Patent ID: 12225228

DESCRIPTION OF EMBODIMENTS

Underlying Knowledge Forming Basis of the Present Disclosure

In relation to the image coding method disclosed in the Background Art section, the inventors have found the following problem. Note that, in the following description, an image may be any of a moving image composed of a plurality of pictures, a still image composed of one picture, a part of a picture, and the like.

Image coding schemes in recent years include MPEG-4 AVC/H.264 and HEVC (High Efficiency Video Coding). In these image coding schemes, inter prediction using coded reference pictures is available.

Moreover, in these image coding schemes, a reference picture called a long-term reference picture may be used. For example, in the case where a reference picture is retained in a DPB (Decoded Picture Buffer) for a long time, the reference picture may be used as a long-term reference picture.

In HEVC, there is a mode called a merge mode. In the merge mode, a motion vector predictor obtained by predicting a motion vector of a current block from a motion vector of an adjacent block or the like is used for coding the current block as the motion vector of the current block. That is, in the merge mode, the motion vector predictor is treated as the motion vector of the current block. The motion vector predictor and the motion vector of the current block in the merge mode are also referred to as a merge vector.

In HEVC, a temporal motion vector predictor can be used, too. The temporal motion vector predictor is derived from a motion vector of a co-located block in a coded co-located picture. Coordinates of the co-located block in the co-located picture correspond to coordinates of the current block in the current picture to be coded.

Hereafter, the motion vector of the co-located block is also referred to as a co-located motion vector, and a reference picture of the co-located block is also referred to as a co-located reference picture. The co-located block is coded using the co-located motion vector and the co-located reference picture. Note that “co-located” may also be written as “collocated”.

Likewise, the motion vector of the current block is also referred to as a current motion vector, and a reference picture of the current block is also referred to as a current reference picture. The current block is coded using the current motion vector and the current reference picture.

The current block and the co-located block mentioned above are each a prediction unit (PU). The prediction unit is a block of an image, and is defined as a data unit for prediction. In HEVC, a coding unit (CU) is defined as a data unit for coding, separately from the prediction unit. The prediction unit is a block in the coding unit. In the following description, the term “block” may be replaced with “prediction unit” or “coding unit”.

The coding unit and the prediction unit are not fixed in size. For example, one picture may include a plurality of coding units of various sizes, and one picture may include a plurality of prediction units of various sizes.

This can cause a situation where a block that exactly matches an area of the current block is not defined in the co-located picture. Accordingly, in HEVC, the co-located block is selected from a plurality of blocks included in the co-located picture by a predetermined selection method.

The temporal motion vector predictor is generated by scaling the motion vector of the selected co-located block based on a POC (Picture Order Count) distance. POCs are ordinal numbers assigned to pictures in display order. A POC distance corresponds to a temporal distance between two pictures. Scaling based on a POC distance is also referred to as POC-based scaling. Expression 1 below is an arithmetic expression for performing POC-based scaling on the motion vector of the co-located block.
pmv=(tb/td)×colmv  (Expression 1).

Here, colmv is the motion vector of the co-located block. pmv is the temporal motion vector predictor derived from the motion vector of the co-located block. tb is a signed POC distance, representing a difference between the current picture and the current reference picture. td is a signed POC distance, representing a difference between the co-located picture and the co-located reference picture.

In the case where a valid temporal motion vector predictor is present, the temporal motion vector predictor is inserted into an ordered list of current motion vector candidates. The motion vector used for coding the current block is selected from the ordered list of current motion vector candidates. The selected motion vector is indicated by a parameter in a bitstream.

FIG.1is a flowchart showing an operation of an image coding apparatus according to a reference example. In particular,FIG.1shows a process of coding an image by inter prediction.

First, the image coding apparatus classifies each of reference pictures as a short-term reference picture or a long-term reference picture (Step S101). The image coding apparatus writes information indicating the classification of each of the reference pictures, to a header of the bitstream (Step S102).

Next, the image coding apparatus identifies the current reference picture (Step S103). The image coding apparatus then derives the current motion vector (Step S104). A derivation process will be described in detail later.

Following this, the image coding apparatus generates a prediction block, by performing motion compensation using the current reference picture and the current motion vector (Step S105).

The image coding apparatus subtracts the prediction block from the current block, to generate a residual block (Step S106). Lastly, the image coding apparatus codes the residual block, to generate the bitstream including the coded residual block (Step S107).

FIG.2is a flowchart showing an operation of an image decoding apparatus according to the reference example. In particular,FIG.2shows a process of decoding an image by inter prediction.

First, the image decoding apparatus obtains the bitstream, and obtains the information indicating the classification of each of the reference pictures by parsing the header of the bitstream (Step S201). The image decoding apparatus also obtains the residual block, by parsing the bitstream (Step S202).

Next, the image decoding apparatus identifies the current reference picture (Step S203). The image decoding apparatus then derives the current motion vector (Step S204). A derivation process will be described in detail later. Following this, the image decoding apparatus generates the prediction block, by performing motion compensation using the current reference picture and the current motion vector (Step S205). Lastly, the image decoding apparatus adds the prediction block to the residual block, to generate a reconstructed block (Step S206).

FIG.3is a flowchart showing details of the derivation process shown inFIGS.1and2. The following describes the operation of the image coding apparatus. The operation of the image decoding apparatus is the same as the operation of the image coding apparatus, with “coding” being replaced with “decoding”.

First, the image coding apparatus selects the co-located picture (Step S301). Next, the image coding apparatus selects the co-located block in the co-located picture (Step S302). The image coding apparatus then identifies the co-located reference picture and the co-located motion vector (Step S303). After this, the image coding apparatus derives the current motion vector by a derivation scheme that involves POC-based scaling (Step S304).

FIG.4is a diagram for explaining the co-located block used in the derivation process shown inFIG.3. The co-located block is selected from a plurality of blocks in the co-located picture.

The co-located picture is different from the current picture that includes the current block. For example, the co-located picture is a picture immediately preceding or immediately following the current picture in display order. In more detail, for example, the co-located picture is a reference picture listed first in any of two reference picture lists used for coding of B pictures (bi-predictive coding).

A first block including a sample c0in the co-located picture is a leading candidate for the co-located block, and is also referred to as a primary co-located block. A second block including a sample c1in the co-located picture is a second leading candidate for the co-located block, and is also referred to as a secondary co-located block.

Let (x, y) be coordinates of a top left sample tl in the current block, w be a width of the current block, and h be a height of the current block. Coordinates of the sample c0are (x+w, y+h). Coordinates of the sample c1are (x+(w/2)−1, y+(h/2)−1).

In the case where the first block is not available, the second block is selected as the co-located block. Examples of the case where the first block is not available include the case where the first block is not present because the current block is located rightmost or bottommost in the picture, and the case where the first block is coded by intra prediction.

The following describes a more specific example of the process of deriving the temporal motion vector predictor as the current motion vector with reference toFIG.3again.

First, the image coding apparatus selects the co-located picture (Step S301). Next, the image coding apparatus selects the co-located block (Step S302). In the case where the first block including the sample c0shown inFIG.4is available, the first block is selected as the co-located block. In the case where the first block is not available and the second block including the sample c1shown inFIG.4is available, the second block is selected as the co-located block.

In the case where the available co-located block is selected, the image coding apparatus sets the temporal motion vector predictor as available. In the case where the available co-located block is not selected, the image coding apparatus sets the temporal motion vector predictor as not available.

In the case where the temporal motion vector predictor is set as available, the image coding apparatus identifies the co-located motion vector as a base motion vector. The image coding apparatus also identifies the co-located reference picture (Step S303).

The image coding apparatus then derives the temporal motion vector predictor from the base motion vector by scaling according to Expression 1 (Step S304).

Through the process described above, the image coding apparatus and the image decoding apparatus each derive the temporal motion vector predictor as the current motion vector.

There are, however, cases where it is difficult to derive the appropriate current motion vector, depending on the relations between the current picture, the current reference picture, the co-located picture, and the co-located reference picture.

For instance, in the case where the current reference picture is a long-term reference picture, there is a possibility that the temporal distance between the current reference picture and the current picture is long. In the case where the co-located reference picture is a long-term reference picture, there is a possibility that the temporal distance between the co-located reference picture and the co-located picture is long.

These cases incur a possibility that an extremely large or small current motion vector is generated as a result of POC-based scaling. This causes degradation in prediction accuracy and degradation in coding efficiency. In particular, the extremely large or small current motion vector cannot be appropriately expressed with a fixed number of bits, leading to significant prediction accuracy degradation and coding efficiency degradation.

An image coding method according to an exemplary embodiment disclosed herein is an image coding method of coding each of blocks of pictures, the image coding method including: deriving a candidate for a motion vector of a current block to be coded, from a motion vector of a co-located block which is a block included in a picture different from a picture that includes the current block; adding the derived candidate to a list; selecting the motion vector of the current block from the list to which the candidate is added; and coding the current block using the selected motion vector and a reference picture of the current block, wherein the deriving includes: determining whether the reference picture of the current block is a long-term reference picture or a short-term reference picture, and whether a reference picture of the co-located block is a long-term reference picture or a short-term reference picture; deriving the candidate from the motion vector of the co-located block by a first derivation scheme that does not involve scaling based on a temporal distance, in the case of determining that each of the reference picture of the current block and the reference picture of the co-located block is a long-term reference picture; and deriving the candidate from the motion vector of the co-located block by a second derivation scheme that involves scaling based on a temporal distance, in the case of determining that each of the reference picture of the current block and the reference picture of the co-located block is a short-term reference picture.

Thus, the candidate for the current motion vector is appropriately derived without being extremely large or small. This contributes to improved prediction accuracy and improved coding efficiency.

For example, in the deriving: the deriving of the candidate from the motion vector of the co-located block may not be performed in the case of determining that one of the reference picture of the current block and the reference picture of the co-located block is a long-term reference picture and the other one of the reference picture of the current block and the reference picture of the co-located block is a short-term reference picture; and the deriving of the candidate from the motion vector of the co-located block may be performed in the case of determining that each of the reference picture of the current block and the reference picture of the co-located block is a long-term reference picture or in the case of determining that each of the reference picture of the current block and the reference picture of the co-located block is a short-term reference picture.

Thus, in the case where low prediction accuracy is expected, the candidate for the current motion vector is not derived from the motion vector of the co-located block. Prediction accuracy degradation can be prevented in this way.

For example, the coding may further include coding information indicating whether the reference picture of the current block is a long-term reference picture or a short-term reference picture, and information indicating whether the reference picture of the co-located block is a long-term reference picture or a short-term reference picture.

Thus, the information indicating, for each reference picture, whether the reference picture is a long-term reference picture or a short-term reference picture is provided from the coding side to the decoding side. This enables the coding side and the decoding side to obtain the same determination result and perform the same process.

For example, the deriving may include: determining whether the reference picture of the current block is a long-term reference picture or a short-term reference picture, using a temporal distance between the reference picture of the current block and the picture that includes the current block; and determining whether the reference picture of the co-located block is a long-term reference picture or a short-term reference picture, using a temporal distance between the reference picture of the co-located block and the picture that includes the co-located block.

Thus, for each reference picture, whether the reference picture is a long-term reference picture or a short-term reference picture is simply and appropriately determined based on the temporal distance.

For example, the deriving may include determining whether the reference picture of the co-located block is a long-term reference picture or a short-term reference picture, in a period during which the co-located block is coded.

Thus, whether the reference picture of the co-located block is a long-term reference picture or a short-term reference picture is determined more accurately.

For example, the deriving may include determining whether the reference picture of the co-located block is a long-term reference picture or a short-term reference picture, in a period during which the current block is coded.

Thus, information indicating whether the reference picture of the co-located block is a long-term reference picture or a short-term reference picture need not be retained for a long time.

For example, the deriving may include: deriving the motion vector of the co-located block as the candidate, in the case of determining that each of the reference picture of the current block and the reference picture of the co-located block is a long-term reference picture; and deriving the candidate by scaling the motion vector of the co-located block using a ratio, in the case of determining that each of the reference picture of the current block and the reference picture of the co-located block is a short-term reference picture, the ratio being a ratio of a temporal distance between the reference picture of the current block and the picture that includes the current block to a temporal distance between the reference picture of the co-located block and the picture that includes the co-located block.

Thus, in the case where the two reference pictures are each a long-term reference picture, scaling is omitted, with it being possible to reduce computation. In the case where the two reference pictures are each a short-term reference picture, the candidate for the current motion vector is appropriately derived based on the temporal distance.

For example, the deriving may further include, without deriving the candidate from the co-located block, selecting another co-located block and deriving the candidate from a motion vector of the other co-located block by the second derivation scheme, in the case of determining that the reference picture of the current block is a short-term reference picture and the reference picture of the co-located block is a long-term reference picture, the other co-located block being coded with reference to a short-term reference picture.

Thus, the block for deriving the candidate of high prediction accuracy is selected. This contributes to improved prediction accuracy.

Moreover, an image decoding method according to an exemplary embodiment disclosed herein is an image decoding method of decoding each of blocks of pictures, the image decoding method including: deriving a candidate for a motion vector of a current block to be decoded, from a motion vector of a co-located block which is a block included in a picture different from a picture that includes the current block; adding the derived candidate to a list; selecting the motion vector of the current block from the list to which the candidate is added; and decoding the current block using the selected motion vector and a reference picture of the current block, wherein the deriving includes: determining whether the reference picture of the current block is a long-term reference picture or a short-term reference picture, and whether a reference picture of the co-located block is a long-term reference picture or a short-term reference picture; deriving the candidate from the motion vector of the co-located block by a first derivation scheme that does not involve scaling based on a temporal distance, in the case of determining that each of the reference picture of the current block and the reference picture of the co-located block is a long-term reference picture; and deriving the candidate from the motion vector of the co-located block by a second derivation scheme that involves scaling based on a temporal distance, in the case of determining that each of the reference picture of the current block and the reference picture of the co-located block is a short-term reference picture.

Thus, the candidate for the current motion vector is appropriately derived without being extremely large or small. This contributes to improved prediction accuracy and improved coding efficiency.

For example, in the deriving: the deriving of the candidate from the motion vector of the co-located block may not be performed in the case of determining that one of the reference picture of the current block and the reference picture of the co-located block is a long-term reference picture and the other one of the reference picture of the current block and the reference picture of the co-located block is a short-term reference picture; and the deriving of the candidate from the motion vector of the co-located block may be performed in the case of determining that each of the reference picture of the current block and the reference picture of the co-located block is a long-term reference picture or in the case of determining that each of the reference picture of the current block and the reference picture of the co-located block is a short-term reference picture.

Thus, in the case where low prediction accuracy is expected, the candidate for the current motion vector is not derived from the motion vector of the co-located block. Prediction accuracy degradation can be prevented in this way.

For example, the decoding may further include decoding information indicating whether the reference picture of the current block is a long-term reference picture or a short-term reference picture, and information indicating whether the reference picture of the co-located block is a long-term reference picture or a short-term reference picture, wherein the deriving includes: determining whether the reference picture of the current block is a long-term reference picture or a short-term reference picture, using the information indicating whether the reference picture of the current block is a long-term reference picture or a short-term reference picture; and determining whether the reference picture of the co-located block is a long-term reference picture or a short-term reference picture, using the information indicating whether the reference picture of the co-located block is a long-term reference picture or a short-term reference picture.

Thus, the information indicating, for each reference picture, whether the reference picture is a long-term reference picture or a short-term reference picture is provided from the coding side to the decoding side. This enables the coding side and the decoding side to obtain the same determination result and perform the same process.

For example, the deriving may include: determining whether the reference picture of the current block is a long-term reference picture or a short-term reference picture, using a temporal distance between the reference picture of the current block and the picture that includes the current block; and determining whether the reference picture of the co-located block is a long-term reference picture or a short-term reference picture, using a temporal distance between the reference picture of the co-located block and the picture that includes the co-located block.

Thus, for each reference picture, whether the reference picture is a long-term reference picture or a short-term reference picture is simply and appropriately determined based on the temporal distance.

For example, the deriving may include determining whether the reference picture of the co-located block is a long-term reference picture or a short-term reference picture, in a period during which the co-located block is decoded.

Thus, whether the reference picture of the co-located block is a long-term reference picture or a short-term reference picture is determined more accurately.

For example, the deriving may include determining whether the reference picture of the co-located block is a long-term reference picture or a short-term reference picture, in a period during which the current block is decoded.

Thus, information indicating whether the reference picture of the co-located block is a long-term reference picture or a short-term reference picture need not be retained for a long time.

For example, the deriving may include: deriving the motion vector of the co-located block as the candidate, in the case of determining that each of the reference picture of the current block and the reference picture of the co-located block is a long-term reference picture; and deriving the candidate by scaling the motion vector of the co-located block using a ratio, in the case of determining that each of the reference picture of the current block and the reference picture of the co-located block is a short-term reference picture, the ratio being a ratio of a temporal distance between the reference picture of the current block and the picture that includes the current block to a temporal distance between the reference picture of the co-located block and the picture that includes the co-located block.

Thus, in the case where the two reference pictures are each a long-term reference picture, scaling is omitted, with it being possible to reduce computation. In the case where the two reference pictures are each a short-term reference picture, the candidate for the current motion vector is appropriately derived based on the temporal distance.

For example, the deriving may further include, without deriving the candidate from the co-located block, selecting another co-located block and deriving the candidate from a motion vector of the other co-located block by the second derivation scheme, in the case of determining that the reference picture of the current block is a short-term reference picture and the reference picture of the co-located block is a long-term reference picture, the other co-located block being decoded with reference to a short-term reference picture.

Thus, the block for deriving the candidate of high prediction accuracy is selected. This contributes to improved prediction accuracy.

Moreover, a content providing method according to an exemplary embodiment disclosed herein is a content providing method of transmitting, from a server in which image data coded by the image coding method described above is recorded, the image data in response to a request from an external terminal.

These general and specific aspects may be implemented using a system, an apparatus, an integrated circuit, a computer program, or a non-transitory computer-readable recording medium such as a CD-ROM, or any combination of systems, apparatuses, methods, integrated circuits, computer programs, and recording media.

Hereinafter, certain exemplary embodiments are described in greater detail with reference to the accompanying Drawings. Each of the exemplary embodiments described below shows a general or specific example. The numerical values, shapes, materials, structural elements, the arrangement and connection of the structural elements, steps, the processing order of the steps etc. shown in the following exemplary embodiments are mere examples, and therefore do not limit the scope of the appended Claims and their equivalents. Therefore, among the structural elements in the following exemplary embodiments, structural elements not recited in any one of the independent claims are described as arbitrary structural elements.

Embodiment 1

FIG.5is a block diagram of an image coding apparatus according to Embodiment 1. An image coding apparatus500shown inFIG.5codes an image on a block basis, and outputs a bitstream including the coded image. In detail, the image coding apparatus500includes a subtracting unit501, a transforming unit502, a quantizing unit503, an entropy coder504, an inverse quantizing unit505, an inverse transforming unit506, an adding unit507, a block memory508, a picture memory509, an intra predicting unit510, an inter predicting unit511, and a selecting unit512.

The subtracting unit501subtracts a prediction image from an image provided to the image coding apparatus500, to generate a differential image. The transforming unit502frequency-transforms the differential image generated by the subtracting unit501, to generate a plurality of frequency coefficients. The quantizing unit503quantizes the plurality of frequency coefficients generated by the transforming unit502, to generate a plurality of quantization coefficients. The entropy coder504codes the plurality of quantization coefficients generated by the quantizing unit503, to generate a bitstream.

The inverse quantizing unit505inverse-quantizes the plurality of quantization coefficients generated by the quantizing unit503, to restore the plurality of frequency coefficients. The inverse transforming unit506inverse-frequency-transforms the plurality of frequency coefficients restored by the inverse quantizing unit505, to restore the differential image. The adding unit507adds the prediction image to the differential image restored by the inverse transforming unit506, to restore (reconstruct) the image. The adding unit507stores the restored image (reconstructed image) in the block memory508and the picture memory509.

The block memory508is a memory for storing the image restored by the adding unit507, on a block basis. The picture memory509is a memory for storing the image restored by the adding unit507, on a picture basis.

The intra predicting unit510performs intra prediction by referencing to the block memory508. That is, the intra predicting unit510predicts a pixel value in a picture from another pixel value in the picture. The intra predicting unit510thus generates the prediction image. The inter predicting unit511performs inter prediction by referencing to the picture memory509. That is, the inter predicting unit511predicts a pixel value in a picture from a pixel value in another picture. The inter predicting unit511thus generates the prediction image.

The selecting unit512selects any of the prediction image generated by the intra predicting unit510and the prediction image generated by the inter predicting unit511, and outputs the selected prediction image to the subtracting unit501and the adding unit507.

Though not shown inFIG.5, the image coding apparatus500may include a deblocking filtering unit. The deblocking filtering unit may perform a deblocking filtering process on the image restored by the adding unit507, to remove noise near block boundaries. The image coding apparatus500may also include a controlling unit that controls each process in the image coding apparatus500.

FIG.6is a block diagram of an image decoding apparatus according to this embodiment. An image decoding apparatus600shown inFIG.6obtains the bitstream, and decodes the image on a block basis. In detail, the image decoding apparatus600includes an entropy decoder601, an inverse quantizing unit602, an inverse transforming unit603, an adding unit604, a block memory605, a picture memory606, an intra predicting unit607, an inter predicting unit608, and a selecting unit609.

The entropy decoder601decodes the coded plurality of quantization coefficients included in the bitstream. The inverse quantizing unit602inverse-quantizes the plurality of quantization coefficients decoded by the entropy decoder601, to restore the plurality of frequency coefficients. The inverse transforming unit603inverse-frequency-transforms the plurality of frequency coefficients restored by the inverse quantizing unit602, to restore the differential image.

The adding unit604adds the prediction image to the differential image restored by the inverse transforming unit603, to restore (reconstruct) the image. The adding unit604outputs the restored image (reconstructed image). The adding unit604also stores the restored image in the block memory605and the picture memory606.

The block memory605is a memory for storing the image restored by the adding unit604, on a block basis. The picture memory606is a memory for storing the image restored by the adding unit604, on a picture basis.

The intra predicting unit607performs intra prediction by referencing to the block memory605. That is, the intra predicting unit607predicts a pixel value in a picture from another pixel value in the picture. The intra predicting unit607thus generates the prediction image. The inter predicting unit608performs inter prediction by referencing to the picture memory606. That is, the inter predicting unit608predicts a pixel value in a picture from a pixel value in another picture. The inter predicting unit608thus generates the prediction image.

The selecting unit609selects any of the prediction image generated by the intra predicting unit607and the prediction image generated by the inter predicting unit608, and outputs the selected prediction image to the adding unit604.

Though not shown inFIG.6, the image decoding apparatus600may include a deblocking filtering unit. The deblocking filtering unit may perform a deblocking filtering process on the image restored by the adding unit604, to remove noise near block boundaries. The image decoding apparatus600may also include a controlling unit that controls each process in the image decoding apparatus600.

The coding process and the decoding process mentioned above are performed on a coding unit basis. The transformation process, the quantization process, the inverse transformation process, and the inverse quantization process are performed on a transform unit (TU) basis where the transform unit is included in the coding unit. The prediction process is performed on a prediction unit basis where the prediction unit is included in the coding unit.

FIG.7is a flowchart showing an operation of the image coding apparatus500shown inFIG.5. In particular,FIG.7shows a process of coding an image by inter prediction.

First, the inter predicting unit511classifies each of reference pictures as a short-term reference picture or a long-term reference picture (Step S701).

The long-term reference picture is a reference picture suitable for long-term use. The long-term reference picture is defined as a reference picture for longer use than the short-term reference picture. Accordingly, there is a high possibility that the long-term reference picture is retained in the picture memory509for a long time. The long-term reference picture is designated by an absolute POC that does not depend on the current picture. Meanwhile, the short-term reference picture is designated by a POC relative to the current picture.

Next, the entropy coder504writes information indicating the classification of each of the reference pictures, to a header of the bitstream (Step S702). That is, the entropy coder504writes information indicating, for each of the reference pictures, whether the reference picture is a long-term reference picture or a short-term reference picture.

Following this, the inter predicting unit511identifies the reference picture of the current block to be coded (to be predicted) (Step S703). The inter predicting unit511may identify a reference picture of a block adjacent to the current block, as the current reference picture. Alternatively, the inter predicting unit511may identify the current reference picture by a predetermined reference index. The inter predicting unit511then derives the current motion vector (Step S704). A derivation process will be described in detail later.

The inter predicting unit511generates the prediction block, by performing motion compensation using the current reference picture and the current motion vector (Step S705). After this, the subtracting unit501subtracts the prediction block from the current block (original image), to generate the residual block (Step S706). Lastly, the entropy coder504codes the residual block, to generate the bitstream including the residual block (Step S707).

FIG.8is a flowchart showing an operation of the image decoding apparatus600shown inFIG.6. In particular,FIG.8shows a process of decoding an image by inter prediction.

First, the entropy decoder601obtains the bitstream, and obtains the information indicating the classification of each of the reference pictures by parsing the header of the bitstream (Step S801). That is, the entropy decoder601obtains the information indicating, for each of the reference pictures, whether the reference picture is a long-term reference picture or a short-term reference picture. The entropy decoder601also obtains the residual block, by parsing the bitstream (Step S802).

Next, the inter predicting unit608identifies the current reference picture (Step S803). The inter predicting unit608may identify a reference picture of a block adjacent to the current block, as the current reference picture. Alternatively, the inter predicting unit608may identify the current reference picture by a predetermined reference index.

Following this, the inter predicting unit608derives the current motion vector (Step S804). A derivation process will be described in detail later. The inter predicting unit608then generates the prediction block, by performing motion compensation using the current reference picture and the current motion vector (Step S805). Lastly, the adding unit604adds the prediction block to the residual block, to generate the reconstructed block (Step S806).

FIG.9is a flowchart showing details of the derivation process shown inFIGS.7and8. The following mainly describes the operation of the inter predicting unit511shown inFIG.5. The operation of the inter predicting unit608shown inFIG.6is the same as the operation of the inter predicting unit511shown inFIG.5, with “coding” being replaced with “decoding”.

First, the inter predicting unit511selects the co-located picture from a plurality of available reference pictures (Step S901). The plurality of available reference pictures are coded pictures, and are retained in the picture memory509.

Next, the inter predicting unit511selects the co-located block in the co-located picture (Step S902). The inter predicting unit511then identifies the co-located reference picture and the co-located motion vector (Step S903).

Following this, the inter predicting unit511determines whether or not any of the current reference picture and the co-located reference picture is a long-term reference picture (Step S904). In the case of determining that any of the current reference picture and the co-located reference picture is a long-term reference picture (Step S904: Yes), the inter predicting unit511derives the current motion vector by a first derivation scheme (Step S905).

The first derivation scheme is a scheme using the co-located motion vector. In more detail, the first derivation scheme is a scheme of directly deriving the co-located motion vector as the current motion vector, without POC-based scaling. The first derivation scheme may be a scheme of deriving the current motion vector by scaling the co-located motion vector at a predetermined ratio.

In the case of determining that none of the current reference picture and the co-located reference picture is a long-term reference picture (Step S904: No), the inter predicting unit511derives the current motion vector by a second derivation scheme (Step S906). That is, in the case of determining that the current reference picture and the co-located reference picture are each a short-term reference picture, the inter predicting unit511derives the current motion vector by the second derivation scheme.

The second derivation scheme is a scheme using the current reference picture, the co-located reference picture, and the co-located motion vector. In more detail, the second derivation scheme is a scheme of deriving the current motion vector by performing POC-based scaling (Expression 1) on the co-located motion vector.

The following describes a more specific example of the process of deriving the current motion vector with reference toFIG.9again. The derivation process described earlier may be changed as follows.

First, the inter predicting unit511selects the co-located picture (Step S901). In more detail, in the case where a slice header parameter slice_type is B and a slice header parameter collocated_from_I0_flag is 0, a picture RefPicList1[0] is selected as the co-located picture. The picture RefPicList1[0] is a reference picture listed first in an ordered reference picture list RefPicList1.

In the case where the slice header parameter slice_type is not B or in the case where the slice header parameter collocated_from_I0_flag is not 0, a picture RefPicList0[0] is selected as the co-located picture. The picture RefPicList0[0] is a reference picture listed first in an ordered reference picture list RefPicList0.

Next, the inter predicting unit511selects the co-located block (Step S902). In the case where the first block including the sample c0shown inFIG.4is available, the first block is selected as the co-located block. In the case where the first block is not available and the second block including the sample c1shown inFIG.4is available, the second block is selected as the co-located block.

In the case where the available co-located block is selected, the inter predicting unit511sets the temporal motion vector predictor as available. In the case where the available co-located block is not selected, the inter predicting unit511sets the temporal motion vector predictor as not available.

In the case where the temporal motion vector predictor is set as available, the inter predicting unit511identifies the co-located motion vector as the base motion vector. The inter predicting unit511also identifies the co-located reference picture (Step S903). In the case where the co-located block has a plurality of motion vectors, that is, in the case where the co-located block is coded using a plurality of motion vectors, the inter predicting unit511selects the base motion vector according to predetermined priority order.

For example, in the case where the current reference picture is a short-term reference picture, the inter predicting unit511may preferentially select a motion vector that points to a location in a short-term reference picture from among the plurality of motion vectors, as the base motion vector.

In detail, in the case where a motion vector that points to a location in a short-term reference picture is present, the inter predicting unit511selects the motion vector as the base motion vector. In the case where a motion vector that points to a location in a short-term reference picture is not present, the inter predicting unit511selects a motion vector that points to a location in a long-term reference picture, as the base motion vector.

After this, in the case where any of the current reference picture and the co-located reference picture is a long-term reference picture (Step S904: Yes), the inter predicting unit511derives the base motion vector as the temporal motion vector predictor (Step S905).

In the case where none of the two reference pictures is a long-term reference picture (Step S904: No), on the other hand, the inter predicting unit511derives the temporal motion vector predictor from the base motion vector by POC-based scaling (Step S906).

As described above, the temporal motion vector predictor is set as available or not available. The inter predicting unit511inserts the temporal motion vector predictor set as available, into an ordered list of current motion vector candidates. The ordered list holds not only the temporal motion vector predictor but various motion vectors as candidates.

The inter predicting unit511selects one motion vector from the ordered list, as the current motion vector. Here, the inter predicting unit511selects a motion vector of highest prediction accuracy for the current block or a motion vector that allows the current block to be coded with highest coding efficiency, from the ordered list. An index corresponding to the selected motion vector is written to the bitstream.

Through the process described above, the current motion vector is appropriately derived from the co-located motion vector, without being extremely large or small. This contributes to improved prediction accuracy and improved coding efficiency.

Note that the status of each reference picture as to whether the reference picture is a long-term reference picture or a short-term reference picture may be changed according to time. For example, a short-term reference picture may later be changed to a long-term reference picture, and a long-term reference picture may later be changed to a short-term reference picture.

Moreover, the inter predicting unit511may determine whether the co-located reference picture is a long-term reference picture or a short-term reference picture, in a period during which the co-located block is coded. The image coding apparatus500may then include an additional memory for holding the determination result from when the co-located block is coded to when the current block is coded.

In this way, whether the co-located reference picture is a long-term reference picture or a short-term reference picture is determined more accurately.

As an alternative, the inter predicting unit511may determine whether the co-located reference picture is a long-term reference picture or a short-term reference picture, in a period during which the current block is coded.

In this way, the information of whether the co-located reference picture is a long-term reference picture or a short-term reference picture need not be retained for a long time.

Moreover, the inter predicting unit511may determine whether the current reference picture is a long-term reference picture or a short-term reference picture, using a temporal distance between the current reference picture and the current picture.

As an example, in the case where the temporal distance between the current reference picture and the current picture is more than a predetermined threshold, the inter predicting unit511determines that the current reference picture is a long-term reference picture. In the case where the temporal distance is not more than the predetermined threshold, the inter predicting unit511determines that the current reference picture is a short-term reference picture.

Likewise, the inter predicting unit511may determine whether the co-located reference picture is a long-term reference picture or a short-term reference picture, using a temporal distance between the co-located reference picture and the co-located picture.

As an example, in the case where the temporal distance between the co-located reference picture and the co-located picture is more than a predetermined threshold, the inter predicting unit511determines that the co-located reference picture is a long-term reference picture. In the case where the temporal distance is not more than the predetermined threshold, the inter predicting unit511determines that the co-located reference picture is a short-term reference picture.

The inter predicting unit608in the image decoding apparatus600may determine, for each reference picture, whether or not the reference picture is a long-term reference picture or a short-term reference picture based on a temporal distance, in the same manner as the inter predicting unit511in the image coding apparatus500. In such a case, the information indicating, for each reference picture, whether the reference picture is a long-term reference picture or a short-term reference picture need not be coded.

Regarding each of the other processes described in this embodiment, too, each structural element in the image decoding apparatus600performs the same process as the corresponding structural element in the image coding apparatus500, as a result of which the image coded with high coding efficiency is appropriately decoded.

The operations described above are also applicable to the other embodiments. Any of the structures and operations described in this embodiment may be incorporated in the other embodiments, and any of the structures and operations described in the other embodiments may be incorporated in this embodiment.

Embodiment 2

An image coding apparatus and an image decoding apparatus according to Embodiment 2 have the same structures as those in Embodiment 1. Hence, the operations of the image coding apparatus and the image decoding apparatus according to this embodiment are described below, using the structure of the image coding apparatus500shown inFIG.5and the structure of the image decoding apparatus600shown inFIG.6.

The image coding apparatus500according to this embodiment performs the operation shown inFIG.7, as in Embodiment 1. The image decoding apparatus600according to this embodiment performs the operation shown inFIG.8, as in Embodiment 1. This embodiment differs from Embodiment 1 in the current motion vector derivation process. This is described in detail below.

FIG.10is a flowchart showing details of the derivation process according to this embodiment. The inter predicting unit511according to this embodiment performs the operation shown inFIG.10, instead of the operation shown inFIG.9. The following mainly describes the operation of the inter predicting unit511shown inFIG.5. The operation of the inter predicting unit608shown inFIG.6is the same as the operation of the inter predicting unit511shown inFIG.5, with “coding” being replaced with “decoding”.

First, the inter predicting unit511selects the co-located picture from the plurality of available reference pictures (Step S1001). Next, the inter predicting unit511selects the co-located block in the co-located picture (Step S1002). The inter predicting unit511then identifies the co-located reference picture and the co-located motion vector (Step S1003).

Following this, the inter predicting unit511determines whether or not the current reference picture is a long-term reference picture (Step S1004). In the case of determining that the current reference picture is a long-term reference picture (Step S1004: Yes), the inter predicting unit511derives the current motion vector by the first derivation scheme same as in Embodiment 1 (Step S1005).

In the case of determining that the current reference picture is not a long-term reference picture (Step S1004: No), the inter predicting unit511determines whether or not the co-located reference picture is a long-term reference picture (Step S1006).

In the case of determining that the co-located reference picture is not a long-term reference picture (Step S1006: No), the inter predicting unit511derives the current motion vector by the second derivation scheme same as in Embodiment 1 (Step S1007). That is, in the case of determining that the current reference picture and the co-located reference picture are each a short-term reference picture, the inter predicting unit511derives the current motion vector by the second derivation scheme.

In the case of determining that the co-located reference picture is a long-term reference picture (Step S1006: Yes), the inter predicting unit511selects another co-located block in the co-located picture (Step S1008). In the example shown inFIG.10, a block coded with reference to a short-term reference picture is selected as the other co-located block.

After this, the inter predicting unit511identifies the co-located reference picture and the co-located motion vector corresponding to the other co-located block (Step S1009). The inter predicting unit511then derives the current motion vector by the second derivation scheme that uses POC-based scaling (Step S1010).

In detail, in the case where the reference picture of the current block is a short-term reference picture and the reference picture of the co-located block is a long-term reference picture, the inter predicting unit511does not derive the current motion vector from the motion vector of the co-located block. The inter predicting unit511instead selects another co-located block coded with reference to a short-term reference picture, and derives the current motion vector from the motion vector of the selected other co-located block.

As an example, in the case where the reference picture of the current block is a short-term reference picture and the reference picture of the co-located block is a long-term reference picture, the inter predicting unit511searches for a block coded with reference to a short-term reference picture. The inter predicting unit511selects the block coded with reference to the short-term reference picture, as the other co-located block.

As another example, in the case where the reference picture of the current block is a short-term reference picture and the reference picture of the co-located block is a long-term reference picture, the inter predicting unit511first searches for a block coded with reference to a short-term reference picture.

In the case where the block coded with reference to the short-term reference picture is present, the inter predicting unit511selects the block as the other co-located block. In the case where the block coded with reference to the short-term reference picture is not present, the inter predicting unit511searches for a block coded with reference to a long-term reference picture. The inter predicting unit511selects the block coded with reference to the long-term reference picture, as the other co-located block.

For example, the inter predicting unit511first selects the first block shown inFIG.4as the co-located block. In the case where the current reference picture is a short-term reference picture and the co-located reference picture is a long-term reference picture, then the inter predicting unit511newly selects the second block shown inFIG.4as the co-located block.

In the above-mentioned example, the inter predicting unit511may select the second block shown inFIG.4as the co-located block only in the case where the reference picture of the second block is a short-term reference picture. The block selected as the co-located block here is not limited to the second block shown inFIG.4, and a block other than the second block may be selected as the co-located block.

FIG.11is a diagram for explaining the co-located block according to this embodiment. Samples c0, c1, c2, and c3in the co-located picture are shown inFIG.11. The samples c0and c1inFIG.11are equal to the samples c0and c1inFIG.4. Not only the second block including the sample c1but also a third block including the sample c2or a fourth block including the sample c3may be selected as the other co-located block.

Coordinates of the sample c2are (x+w−1, y+h−1). Coordinates of the sample c3are (x+1, y+1).

The inter predicting unit511determines, for each of the first, second, third, and fourth blocks in this order, whether or not the block is available. The inter predicting unit511determines the available block as the final co-located block. Examples of the case where the block is not available include the case where the block is not present and the case where the block is coded by intra prediction.

In the case where the current reference picture is a short-term reference picture, the inter predicting unit511may determine that a block coded with reference to a long-term reference picture is not available.

Though the above describes the example of the co-located block selection method, the co-located block selection method is not limited to the above example. A block including a sample other than the samples c0, c1, c2, and c3may be selected as the co-located block. Besides, the priority order of the blocks is not limited to the example described in this embodiment.

The following describes a more specific example of the process of deriving the current motion vector with reference toFIG.10again. The derivation process described earlier may be changed as follows.

First, the inter predicting unit511selects the co-located picture as in Embodiment 1 (Step S1001). Next, the inter predicting unit511selects the first block including the sample c0shown inFIG.11as the co-located block, and identifies the co-located reference picture (Steps S1002and S1003).

Following this, the inter predicting unit511determines whether or not the co-located block is available. In the case where the current reference picture is a short-term reference picture and the co-located reference picture is a long-term reference picture, the inter predicting unit511determines that the co-located block is not available (Steps S1004and S1006).

In the case where the co-located block is not available, the inter predicting unit511searches for and selects another co-located block which is available (Step S1008). In detail, the inter predicting unit511selects a block coded with reference to a short-term reference picture, from among the second block including the sample c1, the third block including the sample c2, and the fourth block including the sample c3inFIG.11. The inter predicting unit511then identifies the reference picture of the co-located block (Step S1009).

In the case where the available co-located block is selected, the inter predicting unit511sets the temporal motion vector predictor as available. In the case where the available co-located block is not selected, the inter predicting unit511sets the temporal motion vector predictor as not available.

In the case where the temporal motion vector predictor is set as available, the inter predicting unit511identifies the co-located motion vector as the base motion vector (Steps S1003and S1009). In the case where the co-located block has a plurality of motion vectors, that is, in the case where the co-located block is coded using a plurality of motion vectors, the inter predicting unit511selects the base motion vector according to predetermined priority order as in Embodiment 1.

In the case where any of the current reference picture and the co-located reference picture is a long-term reference picture (Step S1004: Yes), the inter predicting unit511derives the base motion vector as the temporal motion vector predictor (Step S1005).

In the case where none of the current reference picture and the co-located reference picture is a long-term reference picture (Step S1004: No), on the other hand, the inter predicting unit511derives the temporal motion vector predictor from the base motion vector by POC-based scaling (Steps S1007and S1010).

In the case where the temporal motion vector predictor is set as not available, the inter predicting unit511does not derive the temporal motion vector predictor.

As in Embodiment 1, the inter predicting unit511adds the temporal motion vector predictor set as available, to the list as the candidate for the current motion vector. The inter predicting unit511then selects the current motion vector from the list.

As described above, in this embodiment, in the case where the reference picture of the current block is a short-term reference picture and the reference picture of the co-located block is a long-term reference picture, the current motion vector is not derived from the motion vector of the co-located block.

It is extremely difficult to derive the current motion vector of high prediction accuracy, in the case where one of the current reference picture and the co-located reference picture is a long-term reference picture and the other one of the current reference picture and the co-located reference picture is a short-term reference picture. In view of this, the image coding apparatus500and the image decoding apparatus600according to this embodiment prevent prediction accuracy degradation by the operation described above.

Embodiment 3

An image coding apparatus and an image decoding apparatus according to Embodiment 3 have the same structures as those in Embodiment 1. Hence, the operations of the image coding apparatus and the image decoding apparatus according to this embodiment are described below, using the structure of the image coding apparatus500shown inFIG.5and the structure of the image decoding apparatus600shown inFIG.6.

The image coding apparatus500according to this embodiment performs the operation shown inFIG.7, as in Embodiment 1. The image decoding apparatus600according to this embodiment performs the operation shown inFIG.8, as in Embodiment 1. This embodiment differs from Embodiment 1 in the current motion vector derivation process. This is described in detail below.

FIG.12is a flowchart showing details of the derivation process according to this embodiment. The inter predicting unit511according to this embodiment performs the operation shown inFIG.12, instead of the operation shown inFIG.9. The following mainly describes the operation of the inter predicting unit511shown inFIG.5. The operation of the inter predicting unit608shown inFIG.6is the same as the operation of the inter predicting unit511shown inFIG.5, with “coding” being replaced with “decoding”.

First, the inter predicting unit511selects the co-located picture from the plurality of available reference pictures (Step S1201). Next, the inter predicting unit511selects the co-located block in the co-located picture (Step S1202). The inter predicting unit511then identifies the co-located reference picture and the co-located motion vector (Step S1203).

Following this, the inter predicting unit511determines whether or not the current reference picture is a long-term reference picture (Step S1204). In the case of determining that the current reference picture is a long-term reference picture (Step S1204: Yes), the inter predicting unit511derives the current motion vector by the first derivation scheme same as in Embodiment 1 (Step S1205).

In the case of determining that the current reference picture is not a long-term reference picture (Step S1204: No), the inter predicting unit511determines whether or not the co-located reference picture is a long-term reference picture (Step S1206).

In the case of determining that the co-located reference picture is not a long-term reference picture (Step S1206: No), the inter predicting unit511derives the current motion vector by the second derivation scheme same as in Embodiment 1 (Step S1207). That is, in the case of determining that the current reference picture and the co-located reference picture are each a short-term reference picture, the inter predicting unit511derives the current motion vector by the second derivation scheme.

In the case of determining that the co-located reference picture is a long-term reference picture (Step S1206: Yes), the inter predicting unit511selects another co-located picture (Step S1208). The inter predicting unit511then selects another co-located block in the other co-located picture (Step S1209). In the example shown inFIG.12, a block coded with reference to a short-term reference picture is selected as the other co-located block.

After this, the inter predicting unit511identifies the co-located reference picture and the co-located motion vector corresponding to the other co-located block (Step S1210). The inter predicting unit511then derives the current motion vector by the second derivation scheme that uses POC-based scaling (Step S1211).

In detail, in the case where the reference picture of the current block is a short-term reference picture and the reference picture of the co-located block is a long-term reference picture, the inter predicting unit511does not derive the current motion vector from the motion vector of the co-located block.

The inter predicting unit511instead selects another co-located picture. The inter predicting unit511further selects another co-located block coded with reference to a short-term reference picture, from the selected other co-located picture. The inter predicting unit511derives the current motion vector from the motion vector of the selected other co-located block.

As an example, in the case where the current reference picture is a short-term reference picture and the co-located reference picture is a long-term reference picture, the inter predicting unit511searches for a picture that includes a block coded with reference to a short-term reference picture. The inter predicting unit511selects the picture that includes the block coded with reference to the short-term reference picture, as the other co-located picture.

As another example, in the case where the current reference picture is a short-term reference picture and the co-located reference picture is a long-term reference picture, the inter predicting unit511first searches for a picture that includes a block coded with reference to a short-term reference picture.

In the case where the picture that includes the block coded with reference to the short-term reference picture is present, the inter predicting unit511selects the picture as the other co-located picture.

In the case where the picture that includes the block coded with reference to the short-term reference picture is not present, the inter predicting unit511searches for a picture that includes a block coded with reference to a long-term reference picture. The inter predicting unit511selects the picture that includes the block coded with reference to the long-term reference picture, as the other co-located picture.

For example, in the case where the picture RefPicList0[0] is the co-located picture, the picture RefPicList1[0] is the other co-located picture. In the case where the picture RefPicList1[0] is the co-located picture, the picture RefPicList0[0] is the other co-located picture.

In other words, the picture listed first in one of the two reference picture lists used for coding of B pictures (bi-predictive coding) is the co-located picture, and the picture listed first in the other one of the two reference picture lists is the other co-located picture.

The following describes a more specific example of the process of deriving the current motion vector with reference toFIG.12again. The derivation process described earlier may be changed as follows.

First, the inter predicting unit511selects one of the picture RefPicList0[0] and the picture RefPicList1[0], as the co-located picture (Step S1201). The inter predicting unit511selects, from the selected co-located picture, the first block including the sample c0shown inFIG.11as the co-located block, and identifies the co-located reference picture (Steps S1202and S1203).

Following this, the inter predicting unit511determines whether or not the co-located block is available. In the case where the current reference picture is a short-term reference picture and the co-located reference picture is a long-term reference picture, the inter predicting unit511determines that the co-located block is not available (Steps S1204and S1206).

In the case where the co-located block is not available, the inter predicting unit511newly selects an available co-located block. For example, the inter predicting unit511selects the second block including the sample c1shown inFIG.11, as the co-located block. The inter predicting unit511then identifies the co-located reference picture.

In the case where the available co-located block is not selected, the inter predicting unit511selects another co-located picture. Here, the inter predicting unit511selects the other one of the picture RefPicList0[0] and the picture RefPicList1[0], as the co-located picture (Step S1208).

The inter predicting unit511selects, from the selected co-located picture, the first block including the sample c0shown inFIG.1as the co-located block, and identifies the co-located reference picture (Steps S1209and S1210).

Following this, the inter predicting unit511determines whether or not the co-located block is available. As in the previous determination, in the case where the current reference picture is a short-term reference picture and the co-located reference picture is a long-term reference picture, the inter predicting unit511determines that the co-located block is not available.

In the case where the co-located block is not available, the inter predicting unit511newly selects an available co-located block (Step S1209). In detail, the inter predicting unit511selects the second block including the sample c1shown inFIG.11, as the co-located block. The inter predicting unit511then identifies the co-located reference picture (Step S1210).

In the case where the available co-located block is eventually selected, the inter predicting unit511sets the temporal motion vector predictor as available. In the case where the available co-located block is eventually not selected, the inter predicting unit511sets the temporal motion vector predictor as not available.

In the case where the temporal motion vector predictor is set as available, the inter predicting unit511identifies the motion vector of the co-located block as the base motion vector (Steps S1203and S1210). In the case where the co-located block has a plurality of motion vectors, that is, in the case where the co-located block is coded using a plurality of motion vectors, the inter predicting unit511selects the base motion vector according to predetermined priority order as in Embodiment 1.

In the case where any of the current reference picture and the co-located reference picture is a long-term reference picture (Step S1204: Yes), the inter predicting unit511derives the base motion vector as the temporal motion vector predictor (Step S1205).

In the case where none of the current reference picture and the co-located reference picture is a long-term reference picture (Step S1204: No), on the other hand, the inter predicting unit511derives the temporal motion vector predictor from the base motion vector by POC-based scaling (Steps S1207and S1211).

In the case where the temporal motion vector predictor is set as not available, the inter predicting unit511does not derive the temporal motion vector predictor.

As in Embodiment 1, the inter predicting unit511adds the temporal motion vector predictor set as available, to the list as the candidate for the current motion vector. The inter predicting unit511then selects the current motion vector from the list.

As described above, the image coding apparatus500and the image decoding apparatus600according to this embodiment select the block suitable for current motion vector derivation from a plurality of pictures, and derive the current motion vector from the motion vector of the selected block. This contributes to improved coding efficiency.

Embodiment 4

Embodiment 4 confirmatorily describes the characteristic structures and the characteristic procedures included in Embodiments 1 to 3.

FIG.13Ais a block diagram of an image coding apparatus according to this embodiment. An image coding apparatus1300shown inFIG.13Acodes each of blocks of pictures. The image coding apparatus1300includes a deriving unit1301, an adding unit1302, a selecting unit1303, and a coder1304.

For example, the deriving unit1301, the adding unit1302, and the selecting unit1303correspond to the inter predicting unit511shown inFIG.5and the like, and the coder1304corresponds to the entropy coder504shown inFIG.5and the like.

FIG.13Bis a flowchart showing an operation of the image coding apparatus1300shown inFIG.13A.

The deriving unit1301derives a candidate for a motion vector of a current block, from a motion vector of a co-located block (Step S1301). The co-located block is a block included in a picture different from a picture that includes the current block to be coded.

In the derivation of the candidate, the deriving unit1301determines whether a reference picture of the current block is a long-term reference picture or a short-term reference picture. The deriving unit1301also determines whether a reference picture of the co-located block is a long-term reference picture or a short-term reference picture.

In the case of determining that the reference picture of the current block and the reference picture of the co-located block are each a long-term reference picture, the deriving unit1301derives the candidate from the motion vector of the co-located block by a first derivation scheme. The first derivation scheme is a derivation scheme that does not involve scaling based on a temporal distance.

In the case of determining that the reference picture of the current block and the reference picture of the co-located block are each a short-term reference picture, on the other hand, the deriving unit1301derives the candidate from the motion vector of the co-located block by a second derivation scheme. The second derivation scheme is a derivation scheme that involves scaling based on a temporal distance.

The adding unit1302adds the derived candidate to a list (Step S1302). The selecting unit1303selects the motion vector of the current block from the list to which the candidate is added (Step S1303).

The coder1304codes the current block using the selected motion vector and the reference picture of the current block (Step S1304).

FIG.14Ais a block diagram of an image decoding apparatus according to this embodiment. An image decoding apparatus1400shown inFIG.14Adecodes each of blocks of pictures. The image decoding apparatus1400includes a deriving unit1401, an adding unit1402, a selecting unit1403, and a decoder1404.

For example, the deriving unit1401, the adding unit1402, and the selecting unit1403correspond to the inter predicting unit608shown inFIG.6and the like, and the decoder1404corresponds to the entropy decoder601shown inFIG.6and the like.

FIG.14Bis a flowchart showing an operation of the image decoding apparatus1400shown inFIG.14A.

The deriving unit1401derives a candidate for a motion vector of a current block, from a motion vector of a co-located block (Step S1401). The co-located block is a block included in a picture different from a picture that includes a current block to be decoded.

In the derivation of the candidate, the deriving unit1401determines whether a reference picture of the current block is a long-term reference picture or a short-term reference picture. The deriving unit1401also determines whether a reference picture of the co-located block is a long-term reference picture or a short-term reference picture.

In the case of determining that the reference picture of the current block and the reference picture of the co-located block are each a long-term reference picture, the deriving unit1401derives the candidate from the motion vector of the co-located block by a first derivation scheme. The first derivation scheme is a derivation scheme that does not involve scaling based on a temporal distance.

In the case of determining that the reference picture of the current block and the reference picture of the co-located block are each a short-term reference picture, on the other hand, the deriving unit1401derives the candidate from the motion vector of the co-located block by a second derivation scheme. The second derivation scheme is a derivation scheme that involves scaling based on a temporal distance.

The adding unit1402adds the derived candidate to a list (Step S1402). The selecting unit1403selects the motion vector of the current block from the list to which the candidate is added (Step S1403).

The decoder1404decodes the current block using the selected motion vector and the reference picture of the current block (Step S1404).

Through the process described above, the candidate for the current motion vector is appropriately derived from the motion vector of the co-located block, without being extremely large or small. This contributes to improved prediction accuracy and improved coding efficiency.

Here, the deriving units1301and1401may each not derive the candidate from the motion vector of the co-located block, in the case of determining that one of the reference picture of the current block and the reference picture of the co-located block is a long-term reference picture and the other one of the reference picture of the current block and the reference picture of the co-located block is a short-term reference picture.

In this case, the deriving units1301and1401may each further select another co-located block coded or decoded with reference to a short-term reference picture, and derive the candidate from the other co-located block by the second derivation scheme. As an alternative, the deriving units1301and1401may each derive the candidate by another derivation scheme. As another alternative, the deriving units1301and1401may each eventually not derive the candidate corresponding to the temporal motion vector predictor.

The deriving units1301and1401may determine whether the reference picture of the current block is a long-term reference picture or a short-term reference picture, using a temporal distance between the reference picture of the current block and the picture that includes the current block.

The deriving units1301and1401may each determine whether the reference picture of the co-located block is a long-term reference picture or a short-term reference picture, using a temporal distance between the reference picture of the co-located block and the picture that includes the co-located block.

The deriving units1301and1401may each determine whether the reference picture of the co-located block is a long-term reference picture or a short-term reference picture, in a period during which the co-located block is coded or decoded.

The deriving units1301and1401may each determine whether the reference picture of the co-located block is a long-term reference picture or a short-term reference picture, in a period during which the current block is coded or decoded.

The first derivation scheme may be a scheme of deriving the motion vector of the co-located block as the candidate. The second derivation scheme may be a scheme of deriving the candidate by scaling the motion vector of the co-located block using a ratio of the temporal distance between the reference picture of the current block and the picture that includes the current block to the temporal distance between the reference picture of the co-located block and the picture that includes the co-located block.

The coder1304may further code information indicating whether the reference picture of the current block is a long-term reference picture or a short-term reference picture, and information indicating whether the reference picture of the co-located block is a long-term reference picture or a short-term reference picture.

The decoder1404may further decode information indicating whether the reference picture of the current block is a long-term reference picture or a short-term reference picture, and information indicating whether the reference picture of the co-located block is a long-term reference picture or a short-term reference picture.

The deriving unit1401may then determine whether the reference picture of the current block is a long-term reference picture or a short-term reference picture using the decoded information, and determine whether the reference picture of the co-located block is a long-term reference picture or a short-term reference picture using the decoded information.

Information indicating classification of each reference picture may be stored, as a parameter, in a bitstream at a location described below.

FIG.15Ais a diagram showing a first example of the storage location of the parameter indicating the reference picture classification. As shown inFIG.15A, the parameter indicating the reference picture classification may be stored in a sequence header. The sequence header is also referred to as a sequence parameter set.

FIG.15Bis a diagram showing a second example of the storage location of the parameter indicating the reference picture classification. As shown inFIG.15B, the parameter indicating the reference picture classification may be stored in a picture header. The picture header is also referred to as a picture parameter set.

FIG.15Cis a diagram showing a third example of the storage location of the parameter indicating the reference picture classification. As shown inFIG.15C, the parameter indicating the reference picture classification may be stored in a slice header.

Information indicating a prediction mode (inter prediction or intra prediction) may be stored, as a parameter, in the bitstream at a location described below.

FIG.16is a diagram showing an example of the storage location of the parameter indicating the prediction mode. As shown inFIG.16, the parameter may be stored in a CU header (coding unit header). The parameter indicates whether a prediction unit in a coding unit is coded by inter prediction or intra prediction. This parameter may be used to determine whether or not the co-located block is available.

Each of the structural elements in each of the above-described embodiments may be configured in the form of an exclusive hardware product, or may be realized by executing a software program suitable for the structural element. Each of the structural elements may be realized by means of a program executing unit, such as a CPU and a processor, reading and executing the software program recorded on a recording medium such as a hard disk or a semiconductor memory. Here, the software program for realizing the image coding apparatus and the like according to each of the embodiments is a program described below.

The program causes a computer to execute an image coding method of coding each of blocks of pictures, the image coding method including: deriving a candidate for a motion vector of a current block to be coded, from a motion vector of a co-located block which is a block included in a picture different from a picture that includes the current block; adding the derived candidate to a list; selecting the motion vector of the current block from the list to which the candidate is added; and coding the current block using the selected motion vector and a reference picture of the current block, wherein the deriving includes: determining whether the reference picture of the current block is a long-term reference picture or a short-term reference picture, and whether a reference picture of the co-located block is a long-term reference picture or a short-term reference picture; deriving the candidate from the motion vector of the co-located block by a first derivation scheme that does not involve scaling based on a temporal distance, in the case of determining that each of the reference picture of the current block and the reference picture of the co-located block is a long-term reference picture; and deriving the candidate from the motion vector of the co-located block by a second derivation scheme that involves scaling based on a temporal distance, in the case of determining that each of the reference picture of the current block and the reference picture of the co-located block is a short-term reference picture.

The program may cause the computer to execute an image decoding method of decoding each of blocks of pictures, the image decoding method including: deriving a candidate fora motion vector of a current block to be decoded, from a motion vector of a co-located block which is a block included in a picture different from a picture that includes the current block; adding the derived candidate to a list; selecting the motion vector of the current block from the list to which the candidate is added; and decoding the current block using the selected motion vector and a reference picture of the current block, wherein the deriving includes: determining whether the reference picture of the current block is a long-term reference picture or a short-term reference picture, and whether a reference picture of the co-located block is a long-term reference picture or a short-term reference picture; deriving the candidate from the motion vector of the co-located block by a first derivation scheme that does not involve scaling based on a temporal distance, in the case of determining that each of the reference picture of the current block and the reference picture of the co-located block is a long-term reference picture; and deriving the candidate from the motion vector of the co-located block by a second derivation scheme that involves scaling based on a temporal distance, in the case of determining that each of the reference picture of the current block and the reference picture of the co-located block is a short-term reference picture.

Each of the structural elements may be a circuit. These circuits may wholly constitute one circuit, or be separate circuits. Each of the structural elements may be realized by a general-purpose processor or realized by a special-purpose processor.

The herein disclosed subject matter is to be considered descriptive and illustrative only, and the appended Claims are of a scope intended to cover and encompass not only the particular embodiments disclosed, but also equivalent structures, methods, and/or uses.

For example, an image coding and decoding apparatus may include the image coding apparatus and the image decoding apparatus. A process executed by a specific processing unit may be executed by another processing unit. Processes may be executed in different order, and two or more processes may be executed in parallel.

Embodiment 5

The processing described in each of embodiments can be simply implemented in an independent computer system, by recording, in a recording medium, a program for implementing the configurations of the moving picture coding method (image coding method) and the moving picture decoding method (image decoding method) described in each of embodiments. The recording media may be any recording media as long as the program can be recorded, such as a magnetic disk, an optical disk, a magnetic optical disk, an IC card, and a semiconductor memory.

Hereinafter, the applications to the moving picture coding method (image coding method) and the moving picture decoding method (image decoding method) described in each of embodiments and systems using thereof will be described. The system has a feature of having an image coding and decoding apparatus that includes an image coding apparatus using the image coding method and an image decoding apparatus using the image decoding method. Other configurations in the system can be changed as appropriate depending on the cases.

FIG.17illustrates an overall configuration of a content providing system ex100for implementing content distribution services. The area for providing communication services is divided into cells of desired size, and base stations ex106, ex107, ex108, ex109, and ex110which are fixed wireless stations are placed in each of the cells.

The content providing system ex100is connected to devices, such as a computer ex111, a personal digital assistant (PDA) ex112, a camera ex113, a cellular phone ex114and a game machine ex115, via the Internet ex101, an Internet service provider ex102, a telephone network ex104, as well as the base stations ex106to ex110, respectively.

However, the configuration of the content providing system ex100is not limited to the configuration shown inFIG.17, and a combination in which any of the elements are connected is acceptable. In addition, each device may be directly connected to the telephone network ex104, rather than via the base stations ex106to ex110which are the fixed wireless stations. Furthermore, the devices may be interconnected to each other via a short distance wireless communication and others.

The camera ex113, such as a digital video camera, is capable of capturing video. A camera ex116, such as a digital camera, is capable of capturing both still images and video. Furthermore, the cellular phone ex114may be the one that meets any of the standards such as Global System for Mobile Communications (GSM) (registered trademark), Code Division Multiple Access (CDMA), Wideband-Code Division Multiple Access (W-CDMA), Long Term Evolution (LTE), and High Speed Packet Access (HSPA). Alternatively, the cellular phone ex114may be a Personal Handyphone System (PHS).

In the content providing system ex100, a streaming server ex103is connected to the camera ex113and others via the telephone network ex104and the base station ex109, which enables distribution of images of a live show and others. In such a distribution, a content (for example, video of a music live show) captured by the user using the camera ex113is coded as described above in each of embodiments (i.e., the camera functions as the image coding apparatus according to an aspect of the present disclosure), and the coded content is transmitted to the streaming server ex103. On the other hand, the streaming server ex103carries out stream distribution of the transmitted content data to the clients upon their requests. The clients include the computer ex111, the PDA ex112, the camera ex113, the cellular phone ex114, and the game machine ex115that are capable of decoding the above-mentioned coded data. Each of the devices that have received the distributed data decodes and reproduces the coded data (i.e., functions as the image decoding apparatus according to an aspect of the present disclosure).

The captured data may be coded by the camera ex113or the streaming server ex103that transmits the data, or the coding processes may be shared between the camera ex113and the streaming server ex103. Similarly, the distributed data may be decoded by the clients or the streaming server ex103, or the decoding processes may be shared between the clients and the streaming server ex103. Furthermore, the data of the still images and video captured by not only the camera ex113but also the camera ex116may be transmitted to the streaming server ex103through the computer ex111. The coding processes may be performed by the camera ex116, the computer ex111, or the streaming server ex103, or shared among them.

Furthermore, the coding and decoding processes may be performed by an LSI ex500generally included in each of the computer ex111and the devices. The LSI ex500may be configured of a single chip or a plurality of chips. Software for coding and decoding video may be integrated into some type of a recording medium (such as a CD-ROM, a flexible disk, and a hard disk) that is readable by the computer ex111and others, and the coding and decoding processes may be performed using the software. Furthermore, when the cellular phone ex114is equipped with a camera, the video data obtained by the camera may be transmitted. The video data is data coded by the LSI ex500included in the cellular phone ex114.

Furthermore, the streaming server ex103may be composed of servers and computers, and may decentralize data and process the decentralized data, record, or distribute data.

As described above, the clients may receive and reproduce the coded data in the content providing system ex100. In other words, the clients can receive and decode information transmitted by the user, and reproduce the decoded data in real time in the content providing system ex100, so that the user who does not have any particular right and equipment can implement personal broadcasting.

Aside from the example of the content providing system ex100, at least one of the moving picture coding apparatus (image coding apparatus) and the moving picture decoding apparatus (image decoding apparatus) described in each of embodiments may be implemented in a digital broadcasting system ex200illustrated inFIG.18. More specifically, a broadcast station ex201communicates or transmits, via radio waves to a broadcast satellite ex202, multiplexed data obtained by multiplexing audio data and others onto video data. The video data is data coded by the moving picture coding method described in each of embodiments (i.e., data coded by the image coding apparatus according to an aspect of the present disclosure). Upon receipt of the multiplexed data, the broadcast satellite ex202transmits radio waves for broadcasting. Then, a home-use antenna ex204with a satellite broadcast reception function receives the radio waves. Next, a device such as a television (receiver) ex300and a set top box (STB) ex217decodes the received multiplexed data, and reproduces the decoded data (i.e., functions as the image decoding apparatus according to an aspect of the present disclosure).

Furthermore, a reader/recorder ex218(i) reads and decodes the multiplexed data recorded on a recording medium ex215, such as a DVD and a BD, or (i) codes video signals in the recording medium ex215, and in some cases, writes data obtained by multiplexing an audio signal on the coded data. The reader/recorder ex218can include the moving picture decoding apparatus or the moving picture coding apparatus as shown in each of embodiments. In this case, the reproduced video signals are displayed on the monitor ex219, and can be reproduced by another device or system using the recording medium ex215on which the multiplexed data is recorded. It is also possible to implement the moving picture decoding apparatus in the set top box ex217connected to the cable ex203for a cable television or to the antenna ex204for satellite and/or terrestrial broadcasting, so as to display the video signals on the monitor ex219of the television ex300. The moving picture decoding apparatus may be implemented not in the set top box but in the television ex300.

FIG.19illustrates the television (receiver) ex300that uses the moving picture coding method and the moving picture decoding method described in each of embodiments. The television ex300includes: a tuner ex301that obtains or provides multiplexed data obtained by multiplexing audio data onto video data, through the antenna ex204or the cable ex203, etc. that receives a broadcast; a modulation/demodulation unit ex302that demodulates the received multiplexed data or modulates data into multiplexed data to be supplied outside; and a multiplexing/demultiplexing unit ex303that demultiplexes the modulated multiplexed data into video data and audio data, or multiplexes video data and audio data coded by a signal processing unit ex306into data.

The television ex300further includes: a signal processing unit ex306including an audio signal processing unit ex304and a video signal processing unit ex305that decode audio data and video data and code audio data and video data, respectively (which function as the image coding apparatus and the image decoding apparatus according to the aspects of the present disclosure); and an output unit ex309including a speaker ex307that provides the decoded audio signal, and a display unit ex308that displays the decoded video signal, such as a display. Furthermore, the television ex300includes an interface unit ex317including an operation input unit ex312that receives an input of a user operation. Furthermore, the television ex300includes a control unit ex310that controls overall each constituent element of the television ex300, and a power supply circuit unit ex311that supplies power to each of the elements. Other than the operation input unit ex312, the interface unit ex317may include: a bridge ex313that is connected to an external device, such as the reader/recorder ex218; a slot unit ex314for enabling attachment of the recording medium ex216, such as an SD card; a driver ex315to be connected to an external recording medium, such as a hard disk; and a modem ex316to be connected to a telephone network. Here, the recording medium ex216can electrically record information using a non-volatile/volatile semiconductor memory element for storage. The constituent elements of the television ex300are connected to each other through a synchronous bus.

First, the configuration in which the television ex300decodes multiplexed data obtained from outside through the antenna ex204and others and reproduces the decoded data will be described. In the television ex300, upon a user operation through a remote controller ex220and others, the multiplexing/demultiplexing unit ex303demultiplexes the multiplexed data demodulated by the modulation/demodulation unit ex302, under control of the control unit ex310including a CPU. Furthermore, the audio signal processing unit ex304decodes the demultiplexed audio data, and the video signal processing unit ex305decodes the demultiplexed video data, using the decoding method described in each of embodiments, in the television ex300. The output unit ex309provides the decoded video signal and audio signal outside, respectively. When the output unit ex309provides the video signal and the audio signal, the signals may be temporarily stored in buffers ex318and ex319, and others so that the signals are reproduced in synchronization with each other. Furthermore, the television ex300may read multiplexed data not through a broadcast and others but from the recording media ex215and ex216, such as a magnetic disk, an optical disk, and a SD card. Next, a configuration in which the television ex300codes an audio signal and a video signal, and transmits the data outside or writes the data on a recording medium will be described. In the television ex300, upon a user operation through the remote controller ex220and others, the audio signal processing unit ex304codes an audio signal, and the video signal processing unit ex305codes a video signal, under control of the control unit ex310using the coding method described in each of embodiments. The multiplexing/demultiplexing unit ex303multiplexes the coded video signal and audio signal, and provides the resulting signal outside. When the multiplexing/demultiplexing unit ex303multiplexes the video signal and the audio signal, the signals may be temporarily stored in the buffers ex320and ex321, and others so that the signals are reproduced in synchronization with each other. Here, the buffers ex318, ex319, ex320, and ex321may be plural as illustrated, or at least one buffer may be shared in the television ex300. Furthermore, data may be stored in a buffer so that the system overflow and underflow may be avoided between the modulation/demodulation unit ex302and the multiplexing/demultiplexing unit ex303, for example.

Furthermore, the television ex300may include a configuration for receiving an AV input from a microphone or a camera other than the configuration for obtaining audio and video data from a broadcast or a recording medium, and may code the obtained data. Although the television ex300can code, multiplex, and provide outside data in the description, it may be capable of only receiving, decoding, and providing outside data but not the coding, multiplexing, and providing outside data.

Furthermore, when the reader/recorder ex218reads or writes multiplexed data from or on a recording medium, one of the television ex300and the reader/recorder ex218may decode or code the multiplexed data, and the television ex300and the reader/recorder ex218may share the decoding or coding.

As an example,FIG.20illustrates a configuration of an information reproducing/recording unit ex400when data is read or written from or on an optical disk. The information reproducing/recording unit ex400includes constituent elements ex401, ex402, ex403, ex404, ex405, ex406, and ex407to be described hereinafter. The optical head ex401irradiates a laser spot in a recording surface of the recording medium ex215that is an optical disk to write information, and detects reflected light from the recording surface of the recording medium ex215to read the information. The modulation recording unit ex402electrically drives a semiconductor laser included in the optical head ex401, and modulates the laser light according to recorded data. The reproduction demodulating unit ex403amplifies a reproduction signal obtained by electrically detecting the reflected light from the recording surface using a photo detector included in the optical head ex401, and demodulates the reproduction signal by separating a signal component recorded on the recording medium ex215to reproduce the necessary information. The buffer ex404temporarily holds the information to be recorded on the recording medium ex215and the information reproduced from the recording medium ex215. The disk motor ex405rotates the recording medium ex215. The servo control unit ex406moves the optical head ex401to a predetermined information track while controlling the rotation drive of the disk motor ex405so as to follow the laser spot. The system control unit ex407controls overall the information reproducing/recording unit ex400. The reading and writing processes can be implemented by the system control unit ex407using various information stored in the buffer ex404and generating and adding new information as necessary, and by the modulation recording unit ex402, the reproduction demodulating unit ex403, and the servo control unit ex406that record and reproduce information through the optical head ex401while being operated in a coordinated manner. The system control unit ex407includes, for example, a microprocessor, and executes processing by causing a computer to execute a program for read and write.

Although the optical head ex401irradiates a laser spot in the description, it may perform high-density recording using near field light.

FIG.21illustrates the recording medium ex215that is the optical disk. On the recording surface of the recording medium ex215, guide grooves are spirally formed, and an information track ex230records, in advance, address information indicating an absolute position on the disk according to change in a shape of the guide grooves. The address information includes information for determining positions of recording blocks ex231that are a unit for recording data. Reproducing the information track ex230and reading the address information in an apparatus that records and reproduces data can lead to determination of the positions of the recording blocks. Furthermore, the recording medium ex215includes a data recording area ex233, an inner circumference area ex232, and an outer circumference area ex234. The data recording area ex233is an area for use in recording the user data. The inner circumference area ex232and the outer circumference area ex234that are inside and outside of the data recording area ex233, respectively are for specific use except for recording the user data. The information reproducing/recording unit400reads and writes coded audio, coded video data, or multiplexed data obtained by multiplexing the coded audio and video data, from and on the data recording area ex233of the recording medium ex215.

Although an optical disk having a layer, such as a DVD and a BD is described as an example in the description, the optical disk is not limited to such, and may be an optical disk having a multilayer structure and capable of being recorded on a part other than the surface. Furthermore, the optical disk may have a structure for multidimensional recording/reproduction, such as recording of information using light of colors with different wavelengths in the same portion of the optical disk and for recording information having different layers from various angles.

Furthermore, a car ex210having an antenna ex205can receive data from the satellite ex202and others, and reproduce video on a display device such as a car navigation system ex211set in the car ex210, in the digital broadcasting system ex200. Here, a configuration of the car navigation system ex211will be a configuration, for example, including a GPS receiving unit from the configuration illustrated inFIG.19. The same will be true for the configuration of the computer ex111, the cellular phone ex114, and others.

FIG.22Aillustrates the cellular phone ex114that uses the moving picture coding method and the moving picture decoding method described in embodiments. The cellular phone ex114includes: an antenna ex350for transmitting and receiving radio waves through the base station ex110; a camera unit ex365capable of capturing moving and still images; and a display unit ex358such as a liquid crystal display for displaying the data such as decoded video captured by the camera unit ex365or received by the antenna ex350. The cellular phone ex114further includes: a main body unit including an operation key unit ex366; an audio output unit ex357such as a speaker for output of audio; an audio input unit ex356such as a microphone for input of audio; a memory unit ex367for storing captured video or still pictures, recorded audio, coded or decoded data of the received video, the still pictures, e-mails, or others; and a slot unit ex364that is an interface unit for a recording medium that stores data in the same manner as the memory unit ex367.

Next, an example of a configuration of the cellular phone ex114will be described with reference toFIG.22B. In the cellular phone ex114, a main control unit ex360designed to control overall each unit of the main body including the display unit ex358as well as the operation key unit ex366is connected mutually, via a synchronous bus ex370, to a power supply circuit unit ex361, an operation input control unit ex362, a video signal processing unit ex355, a camera interface unit ex363, a liquid crystal display (LCD) control unit ex359, a modulation/demodulation unit ex352, a multiplexing/demultiplexing unit ex353, an audio signal processing unit ex354, the slot unit ex364, and the memory unit ex367.

When a call-end key or a power key is turned ON by a user's operation, the power supply circuit unit ex361supplies the respective units with power from a battery pack so as to activate the cell phone ex114.

In the cellular phone ex114, the audio signal processing unit ex354converts the audio signals collected by the audio input unit ex356in voice conversation mode into digital audio signals under the control of the main control unit ex360including a CPU, ROM, and RAM. Then, the modulation/demodulation unit ex352performs spread spectrum processing on the digital audio signals, and the transmitting and receiving unit ex351performs digital-to-analog conversion and frequency conversion on the data, so as to transmit the resulting data via the antenna ex350. Also, in the cellular phone ex114, the transmitting and receiving unit ex351amplifies the data received by the antenna ex350in voice conversation mode and performs frequency conversion and the analog-to-digital conversion on the data. Then, the modulation/demodulation unit ex352performs inverse spread spectrum processing on the data, and the audio signal processing unit ex354converts it into analog audio signals, so as to output them via the audio output unit ex357.

Furthermore, when an e-mail in data communication mode is transmitted, text data of the e-mail inputted by operating the operation key unit ex366and others of the main body is sent out to the main control unit ex360via the operation input control unit ex362. The main control unit ex360causes the modulation/demodulation unit ex352to perform spread spectrum processing on the text data, and the transmitting and receiving unit ex351performs the digital-to-analog conversion and the frequency conversion on the resulting data to transmit the data to the base station ex110via the antenna ex350. When an e-mail is received, processing that is approximately inverse to the processing for transmitting an e-mail is performed on the received data, and the resulting data is provided to the display unit ex358.

When video, still images, or video and audio in data communication mode is or are transmitted, the video signal processing unit ex355compresses and codes video signals supplied from the camera unit ex365using the moving picture coding method shown in each of embodiments (i.e., functions as the image coding apparatus according to the aspect of the present disclosure), and transmits the coded video data to the multiplexing/demultiplexing unit ex353. In contrast, during when the camera unit ex365captures video, still images, and others, the audio signal processing unit ex354codes audio signals collected by the audio input unit ex356, and transmits the coded audio data to the multiplexing/demultiplexing unit ex353.

The multiplexing/demultiplexing unit ex353multiplexes the coded video data supplied from the video signal processing unit ex355and the coded audio data supplied from the audio signal processing unit ex354, using a predetermined method. Then, the modulation/demodulation unit (modulation/demodulation circuit unit) ex352performs spread spectrum processing on the multiplexed data, and the transmitting and receiving unit ex351performs digital-to-analog conversion and frequency conversion on the data so as to transmit the resulting data via the antenna ex350.

When receiving data of a video file which is linked to a Web page and others in data communication mode or when receiving an e-mail with video and/or audio attached, in order to decode the multiplexed data received via the antenna ex350, the multiplexing/demultiplexing unit ex353demultiplexes the multiplexed data into a video data bit stream and an audio data bit stream, and supplies the video signal processing unit ex355with the coded video data and the audio signal processing unit ex354with the coded audio data, through the synchronous bus ex370. The video signal processing unit ex355decodes the video signal using a moving picture decoding method corresponding to the moving picture coding method shown in each of embodiments (i.e., functions as the image decoding apparatus according to the aspect of the present disclosure), and then the display unit ex358displays, for instance, the video and still images included in the video file linked to the Web page via the LCD control unit ex359. Furthermore, the audio signal processing unit ex354decodes the audio signal, and the audio output unit ex357provides the audio.

Furthermore, similarly to the television ex300, a terminal such as the cellular phone ex114probably have3types of implementation configurations including not only (i) a transmitting and receiving terminal including both a coding apparatus and a decoding apparatus, but also (ii) a transmitting terminal including only a coding apparatus and (iii) a receiving terminal including only a decoding apparatus. Although the digital broadcasting system ex200receives and transmits the multiplexed data obtained by multiplexing audio data onto video data in the description, the multiplexed data may be data obtained by multiplexing not audio data but character data related to video onto video data, and may be not multiplexed data but video data itself.

As such, the moving picture coding method and the moving picture decoding method in each of embodiments can be used in any of the devices and systems described. Thus, the advantages described in each of embodiments can be obtained.

Furthermore, various modifications and revisions can be made in any of the embodiments in the present disclosure.

Embodiment 6

Video data can be generated by switching, as necessary, between (i) the moving picture coding method or the moving picture coding apparatus shown in each of embodiments and (ii) a moving picture coding method or a moving picture coding apparatus in conformity with a different standard, such as MPEG-2, MPEG-4 AVC, and VC-1.

Here, when a plurality of video data that conforms to the different standards is generated and is then decoded, the decoding methods need to be selected to conform to the different standards. However, since to which standard each of the plurality of the video data to be decoded conform cannot be detected, there is a problem that an appropriate decoding method cannot be selected.

In order to solve the problem, multiplexed data obtained by multiplexing audio data and others onto video data has a structure including identification information indicating to which standard the video data conforms. The specific structure of the multiplexed data including the video data generated in the moving picture coding method and by the moving picture coding apparatus shown in each of embodiments will be hereinafter described. The multiplexed data is a digital stream in the MPEG-2 Transport Stream format.

FIG.23illustrates a structure of the multiplexed data. As illustrated inFIG.23, the multiplexed data can be obtained by multiplexing at least one of a video stream, an audio stream, a presentation graphics stream (PG), and an interactive graphics stream. The video stream represents primary video and secondary video of a movie, the audio stream (IG) represents a primary audio part and a secondary audio part to be mixed with the primary audio part, and the presentation graphics stream represents subtitles of the movie. Here, the primary video is normal video to be displayed on a screen, and the secondary video is video to be displayed on a smaller window in the primary video. Furthermore, the interactive graphics stream represents an interactive screen to be generated by arranging the GUI components on a screen. The video stream is coded in the moving picture coding method or by the moving picture coding apparatus shown in each of embodiments, or in a moving picture coding method or by a moving picture coding apparatus in conformity with a conventional standard, such as MPEG-2, MPEG-4 AVC, and VC-1. The audio stream is coded in accordance with a standard, such as Dolby-AC-3, Dolby Digital Plus, MLP, DTS, DTS-HD, and linear PCM.

Each stream included in the multiplexed data is identified by PID. For example, 0x1011 is allocated to the video stream to be used for video of a movie, 0x1100 to 0x111F are allocated to the audio streams, 0x1200 to 0x121F are allocated to the presentation graphics streams, 0x1400 to 0x141F are allocated to the interactive graphics streams, 0x1B00 to 0x1B1F are allocated to the video streams to be used for secondary video of the movie, and 0x1A00 to 0x1A1F are allocated to the audio streams to be used for the secondary audio to be mixed with the primary audio.

FIG.24schematically illustrates how data is multiplexed. First, a video stream ex235composed of video frames and an audio stream ex238composed of audio frames are transformed into a stream of PES packets ex236and a stream of PES packets ex239, and further into TS packets ex237and TS packets ex240, respectively. Similarly, data of a presentation graphics stream ex241and data of an interactive graphics stream ex244are transformed into a stream of PES packets ex242and a stream of PES packets ex245, and further into TS packets ex243and TS packets ex246, respectively. These TS packets are multiplexed into a stream to obtain multiplexed data ex247.

FIG.25illustrates how a video stream is stored in a stream of PES packets in more detail. The first bar inFIG.25shows a video frame stream in a video stream. The second bar shows the stream of PES packets. As indicated by arrows denoted as yy1, yy2, yy3, and yy4inFIG.25, the video stream is divided into pictures as I pictures, B pictures, and P pictures each of which is a video presentation unit, and the pictures are stored in a payload of each of the PES packets. Each of the PES packets has a PES header, and the PES header stores a Presentation Time-Stamp (PTS) indicating a display time of the picture, and a Decoding Time-Stamp (DTS) indicating a decoding time of the picture.

FIG.26illustrates a format of TS packets to be finally written on the multiplexed data. Each of the TS packets is a 188-byte fixed length packet including a 4-byte TS header having information, such as a PID for identifying a stream and a 184-byte TS payload for storing data. The PES packets are divided, and stored in the TS payloads, respectively. When a BD ROM is used, each of the TS packets is given a 4-byte TP_Extra_Header, thus resulting in 192-byte source packets. The source packets are written on the multiplexed data. The TP_Extra_Header stores information such as an Arrival_Time_Stamp (ATS). The ATS shows a transfer start time at which each of the TS packets is to be transferred to a PID filter. The source packets are arranged in the multiplexed data as shown at the bottom ofFIG.26. The numbers incrementing from the head of the multiplexed data are called source packet numbers (SPNs).

Each of the TS packets included in the multiplexed data includes not only streams of audio, video, subtitles and others, but also a Program Association Table (PAT), a Program Map Table (PMT), and a Program Clock Reference (PCR). The PAT shows what a PID in a PMT used in the multiplexed data indicates, and a PID of the PAT itself is registered as zero. The PMT stores PIDs of the streams of video, audio, subtitles and others included in the multiplexed data, and attribute information of the streams corresponding to the PIDs. The PMT also has various descriptors relating to the multiplexed data. The descriptors have information such as copy control information showing whether copying of the multiplexed data is permitted or not. The PCR stores STC time information corresponding to an ATS showing when the PCR packet is transferred to a decoder, in order to achieve synchronization between an Arrival Time Clock (ATC) that is a time axis of ATSs, and an System Time Clock (STC) that is a time axis of PTSs and DTSs.

FIG.27illustrates the data structure of the PMT in detail. A PMT header is disposed at the top of the PMT. The PMT header describes the length of data included in the PMT and others. A plurality of descriptors relating to the multiplexed data is disposed after the PMT header. Information such as the copy control information is described in the descriptors. After the descriptors, a plurality of pieces of stream information relating to the streams included in the multiplexed data is disposed. Each piece of stream information includes stream descriptors each describing information, such as a stream type for identifying a compression codec of a stream, a stream PID, and stream attribute information (such as a frame rate or an aspect ratio). The stream descriptors are equal in number to the number of streams in the multiplexed data.

When the multiplexed data is recorded on a recording medium and others, it is recorded together with multiplexed data information files.

Each of the multiplexed data information files is management information of the multiplexed data as shown inFIG.28. The multiplexed data information files are in one to one correspondence with the multiplexed data, and each of the files includes multiplexed data information, stream attribute information, and an entry map.

As illustrated inFIG.28, the multiplexed data information includes a system rate, a reproduction start time, and a reproduction end time. The system rate indicates the maximum transfer rate at which a system target decoder to be described later transfers the multiplexed data to a PID filter. The intervals of the ATSs included in the multiplexed data are set to not higher than a system rate. The reproduction start time indicates a PTS in a video frame at the head of the multiplexed data. An interval of one frame is added to a PTS in a video frame at the end of the multiplexed data, and the PTS is set to the reproduction end time.

As shown inFIG.29, a piece of attribute information is registered in the stream attribute information, for each PID of each stream included in the multiplexed data. Each piece of attribute information has different information depending on whether the corresponding stream is a video stream, an audio stream, a presentation graphics stream, or an interactive graphics stream. Each piece of video stream attribute information carries information including what kind of compression codec is used for compressing the video stream, and the resolution, aspect ratio and frame rate of the pieces of picture data that is included in the video stream. Each piece of audio stream attribute information carries information including what kind of compression codec is used for compressing the audio stream, how many channels are included in the audio stream, which language the audio stream supports, and how high the sampling frequency is. The video stream attribute information and the audio stream attribute information are used for initialization of a decoder before the player plays back the information.

In the present embodiment, the multiplexed data to be used is of a stream type included in the PMT. Furthermore, when the multiplexed data is recorded on a recording medium, the video stream attribute information included in the multiplexed data information is used. More specifically, the moving picture coding method or the moving picture coding apparatus described in each of embodiments includes a step or a unit for allocating unique information indicating video data generated by the moving picture coding method or the moving picture coding apparatus in each of embodiments, to the stream type included in the PMT or the video stream attribute information. With the configuration, the video data generated by the moving picture coding method or the moving picture coding apparatus described in each of embodiments can be distinguished from video data that conforms to another standard.

Furthermore,FIG.30illustrates steps of the moving picture decoding method according to the present embodiment. In Step exS100, the stream type included in the PMT or the video stream attribute information included in the multiplexed data information is obtained from the multiplexed data. Next, in Step exS101, it is determined whether or not the stream type or the video stream attribute information indicates that the multiplexed data is generated by the moving picture coding method or the moving picture coding apparatus in each of embodiments. When it is determined that the stream type or the video stream attribute information indicates that the multiplexed data is generated by the moving picture coding method or the moving picture coding apparatus in each of embodiments, in Step exS102, decoding is performed by the moving picture decoding method in each of embodiments. Furthermore, when the stream type or the video stream attribute information indicates conformance to the conventional standards, such as MPEG-2, MPEG-4 AVC, and VC-1, in Step exS103, decoding is performed by a moving picture decoding method in conformity with the conventional standards.

As such, allocating a new unique value to the stream type or the video stream attribute information enables determination whether or not the moving picture decoding method or the moving picture decoding apparatus that is described in each of embodiments can perform decoding. Even when multiplexed data that conforms to a different standard is input, an appropriate decoding method or apparatus can be selected. Thus, it becomes possible to decode information without any error. Furthermore, the moving picture coding method or apparatus, or the moving picture decoding method or apparatus in the present embodiment can be used in the devices and systems described above.

Embodiment 7

Each of the moving picture coding method, the moving picture coding apparatus, the moving picture decoding method, and the moving picture decoding apparatus in each of embodiments is typically achieved in the form of an integrated circuit or a Large Scale Integrated (LSI) circuit. As an example of the LSI,FIG.31illustrates a configuration of the LSI ex500that is made into one chip. The LSI ex500includes elements ex501, ex502, ex503, ex504, ex505, ex506, ex507, ex508, and ex509to be described below, and the elements are connected to each other through a bus ex510. The power supply circuit unit ex505is activated by supplying each of the elements with power when the power supply circuit unit ex505is turned on.

For example, when coding is performed, the LSI ex500receives an AV signal from a microphone ex117, a camera ex113, and others through an AV IO ex509under control of a control unit ex501including a CPU ex502, a memory controller ex503, a stream controller ex504, and a driving frequency control unit ex512. The received AV signal is temporarily stored in an external memory ex511, such as an SDRAM. Under control of the control unit ex501, the stored data is segmented into data portions according to the processing amount and speed to be transmitted to a signal processing unit ex507. Then, the signal processing unit ex507codes an audio signal and/or a video signal. Here, the coding of the video signal is the coding described in each of embodiments. Furthermore, the signal processing unit ex507sometimes multiplexes the coded audio data and the coded video data, and a stream IO ex506provides the multiplexed data outside. The provided multiplexed data is transmitted to the base station ex107, or written on the recording medium ex215. When data sets are multiplexed, the data should be temporarily stored in the buffer ex508so that the data sets are synchronized with each other.

Although the memory ex511is an element outside the LSI ex500, it may be included in the LSI ex500. The buffer ex508is not limited to one buffer, but may be composed of buffers. Furthermore, the LSI ex500may be made into one chip or a plurality of chips.

Furthermore, although the control unit ex501includes the CPU ex502, the memory controller ex503, the stream controller ex504, the driving frequency control unit ex512, the configuration of the control unit ex501is not limited to such. For example, the signal processing unit ex507may further include a CPU. Inclusion of another CPU in the signal processing unit ex507can improve the processing speed. Furthermore, as another example, the CPU ex502may serve as or be a part of the signal processing unit ex507, and, for example, may include an audio signal processing unit. In such a case, the control unit ex501includes the signal processing unit ex507or the CPU ex502including a part of the signal processing unit ex507.

The name used here is LSI, but it may also be called IC, system LSI, super LSI, or ultra LSI depending on the degree of integration.

Moreover, ways to achieve integration are not limited to the LSI, and a special circuit or a general purpose processor and so forth can also achieve the integration. Field Programmable Gate Array (FPGA) that can be programmed after manufacturing LSIs or a reconfigurable processor that allows re-configuration of the connection or configuration of an LSI can be used for the same purpose.

In the future, with advancement in semiconductor technology, a brand-new technology may replace LSI. The functional blocks can be integrated using such a technology. The possibility is that the present disclosure is applied to biotechnology.

Embodiment 8

When video data generated in the moving picture coding method or by the moving picture coding apparatus described in each of embodiments is decoded, compared to when video data that conforms to a conventional standard, such as MPEG-2, MPEG-4 AVC, and VC-1 is decoded, the processing amount probably increases. Thus, the LSI ex500needs to be set to a driving frequency higher than that of the CPU ex502to be used when video data in conformity with the conventional standard is decoded. However, when the driving frequency is set higher, there is a problem that the power consumption increases.

In order to solve the problem, the moving picture decoding apparatus, such as the television ex300and the LSI ex500is configured to determine to which standard the video data conforms, and switch between the driving frequencies according to the determined standard.FIG.32illustrates a configuration ex800in the present embodiment. A driving frequency switching unit ex803sets a driving frequency to a higher driving frequency when video data is generated by the moving picture coding method or the moving picture coding apparatus described in each of embodiments. Then, the driving frequency switching unit ex803instructs a decoding processing unit ex801that executes the moving picture decoding method described in each of embodiments to decode the video data. When the video data conforms to the conventional standard, the driving frequency switching unit ex803sets a driving frequency to a lower driving frequency than that of the video data generated by the moving picture coding method or the moving picture coding apparatus described in each of embodiments. Then, the driving frequency switching unit ex803instructs the decoding processing unit ex802that conforms to the conventional standard to decode the video data.

More specifically, the driving frequency switching unit ex803includes the CPU ex502and the driving frequency control unit ex512inFIG.31. Here, each of the decoding processing unit ex801that executes the moving picture decoding method described in each of embodiments and the decoding processing unit ex802that conforms to the conventional standard corresponds to the signal processing unit ex507inFIG.31. The CPU ex502determines to which standard the video data conforms. Then, the driving frequency control unit ex512determines a driving frequency based on a signal from the CPU ex502. Furthermore, the signal processing unit ex507decodes the video data based on the signal from the CPU ex502. For example, the identification information described in Embodiment 6 is probably used for identifying the video data. The identification information is not limited to the one described in Embodiment 6 but may be any information as long as the information indicates to which standard the video data conforms. For example, when which standard video data conforms to can be determined based on an external signal for determining that the video data is used for a television or a disk, etc., the determination may be made based on such an external signal. Furthermore, the CPU ex502selects a driving frequency based on, for example, a look-up table in which the standards of the video data are associated with the driving frequencies as shown inFIG.34. The driving frequency can be selected by storing the look-up table in the buffer ex508and in an internal memory of an LSI, and with reference to the look-up table by the CPU ex502.

FIG.33illustrates steps for executing a method in the present embodiment. First, in Step exS200, the signal processing unit ex507obtains identification information from the multiplexed data. Next, in Step exS201, the CPU ex502determines whether or not the video data is generated by the coding method and the coding apparatus described in each of embodiments, based on the identification information. When the video data is generated by the moving picture coding method and the moving picture coding apparatus described in each of embodiments, in Step exS202, the CPU ex502transmits a signal for setting the driving frequency to a higher driving frequency to the driving frequency control unit ex512. Then, the driving frequency control unit ex512sets the driving frequency to the higher driving frequency. On the other hand, when the identification information indicates that the video data conforms to the conventional standard, such as MPEG-2, MPEG-4 AVC, and VC-1, in Step exS203, the CPU ex502transmits a signal for setting the driving frequency to a lower driving frequency to the driving frequency control unit ex512. Then, the driving frequency control unit ex512sets the driving frequency to the lower driving frequency than that in the case where the video data is generated by the moving picture coding method and the moving picture coding apparatus described in each of embodiment.

Furthermore, along with the switching of the driving frequencies, the power conservation effect can be improved by changing the voltage to be applied to the LSI ex500or an apparatus including the LSI ex500. For example, when the driving frequency is set lower, the voltage to be applied to the LSI ex500or the apparatus including the LSI ex500is probably set to a voltage lower than that in the case where the driving frequency is set higher.

Furthermore, when the processing amount for decoding is larger, the driving frequency may be set higher, and when the processing amount for decoding is smaller, the driving frequency may be set lower as the method for setting the driving frequency. Thus, the setting method is not limited to the ones described above. For example, when the processing amount for decoding video data in conformity with MPEG-4 AVC is larger than the processing amount for decoding video data generated by the moving picture coding method and the moving picture coding apparatus described in each of embodiments, the driving frequency is probably set in reverse order to the setting described above.

Furthermore, the method for setting the driving frequency is not limited to the method for setting the driving frequency lower. For example, when the identification information indicates that the video data is generated by the moving picture coding method and the moving picture coding apparatus described in each of embodiments, the voltage to be applied to the LSI ex500or the apparatus including the LSI ex500is probably set higher. When the identification information indicates that the video data conforms to the conventional standard, such as MPEG-2, MPEG-4 AVC, and VC-1, the voltage to be applied to the LSI ex500or the apparatus including the LSI ex500is probably set lower. As another example, when the identification information indicates that the video data is generated by the moving picture coding method and the moving picture coding apparatus described in each of embodiments, the driving of the CPU ex502does not probably have to be suspended. When the identification information indicates that the video data conforms to the conventional standard, such as MPEG-2, MPEG-4 AVC, and VC-1, the driving of the CPU ex502is probably suspended at a given time because the CPU ex502has extra processing capacity. Even when the identification information indicates that the video data is generated by the moving picture coding method and the moving picture coding apparatus described in each of embodiments, in the case where the CPU ex502has extra processing capacity, the driving of the CPU ex502is probably suspended at a given time. In such a case, the suspending time is probably set shorter than that in the case where when the identification information indicates that the video data conforms to the conventional standard, such as MPEG-2, MPEG-4 AVC, and VC-1.

Accordingly, the power conservation effect can be improved by switching between the driving frequencies in accordance with the standard to which the video data conforms. Furthermore, when the LSI ex500or the apparatus including the LSI ex500is driven using a battery, the battery life can be extended with the power conservation effect.

Embodiment 9

There are cases where a plurality of video data that conforms to different standards, is provided to the devices and systems, such as a television and a cellular phone. In order to enable decoding the plurality of video data that conforms to the different standards, the signal processing unit ex507of the LSI ex500needs to conform to the different standards. However, the problems of increase in the scale of the circuit of the LSI ex500and increase in the cost arise with the individual use of the signal processing units ex507that conform to the respective standards.

In order to solve the problem, what is conceived is a configuration in which the decoding processing unit for implementing the moving picture decoding method described in each of embodiments and the decoding processing unit that conforms to the conventional standard, such as MPEG-2, MPEG-4 AVC, and VC-1 are partly shared. Ex900inFIG.35Ashows an example of the configuration. For example, the moving picture decoding method described in each of embodiments and the moving picture decoding method that conforms to MPEG-4 AVC have, partly in common, the details of processing, such as entropy coding, inverse quantization, deblocking filtering, and motion compensated prediction. The details of processing to be shared probably include use of a decoding processing unit ex902that conforms to MPEG-4 AVC. In contrast, a dedicated decoding processing unit ex901is probably used for other processing unique to an aspect of the present disclosure. Since the aspect of the present disclosure is characterized by inter prediction in particular, for example, the dedicated decoding processing unit ex901is used for inter prediction. Otherwise, the decoding processing unit is probably shared for one of the entropy decoding, deblocking filtering, and inverse quantization, or all of the processing. The decoding processing unit for implementing the moving picture decoding method described in each of embodiments may be shared for the processing to be shared, and a dedicated decoding processing unit may be used for processing unique to that of MPEG-4 AVC.

Furthermore, ex1000inFIG.35Bshows another example in that processing is partly shared. This example uses a configuration including a dedicated decoding processing unit ex1001that supports the processing unique to an aspect of the present disclosure, a dedicated decoding processing unit ex1002that supports the processing unique to another conventional standard, and a decoding processing unit ex1003that supports processing to be shared between the moving picture decoding method according to the aspect of the present disclosure and the conventional moving picture decoding method. Here, the dedicated decoding processing units ex1001and ex1002are not necessarily specialized for the processing according to the aspect of the present disclosure and the processing of the conventional standard, respectively, and may be the ones capable of implementing general processing. Furthermore, the configuration of the present embodiment can be implemented by the LSI ex500.

As such, reducing the scale of the circuit of an LSI and reducing the cost are possible by sharing the decoding processing unit for the processing to be shared between the moving picture decoding method according to the aspect of the present disclosure and the moving picture decoding method in conformity with the conventional standard.

INDUSTRIAL APPLICABILITY

One or more exemplary embodiments disclosed herein are applicable to a television receiver, a digital video recorder, a car navigation system, a cellular phone, a digital camera, a digital video camera, and the like.