Images

From modwiki

The textures you see in Doom 3 are images that are applied - by use of materials - to the different surfaces of the game, from walls in a map, to models in the world, to the elements of the GUI.

Doom 3 supports images in .JPG and .TGA formats. The correct format for your image depends on the image itself. JPEG does not support an alpha channel, and its compression format can cause a loss in the quality of your image. If, however, you decide it is the best format for your image, Doom 3 does support it. For game quality settings other than Ultra, Doom 3 also uses the .DDS image format in place of the high quality formats (except for normal maps in High Quality mode, which still use .TGA).

The dimensions of your image (width and height) should be a power of two in pixels. In other words, your width and height should be 2, 4, 8, 16, 32, 64, 128, ... etc. Your images do not have to be square, so you can have an image that is 32px by 128px. If you do supply the engine with non-power-of-two textures they will be automatically scaled to fit a power of two size, how the scaling is performed (downwards or upwards) is controlled by the image_roundDown CVar.