You may feel that your mirror already gives you more information than you really want first thing in the morning.
But an MIT team has developed a bathroom mirror that tells you your pulse rate, and is working on extending it to include respiration and blood-oxygen measurements.
The mirror, developed by graduate student Ming-Zher Poh, takes its measurements using a simple webcam to measure slight variations in brightness produced by the flow of blood in the face.
Public-domain software is used to identify the position of the face in the image, and then the digital information from this area is broken down into the separate red, green and blue portions of the video image.
The big challenge was dealing with movements of the subject and variations in the ambient lighting. But Poh was able to adapt Independent Component Analysis – signal-processing techniques originally developed to extract a single voice from a roomful of conversations – to extract the pulse signal from the ‘noise’ of these other variations.
The system produced pulse rates that agreed to within about three beats per minute with the rates obtained from an approved monitoring device, even when the subject was moving. It was even able to get accurate pulse signals from three people in the camera’s view at the same time.
Fokko Wieringa, senior scientist at TNO Science & Industry in the Netherlands, developed a similar system in 2005. But, he says, “the exciting thing about this new method is that they identify a fixed region on the face and track it (thus improving motion artifact tolerance), plus the clever processing method.”
It’s this that allows the use of a cheap and simple camera.
Poh says he’s now working on improving the system to allow blood pressure and blood-oxygen measurements to be extracted from the same video images. It should be possible, he says, since conventional blood oxygen sensors already work by using optical detection, although they use a dedicated light source rather than ambient lighting.
