METHOD OF SPECKLE-NOISE PATTERN REDUCTION AND APPARATUS THEREFOR BASED ON REDUCING THE SPATIAL-COHERENCE OF THE PLANAR LASER ILLUMINATION BEAM BEFORE THE BEAM ILLUMINATES THE TARGET OBJECT BY APPLYING SPATIAL PHASE SHIFTING TECHNIQUES DURING THE TRANSMISSION OF THE PLIB THERETOWARDS

摘要

A planar laser illumination and imaging (PLIIM) based camera system capable of producing digital images with reduced levels of speckle-pattern noise. The PLIIM based camera system comprises 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 camera system. An image formation and detection (IFD) module is provided having a image detection array and imaging forming optics for providing said image detection array with a field of view (FOV). The PLIB and FOV are arranged in a coplanar relationship along the working range of the PLIIM based camera system so that the PLIB illuminates primarily within the FOV of the IFD module. A speckle-pattern noise reduction subsystem is integrated with the PLIA, for reducing the spatial-coherence of said planar laser illumination beam (PLIB) before the PLIB illuminates a target object. The speckle-pattern noise reduction subsystem carries out a spatial phase shifting technique during the transmission of the PLIB towards the target, so that the object is illuminated with a spatially coherent-reduced planar laser illumination beam (PLIB) and numerous substantially different time-varying speckle-noise patterns are produced at the image detection array over the photo-integration time period thereof. The numerous substantially different time-varying speckle-noise patterns are detected at the image detection array over the photo-integration time period, and the detected speckle-noise patterns are temporally averaged at said image detection array during the photo-integration time period thereof. As a result of such temporal averaging, the power of observable speckle-noise patterns is reduced at the image detection array. By virtue of the present invention, it is now possible to enjoy the benefits of laser-based illumination during high-speed imaging operations, without the adverse effects of speckle-pattern noise.