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This study evaluates the recoverability of physiological properties from contact photoplethysmography (PPG) to camera-derived remote photoplethysmography (rPPG) across 655 recordings, revealing that property-specific discrepancies exist under varying observation conditions. The analysis employed CHROM as a fixed observation pathway, yielding a heart-rate mean absolute error (MAE) of 15.26 bpm and a low Pearson correlation of 0.0801, indicating limited correspondence between PPG and rPPG. Notably, while endpoint performance varied significantly with skin type and environmental factors, the study found that population-level correlations do not guarantee individual recording fidelity, highlighting the complexity of translating PPG data to rPPG in real-world applications.
Property-specific discrepancies in PPG-to-rPPG recoverability reveal that not all physiological signals are equally preserved under varying observation conditions.
Camera-derived remote photoplethysmography (rPPG) is commonly validated through endpoint accuracy, but endpoint performance does not establish whether other physiological properties of source contact photoplethysmography (PPG) remain preserved recording by recording. We evaluated property-specific PPG-to-rPPG recoverability on 655 recordings from the Multi-Domain Mobile Video Physiology Dataset using CHROM as a fixed camera-rPPG observation pathway. The pathway reproduced the published CHROM correlation regime, with heart-rate MAE of 15.26 bpm and Pearson correlation of 0.0801. Matched-versus-shuffled validation revealed modest recording-specific autocorrelation correspondence, while spectral and recurrence-rate measures showed little matched discrimination. Maximal Lyapunov exponents showed essentially no recording-specific PPG-to-rPPG correspondence, with correlation of 0.0231 and permutation p-value of 0.5584, despite population-level overlap. Endpoint discrepancy exhibited Fitzpatrick-associated heterogeneity after adjustment for lighting and motion, including a Fitzpatrick VI versus III contrast of 9.32 bpm, while dynamical discrepancy showed no corresponding gradient. Aggregate RGB signal-to-noise ratio did not materially account for the endpoint contrast. In subject-held-out analysis, adding motion and lighting consistently reduced MAE across linear, ridge, and random-forest learners relative to rPPG-HR-only calibration, with reductions up to 13.32 percent. These findings show that recoverability is property-specific: physiological properties differ in recording-specific preservation and dependence on observation conditions, and population-level plausibility does not establish preservation of individual recordings.
