A novel color-to-grayscale method is presented for converting color images to grayscale images by reducing dimensions. The proposed method converts three-dimensional (3-D) RGB color vectors into one-dimensional (1-D) grayscale values by projecting the 3-D vector into a two-dimensional (2-D) intermediate one followed by compressing the 2-D vector into the 1-D value. Characteristics of color are introduced to facilitate the final determination of the 1-D values in the reducing dimensions. The proposed method has the advantages of preserving chromatic contrasts, maintaining luminance consistency, and having a low computational cost. Furthermore, the proposed method has high resistance to artifacts, such as halos, which can occur when using local contents.