IMAGE DATA DECOMPRESSION USING DIFFERENCE VALUES BETWEEN DATA VALUES AND ORIGIN VALUES FOR IMAGE DATA CHANNELS

A decompression method determines image element values from compressed data representing a block of image element values relating to a respective one or more channels. For each of the channels, an indication of a first number of bits representing difference values between the data values and an origin value for the channel is read from the compressed data. For each of the channels, a second number of bits is obtained, wherein representations of the difference values for each of the channels are included in the compressed data using the second number of bits for that channel. The obtained second numbers of bits for the respective channels are used to read the representations of the difference values for the image element values being decompressed. Based on the representations of the difference values, a difference value is determined in accordance with the first number of bits for the channel. For each of the one or more channels, the data value relating to the channel for each of the image element values being decompressed is determined using: (i) the origin value for the channel, and (ii) the determined difference value for the channel for the image element value.