| CPC H04N 19/12 (2014.11) [H04N 19/129 (2014.11); H04N 19/132 (2014.11); H04N 19/176 (2014.11); H04N 19/46 (2014.11); H04N 19/18 (2014.11)] | 24 Claims |
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1. A decoder configured to:
select, from a group of transforms, a transform for a transform block, the group of transforms including an identity transform and at least one non-identity transforms;
derive, a plurality of coefficients within the transform block, wherein to derive the plurality of coefficients the decoder is configured to:
for a current coefficient of the plurality of coefficients, determine a context for decoding a significance flag based on whether the selected transform is the identity transform or one of the at least one non-identity transforms, the significance flag indicating whether the current coefficient is zero, wherein when the selected transform is:
the identity transform, the context depends on a number of non-zero coefficients at first positions that are adjacent to the current coefficient, and
one of the at least one non-identity transforms, the context depends on a position of the current coefficient within the transform block and respective sums of context coded flags corresponding to coefficients at second positions, the second positions including positions adjacent to the current coefficient and positions not adjacent to the current coefficient, and
decode the significance flag based on the determined context;
transform the plurality of coefficients into a residual sample array based on the selected transform; and
reconstruct a block based on the residual sample array and a prediction of the block.
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