[Devel] Gamma correction implementation

[Simon Harvey]

I've been looking at the experimental GRAYS_USE_GAMMA part of ftgrays.c
and I can't see how it solves the following problem:

If white text is being rendered on a black background and a pixel is
deemed to have 50% coverage, then the RGB value when gamma corrected might
need to be 192,192,192 to achieve 50% brightness. If the same pixel is
part of black text being rendered on a white background, it should also
have RGB=192,192,192. However, the scheme in ftgrays.c would correct the
*coverage* to 192, ultimately being rendered as 63,63,63 and exacerbating
the aliasing problem by making the glyph "ink heavy".

For black backgrounds the gamma correction works really well; for lighter
backgrounds it's worse (the "u" in "cruncher", "G"  in alphabet of
attached). I'm not sure the problem really lies with freetype;  shouldn't
gamma correction be performed only when the two colours involved are
known.

Any thoughts?
Simon

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