C-3
Appendix - C --- Scanner Terms
Color Balance
The visual effect of an image when the amount of
each color and the overall amount of color are bal-
anced.
Color bit depth
The simplest pixel has two options: black or white.
(A pixel with two choices is known as a 1-bit image,
or two raised to the power of one). Adding more bit
information increases the number of color options.
The number of potential color options for a pixel
is called color bit depth. For example a 4-bit pixel
would have 16 color options, and an 8-bit pixel
would have 256 color options, while a 24-bit pixel
would have 16,777,216 color options.
Color Cast
An image is said to have a color cast if its colors
are not true. A color cast will usually be described
by stating the particular color predominant in the
image, e.g., the grass appears to have a red color
cast.
Color Correction
To improve the color rendition. Correcting for, and
eliminating an unwanted color cast.
Color Management System
Color Management System (CMS) software in-
creases the accuracy of color interchange between
scanners, displays and printers based on proles
for each device. The CMS is a layer of software
resident on the computer that negotiates color
reproduction between the application and color de-
vices. The CMS performs the color transformations
necessary to exchange accurate color between
diverse devices. The Color manager needs access
to characterization data for the device. The format
and content of such device proles is standardized
by the International Color Consortium (ICC.)
Color Separation
Process of separating colors, in an image, into
primary color components for printing. Converting
an RGB color image into CMYK color image. Color
separation is a technical function during which criti-
cal settings such as GCR, black ink limit and total
ink limit are applied to the image.
Color Space
A color space is a particular language used to de-
scribe color. Examples of color spaces are: RGB,
CMYK, HSV, CIE LAB.
Contrast
The difference between the lightest and darkest
signicant areas in a picture. A picture with high
contrast has nearly white areas and nearly black
areas with sharp changes in brightness between
them. The picture seems dominated by stark light
and dark tones.
Density units
Photographers and printers measure transmis-
sion in base-10 logarithmic density units, where
transmission of unity corresponds to a density of 0,
transmission of 0.1 corresponds to a density of 1,
transmission of 0.01 corresponds to a density of 2,
and so on
Density
The light stopping ability of a lm. Density is in-
versely proportional to the amount of light reected
or transmitted by an image.
Device Dependent Color Space
For example RGB. A device dependent color
space, e.g., the same scan le will appear differ-
ent when viewed on different computer displays.
For example CIE LAB. A device independent color
space is one in which color values are absolute,
e.g., dened by CIE standard. CIE LAB is the
central color space in color management systems
(CMS) and is used to translate between different
device dependent color spaces such as scanner
RGB and display RGB.
CCD
Charge Coupled Device, CCD is the image sen-
sor in the scanner that converts light to voltages.
These voltages are converted by the scanner into
the image.
CCITT Group3
Standard runlength compression format used with
FAX transmission. It utilizes modied Huffman
coding to further compress the runlength num-
bers. Most scanner le formats are dialects of this
format.
CCITT Group4
Two-dimensional compression format, giving very
compact image les. Standardized by CALS (MIL
28002) and ISO-ODA for Drawing Archival and
Interchange.
CIE LAB
A device-independent color space specied by
CIE, used in modern color management software
to facilitate conversion of data from a scanner to a
display, or from a display to an output device.
CIE
Centre Internationale d’Eclairage (CIE) is an inter-
national organization that establishes methods for
measuring color. These color standards for color-
metric measurements are internationally accepted
specications that dene color values mathemati-
cally. The rst color space model, the CIE xyz,
was developed in 1931. CIE denes color as a
combination of three axes: x, y,and z. The two color
spaces released in 1978 are CIE Lab and CIE Luv.
The goal was to provide an accurate and uniform
reference of visual perception.
CMYK
The subtractive printing colors. Cyan, Magenta,
Yellow, Black.
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