Patent Publication Number: US-11032545-B2

Title: Reducing seam artifacts in 360-degree video

Description:
CLAIM OF PRIORITY UNDER 35 U.S.C. § 119 
     This application claims the benefit of U.S. Provisional Application No. 62/526,700, filed Jun. 29, 2017, the entire contents of which are hereby incorporated by reference. 
    
    
     RELATED PATENT APPLICATIONS 
     This application is related to the following earlier filed applications: application No. 62/473,822 filed Mar. 20, 2017, titled “ADAPTIVE PERTURBED CUBEMAP PROJECTION”, application No. 62/479,843 filed Mar. 31, 2017, titled “ADAPTIVE PERTURBED CUBEMAP PROJECTION”, application Ser. No. 15/925,674 filed Mar. 19, 2018, titled “ADAPTIVE PERTURBED CUBE MAP PROJECTION”, application Ser. No. 15/925,681 filed Mar. 19, 2018, titled “ADAPTIVE PERTURBED CUBE MAP PROJECTION”, application No. 62/474,767 filed Mar. 22, 2017, titled “SPHERE POLE PROJECTIONS FOR EFFICIENT COMPRESSION OF 360-DEGREE VIDEO”, application No. 62/528,264 filed Jul. 3, 2017, titled “SPHERE POLE PROJECTIONS FOR EFFICIENT COMPRESSION OF 360-DEGREE VIDEO”, application Ser. No. 15/926,957 filed Mar. 20, 2018, titled “SPHERE POLE PROJECTIONS FOR EFFICIENT COMPRESSION OF 360-DEGREE VIDEO”, application No. 62/475,103 filed Mar. 22, 2017, titled “SPHERE EQUATOR PROJECTION FOR EFFICIENT COMPRESSION OF 360-DEGREE VIDEO”, and application Ser. No. 15/926,732 filed Mar. 20, 2018, titled “SPHERE EQUATOR PROJECTION FOR EFFICIENT COMPRESSION OF 360-DEGREE VIDEO”. This application hereby incorporates by reference the full contents of each of the above list of earlier filed applications. 
     FIELD 
     This application is related to 360-degree video content. For example, systems and methods are described for encoding and/or decoding 360-degree formatted pictures having circular poles of a sphere projected onto square regions, and for efficient and artifact reduced compression and/or decompression of 360 video. 
     BACKGROUND 
     Video coding standards include Joint Video Exploration Team (JVET) of MPEG and VCEG, ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-T H.262 or ISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual, ITU-T H.264 (also known as ISO/IEC MPEG-4 AVC), including its Scalable Video Coding (SVC) and Multiview Video Coding (MVC) extensions and ITU-T H.265 (also known as ISO/IEC MPEG-4 HEVC) with its extensions. 
     SUMMARY 
     In various implementations, methods, devices, apparatus, and computer-readable media for processing 360-degree video data to obtain better coding efficiency are described herein. 
     A method can include obtaining at least one 360-degree rectangular formatted projected picture; detecting a projection boundary in the at least one 360-degree rectangular formatted projected picture; disabling at least one of an in-loop filtering, an intra-prediction, or an inter-prediction, based on detecting the at least one 360-degree rectangular formatted projected picture comprises the projection boundary; and generating an encoded video bitstream. 
     In some embodiments, the method can include determining that the 360-degree rectangular formatted projected picture contains a first picture half and a second picture half, wherein the first picture half and the second picture half are separated by a projection boundary; and disabling in-loop filtering in response to determining that the 360-degree rectangular formatted picture contains the first picture half and the second picture half. 
     In further embodiments, disabling in-loop filtering further comprises: disabling in-loop filtering for the entire at least one 360-degree rectangular formatted projected picture by disabling in-loop filtering in parameter sets for the at least one 360-degree rectangular formatted projected picture. 
     In additional embodiments, disabling in-loop filtering further comprises: disabling in-loop filtering within a slice of the at least one 360-degree rectangular formatted projected picture. 
     In some implementations, disabling in-loop filtering further comprises: identifying at least two coding tree units (CTUs) adjacent one another about the projection boundary; and disabling in-loop filtering for the identified at least two CTUs adjacent one another about the projection boundary. 
     In further implementations, disabling in-loop filtering further comprises: identifying at least two coding tree units (CTUs) adjacent one another about the projection boundary; and disabling in-loop filtering for the identified at least two CTUs by disabling sample adaptive offset (SAO) band offsets or SAO edge offsets across the at least two CTUs. 
     In additional implementations, the 360-degree rectangular formatted projected picture is a 3×2 packed projected picture. 
     In some embodiments, the 360-degree rectangular formatted projected picture is a 6×1 packed projected picture. 
     In further embodiments, the method can include determining the 360-degree rectangular formatted projected picture comprises at least a first region and a second region, wherein the first region and second region are separated by the projection boundary; determining a plurality of coding tree units (CTUs) across the 360-degree rectangular formatted projected picture; determining a plurality of coding units (CUs) from within the plurality of CTUs; performing intra-frame prediction across at least two of the plurality of CUs; identifying a first CU located within the first region and a second CU located within the second region; and disabling intra-frame prediction across the first CU and second CU, based on identifying the first CU located within the first region and the second CU located within the second region. 
     In additional embodiments, the first CU and second CU share a common boundary, and the common boundary is the projection boundary. 
     In some implementations, the method can include determining a 360-degree rectangular formatted projected picture QP value for the 360-degree rectangular formatted projected picture; and wherein disabling intra-frame prediction across the first CU and second CU is performed only when the 360-degree rectangular formatted projected picture QP value is above a threshold QP level. 
     In further implementations, the threshold QP level is 20. 
     In additional implementations, obtaining the at least one 360-degree rectangular formatted projected picture comprises obtaining a first temporal 360-degree rectangular formatted projected picture and a second temporal 360-degree rectangular formatted projected picture, wherein the first temporal 360-degree rectangular formatted projected picture temporally precedes the second temporal 360-degree rectangular formatted projected picture, wherein the first temporal 360-degree rectangular formatted projected picture comprises at least a first region, and wherein the second temporal 360-degree rectangular formatted projected picture comprises at least a second region, wherein the first region and second region are located on opposite sides of the projection boundary, the method can further include: determining a plurality of first temporal coding tree units (CTUs) across the first temporal 360-degree rectangular formatted projected picture; determining a plurality of second temporal coding tree units (CTUs) across the second temporal 360-degree rectangular formatted projected picture; determining a plurality of first temporal coding units (CUs) from within the plurality of first temporal CTUs; determining a plurality of second temporal coding units (CUs) from within the plurality of second temporal CTUs; performing inter-frame prediction across at least one of the CUs from the plurality of first temporal CUs and at least one CU from the plurality of second temporal CUs; identifying a first temporal CU located within the first region and a second temporal CU located within the second region; and disabling inter-frame prediction across the first temporal CU and the second temporal CU based on the identifying a first temporal CU located within the first region and a second temporal CU located within the second region. 
     In some embodiments, disabling inter-frame prediction across the first temporal CU and the second temporal CU, further comprises not performing motion based prediction across the first temporal CU and the second temporal CU. 
     In further embodiments, the projection boundary comprises a boundary wherein a first region and a second region disposed adjacent to one another along the boundary in a projection domain are not disposed adjacent to one another in a spatial domain. 
     A device can include a memory and a processor configured to perform a method that includes obtaining at least one 360-degree rectangular formatted projected picture; detecting a projection boundary in the at least one 360-degree rectangular formatted projected picture; disabling at least one of an in-loop filtering, an intra-prediction, or an inter-prediction, based on detecting the at least one 360-degree rectangular formatted projected picture comprises the projection boundary; and generating an encoded video bitstream. 
     A computer-readable medium can a non-transitory computer-readable medium storing a program containing instructions that, when executed by a processor of a device, cause the device to perform a method that includes obtaining at least one 360-degree rectangular formatted projected picture; detecting a projection boundary in the at least one 360-degree rectangular formatted projected picture; disabling at least one of an in-loop filtering, an intra-prediction, or an inter-prediction, based on detecting the at least one 360-degree rectangular formatted projected picture comprises the projection boundary; and generating an encoded video bitstream. 
     An apparatus can include means for obtaining at least one 360-degree rectangular formatted projected picture; means for detecting a projection boundary in the at least one 360-degree rectangular formatted projected picture; means for disabling at least one of an in-loop filtering, an intra-prediction, or an inter-prediction, based on detecting the at least one 360-degree rectangular formatted projected picture comprises the projection boundary; and means for generating an encoded video bitstream. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Illustrative embodiments of the present application are described in detail below with reference to the following drawing figures: 
         FIG. 1A  is an image illustrating an example of an equirectangular projected frame, in accordance with some examples. 
         FIG. 1B  is an image illustrating an example of a cubemap projected frame, in accordance with some examples. 
         FIG. 1C  is an image illustrating an example of an adjusted cubemap projected frame, in accordance with some examples. 
         FIG. 1D  is an image illustrating an example of an equatorial cylindrical projected frame, in accordance with some examples. 
         FIG. 2A  is a diagram illustrating an example of an equirectangular projection, in accordance with some examples. 
         FIG. 2B  is a diagram illustrating an example of a cubemap or an adjusted cubemap projection, in accordance with some examples. 
         FIG. 2C  is a diagram illustrating an example of a cubemap or an adjusted cubemap projection, in accordance with some examples. 
         FIG. 2D  is a diagram illustrating an example of an equatorial cylindrical projection, in accordance with some examples. 
         FIG. 2E  is a diagram illustrating an example of an equatorial cylindrical projection, in accordance with some examples. 
         FIG. 3A  is an image illustrating an example of a rendered viewport seam/boundary due to motion, in accordance with some examples. 
         FIG. 3B  is an image illustrating an example of viewport seam/boundary due to filtering, in accordance with some examples. 
         FIG. 4A  is a diagram illustrating an example of a guard band scheme for a 3×2 packed cubemap or an adjusted cubemap projection, in accordance with some examples. 
         FIG. 4B  is a diagram illustrating an example of a guard band scheme for a 3×2 packed cubemap or an adjusted cubemap projection, in accordance with some examples. 
         FIG. 4C  is a diagram illustrating an example of a guard band scheme for a 3×2 packed cubemap or an adjusted cubemap projection, in accordance with some examples. 
         FIG. 5A  is a diagram illustrating an example of a guard band scheme for a 3×2 packed equirectangular projection, in accordance with some examples. 
         FIG. 5B  is a diagram illustrating an example of a guard band scheme for a 3×2 packed equirectangular projection, in accordance with some examples. 
         FIG. 5C  is a diagram illustrating an example of a guard band scheme for a 3×2 packed equirectangular projection, in accordance with some examples. 
         FIG. 5D  is a diagram illustrating an example of a guard band scheme for a 6×1 packed equirectangular projection, in accordance with some examples. 
         FIG. 5E  is a diagram illustrating an example of a guard band scheme for a 6×1 packed equirectangular projection, in accordance with some examples. 
         FIG. 6  is a diagram illustrating an example of CTU splitting down to 8×8 CUs along the upper and lower picture halves, in accordance with some examples. 
         FIG. 7  is a block diagram illustrating an example video encoding device, in accordance with some examples. 
         FIG. 8  is a block diagram illustrating an example video decoding device, in accordance with some examples. 
         FIG. 9  is a flowchart illustrating an example of a process for processing video data according to the techniques discussed herein. 
     
    
    
     DETAILED DESCRIPTION 
     Certain aspects and embodiments of this disclosure are provided below. Some of these aspects and embodiments may be applied independently and some of them may be applied in combination as would be apparent to those of skill in the art. In the following description, for the purposes of explanation, specific details are set forth in order to provide a thorough understanding of embodiments of the application. However, it will be apparent that various embodiments may be practiced without these specific details. The figures and description are not intended to be restrictive. 
     The ensuing description provides exemplary embodiments only, and is not intended to limit the scope, applicability, or configuration of the disclosure. Rather, the ensuing description of the exemplary embodiments will provide those skilled in the art with an enabling description for implementing an exemplary embodiment. It should be understood that various changes may be made in the function and arrangement of elements without departing from the spirit and scope of the application as set forth in the appended claims. 
     Specific details are given in the following description to provide a thorough understanding of the embodiments. However, it will be understood by one of ordinary skill in the art that the embodiments may be practiced without these specific details. For example, circuits, systems, networks, processes, and other components may be shown as components in block diagram form in order not to obscure the embodiments in unnecessary detail. In other instances, well-known circuits, processes, algorithms, structures, and techniques may be shown without unnecessary detail in order to avoid obscuring the embodiments. 
     Also, it is noted that individual embodiments may be described as a process which is depicted as a flowchart, a flow diagram, a data flow diagram, a structure diagram, or a block diagram. Although a flowchart may describe the operations as a sequential process, many of the operations can be performed in parallel or concurrently. In addition, the order of the operations may be re-arranged. A process is terminated when its operations are completed, but could have additional steps not included in a figure. A process may correspond to a method, a function, a procedure, a subroutine, a subprogram, etc. When a process corresponds to a function, its termination can correspond to a return of the function to the calling function or the main function. 
     The term “computer-readable medium” includes, but is not limited to, portable or non-portable storage devices, optical storage devices, and various other mediums capable of storing, containing, or carrying instruction(s) and/or data. A computer-readable medium may include a non-transitory medium in which data can be stored and that does not include carrier waves and/or transitory electronic signals propagating wirelessly or over wired connections. Examples of a non-transitory medium may include, but are not limited to, a magnetic disk or tape, optical storage media such as compact disk (CD) or digital versatile disk (DVD), flash memory, memory or memory devices. A computer-readable medium may have stored thereon code and/or machine-executable instructions that may represent a procedure, a function, a subprogram, a program, a routine, a subroutine, a module, a software package, a class, or any combination of instructions, data structures, or program statements. A code segment may be coupled to another code segment or a hardware circuit by passing and/or receiving information, data, arguments, parameters, or memory contents. Information, arguments, parameters, data, etc. may be passed, forwarded, or transmitted via any suitable means including memory sharing, message passing, token passing, network transmission, or the like. 
     Furthermore, embodiments may be implemented by hardware, software, firmware, middleware, microcode, hardware description languages, or any combination thereof. When implemented in software, firmware, middleware or microcode, the program code or code segments to perform the necessary tasks (e.g., a computer-program product) may be stored in a computer-readable or machine-readable medium. A processor(s) may perform the necessary tasks. 
     Virtual reality (VR) provides the ability to be virtually present in a non-physical world created by the rendering of natural and/or synthetic images and sound correlated by the movements of the immersed user, allowing the user to interact with that world. With the recent progress made in rendering devices (e.g., head mounted displays (HMD)) and in 360-degree video (also referred to as VR or Augmented reality (AR) video in some cases) creation, a significant quality of experience can be offered. VR and/or AR applications include gaming, training, education, sports video, online shopping, and so on. 
     In some examples, a 360-degree video system can include various components and can perform various steps. For example, a 360-degree video system can include a camera set. The camera set can include multiple individual cameras (virtual or real cameras) pointing to different directions (with different views) and collectively covering various viewpoints around the camera set (or virtual reality scene). 
     The 360-degree video system can obtain the video pictures captured by the cameras of the camera set, and can perform image stitching. For example, an image stitching device can receive the video pictures from the camera set. In some examples, image stitching includes obtaining the video pictures taken by the multiple individual cameras and synchronizing the video pictures in the time domain and stitching the video pictures in the space (spatial) domain to be a spherical video, but mapped to a rectangular format, such as equi-rectangular (e.g., a world map), cube map, or other shape. 
     The video in the mapped rectangular format can then be encoded (or compressed) using a video codec (e.g., an MPEG codec, a H.265/HEVC codec, a H.264/AVC codec, or other suitable codec). Details regarding encoding of video data using a video codec are described below. 
     The compressed video bitstream(s) may be stored and/or encapsulated in a media format and transmitted through a network to a receiver. For example, a transmission side of the 360-degree video system can generate encapsulated files from the encoded video data (e.g., using a ISO base media file format and/or derived file formats). For instance, the video codec can encode the video data and an encapsulation engine can generate the media files by encapsulating the video data in one or more ISO format media files. In some implementations, the compressed bitstream is not stored and/or encapsulated in a media format. 
     A receiver can then receive the encoded (or compressed) video bitstream(s), possibly encapsulated in a format. A codec in the receiver can decode (or decompress) the encoded video bitstream(s). In some instances, the receiver can parse the media files with encapsulated video data to generate the encoded video data. For example, when a media format is used, the receiver can parse the media files with the encapsulated video data to generate the encoded video data, and the codec in the receiver can decode the encoded video data. 
     The receiver can then send the decoded video signal to a rendering device. The rendering device can be, for example, an HMD or other rendering device. An HMD can track head movement and eye movement, and can render the corresponding part of the video such that an immersive experience is presented to the user. 
     Projections and geometric mappings are used to represent three-dimensional (3D) surfaces on two-dimensional (2D) maps using a 3D-to-2D process. For example, in 360-degree video applications, projections and mappings are used to map a 360-degree video represented on a sphere onto a two-dimensional video frame. Examples of 3D-to-2D projections and mappings include, but are not limited to: equirectangular (ERP), cubemap (CMP), adjusted cubemap (ACP), and equatorial cylindrical (ECP). In some geometric mappings (e.g., CMP and ACP), six sided cube images, spatially related to one another, are transformed into a rectangular 2D projections and mappings. In other geometric mappings (e.g., ECP), cylinder geometry can be used. 
     After stitching of multiple input camera pictures, 360-degree video pictures are typically represented in the ERP format. An equirectangular projection maps points on a sphere to a 2D map by linearly mapping the latitude and longitude of the points on the sphere to x-y coordinates on a picture. A cubemap projection projects the points on the surface of the sphere to points on planes (faces of the cube) that are tangent to the sphere surface. The cubemap projection projects the surface of the sphere onto planes (six faces of the cube) that are tangent to the sphere surface. Adjusted cubemap projection is an enhancement of CMP, which adjusts the sampling on the cube faces to be nearly uniform. Besides the cube geometry, the cylindrical geometry has been utilized to achieve equal-area mapping of the sphere surface onto the projected picture. An equatorial cylindrical projection maps an equatorial sphere segment onto a cylinder. In one example, the ECP operates to project the equatorial region of the sphere between latitudes ±sin −1 (⅔)≈±41.81° onto the cylinder geometry, while the circular sphere pole regions are warped into square regions in the projected picture. 
       FIG. 1  ( FIGS. 1A-1D ) shows video pictures of the ‘PoleVault’ sequence obtained with ERP, CMP, ACP and ECP projections. Shown in  FIG. 1A , is an ERP frame projection  100 , shown in  FIG. 1B , is a CMP 3×2 frame projection  102 , shown in  FIG. 1C , is an ACP 3×2 frame projection  104 , and shown in  FIG. 1D , is an ECP 3×2 frame projection  106 . 
       FIG. 1B &#39;s CMP 3×2 frame projection  102  includes an upper picture half  130  and a bottom picture half  132 , and the halves are separated by a horizontal projection boundary  160  (in other projection types it may be vertical). As used herein, a “projection boundary” can represent a boundary between multiple regions (e.g., upper picture half  130  and bottom picture half  132 ) disposed adjacent to one another along the boundary within the projection domain (e.g., as shown in frame projection  102 ). In some embodiments, a projection boundary can also represent a boundary between multiple regions (e.g., upper picture half  130  and bottom picture half  132 ) that are not disposed adjacent to one another along the boundary within the spatial domain. 
     The upper picture half  130  is divided into the following set of adjacent camera picture regions: a left region  110 , a front region  111  and a right region  112 , and each of such regions in the upper half  130  are separated from one another by vertical spatial-domain-adjacent region boundaries  150  &amp;  151 . The bottom picture half  132  is divided into the following set of adjacent camera picture regions: a bottom region  120 , a back region  121 , and a top region  122 , and each of such regions in the bottom half  132  are separated from one another by vertical spatial-domain-adjacent region boundaries  150  &amp;  151 . 
       FIG. 1C &#39;s ACP 3×2 frame projection  104  includes an upper picture half  134  and a bottom picture half  136 , and the halves are separated by a horizontal projection boundary  162 . The upper picture half  134  is divided into the following set of spatially and projection adjacent camera picture regions: a left region  113 , a front region  114  and a right region  115 , and each of such regions in the upper picture half  134  are separated from one another by vertical spatial-domain-adjacent region boundaries  152  &amp;  153 . The bottom picture half  136  is divided into the following set of spatially and projection adjacent camera picture regions: a bottom region  123 , a back region  124 , and a top region  125 , and each of such regions in the bottom picture half  136  are separated from one another by vertical spatial-domain-adjacent region boundaries  152  &amp;  153 . 
       FIG. 1D &#39;s ECP 3×2 frame projection  106  includes an upper picture half  138  and a bottom picture half  139 , and the halves are separated by a horizontal projection boundary  163 . The upper picture half  138  is divided into the following set of specially and projection adjacent camera picture regions: a left region  116 , a front region  117  and a right region  118 , and each of such regions in the upper picture half  138  are separated from one another by vertical spatial-domain-adjacent region boundaries  154  &amp;  155 . The bottom picture half  139  is divided into the following set of spatially and projection adjacent camera picture regions: a bottom region  126 , a back region  127 , and a top region  128 , and each of such regions in the bottom picture half  139  are separated from one another by vertical spatial-domain-adjacent region boundaries  154  &amp;  155 . 
     Various problems exist in the rendering of 360-degree video via known projections and mappings techniques that transform three-dimensional (3D) surfaces on two-dimensional (2D) maps using a 3D-to-2D process. For example, the existing level of seam/boundary artifacts resulting from the use of such techniques. The seam/boundary artifacts tend to appear when the projected picture consists of adjacent discontinuous regions. 
     After the projection process, the video pictures are typically compressed with a video encoder (AVC, HEVC, etc.), stored or transmitted, and decoded at the receiver side where the renderer generates the viewport that matches the viewer&#39;s head orientation. Depending on this orientation and the field of view, the viewport may cross the outer picture boundaries or inner boundaries within the picture. For boundaries within the picture, the boundaries may be between continuous adjacent regions or discontinuous non-adjacent regions as is shown in  FIG. 2 . 
       FIG. 2  ( FIGS. 2A-2D ), shows in  FIG. 2A , an ERP picture  200 .  FIG. 2B  shows a 3×2 CMP/ACP picture  201 .  FIG. 2C  shows a 3×2 CMP/ACP picture  202 .  FIG. 2D  shows a ECP picture  203 .  FIG. 2E  shows an ECP picture  204 . 
       FIG. 2A , shows an ERP picture  200  that contains outer picture edge boundaries  290 - 296 . ERP picture  200  includes a viewport  205 , where the viewport  205  intersects outer picture edge boundary  294  along viewport boundary intersecting edge segment  220  and outer picture edge boundary  292  along viewport boundary intersecting edge segment  221 . Here, the full area of the ERP picture  200 , in one example, equates to one single region. As an ERP picture, the ERP picture  200 , is a full wrap around 360 degree projected picture, the two vertical outer picture boundaries  292 ,  294 , although shown as separate outer picture boundaries, can be said to represent a single vertical spatial-domain-adjacent boundary at the back edge of the ERP picture  200  where pixels alongside the right outer picture boundary  292  represent pixels that are spatially associated with other corresponding pixels alongside the left outer picture boundary  294 . 
       FIG. 2B  shows a CMP/ACP picture  201  that contains four outer picture edge boundaries  242 - 245 . CMP/ACP picture  201  contains six regions  270 - 272 ,  278 - 280 , where the top half of the CMP/ACP picture  201  is made up of three spatially continuous adjacent regions  270 - 272 , and where the spatially continuous adjacent regions  270 - 272  are separated from one another along vertical spatial-domain-adjacent boundaries  258 ,  259 . The bottom half of the CMP/ACP picture  201  contains three spatially continuously adjacent regions  278 - 280 , where the spatially continuously adjacent regions are separated from one another along vertical spatial-domain-adjacent boundaries  258 ,  259 . The CMP/ACP picture&#39;s  201  top half ( 270 - 272  together) and bottom half ( 278 - 280  together) are separated from one another by a horizontal projection boundary  266 . CMP/ACP picture  201  includes a viewport  206 , where the viewport  206 , for its portion located within a left region  270 , intersects the left outer picture edge boundary  244  along viewport boundary intersecting edge segment  222 , and also intersects the top outer picture edge boundary  242  along viewport boundary intersecting edge segment  223 . The viewport  206 , for its portion located within back region  279 , intersects bottom outer picture boundary  245  along viewport boundary intersecting edge segment  224  and intersects vertical spatial-domain-adjacent region boundary  259  along viewport boundary intersecting edge segment  225 . The viewport  206 , for its portion located within top region  280 , intersects bottom outer picture boundary  245  along viewport boundary intersecting edge segment  226  and intersects vertical spatial-domain-adjacent adjacent picture boundary  259  along viewport boundary intersecting edge segment  225 . 
       FIG. 2C  shows a CMP/ACP picture  202  that contains four outer picture edge boundaries  246 - 249 . CMP/ACP picture  202  contains six regions  273 - 275 ,  281 - 283 , where the top half of the CMP/ACP picture  202  contains three spatially continuous adjacent regions  273 - 275 , and where the spatially continuous adjacent regions are separated from their adjacent counterparts along vertical spatial-domain-adjacent region boundaries  260 ,  261 . The bottom half of the CMP/ACP picture  202  contains three spatially continuous adjacent regions  281 - 283 , where the spatially continuously adjacent regions are separated from their adjacent counterpart regions along vertical spatial-domain-adjacent region boundaries  260 ,  261 . The CMP/ACP picture&#39;s  202  top half ( 273 - 275  together) and bottom half ( 281 - 283  together) are separated from one another by a horizontal projection boundary  267 . CMP/ACP picture  202  includes a viewport  207 , where the viewport  207 , for its portion located within a front region  274 , intersects the horizontal projection boundary  267  along viewport boundary intersecting edge segment  229 , and also intersects the vertical spatial-domain-adjacent region boundary  261  along viewport boundary intersecting edge segment  230 . The viewport  207 , for its portion located within right region  275 , intersects horizontal projection boundary  267  along viewport boundary intersecting edge segment  231 , and intersects vertical spatial-domain-adjacent picture/region boundary  261  along viewport boundary intersecting edge segment  230 . The viewport  207 , for its portion located within bottom region  281 , intersects left outer picture boundary  248  along viewport boundary intersecting edge segment  227 , and intersects horizontal projection boundary  267  along viewport boundary intersecting edge segment  228 . 
       FIG. 2D  shows an ECP picture  203  that contains four outer picture edge boundaries  250 - 253 . ECP picture  203  contains four regions  276 ,  284 - 286 , where the top half of the ECP picture  203  comprises front region  276 , where front region  276  represents three-fourths of a cylinder and spans the top half of the ECP picture  203 . The bottom half of the ECP picture  203  contains three spatially continuous adjacent regions  284 - 286 , where the spatially continuous adjacent regions are separated from their adjacent counterpart regions along vertical spatial-domain-adjacent region boundaries  262 ,  263 . The ECP picture&#39;s  203  top half  276  and bottom half ( 284 - 286  together) are separated from one another by a horizontal projection boundary  268 . ECP picture  203  includes a viewport  208 , where the viewport  208 , for its portion located within a front region  276 , intersects the left outer picture boundary  252  along viewport boundary intersecting edge segment  232 , and also intersects the top outer picture boundary  250  along viewport boundary intersecting edge segment  233 . The viewport  208 , for its portion located within back region  285 , intersects bottom outer picture boundary  253  along viewport boundary intersecting edge segment  234  and intersects vertical spatial-domain-adjacent region/picture boundary  263  along viewport boundary intersecting edge segment  235 . The viewport  208 , for its portion located within top region  286 , intersects bottom outer picture boundary  253  along viewport boundary intersecting edge segment  236  and intersects vertical spatial-domain-adjacent region/picture boundary  263  along viewport boundary intersecting edge segment  235 . 
       FIG. 2E  shows an ECP picture  204  that contains four outer picture edge boundaries  254 - 257 . ECP picture  204  contains four regions  277 ,  287 - 289 , where the top half of the ECP picture  204  comprises front region  277 , where front region  276  represents three-fourths of a cylinder and spans the top half of the ECP picture  204 . The bottom half of the ECP picture  204  contains three spatially continuous adjacent regions  287 - 289 , where the spatially continuous adjacent regions are separated from their adjacent counterpart regions along vertical spatial-domain-adjacent region boundaries  264 ,  265 . The ECP picture&#39;s  204  top half  277  and bottom half ( 287 - 289  together) are separated from one another by a horizontal projection boundary  269 . ECP picture  204  includes a viewport  209 , where the viewport  209 , for its portion located within a front region  277 , intersects the horizontal projection boundary  269  along two viewport edge segments  239  &amp;  240 . The viewport  209 , for its portion located within bottom region  287 , intersects left outer picture boundary  256  along viewport boundary intersecting edge segment  237 , and intersects horizontal projection boundary  269  along viewport boundary intersecting edge segment  238 . 
     Depending on the orientation and the field of view, and as shown in  FIG. 2  ( FIGS. 2A-2E ), the viewports  205 - 209  may cross (1) the outer edge picture boundaries  242 - 257 ,  290 - 296  or (2) vertical spatial-domain-adjacent region boundaries  258 - 265  within the picture between groups of adjacent regions (e.g., ( 270 / 271 / 272 ), ( 273 / 274 / 275 ), ( 278 / 279 / 280 ), ( 281 / 282 / 283 ), ( 284 / 285 / 286 ), ( 287 / 288 / 289 )) or (3) horizontal projection boundaries  266 - 269  between non-spatially-adjacent regions (e.g.,  270 / 278 ,  271 / 279 ,  272 / 280 ,  273 / 281 ,  274 / 282 ,  275 / 283 ,  276 / 284 ,  276 / 285 ,  276 / 286 ,  277 / 287 ,  277 / 288 ,  277 / 289 ). The viewport edge segments  220 - 240 , as shown, are where the viewport regions  202 - 210  cross such boundaries (outer picture, adjacent &amp; non-adjacent). 
     In at least one example, for example the ERP case in  FIG. 2A  showing projected picture  200 , the left  294  and right  292  outer picture boundaries wrap around the back of the sphere, hence, a viewport  205  that is orientated towards the back of the sphere may cross the left  294  and right  292  outer picture boundaries. The region in the ERP picture that is available, and in some examples, required to render the viewport is represented by shaded rectangles  205  for illustrative purposes (generally the shape may not be rectangular). The boundaries within the region required for rendering are represented, in  FIG. 2A , by two line segments  220 ,  221 . 
     In at least one example, the case of 3×2 frame packing of the CMP or ACP cube faces as illustrated in  FIGS. 1B and 1C , the viewport, as shown in  FIGS. 2B and 2C , ( 206  &amp;  207 ) may cross various boundaries as shown as bold boundary edge segments  222 - 226  and  227 - 231 , ( FIGS. 2B and 2C  respectively). Although, as shown, the left  270 ,  273 , front  271 ,  274 , and right  272 ,  275  cube faces/regions are placed adjacent in the top picture half, there is exists a vertical spatial-domain-adjacent region boundary  258 ,  260  between the left  270 ,  273  and front faces/regions  271 ,  274 , and between the front  271 ,  274  and right  272 ,  275  faces/regions where, for example, lines are broken as is visible in  FIGS. 1B and 1C , and similarly for the bottom picture half, where there is a vertical spatial-domain-adjacent region boundaries  259 ,  261  between the top  280 ,  283  and back  279 ,  282  region/faces, and a vertical spatial-domain-adjacent region boundary  258 ,  260  between the bottom  278 ,  281  and back  279 ,  282  face/regions. These vertical spatial-domain-adjacent region boundaries  258 - 265  ( FIGS. 2B-2E ) between adjacent cube faces are less discontinuous than (1) the actual picture boundaries  242 - 257  and (2) the horizontal projection boundaries  266 - 269  between the top  270 / 271 / 272 ,  273 / 274 / 275 ,  276 ,  277  ( FIGS. 2B-2E ) and bottom  278 / 279 / 280 ,  281 / 282 / 283 ,  284 / 285 / 286 ,  287 / 288 / 289 ) halves of the picture.  FIGS. 2B and 2C  illustrate two viewports  206 ,  207  with regions used for rendering that cross various boundaries. In these examples, a 3×2 packing of the cube faces is chosen, however, alternative packing schemes exist that have different boundaries (e.g., 1×6, 6×1, etc.) which represent other alternative examples. The 3×2 packing has one of the fewest boundaries of the packing schemes. 
     In at least one example, for example the case of the ECP boundaries illustrated in  FIGS. 2D and 2E  with packing that is similar to the 3×2 packing of CMP and ACP. In this example, the main difference is that the top picture half, containing “front” region  276 ,  277 , is a continuous region corresponding with a full three quarters of the unwrapped cylinder which is used to project the equatorial region of the sphere. In this packing, one quarter of the unwrapped cylinder, as contained in back regions  284 - 286 ,  287 - 289 , is placed in the back position. Compared with CMP and ACP ( FIGS. 2B &amp; 2C ), for example, lines are not broken at any boundary within the front region  276 ,  277  ( FIGS. 2D &amp; 2E ), however, lines are curved due to the cylindrical projection. In this ECP example ( FIGS. 2D &amp; 2E ), other boundaries are equivalent with CMP and ACP ( FIGS. 2B &amp; 2C ) boundaries, with some additional discontinuity between the top ( 280 ,  283  ( FIGS. 2B &amp; 2C )) ( 286 ,  289  ( FIGS. 2D &amp; 2E )) and back ( 279 ,  282  ( FIGS. 2B &amp; 2C )), ( 285 ,  288  ( FIGS. 2D &amp; 2E )) regions, and the bottom ( 278 ,  281  ( FIGS. 2B &amp; 2C )), ( 284 ,  287  ( FIGS. 2D &amp; 2E )) and back ( 279 ,  282  ( FIGS. 2B &amp; 2C )), ( 285 ,  288  ( FIGS. 2D &amp; 2E )) regions due to minor misalignment in the ECP scheme. Other alternative exemplary packing schemes (not shown), such as 6×1 or 1×6, keep the unwrapped cylinder region connected, however, in such examples, additional boundaries are present between the cylindrical region and the pole regions. 
     The three types of picture boundaries, (1) the outer picture boundaries, (2) the vertical spatial-domain-adjacent region boundaries located between pictures that are adjacent to one another in the pre-stitched camera pictures and where such boundary represents a stitched boundary between two spatially adjacent regions, and (3) the horizontal projection boundaries located between pictures, where such pictures are not spatially adjacent to one another in in the pre-stitched camera pictures, and all three types of picture boundaries are within the projected picture, and may be associated with visible seam/boundary artifacts within the rendered viewport. The following are two examples of potential causes: Example 1 potential cause, is related to motion. In at least one example, for example the case of motion across the outer picture boundary directed into the region, the motion estimation process may select a block that partially includes the padded samples that the encoder adds to extend the reference pictures. At higher quantization parameter (QP) values, those padded samples appear on one side of the boundary in the viewport, while the other side of the boundary is different as illustrated in  FIG. 3A . ( FIG. 3A  represents an example of rendered viewport seam/boundary  301  (vertically down the center of the image) due to motion). This type of seam/boundary artifact is strong at higher QP values. A similar problem occurs, in some examples, inside the CMP or ACP picture (3×2 packing)( FIGS. 2B &amp; 2C ), when motion estimation selects a block that is located partially across the middle picture boundary. In some examples a similar problem occurs related to In-loop filtering (deblocking, sample adaptive offset). In at least one example, where filtering is disabled on the picture boundaries, a sharp unfiltered seam/boundary may be visible in the rendered viewport especially at higher QP values. In the CMP or ACP picture (3×2 packing), the filtering may occur across the middle picture boundary resulting in visible seam/boundary artifacts as illustrated in  FIG. 3B . ( FIG. 3B  shows a viewport seam/boundary  310 ,  312  due to filtering). 
     Systems and methods are disclosed herein that address problems such as those noted above. For example, to address the problems associated with relatively numerous seam/boundary artifacts, multiple systems and methods are proposed such as (1) projected picture adaptations (encoder/decoder), (2) video encoder only modifications, and (3) a hybrid model. In a projected picture adaptations exemplary approach, the projected picture is adapted such that during the rendering stage the seams/boundaries are prevented. An example of such an approach is the use of guard bands. In a video encoder only modifications exemplary approach, the encoder may be projection aware and may make internal modifications that are standard compliant (AVC, HEVC, etc.) to prevent the projection seams/boundaries in the rendering stage. In a hybrid exemplary approach, both video encoder and projected picture modifications may be combined to achieve improved seam/boundary artifact reduction results. 
     The following are further detailed examples of the projected picture adaptations exemplary approach including a 1 st  example titled guard bands symmetrically distributed around the regions of the projected picture, and a 2 nd  example titled guard bands asymmetrically distributed in the projected picture. 
     Guard bands are regions/areas added into the projected picture consisting of additional samples (seam artifact reducing samples) (e.g., pixels) that are not essential for projecting the picture back onto the sphere, but they can be helpful in reducing artifacts such as seams/boundaries on the sphere or in the rendered viewport with the artifacts being the result of the video encoder actions such as motion compensated prediction, in-loop filtering, quantization, etc. Samples that are not essential for projecting the picture back onto the sphere and that are used to reduce artifacts associated with seams/boundaries are described herein as seam artifact reducing samples. The samples in the guard band may include additional seam artifact reducing projected samples, i.e., samples obtained around (spatially nearby) the projected regions with the same projection process, for example, the CMP, ACP, or ECP processes. For example, where a first point is located near an edge of a front region/face cube in a cube geometry, and where there exists a second point/sample in a spatially nearby location on a neighboring top region/face, such spatially nearby points may be relocated away from one another in an associated CMP, ACP or ECP projection including such regions/faces. The spatial proximity and location of all the pixels generated in associated CMP, ACP or ECP algorithms/calculations can be used in the associated projection process and can be used to identify the spatial proximity between any two locations regardless of where they are located on the projected picture. 
     There are other options for guard band seam artifact reducing samples such as gradient samples (e.g., via a gradient operation) that transition from one region to a second region in the projected picture, or a combination of projected samples with gradients or blends, or duplicated samples where the boundary samples of the projected region (e.g., around an edge of the region) are duplicated to the guard band region. In general, the guard band seam artifact reducing samples may be obtained so that the compression efficiency is preserved while reducing the seam/boundary artifacts. The guard band regions typically are defined by a width and a location around the perimeter of the projected region in the picture, and can be further described as, the location being alongside a particular region boundary and the width extending from such particular region boundary&#39;s edge into such region. For example, the guard bands may be present along all sides/edges/boundaries (perimeter) of a cube face, which is the symmetric case, or the guard bands may be placed along only some sides/edges/boundaries that contribute most to the artifact reduction in the viewport, which is the asymmetric case. Since the guard band regions (including additional guard band seam artifact reducing samples) are added to the projected picture before the video encoding, the guard band regions are available to the video encoding processes for prediction such as motion compensated prediction, etc., which may improve prediction. However, the use of the samples for prediction in the video encoding processes may be prohibited by signalled information, for example, in the file format, etc., as further described in Miska M. Hannuksela, Igor D. D. Curcio, “OMAF: Guard band signalling”, MPEG Doc. M40408, Hobart, Australia, April 2017, and Byeongdoo Choi, Ye-Kui Wang, Miska M. Hannuksela, Youngkwon Lim, “Text of ISO/IEC DIS 23090-2 Omnidirectional Media Format”, MPEG Doc. N16824, Hobart, Australia, April 2017. 
       FIG. 4  ( FIGS. 4A-4C ) illustrates various guard band exemplary schemes for 3×2 packed CMP and ACP pictures  400 - 406 , which may be based on the cube geometry with six faces/regions,  410 - 412 ,  419 - 421 , as shown in  FIG. 4A .  FIG. 4A  shows projected picture  400 , there is a guard band  430 - 453  alongside every cube face/region ( 410 - 412 ,  419 - 421 ) boundary ((areas outside of dashed lines) ( 430 - 435 )) such that the cube face/region (non-guard band area) area remains square. This is an example of a symmetric guard band case. In general, the guard band width may vary depending on the cube face side, which is the asymmetric guard band case. Examples are depicted in  FIGS. 4B and 4C .  FIG. 4B , showing projected picture  402 , is an example of the case where the guard bands  454 - 469  are added alongside the top ( 413 - 415  together) and bottom ( 422 - 424  together) 3×1 halves of the projected picture  402 . The reason is that the cube faces/regions within each of the top ( 413 - 415  together) and bottom ( 422 - 424  together) halves are adjacent to one another in the respective halves, along vertical spatial-domain-adjacent region boundaries, is to avoid discontinuous edges within such respective halves. The assumption to support this type of guard band regions is that the seam/boundary artifacts corresponding with the camera picture adjacent to one another in the space domain are often less visible in the rendered viewport and, hence, in at least one example, need no guard band. Note that for each face/region in the top half ( 413 - 415  together), for example, the non-guard band areas (the areas cut out from the original face/region: face/region minus the guard band) represent rectangular non-square areas which is different from their original square geometry before the application of the associated guard area. Other original square faces/regions in many of the examples herein are also changed to non-square areas (non-guard band areas) after the application of the associated guard regions. In  FIG. 4C , showing projected picture  406 , the guard band regions  470 - 475  may be only applied around and alongside the horizontal projection boundary between top ( 416 - 418  together) and bottom ( 425 - 427  together) picture halves to avoid the in-loop filtering that may occur in the encoding process across this non-spatial-domain-adjacent middle boundary. This type of seam/boundary artifacts is known to be typically very problematic in the rendered viewport and, therefore, this guard band type may be recommended in case, for example, the in-loop filtering cannot be disabled by other means in the encoder. Further discussion can be found in the discussion below on Video Encoder-Only Modifications. 
       FIG. 5  ( FIGS. 5A-5E ), showing projected pictures  500 - 508 , depicts guard band regions  530 - 591 ,  330 - 346  for ECP pictures and a CMP/ACP picture (e.g., 3×2 packed ECP in  FIGS. 5A-5C ; 6X1 packed ECP in  FIG. 5D ; and 6×1 packed CMP/ACP in  FIG. 5E ). A difference with guard bands for the cube geometry (e.g.,  FIG. 5E ) may be exemplified in that in ECP packing, there is a three-fourths of a cylinder region (labeled “Front” in these examples) that is not split (e.g.,  FIGS. 5A-5D ). 
       FIG. 5A , showing projected picture  500 , depicts a symmetric guard band region case with a guard band area ( 530 - 536  together) around top picture half  510 , and guard bands ( 537 - 548  together) within the bottom picture half ( 516 - 518  together), and more specifically, a guard band  544 - 546 ,  549  around top region  518 , a guard band  538 - 540 ,  547  around bottom region  516 , and a guard band  541 - 543 ,  548  around back region  517 . Here, top picture half  510  comprises, in the same location and area, a three-fourths of a cylinder front region.  FIGS. 5B and 5C , showing projected pictures  502 ,  504 , depict asymmetric case examples, with  FIG. 5B  showing guard bands  550 - 565  around the top  511  and bottom ( 519 - 521  together) 3×1 picture halves, and with  FIG. 5C  showing guard bands  566 - 571  alongside (above and below) a horizontal projection boundary between top  512  and bottom ( 522 - 524  together) picture halves. 
     In other examples, ECP may be packed 1×6 or 6×1 as depicted in  FIG. 5D , showing projected picture  506 , where the cylinder region ( 316 - 320  together) is not split (6×1 packed ECP with guard regions).  FIG. 5D  shows projected picture  506 , with three faces/regions, a 360 cylinder region face ( 316 - 320  together), a top face  321  and a bottom face  322 , and each face having respective guard band areas  572 - 591 . In  FIG. 5D , two vertical projection boundaries  595 ,  596  are shown, a first boundary  595  between the 360 cylinder region face ( 316 - 320  together) and the top face/region  321 , and a second boundary  596  between the top face/region  321  and the bottom face/region  322 . Although the cylinder region is not split and is represented in the form of front face ( 316 - 20  together), such front face ( 316 - 20  together) corresponds to the four: front, left, right and back, of the original cube geometry (i.e., a 360 cylinder region). 
     In another example, CMP/ACP may be backed 1×6 or 6×1 as depicted in  FIG. 5E , showing projected picture  508 .  FIG. 5E  shows projected picture  508 , with six faces/regions  1010 - 1015  and each face having guard bands  330 - 346 . In  FIG. 5E , a vertical discontinuous projection-only-adjacent region boundary  360  is shown between bottom region  1013  and right region  1012 . 
     Depending on the packing type, the number of guard bands may be different. For example, the case represented in  5 B is shown as having 16 guard bands ( 550 ,  551 ,  552 ,  553 ,  554 ,  555 ,  556 ,  557 ,  558 ,  559 ,  560 ,  561 ,  562 ,  563 ,  564 ,  565 )(one guard band counted per face side (noting that there are 3 face sides within the top picture (front) half)) while the case represented in  5 D is shown as having 18 guard bands (( 572 ,  573 ,  574 ,  575 ,  577 ,  578 ,  579 ,  580 ,  581 ,  582 ,  583 ,  584 ,  586 ,  587 ,  588 ,  589 ,  590 ,  591 ) (noting that there are 4 face sides within face region ( 316 - 320  together). Hence, for similar guard band protection, in some examples, the 3×2 packing type could be more favorable. 
     The presence of guard bands per region and the guard band width may be signaled, for example, in the file format, etc. The presence of guard bands may also be QP dependent. For example, at low QP values, the guard band may be avoided or its width may be reduced. 
     The following represent examples of implementations of guard bands utilizing projected samples, i.e., samples obtained around the projected regions with the same projection process. Such examples are applicable to both ACP and CMP approaches. Although many of the following examples and example calculations correspond to specific 3×2 cube geometries, other examples can include other example calculations and where those example calculations can correspond to other cube geometries, for example, 6×1, 1×6, 2×3 cube geometries. 
     Denote the dimension of any square face as A×A in sample units. For 2D-to-3D coordinate conversion, given the position (m,n) on a given face f, (u,v) is first calculated as:
 
 u =( m+ 0.5)*2/ A− 1, 0≤ m&lt;A, − 1&lt; u&lt; 1
 
 v =( n+ 0.5)*2/ A− 1, 0≤ n&lt;A, − 1&lt; v&lt; 1.
 
     For symmetrical guard bands, i.e., guard bands applied to the four sides of the cube faces, the following padfactor is defined: 
             padfactor   =     1   +       2   ×   padmargin       A   -     2   ×   padmargin                 
with padmargin specifying the width of the guard bands in sample units (being smaller than A/2), for example, 4 samples. Subsequently, the (u, v) coordinates are scaled into (u′, v′) with padfactor as follows:
 
 u′=u ×padfactor,  v′=v ×padfactor
 
     This extends the cube face to sample additional boundary samples from the sphere. In the ACP case, the scaling is followed by the adjustment formulas. Subsequently, the 3D coordinates (X, Y, Z) are derived using the position (u′, v′) and the face index f (see Table 1 below). 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 (X, Y, Z) derivation given (u, v) and the face index f 
               
            
           
           
               
               
               
               
               
            
               
                   
                 f 
                 X 
                 Y 
                 Z 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 0 
                 1.0 
                 −v 
                 −u 
               
               
                   
                 1 
                 −1.0 
                 −v 
                 u 
               
               
                   
                 2 
                 u 
                 1.0 
                 v 
               
               
                   
                 3 
                 u 
                 −1.0 
                 −v 
               
               
                   
                 4 
                 u 
                 −v 
                 1.0 
               
               
                   
                 5 
                 −u 
                 −v 
                 −1.0 
               
               
                   
                   
               
            
           
         
       
     
     In case of 3D-to-2D coordinate conversion, given (X, Y, Z), the (u, v) and face index f is calculated per Table 2 below. Subsequently, the (u, v) coordinates are divided by the padfactor. In the ACP case, the scaling is performed after the adjustment formulas. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Derivation of (u, v) and the face index f given (X, Y, Z) 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Condition 
                 f 
                 u 
                 v 
               
               
                   
                   
               
               
                   
                 |X| ≥ |Y| and |X| ≥ |Z| and X &gt; 0 
                 0 
                 −Z/|X| 
                 −Y/|X| 
               
               
                   
                 |X| ≥ |Y| and |X| ≥ |Z| and X &lt; 0 
                 1 
                 Z/|X| 
                 −Y/|X| 
               
               
                   
                 |Y| ≥ |X| and |Y| ≥ |Z| and Y &gt; 0 
                 2 
                 X/|Y| 
                 Z/|Y| 
               
               
                   
                 |Y| ≥ |X| and |Y| ≥ |Z| and Y &lt; 0 
                 3 
                 X/|Y| 
                 −Z/|Y| 
               
               
                   
                 |Z| ≥ |X| and |Z| ≥ |X| and Z &gt; 0 
                 4 
                 X/|Z| 
                 −Y/|Z| 
               
               
                   
                 |Z| ≥ |X| and |Z| ≥ |Y| and Z &lt; 0 
                 5 
                 −X/|Z| 
                 −Y/|Z| 
               
               
                   
                   
               
            
           
         
       
     
     For the asymmetrical guard band case depicted in  FIG. 4B , where guard bands ( 454 - 469 ) are added around the top ( 413 - 315  together) and bottom ( 422 - 424  together) picture halves, scaling in Table 3 is applied per cube face f with asymmetrical apadfactor defined as follows: 
     
       
         
           
             apadfactor 
             = 
             
               A 
               
                 A 
                 - 
                 padmargin 
               
             
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Scaling of (u, v) coordinates in 2D-to-3D conversion of 
               
               
                 CMP and ACP. 
               
            
           
           
               
               
               
               
            
               
                   
                 Face 
                 Index f 
                 2D-to-3D Conversion 
               
               
                   
                   
               
               
                   
                 Front 
                 0 
                 u′ = u 
               
               
                   
                   
                   
                 v′ = v × padfactor 
               
               
                   
                 Back 
                 1 
                 u′ = u × padfactor 
               
               
                   
                   
                   
                 v′ = v 
               
               
                   
                 Top 
                 2 
                 u′ = (u + 1) × apadfactor − 1 
               
               
                   
                   
                   
                 v′ = v × padfactor 
               
               
                   
                 Bottom 
                 3 
                 u′ = (u + 1) × apadfactor − 1 
               
               
                   
                   
                   
                 v′ = v × padfactor 
               
               
                   
                 Left 
                 4 
                 u′ = (u − 1) × apadfactor + 1 
               
               
                   
                   
                   
                 v′ = v × padfactor 
               
               
                   
                 Right 
                 5 
                 u′ = (u + 1) × apadfactor − 1 
               
               
                   
                   
                   
                 v′ = v × padfactor 
               
               
                   
                   
               
            
           
         
       
     
     In case of 3D-to-2D coordinate conversion, the scaling in Table 4 is applied to obtain the final (u′, v′) coordinates. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Scaling of (u, v) coordinates in 3D-to-2D conversion of 
               
               
                 CMP and ACP. 
               
            
           
           
               
               
               
               
            
               
                   
                 Face 
                 Index f 
                 3D-to-2D Conversion 
               
               
                   
                   
               
               
                   
                 Front 
                 0 
                 u′ = u 
               
               
                   
                   
                   
                 v′ = v/padfactor 
               
               
                   
                 Back 
                 1 
                 u′ = u/padfactor 
               
               
                   
                   
                   
                 v′ = v 
               
               
                   
                 Top 
                 2 
                 u′ = (u + 1)/apadfactor − 1 
               
               
                   
                   
                   
                 v′ = v/padfactor 
               
               
                   
                 Bottom 
                 3 
                 u′ = (u + 1)/apadfactor − 1 
               
               
                   
                   
                   
                 v′ = v/padfactor 
               
               
                   
                 Left 
                 4 
                 u′ = (u − 1)/apadfactor + 1 
               
               
                   
                   
                   
                 v′ = v/padfactor 
               
               
                   
                 Right 
                 5 
                 u′ = (u + 1)/apadfactor − 1 
               
               
                   
                   
                   
                 v′ = v/padfactor 
               
               
                   
                   
               
            
           
         
       
     
     For the asymmetrical guard band case depicted in  FIG. 4C , where guard bands ( 470 - 475 ) are added to the middle picture boundary only, Table 3 is replaced with Table 5 below and Table 4 is replaced with Table 6 below. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Scaling of (u, v) coordinates in 2D-to-3D conversion of 
               
               
                 CMP and ACP. 
               
            
           
           
               
               
               
               
            
               
                   
                 Face 
                 Index f 
                 2D-to-3D Conversion 
               
               
                   
                   
               
               
                   
                 Front 
                 0 
                 u′ = u 
               
               
                   
                   
                   
                 v′ = (v + 1) × apadfactor − 1 
               
               
                   
                 Back 
                 1 
                 u′ = (u − 1) × apadfactor + 1 
               
               
                   
                   
                   
                 v′ = v 
               
               
                   
                 Top 
                 2 
                 u′ = u 
               
               
                   
                   
                   
                 v′ = (v − 1) × apadfactor + 1 
               
               
                   
                 Bottom 
                 3 
                 u′ = u 
               
               
                   
                   
                   
                 v′ = (v + 1) × apadfactor − 1 
               
               
                   
                 Left 
                 4 
                 u′ = u 
               
               
                   
                   
                   
                 v′ = (v + 1) × apadfactor − 1 
               
               
                   
                 Right 
                 5 
                 u′ = u 
               
               
                   
                   
                   
                 v′ = (v + 1) × apadfactor − 1 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 Scaling of (u, v) coordinates in 3D-to-2D conversion of 
               
               
                 CMP and ACP. 
               
            
           
           
               
               
               
               
            
               
                   
                 Face 
                 Index f 
                 3D-to-2D Conversion 
               
               
                   
                   
               
               
                   
                 Front 
                 0 
                 u′ = u 
               
               
                   
                   
                   
                 v′ = (v + 1)/apadfactor − 1 
               
               
                   
                 Back 
                 1 
                 u′ = (u − 1)/apadfactor + 1 
               
               
                   
                   
                   
                 v′ = v 
               
               
                   
                 Top 
                 2 
                 u′ = u 
               
               
                   
                   
                   
                 v′ = (v − 1)/apadfactor + 1 
               
               
                   
                 Bottom 
                 3 
                 u′ = u 
               
               
                   
                   
                   
                 v′ = (v + 1)/apadfactor − 1 
               
               
                   
                 Left 
                 4 
                 u′ = u 
               
               
                   
                   
                   
                 v′ = (v + 1)/apadfactor − 1 
               
               
                   
                 Right 
                 5 
                 u′ = u 
               
               
                   
                   
                   
                 v′ = (v + 1)/apadfactor − 1 
               
               
                   
                   
               
            
           
         
       
     
     Scaling is applied for ECP with padfactor and apadfactor defined for CMP and ACP. 
     In the asymmetric guard band case of  FIG. 5B , where guard bands ( 550 - 565 ) are applied to the upper ( 511 ) and lower picture ( 519 - 521  together) halves, the following scaling in Table 7 and Table 8 is applied. 
     
       
         
           
               
             
               
                 TABLE 7 
               
             
            
               
                   
               
               
                 Scaling of (u, v) coordinates in 2D-to-3D conversion of ECP. 
               
            
           
           
               
               
            
               
                 Index f 
                 2D-to-3D Conversion 
               
               
                   
               
               
                 0 
                 u′ = u × padfactor 
               
               
                   
                 v′ = (v + 1) × apadfactor − 1 
               
               
                 1 
                 u′ = u × padfactor 
               
               
                   
                 v′ = (v − 1) × apadfactor + 1 
               
               
                 2 
                 u′ = (u − 1) × apadfactor + 1 
               
               
                   
                 v′ = v × padfactor 
               
               
                 3 
                 u′ = u 
               
               
                   
                 v′ = v × padfactor 
               
               
                 4 
                 u′ = (u + 1) × apadfactor − 1 
               
               
                   
                 v′ = v × padfactor 
               
               
                 5 
                 u′ = u × padfactor 
               
               
                   
                 v′ = v 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 8 
               
             
            
               
                   
               
               
                 Scaling of (u, v) coordinates in 3D-to-2D conversion of ECP. 
               
            
           
           
               
               
            
               
                 Index f 
                 3D-to-2D Conversion 
               
               
                   
               
               
                 0 
                 u′ = u/padfactor 
               
               
                   
                 v′ = (v + 1)/apadfactor − 1 
               
               
                 1 
                 u′ = u/padfactor 
               
               
                   
                 v′ = (v − 1)/apadfactor + 1 
               
               
                 2 
                 u′ = (u − 1)/apadfactor + 1 
               
               
                   
                 v′ = v/padfactor 
               
               
                 3 
                 u′ = u 
               
               
                   
                 v′ = v/padfactor 
               
               
                 4 
                 u′ = (u + 1)/apadfactor − 1 
               
               
                   
                 v′ = v/padfactor 
               
               
                 5 
                 u′ = u/padfactor 
               
               
                   
                 v′ = v 
               
               
                   
               
            
           
         
       
     
     The following are further detailed examples of the video encoder-only modifications exemplary approach including a 1 st  example titled quantization parameter adjustment, a 2 nd  example titled in-loop filter disabling, and a 3 rd  example titled preventing predictions from non-adjacent regions. Such examples are video coding standard compliant with at least HEVC, and may be compliant with other standards having functionality applicable or analogous to the functionality addressed here. 
       FIG. 6  shows a picture  600  an upper picture half  604  and lower picture half  608 . Picture  600  is also shown with an exemplary 64×64 coding tree unit (CTU) and an exemplary 8×8 coding unit (CU). One CTU side  610  of the exemplary CTU is shown, as well as one 8×8 CU side  620  of exemplary CU. The picture  600  has four outer edge picture boundaries  630 - 633  at its perimeters, four upper picture region boundaries  630 ,  631 ,  632 ,  634  about the perimeter of the upper picture half  604 , and four lower picture region boundaries  631 ,  632 ,  633 ,  634  about the perimeter of the lower picture half  608 . 
     The quantization parameter (QP) adjustment along projected picture regions exemplary approach can contain the following functionality. The QP value may be adjusted along the projected picture region boundaries of CMP, ACP, or ECP. Additionally, the QP value may be adjusted for a set of CUs with the first CU adjacent to the projected picture region boundary and at least one other CU adjacent to the first CU or another CU in the set but not adjacent to the projected picture region boundary. The region QP area boundaries where QP is adjusted may resemble the guard band regions as discussed above, i.e., symmetric or asymmetric, with the difference being that the width of the QP area boundary depends on the coding unit size that allows for the QP change through delta-QP coding, if a residual is present (e.g., HEVC). The coding unit size for QP adjustment may be as large as the CTU or as small as the 8×8 CU, or any CU size combination therebetween. Note that the QP adjustment typically does not add projected samples to the projected picture, however, QP adjustment may be combined with the guard band approach.  FIG. 6  illustrates CTU splitting of a picture  600  down to 8×8 CUs along the upper and lower picture halves. The idea is to reduce the QP value of the 8×8 CUs along the boundaries. Such an approach would increase the number of bits assigned to the boundaries, hence, increasing the quality of the boundaries and reducing the seam/boundary artifacts in the rendered viewport. 
     The QP adjustment may be applied to all picture types such as intra coded, P (predictive coded picture) or B (bidirectional predictive coded picture) pictures generated in the random-access (RA) configuration of the video encoder, for example. Alternatively, the QP adjustment may be limited to intra-coded pictures only, or limited to certain levels of the picture prediction hierarchy in the RA configuration, for example, only intra coded pictures and first level B pictures. The QP adjustment may also be dependent on the QP value of the picture, for example. In case of a low (below a threshold value (e.g., less than 20)) QP value, the QP adjustment may be avoided or reduced. 
     The in-loop filter (deblocking, sample adaptive offset, etc.) disabling with tiles, slices, or QP changes exemplary approach can contain the following functionality. In at least one example, in the 3×2 packing of the CMP, ACP, or ECP projected picture, the in-loop filtering may affect the boundary between the upper and lower picture halves, resulting in severe seam/boundary artifacts in the rendered viewport. The in-loop filtering may be disabled on certain edges under the following five scenarios: In a 1 st  scenario, disable in-loop filtering (deblocking, SAO) in the entire picture by disabling in-loop filtering in the parameter sets (sequence parameter set (SPS), picture parameter set (PPS), etc.). In a 2 nd  scenario, disable in-loop filtering within a slice. In an example, one slice may consist of the CTUs containing the boundary. In-loop filtering may be disabled in the slice header. In a 3 rd  scenario, disable in-loop filtering across the tile boundary. In one example, two tiles may be defined containing the CTUs (or two CUs separated across the middle boundary, where the middle boundary may not be CTU aligned but the tile height is an integer multiple of the CTUs) in the upper and lower picture halves, respectively. In a 4 th  scenario, disable in-loop filtering by reducing the QP value of CUs along the boundary. If the QP is reduced below a threshold value (e.g., 15) then the deblocking filter does not affect edge samples. In a 5 th  scenario, the encoder can disable in-loop filtering by choosing not to apply a sample adaptive offset (SAO) band or edge offsets to CTUs along the boundary. 
     The preventing frame predictions from non-adjacent regions (intra prediction, motion compensation prediction (inter prediction), etc.) exemplary approach can contain the following functionality. Since intra prediction utilizes neighboring samples, which are potentially located in non-adjacent regions in the projected picture, a goal would be to prevent the encoder from utilizing these samples. Especially at higher QP value levels, artifacts may be visible. One approach to prevent the encoder from utilizing the neighboring samples is to define tiles with boundaries between non-adjacent regions in the projected picture. Preventing motion compensation (inter prediction) from non-adjacent regions can be accomplished by restricting the search area of the motion estimation process in the encoder. 
     The video data captured by a camera (e.g., a fisheye camera, or other suitable camera or cameras) can be coded to reduce the amount of data needed for transmission and storage. Coding techniques may be implemented in an example video encoding and decoding system. In some examples, a system includes a source device that provides encoded video data to be decoded at a later time by a destination device. In particular, the source device provides the video data to destination device via a computer-readable medium. The source device and the destination device may comprise any of a wide range of devices, including desktop computers, notebook (i.e., laptop) computers, tablet computers, set-top boxes, telephone handsets such as so-called “smart” phones, so-called “smart” pads, televisions, cameras, display devices, digital media players, video gaming consoles, video streaming device, or the like. In some cases, the source device and the destination device may be equipped for wireless communication. 
     The destination device may receive the encoded video data to be decoded via the computer-readable medium. The computer-readable medium may comprise any type of medium or device capable of moving the encoded video data from source device to destination device. In one example, computer-readable medium may comprise a communication medium to enable source device to transmit encoded video data directly to destination device in real-time. The encoded video data may be modulated according to a communication standard, such as a wireless communication protocol, and transmitted to destination device. The communication medium may comprise any wireless or wired communication medium, such as a radio frequency (RF) spectrum or one or more physical transmission lines. The communication medium may form part of a packet-based network, such as a local area network, a wide-area network, or a global network such as the Internet. The communication medium may include routers, switches, base stations, or any other equipment that may be useful to facilitate communication from source device to destination device. 
     In some examples, encoded data may be output from output interface to a storage device. Similarly, encoded data may be accessed from the storage device by input interface. The storage device may include any of a variety of distributed or locally accessed data storage media such as a hard drive, Blu-ray discs, DVDs, CD-ROMs, flash memory, volatile or non-volatile memory, or any other suitable digital storage media for storing encoded video data. In a further example, the storage device may correspond to a file server or another intermediate storage device that may store the encoded video generated by source device. Destination device may access stored video data from the storage device via streaming or download. The file server may be any type of server capable of storing encoded video data and transmitting that encoded video data to the destination device. Example file servers include a web server (e.g., for a website), an FTP server, network attached storage (NAS) devices, or a local disk drive. Destination device may access the encoded video data through any standard data connection, including an Internet connection. This may include a wireless channel (e.g., a Wi-Fi connection), a wired connection (e.g., DSL, cable modem, etc.), or a combination of both that is suitable for accessing encoded video data stored on a file server. The transmission of encoded video data from the storage device may be a streaming transmission, a download transmission, or a combination thereof. 
     The techniques of this disclosure are not necessarily limited to wireless applications or settings. The techniques may be applied to video coding in support of any of a variety of multimedia applications, such as over-the-air television broadcasts, cable television transmissions, satellite television transmissions, Internet streaming video transmissions, such as dynamic adaptive streaming over HTTP (DASH), digital video that is encoded onto a data storage medium, decoding of digital video stored on a data storage medium, or other applications. In some examples, system may be configured to support one-way or two-way video transmission to support applications such as video streaming, video playback, video broadcasting, and/or video telephony. 
     In one example the source device includes a video source, a video encoder, and an output interface. The destination device may include an input interface, a video decoder, and a display device. The video encoder of source device may be configured to apply the techniques disclosed herein. In other examples, a source device and a destination device may include other components or arrangements. For example, the source device may receive video data from an external video source, such as an external camera. Likewise, the destination device may interface with an external display device, rather than including an integrated display device. 
     The example system above is merely one example. Techniques for processing video data in parallel may be performed by any digital video encoding and/or decoding device. Although generally the techniques of this disclosure are performed by a video encoding device, the techniques may also be performed by a video encoder/decoder, typically referred to as a “CODEC.” Moreover, the techniques of this disclosure may also be performed by a video preprocessor. Source device and destination device are merely examples of such coding devices in which source device generates coded video data for transmission to destination device. In some examples, the source and destination devices may operate in a substantially symmetrical manner such that each of the devices include video encoding and decoding components. Hence, example systems may support one-way or two-way video transmission between video devices, e.g., for video streaming, video playback, video broadcasting, or video telephony. 
     The video source may include a video capture device, such as a video camera, a video archive containing previously captured video, and/or a video feed interface to receive video from a video content provider. As a further alternative, the video source may generate computer graphics-based data as the source video, or a combination of live video, archived video, and computer-generated video. In some cases, if the video source is a video camera, source device and destination device may form so-called camera phones or video phones. As mentioned above, however, the techniques described in this disclosure may be applicable to video coding in general, and may be applied to wireless and/or wired applications. In each case, the captured, pre-captured, or computer-generated video may be encoded by the video encoder. The encoded video information may then be output by output interface onto the computer-readable medium. 
     As noted the computer-readable medium may include transient media, such as a wireless broadcast or wired network transmission, or storage media (that is, non-transitory storage media), such as a hard disk, flash drive, compact disc, digital video disc, Blu-ray disc, or other computer-readable media. In some examples, a network server (not shown) may receive encoded video data from the source device and provide the encoded video data to the destination device, e.g., via network transmission. Similarly, a computing device of a medium production facility, such as a disc stamping facility, may receive encoded video data from the source device and produce a disc containing the encoded video data. Therefore, the computer-readable medium may be understood to include one or more computer-readable media of various forms, in various examples. 
     The input interface of the destination device receives information from the computer-readable medium. The information of the computer-readable medium may include syntax information defined by the video encoder, which is also used by the video decoder, that includes syntax elements that describe characteristics and/or processing of blocks and other coded units, e.g., group of pictures (GOP). A display device displays the decoded video data to a user, and may comprise any of a variety of display devices such as a cathode ray tube (CRT), a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display device. Various embodiments of the application have been described. 
     Specific details of an example encoding device  104  and decoding device  112  are shown in  FIG. 7  and  FIG. 8 , respectively.  FIG. 7  is a block diagram illustrating an example encoding device  104  that may implement one or more of the techniques described in this disclosure. Encoding device  104  may, for example, generate the syntax structures described herein (e.g., the syntax structures of a video parameter set (VPS), sequence parameter set (SPS), picture parameter set (PPS), or other syntax elements). Encoding device  104  may perform intra-prediction and inter-prediction coding of video blocks within video slices. As previously described, intra-coding relies, at least in part, on spatial prediction to reduce or remove spatial redundancy within a given video frame or picture. Inter-coding relies, at least in part, on temporal prediction to reduce or remove temporal redundancy within adjacent or surrounding frames of a video sequence. Intra-mode (I mode) may refer to any of several spatial based compression modes. Inter-modes, such as uni-directional prediction (P mode) or bi-prediction (B mode), may refer to any of several temporal-based compression modes. 
     The encoding device  104  includes a partitioning unit  35 , prediction processing unit  41 , filter unit  63 , picture memory  64 , summer  50 , transform processing unit  52 , quantization unit  54 , and entropy encoding unit  56 . Prediction processing unit  41  includes motion estimation unit  42 , motion compensation unit  44 , and intra-prediction processing unit  46 . For video block reconstruction, encoding device  104  also includes inverse quantization unit  58 , inverse transform processing unit  60 , and summer  62 . Filter unit  63  is intended to represent one or more loop filters such as a deblocking filter, an adaptive loop filter (ALF), and a sample adaptive offset (SAO) filter. Although filter unit  63  is shown in  FIG. 7  as being an in loop filter, in other configurations, filter unit  63  may be implemented as a post loop filter. A post processing device  57  may perform additional processing on encoded video data generated by the encoding device  104 . The techniques of this disclosure may in some instances be implemented by the encoding device  104 . In other instances, however, one or more of the techniques of this disclosure may be implemented by post processing device  57 . 
     As shown in  FIG. 7 , the encoding device  104  receives video data, and partitioning unit  35  partitions the data into video blocks. The partitioning may also include partitioning into slices, slice segments, tiles, or other larger units, as wells as video block partitioning, e.g., according to a quadtree structure of LCUs and CUs. The encoding device  104  generally illustrates the components that encode video blocks within a video slice to be encoded. The slice may be divided into multiple video blocks (and possibly into sets of video blocks referred to as tiles). Prediction processing unit  41  may select one of a plurality of possible coding modes, such as one of a plurality of intra-prediction coding modes or one of a plurality of inter-prediction coding modes, for the current video block based on error results (e.g., coding rate and the level of distortion, or the like). Prediction processing unit  41  may provide the resulting intra- or inter-coded block to summer  50  to generate residual block data and to summer  62  to reconstruct the encoded block for use as a reference picture. 
     Intra-prediction processing unit  46  within prediction processing unit  41  may perform intra-prediction coding of the current video block relative to one or more neighboring blocks in the same frame or slice as the current block to be coded to provide spatial compression. Motion estimation unit  42  and motion compensation unit  44  within prediction processing unit  41  perform inter-predictive coding of the current video block relative to one or more predictive blocks in one or more reference pictures to provide temporal compression. 
     Motion estimation unit  42  may be configured to determine the inter-prediction mode for a video slice according to a predetermined pattern for a video sequence. The predetermined pattern may designate video slices in the sequence as P slices, B slices, or GPB slices. Motion estimation unit  42  and motion compensation unit  44  may be highly integrated, but are illustrated separately for conceptual purposes. Motion estimation, performed by motion estimation unit  42 , is the process of generating motion vectors, which estimate motion for video blocks. A motion vector, for example, may indicate the displacement of a prediction unit (PU) of a video block within a current video frame or picture relative to a predictive block within a reference picture. 
     A predictive block is a block that is found to closely match the PU of the video block to be coded in terms of pixel difference, which may be determined by sum of absolute difference (SAD), sum of square difference (SSD), or other difference metrics. In some examples, the encoding device  104  may calculate values for sub-integer pixel positions of reference pictures stored in picture memory  64 . For example, the encoding device  104  may interpolate values of one-quarter pixel positions, one-eighth pixel positions, or other fractional pixel positions of the reference picture. Therefore, motion estimation unit  42  may perform a motion search relative to the full pixel positions and fractional pixel positions and output a motion vector with fractional pixel precision. 
     Motion estimation unit  42  calculates a motion vector for a PU of a video block in an inter-coded slice by comparing the position of the PU to the position of a predictive block of a reference picture. The reference picture may be selected from a first reference picture list (List  0 ) or a second reference picture list (List  1 ), each of which identify one or more reference pictures stored in picture memory  64 . Motion estimation unit  42  sends the calculated motion vector to entropy encoding unit  56  and motion compensation unit  44 . 
     Motion compensation, performed by motion compensation unit  44 , may involve fetching or generating the predictive block based on the motion vector determined by motion estimation, possibly performing interpolations to sub-pixel precision. Upon receiving the motion vector for the PU of the current video block, motion compensation unit  44  may locate the predictive block to which the motion vector points in a reference picture list. The encoding device  104  forms a residual video block by subtracting pixel values of the predictive block from the pixel values of the current video block being coded, forming pixel difference values. The pixel difference values form residual data for the block, and may include both luma and chroma difference components. Summer  50  represents the component or components that perform this subtraction operation. Motion compensation unit  44  may also generate syntax elements associated with the video blocks and the video slice for use by the decoding device  112  in decoding the video blocks of the video slice. 
     Intra-prediction processing unit  46  may intra-predict a current block, as an alternative to the inter-prediction performed by motion estimation unit  42  and motion compensation unit  44 , as described above. In particular, intra-prediction processing unit  46  may determine an intra-prediction mode to use to encode a current block. In some examples, intra-prediction processing unit  46  may encode a current block using various intra-prediction modes, e.g., during separate encoding passes, and intra-prediction unit processing  46  may select an appropriate intra-prediction mode to use from the tested modes. For example, intra-prediction processing unit  46  may calculate rate-distortion values using a rate-distortion analysis for the various tested intra-prediction modes, and may select the intra-prediction mode having the best rate-distortion characteristics among the tested modes. Rate-distortion analysis generally determines an amount of distortion (or error) between an encoded block and an original, unencoded block that was encoded to produce the encoded block, as well as a bit rate (that is, a number of bits) used to produce the encoded block. Intra-prediction processing unit  46  may calculate ratios from the distortions and rates for the various encoded blocks to determine which intra-prediction mode exhibits the best rate-distortion value for the block. 
     In any case, after selecting an intra-prediction mode for a block, intra-prediction processing unit  46  may provide information indicative of the selected intra-prediction mode for the block to entropy encoding unit  56 . Entropy encoding unit  56  may encode the information indicating the selected intra-prediction mode. The encoding device  104  may include in the transmitted bitstream configuration data definitions of encoding contexts for various blocks as well as indications of a most probable intra-prediction mode, an intra-prediction mode index table, and a modified intra-prediction mode index table to use for each of the contexts. The bitstream configuration data may include a plurality of intra-prediction mode index tables and a plurality of modified intra-prediction mode index tables (also referred to as codeword mapping tables). 
     After prediction processing unit  41  generates the predictive block for the current video block via either inter-prediction or intra-prediction, the encoding device  104  forms a residual video block by subtracting the predictive block from the current video block. The residual video data in the residual block may be included in one or more TUs and applied to transform processing unit  52 . Transform processing unit  52  transforms the residual video data into residual transform coefficients using a transform, such as a discrete cosine transform (DCT) or a conceptually similar transform. Transform processing unit  52  may convert the residual video data from a pixel domain to a transform domain, such as a frequency domain. 
     Transform processing unit  52  may send the resulting transform coefficients to quantization unit  54 . Quantization unit  54  quantizes the transform coefficients to further reduce bit rate. The quantization process may reduce the bit depth associated with some or all of the coefficients. The degree of quantization may be modified by adjusting a quantization parameter. In some examples, quantization unit  54  may then perform a scan of the matrix including the quantized transform coefficients. Alternatively, entropy encoding unit  56  may perform the scan. 
     Following quantization, entropy encoding unit  56  entropy encodes the quantized transform coefficients. For example, entropy encoding unit  56  may perform context adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), syntax-based context-adaptive binary arithmetic coding (SBAC), probability interval partitioning entropy (PIPE) coding or another entropy encoding technique. Following the entropy encoding by entropy encoding unit  56 , the encoded bitstream may be transmitted to the decoding device  112 , or archived for later transmission or retrieval by the decoding device  112 . Entropy encoding unit  56  may also entropy encode the motion vectors and the other syntax elements for the current video slice being coded. 
     Inverse quantization unit  58  and inverse transform processing unit  60  apply inverse quantization and inverse transformation, respectively, to reconstruct the residual block in the pixel domain for later use as a reference block of a reference picture. Motion compensation unit  44  may calculate a reference block by adding the residual block to a predictive block of one of the reference pictures within a reference picture list. Motion compensation unit  44  may also apply one or more interpolation filters to the reconstructed residual block to calculate sub-integer pixel values for use in motion estimation. Summer  62  adds the reconstructed residual block to the motion compensated prediction block produced by motion compensation unit  44  to produce a reference block for storage in picture memory  64 . The reference block may be used by motion estimation unit  42  and motion compensation unit  44  as a reference block to inter-predict a block in a subsequent video frame or picture. 
     In this manner, the encoding device  104  of  FIG. 7  represents an example of a video encoder configured to generate syntax for an encoded video bitstream. The encoding device  104  may, for example, generate VPS, SPS, and PPS parameter sets as described above. The encoding device  104  may perform any of the techniques described herein, including the processes described above. The techniques of this disclosure have generally been described with respect to the encoding device  104 , but as mentioned above, some of the techniques of this disclosure may also be implemented by post processing device  57 . 
       FIG. 8  is a block diagram illustrating an example decoding device  112 . The decoding device  112  includes an entropy decoding unit  80 , prediction processing unit  81 , inverse quantization unit  86 , inverse transform processing unit  88 , summer  90 , filter unit  91 , and picture memory  92 . Prediction processing unit  81  includes motion compensation unit  82  and intra prediction processing unit  84 . The decoding device  112  may, in some examples, perform a decoding pass generally reciprocal to the encoding pass described with respect to the encoding device  104  from  FIG. 7 . 
     During the decoding process, the decoding device  112  receives an encoded video bitstream that represents video blocks of an encoded video slice and associated syntax elements sent by the encoding device  104 . In some embodiments, the decoding device  112  may receive the encoded video bitstream from the encoding device  104 . In some embodiments, the decoding device  112  may receive the encoded video bitstream from a network entity  79 , such as a server, a media-aware network element (MANE), a video editor/splicer, or other such device configured to implement one or more of the techniques described above. Network entity  79  may or may not include the encoding device  104 . Some of the techniques described in this disclosure may be implemented by network entity  79  prior to network entity  79  transmitting the encoded video bitstream to the decoding device  112 . In some video decoding systems, network entity  79  and the decoding device  112  may be parts of separate devices, while in other instances, the functionality described with respect to network entity  79  may be performed by the same device that comprises the decoding device  112 . 
     The entropy decoding unit  80  of the decoding device  112  entropy decodes the bitstream to generate quantized coefficients, motion vectors, and other syntax elements. Entropy decoding unit  80  forwards the motion vectors and other syntax elements to prediction processing unit  81 . The decoding device  112  may receive the syntax elements at the video slice level and/or the video block level. Entropy decoding unit  80  may process and parse both fixed-length syntax elements and variable-length syntax elements in one or more parameter sets, such as a VPS, SPS, and PPS. 
     When the video slice is coded as an intra-coded (I) slice, intra prediction processing unit  84  of prediction processing unit  81  may generate prediction data for a video block of the current video slice based on a signaled intra-prediction mode and data from previously decoded blocks of the current frame or picture. When the video frame is coded as an inter-coded (e.g., B, P or GPB) slice, motion compensation unit  82  of prediction processing unit  81  produces predictive blocks for a video block of the current video slice based on the motion vectors and other syntax elements received from entropy decoding unit  80 . The predictive blocks may be produced from one of the reference pictures within a reference picture list. The decoding device  112  may construct the reference frame lists, List  0  and List  1 , using default construction techniques based on reference pictures stored in picture memory  92 . 
     Motion compensation unit  82  determines prediction information for a video block of the current video slice by parsing the motion vectors and other syntax elements, and uses the prediction information to produce the predictive blocks for the current video block being decoded. For example, motion compensation unit  82  may use one or more syntax elements in a parameter set to determine a prediction mode (e.g., intra- or inter-prediction) used to code the video blocks of the video slice, an inter-prediction slice type (e.g., B slice, P slice, or GPB slice), construction information for one or more reference picture lists for the slice, motion vectors for each inter-encoded video block of the slice, inter-prediction status for each inter-coded video block of the slice, and other information to decode the video blocks in the current video slice. 
     Motion compensation unit  82  may also perform interpolation based on interpolation filters. Motion compensation unit  82  may use interpolation filters as used by the encoding device  104  during encoding of the video blocks to calculate interpolated values for sub-integer pixels of reference blocks. In this case, motion compensation unit  82  may determine the interpolation filters used by the encoding device  104  from the received syntax elements, and may use the interpolation filters to produce predictive blocks. 
     Inverse quantization unit  86  inverse quantizes, or de-quantizes, the quantized transform coefficients provided in the bitstream and decoded by entropy decoding unit  80 . The inverse quantization process may include use of a quantization parameter calculated by the encoding device  104  for each video block in the video slice to determine a degree of quantization and, likewise, a degree of inverse quantization that should be applied. Inverse transform processing unit  88  applies an inverse transform (e.g., an inverse DCT or other suitable inverse transform), an inverse integer transform, or a conceptually similar inverse transform process, to the transform coefficients in order to produce residual blocks in the pixel domain. 
     After motion compensation unit  82  generates the predictive block for the current video block based on the motion vectors and other syntax elements, the decoding device  112  forms a decoded video block by summing the residual blocks from inverse transform processing unit  88  with the corresponding predictive blocks generated by motion compensation unit  82 . Summer  90  represents the component or components that perform this summation operation. If desired, loop filters (either in the coding loop or after the coding loop) may also be used to smooth pixel transitions, or to otherwise improve the video quality. Filter unit  91  is intended to represent one or more loop filters such as a deblocking filter, an adaptive loop filter (ALF), and a sample adaptive offset (SAO) filter. Although filter unit  91  is shown in  FIG. 8  as being an in loop filter, in other configurations, filter unit  91  may be implemented as a post loop filter. The decoded video blocks in a given frame or picture are then stored in picture memory  92 , which stores reference pictures used for subsequent motion compensation. Picture memory  92  also stores decoded video for later presentation on a display device, such as a video destination device  122 . 
       FIG. 9  illustrates an example of a process  900  for processing video data according to the techniques discussed above. At  902 , the process  900  includes obtaining at least one 360-degree rectangular formatted projected picture. 
     At  904 , the process  900  includes detecting a projection boundary in the at least one 360-degree rectangular formatted projected picture. 
     At  906 , the process  900  includes disabling at least one of an in-loop filtering, an intra-prediction, or an inter-prediction, based on detecting the at least one 360-degree rectangular formatted projected picture comprises the projection boundary. 
     At  908 , the process  900  includes generating an encoded video bitstream. 
     In the foregoing description, aspects of the application are described with reference to specific embodiments thereof, but those skilled in the art will recognize that the application is not limited thereto. Thus, while illustrative embodiments of the application have been described in detail herein, it is to be understood that the inventive concepts may be otherwise variously embodied and employed, and that the appended claims are intended to be construed to include such variations, except as limited by the prior art. Various features and aspects of the above-described application may be used individually or jointly. Further, embodiments can be utilized in any number of environments and applications beyond those described herein without departing from the broader spirit and scope of the specification. The specification and drawings are, accordingly, to be regarded as illustrative rather than restrictive. For the purposes of illustration, methods were described in a particular order. It should be appreciated that in alternate embodiments, the methods may be performed in a different order than that described. 
     Where components are described as being “configured to” perform certain operations, such configuration can be accomplished, for example, by designing electronic circuits or other hardware to perform the operation, by programming programmable electronic circuits (e.g., microprocessors, or other suitable electronic circuits) to perform the operation, or any combination thereof. 
     The various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, firmware, or combinations thereof. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present application. 
     The techniques described herein may also be implemented in electronic hardware, computer software, firmware, or any combination thereof. Such techniques may be implemented in any of a variety of devices such as general purposes computers, wireless communication device handsets, or integrated circuit devices having multiple uses including application in wireless communication device handsets and other devices. Any features described as modules or components may be implemented together in an integrated logic device or separately as discrete but interoperable logic devices. If implemented in software, the techniques may be realized at least in part by a computer-readable data storage medium comprising program code including instructions that, when executed, performs one or more of the methods described above. The computer-readable data storage medium may form part of a computer program product, which may include packaging materials. The computer-readable medium may comprise memory or data storage media, such as random access memory (RAM) such as synchronous dynamic random access memory (SDRAM), read-only memory (ROM), non-volatile random access memory (NVRAM), electrically erasable programmable read-only memory (EEPROM), FLASH memory, magnetic or optical data storage media, and the like. The techniques additionally, or alternatively, may be realized at least in part by a computer-readable communication medium that carries or communicates program code in the form of instructions or data structures and that can be accessed, read, and/or executed by a computer, such as propagated signals or waves. 
     The program code may be executed by a processor, which may include one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, an application specific integrated circuits (ASIC s), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Such a processor may be configured to perform any of the techniques described in this disclosure. A general-purpose processor may be a microprocessor; but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. Accordingly, the term “processor,” as used herein may refer to any of the foregoing structure, any combination of the foregoing structure, or any other structure or apparatus suitable for implementation of the techniques described herein. In addition, in some aspects, the functionality described herein may be provided within dedicated software modules or hardware modules configured for encoding and decoding, or incorporated in a combined video encoder-decoder (CODEC).