Posted by Richard Crowley on 09/11/06 17:31

"Luis Ortega" wrote ...
>I have some cel animation drawings done on white paper that I will scan or
>photograph and import into Photoshop and Premiere and I was wondering what
>is the best way to create a blue screen effect so that I can drop a
>background photo behind the cel drawings into the white of the paper.
> Since there are quite a few cels in the animation, I can't really make a
> selection of the backgrounds in each drawing in Photoshop and delete them
> so I get a clear background for Premiere. I have tried several of the
> keying filters (alpha, chroma, colour) and they each do a mediocre job of
> creating a nice crisp knockout of the white background.

How about "luma" (luminence, i.e. brightness). That is what usually
works for me to knock out a white background. Of course, that
assumes you don't have any white (or near-white) in the image itself.
You muse carefuly chose your background so that is distinct from
any part of the desired image.

> One weird effect is that in chroma key, as soon as I select the white
> background and bring up the similarity slider a tiny bit, the blacks also
> disappear! So far, the colour key filter seems the best but it's not
> perfect.

But white, black, and every shade of gray inbetween have exactly the
same "chroma", namely *no chroma* (else it wouldn't be white, black,
or gray). You can;t use any kind of color discrimination to knock out
white (which is ALL colors).

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