Composite modeling of optical flow for artifacts reduction
Because of the outstanding contribution in removing pixel correlation, block-based transform and quantization has been widely accepted in the state-of-art image/video coding standards. However, artifacts are introduced, which result in reducing the subjective quality of the decoded image/video. In this paper, a composite model of the optical flow velocity is mathematically derived and proved to further reduce the blocking artifacts by compensating the DC surface of the decoded image according to the model. The functional relationship among the optical flow velocity of the DC surface of the decoded image, the value discontinuity across the block boundary in the decoded image and the quantity of DC surface adjustment is analyzed and mathematically modeled as a composite function with second-degree polynomial. Four feature points on the model with the corresponding criteria in artifacts reduction are compared to show a good consistency between the model and the actual filtering effects. Finding a point on the model with a better trade-off between the optical flow smoothness and the edge smoothness is promising in producing a more pleasing and natural looking image/video.