Page printer having adaptive data compression for memory minimization

A method for data compressing a raster pixel image, comprising the steps of:

• a. performing run-length encoding for data segments in an initial raster row of said image and outputting, for each run of a data segment in said row, a run length command indicating a run count and an identification of the run data segment;
• and
• b. for data segments in a subsequent row of said image, comparing whether said data segments are the same as or different from data segments in an immediately previous raster row;
• and
• c. issuing commands which identify for said subsequent raster row, which of said data segments exhibit said "same" condition and further indicate said different said data segments.

A method for data compressing a raster-arranged pixel image, comprising the steps of:

• a. providing a first table of data segment patterns indicative of an image comprised of clustered bit patterns and of an image comprised of dispersed bit patterns;
• b. comparing data segments of an image to said data segment patterns in said first table to determine a classification of said image, said classification comprising clustered or dispersed;
• c. compressing said image by reducing each n.times.n bit block of said pixel image to an n-bit data segment and accompanying said compressed image by a classification indicator;
• and
• d. decompressing said image by employing said n-bit data segment to access a stored n.times.n pixel matrix from a pair of matrix tables in accordance with said classification indicator, one said tables including n.times.n-bit images classified as clustered and another said table including n.times.n-bit images classified as dispersed, each said table addresses in accordance with said n-bit data segment.

In a peripheral unit for converting an input data flow to a page--arranged output, said peripheral unit having insufficient random access memory allocated to store an entire video raster image of said page arranged output, a method for converting said input data flow to a page intermediate form that includes a plurality of image strips that make up said page arranged output, each image strip including image processing commands that enable subsequent conversion of each said image strip to a raster video form, said method comprising:

• a. establishing a threshold value of data segments in an image strip;
• b. determining (1) if a number of data segments in an image strip exceeds said threshold value, and (2) if remaining memory in said random access memory is less than a predetermined level and if said determinations 1 and 2 are affirmative;
• c. converting said image strip immediately to raster video and attempting a compression thereof;
• d. storing in said random access memory, compressed raster video that results from step c;
• e. adjusting said threshold value to a smaller value to account for remaining random access memory in said random access memory;
• and
• f. repeating steps a-e for remaining image strip of said page.