#Targa + Underscan
If that smear shows up on a texture, then you've got a board (or
input source) problem, nothing to do with overscan. Again, as I said,
512×400 is an underscan resolution, but border is all around. The 512×482
resolution in underscan, with borders left & right, I don't believe is
available anymore. Other than being a different aspect ratio, there really
is no reason not to be able to use overscan for all operations.