Pattern projection using microlenses
An illumination assembly includes a light source, which is configured to emit optical radiation. A transparency containing a plurality of micro-lenses, which are arranged in a non-uniform pattern and are configured to focus the optical radiation to form, at a focal plane, respective focal spots in the non-uniform pattern. Optics are configured to project the non-uniform pattern of the focal spots from the focal plane onto an object.
1. Apparatus for mapping an object, comprising:
an illumination assembly, comprising:
a transparency containing a plurality of parallel bands, repeating periodically in a first direction, each band containing a replica of an uncorrelated pattern of spots extending across at least a part of the transparency in a second direction, perpendicular to the first direction; and
a light source, which is configured to transilluminate the transparency with optical radiation so as to project the uncorrelated pattern onto the object;
an image capture assembly, which is configured to capture an image of the uncorrelated pattern that is projected onto the object; and
a processor, which is coupled to process the image captured by the image capture assembly so as to reconstruct a three-dimensional (3D) map of the object.
2. The apparatus according to claim 1 , wherein the uncorrelated pattern comprises a pseudo-random pattern.
3. The apparatus according to claim 1 , wherein the uncorrelated pattern comprises a quasi-periodic pattern.
4. The apparatus according to claim 3 , wherein the quasi-periodic pattern has an n-fold symmetry, with n=5 or n>7.
5. The apparatus according to claim 1 , wherein the uncorrelated pattern has a duty cycle that is less than 1/e.
6. The apparatus according to claim 1 , wherein the spots have a local duty cycle that varies across the pattern.
7. The apparatus according to claim 1 , wherein the processor is configured to derive the 3D map by finding respective offsets between the pattern of the spots on multiple areas of the object captured in the image of the pattern that is projected onto the object and a reference image of the pattern, wherein the respective offsets are indicative of respective distances between the areas and the image capture assembly.
8. The apparatus according to claim 7 , wherein the spots have a local duty cycle that varies monotonically along an axis across the pattern, and wherein the processor is configured to determine local gray levels of the multiple areas in the image responsively to the local duty cycle, and to estimate the respective offsets based on the local gray levels.
9. The apparatus according to claim 1 , wherein the spots in the transparency comprise micro-lenses arranged in the uncorrelated pattern.
10. The apparatus according to claim 1 , wherein the illumination assembly comprises a first optic positioned between the light source and a first side of the transparency and a second optic positioned on a second side of the transparency, opposite the first side.
11. A method for mapping an object, comprising:
transilluminating a transparency containing an uncorrelated pattern of spots so as to project the uncorrelated pattern onto the object;
capturing an image of the uncorrelated pattern that is projected onto the object; and
processing the captured image so as to estimate respective depth coordinates of different parts of the object based on local gray levels in the image of the uncorrelated pattern and thereby reconstruct a three-dimensional (3D) map of the object.
12. The method according to claim 11 , wherein the uncorrelated pattern comprises a pseudo-random pattern.
13. The method according to claim 11 , wherein the uncorrelated pattern comprises a quasi-periodic pattern.
14. The method according to claim 13 , wherein the quasi-periodic pattern has an n-fold symmetry, with n=5 or n≥7.
15. The method according to claim 11 , wherein the uncorrelated pattern has a duty cycle that is less than 1/e.
16. The method according to claim 11 , wherein the spots have a local duty cycle that varies across the pattern.
17. The method according to claim 11 , wherein the transparency contains a plurality of parallel bands, repeating periodically in a first direction, each band containing a replica of the uncorrelated pattern extending across at least a part of the transparency in a second direction, perpendicular to the first direction.
18. The method according to claim 11 , wherein processing the captured image comprises finding respective offsets between the pattern of the spots on multiple areas of the object captured in the image of the pattern that is projected onto the object and a reference image of the pattern, and determining respective distances to the areas responsively to the respective offsets.
19. The method according to claim 11 , wherein the spots have a local duty cycle that varies monotonically along an axis across the pattern, and wherein processing the captured image comprises determining the local gray levels of multiple areas in the image responsively to the local duty cycle.
20. The method according to claim 11 , wherein the spots in the transparency comprise micro-lenses arranged in the uncorrelated pattern.