A problem with Primary Visibility and Photoshop

[Jozvex]

Sounds like a 'pre-multiplied alpha' issue. By default when you render something, the alpha channel is multiplied over the render to... make it look nicer, hehe. For compositing this is bad though as you've discovered. Other apps like Digital Fusion can remedy this with the push of a button but I can't remember if Photoshop has a similar feature. Anyway, in the Render Globals (at least for Mental Ray) you can turn off the Pre-Multiply flag in the Framebuffer area.

:thumbsup:

[basquiat]

Thanks Jozvex, I'll try your suggestion :) .

I'm posting a small example, if you have any other insight:

http://i14.photobucket.com/albums/a336/basquiat/example.jpg

Left is the normal render. Right is the layered composite of background and ball.

[djx]

In photoshop you can do layer-matting-"remove black matte" to make it deal with the edge correctly. (Of course this assumes you rendered on a black background)


edit:
I spoke too soon. Photoshop CS 2 seems to over-compensate for the black and you end up with a light colored fringe instead. You can use the layer-matting-"defringe..." to remove it but its not ideal.

Until recently I have been doing this un-premultiply using aftereffects and saving as a layered photoshop file. I think I'll go back to that, since it gives a cleaner result.

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