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adaptive sampling A method to accelerate the anti-aliasing process within the bounds of
the sample matrix size. See also anti-aliasing.
adjacent cell selection A selection of table cells that share at least one boundary with
another cell in the same selection.
affine calibration A tablet calibration method that provides an arbitrary linear
transformation in two-dimensional space. Affine calibration requires three calibration points
to allow a tablet transformation that combines translation, independent X and Y scaling,
rotation, and some skewing. Use affine calibration if a drawing has been stretched differently
in the horizontal or vertical direction. (TABLET)
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)
2644 | Chapter 52 Glossary