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Re: Getting a good bluescreen effect in cel animation drawings

Posted by PTravel on 09/11/06 18:52

"Luis Ortega" <lortega@ntlworld.com> wrote in message
news:e4iNg.6198$s4.3494@newsfe3-win.ntli.net...
>
> "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.

Okay, here's how I handle keying out material that hasn't been specifically
prepared for keying. I'll explain this by example, because I think it's
clearer.

Imagine a black box on a white background. The center of the black box is
white.

Obviously, if I use a luma or color key to key out the background, I'll also
lose the center of the box, which I don't want to do.

So, I create a garbage the covers, roughly, the center of the box. I either
pin it to the center so that it tracks movement automatically, or I use key
frames and manually track. It doesn't have to be exact -- it just needs to
cover up that which I don't want keyed out.

I think apply my luminance (or color key) and key out the background BUT I
reverse the key, i.e. everything but the background gets keyed out. I've
now created a matte the eliminates, exactly, the background.

I change the color of the matter to green and super it over the original
clip. Using my box example, I now a black box with a white center and a
green background.

NOW I can use chromakeying to alpha out the green background.

I find this works pretty well.


> 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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