JP2011024001A - Context-adaptive entropy coding method and apparatus, context-adaptive entropy decoding method and apparatus, and programs therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve efficiency of coding by making available a context table adaptively initialized in accordance with an input image in adaptive entropy coding based on context sorting. <P>SOLUTION: In a space-time domain, macro blocks are sorted into classes each having the same statistical character, and a class sorting information memory 10 stores therein class sorting information and context information. When starting coding for each coding unit such as a slice, the class sorting information memory 10 is referenced by a context table initial value setter 11 and a context table, that a macro block belonging to the same class as a macro block to be coded has is succeeded as information to be used for updating the context table and the context table is initialized. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a context adaptive entropy encoding / decoding technique in high-efficiency image signal encoding.

  H. In a moving picture coding apparatus corresponding to a typical moving picture coding method such as H.264 / AVC, various coded symbols such as quantized DCT coefficients and motion vectors (this is called a syntax element) The entropy encoding unit performs entropy encoding processing.

  In the moving image decoding apparatus, the encoded data encoded by the entropy encoding unit of the moving image encoding apparatus is decoded into a syntax element by the entropy decoding unit.

H. In H.264 / AVC, a method called CABAC (see Non-Patent Document 1) is adopted as the entropy encoding process. CABAC (Context-Adaptive Binary Arithmetic Coding) is a method classified as a context-adaptive arithmetic code, and includes the following three processes.
(1) binarization: a process of converting a multilevel syntax element into a binary signal.
(2) context modeling: a process of selecting a probability model (context table) of a symbol to be encoded for encoding a binary signal. The context table is updated using the encoded binary signal.
(3) binary arithmetic coding: a process of performing binary arithmetic coding on a binary signal using a selected context table.

  The context table models conditional occurrence probabilities with surrounding symbols for the encoding target symbol. The state determined by the surrounding symbols is called a context, and the context is further subdivided (called context classification), and an appropriate probability model is assigned to each context to improve coding efficiency. Yes.

  FIG. 11 shows a configuration example of CABAC. The CABAC 100 includes a binarization unit 101 that converts a multilevel signal, which is a syntax element, into a binary signal, and a context calculation unit 102 that calculates and updates the occurrence probability of the binary signal to be encoded according to the surrounding situation. And a binary arithmetic encoding unit 103 that arithmetically encodes the binary signal based on the binary signal occurrence probability given from the context calculation unit 102.

  The context calculation unit 102 holds a plurality of binary signal generation probabilities, and switches the generation probabilities according to the current encoding target and the surrounding situation, and gives them to the binary arithmetic encoding unit 103. The occurrence probability of a binary signal is one of 0 and 1 symbols (MPS: Most Probable Symbol) having a high occurrence probability and its occurrence probability table (a table having the occurrence probability of MPS. When a number is specified, the corresponding occurrence probability is Obtained) number pStateIdx (see FIG. 11B).

  The MPS occurrence probability corresponding to the occurrence probability table number pStateIdx corresponds to a higher MPS occurrence probability as the value of pStateIdex increases.

  In CABAC, the context calculation unit 102 adaptively switches the occurrence probability of a binary signal by updating pStateIdx for each encoding operation. FIG. 11C shows a table of update values of occurrence probability table numbers. In this table, the updated pStateIdx value when MPS (Most Probable Symbol: 0, 1 which has a higher probability of occurrence) is encoded is transIdxMPS, LPS (Least Probable Symbol: 0, 1). The value of the updated pStateIdx when the symbol with the lower occurrence probability is encoded as transIdxLPS. According to this table, the occurrence probability table number pStateIdx is updated and the occurrence probability table is switched for each encoding operation depending on whether the MPS is encoded or the LPS is encoded.

  This occurrence probability table number pStateIdx, current MPS, encoding state, and other information are set as one set and switched for each syntax element to be encoded such as macroblock (MB) type, CBP, BCBP, MAP, MVD, etc. Thus, entropy encoding by CABAC is performed.

  A state determined by its surrounding symbols for a coding target symbol is called a context. Information on a probability model obtained by modeling the conditional occurrence probability of such a coding symbol (in CABAC, occurrence probability table number pStateIdx) And the occurrence probability table, information on the current MPS, etc.) will be described here as a context table.

D. Marpe, H. Schwarz, and T. Wiegand, “Context-Based Adaptive Binary Arithmetic Coding in the H.264 / AVC Video Compression Standard”, IEEE trans. CSVT, Vol. 13, No. 7, pp. 620- 636, July 2003.

  CABAC initializes the contents of the context table in units called slices, which are sets of macroblocks (MB). That is, a fixed table value given in advance is used as an initial value at the start of slice encoding. However, the signal in the slice is not necessarily a signal having similar statistical properties. For example, when a moving object region and a background region coexist, both have statistically different properties.

  Originally, signals with different statistical properties can be further classified into different contexts to further improve coding efficiency. That is, under the condition where signals having different statistical properties are mixed as described above, there is still room for improvement in improving coding efficiency by context classification.

  The present invention has been made in view of such circumstances, and in adaptive entropy coding based on context classification, an adaptive entropy that classifies macroblocks into classes in the space-time domain and performs adaptive processing based on context classification for each class. The purpose is to establish an encoding method.

  In the present invention, macroblocks (hereinafter sometimes referred to as MB) are classified into sets (called classes) having similar properties in the spatio-temporal region. This classification may be performed for each encoded symbol of the macroblock. Note that the number M of classes to be classified is a value determined in advance between the encoder and the decoder. When a value other than this value is used, it is transmitted to the decoder as additional information of encoded data. Here, to classify into a set with similar properties means to classify according to some predetermined classification criteria such as the same statistical properties of the image or a specific region where the position in the image is. .

  When starting encoding in units such as slices, the information used for initial setting of the context table shall be inherited from the encoded macroblock belonging to the same class as the encoding target macroblock at the start of encoding. . The encoded macroblock that is the inheritance source is referred to as a reference macroblock. The reference macroblock is identified based on the frame number, slice number, and MB number.

The reference macroblock is specified as follows.
[Frame number specifying method 1]: Information specifying a frame number is transmitted as additional information.
[Frame number designation method 2]: When the target macroblock is a P picture (p-picuture), a reference frame for interframe prediction is used. In this case, since the information specifying the reference macroblock shares the inter-frame prediction information, no new additional information is generated.
[Slice number specification method 1]: Information specifying a slice number is transmitted as additional information.
[Slice number designation method 2]: When the target macroblock is a P picture, a slice having the same number as the slice number of the target macroblock is used in a reference frame for interframe prediction. In this case, since the information specifying the reference macroblock shares the inter-frame prediction information, no new additional information is generated.
[Slice number designation method 3]: “Slice number designation method 1” and “slice number designation method 2” are switched as appropriate. In this method, switching is specified by a 1-bit flag.
[MB number specification method 1]: Information specifying the MB number is transmitted as additional information.
[MB number designation method 2]: When the target macroblock is a P picture, the reference macroblock is identified based on the reference region in the inter-frame prediction. When the reference region straddles a plurality of macroblocks, the macroblock occupying the maximum area is set as the reference macroblock. In this case, since the information specifying the reference macroblock shares the inter-frame prediction information, no new additional information is generated.

  As described above, in the present invention, information is inherited in the same class, and the initial setting of the context table is performed. Class classification criteria and specific classification methods can be freely set on the encoder side. Since the class classification method has a trade-off between coding efficiency and computational complexity, what kind of solution is given to this trade-off is at the discretion of the encoder, and a class classification framework is provided. Is the purpose. This is a design philosophy similar to a framework in which the encoder can design the motion vector estimation with a certain degree of freedom in moving picture coding.

  For example, a slice is a H.264 as a set of macroblocks. H.264. In the present invention, a slice can be used as an example of a class.

  Also at the time of decoding, information used for initial setting of the context table when starting decoding of a slice or the like is inherited from a decoded macroblock belonging to the same class as the decoding target macroblock at the start of decoding, and thereby the context table. Initialize the.

  According to the present invention, since the context table is initialized for a class composed of macroblocks having the same statistical properties, adaptive processing specialized for signals within the class becomes possible, and the code amount can be reduced. I can expect.

It is a figure which shows the structural example of the context adaptive entropy encoding apparatus which concerns on one Embodiment of this invention. It is a flowchart of the encoding process by a context adaptive entropy encoding apparatus. It is a figure which shows the structural example of the context adaptive entropy decoding apparatus which concerns on one Embodiment of this invention. It is a flowchart of the decoding process by a context adaptive entropy decoding apparatus. It is a flowchart of the context table initial value setting process (the 1). It is a flowchart of the context table initial value setting process (the 2). It is a flowchart of a context table initial value setting process (the 3). It is a flowchart of a context table initial value setting process (the continuation of the 3). It is a flowchart of a context table initial value setting process (the 4). It is a figure which shows the hardware structural example when implement | achieving with a software program. It is explanatory drawing of the conventional CABAC.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a configuration example of a context adaptive entropy encoding apparatus according to an embodiment of the present invention.

  The context adaptive entropy encoding device 1 includes a class classification information storage unit 10, a context table initial value setting unit 11, a context calculation unit 12, a binarization unit 14, and a binary arithmetic encoding unit 15. The context calculation unit 12 includes a context table storage unit 13 that stores a context table in an internal memory area.

  This context adaptive entropy encoding device 1 is an H.264 standard. This is used when entropy-encoding various encoded symbols such as quantized DCT coefficients and motion vectors in a moving image encoding apparatus such as H.264 / AVC. Here, as an example, a processing example in which the present invention is incorporated will be described mainly based on CABAC. However, the object of the present invention is not limited to CABAC, and any other system can be used as long as it is context adaptive coding. Is equally applicable.

  Similar to the binarization unit 101 in the conventional CABAC 100 shown in FIG. 11, the binarization unit 14 performs processing to convert a multilevel signal of a syntax element to be encoded into a binary signal. If the signal to be encoded is not a multilevel signal, the binarization unit 14 may be omitted.

  The binary arithmetic encoding unit 15 arithmetically encodes the binary signal output from the binarizing unit 14 according to the binary signal occurrence probability given from the context calculation unit 12, and outputs the encoded bit of the encoded stream. To do. The binary arithmetic encoding unit 15 can also be configured by the same one as the conventional binary arithmetic encoding unit 103 shown in FIG.

  The context calculation unit 12 also switches the occurrence probability stored in the context table storage unit 13 according to the current encoding target and the surrounding situation, and gives a binary signal generation probability to the binary arithmetic encoding unit 15 The point of performing is basically the same as in the prior art. However, it differs from the prior art in that the context table initialized by the context table initial value setting unit 11 is used for each coding unit such as at the start of slice coding.

  The class classification information storage unit 10 stores information on which class each encoded macroblock for a plurality of frames or slices is classified, and information on a context table at the end of encoding of the macroblock (for example, Information such as occurrence probability table number and MPS) is stored.

  The context table initial value setting unit 11 classifies the information of the context table of the reference macroblock belonging to the same class as the encoding target macroblock at the start of encoding at the start of encoding of a certain encoding unit, for example, slice. The context table acquired from the storage unit 10 and stored in the context table storage unit 13 is initialized based on the information. For example, in the case of CABAC, the occurrence probability table number pStateIdx is set to the occurrence probability table number pStateIdx updated by the reference macroblock encoding result as an initial value.

  As a result, the binary arithmetic encoding unit 15 performs adaptive encoding specialized for signals in the class, and the encoding efficiency is improved.

  Next, the processing flow of the context adaptive entropy encoding device 1 will be described with reference to the flowchart shown in FIG. Here, the flow of processing when the context table is initialized at the start of slice encoding will be described. However, the context table may be initialized at the start of another encoding unit. Also, the context table may be initialized when the class of the encoding target macroblock is changed to another class.

  [Step S10]: The following steps S11 to S110 are repeated for all slices.

  [Step S11]: For all macroblocks in the encoding target slice, a syntax element to be subjected to context adaptive entropy encoding is read. This is, for example, DCT coefficients, macroblock mode information, motion vectors, and the like.

  [Step S12]: For each syntax element, specify the context table information of the syntax element in the encoded slice used for updating the context table. The update of the context table here means initialization of the context table. When the context table information is designated, the context table information of the corresponding class stored in the class classification information storage unit 10 shown in FIG. Means to specify. In the conventional CABAC, a context table is initialized using a fixed table for each syntax element. In the present invention, the context table is initialized using context table information tuned to a class. . Details of the processing for designating the context table information will be described later with reference to FIGS.

  [Step S13]: Next, the following steps S14 to S19 are repeated for every macroblock (MB) in the current slice.

  [Step S14]: The binarization unit 14 converts the multi-value syntax element into a binary signal. This binary signal is hereinafter referred to as a binary symbol.

  [Step S15]: For a binary symbol, a context table is selected by using the same type of binary symbol information of the encoded peripheral macroblock. When CABAC is used, the CABAC regulations shown in Non-Patent Document 1 are followed.

  [Step S16]: The context table is updated using encoded binary symbols belonging to the same class. When using CABAC, follow the CABAC regulations. In the case of CABAC, the occurrence probability table number is updated according to the update value of the occurrence probability table number shown in FIG. At the head of the slice, the context table is updated using the context table information specified in step S12.

  [Step S17]: The binary symbol to be encoded is entropy-encoded by the binary arithmetic encoding unit 15 using the updated context table.

  [Step S18]: The updated context table information is written in the memory of the class classification information storage unit 10. This writing is performed to refer to the context table updated in this MB as reference information at the start of encoding of the subsequent slice. When the slice MB set is one class, that is, when the information specifying method of the context table initial value setting process (part 1) shown in FIG. 5 described later is used, the context table information is written in units of slices. Do. In other cases, the context table information is written in MB units.

  [Steps S19, S110]: The above processing is repeated for all MBs in the slice, and the processing is repeated in the same manner for all slices. When the slice is completed, the processing ends.

  FIG. 3 shows a configuration example of a context adaptive entropy decoding apparatus according to an embodiment of the present invention.

  The context adaptive entropy decoding device 2 includes a class classification information storage unit 20, a context table initial value setting unit 21, a context calculation unit 22, a binary arithmetic decoding unit 24, and a syntax element conversion unit 25. The context calculation unit 22 includes a context table storage unit 23 that stores a context table in an internal memory area.

  This context adaptive entropy decoding device 2 is an H.264 standard. It is used when decoding a moving image encoded stream in a moving image decoding apparatus such as H.264 / AVC. Here, as in the case of encoding, a processing example based on CABAC will be described. However, if it is context adaptive decoding, it can be similarly applied to other systems.

  The binary arithmetic decoding unit 24 arithmetically decodes the encoded data to be decoded according to the binary signal occurrence probability given from the context calculation unit 22, and outputs a binary signal (binary symbol) as a result of decoding. The syntax element conversion unit 25 converts a binary signal obtained by arithmetic decoding into a multi-value syntax element. These are the same as the decoding method in the conventional CABAC.

  The context calculation unit 22 also performs a process of switching the occurrence probability stored in the context table storage unit 23 according to the current decoding target and the surrounding situation and giving the binary arithmetic decoding unit 24 the binary signal occurrence probability. The point is basically the same as that of the prior art. However, it differs from the prior art in that the context table initialized by the context table initial value setting unit 21 is used for each decoding unit such as when slice decoding starts.

  In the class classification information storage unit 20, information on which class each decoded macroblock for a plurality of frames or slices is classified into, and information on a context table at the end of decoding of the macroblock (for example, occurrence probability) Information such as table number and MPS) is stored.

  The context table initial value setting unit 21 obtains information on the context table of a reference macroblock belonging to the same class as the decoding target macroblock at the start of decoding from a class classification information storage unit 20 at the start of decoding a certain decoding unit, for example, a slice. Based on the acquired information, the context table stored in the context table storage unit 23 is initialized. For example, in the case of CABAC, the occurrence probability table number pStateIdx is set with the occurrence probability table number pStateIdx updated by the decoding result of the reference macroblock as an initial value.

  Next, the flow of processing of the context adaptive entropy decoding device 2 will be described with reference to the flowchart shown in FIG. Here, the flow of processing when the context table is initialized at the start of slice decoding will be described. However, the context table can be initialized at the start of another decoding unit as well. Also, the context table may be initialized when the class of the macroblock to be decoded is changed to another class. However, this initialization unit needs to match the processing at the time of encoding.

  [Step S20]: The following steps S21 to S210 are repeated for all slices.

  [Step S21]: For all macroblocks in the decoding target slice, the encoded data of the syntax element to be subjected to context adaptive entropy decoding is read. This is, for example, data obtained by entropy encoding DCT coefficients, macroblock mode information, motion vectors, and the like.

  [Step S22]: For each syntax element, specify the context table information of the syntax element in the decoded slice to be used for updating the context table. The update of the context table here means the initialization of the context table. When the context table information is designated, the context table information of the corresponding class stored in the class classification information storage unit 20 shown in FIG. Means to specify. In the conventional CABAC, a context table is initialized using a fixed table for each syntax element. In the present invention, the context table is initialized using context table information tuned to a class. . Details of the processing for designating the context table information will be described later with reference to FIGS.

  [Step S23]: Next, the following steps S24 to S29 are repeated for every macroblock (MB) in the current slice.

  [Step S24]: A context table is selected by using the same kind of binary symbol information of the decoded neighboring macroblocks. When CABAC is used, the CABAC regulations shown in Non-Patent Document 1 are followed.

  [Step S25]: The context table is updated using decoded binary symbols belonging to the same class. When using CABAC, follow the CABAC regulations. At the head of the slice, this context table is updated using the context table information specified in step S22.

  [Step S26]: The binary symbol to be decoded is entropy-decoded by the binary arithmetic decoding unit 24 using the updated context table.

  [Step S27]: The decoded binary symbol is converted into a multi-value syntax element by the syntax element conversion unit 25 and output.

  [Step S <b> 28]: The updated context table information is written in the memory of the class classification information storage unit 20. This writing is performed to refer to the context table updated in this MB as reference information at the start of decoding of the subsequent slice. When the slice MB set is one class, that is, when the information specifying method of the context table initial value setting process (part 1) shown in FIG. 5 described later is used, the context table information is written in units of slices. Do. In other cases, the context table information is written in MB units.

  [Steps S29 and S210]: The above processing is repeated for all MBs in the slice, and the processing is repeated in the same manner for all slices. When the slice is completed, the processing ends.

  Next, some examples of detailed processing in step S12 shown in FIG. 2 and step S22 shown in FIG. 4 will be described. The difference between these examples is the difference in the method of specifying information used for updating (initializing) the context table, and the difference in the method of specifying which reference macroblock's context table information is inherited.

  When specifying a reference macroblock, it is basically necessary to specify the frame number, slice number, and MB number. For example, if other information can be specified, specification of the number is omitted. Thus, generation of additional information in encoding can be suppressed. For example, when using information in a frame for which reference is specified in inter-frame prediction, specification of a frame number can be omitted. Further, for example, when one class corresponds to one slice, it is possible to specify in units of slices and omit specification in units of macroblocks.

  The context table initial value setting process (part 1) in FIG. 5 is a process performed in step S12 (FIG. 2) and step S22 (FIG. 4), and is a method of designating information used for updating the context table in units of slices. This is a case, and designation in MB units is not performed.

  In the processing of FIG. 5, the reference frame designation method flag F1 and the reference slice designation method flag F2 are used. The reference frame designation method flag F1 specifies that information specifying the frame number is transmitted as additional information when “1”, and shares the frame number referenced in inter-frame prediction when “0”. The flag to specify. The reference slice designation method flag F2 specifies that information specifying a slice number is transmitted as additional information when “1”, and information of interframe prediction as information specifying a reference macroblock when “0”. Is a flag that specifies sharing. These flags F1 and F2 are set in advance before encoding such as a slice depending on which designation method is used. Alternatively, it is possible to perform switching according to the coding situation.

  First, it is determined whether or not the reference frame designation method flag F1 is “1” (step S50). When the flag F1 is “1”, information specifying the frame number is read as a reference frame index (step S51). If the flag F1 is “0”, the frame number referred to by the encoding target MB in inter-frame prediction is read as a reference frame index (step S52).

  Next, it is determined whether or not the reference slice designation method flag F2 is “1” (step S53). When the flag F2 is “1”, information specifying the slice number is read as a reference slice index (step S54). Thereafter, in the frame specified by the reference frame index, the context table of the last MB of the slice specified by the reference slice index is read and used as information used for updating (initializing) the context table (step S55). When the flag F2 is “0”, in the frame specified by the reference frame index, the encoding target MB reads the context table of the last MB of the slice having the same number as the inter-frame prediction slice number, and updates the context table. This is used as information used for (initialization) (step S56).

  The context table initial value setting process (part 2) in FIG. 6 is a process performed in step S12 (FIG. 2) and step S22 (FIG. 4). In FIG. 5, information used for updating the context table in units of slices. In contrast to this, in FIG. 6, it is specified in units of MB.

  In the example of FIG. 6, in addition to the above-described reference frame designation method flag F1 and reference slice designation method flag F2, a reference macroblock designation method flag F3 is used. The reference macroblock specifying method flag F3 specifies that information specifying the MB number is transmitted as additional information when “1”, and uses the motion vector information in the inter-frame prediction when “0”, and sets the MB number. Specifies that new additional information is not used as the information to be specified.

  First, it is determined whether or not the reference frame designation method flag F1 is “1” (step S60). When the flag F1 is “1”, information specifying the frame number is read as a reference frame index (step S61). When the flag F1 is “0”, the frame number referred to by the encoding target MB in inter-frame prediction is read as a reference frame index (step S62).

  Next, it is determined whether the reference slice designation method flag F2 is “1” (step S63). When the flag F2 is “1”, information specifying the slice number is read as a reference slice index (step S64). When the flag F2 is “0”, the slice number of the encoding target MB is read as the reference slice index in the frame specified by the reference frame index (step S65).

  Next, it is determined whether or not the reference macroblock specifying method flag F3 is “1” (step S66). When the flag F3 is “1”, information specifying the MB number is read as a reference MB index (step S67). Thereafter, in the frame specified by the reference frame index, in the slice specified by the reference slice index, the context table of the MB specified by the reference MB index is read and used for updating (initializing) the context table. (Step S68). When the flag F3 is “0”, motion vector information for inter-frame prediction is read for the encoding target MB (step S69). After that, in the slice specified by the reference slice index in the frame specified by the reference frame index, the context table of the MB occupying the maximum area in the area specified as the reference area for inter-frame prediction is read by the motion vector, It is used as information used for updating (initializing) the context table (step S610).

  The context table initial value setting process (part 3) in FIGS. 7 and 8 is the process performed in step S12 (FIG. 2) and step S22 (FIG. 4), as in FIG. 6, and is information used for updating the context table. This is an example of designating in MB units. However, in this example, the slice number designation method is switched as appropriate.

  First, it is determined whether or not the reference frame designation method flag F1 is “1” (step S70). When the flag F1 is “1”, information specifying the frame number is read as a reference frame index (step S71). When the flag F1 is “0”, the frame number referred to by the encoding target MB in inter-frame prediction is read as a reference frame index (step S72).

  Next, it is determined whether or not the reference slice designation method flag F2 is “1” (step S73). If the flag F2 is not “1”, the process proceeds to step S710 in FIG. If the flag F2 is “1”, information specifying the slice number is read as a reference slice index (step S74).

  Next, it is determined whether or not the reference macroblock designation method flag F3 is “1” (step S75). When the flag F3 is “1”, information specifying the MB number is read as a reference MB index (step S76). Thereafter, in the frame specified by the reference frame index, in the slice specified by the reference slice index, the context table of the MB specified by the reference MB index is read and used for updating (initializing) the context table. (Step S77). When the flag F3 is “0”, motion vector information for inter-frame prediction is read for the encoding target MB (step S78). After that, in the slice specified by the reference slice index in the frame specified by the reference frame index, the context table of the MB occupying the maximum area in the area specified as the reference area for inter-frame prediction is read by the motion vector, It is used as information used for updating (initializing) the context table (step S79).

  If the reference slice designation method flag F2 is “0”, it is next determined whether or not the reference macroblock designation method flag F3 is “1” (step S710 in FIG. 8). When the flag F3 is “1”, the same number as the slice number of the encoding target MB is set as the reference slice index in the frame specified by the reference frame index (step S711). Also, information specifying the MB number is read as a reference MB index (step S712). Thereafter, in the frame specified by the reference frame index, in the slice specified by the reference slice index, the context table of the MB specified by the reference MB index is read and used for updating (initializing) the context table. (Step S713).

  When the flag F3 in the determination in step S710 is “0”, motion vector information for inter-frame prediction is read for the encoding target MB (step S714). After that, in the slice specified by the reference slice index in the frame specified by the reference frame index, the context table of the MB occupying the maximum area in the area specified as the reference area for inter-frame prediction is read by the motion vector, It is used as information used for updating (initializing) the context table (step S715).

  The context table initial value setting process (part 4) in FIG. 9 is the process performed in step S12 (FIG. 2) and step S22 (FIG. 4) as in FIG. 6, and information used for updating the context table is stored in MB units. It is an example specified by. However, the example of FIG. 9 is a method in which the designation of MBs in a slice is fixed to a method of determining a reference macroblock based on a reference region in inter-frame prediction. Therefore, in this example, the reference macroblock designation method flag F3 is not used.

  First, it is determined whether or not the reference frame designation method flag F1 is “1” (step S80). When the flag F1 is “1”, information specifying the frame number is read as a reference frame index (step S81). When the flag F1 is “0”, the frame number referred to by the encoding target MB in inter-frame prediction is read as a reference frame index (step S82).

  Next, it is determined whether or not the reference slice designation method flag F2 is “1” (step S83). When the flag F2 is “1”, information specifying the slice number is read as a reference slice index (step S84). When the flag F2 is “0”, the slice number of the encoding target MB is read as the reference slice index in the frame specified by the reference frame index (step S85).

  Next, motion vector information for inter-frame prediction is read into the encoding target MB (step S86). After that, in the slice specified by the reference slice index in the frame specified by the reference frame index, the context table of the MB occupying the maximum area in the area specified as the reference area for inter-frame prediction is read by the motion vector, It is used as information used for updating (initializing) the context table (step S87).

  As shown in the examples of various specification methods shown in FIG. 5 to FIG. 9, a context number is switched by using a flag or the like as a frame number specification method, a slice number specification method, or an MB specification method. Information used to update the table can be specified.

  As to which specification method is used, for example, a method of fixing to one of various specification methods, a method of selecting a specification method that can minimize the code amount by brute force search, and a specification of a macro block The method is fixed to either, and the frame number and slice number can be specified before encoding or encoding of each slice from among the selection methods that can minimize the code amount by brute force search. Implementations such as selecting at the start are possible.

  When fixing to one designation method before the start of encoding, for example, a preliminary experiment is performed using a training image before encoding, and as a result, a specification method with the smallest code amount is selected. Good.

  Entropy coding using the context table adaptively tuned to the class by inheriting the macroblock context table determined by the above-mentioned various reference macroblock specification methods and updating (initializing) the context table Will be able to do.

  FIG. 10 shows an example of a hardware configuration when this system is realized by using a software program. This system includes a CPU 30 that executes a program, a memory 31 such as a RAM that stores programs and data accessed by the CPU 30, and an image signal input unit 32 (disk device) that inputs an image signal to be encoded from a camera or the like. Or a storage unit for storing image signals obtained from the CPU 30 or the like), and a software program to be executed by the CPU 30. An encoded stream generated by executing the program storage device 33 in which a moving image encoding program 34 represented by H.264 is stored and the moving image encoding program 34 loaded in the memory 31 by the CPU 30; For example, an encoded stream output unit 36 (which may be a storage unit that stores an encoded stream by a disk device or the like) that outputs via a network is connected by a bus.

  In particular, the context adaptive entropy encoding program 35 for causing the CPU 30 to execute the context adaptive entropy encoding according to the present embodiment is a part of the video encoding program 34 or separately from the video encoding program 34. It is stored in the program storage device 33 and loaded into the memory 31 for execution at the time of encoding.

  Even when the context adaptive entropy decoding method according to the present embodiment is realized by a software program, it can be realized by using a similar hardware configuration.

DESCRIPTION OF SYMBOLS 1 Context adaptive entropy encoding apparatus 2 Context adaptive entropy decoding apparatus 10,20 Class classification information storage part 11,21 Context table initial value setting part 12,22 Context calculation part 13,23 Context table storage part 14 Binary part 15 2 Value arithmetic coding unit 24 Binary arithmetic decoding unit 25 Syntax element conversion unit

Claims (8)

In a context adaptive entropy encoding method for entropy encoding encoding target data using a context table holding probability model information that models conditional occurrence probability of encoding target symbols,
Class classification information that stores information that classifies the data to be encoded of a block or symbol to be encoded into a plurality of classes according to a predetermined classification standard, and probability model information for the encoded data that has already been encoded Referring to the storage means, at the start of encoding of a certain encoding unit, the context table is initialized by using the probability model information of the encoded target data that belongs to the same class as the target data to be encoded. The context table initial value setting process,
The encoding target data is encoded according to the probability model information of the context table initialized by the context table initial value setting process, the probability model information of the context table is updated according to the encoding result, and the updated A context adaptive entropy encoding method comprising: an encoding step of writing probability model information to the class classification information storage means. The context adaptive entropy encoding method according to claim 1,
In the context table initial value setting process, when referring to the probability model information of the encoded target data that belongs to the same class as the target data to be encoded, the reference is specified in the inter-frame prediction. A context adaptive entropy encoding method characterized by referring to probability model information of encoding target data corresponding to a position indicated by reference position information of a frame. In a context adaptive entropy encoding device that entropy-encodes encoding target data using a context table that stores probability model information that models the conditional occurrence probability of the encoding target symbol,
Class classification information that stores information that classifies the data to be encoded of a block or symbol to be encoded into a plurality of classes according to a predetermined classification standard, and probability model information for the encoded data that has already been encoded Storage means;
At the start of encoding of a certain encoding unit, referring to the class classification information storage means, using the probability model information of the encoded target data that belongs to the same class as the target data to be encoded, A context table initial value setting means for initializing the context table;
The encoding target data is encoded according to the probability model information of the context table initialized by the context table initial value setting means, the probability model information of the context table is updated according to the encoding result, and the updated A context adaptive entropy encoding device, comprising: encoding means for writing the probability model information to the class classification information storage means. In a context adaptive entropy decoding method for entropy decoding decoding target data using a context table holding probability model information that models a conditional occurrence probability of a decoding target symbol,
Refers to the class classification information storage means for storing information obtained by classifying decoding target data of a block or symbol to be decoded into a plurality of classes according to a predetermined classification criterion and probability model information for the decoded decoding target data A context table initial value setting process for initializing a context table using probability model information of decoded decoding target data belonging to the same class as the decoding target data to be decoded at the start of decoding of a certain decoding unit;
The decoding target data is decoded according to the probability model information of the context table initialized by the context table initial value setting process, the probability model information of the context table is updated according to the decoding result, and the updated probability model A context adaptive entropy decoding method, comprising: a decoding step of writing information to the class classification information storage means. The context adaptive entropy decoding method according to claim 4,
In the context table initial value setting process, when referring to the probability model information of the decoded decoding target data belonging to the same class as the decoding target data to be decoded, the reference position of the frame for which reference is specified in inter-frame prediction A context adaptive entropy decoding method characterized by referring to probability model information of decoding target data corresponding to a position indicated by information. In a context adaptive entropy decoding device that entropy decodes decoding target data using a context table that stores probability model information that models a conditional occurrence probability of a decoding target symbol,
Class classification information storage means for storing information obtained by classifying decoding target data of a block or symbol to be decoded into a plurality of classes according to a predetermined classification criterion, and probability model information for decoded decoding target data;
At the start of decoding of a certain decoding unit, the class classification information storage means is referred to, and the context table is initialized by using the probability model information of decoded decoding target data belonging to the same class as the decoding target data to be decoded. A context table initial value setting means;
The decoding target data is decoded according to the probability model information held by the context table initialized by the context table initial value setting means, the probability model information held by the context table is updated according to the decoding result, and the updated probability model A context adaptive entropy decoding apparatus comprising: decoding means for writing information to the class classification information storage means.   A context adaptive entropy encoding program for causing a computer to execute the context adaptive entropy encoding method according to claim 1 or 2.   A context adaptive entropy decoding program for causing a computer to execute the context adaptive entropy decoding method according to claim 4 or 5.

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