Gamma correction for glyph coverage values.
FreeType glyph rendering gives us a bitmap of coverage amounts, not alpha values. This means that a pixel that is half-covered will have a value of 0.5. But our output devices don't have such a linear response so FreeType expects us to gamma correct these values. Without doing so the antialiasing drops off too quickly and gives us results that look too thin.
This uses the highly-recommended gamma of 1.43, rather than more normal values of 2.2 or 1.8. This is best described here: https://www.puredevsoftware.com/blog/2019/01/22/sub-pixel-gamma-correct-font-rendering/
The reasons are historical. Because so many programmers have neglected gamma blending for so long, people who have created fonts have tried to work around the problem of fonts looking too thin by just making the fonts thicker! Obviously it doesn’t help the jaggedness, but it does make them look the proper weight, as originally intended. The obvious problem with this is that if we want to gamma blend correctly many older fonts will look wrong. So we compromise, and use a lower gamma value, so we get a bit better antialiasing, but the fonts don’t look too heavy.
Following shows the change. The gamma-corrected one is the "brighter" one:
It makes the characters look a bit smoother and fuller with better antialiasing. But because it is a change it might be best to pair this with a change of font too.
