20 February 2007 Adaptive nonlinear imaging characteristic for wide-dynamic-range image sensor using variable integration time
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Abstract
As the issue of wide dynamic range imaging, some adjustments are needed to display an image with wider dynamic range than that of displays. Because the dynamic range of existing displays is limited to 10 from 8 bits for each color, the image quality degrades when the characteristic is not suitable for the objects. One of our smart image sensors can control the integration time of each pixel. In the sensor, the intermediate photodiode value is compared with arbitrary threshold at arbitrary timing and reset depending on the result. We call this "judgment and reset process". The characteristic for wide dynamic range imaging is decided by thresholds and timings. So optimization of the parameters adapted to the brightness distribution of objects and the new sensor which realizes the proposed method are reported. Before the first judgment, the PD values are read out and passed to the external circuit in order to estimate the rough histogram of the image at a frame end. In the histogram, successive pixels are recognized as the detected block. Quota of output values in the characteristic is mainly decided by the block width. In consequence, the dynamic range is widened and the contrast is dramatically improved.
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Fumitsugu Suzuki, Takayuki Hamamoto, "Adaptive nonlinear imaging characteristic for wide-dynamic-range image sensor using variable integration time", Proc. SPIE 6502, Digital Photography III, 65020Z (20 February 2007); doi: 10.1117/12.705245; https://doi.org/10.1117/12.705245
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