A Novel Technique For Face Recognition Across Variable Illuminations And Poses

DOI : 10.17577/IJERTV2IS4927

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A Novel Technique For Face Recognition Across Variable Illuminations And Poses

Ms. Khushboo B. Trivedi, Prof. V. T. Gaikwad,

      1. inal Year Appearing, Associate Professor, Dept. of Information Technology, Dept. of Information Technology,

        Sipna College of Engineering & Technology, Sipna College of Engineering & Technology, Amravati. Amravati.

        Prof. H. N. Datir

        Assistant Professor

        Dept.of Computer Science and Engineering, Sipna College of Engineering & Technology,



        In this paper a face recognition algorithm based on simultaneous sparse approximations under varying illumination and pose is given. A dictionary is learned for each class based on given training examples which minimizes the representation error with a sparseness constraint. A novel test image is projected onto the span of the atoms in each learned dictionary. The resulting residual vectors are then used for classification. To handle variations in lighting conditions and pose, an image relighting technique based on pose-robust albedo estimation is used to generate multiple frontal images of the same person with variable lighting. As a result, the proposed algorithm has the ability to recognize human faces with high accuracy even when only a single or a very few images per person are provided for training.

        Index Terms-Biometrics, dictionary learning, illumination variation, Albedo, relighting, simultaneous sparse signal representation.


          As one of the most successful applications of image analysis and understanding, face recognition has recently received significant attention, especially during the past several years. At least two reasons account for this trend: the first is the wide range of commercial and law enforcement applications, and the second is the availability of feasible technologies after 30 years of research. Even though current machine recognition systems have reached a certain level of maturity, their success is limited by the conditions imposed by many real applications. For example, recognition of face images acquired in an outdoor environment with changes in illumination and/or pose remains a largely unsolved problem. In other words, current systems are still far away from the capability of the human perception system [1]. In face recognition system there are some training images and a test image. Training images are

          those images which have specific controlled conditions, while test image is that image which is used to match with given training image for recognition. Current systems work very well when the test image is captured under controlled conditions. The performance degrades significantly when the test image contains variations that are not present in the training images. Some of these variations include illumination, pose, expression, cosmetics and aging.

          In recent years, the theories of Sparse Representation (SR) and Compressed Sensing (CS) have emerged as powerful tools for efficiently processing data in non-traditional ways. This has led to recovery in interest in the principles of SR and CS for face recognition [2, 3, 4, 5, 6]. Phillips [2] proposed matching pursuit filters for face feature detection and identification. The filters were designed through a simultaneous decomposition of a training set into a 2D wavelet expansion designed to discriminate among faces. It was shown that the resulting algorithm was robust to facial expression and the surrounding environment. Wright et al. [3] introduced an algorithm, called Sparse Representation based Classification (SRC), where the training face images constitute the dictionary and a test image is classified by finding its sparse representation with respect to this dictionary. This work was later extended to handle pose and illumination variations [4], [5]. Also, an expression- invariant face recognition method based on ideas from the distributed compressed sensing and joint sparsity models was proposed in [6].

          There are a number of hurdles that face recognition systems based on sparse representation must overcome. One is designing algorithms that are robust to changes in illumination; a second is that algorithms need to efficiently scale as the number of people enrolled in the system increases. The SRC approach recognizes faces by solving an optimization problem over the set of images enrolled into the database. This solution trades robustness and size of the database against computational efficiency.

          In this paper, an algorithm to perform face recognition across varying illumination based on learning

          class specific dictionaries. Using a relighting method, many elements to the dictionary can be added so that robustness to illumination changes can be realized. This method consists of two stages. In the first stage, given training samples from each class, class specific dictionaries are trained with some fixed number of atoms. Then, a test image is projected onto the span of the atoms in each learned dictionaries. The residual vectors are then used for classification. The paper is divided in following way. The dictionary based face recognition algorithm is detailed in Section 2. Section 3 presents experimental results and Section 4 concludes the paper with a brief summary and discussion.


          Let D~ = [d , , d ] RNxK be a redundant

          where i represent the columns of and the 0 sparsity measure . 0 counts the number of nonzero elements in the

          representation. Here, A F denotes the Frobenius norm

          defined as A F = ijAij . The K-SVD algorithm alternates between sparse-coding and dictionary update steps. In the sparse-coding step, D is fixed and the representation vectors is are found for each example xi. Then, the dictionary is updated atom-by-atom in an efficient way.

          Classification based on Learned Dictionaries:

          Suppose that C distinct face classes and a set of mi training images per class, i {1, ,C} are

          given. An l × q grayscale image as an N-dimensional

          1 K vector, x, which can be obtained by stacking its columns,

          dictionary with K atoms represented as columns dj RN

          where N = l × q. Let B = [x , , x

          ] RN×mi be

          i i1 imi

          with K » N. The choice of dictionary usually depends on

          the specific application. A dictionary may be chosen such that it favors sparse approximations or it can be chosen to resemble the structure that may appear in the input samples. For face recognition, in [2] the dictionary contained steerable wavelet bases elements. while in [3] the dictionary consisted of the gallery images .

          Given a data matrix B = [x1, , xm]

          RNxm and a fixed dictionary D~ RNxK, simultaneous

          an N × mi matrix of training images corresponding to the

          ith class.

          For training, C class specific dictionaries is being learned, Di, to represent the training samples in each Bi, with some sparsity level T0, using the K-SVD algorithm. Once the dictionaries have been learned for each class, given a test sample y, to be projected onto the span of the atoms in each Di using the orthogonal projector

          Pi = D (D T D )1D T . The approximation and residual

          i i i i



          sparse approximation attempts to find a matrix such that B ~ D . Where D RNxP , P < N, is a dictionary matrix whose atoms are selected from ~ and = [1, , m] is the matrix whose columns i are the coefficients corresponding to each data vector xi. In other words, simultaneous sparse approximation attempts to approximate all th samples in B at once as a linear combination of a common subset of atoms with cardinality

          vectors can then be calculated as

          y i = Piy = Dii (2)


          ri(y) = y y i = (I Pi)y, (3)



          respectively, where I is the identity matrix and i = (D T

          D )1D T y are the coefficients. Since the K-SVD algorithm

          much smaller than N. In fact, by keeping the sparsity low i i

          enough, one can eliminate the internal variation of the finds the dictionary, I, that leads to the best representation

          samples in B which may lead to more robust representation. It has been shown that instead of using a predetermined

          for each examples in Bi,

          r i (y)


          can be small if y were to

          dictionary, learning dictionaries from the training data provides much better representation and hence can improve the performance of reconstructive approach to discrimination.

          Learning Class Specific Reconstructive Dictionaries:

          belong to the ith class and large for the other classes. Based on this, one can classify y by assigning it to the class, d

          {1, ,C}, that gives the lowest reconstruction error,

          r i (y) :


          Designing dictionaries based on training is a much recent approach to dictionary design which is

          d = identity(y) = arg mini

          r i (y)



          strongly motivated by the advances in the sparse representation theory [7]. The K-SVD [8] algorithm for learning dictionaries for face images.

          Given a set of examples B = [x1, , xm],



          the goal of the K-SVD algorithm is to find a dictionary D and a sparse matrix that minimize the following representation error

          Fig 1. Shows example of how DFR algorithm works.

          ( D , )= arg min


          B D

          1. subject to i

            i 0 T0 (1)

            Dictionary-based face recognition (DFR) algorithm is Summarized in Fig. 2.

            2.2Pose-Robust Albedo Estimation

            The method presented previously can be generalized such that it can handle pose variations . Let n i

            ,j, s and be some initial estimates of the surface normals, illumination direction and initial estimate of surface normals in pose , respectively. Then, the initial albedo

            at pixel(i,j) can be obtained by

            Fig 1. Exapmle of working of DFR algorithm

            1. Image Relighting

          Recognizing faces under varying illumination given a single training image is a difficult problem. In this

          xi, j

          i,j= n i,j s

          where n i,j denotes the initial estimate of surface normals in pose . Using this model, reformulate the problem of recovering albedo as a signal estimation problem. Formulation for the albedo estimation problem in the presence of pose is as follows:

          i,j = i,j hi ,j+ i,j


          section, here a method was proposed to deal with this

          illumination problem. The idea is to capture illumination conditions that might occur in the test sample in the

          i,j = n

          i, j

          s n

          i, j s

          i, j

          training samples. The Lambertian reflectance model for the facial surface is assumed. The surface normals, albedo and the intensity image are related by an image formation model. For Lambertian objects, the diffused component of the surface reflection is modeled using the Lamberts Cosine Law given by

          I = max(nT s, 0), (5)

          where I is the pixel intensity, s is the light source direction, is the surface albedo and n is the surface normal of the corresponding surface point. Using this model, a nonstationary stochastic filter was recently proposed in [9] to estimate the albedo map from a single face image. We adapt this method to first estimate the albedo map from a given face image. Then, using the estimated albedo map, new images under any illumination condition using the image formation model is generated (5). This can be done by combining the estimated albedo map with the average facial information [10].It was shown in [11] that an image of an arbitrarily illuminated object can be approximated by a linear combination of the image of the same object in the same pose, illuminated by nine different light sources placed at preselected positions. Hence, the image formation



          i, j s



          h i,j = n j s



          i, j s

          i, j is the true albedo and i, j is the degraded albedo. In the case when the pose is known accurately, =

          and h i,j=1. Hence, this can be viewed as a

          generalization in the case of unknown pose. Using this model, a stochastic filtering framework was recently presented to estimate the albedo from a single nonfrontal face image. Once pose and illumination have been normalized, one can use the relighting method described in the previous section to generate multiple frontal images with different lighting to achieve illumination and pose- robust recognition.

          Note that a K-SVD based face recognition algorithm was recently proposed in [12]. Unlike [12], there is no discriminative approach to face recognition. The method is a reconstructive approach to discrimination and



          equation can be rewritten as I = 9


          where Ii =

          does not require multiple images to be available.

          Given a test sample y and C training matrices B1,

          ,BC where each Bi RN×mi contains mi training samples.


          1. For each training image, use the relighting approach described in section 2.1 to generate multiple images with different illumination conditions and use them in the gallery.

          Given a test sample y and C training matrices B1,

          ,BC where each Bi RN×mi contains mi training samples.


          1. For each training image, use the relighting approach described in section 2.1 to generate multiple images with different illumination conditions and use them in the gallery.

          max(nT si, 0) and {s1, , s9} are the pre-specified illumination directions. Since, the objective is to generate gallery images which will be sufficient to account for any illumination in the new image, images under the nine pre- specified illumination conditions were generated and used in the gallery. As a result, this algorithm has the ability to recognize human faces with good accuracy even when only a single or a very few images are provided for training.

          1. Learn the best dictionaries Di, to represent the face images in Bi, using the K-SVD algorithm.

          2. Compute the approximation vectors, y i and the residual vectors, ri(y), using (2) and (3),

            respectively for i = 1, ,C.

          3. Identify y using (4).

          1. Learn the best dictionaries Di, to represent the face images in Bi, using the K-SVD algorithm.

          2. Compute the approximation vectors, y i and the residual vectors, ri(y), using (2) and (3),

            respectively for i = 1, ,C.

          3. Identify y using (4).

          Fig. 2. DFR algorithm.


          In this section, an experimental results on some of the publicly available databases for face recognition such as Extended Yale B dataset [13] . The comparison with other existing face recognition methods in [3] suggests that the SRC algorithm is among the best. Hence, it is used as a bench mark for comparisons in this paper. In all of our experiments, the K-SVD [8] algorithm is used to train the dictionaries with 15 atoms. The performance of our algorithm is compared with that of five different methods: SRC, nearest neighbor (NN), nearest subspace (NS), support vector machines (SVM) and class dependent principal component analysis (CDPCA) . This algorithm is also tested using several features, namely, Eigenfaces, Fisherfaces, Randomfaces, and downsampled images.

          Results on Extended Yale B Database: There are a total of 2, 414 frontal face images o 38 individuals in the Extended Yale B database. These images were captured under various controlled indoor lighting conditions. They were manually cropped and normalized to the size of 192 × 168 . First set of experiments on the Extended Yale B data set consist of testing the performance of our algorithm with different features and dimensions. The objective is to verify the ability of our algorithm in recognizing faces with different illumination conditions. The experimental setup as considered in [3] is followed. The feature space dimensions of 30, 56, 120, and 504 corresponding to the downsampling ratios of, 1/32, 1/24, 1/16, and 1/8, respectively are computed. Randomly 32 images per subject (i.e. half of the images) for training and the other half for testing is selected. Then train dictionaries on the feature space. The best recognition rates of different methods with different dimensions and features are compared in Table1.

          Table 1. Recognition Rates (RR) (in %) of different methods on the Extended Yale B database .















          The maximum recognition rates achieved by DFR are 95.99%, 97.16%, 98.58% and 99.17% for all 30,

          56, 120 and 504 dimensional feature spaces, respectively. The maximum recognition rate achieved by SRC is 98.1% with 504D randomfaces [3]. Also, NN, NS, SVM and CDPCA achieve the maximum recognition rates of 90.7%,

          94.1%, 97.7%, and 98.83%, respectively . As can be seen from this experiment that DFR performs favorably over some of the competitive methods for face recognition on the Extended Yale B database.

          Recognition with partial face features: In this section, the ability of our algorithm in recognizing faces from the partial face features is shown. Partial face features have been used in recovering the identity of human faces before [3]. The images in the Extended Yale B database for this experiment was used. The experimental setup of [3] was used. For each subject, 32 images are randomly selected for training, and the remaining images are used for testing. The region of eye, nose and mouth are selected as partial face features. For this experiment, the relighting step of our algorithm was omitted. Examples of these features are shown in Fig. 3. Table 2 compares the results obtained by using our method with other methods presented in [3]. As can be seen from the table, our method achieves

          recognition rates of 99.3%, 98.8% and 99.8% on eye,

          nose and mouth region, respectively and it outperforms other methods such as SRC, NN, NS and SVM [3].

          Fig. 3. Examples of partial facial features.

          Table 3. Recognition results with partial facial features.

          Right Eye




























          A face recognition algorithm based on dictionary a learning method that is robust to changes in lighting. This entails using a relighting approach based on robust albedo estimation. Various experiments on popular face recognition data sets have shown that this method is efficient and can perform significantly better than many competitive face recognition algorithms. Even though, in this paper, a reconstructive approach to dictionary learning is taken, it is possible to learn discriminative dictionaries for the task of face recognition. It remains an interesting topic for future work to develop a discriminative dictionary learning algorithm that is robust to pose, expression and illumination variations.

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