Method for correcting luminance gradation in an image pickup apparatus
First Claim
1. A luminance gradation correcting method in an image pickup apparatus having a dynamic range, comprising the steps of:
- detecting pieces of histogram data respectively indicating the number of pixels of a luminance level from an input picture signal produced in the image pickup apparatus, the input picture signal indicating a particular image;
detecting a maximum luminance level from the luminance levels of the pieces of histogram data;
detecting a luminance gradation characteristic of the particular image indicated by the input picture signal from the pieces of histogram data corresponding to the luminance levels;
producing a corrected luminance gradation characteristic of the particular image from the luminance gradation characteristic of the particular image according to the maximum luminance level and the dynamic range of the image pickup apparatus;
correcting the luminance levels of the pieces of histogram data to a plurality of gradation corrected luminance levels according to the corrected luminance gradation characteristic of the particular image to set the gradation corrected luminance levels corresponding to the pieces of histogram data within the dynamic range of the image pickup apparatus; and
producing a luminance gradation corrected picture signal composed of the pieces of histogram data corresponding to the gradation corrected luminance levels to reproduce the particular image, in which each of the pixels has one corresponding gradation corrected luminance level, from the luminance gradation corrected picture signal.
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Abstract
A synthesized picture signal of a dynamic image is produced by combining a long-time picture signal representing a low luminance and a short-time picture signal representing a high luminance, pieces of histogram data corresponding to a plurality of luminance levels are detected from the synthesized picture signal, a sum of values of pieces of histogram data is repeatedly calculated as a summed value of a piece of summed histogram data while the number of pieces of histogram data is increased, and an inclination of a line indicated by a series of summed values is detected as a luminance gradation characteristic. Thereafter, the luminance gradation characteristic is corrected to a corrected luminance gradation characteristic according to a relationship between a maximum luminance level and an upper limit luminance level of a dynamic range, and a luminance gradation corrected signal composed of the pieces of histogram data corresponding to gradation corrected luminance levels is produced according to the corrected luminance gradation characteristic to make a maximum gradation corrected luminance level equal to or lower than the upper limit luminance level. Therefore, a low luminance object and/or a high luminance object can be clearly reproduced within the dynamic range.
47 Citations
14 Claims
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1. A luminance gradation correcting method in an image pickup apparatus having a dynamic range, comprising the steps of:
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detecting pieces of histogram data respectively indicating the number of pixels of a luminance level from an input picture signal produced in the image pickup apparatus, the input picture signal indicating a particular image; detecting a maximum luminance level from the luminance levels of the pieces of histogram data; detecting a luminance gradation characteristic of the particular image indicated by the input picture signal from the pieces of histogram data corresponding to the luminance levels; producing a corrected luminance gradation characteristic of the particular image from the luminance gradation characteristic of the particular image according to the maximum luminance level and the dynamic range of the image pickup apparatus; correcting the luminance levels of the pieces of histogram data to a plurality of gradation corrected luminance levels according to the corrected luminance gradation characteristic of the particular image to set the gradation corrected luminance levels corresponding to the pieces of histogram data within the dynamic range of the image pickup apparatus; and producing a luminance gradation corrected picture signal composed of the pieces of histogram data corresponding to the gradation corrected luminance levels to reproduce the particular image, in which each of the pixels has one corresponding gradation corrected luminance level, from the luminance gradation corrected picture signal. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A gradation correction apparatus comprising:
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an imaging device which has at least double sampling speed; a time-axis converter receiving signals of said imaging device; a synthesizer receiving signals of said time-axis converter and outputting a synthesized image signal; a histogram detector which detects histogram data of said synthesized image signal input from said synthesizer; a maximum luminance level detector which detects a maximum luminance level from said histogram data; a gradation characteristic calculator which calculates a gradation characteristic based on said histogram data; a corrected gradation characteristic calculator which calculates a corrected gradation characteristic according to said maximum luminance level; and a gradation corrector which corrects a gradation of said synthesized image signal according to said corrected gradation characteristic. - View Dependent Claims (8, 9, 10, 11, 12)
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13. A video camera comprising a gradation correction apparatus, said gradation correction apparatus including:
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an image device which has at least double sampling speed; a time-axis converter; a synthesizer outputting a synthesized image signal; a histogram detector which detects histogram data of said synthesized signal input from said synthesizer, said histogram data including a maximum luminance level; a maximum luminance level detector which detects the maximum luminance level from said histogram data; a gradation characteristic calculator which calculates a gradation characteristic based on said histogram data; a corrected gradation characteristic calculator which calculates a corrected gradation characteristic according to said maximum luminance level; and a gradation corrector which corrects a gradation of said synthesized image signal according to said corrected gradation characteristic.
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14. A gradation correction method comprising the steps of:
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generating a long exposed image signal and a short exposed image signal in at least said double sampling speed; converting a time-axis of said long exposed image signal and said short exposed image signal in a same time-axis; synthesizing said long exposed signal and said short exposed signal in a synthesized image signal; detecting histogram data of said synthesized picture signal; detecting a maximum luminance level from said histogram data; calculating a gradation characteristic based on said histogram data; calculating a corrected gradation characteristic according to said maximum luminance level; and correcting a gradation of said synthesized image signal according to said corrected gradation characteristic.
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Specification