Method for reducing mosquito noise
View Patent ↗A method of reducing mosquito noise in a digital image. As mosquito noise is often most plainly visible in the “background” of an image (e.g., the sky or some other backdrop to objects within an image), the luminance value of the background of the image is first determined. Then, the luminances of the pixels of the image are compared against this “background luminance” to determine which should be considered as part of this background. The luminances of these background pixels are then averaged so as to smooth out the representation of the background, and reduce mosquito noise.
1. A method of reducing mosquito noise in an image having pixels and a representation of a background, comprising:
determining a representative luminance value corresponding to the background, wherein the representative luminance value is a function of a comparison between a luminance value of a selected pixel in the image with a set of adjacent luminance values corresponding to luminance values of pixels that are proximate to the selected pixel;
comparing luminance values of the pixels to the representative luminance value corresponding to the background, so as to determine a set of background pixels; and
assigning to pixels of the set of background pixels average luminance values determined according to luminance values of adjacent pixels.
2. The method of claim 1 wherein determining a representative luminance value corresponding to the background further comprises:
(A) receiving the luminance value of the selected pixel;
(B) determining the adjacent luminance values corresponding to luminance values of pixels that are proximate to the selected pixel;
(C) calculating a difference value according to differences between the luminance value of the selected pixel and the adjacent luminance values;
(D) comparing the difference value to a difference value threshold;
(E) if the difference value exceeds the difference value threshold, incrementing an element of an array of luminance values, the element corresponding to the luminance value of the selected pixel; and
(F) selecting the luminance value corresponding to the numerically largest element of the elements, so as to select the luminance value corresponding to the background.
3. The method of claim 2 further comprising, prior to (F), repeating (A), (B), (C), (D), and (L) for each of the pixels.
4. The method of claim 2 wherein (C) further comprises setting the difference value equal to an average of the differences between the luminance value of the selected pixel and the adjacent luminance values.
5. The method of claim 2 wherein the difference value threshold is about 15.
6. The method of claim 5 wherein the assigning further comprises leaving the luminance value of the selected pixel unchanged when the difference threshold value does not exceed the luminance difference corresponding to the difference between the luminance value of the selected pixel and the representative luminance value corresponding to the background.
7. The method of claim 1 :
wherein the comparing further comprises computing luminance differences between the luminance values of the pixels and the representative luminance value corresponding to the background, and comparing the luminance differences to a first luminance difference threshold; and
wherein the assigning further comprises assigning the average luminance values when the first luminance difference threshold exceeds the luminance differences.
8. The method of claim 7 wherein the first luminance difference threshold is about 10.
9. The method of claim 7 wherein the assigning further comprises:
(A) determining the luminance values of the selected pixel and of the pixels adjacent to the selected pixel;
(B) flagging those pixels of the pixels adjacent to the selected pixel that have luminance values that are different from the luminance value of the selected pixel by an amount less than a second luminance difference threshold; and
(C) setting the luminance value of the selected pixel substantially equal to the average of the luminance values of the flagged pixels.
10. The method of claim 9 wherein the second luminance difference threshold is about 10.
11. A computer readable medium encoded with computer-executable instructions for performing a method for reducing mosquito noise in an image having pixels and a representation of a background, the method comprising:
a first set of instructions for determining a representative luminance value corresponding to the background, wherein the representative luminance value is a function of a comparison between a luminance value of a selected pixel in the image with a set of adjacent luminance values corresponding to luminance values of pixels that are proximate to the selected pixel;
a second set of instructions for comparing representative luminance values of the pixels to the luminance value corresponding to the background, so as to determine a set of background pixels; and
a third set of instructions for assigning to pixels of the set of background pixels average luminance values determined according to luminance values of adjacent pixels.
12. The computer readable medium of claim 11 wherein the first set of instructions further comprises instructions for:
(A) determining the luminance value of the selected pixel;
(B) determining the adjacent luminance values corresponding to luminance values of pixels that are proximate to the selected pixel;
(C) calculating a difference value according to differences between the luminance value of the selected pixel and the adjacent luminance values;
(D) comparing the difference value to a difference value threshold;
(E) if the difference value exceeds the difference value threshold, incrementing an element of an array of luminance values, the element corresponding to the luminance value of the selected pixel; and
(F) selecting the luminance value corresponding to the numerically largest element of the elements, so as to select the luminance value corresponding to the background.
13. The computer readable medium of claim 12 wherein the first set of instructions further comprises, prior to (F), repeating (A), (B), (C), (D), and (E) for each of the pixels.
14. The computer readable medium of claim 12 wherein (C) further comprises instructions for setting the difference value equal to an average of the differences between the luminance value of the selected pixel and the adjacent luminance values.
15. The computer readable medium of claim 12 wherein the difference value threshold is about 15.
16. The computer readable medium of claim 15 wherein the third set of instructions further comprises instructions for leaving the luminance value of the selected pixel unchanged when the difference threshold value does not exceed the luminance difference corresponding to the difference between the luminance value of the selected pixel and the representative luminance value corresponding to the background.
17. The computer readable medium of claim 11 :
wherein the second set of instructions further comprises instructions for computing luminance differences between the luminance values of the pixels and the representative luminance value corresponding to the background, and comparing the luminance differences to a first luminance difference threshold; and
wherein the third set of instructions further comprises instructions for assigning the average luminance values when the first luminance difference threshold exceeds the luminance differences.
18. The computer readable medium of claim 17 wherein the first luminance difference threshold is about 10.
19. The computer readable medium of claim 17 wherein the third set of instructions further comprises instructions for:
(A) determining the luminance values of the selected pixel and of the pixels adjacent to the selected pixel;
(B) flagging those pixels of the pixels adjacent to the selected pixel that have luminance values that are different from the luminance value of the selected pixel by an amount less than a second luminance difference threshold; and
(C) setting the luminance value of the selected pixel substantially equal to the average of the luminance values of the flagged pixels.
20. The computer readable medium of claim 19 wherein the second luminance difference threshold is about 10.