Branched path tracer workflow

Support Lighting and Rendering
1

Hey friends, I have a question I couldn’t find an answer to using forum search. Sorry if its very common.

Can anyone explain please what the workflow for BPT is? How to estimate amount of samples and WHICH samples you need, to get the same result as with PT? The documentation gives only a simple math: PT Diffuse 250 = BPT 25AA*10 Diffuse. But that doesn’t explain how it works. The default AA value is 4, why?

For example. Lets make it simple, there is scene with an area light, cube and all diffuse materials. PT = 40 samples gives some result, not good not bad. 3.81s.

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BPT with 4AA and 10 Diffuse (4*10=40) gives a much worse result in shadows and better result in directly lit areas. 3.03s.

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BPT with 10AA and 4 Diffuse (10*4=40) gives a better result in shadows than the previous one (but still worse than PT) and same for directly lit areas. 3.14s.

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And then you find out that its not only all about samples in path tracing: light sources also have their sampling. The default is 1. (I suppose that’s why 10AA4D is better than 4AA10D). If you increase it to 2 and have BPT 10AA*4 then we get approximately the same result as PT 40. 3.82s.

But this is just guessing… Where is the truth, how to actually use it? Is there any tutorial explaining how AA, Diffuse etc and lighting samples are connected for Branched Path Tracing? And what is the proper workflow?

Thank you.

2

Does nobody know how to use Branched Path Tracer properly…? :frowning:

3

This video seems to explain it quite well - although like you I cannot get identical results from branched.

4

Yeah, I saw this video many times, but it looks like the author didn’t really know what he was talking about back in 2015 regarding Branched path tracing: same common facts, nothing specific and he set 1AA sample changing other components as if it doesn’t matter. which… matters a lot. So it doesn’t answer the question at all unfortunately. But thanks)

5

I’ve conducted more tests and now the picture is getting clear. Probably I’ll make a short video explaining what’s going on there.

Looks like the story repeats: once I was confused about RenderMan renderer and after not finding proper answers, conducted my own research and made this video on PBR in RenderMan (based on Blender) which seems to be helpful:

So I’ll try to make a tutorial in the same way on Branched Path Tracing.

6

Ok, this is it. The tutorial on Branched path tracing in Cycles.

I hope it will be helpful to someone.

1 Like
7

Hi Alex,
Thank you very much for your tutorial, and very kind of you to make it for us. The BPT was always a mystery to me.
And don’t worry about your accent, I understand it better than most native speakers.

8

I’m glad it was useful =) yet, right after finishing and uploading this video to YouTube I’ve got a problem with Principled shader I was talking about which I don’t know how to solve =))

Does anyone know why the colours in the scene and the light distribution changes a lot when all the materials are based on Principled shaders, WHEN you switch from Path Tracing to Branched Path Tracing?? It doesn’t happen when materials are based on Diffuse+Glossy materials. I’ll make a separate thread about in another branch with examples, but hope that someone could reply here as well.