Pixel-wise noise reduction in thermal images
View Patent ↗Methods and systems are provided to reduce noise in thermal images. In one example, a method includes receiving an image frame comprising a plurality of pixels arranged in a plurality of rows and columns. The pixels comprise thermal image data associated with a scene and noise introduced by an infrared imaging device. The image frame may be processed to determine a plurality of column correction terms, each associated with a corresponding one of the columns and determined based on relative relationships between the pixels of the corresponding column and the pixels of a neighborhood of columns. In another example, the image frame may be processed to determine a plurality of non-uniformity correction terms, each associated with a corresponding one of the pixels and determined based on relative relationships between the corresponding one of the pixels and associated neighborhood pixels within a selected distance.
1. A method comprising:
receiving an image frame comprising a plurality of pixels arranged in a plurality of rows and columns, wherein the pixels comprise thermal image data associated with a scene and noise introduced by an infrared imaging device; and
processing the image frame to determine a plurality of non-uniformity correction (NUC) terms to reduce at least a portion of the noise, wherein each NUC term is associated with a corresponding one of the pixels and is determined based on relative relationships between the corresponding one of the pixels and associated neighborhood pixels within a selected distance from the corresponding one of the pixels, wherein the processing comprises:
for each pixel of the image frame, comparing the pixel to each of its associated neighborhood pixels,
for each comparison, adjusting a first counter if the pixel has a value greater than the compared neighborhood pixel,
for each comparison, adjusting a second counter if the pixel has a value less than the compared neighborhood pixel, and
selectively updating the NUC term associated with the pixel based on the first and second counters.
2. The method of claim 1 , further comprising, for each comparison, adjusting a third counter if the pixel has a value equal to the compared neighborhood pixel, wherein the updating is also based on the third counter.
3. A method comprising:
receiving an image frame comprising a plurality of pixels arranged in a plurality of rows and columns, wherein the pixels comprise thermal image data associated with a scene and noise introduced by an infrared imaging device; and
processing the image frame to determine a plurality of non-uniformity correction (NUC) terms to reduce at least a portion of the noise, wherein each NUC term is associated with a corresponding one of the pixels and is determined based on relative relationships between the corresponding one of the pixels and associated neighborhood pixels within a selected distance from the corresponding one of the pixels, wherein the processing comprises:
for each pixel of the image frame, comparing the pixel to each of its associated neighborhood pixels,
for each comparison, adjusting a counter in a first manner if the pixel has a value greater than the compared neighborhood pixel or a second manner if the pixel has a value less than the compared neighborhood pixel, and
selectively updating the NUC term associated with the pixel based on the counter.
4. The method of claim 1 , wherein the associated neighborhood pixels comprise at least one pixel in a different column and a different row than the corresponding one of the pixels.
5. The method of claim 1 , wherein the distance is a first distance, wherein the portion of the noise is a first portion, the method further comprising repeating the processing using a second distance to update the NUC terms to reduce at least a second portion of the noise.
6. The method of claim 1 , wherein the noise comprises spatially uncorrelated fixed pattern noise (FPN) and spatially correlated FPN.
7. The method of claim 1 , further comprising applying the NUC terms to the image frame to remove the portion of the noise.
8. The method of claim 1 , further comprising temporally damping the NUC terms.
9. The method of claim 1 , further comprising weighting the NUC terms based on gradients between the pixels.
10. The method of claim 1 , further comprising:
processing the image frame to determine a plurality of spatially correlated fixed pattern noise (FPN) terms to reduce a portion of the noise comprising spatially correlated FPN associated with rows or columns of infrared sensors of the infrared imaging device; and
applying the spatially correlated FPN terms to the image frame before the NUC terms are determined.
11. The method of claim 1 , wherein the image frame is an intentionally blurred image frame, wherein the thermal image data is blurred thermal image data.
12. A system comprising:
a memory component adapted to receive an image frame comprising a plurality of pixels arranged in a plurality of rows and columns, wherein the pixels comprise thermal image data associated with a scene and noise introduced by an infrared imaging device; and
a processor adapted to execute instructions to process the image frame to determine a plurality of non-uniformity correction (NUC) terms to reduce at least a portion of the noise, wherein each NUC term is associated with a corresponding one of the pixels and is determined based on relative relationships between the corresponding one of the pixels and associated neighborhood pixels within a selected distance from the corresponding one of the pixels, wherein the instructions to process the image frame are adapted to cause the processor to:
for each pixel of the image frame, compare the pixel to each of its associated neighborhood pixels,
for each comparison, adjust a first counter if the pixel has a value greater than the compared neighborhood pixel,
for each comparison, adjust a second counter if the pixel has a value less than the compared neighborhood pixel, and
selectively update the NUC term associated with the pixel based on the first and second counters.
13. The system of claim 12 , wherein:
the processor is adapted to execute instructions to, for each comparison, adjust a third counter if the pixel has a value equal to the compared neighborhood pixel; and
the instructions to update the NUC term are adapted to cause the processor to selectively update the NUC term also based on the third counter.
14. A system comprising:
a memory component adapted to receive an image frame comprising a plurality of pixels arranged in a plurality of rows and columns, wherein the pixels comprise thermal image data associated with a scene and noise introduced by an infrared imaging device; and
a processor adapted to execute instructions to process the image frame to determine a plurality of non-uniformity correction (NUC) terms to reduce at least a portion of the noise, wherein each NUC term is associated with a corresponding one of the pixels and is determined based on relative relationships between the corresponding one of the pixels and associated neighborhood pixels within a selected distance from the corresponding one of the pixels, wherein the instructions to process the image frame are adapted to cause the processor to:
for each pixel of the image frame, compare the pixel to each of its associated neighborhood pixels,
for each comparison, adjust a counter in a first manner if the pixel has a value greater than the compared neighborhood pixel or a second manner if the pixel has a value less than the compared neighborhood pixel, and
selectively update the NUC term associated with the pixel based on the counter.
15. The system of claim 12 , wherein the associated neighborhood pixels comprise at least one pixel in a different column and a different row than the corresponding one of the pixels.
16. The system of claim 12 , wherein the distance is a first distance, wherein the portion of the noise is a first portion, wherein the processor is adapted to execute instructions to repeat the process using a second distance to update the NUC terms to reduce at least a second portion of the noise.
17. The system of claim 12 , wherein the noise comprises spatially uncorrelated fixed pattern noise (FPN) and spatially correlated FPN.
18. The system of claim 12 , wherein the processor is adapted to execute instructions to apply the NUC terms to the image frame to remove the portion of the noise.
19. The system of claim 12 , wherein the processor is adapted to execute instructions to temporally damp the NUC terms.
20. The system of claim 12 , wherein the processor is adapted to execute instructions to weight the NUC terms based on gradients between the pixels.
21. The system of claim 12 , wherein the processor is adapted to execute instructions to:
process the image frame to determine a plurality of spatially correlated fixed pattern noise (FPN) terms to reduce a portion of the noise comprising spatially correlated FPN associated with rows or columns of infrared sensors of the infrared imaging device; and
apply the spatially correlated FPN terms to the image frame before the NUC terms are determined.
22. The system of claim 12 , wherein the image frame is an intentionally blurred image frame, wherein the thermal image data is blurred thermal image data.
23. The system of claim 12 , further comprising a focal plane array (FPA) adapted to provide the image frame, wherein the FPA comprises an array of microbolometers adapted to receive a bias voltage selected from a range of approximately 0.2 to approximately 0.7 volts.