Image data compression

A method of forming a sequence of arrays of pixel display values for driving a display device from a stream of compressed data containing compressed data codes, each of said arrays of pixel display vales representing a frame of a moving image, said pixel display values being decoded in a predetermined sequence of positions within each array of pixel values each compressed data code representing one or more pixel values extending from a current position reached within said predetermined sequence of positions, said method comprising the steps of:

• (i) in response to a pixel copy code within said stream of compressed data, copying each pixel value of a sequence of a plurality of previously formed pixel display values from respective positions extending from a position different from said current position to respective positions extending from said current position within said array, pixel display values being permitted to vary randomly within said sequence of a plurality of previously formed pixel display values;
• (ii) in response to a new pixel code within said stream of compressed data, mapping one or more pixel appearance values specified by said new pixel code to respective pixel display values;
• and
• (iii) writing said pixel display values derived from said new pixel code to said current position within said array.

Apparatus for forming a stream of compressed data containing compressed data codes from a sequence of arrays of pixel values, each of said arrays of pixel values representing a frame of a moving image, said pixel display values being encoded in a predetermined sequence of positions within each array of pixel values, each compressed data code representing one or more pixel values extending from a current position within said predetermined sequence of positions, said apparatus comprising:

• (i) means for searching through previously compressed pixel values from a preceding frame to identify one or more preceding frame pixel values matching one or more pixel values at a current position within an array of pixel values being compressed and in response to such identification generating a temporal copy code for controlling copying of said preceding frame pixel values to said current position upon subsequent decompression;
• (ii) means for searching through previously compressed pixel values from that frame currently being compressed to identify one or more current frame pixel values matching one or more pixel values at a current position within an array of pixel values being compressed and in response to such identification generating a spatial copy code for controlling copying of said current frame pixel values to said current position upon subsequent decompression;
• and
• (iii) means for generating a new pixel code representing any non-matching pixel to be compressed that cannot be represented by a temporal copy code and cannot be represented by a spatial copy code, said new pixel code specifying pixel appearance.

A method of forming a stream of compressed data containing compressed data codes from a sequence of arrays of pixel values, each of said arrays of pixel values representing a frame of a moving image, said pixel display values being encoded in a predetermined sequence of positions within each array of pixel values, each compressed data code representing one or more pixel values extending from a current position within said predetermined sequence of positions, said method comprising the steps of:

• (i) searching through previously compressed pixel values from a preceding frame to identify one or more preceding frame pixel values matching one or more pixel values at a current position within an array of pixel values being compressed and in response to such identification generating a temporal copy code for controlling copying of said preceding frame pixel values to said current position upon subsequent decompression;
• (ii) searching through previously compressed pixel values from that frame currently being compressed to identify one or more current frame pixel values matching one or more pixel values at a current position within an array of pixel values being compressed and in response to such identification generating a spatial copy code for controlling copying of said current frame pixel values to said current position upon subsequent decompression;
• and
• (iii) generating a new pixel code representing any non-matching pixel to be compressed that cannot be represented by a temporal copy code and a spatial copy code, said new pixel code specifying pixel appearance.