# Motion Capture Technology of Digital Animation Art Based on Machine Learning

Authors: Yi Liu; Guoyu Wang; Ning Wei
Journal: International Transactions on Electrical Energy Systems
 (2022)

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## Abstract

With the progress of society and the increasing development of science and technology, digital animation technology is also constantly innovating. Motion capture technology is widely used in film, television, media, and other fields and has the characteristics of the times. The use of motion capture technology in animation production can greatly improve the accuracy and professionalism of animation performances. It plays an important role in the development of animated character activities, especially in the creation of martial arts and professional dance performances. It uses motion capture technology to create animated character performances and composite effects. In this paper, four feature selection algorithms such as document frequency (DF), information gain (IG), mutual information (MI), and the chi-square test (CHI) were used, and they were used to capture action features and feature selection application steps based on the support vector machine (SVM) algorithm and the naive Bayes (NB) algorithm. The results of the experimental study showed that the TF-CHI algorithm in the improved algorithm had an accuracy rate of 89%, and the feature selection accuracy it made was better than the traditional algorithm. Therefore, the effectiveness of the animation motion capture technology based on the machine learning motion improvement algorithm has been confirmed.


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## Body

## 1. Introduction

The art of animation has a profound impact on the television media industry. The advancement of science and technology and the improvement of living standards have made people’s pursuit of culture and art higher and higher. Animation art is no longer limited to a single group of children, and young people are paying more and more attention and love. Because the form of traditional animation tends to be single and the animation’s action coherence is poor, the texture of the picture is not enough, which affects the viewing experience and is not conducive to the development and dissemination of animation art. As the audience for animation art has expanded, so have its requirements. With the improvement of technical level, motion capture technology emerges over time. Dynamic capture technology is the product of the development of social science and technology, and it has the characteristics of the times. This technology plays a key role in the animation character performance activities involved in the production of animation projects, and also improves the quality of animation pictures and the overall production efficiency of animation. It has played a key role in the establishment of an information-based digital platform and can truly realize resource sharing.The dynamic capture technology can analyze and save the change information of different subjects in the animation so that the animation can be played back and spread at a specific time. This technology mainly uses the position change, space change, angle change, speed change, and facial emotion change of the performer’s body to capture. After careful observation of their emotions and movement changes, a three-dimensional dynamic display is carried out on the system equipment and digital platform, which can enhance the visualization and smoothness of the animation, and enhance the authenticity and naturalness of the performers. Then, the use of dynamic capture technology can intelligently identify and record different characters in the animation and accumulate rich materials for the production of animation. Motion capture technology mainly studies regression optimization problems involving machine learning and computer vision. The key issues of motion capture research based on monocular video are face tracking, key point location, and 3D pose. Focusing on these problems, the key point localization and multipose regression problems are further studied in view of the problems existing in the current method in complex scenes.


## 2. Related Work

With the continuous development of science and technology, digital technology has also developed rapidly. At present, more and more attention is paid to the digital research of animation art. According to Esposito’s analyses of cultural and arts education, cultural and arts education programs guide people to engage in emotional growth and social interaction, including participatory activities such as painting, games, singing, photography, dancing, and cartoon animation [1]. Wilkinson et al. emphasized the need to consider sociocultural values and attitudes when designing digital media [2]. Dalope and Woods pointed out that through the media arts discipline, both students and the community are able to engage in practical exchange with the rich culture around them [3]. Ceranoglu noted that as adolescents’ access to digital media (DM) continues to surge, caregivers and clinicians are concerned about adolescent overuse [4]. Romer and Moreno’s research found that digital media provided more opportunities for marketing and social communication of risky products and behaviors [5]. These studies demonstrate the importance of the digital development of animation art today. But at the same time, the application of the digital representation of animation art to the real world would have excessive risks due to the lack of standard and technical support. It is necessary to use technological progress to promote the dissemination of animation art.There have been a lot of research results on the application of motion capture technology for digital animation art. Wang pointed out that motion capture technology is a digital technology that is mainly used to set the key parts of tracking moving objects and obtain their motion data [6]. Jiang et al. research showed that in the context of future networks, the motivation, problem formulation, and methodology of powerful machine learning algorithms need to be refined to take advantage of hitherto untapped animation applications and services [7]. The motion capture algorithm proposed by Fang et al. confirmed its superior results by demonstrating that it compensated for the shortcomings of incomplete gesture information in animation [8]. Baydin et al. researched and investigated automatic differentiation (AD) in machine learning, which is critical to technical research in digital animation art [9]. The Lamperti et al. study found that by combining machine learning and intelligent iterative sampling, the problem of parameter space exploration and calibration for ABM was explicitly addressed. A fast surrogate metamodel was “learned” using a limited number of ABM evaluations [10]. The aforementioned research contains a large number of machine learning applications. Some are for program development and some are used for building alternative models, but they are basically for research with a large number of data samples, which can continuously improve the operation of the feature selection algorithm. In this paper, the feature selection algorithm was applied to the construction of the motion capture technology of digital animation art, which makes the machine learning algorithm be able to achieve a full range of applications.


## 3. Construction and Application of Digital Animation Art System

### 3.1. Composition and Tools of Digital Animation Art

#### 3.1.1. Construction of Animation Art

“Animation” exists as a technical term in traditional technical understanding, which refers to the laws of motion of animation. That is to give motion and life to static painting art in the process of animation creation [11]. Animation is recognized as a comprehensive art form, which is “a film style with stop-motion shooting as the basic setting method and a certain art form as the content carrier.” It makes inanimate things move as if they were given life. Therefore, the animation uses the technique of “stop-motion shooting” to move things that are “original lifeless,” thereby producing a film style with the art form as the content carrier, as shown in Figure 1.Figure 1
Composition of animation art.Animation culture and its living environment together constitute an art ecosystem. The concept of art ecology comes from art and ecology. Due to its complexity and variability, the artistic ecology of animation culture is characterized by complexity and variability. Because of the spatial intersection and penetration between animation art and other art forms, the ecology of animation art also has a certain topology. The topological structure of animation art ecology is mainly reflected in the diversity of environmental factors. The ecological environment of animation art includes multiple factors such as audience factors, national policy factors, social and cultural environmental factors, natural environmental factors, economic environmental factors, and resource and environmental factors [12, 13]. There is a certain intersection and mutual influence between these factors, which makes the ecology of animation art more complicated, as shown in Figure 2.Figure 2
The ecological components of animation art.Therefore, the use of motion capture technology in animation production can greatly improve the level of animation production and can also improve the efficiency of animation production and reduce costs. Moreover, the animation production process is more intuitive and the effect is more vivid. With the further maturity of technology, performance animation technology will be more and more widely used. As an indispensable and critical part of the performance animation system, motion capture technology would inevitably show a more important position.


#### 3.1.2. Evolution of Object-Oriented Digital Tools

The virtual nature of digital animation technology determines that the technology itself must complete the mimicry of tools in order to realize the connection with the creator. Computer programs usually implement functional integration in the form of a graphical interface. The advancement of tools is the most direct reflection of technological progress. In the late 1970s, computer graphics software began to appear on home computers [14]. The 1980s saw many notable new business software products, and the 1990s and beyond saw many developments, mergers, and deals in the software industry. In 1995, SGI acquired Alias Research and Wavefront, which merged to form Alias Wavefront. The company focused on developing digital content creation tools, and PowerAnimator continues to be used in visual effects and films (such as Toy Story, Casper, and Batman Forever) and video games. After Maya software added new technologies such as motion capture, facial animation, motion blur, and time warping, the computer-aided design of industrial design products was standardized.In the 2010s, the core technology of animation became more and more mature, and the segmentation of the software application market was basically finalized. Major software development companies were committed to the iterative update of the main product version, and constantly improved the function and optimize the algorithm. A large number of plug-in programs developed by small and medium-sized manufacturers and individuals were supplemented as auxiliary creation tools, which fundamentally supported animation creation. After the continuous testing of the application market and capital merger and reorganization, the current mainstream animation software can basically cover most of the key links of the creative process, or focus on a certain type of technical solutions, as shown in Table1.Table 1
List of mainstream animation software.
Serial numberApplicationRelease date latest versionR&D manufacturers1Alibre design2018/07/16 v2018Alibre, LLC2AutoCAD2018/09/10 v2019.1.2Autodesk3Blender2017/11/9 v2.79 bBlender foundation4Carrara2013/08/26 v8.5.1.19DAZ 3D5CityEngine2018/09/18 v2018.1Procedural6Clara.ioRedesigned in 2015/03/31Exocortex


### 3.2. Establishment of Digital Animation Creation Process

The American Disney Company has a set of rigorous process mechanisms for the creation and production of animation, which divides animation production into three stages: the creative design stage, the production stage, and the synthesis stage. When compared with the creative process of traditional animation, the working mode of digital animation adopts digital tools, and its workflow links are relatively independent and less restrained from each other. After the model is created, the links such as coloring and animation can be advanced in parallel, and the animation industry process gradually matures [15]. Since the technical foundation and purpose of mainstream animation creation have not fundamentally changed, the basic framework of the process is stable to a certain extent and has not undergone major changes. However, the specific creative process would be flexibly adjusted and changed locally according to the project category and content to ensure the steady improvement of efficiency and quality. The subsequent creation process is more detailed and complete in specific links, as shown in Figure 3.Figure 3
Digital animation process.


### 3.3. Motion Capture Technology of Digital Animation

#### 3.3.1. System Structure

Motion capture records the movements of performers in filmmaking and video game development, and it uses these movement data to drive digital character models in computers to perform in 2D or 3D computer animation [16, 17]. Generally speaking, there are four kinds of commonly used dynamic capture systems, namely, inertial, optical, electromagnetic, and mechanical systems.When compared with traditional animation production methods, motion capture has the following advantages: its low latency means it obtains results in near real-time, which can effectively reduce the cost of action production; the workload does not vary with the complexity or length of the performance content, and is only limited by the actor’s ability to perform; it is easy to reconstruct complex movements and real physical interactions in a physically accurate way, such as secondary movements, weight, and force exchanges; it is compared with traditional animation action production methods, the amount of animation data that can be generated per unit time is large, which helps to meet cost-effectiveness and production deadline requirements [18, 19]. Motion capture technology also has shortcomings and deficiencies: it depends on specific site, hardware, and software program conditions [20], and requires high up-front investment costs; the way of recording frame by frame is not easy to modify and edit, and it is easier to recapture in case of error than to modify the action file; it is impossible to capture movements that do not follow the laws of physics, and the difference in proportions between the performer’s structure and the digital model’s structure can easily lead to movement errors. It is impossible to capture the exaggerated action style in the traditional animation motion law, and action effects such as elasticity, squeezing, and stretching must be added in the subsequent links. For motion capture, the capture of continuous motion is the key and then the tracking of key optical points is its core. The tracking of 2D points is complicated by factors such as occlusion, absence, and proximity of marker points. At present, the 4-frame tracking principle is mostly used; that is, for the current frame point trajectory, it is necessary to comprehensively judge according to the first frame and the last two frames, as shown in Figure 4.Figure 4
Example of motion capture pair point cloud and optical mark points.The key to 3D Marker Reconstruction is that the data output from each camera is the identified 2D optical point information, as shown in Figure4. If the position and rotation information of each camera in the 3D space are known, according to the operation of 3D geometry, the position information of the corresponding 2D point in the 3D space can be obtained. Of course, there are still many optimized algorithms in this; that is, the part of correcting the data.


#### 3.3.2. Model Application

Digital modeling is the use of professional software to mathematically represent the surface of an object in virtual space [21, 22]. The model is transformed into an image through the rendering process, which can be used for computer simulation of physical phenomena and can be printed and physically created using 3D equipment. The dynamic capture technology model can be created automatically or manually, or the digital information collection of the solid model can be realized by using digital scanning technology [23, 24]. Common model creation methods include surface modeling, 3D scanning, digital sculpting, and polygon modeling.The basic principle of the moving images is based on the phenomenon of persistence of vision. Based on this principle, people can see smooth dynamic images, which at least need to have enough consecutive images. Typically, movies have a frame rate of 24 frames per second; TV has a frame rate of 30 frames per second (NTSC format). Traditional hand-drawn 2D animation typically uses 8 or 12 frames per second to save on the number of drawings required and control costs, and digital animation uses higher frame rates for smoother results. Production can be divided into keyframe animation and algorithm animation, as shown in Table2.Table 2
Performance and comparison of keyframe animation and algorithmic animation.
Animation ttypesKeyframe animationAlgorithmic animationShape differenceParameter differenceKinematicsDynamicsAnimation qualityDepends on the number of keyframesDepends on the number of keyframesDepends on the gauge used lawVery realisticSystem resourcesDepends on the number of points and difference law typeDepends on the number of parametersDepends on the law and saves system resourcesConsume system resourcesPerformance ratio27%54%75%92%By summarizing the above two productions, it can be seen that keyframe animation production has certain advantages, but also obvious disadvantages and limitations. At present, algorithm animation is more commonly used because it can save the consumption of system resources and the effect is also very good. If we want to add more flexible and rich interactions, the algorithmic animation solutions can be used.


### 3.4. Application of Motion Capture Technology

#### 3.4.1. Color Construction

Color vision consistency is one of the basic abilities of human vision. People consistently perceive the target object as a color-consistent whole, even when temporal and spatial lighting conditions change. Perceived color at a point in the scene depends on a number of reasons, including the physical properties of the target surface at that location [25]. In the color vision, an important physical feature of a surface is the spectral reflectance of the surface, which does not change with illumination, structure, and shape. It can be known from the model that the color of visual perception is the product of illuminance and surface specular reflection. The RGB model is also known as the additive color mixing model. It is a method in which RGB three-color light is superimposed on each other to realize color mixing, so it is suitable for the display of illuminants such as monitors. The color mixing rule is as follows: mixing with equal amounts of red, green, and blue primary colors, as shown in Figure 5.Figure 5
Schematic diagram of RGB color model segmentation.The starting point for establishing the color model below is how to decompose the color perceived by vision into two parts: luminance and chrominance.Figure5 shows a schematic diagram of the color model in the RGB color space. At some point (x,y), Mi=MR,MG,MB represents the expected RGB value in the background or reference image at that point. The straight line OMi from the coordinate origin 0 to Mi represents the desired chromaticity line. Ni=NR,NG,NB represents the RGB color value at that point in the foreground image. The distortion produced by Ni relative to Mi is then measured and decomposed into two parts.Luminance distortion: among them, luma distortionβ is a scalar:(1)βi=minNi−βiMi,where βi represents the relative value of the brightness at the point (x,y) in the foreground to the brightness at the corresponding point in the background. If βi 1, the brightness of the point in the foreground is the same as that in the background; if βi is less than 1, the brightness of the point in the foreground is less than the brightness of the background; if βi is greater than 1, the brightness of the point in the foreground is greater than the brightness of the background.Chroma distortion: (EF) is defined as the vertical distance from a point Ni to the chromaticity line:(2)EFi=Ni−βiMi.


#### 3.4.2. Space Conversion

The acquisition and display of images currently used in image processing are mainly based on the RGB color space. Therefore, when the HSI color space is used in the processing, they can be obtained through the corresponding transformation. The mutual transformation relationship between HSI color space and RGB color space is given [26]. The HSI color space starts from the human visual system and uses hue, color saturation, and brightness to describe colors, and it can clearly show the changes in hue, brightness and color saturation. Since human vision is far more sensitive to brightness than to color shades, in order to facilitate color processing and identification, the human visual system often uses HSI color space, which is more in line with human visual characteristics than RGB color space. A large number of algorithms in image processing and computer vision are conveniently available in the HSI color space, which can be processed separately and independently of each other.Color conversion of RGB to HSI:An RGB color image is given, and each RGB pixel and HSI component can be converted by the following formulas:Hue components:(3)S=θ,T≤R,2π−θ,T>R.Among them,(4)θ=arccosM−R+M−T2M−R2+M−TR−M1/2.Saturation component:(5)Z=1−3M+R+TminM,R,T.Intensity component:(6)L=M+R+T3.This shows that the HSI color space and the RGB color space are just different representations of the same physical quantity, and there is a conversion relationship between them. Therefore, the workload of image analysis and processing can be greatly simplified in the HSI color space.


#### 3.4.3. Boundary-Based Segmentation

Image edges are especially important for image recognition and motion capture for animation. Edges are used in animation techniques to outline the target object. Edges contain intrinsic information such as direction, step characteristics, and shape, which are important attributes for extracting dynamic features of objects in motion production [27]. The use of the derivative operator can take the derivative value as the “boundary strength” of the corresponding point, and then extract the boundary point set by setting the threshold. Boundary-based segmentation is the basis for model retrieval, classification, and reconstruction. In order to solve the problems of poor robustness, oversegmentation and undersegmentation in the boundary segmentation algorithm, a boundary derivative operator algorithm based on boundary features is proposed. It is proved by mainstream evaluation methods and experiments that most models can achieve good segmentation results. Therefore, it can be known that the algorithm for extracting the edge is to detect the mathematical operator that conforms to the edge characteristics of the edge pixel, as shown in Figure 6.Figure 6
Common edge types.The first-order partial derivative operator is∂p/∂a,∂p/∂b, and the grayscale change rate is ∂p/∂β=∂p/∂acosβ+∂p/∂bsinβ. Using difference instead of derivative (discrete quantity instead of continuous quantity) based on boundary segmentation, the corresponding expression is as follows:(7)Δpm,n=pm,n−pm−1,n.Among them,(8)Δapm,n=pm,n−pm,n−1.The maximum value of the directional derivative of a function at a point istan−1∂p/∂b/∂p/∂a, and the maximum value of the directional derivative is ∂p/∂a2+∂p/∂b2, so the vector in this direction is called the gradient of the function p.(9)Δβpm,n=Δbpm,ncosβ−Δbpm,nsinβ.Thus, the gradient operatorwpa,b=∂p/∂a2+∂p/∂b2. can detect the boundary in any direction with the same sensitivity, and tan∂p/∂b/∂p/∂a gives the direction information of the boundary.In digital animation processing, the ladder operator is defined as(10)WPm,n=Δapm,n2+(Δbpm,n2.In practical applications, it generally means(11)Δapm,n+Δbpm,n.For the convenience of calculation, the following gradient simulation calculation expression is used:(12)maxΔapm,n,Δbpm,n,maxpm,n−py,q.


#### 3.4.4. Maintenance of Dynamic Background and Capture Technology

The maintenance and updating of dynamic backgrounds are particularly important for capture technology. It must adapt to the background changing conditions including the moving in and out of the scene and the change of the shape of the object itself, as well as the sudden change of light, or the change of shadow introduced by the occlusion of the angle. The following uses the median estimation method to construct a dynamic background: the median filter is a simple order statistic. Median filtering is a nonlinear signal processing technique based on ranking statistics theory that can effectively suppress noise. The basic principle of median filtering is to replace the value of a point in a digital image or digital sequence with the median value of each point value in a neighborhood of the point, so that the surrounding pixel values are close to the true value, thereby eliminating isolated noise points.It is supposed that (X1,X2,…,Xn) are simple samples taken from a population with a continuous distribution T. (X1,X2,…,Xn) are rearranged as X1≤X2≤…≤Xn, that is, Xi is the i-th smallest among X1,X2,…,Xn, i=1,2,…,n. Then, X1≤X2≤…≤Xn is called the order statistic, generated by the samples X1,X2,…,Xn.Due to the following theorem, it is assumed that the sample population has a continuous distribution functionF (x), and the corresponding density function is F (x). X1≤X2≤…≤Xn is the order statistic generated by simple samples:(13)Fqx=∑w=qnnwFxw1−Fxn−w.Then, forq ≤ n, the distribution function and density function of Xq are:(14)fqx=n!q−1!n−q!Fq−1x1−Fxn−qfx.The median is defined as(15)medXi=Xe+1n=2e+1,Xe+1+Xe/2n=2e.Sincen is usually odd in practical applications, only the case where n is odd is discussed:(16)Fmedx=∑w=n+1/2nnwFxw1−Fxn−w.From the theorem, the distribution function and density function of med (Xi) can be obtained as(17)fqx=n!q−1!n−q!Fn−1/2x1−Fxn−1/2fx.Formula (17) has high precision for all odd n. When capturing the chi-square information value of an action, if the action only occurs frequently in a certain category, even if the frequency of occurrence is very high, the result value obtained would not be too large according to the feature selection. This may result in the action not being preferentially selected, but often the action has good category classification information and can better represent dynamic content. Therefore, in view of the occurrence of the above situation, in order to select better feature actions, the algorithm needs to be improved. Aiming at the frequency relationship of the action appearing in the animation in the feature selection algorithm formula, an action factor is proposed, and its magnitude is equal to the ratio of the number of frames that the action appears in the frequency band to the frequency of the action in the overall data set. Its calculation is shown in the following equation:(18)θpx,qy=mpx,qympx.The motion in the animation affects the animation speed. The shape of the action is presented in the animation by the change of position and the change of shape, and these changes depend on the reasonable distribution of animation time, such as fast and slow, acceleration and deceleration, delay and stop motion, and other animation speeds.For example, by (18), it can be calculated that the action factor of “action 1” is θp1=4, and the action factor of “action 2” is θp2=7/8≈0.87. Therefore, according to the calculation result of the action factor, special attention should be paid to the action factor of “action 1.” Then, it is combined with the chi-square statistic; we get(19)“A1”CHIθ∗p1=12,“A2”CHIθ∗p2=98/9≈10.9.Therefore, the result after introducing the action factor should preferentially select “action 1” instead of “action 2” as the feature, which is consistent with the selection result in the real case.


## 3.1. Composition and Tools of Digital Animation Art

### 3.1.1. Construction of Animation Art

“Animation” exists as a technical term in traditional technical understanding, which refers to the laws of motion of animation. That is to give motion and life to static painting art in the process of animation creation [11]. Animation is recognized as a comprehensive art form, which is “a film style with stop-motion shooting as the basic setting method and a certain art form as the content carrier.” It makes inanimate things move as if they were given life. Therefore, the animation uses the technique of “stop-motion shooting” to move things that are “original lifeless,” thereby producing a film style with the art form as the content carrier, as shown in Figure 1.Figure 1
Composition of animation art.Animation culture and its living environment together constitute an art ecosystem. The concept of art ecology comes from art and ecology. Due to its complexity and variability, the artistic ecology of animation culture is characterized by complexity and variability. Because of the spatial intersection and penetration between animation art and other art forms, the ecology of animation art also has a certain topology. The topological structure of animation art ecology is mainly reflected in the diversity of environmental factors. The ecological environment of animation art includes multiple factors such as audience factors, national policy factors, social and cultural environmental factors, natural environmental factors, economic environmental factors, and resource and environmental factors [12, 13]. There is a certain intersection and mutual influence between these factors, which makes the ecology of animation art more complicated, as shown in Figure 2.Figure 2
The ecological components of animation art.Therefore, the use of motion capture technology in animation production can greatly improve the level of animation production and can also improve the efficiency of animation production and reduce costs. Moreover, the animation production process is more intuitive and the effect is more vivid. With the further maturity of technology, performance animation technology will be more and more widely used. As an indispensable and critical part of the performance animation system, motion capture technology would inevitably show a more important position.


### 3.1.2. Evolution of Object-Oriented Digital Tools

The virtual nature of digital animation technology determines that the technology itself must complete the mimicry of tools in order to realize the connection with the creator. Computer programs usually implement functional integration in the form of a graphical interface. The advancement of tools is the most direct reflection of technological progress. In the late 1970s, computer graphics software began to appear on home computers [14]. The 1980s saw many notable new business software products, and the 1990s and beyond saw many developments, mergers, and deals in the software industry. In 1995, SGI acquired Alias Research and Wavefront, which merged to form Alias Wavefront. The company focused on developing digital content creation tools, and PowerAnimator continues to be used in visual effects and films (such as Toy Story, Casper, and Batman Forever) and video games. After Maya software added new technologies such as motion capture, facial animation, motion blur, and time warping, the computer-aided design of industrial design products was standardized.In the 2010s, the core technology of animation became more and more mature, and the segmentation of the software application market was basically finalized. Major software development companies were committed to the iterative update of the main product version, and constantly improved the function and optimize the algorithm. A large number of plug-in programs developed by small and medium-sized manufacturers and individuals were supplemented as auxiliary creation tools, which fundamentally supported animation creation. After the continuous testing of the application market and capital merger and reorganization, the current mainstream animation software can basically cover most of the key links of the creative process, or focus on a certain type of technical solutions, as shown in Table1.Table 1
List of mainstream animation software.
Serial numberApplicationRelease date latest versionR&D manufacturers1Alibre design2018/07/16 v2018Alibre, LLC2AutoCAD2018/09/10 v2019.1.2Autodesk3Blender2017/11/9 v2.79 bBlender foundation4Carrara2013/08/26 v8.5.1.19DAZ 3D5CityEngine2018/09/18 v2018.1Procedural6Clara.ioRedesigned in 2015/03/31Exocortex


## 3.1.1. Construction of Animation Art

“Animation” exists as a technical term in traditional technical understanding, which refers to the laws of motion of animation. That is to give motion and life to static painting art in the process of animation creation [11]. Animation is recognized as a comprehensive art form, which is “a film style with stop-motion shooting as the basic setting method and a certain art form as the content carrier.” It makes inanimate things move as if they were given life. Therefore, the animation uses the technique of “stop-motion shooting” to move things that are “original lifeless,” thereby producing a film style with the art form as the content carrier, as shown in Figure 1.Figure 1
Composition of animation art.Animation culture and its living environment together constitute an art ecosystem. The concept of art ecology comes from art and ecology. Due to its complexity and variability, the artistic ecology of animation culture is characterized by complexity and variability. Because of the spatial intersection and penetration between animation art and other art forms, the ecology of animation art also has a certain topology. The topological structure of animation art ecology is mainly reflected in the diversity of environmental factors. The ecological environment of animation art includes multiple factors such as audience factors, national policy factors, social and cultural environmental factors, natural environmental factors, economic environmental factors, and resource and environmental factors [12, 13]. There is a certain intersection and mutual influence between these factors, which makes the ecology of animation art more complicated, as shown in Figure 2.Figure 2
The ecological components of animation art.Therefore, the use of motion capture technology in animation production can greatly improve the level of animation production and can also improve the efficiency of animation production and reduce costs. Moreover, the animation production process is more intuitive and the effect is more vivid. With the further maturity of technology, performance animation technology will be more and more widely used. As an indispensable and critical part of the performance animation system, motion capture technology would inevitably show a more important position.


## 3.1.2. Evolution of Object-Oriented Digital Tools

The virtual nature of digital animation technology determines that the technology itself must complete the mimicry of tools in order to realize the connection with the creator. Computer programs usually implement functional integration in the form of a graphical interface. The advancement of tools is the most direct reflection of technological progress. In the late 1970s, computer graphics software began to appear on home computers [14]. The 1980s saw many notable new business software products, and the 1990s and beyond saw many developments, mergers, and deals in the software industry. In 1995, SGI acquired Alias Research and Wavefront, which merged to form Alias Wavefront. The company focused on developing digital content creation tools, and PowerAnimator continues to be used in visual effects and films (such as Toy Story, Casper, and Batman Forever) and video games. After Maya software added new technologies such as motion capture, facial animation, motion blur, and time warping, the computer-aided design of industrial design products was standardized.In the 2010s, the core technology of animation became more and more mature, and the segmentation of the software application market was basically finalized. Major software development companies were committed to the iterative update of the main product version, and constantly improved the function and optimize the algorithm. A large number of plug-in programs developed by small and medium-sized manufacturers and individuals were supplemented as auxiliary creation tools, which fundamentally supported animation creation. After the continuous testing of the application market and capital merger and reorganization, the current mainstream animation software can basically cover most of the key links of the creative process, or focus on a certain type of technical solutions, as shown in Table1.Table 1
List of mainstream animation software.
Serial numberApplicationRelease date latest versionR&D manufacturers1Alibre design2018/07/16 v2018Alibre, LLC2AutoCAD2018/09/10 v2019.1.2Autodesk3Blender2017/11/9 v2.79 bBlender foundation4Carrara2013/08/26 v8.5.1.19DAZ 3D5CityEngine2018/09/18 v2018.1Procedural6Clara.ioRedesigned in 2015/03/31Exocortex


## 3.2. Establishment of Digital Animation Creation Process

The American Disney Company has a set of rigorous process mechanisms for the creation and production of animation, which divides animation production into three stages: the creative design stage, the production stage, and the synthesis stage. When compared with the creative process of traditional animation, the working mode of digital animation adopts digital tools, and its workflow links are relatively independent and less restrained from each other. After the model is created, the links such as coloring and animation can be advanced in parallel, and the animation industry process gradually matures [15]. Since the technical foundation and purpose of mainstream animation creation have not fundamentally changed, the basic framework of the process is stable to a certain extent and has not undergone major changes. However, the specific creative process would be flexibly adjusted and changed locally according to the project category and content to ensure the steady improvement of efficiency and quality. The subsequent creation process is more detailed and complete in specific links, as shown in Figure 3.Figure 3
Digital animation process.


## 3.3. Motion Capture Technology of Digital Animation

### 3.3.1. System Structure

Motion capture records the movements of performers in filmmaking and video game development, and it uses these movement data to drive digital character models in computers to perform in 2D or 3D computer animation [16, 17]. Generally speaking, there are four kinds of commonly used dynamic capture systems, namely, inertial, optical, electromagnetic, and mechanical systems.When compared with traditional animation production methods, motion capture has the following advantages: its low latency means it obtains results in near real-time, which can effectively reduce the cost of action production; the workload does not vary with the complexity or length of the performance content, and is only limited by the actor’s ability to perform; it is easy to reconstruct complex movements and real physical interactions in a physically accurate way, such as secondary movements, weight, and force exchanges; it is compared with traditional animation action production methods, the amount of animation data that can be generated per unit time is large, which helps to meet cost-effectiveness and production deadline requirements [18, 19]. Motion capture technology also has shortcomings and deficiencies: it depends on specific site, hardware, and software program conditions [20], and requires high up-front investment costs; the way of recording frame by frame is not easy to modify and edit, and it is easier to recapture in case of error than to modify the action file; it is impossible to capture movements that do not follow the laws of physics, and the difference in proportions between the performer’s structure and the digital model’s structure can easily lead to movement errors. It is impossible to capture the exaggerated action style in the traditional animation motion law, and action effects such as elasticity, squeezing, and stretching must be added in the subsequent links. For motion capture, the capture of continuous motion is the key and then the tracking of key optical points is its core. The tracking of 2D points is complicated by factors such as occlusion, absence, and proximity of marker points. At present, the 4-frame tracking principle is mostly used; that is, for the current frame point trajectory, it is necessary to comprehensively judge according to the first frame and the last two frames, as shown in Figure 4.Figure 4
Example of motion capture pair point cloud and optical mark points.The key to 3D Marker Reconstruction is that the data output from each camera is the identified 2D optical point information, as shown in Figure4. If the position and rotation information of each camera in the 3D space are known, according to the operation of 3D geometry, the position information of the corresponding 2D point in the 3D space can be obtained. Of course, there are still many optimized algorithms in this; that is, the part of correcting the data.


### 3.3.2. Model Application

Digital modeling is the use of professional software to mathematically represent the surface of an object in virtual space [21, 22]. The model is transformed into an image through the rendering process, which can be used for computer simulation of physical phenomena and can be printed and physically created using 3D equipment. The dynamic capture technology model can be created automatically or manually, or the digital information collection of the solid model can be realized by using digital scanning technology [23, 24]. Common model creation methods include surface modeling, 3D scanning, digital sculpting, and polygon modeling.The basic principle of the moving images is based on the phenomenon of persistence of vision. Based on this principle, people can see smooth dynamic images, which at least need to have enough consecutive images. Typically, movies have a frame rate of 24 frames per second; TV has a frame rate of 30 frames per second (NTSC format). Traditional hand-drawn 2D animation typically uses 8 or 12 frames per second to save on the number of drawings required and control costs, and digital animation uses higher frame rates for smoother results. Production can be divided into keyframe animation and algorithm animation, as shown in Table2.Table 2
Performance and comparison of keyframe animation and algorithmic animation.
Animation ttypesKeyframe animationAlgorithmic animationShape differenceParameter differenceKinematicsDynamicsAnimation qualityDepends on the number of keyframesDepends on the number of keyframesDepends on the gauge used lawVery realisticSystem resourcesDepends on the number of points and difference law typeDepends on the number of parametersDepends on the law and saves system resourcesConsume system resourcesPerformance ratio27%54%75%92%By summarizing the above two productions, it can be seen that keyframe animation production has certain advantages, but also obvious disadvantages and limitations. At present, algorithm animation is more commonly used because it can save the consumption of system resources and the effect is also very good. If we want to add more flexible and rich interactions, the algorithmic animation solutions can be used.


## 3.3.1. System Structure

Motion capture records the movements of performers in filmmaking and video game development, and it uses these movement data to drive digital character models in computers to perform in 2D or 3D computer animation [16, 17]. Generally speaking, there are four kinds of commonly used dynamic capture systems, namely, inertial, optical, electromagnetic, and mechanical systems.When compared with traditional animation production methods, motion capture has the following advantages: its low latency means it obtains results in near real-time, which can effectively reduce the cost of action production; the workload does not vary with the complexity or length of the performance content, and is only limited by the actor’s ability to perform; it is easy to reconstruct complex movements and real physical interactions in a physically accurate way, such as secondary movements, weight, and force exchanges; it is compared with traditional animation action production methods, the amount of animation data that can be generated per unit time is large, which helps to meet cost-effectiveness and production deadline requirements [18, 19]. Motion capture technology also has shortcomings and deficiencies: it depends on specific site, hardware, and software program conditions [20], and requires high up-front investment costs; the way of recording frame by frame is not easy to modify and edit, and it is easier to recapture in case of error than to modify the action file; it is impossible to capture movements that do not follow the laws of physics, and the difference in proportions between the performer’s structure and the digital model’s structure can easily lead to movement errors. It is impossible to capture the exaggerated action style in the traditional animation motion law, and action effects such as elasticity, squeezing, and stretching must be added in the subsequent links. For motion capture, the capture of continuous motion is the key and then the tracking of key optical points is its core. The tracking of 2D points is complicated by factors such as occlusion, absence, and proximity of marker points. At present, the 4-frame tracking principle is mostly used; that is, for the current frame point trajectory, it is necessary to comprehensively judge according to the first frame and the last two frames, as shown in Figure 4.Figure 4
Example of motion capture pair point cloud and optical mark points.The key to 3D Marker Reconstruction is that the data output from each camera is the identified 2D optical point information, as shown in Figure4. If the position and rotation information of each camera in the 3D space are known, according to the operation of 3D geometry, the position information of the corresponding 2D point in the 3D space can be obtained. Of course, there are still many optimized algorithms in this; that is, the part of correcting the data.


## 3.3.2. Model Application

Digital modeling is the use of professional software to mathematically represent the surface of an object in virtual space [21, 22]. The model is transformed into an image through the rendering process, which can be used for computer simulation of physical phenomena and can be printed and physically created using 3D equipment. The dynamic capture technology model can be created automatically or manually, or the digital information collection of the solid model can be realized by using digital scanning technology [23, 24]. Common model creation methods include surface modeling, 3D scanning, digital sculpting, and polygon modeling.The basic principle of the moving images is based on the phenomenon of persistence of vision. Based on this principle, people can see smooth dynamic images, which at least need to have enough consecutive images. Typically, movies have a frame rate of 24 frames per second; TV has a frame rate of 30 frames per second (NTSC format). Traditional hand-drawn 2D animation typically uses 8 or 12 frames per second to save on the number of drawings required and control costs, and digital animation uses higher frame rates for smoother results. Production can be divided into keyframe animation and algorithm animation, as shown in Table2.Table 2
Performance and comparison of keyframe animation and algorithmic animation.
Animation ttypesKeyframe animationAlgorithmic animationShape differenceParameter differenceKinematicsDynamicsAnimation qualityDepends on the number of keyframesDepends on the number of keyframesDepends on the gauge used lawVery realisticSystem resourcesDepends on the number of points and difference law typeDepends on the number of parametersDepends on the law and saves system resourcesConsume system resourcesPerformance ratio27%54%75%92%By summarizing the above two productions, it can be seen that keyframe animation production has certain advantages, but also obvious disadvantages and limitations. At present, algorithm animation is more commonly used because it can save the consumption of system resources and the effect is also very good. If we want to add more flexible and rich interactions, the algorithmic animation solutions can be used.


## 3.4. Application of Motion Capture Technology

### 3.4.1. Color Construction

Color vision consistency is one of the basic abilities of human vision. People consistently perceive the target object as a color-consistent whole, even when temporal and spatial lighting conditions change. Perceived color at a point in the scene depends on a number of reasons, including the physical properties of the target surface at that location [25]. In the color vision, an important physical feature of a surface is the spectral reflectance of the surface, which does not change with illumination, structure, and shape. It can be known from the model that the color of visual perception is the product of illuminance and surface specular reflection. The RGB model is also known as the additive color mixing model. It is a method in which RGB three-color light is superimposed on each other to realize color mixing, so it is suitable for the display of illuminants such as monitors. The color mixing rule is as follows: mixing with equal amounts of red, green, and blue primary colors, as shown in Figure 5.Figure 5
Schematic diagram of RGB color model segmentation.The starting point for establishing the color model below is how to decompose the color perceived by vision into two parts: luminance and chrominance.Figure5 shows a schematic diagram of the color model in the RGB color space. At some point (x,y), Mi=MR,MG,MB represents the expected RGB value in the background or reference image at that point. The straight line OMi from the coordinate origin 0 to Mi represents the desired chromaticity line. Ni=NR,NG,NB represents the RGB color value at that point in the foreground image. The distortion produced by Ni relative to Mi is then measured and decomposed into two parts.Luminance distortion: among them, luma distortionβ is a scalar:(1)βi=minNi−βiMi,where βi represents the relative value of the brightness at the point (x,y) in the foreground to the brightness at the corresponding point in the background. If βi 1, the brightness of the point in the foreground is the same as that in the background; if βi is less than 1, the brightness of the point in the foreground is less than the brightness of the background; if βi is greater than 1, the brightness of the point in the foreground is greater than the brightness of the background.Chroma distortion: (EF) is defined as the vertical distance from a point Ni to the chromaticity line:(2)EFi=Ni−βiMi.


### 3.4.2. Space Conversion

The acquisition and display of images currently used in image processing are mainly based on the RGB color space. Therefore, when the HSI color space is used in the processing, they can be obtained through the corresponding transformation. The mutual transformation relationship between HSI color space and RGB color space is given [26]. The HSI color space starts from the human visual system and uses hue, color saturation, and brightness to describe colors, and it can clearly show the changes in hue, brightness and color saturation. Since human vision is far more sensitive to brightness than to color shades, in order to facilitate color processing and identification, the human visual system often uses HSI color space, which is more in line with human visual characteristics than RGB color space. A large number of algorithms in image processing and computer vision are conveniently available in the HSI color space, which can be processed separately and independently of each other.Color conversion of RGB to HSI:An RGB color image is given, and each RGB pixel and HSI component can be converted by the following formulas:Hue components:(3)S=θ,T≤R,2π−θ,T>R.Among them,(4)θ=arccosM−R+M−T2M−R2+M−TR−M1/2.Saturation component:(5)Z=1−3M+R+TminM,R,T.Intensity component:(6)L=M+R+T3.This shows that the HSI color space and the RGB color space are just different representations of the same physical quantity, and there is a conversion relationship between them. Therefore, the workload of image analysis and processing can be greatly simplified in the HSI color space.


### 3.4.3. Boundary-Based Segmentation

Image edges are especially important for image recognition and motion capture for animation. Edges are used in animation techniques to outline the target object. Edges contain intrinsic information such as direction, step characteristics, and shape, which are important attributes for extracting dynamic features of objects in motion production [27]. The use of the derivative operator can take the derivative value as the “boundary strength” of the corresponding point, and then extract the boundary point set by setting the threshold. Boundary-based segmentation is the basis for model retrieval, classification, and reconstruction. In order to solve the problems of poor robustness, oversegmentation and undersegmentation in the boundary segmentation algorithm, a boundary derivative operator algorithm based on boundary features is proposed. It is proved by mainstream evaluation methods and experiments that most models can achieve good segmentation results. Therefore, it can be known that the algorithm for extracting the edge is to detect the mathematical operator that conforms to the edge characteristics of the edge pixel, as shown in Figure 6.Figure 6
Common edge types.The first-order partial derivative operator is∂p/∂a,∂p/∂b, and the grayscale change rate is ∂p/∂β=∂p/∂acosβ+∂p/∂bsinβ. Using difference instead of derivative (discrete quantity instead of continuous quantity) based on boundary segmentation, the corresponding expression is as follows:(7)Δpm,n=pm,n−pm−1,n.Among them,(8)Δapm,n=pm,n−pm,n−1.The maximum value of the directional derivative of a function at a point istan−1∂p/∂b/∂p/∂a, and the maximum value of the directional derivative is ∂p/∂a2+∂p/∂b2, so the vector in this direction is called the gradient of the function p.(9)Δβpm,n=Δbpm,ncosβ−Δbpm,nsinβ.Thus, the gradient operatorwpa,b=∂p/∂a2+∂p/∂b2. can detect the boundary in any direction with the same sensitivity, and tan∂p/∂b/∂p/∂a gives the direction information of the boundary.In digital animation processing, the ladder operator is defined as(10)WPm,n=Δapm,n2+(Δbpm,n2.In practical applications, it generally means(11)Δapm,n+Δbpm,n.For the convenience of calculation, the following gradient simulation calculation expression is used:(12)maxΔapm,n,Δbpm,n,maxpm,n−py,q.


### 3.4.4. Maintenance of Dynamic Background and Capture Technology

The maintenance and updating of dynamic backgrounds are particularly important for capture technology. It must adapt to the background changing conditions including the moving in and out of the scene and the change of the shape of the object itself, as well as the sudden change of light, or the change of shadow introduced by the occlusion of the angle. The following uses the median estimation method to construct a dynamic background: the median filter is a simple order statistic. Median filtering is a nonlinear signal processing technique based on ranking statistics theory that can effectively suppress noise. The basic principle of median filtering is to replace the value of a point in a digital image or digital sequence with the median value of each point value in a neighborhood of the point, so that the surrounding pixel values are close to the true value, thereby eliminating isolated noise points.It is supposed that (X1,X2,…,Xn) are simple samples taken from a population with a continuous distribution T. (X1,X2,…,Xn) are rearranged as X1≤X2≤…≤Xn, that is, Xi is the i-th smallest among X1,X2,…,Xn, i=1,2,…,n. Then, X1≤X2≤…≤Xn is called the order statistic, generated by the samples X1,X2,…,Xn.Due to the following theorem, it is assumed that the sample population has a continuous distribution functionF (x), and the corresponding density function is F (x). X1≤X2≤…≤Xn is the order statistic generated by simple samples:(13)Fqx=∑w=qnnwFxw1−Fxn−w.Then, forq ≤ n, the distribution function and density function of Xq are:(14)fqx=n!q−1!n−q!Fq−1x1−Fxn−qfx.The median is defined as(15)medXi=Xe+1n=2e+1,Xe+1+Xe/2n=2e.Sincen is usually odd in practical applications, only the case where n is odd is discussed:(16)Fmedx=∑w=n+1/2nnwFxw1−Fxn−w.From the theorem, the distribution function and density function of med (Xi) can be obtained as(17)fqx=n!q−1!n−q!Fn−1/2x1−Fxn−1/2fx.Formula (17) has high precision for all odd n. When capturing the chi-square information value of an action, if the action only occurs frequently in a certain category, even if the frequency of occurrence is very high, the result value obtained would not be too large according to the feature selection. This may result in the action not being preferentially selected, but often the action has good category classification information and can better represent dynamic content. Therefore, in view of the occurrence of the above situation, in order to select better feature actions, the algorithm needs to be improved. Aiming at the frequency relationship of the action appearing in the animation in the feature selection algorithm formula, an action factor is proposed, and its magnitude is equal to the ratio of the number of frames that the action appears in the frequency band to the frequency of the action in the overall data set. Its calculation is shown in the following equation:(18)θpx,qy=mpx,qympx.The motion in the animation affects the animation speed. The shape of the action is presented in the animation by the change of position and the change of shape, and these changes depend on the reasonable distribution of animation time, such as fast and slow, acceleration and deceleration, delay and stop motion, and other animation speeds.For example, by (18), it can be calculated that the action factor of “action 1” is θp1=4, and the action factor of “action 2” is θp2=7/8≈0.87. Therefore, according to the calculation result of the action factor, special attention should be paid to the action factor of “action 1.” Then, it is combined with the chi-square statistic; we get(19)“A1”CHIθ∗p1=12,“A2”CHIθ∗p2=98/9≈10.9.Therefore, the result after introducing the action factor should preferentially select “action 1” instead of “action 2” as the feature, which is consistent with the selection result in the real case.


## 3.4.1. Color Construction

Color vision consistency is one of the basic abilities of human vision. People consistently perceive the target object as a color-consistent whole, even when temporal and spatial lighting conditions change. Perceived color at a point in the scene depends on a number of reasons, including the physical properties of the target surface at that location [25]. In the color vision, an important physical feature of a surface is the spectral reflectance of the surface, which does not change with illumination, structure, and shape. It can be known from the model that the color of visual perception is the product of illuminance and surface specular reflection. The RGB model is also known as the additive color mixing model. It is a method in which RGB three-color light is superimposed on each other to realize color mixing, so it is suitable for the display of illuminants such as monitors. The color mixing rule is as follows: mixing with equal amounts of red, green, and blue primary colors, as shown in Figure 5.Figure 5
Schematic diagram of RGB color model segmentation.The starting point for establishing the color model below is how to decompose the color perceived by vision into two parts: luminance and chrominance.Figure5 shows a schematic diagram of the color model in the RGB color space. At some point (x,y), Mi=MR,MG,MB represents the expected RGB value in the background or reference image at that point. The straight line OMi from the coordinate origin 0 to Mi represents the desired chromaticity line. Ni=NR,NG,NB represents the RGB color value at that point in the foreground image. The distortion produced by Ni relative to Mi is then measured and decomposed into two parts.Luminance distortion: among them, luma distortionβ is a scalar:(1)βi=minNi−βiMi,where βi represents the relative value of the brightness at the point (x,y) in the foreground to the brightness at the corresponding point in the background. If βi 1, the brightness of the point in the foreground is the same as that in the background; if βi is less than 1, the brightness of the point in the foreground is less than the brightness of the background; if βi is greater than 1, the brightness of the point in the foreground is greater than the brightness of the background.Chroma distortion: (EF) is defined as the vertical distance from a point Ni to the chromaticity line:(2)EFi=Ni−βiMi.


## 3.4.2. Space Conversion

The acquisition and display of images currently used in image processing are mainly based on the RGB color space. Therefore, when the HSI color space is used in the processing, they can be obtained through the corresponding transformation. The mutual transformation relationship between HSI color space and RGB color space is given [26]. The HSI color space starts from the human visual system and uses hue, color saturation, and brightness to describe colors, and it can clearly show the changes in hue, brightness and color saturation. Since human vision is far more sensitive to brightness than to color shades, in order to facilitate color processing and identification, the human visual system often uses HSI color space, which is more in line with human visual characteristics than RGB color space. A large number of algorithms in image processing and computer vision are conveniently available in the HSI color space, which can be processed separately and independently of each other.Color conversion of RGB to HSI:An RGB color image is given, and each RGB pixel and HSI component can be converted by the following formulas:Hue components:(3)S=θ,T≤R,2π−θ,T>R.Among them,(4)θ=arccosM−R+M−T2M−R2+M−TR−M1/2.Saturation component:(5)Z=1−3M+R+TminM,R,T.Intensity component:(6)L=M+R+T3.This shows that the HSI color space and the RGB color space are just different representations of the same physical quantity, and there is a conversion relationship between them. Therefore, the workload of image analysis and processing can be greatly simplified in the HSI color space.


## 3.4.3. Boundary-Based Segmentation

Image edges are especially important for image recognition and motion capture for animation. Edges are used in animation techniques to outline the target object. Edges contain intrinsic information such as direction, step characteristics, and shape, which are important attributes for extracting dynamic features of objects in motion production [27]. The use of the derivative operator can take the derivative value as the “boundary strength” of the corresponding point, and then extract the boundary point set by setting the threshold. Boundary-based segmentation is the basis for model retrieval, classification, and reconstruction. In order to solve the problems of poor robustness, oversegmentation and undersegmentation in the boundary segmentation algorithm, a boundary derivative operator algorithm based on boundary features is proposed. It is proved by mainstream evaluation methods and experiments that most models can achieve good segmentation results. Therefore, it can be known that the algorithm for extracting the edge is to detect the mathematical operator that conforms to the edge characteristics of the edge pixel, as shown in Figure 6.Figure 6
Common edge types.The first-order partial derivative operator is∂p/∂a,∂p/∂b, and the grayscale change rate is ∂p/∂β=∂p/∂acosβ+∂p/∂bsinβ. Using difference instead of derivative (discrete quantity instead of continuous quantity) based on boundary segmentation, the corresponding expression is as follows:(7)Δpm,n=pm,n−pm−1,n.Among them,(8)Δapm,n=pm,n−pm,n−1.The maximum value of the directional derivative of a function at a point istan−1∂p/∂b/∂p/∂a, and the maximum value of the directional derivative is ∂p/∂a2+∂p/∂b2, so the vector in this direction is called the gradient of the function p.(9)Δβpm,n=Δbpm,ncosβ−Δbpm,nsinβ.Thus, the gradient operatorwpa,b=∂p/∂a2+∂p/∂b2. can detect the boundary in any direction with the same sensitivity, and tan∂p/∂b/∂p/∂a gives the direction information of the boundary.In digital animation processing, the ladder operator is defined as(10)WPm,n=Δapm,n2+(Δbpm,n2.In practical applications, it generally means(11)Δapm,n+Δbpm,n.For the convenience of calculation, the following gradient simulation calculation expression is used:(12)maxΔapm,n,Δbpm,n,maxpm,n−py,q.


## 3.4.4. Maintenance of Dynamic Background and Capture Technology

The maintenance and updating of dynamic backgrounds are particularly important for capture technology. It must adapt to the background changing conditions including the moving in and out of the scene and the change of the shape of the object itself, as well as the sudden change of light, or the change of shadow introduced by the occlusion of the angle. The following uses the median estimation method to construct a dynamic background: the median filter is a simple order statistic. Median filtering is a nonlinear signal processing technique based on ranking statistics theory that can effectively suppress noise. The basic principle of median filtering is to replace the value of a point in a digital image or digital sequence with the median value of each point value in a neighborhood of the point, so that the surrounding pixel values are close to the true value, thereby eliminating isolated noise points.It is supposed that (X1,X2,…,Xn) are simple samples taken from a population with a continuous distribution T. (X1,X2,…,Xn) are rearranged as X1≤X2≤…≤Xn, that is, Xi is the i-th smallest among X1,X2,…,Xn, i=1,2,…,n. Then, X1≤X2≤…≤Xn is called the order statistic, generated by the samples X1,X2,…,Xn.Due to the following theorem, it is assumed that the sample population has a continuous distribution functionF (x), and the corresponding density function is F (x). X1≤X2≤…≤Xn is the order statistic generated by simple samples:(13)Fqx=∑w=qnnwFxw1−Fxn−w.Then, forq ≤ n, the distribution function and density function of Xq are:(14)fqx=n!q−1!n−q!Fq−1x1−Fxn−qfx.The median is defined as(15)medXi=Xe+1n=2e+1,Xe+1+Xe/2n=2e.Sincen is usually odd in practical applications, only the case where n is odd is discussed:(16)Fmedx=∑w=n+1/2nnwFxw1−Fxn−w.From the theorem, the distribution function and density function of med (Xi) can be obtained as(17)fqx=n!q−1!n−q!Fn−1/2x1−Fxn−1/2fx.Formula (17) has high precision for all odd n. When capturing the chi-square information value of an action, if the action only occurs frequently in a certain category, even if the frequency of occurrence is very high, the result value obtained would not be too large according to the feature selection. This may result in the action not being preferentially selected, but often the action has good category classification information and can better represent dynamic content. Therefore, in view of the occurrence of the above situation, in order to select better feature actions, the algorithm needs to be improved. Aiming at the frequency relationship of the action appearing in the animation in the feature selection algorithm formula, an action factor is proposed, and its magnitude is equal to the ratio of the number of frames that the action appears in the frequency band to the frequency of the action in the overall data set. Its calculation is shown in the following equation:(18)θpx,qy=mpx,qympx.The motion in the animation affects the animation speed. The shape of the action is presented in the animation by the change of position and the change of shape, and these changes depend on the reasonable distribution of animation time, such as fast and slow, acceleration and deceleration, delay and stop motion, and other animation speeds.For example, by (18), it can be calculated that the action factor of “action 1” is θp1=4, and the action factor of “action 2” is θp2=7/8≈0.87. Therefore, according to the calculation result of the action factor, special attention should be paid to the action factor of “action 1.” Then, it is combined with the chi-square statistic; we get(19)“A1”CHIθ∗p1=12,“A2”CHIθ∗p2=98/9≈10.9.Therefore, the result after introducing the action factor should preferentially select “action 1” instead of “action 2” as the feature, which is consistent with the selection result in the real case.


## 4. Animation Motion Capture Technology Based on Machine Learning

### 4.1. Motion Capture Technology Algorithm Experiment

For a computer database, it is relatively easy to obtain statistical data such as action frequency, information class ratio, and action item distribution, and these basic data often have very strong characteristic information. Therefore, the feature selection algorithm mainly collects these statistical values and participates in the calculation. Generally, four commonly used feature selection algorithms, DF, IG, MI, and CHI, are used to capture action features. The quality of the feature capture method often determines the subsequent classification effect. However, in actual use, due to the large differences in the characteristics of different types of dynamic data sets, direct use of any of the above algorithms cannot guarantee a good classification effect. Therefore, there is still a lot of room to improve the feature selection algorithm in the capture process.By exploiting algorithmic functions, the computations are performed on action datasets in practical applications. At the same time, combining with the feature data, an improved method is proposed to solve the problems and deficiencies in the above algorithms, and a new feature selection algorithm function is formed. TF-IDF, TFC, and TLC algorithms are all traditional feature weighting calculation methods, and some problems have also been found in daily use. Next, an example is given, it is assumed that there are three categories in an action dataset: “Action 1,” “Action 2,” and “Action 3,” and there are 6 pieces of content in each category. The distribution of the three categories “a,” “b,” and “c” in each category of actions in the dataset is shown in Table 3.Table 3
Distribution of “Action 1,” “Action 2,” and “Action 3” in each category of frequency band.
abc123456123456123456Action 1967888112433222311Action 2222222222331111112Action 3200000233321221120According to the data in Table3, the action analysis coefficient of Action 1 in the data set of class a is higher than that of classes b and c; the action number set of Action 2 has the most stable distribution in the frequency bands of each class. For the convenience of calculation, it is assumed that the length of each segment set in the action data set is 60. At this time, the TLC algorithm can be used to calculate the weight, as shown in Figure 7, log9/15=s:Figure 7
The weight values of “Action 1,” “Action 2,” and “Action 3” under the TF-IDF algorithm.According to the frequency distribution in Figure7, it can be judged that the weight values of “Action 1” and category “a,” “Action 2” and category “c” should be larger. Since action 1 has the same distribution characteristics in each category data set, it cannot provide help for judging classification, so the weight value should be set to 0. And the term “Action 3” appears in the category “c,” which is very helpful for judging classification, and should try to improve its weight. This contradicts the obtained data results in Table 4, so it showed that the TLC algorithm needs to be improved. In addition, because the chi-square statistical calculation formula fully considers the interclass distribution of terms, it should have positive significance for solving the TLC algorithm in theory. When the degree of deviation between the actual observed value of the sample and the theoretically inferred value is counted, the degree of deviation between the actual observed value and the theoretically inferred value determines the size of the chi-square value. The larger the chi-square value, the less consistent it is, and the smaller the deviation, the smaller the chi-square value, and the more consistent it is.Table 4
Dynamic metrics based on SVM algorithm.
CHICHMITF-CHITF-XGBD182%72%89%81%Px0.770.770.930.88Qy0.860.850.950.83


### 4.2. Experimental Results of Dynamic Capture Algorithm

#### 4.2.1. Traditional Machine Learning Algorithm Experiments

An experimental corpus for testing and classification is established in the experiments in this section. The video resources in the experimental database are all derived from some network animation clips. The data in the experimental database is divided into a training action set and a test action set according to the ratio of 1 : 1. The training action set and the test action set save the content of different actions and the category information they belong to. First, the four traditional machine learning classification algorithms, SVM, NB, KNN, and DT, are used to classify the experimental database in this experiment. Machine learning models are divided into two categories: supervised learning and unsupervised learning, according to the types of data that can be used. Supervised learning mainly includes models for classification and for regression. Classification: Support Vector Machine (SVM), Naive Bayes (NB),K-Nearest Neighbor (KNN), Decision Tree (DT); regression: Linear Regression, Support Vector Machine (SVM), K-Nearest Neighbors (KNN), Regression Tree (DT). The experimental method is carried out in sequence according to a text classification processing step shown in Figure 8.Figure 8
Classification steps under machine learning algorithm.The results shown in Figure9 can be obtained in turn by performing a classification test through the several common classification algorithms. The alpha is a smoothing parameter that can be used to control the number of iterations in SVM algorithm experiments. In the linear relationship, the smaller the alpha value is, the higher the classification accuracy is obtained in the experiment. The powerful algorithm based on SVM is decomposed into multiple small optimization problems to solve. These small optimization problems tend to be easy to solve, and solving them sequentially is consistent with the overall solution, where the goal is to find a range of alpha and b. By finding these alphas, the weight W can be found. In this way, the separating hyperplane can be obtained to complete the classification task. In this NB algorithm experiment, the alpha value was finally set to 0.001. In this action dataset, both the SVM algorithm and the NB algorithm have good text classification results.Figure 9
Classification results of four classes of algorithms.In Figure10, the data in the video library are counted under the SVM algorithm and the NB algorithm, respectively. In the experiment, the corpus is randomly selected from the data set, the training set and the test set are composed according to the ratio of 5 : 2, and the classification results of the test data are obtained. The purpose of this experiment is to verify the superiority of the improved feature selection algorithm. First, it is necessary to determine the feature dimension through experiments, and then use several feature selection algorithms such as CHI, CHMI, TF-CHI, and TF-XGB to conduct classification experiments and obtain classification results.Figure 10
Number of features vs. categorical D1 value under SVM.Classification experiments are performed on the action dataset under the SVM algorithm. First of all, through experiments, it can be concluded that the text classification results based on the linear kernel function in this dataset are significantly better than other commonly used kernel functions, so the kernel function is determined as a unified linear kernel function (linear) in the experiments in this section. The CHI and three improved CHMI, TF-CHI, and TF-XGB algorithms are used respectively in the feature selection process. First, the experimental design of the first part is carried out: according to the characteristics of the action dataset selected in this paper, the capture accuracy and D1 value under different actions can be obtained by continuously adjusting the parameters. The purpose of this part of the experiment is to verify the relationship between the captured results and the feature actions under different feature selection methods. Finally, the D1 value index of the classification result is graphically displayed as the four relationship curves shown in Figure10.In the experiment, the classification experiment with a number of feature words in the range of 200–2000 was carried out. As can be seen from the relationship curve in Figure10, within the range of 200–1000 feature words, the D1 value increases linearly with the increase of the number of feature words; until the number of features exceeds 600, the D1 value under the CHI algorithm begins to decrease gradually. Based on the above four relationship curves and mainly based on the D1 value characteristics under the CHI algorithm, 600 is finally selected as the feature dimension under the support vector machine algorithm in this experiment and determined as the subsequent experimental standard. After the feature dimension is determined to be 600, the above several feature selection algorithms are respectively applied to the motion data set for motion capture experiments, then, the accuracy, recall, and D1 value of motion capture under four different feature selection algorithms can be obtained. In this experiment, the accuracy of the classification results and the D1 value are selected as the main reference indicators of this experiment. The data shown in Table 4 are obtained by using different feature selection algorithms under the SVM algorithm.By observing Table4, it can be obtained that the classification results under the SVM algorithm have these statistical characteristics: it is compared with the CHI algorithm, the overall average accuracy and D1 value of the three algorithms based on the improved CHMI, TF-CHI, and TF-XGB have been significantly improved, and they have obtained 2%, 5%, and 3% accuracy improvements, respectively; among the three improved algorithms, TF-CHI has a greater improvement effect, and can achieve an overall average accuracy and D1 value of more than 85%; according to D1 data, TF-CHI is better than the CHMI and TF-XGB algorithms, and its accuracy rate is 89%, which is 7% higher than CHI. After analyzing the above statistical information, it can be considered that the TF-CHI algorithm in the improved feature selection algorithm is better than the CHMI and TF-XGB algorithms, and the three feature selection algorithms have a greater improvement than the single CHI algorithm, thus, confirming the effectiveness of the improved algorithm.


## 4.1. Motion Capture Technology Algorithm Experiment

For a computer database, it is relatively easy to obtain statistical data such as action frequency, information class ratio, and action item distribution, and these basic data often have very strong characteristic information. Therefore, the feature selection algorithm mainly collects these statistical values and participates in the calculation. Generally, four commonly used feature selection algorithms, DF, IG, MI, and CHI, are used to capture action features. The quality of the feature capture method often determines the subsequent classification effect. However, in actual use, due to the large differences in the characteristics of different types of dynamic data sets, direct use of any of the above algorithms cannot guarantee a good classification effect. Therefore, there is still a lot of room to improve the feature selection algorithm in the capture process.By exploiting algorithmic functions, the computations are performed on action datasets in practical applications. At the same time, combining with the feature data, an improved method is proposed to solve the problems and deficiencies in the above algorithms, and a new feature selection algorithm function is formed. TF-IDF, TFC, and TLC algorithms are all traditional feature weighting calculation methods, and some problems have also been found in daily use. Next, an example is given, it is assumed that there are three categories in an action dataset: “Action 1,” “Action 2,” and “Action 3,” and there are 6 pieces of content in each category. The distribution of the three categories “a,” “b,” and “c” in each category of actions in the dataset is shown in Table 3.Table 3
Distribution of “Action 1,” “Action 2,” and “Action 3” in each category of frequency band.
abc123456123456123456Action 1967888112433222311Action 2222222222331111112Action 3200000233321221120According to the data in Table3, the action analysis coefficient of Action 1 in the data set of class a is higher than that of classes b and c; the action number set of Action 2 has the most stable distribution in the frequency bands of each class. For the convenience of calculation, it is assumed that the length of each segment set in the action data set is 60. At this time, the TLC algorithm can be used to calculate the weight, as shown in Figure 7, log9/15=s:Figure 7
The weight values of “Action 1,” “Action 2,” and “Action 3” under the TF-IDF algorithm.According to the frequency distribution in Figure7, it can be judged that the weight values of “Action 1” and category “a,” “Action 2” and category “c” should be larger. Since action 1 has the same distribution characteristics in each category data set, it cannot provide help for judging classification, so the weight value should be set to 0. And the term “Action 3” appears in the category “c,” which is very helpful for judging classification, and should try to improve its weight. This contradicts the obtained data results in Table 4, so it showed that the TLC algorithm needs to be improved. In addition, because the chi-square statistical calculation formula fully considers the interclass distribution of terms, it should have positive significance for solving the TLC algorithm in theory. When the degree of deviation between the actual observed value of the sample and the theoretically inferred value is counted, the degree of deviation between the actual observed value and the theoretically inferred value determines the size of the chi-square value. The larger the chi-square value, the less consistent it is, and the smaller the deviation, the smaller the chi-square value, and the more consistent it is.Table 4
Dynamic metrics based on SVM algorithm.
CHICHMITF-CHITF-XGBD182%72%89%81%Px0.770.770.930.88Qy0.860.850.950.83


## 4.2. Experimental Results of Dynamic Capture Algorithm

### 4.2.1. Traditional Machine Learning Algorithm Experiments

An experimental corpus for testing and classification is established in the experiments in this section. The video resources in the experimental database are all derived from some network animation clips. The data in the experimental database is divided into a training action set and a test action set according to the ratio of 1 : 1. The training action set and the test action set save the content of different actions and the category information they belong to. First, the four traditional machine learning classification algorithms, SVM, NB, KNN, and DT, are used to classify the experimental database in this experiment. Machine learning models are divided into two categories: supervised learning and unsupervised learning, according to the types of data that can be used. Supervised learning mainly includes models for classification and for regression. Classification: Support Vector Machine (SVM), Naive Bayes (NB),K-Nearest Neighbor (KNN), Decision Tree (DT); regression: Linear Regression, Support Vector Machine (SVM), K-Nearest Neighbors (KNN), Regression Tree (DT). The experimental method is carried out in sequence according to a text classification processing step shown in Figure 8.Figure 8
Classification steps under machine learning algorithm.The results shown in Figure9 can be obtained in turn by performing a classification test through the several common classification algorithms. The alpha is a smoothing parameter that can be used to control the number of iterations in SVM algorithm experiments. In the linear relationship, the smaller the alpha value is, the higher the classification accuracy is obtained in the experiment. The powerful algorithm based on SVM is decomposed into multiple small optimization problems to solve. These small optimization problems tend to be easy to solve, and solving them sequentially is consistent with the overall solution, where the goal is to find a range of alpha and b. By finding these alphas, the weight W can be found. In this way, the separating hyperplane can be obtained to complete the classification task. In this NB algorithm experiment, the alpha value was finally set to 0.001. In this action dataset, both the SVM algorithm and the NB algorithm have good text classification results.Figure 9
Classification results of four classes of algorithms.In Figure10, the data in the video library are counted under the SVM algorithm and the NB algorithm, respectively. In the experiment, the corpus is randomly selected from the data set, the training set and the test set are composed according to the ratio of 5 : 2, and the classification results of the test data are obtained. The purpose of this experiment is to verify the superiority of the improved feature selection algorithm. First, it is necessary to determine the feature dimension through experiments, and then use several feature selection algorithms such as CHI, CHMI, TF-CHI, and TF-XGB to conduct classification experiments and obtain classification results.Figure 10
Number of features vs. categorical D1 value under SVM.Classification experiments are performed on the action dataset under the SVM algorithm. First of all, through experiments, it can be concluded that the text classification results based on the linear kernel function in this dataset are significantly better than other commonly used kernel functions, so the kernel function is determined as a unified linear kernel function (linear) in the experiments in this section. The CHI and three improved CHMI, TF-CHI, and TF-XGB algorithms are used respectively in the feature selection process. First, the experimental design of the first part is carried out: according to the characteristics of the action dataset selected in this paper, the capture accuracy and D1 value under different actions can be obtained by continuously adjusting the parameters. The purpose of this part of the experiment is to verify the relationship between the captured results and the feature actions under different feature selection methods. Finally, the D1 value index of the classification result is graphically displayed as the four relationship curves shown in Figure10.In the experiment, the classification experiment with a number of feature words in the range of 200–2000 was carried out. As can be seen from the relationship curve in Figure10, within the range of 200–1000 feature words, the D1 value increases linearly with the increase of the number of feature words; until the number of features exceeds 600, the D1 value under the CHI algorithm begins to decrease gradually. Based on the above four relationship curves and mainly based on the D1 value characteristics under the CHI algorithm, 600 is finally selected as the feature dimension under the support vector machine algorithm in this experiment and determined as the subsequent experimental standard. After the feature dimension is determined to be 600, the above several feature selection algorithms are respectively applied to the motion data set for motion capture experiments, then, the accuracy, recall, and D1 value of motion capture under four different feature selection algorithms can be obtained. In this experiment, the accuracy of the classification results and the D1 value are selected as the main reference indicators of this experiment. The data shown in Table 4 are obtained by using different feature selection algorithms under the SVM algorithm.By observing Table4, it can be obtained that the classification results under the SVM algorithm have these statistical characteristics: it is compared with the CHI algorithm, the overall average accuracy and D1 value of the three algorithms based on the improved CHMI, TF-CHI, and TF-XGB have been significantly improved, and they have obtained 2%, 5%, and 3% accuracy improvements, respectively; among the three improved algorithms, TF-CHI has a greater improvement effect, and can achieve an overall average accuracy and D1 value of more than 85%; according to D1 data, TF-CHI is better than the CHMI and TF-XGB algorithms, and its accuracy rate is 89%, which is 7% higher than CHI. After analyzing the above statistical information, it can be considered that the TF-CHI algorithm in the improved feature selection algorithm is better than the CHMI and TF-XGB algorithms, and the three feature selection algorithms have a greater improvement than the single CHI algorithm, thus, confirming the effectiveness of the improved algorithm.


## 4.2.1. Traditional Machine Learning Algorithm Experiments

An experimental corpus for testing and classification is established in the experiments in this section. The video resources in the experimental database are all derived from some network animation clips. The data in the experimental database is divided into a training action set and a test action set according to the ratio of 1 : 1. The training action set and the test action set save the content of different actions and the category information they belong to. First, the four traditional machine learning classification algorithms, SVM, NB, KNN, and DT, are used to classify the experimental database in this experiment. Machine learning models are divided into two categories: supervised learning and unsupervised learning, according to the types of data that can be used. Supervised learning mainly includes models for classification and for regression. Classification: Support Vector Machine (SVM), Naive Bayes (NB),K-Nearest Neighbor (KNN), Decision Tree (DT); regression: Linear Regression, Support Vector Machine (SVM), K-Nearest Neighbors (KNN), Regression Tree (DT). The experimental method is carried out in sequence according to a text classification processing step shown in Figure 8.Figure 8
Classification steps under machine learning algorithm.The results shown in Figure9 can be obtained in turn by performing a classification test through the several common classification algorithms. The alpha is a smoothing parameter that can be used to control the number of iterations in SVM algorithm experiments. In the linear relationship, the smaller the alpha value is, the higher the classification accuracy is obtained in the experiment. The powerful algorithm based on SVM is decomposed into multiple small optimization problems to solve. These small optimization problems tend to be easy to solve, and solving them sequentially is consistent with the overall solution, where the goal is to find a range of alpha and b. By finding these alphas, the weight W can be found. In this way, the separating hyperplane can be obtained to complete the classification task. In this NB algorithm experiment, the alpha value was finally set to 0.001. In this action dataset, both the SVM algorithm and the NB algorithm have good text classification results.Figure 9
Classification results of four classes of algorithms.In Figure10, the data in the video library are counted under the SVM algorithm and the NB algorithm, respectively. In the experiment, the corpus is randomly selected from the data set, the training set and the test set are composed according to the ratio of 5 : 2, and the classification results of the test data are obtained. The purpose of this experiment is to verify the superiority of the improved feature selection algorithm. First, it is necessary to determine the feature dimension through experiments, and then use several feature selection algorithms such as CHI, CHMI, TF-CHI, and TF-XGB to conduct classification experiments and obtain classification results.Figure 10
Number of features vs. categorical D1 value under SVM.Classification experiments are performed on the action dataset under the SVM algorithm. First of all, through experiments, it can be concluded that the text classification results based on the linear kernel function in this dataset are significantly better than other commonly used kernel functions, so the kernel function is determined as a unified linear kernel function (linear) in the experiments in this section. The CHI and three improved CHMI, TF-CHI, and TF-XGB algorithms are used respectively in the feature selection process. First, the experimental design of the first part is carried out: according to the characteristics of the action dataset selected in this paper, the capture accuracy and D1 value under different actions can be obtained by continuously adjusting the parameters. The purpose of this part of the experiment is to verify the relationship between the captured results and the feature actions under different feature selection methods. Finally, the D1 value index of the classification result is graphically displayed as the four relationship curves shown in Figure10.In the experiment, the classification experiment with a number of feature words in the range of 200–2000 was carried out. As can be seen from the relationship curve in Figure10, within the range of 200–1000 feature words, the D1 value increases linearly with the increase of the number of feature words; until the number of features exceeds 600, the D1 value under the CHI algorithm begins to decrease gradually. Based on the above four relationship curves and mainly based on the D1 value characteristics under the CHI algorithm, 600 is finally selected as the feature dimension under the support vector machine algorithm in this experiment and determined as the subsequent experimental standard. After the feature dimension is determined to be 600, the above several feature selection algorithms are respectively applied to the motion data set for motion capture experiments, then, the accuracy, recall, and D1 value of motion capture under four different feature selection algorithms can be obtained. In this experiment, the accuracy of the classification results and the D1 value are selected as the main reference indicators of this experiment. The data shown in Table 4 are obtained by using different feature selection algorithms under the SVM algorithm.By observing Table4, it can be obtained that the classification results under the SVM algorithm have these statistical characteristics: it is compared with the CHI algorithm, the overall average accuracy and D1 value of the three algorithms based on the improved CHMI, TF-CHI, and TF-XGB have been significantly improved, and they have obtained 2%, 5%, and 3% accuracy improvements, respectively; among the three improved algorithms, TF-CHI has a greater improvement effect, and can achieve an overall average accuracy and D1 value of more than 85%; according to D1 data, TF-CHI is better than the CHMI and TF-XGB algorithms, and its accuracy rate is 89%, which is 7% higher than CHI. After analyzing the above statistical information, it can be considered that the TF-CHI algorithm in the improved feature selection algorithm is better than the CHMI and TF-XGB algorithms, and the three feature selection algorithms have a greater improvement than the single CHI algorithm, thus, confirming the effectiveness of the improved algorithm.


## 5. Conclusions

The digital age has had varying degrees of impact on all aspects of life and has also had a greater impact on art and even animation design. The powerful influence of digital technology is on full display from the many breathtaking motion shots in TV films and digital animation, which relies entirely on digital media. The use of motion capture technology increases the consistency and smoothness of different aspects of the animation. It is compared with traditional technology; this technology is more convenient for the relevant personnel. The details of different frames can be captured and adjusted from different local angles, and the recording record is maintained. The use of motion capture technology in the art of animation is becoming more and more common. At the same time, in order to meet the demand for high-quality animation works and make the visual effects more vivid, the improvement and innovation of animation production technology can promote the sustainable development of animation art.



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*Source: 4857250-2022-09-16.xml*