Mental Ray Motion Files W/ Vector Blur

[user_deleted]

Hey gang,

I'm getting the mental ray .mt (motion) image files out of an animation hoping to use them as uv channels in vector blur. I've got them coming out of MR as .exr and nuke reads them just fine. I then shuffle the r and g channels into the uv channels of the beauty pass, throw in a vector blur, set it to blur on the uv's and get only a tiny bit of blur. The blur looks correct but it's so minute and I can't seem to increase or decrease it. Any thoughts?

~Scott

[user_deleted]

the multiply knob in the VectorBlur node should work for increasing the effect.
I don't know how MR is storing motion data though. If you want you can send me an example image to my private email and I'll have a closer look.

frank

[maya-man]

Does anyone know of what Nuke expects or better still have a Renderman shader that will output the required uv/vector pass?

Thanks

Michael

[user_deleted]

the motion data usually consists of horizontal movement in one channel and vertical in another. where positive pixel values indicate a movement to the right/up and negative values represent movement to the left/down. the actual value of the pixel will tell you how fast a pixel is moving.
however, since this data is in floating point values it can easily be adjusted by grading it to put it into the right "uv space".

hope that helps.
frank

[maya-man]

Thanks for the general info (am just starting out on a Nuke eval here), if I'm outputting mentalray I will try the .mt files, or the la maison revisionfx rsmb-compatible shader. I'm not clear on the difference between the two, except that the RSMB format can work in 16 bit integer if necessary.
I have some rsmb-format vectors in float depth from an older project, I might throw them into Nuke and see what it does, grading upstream to edit the blur length.

I found a bit of info on outputting motion vectors from renderman, but will see if someone else here knows how to implement that.

Also I see you can output Nuke's 3D renders as vectors to pipe back in, could be good as a how-to reference of what the data is meant to be.

Cheers
Michael

[user_deleted]

I've never used the "output vectors" option. they weren't working at all when I tried them last year.
Let me know if you have any luck with them, meybe they are functioning now?!
A quick mail to support@d2software.com could help there.

[maya-man]

I couldn't get them working but I've only been using the app for a few days.