1. A method of processing an image to create a grayscale image, the method comprising: converting, in a color image consisting of a plurality of pixels, a pixel value of each pixel in a RGB color space into a pixel value in a new color space through linear conversion; extracting color information using the pixel value in the new color space; calculating a luminance change amount of each pixel using the extracted color information; and calculating a luminance value for the grayscale image by combining an original luminance value of each pixel and the luminance change amount, and creating the grayscale image according to the calculated luminance value.