I saw a video showcasing this idea some time back. They showed slowed-down video that exaggerated both the colour red, and the lines on your face, neck and hands, following a steep logarithmic slope.

Basically it showed that we imperceptibly blink and undulate like freaky globular aliens, and even consumer level cameras can pick it up. Not so different than a deep ocean jellyfish. Really fascinating stuff, so I'm looking forward to the Android version of your app.

Let me know if you want a beta tester for Android. I can test if it matches the heart rate monitor on the stationary bike, and there's all kinds of weird lighting at the gym I go to. Plus I do HIIT, so my heart is purposely increased/decreased to significantly different target rates every few minutes.