Warp <war### [at] tagpovrayorg> wrote:
>   1) What exactly is the purpose of File_Gamma, given that it makes no
> difference (when creating a PNG file)?

>   2) Where is POV-Ray conjuring a gamma setting of 2.2 even though neither
> Display_Gamma nor File_Gamma were even close to that value?

>   3) Why do Display_Gamma and File_Gamma produce different results even
> if they are set to be the same (when creating a PNG file)?

>   4) Why does POV-Ray produce different results depending on the output
> image format? For example, rendering to a TGA file results in a different
> result than rendering to a PNG file when File_Gamma = 1.0 (the pixels are
> the same, but the gamma metadata makes the PNG different from the TGA).

>   5) How do I make POV-Ray 3.7 to produce a PNG which looks the same as
> what it displayed on screen and as it produces when outputting to a TGA
> file?

  Why is it so hard to answer these questions? I think the questions are
rather simple and straightforward.

  I'm especially interested in question number 4. If the PNG file that
POV-Ray 3.7 currently writes is always correct, as seems to be the claim,
then why is POV-Ray 3.7 writing an "incorrect" result to eg. a TGA file?
Does that mean that outputting to a TGA file is currently broken?

  If the answer to that is "yes", then that brings up question #1 above.

  That answer also implies the same answer for question #3: That the image
preview is currently broken. If this is so, then what purpose does
Display_Gamma serve?

  It also implies something else: That POV-Ray 3.7 should always force a
gamma correction of 2.2 regardless of what Display_Gamma and File_Gamma are.
Wouldn't this kind of defeat the entire purpose of gamma correction in the
first place (in other words, that the image could be created in hardware
which has a gamma correction different from 2.2, and thus you should have
a way of specifying what that gamma is)?

  However, if the output to TGA is *not* broken, that means that the output
to PNG *is* broken because POV-Ray 3.7 is currently writing different things
to these two image formats.

  You can't have it both ways (ie. the output to PNG and TGA being both
correct at the same time). Either one or the other is broken. If your
opinion is that the output to TGA is broken, that raises a whole lot of
issues, as I wrote above.

  If the output to PNG is currently broken, it should be fixed.

-- 
                                                          - Warp

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