| CPC H04N 19/18 (2014.11) [H04N 19/124 (2014.11); H04N 19/129 (2014.11); H04N 19/13 (2014.11); H04N 19/136 (2014.11); H04N 19/139 (2014.11); H04N 19/176 (2014.11); H04N 19/46 (2014.11); H04N 19/50 (2014.11); H04N 19/51 (2014.11); H04N 19/59 (2014.11); H04N 19/61 (2014.11); H04N 19/70 (2014.11); H04N 19/91 (2014.11)] | 20 Claims |

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1. An apparatus for decoding a transform coefficient block, the apparatus comprising:
a decoder configured to extract, from a data stream, a significance map that indicates positions of significant transform coefficients within the transform coefficient block, and the significant transform coefficients within the transform coefficient block; and
an associator configured to associate the significant transform coefficients with their respective positions in the transform coefficient block, wherein transform coefficients within each of a plurality of sub-blocks of the transform coefficient block are scanned in a position sub-scan order, and each sub-block includes information about a plurality of pixels,
wherein the decoder is configured to use, in extracting the significant transform coefficients, context-adaptive entropy decoding such that each of the plurality of sub-blocks is entropy decoded using one or more contexts determined for that sub-block separately from the other of the plurality of sub-blocks, and wherein, for entropy decoding the significant transform coefficients of a sub-block of the plurality of sub-blocks, a selected set of contexts from a plurality of sets of contexts is determined based on a specific value related to one or more of the significant transform coefficients of a previously traversed sub-block of the transform coefficient block, wherein the specific value depends on a number of significant transform coefficients of all previously traversed sub-blocks in a predetermined neighborhood of the sub-block.
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