Alpha: Difference between revisions

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(cleanup...also example was bad because the combine forcefields use additive blending, not alpha channels)
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[[category:Glossary]][[category:Material System]]
[[category:Glossary]][[category:Material System]]
'''Alpha''' is an [[Integer]] [[variable]] that is often included as the "fourth" number in a [[RGB]] color format. '''Alpha''' is an [[opacity]] rating from 0 - 255. Smaller '''alpha''' numbers make objects appear more faded whereas larger numbers make objects appear more visable.
'''Alpha''' is an [[integer]] [[variable]] that is often included as the "fourth" number in a [[RGB]] color format. '''Alpha''' is an [[opacity]] rating from 0 - 255, where 0 is completely invisible and 255 is completely visible. In a VMT file, the "$alpha" parameter is normalized from 0 to 1.0 instead.


0 is completely invisible.
To store an individual alpha value in each pixel, an [[alpha channel]] is used as the fourth channel of the [[TGA]] file. This allows variable opacity, for example, in a single texture, such as the lettered Petrol signs in Half-Life 2. The texture's alpha channel can also be used to define self illumination instead of transparency.
255 is completely visable.
 
[[Alpha Channel]]s are also included inside of textures. A classic graphic format that supports [[alpha channel]]s is the Targa Graphics Format ([[tga]]).
 
[[Alpha channel]]s will let you specify individual opacity values for each pixel.
 
An example of where [[alpha channel]]s are used can be found in the Combine Forcefields.
 
Even though parts of the forcefields are visable, other parts are not. That is because the [[alpha channel]] is hiding certain parts of the texture.

Revision as of 12:01, 15 July 2005

Alpha is an integer variable that is often included as the "fourth" number in a RGB color format. Alpha is an opacity rating from 0 - 255, where 0 is completely invisible and 255 is completely visible. In a VMT file, the "$alpha" parameter is normalized from 0 to 1.0 instead.

To store an individual alpha value in each pixel, an alpha channel is used as the fourth channel of the TGA file. This allows variable opacity, for example, in a single texture, such as the lettered Petrol signs in Half-Life 2. The texture's alpha channel can also be used to define self illumination instead of transparency.

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