noisy render problem

[catchyid]

Hi,

I think this is basic, but I cannot figure it out myself! I have couple pyro smoke objects (pyro shader) and one mesh (mantra surface shader). When I render this scene using physical based rendering, smoke objects look good, however some parts of the solid object (i.e. a building) become noisy. What is the best way to remove this noise from this object?

I "think" increasing the pixel sampling rate would solve it (currently it's 2x2, so 3x3 would fix it, but this means I have to wait 6 days to render the scene and I don't wish to do that). I looked at mantra shader SHOP and the object rendering pane SOP but I could not find a way to increase the sampling rate only for this particular shader/object? It's an outdoor scene where there is only direct sun (directional light) and a sky model, so there is no much diffuse lighting, however I thought increasing light sampling to 8 would help but I am not sure?! Finally, in mantra node, I lowered noise level to 0.01.

In summary: Is there a way to improve only the rendering for a specific object that has mantra shader without improving the entire rendering in Mantra?

Thank you

 

Edited January 6, 2017 by catchyid

[davpe]

hi, well pixel samples 2x2 is extremely low value that I wouldn't recommend for even a fast previews. for a clean image you want to go up to 6x6 or 8x8 in typical cases. of course, the sampling method involves much more than just increasing pixel samples. some of what you have mentioned suggests you will learn a lot from reading the docs (no offense ) the sampling methodology is covered pretty well there.

http://www.sidefx.com/docs/houdini/render/sampling

http://www.sidefx.com/docs/houdini/render/noise

http://www.sidefx.com/docs/houdini/render/quality

rendering anything for 6 days sounds ridiculous, you haven't stated though what is it that takes 6 days to render. is it a single frame? in that case there certainly is something very wrong in your setup. if we are talking about a long sequence that involves some heavy raytracing, decent resolution and noise-free quality and you only have a laptop to do the job, then it's not unreasonable anymore

some general tips:

1 - you can adjust per-shader sampling by adding Properties VOP, via Edit rendering properties dialog. in this particular case, what you'll be looking for are Ray samples. you can't adjust pixel sampling per shader. find list of the properties you can override in the link below (overwhelming)

http://www.sidefx.com/docs/houdini/props/mantra

2 - 8 samples on light are, in general, unreasonably high. I almost never go over 2 or maybe 3 sometimes. it will only help you to clean shadow areas and direct spec (to some extent)

3 - sampling noise 0.01 may not be small number enough. try 0.002 for really fine sampling threshold (but it is directly tied to your min/max ray samples so you have to dial those in reasonably)

4 - for volumes you may have a better performance with similar or the same look with Raytrace engine rather than PBR or maybe even with Micropoly sometimes. it depends what exactly are you looking for.

5 - when rendering volumes, Indirect volume rays are the biggest killer. Second worst thing are transparent shadows on lights. Both of these things may play a vital role in how your render look like but in most cases it is possible to successfully cheat with multiple lights setup and achieve much lower render times (like an hour vs 5 mins, that kind of a difference).

6 - for volumes you usually don't want to play ray samples too high. depends on the particular case but I find myself frequently rendering just 1 or 2 rays and using more pixel samples and playing around a lot with transparent samples (Stochastic transparency - that is really important for rendering volumes and not going crazy), and volume/volume shadow quality.

http://www.sidefx.com/docs/houdini/render/volumes

 

cheers. D.

[catchyid]

Okay David Looks like I need to read more Well, I admit it, I skimmed through documentation quickly.

As per the 6 days, I am talking about a sequence of 390 frames Full HD, so I want each frame to take max 20 minutes on my PC (and the only machine I have, basically working on my demo reel). The scene has around 15 pyro objects (fire, smoke, debris,...)  and one mesh (a building). One last note, I am okay with having some noise in my final render as I will composite it onto an old footage that is already noisy, so they will all fit nicely

Alright, I will read the docs, re-read your reply and take it from there...

Thanks David

[davpe]

good luck then