WO2022042538A1 - Procédé de prédiction inter-trame géométrique en nuage de points à base de blocs et procédé de décodage - Google Patents

Procédé de prédiction inter-trame géométrique en nuage de points à base de blocs et procédé de décodage Download PDF

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WO2022042538A1
WO2022042538A1 PCT/CN2021/114282 CN2021114282W WO2022042538A1 WO 2022042538 A1 WO2022042538 A1 WO 2022042538A1 CN 2021114282 W CN2021114282 W CN 2021114282W WO 2022042538 A1 WO2022042538 A1 WO 2022042538A1
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frame
point cloud
block
node
prediction
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Chinese (zh)
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李革
金佳民
赵文博
张琦
王静
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北京大学深圳研究生院
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/90—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using coding techniques not provided for in groups H04N19/10-H04N19/85, e.g. fractals
    • H04N19/96—Tree coding, e.g. quad-tree coding
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/50—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding
    • H04N19/503—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding involving temporal prediction
    • H04N19/51—Motion estimation or motion compensation
    • H04N19/513—Processing of motion vectors
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/50—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding
    • H04N19/503—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding involving temporal prediction
    • H04N19/51—Motion estimation or motion compensation
    • H04N19/56—Motion estimation with initialisation of the vector search, e.g. estimating a good candidate to initiate a search

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  • the invention belongs to the technical field of point cloud data processing, and in particular relates to a block-based point cloud geometric inter-frame prediction method and a decoding method.
  • Inter-frame prediction of point clouds has always been a technical difficulty in the field of point cloud encoding and decoding. Since point clouds do not have a fixed spatial structure, it is difficult to intuitively obtain a regular block structure like traditional video encoding and decoding. Moreover, the sparsity and flexibility of the spatial distribution of point clouds also bring great difficulties to motion estimation and motion compensation based on block division.
  • the existing point cloud inter-frame prediction framework mainly includes the following:
  • Prediction method based on occupancy code XOR operation This method performs XOR operation on the occupancy code of the current frame and the predicted frame to obtain the residual of two frames of geometric information, and then encodes the residual, but this method cannot capture the time series of point cloud objects When the motion information of the object is large, the residual error of the occupancy code obtained is also large.
  • Mapping-based prediction method This method first maps the 3D point cloud to a multi-angle 2D plane to obtain multiple 2D images, and then uses the existing video coding tools for compression. This method depends on the advantages and disadvantages of the mapping method. , and such mapping-based compression methods are mainly for 3D human object surface scanning datasets, and for sparse datasets such as lidar scanning maps, the effect of inter-frame prediction is limited.
  • Inter-frame prediction method based on block division This method first directly divides the point cloud into blocks, and then searches for the matching block with the smallest error from the reference frame as the prediction block, and uses the prediction block to improve the coding efficiency of the current block.
  • the prediction block For the use of the prediction block, there are currently two ways. One is to directly replace the current block with the prediction block, calculate the prediction residual, and finally encode the obtained residual coefficient. However, due to the sparsity of the spatial distribution of point clouds, the residual coefficient of the predicted block is often still relatively large. The second is to use the geometric occupancy information of the predicted block as a context to improve the entropy coding efficiency of the current block.
  • the exploration platform EM13 proposed by the MPEG point cloud topic group is such a prediction method, but it only supports the cube-shaped bounding box.
  • the octree is divided, so the bounding box range is too large, which leads to the introduction of too many empty blocks, and there are defects such as excessive motion estimation complexity.
  • the present invention provides a block-based point cloud geometric inter-frame prediction method, which combines the point cloud quadtree and
  • the binary tree division technology supports block division of non-cube bounding boxes, which greatly reduces the waste of code words caused by empty blocks.
  • the computational time complexity of motion estimation is greatly reduced; in addition, the present invention simplifies the inter-frame context model. Fusion, without increasing the number of contexts, significantly improves the entropy coding efficiency.
  • One of the objectives of the present invention is to disclose a block-based point cloud geometry inter-frame predictive coding method.
  • the second purpose of the present invention is to disclose a block-based point cloud geometric inter-frame prediction decoding method.
  • One of the objectives of the present invention is to implement the following scheme, a block-based point cloud geometric inter-frame predictive coding method, characterized in that it includes the following steps: S110 : Setting the same enclosing frame for the frame to be coded and the reference frame box, as the root node of tree division; S120: Perform tree division on the to-be-coded frame and the reference frame respectively according to the bounding box, and obtain the current node in the to-be-coded frame and the corresponding reference frame respectively S130: For each child node of the current node, encode the occupancy information of each child node of the current node according to the occupancy information of the corresponding position child node in the prediction block to obtain a code stream.
  • the same bounding box is set for the frame to be encoded and the reference frame as described in S110, which specifically includes the first method or the second method.
  • the tree division in S120 includes octree, quadtree, and binary tree division.
  • the methods for obtaining the current node in the to-be-coded frame and the corresponding prediction block in the reference frame include but are not limited to the following mode 1 or mode 2; the mode 1: setting the prediction block If the shortest side length of the block obtained by the tree division of the frame to be encoded is equal to or less than the size of the predicted block, it is considered that the tree division is completed, and the current node is obtained; In the block, the block at the corresponding position of the current node is directly used as the prediction block; this way 2: the size PTU size of the initial prediction block PTU is set, if the shortest side length of the block obtained by the tree division of the frame to be encoded is When it is equal to or smaller than the PTU size, the initial prediction block PTU is obtained; according to the coding cost, it is decided whether to further divide the PTU, record the flag information, and split flags indicate whether each node of the PTU is further divided, The occupied flags indicates the occupancy information of the divided sub-nodes
  • calculating the most matching prediction block and the corresponding motion vector MV for each of the PUs specifically includes: determining a search window W; according to the search window W, in the reference frame Obtain a local point cloud; in the local point cloud, for the prediction basic unit PU, that is, the current node, the simplified ICP algorithm is used to obtain the matching block with the smallest error and the corresponding motion vector MV, and the error is the smallest.
  • the matching block and the corresponding motion vector MV of the current node are used as the prediction block and the corresponding motion vector MV of the current node, and the motion vector MV is encoded.
  • the determining of the search window W includes: the size of the search window W is set according to different distribution characteristics of the data set and different code rate points, and if the point cloud distribution is relatively discrete, a larger window range is set; If it is tighter, set a smaller window range.
  • the simplified ICP algorithm is used to obtain the matching block with the smallest error and the corresponding motion vector MV, including:
  • the simplified ICP algorithm only considers translation transformation, and the calculation method of the error is the Lagrangian cost, and the calculation formula is as follows:
  • B is the current node of the frame to be encoded
  • W is the search window
  • Q is the nearest neighbor point set obtained by the current node B after the motion vector MV is translated
  • Est(MV) is the estimated and encoded motion
  • Dist is the block matching loss function of the codeword size required to estimate the coding matching deviation.
  • the Dist is a block matching loss function, including: the calculation formula of the block matching loss function Dist is as follows:
  • w is the point in the local point cloud corresponding to the search window W in the reference point cloud
  • q is the point in the nearest neighbor point set Q found by the current node B after the motion vector MV is translated.
  • each child node of the current node encoding the occupancy information of each child node of the current node according to the occupancy information of the child node corresponding to the position in the prediction block, including method 1 or method 2; the method 1: for each child node , on the basis of the original intra-frame context, an additional inter-frame context bit is added to indicate whether the corresponding position in the prediction block is occupied, and the occupancy information of the child nodes of the current node is encoded; The corresponding position child node in the prediction block is occupied, and the occupation codes of the N child nodes in the corresponding intra-frame context mode are set to 1 as the context information, and the occupancy information of the child nodes of the current node is encoded; The location child node is not occupied, and the occupancy information of the child node of the current node is encoded by using the context information in the frame.
  • a block-based point cloud geometric inter-frame prediction decoding method is characterized in that, it includes the following steps: S210: obtaining the same bounding box of the frame to be decoded and the reference frame, As the root node of tree division; S220: Perform tree division on the frame to be decoded and the reference frame respectively according to the bounding box, and obtain the frame to be decoded according to the tree division and/or the point cloud code stream. The current node and the corresponding prediction block in the reference frame; S230: Decode according to the point cloud code stream to obtain the occupancy information of each child node of the node to be decoded, and obtain a point cloud.
  • obtaining the same bounding box of the frame to be decoded and the reference frame described in S210 specifically includes method 1 or method 2:
  • Method 1 Obtain the minimum bounding box of all frames of the entire point cloud sequence, as the frame to be decoded and The bounding box of the reference frame;
  • the second method obtain the minimum bounding box of the frame to be decoded and the reference frame, as the bounding box of the frame to be decoded and the reference frame.
  • the tree division in S220 includes octree, quadtree, and binary tree division.
  • the method of obtaining the current node in the frame to be decoded and the corresponding prediction block in the reference frame described in S220 includes and is not limited to the following method 1 or method 2; this method 1, according to the prediction block If the shortest side length of the block obtained by the tree division of the frame to be decoded is equal to or less than the size of the predicted block, it is considered that the tree division is completed, and the current node is obtained; In the block, the block at the corresponding position of the current node is directly used as the prediction block; In this way 2, according to the size PTU size of the initial prediction block PTU, if the shortest side length of the block obtained by the tree division of the frame to be decoded is equal to When it is smaller than the PTU size, the initial prediction block PTU is obtained; the flag information split flags and occupied flags are obtained by decoding, and the PTU is further divided according to the flag information, and the prediction basic unit PU obtained after all division is completed is used as the current node; the motion vector MV
  • the motion vector MV of each PU is obtained by decoding and the corresponding prediction block is obtained by calculation, which specifically includes: decoding the code stream to obtain the motion vector MV; passing the current node through the motion vector MV translation, calculating the nearest neighbor point set in the reference point cloud, and obtaining the prediction block corresponding to the current node in the reference point cloud;
  • decoding the occupancy information of each child node of the current node according to the occupancy information of the child node corresponding to the position in the prediction block including method 1 or method 2: the method 1: for each child node , on the basis of the original intra-frame context, an additional inter-frame context bit is added to indicate whether the corresponding position in the prediction block is occupied, and the occupancy information of the child nodes of the current node is decoded; The corresponding position child node in the prediction block is occupied, and the N child node occupation codes in the corresponding intra-frame context mode are set to 1 as the context information, and the occupation information of the child node of the current node is decoded; If the location child node is not occupied, the occupancy information of the child node of the current node is decoded by using the context information in the frame.
  • a block-based point cloud geometry inter-frame prediction method of the present invention mainly has the following advantages:
  • non-cubic point cloud bounding boxes can be supported to further reduce the space ratio of empty blocks and reduce codeword waste.
  • the MV is not limited to a fixed search direction, and the optimal matching block can be found more accurately, while avoiding the complex motion vector search process.
  • FIG. 1 is a flow chart of the block-based point cloud geometry inter-frame predictive coding method proposed by the present invention.
  • FIG. 2 is a flow chart of the block-based point cloud geometry inter-frame prediction decoding method proposed by the present invention.
  • FIG. 3 is a flowchart of an embodiment of a block-based point cloud geometry inter-frame predictive coding method proposed by the present invention.
  • FIG. 4 is a flowchart of an embodiment of a block-based point cloud geometry inter-frame prediction decoding method proposed by the present invention.
  • FIG. 5 is a performance diagram of an embodiment of the block-based point cloud geometry inter-frame predictive coding method proposed by the present invention.
  • FIG. 6 is a performance diagram of the block-based point cloud geometric inter-frame prediction decoding method proposed in the present invention under the condition of geometric lossy compression.
  • FIG. 7 is a performance diagram of the block-based point cloud geometric inter-frame prediction decoding method proposed in the present invention under the condition of geometric lossless compression.
  • the block division-based point cloud geometry inter-frame prediction method of the present invention uses block motion estimation to capture point cloud time series motion information, and improves the point cloud geometry information compression performance; for three-dimensional point cloud geometry information compression, for point cloud data, using the previous method
  • the space occupancy information of the coded frame is used to predict the geometric occupancy information of the current block to be coded, and as a context, the entropy coding efficiency of the occupancy code is improved to improve the compression performance of the point cloud geometric information.
  • the method includes the following steps:
  • Embodiment 1 A block-based point cloud geometry inter-frame predictive coding method
  • FIG. 1 is a schematic flowchart of a block-based point cloud geometry inter-frame predictive coding method provided by the present invention. As shown in FIG. 1 , the block-based point cloud geometry inter-frame predictive coding method provided by the present invention includes the following steps:
  • S120 Perform tree division on the to-be-coded frame and the reference frame respectively according to the bounding box, to obtain a current node in the to-be-coded frame and a corresponding prediction block in the reference frame;
  • the same bounding box is set for the frame to be encoded and the reference frame as described in S110, which specifically includes the first method or the second method.
  • the tree division in S120 includes octree, quadtree, and binary tree division.
  • the methods for obtaining the current node in the to-be-coded frame and the corresponding prediction block in the reference frame include but are not limited to the following mode 1 or mode 2; the mode 1: setting the prediction block If the shortest side length of the block obtained by the tree division of the frame to be encoded is equal to or less than the size of the predicted block, it is considered that the tree division is completed, and the current node is obtained; In the block, the block at the corresponding position of the current node is directly used as the prediction block; this way 2: the size PTU size of the initial prediction block PTU is set, if the shortest side length of the block obtained by the tree division of the frame to be encoded is When it is equal to or smaller than the PTU size, the initial prediction block PTU is obtained; according to the coding cost, it is decided whether to further divide the PTU, record the flag information, and split flags indicate whether each node of the PTU is further divided, The occupied flags indicates the occupancy information of the divided sub-nodes
  • calculating the most matching prediction block and the corresponding motion vector MV for each of the PUs specifically includes: determining a search window W; according to the search window W, in the reference frame Obtain a local point cloud; in the local point cloud, for the prediction basic unit PU, that is, the current node, the simplified ICP algorithm is used to obtain the matching block with the smallest error and the corresponding motion vector MV, and the error is the smallest.
  • the matching block and the corresponding motion vector MV of the current node are used as the prediction block and the corresponding motion vector MV of the current node, and the motion vector MV is encoded.
  • the determining of the search window W includes: the size of the search window W is set according to different distribution characteristics of the data set and different code rate points, and if the point cloud distribution is relatively discrete, a larger window range is set; If it is tighter, set a smaller window range.
  • the simplified ICP algorithm is used to obtain the matching block with the smallest error and the corresponding motion vector MV, including:
  • the simplified ICP algorithm only considers translation transformation, and the calculation method of the error is the Lagrangian cost, and the calculation formula is as follows:
  • B is the current node of the frame to be encoded
  • W is the search window
  • Q is the nearest neighbor point set obtained by the current node B after the motion vector MV is translated
  • Est(MV) is the estimated and encoded motion
  • Dist is the block matching loss function of the codeword size required to estimate the coding matching deviation.
  • the Dist is a block matching loss function, including: the calculation formula of the block matching loss function Dist is as follows:
  • w is the point in the local point cloud corresponding to the search window W in the reference point cloud
  • q is the point in the nearest neighbor point set Q found by the current node B after the motion vector MV is translated.
  • each child node of the current node encoding the occupancy information of each child node of the current node according to the occupancy information of the child node corresponding to the position in the prediction block, including method 1 or method 2; the method 1: for each child node , on the basis of the original intra-frame context, an additional inter-frame context bit is added to indicate whether the corresponding position in the prediction block is occupied, and the occupancy information of the child nodes of the current node is encoded; The corresponding position child node in the prediction block is occupied, and the occupation codes of the N child nodes in the corresponding intra-frame context mode are set to 1 as the context information, and the occupancy information of the child nodes of the current node is encoded; The location child node is not occupied, and the occupancy information of the child node of the current node is encoded by using the context information in the frame.
  • Embodiment 2 A block-based point cloud geometry inter-frame prediction decoding method
  • Figure 2 shows a schematic flowchart of a block-based point cloud geometry inter-frame predictive coding method provided by the present invention.
  • the block-based point cloud geometry inter-frame predictive coding method provided by the present invention includes the following steps:
  • S220 Perform tree division on the frame to be decoded and the reference frame respectively according to the bounding box, and obtain the current node in the frame to be decoded and the corresponding the prediction block in the reference frame;
  • S230 Decode the point cloud code stream to obtain the occupancy information of each child node of the node to be decoded, and obtain a point cloud.
  • obtaining the same bounding box of the frame to be decoded and the reference frame described in S210 specifically includes method 1 or method 2:
  • Method 1 Obtain the minimum bounding box of all frames of the entire point cloud sequence, as the frame to be decoded and the minimum bounding box of all frames.
  • the second method obtain the minimum bounding box of the frame to be decoded and the reference frame, as the bounding box of the frame to be decoded and the reference frame.
  • the tree division in S220 includes octree, quadtree, and binary tree division.
  • the method of obtaining the current node in the frame to be decoded and the corresponding prediction block in the reference frame described in S220 includes and is not limited to the following method 1 or method 2; this method 1, according to the prediction block If the shortest side length of the block obtained by the tree division of the frame to be decoded is equal to or less than the size of the predicted block, it is considered that the tree division is completed, and the current node is obtained; In the block, the block at the corresponding position of the current node is directly used as the prediction block; In this way 2, according to the size PTU size of the initial prediction block PTU, if the shortest side length of the block obtained by the tree division of the frame to be decoded is equal to When it is smaller than the PTU size, the initial prediction block PTU is obtained; the flag information split flags and occupied flags are obtained by decoding, and the PTU is further divided according to the flag information, and the prediction basic unit PU obtained after all division is completed is used as the current node; the motion vector MV
  • the motion vector MV of each PU is obtained by decoding and the corresponding prediction block is obtained by calculation, which specifically includes: decoding the code stream to obtain the motion vector MV; passing the current node through the motion vector MV Translate, calculate the nearest neighbor point set in the reference point cloud, and obtain the prediction block corresponding to the current node in the reference point cloud;
  • the occupancy information of each child node of the node to be decoded is obtained by decoding according to the point cloud code stream, including method 1 or method 2: the method 1: for each child node, in the original frame On the basis of the context, an additional inter-frame context bit is added to indicate whether the corresponding position in the predicted block is occupied, and the occupancy information of the child nodes of the current node is decoded; this method 2: If the corresponding position in the predicted block is occupied If the child node is occupied, the occupation codes of the N child nodes in the corresponding intra-frame context mode are set to 1 as the context information, and the occupancy information of the child node of the current node is decoded; if the corresponding position child node in the prediction block is not Occupancy, using intra-frame context information to decode the occupancy information of the child nodes of the current node.
  • Embodiment 3 A block-based point cloud geometry inter-frame predictive coding method
  • FIG. 3 is a flowchart of an embodiment of a block-based point cloud geometry inter-frame predictive coding method proposed by the present invention, as shown in FIG. 3 .
  • S310 Set the same bounding box for the frame to be encoded and the reference frame as the root node of the tree division.
  • Input the geometric information of the frame to be encoded and the frame to be encoded as the reference frame.
  • the frame to be encoded and the reference frame are synchronized for tree division.
  • the calculation methods of the bounding boxes of the reference frame and the frame to be encoded include but are not limited to the following two schemes: the first method is to count all the frames of the entire sequence, and calculate the maximum bounding box size that can include all the frames as the current entire sequence. The second method is to calculate the size of the bounding box only in the reference frame and the current frame, and take the largest bounding box size as the root node of the tree division in the current frame encoding process.
  • S320 Perform tree division on the to-be-coded frame and the reference frame respectively according to the bounding box, to obtain a current node in the to-be-coded frame and a corresponding prediction block in the reference frame, respectively.
  • the space of the obtained point cloud bounding box is divided into trees. According to the different shapes of the bounding box, the tree division modes such as octree, quadtree and binary tree can be used to decompose the space of the point cloud, and several coding blocks can be obtained.
  • the tree division modes such as octree, quadtree and binary tree can be used to decompose the space of the point cloud, and several coding blocks can be obtained.
  • PTU Prediction Tree Unit
  • a PTU can continue to be divided into multiple PUs (Prediction Units) through the octree, and it is decided whether to further divide according to the coding cost. After the division, the PU tree structure can be obtained.
  • PU is the basic unit of prediction, and each PU calculates a motion vector MV, which is used to find the most matching prediction block in the reference frame.
  • PTU size as PTU_size
  • first perform tree division on the current point cloud and if the minimum side length of the node is equal to PTU_size, the current node is regarded as a PTU.
  • PTU can be divided into PU tree and multiple PUs by octree division.
  • the PU tree contains two flag information. The split flags is used to indicate whether each layer of the PU tree is further divided. If the division is continued, the occupied flags is used to indicate that the division The occupancy information of the child nodes of .
  • Each PU computes a motion vector MV, encodes the resulting PU tree and MV so that the decoder can also generate this prediction block and drives the arithmetic entropy encoder in the same way as the encoder.
  • the ICP algorithm finds the matching block that is the closest to the current coded node, even if the Lagrangian cost is the smallest, and obtains the corresponding MV.
  • the local point set of the MV mapping with the smallest cost is the optimal prediction block. If there is no corresponding prediction block, the node at the corresponding position in the reference frame is directly used as the prediction block.
  • the defined window size can be set according to different distribution characteristics of the data set and different code rate points. If the point cloud distribution is relatively discrete, a larger window range can be set; if the point cloud is relatively tight, a smaller window size can be set .
  • B is the current block to be encoded
  • W is the search window
  • Q is the nearest neighbor point set found by B after MV translation
  • Est() estimates the code word required for encoding MV, and is obtained by calculating the code word required for exponential Golomb encoding
  • Dist is the block matching loss function
  • searching for a matching block involves searching for the nearest neighbors of each point in the window in the block to be coded.
  • the present invention accelerates the searching process by establishing a KD tree.
  • the occupancy information of the prediction block obtained in S323 is used as the context to help encode the occupancy information of the current node.
  • This scheme is based on the point cloud intra-frame context entropy coding tool in , which adds inter-frame context information to help further improve the entropy coding efficiency.
  • the second method is that if the corresponding prediction sub-node is occupied, it is considered as a strong prediction, and the prediction confidence is the same as that of the first 7 neighbor sub-nodes in the frame, and the corresponding intra-frame context mode [1]
  • the occupancy codes of the first seven sub-nodes in the frame sequence are all set to 1, and if the corresponding predicted sub-node is not occupied, the original intra-frame context information is retained.
  • the third method is that if the corresponding prediction sub-node is occupied, it is considered as a strong prediction, and the prediction confidence is the same as that of the first three neighbor sub-nodes in the frame, and the Morton order in the corresponding intra-frame context mode is pre-ordered.
  • the occupancy codes of the three sub-nodes are all set to 1. If the corresponding prediction sub-node is not occupied, the original intra-frame context information is retained.
  • the occupancy code information is encoded using the context information obtained in S331 to obtain the code stream of the point cloud.
  • Embodiment 4 A block-based point cloud geometry inter-frame prediction decoding method
  • the same bounding box of the frame to be decoded and the reference frame is obtained by decoding the code stream or external input, and the frame to be decoded and the reference frame are synchronized to perform tree division.
  • the calculation methods of the bounding boxes of the reference frame and the frame to be decoded include but are not limited to the following two methods: Method 1: Obtain the smallest bounding box of all frames of the entire point cloud sequence as the bounding box of the frame to be decoded and the reference frame; Method 2: Obtain the minimum bounding box of the frame to be decoded and the reference frame, as the bounding box of the frame to be decoded and the reference frame.
  • S420 Perform tree division on the frame to be decoded and the reference frame respectively according to the bounding box, and obtain the current node in the frame to be decoded and the corresponding A prediction block in a reference frame.
  • the space of the obtained point cloud bounding box is divided into trees. According to the different shapes of the bounding box, the point cloud can be decomposed spatially by using tree division modes such as octree, quadtree and binary tree to obtain several decoding blocks.
  • tree division modes such as octree, quadtree and binary tree to obtain several decoding blocks.
  • the division of the prediction unit (the current block and the prediction block) has but is not limited to the following two ways:
  • Method 1 Obtain the size of the predicted block by decoding the code stream or inputting time. If the shortest side length of the block obtained by the tree division of the frame to be decoded is equal to or less than the size of the predicted block, the tree division is considered to be completed, and the current node is obtained; In the blocks obtained by reference frame synchronization division, the block corresponding to the current node is directly used as the prediction block;
  • Method 2 Obtain the size PTU size of the initial prediction block PTU by decoding the code stream or time input. If the shortest side length of the block obtained by the tree division of the frame to be decoded is equal to or less than the PTU size, the initial prediction block PTU is obtained; decoding; The flag information split flags and occupied flags are obtained, the PTU is further divided according to the flag information, and the prediction basic unit PU obtained after all division is completed is used as the current node.
  • S430 Decode the point cloud code stream to obtain the occupancy information of each child node of the node to be decoded, and obtain a point cloud.
  • the prediction block obtained in S423 is synchronized with the current node to be decoded to perform octree division, and the occupancy information of each child node of the current node is decoded according to the occupancy information of the corresponding position child node in the prediction block to obtain a point cloud. It includes the following two methods:
  • Method 1 For each child node, based on the original intra-frame context, an additional inter-frame context bit is added to indicate whether the corresponding position in the prediction block is occupied, and the occupancy information of the child node of the current node is decoded;
  • Method 2 If the child node at the corresponding position in the prediction block is occupied, set the occupation codes of the N child nodes in the corresponding intra-frame context mode to 1 as the context information, and decode the occupancy information of the child node of the current node; The child node at the corresponding position is not occupied, and the occupancy information of the child node of the current node is decoded by using the context information in the frame.
  • Embodiment 5 A block-based point cloud geometry inter-frame predictive coding method
  • the method of the present invention is used to perform lossless compression of point cloud geometric information, and the specific implementation steps are:
  • S110 Set the same bounding box for the frame to be encoded and the reference frame as the root node of the tree division.
  • the bounding box can be determined by the three-dimensional coordinates of the starting point and the two sets of information of length, width, height, and side length. Taking this sequence as an example, The corresponding bounding box information is: the xyz coordinate values of the starting point are (-115100, -115025, -44140), and the side lengths are (230239, 230316, 48208). For all frames in the sequence, the tree partition uses this bounding box as the root node.
  • S120 Perform tree division on the to-be-coded frame and the reference frame respectively according to the bounding box, to obtain a current node in the to-be-coded frame and a corresponding prediction block in the reference frame, respectively.
  • first frame as a reference frame and encoding the second frame as an example
  • full intra-frame encoding is adopted.
  • input the reconstructed first frame as the reference frame and use the frame to be encoded as the benchmark to perform a synchronous tree division operation on the point cloud space of the two frames, and then two identical tree structures can be obtained.
  • a tree node corresponds to a space block area.
  • a space block can be further divided into eight, four or two sub-block spaces, and occupancy codes of different lengths are used to identify the corresponding sub-blocks. Whether it is a point or not, each layer only further divides the nodes with a point.
  • the PTU_size+2*512 that is, for the current PTU range, expand the length of 512 in the three coordinate directions.
  • the PTU can continue to be divided into a PU tree structure and corresponding multiple PUs through the octree division.
  • the PTU can also be regarded as a PU with a larger size.
  • the PU tree contains two flag information, and the split flags are used to indicate the nodes of each layer of the PU tree. Whether to further divide, if continue to divide, the occupied flags is used to indicate the occupancy information of the divided child nodes. For each PU, first calculate the encoding cost when it is not further divided. The cost calculation formula is as follows:
  • B is the current block to be coded
  • W is the search window
  • MV is the motion vector corresponding to the closest matching block obtained by the iterative nearest point algorithm for the current node within the search window
  • Q is the nearest neighbor found by B after MV translation Point set
  • Est() estimates the codeword required for encoding MV, which is obtained by calculating the codeword required for exponential Golomb encoding
  • Dist is the block matching loss function, and the formula is as follows:
  • each PU can obtain an MV and a corresponding prediction block, and then perform motion compensation, that is, use the prediction block to replace the node at the corresponding position in the reference frame, and encode the corresponding motion vector and PU tree structure information , so that the decoding end can also generate the same prediction block.
  • a PU to be coded after obtaining the prediction block through step 3 or step 4, further tree division is performed on the prediction block and the PU, and the corresponding prediction occupancy code can be obtained, which is used as the context to help encode the occupancy information of the current PU.
  • the child nodes divided by the PU there are two kinds of inter-frame prediction context situations: 1) the child node at the corresponding position in the prediction block is occupied, and 2) the child node at the corresponding position in the prediction block is not occupied.
  • the first way is to add an additional context bit to each child node based on the original intra-frame context, which is used to indicate the corresponding position in the prediction block is occupied.
  • the second method is that if the corresponding prediction sub-node is occupied, it is considered as a strong prediction, and the prediction confidence is the same as that of the first 7 neighbor sub-nodes in the frame.
  • the occupancy codes of the seven sub-nodes are all set to 1. If the corresponding predicted sub-node is not occupied, the original intra-frame context information is retained.
  • the third method is that if the corresponding prediction sub-node is occupied, it is considered as a strong prediction, and the prediction confidence is the same as that of the first three neighbor sub-nodes in the frame, and the Morton order in the corresponding intra-frame context mode is pre-ordered.
  • the occupancy codes of the three sub-nodes are all set to 1. If the corresponding prediction sub-node is not occupied, the original intra-frame context information is retained.
  • FIG. 6 shows the performance results of implementing the method of the present invention under the condition of geometric lossy compression based on the AVS point cloud compression platform PCRMv3.0, and stable performance gains are obtained on different data sets.
  • FIG. 7 is a performance result of implementing the method of the present invention under the condition of geometric lossless compression based on the AVS point cloud compression platform PCRMv3.0.
  • the block-based point cloud geometric inter-frame prediction method of the present invention can be used to realize the geometric compression of the point cloud.
  • the method first calculates the bounding box information of the point cloud, and then divides the octree or quadtree and binary tree. When the size of the divided sub-nodes reaches the set prediction unit requirements, the search error in the reference frame for the current node is small.

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Abstract

La présente invention concerne un procédé de décodage de prédiction inter-trame géométrique et un procédé de codage de prédiction inter-trame géométrique en nuage de points à base de blocs. Le procédé de codage comprend les étapes suivantes : S110, définir la même boîte englobante pour une trame à coder et pour une trame de référence, et prendre la boîte englobante en tant que nœud racine pour une division d'arbre ; S120, selon la boîte englobante, réaliser respectivement une division d'arbre sur la trame à coder et sur la trame de référence, et obtenir respectivement le nœud actuel dans la trame à coder et un bloc de prédiction correspondant dans la trame de référence ; et S130, pour chaque sous-nœud du nœud actuel, coder des informations d'occupation de chaque sous-nœud du nœud actuel selon des informations d'occupation d'un sous-nœud à une position correspondante dans le bloc de prédiction de façon à obtenir un flux de codes. Le procédé de décodage comprend les étapes suivantes : S210, obtenir la même boîte englobante d'une trame à décoder et d'une trame de référence, et prendre la boîte englobante en tant que nœud racine pour une division d'arbre ; S220, selon la boîte englobante, réaliser respectivement une division d'arbre sur la trame à décoder et sur la trame de référence, et selon une division d'arbre et/ou un flux de codes en nuage de points, obtenir le nœud actuel dans la trame à décoder et un bloc de prédiction correspondant dans la trame de référence ; et S230, réaliser un décodage selon le flux de codes en nuage de points pour obtenir des informations d'occupation de chaque sous-nœud du nœud à décoder de façon à obtenir un nuage de points.
PCT/CN2021/114282 2020-08-24 2021-08-24 Procédé de prédiction inter-trame géométrique en nuage de points à base de blocs et procédé de décodage WO2022042538A1 (fr)

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