Image analysis – Image compression or coding – Transform coding
Reexamination Certificate
1998-07-31
2001-05-22
Couso, Yon J. (Department: 2723)
Image analysis
Image compression or coding
Transform coding
C382S281000
Reexamination Certificate
active
06236761
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to performing Haar transforms of image data.
2. Description of Related Art
Image processing is used in many different types of devices such as computers, digital cameras and digital television for displaying and storing image data. After images are captured and converted into image data, the image data are usually stored, transmitted or displayed. Because uncompressed image data consumes large amounts of storage and requires large bandwidths for transmission, various compression techniques have been applied to reduce the volume of data and, thus, reduce memory and bandwidth requirements as well as the amount of time to handle the image data.
Conventional image compression methods uses Joint Photographic Experts Group (JPEG) algorithms. Thus, image compression devices using JPEG algorithms are readily available. However, image processing devices are achieving ever higher resolutions and image delivery rates resulting in a demand for image compression performance that exceeds image compression capability achieved by conventional devices. Accordingly, new image compression technology is required to provide greater image compression performance.
SUMMARY OF THE INVENTION
This invention provides a method and apparatus for performing Haar transforms that processes one image pixel for each clock cycle. The Haar transform is performed by cascading successive Haar transforms cells where each Haar transform cell processes a 2×2 block of input values and outputs a 2×2 block of Haar transform coefficients.
The four input values are processed by a first stage of two adders and two subtractors and a second stage of two adders and two subtractors. A first adder of the first stage generates a sum of a first row of two input values of a first row of the 2×2 block and a second adder generates a sum of two input values of a second row of the 2×2 block. A first subtractor of the first stage generates a difference between the two input values of the first row of the 2×2 block and a second subtractor generates a difference between the two input values of the second row of the 2×2 block.
A first adder of the second stage sums the output of the first and second adders of the first stage to generate a low frequency coefficient of the Haar transform. A second adder of the second stage generates a sum of the outputs of the subtractors of the first stage to produce a third coefficient of the Haar transform. A first subtractor of the second stage generates a difference of the results of the adders of the first stage to generate a second coefficient of the Haar transform. A second subcontractor of the second stage generates a difference of the outputs of the first and second subtractors of the first stage to generate a fourth coefficient of the Haar transform.
The output coefficient of the Haar transform may be quantized, run length encoded and then compressed to achieve a high compression ratio of greater than 20 to 1 for near lossless image compression. The above Haar transform cell may be incorporated into any type of image capture, processing and reproduction devices such as cameras, scanners and printers to achieve high speed image data compression to reduce storage and bandwidth requirements.
REFERENCES:
patent: 3981443 (1976-09-01), Lynch et al.
“Embedded Image Coding Using Zerotrees of Wavelet Coefficients”, Jerome M. Shapiro,IEEE Transactions On Signal Processing, vol. 41, No. 12, pp. 3445-3462, Dec. 1993.
“Image Coding Using Wavelet Transform”, Marc Antonini, et al,IEEE Transactions On Signal Processing, vol. 1, No. 2, pp. 205-220, Apr. 1992.
“Wavelet Transforms in a JPEG-Like Image Coder”, R. de Queiroz, et al.SPIE, pp. 1662-1673, vol. 2308.
“Predictor Optimization”,Digital Image Compression Techniques, M. Rabbani, P.W. Jones, Chapter 9, pp. 81-83, SPIE Press 1991.
Couso Yon J.
Oliff & Berridg,e PLC
Xerox Corporation
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