Am 07.03.2013 19:16, schrieb s.day:

> I initially set error_bound to 0.8 but had so many artifacts it looked like an
> oil painting (an interesting effect but not what I was after). I just copied the
> radiosity settings from an old image that did not use HDR then started
> tweaking...

Good that you mention this, because I completely forgot about this problem:

Radiosity currently doesn't do a good job with HDR light probes having 
rather small bright regions (e.g. direct sunlight). There are two ways 
to approach this problem:


(A) Create a blurred version of the light probe using an external 
program, and use this one for radiosity:

sphere { <0,0,0>, 10000 // or some other large value
   texture {
     pigment { image_map  {...} }
     finish { emission 1 diffuse 0 specular 0 }
   }
   no_image
   no_reflection
}

For reflections and background, the classic sky_sphere will be visible.


(B) Crank up the radiosity "count" value like mad; setting 
"nearest_count" to the maximum value of 20 should also help.


> Two more questions though..
>
> 1) Is variable reflection advised for most objects, I have previously only used
> this for glass/water?

For realism, yes - variable reflection does improve the credibility of 
any polished surface, and it doesn't slow down the render noticeably.


> 2) Without specular does roughness have an effect on the surface?

No; in radiosity-lit scenes, highlights will always be infinitely sharp 
(unless you know how to achieve blurred reflections. There are ways, but 
they come at a significant cost in render time; and even then the 
blurriness will not be controlled by the roughness keyword.)

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