Method of shutterless non-uniformity correction for infrared imagers

1. A method of correcting an infrared image, the method comprising:

providing a processor;

receiving the infrared image from a camera, the infrared image comprising a plurality of pixels arranged in an input image array, a first pixel in the plurality of pixels having a first pixel value and one or more neighbor pixels with one or more neighbor pixel values, wherein the first pixel and the one or more neighbor pixels are associated with an object in the infrared image, the one or more neighbor pixels being adjacent to the first pixel in the input image array;

processing the infrared image to generate a processed image;

determining, by the processor, whether the processed image is a first frame;

in the event that the processed image is the first frame:

initializing a correction table to an initialized correction table;

initializing a mean image counter to zero;

determining, by the processor, whether the camera is moving;

in the event that the camera is moving:

determining whether a motion of the camera is greater than or equal to a motion threshold;

in the event that the motion of the camera is greater than or equal to the motion threshold:

updating the correction table using a motion-based algorithm; and

providing an output image based on the updated correction table using the motion-based algorithm and the processed image.

2. The method of claim 1 , further comprising:

in the event that the motion of the camera is less than the motion threshold:

initializing a mean image to the processed image; and

initializing the mean image counter to zero.

3. The method of claim 2 , further comprising:

determining whether the mean image counter is greater than a count threshold;

in the event that the mean image counter is greater than the count threshold:

updating the correction table using a motionless algorithm; and

providing the output image based on the updated correction table using the motionless algorithm and the processed image.

4. The method of claim 3 , further comprising:

in the event that the mean image counter is not greater than the count threshold:

providing the output image based on the initialized correction table and the processed image.

5. The method of claim 1 , wherein updating the correction table using the motion-based algorithm comprises:

for each correction pixel value, determining that the first pixel value is not an edge;

for each of the one or more neighbor pixel values, determining that a neighbor pixel value is not an edge;

computing a difference between the first pixel value and the one or more neighbor pixel values; and

determining a correction pixel value based on the difference.

6. The method of claim 5 , wherein updating the correction table using the motion-based algorithm further comprises:

adding the difference to a previous neighbor correction value to update a neighbor correction value; and

subtracting the difference from a previous correction value to update a correction value.

7. The method of claim 1 , wherein updating the correction table using the motion-based algorithm comprises:

for each correction pixel value, determining correction values for the one or more neighbor pixels;

computing a difference between the first pixel value and the one or more neighbor pixel values; and

updating the correction pixel value using the difference.

8. The method of claim 7 , wherein updating the correction table using the motion-based algorithm further comprises:

determining whether an absolute value of the difference is within a range;

in the event that the absolute value of the difference is within the range:

updating a current first correction value of the first pixel value by subtracting a fraction of the difference from a previous first correction value of the first pixel; and

updating one or more current correction pixel values for the one or more neighbor pixels by adding the fraction of the difference to one or more respective previous pixel values for the one or more neighbor pixels.

9. The method of claim 8 , wherein the range is defined by a lower threshold and an upper threshold that are predetermined values.

10. The method of claim 8 , wherein updating the correction table using the motion-based algorithm further comprises:

adding a fraction of the difference to a previous neighbor correction value to update a neighbor correction value; and

subtracting the fraction of the difference from a previous correction value to update a correction value.

11. The method of claim 10 , wherein the fraction of the difference comprises dividing the difference by a denominator, wherein the denominator is a predetermined value.

12. The method of claim 1 , wherein the motion threshold is defined by a plurality of pixel units.

13. A method of correcting an infrared image, the method comprising:

providing a processor;

receiving the infrared image from a camera, the infrared image comprising a plurality of pixels arranged in an input image array, a first pixel in the plurality of pixels having a first pixel value and one or more neighbor pixels with one or more neighbor pixel values, wherein the first pixel and the one or more neighbor pixels are associated with an object in the infrared image, the one or more neighbor pixels being adjacent to the first pixel in the input image array;

processing the infrared image to generate a processed image;

determining, by the processor, whether the processed image is a first frame;

in the event that the processed image is the first frame:

initializing a correction table to an initialized correction table;

initializing a mean image counter to zero;

determining, by the processor, whether the camera is not moving;

in the event that the camera is not moving:

computing a percentage change in a grayscale value of each pixel relative to a corresponding pixel in a mean image;

marking pixels having a percentage change greater than a grayscale threshold as moving pixels; and

counting a number of moving pixels.

14. The method of claim 13 , further comprising:

determining whether the number of moving pixels is greater than a change threshold;

in the event that the number of moving pixels is greater than the change threshold:

initializing the mean image to the processed image;

initializing the mean image counter to zero; and

providing an output image based on the initialized correction table and the processed image.

15. The method of claim 14 , further comprising:

in the event that the number of moving pixels is not greater than the change threshold:

initializing the mean image to a sum of the processed image multiplied by a constant and a fraction of a previous mean image; and

incrementing the mean image counter,

wherein the constant is less than unity, and a sum of the constant and the fraction is equal to unity.

16. The method of claim 15 , further comprising:

determining whether the mean image counter is greater than a count threshold;

in the event that the mean image counter is greater than the count threshold:

updating the correction table using a motionless algorithm; and

providing an output image based on the updated correction table using the motionless algorithm and the processed image.

17. The method of claim 16 , wherein updating the correction table using the motionless algorithm comprises:

for each correction pixel value, determining correction values for the one or more neighbor pixels;

computing a difference between the first pixel value and the one or more neighbor pixel values; and

updating the correction pixel value using the difference.

18. The method of claim 17 , wherein updating the correction table using the motionless algorithm further comprises:

determining whether an absolute value of the difference is within a range;

in the event that the absolute value of the difference is within the range:

updating a current first correction value of the first pixel value by subtracting a fraction of the difference from a previous first correction value of the first pixel; and

updating one or more current correction pixel values for the one or more neighbor pixels by adding the fraction of the difference to one or more respective previous pixel values for the one or more neighbor pixels.

19. The method of claim 17 , wherein updating the correction table using the motionless algorithm further comprises:

adding a fraction of the difference to a previous neighbor correction value to update a neighbor correction value; and

subtracting the fraction of the difference from a previous correction value to update a correction value, wherein the fraction of the difference comprises dividing the difference by a denominator, wherein the denominator is a predetermined value.

20. The method of claim 16 , further comprising:

in the event that the mean image counter is not greater than the count threshold:

providing an output image based on the initialized correction table and the processed image.