Decoding apparatus including a filtering unit configured to determine a pixel value using a weighted average operation

Abstract

A method and apparatus to remove a block effect and a ring effect appearing in a compression-coded image is disclosed. The present invention is especially applicable to an image compression-coded at a low bit rate. In particular, the present invention includes a variety of masks for the removal of the block/ring effect. Thus, one mask is select for a pixel to be filtered. Moreover, candidate pixels to be averaged with the pixel to be filtered is selected from the pixels of the selected mask to better maintain the details of the image, and a weight is applied to improve the calculation speed of the averaging operation. More particularly, the masks according to the present invention have longer tabs toward adjacent blocks at boundaries of the given block to remove the block and ring effect. In an embodiment, the decoding apparatus includes a filtering unit configured to determine a value of a pixel of an image. The filtering unit is configured to determine the value by selecting a filtering mask including eight pixels based on a position of the pixel of the image, and applying a weighted averaging operation to a number of the eight pixels included in the filtering mask.

Description

Claims

1. A filtering method for a pixel P of a block B in a reconstructed image, comprising:

selecting one of a plurality of filtering masks based upon a position of said pixel P in said block B; and

averaging said pixel P and candidate pixels within the selected filtering mask.

2. A method of claim 1, wherein each of the plurality of filtering masks has 8 tabs.

3. A method of claim 1, wherein a filtering mask with more tabs toward a block adjacent said block B is selected.

4. A method of claim 1, further comprising selecting a pixel within the selected filtering mask P_m as a candidate pixel if the value of the pixel P_m meets a predetermined condition.

5. A method of claim 4, wherein the pixel P_m is selected as a candidate pixel if the absolute value of the difference between said pixel P and pixel P_m is less than a threshold value.

6. A method of claim 5, wherein the threshold value is calculated by an equation below,

δ=k×q

7. A method of claim 6, wherein the value of k is 1.0 for filtering boundary pixels of said block B and 0.6 for filtering pixels within the boundary pixels of said block B.

8. A method of claim 4, further comprising adding a weight value to said pixel P prior to the averaging, wherein said weight value is based upon a number of pixels P_m not selected as candidate pixels.

9. A method of claim 8, wherein said weight value is the number of pixels P_m not selected multiplied by the value of said pixel P.

10. A filtering apparatus to filter a pixel P of a block B in a reconstructed image, comprising:

a filtering masking unit selecting one of a plurality filtering masks based upon a position of said pixel P in said block B; and

an averaging unit averaging said pixel P and candidate pixels within the selected mask.

11. An apparatus of claim 10, wherein each of the plurality of filtering masks has 8 tabs.

12. An apparatus of claim 11, wherein the plurality of filtereing masks are modified 3×3 mask forms including:

a filtering mask in which eight tabs are selected from the 3×3 mask form, discarding one corner tab;

a filtering mask in which more tabs are selected in a vertical direction than a horizontal direction, and more vertical lower tabs are selected than vertical upper tabs;

a filtering mask in which more tabs are selected in the vertical direction than the horizontal direction, and more vertical upper tabs are selected than vertical lower tabs;

a filtering mask in which more tabs are selected in the horizontal direction than the vertical direction, and more horizontal left tabs are selected than horizontal right tabs; and

a filtering mask in which more tabs are selected in the horizontal direction than the vertical direction, and more horizontal right tabs are selected than horizontal left tabs.

13. An apparatus of claim 10, wherein a filtering mask with more tabs toward a block adjacent said block B is selected.

14. An apparatus of claim 10, further comprising:

a comparison unit selecting a pixel within the selected mask P_m as a candidate pixel if the value of the pixel P_m meets a predetermined condition.

15. An apparatus of claim 14, wherein the pixel P_m is selected as a candidate pixel if the absolute value of the difference between said pixel P and pixel P_m is less than a threshold value.

16. An apparatus of claim 15, wherein the threshold value is calculated by an equation below,

δ=k×q

17. An apparatus of claim 16, wherein the value of k is 1.0 for filtering boundary pixels of said block B and 0.6 for filtering pixels within the boundary pixels of said block.

18. An apparatus of claim 14, wherein the averaging unit adds a weight value to said pixel P prior to the averaging, wherein said weight value is based upon a number of pixels P_m not selected as candiate pixels.

19. An apparatus of claim 18, wherein said weight value is the number of pixels P_m not selected multiplied by the value of said pixel P.

20. A coding and decoding method comprising:

a discrete cosine transform (DCT) unit performing a DCT operation with respect to divided blocks of an image to generate DCT coefficients;

a quantization unit quantizing the DCT coefficients and transmitting the DCT coefficients in a form of a bit stream through a transmission channel;

a dequantization unit dequantizing the DCT coefficients received through the transmission channel;

an inverse DCT unit performing an inverse DCT operation with respect to the dequantized DCT coefficients to form a reconstructed image, and

a filtering process unit filtering each pixel of each block of the reconstructed image by selecting one of a plurality of filtering masks based upon a position of said pixel in said block; and averaging said pixel and candidate pixels within the selected filtering mask.

21. A decoding apparatus, comprising:

a filtering unit configured to determine a value of a pixel to be filtered, the filtering unit configured to determine the value by selecting a filtering mask based on a position of the pixel to be filtered, the filtering mask including eight pixels, the filtering unit configured to compare a difference value with a threshold, the difference value being based on the pixel to be filtered and a pixel in the selected filtering mask, the threshold being based on quantization information of at least a portion of the image including the pixel to be filtered, and the filtering unit configured to determine the value by applying a weighted averaging operation to a number of the eight pixels included in the filtering mask, the applying being based on the comparing.

22. The apparatus of claim 21, wherein the filtering mask includes the pixel to be filtered.

23. The apparatus of claim 21, wherein the filtering mask covers the pixel to be filtered.

24. The apparatus of claim 21, wherein the filtering mask includes pixels in a first block and pixels in a second block, the second block being adjacent the first block.

25. The apparatus of claim 24, wherein the filtering mask includes at least one pixel from the first block, and three pixels from the second block.

26. The apparatus of claim 25, wherein the pixel to be filtered is in the second block.

27. The apparatus of claim 25, wherein the pixel to be filtered is in the first block.

28. A decoding apparatus, comprising:

a filtering unit configured to determine a value of a pixel to be filtered, the filtering unit configured to determine the value by selecting a filtering mask based on a position of the pixel to be filtered, the filtering mask including eight pixels, the filtering unit configured to compare a difference value with a threshold, the difference value being based on the pixel to be filtered and a pixel in the selected filtering mask, the threshold being based on quantization information of at least a portion of the image including the pixel to be filtered, the filtering unit configured to determine the value by applying weights to a number of pixels included in the filtering mask and performing an averaging operation on the number of weighted pixels, the applying being based on the comparing.

29. The apparatus of claim 21, wherein the filtering unit is configured to apply the weighted averaging operation to non-adjacent pixels.

30. The apparatus of claim 28, wherein the filtering unit is configured to apply the averaging operation to non-adjacent pixels.