Nova Patents
EP0349847B1

Method of and apparatus for compressing image data

Abstract

This record has no abstract on file.

EP0349847B1, drawing sheet 1
Sheet 1 of 41

Term

Term ended

Expired 22 June 2009, 17.3 years ago.

  1. Priority
  2. Filed
  3. Granted
  4. Expired
  5. Today

4 claims: 2 independent, 2 dependent

  1. 1
    A method of compressing image data depicting an image which is divided into blocks (B vh ), each block including a plurality of pixels, said method comprising the steps of:(a) executing an orthogonal transformation operation on said blocks of image data, to thereby obtain a coefficient table (FT) including coefficients of a series of orthogonal functions indicative of said image data for each block, and (b) coding said coefficients of said coefficient table to obtain compressed image data;characterized in that:    the coding step comprises the steps of: (b-1) preparing a plurality of code table groups, each group consisting of a plurality of code tables (CT), each code table being defined for determining which of said coefficients of said coefficient table are to be selected for further coding, wherein the number of said coefficients selected by said code tables is the same in each code table group but is different among said plurality of code table groups;(b-2) obtaining a statistical value (σ) representative of a distribution of said image data in each block;(b-3) comparing said statistical value with thresholds (σ 1 , σ 2 , σ 3 ) which are determined for said code table groups, to select one of said code table groups having the numbers of effective codes corresponding to said statistical value;(b-4) calculating a sum of respective absolute values of said coefficients selected by each code table included in said one of said code table groups, to thereby obtain a plurality of sums for respective code tables included in said one of said code table groups;(b-5) comparing said plurality of sums with each other to determine one of said plurality of code tables which provides the maximum of said plurality of sums, to thereby select a most relevant code table most relevant for coding said coefficients of said coefficient table among said one of code table groups;and (b-6) applying said most relevant code table to said coefficient table for coding said coefficients of said coefficient table to thereby obtain compressed image data (D f ).
  2. 2
    A method in accordance with claim 1, wherein    said coefficients of said coefficient table (FT) are expressed by means of digital data, and respective code elements in said code table (CT) further designate respective numbers of effective digits for respective valid coefficients.
  3. 3
    A method in accordance with claim 1, wherein the step (b-6) comprises the step of:adding a group number of said one code table group to said compressed image data.
  4. 4
    An apparatus (AP) for compressing image data depicting an image which is divided into blocks (B vh ), each block including a plurality of pixels, said apparatus comprising:(a) means (8) for executing an orthogonal transformation operation on said blocks (B vh ) of image data, to thereby obtain a coefficient table (FT) including coefficients of a series of orthogonal functions indicative of said image data for each block, and (b) means for coding said coefficients of said coefficient table to obtain compressed image data;characterized in that:    the coding means comprises: (b-1) means for preparing a plurality of code table groups, each group consisting of a plurality of code tables (CT), each code table being defined for determining which of said coefficients of said coefficient table are to be selected for further coding, wherein the number of said coefficients selected by said code tables is the same in each code table group but is different among said plurality of code table groups;(b-2) means (14) for obtaining a statistical value (σ) representative of a distribution of said image data in each block;(b-3) means (15) for comparing said statistical value with thresholds (σ 1 , σ 2 , σ 3 ) which are determined for said code table groups, to select one of said code table groups having the numbers of effective codes corresponding to said statistical value;(b-4) means (10) for calculating a sum of respective absolute values of said coefficients selected by each code table included in said one of said code table groups, to thereby obtain a plurality of sums for respective code tables included in said one of said code table groups;(b-5) means (10) for comparing said plurality of sums with each other to determine one of said plurality of code tables which provides the maximum of said plurality of sums, to thereby select a most relevant code table most relevant for coding said coefficients of said coefficient table among said one of code table group;and (b-6) means (10) for applying said most relevant code table to said coefficient table for coding said coefficients of said coefficient table to thereby obtain compressed image data (D f ).
Independent claims4