Extended depth of field imaging system using chromatic aberration

• US 7,626,769 B2
• Filed: 03/22/2007
• Issued: 12/01/2009
• Est. Priority Date: 01/31/2005
• Status: Active Grant

• Current Assignee: Datalogic Scanning Incorporated (Datalogic S.p.A.)
• Original Assignee: Datalogic Scanning Incorporated (Datalogic S.p.A.)
• Inventors: Olmstead, Bryan L., Shearin, Alan
• Primary Examiner(s): SCHWARTZ, JORDAN MARC
• Application Number:
  US11/728,038
• Publication Number:
  US 20080212168A1
• Time in Patent Office: 985 Days
• Field of Search: 359/721, 359/719, 250/339.01, 250/339.05
• US Class Current: 359/721
• CPC Class Codes: G02B 27/0075 with means for altering, e.g. increasing, the depth of field or depth of focus
• CPC Class Codes: G06K 7/10702 Particularities of propagating elements, e.g. lenses, mirrors G06K7/10831 takes precedence

Abstract

An imaging system (FIG. 3) is disclosed that has a wavelength dependent focal shift caused by longitudinal chromatic aberration in a lens assembly (203) that provides extended depth of field imaging due to focal shift (213,214) and increased resolution due to reduced lens system magnification. In use, multiple wavelengths of quasi-monochromatic illumination, from different wavelength LEDs (206,207) or the like, illuminate the target, either sequentially, or in parallel in conjunction with an imager (200) with wavelength selective (colored) filters. Images are captured with different wavelengths of illumination that have different focus positions (208,209), either sequentially or by processing the color planes of a color imager separately. Extended depth of field, plus high resolution are achieved. Additionally, information about the range to the target can be determined by analyzing the degree of focus of the various colored images.

Claims

1. An extended depth of field imaging method, comprising:

illuminating a target with a light of a first quasi-monochromatic wavelength in the infrared range;

illuminating the target with a light of a second quasi-monochromatic wavelength different from the first wavelength;

receiving light reflected from the target at an electronic imaging location;

extending depth of target field within which an image of the illuminated target received is substantially in focus by interposing a collection lens constructed and arranged to accentuate chromatic aberration between the illuminated target and the electronic imaging location and by interposing a wavelength dependent aperture between the collection lens and an imaging sensor for receiving the light reflected from the target.

17. A method according to claim 1, wherein the first quasi-monochromatic wavelength is about 850 nm.

18. A method according to claim 1, wherein the target comprises a bar code.

19. A method according to claim 1, wherein an imaging sensor for receiving the light reflected from the target is a solid-state imaging array.

20. A method according to claim 1, wherein the lens comprises a plano-concave lens element and/or a plano-convex lens element.

21. A method according to claim 18, wherein the lens comprises a plano-concave lens element and a plano-convex lens element, and wherein a wavelength dependent aperture is disposed between the plano-convex lens element and the plano-concave lens element.

2. A system for imaging an object, comprising:

an illumination system generating light of first and second different quasi-monochromatic wavelengths wherein at least one of the first and second quasi-monochromatic wavelengths is in the infrared range;

a chromatically aberrant lens system constructed and arranged to accentuate chromatic aberration, the lens system having a first focal distance for the first wavelength light and a second focal distance for the second wavelength light, the second focal distance being different from the first focal distance; and

an imaging sensor receiving, via the lens system, first and second wavelength light reflected from an object to be imaged, the imaging sensor generating an image of the object by assembling first wavelength light focused thereon when a distance of the object from the lens system is the first focal distance and second wavelength light focused thereon when the distance of the object from the lens system is the second focal distance, wherein the imaging sensor is a solid-state imaging array responsive to both the first and second wavelengths of light, wherein the solid-state imaging array comprises an array of pixel elements and is arranged to capture sequential frames of data, each frame comprising data responsive to light incident on substantially all of the array of pixel elements.

3. A system according to claim 2, wherein the lens system comprises one or more lenses.

4. A system according to claim 3 further comprising a wavelength dependent aperture disposed between one of the lenses and the imaging sensor.

5. A system according to claim 2, wherein the first wavelength is about 850 nm, and the second wavelength is about 590 nm.

6. A system according to claim 2, wherein the object comprises a bar code.

7. A system according to claim 2, wherein the lens system comprises a plano-concave lens element and/or a plano-convex lens element.

8. A system according to claim 7 wherein the lens system comprises a plano-concave lens element and a plano-convex lens element, further comprising a wavelength dependent aperture disposed between the plano-convex lens element and the plano-concave lens element.

9. The system according to claim 2, wherein the illumination system includes a first light source generating light of the first wavelength and a second light source generating light of the second wavelength.

10. A system according to claim 2 wherein:

solid-state imaging array includes an array of pixels;

a first subset of the pixels are sensitive to a first set of wavelengths of light that includes the first wavelength light; and

a second subset of the pixels are sensitive to a second set of wavelengths of light that includes the second wavelength light.

11. A system according to claim 2 wherein the illumination system comprises at least a plurality of visible light emitting LEDs and a plurality of infrared light emitting LEDs.

12. A system according to claim 2 wherein the solid-state imaging array comprises an array of pixel elements and further includes wavelength selective filters over at least a subset of the array of pixel elements for distinguishing between the first and second wavelength light.

13. A system according to claim 2 wherein the lens system comprises at least one glass lens that is highly dispersive and uncorrected for chromatic aberration.

14. A system according to claim 2 wherein the lens system comprises:

a first rotationally symmetric lens;

a second rotationally symmetric lens substantially axially aligned with the first lens; and

an aperture element positioned in between the first and second lenses.

15. A system according to claim 2 wherein:

the illumination system controllably emits at least one of the first and second wavelength light during the capture of a frame of data.

16. A system according to claim 4, wherein the lens system comprises a collection lens.

22. A system for imaging an object, comprising:

an illumination system generating light of first and second different quasi-monochromatic wavelengths wherein at least one of the first and second quasi-monochromatic wavelengths is in the infrared range;

a chromatically aberrant lens system having a first focal distance for the first wavelength light and a second focal distance for the second wavelength light, the second focal distance being different from the first focal distance, the lens system comprising a plano-convex lens element and a plano-concave lens element;

a wavelength dependent aperture disposed between the plano-convex lens element and the plano-concave lens element; and

an imaging sensor receiving, via the lens system, light reflected from an object to be imaged, the sensor generating an image of the object by assembling first wavelength light focused thereon when a distance of the object from the lens system is the first focal distance and second wavelength light focused thereon when the distance of the object from the lens system is the second focal distance.

23. A system for imaging an object, comprising:

an illumination system generating light of first and second different quasi-monochromatic wavelengths wherein at least one of the first and second quasi-monochromatic wavelengths is about 850 nm;

a chromatically aberrant lens system having a first focal distance for the first wavelength light and a second focal distance for the second wavelength light, the second focal distance being different from the first focal distance; and

an imaging sensor receiving, via the lens system, light reflected from an object to be imaged, the sensor generating an image of the object by assembling first wavelength light focused thereon when a distance of the object from the lens system is the first focal distance and second wavelength light focused thereon when the distance of the object from the lens system is the second focal distance.