On Thu, 27 Apr 2000 11:29:37 +0200, Gilles Tran <tra### [at] inapginrafr>
wrote:

>In addition to all the post-process requests that have been made in the
>past few days, there is one that is particularly important to me, which
>is the ability to manipulate separately the highlights/midtone/shadows
>proportions (?) of the image. (if this was already mentioned under
>another name in one of Glen Berry's message, forget about it).

If we get the ability to alter tonality using things like
"iso-functions", we can achieve much of what you want, if not all.
Some of the toning filters I suggested affect shadows the most ,
midtones somewhat, and the highlights were practically untouched. I'm
sure that different functions could be implemented to affect whatever
portion of the tonal range you want to selectively enhance.

There is also a function in both Photoshop and Gimp called "Auto
Levels" I'm not sure how it works in detail, but it often helps a
typical POV render to perform this function on it. Perhaps a similar
feature could be done inside POV? Basically, it would set the black
point and white point of the image, and scale the tonal range of
everything else to fit between those two points. This makes sure that
the areas that should be black are truely black, the areas that should
be white are truly white, and all the grays in between are evenly
distributed between them.

There is one side-effect of the Photoshop and Gimp filters. They will
sometimes alter the color balance of an image, because they perform
this tonal range optimization on each RGB channel independently. I
suggest that we explore altering each RGB channel the same amount, in
unison. We alter them based upon their value when averaged together.
This would avoid all color shifts.

Gilles, have you tried "auto levels" ?  Does it do anything similar to
what you want?


Later,
Glen Berry

( Remove the "7" from 7no### [at] ezwvcom to email me. )

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