Channel (Image) Last edited 10 months ago2023-12-16 20:56:49 UTC

Image channels contain primary colour information.

Images are generally made out of three channels: Red, Green and Blue (aka RGB).
It can also be a single channel, where the values either indicate one scale of intensity (aka I mode), or an index into a palette, the entries of which are usually composed of RGB values (P mode).
Transparent images usually have one more channel called Alpha (or A).

In GoldSrc

GoldSrc for the most part allow for only a single indexed channel image; all the colour values are defined in an accompanying palette.
This is the case for textures in WADs, texture in models, and sprites. The common source image format for these textures are P-mode BMP files.
Textures in decals.wad are in pseudo-I mode; the values are linear ramping up or down of intensity values, reflected in its palette, but only the last value of the palette defines the base colour to be applied to the whole decal.
Spraypaint .bmps are in I mode.
The exception to all this is TGA files which can be RGB or RGBA.