Enhanced contrast for object detection and characterization by optical imaging
View Patent ↗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.
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.