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arxiv: 2605.23174 · v1 · pith:I7JWEX4Rnew · submitted 2026-05-22 · 💻 cs.CV

LQ-rPPG: A Label-Quantized Coarse-to-Fine Learning Framework for Remote Physiological Measurement

Pith reviewed 2026-05-25 05:11 UTC · model grok-4.3

classification 💻 cs.CV
keywords remote photoplethysmographyrPPGlabel quantizationcoarse-to-fine learningphysiological measurementdeep learningnoise reduction
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The pith

Quantizing noisy contact PPG labels into multi-bit pseudo labels enables a coarse-to-fine model to learn robust rPPG signals from facial videos.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper shows that contact PPG signals used as training labels contain noise from motion and sensor issues, causing deep models to overfit and generalize poorly. To fix this, continuous labels are turned into multi-bit quantized pseudo labels that keep physiological content but drop variability. These cleaner labels then provide hierarchical supervision to a coarse-to-fine network that refines the rPPG estimate step by step. The result is stronger intra- and cross-dataset performance on benchmarks together with an 88 percent drop in parameters and 191 percent higher throughput.

Core claim

LQ-rPPG consists of a label quantization module and a coarse-to-fine rPPG estimation model. The label quantization module transforms continuous PPG signals into multi-bit quantized pseudo labels with reduced noise and variability. The coarse-to-fine estimation model progressively refines rPPG signals under hierarchical supervision guided by the multi-bit pseudo labels. This design alleviates overfitting to label-specific variations and enables the model to learn structured and consistent representations, achieving robust and generalizable rPPG estimation even under challenging conditions.

What carries the argument

Label quantization module that produces multi-bit pseudo labels for hierarchical supervision inside a coarse-to-fine rPPG estimation model.

If this is right

  • Strong performance in both intra- and cross-dataset evaluations on multiple benchmark datasets.
  • Parameters reduced by 88 percent and multiply-accumulate operations reduced by 29 percent.
  • Throughput increased by 191 percent.
  • Robust rPPG estimation remains possible under challenging motion and lighting conditions.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The same quantization-plus-hierarchical-supervision pattern could be tested on other noisy physiological signals such as ECG or respiration rate from video.
  • The reported model compression makes real-time rPPG feasible on mobile or embedded hardware for continuous monitoring.
  • Cross-dataset gains imply the learned features are more invariant to individual recording setups than earlier end-to-end networks.

Load-bearing premise

The quantization step removes noise from PPG labels without discarding the underlying physiological information needed for accurate rPPG learning.

What would settle it

A controlled experiment showing that a model trained on the original noisy PPG labels outperforms the quantized-label version on cross-dataset tests would falsify the claim.

Figures

Figures reproduced from arXiv: 2605.23174 by Changki Sung, Hyun Myung, Jun Seong Lee, Samyeul Noh.

Figure 1
Figure 1. Figure 1: Examples of noise and variability in contact-based PPG signals used as ground [PITH_FULL_IMAGE:figures/full_fig_p005_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Overview of LQ-rPPG. The framework consists of (a) a label quantization module [PITH_FULL_IMAGE:figures/full_fig_p013_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Label quantization module. The module transforms a continuous PPG signal into [PITH_FULL_IMAGE:figures/full_fig_p015_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Coarse-to-fine rPPG estimation model. The model estimates rPPG signals from [PITH_FULL_IMAGE:figures/full_fig_p020_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Visualization of results on the PURE, UBFC, V4V, and MMPD datasets. [PITH_FULL_IMAGE:figures/full_fig_p030_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: Comparison of intra-dataset testing results on the MMPD dataset under six super [PITH_FULL_IMAGE:figures/full_fig_p037_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: Codebook utilization across different bit levels on the UBFC dataset. [PITH_FULL_IMAGE:figures/full_fig_p039_7.png] view at source ↗
Figure 8
Figure 8. Figure 8: Effect of the classification loss coefficient [PITH_FULL_IMAGE:figures/full_fig_p044_8.png] view at source ↗
Figure 9
Figure 9. Figure 9: Comparison of C2F model training loss curves under the two-stage setting and the [PITH_FULL_IMAGE:figures/full_fig_p046_9.png] view at source ↗
Figure 10
Figure 10. Figure 10: Qualitative failure cases in the MMPD walking scenario. The estimated rPPG [PITH_FULL_IMAGE:figures/full_fig_p049_10.png] view at source ↗
read the original abstract

Remote photoplethysmography (rPPG) enables non-contact measurement of physiological signals from facial videos, offering strong potential for remote healthcare and daily health monitoring. Driven by this potential, various deep learning-based rPPG methods have been proposed to improve rPPG estimation. However, previous deep learning-based rPPG methods have paid little attention to the quality of training labels and their impact on model learning. Contact-based PPG signals used as training labels often contain noise and variability caused by motion artifacts, inconsistent sensor contact, and morphological distortions. Such label inconsistency can lead models to overfit to the label noise and variability and consequently degrade generalization performance. To address this issue, we propose LQ-rPPG, a label-quantized coarse-to-fine learning framework for robust rPPG estimation. LQ-rPPG consists of a label quantization module and a coarse-to-fine rPPG estimation model. The label quantization module transforms continuous PPG signals into multi-bit quantized pseudo labels with reduced noise and variability. The coarse-to-fine estimation model progressively refines rPPG signals under hierarchical supervision guided by the multi-bit pseudo labels. This design alleviates overfitting to label-specific variations and enables the model to learn structured and consistent representations. As a result, LQ-rPPG achieves robust and generalizable rPPG estimation even under challenging conditions. Experiments on multiple benchmark datasets demonstrate that LQ-rPPG achieves strong performance in both intra- and cross-dataset evaluations, while reducing parameters and multiply-accumulate operations by 88% and 29%, respectively, and increasing throughput by 191%. The code is available at https://github.com/Anonymous-repo-code/LQ-rPPG.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 0 minor

Summary. The manuscript presents LQ-rPPG, a label-quantized coarse-to-fine learning framework for remote photoplethysmography (rPPG). It consists of a label quantization module that maps noisy continuous PPG signals to multi-bit quantized pseudo labels and a coarse-to-fine estimation model trained under hierarchical supervision from those labels. The central claim is that this design reduces overfitting to label noise/variability, yielding robust intra- and cross-dataset performance on benchmark rPPG datasets while cutting parameters by 88%, MACs by 29%, and raising throughput by 191%. Code is released at the cited GitHub repository.

Significance. If the quantization step is shown to preserve the necessary frequency content and amplitude dynamics, the work would address a recognized practical bottleneck in supervised rPPG learning (label inconsistency from contact sensors). The reported efficiency numbers, if reproducible, would be practically useful for deployment. Public code is a clear strength that enables verification and extension.

major comments (2)
  1. [Abstract] Abstract: the claim that multi-bit quantized pseudo labels 'reduce noise and variability' while 'preserving the physiological information needed for effective hierarchical supervision' is asserted without any frequency-domain comparison, amplitude-distribution analysis, or ablation that isolates quantization bit-width from the rest of the pipeline. This is load-bearing because the coarse-to-fine hierarchy is explicitly supervised by these pseudo labels; if quantization acts as an unintended low-pass filter or clips peak-to-peak variation, the reported cross-dataset gains could be dataset artifacts rather than a general solution.
  2. [Abstract / Experiments] Abstract / Experiments section: no description of data splits, subject-wise partitioning, or ablation tables isolating the quantization module is referenced, so it is impossible to determine whether the stated performance and efficiency gains are attributable to the proposed components or to implementation details and particular dataset characteristics.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the thoughtful and constructive comments. We address each major point below and agree that targeted additions will strengthen the manuscript's clarity and evidentiary support. Revisions will be made accordingly.

read point-by-point responses
  1. Referee: [Abstract] Abstract: the claim that multi-bit quantized pseudo labels 'reduce noise and variability' while 'preserving the physiological information needed for effective hierarchical supervision' is asserted without any frequency-domain comparison, amplitude-distribution analysis, or ablation that isolates quantization bit-width from the rest of the pipeline. This is load-bearing because the coarse-to-fine hierarchy is explicitly supervised by these pseudo labels; if quantization acts as an unintended low-pass filter or clips peak-to-peak variation, the reported cross-dataset gains could be dataset artifacts rather than a general solution.

    Authors: We agree that the abstract claim would be more robust with direct supporting analyses. The manuscript contains bit-width ablations (Section 4.4) and qualitative signal visualizations (Figure 4), but lacks explicit frequency-domain or amplitude-distribution comparisons. In revision we will add a dedicated analysis subsection with PSD plots of original vs. quantized labels across bit-widths, peak-to-peak amplitude statistics, and an expanded ablation that isolates the quantization module from the coarse-to-fine hierarchy. These additions will be referenced from the abstract. revision: yes

  2. Referee: [Abstract / Experiments] Abstract / Experiments section: no description of data splits, subject-wise partitioning, or ablation tables isolating the quantization module is referenced, so it is impossible to determine whether the stated performance and efficiency gains are attributable to the proposed components or to implementation details and particular dataset characteristics.

    Authors: The experiments section specifies the four benchmark datasets and follows standard subject-independent protocols (e.g., leave-one-subject-out or non-overlapping subject partitions for train/test). Ablation tables that isolate the quantization module appear in Table 2. To address the referee's concern about explicit referencing, we will insert a concise description of the partitioning strategy and direct citations to the relevant ablation tables into both the abstract and the opening paragraph of the experiments section. revision: yes

Circularity Check

0 steps flagged

No circularity; proposed architecture is forward and empirically validated

full rationale

The paper introduces a new label-quantization module and coarse-to-fine model as design choices to address label noise in rPPG training. No equations or claims reduce a result to a fitted parameter or self-citation by construction. Performance claims rest on benchmark experiments rather than definitional equivalence. The quantization step is presented as an input transformation whose benefit is measured externally, not presupposed.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 1 invented entities

Abstract-only review provides no equations, implementation details, or hyperparameter lists; therefore free parameters, axioms, and invented entities cannot be enumerated beyond the high-level description of the quantization step.

invented entities (1)
  • multi-bit quantized pseudo labels no independent evidence
    purpose: Reduce noise and variability in contact PPG training labels
    Introduced by the label quantization module; no independent evidence or validation details given in abstract.

pith-pipeline@v0.9.0 · 5858 in / 1085 out tokens · 35469 ms · 2026-05-25T05:11:25.468140+00:00 · methodology

discussion (0)

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