Video Codes with Directional Transforms

[0052]FIG. 7 schematically shows the DIEM 600. For example, there are eight possible transform directions 701 and corresponding predictions 702. The transform direction is selected by the selected transform indicator 145, and the prediction is selected by the PTI 501. The transform indicators are mapped to a Gray code, in which adjacent directions differ only by one bit. The code words for the selected and the predicted directions are compared bit by bit with an exclusive-OR (XOR) 610 operation to obtain the difference 611. For a precise predictor, this yields in a bit stream with mostly zeros for a low entropy. Because the indicator mappings 605-606 use binary representations, the binarization 620 is not used.

[0053]FIG. 8 shows the DIEM. In this embodiment, the directions are represented by a uniformly continuous sequence of numbers. The difference 610 is

Δ=(IS−IP+N)mod N,

[0054]where IS and IP are the mapped indices of the selected and predicted direction indicators, respectively, and N is the number of possible direction, e.g., eight. Because small differences are more probable, the binarization 620 codes differences close to zero (0, 1, N−1, 2, N−2, . . . ) with fewer bits. The difference calculation can be bypassed 611 and the mapped transform indicator is forwarded directly to the binarization module 620. In this case, the context generation module 900 uses the predicted transform indicator to select an appropriate context.

[0055]Context Generation Module

[0056]FIGS. 9-10 show embodiments of the CGM 900. The CGM selects contexts 921-922 for the CABAC 190. More than two contexts can also be selected. To determine the contexts, the CGM can use the preferred processed block information 16...