Fixed pattern noise mitigation for a thermal imaging system

Patent metadata

Field	Value
Publication number	US-10867371-B2
Application number	US-201816195593-A
Country	US
Kind code	B2
Filing date	Nov 19, 2018
Priority date	Jun 28, 2016
Publication date	Dec 15, 2020
Grant date	Dec 15, 2020

Abstract

An imaging system whose Field of View FOV experiences occasional motion in relation to viewed scenes may be configured to reduce Fixed Pattern Noise (FPN) of acquired image data. FPN may be reduced by developing a pixel by pixel FPN correction term through a series of steps including blurring the image, identifying pixels to exclude from some calculations, a motion detector and an FPN updater for frames under motion and an FPN decay element for frames that are still.

First claim

What is claimed is:

1. A method for reducing at least one of Row Noise and Column Noise in an imaging system including at least one imaging sensor and associated image signal processing chain, wherein successive frames of image pixel data are generated and passed to the image signal processing chain, wherein the image frame is arranged as a rectilinear array of rows and columns of pixels, the method comprising:
selecting a group of pixels, the group of pixels comprising at least a portion of an image frame;
applying a blurring function to the group of pixels to generate a group of blurred pixels;
applying criteria to at least one of the group of pixels or the group of blurred pixels to exclude pixels meeting the criteria to create at least one active pixel or blurred active pixel map of non-excluded pixels;
creating a row or column offset correction by at least one of:
creating at least one of a row or column mean or median of active pixels and blurred active pixels, and subtracting the row or column mean or median of the blurred active pixels from the row or column mean or median of the active pixels; or
subtracting the active blurred pixels from a row or column from the corresponding active row or column active pixels, and creating at least one of a row or column mean or median of the differences; and

subtracting the row or column offset correction from each pixel in each corresponding row or column in the group of pixels.

2. The method of claim 1 , wherein the blurring comprises:
applying a rolling kernel to the pixels; and
replacing a center pixel of each kernel of the rolling kernel with a pixel value derived from nearest neighbor pixels of the center pixel to create a blurred pixel.

3. The method of claim 2 , wherein creating the blurred pixel comprises calculating at least one of a mean, a median, a scaled mean, or a scaled median of the nearest neighbor pixels.

4. The method of claim 3 , wherein the kernel is a 3×3 kernel and the blurred pixel is the median of the 8 pixels adjacent the center pixel in each kernel.

5. The method of claim 1 , wherein applying the criteria comprises at least one of:
executing an amplitude filter on at least one of the group of pixels or the group of blurred pixels and excluding pixels above a predetermined amplitude; or
executing an edge filter on at least one of the group of pixels or the group of blurred pixels and excluding pixels whose edge filter results exceed a predetermined value.

6. The method of claim 5 , wherein the edge filter comprises at least one of a high-pass filter or a cross filter.

7. The method of claim 6 , wherein the amplitude filter comprises eliminating all pixels having a value greater than 1.2 times the average of at least one of the group of pixels or the group of blurred pixels.

8. The method of claim 1 , wherein any row or column with less than a predetermined number of active pixels is excluded.

9. The method of claim 8 , wherein the predetermined number is 4.

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

11. An imaging system including at least one imaging sensor and associated image signal processing chain, wherein successive frames of image pixel data are generated and passed to the image signal processing chain, wherein the image frame is arranged as a rectilinear array of rows and columns of pixels, configured to:
select a group of pixels, the group of pixels comprising at least a portion of an image frame;
apply a blurring function to the group of pixels to generate a group of blurred pixels;
apply criteria to at least one of the group of pixels or the group of blurred pixels to exclude pixels meeting the criteria to create at least one active pixel or blurred active pixel map of non-excluded pixels;
create a row or column offset correction by at least one of:
creating at least one of a row or column mean or median of active pixels and blurred active pixels, and subtracting the row or column mean or median of the blurred active pixels from the row or column mean or median of the active pixels; or
subtracting the active blurred pixels from a row or column from the corresponding active row or column active pixels, and creating at least one of a row or column mean or median of the differences; and

subtract the row or column offset correction from each pixel in each corresponding row or column in the group of pixels to reduce at least one of Row Noise and Column Noise.

12. The system of claim 11 , further configured to:
apply a rolling kernel to the pixels; and
replace a center pixel of each kernel of the rolling kernel with a pixel value derived from nearest neighbor pixels of the center pixel to create a blurred pixel.

13. The system of claim 12 , further configured to calculate at least one of a mean, a median, a scaled mean, or a scaled median of the nearest neighbor pixels.

14. The system of claim 13 , wherein the kernel is a 3×3 kernel and the blurred pixel is the median of the 8 pixels adjacent the center pixel in each kernel.

15. The system of claim 1 , further configured to at least one of:
execute an amplitude filter on at least one of the group of pixels or the group of blurred pixels and exclude pixels above a predetermined amplitude; or
execute an edge filter on at least one of the group of pixels or the group of blurred pixels and exclude pixels whose edge filter results exceed a predetermined value.

16. The system of claim 15 , wherein the edge filter comprises at least one of a high-pass filter or a cross filter.

17. The system of claim 15 , wherein the amplitude filter comprises eliminating all pixels having a value greater than 1.2 times the average of at least one of the group of pixels or the group of blurred pixels.

18. The system of claim 11 , wherein any row or column with less than a predetermined number of active pixels is excluded.

19. The system of claim 18 , wherein the predetermined number is 4.

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

Assignees

• Seek Thermal Inc

Inventors

• Williams Ross
• Parrish William J
• Wolfe Jason

Classifications

• H04N25/76

  Addressed sensors, e.g. MOS or CMOS sensors · CPC title

• G06T2207/20032

  Median filtering · CPC title

• G06T5/20

  using local operators · CPC title

• G06T2207/10048

  Infrared image · CPC title

• G06T5/10

  using non-spatial domain filtering · CPC title