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A P P E N D I C E S
Glossary
8-bit Gray Image (Grayscale)
An image created using the 8-bit Grayscale mode. Each dot of the image is
allocated 8 bits of data, allowing a single dot to be expressed in one of 256 distinct
shades.
24-bit Color Image (Color, High Definition Color)
An image created using the 24-bit Color mode. Each dot of the image is formed by
allocating 8 bits of data to each of the red, green and blue (RGB) channels for a
total of 24 bits. Each channel can produce up to 256 colors, providing the potential
of approximately 16.7 million color tones.
Brightness
The amount of light in an image when it is scanned. Increasing the Brightness
setting makes the entire image lighter, and decreasing the Brightness setting makes
the entire image darker (p. 44).
Contrast
The degree of difference between the dark and light portions of a document being
scanned. Raising the contrast of an image tends to sharpen it, lowering the contrast
tends to blur it (p. 44).
Dot
The fundamental element of a letter, object or image. The number of dots per inch
(dpi) determines the resolution (or density) of a letter, object or image.
Diffusion Dither
One of the methods used to simulate tones in black and white images. First, the
darkness of the original greyscale image is checked and the mid-range tones are
judged to be either black or white. Then the difference between the original
density and converted density is calculated and black dots are dispersed randomly
over the entire image to simulate graduated shading (p. 28).
Gamma Correction
The process whereby variations in color tones from the output of monitors, printers
and other output devices are made consistent with the source (input) document.
In Plug-in Module CS-U you can use the gamma curve menu setting, or enter a
gamma value directly, to set a value to match the gamma value for your monitor.
Gamma values are expressed as numbers: 1 is the standard value, numbers lower
than 1 brighten the output and numbers higher than one darken the output.
A graph function, the Tone Curve (gamma curve), is also available in Plug-in Module
CS-U to make adjustments to gamma values (p. 42).
Gamma Curve
See the entry for Gamma Correction.