Adaptive image filter for filtering image information

• US 7,860,334 B2
• Filed: 02/09/2006
• Issued: 12/28/2010
• Est. Priority Date: 02/09/2006
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Li, Hsiang-Tsun, Hung, Szepo Robert
• Primary Examiner(s): Bali; Vikkram
• Assistant Examiner(s): ENTEZARI, MICHELLE M
• Application Number:
  US11/352,483
• Publication Number:
  US 20070183681A1
• Time in Patent Office: 1,783 Days
• Field of Search: 382/260
• US Class Current: 382/261
• CPC Class Codes: H04N 23/12 with one sensor only
• CPC Class Codes: H04N 23/843 Demosaicing, e.g. interpolating colour pixel values
• CPC Class Codes: H04N 25/134 based on three different wavelength filter elements
• CPC Class Codes: H04N 25/683 by defect estimation performed on the scene signal, e.g. real time or on the fly detection

Abstract

This disclosure describes adaptive filtering techniques to improve the quality of captured imagery, such as video or still images. In particular, this disclosure describes adaptive filtering techniques that filter each pixel as a function of a set of surrounding pixels. An adaptive image filter may compare image information associated with a pixel of interest to image information associated with a set of surrounding pixels by, for example, computing differences between the image information associated with the pixel of interest and each of the surrounding pixels of the set. The computed differences can be used in a variety of ways to filter image information of the pixel of interest. In some embodiments, for example, the adaptive image filter may include both a low pass component and high pass component that adjust as a function of the computed differences.

Claims

1. A method comprising:

computing differences between image information associated with a pixel of interest and image information associated with pixels that surround the pixel of interest by adaptive image filter logic implemented at an electronic device;

determining a low pass component and a high pass component of a filter with respect to the pixel of interest based on the differences computed by the adaptive image filter logic; and

applying the filter to the image information associated with the pixel of interest by filtering the image information according to the equation;

2. The method of claim 1, wherein determining the low pass component of the filter comprises:

comparing each of the computed differences to the low pass threshold;

summing the computed differences that are less than the low pass threshold to obtain a low pass component value; and

determining the low pass component based on the low pass component value.

3. The method of claim 1, wherein determining the high pass component of the filter comprises:

comparing each of the computed differences to the high pass threshold; and

summing the computed differences that are greater than the high pass threshold to obtain a high pass component value; and

determining the high pass component based on the high pass component value.

4. The method of claim 1, further comprising:

buffering image information associated with the pixel of interest and the pixels that surround the pixel of interest; and

correcting image information associated with one or more defective pixels using the buffered image information, wherein computing the differences between image information associated with the pixel of interest and image information associated with each of the pixels that surround the pixel of interest comprises computing the differences using the buffered image information.

5. The method of claim 1, wherein computing differences between image information associated with the pixel of interest and image information associated with each of the pixels that surround the pixel of interest comprises computing differences in an intensity value associated with the pixel of interest and intensity values associated with the pixels that surround the pixel of interest.

6. The method of claim 1, wherein the image information associated with the pixels that surround the pixel of interest represents only a single color.

7. The method of claim 1, wherein identifying the pixels that surround the pixel of interest comprises identifying an n by n array of pixels that surround the pixel of interest.

22. The method of claim 1, wherein applying the filter to the image information associated with the pixel of interest reduces noise and enhaces an image concurrently.

23. The method of claim 1, wherein applying the filter to the image information associated with the pixel of interest comprises modifying a value associated with the pixel of interest by adding the low pass component to the value associated with the pixel of interest and subtracting the high pass component from the value associated with the pixel of interest, wherein the low pass component includes a first scaled sum of computed differences that are less than the low pass threshold and wherein the high pass component includes a second scaled sum of computed differences that are greater than the high pass threshold.

8. A device comprising:

an image sensor array that captures image information, wherein the image sensor array includes a plurality of image sensors that capture image information associated with a plurality of pixels; and

an adaptive image filter that computes differences between image information associated with a pixel of interest and image information associated with pixels that surround the pixel of interest, determines a low pass component and a high pass component of a filter based on the computed differences, and applies the filter to the image information associated with the pixel of interest according to the equation;

9. The device of claim 8, wherein the adaptive image filter compares each of the computed differences to the low pass threshold, sums the computed differences that are less than the low pass threshold to obtain a low pass component value, and determines the low pass component based on the low pass component value.

10. The device of claim 8, wherein the adaptive image filter compares each of the computed differences to the high pass threshold, sums the computed differences that are greater than the high pass threshold to obtain a high pass component value, and determines the high pass component based on the high pass component value.

11. The device of claim 8, further comprising a defective pixel correction unit that buffers image information associated with the pixel of interest and the pixels that surround the pixel of interest, and corrects image information associated with one or more defective pixels using the buffered image information, wherein the adaptive image filter computes the differences using the buffered image information.

12. The device of claim 8, wherein the adaptive image filter computes differences in an intensity value associated with the pixel of interest and intensity values associated with the pixels that surround the pixel of interest.

13. The device of claim 8, wherein the image information associated with the pixels that surround the pixel of interest is in one of the RGB domain and the YCbCr domain.

14. The device of claim 8, wherein the adaptive image filter identifies pixels that utilize a same color filter as the pixels that surround the pixel of interest.

24. The device of claim 8, wherein the adaptive image filter is a single filter that determines the high pass component, determines the low pass component, and applies the high pass component concurrently with applying the low pass component to adjust a value associated with the pixel of interest.

25. The device of claim 8, wherein the low pass component is determined by applying a first scaling factor to a first sum of computed differences that are less than the low pass threshold and wherein the high pass component is determined by applying a second scaling factor to a second sum of computed differences that are greater than the high pass threshold.

15. A computer-readable medium comprising instructions to cause a processor to:

compute differences between image information associated with a pixel of interest and image information associated with pixels that surround the pixel of interest;

determine a low pass component and a high pass component of a filter based on the computed differences; and

apply the filter to the image information associated with the pixel of interest according to the equation;

16. The computer-readable medium of claim 15, wherein the instructions to cause the processor to determine the low pass component of the filter further comprise instructions to cause the processor to:

compare each of the computed differences to the low pass threshold;

sum the computed differences that are less than the low pass threshold to obtain a low pass component value; and

determine the low pass component based on the low pass component value.

17. The computer-readable medium of claim 16, wherein the instructions to cause the processor to determine a high pass component of the filter further comprise instructions to cause the processor to:

compare each of the computed differences to the high pass threshold;

sum the computed differences that are greater than the high pass threshold to obtain a high pass component value; and

determine the high pass component based on the high pass component value.

18. The computer-readable medium of claim 15, wherein the instructions cause the processor to:

buffer image information associated with the pixel of interest and the pixels that surround the pixel of interest; and

correct image information associated with one or more defective pixels using the buffered image information, wherein computing the differences between image information associated with the pixel of interest and image information associated with the pixels that surround the pixel of interest comprises computing the differences using the buffered image information.

19. The computer-readable medium of claim 15, wherein the image information associated with the pixels that surround the pixel of interest is in one of the RGB domain and the YCbCr domain.

20. The computer-readable medium of claim 15, wherein the instructions cause the processor to identify an n by n array of pixels that surround the pixel of interest.

21. The computer-readable medium of claim 15, wherein the pixels that surround the pixel of interest utilize a same color filter.

26. The computer-readable medium of claim 15, wherein the instructions to determine the low pass component and the high pass component include instructions to cause the processor to:

perform a first programmable bit shift operation to a first sum of computed differences that are less than the low pass threshold; and

perform a second programmable bit shift operation to a second sum of computed differences that are greater than the high pass threshold.

27. The computer-readable medium of claim 15, wherein the instructions to apply the filter to the image information associated with the pixel of interest include instructions to apply the high pass component to an intensity value of the pixel of interest concurrently with applying the low pass component to the intensity value of the pixel of interest.

28. A method comprising:

at an electronic device;

computing differences between image information associated with a pixel of interest and image information associated with pixels that surround the pixel of interest;

determining a low pass component and a high pass component of a filter as a function of the computed differences; and

applying the filter to the image information associated with the pixel of interest, wherein applying the filter to the image information associated with the pixel of interest comprises filtering the image information according to the equation;

29. The method of claim 28, wherein the low pass component and the high pass component are determined by a hardware processor of the electronic device.

30. The method of claim 28, wherein the electronic device further comprises an image sensor array, and wherein the pixel of interest corresponds to an image sensor of the image sensor array.

31. A device comprising:

an adaptive image filter that computes differences between image information associated with a pixel of interest and image information associated with pixels that surround the pixel of interest, determines a low pass component and a high pass component of a filter as a function of the computed differences, and applies the filter to the image information associated with the pixel of interest according to the equation;

32. The device of claim 31, further comprising:

an image sensor array configured to capture image information, wherein the image sensor array includes a plurality of image sensors to capture image information associated with a plurality of pixels.

33. The device of claim 31, wherein the adaptive image filter includes:

an adder having a first input coupled to receive the low pass component, an inverting input coupled to receive the high pass component, and a third input coupled to receive the value of the unfiltered image information, wherein the adder is configured to output the value of the filtered image information.