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Simplified image correlation method using off-the-shelf signal processors to extract edge information using only spatial data
Simplified image correlation method using off-the-shelf signal processors to extract edge information using only spatial data
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机译：使用现有信号处理器仅使用空间数据提取边缘信息的简化图像相关方法
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摘要
Provided is an approach to efficiently correlate a previously captured digitally created image to one provided in real-time. The real-time digitally created image is represented by the digitally processed image of just the edges of objects within a scene. This is accomplished via digital edge extraction and subsequent digital data compression, based on comparing only the spatial differences (e.g., range values) among pixels. That is, digital data representative of signal intensity are not used. An application is the efficient correlation of real-time digitally processed 3-D images generated from laser scans, in particular, scans of laser “radars” or LADARS. The process simplifies and improves on conventional techniques by iterating three sequential steps. A “hard” edge or a corner of an object is detected via a “corner-detector” algorithm that assigns a raw edge-strength value to each pixel in the image digitally created from the LADAR return. This is accomplished via a spatial numerical second-derivative operation performed on only the range value (distance from the LADAR to a specific location on an object scanned by the LADAR) assigned to each pixel's neighboring pixels. Next, all edge-strength values greater than a pre-specified value representative of that obtained by a laser (light) reflection from a right angle (90°), i.e., a hard edge or a corner, are reset to the pre-specified edge-strength value. If this second step were omitted, the image correlation process would be dominated by large edge-strength values representative of actual discontinuities in an adjacent pixel's range value, such as those produced when a tall object (building, vehicle, or promontory) shadows the area behind it from a laser scanning it obliquely. Finally, when a discontinuity in range values between two adjacent pixels is detected, the edge-strength value of the pixel representing the larger range value is set to zero. This last step validates the perspective transformation from an oblique view to an overhead view by avoiding the designation of a strong “phantom edge” on the ground. This phantom edge results from the laser beam forming a “shadow” when obliquely radiating a tall vertical object. The data needed to accomplish this correlation are minimized for subsequent storage and manipulation by storing only the two end points of the straight lines digitally generated to depict the edges of objects within a scene. This simple method, using inexpensive commercial off-the-shelf signal processors, enables reliable real-time identification of objects by comparison to a previously obtained reconnaissance library of digital images that have been stored for the purpose of future targeting. To enable each object in this library of digital images to be efficiently stored in memory, each digital image is defined by a greatly reduced and then compressed data set. Using this method, object identification may be accomplished quickly and reliably during such time-critical events as the terminal portion of a guided weapon's trajectory.
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