Under [core] section ( must be created if it doesn't exist ):
texture_quality = 4
to set the quality of loaded textures.
The possible values are:
0 -> uncompressed, OpenGL default
1 -> uncompressed, 32 bits
2 -> uncompressed, 16 bits
3 -> compressed, OpenGL driver
4 -> compressed ( the default value )
1 gives the better quality and much faster loading times, at the expense of video ram usage and a performance hit.