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A JPEG Corner Artifact from Directed Rounding of DCT Coefficients
Shruti Agarwal, Hany Farid
Dartmouth TR2018-838

Abstract: JPEG compression introduces a number of well known artifacts including blocking and ringing. We describe a lesser known or understood artifact consisting of a slightly darker or lighter pixel in the corner of 8 x 8 pixel blocks. This artifact is introduced by the directed rounding of DCT coefficients. In particular, we show that DCT coefficients that are uniformly rounded down or up (but not to the nearest neighbor) give rise to this artifact. An analysis of thousands of different camera models reveals that this artifact is present in approximately 61% of cameras. We also propose a simple filtering technique for removing this artifact.


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   Shruti Agarwal and Hany Farid, "A JPEG Corner Artifact from Directed Rounding of DCT Coefficients." Dartmouth Computer Science Technical Report TR2018-838, February 2018.


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