Ain't this sweet?

PNG properly defines how gamma should be handled in the presence of a 
gAMA chunk.

POV-Ray 3.6, when used with assumed_gamma, respects this definition 
flawlessly... for 24- and 32-bit images, that is.

For 8-bit color palette PNG images, POV-Ray 3.6 doesn't give a damn 
about gamma correction.

Likewise, the PPM format properly defines how gamma should be handled 
*always*.

POV-Ray 3.6 gives a piece of sh*t about this definition.


So, how should one go about this in POV-Ray 3.7? Emulate all those 
crappy details? If so, when? Only when #version is set to 3.6? Always 
when the legacy assumed_gamma statement is used (which is supposed to 
not be used for new scenes)?


Can of worms indeed...

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clipka wrote:
> Likewise, the PPM format properly defines how gamma should be handled 
> *always*.

Err, where did you get this from. In case you are referring to the 
NETPPM toolkit and its CIE/ITU Rec. 709 specification you should be 
aware that this is only valid for files written by this toolkit and not 
for pgm/ppb/pbm/pnm files written by one of the numerous other 
applications in the UNIX world. Therefor pnmgamma (to gamma-correct 
other files) is part of this toolkit.

-Ive

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Ive schrieb:
> clipka wrote:
>> Likewise, the PPM format properly defines how gamma should be handled 
>> *always*.
> 
> Err, where did you get this from. In case you are referring to the 
> NETPPM toolkit and its CIE/ITU Rec. 709 specification you should be 
> aware that this is only valid for files written by this toolkit and not 
> for pgm/ppb/pbm/pnm files written by one of the numerous other 
> applications in the UNIX world. Therefor pnmgamma (to gamma-correct 
> other files) is part of this toolkit.

Yes, that's exactly the source I had it from, and even that actually 
also notes that "a common variation on the PPM format is to have the 
sample values be 'linear,'", which I had perfectly failed to notice.

As I said, the summary you provided on gamma handling in various file 
formats is greatly appreaciated :-)

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