I wrote:
RasterizeWord[word_, font_, size_] :=
Rasterize[Style[word, FontFamily -> font, Black],RasterSize -> size,Background -> Gray]
f=RasterizeWord["A", "Arial", 20]
and I got (after zoom):

with 18 pixels (easy to calculate). Why??
How to make it the grayscale?
I set antialising to none in Unity Tweak Tool (Linux) and I got:

So I tried:
RasterSize -> size, ImageSize -> size
I got the same result. But it is interesting that in GIMP:

when I Export["f.png", f]. I think something is wrong with the zoom.
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– Nov 06 '14 at 16:06