The invention relates to a spectral photometry method for determining the 
oxygen saturation of the blood in optically accessible blood vessels, by determining the intensity of the reflection of the blood vessels and of their environment that is devoid of vessels, using at least two spectrally diverse images. The aim of the invention is to reduce the stress on the patient during the capture of the spectrally diverse images, achieving at the same time an improved 
signal-to-
noise ratio. In addition, the 
improved method aims to guarantee a clear association of arteries and veins in the images and to deliver more meaningful values for the 
oxygen saturation. To capture the spectrally diverse images, the blood vessels and their environment are simultaneously illuminated by illumination 
radiation of at least one measuring 
wavelength and at least one reference 
wavelength, each measuring and reference 
wavelength being tuned to a respective color channel of a color camera that captures the images, in order to be received by said color channel.