WO2015053525A1 - Method for encoding/decoding image and device using same - Google Patents

Abstract

A method for decoding a bitstream including a plurality of layers, according to the present invention, comprises the steps of: setting a parameter for decoding the bitstream from a point at which a random access has occurred if the random access has occurred; and decoding a picture to be decoded, wherein the step of setting a parameter can comprise the steps of: setting an initialization flag indicating whether the picture to be decoded can be outputted since the picture to be decoded is an intra random access point (IRAP) picture, and all reference layers of a target layer to which the picture to be decoded belongs are normally decoded, if the random access has occurred; setting a flag variable (NoRaslOutputFlag) indicating whether the picture to be decoded has been used as a random access point; and resetting the initialization flag if the picture to be decoded is an IRAP picture and the flag variable is 1.

Description

Image encoding / decoding method and apparatus using same

The present invention relates to video encoding and decoding processing, and more particularly, to a video encoding / decoding method and apparatus for supporting bitstream random access.

Recently, as broadcasting services having high definition (HD) resolution have been expanded not only in Korea but also in the world, many users are accustomed to high resolution and high quality images, and many organizations are accelerating the development of next generation video equipment. In addition, as interest in Ultra High Definition (UHD), which has four times the resolution of HDTV, is increasing along with HDTV, a compression technology for higher resolution and higher quality images is required.

For image compression, an inter prediction technique for predicting pixel values included in a current picture from a previous and / or subsequent picture in time, and predicting pixel values included in a current picture using pixel information in the current picture. An intra prediction technique, an entropy encoding technique of allocating a short code to a symbol with a high frequency of appearance and a long code to a symbol with a low frequency of appearance may be used.

Video compression technology is a technology that provides a constant network bandwidth under a limited operating environment of hardware without considering a fluid network environment. However, a new compression technique is required to compress image data applied to a network environment in which bandwidth changes frequently, and a scalable video encoding / decoding method may be used for this purpose.

The present invention provides a method for enabling decoding from an arbitrary point in a bitstream and an apparatus using the same.

In detail, an embodiment of the present invention includes an intra-random access point (IRAP) picture and a non-intra-random random access point picture (IRAP) picture or only an IRAP picture in an AU (access unit) at a random access point. However, when there are two or more NAL unit types, the bitstream may be gradually decoded from a random access point.

According to an embodiment of the present invention, a method of decoding a bitstream including a plurality of layers may include: setting a parameter for decoding the bitstream from a time point when the random access occurs when random access occurs; And decoding the picture to be decoded, and setting the parameter comprises setting an initialization flag indicating whether or not the picture to be decoded can be normally decoded and output when the random access occurs. Steps; Setting a flag variable (NoRaslOutputFlag) indicating whether the decoding target picture is used as a random access point; If the decoding target picture is an IRAP picture, the flag variable is 1, the initialization flag for the decoding target picture is 0, and the initialization flag for all the reference layers of the target layer is 1, for the target layer And resetting the initialization flag to 1.

The setting of the initialization flag may be set to 1 for a base layer of the access unit in which the random access has occurred and to 0 for a layer higher than the base layer.

The setting of the flag variable NoRaslOutputFlag may include setting the flag variable to 1 when the decoding target picture is an IDR picture or a BLA picture or an IRAP picture and is the first picture of the target layer of the corresponding bitstream.

The setting of the flag variable (NoRaslOutputFlag) may include: an initialization flag set to a layer to which the target picture belongs, an initial flag set to 0, and an initialization flag for all reference layers of the layer to which the target picture belongs to 1 In this case, the flag variable may be set to one.

Calculating a POC that is an identifier of the decoding target picture; Constructing a reference picture set and displaying a reference picture type for inter prediction of the picture to be decoded; Determining whether to output the decoding target picture based on the initialization flag; The method may further include performing motion prediction and motion compensation on the decoding target picture by using a reference picture in a reference picture list generated based on the reference picture set.

The determining of whether to output the decoding target picture may include determining that the decoding target picture is not output when the decoding target picture is an IRAP picture and the initialization flag value of the target layer is 0.

The determining of whether to output the decoding target picture includes determining that an output target picture belonging to the output layer is not output in an access unit to which the target layer belongs, rather than an output layer to which the target layer belongs. And the target layer is used as a reference of the output layer so that the decoded picture is used as a reference picture of the output target picture and the flag information indicating whether or not to output a picture signaled in the slice header is decoded with 1 is decoded. In the case of the highest picture among the pictures, it may be determined to output the decoding target picture.

The determining of whether to output the decoding target picture includes determining that an output target picture belonging to the output layer is not output in an access unit to which the target layer belongs, rather than an output layer to which the target layer belongs. The target layer is used as a reference of the output layer such that the decoding target picture is used as a reference picture of the output target picture, the initialization flag value for the target layer is 1, and the decoding target picture is signaled in a slice header. When flag information indicating whether to output a picture is output is the highest picture among decoded pictures of 1, it may be determined that the decoding target picture is output.

Decoding pictures included in a first access unit corresponding to a time point at which the random access occurs; Determining whether to individually output pictures included in the first access unit; Decoding pictures included in a second access unit after the first access unit; The method may further include determining whether to individually output pictures included in the second access unit next to the first access unit.

And outputting a first access unit picture outputting a picture determined to be output among the pictures included in the first access unit, wherein the first access unit picture outputting step comprises: the bitstream being the highest layer to the highest layer. And output an output picture of the output layer when the base layer is an intra random access point (IRAP) picture from the base layer to an nth (0 ≦ n) layer and an output layer belongs to the base layer to the nth layer. When the output layer is included in the top layer from the n + 1 th layer, the decoded picture of the n th layer may be output.

And a second access unit picture outputting step of outputting a picture determined to be output among the pictures included in the second access unit, wherein the second access unit picture outputting step is performed by the second access unit. If the (n + 1≤k) IRAP picture is included in the n + 1 th layer to the k th layer, and the output layer is included in the k th layer from the base layer, the output picture of the output layer is output. When the output layer is included in the highest layer from the k + 1 th layer, a decoded picture of the k th layer or a picture determined to be output may be output.

The calculating of the POC may include setting the POC of the decoding target picture to 0 when the picture of the base layer of the same access unit is an IDR picture, and when the picture of the base layer is the BLA picture or the first CRA picture of the bitstream, POC_MSB of the decoding target picture may be set to zero.

According to another embodiment of the present invention, when a random access occurs, a decoding apparatus of a bitstream includes setting parameters for decoding the bitstream from a time point when the random access occurs, and decoding a picture to be decoded. A prediction unit which decodes a signal, and when the random access occurs, the prediction unit sets an initialization flag indicating whether a target picture to be decoded can be decoded and output normally, and the decoding target picture is randomly accessed. Set a flag variable (NoRaslOutputFlag) indicating whether or not it is used as a point, wherein the decoding target picture is an IRAP picture, the flag variable is 1, the initialization flag for the decoding target picture is 0, and all of the target layers If the initialization flag for the reference layer is 1, the The initialization flag for the layer may be reset to one.

According to an embodiment of the present invention, a method and an apparatus using the same are provided so that decoding is possible from any point in the bitstream.

Specifically, according to one embodiment of the present invention, an intra random access point (IRAP) picture and a non-intra random random access point picture (IRAP) are present in an access unit (AU) at a random access point, or an IRAP picture There is provided a method and an apparatus using the same that can gradually decode a bitstream from a randomly accessible point of time when only two NAL unit types exist.

1 is a block diagram illustrating a configuration of an image encoding apparatus according to an embodiment.

2 is a block diagram illustrating a configuration of an image decoding apparatus according to an embodiment.

3 is a conceptual diagram schematically illustrating an embodiment of a scalable video coding structure using multiple layers to which the present invention can be applied.

4 is a diagram for describing a method of gradually decoding a bitstream according to the present invention.

5 is a diagram illustrating a bitstream structure including a randomly accessible point of time according to an embodiment of the present invention.

6 is a diagram illustrating a bitstream structure including randomly accessible viewpoints according to another embodiment of the present invention.

7 is a diagram illustrating a bitstream structure including randomly accessible viewpoints according to another embodiment of the present invention.

8 is a diagram illustrating a bitstream structure including a randomly accessible time point according to another embodiment of the present invention.

9 is a control flowchart illustrating a method of decoding an image according to an embodiment of the present invention.

10 is a diagram for describing a method of setting a decoding parameter according to an embodiment of the present invention.

11 is a control flowchart illustrating a decoding method of an inter-layer video according to an embodiment of the present invention.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described concretely with reference to drawings. In describing the embodiments of the present specification, when it is determined that a detailed description of a related well-known configuration or function may obscure the gist of the present specification, the detailed description thereof will be omitted.

When a component is said to be “connected” or “connected” to another component, it may be directly connected to or connected to that other component, but it may be understood that another component may exist in between. Should be. In addition, the description "include" a specific configuration in the present invention does not exclude a configuration other than the configuration, it means that additional configuration may be included in the scope of the technical spirit of the present invention or the present invention.

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as the second component, and similarly, the second component may also be referred to as the first component.

In addition, the components shown in the embodiments of the present invention are shown independently to represent different characteristic functions, and do not mean that each component is made of separate hardware or one software component unit. In other words, each component is included in each component for convenience of description, and at least two of the components may be combined into one component, or one component may be divided into a plurality of components to perform a function. Integrated and separate embodiments of the components are also included within the scope of the present invention without departing from the spirit of the invention.

In addition, some of the components may not be essential components for performing essential functions in the present invention, but may be optional components for improving performance. The present invention can be implemented including only the components essential for implementing the essentials of the present invention except for the components used for improving performance, and the structure including only the essential components except for the optional components used for improving performance. Also included in the scope of the present invention.

1 is a block diagram illustrating a configuration of an image encoding apparatus according to an embodiment. A scalable video encoding / decoding method or apparatus may be implemented by an extension of a general video encoding / decoding method or apparatus that does not provide scalability, and the block diagram of FIG. 1 is scalable. An embodiment of an image encoding apparatus that may be the basis of a video encoding apparatus is illustrated.

Referring to FIG. 1, the image encoding apparatus 100 may include a motion predictor 111, a motion compensator 112, an intra predictor 120, a switch 115, a subtractor 125, and a converter 130. And a quantization unit 140, an entropy encoding unit 150, an inverse quantization unit 160, an inverse transform unit 170, an adder 175, a filter unit 180, and a reference image buffer 190.

The image encoding apparatus 100 may perform encoding in an intra mode or an inter mode on an input image and output a bit stream. Intra prediction means intra prediction and inter prediction means inter prediction. In the intra mode, the switch 115 is switched to intra, and in the inter mode, the switch 115 is switched to inter. The image encoding apparatus 100 may generate a prediction block for an input block of an input image and then encode a difference between the input block and the prediction block.

In the intra mode, the intra predictor 120 may generate a prediction block by performing spatial prediction using pixel values of blocks that are already encoded around the current block.

In the inter mode, the motion predictor 111 may obtain a motion vector by searching for a region that best matches an input block in the reference image stored in the reference image buffer 190 during the motion prediction process. The motion compensator 112 may generate a prediction block by performing motion compensation using the motion vector and the reference image stored in the reference image buffer 190.

The subtractor 125 may generate a residual block by the difference between the input block and the generated prediction block. The transform unit 130 may output a transform coefficient by performing transform on the residual block. The quantization unit 140 may output the quantized coefficient by quantizing the input transform coefficient according to the quantization parameter.

The entropy encoding unit 150 entropy encodes a symbol according to a probability distribution based on values calculated by the quantization unit 140 or encoding parameter values calculated in the encoding process, thereby generating a bit stream. You can print The entropy encoding method is a method of receiving a symbol having various values and expressing it in a decodable column while removing statistical redundancy.

Here, the symbol means a syntax element, a coding parameter, a residual signal value, or the like that is to be encoded / decoded. The encoding parameter is a parameter necessary for encoding and decoding, and may include information that may be inferred in the encoding or decoding process as well as information encoded by the encoding apparatus and transmitted to the decoding apparatus, such as syntax elements. This means the information you need to do. Coding parameters may be, for example, intra / inter prediction modes, moving / motion vectors, reference picture indexes, coding block patterns, presence or absence of residual signals, transform coefficients, quantized transform coefficients, quantization parameters, block sizes, block partitioning information, or the like. May include statistics. In addition, the residual signal may mean a difference between the original signal and the prediction signal, and a signal in which the difference between the original signal and the prediction signal is transformed or a signal in which the difference between the original signal and the prediction signal is converted and quantized It may mean. The residual signal may be referred to as a residual block in block units.

When entropy encoding is applied, a small number of bits are allocated to a symbol having a high probability of occurrence and a large number of bits are allocated to a symbol having a low probability of occurrence, whereby the size of the bit string for the symbols to be encoded is increased. Can be reduced. Therefore, compression performance of image encoding may be increased through entropy encoding.

For entropy coding, coding methods such as exponential golomb, context-adaptive variable length coding (CAVLC), and context-adaptive binary arithmetic coding (CABAC) may be used. For example, the entropy encoder 150 may store a table for performing entropy encoding, such as a variable length coding (VLC) table, and the entropy encoder 150 may store the stored variable length encoding. Entropy encoding may be performed using the (VLC) table. In addition, the entropy encoder 150 derives a binarization method of a target symbol and a probability model of a target symbol / bin, and then performs entropy encoding using the derived binarization method or a probability model. You may.

The quantized coefficients may be inversely quantized by the inverse quantizer 160 and inversely transformed by the inverse transformer 170. The inverse quantized and inverse transformed coefficients are added to the prediction block through the adder 175 and a reconstruction block can be generated.

The reconstruction block passes through the filter unit 180, and the filter unit 180 applies at least one or more of a deblocking filter, a sample adaptive offset (SAO), and an adaptive loop filter (ALF) to the reconstruction block or the reconstruction picture. can do. The reconstructed block that has passed through the filter unit 180 may be stored in the reference image buffer 190.

2 is a block diagram illustrating a configuration of an image decoding apparatus according to an embodiment. As described above with reference to FIG. 1, a scalable video encoding / decoding method or apparatus may be implemented by extension of a general video encoding / decoding method or apparatus that does not provide scalability, and the block diagram of FIG. 2 is scalable video decoding. An embodiment of an image decoding apparatus that may be the basis of an apparatus is shown.

2, the image decoding apparatus 200 may include an entropy decoder 210, an inverse quantizer 220, an inverse transformer 230, an intra predictor 240, a motion compensator 250, and a filter. 260 and a reference picture buffer 270.

The image decoding apparatus 200 may receive a bitstream output from the encoding apparatus, perform decoding in an intra mode or an inter mode, and output a reconstructed image, that is, a reconstructed image. In the intra mode, the switch may be switched to intra, and in the inter mode, the switch may be switched to inter. The image decoding apparatus 200 may generate a reconstructed block, that is, a reconstructed block by obtaining a residual block reconstructed from the received bitstream, generating a prediction block, and adding the reconstructed residual block and the prediction block.

The entropy decoder 210 may entropy decode the input bitstream according to a probability distribution to generate symbols including symbols in the form of quantized coefficients. The entropy decoding method is a method of generating each symbol by receiving a binary string. The entropy decoding method is similar to the entropy coding method described above.

The quantized coefficients are inversely quantized by the inverse quantizer 220 and inversely transformed by the inverse transformer 230, and as a result of the inverse quantization / inverse transformation of the quantized coefficients, a reconstructed residual block may be generated.

In the intra mode, the intra predictor 240 may generate a predictive block by performing spatial prediction using pixel values of an already encoded block around the current block. In the inter mode, the motion compensator 250 may generate a prediction block by performing motion compensation using the motion vector and the reference image stored in the reference image buffer 270.

The reconstructed residual block and the prediction block are added through the adder 255, and the added block passes through the filter unit 260. The filter unit 260 may apply at least one or more of the deblocking filter, SAO, and ALF to the reconstructed block or the reconstructed picture. The filter unit 260 outputs a reconstructed image, that is, a reconstructed image. The reconstructed picture may be stored in the reference picture buffer 270 to be used for inter prediction.

The entropy decoder 210, the inverse quantizer 220, the inverse transformer 230, the intra predictor 240, the motion compensator 250, and the filter 260 included in the image decoding apparatus 200. And components directly related to the decoding of an image in the reference image buffer 270, for example, an entropy decoder 210, an inverse quantizer 220, an inverse transformer 230, an intra predictor 240, and motion compensation. The unit 250, the filter unit 260, and the like may be distinguished from other components and expressed as a decoder or a decoder.

Also, the image decoding apparatus 200 may further include a parsing unit (not shown) which parses information related to an encoded image included in a bitstream. The parser may include the entropy decoder 210 or may be included in the entropy decoder 210. Such a parser may also be implemented as one component of the decoder.

3 is a conceptual diagram schematically illustrating an embodiment of a scalable video coding structure using multiple layers to which the present invention can be applied. In FIG. 3, a group of pictures (GOP) represents a picture group, that is, a group of pictures.

In order to transmit image data, a transmission medium is required, and its performance varies depending on the transmission medium according to various network environments. A scalable video coding method may be provided for application to such various transmission media or network environments.

The scalable video coding method is a coding method that improves encoding / decoding performance by removing inter-layer redundancy by using texture information, motion information, and residual signals between layers. The scalable video coding method may provide various scalability in terms of spatial, temporal, and image quality according to ambient conditions such as a transmission bit rate, a transmission error rate, and a system resource.

Scalable video coding may be performed using multiple layers structure to provide a bitstream applicable to various network situations. For example, the scalable video coding structure may include a base layer that compresses and processes image data by using a general image encoding method, and compresses the image data by using the encoding information of the base layer and a general image encoding method together. May include an enhancement layer for processing.

In this case, a layer is an image and a bit divided based on spatial (eg, image size), temporal (eg, coding order, image output order, frame rate), image quality, complexity, and the like. Means a set of bitstreams. In addition, the base layer may mean a lower layer, a reference layer or a base layer, and the enhancement layer may mean an upper layer and an enhancement layer. In addition, the plurality of layers may have a dependency between each other.

Referring to FIG. 3, for example, the base layer may be defined as a standard definition (SD), a frame rate of 15 Hz, and a 1 Mbps bit rate, and the first enhancement layer may be a high definition (HD), a frame rate of 30 Hz, and a 3.9 Mbps bit rate. The second enhancement layer may be defined as 4K-UHD (ultra high definition), a frame rate of 60 Hz, and a bit rate of 27.2 Mbps. The format, frame rate, bit rate, etc. are exemplary and may be determined differently as necessary. In addition, the number of hierarchies used is not limited to this embodiment and may be determined differently according to a situation.

For example, if the transmission bandwidth is 4 Mbps, the frame rate of the first enhancement layer HD may be reduced and transmitted at 15 Hz or less. The scalable video coding method can provide temporal, spatial and image quality scalability by the method described above in the embodiment of FIG. 3.

In the case of encoding and decoding video supporting a plurality of layers in a bitstream, that is, scalable coding, since there is a strong correlation between the plurality of layers, the prediction is performed by using the correlation. Duplicate elements can be removed and the encoding performance of the image can be improved. Performing prediction of the current layer to be predicted using information of another layer is referred to as inter-layer prediction in the following. Scalable video coding has the same meaning as scalable video coding from a coding point of view and scalable video decoding from a decoding point of view.

At least one of a resolution, a frame rate, and a color format may be different from each other, and upsampling or downsampling of a layer may be performed to adjust resolution when inter-layer prediction is performed.

The following points may be considered to describe arbitrary approaches in scalable video coding / decoding (SVC).

The bitstream may support at least one scalability, for example, spatial, image quality, and view scalability, and thus, a video having at least one or more hierarchical structures may be encoded / decoded to allow random access.

The number of layers may be one or more, and the lowest layer may be referred to as a base layer. Hereinafter, a case where the number of layers is three will be described as an example. Of course, the present invention can be applied without being limited to the number of layers.

The upper layer and the lower layer may be encoded / decoded in a single loop or multiple loops.

When a random access point of the bitstream is generated in the encoding apparatus, the decoding apparatus may decode the bitstream from the random access point generated in the encoding apparatus.

The base layer included in an access unit (AU) at random access time is encoded as an intra random access point (IRAP) picture, and upper layers are non-IRAP picture (hereinafter referred to as non-IRAP picture) or IRAP pictures. Can be encoded by. An access unit refers to a set of NAL units or pictures that can be displayed at the same time.

On the other hand, when all pictures of a layer corresponding to a random access time point are encoded in a random access manner, the bitstream can be decoded from this time point. In other words, when a picture that cannot be randomly accessed is included among layers corresponding to a randomly accessible time, a problem may occur that the bitstream cannot be decoded from that time.

The present invention proposes a method for enabling decoding of a bitstream from a corresponding point of time even when a picture of a layer corresponding to a random access point includes a picture that is not accessible randomly.

4 is a diagram for describing a method of gradually decoding a bitstream according to the present invention.

As shown, there are three layers (layer 0, layer 1, layer 2), and each layer may include an IRAP picture and a non-IRAP picture.

The picture of the first layer (layer 0) among the pictures included in the AU A is an IRAP picture, but the pictures of the second layer (layer 1) and the third layer (layer 2) are non-IRAP pictures. Meanwhile, the picture of the second layer (layer 1) among the pictures included in the AU B is an IRAP picture, but the pictures of the first layer (layer 0) and the third layer (layer 2) are non-IRAP pictures. The picture of the third layer (layer 2) of the pictures included in the AU C is an IRAP picture, but the pictures of the first layer (layer 0) and the second layer (layer 1) are non-IRAP pictures.

In the case of the present invention, as shown in FIG. 4, the bitstream may be encoded / decoded so as to be displayed gradually from the lower layer normally decoded to the final highest layer.

5 to 8 illustrate a bitstream structure including a randomly accessible view point according to an embodiment of the present invention.

In the case of FIG. 5, one IRAP picture is included in the AU as shown in FIG. 4, and the IRAP pictures are sequentially included in order from the lowest lower layer to the higher layer. In the bitstream of FIG. 5, a first layer (layer 0) is decoded from AU A, a first layer (layer 0) and a second layer (layer 1) are decoded from AU B, and all layers from AU C. (layer 0, layer 1, layer 2) may be decoded.

In the case of FIG. 6, the pictures of the first layer (layer 0) and the second layer (layer 1) of the pictures included in the AU A are IRAP pictures, and in the case of the next AU B, the pictures of the second layer (layer 1) Only an IRAP picture.

In the case of the bitstream of FIG. 6, the first layer (layer 0) and the second layer (layer 1) are decoded from AU A, and from AU C to the third layer (layer 2), that is, all layers (layer 0, layer 1, layer 2) may be decoded.

In the case of FIG. 7, the picture of the first layer (layer 0) among the pictures included in the AU A is an IRAP picture, and the pictures of the second layer (layer 1) and the third layer (layer 2) are non-IRAP pictures. . Meanwhile, pictures of the first layer (layer 0) and the second layer (layer 1) of the pictures included in the AU B are IRAP pictures, and the second layer (layer 1) and the third of the pictures included in the AU C are included. The picture of the layer (layer 2) is an IRAP picture.

In the case of FIG. 7, the first layer (layer 0) is decoded from AU A, the first layer (layer 0) and the second layer (layer 1) are decoded from AU B, as shown in FIG. Layers (layer 0, layer 1, layer 2) may be decoded.

In the case of FIG. 8, only pictures of a first layer (layer 0) among pictures included in AU A are IRAP pictures, and pictures of a second layer (layer 1) and a third layer (layer 2) are non-IRAP pictures. to be. Meanwhile, the pictures of the first layer (layer 0) and the third layer (layer 2) of the pictures included in the AU B are IRAP pictures, and only the pictures of the second layer (layer 1) of the pictures included in the AU C are included. This is an IRAP picture. In the AU D, only pictures of the third layer (layer 2) are IRAP pictures.

In the case of FIG. 8, the first layer (layer 0) is decoded from AU A, and in AU B, the second layer (layer 1) is a picture because the picture of the second layer (layer 1) is a non-IRAP picture and is not an IRAP picture. Cannot be decrypted. In this case, the pictures of the third layer (layer 2) referring to the second layer (layer 1) may not be normally output. Accordingly, the first layer (layer 0) and the second layer (layer1) can be decoded from AU C, and then all layers (layer 0) from AU D including the IRAP picture in the second layer (layer 1). , layer 1, layer 2) may be decoded.

The present invention provides an encoding and decoding method capable of random access from AU A in a bitstream having the structure of FIGS. 5 to 8. However, the encoding and decoding method of the present invention is not limited to the bitstream structure of FIGS. 5 to 8.

When decoding the bitstream from the random access point, the encoding / decoding process from the corresponding AU is described below when the base layer is an IRAP picture and the AU in which the upper layer is present is the first AU of the bitstream.

According to the present invention, a method of decoding a bitstream from a randomly accessible point of time receives a bitstream up to nth layer, decodes nth layer, and then decodes the layer up to (n + k) th layer (where k> 0). The same may be applied to the case of starting input reception, that is, in case of layer-switching.

When the layer-wise startup is started from the randomly accessible point of view, the structure of the bitstream may have a shorter IRAP picture period in which the nth layer is (0 <= n <= 62) than the n + 1th layer.

9 is a control flowchart illustrating a method of decoding an image according to an embodiment of the present invention. 9 may be equally applied to an image encoding method as well as an image decoding method.

First, the apparatus for decoding an image may set parameters necessary for decoding (S910).

When decoding a bitstream from a random access point, parameters necessary for decoding may be initialized or reset in the following order. The order of (4) and (5) does not change. Specifically, the initialization process for (5) should be performed after (3) and (4), and the initialization process of (5) may be performed only when NoRaslOutputFlag is '1' in (3) or (4). have.

(1) When the base layer included in the AU at the randomly accessible time point is an IRAP picture, that is, an instantaneous decoding refresh (IDR) picture, a broken link access (BLA) picture, or a clean random access (CRA) picture, the random access time point A flag indicating that all pictures included in the AU of are the first pictures of each layer included in the bitstream, for example, a flag such as FirstPicInLayerDecodedFlag may be initialized as follows.

When the current sub / decoding target picture is an IRAP picture and is a picture of a base layer (nuh_layer_id = 0) included in an AU at random access time, the flag value, FirstPicInLayerDecodedFlag, of all possible higher layers can be initialized to '0'. have.

That is, for example, FirstPicInLayerDecodedFlag [i] may be set to 0 for 0 <i <= 63 when the maximum possible number of upper layers is 63, that is, when nuh_layer_id = 63.

(2) When decoding a bitstream whose base layer included in the AU at random access time is an IRAP picture (ie, an IDR picture, a BLA picture, or a CRA picture) from the random access time, the layer included in the bitstream Among these, an initialization flag (for example, named LayerInitialisedFlag) that indicates whether the layer is an IRAP picture and all reference layers in that layer are normally initialized so that the decoded picture of that layer can be used as the output of the decoder. It can be set as That is, the initialization flag indicates whether the target picture to be decoded can be normally decoded and output.

If the current encoding / decoding target picture is an IRAP picture and is a picture of the base layer (nuh_layer_id = 0) included in the AU at random access time, LayerInitialisedFlag [0] is set to 1, and the remaining layers (1 <= i < For Layer 63), LayerInitialisedFlag [i] may be set to 0.

After the initialization flag is set to 0 or 1 for an individual layer at the start of bitstream decoding, the value can be reset according to whether the flag variable and the reference layer referenced by the layer are normally decoded as described below.

(3) When the current encoding / decoding target picture is an IDR picture, a BLA picture or an IRAP picture, and the first picture of the corresponding layer (nuh_layer_id is the same layer as the current encoding / decoding target picture) in the corresponding bitstream (even if it is a CRA picture). NoRaslOutputFlag can be set to '1'. NoRaslOutputFlag is a flag variable indicating whether the corresponding IRAP picture is used as a random access point.

(4) The current encoding or decoding target picture belonging to the AU decoded after the random access point in decoding order is an IRAP (IDR, BLA or CRA) picture, nuh_layer_id = n, and LayerInitialisedFlag [n] is 0, and the current encoding and decoding is performed. All lower reference layers of the layer containing the target picture are correctly initialized (i.e., LayerInitialisedFlag [RefLayerId [n] [j]] = 1, where RefLayerId [n] [j] is the nth higher layer (nuh_layer_id = n). In the case of the nuh_layer_ids of the j th reference layer of the current decoding / decoding target picture), NoRaslOutputFlag may be set to '1'.

That is, if the decoding target picture is an IRAP picture, the initialization flag set in the layer to which the decoding target picture belongs is 0, and the initialization flag for all reference layers of the layer to which the decoding target picture belongs is 1, the flag variable is set to 1.

(5) The current encoded and decoded picture is the nth upper layer (nuh_layer_id = n), the IRAP picture, the NoRaslOutputFlag is '1', the picture is not a picture of the base layer (nuh_layer_id = 0), and the LayerInitialisedFlag [n of the current encoded and decoded picture. ] Is 0, if all the lower reference layers of the layer containing the current encoding and decoding target picture are normally initialized (that is, LayerInitialisedFlag [RefLayerId [n] [j] is 1, where RefLayerId [n] [j] is 1). Denotes nuh_layer_ids of the j-th reference layer of the current sub / decoding target picture, which is the nth upper layer (nuh_layer_id = n). LayerInitialisedFlag [n] may be set to '1'.

That is, if the decoding target picture is an IRAP picture, the flag variable is 1, the initialization flag set for the decoding target picture is 0, and the initialization flags for all the reference layers of the layer to which the decoding target picture belongs are 1, initialization for the target layer. The flag is reset from 0 to 1.

The decoding apparatus calculates a POC, which is an identifier of a picture to be currently encoded / decoded, so that a value increases according to the output order (S920).

The Picture Order Counter (POC) is an identifier for identifying pictures in a layer having the same nuh_layer_id in a coded video stream. The value may increase as the output order from the DPB becomes late. have. That is, the POC is a display order in which pictures may be output from the DPB and displayed, and the POC of the IDR picture may have a value of '0'.

All pictures in the same AU may have the same POC value.

If the IRAP picture and the non-IRAP picture do not exist together in the same AU, or only the IRAP pictures exist and the NAL unit types of the IRAP pictures are the same, the POC value may be calculated by the following conventional method.

The POC value consists of POC_MSB (most significant bit) and POC_LSB (least significant bit), and the total POC can be calculated as the sum of the MSB and LSB (POC = POC_MSB + POC_LSB). In this case, the POC_LSB value may be signaled in the slice header of the picture, and the MaxPOCLSB value indicating the maximum LSB may be signaled in the sequence parameter set.

For non-IRAP pictures, POC_MSB is the POC_MSB (hereinafter referred to as prevPOCMSB) and POC_LSB (hereinafter referred to as prevPOCLSB) of the picture closest to the current picture among temporal_id '0' indicating an identifier of a temporal sublayer previously encoded / decoded. And POC_LSB of the picture to be currently encoded / decoded.

The POC value of an IDR picture can always be assumed to be '0', if the CRA picture is the first picture of the bitstream or for a BLA picture, the POC_MSB value of the picture is assumed to be '0' and the POC_LSB value is defined in the slice header. May be signaled. If the CRA picture is not the first picture of the bitstream, the POC value may be calculated in the same way as the non-IRAP picture.

In the same AU, when the IRAP picture and the non-IRAP picture exist at the same time or only the IRAP picture exists but the NAL unit types of the IRAP pictures are two or more, the POC value may be the same. To this end, flag information such as poc_reset_flag may be signaled in the slice header. When the poc_reset_flag value is '1', the decoding apparatus may set POC values of all pictures in the AU including the slice to '0'. In this case, the decoding apparatus calculates an original POC value (POC 1) calculated by a conventional method of a current encoding / decoding target picture, and POC values of reference layers existing in the decoded picture buffer of the corresponding layer including the picture. It decreases by 1 and sets the POC value of the current target picture to '0'.

Hereinafter, the POC calculation of the picture will be described in detail in two cases.

The first case

If a bitstream including previously encoded AUs is decoded because the corresponding AU is not switched, that is, is not used as a random access time point, decoding of pictures included in the corresponding AU may be performed in the following order.

(a) The initial POC value of the target picture to be currently encoded / decoded may be set as follows.

If the picture is an IDR picture, the POC value may be set to '0'.

When the picture is a BLA picture or a CRA picture as the first picture of the layer of the bitstream, the POC_MSB value is 0 and the POC value may be set to the POC_LSB value signaled in the slice header.

If the picture is a CRA picture or a non-IRAP picture, the general POC configuration method using the POC_LSB value signaled in the slice header (as described above, the current picture among previously encoded / decoded temporal_id '0') The POC value ('POC1') may be set according to POC_MSB (named prevPOCMSB) and POC_LSB (named prevPOCLSB) and POC_LSB value of a picture to be currently encoded / decoded.

(b) With respect to a picture including a slice having a poc_reset_flag of '1', when there are pictures in a DPB, POC values of all pictures in a DPB may be reduced by a value of 'POC1'.

(c) The POC value of the picture including the slice having poc_reset_flag of '1' may be set to '0'.

The second case

When the AU is switched and used as a random access point, that is, decoded as the first AU of the bitstream. For example, the picture of the base layer (layer 0) is an IRAP picture and is the first picture of the coded bitstream. In the case of a BLA picture or a BLA picture, decoding of pictures included in a corresponding AU may be performed in the following order.

(a) The initial POC value of the target picture to be currently encoded / decoded may be set as follows.

If the picture is an IDR picture, the POC value may be set to '0'.

If the picture is a BLA picture or the first picture of the corresponding layer of the bitstream and is a CRA picture, the POC_MSB value is 0 and the POC value may be set to the POC_LSB value signaled in the slice header.

If the picture is a non-IRAP picture (for example, nuh_layer_id = i of the current layer and FirstPicInLayerDecodedFlag [i] = 0), the POC value ('POC1') can be set using one of the following methods: Can be.

(a-1) The POC value 'POC1' may be set according to the conventional POC setting method described above using the POC_LSB value signaled in the slice header. In this case, as the current AU is used as a random access time point, since there are no pictures having the previously encoded / decoded temporal_id of '0', both prevPOCMSB and prevPOCLSB values may be set to '0'.

(a-2) When a BLA or CRA picture exists in the base layer of the same AU, the POC_MSB value of the current decoding target picture may be set to '0'. In this case, the POC value ('POC1') of the picture to be currently decoded is set to the POC_LSB value signaled in the slice header of the current picture.

(a-3) The POC value of the current decoding target picture may not be calculated.

(a-4) When an IDR picture exists in the base layer of the same AU, the POC value of the current decoding target picture may be set to '0' without being calculated.

(b) When the POC value of the current decoding target picture is calculated, for a picture including a slice whose poc_reset_flag is '1', when there are pictures in the DPB, the POC values of all pictures in the DPB are reduced by 'POC1' value. You can.

(c) The POC value of the picture including the slice having poc_reset_flag of '1' may be set to '0'.

Next, the apparatus for decoding an image configures a reference picture set and performs reference picture marking for inter prediction of the current sub / decoding target picture (S930).

When poc_reset_flag for initializing a POC is '0', the POC value or the POC_LSB value of the slice reference pictures of the picture may be calculated as follows.

(1) For short-term reference pictures, POC values of short-term reference pictures are calculated using a delta_POC value indicating each short-term reference picture signaled in the corresponding slice header and a 'POC1' value, which is a POC value of the current picture. do.

In this case, the delta_POC value may be a difference between the POC of the current picture and the i-th short-term reference picture or a difference between the (i + 1) th short-term reference picture and the i-th short-term reference picture.

(2) In the case of long-term reference pictures, a long-term reference picture is referred to using a POC_LSB value for each long-term reference picture, a value for calculating a POC_MSB value (delta_poc_msb_cycle_lt), and a 'POC1' value, which is a POC value of the current picture. The POC_LSB or POC value of the pictures is calculated. delta_poc_msb_cycle_lt may be signaled in the corresponding slice header.

Basically, only the POC_LSB is signaled for the long-term reference picture, and only the POC_LSB value signaled identifies the long-term POC. However, when there is a reference picture having the same POC_LSB value as the POC_LSB of the corresponding long-term reference picture among the plurality of reference pictures, a value (delta_poc_msb_cycle_lt) for calculating the POC_MSB value is additionally signaled, thereby identifying the POC of each reference picture. Do it.

Meanwhile, when poc_reset_flag is '1', POC values or POC_LSB values of slice reference pictures of the picture may be calculated as follows.

(1) In the case of short-term reference pictures, POC values of short-term reference pictures are calculated using a delta_POC value indicating each short-term reference picture signaled in the corresponding slice header and a '0' value, which is a POC value of the current picture. do.

In this case, the delta_POC value may be a difference between the POC of the current picture and the i-th short-term reference picture or a difference between the (i + 1) th short-term reference picture and the i-th short-term reference picture.

(2) In the case of long-term reference pictures, a value for calculating a POC_LSB value and a POC_MSB value for each long-term reference picture (delta_poc_msb_cycle_lt), a '0' value that is a POC value of the current picture, and a slice header of the current picture The POC_LSB value or the POC value of the long term reference pictures is calculated using the POC_LSB value signaled at. delta_poc_msb_cycle_lt may be signaled in the slice header of the corresponding long-term reference picture.

Basically, only the POC_LSB is signaled for the long-term reference picture, and only the POC_LSB value signaled identifies the long-term POC. However, when there is a reference picture having the same POC_LSB value as the POC_LSB of the corresponding long-term reference picture among the plurality of reference pictures, a value (delta_poc_msb_cycle_lt) for calculating the POC_MSB value is additionally signaled, thereby identifying the POC of each reference picture. Do it.

As such, when poc_reset_flag is '1', the POC value or POC_LSB value of the reference pictures signaled to the slice header of the picture including the slice having poc_reset_flag '1' matches the POC value of the pictures existing in the DPB. Can be adjusted using the 'POC1' value of the current picture.

When the POC of the reference picture is calculated, a reference picture set may be configured and the shape of the reference picture may be displayed according to the presence or absence of the reference picture in the DPB.

The image decoding apparatus may generate a virtual reference picture for a picture included in the reference picture set but not present in the DPB (S940).

nuh_layer_id = 0 and the current encoded / decoded picture is an IRAP picture and NoRaslOutputFlag = 1, or nuh_layer_id> 0 (in this case, the IRAP picture with FirstPicInLayerDecodedFlag [nuh_layer_id] = 1 and NoRaslOutputFlag = 1 Or, if FirstPicInLayerDecodedFlag [nuh_layer_id] = 0), virtualizes the pictures that are not present in the current decoded picture buffer among the pictures included in the reference picture set of the current encoding / decoding target picture (that is, the reference pictures configured in step S930). Can be created and stored in the decoded picture buffer.

The POC values of the generated virtual pictures have the POC values of the respective reference pictures calculated in step S920. The PicOutputFlag value indicating whether the virtual reference picture is output in the DPB is set to '0', and the virtual reference picture generated thereby is not output.

The generated virtual reference pictures may be represented as short-term reference pictures or long-term reference pictures as content signaled in the reference picture set. Specifically, the short-term reference picture referenced by the current picture and before the current picture in display order, the short-term reference picture referenced by the current picture and displayed in the display order after the current picture, the long-term reference picture referenced by the current picture, and pictures after the current picture. It may be indicated as a short-term reference picture referenced by, a long-term reference picture referenced by pictures after the current picture.

Next, the image decoding apparatus may determine whether to output the current encoding / decoding target picture (S950). PicOutputFlag, which indicates whether to output the decoded picture, can be set in the following order.If the PicOutputFlag value is '1', the decoded picture buffer is exported to the decoder output, and if it is '0', the decoded picture buffer is output to the decoder output. You can not send.

(1) If the current picture is a RASL (random access skipped leading) picture and the NoRaslOutputFlag value of the IRAP picture closest to the current picture among the sub-decoded / decoded IRAP pictures before the current picture is '1', PicOutputFlag is '0'. Can be set to '.

In this case, the RASL picture is a leading picture in which the encoding / decoding order is later than the IRAP picture closest to the current picture among the IRAP pictures decoded / decoded before the current picture, but the display order is first, and before the IRAP picture. A picture decoded / decoded using a sub / decoded picture as a reference picture.

(2) If the nuh_layer_id value of the picture is n and LayerInitialisedFlag [n] = 0 is not satisfied, the PicOutputFlag may be set to '0'.

(3) If the conditions of (1) and (2) above are not satisfied, the PicOutputFlag value may be set by one of the following methods.

a. The PicOutputFlag value may be set to a pic_output_flag value signaled in the slice header.

b. The PicOutputFlag value may be set to a pic_output_flag value signaled in the slice header when the corresponding layer is an output layer, and set to '0' when the corresponding layer is not an output layer.

c. If the layer is not the output layer, and the immediate upper layer of the layer is an IRAP picture and the LayerInitialisedFlag values of the lower reference layers of the upper layer are all '1', PicOutputFlag may be set to zero.

d. The layer is not an output layer, and there is a layer whose immediate upper layer is the IRAP picture and among the lower reference layers of the upper layer, the layerInitialisedFlag value is '0', and the upper layer of the layer is the output layer. If present, PicOutputFlag of the layer may be set to a pic_output_flag value signaled in the slice header. At this time, if there is a layer having a PicOutputFlag value of '1' among the lower layers close to the corresponding layer, the PicOutputFlag value of the corresponding layer may be set to '0'.

e. The layer is not an output layer, and there is no picture corresponding to the output layer within the same AU, and the layer is either a direct reference picture (a picture of a layer directly referenced by the layer) or an indirect reference picture of the output layer picture. A layer required for encoding / decoding a layer directly referenced by the corresponding layer), and a picture that is a direct or indirect reference picture of an output layer picture and a pic_output_flag value signaled in the slice header is '1' In the case of the highest picture (ie, the picture having the highest nuh_layer_id value) among the pictures, the PicOutputFlag value of the picture may be set to '1'. Otherwise, PicOutputFlag value may be set to '0'.

f. The layer is not an output layer, and there is no picture corresponding to the output layer within the same AU, and the layer is either a direct reference picture (a picture of a layer directly referenced by the layer) or an indirect reference picture of the output layer picture. Layer required when encoding / decoding a layer directly referenced by the corresponding layer), the picture is a direct or indirect reference picture of an output layer picture, the LayerInitializedFlag value is '1', and the pic_output_flag value signaled in the slice header is In the case of the highest picture among the decoded pictures that are '1' (ie, the picture having the highest nuh_layer_id value), the PicOutputFlag value of the picture may be set to '1'. Otherwise, PicOutputFlag value may be set to '0'.

In the case of c, d, e, and f described above, the decoding apparatus may control the output of the pictures in the decoded picture buffer so that not only the set PicOutputFlag value but also the same result as described.

When it is determined whether to output the picture, the image decoding apparatus performs motion prediction and motion compensation on the current sub / decoding target image by using the reference picture in the reference picture list (S960).

In this step, motion prediction and motion compensation may be performed on the current sub / decoded target image using a reference picture in the reference picture list using a conventional inter-picture prediction method.

When inter prediction using the reference picture is performed, a parameter required for decoding may be reset (S970). The image decoding apparatus may set FirstPicInLayerDecodedFlag [i] to 1 when FirstPicInLayerDecodedFlag [i] of the layer including the current sub / decoding target picture, for example, a layer where nuh_layer_id = i is 0.

The decoding apparatus may perform the decoding process for steps S910 to S970 for each layer. After the decoding process in the first AU is finished, pictures having a PicOutputFlag of 1 among the layers in the first AU may be output.

For example, if the base layer consists of IRAP pictures from the nth layer, and the output layer is originally included in the base layer to the nth layer (0 <= n), the decoded picture of the layer And decoded pictures of the n th layer if the n + 1 th layer to the top layer are included in the output layer.

Then, when decoding the AU including the (n + 1 <= k) IRAP picture from the n + 1 th layer to the k th layer in decoding the next AUs, from the 0 th to the k th layer within the AU If the layer to be originally output is included in the kth layer from the base layer among the decoded pictures of the decoded pictures, the decoded pictures of the corresponding layer are output, and if the k + 1th layer to the top layer are included in the output layer In this case, a decoded picture of the k-th layer or a picture having PicOutputFlag of 1 can be output.

The decoding apparatus may decode the bitstream by repeatedly performing the above process up to the AU where the picture of the highest layer is decoded.

10 is a diagram for describing a method of setting a decoding parameter according to an embodiment of the present invention.

When the first random access occurs in the bitstream, the decoding apparatus may set the initialization flag to 1 for the base layer and the initialization flag to 0 for the layer higher than the base layer (S1110).

The initialization flag (LayerInitialisedFlag) is used in the bitstream when the base layer included in the AU at the randomly accessible point is decoded from the randomly accessible point as the bitstream whose IRAP picture (ie, IDR picture, BLA picture, or CRA picture) is decoded from the randomly accessible point. Among the layers included, this layer is an IRAP picture, and all reference layers of the layer are normally initialized to indicate whether a decoded picture of the layer can be used as an output of the decoder. The normalization of the reference layers may mean that the picture may be normally decoded and output from the decoder.

The decoding apparatus may set an initialization flag indicating whether a decoded picture of a corresponding layer can be used as an output of the decoder before bitstream decoding, and the current sub / decoding target picture is an IRAP picture and is assigned to the AU at the time of random access. If the picture is in the base layer (nuh_layer_id = 0), the initialization flag LayerInitialisedFlag [0] is set to 1, and the initialization flag LayerInitialisedFlag [i] for the remaining layers (1 <= i <= 63) is initialized to 0. can do.

After setting the initialization flag, the decoding apparatus may set a flag variable (NoRaslOutputFlag) indicating whether the picture is used as a random access point.

The decoding apparatus may set the flag variable to 1 when the target picture is an IDR picture or a BLA picture or an IRAP picture and the first picture of the corresponding layer (nuh_layer_id is the same layer as the current encoding and decoding target picture) in the corresponding bitstream. If the target picture is an IRAP picture, the initialization flag set in the layer to which the target picture belongs is 0, and the initialization flag for all reference layers of the layer to which the target picture belongs is 1, the flag variable may be set to 1 (S1020).

If the target picture is an IRAP picture, and the flag variable for the target picture is set to 1, the decoding apparatus determines whether the initialization flag set for the target picture is 0 and the initialization flag for all reference layers of the layer to which the target picture belongs is 1. If it is determined that the initialization flag for the target picture is 0 and the initialization flag for all reference layers of the layer to which the target picture belongs is 1, the initialization flag for the target layer may be set from 0 to 1 (S1030).

That is, if the condition that the layer to which the target picture belongs is normally decoded is satisfied, the initialization flag set to 0 in step S1010 may be changed to 1.

When the initialization flag is set, decoding of the target picture may be performed as in the remaining steps of FIG. 9, and a picture of a higher layer may be gradually output depending on whether the decoded picture is output.

11 is a control flowchart illustrating a decoding method of an inter-layer video according to an embodiment of the present invention. A method of finally decoding a bitstream by decoding an image for each access unit and applying the same to a plurality of layers will be described with reference to FIG. 11.

When a random access occurs, the decoding apparatus sets parameters for decoding as shown in steps S910 and 10 of FIG. 9 and decodes pictures included in the first access unit (S1110). The decoding process of the picture may correspond to steps S910 to S970 of FIG. 9, and overlapping description is omitted.

When decoding of the pictures included in the first access unit is completed, the decoding apparatus may determine whether to individually output the pictures included in the first access unit (S1120).

When the decoding apparatus determines whether to individually output the pictures, when the initialization flag value of the target layer to which the decoding target picture belongs is 0, the decoding apparatus may determine that the target picture is not output.

In addition, the decoding apparatus determines that the target layer to which the decoding target picture belongs is not the output layer, and there is no output target picture belonging to the output layer in the access unit to which the target layer belongs, that is, the output target picture is not output. When a layer is used as a reference of an output layer and a target picture is used as a reference picture of the output picture, and the target picture is the highest picture among decoded pictures having flag information indicating whether or not the picture signaled in the slice header is output is 1, It may be determined to output the target picture.

In addition, the decoding apparatus determines that the target layer to which the decoding target picture belongs is not the output layer, and there is no output target picture belonging to the output layer in the access unit to which the target layer belongs, that is, the output target picture is not output. The layer is used as a reference of the output layer, the target picture is used as the reference picture of the output picture, the initialization flag value for the target layer is 1, and the flag information indicating whether the target picture is outputted in the picture signaled in the slice header is 1 In the case of the highest picture among the decoded pictures, the target picture may be determined to be output.

When the output determination process for the first access unit is completed, the decoding apparatus may decode the pictures included in the second access unit, which is the next access unit (S1130), and determine whether to output each of them separately (S1140).

The method of determining whether to output pictures included in the second access unit is the same as the method of determining whether to output pictures included in the first access unit.

The decoding apparatus may output a picture determined to be output in correspondence with an output time point of each picture.

As described above, when random access occurs, the decoding apparatus individually determines whether to output the pictures included in the access unit, and outputs pictures that can be output, and sequentially determines whether to output the pictures of the next access unit, and then decodes normally. Output pictures of a layer that can be output. Through this process, pictures of a higher layer may be gradually decoded and output.

As described above, according to the present invention, an intra-random access point (IRAP) picture and a non-intra-random random access point picture (IRAP) picture or only an IRAP picture exist in an access unit (AU) at a random access point. Provided are methods for decoding a bitstream from a corresponding time point when two or more NAL unit types are provided, and an apparatus using the same.

In the above-described embodiment, the methods are described based on a flowchart as a series of steps or blocks, but the present invention is not limited to the order of steps, and any steps may occur in a different order or at the same time than the other steps described above. have. Also, one of ordinary skill in the art appreciates that the steps shown in the flowcharts are not exclusive, that other steps may be included, or that one or more steps in the flowcharts may be deleted without affecting the scope of the present invention. I can understand.

The above-described embodiments include examples of various aspects. Although not all possible combinations may be described to represent the various aspects, one of ordinary skill in the art will recognize that other combinations are possible. Accordingly, the invention is intended to embrace all other replacements, modifications and variations that fall within the scope of the following claims.

Claims (20)

In the decoding method of a bitstream including a plurality of layers, When a random access occurs, setting a parameter for decoding the bitstream from a time point when the random access occurs; Performing decoding of a decoding target picture, Setting the parameter, Setting an initialization flag indicating whether a target picture to be decoded can be normally decoded and output when the random access occurs; Setting a flag variable (NoRaslOutputFlag) indicating whether the decoding target picture is used as a random access point; If the decoding target picture is an IRAP picture, the flag variable is 1, the initialization flag for the decoding target picture is 0, and the initialization flag for all the reference layers of the target layer is 1, for the target layer And resetting the initialization flag to one. The method of claim 1, Setting the initialization flag, And a value of 1 for a base layer of the access unit in which the random access has occurred, and a value of 0 for a layer higher than the base layer. The method of claim 2, Setting the flag variable (NoRaslOutputFlag), And if the decoding target picture is an IDR picture or a BLA picture or an IRAP picture and is the first picture of a target layer of the corresponding bitstream, the flag variable is set to 1. The method of claim 2, Setting the flag variable (NoRaslOutputFlag), The flag variable is set to 1 when the target picture is an IRAP picture, an initialization flag set in a layer to which the target picture belongs is 0, and an initialization flag for all reference layers of the layer to which the target picture belongs is 1. Decryption method. The method of claim 1, Calculating a POC that is an identifier of the decoding target picture; Constructing a reference picture set and displaying a reference picture type for inter prediction of the picture to be decoded; Determining whether to output the decoding target picture based on the initialization flag; And performing motion prediction and motion compensation on the decoding target picture by using a reference picture in the reference picture list generated based on the reference picture set. The method of claim 5, Determining whether to output the decoding target picture, And when the decoding target picture is an IRAP picture and the initialization flag value of the target layer is 0, determining that the decoding target picture is not output. The method of claim 5, Determining whether to output the decoding target picture, It is determined that the target layer is not an output layer to be output, and that an output target picture belonging to the output layer is not output in an access unit to which the target layer belongs, and the target layer is used as a reference of the output layer. When the decoded picture is used as a reference picture of the output target picture and the decoded picture is the highest picture among decoded pictures having flag information indicating whether or not the picture signaled in the slice header is output is 1, the decoded picture is decoded. The decoding method characterized in that it is determined to output. The method of claim 5, Determining whether to output the decoding target picture, It is determined that the target layer is not an output layer to be output, and that an output target picture belonging to the output layer is not output in an access unit to which the target layer belongs, and the target layer is used as a reference of the output layer. The decoded picture is used as a reference picture of the output target picture, the initialization flag value for the target layer is 1, and the decoded flag information indicating whether the decoding target picture is outputted from the picture signaled in the slice header is 1 And in the case of the highest picture among the pictures, determining to output the decoding target picture. According to claim 1, Decoding pictures included in a first access unit corresponding to a time point at which the random access occurs; Determining whether to individually output pictures included in the first access unit; Decoding pictures included in a second access unit after the first access unit; And determining whether to individually output pictures included in a second access unit next to the first access unit. The method of claim 9, A first access unit picture output step of outputting a picture determined to be output from among pictures included in the first access unit, The outputting of the first access unit picture may include: When the bitstream includes a base layer to a top layer, and is an intra random access point (IRAP) picture from the base layer to an nth (0≤n) layer, and the output layer belongs to the base layer to the nth layer Output an output picture of the output layer, And if the output layer is included in the highest layer from the n + 1 th layer, the decoded picture of the n th layer is output. A second access unit picture output step of outputting a picture determined to be output among the pictures included in the second access unit; The outputting of the second access unit picture may include: An (n + 1 ≦ k) IRAP picture is included in the n + 1 th layer to the k th layer included in the second access unit, If the output layer is included from the base layer to the k-th layer, output pictures of the output layer, And outputting a decoded picture of a k-th layer or a picture determined to be output if the output layer is included in the highest layer from a k + 1 th layer. The method of claim 5, The calculating of the POC may include setting the POC of the decoding target picture to 0 when the picture of the base layer of the same access unit is an IDR picture, and when the picture of the base layer is the BLA picture or the first CRA picture of the bitstream. And the MSB of the decoding target picture is set to zero. In the bitstream decoding apparatus including a plurality of layers, If a random access is generated, a prediction unit for setting a parameter for decoding the bitstream from the time when the random access is generated, and decoding the decoding target picture, When the random access occurs, the prediction unit sets an initialization flag indicating whether a target picture to be decoded can be decoded and output normally, and a flag variable indicating whether the decoded picture is used as a random access point ( NoRaslOutputFlag), the decoding target picture is an IRAP picture, the flag variable is 1, the initialization flag for the decoding target picture is 0, and the initialization flag for all reference layers of the target layer is 1; And resetting the initialization flag for the target layer to one. The method of claim 13, And the prediction unit is set to 1 for a base layer of the access unit in which the random access has occurred, and is set to 0 for a layer higher than the base layer. The method of claim 14, And the predictor sets the flag variable to 1 when the decoding target picture is an IDR picture or a BLA picture or an IRAP picture and is the first picture of the target layer of the corresponding bitstream. The method of claim 14, The prediction unit sets the flag variable to 1 when the target picture is an IRAP picture, the initialization flag set in the layer to which the target picture belongs is 0, and the initialization flags for all reference layers of the layer to which the target picture belongs is 1. Decoding apparatus, characterized in that. The method of claim 13, The prediction unit calculates a POC which is an identifier of the decoding target picture, configures a reference picture set for displaying inter-screen prediction of the decoding target picture, displays a reference picture type, and outputs the decoding target picture based on the initialization flag. And determining, and performing motion prediction and motion compensation on the decoding target picture by using a reference picture in the reference picture list generated based on the reference picture set. The method of claim 17, And if the decoding target picture is an IRAP picture and the initialization flag value of the target layer is 0, the prediction unit determines that the decoding target picture is not output. The method of claim 17, The prediction unit determines that an output target picture belonging to the output layer is not output in an access unit to which the target layer belongs, rather than an output layer to which the target layer is an output target, and the target layer refers to the output layer. When the decoding target picture is used as a reference picture of the output target picture and the decoding target picture is the highest picture among decoded pictures having flag information indicating whether or not the picture signaled in the slice header is output is 1, And determining to output the decoding target picture. The method of claim 17, The prediction unit determines that an output target picture belonging to the output layer is not output in an access unit to which the target layer belongs, rather than an output layer to which the target layer is an output target, and the target layer refers to the output layer. The decoding target picture is used as a reference picture of the output target picture, the initialization flag value for the target layer is 1, and the flag information indicating whether to output the picture signaled in the slice header is 1 is the decoding target picture. And the highest picture among the decoded pictures is determined to output the decoding target picture.

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