Gimp - 2.2 Guía Del Usuario

CHAPTER17

Glossary

Alpha Refers to transparency. An Alpha Channel allows transparency control. Certain

image formats may only contain a single Alpha Channel allowing a transparency

of on or off. Other formats allow a variable level of transparency.

Anti Aliasing A technique used to make diagonal or curved edges appear smoother by

setting pixels near the edge to intermediate colors according to where the edge

crosses the underlying color.

Channels Each image is divided up into separate channels and then recombined be-

fore being sent to the output device. An output device is most usually a screen.

The channels that are used when rendering images to a screen are Red, Green,

and Blue. Other output devices may use different channels. Channels can be

useful when working on images that need adjustment to one particular color. If,

for example, the removal of “red-eye” is the goal, work on the Red channel is most

obviously a ready solution. Channels can be seen as masks that allow or restrict

the output of the color that the channel represents. By running filters against this

channel information, many varied and subtle effects can be put in to play by the

experienced GIMP user.

Dithering Dithering refers to the math and voodoo involved in rendering an image that

has few colors seem like it has many. Dithering is accomplished in different

ways depending on the output device and the program. One particularly effec-

tive method is clustering pixels of color together in an attempt to simulate another

color. This is achieved by the human eye and the tendency for it to mix colors

while viewing complex color patterns. A common dithering effect is seen on tele-

vision screens or in newspaper print. From a distance the images seem to be

constructed of many varied colors or shades, but upon closer inspection this is

certainly not the case. A color television uses only three colors clustered together

in various states of on or off. A black and white newspaper uses only black ink,

yet pictures in newspapers appear to be constructed of grey tones. Furthermore,

there are techniques used to achieve greater success in dithering. T

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