Enhanced contrast for object detection and characterization by optical imaging based on differences between images

1. A computer implemented method for of capturing and analyzing images within a field of view, the method comprising:

defining a first difference image comprising absolute values of second image pixel values of a second image less corresponding first image pixel values of a first image and defining a second difference image comprising absolute values of second image pixel values less third image pixel values of a third image;

defining an enhanced difference image by selecting a smaller of each of corresponding pixel values from the first difference image and the second image pixel values;

distinguishing, in the enhanced difference image, between (i) foreground image components, and (ii) background image components; and

selecting, from the enhanced difference image, an object of interest based on the foreground image components distinguished from the background image components.

2. The computer implemented method of claim 1 , wherein the first image is captured, by a camera, at a time when a light source is in an off state, the second image is captured, by the camera, at a time when the light source is illuminating the field of view and the third image is captured, by the camera, at a time when the light source is in the off state.

3. The computer implemented method of claim 2 , wherein at least two light sources flank the camera and are substantially coplanar therewith.

4. The computer implemented method of claim 2 , wherein the camera and the light source are oriented vertically upward or horizontally outward.

5. The computer implemented method of claim 2 , wherein an image analyzer controls the camera to provide an exposure time no greater than 100 microseconds and wherein the image analyzer activates the light source during the exposure time at a power level of at least 5 watts.

6. The computer implemented method of claim 2 , wherein a holographic diffraction grating is positioned between a lens of the camera and the field of view.

7. The computer implemented method of claim 2 , wherein the light source is a diffuse emitter.

8. The computer implemented method of claim 2 , wherein the light source is an infrared light-emitting diode and the camera is an infrared-sensitive camera.

9. The computer implemented method of claim 2 ,

wherein the foreground image components correspond to objects located within a proximal zone of the field of view, the proximal zone extending from the camera and having a depth relative to an expected maximum distance between the objects corresponding to the foreground image components and the camera, and

wherein the background image components correspond to objects located within a distal zone of the field of view, the distal zone being located, relative to the camera, beyond the proximal zone.

10. The computer implemented method of claim 9 , wherein the proximal zone has a depth of at least four times the expected maximum distance.

11. A wearable goggle, comprising:

a camera oriented toward a field of view containing a background and a hand including fingers;

a 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 camera and the light source and configured to:

define a first difference image comprising absolute values of second image pixel values of a second image less corresponding first image pixel values of a first image and define a second difference image comprising absolute values of second image pixel values less third image pixel values of a third image;

define an enhanced difference image by selecting a smaller of each of corresponding pixel values from the first difference image and the second image pixel values;

distinguish, in the enhanced difference image, between (i) foreground image components, and (ii) background image components; and

selecting, from the enhanced difference image, an object of interest based on the foreground image components distinguished from the background image components.

12. The wearable goggle of claim 11 , wherein the first image is captured, by the camera, at a time when the light source is in an off state, the second image is captured, by the camera, at a time when the light source is illuminating the field of view and the third image is captured, by the camera, at a time when the light source is in the off state.

13. The wearable goggle of claim 11 , wherein the light source is a diffuse emitter.

14. The wearable goggle of claim 11 , wherein the light source is an infrared light-emitting diode and the camera is an infrared-sensitive camera.

15. The wearable goggle of claim 11 ,

wherein the foreground image components correspond to objects located within a proximal zone of the field of view, the proximal zone extending from the camera and having a depth relative to an expected maximum distance between the objects corresponding to the foreground image components and the camera, and

wherein the background image components correspond to objects located within a distal zone of the field of view, the distal zone being located, relative to the camera, beyond the proximal zone.

16. The wearable goggle of claim 15 , wherein the proximal zone has a depth of at least four times the expected maximum distance.

17. The wearable goggle of claim 11 , wherein at least two light sources flank the camera and are substantially coplanar therewith.

18. The wearable goggle of claim 11 , wherein the camera and the light source are oriented vertically upward or horizontally outward.

19. The wearable goggle of claim 11 , wherein an image analyzer controls the camera to provide an exposure time no greater than 100 microseconds and wherein the image analyzer activates the light source during the exposure time at a power level of at least 5 watts.

20. The wearable goggle of claim 11 , wherein a holographic diffraction grating is positioned between a lens of the camera and the field of view.