Imaging system

• US 8,890,952 B2
• Filed: 07/29/2009
• Issued: 11/18/2014
• Est. Priority Date: 07/29/2008
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Katz, Sagi
• Primary Examiner(s): Anyikire, Chikaodili E
• Assistant Examiner(s): BAILEY, FREDERICK D
• Application Number:
  US12/511,074
• Publication Number:
  US 20100026850A1
• Time in Patent Office: 1,938 Days
• Field of Search: None
• US Class Current: 348/135
• CPC Class Codes: G01S 17/18 wherein range gates are used
• CPC Class Codes: G01S 17/894 3D imaging with simultaneous measurement of time-of-flight at a 2D array of receiver pixels, e.g. time-of-flight cameras or flash lidar

Abstract

An imaging system comprising: a light source for illuminating a scene with a known intensity light; a camera having an optic axis and center that images the scene responsive to light reflected by the scene from the illuminating, known intensity light; a range finder controllable to determine distances to surface elements of the scene imaged by the camera; a controller configured to determine reflectivity of a surface element of the scene imaged by the camera responsive to a distance of the surface element from the camera, the known intensity of illuminating light and light from the surface element imaged by the camera.

Claims

1. An imaging system comprising:

a light source for illuminating a scene with a known intensity light;

a camera having an optic axis and center that images the scene responsive to light reflected by surface elements in the scene from the illuminating, known intensity light;

a range finder controllable to determine distances to the surface elements of the scene imaged by the camera;

a controller configured to determine an imaging direction for respective ones of the surface elements imaged by the camera along which imaging direction the camera images light from the respective ones of the surface elements, define normals to the surface elements of the scene imaged by the camera based on the distances to the surface elements, the controller configured to determine reflectivities of the surface elements based on respective distances of the surface elements from the camera, a dot product of the normal to the respective surface elements and a vector parallel to the imaging direction for respective ones of the surface elements, the known intensity of illuminating light, and light from the surface elements imaged by the camera, the controller is configured to provide an image of the scene comprising image pixels whose gray levels are based on the determined reflectivities of the surface elements, the controller configured to identify candidates for a feature in the scene by determining whether the determined reflectivities of the surface elements match a particular reflectivity of the feature,

wherein ones of the surface elements being considered as a candidate for the feature have a value of Rcosθ

that satisfies a constraint;

R*≧

R cosθ

≧

R′

cosθ

_T, wherein R* is the particular reflectivity of the feature, Rcosθ

is the determined reflectivity (R) for the surface element being considered as a candidate times a cosine of an angle (θ

) between the candidate surface element'"'"'s imaging direction and the normal to the candidate surface element, and θ

_T is a threshold angle between the candidate surface element'"'"'s imaging direction and the normal to the candidate surface element.

2. An imaging system according to claim 1, wherein the imaging direction is parallel to a line from a first surface element to the optic center of the camera.

3. An imaging system according to claim 1, wherein the imaging direction is parallel to the optic axis of the camera.

4. An imaging system according to claim 1, wherein the controller is configured to identify the feature in the scene based on a product of the reflectivity determined for a first surface element imaged by the camera times a cosine of an angle between the first surface element'"'"'s imaging direction and the normal to the first surface element.

5. An imaging system according to claim 1, wherein the controller is configured to provide the image of the scene comprising the image pixels wherein a gray level of a first pixel in the image is substantially equal to a product of the reflectivity determined for a first surface element imaged on the pixel times a cosine of an angle between the first surface element'"'"'s imaging direction and normal.

6. An imaging system according to claim 1, wherein the range finder comprises a gated time of flight range finder.

7. An imaging system according to claim 1 further comprising a light source controllable to illuminate different regions of the scene independently of each other with intensities of light responsive to their respective normals.

8. An imaging system according to claim 1 further comprising a light source controllable to illuminate different regions of the scene independently of each other with intensities of light responsive to their respective reflectivities.

9. A method comprising:

illuminating a scene including surface elements with known intensity light;

imaging the surface elements at a camera with light reflected by the surface elements from the known intensity light;

determining distances to the surface elements of the scene from the camera based on the imaging;

determining an imaging direction for respective ones of the surface elements imaged by the camera along which imaging direction the camera images light from the respective ones of the surface elements;

determining normals to the surface elements responsive to the determined distances;

determining reflectivities of respective ones of the surface elements responsive to the respective distances of the surface elements from the camera, a dot product of the normal of respective ones of the surface elements and a vector parallel to the imaging direction for respective ones of the surface elements, the known intensity of illuminating light, and light that is reflected by the surface elements and imaged by the camera;

providing a gray level image of the scene in which a gray level of pixels are substantially proportional to the determined reflectivity of the surface elements or substantially equal to a product of the determined reflectivity of the respective surface elements times a cosine of an angle between the imaging direction for respective ones of the surface elements,

identifying candidates for a feature in the scene based on the gray level image,

wherein ones of the surface elements being considered as a candidate for the feature have a value of Rcosθ

that satisfies a constraint;

R*≧

Rcosθ

≧

R′

cosθ

_T, wherein R* is the particular reflectivity of the feature, Rcosθ

is the determined reflectivity (R) for the surface element being considered as a candidate times a cosine of an angle (θ

) between the candidate surface element'"'"'s imaging direction and the normal to the candidate surface element, and θ

_T is a threshold angle between the candidate surface element'"'"'s imaging direction and the normal to the candidate surface element.

10. A method according to claim 9 and comprising imaging the scene with a camera having an optic center and determining the imaging direction comprises determining the imaging direction to be a direction parallel to a line from a first of the surface elements to the optic center of the camera.

11. A method according to claim 9 and comprising imaging the scene with a camera having an optic axis and determining the imaging direction comprises determining the imaging direction to be a direction parallel to the optic axis.

12. A method according to claim 9, wherein the gray level of a first pixel in the image that images a first of the surface elements is substantially equal to a product of the reflectivity determined for the first surface element times a cosine of an angle between the imaging direction and normal for the first surface element.

13. A method according to claim 9, wherein the gray level of a first pixel in the image that images a first of the surface elements is substantially proportional to the reflectivity of the first surface element.

14. A method comprising:

illuminating a scene including surface elements with known intensity light;

imaging the surface elements at a camera with light reflected by the surface elements from the known intensity light;

determining distances to the surface elements of the scene from the camera based on the imaging;

determining imaging directions substantially along which light from respective ones of the surface elements are imaged;

determining normals to the surface elements responsive to the determined distances;

determining reflectivities of respective ones of the surface elements responsive to respective distances of the surface elements from the camera, a dot product of the normal of respective ones of the surface elements and a vector parallel to the imaging direction for respective ones of the surface elements, the known intensity of illuminating light, and light that is reflected by the surface elements and imaged by the camera; and

identifying candidates for a feature in the scene based on a product of the reflectivity determined for a first surface element imaged by the camera times a cosine of an angle between the first surface element'"'"'s imaging direction and the normal to the first surface element,

wherein the candidates for the feature have a value of Rcosθ

that satisfies a constraint;

R*≧

Rcosθ

≧

R′

cosθ

_T, wherein R* is a particular reflectivity of the feature, Rcosθ

is the determined reflectivity (R) for the candidate times a cosine of an angle (θ

) between the candidate'"'"'s imaging direction and the normal to the candidate, and θ

_T is a threshold angle between the candidate'"'"'s imaging direction and the normal to the candidate.

15. The method of claim 14, wherein the identifying candidates for a feature in the scene based on a product of the reflectivity determined for a first surface element imaged by the camera times a cosine of an angle between the first surface element'"'"'s imaging direction and the normal to the first surface element comprises:

determining whether the scene comprises a feature oriented such that the angle between the normal of the first surface element and the imaging direction for the first surface element is less than θ

_T.