Method of and apparatus for correcting gradation of image represented by image data
AssigneeDainippon Screen Mfg. Co., Ltd.
InventorsAkihiro Nomura, Yasuo Kurusu
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Abstract
A standard gradation correction curve independent of characteristics of an original image is prepared in advance. An accumulated density historgram curve of the original is obtained from image data of the original. A first gradation correction curve is obtained by modifying the standard gradation correction curve, while a second gradation correction curve is obtained by modifying the accumulated density histogram curve. A third gradation correction curve is obtained by linear combination of the first and second gradation conversion curves to perform gradation correction of the image data on the basis of the third gradation correction curve.
Claims10
A method for correcting the gradation of an image comprising the steps of:
- preparing a standard gradation correction curve expressing an arbitrarily defined gradation correction rule;
- receiving image data obtained by reading an image of an original with a photoelectric scanning mechanism;
- statistically obtaining a density distribution curve of said image on the basis of said image data;
- obtaining a first gradation correction curve on the basis of a said standard gradation correction curve;
- obtaining a second gradation correction curve on the basis of said density distribution curve of said image;
- obtaining a third gradation correction curve by composing said first and second gradation correction curves at an arbitrary ratio;
- and
- correcting said gradation of said image through said third gradation correction curve to obtain a gradation corrected image.
An apparatus for correcting the gradation of an image represented by image data, said apparatus comprising:
- memory means for storing a previously prepared standard gradation correction curve;
- counting means for counting the frequency of occurrences of density levels in said image data thereby to obtain statistical data statistically expressing a density distribution of said image;
- first gradation correction curve generating means for generating a first gradation correction curve on the basis of said standard gradation correction curve;
- second gradation correction curve generating means for generating a second gradation correction curve on the basis of said statistic data;
- composing means for composing said first and second gradation correction curves at an arbitrary ratio to give a third gradation correction curve;
- and
- gradation correction means for correcting the gradation of said image on the basis of said third gradation correction curve to generate a gradation corrected image.
Dependencies are inferred from the claim text.