PROCESSING OF TIME-OF-FLIGHT SIGNALS
First Claim
1. A method of determining the presence of aliasing or avoiding aliasing within certain limits in correlation measurements in a time-of-flight system having an imaging sensor and being for use with an illumination unit, the illumination unit being adapted to illuminate a scene with modulated light, the system being adapted to obtain correlation measurements between a correlation signal and modulated light reflected from the scene,the method comprising:
- a) detecting reflected light from at least one object in the scene;
b) determining by one or more first correlation measurements a first correlation between a first correlation signal and the reflected light received at the imaging sensor the first correlation signal having a periodic waveform of a first frequency and the first correlation measurement providing a value of a parameter related to a distance from the imaging sensor to the at least one object;
c) determining by one or more second correlation measurements a second correlation between the reflected light received at the imaging sensor and a second correlation signal, the second correlation signal having a periodic waveform of a second frequency lower than the first frequency;
d) determining for that value of the parameter the presence of aliasing from the second correlation measurement, andwherein the first and/or second correlation measurements are combined into aliasing indicators, the presence of aliasing is determined from indicators being the sign of the in-phase and/or quadrature components of the detected reflected light.
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Accused Products
Abstract
Described herein is a method and sensor of processing time-of-flight (TOF) signals in a TOF camera system including an illumination unit and an imaging sensor. The method comprises illuminating the scene with light at a first frequency, detecting reflected light from at least one object in the scene at the first frequency, and determining a phase measurement using I and Q values. In addition, the scene is illuminated with light at a second frequency, the second frequency being 2−n of the first frequency where n=1, 2, . . . , etc., and the signs of I and Q values for both the first and second frequencies is used to determine the presence of aliasing in the phase measurement so that it can be corrected. The phase measurement is then corrected for aliasing and the effective range of the TOF camera system is extended by multiples of 2n. In addition, relative signal strength needs to be considered in accordance with the reflectivity of objects within the scene. For a reflectivity of 4% and no aliasing, the ability to detect an object decreases with distance (30). For an aliased phase measurement for an object with a reflectivity of 100%, the ability to detect the object is substantially constant (35).
55 Citations
24 Claims
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1. A method of determining the presence of aliasing or avoiding aliasing within certain limits in correlation measurements in a time-of-flight system having an imaging sensor and being for use with an illumination unit, the illumination unit being adapted to illuminate a scene with modulated light, the system being adapted to obtain correlation measurements between a correlation signal and modulated light reflected from the scene,
the method comprising: -
a) detecting reflected light from at least one object in the scene; b) determining by one or more first correlation measurements a first correlation between a first correlation signal and the reflected light received at the imaging sensor the first correlation signal having a periodic waveform of a first frequency and the first correlation measurement providing a value of a parameter related to a distance from the imaging sensor to the at least one object; c) determining by one or more second correlation measurements a second correlation between the reflected light received at the imaging sensor and a second correlation signal, the second correlation signal having a periodic waveform of a second frequency lower than the first frequency; d) determining for that value of the parameter the presence of aliasing from the second correlation measurement, and wherein the first and/or second correlation measurements are combined into aliasing indicators, the presence of aliasing is determined from indicators being the sign of the in-phase and/or quadrature components of the detected reflected light. - View Dependent Claims (2, 3, 4, 5, 6, 16)
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7-15. -15. (canceled)
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17. A method of determining the presence of aliasing or avoiding aliasing within certain limits in correlation measurements in a time-of-flight system having an imaging sensor and being for use with an illumination unit, the illumination unit being adapted to illuminate a scene with modulated light, the system being adapted to obtain correlation measurements between a correlation signal and modulated light reflected from the scene,
the method comprising: -
a) detecting reflected light from at least one object in the scene; b) determining by one or more first correlation measurements a first correlation between a first correlation signal and the reflected light received at the imaging sensor the first correlation signal having a periodic waveform of a first frequency and the first correlation measurement providing a value of a parameter related to a distance from the imaging sensor to the at least one object; c) determining by one or more second correlation measurements a second correlation between the reflected light received at the imaging sensor and a second correlation signal, the second correlation signal having a periodic waveform of a second frequency lower than the first frequency; d) determining for that value of the parameter the presence of aliasing from the second correlation measurement; and wherein the second correlation signal is a pulse-shaped MIX signal, starting with a pulse of a first length, followed by a pulse of a second length and ended with a pulse of a third length to balance the duty cycle of the second correlation signal to be 50%. - View Dependent Claims (18)
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19. A time of flight or range finding sensor unit, having means for determining the presence of aliasing or to avoid aliasing within certain limits, the sensor being for use with an illumination unit, the illumination unit being adapted to illuminate the scene with modulated light, the system being adapted to obtain correlation measurements between a correlation signal and modulated light reflected from the scene,
the sensor unit comprising: -
a) first means for detecting reflected light from at least one object in the scene; b) second means for determining by a first correlation measurement a first correlation between the first signal and the reflected light received at the imaging sensor, the first correlation measurement providing a value of a parameter related to a distance from the imaging sensor to the scene; c) third means for determining by a second correlation measurement a second correlation between the reflected light received at the imaging sensor and a second signal, the second signal having a periodic waveform of a second frequency lower than the first frequency; d) fourth means for determining, for that value, the presence of aliasing from the second correlation measurement, and wherein; the third means for determining the second correlation is adapted to perform the second correlation measurement at different phase offsets for the second frequency; and wherein the sensor unit is adapted to determine in-phase and/or quadrature components of the detected reflected light from the second correlation measurement, and the fourth means using the in-phase and/or quadrature components to determine the presence of aliasing, whereby the presence of aliasing is determined optionally by using a confidence level determined from a distance related factor, the distance related factor optionally being the amount of reflected light modulated at the first frequency and/or second frequency, the size of a speckle pattern, the size of an imposed pattern and wherein the means for determining in-phase and/or quadrature components is optionally adapted to determine the presence of aliasing from the sign of the in-phase and/or quadrature components of the detected reflected light. - View Dependent Claims (20, 21, 22, 23, 24)
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Specification