Image data decompression

A decompression unit configured to perform 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 a plurality of data values relating to a respective plurality of channels, wherein the plurality of channels comprises at least one reference channel and a plurality of non-reference channels, the decompression unit comprising:

• decompression logic configured to:
• read, from the compressed data, compressed channel data for each of the channels, and
• for each of the channels, use the compressed channel data for the channel to determine an initial data value relating to the channel for each of the one or more image element values being decompressed;
• and
• channel decorrelation logic configured to determine, for each of the one or more image element values being decompressed, a decompressed data value for each of the non-reference channels by:
• reading, from the compressed data, an indication of a compression mode for the non-reference channel for the block, wherein the compression mode is either a channel decorrelating mode or a non-channel decorrelating mode,
• if the compression mode for the non-reference channel is the non-channel decorrelating mode, determining the decompressed data value for the non-reference channel to be the determined initial data value relating to the non-reference channel for the image element value, and
• if the compression mode for the non-reference channel is the channel decorrelating mode, determining the decompressed data value for the non-reference channel to be a function of the determined initial data value relating to the non-reference channel and the determined initial data value relating to one of the at least one reference channel for the image element value.

A non-transitory computer readable storage medium having stored thereon an integrated circuit definition dataset that, when processed in an integrated circuit manufacturing system, configures the integrated circuit manufacturing system to manufacture a decompression unit which is configured to perform 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 a plurality of data values relating to a respective plurality of channels, wherein the plurality of channels comprises at least one reference channel and a plurality of non-reference channels, the decompression unit comprising:

• decompression logic configured to:
• read, from the compressed data, compressed channel data for each of the channels, and
• for each of the channels, use the compressed channel data for the channel to determine an initial data value relating to the channel for each of the one or more image element values being decompressed;
• and
• channel decorrelation logic configured to determine, for each of the one or more image element values being decompressed, a decompressed data value for each of the non-reference channels by:
• reading, from the compressed data, an indication of a compression mode for the non-reference channel for the block, wherein the compression mode is either a channel decorrelating mode or a non-channel decorrelating mode,
• if the compression mode for the non-reference channel is the non-channel decorrelating mode, determining the decompressed data value for the non-reference channel to be the determined initial data value relating to the non-reference channel for the image element value, and
• if the compression mode for the non-reference channel is the channel decorrelating mode, determining the decompressed data value for the non-reference channel to be a function of the determined initial data value relating to the non-reference channel and the determined initial data value relating to one of the at least one reference channel for the image element value.