This invention relates to a face recognition system. More particularly the invention relates to a face recognition system which improves the quality of images acquired by the face recognition system.

In a typical face recognition system the subjects' face is illuminated by a light source incident on the subjects face, and an image of the subjects' face is then captured by a camera. This image of the subjects' face can be used to confirm the identity of the subject, and/or to verify the existence of the subject.

If the subject is wearing spectacles, or has oily/shiny patches on their face, then these highly reflective surfaces/face regions will reflect the light incident on the subjects' face in a particular way. Specifically, the light reflected from the spectacles, or from oily/shiny regions of the face will be specularly reflected. By contrast, light which is reflected from matt regions of the subjects' face will be diffusely reflected.

The specularly reflected light and the diffusely reflected light are then incident on a camera to produce an image of the subjects' face. In an ordinary system, the specularly reflected light will saturate the camera, where it is incident on the lens. This saturation of the camera by the specular reflection will product bright spots on the acquired image of the subjects' face. Acquired images which include these bright spots resulting from the specular reflection are of a low quality and are less useful for analysis carried out in a face recognition system. Better quality images will be obtained by a face recognition system which uses images produced from using only the diffusely reflected light from the subjects' face.

According to the invention there is provided a face recognition system comprising at least one source of optical radiation for illuminating the face of a subject and image capture means for acquiring an image of said illuminated face; characterized in that said at least one source of optical radiation and said image capture means are provided with means to modify said optical radiation, whereby to reduce specular reflection in the acquired image of said face.

In a preferred embodiment of the invention the means to modify said optical radiation are polarizing filters located in front of said source of optical radiation and said image capture means. The plane of polarization of the polarizing filter provided to said at least one source of optical radiation is orthogonal to the plane of polarization of the polarizing filter provided to the image capture means. In the preferred embodiment, the image capture means is a camera, and the polarizing filter provided in front of the camera covers at least the lens of the camera. The polarizing filter provided to the source of optical radiation covers the source of optical radiation.

Preferred embodiments of the invention are now described by way of example only, with reference to the sole accompanying figure which:

shows a face recognition system according to the invention.

The figure shows a face recognition system 2 which is used for acquiring an image of the face 10 of a subject 1. The face recognition system includes light sources 3, a camera 4, computer control means 7 and polarizing filters 5 and 6.

The subjects' face 10, is illuminated by the light sources 3. The light sources 3 are typically visible light sources, with an illumination intensity of between 700-2000 lux, but other sources of optical radiation may be used (e.g. infra-red) and other intensity ranges could also be used. The light emitted from the light sources 3 passes through polarizing filters 6, positioned directly in front of light sources 3. The polarizing filters 6 can be located immediately in front of the light sources 3, or up to 2 metres away from the light sources 3. The polarizing filters 6 can be positioned in any orientation with respect to light sources 3. However, the polarizing filters 6 should preferably cover all of the light source 3. If regions of light sources 3 are not covered by the polarizing filters 6, this will lead to unwanted or unusual effects in the image of the subjects' face acquired by the camera 4. The light that passes through polarizing filters 6 to illuminate the subjects' face 10 is now polarized light. The polarized light that is incident on matt regions (e.g. region 12) of the subjects' face 10 will be diffusely reflected. By contrast, polarized light that is incident on oily/shiny regions 11 of the subjects' face 10, or on spectacles 13 that the subject may be wearing, is specularly reflected from the surface and/or spectacles.

The total reflected light (both specular and diffuse) is reflected from the face back to the polarizing filter 5 positioned in front of camera 4. Filter 5 is another polarizing filter, and is positioned so as to have a plane of polarization that is orthogonal to the plane of polarization of polarizing filters 6 positioned in front of lights sources 3. Again, filter 5 can be positioned immediately in front of camera 4, or up to 10 cm in front of camera 4. This polarizing filter 5 will prevent the light which has been specularly reflected from the subjects' face from passing through polarizing filter 5 to reach the camera 4.

Preferably, the polarizing filter 5 only has to cover the lens 8 of camera 4 completely, but it can extended to cover the whole of the camera 4 if desired. The polarizing filter 5 allows the diffusely reflected light to pass through the filter 5 to reach lens 8 of camera 4. The diffusely reflected light then produces an image of the subjects' face 1.

Bright spots in the image which would be caused by specularly reflected light are minimised, since the specularly reflected light is prevented from reaching the camera 4 by provision of polarizing filter 5. The camera 4 and light sources 3 are typically controlled by computer control means 7, but they can be independently controlled by separate control means.

In the face recognition system of the figure I5 the light source 3 and camera 4 are all arranged in the same plane. Alternatively, the light source 3 and camera 4 may be arranged to be aligned in the same direction but not in the same plane, or they may be arranged so that the light source 3 is angled with respect to the camera 4.