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Vector Pass out of Air

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champ_2007
Vector Pass out of Air
on Mar 5, 2007 at 10:50:24 pm

We are rendering through maya with Air and we can't seem to get the vector pass to render properly. We have tweaked values in the RSMB shader that was supplied by air and we always seem to get the same result. Just a solid yellowish colour. Is the shader in air correct? or will we have to use mental ray(which isn't viable in our situation)? Any help on this matter would be appreciated.


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Pierre Jasmin
Re: Vector Pass out of Air
on Mar 5, 2007 at 11:43:44 pm


Air supplied an RSMB shader? What is it, a Renderman shader?
It's yellowish as it uses R=0.5 and G=0.5 as 0 motion to map -1 to 1 within 0 to 1 for 16 bpc and other clamping contexts.

If you render the frame in 16 bpc or float does it have variance in the yellow when you load it somewhere and pass the cursor over it, also is there a control in the shader (eg Max Displace or Scale).

Also with Mental Ray as per http://revisionfx.com/support/faqs/generalfaqs/motion_vectors/#Maya one has to "To get an alpha from the shader, one has to check in Custom Entities in the Render Settings the "Pass Current Alpha Channel" option. Do not try to use the beauty pass alpha in Maya. It won't perfectly align."

With MR it will be affected by the actual shutter setting as well.
If you just give me two frames of a sphere moving with what the shader exports I can see what happens. (techsupport@revisionfx.com)
Feel free to put me in contact with Sitex support as well if they have an mv export shader.


Alpha from the shader?
http://revisionfx.com/support/faqs/generalfaqs/motion_vector_alpha/



Pierre


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champ_2007
Re: Vector Pass out of Air
on Mar 5, 2007 at 11:58:40 pm

Thanks for the response. Yes, air supplied a renderman shader. It has 3 attributes. Light shadow fraction, max displace, and target space. Our renders are currently solid flat yellow (0.5 in the red and greens throughout the image). Changing the attributes in the shader provides the same results in the render. Our alpha pass lines up with our beauty pass. We aren't sure what settings to use in the shader and in Air's motion blur to get the correct result. I am emailing you two frames right now with our results thus far.


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Pierre Jasmin
Re: Vector Pass out of Air
on Mar 6, 2007 at 12:38:14 am


What's the Max Displace Amount?
It should essentially scale towards or from 0.5 0.5 depending on that value

We recommand to work in 16 bpc and type in for Max Displace the most common resolution you use in-house : eg 1280
as in 1280.0 x 1/32767.0 is plenty of subpixel precision for motion blur. Some people prefer to make this value much smaller and work with floating point renders so they can then see color variations in the MV pass.

Not clear what Target Space they offer (screen and pixel?). There must be a way to trigger computation of Motion for the shader somewhere (without Motion blurring the motion vectors).

Pierre


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