KR20190113655A - Method and apparatus for processing video signal - Google Patents

Abstract

A method for decoding an image according to the present invention may include: a step of reconstructing a 360-degree video; a step of decoding view path-related information from a bitstream; and a step of setting a view port corresponding to the view path in the 360-degree video. At this time, the view path-related information may include information about the number of view paths. It is possible to improve the encoding/decoding efficiency of the 360-degree video.

Description

Method and apparatus for processing video signal {METHOD AND APPARATUS FOR PROCESSING VIDEO SIGNAL}

The present invention relates to a video signal processing method and apparatus.

Recently, the demand for high resolution and high quality images such as high definition (HD) and ultra high definition (UHD) images is increasing in various applications. As the video data becomes higher resolution and higher quality, the amount of data increases relative to the existing video data. Therefore, when the video data is transmitted or stored using a medium such as a conventional wired / wireless broadband line, The storage cost will increase. High efficiency image compression techniques can be used to solve these problems caused by high resolution and high quality image data.

An inter-screen prediction technique for predicting pixel values included in the current picture from a picture before or after the current picture using an image compression technique, an intra prediction technique for predicting pixel values included in a current picture using pixel information in the current picture, Various techniques exist, such as an entropy encoding technique for allocating a short code to a high frequency of appearance and a long code to a low frequency of appearance, and the image data can be effectively compressed and transmitted or stored.

Meanwhile, as the demand for high resolution video increases, the demand for stereoscopic video content also increases as a new video service. There is a discussion about a video compression technology for effectively providing high resolution and ultra high resolution stereoscopic image contents.

An object of the present invention is to encode / decode viewport information to improve encoding / decoding efficiency of 360 degree video.

An object of the present invention is to enable a plurality of viewports to be set for 360 degree video.

An object of the present invention is to improve the encoding / decoding efficiency of 360-degree video by encoding / decoding the rotation information of the viewport.

It is an object of the present invention to be able to output a view path on video.

The technical problems to be achieved in the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned above will be clearly understood by those skilled in the art from the following description. Could be.

The image decoding method and apparatus according to the present invention may reconstruct a 360 degree video, decode view path related information from a bitstream, and set a view port corresponding to the view path in the 360 degree video. In this case, the view path related information may include information about the number of view paths.

The image encoding method and apparatus according to the present invention may set a view port corresponding to a view path in 360 degree video, and encode the 360 degree video and the view path related information. In this case, the view path related information may include information about the number of view paths.

In the image decoding / encoding method and apparatus according to the present invention, the position and range of the view path may be set to be the same as the position and range of the view port.

In the image decoding / encoding method and apparatus according to the present invention, the position of the view port may be determined based on information representing a yaw center position, information representing a pitch center position, and information representing a roll center position.

In the image decoding / encoding method and apparatus according to the present invention, the range of the view port may be determined based on information representing a yaw range and information representing a pitch range.

In the image decoding / encoding method and apparatus according to the present invention, the view path may be mapped to a plurality of view ports.

The features briefly summarized above with respect to the present invention are merely exemplary aspects of the detailed description of the invention that follows, and do not limit the scope of the invention.

According to the present invention, there is an advantage in that the view port information is encoded / decoded to improve the encoding / decoding efficiency of the 360 degree video.

According to the present invention, it is possible to set a plurality of view ports for the 360-degree video, there is an advantage that can provide user convenience when playing 360-degree video.

According to the present invention, there is an advantage in that the rotation information of the viewport is encoded / decoded to improve the encoding / decoding efficiency of the 360 degree video.

According to the present invention, by outputting a view path to a 360 degree video, there is an advantage that can provide user convenience when playing a 360 degree video.

The effects obtainable in the present invention are not limited to the above-mentioned effects, and other effects not mentioned above may be clearly understood by those skilled in the art from the following description. will be.

1 is a block diagram illustrating an image encoding apparatus according to an embodiment of the present invention.
2 is a block diagram illustrating an image decoding apparatus according to an embodiment of the present invention.
3 is a diagram illustrating a partition mode that can be applied to a coding block when the coding block is encoded by inter-screen prediction.
4 to 6 are diagrams illustrating a camera apparatus for generating a panoramic image.
7 is a block diagram of a 360 degree video data generating device and a 360 degree video playing device.
8 is a flowchart illustrating operations of a 360 degree video data generating device and a 360 degree video playing device.
9 illustrates a 2D projection method using an isotonic method.
10 illustrates a 2D projection method using a cube projection technique.
11 illustrates a 2D projection method using a icosahedron projection technique.
12 illustrates a 2D projection method using an octahedron projection technique.
13 illustrates a 2D projection method using a truncated pyramid projection technique.
14 is a diagram for explaining the conversion between the face 2D coordinates and the three-dimensional coordinates.
15 is a diagram for explaining a viewport mode.
16 is a diagram illustrating an example in which a position and a size of a view port are specified.
17 is a diagram illustrating syntax associated with a viewport encoded in a bitstream.
18 is a diagram illustrating an example in which a syntax indicating the number of view ports is encoded.
19 is a diagram illustrating an example of deriving current view port information using a reference view port.
20 is a diagram illustrating an example in which information related to rotation of a sphere is encoded.
21 illustrates the concept of 3DoF, 3DoF +, and 6DoF images.
22 is a diagram illustrating an example of overlaying a view path on a video.
FIG. 23 is a diagram for describing syntax related to route information. FIG.

As the invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description. However, this is not intended to limit the present invention to specific embodiments, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention. In describing the drawings, similar reference numerals are used for similar elements.

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. The term and / or includes a combination of a plurality of related items or any item of a plurality of related items.

When a component is referred to as being "connected" or "connected" to another component, it may be directly connected to or connected to that other component, but it may be understood that other components may exist in the middle. Should be. On the other hand, when a component is referred to as being "directly connected" or "directly connected" to another component, it should be understood that there is no other component in between.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprise" or "have" are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, components, or a combination thereof.

Hereinafter, with reference to the accompanying drawings, it will be described in detail a preferred embodiment of the present invention. Hereinafter, the same reference numerals are used for the same components in the drawings, and duplicate descriptions of the same components are omitted.

1 is a block diagram illustrating an image encoding apparatus according to an embodiment of the present invention.

Referring to FIG. 1, the image encoding apparatus 100 may include a picture splitter 110, a predictor 120 and 125, a transformer 130, a quantizer 135, a realigner 160, and an entropy encoder. 165, an inverse quantizer 140, an inverse transformer 145, a filter 150, and a memory 155.

Each of the components shown in FIG. 1 is independently illustrated to represent different characteristic functions in the image encoding apparatus, and does not mean that each of the components 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.

The picture dividing unit 110 may divide the input picture into at least one processing unit. In this case, the processing unit may be a prediction unit (PU), a transform unit (TU), or a coding unit (CU). The picture dividing unit 110 divides one picture into a combination of a plurality of coding units, prediction units, and transformation units, and combines one coding unit, prediction unit, and transformation unit on a predetermined basis (eg, a cost function). You can select to encode the picture.

For example, one picture may be divided into a plurality of coding units. In order to split a coding unit in a picture, a recursive tree structure such as a quad tree structure may be used, and coding is divided into other coding units by using one image or a largest coding unit as a root. The unit may be split with as many child nodes as the number of split coding units. Coding units that are no longer split according to certain restrictions become leaf nodes. That is, when it is assumed that only square division is possible for one coding unit, one coding unit may be split into at most four other coding units.

Hereinafter, in an embodiment of the present invention, a coding unit may be used as a unit for encoding or may be used as a unit for decoding.

The prediction unit may be split in the form of at least one square or rectangle having the same size in one coding unit, or the prediction unit of any one of the prediction units split in one coding unit is different from one another. It may be divided to have a different shape and / or size than the unit.

When generating a prediction unit that performs intra prediction based on the coding unit, the intra prediction may be performed without splitting into a plurality of prediction units NxN when the prediction unit is not the minimum coding unit.

The predictors 120 and 125 may include an inter predictor 120 that performs inter prediction and an intra predictor 125 that performs intra prediction. Whether to use inter prediction or intra prediction on the prediction unit may be determined, and specific information (eg, an intra prediction mode, a motion vector, a reference picture, etc.) according to each prediction method may be determined. In this case, the processing unit in which the prediction is performed may differ from the processing unit in which the prediction method and the details are determined. For example, the method of prediction and the prediction mode may be determined in the prediction unit, and the prediction may be performed in the transform unit. The residual value (residual block) between the generated prediction block and the original block may be input to the transformer 130. In addition, prediction mode information and motion vector information used for prediction may be encoded by the entropy encoder 165 together with the residual value and transmitted to the decoder. When a specific encoding mode is used, the original block may be encoded as it is and transmitted to the decoder without generating the prediction block through the prediction units 120 and 125.

The inter prediction unit 120 may predict the prediction unit based on the information of at least one of the previous picture or the next picture of the current picture. In some cases, the inter prediction unit 120 may predict the prediction unit based on the information of the partial region in which the encoding is completed in the current picture. You can also predict units. The inter predictor 120 may include a reference picture interpolator, a motion predictor, and a motion compensator.

The reference picture interpolator may receive reference picture information from the memory 155 and generate pixel information of an integer pixel or less in the reference picture. In the case of luminance pixels, a DCT based 8-tap interpolation filter having different filter coefficients may be used to generate pixel information of integer pixels or less in units of 1/4 pixels. In the case of a chrominance signal, a DCT-based interpolation filter having different filter coefficients may be used to generate pixel information of an integer pixel or less in units of 1/8 pixels.

The motion predictor may perform motion prediction based on the reference picture interpolated by the reference picture interpolator. As a method for calculating a motion vector, various methods such as full search-based block matching algorithm (FBMA), three step search (TSS), and new three-step search algorithm (NTS) may be used. The motion vector may have a motion vector value of 1/2 or 1/4 pixel units based on the interpolated pixels. The motion prediction unit may predict the current prediction unit by using a different motion prediction method. As the motion prediction method, various methods such as a skip method, a merge method, an advanced motion vector prediction (AMVP) method, an intra block copy method, and the like may be used.

The intra predictor 125 may generate a prediction unit based on reference pixel information around the current block, which is pixel information in the current picture. If the neighboring block of the current prediction unit is a block that has performed inter prediction, and the reference pixel is a pixel that has performed inter prediction, the reference pixel of the block that has performed intra prediction around the reference pixel included in the block where the inter prediction has been performed Can be used as a substitute for information. That is, when the reference pixel is not available, the unavailable reference pixel information may be replaced with at least one reference pixel among the available reference pixels.

In intra prediction, a prediction mode may have a directional prediction mode using reference pixel information according to a prediction direction, and a non-directional mode using no directional information when performing prediction. The mode for predicting the luminance information and the mode for predicting the color difference information may be different, and the intra prediction mode information or the predicted luminance signal information used for predicting the luminance information may be utilized to predict the color difference information.

When performing intra prediction, if the size of the prediction unit and the size of the transform unit are the same, the intra prediction on the prediction unit is performed based on the pixels on the left of the prediction unit, the pixels on the upper left, and the pixels on the top. Can be performed. However, when performing intra prediction, if the size of the prediction unit is different from that of the transform unit, intra prediction may be performed using a reference pixel based on the transform unit. In addition, intra prediction using NxN division may be used only for a minimum coding unit.

The intra prediction method may generate a prediction block after applying an adaptive intra smoothing (AIS) filter to a reference pixel according to a prediction mode. The type of AIS filter applied to the reference pixel may be different. In order to perform the intra prediction method, the intra prediction mode of the current prediction unit may be predicted from the intra prediction mode of the prediction unit existing around the current prediction unit. When the prediction mode of the current prediction unit is predicted by using the mode information predicted from the neighboring prediction unit, if the intra prediction mode of the current prediction unit and the neighboring prediction unit is the same, the current prediction unit and the neighboring prediction unit using the predetermined flag information If the prediction modes of the current prediction unit and the neighboring prediction unit are different, entropy encoding may be performed to encode the prediction mode information of the current block.

Also, a residual block may include a prediction unit performing prediction based on the prediction units generated by the prediction units 120 and 125 and residual information including residual information that is a difference from an original block of the prediction unit. The generated residual block may be input to the transformer 130.

The transform unit 130 converts the residual block including residual information of the original block and the prediction unit generated by the prediction units 120 and 125 into a discrete cosine transform (DCT), a discrete sine transform (DST), and a KLT. You can convert using the same conversion method. Whether to apply DCT, DST, or KLT to transform the residual block may be determined based on intra prediction mode information of the prediction unit used to generate the residual block.

The quantization unit 135 may quantize the values converted by the transformer 130 into the frequency domain. The quantization coefficient may change depending on the block or the importance of the image. The value calculated by the quantization unit 135 may be provided to the inverse quantization unit 140 and the reordering unit 160.

The reordering unit 160 may reorder coefficient values with respect to the quantized residual value.

The reordering unit 160 may change the two-dimensional block shape coefficients into a one-dimensional vector form through a coefficient scanning method. For example, the reordering unit 160 may scan from DC coefficients to coefficients in the high frequency region by using a Zig-Zag scan method and change them into one-dimensional vectors. Depending on the size of the transform unit and the intra prediction mode, a vertical scan that scans two-dimensional block shape coefficients in a column direction instead of a zig-zag scan may be used, and a horizontal scan that scans two-dimensional block shape coefficients in a row direction. That is, according to the size of the transform unit and the intra prediction mode, it is possible to determine which scan method among the zig-zag scan, the vertical scan, and the horizontal scan is used.

The entropy encoder 165 may perform entropy encoding based on the values calculated by the reordering unit 160. Entropy encoding may use various encoding methods such as, for example, Exponential Golomb, Context-Adaptive Variable Length Coding (CAVLC), and Context-Adaptive Binary Arithmetic Coding (CABAC).

The entropy encoder 165 receives residual value coefficient information, block type information, prediction mode information, partition unit information, prediction unit information, transmission unit information, and motion of the coding unit from the reordering unit 160 and the prediction units 120 and 125. Various information such as vector information, reference frame information, interpolation information of a block, and filtering information can be encoded.

The entropy encoder 165 may entropy encode a coefficient value of a coding unit input from the reordering unit 160.

The inverse quantizer 140 and the inverse transformer 145 inverse quantize the quantized values in the quantizer 135 and inversely transform the transformed values in the transformer 130. The residual value generated by the inverse quantizer 140 and the inverse transformer 145 is reconstructed by combining the prediction units predicted by the motion estimator, the motion compensator, and the intra predictor included in the predictors 120 and 125. You can create a Reconstructed Block.

The filter unit 150 may include at least one of a deblocking filter, an offset correction unit, and an adaptive loop filter (ALF).

The deblocking filter may remove block distortion caused by boundaries between blocks in the reconstructed picture. In order to determine whether to perform deblocking, it may be determined whether to apply a deblocking filter to the current block based on the pixels included in several columns or rows included in the block. When the deblocking filter is applied to the block, a strong filter or a weak filter may be applied according to the required deblocking filtering strength. In addition, in applying the deblocking filter, horizontal filtering and vertical filtering may be performed in parallel when vertical filtering and horizontal filtering are performed.

The offset correction unit may correct the offset with respect to the original image on a pixel-by-pixel basis for the deblocking image. In order to perform offset correction for a specific picture, the pixels included in the image are divided into a predetermined number of areas, and then, an area to be offset is determined, an offset is applied to the corresponding area, or offset considering the edge information of each pixel. You can use this method.

Adaptive Loop Filtering (ALF) may be performed based on a value obtained by comparing the filtered reconstructed image with the original image. After dividing the pixels included in the image into a predetermined group, one filter to be applied to the group may be determined and filtering may be performed for each group. For information related to whether to apply ALF, a luminance signal may be transmitted for each coding unit (CU), and the shape and filter coefficient of an ALF filter to be applied may vary according to each block. In addition, regardless of the characteristics of the block to be applied, the same type (fixed form) of the ALF filter may be applied.

The memory 155 may store the reconstructed block or picture calculated by the filter unit 150, and the stored reconstructed block or picture may be provided to the predictors 120 and 125 when performing inter prediction.

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

Referring to FIG. 2, the image decoder 200 includes an entropy decoder 210, a reordering unit 215, an inverse quantizer 220, an inverse transformer 225, a predictor 230, 235, and a filter unit ( 240, a memory 245 may be included.

When an image bitstream is input from the image encoder, the input bitstream may be decoded by a procedure opposite to that of the image encoder.

The entropy decoder 210 may perform entropy decoding in a procedure opposite to that of the entropy encoding performed by the entropy encoder of the image encoder. For example, various methods such as Exponential Golomb, Context-Adaptive Variable Length Coding (CAVLC), and Context-Adaptive Binary Arithmetic Coding (CABAC) may be applied to the method performed by the image encoder.

The entropy decoder 210 may decode information related to intra prediction and inter prediction performed by the encoder.

The reordering unit 215 may reorder the entropy decoded bitstream in the entropy decoding unit 210 based on a method of rearranging the bitstream. Coefficients expressed in the form of a one-dimensional vector may be reconstructed by reconstructing the coefficients in a two-dimensional block form. The reordering unit 215 may be realigned by receiving information related to coefficient scanning performed by the encoder and performing reverse scanning based on the scanning order performed by the corresponding encoder.

The inverse quantization unit 220 may perform inverse quantization based on the quantization parameter provided by the encoder and the coefficient values of the rearranged block.

The inverse transform unit 225 may perform an inverse transform, i.e., an inverse DCT, an inverse DST, and an inverse KLT, for a quantization result performed by the image encoder, that is, a DCT, DST, and KLT. Inverse transformation may be performed based on a transmission unit determined by the image encoder. The inverse transform unit 225 of the image decoder may selectively perform a transform scheme (eg, DCT, DST, KLT) according to a plurality of pieces of information such as a prediction method, a size of a current block, and a prediction direction.

The prediction units 230 and 235 may generate the prediction block based on the prediction block generation related information provided by the entropy decoder 210 and previously decoded blocks or picture information provided by the memory 245.

As described above, when performing the intra prediction in the same manner as the operation in the image encoder, when the size of the prediction unit and the size of the transformation unit are the same, the pixel existing on the left side, the pixel present on the upper left side, and the upper side Intra prediction is performed on a prediction unit based on a pixel, but when intra prediction is performed, when the size of the prediction unit and the size of the transformation unit are different, intra prediction may be performed using a reference pixel based on the transformation unit. Can be. In addition, intra prediction using NxN division may be used only for a minimum coding unit.

The predictors 230 and 235 may include a prediction unit determiner, an inter predictor, and an intra predictor. The prediction unit determiner receives various information such as prediction unit information input from the entropy decoder 210, prediction mode information of the intra prediction method, and motion prediction related information of the inter prediction method, and distinguishes the prediction unit from the current coding unit, and predicts It may be determined whether the unit performs inter prediction or intra prediction. The inter prediction unit 230 predicts the current prediction based on information included in at least one of a previous picture or a subsequent picture of the current picture including the current prediction unit by using information required for inter prediction of the current prediction unit provided by the image encoder. Inter prediction may be performed on a unit. Alternatively, inter prediction may be performed based on information of some regions pre-restored in the current picture including the current prediction unit.

In order to perform inter prediction, a motion prediction method of a prediction unit included in a coding unit based on a coding unit includes a skip mode, a merge mode, an AMVP mode, and an intra block copy mode. It can be determined whether or not it is a method.

The intra predictor 235 may generate a prediction block based on pixel information in the current picture. When the prediction unit is a prediction unit that has performed intra prediction, intra prediction may be performed based on intra prediction mode information of the prediction unit provided by the image encoder. The intra predictor 235 may include an adaptive intra smoothing (AIS) filter, a reference pixel interpolator, and a DC filter. The AIS filter is a part of filtering the reference pixel of the current block and determines whether to apply the filter according to the prediction mode of the current prediction unit. AIS filtering may be performed on the reference pixel of the current block by using the prediction mode and the AIS filter information of the prediction unit provided by the image encoder. If the prediction mode of the current block is a mode that does not perform AIS filtering, the AIS filter may not be applied.

When the prediction mode of the prediction unit is a prediction unit that performs intra prediction based on a pixel value interpolating the reference pixel, the reference pixel interpolator may generate a reference pixel having an integer value or less by interpolating the reference pixel. If the prediction mode of the current prediction unit is a prediction mode for generating a prediction block without interpolating the reference pixel, the reference pixel may not be interpolated. The DC filter may generate the prediction block through filtering when the prediction mode of the current block is the DC mode.

The reconstructed block or picture may be provided to the filter unit 240. The filter unit 240 may include a deblocking filter, an offset correction unit, and an ALF.

Information about whether a deblocking filter is applied to a corresponding block or picture, and when the deblocking filter is applied to the corresponding block or picture, may be provided with information about whether a strong filter or a weak filter is applied. In the deblocking filter of the image decoder, the deblocking filter related information provided by the image encoder may be provided and the deblocking filtering of the corresponding block may be performed in the image decoder.

The offset correction unit may perform offset correction on the reconstructed image based on the type of offset correction and offset value information applied to the image during encoding.

The ALF may be applied to a coding unit based on ALF application information, ALF coefficient information, and the like provided from the encoder. Such ALF information may be provided included in a specific parameter set.

The memory 245 may store the reconstructed picture or block to use as a reference picture or reference block, and may provide the reconstructed picture to the output unit.

As described above, in the embodiment of the present invention, a coding unit is used as a coding unit for convenience of description, but may also be a unit for performing decoding as well as encoding.

In addition, the current block represents a block to be encoded / decoded, and according to the encoding / decoding step, a coding tree block (or a coding tree unit), an encoding block (or a coding unit), a transform block (or a transform unit), or a prediction block. (Or prediction unit) or the like. In the present specification, 'unit' may indicate a basic unit for performing a specific encoding / decoding process, and 'block' may indicate a sample array having a predetermined size. Unless otherwise specified, 'block' and 'unit' may be used interchangeably. For example, in the embodiments described below, the coding block (coding block) and the coding unit (coding unit) may be understood to have the same meaning.

One picture may be divided into square or non-square basic blocks and encoded / decoded. In this case, the basic block may be referred to as a coding tree unit. A coding tree unit may be defined as the largest coding unit allowed in a sequence or slice. Information regarding whether the coding tree unit is square or non-square or the size of the coding tree unit may be signaled through a sequence parameter set, a picture parameter set or a slice header. The coding tree unit may be divided into smaller sized partitions. In this case, when the partition generated by dividing the coding tree unit is called depth 1, the partition generated by dividing the partition having depth 1 may be defined as depth 2. That is, a partition generated by dividing a partition that is a depth k in a coding tree unit may be defined as having a depth k + 1.

A partition of any size generated as the coding tree unit is split may be defined as a coding unit. The coding unit may be split recursively or split into basic units for performing prediction, quantization, transform, or in-loop filtering. For example, an arbitrary size partition generated as a coding unit is divided may be defined as a coding unit or a transform unit or a prediction unit that is a basic unit for performing prediction, quantization, transform, or in-loop filtering.

Alternatively, when the coding block is determined, a prediction block having the same size as the coding block or a size smaller than the coding block may be determined through prediction division of the coding block. Predictive partitioning of a coding block may be performed by a partition mode (Part_mode) indicating a partition type of a coding block. The size or shape of the prediction block may be determined according to the partition mode of the coding block. The division type of the coding block may be determined through information specifying any one of partition candidates. In this case, the partition candidates available to the coding block may include an asymmetric partition shape (eg, nLx2N, nRx2N, 2NxnU, 2NxnD) according to the size, shape, or coding mode of the coding block. As an example, a partition candidate available to a coding block may be determined according to an encoding mode of the current block. As an example, FIG. 3 is a diagram illustrating a partition mode that may be applied to a coding block when the coding block is encoded by inter prediction.

When the coding block is encoded by inter prediction, any one of eight partition modes may be applied to the coding block, as shown in the example illustrated in FIG. 3.

On the other hand, when a coding block is encoded by intra prediction, partition mode PART_2Nx2N or PART_NxN may be applied to the coding block.

PART_NxN may be applied when the coding block has a minimum size. Here, the minimum size of the coding block may be predefined in the encoder and the decoder. Alternatively, information about the minimum size of the coding block may be signaled through the bitstream. As an example, the minimum size of the coding block is signaled through the slice header, and accordingly, the minimum size of the coding block may be defined for each slice.

As another example, the partition candidates available to the coding block may be determined differently according to at least one of the size or shape of the coding block. For example, the number or type of partition candidates that a coding block may use may be differently determined according to at least one of the size or shape of the coding block.

Alternatively, the type or number of asymmetric partition candidates among partition candidates available to the coding block may be limited according to the size or shape of the coding block. As an example, the number or type of asymmetric partition candidates that a coding block may use may be differently determined according to at least one of the size or shape of the coding block.

In general, the size of the prediction block may have a size of 64x64 to 4x4. However, when the coding block is encoded by inter prediction, when the motion compensation is performed, the prediction block may not have a 4x4 size in order to reduce the memory bandwidth.

The field of view of the camera limits the field of view of the video taken by the camera. In order to overcome this problem, a plurality of cameras may be used to capture an image, and the captured image may be stitched to configure one video or one bitstream. For example, FIGS. 4 to 6 illustrate an example of capturing up, down, left, and right sides simultaneously using a plurality of cameras. As such, a video generated by stitching a plurality of videos may be referred to as a panoramic video. In particular, an image having a degree of freedom based on a predetermined central axis may be referred to as 360 degree video. For example, the 360 degree video may be an image having rotation degrees of freedom for at least one of Yaw, Roll, and Pitch.

The camera structure (or camera arrangement) for acquiring 360-degree video has a circular arrangement, as in the example shown in FIG. 4, or a one-dimensional vertical / horizontal arrangement, as in the example shown in FIG. 5A. Alternatively, as in the example shown in FIG. 5B, a two-dimensional arrangement (that is, a mixture of vertical and horizontal arrangements) may be used. Alternatively, as shown in FIG. 6, a spherical device may be equipped with a plurality of cameras.

An embodiment to be described later will be described based on 360 degree video, but it will be included in the technical scope of the present invention to apply the embodiment to be described later to a panoramic video which is not a 360 degree video.

FIG. 7 is a block diagram of a 360 degree video data generating apparatus and a 360 degree video playing apparatus, and FIG. 8 is a flowchart illustrating operations of the 360 degree video data generating apparatus and 360 degree video playing apparatus.

Referring to FIG. 7, the 360-degree video data generating apparatus includes a projection unit 710, a frame packing unit 720, an encoding unit 730, and a transmission unit 740. It may include a parser 750, a decoder 760, a frame depacking unit 770, and a reverse projection unit 780. The encoding unit and the decoding unit illustrated in FIG. 7 may correspond to the image encoding apparatus and the image decoding apparatus illustrated in FIGS. 1 and 2, respectively.

The data generating apparatus may determine a projection conversion technique of the 360 degree image generated by stitching the images photographed by the plurality of cameras. The projection unit 710 may determine the 3D form of the 360 degree video according to the determined projection transformation technique, and project the 360 degree video onto the 2D plane according to the determined 3D form (S801). Here, the projection transformation technique may represent an aspect in which the 360 degree video is developed on the 3D form and the 2D plane of the 360 degree video. The 360-degree image may be approximated as having a form of sphere, cylinder, cube, octahedron or icosahedron in 3D space, according to a projection transformation technique. According to a projection transformation technique, an image generated by projecting a 360 degree video onto a 2D plane may be referred to as a 360 degree projection image.

The 360 degree projection image may be composed of at least one face according to a projection conversion technique. For example, when the 360 degree video is approximated as a polyhedron, each face constituting the polyhedron may be defined as a face. Alternatively, the specific surface constituting the polyhedron may be divided into a plurality of regions, and the divided regions may be set to form separate faces. The 360 degree video approximated in the shape of a sphere may have a plurality of faces according to the projection transformation technique.

In order to increase the encoding / decoding efficiency for the 360 degree video, the frame packing may be performed in the frame packing unit 720 (S802). Frame packing may include at least one of reordering, resizing, warping, rotating, or flipping a face. Through frame packing, the 360-degree projection image may be converted into a form (eg, a rectangle) having high encoding / decoding efficiency, or discontinuity data between faces may be removed. Frame packing may also be referred to as frame reordering or region-wise packing. Frame packing may be selectively performed to improve encoding / decoding efficiency for the 360 degree projection image.

The encoding unit 730 may perform encoding on the 360 degree projection image or the 360 degree projection image on which the frame packing is performed (S803). In this case, the encoder 730 may encode information indicating a projection transformation technique for the 360 degree video. Here, the information indicating the projection transformation technique may be index information indicating any one of the plurality of projection transformation techniques.

In addition, the encoder 730 may encode information related to frame packing for the 360 degree video. Here, the information related to the frame packing may include at least one of whether frame packing is performed, the number of faces, the position of the face, the size of the face, the shape of the face, or the rotation information of the face.

The transmitter 740 may encapsulate and transmit the encapsulated data to the player terminal (S804).

The file parsing unit 750 may parse the file received from the content providing device (S805). The decoding unit 760 may decode the 360 degree projection image using the parsed data (S806).

When frame packing is performed on the 360-degree projection image, the frame depacking unit 760 may perform frame depacking (Region-wise depacking) opposite to the frame packing performed on the content providing side (S807). Frame depacking may be to restore the frame packed 360 degree projection image to before frame packing is performed. For example, frame depacking may be to reverse the reordering, resizing, warping, rotation, or flipping of a face performed in the data generating device.

The inverse projection unit 780 may inversely project the 360 degree projection image on the 2D plane in a 3D form according to a projection transformation technique of the 360 degree video (S808).

Projection transformation techniques include isotropic rectangular projection (ERP), cubic projection transformation (Cube Map Projection, CMP), isosahedral projection transformation (ISP), octahedron projection transformation (Octahedron Projection, OHP), truncated pyramid It may include at least one of a projection transform (Truncated Pyramid Projection, TPP), a Segment Projection (SSP), an Equatorial cylindrical projection (ECP), or a rotated sphere projection (RSP).

9 illustrates a 2D projection method using an isotonic method.

The isotropic method is a method of projecting a pixel corresponding to a sphere into a rectangle having an aspect ratio of N: 1, which is the most widely used 2D transformation technique. Here, N may be two, and may be two or less or two or more real numbers. With isotonicity, the actual length of the sphere corresponding to the unit length on the 2D plane becomes shorter toward the pole of the sphere. For example, the coordinates of both ends of the unit length on the 2D plane may correspond to a distance difference of 20 cm near the equator of the sphere, while corresponding to a distance difference of 5 cm near the pole of the sphere. As a result, the isotropic rectangular method has a disadvantage in that the image distortion is large and coding efficiency is lowered near the poles of the sphere.

10 illustrates a 2D projection method using a cube projection technique.

The cube projection technique involves approximating a 360-degree video to a cube and then converting the cube into 2D. When projecting a 360 degree video onto a cube, one face (or plane) is configured to adjoin four faces. The continuity between the faces is high, and the cube projection method has an advantage of higher coding efficiency than the isotonic diagram method. After projection-converting the 360-degree video to 2D, encoding / decoding may be performed by rearranging the 2D projection-converted image into a quadrangle form.

11 illustrates a 2D projection method using a icosahedron projection technique.

The icosahedron projection technique is a method of approximating a 360 degree video to an icosahedron and converting it into 2D. The icosahedral projection technique is characterized by strong continuity between faces. As in the example shown in FIG. 11, encoding / decoding may be performed by rearranging faces in the 2D projection-converted image.

12 illustrates a 2D projection method using an octahedron projection technique.

The octahedral projection method is a method of approximating a 360 degree video to an octahedron and converting it into 2D. The octahedral projection technique is characterized by strong continuity between faces. As in the example shown in FIG. 12, encoding / decoding may be performed by rearranging faces in the 2D projection-converted image.

13 illustrates a 2D projection method using a truncated pyramid projection technique.

The truncated pyramid projection technique is a method of approximating a 360 degree video to a truncated pyramid and converting it into 2D. Under a truncated pyramid projection technique, frame packing may be performed such that the face at a particular point in time has a different size than the neighboring face. For example, as in the example shown in FIG. 13, the front face may have a larger size than the side face and the back face. When the truncated pyramid projection technique is used, image data of a specific viewpoint is large, and thus the encoding / decoding efficiency of the specific viewpoint is higher than that of other viewpoints.

SSP is a method of dividing a spherical 360-degree video into high- and mid-latitude regions and performing 2D projection transformation. Specifically, when the SSP is followed, the two high latitude regions of the sphere may be mapped to two circles on the 2D plane, and the mid-latitude regions of the sphere may be mapped to the rectangles on the 2D plane like the ERP.

ECP converts spherical 360-degree video into cylindrical form and then converts cylindrical 360-degree video into 2D projection. Specifically, when the ECP is followed, the top and bottom of the cylinder can be mapped to two circles on the 2D plane, and the body of the cylinder can be mapped to the rectangle on the 2D plane.

RSP represents a method of converting a spherical 360 degree video of a tennis ball into two ellipses on a 2D plane.

Each sample of the 360 degree projection image may be identified by face 2D coordinates. The face 2D coordinates may include an index f for identifying the face where the sample is located, a coordinate (m, n) representing a sample grid in a 360 degree projection image.

Through the transformation between the face 2D coordinates and the 3D coordinates, 2D projection transformation and image rendering may be performed. As an example, FIG. 14 is a diagram illustrating a conversion between a face 2D coordinate and a 3D coordinate. When a 360 degree projection image is generated based on the ERP, conversion between three-dimensional coordinates (x, y, z) and face 2D coordinates (f, m, n) may be performed using Equations 1 to 3 below. have.

The current picture in the 360 degree projection image may include at least one or more faces. In this case, the number of faces may be 1, 2, 3, 4 or more natural numbers, depending on the projection method. Among the face 2D coordinates, f may be set to a value equal to or smaller than the number of faces. The current picture may include at least one or more faces having the same temporal order or output order (POC).

Alternatively, the number of faces constituting the current picture may be fixed or variable. For example, the number of faces constituting the current picture may be limited not to exceed a predetermined threshold. Here, the threshold value may be a fixed value previously promised by the encoder and the decoder. Alternatively, information about the maximum number of faces constituting one picture may be signaled through a bitstream.

The faces may be determined by partitioning the current picture using at least one of a horizontal line, a vertical line, or a diagonal line, depending on the projection method.

Each face within a picture may be assigned an index to identify each face. Each face may be parallelized, such as a tile or a slice. Accordingly, when performing intra prediction or inter prediction of the current block, neighboring blocks belonging to different faces from the current block may be determined to be unavailable.

Paces (or non-parallel regions) where parallelism is not allowed may be defined, or faces with interdependencies may be defined. For example, faces that do not allow parallel processing or faces with interdependencies may be coded / decoded sequentially instead of being parallel coded / decoded. Accordingly, even neighboring blocks belonging to different faces from the current block may be determined to be available for intra prediction or inter prediction of the current block, depending on whether parallel processing between faces or dependencies is possible.

In the embodiments described below, although the embodiments are described based on the specific projection method, the embodiments described below may be extended to the projection methods other than the specific projection method.

Since the human viewing angle is limited to about 120 degrees, the user cannot see the entire 360 degree video at once. Due to the limited viewing angle, the user sees only partial images of 360 degree video. The partial image corresponding to the viewing area of the user among the entire areas of the 360 degree video may be defined as a view port. The play device may decode the 360 degree image and render a portion corresponding to the view port in the 360 degree video.

View ports may be classified into static view ports and dynamic view ports according to fluidity. The static view port refers to a view port with no change in position, and the dynamic view port refers to a view port whose position changes as the user's gaze changes. It is rare to use static viewports for an entire sequence of 360-degree video, and most of them use dynamic viewports that change position as the user's eyes move.

The area in the 360 degree video that the user should watch carefully can be set. For example, the content producer may set a view port trajectory that should be viewed in a 360 degree video. A viewport corresponding to an area of interest to a producer or viewer in a 360 degree video may be referred to as a region of interest (ROI), a recommended view port, a director's cut, or the like. .

In view of the viewport, only a part of the 360 degree video may be encoded. For example, 360 degree video may be encoded around a view port among 360 degree videos. Here, the meaning of encoding the 360 degree video around the view port may mean encoding a rectangular area corresponding to the view port, a predetermined size area including the view port, or a tile / slice including the view port. .

For example, the 360 degree video may be encoded based on the ROI of the entire area of the 360 degree video. Encoding the 360 degree video around the ROI may be referred to as ROI mode.

Alternatively, after encoding and decoding the entire 360-degree video, only the partial image corresponding to the view port may be extracted from the decoded 360-degree image, and the extracted partial image may be re-encoded. As such, after encoding and decoding the entire 360-degree video, recoding only a portion corresponding to the view port in the decoded 360-degree image may be referred to as a view port mode.

In the region of interest mode, there is a limit to watching the region of interest provided by the content producer instead of watching the region to which the user's eyes are directed. However, in the viewport mode, there is an advantage of providing a dynamic viewport according to the viewer's eye movement.

15 is a diagram for explaining a viewport mode.

In the example shown in FIG. 15, the encoders (Encoder A) 1510 of the server may encode the entire 360 degree video. The encoded 360 degree video may be transmitted to an intermediate node via a network.

If the server transmits the bitstream for the entire 360-degree video, the decoder (Decoder A, 1520) of the intermediate node may decode the entire 360-degree video through the bitstream received from the server. Here, the intermediate node may include a media aware network element (MANE) complying with the MMT transmission standard. In addition, the linear region extractor 1530 of the intermediate node may receive position data related to the view port from the play device, and extract a rectangular area corresponding to the view port from the decoded 360 degree video. When the rectangular region corresponding to the viewport is extracted, the encoder B (1540) of the intermediate node may encode the extracted rectangular partial image and transmit a bitstream of the encoded partial image through a network. .

The decoder B (Decoder B) 1550 of the play device may receive a bitstream of a partial image received through a network and decode the received partial image. The play device may output an area corresponding to the view port in the 360 degree video.

As in the above-described example, in order to encode / decode / render the partial image corresponding to the view port, it is necessary to specify the position, size or width of the view port. The location and size (or width) of the viewport may be defined based on at least one of the coordinates of the viewport, the width and height of the viewport, and the angle between the predetermined central axis and the viewport. As an example, the location and size of the view port may be determined by an angle difference between the view point center point and the view port center point and the view port boundary.

The center point of the viewport may be specified by spherical coordinates including a rotation angle Yaw about the z axis, a rotation angle Pitch about the x axis, and a rotation angle Roll about the z axis. In addition, the width and height of the viewport may be specified by information indicating the range of the viewport. Here, the range of the view port may include a Yaw range indicating an angle between the left boundary and the right boundary of the view port, and a pitch range indicating the angle between the upper boundary and the lower boundary of the view port.

16 is a diagram illustrating an example in which a position and a size of a view port are specified.

For convenience of description, it is assumed that the position of the viewport center point and the range of the viewport are defined using sphere coordinates represented by (Yaw, Picth, Roll), as in the example shown in FIG. .

As in the example shown in FIG. 16B, the position and size of the view port may be specified by the center point of the view port and the view port range. As an example, the position and size of the viewport may be specified by the center coordinates (Yaw, Roll, Pitch) of the viewport, the Yaw range and the Pitch range. Here, the left and right ranges of the view port may be specified using the Yaw range, and the upper and lower ranges of the view port may be specified using the pitch range.

The image encoding apparatus encoding the 360 degree image may encode view port related information in order to specify the position and size of the view port, and transmit the information to the image decoding apparatus through the bitstream. Here, the view port related information may include information indicating the position of the view port center point and information for specifying the view port range. In addition, the view port related information may further include at least one of angular precision related information, information for determining a picture range to which the view port is applied, and encoding mode information related to the view port.

17 is a diagram illustrating syntax associated with a viewport encoded in a bitstream.

The video encoding apparatus may encode information indicating the angle precision. For example, in the example shown in FIG. 17, spherical_viewport_precision may be a syntax indicating angular precision. The angular precision may be set to a value obtained by multiplying the value of spherical_viewport_precision by 10 ⁻² . For example, when the value of spherical_viewport_precision is 1, the angular precision may be set to 0.01 degree. This indicates that the position and range of the viewport can be displayed in units of 0.01 degree.

Alternatively, one of the plurality of angular precision candidates may be selected based on the signaled information. For example, spherical_viewport_precision may be an index specifying any one of a plurality of angular precision candidates.

The video encoding apparatus may encode information indicating the center point of the viewport. For example, in the example illustrated in FIG. 17, spherical_viewport_yaw may represent Yaw coordinates of the viewport center point, spherical_viewport_pitch may represent Pitch coordinates of the viewport center point, and spherical_viewport_roll may represent Roll coordinates of the viewport center point.

The video encoding apparatus may encode information for specifying the viewport range. For example, in the example shown in FIG. 17, spherical_viewport_range_yaw is for specifying a left and right range (ie, Yaw range) of the view port, and spherical_viewport_range_pitch is for specifying an upper and lower range (ie, Pitch range) of the view port.

spherical_viewport_range_yaw and spherical_viewport_range_pictch may indicate angles from the viewport center point to one side boundary of the viewport. For example, spherical_viewport_range_yaw may represent an angle from the center of the viewport to the left or right border of the viewport, and spherical_viewport_range_pictch may represent an angle from the center of the viewport to the top or bottom boundary of the viewport. In this case, the Yaw range can be extended to the left and right symmetrical regions of the region designated by spherical_viewport_range_yaw, and the pitch range can be extended to the vertically symmetrical region of the region designated by spherical_viewport_range_pitch. As described above, by encoding information corresponding to half of the view port range, the amount of bits required to determine the view port range may be reduced.

Equations 4 and 5 show examples of deriving a half view port range based on syntax associated with the view port.

When the value of spherical_viewport_precision is 1, the value of spherical_viewport_range_yaw is 4000, and the value of spherical_viewport_range_pitch is 5000, the half Yaw range can be derived as 40 and the half pitch range as 50. Accordingly, the viewport may be defined as a Yaw region between -40 degrees and 40 degrees left and right with respect to the center point of the viewport, and a pitch region between -50 degrees and 50 degrees up and down with respect to the center point of the viewport.

As another example, spherical_viewport_range_yaw and spherical_viewport_range_pictch may be set to indicate an angle between both sides of the viewport. For example, the value obtained by multiplying the spherical_viewport_range_yaw value by the angular precision may be derived into the Yaw range, or the value obtained by multiplying the spherical_viewport_range_pitch value by the angular precision may be derived into the pitch range.

The image encoding apparatus may encode information representing a picture range to which the view port information is applied. As an example, in the example shown in FIG. 17, spherical_viewport_persistence_flag is a syntax indicating whether view port information is applied only to the current picture or to another picture. For example, when the value of spherical_viewport_persistence_flag is 0 (or 1), view port related syntax (eg, angular precision, view port center point, and view port range related information) may be applied only to the current picture. On the other hand, when the value of spherical_viewport_persistence_flag is 1 (or 0), the view port syntax of the current picture may be applied to other pictures until a new view port syntax is introduced. Here, the other picture may be a picture having a different output order (eg, Picture Order Count, POC) or decoding order from the current picture. For example, when spherical_viewport_persistence_flag is 1, the view port related syntax of the current picture may be applied to a POC larger than the current picture or a picture decoded later than the current picture.

The image encoding apparatus may encode information associated with an encoding mode. For example, in the example illustrated in FIG. 17, spherical_viewport_mode may indicate an encoding mode of a current sequence or a current picture. For example, spherical_viewport_mode equal to 0 (or 1) may indicate that region of interest mode is applied to the current sequence or current picture, and spherical_viewport_mode equal to 1 (or 0) indicates that view port mode is applied to the current sequence or current picture. Can be represented.

In the example shown in FIG. 17, the encoding / decoding for the angle precision may be omitted, and the angle precision predefined in the encoding apparatus and the decoding apparatus may be used.

The view port related information illustrated in FIG. 17 may be encoded through at least one of a Supplementary Enhancement Information (SEI) message, a sequence header, a picture header, or a slice header.

It is also possible to set a plurality of view ports in one picture. Referring to the viewport mode as an example, when a plurality of viewers watch a 360 degree video, the view ports of the plurality of viewers may be different. In this case, the intermediate node may re-encode the partial region corresponding to each viewer's view port from the decoded 360 degree video and transmit the re-encoded plural partial images to each play apparatus.

Alternatively, a plurality of ROIs may be set in the 360 degree video. For example, when a plurality of regions of interest are set in a sporting event, the viewer may select one of the plurality of regions of interest and watch a partial image corresponding to the selected region of interest. In the ROI mode, the encoding apparatus may encode a partial image corresponding to each ROI, and transmit any one of the encoded partial images to the play apparatus according to the ROI selected by the user.

When a plurality of view ports are available, the view port information may further include information about the number of view ports. In this case, the image encoding apparatus may further encode information about the number of view ports.

18 is a diagram illustrating an example in which a syntax indicating the number of view ports is encoded.

The video encoding apparatus may encode information indicating the number of view ports. For example, in the example illustrated in FIG. 18, viewport_num may represent the number of view ports. Unlike in the illustrated example, it is also possible to encode a syntax obtained by subtracting a predefined integer from the number of view ports. For example, viewport_num_minus1 may represent a value obtained by subtracting 1 from the number of view ports.

The number of view ports may represent at least one of the maximum number or the minimum number of view ports allowable in the current picture. Alternatively, the number of view ports may represent a number applied at at least one level of a sequence, a temporal layer, a picture, or a slice including a current picture.

When a plurality of view ports are used, position and range information of each view port may be encoded. Different view port indexes (viewport_idx) may be allocated to the plurality of view ports, and location and range information may be encoded for each view port index.

For example, in the example illustrated in FIG. 18, spherical_viewport_yaw [viewport_idx], spherical_viewport_pitch [viewport_idx], and spherical_viewport_roll [viewport_idx] represent center point spherical coordinates (Yaw, Pitch, Roll) of the viewport having the viewport index [viewport_idx], respectively. .

In addition, spherical_viewport_range_yaw [viewport_idx] and spherical_viewport_range_pitch [viewport_idx] are used to determine the Yaw range and the Pitch range of the viewport having the viewport index [viewport_idx], respectively.

The image decoding apparatus may decode information indicating the number of view ports, and when the number of view ports is plural, may decode position and range information of each view port and determine the position and size of each view port.

Although not shown, information (eg, a flag) indicating whether a plurality of view ports are allowed may be signaled via the bitstream.

When there are a plurality of view ports, information of each view port may be independently encoded. For example, in the example illustrated in FIG. 18, location information and range information are signaled for each of the plurality of view ports.

As another example, new view port information may be encoded / decoded using a pre-coded / decoded viewport or a predefined viewport. In detail, after selecting the reference view port from among the plurality of view ports, the current view port information may be derived by using the reference view port information. Here, the current view port information derived from the reference view port may include at least one of the view port related syntax described with reference to FIGS. 17 and 18.

The reference view port may mean a view port that is a reference of encoding or decoding among a plurality of view ports. For example, the reference view port may mean a view port that is first encoded or decoded in a picture, a view port of a specific position in a picture, or a view port having a view port index of a predetermined value (eg, 0). The specific position for determining the reference view port may be predefined in the image encoding apparatus and the image decoding apparatus. Alternatively, information indicating a specific location for determining the reference view port may be signaled via the bitstream.

Alternatively, an adjacent view port adjacent to the current view port and a view port encoded / decoded before the current view port may be set as the reference view port.

The number of reference view ports may be one or more.

19 is a diagram illustrating an example of deriving current view port information using a reference view port.

When the plurality of view ports are supported in the view port mode or the ROI mode, the image encoding apparatus encodes information about the reference view port or the specific view port, and for the remaining view ports except for the reference view port, the reference view port The difference value with can be encoded.

For example, in the example illustrated in FIG. 19, spherical_viewport_yaw [0], spherical_viewport_pitch [0], and spherical_viewport_roll [0] may represent center point coordinates of the viewport having an index [0]. In addition, spherical_viewport_range_yaw [0] and spherical_viewport_range_pitch [0] may indicate a half Yaw range and a half pitch range of the view port having an index [0].

The information about the remaining view port may be encoded as a difference value from the reference view port information. For example, in the example illustrated in FIG. 19, delta_viewport_yaw, delta_viewport_pitch, and delta_viewport_roll may indicate a coordinate difference between the center point of the reference view port and the center point of the current view port. When the viewport has a viewport index [0], the viewport is a reference viewport, delta_viewport_yaw, delta_viewport_pitch, and delta_viewport_roll of the viewport having [viewport_idx] may be defined as in Equation 6 below.

In addition, in the example illustrated in FIG. 19, delta_viewport_range_yaw and delta_viewport_range_pitch may indicate a half Yaw range difference value and a half Pitch range difference value between the reference view port and the current view port. For example, delta_viewport_range_yaw and delta_viewport_range_pitch of the viewport having [viewport_idx] may be defined as in Equation 7 below.

As another example, the previous view port of the current view port (that is, the view port whose view port index is 1 lower than the current index) may be set as the reference view port. In this case, delta_viewport_yaw, delta_viewport_pitch, and delta_viewport_roll of the viewport having [viewport_idx] may be defined as a difference value from the viewport having [viewport_idx-1] as shown in Equation 8.

In addition, delta_viewport_range_yaw and delta_viewport_range_pitch of the viewport having [viewport_idx] may be defined as a difference value from the viewport having [viewport_idx-1] as shown in Equation 9 below.

The image decoding apparatus may determine the position and range of the current view port by adding the position and range information of the reference view port and the position and range difference values of the current view port.

After applying the 3D rotation in the viewport unit, the image may be encoded / decoded. Specifically, at the initial position of the viewport, the sphere may be rotated in at least one direction of Yaw, Pitch, or Roll to obtain the position of the final viewport.

The image encoding apparatus may encode information related to the rotation of the viewport in the bitstream. The image decoding apparatus may obtain the rotated view port by applying the decoded view port rotation information to the view port set based on the position and range information of the view port.

20 is a diagram illustrating an example in which information related to rotation of a sphere is encoded.

The video encoding apparatus may encode information indicating the rotation angle precision. For example, in the example shown in FIG. 20, spherical_viewport_orientation_precision may be a syntax indicating rotation angle precision. Rotation angle precision can be applied to a syntax that indicates the rotation angle of the viewport. The rotation angle precision may be set to a value obtained by multiplying the value of spherical_viewport_orientation_precision by 10 ⁻² . For example, when the value of spherical_viewport_orientation_precision is 1, the angle precision may be set to 0.01 degree. This indicates that the rotation angle of the viewport can be displayed in units of 0.01 degree.

Alternatively, one of the plurality of rotation angle precision candidates may be selected based on the signaled information. For example, spherical_viewport_orientation_precision may be an index specifying any one of a plurality of rotation angle precision candidates.

The video encoding apparatus may encode information indicating the rotation angle of the viewport. As an example, in the example shown in FIG. 20, spherical_viewport_orientation_yaw may indicate the rotation degree of the view port in the Yaw direction, spherical_viewport_orientation_pitch may indicate the rotation degree of the view port in the pitch direction, and spherical_viewport_orientation_roll may indicate the rotation direction of the view port in the roll direction.

Rotation angle precision and viewport rotation information can be used to specify the rotation angle of the viewport. For example, Equation 10 illustrates an example of inducing a viewport rotation angle.

Although not shown, information indicating whether the viewport is rotated may be further encoded. Rotation information of the viewport may be selectively signaled based on information indicating whether the viewport is rotated.

In the example shown in FIG. 20, the encoding / decoding for the rotation angle precision may be omitted, and the rotation angle precision predefined in the encoding apparatus and the decoding apparatus may be used. Alternatively, the encoding / decoding for the rotation angle precision may be omitted, and the rotation angle precision may be set in the same manner as the angle precision.

In the example shown in FIG. 20, spherical_viewport_orientation_yaw, spherical_viewport_orientation_pitch, and spherical_viewport_orientation_roll simultaneously indicate the rotation direction and the rotation angle. As an example, spherical_viewport_orientation_yaw represents a rotation angle with respect to Yaw. Instead of encoding the syntax indicating both the rotation direction and the rotation angle, it is also possible to encode the rotation direction and the rotation angle as separate information. As an example, after encoding the information indicating whether the viewport is rotated in a predetermined direction, if it is determined that the viewport is rotated in a predetermined direction, the information indicating the rotation angle with respect to the predetermined direction may be encoded. For example, spherical_viewport_yaw_oriented_flag may be a flag indicating whether the viewport is rotated in the Yaw direction. If the flag is 1, spherical_viewport_orientation_yaw indicating the yaw direction rotation angle of the viewport may be further signaled.

The 360-degree image may be a 3DoF (Degree of Freedom) image, a 3DoF + image, or a 6DoF image. The 3DoF image can have rotational degrees of freedom about three axes. For example, the 3DoF image may support free rotation for Yaw, Roll, and Pitch. The 3DoF + image adds a limited linear degree of freedom to the 3DoF image. For example, the 3DoF + image may support free rotation about Yaw, Roll, and Picth, and limited movement along at least one of the x-axis, y-axis, or z-axis. The 6DoF image adds complete linear degrees of freedom to the 3DoF image. For example, the 6DoF image may support free rotation about Yaw, Roll, and Pitch, and free movement about the x-axis, y-axis, and z-axis.

21 illustrates the concept of 3DoF, 3DoF +, and 6DoF images.

When using the 3DoF video service, the user can move and look at the realistic media while sitting or standing. The 360 degree video provided by the 3DoF video service may be referred to as omnidirectional video.

When using 3DoF + video service, users can move their heads and watch the realistic media. In addition, the user can move within a limited area and enjoy the sensory media.

When using 6DoF video service, users can move their heads and watch realistic media. In addition, the user can move and enjoy the realistic media.

In an image service supporting limited movement of a user or free movement of a user, path information intended by a content producer may be encoded and signaled. By providing the path information intended by the content producer to the user, an optimal moving path for viewing an image may be provided to the user. Information on a single path may be encoded and signaled, or information on multiple paths may be encoded and signaled.

22 is a diagram illustrating an example of overlaying a view path on a video.

Overlay the view path determined by the path information on the video. For example, as in the example illustrated in FIG. 22, the directions of the first path Path 1 and the second path Path 2 may be overlayed on the virtual space provided by the video.

Alternatively, the viewer may provide an interface for selecting any one of a plurality of paths.

The path information may include at least one of information indicating whether the plurality of view paths are supported or the number of view paths. The view port related information described above may be used to indicate the location and range of the view path.

One view path may support multiple view ports, or multiple view paths may support one view port.

FIG. 23 is a diagram for describing syntax related to route information. FIG.

viewpath_num_minus1 + 1 indicates the number of view paths. viewpath_idx represents the index of the view path.

spherical_viewport_yaw [view_path_idx] [viewport_idx] indicates the yaw center position of the view path whose view path index is view_path_idx and view port index is viewport_idx.

spherical_viewport_pitch [view_path_idx] [viewport_idx] indicates the pitch center position of the view path whose view path index is view_path_idx and view port index is viewport_idx.

spherical_viewport_roll [view_path_idx] [viewport_idx] indicates the roll center position of the view path whose view path index is view_path_idx and view port index is viewport_idx.

spherical_viewport_range_yaw [view_path_idx] [viewport_idx] indicates the yaw range of the view path whose view path index is view_path_idx and view port index is viewport_idx.

spherical_viewport_range_pitch [view_path_idx] [viewport_idx] indicates the pitch range of the view path whose view path index is view_path_idx and view port index is viewport_idx.

The number of viewport_idx corresponding to view_path_idx may be one or more. In addition, the mapping relationship between view_path_idx and viewport_idx may be changed depending on the playback time.

When the user selects one view path, a view port image corresponding to the selected view path may be output. When there are a plurality of view ports corresponding to the selected view path, a representative view port image of the plurality of view ports may be output, or an interface for selecting one of the plurality of view ports may be output. The representative view port image may correspond to a view port having a predefined index, or may correspond to a view port having the smallest index or the smallest index.

Although the above-described embodiments are described based on a series of steps or flowcharts, this does not limit the time-series order of the invention and may be performed simultaneously or in a different order as necessary. In addition, in the above-described embodiment, each component (for example, a unit, a module, etc.) constituting the block diagram may be implemented as a hardware device or software, and a plurality of components are combined into one hardware device or software. It may be implemented. The above-described embodiments may be implemented in the form of program instructions that may be executed by various computer components, and may be recorded in a computer-readable recording medium. The computer-readable recording medium may include program instructions, data files, data structures, etc. alone or in combination. Examples of computer-readable recording media include magnetic media such as hard disks, floppy disks and magnetic tape, optical recording media such as CD-ROMs, DVDs, and magneto-optical media such as floptical disks. media), and hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, flash memory, and the like. The hardware device may be configured to operate as one or more software modules to perform the process according to the invention, and vice versa.

Claims (10)

Restoring a 360 degree video;
Decoding view path related information from the bitstream; And
Setting a viewport corresponding to the view path to the 360 degree video,
And the view path related information includes information about the number of view paths. The method of claim 1,
The position and the range of the view path is set equal to the position and the range of the view port, the image decoding method. The method of claim 2,
And the position of the view port is determined based on the information representing the yaw center position, the information representing the pitch center position, and the information representing the roll center position. The method of claim 3, wherein
The range of the view port is determined based on the information indicating the Yaw range and the information indicating the pitch range, image decoding method. The method of claim 1,
And the view path is mapped to a plurality of view ports. Setting a viewport corresponding to the view path to the 360 degree video; And
Encoding the 360 degree video and the view path related information,
And the view path related information includes information about the number of view paths. The method of claim 6,
The position and range of the view path is set equal to the position and range of the view port, the image encoding method. The method of claim 7, wherein
And the position of the view port is determined based on information representing a yaw center position, information representing a pitch center position, and information representing a roll center position. The method of claim 8,
And the range of the view port is determined based on the information representing the yaw range and the information representing the pitch range. The method of claim 6,
And the view path is mapped to a plurality of view ports.

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