1. A method of suppressing ambient light interference in a photoplethysmographic (PPG) image signal, the method comprising: imaging a first region of interest on a skin of a subject using a video camera to obtain a PPG image signal, wherein the PPG image signal comprises periodic intensity variations corresponding to ambient light reflected from the region of interest; imaging a first reference region of interest not on the skin using the video camera to obtain a reference signal; spectrally analyzing, via a computer, the reference signal using a first auto-regressive (AR) all pole model to identify poles corresponding to spectral components in the first AR all pole model for the reference signal; and spectrally analyzing, via a computer, the PPG image signal using a second auto-regressive (AR) all pole model to identify poles corresponding to spectral components in the second AR all pole model for the PPG image signal and removing poles in the second AR all pole model corresponding to the spectral components of the reference signal to suppress the ambient light interference; estimating, via the computer, a first vital-sign of the subject based on a remaining portion of the second AT all pole model and after removal of the selected ones of the poles from the second AR all pole model corresponding to the spectral components of the reference signal; and storing, displaying or transmitting, via the computer, the estimated first vital sign.