DEPTH MEASUREMENT USING A PHASE GRATING

• US 20180031372A1
• Filed: 01/25/2016
• Published: 02/01/2018
• Est. Priority Date: 02/24/2015
• Status: Active Grant

• Current Assignee: Rambus Inc.
• Original Assignee: Rambus Inc.
• Inventors: Gill, Patrick R.
• Granted Patent: US 10,317,205 B2
• Time in Patent Office: Days
• CPC Class Codes: G01C 3/14 with binocular observation at a single point, e.g. stereoscopic type G01C3/20 takes precedence
• CPC Class Codes: G02B 27/1086 operating by diffraction only
• CPC Class Codes: G06T 7/593 from stereo images
• CPC Class Codes: H04N 13/10 Processing, recording or transmission of stereoscopic or multi-view image signals
• CPC Class Codes: H04N 13/271 wherein the generated image signals comprise depth maps or disparity maps

Abstract

Binocular depth-perception systems use binary, phase-antisymmetric gratings to cast point-source responses onto an array of photosensitive pixels. The gratings and arrays can be manufactured to tight tolerances using well characterized and readily available integrated-circuit fabrication techniques, and can thus be made small, cost-effective, and efficient. The gratings produce point-source responses that are large relative to the pitch of the pixels, and that exhibit wide ranges of spatial frequencies and orientations. Such point-source responses make it easy to distinguish the point-source responses from fixed-pattern noise the results from spatial frequencies of structures that form the array.

Claims

1. A method of measuring a depth to an object in a scene, the method comprising:

receiving light in a wavelength band of interest from the scene at a phase grating, the phase grating inducing near-field spatial modulations producing a diffraction pattern;

capturing an image of the diffraction pattern;

computing a disparity between the image and a reference; and

estimating the depth to the object based on the disparity.

2. The method of claim 1, wherein the phase grating is a first phase grating, the method further comprising:

receiving the light from the scene at a second phase grating, the second phase grating inducing second near-field spatial modulations producing a second diffraction pattern;

capturing a second image of the second diffraction pattern; and

using the second image as the reference.

3. The method of claim 2, wherein estimating the depth comprises computed a distance between the image and the second image.

4. The method of claim 1, further comprising shining a laser source of the light on the object.

5. The method of claim 4, further comprising filtering out second light outside the wavelength band of interest.

6. The method of claim 5, wherein the filtering uses at least one of a color filter and a cross-polarized filter.

7. The method of claim 1, wherein capturing the image comprises sampling the diffraction pattern with an array of pixels of a pixel pitch.

8. The method of claim 7, wherein computing the disparity comprises measuring a lateral shift of the diffraction pattern on the pixels.

9. The method of claim 7, wherein the diffraction pattern produces a point-source response with a maximum dimension of at least six times the pixel pitch on the array and features with smaller dimensions less than a third the maximum dimension.

10. The method of claim 9, wherein the image includes band-limited noise at spatial frequencies that correspond to known attributes of the pixel array, the method further comprising filtering out the band-limited noise at those frequencies.

11. The method of claim 10, wherein computing the disparity comprises computing a Fourier cross-correlation of the captured image.

12. An imaging system comprising:

an array of photosensitive pixels having a pixel pitch;

a phase grating that exhibits a point-source response on the array, the array to capture an image of the response, the response having a maximum response dimension at least six times the pixel pitch and features with smaller dimensions less than a third the maximum dimension; and

a processor for;

computing a position of the response in the image and with respect to a reference; and

estimating a depth between the phase grating and the point source based on the computed position.

13. The imaging system of claim 12, further comprising a second phase grating that exhibits a second point-source response, the processor computing a second position of the second response and estimating the depth based on the second position.

14. The imaging system of claim 12, wherein the array exhibits band-limited noise arising from known attributes of the geometry of the pixel array, the system further comprising a filter for removing the band-limited noise.

15. A method of detecting a position of a point source, the method comprising:

directing light from the point source through an optical element that exhibits a point-source response on an array of photosensitive pixels spaced by a pixel pitch, the point-source response having a maximum response dimension at least six times the pixel pitch and features with smaller dimensions less than a third the maximum dimension;

capturing the point-source response;

computing a position of the point-source response on the array; and

estimating the position of the point source using the computed position.

16. The method of claim 15, further comprising computing a depth from the optical element to the point source using the estimated position.

17. The method of claim 15, further comprising:

directing the light through a second optical element that exhibits a second point-source response;

computing a second position of the second point-source response; and

estimating a depth between the second optical element and the point source using the computed second position.

18. The method of claim 15, wherein the optical element comprises a grating.

19. The method of claim 18, wherein the grating comprises a phase grating.

20. The method of claim 15, further comprising passing the light through a lens between the point source and the array.