Optical expression detection
Some embodiments are directed to a biometric authentication system including headwear having a plurality of biosensors each configured to sample muscle activity so as to obtain a respective time-varying signal, a data store for storing a data set representing characteristic muscle activity for one or more users, and a processor configured to process the time-varying signals from the biosensors in dependence on the stored data set so as to determine a correspondence between a time-varying signal and characteristic muscle activity of one of the one or more users, and in dependence on the determined correspondence, authenticate the time-varying signals as being associated with that user.
1. A system for detecting facial muscle activity comprising:
wearable apparatus comprising an optical flow sensors located so as to, in use when the apparatus is worn, image an area of skin associated with one or more facial muscles, the optical flow sensor being configured to capture time-varying data describing movement of the respective area of skin substantially in the plane of the imaged area of skin, wherein the optical flow sensor is configured to receive light from a plurality of areas of skin over one or more optical fibres; and
wherein the wearable apparatus further comprises an optical switch configured to alternately provide light received from each of at least two of the plurality of areas of skin to the optical flow sensor, the optical switch being synchronised with the sampling rate of the optical flow sensor such that the optical flow sensor is configured to alternately sample different areas of skin.
2. The system as claimed in claim 1 , wherein the optical flow sensors are located at the wearable apparatus so as to, in use when the apparatus is worn, image an area of skin overlying or adjacent to an insertion point of at least one of the one or more associated facial muscles.
3. The system as claimed in claim 1 , further comprising a processor configured to process the time-varying data in dependence on a predetermined dataset relating facial muscle activity to movement of the areas of skin so as to determine activity of the facial muscles.
4. The system as claimed in claim 3 , wherein the time-varying data comprises one or more of: vector information describing the magnitude and direction of movement of the area of skin; and a time series of images of the area of skin.
5. The system as claimed in claim 1 , wherein the optical switch is configured to effect the switching using one or more liquid crystal filters or one or more controllable mirrors.
6. The system as claimed in claim 4 , wherein the time-varying data comprises a time series of images and the processor is configured to process the time-varying data by identifying changes in texture in the images indicative of facial muscle activity according to the predetermined dataset.
7. The system as claimed in claim 3 , wherein the processor is configured to determine activation of a facial muscle associated with an area of skin when the magnitude of movement of the area of skin in a predefined direction exceeds a predetermined threshold.
8. The system as claimed in claim 3 , wherein the processor is configured to process time-varying data from the optical flow sensor so as to determine facial expression of the wearer of the wearable apparatus.
9. The system as claimed in claim 8 , wherein the processor is configured to identify a facial expression when the magnitude and direction of movement detected at the optical flow sensor matches within predefined bounds a respective stored magnitude and direction of movement for the optical flow sensor for that facial expression.
10. The system as claimed in claim 9 , wherein the system comprises a plurality of optical flow sensors each located so as to, in use when the apparatus is worn, image an area of skin associated with one or more facial muscles, wherein the processor is configured to, on identifying that two or more of the plurality of optical flow sensors capture substantially similar skin movements in both magnitude and direction, not determine a facial expression of the wearer of the wearable apparatus.
11. The system as claimed in claim 3 , wherein the processor is configured to process the determined activity of the set of facial muscles so as to infer facial expression of the wearer of the wearable apparatus.
12. The system as claimed in claim 3 , wherein the processor is provided at one or more of: the wearable apparatus and a device external to the wearable apparatus and configured to receive the time-varying data by a wired or wireless connection.
13. The system as claimed in claim 1 , the wearable apparatus further comprising one or more lenses adapted to, in use when the apparatus is worn, focus light reflected from an area of skin onto the optical flow sensor.
14. The system as claimed in claim 1 , the wearable apparatus comprising one or more light sources arranged to illuminate the areas of skin.
15. The A system as claimed in claim 1 , wherein one or more of the light sources are configured to illuminate the at least two of the plurality of areas of skin synchronously with the sampling rate of the optical flow sensor.
16. The system as claimed in claim 1 , wherein the wearable apparatus further comprises one or more first mirrors each configured to direct light reflected from the skin to the optical flow sensor.
17. The system as claimed in claim 3 , wherein the wearable apparatus further comprises one or more motion sensors and the processor is configured to filter the time-varying data describing movement of the respective areas of skin in dependence on the output of the one or more motion sensors.
18. The system as claimed in claim 3 , wherein the system comprises a plurality of optical flow sensors each located so as to, in use when the apparatus is worn, image an area of skin associated with one or more facial muscles and wherein the plurality of optical flow sensors includes an optical flow sensor arranged at the wearable apparatus so as to detect movement of an area of skin on or below the supraorbital ridge and the processor is configured to interpret elevation of that area of skin as activation of the frontalis muscle.
19. The system as claimed in claim 18 , wherein, in use, no part of the wearable apparatus overlies the frontalis muscle.
20. A wearable apparatus for detecting facial skin movement comprising an optical flow sensor located so as to, in use when the apparatus is worn, image an area of skin associated with one or more facial muscles, the optical flow sensor being configured to capture time-varying data describing movement of the respective area of skin substantially in the plane of the imaged area of skin; and
wherein the optical flow sensor is configured to receive light from a plurality of areas of skin over one or more optical fibres; and
wherein the wearable apparatus further comprises an optical switch configured to alternately provide light received from each of at least two of the plurality of areas of skin to the optical flow sensor, the optical switch being synchronised with the sampling rate of the optical flow sensor such that the optical flow sensor is configured to alternately sample different areas of skin.