I use POV for graphics work, so I often rely on it to match rgb values
irrespective of lighting conditions. For example, in 3.6 a 50% gray with no
light source and ambient 1 is always accurately rendered as RGB 128, 128, 128,
as long as Display_Gamma in povray.ini is the same as assumed_gamma in
global_settings or if no assumed_gamma is declared. This is true of image-mapped
pigments or declared colors.

In 3.7, however, with the suggested Display_Gamma and File_Gamma set to 2.2, a
50% gray (rgb 0.5) with no light source and ambient 1 comes out as RGB
186,186,186 or a gray of about 0.73, much lighter. This does not make sense to
me. I would expect that if ambient is set to 1 with nothing else affecting the
color, that the rendered output would match the value called for.

This can be corrected. I know, by modifying the pigment with "gamma 2.2" but
shouldn't this be done internally? What a pain! With Display_Gamma and
File_Gamma set to 1 and no pigment gamma correction, however, gray 50 comes out
gray 50. But this doesn't seem to be the accepted wisdom nor does it match the
gamma of my system. The gAMA chunk in the PNG is written as 1.00 rather than the
usual 0.45454.

There is also a discrepancy in the beta between declared color values and color
values taken from image maps. With Display_Gamma & File_Gamma = 2.2 and no color
correction, an image map of RGB 128 comes out as RGB 128, as expected, but a
square box with pigment {rgb 0.5} finish {ambient 1} comes out as RGB 186.

What am I missing here? I've read the relevant posts and wikis and do not really
want to get into the debate over what's "realistic" versus what "looks good" but
I'm having considerable trouble converting all the years of pigments and
textures and materials into something close to what they were originally meant
to look like. Running everything as #version 3.6 doesn't really seem feasible
and without some simple conversion solution there's a lot of experimentation and
techniques that will be broken.

(Using Window 7 64-bit with Photoshop to test file output, ColorPix to test
display, and pngcheck to test the PNG files.)

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