EP1405268A1

EP1405268A1 - Method of wavelet coding a mesh object

Info

Publication number: EP1405268A1
Application number: EP02762522A
Authority: EP
Inventors: Patrick Gioia
Original assignee: France Telecom SA
Current assignee: Orange SA
Priority date: 2001-07-10
Filing date: 2002-07-04
Publication date: 2004-04-07
Also published as: FR2827409B1; CA2453283C; AU2002328371A1; KR20040018450A; CN1276390C; CN1526120A; FR2827409A1; KR100922511B1; CA2453283A1; BR0210974A; US20040208382A1; MXPA04000217A; US7555168B2; WO2003009234A1; JP2004535644A; WO2003009234A8; JP4064345B2

Abstract

The invention relates to a method of coding an object having at least two dimensions which is associated with a basic mesh comprising a set of basic surfaces and with coefficients in a base of wavelets corresponding to local modifications to said basic mesh. The inventive method delivers a global data flow that can be used to reconstruct the object. According to the invention, said wavelet coefficients are partitioned into at least two disjoint subsets each of which is encoded independently. Subsequently, positional data are inserted by the method into the global data flow which can be used to locate wavelet coefficients relative to a portion of the object in said global data flow, in such a way as to enable a selective reconstruction of said portion using the coefficients of at least one of said subsets.

Description

WAVES CODING METHOD OF A MESH OBJECT

The field of the invention is that of coding mesh objects with at least two dimensions. More specifically, the invention relates to the representation and coding of meshes, or of textures coded by meshes, associated with objects of a graphic scene implementing a method called "wavelet". The invention applies more particularly, but not exclusively to ^2nd generation wavelets, presented in particular in the document by Wim Sweldens, entitled "The Lifting Scheme: A Construction of Second Generation Wavelets" (in French, "The process of elevation: a construction of second generation wavelets "), SIAM Journal on Mafhematical Analysis, Volume 29, number 2, pp 511-546, 1998.

The invention finds applications in all fields where it is desirable to optimize the storage and / or transmission of images. The invention applies in particular, but not exclusively, to the storage and transmission of three-dimensional models, elevation grids, and of objects and textures coded by two-dimensional meshes.

It is recalled that the so-called "wavelet" coding methods make it possible to represent a mesh as a succession of details added to a basic mesh. The general theory of this technique is described in particular in the article by M. Lounsbery, T. DeRose and J. Warren, "Multiresolution Analysis for Surfaces of Arbitrary Topological Type" (ACM Transaction on Graphics, Vol. 16, No. 1, pp. 34-73, January 1997). The general principle of this technique consists in developing a homeomorphism between an object to be coded (such as a 3D mesh for example) and a simple mesh (more generally called "basic mesh") in a base of particular functions, called wavelets of second generation. According to this technique, a mesh is therefore represented by a series of coefficients which correspond to the coordinates in a wavelet base of a parametrization of said mesh by a simple polyhedron.

Thus, an object coded according to such a technique is presented as the union of the following two elements: the basic mesh, which generally has few facets, and represents a coarse version of the object to be coded; the wavelet coefficients, which are triplets of real numbers assigned simultaneously to a precise area of the basic mesh and to a given level of subdivision of this mesh. These wavelet coefficients represent the refinements to be made to the zone with which they are associated in order to converge towards the geometry of the initial object.

To be able to reconstruct a representation of the coded object on a display terminal, it is necessary to transmit to the latter, on the one hand the basic mesh, and on the other hand the associated wavelet coefficients. For this purpose, it is necessary to determine an effective coding method for the wavelet coefficients, with a view to their compression and their transmission, for example via communication networks, to the display terminal, possibly remote.

To date, it is the so-called "zero-trees" coding technique which achieves the best results in terms of compression of the wavelet coefficients to be transmitted. One such technique consists in describing an order of coding of the wavelet coefficients, which is predetermined and known in advance by the transmitter and receiver terminals (for example of a server and of a client display terminal). Such a technique therefore makes it possible, during the transmission of wavelet coefficients, to avoid transmitting information relating to the ranges of non-significant coefficients for the coding of the object considered. Such zero-tree coding is generally coupled to a "bit-plane" coding, which makes it possible, when transmitting the coefficients, to transmit the most significant bits of each coefficient first.

For a more detailed description of the techniques by "zero-trees", one can refer to the articles by Jérôme M. Shapiro, "Embedded Image Coding

Using Zerotrees of Wavelet Coefficients "(IEEE Trans. Sig. Proc. 41 (12),

Dec.1993) and A. Said, W. A. Pearlman, "A New, Fast, and Efficient Image

Coded Based on Set Partitioning in Hierarchical Trees "(IEEE Trans. Cire.

System. For Video Tech., 6 (3), June 1996). These techniques, originally developed for the coding of two-dimensional images, have recently been applied to second generation wavelet coefficients, as described in the publications "Progressive

Geometry Compression "(SIGGRAPH 2000 proceedings) by A. Khodakovsky, P.

Schroder and W. Sweldens, and "Hierarchical Coding of 3D Models with Subdivision Surfaces" (IEEE ICIP 2000 Proceedings) by F. Moran and N. Garcia.

In these last two references, the coding techniques are based on the arbitrary adoption of a hierarchy between the wavelet coefficients to be transmitted, making it possible to determine their order of transmission to a remote display or storage terminal. This order, known to the receiving terminal, allows the latter to reconstruct the entire transmitted object.

A disadvantage of these techniques of the prior art is that the server in charge of transmitting the wavelet coefficients to a display terminal cannot make a selection of the coefficients which it wishes to send, and therefore systematically transmits the whole coefficients at the client terminal.

However, it is frequent that the customer need only receive the refinements associated with a portion of the basic mesh. For example, during a virtual museum visit, a client may wish, first, to observe an overview of a sculpture, then to visualize only a detail of his face. Only the wavelet coefficients corresponding to the refinements of the basic mesh on this portion of the face are therefore necessary.

Using the techniques of the prior art, it is impossible for the server to make a selection of the useless coefficients and to send only the coding portion corresponding to the area that the client wishes to view.

A disadvantage of these techniques of the prior art is therefore that the client receives all the wavelet coefficients, including those corresponding to the coding of portions of the object which he does not wish to visualize, and of which he therefore no need. The communication network used for the transmission of the wavelet coefficients is therefore unnecessarily overloaded, and the transmission rate of the useful coefficients decreases accordingly.

In addition, in the case where the display terminal has low processing capacities, the reconstruction of a representation of the object from all of the wavelet coefficients is long, which is a source of inconvenience for the customer.

Another disadvantage of these techniques of the prior art is therefore that, if the client wishes to carry out an adaptive decoding, so as to view only the portions of the object which interest him, he must perform a sorting himself transmitted wavelet coefficients. The client must therefore decode the entire data stream transmitted by the server, or coming from a data carrier, then judge the relevance of the wavelet coefficients thus decoded, according to the portion of the mesh to which they are associates.

Consequently, a disadvantage of these techniques of the prior art is that, in order to carry out an adaptive decoding, the client must have a display terminal having sufficient processing capacities to carry out the decoding operations of the global stream, selection of the relevant coefficients, and reconstruction of a representation of the object from the coefficients thus selected. In other words, a disadvantage of these techniques of the prior art is that it is impossible, for a client having a display terminal having reduced processing capacities, to carry out an adaptive decoding.

The invention particularly aims to overcome these drawbacks of the prior art.

More specifically, an objective of the invention is to implement a technique of coding an object by wavelets, allowing a display terminal to carry out an adaptive decoding of the object.

Another objective of the invention is to provide a technique for coding an object by wavelets, allowing a server to select certain wavelet coefficients, and to transmit the selected coefficients, according to an area of the basic mesh. with which they are associated. In particular, an objective of the invention is to allow a server to transmit only certain wavelet coefficients, according to a request from a client. The invention also aims to implement a technique of coding meshes representative of objects or 3D scenes, allowing an adaptive reconstruction of a mesh within a display terminal.

Another objective of the invention is to provide a coding technique for an object using wavelets which is suitable for display terminals having low processing capacities.

The invention also aims, of course, to provide a reconstruction and transmission technique over a communication network of an object coded according to this coding method. In particular, during such a transmission, an objective of the invention is not to unnecessarily overload the communication networks.

Another objective of the invention is to implement a technique for coding an object by wavelets which is suitable for transmission via a communication network with limited bit rate.

These objectives, as well as others which will appear subsequently, are achieved using a method of coding an object with at least two dimensions associated with a basic mesh made up of a set of basic facets, and with coefficients in a wavelet base corresponding to local modifications of said basic mesh, said method delivering a global data stream making it possible to reconstruct said object. According to the invention, said wavelet coefficients are partitioned into at least two disjoint subsets each undergoing independent coding, and said method inserts, into said global data stream, location data making it possible to identify wavelet coefficients relating to a portion of said object in said global data flow, so as to allow a selective reconstruction of said portion using the coefficients of at least one of said subsets.

Thus, the invention is based on a completely new and inventive approach to the coding of an object by wavelets and the shaping of the data thus coded within a global data stream. Indeed, the invention is notably based on the generation of a global data flow, within which one can easily identify the wavelet coefficients, as a function of the portion of the mesh object with which they are associated. This is in particular allowed, within the framework of the invention, by the insertion of location data within the data stream, so as to allow an adaptive visualization of the coded object by a client terminal.

Advantageously, each of said disjoint subsets is a basic facet.

Thus, it is easy to identify, within the global data stream, the wavelet coefficients associated with each of the basic facets, thanks to the presence in the location data stream. It is thus possible to selectively reconstruct a portion of a meshed object, from the wavelet coefficients associated with the facet (s) of the portion considered.

Preferably, said coding implements the following steps: detection of at least one non-significant part; - specific treatment of each of said non-significant parts. Indeed, a coding of the subsets of wavelet coefficients (that is to say a transformation of these coefficients into a binary sequence) taking into account the non-significant parts makes it possible to achieve a better compression rate of these coefficients, with a view to their transmission. Preferably, said coding implements a "zero-tree" type technique.

Indeed, the "zero-tree" technique is to date the technique for achieving the best compression results. It is of course also possible to envisage using any other technique for coding the wavelet coefficients within the overall data stream, adapted to the implementation of the invention.

According to a first variant of the invention, said global data stream comprises a header, comprising at least some of said location data, and a zone of wavelet coefficients, comprising a sub-area identified by said location data for each of said disjoint subsets.

Thus, if the list of wavelet coefficients has been partitioned into N subsets, each corresponding to a portion of the meshed object, the wavelet coefficients zone of the global data stream includes N identifiable sub-zones, within the flow, using location data. It will be noted here that the location data making it possible to identify a sub-zone of the flow can be included in the header and / or in any other part of the data flow.

Advantageously, said location data contained in said header identifies a sub-area, by defining a distance between the position of a reference element and the start of said sub-area in said flow.

Such a reference element can for example be the start or the end of the header, or any other element whose position in the flow can easily be known. The distance can for example be expressed in number of bits.

Advantageously, said header further comprises at least some of the information belonging to the group comprising: the number of basic facets; the type of wavelet; information relating to said object; information relating to the coding of said location data. This information can be used by a display terminal to reconstruct, from the flow, a representation of a portion, or of the whole, of the meshed object.

According to a second variant of the invention, said global data stream comprises at least one area of wavelet coefficients, comprising a sub-area identified by said location data for each of said disjoint subsets, said location data comprising at least minus one marker at the beginning and / or at the end of each of the sub-areas.

Thus, the location data is distributed throughout the overall data flow, and not grouped in a header, as before. Preferably, said sub-areas are organized in said stream in order of increasing basic facet.

Thus, when each of the basic facets undergoes independent coding (for example of the "zero-tree" type), provision is made to order the sub-zones within the stream as a function of the number of the basic facet to which they are associated, for example in ascending order.

The invention also relates to a method for transmitting a data stream, between, on the one hand, at least one server and / or at least one data carrier, and, on the other hand, at least one display terminal , said data flow making it possible to reconstruct an object associated on the one hand with a basic mesh made up of a set of basic facets, and on the other hand with coefficients in a wavelet base corresponding to local modifications of said basic mesh.

According to the invention, such a transmission method comprises: a step of receiving a request defining a portion of said object to be displayed; a step of analyzing location data present in said stream, as a function of said request, making it possible to identify wavelet coefficients relating to said portion in said data stream; a step of extracting said identified wavelet coefficients to form a reduced data stream; a step of transmitting said reduced data stream.

Thus, a server, on receipt of a request from a client relating to a portion of the object, can select, within the global data flow, the subset or coefficients associated with the portion of the object considered. It can then construct a reduced flow, from the coefficients of the sub-assembly (s) concerned, and transmit it to the customer's display terminal.

The invention also relates to a signal representative of an object associated with a basic mesh consisting of a set of basic facets, and with coefficients in a wavelet base corresponding to local modifications of said basic mesh, comprising at at least one area of wavelet coefficients and at least one location area, comprising location data making it possible to locate wavelet coefficients relating to a portion of said object in said signal.

According to a first embodiment of the invention, said wavelet coefficients being partitioned into at least two disjoint subsets each undergoing independent coding, such a signal comprises a header, comprising at least some of said location data, and a wavelet coefficient area, comprising a sub-area identified by said location data for each of said subsets. According to a second embodiment of the invention, said wavelet coefficients being partitioned into at least two disjoint subsets each undergoing independent coding, such a signal comprises at least one area of wavelet coefficients, comprising a sub- area identified by said location data for each of said subsets, said location data location comprising at least one marker at the start and / or at the end of each of the sub-areas.

The invention also relates to a data medium intended to store at least one object coded according to the method described above. The invention also relates to a system for transmitting a data stream, between, on the one hand, at least one server and / or at least one data carrier, and, on the other hand, at least one display terminal , said data flow making it possible to reconstruct an object associated on the one hand with a basic mesh made up of a set of basic facets, and on the other hand with coefficients in a wavelet base corresponding to local modifications of said basic mesh.

According to the invention, such a system comprises: means for receiving a request defining a portion of said object to be displayed; means for analyzing location data present in said stream, as a function of said request, making it possible to identify wavelet coefficients relating to said portion in said data stream; means for extracting said identified wavelet coefficients to form a reduced data flow; - means for transmitting said reduced data flow.

The invention also relates to a terminal for viewing an object associated with a basic mesh consisting of a set of basic facets, and with coefficients in a wavelet base corresponding to local modifications of said basic mesh, comprising means for receiving a global data stream making it possible to reconstruct said object, further comprising means for formulating a request defining a portion of said object to be viewed intended for a server and / or a data medium , and means for reconstructing said portion from a reduced data stream, comprising wavelet coefficients relating to said portion, received from said server and / or from said data medium. Such a terminal therefore differs greatly from the display terminals of the prior art. Indeed, it can send a request to a server, identifying the portion (s) of the mesh object that the client wishes to view, and reconstruct from the only wavelet coefficients associated with this or these portion (s) , that it will have previously decoded, a corresponding representation of the object (s) ρortion (s). Such a terminal therefore differs from the terminals of the prior art in that it no longer decodes the whole of a global data stream in order to be able to select the wavelet coefficients associated with a portion of the object, and reconstruct a representation of this portion. The invention also relates to a server comprising means for storing at least one object coded according to the coding method described above and transmission means implementing the transmission method described above.

The invention finally relates to a device for coding an object associated with a basic mesh consisting of a set of basic facets, and with coefficients in a wavelet base corresponding to local modifications of said basic mesh, said device generating a global data stream making it possible to reconstruct said object, partitioning said wavelet coefficients into at least two disjoint subsets, and applying independent coding to each of said subsets, and comprising means of insertion, into said global data flow, of localization data making it possible to locate wavelet coefficients relating to a portion of said object in said global data flow, so as to allow selective reconstruction of said portion using coefficients of at least one of said subsets. Other characteristics and advantages of the invention will appear more clearly on reading the following description of a preferred embodiment, given by way of simple illustrative and nonlimiting example, and of the appended drawings, among which: FIG. 1 presents a synoptic of the different steps implemented during the coding of a mesh object with at least two dimensions according to the invention; FIG. 2 illustrates an example of the structure of a data stream generated during the coding presented in FIG. 1, and comprising location data, according to a first variant of the invention; - Figure 3 details the structure of the data flow of Figure 2, when the location data is indicative of a distance within the flow; FIG. 4 describes an example of the structure of a data stream generated during the coding of a meshed object with at least two dimensions, and comprising location data distributed within the stream, according to a second variant of the invention; FIG. 5 presents a block diagram of the different steps implemented by a server for transmitting the data flow of FIGS. 2 to 4, on receipt of a request from a client terminal.

The general principle of the invention is based on the insertion of location data within a data stream generated during the wavelet coding of a mesh object with at least two dimensions, so as to allow selection and transmission. selective coefficients according to the area of the object with which they are associated.

Referring to FIG. 1, a particular embodiment of the coding method of the invention is presented.

We consider here the case of an object with at least two dimensions coded according to a method called "wavelets". It is recalled that, according to such a method, a basic mesh is associated with the object, and a plurality of wavelet coefficients, corresponding to the refinements to be made to the basic mesh in order to reconstruct a representation of the object. Each node of the basic mesh is thus associated with a wavelet coefficient.

It is assumed that the stages of construction of the basic mesh and of determination of the associated wavelet coefficients have already been implemented by a coding device, which therefore has a list of wavelet coefficients associated with the object to code. We recall that a wavelet coefficient is a triplet of reals (x, y, z), accompanied by information I of spatial and frequency location, making it possible to know to which wavelet a coefficient is associated. This information I can for example be a quadruplet (F0, a, b, c), where F0 represents a facet of the basic mesh, and (a, b, c) represent barycentric coordinates on this face.

During a step referenced 20, the coding device performs a partition of the set of wavelet coefficients associated with the mesh object to be coded, into subsets M ₁₅ M ₂ , ..., M _N. These subsets are preferably disjoint. They can be constructed based, for example, on visual criteria. They each include the wavelet coefficients used to reconstruct a representation of a portion of the mesh object to be coded.

For example, if the mesh object to be coded is a three-dimensional character, one can envisage partitioning the list of wavelet coefficients into five subsets corresponding respectively to the face, to each of the members, and to the bust of the character.

During a step referenced 21, the coding device defines, on each subset M _i5 an arbitrary hierarchy by determining parentage links between the different vertices of the subset, if necessary. Of course, there is not necessarily a filiation between two vertices of the same subset, which can be sister vertices.

The coding device then performs (22) an independent coding of the wavelet coefficients of each of the subsets M _i5 for i varying from 1 to N. Such coding is for example a "zero-tree" type coding, and allows to compress the representation of the wavelet coefficients, and therefore of the associated mesh nodes, of each of the subsets M _; .

During a step referenced 23, the coding device generates a global data stream, comprising, on the one hand, the result of the coding (for example of the "zero-tree" type) of each of the subsets M _i5 and secondly, location data making it possible to determine the position of each of the subsets M; in the stream. The structure of such a flow makes it possible to obtain great flexibility in sending one or more JV1 subsets to a display terminal, according to a request from a client.

Referring to FIG. 2, an embodiment of a data stream 1, generated according to the method of FIG. 1, is presented.

For the sake of simplification, we limit ourselves, throughout the rest of the document, to the case where each of the subsets M; includes the wavelet coefficients associated with a basic facet of the object. It will of course be easy for a person skilled in the art to generalize the description below in the event that a subset M _; includes the wavelet coefficients associated with a plurality of basic facets, or with a plurality of nodes of the basic mesh.

It is assumed here, and throughout the rest of the document, that the facets of the basic mesh are ordered in ascending order. For example, one arbitrarily chooses a starting facet, and one chooses an order of course of the set of basic facets (for example in the trigonometric, or anti-trigonometric direction), so that the starting facet is considered as the first facet, and so on until the last facet of the basic mesh traversed according to the order of course, which becomes the M ^lth basic facet.

According to the invention, a data stream 1 is generated by a coding device during the wavelet coding of an object, for example three-dimensional. In a particular embodiment of the invention, the data stream 1 comprises a header 10, and a zone of wavelet coefficients 11.

The wavelet coefficients area 11 is preferably divided into a plurality of sub-areas (not shown in FIG. 1), each grouping the wavelet coefficients associated with a facet of the basic mesh of the object. As recalled previously, a wavelet coefficient is a triplet of reals (x, y, z), accompanied by information I of spatial and frequency location, making it possible to know which wavelet a coefficient is associated with. This information I can for example be a quadruplet (F0, a, b, c), where F0 represents a facet of the basic mesh, and (a, b, c) represent barycentric coordinates on this face.

In a preferred embodiment of the invention, each sub-zone comprises the "zero-tree" coding of the wavelet coefficients associated with a basic facet. Thus, we perform a partition of the wavelet coefficients according to the facet FO with which they are associated, and we perform as many "zero-tree" codings as there are partitions. (It will be recalled that, in another embodiment of the invention described in relation to FIG. 1, the coefficients are partitioned into a plurality of subsets M _{;, the} same subset being able to group together several basic facets FO, and an independent “zero-tree” coding is carried out for each of the subsets Mi. Each sub-zone then comprises the “zero-tree” coding of the wavelet coefficients associated with a subset M;). It is of course also possible to envisage using any other coding technique allowing satisfactory compression and transmission of the wavelet coefficients. We preferentially use a coding technique allowing a specific coding of the insignificant parts of the object considered.

The header 10 includes the location data, making it possible to locate each of the sub-areas within the wavelet coefficient area 11. It also includes information relating to the type of coding implemented, such as information on the type of wavelet functions used, the number of wavelet coefficients, the characteristics of the basic mesh (number of basic facets, ...), or even the maximum level of subdivision of the basic mesh. In the particular embodiment presented in relation to the figure

3, the area of the wavelet coefficients 11 is divided into a plurality of sub-areas referenced 111 to 113. Thus the sub-area referenced 111 is the "sub-area 1" associated with the first facet of the basic mesh, the sub-area referenced 112 is associated with the second basic facet, and sub-area referenced 113 is associated with the ^{m th} base facet. It will of course be noted that, for the sake of simplification of the figure, not all the sub-zones have been represented.

The header 10 comprises a preamble 101, and a plurality of location data referenced 102 to 104. The preamble 101 comprises for example data relating to the type of mesh and to the type of wavelets used, mentioned above.

The area referenced 102, entitled "offset 1", provides information on the position of the wavelet coefficients associated with the first basic facet in bit stream 1, that is to say that it provides information, for example, on the distance separating the end of the preamble 101 and the beginning of the "sub-area 1" referenced 111.

In a particular embodiment of the invention, such a distance is expressed in number of bits. In another embodiment of the invention, the location data area referenced 102 can of course also provide information on the distance separating the start of the "sub-area 1" referenced 111 from any other reference element of the data stream 1 , so as to allow the localization of the wavelet coefficients of the "sub-area 1" 111 in the bit stream 1.

In FIG. 3, the "offset 2" area 103 (respectively the "offset M" area 104) provides information on the number of bits separating the start of the "sub area 2" 112 (respectively of the "sub area M" 113) and the end of the preamble 101.

Thus, when a server, in response to a request from a client terminal, wishes to transmit to the latter the wavelet coefficients associated with the M ^th basic facet, it consults the location data "M shift" 104 of the 'header 10. The "M shift" area 104 indicates to the server the number of bits separating the end of the preamble 101 from the start of the "M sub-area" 113, and the server can therefore go directly to the start of the " sub-area M "113, so as to extract and then transmit these only coefficients to the client terminal.

The data stream 1 of FIG. 4 comprises a header 10 and a wavelet coefficient area 11, comprising on the one hand sub-areas of wavelet coefficients referenced 111 to 113 and location data areas referenced 120 to 123. In such an alternative embodiment, the location data referenced 120 to 123 are therefore distributed in the data stream 1, and not grouped in the header 10 as previously.

The location data 120 to 123 are for example markers indicating the start and / or the end of a wavelet coefficient sub-area. Thus, the area "mark 1" referenced 120 indicates the beginning of the "sub-area 1" 111, comprising the wavelet coefficients associated with the first facet of the basic mesh. The zone "mark 2" referenced 121 marks the beginning of the "sub-zone 2" referenced 112, and the "mark M" referenced 123 marks the beginning of the "sub-zone M" referenced 113.

In a particular embodiment of the invention, the information contained in the fields "mark 1" 120, "mark 2" 121 and so on up to "mark M" 123 are identical. In other words, a plurality of identical markers is inserted into the zone of wavelet coefficients 11 of the data stream 1, so as to separate the different sub-zones each associated with a facet of the basic mesh. Thus, when a server wishes to send the wavelet coefficients associated with the "M sub-area" 113 to a display terminal, it traverses all of the flow 1, and counts the markers that it encounters, so as to determine the M ^-th marker 123, and thus determine where begins the "subfield M" 113, comprising code "zero-tree" wavelet coefficients associated with the ^{m th} base facet. Thus, the client terminal receives only the wavelet coefficients of the "sub-area M" 113, and does not need to decode the entire stream 1 to access the wavelet coefficients it needs. In another embodiment of the invention, the markers referenced

120 to 123 are specific to a given sub-area of the wavelet coefficient area 11. The marker "mark 1" 120 specifically indicates the start of "sub-area 1" 111, the marker "mark 2" 121 specifically indicates the start of "Subarea 2" 112, and so on. (We can of course also consider, for example, that the markers referenced 120 to 123 indicate the end of the associated sub-areas 111 to 113.)

Thus, a server wishing to transmit the coefficients of the "M sub-area" 113 in response to a request from a client traverses the data stream 1, until it finds the marker "mark M" 123, and deduces the position therefrom. from the start of "M sub-area" 113.

It is also possible to envisage any other embodiment of the invention, not illustrated in FIGS. 3 and 4, but which makes it possible to construct a data stream 1, in which location data are inserted allowing a server to determine the location a sub-area of wavelet coefficients associated with a basic facet, or more generally with a subset M _; grouping a plurality of nodes or basic facets, with a view to its extraction and its selective transmission in response to a request from a client.

For example, one can envisage an embodiment combining the variants of the invention presented in relation to FIGS. 3 and 4, in which the sub-zones referenced 111 to 113 would be grouped into sets of three or four sub-zones. Location data, inserted in the header 10, would provide information on the distance between a reference element (for example the end of the preamble 101) and the start of a set of sub-areas. Markers would be inserted within such a set, so as to indicate the beginning and / or the end of each of the sub-areas of the set.

Thus, thanks to the location data located in the header 10, a server could go to position itself directly at the start of a set of sub-areas, then browse this set, and determine, using the markers, the position of or sub-area (s) of the set that it must transmit in response to a request from a client.

We now present, in relation to FIG. 5, the different steps implemented by a server, or by a terminal connected to a data medium, and responsible for transmitting the wavelet coefficients associated with an area of the basic mesh, in response to a client request. For the sake of simplification, we will only describe in the following the case of the processing implemented by a server in response to a request from a display terminal. Those skilled in the art will easily deduce therefrom the processing operations to be carried out when the object data come from a data carrier connected, directly or indirectly, to the display terminal.

It is assumed that a customer wishes to observe a detail of a scene that he is viewing on his terminal. The terminal therefore sends a request to the server specifying the portion of the scene for which it wishes to obtain the wavelet coefficients determining the refinements to be made to the basic mesh in order to obtain a satisfactory reconstruction of the portion.

During a step referenced 40, the server receives the request from the client terminal, and determines the facets of the basic mesh concerned by the request. During a step referenced 41, the server browses the data stream generated at the output of a scene coding device, and analyzes the location data present in this stream. For example, it consults the location data contained in the header of the stream.

During a step referenced 42, it determines the position of the sub-areas of wavelet coefficients associated with the portion of the scene considered, as a function of the location data which it has previously analyzed. After identification (42) of the wavelet coefficients relating to the portion of object to be displayed, the server extracts (43) these coefficients from the global data flow, so as to form a reduced flow intended for the client terminal.

During a step referenced 44, the server transmits this reduced stream to the client's viewing terminal, so that the latter can reconstruct the portion of the scene that the client wishes to view, without having to decode the entire stream of global data.

Claims

1. Method for coding an object with at least two dimensions associated with a basic mesh made up of a set of basic facets, and with coefficients in a wavelet base corresponding to local modifications of said basic mesh, said method delivering a global data stream making it possible to reconstruct said object, characterized in that said wavelet coefficients are partitioned into at least two disjoint subsets each undergoing independent coding, and in that said method inserts into said stream global data, location data making it possible to locate wavelet coefficients relating to a portion of said object in said global data stream, so as to allow selective reconstruction of said portion using coefficients of at least one said subsets.

2. Method according to claim 1, characterized in that each of said subsets is a basic facet.

3. Method according to any one of claims 1 and 2, characterized in that said coding implements the following steps: detection of at least a non-significant part; - specific treatment of each of said non-significant parts.

4. Method according to any one of claims 1 to 3, characterized in that said coding implements a "zero-tree" type technique.

5. Method according to any one of claims 1 to 4, characterized in that said global data stream comprises a header, comprising at least some of said location data, and a zone of wavelet coefficients, comprising a sub area identified by said location data for each of said subsets.

6. Method according to claim 5, characterized in that said location data contained in said header identifies a sub-area, by defining a distance between the position of a reference element and the start of said sub-area in said flow.

7. Method according to any one of claims 5 and 6, characterized in that said header further comprises at least some of the information belonging to the group comprising: the number of basic facets; the type of wavelet; information relating to said object; information relating to the coding of said location data.

8. Method according to any one of claims 1 to 4, characterized in that said global data stream comprises at least one area of wavelet coefficients, comprising a sub-area identified by said location data for each of said sub- together, said location data comprising at least one marker at the start and / or at the end of each of the sub-areas.

9. Method according to any one of claims 5 to 8, characterized in that said sub-zones are organized in said flow in order of increasing basic facet.

10. Method for transmitting a data stream, between, on the one hand, at least one server and / or at least one data carrier, and, on the other hand, at least one display terminal, said stream of data making it possible to reconstruct an object associated on the one hand with a basic mesh made up of a set of basic facets, and on the other hand with coefficients in a wavelet base corresponding to local modifications of said basic mesh, characterized in that it comprises: a step of receiving a request defining a portion of said object to be displayed; a step of analyzing location data present in said stream, as a function of said request, making it possible to identify wavelet coefficients relating to said portion in said data stream; a step of extracting said identified wavelet coefficients to form a reduced data stream; a step of transmitting said reduced data stream.

11. Signal representative of an object with at least two dimensions associated with a basic mesh consisting of a set of basic facets, and with coefficients in a wavelet base corresponding to local modifications of said basic mesh, characterized in that it comprises at least one area of wavelet coefficients and at least one location area, comprising location data making it possible to locate wavelet coefficients relating to a portion of said object in said signal.

12. Signal according to claim 11, characterized in that, said wavelet coefficients being partitioned into at least two disjoint subsets each undergoing independent coding, it comprises a header, comprising at least some of said location data, and a wavelet coefficient area, comprising a sub-area identified by said location data for each of said subsets.

13. Signal according to claim 11, characterized in that, said wavelet coefficients being partitioned into at least two disjoint subsets each undergoing independent coding, it comprises at least one area of wavelet coefficients, comprising a sub- zone identified by said location data for each of said subsets, said location data comprising at least one marker at the start and / or at the end of each of the sub-areas.

14. Global data flow recorded on a support usable in a computer and allowing to reconstruct an object coded in at least two dimensions, associated with a basic mesh made up of a set of facets of base, and to coefficients in a wavelet base corresponding to local modifications of said basic mesh, characterized in that said wavelet coefficients are partitioned into at least two disjoint subsets each undergoing independent coding, and in that that, in said recorded global data stream, location data are inserted making it possible to locate wavelet coefficients relating to a portion of said object in said global data stream, so as to allow selective reconstruction of said portion at using coefficients of at least one of said subsets.

15. Global data flow according to claim 14, characterized in that it makes it possible to reconstruct an object with at least two dimensions coded according to the method of any one of claims 1 to 9.

16. System for transmitting a data stream, between, on the one hand, at least one server and / or at least one data carrier, and, on the other hand, at least one display terminal, said stream of data making it possible to reconstruct an object with at least two dimensions associated on the one hand with a basic mesh made up of a set of basic facets, and on the other hand with coefficients in a wavelet base corresponding to local modifications of said basic mesh, characterized in that it comprises: means for receiving a request defining a portion of said object to be displayed; means for analyzing location data present in said stream, as a function of said request, making it possible to identify wavelet coefficients relating to said portion in said data stream; means for extracting said identified wavelet coefficients to form a reduced data flow; means for transmitting said reduced data stream.

17. Terminal for viewing an object with at least two dimensions associated with a basic mesh consisting of a set of basic facets, and with coefficients in a wavelet base corresponding to local modifications of said basic mesh, comprising means for receiving a global data stream making it possible to reconstruct said object, characterized in that it further comprises means for formulating a request defining a portion of said object to be viewed intended for a server and / or a data medium, and means for reconstructing said portion from a reduced data flow, comprising relative wavelet coefficients to said portion, received from said server and / or from said data medium.

18. Server comprising means for storing at least one object with at least two dimensions coded according to the method of any one of claims 1 to 9 and transmission means implementing the method of claim 10.

19. Device for coding an object with at least two dimensions associated with a basic mesh made up of a set of basic facets, and with coefficients in a wavelet base corresponding to local modifications of said basic mesh, said device generating a global data stream making it possible to reconstruct said object, characterized in that it partitions said wavelet coefficients into at least two disjoint subsets, and in that it applies independent coding to each of said subsets sets, and in that it comprises means for inserting, into said global data stream, location data making it possible to locate wavelet coefficients relating to a portion of said object in said global data stream, so as to allow a selective reconstruction of said portion using the coefficients of at least one of said subsets.