From the creatives folks at Fitbit:
The basic idea is that the color of your face fluctuates slightly as blood perfusion under the skin changes from your heart’s pumping. If you measure the color change, you can measure heart rate. It sounds simple, but it’s not. One thing that makes this difficult is user motion: if the person being measured moves, it becomes difficult to disentangle cardiac-induced color changes from changes in lighting conditions on the face, rotations of the face, etc. But in some cases, we’re actually able to filter out some of this motion. Pretty cool, right?
This is hardly polished technology, but the idea is that you can get heart rate by looking at skin color changes. This is really pretty impressive. It’s a pretty clever approach. I’d be curious how well it transfers from using older film to using some modern 1080p broadcast quality video. Does the accuracy improve?