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Cycles produces banded render artifacts in dense or sharp volume renders.
Confirmed, NormalPublicTO DO

Description

System Information
Windows 10, Nvidia GTX 1070 8gb

Blender Version
Broken: 2.90.0 f4dc9f9d68b
*2.72a also has this issue, suggesting most if not all cycles+volume builds produce this artifact.
*2.8 also has this issue.
*2.9 still has this issue. (replaced sample file with a new one that is more noticeable, and easier to compute and render.)

Sharply surfaced volumes (more noticeably from simulations) display banding from what seems to be non-homogeneous sampling at each step. While it can appear, and is most noticeable on smooth surfaces, it is exacerbated by volume density multiplication, having 0 volume bounces, non-identical max and min bounces, and nodes that remap density values. Animating the camera makes it even more noticeable, as the bands trace out concentric spheres radiating from the camera. This may be a bug, but it may also reveal some larger issue in the rendering system, or require more than a patch to correct.

Exact steps for others to reproduce the error (Optionals in parentheses are what I did to make the issue more visible)

  1. make a smoke simulation with a visible flow object
  2. simulate to some frame (Optional: limit the cache end to be able to move the camera around a still simulation)
  3. make a scattering volume material for the domain that both multiplies density by a high number. (Optional: add a color ramp after the density value or after the multiplication value, move the white value a bit closer to the middle, and set to constant)

(updated to 2.90)
please let it simulate to frame 21 or higher to get identical results to me.
file result preview:

Event Timeline

Brecht Van Lommel (brecht) lowered the priority of this task from 90 to 50.
Nick Dorn (Nubnubbud) renamed this task from Cycles does not appear to treat step boundaries vs between step boundaries homogeneously in volumes, produces render artifacts. to Cycles produces banded render artifacts in dense or sharp volume renders..Wed, Sep 9, 11:30 PM

renamed for clarity of scope and succinctness- the description should probably be where the supposed cause or influencing variables go, not the title, and it was overly redundant. Apologies for the multiple edits- kept finding out of date information, files, and redundant text, and my current test file was far better at exposing the bug/artifact. >