Andrew Cocker wrote:
 >
> Whilst rendering internal room scenes with plane walls, I have noticed (as have many
others
> I'm certain) that using a high error_bound gives better (ie non-blotchy) results on
the large
> flat areas, but poor (ie too light) shadows. However, a very low error_bound creates
> blotchiness on the large flat areas, but great shadows.

What's happening, very basically, is that with high error_bound, you're 
really getting the same artifact-causing blotches, but because they're 
so much bigger, they tend to pile up on top of each other and average out.

Increae your count. Alternately, you could try raising nearest_count, 
which will tend to smooth out the artifacts at the expense of render 
time. You might also try using a very large pretrace_start and a very 
small pretrace_end; the additional radiosity passes also tend to smooth 
out the artifacts.

> Would it be possible (and I am no expert on how radiosity works) to specify
different values
> for error_bound for different areas of the image, and have POV-Ray interpolate
between them to
> give smooth transitions?

It would probably be *possible*, but I don't think a 2D map would be 
very useful for controlling radiosity in a 3D space.. not to mention it 
would be a huge pain in the ass to use, and would break if you changed 
the resolution or aspect ratio of the image.

> hopefully in version 4, a better quality of radiosity could be
> achieved without the above being neccessary.)

I don't see anything particularly wrong with the current implementation. 
If you stop and think about what it's simulating, I suspect you'll find 
that there's really no good way to get around the fact that it's slow.

There's at least one other way to implement radiosity lighting, but it 
requires everything in your scene to be made up of triangles (obviously 
this is impractical for POV-Ray), and I don't get the impression that 
it's terribly fast either.

-Xplo

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