WO2011125729A1 - 画像処理装置と画像処理方法 - Google Patents
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T5/00—Image enhancement or restoration
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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
- H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
- H04N19/102—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
- H04N19/117—Filters, e.g. for pre-processing or post-processing
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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
- H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
- H04N19/134—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or criterion affecting or controlling the adaptive coding
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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
- H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
- H04N19/169—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
- H04N19/17—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object
- H04N19/176—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object the region being a block, e.g. a macroblock
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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
- H04N19/80—Details of filtering operations specially adapted for video compression, e.g. for pixel interpolation
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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 present invention relates to an image processing apparatus and an image processing method. Specifically, a decoded image of good image quality is obtained.
- devices that handle image information as digital and perform efficient transmission and storage of information at that time for example, devices conforming to a method such as MPEG that performs compression by orthogonal transformation such as discrete cosine transformation and motion compensation are broadcast stations And it is getting popular in general homes.
- MPEG2 ISO / IEC 13818-2
- MPEG2 ISO / IEC 13818-2
- MPEG2 compression method for example, in the case of an interlace scan image of standard resolution having 720 ⁇ 480 pixels, it is possible to realize good image quality by allocating a 4 to 8 Mbps code amount (bit rate). Further, in the case of a high resolution interlaced scanning image having 1920 ⁇ 10 88 pixels, it is possible to realize good image quality by allocating a code amount (bit rate) of 18 to 22 Mbps.
- MPEG2 was mainly intended for high-quality coding suitable for broadcasting, it did not correspond to a coding amount (bit rate) lower than that of MPEG1, that is, a coding method with a higher compression rate.
- bit rate bit rate
- MPEG4 coding amount
- image coding method that standard was approved as an international standard as ISO / IEC 14496-2 in December 1998.
- H.26L ITU-T Q6 / 16 VCEG
- H.264 ISO-T Q6 / 16 VCEG
- FRExt including RGB, 4: 2: 2, 4: 4: 4, etc., necessary coding tools necessary for business use, and 8 ⁇ 8 DCT and quantization matrix defined in MPEG2 Standardization of Fidelity Range Extension was completed in February 2005.
- H.264 / AVC system has become a coding system capable of well representing film noise included in a movie, and has been used for a wide range of applications such as Blu-Ray (trademark).
- encoding of image data is performed in block units. Further, in decoding of encoded data, as shown in, for example, Patent Document 1, performing block processing on the basis of block boundary strength and a quantization parameter is performed to suppress block distortion.
- Non-Patent Document 1 the macroblock size is set to MPEG2, H.264, H.264, and so forth. It has been proposed to make the size larger than H.264 / AVC, for example, 32 pixels ⁇ 32 pixels. That is, according to Non-Patent Document 1, H.264 and H.264 are applied to 16 ⁇ 16 pixel blocks and below by adopting a hierarchical structure for macroblocks. It is compatible with macroblocks in H.264 / AVC, and larger blocks are defined as its superset.
- block distortion becomes large especially at a low bit rate. For this reason, when block distortion is removed by the conventional deblocking filter, block distortion may not be sufficiently removed and image quality may be degraded.
- a decoding unit that decodes a coded stream in which image data is coded block by block to generate decoded image data, and decoded image data generated by the decoding unit.
- an image processing apparatus including: a filter that performs filtering processing for removing block distortion;
- the filter strength in the filter processing is adjusted according to a filter that performs filtering processing for removing block distortion from decoded image data and a block size of an adjacent block adjacent to a block boundary.
- an image processing apparatus including: a filter strength adjustment unit; and an encoding unit that encodes image data using decoded image data that has been subjected to filter processing by the filter.
- Filter processing to remove block distortion from decoded image data obtained by performing inverse quantization of inverse quantization and data after inverse quantization of quantized data obtained by performing decoding To be done.
- the filter strength is adjusted so that the filtering process is more likely to be performed as the block size is larger.
- parameter values for adjusting the filter strength are set according to the block size.
- the filter strength is adjusted according to the larger block size.
- the values of syntax elements of the encoding standard are adjusted.
- H The filter strength is adjusted by adjusting the values of FilterOffsetA and FilterOffsetB specified by slice_alpha_c0_offset_div2 and slice_beta_offset_div2 which are syntax elements of the H.264 / AVC standard.
- the value of deblocking_filter_control_present_flag of the picture parameter set which is a syntax element is set to a predetermined value, for example, “1”, and FilterOffsetA and FilterOffsetB in the slice header. Describes the value of.
- a method of decoding an encoded stream in which image data is encoded for each block to generate decoded image data, and for the decoded image data generated by the decoding unit comprising the steps of: filtering for removing distortion; and adjusting the filter strength in the filtering according to the block size of the adjacent block adjacent to the block boundary.
- an image processing method comprising: a step of encoding image data using the decoded image data subjected to filter processing by the filter.
- the filter strength is adjusted in accordance with the block size of the adjacent block adjacent at the block boundary. For this reason, even if a macro block having an expanded size is used, it is possible to obtain a high quality decoded image with reduced block distortion by adjusting the filter strength according to the block size.
- the image processing apparatus is applied to an image coding apparatus that codes image data for each block, an image decoding apparatus that decodes a coded stream in which image data is coded for each block, and the like.
- the case where it is possible and it applies to an image coding apparatus and the case where it applies to an image decoding apparatus is demonstrated in the following order.
- Configuration of image coding apparatus About filtering process of deblocking filter 3.
- Configuration of deblocking filter and filter strength adjustment unit in image coding apparatus Operation of image coding device 5.
- FIG. 1 shows the configuration of the image coding apparatus.
- the image coding apparatus 10 includes an analog / digital conversion unit (A / D conversion unit) 11, a screen rearrangement buffer 12, a subtraction unit 13, an orthogonal conversion unit 14, a quantization unit 15, a lossless encoding unit 16, and an accumulation buffer 17. , Rate control unit 18. Furthermore, the image coding apparatus 10 includes an inverse quantization unit 21, an inverse orthogonal transformation unit 22, an addition unit 23, a deblocking filter 24, a frame memory 25, a selector 26, an intra prediction unit 31, a motion prediction / compensation unit 32, a prediction. An image / optimum mode selection unit 33 is provided.
- the A / D conversion unit 11 converts an analog image signal into digital image data and outputs the digital image data to the screen rearrangement buffer 12.
- the screen rearrangement buffer 12 rearranges frames of the image data output from the A / D converter 11.
- the screen rearrangement buffer 12 rearranges the frames according to the GOP (Group of Pictures) structure related to the encoding process, and the image data after the rearrangement is subjected to the subtraction unit 13, the intra prediction unit 31, and the motion prediction / compensation unit Output to 32.
- GOP Group of Pictures
- the subtraction unit 13 is supplied with the image data output from the screen rearrangement buffer 12 and the prediction image data selected by the prediction image / optimum mode selection unit 33 described later.
- the subtraction unit 13 calculates prediction error data, which is the difference between the image data output from the screen rearrangement buffer 12 and the prediction image data supplied from the prediction image / optimum mode selection unit 33, to the orthogonal transformation unit 14. Output.
- the orthogonal transformation unit 14 performs orthogonal transformation processing such as discrete cosine transformation (DCT; Discrete Cosine Transform), Karhunen-Loeve transformation, or the like on the prediction error data output from the subtraction unit 13.
- the orthogonal transform unit 14 outputs transform coefficient data obtained by performing orthogonal transform processing to the quantization unit 15.
- the quantization unit 15 is supplied with the transform coefficient data output from the orthogonal transformation unit 14 and a rate control signal from a rate control unit 18 described later.
- the quantization unit 15 quantizes the transform coefficient data, and outputs the quantized data to the lossless encoding unit 16 and the inverse quantization unit 21. Further, the quantization unit 15 switches the quantization parameter (quantization scale) based on the rate control signal from the rate control unit 18 to change the bit rate of the quantization data.
- the lossless encoding unit 16 receives the quantization data output from the quantization unit 15, and prediction mode information from the intra prediction unit 31, the motion prediction / compensation unit 32, and the prediction image / optimum mode selection unit 33 described later. Ru.
- the prediction mode information includes, for example, a macroblock type capable of identifying a prediction block size, a prediction mode, motion vector information, reference picture information and the like according to intra prediction or inter prediction.
- the lossless encoding unit 16 performs lossless encoding processing on the quantized data by, for example, variable-length encoding or arithmetic encoding, and generates an encoded stream and outputs the encoded stream to the accumulation buffer 17. Also, the lossless encoding unit 16 losslessly encodes the prediction mode information and adds it to the header information of the encoded stream.
- the accumulation buffer 17 accumulates the coded stream from the lossless coding unit 16. Further, the accumulation buffer 17 outputs the accumulated encoded stream at a transmission rate according to the transmission path.
- the rate control unit 18 monitors the free space of the accumulation buffer 17, generates a rate control signal according to the free space, and outputs the rate control signal to the quantization unit 15.
- the rate control unit 18 acquires, for example, information indicating the free space from the accumulation buffer 17.
- the rate control unit 18 reduces the bit rate of the quantized data by the rate control signal when the free space is reduced. Further, when the free space of the accumulation buffer 17 is sufficiently large, the rate control unit 18 increases the bit rate of the quantized data by the rate control signal.
- the inverse quantization unit 21 performs inverse quantization processing of the quantized data supplied from the quantization unit 15.
- the inverse quantization unit 21 outputs transform coefficient data obtained by performing the inverse quantization process to the inverse orthogonal transform unit 22.
- the inverse orthogonal transformation unit 22 outputs data obtained by performing inverse orthogonal transformation processing of the transform coefficient data supplied from the inverse quantization unit 21 to the addition unit 23.
- the addition unit 23 adds the data supplied from the inverse orthogonal transformation unit 22 and the predicted image data supplied from the predicted image / optimum mode selection unit 33 to generate decoded image data, and the deblocking filter 24 and the frame memory Output to 25
- the deblocking filter 24 performs a filtering process to reduce block distortion that occurs during image coding.
- the deblocking filter 24 performs filter processing for removing block distortion from the decoded image data supplied from the addition unit 23, and outputs the decoded image data after filter processing to the frame memory 25.
- the deblocking filter 24 adjusts the filter strength based on the parameter value supplied from the filter strength adjustment unit 41 described later.
- the frame memory 25 holds the decoded image data supplied from the adding unit 23 and the decoded image data after filter processing supplied from the deblocking filter 24.
- the selector 26 supplies the decoded image data before the filtering process read out from the frame memory 25 to perform the intra prediction to the intra prediction unit 31. Further, the selector 26 supplies the decoded image data after filter processing read from the frame memory 25 to the motion prediction / compensation unit 32 in order to perform inter prediction.
- the intra prediction unit 31 uses the image data of the image to be encoded output from the screen rearrangement buffer 12 and the decoded image data before filter processing read from the frame memory 25 to generate the intra for all candidate intra prediction modes. Perform prediction processing. Furthermore, the intra prediction unit 31 calculates a cost function value for each intra prediction mode, and optimizes the intra prediction mode in which the calculated cost function value is the smallest, that is, the intra prediction mode in which the coding efficiency is the best. Select as intra prediction mode. The intra prediction unit 31 outputs predicted image data generated in the optimal intra prediction mode, prediction mode information on the optimal intra prediction mode, and a cost function value in the optimal intra prediction mode to the predicted image / optimum mode selection unit 33. Further, as described later, the intra prediction unit 31 obtains prediction code information on the intra prediction mode in the lossless encoding unit 16 in the intra prediction process of each intra prediction mode in order to obtain the generated code amount used for calculating the cost function value. Output.
- the motion prediction / compensation unit 32 performs motion prediction / compensation processing on all prediction block sizes corresponding to the macro block.
- the motion prediction / compensation unit 32 uses the decoded image data after filter processing read from the frame memory 25 for each image of each prediction block size in the encoding target image read from the screen rearrangement buffer 12. Detect motion vectors. Furthermore, the motion prediction / compensation unit 32 performs motion compensation processing on the decoded image based on the detected motion vector to generate a predicted image. Also, the motion prediction / compensation unit 32 calculates a cost function value for each prediction block size, and calculates a prediction block size that minimizes the calculated cost function value, that is, a prediction block size that achieves the best coding efficiency. , Select as the optimal inter prediction mode.
- the motion prediction / compensation unit 32 outputs predicted image data generated in the optimal inter prediction mode, prediction mode information on the optimal inter prediction mode, and a cost function value in the optimal inter prediction mode to the predicted image / optimum mode selection unit 33. Do. Also, the motion prediction / compensation unit 32 outputs prediction mode information related to the inter prediction mode to the lossless encoding unit 16 in the inter prediction processing with each prediction block size, in order to obtain the generated code amount used for calculating the cost function value. Do. The motion prediction / compensation unit 32 also performs prediction in skipped macroblocks or direct mode as the inter prediction mode.
- the predicted image / optimum mode selection unit 33 compares the cost function value supplied from the intra prediction unit 31 with the cost function value supplied from the motion prediction / compensation unit 32 in units of macroblocks, and the cost function value is smaller. Is selected as the optimal mode in which the coding efficiency is the best. Further, the predicted image / optimum mode selection unit 33 outputs the predicted image data generated in the optimum mode to the subtraction unit 13 and the addition unit 23. Further, the predicted image / optimum mode selection unit 33 outputs the prediction mode information of the optimum mode to the lossless encoding unit 16 and the filter strength adjustment unit 41. The predicted image / optimum mode selection unit 33 performs intra prediction or inter prediction on a slice basis.
- the filter strength adjustment unit 41 sets a parameter value for adjusting the filter strength in accordance with the prediction block size indicated by the prediction mode information of the optimum mode, and outputs the parameter value to the deblocking filter 24.
- deblocking filter filtering In the filtering process of the deblocking filter, H264.
- deblocking_filter_control_present_flag of Picture Parameter Set RBSP included in image compression information and disable_deblocking_filter_idc included in Slice Header are used. It is possible to specify three ways: (a) applied to block boundaries and macroblock boundaries, (b) applied only to Macroblock boundaries, and (c) not applied.
- QP when applying the following processing to luminance data, QPY is used, and when applying to chrominance data, QPC is used. Also, in motion vector coding, intra prediction, and entropy coding (CAVLC / CABAC), pixel values belonging to different slices are processed as “not available”. Furthermore, in the filtering process, even when pixel values belonging to different slices belong to the same picture, processing is performed as “available”.
- pixel data before filter processing at block boundaries are p0 to p3 and q0 to q3 as shown in FIG. 2A.
- the pixel data after processing is p0 'to p3' and q0 'to q3'.
- block boundary strength data Bs (Boundary Strength) is defined for the pixels p and q in FIG.
- the block boundary strength data Bs belongs to the macro block MB in which either the pixel p or the pixel q is intra-coded and the pixel is located at the boundary of the macro block MB. , "4" with the highest filter strength is assigned.
- the block boundary strength data Bs is next to “4” when the pixel p or the pixel q belongs to the macroblock MB to be intra-coded and the pixel is not located at the boundary of the macroblock MB.
- a high filter strength "3" is assigned.
- the block boundary strength data Bs does not belong to the macro block MB in which both the pixel p and the pixel q are intra-coded, and when any pixel has a transform coefficient, the filter following “3” A high strength "2" is assigned.
- the block boundary strength data Bs does not belong to the macroblock MB in which both the pixel p and the pixel q are intra-coded, and satisfies the condition that one of the pixels has no transform coefficient, and “1” is assigned when either the reference frame is different, the number of reference frames is different, or the motion vector is different.
- the block boundary strength data Bs does not belong to the macroblock MB in which both the pixels p and q are intra-coded, and both pixels do not have transform coefficients, and the filter processing is performed when the reference frame and motion vector are the same. "0" is assigned, which means not to perform.
- the threshold values ⁇ and ⁇ which are parameter values for adjusting the filter strength, that is, the ease of application of the filter, are determined by default according to the quantization parameter QP as follows.
- the user can adjust the strength by two parameters of slice_alpha_c0_offset_div2 and slice_beta_offset_div2 included in Slice Header in the image compression information.
- FIG. 3 shows the relationship between the quantization parameter QP and the threshold value ⁇ . When an offset amount is added to the quantization parameter QP, the curve showing the relationship between the quantization parameter QP and the threshold value ⁇ moves in the direction of the arrow. From the above, it is clear to adjust the filter strength.
- index A and index B are calculated from the equations (2) to (4) using the quantization parameters qPp and qPq of the adjacent block P and block Q, respectively, and the thresholds ⁇ and ⁇ are determined from the table shown in Table 2.
- qPav (qPp + qPq + 1) >> 1
- indexA Clip3 (0, 51, qPav + FilterOffsetA)
- index B Clip 3 (0, 51, qPav + FilterOffset B) (4)
- the deblocking filter performs operations shown in equations (5) to (7) to calculate pixel data p0 ′ and q0 ′ after filter processing.
- Clip3 indicates clipping processing.
- p0 ′ Clip 1 (p 0 + ⁇ ) (5)
- q0 ' Clip1 (q0 + ⁇ ) (6)
- ⁇ Clip 3 ( ⁇ tc, tc ((((q0 ⁇ p0) ⁇ 2) + (p1 ⁇ q1) +4) >> 3)) (7))
- the deblocking filter calculates “tc” in the equation (7) based on the equation (8) when the chromaEdgeFlag indicates “0”, and calculates based on the equation (9) otherwise.
- (10) aq
- the deblocking filter calculates the pixel data p1 ′ after filter processing by performing the operation shown in equation (12) when chromaEdgeFlag is “0” and ap is “ ⁇ ” or less, and other than that In this case, it is acquired by equation (13).
- p1 ' p1 + Clip3 (-tc0, tc0, (p2 + ((p0 + q0 + 1) >> 1)-(p1 ⁇ 1)) >> 1) (12)
- p1 ' p1 (13)
- the deblocking filter calculates the pixel data q1 ′ after filter processing by performing the operation shown in equation (14) when the chromaEdgeFlag is “0” and aq is “ ⁇ ” or less, and other than that In this case, it is acquired by equation (15).
- q1 ' q1 + Clip3 (-tc0, tc0, (q2 + ((p0 + q0 + 1) >> 1)-(q1 ⁇ 1)) >> 1) (14)
- q1 ' q1 (15)
- the deblocking filter calculates pixel data p0 ′, p1 ′, p2 ′ according to equations (17) to (19) when the chromaEdgeFlag indicates “0” and the condition of equation (16) is satisfied.
- the deblocking filter calculates pixel data q0 ′, q1 ′, q2 ′ according to equations (24) to (26) when the chromaEdgeFlag indicates “0” and the condition of equation (23) is satisfied.
- q0 ' (p1 + 2 ⁇ p 0 + 2 ⁇ q 0 + 2 + q 2 + 4)
- q1 ′ (p0 + q0 + q1 + q2 + 2) >> 2 (25)
- q2 ' (2 * q3 + 3 * q2 + q1 + q0 + p4 + 4) >> 3 (26)
- the deblocking filter calculates pixel data q0 ′, q1 ′, q2 ′ according to equations (27) to (29) when chromaEdgeFlag indicates “0” and the condition of equation (23) is not satisfied. .
- q0 ' (2 * q1 + q0 + p1 + 2) >> 2
- q1 ' q1
- q2 ' q2
- the filter strength adjustment unit 41 adjusts the filter strength in the deblocking filter 24 according to the prediction block size in the optimum mode in the macroblock.
- block distortion is more noticeable to human eyes when the block size is larger. Also, larger block sizes are more likely to be selected for flat areas that do not contain much texture information.
- the filtering process of the deblocking filter is a low-pass filter process, and thus the sharpness of the image is lost.
- the filter strength adjustment unit 41 adjusts the filter strength in the deblocking filter 24 by setting parameter values for adjusting the filter strength in accordance with the prediction block size.
- the filter strength adjustment unit 41 adjusts the filter strength in accordance with the larger prediction block size when the prediction block size in the optimum mode is the expanded block size in either the relevant block or the adjacent block. .
- the filter strength adjustment unit 41 sets prediction block sizes of two adjacent blocks so that the filter strength becomes stronger as the block size is larger. Adjust the filter strength according to the combination of
- FIG. 4 shows the configuration of the deblocking filter and the filter strength adjustment unit.
- the filter strength adjustment unit 41 includes a block size buffer 411 and a parameter selection unit 412.
- the block size buffer 411 accumulates information indicating the predicted block size in the optimum mode selected by the predicted image / optimum mode selection unit 33 for one frame image. That is, in the block size buffer 411, information regarding the predicted block size of each macro block in the one frame image to be encoded is stored.
- the parameter selection unit 412 sets a parameter value based on the information of the predicted block size of the block size buffer 411 so that filtering processing is likely to be applied to the decoded image portion of a larger block size.
- the parameter selection unit 412 is, for example, H.264.
- the values of FilterOffsetA and FilterOffsetB specified by slice_alpha_c0_offset_div2 and slice_beta_offset_div2 which are syntax elements of the H.264 / AVC standard are set to larger values.
- the parameter selection unit 412 sets FilterOffsetA and FilterOffsetB in advance according to the combination of adjacent prediction block sizes, and determines which prediction block size is the adjacent block based on information of the prediction block size. Do. Furthermore, a value corresponding to the combination of the determined prediction block sizes is used.
- parameter selection unit 412 calculates index A and index B from the above equations (2) to (4), and uses the table shown in Table 2 to set threshold values ⁇ and ⁇ which are parameter values for setting the filter strength. It is set according to the predicted block size, and is output to the filter strength determination unit 241 of the deblocking filter 24.
- the filter strength determination unit 241 determines the block boundary strength data Bs based on the prediction mode information supplied from the lossless encoding unit 16 and determines the determined block boundary strength data Bs and the threshold value ⁇ supplied from the parameter selection unit 412. And ⁇ are output to the filter processing unit 242.
- the filter processing unit 242 performs the above-described filter operation using the block boundary strength data Bs, the threshold values ⁇ and ⁇ , and the pixel data p3, p2, p1, p0, q0, q1, and q3 of the block boundary portion, and performs filter processing
- the subsequent pixel data p3 ', p2', p1 ', p0', q0 ', q1', q2 ', q3' are calculated.
- FIG. 5 shows predicted block sizes used in the image coding process.
- H. In the H.264 / AVC system, as shown in (C) and (D) of FIG. 5, predicted block sizes of 16 ⁇ 16 pixels to 4 ⁇ 4 pixels are defined.
- H. In the case of using a macro block of a size expanded than the H.264 / AVC system, for example, in the case of using a 32 ⁇ 32 pixel macro block, a predicted block size shown in FIG. 5B is defined, for example.
- the predicted block size shown in (A) of FIG. 5 is defined.
- “Skip / direct” indicates that the motion prediction / compensation unit 32 is the predicted block size when the skipped macroblock or the direct mode is selected. Also, “ME” indicates that it is a motion compensation block size. Also, “P8 ⁇ 8” indicates that further division can be performed in the lower layer in which the size of the macro block is reduced.
- H. In order to improve coding efficiency further than H.264 / AVC, with ITU-T and JCTVC (Joint Collaboration Team-Video Coding), which is a joint standardization body of ISO / IEC, High Efficiency Video Coding (HEVC) and The standardization of the called coding scheme is in progress.
- JCTVC Joint Collaboration Team-Video Coding
- HEVC High Efficiency Video Coding
- H.264 is used. It is possible to use a macroblock of a size expanded than the H.264 / AVC system, and a CU (Coding Unit) is defined.
- the CU is also referred to as a CTB (Coding Tree Block), and the H. It plays the same role as a macroblock in the H.264 / AVC system.
- the macroblock In the H.264 / AVC system, the macroblock is fixed at a size of 16 ⁇ 16 pixels, whereas the HEVC coding system is not fixed in size, and in each sequence, in the image compression information It will be specified.
- LCU Large Coding Unit
- SCU Smallest Coding Unit
- FIG. 6 shows an example of a CU defined in the HEVC coding scheme.
- the size of the LCU is 128, and the maximum hierarchical depth is 5.
- split_flag is 1, a 2N ⁇ 2N sized CU is divided into an N ⁇ N sized CU, which is one level lower.
- CU is divided into PU (Prediction Unit) which is a unit of intra or inter prediction, and is divided into TU (Transform Unit) which is a unit of orthogonal transformation.
- PU Prediction Unit
- TU Transform Unit
- the CU is further divided into PUs, which are units of intra or inter prediction, and divided into TUs, which are units of orthogonal transformation, and prediction processing and orthogonal transformation processing are performed.
- PUs which are units of intra or inter prediction
- TUs which are units of orthogonal transformation
- prediction processing and orthogonal transformation processing are performed.
- 16 ⁇ 16 and 32 ⁇ 32 orthogonal transformations in addition to 4 ⁇ 4 and 8 ⁇ 8.
- blocks and macroblocks include the concepts of CUs, PUs, and TUs as described above, and are not limited to blocks of fixed sizes.
- FIG. 7 is a flowchart showing the image coding processing operation.
- the A / D conversion unit 11 A / D converts the input image signal.
- step ST12 the screen rearrangement buffer 12 performs image rearrangement.
- the screen rearrangement buffer 12 stores the image data supplied from the A / D converter 11, and performs rearrangement from the display order of each picture to the coding order.
- step ST13 the subtraction unit 13 generates prediction error data.
- the subtraction unit 13 generates a prediction error data by calculating the difference between the image data of the image rearranged in step ST12 and the prediction image data selected by the prediction image / optimum mode selection unit 33.
- the prediction error data has a smaller amount of data than the original image data. Therefore, the amount of data can be compressed as compared to the case of encoding the image as it is.
- the orthogonal transformation unit 14 performs orthogonal transformation processing.
- the orthogonal transformation unit 14 orthogonally transforms the prediction error data supplied from the subtraction unit 13. Specifically, orthogonal transformation such as discrete cosine transformation and Karhunen-Loeve transformation is performed on the prediction error data to output transformation coefficient data.
- step ST15 the quantization unit 15 performs quantization processing.
- the quantization unit 15 quantizes transform coefficient data.
- rate control is performed as described in the process of step ST25 described later.
- step ST16 the inverse quantization unit 21 performs inverse quantization processing.
- the inverse quantization unit 21 inversely quantizes the transform coefficient data quantized by the quantization unit 15 with a characteristic corresponding to the characteristic of the quantization unit 15.
- the inverse orthogonal transform unit 22 performs inverse orthogonal transform processing.
- the inverse orthogonal transformation unit 22 inversely orthogonally transforms the transform coefficient data inversely quantized by the inverse quantization unit 21 with the characteristic corresponding to the characteristic of the orthogonal transformation unit 14.
- step ST18 the addition unit 23 generates decoded image data.
- the addition unit 23 adds the predicted image data supplied from the predicted image / optimum mode selection unit 33 and the data after inverse orthogonal transformation of the position corresponding to the predicted image to generate decoded image data.
- step ST19 the deblocking filter 24 performs filter processing.
- the deblocking filter 24 filters the decoded image data output from the adding unit 23 to remove block distortion.
- step ST20 the frame memory 25 stores the decoded image data.
- the frame memory 25 stores the decoded image data before the filtering process and the decoded image data after the filtering process.
- step ST21 the intra prediction unit 31 and the motion prediction / compensation unit 32 perform prediction processing. That is, the intra prediction unit 31 performs intra prediction processing in the intra prediction mode, and the motion prediction / compensation unit 32 performs motion prediction / compensation processing in the inter prediction mode.
- this process performs prediction processes in all candidate prediction modes, and the cost function values in all candidate prediction modes are respectively It is calculated. Then, based on the calculated cost function value, the optimal intra prediction mode and the optimal inter prediction mode are selected, and the predicted image generated in the selected prediction mode and its cost function and prediction mode information are predicted image / optimum mode The selection unit 33 is supplied.
- the prediction image / optimum mode selection unit 33 selects prediction image data. Based on the cost function values output from the intra prediction unit 31 and the motion prediction / compensation unit 32, the predicted image / optimum mode selection unit 33 determines the optimal mode with the best coding efficiency. Further, the prediction image / optimum mode selection unit 33 selects prediction image data of the determined optimum mode and supplies the selected prediction image data to the subtraction unit 13 and the addition unit 23. This predicted image is used for the calculation of steps ST13 and ST18 as described above. The prediction mode information corresponding to the selected prediction image data is output to the lossless encoding unit 16 and the filter strength adjustment unit 41.
- the lossless encoding unit 16 performs lossless encoding processing.
- the lossless encoding unit 16 losslessly encodes the quantized data output from the quantization unit 15. That is, lossless coding such as variable-length coding or arithmetic coding is performed on the quantized data to perform data compression.
- prediction mode information for example, including macroblock type, prediction mode, motion vector information, reference picture information, and the like
- the lossless encoded data of the prediction mode information is added to the header information of the encoded stream generated by the lossless encoding of the quantized data.
- step ST24 the accumulation buffer 17 performs accumulation processing to accumulate a coded stream.
- the encoded stream stored in the storage buffer 17 is appropriately read and transmitted to the decoding side through the transmission path.
- step ST25 the rate control unit 18 performs rate control.
- the rate control unit 18 controls the rate of the quantization operation of the quantization unit 15 so that overflow or underflow does not occur in the accumulation buffer 17 when the accumulation buffer 17 accumulates the encoded stream.
- step ST21 of FIG. 7 will be described with reference to the flowchart of FIG.
- the intra prediction unit 31 performs an intra prediction process.
- the intra prediction unit 31 performs intra prediction on the image of the block to be processed in all candidate intra prediction modes.
- the decoded image data stored in the frame memory 25 without being subjected to the filtering process by the deblocking filter 24 is used as the image data of the decoded image referred to in intra prediction.
- this process performs intra prediction in all candidate intra prediction modes, and calculates cost function values for all candidate intra prediction modes. Then, based on the calculated cost function value, one intra prediction mode with the best coding efficiency is selected from all the intra prediction modes.
- step ST32 the motion prediction / compensation unit 32 performs inter prediction processing.
- the motion prediction / compensation unit 32 performs inter prediction processing of all candidate inter prediction modes (all prediction block sizes) using the decoded image data after filter processing stored in the frame memory 25.
- the prediction process is performed in all candidate inter prediction modes, and cost function values are calculated for all candidate inter prediction modes. Then, based on the calculated cost function value, one inter prediction mode with the best coding efficiency is selected from all the inter prediction modes.
- step ST41 the intra prediction unit 31 performs intra prediction in each prediction mode.
- the intra prediction unit 31 generates predicted image data for each intra prediction mode using the decoded image data before filter processing stored in the frame memory 25.
- the intra prediction unit 31 calculates cost function values for each prediction mode.
- H.1 As defined in JM (Joint Model), which is reference software in the H.264 / AVC system, this is performed based on either the High Complexity mode or the Low Complexity mode.
- ⁇ indicates the entire set of prediction modes to be candidates for encoding the block or macroblock.
- D indicates the difference energy (distortion) between the decoded image and the input image when encoding is performed in the prediction mode.
- R is a generated code amount including orthogonal transform coefficients, prediction mode information and the like, and ⁇ is a Lagrange multiplier given as a function of the quantization parameter QP.
- Cost (Mode ⁇ ) D + QPtoQuant (QP) ⁇ Header_Bit (31)
- ⁇ indicates the entire set of prediction modes to be candidates for encoding the block or macroblock.
- D indicates the difference energy (distortion) between the decoded image and the input image when encoding is performed in the prediction mode.
- Header_Bit is a header bit for the prediction mode, and QPtoQuant is a function given as a function of the quantization parameter QP.
- the intra prediction unit 31 determines the optimal intra prediction mode.
- the intra prediction unit 31 selects one intra prediction mode in which the cost function value is the minimum value among them based on the cost function value calculated in step ST42, and determines it as the optimal intra prediction mode.
- step ST32 in FIG. 8 will be described with reference to the flowchart in FIG.
- step ST51 the motion prediction / compensation unit 32 determines a motion vector and a reference image for each prediction mode. That is, the motion prediction / compensation unit 32 determines a motion vector and a reference image for the block to be processed in each prediction mode.
- step ST52 the motion prediction / compensation unit 32 performs motion compensation on each prediction mode.
- the motion prediction / compensation unit 32 performs motion compensation on the reference image for each prediction mode (each prediction block size) based on the motion vector determined in step ST51, and generates predicted image data for each prediction mode.
- the motion prediction / compensation unit 32 In step ST53, the motion prediction / compensation unit 32 generates motion vector information for each prediction mode.
- the motion prediction / compensation unit 32 generates motion vector information to be included in the coded stream for the motion vector determined in each prediction mode. For example, a prediction motion vector is determined using median prediction or the like, and motion vector information indicating the difference between the motion vector detected by motion prediction and the prediction motion vector is generated.
- the motion vector information generated in this manner is also used to calculate the cost function value in the next step ST54, and finally, when the corresponding prediction image is selected by the prediction image / optimum mode selection unit 33. Is included in the prediction mode information and output to the lossless encoding unit 16.
- step ST54 the motion prediction / compensation unit 32 calculates cost function values for each inter prediction mode.
- the motion prediction / compensation unit 32 calculates the cost function value using the equation (30) or the equation (31) described above. Note that the calculation of the cost function value for the inter prediction mode is based on H.264. The evaluation of cost function values of Skip Mode and Direct Mode defined in the H.264 / AVC system is also included.
- step ST55 the motion prediction / compensation unit 32 determines the optimal inter prediction mode.
- the motion prediction / compensation unit 32 selects one prediction mode in which the cost function value is the minimum value among them based on the cost function value calculated in step ST54, and determines it as the optimal inter prediction mode.
- deblocking_filter_control_present_flag is present in the picture parameter set.
- slice_alpha_c0_offset_div2 and slice_beta_offset_div2 are present in the slice header, and when they do not exist, "0" is used as a default value.
- the offset values SZa and SZb are, for example, integers satisfying 0 ⁇ SZa ⁇ SZb ⁇ 6 according to the combination of the sizes of two adjacent blocks, together with FilterOffsetA and FilterOffsetB as shown in Table 4 It is assumed that the value is defined as follows.
- Table 4 shows an offset for each combination of prediction block sizes of adjacent two blocks so that the filter strength becomes stronger as the block size is larger when a plurality of macroblocks having a block size larger than a predetermined macroblock are used. It shows the value. Further, the offset values in Table 4 are set to adjust the filter strength in accordance with the larger prediction block size, when the prediction block size is different between two adjacent blocks. That is, the values of FilterOffsetA and FilterOffsetB are set in accordance with the larger sized block of the two adjacent blocks. For example, when the larger block is 64 pixels, the offset value SZb is set. When the larger block is 32 pixels, the offset value SZa is set. When the larger block is 16 ⁇ 16 pixels, the offset value is “0”.
- FIG. 11 is a flowchart showing the filter setting process.
- the filter strength adjustment unit 41 acquires the prediction block size in the optimum mode.
- the filter strength adjustment unit 41 acquires the prediction block size corresponding to the prediction image selected in step ST22 of FIG. 7, that is, the prediction block size when encoding is performed in the optimal mode.
- step ST62 the filter strength adjustment unit 41 determines whether the boundary portion of the block or the adjacent block is 64 pixels. The filter strength adjustment unit 41 proceeds to step ST63 when the boundary portion of the block or the adjacent block is 64 pixels, and proceeds to step ST64 when the boundary portion of the block and the adjacent block is smaller than 64 pixels.
- step ST63 the filter strength adjustment unit 41 selects the offset value SZb, and proceeds to step ST67 as FilterOffsetA and FilterOffsetB.
- step ST64 the filter strength adjustment unit 41 determines whether the boundary portion of the block or the adjacent block is 32 pixels. The filter strength adjustment unit 41 proceeds to step ST65 when the boundary portion of the block or the adjacent block is 32 pixels, and proceeds to step ST66 when the boundary portion of the block and the adjacent block is smaller than 32 pixels.
- step ST65 the filter strength adjustment unit 41 selects the offset value SZa ( ⁇ SZb), and proceeds to step ST67 as FilterOffsetA and FilterOffsetB.
- step ST66 the filter strength adjustment unit 41 selects the offset value 0 ( ⁇ SZa), and proceeds to step ST67 as FilterOffsetA and FilterOffsetB.
- the filter strength adjustment unit 41 performs filter strength adjustment.
- the filter strength adjustment unit 41 determines threshold values ⁇ and ⁇ that are parameter values for setting the filter strength using the FilterOffsetA and FilterOffsetB set in steps ST63, 65 and 66, and outputs them to the deblocking filter 24.
- the deblocking filter 24 can easily apply the filter processing by setting the thresholds ⁇ and ⁇ by increasing the offset amount. it can.
- Table 4 and FIG. 11 illustrate combinations of 64 ⁇ 64 images, 32 ⁇ 32 pixels, and 16 ⁇ 16 pixels, the combination is not limited to these sizes.
- the offset value SZb is used when the larger block is 64 pixels, the offset value SZa when the larger block is 32 pixels, and the offset value “0” when 16 ⁇ 16 pixels are used. Is not limited to the combination described above as long as it is easy to apply a filter to a large block and obtain good image quality.
- the user when the user wants to set a value different from Table 4 independently, the user sets the value of deblocking_filter_control_present_flag in the picture parameter set to the predetermined value “1”, and the user sets FilterOffsetA16, FilterOffsetA32, FilterOffsetA64 and FilterOffsetB16, in the slice header. It is possible to set values of FilterOffsetB32 and FilterOffsetB64.
- Each parameter corresponds to the case where the larger one of two adjacent blocks is 16 ⁇ 16, 32 ⁇ 32, 64 ⁇ 64.
- the block size at which the coding efficiency is the best is determined, and the coding process of the image data is performed with the determined block size.
- the information indicating the block size is accumulated in the block size buffer 411 of the filter strength adjustment unit 41. Therefore, when decoded image data is generated by decoding image data that has been subjected to the encoding process with the block size with the highest encoding efficiency, the position of the predicted block in the decoded image becomes clear. Therefore, block distortion can be reduced even if the block size is large by adjusting the filter strength for a large block size to make it easy to apply a filter based on the information stored in the block size buffer 411. Further, since block distortion in the decoded image data can be reduced, it is possible to prevent the prediction error data from becoming large due to the influence of the block distortion, and hence the amount of data after the encoding process can be further reduced.
- An encoded stream generated by encoding an input image is supplied to an image decoding apparatus via a predetermined transmission path, a recording medium, and the like, and is decoded.
- FIG. 12 shows the configuration of the image decoding apparatus.
- the image decoding apparatus 50 includes an accumulation buffer 51, a lossless decoding unit 52, an inverse quantization unit 53, an inverse orthogonal transformation unit 54, an addition unit 55, a deblocking filter 56, a screen rearrangement buffer 57, and a D / A conversion unit 58. Is equipped. Further, the image decoding apparatus 50 includes a frame memory 61, selectors 62 and 65, an intra prediction unit 63, a motion compensation unit 64, and a filter strength adjustment unit 71.
- the accumulation buffer 51 accumulates the transmitted encoded stream.
- the lossless decoding unit 52 decodes the coded stream supplied from the accumulation buffer 51 by a method corresponding to the coding method of the lossless coding unit 16 in FIG. 1. Further, the lossless decoding unit 52 outputs prediction mode information obtained by decoding header information of the encoded stream to the intra prediction unit 63, the motion compensation unit 64, and the deblocking filter 56.
- the inverse quantization unit 53 inversely quantizes the quantized data decoded by the lossless decoding unit 52 in a method corresponding to the quantization method of the quantization unit 15 in FIG. 1.
- the inverse orthogonal transform unit 54 performs inverse orthogonal transform on the output of the inverse quantization unit 53 according to a scheme corresponding to the orthogonal transform scheme of the orthogonal transform unit 14 in FIG.
- the addition unit 55 adds the data after the inverse orthogonal transform and the predicted image data supplied from the selector 65 to generate decoded image data, and outputs the decoded image data to the deblocking filter 56 and the frame memory 61.
- the deblocking filter 56 performs a filtering process on the decoded image data supplied from the adding unit 55, removes block distortion, supplies it to the frame memory 61, stores it, and outputs it to the screen rearrangement buffer 57. Further, the deblocking filter 56 adjusts the filter strength based on the prediction mode information supplied from the lossless decoding unit 52 and the threshold values ⁇ and ⁇ for filter strength adjustment supplied from the filter strength adjustment unit 71 described later. .
- the screen rearranging buffer 57 rearranges the images. That is, the order of the frames rearranged for the encoding order by the screen rearrangement buffer 12 in FIG. 1 is rearranged in the original display order and output to the D / A conversion unit 58.
- the D / A converter 58 D / A converts the image data supplied from the screen rearrangement buffer 57 and outputs the data to a display (not shown) to display the image.
- the frame memory 61 holds the decoded image data before the filtering process supplied from the adding unit 55 and the decoded image data after the filtering process supplied from the deblocking filter 24.
- the selector 62 decodes decoded image data before filter processing read from the frame memory 61 when decoding of a prediction block for which intra prediction has been performed is performed based on prediction mode information supplied from the lossless decoding unit 52. Are supplied to the intra prediction unit 63. Also, when decoding of the prediction block for which inter prediction has been performed is performed based on the prediction mode information supplied from the lossless decoding unit 52, the selector 26 performs decoding after filter processing read from the frame memory 61. The image data is supplied to the motion compensation unit 64.
- the intra prediction unit 63 generates a prediction image based on the prediction mode information supplied from the lossless decoding unit 52, and outputs the generated prediction image data to the selector 65.
- the intra prediction unit 63 also outputs information indicating the block size of the generated predicted image to the filter strength adjustment unit 71.
- the motion compensation unit 64 performs motion compensation based on the prediction mode information supplied from the lossless decoding unit 52, generates prediction image data, and outputs the prediction image data to the selector 65. That is, the motion compensation unit 64 performs motion compensation on the reference image indicated by the reference frame information based on the motion vector information and the reference frame information based on the motion vector information and the reference frame information included in the prediction mode information. Generate predicted image data. Further, the motion compensation unit 64 outputs information indicating the block size of the generated predicted image to the filter strength adjustment unit 71.
- the selector 65 supplies the predicted image data generated by the intra prediction unit 63 to the addition unit 55. Further, the selector 65 supplies the prediction image data generated by the motion compensation unit 64 to the addition unit 55.
- the filter strength adjustment unit 71 is configured similarly to the filter strength adjustment unit 41 shown in FIG. 4 and performs the same operation.
- the filter strength adjustment unit 71 adjusts the filter strength in the deblocking filter 56 by setting parameter values for adjusting the filter strength in accordance with the prediction block size. Further, the filter strength adjustment unit 71 adjusts the filter strength in accordance with the larger predicted block size when the predicted block size in the optimum mode is a block size expanded in either the relevant block or the adjacent block. . Furthermore, when a plurality of macroblocks having a block size larger than that of a predetermined macroblock is used, the filter strength adjustment unit 71 predicts the block sizes of two adjacent blocks so that the filter strength becomes stronger as the block size becomes larger.
- the filter strength adjustment unit 71 sets threshold values ⁇ and ⁇ which are parameter values for adjusting the filter strength according to the block size supplied from the intra prediction unit 63 and the motion compensation unit 64, and performs the deblocking filter. Output to 56
- step ST71 the accumulation buffer 51 accumulates the transmitted encoded stream.
- step ST72 the lossless decoding unit 52 performs lossless decoding processing.
- the lossless decoding unit 52 decodes the encoded stream supplied from the accumulation buffer 51. That is, quantized data of each picture encoded by the lossless encoding unit 16 of FIG. 1 is obtained. Further, the lossless decoding unit 52 performs lossless decoding of prediction mode information included in header information of the encoded stream, and supplies the obtained prediction mode information to the deblocking filter 56 and the selectors 62 and 65. Furthermore, the lossless decoding unit 52 outputs prediction mode information to the intra prediction unit 63 when the prediction mode information is information related to the intra prediction mode. In addition, when the prediction mode information is information related to the inter prediction mode, the lossless decoding unit 52 outputs the prediction mode information to the motion compensation unit 64.
- step ST73 the inverse quantization unit 53 performs inverse quantization processing.
- the inverse quantization unit 53 inversely quantizes the quantized data decoded by the lossless decoding unit 52 with a characteristic corresponding to the characteristic of the quantization unit 15 in FIG. 1.
- the inverse orthogonal transform unit 54 performs inverse orthogonal transform processing.
- the inverse orthogonal transformation unit 54 performs inverse orthogonal transformation on the transform coefficient data inversely quantized by the inverse quantization unit 53 with a characteristic corresponding to the characteristic of the orthogonal transformation unit 14 in FIG. 1.
- step ST75 the addition unit 55 generates decoded image data.
- the addition unit 55 adds the data obtained by performing the inverse orthogonal transformation process and the predicted image data selected in step ST79 described later to generate decoded image data. The original image is thus decoded.
- step ST76 the deblocking filter 56 performs filter processing.
- the deblocking filter 56 performs filter processing of the decoded image data output from the adding unit 55 to remove block distortion included in the decoded image.
- step ST77 the frame memory 61 performs storage processing of the decoded image data.
- step ST78 the intra prediction unit 63 and the motion compensation unit 64 perform prediction processing.
- the intra prediction unit 63 and the motion compensation unit 64 respectively perform prediction processing corresponding to the prediction mode information supplied from the lossless decoding unit 52.
- the intra prediction unit 63 performs intra prediction processing based on the prediction mode information, and generates prediction image data. Also, when prediction mode information of inter prediction is supplied from the lossless decoding unit 52, the motion compensation unit 64 performs motion compensation based on the prediction mode information to generate prediction image data.
- step ST79 the selector 65 selects prediction image data. That is, the selector 65 selects the prediction image supplied from the intra prediction unit 63 and the prediction image data generated by the motion compensation unit 64 and supplies it to the addition unit 55, and as described above, the reverse orthogonality is made in step ST75. The output of the conversion unit 54 is added.
- step ST80 the screen rearrangement buffer 57 performs image rearrangement. That is, in the screen rearrangement buffer 57, the order of the frames rearranged for encoding by the screen rearrangement buffer 12 of the image encoding device 10 of FIG. 1 is rearranged in the original display order.
- step ST81 the D / A conversion unit 58 D / A converts the image data from the screen rearrangement buffer 57. This image is output to a display not shown, and the image is displayed.
- the filter strength adjustment unit 71 performs the filter strength adjustment process shown in FIG. 11 described above.
- the filter strength adjustment unit 71 is, for example, H.264.
- FilterOffsetA and FilterOffsetB specified by slice_alpha_c0_offset_div2 and slice_beta_offset_div2 which are syntax elements of the H.264 / AVC standard, parameter values for adjusting the filter strength so that the filter is more likely to be applied as the prediction block size becomes larger. Threshold values ⁇ and ⁇ are set.
- the filter strength adjustment unit 71 generates threshold values ⁇ and ⁇ that are parameter values for adjusting the filter strength according to the predicted block size when encoding is performed, and outputs the threshold values ⁇ and ⁇ to the deblocking filter 56.
- the deblocking filter 56 determines block boundary strength data Bs based on prediction mode information, and performs filtering on the decoded image data using the threshold values ⁇ and ⁇ .
- the filter strength adjustment unit 71 sets the value of deblocking_filter_control_present_flag of the picture parameter set that is a syntax element to a predetermined value and the values of FilterOffsetA and FilterOffsetB are described in the slice header, this is described.
- the threshold values ⁇ and ⁇ are generated using the above values and output to the deblocking filter 56. If such adjustment of the filter strength is performed, if the user independently sets a value different from that in Table 4 in the image encoding device, the image decoding device may perform filter processing according to the user's setting. become able to.
- the information indicating the block size used in the encoding process is accumulated in the block size buffer of the filter strength adjustment unit 71. Therefore, when the coded stream is decoded to generate decoded image data, the position of the prediction block in the decoded image becomes clear. Therefore, block distortion can be reduced even if the block size is large by adjusting the filter strength for a large block size to make it easy to apply a filter based on the information stored in the block size buffer. Therefore, it is possible to obtain a decoded image with good image quality.
- the series of processes described in the specification can be performed by hardware, software, or a combined configuration of both.
- a program recording the processing sequence is installed and executed in a memory in a computer incorporated in dedicated hardware.
- the program may be installed and executed on a general-purpose computer that can execute various processes.
- the program can be recorded in advance on a hard disk or ROM (Read Only Memory) as a recording medium.
- the program may be temporarily or permanently stored in a removable recording medium such as a flexible disk, a compact disc read only memory (CD-ROM), a magneto optical disc (MO), a digital versatile disc (DVD), a magnetic disc, or a semiconductor memory. It can be stored (recorded).
- a removable recording medium such as a flexible disk, a compact disc read only memory (CD-ROM), a magneto optical disc (MO), a digital versatile disc (DVD), a magnetic disc, or a semiconductor memory. It can be stored (recorded).
- Such removable recording media can be provided as so-called package software.
- the program is installed on the computer from the removable recording medium as described above, and is wirelessly transferred from the download site to the computer or transferred to the computer via a network such as LAN (Local Area Network) or the Internet by wire.
- the computer can receive the program transferred as such, and can install it on a recording medium such as a built-in hard disk.
- the filter strength is adjusted according to the block size of the adjacent block adjacent at the block boundary. For this reason, even if a macro block having an expanded size is used, it is possible to obtain a high quality decoded image with reduced block distortion by adjusting the filter strength according to the block size. Therefore, as in MPEG, H. 26x, etc., image information (bit stream) obtained by encoding in block units is transmitted / received via network media such as satellite broadcasting, cable TV, Internet, mobile phone etc. It is suitable for an image coding apparatus, an image decoding apparatus, etc. used when processing on storage media such as optical, magnetic disk, flash memory, etc.
- lossless decoding unit 58 ⁇ ⁇ D / A converter, 64 ⁇ ⁇ ⁇ motion compensation unit, 71 ⁇ ⁇ ⁇ ⁇ filter strength adjustment unit 241 ... filter strength decision unit, 242 ... filter processing unit, 411 ... block size buffer, 412 ... parameter selector
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Abstract
Description
1.画像符号化装置の構成
2.デブロッキングフィルタのフィルタ処理について
3.画像符号化装置におけるデブロッキングフィルタとフィルタ強度調整部の構成
4.画像符号化装置の動作
5.画像復号化装置の構成
6.画像復号化装置の動作
図1は、画像符号化装置の構成を示している。画像符号化装置10は、アナログ/ディジタル変換部(A/D変換部)11、画面並び替えバッファ12、減算部13、直交変換部14、量子化部15、可逆符号化部16、蓄積バッファ17、レート制御部18を備えている。さらに、画像符号化装置10は、逆量子化部21、逆直交変換部22、加算部23、デブロッキングフィルタ24、フレームメモリ25、セレクタ26、イントラ予測部31、動き予測・補償部32、予測画像・最適モード選択部33を備えている。
デブロッキングフィルタのフィルタ処理において、H264./AVCの符号化方式では、画像圧縮情報に含まれるPicture Parameter Set RBSPのdeblocking_filter_control_present_flagおよびSlice Headerに含まれるdisable_deblocking_filter_idcという2つのパラメータによって、
(a) ブロック境界、およびマクロブロック境界に施す
(b) Macroblock境界にのみ施す
(c) 施さない
の3通りを指定することが可能である。
Bs>0
|p0-q0|<α;|p1-p0|<β;|q1-q0|<β
・・・(1)
qPav=(qPp+qPq+1)>>1 ・・・(2)
indexA=Clip3(0,51,qPav+FilterOffsetA) ・・・(3)
indexB=Clip3(0,51,qPav+FilterOffsetB) ・・・(4)
p0’=Clip1(p0+Δ) ・・・(5)
q0’=Clip1(q0+Δ) ・・・(6)
Δ=Clip3(-tc,tc((((q0-p0)<<2)+(p1-q1)+4)>>3)) ・・・(7)
tc=tc0+((ap<β)?1:0)+(aq<β)?1:0) ・・・(8)
tc=tc0+1 ・・・(9)
このtcの値は、BsとindexAの値に応じて表3のように定義される。
ap=|p2-p0| ・・・(10)
aq=|q2-q0| ・・・(11)
p1’=p1+Clip3(-tc0,tc0,(p2+((p0+q0+1)>>1)-(p1<<1))>>1) ・・・(12)
p1’=p1 ・・・(13)
q1’=q1+Clip3(-tc0,tc0,(q2+((p0+q0+1)>>1)-(q1<<1))>>1) ・・・(14)
q1’=q1 ・・・(15)
ap<β && |p0-q0|<((α>>2)+2) ・・・(16)
p0’=(p2+2・p1+2・p0+2・q0+q1+4)>>3 ・・・(17)
p1’=(p2+p1+p0+q0+2)>>2 ・・・(18)
p2’=(2・p3+3・p2+p1+p0+q0+4)>>3 ・・・(19)
p0’=(2・p1+p0+q1+2)>>2 ・・・(20)
p1’=p1 ・・・(21)
p2’=p2 ・・・(22)
aq<β && |p0-q0|<((α>>2)+2) ・・・(23)
q0’=(p1+2・p0+2・q0+2・q1+q2+4)>>3 ・・・(24)
q1’=(p0+q0+q1+q2+2)>>2 ・・・(25)
q2’=(2・q3+3・q2+q1+q0+p4+4)>>3 ・・・(26)
q0’=(2・q1+q0+p1+2)>>2 ・・・(27)
q1’=q1 ・・・(28)
q2’=q2 ・・・(29)
フィルタ強度調整部41は、当該マクロブロックにおける最適モードの予測ブロックサイズに応じて、デブロッキングフィルタ24におけるフィルタ強度の調整を行う。
次に、画像符号化処理動作について説明する。図5は、画像符号化処理で用いる予測ブロックサイズを示している。H.264/AVC方式では、図5の(C)(D)に示すように16×16画素~4×4画素の予測ブロックサイズが規定されている。また、H.264/AVC方式よりも拡張された大きさのマクロブロックを用いる場合、例えば32×32画素のマクロブロックを用いる場合、例えば図5の(B)に示す予測ブロックサイズが規定される。また、例えば64×64画素のマクロブロックを用いる場合、例えば図5の(A)に示す予測ブロックサイズが規定される。
Cost(Mode∈Ω)=D+λ・R ・・・(30)
Cost(Mode∈Ω)=D+QPtoQuant(QP)・Header_Bit ・・・(31)
ステップST61でフィルタ強度調整部41は、最適モードの予測ブロックサイズを取得する。フィルタ強度調整部41は、図7のステップST22で選択された予測画像に対応する予測ブロックサイズ、すなわち最適モードで符号化を行うときの予測ブロックサイズを取得する。
FilterOffsetA32=FilterOffsetA16+SZa
FilterOffsetA64=FilterOffsetA16+SZb
FilterOffsetB32=FilterOffsetB16+SZa
FilterOffsetB64=FilterOffsetB16+SZb
のような値を用いればよい。
入力画像を符号化して生成された符号化ストリームは、所定の伝送路や記録媒体等を介して画像復号化装置に供給されて復号される。
次に、図13のフローチャートを参照して、画像復号化装置50で行われる画像復号処理動作について説明する。
Claims (20)
- 画像データがブロック毎に符号化されている符号化ストリームを復号化して復号画像データを生成する復号部と、
前記復号部により生成された復号画像データに対してブロック歪みを除去するフィルタ処理を行うフィルタと、
ブロック境界で隣接する隣接ブロックのブロックサイズに応じて、前記フィルタ処理におけるフィルタ強度を調整するフィルタ強度調整部と
を設けた画像処理装置。 - 前記フィルタ強度調整部は、前記隣接ブロックのブロックサイズが大きいほどフィルタ処理をかかりやすくするようにフィルタ強度を調整する請求項1記載の画像処理装置。
- 前記フィルタ強度調整部は、前記フィルタ強度を調整するパラメータ値を前記ブロックサイズに応じて設定する請求項2記載の画像処理装置。
- 前記フィルタ強度調整部は、隣接ブロックのブロックサイズの組み合わせに応じて、前記フィルタ処理におけるフィルタ強度を調整する請求項3に記載の画像処理装置。
- 前記フィルタ強度調整部は、隣接ブロックでブロックサイズが異なる場合、大きい方のブロックサイズに応じてフィルタ強度を調整する請求項4記載の画像処理装置。
- 前記フィルタ強度調整部は、所定のマクロブロックよりもブロックサイズが大きいマクロブロックが用いられる場合、ブロックサイズが大きいほどフィルタ強度が強くなるように、隣接ブロックのブロックサイズの組み合わせに応じて、パラメータ値を設定する請求項5記載の画像処理装置。
- 前記フィルタ強度調整部は、符号化規格のシンタックス・エレメントの値を調整して、前記フィルタ強度を調整する請求項3記載の画像処理装置。
- 前記フィルタ強度調整部は、H.264/AVC規格のシンタックス・エレメントであるslice_alpha_c0_offset_div2およびslice_beta_offset_div2で指定するFilterOffsetAおよびFilterOffsetBの値を調整して、前記フィルタ強度を調整する請求項7記載の画像処理装置。
- 前記フィルタ強度調整部は、予め設けられているパラメータ値と異なるパラメータ値を用いる場合に、前記シンタックス・エレメントであるピクチャパラメータセットのdeblocking_filter_control_present_flagの値を所定の値に設定し、スライスヘッダに、前FilterOffsetAおよびFilterOffsetBの値を記述する請求項7記載の画像処理装置。
- 画像データがブロック毎に符号化されている符号化ストリームを復号化して復号画像データを生成する工程と、
前記復号部により生成された復号画像データに対してブロック歪みを除去するフィルタ処理を行う工程と、
ブロック境界で隣接する隣接ブロックのブロックサイズに応じて、前記フィルタ処理におけるフィルタ強度を調整する工程と
を設けた画像処理方法。 - 復号画像データに対してブロック歪みを除去するフィルタ処理を行うフィルタと、
ブロック境界で隣接する隣接ブロックのブロックサイズに応じて、前記フィルタ処理におけるフィルタ強度を調整するフィルタ強度調整部と、
前記フィルタによりフィルタ処理が行われた復号画像データを用いて、画像データを符号化する符号化部と、
を設けた画像処理装置。 - 前記フィルタ強度調整部は、前記隣接ブロックのブロックサイズが大きいほどフィルタ処理をかかりやすくするようにフィルタ強度を調整する請求項11記載の画像処理装置。
- 前記フィルタ強度調整部は、前記フィルタ強度を調整するパラメータ値を前記ブロックサイズに応じて設定する請求項12記載の画像処理装置。
- 前記フィルタ強度調整部は、隣接ブロックのブロックサイズの組み合わせに応じて、前記フィルタ処理におけるフィルタ強度を調整する請求項13に記載の画像処理装置。
- 前記フィルタ強度調整部は、隣接ブロックでブロックサイズが異なる場合、大きい方のブロックサイズに応じてフィルタ強度を調整する請求項14記載の画像処理装置。
- 前記フィルタ強度調整部は、所定のマクロブロックよりもブロックサイズが大きいマクロブロックが用いられる場合、ブロックサイズが大きいほどフィルタ強度が強くなるように、隣接ブロックのブロックサイズの組み合わせに応じて、パラメータ値を設定する請求項15記載の画像処理装置。
- 前記フィルタ強度調整部は、符号化規格のシンタックス・エレメントの値を調整して、前記フィルタ強度を調整する請求項13記載の画像処理装置。
- 前記フィルタ強度調整部は、H.264/AVC規格のシンタックス・エレメントであるslice_alpha_c0_offset_div2およびslice_beta_offset_div2で指定するFilterOffsetAおよびFilterOffsetBの値を調整して、前記フィルタ強度を調整する請求項17記載の画像処理装置。
- 前記フィルタ強度調整部は、予め設けられているパラメータ値と異なるパラメータ値を用いる場合に、前記シンタックス・エレメントであるピクチャパラメータセットのdeblocking_filter_control_present_flagの値を所定の値に設定し、スライスヘッダに、前FilterOffsetAおよびFilterOffsetBの値を記述する請求項17記載の画像処理装置。
- 復号画像データに対してブロック歪みを除去するフィルタ処理を行う工程と、
ブロック境界で隣接する隣接ブロックのブロックサイズに応じて、前記フィルタ処理におけるフィルタ強度を調整する工程と、
前記フィルタによりフィルタ処理が行われた復号画像データを用いて、画像データを符号化する工程と
を設けた画像処理方法。
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