Methods and decompression units for decompressing a compressed block of image data

A decompression unit configured to decompress data from a compressed block of image data, the compressed block of image data representing a 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 decompression unit comprising:

• a header analysis unit configured to:
• receive a header of the compressed block of image data, the header comprising common base information that is common to a first set of values and information identifying a size of fixed-length parameters for the first set of values, the first set of values comprising all or a portion of the two-dimensional block of first values, and
• analyse the header to identify (i) a location in a body of the compressed block of image data of a fixed-length parameter for a first selected value of the first set of values, and (ii) the common base information for the first set of values;
• a body analysis unit configured to:
• receive the body, the body comprising a fixed-length parameter for each value in the first set of values that that is zero, one or more than one bits, each value in the first set of values being obtainable from the common base information for the first set of values and the fixed-length parameter for that value, and
• retrieve the fixed-length parameter for the first selected value from the identified location of the body;
• and
• a value generation unit configured to generate the first selected value from the common base information for the first set of values and the fixed-length parameter for the first selected value.