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A CMOS image sensor with local brightness adaptation and high intrascene dynamic range
An integrated CMOS image sensor with 128x128 pixels and local brightness adaptation suitable for machine vision and surveillance applications has been developed and successfully tested. Local brightness adaptation is achieved by dividing the input photocurrent of each sensor pixel by its local average. Since the irradiance at the imager is based on a nonlinear multiplicative combination of scene illumination and object surface reflectance, the output signal of the imager will depend only on the visually relevant reflectance component if the illumination does not significantly vary within the averaging areas. The computation of local average is realized by spatial lo-pass filtering the input photocurrent distribution using a 2D pseudo-resistive diffusion network. Division by local average inside each pixel is based on a translinear divider. The chip has been realized in a 1mu m n-well standard CMOS process. The pixel pitch is 53,4 mu m and the total chip area is 68mm2.