Clean and Convert Your Raster Scans30 Jun, 2001 By: David Byrnes
Five raster-to-vector solutions speed up conversion of paper drawings to digital files
Scanning in paper drawings is the easy part. To convert the raster (bitmapped) images that result into vector graphics that you can manipulate in your CAD program, you need raster-to-vector software. Scanners capture drawing data in binary files. Service bureaus and large organizations with thousands of paper drawings typically use large-format document scanners from companies such as Vidar and IDEAL (see the hardware review of current models), but desktop scanners that costs about $100 work just as well to capture details or letter-size areas from larger documents. Scanning alone is rarely enough to generate satisfactory electronic drawings. At a minimum, you must clean up the scanned drawings, remove excessive speckles, and deskew the image so horizontal and vertical linework looks straight. Once raster images are clean, you can edit them. For example, you can rubbersheet a scanned contour mapstretch it over any number of points until the image ends up in an almost exact correlation with the real topography.
For some jobs, raster editing alone produces an image useful enough to attach to an AutoCAD drawing. AutoCAD Release 14 introduced the capability to combine raster and vector images in a single drawing, although you have to store the images in separate files. Sometimes, however, scanned and edited raster image files must be vectorized. This process literally turns a scanned image into a drawing file.
Today's scanners often print directly from the scan (scan-to-print) and offer the option of scan-to-file. To generate better-looking printed documents, they use error diffusion that adjusts the raster image. Unfortunately, image files with error diffusion are much more difficult to vectorize satisfactorily, and many people get turned off because of poor results.
The five software programs we review offer tools to clean up raster images, edit raster images more substantially, and convert the raster data to vectors that you can work on in a CAD program. Two programs are AutoCAD 2000i plug-ins, and the other three are stand-alone programs. They range in price from $249 to $3,900.
We invited eight raster-to-vector program vendors to participate. Autodesk, GTX, Rasterex International, Softcover International, and softelec sent in software. Hitachi wasn't able to get its software to us in time for the comparative review, but see the sidebar to the right for more on its new product.
In December 1999, we looked at an even dozen programs, all of which were capable of fully automatic raster-to-vector conversion. This time, one program (Autodesk CAD Overlay 2000i) doesn't offer automatic vectorizationbut that doesn't mean it's a poor choice compared with the other four programs. CAD Overlay offers an extensive set of tools for raster cleanup and editing. It simply takes a different philosophical approach to the vectorization side of the process. Surprisingly few of the programs have been substantially revised since we last looked at them.
One big change involves Rasterex's RxAutoImage COLOR PRO R5. Rasterex ended its relationship with Consistent Software, the Russian company that coded its software for the last decade, and licensed a different line of software from softelec GmbH in Germany. Yes, that's the same softelec that produces VPStudio. In other words, softelec GmbH is now in the curious position of competing with its own distribution channel.
How I tested the software
I evaluated the five programs on my aging 266MHz Dell Pentium II desktop machine with 128MB and SCSI peripherals. This system runs Windows NT 4, service pack 5.
As with previous reviews, I broke the desired feature sets into three broad categories: image cleanup, raster editing, and raster-to-vector conversion.
Image cleanup covers despeckling, deskewing, and other tasks that affect the image as a whole. Raster editing moves from the whole image to specific areas and includes raster object recognition and raster snap, raster layering, merging raster data into a single file, and rasterization.
Raster-to-vector conversion is the main course. The standard features I look for are the type of vectorization the software performs and advanced features such as text and pattern recognition. For a complete feature comparison table, see the features index.
Excellence in raster-to-vector software
This is a uniformly excellent batch of raster-to- vector software. Because vectorization isn't as necessary as in the past, all the programs have focused on their raster features. All do a good job, but softelec has worked on the error diffusion problems that many new scanners introduce and Softcover International virtually doubled its cleanup and raster-editing features.
I still don't like dongles. I believe that any form of copy protection inconveniences the legitimate user while doing nothing to stop illegitimate ones from using cracked software.
You won't go wrong with any program hereeach one has many strengths and very few weaknesses, as you can see from the minor quibbles I mention.
Reviewer's Report Card