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:
- things like White's illusion
<https://en.wikipedia.org/wiki/White%27s_illusion> show that the
perception works in strange ways
- "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
<https://www.researchgate.net/publication/225063899_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
- may be the alpha should also depend on the ppem.
I have not found much in the literature. Opinions, pointers?
Thanks,
Eric.
