1. An image processing method for converting a color signal representing a color in a first color gamut to a color signal representing a color in a color gamut of an image forming apparatus, the image processing method comprising: modifying a shape of the color gamut of the image forming apparatus according to a shape of the first color gamut so as to change the shape of the color gamut of the image forming apparatus to a shape similar to the shape of the first color gamut; and converting a color signal representing a color in the first color gamut to a color signal representing a color in the color gamut of the image forming apparatus.