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Gray Scale Image Compression Algorithm

IP.com Disclosure Number: IPCOM000047226D
Original Publication Date: 1983-Oct-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Greenhalgh, RC: AUTHOR

Abstract

This article describes a run-length encoding algorithm including vertical reference coding. Unique code patterns are transmitted where a current string of black or white pel values correlate with a string in the preceding or history line. Correlation is defined as a condition where successive lines have strings of the same value (black or white) which begin at the same pel and end within one pel of each other. Table 1 below defines eight (type A - type H) signal types. A type A signal specifies a gray scale value for a single pel. Signal types B, C, and D are used where a correlation is found between the current line and the history line. Signal types E, F, G and H define both short and long runs of white and black pels in those instances where no correlation exists.

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Gray Scale Image Compression Algorithm

This article describes a run-length encoding algorithm including vertical reference coding. Unique code patterns are transmitted where a current string of black or white pel values correlate with a string in the preceding or history line.

Correlation is defined as a condition where successive lines have strings of the same value (black or white) which begin at the same pel and end within one pel of each other. Table 1 below defines eight (type A - type H) signal types. A type A signal specifies a gray scale value for a single pel. Signal types B, C, and D are used where a correlation is found between the current line and the history line. Signal types E, F, G and H define both short and long runs of white and black pels in those instances where no correlation exists. CODES TYPE REPRESENTATION

A Single Pel

B Correlation - ends even with history line

C Correlation - ends 1 pel short of history line

D Correlation - ends 1 pel past history line

E Short white run of NNNN count

F Long white run of NNNN NNNN count

G Short black run of NNNN count

H Long black run of NNNN NNNN count

TABLE 1 Table 2 below defines preferred bit patterns for the signal types A - H. Each signal type may consist of 1 to 4 four-bit words. For signal types E, F, G and H, an NNNN word may have any non-zero value. For signal type A, the NNNN word may have any value. CODES TYPE PATTERN

A NNNN

B 0000 1000

C 0000 0100

D 0000 1100

E 0000 0000 NNNN

F 0000 0010 NNN...