# Application of Multitask Joint Sparse Representation Algorithm in Chinese Painting Image Classification

Authors: Dongyu Yang; Xinchen Ye; Baolong Guo
Journal: Complexity
 (2021)

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## Abstract

This paper presents an in-depth study and analysis of Chinese painting image classification by a multitask joint sparse representation algorithm for texture feature extraction of Chinese painting images and proposes a method to extract texture features directly for the original images. It simplifies the process of image grayscale conversion and preserves the information contained in the original Chinese painting images to the greatest extent. The algorithm uses the ideas of multicolor domain analysis and multiscale analysis, combined with the traditional grayscale coeval matrix to extract texture features. Experiments show that the multiscale grayscale cooccurrence matrix algorithm outperforms the traditional grayscale cooccurrence matrix algorithm and the color grayscale cooccurrence matrix algorithm. The discriminative ability of multiple features for target recognition is integrated by multitask learning, thus improving the robustness and generalization ability of the algorithm; meanwhile, the recognition accuracy is improved by using a two-level multitask learning mode to exclude the interference of a large number of irrelevant dictionary atoms. The experimental results show that the algorithm has higher recognition accuracy and better robustness than the existing sparse representation SAR target recognition algorithm. Configuration recognition experiments are conducted on different configurations of target data, and the experimental results show that the algorithm achieves better configuration recognition accuracy than existing algorithms.


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## Body

## 1. Introduction

The concept of Chinese painting began to be widely used at the beginning of this century [1], and the concept was introduced as an affirmation of the ancient art of painting in China and as a way to preserve the national painting. Chinese painting has created a form of painting that belongs exclusively to China. Classifying Chinese paintings can manage the database of Chinese paintings efficiently, and a reasonable classification can retrieve the specified works from the huge database of Chinese paintings easily and quickly. Therefore, Chinese painting feature extraction algorithms are a focus of research for most Chinese painting classification researchers at present. Texture, color, and shape features are the three most used features for images [2]. Using shape features to classify and recognize Chinese paintings does not achieve ideal results because it is affected by many factors, and there are limitations in using it for image classification and recognition. Texture feature is one of the most frequently used features of the image, and it is also a feature that can best reflect the distribution pattern of the image. The color feature mainly represents the color information contained in the image and is more inclined to describe the overall characteristics of the image, which is a feature that cannot be ignored. The color and texture features can well represent the information contained in the image, and they are also the most frequently used features in the current classification and recognition of Chinese painting images [3].With the rapid development of computer technology, more and more precious materials can be preserved in digital form. The digitization of Chinese paintings drawn on rice paper or silk is conducive to the long-term preservation of these precious materials. This is why the digital management of Chinese paintings is particularly important [4]. Therefore, it is important to retrieve the specific images needed in the huge database of Chinese paintings, which has become a hot topic of research by researchers in [5–7]. The color and texture features can well represent the information contained in the image, and they are also the most frequently used features in the current classification and recognition of Chinese painting images.The main problem studied in this paper is the automatic image annotation algorithm based on deep learning. The main process of image annotation model based on deep learning is as follows: using the annotated dataset as a training sample, constructing a semantic concept model using a deep learning network, then using the training sample to train the model to get a model that can perform image multilabel classification, and finally using the already trained model to determine the image semantic label of the sample to be annotated and output the label type of the image. First, a parallel classification strategy is proposed, which combines two features and sends them to the Softmax classifier to achieve classification. The experimental results on the dataset constructed in the article containing 1015 Chinese painting works show that the proposed method is based on five types of images. A good classification effect is achieved, with a classification accuracy of 96%. The most critical issue is to establish an effective semantic concept model. In recent years, many scholars have proposed many image auto-labeling algorithms and auto-classifier models based on existing conditions; for example, the proposed SVM model-based binary classification method, graph model classification method, and Gaussian mixture model. These methods can be directly applied to image auto-labeling. Many of these methods ignore the characteristics of the image annotation problem and the correlation between labels, and the annotation results are not very satisfactory. Therefore, this paper presents some research work on how to make full use of the characteristics of the automatic image annotation problem, make full use of the inter-label association relationship, and realize automatic image annotation based on deep learning techniques. Chinese painting image classification is an important part of the digital art work management system. To obtain the overall style and local brushstroke characteristics of Chinese painting, a Chinese painting image classification algorithm that combines global and local features is proposed.


## 2. Related Works

He et al. studied Chinese painting modeling, designed a framework, and used it to test various current algorithms so that they could be applied to the classification and recognition of Chinese paintings [8]. She et al. combined global and local features to classify western paintings and achieved quite satisfactory results [9]. Cheng et al. proposed the heterogeneous feature group selection method and improved the regression model. Cheng et al. extracted a subset of heterogeneous features to characterize the artistic style of ink painting and finally achieved the classification recognition of ink painting with an average accuracy of 87% [10]. Nie et al. applied complex network theory to texture feature extraction of images and proposed a chunking filtering method based on image entropy to extract texture features of Chinese paintings in combination with complex network theory, and the average detection rate reached 84.5% [11]. Zhao et al. extracted the style features of Chinese paintings by different authors, then selected the most representative feature subset to achieve the author prediction of Chinese paintings with an average finding rate of 87%, and used a convolutional neural network to achieve the sentiment classification of Chinese painting images [12].Earlier image annotation was done in a discriminative way, and the image annotation results were obtained mainly by determining the correctness of the labels. Gao et al. mined the association relationship between labels and tags in images and proposed a multilevel group sparse coding image automatic annotation model for simultaneous single-label images [13]. Jiang et al. used the sparse representation of features to add an intergroup constraint term to the original sparse representation model to achieve image annotation and proposed an automatic annotation framework based on distance constraint/group sparse coding [14]. The model first learns the corresponding feature weights in the training samples, then the weights are used to compute the K-Nearest Neighbor (KNN) images of the test samples, and, finally, a label transfer strategy is used to achieve automatic labeling of unknown images [15]. Subsequently, Support Vector Machine (SVM)-based image labeling algorithms and Bayesian classification image labeling methods emerged [16]. The algorithm is more effective in small-scale sample classification learning because SVM algorithms based on small-scale samples avoid problems such as the law of large numbers and probability metric measures. Generally, the image is segmented into multiple regions, with each region corresponding to the labeled words of the image, then a binary classifier is trained for each word, and, finally, the trained classifier is used to classify the image. Since this algorithm cannot solve the multilabel classification problem, some scholars have proposed an improved algorithm based on this method [17]. This algorithm uses a multivariate classifier for classification learning, the multivariate classifier takes into account the association links between labeled words and image regions, and to a certain extent its classification results are more perfect and more credible. The above methods are all discriminative model-based image annotation methods. Discriminative model-based image annotation methods are simple to construct and easy to implement. However, the problem of “semantic gap” is easy to occur in the annotation process.


## 3. Multitask Joint Sparse Representation Algorithm for Chinese Painting Image Classification Design

### 3.1. Multitask Joint Sparse Representation Algorithm

Sparse representation (SR) is a signal consisting of few nonzero elements in a smaller vector space. Due to its ability to represent high-dimensional data, SR has become an unavoidable feature extraction concept, and it is a signal sampling technique used to compress images. The process of sparse representation can be thought of as projecting the target signal into a space consisting of a set of nonorthogonal bases, and the coefficients projected on each base are sparsely coded. The term “sparse” conveys the idea that only individual numbers are zero or differ significantly from zero in the coefficients obtained by using a dictionary to represent the information. Thus, it can be stated briefly that the important information of the signal can be expressed with few nonzero elements and that it is easier to solve in this way [18]. From a mathematical point of view, a sparse representation is a multidimensional data representation. As represented in Figure 1 it is the small number of atoms in the matrix D that can be used to represent the signal y by a linear combination.Figure 1
Diagram of the joint sparse representation model for sparse multitasking.The model is linearly expressed as(1)Y=MX.Since the image is usually noisy, (1) can be rewritten as(2)Y=MX+D,where z is the noise. Equation (1) is an underdetermined linear equation, by which it is impossible to obtain a unique representation of the input signal y on the dictionary D. Therefore, in obtaining the sparse representation, it is necessary to constrain other coefficients by imposing constraints on the coefficient x. The sparser the coefficients x are, the easier it is to accurately predict the class labels of the input signal y. This motivates us to find the sparsest solution. The following optimization problem can solve the coefficients. In (3), we generally adopt the method of controlling variables to determine(3)G=argminfEyfx−y2,L=1−aLmse+aLKL.It refers to the number of nonzero elements of a vector and is also used to control the strength of the sparse model.x does not have an exact sparse representation, but it can be represented in such a way as to ensure that the result is as close as possible to the original signal y. There is a different form of the sparse representation of the model that uses Lagrange multipliers to combine two constraints into one inequality:(4)kj|i=exp−xi−xi¯2/2σi2∑k≠iexp−xi−xi¯2/2σi2.However, in practice, finding the sparsest solution of the L0 parametrization is an NP-hard problem. In such cases, the test samples presumably cannot be sparsely represented as a linear combination of the training samples. Several studies have shown that when the solution is sparse and when the signal and the dictionary satisfy certain conditions, it is possible to constrain the L1 parametrization instead of the L0 parametrization and then approximate the sparse solution by solving for a stable solution of the L1 parametrization that minimizes the sparse solution; then, the sparse representation model based on the L1 parametrization has the following formulation:(5)L1=exp−xi−yj¯2/2σi2∑k≠iexp−xi−xi¯2/2σi2,L2=exp−xi−yj¯2/2σi2∑k≠iexp−xi−yi¯2/2σi2,L0=exp−xi−zj¯2/2σi2∑k≠iexp−xi−zi¯2/2σi2.The delta_i is the gradient at positioni. In sparse representation, the construction of dictionaries has been a key aspect of sparse representation, which directly affects whether sparse representation can be performed efficiently. The dictionary atoms must satisfy two requirements: first, they need to form the entire M-dimensional space and thus can represent the original signal linearly; second, the individual dictionary atoms are linearly independent [19]. Therefore, how to construct the dictionary is one of the key research problems in sparse representation theory, and no matter how to construct the dictionary, the goal is to make the dictionary itself contain more and more rich information, and different signals can be represented adaptively.At present, the construction of dictionaries is divided into three categories: directly using the original training samples as dictionaries, analyzing dictionaries, and learning dictionaries. The method of using original training samples to form dictionaries is simpler, but the dictionary capacity increases with the number of training samples or categories, which makes the computational burden increase and the efficiency decrease, and the redundant information cannot be effectively expressed for the original signal, thus leading to the decrease of detection accuracy. Analytical dictionaries refer to the dictionaries obtained by using certain mathematical models. Frequently used analytical dictionaries are wavelet dictionaries, Fourier transforms dictionaries, and discrete cosine transform dictionaries (DCT dictionaries). The advantage of this dictionary is that the principle is simple and easy to implement, but it also has the disadvantage that its representation of the signal is too homogeneous and does not have self-adaptability. When facing complex remote sensing images, the dictionary is not flexible enough to adapt to sample changes and cannot accurately represent the sparse features of the images, and then the analytical dictionary is not a suitable choice. Learning dictionaries, i.e., dictionaries obtained by training and learning a large amount of data similar to the target data, in contrast, are more practical than analytic dictionaries. The dictionaries obtained by learning are morphologically rich, with the structured, discriminative ability and better flexibility to better adapt to different image data and obtain sparser representations. We are discussing Chinese paintings, but the drawings are all similar, so our algorithm can be used for other types of paintings as well.Multitask learning (MTL) is an approach to inductive transfer that can ensure that related tasks learn from each other by using the information contained in the training signals of the related tasks and makes the inductive transfer approach effective. It does this by learning tasks in parallel using a shared representation, allowing what each task learns to better help learn other tasks. One type of construction is the construction of multiple tasks with commonality. Multiple tasks can be constructed in various ways, which may depend on the particular application. Another key technique is the correlation analysis of multiple tasks. Tasks can be correlated in various ways. There are two common approaches: tasks can be related by assuming that all learned functions are close to each other in some specification, and tasks can also be related to each other because they all share a base representation. For the first type of task correlation, the typical approach is a linear regression function. For the second type of task correlation, there are some widely used representations, such as sparsity.In multitask learning, multiple tasks with similarity can be solved, and a linear representation model can be constructed for the sparse representation of each task, while information can be shared among different tasks with similarity, thus effectively utilizing the potential information between different tasks and improving the accuracy of recognition, thus constructing a multitask sparse representation model:(6)Mr=limΔr⟶0r+Δrn−rnΔr.The traditional multitask sparse model only considers the features of each pixel itself and ignores the spatial correlation between neighboring pixels. In remote sensing images, neighboring pixels usually belong to the same material. Therefore, the image pixels in a small spatial neighborhood are highly similar and have many similarities. By the same token, these near-neighbor pixels can be represented simultaneously and have similar structures. The spatial information can also be combined in the same way in the framework of a multitask sparse representation model.According to the principle of joint sparse representation, when adjacent pixels are sparsely represented at the same time, the sparse coefficient can easily solve the following optimization problems:(7)Fr=∫0Tprdr=rn.Two constraints need to be considered here: the first constraint is the assumption that similar pixels are approximately distributed in the same low-dimensional subspace that also consists of the same class of training samples; the second constraint is the assumption that the nearest neighbor pixels have the same low-dimensional subspace domain. Here, the constraint of joint sparsity across different tasks can provide other useful information for the classification problem because different tasks may support different sparse representation coefficients, and joint sparsity may enhance the robustness of coefficient estimation. The joint orthogonal match-tracking method is a generalization of the orthogonal match-tracking algorithm under the L2 parametric model, and its basic idea is to select the atom that simultaneously produces the best approximation to all residual vectors in each iteration and then estimate the signal and update the residuals. In particular, at thekth iteration, a correlation matrix is computed and the data matrix is the residuals between X and its approximation.The concept of sparse representation theory, the mathematical model, and the breakthrough of sparse representation solution are introduced, based on which the proposed collaborative representation and the detailed solution process are presented. The advantages of collaborative representation are derived by comparing algorithms with different solving methods that have a unified theoretical basis. The multitask learning theory and the multitask joint sparse representation model combined with the sparse representation theory are introduced. Finally, the solution process of the joint orthogonal matching algorithm is described in detail.


### 3.2. Design and Analysis of Chinese Painting Image Classification System

Influenced by the five elements of yin and yang, Buddhism, Taoism, Confucianism, and other cultures, Chinese painting is not only black and white and gray; it also includes certain color components, such as the heavy color paintings and murals of the Tang Dynasty, which are outstanding representatives [20–23]. According to statistics, traditional Chinese paintings use as many as 60 or 70 types of pigments, mainly taken from plants, and many modern painters have a richer use of color. Therefore, the classification and recognition of Chinese paintings cannot ignore the color features, but most current researchers focus on the study of texture features for the classification and recognition of Chinese paintings, and few researchers have conducted relevant studies on the color features of Chinese paintings. The image weighted chunking method is a simple and effective method, which firstly chunks the image, then extracts the color features for each small chunk, and finally fuses the color features of each chunk by different weight assignments. It can make up for the lack of spatial information of image color features and can classify and recognize images more effectively by using color features. In the paper, the image is chunked, and then the color features of the image are extracted; that is, the value of its color moment is calculated, which can compensate for the shortcoming of the color moment for the lack of spatial information description of the image. The result of extracting color features of images is more accurate.Every painter already has a primary color before painting, and this primary color is related to the content of the painting; for example, landscape painting will be dominated by lime green, while flower and bird painting will be dominated by green and red, and figure painting will be mostly pink and white, jade. Therefore, the color characteristic of Chinese paintings is also an indispensable feature in the classification and identification of Chinese paintings. Based on the ideas of mixed color space and image chunking explained in the previous subsection, this paper proposes a chunking color feature extraction algorithm based on mixed color space and uses the algorithm to extract color features of Chinese painting images. This subsection will address the algorithm in detail.For the feature fusion of mixed color space, a weighted fusion is adopted, and the specific weight assignment is decided according to the contribution rate of different color spaces for the classification and recognition of Chinese painting images. The accuracy rate of Chinese painting image recognition is obtained by extracting the chunked color moment features of the image under different color spaces, respectively, according to the first, and using the color moments of this color space to classify and recognize the Chinese painting images, as shown in Table1.Table 1
Checking rate in different color spaces.
CategoryLuminance-bandwidth-chrominance (YUV)Hue saturation intensity (HIS)Hue saturation value (HSV)Landscape painting2333.58.2Flower and bird painting10.224.85.5Figure painting27.48.624.9Bamboo painting6.717.720.2Pommel horse painting6.4815.8Average value25.228.811Finally, the average values of the three color space check rates are normalized to determine the corresponding weights of the three color spaces as 0.314, 0.342, and 0.344, respectively. Using the obtained weight values, the corresponding order moments of the corresponding components of the three color spaces are weighted and fused to obtain the color moments of the mixed color space. The specific feature fusion flow chart is shown in Figure2.Figure 2
Feature fusion block flow chart.The feature extraction module input is one pair of images after another, which uses the improved ResNeXt101 network for image feature learning, and then, after a maximum pooling layer, a 2048-dimensional image feature can be obtained through a fully connected layer; secondly, the second step word embedding vector is input to the first layer of the graph convolutional network, and the label is output after the stacking of layer after layer of the graph convolutional network feature classifier, which is a collection of label pairs with multiple label association relations; each element of the collection is a combination of labels, and a label may have many combination relations in it. Finally, the dot product process refers to the process of doing fast matching between the image features and the elements in the classifier. Based on the case of the image features and each element in the classifier, the one with the highest correlation is output, which is the multilabel classification result of the image, and then the judgment is done with the original labels of the dataset to achieve both the accuracy and error rate of image classification. As shown in Figure3, the process of the dot product is represented: the left side of the figure shows an instance of an image feature that is continuously matched in the classifier and matched to the set of labels with high relevance as the final label classification result for that image feature. Its main idea is to use moments to represent the distribution of various colors in an image, and then use the statistical parameters of different color components as parameters. The low-order moments concentrate the main information of the color distribution, second- and third-order moments of color, and the higher-order moments hardly contain color information. Among them, the first-order moment can indicate the overall overview of the image, that is, mean information; the second-order moment can indicate the change in image details, that is, variance information; the third-order moment can indicate the slope information of the image.Figure 3
Schematic diagram of the dot product process.To verify the effectiveness and feasibility of the algorithm for classification and recognition of Chinese paintings, 600 paintings of different dynasties and categories were randomly selected from Chinese painting websites to form another database of Chinese paintings, including 126 bird paintings, 123 landscape paintings, 114 figure paintings, 118 bamboo paintings, and 119 horse and saddle paintings. The remaining paintings include 96 bird paintings, 93 landscape paintings, 84 figure paintings, 88 bamboo paintings, and 89 horse and saddle paintings. The color features of the Chinese painting images were extracted in HSV, HIS, YUV, and mixed color space, respectively, where the mixed color space was divided into two directions, blocked and unblocked, when extracting the color features of the images. Then, the grayscale cogeneration matrix feature parameters of the Chinese painting image are calculated as texture features, and they are stitched with the 9 color features to obtain the final 13 hybrid feature vectors characterizing the Chinese painting image. Finally, the vectors are used for the classification recognition of Chinese paintings.After the feature fusion of the low-frequency feature extraction results and the globally extracted features, since the low-frequency features are extracted twice, it is equivalent to increasing the training weights of the low-frequency words in the weights. The algorithm in this paper uses the SGD algorithm as the optimization algorithm, the decay of weights is set to 0.005, and the initial learning rate (LR) is also set to 0.1. During the training process, the learning rate is also dynamically reduced according to the loss of the validation set, and the learning rate of the dataset is dynamically reduced by a factor of 10 every 5 epochs. The algorithm in this section and the two models extracted using the ResNeXt101 network in Section 4 are trained 100 times, then the highest and lowest word frequencies are removed and averaged, and several low-frequency labels are selected for comparison. The accuracy of the current solution is very high, but the efficiency is not very good.


## 3.1. Multitask Joint Sparse Representation Algorithm

Sparse representation (SR) is a signal consisting of few nonzero elements in a smaller vector space. Due to its ability to represent high-dimensional data, SR has become an unavoidable feature extraction concept, and it is a signal sampling technique used to compress images. The process of sparse representation can be thought of as projecting the target signal into a space consisting of a set of nonorthogonal bases, and the coefficients projected on each base are sparsely coded. The term “sparse” conveys the idea that only individual numbers are zero or differ significantly from zero in the coefficients obtained by using a dictionary to represent the information. Thus, it can be stated briefly that the important information of the signal can be expressed with few nonzero elements and that it is easier to solve in this way [18]. From a mathematical point of view, a sparse representation is a multidimensional data representation. As represented in Figure 1 it is the small number of atoms in the matrix D that can be used to represent the signal y by a linear combination.Figure 1
Diagram of the joint sparse representation model for sparse multitasking.The model is linearly expressed as(1)Y=MX.Since the image is usually noisy, (1) can be rewritten as(2)Y=MX+D,where z is the noise. Equation (1) is an underdetermined linear equation, by which it is impossible to obtain a unique representation of the input signal y on the dictionary D. Therefore, in obtaining the sparse representation, it is necessary to constrain other coefficients by imposing constraints on the coefficient x. The sparser the coefficients x are, the easier it is to accurately predict the class labels of the input signal y. This motivates us to find the sparsest solution. The following optimization problem can solve the coefficients. In (3), we generally adopt the method of controlling variables to determine(3)G=argminfEyfx−y2,L=1−aLmse+aLKL.It refers to the number of nonzero elements of a vector and is also used to control the strength of the sparse model.x does not have an exact sparse representation, but it can be represented in such a way as to ensure that the result is as close as possible to the original signal y. There is a different form of the sparse representation of the model that uses Lagrange multipliers to combine two constraints into one inequality:(4)kj|i=exp−xi−xi¯2/2σi2∑k≠iexp−xi−xi¯2/2σi2.However, in practice, finding the sparsest solution of the L0 parametrization is an NP-hard problem. In such cases, the test samples presumably cannot be sparsely represented as a linear combination of the training samples. Several studies have shown that when the solution is sparse and when the signal and the dictionary satisfy certain conditions, it is possible to constrain the L1 parametrization instead of the L0 parametrization and then approximate the sparse solution by solving for a stable solution of the L1 parametrization that minimizes the sparse solution; then, the sparse representation model based on the L1 parametrization has the following formulation:(5)L1=exp−xi−yj¯2/2σi2∑k≠iexp−xi−xi¯2/2σi2,L2=exp−xi−yj¯2/2σi2∑k≠iexp−xi−yi¯2/2σi2,L0=exp−xi−zj¯2/2σi2∑k≠iexp−xi−zi¯2/2σi2.The delta_i is the gradient at positioni. In sparse representation, the construction of dictionaries has been a key aspect of sparse representation, which directly affects whether sparse representation can be performed efficiently. The dictionary atoms must satisfy two requirements: first, they need to form the entire M-dimensional space and thus can represent the original signal linearly; second, the individual dictionary atoms are linearly independent [19]. Therefore, how to construct the dictionary is one of the key research problems in sparse representation theory, and no matter how to construct the dictionary, the goal is to make the dictionary itself contain more and more rich information, and different signals can be represented adaptively.At present, the construction of dictionaries is divided into three categories: directly using the original training samples as dictionaries, analyzing dictionaries, and learning dictionaries. The method of using original training samples to form dictionaries is simpler, but the dictionary capacity increases with the number of training samples or categories, which makes the computational burden increase and the efficiency decrease, and the redundant information cannot be effectively expressed for the original signal, thus leading to the decrease of detection accuracy. Analytical dictionaries refer to the dictionaries obtained by using certain mathematical models. Frequently used analytical dictionaries are wavelet dictionaries, Fourier transforms dictionaries, and discrete cosine transform dictionaries (DCT dictionaries). The advantage of this dictionary is that the principle is simple and easy to implement, but it also has the disadvantage that its representation of the signal is too homogeneous and does not have self-adaptability. When facing complex remote sensing images, the dictionary is not flexible enough to adapt to sample changes and cannot accurately represent the sparse features of the images, and then the analytical dictionary is not a suitable choice. Learning dictionaries, i.e., dictionaries obtained by training and learning a large amount of data similar to the target data, in contrast, are more practical than analytic dictionaries. The dictionaries obtained by learning are morphologically rich, with the structured, discriminative ability and better flexibility to better adapt to different image data and obtain sparser representations. We are discussing Chinese paintings, but the drawings are all similar, so our algorithm can be used for other types of paintings as well.Multitask learning (MTL) is an approach to inductive transfer that can ensure that related tasks learn from each other by using the information contained in the training signals of the related tasks and makes the inductive transfer approach effective. It does this by learning tasks in parallel using a shared representation, allowing what each task learns to better help learn other tasks. One type of construction is the construction of multiple tasks with commonality. Multiple tasks can be constructed in various ways, which may depend on the particular application. Another key technique is the correlation analysis of multiple tasks. Tasks can be correlated in various ways. There are two common approaches: tasks can be related by assuming that all learned functions are close to each other in some specification, and tasks can also be related to each other because they all share a base representation. For the first type of task correlation, the typical approach is a linear regression function. For the second type of task correlation, there are some widely used representations, such as sparsity.In multitask learning, multiple tasks with similarity can be solved, and a linear representation model can be constructed for the sparse representation of each task, while information can be shared among different tasks with similarity, thus effectively utilizing the potential information between different tasks and improving the accuracy of recognition, thus constructing a multitask sparse representation model:(6)Mr=limΔr⟶0r+Δrn−rnΔr.The traditional multitask sparse model only considers the features of each pixel itself and ignores the spatial correlation between neighboring pixels. In remote sensing images, neighboring pixels usually belong to the same material. Therefore, the image pixels in a small spatial neighborhood are highly similar and have many similarities. By the same token, these near-neighbor pixels can be represented simultaneously and have similar structures. The spatial information can also be combined in the same way in the framework of a multitask sparse representation model.According to the principle of joint sparse representation, when adjacent pixels are sparsely represented at the same time, the sparse coefficient can easily solve the following optimization problems:(7)Fr=∫0Tprdr=rn.Two constraints need to be considered here: the first constraint is the assumption that similar pixels are approximately distributed in the same low-dimensional subspace that also consists of the same class of training samples; the second constraint is the assumption that the nearest neighbor pixels have the same low-dimensional subspace domain. Here, the constraint of joint sparsity across different tasks can provide other useful information for the classification problem because different tasks may support different sparse representation coefficients, and joint sparsity may enhance the robustness of coefficient estimation. The joint orthogonal match-tracking method is a generalization of the orthogonal match-tracking algorithm under the L2 parametric model, and its basic idea is to select the atom that simultaneously produces the best approximation to all residual vectors in each iteration and then estimate the signal and update the residuals. In particular, at thekth iteration, a correlation matrix is computed and the data matrix is the residuals between X and its approximation.The concept of sparse representation theory, the mathematical model, and the breakthrough of sparse representation solution are introduced, based on which the proposed collaborative representation and the detailed solution process are presented. The advantages of collaborative representation are derived by comparing algorithms with different solving methods that have a unified theoretical basis. The multitask learning theory and the multitask joint sparse representation model combined with the sparse representation theory are introduced. Finally, the solution process of the joint orthogonal matching algorithm is described in detail.


## 3.2. Design and Analysis of Chinese Painting Image Classification System

Influenced by the five elements of yin and yang, Buddhism, Taoism, Confucianism, and other cultures, Chinese painting is not only black and white and gray; it also includes certain color components, such as the heavy color paintings and murals of the Tang Dynasty, which are outstanding representatives [20–23]. According to statistics, traditional Chinese paintings use as many as 60 or 70 types of pigments, mainly taken from plants, and many modern painters have a richer use of color. Therefore, the classification and recognition of Chinese paintings cannot ignore the color features, but most current researchers focus on the study of texture features for the classification and recognition of Chinese paintings, and few researchers have conducted relevant studies on the color features of Chinese paintings. The image weighted chunking method is a simple and effective method, which firstly chunks the image, then extracts the color features for each small chunk, and finally fuses the color features of each chunk by different weight assignments. It can make up for the lack of spatial information of image color features and can classify and recognize images more effectively by using color features. In the paper, the image is chunked, and then the color features of the image are extracted; that is, the value of its color moment is calculated, which can compensate for the shortcoming of the color moment for the lack of spatial information description of the image. The result of extracting color features of images is more accurate.Every painter already has a primary color before painting, and this primary color is related to the content of the painting; for example, landscape painting will be dominated by lime green, while flower and bird painting will be dominated by green and red, and figure painting will be mostly pink and white, jade. Therefore, the color characteristic of Chinese paintings is also an indispensable feature in the classification and identification of Chinese paintings. Based on the ideas of mixed color space and image chunking explained in the previous subsection, this paper proposes a chunking color feature extraction algorithm based on mixed color space and uses the algorithm to extract color features of Chinese painting images. This subsection will address the algorithm in detail.For the feature fusion of mixed color space, a weighted fusion is adopted, and the specific weight assignment is decided according to the contribution rate of different color spaces for the classification and recognition of Chinese painting images. The accuracy rate of Chinese painting image recognition is obtained by extracting the chunked color moment features of the image under different color spaces, respectively, according to the first, and using the color moments of this color space to classify and recognize the Chinese painting images, as shown in Table1.Table 1
Checking rate in different color spaces.
CategoryLuminance-bandwidth-chrominance (YUV)Hue saturation intensity (HIS)Hue saturation value (HSV)Landscape painting2333.58.2Flower and bird painting10.224.85.5Figure painting27.48.624.9Bamboo painting6.717.720.2Pommel horse painting6.4815.8Average value25.228.811Finally, the average values of the three color space check rates are normalized to determine the corresponding weights of the three color spaces as 0.314, 0.342, and 0.344, respectively. Using the obtained weight values, the corresponding order moments of the corresponding components of the three color spaces are weighted and fused to obtain the color moments of the mixed color space. The specific feature fusion flow chart is shown in Figure2.Figure 2
Feature fusion block flow chart.The feature extraction module input is one pair of images after another, which uses the improved ResNeXt101 network for image feature learning, and then, after a maximum pooling layer, a 2048-dimensional image feature can be obtained through a fully connected layer; secondly, the second step word embedding vector is input to the first layer of the graph convolutional network, and the label is output after the stacking of layer after layer of the graph convolutional network feature classifier, which is a collection of label pairs with multiple label association relations; each element of the collection is a combination of labels, and a label may have many combination relations in it. Finally, the dot product process refers to the process of doing fast matching between the image features and the elements in the classifier. Based on the case of the image features and each element in the classifier, the one with the highest correlation is output, which is the multilabel classification result of the image, and then the judgment is done with the original labels of the dataset to achieve both the accuracy and error rate of image classification. As shown in Figure3, the process of the dot product is represented: the left side of the figure shows an instance of an image feature that is continuously matched in the classifier and matched to the set of labels with high relevance as the final label classification result for that image feature. Its main idea is to use moments to represent the distribution of various colors in an image, and then use the statistical parameters of different color components as parameters. The low-order moments concentrate the main information of the color distribution, second- and third-order moments of color, and the higher-order moments hardly contain color information. Among them, the first-order moment can indicate the overall overview of the image, that is, mean information; the second-order moment can indicate the change in image details, that is, variance information; the third-order moment can indicate the slope information of the image.Figure 3
Schematic diagram of the dot product process.To verify the effectiveness and feasibility of the algorithm for classification and recognition of Chinese paintings, 600 paintings of different dynasties and categories were randomly selected from Chinese painting websites to form another database of Chinese paintings, including 126 bird paintings, 123 landscape paintings, 114 figure paintings, 118 bamboo paintings, and 119 horse and saddle paintings. The remaining paintings include 96 bird paintings, 93 landscape paintings, 84 figure paintings, 88 bamboo paintings, and 89 horse and saddle paintings. The color features of the Chinese painting images were extracted in HSV, HIS, YUV, and mixed color space, respectively, where the mixed color space was divided into two directions, blocked and unblocked, when extracting the color features of the images. Then, the grayscale cogeneration matrix feature parameters of the Chinese painting image are calculated as texture features, and they are stitched with the 9 color features to obtain the final 13 hybrid feature vectors characterizing the Chinese painting image. Finally, the vectors are used for the classification recognition of Chinese paintings.After the feature fusion of the low-frequency feature extraction results and the globally extracted features, since the low-frequency features are extracted twice, it is equivalent to increasing the training weights of the low-frequency words in the weights. The algorithm in this paper uses the SGD algorithm as the optimization algorithm, the decay of weights is set to 0.005, and the initial learning rate (LR) is also set to 0.1. During the training process, the learning rate is also dynamically reduced according to the loss of the validation set, and the learning rate of the dataset is dynamically reduced by a factor of 10 every 5 epochs. The algorithm in this section and the two models extracted using the ResNeXt101 network in Section 4 are trained 100 times, then the highest and lowest word frequencies are removed and averaged, and several low-frequency labels are selected for comparison. The accuracy of the current solution is very high, but the efficiency is not very good.


## 4. Analysis of Results

### 4.1. Analysis of Results of Joint Sparse Representation of Multitask

Figure4 shows the comparison of the accuracy of the ML-GCN algorithm and the two-channel improved ML-GCN algorithm on the PASCAL VOC2012 dataset before and after the improvement. From these two figures, it can be seen that the improved ML-GCN algorithm based on two channels is effective in improving the accuracy and completeness in image annotation, the accuracy OP of the improved ML-GCN algorithm based on two channels reaches 91.79%, and the completeness OR reaches 94.05%. Compared with the improved ML-GCN algorithm, the accuracy is improved by 1.61%, and the completeness is improved by 2.44%.Figure 4
Comparison of ML-GCN before and after improvement algorithm and two-channel improvement algorithm for checking accuracy values.
(a)(b)The average accuracy of the ML-GCN algorithm based on the two-channel improvement is shown in Figure4, where the horizontal coordinates indicate the number of training sessions and the vertical coordinates indicate the mAP values. The improved ML-GCN algorithm obtains the best mAP value after the 11th training, and the training stabilizes after that.Figure5 shows the change curves of loss during the training process of the three algorithms, compared with the two algorithms ML-GCN and improved ML-GCN; it can be seen that the improved algorithm after feature fusion can effectively reduce the loss and is effective in improving the image annotation performance. It can be seen that the accuracy of drapery-coronal Chinese painting images improves from 93.2% to 96.3%, the accuracy of hotspot Chinese painting images improves from 90.8% to 95.1%, and the accuracy of radiation-coronal Chinese painting images improves from 91.5% to 95.9%. All three types of Chinese painting images improved by about 3 to 4 percentage points each, while the arc-shaped Chinese painting images decreased from 97.6% to 97.2%, a difference of 0.4 percentage points, presumably due to the error in the experiment. Its average test accuracy improved from 94.20% before the network improvement to 96.54% after the network improvement, which indicates that the improved version of the densely connected network structure can indeed greatly improve the classification accuracy of Chinese painting images. The training accuracy of the network increases until it finally plateaus, while the training loss also decreases and finally stabilizes.Figure 5
Network training on 3000 epochs.Next, experiments were conducted on the 8001 Chinese painting image database and the 38044 Chinese painting image database with different ratios of 8 : 2, 2 : 1, 4 : 6, 2 : 8, and 1 : 9, respectively. The experimental results are shown in Figure6. From Figure 6, it can be seen that the training results of the network model are the best when the ratio of the training set to test set is 8 : 2, and the classification accuracy of Chinese paintings is the highest for both the 8001 Chinese painting image database and 38044 Chinese painting image database, which is indicated by the red line in the figure. When the ratio of training to testing data in the network model is 8 : 2, the average test accuracy of the 8001 Chinese painting image database is 96.54%, while the average accuracy of 38044 paintings is 98.99%.Figure 6
(a) 8001 database and (b) 38044 database.Because of the unique band structure of the arc-shaped Chinese painting images, which is clearer than the other shapes, and the relatively large amount of data, about two to five times more than the other categories, the classification accuracy of the arc-shaped Chinese painting images is the highest in both Figures6(a) and 6(b) at different scales. In contrast, the classification accuracy of hotspot Chinese painting images is lower, roughly due to its complex morphological structure and the fact that it has the least amount of data among the four categories of Chinese paintings due to its shortest appearance time, as shown in Figure 6.The comparison chart shows that the average accuracy rate of 38044 Chinese painting database is higher and the accuracy rate of each category is higher compared with the same proportion of 8001 Chinese painting database. This is because the 38044 Chinese painting database has a larger amount of data; it can provide richer data information and its Chinese painting image features are more expressive.


### 4.2. Classification Results of Chinese Painting Graphics

The experiments for classification and recognition of Chinese paintings are divided into two parts, the classification experiments based on the subject matter of Chinese paintings and the classification experiments based on the authors of Chinese paintings, and the databases are selected from the two databases described in Sections3 and 4. SVM is selected for training and classification of the Chinese painting database. The selection of SVM kernel functions and parameters is the same as in the first two sections. The judging criteria are the same as those in the first two sections, and the experimental effects are still evaluated according to the average completion rate, the average accuracy rate, and the average classification accuracy.The fusion method is used to fuse the chunked mixed color space color features with the multiscale grayscale coeval matrix texture features to generate a comprehensive feature vector, select the Chinese painting database described in Section3, and classify the Chinese painting database by author. The effect of this paper’s algorithm is compared with GLCM combined color moments, CGLCM combined color moments, and multiscale GLCM combined color moments for the classification and recognition of Chinese paintings. To keep the consistency of the evaluation criteria, the average accuracy rate and the average completeness rate are still selected as the evaluation criteria, and the experimental results are shown in Figure 7.Figure 7
Comparison of the average accuracy and average completeness of the original images.
(a)(b)(c)(d)From the data in Figure7, it can be seen that the combination of the two features in this paper is the most effective for the classification of Chinese paintings, the average detection rate is improved by 11%, and the average detection rate is improved by 13.3% compared with the GLCM combined with color moments. Compared with CGLCM combined with color moments, the average detection rate is improved by 8.9% and the average detection rate is improved by 10.4%. Compared with the multiscale GLCM combined color moments, the average accuracy is improved by 5.1%, and the average completeness is improved by 5.1%. To verify the improvement of the combined vectors for classification and recognition of works by different authors, the above table was converted into a bar chart, and the results are shown in Figure 8.Figure 8
Comparison of the average correct classification rate of integrated vector authors.From Figure8, it can be seen that the average classification accuracy of the integrated feature vector after the combination of the two algorithms in this paper also has a corresponding improvement for the paintings of Zhou Qingbo and Liu Haisu. This indicates that the integrated vector features can make up for the lack of single texture features in the classification recognition of modern painters’ colorful paintings and effectively improve the classification recognition of the Chinese painting database by the author. From the line graph, we can see that the decreasing slope of the algorithm combining the two features in this paper is slow compared with other combining methods; in particular, in the case where the mean square value of noise is 20 and 30, the recognition effect of GLCM combining color moments, CGLCM combining color moments, and multiscale GLCM combining color moments decreases rapidly. The algorithm of this paper can maintain a slow decreasing slope, which indicates that the combination of the two algorithms is more resistant to noise than the GLCM combined color moment, CGLCM combined color moment, and multiscale GLCM combined color moment algorithms.The time taken to classify Chinese paintings with the proposed composite feature vector of mixed color space chunked color features combined with texture features of multiscale grayscale cogeneration matrix is 11.2 s higher than other algorithms on average, but the average accuracy of classification recognition is significantly higher than other composite feature vectors. Therefore, the proposed integrated feature vector with the fusion of two features has significantly improved the recognition accuracy of Chinese paintings by subject matter at the expense of some time. The existing solutions have a higher accuracy rate, but compared to the previous solutions and preventions, the processing time will be relatively longer.The described texture features and the color features introduced in Section4 are fused to form hybrid features for the classification and recognition of Chinese paintings, and a large number of experiments are conducted to verify the effectiveness of the hybrid features used in this paper for the recognition of Chinese paintings. The final classification results show that the proposed hybrid features outperform the GLCM combined with traditional color moments, CGLCM combined with color moments, and multiscale GLCM combined with color moments algorithms in the classification and recognition of Chinese paintings in terms of average accuracy, average completeness, and average correct classification rate. Finally, the time consumed by the hybrid features proposed in this paper is counted. Although the running time of the algorithm with the integrated feature vector fused with the two features proposed in this paper is significantly higher than that of other algorithms, the recognition accuracy for the classification of Chinese paintings by subject matter is significantly improved at the expense of some time.


## 4.1. Analysis of Results of Joint Sparse Representation of Multitask

Figure4 shows the comparison of the accuracy of the ML-GCN algorithm and the two-channel improved ML-GCN algorithm on the PASCAL VOC2012 dataset before and after the improvement. From these two figures, it can be seen that the improved ML-GCN algorithm based on two channels is effective in improving the accuracy and completeness in image annotation, the accuracy OP of the improved ML-GCN algorithm based on two channels reaches 91.79%, and the completeness OR reaches 94.05%. Compared with the improved ML-GCN algorithm, the accuracy is improved by 1.61%, and the completeness is improved by 2.44%.Figure 4
Comparison of ML-GCN before and after improvement algorithm and two-channel improvement algorithm for checking accuracy values.
(a)(b)The average accuracy of the ML-GCN algorithm based on the two-channel improvement is shown in Figure4, where the horizontal coordinates indicate the number of training sessions and the vertical coordinates indicate the mAP values. The improved ML-GCN algorithm obtains the best mAP value after the 11th training, and the training stabilizes after that.Figure5 shows the change curves of loss during the training process of the three algorithms, compared with the two algorithms ML-GCN and improved ML-GCN; it can be seen that the improved algorithm after feature fusion can effectively reduce the loss and is effective in improving the image annotation performance. It can be seen that the accuracy of drapery-coronal Chinese painting images improves from 93.2% to 96.3%, the accuracy of hotspot Chinese painting images improves from 90.8% to 95.1%, and the accuracy of radiation-coronal Chinese painting images improves from 91.5% to 95.9%. All three types of Chinese painting images improved by about 3 to 4 percentage points each, while the arc-shaped Chinese painting images decreased from 97.6% to 97.2%, a difference of 0.4 percentage points, presumably due to the error in the experiment. Its average test accuracy improved from 94.20% before the network improvement to 96.54% after the network improvement, which indicates that the improved version of the densely connected network structure can indeed greatly improve the classification accuracy of Chinese painting images. The training accuracy of the network increases until it finally plateaus, while the training loss also decreases and finally stabilizes.Figure 5
Network training on 3000 epochs.Next, experiments were conducted on the 8001 Chinese painting image database and the 38044 Chinese painting image database with different ratios of 8 : 2, 2 : 1, 4 : 6, 2 : 8, and 1 : 9, respectively. The experimental results are shown in Figure6. From Figure 6, it can be seen that the training results of the network model are the best when the ratio of the training set to test set is 8 : 2, and the classification accuracy of Chinese paintings is the highest for both the 8001 Chinese painting image database and 38044 Chinese painting image database, which is indicated by the red line in the figure. When the ratio of training to testing data in the network model is 8 : 2, the average test accuracy of the 8001 Chinese painting image database is 96.54%, while the average accuracy of 38044 paintings is 98.99%.Figure 6
(a) 8001 database and (b) 38044 database.Because of the unique band structure of the arc-shaped Chinese painting images, which is clearer than the other shapes, and the relatively large amount of data, about two to five times more than the other categories, the classification accuracy of the arc-shaped Chinese painting images is the highest in both Figures6(a) and 6(b) at different scales. In contrast, the classification accuracy of hotspot Chinese painting images is lower, roughly due to its complex morphological structure and the fact that it has the least amount of data among the four categories of Chinese paintings due to its shortest appearance time, as shown in Figure 6.The comparison chart shows that the average accuracy rate of 38044 Chinese painting database is higher and the accuracy rate of each category is higher compared with the same proportion of 8001 Chinese painting database. This is because the 38044 Chinese painting database has a larger amount of data; it can provide richer data information and its Chinese painting image features are more expressive.


## 4.2. Classification Results of Chinese Painting Graphics

The experiments for classification and recognition of Chinese paintings are divided into two parts, the classification experiments based on the subject matter of Chinese paintings and the classification experiments based on the authors of Chinese paintings, and the databases are selected from the two databases described in Sections3 and 4. SVM is selected for training and classification of the Chinese painting database. The selection of SVM kernel functions and parameters is the same as in the first two sections. The judging criteria are the same as those in the first two sections, and the experimental effects are still evaluated according to the average completion rate, the average accuracy rate, and the average classification accuracy.The fusion method is used to fuse the chunked mixed color space color features with the multiscale grayscale coeval matrix texture features to generate a comprehensive feature vector, select the Chinese painting database described in Section3, and classify the Chinese painting database by author. The effect of this paper’s algorithm is compared with GLCM combined color moments, CGLCM combined color moments, and multiscale GLCM combined color moments for the classification and recognition of Chinese paintings. To keep the consistency of the evaluation criteria, the average accuracy rate and the average completeness rate are still selected as the evaluation criteria, and the experimental results are shown in Figure 7.Figure 7
Comparison of the average accuracy and average completeness of the original images.
(a)(b)(c)(d)From the data in Figure7, it can be seen that the combination of the two features in this paper is the most effective for the classification of Chinese paintings, the average detection rate is improved by 11%, and the average detection rate is improved by 13.3% compared with the GLCM combined with color moments. Compared with CGLCM combined with color moments, the average detection rate is improved by 8.9% and the average detection rate is improved by 10.4%. Compared with the multiscale GLCM combined color moments, the average accuracy is improved by 5.1%, and the average completeness is improved by 5.1%. To verify the improvement of the combined vectors for classification and recognition of works by different authors, the above table was converted into a bar chart, and the results are shown in Figure 8.Figure 8
Comparison of the average correct classification rate of integrated vector authors.From Figure8, it can be seen that the average classification accuracy of the integrated feature vector after the combination of the two algorithms in this paper also has a corresponding improvement for the paintings of Zhou Qingbo and Liu Haisu. This indicates that the integrated vector features can make up for the lack of single texture features in the classification recognition of modern painters’ colorful paintings and effectively improve the classification recognition of the Chinese painting database by the author. From the line graph, we can see that the decreasing slope of the algorithm combining the two features in this paper is slow compared with other combining methods; in particular, in the case where the mean square value of noise is 20 and 30, the recognition effect of GLCM combining color moments, CGLCM combining color moments, and multiscale GLCM combining color moments decreases rapidly. The algorithm of this paper can maintain a slow decreasing slope, which indicates that the combination of the two algorithms is more resistant to noise than the GLCM combined color moment, CGLCM combined color moment, and multiscale GLCM combined color moment algorithms.The time taken to classify Chinese paintings with the proposed composite feature vector of mixed color space chunked color features combined with texture features of multiscale grayscale cogeneration matrix is 11.2 s higher than other algorithms on average, but the average accuracy of classification recognition is significantly higher than other composite feature vectors. Therefore, the proposed integrated feature vector with the fusion of two features has significantly improved the recognition accuracy of Chinese paintings by subject matter at the expense of some time. The existing solutions have a higher accuracy rate, but compared to the previous solutions and preventions, the processing time will be relatively longer.The described texture features and the color features introduced in Section4 are fused to form hybrid features for the classification and recognition of Chinese paintings, and a large number of experiments are conducted to verify the effectiveness of the hybrid features used in this paper for the recognition of Chinese paintings. The final classification results show that the proposed hybrid features outperform the GLCM combined with traditional color moments, CGLCM combined with color moments, and multiscale GLCM combined with color moments algorithms in the classification and recognition of Chinese paintings in terms of average accuracy, average completeness, and average correct classification rate. Finally, the time consumed by the hybrid features proposed in this paper is counted. Although the running time of the algorithm with the integrated feature vector fused with the two features proposed in this paper is significantly higher than that of other algorithms, the recognition accuracy for the classification of Chinese paintings by subject matter is significantly improved at the expense of some time.


## 5. Conclusion

This paper gives a relevant description of the research significance and the purpose of the research on feature extraction algorithm and classification recognition of Chinese paintings. The theoretical knowledge related to feature extraction of images is elaborated, including several algorithms for texture feature extraction and several algorithms commonly used for color feature extraction; the image classification and recognition process is briefly outlined; and the methods of image classification and recognition are explained. For unimportant targets and unfocused target distribution occlusion problems in complex backgrounds, we only use the attention mechanism of local correlation between image regions in image single-label classification. In this paper, we propose an improved ML-GCN-based image auto-labeling algorithm based on the ML-GCN network model, using the dependency between multiple labels. Based on the above proposed two feature extraction algorithms, the feature fusion is performed and the classification recognition of national paintings is experimentally verified using the integrated feature vector. It is proved that the proposed hybrid feature vector has a good effect on the classification recognition of Chinese paintings. Finally, the time consumed for the classification recognition of Chinese paintings according to the subject matter is counted, and although the algorithm of the proposed two-feature fusion of the integrated feature vector in the paper consumes more time than other algorithms, its recognition accuracy has been significantly improved.



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*Source: 5546338-2021-03-25.xml*