A computer-implemented method of performing decompression to determine one or more image element values from compressed data, wherein the compressed data represents a block of image data comprising a plurality of image element values, each image element value comprising one or more data values relating to a respective one or more channels, the method comprising: reading (S712), from the compressed data, an indication of an origin value for each of the one or more channels; reading (S704), from the compressed data, for each of the one or more channels, an indication of a first number of bits for representing difference values which represent differences between the data values and the origin value for the channel; obtaining (S706), for each of the one or more channels, a second number of bits, wherein representations of the difference values for each of the one or more channels are included in the compressed data using the second number of bits for that channel; using (S708) the obtained one or more second numbers of bits for the respective one or more channels to read the representations of the difference values for the one or more image element values being decompressed from the compressed data; based on the representations of the difference values read from the compressed data, determining (S710), for each of the one or more channels and for each of the one or more image element values being decompressed, a difference value in accordance with said first number of bits for the channel; and for each of the one or more channels, determining (S714) the data value relating to the channel for each of the one or more image element values being decompressed using: (i) the origin value for the channel, and (ii) the determined difference value for the channel for the image element value. reading (S712), from the compressed data, an indication of an origin value for each of the one or more channels; reading (S704), from the compressed data, for each of the one or more channels, an indication of a first number of bits for representing difference values which represent differences between the data values and the origin value for the channel; obtaining (S706), for each of the one or more channels, a second number of bits, wherein representations of the difference values for each of the one or more channels are included in the compressed data using the second number of bits for that channel; using (S708) the obtained one or more second numbers of bits for the respective one or more channels to read the representations of the difference values for the one or more image element values being decompressed from the compressed data; based on the representations of the difference values read from the compressed data, determining (S710), for each of the one or more channels and for each of the one or more image element values being decompressed, a difference value in accordance with said first number of bits for the channel; and for each of the one or more channels, determining (S714) the data value relating to the channel for each of the one or more image element values being decompressed using: (i) the origin value for the channel, and (ii) the determined difference value for the channel for the image element value. <EOS>