An image processing method for forming a color conversion table to convert plural input colors into output colors, the method including the steps of: extracting color values of plural gray scales wherein in input and output characteristic data, a signal value of one color is variable and signal values of other colors are fixed; creating a model with which difference values between input and output color values are outputted by inputting the extracted color values; and estimating the output color values corresponding to the input color values to create the color conversion table to convert plural input colors into output colors, after shifting the color values by adding or subtracting the difference values which are obtained by inputting the color values into the model with respect to every output color values.