[Radiance-general] Blotching caused by translucent material

[Andrew McNeil]

Hi Orn,

It looks like the specular transmission component is sampled
stochastically, this happens because you have non-zero roughness in your
trans definition. To reduce the blotches in your sun patches you'll need to
crank ad, reduce aa and set st to zero. I'd keep lw at roughly 1/ad because
you want to heavily sample the window but with so many rays you don't need
them to split much further. You could also consider turning off the ambient
cache by setting -aa 0. This changes the effect from blotches to noise,
which sometimes has a better appearance.

Or you could change roughness from 0.010 to 0. I'm not sure how important
the roughness is to you simulation, but I don't expect it'll have much
affect on your illuminance result. But if you're interested in simulating
appearance accurately then the roughness is important.

I'd also suggest double checking your trans definition. It has a very low
total transmission (~9%) and is mostly specular.

Best,
Andy


On Fri, Jun 12, 2015 at 5:47 AM, Örn Erlendsson <orn.e at live.com> wrote:

> Hi,
>
> Can someone help me to set the Radiance parameters to eliminate blotching
> in my images? I am running renderings, DGP and glare simulations for a
> simple geometry. I have had no issues with the images when I use clear
> glazing. One of the tests that I am conducting, however, uses translucent
> glazing with the following parameters:
>
> void trans testTrans
> 0
> 0
> 7 0.478 0.478 0.478 0.000 0.010 0.178 0.635
>
> I've run radiance with two different parameter sets, the first with
>
> _av_ is set to 0
> xScale is set to 2
> _ab_ is set to 6
> _dc_ is set to 0.5
> _aa_ is set to 0.2
> _ad_ is set to 2048
> _st_ is set to 0.5
> yScale is set to 2
> _ps_ is set to 4
> _ar_ is set to 64
> _as_ is set to 2048
> _ds_ is set to 0.25
> _pt_ is set to 0.1
> _dr_ is set to 1
> _pj_ is set to 0.9
> _dp_ is set to 256
> _dt_ is set to 0.25
> _lr_ is set to 6
> _dj_ is set to 0.5
> _lw_ is set to 0.01
>
> resulting in the image named Blotching001
>
> The second case has the following parameters:
>
> _av_ is set to 0
> xScale is set to 6
> _ab_ is set to 6
> _dc_ is set to 0.75
> _aa_ is set to 0.1
> _ad_ is set to 4096
> _st_ is set to 0.15
> yScale is set to 6
> _ps_ is set to 2
> _ar_ is set to 128
> _as_ is set to 4096
> _ds_ is set to 0.05
> _pt_ is set to 0.05
> _dr_ is set to 3
> _pj_ is set to 0.9
> _dp_ is set to 512
> _dt_ is set to 0.15
> _lr_ is set to 8
> _dj_ is set to 0.7
> _lw_ is set to 0.005
>
> resulting in the image named Blotching002. I have also attached an image
> with no blotching. This case uses glazing with 65% light transmittance.
>
> Although the second case is much better, it is still very bad for hours
> when the sun is lower in the sky. The two above images are rendered for a
> clear sky at 18:00 in Germany.
>
> Can someone help?
>
> Kind regards,
> Orn Erlendsson
>
>
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>
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