[Radiance-general] illum-like behaviour for sky dome

[Rob Guglielmetti]

I love how you can whip up these fun image recipes, Greg!

On May 24, 2010, at 10:46 AM, Greg Ward wrote:

> Hi Axel,
> 
> Your sky is probably twice as bright because without turning on direct jittering, all ray samples will be taken from the zenith, neglecting to integrate the cosine factor.  You can try again with -dj 1, but I don't think you'll like the noisy results.
> 
> A better approach is to remove the significant low frequencies from your sky, replacing them with the desired gensky or gendaylit distribution.  See the following entry in a thread from a couple years ago:
> 
> 	http://www.radiance-online.org/pipermail/radiance-general/2008-May/005046.html
> 
> Christopher's suggestion is also a good one.  You can save the depth buffer using the -z option, convert it to an image, then use pcomb to select for depths greater than 1e9 as the sky, like so:
> 
> 	rpict ... -x 1024 -y 768 -pa 0 -pj 0 -vf view1.vf -z view1.zbf scene.oct > view1.hdr
> 	rpict ... -x 1024 -y 768 -pa 0 -pj 0 -vf view1.vf sky_only.oct > view1sky.hdr
> 	pvalue -r -h -y 768 +x 1024 -df view1.zbf | pcomb -e 'sel=if(gi(3)-1e9,2,1)' \
> 			-e 'ro=ri(sel);go=gi(sel);bo=bi(sel)' view1.hdr view1sky.hdr - \
> 			| pfilt -1 -r .6 -x /3 -y /3 > filtered.hdr
> 
> The sky_only.oct contains the nice, captured sky you wish to reproduce.  The final pfilt improves the appearance substantially.  The -pj 0 turns off the usual pixel jittering, which can lead to some aliasing but is necessary to get exact pixel correspondence between renderings.  I'm sure you can figure out the rest, fixing any mistakes I made above.
> 
> Cheers,
> -Greg
> 
>> From: Axel Jacobs <jacobs.axel at gmail.com>
>> Date: May 23, 2010 2:51:52 PM PDT
>> 
>> Dear list,
>> 
>> I have a brightfunc applied to the glow of the sky dome. I would like this pattern to be visible to the camera, but use a normal gensky generated sky for all sample rays.
>> 
>> Conceptually, this is similar to the illum type where a different material is applied when the object (the sky in my case) is viewed directly.
>> 
>> I did try with illum:
>> 
>> skyfunc glow skyglow
>> 0
>> 0
>> 4  1 1 1  0
>> 
>> skyglow brightfunc bracelet
>> 2 band bracelet.cal
>> 0
>> 0
>> 
>> skyfunc illum skymat
>> 1 bracelet
>> 0
>> 3  1 1 1
>> 
>> skymat source sky
>> 0
>> 0
>> 4  0 0 1  180
>> 
>> This works, but results in about twice the horizontal illuminance compared to a normal glow sky. The sky now takes part in the direct calculation (this works with -ab 0), and all light expectedly emenates from the zenith. So using illum is not an option.
>> 
>> Many thanks for your ideas
>> 
>> Axel
> 
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