View Full Version : use background not transparent but black??

01 January 2007, 05:04 AM
Hi there
Could someone please help me would be much aprreatiated.

I have rendered the first jpeg "render lambert" which has lambert applied to the plane. That succesfully rendered I am now trying to render the same picture but with "use background " material applied to the plane. See jpeg 2 "render use background.
There seems to be a problem in that the plane renders as black when it should be transparent with only the shadow on the transparent plane and the picture showing underneath. I havent used "suface shader' or anything like that. In the scene view the plane is grey when I think its supposed to be green when the use background is applied. I have a directional light for the shadow of the ball with depth map shadow turned on. Also have a ambient light to brighten the scene. Have tried maya software and mental ray to rendering.
Still cannot get the plane to be transparent like it is suppose to be. See attachments below.

Thanks again :)

01 January 2007, 05:18 AM
That shader uses the background color as it's color. Your background color is black, therefore, so is your plane.

01 January 2007, 06:53 AM
I see your problem.

What you are trying to do basically is to have a shadow effect from the sphere on the ground of your image plane. You were trying to do this within maya itself. This isn't an unheard of workflow, but generally you render output from maya (without image planes) and comp it to any existing footage you had in mind in a compositing or paint software such as shake, after effects, or photoshop if you're just handling single frames.

useBackground will as Sacslacker said adapt the color of the background. It basically masks out any geomtery you do not want to render out at the time (for matte work or layering), but it can also be used to catch the shadow or reflections off an object without actually rendering the object. What you should do is zero out all values of the useBackground shader except shadow mask, which will make it render out black in rgb mode, but you'll be able to see the alpha if you go to alpha mode.

01 January 2007, 02:53 PM
Use Background shader will use the color from your render camera -> environment.

So if you put a backplane into this node, you get the effect.

01 January 2007, 08:52 PM
Thanks for your replies.
I tried the isoparmB solution and it didn't work. Did not really know how to implement mickna solution. I suppose when you say "put the backplane into this node" you are referring to using the connection editor. Not sure which nodes to connect.

01 January 2007, 09:32 AM
While in the render view, click the display alpha channel button in the panel menu bar. This should show you wether the shadow exists in your render. If it does, you can comp it. Also make sure your light is set to cast shadows and is positioned correctly relative to the sphere and plane.

Also, try setting your current render to maya software just to test.

01 January 2007, 08:33 AM

I guess your backplane (the image with the road) is a nurbs or polyplane in the scene, isn't it?

So delete this from the scene.
- Select your camera (the camera you are rendering)
- press [Strg]+[a] to open the attribute editor
- scroll down and open Environment
- click on [Create]
- now you should see a yellow square in the viewport
- The Attribute editor change to imageplane
- In the second section you should see there "Image Name"
- click on the smal icon (folder) on the right side
- select your image

Hope this helps?

01 January 2007, 01:42 AM
What IsoparmB is talking about is correct. He is describing the steps to set this up to later be composited in a compositing application such at after effects. It really is good practice to think in terms of compositing when setting up scenes and lighting. I think this is one of those things that's hard to wrap your mind around when starting out.

01 January 2007, 05:47 AM
here.. using your image as an example......... (
When using the use Background shader...Reflectivity 0
is that what you are looking for?
If not im sorry...

01 January 2007, 02:43 PM
What you posted in the first image would work if the background were an image plane assigned to that camera view, not if it were just a texture mapped surface. mickna seems to have posted the keystrokes involved to fix it, although I don't know where he found a [strg] key. :)


01 January 2007, 03:12 PM
Hey Jeremy!

My [strg] key is near the "any"-key *lol*
BTW: Is it possible, that you gave a seminar on the filmakademie in Ludwigsburg?
I think we met there (six or seven years ago)?

Take care,

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