A method for determining one or more physiological parameters of a subject. The method includes providing a plurality of images of a vessel of the subject in response to illumination of the vessel to light of different wavelengths; converting each of the plurality of images of the vessel into at least two grayscale images, thereby generating a plurality of first grayscale images of a first wavelength range and a plurality of second grayscale images of a second wavelength range, the first wavelength range and the second wavelength range being different from each other; and determining the one or more physiological parameters of the subject based on at least the plurality of first grayscale images and the plurality of second grayscale images.