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Am 05.08.2017 um 06:28 schrieb Kenneth:
> "Kenneth" <kdw### [at] gmail com> wrote:
>> One more image test, again for my own purposes: This PNG is *directly* from
>> POV-Ray (and NOT post-processed in Photoshop.) If it shows up correctly here
>> both as a small preview AND as the larger hi-rez image, then the problem will be
>> in my use of Photoshop, for some strange reason. An interesting experiment...
>
> Confirmed(!) THIS PNG image looks correct to me--both the small preview as
> well as the larger hi-rez version, when clicking on the preview.
... and this one carries not only a `gAMA` chunk indicating an encoding
gamma of 1/2.2, but also a `sRGB` chunk indicating that in fact the
encoding doesn't use a gamma-law function but rather the sRGB transfer
function.
> This is indeed strange-- but at least I now have a clue as to what might be
> going on, within Photoshop (and how it treats POV-Ray-generated PNG
> renders--possibly changing their gamma when I certainly wasn't expecting that.)
> I need to test this further.
>
> However...this does NOT explain the difference in appearance here of my
> originally posted PNG's-- the previews vs. the hi-rez versions. The only
> possible explanation I can come up with is that the newsgroup 'previews' are at
> one gamma setting, while the hi-rez versions are shown with a different setting.
> Sounds a bit crazy, I know...
The previews are most certainly generated without worrying too much
about gamma, effectively generating a JPEG image gamma pre-corrected for
whatever would have been the decoding gamma of the PNG file (4.4 in your
case).
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