Spoof detection based on specular and diffuse reflections

An optical biometric imaging arrangement configured to capture an image of an object, the biometric imaging arrangement comprising:

• an image sensor comprising a photodetector pixel array, the image sensor being arranged under a controllable light source comprising light source units, wherein the photodetector pixel array comprises a first set of pixels to acquire a first type of image portion, pixels of the first set of pixels being configured to capture light of a first distinguishable color and being arranged directly under a light source unit of the controllable light source that is active during image acquisition to capture predominantly specular light reflected off the object, and a second set of pixels to acquire a second type of image portion, pixels of the second set of pixels being configured to capture light of a second distinguishable color and being arranged directly under a portion of the controllable light source that is at least partly in-active during image acquisition to capture predominantly diffuse light reflected off the object,
• the optical biometric imaging arrangement being configured to:
• illuminate the object with a light pattern comprising portions of different light intensity using the controllable light source;
• acquire an image of the object, the image comprising image portions of the first type and of the second type corresponding to the portions of different light intensity of the light pattern illuminating the object,
• perform biometric authentication including spoof detection based on metrics extracted from the image portions of both the first type and the second type.

A control unit configured to perform biometric authentication using an optical biometric arrangement comprising an image sensor comprising a photodetector pixel array configured to capture an image of an object, the image sensor being arranged under a controllable light source comprising light source units, the control unit being configured to:

• obtain an image of the object, the image being acquired while illuminating the object with a light pattern comprising portions of different light intensity, whereby the obtained image comprises image portions corresponding to the portions of different light intensity of the light pattern illuminating the object,
• at least one image portion of a first type being captured by pixels in the photodetector pixel array configured to capture light of a first distinguishable color and arranged directly under a light source unit being active during image acquisition to capture predominantly specular light reflected off the object, and
• at least one image portion of a second type being captured by pixels in the photodetector pixel array configured to capture light of a second distinguishable color and arranged under an at least partly in-active illumination area of the controllable light source during image acquisition to capture predominantly diffuse light reflected off the object, and
• perform biometric authentication including spoof detection based on metrics extracted from the image portions of both the first type and the second type.