Image processing apparatus, image processing method, and computer-readable medium

• US 8,457,397 B2
• Filed: 12/08/2010
• Issued: 06/04/2013
• Est. Priority Date: 07/16/2010
• Status: Active Grant

• Current Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Original Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Inventors: Sakai, Hiroyuki, Nakagawa, Junichi, Umeda, Kiyoshi
• Primary Examiner(s): COUSO, JOSE L
• Application Number:
  US12/962,889
• Publication Number:
  US 20120013764A1
• Time in Patent Office: 909 Days
• Field of Search: 382162-168, 382/190, 382/254, 382274-275, 358/1.9, 358/3.27, 358/516, 358518-520, 358/523, 348/221.1, 348/223.1
• US Class Current: 382/167
• CPC Class Codes: G06T 5/00 Image enhancement or restoration
• CPC Class Codes: H04N 1/6077 Colour balance, e.g. colour cast correction
• CPC Class Codes: H04N 1/6086 by scene illuminant, i.e. conditions at the time of picture capture, e.g. flash, optical filter used, evening, cloud, daylight, artificial lighting, white point measurement, colour temperature
• CPC Class Codes: H04N 9/643 Hue control means, e.g. flesh tone 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 processing apparatus for applying a color balance correction to input image data, comprises a holding unit which holds information indicating a locus of a change in highlight color when a color temperature for image data is changed on a color space; a highlight color calculation unit which calculates a highlight color from the image data; a distance calculation unit which calculates a distance between the highlight color and the highlight color locus held in the holding unit on the color space; a reliability calculation unit which calculates a reliability for a value of the highlight color calculated by the highlight color calculation unit in accordance with the distance calculated by the distance calculation unit; and a color balance correction unit which applies the color balance correction to the image data using the highlight color and the reliability.

Claims

1. An image processing apparatus for applying a color balance correction to input image data, comprising:

a highlight color calculation unit which calculates a highlight color from image data;

a distance calculation unit which calculates a distance between the highlight color and a highlight color blackbody locus held preliminary on a color space;

a reliability calculation unit which calculates a reliability for a value of the highlight color calculated by said highlight color calculation unit in accordance with the distance calculated by said distance calculation unit; and

a color balance correction unit which applies the color balance correction to the image data using the highlight color and the reliability.

2. The apparatus according to claim 1, wherein the reliability is lower with increasing distance between the highlight color calculated by said highlight color calculation unit and the locus.

3. The apparatus according to claim 1, wherein the reliability is calculated using a nonlinear function.

4. The apparatus according to claim 3, wherein in the nonlinear function, an amount of change of the reliability is changed based on a pre-set threshold with respect to the distance.

5. The apparatus according to claim 3, wherein in the nonlinear function, the reliability calculated based on the distance is changed based on a pre-set curve.

6. The apparatus according to claim 1, wherein said color balance correction unit applies the color balance correction to make the highlight color calculated by said highlight color calculation unit be closer to an origin as the reliability is lower.

7. The apparatus according to claim 1, wherein said color balance correction unit suppresses an amount of change by the color balance correction to respective pixels of the image data as the reliability is lower.

8. The apparatus according to claim 1, wherein said color balance correction unit applies the color balance correction using a 3DLUT.

9. The apparatus according to claim 8, wherein said color balance correction unit suppresses an amount of change by the color balance correction for respective grids of the 3DLUT as the reliability is lower.

10. The apparatus according to claim 1, wherein said color balance correction unit applies the color balance correction based on human visual characteristics.

11. The apparatus according to claim 1, wherein the highlight color calculated by said highlight color calculation unit is calculated by calculating a histogram for a predetermined component.

13. A non-transitory computer-readable medium storing a program for controlling a computer to function as an image processing apparatus according to claim 1.

12. An image processing method, executed by one or more processors, for applying a color balance correction to input image data, the method comprising:

a highlight color calculation step of calculating a highlight color from image data;

a distance calculation step of calculating a distance between the highlight color and a highlight color blackbody locus held preliminarily on a color space;

a reliability calculation step of calculating a reliability for a value of the highlight color calculated in the highlight color calculation step in accordance with the distance calculated in the distance calculation step; and

a color balance correction step of applying the color balance correction to the image data using the highlight color and the reliability.

14. An image processing apparatus comprising:

a highlight color calculation unit which calculates a highlight color from image;

a distance calculation unit which calculates a distance between the highlight color and a highlight color blackbody locus held preliminarily on a color space; and

a correction unit which corrects the highlight color calculated by said highlight color calculation unit in accordance with the distance calculated by said distance calculation unit.

15. The apparatus according to claim 14, further comprising a color balance correction unit which performs color balance correction for the image based on the highlight color corrected by said correction unit.

16. The apparatus according to claim 14, wherein the color space is a space for a color difference component.

17. The apparatus according to claim 14, wherein an amount of correction for the highlight color calculated by said highlight color calculation unit is larger with increasing distance.

18. The apparatus according to claim 14, wherein said correction unit corrects the highlight color calculated by said highlight color calculation unit so as to be closer to an origin on the color space.

19. The apparatus according to claim 14, wherein the highlight color calculation unit calculates the highlight color by calculating a histogram for a predetermined component.

21. A non-transitory computer-readable medium storing a program for controlling a computer to function as an image processing apparatus according to claim 14.

20. An image processing method executed by one or more processors, the method comprising:

a highlight color calculation step of calculating a highlight color from image;

a distance calculation step of calculating a distance between the highlight color and a highlight color blackbody locus held preliminarily on a color space; and

a correction step of correcting the highlight color calculated in the highlight color calculation step in accordance with the distance calculated in the distance calculation step.