WO2001041453A1 - Blocking artifact reduction in the dct domain - Google Patents
Blocking artifact reduction in the dct domain Download PDFInfo
- Publication number
- WO2001041453A1 WO2001041453A1 PCT/EP2000/011295 EP0011295W WO0141453A1 WO 2001041453 A1 WO2001041453 A1 WO 2001041453A1 EP 0011295 W EP0011295 W EP 0011295W WO 0141453 A1 WO0141453 A1 WO 0141453A1
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- frequency domain
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/90—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using coding techniques not provided for in groups H04N19/10-H04N19/85, e.g. fractals
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/48—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using compressed domain processing techniques other than decoding, e.g. modification of transform coefficients, variable length coding [VLC] data or run-length data
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/50—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding
- H04N19/503—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding involving temporal prediction
- H04N19/51—Motion estimation or motion compensation
- H04N19/527—Global motion vector estimation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/85—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using pre-processing or post-processing specially adapted for video compression
- H04N19/86—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using pre-processing or post-processing specially adapted for video compression involving reduction of coding artifacts, e.g. of blockiness
Definitions
- the invention relates in general to the reduction of blocking artifacts in image data and in particular to a method and device for reducing blocking artifacts in image data using only frequency domain operations.
- Discrete Cosine Transform (DCT) coding is one well-known compression scheme.
- the image is divided into small rectangular regions or "blocks". Each block is transform coded and transmitted through a communications channel.
- the blocks are decoded and reassembled into the original image. Typically these blocks are formed by an array of 8X8 pixels.
- the DCT is applied to each block and then each block is quantized.
- the DCT is a linear transformation that creates a new block of pixels; each new pixel is a linear combination of all the incoming pixels of the original block.
- the DCT based block image coding technique causes degradation of the received image in the form of blocking artifacts.
- an image is block coded the reconstructed blocks can be visible in the reconstructed image resulting in the viewer seeing the block boundaries, which in general are due to uncorrelated quantization noise.
- Quantization noise is independent between blocks yielding a jump or step at the block boundaries.
- the greater the compression the greater the blocking artifacts. The blocking effect is quite visible to the viewer and can become quite annoying since the eye is so sensitive to the "step" at the block boundary.
- a method and device for reducing blocking artifacts which analyzes the DCT characteristics of the boundary between two blocks and reduces the blocking artifacts by smoothing out the abrupt discontinuities at the block boundaries in the frequency domain.
- a first frequency domain block (A) and a second frequency domain block (B) are received in the video stream.
- a third frequency domain block (C) is then computed which overlaps the first and second frequency domain blocks at the boundary between the first and second block.
- the third block is used to smooth the discontinuity at blocks A and B's boundary by adjusting the DCT coefficients of the third block.
- the computed change in the third block's coefficients is then translated into a change in coefficients of the first and second blocks (A, B). It is an object of the invention to perform this smoothing in the frequency domain only, by using the third block C.
- Yet another object of the invention is to choose, ⁇ A and ⁇ B to minimize the change to the first and second blocks.
- Yet a further object of the invention is to make ⁇ A substantially opposite to ⁇ B.
- Another object of the invention concerns blocks A and B when they are not relatively uniform. This object is achieved by reducing large DCT coefficients of high frequency components in the third block C.
- Yet a further object of the invention is to change the coefficients of the third block C by reducing large high frequency coefficients in the third block C if their respective coefficients in the first and second blocks are substantially zero. Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
- the invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the apparatus embodying features of construction, combinations of elements and arrangement of parts which are adapted to effect such steps, all as exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.
- the embodiments of the invention pertain to reducing blocking artifacts by analyzing the DCT characteristics of the boundary between two blocks and smoothing the abrupt discontinuities at the block boundaries in the frequency domain.
- Two frequency domain blocks A and B are received in the video stream and a third block C is computed which overlaps the boundary between the two blocks A and B.
- the third block is used to smooth the discontinuity at block A and B's boundary by changing the DCT coefficients of the third block and translating this change into a change in coefficients of blocks A and B.
- This blocking artifact reduction is explained in a first instance with reference to two blocks A and B which each have uniform pixels values in the spatial domain but a step or jump in pixel value occurs across the blocks' boundary and in a second instance with reference to two blocks A and B which do not necessarily have uniform pixels in the spatial domain.
- Figure la shows two 8X8 pixel blocks 'a' and 'b' and a third pixel block 'c' which overlaps 'a' and 'b' and covers the boundary 'e'.
- Figure lb shows an example of the elements of blocks 'a', ay and 'b', b in a first embodiment of the invention.
- the step edge must be smoothed to a ramp edge such as the one shown in Figure 2b.
- the object of the present invention is to smooth the DCT of block 'c', C, in the frequency domain thereby removing the step in the middle of the block 'c' and translate this smoothing into a change in coefficients of DCT blocks A and B.
- the DCT blocks A and B are readily available from the compressed bitstream after performing variable length decoding, but the DCT block C is not. Therefore, to smooth the DCT block C it is first necessary to compute the DCT coefficients of block C.
- This computation does not merely involve merging the DCT values of the right hand portion of block A and the DCT values of the left hand portion of Block B because each DCT block is a linear combination of all the incoming pixels of a block, making the computation of the DCT block C quite complex.
- One way to find the DCT coefficients of block C is to convert blocks A and B into the spatial domain and compute block C by linearly combining all of the pixels of block 'c'. This is a cumbersome technique and requires decompressing the blocks.
- the DCT block C is obtained from DCT blocks A and B without performing inverse DCT. Since blocks 'a', 'b' and 'c' can simply be considered as matrices having elements consisting of pixel values ay, by, respectively, the matrix 'c' can be written in terms of matrices 'a' and 'b' as follows:
- Ki and K 2 are 8X8 matrices.
- Ki is given by:
- Mi and M 2 are fixed and do not depend on either matrices 'a', 'b', or 'c'.
- FIG. 4a and Figure 4b show the matrices Mi and M 2 respectively. Looking at these matrices it is seen that in the odd rows the 1st, 3rd, 5th and 7th elements of M] are the same as that of M 2 , and the 2nd, 4th, 6th and 8th elements of Mi are the negative of M 2 . In the even rows the converse is true. Therefore Mi and M 2 can be written as follows:
- equation 11 Since matrix Com contains only the common elements it has less than 32 non-zero elements. Similarly the matrix Dif contains only 32 non-zero entries. Computing C using equation 11 instead of equation 8 saves on computation since although equation 8 requires two matrix multiplications and so does equation 11, equation 11 performs a multiplication with matrix elements that are mostly zero.
- Equation 11 therefore has provided the DCT coefficients of the DCT transform of block c without having to convert blocks A and B back into the pixel domain.
- this block must be "smoothed" to remove the step edge that exists in the middle of the block in the spatial domain.
- an analysis was performed to see how the coefficients in block C change when the block 'c' in the spatial domain is changed from having a step edge to one which exhibits a ramp type edge.
- Figure 6a shows a pixel matrix 'c' which has a step edge at columns 4 and 5.
- Figure 6b shows a matrix newc that contains a linear interpolation of the values of pixel matrix c in Figure 6a. This newc is the smoothed block in the pixel domain that exhibits a ramp type edge across the block.
- the first column contains the pixel values ay of block 'a' and the last column contains the pixel values by of block 'b'.
- the pixel values in columns 2-7 vary in accordance with a linear interpolation from left to right. As can be seen from Figure 6b there is no longer a step edge between columns 4 and 5. Obviously a linear interpolation is not the only method of removing this step edge but it is the one chosen here for ease of description.
- the DCT of newc is NEWC as shown in Figure 7c.
- the DCT of * c' is C as shown in Fig. 7a.
- Formula 12 requires the spatial domain values ⁇ , j and i ⁇ however these are easily obtained from the coefficients of A and B without conversion into the spatial domain.
- Figures 9A and 9B show the blocks A and B (the DCT transforms of blocks 'a' and 'b' shown in Fig lb). DCT blocks A and B have only one non-zero coefficient which when divided by 8 yields the pixel values 9 and - of their respective spatial domain blocks 'a' and 'b', e.g.
- NEWC-C ⁇ AM ⁇ + ⁇ BM 2
- a system that uses the method and/or device of the current invention is shown in Fig. 14.
- a variable length decoder 10 decodes the incoming video stream and inverse quantizer 20 computes the DCT blocks that have the blocking artifacts.
- the blocking artifact removal system 30 removes the blocking artifacts from the DCT blocks and provides the DCT blocks for display or storage.
- a first method of reducing the blocking artifacts when the blocks do not contain uniform pixels is to reduce the high frequency components in block C which are the result of the block boundary.
- Smoothing can be obtained by setting the large high-frequency coefficient values in block C to zero or reducing their values. Once this modification to C has been performed the change to C is translated into a change in blocks A and B as described above. This method can be used for uniform pixel blocks but a more accurate result for uniform blocks is obtained from the method above which uses linear interpolation.
- block C is smoothed by changing the individual coefficient values in C to zero if their corresponding value in block A and B are also zero.
- the reason this provides smoothing is that it assumes that blocks A and B belong to the same image region and therefore the frequency characteristics of A and B should be similar to each other. Since block C also belongs to the same image region, the frequency characteristics of block C should be similar to the frequency characteristics of blocks A and B. However, since there is a boundary introduced into block C there will be some high frequency characteristics of block C which represent the boundary and these will not be found in blocks A and B and therefore should be set to zero. Accordingly the high frequency components that are zero in both A and B are set to zero in block C.
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- Engineering & Computer Science (AREA)
- Multimedia (AREA)
- Signal Processing (AREA)
- Compression Or Coding Systems Of Tv Signals (AREA)
- Compression Of Band Width Or Redundancy In Fax (AREA)
- Image Processing (AREA)
- Compression, Expansion, Code Conversion, And Decoders (AREA)
Abstract
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Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
KR1020017009617A KR20010101882A (en) | 1999-11-30 | 2000-11-10 | Blocking artifact reduction in the DCT domain |
JP2001541255A JP2003516054A (en) | 1999-11-30 | 2000-11-10 | Method and apparatus for reducing blocking artifacts in DCT domain |
EP00981258A EP1157558A1 (en) | 1999-11-30 | 2000-11-10 | Blocking artifact reduction in the dct domain |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
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US45127799A | 1999-11-30 | 1999-11-30 | |
US09/451,277 | 1999-11-30 |
Publications (1)
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WO2001041453A1 true WO2001041453A1 (en) | 2001-06-07 |
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PCT/EP2000/011295 WO2001041453A1 (en) | 1999-11-30 | 2000-11-10 | Blocking artifact reduction in the dct domain |
Country Status (5)
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EP (1) | EP1157558A1 (en) |
JP (1) | JP2003516054A (en) |
KR (1) | KR20010101882A (en) |
CN (1) | CN1191717C (en) |
WO (1) | WO2001041453A1 (en) |
Families Citing this family (4)
Publication number | Priority date | Publication date | Assignee | Title |
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KR100561462B1 (en) * | 2003-07-09 | 2006-03-16 | 삼성전자주식회사 | Image processing method and apparatus in image forming system |
CA2674164A1 (en) * | 2006-12-28 | 2008-07-17 | Thomson Licensing | Detecting block artifacts in coded images and video |
CN105279742B (en) * | 2015-11-19 | 2018-03-30 | 中国人民解放军国防科学技术大学 | A kind of image de-noising method quickly based on piecemeal estimation of noise energy |
CN105279743B (en) * | 2015-11-19 | 2018-03-30 | 中国人民解放军国防科学技术大学 | A kind of picture noise level estimation method based on multistage DCT coefficient |
Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5787204A (en) * | 1991-01-10 | 1998-07-28 | Olympus Optical Co., Ltd. | Image signal decoding device capable of removing block distortion with simple structure |
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2000
- 2000-11-10 KR KR1020017009617A patent/KR20010101882A/en not_active Application Discontinuation
- 2000-11-10 WO PCT/EP2000/011295 patent/WO2001041453A1/en active Application Filing
- 2000-11-10 CN CNB008031673A patent/CN1191717C/en not_active Expired - Fee Related
- 2000-11-10 EP EP00981258A patent/EP1157558A1/en not_active Withdrawn
- 2000-11-10 JP JP2001541255A patent/JP2003516054A/en active Pending
Patent Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5787204A (en) * | 1991-01-10 | 1998-07-28 | Olympus Optical Co., Ltd. | Image signal decoding device capable of removing block distortion with simple structure |
Non-Patent Citations (6)
Title |
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JEON B ET AL: "BLOCKING ARTIFACTS REDUCTION IN IMAGE COMPRESSION WITH BLOCK BOUNDARY DISCONTINUITY CRITERION", IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS FOR VIDEO TECHNOLOGY,US,IEEE INC. NEW YORK, vol. 8, no. 3, 1 June 1998 (1998-06-01), pages 345 - 357, XP000767704, ISSN: 1051-8215 * |
KWAK H Y ET AL: "PROJECTION-BASED EIGENVECTOR DECOMPOSITION FOR REDUCTION OF BLOCKING ARTIFACTS OF DCT CODED IMAGE", PROCEEDINGS OF THE INTERNATIONAL CONFERENCE ON IMAGE PROCESSING. (ICIP),US,LOS ALAMITOS, IEEE COMP. SOC. PRESS, 23 October 1995 (1995-10-23), pages 527 - 530, XP000624022, ISBN: 0-7803-3122-2 * |
PAEK H ET AL: "ON THE POCS-BASED POSTPROCESSING TECHNIQUE TO REDUCE THE BLOCKING ARTIFACTS IN TRANSFORM CODED IMAGES", IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS FOR VIDEO TECHNOLOGY,US,IEEE INC. NEW YORK, vol. 8, no. 3, 1 June 1998 (1998-06-01), pages 358 - 367, XP000767705, ISSN: 1051-8215 * |
TIEN C -N ET AL: "TRANSFORM-DOMAIN POSTPROCESSING OF DCT-CODED IMAGES", SPIE VISUAL COMMUNICATIONS AND IMAGE PROCESSING, vol. 2094, no. PART 03, 8 November 1993 (1993-11-08), pages 1627 - 1638, XP002057987 * |
WEIDONG KOU ET AL: "A DIRECT COMPUTATION OF DCT COEFFICIENTS FOR A SIGNAL BLOCK TAKEN FROM TWO ADJACENT BLOCKS", IEEE TRANSACTIONS ON SIGNAL PROCESSING,US,IEEE, INC. NEW YORK, vol. 39, no. 7, 1 July 1991 (1991-07-01), pages 1692 - 1695, XP000240169, ISSN: 1053-587X * |
WING-KUEN LING ET AL: "A novel method for blocking effect reduction in DCT-coded images", ISCAS'99. PROCEEDINGS OF THE 1999 IEEE INTERNATIONAL SYMPOSIUM ON CIRCUITS AND SYSTEMS VLSI (CAT. NO.99CH36349), ISCAS'99. PROCEEDINGS OF THE 1999 IEEE INTERNATIONAL SYMPOSIUM ON CIRCUITS AND SYSTEMS. VLSI, ORLANDO, FL, USA, 30 MAY-2 JUNE 1999, 1999, Piscataway, NJ, USA, IEEE, USA, pages 46 - 49 vol.4, XP002161834, ISBN: 0-7803-5471-0 * |
Also Published As
Publication number | Publication date |
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EP1157558A1 (en) | 2001-11-28 |
CN1338182A (en) | 2002-02-27 |
KR20010101882A (en) | 2001-11-15 |
JP2003516054A (en) | 2003-05-07 |
CN1191717C (en) | 2005-03-02 |
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