1. An apparatus for decoding a transform coefficient block, the apparatus comprising: a decoder configured to extract, from a data stream, a significance map indicating 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 extracted significant transform coefficients with their respective positions in the transform coefficient block in a coefficient scan order, wherein according to the coefficient scan order, a plurality of sub-blocks of the transform coefficient block are scanned in a sub-block scan order, wherein each sub-block includes more than one pixel, and the transform coefficients within each sub-block are scanned in a position sub-scan order, wherein the position sub-scan order is adaptively selected from a plurality of scan orders including a diagonal scan order, wherein the decoder is configured to use, in extracting the significant transform coefficients, context-adaptive entropy decoding wherein, for each sub-block, a selected set of contexts from a plurality of sets of contexts is determined based on a statistic of the transform coefficients within a previously traversed sub-block of the transform coefficient block, or a statistic of the transform coefficients of a co-located sub-block in a previously decoded transform coefficient block.