On Tue, Jun 8, 2021 at 11:14 AM Eric Muller <[email protected]> wrote: > > On the one hand, we have a coverage map, i.e. for each pixel how much of it > is covered by the outline. > > On the other hand, we are blending a foreground (text) color with a > background color. So we need some alpha, and use it for a linear blending, in > a linear colorspace. > > What is not clear to me is how to go from coverage to alpha. Identity is > plausible, but there are also reasons to believe it is not:
Coverage is a pixel proportion that draws the outline foreground color: Coverage == opacity (aka alpha). It is more than plausible, it is justifiable. It certainly helps to use gamma correction too so that blending is linear. > - things like White's illusion show that the perception works in strange ways I do not know why you are concerned, or how, or why you want to compensate for this using coverage or alpha. > - "One usually begins by assuming that nothing is known about the object > world and then the diffraction limit outlines the range of object details > that an image transfer allows to be gained and, by exclusion, those that it > leaves undetermined. On the other hand, it might be known ahead of time that > the ensemble of possible objects is restricted. Then distinctions can be made > by concentrating on the expected differences and disregarding image aspects > that might have arisen from sources known beforehand to be absent." (Optical > superresolution and visual hyperacuity, Westheimer), which can explain how > readers can perceive gray pixels differently (i.e. expecting black and white, > and therefore perceiving gray as width) > > - may be the alpha should also depend on the foreground/background color FreeType prefers to stay out of it. We sell *coverage*. Take it or leave it. Once bought, you can do whatever you want with it in the context of your perception experiments :) > - may be the alpha should also depend on the ppem. Again, we sell coverage. It looks great as alpha with gamma correction.
