Mirror & Caustics with BiDir

[Vutshi]

I was curious whether it is possible to see a mirror reflection of caustics with BiDir renderer or not. In theory they should be there. In practice (viewtopic.php?f=16&t=8119#p79937) it is recommended to use SPPM renderer. So I did the simplest scene I can imagine and render it in low resolution up to insane samples per pixel numbers. It was expected to see some caustics at 10^5 S/p. Here are the results.

18 kS/p

mirror_caustics 18ksp no over.png (26.86 KiB) Viewed 873 times

200 kS/p

mirror_caustics 200ksp no over.png (27.2 KiB) Viewed 865 times

P.S. The scene is illuminated by sun. So, if someone wants to see sun light caustics reflected in a scene one should aim for hundreds of kS/p in BiDir case.

UPDATE: SPPM produces good result almost infinitely fast compared to BiDir, but it is still a little bit blurred.

310 MPhotons

mirror_caustics2 sppm 310Mp.png (45.32 KiB) Viewed 865 times

1.7 GPhotons

mirror_caustics2 sppm 1.7Gp.png (44.24 KiB) Viewed 857 times

15.35 GPhotons

mirror_caustics2 sppm 15.35Gp.png (43.44 KiB) Viewed 810 times

SPPM settings:
startradius 1.5
photonperpass 500k
alpha 0.9

[SATtva]

Nice test. Maybe you'll add a SPPM render as a reference?

[Vutshi]

Nice test. Maybe you'll add a SPPM render as a reference?

Good idea. Now I wonder how soon SPPM will become as sharp as BiDir.

[SATtva]

This depends on SPPM settings. You can lower start radius to reduce initial bias.

[Vutshi]

This depends on SPPM settings. You can lower start radius to reduce initial bias.

I updated the first post with 1.7Gphotons SPPM image. It looks a bit sharper than the 310Mphotons... but the difference is so tiny. Is there any estimation on how long one needs to calculate to get image converged to the proper solution?

[A-man]

In my experience, using a very small (0.25-0.5) starting radius yeilds the best result if you are going to render it for a while (12+ hours).
See Eros's post here viewtopic.php?f=8&t=5525&start=240 (He used .75, which seemed to work fairly well)