Methods and apparatuses for addressing chromatic aberrations and purple fringing

• US 8,797,418 B2
• Filed: 07/22/2011
• Issued: 08/05/2014
• Est. Priority Date: 01/28/2008
• Status: Expired due to Fees

• Current Assignee: FotoNation Limited (Adeia Inc.)
• Original Assignee: DigitalOptics Corporation Europe Limited (Adeia Inc.)
• Inventors: Stec, Piotr, Murray, Larry, Drimbarean, Alexandru
• Primary Examiner(s): CUTLER, ALBERT H
• Application Number:
  US13/189,477
• Publication Number:
  US 20120057041A1
• Time in Patent Office: 1,110 Days
• Field of Search: 348/187, 348/188
• US Class Current: 348/222.1
• CPC Class Codes: G06T 5/006 Geometric correction correction of chromatic aberrations adapted to be used in an image pickup device containing an electronic image sensor H04N23/10; detecting, correcting, reducing or removing artefacts resulting only from the lens unit, e.g. flare, shading, vignetting or "cos4" H04N25/61
• 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
• CPC Class Codes: H04N 25/611 Correction of chromatic aberration

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:

acquiring a digital image;

calculating vertical and horizontal gradients for each color component of at least a portion of the 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; 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 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.

3. The method of claim 2, wherein the new red R′

and blue B′

color values comprise;

R′

=R·

(1−

Rcorr)+G·

Rcorr; and

B′

=B·

(1−

Bcorr)+G·

Bcorr.

4. One or more non-transitory 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.

5. The one or more non-transitory processor-readable media of claim 4, 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.

6. The one or more non-transitory processor-readable media of claim 5, wherein the new red R′

and blue B′

color values comprise;

R′

=R·

(1−

Rcorr)+G·

Rcorr; and

B′

=B·

(1−

Bcorr)+G·

Bcorr.

7. 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 of at least a portion of the 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.

8. The device of claim 7, 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.

9. The device of claim 8, wherein the new red R′

and blue B′

color values comprise;

R′

=R·

(1−

Rcorr)+G·

Rcorr; and

B′

=B·

(1−

Bcorr)+G·

Bcorr.