Image apparatus for principal components analysis based illuminant estimation

• US 9,118,880 B2
• Filed: 09/24/2008
• Issued: 08/25/2015
• Est. Priority Date: 09/24/2008
• Status: Active Grant

• Current Assignee: Nikon Corporation
• Original Assignee: Nikon Corporation
• Inventors: Hong, Li
• Primary Examiner(s): PRABHAKHER, PRITHAM DAVID
• Application Number:
  US13/119,641
• Publication Number:
  US 20110169979A1
• Time in Patent Office: 2,526 Days
• Field of Search: 3482221-238, 382/165
• US Class Current: 1/1
• CPC Class Codes: H04N 23/88 for colour balance, e.g. white-balance circuits or colour temperature control
• CPC Class Codes: H04N 9/73 Colour balance circuits, e.g. white balance circuits or colour temperature control camera processing pipelines for colour balance H04N23/88

Abstract

An image apparatus for providing an estimated illuminant of a scene and subsequently providing an adjusted image of the scene includes a capturing system and an illuminant database. The capturing system captures information for an input image of the scene. The input image is defined by a plurality of input colors. The illuminant database includes a separate subspace of information for a plurality of possible illuminants. The subspaces can be created from multi-dimensional color information from its respective possible illuminant that is computed using Principal Components Analysis. This allows for more accurate illuminant estimation of the scene and the use of Principal Components Analysis to generate the one or more subspaces allows for accurate and relatively easy generation of the subspaces. Additionally, the image apparatus can include a control system that compares the input colors to the subspaces in the illuminant database.

Claims

1. An image apparatus for determining an estimated illuminant of a scene, the image apparatus comprising:

a capturing system including an image sensor that captures an input image of the scene, the input image including a plurality of input colors, including a first input color and a second input color;

a storage system that includes a memory that stores an illuminant database that includes a one-dimensional chromatic subspace for a first illuminant and a one-dimensional chromatic subspace for a second illuminant that is different from the first illuminant; and

a control system including a processor that accesses the illuminant database from the storage system to estimate the estimated illuminant of the scene, wherein the control system (i) compares the first input color to the one-dimensional chromatic subspace for the first illuminant to compute a first, first separation distance that represents how far or close the first input color is to the one-dimensional chromatic subspace for the first illuminant; and

(ii) compares the first input color to the one-dimensional chromatic subspace for the second illuminant to compute a first, second separation distance that represents how far or close the first input color is to the one-dimensional chromatic subspace for the second illuminant.

2. The image apparatus of claim 1 wherein the control system (i) compares the second input color to the one-dimensional chromatic subspace for the first illuminant to compute a second, first separation distance that represents how far or close the second input color is to the one-dimensional chromatic subspace for the first illuminant;

and (ii) compares the second input color to the one-dimensional chromatic subspace for the second illuminant to compute a second, second separation distance that represents how far or close the second input color is to the one-dimensional chromatic subspace for the second illuminant.

3. The image apparatus of claim 2 wherein the control system adds the first separation distances to determine a total consistency matching error for the first illuminant, and adds the second separation distances to determine a total consistency matching error for the second illuminant.

4. The image apparatus of claim 2 wherein the control system takes a non-uniform summation of the first separation distances to determine a total consistency matching error for the first illuminant, and a non-uniform summation of the second separation distances to determine a total consistency matching error for the second illuminant.

5. The image apparatus of claim 2 wherein at least one of the separation distances is a root mean square distance.

6. The image apparatus of claim 2 wherein at least one of the separation distances is an absolute mean distance.

7. The image apparatus of claim 2 wherein the control system utilizes brightness level information of the input colors for scaling the separation distances.

8. The image apparatus of claim 7 wherein the one-dimensional chromatic subspace for the first illuminant is created from two-dimensional color information in chromatic space for the first illuminant that is reduced using Principal Component Analysis, and the one-dimensional chromatic subspace for the second illuminant is created from two-dimensional color information in chromatic space for the second illuminant that is reduced using Principal Component Analysis.

9. An image apparatus for determining an estimated illuminant of a scene, the image apparatus comprising:

a capturing system including an image sensor that captures an input image of the scene, the input image including a plurality of input colors;

a storage system that incldues a memory that stores an illuminant database that includes a one-dimensional chromatic subspace for a first illuminant and a one-dimensional chromatic subspace for a second illuminant that is different from the first illuminant; and

a control system including a processor that accesses the illuminant database from the storage system to estimate the estimated illuminant of the scene, wherein the control system (i) generates a non-redundant list of non-redundant input colors from the plurality of input colors;

(ii) computes a separate, first separation distance for each non-redundant input color that represents how far or close that particular non-redundant input color is to the one-dimensional chromatic subspace for the first illuminant; and

(iii) computes a separate, second separation distance for each non-redundant input color that represents how far or close that particular non-redundant input color is to the one-dimensional chromatic subspace for the second illuminant.

10. The image apparatus of claim 9 wherein the control system adds the first separation distances to determine a total consistency matching error for the first illuminant, and adds the second separation distances to determine a total consistency matching error for the second illuminant.

11. The image apparatus of claim 9 wherein the control system takes a non-uniform summation of the first separation distances to determine a total consistency matching error for the first illuminant, and a non-uniform summation of the second separation distances to determine a total consistency matching error for the second illuminant.

12. The image apparatus of claim 9 wherein the one-dimensional chromatic subspace for the first illuminant is created from two-dimensional color information in chromatic space for the first illuminant that is reduced using Principal Component Analysis, and the one-dimensional chromatic subspace for the second illuminant is created from two-dimensional color information in chromatic space for the second illuminant that is reduced using Principal Component Analysis.

13. A method for determining an estimated illuminant of a scene comprising:

creating an illuminant database comprising (i) providing two-dimensional color information in chromatic space for a first illuminant;

(ii) providing two-dimensional color information in chromatic space for a second illuminant;

(iii) creating the illuminant database using a control system that includes a processor, the control system reducing the two-dimensional color information in chromatic space for the first illuminant to a one-dimensional chromatic subspace for the first illuminant; and

reducing the two-dimensional color information in chromatic space for the second illuminant to a one-dimensional chromatic subspace for the second illuminant; and

transferring the illuminant database to a storage system that includes a memory;

capturing an input image of the scene with an image sensor, the input image including a first input color and a second input color; and

comparing the first input color and the second input color to each of the one-dimensional chromatic subspaces of the illuminant database;

wherein the step of comparing includes (i) comparing the first input color to the one-dimensional chromatic subspace for the first illuminant to compute a first, first separation distance that represents how far or close the first input color is to the one-dimensional chromatic subspace for the first illuminant;

(ii) comparing the first input color to the one-dimensional chromatic subspace for the second illuminant to compute a first, second separation distance that represents how far or close the first input color is to the one-dimensional chromatic subspace for the second illuminant;

(iii) comparing the second input color to the one-dimensional chromatic subspace for the first illuminant to compute a second, first separation distance that represents how far or close the second input color is to the one-dimensional chromatic subspace for the first illuminant; and

(iv) comparing the second input color to the one-dimensional chromatic subspace for the second illuminant to compute a second, second separation distance that represents how far or close the second input color is to the one-dimensional chromatic subspace for the second illuminant.

14. The method of claim 13 wherein the step of creating includes (i) the two-dimensional color information in chromatic space for the first illuminant being reduced using Principal Component Analysis to the one-dimensional chromatic subspace for the first illuminant;

and (ii) the two-dimensional color information in chromatic space for the second illuminant being reduced using Principal Component Analysis to the one-dimensional chromatic subspace for the second illuminant.

15. The method of claim 13 further comprising the steps of adding the first separation distances to determine a total consistency matching error for the first illuminant, and adding the second separation distances to determine a total consistency matching error for the second illuminant.