Eevee motion blur causes ghosting on image sequences when steps are greater than one #80452

New Issue

Mister Krinkle · 2020-09-04T01:54:58+02:00

Mister Krinkle commented

2020-09-04 01:54:58 +02:00

System Information
Operating system: Darwin-19.6.0-x86_64-i386-64bit 64 Bits
Also tested on Windows-10-10.0.19041
Graphics card: AMD Radeon Pro Vega 48 OpenGL Engine ATI Technologies Inc. 4.1 ATI-3.10.16

Blender Version
Broken: version: 2.90.0, branch: master, commit date: 2020-08-31 11:26, hash: 0330d1af29
Worked: (newest version of Blender that worked as expected)

Short description of error
The next frame of an image sequence/video texture is added onto the current one when the step count in Eevee's motion blur is any value greater than one.

Demo file: blur.blend
Video used: demo.mov.zip

Exact steps for others to reproduce the error

Create a material that references a video or image sequence in any form
Turn on motion blur and set step count to any value greater than one
Render

**System Information** Operating system: Darwin-19.6.0-x86_64-i386-64bit 64 Bits Also tested on Windows-10-10.0.19041 Graphics card: AMD Radeon Pro Vega 48 OpenGL Engine ATI Technologies Inc. 4.1 ATI-3.10.16 **Blender Version** Broken: version: 2.90.0, branch: master, commit date: 2020-08-31 11:26, hash: `0330d1af29` Worked: (newest version of Blender that worked as expected) **Short description of error** The next frame of an image sequence/video texture is added onto the current one when the step count in Eevee's motion blur is any value greater than one. ![image.png](https://archive.blender.org/developer/F8838153/image.png) Demo file: [blur.blend](https://archive.blender.org/developer/F8838158/blur.blend) Video used: [demo.mov.zip](https://archive.blender.org/developer/F8838163/demo.mov.zip) **Exact steps for others to reproduce the error** 1. Create a material that references a video or image sequence in any form 2. Turn on motion blur and set step count to any value greater than one 3. Render

Mister Krinkle commented

2020-09-04 01:54:58 +02:00

Added subscriber: @moid

Richard Antalik commented

2020-09-09 03:32:10 +02:00

Changed status from 'Needs Triage' to: 'Confirmed'

Mister Krinkle commented

2020-09-15 15:13:30 +02:00

This issue also appears to affect objects when Disable in Render is keyframed. Behavior on the frame when the value changes from -1 (visible) to 1 (invisible):

1 step

2 steps

This issue also appears to affect objects when Disable in Render is keyframed. Behavior on the frame when the value changes from -1 (visible) to 1 (invisible): 1 step ![image.png](https://archive.blender.org/developer/F8883244/image.png) 2 steps ![image.png](https://archive.blender.org/developer/F8883231/image.png)

RedMser commented

2020-10-11 14:04:27 +02:00

Added subscriber: @RedMser

Clément Foucault commented

2020-10-13 17:28:02 +02:00

Added subscribers: @brecht, @fclem

Clément Foucault commented

2020-10-13 17:28:02 +02:00

If I understand the issue correctly, the expected behavior should be that the animation would not be "multisampled" in time and just use the value from the initial frame (just like in cycles).

I'm unsure how to fix the issue, or even if Cycles behavior is normal / wanted. @brecht any opinion?

If I understand the issue correctly, the expected behavior should be that the animation would not be "multisampled" in time and just use the value from the initial frame (just like in cycles). I'm unsure how to fix the issue, or even if Cycles behavior is normal / wanted. @brecht any opinion?

Brecht Van Lommel commented

2020-10-13 17:56:43 +02:00

Cycles does not support motion blur of visibility and image sequences, it always uses the value from the render frame. That's a known limitation, it's only the object matrix and mesh vertex locations that change in motion blur, everything else remains fixed.

It's not obvious how you would interpolate image sequences or visibility, there is no sub-frame data for that, so we just don't do it.

I guess this could be done in Eevee by evaluating 4 frames instead of 3? Basically treating the center motion step the same as the previous and next motion step, using it only for storing object matrices and vertex coordinates. If the center and render frame match, you can of course only evaluate 3 frames as an optimization.

Cycles does not support motion blur of visibility and image sequences, it always uses the value from the render frame. That's a known limitation, it's only the object matrix and mesh vertex locations that change in motion blur, everything else remains fixed. It's not obvious how you would interpolate image sequences or visibility, there is no sub-frame data for that, so we just don't do it. I guess this could be done in Eevee by evaluating 4 frames instead of 3? Basically treating the center motion step the same as the previous and next motion step, using it only for storing object matrices and vertex coordinates. If the center and render frame match, you can of course only evaluate 3 frames as an optimization.

Clément Foucault commented

2020-10-13 19:09:38 +02:00

Well EEVEE just re-evaluate everything for each motion blur substep and changing the center step, so an object that becomes visible inside the shutter time might appear partially visible.

So EEVEE is just doing the "right" thing in my opinion. I'm going to clasify this a technical limitation / known issue as I don't see how I could implement this with the subframe evaluation method we currently have.

I understand your suggestion of evaluating the original frame once more to reload the correct images & visibility but this create much more issue with some data pointers & resources.

Well EEVEE just re-evaluate everything for each motion blur substep and changing the center step, so an object that becomes visible inside the shutter time might appear partially visible. So EEVEE is just doing the "right" thing in my opinion. I'm going to clasify this a technical limitation / known issue as I don't see how I could implement this with the subframe evaluation method we currently have. I understand your suggestion of evaluating the original frame once more to reload the correct images & visibility but this create much more issue with some data pointers & resources.

Philipp Oeser removed the

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Eevee motion blur causes ghosting on image sequences when steps are greater than one #80452