I did a quick test on this and it seems diffuse reflection
from a surface is clipped to the diffuse value.

// output as 48bit and adjust histogram to compare

#declare M=1; // set levels max point to 255/51=5
//#declare M=51; 

global_settings{
  max_trace_level 6
  radiosity{
    pretrace_start 0.04
    pretrace_end 0.01
    count 800
    recursion_limit 5
    nearest_count 3
    error_bound 0.2
    max_sample 100
  }
}

camera{
  location <0,0,-39>
  direction 1.5*z
}


box{<-3,-3,-40>,<3,3,2>
  pigment{rgb 1}
  finish{diffuse 0.75 ambient 0}
}

light_source{
  <2.5,2.5,1>
  rgb 1/0.75
  spotlight radius 10 falloff 30 tightness 1 point_at<-2.5,-2.5,-1>
}


_____________
Kari Kivisalo

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Kari Kivisalo wrote:
> 
> I did a quick test on this and it seems diffuse reflection
> from a surface is clipped to the diffuse value.
> 

You have to elaborate a bit more on that - the scene renders just fine
here and i have no idea what this 'M' is meant for.

Christoph

-- 
POV-Ray tutorials, include files, Sim-POV,
HCR-Edit and more: http://www.tu-bs.de/~y0013390/
Last updated 28 Feb. 2003 _____./\/^>_*_<^\/\.______

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Christoph Hormann wrote:
> 
> You have to elaborate a bit more on that - the scene renders just fine
> here and i have no idea what this 'M' is meant for.

The idea is that M=1 limits all the reflected rays below 1.
The directly lit area is the brigtest and emits at intensity 1 which
should be ok even if there is clipping done anywhere.

M=51 should look equal to M=1 when M=1 image is adjusted to same
brightness. It doesn't so there is clipping present. You'll notice
the back wall intensity is clipped to 0.75. The corridor is also
darker.



_____________
Kari Kivisalo

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Kari Kivisalo wrote:
> 
> > You have to elaborate a bit more on that - the scene renders just fine
> > here and i have no idea what this 'M' is meant for.
> 
> The idea is that M=1 limits all the reflected rays below 1.
> The directly lit area is the brigtest and emits at intensity 1 which
> should be ok even if there is clipping done anywhere.
> 
> M=51 should look equal to M=1 when M=1 image is adjusted to same
> brightness. It doesn't so there is clipping present. You'll notice
> the back wall intensity is clipped to 0.75. The corridor is also
> darker.

Fine but 'M' is not used anywhere in your code - the image will always
look the same.

Christoph

-- 
POV-Ray tutorials, include files, Sim-POV,
HCR-Edit and more: http://www.tu-bs.de/~y0013390/
Last updated 28 Feb. 2003 _____./\/^>_*_<^\/\.______

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Christoph Hormann wrote:
> 
> Fine but 'M' is not used anywhere in your code - the image will always
> look the same.

Should be like:

light_source{
  <2.5,2.5,1>
  rgb 1/0.75*M
  spotlight radius 10 falloff 30 tightness 1 point_at<-2.5,-2.5,-1>
}

Posted image to binaries.images where M=1 is adjusted to same
brightness.


_____________
Kari Kivisalo

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Kari Kivisalo wrote:
> 
> Should be like:
> 
> light_source{
>   <2.5,2.5,1>
>   rgb 1/0.75*M
>   spotlight radius 10 falloff 30 tightness 1 point_at<-2.5,-2.5,-1>
> }

All right, i already assumed something like that.

This effect is cause by the clipping of prediction values (stored
illuminance values plus gradients) in ra_average_near() (line 461 ff. in
radiosit.cpp).  I am not completely sure why this clipping is used but i
suppose it was meant to reduce artefacts when there was no
Maximum_Sample_Brightness yet.  Using max_sample you can achieve about the
same effect.

Christoph

-- 
POV-Ray tutorials, include files, Sim-POV,
HCR-Edit and more: http://www.tu-bs.de/~y0013390/
Last updated 28 Feb. 2003 _____./\/^>_*_<^\/\.______

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> This effect is cause by the clipping of prediction values (stored
> illuminance values plus gradients) in ra_average_near() (line 461 ff. in
> radiosit.cpp).  I am not completely sure why this clipping is used but i
> suppose it was meant to reduce artefacts when there was no
> Maximum_Sample_Brightness yet.  Using max_sample you can achieve about the
> same effect.

Nope :)

You simply do not understand gradients in the Ward's method....
It does not limit the interpolated values.. it limits overestimation by
gradient method and
has no connection to the Kari's sample.

I will show you in a few days all clipping places in the radiosit.cpp and
more :)

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"T.J.Viking" wrote:
> 
> [...]
> 
> You simply do not understand gradients in the Ward's method....
> It does not limit the interpolated values.. it limits overestimation by
> gradient method and
> has no connection to the Kari's sample.

Well, in contrast to you i changed it and tested the results...

Christoph

-- 
POV-Ray tutorials, include files, Sim-POV,
HCR-Edit and more: http://www.tu-bs.de/~y0013390/
Last updated 28 Feb. 2003 _____./\/^>_*_<^\/\.______

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> > You simply do not understand gradients in the Ward's method....
> > It does not limit the interpolated values.. it limits overestimation by
> > gradient method and
> > has no connection to the Kari's sample.
>
> Well, in contrast to you i changed it and tested the results...

And you led to the overestimation of interpolated samples....

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Some info 4 you Chris.
I would really appreciate if you read that:

http://radsite.lbl.gov/radiance/papers/erw92/paper.html

http://positron.cs.berkeley.edu/~gwlarson/papers.html

Those are papers of Greg Ward, and current POVRAY "radiosity" is
modified Ward's Irradiance Cache.

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