Image analysis – Image enhancement or restoration – Edge or contour enhancement
Reexamination Certificate
1996-07-02
2002-05-14
Lee, Thomas D. (Department: 2624)
Image analysis
Image enhancement or restoration
Edge or contour enhancement
C382S275000, C382S168000
Reexamination Certificate
active
06389177
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to image postprocessing techniques and more particularly to a system and method using edge processing to remove blocking artifacts from decompressed images.
2. Description of the Background Art
Producing high-quality visual images using modern computer techniques is an important consideration of many computer manufacturers and designers. When displayed on a video monitor, an image frame typically comprises many separate picture elements or pixels which are each represented using a corresponding binary value. The computer system thus requires large amounts of digital information to represent each displayed image frame. To conserve memory space and expedite transmission of the digital information, modern computer systems typically code the image frames using a variety of compression techniques. One popular compression coding technique uses an encoder device to divide an image into a number of discrete blocks which are each processed and compressed independently. A corresponding decoder device subsequently decompresses the compressed image prior to display on a video monitor. Examples of conventional formats which utilize block-based image coding and decoding include JPEG, MPEG, H.261 and H263.
Referring now to
FIG. 1
, a block diagram of a sample blocked image
110
processed by a conventional block-based image decoder is shown. Sample blocked image
110
includes adjacent blocks
112
and
116
which are separated by boundary
114
. Sample blocked image
110
contains sixteen blocks for reasons of clarity, however, in practice, a blocked image may typically contain a greater number of discrete blocks.
Blocking artifacts are relatively common to block-based encoder/decoder systems. Each discrete image block is processed and compressed separately, resulting in frequent variations in average pixel intensity between the various blocks. This causes the human eye to perceive the resultant image frame as a collection of individual blocks, as illustrated in FIG.
1
.
For example, block
112
lies adjacent to block
116
along boundary
114
. If block
112
and block
116
have different pixel intensities, the human eye will perceive an “edge” along boundary
114
. This edge is created by the discontinuity in pixel intensity across boundary
114
between block
112
and block
116
. Furthermore, this edge will have an edge intensity proportional to the magnitude of the average difference between the pixel intensity of block
112
and the pixel intensity of block
116
.
One conventional postprocessing technique for reducing the block edges is low-pass filtering. The low-pass filter, however, smoothes both the block edges and the perceptually important features of the image, resulting in a blurred image. Adaptive filtering and image restoration techniques may also be used to reduce block edges, however, these techniques may also create new artifacts in the image. Therefore, in accordance with the present invention, an improved system and method is needed for using edge processing to remove blocking artifacts in image decoder devices.
SUMMARY OF THE INVENTION
In accordance with the present invention, a system and method are disclosed for using edge processing to remove blocking artifacts from decompressed images. The present invention comprises an edge processor device which preferably includes an image converter, a statistics analyzer, a reference calculator and an artifact remover.
Initially, the edge processor receives an image containing blocking artifacts such as block edges along boundaries. The image converter then accesses the received image and builds a corresponding edge representation which includes information about edge intensity and edge location. Next, the statistics analyzer constructs a histogram which shows edge intensities along block boundaries within the edge representation.
The reference calculator then derives reference values from the compiled histogram The reference values correspond to edge intensities which have a high number of occurrences along the block boundaries. The present invention thus identifies the blocking artifacts by determining their corresponding reference values, since the blocking artifacts typically occur at a greater frequency than other edges which fall along block boundaries in the received image.
The artifact remover then removes the blocking artifacts by setting their edge intensities to zero. Finally, the image converter reconstructs the originally-received image after the blocking artifacts have been deleted. The present invention thus effectively removes the blocking artifacts to provide an improved image through the use of the foregoing edge-processing technique.
REFERENCES:
patent: 4939645 (1990-07-01), Hopkinson
patent: 5065444 (1991-11-01), Garber
patent: 5819035 (1998-10-01), Devaney et al.
patent: 5850294 (1998-12-01), Apostolopoulos et al.
Stephane Mallat and Sifen Zhong, Characterization of Signals from Multiscale Edges, IEEE Transactions on Pattern Analysis and Machine Intelligence, vol. 14, No. 7. pp. 710-732, Jul. 1992.
Dennis M. Healy, Jr., Jian Lu, and John B. Weaver, Two Applications of Wavelets and Related Techniques in Medical Imaging, Annals of Biomedical Engineering, vol. 23, pp. 637-665, 1995.
Chu Ke-Chiang
Lu Jian
Tian Yu Tina
Wu Hsi-Jung
Apple Computer Inc.
Blakely & Sokoloff, Taylor & Zafman
Lee Thomas D.
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