With significant achievements and improvements in imaging hardware and software, the past decade has witnessed a rapid growth in the literature pertaining to imaging PPG techniques. The use of an imaging sensor in a PPG system provides additional functionality with respect to a single diffuse sensor, particularly motion compensation and region of interest selection, both of which enable a robust and flexible noncontact PPG system. For instance, Wieringa and colleagues have introduced a complementary metal oxide semiconductor (CMOS) camera-based multiple wavelength imaging PPG device that provides a potential route toward contactless assessment of blood oxygen saturation,8 and Poh et al. have reported a webcam-based technique for remote acquisition of PPG signals that uses ambient light as a source of illumination.6 These examples indicate two research directions within imaging PPG: high-definition camera-based imaging PPG (iPPG) and webcam-based imaging PPG (wPPG). The first of these two examples, which typically comprises a high sample rate and is coupled with a custom light source, has proven to be superior in sensitivity and the ability to assess multiple physiological parameters, while the second, which normally uses ambient light as the illumination source, shows its advantage in terms of simplicity and low cost but lacks the ability to extract several clinically important parameters, including blood oxygen saturation. However successful it has been in acquiring physiological parameters, e.g., heart/respiration rate, a number of key questions still remain for the wPPG technique. Particularly, we have to address the practical issue of how variations in ambient light intensity could influence the performance of the system during physiological assessment. Moreover, compared to the accumulated literature regarding imaging PPG,5–12 there are few studies that compare these two techniques and appraise their performance within the same experiment. In our previous work,5,11 a high-resolution CMOS camera-based imaging PPG system has been introduced, and its practicability and reliability in terms of remote assessment of the cardiovascular system has been shown. Therefore, in the present study, the remote imaging PPG systems, including a high-speed CMOS color camera, a webcam, an optical spectrometer, and a contact PPG (cPPG) sensor, have been set up to compare the reliability and sensitivity of ambient light-based imaging PPG measurements in accessing the cardiovascular system. Measurements were taken from subjects undergoing various intensities of exercise in order to make these comparative assessments under different physiological conditions.