Motion blur issue on fast spinning objects

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Motion blur issue on fast spinning objects

Postby tobywe » Sat Feb 02, 2019 1:14 pm

tobywe Sat Feb 02, 2019 1:14 pm
Hi,

I've been having trouble with getting the motion blur samples to work on spinning objects. I've done a test with an object-level very fast spinning motion on a box. I did a render with Mantra where it seems to sample as you'd expect with 360 degrees of blur and then the same settings with Octane and it never seems to give the expected results. Is this something I've missed or is it a limitation?

Octane:
octane_mb.PNG


Mantra:
mantra_mb.PNG


Secondly, I was wondering if there's a way of setting the sample rate for the Deformations MB, or does it inherit the Objects MB?

Many thanks,

Toby
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Re: Motion blur issue on fast spinning objects

Postby juanjgon » Mon Feb 04, 2019 10:32 am

juanjgon Mon Feb 04, 2019 10:32 am
Hi,

To render fast spinning motion blur effects at the OBJ level, you need to increase the transformations MB steps. Sometimes you could need 10 or 20 steps to make it work fine. On the other hand, the fast spinning deformation MB at SOP level (from mesh deformations) is not possible currently because the deformations MB is using only two steps.

Hope it helps,
-Juanjo
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Octane plugin development and support: LightWave and Houdini
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Re: Motion blur issue on fast spinning objects

Postby tobywe » Mon Feb 04, 2019 4:03 pm

tobywe Mon Feb 04, 2019 4:03 pm
Hi Juanjo,

Thanks for getting back to me about this and that's good to know about the deformation mb step limit.

With regards to the object level steps etc.,I did play around with the mb samples and cranked it all the way up to 16 but still not getting it to behave as expected (it doesn't seem possible to push it up as high as 20). The only way I was able to get the full radial blur was to use the camera shutter time instead of the octane one and push it up to 4, but then this would mess up the motion blur on any other moving objects.

Again, it seems that Mantra on 16 steps renders with the full radial blur.

I've attached the scene file, in case you have a moment to take a look.

Many thanks!

Toby
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spinning_mb_test.zip
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Re: Motion blur issue on fast spinning objects

Postby juanjgon » Mon Feb 04, 2019 9:54 pm

juanjgon Mon Feb 04, 2019 9:54 pm
Thanks for the scene. Yes, it seems that there is a weird behavior with the MB when there are more than two transformations MB steps. Investigating ...

Thanks,
-Juanjo
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Octane plugin development and support: LightWave and Houdini
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Re: Motion blur issue on fast spinning objects

Postby tobywe » Tue Feb 05, 2019 12:10 pm

tobywe Tue Feb 05, 2019 12:10 pm
Thanks for having a look at it :)
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Re: Motion blur issue on fast spinning objects

Postby juanjgon » Tue Feb 05, 2019 9:52 pm

juanjgon Tue Feb 05, 2019 9:52 pm
Ok. I've fixed all these issues with the motion blur for the next build. It was indeed a critical bug introduced in the latest changes made in the code to make the IPR scene update faster, so thanks for reporting it!

I've also raised the max. number of motion blur steps to 64, something that could help also in these kinds of scenes.

Thanks,
-Juanjo
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2019_02_05-20_17_58.jpg
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Re: Motion blur issue on fast spinning objects

Postby tobywe » Tue Feb 05, 2019 11:36 pm

tobywe Tue Feb 05, 2019 11:36 pm
Hi Juanjo,

That's great and so fast! Thanks for looking into it and I'll look out for the next build.

Best wishes,

Toby
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