Image diff for later reconstruction

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Hi,

I try to realise video transmission over network with minimal traffic. I don't want to send every single frame, but just the differences between the current frame and the previous one, so that the current frame can be reconstructed by current frame = previousFrame + diff. This difference will be mainly black, so JPG encoding will utilize its full compression capability.

Now my problem: If I just send the result of absdiff(currentFrame, previousFrame), the reconstruction approach is not possible, because I lose the sign. Does anybody have an idea, how I could realise such a reconstruction with OpenCV?