# Contact Surface Area: A Novel Signal for Heart Rate Estimation in Smartphone Videos

## TL;DR

This paper introduces fingertip contact surface area as a new signal for smartphone-based heart rate estimation, demonstrating its correlation with green color intensity and improving accuracy over existing methods.

## Contribution

It presents a novel contact surface area signal, models its relation to pressure, and shows enhanced heart rate estimation accuracy combining area and color signals.

## Key findings

- Lower error rates with the combined algorithm (4.1%)
- Significant correlation between contact area and green intensity
- Outperforms commercial color-based apps (>6%)

## Abstract

We consider the problem of smartphone video-based heart rate estimation, which typically relies on measuring the green color intensity of the user's skin. We describe a novel signal in fingertip videos used for smartphone-based heart rate estimation: fingertip contact surface area. We propose a model relating contact surface area to pressure, and validate it on a dataset of 786 videos from 62 participants by demonstrating a statistical correlation between contact surface area and green color intensity. We estimate heart rate on our dataset with two algorithms, a baseline using the green signal only and a novel algorithm based on both color and area. We demonstrate lower rates of substantial errors (>10 beats per minute) using the novel algorithm (4.1%), compared both to the baseline algorithm (6.4%) and to published results using commercial color-based applications (>6%).