Alpha: Difference between revisions

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[[category:Glossary]][[category:Material System]]
:''For the VMT parameter, see {{ent|$alpha}}.
{{mergeto|alpha channel}}
'''Alpha''' is a [[byte]] {{wiki|variable}} that is often included as the "fourth" byte in a [[RGB]] color format. '''Alpha''' is usually an [[opacity]] rating from 0 - 255, where 0 is completely invisible and 255 is completely visible. Alpha is sometimes also used for other things, such as a self-illumination mask.
'''Alpha''' is a [[byte]] {{wiki|variable}} that is often included as the "fourth" byte in a [[RGB]] color format. '''Alpha''' is an [[opacity]] rating from 0 - 255, where 0 is completely invisible and 255 is completely visible. In a [[VMT]] file, the "$alpha" parameter is normalized from 0 to 1.0. The value used in the in-game texture is $alpha * 255. That is, an $alpha of 0.7 will convert to a texture alpha of 178 ( 0.7 * 255 = 178.5, floor rounded to 178 ).


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 opacity.
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.


{{note|Some graphics editors (such as Photoshop Elements) will not be able to save alpha into TGA format. Some free alternatives that are able to save 32-Bit alpha TGA are [http://www.getpaint.net Paint.Net], [http://files.filefront.com/TOTGA32/;5347390;/fileinfo.html TOTGA32] and [http://www.gimp.org/ The Gimp].}}
[http://www.getpaint.net Paint.net] is a good program for adding alpha to a texture. Be aware that a pixel with alpha set to 0 still has R, G, and B values, which may affect the texture in some cases.
 
[[Category:Glossary]]
[[Category:Material System]]

Revision as of 08:26, 29 August 2018

For the VMT parameter, see $alpha.

Alpha is a byte Wikipedia icon variable that is often included as the "fourth" byte in a RGB color format. Alpha is usually an opacity rating from 0 - 255, where 0 is completely invisible and 255 is completely visible. Alpha is sometimes also used for other things, such as a self-illumination mask.

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.

Paint.net is a good program for adding alpha to a texture. Be aware that a pixel with alpha set to 0 still has R, G, and B values, which may affect the texture in some cases.

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