Warp <war### [at] tagpovrayorg> wrote:
>   One reason can be that I want to match exactly the image pixel values with
> HTML colors. If I want the color scheme of an image to match, for example,
> the background color of a HTML page, I should be able to do that.

  Consider, for example, this:
http://warp.povusers.org/pov_imagemap_test/index2.html

  When outputting to PNG, File_Gamma has basically no effect. While the
pixel values written to the file are different, POV-Ray still manages to
make the PNG behave exactly as if a File_Gamma of 2.2 was always defined.
It doesn't matter if File_Gamma is 1.0 or 2.2, the result will always look
the same.

  If the user really wants the output file to look the same as what
POV-Ray displayed on screen when Display_Gamma was set to 1.0, he has
to either use some other image format (eg. TGA) or he has to manually
remove the gamma metadata from the PNG file.

  So I have a few questions:

  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?

-- 
                                                          - Warp

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