Image analysis – Color image processing – Compression of color images
Reexamination Certificate
1998-11-03
2001-07-24
Au, Amelia M. (Department: 2623)
Image analysis
Color image processing
Compression of color images
C382S251000, C375S240030
Reexamination Certificate
active
06266440
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a technology of compressing and coding color image data for its storage or transmission.
BACKGROUND OF THE INVENTION
When color image data is to be transmitted or accumulated, the color image data is subjected to the processing for compression and coding in order to suppress an amount of information to be processed.
A conventional type of image data compression method is generally a method, as typified by JPEG (Joint Photographic Expert Group) method, of dividing image data into blocks each having a plurality of pixels, subjecting each of the blocks to specified conversion and then compressing the data by quantization. A technology related to the color image data converting apparatus is disclosed in Japanese Patent Laid-Open Publication No. SHO 63-185163.
In the color image data converting apparatus disclosed in this Publication, as shown in
FIG. 7
, at first, image data for inputted three colors of RGB is converted into data for lightness (Y) and chromaticity (u, v) in a color space converting section
510
. Then, each of the data (Y, u, v) is inputted into corresponding space converting sections
521
,
522
and
523
, where it is subjected to space conversion for each block having a plurality of pixels. Then, the data is quantized in corresponding quantizing sections
531
,
532
and
533
and coded in a coding section
540
. By converting an input color image data into information for lightness and color, and then subjecting the data to space conversion, quantization and coding, compression efficiency of color image data can be enhanced.
In the conventional type of technology as disclosure in the above Publication, however, the data for lightness (Y) and chromaticity (u, v) converted in the color space converting section
510
is uniformly quantized in each of the quantizing sections
531
,
532
and
533
regardless of characteristics of input color image data such as a difference in its lightness or the like. Therefore, the compression may be insufficient or it may be too heavy depending on color, and hence image quality may be degraded.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide, for solving the problems described above, a color image data compressing apparatus which can efficiently compress color image data with suppression of image degradation due to data compression by changing quantization efficiency of the data according to a type of input color image data.
In the present invention, when the data for the input color image data is quantized, the degree of quantization is changed according the input color image data, so that degradation of image quality due to data compression can be suppressed.
REFERENCES:
patent: 4887151 (1989-12-01), Wataya
patent: 5341441 (1994-08-01), Maeda et al.
patent: 5369439 (1994-11-01), Matsuda et al.
patent: 5930386 (1999-07-01), Saito
patent: 6058217 (2000-05-01), Kondo
patent: 6075619 (2000-06-01), Iizuka
patent: 63-185163 (1988-07-01), None
Au Amelia M.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
Wu J.
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