- Research
- Open Access
Projective complex matrix factorization for facial expression recognition
- Viet-Hang Duong^{1},
- Yuan-Shan Lee^{1},
- Jian-Jiun Ding^{2},
- Bach-Tung Pham^{1},
- Manh-Quan Bui^{1},
- Pham The Bao^{2} and
- Jia-Ching Wang^{1, 3}Email author
https://doi.org/10.1186/s13634-017-0521-9
© The Author(s). 2018
Received: 28 June 2017
Accepted: 11 December 2017
Published: 2 February 2018
Abstract
In this paper, a dimensionality reduction method applied on facial expression recognition is investigated. An unsupervised learning framework, projective complex matrix factorization (proCMF), is introduced to project high-dimensional input facial images into a lower dimension subspace. The proCMF model is related to both the conventional projective nonnegative matrix factorization (proNMF) and the cosine dissimilarity metric in the simple manner by transforming real data into the complex domain. A projective matrix is then found through solving an unconstraint complex optimization problem. The gradient descent method was utilized to optimize a complex cost function. Extensive experiments carried on the extended Cohn-Kanade and the JAFFE databases show that the proposed proCMF model provides even better performance than state-of-the-art methods for facial expression recognition.
Keywords
1 Introduction
Facial expression recognition (FER) plays an important role in many applications related to computer vision and pattern recognition, such as human computer interface, surveillance, and multimedia [1–5]. Intensive techniques have been proposed for FER problem [6–14]. Much attention is put on the facial action coding system (FACS) approach which attempts to decompose facial expressions into varied action units and facial expression could be recognized based on the mixture of action units [6, 7]. A new perspective of using deep neural networks [8–11] to extract powerful temporal features hidden in facial images is also an interesting approach for FER, in particular for dynamic facial expression recognition. The dimensionality reduction technique that reduces the size of the feature space has been widely utilized because of its effectiveness on feature representation [12–14]. It is known that the changes of local appearance (e.g., eyes, nose, mouth) are usually related to facial expression variations; meanwhile, the global features that are related to the whole facial image may fail on expression analysis. Local facial components contain more discriminative information and outperform global features for face recognition [15]. A nonholistic representation and a low rank approximation of the data make better performance for an FER system [16].
Nonnegative matrix factorization (NMF) [12, 13] is among the most popular dimensionality reduction methods by its natural part-based representation ability. NMF decomposes the high-dimensional nonnegative data matrix into two low-rank nonnegative matrices with additional non-negativity constraints. Most NMF techniques estimate the linear subspace of the given data by the square of the Euclidean distance or the generalized Kullback-Leibler divergence. They work well when image noise is independent and identically distributed. However, for the data corrupted by outliers, the estimated subspace can be arbitrarily biased [17]. To overcome this drawback, researchers improved NMF in different distance metrics. Specifically, D. Kong et al. proposed a robust NMF by using L_{2} and L_{1} norms, where the noise was assumed to follow the Laplacian distribution [18]. Similarly, Earth Mover’s distance (EMD) and the Manhattan distance were also suggested in the work of Sandler et al. [19] and N. Guan et al. [20], respectively.
Besides, integrating constraints or using different metrics to modify the structure is also another attractive strategy to extend NMF. Starting from the ideas of SVD and NMF, for instance, Yuan et al. proposed a novel method called projective nonnegative matrix factorization (proNMF) [21]. Instead of operating two parameter matrices as NMF, there is only one computed matrix in proNMF. The coefficient matrix is replaced by the inner product of the base and the input matrix. As a result, there exists much fewer free-learned parameters. Furthermore, inspite of having no any extra regularization term, proNMF is still able to learn more spatially localized and part-based representations of visual patterns.
Recently, many FER algorithms have adopted NMF. Buciu and Pitas employed NMF for FER by enforcing local constraints to create a local NMF (LMF) model [22]. Nikitidis et al. incorporated discriminant constraints to build the supervised NMF learning method [23, 24]. Based on clustering-based discriminant analysis (CDA), the algorithm in [25] efficiently decomposes the provided data to discriminant parts and successfully extended the well-known NMF to subclass discriminant NMF (SDNMF). R. Zhi et al. [26] provided another extended NMF which imposed both sparse constraints on the basis matrix and graph-preserving criterions to improve the classification performance. Interpreting expressive images into two subspaces including the identity subspace and the expression subspace was a new model investigated in dual subspace nonnegative matrix factorization (DSNMF) [27] and dual subspace nonnegative graph embedding [28]. It can be seen that, in order to extract representative expression facial features, most existing algorithms tried to integrate label information via different constraints to derive supervised NMF. Therefore, the overall performance highly depends on the expression label which is insufficient to characterize data by the variations of pose, illumination, etc.
How to develop an unsupervised learning algorithm that performs efficiently FER was aimed in this paper. Encouraged by the localized and part-based representations of proNMF as well as the challenges on choosing a suitable metric that quantifies the approximation error in the NMF model, we proposed a new dimensionality reduction approach, named projective complex matrix factorization (proCMF). The proCMF model attempts to learn the localized basis that highlights the salient features of facial expressions; meanwhile, the reconstruction error affected by outliers was also minimized as much as possible. Moreover, the underlying intrinsic cosine dissimilarity referenced from the equivalence between two different metrics is also exploited. We also adopt a cosine-based distance measure to define an explicit mapping function from the space of pixel intensity into a high-dimensional sphere where complex projection is performed. The Euler formula was used for constructing isomorphism mapping from the real space to the complex space. In this context, the cosine dissimilarity for approximating real data was replaced by the Frobenius norm to evaluate the reconstruction error of complex approximation. After transforming the real data into the complex field, the obtained complex matrix was approximately factorized into a product of two low-rank matrices through an unconstraint complex optimization problem. The proposed method addresses the general problem of finding projections that enhance class separability without attached label information in the reduced dimensional space. There is no any extra regularization term in the objective functions that reduce the complication on solving the optimization problem. Furthermore, the representation of newly coming samples in the FER framework by using only the trained projection matrix is one of the important factors on decreasing the computational complexity.
In summary, the contributions of this paper are shown as follows.
First, we construct a new dimensionality reduction model for learning low rank projection in the complex domain. The adoption of cosine dissimilarity and the Frobenius norm significantly enhance the performance of the FER system.
Second, proCMF can be performed without limiting the sign of data. Our proposed method can be applied to both negative and positive data, which yields extension on real-world applications. Therefore, several operations that can extract complex features, such as the short-time Fourier transform, are going to be utilized directly instead of their absolute values (magnitude/power spectrogram) on sound processing.
To satisfy nonnegative requirement, NMF usually uses various strategies on minimizing a function, which leads to computational complexity. On the contrary, the significant superiority compared to NMF approaches of the proposed proCMF is to construct an unconstraint optimization problem that simplified the framework of extracting the basis and intrinsic features.
The rest of this paper is organized as follows. In Section 2, we recall some basic facts about proNMF. The motivation, formulation, and algorithms of the proposed model as well as its optimal solution are presented in Section 3. Some optimization techniques and computation methods are also described in this section. The convincing experimental results of the proposed approach on FER are depicted in Section 4. Finally, conclusion and future work are drawn in Section 5.
2 Projective nonnegative matrix factorization
3 Projective complex matrix factorization
3.1 Observations on cosine dissimilarity
It can be seen that, if I_{1} ≈ I_{2}, e.g., ∀c, x_{1}(c) − x_{2}(c) ≈ 0, then d(Z(x_{1}), Z(x_{2})) → 0. This implies that if the two images are unrelated, then their local elements are unmatched.
Therefore, the cosine dissimilarity of a data pair in the input real space equals to the Frobenious distance of the corresponding data pair in the complex domain. It is known that the robustness of cosine dissimilarity in the real domain has been found to suppress outliers [32]. With the idea of utilizing different robust similarity metrics to extend NMF, we introduce a new dimensionality reduction method (proCMF) which relates to conventional proNMF and uses the cosine dissimilarity metric as a measurement of the reconstruction error. However, the complexity of optimizing the real function with the cosine distance is wisely addressed by converting to a complex optimization problem with the Frobenius norm which is described in the next sections.
3.2 Problem formulation
In this section, we formulate the problem of multi-variants data factorization within the framework of complex data decomposition. Given the sample dataset X = [x_{1}, x_{2}, …, x_{ M }], x_{ i } ∈ ℝ^{ N }, we convert the real data matrix X ∈ ℝ^{N × M} to a complex matrix Z ∈ ℂ^{N × M} by the mapping (8) and perform matrix factorization in this complex feature space.
3.3 Complex-valued gradient decent method
It can be seen that (10) is a nonconvex minimization problem with respect to both variables W and V. Therefore, they are impractical to obtain the optimal solution. This NP-hard problem can be tackled by applying the block coordinate descent (BCD) with two matrix blocks [33] to obtain a local solution by the following scheme:
Let V = Re(V) + iIm(V) where i is the imaginary unit and i^{2} = − 1. Then, f(V) can be viewed as a real bivariate function of its real and imaginary components.
4 Experiments
We evaluated the proposed proCMF on FER. The classification capability of the derived encoding coefficient vectors was compared with various NMF-based methods.
Here, the minimization of the objective function \( \frac{1}{2}{\left\Vert {\mathbf{Z}}_{tr}-{\mathbf{W}}_{tr}{\mathbf{V}}_{tr}{\mathbf{Z}}_{tr}\right\Vert}^2 \) of proCMF was operated on the training phase that extracts new feature H_{ tr }=V_{ tr }Z_{ tr } from the image training set Z_{ tr }. After creating a projection matrix V_{ tr }, for each new testing sample z_{ te } in a query face image Z_{ te }, we can easily obtain its corresponding projection h_{ te } such that h_{ te }=V_{ tr }z_{ te }. To make a decision about the facial expression class, the projected expression representation h_{ te } will be fed to the nearest neighbor classifier. Then, the Euclidean distance between h_{ te } and each training datum of H_{ tr } is computed. The tested image is assigned to the class with the closest training datum.
4.1 Data description
The proposed algorithm is tested on two well-known datasets, the extended Cohn-Kanade (CK+) [38] and the Japanese Female Facial Expression (JAFFE) [39] datasets of six “basic” facial expressions (happiness, sadness, surprise, anger, disgust, and fear).
Each cropped facial image in the datasets was isotropically scaled to the fixed size of 32 × 32 pixels.
4.2 Baselines and experiment settings
The proposed algorithm is compared to the following popular PCA and NMF algorithms: (1) basic NMF [4]; (2) projective NMF (proNMF) [9]; (3) convex NMF (conNMF) [40]; (4) weighted NMF (weiNMF), which assigns binary weights to the data matrix [41]; (5) NeNMF, which applies efficient Nesterov’s optimal gradient method in the optimization process [42]; (6) principal component analysis (PCA) [43]; (7) graph preserving sparse nonnegative matrix factorization (GSNMF) [26]; (8)(9) unsupervised and supervised robust nonnegative graph embedding (uRNGE) and (sRNGE), which are robust nonnegative graph embedding methods that replace the L_{2}-norm with the L_{21}-norm [44, 45]; and (10)(11) unsupervised and supervised robust semi-nonnegative graph embedding (usRNGE) and (ssRNGE), which are robust semi-nonnegative graph embedding methods that impose no constraint on the base matrix [44].
In the implementation of the complex valued conjugate gradient decent method with the Amijo rule (CGD), we set the decreasing rate of the step size μ to satisfy (19) with the sufficient decreasing condition at 0.01 and the stopping criteria of 10,000 times of iterations or that the error ε is smaller than 10^{−4}.
4.3 Visualization of learned basis components and reconstructed images
4.4 Facial expression recognition on CK+ dataset
Facial expression recognition rate (%) using the CK+ dataset with different subspace dimensionalities (case 1: no. training = 1)
No. base | proCMF | NMF | proNMF | conNMF | weiNMF | NeNMF | PCA | GSNMF | uRNGE | usRNGE | sRNGE | ssRNGE |
---|---|---|---|---|---|---|---|---|---|---|---|---|
20 | 94.86 | 85.41 | 73.78 | 41.28 | 85.06 | 94.30 | 66.94 | 95.60 | 30.87 | 32.35 | 48.82 | 87.00 |
30 | 96.09 | 90.99 | 78.74 | 58.99 | 91.07 | 89.30 | 78.93 | 96.69 | 40.93 | 71.97 | 56.84 | 92.98 |
40 | 96.55 | 93.88 | 82.21 | 73.55 | 94.17 | 90.27 | 80.99 | 96.01 | 45.37 | 92.65 | 62.54 | 94.34 |
50 | 97.02 | 94.50 | 84.84 | 80.27 | 94.75 | 91.80 | 86.78 | 96.71 | 51.94 | 93.18 | 66.94 | 95.08 |
60 | 97.02 | 95.06 | 83.66 | 87.40 | 94.92 | 92.34 | 88.02 | 96.57 | 55.45 | 94.88 | 72.44 | 95.31 |
70 | 97.21 | 95.18 | 85.31 | 90.42 | 95.62 | 93.31 | 89.05 | 96.71 | 55.19 | 95.25 | 73.45 | 94.77 |
80 | 97.21 | 95.93 | 85.89 | 91.57 | 95.58 | 93.27 | 91.12 | 96.84 | 60.29 | 94.70 | 75.12 | 94.65 |
90 | 97.29 | 95.95 | 86.53 | 92.42 | 95.87 | 93.26 | 91.53 | 96.82 | 62.46 | 94.74 | 77.87 | 94.30 |
100 | 97.15 | 96.03 | 88.55 | 92.03 | 95.62 | 94.17 | 91.53 | 96.86 | 78.60 | 94.65 | 78.99 | 93.68 |
Ave. | 96.71 | 93.66 | 83.28 | 78.66 | 93.63 | 92.45 | 84.99 | 96.54 | 53.46 | 84.93 | 68.11 | 93.57 |
Facial expression recognition rate (%) using the CK+ dataset with different subspace dimensionalities (case 2: no. training = 2)
No. base | proCMF | NMF | proNMF | conNMF | weiNMF | NeNMF | PCA | GSNMF | uRNGE | usRNGE | sRNGE | ssRNGE |
---|---|---|---|---|---|---|---|---|---|---|---|---|
20 | 96.78 | 84.44 | 77.25 | 29.37 | 84.49 | 94.75 | 72.73 | 98.04 | 28.95 | 78.18 | 41.74 | 91.76 |
30 | 97.99 | 91.38 | 80.83 | 41.85 | 91.32 | 94.08 | 78.24 | 98.26 | 35.65 | 87.19 | 53.28 | 96.69 |
40 | 98.40 | 94.55 | 81.30 | 53.83 | 94.60 | 94.41 | 85.67 | 98.71 | 42.56 | 95.43 | 61.18 | 97.02 |
50 | 98.57 | 96.03 | 85.32 | 65.37 | 95.15 | 94.52 | 90.36 | 98.54 | 47.77 | 97.33 | 66.39 | 97.66 |
60 | 98.68 | 97.02 | 84.54 | 76.78 | 96.47 | 94.38 | 92.56 | 96.36 | 51.93 | 98.07 | 70.39 | 97.93 |
70 | 98.76 | 96.70 | 86.39 | 82.26 | 97.11 | 93.72 | 92.84 | 95.65 | 54.66 | 98.29 | 70.74 | 97.91 |
80 | 98.59 | 97.91 | 87.47 | 86.28 | 97.66 | 94.21 | 93.94 | 97.74 | 59.26 | 98.21 | 74.74 | 98.18 |
90 | 98.76 | 97.88 | 86.89 | 89.84 | 97.49 | 94.16 | 95.32 | 98.21 | 66.25 | 98.29 | 74.68 | 98.15 |
100 | 98.79 | 97.85 | 87.99 | 92.78 | 97.47 | 93.28 | 95.87 | 98.21 | 70.74 | 98.29 | 74.35 | 98.24 |
Ave. | 98.37 | 94.86 | 84.22 | 68.71 | 94.64 | 94.17 | 88.61 | 97.75 | 50.86 | 94.36 | 65.28 | 97.06 |
Most of the algorithms tend to get higher recognition rates when the subspace dimension increases. NMF performs better than proNMF and conNMF but worse than weiNMF and NeNMF. As mentioned in Section 4.3, the facial bases extracted by proNMF are spatially localized and lack expression-related information. These small basis regions of proNMF are clearly not appropriate for facial expression discrimination and result in unsatisfactory performance. The eigenface approach PCA, a well-known framework for dimensionality reduction, just rated at 86.80% in average achievement. The supervised scheme of the NGE model herein is better than unsupervised ones in all cases, and no nonnegative constraint on the base matrix of semi-NMF has significant effect on FER. GSNMF and the proposed proCMF are superior to baseline methods. Their average performances are over 97% with the highest rate of 97.51% is achieved by the proposed proCMF algorithm.
4.5 Facial expression recognition on JAFFE dataset
Facial expression recognition rate (%) using the JAFFE dataset with different subspace dimensionalities (case 1: no. training = 1)
No. base | proCMF | NMF | proNMF | conNMF | weiNMF | NeNMF | PCA | GSNMF | uRNGE | usRNGE | sRNGE | ssRNGE |
---|---|---|---|---|---|---|---|---|---|---|---|---|
20 | 71.33 | 68.11 | 50.00 | 45.53 | 63.36 | 66.85 | 51.05 | 68.11 | 22.38 | 31.68 | 27.62 | 60.77 |
30 | 71.19 | 70.84 | 56.01 | 49.09 | 68.32 | 61.05 | 57.34 | 70.07 | 22.10 | 60.77 | 33.78 | 62.31 |
40 | 71.47 | 71.68 | 57.83 | 48.60 | 68.95 | 63.28 | 58.74 | 69.23 | 28.18 | 64.27 | 39.79 | 60.28 |
50 | 70.14 | 71.12 | 60.21 | 52.17 | 69.02 | 61.82 | 57.34 | 69.09 | 32.66 | 63.50 | 43.15 | 62.73 |
60 | 69.65 | 69.79 | 57.34 | 46.36 | 72.38 | 63.71 | 57.34 | 70.28 | 36.78 | 64.41 | 47.41 | 61.82 |
70 | 70.07 | 26.15 | 60.56 | 27.34 | 69.16 | 62.52 | 57.34 | 70.98 | 42.24 | 71.40 | 51.19 | 70.77 |
80 | 69.09 | 16.01 | 62.03 | 27.90 | 23.50 | 62.87 | NA | 69.93 | 46.64 | 13.43 | 59.86 | 12.31 |
90 | 70.28 | 18.60 | 63.64 | 26.01 | 26.71 | 61.40 | NA | 70.91 | 49.37 | 13.15 | 64.55 | 15.38 |
100 | 70.56 | 52.94 | 61.54 | 35.59 | 15.25 | 63.36 | NA | 70.56 | 53.64 | 14.06 | 66.36 | 15.17 |
Ave. | 70.42 | 51.69 | 58.80 | 39.84 | 52.96 | 62.98 | 57.62 | 69.91 | 37.11 | 44.07 | 48.19 | 46.84 |
Facial expression recognition rate (%) using the JAFFE dataset with different subspace dimensionalities (case 2: no. training = 2)
No. base | proCMF | NMF | proNMF | conNMF | weiNMF | NeNMF | PCA | GSNMF | uRNGE | usRNGE | sRNGE | ssRNGE |
---|---|---|---|---|---|---|---|---|---|---|---|---|
20 | 77.53 | 70.55 | 52.60 | 44.66 | 67.39 | 74.79 | 60.27 | 75.34 | 20.27 | 39.32 | 29.59 | 70.68 |
30 | 80.96 | 73.70 | 52.87 | 44.93 | 75.48 | 74.93 | 64.38 | 78.77 | 27.53 | 73.01 | 33.15 | 75.07 |
40 | 82.33 | 75.61 | 55.07 | 47.67 | 77.26 | 73.70 | 68.49 | 79.59 | 30.82 | 74.66 | 42.47 | 75.75 |
50 | 82.05 | 78.49 | 56.57 | 50.68 | 80.00 | 75.34 | 69.86 | 81.51 | 34.52 | 76.44 | 43.29 | 75.34 |
60 | 82.46 | 79.31 | 58.35 | 55.20 | 80.55 | 70.68 | 71.23 | 79.86 | 38.9 | 75.75 | 47.67 | 75.34 |
70 | 81.51 | 80.68 | 59.86 | 58.49 | 82.19 | 72.05 | 68.49 | 81.23 | 42.6 | 76.3 | 54.66 | 77.26 |
80 | 83.84 | 81.51 | 56.57 | 56.71 | 82.05 | 70.82 | 69.86 | 81.51 | 52.33 | 78.08 | 60.68 | 74.38 |
90 | 83.84 | 82.46 | 60.96 | 55.61 | 82.46 | 68.35 | 68.49 | 82.74 | 67.4 | 75.89 | 64.93 | 74.11 |
100 | 84.38 | 82.46 | 59.45 | 56.30 | 82.88 | 67.39 | 71.23 | 82.33 | 73.97 | 75.07 | 71.37 | 74.79 |
Ave. | 82.10 | 78.31 | 56.92 | 52.25 | 78.92 | 72.01 | 68.03 | 80.32 | 43.15 | 71.61 | 49.76 | 74.75 |
4.6 Facial expression recognition on occluded CK+ images
Facial expression recognition rate (%) using the occluded CK+ with different subspace dimensionalities (case of occluded randomly images)
No. base | proCMF | NMF | proNMF | conNMF | weiNMF | NeNMF | PCA | GSNMF | uRNGE | usRNGE | sRNGE | ssRNGE |
---|---|---|---|---|---|---|---|---|---|---|---|---|
20 | 66.82 | 50.62 | 34.38 | 20.04 | 48.60 | 68.97 | 53.31 | 50.50 | 21.78 | 45.54 | 26.9 | 59.13 |
30 | 73.43 | 58.39 | 35.87 | 24.59 | 58.97 | 63.88 | 60.33 | 75.21 | 22.93 | 52.02 | 32.69 | 70.7 |
40 | 79.42 | 62.27 | 43.93 | 26.16 | 63.43 | 61.07 | 62.81 | 74.09 | 28.55 | 58.93 | 35.33 | 72.85 |
50 | 80.95 | 65.29 | 44.05 | 27.52 | 65.00 | 59.71 | 66.12 | 68.22 | 28.06 | 62.85 | 39.21 | 73.26 |
60 | 82.23 | 70.37 | 45.91 | 27.19 | 67.85 | 55.54 | 68.18 | 59.01 | 34.17 | 68.06 | 40.95 | 73.47 |
70 | 83.51 | 70.33 | 46.61 | 26.82 | 72.36 | 52.98 | 69.01 | 67.85 | 34.92 | 73.18 | 45.08 | 76.07 |
80 | 83.39 | 73.31 | 49.88 | 27.81 | 72.40 | 47.23 | 73.55 | 65.62 | 38.60 | 75.79 | 46.61 | 78.55 |
90 | 84.96 | 73.39 | 52.64 | 27.73 | 73.31 | 39.09 | 77.69 | 72.98 | 41.78 | 78.10 | 48.97 | 79.71 |
100 | 86.03 | 75.25 | 51.36 | 29.34 | 74.38 | 37.60 | 78.51 | 70.08 | 40.54 | 75.58 | 54.79 | 80.08 |
Ave. | 80.08 | 66.58 | 44.96 | 26.36 | 66.26 | 54.01 | 67.72 | 67.06 | 32.37 | 65.56 | 41.17 | 73.76 |
Facial expression recognition rate (%) using the occluded CK+ with different subspace dimensionalities (case of occluded mouth)
No. Base | proCMF | NMF | proNMF | conNMF | weiNMF | NeNMF | PCA | GSNMF | uRNGE | usRNGE | sRNGE | ssRNGE |
---|---|---|---|---|---|---|---|---|---|---|---|---|
20 | 76.28 | 55.21 | 40.83 | 21.74 | 53.36 | 62.75 | 61.57 | 61.57 | 24.30 | 46.28 | 31.98 | 60.80 |
30 | 81.92 | 63.39 | 45.29 | 25.87 | 56.26 | 59.68 | 70.66 | 74.73 | 30.83 | 55.19 | 37.69 | 67.48 |
40 | 77.85 | 68.18 | 47.85 | 31.69 | 65.35 | 63.52 | 69.83 | 77.80 | 29.67 | 63.34 | 43.06 | 72.03 |
50 | 85.21 | 67.58 | 50.66 | 33.64 | 69.78 | 65.53 | 70.66 | 75.74 | 32.48 | 74.26 | 45.87 | 77.20 |
60 | 85.87 | 71.61 | 48.26 | 37.48 | 69.19 | 69.72 | 76.45 | 62.51 | 37.85 | 79.81 | 47.52 | 80.63 |
70 | 84.85 | 73.42 | 47.60 | 43.22 | 76.27 | 71.25 | 77.69 | 75.09 | 41.65 | 84.77 | 48.93 | 82.10 |
80 | 85.21 | 74.91 | 49.92 | 45.79 | 76.62 | 63.05 | 79.34 | 74.20 | 45.95 | 87.66 | 51.82 | 84.41 |
90 | 86.03 | 78.29 | 50.00 | 49.30 | 78.93 | 58.74 | 79.34 | 77.86 | 47.36 | 89.73 | 53.80 | 86.36 |
100 | 87.60 | 81.90 | 49.83 | 50.91 | 78.87 | 43.80 | 81.82 | 75.03 | 46.42 | 89.02 | 58.93 | 88.12 |
Ave. | 83.42 | 70.50 | 47.81 | 37.74 | 69.40 | 62.00 | 74.15 | 72.73 | 37.39 | 74.45 | 46.62 | 77.68 |
Facial expression recognition rate (%) using the occluded CK+ with different subspace dimensionalities (case of occluded eyes)
No. base | proCMF | NMF | proNMF | conNMF | weiNMF | NeNMF | PCA | GSNMF | uRNGE | usRNGE | sRNGE | ssRNGE |
---|---|---|---|---|---|---|---|---|---|---|---|---|
20 | 75.50 | 58.93 | 38.00 | 21.43 | 50.41 | 70.43 | 38.43 | 76.39 | 28.93 | 25.62 | 25.80 | 65.58 |
30 | 78.02 | 69.70 | 47.41 | 24.09 | 62.57 | 65.29 | 49.17 | 71.72 | 24.88 | 38.10 | 37.01 | 71.19 |
40 | 77.52 | 73.88 | 51.95 | 28.93 | 67.00 | 69.01 | 54.55 | 70.48 | 26.94 | 42.89 | 41.15 | 75.97 |
50 | 86.86 | 72.26 | 55.32 | 31.94 | 67.83 | 64.76 | 57.02 | 73.38 | 35.45 | 45.21 | 42.80 | 81.88 |
60 | 83.26 | 74.38 | 51.90 | 39.43 | 71.66 | 65.11 | 56.20 | 62.46 | 39.09 | 48.51 | 48.64 | 85.06 |
70 | 84.46 | 78.29 | 62.00 | 39.32 | 75.62 | 66.35 | 56.61 | 69.54 | 44.38 | 51.98 | 50.41 | 83.53 |
80 | 80.50 | 75.93 | 63.67 | 45.51 | 78.39 | 59.15 | 60.74 | 73.49 | 46.61 | 50.74 | 53.31 | 87.60 |
90 | 80.41 | 82.64 | 63.62 | 45.69 | 79.75 | 44.86 | 64.88 | 79.99 | 49.75 | 53.97 | 57.62 | 90.20 |
100 | 84.05 | 81.17 | 63.53 | 45.45 | 79.75 | 44.27 | 66.53 | 82.05 | 52.94 | 59.67 | 60.33 | 87.43 |
Ave. | 81.18 | 74.13 | 55.27 | 35.75 | 70.33 | 61.03 | 56.01 | 73.28 | 38.77 | 46.30 | 46.34 | 80.94 |
Confusion matrix of 7-class facial expression recognition using proCMF on CK+ dataset with unocclusion and eyes and mouth occlusions (%)
Anger | Disgust | Fear | Happiness | Sadness | Surprise | Neutral | ||
---|---|---|---|---|---|---|---|---|
Anger | 96.08 | 1.96 | 0 | 1.96 | 0 | 0 | 0 | Unocclusion |
94.12 | 2.94 | 0 | 2.94 | 0 | 0 | 0 | Mouth | |
100 | 0 | 0 | 0 | 0 | 0 | 0 | Eyes | |
Disgust | 0 | 98.25 | 0 | 0 | 1.75 | 0 | 0 | Unocclusion |
2.63 | 92.11 | 0 | 0 | 0 | 5.26 | 0 | Mouth | |
13.16 | 63.16 | 0 | 0 | 23.68 | 0 | 0 | Eyes | |
Fear | 2.22 | 0 | 97.78 | 0 | 0 | 0 | 0 | Unocclusion |
0 | 6.67 | 86.67 | 3.33 | 0 | 3.33 | 0 | Mouth | |
0 | 0 | 100 | 0 | 0 | 0 | 0 | Eyes | |
Happiness | 0 | 0 | 0 | 100 | 0 | 0 | 0 | Unocclusion |
4.00 | 6.00 | 0 | 86.00 | 0 | 4.00 | 0 | Mouth | |
4.00 | 2.00 | 0 | 90.00 | 4.00 | 0 | 0 | Eyes | |
Sadness | 2.08 | 0 | 0 | 0 | 97.92 | 0 | 0 | Unocclusion |
3.13 | 12.50 | 0 | 0 | 71.86 | 9.38 | 3.13 | Mouth | |
9.37 | 0 | 0 | 0 | 90.63 | 0 | 0 | Eyes | |
Surprise | 0 | 0 | 1.28 | 0 | 0 | 98.72 | 0 | Unocclusion |
0 | 0 | 0 | 0 | 1.92 | 98.08 | 0 | Mouth | |
1.92 | 0 | 5.77 | 0 | 9.62 | 82.69 | 0 | Eyes | |
Neutral | 0 | 0 | 0 | 0 | 0 | 0 | 100 | Unocclusion |
0 | 0 | 0 | 0 | 0 | 0 | 100 | Mouth | |
0 | 0 | 0 | 0 | 16.67 | 0 | 83.33 | Eyes |
5 Conclusions
We explored a new dimensionality reduction model which employs an implicitly cosine dissimilarity metric by transforming the real data to the complex domain and sets up a complex projection matrix in the setting of an unbounded optimization problem. Under the simple framework without any added label information, the proposed method, proCMF, successfully extracted local facial features which are salient areas in facial expression formation. The experiments validate convincingly that the proposed proCMF algorithm can much outperform the popular NMF algorithms for facial expression recognition. The proposed model shows its potential on dealing with diverse scenarios that involve a whole face and an occluded face. In the future, we will develop the current model by incorporating more constraints and improving optimization methods to enhance the FER performance. In order to firm the effectiveness of the proposed method, we will extend evaluation on spontaneous facial expressions and apply directly complex spectrogram features on sound processing, especially the problems about sound source separation.
Declarations
Acknowledgements
This research was financially supported in part by the National Central University, Taiwan, through the NCU International Student Scholarship. The authors would like to thank the anonymous reviewers for their valuable comments that significantly improved the quality of this paper.
Authors’ contributions
VHD made the main contributions to the conception and tracking algorithms’ design, as well as drafting the article. BTP contributed to the design of experiments. YSL, JJD, and PTB provided the technical advices. MQB checked the manuscript and contributed to the rearrangement of the materials. JJW offered critical suggestions on the algorithms’ design, provided significant revising for important intellectual content, and gave final approval of the current version to be submitted. All authors read and approved the final manuscript.
Consent for publication
Informed consent was obtained from all authors included in the study.
Competing interests
The authors declare that they have no competing interests.
Ethical approval
All data and procedures performed in paper were in accordance with the ethical standards of research community. This paper does not contain any studies with human participants or animals performed by any of the authors.
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Authors’ Affiliations
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