Hi folks,

I keep running into a problem with radiosity and I'd like to ask, why it
behaves that way. Lets say I have a sky_sphere to illuminate a scene like
this:

sky_sphere { pigment { rgb 1 } } // Light
sphere { 0,1 pigment { rgb 1 } }
plane { y,-1 pigment { rgb .6 } }

Now, lets say I want to increase the light, so I set a higher pigment in
sky_sphere. But no matter how high I go, the scene doesn't turn white....
Why?

If I increase the pigment in the light-absorbing objects (plane and sphere)
it works, and the scene is able to turn white! Also, by setting a higher
brightness in the radiosity block, I can get more light in the scene.. BUT..
After much experimentation it seems, I am limited when objects can't really
emit light with strength above 1.. Somewhere the value is clipped and I
don't understand why.

It's not due to "max_sample" in the radiosity block that is turned off by
default.

Best regards,
Hugo

Post a reply to this message

You might want to look at the radiosity tutorial.  Your objects need a full
texture, including a finish:

sky_sphere { pigment { rgb 1 } } // Light
sphere { 0,1 texture { pigment { rgb 1 } finish { ambient 0.5 diffuse 1
brilliance 3 } } }
plane { y,-1 texture { pigment { rgb .6 } finish { ambient 0.2 diffuse 1
brilliance 2 } } }


"Hugo Asm" <hua### [at] post3teledk> wrote in message
news:3f3178be@news.povray.org...
> Hi folks,
>
> I keep running into a problem with radiosity and I'd like to ask, why it
> behaves that way. Lets say I have a sky_sphere to illuminate a scene like
> this:
>
> sky_sphere { pigment { rgb 1 } } // Light
> sphere { 0,1 pigment { rgb 1 } }
> plane { y,-1 pigment { rgb .6 } }
>
> Now, lets say I want to increase the light, so I set a higher pigment in
> sky_sphere. But no matter how high I go, the scene doesn't turn white....
> Why?
>
> If I increase the pigment in the light-absorbing objects (plane and
sphere)
> it works, and the scene is able to turn white! Also, by setting a higher
> brightness in the radiosity block, I can get more light in the scene..
BUT..
> After much experimentation it seems, I am limited when objects can't
really
> emit light with strength above 1.. Somewhere the value is clipped and I
> don't understand why.
>
> It's not due to "max_sample" in the radiosity block that is turned off by
> default.
>
> Best regards,
> Hugo
>
>

Post a reply to this message

> Your objects need a full texture, including a finish:
>
> sky_sphere { pigment { rgb 1 } } // Light
> sphere { 0,1 texture { pigment { rgb 1 } finish { ambient 0.5 diffuse 1
> brilliance 3 } } }
> plane { y,-1 texture { pigment { rgb .6 } finish { ambient 0.2 diffuse 1
> brilliance 2 } } }

Thanks for your reply, but why have you increased the ambient value in the
sphere and plane? That way, they will emit light. I only want the sky to
emit light. Raising the diffuse parameters is going to brighten the scene
too, but it still doesn't allow the *light* to increase. Lets say I have a
dark material somewhere; an object that is rather dark. Shouldn't it still
be able to respond to a strong lightsource?

Regards,
Hugo

Post a reply to this message

Hugo Asm wrote:
> 
> If I increase the pigment in the light-absorbing objects (plane and sphere)
> it works, and the scene is able to turn white! Also, by setting a higher
> brightness in the radiosity block, I can get more light in the scene.. BUT..
> After much experimentation it seems, I am limited when objects can't really
> emit light with strength above 1.. Somewhere the value is clipped and I
> don't understand why.

It is actually not a limitation of the brightness objects can have, it is
a limitation of the radiosity estimation values.  A small and very bright
object will have a significant effect but if you make the whole sky sphere
brighter than white this will be clipped.  It will be changed in POV-Ray
3.5.1.  To work around the problem you can render your scene on a lower
lighting level and post process the result (16 bit output would be
recommended for this of course).

Christoph

-- 
POV-Ray tutorials, include files, Sim-POV,
HCR-Edit and more: http://www.tu-bs.de/~y0013390/
Last updated 17 Jun. 2003 _____./\/^>_*_<^\/\.______

Post a reply to this message

> It is actually not a limitation of the brightness objects can have, it is
> a limitation of the radiosity estimation values.  A small and very bright
> object will have a significant effect but if you make the whole sky sphere
> brighter than white this will be clipped.  It will be changed in POV-Ray
> 3.5.1.  To work around the problem you can render your scene on a lower
> lighting level and post process the result (16 bit output would be
> recommended for this of course).

Thank you! Sounds very nice. Meanwhile, I've begun to use Kari Kivisalo's
exposure patch to gain some brightness right before the final output. That
saves me the manual PP and seems to work.  :o)

Regards,
Hugo

Post a reply to this message