1. A method of encoding a set of texture data elements to be used in a graphics processing system, the method comprising: determining a lower resolution representation of the set of texture data elements; determining a full resolution set of difference data for representing the difference between an up scaled version of the determined lower resolution representation of the set of texture data elements, and the original set of texture data elements; and encoding the set of texture data elements as one or more blocks of texture data representing the texture data elements, each such block of texture data: representing a block of texture data elements from the set of texture data elements and including: data indicating a base data value for the block taken from the determined lower resolution representation of the set of texture data elements; and data indicating the difference data from the determined set of difference data to be used when decoding the block of texture data to generate the data values to be used for the texture data elements that the block of texture data represents.