Do you suppose this is related to gamma correction issues? I just don't see what could possibly wrong. I'm using the output of my tonemapping as the input scene which is in regular 32 bit unsigned format and being output to an srgb target after being linear.
update: Gamma correction does not seem to be the problem. I've tried using regular R8G8B8A8_UNORM for both outputs. Besides being in the wrong color space the border issue was still there. Maybe it's the LUT texture ?
update2: I just tried making it the only post effect in my chain, and I've tried using regular LDR for shading. The pixel border still appears. This has to be either an issue with the input texture or the sampling process..
If I just output rawColor inside the color correction shader I get the perfect original scene. But using the LUT I get the border.
It looks almost like an edge highlighting. Using LinearWrap makes it even more apparent.