Loop-filtering method for image data and apparatus therefor

Abstract

A loop-filtering method for reducing quantization effect generated when an image data is encoded and decoded, and an apparatus therefor. The loop-filtering method includes the steps of extracting a flag indicating whether the image data requires loop-filtering using the distribution of inverse quantized coefficients (IQCs) of an inverse quantized image data and a motion vector indicating the difference between the previous frame and the current frame. The image data corresponding to the flag is then filtered by a predetermined method if the extracted flag indicates a need for the loop-filtering. Using the flags and an adaptive filter reduces the quantization effect and is useful to reduce the amount of computation required for the filtering. Also, the filtering can be performed through parallel processing without multiplication and division, so that the complexity of hardware can be reduced.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This is a divisional of application Ser. No. 10 / 405,642 filed Apr. 3, 2003, which is a Continuation Application of U.S. application Ser. No. 09 / 302,989 filed Apr. 30, 1999. The entire disclosures of the prior applications, U.S. patent application Ser. Nos. 10 / 405,642 and 09 / 302,989 are hereby incorporated by reference.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The present invention relates to image data processing, and more particularly, to a method for loop-filtering image data to reduce a quantization effect and an apparatus therefor.[0004]2. Description of the Related Art[0005]Generally, picture encoding standards such as MPEG of the International Standardization Organization (ISO) and H.263 recommended by the International Telecommunication Union (ITU) adopt block-based motion estimation and discrete cosine transform (DCT) blocks. Most picture encoding standards utilize the DCT in 8.times.8 pixel block units in ord...

AI Technical Summary

Benefits of technology

[0010]To solve the above problems, it is an object of the present invention is to provide a method for loop-filtering image data and an apparatus therefor, capable of encoding at a low bit rate without need for complicated computations, by which quantization effects such as blocking artifacts, corner outliers and ringing noise caused by block-based decoding can be reduced.

[0011]According to one aspect of the object, there is provided a loop-filtering method for reducing quantization effect generated when an image data is encoded and decoded, the method comprising the steps of: extracting a flag indicating whether the image data requires loop-filtering using the distribution of inverse quantized coefficients (IQCs) of an inverse quantized image data and a motion vector indicating the difference between the previous frame and the current frame; and filtering the image data corresponding to the flag by a predetermined method if the extracted flag indicates a need for the loop-filtering.

[0032]According to another aspect of the object, there is provided an apparatus for loop-filtering image data, capable of reducing quantization effect generated when an image data is encoded and decoded, the apparatus comprising: a flag extractor for extracting a flag indicating whether the image data requires loop-filtering, using distribution of inverse quantized coefficients (IQCS) of the image data, and a motion vector indicating the difference between the previous frame and the current frame; a deblocking filter for deblocking filtering the image data by investigating the blocking flag extracted by the flag extractor; a corner outlier compensator for detecting the corner outlier of the deblocking-filtered data and compensating for the detected corner outlier; and a deringing filter for deringing-filtering the corner outlier compensated data by investigating the ringing flag extracted by the flag extractor, and wherein the flags comprise a blocking flag indicating whether a need for reducing blocking artifacts near block boundaries exists, and a ringing flag indicating whether there is a need for reducing ringing noise near image edges.

[0034]According to still another aspect of the present invention, there is provided a computer readable medium having embodied thereon a computer program for loop-filtering image data, capable of reducing quantization effect generated when the image data is block-based encoded and decoded, wherein the loop-filtering comprises the steps of: (a) extracting a flag indicating whether the image data requires loop-filtering using the distribution of inverse quantized coefficients (IQCs) of an inverse quantized image data and a motion vector indicating the difference between the previous frame and the current frame; and (b) filtering the image data corresponding to the flag by a predetermined method if the extracted flag indicates a need for the loop-filtering, wherein in the step (a) the flag is extracted from a discrete cosine transform (DCT) domain of each block if an image frame to be loop-filtered is an intra frame, and from a residual signal and a reference frame if the image frame to be loop-filtered is an inter frame.

Problems solved by technology

However, when the block-based image data is restored, considerable image deterioration, for example, blocking artifacts near the block boundary, corner outliers at the cross points of blocks, and ringing noise near the image edges, occurs.

Such deterioration is serious when the image is highly compressed.

Blocking artifacts are caused by grid noise generated along the block boundary in a relatively homogeneous area.

However, the above methods require complicated computations.

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