B
blending : The transitioning of one line,
surface or color into another smoothly without an observable joining edge.
blending function : The weights that are
applied to two curves to assure continuity without an observable junction.
They are usually in the form of cubic polinomials.
box filter : A method for modifying the
color value of a pixel by averaging it with the color values of those pixels
surrounding it. Used in anti-aliasing.
Bresenham's algorithm : A mathematical
algorithm for determining which pixels should be illuminated for the most
accurate representation of straight line, given a
specified pixel resolution.
brightness : 1: The average light intensity
of an image. 2: The perceived amount of light as determined by luminance
and chrominance of the source. Brightness is
based upon the perception of the human eye, which
varies with frequency, so that is not proportional to physical energy emitted.
byte : A unit of computer data consisting
of eight bits.
C
CCD : Charge-Coupled Device;
a semiconductor device configured in shift-register arrays for sensing
light. Used in some television cameras and scanners.
CD-ROM : Compact Disk Read
Only
Memory;
an interchangeable digital storage media having data encoded optically
on a disk for readback by laser in a drive that rotates the disk. The technology
is similar to discs used for digital audio recording, but encoded differently.
cellular automata :
A technique for modeling of growth. Cellular automata are made up of mahematical
cells in an array. Each cell changes its value or state according to some
specified set of algorithms. The state of each cell is affected by the
states of neighboring cells.
CGA : Color Graphics Adapter; a graphics
adapter card that interfaces the IBM PC and compatibles to a color monitor
using a low-resolution (200x320) color graphics standard.
compositing : Composititing of images is combining images to
create new images. The value of each pixel in the composited image is computed
from the component images in some fashion. In an ovelay, the pixels of
the foreground image must be given transparency values. A pixel's value
in the composited image is taken from the background image unless the foreground
image has a nontrasparent value at that point, in which case the value
is taken from the foreground image. In a blending of two images, the resulting
pixel value is a linear combination of the values of the two component
pixels.
D
dithering : Simulating gray tones
by the use of varying patterns and sizes of background data.
dither matrix : An array of numbers, used
in adjacent blocks repeated over the screen, providing the pattern for
dithering. The matrix number associated with the screen coordinates is
added to the pixel value before rounding.
dot : 1: A display of one pixel. 2: A circular marker of selectable
size on an image.
dpi : Dots per inch. A measure of the quality and resolution
of a display or printer. This is the number of horizontal or vertical dots
that can be displayed or printed in a linear inch.
G
Gupta-Sproull algorithm : A technique for drawing antialiased
lines. The algorithm draws three pixel wide lines using the Bresenham algorithm.
It determines the proper pixel color by determining the perpendicular distance
from the pixel center to the line center and then using a table lookup.
H
halftone : A graphic in which dots are used to represent continuous
tones, with large, closely spaced dots representing darker areas and smaller,
widely spaced dots representing lighter tones. This permits the
printing processes, which cannot handle continuous tone images. A halftone
can be created from a photograph by rephotographing it through a screen
that breaks the picture up into dots.
L
Life game : A game which provides
a visual example of the use of cellular automata. The player sets up an
array of cells and they then are born, grow, decay, or die according to
simple rules. The continually changing cell pattern in displayed on the
display screen.
M
morphing : The process of converting one image to another by
warping the original image to some intermediate distorted shape and then
warping this distorted shape back to the second image over the course of
a number of animation frames.
P
pixel [from picture element] 1: One of individually addressable
elements of an array of color or intensity data forming a digital image.
2: The smallest element on raster display for which the color or intensity
may be independently set.
point 1: A location in space, specified by coordinates. 2: In
typesetting, the smallest unit of measure, equal to 1/72
of an inch.
Q
quantization technique : A method for reducing a large number
of colors to the limited number available for a particular display mode.
Such techniques include uniform quantization, use of popularity
algorithm,
median cut, and octree quanization.
S
spline : A mathematically defined curve that provides a smooth
path from one point to another with a shape controlled by a number of control
points. See B-spline.
W
warping : 1: The two-dimensional mapping of an image to produce
an image for display. 2: The distorting of an image to give an unusual
effect. The technique used produces the same results as if the image
were on a sheet of rubber that is stretched in some areas and compressed
in others. It is accomplished by remappping the pixels of the image using
affine transformations that are determined by the relation of each original
pixel to some established control points. Often warping is used in association
with animation, with the image being slowly distorted from its original
shape to the final shape over a period of time.
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