Image data compression/decompression

A method of encoding digital data representative of a document to be duplicated and obtained by scanning said document, said data representing either text data or continuous tone data and said method resulting in compressed data which can be decompressed in either direction to recover the original digital data and comprising the steps of:

• assembling said digital data into scanned strips of said document with each scanned strip comprising a plurality of scan lines of said document;
• reading the scan lines of said scanned strips in parallel to form data words defining columns of said scanned strips;
• defining at least the first and last data words of each scanned strip as text data;
• counting the number of consecutive data words in each scanned strip which are identical to one another to determine the run lengths of said identical data words;
• encoding each run of data words read and the corresponding run length into fixed length coded words;
• concatenating all fixed length code words for each scanned strip to form coded scanned strips;
• reviewing each coded scanned strip;
• substituting uncoded scanned strip data for any coded scanned strip which exceeds its corresponding uncoded scanned strip data;
• concatenating all coded and uncoded scanned strips to form a coded representation of said document;
• inserting synchronization words before each coded scanned strip and before and after each uncoded scanned strip;
• and
• inserting synchronization words into said coded scanned strips to separate text data from continuous tone data and continuous tone data.

A method of handling digital data representative of a document to be duplicated and obtained by scanning said document comprising the steps of:

• assembling said digital data into scanned strips of said document with each scanned strip comprising a plurality of scanned lines of said document;
• reading the scanned lines in parallel to form data words defining columns of said scanned strips;
• counting the number of consecutive data words in each scanned strip which are identical to one another to determine the run length of said identical words;
• encoding each run of data words read and the corresponding run length into a fixed-length coded word;
• storing all fixed-length coded words in a concatenated form to represent said document;
• reading said concatenated fixed-length coded words;
• and
• decoding said fixed-length coded words to obtain the digital data representative of the document to be duplicated.

Apparatus for encoding digital data representative of a document to be duplicated and obtained by scanning said document, said apparatus comprising:

• buffer means for assembling said digital data into scanned strips of said document with each scanned strip comprising a plurality of scanned lines of said document;
• pattern recognition means connected to said buffer means for identifying data words representative of columns of said scanned strips;
• counter means responsive to said pattern recognition means for determining the run length of consecutive data words in each scanned strip which are identical to one another;
• encoder means responsive to the identified data words and run lengths for forming fixed-length coded words representative thereof;
• and
• output buffer means for concatenating all fixed-length coded words to form a coded representation of said document.

A method of encoding digital data representative of a document to be duplicated and obtained by scanning said document comprising the steps of:

• assembling said digital data into scanned strips of said document with each scanned strip comprising a plurality of scan lines of said document;
• reading the scan lines in parallel to form data words defining columns of said scanned strips;
• counting the number of consecutive data words in each scanned strip which are identical to one another to determine the run lengths of said identical data words;
• encoding runs of data words read and the corresponding run lengths into fixed length coded words, said run lengths being equal to or less than one of a number of maximum run lengths associated with said fixed length coded words;
• and
• concatenating all fixed length coded words to represent said document.