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Agreement of Light Tracing and Path Tracing with a Thin Lens

Posted: Thu Aug 14, 2014 3:30 am
by Geometrian
Hi,

I have implemented a light tracer and a path tracer. For every scene I have tried with a finite-aperture camera containing no lens (i.e., the aperture is just a hole) and a single light, the results match exactly.

However, if a thin lens is added, the results differ. Specifically:
--If the sensor and light are the same distance from the lens, the results agree
--If the light is moved closer, it appears darker in the light tracer render
--If the light is moved farther, it appears brighter in the light tracer render

I have confirmed that the paths generated by both algorithms are plausible by visualizing the generated rays in another program.

The lens is technically a BSDF, which do not, in general preserve radiance (nor, I assume, importance). Could this be the source of the problem?

-G

Re: Agreement of Light Tracing and Path Tracing with a Thin

Posted: Thu Aug 14, 2014 3:39 am
by MohamedSakr
I guess what you mean by:
Geometrian wrote: --If the sensor and light are the same distance from the lens, the results agree
--If the light is moved closer, it appears darker in the light tracer render
--If the light is moved farther, it appears brighter in the light tracer render
is that at case 2 and 3 the camera path tracer gives the same brightness, while the light tracer gives darker/brighter results

this makes sense, assuming you are doing a random sampling, if the light is closer to the sensor, this means more samples will get missed (so only samples that hits the sensor will be counted) which means darker result, and if it is further then more samples will hit the sensor so brighter results

Re: Agreement of Light Tracing and Path Tracing with a Thin

Posted: Thu Aug 14, 2014 3:51 am
by Geometrian
My concern here is that the results from the path tracer and the results from the light tracer disagree.

Re: Agreement of Light Tracing and Path Tracing with a Thin

Posted: Thu Aug 14, 2014 4:23 am
by MohamedSakr