KR101685556B1 - Method and apparatus for image encoding/decoding - Google Patents

Abstract

A video encoding / decoding method and apparatus supporting a plurality of layers is disclosed. The video decoding method includes analyzing a layer dependency of a current layer based on a VPS (Video Parameter Set) extension, analyzing layer dependency of a current slice based on information coded on a slice-by-slice basis, Constructing a reference picture list for the current layer based on an analysis of at least one of a layer dependency and a layer dependency on the current slice.

Description

METHOD AND APPARATUS FOR IMAGE ENCODING / DECODING [0002]

The present invention relates to image coding and decoding, and more particularly, to image coding and decoding based on video coding.

Recently, as a multimedia environment has been established, a variety of terminals and networks have been used, and user demands have been diversified accordingly.

For example, as the performance and computing capability of a terminal are diversified, the performance to be supported varies depending on a device. In addition, the network in which the information is transmitted is also diversified not only by the external structure such as a wired / wireless network, but also by the type of information to be transmitted, information amount and speed, and the like. The user selects the terminal and the network to be used according to the desired function, and the spectrum of the terminal and the network provided by the enterprise to the user is also diversified.

In this regard, recently, broadcasting having a high definition (HD) resolution has been expanded not only in the domestic market but also in the world, so that many users are accustomed to high resolution and high quality video. Accordingly, many video service related organizations are making efforts to develop next generation video equipment.

In addition, with the increasing interest in UHD (Ultra High Definition), which has a resolution more than four times that of HDTV in addition to HDTV, there is a growing demand for a technology for compressing and processing higher resolution and higher quality images.

An inter prediction technique for predicting a pixel value included in a current picture from a previous and / or a temporal picture in order to compress and process an image, an inter prediction technique for predicting a pixel value included in a current picture, An entropy encoding technique for assigning a short code to a symbol having a high appearance frequency and a long code to a symbol having a low appearance frequency can be used.

As described above, considering the requirements of each terminal, network, and diversified user with different functions to be supported, the quality, size, and frame of a supported image need to be diversified accordingly.

As described above, scalability that supports various image quality, resolution, size, frame rate, etc. due to heterogeneous communication networks and various functions and types of terminals has become an important function of a video format.

Therefore, it is necessary to provide a scalability function to enable efficient video encoding and decoding in terms of time, space, and image quality in order to provide a service required by a user in various environments based on a highly efficient video encoding method.

The present invention provides an image encoding / decoding method and apparatus capable of improving image encoding / decoding efficiency.

The present invention provides a method and apparatus for performing hierarchical switching in scalable video coding capable of improving coding / decoding efficiency.

The present invention provides a method and apparatus for encoding / decoding scalable reference picture set information capable of improving image coding / decoding efficiency.

The present invention provides a reference image management method and apparatus in scalable video coding capable of improving image encoding / decoding efficiency.

According to an aspect of the present invention, an image decoding method supporting a plurality of layers is provided. The video decoding method includes analyzing a layer dependency of a current layer based on a VPS (Video Parameter Set) extension, analyzing layer dependency of a current slice based on information coded on a slice-by-slice basis, Constructing a reference picture list for the current layer based on an analysis of at least one of a layer dependency and a layer dependency on the current slice.

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According to another aspect of the present invention, an image encoding method supporting a plurality of layers is provided. The method includes the steps of determining a layer dependency of a current layer and encoding the layer dependency of a current layer using a VPS (Video Parameter Set) extension, determining a layer dependency of a current slice and encoding the slice according to a slice, And constructing a reference picture list for the current layer based on at least one of the layer dependencies for the current slice.

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According to another aspect of the present invention, there is provided an image decoding apparatus that supports a plurality of layers. The image decoding apparatus includes a decoding unit for analyzing a layer dependence of a current layer based on a VPS (Video Parameter Set) extension, analyzing layer dependency of a current slice based on information encoded for each slice, And a prediction unit configured to construct a reference picture list for the current layer based on an interpretation of at least one of the layer dependency and the layer dependency for the current slice, and to perform prediction based on the reference picture list.

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The present invention can provide a reference image management method in a hierarchical coding scheme capable of providing space, time, image quality, and viewability scalability. When inter-layer prediction including at least one reference layer is performed, a reference image including decoded images of the reference layer can be efficiently managed. In addition, according to the present invention, it is possible to efficiently manage the reference layer and to select the reference layer so as to maximize the coding efficiency even if it is the same layer.

1 is a block diagram illustrating a configuration of an image encoding apparatus according to an embodiment of the present invention.
2 is a block diagram illustrating a configuration of an image decoding apparatus according to an embodiment of the present invention.
3 is a conceptual diagram schematically showing an example of a scalable video coding structure using a plurality of layers to which the present invention can be applied.
4 is a diagram showing a configuration of a reference picture list.
5 is a flowchart schematically showing a method of managing reference pictures in scalable video coding according to an embodiment of the present invention.
FIG. 6 is a diagram for explaining a method of constructing a scalable reference layer set (SRLS) or a layer dependency set according to the present invention.
7 is a diagram for explaining a method of constructing a reference picture list (reference picture list) according to the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In describing the embodiments of the present invention, if the detailed description of related known structures or functions is deemed to obscure the subject matter of the present specification, the description may be omitted.

When an element is referred to herein as being "connected" or "connected" to another element, it may mean directly connected or connected to the other element, Element may be present. In addition, the content of " including " a specific configuration in this specification does not exclude a configuration other than the configuration, and means that additional configurations can be included in the scope of the present invention or the scope of the present invention.

The terms first, second, etc. may be used to describe various configurations, but the configurations are not limited by the term. The terms are used for the purpose of distinguishing one configuration from another. For example, without departing from the scope of the present invention, the first configuration may be referred to as the second configuration, and similarly, the second configuration may be named as the first configuration.

In addition, the constituent elements shown in the embodiments of the present invention are shown independently to represent different characteristic functions, which do not mean that each constituent element is composed of separate hardware or a single software constituent unit. That is, each constituent unit is included in each constituent unit for convenience of explanation, and at least two constituent units of each constituent unit may form one constituent unit or one constituent unit may be divided into a plurality of constituent units to perform a function. The integrated embodiments and the separate embodiments of each component are also included in the scope of the present invention unless they depart from the essence of the present invention.

In addition, some of the components are not essential components to perform essential functions in the present invention, but may be optional components only to improve performance. The present invention can be implemented only with components essential for realizing the essence of the present invention except for the components used for performance improvement, Are 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 of the present invention.

A scalable video encoding / decoding method or apparatus may be implemented by a general image encoding / decoding method or apparatus extension that does not provide scalability, and the block diagram of FIG. 1 shows an embodiment of a video encoding apparatus that can be a basis of a good video encoding apparatus.

1, the image encoding apparatus 100 includes a motion prediction unit 111, a motion compensation unit 112, an intra prediction unit 120, a switch 115, a subtractor 125, a transform unit 130, A quantization unit 140, an entropy encoding unit 150, an inverse quantization unit 160, an inverse transformation unit 170, an adder 175, a filter unit 180, and a reference picture buffer 190.

The image encoding apparatus 100 may encode an input image in an intra mode or an inter mode and output a bit stream. In the intra mode, the switch 115 is switched to the intra mode, and in the inter mode, the switch 115 can be switched to the inter mode. Intra prediction is intra prediction, and inter prediction is inter prediction. The image encoding apparatus 100 may generate a prediction block for an input block of an input image, and then may code a residual between the input block and the prediction block. At this time, the input image may mean an original picture.

In the intra mode, the intraprediction unit 120 may generate a prediction block by performing spatial prediction using the pixel values of the already coded / decoded blocks around the current block.

In the inter mode, the motion predicting unit 111 can obtain a motion vector by searching an area of the reference picture stored in the reference picture buffer 190 that is best matched with the input block. The motion compensation unit 112 may generate a prediction block by performing motion compensation using a motion vector. Here, the motion vector is a two-dimensional vector used for inter prediction, and can represent the offset between the current image to be encoded / decoded and the reference image.

The subtractor 125 may generate a residual block by a difference between the input block and the generated prediction block.

The transforming unit 130 may perform a transform on the residual block to output a transform coefficient. Here, the transform coefficient may mean a coefficient value generated by performing a transform on a residual block and / or a residual signal. Hereinafter, a quantized transform coefficient level generated by applying quantization to a transform coefficient may also be referred to as a transform coefficient.

The quantization unit 140 may quantize the input transform coefficient according to a quantization parameter (or a quantization parameter) to output a quantized coefficient. The quantized coefficients may be referred to as quantized transform coefficient levels. At this time, the quantization unit 140 can quantize the input transform coefficients using the quantization matrix.

The entropy encoding unit 150 may perform entropy encoding based on the values calculated by the quantization unit 140 or the encoding parameter values calculated in the encoding process to output a bitstream. 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, thereby expressing symbols, The size of the column can be reduced. Therefore, the compression performance of the image encoding can be enhanced through the entropy encoding. The entropy encoding unit 150 may use an encoding method such as Exponential-Golomb, Context-Adaptive Variable Length Coding (CAVLC), and Context-Adaptive Binary Arithmetic Coding (CABAC) for entropy encoding.

Since the image encoding apparatus 100 according to the embodiment of FIG. 1 performs inter-prediction encoding, that is, inter-view prediction encoding, the currently encoded image needs to be decoded and stored for use as a reference image. Accordingly, the quantized coefficients are inversely quantized in the inverse quantization unit 160 and inversely transformed in the inverse transformation unit 170. The inverse quantized and inverse transformed coefficients are added to the prediction block through the adder 175 and a reconstructed block is generated.

The restoration block passes through the filter unit 180 and the filter unit 180 applies at least one of a deblocking filter, a sample adaptive offset (SAO), and an adaptive loop filter (ALF) can do. The filter unit 180 may be referred to as an adaptive in-loop filter. The deblocking filter can remove block distortion occurring at the boundary between the blocks. The SAO may add a proper offset value to the pixel value to compensate for coding errors. ALF can perform filtering based on the comparison between the reconstructed image and the original image. The reconstruction block having passed through the filter unit 180 can be stored in the reference picture buffer 190.

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

As described above with reference to FIG. 1, the scalable video encoding / decoding method or apparatus can be implemented by expanding a general image encoding / decoding method or apparatus that does not provide scalability, and the block diagram of FIG. 2 shows a scalable 1 shows an embodiment of an image decoding apparatus which can be a basis of a video decoding apparatus.

2, the image decoding apparatus 200 includes an entropy decoding unit 210, an inverse quantization unit 220, an inverse transform unit 230, an intra prediction unit 240, a motion compensation unit 250, an adder 255 A filter unit 260, and a reference picture buffer 270.

The video decoding apparatus 200 receives the bit stream output from the encoder and decodes the video stream into the intra mode or the inter mode, and outputs the reconstructed video, that is, the reconstructed video. In the intra mode, the switch is switched to the intra mode, and in the inter mode, the switch can be switched to the inter mode.

The image decoding apparatus 200 may obtain a reconstructed residual block from the input bitstream, generate a prediction block, and add the reconstructed residual block and the prediction block to generate a reconstructed block, i.e., a reconstructed block .

The entropy decoding unit 210 may entropy-decode the input bitstream according to a probability distribution to generate symbols including a symbol of a quantized coefficient type.

When the entropy decoding method is applied, a small number of bits are assigned to a symbol having a high probability of occurrence, and a large number of bits are assigned to a symbol having a low probability of occurrence, so that the size of a bit string for each symbol is Can be reduced.

The quantized coefficients are inversely quantized in the inverse quantization unit 220 and inversely transformed in the inverse transformation unit 230. The reconstructed residual block can be generated as a result of inverse quantization / inverse transformation of the quantized coefficients. At this time, the inverse quantization unit 220 can apply the quantization matrix to the quantized coefficients.

In the intra mode, the intraprediction unit 240 may generate a prediction block by performing spatial prediction using the pixel value of the already decoded block around the current block. In the inter mode, the motion compensation unit 250 may generate a prediction block by performing motion compensation using a motion vector and a reference image stored in the reference picture buffer 270. [

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

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

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

A video coding method supporting scalability (hereinafter, referred to as 'scalable coding' or 'scalable video coding') removes redundancy between layers by utilizing texture information, motion information, residual signals, etc. between layers Thereby improving the encoding and decoding performance. The scalable video coding method can be applied to various scalers in terms of spatial, temporal, image quality (or quality, quality), and viewpoint according to the surrounding conditions such as transmission bit rate, transmission error rate, It is possible to provide the capability.

Scalable video coding can 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 for compressing and processing image data using a general image decoding method, and compressing and compressing the image data using the decoding information of the base layer and a general image decoding method. Lt; RTI ID = 0.0 > layer. ≪ / RTI >

Here, the layer may be divided into a plurality of layers based on spatial (e.g., image size), temporal (e.g., decoding order, image output order, frame rate), image quality, complexity, Means a set of separated video and bitstreams.

The base layer may be referred to as a base layer or may be referred to as a lower layer. The enhancement layer may be referred to as an enhancement layer or a higher layer. In this case, the lower layer may mean a layer supporting lower scalability than the specific layer, and the upper layer may mean a layer supporting higher scalability than a specific layer. A layer that a particular layer refers to in encoding or decoding may be referred to as a reference layer (or a reference layer).

Referring to FIG. 3, for example, the base layer may be defined by a standard definition (SD), a frame rate of 15 Hz, a bit rate of 1 Mbps, and a first enhancement layer may be defined as high definition (HD), a frame rate of 30 Hz, And 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, the frame rate, the bit rate, and the like are one example, and can be determined as needed. Also, the number of layers to be used is not limited to the present embodiment, but can be otherwise determined depending on the situation. For example, if the transmission bandwidth is 4 Mbps, the frame rate of the first enhancement layer HD may be reduced to 15 Hz or less.

The scalable video coding method can provide temporal, spatial, picture quality, and viewability scalability by the above-described method in the embodiment of FIG.

In this specification, scalable video coding has the same meaning as scalable video encoding in terms of encoding and scalable video decoding in decoding.

On the other hand, in the scalable video coding structure, since there is a strong correlation between layers, if the prediction is performed by using such a relation, it is possible to remove redundant elements of data and improve the coding performance of an image. Therefore, when predicting a picture (picture) of a current layer (upper layer) to be coded or decoded, inter prediction or intra prediction using information of the current layer, inter-layer prediction using information of another layer, Or inter-layer prediction).

Since inter-layer prediction, that is, inter-layer prediction uses information of different layers, information of other layers used for inter-layer prediction is needed. That is, information of another layer (reference layer) used for interlayer prediction of the current layer, information of reference pictures to be referred to in the reference layer, and the like are required. When using such interlayer prediction, it is necessary to manage the reference layer and the reference picture referred to by the current layer.

Information related to management of reference pictures (hereinafter, referred to as inter-layer reference picture management) used for inter-layer prediction is transmitted by the encoder, thereby indicating how many layers each layer refers to using the inter-layer dependency set here You can send information and information that tells you which layer each layer has referenced. The portion for transmitting the management information for the reference picture can be transmitted in various forms, and one example of them can be a Video Parameter Set (VPS) extension. For example, a VPS extension may contain information that tells how many layers each layer refers to, and information that tells which layer each layer refers to.

For example, in the decoder, num_direct_ref_layers [layerID] indicating the number of reference layers referred to by each layer from the VPS extension can be analyzed and ref_layer_id [i] indicating a reference layer to be referred to for each layer can be analyzed. In this case, i in ref_layer_id [i] may range from '0' to a value specified by num_direct_ref_layers indicating how many layers each layer refers to. In other words, you can see how many layers the current layer refers to from the VPS extension, and also know the reference layer of the current layer.

When the analysis of the layer to be referred to by each layer is completed, a reference picture list (or a reference picture list) can be constructed. At this time, not only reference pictures used for inter-prediction but also reference pictures used for inter-layer prediction can be added to the reference picture list.

4 is a diagram showing a configuration of a reference picture list.

4, the reference picture list includes a long-term reference picture set RefPicSetLtCurr referred to by the current picture, a long-term reference picture set RefPicSetLtFoll not referred to by the current picture, a forward short- (RefPicSetStCurrBefore), a backward reference picture set (RefPicSetStCurrAfter) referenced by the current picture, a short reference picture set (RefPicSetStFoll) not referred to by the current picture, and a reference picture set RefPicSetIvCurr ).

The reference picture set (RefPicSetIvCurr) referred to for interlayer prediction may include as many reference layers as the num_direct_ref_layers signaled in the VPS extension.

A reference picture set (RefPicSetIvCurr) referred to for interlayer prediction includes a picture having a picture identifier (layer_id) equal to ref_layer_id [i] signaled in the VPS extension and having a Picture Order Count (POC) identical to the current picture of the current layer . The POC may be a value capable of identifying pictures belonging to the same layer, and may be a value indicating an output order.

All the pictures constituting the reference picture set (RefPicSetIvCurr) referred to for inter-layer prediction are all indicated as " used for long-term reference ".

Hereinafter, a method for efficiently managing a reference picture when interlaced prediction is performed by including at least one reference layer in a scalable video coding structure will be described.

5 is a flowchart schematically showing a method of managing reference pictures in scalable video coding according to an embodiment of the present invention. The method of FIG. 5 can be performed by the encoding apparatus of FIG. 1 or the decoding apparatus of FIG. 2 described above.

Referring to FIG. 5, an encoder or a decoder analyzes a layer dependency in a VPS extension (S500).

As described above, the layer dependency analysis means to grasp the inter-layer dependency in order to encode or decode the current layer. When the current layer is encoded or decoded, .

When coding the layer dependency using the VPS extension, the encoder can (1) use the existing layer dependency representation method, (2) use the existing layer dependency representation method and One can use one of the methods of representing a layer dependency using a scalable reference layer set (SRLS).

The method of expressing the layer dependency using the SRLS is as follows. Namely, the number of reference layers (num_direct_ref_layers) and the reference layer (ref_layer_id) that can be referred to by the current layer are designated in advance by SRLS How to say.

In the case of encoding using the existing layer dependency representation method, the encoder can encode the layer dependency according to the conventional method as shown in FIG.

When encoding is performed using the existing layer dependency representation method and the layer dependency expression method using SRLS, the encoder first encodes a flag (for example, vps_srls_present_flag) indicating which method is used and encodes the layer dependency according to the flag .

For example, when using the existing layer dependency representation method, it is possible to encode vps_srls_present_flag to 0 and encode the layer dependency through the existing syntax. (For example, num_scalable_ref_layer_sets) and information (scalable_ref_layer_set ()) for each layer dependency set, which encodes vps_srls_present_flag to 1, and indicates how many layer dependency sets (SRLS) Can be encoded.

In view of the decoder, when the encoder is coded using the existing layer dependency representation method, the decoder can decode the layer dependency in a conventional manner without converting the syntax.

When encoding is performed using either the existing layer dependency representation method or the layer dependency representation method using SRLS in the encoder, the decoder decodes a flag (for example, vps_srls_present_flag) indicating that the layer dependency is encoded using a certain method And decrypt the layer dependency information according to the flag.

Table 1 is an example of a syntax that describes how to interpret layer dependencies in VPS extensions.

Referring to Table 1, vps_srls_present_flag is a flag that indicates whether the layer dependency is encoded using any of the existing layer dependency rendering method and the layer dependency rendering method using SRLS. For example, when vps_srls_present_flag is 0, it is indicated that it is coded by the existing layer dependency representation method, and when vps_srls_present_flag is 1, it can be indicated that it is coded by the layer dependency representation method using SRLS.

num_scalable_ref_layer_sets represents the number of layer dependency sets (SRLS).

scalable_ref_layer_set () represents the configuration of each layer dependency set.

The decoder may decode vps_srls_present_flag to interpret the layer dependencies in the VPS.

When vps_srls_present_flag is 0, the decoder can decode the syntax using an existing layer dependency representation method.

If vps_srls_present_flag is 1, the decoder can decrypt the syntax with a layer dependency representation method using SRLS. At this time, the decoder can decode num_scalable_ref_layer_sets to determine the number of layer dependency sets (SRLS), and decode scalable_ref_layer_set () to construct each layer dependency set (SRLS).

A method of constructing the layer dependency set (SRLS) according to the present invention will be described in detail with reference to FIG.

The encoder or decoder analyzes the layer dependency in the slice (S510).

When analyzing the layer dependency through a slice, the encoder or decoder can use (1) a method of using / changing the layer dependency interpreted by the conventional method in the current slice in the VPS extension, and (2) You can use one of the ways to use / change the current slice using dependencies.

When a layer dependency that is resolved in the existing method in the VPS extension is used / changed in the current slice, the encoder discriminates whether to use the layer dependency for the current slice or set a new layer dependency for the current slice, Information can be encoded for each slice using a flag (for example, slice_srls_present_flag).

If a method of setting a new layer dependency for the current slice is used, the encoder encodes the number of layers that can be referred to by the current slice into syntax information (for example, num_scalable_ref_layer) (Layer_id or identifiable information) to be referred to can be encoded with syntax information (for example, scalable_ref_layer [i]) and transmitted. New layer dependencies can be set within the inter-layer dependencies set in the VPS extension.

If a layer dependency that has been resolved in a conventional way in the VPS extension is used / changed in the current slice, the decoder may use a flag (not shown) to indicate whether to use the layer dependency for the current slice or set a new layer dependency for the current slice For example, slice_srls_present_flag) may be decoded first, and the layer dependency information for the current slice may be decoded according to the flag.

Table 2 is an example of a syntax indicating how to use / change the layer dependency interpreted by the existing method in the current slice in the VPS extension.

Referring to Table 2, slice_srls_present_flag is a flag that indicates whether to use the layer dependency for the current slice or set a new layer dependency for the current slice.

num_scalable_ref_layer represents the number of layers that the current slice will reference.

The scalable_ref_layer [i] indicates the layer_id of the layer to be referred to or information for identifying the layer to be referred to.

 Table 3 shows an embodiment of the syntax shown in Table 2. Referring to Table 3, slice_srls_present_flag is a flag that indicates whether to use the layer dependency for the current slice or set a new layer dependency for the current slice. For example, if slice_srls_present_flag is 1, it indicates that a new layer dependency is set in the current slice, and if slice_srls_present_flag is 0, it means that layer dependency is not used for the current slice. If slice_srls_present_flag is 0, num_scalable_ref_layer is set to 0 and the current slice does not use inter layer reference.

 slice_srls_present_flag is used when the current layer to be coded is not the base layer, when the interlayer dependency set in the VPS extension is not always used, and when the number of layers that the current layer can refer to in the interlayer dependency set in the VPS extension is 1 If satisfactory, interpretation is possible.

num_scalable_ref_layer represents the number of layers that the current slice will reference. num_scalable_ref_layer is interpretable when slice_srls_present_flag is 1 and the number of layers that can be referenced in the inter-layer dependency set in the VPS extension is 2 or more. num_scalable_ref_layer is greater than 1 and may have a value less than the number of layers the current layer can reference in inter-layer dependencies set in the VPS extension. In the inter-layer dependency set in the VPS extension, num_scalable_ref_layer is set to 1 even if it is not interpreted, when the number of layers that the current layer can refer to is 1.

The scalable_ref_layer [i] indicates the layer_id of the layer to be referred to or information for identifying the layer to be referred to. If the num_scalable_ref_layer is equal to the number of layers that can be referenced by the current layer in the inter-layer dependency set in the VPS extension, scalable_ref_layer [i] can identify equally the reference layer specified by inter-layer dependency set in the VPS extension Information.

The decoder can decode slice_srls_present_flag to interpret the layer dependency on the slice. If slice_srls_present_flag is 1, a new layer dependency is set in the current slice. If slice_srls_present_flag is 0, layer dependency is not used.

When a new layer dependency is used for the current slice, the decoder decodes num_scalable_ref_layer to find the number of layers to be referred to by the current slice, decodes scalable_ref_layer [i] by the number of layers to be referred to by the current slice, You can identify the layer_id or the information that identifies the layer to be referenced.

On the other hand, when the layer dependency expressed by SRLS in the VPS extension is used / changed in the current slice, the encoder decides whether to use the layer dependency set in the VPS extension or the new layer dependency in the current slice, Can be encoded for each slice using a flag (e.g., scalable_ref_layer_set_vps_flag).

Here, the encoder can distinguish whether it is coded according to the existing layer dependency representation method or the layer dependency representation method using SRLS according to the flag information (for example, vps_srls_present_flag) set in the VPS extension.

If the encoding is performed by the layer dependency representation method using SRLS, the encoder encodes the new layer dependency in the current slice according to the scalable_ref_layer_set_vps_flag or syntax information indicating the layer dependency set to be used in the layer dependency set set in the VPS extension For example, scalable_ref_layer_set_Idx).

If the method used in the VPS extension is coded using the existing layer dependency representation method, the layer dependency to be used in the current slice according to the scalable_ref_layer_set_vps_flag can be used or changed in the current slice by the existing method in the VPS extension described above You can set it up like this.

Table 4 is an example of a syntax indicating a method of using / changing in the current slice using the layer dependency expressed by SRLS in the above-mentioned VPS extension.

The encoder or decoder composes a reference picture list (S520).

The inter-layer reference picture list can be managed by the inter-layer dependency set in the VPS extension or slice header. At this time, the layer dependency in the VPS extension and the slice header can be analyzed by the method described in steps S500 to S510.

The encoder or decoder can add a layer dependency set (SRLS) when constructing the reference picture list after analyzing the layer to which each layer refers. SRLS can specify the number of layers to reference as the number of reference layers interpreted in the VPS extension or slice header. SRLS can also specify an image with the same POC as the current picture in the reference layer with the dependency interpreted in the VPS extension or slice header. All pictures in SRLS are marked as "used for long-term reference".

A method of constructing a reference picture list including the SRLS according to the present invention will be described in detail with reference to FIG.

FIG. 6 is a diagram for explaining a method of constructing a scalable reference layer set (SRLS) or a layer dependency set according to the present invention.

Referring to FIG. 6, M scalable reference layer sets may exist, and each scalable reference layer set may be composed of a plurality of layer IDs.

The scalable reference layer set 1 may be composed of A layer IDs, the scalable reference layer set 2 may be composed of B layer IDs, and the scalable reference layer set M may be composed of K layer IDs.

The layer ID constituting the scalable reference layer set can be specified by the difference value between the current layer ID and the reference layer ID.

The encoder may encode scalable_ref_layer_set () as described above to construct a scalable reference layer set. The scalable_ref_layer_set () includes syntax information (e.g., num_ref_layer) indicating the number of reference layers, syntax information (e.g., delta_layer_id_sign) indicating the sign of the layer_id difference value between the current layer and the reference layer by the number of reference layers, (For example, abs_delta_layer_id [i]) indicating the absolute value of the difference value can be sequentially encoded and transmitted. At this time, the syntax information (e.g., num_ref_layer, delta_layer_id_sign, abs_delta_layer_id [i]) encoded by scalable_ref_layer_set () can be specified and encoded for each scalable reference layer set.

Table 5 shows a syntax table of scalable_ref_layer_set () for constructing a scalable reference layer set.

Referring to Table 5, num_scalable_ref_layer_set represents the number of scalable reference layer sets.

The value of 1 added to delta_srls_idx_mimus1 is a value specifying the scalable reference layer set, and indicates the difference value with the previous scalable reference layer set.

num_ref_layer indicates the number of reference rails.

delta_layer_id_sign represents the sign of the difference between the current layer and the reference layer.

abs_delta_layer_id [i] represents the absolute value of the difference between the current layer and the reference layer.

The decoder recognizes the number of reference layers constituting the reference layer set through the num_ref_layer and grasps the layer_id difference value between the current layer and the reference layer through delta_layer_id_sign and abs_delta_layer_id [i] signaled by the number of reference rails.

7 is a diagram for explaining a method of constructing a reference picture list (reference picture list) according to the present invention.

Referring to FIG. 7, five lists of POC values and one list used for inter-layer prediction may be configured to derive a reference image set included in the current layer before decoding the current image.

The POC value list (Picture order count list) may include PocLtCurr, PocLtFoll, PocStCurrBefore, PocStCurrAfter, and PocStFoll. Each list contains a number of components (i.e., POC values) specified by NumPocStCurrBefore, NumPocStCurrAfter, NumPocStFoll, NumPocLtCurr, and NumPocLtFoll, respectively.

PocLtCurr is a list including a POC of a long-term reference picture that is used by the current picture and has a POC larger than the POC of the current picture, and PocLtFoll includes a POC of the long-term reference picture that is not used by the current picture . PocLtCurr and PocLtFoll are used to construct a long-term reference picture set.

PocStCurrBefore is a list including the POC of a short-term reference picture having a POC smaller than the POC of the current picture, which is used by the current picture. PocStCurrAfter is a list including the POC of a short-term reference picture that is used by the current picture and has a POC that is larger than the POC of the current picture. PocStFoll is a list including POCs of short-term reference pictures not used by the current picture. PocStCurrBefore, PocStCurrAfter, and PocStFoll are used to construct a short-term reference picture set.

One list used for inter-layer prediction may include reference layer candidates to support scalability. The reference layer candidate may be composed of a layer ID (LayerIDScalableCurr) for a reference layer candidate for interlayer prediction. LayerIDScalableCurr is used to construct a set of scalable reference layers.

The encoder or decoder can check the DPB (Decoded Picture Buffer) storing the decoded picture with respect to the current layer to derive a set of five reference pictures from the five POC lists, check the DPB of the other layer, (LayerIDScalableCurr), a reference layer set (ScalableRefLayerSet) to be used for interlayer prediction.

The scalable reference layer set (ScalableRefLayerSet) may comprise a reference layer corresponding to the number of reference layers signaled in the VPS extension or slice header.

A scalable reference layer set (ScalableRefLayerSet) may specify an image having the same POC as the current picture in the reference layer with a dependency signaled in the VPS extension or slice header.

All images that make up a scalable reference layer set (ScalableRefLayerSet) are marked as used for long-term reference.

The encoder or decoder may derive a reference picture list based on the reference picture set and the scalable reference layer set, and perform inter prediction or inter-layer prediction using the reference picture list.

According to the present invention, a scalable reference layer set (SRLS) is added to an existing reference picture set (RPS) to construct a reference picture in a different layer, The reference image can be integrated and managed. Also, the DPB management in the current layer does not affect the DPB of the other layer.

In the above-described embodiments, the methods are described on the basis of a flowchart as a series of steps or blocks, but the present invention is not limited to the order of the steps, and some steps may occur in different orders or simultaneously . It will also be understood by those skilled in the art that the steps depicted in the flowchart illustrations are not exclusive and that other steps may be included or that one or more steps in the flowchart may be deleted without affecting the scope of the invention You will understand.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the claims, and all technical ideas within the scope of the claims should be construed as being included in the scope of the present invention.

Claims (18)

A video decoding method for supporting a plurality of layers,
Analyzing a layer dependency for a current layer based on a VPS (Video Parameter Set) extension;
Analyzing the layer dependency for the current slice based on the information encoded on a slice-by-slice basis; And
Constructing a reference picture list for the current layer based on an analysis of at least one of a layer dependency for the current layer and a layer dependency for the current slice,
Analyzing the layer dependency of the current slice based on the slice-
And determining whether to use a new layer dependency for the current slice. The method according to claim 1,
The layer dependency includes:
Wherein the reference layer comprises at least one reference layer set including a number of reference layers referred to by the current layer and identification information of the reference layer. delete delete delete The method according to claim 1,
Wherein the step of analyzing the layer dependency of the current slice based on the slice-
Determining whether to use the new layer dependency for the current slice according to information indicating whether a new layer dependency is to be used for the current slice. The method according to claim 1,
Wherein the step of analyzing the layer dependency of the current slice based on the slice-
If it is determined to use the new layer dependency on the current slice,
Analyzing the number of reference layers referred to by the current slice;
Analyzing identification information of a reference layer referred to by the current slice by the number of reference layers referenced by the current slice; And
And constructing a reference layer set for the current slice based on identification information of a reference layer referenced by the current slice. delete A video encoding method for supporting a plurality of layers,
Determining a layer dependency for a current layer and encoding the layer dependency using a VPS (Video Parameter Set) extension;
Determining a layer dependency for a current slice and encoding the slice for each slice; And
Constructing a reference picture list for the current layer based on at least one of a layer dependency for the current layer and a layer dependency for the current slice,
Determining a layer dependency for the current slice and encoding the slice for each slice,
Determining whether to set a new layer dependency for the current slice. 10. The method of claim 9,
The layer dependency includes:
Wherein the reference layer comprises at least one reference layer set including a number of reference layers referred to by the current layer and identification information of the reference layer. delete delete delete 10. The method of claim 9,
Determining a layer dependency for the current slice and encoding the slice for each slice,
Determining whether to set the new layer dependency for the current slice according to information indicating whether to set a new layer dependency for the current slice. 10. The method of claim 9,
Determining a layer dependency for the current slice and encoding the slice for each slice,
If it is determined to set the new layer dependency on the current slice,
Determining a number of reference layers referred to by the current slice;
Determining identification information of a reference layer referred to by the current slice by the number of reference layers referenced by the current slice; And
And constructing a reference layer set for the current slice based on identification information of a reference layer referenced by the current slice. delete delete delete

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