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Accuracy & Guidelines

TL;DR: VitalLens achieves high fidelity on high-quality video inputs, but input quality matters.

In our study conducted on a diverse benchmark of 422 unique individuals, we observed a mean absolute error of:

  • Heart Rate: 1.57 bpm
  • Respiratory Rate: 1.08 breaths/min
  • HRV-SDNN: 10.18 ms

Guidelines for Best Accuracy

The "Garbage In, Garbage Out" rule applies strictly to rPPG. To maximize the confidence scores and accuracy of estimates returned by the API, adhere to these guidelines:

1. Lighting Environment

  • Even Illumination: Ensure the face is evenly lit. Shadows moving across the face will create artifacts.
  • Avoid Flickering: Older fluorescent tubes and some LED lights flicker at frequencies that interfere with pulse detection.
  • Monitor Glare: Avoid having the subject sit in a dark room illuminated only by a computer monitor. Screens refresh at specific rates and emit changing colors that can corrupt the rPPG signal on the subject's face.

2. Video Quality

  • Compression: Avoid heavy video compression (low bitrate). rPPG relies on imperceptible skin color changes. Compression algorithms are designed to remove exactly these "redundant" color details.
  • Resolution: While the API downsamples images internally, inputting uncompressed or high-bitrate video (even at 480p) is preferred over 4K video with high compression artifacts.

3. Motion & Positioning

While VitalLens is robust to natural movement, signal quality is directly related to stability. The more motion introduced, the lower the confidence score and accuracy of the estimates.

  • Camera Stability: Handheld use is supported, but using a tripod or stable surface will always yield the highest accuracy.
  • Subject Movement: Normal behavior (like blinking or shifting weight) is fine. However, significant activity impacts the signal:
    • Talking/Chewing: Adds noise that may slightly degrade precision.
    • Walking/Exercise: Heavy body motion can overpower the rPPG signal and should be minimized where possible.
  • Orientation: The subject should face the camera directly.
  • Framing: Include the upper chest in the frame.
    • Face Only: Sufficient for Heart Rate.
    • Face + Upper Chest: Required for Respiratory Rate to detect breathing motion.

For a deeper technical analysis of how environmental factors impact signal integrity, read our technical paper.