PRINCIPAL COMPONENTS ANALYSIS BASED ILLUMINANT ESTIMATION

• US 20110169979A1
• Filed: 09/24/2008
• Published: 07/14/2011
• Est. Priority Date: 09/24/2008
• Status: Active Grant

• Current Assignee: Nikon Corporation
• Original Assignee: Nikon Corporation
• Inventors: Hong, Li
• Granted Patent: US 9,118,880 B2
• Time in Patent Office: Days
• US Class Current: 348/222.1
• 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 providing an estimated illuminant of a scene, the image apparatus comprising:

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

an illuminant database that includes a separate subspace for each of a plurality of possible illuminants, wherein at least one of the subspaces is created from multi-dimensional color information from its respective possible illuminant that is reduced to the subspace using Principal Components Analysis.

2. The image apparatus of claim 1 wherein the multi-dimensional color information is in chromatic space.

3. The image apparatus of claim 1 further comprising a control system that compares the input colors of the input image to the subspace for each of the possible illuminants.

4. The image apparatus of claim 3 wherein the control system computes a separation distance between at least one of the input colors and the subspace for each of the possible illuminants.

5. The image apparatus of claim 3 wherein the control system computes a separation distance between a plurality of the input colors and the subspace for each of the possible illuminants.

6. The image apparatus of claim 5 wherein the separation distance is a root mean square distance.

7. The image apparatus of claim 5 wherein the separation distance is an absolute mean distance.

8. The image apparatus of claim 5 wherein the control system incorporates brightness information of the input colors when computing the separation distance from the input colors and the subspace for each of the possible illuminants.

9. The image apparatus of claim 5 wherein the control system takes a non-uniform summation of the separation distances from the input colors to the subspace.

10. The image apparatus of claim 5 wherein the control system selects the possible illuminant that has the best total consistency error as the estimated illuminant.

11. The image apparatus of claim 10 wherein the control system performs color correction on the input image based on the estimated illuminant.

12. An image apparatus for providing an estimated illuminant of a scene, the image apparatus comprising:

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

an illuminant database that includes a separate subspace for each of a plurality of possible illuminants, wherein each the subspaces is created from multi-dimensional, chromatic color information from its respective possible illuminant that is reduced to the subspace using Principal Components Analysis; and

a control system that compares the input colors of the input image to the subspace for each of the possible illuminants, and the control system computes a separation distance between the input colors and the subspace for each of the possible illuminants.

13. The image apparatus of claim 12 wherein the control system incorporates brightness information of the input colors when computing the separation distance from the input colors and the subspace for each of the possible illuminants.

14. The image apparatus of claim 12 wherein the control system takes a non-uniform summation of the scaled distance from the input colors to the subspace.

15. A method for estimating a possible illuminant of a scene, the method comprising the steps of:

creating an illuminant database that includes a separate subspace for each of a plurality of possible illuminants, wherein at least one of the subspaces is created from multi-dimensional color information from its respective possible illuminant that is reduced to the subspace using Principal Components Analysis.

16. The method of claim 15 wherein the step of creating includes the step of converting the multi-dimensional color information into chromatic space.

17. The method of claim 15 further comprising the steps of captures an input image of the scene, the input image including a plurality of input colors;

and comparing the input colors of the input image to the subspace for each of the possible illuminants with a control system.

18. The method of claim 17 wherein the step of comparing includes the step of computing a separation distance between the input colors and the subspace for each of the possible illuminants.

19. The method of claim 18 wherein the step of computing a separation distance include incorporating brightness information of the input colors when computing the separation distance from the input colors and the subspace for each of the possible illuminants.

20. The method of claim 18 wherein the step of computing a separation distance includes taking a non-uniform summation of the scaled distance from the input colors to the subspace.