METHOD AND APPARATUS FOR CALCULATING A DISTANCE BETWEEN AN OPTICAL APPARATUS AND AN OBJECT

• US 20110176709A1
• Filed: 07/16/2010
• Published: 07/21/2011
• Est. Priority Date: 01/21/2010
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: YOU, Jang-woo, PARK, Yong-hwa
• Granted Patent: US 8,611,610 B2
• Time in Patent Office: Days
• US Class Current: 382/106
• CPC Class Codes: G06T 2207/20056 Discrete and fast Fourier transform, [DFT, FFT]
• CPC Class Codes: G06T 7/521 from laser ranging, e.g. using interferometry; from the projection of structured light

Abstract

A method and apparatus for determining a distance between an optical apparatus and an object by considering a measured nonlinear waveform, as opposed to a mathematically ideal waveform. The method and apparatus may accurately calculate distance information without being affected by a type of waveform projected onto the object and may not require an expensive light source or a light modulator for generating a light with little distortion and nonlinearity. Further, since the method may be able to use a general light source, a general light modulator, and a general optical apparatus, additional costs do not arise. Furthermore, a lookup table, in which previously calculated distance information is stored, may be used, and thus the amount of computation required to be performed to calculate the distance is small, thereby allowing for quick calculation of the distance information in real time.

Claims

1. A method of extracting distance information, the method comprising:

projecting a plurality of different lights onto an object;

modulating, by a light modulator having a gain, reflected lights reflected from the object into modulated images;

detecting, by a photodetector, the modulated images and obtaining from the modulated images a plurality of intensity images respectively corresponding to the plurality of different lights;

obtaining a phase delay of each of the reflected lights from the plurality of intensity images; and

calculating a distance to the object from the obtained phase delay,

wherein the obtaining of the phase delay comprises referring to a lookup table that stores information obtained by measuring the waveforms of the plurality of different lights and the gain of the light modulator.

2. The method of claim 1, wherein the waveforms of the plurality of different lights and the gain of the light modulator have the same period.

3. The method of claim 2, wherein the plurality of different lights have one of the same waveform and different phases or different waveforms.

4. The method of claim 2, wherein the plurality of different lights are controlled to have the same average value.

5. The method of claim 1, wherein the photodetector forms the plurality of intensity images respectively corresponding to the plurality of different lights by accumulating a plurality of modulated images, which respectively correspond to the plurality of different lights, respectively for predetermined exposure times.

6. The method of claim 1, further comprising obtaining reflectance of the object and an intensity of an ambient light from the phase delay.

7. The method of claim 1, wherein the obtaining of the phase delay comprises:

quantizing an intensity image vector in a three-dimensional (3D) space by using the plurality of intensity images;

obtaining a rotation angle of the intensity image vector from a reference vector in the 3D space; and

obtaining from the rotation angle α

phase delay of each of the reflected lights by referring to the lookup table.

8. The method of claim 7, wherein the lookup table comprises a previously determined relationship between the phase delay of each of the reflected lights and the rotation angle.

9. The method of claim 7, wherein the intensity image vector is quantized as a combination of differences between the plurality of intensity images.

10. The method of claim 1, wherein the lookup table comprises plural different lookup tables corresponding to various combinations of the plurality of different lights and the gain, and

wherein the obtaining comprises referring to a lookup table among the plural lookup tables corresponding to a specific combination of the plurality of different lights and the gain.

11. The method of claim 1, further comprising creating the lookup table, wherein creating comprises:

obtaining polynomial expressions representing the gain and the plurality of different lights by measuring waveforms of the plurality of different lights and the gain of the light modulator;

obtaining polynomial expressions with respect to the plurality of intensity images by using the polynomial expressions with respect to the waveforms of the plurality of different lights and the gain of the light modulator;

representing each of the polynomial expressions with respect to the plurality of intensity images as a sum of a function of the phase delay and a constant term that is not related to the phase delay;

defining a vector function of the phase delay in a three-dimensional (3D) space by using a combination of differences between a plurality of functions of the phase delay, and defining a specific vector as a reference vector;

defining an intensity image vector in the 3D space as a combination of differences between the polynomial expressions with respect to the plurality of intensity images;

determining a relationship between a rotation angle of the intensity image vector from the reference vector and a phase delay corresponding to the rotation angle; and

creating the lookup table including the determined relationship.

12. The method of claim 11, wherein the obtaining the polynomial expressions comprises:

inducing general polynomial expressions with respect to the reflected lights from the polynomial expressions with respect to the plurality of different lights;

obtaining polynomial expressions with respect to the modulated images by multiplying the polynomial expressions with respect to the reflected lights by the polynomial expression with respect to the gain; and

obtaining polynomial expressions with respect to the plurality of intensity images respectively corresponding to the plurality of different lights by integrating the polynomial expressions with respect to the modulated images with an exposure time of the photodetector.

13. The method of claim 11, wherein the obtaining the polynomial expressions representing the gain and the plurality of different lights by measuring the waveforms of the plurality of different lights and the gain of the light modulator comprises:

measuring the waveform of each of the plurality of different lights;

expressing a result of the measuring of the waveform of each of the plurality of different lights as an orthogonal function on a time axis;

measuring the waveform of the gain of the light modulator; and

expressing a result of the measuring of the waveform of the gain of the light modulator as an orthogonal function on the time axis.

14. The method of claim 13, wherein the expressing of the result of the measuring of the waveform of each of the plurality of different lights as the orthogonal function on the time axis comprises obtaining a polynomial expression with respect to each of the plurality of different lights by determining coefficients of sine terms and coefficients of cosine terms of a Fourier series or coefficients of a Chebyshev polynomial expression.

15. The method of claim 13, wherein the expressing of the result of the measuring of the waveform of the gain of the light modulator as the orthogonal function on the time axis comprises obtaining a polynomial expression with respect to the gain by determining coefficients of sine terms and coefficients of cosine terms of a Fourier series or coefficients of a Chebyshev polynomial expression.

16. The method of claim 13, further comprising determining average values of the plurality of different lights and an average value of the gain from the results of the measuring of the waveform of each of the plurality of different lights and the waveform of the gain.

17. The method of claim 11, wherein the representing comprises representing each of the polynomial expressions with respect to the plurality of intensity images as the sum of the function of the phase delay and the constant term that is not related to the phase delay by considering only a direct current (DC) term present in each of the polynomial expressions with respect to the plurality of intensity images.

18. The method of claim 11, wherein the vector function of the phase delay in the 3D space is defined by

{right arrow over (F)}(φ

_TOF)=[F⁽¹²⁾(φ

_TOF),F⁽²³⁾(φ

_TOF),F⁽³¹⁾(φ

_TOF)]^T

where F^(ij)(φ

_TOF)=F⁽ⁱ⁾(φ

_TOF)−

F^(j)(φ

_TOF), i,j=1, 2, 3, and F⁽ⁱ⁾(Φ

_TOF) is a function of a phase delay of an i^th projected light.

19. The method of claim 18, wherein a vector {right arrow over (F)}(0°

) having a phase delay Φ

_TOF=0 in the vector function of the phase delay is defined as a reference vector.

20. The method of claim 11, wherein the intensity image vector in the 3D space is defined by {right arrow over (I)}_CCD=[I_CCD⁽¹²⁾, I_CCD⁽²³⁾, I_CCD⁽³¹⁾]^T

where I_CCD^(ij)=I_CCD⁽ⁱ⁾−

I_CCD^(j), i,j=1, 2, 3, and I⁽ⁱ⁾_CCD is an intensity image corresponding to an i^th projected light.

21. The method of claim 11, wherein different lookup tables are created according to various combinations of the plurality of different lights and the gain.

22. A method of extracting distance information, the method comprising:

projecting light having a periodic waveform onto an object;

modulating, by a light modulator having a plurality of different gains, a light reflected from the object into modulated images;

detecting, by a photodetector, the modulated images to obtain a plurality of intensity images respectively corresponding to the plurality of different gains;

obtaining a phase delay of the reflected light by using the plurality of intensity images; and

calculating a distance to the object from the obtained phase delay,

wherein the obtaining of the phase delay comprises obtaining the phase delay by referring to a lookup table having information obtained by measuring waveforms of the projected light and the plurality of different gains of the light modulator.

23. The method of claim 22, wherein the waveform of the projected light and the plurality of different gains have the same period.

24. The method of claim 22, wherein the photodetector forms the plurality of intensity images respectively corresponding to the plurality of different gains by accumulating the plurality of modulated images, which respectively correspond to the plurality of different gains, respectively for predetermined exposure times.

25. The method of claim 22, wherein the obtaining of the phase delay comprises:

quantizing an intensity image vector in a three-dimensional (3D) space by using the plurality of intensity images;

obtaining a rotation angle of the intensity image vector from a reference vector in the 3D space; and

obtaining, from the rotation angle, a phase delay of the reflected light by referring to the lookup table.

26. The method of claim 25, wherein the lookup table comprises a previously determined relationship between the phase delay of the reflected light and the rotation angle.

27. The method of claim 25, wherein the intensity image vector is quantized as a combination of differences between the plurality of intensity images.

28. The method of claim 22, wherein the lookup table comprises plural different lookup tables corresponding to various combinations of the plurality of different gains and the projected light, and

wherein the obtaining comprises referring to a lookup table among the plural lookup tables corresponding to a specific combination of the plurality of different gains and the projected light.

29. An optical apparatus that determines a distance between the optical apparatus and an object, the optical apparatus comprising:

a light source that generates a plurality of different lights and projects the plurality of different lights onto the object, each of the plurality of different lights having a periodic waveform;

a light modulator having a gain that modulates reflected lights reflected from the object into modulated images, each of the modulated images having a periodic waveform;

a photodetector that detects the modulated images obtained by the light modulator and obtains, from the modulated images, a plurality of intensity images respectively corresponding to the plurality of different lights; and

a distance information image processor obtains a phase delay of each of the reflected lights from the plurality of intensity images, and calculates the distance between the optical apparatus and the object by referring to a lookup table that stores information obtained by measuring the waveforms of the plurality of different lights and the gain of the light modulator.

30. The optical apparatus of claim 29, further comprising:

a light source driving unit that controls waveforms of the plurality of different lights by driving the light source;

a light modulator driving unit that controls a waveform of a gain by driving the light modulator; and

a control unit that controls operations of the light source driving unit, the light modulator driving unit, and the photodetector.

31. The optical apparatus of claim 29, further comprising:

a first lens, disposed near a light incident surface of the light modulator, that focuses the reflected lights within an area of the light modulator;

a filter, disposed between the first lens and the light modulator, that transmits only lights having specific wavelengths; and

a second lens, disposed between the light modulator and the photodetector, that focuses the modulated images obtained by the light modulator within an area of the photodetector.

32. The optical apparatus of claim 29, wherein the photodetector comprises a charge-coupled diode (CCD) image sensor or a complementary metal-oxide semiconductor (CMOS) image sensor including a two-dimensional (2D) or one-dimensional (1D) array, a photodetector comprising an array of photodiodes, or a photodetector comprising one photodiode for measuring a distance to a single point.

33. A 3D camera comprising the optical apparatus of claim 29.

34. A laser radar comprising the optical apparatus of claim 29.

35. A method of creating a lookup table for calculating distance information between an optical apparatus and an object, the method comprising:

measuring waveforms of a plurality of different lights projected onto the object and a gain of a light modulator;

obtaining polynomial expressions representing the plurality of different lights and the gain of a light modulator from the measured waveforms and the gain;

obtaining polynomial expressions with respect to a plurality of intensity images from the polynomial expressions with respect to the waveforms of the plurality of different lights and the gain of the light modulator;

representing each of the polynomial expressions with respect to the plurality of intensity images as a sum of a function of a phase delay and a constant term that is not related to the phase delay;

defining a vector function of the phase delay in a three-dimensional (3D) space from a combination of differences between a plurality of functions of the phase delay, and defining a specific vector as a reference vector;

defining an intensity image vector in the 3D space as a combination of differences between the polynomial expressions with respect to the plurality of intensity images;

determining a relationship between a rotation angle of the intensity image vector from the reference vector and a phase delay corresponding to the rotation angle; and

expressing the determined relationship in the form of a table or a function.

37. A computer-readable storage medium storing the lookup table created by the method of claim 35.

36. A method of creating a lookup table for calculating distance information between an optical apparatus and an object, the method comprising:

measuring waveforms light projected onto the object and a plurality of different gains of a light modulator;

obtaining polynomial expressions representing the light and the plurality of different gains of the light modulator from the measured light and the plurality of different gains;

obtaining polynomial expressions with respect to a plurality of intensity images from the polynomial expressions with respect to the light and the plurality of different gains of the light modulator;

quantizing each of polynomial expressions with respect to the plurality of intensity images as a sum of a function of a phase delay and a constant term that is not related to the phase delay;

defining a vector function of the phase delay in a three-dimensional (3D) space from a combination of differences of a plurality of functions of the phase delay, and defining a specific vector as a reference vector;

defining an intensity image vector in the 3D space as a combination of differences between the polynomial expressions with respect to the plurality of intensity images;

determining a relationship between a rotation angle of the intensity image vector from the reference vector and a phase delay corresponding to the rotation angle; and

expressing the determined relationship in the form of a table or a function.

38. A computer-readable storage medium storing the lookup table created by the method of claim 36.

39. A method of calculating a distance between an optical apparatus and an object, the method comprising:

projecting light onto the object, the light having a waveform;

modulating, by a light modulator of the optical apparatus, the light modulator having a gain, light reflected from the object into modulated images;

obtaining, from the modulated images, an intensity image corresponding to the light projected onto the object;

obtaining, from the intensity image, a phase delay of the light reflected from the object; and

calculating, by a processor of the optical apparatus, the distance between the optical apparatus and the object from the phase delay, the waveform of the light projected onto the object, and the gain of the light modulator.

40. The method according to claim 39, wherein the calculating comprises calculating the distance by referring to a lookup table that associates the phase delay, the waveform of the light projected onto the object, and the gain of the light modulator with each other.