Agreement of Light Tracing and Path Tracing with a Thin Lens

Practical and theoretical implementation discussion.
Geometrian
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Joined: Sun Jul 28, 2013 6:53 pm
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Agreement of Light Tracing and Path Tracing with a Thin Lens

Postby Geometrian » Thu Aug 14, 2014 3:30 am

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

MohamedSakr
Posts: 83
Joined: Thu Apr 24, 2014 2:27 am

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

Postby MohamedSakr » Thu Aug 14, 2014 3:39 am

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

Geometrian
Posts: 29
Joined: Sun Jul 28, 2013 6:53 pm
Contact:

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

Postby Geometrian » Thu Aug 14, 2014 3:51 am

My concern here is that the results from the path tracer and the results from the light tracer disagree.

MohamedSakr
Posts: 83
Joined: Thu Apr 24, 2014 2:27 am

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

Postby MohamedSakr » Thu Aug 14, 2014 4:23 am



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