Method of converting color image into grayscale image and recording medium storing program for performing the same

A non-transitory recording medium in which a program of commands executable by a digital processor performing image color conversion is materially embodied and recording the program readable by the digital processor, the program comprising:

• acquiring a target gradient including features of an input original color image;
• determining a global mapping function for converting the original color image into a grayscale image based on the acquired target gradient;
• and
• converting the original color image into a grayscale image using the determined global mapping function,
• wherein determining the global mapping function for converting the original color image into the grayscale image based on the acquired target gradient includes modeling the global mapping function as g=L+f(H)C, L, C, and H denote luminance, chroma, hue components of a color in a CIE LCH color space, respectively, and f(H) denotes a trigonometric polynomial of H.