1. A method of determining which one of a set of plural predefined partitioning patterns to use to divide data elements of a block of data elements to be encoded into separate partitions within the block for encoding purposes, the method comprising: generating a reference partitioning pattern for the block of data elements using a partitioning function, the partitioning function comprises a clustering function that partitions the data element values into a given number of partitions of data values, and the step of generating a reference partitioning pattern for the block of data elements using a partitioning function comprises using the clustering function to partition the data element values into a given number of partitions of data values, and then allocating each data element in the block to a respective data value partition based on its value, to thereby give the reference partitioning pattern for the block; comparing some or all of the predefined partitioning patterns in the set of plural predefined partitioning patterns to the generated reference partitioning pattern; and selecting one of the predefined partitioning patterns in the set of plural predefined partitioning patterns as the partitioning pattern to use when encoding the block of data elements on the basis of the comparison.