Re: Black edges around objects when I enable motion blur!? Help!

Hi,

This may only confuse the issue further, but it looks like the left image is not pre-multiplied with the alpha channel.

For elements of the image to appear transparent, a pixel's value must be multiplied by the alpha pixel's value. For example if your image's pixel value is 256,256,256 (white) and the alpha pixel's value is 0,0,0 (black) then the image pixel value will become 0,0,0 (Multiplying by 0 leaves 0)

If the image is not pre-multiplied by the alpha, you will see the image pixel values at whatever they are set to with no transparency. Maya may leave the pixels in the blurred, semi-transparent area around the moving object black, relying on the final compositing operation to blend them with the background. This would create the ring of black around your object.

Very often in compositing situations if you try to adjust the levels of an image that is pre-multiplied by the alpha, you will start to see a ring around the non-transparent part of the image. This is because as you adjust the image, you are affecting the final multiplied version of the image.

In your case, without actually knowing what I'm talking about, I would guess that for some reason, Maya is outputting an un-pre-multiplied image. There may be a way of adjusting this setting. Usually 3D graphics renders are pre-multiplied, but because programs like Shake allow a great deal of control over how the alpha is combined with the image, there may be times when you might want to output an un-pre-multiplied image.

Of course, this may not have anything to do with your problem. I only know enough to be a danger to myself and others...

If you could post an iff file with the alpha, I'd be happy to look at it in Shake and see if I can figure out it's multiplication status.

Hope this helps.

Lars