Plotters have been use for many years, and these specialty printers are still Plotters are the perfect tool for producing precise output
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ĎA Degree In Thresholdingí
By Bruce D. Vallillee

I am sixty three years old, and over the 30 years I have spent in the reprographics industry, I have seen many changes. I cannot claim to have seen it all (that my years in this industry have taught me clearly). Running a small reprographics firm has meant offering almost 20 distinctly different services to insure survival. Each group of services and technologies requires its own specialist. I have often felt like someone who owns an auto repair shop, but is not an auto mechanic himself. Its an awfully frustrating feeling of helplessness.




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The one area where I finally cease to be overwhelmed is scanning. Scanning, they always told me was not meant to be as easy as plotting. Scanning is best left to the scanning professionals, they said. The only ones allowed to scan are the experts in multiple pass interactive 2D adaptive thresholding technologies (try saying that three times fast). Discoloring is a common effect as paper documents age. The problems is the ability to differentiate between the background and the foreground. This is compounded by the uneven discoloring across the page. An analog copier creates one level of exposure or contrast for the whole page, resulting in some areas that might be adequate, but the majority of the sections on the page producing an unacceptable image quality. Digital scanners have the ability to vary the contrast and level of exposure throughout the drawing, creating a more optimum image quality. This process is called thresholding. Generally the machine doesnít get it right on its own, and requires the user to set it interactively by viewing pre-scans on the screen, and adjusting thresholding, speckling and other controls. The scan time skyrockets as the drawing is fed into the scanner over and over again (multiple pass). Most scanners use area averaging circuits, creating a two-dimensional map of the image to determine exposure levels at various points across the page. Small areas of analysis are used to measure the amount of light reflection. Each pixel that reflects less light than the average reflection off the specific area represents the foreground, the remaining is the background. Vidarís new scanners claim to have introduced a smaller area of analysis, thereby supposedly creating a better image quality. Although the race now between scanner manufacturers is to create a smaller area of analysis, the problems inherent to this process are compounded.

Difficult matters associated with area averaging circuits are being addressed by some strange methods. One of the solutions adopted by most is to use greyscale. Besides substantially exploding the file size or creating unnecessary speckle, greyscale has not produced a solution.


Changes in the background that are common in most sepia originals, cannot be recognized adequately by area averaging circuits, resulting in most scanners losing part of the image.
Some months ago I saw an advertisement by Canon in WIRED magazine. I thought if color scanning can be simplified in this manner, there must be a user friendly solution for engineering scanners.

Plotters have been use for many years, and these specialty printers are still Plotters are the perfect tool for producing precise output

I found this solution in WideComís line of SLC836 large document scanners. WideComís solution meant doing away with area averaging circuits, and instead creating a mathematical curve to map the background. This resulted in not only better image quality, but also eliminated the need for multiple passes and interactive thresholding adjustments. Imagine optimum image quality with a single pass, and all I press is "ENTER" on my computer. Now I cease to be over whelmed by scanning.

WideComís thresholding technology does not utilize area averaging circuits, but instead maps the document background by creating a mathematical continuom, providing substantially better image quality. Plotters have been use Specialty printers are still Plotters are the perfect tool for Producing precise

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