Motion compensation in range imaging

1. A method of determining a distance between a range imaging device and at least one moving object, the method comprising:

modulating an image sensor according to a coded exposure;

while modulating the image sensor, acquiring, at the image sensor, an image of at least a portion of a modulated illumination signal reflected from a scene containing at least one moving object;

generating phase step range image data based on the image of the modulated illumination signal reflected from the scene, the phase step range image data comprising a first phase step image and at least a second phase step image;

calculating an initial estimate of a distance between the image sensor and the at least one moving object, and an initial estimate of a brightness of the at least one moving object using a processor, wherein the estimates are based on the acquired phase step range image data;

calculating an optical flow of the moving object based on: i) the initial estimate of the distance between the image sensor and the at least one moving object; ii) the initial estimate of the brightness of the at least one moving object; iii) the first phase step image; and iv) the second phase step image;

generating motion corrected image data by applying an inverted coded exposure to the phase step range image data to correct for the calculated optical flow; and

calculating a distance between the image sensor and the at least one moving object based on the corrected image data.

2. The method of claim 1 , wherein the coded exposure comprises a sine function.

3. The method of claim 1 , wherein the coded exposure comprises a square wave.

4. The method of claim 1 , wherein the initial estimate of a distance between the image sensor and the at least one moving object is a two phase estimate.

5. The method of claim 1 , wherein the calculating of the optical flow comprises a linear approximation.

6. The method of claim 1 , wherein the calculating of the optical flow comprises a non-equispaced inverse Fourier transform.

7. The method of claim 1 , wherein the method further comprises illuminating the scene using an amplitude modulated continuous wave signal.

8. A method of determining a distance between a range imaging camera and a plurality of moving objects, the method comprising:

modulating an image sensor according to a coded exposure;

while modulating the image sensor according to the coded exposure, capturing, at the image sensor, an image of at least a portion of a modulated illumination signal reflected from the plurality of moving objects;

generating raw sequence image data based on the captured image at an image, the raw sequence image data comprising a plurality of sequential phase step images of a scene comprising the moving objects;

receiving the raw sequence image data at a processor;

estimating a two phase estimate of a distance between the range imaging camera and each of the moving objects;

generating a motion mask, utilizing the sequential phase step images, to identify areas in the raw sequence image data that include image data related to the moving objects;

segmenting the raw image data utilizing the motion mask to isolate an area of the raw image data corresponding to each of the moving objects;

determining an optical flow of each of the moving objects based on the two phase estimates and the object segmentation;

calculating a magnitude and a direction of the optical flow of each of the moving objects;

rotating and scaling the sequential phase step images based on the calculated magnitude and direction of the optical flow of each of the moving objects;

motion inverting the rotated and scaled sequential phase step images to compensate for the motion of the moving objects;

reversing the rotating and the scaling of the sequential phase step images to generate motion corrected sequential phase step images;

decoding the motion corrected sequential phase step images using the coded exposure to generate a motion corrected phase step sequence; and

calculating the distance between the range imaging camera and each of the moving objects based on the motion corrected phase step sequence.

9. The method of claim 8 , wherein the image sensor is a CMOS sensor.

10. The method of claim 8 , wherein the two phase estimate comprises estimated distance data for each of a plurality of pixels.

11. The method of claim 8 , wherein the two phase estimate comprises estimated brightness data for each of a plurality of pixels.

12. The method of claim 8 , wherein the optical flow is represented by a plurality of vectors, each of the plurality of vectors associated with one of the plurality of pixels.

13. The method of claim 8 , wherein the determining the optical flow comprises a linear approximation.

14. The method of claim 8 , wherein the calculating of the optical flow comprises a non-equispaced inverse Fourier transform.

15. The method of claim 8 , wherein the coded exposure comprises a square wave.

16. The method of claim 8 , wherein the coded exposure comprises a sine wave.

17. The method of claim 8 , further comprising illuminating the scene using a modulated illumination signal.

18. The method of claim 17 , further comprising generating the modulated illumination signal using a signal generator.

19. The method of claim 8 , wherein calculating the distance between the range imaging camera and each of the moving objects comprises decoding a distance for each pixel in the motion corrected phase step sequence.

20. A range imaging camera, comprising:

an illumination source to illuminate a scene using a modulated illumination signal;

an image sensor to capture raw sequence image data from the illuminated scene using a coded exposure, wherein the image sensor is configured to capture at least a portion of the modulated illumination signal reflected from at least one moving object in the illuminated scene; and

a processor to process the raw sequence image data to correct for motion in the captured raw sequence image data, wherein the processor is configured to perform the following:

calculating a two phase estimate of a distance between the range imaging camera and the moving object based on the raw sequence image data;

generating a motion mask, based on the raw sequence image data, to identify areas in the raw sequence image data that includes image data related to the moving object;

segmenting the raw sequence image data to isolate an area of the raw sequence image data corresponding to the moving object based on the motion mask;

determining an optical flow of the moving object based on the two phase estimate and the segmented raw sequence image data;

calculating a magnitude and a direction of the optical flow of the moving object;

rotating and scaling the raw sequence image data based on the calculated magnitude and direction of the optical flow of the moving object;

motion inverting the rotated and scaled raw sequence image data to compensate for the motion of the moving object;

reversing the rotating and the scaling of the raw sequence image data to generate motion corrected sequence image data;

decoding the motion corrected sequence image data using the coded exposure to generate decoded motion corrected sequence image data; and

calculating the distance between the range imaging camera and the moving object based on the decoded motion corrected sequence image data.

21. The range imaging camera of claim 20 , wherein the illumination signal is modulated with an amplitude modulated continuous wave.

22. The range imaging camera of claim 20 , wherein the image sensor is a CMOS sensor.

23. The range imaging camera of claim 20 , wherein the coded exposure comprises a square wave.

24. The range imaging camera of claim 20 , wherein the coded exposure comprises a sinusoidal wave.

25. The range imaging camera of claim 20 , wherein the image sensor transmits the raw sequence image data to the processor.

26. The range imaging camera of claim 20 , wherein the image sensor comprises a pixel array.

27. The range imaging camera of claim 26 , wherein the two phase estimate comprises estimated distance data for each of a plurality of pixels.

28. The range imaging camera of claim 26 , wherein the two phase estimate comprises estimated brightness data for each of a plurality of pixels.

29. The range imaging camera of claim 20 , wherein the optical flow is represented by a plurality of vectors, each of the plurality of vectors associated with one of the plurality of pixels.

30. The range imaging camera of claim 20 , wherein the determining the optical flow comprises a linear approximation.

31. The range imaging camera of claim 20 , wherein the determining the optical flow comprises a non-equispaced inverse Fourier transform.

32. The range imaging camera of claim 20 , further comprising a signal generator to generate the modulated illumination signal.

33. The range imaging camera of claim 20 , wherein the calculating the distance between the range imaging camera and the moving object comprises decoding a distance for each pixel in the decoded motion corrected sequence image data.