This tutorial is to get beginners into the basics of ArmA 2 texturing. Take a note that this applies to ArmA as well.

_CO suffix is for basic texture (diffuse).
_CA suffix is for transparent alpha channel textures.
_NOHQ suffix is for normal maps.
_SMDI suffix is for specular maps.

Use only Texview2 or pal2pace to save your textures and always remember to use the suffix like _CO or _CA in the file names. Do not use Kegety's PAA plugin for Photoshop, simply because the previously mentioned method is better.

The “suffix” in file name determines the texture type. For example MyTexture_co.paa and MyTexture_ca.paa are nice examples. You should not leave out the suffix on any texture.

Always try to achieve 1 texture / 1 model. That is the golden rule. Even BIS sometimes cannot use only single texture, but this rule is very strict on the last resolution LOD of the model. Do NOT have more than one texture in last res LOD.

You have to separate normal textures and alpha channel transparent textures, because either you do not get any transparency in _CO texture or with _CA texture the whole texture is transparent. So split your transparent (windows, etc) parts of the model into one single texture.

Vehicles usually have interior like cockpit or so in separate texture if there is lot of details. Usually this texture need only to be applied for View - Pilot / Gunner / Cargo so it stays separate from the main model shown to outside world.

If you get transparent bug that your normal model (weapon, tank, house etc) is just slightly transparent, then it means there is alpha channel in the _CO texture or that your texture indeed is _CA transparent texture.

Open the .paa texture in Texview2, save to TGA. Then open the TGA in decent image editor and fill all of the alpha channel to pure white color. Save TGA, load it up on Texview2 and save to _CO.paa or use pal2pace to convert it to paa format.