Pitel added a comment.
I finally got to do some testing and it is not looking good for luminance formula `0.2126*r + 0.7152*g + 0.0722*b`. Screenshot with background color `#5500FF` (blueish, button background on picture), you can see that black text is readable on it, but it has luminance only 0.14 so in overlay it is replaced by black. F5769603: Screenshot_20180327_174715.png <https://phabricator.kde.org/F5769603> So I would rather stay conservative, and used formula `max(r, g, b)`. I am still not sure whether the threshold should be `0.5` or a bit lower... REPOSITORY R120 Plasma Workspace REVISION DETAIL https://phabricator.kde.org/D11262 To: Pitel, mart, #plasma Cc: fredrik, ngraham, abetts, broulik, mvourlakos, plasma-devel, ragreen, ZrenBot, lesliezhai, ali-mohamed, jensreuterberg, sebas, apol, mart
