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Flatbed Scanning Hints

CONTRAST, BRIGHTNESS for LINE SCANS
 
Normal Line ScanManual use of Brightness and Contrast controls is always necessary when scanning Line or 1bit Bitmaps. Another control, Threshold or the Cut-Off Point may be available in the software window in place of a Brightness control when scanning Line pictures.

Even though the scanning software has been setup to reproduce the art as a Line drawing, the scanner always sees the image initially as a Greyscale. Areas or edges of fine detail may actually cut through the middle of virtual pixels and the software will see these pixels with values other than just black or white. The scanning software will then have to make a decision – is the grey pixel to be black or is it to be white.

The result can often be controlled by using a combination of the Brightness and Contrast controls if that's all you have. While these controls will alter the greyness of the above mentioned virtual pixels, a Threshold Control will more easily allow the operator to control the point at which the software decides a grey value will either become white (RGB 255) or be recorded as black (RGB 0).

Accepting the picture at the top of the page as normal, study the detail changes throughout all 3 pictures on this page. If the operator has the controls that allow intervention during the scanning process, then decisions have to be made about the original and which, if any, are the more important areas of the picture - should some detail have to be lost or at least degraded.

The effect is not unlike the increasing or reducing of the exposure on film in a camera, but we cannot also vary the developing time as we can with photography.

NOTE: The best way to capture fine detail is to scan at the highest resolution the system will allow, or cope with. Resolutions of 2000+ pxl/Inch are not uncommon for quality work. Because software does the interpolating of recorded values, there is a limit to the enhancement which mostly depends on the device resolution - number of CCDs per inch.

Over exposed Line Scan
Increasing the Threshold will enhance the fine white detail in the black areas.
Under exposed Line Scan
Reducing the Threshold will preserve the fine detail in larger white areas

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