Attractors from Black & White image

Hi all !

I'm tracking a body with IR then obtain a sort of shadow. I would like the black borders of the tracked body to attract objects, then I have to get some coordinates.

My idea for the first step was that I can apply a PixelS treatment on a reduced image, then convert to the QC coordinate system.

But I can't manage to track these borders. I always get the whole black/white part.

Does anyone have an idea on testing something like "if one of the surrounding pixels is white, then your black pixel is a border" ?

Thanks !!!