TWAIN and WIA are standards for communicating between imaging devices (e.g. scanners) and software applications.

TWAIN

If you have a scanner and it is “TWAIN compliant”, you can use it to scan directly into any software application that supports TWAIN, like our Scan2CAD raster to vector conversion software. This means that after you scan, the scanned image will appear in the application already open.

When you scan using an application that supports TWAIN, the scanning dialog and the options it contains are specified by your scanner’s manufacturer (Canon, Epson, HP, Contex, Graphtec etc.) and will therefore vary depending on the type of scanner you have.

TWAIN scanning dialogs can be extremely comprehensive. For example, the TWAIN interface supplied with Contex SD and HD large format scanners is an exact replica of Contex’s NextImage scanning software minus the print, copy and color management components. If you have a Contex scanner and all you want to do is scan technical drawings, Contex’s free TWAIN interface will do everything you need.

“The word ‘twain’ is an archaic form meaning ‘two’. It appears in Kipling’s ‘The Ballad of East and West’ – ‘… and never the twain shall meet …’, reflecting the difficulty, at the time, of connecting scanners and personal computers. It was up-cased to TWAIN to make it more distinctive. This led people to believe it was an acronym, and then to a contest to come up with an expansion. None were selected, but the entry ‘Technology Without An Interesting Name’ continues to haunt the standard.” (From the Free On-line Dictionary of Computing.)

WIA

WIA (Windows Image Acquisition) is a Microsoft utility that is supplied as part of Windows. Like TWAIN, WIA allows you to scan directly with a “WIA compliant” scanner into any application that supports WIA or TWAIN – all TWAIN compliant applications like Scan2CAD raster to vector conversion software support WIA as well.

Unlike TWAIN, however, the scanning dialog that appears when you scan and the controls on it are variations on a basic Microsoft design. This means that the level of functionality and scanning control that are available in a WIA interface are less comprehensive than in a well-written TWAIN interface.

Colortrac large format scanners support WIA rather than TWAIN. If you have a Colortrac scanner we suggest you purchase Colortrac’s (excellent) ScanWorks scanning software rather than attempt to use the WIA scanning interface.

Which scanners support TWAIN and WIA?

To the best of our knowledge all desktop scanners support TWAIN and WIA, as do most modern large format scanners. For example, modern Contex and Graphtec large format scanners support TWAIN, and modern Colortrac scanners support WIA.

However, if you have an older large format scanner, it is unlikely to support TWAIN or WIA. In this case you will not be able to scan directly into TWAIN/WIA compliant applications such as Scan2CAD raster to vector conversion software.

If your scanner doesn’t support TWAIN/WIA and you want to get scanned images into a TWAIN/WIA compliant application you need to use the software supplied with your scanner to scan your drawings, save them as TIFF, BMP or similar, then load the saved scan into your application.

Alternatively, there is a German software program from SCP called EasyTWAIN that makes non-TWAIN compliant scanners TWAIN compliant so you can use them to scan images directly into your TWAIN compliant software applications. EasyTWAIN supports a wide range of older large format scanners.

Generally*, no.

Once you have scanned an image at too low a resolution, the damage has been done and the information you need in order to do a successful raster to vector conversion has been lost.

Increasing the resolution of the low resolution image won’t bring back the details of a shape, or separate two touching entities.

To take an example from a previous post:

Original drawing		Desired vectors
Scanned at good resolution: Circle looks like a circle		Scanned at too low resolution: Circle looks like a diamond

If you take the too low resolution image and simply double its resolution in a program like Photoshop, you will end up with this:

The circle still looks like a diamond – its shape has not been improved – but now each “step” in the diamond is made up of four pixels instead of just one.

The only way to increase the resolution of most low resolution images is to re-scan the original drawing using a higher resolution.

 
* There are some circumstances where you can increase the resolution of a low resolution image to give better raster to vector conversion results. I will examine these in a future post.

The logo below looks absolutely fine. It is clear and legible.

You may think you can just download it and vectorize it, but if you try to vectorize this logo, you’ll find it won’t work. Why?

The main reason is that it is too low resolution.

If you read the logo into our Scan2CAD raster to vector converter, into Photoshop or into any program that reads raster images, then zoom into it, you will see that although the image makes sense when viewed on the web, it doesn’t make sense when viewed close up.

For example, here is a zoomed in view of the “r” from the logo above.

The letter “r” from the logo above, zoomed in		Desired vectors

If you did not know this was an “r”, you could not say, this is an “r”. It doesn’t look like an “r”, it looks like a blob. There are not enough pixels in the “r” to adequately define its shape – for example, there are no curves. A raster to vector converter would be unable to create the desired vectors from it.

Web images are of necessity very low resolution.

Web sites are designed to be viewable on most peoples’ screens.

Like raster images, screen displays are made up of squares, or pixels.

Our web use statistics tell us that the majority of people visiting this web site are using screens with 1024 pixels displayed across the screen area and 768 down it. Most web site designs, then, are made up to a 1024 pixel width size or thereabouts.

As a logo on a web site normally takes up only a small portion of the web site’s design, it will be considerably smaller that 1024 x 768 pixels in size. The logo at the top of this page for example is 120 x 80 pixels.

The “r” is only a small portion of the 120 x 80 pixel logo – about 9 x 5 pixels. To get a good conversion of the “r”, you would probably be looking at it being made up out of about 150 x 200 pixels:

High resolution raster image with well-defined outline and curves

The bottom line is that images on the web are designed to look good on the web. An image that looks good on the web needs different attributes from an image that will convert well to vectors. Most specifically, an image on the web will almost certainly be too low resolution to convert.

The right resolution for raster to vector conversion depends on the drawing you want to convert. If you are vectorizing small details you will need a higher resolution than if you are vectorizing large details.

For example, let’s say you scanned the two drawings of circles below at the same resolution.

Original drawing: Large circle		Original drawing: Small circle
After scanning: Recognizable circle		After scanning: No circle shape

After scanning, the large circle is still recognizable as a circle. If you were to vectorize it, it would vectorize to a circle vector.

If you were to vectorize the scanned small circle however, it would not vectorize to a circle vector. Why? Because there is no circle there for the raster to vector converter to convert.

The pixels at this resolution are too large with respect to the size of the small circle to be able to represent the circle shape. In order to be able to vectorize the small circle to a circle vector, you would need to scan it at a much higher resolution so that it was represented as a circle on the raster image.

As a general rule, a resolution of 200 to 400 dpi will be enough to properly represent the shapes on most technical drawings. For small artwork such as logos, you may need a much higher resolution – 600 dpi, 1200 dpi or even more.

After you’ve scanned a drawing, you should zoom into your scan, look at it, and ask yourself the following questions:

1. Do the shapes on the raster image look like the shapes you’re expecting in the vector image?

Original drawing		Desired vectors
Good resolution: Circle looks like a circle		Too low resolution: Circle looks like a diamond

2. Are adjacent / concentric shapes separated by clear white space?

Original drawing		Desired vectors
Good resolution: Concentric circles completely separated		Too low resolution: Concentric circles touching

Original drawing		Desired vectors
Good resolution: Adjacent text characters and underlining completely separated		Too low resolution: Adjacent text characters and underlining touching

Note that touching adjacent or concentric entities can also be caused by scanning with an inappropriate threshold. See Explaining the threshold – a vital setting for successful raster to vector conversion.

3. Do curves look like curves? (Not staircases!)

Original drawing		Desired vectors
Good resolution: Curves look like curves		Too low resolution: Curves look like staircases

If your answer to 1, 2 or 3 above is NO, you need to re-scan your drawing at a higher resolution.

Low resolution raster images are one of the most frequent causes of poor raster to vector conversion results.

As stated in a previous post, raster images are made up of little squares called pixels.

The number of pixels per inch of a raster image is called its resolution. Resolution is measured in dpi (dots per inch). An image with a resolution of 300 dpi has 300 pixels along each inch. An image with a resolution of 600 dpi has 600 pixels along each inch, etc.

The term dots per inch comes from printer terminology – printers print dots. Because raster images are made up of square pixels rather than round dots, a more accurate term would be ppi, or pixels per inch. However, although the term ppi does exist, no-one uses it.

The resolution of a raster image is very important for raster to vector conversion because it determines how well the shapes on the image are defined. The better the shapes are defined, the better the raster to vector conversion will be.

For example, consider the curve below.

On a raster image, the curve must be represented by square pixels.

The images below show the pixel representation of the curve at lower and lower resolutions.

At the higher resolutions, the pixels are small and are able to represent the shape of the curve well. If you were to vectorize these images, you would get a vector curve.

As the resolution gets lower and lower, the pixels become too large to be able to represent the curve and no longer form a curve shape. If you were to vectorize these images, you would not get a vector curve, because there is no curve shape on the image.

If you want to do a raster to vector conversion, you must make sure that the resolution of the raster image you want to vectorize is high enough to adequately represent the shapes on your drawing. (But not too high – that’s a subject for another post!)

In my next posts I’ll be looking at what resolution is right for raster to vector conversion, how to tell if your image is too low resolution for raster to vector conversion and other resolution related issues.

If you want to convert a PDF file to CAD, you need to be aware that there are two types of PDF file, raster and vector.

Internally, the two types of PDF file are quite different. Converting them to a CAD file format such as DXF requires different processes.

If your PDF file was created by scanning a drawing, it will be a raster PDF file. A raster PDF file is essentially a raster image – usually TIFF or JPEG – held within a PDF wrapper. Because it is a raster image, it needs to be converted to CAD using a raster to vector converter such as our Scan2CAD product.

If your PDF file was created by saving PDF from a CAD program, it will most likely be a vector PDF file. Unlike raster PDF files, vector PDF files already contain vectors, although not in a format that most CAD programs can understand. To convert a vector PDF file to CAD you need a vector PDF to CAD converter such as PDF2CAD from Visual Integrity.

How to tell if your PDF file is raster or vector

Here are three ways to tell if your PDF file is raster or vector:

• Load your PDF file into our Scan2CAD raster to vector converter or the Scan2CAD Trial version.
   

  If Scan2CAD loads it in and the drawing is displayed, it is raster.

  If Scan2CAD displays the message “Scan2CAD found no raster images”, it is vector.

  Note that there are also PDF files that are vector but that contain raster images within them. In this case, Scan2CAD will load the raster images.

• Load your PDF file into Adobe Reader, then click on it.
   

  

  If nothing happens, the PDF file is vector.

  
  
  

  If the drawing is highlighted in blue when clicked on, it is raster.

  
  
  Note that this does not work in all versions of Adobe Reader.

• Load your PDF file into Adobe Reader, then zoom into it.
   

  

  If lines and arcs continue to appear smooth as you zoom further and further in, the PDF file is vector.

  
  
  

  If lines and arcs begin to look “stepped” as you zoom further and further in, it is raster.

  
   

For more information on PDF files, see our Scanners4CAD article
SCAN-TO-PDF: Benefits and Considerations.

If you are vectorizing curvy shapes such as contour maps, aerofoils, ship hulls or freeform artwork, it’s a good idea to set your raster to vector conversion software to convert them to a type of vector called a Bezier curve.

Bezier curves are a type of spline vector – a way of mathematically representing smooth, flowing curves. They were defined by Pierre Etienne Bézier (1910 – 1999), who was an engineer and designer at the French car manufacturer Renault for 42 years. Interestingly, Wikipedia states that although Bézier patented the Bezier curve, it is based on de Casteljau’s algorithm, by Paul de Casteljau. de Casteljau worked for rival French car manufacturer Citroën.

What makes Bezier curves so great?

First, they are a simple way of smoothly representing what you might call "irregular" curves. For example, take the raster curve below (black).

It is possible to represent a curve like this using a single Bezier curve, although if you vectorize it using our Scan2CAD raster to vector converter it will most likely be represented by several Bezier curves to keep the fit to the raster image tight. In this example, Scan2CAD has used three bezier curves (blue). The nature of the curves makes it easy for each curve to attach smoothly to the next.

It would be much more difficult to represent this irregular curve using arcs, which, with their fixed radii, are what you might call "regular" curves. To get a smooth representation of the curve using arcs, with each arc attaching smoothly to the next, you would need to use eight arcs (pink).

Second, once created, Bezier curves are very easy to edit. Each curve has a start point, an end point and two control points. The control points are attached to the start and end points by control lines. By manipulating the control points to change the angle and length of the control lines, you can very easily change the shape of the curve.

Bezier curves and CNC software

Although Pierre Bézier was heavily involved in CNC, even designing and producing an early milling and drilling machine, most CNC software does not support Bezier curves.

If you have Scan2CAD, this is not a problem as you can ask Scan2CAD to export the Bezier curves to the DXF file as a series of arcs or line segments, which your CNC software will be able to read. These arcs or line segments will not be as easy to edit as the original Bezier curves but they will retain their smooth fit.

Along with resolution, the threshold is the most important setting you need to choose when scanning a drawing for raster to vector conversion. Choosing the correct threshold can make the difference between raster to vector conversion success and failure.

Choose a threshold that is too low, and parts of your drawing will be missing from the scan.

Choose a threshold that is too high, and parts of your drawing will merge together.

In either event, valuable information is lost and you will not be able to produce a successful conversion.

Below is a video I’ve created that explains what the threshold is and how to set it.

You normally set the threshold at the time of scanning, using your scanner’s scanning software. On our Scanners4CAD large format scanner web site you’ll find information on the thresholding available in the scanning software from the three major large fomat scanner manufacturers:

Nextimage (Contex)
Scanning Master (Graphtec)
ScanWorks (Colortrac)

Free thresholding

If you scan your drawing in greyscale, you can also threshold it within our Scan2CAD raster to vector converter. Thresholding is included in the trial version of Scan2CAD, which provides free and unlimited raster editing.

DXF stands for Data eXchange Format. DXF is a vector image file type.

Unlike raster image file types such as TIFF and BMP which are compatible with most raster-based programs, vector image file types vary wildly. Any given vector-based program will probably have its own unique and exclusive file type. It will probably only read a handful of other vector file types – and probably some of these incorrectly.

Of the vector file types, DXF is the most ubiquitous, at least in the CAD world. Developed by Autodesk, it is designed for exchanging drawings between different CAD programs.

Our raster to vector converter Scan2CAD saves vectors as DXF. It uses a very simple implementation of DXF that can be read into, and edited in, all CAD and CNC packages that we know of, including all versions of AutoCAD.

This means that Scan2CAD can be used with any CAD and CNC program.

As the song says, “Let’s start at the very beginning, it’s a very good place to start” …

So what is raster to vector conversion (vectorization) anyway, and why do you need it?

If the following explanation sounds familiar, that’s because it’s based on my original explanation which I wrote back in 1995. The original has been copied many times – sometimes verbatim, sometimes edited, always uncredited – on other raster to vector conversion sites across the web!

A raster to vector converter converts a raster image to a vector image.

What is a raster image?

A raster image is essentially an image made up of a grid of little squares called pixels. Lines and arcs are represented by colouring the appropriate pixels.

Raster images are created when you scan a drawing, take a photograph with a digital camera or create an image in a raster-based software program such as Adobe Photoshop.

Raster images can be saved as various sorts of file including BMP, CALS, GIF, IMG, JPEG, PCX, PDF, PNG and TIFF. I will look at these file types in more detail in a later post.

What is a vector image?

A vector image is an image made up of vectors – mathematically defined entities drawn between coordinates.

Vector images are created by CAD programs and other vector-based software programs such as Adobe Illustrator.

Vector image file types include DXF, DWG, DGN, HPGL, SVG, EMF, WMF and PDF (which can contain raster images, vector images or both).

Why convert raster images to vector images?

You will probably be able to load a raster image into your CAD program – most CAD programs can import and display raster images. However, once you have imported a raster image into your CAD program you will find that all you can do is look at it or trace over it. You will not be able to make any changes to it.

This is because CAD and CNC programs can only work with vectors. If you want to edit a raster image in your CAD program or cut it in your CNC program you must first convert it to a vector image. You do this using a raster to vector converter such as our Scan2CAD program.

Once you have converted the raster image to a vector image and saved it as a vector file you will be able to import it into your CAD or CNC program and edit it just like any other drawing you have created using your CAD program.