Fredrik Eriksson <fe79}--at--{yahoo}--dot--{com> wrote:
> On Thu, 03 Sep 2009 16:42:46 +0200, Warp <war### [at] tagpovrayorg> wrote:
> > Warp <war### [at] tagpovrayorg> wrote:
> >>   However, there are situations where you precisely *don't want* that.
> >> You want raw pixel values, and nothing else, as I exemplified above.
> >
> >   I just figured out the *perfect* example of a situation where you want
> > raw, linear pixel values which are *not* gamma-corrected: When you are
> > rendering an image which will be used as input to create a heightfield.
> >
> >   There 0.5 should mean exactly half height, not a height of 0.73.

> Which is exactly what you should get if you use a gamma-aware image  
> format, regardless of what you set File_Gamma to.

  No, because gamma correction will change the actual values of the
pixels before they are used/displayed. Thus, for example, a pixel which
in the image file has values <0.5, 0.5, 0.5> will be converted to
<0.73, 0.73, 0.73> before being displayed on screen, for a gamma correction
value of 2.2.

  However, when you are using an image to generate a heightfield, you are
not *displaying* the pixels. It's actually not an image supposed to be
shown on screen. It's just an image file being used to represent height
values. (One could say that an image file is being "abused" for a different
purpose than it was originally intended.) However. this is a very common
technique because image files are both very common with a lot of support,
and a practical way of storing height information.

  In this situation gamma correction makes no sense because the image file
does not actually contain an image.

-- 
                                                          - Warp

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