Method and system for robust and extended illumination waveforms for depth sensing in 3D imaging
The methods and systems disclosed herein improve upon previous 3D imaging techniques by making use of a longer illumination pulse to obtain the same or nearly the same range resolution as can be achieved by using a much shorter, conventional laser pulse. For example, a longer illumination pulse can be produced by one or more Q-switched lasers that produce, for example, 5, 10, 20 ns or longer pulses. In some instances, the laser pulse can be longer than the modulation waveform of a MIS-type imaging system and still produce a repeatable response function. The light pulse generation technologies required to achieve longer pulse lengths can be significantly less expensive and less complex than known technologies presently used to generate shorter illumination pulse lengths. Lower-cost, lower-complexity light pulse sources may facilitate lower-cost, commercial 3D camera products.
1. A three-dimensional imaging system, comprising:
an illumination source configured to emit a light pulse having a length;
a light receiving subsystem configured to receive a portion of the light pulse reflected or scattered by a scene and also including:
a modulator configured to temporally modulate the received portion of the light pulse with a predetermined modulation waveform having a predetermined length, wherein the length of the light pulse is greater than or equal to 10% of the length of the length of the modulation waveform;
a first imaging sensor array configured to generate a first set of image pixel intensity values in response to the modulated received portion of the light pulse; and
a second imaging sensor array configured to generate a second set image pixel intensity values in response to the modulated received portion of the light pulse or a non-modulated received portion of the light pulse; and
a processor subsystem configured to obtain three-dimensional image range data by calculating time-of-flight (TOF) measurements regarding the light pulse based on a ratio involving the first set of image pixel intensity values and the second set of image pixel intensity values.
2. The three-dimensional imaging system of claim 1 , wherein the length of the light pulse is greater than or equal to 5 nanoseconds.
3. The three-dimensional imaging system of claim 1 , wherein the length of the light pulse is greater than or equal to 10 nanoseconds.
4. The three-dimensional imaging system of claim 1 , wherein the length of the light pulse is greater than or equal to 20 nanoseconds.
5. The three-dimensional imaging system of claim 1 , wherein the illumination source is selected from the group consisting of one or more Q-switched lasers, one or more semiconductor lasers, one or more laser diodes, and one or more light emitting diodes (LEDs).
6. The three-dimensional imaging system of claim 1 , wherein the light pulse emitted by the illumination source has a leading edge or falling edge that is non-monotonic.
7. The three-dimensional imaging system of claim 1 , further comprising means for producing monotonic convolution signal when either the illumination source or the modulation waveform has a high frequency modulation.
8. The three-dimensional imaging system of claim 1 , further comprising:
means for producing a convolved signal based on the light pulse and the modulation waveform; and
means for determining a range of at least one object in the scene based on the convolved signal.
9. The three-dimensional imaging system of claim 8 , wherein the range is determined using an analytic approximation to range as a function of the convolved signal.
10. The three-dimensional imaging system of claim 8 , wherein the range is calculated using a lookup table of values relating the convolved signal to the range or time.
11. The three-dimensional imaging system of claim 10 , further comprising means for interpolating between values stored in the lookup table.
12. The three-dimensional imaging system of claim 10 , wherein the lookup table values corresponds to regions of pixels.
13. The three-dimensional imaging system of claim 1 , wherein the system is configured so that smallest achievable range resolution is less than 10% of the light pulse length.
14. The three-dimensional imaging system of claim 1 , wherein the system is configured so that smallest achievable range resolution is less than 1% of the light pulse length.
15. A method of three-dimensional imaging, comprising:
emitting a light pulse having a length to illuminate a scene, at least in part;
receiving a portion of the light pulse reflected or scattered by the scene;
temporally modulating the received portion of the light pulse as a function of time, according to a predetermined modulation waveform having a predetermined length, wherein the length of the light pulse is greater than or equal to 10% of the length of the modulation waveform;
generating a first set of image pixel intensity values in response to the modulated received portion of the light pulse;
generating a second set image pixel intensity values in response to the modulated received portion of the light pulse or a non-modulated received portion of the light pulse; and
obtaining three-dimensional image range data by calculating time-of-flight (TOF) measurements regarding the light pulse based on a ratio involving the first set of image pixel intensity values and the second set of image pixel intensity values.
16. The method of claim 15 , wherein the length of the light pulse is greater than or equal to 5 nanoseconds.
17. The method of claim 15 , wherein the length of the light pulse is greater than or equal to 10 nanoseconds.
18. The method of claim 15 , wherein the length of the light pulse is greater than or equal to 20 nanoseconds.
19. The method of claim 15 , wherein the light pulse is produced by an illumination source selected from the group consisting of one or more Q-switched lasers, one or more semiconductor lasers, one or more laser diodes, and one or more light emitting diodes (LEDs).
20. The method of claim 15 , further comprising:
producing a convolved signal based on the light pulse and the modulation waveform; and
determining a range of at least one object in the scene based on the convolved signal.