d 8 bpp colormapped
   (bpp == bits/pixel).  Scaling operations with simple sampling
   can be done at 1, 2, 4, 8, 16 and 32 bpp.  Linear interpolation
   is slower but gives better results, especially for upsampling.
   For moderate downsampling, best results are obtained with area
   mapping scaling.  With very high downsampling, either area mapping
   or antialias sampling (lowpass filter followed by sampling) give
   good results.  Fast area map with power-of-2 reduction are also
   provided.  Optional 