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Rendering with Arnold in 3ds Max using the MaxtoA plug-in.
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I have a doubt about specular reflection

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Message 1 of 7
Francesco_Furneri
266 Views, 6 Replies

I have a doubt about specular reflection

spec-reflection.jpg


Hello. I would like to hear your thoughts on this doubt that I have.

Let's say we have a light source that bounces several times, creating diffuse and specular reflections before reaching the eye, as shown in figure.

After the first bounce part of the radiation is being diffused and part of it is being reflected like a mirror (let's say the roughness is ideally 0 and the surfaces also diffuse color) and so on for the other bounces until the light reaches the eye.

What I don't understand is why the first reflected ray, after hitting the "ceiling" is not diffused by the surface like the other diffused rays but it's reflected again and so for the other reflected rays. Shouldn't it be in part reflected and in part diffused like the secondary diffused rays?

does that happen because the reflected rays only continue to reflect after hitting a surface?

I hope I explained my doubt well.



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Message 2 of 7

When the camera ray hits the object, you'll get 4 specular rays (with the default specular samples set to 2). Then for each of those specular rays, you'll get 1 specular ray (eg specular samples becomes 1 after the first bounce)



// Stephen Blair
// Arnold Renderer Support
Message 3 of 7

@Stephen Blair thank you very much for your answer!

Maybe I didn't explain well my doubt. It's not very specific of Arnold but I would like to to know this.

ARNOLD: rays are separated in diffuse, specular, SSS etc...

REALITY: when a rspecular reflected ray (and not diffused ray) hits another surface is it only reflected or also diffused?

In Arnold it seems that specular rays are always reflected as they are separated from diffuse rays.

In reality do specular rays continue reflecting (in a specular way) or do they also diffuse light when they keep bouncing?

I hope I explained better now


Message 4 of 7

In reality? Ok, so this is a light physics question 😉
I would say you get everything at each bounce...but I didn't check on that



// Stephen Blair
// Arnold Renderer Support
Message 5 of 7

Ok thanks, I had that doubt because I was wondering if Arnold ignores diffuse bounces from specular reflected rays or the specular reflected rays didnt' emit diffuse reflections for some reason

🙂

Message 6 of 7

Hi Francesco, in reality there are a huge amount of photons that bounce a huge amount of times, with all the possible combinations, and different probabilities. The renderers try to mimic this by "sending rays", but there's no distinction between a reflection ray or a diffuse ray in real life. Any ray can bounce in any possible way next time it hits a surface. The only reason why some ray combinations can be ignored by renderers is for efficiency.

Cheers

Message 7 of 7

Oooh thanks Sebastien. That's great! So, in your opinion, ignoring some rays doesn't make any huge difference from reality, right?

I mean, If Arnold ignores any diffuse rays from indirect specular reflected rays, we obtain a render which is so close to reality, even without those ignored rays

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