A Comparative Study of Compensation Techniques in Directional DCT´s

A block-based directional DCT framework has been developed recently in which the first transform may choose to follow a direction other than the vertical or horizontal one - the default direction in the conventional 2D DCT, while the second transform is selected according to the first one. However, these directional DCT´s would suffer from the so-called mean weighting defect because DCT´s of different lengths have to be used at the first step along different directional lines within each image block, thus resulting in some unnecessary non-zero components during the second transform. This paper presents a comparative study of various techniques for compensating such defect, including different ways of modifying the scaling factors used in the DCT matrices and the so-called DeltaDC correction method. These techniques are compared with each other in terms of coding performance and computational complexity.