Compared: Splines vs. polylines

Splines vs. polylines. Image source: knowledge.autodesk.com

Polyline

Polylines are entities that are made up of lots of shorter lines and arcs that have been joined into one.

In Scan2CAD, you can create a polyline from consecutive lines and arcs by selecting Vector Edit Menu > Modify > Make Polylines.

Spline

A spline is a smooth curve that passes through two or more specific points. The term has its roots from the good old days of mechanical drafting. Back then, a flexible metal or wooden strip (called a spline) was used to construct mathematical graphs. In the world of computer graphics today, splines are easily edited by moving control points; you can add, remove or move control points to alter the size and shape of the spline.

Another term that you might come across often in CAD is Bezier curve. A Bezier curve is a special type of spline, which is defined by only one polynomial function. In layman’s terms, a Bezier curve is defined by only four points (two end points and two control points). Meanwhile, a spline is a more general term; a spline can comprise of multiple Bezier curves linked together.

Why convert splines to polylines?

While CNC incompatibility is the most popular reason for converting splines to polylines, there are some users who do so to get a more optimized design. In the image below, the curvefitted polyline is 38% more compact than the original spline! The original spline had 70 control points, which was later converted to just 43 arcs and lines. The resulting drawing matches very closely too!

The letter ‘C’ on the top is a spline, whereas the bottom image is a polyline. In this case, the polyline is more compact than the spline. Image source: TCICorp.com

Finally, there are some vector editing actions that you just can’t do to a spline (e.g. changing the width). Of course, these features depend on the CAD software you’re working with. Therefore, some people find it easier to work with polylines, as these are simpler vector entities that are supported by all CAD programs.

Step-by-step guide using Scan2CAD

1. Select Vector Edit Menu > Modify > Bezier to Line
2. Select the spline that you’d like to convert with your mouse.
3. That’s it!

Tip on selecting vectors in Scan2CAD: A little box will appear on your graphic cursor; this indicates whether your vector is within Grab Snap Distance. Make sure that the vector you want to edit falls inside this box, then click!)

Using AutoCAD? Here is a guide on how to convert splines to polylines using AutoCAD.

Handy Tips for Conversion

You can compare any vectors after editing using Scan2CAD’s View Vector Ghosts function. The original Bezier curve is shown as a pale gray “ghost”. This “ghost” disappears when you change the zoom levels or pan across the screen. Turn this cool function on by hitting Shift+G on your keyboard.

The lower the precision, the larger the variation between the original spline and the new shape constructed from polylines. If you select a low precision/large tolerance value, the original spline profile will be made up of fewer and longer line segments. Conversely, a high precision value results in many short line segments.

• If you’re using your design in a CNC application, don’t convert your splines using too high precision. The CNC machine will have a very hard time tracing many short segments. The machine will jerk a lot and you’ll end up with a very ragged edge.
• On the flip side, you will want to retain your free-form curve shape to a reasonable degree of accuracy and not lose any intended smoothness.
• Consider the type of design that you’re working with. If you’re producing an object that will get heavily sanded into shape, you have more room to work with and can use lower precision when converting splines into polylines.

For more handy tips, follow Scan2CAD’s Tips and Tricks for Users blog.

Can I convert this scanned technical drawing to vector?

This engineering schematic is a terrible candidate for raster-to-vector conversion

Nope, not this one! It is common for folks to scan a floorplan or technical drawing and convert it to vector, so that the drawing can be used in another CAD application (such as AutoCAD). However, you cannot achieve that with this image above. First, it’s a very poor quality JPG file – zoom in and you’ll get a blurry, distorted mess of pixels. Lots of data would also have been lost when the JPG file is saved, as JPG uses file compression to minimize the file size. Secondly, the image holds up to 16.7 million colors. Ideally, it would be just black and white. If there are too many colors (such as many shades of gray), vectorization software would pick out different zones of colors as different vector elements. Finally, the text is completely unreadable, even to the human eye. The Optical Character Recognition (OCR) software would find it almost impossible to read and retype this into vector text.

Meanwhile, this floorplan would be converted to vector without a hitch!

Instead, you need to use a technical drawing that looks like this one. This floor plan that is perfect for vector conversion.

• It is clear of any noise (such as speckles).
• The image is in pure black and white.
• The text characters that make up the labels of the floorplan are also well-isolated from each other (i.e. the characters do not touch or overlap).
• Another best practice is to save the image as a TIFF file format. Click to download the sample floorplan.tif generated by Scan2CAD.

Can I convert this photo for 3D CAD use?

Image source: nps.gov

Don’t bother trying to scan a photo of a house to create 3D vector plans of the building. It is simply not possible; no one can write software to achieve that—ever! Consider all the information that is missing – one cannot tell the scale of the house from the photo without making some assumptions, and the image doesn’t reveal the part of the house that faces away from the photographer. A more realistic option is to work with a skilled designer to create a 3D vector plan, using the photo as inspiration. There are also 3D scanners that can be used to construct 3D models, but this doesn’t sit in the realm of raster-to-vector conversion.

Can I trace the outlines of shapes from photos?

The left-most image is completely unsuitable. The middle image is somewhat more suitable, but the right-most image is ideal

Check out the image above, on the left. Automatic vectorization software cannot trace clean outlines of these individual flowers—the image is simply too busy. If you’re looking to achieve this, your best bet may be to manually trace the image—for example, by using the Pen tool in Scan2CAD.

A better option could be to find an image of a single flower, with no overlap, such as the image in the middle above. Using such an image, you could then increase the threshold until you remove any unnecessary detail, leaving you with a usable outline.

The ideal candidate would be the image on the right. As it is a silhouette, made up of only two colors, with no distortion, it’s perfect for vectorization.

If you’re looking to create a more photo-realistic vector image, rather than an outline, then this is possible with Scan2CAD. We opened the original image, seen below on the left, in Scan2CAD, and reduced the number of colors in order to create an image with solid regions of color. We then created a simpler vector image from the original.

Using Scan2CAD, you can alter a number of settings during the vectorization process, such as vector definition, profile and types. You can see the effect of changing each setting in the Live Preview window which appears in your dialog box. Learn more about vectorizing pictures and photos in our User Manual.

Can I convert these logos into vector format?

It is best to use the clean logo file on the right, instead of a photo of the logo against a full background (left). Do note, however, that the logo on the right needs some cleaning. The image looks great viewed at this scale, but when you zoom in a little closer, you’ll notice some blurred lines and distortion. We recommend using Scan2CAD’s Color Segment tool to reduce the colors.

Can I reverse-engineer these tools from a scan?

Image source: Into The Woods blog and Alloy Artifacts

You will not yield an accurate vector outline of the tool from the image on the left. There are two main problems. First, the photo was not taken directly above the tool, therefore the different aspects of the tool are not shown in the correct scale. Secondly, the image does not have a clear contrast between the tool and the background. You should try scanning or photographing the tool on a clean, white background. As an extra tip, try your best to minimize the shadows in the photo.

The photo on the right gets extra credit because they included a ruler as reference of measurement. Another tip could be to scan the tool with a piece of graph paper in the background. We’ve also written a step-by-step guide on How to Reverse Engineer a Part from a 2D Scan.

We hope that this post has shed some light on what conversion software can do, and what it can’t. Here are some resources that you might find handy:

• Find out what is and isn’t possible when converting photos to CAD
• Check out our Raster quality checklist to help you choose the right image to begin with
• Learn about our top 10 raster effects to clean and optimize your raster image before conversion

Scan2CAD is the market-leading vectorization software, and comes complete with a full raster and vector editing suite. Plus, a blog covering all the latest news—from Top 3D CAD models to CNC Projects to CAD Freeware. You can try out all of Scan2CAD’s features for yourself, with our 14-day free trial.

You can either convert from raster to vector manually or using an automated computer algorithm. When converting manually, an artist would need to trace over the raster image using drawing software, a tablet, and a stylus (or even a mouse, if they were incredibly proficient!). Alternatively, a computer programmer can write an algorithm: a set of rules or instructions that a computer follows in order to perform a calculation. Read on to learn how this process works.

To a human, vectorization appears to be a single process. From a computer’s point of view, however, it is a combination of several smaller algorithms, each of which controls a specific part of the process. The software uses these algorithms to analyze the raster image, before creating a vector representation of it. The procedure involves three main stages: pre-processing, processing, and post-processing.

Step 1: Pre-processing

The purpose of pre-processing is, quite simply, to prepare the raster image for vectorization. The type of pre-processing work that needs to be done depends on the type and quality of the input image. Here are a few techniques that the vectorization software employs to produce optimum vector output:

• Reduce color. Vectorization works best when the initial raster image has as few colors as possible. To achieve this, grayscale images are binarized, and all gray elements in the image are converted to black or white pixels. Meanwhile, the software reduces the number of colors present in a color image to the minimum possible.

• Reduce noise. You may not be able to notice the effects of noise when viewing your raster image, but it can have a serious impact on the quality of your vector output. There are many reasons why noise appears in a raster image—especially in scanned images—from the low quality of your original sketch, to paper defects, non-optimal threshold settings, or non-uniform lighting in your scanner. Vectorization software, meanwhile, removes dust, speckles and unwanted spots. Noise pixels are identified by comparing them with the neighbouring pixels—shapes and objects are structured, whereas noise pixels are random and usually smaller in size. Filters use rules to accept or reject the pixel; smarter algorithms can analyze the local pixel neighbourhood and define the filter dynamically.

• Increase threshold. Thresholding involves dividing the shades of gray in an image into black and white pixels. This creates a sharp distinction between a white background and black foreground, making the image easier to vectorize.

Check out the difference threshold levels make to your image! You can include as much or as little detail as you want.

Step 2: Processing

This stage is where the conversion from raster to vector happens. First, the program finds the lines in the raster image, where each line is essentially a chain of pixels. There are two main approaches to “find the line”:

Here’s a comparison between both thinning-based and contour-based methods. Image source: www.loria.fr/en/

Again, the type of method we’d use depends on the type of image. For example, thinning-based methods are very sensitive to noise. Contour-based methods, meanwhile, are more noise-tolerant, but rely on complex matching schemes. Many programs also apply two-step vectorization procedures that combine a few methods. There are also other methods such as orthogonal zig-zag, run-length encoding and sparse pixel tracking.

After the program “finds the line”, the program approximates the lines found into a set of vectors. It creates a vector-based representation using elements like text, polygons, circles, arcs, Bezier curves and lines (including dotted lines, dash-dot lines, arrows and polylines).

Step 3: Post-processing

In this stage, the software seeks to analyze and interpret the vector data. The goal here is to remove noise from the vector model, recognize objects, and recover entities from vector data. There are various goals to achieve in this step, including:

• Filling gaps
• Classifying vectors
• Eliminating false branches
• Rectifying right-angled corners
• Finding the best position for junction points
• Simplifying vectors using polygonal approximation
• Checking for duplicates and removing/merging identical vectors that are lying on top of each other
• Lengthening vectors and combining multiple vectors into a single vector

One example of post-processing: the software converts two lines into a polyline

There you have it! When you convert an image from raster to vector, there’s a whole lot going on in the background—all of which is controlled by pre-programmed algorithms. From a user’s point of view, though, it only takes a single mouse click.

Creating a CAD drawing can be time-consuming. It can take an age to master each different piece of CAD software; even simple CAD projects require experience with lots of different tools. Choosing Scan2CAD is just one way to help speed up the design process. If you want to really turbo-charge your CAD work, though, you’ll need to get to grips with some hand keyboard shortcuts. Check out our useful slideshow, and we’ll teach you how to navigate Scan2CAD like a keyboard ninja!

Transcript:

Scan2CAD already helps CAD users around the world save hours of time every working day by automating the raster-to-vector conversion process. But what if I told you that you could save even more time? Scan2CAD has a number of great keyboard shortcuts that can help to speed up your workflow and boost your productivity. Want to learn how to use them? Here’s a guide to our top 10 shortcuts. You’ll learn how to…

• Move around the screen
• Zoom in and out
• Get set up
• View vectors
• View vector grab points
• View vectors by color or type
• Vectorize
• Undo
• Rotate raster image
• Tidy up vectors

1. Moving around the screen

Thoroughly checking your image before and after conversion is the best way to avoid errors and ensure best results. Using the keyboard shortcuts in the list on the right means that you can view your image in great detail whilst still ensuring no part of the image is left unchecked. This means you can take a systematic approach to checking your image.

2. Zooming in and out

Zooming is an intuitive and simple process—just click on the magnifying glass, or use a keyboard shortcut! Please note, though, that these shortcuts are different to those you may be familiar with from programs such as Google Chrome or Microsoft Office. When you select an area of your image, you can also use the F key to enlarge it to fill the screen.

3. Getting set up

Every designer will have different preferences as to how their workspace is set up. Scan2CAD is no different—that’s why you can select from a number of different viewing settings. In the next few slides, we’ll also be going into detail on how some of these settings can be used.

4. Viewing vectors

You can choose whether to display your vector image only, raster image only, or both. This is a useful tool for comparing your original raster image with the vector image created by the conversion process. These keyboard shortcuts are a quick and easy way to toggle between the different views and compare and contrast between the images.

5. View vector grab points

It’s easy to see where your vectors start and end by viewing grab points. Grab points are placed:

• at the ends of a vector line
• at the centre and 12 o’clock points of a vector circle
• at the mid points of an arc
• at text origin points

You also use Grab Points to move vectors around the screen – just position your cursor over the grab point and drag the vector to its new position.

6. View vector elements by type

Choosing to view vectors by type means that different types of vectors will be differentiated from one another on screen by being displayed in different colors. The full list of colors for each line type is:

• Continuous lines: Red
• Dash lines: Black
• Arrow lines: Gray
• Hatch lines: Brown
• Polylines: Green
• Circles: Dark blue
• Arcs: Magenta
• Bezier curve: Pale blue
• Text: Magenta

7. Vectorize

Scan2CAD makes vectorization a one-click process — but if you’d rather use your keyboard, it can just as easily be a one-stroke process using the commands on the right. You can choose whether to vectorize text, lines, or both — and if things don’t go to plan, it’s just as easy to undo them by hitting the same key again + Ctrl.

8. Undo

Everyone makes mistakes from time to time, so you’re almost definitely familiar with this one. If not, then say hello to the most useful keyboard shortcut on your computer. Using Ctrl + Z gives you the freedom to take a trial-and-error approach whilst perfecting your vector image. With Scan2CAD, you can undo up to 256 actions!

9. Rotate raster image

Using the Deskewing tool on very skewed images usually results in a significant loss of quality, so best to avoid that!

Need to deskew a raster image before you vectorize it? This is one of our favourite tips to do just that! When you select the Rotate by Line tool, Scan2CAD will prompt you to draw a reference line. Draw this line on top of a skewed line which should be exactly horizontal or vertical. Scan2CAD will use this line as a reference to detect the angle by which the image is skewed. The tool will then automatically rotate the image, giving you perfect alignment!

10. Tidy up vectors

Attach End Point determines which grab points are moved together. Extend Grab Point ‘stretches’ one vector to meet another vector. Grab Snap Distance defines how close two vector end points must be for them to snap together.

Can’t tell whether Attach End Points is switched on or off?
Just check at the bottom of your screen!

For more tips and tricks, be sure to check out our blog! Each week, our team explores a different topic from the world of CAD and its related fields. We’ve got guides to file conversion, introduction to the different CAD file types, as well as DIY tutorials to get you started with Scan2CAD!

What is reverse engineering?

Reverse engineering is the reproduction of another manufacturer’s product based on a detailed examination of the product’s construction. This process usually involves taking apart a device to see how it works, or producing 3D images of the original part. It’s possible to reverse-engineer almost anything—a mechanical device, an electronic component, computer software or even organic matter! However, whilst some reasons for extracting design information can be socially beneficial (detecting vulnerabilities, or competitive analysis), other uses of reverse engineering are criminal (creating knock-off software or parts). Make sure, therefore, that you’re acting within the law when reverse-engineering a part.

On the left is a simple part made from sheet metal. On the right, we’ve converted the part into CAD format for reproduction. Image source: inspecvision.com

What you need:

• A simple part you’d like to reverse engineer
• Access to a good quality scanner that can scan the dimensions you need
• A raster-to-vector converter like Scan2CAD
• A CNC machine (or access to a CNC machining service) — check out our guide to CNC kits for beginners for tips!

Bonus Video: How To Reverse Engineer A Tool

In this video, Luke will demonstrate how to take an image of a tool and convert it to an accurate vector outline.

Step 1: Scan the product

A critical element of the reverse engineering process is getting a good scan. Since we’re reverse engineering parts based on a 2D scan, you can only choose parts that have details in 2D. We’re only tracing part outlines here, so this technique won’t work for molded parts with extruding 3D detail. You should also take note of the requirements and limitations of your CNC cutting system. For example, the cut width of the tools in your CNC cutting system may limit the amount of detail you want to reproduce.

This is a Deskan Fast Parts scanner, which can scan parts up to A0 in size, for more niche reverse engineering situations. For the simplest parts, you could even use your regular desktop scanner!

Step 2: Convert image to vector

Once upon a time, this would have been one of the most difficult parts of the process, as you would have had to trace over the image by hand. Thanks to Scan2CAD, it now takes just a few seconds. Simply open your scanned raster image file in Scan2CAD, choose the right vectorization settings, and convert your image in a few clicks! Here’s a quick and easy guide on how to convert your image from raster to vector.

Step 3: Check the vector file

New users sometimes make the mistake of expecting their converted vector image to be the finished article. Before machining your design, you’ll need to spend some time checking and cleaning your vector image. How long this takes will depend on the complexity of your image.

Once your image is cleaned up, save your image type using the CNC file format. This ensures that it can be fed into a CNC machine. If you’re not experienced with CNC, then consult with a CNC machinist, who will be able to advise you on the best steps to take for your design.

Want extra tips on how to convert to vector? Check out our Ultimate Guide to Raster to Vector Conversion! Plus, get great tips on turning your ideas into reality with CNC! Having some trouble? Visit our guide to common conversion problems.

What is a bitmap graphic?

Image source: prepressure.com

Bitmap images (also known as raster images) are made up of pixels in a grid; each pixel containing a color value. These pixels (short for picture elements) are tiny, individual squares of color that are arranged in a grid to form an image. It is easy to identify a bitmap image by zooming into the image. If you enlarge the photo enough, you can clearly see the individual dot of color, as you can see on the image on the left.

The term bitmap quite literally means “map of bits”. A “bit” is essentially a value of either 0 or 1. The “map” therefore refers to how these bits are arranged in a rectangular grid. In the simplest images, which contain only black and white, it is possible to use just 1 bit per pixel. However, most images use more than one bit per pixel—a “true color” image, for example, uses 24 bits per pixel. A very large image with many colors would therefore have a very large file size. To combat this, bitmap images can be slimmed down using lossy or lossless compression methods.

How are bitmaps created?

When you take a photo using a digital camera or scan a drawing into your PC, you’re creating a bitmap image. You can also create bitmap graphics using software like Microsoft Paint and Adobe Photoshop. When you edit a bitmap image, you’re editing the color values of individual pixels. This makes it difficult to edit individual elements within the image. It’s simpler to edit a bitmap image as a whole—for example, by editing its contrast or brightness, or by applying a filter (like the ones you can find on Instagram).

In a 1 bit image, every pixel is either black or white. Image source: bbc.co.uk/education/guides

What characteristics define a bitmap?

Bitmap images are characterized by two parameters: the number of pixels (resolution) and the color depth per pixel.

• Color depth refers to the information contained within the image. For example, a 1-bit image means that a pixel could either be black or white. An 8-bit image means that each pixel can consist of any one out of 256 color values (2 to the power of 8). “True color” images use 24-bit RGB, in which there are 8 bits allocated to each red, green and blue component.

8 bits each for red, green, and blue, for a total of 24 bits per pixel

• The number of pixels is a measure of how many pixels there are in a given area, or pixel density. This is measured in pixels per inch (PPI) or dots per inch (DPI). The resolution of an image affects the quality of the bitmap being displayed or printed. The higher the resolution, the less apparent the pixel nature of the bitmap will be.

The size of the bitmap image is closely linked to the graphics display resolution—the number of pixels that an electronic visual display device or printer can display. This is because the pixels themselves have no explicit dimension. The quality with which a bitmap is printed or displayed depends on the resolution of the device. For example, the image below has the same color depth and information content. However, the smaller image is 80DPI while the larger image is 30DPI. The pixelation is more evident in the larger image.

Which image has the higher resolution? (It’s the one on the left!) Image source: paulbourke.net

How is bitmap data stored?

Bitmap data can be stored in a variety of file formats. There’s the BMP file format, which allows Windows to display bitmap images on any device. (Learn more about converting BMP to DXF.) However, this file format lacks compression and are generally large in file size, and hence, a largely outdated file format. Many of the most common image file formats, such as JPEG, PNG, GIF and TIFF, store bitmap graphics. However, since they use compression, they are not usually referred to as bitmaps, but are instead called raster images. To learn more about each file format, click over to read our infographic about raster and vector images.

What is a vector graphic?

Image source: serif.com

Vector graphics consist of shapes called objects. They can include lines, curves, shapes and text. Rather than being made up of pixels, vector objects can be thought of as a set of instructions. These ‘instructions’ contain information about the position of an object within the image; line width and length, and any color information. Taken together, these objects contain the information required to correctly display the image on screen.

A key difference between bitmaps and vector images is the ability to edit individual elements. Individual elements within a vector image can be edited and transformed separately. This makes it easy to move, enlarge, and rotate each element—and much more. In a bitmap, this would be close to impossible. Another distinguishing characteristic of vector graphics is their scalability. You can zoom into or enlarge a vector image without losing any quality. Take, for example, the image above. Even when enlarged, the image appears crisp, and all its details have been preserved.

How are vectors created?

Vector graphics are created in graphics packages such as Adobe Illustrator, AutoCAD or Scan2CAD.

How is vector data stored?

There are a wide range of vector file types available. Many are specialized for a particular use—DXF and DWG, for example, are intended for use in CAD programs, while AI is used primarily with Adobe Illustrator. Web browsers generally do not support a wide range of vector image files; Scalable Vector Graphics (SVG) files are a notable exception. One of the most well-known vector file types is actually PDF, though this format only supports a very limited range of vector entities, and can also support raster elements.

Using vector images in CAD? Check out our comparison of the DWG and DXF file formats.

When is it best to use bitmap graphics?

Image storage technology is constantly evolving and as it involves we see how vector graphics are becoming a preferable format where there is a choice. 

However, bitmap graphics continue to be the vastly dominant format in many areas. For example, the vast majority of websites that you view continue to display images in bitmap format. This is not only due to the dominant legacy of bitmap images but also because it is much more computationally easy for all browsers to support common bitmap graphics, compared to the mathematically-composed vector graphics. It is expected that vector graphics will become more common in websites over the following decade and indeed many websites already use vector formats such as SVG.

Bitmap images are also used for image acquisition, such as scanning a document or photography. This is unlikely to change because cameras are pixel-based tools. And there’s little benefit in representing a scanned document in vector format – Unless of course you are dealing with something like a paper CAD drawing. 

When is it best to use vector graphics

Vector graphics should be the format of choice when the accuracy, perceived quality or scalability of the image is more important the cross-compatible benefits of bitmap graphics.

For example, if you wish to have your company logo printed on a large sign you should first convert your logo to vector before sending it to the printing company. This is because your image will need to be scaled-up to very large dimensions prior to printing. A respectable printing company will not accept a bitmap image for this purpose because the printed image would be distorted and pixelated.

Vector graphics are also imperative when you need a graphic to store accurate data. For example in Computer-Aided Design a designer or engineer will typically use DXF or DWG files. These are vector files which contain mathematic representations of the graphics with additional data such as scaling information, text strings, CAD object data and much more. It would be impossible for bitmap graphics to store this information.

Comparison of bitmap and vector graphics

Bitmap graphics are formed of pixels whereas vector graphics are generated from mathematically-defined equations. The quality of vector graphics are not dependent on the resolution, they can be scaled up or down infinitely and at whichever scale, the resolution will always be perfect. Whereas the perceived quality of a bitmap depends totally on the resolution of the image. The higher the bitmaps’ DPI/PPI the higher the perceived quality. 

In the below table we provide a detailed comparison of bitmap vs vector graphics.

If you’re choosing between graphic file types, here are a few questions you should think about:

• Does the image need to be resized?
• Does the image need to look photo-realistic?
• Do you have any restrictions on file size?
• What are you using the image for?

Most design projects will involve a combination of vector and bitmap images. For example, a web designer may use a vector logo whilst using bitmaps to store photos and other graphics. Architects, meanwhile, could use both bitmap and vector elements to create a blueprint, and save their image in a format which supports both (such as PDF).

It is also possible to convert a bitmap graphic to vector, using a process called vectorization or image tracing. This is usually done when users want to import scanned drawings into Computer Aided Design (CAD) packages. Software packages like Scan2CAD can automatically trace the lines, curves and text within an image and recreate bitmap graphics using vector objects. Converting vector graphics to bitmap is much, much easier—you just need to use the Save As command in any graphic package. Vector graphics are converted to bitmap graphics so they can be shared easily or used on a web page.

How Scan2CAD and other raster-to-vector conversion programs trace images

Conclusion

As we’ve learned, there are quite vast differences between bitmap and vector graphics even when side-by-side the images could appear to be very similar. Vector graphics continue to be a preferable choice in graphic format when the perceived quality, associated data and scalability of the image are important to the user. We have observed how vector graphics are the norm for such industries as CAD. However, bitmap graphics continue to be dominant in image acquisition – such as document scanning and photography – and where cross-compatibility is important such as imagery on websites.

Filling a market need

Like many of the greatest software ideas, Scan2CAD started life as a solution to a personal problem. The Knoll brothers, for example, created Photoshop because they were frustrated with the lack of color correction software; MATLAB, meanwhile, was created by three American mathematicians to compute calculations that they’d otherwise have to do by hand. In the same vein, George Kennedy designed Scan2CAD because his brother needed to transfer his paper drawings to CAD.

George’s brother was an architect who had stacks of hand-drawn blueprints. He’d been searching for an application that could convert these paper sketches into vector data, so that he could use powerful CAD software in his work and save time. Unfortunately, there was no simple solution available at the time. George decided it was up to him to provide that solution – and so, the idea for Scan2CAD was born.

Building the product with the user’s specifications in mind

Transforming an image from raster to vector is a tricky process. This meant that creating Scan2CAD was no cakewalk. First, George had to learn how to write software. He bought himself a bookshelf full of guides to C, the programming language used to write Scan2CAD. He also taught himself how to write the mathematical algorithms required to create vector data.

Once created, the product needed a name. The aim of the software was to take scanned images and convert them into editable vector information, for use in CAD applications. In other words, taking an image from a scan to CAD – hence the name Scan2CAD! To this day, George Kennedy continues to be the lead developer of Scan2CAD.

Bringing image conversion to everyone

A blast from the past: an early 2000s CD-ROM version of Scan2CAD!

The first version of Scan2CAD was released in 1997. To buy the software, customers had to send a cheque in the post. The software would then be sent out to the customer on a floppy disk.

Cheques and floppy disks may have largely disappeared nowadays, but Scan2CAD is still around. There’s no longer any waiting around: customers can simply visit Scan2CAD’s website and download it in a few seconds. Scan2CAD has enabled big businesses and creative individuals alike to turn their paper sketches into CAD-ready files. Before Scan2CAD, this process would have taken hours or even days of painstaking manual work. Now, vectorization takes just a few clicks and a few seconds. With its wide range of settings, Scan2CAD also gives users maximum control over vectorization – so you can get great results in no time.

Evolving over the years

Over the course of two decades, Scan2CAD has grown and changed radically. The first version of Scan2CAD introduced the ability to trace raster images. Over time, Scan2CAD began to support more and more file types – full PDF support was introduced in version 8 (2010) while DWG compatibility arrived in 2016.

Scan2CAD’s features have undergone significant overhauls as time has gone on. The conversion tools became more and more powerful too, with improved Bezier curve drawing and enhanced vector drawing tools. Its development road map has also adapted to meet the changing needs of the market. Scan2CAD introduced flexible licensing as other software moved to the cloud. Feedback from the Scan2CAD community has also driven the development of innovative new features. When Scan2CAD’s developers heard that many of their users were using Scan2CAD for CNC work, they immediately built in support for G code file formats!

The Scan2CAD website looked like this back in 2009!

What’s next?

Scan2CAD can’t and won’t stand still. Its focus on converting raster images to vector has remained the same, but the software continues to evolve and adapt to customers’ needs. Scan2CAD is also working on releasing a Mac version of Scan2CAD in the near future.

The Scan2CAD team is continuously improving the quality of the conversion software, meaning greater ease-of-use and better vector outputs. Scan2CAD is now the vectorization software of choice across a wide range of industries, from architects to space shuttle developers. As the software’s functionality expands, so too will its relevance to CAD customers.

Table of Contents

• When would you convert PNG images to DWG?
• How to convert a PNG file to DWG?
• What is a PNG file?
• What is a DWG file?
• Behind the scenes: How are PNG files converted to DWG?
• Why choose Scan2CAD over an online converter?
• Using Scan2CAD to convert PNG to DWG

Transcript

When would you convert PNG images to DWG?

…when you want to edit individual elements within the image.
Working with PNGs is much like painting with actual paint – editing involves ‘painting over’ the original image. The image is made up of pixels, instead of vector shapes. Editing it would involve making changes which affect the entire image. Singling out a single element to be edited is close to impossible.

In contrast, vector files, like DWG, are much more versatile. They allow you to edit individual elements within the image. You can change colors, resize a particular object within the drawing, move elements around, copy objects into other drawings, and more. It is this versatility that makes DWG vector files invaluable to CAD work.

…when you want to edit or reuse the image (or certain parts of the image)
PNG-to-DWG conversion comes in handy when you have a stack of hard- copy images, or a folder full of PNG images on your computer that you’d like to digitize. Converting to DWG allows you to reuse parts of older drawings in modern formats. For example, a group of architects working together can reuse certain drawing objects, like doors or windows, in new projects. They can also share the floorplan with interior designers, electricians, building contractors, and others. Vectors are also scalable, meaning that you can resize a vector drawing as many times as you wish, without any loss in quality.

…when you want to transcribe the drawing into operable instructions.
An artist designs signboards or sculptures using the software that they know best, such as Adobe Illustrator or Photoshop. This design is then converted to a DWG file, using applications like Scan2CAD. Then, the design is sent off to a CNC cutting machine vendor, who will manufacture the actual product from the DWG drawing. These machines use the vector files to generate automatic cutting instructions.

CAD programs also allow you to bring your PNG images to life in other ways. You can upload CAD drawings into 3D modelling software, or even create animations from your converted files.

You have two options to convert PNG files to DWG:

• Convert manually, by tracing the PNG image with a Vector Pen tool.
  You could manually draw vectors. This could take hours, or even days! It’s also extremely difficult to get an accurate vector drawing using this approach. There’s lots of fiddling about with pens and grab points.
• Convert automatically, using a PNG-to-DWG file conversion program
  Simply load the file into the conversion program, click a few buttons and voilà! You’ll have to complete some post-processing steps, but it’s still much faster than drawing manually. By using the right file conversion software, you’ll save precious hours of your workday… and convert in a few clicks!

Once the PNG is converted into DWG, you can load the drawing into almost any CAD program The world is now your oyster. You can cut, copy and paste certain elements of an existing drawing. You can edit specific elements of the drawing, such as reshaping Bezier curves, stretching vectors, converting lines to arcs, and more. CAD software makes it easy to revise and edit drawings. All sorts of CAD editing tools in your arsenal!

Most users use DWG files as an intermediary file format

For example, an architectural designer can scan a hard copy floorplan. Once it’s converted to DWG, they can share it with an electrical engineer for wiring plans, a structural contractor for structural renovations, a landscape designer, and anyone else who may be involved in the project.

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How to convert a PNG file to DWG

The entire conversion process takes about ten clicks. Here are the steps to converting a PNG file to DWG using Scan2CAD:

1. Load the PNG image file that you’d like to convert.
2. Select the conversion settings. In Scan2CAD, there are pre-programmed
   vectorization settings to help correctly identify the objects in your drawing. For example, the “Architectural” option is designed to detect straight lines and right angles.
3. Click “Convert”. Almost immediately, you’ll have a DWG file that you can load into another CAD software. It’s always best to spend a few minutes to thoroughly check your DWG file, examine the outputs and clean it up as necessary.
4. Save the DWG file. Now, you can edit the DWG file with any supported CAD software.

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What is PNG?

PNG is a raster image file format. A raster image stores image information in small squares of color called pixels. PNG supports lossless data compression, which means that it does not lose quality during editing. In CAD, PNG is commonly used to capture a screenshot of the CAD drawing whilst edits are being made. This is because PNG images are easily shareable.

Did you know? PNG is pronounced “ping”! The acronym stands for “PNG Not GIF”, to oppose the patenting of GIF.

However, you should always choose TIFF over PNG. TIFF or Tagged Image File Format, is an image file format for high quality graphics. It is the most popular format amongst graphic artists, the publishing industry, and photographers – anyone who regularly deals with image editing and manipulation. TIFFs can either be compressed or decompressed using lossless compression, helping you preserve every single detail of your image. Hence, it is the preferred format when scanning photographs and sketches for raster-to-vector conversion. Of course, greater detail comes at the expense of file size. In addition, TIFF is quite a complex file format, and as a result it is less likely to be supported by more general applications such as web browsers.

Check out our ultimate guide to learn everything you need to know about converting from TIFF to DWG.

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What is DWG?

DWG is a vector graphic file format. We’ve written about on the DWG file format extensively on our Scan2CAD blog. DWG files store both 2D and 3D data, as well as a database of dimensional data and metadata.

Here are some programs that you can use to view and edit DWG files. AutoCAD, Scan2CAD, some versions of Google Sketchup, DraftSight, IntelliCAD, CorelCAD, A360 Viewer (online viewer), DWG TrueViewTM (online viewer) and AutoCAD 360 (mobile and web app).

Some examples of CAD software that you can use to view and edit DWG files

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How does the software convert a PNG image to DWG?

Raster-to-vector conversion software basically traces the raster image and reproduces the drawing using vector entities. It also allows you to trace outlines, or retain information pertaining to whether a line is solid or hatched. It includes algorithms that can detect image edges, recognize different types of lines; angles at which the lines are joined, different shapes, and different colors, as well as text.

Here is how Scan2CAD and other raster-to-vector conversion programs trace images

In order to create the best quality vector image, the software employs a few processing techniques…

• “gap jumping” fills in gaps in the scanned raster image, helping create unbroken vectors
• corner sharpening to capture right-angles
• line thickening
• removal of unwanted spots and speckles

To learn more, check out our article on how vectorization software converts images to DWG.

The conversion software can also “read” text and “type” it out into editable vector text. If a scanned document contains text, the text is saved as a raster image. Hence, the file conversion software has to regenerate the text in the document using smart OCR (Optical Character Recognition) technology. It’s the same concept as tracing shapes and lines, except that the OCR algorithm detects letters and numbers. Click here to learn more about OCR and how it works.

Each program that is capable of OCR will treat text differently. Great ones save whole phrases of text in a single layer – this makes the text easily editable. However, subpar conversion software may split the string of text into separate characters and jumble the positioning of the text. This makes the text extremely difficult to edit.
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Why choose Scan2CAD over an online converter?

When deciding how to convert from PNG to DWG, it might be tempting to think that all converters are the same. You might instinctively head straight to Google, type in “convert png to dwg”, and head to the first free online tool that appears. These online converters often claim to offer great results with no downloads—but the truth is that they simply can’t live up to their claims.

Converting from PNG to DWG is a complex process that requires a lot of computing power. By their nature, online tools simply aren’t able to offer the same amount of processing power as a local application can—and as a result, they tend to cut corners. You may find yourself unable to upload complex files due to size restrictions—and when you finally can convert something, you may find that the results are poor. The problems with online converters can range from being unable to open your file to serious security issues.

Choosing Scan2CAD means choosing a fast, secure and accurate conversion program. Tried and trusted by users in a wide range of industries, Scan2CAD offers great vectorization results—and a whole lot more.

Using an online converter is risky—but using cracked software can be even worse. Learn about the risks of downloading a Scan2CAD crack.

Using Scan2CAD to convert PNG to DWG

There are various features offered by Scan2CAD that would come in handy during conversion:

• Support for over 40 file formats including DWG, DXF, SVG, PDF, TIFF, and more
• Full set of editing tools for both raster and vector images
• Smart OCR to recognize and edit text
• Built-in vector recognition presets to correctly identify shapes and line types
• Raster and vector viewing tools
• Command line
• Batch processing
• Flexible licensing
• Excellent support 24/7

Need to convert a different file format to DWG instead? Check out our Ultimate Guide covering how to convert PDF to DWG.

How is G-code used in CNC machining?

CNC machinists use G-code to instruct CNC machines where and how to move. The code dictates which direction the machine should move in, how fast it should move, how deep it should cut, and so on. The instructions are described using Cartesian coordinate locations (e.g. two units left and three units up.)

To begin with, an initial block of material will be loaded into the machine. Then, following the instructions given by the G-code, the cutting tool cuts away material from the block to produce the finished product.

G-code is one of the most widely used programming languages used to control automated machine tools. Most CNC machines execute G-code, although other CNC languages exist, such as Heidenhain, Mazak, and other proprietary formats.

CNC machinists can either write G-code from scratch, modify existing G-code, or generate G-code using CAM software. CAM software can generate G-code from either images or CAD files. In today’s extensive CAD industry, there are also CAD editing programs that automatically convert CAD files into G-code. There are also richly-featured G-code editors that can be used to simulate G-code, or to translate G-code into conversational CNC.

An example of a CNC editor, where CAM programmers can edit G-code before manufacturing

How to read and write G-code

A typical line of G-code is quite cryptic for newcomers – it takes years for a CNC machinist to master the language. Whilst the entire language is referred to as G-code, technically speaking a ‘code’ refers to just a single instruction in the language. Each ‘code’ consists of a letter address and a number, and gives a specific instruction to the machine.

Most lines of G-code will begin with the letter G – hence why the language got the name! This is because the letter G signifies preparatory codes. They tell the machine which kind of motion is required, or which offset values to use. The codes beginning with G are therefore almost always found at the start of a line of G-code. G00, for example, tells the machine to move at maximum speed, while G02 tells it to move in a clockwise, circular motion.

Try and read this snippet of G-code! It’s a simple drawing of straight lines

Not all G-codes start with the letter G!

Whilst codes beginning with G are extremely common, all 26 letters of the alphabet are used in G-code. S, for example, defines speed, while F defines feed rate. There are some other important basics to know, such as:

• The letter X controls the horizontal position or X-axis of the machine
• The letter Y controls the vertical position or Y-axis of the machine
• The letter Z controls the depth or Z-axis of the machine
• The numbers next to these letters determine the distance moved by the machine

You can view a full list of standard G-codes here. Be aware, however, that codes vary by machine type, make, and model.

G-code File Types supported by Scan2CAD

There are dozens of known G-code file extensions. Which file type your CNC machine will support depends on its setup, as well as the make and model. Scan2CAD supports three of the most popular G-code file types – .CNC, .NC and .TAP. The latest release of Scan2CAD, v9, allows you to directly export a vector image file to G-code file format. Now, you can convert scanned sketches and images to vector using Scan2CAD, before saving it as G-code. These files can then be transferred to a CNC machine and used for production.

The CNC Export dialog in Scan2CAD provides you with a range of options:

• G-code Bezier options – cubic splines (G-code G05), arcs (G-code G02/G03) or polylines (G-code G01). If you select polylines, Bezier curves will be broken into straight-line segments
• Arc and circle rotation – clockwise or anti-clockwise
• Z-settings – various parameters relating to the cutting of the exported vectors
• Scale settings – the relation between vector points and a distance in real-life – e.g. two points on a vector image could represent an inch

The CNC Export Settings dialog box in Scan2CAD. There are four different settings which can be defined.

Recommended reading:

• Easy G-codes every machinist must know
• How to go from CAD, Image or STL to G-code
• CNC Programming with G-code for Beginners

What is DWG?

Developed by Autodesk in the early 1980s, DWG files are best known as the native file format for AutoCAD, though they are used by several other CAD packages as well. The name DWG is an abbreviation of drawing, which gives a clue as to its intended use – storing design data and metadata. Besides storing CAD drawing designs, the format can also be used to store vectors, and geographic information. In short, DWG files can hold all the relevant vector data in your designs. The file format is proprietary, meaning that Scan2CAD does not publish the file specification publicly and not many programs don’t support it. Luckily, Scan2CAD lets you view and edit DWG files. To delve deeper into the details of this file format, you can visit our Overview of DWG Files.

Step-by-Step Guide to Viewing DWG Files using Scan2CAD

While a DWG file is a more complex beast than a familiar PNG or JPEG, opening a DWG file is easy as pie. To open a DWG file in Scan2CAD, simply…

1. Click on the “File” menu at the top-left hand corner of the screen.
2. Click “Vector”, followed by “Load”.
3. Browse to the file you want to load and click “Open”

Scan2CAD can open any DWG file version from R2000 to R2014. It will not, however, load any layer and block information stored in the DWG file. Scan2CAD only loads parts of the file that it supports, including lines, polylines, polygons, polypolygons, arcs, splines (Bezier curves), polybeziers, circles and text. Finally, Scan2CAD will preserve any scale information (viewable in the Vector Scale Settings dialog).

Here are a few screenshots, demonstrating how to load DWG files in Scan2CAD. Click to view full-size image.

Keyboard Shortcuts to Use When Viewing DWG Files on Scan2CAD

• Ctrl+Shift+Z to ensure that the correct 0,0 origin is applied to the vectors as it is loaded. You should press this as the DWG file is loaded.
• Ctrl+Shift+F to ensure that all of the vectors which are loaded are fully displayed.
• Arrow keys to pan around the image. You can also hold down the mouse scroll wheel or space bar when moving your mouse.
• M to zoom in, and D to zoom out
• G to turn vector grab points on or off. These could be your vector end points, circle center points, circle 12 o’clock points, arc midpoints and text origin points.
• E to view Bezier control points – these are the handles which you can move to edit the size and shape of a Bezier curve.
• T to view text extents.
• Shift+L to view vector line widths. Don’t let your eyes deceive you – vector lines may appear to be the same width, but this may not reflect the true line width values.
• C to view vector colours or type. If you turn this feature off, Scan2CAD displays each vector element in a different colour.

Before we begin…

Are you looking for free designs which are ‘cut-ready’ for your CNC projects? Check out our library of free DXF designs for CNC. We release new packs every week and they’re all free to use in hobbyist or commercial projects.

Table of Contents:

• What is CNC
• The Design Process: From CAD to CNC
• 8 Tips for Designing for CNC
• Using Scan2CAD to Convert Images for CNC
• Case Study: Reverse-engineering CNC parts

What is CNC?

CNC stands for Computer Numeric Control. The computer converts the CAD design into numbers – graphic coordinates – which control the movement of the cutter. In the diagram on the left, the cutter is at point A (18, 8, 23). The computer-controlled cutter will travel to different sets of coordinates, in sequence, until the desired shape has been manufactured.

Some of the most common types of CNC machines…

From design to CNC fabrication…

It all begins as a drawing, perhaps in CAD software. The design is usually saved as a DXF or DWG – you may need to convert your image to one of these formats first. Then, you’d import your drawing into CAM/CNC software to generate the G-code which will control the CNC machine.

Tip: You can create G-Code formats from you designs directly in Scan2CAD.

There are a few ways you can create your CAD design. In the next two slides, we’ll walk you through the most common workflows.

Example 1:  Manually trace an image creating the vector cut paths 
We’ll start with a photograph of a tractor. Trace around the silhouette and the main features that you want to cut out. Save your design as a DXF file and import it into a CAM program to generate the G-code.

Example 2:  Automatically Converting an image into DXF drawing format
Scan your sketch and save it as a PDF or image format (e.g. JPEG, TIFF). Convert the file to DXF format using conversion software like Scan2CAD. Import the vector DXF file into a CAM/CNC program to generate G-code. In fact, you can also convert and image directly to G-code formats in Scan2CAD.

8 Tips for Designing for CNC

1. Don’t forget to define the scale of your vector image
For precision CNC work, it’s good practice to set the system units to millimeters; and precision or tolerance to 0.5 µm. Scan2CAD has three different ways to scale vectors when exporting them to DXF file format. Check out this article in our User Manual to learn more.

Vector Scale Options in Scan2CAD

2. Place your geometry on a single layer
After designing your CAD drawing, you should make sure it’s been cleaned up before importing it to CAM. For best results, you should:

• Reduce the vector lines to the lowest number of nodes without being detrimental to the design quality
• Only export the relevant parts of your drawing into the final DXF file
• If you need to edit in your CNC software, lock layers that you don’t want to accidentally select or move around

3. Convert splines and arcs
Many CNC machines prefer to work with polylines (i.e. many lines as a single vector entity), rather than a series of broken entities like arcs, beziers and lines. In Scan2CAD, you can convert a spline into a polyline using the vector editing tools. To do so, select Vector Edit Menu, then Modify, then Bezier to Line. Finally, click on the Bezier curve you’d like to convert.

4. Remove spaces and draw one coherent cut path
If you want clean, connected cut lines, then you must ensure that your relevant vector lines are connected. This is especially important when you turn lines and arcs into polylines. Make sure that the lines and arcs join together perfectly by using Snap tools (do not approximate!) AutoCAD users would find the PEDIT command handy for this purpose. In Scan2CAD, you can define a Grab Snap Distance between grab points.

5. Select touching objects and convert them into a single entity
In Scan2CAD, select the Vector Edit Menu, then Modify, then Make Polylines. If there are arcs in your drawings, you must check Include Arcs before converting them into polylines. This function is found by clicking Vector Edit Menu, then Modify > Polylines Options > Include Arcs.

6. Remove overlapping geometry
If there are overlapping vectors in your design, you’re basically instructing the CNC machine to go back and forth in the same area. This is may be OK for some laser etching designs but in most cases it is not practical. Delete duplicate copies of objects. Combine lines that partially overlap (for example, arcs drawn over portions of circles) Combine objects when aligned end-to-end.

7. Set your default Z-Axis Value
In Scan2CAD, you can set the default Z value for all vectors in the CNC export options. (File > Vector > CNC Export Options) You can also set the Z value for individual vector elements should you wish to.

8. Familiarize yourself with the cut width of tools on your CNC cutting system
The depth and width of cut are crucial variables when milling pockets, profiling, facing and performing other machining operations. Understanding your cut width will help you control your feeds and speeds, the Material Removal Rate and how long it will take to complete the operation; as well as the surface finish. The spacing between your toolpaths should be comparable to the diameter of the tool. Also take note that machined corners depend on the size of the end mill, and this affects how to parts fit together. To learn more about CAD and milling strategies, check out this guide to Mastering CAD and CAM for CNC Machining by Michael Zalewski.

Using Scan2CAD to Convert Images for CNC

Why use Scan2CAD to prepare your CNC drawing file? You could either trace an image manually or convert that image automatically! The first option could take hours, or even days – time that could be better spent working on other things! Alternatively, you could load the image file into a raster-to-vector conversion program like Scan2CAD. A few clicks later and voilà! Out comes a DXF file that’s ready to edit in CAD software. Once the image is converted into DXF, you can easily edit it using any CAD program. The Scan2CAD vector editing toolbox offers all the basic functions:

• You can cut, copy and paste certain elements of an existing drawing.
• You can edit specific elements of the drawing, including stretching vectors, converting lines to arcs, and more.

Converting your image to DXF is easy with Scan2CAD!

1. Load the image or PDF file that you’d like to convert.
2. Select the conversion settings. Scan2CAD comes with pre-programmed settings. For example, there is an “Architectural” option that is designed to trace straight lines and right angles, whereas the “Contour Map” setting traces curves well.
3. Click “Convert”. Wait a few seconds and voilà! You have a DXF file that is compatible with any CAD software on the market. After conversion, you can choose whether to display only vector information or to overlay the original raster image as well.
4. Save the DXF file. Now, you can view, edit and clean up the DXF file with any CAD program, before importing it into CAM software. Tip: You can also save in a G-code formats (.nc, .cnc. .tap)

Case Study: Reverse-engineering CNC parts

Shapemakers is an Australian CNC company that manufactures an A0-size scanning system called Deskan Color Express 6. Its clients turn to Shapemakers to scan old gaskets, drawings and seals (up to 1180x870mm in size!) The Deskan 6 software can scan the A0 drawing in strips and stitch these together using the proprietary software.

However, its clients require the drawings in DXF vector format for editing in CAD or cutting on a CNC machine. That’s where Scan2CAD comes in. Our software allows Shapemakers to vectorize their large scans and cut out the parts quickly and easily.

Grab this post as a slideshow

If you’re interested in creating parts yourself, check out our guide to the best CNC kits for beginners.

This guide is brought to you by Scan2CAD, the market leading file conversion and editing software. Scan2CAD includes conversion tools, image editing and cleaning tools, smart OCR, full PDF support, as well as vector recognition and editing. Download your free trial for 14 days, with full access to all of Scan2CAD’s features.

These PDF files contain valuable information required for your CAD work. However, in order to extract the information and make edits to the drawing, you’ll need to convert PDF to DXF or DWG. In this article, we’ll walk you through everything you need to know about Scan2CAD, the market leading file conversion software that you can download for free. With its 20-year track record and clients such as Shell, BBC and Intel, it’s the file conversion brand that you can trust.

1. Highly Accurate PDF-to-DXF conversion

Scan2CAD can extract both raster and vector information contained within your PDF file, including vector entities like polylines, polygons and text; as well as embedded raster images and metadata. It also includes an OCR text recognition engine to extract text from images. Scan2CAD also lets you…

• Save vector entities on one single DXF layer or on multiple layers (each layer defined by either color or type)
• Automatically retain any user-defined line types (such as dashes and dots) when converting vector PDF files. It also preserves line width information, which is especially handy when converting electrical diagrams
• Save vector files in the correct size and scale
• Save vectors as True Color (i.e. the exact original color)

The most powerful feature in Scan2CAD has to be our raster to vector conversion engine. The software comes pre-loaded with automatic settings for a wide range of drawings, including architectural, electrical, and mechanical drawings, amongst many others. This enables the software to create the most accurate vector entities possible, giving you optimal results.

Scan2CAD’s raster-to-vector conversion engine comes in handy when dealing with circles and arcs

The PDF file format only supports a limited number of vector entities – and these don’t include arcs or circles. As a result, any circular shapes are converted into short lines or Bezier curves. This output is incredibly difficult to edit. If your drawing includes arcs and circles, be sure to choose software like Scan2CAD that can replace the short lines or Bezier curves with true arcs and circles that are easy to edit.

These circles were imported from a PDF using another conversion program. Instead of appearing as two vector circles, they have been reproduced as a series of small vector lines, making them very hard to edit in CAD.	These circles were imported from a PDF using Scan2CAD. Scan2CAD detected them and reproduced them as easy-to-edit vector circles. Just select the Make Vector Circles option when importing your file into Scan2CAD.

2. CAD & CNC-ready files

After vector conversion, you can export your file as DXF or DWG (and a number of other vector file types). These are the two most widely-used CAD file types in the industry. Not only that, but Scan2CAD is able to read and write files from many different versions of DXF and DWG files. It supports DXF files pre-R14 and DXF R14/LT97 and later, and it supports DWG files for all versions between R12 and R2007-2010. As for input, Scan2CAD accepts both single page and multi-page PDF input. What’s more, when importing your PDF, you can choose to import raster images only, vector images only, or both – and whether it’s a scanned document or a drawing file that’s saved as PDF, Scan2CAD can convert your file to DXF. You can even rotate the PDF page when loading it! After you’ve vectorized your files, they’re ready for use in CNC machining.

Still deciding which CNC machine to start with? Check out our guide to the best CNC kits for beginners!
download scan2cad for free here

3. Full set of vector and raster editing tools

Scan2CAD is an end-to-end file conversion solution. Using just one program, you can scan, edit, and convert your image. You can clean up raster images and prep them for optimal raster-to-vector conversion. After conversion, there’s an entire suite of vector editing tools, meaning you can cut, copy, move, and paste elements within your image, draw new vectors, add text, and more. This can be useful for optimizing poor raster images before conversion, e.g. converting GIF to DXF. 

Scan2CAD comes with a complete suite of raster and vector editing tools

4. Convenient

Using Scan2CAD’s intelligent conversion software can you save hours of precious time. Once you experience the convenience of using raster-to-vector conversion software, you’ll never go back to tracing over raster images manually on your CAD software.

Scan2CAD also supports batch processing so you can automate conversions of thousands of files in a few clicks! All you have to do is select the files or folders you want to convert and choose the right settings. Learn more about batch conversion and automation here.

Scan2CAD is leaps and bounds ahead of competitors when it comes to dealing with raster images. Other conversion software will simply extract the raster images from your PDF, potentially leaving you with a huge number of different raster images for each page of your PDF. It’s not very efficient, and it makes it really hard to edit. Scan2CAD, meanwhile, saves all the raster images on one page as a single image, letting you get on with editing it as normal.

5. Safe and secure

There are plenty of online conversion tools promising great results, absolutely free! It sounds too good to be true – and unfortunately, that’s because it almost always is. Uploading your files to an online tool might not only leave you with a poor quality image – it can compromise the security of your file, leave your company’s intellectual property vulnerable, and comes with the risk of malware being downloaded to your PC. Check out our article on the problems of online file converters to find out more – and find out why it’s better to stick with Scan2CAD.

Try every feature for free

Try the full version of Scan2CAD with our free 14-day trial. This trial version allows you to try every single feature in the professional version of Scan2CAD, all for free. Unlike some other free PDF to DXF and PDF to DWG converters, there are no watermarks printed onto your output files. Click on the image below to download your unlimited trial now.

One of the easiest ways is to simply convert your DWG file into the almost universally-accepted DXF format. DXF was specifically invented to allow sharing between those using AutoCAD and those using other software – it’s the perfect format for collaboration. So how do you go about converting to DXF? Read all about it in our Ultimate Guide on converting DWG to DXF – complete with a few handy tips to make the process smooth and efficient.

Video: How to convert DWG to DXF Without AutoCAD

Let’s kick things off with a demonstration how to quickly and accurately convert your DWG files to DXF with conversion software – Scan2CAD. Converting your DWG with Scan2CAD will ensure that you do not lose any data in the file conversion. 

You can follow along with the steps in the video by downloading the Scan2CAD free trial.

Why would you convert a DWG file to DXF?

For sharing! After all, there are dozens of different file types used by CAD software. It’s common to be asked to provide an image file in a particular format. Other times, someone may have provided a file in a format they’re already used to, but which is entirely different from the CAD software that you use. In both cases, you’ll need a file that can be opened and edited by both parties. Of all the file types, DWG and DXF files are the most commonly shared, with DWG being the standard file format for AutoCAD, and DXF being the de facto file exchange format.

Another important reason to convert files to DXF is to convert complex entities into simpler entity types – a feature which is especially useful when you’re loading a DXF file into a CAM program. Many of the more complex vector entities, eg. Attrib, Table, Spline, Region, or 3DSolid, are not supported by all CAD packages. To ensure that your file is compatible with all programs, you’ll need to convert these into simpler entities like lines and shapes. By using a file converter such as Scan2CAD, you can extract the simpler elements like lines, polylines, arcs, circles and text.

What is DXF?

The DXF file format is a drawing interchange format used to transfer data between CAD programs. After all, its acronym, DXF, stands for Drawing eXchange Format. DXF is the most commonly used format for Computer Aided Design (CAD). Whereas DWG was designed as proprietary software, DXF is openly documented, and compatible with a much greater range of software packages. The collaboration-friendly nature of DXFs has made them ubiquitous, and in turn this ubiquity makes them a great medium for collaboration. If you’re not sure what software a recipient is using, just save your drawing as a DXF and you can rest assured that the recipient will be able to open it in their CAD program.

What is DWG?

DWG is the native file format for AutoCAD drawing files. The acronym DWG stands for DraWinG! A DWG file can store all sorts of image data, including images, geometric data, maps, photos, and more. It is a proprietary file format, which means that the specifications for DWG are not publicly documented. Programs like AutoCAD, IntelliCAD, CorelCAD, Adobe Illustrator and of course Scan2CAD can all read and write DWG files.

A drawing of a house, saved as a DWG file. DWGs store both 2D and 3D data, as well as a database of dimensional data

How to convert DWG to DXF

You can export the entire DWG drawing file, or selected objects within a drawing, as a DXF file. However, the conversion process varies depending on the CAD program you have installed on your computer. If you have AutoCAD, the conversion process is extremely simple.

Steps to convert DWG to DXF files using AutoCAD:

1. Open the DWG in AutoCAD
2. Hit ‘File’ the select ‘Save As’ to bring up the file saving options.
3. In the next dialog you can select DXF as the required output.
4. Select ‘Save’ to create your DWG file.

The process is slightly more complicated if you’ve received a DWG file from someone else, and you don’t have AutoCAD installed on your computer. Thankfully, Scan2CAD allows you to convert DWG files to DXF easily. With Scan2CAD users can view the latest DWG and DXF files with full fidelity, whilst also making use of its powerful editing capabilities. Conversion from DWG to DXF takes just five simple steps.

Steps to convert DWG to DXF using Scan2CAD:

1. Open your DWG file. By clicking the big, green ‘Open a File’ button.
2. Export the DWG to DXF by clicking the ‘Export’ button in the upper right corner.
3. Select your desired file format (i.e. DXF) and click Save.
4. That’s it! You’ve accurately converted your DWG to DXF.

The file will then be saved as a DXF in the indicated directory. Voilà! Now you have a CAD drawing file that you can load onto any CAD program.

Converting DWG to DXF in Scan2CAD

Online DWG to DXF converters

In addition to CAD programs and dedicated conversion software such as Scan2CAD, there are a number of online file converters which offer free DWG to DXF conversion. However, quite often, these converters turn out to be too good to be true.

There are many advantages to dedicated, local applications—such as batch conversion and post-processing tools—that online converters simply can’t replicate. Online tools also frequently impose limits on file sizes, making it difficult to convert complex files.

Worse still, converting your files using an online tool can put them at risk of being stolen—and can leave your computer vulnerable to being infected by viruses and Trojans. For more information, check out our guide to the risks of online converters.

Batch Converting DWG files to DXF

Scan2CAD offers the ability to automate all features of the software by utilising the Python API. This powerful API gives you the ability to replicate repetitive tasks and convert a large number of files in a few clicks. This is the perfect option for you if you have a large number of DWG files to convert to DXF.

Converting to and from different file versions

DWG and DXF files are versioned. About every three years, AutoCAD changes the DWG file format and older versions of the software become incompatible with the newer versions. Scan2CAD can read DWG versions as early as 2.5 and can save to any version from R12 to R2007-2010. As for DXF, Scan2CAD can read DXF pre-R14, as well as DXF R14/LT97 and later. You can select which file version you’d like to save as when you save your vector file.

You can also use Autodesk’s free file viewing software, DWG TrueView to convert your DWG file to a previous format. This function can be found in the “Save Drawing As” dialog box. Simply add your file into the DWG convert window, select the format you’d like your files to be converted to, and hit “Convert”.

Tips and tricks for DWG to DXF conversion

1. Learn which CAD elements your file converter supports.
When you load a DWG file in Scan2CAD, all layer and block information is lost. Scan2CAD only loads elements that it supports, which includes lines, polylines, polygons, polypolygons, arcs, splines, Bezier curves, polybeziers, circles and text. The same principle applies to all other CAD packages, so be sure to check the user manual before converting.

2. Define different DXF export options depending on your needs and requirements.
You can select whether or not to extract Bezier curves as splines, arcs or polylines, whether to include line width data, or attach a raster image. Another setting that may come in handy is how you group your vectors into layers, which can be done either by color layers or layer types.

3. Define the scale and units you want to use.
This will save you time later on when you try to edit the drawing in another CAD program. To do this, use the Vector Scale Settings dialog. You’ll be presented with three options: DPI scaling, Distance scaling or Geo scaling. You can then map a distance in pixels to an absolute measurement unit such as inches or millimetres. Finally, press Ctrl+Shift+S to save the scaling information before loading or merging the file.

4. Adjust the origin of the file.
If the DWG file was produced by another CAD program, chances are the default origin is not set to 0,0. This can lead to incorrect display problems. To fix this, simply hit Ctrl+Shift+Z before loading the DWG file to ensure that the correct 0,0 origin is set when the file loads.

5. Make sure all vectors are loaded.
This is another quick keyboard shortcut fix. Press Ctrl+Shift+E after loading the DWG file to ensure that the parameters are set to fully display all vectors that are loaded.

6. Manage your files properly.
Here’s a no-brainer. It’s always good practice to backup your files prior to doing any file conversion. You may accidentally overwrite the original file if you’re converting between file format versions, because the file extension will be the same for both versions. It’s also worth remembering that some data is always lost during file conversion, so if you need to convert a file multiple times, try to convert from the original where possible.

Scan2CAD is the market leading file conversion software. It can support more than 20 different file types and comes with a full raster and vector editing suite. Check out all of Scan2CAD’s features here – you can try all of them for free with our 14-day free trial. Click on the image below to find out more.

“I’ve lost the scale information after converting my file to DXF”

The first thing to consider is which type of file you converted to DXF. One of the most common uses of Scan2CAD is conversion from PDF to DXF. As PDFs can be opened universally, images saved under proprietary CAD file types are often converted to PDF before going on to be converted to DXF. The trouble with this approach is that PDFs only store print dimensions, and discard the scaling information from CAD software. PDFs only preserve the relationship between objects (e.g. point A is 20 pixels away from point B). This problem is compounded by the fact that DXFs don’t define physical dimensions using measurements like millimetres or inches.

Define the scale of a DXF file with Scan2CAD

To solve this issue, you’ll have to set the scale again after DXF conversion. Scan2CAD offers three different ways to add scale to your DXF image: DPI, distance or geo scaling. Check out this article in our User Manual for detailed instructions on changing the scale on a vector image.

If you’re converting a PDF file into DXF, you may also lose hatching information. This is because PDF files stores the hatch as a pattern fill, a feature which isn’t supported by DXF. This is also easy to fix post-conversion – just map the resulting value into a hatch entity.

“I want to convert from JPG to DXF”

It’s difficult to extract a clean vector from a pixelated image

Although JPG is one of the most popular image file formats around, it’s not always ideal for conversion to vector formats such as DXF. JPG is a compressed file format, which means that some information is discarded in the interest of saving file space. The downside, however, is that JPG images are usually very distorted when zoomed in. This is an even greater problem for images which could be 2 color (black and white) for example, line drawings for part schematics, or architectural floor plans. This is because JPGs don’t save these drawings in black and white, but as grayscale images, with blocks of pixels in varying shades of gray. Conversion software is unable to group together these pixels, and thus distinguishes the black parts and gray parts as separate vector entities.

We always recommend using a high quality image format like the TIFF file format if possible, which is the standard file format used to exchange raster images between programs. TIFF, or Tagged Image File Format, is commonly used among graphic artists and photographers, as well as in the printing and publishing industry. PNG and GIF formats are also acceptable for images with few colors—to learn more about GIF to DXF conversion click here.

Struggling with converting your JPEG file? Don’t despair—check out our ultimate guides to converting JPEG to DWG and JPEG to DXF to help tackle your vectorization issues!

“I can’t import my DXF file”

Not every DXF file is the same. Every third version of AutoCAD comes with a new version of the DXF file format. Think of it like MS Office – you couldn’t open a Word 2016 file in Word 97. CAD software is much the same – whilst backward compatibility comes as standard, an older version of your software won’t necessarily be compatible with more recent versions of DXF. This issue is especially common when transferring files to a milling machine. It’s good practice to save the file in AutoCAD 2000/DXF format, as this avoids compatibility issues. You can use Scan2CAD to convert between versions of DXF, with support for all versions back to DXF 2000.

When converting a DXF file to an older version, the conversion program either strips out information that is specific to the current version or converts it to another object type. Always remember that converting a drawing to an earlier release format may cause some data loss. To avoid overwriting the original file and losing this data altogether, remember to save the file using a different file name.

“I’ll design my drawing in one CAD program and export it to another using DXF format”

Often, a designer will forget to check the requirements of the output CAD program. This is a common problem if your converted DXF file is meant for manufacturing. DXF files support hundreds of entity types such as hatches, blocks, tapered polylines, TrueType fonts, multi-line text, splines, regions – and many, many more. All of these are very fancy entity types. (For more info, check out our overview of the DXF file format.) In contrast, simple manufacturing formats only contain X-Y coordinates and shapes. It’s therefore very important to make sure that your DXF file contains the necessary information for its intended use.

“It doesn’t matter which file converter I use, they’ll all give me a usable DXF file”

Not all file converters are created equal. It’s tempting to go for an online converter – after all, it’s free, and there’s no need to download any software. Unfortunately, the output is unlikely to be good enough for use in CAD. Often, dashed lines, arcs, and curves will be converted into a series of short straight lines instead of the appropriate line type.

There’s a right way to convert to vector – and a wrong way.

Not only is the choice of converter important, but choosing the right image is key too. You know what they say – “garbage in, garbage out” – and it’s especially true when it comes to file conversion. Make sure to clean up your image before conversion – a few quick retouches can work wonders, and give you vastly improved results. Want to know more about getting rid of speckles, getting crisp lines, and fixing that annoying skew? Head over to our Ultimate Guide to PNG-to-DXF Conversion for all this – and more!

1. Change your raster image’s resolution

The rule of thumb is that lines should be 4-5 pixels thick. You can zoom into your image to check. For best results, we recommend an image resolution of at least 300 dpi. If your image has a particularly low DPI you can increase the scale in Scan2CAD (by clicking Raster Effects > Scale).

2. Reduce colors

In an ideal world, all images that you’re converting to vector would be monocolor (black and white). This gives you the clearest possible contrast between the background (typically white) and the foreground (typically black – these being the elements you wish to vectorize).

Commonly, however, even an image that appears black and white may be formed of hundreds of colors on the grayscale.

Reducing colors is important because a conversion engine will detect every shade as a separate region in the image. Therefore, if you converted an image with complex colors into vector then you will have a large number of separate vector entities in your image, rather than smooth, solid lines, text, and polygons.

Of course, it is common that you wish to keep multiple colors in your image (for example, maps containing several colors). For these images, reducing to black and white is likely to be inappropriate – instead, you should reduce the image to as few colors as possible whilst still maintaining the necessary detail of the image. Scan2CAD comes equipped with a function to reduce colors automatically – it will map all colors in an image to a number of colors of your choosing. Learn more about editing raster colors here.

If you zoom into the rectangular marked part of the image on the left, you can see that ‘areas’ of the same apparent color are made up of pixels of many similar colors. To produce areas of consistent color we can use the Scan2CAD Segmentation tool. This will group areas of adjacent pixels of similar color/intensity into zones of color that best represent the original image. Here, we have segmented to just 16 colors to illustrate the process.

3. Clean the background

In the same vein as color reduction, you may need to clean your background even if it looks clear when zoomed out. If, for example, you have an image with a white background, you may have distortion bleeding into the white background. If you do not remove these distorted areas prior to vectorization, you will convert them to vector. In these cases, the fastest way to clean the image background is by reducing the colors.

Simple or Adaptive Threshold in the Raster Effects Menu will do the job for black and white images. The color segment tool will also achieve this for images formed of multiple colors.

4. Negate the image

This raster effect can be applied if you’ve got a negative image (white lines on black). Scan2CAD assumes that all images are positive images (black lines on white), so you may end up having very different results after vectorization.

Black on white or white on black?

5. Thicken lines

Gaps or broken lines are especially common when scanning pencil-drawn sketches or faint prints. Thickening the lines/pixels should be done with care since using this tool too liberally can result in unwanted joined lines or touching entities which would deteriorate the quality of your vector.

Even a beginner can easily clean up an image using the sliders and preview windows in Scan2CAD

6. Remove speckles

There are two ways to do this: either by using the Despeckle Tool or by manually erasing them using the Freehand Erase Tool. With the former, you can define how large the speckles are (in terms of pixels) and any marks of this size or larger would be automatically erased.

7. Remove holes

Just as there are stray pixels to remove, there are also gaps to fill in solid objects. Holes usually appear when the scan is too faint. The steps really are self-explanatory—just click Raster Effects > Clean > Remove Holes.

8. Smooth the image

How closely do you want to trace around the edges of your raster image? The Smooth Raster Effect removes “hairs” on your image, which are usually a result of scanning at too high a resolution, or when scanning a pencil-drawn sketch. The scanner then picks out details that aren’t usually visible by the human eye. If left un-smoothed, the conversion engine will draw vectors at these loose ends.

Notice the bumpy lines around the edges of the shape—these must be smoothed out in order to create a precise vector representation of your raster image.

9. Deskew the image

If images are scanned at a slight angle, what appears as straight lines in the raster image won’t be converted into clean, straight lines in the vector. Scan2CAD comes equipped with deskewing tools to fix these issues. However, heavy use of deskewing tools can have a negative impact on image quality, so if your image is very heavily skewed, it would be better to rescan the image (if possible) for optimum results.

10. Adding a border

Conversion engines cannot vectorize shapes that are right at the image edge. Luckily, this is quick to fix: simply select Raster Effects Menu > Border. Then, insert a suitable border width in pixels. Of course, if your scanned image has a large border or if you’ve inserted a border with too large a width, simply cropping the image would remove the unnecessary border.

Often times, it is necessary to apply few raster effects on the same image. Here’s an example. The higher zoom level reveals that the image is simply a series of irregular disconnected dots. We can improve this by thickening the pixels, removing speckles and holes and finally smoothening the edges before vectorization.

To learn more about each of these effects, check out our comprehensive user manual. On the other hand, if you’re curious and just want to test each feature out, then you can—you don’t even have to read the instructions! It’s easy to click on them and see how each feature works with your very own eyes.

All of these raster effects can be found in the Scan2CAD toolbar

1. Project Collaboration

In order for engineers, architects, graphic designers and the like to work alongside each other – and with their clients – it is integral that common ground be established with regards to file formats. Native to AutoCAD, DWG files are widely used across the design industry, and are operational on almost any top CAD platform, ensuring that individuals at any point in the design process or supply chain are able to open and work on files in their preferred program.

Even clients who are not looking to edit the files, or those who have no desire to invest in CAD software, can participate effectively: it is possible to both view and edit DWG files for free without AutoCAD, using software such as A360 Viewer by Autodesk, DWG TrueView, or AutoCAD 360.

Some examples of CAD software that can be used to view and edit DWG files

2. Vector Quality

Those familiar with CAD will know that, due to their nature as vector images, DWG files are scalable, retaining their quality at any scale.

Converting to a DWG from any raster format, such as BMP, not only brings about a huge improvement in quality, but is necessary for the files to be edited and worked upon. For those clients who do, inevitably, send over files from other contractors in raster versions – possibly to combat many of the perceived problems caused by sharing large files – it is essential that you have the resources to convert them into vector for the purposes of CAD.

Software such as Scan2CAD resolves this issue; through automatic, high quality conversion, the involvement of multiple working parties need not hinder the design process. Rather, it aids the effective combination of skill sets to enhance results.

3. From Paper to CAD

The ability to convert images from JPG, PNG or TIFF to DWG—or to convert from PDF to DWG—opens up a wide array of potential for those who begin the design process by putting pencil to paper.

Sketches can be transformed into vector lines, forming the basis of a CAD drawing. While these files may require some post raster-to-vector conversion clean up, this process is much more efficient than re-creating the image from scratch in CAD.

Converting to DWG is therefore the ideal solution for people who work both on paper and in CAD software, offering a level of integration and flexibility that allows for less time wastage and a more streamlined design process.

4. 2D – 3D Potential

Designers can turn their sketches and concepts into reality

One of the greatest benefits of converting to DWG is the ability for both two- and three-dimensional files to work in unison, increasing the potential uses for designs beyond their original scope.

One practical application of this might involve a graphic designer producing a 2D logo, which is subsequently imported into CAD by a product designer to use as a 3D design. This provides developers with the flexibility to utilize the design in different ways: to emboss onto a product, for example.

DWG files can also be opened in Google’s Sketchup packages, allowing 3D models to be produced quickly and accurately from CAD drawings.

5. Situation Appropriate

We’ve already had the DWG vs DXF debate, but the conclusions we drew are certainly relevant here. DWG ensures that all specialized data remains present, which cannot be guaranteed when exporting to DXF.

Equally, while there is a limited difference between the file sizes produced by DWG and DXF, it’s worth noting that DWG files are stored slightly more efficiently, making them optimal for the sort of collaboration discussed above.

Scan2CAD v9 offers the facility to import and export DWG files. Not only does it offer improved vector conversion, but with its wide range of features, it’s the ideal tool for all your image editing and conversion needs. Try out all the features of Scan2CAD with our 14-day free trial.

This technology is employed for a variety of applications, such as data entry of documents, automatic number plate recognition, digitisation of printed documents in Google Books, and even beating CAPTCHA anti-bot systems!

In the CAD world, OCR plays a crucial role in converting raster sketches into editable CAD drawings. In this article, we’ll go behind the scenes to understand how OCR works!

There are two different techniques (or algorithms) in optical character recognition: pattern recognition and feature extraction, and each technique is worth looking at in a little bit more detail.

Pattern recognition

The computer matches the text with its dictionary of characters.

Using this technique, the computer tries to recognize the entire character and matches it to the matrix of characters stored in the software. As a result, this technique is also known as pattern matching or matrix matching. The drawback of this technique is that it relies on the input characters and the stored characters being of the same font and same scale. Check out the photo on the left — it’s the first font created in the 1960s for OCR — the OCR-A — where every letter had the same width. All cheques were printed using this font to allow banking computers to process them!

Scan2CAD applies Neural Networks to the task of pattern matching. Neural networks work in an analogous way to the human brain. They learn to recognize shapes and patterns from a range of examples. Scan2CAD includes a feature allowing the user to train their own Neural Networks to recognize font styles unique to their drawings.

Feature extraction

Letter A = two angled lines + one horizontal line

This one is a much more sophisticated way of spotting characters. It decomposes characters into “features” like lines, closed loops, line directions and intersections.

Let’s take letter A as an example. If the computer sees two angled lines that meet at the top, and both lines are joined together by a horizontal line in the middle, that’s a letter A.

By using rules like these, the program can identify most capital ‘A’s, regardless of the font that it is written in.

Pre-processing to improve text recognition

In order to recognize text effectively, the software must pre-process the image using techniques such as:

• De-skew – Titlting the image a few degrees in order to make the lines of text perfectly horizontal or vertical
• Despeckle – Removing spots and smoothing the edges of the characters
• Character isolation – Split touching characters that may have bled into each other
• Layout analysis – Identifying text positions, columns and paragraphs
• Line removal – Removing overlying lines or boxes

More sophisticated software conducts post-processing steps as well. The software would match the transcribed output to a lexicon (a dictionary of allowed characters), or conduct near-neighbor analysis to identify words that are usually seen together (for example, the phrase “living doom” will be automatically corrected to “living room”, since the word “living” and “room” often occur together).

OCR Technology in Scan2CAD

Scan2CAD is a raster-to-vector conversion engine. It converts images into vector drawings, so that it can be edited using other CAD/CAM and CNC software. Since many images contain text, OCR is a vital part of the raster-to-vector conversion process. Unlike many CAD image converters, Scan2CAD converts text in raster images into proper editable vector text strings, instead of constructing it out of individual vector entities (such as lines and arcs.)

You can help ensure that the text on your raster image is ready for vectorization by following Scan2CAD’s Raster Text Quality Checklist.

On the left is CAD text that’s converted using Scan2CAD. On the right is text converted using another software, that isn’t reassembled into the logical sentences very accurately.

With OCR, there’s no need to manually retype the labels, and these text vectors are easily editable too. In many cases, all you have to do is click “OCR” on the ribbon at the top of your workspace, and voila! Try OCR for yourself using our 14-day FREE trial of Scan2CAD.

Further reading:

• Best practices for improving OCR accuracy
• Convert handwritten notes into Word documents
• Build your own OCR application using kNN

Before you resort to the standard email sharing, read our guide to sharing DWG files the smart way.

Does the recipient need to edit the DWG drawing?

Before you hit “Send”, it’s worth taking a moment to answer this question: what is the intent of sharing the file? If it’s not important to convey the actual CAD geometry, it is easier to save and share the drawing as a PDF or TIFF file.

PDF and TIFF convey a picture of what the CAD data looks like, with PDF saving the drawing using vectors, and TIFF doing so in pixels. This is usually sufficient if you’re just sharing the drawing for review and markup. On the other hand, DWG drawings are the better option if the recipient needs to take certain elements (or blocks) and apply them to other drawings.

Sharing DWG files using a shared drive

If you work in a larger company, it’s usually best to share DWG files to a shared folder in your company network, or using cloud storage services like Drive and Dropbox. This way you can collaborate and work simultaneously by using file references. Of course, there are several best practices to this sort of file management, such as limiting users who can modify the files, keeping backups, and maintaining file-naming conventions. This method of sharing files can get a little messy, especially when multiple collaborators are working on one same project and sharing many versions of the file back and forth.

AutoCAD and AutoCAD LT also come with a cloud service called Autodesk 360, so you can share the file within the program itself. It works like Office 360 or Google Docs – you can invite collaborators or clients via email; whoever is invited can view or edit the DWG file from their web browser or mobile device.

The AutoCAD 360 File Manager shares a similar interface with Google Drive

Sharing DWG files using data management applications

If you’re looking for more robust solutions for collaboration, tailored to your needs, you should consider CAD data management applications. These are complete software solutions that you can use to share files, organize design data, manage documentation, and track revisions. To name a few, there’s Vault by Autodesk, Project Wise by Bentley, Teamcenter by Siemens, and Enovia by Dassault Systèmes.

Here’s a screenshot of Project Wise on a Mac. There’s a DWG file management system for every major industry

To round things up, here are three top tips for sharing DWG files.

1. Be careful when sharing referenced drawings

AutoCAD allows you to attach one drawing file to another using external references or xref. This allows you to coordinate your work with others – you can reference another designer’s drawing to yours and keep up with any changes he makes). At the same time, you can keep the names of your layers, text styles and named elements in your drawing separate from the referenced drawings.

The only thing to note when sharing files with xref is that you need to bind the files first, or use the e-transmit command.

2. Manage your DWG file size

There are few commands you can use to get rid of references that bloat your file size. Here are the AutoCAD commands for making DWG files smaller: AUDIT, PURGE, -PURGE AND OVERKILL. Just be careful you aren’t removing things you actually need!

A relatively simple drawing should be about 10MB in file size.

3. Save reusable content as blocks in separate DWG files

It is common to save reusable content as blocks, so that you and your colleagues can use them repeatedly and maintain your drawing standards. For example, architects can save doors and windows as blocks. Here’s a tip: share these blocks with your colleagues.

Here are a few popular file conversions involving DWG; we’ll explain when and why someone would require such a file conversion, and offer a few pieces of advice for the process.

Convert DWG to DXF—and vice versa

The first most common scenario is to receive CAD drawing files in DXF file format. The DXF file format is a drawing interchange file, and is often used for sharing drawing data between CAD programs.

You can usually load DXF files directly into any CAD program, however, if your CAD program doesn’t support DWG, you’ll first need to convert it to DWG using a file converter like Scan2CAD. It’s an extremely simple process, which involves opening the DWG file in Scan2CAD and saving it as a DXF.

There are two other CAD file formats you may come across – DXB (a binary file used for plotting) and DWF (a publishing file format used to distribute designs over the Internet). The steps you’d follow during conversion are the same. Do note that the DWF cannot be fully recovered or converted into a standard DWG drawing. The converted output will not have the full prevision of the original.

When converting between CAD file types, you must check what CAD object types are supported by the conversion software. You’ll want to make sure it preserves all of the entities in your drawing, such as arcs, polylines, true type fonts, Bezier curves, embedded images, etc.. Also, don’t forget to define the treatment of these entities, for example, Scan2CAD allows you to choose whether to convert curves into Bezier splines or multiple arc segments, depending on your CAD software requirement.

Convert DWG to PDF

If you have a DWG drawing file that you’d like to share with your colleagues, collaborators or peers online, PDF files are the way to go. Everyone can view PDF files using free file viewers, and they’re easy to annotate. You can convert DWG to PDF from within AutoCAD. A feature that will come in handy during DWG to PDF conversion is the ability to include metadata (title, keywords, add bookmarks, etc.), so that your PDF is searchable and easily indexed.

Convert PDF to DWG

Let’s consider the reverse scenario – receiving PDF drawings. PDF files are read-only drawings, so it is not suitable format if the recipient needs to edit the drawing directly. In order to edit the file, you’d first have to convert it to DWG format.

The first question to consider when converting PDF files to DWG is whether the PDF file contain raster or vector information. Vector information is easy to extract, raster information less so. In the latter case, the conversion software has to convert images to vector format first, which brings us to the next conversion process.

Lots of Scan2CAD’s users use DWG/DXF files as an intermediary

Convert image files to DWG

This file conversion is common when you have a hard-copy drawing (on paper!) that you’d like to digitise. By scanning and converting the sketch into DWG format, you can reuse elements of the drawing and save time producing the drawing from scratch. This is the hardest type of conversion of all (from the computer’s perspective), as it involves tracing the image and replicating it with new CAD entities. This process is called raster-to-vector conversion, or image tracing.

A few tips here: clean up the image as much as possible, experiment with a couple of vectorization settings, and check the vector output thoroughly after conversion. Head over to our ultimate guides to learn more about converting JPG, PNG and TIFF files to DWG.

After converting the image to DWG, you can edit the vector using Scan2CAD’s complete suite of vector editing tools

Convert DWG to an earlier format

Say you receive a drawing from a vendor in DWG 2013 file format, but you’re running AutoCAD 2010 on your computer. To open the drawing, you’d need to convert the DWG file into an older version of DWG. Scan2CAD can handle convert DWG files between versions R2000 through R2014.

Scan2CAD can handle all of the file conversions mentioned above. It allows you to convert any file into DWG without the need for AutoCAD, and the resulting file can be used with AutoCAD or any CAD program just like any other drawing file.

You can try out Scan2CAD’s full range of features completely free for 14 days.

You could also elect to purchase tokens under the Autodesk Flex program that let you use AutoCAD (or any Autodesk software) for a day. But given Autodesk requires you to buy the tokens in bulk, with the minimum number of tokens available for purchase being 500, which amounts to $1,500, this would still be an expensive alternative. (You can learn more about Autodesk Flex in our AutoCAD pricing article.)

Could there be another way? The answer is yes! And in fact, there are five of them. In this guide, we’ll show you five approaches that will open your world up to the various alternatives to viewing DWG without AutoCAD. Read on!

What is DWG?

DWG is a proprietary file format native to AutoCAD. The .dwg file format contains the data and metadata that describes and stores the content of 2D designs and 3D models. Typically, a .dwg file includes numerous sections, including a header, classes, object data (which includes graphical objects, such as lines, circles, and more, as well as non-graphical objects), and handles (also known as object maps). For more on what each of these sections is all about, click here.

As a file format owned by Autodesk, companies must seek permission in the form of licensing agreements if they wish to create software that can read or write .dwg files. Unfortunately, this means that only a few software applications support this capability. So, what programs allow you to view .dwg without AutoCAD?

Approaches to Viewing DWG without AutoCAD

As stated, you can select one of five main approaches if you wish to view DWG without AutoCAD:

1. Convert the DWG file to PDF
2. Conversion software
3. Software that can read or write .dwg files
4. View-only software
5. DWG-viewing applications on mobile

Approach #1: Conversion Software

Scan2CAD

The first on our list and – in our humble opinion – possibly the best is our very own Scan2CAD. Scan2CAD is market-leading software for conversion, vectorization, and image editing. Scan2CAD’s main feature is to convert image files into DWG (and DXF) – but it has a whole lot more. Not only can you use Scan2CAD to view DWGs and DXFs, but its complete image-editing suite also allows you to edit them. What’s more, you can try out Scan2CAD’s full range of features completely free for 14 days.

Scan2CAD especially stands out from other offline conversion software like Anydwg or Autodwg. That’s because its graphical user interface (GUI) features a workspace that displays the .dwg drawing in real time. While other software programs perform the conversion in the background, only allowing you to upload the .dwg file without offering you the option to view or edit the drawing, Scan2CAD definitely has a one-up over its competitors. It not only lets you view the drawing but also enables you to modify a few aspects of the drawing.

The Scan2CAD file-viewer interface

Pros of Scan2CAD

• The software enables you to view and edit the .dwg drawing
• Scan2CAD is fast – it seamlessly and speedily opens large file
• It lets you convert the .dwg files to .dxf or .cnc file formats
• You can use Scan2CAD to open and view a variety of file formats, including .pdf, .jpeg, .png, .bmp, .tiff, .dxf and, of course, .dwg
• Scan2CAD is available for free throughout a 14-day trial period

Cons of Scan2CAD

• Scan2CAD cannot be used to convert a .dwg or .dxf file to .pdf

Approach #2: DWG to PDF Conversion Tools

The second approach involves converting the .dwg file to a .pdf format using online or offline converters. Some converters are free, while the rest require you to shell out a few coins. Regardless, this is a decent ‘roundabout’ solution to viewing .dwg files, albeit indirectly. In fact, most of these tools do not let you preview or view the .dwg drawing. Instead, they only allow you to upload the file, upon which you have to hit the ‘convert’ button without previewing the drawing.

A quick Google search will reveal a bunch of free options you can use to convert your .dwg file, but please be wary of the common pitfalls of using these free online file converters. Besides the possibility of compromising the safety and privacy of your files, you’ll often find that these converters offer very limited functionality. Some of your file’s data may also get lost in translation, and the files cannot be edited once converted. If the converter converts your vector images to raster pixel-based files, you may lose quality as well – the more you zoom in, the more pixelated the image will be.

That said, a few reliable options exist. And as discussed more broadly in our article on the pitfalls of using free online file converters, the top 3 reliable and safe online file converters include:

1. Zamzar
2. Cloudconvert
3. Anyconv

If you already use Adobe Acrobat DC, however, you could make use of its ability to convert DWG files to PDF. Adobe Acrobat DC is a PDF solution that allows you to convert, sign, send and manage documents. It’s really easy to use, too – from Windows Explorer, simply locate the DWG file, right-click, and select “Convert to Adobe PDF.” With one click, you now have a PDF file that can be viewed by anyone with Adobe Reader.

Acrobat DC ensures that all layers, scaling options, and links are preserved. The content is tagged, too, so your file remains searchable. Another great benefit to converting from DWG to PDF is reduced file size. I converted a 1MB DWG file into a 330kB PDF – slicing two-thirds off the file size. However, this is only a viable option if you already have a pro subscription for Adobe Acrobat DC; prices start from $14.99 or £13.33 per month.

Need to convert back? Learn everything you need to know about converting your PDF file to DWG.

Approach #3: Viewer Software

If you opt for this third approach, you can choose between Autodesk products or tools developed and sold by other developers.

Autodesk Products

Autodesk develops and offers free tools that enable users to view 2D and 3D files. These tools include:

1. Autodesk viewer (online)
2. DWG Trueview (desktop software)
3. Autodesk Drive (free to use for existing subscribers who’ve purchased one of Autodesk’s products)

You can also use the AutoCAD web app and AutoCAD mobile app, though you have to pay a yearly subscription to access and use the latter. In contrast, you must have an AutoCAD or AutoCAD LT subscription to use the AutoCAD web app.

1. Autodesk Viewer

Autodesk Viewer is a free, cross-platform browser-based online viewer that supports more than 80 file types, including Autodesk’s very own .dwg. With this tool, you can view a large selection of 2D and 3D files, even those created using software outside Autodesk’s stable, such as SolidWorks. In addition to viewing the drawings and models, Autodesk Viewer lets you measure, mark up, review, and share.

Pros of Autodesk Viewer

• It is a cross-platform tool: it works on Windows, macOS, and Chrome OS
• Autodesk Viewer supports more than 80 file types, including .dwg, .step, .dwf, .rvt
• The tool works with around 15 Autodesk products, including AutoCAD, 3ds Max, Fusion 360, Revit, InfraWorks, BIM360, Civil 3D, Maya, Formit, Inventor, Navisworks, Netfabb, Character Generator, Eagle, and Tinkercad
• Autodesk Viewer is free
• The support for markups, annotation, and drawing tools facilitate collaboration and fast feedback

Cons of Autodesk Viewer

• Autodesk Viewer still ties you to the Autodesk ecosystem

2. DWG TrueView

Autodesk DWG TrueView is a free desktop software that allows you to view, review, measure, and share 2D and 3D files. In addition, this tool lets you convert .dwg files to ensure they can be opened using older versions of AutoCAD. However, unlike the Autodesk Viewer tool, DWG TrueView only supports two file types: .dwg and .dxf. Additionally, it only works with a few Autodesk products, plus it is only available on Windows.

Pros of DWG TrueView

• It lets you view, measure, review, and share .dwg files
• DWG TrueView enables you to convert .dwg files to ensure they can be opened by older versions of AutoCAD
• This tool is free

Cons of DWG TrueView

• DWG TrueView is only available to users of Windows OS
• It supports only two file formats

3. Autodesk Drive

To support collaboration, Autodesk offers Autodesk Drive, which is free to use for subscribers who have already purchased one of Autodesk’s products. This solution enables you to view, store, and share .dwg, .dxf, .pdf, Microsoft Office files, .rvt, and more. And as the data is stored in a cloud, you can access the design files on any device and from any geographic location.

Pros of Autodesk Drive

• It is free to use for existing Autodesk subscribers
• Autodesk Drive allows users to access and view design files using any device
• This tool supports multiple file formats
• It supports syncing of design files using the PC Connector software

Cons of Autodesk Drive

• Users must have an existing subscription to use it

Non-Autodesk Products

Autodwg’s DWGSee

DWGSee User Interface (source)

Developed and sold by Autodwg, DWGSee enables users to view, measure, modify, mark up, annotate, and print .dwg files. It also supports additional file formats such as .dxf and .dwf. What’s more, this solution can open raster image files saved using the .tif, .gif, .png, .jpeg, and .bmp file formats.

To use this solution, however, Autodwg requires you to purchase a lifetime license that includes a year’s supply of free updates. There are three pricing tiers:

Source: Autodwg

Pros of DWGSee

• It enables users to view, measure, modify, mark up, print, and annotate design files
• DWGSee supports the .dwg, .dxf, and .dwf file formats
• It can open raster image files
• DWGSee Pro users can export .dwg drawings as PDFs or raster images
• It works with the drawings saved using AutoCAD 2022
• DWGSee can save drawing files using different versions of .dxf or .dwg file formats

Cons of DWGSee

• It is not a free offering

If you already use CAD software, there’s no harm in checking whether the CAD software that you’re familiar with handles DWG files. Most of the major CAD software applications can open, view, and share DWG files. A few examples include:

1. DraftSight
2. IntelliCAD
3. CorelCAD
4. Sketchup
5. Microsoft Visio
6. Adobe Illustrator

Due to the proprietary nature of the DWG format, you may struggle to find software that will let you edit the files themselves, however.

A few examples of CAD software that can be used to open DWGs

Approach #5: View DWG Files on Mobile

Companies are jostling to tap the growing worldwide smartphone market, with projections showing that by 2025, there’ll be 7.33 billion smartphones, up from 6.37 billion in 2021. So, they are increasingly developing solutions that cater to smartphone users. Companies in the CAD software market are not being left behind. And with the mobile phone applications they have created, you, the user, can view DWG files on mobile. Our roundup of the various apps you can use to view CAD files on mobile lists five applications, namely:

1. ZWCAD Mobile
2. DWG Fastview
3. A360
4. Onshape 3D CAD
5. eDrawings Pro

Nonetheless, of these five options, you can only view DWG files on just three of them. These include Autodesk’s A360, ZWCAD Mobile, and DWG Fastview.

Parting Shot

You do not need to buy an AutoCAD license if your only intention is to view a DWG file. Instead, you can choose one of the five approaches described herein, some of which are free – either throughout the service life or for a limited period during a free trial. The different alternatives provide enhanced capabilities beyond merely acting as tools that enable you to view DWG without AutoCAD. For example, you can modify, annotate, mark up, or share drawings. What’s more, the alternatives also enable you to view designs saved using other CAD formats such as DXF and DWF.