- pix-color-magnitudeprocedure
- in - PPIX - 32bpp or 8bpp w/cmap
- in - RREF GREF BREF: int32
- Reference values for red, green, blue components, representing unbalanced white or avg background color of a scanned image. Image colors are adjusted according to the ref values. Set all to 0 to skip this adjustment.
- in - TYPE - one of intermediate-diff: 1, avg-max-diff: 2, max_diff: 3
- returns: 8bpp ppix (amt of color in each src pixel) or #f on error.