Filtering mode for intra prediction inferred from statistics of surrounding blocks
The present invention relates to intra prediction which may be performed during encoding and/or decoding of an image signal. In particular, the present invention relates to intra prediction of a current block, during which filtering is applied to the prediction signal and/or to signal used for the prediction. The filtering is applied in accordance with a decision based on characteristics of image signal included in block(s) spatially adjacent to the current block.
1. A method for decoding, on a block-by-block basis, encoded image data partitioned into a plurality of blocks, said method comprising:
detecting a location and a direction of a dominant edge within each image data of a plurality of previously decoded blocks spatially adjacent to a current block, the edge intersecting the current block and the plurality of the previously decoded blocks being used for intra prediction of the current block;
deciding on the basis of the detected dominant edge whether either a first filtering or a second filtering is to be applied to pixels of the previously decoded blocks to be used as reference pixels for intra-prediction depending on the proximity of said pixels of the previously decoded blocks relative to the detected dominant edge; and
predicting the current block from the image data of the previously decoded blocks by intra prediction,
wherein in said predicting of the current block, intra prediction is performed using filtered image data of the previously decoded blocks to which the first filtering is applied as reference for the prediction, when it is decided in said deciding that the first filtering is to be applied, and
wherein in said predicting of the current block, intra prediction is performed using filtered image data of the previously decoded blocks to which the second filtering is applied as reference for the prediction, when it is decided in said deciding that the first filtering is not to be applied, the second filtering being edge-sharpening filtering applied to n pixels to be used as reference pixels for intra-prediction of the current block around the edge intersection with the current block and the first filtering being low-pass filtering applied to the remaining pixels to be used as reference pixels for intra-prediction of the current block.
2. An apparatus for decoding, on a block-by-block basis, encoded image data partitioned into a plurality of blocks, said apparatus comprising: a controller; a processor; and a memory, said processor configured to perform:
detecting a location and a direction of a dominant edge within each image data of plurality of previously decoded blocks spatially adjacent to a current block, the edge intersecting the current block and the plurality of the previously decoded blocks being used for intra prediction of the current block;
deciding on the basis of the detected dominant edge whether either a first filtering or a second filtering is to be applied to pixels of the previously decoded blocks to be used as reference pixels for intra-prediction depending on the proximity of said pixels of the previously decoded blocks relative to the detected dominant edge; and
predicting the current block from the image data of the previously decoded blocks by intra prediction,
wherein in said predicting of the current block, intra prediction is performed using filtered image data of the previously decoded blocks to which the first filtering is applied as reference for the prediction, when it is decided in said deciding that the first filtering is to be applied, and
wherein in said predicting of the current block, intra prediction is performed using filtered image data of the previously decoded blocks to which the second filtering is applied as reference for the prediction, when it is decided in said deciding that the first filtering is not to be applied, the second filtering being edge-sharpening filtering applied to n pixels to be used as reference pixels for intra-prediction of the current block around the edge intersection with the current block and the first filtering being low-pass filtering applied to the remaining pixels to be used as reference pixels for intra-prediction of the current block.