Loop-filtering method for image data and apparatus therefor

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, wherein the flag comprises 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;
• 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.

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.