Here is what I hope to do:

Chroma key out parts of one gemhead film layer,
to reveal parts a film playing behind it (another gemhead layer)...
(Can i ) flatten these two gemheads and then manipulate it further, i.e.:
chroma key out more parts (originally from the top gemhead layer),
to reveal another film playing in the background?

Any help would be much appreciated!
Thanks

@cocobryce Hello there...... You could try this...........pd/extra/gem/pix_chroma_key-help.pd
But using [pix_film] instead of [pix_image].......... maybe?
I cannot find two videos of the same size to test at the moment. You might be lucky.
David.

Thanks @whale-av this helped.

What I am after is being able to key out the background just like green-screening (where the background is keyed out and you see a video behind a person)... Then I want to key out the person to reveal another video in their silhouette.

This works but gemhead 1 and 2 are easily key out together in the second round (of keying).

@cocobryce Hello again........
You might have to do some clever stuff with the rendering order. I am no expert in GEM. Look at pd\extra\Gem\examples\02.advanced/14.RenderOrder.pd.

Have a look also at........... pd/extra/Gem/gemframebuffer-help.pd
and.... pd/extra/Gem/examples/07.texture/11.multiples_gemhead_in_a_framebuffer.pd
which can allow you to do more to an image before the next chain is rendered.

Also, if you upload your patch then others, who know more than me about Gem, might modify it for you and re-upload into the thread!
David.

Thanks @whale-av .

I tried each of the patches suggested - got close. Each had some issues i couldn't figure out.

Here's where i'm at and it's working pretty good for now... alpha and chroma key...

Thanks again for your help!