Face detection in gray scale images using locally linear embeddings

The problem of face detection remains challenging because faces are non-rigid objects that have a high degree of variability with respect to head rotation, illumination, facial expression, occlusion, and aging. This paper employs a novel technique, known as Locally Linear Embedding (LLE), for solving the face detection problem. The LLE method performs dimensionality reduction on data for learning and classification purposes. Proposed by Roweis and Saul, the intent of LL is to determine a locally linear fit so that each data point can be represented by a linear combination of its closest neighbors. The first objective of this research is to apply the LLE algorithm to 2D facial images to obtain their representation in a sub-space under the specific conditions stated above. The low-dimensional data are then used to train Support Vector Machine (SVM) classifiers to label windows in images as being either face or non-face. Six different databases of cropped facial images, corresponding to variations in head rotation, illumination, facial expression, occlusion and aging, were used to train and test the classifiers. The second objective was to evaluate the feasibility of using the combined efficacy of the six SVM classifiers in a two-stage face detection approach. Experimental results obtained demonstrated that the performance of the proposed method was similar and sometimes better when compared to other face detection methods, thus indicating a viable and accurate technique.