Image data decompression

A compression unit configured to perform lossy compression on a block of image data in accordance with a multi-level difference table, wherein the block of image data comprises a plurality of image element values, and wherein each level of the multi-level difference table comprises a plurality of entries, the compression unit comprising:

• origin value determination logic configured to determine an origin value for the block of image data;
• level determination logic configured to determine a level within the multi-level difference table for the block of image data by:
• determining a maximum difference between the determined origin value and any one of the image element values in the block of image data, and
• selecting, from the multi-level difference table, the level whose largest entry most closely represents the determined maximum difference;
• entry selection logic configured to select, for each image element value in the block of image data, one of the entries at the determined level within the multi-level difference table;
• and
• compressed block formation logic configured to form a compressed block of data for the block of image data, the compressed block of data comprising:
• (i) data representing the determined origin value, (ii) an indication of the determined level, and (iii) for each image element value in the block of image data, an indication of the selected entry for that image element value.

A non-transitory computer readable storage medium having stored thereon a computer readable dataset description of a compression unit that, when processed in an integrated circuit manufacturing system, causes the integrated circuit manufacturing system to manufacture an integrated circuit embodying the compression unit, wherein the compression unit is configured to perform lossy compression on a block of image data in accordance with a multi-level difference table, wherein the block of image data comprises a plurality of image element values, and wherein each level of the multi-level difference table comprises a plurality of entries, the compression unit comprising:

• origin value determination logic configured to determine an origin value for the block of image data;
• level determination logic configured to determine a level within the multi-level difference table for the block of image data by:
• determining a maximum difference between the determined origin value and any one of the image element values in the block of image data, and
• selecting, from the multi-level difference table, the level whose largest entry most closely represents the determined maximum difference;
• entry selection logic configured to select, for each image element value in the block of image data, one of the entries at the determined level within the multi-level difference table;
• and
• compressed block formation logic configured to form a compressed block of data for the block of image data, the compressed block of data comprising:
• (i) data representing the determined origin value, (ii) an indication of the determined level, and (iii) for each image element value in the block of image data, an indication of the selected entry for that image element value.