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--></style><title>Re: [PD] color keying using pd and Gem for
OSX</title></head><body>
<blockquote type="cite" cite>hi,<br>
<x-tab> </x-tab>i am having limited success
achieving color keying using 2 stream of video. Have tried using the
[pix_alpha] method and can achieve color keying using to picture
sources<br>
or using video as the background and an image as the keyed foreground,
but replacing the foreground image with a movie does not work.<br>
<x-tab> </x-tab>tried converting the foreground movie using
[pix_rgba] but no use, it just screws up the color. using
[pix_hsv2rgb] results in some sort of keying but not through the
pix_alpha method just as a result of shifting the color fields
around.<br>
<x-tab> </x-tab>i was wondering if<br>
<x-tab>
</x-tab><x-tab> </x-tab>a)
what i am trying to do is just wrong<br>
<x-tab> </x-tab><x-tab>
</x-tab>b) some crucial step is missing<br>
<x-tab> </x-tab><x-tab>
</x-tab>c) GEM implementation on OS X is lacking</blockquote>
<div><br></div>
<div>which version of GEM are you using? there's not a final
release for OSX yet so you might be using a broken or outdated
version. try the one here:
http://taproot.dyndns.org/~cgc/downloads/index.html (make sure
you grab the appropriate one for either G3 or G4 cpu).</div>
<div><br></div>
<div>it has an object called pix_chroma_key that i wrote and it does
keying on both RGB and YUV sources. it's usage is quite simple
it takes a message for the key 'value' with three arguments for each
color channel, and a 'range' message which is the range of values +/-
the center value.</div>
<div><br></div>
<div>example for RGB:</div>
<div>value 150 100 50</div>
<div>range 20 10 10</div>
<div><br></div>
<div>would key using the red channel for a range of 130 to 170 the
green from 90 to 110 and blue 40 to 50. if this was for YUV it
would be the same ranges for Y (luma) Cb (chroma-blue) and Cr
(chroma-red) in that order.</div>
<div><br></div>
<div>there's also a 'direction' message that flips the keyed
areas.</div>
<div><br></div>
<div><br></div>
<div>cheers, tim</div>
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