IMAGE PROCESSING METHOD AND APPARATUS

• US 20090185753A1
• Filed: 05/06/2008
• Published: 07/23/2009
• Est. Priority Date: 01/18/2008
• Status: Active Grant

• Current Assignee: FotoNation Limited (Adeia Inc.)
• Original Assignee: FotoNation Ireland Limited (Adeia Inc.)
• Inventors: Zamfir, Adrian, Florea, Corneliu, Drimbarean, Alexandru, Albu, Felix
• Granted Patent: US 7,995,855 B2
• Time in Patent Office: Days
• US Class Current: 382/260
• CPC Class Codes: G06T 2207/10024 Color image
• CPC Class Codes: G06T 2207/20012 Locally adaptive
• CPC Class Codes: G06T 5/20 using local operators
• CPC Class Codes: G06T 5/94 based on local image properties, e.g. for local contrast enhancement
• CPC Class Codes: H04N 1/56 Processing of colour picture signals H04N1/52 takes precedence
• CPC Class Codes: H04N 1/60 Colour correction or control H04N1/54 takes precedence

Abstract

A method of processing an image includes traversing pixels of an image in a single pass over the image. An inverting function is applied to the pixels. A recursive filter is applied to the inverted pixel values. The filter has parameters which are derived from previously traversed pixel values of the image. A pixel value is combined with a filter parameter for the pixel to provide a processed pixel value for a processed image.

Claims

1. A method of processing an image comprising:

a) traversing multiple pixels of the image in a single pass over the image;

b) applying an inverting function to said pixels;

c) applying a recursive filter to one or more inverted pixel values, said filter having one or more parameters derived from previously traversed pixel values of said image; and

d) combining said one or more pixel values with said one or more parameters to provide processed pixel values for a processed image.

2. A method according to claim 1 wherein said image comprises one or a combination of YCC or RGB format.

3. A method according to claim 2 wherein said image comprises RGB format and wherein said inverting function inverts a combination of one or more color plane values for a pixel.

4. A method according to claim 2 wherein said image comprises YCC format and wherein said inverting function inverts an intensity value for a pixel.

5. A method according to claim 1 wherein said traversing comprises one or a combination of row wise;

column wise;

or traversing an arbitrary path across the image.

6. A method according to claim 3 further comprising:

providing an estimate of the average of the red, green and blue planes from previously traversed pixel values of said image;

providing correction terms for one or more of said planes, said correction terms being dependent on said color channel average estimates;

and

wherein said combining includes multiplying a pixel value with a correction term.

7. A method according to claim 6 wherein said correction terms are limited by respective upper and lower thresholds.

8. A method according to claim 1 wherein said combining comprises one of a linear or a logarithmic combination, or a combination thereof.

9. A method according to claim 8 wherein said combining comprises multiplying said pixel value, a correction term and said filter parameter for said pixel to provide a pixel value for a processed image.

10. A method according to claim 6 wherein said providing an estimate of the average of said red, green and blue channels comprises:

R=β

·

R+(1−

β

)·

G(i,j,1)

G=β

·

G+(1−

β

)·

G(i,j,2)

B=β

·

B+(1−

β

)·

G(i,j,3),

where;

G(i,j,k) is the pixel value for the respective red (R), green (G) or blue (B) color plane; and

β

is a coefficient between 0 and 1.

11. A method according to claim 6 wherein said correction terms γ

_R, γ

_B for each of said red and blue color planes comprise;

12. A method as claimed in claim 11 wherein γ

_R and γ

_B are limited to between 0.95 and 1.05

13. A method according to claim 1 wherein said recursive filter parameters H(i,j) comprise:

H(i,j)=α

H(i,j−

1)+(1−

α

)(ƒ

(G(i,j,k)))

where;

α

is the pole of the filter;

G(i,j,k) is the pixel value for the respective red (R), green (G) or blue (B) color plane, or combinations thereof; and

ƒ

(G(i, j, k)) is said inverting function.

14. A method according to claim 13 wherein α

is between 0.05 and 0.8.

15. A method according to claim 13 wherein said inverting function comprises:

16. A method according to claim 4 wherein said inverting function comprises:

17. A method according to claim 6 wherein combining comprises:

G₁(i,j,1)=G(i,j,1)·

H(i,j)·

γ

_R

G₁(i,j,2)=G(i,j,2)·

H(i,j)

G₁(i,j,3)=G(i,j,3)·

H(i,j)·

γ

_B

where;

γ

_R, γ

_B are said correction terms;

H(i,j) is said filter parameter; and

G(i,j,k) is the pixel value for the respective red (R), green (G) or blue (B) color plane, or combinations thereof.

18. A method according to claim 6 wherein combining comprises:

19. A method according to claim 1 wherein said image is in YCC format and said recursive filter parameters H(i,j) comprise:

H(i,j)=α

H(i,j−

1)+(1−

α

)(ƒ

(Y(i,j)))

where;

α

is the pole of the IIR filter;

Y(i,j) is said pixel intensity value; and

ƒ

(Y(i, j)) is said inverting function.

20. A method according to claim 19 wherein said inverting function comprises:

21. A method according to claim 19 wherein said combining comprises:

Y₁(i,j)=Y(i,j)[1+ε

(i,j)·

(1−

H(i,j))]

where;

H(i,j) is said filter parameter; and

ε

(i, j) is a gain factor.

22. A method according to claim 21 wherein ε

(i,j) is either constant or varies for said image.

23. A method comprising iteratively applying steps a) to d) to one or more successively processed images each of steps b), c) and d) being respectively adapted to improve image luminance or image sharpness or both.

24. An image processing apparatus comprising:

a) one or more optics and a sensor for acquiring a digital image;

b) a processor; and

c) one or more storage media having digital code embodied therein for programming the processor to perform an image processing method comprising;

i)traversing multiple pixels of the image in a single pass over the image;

ii) applying an inverting function to said pixels;

iii) applying a recursive filter to one or more inverted pixel values, said filter having one or more parameters derived from previously traversed pixel values of said image; and

iv) combining said one or more pixel values with said one or more parameters to provide processed pixel values for a processed image.

25. The apparatus of claim 24, wherein said image is in one of YCC or RGB format.

26. The apparatus of claim 25, wherein said images comprise RGB format and wherein said inverting function inverts a combination of one or more color plane values for a pixel.

27. The apparatus of claim 26, further comprising:

providing an estimate of an average of red, green and blue planes from previously traversed pixel values of said image;

providing correction terms for one or more of said planes, said correction terms being dependent on said average;

and

wherein said combining includes multiplying a pixel value with a correction term.

28. The apparatus of claim 27, wherein said correction terms are limited by respective upper and lower thresholds.

29. The apparatus of claim 25, wherein said image comprises YCC format and wherein said inverting function inverts an intensity value for a pixel.

30. The apparatus of claim 24, wherein said combining comprises a linear or a logarithmic combination, or a combination thereof.

31. The apparatus of claim 30, wherein said combining comprises multiplying said pixel value, a correction term and said filter parameter for said pixel to provide a pixel value for a processed image.

32. The apparatus of claim 24, wherein said traversing comprises one or a combination of row wise;

column wise;

or traversing an arbitrary path across the image.