In article <3909A3B3.BF05149C@inapg.inra.fr>, Gilles Tran 
<tra### [at] inapginrafr> wrote:

> For what I read here,
> http://www.geocities.com/SiliconValley/Haven/5179/
> it's equivalent to PSP and Picture Publisher H/M/S modification, 
> including the color balancing alteration. So we're basically talking 
> about the same thing.
> The really nice thing about H/M/S balancing, for a non specialist of 
> photo touch-up, is that it is very simple to use (unlike color 
> balancing or even color saturation) and, usually, a subtle extension 
> of the shadow range is quite enough to enhance nicely a picture. So 
> if something of that sort could be implemented in pov, it would be 
> nice to have it done along the same lines, or, if this can be done 
> with a generic model, to ensure that this model can be used in a 
> macro that does it with the H/M/S logic. Obviously, such a generic 
> model could be extremely powerful and improve many pov renders in a 
> dramatic way.

A dynamic_range filter, which would take two values and scale the input 
so that the min value is at 0 and the max at 1? I think it could 
probably be done easily with the add and multiply filters, though. Maybe 
package it in a macro, this seems to work right:
#macro DynamicRange(Min, Max)
    clip_colors {Min, Max}
    add {rgb -Min}
    multiply {rgb 1/(Max-Min)}
#end
Another filter that might be useful would be a "curves" filter, that 
takes a spline(or a color_map?) and adjusts the image according to it.


> In fact, I wonder why most pov pictures use such a narrow range. I 
> have always noticed that pics from other renderers tend to be 
> crispier : is it possible that these renderers include some 
> self-correcting algorithm that would stretch the range whenever it's 
> needed ? Note that this is a general statement : HE Day pics, for 
> instance, always seem quite contrasted already.

I think that is mostly because HE Day is better at lighting than most 
people. I tend to use ambient 0 when possible, and rely on multiple 
lights and radiosity(thanks to Nathan Kopp!) to get good lighting. I 
find it greatly improves shading and shadows.

-- 
Christopher James Huff - Personal e-mail: chr### [at] yahoocom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://chrishuff.dhs.org/
TAG Web page: http://tag.povray.org/

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