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I want to change the opacity of the edge of an object so that when I render it and import to After Effects, it would match with the background video and feather at the edge of objects.

Cant place images yet.

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2 Answers 2

When you render in 3D Max make sure pre-multiplying is turned off.

Given the situation you want to render an object to be used for post-production within Photoshop, then…

  • Be sure you set the background to complete black: Rendering > Environment > Background > Colour (click on the colour field and set red, green and blue to 0)
  • Set the antialising in your render settings to Blackman - this type of antialising is quite sharp and doesn’t blur the edges. In V-Ray this is located in Renderer > Image sampler > Antialiasing Filter.
  • Set the file type in the common rendering dialog to tga, 32-bit, premultiplied and alpha split off, compress on.
  • In Photoshop, load the TGA image, double click the layer to convert it from a background layer into a normal layer.
  • Go to channels, CTRL-select the alpha channel, invert the selection, go back to layers and hit the delete button.

[...]

If you already have rendered your image and your alpha is accidentally pre-multiplied, you can add a 6th step to the 5 I mentioned above. In Photoshop go to Layer > Matting > Remove Black Matte. Voilà, you got rid of the black ‘halo’ again.

Full article:
http://www.onoff.ch/2007/01/04/premultiplied-alpha-problems/

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You can use simplechoker module in After Effects to crop unmatched edges.

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