US 7,099,056 B1 · Automatically balanced exposure time and gain in an image sensor

Abstract

An automatic exposure system is arranged to dynamically adjust the exposure time and gain of a pixel array in an imaging system. A selected group of pixels from the pixel array are evaluated while the pixel array is exposed to light that is reflected from a scene. The signal levels associated with the selected pixels are compared to a dynamically adjusted exposure threshold level, while the current exposure time is compared to a dynamic adjusted exposure time limit. The exposure threshold level and exposure time limit are selected using a method that is optimized for lower noise and less blur in the resulting image. The optimization method includes an optimal exposure method, an extrapolative method, an iterative method, and an alternative iterative method. The optimization methods are arranged to find an optimum balance between exposure time and gain such that noise and motion blur are minimized in the resulting image.

Claims25

Dependent claims

A method for balancing an exposure time and a gain for pixels in a pixel array system, the method comprising:

starting an exposure time interval;
selecting an exposure threshold in response to a current exposure time;
scanning the signal levels associated with sparse pixels, wherein the sparse pixels corresponds to a selected group of pixels from the pixel array;
repeating the steps of selecting the exposure threshold and scanning the signal levels when the scanned signal levels fail to exceed the selected exposure threshold;
terminating the exposure time interval when at least one of the scanned signal levels exceed the selected exposure threshold;
and
selecting a gain setting that is associated with the selected exposure threshold when the exposure time interval is terminated.

4 more elements

A method for balancing an exposure time and a gain for pixels in a pixel array system, the method comprising:

starting an exposure time interval;
selecting an exposure threshold that corresponds to a minimum threshold level;
selecting an exposure time limit that corresponds to a minimum exposure time;
scanning the signal levels associated with sparse pixels until an initial scan condition is satisfied, wherein the sparse pixels corresponds to a selected group of pixels from the pixel array, wherein the initial scan condition is satisfied when at least one of a first condition and a second condition are satisfied, wherein the first condition is satisfied when at least one of the scanned signal levels exceeds the selected exposure threshold, and wherein the second condition is satisfied when an exposure time exceeds the selected exposure time limit;
terminating the exposure time interval when a termination condition is satisfied, wherein the termination condition is satisfied when the initial scan condition is satisfied, the first condition fails, and the current exposure time limit corresponds to the last available exposure time limit;
selecting a higher exposure time limit when the termination condition fails, the initial scan condition is satisfied, the first condition fails, and the current exposure time limit is different from the maximum exposure time limit, wherein that the selected exposure time limit is greater than the previously selected exposure time limit;
repeating the step of scanning the signal levels associated with sparse pixels until an initial scan condition is satisfied after the higher exposure time limit is selected;
initiating a final scan procedure when the initial scan condition is satisfied and the first condition is satisfied, wherein the final scan procedure comprises:
selecting an exposure threshold that is associated with the selected exposure time limit;
scanning the signal levels associated with sparse pixels until a final scan condition is satisfied, wherein the final scan condition is satisfied when at least one of a third condition and a fourth condition are satisfied, wherein the third condition is satisfied when at least one of the scanned signal levels exceeds the selected exposure threshold, and wherein the second condition is satisfied when the exposure time exceeds an exposure timeout limit;
and
terminating the exposure time interval when the final scan condition is satisfied;
selecting a gain setting that is associated with the selected exposure threshold when the exposure time interval is terminated.

10 more elements

A method for balancing an exposure time and a gain for pixels in a pixel array system, the method comprising:

starting an exposure time interval;
selecting an exposure threshold that is greater than a minimum threshold level;
selecting an exposure time limit that corresponds to the selected exposure threshold;
scanning the signal levels associated with sparse pixels until an initial scan condition is satisfied, wherein the sparse pixels corresponds to a selected group of pixels from the pixel array, wherein the initial scan condition is satisfied when at least one of a first condition and a second condition are satisfied, wherein the first condition is satisfied when at least one of the scanned signal levels exceeds the selected exposure threshold, and wherein the second condition is satisfied when an exposure time exceeds the selected exposure time limit;
selecting a lower exposure threshold and corresponding exposure time limit when the initial scan condition is satisfied, the first condition fails, and the current exposure time limit is different from the maximum exposure time limit, wherein the selected exposure threshold is less than the previously selected exposure threshold, and the corresponding exposure time limit is greater than the previously selected exposure time limit;
repeating the step of scanning the signal levels associated with sparse pixels until the initial scan condition is satisfied after the lower exposure threshold and the corresponding exposure time limit are selected;
initiating a final scan procedure when the initial scan condition is satisfied and the first condition is satisfied, wherein the final scan procedure comprises:
selecting a higher exposure threshold that is greater than the previously selected exposure threshold;
scanning the signal levels associated with sparse pixels until a final scan condition is satisfied, wherein the final scan condition is satisfied when at least one of a third condition and a fourth condition are satisfied, wherein the third condition is satisfied when at least one of the scanned signal levels exceeds the selected exposure threshold, and wherein the second condition is satisfied when the exposure time exceeds an exposure timeout limit;
and
terminating the exposure time interval when the final scan condition is satisfied;
and
selecting a gain setting that is associated with the selected exposure threshold when the exposure time interval is terminated.

10 more elements

A method for balancing an exposure time and a gain for pixels in a pixel array system, the method comprising:

starting an exposure time interval;
selecting an exposure threshold that corresponds to a minimum threshold level;
selecting an exposure time limit that is associated with a next exposure threshold that is greater than the minimum threshold level;
scanning the signal levels associated with sparse pixels until an scan condition is satisfied, wherein the sparse pixels corresponds to a selected group of pixels from the pixel array, wherein the scan condition is satisfied when at least one of a first condition and a second condition are satisfied, wherein the first condition is satisfied when an exposure time exceeds the selected exposure time limit, and wherein the second condition is satisfied when at least one of the scanned signal levels exceeds the selected exposure threshold;
selecting a higher exposure threshold and another exposure time when the scan condition is satisfied, the first condition fails, and a third condition is satisfied, wherein the third condition is satisfied when the exposure time fails to exceed the previously selected exposure time limit, and the currently selected exposure threshold is different from a maximum exposure threshold;
repeating the step of scanning the signal levels associated with sparse pixels until the scan condition is satisfied after the higher exposure threshold and the other exposure time limit are selected;
terminating the exposure time interval when the at least one of the first condition is satisfied, the scan condition is satisfied and the exposure time exceeds the previously selected exposure time limit, and the scan condition is satisfied and the currently selected exposure threshold corresponds to the maximum exposure threshold;
and
selecting a gain setting that is associated with the selected exposure threshold when the exposure time interval is terminated.

6 more elements

Dependencies are inferred from the claim text.

Automatically balanced exposure time and gain in an image sensor

Life of this patent

Automatically balanced exposure time and gain in an image sensor

Life of this patent

Abstract

Claims25