Characterization and Simple Fixed Pattern Noise Correction in Wide Dynamic Range “Logarithmic” Imagers

Wide dynamic range logarithmic imagers can render naturally illuminated scenes while preserving detail and contrast information at a lower cost than high dynamic range linear sensors. However, the quality of the output is severely degraded by fixed pattern noise (FPN). Although previous FPN correction techniques can eliminate the dominant additive form of this noise, the contrast threshold of the imager over a wide illumination range is poor compared to the human visual system. In this paper, it is shown that a four-parameter model fits the measured characteristic response of wide dynamic range pixels over 11 decades of input current. A comparison of the responses of 200 pixels shows that there are significant variations in all four parameters. A procedure is described that allows the four pixel parameters to be obtained from the response of each pixel to five input currents. However, a much simpler procedure is shown to correct FPN, leading to a contrast threshold comparable to the human visual system over the five decades required to image wide-dynamic-range, naturally illuminated scenes.