Methods for compressing and re-constructing a color image in a computer system
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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Abstract
We discloses an efficient method for compressing a color image, visual block pattern truncation coding (VBPTC), in which the conventional block truncation coding (BTC) serves to encode an original image. This method defines the edge block according to human visual perception. If the difference between the two quantized values of BTC in a block is larger than a threshold which is defined by visual characteristics, the block will be identified as an edge block. In an edge block, the bitmap is adapted to compute block gradient orientation and to match the block pattern.
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Citations
8 Claims
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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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
- a) decomposing said image into non-overlapping contiguous rectangular blocks wherein each of said block comprises an array of 4×
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Current AssigneeNational Science Council
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Original AssigneeNational Science Council
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InventorsLee, Yung-Pin, Chen, Hsu-Tung, Wu, Po-Cheng, Chen, Liang-Gee, Liu, Yuan-Chen
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Primary Examiner(s)Mancuso, Joseph
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Assistant Examiner(s)COOPERRIDER, FRED E
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Application NumberUS09/042,061Time in Patent Office984 DaysField of Search382/166, 382/162, 382/180, 382/272US Class Current382/166CPC Class CodesG06T 9/005 Statistical coding, e.g. Hu...
