Compositing problem

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  01 January 2013
Compositing problem


I'm working on a project to incorporate 3d objects into a photograph, it is all new for me, so i have been learning a lot about it.
And i think i have grasped the basics a bit, but i have run into a issue...

I have the picture set as a background object, and the particles are in front of them.
If i render this everything is fine, but when i turn of primary visibility of the background and only render the particles in a transparant layer the antialiassing bits get very dark, so i get the result you see in the picture i included.

I render with mentalray with Final Gathering enabled to get nice illumination and shadows on the particles, and from particles to the background.

Can anyone tell me what i am doing wrong?
In this case i turned the primary visibility of the background off, but i get the same result when using the background shader.
Life begins at +1 g lateral.
  01 January 2013
Your problem is that your render is premultiplied and your compositing app is expecting straight (aka unpremultiplied).

You can either tell Maya not to premultiply (in Render Settings) or tell your comping app your render is premultiplied. I'm guessing you're using After Effects and the setting you need is somewhere in the Interpret Footage options.

  01 January 2013
Aaaaaah, thnx a million for your explanation, i used Photoshop because that's the program my photographer uses, and it had the same problem.
In Photoshop i fixed it using [Layers, Matting, Remove black matte].
I really thought i was doing something wrong in maya..

Thnx again, you are a lifesaver!
Life begins at +1 g lateral.
  01 January 2013
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