On Thu, 01 Jun 2000 23:52:35 +0200, Stephane Marty <alb### [at] wanadoofr>
wrote:

>As I proposed to you a few days ago, I've converted the original
>"cornell box" scene to PoV. Both have exactly the same frame. However,
>don't forget that the original rendering was done in spectral space so,
>because of the loss of accuracy, we have a visible colorimetric
>difference.

I have a few comments about your adaptation of the Cornell Box. I
noticed that in your POV code, you scaled the box dimensions down by a
factor of 10. If we will be treating this as a standard, why not keep
the same box size as the original? (Some might say the scaling has no
effect, but then I want to know even more why it was changed, if it
makes no difference?)

I noticed that you are using Cornell's synthetic rendering as your
standard. It would be better to use the actual photo of the physical
Cornell Box for comparisons. (The goal is to reproduce reality with
POV-Ray, not to emulate another rendering.) It's unfortunate that
Cornell didn't provide a nice RGB image of the original box. The only
one I found was in a 7-channel IPLab format, instead of a typical RGB
image. They offer a Matlab function to work with the IPLab format, but
I have no idea how to use it. 

Can anyone figure out how to accurately convert the 7 channel IPLab
reference image into an RGB image?

What sort of procedure did you use to convert their spectral data into
RGB values? I think it needs a bit of revision. Your "white" is a bit
too pure. The original looked a bit yellowish in comparison. Your
"red" looks too pure. The original is closer to red-orange than a
simple red. The green is also different, but I'm not sure the best way
to describe it. 

Don't misunderstand, I do appreciate the effort you have put into this
so far. It would just be nice to improve things a bit. For a long
time, people have been judging the rendering quality of POV-Ray, as if
they lived in a total vacuum. I think it's time we started comparing
POV to actual samples of the real world, when we want to judge its
rendering quality. What looks more interesting is not always more
accurate. Reality and people's recollection of it, are almost always
significantly different.

As for the rendering comparison, I like your illumination model the
best. It's a shame it takes so long. Perhaps a way will be found to
increase the speed? 

Thanks for sharing your results with us.

Later,
Glen Berry

( Remove the "7" from 7no### [at] ezwvcom to email me. )

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