Sorry Robert for having occupied your thread with this partial off topic 
matter and I already wish I would have kept my mouth shut in the first 
place.
But this observation is at least on topic for people using Photoshop to 
prepare image maps for the use within POV-Ray (and other rendering 
software).

The image is the original PNG file you did post and I strongly assume 
this was written by Photoshop.

Top row left to right:
Photoshop CS5,
Firefox,
Windows 7 build in Picture Viewer

Bottom row left to right:
Quicktime for Windows, (looks the same as on my MacBook)
Google Chrome,
POV-Ray render window (used as image_map with {ambient 1 diffuse 0})

I'm too lazy to do a similar compare on Linux right now but I am pretty 
sure it will show the same discrepancy.
And actually it is hard to tell what would be the "right" interpretation.
IC follows exactly the PNG specification. It does both, it handles the 
specified color primaries and it does handle the transformation of the 
gamma 2.2 to sRGB response function.
But this also means that IC (and POV-Ray!!!) does show it different then 
"meant" within Photoshop as Photoshop itself ignores its own tags when 
importing the file again (and is as such consistent within itself but 
not necessarily with the rest of the world).
Why Photoshop writes this tags that it ignores itself and not writes the 
PNG in the same same way it does e.g. JPEG by simply adding an ICC color 
profile will stay a secret of the Adobe developers.
Anyway, bottom line and to be at least a bit on topic: when you care 
about your colors within POV-Ray do not use PNG files written by Photoshop.
And do not get me wrong, the PNG file format is fine and you should not 
have trouble with PNG files written by any other application. And 
besides that I strongly dislike the company politics of Adobe*, 
Photoshop as image processing software keeps completely unrivaled.

It is really sad that color management on PC systems is still such a 
mess. And I fear with the latest release of LibPNG (1.5.6) that has 
finally and for the first time an in-build mechanism for transforming 
exponential to sRGB gamma (and visa versa) the situation will become 
even worse and not better as programmers are often not color experts at 
the same time.

-Ive

*I never understood why so many people agree in bashing Microsoft. 
Compared to the iron fist Adobe is ruling its market segment and is 
continuously expanding in all directions, Microsoft appears more like a 
bunch of 70ies hippies to me, well apparently rich ones, given that.

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