If I understand it correctly, the purpose of radiosity is to compensate for
light scattered by rough surfaces. Normals, as I understand don't do this
right without radiosity which is why you need to add radiosity.

Therefore if you were to use isosurfaces or heightfields to make rough
textures with a relatively low reflection level and a high maximum iteration
level, you wouldn't need to add radiosity.

Am I correct or do I have I gone wrong somewhere?

Nekar

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Nekar Xenos <vir### [at] iconcoza> wrote:
: If I understand it correctly, the purpose of radiosity is to compensate for
: light scattered by rough surfaces. Normals, as I understand don't do this
: right without radiosity which is why you need to add radiosity.

: Therefore if you were to use isosurfaces or heightfields to make rough
: textures with a relatively low reflection level and a high maximum iteration
: level, you wouldn't need to add radiosity.

: Am I correct or do I have I gone wrong somewhere?

  I'm not completely sure what you are talking about.
  Radiosity (or better called "global illumination") is a process of
calculating the interreflection of light between surfaces, which happens
in the real world.

  A small example of what this is:
  Suppose that you are in a completely dark room, with absolutely no light.
Then you turn on a flashlight torch and point it towards a wall. Immediately
you begin to see other details in the room (for example yourself) although
the flashlight is not directly illuminating anything but part of the wall.
It's the light reflected from the wall that is illuminating other parts of
the room (such as the other walls and yourself) and that's why you are able
to see them.
  Suppose that the wall is red instead of white (as supposed in the example
above). The light reflected from the wall will be mostly pure red (in
practice it will reflect a bit of other frequencies as well, since it's
not possible in practice to get a material with 100% red reflectance, but
the other light frequencies are quite minimal). Thus, you will see the other
details in the room illuminated with red light (although the flaslight
itself emits white light).

  This is what radiosity does: It calculates how the light bounces between
surfaces, illuminating other surfaces (which may not be otherwise directly
illuminated at all).
  This can make visible (3D) shapes which are in shadows, as well as affecting
the illumination of everything, even the lit parts (the so-called
"color-bleeding"): If a white chair is in a red room, the chair will get
a reddish tint even if it's directly illuminated by the light source.
  When done right, this adds even a suprising amount of realism to an image.

  I don't understand your talks about normals and isosurfaces in this
context.

-- 
char*i="b[7FK@`3NB6>B:b3O6>:B:b3O6><`3:;8:6f733:>::b?7B>:>^B>C73;S1";
main(_,c,m){for(m=32;c=*i++-49;c&m?puts(""):m)for(_=(
c/4)&7;putchar(m),_--?m:(_=(1<<(c&3))-1,(m^=3)&3););}    /*- Warp -*/

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"Warp" <war### [at] tagpovrayorg> wrote in message
news:3ab9f34b@news.povray.org...
> Nekar Xenos <vir### [at] iconcoza> wrote:
> : If I understand it correctly, the purpose of radiosity is to compensate
for
> : light scattered by rough surfaces. Normals, as I understand don't do
this
> : right without radiosity which is why you need to add radiosity.
>
> : Therefore if you were to use isosurfaces or heightfields to make rough
> : textures with a relatively low reflection level and a high maximum
iteration
> : level, you wouldn't need to add radiosity.
>
<snip>
>
>   I don't understand your talks about normals and isosurfaces in this
> context.
>

I do! (I think).

In the real world, radiosity is generated by any surface that isn't 100%
reflective. However, in Pov-world, this scattering of light is not normally
simulated. In other words, it doesn't matter how bumpy/diffuse/whatever you
make your surfaces - if you don't turn radiosity on, you won't get any
radiosity.

Of course, once you turn it on, then, yes, the shapes and materials of your
objects will affect the radiosity in your scene.

So, the lack of radiosity in standard scenes is nothing to do with lack of
appropriate objects, but is associated with the lack of appropriate
calculations.

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Warp wrote:
> 
> Nekar Xenos <vir### [at] iconcoza> wrote:
> : If I understand it correctly, the purpose of radiosity is to compensate for
> : light scattered by rough surfaces. Normals, as I understand don't do this
> : right without radiosity which is why you need to add radiosity.
> 
> : Therefore if you were to use isosurfaces or heightfields to make rough
> : textures with a relatively low reflection level and a high maximum iteration
> : level, you wouldn't need to add radiosity.
> 
> : Am I correct or do I have I gone wrong somewhere?
> 
>   I'm not completely sure what you are talking about.
>   Radiosity (or better called "global illumination") is a process of
> calculating the interreflection of light between surfaces, which happens
> in the real world.
> 

It should be added that radiosity only calculates the diffuse
interreflection.  For the specular aspects there is photon mapping.  

That's probably also the point Nekar referred to.  Since raytracing
generally does not involve calculation of light reflection, neither
diffuse nor specular, photon mapping and radiosity are both necessary no
matter whether normals or real geometric roughness is used.

Christoph

-- 
Christoph Hormann <chr### [at] gmxde>
IsoWood include, radiosity tutorial, TransSkin and other 
things on: http://www.schunter.etc.tu-bs.de/~chris/

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Ok, let's use some examples on the radiosity sample that comes with Povray :

A) Rendered with the best known settings for radiosity.

B) Use isosurfaces or heightfields to make the roughness of real world
texture, such as wall paint, etc. Use photon packs for lighting and no
radiosity.

Which should look more real?

Nekar

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I forgot to add that B) has a relatively low reflection of say 0.2.

Another thing about radiosity, If you have only smooth reflective surfaces
in a scene, adding radiosity should make basically no difference to the
scene. Right?

Nekar

"Nekar Xenos" <vir### [at] iconcoza> wrote in message
news:3aba0ecd@news.povray.org...
> Ok, let's use some examples on the radiosity sample that comes with Povray
:
>
> A) Rendered with the best known settings for radiosity.
>
> B) Use isosurfaces or heightfields to make the roughness of real world
> texture, such as wall paint, etc. Use photon packs for lighting and no
> radiosity.
>
> Which should look more real?
>
> Nekar
>
>
>

Post a reply to this message

Nekar Xenos wrote:
> 
> Ok, let's use some examples on the radiosity sample that comes with Povray :
> 
> A) Rendered with the best known settings for radiosity.
> 
> B) Use isosurfaces or heightfields to make the roughness of real world
> texture, such as wall paint, etc. Use photon packs for lighting and no
> radiosity.
> 
> Which should look more real?
> 

Your B-version would not be a feasible solution.  The surface structures
leading to diffuse scattering of light in reality are in micrometer
scale.  Even if you use that accurate geometry there would be no effect in
Povray.  

Photon mapping right now is good for large scale computation of reflection
and refraction, but not for realistic simulation of the detail effects.  

Christoph

-- 
Christoph Hormann <chr### [at] gmxde>
IsoWood include, radiosity tutorial, TransSkin and other 
things on: http://www.schunter.etc.tu-bs.de/~chris/

Post a reply to this message

Nekar Xenos wrote:
> 
> I forgot to add that B) has a relatively low reflection of say 0.2.
> 
> Another thing about radiosity, If you have only smooth reflective surfaces
> in a scene, adding radiosity should make basically no difference to the
> scene. Right?
> 

Radiosity (in megapov) uses the diffuse finish component for calculation
(and of course ambient for emission).  If you set diffuse and ambient to 0
on all objects, there will be no effect.  This has nothing to do with the
surfaces being smooth or not.

Christoph

-- 
Christoph Hormann <chr### [at] gmxde>
IsoWood include, radiosity tutorial, TransSkin and other 
things on: http://www.schunter.etc.tu-bs.de/~chris/

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As I understand you B) would work  with a ridiculously high resolution?

Nekar

"Christoph Hormann" <chr### [at] gmxde> wrote in message
news:3ABA1641.D8617F72@gmx.de...
>
>
> Nekar Xenos wrote:
> >
> > Ok, let's use some examples on the radiosity sample that comes with
Povray :
> >
> > A) Rendered with the best known settings for radiosity.
> >
> > B) Use isosurfaces or heightfields to make the roughness of real world
> > texture, such as wall paint, etc. Use photon packs for lighting and no
> > radiosity.
> >
> > Which should look more real?
> >
>
> Your B-version would not be a feasible solution.  The surface structures
> leading to diffuse scattering of light in reality are in micrometer
> scale.  Even if you use that accurate geometry there would be no effect in
> Povray.
>
> Photon mapping right now is good for large scale computation of reflection
> and refraction, but not for realistic simulation of the detail effects.
>
> Christoph
>
> --
> Christoph Hormann <chr### [at] gmxde>
> IsoWood include, radiosity tutorial, TransSkin and other
> things on: http://www.schunter.etc.tu-bs.de/~chris/

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Nekar Xenos wrote:
> 
> As I understand you B) would work  with a ridiculously high resolution?
> 

Maybe if you want the view of a painted wall under a microscope :-)

Christoph

-- 
Christoph Hormann <chr### [at] gmxde>
IsoWood include, radiosity tutorial, TransSkin and other 
things on: http://www.schunter.etc.tu-bs.de/~chris/

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