The Impact of Video Compression on Remote Cardiac Pulse Measurement Using Imaging Photoplethysmography

Remote physiological measurement technique leverages digital cameras to recover the blood volume pulse from the human body.

Air Force Research Laboratory, Wright Patterson Air Force Base, Ohio

Remote measurement of physiological signals has a number of advantages over traditional contact methods. It allows the measurement of vital signals unobtrusively and concomitantly. In recent years, a number of approaches for imaging-based measurement of physiology using digital cameras have been proposed. Imaging photoplethysmography (iPPG) captures variations in light reflected from the body due to blood volume changes in microvascular tissue. It has been demonstrated that sub-pixel variations in color channel measurements from a digital single lens reflex (DSLR) camera, when aggregated, could be used to recover the blood volume pulse. Subsequently, it was shown that iPPG methods can allow accurate measurement of heart rate, heart rate variability, breathing rate, blood oxygenation and pulse transit time.

A number of parameters influence the accuracy of iPPG measurements. These include the imager quality, and the frame rate and resolution of the images. Previous research compared remote physiological measurement using a low cost webcam and a high-speed color CMOS and showed similar signals were captured from both cameras, further supporting that iPPG is a practical method for scalable applications such as telemedicine. It was also found that reducing frame rate from 120Hz to 30Hz and/or reducing image resolution from 658×492 pixels to 329×246 pixels had little impact on the accuracy of pulse rate measurements. Video compression is an important parameter that has not been systematically studied with regard to iPPG.