1. A colorimetric value calculating method for calculating a colorimetric value of a printed object including an image formed on a light-transmissive medium in an observational environment in which both a transmissive light source and a reflective light source coexist, comprising: a first acquisition step for acquiring a spectral transmittance of the printed object and a spectral reflectance of the printed object; a second acquisition step for acquiring a spectral distribution of the transmissive light source and a spectral distribution of the reflective light source; and a calculating step for calculating the colorimetric value of the printed object in the observational environment, using the obtained spectral transmittance of the printed object, the obtained spectral reflectance of the printed object, the obtained spectral distribution of the transmissive light source, and the obtained spectral distribution of the reflective light source.