JP2021057730A - Image coding method, image coding device, image decoding method, and image decoding device - Google Patents

Abstract

To provide an image coding method and an image decoding method capable of achieving a high compression rate and better image quality.SOLUTION: An inter-prediction unit 105 in an image coding device includes: a history list that stores motion prediction information for blocks that have been coded according to a history list size regulation; a history list size reference unit 603 that manages the size of the history list; a merge mode list creation unit 601 that adds the motion prediction information in the history list as a merge mode candidate in addition to the motion prediction information on a surrounding block of a coding object block and the motion prediction information on a collocated block, and creates a merge mode candidate list; and a merge mode prediction unit 602 that selects optimum motion prediction information on the basis of the merge mode candidate list created by the merge mode list creation unit 601 and performs inter-prediction by the merge mode.SELECTED DRAWING: Figure 6

Description

The present invention relates to an image coding method for encoding an image, an image coding device, an image decoding method for decoding encoded image data, and an image decoding device.

As a method of converting image and audio information into digital data, recording and transmitting it, H. 264 / AVC (Advanced Video Coding) and H.A. 265 / HEVC (High Efficiency Video Coding) standards and the like have been formulated so far. ISO / IEC MPEG and ITU-T VCEG are studying a next-generation method called VVC (Versatile Video Coding) that realizes a compression ratio exceeding these (see Non-Patent Document 1).

As one of the technical candidates for VVC, a method called a merge mode in inter-screen prediction (inter-prediction) has been proposed. In the merge mode, the motion prediction information is acquired from the coded blocks around the coded block. In HEVC's merge mode, motion prediction information of peripheral blocks was listed to create a merge mode candidate list, and motion prediction information was specified by the number of this list, but in VVC, history-based motion prediction information is added. Has been proposed. In this method, a list for history is separately prepared, the motion prediction information of the encoded blocks is sequentially stored, and the list is added to the merge mode candidate list.

Xiaozhong Xu and Shan Liu, “Recent advances in video coding beyond the HEVC standard” SIP (2019), vol.8

However, in the currently proposed method, the history list is fixed at size 6. If the size is fixed, even a system with a small amount of memory such as a mobile terminal must keep a certain list, which makes resources inefficient. On the other hand, in resource-rich large-scale systems, it may be possible to improve coding efficiency by holding a longer list. As described above, the fixed length list has a problem that the system lacks flexibility and the coding efficiency cannot be optimized.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a more suitable image coding / decoding technique.

In order to achieve the above object, one embodiment of the present invention may be configured as described in the claims, for example.

According to the present invention, it is possible to provide a more suitable image coding technique and image decoding technique.

It is explanatory drawing of an example of the image coding apparatus which concerns on Example 1 of this invention. It is explanatory drawing of an example of the image decoding apparatus which concerns on Example 2 of this invention. It is explanatory drawing of an example of the image coding method which concerns on Example 1 of this invention. It is explanatory drawing of an example of the image decoding method which concerns on Example 2 of this invention. It is explanatory drawing of an example of the data recording medium which concerns on Example 3 of this invention. It is a detailed explanatory drawing of an example of the image coding apparatus which concerns on Example 1 of this invention. It is a detailed explanatory drawing of an example of the image decoding apparatus which concerns on Example 2 of this invention. It is a detailed explanatory drawing of an example of the image coding method which concerns on Example 1 of this invention. It is a detailed explanatory drawing of an example of the image decoding method which concerns on Example 2 of this invention. It is explanatory drawing of the method of making a history list which concerns on one Example of this invention.

Hereinafter, examples of the present invention will be described with reference to the drawings.

Further, in each drawing, the components having the same reference numerals have the same functions.

The "0 vc" or "0 vector" in each description and each drawing of the present specification means that the value of each component is 0, or is converted and set to such a vector.

In addition, "not referenceable" in each description and each drawing of the present specification means that the block information cannot be acquired because the block position is outside the range of the screen. “Referenceable” means that block information can be acquired, and the block information includes information such as a pixel value, a vector, a reference frame number, and / or a prediction mode.

In addition, the expression "residual component" in each description and each drawing of the present specification also includes the same meaning as "prediction error".

In addition, the expression "area" in each description and each drawing of the present specification also includes the same meaning as "image".

In addition, the expression "transmitted with a flag" in each description and each drawing of the present specification also includes the meaning of "transmission included in the flag".

(Example 1)
First, Example 1 of the present invention will be described with reference to the drawings.

FIG. 1 shows an example of a block diagram of the image coding apparatus according to the first embodiment of the present invention.

The image coding device includes, for example, an image input unit 101, a block division unit 102, a mode management unit 103, an intra prediction unit 104, an inter prediction unit 105, a block processing unit 106, a conversion / quantization unit 107, and an inverse quantization / inverse conversion. A unit 108, an image composition / filter unit 109, a decoded image management unit 110, an entropy coding unit 111, and a data output unit 112 are provided.

The operation of each component of the image coding apparatus will be described in detail below.

The operation of each component of the image coding device may be, for example, an autonomous operation of each component as described below. Further, for example, it may be realized by cooperating with software stored in the control unit or the storage unit.

First, the image input unit 101 acquires and inputs the original image to be encoded. Next, the block division unit 102 divides the input original image into blocks of a certain size called a CTU (Coding Tree Unit), and further analyzes the input image to make each CTU according to its characteristics. And divide it into more detailed blocks. The block that is the unit of these coding is called a CU (Coding Unit). The division of the CTU into CUs is managed by a tree structure such as a quadtree, a ternary tree, or a binary tree. The inside of the CU may be further divided into subblocks for prediction and TUs (Transform Units) for frequency conversion, quantization, and the like.

The mode management unit 103 manages a mode that determines a coding method for each CU. Coding processing is performed using a plurality of intra-prediction methods and inter-prediction methods, and the most efficient mode for coding the CU is determined. The most efficient mode is a mode in which the coding error can be minimized for a certain amount of code. There may be a plurality of optimum modes, which may be selected as appropriate according to the situation. To determine which mode is efficient, the intra-prediction unit 104 and the inter-prediction unit 105 perform prediction processing of multiple modes, measurement of residual components and code amounts of various flags using other processing units, and reproduction at the time of decoding. It is performed in combination with image error prediction. Generally, the mode is determined in units of CU, but the CU may be divided into sub-blocks and the mode may be determined for each.

The method of predicting the coded block (CU or subblock) generally includes intra (intra-frame) prediction and inter (inter-frame) prediction, which are performed by the intra prediction unit 104 and the inter prediction unit 105, respectively. The intra prediction uses the information of the same frame encoded before the coded block, and the inter prediction uses the information of the frame before or after the coded frame before the coded frame. Use. Here, although only one intra prediction unit 104 and one inter prediction unit 105 are described for the sake of explanation, they may be provided for each coding mode and each frame.

The intra prediction unit 104 performs in-screen prediction processing. In the "prediction processing", a prediction image is generated. The in-screen prediction process predicts the pixels of the coded block using the information of the same frame encoded before the coded block. Intra prediction includes direction prediction, matrix prediction, cross-component prediction, multi-line prediction, in-screen block copy, and the like. In the transmission of the intra prediction mode, the most probable mode is estimated from the intra prediction mode of the encoded block.

The inter-screen prediction unit 105 performs inter-screen prediction processing. In the "prediction processing", a prediction image is generated. The inter-screen prediction process predicts the pixels of the coded block by using the information of the frames before or after the coded frame, which is coded before the coded frame. In this embodiment, we propose an improvement method of the merge mode in inter-prediction. The inter-prediction method added by this embodiment will be described later. Inter-prediction includes motion compensation prediction, merge mode prediction, affine transformation prediction, triangle block division prediction, intra-inter-combination prediction, optical flow prediction, decoder-side movement prediction, and the like.

The block processing unit 106 is obtained from the block division unit 102 and the prediction image generated by the intra prediction by the intra prediction unit 104 or the prediction image generated by the inter prediction unit 105 for each coded block. The residual component is calculated and output by taking the difference from the original image of the coded block.

The conversion / quantization unit 107 performs frequency conversion and quantization processing on the residual component input from the block processing unit 106, and outputs a coefficient sequence. For frequency conversion, DCT (Discrete Cosine Transform), DST (Discrete Sine Transform), or those converted so that they can be processed by integer arithmetic may be used. The coefficient sequence is sent to both the process of restoring the image to create the decoded image used for prediction and the process of outputting the data. Conversion and quantization may be skipped by specifying the mode.

The inverse quantization / inverse conversion unit 108 performs inverse quantization and inverse conversion in order to create a decoded image using the coefficient sequence obtained from the transformation / quantization unit 107 for prediction, and outputs the restored residual component. To do. Inverse quantization and inverse conversion may be performed in the opposite directions corresponding to the quantization and transformation of the conversion / quantization unit, respectively. Inverse quantization and inverse transformation may be skipped by specifying the mode.

The image composition / filter unit 109 is restored by the inverse quantization / inverse conversion unit 108 with the prediction image generated by the intra prediction by the intra prediction unit 104 or the prediction image generated by the inter prediction by the inter prediction unit 105. The residual component is synthesized, and further processing such as a loop filter is performed to generate a decoded image.

The decoded image management unit 110 holds the decoded image and manages the image referred for the intra prediction and the inter prediction, the mode information, and the like.

The entropy coding unit 111 performs entropy coding processing on the mode information and the coefficient string information and outputs the bit string. As the entropy coding method, a method such as CABAC (Context Adaptive Binary Arithmetic Code) may be used. A variable length code and a fixed length code may be used in combination. To determine the context, refer to the specified table.

The data output unit 112 outputs the encoded data to the recording medium or the transmission line.

Next, the flow of the coding method in the image coding apparatus according to the first embodiment of the present invention will be described with reference to FIG.

First, in step 301, the original image to be encoded is input, the content of the image is analyzed, the division method is determined, and the image is divided into blocks. The analysis of the image content may be performed on the entire image, may be performed by combining a plurality of frames, or may be performed in units of blocks such as slices, tiles, bricks, and CTUs in which the image is divided. The block is generally divided into CTUs of a certain size and then divided into CUs by a tree structure.

Next, in step 302, intra-prediction is performed for the coded target block of the original image acquired in step 301. The intra prediction mode is as described above. Prediction is performed for a plurality of modes according to each intra prediction mode.

Next, in step 303, inter-prediction is performed for the coded target block of the original image acquired in step 301. In this embodiment, we propose an improvement method of the merge mode in inter-prediction. The inter-prediction method added by this embodiment will be described later. The inter-prediction mode is as described above. Prediction is performed for a plurality of modes according to each inter-prediction mode.

Next, in step 304, for each mode, the residual components are separated for the pixels of the coded block to be intra-predicted and inter-predicted, and the residual component conversion processing, the quantization processing, and the entropy coding processing are performed. To calculate the coded data.

Next, in step 305, a decoded image is created by performing inverse quantization and inverse conversion processing for each mode and synthesizing the residual component with the predicted image. The decoded image is managed together with the prediction data and various coding data in the intra prediction and the inter prediction, and is used for the prediction of other coding target blocks.

Next, in step 306, each mode is compared to determine the mode that can be most efficiently encoded. The mode includes an intra prediction mode, an inter prediction mode, and the like, and these are collectively called a coding mode. The mode selection method is as described above.

In step 307, the coded data of the coded block is output according to the determined coding mode. The coding process of each of the above coding target blocks is repeated for the entire image to encode the image.

The merge mode prediction method and the merge mode candidate list creation method according to this embodiment will be described with reference to FIG. This is a detailed description of a part of the operation of the inter-prediction unit 105. The inter-prediction unit 105 performs various inter-predictions, and the inter-prediction by the merge mode will be described below as an example.

The merge mode list creation unit 601 creates a merge mode candidate list for the coded block. At this time, the motion prediction information using the history list created up to this point is also added as a candidate to the list. The list for history is managed as a list whose history list is sized by the history list size reference unit 603. The history list size reference unit 603 has a memory for storing the size of the history list. The merge mode list creation unit 601 has a memory for managing a list such as a merge mode list and a history list. It has a mechanism to determine whether the motion prediction information registered in the list is the same as the motion prediction information stored in the list. The method of creating the history list will be described later.

The merge mode prediction unit 602 selects the optimum motion prediction information based on the merge mode candidate list created by the merge mode list creation unit 601, records the list number information, and performs inter-prediction by the merge mode. As the inter-prediction method in the merge mode, a conventional method may be used.

The merge mode prediction method and the merge mode candidate list creation method according to this embodiment will be described with reference to FIG. This describes in detail a part of step 303 for performing inter-prediction. In step 303 for performing inter-prediction, various inter-predictions are performed, but in the following, inter-prediction by the merge mode will be described as an example.

In step 801, a history list is created according to the history list size regulation. In the existing method, the history list size is fixed, but in this embodiment, the history list size is variable. The history list size may be implicitly determined by equipment, terminals, etc., indirectly or implicitly according to profile, tier, level, etc., or directly or explicitly by header flags, etc. You may decide on. It may be specified as a numerical value, or it may be specified as a flag or a table. The same value may be maintained depending on the method, equipment, etc., or may be changed in the middle of the stream.

The history list sequentially stores the motion prediction information of the encoded blocks. When registering the motion prediction information in the list, it is determined whether or not the motion prediction information is the same as the motion prediction information stored in the list.

The procedure for registering the list is as follows. Check if the motion prediction information in the list is the same as the motion prediction information to be registered, from the oldest to the number stored in the list. The oldest list is set as list number 0, and if there is the same list, the check number is updated with that list number. If none are the same, the check number remains 0. The size of the list is determined by the specified list size. The maximum number of stored items in the list is the specified list size. Next, the list is updated. If there is no same thing in the list and the number of stored items in the list is smaller than the list size, the motion prediction information is registered at the end (latest part) of the current list, and the number of stored items in the list is increased by 1. In other cases, that is, if there is the same thing in the list or the number of stored items in the list has reached the list size, the movement prediction information of the position of the check number is deleted, and in the subsequent (newer) list. Move forward the motion prediction information of (store the list number in the place where -1 is done). Finally, the motion prediction information is registered at the end (latest part) of the list. The number of stored items in the list is -1, and the number of stored items in the list is the same.

In step 802, the merge mode is predicted for the coded block with reference to the history list created in step 801. As the inter-prediction method in the merge mode, a conventional method may be used. At this time, if there is space in the merge mode candidate list, the motion prediction information is copied from the history list and used as the merge mode candidate. The method of creating the merge mode candidate list will be described later.

A method of creating a history list according to this embodiment will be described with reference to FIG.

The history list is for sequentially storing the motion prediction information of the encoded blocks and adding them to the merge mode candidate list.

In the existing method, the history list size is fixed, but in this embodiment, the history list size is variable. The history list size may be implicitly determined by equipment, terminals, etc., indirectly or implicitly by profile, tier, level, etc., or directly or explicitly by header flags, etc. You may. It may be specified as a numerical value, or it may be specified as a flag or a table. The same value may be maintained depending on the method, equipment, etc., or may be changed in the middle of the stream.

The procedure for registering the list is as follows. Check if the motion prediction information in the list is the same as the motion prediction information to be registered, from the oldest to the number stored in the list. The oldest list is set as list number 0, and if there is the same list, the check number is updated with that list number. If none are the same, the check number remains 0. The size of the list is determined by the specified list size. The maximum number of stored items in the list is the specified list size. Next, the list is updated. If there is no same thing in the list and the number of stored items in the list is smaller than the list size, the motion prediction information is registered at the end (latest part) of the current list, and the number of stored items in the list is increased by 1. In other cases, that is, if there is the same thing in the list or the number of stored items in the list has reached the list size, the movement prediction information of the position of the check number is deleted, and in the subsequent (newer) list. Move forward the motion prediction information of (store the list number in the place where -1 is done). Finally, the motion prediction information is registered at the end (latest part) of the list. The number of stored items in the list is -1, and the number of stored items in the list is the same.

The method of creating the merge mode candidate list is as follows: after the motion prediction information of the peripheral blocks of the coded block and the motion prediction information of the colocted block are stored, the motion prediction information of the history list is stored, and then in the list. Stores the average value of motion prediction information, and stores the zero vector if there is space.

Here, when storing the motion prediction information of the history list in the merge mode candidate list, check the availability of the merge mode candidate list at that time. If there is space in the merge mode candidate list, among the motion information stored in the history list, the number of motion information corresponding to the number of spaces in the merge mode candidate list is copied in order from the new motion information. Here, "in order from the newest motion information" has the same meaning even if it is expressed as "in order from the motion information having the largest index" among the motion information stored in the history list. At this time, as described above, the history list size is variable in this embodiment. Therefore, when the motion information is stored in the history list without any space, the maximum index of the motion information to be copied to the above-mentioned merge mode candidate list changes according to the history list size unlike the conventional case. When copying the motion information stored in the history list to the merge mode candidate list, the motion information already existing in the merge mode candidate list is not copied for the same motion information. Further, when copying the motion information stored in the history list to the merge mode candidate list, the maximum value of the number of copies may be determined separately from the history list size. At this time, the maximum value of the number of copies may be set so as to be always equal to or less than the history list size. Alternatively, the maximum number of copies and the variable history list size, whichever is smaller, may be set to allow copying.

In this way, the motion prediction information of the coded block is stored in the history list. The motion prediction information stored in the history list is copied to the merge mode candidate list of the block to be coded thereafter. In this way, more suitable candidates can be added to the motion prediction information that can be selected in the merge mode.

As described above, the coding process in this embodiment is performed.

According to the image coding apparatus and the image coding method according to the first embodiment described above, the list size can be adjusted according to the situation, the system is more flexible than the existing method, and the compression efficiency is high. It becomes possible to realize an image coding device and an image coding method.

Further, the image coding device and the image coding method according to the first embodiment can be applied to a recording device, a mobile phone, a digital camera, or the like using them.

According to the image coding apparatus and the image coding method according to the first embodiment of the present invention described above, the amount of coded data is reduced and the image quality of the decoded image is deteriorated when the coded data is decoded. It becomes possible to prevent it. That is, a high compression rate and a better image quality can be realized.

Therefore, according to the image coding apparatus and the image coding method according to the first embodiment of the present invention, a more suitable image coding technique can be provided.

(Example 2)
Next, FIG. 2 shows an example of a block diagram of the image decoding apparatus according to the second embodiment of the present invention.

The image decoding device is, for example, a stream analysis unit 201, a block management unit 202, a mode determination unit 203, an intra prediction unit 204, an inter prediction unit 205, a coefficient analysis unit 206, an inverse quantization / inverse conversion unit 207, and an image composition / filter unit. It includes 208, a decoded image management unit 209, and an image output unit 210.

The operation of each component of the image decoding device will be described in detail below.

The operation of each component of the image decoding device may be, for example, an autonomous operation of each component as described below. Further, for example, it may be realized by cooperating with software stored in the control unit or the storage unit.

First, the stream analysis unit 201 analyzes the input coded stream. Here, the stream analysis unit 201 also performs data extraction processing from packets and information acquisition processing of various headers and flags.

Further, at this time, the coded stream input to the stream analysis unit 201 is, for example, a coded stream generated by the image coding device and the image coding method according to the first embodiment. Since the generation method is as shown in the first embodiment, the description thereof will be omitted. It may be a coded stream read from the data recording medium shown in Example 3. The recording method will be described later.

Next, the block management unit 202 manages the block processing according to the block division information analyzed by the stream analysis unit 201. Generally, the coded image is divided into blocks, and each coded block is managed by a tree structure or the like. The block processing order is often the raster scan order, but the blocks may be processed in an arbitrary predetermined order such as a zigzag scan. The block division method is as described above.

Next, the mode determination unit 203 determines the coding mode specified by the flag or the like for each coding target block. The following decoding process is performed according to the coding mode of the determination result. The processing for each coding mode will be described below.

First, when the coding mode is intra-coding, the intra-prediction unit 204 synthesizes the intra-prediction and the predicted image. The intra prediction mode is as described in the first embodiment.

When the coding mode is coding by inter-prediction, the inter-prediction unit 205 synthesizes the inter-prediction and the predicted image. In this embodiment, we propose an improvement method of the merge mode in inter-prediction. The inter-prediction method added by this embodiment will be described later. The inter-prediction mode is as described in the first embodiment.

On the other hand, the coefficient analysis unit 206 analyzes the coded data of each coded block included in the input coded stream, decodes the entropy-coded data, and encodes the coded data including the coefficient sequence of the residual component. Is output. At this time, the process corresponding to the coding mode of the determination result of the mode determination unit 203 is performed.

The inverse quantization / inverse conversion unit 207 performs inverse quantization processing and inverse conversion on the coded data including the coefficient sequence of the residual component, and restores the residual component. The methods of inverse quantization and inverse conversion are as described above. Inverse quantization and inverse transformation may be skipped by specifying the mode.

The residual component restored as described above is combined with the predicted image output from the intra prediction unit 204 and the inter prediction unit 205 by the image composition / filter unit 208, and further processed by a loop filter or the like to perform the decoded image. Is output as.

The decoded image management unit 209 holds the decoded image and manages the image referred for the intra prediction and the inter prediction, the mode information, and the like.

The last decoded image is output by the image output unit 210, and the image is decoded.

Next, the flow of the image decoding method in the image decoding apparatus according to the second embodiment of the present invention will be described with reference to FIG.

First, in step 401, the coded stream to be decoded is acquired and the data is analyzed. It also manages block processing according to the analyzed block division information. The block division method is as described in the first embodiment.

Next, in step 402, the coding mode for one coding unit (block unit, pixel unit, etc.) included in the coded data is determined by using the coding mode information analyzed in step 401. Here, in the case of the intra-coding mode, the process proceeds to step 403, and in the case of the inter-coding mode, the process proceeds to step 404.

In step 403, the intra prediction and the prediction image are combined according to the method specified by the coding mode. The intra prediction mode is as described in the first embodiment.

In step 404, inter-prediction and prediction image composition are performed according to the method specified by the coding mode. In this embodiment, we propose an improvement method of the merge mode in inter-prediction. The inter-prediction method added by this embodiment will be described later. The inter-prediction mode is as described in the first embodiment.

In step 405, the coded data of each coded block is analyzed according to the method specified by the coding mode, the entropy-coded data is decoded, and the coded data including the coefficient sequence of the residual component is output. To do. Further, the coded data including the coefficient sequence of the residual component is subjected to inverse quantization processing and inverse conversion to restore the residual component. The methods of inverse quantization and inverse conversion are as described above. Inverse quantization and inverse transformation may be skipped by specifying the mode.

In step 406, for each coded block, the predicted image created by intra-prediction or inter-prediction and the restored residual component are combined, and the decoded image is further processed by a loop filter or the like to obtain a decoded image. create. A decoded image is created by performing the decoding process performed for each coded block for the entire image.

In step 407, the generated decoded image is output and displayed.

The merge mode prediction method and the merge mode candidate list creation method according to this embodiment will be described with reference to FIG. 7. This is a detailed description of a part of the operation of the inter-prediction unit 205. The inter-prediction unit 205 performs various inter-predictions, and the inter-prediction by the merge mode will be described below as an example.

The merge mode list creation unit 701 creates a merge mode candidate list for the block to be decrypted. At this time, the motion prediction information using the history list created up to this point is also added as a candidate to the list. The list for history is managed as a list whose history list is sized by the history list size reference unit 703. The history list size reference unit 703 has a memory for storing the size of the history list. The merge mode list creation unit 701 has a memory for managing a list such as a merge mode list and a history list. It has a mechanism to determine whether the motion prediction information registered in the list is the same as the motion prediction information stored in the list. The method of creating the history list is as described in the first embodiment.

The merge mode prediction unit 702 selects the optimum motion prediction information based on the merge mode candidate list created by the merge mode list creation unit 701, records the list number information, and performs inter-prediction by the merge mode. As the inter-prediction method in the merge mode, a conventional method may be used.

The merge mode prediction method and the merge mode candidate list creation method according to this embodiment will be described with reference to FIG. This describes in detail a part of step 404 for making an inter-prediction. In step 404 for performing inter-prediction, various inter-predictions are performed, but in the following, inter-prediction by the merge mode will be described as an example.

In step 901, a history list is created according to the history list size regulation. In the existing method, the history list size is fixed, but in this embodiment, the history list size is variable. The history list size may be implicitly determined by equipment, terminals, etc., indirectly or implicitly according to profile, tier, level, etc., or directly or explicitly by header flags, etc. You may decide on. It may be specified as a numerical value, or it may be specified as a flag or a table. The same value may be maintained depending on the method, equipment, etc., or may be changed in the middle of the stream.

The history list sequentially stores the motion prediction information of the decoded blocks. When registering the motion prediction information in the list, it is determined whether or not the motion prediction information is the same as the motion prediction information stored in the list.

The procedure for registering the list is as follows. Check if the motion prediction information in the list is the same as the motion prediction information to be registered, from the oldest to the number stored in the list. The oldest list is set as list number 0, and if there is the same list, the check number is updated with that list number. If none are the same, the check number remains 0. The size of the list is determined by the specified list size. The maximum number of stored items in the list is the specified list size. Next, the list is updated. If there is no same thing in the list and the number of stored items in the list is smaller than the list size, the motion prediction information is registered at the end (latest part) of the current list, and the number of stored items in the list is increased by 1. In other cases, that is, if there is the same thing in the list or the number of stored items in the list has reached the list size, the movement prediction information of the position of the check number is deleted, and in the subsequent (newer) list. Move forward the motion prediction information of (store the list number in the place where -1 is done). Finally, the motion prediction information is registered at the end (latest part) of the list. The number of stored items in the list is -1, and the number of stored items in the list is the same.

In step 902, the merge mode is predicted for the decryption target block with reference to the history list created in step 901. As the inter-prediction method in the merge mode, a conventional method may be used. At this time, if there is space in the merge mode candidate list, the motion prediction information is copied from the history list and used as the merge mode candidate. The method of creating the merge mode candidate list is as described in the first embodiment.

In this embodiment as well, in addition to the examples, a coded stream in which each coded mode is subdivided and defined by using the size of the block used in the coded mode as a parameter may be used as the decoding target stream.

As described above, the decoding process in this embodiment is performed.

According to the image decoding apparatus and the image decoding method according to the second embodiment described above, the list size can be adjusted according to the situation, the system is more flexible than the existing method, and the image decoding has high compression efficiency. It becomes possible to realize an apparatus and an image decoding method.

Further, the image decoding device and the image decoding method according to the second embodiment can be applied to a reproduction device, a mobile phone, a digital camera, or the like using them.

According to the image decoding apparatus and the image decoding method according to the second embodiment of the present invention described above, it is possible to decode coded data having a small amount of code with higher image quality.

Therefore, according to the image decoding apparatus and the image decoding method according to the second embodiment of the present invention, a more suitable image decoding technique can be provided.

(Example 3)
Next, FIG. 5 shows an example of the data recording medium according to the third embodiment of the present invention.

The coded stream according to the present embodiment of the present invention is a coded stream generated by the image coding apparatus or the image coding method according to the first embodiment according to the first embodiment. Since the generation method is as shown in the first embodiment, the description thereof will be omitted.

Here, the coded stream according to this embodiment is recorded as a data string 502 on the data recording medium 501, for example. The data string 502 is recorded, for example, as a coded stream according to a predetermined grammar.

First, the coded stream is taken out as a bit string divided into units of a certain size called a NAL (Network Abstraction Layer) unit 503. The bit string of the NAL unit is read out according to a predetermined rule such as a variable length code and converted as an RBSP (Raw Byte Sequence Payload). The RBSP data is composed of information such as a sequence parameter set 504, a picture parameter set 505, a decoding parameter set, a video parameter set, and slice data 506.

Inside each slice, for example, information 507 about each block is contained. Inside the information about the block, for example, there is an area for recording each coding mode for each block, and this is set as a coding mode flag 508.

According to the data recording medium according to the third embodiment described above, the list size can be adjusted according to the situation, and the compression efficiency can be recorded higher than that of the existing method.

According to the data recording medium according to the third embodiment of the present invention described above, the amount of code can be reduced and deterioration of image quality can be prevented. That is, it is possible to realize a data recording medium that has a high compression rate and records a coded stream having better image quality.

It should be noted that any combination of the above-described drawings and examples of each method and the like can be an embodiment of the present invention.

According to each embodiment of the present invention described above, the amount of code can be reduced and deterioration of image quality can be prevented. That is, a high compression rate and a better image quality can be realized.

101 ... Image input unit, 102 ... Block division unit, 103 ... Mode management unit, 104 ... Intra prediction unit, 105 ... Inter prediction unit, 106 ... Block processing unit, 107 ... Conversion / quantization unit, 108 ... Inverse quantization / Inverse conversion unit, 109 ... image composition / filter unit, 110 ... decoded image management unit, 111 ... entropy coding unit, 112 ... data output unit, 201 ... stream analysis unit, 202 ... block management unit, 203 ... mode determination unit, 204 ... Intra prediction unit, 205 ... Inter prediction unit, 206 ... Coefficient analysis unit, 207 ... Inverse quantization / inverse conversion unit, 208 ... Image composition / filter unit, 209 ... Decoded image management unit, 210 ... Image output unit 601 ... Merge mode list creation unit, 602 ... merge mode prediction unit, 603 ... history list size reference unit, 701 ... merge mode list creation unit, 702 ... merge mode prediction unit, 703 ... history list size reference unit.

Claims (6)

An image coding device that encodes an input image.
Equipped with an inter-prediction unit that makes inter-screen predictions
It has a merge prediction mode that uses the motion prediction information of the coded block with reference to the motion prediction information of the coded block.
In merge prediction mode, it has a merge mode candidate list that stores motion prediction information.
It has a history list that holds the motion prediction information of the encoded block according to the history selected so far.
It has a means to copy the motion prediction information of the history list to the merge mode candidate list,
An image encoder that can specify the maximum value of a history list. In the image coding apparatus according to claim 1,
An image coding device having a means for checking whether or not the same motion prediction information is present in the list when registering the motion prediction information in the history list. An image coding method that encodes an input image.
Steps to make inter-screen predictions and
A step of performing prediction in a merge mode in which the motion prediction information of the coded block is used with reference to the motion prediction information of the encoded block.
In the merge prediction mode, it has a merge mode candidate list that stores the movement prediction information, has a history list that holds the movement prediction information of the encoded block according to the history selected so far, and merges the movement prediction information of the history list. With a step to copy to the mode candidate list,
An image coding method that can specify the maximum value of a history list. An image decoding device that decodes a coded stream that encodes an image.
Equipped with an inter-prediction unit that makes inter-screen predictions
It has a merge prediction mode that uses the motion prediction information of the coded block with reference to the motion prediction information of the coded block.
In merge prediction mode, it has a merge mode candidate list that stores motion prediction information.
It has a history list that holds the motion prediction information of the encoded block according to the history selected so far.
It has a means to copy the motion prediction information of the history list to the merge mode candidate list,
An image decoding device that can specify the maximum value of the history list. In the image decoding apparatus according to claim 4,
An image decoding device having a means for checking whether or not the same motion prediction information is present in the list when registering the motion prediction information in the history list. An image decoding method that decodes a coded stream that encodes an image.
Steps to make inter-screen predictions and
A step of performing prediction in a merge mode in which the motion prediction information of the coded block is used with reference to the motion prediction information of the encoded block.
In the merge prediction mode, it has a merge mode candidate list that stores the movement prediction information, has a history list that holds the movement prediction information of the encoded block according to the history selected so far, and merges the movement prediction information of the history list. With a step to copy to the mode candidate list,
An image decoding method that can specify the maximum value of the history list.

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