Motion blur - black transparency problem

[thomes]

hi,

any help why i get this black backgroud effect in the objects motion blur?

its only a white plane and the object rotating at a distance.

any chance to get it as the lower reference picture ?

many thanks for help!
thomes

[etn249]

I would need to know more to guess a cause for this problem.

Which render engine is each image from? Are you using the renderer’s main motion blur, or the compositor’s vector blur? What are the motion blur’s settings?

[thomes]

hi etn, first big thanks for help!
rendermachine or comp for the down i dont know.
the upper is blender 4,.0 cycles motionblur in rendering.
centeronframe,shutter 0,5, rolling shutter none, shuttercurve default.

motionblur.blend (3.0 MB)

[etn249]

I have looked at your scene. The problem happens because of 2 reasons.

First reason, the reference is probably using a shutter curve to soften the edges of the motion blur, you should try using one too.

The other reason you are getting blackness in the motion blur is because your material is transparent and it’s lit in a way that creates dark zones. If you render without motion blur, you will see the object actually has dark areas, and those get stretched when you use motion blur.

That darkness is not unrealistic, but if you don’t want it, you need to place some more lights in your scene so the object has fewer dark areas on it.

[thomes]

@etn249

is not unrealistic, but if you don’t want it, you need to place some more lights in your scene so the object has fewer dark areas on it.

thanks a lot for looking into.

i deleted all the lights,for the initial rendering there were some light in the scene, but when i make world backgrounds both to 1 it gets quite better, also if i use shuttercurve as you said. i try it again tomorrorw at work with the original scene.

can´t see transparency in the material, but i will try all your other inputs tomorrow.

thanks again !

[etn249]

Ah, you are right, there is no transparency. It’s just that the shading looks messed up on my end because the normal map is missing.

[thomes]

for what i found out, its a problem of the ground floor to be a shadow catcher.
the second time these days i have a problem with this shadow catcher interactivity…

plane as shadow catcher:

plane without shadow catcher:

motion blur without plane:

here it was also a problem of the shadow catcher floor plane…

Animate visibility in Blender 4.0 Timeline?

Yea that was really far-fetched. I’m not sure why this happens, but I imagine this is a natural consequence of how the shadow catcher functions. That means you can’t use that solution with shadow catchers. Isn’t that a dealbreaker ?

[etn249]

Maybe it would be possible to do it in 2 passes then?

• The first view layer is just the object on a transparent background, the plane is set to holdout.

• The second view layer is just the shadow catcher, the object is set to “indirect only” so its shadow is visible, but not the object.

Then, the 2 could be combined in the compositor.

[thomes]

Thanks a lot etn! … composed in AE. For me best visual appearance was the third with transparency.

[Hadriscus]

I can see why transparency works like it does with a shadow catcher in the background, but motion blur? I don’t think this is expected behaviour.