Adaptive gain control image processing system and method

1. An image processing system for use with an image sensor and a power supply, the image processing system comprising:

correction circuitry coupled to the image sensor and configured to receive a raw frame of video data from the image sensor;

scene analysis circuitry

(1) coupled to the image sensor and configured to receive the raw frame of video data from the image sensor and

(2) coupled to the correction circuitry and configured to receive a processed frame of video data from the correction circuitry,

wherein the scene analysis circuitry outputs

(1) an average video level of at least one of the raw frame of video data and the processed frame of video data and

(2) scene metrics related to at least one of the raw frame of video data and the processed frame of video data;

setpoint controller circuitry for outputting a setpoint based on at least the scene metrics;

and gain controller circuitry for receiving the average video level and the setpoint and setting a power supply gain as a function of a power supply gain for an earlier frame of video times the ratio of the setpoint to the average video level.

2. The image processing system as claimed in claim 1 , wherein the image sensor is a sensor for night-vision goggles.

3. The image processing system as claimed in claim 1 , wherein the scene metrics comprise at least one of the following characteristics:

a number of pixels that have intensities representing a saturated condition;

a percentage of pixels that have intensities representing the saturated condition;

a number of pixels that have intensities greater than a first threshold;

a percentage of pixels that have intensities greater than the first threshold;

a number of pixels that have intensities less than a second threshold;

and a percentage of pixels that have intensities less than the second threshold.

4. The image processing system as claimed in claim 1 , wherein the setpoint controller circuitry sets the setpoint by assigning the reduction of saturation a higher priority than an adjustment based on any other scene metric of the scene metrics related to at least one of the raw frame of video data and the processed frame of video data.

5. The image processing system as claimed in claim 4 , wherein the setpoint controller circuitry sets the setpoint by assigning the reduction of values in a high bin a higher priority than an adjustment based on any other scene metric, except for saturation, of the scene metrics related to at least one of the raw frame of video data and the processed frame of video data.

6. The image processing system as claimed in claim 1 , wherein at least a portion of at least one of the correction circuitry, the scene analysis circuitry, the setpoint controller circuitry and the gain controller circuitry comprises a field programmable gate array (FPGA).

7. The image processing system as claimed in claim 1 , wherein at least a portion of at least one of the correction circuitry, the scene analysis circuitry, the setpoint controller circuitry and the gain controller circuitry comprises a field programmable gate array (FPGA) connected to a microcontroller.

8. The image processing system as claimed in claim 7 , wherein the field programmable gate array (FPGA) provides the scene metrics to the microcontroller, and wherein the microcontroller implements at least a portion of the setpoint controller circuitry and the gain controller circuitry.

9. A method of providing gain correction in an image processing system, the method being implemented under the control of a microcontroller reading computer instructions from a non-transitory computer memory accessible by the microcontroller and causing the system to perform the steps of:

(a) assigning a setpoint of a system gain controller;

(b) receiving a frame of digital video data;

(c) calculating plural scene metrics from the received frame of digital data, wherein the plural scene metrics include a saturation metric and a high bin metric, the saturation metric having a first threshold indicating a maximum amount of pixels at saturation, and the high bin metric having a second threshold indicating a maximum amount of pixels above a high bin threshold, wherein the first threshold is lower than the second threshold;

(d) calculating an adjustment metric based on the plural scene metrics;

(e) calculating a filter value based on the current setpoint of the system gain controller;

(f) calculating an updated setpoint based on the current setpoint of the system gain controller, the adjustment metric and the filter value; and

(g) repeating steps (b)-(f) for successive frames of digital video data.

10. The method as claimed in claim 9 , wherein calculating the adjustment metric based on the plural scene metrics comprises calculating plural normalized scene metrics from the plural scene metrics.

11. The method as claimed in claim 10 , wherein calculating the adjustment metric comprises calculating metric values based on the plural normalized scene metrics and a prioritization order for adjustments to the setpoint.

12. An image processing system for use with an image sensor and a power supply, the image processing system comprising:

correction circuitry coupled to the image sensor and configured to receive a raw frame of video data from the image sensor;

scene analysis circuitry

(1) coupled to the image sensor and configured to receive the raw frame of video data from the image sensor and

(2) coupled to the correction circuitry and configured to receive a processed frame of video data from the correction circuitry,

wherein the scene analysis circuitry outputs

(1) an average video level of at least one of the raw frame of video data and the processed frame of video data and

(2) scene metrics related to at least one of the raw frame of video data and the processed frame of video data;

setpoint controller circuitry for outputting a setpoint based on at least the scene metrics;

and gain controller circuitry for receiving the average video level and the setpoint and setting an image sensor gain as a function of an image sensor gain for an earlier frame of video times the ratio of the setpoint to the average video level.

13. The image processing system as claimed in claim 1 , wherein the gain controller circuitry sets the power supply gain as a function of a power supply gain for an earlier frame of video, the ratio of the setpoint to the average video level, and an overshoot correction factor, alpha.

14. The image processing system as claimed in claim 12 , wherein the gain controller circuitry sets the image sensor gain as a function of an image sensor gain for an earlier frame of video, the ratio of the setpoint to the average video level, and an overshoot correction factor, alpha.

15. The method as claimed in claim 9 , wherein calculating the updated setpoint comprises constraining the updated setpoint to be within a range of a value for full white.

16. The method as claimed in claim 9 , wherein calculating an adjustment metric based on the plural scene metrics comprises calculating an adjustment metric to decrease the setpoint when an amount of pixels at saturation is greater than the first threshold.

17. The method as claimed in claim 9 , wherein calculating an adjustment metric based on the plural scene metrics comprises calculating an adjustment metric to decrease the setpoint when an amount of pixels above the high bin threshold is above the second threshold.

18. The method as claimed in claim 9 , wherein calculating plural scene metrics from the received frame of digital data comprises calculating a low bin metric having a third threshold indicating a maximum amount of pixels below a low bin threshold.

19. The method as claimed in claim 18 , wherein calculating an adjustment metric based on the plural scene metrics comprises calculating an adjustment metric to increase the setpoint when an amount of pixels below the low bin threshold is greater than the third threshold.

20. The image processing system as claimed in claim 12 , wherein the image sensor is a sensor for night-vision goggles.

21. The image processing system as claimed in claim 12 , wherein the scene metrics comprise at least one of the following characteristics:

a number of pixels that have intensities representing a saturated condition;

a percentage of pixels that have intensities representing the saturated condition;

a number of pixels that have intensities greater than a first threshold;

a percentage of pixels that have intensities greater than the first threshold;

a number of pixels that have intensities less than a second threshold;

and a percentage of pixels that have intensities less than the second threshold.

22. The image processing system as claimed in claim 12 , wherein the setpoint controller circuitry sets the setpoint by assigning the reduction of saturation a higher priority than an adjustment based on any other scene metric of the scene metrics related to at least one of the raw frame of video data and the processed frame of video data.

23. The image processing system as claimed in claim 12 , wherein the setpoint controller circuitry sets the setpoint by assigning the reduction of values in a high bin a higher priority than an adjustment based on any other scene metric, except for saturation, of the scene metrics related to at least one of the raw frame of video data and the processed frame of video data.

24. The image processing system as claimed in claim 12 , wherein at least a portion of at least one of the correction circuitry, the scene analysis circuitry, the setpoint controller circuitry and the gain controller circuitry comprises a field programmable gate array (FPGA).

25. The image processing system as claimed in claim 12 , wherein at least a portion of at least one of the correction circuitry, the scene analysis circuitry, the setpoint controller circuitry and the gain controller circuitry comprises a field programmable gate array (FPGA) connected to a microcontroller.