Face Recognition using Photometric Stereo

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We propose to construct a system for 3D face recognition. We propose to use photometric stereo for face reconstruction in order to by pass the problems of conventional stereo (that needs to solve the matching problem first), structured light (that does not supply colour information) and photometric stereo with spectrally distinct light sources (that relies on the assumption of uniformly coloured imaged objects). Photometric stereo (PS) can reproduce structural details and colour on a per pixel basis in a way that no other 3D system can. The proposed scheme will be appropriate for use in a controlled environment for authentication purposes, but also in a general environment e.g. the entrance of a public event. We shall use two routes: surface reconstruction from the data and direct extraction of facial characteristics from the PS set. In the first approach, once surface normal and albedo is recovered, images of the face may be synthetically rendered under arbitrary new pose and illumination conditions to allow novel viewing conditions. We also aim to use a new multi-scale facial feature matching approach in the recognition process, where facial features range from overall face and head shape to fine skin dermal topography, reflectance and texture. The latter may be thought of as a form of detailed surface bump map forming a unique skin-print or signature and represents a new approach. Hence both the 3D shape and 2D intensity data will be used in recognition or authentication tasks. We propose to use scalable methods for matching, so we can cope with large databases. 3D matching will be done with the newly proposed invaders algorithm which is FFT cross-correlation based, and more detailed matching will be done by using features and classifier combination. The novelty of our approach lies in the use of PS to extract 3D information, the use of detailed facial characteristics like moles, scratches, and skin texture, and in the design of the system so that it can operate while the person is moving, with minimum intrusion and maximum efficiency. We have two industrial collaborators who will contribute in system design, data gathering and exploitation and support from the Home Office. We shall evaluate our system following three possible scenaria: a face searched in the crowd (real time face recognition), a person has to be identified (off-line face recognition) and a person has to be checked against a claimed identity (face authentication). We shall install the first prototype system in the offices of one of our industrial partners in month 12, so that data can be collected. We envisage a door like structure with lights flashing in succession as a person walks through, while a camera is capturing images. We propose to investigate the optimal number of lights in terms of efficiency and accuracy of the reconstruction, and the option of using non-visible light to avoid problems with people sensitive to flashes. We shall also investigate the relationship between detail that has to be captured and the geometry of the construction.