[Cg1] AreaLight

Gereon Fox s9gefoxx at stud.uni-saarland.de
Fri Jan 9 16:57:02 CET 2015

You're right: I tried your approach and a comparison by laying one image
over the other revealed that the bright spots now do match. Plus I don't
have to to that ugly clamp any more...

Thanks for the feedback!

Am 07.01.2015 um 19:42 schrieb Alex Schlosser:
> Hi,
> 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
> Cheers,
> Alex
> 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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