Human Face Recognition

PCA and LDA based Neural Networks for Human Face Recognition

PCA and LDA based Neural Networks for Human Face Recognition


                  After 9/11 tragedy, governments in all over the world started to look more seriously to the levels of security they have at their airports and borders. Countries annual budgets were increased drastically to have the most recent technologies in identification, recognition and tracking of suspects. The demand growth on these applications helped researchers to be able to fund their research projects. One of most common biometric recognition techniques is face recognition. Although face recognition is not as accurate as the other recognition methods such as fingerprints, it still grabs huge attention of many researchers in the field of computer vision. The main reason behind this attention is the fact that the face is the conventional way people use to identify each others.

Over the last few decades, a lot of researchers gave up working in the face recognition

problem due to the inefficiencies of the methods used to represent faces. The face representation was performed by using two categories. The First category is global approach or appearance-based, which uses holistic texture features and is applied to the face or specific region of it. The second category is feature-based or component-based, which uses the geometric relationship among the facial features like mouth, nose, and eyes. A feature-based approach was implemented by a geometrical model of a face by 2-D elastic graph. Another example of feature-based was done by independently matching templates of three facial regions (eyes, mouth and nose) and the configuration of the features was unconstrained since the system didnít include geometrical model . Principal components analysis (PCA) method (Sirovich & Kirby, 1987; Kirby & Sirovich,1990) which is also called eigenfaces (Turk & Pentland, 1991; Pentland & Moghaddam, 1994) is appearance-based technique used widely for the dimensionality reduction and recorded a great performance in face recognition. PCA based approaches typically include two phases: training and classification. In the training phase, an eigenspace is established from the training samples using PCA and the training face images are mapped to the eigenspace for classification. In the classification phase, an input face is projected to the same eigenspace and classified by an appropriate classifier. Contrasting the PCA which encodes information in an orthogonal linear space, the linear discriminant analysis (LDA) method (Belhumeur et al., 1997; Zhao et al., 1998) which also known as fisherfaces method is another example of  appearance-based techniques which encodes discriminatory information in a linear separable space of which bases are not necessarily orthogonal.

                   In this chapter, two face recognition systems, one based on the PCA followed by a

feedforward neural network (FFNN) called PCA-NN, and the other based on LDA followed by a FFNN called LDA-NN, are explained. The two systems consist of two phases which are the PCA or LDA feature extraction phase, and the neural network classification phase. The introduced systems provide improvement on the recognition performances over the conventional LDA and PCA face recognition systems. The neural networks are among the most successful decision making systems that can be trained to perform complex functions in various fields of applications including pattern recognition , optimization, identification, classification, speech, vision, and control systems. In FFNN the neurons are organized in the form of layers. The FFNN requires a training procedure where the weights connecting the neurons in consecutive layers are calculated based on the training samples and target classes. After generating the eigenvectors using PCA or LDA methods, the projection vectors of face images in the training set are calculated and then used to train the neural network. These architectures are called PCA-NN and LDA-NN for eigenfaces and fisherfaces methods respectively. The first part of the chapter introduces PCA and LDA techniques which provide theoretical and practical implementation details of the systems. Both of the techniques are explained by using wide range of illustrations including graphs, flowcharts and face images. The second part of the chapter introduces neural networks in general and FFNN in particular. The training and test phases of FFNN are explained in detail. Finally the PCA-NN and LDA-NN face recognition systems are explained and the performances of the respective methods are compared with conventional PCA and LDA based face recognition systems.

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