C-4
Appendix - C --- Scanner Terms
Gamut Transformation
Color Management System function, where out-of-gamut
colors are converted to colors within the gamut of the targeted
device, e.g., a printer.
Gamut
The color range scanable, printable or displayable by a device;
e.g., if some of the displayable colors are outside of the gamut
of the printer they cannot be printed.
GCR
Gray component replacement. A color separation setting used
on color photographs where cyan, magenta and yellow inks
are replaced by black ink (in a balance that would yield a gray
value). The advantages are a reduction in overall ink usage
and some increase in image detail.
Grayscale
A term for a black and white photographic image or a scanner
setting. Refers to the range of 256 gray tones that make up the
image.
Halftoning
The processes of offset printing and laser printing are intrinsi-
cally bilevel. However, these devices can reproduce a range of
tone levels by halftoning; e.g., an array of widely spaced dots
produces the perception of light gray, and an array of tightly
spaced dots produces dark gray. Halftone dots are usually
placed in a regular grid. In color printing it is conventional to
use cyan, magenta, yellow and black grids that have exactly
the same dot pitch but different carefully-chosen screen
angles.
Highlights
The lightest part of a picture--reproduced as white on the
screen or when printed.
Histogram
A bar graph representing the statistical distribution of Gray-
tones or colors in an image. Each column represents the num-
ber of pixels at that gray level or color.
HLS
A color space with the three variables of Hue, Lightness, Satu-
ration. See HSV.
HSV
A color space with the three variables of Hue, Saturation,
Value. Hue means color (as in the color wheel.) Saturation is
an indication relating to the richness or vibrancy of the color.
Value is a term best related to the intensity of light illuminat-
ing the object.
Hue
A named color. In discussions of color that relate to photogra-
phy, scanning, and printing, six hues are especially important:
red, yellow, green, cyan, blue, and magenta. These hues make
up every color we can see, and are the designated hues on
color wheels.
Hue is also a measurement of color that can be related by
pointing towards a certain color on the color wheel. Hue
indicates the relative redness, blueness, greenness, yellowness,
etc., of a color.
ICC
The International Color Consortium (ICC) was formed to ad-
dress the need for a common color framework. The ICC has
developed a standard device profile that contains information
about how various devices render color. This concept is sup-
ported by Apple (Colorsync), Microsoft for Windows 95, Sun
for Solaris, and by Silicon Graphics for Irix.
Image Editor
A program used to edit pictures to change colors, increase
detail, scale or otherwise alter the picture.
Indexed color
Indexed color (or pseudo-color) is the provision of a relatively
small number, say 256, of discrete colors in a colormap or pal-
ette. For each pixel in the image, the index number of a color
is then stored. When retrieving the image, a lookup table uses
the index to retrieve red, green and blue components that are
then sent to the display. In graphic file formats such as PCX of
TIFF, an indexed color image is accompanied by its colormap.
Interpolation
Using the interpolation method of resampling generates values
for points in between the actual pixels by looking at the sur-
rounding colors or intensities. In a scanner resolution is in-
creased beyond the actual number of CCD cells. As each line
of pixel data arrives from the cameras, new interpolated pixels
are added between original pixels. The added pixels enhance
line edge definition.
JPEG Compression
Joint Photographic Experts Group Compression. A method to
save storage space by compressing files. JPEG achieves a high
degree of compression by discarding non-important picture
detail.
JPEG
A compressed file format for images. Named after the Joint
