Alpha: Difference between revisions

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[[category:Glossary]][[category:Material System]]
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'''Alpha''' is a [[byte]] [[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 $alpha of 0.7 will convert to a texture alpha of 178 ( 0.7 * 255 = 178.5, floor rounded to 178 ).
[[File:Alpha sign.png|300px|thumb|right|This sign from Half-Life 2 is not a model, it's a texture that uses an alpha channel for transparency.]]
:''For the VMT parameter, see {{ent|$alpha}}.
'''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.


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.gimp.org/ The Gimp], [http://www.getpaint.net Paint.Net] and [http://files.filefront.com/TOTGA32/;5347390;/fileinfo.html TOTGA32].}}
{{paintdotnet|4.1}} 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; see [[alpha dilation]] for more information.
 
{{todo|Mention {{code|renderamt}} KV and {{code|Alpha}} [[I/O|input]].}}
 
[[Category:Glossary]]
[[Category:Material System]]

Latest revision as of 04:30, 12 July 2024

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This sign from Half-Life 2 is not a model, it's a texture that uses an alpha channel for transparency.
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 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; see alpha dilation for more information.

Todo: Mention renderamt KV and Alpha input.
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