Glossary

A P P E N D I C E S

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.