KR102246634B1 - Video encoding and decoding method and apparatus using the same - Google Patents

Abstract

The method for decoding an image supporting a plurality of layers according to the present invention includes the steps of initializing parameters required for decoding; Calculating a POC that is an identifier of a picture to be decoded; Constructing a reference picture set and displaying a reference picture shape for inter prediction of the target decoded picture; Determining whether to output the target decoded picture; And performing motion prediction and motion compensation for the target decoded picture using a reference picture in a reference picture list generated based on the reference picture set, and calculating the POC comprises a base layer of the same access unit When the picture of is an IDR picture, the POC of the picture to be decoded is set to 0, and when the picture of the base layer is a BLA picture or a CRA picture, the MSB of the picture to be decoded may be set to 0.

Description

Video encoding/decoding method and apparatus using the same {VIDEO ENCODING AND DECODING METHOD AND APPARATUS USING THE SAME}

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

Recently, as broadcasting services having high definition (HD) resolution are expanded not only domestically but also globally, many users are getting accustomed to high-resolution and high-definition images, and accordingly, many organizations are spurring the development of next-generation video devices. In addition, as interest in UHD (Ultra High Definition) having a resolution of 4 times or more than HDTV in addition to HDTV is increasing, a compression technology for higher resolution and high-definition images is required.

For image compression, an inter prediction technology that temporally predicts a pixel value included in a current picture from a previous and/or subsequent picture, and predicts a pixel value included in the current picture using pixel information in the current picture. An intra prediction technique, an entropy encoding technique in which a short code is assigned to a symbol with a high frequency of appearance, and a long code is assigned to a symbol with a low frequency of occurrence, may be used.

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

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

Specifically, in an embodiment of the present invention, an IRAP (intra random access point) picture and a non-IRAP picture (non-intra random access point picture) exist within an access unit (AU) at a random access point, or only an IRAP picture exists. However, when two or more NAL unit types are used, a method of setting POC values of pictures in a corresponding AU and an apparatus using the same are provided.

According to an embodiment of the present invention, when decoding a bitstream from an arbitrary point in time, even when a picture included in the corresponding point in time includes a picture that cannot be accessed randomly, the POC value in the same AU is set equally to manage pictures in the decoded picture buffer. It provides a method for facilitating and an apparatus using the same.

According to an embodiment of the present invention, a method for decoding an image supporting a plurality of layers includes: initializing parameters necessary for decoding; Calculating a POC that is an identifier of a picture to be decoded; Constructing a reference picture set and displaying a reference picture shape for inter prediction of the target decoded picture; Generating a virtual reference picture for a picture included in the reference picture set but not in a decoded picture buffer; Determining whether to output the target decoded picture; It may include performing motion prediction and motion compensation for the target decoded picture by using a reference picture in a reference picture list generated based on the reference picture set, and calculating the POC comprises: When the picture of the base layer is an IDR picture, the POC of the picture to be decoded is set to 0, and when the picture of the base layer is a BLA picture or a CRA picture, the MSB of the picture to be decoded may be set to 0.

According to an embodiment of the present invention, a method for enabling decoding from an arbitrary point in a bitstream and an apparatus using the same are provided.

Specifically, according to an embodiment of the present invention, an IRAP (intra random access point) picture and a non-IRAP picture (non-intra random access point picture) exist in an access unit (AU) at a random access point, or an IRAP picture However, when there are two or more NAL unit types, a method of setting POC values of pictures in a corresponding AU and an apparatus using the same are provided.

According to an embodiment of the present invention, when decoding a bitstream from an arbitrary point in time, a decoded picture buffer by setting the same POC value in the same AU even when a picture included in the corresponding view includes a picture that cannot be accessed randomly. A method for facilitating management of my pictures and an apparatus using the same are provided.

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 showing 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 an embodiment of the present invention.
5 is a diagram for explaining calculating a POC of a picture 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 specification, when it is determined that a detailed description of a related known configuration or function may obscure the subject matter of the present specification, a detailed description thereof will be omitted.

When a component is referred to as being “connected” or “connected” to another component, it is understood that it may be directly connected or connected to the other component, but other components may exist in the middle. It should be. In addition, the description of "including" a specific configuration in the present invention does not exclude configurations other than the corresponding configuration, and means that additional configurations may be included in the scope of the implementation of the present invention or the scope of the technical idea of the present invention.

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

In addition, the constituent units shown in the embodiments of the present invention are shown independently to represent different characteristic functions, and does not mean that each constituent unit is formed of separate hardware or a single software constituent unit. That is, each constituent part is listed and included as a respective constituent part for convenience of explanation, and at least two of the constituent parts are combined to form one constituent part, or one constituent part is divided into a plurality of constituent parts to perform a function Integrated embodiments and separate embodiments of the components are also included in the scope of the present invention as long as they do not depart from the essence of the present invention.

In addition, some of the components are not essential components that perform essential functions in the present invention, but may be optional components only for improving performance. The present invention can be implemented by including only components essential to implement the essence of the present invention excluding components used for performance improvement, and a structure including only essential components excluding optional components used for performance improvement 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 a general video encoding/decoding method or apparatus that does not provide scalability, and the block diagram of FIG. 1 is scalable. It shows an embodiment of an image encoding apparatus that can be the basis of a video encoding apparatus.

Referring to FIG. 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, and a transform unit 130. , 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 encode an input image in an intra mode or an inter mode 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. After generating a prediction block for an input block of an input image, the image encoding apparatus 100 may encode a difference between the input block and the prediction block.

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

In the case of the inter mode, the motion prediction unit 111 may find a region in the reference image stored in the reference image buffer 190 that best matches the input block in the motion prediction process to obtain a motion vector. The motion compensation unit 112 may generate a prediction block by performing motion compensation using a motion vector and a reference image stored in the reference image buffer 190.

The subtractor 125 may generate a residual block based on a difference between the input block and the generated prediction block. The transform unit 130 may transform the residual block and output a transform coefficient. In addition, the quantization unit 140 may quantize the input transform coefficient according to a quantization parameter and output a quantized coefficient.

The entropy encoding unit 150 entropy-encodes a symbol according to a probability distribution based on values calculated by the quantization unit 140 or an encoding parameter value calculated during an encoding process to generate a bit stream. Can be printed. The entropy encoding method is a method of receiving symbols having various values, removing statistical redundancy, and expressing them as a sequence of decodeable binary numbers.

Here, the symbol means a syntax element to be encoded/decoded, a coding parameter, a value of a residual signal, and the like. An encoding parameter is a parameter necessary for encoding and decoding, and may include information that can be inferred during encoding or decoding as well as information encoded by the encoding device and transmitted to the decoding device, such as a syntax element, and encodes or decodes an image. It means the information you need when doing it. Encoding parameters include values such as intra/inter prediction mode, motion/motion vector, reference image index, coded block pattern, residual signal presence, transform coefficient, quantized transform coefficient, quantization parameter, block size, block division information, etc., or Can include statistics. In addition, the residual signal may mean the difference between the original signal and the predicted signal, and a signal in which the difference between the original signal and the predicted signal is transformed, or the difference between the original signal and the predicted signal is transformed and quantized. It can also mean. The residual signal may be referred to as a residual block in block units.

When entropy coding 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 the symbol, so that the size of the bit string for the symbols to be encoded is reduced. Can be reduced. Accordingly, compression performance of image encoding may be improved through entropy encoding.

For entropy encoding, encoding 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 encoding unit 150 may store a table for performing entropy encoding such as a variable length encoding (VLC) table, and the entropy encoding unit 150 may store the stored variable length encoding Entropy coding can 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 coefficient may be inverse quantized by the inverse quantization unit 160 and may be inversely transformed by the inverse transform unit 170. The inverse quantized and inverse transformed coefficients are added to the prediction block through the adder 175, and a reconstructed block may be 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) to a restoration block or a 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 in FIG. 1, the scalable video encoding/decoding method or apparatus may be implemented by a general video encoding/decoding method or apparatus that does not provide scalability, and the block diagram of FIG. 2 is a scalable video decoding method. It shows an embodiment of an image decoding apparatus that can be the basis of the apparatus.

Referring to FIG. 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, and a filter unit. 260 and a reference image buffer 270.

The image decoding apparatus 200 may receive a bitstream output from the encoding apparatus, perform decoding in an intra mode or an inter mode, and output a reconstructed image, that is, a reconstructed image. In the case of the intra mode, the switch may be switched to intra, and in the case of 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 an input 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 string of binary numbers. The entropy decoding method is similar to the entropy encoding method described above.

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

In the case of the intra mode, the intra prediction unit 240 may generate a prediction block by performing spatial prediction using pixel values of an already coded block around the current block. In the case of 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 image buffer 270.

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

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

In addition, the image decoding apparatus 200 may further include a parsing unit (not shown) for parsing information related to the encoded image included in the bitstream. The parsing unit may include an entropy decoding unit 210 or may be included in the entropy decoding unit 210. This parsing unit may also be implemented as a component of the decoding unit.

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

A transmission medium is required to transmit image data, and its performance is different for each transmission medium according to various network environments. A scalable video coding method may be provided for application to such various transmission media or network environments.

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

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

Here, the layer is an image and a bit divided based on spatial (e.g., image size), temporal (e.g., encoding order, image output order, frame rate), quality, complexity, etc. It means a set of streams (bitstream). In addition, the base layer may refer to a lower layer, a reference layer or a base layer, and an enhancement layer may refer to an upper layer and an enhancement layer. Also, multiple layers may have dependencies on each other.

Referring to FIG. 3, for example, the base layer may be defined as SD (standard definition), a frame rate of 15 Hz, and a 1 Mbps bit rate, and the first enhancement layer is a high definition (HD), a frame rate of 30 Hz, and a bit rate of 3.9 Mbps. 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 one embodiment and may be differently determined as necessary. Also, the number of layers to be used is not limited to this embodiment and may be determined differently according to circumstances.

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

In the case of encoding and decoding video that supports multiple layers in the bitstream, that is, scalable coding, there is a strong correlation between the multiple layers. Redundant elements can be removed and video encoding performance can be improved. Hereinafter, prediction of a current layer to be predicted using information of another layer is referred to as inter-layer prediction. The scalable video coding has the same meaning as the scalable video coding from the viewpoint of encoding and the scalable video decoding from the viewpoint of decoding.

The plurality of layers may have at least one of a resolution, a frame rate, and a color format different from each other, and up-sampling or down-sampling of a layer may be performed to adjust a resolution during inter-layer prediction.

The following points may be considered in order to describe a random approach in scalable video coding (SVC).

The bitstream may support at least one or more scalability, for example, spatial, image quality, and view scalability, and a video having at least one hierarchical structure as described above may be encoded/decoded so that random access is possible.

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

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

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

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

On the other hand, only when all pictures of a layer corresponding to a random access view are encoded in a manner that allows random access, decoding of the bitstream from the corresponding view is possible. In other words, if a picture that cannot be randomly accessed is included among the layers corresponding to the random access point, the POC value in the same access unit is not the same, making it difficult to manage the picture in the decoded picture buffer (DPB). Problems can arise.

In order to solve this problem, the present invention is to decode a bitstream from an arbitrary point in time, and even when a picture included in the corresponding point of time contains a picture that cannot be accessed randomly, the POC value in the same access unit is set equally to facilitate DPB content. It makes it possible to manage one picture. By setting the same POC value, the bitstream can be decoded from a corresponding random access point.

4 is a control flowchart illustrating a video decoding method according to an embodiment of the present invention. The content of the invention described with reference to FIG. 4 can be applied equally to a method of encoding an image as well as a method of decoding an image.

First, the apparatus for decoding an image may initialize parameters necessary for decoding (S410).

In the case of decoding a bitstream from a random access point, parameters necessary for decoding can be initialized in the following order.

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

When the current sub/decoding target picture is an IRAP picture and a picture of a base layer (nuh_layer_id = 0) included in an AU at a random access point, the flag values of all possible upper layers may be initialized to '0'.

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

The POC, which is the identifier of the picture to be currently encoded/decoded, is calculated so that the value increases according to the output order (S420).

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

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

In the case of a non-IRAP picture, POC_MSB is a POC_MSB (hereinafter referred to as prevPOCMSB), POC_LSB (hereinafter referred to as prevPOCLSB) of a picture close to the current picture among pictures whose temporal_id indicating an identifier of a temporal sublayer that has been previously encoded/decoded is '0'. ) And the POC_LSB value of the picture to be currently encoded/decoded.

The POC value of the IDR picture can always be assumed to be '0', and when the CRA picture is the first picture in the bitstream or in the case of a BLA picture, the POC_MSB value of the picture is assumed to be '0', and the POC_LSB value is assumed to be '0' in the slice header. Can be signaled. When the CRA picture is not the first picture in the bitstream, the POC value may be calculated in the same manner as the non-IRAP picture.

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

When an IRAP picture and a non-IRAP picture exist in the same AU at the same time, or only an IRAP picture exists, but two or more NAL unit types of IRAP pictures are present, the POC value may be the same. To this end, flag information such as poc_reset_flag may be signaled in the slice header, and the decoding apparatus may reset the POC value of the picture to '0' or the POC_MSB value to '0' when the poc_reset_flag value is '1'.

5 is a diagram for explaining calculating a POC of a picture according to the present invention. FIG. 5 is a diagram for explaining step S420, and shows an embodiment in which a base layer is an IRAP picture and upper layers are encoded as non-IRAP pictures in an AU (AU A) that is a randomly accessible view. Calculation of the POC of a picture can be described by dividing into the following two cases.

Case 1

When a bitstream including AUs previously coded because the corresponding AU is not switched, that is, is not used as a random access point, is decoded, the decoding process of pictures included in the corresponding AU may proceed in the following order.

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

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

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

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

(b) For a picture including a slice with a poc_reset_flag of '1', when pictures exist in the DPB, the POC values of all the pictures in the DPB may be reduced by a value of'POC1'.

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

Case 2

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

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

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

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

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

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

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

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

(a-4) When an IDR picture exists in the base layer of the same AU, the POC value of the current decoding target picture may not be calculated and may be set to '0'.

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

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

Next, the apparatus for decoding an image configures a reference picture set and performs reference picture marking for inter-screen prediction of the current encoding/decoding target picture (S430).

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

(1) In the case of short-term reference pictures, the POC values of short-term reference pictures are calculated using the delta_POC value representing each short-term reference picture signaled in the corresponding slice header and the POC value of the current picture,'POC1'. do.

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

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

For a long-term reference picture, only POC_LSB is signaled by default, and a long-term POC is identified with only the signaled POC_LSB value. However, if a reference picture having the same POC as the POC_LSB of the corresponding long-term reference picture exists among the plurality of reference pictures, a value for calculating the POC_MSB value (delta_poc_msb_cycle_lt) is additionally signaled, and through this, the POC of each reference picture can be identified. To be able to.

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

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

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

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

For a long-term reference picture, only POC_LSB is signaled by default, and a long-term POC is identified with only the signaled POC_LSB value. However, if a reference picture having the same POC as the POC_LSB of the corresponding long-term reference picture exists among the plurality of reference pictures, a value for calculating the POC_MSB value (delta_poc_msb_cycle_lt) is additionally signaled, and through this, the POC of each reference picture can be identified. To be able to.

As described above, if poc_reset_flag is '1', the POC value or POC_LSB value of reference pictures signaled in the slice header of the picture including the slice with poc_reset_flag '1' coincides with decreasing the POC value of pictures existing in the DPB. It can be adjusted using the'POC1' value of the current picture.

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

The video decoding apparatus may generate a virtual reference picture for a picture that is included in the reference picture set, but does not exist in the DPB (S440).

Pictures that do not exist in the current DPB among the short-term reference pictures and long-term reference pictures configured in step S430 to refer to the current picture or to refer to pictures that are encoded/decoded after the current picture may be virtually generated and stored in the DPB. .

The POC values of the generated virtual pictures have the POC values of each reference picture calculated in step S430. The PicOutputFlag value indicating whether the virtual reference picture is output from the DPB is set to '0', and the virtual reference picture generated thereby is not output.

Next, the video decoding apparatus may determine whether to output the current encoding/decoding target picture (S450).

If the corresponding AU is not switched, that is, is not used as a random access point, and thus the encoded bitstream including previously encoded AUs is decoded as it is, all pictures included in the corresponding AU can be normally decoded. Therefore, the PicOutputFlag of the original output layers is set to '1'.

On the other hand, when the corresponding AU is switched and used as a random access point, for example, when a picture of the base layer (layer 0) is an IRAP picture and is the first picture of an encoded bitstream, or a BLA picture, that is, , When the corresponding AU is decoded as the first AU of the bitstream, whether to output is determined as follows.

(1) Among pictures included in the AU, when only the base layer is an IRAP picture and the picture of the first upper layer (Layer 1) is a non-IRAP picture, the PicOutputFlag of the decoded picture of the base layer is set to '1', and PicOutputFlag of decoded pictures of the remaining layers may be set to '0'.

(2) If the base layer and the first upper layer (Layer 1) of the pictures included in the AU are IRAP pictures and the second upper layer (Layer 2) is a non-IRAP picture, the decoded picture of the first upper layer PicOutputFlag of is set to '1', and if the base layer is an output layer, the PicOutputFlag of the decoded picture of the base layer is also set to '1'.

That is, when the IRAP pictures from the base layer to the nth layer are composed of IRAP pictures from the base layer to the n-th layer, the video decoding apparatus determines the PicOutputFlag of the decoded pictures corresponding to the output layers when the originally intended layer is included in the base layer to the n-th layer. It is set to '1', and if an output layer originally intended to be output is included in the n+1th layer or the uppermost layer, the PicOutputFlag of the decoded picture of the nth layer may be set to '1'.

When it is determined whether to output a picture, the image decoding apparatus performs motion prediction and motion compensation on the current encoding/decoding target image by using the reference picture in the reference picture list (S460).

In this step, motion prediction and motion compensation for a current encoding/decoding target image may be performed using a reference picture in a reference picture list as a conventional inter prediction method.

When inter prediction is performed using a reference picture, a parameter required for decoding may be reset (S470).

The video decoding apparatus may set FirstPicInLayerDecodedFlag[i] to 1 when FirstPicInLayerDecodedFlag[i] of the layer including the current sub/decoding target picture, for example, nuh_layer_id = i is 0.

As described above, according to the present invention, an IRAP (intra random access point) picture and a non-IRAP picture (non-intra random access point picture) or only an IRAP picture exist in the access unit (AU) at the random access point, A method of setting POC values of pictures in a corresponding AU when two or more NAL unit types are used and an apparatus using the same are provided.

In the above-described embodiment, 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 steps, and certain steps may occur in a different order or concurrently with those described above. have. In addition, those of ordinary skill in the art understand that the steps shown in the flowchart are not exclusive, other steps are included, or one or more steps in the flowchart may be deleted without affecting the scope of the present invention. You can understand.

The above-described embodiments include examples of various aspects. It is not possible to describe all possible combinations for representing the various aspects, but one of ordinary skill in the art will recognize that other combinations are possible. Accordingly, the present invention will be said to include all other replacements, modifications and changes falling within the scope of the following claims.

100: image encoding device 111: motion prediction unit
112: motion compensation unit 120: intra prediction unit
115: switch 125: subtractor
130: transform unit 140: quantization unit
150: entropy encoding unit 160: inverse quantization unit
170: inverse transform unit 180: filter unit

Claims (7)

In a video decoding method supporting a plurality of layers,
Initializing parameters necessary for decoding;
Calculating a picture of count (POC) that is an identifier of a current picture;
Generating a reference picture list for inter prediction of the current picture;
Comprising the step of performing inter prediction for the current picture by using a reference picture in the reference picture list,
In the calculating of the POC, when a picture of a base layer of the same access unit is an instantaneous decoding refresh (IDR) picture and at least one non-IDR picture other than the IDR picture exists in the same access unit, the current picture is included. And POCs of all pictures of the same access unit are set to 0.
The method of claim 1,
The step of calculating the POC,
When the picture of the base layer is a broken link access (BLA) picture or a first clean random access (CRA) picture of a bitstream, the MSB (Most Significant Bit) of the current picture is set to 0. Decryption method.
The method of claim 1,
Initializing the parameters required for the decoding,
When the current picture is an intra random access point (IRAP), a flag indicating that the picture is the first picture in the layer is set to a predefined value.
The method of claim 3,
The predetermined value is a value indicating that the picture is the first picture of a layer.
The method of claim 3,
When the current picture is an intra random access point (IRAP), the flags of all layers are set to a predefined value.
The method of claim 1,
After the step of performing inter prediction on the current picture by using a reference picture in the reference picture list, it is determined whether to output the current picture.
The method of claim 1,
After the step of performing inter prediction on the current picture by using a reference picture in the reference picture list, a parameter necessary for the decoding is reset.

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