OK, I tried this :
I changed warp's previous code to add light fading in the light_source
block.
So, that gives :

#version Unofficial MegaPov 0.5;

global_settings
{ ini_option "+QR"
  ambient_light .01
  radiosity
  { pretrace_start 0.08
    pretrace_end   0.02
    count 80
    nearest_count 5
    error_bound 1
    recursion_limit 4
    low_error_factor .5
    gray_threshold 0.0
    minimum_reuse 0.015
    brightness 1.7
    adc_bailout 0.01/2
  }
}

camera { location -z*11.9 look_at 0 angle 60 }

light_source
{ 0, 1*10
  fade_power 1
  fade_distance .21

  looks_like
  { box { <-1,0,-1><1,.4,1> pigment { rgb 1 } finish { ambient
.25*4*1000 } }
  }
  translate y*3.6
}

#macro Wall(Color1, Color2)
  box
  { <-4,-4,0><4,4,.1>
    pigment
    { boxed color_map
      { [0 Color1][.1 Color1][.1 Color2][.2 Color2][.2 Color1][1 Color1]
      }
      translate <1,1,0>
      warp { repeat x*2 }
      warp { repeat y*2 }
    }
  }
#end

object { Wall(rgb 1, rgb .8) translate z*4 }
object { Wall(rgb 1, rgb .8) rotate y*180 translate -z*12 }
object { Wall(rgb x, rgb x*.8) rotate -y*90 translate -x*4 }
object { Wall(rgb x, rgb x*.8) rotate -y*90 translate -x*4-z*8 }
object { Wall(rgb z, rgb <.3,.3,.8>) rotate y*90 translate x*4 }
object { Wall(rgb z, rgb <.3,.3,.8>) rotate y*90 translate x*4-z*8 }
object { Wall(rgb x+y, rgb (x+y)*.8) rotate -x*90 translate y*4 }
object { Wall(rgb x+y, rgb (x+y)*.8) rotate -x*90 translate y*4-z*8 }
box { <-4,-4,-12><4,-4.1,4> pigment { checker rgb 1, rgb .2 scale .5 } }

box { -1,1 pigment { rgb x+y } rotate y*30 translate <-1.5,-3,-1> }
sphere { <-1.8,-.5,0>, .9 pigment { rgb 1 } finish { specular .3 } }
cylinder
{ 0, y, 1 pigment { rgb <1,.8,.6> }
  rotate z*70 rotate y*-20 translate <2.5,-2.5,-1>
}

union
{ torus
  { 1.2, .5
    pigment { rgbf <1,1,1,.95> }
    finish { specular .5 roughness .02 reflection .2 }
    interior { ior 1.5 }
  }
  cone
  { 0, .7, y*2.5, 0 pigment { rgb y+z } finish { specular .2 }
  }
  rotate z*65 rotate y*-40 translate <1,-1,2>
}


You can see the resulting image rendered with MegaPoV 0.5 here :
http://perso.wanadoo.fr/albedo/warp_pov.jpg

Then, I replaced the global_settings block by :

global_settings
{
  ambient 1/1000
  stochastic_global_illumination { samples 300 brightness 0.55 }
}

The rest is unchanged. I implemented my patch in my MegaPoV 0.5 release.
You can see the resulting image rendered with it here :
http://perso.wanadoo.fr/albedo/warp_sgi.jpg

Don't you think there's a bit difference of realism, especially for the
yellow box ?
Try to look at these images successively. It seems to me that the
original radiosity rendering is a bit tasteless compared to my
stochastic radiosity function.
However, the first rendering was twice as fast as the second. But I
don't really know if there's a way to parameter the radiosity { ... }
block to obtain the same results we have easily with the
stochastic_global_illumination function. The main reason is maybe
because algorithms are differents.
What do you think ?

Stephane Marty
- - - - - - - -
Computer Graphics Software
http://perso.wanadoo.fr/albedo

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Yours does have certain aspects which I like, but it seems less realistic
than the other one. Yours almost seems to make the box reflective. I don't
like that. I'm sorry.

Post a reply to this message

On Sun, 28 May 2000 09:19:02 -0500, "Tony[B]"
<ben### [at] panamac-comnet> wrote:

>Yours does have certain aspects which I like, but it seems less realistic
>than the other one.

Tony, this isn't directed at you, but to everyone:

Has anyone reading this news group *ever* actually seen a physical
room identical to the one being used here for these radiosity tests?
If not, how on earth can you debate some of the more minor issues of
realism, when comparing two different radiosity tests?

This sort of room is a standard test subject for radiosity. It even
has an official name. (I think it's a Cornell Box?) Has any of us ever
seen such a room in real life?

I suggest creating some sort of standard *physical* environment to
serve as a reference point for testing your radiosity renderings. To
this end, I'm thinking of building my own physical implementation of
the Cornell Box. It will have the same basic colors and lighting as
these computer simulations. I will also recreate this physical box in
POV script, for use in radiosity testing. When it is done, I can see
which of the radiosity techniques actually look the most realistic.

The only trouble is, not everyone could come to my home and see this
in person. I suppose I'll photograph the box, live with the errors
introduced by the photographic process, and post that image to this
news server. That should still be much more objective than the simple
testing currently being done here.

Comments anyone?

Later,
Glen Berry

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

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I guess you're right. Please post the photo for us, Glen. I would really
appreciate it. But, still, in my experience, colors don't bleed that much in
RL, I think.

Post a reply to this message

On Sun, 28 May 2000 13:19:49 -0500, "Tony[B]"
<ben### [at] panamac-comnet> wrote:

>I guess you're right. Please post the photo for us, Glen. I would really
>appreciate it. But, still, in my experience, colors don't bleed that much in
>RL, I think.

I also think that many of the examples we've seen "bleed" in
unrealistic ways. Sometimes the color bleed seems far too saturated,
and other times it seems to bleed for too great a distance. However,
there *are* circumstances in real life where the color bleed is
dramatic, even if this isn't typical in most cases. 

The trouble is, this example scene everyone is using has no physical
reference that I know of. That's why I suggest building a physical box
for comparison. It might be a little while before I get one built, but
I do intend to get around to it. I would also encourage others to
attempt something similar and let this newsgroup know about your
results. 

If nothing else, accurately model an existing space that you have
access to, (such as a room in your house), and let us know which
radiosity techniques render it the best. It would be a good idea to
back up the results with a high quality photograph of the actual
space. (I realize that to do this properly requires more effort and
discipline than most people are willing to invest. It also prohinits
others from validating your results, unless they also build a room
just like yours. However, I think it could still be educational.)

Later,
Glen Berry


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

Post a reply to this message

Glen Berry wrote:
> 
> I suggest creating some sort of standard *physical* environment to
> serve as a reference point for testing your radiosity renderings. To
> this end, I'm thinking of building my own physical implementation of
> the Cornell Box. It will have the same basic colors and lighting as
> these computer simulations. I will also recreate this physical box in
> POV script, for use in radiosity testing. When it is done, I can see
> which of the radiosity techniques actually look the most realistic.
> 
> The only trouble is, not everyone could come to my home and see this
> in person. I suppose I'll photograph the box, live with the errors
> introduced by the photographic process, and post that image to this
> news server. That should still be much more objective than the simple
> testing currently being done here.
> 
> Comments anyone?

Yes, why not, that sounds great !

Stephane Marty
- - - - - - - -
Computer Graphics Software
http://perso.wanadoo.fr/albedo

Post a reply to this message

Stephane Marty <alb### [at] wanadoofr> wrote:
: Don't you think there's a bit difference of realism, especially for the
: yellow box ?

  I can compare the two images very well by pressing alt+left (back) and
alt+right (forward) successively in Netscape. It changes between the images
very quickly making it very easy to see the differences in the images.

  I'm sorry but I can't see _any_ difference in the yellow box, no matter
how carefully I look.
  Well, in the right face, near the floor, I can see a couple of blotchy
spots which are missing in the megapov image. I can't say that these
blotchy spots are very realistic. They are probably caused by the low
sampling amount (300 if I remember right?).

  Instead, there's a big difference in the white wall. In the megapov version
it's quite well lit, with a reddish tint at the left side and a blueish tint
at the right side. Looks quite good to me.
  However, in the second image created by your patch this wall is pretty dark
and there's no visible color bleeding from the colored side walls.
  I have to say that I like more the megapov version of this wall. It just
looks better, and in my opinion more realistic.
  I think I know what's the problem: What's the recursion level of your
algorithm?

  I would like to see bigger versions of these images. For example 640x480.
And antialiased.

: However, the first rendering was twice as fast as the second.

  Well, this is another advantage of the megapov version. I suppose that if
you had used antialiasing the speed difference might have been even bigger.

-- 
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

Post a reply to this message

Warp wrote:
> 
>   I'm sorry but I can't see _any_ difference in the yellow box, no matter
> how carefully I look.

What about the shading of the yellow box ?

>   Well, in the right face, near the floor, I can see a couple of blotchy
> spots which are missing in the megapov image. I can't say that these
> blotchy spots are very realistic. They are probably caused by the low
> sampling amount (300 if I remember right?).
> 
>   Instead, there's a big difference in the white wall. In the megapov version
> it's quite well lit, with a reddish tint at the left side and a blueish tint
> at the right side. Looks quite good to me.
>   However, in the second image created by your patch this wall is pretty dark
> and there's no visible color bleeding from the colored side walls.
>   I have to say that I like more the megapov version of this wall. It just
> looks better, and in my opinion more realistic.
>   I think I know what's the problem: What's the recursion level of your
> algorithm?

2.

>   I would like to see bigger versions of these images. For example 640x480.
> And antialiased.
> 
> : However, the first rendering was twice as fast as the second.
> 
>   Well, this is another advantage of the megapov version. I suppose that if
> you had used antialiasing the speed difference might have been even bigger.

Well, what is clear to me is that your opinion is a bit influenced by
something I don't understand.
Too bad.

Post a reply to this message

Stephane Marty <alb### [at] wanadoofr> wrote:
: Well, what is clear to me is that your opinion is a bit influenced by
: something I don't understand.
: Too bad.

  I don't think it should be so hard to understand.

  - Your patch certainly makes the so-called "color bleeding" more evident.
This, however, doesn't make the image look better or more realistic, only
kind of overexposed.

  - As seen in the two example images made with my scene, the brightness seems
to need some fixing. At least to me the megapov version looks more like it
should be (I'm talking about the white wall). If you look at the image created
with your patch and compare the brightness of the colored walls to the white
wall, there seems to be an odd discontinuity: The colored walls are well lit
while the white wall is quite dark. In the real word the light reflecting
from the side walls, the floor, the backwall and even the objects should make
the white wall more lit.

  - Your patch seems to have some graininess problem which is somewhat evident
in the example image in the www-page of the patch. If I understood correctly,
it happens when the sample count is too low. In megapov even an extremely
low sample count creates almost perfectly smooth illumination. It was mentioned
that your patch may need even 10 times more samples than megapov needs to
create a non-grainy image (80 samples vs. 800 samples).

  - Your patch is very slow compared to megapov. Even when megapov uses
recursion level 4 and your patch uses only recursion level 2 (which of
course reduces the quality), your patch took twice the render time of
megapov to get an image of approximately the same quality. Even then some
blotchy spots can be seen in some parts of the scene (probably due to the
low sample count?).
  Somehow I also have the feeling that using antialiasing would have made the
render time even longer compared to megapov (I may be wrong here, of course).

  - You haven't rendered the sample image at a higher resolution (eg. 640x480)
and somehow I have the feeling that using the same radiosity settings but
using higher resolution might cause graininess in the image (of course it's
only a hypotesis). Please correct me if I'm wrong.
  The radiosity in megapov is independent of the image size. You can render
that image at any resolution you want and you will probably not get any
graininess, blotchiness or whatever that doesn't appear in the small image.
  If I'm correct in my assumption then I think that you'll have to increase
the sample count for bigger resolutions thus making the rendering times
extremely long.
  (If I'm mistaken here, please forgive me.)

-- 
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

Post a reply to this message

Warp wrote:
> 
>   The radiosity in megapov is independent of the image size. You can render
> that image at any resolution you want and you will probably not get any
> graininess, blotchiness or whatever that doesn't appear in the small image.

That's probably not entirely true. You would get the same amount of radiosity
detail in a larger image, but the inaccuracies would become more conspicuous.

-- 
Margus Ramst

Personal e-mail: mar### [at] peakeduee
TAG (Team Assistance Group) e-mail: mar### [at] tagpovrayorg

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