| 摘要 |
An improved a.c. coupled forward looking infrared (FLIR) system is disclosed. In a.c. coupled FLIR systems utilizing an array of detectors, the video signals produced when scanning "hot targets" are distorted toward the dark end of the display dynamic range. This distortion produces dark image obliterating streaks which are substantially reduced by a streak reduction system. In one embodiment video signals for each scan line are delayed in a delay line; while, the mean voltage is determined in an integrator, the mode voltage calculated from the probability density curve and the two summed in an adder to provide a video correction voltage. A sample and hold circuit then applies the video correction signal to the video voltage output of the delay line to produce video signals absent any streaking voltage. In another embodiment the video signals are connected to a first integrator to determine the mean voltage. The mean voltage is held in a first sample and hold circuit while the mean voltage is compared in a comparator with the video signals and the difference integrated in a second integrator to provide a median voltage of an observed probability distribution function which is sampled and held in a second sample and hold circuit for a comparision in a first difference amplifier with a reference d.c. voltage equal to the 50 percent position on the cumulative probability distribution function curve. The output of the first difference amplifier is a calculation of the incremental probability ( DELTA P). Since horizontal displacements of a family of proportional triangles of moderate skewness can be determined by multiplying vertical displacements by a proportionality constant, DELTA P is multiplied by an observed proportionality constant and the video correction signal DELTA V obtained. The video voltage, the mean voltage and the video correction voltage are added in a second difference amplifier and the corrected video signal applied to an amplifier to restore the gain necessary for display of the corrected video signals on a cathode ray tube.
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