floorChannelDelta

The largest single-channel difference a pixel may have and still be absorbed by minMismatchedPixels; one past it fails the comparison however few there are. Unset by default, leaving viddik's own 96 — twice the measured cross-OS residue (delta 47), and well short of a changed glyph (a full stop: 12 px at delta 223). 255 restores a floor that counts pixels only. Becomes the viddik.floorChannelDelta system property.