Computer readable storage medium, image correction apparatus, and image correction method

• US 20110007192A1
• Filed: 09/15/2010
• Published: 01/13/2011
• Est. Priority Date: 03/18/2008
• Status: Active Grant

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Watanabe, Masahiro
• Granted Patent: US 8,471,934 B2
• Time in Patent Office: Days
• US Class Current: 348/243
• CPC Class Codes: G06T 2207/20008 Globally adaptive
• CPC Class Codes: G06T 5/009 Global, i.e. based on properties of the image as a whole applied in cameras using an electronic image sensor H04N23/80, H04N23/70
• CPC Class Codes: G06T 5/92 based on global image properties
• CPC Class Codes: H04N 1/6027 Correction or control of colour gradation or colour contrast H04N1/6058 takes precedence

Abstract

An image correction apparatus includes a dark-pixel-region extracting unit that extracts a dark pixel region of image data photographed by a photographing unit, a dark-pixel-area calculating unit that calculates an area of the dark pixel region extracted by the dark-pixel-region extracting unit, a luminance-value-variance calculating unit that calculates variance of luminance values of pixels in the dark pixel region extracted by the dark-pixel-region extracting unit, and an image correction unit that corrects brightness of the image data in accordance with the area calculated by the dark-pixel-area calculating unit and in accordance with the variance of the luminance values calculated by the luminance-value-variance calculating unit.

Claims

1. A computer readable storage medium having stored therein an image correction program, the image correction program causing a computer to execute a process comprising:

extracting a dark pixel region of image data photographed by a photographing unit;

firstly calculating an area of the dark pixel region extracted in the extracting;

secondly calculating variance of luminance values of pixels in the dark pixel region extracted in the extracting; and

correcting brightness of the image data in accordance with the area calculated in the firstly calculating and in accordance with the variance of the luminance values calculated in the secondly calculating.

2. The computer readable storage medium according to claim 1, wherein the process further comprises

determining whether the area of the dark pixel region calculated in the firstly calculating is greater than a certain area threshold and whether the variance of the luminance values of the pixels calculated in the secondly calculating is greater than a certain variance threshold,

wherein, the correcting includes correcting the brightness of the image data when it is determined in the determining that the area of the dark pixel region is greater than the certain area threshold and the variance of the luminance values of the pixels is greater than the certain variance threshold.

3. The computer readable storage medium according to claim 1, wherein the process further comprises

thirdly calculating, using information on the photographing unit during photographing, an exposure level,

wherein the correcting includes correcting the brightness of the image data in accordance with the area calculated in the firstly calculating, the variance of the luminance values calculated in the secondly calculating, and the exposure level calculated in the thirdly calculating.

4. The computer readable storage medium according to claim 3, wherein

the determining includes determining whether the exposure level calculated in the thirdly calculating is greater than a first certain threshold, and, determining whether the exposure level is greater than a second certain threshold that is greater than the first threshold when it is determined that the exposure level is greater than the first certain threshold, and

the correcting includes correcting, if it is determined that the exposure level is lower than the second certain threshold, the brightness of the image data.

5. The computer readable storage medium according to claim 3, wherein

the correcting includes correcting the brightness of the image data by making the degree of correction greater as the exposure level calculated in the thirdly calculating gets closer to an intermediate level between a minimum exposure level and a maximum exposure level.

6. An image correction apparatus comprising:

a dark-pixel-region extracting unit that extracts a dark pixel region of image data photographed by a photographing unit;

a dark-pixel-area calculating unit that calculates an area of the dark pixel region extracted by the dark-pixel-region extracting unit;

a luminance-value-variance calculating unit that calculates variance of luminance values of pixels in the dark pixel region extracted by the dark-pixel-region extracting unit; and

an image correction unit that corrects brightness of the image data in accordance with the area calculated by the dark-pixel-area calculating unit and in accordance with the variance of the luminance values calculated by the luminance-value-variance calculating unit.

7. The image correction apparatus according to claim 6, further comprising

an image-state determining unit that determines whether the area of the dark pixel region calculated by the dark-pixel-area calculating unit is greater than a certain area threshold and whether the variance of the luminance values of the pixels calculated by the luminance-value-variance calculating unit is greater than a certain variance threshold,

wherein, when the image-state determining unit determines that the area of the dark pixel region is greater than the certain area threshold and the variance of the luminance values of the pixels is greater than the certain variance threshold, the image correction unit corrects the brightness of the image data.

8. The image correction apparatus according to claim 6, further comprising

an exposure-level calculating unit that calculates, using information on the photographing unit during photographing, an exposure level,

wherein the image correction unit corrects the brightness of the image data in accordance with the area calculated by the dark-pixel-area calculating unit, the variance of the luminance values calculated by the luminance-value-variance calculating unit, and the exposure level calculated by the exposure-level calculating unit.

9. The image correction apparatus according to claim 8, wherein

the image-state determining unit determines whether the exposure level calculated by the exposure-level calculating unit is greater than a first certain threshold, and, if the image-state determining unit determines that the exposure level is greater than the first certain threshold, the image-state determining unit determines whether the exposure level is greater than a second certain threshold that is greater than the first threshold, and

the image correction unit corrects, if the image-state determining unit determines that the exposure level is lower than the second certain threshold, the brightness of the image data.

10. The image correction apparatus according to claim 8, wherein the image correction unit corrects the brightness of the image data by making the degree of correction greater as the exposure level calculated by the exposure-level calculating unit gets closer to an intermediate level between a minimum exposure level and a maximum exposure level.

11. An image correction method comprising:

extracting a dark pixel region of image data photographed by a photographing unit;

firstly calculating an area of the dark pixel region extracted in the extracting;

secondly calculating variance of luminance values of pixels in the dark pixel region extracted in the extracting; and

correcting brightness of the image data in accordance with the area calculated in the firstly calculating and in accordance with the variance of the luminance values calculated in the secondly calculating.

12. The image correction method according to claim 11, further comprising

determining whether the area of the dark pixel region calculated in the firstly calculating is greater than a certain area threshold and whether the variance of the luminance values of the pixels calculated in the secondly calculating is greater than a certain variance threshold,

wherein, the correcting includes correcting the brightness of the image data when it is determined in the determining that the area of the dark pixel region is greater than the certain area threshold and the variance of the luminance values of the pixels is greater than the certain variance threshold.

13. The image correction method according to claim 11, further comprising

thirdly calculating, using information on the photographing unit during photographing, an exposure level,

wherein the correcting includes correcting the brightness of the image data in accordance with the area calculated in the firstly calculating, the variance of the luminance values calculated in the secondly calculating, and the exposure level calculated in the thirdly calculating.

14. The image correction method according to claim 13, wherein

the determining includes determining whether the exposure level calculated in the thirdly calculating is greater than a first certain threshold, and, determining whether the exposure level is greater than a second certain threshold that is greater than the first threshold when it is determined that the exposure level is greater than the first certain threshold, and

the correcting includes correcting, if it is determined that the exposure level is lower than the second certain threshold, the brightness of the image data.

15. The image correction method according to claim 13, wherein

the correcting includes correcting the brightness of the image data by making the degree of correction greater as the exposure level calculated in the thirdly calculating gets closer to an intermediate level between a minimum exposure level and a maximum exposure level.