Jim Holsenback nous apporta ses lumieres en ce 10 / 05 / 2007 19:44:
> Hola,
> 
> I'm working on an idea and I'm not getting the results I expected, so before 
> I flog this any further, I thought I'd post and see if it's even possible. 
> For those who don't know what a cross screen filter is ..... check out this 
> Wikipedia entry: 
> http://en.wikipedia.org/wiki/Filter_(photography)#Cross_screen
> 
> So my question is is this even possible in POV? I've constructed my filter 
> (I'm using the fine wire grating method) and it dosen't work as expected. I 
> think I'm missing the "diffraction" element of my filter. Since this is a 
> pretty sharp group I imagine someone might have a few pointers to get me 
> going in the right direction .... or tell me that it can't be done.
> 
> Cheers Jim 
> 
> 
Strictly, NO. But, you can have something similar.
POV-Ray don't have diffraction.
You can simulate this effect by using a plane placed between the camera and the 
rest of the scene. The filter-box will be totaly transparent (rgbt 1) have some 
averaged rotated gradient pattern (to give the rainbow lines) and a flat normal 
that is stronger than the rest (heavier ponderation) so that the objects 
themself are seen normaly.
You need to give your filter-box an interior with a small ior and a large 
dispersion value, maybe larger than that of the ior. You will probably need to 
increment the dispersion_samples value over it's default value of 7.

Be ready for long render times. Each averaged normal will generate an additional 
ray to be computed, that will bet multiplied by dispersion_samples. So, if you 
want a 6 branches effect, you will have at least 49 rays to sample for each pixel.

There is a tool, the lenseflare macro, that does basicaly that.


-- 
Alain
-------------------------------------------------
An organizer for the "Million Agoraphobics March" expressed disappointment in 
the turnout for last weekend's event.

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