Methods and apparatus for coded time-of-flight camera
In illustrative implementations, a time-of-flight camera robustly measures scene depths, despite multipath interference. The camera emits amplitude modulated light. An FPGA sends at least two electrical signals, the first being to control modulation of radiant power of a light source and the second being a reference signal to control modulation of pixel gain in a light sensor. These signals are identical, except for time delays. These signals comprise binary codes that are m-sequences or other broadband codes. The correlation waveform is not sinusoidal. During measurements, only one fundamental modulation frequency is used. One or more computer processors solve a linear system by deconvolution, in order to recover an environmental function. Sparse deconvolution is used if the scene has only a few objects at a finite depth. Another algorithm, such as Wiener deconvolution, is used is the scene has global illumination or a scattering media.
1. A method comprising, in combination:
(a) an electrical signal controlling modulation of a light source, such that the light source illuminates a scene, the electrical signal is periodic, and each period of the electrical signal comprises an m-sequence;
(b) a time-of-flight (ToF) sensor taking measurements of light that is incident on the ToF sensor and reflected from the scene; and
(c) one or more computers performing an algorithm that takes the measurements as input and that calculates multiple scene depths in the scene for each pixel in a set of mixed pixels;
wherein
(i) the one or more computers calculate a light sweep image, and
(ii) the one or more computers calculate, based on the light sweep image, values of control signals which control a digital image displayed on a screen, such that
(A) the digital image includes light intensities for voxels at a specific depth of the scene, but not at other depths in the scene, and
(B) one or more of the voxels correspond to a scene position that is viewable from the ToF sensor only through a diffuser.
2. The method of claim 1 , wherein the algorithm performs sparse deconvolution.
3. The method of claim 1 , wherein the algorithm includes Weiner deconvolution or Hodrick-Prescott filtering.
4. The method of claim 1 , wherein the scene is static during the modulation and during the measurements.
5. The method of claim 1 , wherein:
(a) the ToF sensor has a correlation waveform that is the cross-correlation of (i) a reference signal that controls modulation of gain of pixels of the ToF sensor and (ii) received light at the ToF sensor; and
(b) the correlation waveform is not substantially sinusoidal.
6. Apparatus comprising, in combination:
(a) a light source,
(b) a time-of-flight (ToF) sensor;
(c) a set of one or more computer processors; and
(d) machine-accessible media;
wherein
(i) the machine-accessible media do not comprise a transitory signal, and
(ii) the machine-accessible media have instructions encoded thereon for the set of processors
(A) to generate an electrical signal to control modulation of a light source, such that the electrical signal comprises an m-sequence, and
(B) to perform an algorithm that takes, as an input, measurements by the ToF sensor, and that calculates, for each pixel in a set of mixed pixels, multiple depths in a scene,
(C) to calculate a light sweep image, and
(D) to calculate, based on the light sweep image, values of control signals which control a digital image displayed on a screen, such that
(I) the digital image includes light intensities for voxels at a specific depth of the scene, but not at other depths in the scene, and
(II) one or more of the voxels correspond to a scene position that is viewable from the ToF sensor only through a diffuser.
7. The apparatus of claim 6 , wherein the algorithm involves sparse deconvolution.
8. The apparatus of claim 6 , wherein the algorithm involves Wiener deconvolution or Hodrick-Prescott filtering.
9. The apparatus of claim 6 , wherein at least one pixel in the ToF sensor comprises a lock-in pixel.
10. The apparatus of claim 6 , wherein at least one pixel in the ToF sensor comprises a single-photon avalanche diode.
11. The apparatus of claim 6 , wherein the algorithm involves sparse deconvolution.
12. The apparatus of claim 6 , wherein the algorithm involves Wiener deconvolution or Hodrick-Prescott filtering.
13. A method comprising, in combination:
(a) an electrical signal controlling modulation of a light source, such that the light source illuminates a scene and that at least a portion of the electrical signal comprises a flat spectrum signal;
(b) a time-of-flight (ToF) sensor taking measurements of light that is incident on the ToF sensor and reflected from the scene; and
(c) one or more computers performing an algorithm that takes the measurements as input and that calculates multiple scene depths for each pixel in a set of mixed pixels; wherein
(i) the one or more computers calculate a light sweep image, and
(ii) the one or more computers calculate, based on the light sweep image, values of control signals which control a digital image displayed on a screen, such that
(A) the digital image includes light intensities for voxels at a specific depth of the scene, but not at other depths in the scene, and
(B) one or more of the voxels correspond to a scene position that is viewable from the ToF sensor only through a diffuser.
14. The method of claim 13 , wherein the algorithm performs sparse deconvolution.
15. The method of claim 13 , wherein the electrical signal is not substantially square.
16. The method of claim 13 , wherein the scene is static during the modulation and during the measurements.
17. The method of claim 13 , wherein:
(a) the ToF sensor has a correlation waveform that is the cross-correlation of (i) a reference signal that controls modulation of gain in pixels of the ToF sensor and (ii) received light at the ToF sensor; and
(b) the correlation waveform is not substantially sinusoidal.
18. Apparatus comprising, in combination:
(a) a light source configured to emit light that illuminates a static scene, which light undergoes modulation;
(b) a time-of-flight (ToF) sensor; and
(c) one or more computers that are programmed
(i) to output an electrical signal that controls the modulation, such that the electrical signal is periodic and each period of the electrical signal comprises a flat spectrum signal, and
(ii) to perform an algorithm that calculates a depth map of the scene, which depth map specifies, for each pixel in a set of mixed pixels of the ToF sensor, multiple depths in the scene,
(iii) to calculate a light sweep image, and
(iv) to calculate, based on the light sweep image, values of control signals which control a digital image displayed on a screen, such that
(I) the digital image includes light intensities for voxels at a specific depth of the scene, but not at other depths in the scene, and
(II) one or more of the voxels correspond to a scene position that is viewable from the ToF sensor only through a diffuser.