Method and device for compressing color images

• Main Authors: SUZUKI NAOKO, KATSUMATA YUKATA, KANAMOTO KOUICHI, EGUCHI SHINICHI
• Format: Patent
• Language: English
• Published: 18.05.2005
• Edition: 7
• Subjects: CALCULATING; COMPUTING; COUNTING; ELECTRIC COMMUNICATION TECHNIQUE; ELECTRICITY; HANDLING RECORD CARRIERS; IMAGE DATA PROCESSING OR GENERATION, IN GENERAL; PHYSICS; PICTORIAL COMMUNICATION, e.g. TELEVISION; PRESENTATION OF DATA; RECOGNITION OF DATA; RECORD CARRIERS

It is an object of the present invention to improve the compression ratio of a color image and to clearly display the outlines of characters and the like. A hue cluster classifying/unifying unit reduces the number of hue values of each pixel in a color image, based on a hue histogram, allocates the number-reduced hue value to each pixel and classifies pixels with the same hue value into one cluster. Furthermore, the unit unifies clusters whose hue values are below a predetermined value. The unit also traces the outline of a cluster whose size is below a reference value and determines that a cluster that has a lot of change points belongs to a character area. An encoding unit determines the characteristic of each cluster, based on both an area determined by an area determining unit and whether the cluster belongs to a ruled line area or a character area, and encodes pixels in each cluster by a coding method suitable for the characteristic of the cluster.