Create alpha channel from gleffects_sobel output

[Chris Whittenburg]

I would like to overlay the edge output from gleffects_sobel element, onto
a thermal RGB image, but I can't find a good way to do it.

If I just use glvideomixer, and set the alpha of both streams to 0.5, then
I get something similar to what I want, but there isn't much contrast.

I think what I want to do is turn the black areas of the sobel output into
an alpha channel, and then use a videomixer with that and the thermal data.


But, how do I generate the alpha channel from the output of gleffects_sobel
element?

Thanks,
Chris
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