Methods and apparatuses providing noise reduction while preserving edges for imagers

• US 20080043124A1
• Filed: 09/17/2007
• Published: 02/21/2008
• Est. Priority Date: 12/07/2005
• Status: Abandoned Application

• Current Assignee: Aptina Imaging Corporation (ON Semiconductor Corporation)
• Original Assignee: Micron Technology, Inc.
• Inventors: Subbotin, Igor
• Application Number:
  US11/898,909
• Publication Number:
  US 20080043124A1
• Time in Patent Office: Days
• US Class Current: 348/250
• CPC Class Codes: G06T 2207/10024 Color image
• CPC Class Codes: G06T 5/20 using local operators
• CPC Class Codes: G06T 5/70 Denoising; Smoothing
• CPC Class Codes: H04N 1/409 Edge or detail enhancement; Noise or error suppression

Abstract

Methods and apparatuses of reducing noise in an image by obtaining a first value for a target pixel, obtaining a respective second value for neighboring pixels surrounding the target pixel, for each neighboring pixel, comparing a difference between the first value and the second value to a threshold value and selectively replacing the first value with an average value obtained from the first value and at least a subset of the second values from the neighboring pixels which have an associated difference which is less than the threshold value based on a result of the comparing step. In a further modification, less than all neighboring pixels which have an associated difference which is less than the threshold value are used in the averaging.

Claims

1. A method of processing an image, comprising the steps of:

selecting a set of pixel signals from pixels surrounding an identified target pixel having a target pixel signal;

for each of the surrounding pixel signals of the set, determining a respective difference value between the target pixel signal and the surrounding pixel signal;

for each of the surrounding pixel signals of the set, determining if the respective difference value is less than a predetermined threshold; and

substituting an average value as a value for the target pixel signal, the average value is based on the target pixel signal and at least a selected subset of the pixel signals having a respective difference value less than a predetermined threshold.

2. The method of claim 1, wherein the average value is an average of 2ⁿ pixel signals where n is an integer.

3. The method of claim 1, wherein the target pixel is one of a red, greenred, greenblue, or blue pixel and each of the pixels in the selected set are the same color as the target pixel.

4. The method of claim 1, wherein at least one of the surrounding pixels has been previously denoised.

5. The method of claim 1, wherein the predetermined threshold is based on at least one of an analog and digital gain used in image capture.

6. The method of claim 1, wherein the predetermined threshold is based on the color of the target pixel.

7. A method of processing an image comprising the steps of:

selecting a target pixel having a first signal value;

replacing a first register value with a sum of the first register value and the first signal value;

incrementing a first counter;

selecting a correction kernel having a number of pixels surrounding the target pixel, each of the kernel pixels having a respective second signal value;

grouping the selected kernel pixels into at least one pixel group;

comparing a difference between the first signal value and a one of the respective second signal values to a threshold value;

replacing the first register value with a sum of the first register value and one of the respective second signal values based on a result of the comparing the difference step;

incrementing the first counter based on a result of the comparing the difference step;

comparing a value of the first counter to a set of at least one predetermined number;

replacing a second register value with the first register value based on a result of the comparing the value step;

replacing a value of a second counter with the value of the first counter based on a result of the comparing the value step; and

replacing the first signal value with the result of a division of the second register value by the second counter.

8. The method of claim 7, further comprising repeating the comparing the difference step through replacing the value of the second counter step for each of the respective second signal values.

9. The method of claim 7, further comprising repeating the comparing the difference step through replacing the value of the second counter step for each of the respective second signal values in a first pixel group before repeating the comparing the difference step through replacing the value of the second counter step for each of the respective second signal values in a second pixel group.

10. The method of claim 7, wherein each selected kernel pixel has a respective distance from the target pixel and are grouped based on each kernel pixels'"'"' distance from the target pixel.

11. The method of claim 7, wherein the set of at least one predetermined number is comprised of integer powers of the number two.

12. The method of claim 7, wherein the target pixel is one of a red, green, or blue pixel and each of the selected kernel pixels are the same color as the target pixel.

13. A method of processing an image, comprising the steps of:

selecting a target pixel having a signal value;

selecting a correction kernel associated with the target pixel containing a set of correction kernel pixels each having a respective pixel signal and a respective distance from the target pixel;

for each of the correction kernel pixel signals, determining a respective difference value between the target pixel signal and the correction kernel pixel signal;

for each of the correction kernel pixel signals, determining if the respective difference value is less than a predetermined threshold; and

substituting an average value as a value for the target pixel signal, the average value being an average of 2ⁿ pixel signals where n is an integer, wherein the 2ⁿ signals are comprised of the target pixel signal and at least a subset of the correction kernel pixel signal having a respective difference value less than a predetermined threshold.

14. The method of claim 13, wherein the at least a subset of correction kernel pixel signals is selected based on the correction kernel pixel signals respective distances from the target pixel.

15. An imager comprising:

a pixel array for capturing an image and comprising a plurality of pixels, each pixel outputting a signal representing an amount of light received; and

a circuit for denoising an image captured by the array,

the circuit being configured to;

select from the captured image a target pixel having a signal value;

select a correction kernel associated with the target pixel containing a set of correction kernel pixels each having a respective pixel signal and a respective distance from the target pixel;

for each of the correction kernel pixel signals, determine a respective difference value between the target pixel signal and the correction kernel pixel signal;

for each of the correction kernel pixel signals, determine if the respective difference value is less than a predetermined threshold; and

substitute an average value as a value for the target pixel signal, the average value being an average of 2ⁿ pixel signals where n is an integer, wherein the 2ⁿ signals are comprised of the target pixel signal and at least a subset of the correction kernel pixel signals having a respective difference value less than a predetermined threshold.

16. The imager of claim 15, wherein the at least a subset of correction kernel pixel signals is selected based on the correction kernel pixel signals respective distances from the target pixel.

17. The imager of claim 15, wherein the imager is part of a camera system.

18. An imager comprising:

a pixel array for capturing an image and comprising a plurality of pixels, each pixel outputting a signal representing an amount of light received; and

a processing circuit for denoising an image captured by the array, the processing circuit being configured to;

select from the captured image a set of pixel signals from pixels surrounding an identified target pixel having a target pixel signal;

for each of the surrounding pixel signals of the set, determine a respective difference value between the target pixel signal and the surrounding pixel signal;

for each of the surrounding pixel signals of the set, determine if the respective difference value is less than a predetermined threshold; and

substitute an average value as a value for the target pixel signal, the average value is based on the target pixel signal and at least a selected subset of the pixel signals having a respective difference value less than a predetermined threshold.

19. The imager of claim 18, wherein the average value is an average of 2ⁿ pixel signals where n is an integer.

20. The imager of claim 18, wherein the target pixel and each pixel in the selected set are the same color.

21. The imager of claim 18, wherein at least one of surrounding pixels has been previously denoised.

22. The imager of claim 18, wherein the imager is part of a camera system.

23. A storage medium containing a program for execution by a processor, the processor when executing the program, performs the steps of:

selecting a set of pixel signals from pixels surrounding an identified target pixel having a target pixel signal;

for each of the surrounding pixel signals of the set, determining a respective difference value between the target pixel signal and the surrounding pixel signal;

for each of the surrounding pixel signals of the set, determining if the respective difference value is less than a predetermined threshold; and

substituting an average value as a value for the target pixel signal, the average value is based on the target pixel signal and at least a selected subset of the pixel signals having a respective difference value less than a predetermined threshold.