Time of flight camera with stripe illumination

• US 9,435,891 B2
• Filed: 02/15/2013
• Issued: 09/06/2016
• Est. Priority Date: 02/15/2012
• Status: Active Grant

• Current Assignee: Ams Sensors Singapore Pte. Ltd. (Ams-Osram AG)
• Original Assignee: Heptagon Micro Optics Pte Ltd
• Inventors: Oggier, Thierry
• Primary Examiner(s): Ratcliffe, Luke
• Assistant Examiner(s): Abraham, Samantha K
• Application Number:
  US13/767,953
• Publication Number:
  US 20140055771A1
• Time in Patent Office: 1,299 Days
• Field of Search: 356/3.01, 356/4.01, 356/5.01, 356/5.09, 356/9, 356/625
• US Class Current: 1/1
• 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

Abstract

A time of flight (TOF) based camera system includes an illumination module that illuminates only portion of the sensor'"'"'s field of view that translates to a given region of the pixels of the imaging sensor. The acquired data of the pixel region is processed and/or readout, typically. After the exposure time of the first pixel region is completed, a second pixel region is illuminated and the second pixel region is processed. This procedure can be repeated a couple of times up to a few hundred even thousand times until the entire pixel array is readout and possibly read-out a number of times. The full depth image is then reconstructed based on the results from the different pixel region acquisitions. This system can be used to reduce stray light. Compared to state-of-the-art TOF camera, the presented method and device show improvements in background light stability and a reduction in multiple reflections.

Claims

1. A time of flight camera comprising:

an imaging sensor including a two-dimensional array of pixels that demodulates received light from a two dimensional field of view of a scene; and

an illumination module arranged for illuminating, sequentially, respective portions of the field of view of the scene with modulated light, wherein each illuminated portion of the field of view corresponds to a plurality of pixels of a horizontal line of the array and a plurality of pixels of a vertical column of the array, each illuminated portion corresponding to fewer than all of the pixels in the array, wherein different groups of pixels corresponding to respective ones of the illuminated portions partially overlap one another,

wherein the time of flight camera further includes a processor operable to perform a depth calculation based on samples from the different groups of pixels corresponding to respective ones of the partially overlapping portions.

2. A camera as claimed in claim 1, wherein illuminated portions are scanned over the field of view.

3. A camera as claimed in claim 1, wherein the imaging sensor reads out pixels that correspond to the illuminated portions of the field of view.

4. A camera as claimed in claim 1, wherein the illuminated portions are stripe-shaped.

5. A camera as claimed in claim 1, wherein the illuminated portions are horizontal stripes.

6. A camera as claimed in claim 1, wherein the illuminated portions are horizontal stripes that are successively scanned over the entire field of view.

7. A camera as claimed in claim 1, wherein the illumination module comprises a light source and a scanning device for scanning the light from the light source over the field of view.

8. A camera as claimed in claim 7, wherein the scanning of the scanning device is synchronized to the acquisition by the imaging sensor.

9. A camera as claimed in claim 1, wherein the illuminated portions of the field of view are less than 10% of the total field of view.

10. A camera as claimed in claim 1, wherein scanning by the illumination module is controlled by an external signal source.

11. A camera as claimed in claim 1, wherein the imaging sensor acquires multiple samples with each of the pixels that correspond to the illuminated portions of the field of view.

12. A camera as claimed in claim 1 wherein the illumination module comprises a diffractive optical element arranged so that light exiting the illumination module corresponds to a respective one of the portions of the field of view.

13. A camera as claimed in claim 1 wherein the illumination module comprises:

a light source;

a micro-mirror operable to scan light form the light source across the entire field of view; and

a diffractive optical element arranged to receive light reflected by the micro-mirror and to shape the light so that light exiting the illumination module corresponds to a respective one of the portions of the field of view.

14. A camera as claimed in claim 1 wherein each illuminated portion of the field of view corresponds to a plurality of horizontal lines or vertical columns of the array.

15. A method of operation for a time of flight camera, the method comprising:

illuminating, sequentially, respective portions of a two dimensional field of view of a scene with modulated light, wherein each portion of the field of view corresponds to a plurality of pixels of a horizontal line of the array and a plurality of pixels of a vertical column of the array, each portion corresponding to fewer than all of the pixels in the array, wherein different groups of pixels corresponding to respective ones of the illuminated portions partially overlap one another; and

using the two dimensional array of pixels to demodulate received light from the two dimensional field of view of the scene;

acquiring multiple samples in each of the pixels that corresponds to the illuminated portions of the field of view, including the different groups of pixels corresponding to respective ones of the illuminated portions that partially overlap one another; and

performing a depth calculation using the multiple samples from the pixels corresponding to the illuminated portions of the field of view, including the different groups of pixels corresponding to respective ones of the illuminated portions that partially overlap one another.

16. A method as claimed in claim 15, further comprising sequentially illuminating different portions of the field of view.

17. A method as claimed in claim 15, further comprising reading out pixels of an imaging sensor that correspond to the illuminated portions of the field of view.

18. A method as claimed in claim 15, wherein the illuminated portions are stripe-shaped.

19. A method as claimed in claim 15, wherein the illuminated portions are horizontal stripes.

20. A method as claimed in claim 15, wherein the illuminated portions are horizontal stripes that are successively scanned over the entire field of view.

21. A method as claimed in claim 15, wherein illuminating portions of the field of view comprises generating light with a light source and then scanning the light over the field of view with a scanning device.

22. A method as claimed in claim 21, further comprising synchronizing the scanning of the scanning device with acquisition of light from the scene by an imaging sensor.

23. A method as claimed in claim 15 wherein each portion of the field of view corresponds to a plurality of horizontal lines or vertical columns of the array.