2007-10-12

Maya: No Alpha channel on mia_material(_x)?

This must rank as the "most frequently asked question ever". (And consequently, the worst use of Google ever, apparently, since CGTalk alone has more threads on the topic than you can shake a stick at).

The problem: You render stuff in Maya, using mia_material(_x) - or any other "mental ray" shader - but you find that those pixels containing that shader has no alpha. What gives?

The reality is that Maya has a very peculiar notion of Alpha... because the Maya software renderer actually has true three-colored "transparency", so transparency gets passed around separately in the most... odd... ways ;)

Hence, to get the Maya system to "understand" a standard shader that uses alpha, you need to check this here little checkbox:



Then, life should be more fun again!

/Z

13 comments:

Peter said...

For the record: that's in Render Settings > Mental Ray.

Tiger said...

hi master Zap

i want to know how to get the alpha channel for glass material using mia_material_x?.. the alpha seems to be solid and the transparent area inside does not contain alpha.

t.q

Locke said...

Thank you so much. You just saved me from wasting more time.

joie said...

Yeah but, What about changing the mia_material own alpha channel?.

What if I have two opaque balls but I want one of them have grey alpha channel?, In MAYA you just change its alpha color, but mia_material doesn't have any. So?.

henna said...

Actually after doing that it didn't work. I also had to do this extra step:

On the mia material settings, under advanced refraction, check the box "propagate alpha". I don't know if that's obvious haha... but well I didn't know! now it's working fine!

-daniel

H.Rosenberg said...

Is there any way to have alphas when you are doing Mental Ray multipass on an Mia_Material_X_Passes?

Yuri.aws said...

Ok, in Maya 2011:
1) pass custom alpha stands by default in mental ray options tab
2) propagate alpha didn't do anything for me
3) in mia material x/ x passes go into advanced and there is cutout opacity, just drop your file while alpha channel in there and you should be good!
Hope this helps...

Yuri.aws said...

Ok, in Maya 2011:
1) pass custom alpha stands by default in mental ray options tab
2) propagate alpha didn't do anything for me
3) in mia material x/ x passes go into advanced and there is cutout opacity, just drop your file while alpha channel in there and you should be good!
Hope this helps...

defmans7 said...

HOLY MOTHER OF GOD!
That was an epic internet trawl to get to this post and finally solve my problem...

Alena Volarevic said...

I have a question about this cutout. If for example I have a feather that I want to cutout, and it's not clean black and white image, instead it has a bit of transition/grey on the edges. In the render it gives me some weird line on the edge. Is there a solution for it or does cutout accept only black and white images without grey in it?

Yuri.aws said...

As far as I know Maya works best with IFF files.So try that. Also alpha channel has to be B&W, not greyscale. However shader transparency can be greyscale. So you might wanna go and clean up your alpha in photoshop or other editor and bring it back to maya as an IFF. Hope this answers your question.

Tornado said...

i only got my glass transparent alpha with .TGA file format ! i other format i just got alpha for contour totaly white no gray parts(.psd,.png,.tiff)

Eduardo Guisandes said...

Is there a way to have alpha on a mia_material_xpasses, with a transparency map connected to it, on render passes? It works fine normally, but not in passes