Method and system to reduce stray light reflection error in time-of-flight sensor arrays

• US 8,675,182 B2
• Filed: 05/01/2012
• Issued: 03/18/2014
• Est. Priority Date: 04/11/2008
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Bamji, Cyrus
• Primary Examiner(s): RATCLIFFE, LUKE D
• Application Number:
  US13/461,443
• Publication Number:
  US 20120229790A1
• Time in Patent Office: 686 Days
• Field of Search: 356 301- 315, 356 401- 41, 356 501- 515, 356 6- 22, 356/28, 356/28.5
• US Class Current: 356/5.01
• CPC Class Codes: G01S 17/36 with phase comparison between the received signal and the contemporaneously transmitted signal
• CPC Class Codes: G01S 17/894 3D imaging with simultaneous measurement of time-of-flight at a 2D array of receiver pixels, e.g. time-of-flight cameras or flash lidar
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating

Abstract

Haze-type phase shift error due to stray light reflections in a phase-type TOF system is reduced by providing a windowed opaque coating on the sensor array surface, the windows permitting optical energy to reach light sensitive regions of the pixels, and by reducing optical path stray reflection. Further haze-type error reduction is obtained by acquiring values for a plurality (but not necessarily all) of pixel sensors in the TOF system pixel sensor array. Next, a correction term for the value (differential or other) acquired for each pixel in the plurality of pixel sensors is computed and stored. Modeling response may be made dependent upon pixel (row,column) location within the sensor array. During actual TOF system runtime operation, detection data for each pixel, or pixel groups (super pixels) is corrected using the stored data. Good optical system design accounts for correction, enabling a simple correction model.

Claims

1. A time of flight (TOF) ranging system comprising:

a source of optical energy for emitting optical energy toward a target object a distance Z away;

an array of light sensitive sensors in an optical path with the target object for detecting reflected optical energy and outputting detection signals, the array of light sensitive sensors having a surface having reflective regions covered with a non-reflective coating, the non-reflective coating surrounding windows for regions for passing the reflected optical energy to the light sensitive sensors; and

a software controlled processor for determining Z distance measurements based on the detection signals of the array of light sensitive sensors.

2. The system of claim 1 further comprising:

a memory accessible to the processor for storing haze correction values for at least some of the light sensitive sensors of the array;

the software controlled processor correcting phase-shift data based on the detection signals from the light sensitive sensors of the array with the haze correction values stored in the memory for at least some of the light sensitive sensors of the array; and

wherein the software controlled processor for determining Z distance measurements based on the detection signals of the array of light sensitive sensors further comprises the software controlled processor for determining Z distance measurements based on the phase-shift data corrected with the haze correction values.

3. The system of claim 1 wherein the windows for the regions for passing the reflected optical energy from the lens to the light sensitive sensors are each oversized relative to an area of a light sensitive portion of a respective light sensitive sensor.

4. The system of claim 2 wherein the light sensitive sensors are pixel sensors and the haze correction values stored in the memory for at least some of the light sensitive sensors of the array comprise correction signal coefficients defined on a super-pixel basis, a super pixel being defined as a pixel plus neighboring pixels within a predetermined radius of pixels in the array.

5. The system of claim 1 wherein the non-reflective coating surrounding the windows includes ink.

6. The system of claim 5 wherein the ink is black ink.

7. The system of claim 1 wherein the non-reflective coating surrounding the windows includes paint.

8. The TOF ranging system of claim 1 wherein the non-reflective coating surrounding the windows is opaque.

9. The time of flight (TOF) ranging system of claim 1 further comprising that the TOF ranging system is a phase shift type TOF ranging system.

10. The TOF ranging system of claim 1 further comprising one or more optical elements, including at least one optical element with an anti-reflective coating facing the array of light sensitive sensors, for receiving the reflected optical energy including reflections of the optical energy emitted from the source.

11. The TOF ranging system of claim 9 further comprising that the at least one optical element with the anti-reflective coating facing the array of light sensitive sensors is at least one lens having the anti-reflective coating.

12. A time of flight (TOF) phase-shift type ranging system comprising:

a source of optical energy for emitting optical energy toward a target object a distance Z away;

an array of pixel sensors in an optical path with the target object for detecting reflected optical energy from the object and outputting detection signals, the array of pixel sensors having a surface having reflective regions covered with a non-reflective coating, the non-reflective coating surrounding windows for regions for passing the reflected optical energy to the pixel sensors; and

a software controlled processor for determining Z distance measurements based on the detection signals of the array of pixel sensors.

13. The system of claim 12 wherein the windows for the regions for passing the reflected optical energy from the lens to the pixel sensors are each oversized relative to an area of a light sensitive portion of a respective pixel sensor.

14. The TOF ranging system of claim 12 further comprising one or more optical elements, including at least one optical element with an anti-reflective coating facing the array of pixel sensors, for receiving the reflected optical energy including reflections of the optical energy emitted from the source.

15. The TOF ranging system of claim 14 further comprising that the at least one optical element with the anti-reflective coating facing the array of pixel sensors is at least one lens having the anti-reflective coating.

16. The system of claim 12 wherein the non-reflective coating surrounding the windows includes ink.

17. The system of claim 12 wherein the non-reflective coating surrounding the windows includes paint.

18. The TOF ranging system of claim 12 wherein the non-reflective coating surrounding the windows is opaque.

19. The system of claim 12 further comprising:

a memory accessible to the processor for storing haze correction values for at least some of the pixel sensors of the array;

the software controlled processor correcting phase-shift data based on the detection signals from the pixel sensors of the array with the haze correction values stored in the memory for at least some of the pixel sensors of the array; and

wherein the software controlled processor for determining Z distance measurements based on the detection signals of the array of pixel sensors further comprises the software controlled processor for determining Z distance measurements based on the phase-shift data corrected with the haze correction values.

20. The system of claim 19 wherein the haze correction values stored in the memory for at least some of the pixel sensors of the array comprise correction signal coefficients defined on a per pixel basis.