There are three ways I know of, to texture a model for a game, are there any other ways? Method 1: Using layers, materials, smart materials (Example: realistic games) Method 2: Hand painting textures (league) Method 3: Using polypaint, mainly in zbrush but blender can also do it (just not as good) (Example: No idea)
It's just bits.. You can even have something like (4 equal-sized channels) RGBA = 8bit + 8bit + 8bit + 8bit = 32 bit = 6bit + 6bit + 6bit + 5bit + 4bit + 4bit + 1bit (7 non-equal-sized channels). There is another example in:
It's pretty common tactic to combine grayscale textures together, saves memory. Most common use is 3-channel packing for Ambient Occlusion (red), Roughness (green), and Metalness (blue). It's extremely rare to pack more than four channels into a single bitmap, since there are no tools optimized for it, and I doubt there…