A method of operating a data processing system 4 is disclosed that comprises producing data in the form of blocks of data, where each block of data represents a particular region of a data array, processing the data using a processing operation in which one or more output data values are each determined using data values from plural different lines of the data array, storing the processed data in a memory 21 of the data processing system, and reading the data from the memory 21 in the form of lines.