Time based offset correction for imaging systems and adaptive calibration control

Patent metadata

Field	Value
Publication number	US-2016198102-A1
Application number	US-201615068405-A
Country	US
Kind code	A1
Filing date	Mar 11, 2016
Priority date	Aug 5, 2014
Publication date	Jul 7, 2016
Grant date	—

Abstract

A method and an imaging system for adaptive shutter control wherein an imaging system can be configured to actuate a calibration element at various times and develop an offset correction or Non-Uniformity Correction (NUC). The system control processing units may acquire information derived from calibration data, regular imaging data or external data, which may be correlated with how fast the NUC is changing over time. How often calibration element is actuated may be adaptively determined from the correlating information and the actuation times may be adaptively controlled to optimally actuate as needed. In some embodiments the calibration element may be a shutter and calibration activation may include closing the shutter and providing a flat field image for calibration purposes.

First claim

What is claimed is:

1 . A method for adaptive calibration control in an imaging system comprising a calibration element, a Focal Plane Array (FPA) comprising an array of photodetectors, and detector electronic circuitry for reading out image data from the array of photodetectors, and one or more control processors, the method comprising:
actuating the calibration element at one or more times under processor control to present a known scene to the array of photodetectors; acquiring image data from the array of photodetectors while the calibration is actuated, the image data comprising an array of pixel values representing the known scene; calculating a non-uniformity correction (NUC); acquiring image data at one or more times with the calibration element de-actuated; generating an estimated rate of change of the NUC based at least in part on one or more of calibration image data, scene image data, elapsed time data, or FPA ambient condition data; based at least in part on the estimated rate of change of the NUC, determining at least one of:
an interval for actuating the calibration element or a next calibration activation time, or
an interval for updating the NUC.

2 . The method of claim 1 , wherein the estimated rate of change of the NUC is based at least in part on a filter operation performed on image data.

3 . The method of claim 2 , wherein the filter operation comprises application of a high-pass filter or a Fixed Pattern Noise (FPN) filter, and the estimated rate of change of the NUC is based at least in part on a change in high spatial frequency noise over time.

4 . The method of claim 1 , wherein FPA ambient temperature information is determined by acquiring data from one or more of an FPA temperature sensor, an imaging system, temperature sensor whose output is related to FPA temperature, a known scene temperature sensor, or an imaging system temperature sensor sensing surrounding environment ambient temperature.

5 . The method of claim 4 , wherein the estimated rate of change of the NUC is based at least in part on one or more of the acquired temperature difference over time or the rate of change of the acquired temperature.

6 . The method of claim 1 further comprising:
generating a predictive function configured to predict the NUC, the predictive function based at least in part on the known scene data acquired at two or more calibration events, wherein a predicted NUC is applied to image data acquired during scene imaging events that are subsequent to the two or more calibration events used to develop the predictive function; and
updating the predictive function based on subsequent calibration events,
wherein the estimated rate of change of the NUC is based at least in part on properties of the predictive function.

7 . The method of claim 6 , wherein the estimated rate of change of the NUC is based at least in part on the rate of change of the predictive function.

8 . The method of claim 1 , wherein elapsed time is acquired from one or more of a real time clock or timer.

9 . The method of claim 1 , wherein the calibration element is a shutter and the known scene is the flat field scene observed by the FPA when the shutter is closed.

10 . The method of claim 1 , wherein the imaging system is a thermal imaging system.

11 . An imaging system comprising:
an imaging FPA comprising an infrared focal plane array; a calibration element configured to expose the FPA to a known scene when actuated; and one or more control processor elements including one or more of a signal processing element, a calibration element controller, a temperature acquisition element, and a timer element, the processor configured to:
actuate the calibration element at one or more times under processor control to present a known scene to the array of photodetectors;
acquire image data from the array of photodetectors, the image data comprising an array of pixel values representing the known scene;
determine a non-uniformity correction (NUC);
acquire image data at one or more times with the calibration element de-actuated;
generate an estimated rate of change of the NUC based at least in part on one or more of calibration image data, scene image data, elapsed time data, or FPA ambient condition data; and
determine, based at least in part on the estimated rate of change of the NUC, at least one of:
an interval for actuating calibration element or next calibration activation time; or
updating NUC based on the correlating information.

12 . The system of claim 11 , wherein the estimated rate of change of the NUC is based at least in part on a filter operation performed on image data.

13 . The system of claim 12 , wherein the filter operation comprises application of a high-pass filter or a Fixed Pattern Noise (FPN) filter, and the estimated rate of change of the NUC is based at least in part on a change in high spatial frequency noise over time.

14 . The system of claim 11 , wherein FPA ambient temperature information is determined by acquiring data from one or more of an FPA temperature sensor, an imaging system temperature sensor whose output is related to FPA temperature, a known scene temperature sensor, or an imaging system temperature sensor sensing surrounding environment ambient temperature.

15 . The system of claim 14 , wherein the estimated rate of change of the NUC is based at least in part on one or more of the acquired temperature difference over time or the rate of change of the acquired temperature.

16 . The system of claim 11 , wherein the processor is further configured to:
generate a predictive function configured to predict the NUC, the predictive function based at least in part on the known scene data acquired at two or more calibration events, wherein a predicted NUC is applied to image data acquired during scene imaging events that are subsequent to the two or more calibration events used to develop the predictive function; and update the predictive function based on subsequent calibration events, wherein the estimated rate of change of the NUC is based at least in part on properties of the predictive function.

17 . The system of claim 16 , wherein the estimated rate of change of the NUC is based at least in part on the rate of change of the predictive function.

18 . The system of claim 11 , wherein elapsed time is acquired from one or more of a real time clock or timer.

19 . The system of claim 11 , wherein the calibration element is a shutter and the known scene is the flat field scene observed by the FPA when the shutter is closed.

20 . The system of claim 11 , wherein the imaging system is a thermal imaging system.

Assignees

• Seek Thermal Inc

Inventors

• Chahine Romeo
• Parrish William J
• Lee Jeffery
• Williams Ross
• Engberg Andreas
• Wolfe Jason

Classifications

• H04N17/002 Primary

  for television cameras · CPC title

• H04N23/73

  by influencing the exposure time · CPC title

• H04N25/672

  between adjacent sensors or output registers for reading a single image · CPC title

• H04N25/671

  for non-uniformity detection or correction · CPC title

• H04N25/63 Primary

  applied to dark current · CPC title