Nuke UV information for vectorblur etc...

[scott212]

What does a nuke-friendly UV file look like? Is it a normal map or something different? If I were coming from maya is it something I could get from a sampler info node and a ramp (r,g)?

Just curious because I have tried both with no luck. I've also pulled motion vectors from mental ray but that doesn't quite seem right either. How do productions derive uv maps for nuke?

[rueter]

it depends on what you want to do with the "UV" data. if you want to use it to apply motion blur red and green channels (or u and v) should contain floating point linear (!) data that defines the speed of every pixel by their respective value. I.e. the bigger the value the faster the motion the bigger the blur. positive numbers usually mean the pixel is traveling left to right (u) or upwards (v) while negative numbers reverse the direction (technically that could be different depending on your shader).
Make sure you read the UV channels in as linear color space otherwise they will be screwed up by an additional LUT.
To adjust the amount of blur you can either use the multiply knob in the VectorBlur or pre grade the UVs first (make sure you don't clamp them though as you will lose important data).

[Diogo Girondi]

Which 3D app are you using?

[scott212]

Maya

[Diogo Girondi]

Try this

[scott212]

I've seen that before but dismissed it since it's so pointed at the Revision plugins, guess I figured it was proprietary data. Have you used this with nuke and can vouch for it?

[Diogo Girondi]

Hey Scott,

I haven't used it with Nuke but you could give it a spin and see if works out for you. I'll do some tests here as well to see how it behaves.


Cheers,

[Diogo Girondi]

Humm...

It doesn't seem to work. Using ReelSmart settings it doesn't seem to be capable of understanding Z, and with SmoothKit settings it seems to get lost with Z at some point.

But maybe I've did something wrong, I'll give it one more look tomorrow.



Cheers,

[scott212]

Yeah - I got the same results. I was reading through the docs to see if I could derive some kind of usable info and found this:

According to the RevisionFX SmoothKit specifications, Red and Green color channels hold normalized direction vectors, and the Blue one holds the normalized intensity - the speed - of the motion.

* Red Channel: X [0,1]
* Green Channel: Y [0,1]
* Blue Channel: Intensity [0,1]

According to the RevisionFX ReelSmart Motion Blur v3 specifications, Red and Green color channels hold direction vectors scaled by normalized intensity - the speed - of the motion.

* Red Channel: X scaled by normalized Intensity [0,1]
* Green Channel: Y scaled by normalized Intensity [0,1]
* Blue Channel: not used.

It seems as though the ReelSmart would be closest to correct but just needs some scaling.

[scott212]

All right - I've got a solution for moVector info from mental ray to nuke. It uses ctrl.buffers shader pack for some specific reasons instead of the Real Smart vector shaders.

If anyone is interested I'll put up a tutorial. Don't have a lot of time but would be happy to if someone needs it.

[scott212]

Now I'm gettin a bit peeved. lol! I've gotten the motion vectors to agree with the vector blur, but for some reason the vector blur is being choked by the alpha. The alpha doesn't get blurred with the color channels. I've got it set to blur the rgba channels with the red & green channels of the motion file piped to uv, so I have no idea why this is happening. Any ideas guys? Thank so much.

[Diogo Girondi]

Cool Scott,

Would be great if you could share your way to deal with it using ctrl.buffer shader pack. I'm taking a look at ctrl.buffer, read and write right now.

Thanks for the tip

[Diogo Girondi]

have you tried to use the Forward with the Alpha set?

There is also Puppet shaders to store buffers and convert MR Motion Vectors to RGB, maybe you could check them out. Don't know don't use Maya my self.

Quick test with the ctrlBuffer shader, it's not quite right yet

[scott212]

well I'll share as soon as I get it workin, don't want to misinform.

Basically you want to write out the mental ray motion file and the coverage file, whatever method you choose. I've been wanting to take a look at puppet's pack but already had ctrl.buffers installed. You don't really need either one but there are a couple features to get the coverage buffer working that mental ray for maya didn't implement unfortunately.

The motion file is unantialiased and the coverage file is basically the contours of the objects where the pixels would generally be antialiased. Through some comp magic you can arrive at an antialiased motion file. The magic is what I'm still workin on.

The problem with the above I found is the black interior lines mess up the blur and the black back should be around middle grey. Not sure entirely why about the grey yet but it works.

[scott212]

I hate to say it but I don't have time right now to keep messing with it, I'm gonna wuss out and jump over to shake for the reelSmart moblur. I'm surely not giving up though.

Cheers