Enhanced contrast for object detection and characterization by optical imaging

• US 8,693,731 B2
• Filed: 01/16/2013
• Issued: 04/08/2014
• Est. Priority Date: 01/17/2012
• Status: Active Grant

• Current Assignee: Lmi Liquidating Co., LLC
• Original Assignee: Leap Motion Incorporated (Ultraleap Limited)
• Inventors: Holz, David, Yang, Hua
• Primary Examiner(s): Park, Chan
• Assistant Examiner(s): Thomas, Mia M
• Application Number:
  US13/742,845
• Publication Number:
  US 20130182077A1
• Time in Patent Office: 447 Days
• Field of Search: 382/103, 382/104, 382/154, 382/168, 382/190, 382/195, 382/289, 382/293, 382/295, 348/14.01, 348/36, 348/143, 348/155, 348/222.1, 378/4, 378/7
• US Class Current: 382/103
• CPC Class Codes: G06F 18/00 Pattern recognition
• CPC Class Codes: G06F 3/017 Gesture based interaction, e.g. based on a set of recognized hand gestures interaction based on gestures traced on a digitiser G06F3/04883
• CPC Class Codes: G06F 3/0304 Detection arrangements using opto-electronic means constructional details of pointing devices not related to the detection arrangement using opto-electronic means G06F3/033; optical digitisers G06F3/042
• CPC Class Codes: G06T 2200/04 involving 3D image data
• CPC Class Codes: G06T 2207/10012 Stereo images
• CPC Class Codes: G06T 2207/10016 Video; Image sequence
• CPC Class Codes: G06T 7/10 Segmentation; Edge detection motion-based segmentation G06T7/215
• CPC Class Codes: G06T 7/11 Region-based segmentation
• CPC Class Codes: G06T 7/194 involving foreground-background segmentation
• CPC Class Codes: G06T 7/215 Motion-based segmentation
• CPC Class Codes: G06T 7/248 involving reference images or patches
• CPC Class Codes: G06T 7/251 involving models
• CPC Class Codes: G06T 7/254 involving subtraction of images
• CPC Class Codes: G06T 7/262 using transform domain methods, e.g. Fourier domain methods
• CPC Class Codes: G06T 7/344 involving models
• CPC Class Codes: G06T 7/37 using transform domain methods
• CPC Class Codes: G06T 7/70 Determining position or orientation of objects or cameras camera calibration G06T7/80
• CPC Class Codes: G06T 7/90 Determination of colour characteristics
• CPC Class Codes: G06V 20/64 Three-dimensional objects
• CPC Class Codes: G06V 40/107 Static hand or arm
• CPC Class Codes: H04N 13/254 : in combination with electromagnetic radiation sources for illuminating objects
• CPC Class Codes: H04N 23/661 : Transmitting camera control signals through networks, e.g. control via the Internet

Abstract

Enhanced contrast between an object of interest and background surfaces visible in an image is provided using controlled lighting directed at the object. Exploiting the falloff of light intensity with distance, a light source (or multiple light sources), such as an infrared light source, can be positioned near one or more cameras to shine light onto the object while the camera(s) capture images. The captured images can be analyzed to distinguish object pixels from background pixels.

Claims

1. An image capture and analysis system for identifying objects of interest in a digitally represented image scene, the system comprising:

at least one camera oriented toward a field of view;

at least one light source disposed on a same side of the field of view as the camera and oriented to illuminate the field of view; and

an image analyzer coupled to the camera and the at least one light source configured to;

operate the at least one camera to capture a sequence of images including a first image captured at a time when the at least one light source is illuminating the field of view;

identify pixels corresponding to the object rather than to a background; and

based on the identified pixels, construct a 3D model of the object, including a position and shape of the object, to geometrically determine whether it corresponds to the object of interest,

wherein the image analyzer distinguishes between (i) foreground image components corresponding to objects located within a proximal zone of the field of view, the proximal zone extending from the at least one camera and having a depth relative thereto of at least twice an expected maximum distance between the objects corresponding to the foreground image components and the at least one camera, and (ii) background image components corresponding to objects located within a distal zone of the field of view, the distal zone being located, relative to the at least one camera, beyond the proximal zone.

2. The system of claim 1 wherein the proximal zone has a depth of at least four times the expected maximum distance.

3. The system of claim 1 wherein the at least one light source is a diffuse emitter.

4. The system of claim 3 wherein the at least one light source is an infrared light-emitting diode and the at least one camera is an infrared-sensitive camera.

5. The system of claim 1 wherein there are at least two light sources flanking the at least one camera and substantially coplanar therewith.

6. The system of claim 1 wherein the at least one camera and the at least one light source are oriented vertically upward.

7. The system of claim 1 wherein the at least one camera is operated to provide an exposure time no greater than 100 microseconds and the at least one light source is activated during exposure time at a power level of at least 5 watts.

8. The system of claim 1 further comprising a holographic diffraction grating positioned between a lens of the at least one camera and the field of view.

9. The system of claim 1 wherein the image analyzer operates the at least one camera to capture second and third images when the at least one light source is not illuminating the field of view and identifies the pixels corresponding to the object based on a difference between the first and second images and a difference between the first and third images, wherein the second image is captured before the first image and the third image is captured after the second image.

10. A method for capturing and analyzing images, the method comprising the steps of:

activating at least one light source to illuminate a field of view containing an object of interest;

capturing a sequence of digital images of the field of view using a camera at a time when the at least one light source is activated;

identifying pixels corresponding to the object rather than to a background; and

based on the identified pixels, constructing a 3D model of the object, including a position and shape of the object, to geometrically determine whether it corresponds to the object of interest,

wherein the at least one light source is positioned such that objects of interest are located within a proximal zone of the field of view, the proximal zone extending from a camera to a distance at least twice an expected maximum distance between the objects of interest and the camera.

11. The method of claim 10 wherein the proximal zone has a depth of at least four times the expected maximum distance.

12. The method of claim 10 wherein the at least one light source is a diffuse emitter.

13. The method of claim 10 wherein the at least one light source is an infrared light-emitting diode and the camera is an infrared-sensitive camera.

14. The method of claim 10 wherein two light sources are activated, the light sources flanking the camera and substantially coplanar therewith.

15. The method of claim 10 wherein the camera and the at least one light source are oriented vertically upward.

16. A method for capturing and analyzing images, the method comprising the steps of:

activating at least one light source to illuminate a field of view containing an object of interest;

capturing a sequence of digital images of the field of view using a camera at a time when the at least one light source is activated;

identifying pixels corresponding to the object rather than to a background;

based on the identified pixels, constructing a 3D model of the object, including a position and shape of the object, to geometrically determine whether the model corresponds to the object of interest; and

capturing a first image when the at least one light source is not activated, a second image when the at least one light source is activated, and a third image when the at least one light source is not activated, wherein pixels corresponding to the object are identified based on a difference between the second and first images and a difference between the second and third images.