User Guide

Chapter 3
70 VRS User’s Manual
Simple Thresholding
Simple thresholding is fine for black text on white paper, but it is tricky when you
have a combination of dark and light text and lines, and dark and light background
surfaces on one page. Figure 3-30 shows a good example of this kind of document.
Figure 3-30. Color Scan of Original Document
A color or 24-bit image is an exact representation of how the original document looks,
much like a photograph of the original. A 24-bit image can contain more than 16
million different colors and is capable of showing all the shades, as well as the darkest
and faintest elements of a document.
It is important, however, to point out that while a 24-bit image can be converted to a
grayscale or a bitonal image, a grayscale or bitonal image cannot be converted to a
color image. Just as a photo taken on black and white film cannot be converted to a
color photograph, an image cannot be converted to color if that original color data
was never captured.
Like the color image, an 8-bit grayscale or 256-level grayscale image also looks like a
photographic representation of the original, but without the color. Because it can
display up to 256 gray levels, it is suited for representing documents containing
different shades of text. Black and white only document scanners capture the