Methods and systems for hierarchical de-aliasing time-of-flight (TOF) systems

• US 8,629,976 B2
• Filed: 02/04/2011
• Issued: 01/14/2014
• Est. Priority Date: 10/02/2007
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Hui, Hua, Bamji, Cyrus
• Primary Examiner(s): RATCLIFFE, LUKE D
• Application Number:
  US13/021,484
• Publication Number:
  US 20110188028A1
• Time in Patent Office: 1,075 Days
• Field of Search: 356 301- 315, 356 401- 41, 356 501- 515, 356 6- 22, 356/28, 356/28.5
• US Class Current: 356/4.01
• 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 7/4915 Time delay measurement, e.g. operational details for pixel components signal extraction and conditioning G01S7/493; Phase measurement

Abstract

A TOF system acquires depth data using n≧3 modulation frequencies f₁, f₂, . . . , f_m separately, associated with separate aliasing interval ranges Z₁, Z₂, . . . , Z_m. Next, n intermediate frequencies f_DE1, f_DE2, . . . , f_DEn are generated sorted by order of f_DE1<f_DE2< . . . <f_DEn and corresponding phases are computed from the data acquired separately using f₁, f₂, . . . , f_m. Hierarchically dealiasing of the thus-acquired data is carried out using the generated intermediate frequencies. Hierarchical dealiasing may be carried out one step at a time, if desired. Thus operated, the TOF system provides an effective aliasing interval range Z_D>Z_k for k=1 . . . n as if said TOF system operated at a very low modulation frequency f_D, while simultaneously providing depth resolution certainty as if said TOF system operated at a high modulation frequency f_E. Preferably high modulation frequency f_E is a function of all modulation frequencies f₁, f₂, . . . , f_m, which function may be an arithmetic mean or a weighted average of f₁, f₂, . . . , f_m.

Claims

1. A processor implemented method to hierarchically dealias distance Z range of a phase-type time of flight system having a processor, the method comprising:

(a) acquiring data from said time of flight system using modulation frequencies f₁, f₂, . . . , f_m separately, wherein if said time of flight time of flight system were operated solely at one of said modulation frequencies, aliasing interval ranges of Z₁, Z₂, . . . , Z_m would result;

(b) generating n intermediate frequencies f_DE1, f_DE2, . . . , f_DEn sorted by order of f_DE1<

f_DE2<

. . . <

f_DEn and computing their corresponding phases from data acquired at step (a); and

(c) hierarchically dealiasing data acquired at step (a) using said intermediate frequencies generated at step (b);

wherein said time of flight system provides an effective aliasing interval range Z_D>

Z_k for k=1 . . . n as if said time of flight system operated at a very low modulation frequency f_D, while simultaneously providing depth resolution certainty as if said time of flight system operated at a high modulation frequency f_E.

2. The method of claim 1, wherein at step (b), selection of said intermediate frequency f_DE1, f_DE2, . . . , f_DEn is based on a ratio between two frequencies

3. The method of claim 1, wherein at step (c), hierarchical dealiasing is done one step at a time.

4. The method of claim 3, wherein at step (c) includes first dealiasing phase data of f_DE1 using phase of f_D, and then dealiasing phase of f_DE2 using phase of f_DE1.

5. The method of claim 4, wherein at each step phase of f_DE(k+1) is dealiased using phase of f_DEk until a last step, at which phase f_E is dealiased using phase of f_DEn to yield unwrapped phase of f_E.

6. The method of claim 1, wherein f_E is a function of all modulation frequencies f₁, f₂, . . . , f_m, said function selected from at least one of (i) an arithmetic mean of f₁, f₂, . . . , f_m, and (ii) a weighted average of f₁, f₂, . . . , f_m.

7. The method of claim 1, wherein unwrapped phase of f_E is computable as follows:

(i) at a last step of hierarchical de-aliasing, dealiasing phase of each said modulation frequency f₁, f₂, . . . , f_m using f_DEn to get unwrapped phase of each modulation frequency; and

(ii) computing unwrapped phase of f_E using a function between f_E and f₁, f₂, . . . , f_m.

8. The method of claim 1, wherein at each step of dealiasing phase of f_DE(k+1) using phase of f_DEk, a corrected phase cycle of f_DEk within the [0, 2π

] cycle of f<sub>DE(k−

1)</sub> from a previous, de-aliasing step is used to find a correct phase cycle of f_DE(k+1) within a cycle of f_DEk;

wherein correct cycle of f_DE(k+1) within a total unambiguous range Z_D, or the cycle of f_D can be found.

9. The method of claim 1, wherein said method is carried out by said time of flight system.

10. A hierarchical dealiasing unit useable with a phase-based time of flight system, the hierarchical dealiasing unit including a memory and a processor and comprising:

code instructing the processor to cause said time of flight system to acquire data using modulation frequencies f₁, f₂, . . . , f_m separately, wherein if said time of flight system were operated solely at one of said modulation frequencies, aliasing interval ranges of Z₁, Z₂, . . . , Z_m would result;

code instructing the processor to generate n intermediate frequencies f_DE1, f_DE2, . . . , f_DEn sorted by order of f_DE1<

f_DE2<

. . . <

f_DEn and computing their corresponding phases from data acquired at step (a); and

code instructing the processor to hierarchically dealias data acquired using said modulation frequencies f₁, f₂, . . . , f_m separately using said n intermediate frequencies f_DE1, f₂, . . . f_DEn;

wherein said time of flight system provides an effective aliasing interval range Z_D>

Z_k for k=1 . . . n as if said time of flight system operated at a very low modulation frequency f_D, while simultaneously providing depth resolution certainty as if said time of flight system operated at a high modulation frequency f_E.

11. The hierarchical dealiasing unit of claim 10, wherein code instructing the processor to generate selects said intermediate frequency f_DE1, f_DE2, . . . , f_DEn based on a ratio between two frequencies

12. The hierarchical dealiasing unit of claim 10, wherein hierarchical dealiasing is done one step at a time.

13. The hierarchical dealiasing unit of claim 10, wherein there first occurs dealiasing phase data of f_DE1 using phase of f_D, followed by dealiasing phase of f_DE2 using phase of f_DE1.

14. The hierarchical dealiasing unit of claim 12, wherein at each step phase of f_DE(k+1) is dealiased using phase of f_DEk until a last step, at which phase f_E is dealiased using phase of f_DEn to yield unwrapped phase of f_E.

15. The hierarchical dealiasing unit of claim 10, wherein f_E is a function of all modulation frequencies f₁, f₂, . . . , f_m, said function selected from at least one of (i) an arithmetic mean of f₁, f₂, . . . , f_m, and (ii) a weighted average of f₁, f₂, . . . , f_m.

16. The hierarchical dealiasing unit of claim 10, wherein:

unwrapped phase of f_E is computable by, at a last step of hierarchical de-aliasing, dealiasing phase of each said modulation frequency f₁, f₂, . . . , f_m using f_DEn to get unwrapped phase of each modulation frequency; and

computing unwrapped phase of f_E using a function between f_E and f₁, f₂, . . . , f_m.

17. The hierarchical dealiasing unit of claim 10, wherein at each step of dealiasing phase of f_DE(k+1) using phase of f_DEk, a corrected phase cycle of f_DEk within the [0,2π

] cycle of f<sub>DE(k−

1)</sub> from a previous de-aliasing step is used to find a correct phase cycle of f_DE(k+1) within a cycle of f_DEk;

wherein correct cycle of f_DE(k+1) within a total unambiguous range Z_D, or the cycle of f_D can be found.

18. A phase-based time-of-flight system including a processor implementing a hierarchical dealiasing unit, said hierarchical dealiasing unit comprising:

a sensor responsive to the processor and causing said time of flight system to acquire data using modulation frequencies f₁, f₂, . . . , f_m separately, wherein if said time of flight system were operated solely at one of said modulation frequencies, aliasing interval ranges of Z₁, Z₂, . . . , Z_in would result;

a clock interface component for generating n intermediate frequencies f_DE1, f_DE2, . . . , f_DEn sorted by order of f_DE1<

f_DE2<

. . . <

f_DEn and computing their corresponding phases from data acquired at step (a); and

the processor hierarchically dealiasing data acquired using said modulation frequencies f₁, f₂, . . . , f_m separately using said n intermediate frequencies f_DE1, f_DE2, . . . , f_DEn;

wherein said time of flight system provides an effective aliasing interval range Z_D>

Z_k for k=1 . . . n as if said time of flight system operated at a very low modulation frequency f_D, while simultaneously providing depth resolution certainty as if said time of flight system operated at a high modulation frequency f_E.

19. The time of flight system of claim 18, wherein said clock interface component selects said intermediate frequency f_DE1, f_DE2, . . . , f_DEn based on a ratio between two consecutive frequencies f_DE(k+1) which is limited by a ratio determined by an uncertainty requirement.

20. The time of flight system of claim 18, wherein said hierarchical dealiasing unit has at least one characteristic selected from a group consisting of (i) hierarchical dealiasing is done one step at a time, (ii) there first occurs dealiasing phase data of f_DE1 using phase of f_D, followed by dealiasing phase of f_DE2 using phase of f_DE1, (iii) at each step phase of f_DE(k+1) is dealiased using phase of f_DEk until a last step, at which phase f_E is dealiased using phase of f_DEn to yield unwrapped phase of f_E, (iv) f_E is a function of all modulation frequencies f₁, f₂, . . . , f_m said function selected from at least one of (i) an arithmetic mean of f₁, f₂, . . . , f_m, and (ii) a weighted average of f₁, f₂, . . . , f_m, (v) unwrapped phase of f_E is computable by, at a last step of hierarchical de-aliasing, dealiasing phase of each said modulation frequency f₁, f₂, . . . , f_m using f_DEn to get unwrapped phase of each modulation frequency;

and computing unwrapped phase of f_E using a function between f_E and f₁, f₂, . . . , f_m, and (vi) at each step of dealiasing phase of f_DE(k+1) using phase of f_DEk, a corrected phase cycle of f_DEk within the [0, 2π

] cycle of f<sub>DE(−

1)</sub> from a previous de-aliasing step is used to find a correct phase cycle of f_DE(k+1) within a cycle of f_DEk such that correct cycle of f_DE(k+1) within a total unambiguous range Z_D, or the cycle of f_D can be found.