Patent Publication Number: US-2021192243-A1

Title: Method, system, and computer-readable medium for generating spoofed structured light illuminated face

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of International Application No. PCT/CN2019/104232, filed on Sep. 3, 2019, which claims priority to U.S. Provisional Application No. 62/732,783, filed on Sep. 18, 2018. The entire disclosures of the aforementioned applications are incorporated herein by reference. 
    
    
     BACKGROUND OF THE DISCLOSURE 
     1. Field of the Disclosure 
     The present disclosure relates to the field of testing security of face recognition systems, and more particularly, to a method, system, and computer-readable medium for generating a spoofed structured light illuminated face for testing security of a structured light-based face recognition system. 
     2. Description of the Related Art 
     Over the past few years, biometric authentication using face recognition has become increasingly popular for mobile devices and desktop computers because of the advantages of security, fast speed, convenience, accuracy, and low cost. Understanding limits of face recognition systems can help developers design more secure face recognition systems that have fewer weak points or loopholes that can be attacked by spoofed faces. 
     SUMMARY 
     An object of the present disclosure is to propose a method, system, and computer-readable medium for generating a spoofed structured light illuminated face for testing security of a structured light-based face recognition system. 
     In a first aspect of the present disclosure, a method includes: 
     determining, by at least one processor, a first spatial illumination distribution using a first image caused by at least first structured light and a second image caused by at least second structured light, wherein a first portion of the first image is caused by a first portion of the at least first structured light traveling a first distance, a first portion of the second image is caused by a first portion of the at least second structured light traveling a second distance, the first portion of the first image and the first portion of the second image cause a same portion of the first spatial illumination distribution, and the first distance is different from the second distance; 
     building, by the at least one processor, a first 3D face model; 
     rendering, by the at least one processor, the first 3D face model using the first spatial illumination distribution, to generate a first rendered 3D face model; and 
     displaying, by a first display, the first rendered 3D face model to a first camera for testing a face recognition system. 
     According to an embodiment in conjunction with the first aspect of the present disclosure, the step of determining the first spatial illumination distribution using the first image caused by the at least first structured light and the second image caused by the at least second structured light includes: determining the first spatial illumination distribution using the first image caused only by the first structured light and the second image caused only by the second structured light, wherein the first portion of the first image is caused by a first portion of the first structured light traveling the first distance, the first portion of the second image is caused by a first portion of the second structured light traveling the second distance; and the method further includes: determining a second spatial illumination distribution using a third image caused only by first non-structured light and a fourth image caused only by second non-structured light, wherein a first portion of the third image is caused by a first portion of the first non-structured light traveling a third distance, a first portion of the fourth image is caused by a first portion of the second non-structured light traveling a fourth distance, the first portion of the third image and the first portion of the fourth image cause a same portion of the second spatial illumination distribution, and the third distance is different from the fourth distance. 
     According to an embodiment in conjunction with the first aspect of the present disclosure, the method further includes: 
     illuminating a first projection surface with the first non-structured light; 
     capturing the third image, wherein the third image reflects a third spatial illumination distribution on the first projection surface illuminated by the first non-structured light; 
     illuminating a second projection surface with the second non-structured light; and 
     capturing the fourth image, wherein the fourth image reflects a fourth spatial illumination distribution on the second projection surface illuminated by the second non-structured light; 
     wherein the first projection surface is or is not the second projection surface. 
     According to an embodiment in conjunction with the first aspect of the present disclosure, the method further includes: 
     projecting to a first projection surface with the at least first structured light, wherein the at least first structured light is unbent by any optical element before traveling to the first projection surface; and 
     capturing the first image, wherein the first image reflects a fifth spatial illumination distribution on the first projection surface illuminated by the at least first structured light; 
     projecting to a second projection surface with the at least second structured light, wherein the at least second structured light is unbent by any optical element before traveling to the second projection surface; and 
     capturing the second image, wherein the second image reflects a sixth spatial illumination distribution on the second projection surface illuminated by the at least second structured light; 
     wherein the first projection surface is or is not the second projection surface. 
     According to an embodiment in conjunction with the first aspect of the present disclosure, the method further includes: 
     projecting to a first projection surface and a second projection surface with at least third structured light, wherein the at least third structured light is reflected by a reflecting optical element and split by a splitting optical element into the at least first structured light and the at least second structured light correspondingly traveling to the first projection surface and the second projection surface; 
     capturing the first image, wherein the first image reflects a seventh spatial illumination distribution on the first projection surface illuminated by the at least first structured light; and 
     capturing the second image, wherein the second image reflects an eighth spatial illumination distribution on the second projection surface illuminated by the at least second structured light. 
     According to an embodiment in conjunction with the first aspect of the present disclosure, the method further includes: 
     capturing the first image and the second image by at least one camera. 
     According to an embodiment in conjunction with the first aspect of the present disclosure, the step of building the first 3D face model includes: 
     perform scaling such that the first 3D face model is scaled in accordance with a fifth distance between the first display and the first camera when the first rendered 3D face model is displayed by the first display to the first camera. 
     According to an embodiment in conjunction with the first aspect of the present disclosure, the step of building the 3D face model includes: 
     extracting facial landmarks using a plurality of photos of a target user; 
     reconstructing a neutral-expression 3D face model using the facial landmarks; 
     patching the neutral-expression 3D face model with facial texture in one of the photos, to obtain a patched 3D face model; 
     scaling the patched 3D face model in accordance with a fifth distance between the first display and the first camera when the first rendered 3D face model is displayed by the first display to the first camera, to obtain a scaled 3D face model; 
     performing gaze correction such that eyes of the scaled 3D face model look straight towards the first camera, to obtain a gaze corrected 3D face model; and 
     animating the gaze corrected 3D face model with a pre-defined set of facial expressions, to obtain the first 3D face model. 
     In a second aspect of the present disclosure, a system includes at least one memory, at least one processor, and a first display. The at least one memory is configured to store program instructions. The at least one processor is configured to execute the program instructions, which cause the at least one processor to perform steps including: 
     determining a first spatial illumination distribution using a first image caused by at least first structured light and a second image caused by at least second structured light, wherein a first portion of the first image is caused by a first portion of the at least first structured light traveling a first distance, a first portion of the second image is caused by a first portion of the at least second structured light traveling a second distance, the first portion of the first image and the first portion of the second image cause a same portion of the first spatial illumination distribution, and the first distance is different from the second distance; 
     building a first 3D face model; and 
     rendering the first 3D face model using the first spatial illumination distribution, to generate a first rendered 3D face model. 
     The first display is configured to display the first rendered 3D face model to a first camera for testing a face recognition system. 
     According to an embodiment in conjunction with the second aspect of the present disclosure, the step of determining the first spatial illumination distribution using the first image caused by the at least first structured light and the second image caused by the at least second structured light includes: determining a first spatial illumination distribution using the first image caused only by the first structured light and the second image caused only by the second structured light, wherein the first portion of the first image is caused by a first portion of the first structured light traveling the first distance, the first portion of the second image is caused by a first portion of the second structured light traveling the second distance; and the method further includes: determining a second spatial illumination distribution using a third image caused only by first non-structured light and a fourth image caused only by second non-structured light, wherein a first portion of the third image is caused by a first portion of the first non-structured light traveling a third distance, a first portion of the fourth image is caused by a first portion of the second non-structured light traveling a fourth distance, the first portion of the third image and the first portion of the fourth image cause a same portion of the second spatial illumination distribution, and the third distance is different from the fourth distance. 
     According to an embodiment in conjunction with the second aspect of the present disclosure, the system further includes: 
     a first projection surface configured to be illuminated with the first non-structured light, wherein a third spatial illumination distribution on the first projection surface is reflected in the third image, and the third image is captured by the first camera; and 
     a second projection surface configured to be illuminated with the second non-structured light, wherein a fourth spatial illumination distribution on the second projection surface is reflected in the fourth image, and the fourth image is captured by the first camera; 
     wherein the first projection surface is or is not the second projection surface. 
     According to an embodiment in conjunction with the second aspect of the present disclosure, the system further includes: 
     a first non-structured light illuminator; 
     a first projection surface and a second projection surface, wherein the first projection surface is or is not the second projection surface; and 
     a second camera, wherein the second camera is or is not the first camera; 
     wherein
         the first non-structured light illuminator is configured to illuminate the first projection surface with the first non-structured light;   the second camera is configured to capture the third image, wherein the third image reflects a third spatial illumination distribution on the first projection surface illuminated by the first non-structured light;   the first non-structured light illuminator is further configured to illuminate the second projection surface with the second non-structured light; and   the second camera is further configured to capture the fourth image, wherein the fourth image reflects a fourth spatial illumination distribution on the second projection surface illuminated by the second non-structured light.       

     According to an embodiment in conjunction with the second aspect of the present disclosure, the system further includes: 
     a first projection surface configured for projection with the at least first structured light to be performed to the first projection surface, wherein the at least first structured light is unbent by any optical element before traveling to the first projection surface, a fifth spatial illumination distribution on the first projection surface is reflected in the first image, and the first image is captured by the first camera; and 
     a second projection surface configured for projection with the at least second structured light to be performed to the second projection surface, wherein the at least second structured light is unbent by any optical element before traveling to the second projection surface, a sixth spatial illumination distribution on the second projection surface is reflected in the second image, and the second image is captured by the first camera; 
     wherein the first projection surface is or is not the second projection surface. 
     According to an embodiment in conjunction with the second aspect of the present disclosure, the system further includes: 
     at least first structured light projector; 
     a first projection surface and a second projection surface, wherein the first projection surface is or is not the second projection surface; and 
     a second camera, wherein the second camera is or is not the first camera; 
     wherein
         the at least first structured light projector is configured to project to the first projection surface with the at least first structured light, wherein the at least first structured light is unbent by any optical element before traveling to the first projection surface;   the second camera is configured to capture the first image, wherein the first image reflects a fifth spatial illumination distribution on the first projection surface illuminated by the at least first structured light;   the at least first structured light projector is further configured to project to the second projection surface with the at least second structured light, wherein the at least second structured light is unbent by any optical element before traveling to the second projection surface; and   the second camera is further configured to capture the second image, wherein the second image reflects a sixth spatial illumination distribution on the second projection surface illuminated by the at least second structured light.       

     According to an embodiment in conjunction with the second aspect of the present disclosure, the system further includes: 
     a first projection surface and a second projection surface configured for projection with at least third structured light to be performed to the first projection surface and the second projection surface; 
     wherein
         the at least third structured light is reflected by a reflecting optical element and split by a splitting optical element into the at least first structured light and the at least second structured light correspondingly traveling to the first projection surface and the second projection surface;   a seventh spatial illumination distribution on the first projection surface is reflected in the first image, and the first image is captured by the first camera; and   an eighth spatial illumination distribution on the second projection surface is reflected in the second image, and the second image is captured by the first camera.       

     According to an embodiment in conjunction with the second aspect of the present disclosure, the system further includes: 
     at least first structured light projector; 
     a first projection surface and a second projection surface; and 
     a second camera; 
     a third camera; 
     wherein
         the at least first structured light projector is configured to project to the first projection surface and the second projection surface with at least third structured light;   the at least third structured light is reflected by a reflecting optical element and split by a splitting optical element into the at least first structured light and the at least second structured light correspondingly traveling to the first projection surface and the second projection surface;   the second camera is configured to capture the first image, wherein the first image reflects a seventh spatial illumination distribution on the first projection surface illuminated by the at least first structured light; and   the third camera is configured to capture the second image, wherein the second image reflects an eighth spatial illumination distribution on the second projection surface illuminated by the at least second structured light.       

     According to an embodiment in conjunction with the second aspect of the present disclosure, the system further includes: 
     at least one camera configured to capture the first image and the second image. 
     According to an embodiment in conjunction with the second aspect of the present disclosure, the step of building the first 3D face model includes: 
     perform scaling such that the first 3D face model is scaled in accordance with a fifth distance between the first display and the first camera when the first rendered 3D face model is displayed by the first display to the first camera. 
     According to an embodiment in conjunction with the second aspect of the present disclosure, the step of building the 3D face model includes: 
     extracting facial landmarks using a plurality of photos of a target user; 
     reconstructing a neutral-expression 3D face model using the facial landmarks; 
     patching the neutral-expression 3D face model with facial texture in one of the photos, to obtain a patched 3D face model; 
     scaling the patched 3D face model in accordance with a fifth distance between the first display and the first camera when the first rendered 3D face model is displayed by the first display to the first camera, to obtain a scaled 3D face model; 
     performing gaze correction such that eyes of the scaled 3D face model look straight towards the first camera, to obtain a gaze corrected 3D face model; and 
     animating the gaze corrected 3D face model with a pre-defined set of facial expressions, to obtain the first 3D face model. 
     In a third aspect of the present disclosure, a non-transitory computer-readable medium with program instructions stored thereon is provided. When the program instructions are executed by at least one processor, the at least one processor is caused to perform steps including: 
     determining a first spatial illumination distribution using a first image caused by at least first structured light and a second image caused by at least second structured light, wherein a first portion of the first image is caused by a first portion of the at least first structured light traveling a first distance, a first portion of the second image is caused by a first portion of the at least second structured light traveling a second distance, the first portion of the first image and the first portion of the second image cause a same portion of the first spatial illumination distribution, and the first distance is different from the second distance; 
     building a first 3D face model; 
     rendering the first 3D face model using the first spatial illumination distribution, to generate a first rendered 3D face model; and 
     causing a first display to display the first rendered 3D face model to a first camera for testing a face recognition system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to more clearly illustrate the embodiments of the present disclosure or related art, the following figures will be described in the embodiments are briefly introduced. It is obvious that the drawings are merely some embodiments of the present disclosure, a person having ordinary skill in this field can obtain other figures according to these figures without paying the premise. 
         FIG. 1  is a block diagram illustrating a spoofed structured light illuminated face generation system used to test a structured light-based face recognition system in accordance with an embodiment of the present disclosure. 
         FIG. 2  is a block diagram illustrating the spoofed structured light illuminated face generation system in accordance with an embodiment of the present disclosure. 
         FIG. 3  is a structural diagram illustrating a first setup for calibrating static structured light illumination in accordance with an embodiment of the present disclosure. 
         FIG. 4  is a structural diagram illustrating a second setup for calibrating the static structured light illumination in accordance with an embodiment of the present disclosure. 
         FIG. 5  is a structural diagram illustrating a first setup for calibrating static non-structured light illumination in accordance with an embodiment of the present disclosure. 
         FIG. 6  is a structural diagram illustrating a second setup for calibrating the static non-structured light illumination in accordance with an embodiment of the present disclosure. 
         FIG. 7  is a block diagram illustrating a hardware system for implementing a software module for displaying a first rendered 3D face model in accordance with an embodiment of the present disclosure. 
         FIG. 8  is a flowchart illustrating a method for building a first 3D face model in accordance with an embodiment of the present disclosure. 
         FIG. 9  is a structural diagram illustrating a setup for displaying the first rendered 3D face model to a camera in accordance with an embodiment of the present disclosure. 
         FIG. 10  is a structural diagram illustrating a setup for calibrating dynamic structured light illumination and displaying a first rendered 3D face model to a camera in accordance with an embodiment of the present disclosure. 
         FIG. 11  is a flowchart illustrating a method for generating a spoofed structured light illuminated face in accordance with an embodiment of the present disclosure. 
         FIG. 12  is a flowchart illustrating a method for generating a spoofed structured light illuminated face in accordance with another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Embodiments of the present disclosure are described in detail with the technical matters, structural features, achieved objects, and effects with reference to the accompanying drawings as follows. Specifically, the terminologies in the embodiments of the present disclosure are merely for describing the purpose of the certain embodiment, but not to limit the invention. 
     As used here, the term “using” refers to a case in which an object is directly employed for performing a step, or a case in which the object is modified by at least one intervening step and the modified object is directly employed to perform the step. 
       FIG. 1  is a block diagram illustrating a spoofed structured light illuminated face generation system  100  used to test a structured light-based face recognition system  200  in accordance with an embodiment of the present disclosure. The spoofed structured light illuminated face generation system  100  is a 3D spoofed face generation system configured to generate a spoofed structured light illuminated face of a target user. The structured light-based face recognition system  200  is a 3D face recognition system configured to authenticate whether a face presented to the structured light-based face recognition system  200  is the face of the target user. By presenting the spoofed structured light illuminated face generated by the spoofed structured light illuminated face generation system  100  to the structured light-based face recognition system  200 , security of the structured light-based face recognition system  200  is tested. The structured light-based face recognition system  200  may be a portion of a mobile device or a desktop computer. The mobile device is, for example, a mobile phone, a tablet, or a laptop computer. 
       FIG. 2  is a block diagram illustrating the spoofed structured light illuminated face generation system  100  in accordance with an embodiment of the present disclosure. Referring to  FIG. 2 , the spoofed structured light illuminated face generation system  100  includes at least structured light projector  202 , at least one projection surface  214 , at least one camera  216 , a software module  220  for displaying a first rendered 3D face model, and a display  236 . The at least structured light projector  202 , the at least one projection surface  214 , the at least one camera  216 , and the display  236  are hardware modules. The software module  220  for displaying the first rendered 3D face model includes an illumination calibrating module  222 , an 3D face model building module  226 , an 3D face model rendering module  230 , and a display controlling module  234 . 
     The at least structured light projector  202  is configured to project to one of the at least one projection surface  214  with at least first structured light. The one of the at least one projection surface  214  is configured to display a first spatial illumination distribution caused by the at least first structured light. One of the at least one camera  216  is configured to capture a first image. The first image reflects the first spatial illumination distribution. A first portion of the first image is caused by a first portion of the at least first structured light traveling a first distance to reach the one of the at least one projection surface  214 . The at least structured light projector  202  is further configured to project to the same one or a different one of the at least one projection surface  214  with at least second structured light. The same one or the different one of the at least one projection surface  214  is further configured to display a second spatial illumination distribution caused by the at least second structured light. The same one or a different one of the at least one camera  216  is further configured to capture a second image. The second image reflects the second spatial illumination distribution. A first portion of the second image is caused by a first portion of the at least second structured light traveling a second distance to reach the same one or the different one of the at least one projection surface  214 . The first distance is different from the second distance. The illumination calibrating module  222  is configured to determine a third spatial illumination distribution using the first image and the second image. The first portion of the first image and the first portion of the second image cause a same portion of the third spatial illumination distribution. The 3D face model building module  226  is configured to build a first 3D face model. The 3D face model rendering module  230  is configured to render the first 3D face model using the third spatial illumination distribution, to generate the first rendered 3D face model. The display controlling module  234  is configured to cause the display  236  to display the first rendered 3D face model to a first camera. The display  236  is configured to display the first rendered 3D face model to the first camera. 
     In an embodiment, the at least structured light projector  202  is a structured light projector  204 . The structured light projector  204  is configured to project to the one of the at least one projection surface  214  with only first structured light. The first spatial illumination distribution is caused only by the first structured light. The first portion of the first image is caused by a first portion of the first structured light traveling the first distance to reach the one of the at least one projection surface  214 . The structured light projector  204  is further configured to project to the same one or the different one of the at least one projection surface  214  with only second structured light. The second spatial illumination distribution is caused only by the second structured light. The first portion of the second image is caused by a first portion of the second structured light traveling the second distance to reach the same one or the different one of the at least one projection surface  214 . The spoofed structured light illuminated face generation system  100  further includes a non-structured light illuminator  208 . The non-structured light illuminator  208  is configured to illuminate the one of the at least one projection surface  214  with only first non-structured light. The one of the at least one projection surface  214  is further configured to display a fourth spatial illumination distribution caused only by the first non-structured light. The one of the at least one camera  216  is further configured to capture a third image. The third image reflects the fourth spatial illumination distribution. A first portion of the third image is caused by a first portion of the first non-structured light traveling a third distance to reach the one of the at least one projection surface  214 . The non-structured light illuminator  208  is further configured to illuminate the same one or the different one of the at least one projection surface  214  with only second non-structured light. The same one or the different one of the at least one projection surface  214  is further configured to display a fifth spatial illumination distribution caused only by the second non-structured light. The same one or the different one of the at least one camera  216  is further configured to capture a fourth image. The fourth image reflects the fifth spatial illumination distribution. A first portion of the fourth image is caused by a first portion of the second non-structured light traveling a fourth distance to reach the same one or the different one of the at least one projection surface  214 . The third distance is different from the fourth distance. The third distance may be same as the first distance. The fourth distance may be same as the second distance. The illumination calibrating module  222  is further configured to determine a sixth spatial illumination distribution using the third image and the fourth image. The first portion of the third image and the first portion of the fourth image cause a same portion of the sixth spatial illumination distribution. The 3D face model rendering module  230  is configured to render the first 3D face model using the third spatial illumination distribution and the sixth spatial illumination distribution, to generate the first rendered 3D face model. 
     Alternatively, the 3D face model rendering module  230  is configured to render the first 3D face model using the third spatial illumination distribution, to generate the first rendered 3D face model, and render the first 3D face model using the sixth spatial illumination distribution, to generate a second rendered 3D face model. The display controlling module  234  is configured to cause the display  236  to display the first rendered 3D face model and the second rendered 3D face model to the first camera. The display  236  is configured to display the first rendered 3D face model and the second rendered 3D face model to the first camera. A person having ordinary skill in the art will understand that other rendering alternatives now known or hereafter developed, may be used for spoofing the corresponding structured light-based face recognition system  200 . 
     Still alternatively, the at least structured light projector  202  includes a structured light projector  204  and a non-structured light illuminator  208 . The structured light projector  204  is configured to project to the one of the at least one projection surface  214  with only first structured light. The non-structured light illuminator  208  is configured to illuminate the one of the at least one projection surface  214  with only first non-structured light. The first spatial illumination distribution is caused by a combination of the first structured light and the first non-structured light. The first portion of the first image is caused by a first portion of the combination of the first structured light and the first non-structured light traveling the first distance to reach the one of the at least one projection surface  214 . The structured light projector  204  is further configured to project to the same one or the different one of the at least one projection surface  214  with only second structured light. The non-structured light illuminator  208  is further configured to illuminate the same one or the different one of the at least one projection surface  214  with only second non-structured light. The second spatial illumination distribution is caused by a combination of the second structured light and the second non-structured light. The first portion of the second image is caused by a first portion of the combination of the second structured light and the second non-structured light traveling the second distance to reach the same one or the different one of the at least one projection surface  214 . A person having ordinary skill in the art will understand that other light source alternatives and illumination calibration alternatives now known or hereafter developed, may be used for rendering the first 3D face model. 
     In an embodiment, the structured light projector  204  is a dot projector. The first spatial illumination distribution and the second spatial illumination distribution are spatial point cloud distributions. A spatial point cloud distribution includes shape information, location information, and intensity information of a plurality of point clouds. Alternatively, the structured light projector  204  is a stripe projector. The first spatial illumination distribution and the second spatial illumination distribution are spatial stripe distributions. A spatial stripe distribution includes shape information, location information, and intensity information of a plurality of stripes. A person having ordinary skill in the art will understand that other projector alternatives now known or hereafter developed, may be used for rendering the first 3D face model. 
     In an embodiment, the structured light projector  204  is an infrared structured light projector. The non-structured light illuminator  208  is an infrared non-structured light illuminator such as a flood illuminator. The at least one camera  216  is at least one infrared camera. The display  236  is an infrared display. The first camera is an infrared camera. Alternatively, the structured light projector  204  is a visible structured light projector. The non-structured light illuminator  208  is a visible non-structured light illuminator. The at least one camera  216  is at least one visible light camera. The display  236  is a visible light display. The first camera is a visible light camera. A person having ordinary skill in the art will understand that other light alternatives now known or hereafter developed, may be used for spoofed structured light illuminated face generation and structured light-based face recognition. 
     In an embodiment, the one and the different one of the at least one projection surface  214  are surfaces of corresponding projection screens. Alternatively, the one of the at least one projection surface  214  is a surface of a wall. A person having ordinary skill in the art will understand that other projection surface alternatives now known or hereafter developed, may be used for rendering the first 3D face model. 
     In an embodiment, the structured light projector  204 , the non-structured light illuminator  208 , and the first camera are parts of the structured light-based face recognition system  200  (shown in  FIG. 1 ) configured to illuminate the face of the target user and capture illuminated face of the target user for authentication. The at least one camera  216  is a camera  306  to be described with reference to  FIG. 3 . The first camera is the camera  306  to be described with reference to  FIG. 9 . Alternatively, the structured light projector  204 , the non-structured light illuminator  208 , and/or the camera  306  are not parts of the structured light-based face recognition system  200 , but are of same corresponding component types as corresponding components of the structured light-based face recognition system  200 . In another embodiment, the structured light projector  204 , the non-structured light illuminator  208 , and the first camera are parts of the structured light-based face recognition system  200 . The at least one camera  216  is a camera  1040  and a camera  1042  to be described with reference to  FIG. 10 , and the first camera is a camera  1006  to be described with reference to  FIG. 10 . The camera  1040  and the camera  1042  are same type of cameras as the camera  1006 . A person having ordinary skill in the art will understand that other source of component alternatives now known or hereafter developed, may be used for spoofed structured light illuminated face generation. 
       FIG. 3  is a structural diagram illustrating a first setup  300  for calibrating static structured light illumination in accordance with an embodiment of the present disclosure. Referring to  FIGS. 2 and 3 , the first setup  300  is for implementing steps related to the first spatial illumination distribution performed by the structured light projector  204 , the at least one projection surface  214 , and the at least one camera  216 . The first setup  300  is a setup at time t 1 . In  FIG. 2 , the structured light projector  204  is configured to project to the one of the at least one projection surface  214  with only the first structured light. In the first setup  300 , a structured light projector  302  is configured to project to a projection screen  308  with only the first structured light. Anon-structured light illuminator  304  is covered by a lens cover. In  FIG. 2 , the one of the at least one projection surface  214  is configured to display the first spatial illumination distribution caused only by the first structured light. In the first setup  300 , the projection screen  308  is configured to display the first spatial point cloud distribution caused only by the first structured light. The first spatial point cloud distribution includes shape information, location information, and intensity information of a plurality of first point clouds. Each first point cloud has, for example, a triangular shape, or a circular shape. One  310  of the first point clouds having a triangular shape is exemplarily illustrated in  FIG. 3 . A portion of the first structured light causing corners of the first point cloud  310  is exemplarily illustrated as dashed lines. Other first point clouds and other portions of the first structured light are not shown in  FIG. 3  for simplicity. The projection screen  308  is located with respect to the structured light projector  302  such that a corner  322  of the first point cloud  310  is caused by a portion  312  of the first structured light traveling a distance d 1  to reach the projection screen  308 . The first structured light is unbent by any optical element before traveling to the projection screen  308 . In  FIG. 2 , the one of the at least one camera  216  is configured to capture the first image. The first image reflects the first spatial illumination distribution. The first portion of the first image is caused by the first portion of the first structured light traveling the first distance to reach the one of the at least one projection surface  214 . In the first setup  300 , a camera  306  is configured to capture an image  320 . The image  320  reflects the entire first spatial point cloud distribution. A portion of the image  320  reflecting the corner  322  of the point cloud  310  is caused by the portion  312  of the first structured light. 
       FIG. 4  is a structural diagram illustrating a second setup  400  for calibrating the static structured light illumination in accordance with an embodiment of the present disclosure. Referring to  FIGS. 2 and 4 , the second setup  400  is for implementing steps related to the second spatial illumination distribution performed by the structured light projector  204 , the at least one projection surface  214 , and the at least one camera  216 . The second setup  400  is a setup at time t 2 . Time t 2  is later than time t 1 . In  FIG. 2 , the structured light projector  202  is further configured to project to the same one or the different one of the at least one projection surface  214  with only the second structured light. In the second setup  400 , the structured light projector  302  is further configured to project to a projection screen  408  with only the second structured light. The non-structured light illuminator  304  is covered by the lens cover. In  FIG. 2 , the same one or the different one of the at least one projection surface  214  is further configured to display the second spatial illumination distribution caused only by the second structured light. In the second setup  400 , the projection screen  408  is further configured to display a second spatial point cloud distribution caused only by the second structured light. The second spatial point cloud distribution includes shape information, location information, and intensity information of a plurality of second point clouds. Each second point cloud has, for example, a triangular shape, or a circular shape. One  410  of the second point clouds having a triangular shape is exemplarily illustrated in  FIG. 4 . A portion of the second structured light causing corners of the second point cloud  410  is exemplarily illustrated as dashed lines. Other second point clouds and other portions of the second structured light are not shown in  FIG. 4  for simplicity. The projection screen  408  is located with respect to the structured light projector  302  such that a corner  422  of the second point cloud  410  is caused by a portion  412  of the second structured light traveling a distance d 2  to reach the projection screen  408 . The distance d 2  is longer than the distance d 1 . The second structured light is unbent by any optical element before traveling to the projection screen  408 . A path of the portion  412  of the second structured light is overlapped with a path of the portion  312  (labeled in  FIG. 3 ) of the first structured light such that the second point cloud  410  is an enlarged version of the first point cloud  310  (labeled in  FIG. 3 ). The projection screen  408  may be the same projection screen  308  in  FIG. 3 . In  FIG. 2 , the same one or the different one of the at least one camera  216  is further configured to capture the second image. The second image reflects the second spatial illumination distribution. The first portion of the second image is caused by the first portion of the second structured light traveling the second distance to reach the same one or the different one of the at least one projection surface  214 . The first distance is different from the second distance. In the second setup  400 , the camera  306  is further configured to capture an image  420 . The image  420  reflects the entire second spatial point cloud distribution. A portion of the image  420  reflecting the corner  422  of the point cloud  410  is caused by the portion  412  of the second structured light. 
     Referring to  FIG. 2 , the illumination calibrating module  222  is configured to determine the third spatial illumination distribution using the first image and the second image. The first portion of the first image and the first portion of the second image cause the same portion of the third spatial illumination distribution. Referring to  FIGS. 2, 3 and 4 , the illumination calibrating module  222  is configured to determine the third spatial point cloud distribution using the image  320  and the image  420 . A portion of the image  320  corresponding to the corner  322  of the point cloud  310  and a portion of the image  420  corresponding to the corner  422  of the point cloud  410  cause a same corner of the third spatial point cloud distribution. The third spatial point cloud distribution is a calibrated version of a spatial point cloud distribution of the structured light projector  302 . The first spatial point cloud distribution and the second spatial point cloud distribution are originated from the spatial point cloud distribution of the structured light projector  302 . Calibration of the spatial point cloud distribution of the structured light projector  302  may involve performing extrapolation on the first spatial point cloud distribution and the second spatial point cloud distribution, to obtain the third spatial point cloud distribution. Other setups such that interpolation is performed for calibrating the spatial point cloud distribution of the structured light projector  302  is within the contemplated scope of the present disclosure. Intensity information of the third spatial point cloud distribution is calibrated using the inverse-square law. Calibration of the spatial illumination distribution of the structured light projector  302  may use the distances d 1  and d 2 . The spatial point cloud distribution of the structured light projector  302  is static throughout the structured light-based face recognition system  200  (shown in  FIG. 1 ) illuminating the face of the target user with structured light and capturing structured light illuminated face of the target user, and therefore may be pre-calibrated using the first setup  300  and the second setup  40 . 
       FIG. 5  is a structural diagram illustrating a first setup  500  for calibrating static non-structured light illumination in accordance with an embodiment of the present disclosure. Referring to  FIGS. 2 and 5 , the first setup  500  is for implementing steps related to the fourth spatial illumination distribution performed by the non-structured light illuminator  208 , the at least one projection surface  214 , and the at least one camera  216 . The first setup  500  is a setup at time  3 . Time t 3  is different from time t 1  and t 2  described with reference to  FIGS. 3 and 4 . In  FIG. 2 , the non-structured light illuminator  208  is configured to illuminate the one of the at least one projection surface  214  with only the first non-structured light. In the first setup  500 , a non-structured light illuminator  304  is configured to illuminate a projection screen  508  with only the first non-structured light. The projection screen  508  may be the same projection screen  308 . The structured light projector  302  is covered by a lens cover. In  FIG. 2 , the one of the at least one projection surface  214  is further configured to display the fourth spatial illumination distribution caused only by the first non-structured light. In the first setup  500 , the projection screen  508  is configured to display the fourth spatial illumination distribution caused only by the first non-structured light. The fourth spatial illumination distribution includes intensity information of the first non-structured light. A portion of the first non-structured light illuminating the projection screen  508  is exemplarily illustrated as dashed lines. Other portions of the first non-structured light are not shown in  FIG. 5  for simplicity. The projection screen  308  is located with respect to the non-structured light illuminator  304  such that an illuminated portion  522  of the projection screen  508  is caused by a portion  514  of the first non-structured light traveling a distance d 3  to reach the projection screen  508 . The first non-structured light is unbent by any optical element before traveling to the projection screen  508 . In  FIG. 2 , the one of the at least one camera  216  is further configured to capture the third image. The third image reflects the fourth spatial illumination distribution. The first portion of the third image is caused by the first portion of first non-structured light traveling the third distance to reach the one of the at least one projection surface  214 . In the first setup  500 , the camera  306  is configured to capture an image  520 . The image  520  reflects the entire fourth spatial illumination distribution. A portion of the image  520  reflecting the illuminated portion  522  of the projection screen  508  is caused by the portion  514  of the first non-structured light. 
       FIG. 6  is a structural diagram illustrating a second setup  600  for calibrating the static non-structured light illumination in accordance with an embodiment of the present disclosure. Referring to  FIGS. 2 and 6 , the second setup  600  is for implementing steps related to the fifth spatial illumination distribution performed by the non-structured light illuminator  208 , the at least one projection surface  214 , and the at least one camera  216 . The second setup  600  is a setup at time t 4 . Time t 4  is later than time t 3 . In  FIG. 2 , the non-structured light illuminator  208  is further configured to illuminate the same one or the different one of the at least one projection surface  214  with only the second non-structured light. In the second setup  600 , the non-structured light illuminator  304  is further configured to illuminate a projection screen  608  with only the second non-structured light. The structured light projector  302  is covered by the lens cover. In  FIG. 2 , the same one or the different one of the at least one projection surface  214  is further configured to display the fifth spatial illumination distribution caused only by the second non-structured light. In the second setup  600 , the projection screen  608  is further configured to display the fifth spatial illumination distribution caused only by the second non-structured light. The fifth spatial illumination distribution includes intensity information of the second non-structured light. A portion of the second non-structured light illuminating the projection screen  608  is exemplarily illustrated as dashed lines. Other portions of the second non-structured light are not shown in  FIG. 6  for simplicity. The projection screen  608  is located with respect to the non-structured light illuminator  304  such that an illuminated portion  622  of the projection screen  608  is caused by a portion  614  of the second non-structured light traveling a distance d 4  to reach the projection screen  608 . The distance d 4  is longer than the distance d 3 . The second non-structured light is unbent by any optical element before traveling to the projection screen  608 . A path of the portion  614  of the second non-structured light is overlapped with a path of the portion  514  (labeled in  FIG. 5 ) of the first non-structured light. The projection screen  608  may be the same projection screen  508  in  FIG. 5 . In  FIG. 2 , the same one or the different one of the at least one camera  216  is further configured to capture the fourth image. The fourth image reflects the fifth spatial illumination distribution. The first portion of the fourth image is caused by the first portion of the second non-structured light traveling a fourth distance to reach the same one or the different one of the at least one projection surface  214 . The third distance is different from the fourth distance. In the second setup  600 , the camera  306  is further configured to capture an image  620 . The image  620  reflects the entire fifth spatial illumination distribution. A portion of the image  620  reflecting the illuminated portion  622  of the projection screen  608  is caused by the portion  614  of the second non-structured light. 
     Referring to  FIG. 2 , the illumination calibrating module  222  is further configured to determine the sixth spatial illumination distribution using the third image and the fourth image. The first portion of the third image and the first portion of the fourth image cause the same portion of the sixth spatial illumination distribution. Referring to  FIGS. 2, 5 and 6 , the illumination calibrating module  222  is configured to determine the sixth spatial illumination distribution using the image  520  and the image  620 . A portion of the image  520  corresponding to the illuminated portion  522  of the projection screen  508  and a portion of the image  620  corresponding to the illuminated portion  622  of the projection screen  608  cause a same portion of the sixth spatial illumination distribution. The sixth spatial illumination distribution is a calibrated version of a spatial illumination distribution of the non-structured light illuminator  304 . The fourth spatial illumination distribution and the fifth spatial illumination distribution are originated from the spatial illumination distribution of non-structured light illuminator  304 . Calibration of the spatial illumination distribution of the non-structured light illuminator  304  may involve performing extrapolation on the fourth spatial illumination distribution and the fifth spatial illumination distribution, to obtain the sixth spatial illumination distribution. Other setups such that interpolation is performed for calibrating the spatial illumination distribution of the non-structured light illuminator  304  is within the contemplated scope of the present disclosure. Intensity information of the sixth spatial illumination distribution is calibrated using the inverse-square law. Calibration of the spatial illumination distribution of the non-structured light illuminator  304  may use the distances d 3  and d 4 . The spatial illumination distribution of the non-structured light illuminator  304  is static throughout the structured light-based face recognition system  200  (shown in  FIG. 1 ) illuminating the face of the target user with non-structured light and capturing non-structured light illuminated face of the target user, and therefore may be pre-calibrated using the to first setup  500  and the second setup  600 . 
       FIG. 7  is a block diagram illustrating a hardware system  700  for implementing a software module  220  (shown in  FIG. 2 ) for displaying the first rendered 3D face model in accordance with an embodiment of the present disclosure. The hardware system  700  includes at least one processor  702 , at least one memory  704 , a storage module  706 , a network interface  708 , an input and output (I/O) module  710 , and a bus  712 . The at least one processor  702  sends signals directly or indirectly and/or receives signals directly or indirectly from the at least one memory  704 , the storage module  706 , the network interface  708 , and the I/O module  710 . The at least one memory  704  is configured to store program instructions to be executed by the at least one processor  702  and data accessed by the program instructions. The at least one memory  704  includes a random access memory (RAM), other volatile storage device, and/or read only memory (ROM), or other non-volatile storage device. The at least one processor  702  is configured to execute the program instructions, which configure the at least one processor  702  as the software module  220  for displaying the first rendered 3D face model. The network interface  708  is configured access program instructions and data accessed by the program instructions stored remotely through a network. The I/O module  710  includes an input device and an output device configured for enabling user interaction with the hardware system  700 . The input device includes, for example, a keyboard, or a mouse. The output device includes, for example, a display, or a printer. The storage module  706  is configured for storing program instructions and data accessed by the program instructions. The storage module  706  includes, for example, a magnetic disk, or an optical disk. 
       FIG. 8  is a flowchart illustrating a method  800  for building the first 3D face model in accordance with an embodiment of the present disclosure. The method  800  is performed by the 3D face model building module  226 . In step  802 , facial landmarks are extracted using a plurality of photos of the target user. The facial landmarks may be extracted using a supervised descent method (SDM). In step  804 , a neutral-expression 3D face model is reconstructed using the facial landmarks. In step  806 , the neutral-expression 3D face model is patched with facial texture in one of the photos, to obtain a patched 3D face model. The facial texture in the one of the photos is mapped to the neutral-expression 3D face model. In step  808 , the patched 3D face model is scaled in accordance with a fifth distance between a first display and the first camera (described with reference to  FIG. 2 ) when the first rendered 3D face model is displayed by the first display to the first camera, to obtain a scaled 3D face model. The first display is the display  236  (shown in  FIG. 2 ). The fifth distance is exemplarily illustrated as a distance d 5  between a display  916  and the camera  306  in  FIG. 9 . The step  808  may further include positioning the display  236  in front of the first camera at the fifth distance before the patched 3D face model is scaled. Alternatively, the display  236  is positioned in front of the first camera at the fifth distance after the step  808 . The step  808  is for geometry information of the first rendered 3D face model (described with reference to  FIG. 2 ) obtained by the structured light-based face recognition system  200  (shown in  FIG. 1 ) to match geometry information of the face of the target user stored in the structured light-based face recognition system  200 . In step  810 , gaze correction is performed such that eyes of the scaled 3D face model look straight towards the first camera, to obtain a gaze corrected 3D face model. In step  812 , the gaze corrected 3D face model is animated with a pre-defined set of facial expressions, to obtain the first 3D face model. Examples of the steps  802 ,  804 ,  806 ,  810 , and  812  are described in more detail in “Virtual U: Defeating face liveness detection by building virtual models from your public photos,” Yi Xu, True Price, Jan-Michael Frahm, and Fabian Monrose, In  USENIX security symposium , pp. 497-512, 2016. 
     In method  800 , scaling is performed on a 3D morphable face model. Alternatively, scaling may be performed on a face model reconstructed using shape from shading (SFS). A person having ordinary skill in the art will understand that other face model reconstruction alternatives now known or hereafter developed, may be used for building the first 3D face model to be rendered. 
       FIG. 9  is a structural diagram illustrating a setup  900  for displaying the first rendered 3D face model to the camera  306  in accordance with an embodiment of the present disclosure. Referring to  FIGS. 2 and 9 , the setup  900  is for implementing a step performed by the display  236 . In  FIG. 2 , the display  236  is configured to display the first rendered 3D face model to the first camera. In the setup  900 , a display  916  is configured to display a rendered 3D face model  909  to the camera  306  during time separated from time of static structured light illumination. The structured light projector  302  and the non-structured light illuminator  304  are covered by the lens covers. The rendered 3D face model  909  is a spoofed face illuminated by structured light with the spatial point cloud distribution of the structured light projector  302  described with reference to  FIG. 4 , and non-structured light with the spatial illumination distribution of the non-structured light illuminator  304  described with reference to  FIG. 6 . The rendered 3D face model  909  includes a plurality of point clouds deformed by the first 3D face model described with reference to  FIG. 2  and a portion  918  of the face illuminated only by the non-structured light with the spatial illumination distribution of the non-structured light illuminator  304 . A point cloud  910  deformed by the first 3D face model is illustrated as an example. Other point clouds deformed by the first 3D face model are not shown in  FIG. 9  for simplicity. 
       FIG. 10  is a structural diagram illustrating a setup  1000  for calibrating dynamic structured light illumination and displaying a first rendered 3D face model to a camera in accordance with an embodiment of the present disclosure. Compared to the first setup  300  in  FIG. 3 , the second setup  400  in  FIG. 4 , and the setup  900  in  FIG. 9  which are for calibrating static structured light illumination and displaying the first 3D face model rendered with the static structured light illumination, the setup  1000  is for calibrating dynamic structured light illumination and displaying the first 3D face model rendered with the dynamic structured light illumination. In  FIG. 2 , the structured light projector  204  is configured to project to the one of the at least one projection surface  214  with only the first structured light. The one of the at least one projection surface  214  is configured to display the first spatial illumination distribution caused only by the first structured light. The structured light projector  204  is further configured to project to the same one or the different one of the at least one projection surface  214  with only the second structured light. The same one or the different one of the at least one projection surface  214  is further configured to display the second spatial illumination distribution caused only by the second structured light. Compared to the first setup  300  and the second setup  400  which generate the first structured light and the second structured light correspondingly at time t 1  and time t 2 , the setup  1000  generate the first structured light and the second structured light at the same time. In the setup  1000 , a structured light projector  1002  is configured to project to a projection screen  1020  and a projection screen  1022  with only third structured light. The third structured light is reflected by a reflecting optical element  1024  and split by a splitting optical element  1026  into the first structured light and the second structured light correspondingly traveling to the projection screen  1020  and the projection screen  1022 . The reflecting optical element  1024  may be a mirror. The splitting optical element  1026  may be a 50:50 beam splitter. The projection screen  1020  is located with respect to the structured light projector  1002  such that a corner  1034  of a first point cloud  1033  is caused by a portion  1032  of the first structured light traveling a distance d 6  (not labeled) to reach the projection screen  1020 . The projection screen  1022  is located with respect to the structured light projector  1002  such that a corner  1037  of a second point cloud  1038  is caused by a portion  1036  of the second structured light traveling a distance d 7  (not labeled) to reach the projection screen  1022 . The distance d 7  is longer than the distance d 6 . In  FIG. 2 , the one of the at least one camera  216  is configured to capture the first image. The first image reflects the first spatial illumination distribution. The same one or the different one of the at least one camera  216  is further configured to capture the second image. The second image reflects the second spatial illumination distribution. Compared to the first setup  300  and the second setup  400  which correspondingly capture the image  320  and the image  420  using the camera  306 , the setup  1000  captures an image  1044  and an image  1046  correspondingly using the camera  1040  and the camera  1042 . The image  1044  reflects an entire first spatial point cloud distribution. The image  1046  reflects an entire second point cloud distribution. 
     Referring to  FIG. 2 , the illumination calibrating module  222  is configured to determine the third spatial illumination distribution using the first image and the second image. Referring to  FIGS. 3, 4 and 10 , compared to the illumination calibrating module  222  that calibrates the spatial point cloud distribution of the structured light projector  302  in  FIGS. 3 and 4  using the distances d 1  and d 2 , the illumination calibrating module  222  for the setup  1000  calibrates a spatial point cloud distribution of the structured light projector  1002  using a first total distance and a second total distance. The first total distance is a sum of a distance of a path between the structured light projector  1002  and the reflecting optical element  1024  along which a portion  1028  of the third structured light travels, a distance of a path between the reflecting optical element  1024  and the splitting optical element  1026  along which a portion  1030  of the third structured light travels, and a distance of a path between the splitting optical element  1026  and the projection screen  1020  along which the portion  1032  of the first structured light travels. The second total distance is a sum of the distance of the path between the structured light projector  1002  and the reflecting optical element  1024  along which the portion  1028  of the third structured light travels, a distance of the path between the reflecting optical element  1024  and the splitting optical element  1026  along which the portion  1030  of the third structured light travels, and a distance of a path between the splitting optical element  1026  and the projection screen  1022  along which the portion  1036  of the second structured light travels. 
     Referring to  FIG. 10 , a spatial illumination distribution of a non-structured light illuminator  1004  may be static and pre-calibrated using the first setup  500  in  FIG. 5  and the second  30  setup  600  in  FIG. 6 . The non-structured light illuminator  1004  is covered by lens cover in the setup  1000 . Alternatively, a spatial illumination distribution of the non-structured light illuminator  1004  may be dynamic and calibrated together with the spatial point cloud distribution of the structured light projector  1002 . The spatial illumination distribution of the non-structured light illuminator  1004  may be calibrated similarly as the spatial point cloud distribution of the structured light projector  1002 . 
     Referring to  FIG. 2 , the display  236  is configured to display the first rendered 3D face model to the first camera. Compared to the setup  900  in  FIG. 9  which displays the rendered 3D face model  909  to the camera  306  during the time separated from the time of the static structured light illumination, a display  1016  in  FIG. 10  is configured display a plurality of rendered 3D face models to the camera  1006  during time overlapped with time of the dynamic structured light illumination. One  1009  of the rendered 3D face models is exemplarily illustrated in  FIG. 10 . The rendered 3D face model  1009  may be rendered similarly as the rendered 3D face model  909 . 
       FIG. 11  is a flowchart illustrating a method for generating a spoofed structured light illuminated face in accordance with an embodiment of the present disclosure. Referring to  FIGS. 2, 3, 4, and 7 , the method for generating the spoofed structured light illuminated face includes a method  1110  performed by or with the at least structured light projector  202 , the at least one projection surface  214 , and the at least one camera  216 , a method  1130  performed by the at least one processor  702 , and a method  1150  performed by the display  236 . 
     In step  1112 , projection with at least first structured light is performed to a first projection surface by the at least structured light projector  202 . The first projection surface is one of the at least one projection surface  214 . The at least first structured light is unbent by any optical element before traveling to the first projection surface using the first setup  300 . In step  1114 , a first image caused by the at least first structured light is captured by the at least one camera  216 . In step  1116 , projection with at least second structured light is performed to a second projection surface by the at least structured light projector  202 . The second projection surface is the same one or a different one of the at least one projection surface  214 . The at least second structured light is unbent by any optical element before traveling to the second projection surface using the second setup  400 . In step  1118 , a second image caused by the at least second structured light is captured by the at least one camera  216 . In step  1132 , a first spatial illumination distribution is determined using the first image and the second image by the illumination calibrating module  222  for the first setup  300  and the second setup  400 . In step  1134 , a first 3D face model is built by the 3D face model building module  226 . In step  1136 , the first 3D face model is rendered using the first spatial illumination distribution, to generate a first rendered 3D face model by the 3D face model rendering module  230 . In step  1138 , a first display is caused to display the first rendered 3D face model to a first camera by the display controlling module  234 . The first display is the display  236 . In step  1152 , the first rendered 3D face model is displayed to the first camera by the display  236 . 
       FIG. 12  is a flowchart illustrating a method for generating a spoofed structured light illuminated face in accordance with another embodiment of the present disclosure. Referring to  FIGS. 2, 7, and 10 , compared to the method for generating the spoofed structured light illuminated face described with reference to  FIG. 11 , the method for generating the spoofed structured light illuminated face includes a method  1210  performed by or with the at least structured light projector  202 , the at least one projection surface  214 , and the at least one camera  216  instead of the method  1110 . 
     In step  1212 , projection with at least third structured light is performed to a first projection surface and a second projection surface by the at least structured light projector  202 . The first projection surface is one of the at least one projection surface  214 . The second projection surface is a different one of the at least one projection surface. The at least third structured light is reflected by a reflecting optical element and split by a splitting optical element into at least first structured light and at least second structured light correspondingly traveling to the first projection surface and the second projection surface using the setup  1000 . In step  1214 , a first image caused by the at least first structured light is captured by the at least one camera  216 . In step  1216 , a second image caused by the at least second structured light is captured by the at least one camera  216 . 
     Some embodiments have one or a combination of the following features and/or advantages. In an embodiment, a spatial illumination distribution of at least structured light projector of a structured light-based face recognition system is calibrated by determining a first spatial illumination distribution using a first image caused by at least first structured light and a second image caused by at least second structure light. A first portion of the first image is caused by a first portion of the at least first structured light traveling a first distance. A first portion of the second image is caused by a first portion of the at least second structured light traveling a second distance. The first portion of the first image and the first portion of the second image cause a same portion of the first spatial illumination distribution. The first distance is different from the second distance. A first 3D face model of a target user is rendered using the first spatial illumination distribution, to generate a first rendered 3D face model. The first rendered 3D face model is displayed by a first display to a first camera of the structured light-based face recognition system. Therefore, a simple, fast, and accurate method for calibrating the spatial illumination distribution of the at least structured light projector is provided for testing the structured light-based face recognition system, which is a 3D face recognition system. In an embodiment, scaling is performed such that the first 3D face model is scaled in accordance with a distance between the first display and the first camera when the first rendered 3D face model is displayed by the first display to the first camera. Hence, geometry information of the first rendered 3D face model obtained by the structured light-based face recognition system may match geometry information of the face of the target user stored in the structured light-based face recognition system during testing. 
     A person having ordinary skill in the art understands that each of the units, modules, algorithm, and steps described and disclosed in the embodiments of the present disclosure are realized using electronic hardware or combinations of software for computers and electronic hardware. Whether the functions run in hardware or software depends on the condition of application and design requirement for a technical plan. A person having ordinary skill in the art can use different ways to realize the function for each specific application while such realizations should not go beyond the scope of the present disclosure. 
     It is understood by a person having ordinary skill in the art that he/she can refer to the working processes of the system, device, and module in the above-mentioned embodiment since the working processes of the above-mentioned system, device, and module are basically the same. For easy description and simplicity, these working processes will not be detailed. 
     It is understood that the disclosed system, device, and method in the embodiments of the present disclosure can be realized with other ways. The above-mentioned embodiments are exemplary only. The division of the modules is merely based on logical functions while other divisions exist in realization. It is possible that a plurality of modules or components are combined or integrated in another system. It is also possible that some characteristics are omitted or skipped. On the other hand, the displayed or discussed mutual coupling, direct coupling, or communicative coupling operate through some ports, devices, or modules whether indirectly or communicatively by ways of electrical, mechanical, or other kinds of forms. 
     The modules as separating components for explanation are or are not physically separated. The modules for display are or are not physical modules, that is, located in one place or distributed on a plurality of network modules. Some or all of the modules are used according to the purposes of the embodiments. 
     Moreover, each of the functional modules in each of the embodiments can be integrated in one processing module, physically independent, or integrated in one processing module with two or more than two modules. 
     If the software function module is realized and used and sold as a product, it can be stored in a readable storage medium in a computer. Based on this understanding, the technical plan proposed by the present disclosure can be essentially or partially realized as the form of a software product. Or, one part of the technical plan beneficial to the conventional technology can be realized as the form of a software product. The software product in the computer is stored in a storage medium, including a plurality of commands for a computational device (such as a personal computer, a server, or a network device) to run all or some of the steps disclosed by the embodiments of the present disclosure. The storage medium includes a USB disk, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a floppy disk, or other kinds of media capable of storing program codes. 
     While the present disclosure has been described in connection with what is considered the most practical and preferred embodiments, it is understood that the present disclosure is not limited to the disclosed embodiments but is intended to cover various arrangements made without departing from the scope of the broadest interpretation of the appended claims.