Cycles motion blur does not interpolate correctly #107482

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opened 2023-04-30 17:28:41 +02:00 by Max Mustermann · 7 comments

Max Mustermann commented

2023-04-30 17:28:41 +02:00

System Information
Operating system: Fedora Linux (Wayland)
Graphics card: AMD GPU (but Cycles renders on AMD CPU)

Blender Version
Broken: 3.5.0
Worked: never? (same results till 2.83)

Cycles motion blur interpolation is strange.
It's very noticeable when an object or the camera is bound to a constraint and the motion blur shutter is set very high (like 60 frames). Cycles motion blur will interpolate it wrong. I will include pictures and .blend files

Exact steps for others to reproduce the error

Open attached .blend file
Render the first frame with EEVEE and Cycles and compare the motion blur.

**System Information** Operating system: Fedora Linux (Wayland) Graphics card: AMD GPU (but Cycles renders on AMD CPU) **Blender Version** Broken: 3.5.0 Worked: never? (same results till 2.83) Cycles motion blur interpolation is strange. It's very noticeable when an object or the camera is bound to a constraint and the motion blur shutter is set very high (like 60 frames). Cycles motion blur will interpolate it wrong. I will include pictures and .blend files **Exact steps for others to reproduce the error** - Open attached .blend file - Render the first frame with EEVEE and Cycles and compare the motion blur.

02-evee_object_moving_on_constraint.jpg

47 KiB

02-object-moving-on-constraint.blend

887 KiB

01-camera-moving-on-constraint.blend

883 KiB

01-cycles_camera_moving_on_constraint.jpg

48 KiB

02-cycles_object_moving_on_constraint.jpg

47 KiB

01-evee_camera_moving_on_constraint.jpg

42 KiB

Max Mustermann added the

labels 2023-04-30 17:28:42 +02:00

Iliya Katushenock added the

label 2023-04-30 17:37:29 +02:00

Pratik Borhade commented

2023-05-01 12:43:22 +02:00

Member

Thanks for the report. Can confirm.

Thanks for the report. Can confirm.

Pratik Borhade added

Render & Cycles

and removed

labels 2023-05-01 12:43:33 +02:00

Fernando Alcala commented

2023-05-02 01:59:44 +02:00

That's because you increased the sub-stepping for Eevee but not Cycles.

That's because you increased the sub-stepping for Eevee but not Cycles.

Max Mustermann commented

2023-05-02 03:21:41 +02:00

Author

That's right. If you can show me where I can do that for Cycles I will change the title of this bug report, but the motion blur in my example has a range of 60 frames.
If Cycles really operates with a sub-step system like Evee does, shouldn't Cycles have at least one step for every frame by default?

That's right. If you can show me where I can do that for Cycles I will change the title of this bug report, but the motion blur in my example has a range of 60 frames. If Cycles really operates with a sub-step system like Evee does, shouldn't Cycles have at least one step for every frame by default?

Fernando Alcala commented

2023-05-02 03:42:04 +02:00

https://docs.blender.org/manual/en/latest/render/cycles/object_settings/object_data.html#bpy-types-cyclesobjectsettings-use-motion-blur

https://docs.blender.org/manual/en/latest/render/cycles/object_settings/object_data.html#bpy-types-cyclesobjectsettings-use-motion-blur

Max Mustermann commented

2023-05-02 04:33:14 +02:00

Author

Thank You!

I'm unsure what to do with this issue.
On the one hand it seems like user error, but it's also unexpected of both Evee and Cycles to not have a step for every frame in the shutter range by default.
I assume a global setting for motion blur like in Evee is not possible for Cycles?
Should cameras (and objects?) have a higher step value by default? The difference seems to be 0.01MB in memory usage during rendering when using 7 steps instead of 1 step.

l will leave the decision to someone else.

Thank You! I'm unsure what to do with this issue. On the one hand it seems like user error, but it's also unexpected of both Evee and Cycles to not have a step for every frame in the shutter range by default. I assume a global setting for motion blur like in Evee is not possible for Cycles? Should cameras (and objects?) have a higher step value by default? The difference seems to be 0.01MB in memory usage during rendering when using 7 steps instead of 1 step. l will leave the decision to someone else.

Max Mustermann commented

2023-05-05 00:18:56 +02:00

Author

To be fair with 10 000 individual objects (cubes) at 7 steps, the extra memory usage is 94MB.

To be fair with 10 000 individual objects (cubes) at 7 steps, the extra memory usage is 94MB.

Max Mustermann commented

2023-06-05 19:49:07 +02:00

Author

I can imagine a default value of 3 steps or more for new objects delivering a much more seamless experience with minimal impact on memory usage.

I can imagine a default value of 3 steps or more for new objects delivering a much more seamless experience with minimal impact on memory usage.

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Animation & Rigging

Asset Browser Project Overview

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EEVEE & Viewport

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Reference: blender/blender#107482

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