Classifications

• • 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
  • H04N19/132—Sampling, masking or truncation of coding units, e.g. adaptive resampling, frame skipping, frame interpolation or high-frequency transform coefficient masking
• • 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
  • H04N19/103—Selection of coding mode or of prediction mode
  • H04N19/107—Selection of coding mode or of prediction mode between spatial and temporal predictive coding, e.g. picture refresh
• • 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
  • H04N19/146—Data rate or code amount at the encoder output
  • H04N19/147—Data rate or code amount at the encoder output according to rate distortion criteria
• • 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
• • 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
  • H04N19/60—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding
  • H04N19/61—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding in combination with predictive coding

Definitions

• Methods and apparatuses consistent with the present invention relate to video encoding, and more particularly, to video encoding in which an encoding mode is rapidly decided in video encoding and video encoding is performed in the decided encoding mode.
• Inter mode is used in inter prediction, which is directed to encoding differences between motion vector information and pixel values for the purpose of encoding macroblocks of a current picture, in which the motion vector information indicates the position of one block or positions of a plurality of blocks , as decided with respect to a reference picture. Since a maximum of 5 reference pictures at any particular time can be obtained in accordance with H.264, blocks to which current macroblocks are to refer to are searched for by investigating reference pictures in a frame memory that stores the reference pictures. The reference pictures stored in the frame memory may be past pictures or future pictures with respect to the current pictures.
• Intra mode is used in intra prediction, which is directed to calculating predicted pixel values of macroblocks to be encoded using pixel values spatially adjacent to the macroblocks to be encoded, instead of referring to reference pictures, and then encoding differences between the predicted pixel values and the pixel values for the purpose of encoding macroblocks of the current picture.
• the present invention provides a method and apparatus for video encoding, in which an encoding mode is rapidly decided by performing an encoding mode decision according to a predetermined order and video encoding is performed in the decided encoding mode.
• FTG 1 is a block diagram of an apparatus for video encoding according to an embodiment of the present invention.
• FTG 2 illustrates various ways of dividing macroblocks in inter prediction
• FTG 3 illustrates an example in which various block types are assigned to each macroblock of a current picture to be encoded
• FTG 4 illustrates a luminance block P to be predicted and adjacent blocks used in prediction
• FTGS. 5 A and 5B are views for explaining calculation of predicted motion vectors (PMVs);
• FTG 6 is a view for explaining calculation of RDcosts
• FTG 7 is a flowchart illustrating a method of deciding an encoding mode
• FTG 8A and 8B are views for explaining calculation of average boundary errors (ABEs);
• FTG 9 is a schematic block diagram of an apparatus for video encoding according to an embodiment of the present invention.
• FTG 10 is a schematic block diagram of an apparatus for video encoding according to another embodiment of the present invention. Best Mode
• the present invention provides a method for video encoding including: (a) determining whether a predetermined block of a predetermined size forming a video satisfies predetermined conditions corresponding to a first mode of a pluraity of video encoding modes; and (b) choosing the first mode as an encoding mode of the predetermined block if the predetermined conditions are satisfied .
• the present invention provides a method for video encoding comprising: (a) calculating temporal similarity of a predetermined block of a predetermined size forming a video with a reference block of a reference picture in an inter mode; and (b) determining whether to orrit an encoding process in an intra mode according to the calculated temporal similarity and spatial similarity between a block of the current picture and an adjacent block.
• the present invention provides an apparatus for video encoding as described above.
• the present invention provides for a computer readable medium having embodied thereon programs for implementing a method for video encoding as described above.
• An apparatus for video encoding according to the present invention encodes video data.
• the video data is composed of a plurality of pictures arranged along a time axis and each picture is composed of a pluraity of blocks.
• the blocks include macroblocks and subblocks that are obtained by halving or quartering the macroblocks in a vertical or horizontal direction. Division of the macroblocks will be described later with reference to FTG 2.
• FTG 1 is a block diagram of an apparatus for video encoding according to an embodiment of the present invention.
• the apparatus for video encoding includes a motion estimator 102, a motion compensator 104, an intra predictor 106, a transformer 108, a quantizer 110, a re- orderer 112, an entropy coder 114, a dequantizer 116, an inverse transformer 118, a filter 120, and a frame memory 122.
• the apparatus for video encoding performs encoding with respect to macroblocks of a current picture in an encoding mode chosen from among various encoding modes.
• RDcosts are calculated by performing encoding in all the possible modes inter prediction and intra prediction can have, a mode having the smallest RDcost is chosen as the optimal encoding mode, and encoding is performed in the chosen encoding mode.
• the RDcost will be described in detail later.
• choosing the optimal encoding mode is not necessarily performed by means of calculation of RDcosts and may be performed using a variety of different methods.
• the motion estimator 102 searches in a reference picture for inter prediction for predicted values of macroblocks of a current picture. If reference blocks are found in half pixel units or quarter pixel units, the motion compensator 104 chooses reference block data values using the found half pixels and quarter pixels. As such, inter prediction is performed by the motion estimator 102 and the motion compensator 104.
• the intra predictor 106 performs intra prediction directed to searching for the predicted values of the macroblocks of the current picture from the current picture. Whether to perform inter prediction or intra prediction for the current macroblocks is determined by RD costs in all the encoding modes. After calculating the RDcosts in all the encoding modes, choosing a mode having the smallest RDcost as the encoding mode for the current macroblocks, and performing encoding of the current macroblocks.
• a quantized picture is dequantized by the dequantizer 116 and then processed by the inverse transformer 118, and thus the current picture is decoded.
• the decoded current picture is stored in the frame memory 122 and used to perform inter prediction on the next picture. Once the decoded picture passes through the filter 120, it is converted to a picture including some encoding errors in addition to those of the original picture.
• FTG 2 illustrates various ways of dividing macroblocks in inter prediction.
• one 16x16 macroblock can be divided into 16x16, 16x8, 8x16, or 8x8 subblocks and each 8x8 block can be divided into 8x4, 4x8, or 4x4 subblocks. Motion estimation and compensation are performed on these subblocks, thereby motion vectors are determined for each subblock. If inter prediction is performed in various block modes, encoding can be effectively performed with respect to the characteristics and movement of object in a video.
• FTG 3 illustrates an example in which various block types are assigned to each of the macroblocks of the current picture to be encoded.
• variable blocks are assigned such that inter prediction is performed using a large block when motion of a video is simple and an object is large and using a small block when motion of a video is complex and an object is small.
• FTG 4 illustrates a luminance block P to be predicted and adjacent blocks to be used in prediction.
• Intra prediction is performed with respect to luminance and chrominance.
• a block P 410 to be predicted is predicted using decoded blocks A through L adjacent to the block P 410. Prediction is performed on not only luminance (luma) blocks but also chrominance (U and V signals) blocks.
• the luminance block P 410 is a l6xl6 block composed of several 4x4 blocks.
• blocks a through p are 4x4 blocks to be predicted and A, B, C, D and I, J, K, L are blocks used in prediction.
• Intra prediction can be classified into two types according to the size of a block to be predicted: 4x4 prediction and 16x16 prediction. Also, according to a prediction direction, there are 9 modes in 4x4 prediction and there are 4 modes in 16x16 prediction. The 9 modes in 4x4 prediction are classified according to prediction directions in which prediction samples are obtained using pixel values of the blocks A, B, C, D and I, J, K, L adjacent to a 4x4 block to be predicted.
• a 4x4 intra luma prediction mode includes a vertical mode, a horizontal mode, a DC mode, a diagonal_down_left mode, a diagonal_down_right mode, a vertical_right mode, a horizontal_down mode, a vertical_up mode, and a horizontal_up mode.
• a 16x16 intra luma prediction mode includes a vertical mode, a horizontal mode, a DC mode, and a plane mode. Since RDcosts should be calculated in various modes such as the above modes, a large amount of calculation is required ike in inter prediction.
• FTGS. 5 A and 5B are views for explaining calculation of PMVs.
• a motion vector of a current macroblock C has a high probab ⁇ ty of being similar to those of adjacent macroblocks.
• the motion vector of the current macroblock C is predicted using the motion vectors of adjacent macroblocks A, B, and D. Prediction may be performed by calculating a median value of the motion vectors of the macroblocks A, B, and D. In encoding, the PMVs are subtracted from actual motion vectors.
• H.264 encoding prediction is performed by selecting a mode chosen during inter prediction or a mode chosen during intra prediction. Compression efficiency of H.264 depends on a chosen mode in which prediction is performed. To select the best mode, prediction of a block is performed using all the modes and RDcosts are calculated.
• FTG 6 is a view for explaining calculation of RDcosts.
• a rate R means a bit rate and indicates the number of bits used in encoding one macroblock.
• the rate R is the sum of the number of bits obtained by processing residual signals left after inter prediction or intra prediction in a transformer and quantizer 610 and a variable length coder 620, the number of bits obtained by processing motion vector information in the variable length coder 620, and the number of bits obtained by processing reference picture information in the variable length coder 620.
• a distortion D indicates a difference between the orignal macroblock and a decoded macroblock when an encoded video is decoded.
• the distortion D can be obtained once the orignal macroblock is decoded after being processed by a dequantizer and inverse-transformer 630.
• the RDcost is calculated by a rate-distortion cost calculator 640 using the obtained rate and distortion as follows.
• Distortion indicates a difference in pixel value between the current macroblock and a corresponding macroblock that is encoded, and then decoded, and is calculated using Equation 2.
• Rate indicates a bit rate calculated using a method as described above.
• Equation 3 B(k, 1) and B'(k, 1) indicate pixel values of (k, 1) of the current macro block and the decoded macroblock, respectively.
• QP indicates an integer rangng from 0 to 51 and is a H.264 quantization value
• Rate indicates the number of bits required for encoding of the current macroblock.
• FTG 7 is a flowchart illustrating a method of deciding an encoding mode.
• a current block is input, it is primarily checked whether the current block is in a skip mode or not.
• the skip mode only encoding mode information of a block to be encoded is transmitted or stored. There is a high probability that a pixel value of a given block of a current block is identical to that of a corresponding block of a reference block because only the encoding mode information is transmitted or stored without a need for transmission or storing of additional encoded data such as residual signals or motion vector information.
• motion estimation is performed on the current block and a reference picture is chosen, in step S705.
• step S710 it is determined whether the current block satisfies all of the following four conditions:
• ® the block size used for inter prediction is 16x16
• ® the reference picture used to encode the current block is temporally closest to the current picture among reference pictures stored in the frame memory(just one previous picture)
• D the motion vector is (0, 0) or the same as its PMV
• ® the transform coefficients of the residual signals that are differences in pixel values of the current block and the reference picture are all quantized to zero.
• the block size used for inter prediction is 8x8
• ® the reference picture and the motion vector that are used to encode the current block are the same as predicted values from the reference picture of a block that is spatially or temporally adjacent to the current block and motion vector information of the block, and (D the transform co- efficients of the residual signals that are differences in pixel values of the current block and the reference picture are all quantized to zero.
• step S720 the block is determined to be in the skip mode and a n encoding mode decision process is terminated without checking to see if the current block has other modes, in step S720.
• inter prediction is performed in other modes inter prediction can have, an inter mode is decided from among the modes of inter prediction, and the number of bits obtained when encoding is performed in the decided inter mode is calculated, in step S725.
• the inter mode is chosen from among a group of some of all the possible modes, instead of from among all the possible modes.
• an average rate (AR) is calculated.
• the AR is calculated using Equation 4 and indicates a rate per pixel. Since inter prediction is already performed, a rate is already known.
• step S730 an average boundary error (ABE) is calculated.
• FIGS. 8A and 8B are views for explaining calculation of the ABE.
• Equation 5 a sum of boundary error (SBE) is calculated using Equation 5. Then, an ABE per pixel is calculated.
• ABE -!-SBE.
• 64 (16 + 16) L ⁇ ma + (8 + 8) Chroma ⁇ 2 64 (5),
• Equation 5 is arranged as follows.
• Equation 5 is arranged as follows.
• the ABE can be calculated using Equation 5.
• step S735 the AR and the ABE are compared. Calculations of the AR and the ABE are examples of calculations of temporal similarity and spatial similarity, respectively. If the ABE is greater than the AR, it means that the current macroblock has higher probability of being in the inter mode rather than the intra mode. Thus, in step S750, the current macroblock is determined to be in the inter mode chosen in step S725 and the process is terminated. If the ABE is not greater than the AR, one mode is chosen from among intra modes in step S740. In step S745, an encoding mode of the current macroblock is chosen from among the decided intra mode and the previously chosen inter mode.
• Another example of a determination of temporal similarity besides the AR is to use differences in pixel values of the macroblock of the current picture and the reference block of the reference picture in the inter mode.
• the differences can be obtained by calculating the differences between respective pixel values of the current macroblock and the reference block of the reference picture, summing the absolute values of the differences or squared values of the differences, and multiplying the sum by a predetermined ratio ⁇ .
• FTG 9 is a schematic block diagram of an apparatus for video encoding according to the embodiment of the present invention.
• the apparatus for video encoding includes a determination unit 910, an encoding mode decision unit 920, and an encoding performing unit 930.
• the determination unit 910 determines whether a block of a predetermined size forming a video satisfies conditions for the skip mode among a pluraity of encoding modes used for video encoding.
• the conditions for the skip mode are already described above.
• the encoding mode decision unit 920 decides the skip mode as the encoding mode of the block if all the conditions as described above are satisfied . If the conditions are not satisfied, the encoding mode decision unit 920 further performs inter prediction or intra prediction and selects one of various encoding modes as the encoding mode of the block.
• the encoding performing unit 930 creates compressed video data according to the encoding mode chosen by the encoding mode decision unit 920.
• FTG 10 is a schematic block diagram of an apparatus for video encoding according to another embodiment of the present invention.
• a temporal similarity calculation unit 1010 calculates temporal similarity of the macroblock of the current picture with the reference block of the reference picture in the inter mode.
• a comparing unit 1020 determines whether to onit an encoding process in the intra mode according to the calculated temporal similarity and spatial similarity between the macroblock of the current picture and the adjacent block. Thus, one encoding mode is decided. Preferably, but not necessarily, the temporal similarity and the spatial similarity are calculated based on the AR and the ABE.
• Another example of calculation of the temporal similarity is to use differences in pixel values of the macroblock of the current picture and the reference block of the reference picture in the inter mode.
• the differences can be obtained by calculating the differences between respective pixel values of the current macroblock and the reference block of the reference picture, summing the absolute values of the differences or squared values of the differences, and multiplying the sum by the predetermined ratio ⁇ .
• the encoding performing unit 1030 creates compressed video data according to the encoding mode decided by the comparing unit 1020.
• the method for video encoding according to the present invention can be written as computer programs. Codes and code segments forming the programs can be easily construed by programmers skilled in the art to which the present invention. Also, the programs are stored in computer readable media and read and implemented by computers, thereby implementing the method for video encoding. Examples of the computer readable media include magnetic recording media, optical recording media, and carrier waves.

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