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Passes artifacts in Cycles when motion blur enabled
Closed, InvalidPublic


System Information
Windows 7 Ultimate 64 bit
GTX 780 Ti

Also checked on GTX 770

Blender Version
Broken: 2.69, 2.71.3, 2.72
Worked: Don't know if it's a bug or a missing future

Short description of error
In Cycles, when the motion blur is enabled - Passes are rendered with artifacts, although the image render is fine.
It happens even when the render samples are high.

Exact steps for others to reproduce the error

  • Just add a monkey
  • Index it as number 1
  • Create a fast moving animation
  • Render at the pick of the speed
  • Add an ID mask converter at the Compositor
  • See the results:

Blend file:



Event Timeline

Serj Maiorov (printerkiller) created this task.
Serj Maiorov (printerkiller) raised the priority of this task from to Needs Triage by Developer.
Lukas Toenne (lukastoenne) claimed this task.

This is not a bug but a technical limitation. The Index pass is by its nature not mixable with results from other objects! This means that in areas where the object is half-transparent (motion blur) the index is either from the background or the object, but can only be one or the other.

If you want to blend the object with the background you have other options, like using a material override or similar.