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From: | Nikolaus Waxweiler |
Subject: | Re: [ft-devel] State of autohinter stem darkening |
Date: | Thu, 22 Oct 2015 21:55:30 +0200 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 |
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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