Glossary.
1-bit color A system for creating raster (bit map) images
on a computer in which each pixel uses only one bit of
memory and disk storage. In 1-bit color, a pixel is either
black or white.
24-bit color A system for creating raster images in which
each pixel uses three bytes of memory and disk storage. In
RGB color, one byte is used by each of the red, green, and
blue components (channels) of a pixel.
8-bit color or 8-bit grayscale A system for creating
raster images in which each pixel uses one byte of memory
and disk storage. This produces 256 colors or shades of
gray, which is enough for a high-quality black-and-white
image or a low-quality color image.
additive colors Red, green, and blue are the additive
colors of film-based photography and digital imaging.
When red, green, and blue lights are mixed in equal
amounts, the result is white light.
aliasing In a digital image, the appearance of jagged,
“staircase” effects along lines and edges, especially diago-
nal lines. Aliasing is accentuated when the pixels in the
image are highly enlarged and visible to the viewer.
alpha channel In Adobe Photoshop software, the
palette where masks are stored.
analog-to-digital conversion The process of convert-
ing the analog information captured by a scanner or cam-
era into computer-readable form. The analog signal is
translated into digital numbers by a computer chip.
antialiasing The process of reducing jagged, aliased
edges by smoothing (gently blurring) pixels along the
edges.
archival paper A high-quality inkjet paper, usually
with a matte or semi-gloss finish, designed for pigment-
based inks. Images on this paper can be displayed behindnon-glare archival glass for many decades or more without
any noticeable fading.
artifact Any visible degradation of the details of a digi-
tal image caused by the methods used to capture, store, or
compress the image. A common form of artifact occurs dur-
ing lossy compression when bogus details appear near the
edges of objects. In other artifacts, bands of solid colors
appear in places that should exhibit subtle gradations.
banding An artifact that spoils the appearance of an
image’s subtle gradations of color and tone. In banding,
bands or blocks of solid color appear in place of gradations.
binary number A number that is the result of changing
information into computer-readable form. A binary num-
ber is composed of one or more single digits, each of which
can represent either one or zero. All information in a com-
puter is stored as binary numbers.
bit A single digit of a binary number, a quantity repre-
senting either 0 or 1.
bit depth The number of bits used to represent the color
of each pixel.
bitmap An image made up of rows and columns of pix-
els. Also called a raster image. Each pixel represents a spot
of solid color.
brightness (value) In digital images, numerical value
of a pixel that represents its brightness level from black to
white. In gray scale images it ranges in value from 0
(black) to 255 (white). In color images, it is a combination
of the values of each color channel. Brightness is one of the
three terms that are used to exactly describe a color (the
others are saturation and hue).
Brush An imaging software tool that paints colors or spe-
cial effects on a layer.
byte In a computer, an organized grouping of eight bits
of memory or storage. A byte is often used to represent the29 0789731207_glossary.qxd 4/6/04 2:16 PM Page 347