An image processing method converts data dependent on a first illuminating light into data dependent on a second illuminating light by, storing conversion conditions for plural illuminating light sources of different color rendering properties, generating data indicating the proportion of synthesis of the stored conversion conditions of the plural light sources, corresponding to the second illuminating light, generating a first conversion condition from the stored conversion conditions for the plural illuminating light sources according to the data indicating the proportion of synthesis, generating a second conversion condition for color temperature conversion based on color temperature information from the second illuminating light, and converting data dependent on the first illuminating light into data dependent on the second illuminating light using the first and second conversion conditions.