| 摘要 |
PROBLEM TO BE SOLVED: To conduct more natural color area compression or expansion where hue is preserved, chroma and lightness are not greatly changed and loss of gradation or the like is not caused. SOLUTION: The lightness L' of a conversion center point D on the L* axis corresponding to a conversion object point T is expressed as a function of the lightness L and chroma C of the conversion object point T where vectors V directed from the conversion object point T to a conversion center point D do not cross each other at points other than the conversion center point. Concretely, an expression of L'= Lc+α.tanΦis employed for the function, whereΦis the angle of a vector V with respect to the C* axis,αis a positive constant, and Lc is the lightness of the conversion center point atΦ=0. The Lc is decided in advance as the L* value within the color area of an output device. The conversion center point D is uniquely decided so that the vectors V do not cross at points other than the conversion center point D each other by calculating the lightness L' of the conversion center point D. On the basis thereof, the conversion object point T at the outside of the color area of the output device is compressed into a cross point S of the vector V and the color area exterior Go of the output device or confined to the inside of the color area of the output device.
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