Put and check the final render in the original sequence with Difference mode

When I put and check the final render in the original sequence with Difference mode, I always get that slight outline all over my texts.

It happens with h.264 and Apple Prores 422 and Animation mov.

It's not something that is driving me crazy bc no one will notice the difference anyway but you know..

My rough guess is that happens when the video gets compressed by the renderer therefore It's unavoidable.

But it remains the question that why my cam footages are completely fine.

Anyone can help me understand this?? 

I'll leave some screenshot examples with some clean color matte and some texts.