wed by either thresholding or dithering.

   There are also image depth converters that don't have scaling,
   such as unpacking operations from 1 bpp to grayscale, and
   thresholding and dithering operations from grayscale to 1, 2 and 4 bpp.

5. Image shear and rotation (and affine, projective, ...)

   Image shear is implemented with both rasterops and linear interpolation.
   The rasterop implementation is faster and has no constraints on image
   depth.  We provide horizontal and vertical shearing abou