When encoding an array of data elements of a stream of arrays of data elements, a set of sample adaptive offset options to be used for encoding the array are selecting on the basis of a distortion value that is determined for a particular set of sample adaptive offset options. The distortion value is determined by generating one or more filtered reconstructed source blocks by applying a sample adaptive offset filter in accordance with the particular set of sample adaptive offset options to one or more reconstructed source blocks corresponding to a source block, and by then determining a distortion value for the particular set of sample adaptive offset options by comparing the one or more filtered reconstructed source blocks with the source block. When the particular set of sample adaptive offset options comprises an edge offset type, the distortion value is determined using a set of error values comprising fewer data elements than the source block of data elements.