color correction confusion

[Mylenium]

Apologies if this seems a stupid question

No, it's not. AE will internally unmultiply the Alpha so in theory this should be no problem. However, on the practical side there is one limitation: In order to retain the blending, the pixels need to be dilated beyond the borders of the Alpha. Since AE has no way of knowing if the resulting RGB color is actually the way it was meant to be. Even though a given pixel is stored in the file multiplied with black, it's intended original color in the renderer might have been a different one. This is more or less an evil combination of the renderers Gamma settings, low bit-depth file formats and obviously the impossibility of storing surface attributes such as luminosity other than in the pixel color itself. So for the most part it's true - if you are interested in massive color corrections, using straigh Alpha would be a better choice. It's possible to get rid of fringes by using additional effects (Remove Color Matting, Matte Choker), but in strict technical terms then you are already degenerating the Alpha, so it is not always advisable.

Mylenium

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