Non-uniformity correction (NUC) gain damping

• US 9,143,709 B1
• Filed: 02/03/2012
• Issued: 09/22/2015
• Est. Priority Date: 05/09/2011
• Status: Active Grant

• Current Assignee: Elbit Systems of America LLC (Elbit Systems Limited)
• Original Assignee: Exelis Incorporated (L3Harris Technologies, Inc.)
• Inventors: Winn, Stuart Martin
• Primary Examiner(s): TUCKER, WESLEY J
• Application Number:
  US13/365,611
• Time in Patent Office: 1,327 Days
• Field of Search: 382274-275
• US Class Current: 1/1
• CPC Class Codes: H04N 25/671 for non-uniformity detection or correction
• CPC Class Codes: H04N 25/68 applied to defects

Abstract

A system of non-uniformity correction (NUC) for a pixel in an imaging array includes: a storage module for storing (a) a first gain coefficient for correcting a gain error of the pixel and (b) multiple damping factors, including a first damping factor, for adjusting the first gain coefficient, in response to multiple respective light levels that the pixel senses during operation. Also included is a NUC corrector module for receiving a first intensity value from the pixel in response to a first light level. The NUC corrector module extracts the first gain coefficient and a first damping factor from the storage module, and then corrects the first intensity value of the pixel using the (a) first gain coefficient and (b) first damping factor.

Claims

1. A system of non-uniformity correction (NUC) for a pixel in an imaging array comprising:

a lens assembly;

an analog to digital converter;

an imaging array, coupled to the analog to digital converter, for providing digital data pixel intensity values in response to a level of the light being received via the lens assembly;

a storage module for storing;

(a) a first gain coefficient for correcting a gain error of the pixel and

(b) multiple damping factors, including a first damping factor, for adjusting the first gain coefficient, in response to multiple respective light levels that the pixel senses during operation, and

a NUC corrector module, coupled to the analog to digital converter, said NUC corrector module comprising a subtractor, a first multiplier, a second multiplier and an adder of the NUC corrector module, the NUC corrector module configured to;

receive a first intensity value as digital data from the analog to digital converter of a pixel in response to a first light level,

extract the first gain coefficient and a first damping factor from the storage module, and

correct the first intensity digital data value of the pixel wherein;

the subtractor reduces a value of 1 by the first gain coefficient to provide a reduced value;

the first multiplier multiplies the first damping factor by the reduced value to provide a multiplied value;

the adder either adds or subtracts the multiplied value from the value of 1 to provide a corrected gain of the pixel; and

a second multiplier multiplying an offset adjustment value by the corrected gain of the pixel to provide a final output data value of the pixel.

2. The system of claim 1 including:

an NUC calibration module for calculating the first gain coefficient and the multiple damping factors and providing the first gain coefficient and the multiple damping factors to the storage module.

3. The system of claim 2 wherein

the first gain coefficient is determined by capturing a flat field image at a predetermined light level, and

the multiple damping factors are determined by capturing multiple flat field images at a plurality of further light levels, and calculating a change in gain at each of the plurality of further light levels.

4. The system of claim 2 wherein

the NUC calibration module is configured to calculate during a calibration mode, and

the NUC corrector module is configured to operate during an operating mode.

5. The system of claim 2 wherein

the NUC calibration module is configured to determine a first offset coefficient for adjusting an offset value of the pixel, and

the storage module is configured to receive and store the first offset coefficient from the NUC calibration module.

6. The system of claim 1 wherein

the storage module includes a look-up table (LUT) of the multiple respective light levels corresponding to the multiple damping factors of the pixel.

7. The system of claim 1 including:

the storage module for storing (a) a second gain coefficient for correcting a gain error of another pixel and (b) multiple damping factors, including a second damping factor, for adjusting the second gain coefficient, in response to multiple respective light levels that the other pixel senses during operation, and

the NUC corrector module correcting a second intensity value of the other pixel using the (a) the second gain coefficient and (b) the second damping factor.

8. A method for non-uniformity correction (NUC) of a pixel in an imaging array, the method comprising the steps of:

capturing a flat field image at a predetermined light level by an imaging array;

based on the predetermined light level of the captured image, determining a gain coefficient of a pixel of the flat field image;

storing, in a storage module, the determined gain coefficient of the pixel;

storing a plurality of damping factors for a corresponding plurality of video levels of the pixel, wherein an individual damping factor of the plurality of damping factors is determined by a ratio between (a) the gain coefficient of a pixel at a predetermined light level and (b) a gain coefficient of the pixel at another light level, the other light level being a determined video level of the pixel;

receiving light via a lens assembly at the imaging array;

generating a pixel intensity value based on the received light;

determining a video level of the generated pixel intensity value; and

correcting the pixel intensity value, at the determined video level, by adjusting the gain coefficient of the pixel intensity value using a stored damping factor that corresponds to the determined video level of the pixel intensity.

9. The method of claim 8 including the steps of:

storing an offset coefficient for the pixel; and

correcting the pixel using the stored offset coefficient for the pixel.

10. The method of claim 8 including the steps of:

storing another plurality of damping factors for a corresponding plurality of video levels of another pixel;

determining another video level of the other pixel; and

correcting the other pixel, at the determined other video level, by adjusting the gain coefficient of the other pixel using a stored damping factor that corresponds to the determined video level of the other pixel.

11. The method of claim 8 wherein

the gain is adjusted by subtraction from a value of 1 to obtain a reduced value, next the reduced value is multiplied by the stored damping factor to provide a multiplied value, and the multiplied value is subtracted from or added to the value of 1 to provide a corrected gain value of the pixel.

12. The method of claim 11 wherein:

the corrected gain value of the pixel is adjusted by an offset coefficient value to obtain a final output data of the pixel.

13. A method for non-uniformity correction (NUC) of a pixel in an imaging array, the method comprising the steps of:

generating, at an imaging array, an intensity value of pixel;

determining a video level of the pixel based on the pixel intensity value;

storing, in a storage module, a damping factor of the pixel based on average video levels of pixel intensity values of the imaging array and at least one function that mathematically expresses multiple gain values of the pixel as a function of respective video levels of the pixel;

selecting a gain value using the at least one function based on the determined pixel video level, wherein the selected gain value is a predetermined NUC gain for the determined pixel video level;

subtracting the selected gain value from a value of 1 to provide a subtracted value;

multiplying the subtracted value by the damping factor of the pixel to provide a multiplied value; and

adding or subtracting the multiplied value from the value of 1 to provide a calculated damped gain;

and

correcting the video level of the pixel using the damped gain.

14. The method of claim 13 including the steps of:

adding an offset value to the video level of the pixel; and

multiplying the offset value with the calculated damped gain to provide the corrected video level of the pixel.

15. The method of claim 13 wherein:

the step of storing includes;

storing a plurality of functions that mathematically express multiple gain values of the pixel as a function of the respective video levels of the pixel; and

the step of selecting includes the step of;

selecting the gain value from the plurality of functions that is adjacent to the predetermined NUC gain for the pixel.

16. The method of claim 15 wherein storing includes:

storing the plurality of functions in a look-up table (LUT) as distinct gain values for corresponding respective video levels of the pixel.