Enhanced contrast for object detection and characterization by optical imaging based on differences between images
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. A method of capturing and analyzing an image, the method comprising:
utilizing an image analyzer coupled to at least one camera and at least one light source 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 a field of view;
based on information obtained from an object of interest, construct at least a position and a shape of the object of interest; and
distinguish 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 to 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 method of claim 1 , wherein the proximal zone has a depth of at least four times the expected maximum distance.
3. The method of claim 1 , wherein the at least one light source is a diffuse emitter.
4. The method 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 method of claim 1 , wherein at least two light sources flank the at least one camera and are substantially coplanar therewith.
6. The method of claim 1 , wherein the at least one camera and the at least one light source are oriented vertically upward or horizontally outward.
7. The method of claim 1 , wherein the image analyzer controls the at least one camera to provide an exposure time no greater than 100 microseconds and wherein the image analyzer activates the at least one light source during the exposure time at a power level of at least 5 watts.
8. The method of claim 1 , wherein a holographic diffraction grating is positioned between a lens of the at least one camera and the field of view.
9. The method of claim 1 , wherein the image analyzer is further configured to operate 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 identify pixels corresponding to the object of interest based on a difference between the first and second images and a difference between the first and third images, and wherein the second image is captured before the first image and the third image is captured after the second image.
10. A wearable goggle, comprising:
at least one camera oriented toward a field of view containing a background and a hand including fingers;
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
a processor coupled to the at least one camera and the light source and configured to:
activate at least one light source to illuminate the field of view containing the hand;
capture a sequence of digital images of the field of view using the at least one camera at a time when the at least one light source is activated; and
based on information obtained from the hand, constructing at least a position and a shape of the hand,
wherein the at least one light source is positioned such that hand is located within a proximal zone of the field of view, the proximal zone extending from the at least one camera to a distance at least twice an expected maximum distance between the hand and the at least one camera.
11. The wearable goggle of claim 10 wherein the proximal zone has a depth of at least four times the expected maximum distance.
12. The wearable goggle of claim 10 wherein the at least one light source is a diffuse emitter.
13. The wearable goggle of claim 10 wherein the at least one light source is an infrared light-emitting diode and the at least one camera is an infrared-sensitive camera.
14. The wearable goggle of claim 10 wherein at least two light sources are activated, and the at least two light sources flank the at least one camera and are substantially coplanar therewith.
15. The wearable goggle of claim 10 wherein the at least one camera and the at least one light source are oriented horizontally outward with respect to a wearable goggle.
16. A wearable goggle, comprising:
at least one camera oriented toward a field of view containing a background and a hand including fingers;
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
a processor coupled to the at least one camera and the light source and configured to:
activate the at least one light source to illuminate the field of view containing the hand;
capture a sequence of digital images of the field of view using that at least one camera at a time when the at least one light source is activated;
based on information obtained from the hand, construct at least a position and shape of the hand; and
capture 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 hand are identified based on a difference between the second and first images and a difference between the second and third images.