>> (B) If (after fixing (A)) you see checkering in the preview window
>> and/or the output file when rendering the scene file below, then your
>> Display_Gamma (POV-Ray 3.6 and 3.7) and/or File_Gamma setting (POV-Ray
>> 3.7 only), respectively, is wrong.
> Well that produces a broken file for me if I choose to output a PNG file (i.e.
> the gray value isn't half the white value). HDR output works though (as I assume
> it's in linear space).
How did you /check/ that the gray value isn't "half the white value"?
If you squint your eyes to "blur" the black-and-white-striped squares,
and it then /appears/ to have the same brightness as the gray value,
then that gray value /is/ half as bright as the white.
Note that Photoshop lies to you about brightness (and so do your eyes).
Photoshop also uses physically wrong math when blurring images (at least
the old version I own does).
The /physical/ blurring by squinting your eyes, however, does indeed
comprise a physically correct "computation" of (black+white)/2 (taking a
few steps back may do the same job, and some people may just need to
take off their glasses), which obviously gives you a grey of /truly/
half the white value (*), which you can then visually compare to the
grey of /allegedly/ half the white value.
(* provided you have set your display's black point properly)
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