From: "Mike Gorchak"

added help and options -mono to force monochrome RGB2YUB conversion and
-lum <percent> - luminance of image during conversion. Also rewritten code
which moves overlay into window. Now it depends on window size.
Also fully rewritten -scale option, image now scaling from 50% from center
of screen until border of window is reached - it really tests scaler, old
-scale test doesn't test downscale.

--HG--
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%40570