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
  • H04N19/60—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
  • H04N19/615—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding in combination with predictive coding using motion compensated temporal filtering [MCTF]
• • 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
  • H04N19/174—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 slice, e.g. a line of blocks or a group of blocks
• • 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
  • H04N19/30—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using hierarchical techniques, e.g. scalability
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/50—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding
  • H04N19/503—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding involving temporal prediction
  • H04N19/51—Motion estimation or motion compensation
  • H04N19/53—Multi-resolution motion estimation; Hierarchical motion estimation
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/50—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding
  • H04N19/503—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding involving temporal prediction
  • H04N19/51—Motion estimation or motion compensation
  • H04N19/577—Motion compensation with bidirectional frame interpolation, i.e. using B-pictures
• • 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
• • 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
  • H04N19/63—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding using sub-band based transform, e.g. wavelets
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/90—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using coding techniques not provided for in groups H04N19/10-H04N19/85, e.g. fractals
  • H04N19/91—Entropy coding, e.g. variable length coding [VLC] or arithmetic coding

Definitions

• Apparatuses and methods consistent with the present invention relate to context- based adaptive arithmetic coding and decoding with improved coding efficiency, and more particularly, to context-based adaptive arithmetic coding and decoding methods and apparatuses providing improved coding efficiency by initializing a context model for a given slice of an input video to a context model for a base layer slice at the same temporal position as the given slice for arithmetic coding and decoding.
• a video encoder performs entropy coding to convert data symbols representing video input elements into bitstreams suitably compressed for transmission or storage.
• the data symbols may include quantized transform coefficients, motion vectors, various headers, and the like.
• Examples of the entropy coding include predictive coding, variable length coding, arithmetic coding, and so on. Particularly, arithmetic coding offers the highest compression efficiency.
• context-based adaptive arithmetic coding utilizes local, spatial or temporal features.
• a Joint Video Team (JVT) scalable video model utilizes the context-based adaptive arithmetic coding in which probability models are adaptively updated using the symbols to be coded. Disclosure of Invention
• the context-based adaptive arithmetic coding method requires an increased number of coded blocks and accumulation of information.
• the conventional context-based adaptive arithmetic coding method has a drawback in that when a context model is intended to be initialized to a predefined probability model for each slice, unnecessary bits may be consumed to reach a predetermined coding efficiency after initialization.
• the present invention provides video coding and decoding methods and ap- paratuses improving coding efficiency and reducing error propagation by initializing a context model for a given slice to a context model for a base layer slice at the same temporal position as the given slice.
• a method for performing context-based adaptive arithmetic coding on a given slice in an enhancement layer frame of a video signal having a multi-layered structure including: resetting a context model for the given slice to a context model for a base layer slice at the same temporal position as the given slice; arithmetically coding a data symbol of the given slice using the reset context model; and updating the context model based on a value of the arithmetically coded data symbol.
• a method for performing context-based adaptive arithmetic decoding on a given slice in an enhancement layer frame of a video signal having a multi-layered structure including: resetting a context model for the given slice to a context model for a base layer slice at the same temporal position as the given slice; arithmetically decoding a bitstream corresponding to the given slice using the reset context model to generate a data symbol of the given slice; and updating the context model based on a value of the data symbol.
• a method for performing context-based adaptive arithmetic coding on a given slice in an enhancement layer frame of a video signal having a multi-layered structure including: resetting a context model for the given slice to at least one of a context model for a base layer slice at the same temporal position as the given slice, a context model for a slice coded temporally before the given slice, and a predetermined value; arithmetically coding a data symbol of the given slice using the reset context model; and updating the context model based on a value of the arithmetically coded data symbol.
• a method for performing context-based adaptive arithmetic decoding on a given slice in an enhancement layer frame of a video signal having a multi-layered structure including: resetting a context model for the given slice to at least one of a context model for a base layer slice at the same temporal position as the given slice, a context model for a slice de coded temporally before the given slice, and a predetermined value; arithmetically decoding a bitstream corresponding to the given slice using the reset context model to generate a data symbol of the given slice; and updating the context model based on a value of the data symbol.
• a video coding method including a method for performing context-based adaptive arithmetic coding on a given slice in an enhancement layer frame having a multi-layered structure, the video coding method including: subtracting a predicted image for the given slice from the given slice and generating a residual image: performing spatial transform on the residual image and generating a transform coefficient; quantizing the transform coefficient; resetting a context model for the given slice to a context model for a base layer slice at the same temporal position as the given slice; arithmetically coding a data symbol of the given slice using the reset context model; updating the context model based on a value of the arithmetically coded data symbol; generating a bitstream containing the arithmetically coded data symbol; and transmitting the bitstream.
• a video decoding method including a method for performing context-based adaptive arithmetic decoding on a given slice in an enhancement layer frame having a multi-layered structure, the video de coding method including: parsing a bitstream and extracting data about the given slice to be reconstructed; resetting a context model for the given slice to a context model for a base layer slice at the same temporal position as the given slice according to the data; arithmetically decoding a data symbol corresponding to the given slice using the reset context model to generate a data symbol of the given slice; updating the context model based on a value of the data symbol; dequantizing the data symbol to generate a transform coefficient; performing inverse spatial transform on the transform coefficient to reconstruct a residual image obtained by subtracting a predicted image from the given slice; and adding the predicted image reconstructed by motion compensation to the reconstructed residual image and reconstructing the given slice.
• a method for coding a given slice in an enhancement layer frame of a video signal having a multi-layered structure including: subtracting a predicted image for the given slice from the given slice and generating a residual image; performing spatial transform on the residual image and generate a transform coefficient; quantizing the transform coefficient; resetting a context model for the given slice to at least one of a context model for a base layer slice at the same temporal position as the given slice, a context model for a slice coded temporally before the given slice, and a predetermined value; arithmetically coding a data symbol of the given slice using the reset context model; updating the context model based on a value of the arithmetically coded data symbol; generating a bitstream containing the arithmetically coded data symbol; and transmitting the bitstream.
• a method for decoding a given slice in an enhancement layer frame of a video signal having a multi-layered structure including: parsing a bitstream and extracting data about the given slice to be reconstructed; resetting a context model for the given slice to at least one of a context model for a base layer slice at the same temporal position as the given slice, a context model for a slice de coded temporally before the given slice, and a predetermined value according to the data; arithmetically decoding a bitstream corresponding to the given slice using the reset context model to generate a data symbol of the given slice; updating the context model based on a value of the data symbol,; dequantizing the data symbol to generate a transform coefficient; performing inverse spatial transform on the transform coefficient to reconstruct a residual image obtained by subtracting a predicted image from the given slice; and adding the predicted image reconstructed by motion compensation to the reconstructed residual image and reconstructing the given slice.
• a video encoder for compressing a given slice in an enhancement layer frame having a multi-layered structure, the encoder including: a unit which subtracts a predicted image for the given slice from the given slice and generates a residual image; a unit which performs spatial transform on the residual image and generates a transform coefficient; a unit which quantizes the transform coefficient; a unit which resets a context model for the given slice to a context model for a base layer slice at the same temporal position as the given slice; a unit which arithmetically codes a data symbol of the given slice using the reset context model; a unit which updates the context model based on a value of the arithmetically coded data symbol; a unit which generates a bitstream containing the arithmetically coded data symbol; and a unit which transmits the bitstream.
• a video decoder for reconstructing a given slice in an enhancement layer frame having a multi- layered structure, the decoder including: a unit which parses a bitstream and extracts data about the given slice to be reconstructed; a unit which resets a context model for the given slice to a context model for a base layer slice at the same temporal position as the given slice according to the data; a unit which arithmetically decodes a bitstream corresponding to the given slice using the reset context model to generate a data symbol of the given slice; a unit which updates the context model based on a value of the data symbol; a unit which dequantizes the data symbol to generate a transform coefficient; a unit which performs inverse spatial transform on the transform coefficient to reconstruct a residual image obtained by subtracting a predicted image from the given slice; and a unit which adds the predicted image reconstructed by motion compensation to the reconstructed residual image and reconstructs the given slice.
• a video encoder for compressing a given slice in an enhancement layer frame having a multi- layered structure, the encoder including: a unit which subtracts a predicted image for the given slice from the given slice and generates a residual image; a unit which performs spatial transform on the residual image and generates a transform coefficient; a unit which quantizes the transform coefficient; a unit which resets a context model for the given slice to at least one of a context model for a base layer slice at the same temporal position as the given slice and a context model for a slice coded temporally before the given slice, and a predetermined value; a unit which arithmetically codes a data symbol of the given slice using the reset context model; a unit which updates the context model based on the value of the arithmetically coded data symbol; a unit which generates a bitstream containing the arithmetically coded data symbol; and a unit which transmits the bitstream.
• a video decoder for reconstructing a given slice in an enhancement layer frame having a multi-layered structure, the decoder including: a unit which parses a bitstream and extracts data about the given slice to be reconstructed; a unit which resets a context model for the given slice to at least one of a context model for a base layer slice at the same temporal position as the given slice and a context model for a slice de coded temporally before the given slice according to the data and a predetermined value; a unit which arithmetically decodes a bitstream corresponding to the given slice using the reset context model to generate a data symbol of the given slice; a unit which updates the context model based on a value of the data symbol, a unit which de- quantizes the data symbol to generate a transform coefficient; a unit which performs inverse spatial transform on the transform coefficient to reconstruct a residual image obtained by subtracting a predicted image from the given slice; and a unit
• FlG. 1 illustrates a context-based adaptive arithmetic coding method according to a first exemplary embodiment of the present invention
• FlG. 2 illustrates a context-based adaptive arithmetic coding method according to a second exemplary embodiment of the present invention
• FlG. 3 illustrates a context-based adaptive arithmetic coding method according to a third exemplary embodiment of the present invention
• FlG. 4 is a flowchart illustrating a video coding method including a context-based adaptive arithmetic coding method according to an exemplary embodiment of the present invention
• FlG. 5 is a flowchart illustrating a video decoding method including a context- based adaptive arithmetic decoding method according to an exemplary embodiment of the present invention
• FlG. 6 is a flowchart illustrating a video coding method including a context-based adaptive arithmetic coding method according to an exemplary embodiment of the present invention
• FlG. 7 is a flowchart illustrating a video decoding method including a context- based adaptive arithmetic decoding method according to an exemplary embodiment of the present invention
• FlG. 8 is a block diagram of a video encoder according to an exemplary embodiment of the present invention.
• FlG. 9 is a block diagram of a video decoder according to an exemplary embodiment of the present invention.
• Context-based Adaptive Binary Arithmetic Coding achieves high compression performance by selecting a probability model for each symbol based on a symbol context, adapting probability estimates corresponding to the probability model based on local statistics and performing arithmetic coding on the symbol.
• the coding process of the data symbol consists of at most four elementary steps: 1. Binarization; 2. Context modeling; 3. Arithmetic coding; and 4. Probability updating.
• CABAC Context-based Adaptive Binary Arithmetic Coding
• CABAC set forth but the invention is not limited thereto.
• a context model which is a probability model for one or more bins of binarized symbols and chosen based on the recently coded data symbol statistics, stores a probability for each bin to be '1 ' or 1 O'.
• An arithmetic encoder codes each bin based on the chosen probability model. Each bin has only two probability sub-ranges corresponding to values of T and 1 O', respectively.
• the chosen probability model is updated using actually coded values. That is to say, if the bin value is T, the frequency count of l's is incremented by one.
• CABAC CABAC since context modeling is performed in units of slices, probability values of context models are initialized using fixed tables at the start of each slice.
• VLC variable length coding
• the CABAC technique is required that a predetermined amount of information accumulate such that context models are constantly updated using the statistics of the recently coded data symbols.
• initializing context models for each slice using predefined probability models may result in unnecessary consumption of bits until degraded performance, which is due to an increase in the number of blocks after initialization, is traded off.
• the present invention proposes improved a CABAC technique by reducing a reduction in the coding efficiency immediately after initializing context models using statistical characteristics of the slice coded temporally before the base layer slice as an initial value of a context model for the given slice.
• FIG. 1 illustrates a context-based adaptive arithmetic coding method according to a first exemplary embodiment of the present invention.
• a context model for a given slice in an enhancement layer high-pass frame is initialized to a context model for a corresponding slice in a base layer high-pass frame at the same temporal position for multi-layered video coding.
• a context model for an enhancement layer high-pass frame 111 can be initialized to a context model for a base layer high-pass frame 121 at the same temporal position.
• the context models for enhancement layer low-pass frames 118 and 119 can also be initialized to context models for base layer low-pass frames 128 and 129 at the same temporal positions, respectively, thereby preventing degradation in coding efficiency during an initial stage of frame coding.
• FlG. 2 illustrates a context-based adaptive arithmetic coding method according to a second exemplary embodiment of the present invention in which a context model for a previously coded frame is used as a context model for an enhancement layer frame having no corresponding base layer frame.
• Context models for enhancement layer frames 111 through 113 having corresponding base layer frames at the same temporal positions are initialized to context models for their corresponding base layer frames 121 through 123 as described above with reference to FlG. 1.
• context models for previously coded frames can be used as context models for enhancement layer frames 114 through 117 having no corresponding base layer frames.
• a context model for a slice coded immediately before the given slice may be used as an initial value of a context model for the given high-pass frame slice.
• the high-pass frames are coded in the order from the lowest level to the highest level consecutively using a context model for a slice coded immediately before the given slice as an initial value of a context model for the given slice.
• the slice coded immediately before the given slice may indicate a corresponding slice of a neighboring high-pass frame in the same temporal level or a slice coded immediately before the given slice in the same high-pass frame.
• the method of coding the given slice using the context model for the slice that has been coded immediately before the given slice may not provide high coding efficiency.
• the present invention can provide for high coding efficiency by using statistical information on a slice in the lower level that is temporally closest to the given slice. Further, the method using the statistical information on a slice in the lower level that is temporally closest to the given slice can reduce error propagation compared to the methods of the first and second exemplary embodiments because an error occurring within a slice can propagate to only a slice at a higher level that uses the slice as a reference.
• the context model for the slice that has been coded immediately before the given slice or the context model for the slice in the lower level that is temporally closest to the given slice may be selectively referred to.
• probability models constituting a context model of a slice may be selectively referred to.
• information about whether or not the respective probability models have been referred to may be inserted into a bitstream for transmission to a decoder part.
• FlG. 3 illustrates a context-based adaptive arithmetic coding method according to a third exemplary embodiment of the present invention.
• a context model for a given slice in an enhancement layer of every high-pass frame is initialized to one selected from context models for a base layer slice at the same temporal position as the given slice and slices coded temporally before the given slice in the same enhancement layer . That is, for slices 114 through 117 without their corresponding base layers at the same temporal position, the context model for the given slice is initialized to one of context models for slices coded temporally before the given slice in the same enhancement layer. For slices 111 through 113 with their corresponding base layers at the same temporal position, the context model for the given slice is initialized to a context model for the corresponding base layer slice or to one of context models for slices coded temporally before the given slice.
• a context model that enhances the coding efficiency of a given slice most is selected for performing arithmetic coding of the given slice.
• This procedure may consist of determining whether or not a slice (e.g., slice 113 ) is to be arithmetically coded using an empirically predefined initial value, determining whether or not a context model, as indicated by an arrow labeled 131, for a corresponding base layer slice is to be referred to, determining whether or not a context model of a slice coded immediately before the given slice 113, as indicated by an arrow labeled 132, and determining whether a context model for a slice that is temporally closest to the given slice is to be referred to, as indicated by an arrow labeled 133.
• Probability models constituting one context model selected for initialization can be selectively used as described above with reference to FIGS. 2 and 3.
• data is inserted into a bitstream and transmitted to a decoder, the data including information about whether or not a predefined value has been used, information about whether or not a context model of a corresponding base layer slice has been used, information about whether or not a slice coded temporally before the given slice has been used. If the given slice is arithmetically coded by the context model for a base layer slice or a slice coded temporally before the given slice, the data may include information about whether or not each of probability models constituting a context model for a slice coded temporally before the given slice has been used as a reference model.
• FIG. 4 is a flowchart illustrating a video coding method including a context-based adaptive coding method according to an exemplary embodiment of the present invention.
• the video coding method includes subtracting a predicted image for a given slice to be compressed from the given slice to generate a residual signal (step S410), performing spatial transform on the residual signal and generate a transform coefficient (step S420), quantizing data symbols containing a transform coefficient and a motion vector obtained during generation of the predicted image (step S430), entropy coding the quantized data symbols (steps S440 through S470), and generating a bitstream for transmission to a decoder (steps S480 and S490).
• the entropy coding process includes binarization (step S440), resetting of a context model (step S454 or S456 ), arithmetic coding (step S460), and update of a context model (step S470).
• binarization step S440 may be skipped.
• a data symbol having a non-binary value is converted or binarized into a binary value.
• a context model for the slice is reset in steps S452 through S456.
• the entropy coding is performed in units of blocks and a context model is reset in units of slices to ensure independence of slices.
• the context model is reset for symbols of the first block in the slice.
• context models corresponding thereto are adaptively updated.
• a selected context model is reset by referring to a context model for the slice coded temporally before the slice, which is as described above with reference to FIGS. 2 and 3.
• it can refer to a part of probability models of the context model.
• the bit stream can be transferred which contains the information of reference of each probability model.
• FIGS. 2 and 3 Examples of a slice that will be used to reset a context model for a given slice are shown in FIGS. 2 and 3.
• a video coding method including the arithmetic coding method according to the second or third exemplary embodiment of the present invention, as shown in FIG. 2 or 3, may further include selecting one of context models available for reference. Criteria of selecting one of context models available for reference include coding efficiency, an error propagation probability, and so on. In other words, a context model having a highest coding efficiency or a context model having a least error propagation probability may be selected among context model candidates.
• step S460 the binarized symbol is subjected to arithmetic coding according to a probability model having a context model for a previously selected slice as an initial value.
• step S470 the context model is updated based on the actual value of the binarized symbol. For example, if one bin of the data symbol has a value of 1 O,' the frequency count of O's is increased. Thus, the next time this model is selected, the probability of a '0' will be slightly higher.
• FIG. 5 is a flowchart illustrating a video decoding method including a context- based adaptive arithmetic decoding method according to an exemplary embodiment of the present invention.
• a decoder parses a received bitstream in order to extract data for reconstructing a video frame in step S510.
• the data may include information about a selected context model, for example, slice information of the selected context model when one of context models of a slice coded temporally before the given slice is selected for initialization of a context model of the given slice during arithmetic coding performed by an encoder.
• a context model for the given slice is reset in steps S522 through 526.
• the context model for the given slice is reset to a context model for the base layer slice in the step S524.
• the context model for the given slice is reset to a context model for a slice de coded temporally before the given slice in the step S526.
• step S530 a bitstream corresponding to the slice is arithmetically decoded according to the context model.
• step S540 the context model is updated based on the actual value of the decoded data symbol.
• the arithmetically decoded data symbol is converted or de- binarized into a non-binary value in step S550.
• step S560 dequantization is performed on the debinarized data symbol and generates a transform coefficient and, in step S570, inverse spatial transform is performed on the transform coefficient to reconstruct a residual signal for the given slice.
• step S580 a predicted image for the given block reconstructed by motion compensation is added to the residual signal, thereby reconstructing the given slice.
• FIG. 6 is a flowchart illustrating a video coding method including a context-based adaptive arithmetic coding method according to an exemplary embodiment of the present invention.
• the video coding method includes subtracting a predicted image for a given slice from the given slice to generate a residual image (step S610), performing spatial transform on the residual image and generate a transform coefficient (step S620), quantizing the transform coefficient (step S630), entropy coding the quantized transform coefficient (steps S640 through S670), generating a bitstream (step S680), and transmitting the bitstream to a decoder (step S690).
• entropy coding is performed in the following manner.
• a context model for the given slice is reset to a context model for a corresponding base layer slice, a context model for a slice coded temporally before the given slice, or a predetermined initial value provided by a video encoder.
• the video coding method may further comprise selecting one of a context model for a base layer slice corresponding to the given slice in an enhancement layer, a context model for a slice coded temporally before the given slice in the same enhancement layer, and a predetermined initial value provided by a video encoder.
• the video coding method according to the illustrative embodiment may further comprise selecting a probability model to be used as a reference model.
• a selected context model among two or more context models is initialized in step
• step S655 and then arithmetically coded in step S660.
• step S670 the context model is updated using an arithmetically coded data symbol value.
• a bitstream generated through the above steps may contain information about a slice used in resetting a context model for the given slice, or information about whether or not each of probability models constituting a context model for a slice coded temporally before the given slice has been used as a reference model.
• FIG. 7 is a flowchart illustrating a video decoding method including a context- based adaptive arithmetic decoding method according to an exemplary embodiment of the present invention.
• a video decoder parses a bitstream in order to extract data about a given slice to be reconstructed in step S710.
• the data about the given slice may include information about a slice used for initializing a context model for the given slice, information about the context model for the given slice, or information about whether or not each of probability models constituting a context model for a slice coded temporally before the given slice has been used as a reference model.
• a context model for the given slice is reset to either a context model for a corresponding base layer slice or a context model for a slice de coded temporally before the given slice according to the information about an initial value of the context model extracted from the bitstream in step S725.
• step S730 a bitstream corresponding to the given slice is arithmetically decoded using the context model.
• step S740 the context model is updated based on the value of arithmetically decoded data symbol.
• step S750 the arithmetically decoded value is converted or debinarized into a non-binary value.
• step S760 dequantization is performed on the debinarized value and a transform coefficient is generated.
• CABAC context-based adaptive binary arithmetic coding
• the video decoder performs inverse spatial transform on the transform coefficient to reconstruct a residual image in step S770 and adds a predicted image reconstructed by motion compensation to the residual image in order to reconstruct the given slice in step S780.
• FlG. 8 is a block diagram of a video encoder 800 according to an exemplary embodiment of the present invention.
• the video encoder 800 includes a spatial transformer 840, a quantizer 850, an entropy coding unit 860, a motion estimator 810, and a motion compensator 820.
• the motion estimator 810 performs motion estimation on a given frame among input video frames using a reference frame to obtain motion vectors.
• a block matching algorithm is widely used for the motion estimation.
• a given motion block is moved in units of pixels within a particular search area in the reference frame, and displacement giving a minimum error is estimated as a motion vector.
• hierarchical variable size block matching HVSBM
• simple fixed block size motion estimation is used.
• the motion estimator 810 transmits motion data such as motion vectors obtained as a result of motion estimation, a motion block size, and a reference frame number to the entropy coding unit 860.
• the motion compensator 820 performs motion compensation on the reference frame using the motion vectors calculated by the motion estimator 810 and generates a predicted frame for the given frame.
• a subtracter 830 calculates a difference between the given frame and the predicted frame in order to remove temporal redundancy within the input video frame.
• the spatial transformer 840 uses spatial transform technique supporting spatial scalability to remove spatial redundancy within the frame in which temporal redundancy has been removed by the subtractor 830.
• the spatial transform method may include a Discrete Cosine Transform (DCT), or wavelet transform. Spatially- transformed values are referred to as transform coefficients.
• DCT Discrete Cosine Transform
• transform coefficients Spatially- transformed values are referred to as transform coefficients.
• the quantizer 850 applies quantization to the transform coefficient obtained by the spatial transformer 840.
• Quantization means the process of expressing the transform coefficients formed in arbitrary real values by discrete values, and matching the discrete values with indices according to the predetermined quantization table.
• the quantized result value is referred to as a quantized coefficient.
• the entropy coding unit 860 losslessly codes data symbols including the quantized transform coefficient obtained by the quantizer 850 and the motion data received from the motion estimator 810.
• the entropy coding unit 860 includes a binarizer 861, a context model selector 862, an arithmetic encoder 863, and a context model updater 864.
• the binarizer 861 converts the data symbols into a binary value that is then sent to the context model selector 862.
• the binarizer 861 may be omitted when CABAC is not used.
• the context model selector 862 selects either an initial value predefined as an initial value of a context model for a given slice or a context model for a slice coded temporally before the given slice. Information about the selected initial value of the c ontext model is sent to a bitstream generator 870 and inserted into a bitstream for transmission. Meanwhile, when a method of referring to slices coded temporally before the given slice in order to initialize a context model for a given slice is predefined between an encoder part and a decoder part, the context model selector 862 may not be provided.
• the arithmetic encoder 863 performs context-based adaptive arithmetic coding on data symbols of a given block using the context model.
• the context model updater 864 updates the context model based on the value of the arithmetically coded data symbol.
• the video encoder 800 may further include a dequantizer and an inverse spatial transformer.
• FlG. 9 is a block diagram of a video decoder 900 according to an exemplary embodiment of the present invention.
• the video decoder 900 includes a bitstream parser 910, an entropy decoding unit
• the bitstream parser 910 parses a bitstream received from an encoder to extract information needed for the entropy decoding unit 920 to decode the bitstream.
• the entropy decoding unit 920 performs lossless decoding that is the inverse operation of entropy coding to extract motion data that are then fed to the motion compensator 950 and texture data that are then fed to the dequantizer 930.
• the entropy decoding unit 920 includes a context model setter 921, an arithmetic decoder 922, a context model updater 923, and a debinarizer 924.
• the context model setter 921 initializes a context model for a slice to be decoded according to the information extracted by the bitstream parser 910.
• the information extracted by the bitstream parser 910 may contain information about a slice having a context model to be used as an initial value of a context model for a given slice and in- formation about a probability model to be used as the initial value of the context model for the given slice.
• context models independent of type of the block in a slice may be initialized.
• the arithmetic decoder 922 performs context-based adaptive arithmetic decoding on a bitstream corresponding to data symbols of the given slice according to the context model set by the context model setter 921.
• the context model updater 923 updates the given context model based on the value of the arithmetically decoded data symbol.
• the debinarizer 924 converts the decoded binary values obtained by the arithmetic decoder 922 into non-binary values.
• the d ebinarizer performs inversely binarizing data.
• the dequantizer 930 dequantizes texture information received from the entropy decoding unit 920.
• the dequantization is a process of obtaining quantized coefficients from matched quantization indices received from the encoder.
• the inverse spatial transformer 940 performs inverse spatial transform on coefficients obtained after the dequantization to reconstruct a residual image in a spatial domain.
• the motion compensator 950 performs motion compensation on the previously reconstructed video frame using the motion data from the entropy decoding unit 920 and generates a motion-compensated frame.
• an adder 960 adds a motion-compensated image received from the motion compensator 950 to the residual image in order to reconstruct a video frame.
• various components mean, but are not limited to, software or hardware components, such as a Field Programmable Gate Arrays (FPGAs) or Application Specific Integrated Circuits (ASICs), which perform certain tasks.
• the components may advantageously be configured to reside on the addressable storage media and configured to execute on one or more processors.
• the functionality provided for in the components and modules may be combined into fewer components and modules or further separated into additional components and modules.
• context-based adaptive arithmetic coding and decoding methods and apparatuses of the present invention according to the exemplary em- bodiments of the present invention provide at least the following advantages.
• the video coding and decoding methods and apparatuses can improve overall coding efficiency and reduce error propagation by initializing a context model for a given slice to a context model for a base layer slice.
• the video coding and decoding methods and apparatuses also provide improved coding performance by initializing a context model for a given slice to one of context models for two or more previously coded slices.

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