Posted by Luis Ortega on 09/11/06 18:40

"Richard Crowley" <richard.7.crowley@intel.com> wrote in message
>
> 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.

Thanks, guys, I'll try luma, but I know that my drawings contain some whites
inside of the drawings.
I'm trying to plan right now for how to advise a class of kids on how to
prepare their own drawings, so nothing is really done yet except for my few
test drawings, which do have lots of white inside the drawn elements.
I could advise the kids to be sure to fill in anything that is not
background in some colour, but if they use weak colours such as colour
pencils, I imagine that there will be enough white in those areas to maybe
give me problems?
I will have to try colouring in my test cels with the same sort of colour
pencils that the kids will use. Markers seem to produce too strong a colour
and tend to cover up the drawing details.
In the end, it might be best just to tell them to do it all in the drawings
and not rely on keying out a background.
Later, we will be doing claymations and cutout stopmotions (a la South Park)
and with these they will probably need to be able to key out the background,
but it's fairly easy to lay the cutouts on some solid colour poster paper
when we photograph them. I've had less luck with clean keying out of
backgrounds in claymation because the lighting on the background paper is
not always perfectly even and then Premiere has problems getting a clean
edge around the claymation figures.


>> 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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