Method and system for lossless dealiasing in time-of-flight (TOF) systems

• US 7,791,715 B1
• Filed: 10/02/2007
• Issued: 09/07/2010
• Est. Priority Date: 10/02/2006
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Canesta Incorporated (Microsoft Corporation)
• Inventors: Bamji, Cyrus
• Primary Examiner(s): COFFA, SERGIO
• Application Number:
  US11/906,609
• Time in Patent Office: 1,071 Days
• Field of Search: 356/4.01, 356/5.01, 356/5.1
• US Class Current: 356/5.1
• CPC Class Codes: G01C 3/08 Use of electric radiation detectors
• 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 7/481 Constructional features, e.g. arrangements of optical elements
• CPC Class Codes: G01S 7/491 Details of non-pulse systems

Abstract

Time-of-flight (TOF) phase-derived data is dealiased by operating the TOF system using at least two close-together modulation frequencies f₁ and f₂ that are close to the TOF system maximum modulation frequency f_m. On one hand, phase data acquired by the TOF is associated with a desirably long aliasing interval range Z_AIR normally associated with a rather low modulation frequency. On the other hand, phase data acquired by the TOF system is also associated with the high precision certainty as to Z value normally associated with high modulation frequency. Preferably the TOF system operates always close to f_m such that TOF operating efficiency is high, and system signal/noise ratio is not substantially degraded using the present invention.

Claims

1. A method of dealiasing distance Z range of a phase-type time of flight (TOF) system operable at a maximum modulation frequency f_m, comprising the following steps:

(a) acquiring data from said TOF system using at least a first modulation frequency f₁ and using a second modulation frequency f₂, wherein operation of said TOF system solely at f₁ would yield an aliasing interval range of Z_AIR1, and operation of said TOF system solely at f₂ would yield an aliasing interval range of Z_AIR2, where Z_AIR2>

Z_AIR1; and

(b) processing phase data acquired at step (a) so as to cause said TOF system to provide an effective aliasing interval range Z_AIRD, where Z_AIRD>

Z_AIR2>

Z_AIR1, said Z_AIRD corresponding to operation of said TOF system at an effective dealiasing frequency f_D that is proportional to;

A·

f₁−

B·

f₂, where A and B are weighting factors, and to provide Z resolution certainty exceeding what said TOF system produces by processing data acquired solely while operating at said modulation frequency f₁ and disregarding data acquired at said modulation frequency f₂, and to provide Z resolution certainty exceeding what said TOF system produces by processing data acquired solely while operating at said modulation frequency f₂ and disregarding data acquired at said modulation frequency f₁.

2. The method of claim 1, wherein at step (b) said weighting factors have a characteristic selected from a group consisting of (i) A and B are both positive, (ii) A and B are both negative, and (iii) A and B have opposite signs.

3. The method of claim 2, wherein at step (b) f_d<

<

f_m.

4. The method of claim 1, wherein at step (b) said TOF system acquiring data at an effective operating modulation frequency f_E where f₂<

f_E≦

f_m.

5. The method of claim 1, wherein at step (a), said first modulation frequency f₁ is within a range of about 60% to 100% of said maximum modulation frequency f_m.

6. The method of claim 1, wherein at step (a), said second modulation frequency f₂ is within a range of about 35% to 99% of said first modulation frequency f₁.

7. The method of claim 1, wherein said TOF system includes an array of pixel detectors, and wherein step (a) includes obtaining said data from said pixel detectors that are adjacent each other in said array.

8. The method of claim 1, wherein said TOF system includes an array of pixel detectors, and wherein step (a) includes obtaining said data from said pixel detectors sequentially in time.

9. The method of claim 1, wherein step (a) is carried out such that offsets associated with said data acquired at said first modulation frequency f₁ are at least partially cancelled using said data acquired at said second modulation frequency f₂.

10. The method of claim 1, wherein step (b) is carried out hierarchically.

11. A dealiasing subsystem to dealias distance Z range, useable with a phase-type time of flight (TOF) system operable at a maximum modulation frequency f_m, the dealiasing subsystem comprising:

means for causing said TOF system to acquire data using at least a first modulation frequency f₁ and using a second modulation frequency f₂, wherein operation of said TOF system solely at f₁ would yield an aliasing interval range of Z_AIR1, and operation of said TOF system solely at f₂ would yield an aliasing interval range of Z_AIR2, where Z_AIR2>

Z_AIR1; and

means for processing phase data acquired by said TOF system to cause said TOF system to provide an effective aliasing interval range Z_AIRD, where Z_AIRD>

Z_AIR2>

Z_AIR1, Z_AIRD corresponding to operation of said TOF system at an effective dealiasing frequency f_D proportional to;

A·

f₁−

B·

f₂, where A and B are weighting factors, and to provide Z resolution certainty exceeding what said TOF system produces by processing data acquired solely while operating at said modulation frequency f₁ and disregarding data acquired at said modulation frequency f₂, and to provide Z resolution certainty exceeding what said TOF system produces by processing data solely while operating at said modulation frequency f₂ and disregarding data acquired at said modulation frequency f₁.

12. The subsystem of claim 11, wherein said means for processing causes said TOF system acquiring data at an effective dealiasing frequency f_D proportional to a function of f₁ and f₂.

13. The subsystem of claim 11, wherein said means for processing causes said TOF system to function as though it were acquiring data at an effective operating modulation frequency f_E where f₂<

f_E≦

f_m.

14. The subsystem of claim 11, wherein said means for causing causes said TOF system to operate such that said first modulation frequency f₁ is within a range of about 60% to 100% of said maximum modulation frequency f_m.

15. The subsystem of claim 11, wherein said means for causing causes said TOF system to operate such that said second modulation frequency f₂ is within a range of about 35% to 99% of said first modulation frequency f₁.

16. The subsystem of claim 11, wherein said TOF system includes an array of pixel detectors, and wherein said means for processing causes said TOF system to obtain said data from said pixel detectors that are adjacent each other in said array.

17. The subsystem of claim 11, wherein said TOF system includes an array of pixel detectors, and wherein said means for processing causes said TOF system to obtain said data from said pixel detectors sequentially in time.

18. The subsystem of claim 11, wherein said means for causing causes offsets associated with said data acquired at said first modulation frequency f₁ are at least partially cancelled using said data acquired at said second modulation frequency f₂.

19. The subsystem of claim 11, wherein said means for processing functions hierarchically.

20. The subsystem of claim 11, wherein at least one of said means for causing and said means for processing includes at least one executable software routine on media.