Why Doesnt The Background Render When I Assign A Surface Shader?

[georgep1]

Whenever I try to assign an object in my scene a maya surface shader and then render it in mental ray, the background doesnt render and I get an image that is a "cutout" without a background. How can I prevent this from happening?

[fortner_mike]

Do you actually have the background (like some plane or something)? If so, what is is?

[georgep1]

no, its just a solid color. I have since fixed the problem, or I should say I am not having the problem anymore, as I have no idea what I did to fix it. I am thinking maybe it had something to do with the near and far clip planes?

[fortner_mike]

Ok. but i don't understand this:

QUOTE
I get an image that is a "cutout" without a background

Thats exactly what you are supposed to get, by default the color is black (but you may have changed it). There always must be some background, white black or whatever... but there is always a background when you render (unless you use alpha but i understand you dont)

[joojaa]

Theres still a color alpha or not!

[fortner_mike]

Yeah, cant argue with that . But i was only thinking of what can user see on the screen by default(and that would be R G B channels, not alpha).

[georgep1]

ok, by cutout, i mean that the objects in the foreground appear in the rendering, but instead of having a black background (which is the set background color), the background is transparent when I open the image (targa) in photoshop. The problem only occurs in batch renders and not preview renders. I do not have a check mark in the render alpha box in the render settings, and I do not have a check mark in the mask box under the output settings of the camera attribute editor. I think this may have something to do with the near and far clip planes but im not totally sure. I cant imagine why the clip planes would effect the background, but changing the near clip plane to .001 from .01 and the far clip plane to 5000 from 1000 has seemingly solved the problem

[fortner_mike]

This may be some photoshop setting, but It really has nothing to do with clipping planes. Now when you put it like this it sure sounds like it has something to do with alpha channel. Anyhow if its a still you can manually fill it with black (but to much work if it's a sequence of images for video). You could bypass that by creating a plane behind the scene and assign a black shader to it, turn of all the reflections and cast and receive shadows and other things. This is not a real solution but its a nice trick which you can use if you cant fix it other way.

[joojaa]

Ahh this its photoshop interpreting (incidentally this was a much requested feature of ps and it annoys the hell out of 55% of users) the image just ditch the alpha.

Why would you want to render without alpha, its just a bonus you can easily choose not to use it anyway (but more importantly like z depth you get it for free.)

[georgep1]

how do i ditch the alpha? I thought this was what I was doing by not rendering with the alpha.

[joojaa]

Sure but why would you rip your tickets beforehand so you must go to a certain predefined flight whan you can decide to take any flight for same fee (at no risk of not getting a good seat, s if you decide to stay one day longer you can)?

select the layer and delte its alpha. Anyway this i quite basicphotoshop functionality so ask photoshops help