A Convolutional Neural Network for Compound Micro-Expression Recognition

Yue Zhao, Jiancheng Xu, Yue Zhao, Jiancheng Xu

Abstract

Human beings are particularly inclined to express real emotions through micro-expressions with subtle amplitude and short duration. Though people regularly recognize many distinct emotions, for the most part, research studies have been limited to six basic categories: happiness, surprise, sadness, anger, fear, and disgust. Like normal expressions (i.e., macro-expressions), most current research into micro-expression recognition focuses on these six basic emotions. This paper describes an important group of micro-expressions, which we call compound emotion categories. Compound micro-expressions are constructed by combining two basic micro-expressions but reflect more complex mental states and more abundant human facial emotions. In this study, we firstly synthesized a Compound Micro-expression Database (CMED) based on existing spontaneous micro-expression datasets. These subtle feature of micro-expression makes it difficult to observe its motion track and characteristics. Consequently, there are many challenges and limitations to synthetic compound micro-expression images. The proposed method firstly implemented Eulerian Video Magnification (EVM) method to enhance facial motion features of basic micro-expressions for generating compound images. The consistent and differential facial muscle articulations (typically referred to as action units) associated with each emotion category have been labeled to become the foundation of generating compound micro-expression. Secondly, we extracted the apex frames of CMED by 3D Fast Fourier Transform (3D-FFT). Moreover, the proposed method calculated the optical flow information between the onset frame and apex frame to produce an optical flow feature map. Finally, we designed a shallow network to extract high-level features of these optical flow maps. In this study, we synthesized four existing databases of spontaneous micro-expressions (CASME I, CASME II, CAS(ME)2, SAMM) to generate the CMED and test the validity of our network. Therefore, the deep network framework designed in this study can well recognize the emotional information of basic micro-expressions and compound micro-expressions.

Keywords: 3D-FFT; CNN; EVM; FACS; TV-L1 optical flow; compound micro-expressions.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
This Compound Facial Expressions of Emotion (CFEE).
Figure 2
Figure 2
The framework of the proposed method.
Figure 3
Figure 3
Compound facial expressions in real environments (left: “disgustedly surprised”, right: “fearfully surprised”).
Figure 4
Figure 4
The generation process of CMED: (a) Description of Positively Surprised; (b) Description of Positively Negative; (c) Description of Negatively Surprised; (d) Description of Negatively Negative.
Figure 4
Figure 4
The generation process of CMED: (a) Description of Positively Surprised; (b) Description of Positively Negative; (c) Description of Negatively Surprised; (d) Description of Negatively Negative.
Figure 5
Figure 5
The compound micro-expression database.
Figure 6
Figure 6
Comparison of ME sequences at different magnification factors.
Figure 7
Figure 7
Optical flow maps of six MEs in CASME Ⅱ database.
Figure 8
Figure 8
Overall framework of proposed network.
Figure 9
Figure 9
Recognition performance using different magnification factor.
Figure 10
Figure 10
Comparison of different magnification method.
Figure 11
Figure 11
Optical flow feature maps with different λ and Nscales.
Figure 12
Figure 12
Recognition performance using different input graph on CMED. Magnified not magnificated.
Figure 13
Figure 13
The measurement of confusion matrix: (a) the basic ME database; (b) the CMED.

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Source: PubMed

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구독하다