Methods and Apparatuses for Addressing Chromatic Abberations and Purple Fringing

• US 20090189997A1
• Filed: 01/27/2009
• Published: 07/30/2009
• Est. Priority Date: 01/28/2008
• Status: Active Grant

• Current Assignee: FotoNation Limited (Adeia Inc.)
• Original Assignee: FotoNation Ireland Limited (Adeia Inc.)
• Inventors: Drimbarean, Alexandru, Murray, Larry, Stec, Piotr
• Granted Patent: US 8,339,462 B2
• Time in Patent Office: Days
• US Class Current: 348/222.100
• CPC Class Codes: G06T 5/80 Geometric correction
• CPC Class Codes: H04N 17/002 for television cameras
• CPC Class Codes: H04N 23/81 for suppressing or minimising disturbance in the image signal generation

Abstract

Methods and systems for detecting and correcting chromatic aberration and purple fringing are disclosed. Chromatic aberration can be addressed by separating an image into color planes and then adjusting these to reduce chromatic aberration by using a specific calibration image (calibration chart) as an empirical method to calibrate the image acquisition device. Purple fringing can be corrected by initially addressing color aberration resulting from the lateral chromatic aberration (LCA). The LCA is first removed and then the correction is extended to purple fringing. A discovery is relied upon that the purple fringing is created in the direction of the chromatic aberration and is more pronounced in the direction of the chromatic aberration.

Claims

1. A processor-implemented method of correcting lateral chromatic aberrations in digital images within a digital image acquisition device, comprising:

calibrating a camera-lens pair;

acquiring a digital image;

correcting lateral chromatic aberrations within the digital image, including;

finding a displacement for a current pixel in a temporary buffer;

designating the displacement as a relative position in a source buffer;

interpolating a displacement value;

store interpolated value in the temporary buffer; and

repeat for next one or more pixels and end after last pixel; and

outputting, storing, displaying, projecting, or transmitting a corrected digital image which has been corrected for lateral chromatic aberrations, or a further processed version of the digital image, or combinations thereof.

2. The method of claim 1, wherein the calibrating comprises:

detecting measurement points of a test image;

measuring aberration; and

interpolating scattered data.

3. The method of claim 2, wherein the measuring aberration comprises thresholding.

4. The method of claim 2, wherein the calibrating further comprises:

finding and storing first and second data points in a first dimension;

applying linear interpolation to empty points between the first and second data points;

substituting value of second point to value of first point; and

increment a second dimension and repeat one or more times.

5. The method of claim 1, wherein the interpolating comprising applying a sinc filter.

6. The method of claim 5, wherein the since filter comprises a 5×

5 sinc filter.

10. The method of claim 1, wherein the interpolating comprises selecting a pixel neighborhood and performing the method in a single pass.

7. A processor-implemented method of correcting lateral chromatic aberrations in digital images within a digital image acquisition device, comprising:

acquiring a digital image;

calculating corrected values for red (R) and blue (B) color channels as follows;

R′

=R+(G−

R)×

corR;

B′

=B+(G−

B)×

corB;

where corR and corB are selected correction ratios for the red and blue color channels, respectively; and

outputting, storing, displaying, projecting, or transmitting a corrected digital image which has been corrected for lateral chromatic aberrations, or a further processed version of the digital image, or combinations thereof.

8. The method of claim 7, wherein the selected correction ratios corR and corB comprise:

CorR={CR=0.1×

clamp ([R(x,y)−

RC(x,y)],10)}×

CRB; and

CorB={CB=0.1×

clamp ([B(x,y)−

BC(x,y)],10)}×

CRB;

where clamp (.,.) returns second term when first term exceeds it; and

CRB=1+cos [abs(Rc(x,y)−

Bc(x,y))π

/200, when abs(Rc(x,y)−

Bc(x,y))<

200; and

CRB=0 when abs(Rc(x,y)−

Bc(x,y))<

200.

9. The method of claim 8, further comprising applying color corruption correction when G<

R′ and

R′

<

B′

.

11. A processor-implemented method of correcting lateral chromatic aberrations in digital images within a digital image acquisition device, comprising:

acquiring a digital image;

calculating vertical and horizontal gradients for each color component;

calculating correction ratios based on a dot product between color component gradient and vector formed by a pixel position and image center;

calculating new red R′ and

blue B′

color values using linear interpolation between current red R and blue B values and green G value using respective correction ratios; and

outputting, storing, displaying, projecting, or transmitting a corrected digital

image which has been corrected for lateral chromatic aberrations, or a further processed version of the digital image, or combinations thereof.

12. The method of claim 11, wherein the correction ratios comprise:

Rcorr=(x·

Gradx(R)+y·

Grady(R))/(abs[x2+y2]·

Rnorm; and

Bcorr=(x·

Gradx(B)+y·

Grady(B))/(abs[x2+y2]·

Bnorm;

where

Rnorm=1+absGrad(G)+max(G,R-min(B,G)); and

Bnorm=1+absGrad(G)+max(G,B-min(R,G));

where

absGrad(G) comprises a length of a green gradient vector.

13. The method of claim 12, wherein the new red R′

and blue B′

color values comprise;

R′

=R·

(1-Rcorr)+G·

Rcorr; and

B′

=B·

(1-Bcorr)+G·

Bcorr

14. One or more processor readable media having code embedded therein for programming a processor to perform a method of correcting lateral chromatic aberrations in digital images, wherein the method comprises:

calibrating a camera-lens pair;

acquiring a digital image;

correcting lateral chromatic aberrations within the digital image, including;

finding a displacement for a current pixel in a temporary buffer;

designating the displacement as a relative position in a source buffer;

interpolating a displacement value; and

store interpolated value in the temporary buffer; and

repeat for next one or more pixels and end after last pixel.

15. The one or more processor-readable media of claim 14, wherein the calibrating comprises:

detecting measurement points of a test image;

measuring aberration; and

interpolating scattered data.

16. The one or more processor-readable media of claim 15, wherein the measuring aberration comprises thresholding.

17. The one or more processor-readable media of claim 15, wherein the calibrating further comprises:

finding and storing first and second data points in a first dimension;

applying linear interpolation to empty points between the first and second data points;

substituting value of second point to value of first point; and

increment a second dimension and repeat one or more times.

18. The one or more processor-readable media of claim 14, wherein the interpolating comprising applying a sinc filter.

19. The one or more processor-readable media of claim 18, wherein the since filter comprises a 5×

5 sinc filter.

23. The one or more processor-readable media of claim 14, wherein the interpolating comprises selecting a pixel neighborhood and performing the method in a single pass.

20. One or more processor readable media having code embedded therein for programming a processor to perform a method of correcting lateral chromatic aberrations in digital images, wherein the method comprises calculating corrected values for red (R) and blue (B) color channels as follows:

R′

=R+(G−

R)×

corR;

B′

=B+(G−

B)×

corB;

where corR and corB are selected correction ratios for the red and blue color channels, respectively.

21. The one or more processor-readable media of claim 20, wherein the selected correction ratios corR and corB comprise:

CorR={CR=0.1×

clamp ([R(x,y)−

RC(x,y)],10)}×

CRB; and

CorB={CB=0.1×

clamp ([B(x,y)−

BC(x,y)],10)}×

CRB;

where clamp (.,.) returns second term when first term exceeds it; and

CRB=1+cos [abs(Rc(x,y)−

Bc(x,y))π

/200, when abs(Rc(x,y)−

Bc(x,y))<

200; and

CRB=0 when abs(Rc (x,y)−

Bc(x,y))<

200.

22. The one or more processor-readable media of claim 21, wherein the method further comprises applying color corruption correction when G<

R′ and

R′

<

B′

.

24. One or more processor readable media having code embedded therein for programming a processor to perform a method of correcting lateral chromatic aberrations in digital images, wherein the method comprises:

calculating vertical and horizontal gradients for each color component of at least a portion of a digital image;

calculating correction ratios based on a dot product between color component gradient and vector formed by a pixel position and image center;

calculating new red R′ and

blue B′

color values using linear interpolation between current red R and blue B values and green G value using respective correction ratios.

25. The one or more processor-readable media of claim 24, wherein the correction ratios comprise:

Rcorr=(x·

Gradx(R)+y·

Grady(R))/(abs[x2+y2]·

Rnorm; and

Bcorr=(x·

Gradx(B)+y·

Grady(B))/(abs[x2+y2]·

Bnorm;

where

Rnorm=1+absGrad(G)+max(G,R-min(B,G)); and

Bnorm=1+absGrad(G)+max(G,B-min(R,G));

where

absGrad(G) comprises a length of a green gradient vector.

26. The one or more processor-readable media of claim 25, wherein the new red R′

and blue B′

color values comprise;

R′

=R·

(1Rcorr)+G·

Rcorr; and

B′

=B·

(1-Bcorr)+G·

Bcorr

27. A portable digital image acquisition device comprising a lens, an image sensor, a processor, and one or more processor readable media having code embedded therein for programming the processor to perform a method of correcting lateral chromatic aberrations in digital images, wherein the method comprises:

calibrating a camera-lens pair;

acquiring a digital image;

correcting lateral chromatic aberrations within the digital image, including;

finding a displacement for a current pixel in a temporary buffer;

designating the displacement as a relative position in a source buffer;

interpolating a displacement value;

store interpolated value in the temporary buffer; and

repeat for next one or more pixels and end after last pixel; and

outputting, storing, displaying, projecting, or transmitting a corrected digital image which has been corrected for lateral chromatic aberrations, or a further processed version of the digital image, or combinations thereof.

28. The device of claim 27, wherein the calibrating comprises:

detecting measurement points of a test image;

measuring aberration; and

interpolating scattered data.

29. The device of claim 28, wherein the measuring aberration comprises thresholding.

30. The device of claim 28, wherein the calibrating further comprises:

finding and storing first and second data points in a first dimension;

applying linear interpolation to empty points between the first and second data points;

substituting value of second point to value of first point; and

increment a second dimension and repeat (ii)-(v) one or more times.

31. The device of claim 27, wherein the interpolating comprising applying a sinc filter.

32. The device of claim 31, wherein the since filter comprises a 5×

5 sinc filter.

36. The device of claim 27, wherein the interpolating comprises selecting a pixel neighborhood and performing the method in a single pass.

33. A portable digital image acquisition device comprising a lens, an image sensor, a processor, and one or more processor readable media having code embedded therein for programming the processor to perform a method of correcting lateral chromatic aberrations in digital images, wherein the method comprises calculating corrected values for red (R) and blue (B) color channels as follows:

R′

=R+(G−

R)×

corR;

B′

=B+(G−

B)×

corB;

where corR and corB are selected correction ratios for the red and blue color channels, respectively.

34. The device of claim 33, wherein the selected correction ratios corR and corB comprise:

CorR={CR=0.1×

clamp ([R(x,y)−

RC(x,y)],10)}×

CRB; and

CorB={CB=0.1×

clamp ([B(x,y)−

BC(x,y)],10)}×

CRB;

where clamp (.,.) returns second term when first term exceeds it; and

CRB=1+cos [abs(Rc(x,y)−

Bc(x,y))π

/200, when abs(Rc(x,y)−

Bc(x,y))<

200; and

CRB=0 when abs(Rc(x,y)−

Bc(x,y))<

200.

35. The device of claim 34, wherein the method further comprises applying color corruption correction when G<

R′ and

R′

<

B′

.

37. A portable digital image acquisition device comprising a lens, an image sensor, a processor, and one or more processor readable media having code embedded therein for programming the processor to perform a method of correcting lateral chromatic aberrations in digital images, wherein the method comprises:

acquiring a digital image;

calculating vertical and horizontal gradients for each color component;

calculating correction ratios based on a dot product between color component gradient and vector formed by a pixel position and image center;

calculating new red R′ and

blue B′

color values using linear interpolation between current red R and blue B values and green G value using respective correction ratios.

38. The device of claim 37, wherein the correction ratios comprise:

Rcorr=(x·

Gradx(R)+y·

Grady(R))/(abs[x2+y2]·

Rnorm; and

Bcorr=(x·

Gradx(B)+y·

Grady(B))/(abs[x2+y2]·

Bnorm;

where

Rnorm=1+absGrad(G)+max(G,R-min(B,G)); and

Bnorm=1+absGrad(G)+max(G,B-min(R,G));

where

absGrad(G) comprises a length of a green gradient vector.

39. The device of claim 38, wherein the new red R′

and blue B′

color values comprise;

R′

=R·

(1-Rcorr)+G·

Rcorr; and

B′

=B·

(1-Bcorr)+G·

Bcorr