A method and apparatus for processing an image to create a grayscale image are provided. The method includes 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 color space 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, 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. In converting color image into grayscale image and representing the grayscale image, the luminance change amount is set according to a property of each color perceived by humans and added to original luminance value, thereby explicitly discriminating among objects.