Synchronizing an illumination sequence of illumination sources with image capture in rolling shutter mode

Abstract

Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for a biometric authentication system. In one aspect, a method includes receiving, at one or more processing devices, data corresponding to a first set of pixels of an image sensor. The first set of pixels are exposed under illumination by a first source. Data corresponding to a second set of pixels of the image sensor is received, at the one or more processing devices. The second set of pixels are exposed under illumination by a second source that is spatially separated from the first source. A three-dimensional image is generated using the data corresponding to the first set of pixels as a first image of a pair of photometric stereo images, and the data corresponding to the second set of pixels as a second image of the pair of photometric stereo images.

What is claimed is: 
     
         1 . A computer-implemented method for generating a three-dimensional (3D) image, the method comprising:
 receiving, at one or more processing devices, data corresponding to a first set of pixels of an image sensor, wherein the first set of pixels are exposed under illumination by a first source;   receiving, at the one or more processing devices, data corresponding to a second set of pixels of the image sensor, wherein the second set of pixels are exposed under illumination by a second source that is spatially separated from the first source; and   generating the 3D image using the data corresponding to the first set of pixels as a first image of a pair of photometric stereo images, and the data corresponding to the second set of pixels as a second image of the pair of photometric stereo images.   
     
     
         2 . The computer-implemented method of  claim 1 , wherein the first and second sets of pixels are partially non-overlapping. 
     
     
         3 . The computer-implemented method of  claim 1 , wherein exposure of the image sensor is controlled by a rolling shutter that exposes the pixels of the image sensor in a row-wise manner. 
     
     
         4 . The computer-implemented method of  claim 1 , wherein exposure of the image sensor is controlled by a rolling shutter that exposes the pixels of the image sensor in a column-wise manner. 
     
     
         5 . The computer-implemented method of  claim 1 , wherein the first source is activated at a higher intensity than the second source at the time of exposure of the first set of pixels. 
     
     
         6 . The computer-implemented method of  claim 1 , wherein the second source is activated at a higher intensity than the first source at the time of exposure of the first set of pixels. 
     
     
         7 . The computer-implemented method of  claim 1 , further comprising:
 determining, by the one or more processing devices, that the 3D image corresponds to an alternative representation of a live person; and   responsive to identifying the subject in the image to be an alternative representation of a live person, preventing access to a secure system.   
     
     
         8 . The computer-implemented method of  claim 1 , wherein the 3D image depicts a user; and the method comprises:
 authenticating the user based on comparing the 3D image of the user to a template image of the user.   
     
     
         9 . The computer-implemented method of  claim 1 , wherein the first source is activated at a different wavelength than the second source at the time of exposure of the first set of pixels. 
     
     
         10 . One or more non-transitory computer-readable storage media coupled to one or more processors and having instructions stored thereon which, when executed by the one or more processors, cause the one or more processors to perform operations comprising:
 receiving data corresponding to a first set of pixels of an image sensor, wherein the first set of pixels are exposed under illumination by a first source;   receiving data corresponding to a second set of pixels of the image sensor, wherein the second set of pixels are exposed under illumination by a second source that is spatially separated from the first source; and   generating the 3D image using the data corresponding to the first set of pixels as a first image of a pair of photometric stereo images, and the data corresponding to the second set of pixels as a second image of the pair of photometric stereo images.   
     
     
         11 . The computer-readable storage media of  claim 10 , wherein the first and second sets of pixels are partially non-overlapping. 
     
     
         12 . The computer-readable storage media of  claim 10 , wherein exposure of the image sensor is controlled by a rolling shutter that exposes the pixels of the image sensor in a row-wise manner. 
     
     
         13 . The computer-readable storage media of  claim 10 , wherein exposure of the image sensor is controlled by a rolling shutter that exposes the pixels of the image sensor in a column-wise manner. 
     
     
         14 . The computer-readable storage media of  claim 10 , wherein the first source is activated at a higher intensity than the second source at the time of exposure of the first set of pixels. 
     
     
         15 . The computer-readable storage media of  claim 10 , wherein the second source is activated at a higher intensity than the first source at the time of exposure of the first set of pixels. 
     
     
         16 . A system, comprising:
 an image sensor;   a first illumination source;   a second illumination source that is spatially separated from the first illumination source;   a one or more processing devices that perform operations comprising:
 receiving data corresponding to a first set of pixels of the image sensor, wherein the first set of pixels are exposed under illumination by the first illumination source; 
 receiving data corresponding to a second set of pixels of the image sensor, wherein the second set of pixels are exposed under illumination by the second illumination source; and 
 generating a three-dimensional (3D) image using the data corresponding to the first set of pixels as a first image of a pair of photometric stereo images, and the data corresponding to the second set of pixels as a second image of the pair of photometric stereo images. 
   
     
     
         17 . The system of  claim 16 , wherein the first and second sets of pixels are partially non-overlapping. 
     
     
         18 . The system of  claim 16 , wherein exposure of the image sensor is controlled by a rolling shutter that exposes the pixels of the image sensor in a row-wise manner. 
     
     
         19 . The system of  claim 16 , wherein exposure of the image sensor is controlled by a rolling shutter that exposes the pixels of the image sensor in a column-wise manner. 
     
     
         20 . The system of  claim 16 , wherein the first illumination source is activated at a higher intensity than the second illumination source at the time of exposure of the first set of pixels.