[Cg1] AreaLight

Alex Schlosser schlosser at st.cs.uni-saarland.de
Wed Jan 7 19:42:18 CET 2015


in the 'Distribution Raytracing' slides it says we should scale the 
light sources intensity by incident cosine and the area of the 
source-solid. As far as I understood it we achieve the behaviour of an 
area light by simulating N pointlights each having an intensity divided 
by N. The integral in the area light equation then gives us N=source area.
I don't think the cosine scaling is done at all in the reference picture 
because the top of the walls should be way darker (Also we cannot easily 
reach the sources normal vector in the given structure).
So what I ended up doing is dividing the intensity by (distance^2 / 
area), mind the paranthesis because the scene is very 'small' and both 
distance and area are below 1.
This achieves a very similar image to the reference, I do not know if 
this is correct though.
Image: http://i.imgur.com/8iBcBXI.png


On 01/07/2015 06:05 PM, Gereon Fox wrote:
> Discussing the issue with a fellow student, I realised that I had
> forgotten to mention the following: Before we apply said division, we
> clamp the radiance we got from the texture. This is what makes our
> approach especially suspicious, because the texture's radiance of 25.f
> seems to have been chosen carefully and we just discard every
> information beyond 1.f through the clamp...
> Am 06.01.2015 um 01:47 schrieb Gereon Fox:
>> Hi,
>> we are having some trouble with the AreaLight: The constant
>> texture/material attached to it in the sample scene emits a radiance of
>> 25.0. Obviously, simply returning this radiance in
>> AreaLight::getIntensity makes the scene much too bright. That is why we
>> tried to follow all the clues we could find and divided that radicane by
>> the (sparsely convincing) divisor pi * irr.distance^2. This made our
>> images look quite similar to the samples, but the bright half-circle on
>> the white back wall is now a little too small (see attachment).
>> What are we doing wrong here?
>> Regards,
>> Gereon.
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