using exr - velocity looks fine in the vr buffer, black when brought into nuke?

[joconnell]

Hi Folks,

I'm finally catching up with 3 years ago and starting to work with nuke ops that like using velocity blur for elements. I'm finding with a few scenes that while my velocity element looks correct in the vray frame buffer, when brought into nuke as part of an exr file, the channel is black when viewed - it doesn't seem to have any alpha values either. I'm using the default values that are added as per Instincts suggestions on another thread and these seem to work fine - admittedly the blur looks like a blurred version of the render at 50% opacity on top of itself but anyway.

Has anyone else gotten these issues or is there a way that the velocity element can be affected by anything else in a scene?

Cheers!

John

[instinct]

Did you check the actual values (using the indicator under the viewer) ?

Had some comp ppl complain and turned out things were moving from top right to bottom left wich naturally results in velocity beeing all negative and not visible in the viewer. The VFB compensated for that if i am not mistaken.

Just a wild guess tho

Regards,
Thorsten

[joconnell]

You're Totally right actually - I'm looking at the colour picker in nuke and despite there not being a visible object, there's something in there alright, albeit with negative values - what was throwing me was that I was expecting to see the same grey bg and colour values on top. In terms of values do you normally render unclamped and let the max value take care of itself via exr float?

Cheers for the help - that was spot on!

[instinct]

Yip render unclamped and to exr float. The velocity element stores velocity as "pixels per frame". So if you leave it at default min/max and use unclamped, than the nuke vectorblur settings are pretty much equivalent to the max moblur settings (duration in frames etc) and hence easy to adopt to real shutter values.

Regards,
Thorsten

[joconnell]

Getcha - so you cane nearly use unclamped from max and then use 0.5 in nuke it'll work for the majority of cameras unless they're using a different shutter angle. Much appreciated Thorsten!