Image processing method and image processing apparatus for making luminance correction
First Claim
1. An image processing method of making luminance correction on the basis of a luminance histogram showing distribution of a luminance level of image data in which an image is expressed by a numerical value, comprising the steps of:
- obtaining a luminance average value in said luminance histogram, a luminance standard deviation indicative of a degree of dispersion of luminance distribution from said luminance average value, and a peak distance value which indicates a longest distance between peaks is calculated in said luminance histogram in the case where plural peaks exist, so that plural distances between respective peaks exist;
comparing a distribution discrimination value which can discriminate whether a distribution deviation of the luminance level exists on a low luminance side or a high luminance side in said luminance histogram or not with the obtained peak distance value, and comparing a halftone presence/absence discrimination value which can discriminate whether the distribution deviation of the luminance levels does not exist in a halftone in said luminance histogram or not with the obtained standard deviation, thereby discriminating whether said image is a backlight image or not on the basis of results of said comparisons; and
comparing each of said luminance average value and said luminance standard deviation by using an exposing state discrimination value which can discriminate the exposing state, thereby discriminating an exposing state of an image other than the backlight image.
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Abstract
An image processing method of making luminance correction on the basis of a luminance histogram showing luminance level distribution of image data expressing an image by a numerical value. A luminance average value, a luminance standard deviation, and a peak distance in the luminance histogram are obtained. A distribution discrimination value which can discriminate whether the luminance level distribution is deviated on the low/high luminance side in the histogram is compared with the peak distance. A halftone presence/absence discrimination value which can discriminate whether the luminance distribution is not deviated in the halftone in the luminance histogram is compared with the standard deviation. A backlight image is discriminated by the comparison results. An exposing state of an image other than a backlight image is discriminated by using an exposing state discrimination value. The proper luminance correction is made in accordance with the exposing state.
37 Citations
17 Claims
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1. An image processing method of making luminance correction on the basis of a luminance histogram showing distribution of a luminance level of image data in which an image is expressed by a numerical value, comprising the steps of:
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obtaining a luminance average value in said luminance histogram, a luminance standard deviation indicative of a degree of dispersion of luminance distribution from said luminance average value, and a peak distance value which indicates a longest distance between peaks is calculated in said luminance histogram in the case where plural peaks exist, so that plural distances between respective peaks exist; comparing a distribution discrimination value which can discriminate whether a distribution deviation of the luminance level exists on a low luminance side or a high luminance side in said luminance histogram or not with the obtained peak distance value, and comparing a halftone presence/absence discrimination value which can discriminate whether the distribution deviation of the luminance levels does not exist in a halftone in said luminance histogram or not with the obtained standard deviation, thereby discriminating whether said image is a backlight image or not on the basis of results of said comparisons; and comparing each of said luminance average value and said luminance standard deviation by using an exposing state discrimination value which can discriminate the exposing state, thereby discriminating an exposing state of an image other than the backlight image. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. An image processing method for discriminating an exposure state of image data on the basis of a luminance histogram which indicates a distribution of luminance level of the image data and is generated from the image data, comprising the steps of:
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calculating a luminance deviation value indicating a distribution state of luminance level from the luminance histogram; detecting one or more peaks from the luminance histogram; calculating a peak distance value which indicates the longest distance between peaks in the case that plural peaks exist so that plural distances between respective peaks exist; and discriminating that the image is a backlight image when the luminance deviation value is greater than or equal to a first predetermined value and the peak distance value is greater than or equal to a second predetermined value.
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15. An image processing apparatus for discriminating an exposure state of image data on the basis of a luminance histogram which indicates a distribution of luminance level of the image data and is generated from the image data, said apparatus comprising:
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a luminance standard deviation unit which calculates a luminance deviation value indicating a distribution state of luminance level from the luminance histogram; a peak distance obtaining unit which detects one or more peaks from the luminance histogram; and an exposure discriminating unit which calculates a peak distance value which indicates the longest distance between peaks in the case that plural peaks exist so that plural distances between respective peaks exist; and
discriminates that the image is a backlight image when the luminance deviation value is greater than or equal to a first predetermined value and the peak distance value is greater than or equal to a second predetermined value. - View Dependent Claims (16, 17)
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Specification