"Tim Nikias" <JUSTTHELOWERCASE:timISNOTnikias(at)gmx.netWARE> wrote:
> (see thread "using assumed_gamma of 1.0... a discussion", located here:
>
http://news.povray.org/povray.general/thread/%3Cweb.439a1b692d1f46002a1c213f0%40news.povray.org%3E/)
>
> Anyways. My experience is this: I have a nice image_map, I follow the docs
> and supply assumed_gamma of 1.0 and have Display_Gamma properly set to 2.2,
> and what happens? The image_maps turn out brighter than their source. Why?
> Due to the internal gamma correction of POV-Ray.
> Personally, I'd like an image-map to look like it's source when its lit with
> 100% white light (e.g. by applying finish{ambient 1 diffuse 0}), but the
> gamma-correction prevents that.

That's exactly what I've been seeing as well.  Which is really the main
reason I
haven't (yet) gone over to using assumed_gamma of 1.0

There seems to be a kind of "either/or" situation in POV, from my own point
of view: Either use assumed_gamma of 1 so that POV can work internally in
an "undistorted" linear color space...in which case an "unprocessed,"
normal .png or .bmp image_map will look too bright...OR use an
assumed_gamma that matches display_gamma (and monitor/OS gamma)..2.2 in
your case...so that the image map will reproduce exactly as it is supposed
to look...but then, apparently, POV itself is no longer working in an ideal
color space.  That's just...weird!

My own solution to the image_map problem (which I've posted elsewhere, if
less succinctly): IF using an assumed_gamma of 1, first bring the .png
image_map image into a graphics program (like Photoshop, or GIMP, or of
course your own gamma macro) where you can re-save the image with a
gamma (gamma correction?) of 1.0 embedded into it.  Only then
will the image_map
render correctly in POV!  This doesn't work with .bmp images (or, for that
matter, any other kind that doesn't support embedded gamma info.)

In reading all the responses so far to my own original post (which you
referenced), I'm coming around to the idea that using an assumed_gamma of
1.0 is, in fact, correct.

But I find this either/or situation to be MOST perplexing!!!

Ken

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