"Main Menu Options

Ultra
Each texture (diffuse, specular, normal) will be at full resolution with no compression. In a typical DOOM 3 level, this can hover around 500 megabyte of texture data. This will run on current hardware but will not fit onto a 256MB card, causing texture thrashing. The amount of texture referenced in a given scene per frame ( 60 times a second ) can easily be 50 megabytes+. This is ideal for 512 megabyte video cards.

High quality
Uses hardware compression ( DXT1,3,5 ) for specular and diffuse textures and no compression for normal textures. This looks very very close to Ultra quality but the compression does cause some loss in quality. This is ideal for 256 megabyte video cards.

Medium quality
Uses hardware compression for all textures (specular, diffuse and normal). While this still looks good, compressing the normal maps can produce a few artifacts especially on hard angled or round edges. This is ideal for 128 megabyte cards.

Low quality
Uses hardware compression for all textures (specular, diffuse and normal) and automatically resizes diffuse and normal textures to no more than 256x256 and specular texture maps to no more than 64x64. This is ideal for 64 megabyte video cards."