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2D motion vector and image cards with alpha

4 REPLIES 4
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Message 1 of 5
dkrelina
508 Views, 4 Replies

2D motion vector and image cards with alpha

I'm using Maya 2015 and metal ray. I'm rendering an image sequence with a 2D Motion Vector pass (mv2DToxik). I'm noticing that the MV pass is not getting the transparency information from the image cards in the scene. How do I render an MV pass that respects the transparency of my shaders?

 

 

motion_vector_alpha_blur_note.0180.jpgmotion_vector_alpha_grey.0180.jpgmotion_vector_alpha_mv.0180.jpgmotion_vector_alpha_rgb.0180.jpgmotion_vector_alpha_blur.0180.jpg

 

 

4 REPLIES 4
Message 2 of 5
mspeer
in reply to: dkrelina

Hi!

 

You can't render "transparent motion". A Pixel can store information for one direction or the other, but not both (it's the same problem as with Z-Depth). You can however use multiple layers with different masks and/or moving objects (motion vectors) and composite them later.

Message 3 of 5
dkrelina
in reply to: mspeer

Ah, I see. That makes sense. So then the solution would be to have multiple MV passes and matte passes and then combine them together to create a "master MV pass" in comp. Correct?

 

So here is the problem... How do I create the matte passes for the objects with transparent shaders? I am trying to render a puzzle matte in metal ray using the Custom Color pass combined with writeToColorBuffer and I'm still getting the same issue. No transparency.

 

motion_vector_mat_id.0181.jpg

 

Is it possible to render a matte pass with transparency using a pass? Or can this only be done with a layer?

 

If with a layer, do I need to create an entirely new set of shaders, and then re-assign one by one? Or is it possible to maintain the transparency with an override?

 

What's the best way to create the matte pass with transparency?

Message 4 of 5
mspeer
in reply to: dkrelina

Hi!

 

"So then the solution would be to have multiple MV passes and matte passes and then combine them together to create a "master MV pass" in comp."

No, at the moment you combine them you still only get one direction.

Think about 2 semi transparent objects, one moves to the left and an other behind moves to the right.

So you need to render object1 + motion and then combine the result with object2 + motion.

 

 

Because of Reflections and Refractions you may not get Transparency in the alpha channel, that's correct.

How to render the different layers/or passes is up to you, everything that works is OK (consider you may need both, semi transparent and full opaque/transparent mattes) .

Message 5 of 5
dkrelina
in reply to: mspeer

Ok I see what you mean about it not being possible to have vectors moving in two opposite directions.

 

In this case, I would be comfortable with using full opaque/transparent mattes, as long as I get the silhouette of the plants (as seen in the image). Perhaps using a threshold, and then everything above or below is either 0% or 100%. Is this possible in the mv2DToxik pass? I have not been able to find how to do this. Or do I need to achieve it using additional mattes?

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