Photocurrent estimation from multiple captures for simultaneous SNR and dynamic range improvement in CMOS image sensors
First Claim
9. An estimation method for non-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 the steps of:
- measuring an illumination indication from said sensor;
storing said illumination indication, wherein said measuring and storing steps occur a multiplicity of times during said exposure period thereby collecting a multiplicity of measurements; and
performing a non-recursive optimal illumination estimation on said sensor from said collected multiplicity of measurements.
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Abstract
The dynamic range and the noise immunity of a digital imaging system are increased by basing an estimate of the illumination on a sensor on a series of measurements of the accumulated illumination at intervals within an exposure period. The measuring may occur destructively, or alternatively the photocurrent of the sensor may continue to accumulate over the exposure period. The estimate may use statistical signal processing of the measurements, based on various noise models and various optimization criteria. The estimate may be computed recursively over the multiplicity of measurements, using a set of recursive values that may include but is not limited to the estimated illumination, a current weighting coefficient, a variance of the current measurement and a variance over the series of measurements.
41 Citations
35 Claims
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9. An estimation method for non-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 the steps of:
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measuring an illumination indication from said sensor;
storing said illumination indication, wherein said measuring and storing steps occur a multiplicity of times during said exposure period thereby collecting a multiplicity of measurements; and
performing a non-recursive optimal illumination estimation on said sensor from said collected multiplicity of measurements. - View Dependent Claims (1, 2, 3, 4, 5, 6, 7, 8, 10, 11, 12, 13, 14, 15)
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16. 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 the steps of:
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measuring an illumination indication from said sensor, said measuring occurs a multiplicity of times at intervals during said exposure period thereby producing a multiplicity of measurements; and
determining an estimated illumination on said sensor from said multiplicity of measurements, 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. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24)
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25. An apparatus configured to estimate illumination on a sensor during an exposure period, said apparatus comprising:
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a sampling means configured to measure, at a multiplicity of time intervals during said exposure period, an illumination indication from a sensor, and configured to thereby produce a multiplicity of measurements; and
an estimation means configured to determine, based on weighted averaging, an estimated illumination on said sensor from said multiplicity of measurements. - View Dependent Claims (26, 27, 28, 29, 30, 31, 32)
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33. An apparatus configured to estimate illumination on a sensor during an exposure period, said apparatus comprising:
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a sampling means configured to measure, at a multiplicity of time intervals during said exposure period, an illumination indication from a sensor, and configured to thereby 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;
means for weighting a particular one of said multiplicity of measurements;
means for indicating variance between said particular one of said multiplicity of measurements and said multiplicity of measurements; and
means for indicating overall variance of said multiplicity of measurements.
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34. An apparatus configured to estimate illumination on a sensor during an exposure period, said apparatus comprising:
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a sampling means configured to measure, at a multiplicity of time intervals during said exposure period, an illumination indication from a sensor, and configured to thereby 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 being 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 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 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.
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35. An apparatus configured to estimate illumination on a sensor during an exposure period for simultaneously reducing noise and improving dynamic range at low illumination end, where said sensor is configured in a complementary metal oxide semiconductor (CMOS) image sensor system capable of capturing multiple image samples during said exposure period, said apparatus comprising:
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means for measuring, at a multiplicity of intervals during said exposure period, actual photocurrent from said sensor, said means for measuring thereby producing a multiplicity of photocurrent measurements; and
means for estimating optimal photocurrent on said sensor from said multiplicity of measurements.
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Specification