Method of and apparatus for reducing speckle-pattern noise in a planar laser illumination and imaging (PLIIM) based system
First Claim
1. A method of reducing speckle-pattern noise at the image detection array of a planar laser illumination and imaging (PLIIM) based system, said method comprising the steps of:
- (a) producing a planar laser illumination laser beam (PLIB) within a planar laser illumination and imaging (PLIIM) based system including an image detection array having image forming optics with a field of view (FOV) arranged in a coplanar relationship with said PLIB;
(b) reducing the spatial-coherence of said PLIB before said PLIB illuminates a target object, so that the object is illuminated with a spatially coherent-reduced planar laser illumination beam (PLIB) and a plurality of substantially different time-varying speckle-noise patterns are produced at said image detection array over the photo-integration time period thereof;
(c) detecting said plurality of substantially different time-varying speckle-noise patterns over said photo-integration time period; and
(d) temporally averaging said detected speckle-noise patterns at said image detection array during said photo-integration time period thereof, thereby reducing the power of observable speckle-noise patterns at said image detection array.
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Abstract
Methods of and systems for illuminating objects using planar laser illumination beams having substantially-planar spatial distribution characteristics that extend through the field of view (FOV) of image formation and detection modules employed in such systems. Each planar laser illumination beam is produced from a planar laser illumination beam array (PLIA) comprising an plurality of planar laser illumination modules (PLIMs). Each PLIM comprises a visible laser diode (VLD, a focusing lens, and a cylindrical optical element arranged therewith. The individual planar laser illumination beam components produced from each PLIM are optically combined to produce a composite substantially planar laser illumination beam having substantially uniform power density characteristics over the entire spatial extend thereof and thus the working range of the system. Preferably, each planar laser illumination beam component is focused so that the minimum beam width thereof occurs at a point or plane which is the farthest or maximum object distance at which the system is designed to acquire images, thereby compensating for decreases in the power density of the incident planar laser illumination beam due to the fact that the width of the planar laser illumination beam increases in length for increasing object distances away from the imaging optics. By virtue of the present invention, it is now possible to use both VLDs and high-speed CCD-type image detectors in conveyor, hand-held and hold-under type scanning applications alike, enjoying the advantages and benefits that each such technology has to offer, while avoiding the shortcomings and drawbacks hitherto associated therewith.
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Citations
18 Claims
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1. A method of reducing speckle-pattern noise at the image detection array of a planar laser illumination and imaging (PLIIM) based system, said method comprising the steps of:
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(a) producing a planar laser illumination laser beam (PLIB) within a planar laser illumination and imaging (PLIIM) based system including an image detection array having image forming optics with a field of view (FOV) arranged in a coplanar relationship with said PLIB; (b) reducing the spatial-coherence of said PLIB before said PLIB illuminates a target object, so that the object is illuminated with a spatially coherent-reduced planar laser illumination beam (PLIB) and a plurality of substantially different time-varying speckle-noise patterns are produced at said image detection array over the photo-integration time period thereof; (c) detecting said plurality of substantially different time-varying speckle-noise patterns over said photo-integration time period; and (d) temporally averaging said detected speckle-noise patterns at said image detection array during said photo-integration time period thereof, thereby reducing the power of observable speckle-noise patterns at said image detection array. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A planar laser illumination and imaging (PLIIM) based system for producing digital images with reduced levels of speckle-pattern noise, said PLIIM based system comprising:
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a planar laser illumination array (PLIA) including a plurality of laser diodes for producing and projecting a planar laser illumination beam (PLIB) through a light transmission aperture, so as to illuminate an object as it is moving past said PLIIM based system; an image formation and detection (IFD) module having a an image detection array and imaging forming optics for providing said image detection array with a field of view (FOV), wherein said PLIB and said FOV are arranged in a coplanar relationship along the working range of said PLIIM based system so that the PLIB illuminates primarily within said FOV of the IFD module; and a speckle-pattern noise reduction subsystem, integrated with said PLIA, for reducing the spatial-coherence of said PLIB before said PLIB illuminates a target object so that the object is illuminated with a spatially coherent-reduced planar laser illumination beam (PLIB) and a plurality of substantially different time-varying speckle-noise patterns are produced at said image detection array over the photo-integration time period thereof; whereby said plurality of substantially different time-varying speckle-noise patterns are detected at said image detection array over said photo-integration time period, and said detected speckle-noise patterns are temporally averaged at said image detection array during said photo-integration time period thereof, thereby reducing the power of observable speckle-noise patterns at said image detection array. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18)
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Specification