IMAGE PROCESSING APPARATUS, IMAGE PROCESSING METHOD, AND COMPUTER-READABLE MEDIUM

• US 20120013763A1
• Filed: 12/08/2010
• Published: 01/19/2012
• Est. Priority Date: 07/16/2010
• Status: Active Grant

• Current Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Original Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Inventors: Umeda, Kiyoshi, Sakai, Hiroyuki, Nakagawa, Junichi
• Granted Patent: US 8,442,315 B2
• Time in Patent Office: Days
• US Class Current: 348/223.1
• 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 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 for applying a color balance correction to input image data, comprising:

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.

2. The apparatus according to claim 1, wherein said first highlight color calculation unit further comprises:

an object detection unit which detects an object included in the image data;

an object color calculation unit which calculates an object color as a color value of the object; and

a first highlight color determination unit which estimates a color temperature of the light source at the time of shooting using a gray color value and the object color in the image data, and determines the first highlight color from a color value of the image data at the estimated color temperature.

3. The apparatus according to claim 1, wherein said second highlight color calculation unit further comprises:

a histogram calculation unit which calculates a histogram by accumulating luminance components of the image data; and

a second highlight color determination unit which determines the second highlight color using a luminance value, an accumulated frequency in the histogram of which exceeds a predetermined value.

4. The apparatus according to claim 1, wherein said third highlight color calculation unit calculates a value of the third highlight color by internally dividing a value of the first highlight color and a value of the second highlight color on the color space using weighting coefficients.

5. The apparatus according to claim 4, wherein the weighting coefficients assume predetermined values.

6. The apparatus according to claim 4, wherein the weighting coefficients are determined according to differences from a reference value in respective processes of said first highlight color calculation unit and said second highlight color calculation unit.

7. The apparatus according to claim 2, wherein said third highlight color calculation unit further comprises:

a highlight color candidate calculation unit which calculates a plurality of highlight color candidates using the first highlight color and the second highlight color;

a candidate correction unit which applies the color balance correction to the object color using each of the plurality of highlight color candidates;

a distance calculation unit which calculates a distance on the color space between each of the object colors after the color balance correction by said candidate correction unit and an ideal object color which is held in advance; and

a third highlight color determination unit which determines, as the third highlight color, a highlight color candidate corresponding to the shortest distance of the distances calculated by said distance calculation unit.

8. The apparatus according to claim 1, wherein the color balance correction by said correction unit is nonlinear processing.

9. The apparatus according to claim 1, wherein the color balance correction by said correction unit uses CIECAM02.

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

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

a first highlight color calculation step of estimating a light source at the time of shooting from pixel values of the image data, converting color values of the image data based on a condition of the estimated light source at the time of shooting, and calculating a first highlight color;

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

a third highlight color calculation step of calculating 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 step of attaining the color balance correction by converting the pixel values of the image data using the third highlight color.