In their advertisements and sales literature the large format scanner manufacturers all claim that their scanners are fast, easy and productive.
We must disagree. We receive hundreds of poorly scanned images every year which are totally unsuitable for raster to vector conversion. Clearly, the people who made these scans did not have a clue. If scanners are so easy and productive to use, why then the plethora of poor quality scanned images?
Essentially, there are three issues.
- Many users (and many large format scanner resellers) do not know what good scanned quality for raster to vector conversion is.
- Many users do not know how to go about achieving a good quality scanned image for raster to vector conversion.
- The large format scanner being used may be equipped with poor quality or difficult to use scanning software, which makes achieving a high quality scan much more difficult.
There is a need for basic training which shows the user what good scanned image quality is. Showing someone how to scan is pointless if that person does not know what they are attempting to achieve. Raster to vector conversion software requires sharp solid lines on a clean white background. It might sound easy enough but without zooming in to interrogate the scanned image, the result may be nothing of the sort. Learn to interrogate every scan you make.
Without some proper training, many new and even long-term users find large format scanning difficult, time-consuming and overly complicated. Many will accept the first result they get rather than persist in spending more precious time trying to get a sharper, cleaner, better image. Because time is money, the least skilled and competent are often tasked to do the scanning after only the briefest of introductions to the process. No quality scan will come of this.
Getting a Demo
All large format scanner manufacturers supply their own proprietary scanning software. None work with other scanners. You are a prisoner of the software supplied with your choice of wide format scanner.
We recommend that you examine the supplied scanning software with a critical eye. It is the front-end of every scanning solution that you will have to work with. Some scanning software programs are decidedly better than others for creating scans suitable for raster to vector conversion.
Getting the best system for your needs means looking at more than one large format scanner – and its software! As viewing more than one scanning system is usually a hassle for busy people, many will buy the first scanner they see if it is well demo-ed to them. It is tempting but try not to make this mistake! Given the competition in the scanner market, it is not difficult to arrange demos from rival suppliers. Try to make the time to do so.
Most large format scanner sales people have their own tried and tested demo routine into which they throw a few tricks calculated to impress you. It is important that you take charge of their demo. Do not let them use their drawings. Use the worst of your own drawings while trying to use the software yourself. As far as possible, turn their demo into a training session. Did you learn enough to use it alone in 10 days time?
Try to learn as much about scanning and scanned image quality as you can when you get a large format scanner demo. Tell the demo jockey that you want to scan drawings for raster to vector conversion. Ignore any who say "raster to vector conversion doesn’t work". Press them to provide the sharp, clean scans which they claim in their product literature. This is what you will need in a large format scanner for raster to vector conversion.
Most importantly, does the reseller understand scanned image quality? We cannot stress how important scanned image quality is. In scanning a monochrome (black and white) drawing for automatic raster to vector conversion, lines need to be sharp and well-defined against a clean white background. This can only be seen by zooming into the image, cleaning it up and making adjustments to the settings. How easy is it to zoom in?
Was the large format scanner salesperson able to show you how a dirty drawing can be cleaned up so that it has sharp lines which will vectorize well in a raster to vector converter like Scan2CAD? Was it an easy matter to get a better result? Did this require a lot of tedious and time-consuming rescanning? Or did the salesperson use an easier, cleverer way to do this?
Thresholding
Having a clean white background with well-defined, unbroken drawing detail is what one aims for when scanning for raster to vector conversion.
As a result, the main features we look for in scanning software are simple and adaptive thresholding, features which allow you to dynamically clean the drawing background while at the same time strengthening the foreground drawing detail. A number of packages offer this, including our own raster to vector converter, Scan2CAD.
Graphtec’s Scanning Master software has thresholding which it calls Intensity Correction. While it works well, it is made difficult to use by the software’s rocker mode. If the scan needs to be improved, you must typically zoom into a part of the image in order to see the effect of changes to the scan settings. To do this, Graphtec scanners must feed the document back and forwards through the scanner which shows the results in a very small and narrow on-screen window. It is a slow, outdated way of scanning.
Both Colortrac’s and Contex’s scanning software offer thresholding which is easier to use. However, Contex’s Nextimage software requires a prescan and a rescan and what you see in the final scanned image is not necessarily the same as what you saw in the prescan.
We think we have good reasons for recommending Colortrac’s ScanWorks software. Its “scan once, edit many” approach is different to and more productive than anything else we’ve used. ScanWorks requires just one scan, (unless you need to change the resolution). Thereafter, you can change settings and see the results dynamically in real-time without any need to rescan. There is no backwards-forwards rocker mode scanning, allowing you to create scans suitable for raster to vector conversion relatively quickly and easily (assuming that the original drawing is itself high enough quality).
For more information on thresholding, see Explaining the threshold – a vital setting for successful raster to vector conversion.
Other Considerations
There are other issues which you may want to consider, like image width, ENERGY STAR® compliance and price.
Large format scanners vary in width from 24″ (scans up to A1 / D-size drawings in portrait) to 56″ (scans A0 / E-size drawings in landscape). Most scanners are in the 36″ to 44″ range and can scan A0 / E-size drawings in portrait.
Most modern scanners now use instant-on LED illumination and are ENERGY STAR compliant. LED illumination and ENERGY STAR compliance do not affect image quality for raster to vector conversion. However, they do affect the speed with which you can walk up to a scanner, switch it on and scan. Left running, ENERGY STAR compliant scanners will go into a cost-saving sleep mode.
Large format scanners that use CIS technology generally cost less than CCD scanners. CCD scanners are better for high quality color scans, but are not necessary for scanning drawings for raster to vector conversion. Contex SD, Colortrac Ci and Graphtec CSX300 CIS-based large format scanners are the most affordable. As stated, it is the software which provides the sharpness and clarity needed for raster to vector conversion.
Some manufacturers / resellers include software for free, while others charge extra. Many manufacturers / resellers are now also including an on-site warranty in the price of their scanners.
Wrapping Up
Don’t get drawn in by sales hype: All current large format scanners have the optical resolution and speed required to create a scan that is suitable for raster to vector conversion.
Scanners that use CIS technology generally cost less than CCD scanners, and so are recommended if price is an issue.
Considerable thought needs to be given to the accompanying software. If the scanner you want to buy has poor scanning software, creating a suitable scan for raster to vector conversion will be more difficult and will take longer.
A way around poor scanning software is to use your scanner’s software to scan in grayscale, then use Scan2CAD’s simple and adaptive thresholding to turn the scan into a usable black and white image suitable for raster to vector conversion.
For further information on the latest large format scanners and to download a large format scanner comparison chart, see www.scanners4cad.com.
