Adaptive gain control image processing system and method
By utilizing scene metrics in an image processing system (such as night vision goggles or a camera), a setpoint controller can set a setpoint used by a gain controller. Using the setpoint and an average video level of a frame, the gain controller can set gain control signals sent to an image sensor and/or a high voltage power supply to adaptively adjust for higher and lower light scenarios. Scene metrics can include an amount of saturation in a frame, a number or percentage of pixels above a first threshold and a number or percentage of pixels below a second threshold.
1. An image processing system for use with an image sensor and a high voltage power supply, the image processing system comprising:
correction circuitry for 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 a 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 at least one of a High Voltage Power Supply (HVPS) gain and an image sensor gain based on a 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 a 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. The image processing system as claimed in claim 1 , wherein the gain controller circuitry sets the HVPS gain as a function of an HPVS gain for an earlier frame of video times the ratio of the setpoint to the average video level.
10. The image processing system as claimed in claim 1 , wherein the gain controller circuitry sets the 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.
11. The image processing system as claimed in claim 1 , wherein the gain controller circuitry sets the HVPS gain as a function of an HPVS gain for an earlier frame of video, the ratio of the setpoint to the average video level, and an overshoot correction factor alpha.
12. The image processing system as claimed in claim 1 , 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.