Classifications

• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T13/00—Animation
  • G06T13/20—Three-dimensional [3D] animation
  • G06T13/40—Three-dimensional [3D] animation of characters, e.g. humans, animals or virtual beings
• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T9/00—Image coding
  • G06T9/001—Model-based coding, e.g. wire frame

Definitions

• the present invention generally relates to the field of virtual reality, and more specifically to the encoding of avatar animation parameters.
• avatar animation parameters offer two great standards offer a structure to animate a character in three dimensions, or avatar.
• This standard defines for avatars a hierarchical articular structure called skeleton, composed of segments. Each segment of the skeleton of an avatar is associated with a portion of the geometric envelope of the avatar. This association corresponds in fact to a segmentation of the avatar into removable elements, which allows to animate the avatar by applying transformations of the type translation, rotation or scaling on these different elements of the same skeleton, or articulated chain. The part of the geometric envelope of the avatar attached to a segment then follows the movement of this segment, either rigidly or elastically using a technique called "skinning". Today most of the computer graphics tools for creating avatars implement the typical skeleton defined by the HAnim standard.
• the second standard is the MPEG4 BBA standard, based on the English "Motion Picture Expert Group 4 Bone Based Animation", which takes the foundations of the HAnim standard, in particular the segmentation of avatars into removable elements.
• the MPEG4 BBA standard does not define a typical skeleton, it offers more flexibility because it allows to build, respecting the principle of the HAnim standard, any skeleton, for example an animal skeleton.
• the MPEG4 BBA standard itself includes a derived standard, the MPEG4 BAP standard, according to the English "Motion Picture Expert Group 4 Body Animation Parameter", which defines frozen animation parameters associated with the standard skeleton of the HAnim standard. .
• This derived standard is therefore again less flexible than the MPEG4 BBA standard, which is not limited to a single skeleton and allows different animation parameters to be defined for a given skeleton.
• the standard HAnim has put in place constraints on the topology of the typical skeleton, and defined a pose of rest of the avatars before animation. This principle is also taken up by the MPEG4 BBA standard.
• articulation levels are defined between the segments of the standard skeletons. These articulation levels have a very precise dimensioning and positioning in the space, which makes it possible to define for each skeleton a rest position. In this rest position, all the animation parameters as defined in HAnim, MPEG4 BAP or MPEG4 BBA have a reference value. Thus, for example, the translation value of a segment of the standard skeleton in its rest position is initialized to the null vector.
• the animation of an avatar is then translated by a succession of transformations made from this position of rest of the skeleton type of the avatar.
• the animation parameters of the different segments of the standard skeleton are expressed in local references to these segments.
• the skeletal scaling parameters, as well as the skeleton related rotation parameters are expressed independently of the global three dimensional Cartesian coordinate system in which the avatar geometry is defined.
• the skeletal translation parameters even expressed in the local landmarks to the skeleton segments, are not totally independent of the scene in which the avatar moves. Indeed the lengths of translation vectors are not expressed relative to the skeleton, but in a system of absolute units of measurement.
• the use of the articulation levels of the HAnim standard allows, for all avatars built according to the rules of these levels, to be animated with the same animation stream compatible with this standard.
• animation streams containing animation parameters are often encoded separately from the morphological data of the characters.
• the morphological data of the avatars and the animation parameters are dissociated so that they can be encoded and streamed separately, which raises many difficulties in terms of implementation.
• the animation parameters are not totally independent of the morphology of the character to be animated.
• translation movements are generally weaker when performed by a small character, than when they are performed by a larger character.
• the object of the present invention is to overcome the drawbacks of the prior art by providing methods and devices for coding and decoding, making it possible to express the animation data of an avatar independently of the dimensions of the scene in which it is located. find.
• the invention proposes a method for coding animation parameters of a character with which morphological values are associated, said animation parameters comprising a translation parameter associated with at least a portion of said character, characterized in that that to encode an intrinsic translation of said part of said character by a translation vector, said translation parameter contains a value which is a function of said vector and one of said morphological values.
• the intrinsic translations to the character to be animated are differentiated from those which are extrinsic to him, such as for example a translation due to a displacement. in an elevator.
• the translation parameters encoding intrinsic translations are expressed, by this method, relative to the skeleton of the character, based on anthropomorphic measurements calculated on the skeleton.
• This makes it possible to encode animation streams separately from the morphology data of the avatars while respecting, in the implementation of the animation, the morphology of the character to be animated.
• the coding according to the invention makes it possible to keep, for the same flow of animation, when changing the character to be animated, realistic translations with respect to the dimensions of the new character, since one takes into account the intrinsic character. translations that are related to this new character.
• the method according to the invention is not limited to encoding human characters, but can be used on any type of animated object for which translation parameters are associated with parts of this object. object.
• the word "character” is indeed used in this application in the sense of any articulated object subject to animation.
• a parameter among said animation parameters makes it possible to determine whether said translation parameter encodes an intrinsic translation to said character or an extrinsic translation to said character. This makes it possible to encode in the same animation flow, the movements relating to the three-dimensional scene in which the character evolves, or extrinsic movements, and movements relating to the character, or intrinsic movements.
• said morphological values are lengths of segments of the skeleton of said character
• said translation parameter is associated with a segment of the skeleton of said character
• said translation parameter contains a value that is proportional to said vector and inversely proportional to the length of said segment.
• the translation vector associated with a segment of the character is normalized by the length of this segment. This allows to fine-code the intrinsic translations to the character to animate, using a plurality of its morphological parameters.
• the invention also relates to a method for decoding animation parameters of a character with which morphological values are associated, said animation parameters comprising a translation parameter associated with at least a part of said character, characterized in that for decoding an intrinsic translation of said part of said character, the value of said translation parameter is multiplied by a factor of one of said morphological values.
• said morphological values are lengths of segments of the skeleton of said character, said translation parameter being associated with a segment of the skeleton of said character, and for decoding an intrinsic translation of a segment.
• said method comprises the steps of: - Calculation of the length of said segment, - Obtaining an estimate of the value of said translation in a system of absolute units of measurement, by multiplying the value of said translation parameter by a factor proportional to the length of said previously calculated segment.
• the invention also relates to a signal conveying animation parameters of a character to which are associated morphological values, said animation parameters comprising a translation parameter containing a translation information of said part of said character in the form of a value included in said translation parameter, characterized in that said value has been evaluated according to one of said morphological values when said translation is intrinsic to the character.
• said signal conveys a parameter making it possible to determine whether said translation is an intrinsic translation to the character or an extrinsic translation to the character.
• the invention also relates to a device for coding animation parameters of a character with which morphological values are associated, characterized in that it comprises means adapted to implement the coding method according to the invention.
• the invention further relates to a device for decoding animation parameters of a character with which are associated morphological values, characterized in that it comprises means adapted to implement the decoding method according to the invention.
• the decoding method, as well as the signal and the devices, have advantages similar to those of the coding method according to the invention.
• the invention also relates to a computer program comprising instructions for implementing the previously presented methods, when these are executed on a computer.
• FIG. 1 represents an avatar on which a standard skeleton of the HAnim standard is applied
• FIG. 2 is a diagram illustrating the uses of the coding method and the decoding method according to the invention on a stream of successive transformations
• FIG. 3 illustrates steps of the coding method according to the invention
• FIG. 4 illustrates steps of the decoding method according to the invention.
• the coding method and the decoding method according to the invention use the MPEG 4 BBA standard for encoding and decoding animation parameters determined from an avatar A represented in FIG. Figure 1. It should be noted that although these animation parameters are determined from the avatar A, they are then reused to animate other avatars having the same skeleton type as the avatar A, as described here. -after.
• This embodiment has the advantage of using without modifications of parameters an existing standard, but other embodiments, for example incorporating additional parameters to an existing standard encoding animation parameters, are conceivable.
• the use of the methods according to the invention is not limited to characters having the standard skeleton defined by the HAnim standard. Indeed, the methods according to the invention can be used on any type of avatar, with morphological criteria potentially different from the lengths of the typical skeleton segment, for example the height or the width of the avatar.
• FIG. 1 In the rest position defined by this standard. It is composed of segments and levels of articulation, which allow the animation of the geometry of the avatar.
• the movements of the left forearm of the avatar A are calculated from the transformations applied on the segment B k
• the movements of the right leg of the avatar A are calculated from the transformations applied on the segment Bi.
• N k and Ni respectively corresponding to the left elbow and the right knee of the avatar, are associated rotation parameters respectively corresponding to the left forearm and the right leg of the avatar.
• the coding and decoding of the animation of the avatar A, or other avatars having the same standard skeleton, are performed by the coding and decoding methods according to the invention according to the steps E1 to E4 shown in FIG. 2.
• Avatar A undergoes a succession of transformations TR 0 to TR n over time.
• a first step E1 of the coding method according to the invention the successive transformations TR j of the avatar are coded in an animation stream composed of successive "SBBone" structures for each segment B 1 of the skeleton of the avatar A.
• Each "SBBone” structure whose nomenclature is defined by the MPEG4 BBA standard and reproduced in Appendix 1, encodes the transformations of a segment identified by the "bonelD" number with respect to its rest position specified by the standard HAnim.
• the values of the animation parameters of the "SBBone" structure of Annex 1 correspond to the initial values of the transformation parameters in relation to the idle position of the avatar. These animation parameters are expressed in the local coordinate system at segment B 1 , the origin of this local coordinate system being defined by the "center” parameter. This origin corresponds in fact to a level of articulation of the skeleton type.
• the parameter "rotation” for example is (0 0 1 0) which indicates a rotation of zero angle with respect to the axis (0 0 1) in this local coordinate system.
• the animation stream processed by the coding method according to the invention contains only transformations intrinsic to the avatar, extrinsic transformations. to the character being encoded separately in a file in BIFS format, according to the English "Blnary Format for Scenes", which encodes the global parameters of the MPEG4 scene to be animated.
• an additional parameter is for example added to the "SBBone" structures of an animation stream, making it possible to determine whether the "translation" parameter of a "SBBone” structure encodes an intrinsic translation
• a single animation stream is thus used to code extrinsic and intrinsic transformations to the avatar A, the "translation" parameter then being modified in the manner described in FIG. step E2 only for translations intrinsic to the avatar.
• a second step E2 of the coding method according to the invention the values of the translation parameters of the animation stream obtained in the step E1 are modified in order to take into account the relative nature of the intrinsic translations of the avatar A.
• each "SBBone" structure of the animation stream is processed according to the steps a1 to a3 of FIG.
• Step ai is the reading of the "endpoint" parameter of the "SBBone" structure considered, encoding the animation parameters of a segment B 1 .
• This parameter "endpoint” contains the coordinates of the end of the segment B 1 which is not the origin of the local coordinate system to the segment B 1 .
• the next step a2 is the calculation of the length L 1 of the segment B 1 . This length is determined by calculating the norm of the vector contained in the "endpoint" parameter previously read.
• the following step a3 is the modification of the translation value T 1 contained in the parameter "translation”, which expresses a translation in a system of absolute measurement units, to replace it with a translation value TN 1 relative to the avatar A, and more precisely to the segment B 1 .
• the relative translation value TN 1 corresponds in fact to the normalization of the absolute translation value T 1 by the length of the segment B 1 , according to the following equation:
• K is a normalization factor.
• the normalization factor K simply makes it possible to express TN 1 on a scale of between 0 and 10 for example. It is the same for all segments B 1 and is fixed in advance by the users of the methods according to the invention. In this way no specific parameter is needed to encode the normalization factor K in the animation stream.
• E1 and E2 are performed in a coding device, for example in a software module of an animation engine.
• This coding device then binary code the animation parameters thus modified in a stream in BIFS format, in order to compress the animation data in a standard way.
• the animation designer adapts the "endpoint" fields of the "SBBone" structures of avatar A to the skeleton of other avatars having the same type skeleton. Indeed, the translation parameters being coded in a relative manner, only the fields "endpoint" coding the length of the segments of the new avatars are to be modified.
• the coding device then creates other BIFS streams corresponding to the animation parameters of these other avatars.
• the animation streams thus obtained in the form of BIFS files at the end of the step E2 are transmitted on a communication network to an animation engine remote from the previous one, separately from the data.
• the information signals corresponding to these animation streams thus convey animation parameters, for which the translation parameters take into account the morphological values of the characters to be animated.
• these information signals only transmit intrinsic animation parameters to the avatars and the morphological values taken into account are the lengths of the segments of the typical skeleton of these avatars.
• the information signals transmit both intrinsic animation parameters to the avatars, and extrinsic animation parameters to the avatars.
• the information signals also each convey a parameter indicating the intrinsic or extrinsic nature of the transmitted translation parameters.
• a third step E3 it is assumed that the remote animation engine receives morphological data from a new avatar different from the avatar A, but having the same type skeleton, as well as the associated BIFS animation stream. It should be noted that the steps E3 and E4 described below, however, can be transposed to the case where the animation engine receives morphological data from the avatar A and the animation stream corresponding to the avatar A. Indeed the BIFS animation stream received in both cases is the same, only the values of the fields "endpoint" are different, since they depend on the avatar to animate.
• the BIFS animation stream received in step E3 is decompressed by the remote client.
• the decoding method according to the invention is then used to perform an animation of the new avatar, from the data that have been decompressed from the previously transmitted BIFS file.
• the decoding method according to the invention is implemented in a specific module of the remote animation engine. For this purpose, each "SBBone" structure corresponding to a segment B ', of the typical skeleton of the new avatar in the file, is processed according to the decoding steps b1 to b3 of FIG. 4:
• Step b1 is the reading of the "endpoint" parameter of the "SBBone" structure considered, encoding the animation parameters of the segment B ',.
• the next step b2 is the calculation of the length L ', the segment B' ,. This length is determined by calculating the norm of the vector contained in the "endpoint" parameter previously read.
• the next step b3 is the modification of the relative translation value TN 1 contained in the "translation" parameter, to replace it with a corresponding translation value T 'expressed in a system of absolute measurement units.
• step E3 The data thus decoded at the end of step E3 comply with the MPEG4 BBA standard for encoding the animation parameters of the new avatar.
• Step E4 is the reading of the data decoded in step E3 by the remote animation engine, and the animation of the new avatar with the animation parameters contained in these data.
• These animation parameters respect the morphology of the new avatar, while having been designed from a different initial Avatar A.
• the translation parameters of the pelvis of the new avatar when it works are adapted to its dimensions.
• SBBonej #% NDT SFSBBoneNode, SF3DNode, SF2DNode eventIN MF3DNode addChildren eventIN MF3DNode removeChildren exposedField SFInt32 bonelD 0 exposedField MFInt32 skinCoordlndex [] exposedField MFFIoat skinCoordWeight [] exposedField SFVec3f endpoint 001 exposedField SFInt32 falloff 1 exposedField MFFIoat sectionPosition [] exposedField MFFIoat sectionlnner [] exposedField MFFIoat sectionOuter [] exposedField SFInt32 rotationOrderO exposedField MFNode children [] exposedField SFVec3f center 000 exposedField SFRotation rotation 0010 exposedField SFVec3f translation 000 exposedField SFVec3f scale 111 exposedField SFRotation scaleOrientation 0010 exposedField

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• 2006
  • 2006-06-27 FR FR0652668A patent/FR2902914A1/fr active Pending
• 2007
  • 2007-06-26 WO PCT/FR2007/051532 patent/WO2008001008A2/fr not_active Ceased
  • 2007-06-26 US US12/305,718 patent/US20090315898A1/en not_active Abandoned
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