Time of flight camera
A method of determining distances to features in a scene comprising transmitting structured light modulated at a modulation frequency to illuminate the scene with a structured illumination pattern and for each combination of a sampling phase offset ψ k and a perturbation phase shift λ n , modulating sensitivity of a photo sensor at the frequency of modulation of the transmitted light, but phase shifted relative to phase of the transmitted light by a phase θ k,n =(ψ k +λ n ), and for each value of θ k,n modulo 360°, registering light reflected by features in the scene during a different exposure and using the registered light to provide a range image of the scene.
1. A continuous wave time of flight (CW-TOF) camera operable to determine distances to features in a scene, the CW-TOF camera comprising:
a light source operable to transmit light to illuminate the scene;
a photosensor having a plurality of pixels configured to register amounts of light reflected from the transmitted light by features in the scene; and
a controller configured to:
control the light source to transmit structured light modulated at a modulation frequency to illuminate the scene with a structured illumination pattern; and
for each combination of a sampling phase offset of a plurality of different sampling phase offsets and a perturbation phase shift of a plurality of different perturbation phase shifts:
modulate sensitivity of the photosensor at the frequency of modulation of the transmitted light but phase shifted relative to phase of the transmitted light by a phase equal to a sum of the sampling phase offset and the perturbation phase;
for each value of the sum modulo 360°, turn on the photosensor for a different exposure period to register light reflected by the features; and
determine distances to the features based on the light registered by the pixels.
2. The CW-TOF camera according to claim 1 wherein turning on the photosensor for a different exposure period comprises for each sampling phase offset turning on the photosensor for a different exposure period for each of the plurality of different perturbation phase shifts.
3. The CW-TOF camera according to claim 2 wherein the controller is configured to control the light source to modify the structured light with a sequence of optical pattern modifiers in synchrony with a sequence of the perturbation phase shifts.
4. The CW-TOF camera according to claim 3 wherein determining a distance to a feature imaged on a pixel of the photosensor comprises summing voltages representing light that the pixel registers during each of the exposure periods to provide a summed voltage that is a function of a propagation phase delay for light to travel from the camera to the feature and back to the camera.
5. The CW-TOF camera according to claim 4 wherein determining distance to the feature comprises using the summed voltages to determine the propagation phase delay and therefrom the distance.
6. The CW-TOF camera according to claim 1 wherein the structured illumination pattern is a stationary illumination pattern comprising a plurality of different types of stationary illumination zones.
7. The CW-TOF camera according to claim 6 wherein turning on the photosensor for a different exposure period for each value of the sum modulo 360° comprises for each sampling phase offset turning on the photosensor for a different exposure period, for each perturbation phase shift of the plurality of different perturbation phase shifts.
8. A continuous wave time of flight (CW-TOF) camera operable to determine distances to features in a scene, the CW-TOF camera comprising:
a light source operable to transmit light to illuminate the scene;
a photosensor having a plurality of pixels configured to register amounts of light reflected from the transmitted light by features in the scene; and
a controller configured to:
control the light source to transmit structured light modulated at a modulation frequency to illuminate the scene with a structured illumination pattern; and
for each combination of a sampling phase offset of a plurality of different sampling phase offsets and a perturbation phase shift of a plurality of different perturbation phase shifts:
modulate sensitivity of the photosensor at the modulation frequency of the transmitted light but phase shifted relative to phase of the transmitted light by a phase equal to a sum of the sampling phase offset and the perturbation phase shift;
for each value of a sum modulo 360°, turn on the photosensor for a different exposure period to register light reflected by the features, wherein turning on the photosensor for a different exposure period for each value of the sum modulo 360° comprises turning on the photosensor for a number of exposure periods less than a number of the plurality of sampling phases times the number of the plurality of perturbation phase shifts; and
determine distances to the features based on the light registered by the pixels.
9. The CW-TOF camera according to claim 1 wherein turning on the photosensor for a different exposure period for each value of the sum modulo 360° comprises turning on the photosensor for a number of exposure periods that is equal to the number of different values of the sum modulo 360°.
10. The CW-TOF camera according to claim 6 wherein determining a distance to a feature located in a stationary illumination zone imaged on a given pixel comprises determining for each sampling phase offset a sum of a plurality of voltages each voltage representing light registered by a pixel in the photosensor for a different perturbation phase.
11. The CW-TOF camera according to claim 10 wherein the plurality of voltages comprises a voltage representing light registered by the given pixel for a first perturbation phase of the plurality of perturbation phases and a voltage representing light that a pixel registers from a feature located in type of stationary illumination zone different from the type of stationary illumination zone in which the feature imaged by the given pixel is located for a second perturbation phase λ n different from the first perturbation phase.
12. The CW-TOF camera according to claim 11 wherein the sum of voltages comprises a voltage for each perturbation phase paired with a stationary illumination zone provided by a pixel that images a feature located in the stationary illumination zone.
13. The CW-TOF camera according to claim 12 wherein a number of different stationary illumination zones is equal to a number of the plurality of perturbation phases and the controller pairs the perturbation phases with stationary illumination zones using a bijective mapping of the perturbation phases to the stationary illumination zones.
14. The CW-TOF camera according to claim 12 wherein a number of the plurality of different stationary illumination zones is less than a number of the plurality of perturbation phases, and the controller pairs the perturbation phases with stationary illumination zones using a surjective mapping of the perturbation phases to the stationary illumination zones.
15. A method of determining distances to features in a scene, the method comprising:
transmitting structured light modulated at a modulation frequency to illuminate a scene with a structured illumination pattern; and
for each combination of a sampling phase offset of a plurality of different sampling phase offsets and a perturbation phase shift of a plurality of different perturbation phase shifts:
modulating sensitivity of a photosensor having pixels configured to register light at the frequency of modulation of the transmitted light, but phase shifted relative to phase of the transmitted light by a phase equal to a sum of a sampling phase offset and a perturbation phase;
for each value of the sum modulo 360°, turning on the photosensor for a different exposure period to register light reflected by features in the scene; and
determining distances to the features based on the light registered by the pixels.
16. The method according to claim 15 wherein turning on the photosensor for a different exposure period for each value of the sum modulo 360° comprises for each sampling phase offset turning on the photosensor for a different exposure period for each perturbation phase of the plurality of different perturbation phase shifts.
17. The method according to claim 15 wherein turning on the photosensor for a different exposure period for each value of the sum modulo 360° comprises turning on the photosensor for a number of exposure periods less than a number of the plurality of sampling phases times the number of the plurality of perturbation phase shifts.
18. The method according to claim 15 wherein turning on the photosensor for a different exposure period for each value of the sum modulo 360° comprises turning on the photosensor for a number of exposure periods that is equal to the number of different values of the sum modulo 360°.
19. The method according to claim 15 wherein illuminating the scene with a structured illumination pattern comprises illuminating the scene with a stationary illumination pattern comprising a plurality of different types of stationary illumination zones.
20. The method according to claim 15 wherein illuminating the scene with a structured illumination pattern comprises illuminating the scene with a dynamic illumination pattern comprising a plurality of different types of dynamic illumination zones for each of which dynamic illumination zone, illumination is controllable to change as a function of time independently of illumination of the other zones.