There is a cool image attached to this bug report:
https://bugreports.qt.io/browse/QTBUG-41590
Gamma correction makes black text lighter and white text heavier,
i.e., has opposite effects, i.e., you cannot use one universal value.
Hold on, that's intended: "Gamma 1.8, darkened" is *exactly* what we
need! It might look alien to you, but that's partly because we've been
looking at non-corrected glyphs for so long in Linux land that we think
it's how things must be. You'll get used to the gamma-corrected look
quickly :)
Non-gamma-corrected dark text on light background is too heavy and light
text on dark background too light. Gamma correction/linear
alpha-blending equalizes this to the eye. Look at
https://imgur.com/a/5YzVM, first pic: gamma correction, second pic: no
gamma correction. Note the lightness, color-fringing and pixelyness.
Also note how red text on green background in the bug report image looks
the cleanest in "Gamma 1.8" and "Gamma 1.8, darkened". So yes, gamma
correction should be done universally.
The stem darkening done by the CFF driver and now the autohinter counter
the lightness of gamma-corrected text (compare "Gamma 1.8" and "Gamma
1.8, darkened"). That's the entire point of the feature. Mac OS X is
probably doing it that way (Dave? ;)).
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