WO2015102271A1

WO2015102271A1 - Method for decoding image and apparatus using same

Info

Publication number: WO2015102271A1
Application number: PCT/KR2014/012495
Authority: WO
Inventors: 이하현; 강정원; 이진호; 최진수; 김진웅
Original assignee: 한국전자통신연구원
Priority date: 2014-01-02
Filing date: 2014-12-17
Publication date: 2015-07-09

Abstract

A method for decoding an image according to an embodiment of the present invention, which supports a plurality of layers, may comprise the steps of: receiving information on a reference layer used to decode a current picture for inter-layer prediction; inducing the number of valid reference layer pictures used to decode the current picture on the basis of the information on the reference layer; and performing inter-layer prediction on the basis of the number of the valid reference layer pictures.

Description

Image decoding method and apparatus using same

The present invention relates to encoding and decoding processing of an image, and more particularly, to a method and apparatus for encoding and decoding an image that supports a plurality of layers in a bitstream.

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 a pixel value included in a current picture from a previous and / or subsequent picture in time, and for predicting a pixel value 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 signaling layer information existing in an image coded bitstream of a plurality of hierarchical structures including a temporal sublayer, an inter-layer prediction method, and a method for obtaining a target output layer.

In addition, the present invention provides a method for accessing layer information described in a VPS in a bitstream without using an entropy decoder for session negotiation and the like, and an apparatus using the same.

In addition, an embodiment of the present invention provides a method for determining an effective number of inter-layer reference pictures required for decoding a current picture, using the method for inter-layer prediction, a method for obtaining a target output layer, and an apparatus using the same.

An embodiment of the present invention provides a method of decoding an image supporting a plurality of layers, the method including: receiving information on a reference layer used for decoding a current picture for inter-layer prediction; Deriving a number of valid reference layer pictures used for decoding the current picture based on the information on the reference layer; And performing inter-layer prediction based on the number of valid reference layer pictures.

The number of valid reference layer pictures of all slices belonging to the current picture may be the same.

When the layer identifier for identifying the current layer to which the current picture belongs is 0, the number of valid reference layer pictures may be derived as zero.

When the number of direct reference layers for the current layer to which the current picture belongs is zero, the number of valid reference layer pictures may be derived as zero.

The same access unit as the current picture derived in consideration of the number of direct reference layers for the current layer, maximum temporal sublayer information of the reference layer, maximum temporal sublayer information allowing inter-layer prediction in the reference layer, and a temporal identifier of the current picture. When the number of reference layer pictures in the frame is 0, the number of valid reference layers may be derived as zero.

The layer identifier identifying the current layer to which the current picture belongs is not 0 or the number of reference pictures available for inter-layer prediction in the same access unit as the current picture is 0, but not in the layer including the current picture. When using all direct reference layer pictures belonging to all direct reference layers for the same picture and present in the same access unit as the current picture and included in the inter-layer reference picture set of the current picture, as the reference layer pictures of the current picture, the valid reference The number of layer pictures is based on a variable indicating the number of direct reference layers for the current layer, maximum temporal sublayer information of each layer, maximum temporal sublayer information allowing interlayer prediction in each layer, and a temporal identifier of the current picture. Can be induced.

The maximum temporal sublayer information of the reference layer among the direct reference layer pictures for the current picture is greater than or equal to the temporal identifier of the current picture, and the maximum temporal sublayer information allowing inter-layer prediction in the reference layer is the temporal identifier of the current picture. The number of pictures of the reference layer corresponding to the larger case may be used as the number of valid reference layer pictures for decoding the current picture.

When inter-layer prediction is not used for decoding the current picture, the number of valid reference layer pictures may be derived as zero.

If at most one picture is used for inter-layer prediction for each picture in a coding video sequence or if the number of direct reference layers of the layer to which the current picture belongs is 1, the number of valid reference layer pictures may be derived as 1. have.

If at most one picture is used for inter-layer prediction for each picture in a coding video sequence or if the number of direct reference layers of the layer to which the current picture belongs is 1, the number of reference layer pictures that can be used for decoding the current picture. If is greater than 0, the number of valid reference layer pictures can be derived as 1, and if the number of reference layer pictures that can be used for decoding the current picture is 0, the number of valid reference layer pictures can be derived to 0.

If the number of reference layer pictures that can be used for inter-layer prediction for each picture in a coding video sequence or can be used for inter-layer prediction in the same access unit as the current picture is 1, then the valid reference layer picture is valid. The number of can be derived as 1.

When the information about the reference layer includes number information indicating the number of pictures used for decoding the current picture for inter-layer prediction, the number of valid reference layer pictures may be derived to a value specified by the number information. have.

According to an embodiment of the present invention, a method of signaling layer information existing in an image coded bitstream of a plurality of hierarchical structures including a temporal sublayer, an inter-layer prediction method, and a method of obtaining a target output layer are provided.

Furthermore, according to an embodiment of the present invention, a method and an apparatus using the same are provided for accessing hierarchical information existing in a bitstream for session negotiation and the like even in a media aware network equipment (MANE) having no entropy decoder.

According to the present invention, there is provided a method of accurately determining the effective number of inter-layer reference pictures required for decoding a current picture and using it for inter-layer prediction, a method of outputting an actual desired output layer, and an apparatus using the same.

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

5 is a diagram for describing a method of deriving the number of valid reference layer pictures 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. Encoding parameters are parameters necessary for encoding and decoding, and may include information that may be inferred during encoding or decoding, as well as information encoded by an encoder and transmitted to a decoder, such as syntax elements. Means necessary information. 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 reconstructed block or reconstructed 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 encoder and 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 GOP (Group of Picture) 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 redundancy between layers 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, image quality, and viewpoint according to ambient conditions such as transmission bit rate, transmission error rate, and system resources.

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.

Here, the layer is an image divided based on spatial (eg, image size), temporal (eg, coding order, image output order, frame rate), image quality, viewpoint, complexity, etc. And a set of bitstreams. In addition, the base layer may mean a lower layer or a reference layer, and an enhancement layer may mean an upper 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 may provide temporal, spatial, image quality, and viewpoint scalability by the method described above in the embodiment of FIG. 3.

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.

The present invention relates to a sub-encoding / de-coding process of an image including a plurality of layers or views, wherein the plurality of layers or views include first, second, third, It may be expressed as an nth layer or a viewpoint. In the following description, a picture in which the first layer and the second layer exist is described as an example, and the same may be applied to more layers or viewpoints. In addition, the first layer may be expressed as a base layer, and the second layer may be expressed as an upper layer. In addition, the first layer may be expressed as a reference layer, and the second layer may be expressed as an enhancement layer.

The picture / block of the first layer corresponding to the picture / block of the second layer may be changed according to the size of the second layer picture / block. That is, when the size of the picture / block of the first layer is smaller than that of the picture / block of the second layer, scaling may be performed using methods such as up-sampling and re-sampling.

In addition, the picture of the first layer may be used for image encoding / decoding of the second layer in addition to the reference picture list of the second layer. In this case, the second layer may perform prediction and encoding / decoding by using the first layer image in the reference picture list as in the normal inter prediction.

The block size for encoding / decoding may be NxN-type squares such as 4x4, 8x8, 16x16, 32x32, 64x64, or NxM-shaped rectangles such as 4x8, 16x8, 8x32, and the unit of the block is a coding block (CB: Coding Block). ), At least one of a prediction block (PB) and a transform block (TB) may have different sizes.

Hereinafter, a prediction block, ie, a prediction signal, of a block that is to be encoded and decoded in a higher layer (hereinafter, referred to as a current block or a target block) of a scalable video, that is, an encoding and decoding method of an image using a multi-layer structure, is generated. See how to do it. In the following, the contents (method or apparatus) of the present invention may be generally applied equally to an encoder and a decoder.

On the other hand, in the current draft of Scalable High Efficiency Video Coding (SHVC) and Multiview-High Efficiency Video Coding (MV-HEVC) standards, profiles, tiers, and levels used for layer sets in video parameter set extensions (VPS extensions) The syntax element (profile_tier_level) indicating is described as shown in Table 1.

Table 1

Referring to Table 1, the value specified by vps_num_profile_tier_level_minus1 indicates the number of profile_tier_level () syntax structures in the VPS.

If vps_profile_present_flag [i] is “1”, it indicates that profile and tier information exists in the i-th profile_tier_level () syntax structure. If “ps”, “v” _profile_present_flag [i] indicates that profile and tier information is present in the i-th profile_tier_level () syntax structure. It does not exist and it is inferred.

profile_ref_minus1 [i] indicates that the profile and tier information for the i-th profile_tier_level () syntax structure is inferred to be the same as the profile and tier information for the (profile_ref_minus1 [i] +1) th profile_tier_level () syntax structure. At this time, profile_ref_minus1 [i] plus 1 should be less than or equal to i.

According to the current standard draft as shown in Table 1, when i is 1 and vps_profile_present_flag [1] has a value of 0, the profile and tier information for the first profile_tier_level () syntax structure is (profile_ref_minus1 [1] +1) th profile_tier_level () Inference must be made from the syntax structure. That is, the value of “profile_ref_minus1 [1] +1” must be equal to 1 or 0. If "profile_ref_minus1 [1] +1" is 0, profile_ref_minus1 [1] has a value of -1, which violates the profile_ref_minus1 [i] syntax definition encoded by u (6).

In addition, when (profile_ref_minus1 [1] +1) has a value of “1”, a problem may arise that the first profile and tier information are inferred from the first profile_tier_level syntax structure.

In order to solve this problem, a constraint such as "the vps_profile_present_flag [1] should always be 1 for the first profile_tier_level syntax structure" may be added to the semantics of the syntax. In this case, semantics for vps_profile_present_flag [i] of Table 1 may be expressed as follows.

If vps_profile_present_flag [i] is “1”, it indicates that profile and tier information exists in the i-th profile_tier_level () syntax structure. If vps_profile_present_flag [i] is “0”, it shows in i-th profile_tier_level () syntax structure. It may indicate that profile and tier information does not exist and is inferred. Vps_profile_present_flag [1] for the first profile_tier_level syntax structure must have a value of 1.

According to another embodiment, in order to solve the above problem, a signaling method as shown in Table 2 may be considered.

TABLE 2

Referring to Table 2, the value specified by vps_num_profile_tier_level_minus1 indicates the number of profile_tier_level () syntax structures in the VPS.

If vps_profile_present_flag [i] is “1”, it indicates that profile and tier information exists in the i-th profile_tier_level () syntax structure. If vps_profile_present_flag [i] is “0”, it shows in i-th profile_tier_level () syntax structure. There is no profile and tier information, and it is inferred from the profile and tier information of the i-1 th profile_tier_level () syntax structure. Vps_profile_present_flag [1] for the first profile_tier_level syntax structure must have a value of 1.

According to Table 2, profile_ref_minus1 [1] is not signaled.

According to another embodiment of the present invention, the syntax structure of the VPS may be changed to parse the VPS extension even in a media aware network equipment (MANE) without an entropy decoder. Tables 3-5 show VPS in accordance with various aspects of the present invention.

TABLE 3

Table 4

Table 5

Referring to Table 3, the syntax element vps_extension_offset transmitted from the VPS is a byte offset from the start point of the VPS NAL unit to the fixed length coded information starting with the “avc_base_layer_flag” syntax. Indicates.

The byte offset defined by vps_extension_offset does not require entropy decoding within the VPS NAL unit and allows access to basic information that enables session negotiation.

For example, a media aware network equipment (MANE) without an entropy decoder may parse basic information that does not require entropy decoding based on the byte offset value described by vps_extension_offset and use it for session negotiation.

MANE without an entropy decoder does not entropy decode information after vps_extension_offset based on vps_extension_offset information for session negotiation, and when parsing output layer sets information in the VPS extension of Table 4, the layer in the layer identifier list The variable NumLayersInIdList indicating the number should be entropy decoded into information about layer sets described after vps_extension_offset in Table 3, that is, a value calculated from layer_id_included_flag [i] [j].

Without entropy decoding, information about layer sets can be described in the VPS extension as shown in Table 5 so that output layer set information in the VPS extension can be used for session negotiation and the like.

Meanwhile, the semantics of the layer sets related syntax elements described in the VPS extension of Table 5 are as follows.

The vps_maximum_layer_id indicates the maximum nuh_layer_id value allowed in all NAL units in the CVS in the same manner as the vps_max_layer_id described in the VPS, and may have the same value as the vps_max_layer_id described in the VPS.

A value specified by vps_number_layer_sets_minus1 may be signaled before vps_vui_offset if it indicates the number of layer sets.

When layer_id_nuh_included_flag [i] [j] is 1, same as layer_id_included_flag [i] [j] described in the VPS, it indicates that nuh_layer_id value equal to j is included in the layer identifier list (layer identifier list, layerSetLayerIdList [i]), and layer_id_nuh_included_flag [i] [j] equal to 0 indicates that a nuh_layer_id value equal to j is not included in the layer identifier list (layerSetLayerIdList [i]). layer_id_nuh_included_flag [i] [j] must have the same value as layer_id_included_flag [i] [j] described in the VPS.

NumLayersInIdList [i] and layer identifier list (layerSetLayerIdList [i]) for i, which may have a value from 1 to vps_number_layer_sets_minus1, can be obtained as follows.

n = 0

for (m = 0; m <= vps_maximum_layer_id; m ++)

if (layer_id_nuh_included_flag [i] [m])

layerSetLayerIdList [i] [n ++] = m

numLayersInIdList [i] = n

In the multi-layer video encoding / decoding method, VPS VUI video usability information bitstream partition hypothetical reference decoder (HRD) parameter syntax and bitstream segmentation HRD (Bitstream) based on layer_id_nuh_included_flag [i] [j] described in the VPS extension. partition HRD) Parameter A supplementary enhancement information message (SEI) syntax may be described or layer set related information may be interpreted.

According to another embodiment of the present invention, as shown in Table 6, information about layer sets may be described in the VPS extension.

Table 6

Table 6 shows information about layer sets in the VPS extension, and the session negotiation may be performed without entropy decoding by using the output layer set information in the VPS extension.

The layer set related syntax (vps_maximum_layer_id, vps_number_layer_sets_minus1, layer_id_nuh_included_flag [i] [j]) may be described above the syntax element vps_vui_offset.

In addition, the position of the syntax element direct_dependency_flag indicating whether there is a dependency between layers may be changed over vps_vui_offset. In this case, even if the syntax element after vps_vui_offset is not parsed, the information about the vps_vui can be grasped using the vps_vui_offset value.

According to another embodiment, as shown in Table 7, information about layer sets in a VPS extension may be described.

TABLE 7

Referring to Table 7, the position of the racer set related syntax elements present in the VPS may be located before vps_extension_offset.

The vps_num_layer_sets_minus1, which was previously encoded with a variable number of bits ue (V), may be encoded with a fixed number of bits u (10) to avoid entropy decoding, and vps_number_layer_sets_minus1 of the same function described in the VPS extension may be deleted.

On the other hand, the video signaling information described in the VPS VUI is information that can be used for session negotiation, the VPS VUI may be as shown in Table 8.

Table 8

Referring to Table 8, indicates that the video_signal_info_idx_present_flag 1 is a syntax element and vps_num_video_signal_info_minus1 vps_video_signal_info_idx [i] exists, it indicates that video_signal_info_idx_present_flag is zero, there is no syntax elements vps_num_video_signal_info_minus1 and vps_video_signal_info_idx [i].

A value obtained by adding 1 to vps_num_video_signal_info_minu1 indicates the number of video_signal_info () syntax structures in the VPS. If vps_num_video_signal_info_minu1 does not exist, the number of vps_num_video_signal_info_minus1 is inferred to be equal to the value of MaxLayersMinus1.

vps_video_signal_info_idx represents an index of the video_signal_info () syntax structure list applied to a layer having nuh_layer_id equal to layer_id_in_nuh [i]. If vps_video_signal_info_idx does not exist, vps_video_signal_info_idx [i] is inferred to (video_signal_info_idx_present_flag? 0: i). vps_video_signal_info_idx [i] may be in a range from 0 to vps_num_video_signal_info_minus1.

In the current SHVC and MV-HEVC standard drafts, video signaling in MANE without an entropy decoder exists because there are syntax elements encoded with exp-golomb codes (ue (v)) before video signaling information, as shown in Table 8. This can cause problems with information (not available for session negotiation).

To solve this problem, that is, video signaling information can be described in a location accessible without entropy decoding, as shown in Table 9, in order to use the video signaling information in the VPS VUI for session negotiation without entropy decoding.

Table 9

To access video signaling information without entropy decoding, as shown in Table 9, syntax elements related to video signaling information next to bit elements (bit_rate) and picture rate (pic_rate) related syntax elements (bit_rate_present_vps_flag, pic_rate_present_vps_flag, bit_rate_present_flag, pic_rate_present_flag, etc.) in VPS_VUI Can be described.

That is, by receiving the flag information indicating the number of video signal information (video_signal_info) and the presence of a signal indicating the index of the video signal information, that is, video_signal_info_idx_present_flag after the signals signaled by using a fixed bit, the video is performed without entropy decoding. Signaling information can be accessed.

Meanwhile, one aspect of the present invention proposes various methods for obtaining the number of valid reference layer pictures used for decoding a current picture for inter-layer prediction.

First method

A variable 'NumActiveRefLayerPics' indicating the number of valid reference layer pictures used for decoding the current picture for inter-layer prediction may be obtained as follows. According to the first method, all slices of the picture may be limited to having the same 'NumActiveRefLayerPics' value.

(1) When the 'nuh_layer_id' corresponding to the layer identifier of the layer to which the current picture belongs is 0 or the number of direct reference layers of the layer to which the current picture belongs is 'NumDirectRefLayers' to 0, the current picture is used for inter-layer prediction. The number of valid reference layer pictures used for decoding 'NumActiveRefLayerPics' may be set to zero. That is, if the layer is a base layer or the number of layers directly referenced is zero, the number of valid reference layer pictures used for decoding the current picture is set to zero.

(2) Otherwise, if the value of the syntax element 'all_ref_layers_active_flag' described in the VPS extension is 1, the number of valid reference layer pictures used for decoding the current picture for inter-layer prediction, 'NumActiveRefLayerPics' The variable 'numRefLayerPics' obtained from Equation 1, Equation 2 or Equation 3 may be set.

If all_ref_layers_active_flag is 1, for each picture referencing a video parameter set, of the direct reference layer pictures belonging to all direct reference layers of the layer containing the picture, they exist in the same access unit as the current picture and It indicates that all direct reference pictures included in the inter-layer reference picture set are used for inter-layer prediction. Whether the same access unit exists and whether the inter-layer reference picture set is included is the maximum temporal sublayer information (sub_layers_vps_minus1 [i]) of each layer and the value for the max temporal sublayer information (max_tid_il_ref_pics_plus1 [i] that allows inter-layer prediction in each layer ] [j]).

An all_ref_layers_active_flag equal to 0 indicates that the constraint may or may not apply.

This all_ref_layers_active_flag may be expressed with syntax such as default_ref_layers_active_flag.

A variable 'numRefLayerPics' indicating the number of reference layer pictures that can be used for inter-layer prediction in the same access unit as the current picture may be derived as follows.

Equation 1

Referring to Equation 1, the variable 'NumDirectRefLayers []' indicates the number of reference layers directly referenced by the current layer calculated from the syntax element 'direct_dependency_flag' described in the VPS extension.

'sub_layers_vps_max_minus1 [i]' indicates maximum temporal sublayer information of each layer, 'max_tid_il_ref_pics_plus1 [i] [j]' indicates maximum temporal sublayer information that allows inter-layer prediction in each layer, and 'TemporalId' is the current Represents a temporal identifier of a picture.

According to Equation 1, of the direct reference layers of the layer including the current picture, the 'sub_layers_vps_max_minus1 [i]' value of the reference layer is greater than or equal to the 'TemporalId' value of the current picture, and the value of the reference layer with respect to the current layer. Only pictures of the reference layer whose 'max_tild_il_ref_pics_plus1 [i] [j]' value is larger than the temporal identifier 'TemporalId' value of the current picture may be regarded as direct reference layer pictures that may be used for decoding the current picture for inter-layer prediction. .

On the other hand, when the syntax element 'max_tid_il_ref_pics_plus1 [i] [j]' is' 0 ', a non-IRAP picture having a' nuh_layer_id 'equal to' layer_id_in_nuh [i] 'is a' layer_id_in_nuh [ j] 'cannot be used as a reference picture for inter-layer prediction for a picture having the same' nuh_layer_id 'value. Equation 1 may be replaced with Equation 2 to reflect this constraint.

Equation 2

In Equation 2, the variable 'NumDirectRefLayers []' represents the number of reference layers directly referenced by the current layer calculated from the syntax element 'direct_dependency_flag' described in the VPS extension.

According to Equation 2, when the value of 'max_tid_il_ref_pics_plus1 [i] [j]' is '0' among the direct reference layers of the layer including the current picture, the temporal identifier 'TemporalId' of the current picture and the reference layer Only pictures in the reference layer whose 'max_tid_il_ref_pics_plus1 [i] [j]' value is equal to '0' and whose 'sub_layers_vps_max_minus1 [i]' value of the reference layer is greater than or equal to the value of the temporal identifier 'TemporalId' of the current picture are used for inter-layer prediction. For reference layer pictures that can be used for decoding the current picture. In this case, the picture of the reference layer may be restricted to be an IRAP picture.

If 'max_tid_il_ref_pics_plus1 [i] [j]' is greater than '0', the 'sub_layers_vps_max_minus1 [i]' value of the reference layer is greater than or equal to the temporal identifier 'TemporalId' value of the current picture, and the 'max_tild_il_ref_pics_plus1 [i]' of the reference layer Only pictures of the reference layer whose value [j] 'is greater than the temporal identifier' TemporalId 'value of the current picture may be regarded as reference layer pictures that may be used for decoding of the current picture for inter-layer prediction.

According to another embodiment, when the syntax element 'max_tid_il_ref_pics_plus1 [i] [j]' is '0', a non-infrared random access point picture having 'nuh_layer_id' equal to 'layer_id_in_nuh [i]' Cannot be used as a reference picture for inter-layer prediction for a picture having a 'nuh_layer_id' value equal to 'layer_id_in_nuh [j]'. Equation 1 may be replaced with Equation 3 to reflect this constraint.

Equation 3

In Equation 3, the variable 'NumDirectRefLayers []' represents the number of reference layers directly referenced by the current layer calculated from the syntax element 'direct_dependency_flag' described in the VPS extension.

According to Equation 3, when the 'sub_layer_vps_max_minus1 [i]' value of the reference layer is greater than or equal to the temporal identifier 'TemporalId' value of the current picture, the temporal identifier 'TemporalId' value of the current picture has '0' or Only when the value of 'max_tid_il_ref_pics_plus1 [i] [j]' is larger than the temporal identifier 'TemporalId' value of the current picture, the picture of the reference layer may be regarded as reference layer pictures that can be used for decoding of the current picture.

(3) Otherwise, if the syntax element 'inter_layer_pred_enabled_flag' described in the slice segment header of the current picture is '0', the number of valid reference layer pictures used for decoding the current picture for inter-layer prediction. 'NumActiveRefLayerPics' may be set to '0'. inter_layer_pred_enabled_flag indicates whether inter-layer prediction is used for decoding the current picture.

(4) Otherwise, if the syntax element 'max_one_active_ref_layer_flag' described in the VPS is 1 or the number of direct reference layers of the layer to which the current picture belongs is 'NumDirectRefLayers' is 1, Equation 1 If the variable 'numRefLayerPics' obtained from Equation 2 or Equation 3 is greater than '0', the number of valid reference layer pictures used for decoding the current picture for inter-layer prediction may be set to '1'. If the variable 'numRefLayerPics' obtained from Equation 1, Equation 2 or Equation 3 is '0', the number of valid reference layer pictures used for decoding the current picture for inter-layer prediction is '0'. Can be set.

A value of 'max_one_active_ref_layer_flag' of '1' indicates that at most one picture is used for inter-layer prediction for each picture in a coding video sequence. A value of 'max_one_active_ref_layer_flag' of '0' indicates that at least one picture is used for inter-layer prediction. Indicates what can be used.

(5) If all the conditions of (1) to (4) are not satisfied, the number of valid reference layer pictures used for decoding the current picture for inter-layer prediction, 'NumActiveRefLayerPics' is the syntax element 'transmitted in the slice segment header'. It may be set to a value obtained by adding '1' to num_inter_layer_ref_pics_minus1 '.

(6) In (1) to (5), numRefLayerPics can be expressed as numRefLayerPics [k] [m] when the nuh_layer_id value of the corresponding layer is 'k' and the TemporalId value of the temporal sublayer identifier is 'm'. , Can be calculated from equation (4) or equation (5).

Equation 1 for deriving a variable 'numRefLayerPics' at the VPS level indicating the number of reference layer pictures that can be used for decoding the sub-layer pictures of each layer for the entire layer included in the bitstream is represented by Equation 4 or Can be replaced by 5. In this case, 'numRefLayerLayerPics' may be replaced with 'numRefLayerPics [nuh_layer_id] [TemporalId]'.

Equation 4

In Equation 4, the variable 'NumDirectRefLayers []' represents the number of reference layers directly referenced by the current layer calculated from the syntax element 'direct_dependency_flag' described in the VPS extension.

'sub_layers_vps_max_minus1 [i]' indicates maximum temporal sublayer information of each layer, 'max_tid_il_ref_pics_plus1 [i] [j]' indicates maximum temporal sublayer information that allows inter-layer prediction in each layer, and vps_max_sub_layers_minus1 'indicates to the VPS. Represents the maximum sublayer information allowable in the described entire layer.

'Layer_id_in_nuh' for reference layer pictures of Equation 4 means 'nuh_layer_id' value present in the VCL NAL unit header.

According to Equation 4, first, from a direct reference layer for sublayers having tid (Temporal) values from 0 to 'vps_max_sub_layers_minus1' for each layer (0 to vps_max_layers_minus1) at a higher level (eg, VPS) It is determined whether there is a possible sublayer.

As a result of the determination, when there is a reference sublayer, the 'layer_id_in_nuh' value for the corresponding sublayer may be assigned to RefLayerIdListForTid [[lId] [tId] [k ++]. numRefLayerPics [lId] [tId] means the number of referenceable sublayers of a sublayer having a tId value with respect to the lId layer.

The existence of a referenceable sublayer indicates that the 'sub_layers_vps_max_minus1 []' value of the reference layer is greater than or equal to the 'TemporalId (tId)' value of the current picture, and the 'max_tild_il_ref_pics_plus1 [] []' value of the reference layer is the 'TemporalId of the current picture. If greater than (tId) 'value or the TemporalId (tId) value of the current picture is 0, only pictures of the reference layer may be determined as a reference layer picture that can be used for decoding of the current picture for inter-layer prediction.

Equation 5

In Equation 5, the variable 'NumDirectRefLayers []' represents the number of reference layers directly referenced by the current layer calculated from the syntax element 'direct_dependency_flag' described in the VPS extension.

'Sub_layers_vps_max_minus1 [i]' indicates maximum temporal sublayer information of each layer, and 'max_tid_il_ref_pics_plus1 [i] [j]' indicates maximum temporal sublayer information that allows inter-layer prediction in each layer.

'Layer_id_in_nuh' for reference layer pictures of Equation 5 means 'nuh_layer_id' value present in the VCL NAL unit header.

According to Equation 5, sublayers having tid (Temporal) values from 0 to the maximum temporal sublayer 'sub_layers_vps_max_minus1' for each layer (0 to vps_max_layers_minus1) at a higher level (for example, VPS). It is determined whether there is a sublayer referable from a direct reference layer.

2nd method

The number of valid reference layer pictures 'NumActiveRefLayerPics' used for decoding the current picture for inter-layer prediction may be derived as follows. All slices of the picture may be limited to having the same 'NumActiveRefLayerPics' value.

(1) interlayer prediction when 'nuh_layer_id' of the layer to which the current picture belongs has a value of 0 or the value of the variable 'numRefLayerPics' obtained from Equation 1, Equation 2 or Equation 3 is '0' For example, the number of valid reference layer pictures used to decode the current picture 'NumActiveRefLayerPics' may be set to '0'.

(2) Otherwise, if the syntax element 'all_ref_layers_active_flag' value described in the VPS is 1, the number of valid reference layer pictures used for decoding the current picture for inter-layer prediction, 'NumActiveRefLayerPics' It may be set to be equal to the value of the variable 'numRefLayerPics' obtained from Equation 1, Equation 2 or Equation 3.

(3) Otherwise, if the syntax element 'inter_layer_pred_enabled_flag' described in the slice segment header of the current picture is' 0 ', the number of valid reference layer pictures used for decoding the current picture for inter-layer prediction' NumActiveRefLayerPics' may be set to '0'.

(4) Otherwise, if the syntax element 'max_one_active_ref_layer_flag' described in the VPS is 1 or the number of direct reference layers of the layer to which the current picture belongs is 1, NumDirectRefLayers is used for decoding the current picture. The number of valid reference layer pictures to be 'NumActiveRefLayerPics' may be set to '1'.

(6) The numRefLayerPics of (1) to (5) may be expressed as numRefLayerPics [k] [m] when the nuh_layer_id value of the layer is 'k' and the TemporalId value of the temporal sublayer identifier is 'm'. Can be derived from Equation 4 or Equation 5.

3rd way

As another example, the number 'NumActiveRefLayerPics' of valid reference layer pictures used for decoding the current picture for inter-layer prediction may be derived as follows. All slices of the picture may be limited to having the same 'NumActiveRefLayerPics' value.

(4) Otherwise, if the value of the syntax element 'max_one_active_ref_layer_flag' described in the VPS is 1 or the value of the variable 'numRefLayerPics' from Equation 1, Equation 2 or Equation 3 is '1', The number of valid reference layer pictures 'NumActiveRefLayerPics' used for decoding a picture may be set to '1'.

Meanwhile, the variable 'NumDirectRefLayers []' indicating the number of reference layers directly referenced by the current layer calculated from the syntax element described in the VPS extension, and the syntax element 'sub_layers_vps_max_minus1 [i' indicating the maximum time sublayer information of each layer. ] ', The syntax element' max_tid_il_ref_pics_plus1 [i] [j] 'information indicating the maximum temporal sublayer information allowing inter-layer prediction in each layer and the current information for inter-layer prediction using the temporal information' TemporalId 'of the current picture. When deriving a variable 'numRefLayerPics' indicating the number of reference layer pictures that can be used for decoding of a picture, a slice segment header signaling information about a picture used for inter-layer prediction will be described as shown in Table 10 below. Can be.

Table 10

Referring to Table 10, when 'nuh_layer_id' is greater than 0, the syntax element 'all_ref_layers_active_flag' described in the VPS extension is 0, and the value of 'numRefLayerPics' derived from Equation 1 or Equation 2 is greater than '0'. Only information about the inter-layer reference picture (inter-layer_pred_enabled_flag) may be signaled.

Also, the syntax element 'num_inter_layer_ref_pics_minus1' and the syntax element indicating the inter-layer reference picture only when the syntax element 'inter_layer_pred_enabled_flag' is 1 and the value of 'numRefLayerPics' is greater than '1'. 'inter_layer_pred_layer_idc [i]' may be signaled.

Under the above conditions, when the syntax element 'max_one_active_ref_layer_flag' described in the VPS extension is 1, the syntax element 'num_inter_layer_ref_pics_minus1' indicating the number of inter-layer reference pictures may not be signaled.

In the above condition, when the values of 'NumActiveRefLayerPics' and 'numRefLayerPics' are the same, the syntax element 'inter_layer_pred_layer_idc [i]' indicating the inter-layer reference picture may not be signaled.

The syntax element 'inter_layer_pred_layer_idc [i]' may have a value from 0 to 'NumDirectRefLayers-1' of the layer to which the current picture belongs, and when 'inter_layer_pred_layer_idc [i]' is not signaled, Equation 1 or Equation 2 Something like 'refLayerPicIdc [i]' derived from can also be inferred.

In this case, information about a valid reference layer picture used for decoding the current picture may be derived as shown in Equation 6 below. 'Nuh_layer_id' is the 'nuh_layer_id' value of the current picture, and RefLayerId [] [] has the 'layer_id_in_nuh []' value of the reference layer.

Equation 6

Meanwhile, in another example, when 'numRefLayerPics' is derived using Equation 4 or Equation 5, a slice segment header signaling information about a picture used for inter-layer prediction may be described as shown in Table 11 below. .

In Table 11, nuh_layer_id is layer identifier information described in a NAL header of a current decoding target picture, and TemporalId represents time information of a current decoding target picture, that is, sublayer layer information.

Table 11

Referring to Table 11, 'nuh_layer_id' is greater than 0, the syntax element 'all_ref_layers_active_flag' described in the VPS extension is 0, and the value of 'numRefLayerPics [nuh_layer_id] [TemporalId]' derived from

Equation

4 or 5 is Only when greater than '0', information about the inter-layer reference picture (inter-layer_pred_enabled_flag) may be signaled.

In addition, the syntax element 'num_inter_layer_ref_pics_minus1' and the inter-layer reference may be used only when the syntax element 'inter_layer_pred_enabled_flag' is 1 and the value of 'numRefLayerPics [nuh_layer_id] [TemporalId]' is greater than '1'. A syntax element 'inter_layer_pred_layer_idc [i]' indicating a picture may be signaled.

Under the above conditions, when the syntax element 'max_one_active_ref_layer_flag' described in the VPS extension is 1, the syntax element 'num_inter_layer_ref_pics_minus1' indicating the number of inter-layer reference pictures may not be signaled. 'Num_inter_layer_ref_pics_minus1' may have a 'numRefLayerPics [nuh_layer_id] [TemporalId] -1' value derived from Equation 4 or Equation 5 from 0.

In the above condition, when the values of 'NumActiveRefLayerPics' and 'numRefLayerPics [nuh_layer_id] [TemporalId]' are the same, the syntax element 'inter_layer_pred_layer_idc [i]' indicating the inter-layer reference picture may not be signaled.

If the syntax element 'inter_layer_pred_layer_idc [i]' can have a value from 0 to 'numRefLayerPics [nuh_layer_id] [TemporalId]' -1 'of the layer to which the current picture belongs, the index if' inter_layer_pred_layer_idc [i] 'is not signaled Can be inferred to be equal to the value of 'i'.

In this case, information about a valid reference layer picture used for decoding the current picture may be derived as shown in Equation 7 below. 'Nuh_layer_id' is a 'nuh_layer_id' value of the current picture, and RefLayerIdListForTid [] [] is a variable having a 'layer_id_in_nuh []' value of a reference layer derived from Equation 4 or (5).

Equation 7

Meanwhile, in the current draft of SHVC and MV-HEVC standards, information on the target decoding layer (TargetDecLayerIdList) and information on the target output layer (TargetOptLayerIdList) are derived as shown in Equation 8.

Equation 8

Referring to Equation 8, the variable TargetOptLayerSetIdx represents a target output layer set index, and may be converted into a layer set index by the syntax element output_layer_set_idx_minus1 [] described in the VPS extension.

NumLayersInIdList indicates the number of layers included in the layer set, and TargetDecLayerIdList indicates the nuh_layer_id value of the layer included in the layer set and to be decoded. TargetOptLayerIdList indicates the nuh_layer_id value of the layer to be included in the layer set and output.

Only nuh_layer_id of the layer whose output_layer_flag is 1 may be included in TargetOptLayerIdList.

output_layer_flag [] [] is signaled in units of an output layer set in the VPS extension.

However, in Equation 8, since the ouput_layer_flag value is determined in a layer set unit rather than an output layer set unit, a problem in that information of an output layer cannot be normally identified may occur.

In addition, since i does not specify the output_layer_flag [i] [j] for the i th output layer set having a value ranging from 0 to vps_number_layer_sets_minus1, the information on the output layer cannot be properly identified. May occur.

In order to solve the above problem, Equation 8 for deriving information on the target decoding layer (TargetDecLayerIdList) and information on the target output layer (TargetOptLayerIdList) may be changed as shown in Equation 9.

Using Equation 9, an output_layer_flag [i] [j] value for an i th output layer set in which i has a value ranging from 0 to vps_number_layer_sets_minus1 may be specified.

Equation 9

In equation (9), output_layer_flag [i] [j] equals 1 to indicate that the jth layer is within the i-th output layer set, and output_layer_flag [i] [j] equals 0 to j-th within the i-th output layer set. Indicates that the layer is not the target output layer.

If the output layer flag (output_layer_flag) indicating whether the j th layer in the output layer set indicated by the target output layer set index (TargetOptLayerSetIdx) is 1, a target output layer ID list (TargetOptLayerIdList) containing information about the target output layer ) May be configured with the layer_id value of the j-th layer in the layer set indicated by the target decoding layer set index (TargetDecLayerSetIdx).

The target decoding layer set index (TargetDecLayerSetIdx) may be specified from output layer set index information signaled in the video parameter set.

The target decoding layer ID list TargetDecLayerIdList containing information on the target decoding layer may be configured as the layer_id value of the j-th layer in the layer set indicated by the target decoding layer set index (TargetDecLayerSetIdx).

The standard document states that output_layer_flag [i] [j] for the i-th output layer set with a value in the range 0 to vps_number_layer_sets_minus1 can be inferred as shown below (a) and (b): can do.

default_one_target_output_layer_idc may have a value of 0 to 3 as a signal signaled to derive an output layer for the output layer set.

If default_one_target_output_layer_idc is 0, it can indicate that all layers included in the output layer set are outputted, and if the default_one_target_output_layer_idc is 1, only the highest layer among the layers included in the output layer set, that is, the layer with the highest layer id, is output. Can be shown.

In addition, when default_one_target_output_layer_idc is 2, it may represent that only a layer having an output_layer_flag of 1 is output. If default_one_target_output_layer_idc is 3, it may indicate a reserved value that can be used in the future (reserved for furture use).

(a) If the default_one_target_output_layer_idc described in the VPS is 1, a layer having “layer count -1” included in the i-th layer set, that is, if j == NumLayersInIdList [i] -1, output_layer_flag [i] [j] is “ Can be inferred as 1 ”. Otherwise, output_layer_flag [i] [j] may be inferred to be zero. At this time, j has a value of 0 from NumLayerInIdList [i] -1.

(b) If default_one_target_output_layer_idc described in the VPS is 0, output_layer_flag [i] [j] may be inferred to 1. At this time, j has a value of 0 from NumLayerInIdList [i] -1.

The vps_number_layer_sets_minus1 described in the VPS extension is information indicating the number of layer sets described in the VPS. The value of vps_number_sets_minus1 is always greater than 1 because the MV-HEVC / SHVC bitstream includes two or more layer sets. Has a value. Accordingly, it can be specified that vps_number_layer_sets_minus1 encoded by u (10) has a value from 1 to 1023. Alternatively, it may be specified that vps_number_layer_sets_minus1 is replaced with vps_number_layer_sets_minus2 and vps_number_layer_sets_minus2 has a value from 0 to 1022.

In addition, the present invention provides a method for representing a non-reference picture that is not necessary for inter-layer prediction.

For a picture having the highest temporal level (Highest Temproal Id), it may be determined whether the reference picture is a non-reference picture or a reference picture based on the max_tid_il_ref_pics_plus1 [] [] value signaled by the VPS extension.

In the current draft of the SHVC and MV-HEVC standards, a picture having the highest temporal level is separately indicated as a reference picture or a non-reference picture as shown in Equation 10 below.

Equation 10

In Equation 10, currTid represents a temporal level of a currently decoded picture, and max_tid_il_ref_pics_plus1 [iLidx] [jLidx] represents information of a maximum temporal level that allows inter-layer prediction in a current layer and is signaled in a VPS. max_tid_il_ref_pics_plus1 [iLidx] [jLidx] is signaled for each higher layer having a dependency relationship with the current layer.

If the temporal level of the current decoded picture is less than or equal to max_tid_il_ref_pics_plus1 [] [] for the upper layer with the dependency, then the remainingInterLayerReferencesFlag value is set to 1 for the upper layer with dependency with the layer to which the currently decoded picture belongs. Set to.

After determining the remainingInterLayerReferencesFlag value for all upper layers having dependency with the current decoded picture, if the remainingInterLayerReferencesFlag value is 0, the current picture is marked as "non-reference picture".

However, if the current decoded picture is used as a reference layer for any one of the upper layers having a dependency, the currently decoded picture should be marked as a “reference picture”.

Therefore, when remainingInterLayerReferencesFlag, which means “reference picture,” is set to 1 for one of the upper layers having a dependency as shown in Equation 10, the process of determining the remainingInterLayerReferenceFlag value for the remaining upper layers is omitted and the current process is omitted. The decoded picture may not be changed to a “non-reference picture”. In other words, the currently decoded picture can be regarded as a "reference picture".

Equation 11

First, the decoding apparatus may receive information about a reference layer used for decoding a current picture for inter-layer prediction (S410).

Information about such a reference layer includes direct_dependency_flag [i] [j] indicating whether the layer having the j index is a direct reference layer for the layer having the i index, and 'sub_layers_vps_max_minus1 [indicating the maximum temporal sublayer information of each layer. i], 'max_tid_il_ref_pics_plus1 [i] [j] indicating maximum temporal sublayer information allowing inter-layer prediction in each layer, a temporal sublayer identifier of the current picture, and all direct reference layers of the current layer including the current picture. A reference layer picture that can be used for inter-layer prediction specified by a value for the maximum temporal sublayer information of each layer and the maximum temporal sublayer information for allowing inter-layer prediction in each layer, and the same access unit as the current picture. All_ref_la that is present in and indicates whether it is included in the inter-layer reference picture set of the current picture. yers_active_flag, inter_layer_pred_enabled_flag indicating whether inter-layer prediction is used for decoding the current picture, max_one_active_ref_layer_flag indicating whether at most one picture is used for inter-layer prediction for each picture in the coding video sequence, current picture for inter-layer prediction Flag information such as num_inter_layer_ref_pics_minus1 and the like indicating the number of pictures used for decoding may be included.

The decoding apparatus derives the number of valid reference layer pictures used for decoding the current picture based on the information on the reference layer (S420).

All slices belonging to the current picture may have the same number of valid reference layer pictures.

5 is a diagram for describing a method of deriving the number of valid reference layer pictures according to an embodiment of the present invention. A process of deriving the number of valid reference layer pictures according to the present embodiment will now be described with reference to FIG. 5.

First, it is determined whether the layer identifier for identifying the current layer to which the current picture belongs is 0 or the number of layers directly referenced by the current layer to which the current picture belongs is 0 (S510).

As a result, when the layer identifier for identifying the current layer to which the current picture belongs is 0 or the number of layers directly referenced by the current layer to which the current picture belongs is 0, the number of valid reference layer pictures is derived as 0 (S520). .

Otherwise, that is, unless the layer identifier that identifies the current layer to which the current picture belongs is zero or the number of layers directly referenced by the current layer to which the current picture belongs is zero, all of the layers that contain that picture. Among direct reference layer pictures belonging to the direct reference layers, it is determined whether all direct reference pictures existing in the same access unit as the current picture and included in the inter-layer reference picture set of the picture are used for inter-layer prediction (S530). ).

In step S530, the present step may be determined based on flag information such as all_ref_layers_active_flag, and if all_ref_layers_active_flag is 1, the number of valid reference layer pictures indicates the number of reference layer pictures that may be used for decoding the current picture. Can be derived to the number (S540).

The reference layer picture count is a variable indicating the number of reference layers directly referenced by the current layer, maximum temporal sublayer information of each layer, maximum temporal sublayer information allowing interlayer prediction in each layer, and a temporal identifier of the current picture. Derived based on. In this case, among the pictures of the direct reference layers belonging to the current picture, the maximum temporal sublayer information of the reference layer is greater than or equal to the temporal identifier of the current picture, and the maximum temporal sublayer information of the reference layer for the current layer is the current picture. If greater than the temporal identifier of, the pictures of the corresponding reference layer may be regarded as reference layer pictures that can be used for decoding the current picture for inter-layer prediction.

If all_ref_layers_active_flag is 0, it is determined whether inter-layer prediction is not used for decoding of the current picture through inter_layer_pred_enabled_flag (S550). If the inter_layer_pred_enabled_flag is 0, the number of valid reference layer pictures is derived as 0 (S520).

Otherwise, it is determined whether at most one picture is used for inter-layer prediction for each picture in the coded video sequence or whether the number of direct reference layers of the layer to which the current picture belongs is one (S560).

If max_one_active_ref_layer_flag is 1 or the number of direct reference layers of the layer to which the current picture belongs is 1, the number of valid reference layer pictures is derived as 1 (S570).

If all of the above determination conditions are not satisfied, the number of valid reference layer pictures is a value specified by number information (num_inter_layer_ref_pics_minus1) indicating that the information about the reference layer is used to decode the current picture for inter-layer prediction. It may be derived (S580).

4 again, if the number of valid reference layer pictures is derived, the decoding apparatus performs inter-layer prediction based on this (S430).

As described above, according to the present invention, a signaling method for notifying layer information present in an image coded bitstream of a plurality of hierarchical structures including a temporal layer, an inter-layer prediction method, and a method for obtaining a target output layer and an apparatus using the same Is provided.

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

In the decoding method of an image supporting a plurality of layers,

Receiving information about a reference layer used for decoding a current picture for inter-layer prediction;

Deriving a number of valid reference layer pictures used for decoding of the current picture based on the information on the reference layer;

Performing inter-layer prediction based on the number of valid reference layer pictures.
The method of claim 1,

And the number of valid reference layer pictures of all slices belonging to the current picture is the same.
The method of claim 1,

And when the layer identifier for identifying the current layer to which the current picture belongs is 0, the number of valid reference layer pictures is derived as zero.
The method of claim 1,

The number of reference layer pictures that can be used for inter-layer prediction in the same access unit as the current picture is derived as 0.
The method of claim 1,

The layer identifier identifying the current layer to which the current picture belongs is not 0 or the number of reference layer pictures that can be used for inter-layer prediction in the same access unit as the current picture is 0,

Inter-layer prediction specified by values of the maximum temporal sublayer information of each layer and the maximum temporal sublayer information allowing interlayer prediction in each layer among the direct reference layer pictures belonging to all the direct reference layers of the current layer. If a reference layer picture that can be used in the same access unit as the current picture and is included in the inter-layer reference picture set of the current picture,

And the number of valid reference layer pictures is derived from the number of reference layer pictures.
The method of claim 5,

The number of reference layer pictures is a variable indicating the number of reference layers directly referenced by the current layer, maximum temporal sublayer information of each layer, maximum temporal sublayer information allowing inter-layer prediction in each layer, and current picture. Derived based on the temporal identifier of,

Among the pictures of the direct reference layers of the current layer to which the current picture belongs, the maximum temporal sublayer information of the reference layer is greater than or equal to the temporal identifier of the current picture, while allowing the inter-layer prediction in the reference layer for the current layer. When the temporal sublayer information is larger than the temporal identifier of the current picture or when the temporal identifier of the current picture is 0, pictures of the corresponding reference layer may be used as reference layer pictures that may be used for decoding of the current picture for inter-layer prediction. Characterized by what is considered.
The method of claim 1,

If the inter-layer prediction is not used to decode the current picture, the number of valid reference layer pictures is derived as zero.
The method of claim 1,

If at most one picture is used for inter-layer prediction for each picture in a coding video sequence, or if the number of direct reference layers of the layer to which the current picture belongs is one,

And the number of valid reference layer pictures is derived as one.
The method of claim 1,

When the information on the reference layer includes number information indicating the number of pictures used for decoding the current picture for inter-layer prediction,

And the number of valid reference layer pictures is derived to a value specified by the number information.
In the method for receiving video parameter set video usability information (VPS VUI),

Receiving information of preset fixed bits;

And receiving flag information indicating whether a signal indicating the number of video signal information (video_signal_info) and an index of the video signal information is present.
In a method of deriving information on a target layer of an image supporting a plurality of layers,

Receiving output layer set index information for the layer set to be output;

Receiving an output layer flag indicating whether the layer is output;

Specifying a target decoding layer set index based on the output layer set index information;

If the output layer flag for the i th layer in the output layer set indicated by the preset target output layer set index is 1, the id of the target output layer is the layer_id value of the i th layer in the layer set indicated by the target decoding layer set index. Constructing a list.
The method of claim 11,

And constructing an id list of a target decoding layer using the layer_id value of the i th layer in the layer set indicated by the target decoding layer set index.
The method of claim 11,

When information indicating that all the layers included in the output layer set including the layers to be outputted are output,

And an output layer flag for all layers included in the output layer set is inferred to 1.
The method of claim 11,

When information indicating that only the highest layer having the highest layer ID among the layers included in the output layer set including the layers to be output is received is received,

The output layer flag for the top layer is inferred to 1,

And an output layer flag for a layer other than the highest layer among layers included in the output layer set is inferred to be zero.
In the image decoding apparatus supporting a plurality of layers,

Derive the number of valid reference layer pictures used for decoding the current picture based on the reference layer used for decoding the current picture for received inter-layer prediction, and inter-layer based on the number of valid reference layer pictures And a decoding unit for performing prediction.
The method of claim 15,

When the layer identifier for identifying the current layer to which the current picture belongs is 0 or the number of layers directly referenced by the current layer to which the current picture belongs is 0, the number of valid reference layer pictures is derived as 0. Device.
The method of claim 15,

And when the number of reference pictures that can be used for inter-layer prediction in the same access unit as the current picture is zero, the number of valid reference layer pictures is derived as zero.
The method of claim 15,

The layer identifier identifying the current layer to which the current picture belongs is not 0 or the number of reference layer pictures that can be used for inter-layer prediction in the same access unit as the current picture is 0,

Among the direct reference layer pictures belonging to all direct reference layers of the current layer, inter-layer prediction specified by a value for the maximum temporal sublayer information of each layer and the maximum temporal sublayer information allowing interlayer prediction in each layer. If a reference layer picture that can be used exists in the same access unit as the current picture and is included in the inter-layer reference picture set of the current picture,

And the number of valid reference layer pictures is derived from the number of reference layer pictures.
The method of claim 15,

And if the inter-layer prediction is not used to decode the current picture, the number of valid reference layer pictures is derived as zero.
The method of claim 15,

If at most one picture is used for inter-layer prediction for each picture in a coding video sequence, or if the number of direct reference layers of the layer to which the current picture belongs is one,

And the number of valid reference layer pictures is derived as one.