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Cycles: using Adaptive Sampling with Progressive Refine causes severe artefacting
Confirmed, HighPublicBUG


System Information
Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: Radeon (TM) RX 470 Graphics ATI Technologies Inc. 4.5.14758 Core Profile Context 21.2.2 27.20.14535.1000

Blender Version
Broken: version: 2.92.0 Release Candidate, branch: master, commit date: 2021-02-19 18:02, hash: rBb1142858d4ca
Worked: 2.91

Short description of error
When rendering with Adaptive Sampling and Progressive Refine both enabled, white artefacts appear in parts of the image. Note that they only appear after a certain number of samples, when adaptivity kicks in, I presume. Also I only tested CPU rendering.
Top is rendered in 2.91, bottom in 2.92 rc, on same exacts settings.

Exact steps for others to reproduce the error

  • Open attached file or:
    • with the default scene set the render engine to Cycles
    • enable Adaptive Sampling and Progressive Refine
  • press F12 to render

Event Timeline

Germano Cavalcante (mano-wii) changed the task status from Needs Triage to Needs Information from User.Feb 24 2021, 9:23 PM

I can't replicate the problem?
Can you provide a file showing it?
Many bugs are fixed between the official releases. Please try the latest development snapshot of blender:

Germano Cavalcante (mano-wii) changed the task status from Needs Information from User to Confirmed.Feb 24 2021, 9:27 PM
Germano Cavalcante (mano-wii) changed the subtype of this task from "Report" to "Bug".

I managed to reproduce the problem!
It starts to appear after 32 frames.
Here the file that I used to test:

It seems that this bug is somehow caused by adaptive sampling and the exact number of samples when these artefacts start appearing is dependent on the total number of render samples, but they do appear eventually.

In case it helps, here's a video of it happening on OSX with the default cube's scene:

Versions from "About Blender" dialog:

Blender version: 2.92.0

Date: 2021-02-24 16:25
Hash: 02948a2cab44
Branch: master

Those actions (specifically disabling "Adaptive Sampling") cured the destroyed cycles renders in 2.9.2 (Mac OS Mojave).

Thank you.