An image processing method includes creating a conversion table for converting a color in a device-independent color space into a color in a device color space based on a colorimetry result of a color patch output by a device. Creating the conversion table includes converting a color in a three-dimensional color space dependent on a device into a color in a four-dimensional device color space including black. Converting a color in the three-dimensional color space includes separating an input color in the three-dimensional device-dependent color space into color components of the four-dimensional device color space based on a gradation from the input color to black, using a black generation curve of a gray line set by a user and black generation curves set for individual primary colors of RGBCMY, and performing saturation-increase conversion on the color components in accordance with an amount of a black colorant.