Intra and inter prediction for point cloud attribute coding by transfer function parameters

Abstract

Intra and inter prediction of attributes of points of 3D blocks of a 3D point cloud is proposed in the context of the encoding or the decoding of the attributes in a parallelisable way, independently of the geometry. The volume of the 3D point cloud is divided in blocks. The geometry is compressed and a 3D image represented as a transform function is generated for each block. According to the present principles, theses 3D images are inter or intra predicted according to a set of prediction modes.

Description

[0001]INTRA AND INTER PREDICTION FOR POINT CLOUD ATTRIBUTE CODING BY TRANSFER FUNCTION PARAMETERS 1. Technical Field The present principles generally relate to the domain of encoding, transmitting and decoding point clouds with attributes. In particular, the present principles relate to formatting the attributes of a point cloud independently of how the geometry is encoded or decoded and in a way that allow a parallel encoding and decoding of the geometry and the attributes of a point cloud. 2. Background The present section is intended to introduce the reader to various aspects of art, which may be related to various aspects of the present principles that are described and / or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present principles. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. Advances in 3D capturing and rendering technologies enables new applications and services in the fields of autonomous driving, cultural heritage archival, immersive telepresence and virtual / augmented reality. Point clouds have arisen as one of the main 3D scene representations for such applications. A point cloud frame consists of a set of 3D points, each point being represented by its 3D location and eventually one or more attributes like color, reflectance, normal vector, or transparency. Compression of dense dynamic point clouds with a geometry-based approach requires a huge amount of information. A 3D-to-2D projection may leverage existing 2D video codecs to encode 3D point clouds or 3D meshes. For example, a Geometric Point Cloud Compression (G-PCC) encoder for dense dynamic point clouds combines several tool modules, comprising pruned occupancy tree (octree) plus triangle soups for geometry coding, Region- Adaptive Hierarchical Transform (RAHT) for color attribute coding, motion compensated inter- frame prediction and context-adaptive arithmetic coding. It is possible to encode / decode the attributes of a point cloud in a parallelisable way, independently of the geometry. However, there is a lack of an intra and inter prediction to take advantage of already encoded / decoded information in the current frame. 3. Summary The following presents a simplified summary of the present principles to provide a basic understanding of some aspects of the present principles. This summary is not an extensive overview of the present principles. It is not intended to identify key or critical elements of the present principles. The following summary merely presents some aspects of the present principles in a simplified form as a prelude to the more detailed description provided below. The present principles relate to a method for encoding a 3D point cloud encompassed in a 3D volume. The points of the 3D point cloud have attributes, for example a color. The method comprises dividing the 3D volume in 3D blocks. For each 3D block comprising at least one point, geometry values of the at least one point are compressed. A first 3D image is generated and coded as a transform function associating coordinates within the 3D block with an attribute value according to the attribute values of the at least one point. A prediction mode for attributes of the 3D block is determined. A second 3D image is generated according to this prediction mode and first 3D images generated for different 3D blocks. The second 3D image is subtracted from the first 3D image to obtain a 3D residue image. Then, compressed geometries, arithmetically coded sequence of the prediction modes and entropy coded transform functions of the 3D residue images are encoded in a data stream. The present principles also relate to a device comprising a processor and a memory associated with the processor that is configured to implement the method above. The present principles also relate to a method for decoding a 3D point cloud encompassed in a 3D volume, points of the 3D point cloud having attributes. The method comprises obtaining compressed geometries of 3D blocks of the 3D volume, arithmetically coded sequence of prediction modes for the 3D blocks and entropy coded transform functions of 3D residue images for the 3D blocks. For each 3D block, geometry values are decompressed for at least one point in the 3D block. A first 3D image is generated for the 3D block by adding a 3D residue image to a 3D predicted image. The 3D residue image is obtained according to the inverse of the transform function of the 3D block and the 3D predicted image is obtained according to the prediction mode of the 3D block and first 3D images generated for different 3D blocks. An attribute value is attributed to the at least one point according to the first 3D image. The present principles also relate to a device comprising a processor and a memory associated with the processor that is configured to implement the method above. 4. Brief Description of Drawings The present disclosure will be better understood, and other specific features and advantages will emerge upon reading the following description, the description making reference to the annexed drawings wherein: ^ Figure 1 illustrates a G-PCC scheme wherein geometry and attributes are sequentially compressed; ^ Figure 2 illustrates how the 3D space of a 3D point cloud to encode is divided in a scheme to encode / decode the attributes of a point cloud independently of how the geometry is encoded / decoded; ^ Figure 3 shows an example architecture of a device 30 which may be configured to implement encoding and / or decoding methods according to an embodiment of the present principles; ^ Figure 4 shows an example of an embodiment of the syntax of a stream when the data are transmitted over a packet-based transmission protocol; ^ Figure 5 illustrates blocks used for intra prediction, according to the present principles; ^ Figure 6 diagrammatically shows how the signalling of prediction modes are signalled to the decoder, according to the present principles. 5. Detailed description of embodiments The present principles will be described more fully hereinafter with reference to the accompanying figures, in which examples of the present principles are shown. The present principles may, however, be embodied in many alternate forms and should not be construed as limited to the examples set forth herein. Accordingly, while the present principles are susceptible to various modifications and alternative forms, specific examples thereof are shown by way of examples in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the present principles to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present principles as defined by the claims. The terminology used herein is for the purpose of describing particular examples only and is not intended to be limiting of the present principles. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises", "comprising," "includes" and / or "including" when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. Moreover, when an element is referred to as being "responsive" or "connected" to another element, it can be directly responsive or connected to the other element, or intervening elements may be present. In contrast, when an element is referred to as being "directly responsive" or "directly connected" to other element, there are no intervening elements present. As used herein the term "and / or" includes any and all combinations of one or more of the associated listed items and may be abbreviated as" / ". 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. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element without departing from the teachings of the present principles. Although some of the diagrams include arrows on communication paths to show a primary direction of communication, it is to be understood that communication may occur in the opposite direction to the depicted arrows. Some examples are described with regard to block diagrams and operational flowcharts in which each block represents a circuit element, module, or portion of code which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that in other implementations, the function(s) noted in the blocks may occur out of the order noted. For example, two blocks shown in succession may, in fact, be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending on the functionality involved. Reference herein to “in accordance with an example” or “in an example” means that a particular feature, structure, or characteristic described in connection with the example can be included in at least one implementation of the present principles. The appearances of the phrase in accordance with an example” or “in an example” in various places in the specification are not necessarily all referring to the same example, nor are separate or alternative examples necessarily mutually exclusive of other examples. Reference numerals appearing in the claims are by way of illustration only and shall have no limiting effect on the scope of the claims. While not explicitly described, the present examples and variants may be employed in any combination or sub-combination. Figure 1 illustrates a G-PCC scheme wherein geometry and attributes are sequentially compressed. In the encoder 11, a point cloud 12 with attributes (for example color or transparency) is obtained from a source. The geometry is first compressed, for example by dividing the 3D space of the 3D point cloud in voxels and representing it as an octree. Then the geometry is decompressed and the attributes are transferred onto the decompressed geometry to be compressed, for example with RAHT techniques. Currently, RAHT is not a parallelisable transform as it encodes the entire frame’s attributes together. In addition, the encoding of the attributes is dependent on the results of the geometry encoder, which introduces errors if the geometry encoding is lossy. Therefore, the encoding of the geometry cannot be executed in parallel with the encoding of the attributes, as one needs to transfer the attributes to the decoded geometry prior to encoding the point cloud attributes. The same problem occurs at the decoder 13 wherein the geometry must be fully decompressed before than the attributes are decompressed on the decompressed geometry to obtain a decoded point cloud 14 with attributes. Figure 2 illustrates how the 3D space of a 3D point cloud to encode is divided in a scheme to encode / decode the attributes of a point cloud independently of how the geometry isencoded / decoded. The point cloud 3D space is divided into 3D-blocks of size ^^ ൈ ^^ ൈ ^^, as shown in a 2D example in Figure 2, where ^^ is an integer, for example a power of 2. The geometry and attribute encoding / decoding is executed for each block individually and only occupied blocks are processed. The signalling of which block is occupied can be conveyed to the decoder using,for example, the octree. Furthermore, each block is subdivided into ^^௫ ൈ ^^௬ ൈ ^^௭ regions where^^௫, ^^௬, and ^^௭are an integer lower than or equal to ^^. From each input point cloud block, an ^^௫ ൈ ^^௬ ൈ ^^௭ image ^^^ is generated, that representsthe attribute ^^ for every possible position (X, Y, Z) inside that block. The value of ^^^^^^, ^^, ^^^ isequal to the value of attribute ^^ of the point at position ^^^,^^,^^^ when there is only one non-empty point of the input point cloud block at (x,y,z). It is set to the average value of the attribute ^^ of allpoints at position ^^^, ^^, ^^^ when there is more than one point of the input point cloud block at thisposition. It is set to an interpolated attribute ^^ based on the average of the closest points when thereare no points at position ^^^, ^^, ^^^, where ^^ ൌ ^^^ ∗ ே^ே^ ே^ே^, ^^ ൌ ^^^ ∗ே^, and ^^ ൌ ^^^ ∗ே ^. According to using already encoded / decoded blocks. Two prediction types are combined: Intra prediction that uses already encoded / decoded blocks on the current frame and inter prediction that uses already encoded / decoded blocks on the previous frame. Figure 5 illustrates blocks used for intra prediction. In a first embodiment, only blocks 52 touching a face of block 51 to be predicted are considered. The blocks used for prediction are occupied blocks in the current frame that are already encoded / decoded and whose image ^^^is already reconstructed after dequantize and inverse transform. In a second embodiment, to limit memory footprint, only the decoded voxels 53 of the 3D images ^^^that are touching block 51 to be predicted are used for prediction. For simplicity of notation, block 51 to be predicted is called “B” in the rest of the present document. The samples voxels used for intra or inter prediction are at position ^^^, ^^, ^^^ where at leastone value of ^^, ^^, or ^^ is equal to െ1. The set of all sample voxels used for prediction is called thesample domain. Let ^^^^^, ^^, ^^^ be the reconstructed attribute for the sample voxel located at^^^, ^^, ^^^. If there is no available sample located at this position, the value of ^^^^^, ^^, ^^^ is the valueof the nearest available sample voxel attribute. According to the present principles, two categories of prediction are proposed: non-angular and angular. For the latter category, the prediction has a preferred direction. The directions used for prediction are defined by the vectors ^^௫, ^^௬, and ^^௭as defined in equation Eq1 and in the following table. Eq1: ^^௫^^^௫^ ൌ ^^ ^ଷଶ ெ^ ^^௫^ , ^^௫ ∈ ^0,1, … ,^^௫ െ 1^ where ^^௫, ^^௬, and ^^௭belongs, for example, to set ^2,4,8,16,32^ and are parameters that determines the number of prediction modes, and where V is, for instance, the following vector: ^^ ൌ ^^32,^29,^26,^23,^20,^18,^16,^14,^12,^10,^8,^6,^4,^3,^2,^1,0,െ1,െ2,െ3,െ4,െ6,െ8,െ10,െ12,െ14,െ16,െ18,െ20,െ23,െ26,െ29^ Parameters may be defined by default, by an operator or automatically, for example on the basis of a rate-distortion optimization. The intra prediction modes are the ones depicted in the following table: Mode Number Index Direction of modes ^^^^^,^^^^,^^^^^ Non- DC 10- angularPlanar11 -Angular X ^^௬ ∗ ^^௭ 2 ^ ^^௬ ∗ ^^௭ ^ ^^௭ ^െ32, ^^௬^^^௬൧, ^^௭^^^௭^^Y ^^௫ ∗ ^^௭ 2 ^ ^^௬ ∗ ^^௭ ^ ^^௫ ∗ ^^௭ ^ ^^௭ ^^^௫^^^௫^,െ32, ^^௭^^^௭^^Z ^^௫ ∗ ^^௬ 2 ^ ^^௬ ∗ ^^௭ ^ ^^௫ ∗ ^^௭ ^ ^^௫ ∗ ^^௬ ^ ^^௬ ൫^^௫^^^௫^, ^^௬^^^௬൧,െ32൯Y-Z plane ^^௫2 ^ ^^௬ ∗ ^^௭ ^ ^^௫ ∗ ^^௭ ^ ^^௫ ∗ ^^௬ ^ ^^௫^^^௫^^^௫^,െ32,െ32^ X-Z plane^^௬2 ^ ^^௬ ∗ ^^௭ ^ ^^௫ ∗ ^^௭ ^ ^^௫ ∗ ^^௬ ^ ^^௫^െ32, ^^௬^^^௬൧,െ32^^^^௬X-Y ^^௭2 ^ ^^௬ ∗ ^^௭ ^ ^^௫ ∗ ^^௭ ^ ^^௫ ∗ ^^௬ ^ ^^௫^െ32,െ32,^^௭^^^௭^^plane ^^^௬^^^௭Diagonal12 ^ ^^௬ ∗ ^^௭ ^ ^^௫ ∗ ^^௭ ^ ^^௫ ∗ ^^௬ ^ ^^௫^െ32,െ32,െ32^ ^^^௬^^^௭The prediction is referred as ^^^^^, ^^, ^^^ and is computed differently depending on theprediction mode. Mode DC is available if there is at least one already encoded / decoded block touching the current block. In this mode, the attribute of each voxel of B is predicted as the average value of all voxels on the sample domain. Mode Planar is available if at least two already encoded / decoded blocks are touching thecurrent block. Each ^^^^^, ^^, ^^^ value in this mode is obtained as the arithmetic mean of linearinterpolations, ^^௫ , ^^௬ , and ^^௭. The prediction ^^^^^,^^, ^^^ is compute according to three differentcases. In a first case, if there is an available block touching the face in the direction -x, and another in the direction -y: ^^௫^^^,^^, ^^^ ൌ ^^^^^^^^^^െ1,^^, ^^^,^^^^^௫ ,െ1, ^^^, ^^, ^^௫^^^௬^^^, ^^, ^^^ ൌ ^^^^^^^^^^^^,െ1, ^^^, ^^൫െ1,^^௬, ^^൯, ^^,^^௬^^ face in the direction -x, and another in the direction -z: ^^௫^^^,^^, ^^^ ൌ ^^^^^^^^^^െ1,^^, ^^^,^^^^^௫, ^^,െ1^, ^^, ^^௫^^^௭^^^, ^^, ^^^ ൌ ^^^^^^^^^^^^, ^^,െ1^,^^^െ1,^^, ^^௭^, ^^, ^^௭^^^௭ ∗ ^^௫^^^, ^^, ^^^ ^ ^^௫ ∗ ^^௭^^^,^^, ^^^ ^ ^^௫ ∗ ^^^^^^^, ^^, ^^^ ൌ ^ ௭^^^ otherwise, in a ^^௬^^^, ^^, ^^^ ൌ ^^^^^^൫^^^^^,െ1, ^^^,^^൫^^, ^^௬ ,െ1൯,^^, ^^௬൯^^௭^^^, ^^, ^^^ ൌ ^^^^^^^^^^^^, ^^,െ1^, ^^^^^,െ1,^^௭^, ^^,^^௭^^^ ∗ ^^ ^^^,^^, ^^^ ^ ^^ ∗ ^^ ^^^, ^^, ^^^ ^ ^^^, ^^ ൌ ^ ௭ ௬ ௬ ௭ ௬ ∗ ^^^^^^^, ^ ^ ௭^^^ The availability of angular modes depends on the availability of already decoded blocks touching a face of the current block: Modes X: available if there is a block touching the face in the direction -x; Modes Y: available if there is a block touching the face in the direction -y; Modes Z: available if there is a block touching the face in the direction -z; Modes Y-Z plane: available if there is a block touching the face in the direction -y and another in the direction -z; Modes X-Z plane: available if there is a block touching the face in the direction -x and another in the direction -z; Modes X-Y plane: available if there is a block touching the face in the direction -x and another in the direction -y; Mode diagonal: available if there is a block touching the face in the direction -x, one in the direction -y and another in the direction -z. The prediction of the attribute value of a voxel depends on the direction ^^ ൌ ^^^௫, ^^௬, ^^௭^of each mode provided in the table above. According to the present principles, there are three different cases of intra predictions depending on the value of ^^௫, ^^௬, and ^^௭, according to the following equations, where ^^ is either ^^, ^^, or ^^: 32 ∗ ^^^ ^ 1^ ^ ⌊െ^^ / 2⌋^^௨െ^^^ ^^^^ ^^௨ ^ 0௨^∞ ^^^^ℎ^^^^^^^^^^^^If ^^௫ ^ ^^௬ and then^^^ ൌ 32 ∗ ^^ ^ ^^௫ ∗ ^^௬ Else ^^^ ൌ 32 ∗ ^^ ^ ^^௭ ∗ ^^௫^^^ ൌ 32 ∗ ^^ ^ ^^௭ ∗ ^^௬ 32 ^^^ ^^^ ൌ ^^ 32 ^^^ ൌ ^^^ െ 32 ∗ ^^^^^ଶ ൌ ^^^ െ 32 ∗ ^^^ଷ ଷ ^^^ ^^^^^^ ^ ^^^ ^ ^ the values provided in the table below. These values are subject to the constraint: ଷ ^^^^^^^^^^^64 ∀ ^^The operator ≫ is a bit shift is equivalent to: ^^ ^^ ≫ ^^ ≡ ^௬^ 2 p\i 0 1 2 3 0 16 32 16 0 1 11 39 15 -1 2 7 45 13 -1 3 2 52 12 -2 4 -2 58 10 -2 5 -3 57 12 -2 6 -3 56 13 -2 7 -4 55 15 -2 8 -4 54 16 -2 9 -5 53 19 -3 10 -5 50 22 -3 11 -5 48 25 -4 12 -6 46 28 -4 13 -6 44 30 -4 14 -5 41 32 -4 15 -5 39 34 -4 16 -4 36 36 -4 17 -4 34 39 -5 18 -4 32 41 -5 19 -4 30 44 -6 20 -4 28 46 -6 21 -4 25 48 -5 22 -3 22 50 -5 23 -3 19 53 -5 24 -2 16 54 -4 25 -2 15 55 -4 26 -2 13 56 -3 27 -2 12 57 -3 28 -2 10 58 -2 29 -2 12 52 2 30 -1 13 45 7 31 -1 15 39 11 For the inter prediction, the previous encoded / decoded frame is used for prediction. The previous frame can be motion compensated to adjust for movement. Image ^^^of the corresponding in the previous frame is used as predicted image for the current block. According to the present principles, the prediction mode, for a block, is determined at the encoder side based on a rate-distortion optimization and signalled to the decoder on the bitstream by means of flags that are encoded using adaptative binary arithmetic encoder. Figure 6 diagrammatically shows how the signalling of prediction modes are signalled to the decoder. If frames of a sequence of point clouds with attributes can be inter predicted, a first information signalling whether the selected prediction mode is intra or inter is encoded, depending on four cases. In a first case, there is no intra prediction modes available nor the inter mode: there is no need to signal if the prediction mode is intra or inter and the prediction is P(x,y,z)=0. In a second case, the inter mode is not available: there is no need to signal if the prediction mode is intra or inter and both the encoder and the decoder infer that one of the intra modes is to be used. In a third case, some of the intra modes are not available. There is no need to signal if the prediction mode is intra or inter and both the encoder and the decoder will infer that the inter mode is to be used. In a fourth case, the selected prediction mode may be intra or inter and is signalled by a flag, following tree 61 of Figure 6. According to the present principles, the flag is sent using adaptive binary arithmetic coding, where the probability of the flag be encoded as true is given by Prob[0]. After encoding / decoding this flag, the probability Prob[0] is updated by increasing the value if the sent true flag is set to true, or by decreasing the value if it is set to false. When the prediction mode is intra, the selected intra prediction mode is signalled. This is performed, for example, by using signalling tree 62 of Figure 6. Starting from the start point, a binary flag determines which direction the decoder is following in the tree branches to decode the prediction mode at each node it passes in the tree. The probability for a flag to be true is determined by the vector Prob. However, as some prediction modes may not be available depending on the availability of neighbouring blocks of the block being predicted, some probabilities of the vector Prob are replaced by default values when encoding / decoding a particular case, for example, as listed in the table below. After encoding / decoding, the values that have being replaced by a default value revert to its previous value. Block available Prob[n] at direction X Y Z [1] [2] [3] [4] [5] [6] [7] [8] F F F 0 0 1 1 0 1 1 1 F F T [1] 0 1 1 0 1 1 1 F T F [1] 0 1 0 0 1 1 1 F T T [1] [2] 1 ½ 0 1 [7] 1 T F F [1] 0 0 0 0 1 1 1 T F T [1] [2] ½ 1 0 1 1 [8] T T F [1] [2] ½ 0 0 [6] 1 1 T T T [1] [2] 2 / 3 ½ [5] [6] [7] [8] Where F stands for False and T for True. If a probability of the vector Prob is not forced to a given default value, the probability is updated while the prediction mode is encoded. If a true flag is encoded, the given probability is increased, otherwise the probability is decreased. For the angular modes, except the diagonal mode, after finishing the signalling using tree 62, the index of the prediction mode is conveyed. Let define that ^^^is the first index of a group of prediction modes (X, Y, Z, Y-Z plane, X-Z plane, or X-Y plane), and that the group has ^^prediction modes. The signalling is performed tree 63, where ^^ is a value such that no twodifferent groups use the same set of probabilities. Finally, prediction ^^^^^,^^, ^^^ is subtracted from the image ^^^^^^, ^^, ^^^ at encoder side toobtain a 3D residue image. The 3D residue image is encoded as a transform function and entropy coded in the stream. At the decoder side, a 3D residue image is retrieved by entropy decoding and inverse transforming, and it is added to the 3D image generated according to the decoded prediction mode. Figure 3 shows an example architecture of a device 30 which may be configured to implement encoding and / or decoding methods according to an embodiment of the present principles. The device is linked with other devices via their bus 31 and / or via I / O interface 36. Device 30 comprises following elements that are linked together by a data and address bus 31:D ^ a processor 32 (or CPU), which is, for example, a DSP (or Digital Signal Processor); ^ a ROM (or Read Only Memory) 33; ^ a RAM (or Random Access Memory) 34; ^ a storage interface 35; ^ an I / O interface 36 for reception of data to transmit, from an application; and ^ a power supply (not represented in Figure 2), e.g. a battery. In accordance with an example, the power supply is external to the device. In each of mentioned memory, the word « register » used in the specification may correspond to area of small capacity (some bits) or to very large area (e.g. a whole program or large amount of received or decoded data). The ROM 33 comprises at least a program and parameters. The ROM 33 may store algorithms and instructions to perform techniques in accordance with present principles. When switched on, the CPU 32 uploads the program in the RAM and executes the corresponding instructions. The RAM 34 comprises, in a register, the program executed by the CPU 32 and uploaded after switch-on of the device 30, input data in a register, intermediate data in different states of the method in a register, and other variables used for the execution of the method in a register. The implementations described herein may be implemented in, for example, a method or a process, an apparatus, a computer program product, a data stream, or a signal. Even if only discussed in the context of a single form of implementation (for example, discussed only as a method or a device), the implementation of features discussed may also be implemented in other forms (for example a program). An apparatus may be implemented in, for example, appropriate hardware, software, and firmware. The methods may be implemented in, for example, an apparatus such as, for example, a processor, which refers to processing devices in general, including, for example, a computer, a microprocessor, an integrated circuit, or a programmable logic device. Processors also include communication devices, such as, for example, computers, cell phones, portable / personal digital assistants ("PDAs"), and other devices that facilitate communication of information between end-users. Device 30 is linked, for example via bus 31 to a set of sensors 37 and to a set of rendering devices 38. Sensors 37 may be, for example, cameras, microphones, temperature sensors, Inertial Measurement Units, GPS, hygrometry sensors, IR or UV light sensors or wind sensors. Rendering devices 38 may be, for example, displays, speakers, vibrators, heat, fan, etc. In accordance with examples, the device 30 is configured to implement a method according to the present principles of encoding, decoding and rendering a 3D point clouds with attributes, and belongs to a set comprising: ^ a mobile device; ^ a communication device; ^ a game device; ^ a tablet (or tablet computer); ^ a laptop; ^ a still picture camera; ^ a video camera. Figure 4 shows an example of an embodiment of the syntax of a stream when the data are transmitted over a packet-based transmission protocol. Figure 4 shows an example structure 4 of a stream encoding point clouds according to the present principle. The structure consists in a container which organizes the stream in independent elements of syntax. The structure may comprise a header part 41 which is a set of data common to every syntax element of the stream. For example, the header part comprises some of metadata about syntax elements, describing the nature and the role of each of them. The structure comprises a payload comprising an element of syntax 42 and at least one element of syntax 43 (there may be an element of syntax 43 for each type of attribute data, for instance one for the color, one for the reflectance, one for the normal vectors, etc.). Syntax element 42 comprises data representative of the geometry of the point cloud, that is, for example, a series of bits representative of the 3D blocks, for example represented as octrees. The implementations described herein may be implemented in, for example, a method or a process, an apparatus, a computer program product, a data stream, or a signal. Even if only discussed in the context of a single form of implementation (for example, discussed only as a method or a device), the implementation of features discussed may also be implemented in other forms (for example a program). An apparatus may be implemented in, for example, appropriate hardware, software, and firmware. The methods may be implemented in, for example, an apparatus such as, for example, a processor, which refers to processing devices in general, including, for example, a computer, a microprocessor, an integrated circuit, or a programmable logic device. Processors also include communication devices, such as, for example, Smartphones, tablets, computers, mobile phones, portable / personal digital assistants ("PDAs"), and other devices that facilitate communication of information between end-users. Implementations of the various processes and features described herein may be embodied in a variety of different equipment or applications, particularly, for example, equipment or applications associated with 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 an encoder, a decoder, a post-processor processing output from a decoder, a pre-processor providing input to an encoder, a video coder, a video decoder, a video codec, a web server, a set-top box, a laptop, a personal computer, a cell phone, a PDA, and other communication devices. As should be clear, the equipment may be mobile and even installed in a mobile vehicle. Additionally, the methods may be implemented by instructions being performed by a processor, and such instructions (and / or data values produced by an 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 diskette (“CD”), an optical disc (such as, for example, a DVD, often referred to as a digital versatile disc or a digital video disc), a random access memory (“RAM”), or a read-only memory (“ROM”). The instructions may form an application program tangibly embodied on a processor-readable medium. Instructions may be, for example, in hardware, firmware, software, or a combination. Instructions may be found in, for example, an operating system, a separate application, or a combination of the two. A processor may be characterized, therefore, as, for example, both a device configured to carry out a process and a device that includes a processor-readable medium (such as a storage device) having instructions for carrying out a process. Further, a processor-readable medium may store, in addition to or in lieu of instructions, data values produced by an implementation. As will be evident to one of skill in the art, implementations may produce a variety of signals formatted to carry information that may be, for example, stored or transmitted. The information may include, for example, instructions for performing a method, or data produced by one of the described implementations. For example, a signal may be formatted to carry as data the rules for writing or reading the syntax of a described embodiment, or to carry as data the actual syntax-values written by a described embodiment. Such a signal may be formatted, for example, as an electromagnetic wave (for example, using a radio frequency portion of spectrum) or as a baseband signal. The formatting may include, for example, encoding a data stream and modulating a carrier with the encoded data stream. The information that the signal carries may be, for example, analog or digital information. The signal may be transmitted over a variety of different wired or wireless links, as is known. The signal may be stored on a processor-readable medium. A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made. For example, elements of different implementations may be combined, supplemented, modified, or removed to produce other implementations. Additionally, one of ordinary skill will understand that other structures and processes may be substituted for those disclosed and the resulting implementations will perform at least substantially the same function(s), in at least substantially the same way(s), to achieve at least substantially the same result(s) as the implementations disclosed. Accordingly, these and other implementations are contemplated by this application.

Claims

CLAIMS 1. A method for encoding a 3D point cloud encompassed in a 3D volume, points of the 3D point cloud having attributes, the method comprising: ^ dividing the 3D volume in 3D blocks; ^ for each 3D block comprising at least one point: ^ compressing geometry values of the at least one point; ^ generating a first 3D image as a transform function associating coordinates within the 3D block with an attribute value according to the attribute values of the at least one point; ^ determining a prediction mode for attributes of the 3D block; generating a second 3D image according to the prediction mode and first 3D images generated for different 3D blocks and subtracting the second 3D image from the first 3D image to obtain a 3D residue image; and ^ encoding compressed geometries, arithmetically coded sequence of the prediction modes and entropy coded transform functions of the 3D residue images in a data stream.

2. The method of claim 1, wherein the prediction mode for a block is determined based on a rate- distortion optimization.

3. The method of claim 1 or 2, wherein a prediction mode belongs to a group comprising an inter prediction mode and intra prediction modes comprising non-angular prediction modes and angular prediction modes for 3D images.

4. A method for decoding a 3D point cloud encompassed in a 3D volume, points of the 3D point cloud having attributes, the method comprising: ^ obtaining compressed geometries of 3D blocks of the 3D volume, arithmetically coded sequence of prediction modes for the 3D blocks and for each 3D block, an entropy coded transform function of 3D residue images for the 3D blocks; ^ for each 3D block: ^ decompressing geometry values of at least one point in the 3D block;^ generating a first 3D image for the 3D block by adding a 3D residue image to a 3D predicted image; the 3D residue image being obtained according to an inverse of the entropy coded transform function of the 3D block; the 3D predicted image being obtained according to the prediction mode of the 3D block and first 3D images generated for different 3D blocks; and ^ attributing an attribute value to the at least one point according to the first 3D image.

5. The method of claim 4, wherein a prediction mode belongs to a group comprising an inter prediction mode and intra prediction modes comprising non-angular prediction modes and angular prediction modes for 3D images.

6. A device for encoding a 3D point cloud encompassed in a 3D volume, points of the 3D point cloud having attributes, the device comprising a memory associated with a processor configured for: ^ dividing the 3D volume in 3D blocks; ^ for each 3D block comprising at least one point: ^ compressing geometry values of the at least one point; ^ generating a first 3D image as a transform function associating coordinates within the 3D block with an attribute value according to the attribute values of the at least one point; ^ determining a prediction mode for attributes of the 3D block; generating a second 3D image according to the prediction mode and first 3D images generated for different 3D blocks and subtracting the second 3D image from the first 3D image to obtain a 3D residue image; and ^ encoding compressed geometries, arithmetically coded sequence of the prediction modes and entropy coded transform functions of the 3D residue images in a data stream.

7. The device of claim 6, wherein the prediction mode for a block is determined based on a rate- distortion optimization.

8. The device of claim 6 or 7, wherein a prediction mode belongs to a group comprising an inter prediction mode and intra prediction modes comprising non-angular prediction modes and angular prediction modes for 3D images.

9. A device for decoding a 3D point cloud encompassed in a 3D volume, points of the 3D point cloud having attributes, the device comprising a memory associated with a processor configured for: ^ obtaining compressed geometries of 3D blocks of the 3D volume, arithmetically coded sequence of prediction modes for the 3D blocks and for each 3D block, an entropy coded transform function of 3D residue images for the 3D blocks; ^ for each 3D block: ^ decompressing geometry values of at least one point in the 3D block; ^ generating a first 3D image for the 3D block by adding a 3D residue image to a 3D predicted image; the 3D residue image being obtained according to an inverse of the entropy coded transform function of the 3D block; the 3D predicted image being obtained according to the prediction mode of the 3D block and first 3D images generated for different 3D blocks; and ^ attributing an attribute value to the at least one point according to the first 3D image.

10. The device of claim 9, wherein a prediction mode belongs to a group comprising an inter prediction mode and intra prediction modes comprising non-angular prediction modes and angular prediction modes for 3D images.

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