Kirk Andrews nous apporta ses lumieres en ce 25-03-2007 20:42:
> My favorite time of day is when the sun hangs low on the horizon and casts
> long rays of warm yellow light on the landscape.  This is just an effort to
> recapture that feeling on a cloudy Sunday.
> 
> The bridge is made of superellipsoids, the trees are from POVTree (and
> aren't my favorite trees--I'll try something different next time I render
> this), and the landscape is made from isosurfaces, of course.
> 
> I used an area light but I'm left with grainy shadows.  Could someone tell
> me how to avoid that?
> 
> 
> ------------------------------------------------------------------------
> 
How many elements in your area_light? The default of 4?
That grainyness is caused by a sparce array coupled with jitter. With jitter, 
the elements of the area_light move around from pixel to pixel, and that 
movement is proportional to the spacing between the various elements. If the 
light is 100*100 unit and is composed of 4*4 elements, they can move about 20 
unit around ther base locations.

Best way is to use a much denser array and use adaptive with as small a value as 
you can get by. With adaptive, it's best to use values like 9, 17, 33, 65,... 
(the powers of 2 plus 1). Start with adaptive 0 (minimum array of 3*3 to be 
helpfull), use adaptive 1 (array at least 5*5) if you get artefacts, up that to 
2 if 1 in still not enough (array at least 9*9). That way, you get nice, smooth 
shading and reasonable rendering speed.

Adaptive 0 start with the 4 corners and, if some are not visible, samples half 
way between them, forming 4 smaler squares. If a square is completely visible, 
or not visible, no more subsampling is done. If there is a fifference, the 
subsampling is repeated, limited with the size of the array.

-- 
Alain
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   A hooker once told me she had a headache.
   	Rodney Dangerfield

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