Hello,

I'm wondering: Would it be feasable to use radiosity with a sky sphere to
generate HDR-ish effects from within Pov-ray?

Since sky_spheres only take pigments, not full textures, I can't see how to
do it directly with a sky_sphere. If I simply apply a sky_sphere pigment to
a scaled up sphere, the pigment gets all messed up, because sky_spheres map
pigments differently than a normal sphere.

I've doodled with running an empty scene (nothing inside but a camera and a
sky_sphere) with a spherical projection, outputting to hdr, then mapping
that to a giant sphere inside the final scene. This doesn't work right at
all unless you use uv mapping on the sphere ;-) but even then I can never
get the textures to look the same as they did originally.

Any chance I piqued the curiousity of someone who knows more about the topic
than I do? :-)

FWIW, this was all prompted by a sunset scene that I'm working on that I
just can't get the lighting right in. :-P

William

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"Afishionado" <afi### [at] gmailcom> wrote in message 
news:web.43c5a940743b370581cca5e40@news.povray.org...
> I'm wondering: Would it be feasable to use radiosity with a sky sphere to
> generate HDR-ish effects from within Pov-ray?
>
> Since sky_spheres only take pigments, not full textures, I can't see how 
> to
> do it directly with a sky_sphere. If I simply apply a sky_sphere pigment 
> to
> a scaled up sphere, the pigment gets all messed up, because sky_spheres 
> map
> pigments differently than a normal sphere.


sky_sphere {
  pigment {image_map {hdr MAP once interpolate 2 map_type 1}}
}


Sky_sphere shouldn't map different then a sphere, but what does happen is 
that a sky_sphere is infinite, whereas a sphere isn't, so depending upon the 
size of the sphere and the location of your camera, the scene can look 
different because of perspective.  Try using a larger sphere to minimize 
this.

One advantage that a sphere has over a sky_sphere is that it has a finish 
block so you can increase the ambient value to increase the radiosity 
influence of the HDR, whereas with sky_sphere, it is much more difficult to 
do.

Hope that helps a little.

-tgq

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"Afishionado" <afi### [at] gmailcom> wrote:
> Hello,
>
> I'm wondering: Would it be feasable to use radiosity with a sky sphere to
> generate HDR-ish effects from within Pov-ray?
>
> Since sky_spheres only take pigments, not full textures, I can't see how to
> do it directly with a sky_sphere. If I simply apply a sky_sphere pigment to
> a scaled up sphere, the pigment gets all messed up, because sky_spheres map
> pigments differently than a normal sphere.

Why use a sky_sphere? A regular sphere works ok. Have a look at Jaime Vives
Piqueres' web page for a simple way to do pseudo-HDRI lighting in standard
POV.

http://www.ignorancia.org/tips.php

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PM 2Ring <nomail@nomail> wrote:
> Why use a sky_sphere?

  Why not? Can you give some reasons?

  For one, sky_sphere is faster than a regular sphere.

-- 
                                                          - Warp

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OK, I have a sky texture made in Pov-Ray (bozo clouds, etc.) that works fine
on a standard sky_sphere. I'm just wondering if I can light the scene using
radiosity from it.

I can't figure out how to "bump up" the radiosity of it with a sky_sphere.
That's really all there is to it.

The radiosity bit from the Pov-Ray tutorial seems to show blue light from a
sky, so maybe there's something really simple here that I'm just too
thick-headed to see. Maybe I just need to stare at the docs longer. :-P

William

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Afishionado <afi### [at] gmailcom> wrote:
> OK, I have a sky texture made in Pov-Ray (bozo clouds, etc.) that works fine
> on a standard sky_sphere. I'm just wondering if I can light the scene using
> radiosity from it.

  Yes.

> I can't figure out how to "bump up" the radiosity of it with a sky_sphere.
> That's really all there is to it.

  You can increase the 'brightness' value of radiosity, if that helps.

  Of course if you really want to brighten up the sky texture and nothing
else, then you'll have to use a real sphere with a proper 'finish'.

-- 
                                                          - Warp

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"Warp" <war### [at] tagpovrayorg> wrote in message 
news:43c6bf83@news.povray.org...
> Afishionado <afi### [at] gmailcom> wrote:
> > OK, I have a sky texture made in Pov-Ray (bozo clouds, etc.) that 
works fine
> > on a standard sky_sphere. I'm just wondering if I can light the 
scene using
> > radiosity from it.
> 
>   Yes.
> 
> > I can't figure out how to "bump up" the radiosity of it with a 
sky_sphere.
> > That's really all there is to it.
> 
>   You can increase the 'brightness' value of radiosity, if that helps.
> 
>   Of course if you really want to brighten up the sky texture and 
nothing
> else, then you'll have to use a real sphere with a proper 'finish'.

Not necesseaeraely (I really hate that word :-/)
You can use the transmit-brighten/darken-trick:

-- start code --

#version unofficial MegaPov 1.1;
sky_sphere {
 pigment {
  image_map {
   hdr "rnl_probe.hdr"
   map_type 7
  }
 }
 pigment {rgb 0 transmit .5}
}

-- end code --

The transmit-value acts like an ambient-value: transmit 0 gives total 
blackness, transmit 1 gives standard brightness, transmit 2 gives double 
brightness and so on.

cu!
-- 
#macro G(b,e)b+(e-b)*C/50#end#macro _(b,e,k,l)#local C=0;#while(C<50)
sphere{G(b,e)+3*z.1pigment{rgb G(k,l)}finish{ambient 1}}#local C=C+1;
#end#end _(y-x,y,x,x+y)_(y,-x-y,x+y,y)_(-x-y,-y,y,y+z)_(-y,y,y+z,x+y)
_(0x+y.5+y/2x)_(0x-y.5+y/2x)            // ZK http://www.povplace.com

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Or, I could use:

color rgb <r, b, b> * n

in my pigment definitions. :-P

My bad.

William

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"Afishionado" <afi### [at] gmailcom> wrote in message 
news:web.43c6e82f3b03bf4bc5653ea60@news.povray.org...
> Or, I could use:
> 
> color rgb <r, b, b> * n
> 
> in my pigment definitions. :-P

yes, but that won't work with image_map's

cu!
-- 
#macro G(b,e)b+(e-b)*C/50#end#macro _(b,e,k,l)#local C=0;#while(C<50)
sphere{G(b,e)+3*z.1pigment{rgb G(k,l)}finish{ambient 1}}#local C=C+1;
#end#end _(y-x,y,x,x+y)_(y,-x-y,x+y,y)_(-x-y,-y,y,y+z)_(-y,y,y+z,x+y)
_(0x+y.5+y/2x)_(0x-y.5+y/2x)            // ZK http://www.povplace.com

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> yes, but that won't work with image_map's

Which I'm not working with right now. :-P

William

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