Starting a news thread just in case ABX is right. ;-)

Please reply to this - if the cross-posting indeed expires i will repost 
the thread summary.

Gilles Tran wrote:
> 
> These are very good looking. On my computer the first one takes 7m50 so it's
> still pretty fast. I started the second one but stopped it after a while and
> I guess it should take somewhere between 1h and 1h30.
> The difference in render time doesn't seem much justified between both
> images as the second one still have large corner artifacts.
> 

There is indeed not much of a difference between those two at the first 
glance but the faster one, although it renders quite fast, is quite far 
away from the 'correct' solution.  If you compare the images directly 
you will see what i mean.

> However, the impressive lack of artifacts on the walls (similar to the one
> observed with C4D) leads to an obvious question : why do the default
> parameters in this case lead to so-so results? Is the trade-off the corner
> artifact problem? Could POV-Ray's radiosity be "adaptive"?

It depends on what kind of results you want.  The aim of any radiosity 
algorithm should be to converge to the correct solution if you increase 
the quality settings.  How it looks in a fast render much depends on the 
settings in POV-Ray.  To me it seems the default settings usually lead 
to a fairly uniform result, meaning the artefacts have similar intensity 
in all parts of the scene.

> Here's a C4D version obtained by boosting the "max resolution" parameter.
> This drove the render time to almost 2 hours but all the artifacts are gone
> except a couple. In fact I think I could get rid of them entirely by
> lowering the "min resolution" parameter but more tests are required. The top
> image is a screen shot of the pre-pass with the sample location visible.
> http://www.oyonale.com/temp/testrad3h.png

A similar view with POV-Ray using the previous 'e' settings:

http://www.tu-bs.de/~y0013390/files/rad_01e3.png
http://www.tu-bs.de/~y0013390/files/rad_01e2.png

Note because of the techique used to display the points the sample 
locations are not as clearly visible as in the C4D image.  If you 
extract the sample locations from the cache file and display the points 
this might lead to better results.

In rad_01e2.png the blue areas show the places where additional samples 
would be required during final trace without 'always_sample off'.  The 
small red stripes in the corners are those parts were additional samples 
were taken despite 'always_sample off'.

If you turn on always_sample you will see that the artefacts are 
slightly diminished (esp. lower right corner) but the render time is 
increased by more than 50% (28846 instead of 21738 samples)

Christoph

-- 
POV-Ray tutorials, include files, Sim-POV,
HCR-Edit and more: http://www.tu-bs.de/~y0013390/
Last updated 25 Oct. 2003 _____./\/^>_*_<^\/\.______

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