Image processing with color balance correction

• US 9,406,003 B2
• Filed: 09/22/2014
• Issued: 08/02/2016
• Est. Priority Date: 07/16/2010
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Umeda, Kiyoshi, Sakai, Hiroyuki, Nakagawa, Junichi
• Primary Examiner(s): COUSO, JOSE L
• Application Number:
  US14/493,334
• Publication Number:
  US 20150009513A1
• Time in Patent Office: 680 Days
• US Class Current: 1/1
• CPC Class Codes: G06K 15/1878 Adjusting colours image colour correction or control for documents in general H04N1/60
• CPC Class Codes: G06T 5/40 using histogram techniques
• CPC Class Codes: H04N 23/88 for colour balance, e.g. white-balance circuits or colour temperature control
• 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 first highlight color calculation unit which estimates a light source at the time of shooting from pixel values of the image data, converts color values of the image data based on a condition of the estimated light source at the time of shooting, and calculates a first highlight color; a second highlight color calculation unit which calculates a second highlight color from the image data; a third highlight color calculation unit which calculates a third highlight color based on a positional relationship between the first highlight color and the second highlight color on a color space; and a correction unit which attains the color balance correction by converting the pixel values of the image data using the third highlight color.

Claims

1. An image processing apparatus comprising:

one or more processors;

an extraction unit configured to extract, from a plurality of pixels included in an image, a pixel having a first color and a pixel having a second color different form the first color;

a calculation unit constructed to calculate a highlight color in the image using at least a value of the pixel having the first color and a value of the pixel having the second color extracted by the extraction unit included in the image and a histogram obtained from a luminance component of the image; and

a correction unit constructed to correct a color balance of the image using the highlight color calculated by the calculation unit.

2. The apparatus according to claim 1, wherein the first color is gray color and the second color is skin color.

3. The apparatus according to claim 1, wherein the calculation unit calculates the highlight color based on a highlight luminance value obtained from the histogram.

4. The apparatus according to claim 2, wherein the skin color is a color of a skin color region of a face included in the image.

7. The apparatus according to claim 1, wherein the calculation unit further calculates the highlight color using a locus of the first color which changes, on a color plane, depending on a change of a color temperature and a locus of the second color which changes, on the color plane, depending on a color temperature.

8. The apparatus according to claim 7, wherein the calculation unit calculates the highlight color based on a relationship on the color plane between the locus of the first color and a value which is obtained by processing the pixel having the first color extracted by the extraction unit.

9. The apparatus according to claim 3, further comprising a generation unit configured to generate a histogram in which luminance components of the image are accumulated, and

wherein the highlight luminance value is a luminance value that a frequency ratio accumulated in turn from smaller luminance values of the histogram is a predetermined frequency ratio.

5. An image processing method comprising:

extracting, from a plurality of pixels included in an image, a pixel having a first color and a pixel having a second color different from the first color;

calculating a highlight color in the image using at least a value of the pixel having the first color and a value of the pixel having the second color extracted in the extracting step included in the image and a histogram obtained from a luminance component of the image; and

correcting a color balance of the image using the highlight color calculated in the calculating step.

10. The method according to claim 5, wherein the first color is gray color and the second color is skin color.

11. The method according to claim 5, wherein in the calculating step, the highlight color is calculated based on a highlight luminance value obtained from the histogram.

12. The method according to claim 5, wherein the skin color is a color of a skin color region of a face included in the image.

13. The method according to claim 5, wherein in the calculating step, the highlight color is further calculated using a locus of the first color which changes, on a color plane, depending on a change of a color temperature and a locus of the second color which changes, on the color plane, depending on a color temperature.

14. The method according to claim 13, wherein in the calculating step, the highlight color is calculated based on a relationship on the color plane between the locus of the first color and a value which is obtained by processing the pixel having the first color extracted in the extracting step.

15. The method according to claim 5, further comprising generating a histogram in which luminance components of the image are accumulated, and

wherein the highlight luminance value is a luminance value that a frequency ratio accumulated in turn from smaller luminance values of the histogram is a predetermined frequency ratio.

6. A non-transitory computer-readable medium storing a program for controlling a computer function as:

an extraction unit configured to extract, from a plurality of pixels included in an image, a pixel having a first color and a pixel having a second color different form the first color;

a calculation unit constructed to calculate a highlight color in the image using at least a value of the pixel having the first color and a value of the pixel having the second color extracted by the extraction unit included in the image and a histogram obtained from a luminance component of the image; and

a correction unit constructed to correct a color balance of the image using the highlight color calculated by the calculation unit.