Single File EXR with Velocity Channel

[frame_michael]

Hi,
we have setup our workflow to incorporate single file exrs with all the render elements we need in it.

We are using Reel Smart Motion blur in After Effects to render Motion Blur in post.
I have managed to get the right results when using pngs (one for each render element) and preserving rgb in AE.
But i am not able to get the same result with the single file exrs. It seems the velocity channel is getting a different
gamma than the other channels.

I would really like to stay with the single file exrs and only one render pass (high rendertimes / animation)

We are using 3dsMAX 2012 64bit Vray 2.20.01. Linear workflow.

This is the VFB velocity channel - looking right


This is how the channel looks like when used in AE - all other channels are ok!



This is our render setup for single file EXRs (to my knowledge it only works this way - save separate render channels produces multiple files)


Does anyone have a solution for this - or is it a bug?

best regards
Michael

[instinct]

The default for velocity is signed (so things moving from right to left will cause negative values) so the negative part is eventually dropped by AE ? Also the element records velocity as pixels/frame by default, so values above one might also be clamped by AE

Regards,
Thorsten

[frame_michael]

@Thorsten, sorry I don't get what you mean with the negative part in AE.
I used the same settings (with headroom for the max veolicity in last frame) and the same numbers within RSMB in AE.
What I don't get is with the same settings it works using multiple pngs as opposed to a single EXR.

[frame_michael]

I checked the EXR's in PDPlayer - in case AE is interpreting the EXR's wrong.
But it's the same there. So it seems like a problem of Vray saving to single file EXR or EXR interpreting it wrong?



Can someone help - please?

[jacksc02]

I use single EXRs with velocity channels in fusion and everything works perfectly

[jacksc02]

here is a screen grab of fusion showing that the velocity channel in a single EXR is working perfectly well.
If you want to try one of my EXRs PM me and I will send it to you to try in AFX.

[frame_michael]

@Chris, could you check your Vray VFB if it looks the same there? My velocity channel inside VFB is way flatter (more desaturated) looking.

[jacksc02]

Here is what it looks like inside the VFB in max

[jacksc02]

Looks quite different in the max VFB and that is because in fusion it is not showing the "blue" velocity information

[vlado]

You don't really need the blue part; most compositing software doesn't use it anyways.

Best regards,
Vlado

[Morbid Angel]

the way the exr looks in after effects appears correct. When vray displays the exr in framebuffer its placed against a neutral gray background. However if you are using a multichannel exr, the gray background does not get written into it, so you see Red and Green on pure black. If you simply take the image out of vray frame buffer and subtract 50% gray, you will get the same result.

[frame_michael]

Thanks Dmitry,

with your idea i was able to get the right result.
I just added 50% gray to the velocity channel and it works the right way in AE!
Without the added gray the velocity calculation is wrong.

[Morbid Angel]

what are you using in AE as the motion vector?

[frame_michael]

I'm not quite sure what you mean - in AE it's just a layer or precomp.
Inside the precomp is the velocity channel with gray added on top.

[Morbid Angel]

i see, i guess its how the reel smart motion blur reads it. Must be ae thing. Glad it works