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
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