Image analysis – Color image processing – Color correction
Reexamination Certificate
2000-11-24
2004-11-23
Tran, Phuoc (Department: 2621)
Image analysis
Color image processing
Color correction
C358S520000
Reexamination Certificate
active
06823083
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for and a method of correcting data representing saturation (color saturation, chromaticness, colorfulness or chroma), an apparatus for and a method of calculating maximum saturation, and an apparatus for and a method of correcting pixel data, and a method of determining a saturation correction curve.
2. Description of the Background Art
A color image read using a color scanner or the like may, in some cases, be insufficient in (color) saturation. In such a color image, correction processing for emphasizing saturation may, in some cases, be performed. In a coordinate system (an L*a*b* coordinate system, an L*u*v* coordinate system, etc.) in a uniform perception color space (uniform perceptual space) which can be handled independently by lightness (luminance), saturation and hue, the saturation is multiplexed by a fixed coefficient (constant value), to perform correction for emphasizing the saturation.
However, saturation which can be expressed is limited. When the (color) saturation (colorfulness) is multiplexed by a uniform fixed coefficient to perform correction for emphasizing the (color) saturation (colorfulness), therefore, data representing the (color) saturation (colorfulness) after the corrected may, in some cases, be saturated. Color compression occurs by the saturation.
SUMMARY OF THE INVENTION
An object of the present invention is to emphasize saturation without causing color compression.
Another object of the present invention is to calculate maximum saturation which can be taken by one pixel.
Still another object of the present invention is to make it possible to change maximum saturation.
A saturation correcting apparatus according to a first aspect of the present invention is characterized by comprising saturation data input means for inputting saturation data relating to an image corresponding to one frame which should be corrected; and correction means for performing, with respect to the saturation data relating to the image corresponding to one frame which has been inputted from the saturation data input means, saturation correction processing based on a correction curve for emphasizing and outputting, when the saturation data relating to one of pixels composing the image corresponding to one frame represents intermediate saturation between maximum saturation and minimum saturation which the saturation data relating to the one pixel can take, the saturation data, while outputting, when the saturation data represents the maximum saturation, the saturation data upon stopping the emphasis processing.
The first aspect of the present invention also provides a method suitable for the above-mentioned apparatus. That is, the method comprises the steps of inputting saturation data relating to an image corresponding to one frame which should be corrected; and performing, with respect to the inputted saturation data relating to the image corresponding to one frame, saturation correction processing based on a correction curve for emphasizing and outputting, when the saturation data relating to one of pixels composing the image corresponding to one frame represents intermediate saturation between maximum saturation and minimum saturation which the saturation data relating to the one pixel can take, the saturation data, while outputting, when the saturation data represents the maximum saturation, the saturation data upon stopping the emphasis processing.
According to the first aspect of the present invention, the saturation data relating to the image corresponding to one frame which should be corrected is inputted. Such correction that the saturation data relating to one of the pixels composing the image corresponding to one frame is emphasized and outputted when it represents the intermediate saturation between the maximum saturation and the minimum saturation which the saturation data relating to the one pixel can take, while being outputted upon stopping the emphasis processing when it represents the maximum saturation is made with respect to the saturation data relating to the image corresponding to one frame.
According to the first aspect of the present invention, when the saturation data relating to the one pixel represents the maximum saturation which the saturation data relating to the one pixel can take, no correction for emphasizing saturation is made. Accordingly, it is possible to prevent the saturation data from being saturated by correction for emphasizing saturation. Consequently, it is possible to prevent color compression from occurring by the saturation emphasis processing. When the saturation data relating to the one pixel represents the intermediate saturation, correction for emphasizing saturation is made. A sharp image is thus obtained.
When the saturation data relating to one of the pixels composing the image corresponding to one frame represents the maximum saturation or the minimum saturation, it may be outputted as it is. When the saturation data represents the maximum saturation, processing for decreasing the saturation may be performed.
The saturation correcting apparatus may further comprise a correction curve producing device for producing the correction curve. The correction curve may be produced in the form of a table and previously stored.
The correction curve may be determined such that the saturation represented by the saturation data after the saturation correction processing is less than the maximum saturation. In the intermediate saturation, it is possible to prevent the saturation data after the correction from being saturated even if the correction for emphasizing saturation is made.
The correction curve can be realized by a circular arc or a polygonal line, for example.
The correction curve can be specifically determined on the basis of the maximum saturation calculated on the basis of luminance data and hue angle data which correspond to the saturation data.
An average of the saturation data relating to the image corresponding to one frame is calculated, to determine the correction curve such that the lower the calculated average is, the higher the degree of correction is, while the higher the calculated average is, the lower the degree of correction is.
The saturation correcting apparatus may further comprise correction value calculation means for calculating a color difference correction value from the characteristics of color difference data relating to the image corresponding to one frame which should be corrected; and subtraction means for subtracting the color difference correction value from the color difference data relating to the image corresponding to one frame which should be corrected. In this case, the correction means will perform the saturation correction processing on the basis of the correction curve with respect to the saturation data corresponding to the color difference data from which the color difference correction value has been subtracted by the subtraction means.
A color based on an imaging light source at the time of imaging may, in some cases, be further overlapped with a subject image (so-called color fogging). In a case where the saturation is emphasized when the color fogging occurs, the color fogging may, in some cases, be further emphasized.
A predetermined color difference correction value is subtracted from the color difference data relating to the image corresponding to one frame which should be corrected. Accordingly, it is possible to prevent the color fogging from being emphasized even if the saturation is corrected.
The saturation correcting apparatus may further comprises range calculation means for respectively finding a first range in which the values of the three primary colors are not more than their maximum values in first luminance of less than the maximum luminance and a second range in which the values of the three primary colors are not less than their minimum values in second luminance of more than the minimum luminance; first saturation calculation means for finding first maximum s
Watanabe Koichi
Yamaguchi Yoshihiro
Birch & Stewart Kolasch & Birch, LLP
Fuji Photo Film Co. , Ltd.
Tran Phuoc
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