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Weird motion blur problem when using SSS and a hard light

Posted: Tue Jun 14, 2016 8:08 am
by thomasderijk
Hi!
This is my first post on the forum.
Couldnt find anything related to this problem.

Im using a character with Sub surface scattering material.
Inside is a skeleton, which also uses the same vertex motion blur setting so the entire body acts as one when it comes to motion blur.
Now when there is a hard backlight in a certain scene, the motion blur messes up in the parts where the hand is directly in front of the light.
When there is geometry between the light and the character, like the other character with the same materials, or the wall next to it, this doesnt happen.

The geometry that does show, is not the skeleton, nor the hand geo.
The actual skeleton is much thinner, and the hand geo is obviously thicker that what it showing.
I had no luck changing the amount of samples, as far is can tell anyway

Any help would be much appreciated, thank you :)

project file
https://www.dropbox.com/s/4egi5yfi3ozad ... m.c4d?dl=0

vimeo render
https://vimeo.com/170588129/dc1a745e1c

Re: Weird motion blur problem when using SSS and a hard light

Posted: Wed Jun 15, 2016 7:56 am
by thomasderijk
anyone?
all the topics getting replies apart from mine haha
:oops:

Re: Weird motion blur problem when using SSS and a hard light

Posted: Wed Jun 15, 2016 2:42 pm
by zoppo
This is no error, it is your scene - the movement is very fast and therefore the motion blur is very strong. The few pixels left are completely "overpowered" by the strong backlight. But they are there, you can see them when you save the frame as 32bit linear and dial down exposure A LOT:

Image

Image

Re: Weird motion blur problem when using SSS and a hard light

Posted: Wed Jun 15, 2016 3:54 pm
by thomasderijk
i see!!!!
thats crazy haha
thank you!

I was thinking this could not be the case because in my belief it would be like this:
Moving mesh -> light -> motion blur
so 2 frames with motion blur blending between them so to speak, would never be able to be faded away by that hard backlight, because lightning acts upon the mesh first, and then two images are then motion blurred
if you know what i mean haha
but it seems it works different than i thought

do you have any suggestions on getting the mesh to show up anyway?

My plan now is to do a second render with softer backlight and then compositing that in

thank you!