MOTION PICTURE ENCODING/DECODING APPARATUS, ADAPTIVE DEBLOCKING FILTERING APPARATUS AND FILTERING METHOD FOR SAME, AND RECORDING MEDIUM

• US 20110200100A1
• Filed: 10/22/2009
• Published: 08/18/2011
• Est. Priority Date: 10/27/2008
• Status: Active Grant

• Current Assignee: SK Telecom Co., Ltd.
• Original Assignee: SK Telecom Co., Ltd.
• Inventors: Choe, Yoonsik, Ahn, Junhyuk, Kim, Hayoon, Kim, Byongho, Choi, Yungho, Kim, Yonggoo
• Granted Patent: US 9,596,485 B2
• Time in Patent Office: Days
• US Class Current: 375/240.02
• 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 19/61 in combination with predictive coding
• CPC Class Codes: H04N 19/82 involving filtering within a prediction loop
• CPC Class Codes: H04N 19/86 involving reduction of coding artifacts, e.g. of blockiness

Abstract

A video encoding/decoding apparatus, an adaptive deblocking filtering apparatus and a filtering method for same, and a recording medium are disclosed. The filtering apparatus includes: a boundary strength determiner for determining strength of boundaries between subblocks of current block; a direction selector for selecting multiple directions preset with reference to the boundary sequentially; a filtering pixel selector for selecting pixels for filtering based on selected directions; a filtering determiner for determining whether to perform the filtering for the selected directions depending on relationships between pixel values of selected pixels; and a filtering unit for filtering the selected pixels in the selected directions depending on the determination of whether to perform filtering to apply pixel-wide deblocking filtering in a plurality of directions as well as in vertical and horizontal directions, thus effectively removing block distortions resulting from a diagonal discontinuity caused byedges in a plurality of diagonal directions.

Claims

1. An adaptive deblocking filtering apparatus comprising:

a boundary strength determiner for determining strength of boundaries between subblocks of a current block;

a direction selector for selecting a number of directions preset with reference to the boundary individually and sequentially;

a filtering pixel selector for selecting pixels for filtering based on selected directions;

a filtering determiner for performing a determination of whether to perform the filtering for the selected directions depending on relationships between pixel values of selected pixels; and

a filtering unit for performing the filtering with respect to the selected pixels in the selected directions depending on the determination of whether to perform the filtering.

2. The adaptive deblocking filtering apparatus of claim 1, wherein the filtering unit determines the selected directions as a filtering direction if the relationships between pixel values of selected pixels satisfies a condition that an absolute value of a pixel value difference between two first pixels facing each other with reference to the boundary, an absolute value of a pixel value difference between a second pixel and a first pixel both at one side with reference to the boundary, and an absolute value of a pixel value difference between a second pixel and a first pixel at another side with reference to the boundary are smaller than thresholds respectively preset.

3. The adaptive deblocking filtering apparatus of claim 2, wherein the filtering unit, in an occasion that the filtering direction is determined to be multiple, performs the filtering in selected one or more of multiple filtering directions depending on pixel value changes between the selected pixels.

4. The adaptive deblocking filtering apparatus of claim 1, wherein the number of directions preset include 45 degrees, 90 degrees, and 135 degrees.

5. The adaptive deblocking filtering apparatus of claim 1, wherein the number of directions preset include 45 degrees, 56.25 degrees, 67.5 degrees, 78.75 degrees, 90 degrees, 101.25 degrees, 112.5 degrees, 123.75 degrees, and 135 degrees.

6. An adaptive deblocking filtering method comprising:

determining strength of boundaries between subblocks of a current block;

selecting a number of directions preset with reference to the boundary individually and sequentially;

selecting pixels for filtering based on selected directions;

determining a filtering by performing a determination of whether to perform the filtering for the selected directions depending on relationships between pixel values of selected pixels; and

performing the filtering with respect to the selected pixels in the selected directions depending on the determination of whether to perform the filtering.

7. The adaptive deblocking filtering method of claim 6, wherein the step of determining the filtering determines the selected directions as a filtering direction if the relationships between pixel values of selected pixels satisfies a condition that an absolute value of a pixel value difference between two first pixels facing each other with reference to the boundary, an absolute value of a pixel value difference between a second pixel and a first pixel both at one side with reference to the boundary, and an absolute value of a pixel value difference between a second pixel and a first pixel at another side with reference to the boundary are smaller than thresholds respectively preset.

8. The adaptive deblocking filtering method of claim 7, wherein the step of performing filtering, in an occasion that the filtering direction is determined to be multiple, performs the filtering in selected one or more of multiple filtering directions depending on pixel value changes between the selected pixels.

9. The adaptive deblocking filtering method of claim 6, wherein the number of directions preset include 45 degrees, 90 degrees, and 135 degrees.

10. The adaptive deblocking filtering method of claim 6, wherein the number of directions preset include 45 degrees, 56.25 degrees, 67.5 degrees, 78.75 degrees, 90 degrees, 101.25 degrees, 112.5 degrees, 123.75 degrees, and 135 degrees.

11. A video encoding apparatus comprising:

a predictor for predicting a current block of an image to generate a predicted block;

a subtractor for subtracting the predicted block from the current block to generate a residual block;

a transformer for performing a transform on the residual block into a frequency domain;

a quantizer for performing a quantization on the residual block after the transform;

an encoder for encoding the residual block after the quantization;

an inverse quantizer for performing an inverse quantization on the residual block;

an inverse transformer for performing an inverse transform on the residual block after the inverse quantization into a residual block having pixel signals on time axis;

an adder for adding the predicted block to the residual block after the inverse transform to perform a reconstruction of the current block; and

a deblocking filtering unit for deblocking-filtering the current block after the reconstruction through selecting pixels for filtering by the number of directions preset with reference to the boundary of the current block having been reconstructed, performing a determination of whether to perform the filtering for corresponding directions depending on relationships between pixel values of selected pixels, and performing the filtering with respect to the selected pixels in the corresponding directions depending on the determination of whether to perform the filtering.

12. The video encoding apparatus of claim 11, wherein the deblocking filtering unit determines the corresponding directions as a filtering direction if the relationships between pixel values of selected pixels satisfies a condition that an absolute value of a pixel value difference between two first pixels facing each other with reference to the boundary, an absolute value of a pixel value difference between a second pixel and a first pixel both at one side with reference to the boundary, and an absolute value of a pixel value difference between a second pixel and a first pixel at another side with reference to the boundary are smaller than thresholds respectively preset.

13. The video encoding apparatus of claim 12, wherein the deblocking filtering unit, in an occasion that the filtering direction is determined to be multiple, performs the filtering in selected one or more of multiple filtering directions depending on pixel value changes between the selected pixels.

14. A video decoding apparatus comprising:

a decoder for decoding a bitstream to extract a residual block;

an inverse quantizer for performing an inverse quantization on the residual block;

an inverse transformer for performing an inverse transform on the residual block after the inverse quantization;

a predictor for predicting a current block to generate a predicted block;

an adder for adding the predicted block to the residual block after the inverse transform to perform a reconstruction of the current block; and

a deblocking filtering unit for deblocking-filtering the current block after the reconstruction by the adder through selecting pixels for filtering by the number of directions preset with reference to the boundary of the current block, performing a determination of whether to perform the filtering for corresponding directions depending on relationships between pixel values of selected pixels, and performing the filtering with respect to the selected pixels in the corresponding directions depending on the determination of whether to perform the filtering.

15. The video decoding apparatus of claim 14, wherein the deblocking filtering unit determines the corresponding directions as a filtering direction if the relationships between pixel values of selected pixels satisfies a condition that an absolute value of a pixel value difference between two first pixels facing each other with reference to the boundary, an absolute value of a pixel value difference between a second pixel and a first pixel both at one side with reference to the boundary, and an absolute value of a pixel value difference between a second pixel and a first pixel at another side with reference to the boundary are smaller than thresholds respectively preset.

16. The video decoding apparatus of claim 15, wherein the deblocking filtering unit, in an occasion that the filtering direction is determined to be multiple, performs the filtering in selected one or more of multiple filtering directions depending on pixel value changes between the selected pixels.

17. A computer readable medium storing a computer program comprising functions of:

determining strength of boundaries between subblocks of a current block;

selecting a number of directions preset with reference to the boundary individually and sequentially;

selecting pixels for filtering based on selected directions;

performing a determination of whether to perform the filtering for the selected directions depending on relationships between pixel values of selected pixels; and

performing the filtering with respect to the selected pixels in the selected directions depending on the determination of whether to perform the filtering.

18. A deblocking filtering apparatus comprising:

a boundary strength determiner for determining strength of boundaries between subblocks of a current block;

a filtering direction determiner for selecting an optimal direction among a number of directions preset respectively for pixels in the boundaries of the subblocks based on pixel value changes between the pixels corresponding respectively to the directions, and determining a most selected direction among a number of selected optimal directions with respect to all of the pixels in the boundaries of the subblocks, as a determined filtering direction of a corresponding subblock; and

a filtering unit for performing a selection of pixels for filtering based on the determined filtering direction with respect to each of the pixels in the boundaries of the subblocks, performing a determination of whether to perform the filtering for the determined filtering direction depending on relationships between pixel values of selected pixels, and performing the filtering with respect to the selected pixels in the determined filtering direction depending on the determination of whether to perform the filtering.

19. The deblocking filtering apparatus of claim 18, wherein the filtering direction determiner calculates the pixel value changes based on an absolute value of a pixel value difference between two first pixels facing each other with reference to a corresponding boundary, an absolute value of a pixel value difference between a second pixel and a first pixel both at one side with reference to the corresponding boundary, an absolute value of a pixel value difference between a second pixel and a first pixel at another side with reference to the corresponding boundary, an absolute value of a pixel value difference between a third pixel and the second pixel at the one side with reference to the corresponding boundary, and an absolute value of a pixel value difference between a third pixel and the second pixel at the another side with reference to the corresponding boundary, and selects among the directions one with a smallest pixel value change as the optimal direction.

20. The deblocking filtering apparatus of claim 18, wherein the filtering unit performs the filtering in the determined filtering direction if the relationships between pixel values of the selected pixels satisfies a condition that an absolute value of a pixel value difference between two first pixels facing each other with reference to a corresponding boundary, an absolute value of a pixel value difference between a second pixel and a first pixel both at one side with reference to the corresponding boundary, and an absolute value of a pixel value difference between a second pixel and a first pixel at another side with reference to the corresponding boundary are smaller than thresholds respectively preset.

21. The deblocking filtering apparatus of claim 20, wherein the filtering unit, in an occasion that the determined filtering direction cannot satisfy the condition, performs a check if vertical direction of the corresponding boundary can, and in accordance with a result of the check, performs the filtering.

22. The deblocking filtering apparatus of claim 18, wherein the number of directions preset include 45 degrees, 56.25 degrees, 67.5 degrees, 78.75 degrees, 90 degrees, 101.25 degrees, 112.5 degrees, 123.75 degrees, and 135 degrees.

23. The deblocking filtering apparatus of claim 18, wherein the filtering direction determiner records the determined filtering direction as additional information for the corresponding subblock or has the pixels after the filtering in the determined filtering direction among the pixels in the boundaries of corresponding subblocks assigned with additional information and recorded.

24. A deblocking filtering apparatus comprising:

a boundary strength determiner for determining strength of boundaries between subblocks of a current block;

a filtering direction determiner for selecting a direction as a determined filtering direction among a number of directions preset, with respect to a first pixel in the boundaries of the subblocks based on pixel value changes between the pixels corresponding respectively to the directions; and

determining a latest and most selected direction for a current subblock as a determined filtering direction, or determining a direction right ahead of the latest and most selected direction as the determined filtering direction, or determining a filtering direction according to the selecting of the direction of the first pixel, with respect to a second and later ones of the pixels in the boundaries of the subblocks; and

a filtering unit for performing a selection of pixels for filtering based on the determined filtering direction with respect to each of the pixels in the boundaries of the subblocks, performing a determination of whether to perform the filtering for the determined filtering direction depending on relationships between pixel values of selected pixels, and performing the filtering with respect to the selected pixels in the determined filtering direction depending on the determination of whether to perform the filtering.

25. The deblocking filtering apparatus of claim 24, wherein the filtering direction determiner calculates the pixel value changes based on an absolute value of a pixel value difference between two first pixels facing each other with reference to a corresponding boundary, an absolute value of a pixel value difference between a second pixel and a first pixel both at one side with reference to the corresponding boundary, an absolute value of a pixel value difference between a second pixel and a first pixel at another side with reference to the corresponding boundary, an absolute value of a pixel value difference between a third pixel and the second pixel at the one side with reference to the corresponding boundary, and an absolute value of a pixel value difference between a third pixel and the second pixel at the another side with reference to the corresponding boundary, and selects among the directions one with a smallest pixel value change as the determined filtering direction.

26. The deblocking filtering apparatus of claim 24, wherein the filtering unit performs the filtering in the determined filtering direction if the relationships between pixel values of the selected pixels satisfies a condition that an absolute value of a pixel value difference between two first pixels facing each other with reference to a corresponding boundary, an absolute value of a pixel value difference between a second pixel and a first pixel both at one side with reference to the corresponding boundary, and an absolute value of a pixel value difference between a second pixel and a first pixel at another side with reference to the corresponding boundary are smaller than thresholds respectively preset.

27. The deblocking filtering apparatus of claim 24, wherein the number of directions preset include 45 degrees, 56.25 degrees, 67.5 degrees, 78.75 degrees, 90 degrees, 101.25 degrees, 112.5 degrees, 123.75 degrees, and 135 degrees.

28. An deblocking filtering method comprising:

determining strength of boundaries between subblocks of a current block;

selecting an optimal direction among a number of directions preset respectively for pixels in the boundaries of the subblocks based on pixel value changes between the pixels corresponding respectively to the directions;

determining a most selected direction among a number of selected optimal directions with respect to all of the pixels in the boundaries of the subblocks, as a determined filtering direction of a corresponding subblock;

performing a selection of pixels for filtering based on the determined filtering direction with respect to each of the pixels in the boundaries of the subblocks;

performing a determination of whether to perform the filtering for the determined filtering direction depending on relationships between pixel values of selected pixels; and

performing the filtering with respect to the selected pixels in the determined filtering direction depending on the determination of whether to perform the filtering.

29. The deblocking filtering method of claim 28, wherein the pixel value changes in the step of selecting the optimal direction are calculated based on an absolute value of a pixel value difference between two first pixels facing each other with reference to a corresponding boundary, an absolute value of a pixel value difference between a second pixel and a first pixel both at one side with reference to the corresponding boundary, an absolute value of a pixel value difference between a second pixel and a first pixel at another side with reference to the corresponding boundary, an absolute value of a pixel value difference between a third pixel and the second pixel at the one side with reference to the corresponding boundary, and an absolute value of a pixel value difference between a third pixel and the second pixel at the another side with reference to the corresponding boundary, and a direction with a smallest pixel value change among the directions is selected as the optimal direction.

30. The deblocking filtering method of claim 28, wherein the step of performing the determination of whether to perform the filtering determines whether to perform the filtering depending on whether the relationships between pixel values of the selected pixels satisfies a condition that an absolute value of a pixel value difference between two first pixels facing each other with reference to a corresponding boundary, an absolute value of a pixel value difference between a second pixel and a first pixel both at one side with reference to the corresponding boundary, and an absolute value of a pixel value difference between a second pixel and a first pixel at another side with reference to the corresponding boundary are smaller than thresholds respectively preset.

31. The deblocking filtering method of claim 30, wherein the step of performing the determination of whether to perform the filtering, in an occasion that the determined filtering direction cannot satisfy the condition, performs a check if vertical direction of the corresponding boundary can, and in accordance with a result of the check, determines whether to perform the filtering for the vertical direction.

32. The deblocking filtering method of claim 28, wherein the number of directions preset include 45 degrees, 56.25 degrees, 67.5 degrees, 78.75 degrees, 90 degrees, 101.25 degrees, 112.5 degrees, 123.75 degrees, and 135 degrees.

33. The deblocking filtering method of claim 28, further comprising recording the determined filtering direction in the step of the determined filtering direction as additional information for the corresponding subblock or having the pixels after the filtering in the determined filtering direction among the pixels in the boundaries of corresponding subblocks assigned with additional information and recorded.

34. An deblocking filtering method comprising:

determining strength of boundaries between subblocks of a current block;

selecting a direction as a first determined filtering direction among a number of directions preset with respect to a first pixel in the boundaries of the subblocks based on pixel value changes between the pixels corresponding respectively to the directions;

determining a latest and most selected direction for a current subblock as a second determined filtering direction, or determining a direction right ahead of the latest and most selected direction as an optimal filtering direction, or determining a filtering direction according to the selecting of the direction of the first pixel with respect to a second and later ones of the pixels in the boundaries of the subblocks;

performing a selection of pixels for filtering based on the determined filtering direction with respect to each of the pixels in the boundaries of the subblocks;

performing a determination of whether to perform the filtering for the determined filtering direction depending on relationships between pixel values of selected pixels; and

performing the filtering with respect to the selected pixels in the determined filtering direction depending on the determination of whether to perform the filtering.

35. The deblocking filtering method of claim 34, wherein the pixel value changes in the step of selecting a first determined filtering direction are calculated based on an absolute value of a pixel value difference between two first pixels facing each other with reference to a corresponding boundary, an absolute value of a pixel value difference between a second pixel and a first pixel both at one side with reference to the corresponding boundary, an absolute value of a pixel value difference between a second pixel and a first pixel at another side with reference to the corresponding boundary, an absolute value of a pixel value difference between a third pixel and the second pixel at the one side with reference to the corresponding boundary, and an absolute value of a pixel value difference between a third pixel and the second pixel at the another side with reference to the corresponding boundary, and a direction with a smallest pixel value change among the directions is selected as the filtering direction.

36. The deblocking filtering method of claim 34, wherein the step of performing the determination of whether to perform the filtering determines whether to perform the filtering depending on whether the relationships between pixel values of the selected pixels satisfies a condition that an absolute value of a pixel value difference between two first pixels facing each other with reference to a corresponding boundary, an absolute value of a pixel value difference between a second pixel and a first pixel both at one side with reference to the corresponding boundary, and an absolute value of a pixel value difference between a second pixel and a first pixel at another side with reference to the corresponding boundary are smaller than thresholds respectively preset.

37. The deblocking filtering method of claim 34, wherein the number of directions preset include 45 degrees, 56.25 degrees, 67.5 degrees, 78.75 degrees, 90 degrees, 101.25 degrees, 112.5 degrees, 123.75 degrees, and 135 degrees.

38. A video encoding apparatus comprising:

a predictor for predicting a current block of an image to generate a predicted block;

a subtractor for subtracting the predicted block from the current block to generate a residual block;

a transformer for performing a transform on the residual block into a frequency domain;

a quantizer for performing a quantization on the residual block after the transform;

an encoder for encoding the residual block after the quantization;

an inverse quantizer for performing an inverse quantization on the residual block;

an inverse transformer for performing an inverse transform on the residual block after the inverse quantization into a residual block having pixel signals on time axis;

an adder for adding the predicted block to the residual block after the inverse transform to perform a reconstruction of the current block; and

a deblocking filtering unit for deblocking-filtering the current block after the reconstruction through selecting an optimal direction among a number of directions preset respectively for pixels in the boundaries of the subblocks of the current block having been reconstructed based on pixel value changes between the pixels corresponding respectively to the directions, determining a most selected direction among a number of selected optimal directions with respect to all of the pixels in the boundaries of the subblocks as a determined filtering direction of a corresponding subblock, performing a selection of pixels for filtering based on the determined filtering direction with respect to each of the pixels in the boundaries of the subblocks, performing a determination of whether to perform the filtering for the determined filtering direction depending on relationships between pixel values of selected pixels, and performing the filtering with respect to the selected pixels in the determined filtering direction depending on the determination of whether to perform the filtering.

39. A video encoding apparatus comprising:

a predictor for predicting a current block of an image to generate a predicted block;

a subtractor for subtracting the predicted block from the current block to generate a residual block;

a transformer for performing a transform on the residual block into a frequency domain;

a quantizer for performing a quantization on the residual block after the transform;

an encoder for encoding the residual block after the quantization;

an inverse quantizer for performing an inverse quantization on the residual block;

an inverse transformer for performing an inverse transform on the residual block after the inverse quantization into a residual block having pixel signals on time axis;

an adder for adding the predicted block to the residual block after the inverse transform to perform a reconstruction of the current block; and

a deblocking filtering unit for deblocking-filtering the current block after the reconstruction through selecting a direction as a determined filtering direction among a number of directions preset, with respect to a first pixel in the boundaries of the subblocks of the current block after the reconstruction based on pixel value changes between the pixels corresponding respectively to the directions;

determining a latest and most selected direction for a current subblock as a determined filtering direction, or determining a direction right ahead of the latest and most selected direction as the determined filtering direction, or determining a filtering direction according to the selecting of the direction of the first pixel, with respect to a second and later ones of the pixels in the boundaries of the subblocks;

performing a selection of pixels for filtering based on the determined filtering direction with respect to each of the pixels in the boundaries of the subblocks;

performing a determination of whether to perform the filtering for the determined filtering direction depending on relationships between pixel values of selected pixels; and

performing the filtering with respect to the selected pixels in the determined filtering direction depending on the determination of whether to perform the filtering.

40. A video decoding apparatus comprising:

a decoder for decoding a bitstream to extract a residual block;

an inverse quantizer for performing an inverse quantization on the residual block;

an inverse transformer for performing an inverse transform on the residual block after the inverse quantization;

a predictor for predicting a current block to generate a predicted block;

an adder for adding the predicted block to the residual block after the inverse transform to perform a reconstruction of the current block; and

a deblocking filtering unit for deblocking-filtering the current block after the reconstruction through selecting a determined optimal direction among a number of directions preset, with respect to a particular pixel corresponding to additional information in receipt among all of pixels in the boundaries of the subblocks of the current block having been reconstructed based on pixel value changes between the pixels corresponding respectively to the directions, determining the determined optimal direction as a determined filtering direction of a corresponding subblock, performing a selection of pixels for filtering based on the determined filtering direction with respect to each of the pixels in the boundaries of the subblocks, performing a determination of whether to perform the filtering for the determined filtering direction depending on relationships between pixel values of selected pixels, and performing the filtering with respect to the selected pixels in the determined filtering direction depending on the determination of whether to perform the filtering.

41. A video encoding apparatus comprising:

a decoder for decoding a bitstream to extract a residual block;

an inverse quantizer for performing an inverse quantization on the residual block;

an inverse transformer for performing an inverse transform on the residual block after the inverse quantization;

a predictor for predicting a current block to generate a predicted block;

an adder for adding the predicted block to the residual block after the inverse transform to perform a reconstruction of the current block; and

a deblocking filtering unit for deblocking-filtering the current block after the reconstruction by the adder through performing a selection of pixels for filtering based on a filtering direction received as additional information of a corresponding subblock with respect to each of the pixels in the boundaries of the subblocks of the current block having been reconstructed, performing a determination of whether to perform the filtering for the determined filtering direction depending on relationships between pixel values of selected pixels, and performing the filtering with respect to the selected pixels in the determined filtering direction depending on the determination of whether to perform the filtering.

42. A video decoding apparatus comprising:

a decoder for decoding a bitstream to extract a residual block;

an inverse quantizer for performing an inverse quantization on the residual block;

an inverse transformer for performing an inverse transform on the residual block after the inverse quantization;

a predictor for predicting a current block to generate a predicted block;

an adder for adding the predicted block to the residual block after the inverse transform to perform a reconstruction of the current block; and

a deblocking filtering unit for deblocking-filtering the current block after the reconstruction by the adder through selecting a direction as a determined filtering direction among a number of directions preset, with respect to a first pixel in the boundaries of the subblocks of the current block after the reconstruction based on pixel value changes between the pixels corresponding respectively to the directions;

determining a latest and most selected direction for a current subblock as a determined filtering direction, or determining a direction right ahead of the latest and most selected direction as the determined filtering direction, or determining a filtering direction according to the selecting of the direction of the first pixel, with respect to a second and later ones of the pixels in the boundaries of the subblocks;

performing a selection of pixels for filtering based on the determined filtering direction with respect to each of the pixels in the boundaries of the subblocks;

performing a determination of whether to perform the filtering for the determined filtering direction depending on relationships between pixel values of selected pixels; and

performing the filtering with respect to the selected pixels in the determined filtering direction depending on the determination of whether to perform the filtering.

43. A computer readable medium storing a computer program comprising functions of:

determining strength of boundaries between subblocks of a current block;

selecting an optimal direction among a number of directions preset respectively for pixels in the boundaries of the subblocks based on pixel value changes between the pixels corresponding respectively to the directions;

determining a most selected direction among a number of selected optimal directions with respect to all of the pixels in the boundaries of the subblocks, as a determined filtering direction of a corresponding subblock;

performing a selection of pixels for filtering based on the determined filtering direction with respect to each of the pixels in the boundaries of the subblocks;

performing a determination of whether to perform the filtering for the determined filtering direction depending on relationships between pixel values of selected pixels; and

performing the filtering with respect to the selected pixels in the determined filtering direction depending on the determination of whether to perform the filtering.

44. A computer readable medium storing a computer program comprising functions of:

determining strength of boundaries between subblocks of a current block;

selecting a direction as a first determined filtering direction among a number of directions preset with respect to a first pixel in the boundaries of the subblocks based on pixel value changes between the pixels corresponding respectively to the directions;

determining a latest and most selected direction for a current subblock as a second determined filtering direction, or determining a direction right ahead of the latest and most selected direction as an optimal filtering direction, or determining a filtering direction according to the selecting of the direction of the first pixel with respect to a second and later ones of the pixels in the boundaries of the subblocks;

performing a selection of pixels for filtering based on the determined filtering direction with respect to each of the pixels in the boundaries of the subblocks;

performing a determination of whether to perform the filtering for the determined filtering direction depending on relationships between pixel values of selected pixels; and

performing the filtering with respect to the selected pixels in the determined filtering direction depending on the determination of whether to perform the filtering.