Missing attribute value transmission for rendering viewport of volumetric scene

Abstract

Methods, devices, and data streams for generating, transmitting, and decoding volumetric scenes are provided. According to the present principles, rendering attribute values, such as color values, are transmitted to a renderer for use as suggested attribute values for pixels for which the attribute is missing. For example, when rendering a viewport image of a volumetric scene, some pixels may lack color information. In such a case, the present principles provide a suggested default color. These principles are applicable to various rendering attributes, such as reflectivity, transparency, material or gloss. In an embodiment, an attribute value is associated with a region of the 3D space. In another embodiment, a quality level associated with a default value helps a renderer select a fill method.

Description

Technical Field

[0001] The present principles generally relate to the field of encoding, transmitting and rendering volumetric scenes, for example when rendering on an end-user device such as a mobile device or a head-mounted display (HMD), such as perspective glasses. In particular, the present principles relate to attributing color values ​​to pixels of a viewport image of a volumetric scene when the color value cannot be retrieved from a representation of the volumetric scene. The present principles apply to various rendering properties, such as reflectivity, transparency, material or glossiness. Background Art

[0002] This section is intended to introduce the reader to various aspects of the technology, which may be related to various aspects of the present principles described and / or claimed below. It is believed that this discussion is helpful in providing the reader with background information to facilitate a better understanding of various aspects of the present principles. Therefore, it should be understood that these statements are to be read in this light, and not as admissions of prior art.

[0003] A volumetric scene is, for example, a three-dimensional (3D) scene that has been captured as a multi-view plus depth image (MVD) using a set of cameras, or is modeled as a point cloud or mesh representation, for example. There are many techniques for acquiring volumetric scenes, and they can be mixed together. The key point of a volumetric scene is that it can be rendered from a different viewpoint than the one used for capture (and / or modeling). The source content type, compression standard, rendering device, and synthesis method may vary from solution to solution. However, in any case, when a viewport is to be synthesized at the decoder side, a virtual camera located in the 3D space of the volumetric scene is used to project the available information onto the viewport image to be rendered. Depending on the completeness of the representation of the volumetric scene (which may depend on the size of the data required to encode it) and on the position of the virtual camera, for a given rendering attribute (also called pixel attribute), some pixels of the viewport image may not have projection data. The missing pixel attribute value may be depth, color, or any other rendering attribute (e.g., reflectivity, transparency, or glossiness).

[0004] There are methods for overcoming the problem of missing values, including repairing parts of the representation of the volumetric scene at the encoder side, or filtering depth values ​​or repairing parts of the viewport image to be rendered at the decoder side. However, these methods are extensive in terms of computational resources at the decoder / renderer side. There is a lack of a format for encoding volumetric scenes that can guide the renderer to the most appropriate solution for the missing pixel values. Summary of the invention

[0005] A simplified summary of the present principles is presented below to provide a basic understanding of some aspects of the present principles. This summary is not an extensive review of the present principles. It is not intended to identify the key or decisive elements of the present principles. The following summary merely presents some aspects of the present principles in a simplified form as a preface to the more detailed description provided below.

[0006] Methods, devices and data streams for generating, transmitting and decoding volumetric scenes are provided. According to the present principles, rendering attribute values ​​(such as color values) are transmitted to a renderer to be used as suggested attribute values ​​for pixels for which the attribute is missing. For example, when rendering a viewport image of a volumetric scene, some pixels may be missing color information. In such a case, the present principles provide suggested default colors. The present principles are applicable to various rendering attributes, such as reflectivity, transparency, material or glossiness. In an embodiment, the attribute value is associated with an area of ​​3D space. In another embodiment, a quality level associated with the default value helps the renderer select a fill method.

[0007] The present principles relate to a method comprising encoding in a data stream a representation of a volumetric scene and metadata comprising a color value, the color value indicating to a renderer to set missing color values ​​to the color value when rendering a viewport image of the volumetric scene. In an embodiment, the color value is associated with a quality level, the quality level indicating to the renderer the level of visibility of visual artifacts when the missing color value is set to the color value. The color value may be determined based on the color values ​​of pixels of a multi-view image used to generate a representation of the volumetric scene. In another embodiment that may be combined with the previous embodiment, the metadata comprises at least two color values, each given color value being associated with a region of the volumetric scene, which indicates to the renderer to use the given color value for a portion of the viewport image representing the region of the volumetric scene. The present principles apply to color values ​​and any other rendering attribute values, such as reflectivity, transparency, glossiness, material, etc.

[0008] The present principles also relate to an apparatus comprising a memory associated with a processor, the processor being configured to implement the above-mentioned method.

[0009] The present principles also relate to a method comprising obtaining a representation of a volumetric scene and metadata including color values ​​from a data stream; and rendering a viewport image of the volumetric scene and setting missing color values ​​to color values.

[0010] In an embodiment, the color value is associated with a quality level, which indicates to the renderer the level of visibility of visual artifacts when setting missing color values ​​to color values. The color value may be determined based on the color values ​​of the pixels of the multi-view image used to generate the representation of the volumetric scene. In another embodiment that may be combined with the previous embodiment, the metadata includes at least two color values, each given color value being associated with a region of the volumetric scene, which indicates to the renderer to use the given color value for the portion of the viewport image representing the region of the volumetric scene. The present principles apply to color values ​​and any other rendering property values, such as reflectivity, transparency, glossiness, material, etc.

[0011] The present principles also relate to an apparatus comprising a memory associated with a processor, the processor being configured to implement the above-mentioned method.

[0012] The present principles also relate to a data stream comprising a representation of a volumetric scene and metadata comprising color values ​​instructing a renderer to set missing color values ​​to color values ​​when rendering a viewport image of the volumetric scene.

[0013] In an embodiment, the color value is associated with a quality level, which indicates to the renderer the level of visibility of visual artifacts when setting missing color values ​​to color values. The color value may be determined based on the color values ​​of the pixels of the multi-view image used to generate the representation of the volumetric scene. In another embodiment that may be combined with the previous embodiment, the metadata includes at least two color values, each given color value being associated with a region of the volumetric scene, which indicates to the renderer to use the given color value for the portion of the viewport image representing the region of the volumetric scene. The present principles apply to color values ​​and any other rendering property values, such as reflectivity, transparency, glossiness, material, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present disclosure will be better understood, and other particular features and advantages will emerge, upon reading the following description, which refers to the accompanying drawings, in which:

[0015] - Figure 1 A general encoding / decoding flow chart of a volumetric scene according to the present principles is illustrated;

[0016] - Figure 2 A viewport image of a volumetric scene is shown in which some color information is missing;

[0017] - Figure 3 An example architecture of an encoding and rendering engine that may be configured to implement the present principles is shown;

[0018] - Figure 4 An example of an embodiment of the syntax of a data stream encoding a volumetric scene description according to the present principles is shown. DETAILED DESCRIPTION

[0019] The present principle will be described more fully below with reference to the accompanying drawings, in which examples of the present principle are shown. However, the present principle can be implemented in a variety of alternative forms and should not be interpreted as being limited to the examples set forth herein. Therefore, although the present principle is susceptible to various modifications and alternative forms, its specific examples are shown by the examples in the accompanying drawings and will be described in detail herein. However, it should be understood that there is no intention to limit the present principle to the specific form disclosed, but on the contrary, the present disclosure will cover all modifications, equivalents and alternatives that fall within the spirit and scope of the present principle as defined by the claims.

[0020] The terms used herein are only used for the purpose of describing specific examples and are not intended to be a limitation of this principle. As used herein, the singular forms "one", "an" and "the" are also intended to include plural forms, unless the context clearly indicates otherwise. It will be further understood that when the terms "include", "include", "contain" and / or "contain" are used in this specification, the existence of the features, integers, steps, operations, elements and / or components is specified, but the existence or addition of one or more other features, integers, steps, operations, elements, components and / or their groups is not excluded. In addition, when an element is referred to as "in response to" or "connected to" another element, it can directly respond to or be connected to another element, or there can be an intermediate element. In contrast, when an element is referred to as "directly responding to" or "directly connected to" another element, there is no intermediate element. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items, and can be abbreviated as " / ".

[0021] It will be understood that although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. For example, without departing from the teaching of the present principles, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element.

[0022] Although some of the figures include arrows on communication paths to illustrate a primary direction of communication, it is to be understood that communication can occur in the opposite direction to the depicted arrows.

[0023] Some examples are described with respect to block diagrams and operational flow charts, wherein each block represents a portion of a circuit element, module, or code, which includes one or more executable instructions for implementing a specified (one or more) logical function. It should also be noted that in other implementations, the (one or more) functions indicated in the blocks may not appear in the order indicated. For example, two blocks shown in succession may actually be executed substantially simultaneously, or the blocks may sometimes be executed in reverse order, depending on the functions involved.

[0024] References herein to "according to an example" or "in an example" mean that a particular feature, structure, or characteristic described in connection with the example may be included in at least one implementation of the present principles. The phrases "according to an example" or "in an example" appearing in various places in the specification are not necessarily all referring to the same example, nor are they necessarily separate or alternative examples that are mutually exclusive of other examples.

[0025] Reference signs appearing in the claims are by way of illustration only and shall have no limiting effect on the scope of the claims.The present examples and variations may be used in any combination or sub-combination although not explicitly described.

[0026] A volumetric scene is a three-dimensional (3D) scene that is to be rendered from a viewpoint belonging to a region of 3D space.

[0027] Figure 1 A general encoding / decoding flow chart for a volumetric scene is illustrated. A 3D scene is captured at step 11. The 3D scene can be captured as a multi-view plus depth image (MVD) using, for example, a set of cameras, or modeled as a point cloud or mesh representation, for example. There are many techniques for acquiring a volumetric scene, and they can be mixed together to generate a model 12 of the 3D scene. At step 13, the model 12 of the 3D scene is encoded as a volumetric scene, i.e., a 3D scene intended to be observed from different viewpoints, such as from any position within a determined area of ​​3D space (or from the entire 3D space). The encoding step 13 generates a bitstream 14, which can be stored in a memory, or it can be transmitted by a transmitter over a network at step 15. Thus, a bitstream 16 is received by a receiver. As is well known, bitstreams 14 and 16 may be slightly different due to transmission problems (e.g., some packets may have been lost or received too late to be decoded in real time). At step 17, the received bitstream 16 is decoded to generate a model 18. Model 18 may be different from model 12 due to transmission problems and / or due to decoding problems. For example, the compression method at encoding step 13 may introduce approximations or may have deleted some information to ensure a given bit rate for the bitstream 14. The decoder may also decode only a portion of the bitstream 16 due to memory or processing resource limitations, and / or it may decode only a portion of the model required to render the viewport image 10 according to the rendering viewpoint at step 19.

[0028] Through this flowchart, the source content type (ie, model 12), encoding and compression method 13, and synthesis method 19 can be varied. When rendering a viewport image of a volumetric scene, some pixels of the viewport may not be filled with information (eg, color).

[0029] Figure 2 A viewport image 20 of a volumetric scene is shown in which some color information is missing. Figure 2 As shown on the viewport image 20, pixels in area 21 are missing color information. For example, the color information of these pixels may not have been retrieved at step 19 due to the sparsity of the model 12 or 18. It may happen that a ray passing from a pixel of the viewport at a given angle does not intersect any 3D point from the un-projection of any of the input views; and this is the case even before encoding, using the entire MVD input 12. The missing color information may also be due to the encoding step 13. In practice, the encoder may discard some areas of the input MVD 12 or shift some points within the point cloud 12. Noise on the geometry may also be introduced during the video encoding step 13 (for example when the volumetric scene is encoded as patch atlases), which potentially leads to a shift of points. Figure 2 In the example above, missing colors are set to gray values ​​by the renderer by default.

[0030] Methods to overcome the problem of missing pixels are proposed in the prior art. For example by filtering the depth at the decoder side. In this method, after the visibility phase (i.e., testing whether a point of the decoded model is visible for a given pixel of the viewport image), some pixels of the depth map of the viewport may still be unfilled. Depth filtering can be performed to fill part of those pixels with depth values ​​from the local neighborhood of the pixel with missing information. This method is called dilation. This solution requires processing resources at the decoder side and may cause artifacts at the contours.

[0031] Inpainting can also be performed at the decoder side. In such an approach, some pixels may remain unfilled in the viewport after it has been synthesized from the decoded data, resulting in small or larger unfilled areas. An additional inpainting step is usually performed after synthesis. There are two general methods for performing inpainting of those unfilled areas: 1) an example-based approach, in which a patch of some similar pixels is searched in the rendered viewport image and adapted to the unfilled area; 2) a diffusion-based approach, in which the neighborhood of the unfilled area is used to gradually fill it. This solution has the advantage that it is independent of the transmitted data and it only relies on post-processing of the viewport image. However, it requires a lot of processing resources to be implemented by the rendering device.

[0032] It is also possible to perform repair at the encoder side. Since the entire captured data is available at the encoder side, there is an opportunity to use this data to build a virtual view that grasps the context of the scene and thus predicts some pixels that will be missing at rendering time. Additional elements (such as patch pictures) are added to the encoded bitstream. This solution has two main disadvantages. First, it is time-consuming at the encoder side, because creating such a patch requires unprojecting / reprojecting all pixels of all source views from the MVD. Secondly, these additional patches cannot ensure that there are no unfilled pixels at the renderer stage.

[0033] According to the present principles, metadata including a color value is encoded in the data stream 14 in association with the representation of the volumetric scene, the color value instructing the renderer to set missing color values ​​to the color value when rendering the viewport image of the volumetric scene. At step 19, the color value is decoded from the received bitstream 16 and used by the renderer as a suggested default color value to fill in the missing pixels of the viewport image 20. In an embodiment, the color value is encapsulated in a Supplemental Enhancement Information (SEI) message for transmission. According to the present principles, the metadata may also include suggested default values ​​for pixel attributes other than color attributes (e.g., transparency, material, reflectivity, glossiness, etc.).

[0034] The following table proposes the syntax for metadata including color (or other attribute) values ​​according to the present principles:

[0035]

[0036] In an example embodiment, the metadata is encoded in the SEI message of the volumetric video standard V3C. In this example, the SEI table in the general SEI message syntax of section F.2.1 of V3C will be updated accordingly:

[0037]

[0038] exist Figure 2 In the example of FIG. 1 , transmitting such information, such as a suggested default color set to black, would help limit annoyance caused by the presence of gray pixels. The color value may be selected by an operator or automatically calculated, for example, as an average value of images or points of the model 12, or as a minimum value of different views or points of the model 12.

[0039] In an embodiment, the 3D space is divided into regions and a color (or other attribute) value is associated with each region of the space. The color value may be determined based on the color of a point in that region of the 3D space. In this embodiment, the metadata associated with the volumetric scene in the data stream includes several pairs of color (or other attribute) values ​​and descriptions of regions of the 3D space of the volumetric video.

[0040] In another embodiment of the present principles, an attribute value (which may be associated with an area of ​​3D space) is associated with a quality level that indicates to the renderer the level of visibility of visual artifacts when a missing color value is set to that color value. For example, a default color value may be determined based on the average color of the points of the point cloud representing the model 12. If the variance of these color data exceeds a given threshold, the quality value is low. If the variance of the considered area is low, the quality level is set to a high value. This is just an example. A large number of and different calculations may be used to determine the quality level. At the decoder side, taking into account the quality level, the renderer may use the given attribute value as a default value, or instead select another filling method, for example, filtering depth or repairing missing parts.

[0041] Figure 3 An example architecture of an encoding and rendering engine 30 that can be configured to implement the present principles is shown. Figure 3 The devices of the architecture are linked to other devices via the bus 31 of other devices and / or via the I / O interface 36.

[0042] The device 30 comprises the following elements linked together by a data and address bus 31:

[0043] - a microprocessor 32 (or CPU), which is for example a DSP (or digital signal processor);

[0044] - ROM (or read-only memory) 33;

[0045] - RAM (or random access memory) 34;

[0046] - storage interface 35;

[0047] - an I / O interface 36 for receiving data to be transmitted from an application; and

[0048] -power supply( Figure 2 not shown), such as batteries.

[0049] According to an example, the power supply is external to the device. In each of the memories mentioned, the word "register" used in the specification can correspond to an area of ​​small capacity (a few bits) or a very large area (such as an entire program or a large amount of received or decoded data). ROM 33 includes at least programs and parameters. ROM 33 can store algorithms and instructions to perform the technology according to the present principles. When turned on, CPU 32 uploads the program to RAM and executes the corresponding instructions.

[0050] RAM 34 includes in registers a program executed by CPU 32 and uploaded after device 30 is turned on, input data in registers, intermediate data in different states of a method in registers, and other variables in registers for executing the method.

[0051] The implementation described herein can be implemented in, for example, a method or process, a device, a computer program product, a data stream, or a signal. Even if only discussed in the context of a single form of implementation (e.g., discussed only as a method or device), the implementation of the discussed features can also be implemented in other forms (e.g., programs). The device can be implemented in, for example, appropriate hardware, software, and firmware. The method can be implemented in, for example, a device (such as, for example, a processor, which generally refers to a processing device, including, for example, a computer, a microprocessor, an integrated circuit, or a programmable logic device). The processor also includes a communication device, such as, for example, a computer, a cellular phone, a portable / personal digital assistant ("PDA"), and other devices that facilitate the communication of information between end users.

[0052] The device 30 is linked, for example, via a bus 31, to a set of sensors 37 and a set of rendering devices 38. The sensors 37 may be, for example, cameras, microphones, temperature sensors, inertial measurement units, GPS, humidity sensors, IR or UV light sensors, or wind sensors. The rendering devices 38 may be, for example, displays, speakers, vibrators, heaters, fans, etc.

[0053] According to an example, the device 30 is configured to implement a method according to the present principles and belongs to the set comprising:

[0054] -mobile device;

[0055] -communication equipment;

[0056] -Gaming equipment;

[0057] - Tablet (or tablet computer);

[0058] - Laptop;

[0059] -Still picture camera;

[0060] -Camcorder.

[0061] Figure 4 An example of an embodiment of the syntax of a data stream encoding a volumetric scene description according to the present principles is shown. Figure 4An example structure 4 of a volumetric scene representation is shown. The structure includes a container that organizes the stream into independent grammatical elements. The structure may include a header portion 41, which is a set of data common to each grammatical element of the stream. For example, the header portion includes some of the metadata about the grammatical elements that describe the properties and effects of each of the grammatical elements. The structure also includes a payload that includes an element 42 of the grammar and an element 43 of the grammar. The element 42 of the grammar includes metadata representing a media content item and includes at least a rendering attribute value, such as a color value, which indicates that the renderer sets the missing color value to the color value when rendering the viewport image of the volumetric scene. In an embodiment, the attribute value is associated with an area of ​​the 3D space of the volumetric scene represented in the element 43 of the grammar. In another embodiment, the attribute value is associated with a quality level that indicates to the renderer the level of visibility of visual artifacts when the missing color value is set to the color value. The element 43 of the grammar is part of the payload of the data stream and includes data encoding the representation of the volumetric scene of the present principles. Various formats can be used for the representation.

[0062] The implementation described herein can be implemented in, for example, a method or process, a device, a computer program product, a data stream, or a signal. Even if only discussed in the context of a single form of implementation (e.g., discussed only as a method or device), the implementation of the discussed features can also be implemented in other forms (e.g., programs). The device can be implemented in, for example, appropriate hardware, software, and firmware. The method can be implemented in, for example, a device (such as, for example, a processor, which generally refers to a processing device, including, for example, a computer, a microprocessor, an integrated circuit, or a programmable logic device). The processor also includes a communication device, such as, for example, a smart phone, a tablet, a computer, a mobile phone, a portable / personal digital assistant ("PDA"), and other devices that facilitate the communication of information between end users.

[0063] The implementation of various processes and features described herein can be implemented in a variety of different equipment or applications, particularly in equipment or applications associated with, for example, data encoding, data decoding, view generation, texture processing and other processing of images and related texture information and / or depth information. Examples of such equipment include encoders, decoders, post-processors for processing outputs from decoders, pre-processors for providing inputs to encoders, video encoders, video decoders, video codecs, web servers, set-top boxes, laptop computers, personal computers, cellular phones, PDAs and other communication devices. As should be clear, the equipment can be mobile and even installed in a mobile vehicle.

[0064] Furthermore, the method may be implemented by instructions executed by a processor, and such instructions (and / or data values ​​resulting from the implementation) may be stored on a processor-readable medium, such as, for example, an integrated circuit, a software carrier, or other storage device, such as, for example, a hard disk, a compact disk ("CD"), an optical disk (such as, for example, a DVD, commonly referred to as a digital versatile disk or digital video disk), a random access memory ("RAM"), or a read-only memory ("ROM"). The instructions may form an application program tangibly implemented on a processor-readable medium. The instructions may, for example, be in hardware, firmware, software, or a combination. The instructions may exist in, for example, an operating system, a separate application, or a combination of both. Thus, a processor may be characterized as, for example, a device configured to perform a process and a device including a processor-readable medium (such as a storage device) having instructions for performing the process. Furthermore, in addition to or in lieu of instructions, the processor-readable medium may store data values ​​resulting from the implementation.

[0065] As will be apparent to one skilled in the art, implementations may generate a variety of formatted signals to carry information that may be stored or transmitted, for example. The information may include, for example, instructions for executing a method, or data generated by one of the implementations. For example, a signal may be formatted to carry as data the rules for writing or reading the grammar of the embodiment, or to carry as data the actual grammar values ​​written by the embodiment. Such a signal may be formatted as, for example, an electromagnetic wave (e.g., using the radio frequency portion of the spectrum) or a baseband signal. Formatting may include, for example, encoding a data stream and modulating a carrier with the encoded data stream. The information carried by the signal may be, for example, analog or digital information. As is well known, signals may be transmitted over a variety of different wired or wireless links. The signal may be stored on a processor-readable medium.

[0066] A number of implementations have been described. However, it will be appreciated that various modifications may be made. For example, elements of different implementations may be combined, supplemented, modified, or removed to produce other implementations. Furthermore, it will be appreciated by those of ordinary skill that other structures and processes may replace those disclosed, and that the resulting implementations will perform at least substantially the same (one or more) functions in at least substantially the same (one or more) manners to achieve at least substantially the same (one or more) results as the disclosed implementations. Therefore, the present application contemplates these and other implementations.

Claims

1. A method comprising encoding in a data stream a representation of a volumetric scene and metadata including color values ​​that instruct a renderer to set missing color values ​​to color values ​​when rendering a viewport image of the volumetric scene. 2 . The method of claim 1 , wherein the color value is associated with a quality level that indicates to a renderer a level of visibility of visual artifacts when setting missing color values ​​to the color value.

3. A method according to claim 1 or 2, wherein the color value is determined from color values ​​of pixels of a multi-view image used to generate the representation of the volumetric scene.

4. A method according to one of claims 1 to 3, wherein the metadata comprises at least two color values, each given color value being associated with a region of the volumetric scene, which instructs the renderer to use the given color value for the portion of the viewport image representing the region of the volumetric scene.

5. The method according to one of claims 1 to 4, wherein the metadata is encoded in a Supplemental Enhancement Information message. 6 . The method according to claim 1 , wherein the metadata further comprises a second value of a rendering attribute other than color, which instructs the renderer to set a missing value of the attribute to the second value when rendering a viewport image of the volumetric scene.

7. A method comprising: - obtain a representation of the volumetric scene and metadata including color values ​​from the data stream; as well as - Renders a viewport image of the volumetric scene and sets the missing color values ​​to color values.

8. The method of claim 7, wherein the color values ​​are associated with a quality level, and wherein the method of setting the missing color values ​​is selected according to the quality level.

9. The method of one of claims 7 to 8, wherein the metadata comprises at least two color values, each given color value being associated with a region of the volumetric scene, and wherein a given color value is used to represent a portion of the viewport image of the region of the volumetric scene.

10. The method according to one of claims 7 to 9, wherein metadata is decoded from a Supplemental Enhancement Information message.

11. The method of one of claims 7 to 10, wherein the metadata further comprises a second value of a rendering property other than color, and wherein missing values ​​of the property of the viewport image are set to the second value.

12. A data stream comprising a representation of a volumetric scene and metadata comprising color values ​​instructing a renderer to set missing color values ​​to color values ​​when rendering a viewport image of the volumetric scene.

13. The data stream of claim 12, wherein the color value is associated with a quality level that indicates to a renderer a level of visibility of visual artifacts when setting missing color values ​​to the color value.

14. A data stream according to claim 12 or 13, wherein the colour value is determined from colour values ​​of pixels of a multi-view image used to generate the representation of the volumetric scene.

15. A data stream according to one of claims 12 to 14, wherein the metadata comprises at least two color values, each given color value being associated with a region of the volumetric scene, which instructs the renderer to use the given color value for the portion of the viewport image representing the region of the volumetric scene.

16. The data stream according to one of claims 12 to 15, wherein the metadata is encoded in a Supplemental Enhancement Information message.

17. The data stream of one of claims 12 to 16, wherein the metadata further comprises a second value of a rendering attribute other than color, which instructs the renderer to set a missing value of the attribute to the second value when rendering a viewport image of the volumetric scene.

18. A device comprising a memory associated with a processor, the processor configured to encode in a data stream a representation of a volumetric scene and metadata including color values, the color values ​​instructing a renderer to set missing color values ​​to color values ​​when rendering a viewport image of the volumetric scene.

19. The apparatus of claim 18, wherein the color value is associated with a quality level that indicates to a renderer a level of visibility of visual artifacts when setting missing color values ​​to the color value.

20. An apparatus according to claim 18 or 19, wherein the colour value is determined from colour values ​​of pixels of the multi-view image used to generate the representation of the volumetric scene.

21. The apparatus of one of claims 19 to 20, wherein the metadata comprises at least two color values, each given color value being associated with a region of the volumetric scene, which instructs the renderer to use the given color value for the portion of the viewport image representing the region of the volumetric scene.

22. The device according to one of claims 18 to 21, wherein the metadata is encoded in a Supplemental Enhancement Information message.

23. The apparatus of one of claims 18 to 22, wherein the metadata further comprises a second value of a rendering attribute other than color, which instructs the renderer to set a missing value of the attribute to the second value when rendering a viewport image of the volumetric scene.

24. An apparatus comprising a memory associated with a processor, the processor being configured to: - obtaining a representation of the volumetric scene and metadata including color values ​​from the data stream; and - Renders a viewport image of the volumetric scene and sets the missing color values ​​to color values.

25. The apparatus of claim 24, wherein the color values ​​are associated with a quality level, and wherein the method of setting the missing color values ​​is selected according to the quality level.

26. Apparatus according to one of claims 24 to 25, wherein the metadata comprises at least two colour values, each given colour value being associated with a region of the volumetric scene, and wherein a given colour value is used to represent a portion of the viewport image of the region of the volumetric scene.

27. The apparatus of one of claims 24 to 26, wherein the metadata is decoded from a Supplemental Enhancement Information message.

28. Apparatus according to one of claims 24 to 27, wherein the metadata further comprises a second value of a rendering property other than colour, and wherein missing values ​​of the property of the viewport image are set to the second value.

Images