[ft-devel] gamma correction and stem darkening

[Derek B. Noonburg]

I've been motivated by the discussion here to work on implementing
proper gamma correction in Xpdf.  I'm running into some issues with
text display using FreeType.

The font types I need to support are:
* Type 1
* CFF
* TrueType

I'm dealing with the fonts that are embedded in PDF files, so it's
common to find subsets, which may or may not have valid encoding
information -- which can cause problems for the autohinter.

The other issue is that I occasionally run into "tricky" TrueType
fonts (in the FT_FACE_FLAG_TRICKY sense: CJK fonts that use hinting
instructions to move points around), with random font names -- which
means there's no way (as far as I know) to detect that they're tricky.

What I'm currently trying:
* use FreeType 2.6.2
* set no-stem-darkening to false for the cff driver
* set no-stem-darkening to false for the autofitter driver
* use FT_LOAD_TARGET_LIGHT

This seems to work pretty well for most fonts (Type 1, CFF, and
TrueType).  It even seems to work for TrueType fonts without a Unicode
cmap (though I still need to double-check that).

But it fails badly on tricky CJK TrueType fonts.

For high-quality output with gamma correction, I think I need both:
(1) native hinting for TrueType fonts -- otherwise tricky CJK fonts
    fail
(2) stem darkening -- otherwise the text is too light after gamma
    correction

But I don't see any way to get both of those.

Does anyone have suggestions?

- Derek