Random accessible image data compression

A compression unit configured to compress a block of image data, the block of image data comprising a plurality of image element values, each image element value being divisible into at least a first value and a second value such that the block of image data comprises a two-dimensional block of first values, the compression unit comprising:

• a header generation unit configured to identify common base information for compressing a first data set according to a first fixed-length compression algorithm, the first data set comprising all or a portion of the two-dimensional block of first values;
• and
• a body generation unit configured to:
• identify a fixed-length parameter for each first value in the first data set according to the first fixed-length compression algorithm, each first value being obtainable from the common base information for the first data set and the fixed-length parameter for that first value, and
• form a compressed block for the block of image data based on the common base information and the fixed-length parameters by:
• forming a header for the compressed block of image data, wherein the header comprises the common base information for the first data set and information that indicates a size of the fixed-length parameter for each first value in the first data set, and
• forming a body for the compressed block of image data, wherein the body comprises the fixed-length parameter for each first value in the first data set.