1. A printing apparatus that prints an image on a print medium based on image data, the printing apparatus comprising: an image processing memory unit that stores image processing data for adjusting the image data depending on a correspondence among the print medium and a plurality of reference print media; an average spectral intensity memory unit that stores an average spectral intensity at a plurality of wavelengths for each reference print media; a covariance information memory unit that stores covariance information of the spectral intensities of each reference print media; a spectral intensity measurement unit that measures a spectral intensity of the print medium at a plurality of wavelengths based on reflected light from the print medium; a Mahalanobis distance acquisition unit that acquires Mahalanobis distances between the print medium and the reference print media based on the spectral intensities of the print medium, the average spectral intensities of the reference print media, and the covariance information of the reference print media; a determination unit that determines which reference print media most closely matches the print medium based on the Mahalanobis distances; and an image printing unit that adjusts the image data using the image processing data corresponding to the reference print media that most closely matches the print medium and then prints the image on the first print medium based on the adjusted image data.