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Giorgio Luciano avatar image
Giorgio Luciano asked ·

Polarised light

I'm doing a scientific research about rendering and I was wondering if there is a way to recreate polarisation in arnold. I know that it already includes "exotic" stuff as the wonderful thin film shader. I hacked a bit a glass shader using normal directions for changing transparency and scatter, but I'm curious to know if there is a more correct approach to it. Not to mention that in theory, a render capable or working also with polarised light can obtain more realistic renderings. (or not ?). Very curious to hear your take on that

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Mike Farnsworth avatar image
Mike Farnsworth answered ·

Arnold does not support polarized light simulation, unfortunately. Arnold's refraction calculations combine both parallel and perpendicular components of light polarization, and they aren't separated out. It might be possible with all custom shaders and BRDFs to attach an orientation to each ray, but the reverse-ray-tracing nature of Arnold will make it difficult to apply the individual polarization results back through ray paths to the camera to finally filter after the fact.

With that said, it might be entirely possible to make it happen, but it's a big project.

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thanks for the detailed answer

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Shawn Kearney avatar image
Shawn Kearney answered ·

To do this "physically accurate" the light rays would have to have a polar attribute attached to them somehow, and to fully simulate, you'd start running some quantum weirdness that definitely goes beyond the scope of what Arnold (or even Maxwell) is designed for.

Is there something specific you're trying to do?

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Trying to recreate the look of a mineral under polarised light.

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Giorgio Luciano avatar image
Giorgio Luciano answered ·

Thanks for the anwer, actually how can I use (or where I can find docs/examples) for simulating seing my obj throught a polarised lens ? Do you also think it is possible to simulate something similar of what we have when we cross two linear polariser ?

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Max Tarpini avatar image
Max Tarpini answered ·

My take is that I don't think it would make more realistic renderings. Light is generally unpolarized if you ain't trying to simulate laser beams or the final phase of a sun eclipse. After some kind of refractions or reflections it could end-up being polarized however light transport in rendering applications is then generally computed over diffuse interreflections so in a general case where caustics are not computed it would still be virtually unpolarized. That said linear polarization with lens filters for example is generally used to tweak reflections but for that we have already ray flags to ctrl independently reflections from eye/camera rays etc and to simulate some kind of polarization.

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