IMAGE PROCESSING APPARATUS AND CONTROL METHOD THEREOF

• US 20100329559A1
• Filed: 06/23/2010
• Published: 12/30/2010
• Est. Priority Date: 06/29/2009
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Kanai, Izumi, Shindo, Yuuki, Saito, Tetsuji
• Granted Patent: US 8,649,597 B2
• Time in Patent Office: Days
• US Class Current: 382/172
• CPC Class Codes: G06T 5/40 using histogram techniques
• CPC Class Codes: G06T 5/92 based on global image properties

Abstract

An image processing apparatus according to the present invention, comprises a histogram creation unit creates a histogram from an input image, a detection unit detects a gradation level of interest from the histogram, a gradation correction parameter generation unit generates a gradation correction parameter to improve a gradation characteristic in a gradation range around the gradation level of interest, and a correction unit corrects the gradation of the image using the gradation correction parameter, wherein the detection unit detects, as the gradation level of interest, a gradation level of which frequency is a peak value equal to or more than a predetermined threshold, and which has variation width of frequencies in a predetermined range including this gradation level to be smaller than a predetermined width in the histogram.

Claims

1. An image processing apparatus, comprising:

a histogram creation unit creates a histogram from an input image;

a detection unit detects a gradation level of interest from the histogram;

a gradation correction parameter generation unit generates a gradation correction parameter to improve a gradation characteristic in a gradation range around the gradation level of interest; and

a correction unit corrects the gradation of the image using the gradation correction parameter, wherein

the detection unit detects, as the gradation level of interest, a gradation level of which frequency is a peak value equal to or more than a predetermined threshold, and which has variation width of frequencies in a predetermined range including this gradation level to be smaller than a predetermined width in the histogram.

2. The image processing apparatus according to claim 1, wherein

when a frequency of a gradation level, which is a target to be judged whether the gradation level is a gradation level of interest or not, is lower than a value obtained by multiplying a total of frequencies of a respective n number of gradation levels (n is an integer of 1 or greater) at lower and higher sides of this gradation level, excluding this gradation level, by a predetermined value, the detection unit regards the variation width of the frequencies in the predetermined range is smaller than the predetermined width.

3. The image processing apparatus according to claim 2, further comprising,

a histogram preprocessing unit analyzes a histogram created by the histogram creation unit, rewrites a frequency of a gradation level of a minimum gradation level plus n to a frequency of the minimum gradation level if the frequency of the minimum gradation level is higher than the frequency of the gradation level of the minimum gradation level plus n, and rewrites a frequency of a gradation level of a maximum gradation level minus n to a frequency of the maximum gradation level if the frequency of the maximum gradation level is higher than the frequency of the gradation level of the maximum gradation level minus n.

4. The image processing apparatus according to claim 1, wherein

when a plurality of gradation levels, each of which has frequency being a peak value equal to or more than the predetermined threshold, and has variation width of frequencies in a predetermined range including this gradation level to be smaller than the predetermined width, exist in the histogram, the detection unit detects at least a gradation level in the lowest gradation level side as the gradation level of interest.

5. The image processing apparatus according to claim 1, wherein

when a plurality of gradation level, each of which has frequency being a peak value equal to or more than the predetermined threshold, and has variation width of frequencies in a predetermined range including this gradation level to be smaller than the predetermined width, exist in the histogram, the detection unit detects at least a gradation level in the highest gradation level side as the gradation level of interest.

6. The image processing apparatus according to claim 1, wherein

the histogram creation unit divides the image into a plurality of areas, and creates a histogram for each area,

the detection unit detects a gradation level of interest from the histogram of each of the areas,

the gradation correction parameter generation unit generates, for each of the areas, a gradation correction parameter for improving a gradation characteristic in a gradation range around the gradation level of interest of the each area, and

the correction unit corrects the gradation of the image by combining, for each pixel, a pixel value which is calculated using a gradation correction parameter generated for a first area to which the pixel belongs, and a pixel value which is calculated using a gradation correction parameter generated for a second area adjacent to the first area, using weights based on a positional relationship between the pixel and the first area and a positional relationship between the pixel and the second area, and setting this combined pixel value as a final pixel value of the pixel.

7. The image processing apparatus according to claim 4, wherein

the histogram creation unit divides the image into a plurality of areas, and creates a histogram for each area,

the detection unit detects a gradation level of interest from the histogram of each of the areas, and

the gradation correction parameter generation unit generates, for the image, a gradation correction parameter for improving a gradation characteristic in a gradation range at least around a gradation level of interest in the lowest gradation level side, out of the plurality of gradation levels of interest detected for each of the areas.

8. The image processing apparatus according to claim 5, wherein

the histogram creation unit divides the image into a plurality of areas, and creates a histogram for each area,

the detection unit detects a gradation level of interest from the histogram of each of the areas, and

the gradation correction parameter generation unit generates, for the image, a gradation correction parameter for improving a gradation characteristic in a gradation range at least around a gradation level of interest in the highest gradation level side, out of the plurality of gradation levels of interest detected for each of the areas.

9. The image processing apparatus according to claim 1, further comprising:

a storage unit stores a plurality of predetermined gradation correction parameters; and

a calculation unit calculates a total of frequencies of from a minimum gradation level to a predetermined gradation level of the histogram, as a frequency in a low gradation level side, wherein

when the gradation level of interest is not detected by the detection unit, the gradation correction parameter generation unit selects any of the plurality of gradation correction parameters depending on the frequency in the low gradation level side, and

the correction unit corrects the gradation of the image using the selected gradation correction parameter.

10. The image processing apparatus according to claim 1, further comprising:

a storage unit stores a plurality of predetermined gradation correction parameters; and

a calculation unit calculates a total of frequencies of from a predetermined gradation level to a maximum gradation level of the histogram, as a frequency in a high gradation level side, wherein

when the gradation level of interest is not detected by the detection unit, the gradation correction parameter generation unit selects any of the plurality of gradation correction parameters depending on the frequency in the high gradation level side, and

the correction unit corrects the gradation of the image using the selected gradation correction parameter.

11. A controlling method of an image processing apparatus, comprising the steps of:

creating a histogram from an input image;

detecting a gradation level of interest from the histogram;

generating a gradation correction parameter to improve a gradation characteristic in a gradation range around the gradation level of interest; and

correcting the gradation of the image using the gradation correction parameter, wherein

a gradation level of which frequency is a peak value equal to or more than a predetermined threshold, and which has variation width of frequencies in a predetermined range including this gradation level to be smaller than a predetermined width in the histogram, is detected as the gradation level of interest in the step of detecting.