sharpening after resampling is provided to
   improve appearance by reducing the visual effect of averaging
   across sharp boundaries.

   For fast analysis of grayscale and color images, it is useful to
   have integer subsampling combined with pixel depth reduction.
   RGB color images can thus be converted to low-resolution
   grayscale and binary images.

   For binary scaling, the dest pixel can be selected from the
   closest corresponding source pixel.  For the special case of
   power-of-2 binary r