Apparatus for converting image signal representing image having gradation
First Claim
1. An image signal conversion apparatus for converting a first image signal obtained by scanning an original image having a gradation into a second image signal to produce a modified gradation, wherein said original image consists of a pixel array which is scanned to obtain a data read region and said first image signal represents respective values of densities of pixels included in said pixel array, said image signal conversion apparatus comprising:
- (a) means for classifying said pixels into a plurality of density ranks in accordance with the respective values of said first image signal and generating a first density histogram representing the number of pixels which belong to the respective density ranks, said first density histogram including at least one peak portion;
(b) means for extracting a peak portion which satisfies a predetermined condition from said at least one peak portion to thereby obtain a detected peak portion;
(c) means for calculating a pixel removal density range in accordance with a density rank value which corresponds to said detected peak portion;
(d) means for extracting pixels whose value of said first image signal belongs to said pixel removal density range from pixels which form said data read region to thereby obtain pixels-to-be-removed;
(e) means for classifying pixels which remain after removal of said pixels-to-be-removed from said pixels which form said data read region into a plurality of density ranks in accordance with the values of said first image signal to thereby generate a second density histogram representing the number of pixels which belong to the respective density ranks;
(f) means for determining a reference point on a gradation conversion coordinate plane in accordance with said second density histogram;
(g) means for determining signal conversion characteristics in accordance with said reference point;
(h) means for setting said signal conversion characteristics in a signal converter; and
(i) means for inputting said first image signal to said signal converter and receiving an output signal from said signal converter as said second image signal, whereby said first image signal is converted into said second image signal.
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Abstract
An apparatus for converting an image signal representing an image having gradation includes a first density histogram generator. The first density histogram generator generates a first density histogram based on a first image signal which is obtained by reading a data read region. Of peak portions formed in the first density histogram, the density rank value of a peak portion which satisfies a predetermined condition is detected. A pixel-to-be-removed detector determines pixels-to-be-removed whose average densities are included in a pixel removal density range which corresponds to the detected peak portion density rank value. A second density histogram is generated from the pixels remaining after the removal of the pixels-to-be-removed. Based on the second density histogram, a cumulative density histogram is generated to thereby find a highlight point and a shadow point through which a gradation curve passes. Then, the gradation curve is established and an image processing part converts the first image signal into a second image signal in accordance with the established gradation curve.
32 Citations
30 Claims
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1. An image signal conversion apparatus for converting a first image signal obtained by scanning an original image having a gradation into a second image signal to produce a modified gradation, wherein said original image consists of a pixel array which is scanned to obtain a data read region and said first image signal represents respective values of densities of pixels included in said pixel array, said image signal conversion apparatus comprising:
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(a) means for classifying said pixels into a plurality of density ranks in accordance with the respective values of said first image signal and generating a first density histogram representing the number of pixels which belong to the respective density ranks, said first density histogram including at least one peak portion; (b) means for extracting a peak portion which satisfies a predetermined condition from said at least one peak portion to thereby obtain a detected peak portion; (c) means for calculating a pixel removal density range in accordance with a density rank value which corresponds to said detected peak portion; (d) means for extracting pixels whose value of said first image signal belongs to said pixel removal density range from pixels which form said data read region to thereby obtain pixels-to-be-removed; (e) means for classifying pixels which remain after removal of said pixels-to-be-removed from said pixels which form said data read region into a plurality of density ranks in accordance with the values of said first image signal to thereby generate a second density histogram representing the number of pixels which belong to the respective density ranks; (f) means for determining a reference point on a gradation conversion coordinate plane in accordance with said second density histogram; (g) means for determining signal conversion characteristics in accordance with said reference point; (h) means for setting said signal conversion characteristics in a signal converter; and (i) means for inputting said first image signal to said signal converter and receiving an output signal from said signal converter as said second image signal, whereby said first image signal is converted into said second image signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. An image signal conversion apparatus for converting a first image signal obtained by scanning an original image having a gradation into a second image signal to produce a modified gradation, wherein said original image consists of a pixel array which is scanned to obtain a data read region, said data read region comprising a subject region and a peripheral region surrounding said subject region, said first image signal represents respective values of densities of pixels included in said pixel array, said image signal conversion apparatus comprising:
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(a) means for classifying said pixels into a plurality of density ranks in accordance with the respective values of said first image signal and generating a first density histogram representing the number of pixels which belong to the respective density ranks, said first density histogram including at least one peak portion; (b) means for extracting a peak portion which satisfies a predetermined first condition which corresponds to said peripheral region from said at least one peak portion to thereby obtain a first removal candidate peak portion; (c) means for classifying pixels which remain after removal of pixels which are included in a pixel distribution surge portion around said first removal candidate peak portion from the pixels which form said data read region into a plurality of density ranks in accordance with the respective values of said first image signal and generating a second density histogram representing the number of pixels which belong to the respective density ranks, said second density histogram including at least one peak portion; (d) means for extracting a peak portion which satisfies a predetermined second condition which corresponds to said peripheral region from said at least one peak portion of said second density histogram to thereby obtain a second removal candidate peak portion; (e) means for comparing the density of said first removal candidate peak portion with the density of said second removal candidate peak portion; (f) means for selecting a removal cancel peak portion from said first and second removal candidate peak portions in accordance with a result of said comparison; (g) means for calculating a pixel removal density range which includes a peak portion which remains after excluding said removal cancel peak portion from said first and said second removal candidate peak portions; (h) means for selecting pixels whose value of said first image signal belongs to said pixel removal density range among the pixels which form said data read region as pixels-to-be-removed; (i) means for classifying pixels which remain after removal of said pixels-to-be-removed from the pixels which form said data read region into a plurality of density ranks in accordance with the values of said first image signal to thereby generate a third density histogram representing the number of pixels which belong to the respective density ranks; (j) means for determining a reference point on a gradation conversion coordinate plane in accordance with said third density histogram; (k) means for determining signal conversion characteristics in accordance with said reference point; (l) means for setting said signal conversion characteristics in a signal converter; and (m) means for inputting said first image signal to said signal converter and receiving an output signal from said signal converter as said second image signal, whereby said first image signal is converted into said second image signal. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28)
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29. An image signal generating and converting apparatus comprising:
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(a) a scanner for scanning an image having a subject region and a peripheral region surrounding the subject region, the scanner scanning the image only once without selectively scanning the subject region and the peripheral region of the image to obtain a data read region, the image having a gradation and including a pixel array formed by a plurality of pixels; (b) an image signal generator for generating a first image signal from said image read region scanned by said scanner, said first image signal representing respective values of densities of said pixel array; (c) an image signal converter for converting said first image signal into a second image signal to produce a modified gradation, said image signal converter comprising; (c-1) a first classifier for classifying said pixels into a plurality of density ranks in accordance with the respective values of said first image signal and generating a first density histogram representing the number of pixels which belong to the respective density ranks, said first density histogram including at least one peak portion; (c-2) a first extractor for extracting a peak portion which satisfies a predetermined condition from said at least one peak portion to thereby obtain a detected peak portion; (c-3) a pixel removal density range calculator for calculating a pixel removal density range in accordance with a density rank value which corresponds to said detected peak portion; (c-4) a second extractor for extracting pixels whose value of said first image signal belongs to said pixel removal density range from pixels which form said data read region to thereby obtain pixels-to-be-removed; (c-5) a second classifier for classifying pixels which remain after removal of said pixels-to-be-removed from said pixels which form said data read region into a plurality of density ranks in accordance with the values of said first image signal to thereby generate a second density histogram representing the number of pixels which belong to the respective density ranks; (c-6) a reference point selector for determining a reference point on a gradation conversion coordinate plane in accordance with said second density histogram; (c-7) a determiner for determining signal conversion characteristics in accordance with said reference point; (c-8) a setter for setting said signal conversion characteristics in a signal converter; (c-9) an image signal input/output device for inputting said first image signal to said converter and receiving an output signal from said signal converter as said second image signal, whereby said first image signal is converted into said second image signal.
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30. An image signal generating and converting apparatus comprising:
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(a) a scanner for scanning an image having a subject region and a peripheral region surrounding the subject region, the scanner scanning the image only once without selectively scanning the subject region and the peripheral region to obtain a data read region, the image having a gradation and including a pixel array formed by a plurality,of pixels; (b) an image signal generator for generating a first image signal from said image read region scanned by said scanner, said first image signal representing respective values of densities of said pixel array; (c) an image signal converter for converting said first image signal into a second image signal to produce a modified gradation, said image signal converter comprising; (c-1) a first classifier for classifying said pixels into a plurality of density ranks in accordance with the respective values of said first image signal and generating a first density histogram representing the number of pixels which belong to the respective density ranks, said first density histogram including at least one peak portion; (c-2) a first extractor for extracting a peak portion which satisfies a predetermined first condition which corresponds to said peripheral region from said at least one peak portion to thereby obtain a first removal candidate peak portion; (c-3) a second classifier for classifying pixels which remain after removal of pixels which are included in a pixel distribution surge portion around said first removal candidate peak portion from the pixels which form said data read region into a plurality of density ranks in accordance with the respective values of said first image signal and generating a second density histogram representing the number of pixels which belong to the respective density ranks, said second density histogram including at least one peak portion; (c-4) a second extractor for extracting a peak portion which satisfies a predetermined second condition which corresponds to said peripheral region from said at least one peak portion of said second density histogram to thereby obtain a second removal candidate peak portion; (c-5) a comparator for comparing the density of said first removal candidate peak portion with the density of said second removal candidate peak portion; (c-6) a first selector for selecting a removal cancel peak portion from said first and second removal candidate peak portions in accordance with a result of said comparison; (c-7) a pixel removal density range calculator for calculating a pixel removal density range which includes a peak portion which remains after excluding said removal cancel peak portion from said first and said second removal candidate peak portions; (c-8) a second selector for selecting pixels whose value of said first image signal belongs to said pixel removal density range among the pixels which form said data read region as pixels-to-be-removed; (c-9) a third classifier for classifying pixels which remain after removal of said pixels-to-be-removed from the pixels which form said data read region into a plurality of density ranks in accordance with the values of said first image signal to thereby generate a third density histogram representing the number of pixels which belong to the respective density ranks; (c-10) a first determiner for determining a reference point on a gradation conversion coordinate plane in accordance with said third density histogram; (c-11) a second determiner for determining signal conversion characteristics in accordance with said reference point; (c-12) a setter for setting said signal conversion characteristics in a signal converter; and (c-13) an image signal input/output device for inputting said first image signal to said signal converter and receiving an output signal from said signal converter as said second image signal, whereby said first image signal is converted into said second image signal.
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Specification