Dumb one for Instinct and the other nuke folks - motion vectors again

[joconnell]

Heya Folks,

I'm having a few hassles with this using instincts method of rendering in vray with the default velocity settings applied and then setting my blur method in nuke to forward. My velocity pass looks okay in vray, comes into nuke a good bit darker and then when I apply the blur it appears like a blurred render overlaid at 50% with the original render. Here's the vray render and settings, then the velocity pass as seen in nuke with the result from those settings. I'm rendering with the dumb "linear workflow" button and baking in gamma to the renders - is it a side effect of doing this rather than using don't affect colours causing the issue? Importing as linear seems to do the same darkening on the velocity channel regardless. No doubt it's something dumb - anyone any thoughts?

[Sushidelic]

You should tick the alpha and set it to RGB.alpha.
Dunno what the linear workflow does to your velocity channel, but as you are saying it looks darker, might be that the exr saver or anything else is burning in a gamma here... so if things still look incorrect, you might try to ad a gamma 2.2 to your vectors before piping them in.

best regards,
Michael

[joconnell]

Ugh - alpha was exactly what it was, it's stopped that ugly 50% blend nonsense. The nuke folks in here had done motion blur some other way before so didn't know their way around the vector node as well. Thanks a million Michael, that's save a lot of hassle and render time in the future!

[instinct]

Given the screenshot you should also uncheck "clamp". Looking at the max velocity of 118 you're gonna see pretty crazy clamping issues. For nuke i'd simply untick clamp and there you go.

Regards,
Thorsten

[joconnell]

I was wondering that - I was using a post you'd put in a while back which mentioned that you just add the velocity pass with the default values and off you go - wasn't sure if vray did some fancy scaling on the pass to make it behave. Cheers for the two pointers, that's that sorted out from now on then!

[instinct]

You can do some "fancy" scaling using the max velocity spinner. This value will be 1.0 in the output image. This is needed for non float images. If you leave the defaults and untick clamp then you end up with absolute pixels/frame velocity values. Which is just what nuke expects. So you can then work with the "film friendly" values of the vector blur.

[joconnell]

Getcha. Unclamped makes far more sense than trying to test each scene for that the max velocity is. Quite nice not taking the hit for render time on motion blur!

[Dariusz Makowski (Dadal)]

Heya

Quick question - how did u chock up velocity pass with vectorblur? - got it to work. But the blur is in wrong dirrection... how do I deal with that? :s

[joconnell]

Is your method set to forward or backward? Tbh the steps outline above have worked perfectly for me every time!

[Dariusz Makowski (Dadal)]

was backward - now I'm using forward and it look better. But I have 1 issue that bother me. It sems that motion blur is applied on top of image as something like screen - u can kinda see the oryginal shape non blured and then blur on top of it... How to fix it ? In after effect motion blur smooth out shape - which is what I'm after...

Thanks, bye.

[instinct]

Be sure to tick alpha and select your alpha channel.

Regards,
Thorsten

[joconnell]

Yep that's the one - that does the weird doubling effect.