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Reduce render times (Redshift)

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ok so the whole point of GPU rendering is to speed up your render pipeline. On a current project however if I cannot improve my 5 -10 minutes per frame render times I have no choice but to revert to Mantra (houdini)
I'm running a Titan X Pascal card on a Ubuntu linux system with 64gb ram
My scene is not too complex and fairly simple to describe.
Animated smoke inside a glass sphere surrounded by some animating geometry(think gyroscope)
Using 3 point lights inside the smoke, 3 area lights outside the glass sphere and 1 environment light.
Outputting to 1080p half float .exr files.

Here are my relevant render settings. Which of these should I focus on to reduce my render times(ie would have the least impact on quality and most impact on reducing render time)?

Unified Sampling
Min Samples 16
Max Samples 128
Adaptive Error Threshold 0.01

Filter Type Gaussian
Filter Size 2
Max Subsample Intensity 2
Max Secondary Ray Intensity 2

Global Illumination settings
Primary GI Engine Brute Force
Secondary GI Engine Irradiance point cloud

Num GI Bounces 2
Conserve Reflections Energy checked

Brute Force GI Rays 1024

Irradiance Point Cloud settings
Frames to Blend 0
Show Calculation checked
Screen radius 16
Samples per Pixel 32
Filter Size 2
Retrace Threshold 3

Volumetric Scattering enabled
Scattering  0.01
Attenuation 0
Phase 0
Fog Emission
Apply Camera Exposure Compensation checked
Fog Height .35
For Horizontal Blur 0.08

Environmental Scale 0.537
Camera Scale 0.087
Reflection Scale 0.027
GU Scale 0.595

Environment Alpha Replace checked

Sampling Overrides
Reflection Samples 512
Refraction Samples 512
Volume Samples 512
(all Samples Scale 1)

Edited by art3mis

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Can you post the slow rendering HIP file?

I typically use IC with IPC and avoid brute force unless there is no other option. Also those 512 over samples seem high. You need to figure out where you are experiencing noise and only over sample in those areas. Turning everything up is like turning on all the faucets in your house and wondering why it is taking so long to fill the bath.

Edited by Atom

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Thanks. Great analogy! I tried turning off volumetric sampling, all oversamples and reduced refraction,  reflection  samples although the latter probably too much since now quite a bit of noise in background. But render time down to average of about a minute.


My understanding is that Irradiance caching, although quite fast, is primarily useful for scenes with large flat areas of low contrast, ie architectural renderings, and not for any scene containing lots of small detail. Will give it a try though

Will post a simplified .hip once I get closer to my target.

Also noticing I'm getting zero motion blur even though enabled in both ROP and Redshift Obj attached to each rapidly rotating gyro part.



Edited by art3mis

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That is looking great!

Do you have a Trail, in Compute Velocity mode, after each transform that moves your parts? Examine your @v attribute in the spreadsheet to make sure it is not 0.0.

Edited by Atom

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39 minutes ago, art3mis said:

Thanks Atom. I'm pretty committed to mastering RS, though I've heard Octane requires less fiddling.

Octane is junk compared to Redshift for Houdini IMO - just check out the way you do attributes.

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