Modelling, calibration and rendition of colour logarithmic CMOS image sensors

Logarithmic CMOS image sensors encode a high dynamic range scene in a manner that roughly approximates human perception whereas linear sensors with equivalent quantisation suffer from saturation or loss of detail. Moreover, the continuous response of logarithmic pixels permit high frame rates and random access, features that are useful in motion detection. This paper describes how to model, calibrate and render pixel responses from a colour logarithmic sensor into a standard colour space. The work unifies colour theory in conventional linear sensors and fixed pattern noise theory in monochromatic logarithmic sensors. Experiments with a Fuga 15RGB sensor demonstrate calibration and rendition using a Macbeth chart and neutral density filters. Colour rendition of the sensor with an empirical model, tested over three decades of dynamic range, competes with conventional digital cameras, tested over 1.5 decades. Photodiode leakage currents complicate modelling and calibration and degrade rendition in dim lighting.