# Department of ECE, JNTU University, Hyderabad, india
*Department of ECE, Institute of Aeronautical Engineering, Hyderabad, India
Abstract— the Face recognition remain a challenging area despite there are numerous face recognition algorithms came up in the last two decades. Lot of efforts went in improving the automated surveillance systems opens the door for inventing innovative face recognition algorithms. Supervised (Fisher faces) and unsupervised (Eigen Faces) face recognition algorithms are taken in to account to evaluate broadly their performances under different pre-processing data sets. Three pre-processing steps are used in considering the facial images with dark or bad lighting, low contrast. The pre-processing steps used here are contrast stretching, Homomorphic filtering and conversion of PGM image to Tagged Image File Format (TIFF), Graphics Interchange Format (GIF) and Portable Network Graphics (PNG). AT&T ORL data base is considered for evaluating the performance of Eigen faces and Fisher faces. The results show that the fisher face performs well when compared with the Eigen face for illumination changes data base. The performance evaluating curves like Cumulative Match Characteristics (CMC), Expected Performance Curve and Receiver Operating Characteristics (ROC) for Face Recognition systems are also drawn both for Eigen faces and Fisher faces for comparison. Keywords— Eigen face, Fisher face, Principle Component Analysis, Fisher Linear Discriminant, Face Recognition System. Introduction
Image enhancement techniques are very much important for face recognition and detection algorithms. Change in illumination conditions may drastically affect the face recognition rate. Before testing and training, the face data base has to be enhanced so that the affect of face recognition algorithms can be effectively seen. After all, image is considered as a bunch of pixels arranged in an array, the manipulation on the pixel may enhance the image. Because of light illumination conditions at the time of taking the face images, there are dark areas and bright areas too in the same image. All these things need to be considered before applying enhancement techniques on the face image data set for recognition rate improvement [1- 3].
In the last three decades, so many face recognition algorithms are proposed, tested and experimented. In all these algorithms, the focus is in extracting the features of the face in the data base. Many algorithms are still working and are being used in surveillance systems [4-5]. Prominent ones are PCA and LDA.
In face recognition and detection literature, different face representation methods are used and they are global features, representing as sub spaces etc.. in face recognition basically the person is recognized by the use of large data set of face images. Two linear techniques namely PCA and LDA are prominently used for face recognition. These linear techniques create feature vector for every face in the face data base. The purpose of creating the feature vector is for dimension reduction.
Principal component analysis (PCA) method achieved the dimension reduction by projecting the original face image data onto lower dimensional subspace crossed by the best eigenvectors of the covariance matrix. Linear Discriminant Analysis (LDA) method looks for the projective axes on which the data points of two or more different classes are distant from each other, this mean LDA searches for the maximizing between class scatter, while constraining the data points of the same class to be as near to each other as possible, this mean searching for the minimizing within class scatter.
An important aspect in improving the performance of face recognition system is the enhancing of face image. The intended aim of face image enhancement is that the resulted images have better visual quality than the input one. Face image can be improved, by enhancing the brightness, contrast and resolution of image . This is a part of pre-processing stage that can affect the feature extraction and finally recognition performance. For instance in, the image enhancement has been considered in face recognition technique. Song et al., calculates, prior to feature extraction stage, the illumination difference between right and left part of face. If there is a spacious amount of difference than take the mirror of average illuminated part.
The aim of this research work is to observe the effect of image pre-processing of face data base in Eigen faces and Fisher faces. The effect of combination of contrast stretching and Homomorphic filtering on the face database for improving the face recognition rate is observed. The effect of GIF, PNG and TIFF file format in improving the face recognition rate are also observed .
The Block diagrams of face recognition system and verification systems are shown in figure 1 and figure 2 respectively. Figure one shows the training stage and figure 2 show the testing stage. The pre-processing includes contrast stretching and Homomorphic filtering . In the feature extraction stage, the scale vector is constructed for each and every face of the data base. If even one face in the data base is similar with the test image, the face is identified as “known”, otherwise “unknown”.