Television – Image signal processing circuitry specific to television – Noise or undesired signal reduction
Reexamination Certificate
1998-04-03
2001-05-01
Hsia, Sherrie (Department: 2614)
Television
Image signal processing circuitry specific to television
Noise or undesired signal reduction
C348S625000, C382S268000, C382S199000, C382S205000
Reexamination Certificate
active
06226050
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to data filtering, and more particularly, to a signal adaptive filtering method for reducing ringing noise, and a signal adaptive filter suitable for implementing the method. This application for a signal adaptive filtering method and signal adaptive filter for reducing ringing noise is based upon Korean Patent Application No. 97-12498 which is incorporated herein by reference for all purposes.
2. Description of the Related Arts
Generally, picture encoding standards such as MPEG of the International Organization for Standardization (ISO) and H.263 recommended by the International Telecommunication Union (ITU) adopt block-based motion estimation and discrete cosine transform (DCT) of blocks. When an image is highly compressed, the block-based coding may cause a blocking effect and ringing noise. A typical blocking effect is grid noise in a homogeneous area in which adjacent pixels have relatively similar pixel values. Another blocking effect is staircase noise which has the shape of a staircase and is generated along the edge of the image. Also, the ringing noise is due to the typical Gibb's phenomenon which results from the truncation of a DCT coefficient by quantization when the image is highly compressed. The ringing noise causes a problem in that an object in the image is displayed as multiple overlapping objects.
SUMMARY OF THE INVENTION
To solve the problems above, it is an object of the present invention to provide a signal adaptive filtering method for reducing the ringing noise in a high compression encoding system, caused when block-based decoding an image data, and a signal adaptive filter for implementing the method.
According to an aspect of the present invention, there is provided a signal adaptive filtering method for reducing ringing noise of an image data, comprising the steps of:
(a) calculating a gradient of the image data to be filtered at each pixel using a one-dimensional horizontal gradient operator of 1×2 size and a one-dimensional vertical gradient operator of 2×1 size, both having a weighted value (1,−1), and comparing the absolute value of the calculated gradient with a predetermined threshold value to generate a binary value;
(b) repeating the step (a) on a pixel block having a predetermined size by a pixel unit to generate a binary edge map with respect to the whole block;
(c) applying a filter window of a predetermined size to the generated binary edge map to determine whether edges are present in the filter window;
(d) filtering the pixel values of the corresponding filter window pixel by pixel by using predetermined first weighted values to generate a new pixel value if it is determined in said step (c) that edges are not present; and
(e) filtering the pixel values of the corresponding filter window pixel by pixel by using predetermined second weighted values to generate a new pixel value if it is determined in said step (c) that edges are present, wherein the filtering is not performed if the pixel located at the center of the filter window represents an edge.
Preferably, the step (a) comprises the sub-steps of:
(a1) initializing upper and left pixels of the filtering target pixel block to information (
0
) meaning a non-edge;
(a2) comparing the absolute value of the gradient with respect to each pixel of the image with the predetermined threshold value; and
(a3) determining the corresponding pixel and adjacent pixel (right pixel when using the horizontal gradient operator, and lower pixel when using the vertical gradient operator) as edge if the absolute value is greater than the threshold value, and as non-edge if the absolute value is less than or equal to the threshold value, to generate the binary value.
According to another aspect of the present invention, a signal adaptive filter is provided which has an image storing unit for temporarily storing decompressed image data and a gradient operation unit for receiving the image data from the image storing unit and calculating a gradient of the image data in the horizontal and vertical directions by a one-dimensional horizontal gradient operator of 1×2 size and a one-dimensional vertical gradient operator of 2×1 size, both having a weighted value (1,−1). The filter also has a binary edge map generator for comparing the absolute value of each result in pixel units, which is gradient-operated in horizontal and vertical directions by the gradient operation unit, with a predetermined threshold value to generate a binary edge map. The filter also has a filter selector for storing the binary edge map provided from the binary edge map generator, and for classifying the input image data into one of an edge area including at least one edge information and a homogeneous area without having edge information, based on the binary edge map. The filter also has an average filter for average-filtering pixel of the filter window, determined as the homogeneous area by the filter selector, to generate a new pixel value, and a weighted filter for weight-filtering pixels of the filter window using a predetermined weighted value, determined as the edge area by the filter selector, to generate a new pixel value.
REFERENCES:
patent: 5883983 (1999-03-01), Lee
patent: 5974197 (1999-10-01), Lee
patent: 3-263977 (1991-11-01), None
patent: 4-20182 (1992-01-01), None
patent: 4-42682 (1992-02-01), None
patent: 4-159869 (1992-06-01), None
patent: 6-105188 (1994-04-01), None
patent: 6-260889 (1994-09-01), None
patent: 6-315104 (1994-11-01), None
Hsia Sherrie
Samsung Electronics Co,. Ltd.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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