Mode-dependent coefficient scanning and directional transforms for different colour sampling formats
A method of coding 4:2:2 or 4:4:4 video data comprises predicting luminance and/or chrominance samples of an image from other respective reference samples derived from the same image according to a prediction mode associated with a sample to be predicted, the prediction mode being selected for each of a plurality of blocks of samples, from a set of two or more candidate prediction modes; detecting differences between the samples and the respective predicted samples; selecting a frequency-separation transform from two or more candidate frequency separation transforms according to the prediction mode associated with a current block of samples using a mapping between transform and prediction mode, the mapping between different, as between chrominance and luminance samples, for at least the 4:4:4 format; and encoding the detected differences by frequency-separating the differences, using the selected frequency-separation transform.
1. A data decoding apparatus comprising:
circuitry configured to
detect from parameters of a received bitstream whether intra prediction is enabled in data and for detecting an intra-prediction mode for a block of samples represented in the bitstream,
determine a scan pattern from a plurality of scan patterns for scanning frequency coefficients, the determined scan pattern being associated with the intra-prediction mode by a mapping, the mapping being different for chrominance and luminance samples, the chrominance and luminance samples being arranged in blocks, the blocks of chrominance samples having a different aspect ratio relative to the blocks of luminance samples, the blocks of chrominance samples having an aspect ratio in which a height is different than a width, and the intra-prediction mode associated with the determined scan pattern being determined in accordance with the aspect ratio such that the intra-prediction mode is remapped from a first intra-prediction mode to a second intra-prediction mode based on the aspect ratio; and
scan the frequency coefficients representing the blocks of chrominance samples and the blocks of luminance samples in an order of the determined scan pattern which depends on the intra-prediction mode associated with the determined scan pattern and decode video data for output.
2. The data decoding apparatus according to claim 1 , where the mapping is stored data in a look up table.
3. The data decoding apparatus according to claim 1 wherein the circuitry is further configured to apply filtering as part of the decoding of the video data.
4. The data decoding apparatus according to claim 1 , wherein the intra-prediction mode for each of the blocks is a prediction direction.
5. The data decoding apparatus according to claim 4 , wherein the intra-prediction mode is selected from 35 predictions, including 33 prediction directions.
6. The data decoding apparatus according to claim 1 , wherein the circuitry is configured to determine a horizontal scan pattern in respect for a predominantly vertical prediction mode, determine a vertical scan pattern in respect of predominantly horizontal prediction modes, and determine a diagonal scan pattern in respect of other prediction modes.
7. The data decoding apparatus according to claim 1 , wherein the bitstream represents 4:2:2 video data, and the mapping is different for 4:2:2 blocks of the luminance samples and 4:2:2 blocks of the chrominance samples.
8. The data decoding apparatus according to claim 7 , wherein the blocks of luminance samples are 8×8 blocks and the blocks of chrominance samples are 4×8 blocks.
9. The data decoding apparatus according to claim 7 , wherein the 4:2:2 blocks of luminance samples and the 4:2:2 blocks of chrominance samples are Transform Units.
10. A data decoding method comprising:
detecting from parameters of a received bitstream whether intra prediction is enabled in the data and for detecting an intra-prediction mode for a block of samples represented in the bitstream;
determining a scan pattern from a plurality of scan patterns for scanning frequency coefficients, the determined scan pattern being associated with the intra-prediction mode by a mapping, the mapping being different for chrominance and luminance samples, the chrominance and luminance samples being arranged in blocks, the blocks of chrominance samples having a different aspect ratio relative to the blocks of luminance samples, the blocks of chrominance samples having an aspect ratio in which a height is different than a width, and the intra-prediction mode associated with the determined scan pattern being determined in accordance with the aspect ratio such that the intra-prediction mode is remapped from a first intra-prediction mode to a second intra-prediction mode based on the aspect ratio;
scanning the frequency coefficients representing the blocks of chrominance samples and the blocks of luminance samples in an order of the determined scan pattern which depends on the intra-prediction mode; and
decoding video data for output.
11. The data decoding method according to claim 10 , comprising determining a horizontal scan pattern in respect for a predominantly vertical prediction mode, determining a vertical scan pattern in respect of predominantly horizontal prediction modes, and determining a diagonal scan pattern in respect of other prediction modes.
12. The data decoding method according to claim 10 , wherein the bitstream represents 4:2:2 video data and the mapping is different for 4:2:2 blocks of the luminance samples and 4:2:2 blocks of the chrominance samples.
13. A non-transitory computer-readable storage medium storing computer-readable instructions that, when executed by a computer, cause the computer to perform a method comprising:
detecting from parameters of a received bitstream whether intra prediction is enabled in data and for detecting an intra-prediction mode for a block of samples represented in the bitstream;
determining a scan pattern from a plurality of scan patterns for scanning frequency coefficients, the determined scan pattern being associated with the intra-prediction mode by a mapping, the mapping being different for chrominance and luminance samples, the chrominance and luminance samples being arranged in blocks, the blocks of chrominance samples having a different aspect ratio relative to the blocks of luminance samples, the blocks of chrominance samples having an aspect ratio in which a height is different than a width, and the intra-prediction mode associated with the determined scan pattern being determined in accordance with the aspect ratio such that the intra-prediction mode is remapped from a first intra-prediction mode to a second intra-prediction mode based on the aspect ratio;
scanning the frequency coefficients representing the blocks of chrominance samples and the blocks of luminance samples in an order of the determined scan pattern which depends on the intra-prediction mode associated with the determined scan pattern; and
decoding video data for output.
14. A video storage, reception, capture or display apparatus comprising the data decoding apparatus of claim 1 .
15. The non-transitory computer-readable storage medium according to claim 13 , wherein the method comprises determining a horizontal scan pattern in respect for a predominantly vertical prediction mode, determining a vertical scan pattern in respect of predominantly horizontal prediction modes, and determining a diagonal scan pattern in respect of other prediction modes.
16. The non-transitory computer-readable storage medium according to claim 13 , wherein the bitstream represents 4:2:2 video data and the mapping is different for 4:2:2 blocks of the luminance samples and 4:2:2 blocks of the chrominance samples.