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Alpha isn't rendering

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Steven J Casey
Alpha isn't rendering
on Nov 2, 2005 at 2:34:04 pm

Newbie not sure what's going on. I'm not getting an alpha channel on my render even though it's turned on in the Image File Output dialog. What is the best image format to use if I'm bringing this into After Effects for compositing? I tried just keying out the black in AE but then of course I'm keying out the shadows/shading on my object. I see someone asked pretty much the same thing a few days ago but there's no replies. Please help the confused! : )

Not sure I understand Z Depth, either. Is there a 1 or 2 sentence basic explanation of this?

Thanks!
Steven


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Sean Fennell
Re: Alpha isn't rendering
on Nov 2, 2005 at 5:19:39 pm

what file format are you rendering to? Tiff and Tga are good formats for bringing images with alpha into after effects.

As for zdepth, you can render to rla format which after effects can read and it will hold color, alpha, and z-depth. Although I though after effects supported maya's native IFF format. If so, iff is the most efficient way to go.



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Chad Briggs
Re: Alpha isn't rendering
on Nov 2, 2005 at 5:32:57 pm

word to the wise on maya 7 and .iff formats for those who care. If you render to .iff from mental ray (inside maya) then those IFF will not open in photoshop or afx. This really sucks, cause I was really starting to like .iff. Apparently it's an adobe issue (so alias claims) and they are trying to sort it out. (Maya Software render IFF's work fine tho, but who uses that anymore :) )
-chad


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Jason Brummett
Re: Alpha isn't rendering
on Nov 3, 2005 at 11:19:42 pm

I do 99 percent of the time..:)

Jason Brummett
Studio Z Inc.


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Ben Insler
Re: Alpha isn't rendering
on Nov 4, 2005 at 7:12:54 pm

As for a 1-2 sentence explaination of what z-depth is, it's a black and white image (just like an alpha channel) that describes the distance of objects from the camera. So, for example, let's assume that you have a plane with a default shader facing your camera, tilted at a 45 degree angle so that the plane is closer to the camera at the bottom and farther from the camera at the top. When you render the scene, you will get:

Chroma: A default gray plane, provided default lighting was turned on

Alpha: A solid white image, provided that your plane filled your camera frame

Depth: A gradient from white to black transitioning vertically up your image, describing that the bottom of the rendered plane is closer to the camera than the top.

Just 2 quick notes on z-depth. You have to render it using .rla or .iff through the Batch Render. In my experience, I've never been able to render out a frame in the render view, save the image out, and have it end up with z-depth when you open it in FCheck or anything else. Also, to my knowledge, z-depth will not anti-alias while rendering, so watch out for very blocky z-depth maps.

Hope that helps a little.

-Ben


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Sean Fennell
Re: Alpha isn't rendering
on Nov 4, 2005 at 7:52:25 pm

Nope, z-depth will not anti-alias because the blending of the values that anti-aliasing does would provide incorrect data at the edges of geometry because the blending of values will, technically, change the distance from the camera for those pixels. You could always render the z-depth pass much larger if necessary.


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GregNeumayer
Re: Alpha isn't rendering
on Dec 10, 2005 at 10:58:24 pm

Sean,
Trying to get z-depth into AE from Maya has been making me crazy. If z-depth info can't be anti-aliased, won't it make all effects that use it look pretty crappy? Is there (could there be) such a thing as a straight z-depth channel?

-Greg

Antifreeze Design
http://www.antifreezemotiongraphics.com


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