A system for estimating a photoplethysmogram waveform of a target includes an image processor configured to obtain images of the target and a waveform analyzer. The waveform analyzer is configured to determine a weight of a portion of the target. The weight is based on a time variation of a light reflectivity of the portion of the target. The time variation of the light reflectivity of the target is based on the images. The waveform analyzer is further configured to estimate a PPG waveform of the target based on the weight of the portion and the time variation of the light reflectivity of the portion.