Image analysis – Image transformation or preprocessing – Walsh – hough – or hadamard transform
Reexamination Certificate
1998-07-13
2001-04-24
Boudreau, Leo (Department: 2621)
Image analysis
Image transformation or preprocessing
Walsh, hough, or hadamard transform
C382S248000, C382S251000
Reexamination Certificate
active
06222946
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to an image compression device by which color still image data is compressed in accordance with an Hadamard's transformation, and also to an image expansion device by which the compressed image data is expanded in accordance with an inverse Hadamard's transformation.
2. Description of the Related Art
A standard algorithm, for the encoding of high resolution images and the transfer of that information through telecommunication transmission channels, has been recommended by the JPEG (Joint Photographic Expert Group). In the JPEG system, a large-scale data compression is performed as follows: the original image data represented by pixel values are divided into a plurality of 8×8 blocks, each of which is subjected to a two dimensional discrete cosine transformation (DCT), so that the original image data are broken down into components on a spatial frequency axis. The components expressed on the spatial frequency axis are quantized by using a quantization table, and are then encoded to become compressed image data.
Although the image data are compressed with a high efficiency by the JPEG system, the image compression is performed using a non-reversible method in which an error exists between the original image data and reproduced image data, which are obtained by expanding the compressed image data. Conversely, for a reversible method in which no error exists between the original image data and the reproduced image data, an image compression using an Hadamard's transformation can be utilized. In the Hadamard's transformation system, the image data is converted or inversely-converted using a symmetric matrix, which is constructed only of components 1 and −1, and the Hadamard's transformation can be performed only by addition and subtraction calculations.
In the Hadamard's transformation, however, in comparison with the JPEG system, the compression ratio is low, and thus the amount of compressed image data is large, which presents a disadvantage when recording and transmitting the compressed image data.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an image compression device and an image expansion device in which original image data are compressed with a reversible method, such that the size of the compressed image data is small, and are expanded.
According to the present invention, there is provided an image compression device comprising an Hadamard's transformation processor and a quantization processor.
The Hadamard's transformation processor applies an Hadamard's transformation to image data inputted to the image compression device to obtain Hadamard's transformation coefficients corresponding to the image data. The quantization processor quantizes the Hadamard's coefficients by a quantization table composed of quantization coefficients, each of which is to the power of 2, to obtain quantized Hadamard's transformation coefficients.
Further, according to the present invention, there is provided an image expansion device comprising an inverse quantization processor, a corrected coefficient generating processor and an image data reproducing processor.
The inverse quantization processor dequantizes quantized Hadamard's transformation coefficients by using a quantization table composed of quantization coefficients, each of which is to the power of 2, to obtain dequantized Hadamard's transformation coefficients. The corrected coefficient generating processor obtains corrected dequantized Hadamard's transformation coefficients, each of which has the same value as each of Hadamard's transformation coefficients, based on the dequantized Hadamard's transformation coefficients. The image data reproducing processor applies inverse Hadamard's transformation to the corrected dequantized Hadamard's transformation coefficients to reproduce image data.
REFERENCES:
patent: 5374958 (1994-12-01), Yanagihara
patent: 5854756 (1998-12-01), Willink
R.C.Gonzalez, R.E.Woods, “Digital immage processing”, Addison-Wesley Publication Company, pp. 374-376,384-387, 1992.*
An article by Ryozo Nishina et al., entitled “Two Types of Distortionless Image Compression Coding Systems Developed”.
The Journal of TIEICE, vol. 79, No. 11, p. 1185, Nov. 1996, along with an English Language Translation.
Asahi Kogaku Kogyo Kabushiki Kaisha
Boudreau Leo
Greenblum & Bernstein P.L.C.
Novik Dmitry A.
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