Block artifact phenomenon eliminating device and eliminating method thereof

• US 20060181740A1
• Filed: 11/09/2005
• Published: 08/17/2006
• Est. Priority Date: 12/08/2004
• Status: Active Grant

• Current Assignee: Electronics and Telecommunications Research Institute
• Original Assignee: Electronics and Telecommunications Research Institute
• Inventors: Kim, Byung-Gyu, Kim, Seon-Tae, Song, Suk-Kyu, Mah, Pyeong-Soo
• Granted Patent: US 7,961,357 B2
• Time in Patent Office: Days
• US Class Current: 358/3.260
• CPC Class Codes: H04N 19/117 Filters, e.g. for pre-processing or post-processing sub-band filter banks H04N19/635
• CPC Class Codes: H04N 19/14 Coding unit complexity, e.g. amount of activity or edge presence estimation H04N19/146 takes precedence
• CPC Class Codes: H04N 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/86 involving reduction of coding artifacts, e.g. of blockiness

Abstract

A device for eliminating a block artifact phenomenon of a decoded image frame, and an eliminating method thereof. A method for eliminating a block artifact phenomenon according to the present invention includes: extracting pixel information including a magnitude of edge response, an edge direction, and an edge position, by applying an edge detector to an arbitrary pixel in an image frame; distinguishing the pixel into a non-edge pixel, an object edge pixel, or a block edge pixel by using the extracted pixel information; and performing filtering according to the distinguishing result. In this manner, an object edge information is selectively protected, so that an improved image quality may be provided.

Claims

1. A method for eliminating a block artifact phenomenon of a block based decoded image frame, the method comprising:

extracting pixel information comprising a magnitude of edge response, an edge direction, and an edge position by applying an edge detector to an arbitrary pixel in the image frame;

distinguishing the pixel between a non-edge pixel, an object edge pixel, or a block edge pixel by using the extracted pixel information; and

performing filtering according to the distinguishing result.

2. The method for eliminating a block artifact phenomenon of claim 1, wherein the magnitude of edge response is an absolute value of a response obtained when applying the edge detector to the pixel.

3. The method for eliminating a block artifact phenomenon of claim 2, wherein the magnitude of edge response is given by the following equation

M(i, j)=|f(i, j)×

K(m, n)|,

wherein;

(i, j) is a position of the arbitrary pixel;

M(i, j) is the magnitude of edge response of the pixel;

f(i, j) is a pixel value of the pixel; and

K(m, n) is a two-dimensional edge detect operator.

4. The method for eliminating a block artifact phenomenon of claim 1, wherein the edge direction information is an arctangent of a ratio between a horizontal component and a vertical component of an edge detector response.

5. The method for eliminating a block artifact phenomenon of claim 1, wherein the edge position is a relative location in a block in which the pixel is comprised, expressed in coordinates.

6. The method for eliminating a block artifact phenomenon of claim 1, wherein the edge detector may be a Sobel edge detector or a Canny edge detector.

7. The method for eliminating a block artifact phenomenon of claim 1, wherein distinguishing the pixel further comprises comparing the magnitude of edge response of the pixel with a predetermined threshold value, and when the predetermined threshold value is greater, distinguishing the pixel as a non-edge pixel.

8. The method for eliminating a block artifact phenomenon of claim 7, wherein distinguishing the pixel further comprises:

when the magnitude of edge response is larger, determining whether the edge direction of the pixel is 0°

or 90°

, and when the edge direction is determined not to be 0°

or 90°

, distinguishing the pixel as an object edge pixel; and

when the edge direction is determined to be 0°

or 90°

, determining whether the pixel is located around a block boundary region by using the edge position information, and when the pixel is determined to be located around the block boundary region, distinguishing the pixel as a block edge pixel.

9. The method for eliminating a block artifact phenomenon of claim 8, the method further comprising, when the edge direction is determined to be 0°

or 90°

, but the edge position is determined not to be located around the block boundary region, determining the pixel to be an object edge pixel.

10. The method for eliminating a block artifact phenomenon of claim 9, wherein, in performing the filtering, a pixel distinguished as a non-edge pixel or a block edge pixel from the pixels in the decoded image frame is processed by low pass filtering.

11. The method for eliminating a block artifact phenomenon of claim 9, wherein, in performing the filtering, a pixel distinguished as an object edge pixel from the pixels in the decoded image frame is processed by all-pass filtering or sharpening filtering.

12. The method for eliminating a block artifact phenomenon of claim 9, the method further comprising adding a distinguishing code to a pixel distinguished as an object edge pixel from the pixels in the decoded image frame.

13. A device for eliminating a block artifact phenomenon of an image frame, comprising:

a pixel information extractor for extracting pixel information comprising a magnitude of edge response, an edge direction, and an edge position by applying an edge detector to an arbitrary pixel in an image frame decoded based on a block;

an edge distinguisher for distinguishing the pixel into a non-edge pixel, an object edge pixel, or a block edge pixel by using the extracted pixel information; and

a filter part for performing filtering according to the distinguishing result.

14. The device for eliminating a block artifact phenomenon of an image frame of claim 13, wherein the filter part comprises:

a low pass filter for eliminating a high frequency component having a non-edge pixel and a block edge pixel; and

an adaptive filter for performing filtering while preserving edge information of the object edge pixel.

15. The device for eliminating a block artifact phenomenon of an image frame of claim 14, wherein the adaptive filter is one of a full band pass filter and a sharpening filter.