IMAGE PROCESSING APPARATUS AND CONTROL METHOD THEREOF
First Claim
1. An image processing apparatus for executing tone correction of luminance values in an image, comprising:
- a generation unit configured to generate, for the image, a luminance histogram in which frequencies indicating numbers of pixels for respective luminance values are arranged in an order of luminance values from a first side to a second side;
a dividing unit configured to generate a plurality of partial histograms by dividing the luminance histogram at downward convex parts in a frequency distribution of the luminance histogram;
a calculation unit configured to select one of the plurality of partial histograms as a partial histogram of interest, to calculate, as a drop candidate, a difference between a maximum frequency in one partial histogram located on the first side of the partial histogram of interest, and a minimum frequency within a range from a luminance level corresponding to the maximum frequency to a luminance level corresponding to a maximum frequency in the partial histogram of interest, and to determine, as a drop of the partial histogram of interest, a maximum one of the drop candidates calculated for all the partial histograms located on the first side of the partial histogram of interest;
a setting unit configured to set, for the partial histogram of interest, a smaller weight with increasing drop; and
a correction unit configured to execute the tone correction using a luminance histogram obtained by applying weights set by said setting unit respectively to the plurality of partial histograms.
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Abstract
An image processing apparatus generates, for an image, partial histograms by dividing a luminance histogram at downward convex parts of a frequency distribution of the luminance histogram. The image processing apparatus calculates, for a partial histogram selected from the partial histograms, a difference between a maximum frequency in each of all the partial histograms located on the first side of the selected partial histogram, and a minimum frequency within a luminance range from a luminance level of the maximum frequency to that of a maximum frequency in the selected partial histogram as a drop, and sets a maximum one of the drops calculated for the respective partial histograms as a drop. The image processing apparatus sets a weight, which becomes smaller as this drop is larger, for the selected partial histogram, and calculates a weighted average of the luminance histogram, thereby acquiring a luminance value for the tone correction.
12 Citations
16 Claims
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1. An image processing apparatus for executing tone correction of luminance values in an image, comprising:
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a generation unit configured to generate, for the image, a luminance histogram in which frequencies indicating numbers of pixels for respective luminance values are arranged in an order of luminance values from a first side to a second side; a dividing unit configured to generate a plurality of partial histograms by dividing the luminance histogram at downward convex parts in a frequency distribution of the luminance histogram; a calculation unit configured to select one of the plurality of partial histograms as a partial histogram of interest, to calculate, as a drop candidate, a difference between a maximum frequency in one partial histogram located on the first side of the partial histogram of interest, and a minimum frequency within a range from a luminance level corresponding to the maximum frequency to a luminance level corresponding to a maximum frequency in the partial histogram of interest, and to determine, as a drop of the partial histogram of interest, a maximum one of the drop candidates calculated for all the partial histograms located on the first side of the partial histogram of interest; a setting unit configured to set, for the partial histogram of interest, a smaller weight with increasing drop; and a correction unit configured to execute the tone correction using a luminance histogram obtained by applying weights set by said setting unit respectively to the plurality of partial histograms. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An image processing apparatus for executing tone correction of luminance values in an image, comprising:
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a generation unit configured to generate, for the image, a luminance histogram including frequencies indicating numbers of pixels for respective luminance values; a second generation unit configured to generate a second luminance histogram by applying weights according to luminance values to the luminance histogram; a setting unit configured to analyze a histogram shape using the second luminance histogram, and to set weight values for respective mountain-shaped distributions in the second luminance histogram; and an acquisition unit configured to acquire a feature amount for the tone correction by applying the weight values set by said setting unit to one of the luminance histogram and the second luminance histogram. - View Dependent Claims (10, 11, 12)
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13. A method of controlling an image processing apparatus for executing tone correction of luminance values in an image, comprising:
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a generation step of generating, for the image, a luminance histogram in which frequencies indicating numbers of pixels for respective luminance values are arranged in an order of luminance values from a first side to a second side; a dividing step of generating a plurality of partial histograms by dividing the luminance histogram at downward convex parts in a frequency distribution of the luminance histogram; a calculation step of selecting one of the plurality of partial histograms as a partial histogram of interest, calculating, as a drop candidate, a difference between a maximum frequency in one partial histogram located on the first side of the partial histogram of interest, and a minimum frequency within a range from a luminance level corresponding to the maximum frequency to a luminance level corresponding to a maximum frequency in the partial histogram of interest, and determining, as a drop of the partial histogram of interest, a maximum one of the drop candidates calculated for all the partial histograms located on the first side of the partial histogram of interest; a setting step of setting, for the partial histogram of interest, a smaller weight with increasing drop; and a correction step of executing the tone correction using a luminance histogram obtained by applying weights set in the setting step respectively to the plurality of partial histograms. - View Dependent Claims (15)
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14. A method of controlling an image processing apparatus for executing tone correction of luminance values in an image, comprising:
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a first generation step of generating, for the image, a luminance histogram including frequencies indicating numbers of pixels for respective luminance values; a second generation step of generating a second luminance histogram by applying weights according to luminance values to the luminance histogram; a setting step of analyzing a histogram shape using the second luminance histogram, and setting weight values for respective mountain-shaped distributions in the second luminance histogram; and an acquisition step of acquiring a feature amount for the tone correction by applying the weight values set in the setting step to one of the luminance histogram and the second luminance histogram. - View Dependent Claims (16)
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Specification