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Methods for compressing and re-constructing a color image in a computer system

  • US 6,151,409 A
  • Filed: 03/13/1998
  • Issued: 11/21/2000
  • Est. Priority Date: 03/13/1998
  • Status: Expired due to Term
First Claim
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1. A method for compressing a color image comprising the following steps performed in a computer system:

  • a) decomposing said image into non-overlapping contiguous rectangular blocks wherein each of said block comprises an array of 4×

    4 pixels;

    b) generating a luminance value for each of said pixels within each of said blocks;

    c) quantizing luminance values of said pixels within one block for each of said blocks in a sequence according to a position thereof into a lower mean value Y0 and an upper mean value Y1 by i) calculating an average luminance value, Yavg, of said pixels within said block;

    ii) calculating an average luminance value of pixels within said block having luminance values lower than or equal to Yavg as said Y0 ; and

    iii) calculating an average luminance value of pixels within said block having luminance values greater than Yavg as said Y1 ;

    d) setting a block as an uniform block when (Y1 -Y0)/Y0 is less than a threshold value within a range of 0.02-0.03, and as an edge block when (Y1 -Y0)/Y0 is not less than said threshold value;

    e) for each uniform block outputting Yavg as the luminance values of said pixels thereof and an index representing an uniform block; and

    f) for each edge block I) creating a bitmap plane by comparing the luminance value of each pixel thereof with Yavg, and assigning its corresponding bit in the bitmap plane a "0" value if the luminance value is less than or equal to Yavg, otherwise assigning the corresponding bit in the bitmap plane a "1" value;

    II) deciding the block pattern of said edge block by computing a luminance gradient direction of the bitmap plane of said edge block and matching said luminance gradient direction with a bitmap plane table which is created by angle quantization using the bit values "0" and "1" of 4×

    4 bitmap plane; and

    III) outputting Y0 and Y1, and an index representing the decided block pattern of said edge block.

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