Provided are a color to grayscale image conversion method of converting a color image into a grayscale image while maintaining original features of the color image, and a recording medium storing a program for performing the same. When an original color image is input, a target gradient with the features of the input original color image is acquired, and a global mapping function for converting the original color image into a grayscale image is determined based on the acquired target gradient. Thereafter, the original color image is converted into a grayscale image using the determined global mapping function. Therefore, it is possible to quickly convert a color image into a grayscale image, and to acquire a high-quality grayscale image with features of color difference included in the original color image.