Velocity pass working in nuke but not in flame...

[evanerichards]

Ok. So, I know many people don't have access to a flame, but I thought I'd throw the question out there as some wise person may have some insight as to what is going on.

We rendered a scene with multichannel EXRs. We bring it into flame, apply the velocity pass the motion blur looks great.
We bring the same scene into flame and it has problems. Certain frames will be severely blurred while others will hardly be blurred at all.

Any idea why that might be the case? Why a pass might work well in one compositing package and not another?

I feel like I've covered this before but when I went back through all my old posts I didn't find any answers.

Thanks!!

[tashko.zashev]

Hi,

Nuke works fine with zero based Velocity channel, I'm not sure if this is the same with Flame.
What about if you use 0.5 based one? You can try it by increasing the brightness for the Velocity pass in Flame with 0.5.

[evanerichards]

That's a good question. I'll test it out and see if that makes a difference. Thanks

Also, can you explain what the "Clamp Velocity" checkbox does? How does it clamp the output? What does it clamp it to?

[Rens]

It clamps to 0-1 (0-255 in 8-bit space).

The max velocity value is a scale factor. If your object is moving 500 pixels and you set the max velocity value to 500.0 then the colour value will be 1.0 instead of 500.0. For writing to non-float.

Unclamped with max velocity at 1.0 will give you the pixel distance travelled.

Keep in mind though that it's still 0.5-based so you need to subtract that first.