inhahe nous apporta ses lumieres en ce 2007/10/16 05:18:
> I'm not an advanced user of POVRay, but I thought only advanced users would
> be knowledgeable enough to answer my question.
> 
> i want to do refraction where colors are separated, like in the prism
> effect.  afaik the feature that does this is photon mapping.  but from a
> little bit of reading I get the impression that photon mapping would only
> project colors onto surfaces, not onto the camera.  so, e.g. if i created a
> diamond i wouldn't see it shine with various colors.
> 
> but i had an idea.  let's say I create a white surface, with a lens-shaped
> refracting object in front of it, and put a black box around it except for
> the lens, like a camera.  then i point this contraption toward the diamond
> or whatever, and put the povray camera inside the contraption pointing
> toward the white surface.  then of course when the image is rendered I flip
> it horizontally and vertically.
Overkill.
> 
> will this work?
Maybe.
> is it necessary?
NO!
> 
> 
Whenever you add dispersion you get coloured difraction. If the camera see, 
directly or not, the dispersing object, you'll see the colours. You don't need 
photons for that. Photons will make the caustics that hit some surface coloured 
also.
To see the colours, you need an interior block like:

interior{ior 2.5 dispersion 1.2}

Here,the default dispersion_samples of 7 is unualy enough.
Diamond's ior is about 2.5 and it have a relatively strong dispersion, over done 
here.
If the diamond is "free floating", that's all you need.
If the diamond is resting on something, and you want to see the effect on that 
surface, THEN you need photons:

object{Diamond interior{ior 2.5 dispersion 1.1 dispersion_samples 
15}photons{target refraction on difraction on collect off}}

A larger number of dispersion samples is needed to get smooth coloured caustics 
unless very close to the diamond.
You don't need to add a photons block to the light_source, nor to the surface.

-- 
Alain
-------------------------------------------------
You know you've been raytracing too long when you read about an algorithm or 
datastructure and your first thought is: "How can I use this to speed up 
raytracing?"
Christoph Rieder

Post a reply to this message