Ahh, I intend that this be my last post on the subject, because it is pretty much OT for this list, but I re-read the bug report and saw a paragraph that was there before, but seems to have sunk in now:
` Fontconfig has nothing to do with presenting the glyphs to the user, it simply selects the fonts. The bug you are seeing (and, yes, I agree that it is a bug even if white text on a black background is wrong) is due to limitations in various rendering libraries, like Xrender, cairo et al. '
On Saturday, February 03, 2018 09:14:45 AM rhkramer@gmail.com wrote:
On Saturday, February 03, 2018 09:02:10 AM rhkramer@gmail.com wrote:
I did find a bug report not too long ago for some application which actually confirmed the bias I described, and described how that worked (in general terms)--I'll make a cursory search or try to remember where I found that, and, if I do, I'll post it here.
Ahh, that was easier than I expected--here are my notes after reading that bug report (some time ago)--I did not re-read it today to see if anything has changed. The comments immediately after the [[<URL>][<Page Title>]] are my own, the things after the ` are quotations from the bug report.
Summary: Gamma not taken into account, white on black hard to read]]--this confirms my observation of the problem, but my explanation (iirc) predates gamma correction (iir/uc)--my theory of the cause of the problem is that anti- aliasing sort of "assumed" that the normal view would be black on white, when it was applied to white on black, it should have somehow considered the other "color" (black or white) to be the basis--because it didn't, fewer pixels are colored white when viewing white on black as opposed to the number of pixels colored black when viewing black on white. I don't know if the problem still exists--it probably does in at least some places, and, I still have more difficulty reading white (or a light color) on a black (or dark background). ` When doing antialiasing, fontconfig-based renderers do not take gamma into account and assume a linear color space. This make black on white text difficult to read at small font sizez.
...
The reason is that the stems of the glyphs are thinner than a whole pixel. Therefore, they get a fractionnal value. For example, the pixels on the lower part of the stem of the 'f' get the pixel value 151/255 in black on white, and 104/255 in white on black (and 104+151=255). With the usual 2.2 gamma, this makes respectively 32% and 14%, which gives a contrast of 68% for black on white, and 14% for white on black. '