Photocurrent estimation from multiple captures for simultaneous SNR and dynamic range improvement in CMOS image sensors

An estimation method for recursively estimating an optimal illumination on a sensor capable of capturing non-destructively a plurality of image samples during an exposure period, said method comprising:

• measuring an illumination indication from said sensor, said measuring occurs two or more times at intervals during said exposure period, producing a multiplicity of measurements;
• determining an estimated illumination on said sensor from all or essentially all of said multiplicity of measurements non-destructively captured before motion/saturation, said determining step occurring recursively over said multiplicity of measurements and including statistical signal processing of said multiplicity of measurements, said signal processing being based on a noise model selected from a fixed pattern noise model, a reset noise model, a shot noise model and a read noise model;
• and
• maintaining a plurality of parameters during said measuring step, said plurality of parameters comprising:
• said estimated illumination;
• a weighting coefficient applied to a difference between a present one of said multiplicity of measurements and said estimated illumination corresponding to a previous one of said multiplicity of measurements;
• a mean square error of said estimated illumination;
• and
• a covariance of said estimated illumination with said present one of said multiplicity of measurements.

An apparatus configured to estimate illumination on a sensor during an exposure period, said apparatus comprising:

• a sampling means configured to measure, at a multiplicity of time intervals during said exposure period, an illumination indication from said sensor, and configured to produce a multiplicity of measurements;
• and
• an estimation means configured to determine an estimated illumination on said sensor from said multiplicity of measurements, said estimation means being configured to compute recursively over said multiplicity of measurements and to maintain recursively a plurality of parameters over said multiplicity of measurements, said plurality of parameters comprising:
• said estimated illumination;
• a weighting coefficient of a particular one of said multiplicity of measurements;
• a variance between said particular one of said multiplicity of measurements and said multiplicity of measurements;
• and
• an overall variance of said multiplicity of measurements.

An apparatus configured to estimate illumination on a sensor during an exposure period, said apparatus comprising:

• a sampling means configured to measure, at a multiplicity of time intervals during said exposure period, an illumination indication from said sensor, and configured to produce a multiplicity of measurements;
• and
• an estimation means configured to determine an estimated illumination on said sensor from said multiplicity of measurements, wherein said estimation means is configured to perform statistical signal processing of said multiplicity of measurements, said signal processing being based on a noise model selected from a fixed pattern noise model, a reset noise model, a shot noise model and a read noise model, and wherein said estimation means is configured to compute recursively over said multiplicity of measurements and to maintain recursively a plurality of parameters over said multiplicity of measurements, said plurality of parameters comprising:
• said estimated illumination;
• a weighting coefficient applied to a difference between a present one of said multiplicity of measurements and said estimated illumination corresponding to a previous one of said multiplicity of measurements;
• a mean square error of said estimated illumination;
• and
• a covariance of said estimated illumination with said present one of said multiplicity of measurements.