Measuring shape of specular objects by local projection of coded patterns

Patent metadata

Field	Value
Publication number	US-2016349046-A1
Application number	US-201615151388-A
Country	US
Kind code	A1
Filing date	May 10, 2016
Priority date	May 29, 2015
Publication date	Dec 1, 2016
Grant date	—

Abstract

The shape of a specular object is measured by illumination of the object by a light field generated by two or more spaced apart layers controllable to display multiple patterns that are predetermined relative to a bounding volume within which the object is positioned. The patterns code a sparse subset of the multitude of light rays that can be generated by the layers to those that can actually reach the bounding volume. A process is described by which a sparse coding of the light rays can be derived.

First claim

1 . A method of measuring shape of a specular object, the method comprising:
positioning the object within a bounding volume at an inspection station; illuminating the object with an illumination field generated by two or more spaced apart liquid crystal layers with largely overlapping fields of view, wherein each liquid crystal layer is controlled to display multiple binary patterns in synchronization with each other layer, and wherein the multiple binary patterns are predetermined for the bounding volume such that relative to a large multitude of light rays in the illumination field, the multiple binary patterns code a sparse subset of the multitude of light rays that can reach the bounding volume; capturing one or more images of the object under the illumination field; and recovering the shape of the object using the captured one or more images.

2 . The method according to claim 1 , further comprising selecting a size for the bounding volume based on size of the object, and selecting the predetermined multiple binary patterns from amongst multiple different pre-stored sets of multiple binary patterns, each different set corresponding to a different size of the bounding volume.

3 . The method according to claim 1 , wherein the liquid crystal layers are sandwiched between a pair of mutually perpendicularly oriented polarization filters and are provided with a backlight light source.

4 . The method according to claim 1 , wherein a polarized light ray passing through a pixel of a liquid crystal layer undergoes a change of polarization based on the binary value of the binary pattern being displayed at the pixel, and a polarized light ray passing through two or more liquid crystal layers undergoes a change of polarization based on a logical XOR combination of the binary values of the binary patterns being displayed at the pixels of the liquid crystal layers through which the light ray passes.

5 . The method according to claim 1 , wherein the binary patterns are predetermined to assign a unique code to each light ray of the illumination field that can reach the bounding volume, and wherein recovering the shape of the object includes recovering the unique codes from the captured one or more images and identifying each corresponding light ray using the unique codes and based on the location of the bounding volume.

6 . The method according to claim 5 , wherein recovering the shape of the object includes determining a correspondence between an exit ray of the illumination field and an incoming ray in the captured one or more images, and using ray-ray intersection to determine position and calculation of half-way vector to determine a normal of each such intersection point.

7 . An apparatus for measuring shape of a specular object, the apparatus comprising:
an illumination source for generating an illumination field for illumination of a bounding volume at an inspection station, wherein the illumination source includes two or more spaced apart liquid crystal layers positioned relative to each other with largely overlapping fields of view, wherein each liquid crystal layer is controllable to display multiple binary patterns; an illumination control module constructed to control the liquid crystal layers to display the multiple binary patterns in synchronization with each other layer, wherein the multiple binary patterns are predetermined for the bounding volume such that relative to a large multitude of light rays in the illumination field, the multiple binary patterns code a sparse subset of the multitude of light rays that can reach the bounding volume; and a shape recovery module constructed to capture one or more images of the object under the illumination field and to recover the shape of the object using the captured one or more images.

8 . The apparatus according to claim 7 , wherein the illumination control module is further constructed to select the predetermined multiple binary patterns from amongst multiple different pre-stored sets of multiple binary patterns, each different set corresponding to a different size of the bounding volume, wherein the selection is based on size of the object.

9 . The apparatus according to claim 7 , wherein the liquid crystal layers are sandwiched between a pair of mutually perpendicularly oriented polarization filters and are provided with a backlight light source.

10 . The apparatus according to claim 7 , wherein the illumination source is constructed such that a polarized light ray passing through a pixel of a liquid crystal layer undergoes a change of polarization based on the binary value of the binary pattern being displayed at the pixel, and a polarized light ray passing through two or more liquid crystal layers undergoes a change of polarization based on a logical XOR combination of the binary values of the binary patterns being displayed at the pixels of the liquid crystal layers through which the light ray passes.

11 . The apparatus according to claim 7 , wherein the binary patterns are predetermined to assign a unique code to each light ray of the illumination field that can reach the bounding volume, and wherein the shape recovery module is further constructed to recover the shape of the object by recovering the unique codes from the captured one or more images and by identifying each corresponding light ray using the unique codes and based on the location of the bounding volume.

12 . The apparatus according to claim 11 , wherein the shape recovery module is further constructed to recover the shape of the object by determining a correspondence between an exit ray of the illumination field and an incoming ray in the captured one or more images, and by using ray-ray intersection to determine position and calculation of half-way vector to determine a normal of each such intersection point.

13 . A method for determining multiple binary patterns for use in measuring shape of a specular object positioned within a bounding volume by illuminating the object with an illumination field generated by two or more spaced apart liquid crystal layers with largely overlapping fields of view, wherein each liquid crystal layer is controlled to display the multiple binary patterns, the method comprising:
choosing multiple starting binary patterns for the liquid crystal layers for which patterns have not yet been determined; deriving a multidimensional binary code vector in a multidimensional binary code vector space for each polarized light ray passing through the two or more liquid crystal layers and reaching the bounding volume using a logical XOR combination of values; finding a multidimensional binary code vector for projection in the multidimensional binary code vector space; determining a projection transformation along the multidimensional binary code vector for projection; and applying the projection transformation to the multiple starting binary patterns to obtain multiple relatively more optimized binary patterns for the liquid crystal layers.

14 . The method according to claim 13 , wherein the projection transformation reduces the dimension of the multidimensional binary code vector space by one, and wherein the dimension of the multidimensional binary code vector space corresponds to the number of captured images.

15 . The method according to claim 13 , further comprising repeating the steps of deriving, finding, determining and applying, after replacing the multiple starting binary patterns with the obtained multiple relatively more optimized binary patterns for the liquid crystal layers to obtain multiple increasingly more optimized binary patterns for the liquid crystal

Assignees

• Canon Kk

Inventors

• Tin Siu-Kei
• Ye Jinwei

Classifications

• G06V10/145

  Illumination specially adapted for pattern recognition, e.g. using gratings · CPC title

• G06K9/4661

  Physics · mapped topic

• G06K9/52

  Physics · mapped topic

• G01B11/2513 Primary

  with several lines being projected in more than one direction, e.g. grids, patterns · CPC title

• G06T7/514

  from specularities · CPC title