An image processing apparatus for converting input image data into output image data for an image forming apparatus configured to output an image with the use of coloring material, the image processing apparatus comprising: a unit configured to perform a coloring-material usage amount reduction process of converting the input image data into the output image data such that an amount of the coloring material used for color-printing the input image data becomes a target coloring-material usage amount defined based on a monochrome-printing coloring-material usage amount, wherein the target coloring-material usage amount is defined by using as a reference the coloring-material usage amount used when printing images that are converted to monochrome images from color images, wherein the coloring-material usage amount reduction process is performed by selecting a color conversion value to be used for a conversion process of converting RGB values into values including at least CMY values, and wherein the conversion process is performed by using a table including color conversion values associated with the RGB values of the input image data, and the color conversion value to be used for the conversion process is selected from among the color conversion values in the table, the selected color conversion value corresponding to one color among plural colors having a higher degree of brightness than that of input data indicating the input image data and having the same hue as that of the input data indicating the input image data, the amount of the coloring material used for color-printing said one color being less than or equal to the amount of the coloring material used for monochrome-printing corresponding to the input data and also being a maximum amount among the amounts of the coloring materials used for color-printing the plural colors. a unit configured to perform a coloring-material usage amount reduction process of converting the input image data into the output image data such that an amount of the coloring material used for color-printing the input image data becomes a target coloring-material usage amount defined based on a monochrome-printing coloring-material usage amount, wherein the target coloring-material usage amount is defined by using as a reference the coloring-material usage amount used when printing images that are converted to monochrome images from color images, wherein the coloring-material usage amount reduction process is performed by selecting a color conversion value to be used for a conversion process of converting RGB values into values including at least CMY values, and wherein the conversion process is performed by using a table including color conversion values associated with the RGB values of the input image data, and the color conversion value to be used for the conversion process is selected from among the color conversion values in the table, the selected color conversion value corresponding to one color among plural colors having a higher degree of brightness than that of input data indicating the input image data and having the same hue as that of the input data indicating the input image data, the amount of the coloring material used for color-printing said one color being less than or equal to the amount of the coloring material used for monochrome-printing corresponding to the input data and also being a maximum amount among the amounts of the coloring materials used for color-printing the plural colors.