1. A system configured to perform a 2D transform on each input data block of a sequence of input data blocks, wherein each said input data block comprises rows and columns of input data values and the 2D transform includes a row transform and a column transform, said system including: row transform circuitry configured to generate a block of partially transformed data in response to each said input data block, by performing the row transform on each row of the input data block; and column transform circuitry configured to perform the column transform on each column of the block of partially transformed data, wherein the row transform circuitry is configured to determine, when performing the row transform on each said row, whether each of different subsets of the data values comprising a partition of the row includes at least one zero value, whether each of different subsets of a first one of the subsets of the partition of the row includes at least one zero value, and whether each of different subsets of a second one of the subsets of the partition of the row includes at least one zero value, and the row transform circuitry is configured to bypass or perform in a reduced-power manner at least one transformation operation on at least one of the data values that is determined to be a zero value.