Strange Velocity Pass...

[evanerichards]

So I've been working on a job with a velocity pass.
I was handed a velocity pass and it works, but it doesn't look like any velocity pass I've ever worked with before. In the past all the velocity passes I've worked with have sort of pastel looking colors on gray. The ones I was handed are bright solid colors (green, red and yellow) on Black.
Why do these look different? Are there two types of velocity passes like there are normals passes? The one I rendered out was a 16bit exr the one I was sent was a 32bit exr but I don't feel like it should look too different. They were both rendered in vray.

Please check the velocity pass I've attached for reference.

[Morbid Angel]

This is correct. What you used to from vray is actually vray renders them on grey bg, but during motion vector extraction you only take the red and green values, so if you were to take the same velocity pass in nuke and extract those channels they would look like this. What you have there is how a velocity pass would look out of a multichannel exr in vray.

[evanerichards]

Interesting. So, I'm not quite certain. Why would the render be different as a multichannel .exr than it would be as a standalone image?

[tashko.zashev]

When you save the velocity pass in floating point images like .exr (Multichannel) or .vrimage then the velocity will be 0 (zero) based.
If you want to get the velocity image with grey background, like the one saved in the other file formats, you can add 50% ( 128,128,128 ) grey on post.

[evanerichards]

Hmmm. Well in both cases the files were saved in .exr formats. But one had a gray background and one had a black background. The only difference was that one was multichannel .exr (the black BG) and one was a regular .exr (gray BG).
I don't care if it has a gray background. It doesn't make a difference in the way they work but I was just wondering why a multichannel pass would look difference from a non-multichannel standalone pass of the same format.

[tashko.zashev]

Hi,

Some compositing applications (node based) require zero based velocity channel some of them don't. So V-Ray can save both.