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Abstract

A FLIR imager is modified to include a hybrid optical/electronic processor for automatic local area dynamic range normalization. FLIR imagers have an objective lens for focusing IR energy emanating from a scene on a detector array. The detector array generates electrical signals representative of the scene. LEDs generate a visible picture of the thermal image of the scene for a video processor for formatting the signals for a particular type display (TV). The hybrid optical/electronic processor is inserted between the LEDs and the video processor; it includes a beamsplitter for directing the image to a pair of CCD cameras. The image at one camera is set in sharp focus to preserve all of the spatial frequency content (allpass) through the image reconstruction optics. While the image at the second camera is slightly defocused for averaging image information over small local regions the size of the defocused point spread function (spatial lowpass filtered). The electrical signal outputs of the CCD cameras are connected to a differential amplifier for subtracting the lowpass image from the allpass image to produce the highpass image and amplification to bring the resulting signal level above the noise level of the CRT display; while the local average image output of the second camera is connected to a limiter for limiting the local average variations. A summing amplifier is used to bring the signal back together for restoring the visual impression of hot and cold objects without saturation or blanking and provide enhancement of image detail.

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First Claim