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adjacent cell selection A selection of table cells that share at least one boundary with
another cell in the same selection.
alias A shortcut for a command. For example, CP is an alias for COPY, and Z is an alias for
ZOOM. You define aliases in the acad.pgp file.
aliasing The effect of discrete picture elements, or pixels, aligned as a straight or curved
edge on a fixed grid appearing to be jagged or stepped. See also anti-aliasing.
aligned dimension A dimension that measures the distance between two points at any
angle. The dimension line is parallel to the line connecting the dimension's definition
points. (DIMALIGNED)
alpha channel Alpha is a type of data, found in 32-bit bitmap files, that assigns transparency
to the pixels in the image.
A 24-bit truecolor file contains three channels of color information: red, green, and blue,
or RGB. Each channel of a truecolor bitmap file is defined by 8 bits, providing 256 levels of
intensity. The intensity of each channel determines the color of the pixel in the image.
Thus, an RGB file is 24-bit with 256 levels each of red, green, and blue.
By adding a fourth, alpha channel, the file can specify the transparency, or opacity, of each
of the pixels. An alpha value of 0 is transparent, an alpha value of 255 is opaque, and values
in between are semi-transparent. An RGBA file (red, green, blue, alpha) is 32-bit, with the
extra 8 bits of alpha providing 256 levels of transparency.
To output a rendered image with alpha, save in an alpha-compatible format such as PNG,
TIFF, or Targa.
ambient color A color produced only by ambient light. Ambient color is the color of an
object where it is in shadow. This color is what the object reflects when illuminated by
ambient light rather than direct light.
ambient light Light that illuminates all surfaces of a model with equal intensity. Ambient
light has no single source or direction and does not diminish in intensity over distance.
angular dimension A dimension that measures angles or arc segments and consists of text,
extension lines, and leaders. (DIMANGULAR)
angular unit The unit of measurement for an angle. Angular units can be measured in
decimal degrees, degrees/minutes/seconds, grads, and radians.
annotation scale A setting that is saved with model space, layout viewports, and model
views. When you create annotative objects, they are scaled based on the current annotation
scale setting and automatically displayed at the correct size.
annotational constraint Dimensional constraint used to control the size of the geometry
as well as annotate the drawing.
1598 | Chapter 51 Glossary