REVIEW 2 major objections 6 minor 39 references
Differentiable Low-computation Global Correlation Loss for Monotonicity Evaluation in Quality Assessment
T0 review · 2 major / 6 minor · reviewed 2026-08-10 · deepseek-v4-flash
Pith's one-line read A differentiable SROCC loss plus a memory bank of past predictions improves quality-assessment metrics without changing their architecture.
desk verdict Plausible differentiable SROCC loss, but complexity claim is wrong, evidence is thin, and the memory bank's staleness is unanalyzed; deserves review only with major revision. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The central object is a differentiable approximation of the ranking operation: $R'(x)=\sum_{x_i\in x^{(k)}}\frac{1+\tanh(k(x-x_i))}{2}$, whose gradient is $\frac{k}{2}\sum\left(1-\tanh^2(k(x-x_i))\right)$. Inserting these soft ranks into the Pearson correlation formula turns SROCC into a smooth loss. The second mechanism is a memory bank of dictionaries storing predicted and ground-truth quality scores keyed by file name; past predictions are detached (gradient-free) scalars, so the loss can be evaluated over a set much larger than the batch while backpropagation cost stays low. The $O(K)$ complexity is what makes direct global SROCC optimization practical compared with pairwise ranking ($O(K^2)$) or linear-programming sorting.
What would settle it
On a fixed quality-assessment benchmark, compare the proposed training with a variant whose memory bank is refreshed every few iterations by recomputing stored predictions with the current network; if the refreshed variant does not match or beat the original in final SROCC, the claimed global-consistency mechanism is not what drives the gain. A direct measurement of the stale-to-current prediction correlation during training would also settle whether the proxy assumption holds.
Extended reading notes
Core claim
The central claim is that global monotonicity can be optimized directly during training by making the sorting operation inside SROCC differentiable. The paper defines soft ranks $r_k = \sum_{q_i \in q^{(k)}} \frac{1+\tanh(k(q - q_i))}{2}$ and $\hat r_k$ analogously for predicted scores, then uses the negative Pearson correlation of these soft ranks as the loss $L_{Mono}$; with $K$ samples this costs $O(K)$ instead of the $O(K^2)$ of pairwise ranking losses. Because each mini-batch sees only a fraction of the data, the authors also maintain two dictionaries, a memory bank keyed by file names, that record ground-truth and predicted scores; only the current batch's predictions carry gradients, while earlier predictions enter the loss as scalars. The paper reports that adding this loss and memory bank to reproduced image and point cloud quality metrics improves PLCC and SROCC on CSIQ, LIVE, SJTU-PCQA, and WPC in most conditions, and concludes that SROCC can be trained directly without changing the metric framework.
Load-bearing premise
The load-bearing premise is that quality scores predicted by earlier versions of the network and stored in the memory bank are a faithful stand-in for the current model's predictions on the whole dataset, so optimizing a loss over that mixed set improves true global SROCC.
Editorial extensions
If this is right
- Existing no-reference quality metrics can adopt the loss as a drop-in training objective, since it does not change the network or the evaluation protocol.
- Larger effective optimization sets become feasible: the memory bank lets the loss see many more samples than a mini-batch, at linear cost in dictionary size.
- Direct SROCC optimization should matter most when monotonic ordering matters more than absolute score accuracy, such as ranking or retrieval-style quality comparisons.
- The same differentiable-sorting loss could be transferred to other rank-correlation-based objectives in quality assessment, such as Kendall's tau or group-wise ranking constraints.
- Observed gains on both image and point cloud benchmarks suggest the mechanism is task-agnostic within perceptual quality prediction.
Reading between the lines
- The paper does not analyze the distribution shift between stale memory-bank predictions and current network outputs; an implicit testable extension is to weight or refresh stored scores by epoch, which could improve or reveal limits of the method.
- Because the loss is a smooth surrogate for SROCC, the steepness parameter $k$ likely controls the bias-variance trade-off of the rank approximation; annealing $k$ during training is a natural extension the paper does not explore.
- The reported gains are small (typically 0.001–0.011 in SROCC), so a reader should treat the method's value as a cheap training addition rather than a large accuracy jump.
- The method could be evaluated on full-reference quality metrics or on video quality assessment, where temporal ordering and global monotonicity are also evaluated by SROCC.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes a training strategy for no-reference quality assessment that directly optimizes a differentiable approximation of SROCC. The method replaces the non-differentiable sorting operation with a tanh-approximated cumulative Heaviside step function (Eqs. (7)-(9)), forms a PLCC-style loss on the approximate ranks (Eq. (10)), and introduces a memory bank that stores predicted quality scores from previous batches as gradient-free scalars to provide a larger evaluation context during training. The approach is evaluated by adding it to four base metrics (DBCNN, HyperIQA, ResSCNN(D), PQA-Net) on image (CSIQ, LIVE) and point cloud (SJTU-PCQA, WPC) datasets. The reported results show small improvements in most conditions, with one regression (HyperIQA/CSIQ SROCC drops from 0.922 to 0.914 in Table I). The paper claims the loss is O(K) rather than O(K^2).
Significance. If validated, a low-computation differentiable SROCC loss would be a practically useful tool for quality assessment training, where SROCC is the standard monotonicity metric. The tanh-based rank approximation is simple, easy to implement, and the derivation in Eqs. (7)-(9) is mathematically sound. However, the significance of the contribution is currently limited by two issues: the claimed O(K) complexity is not supported by the equations (the loss is O(K^2)), and the memory bank mechanism that underpins the 'global consistency' claim is not analyzed for the distribution shift between stale stored predictions and current model outputs. The experimental evidence is also thin, with no error bars or significance tests and most gains at or below 0.01 in SROCC/PLCC. The idea is worth pursuing, but the paper in its present form does not convincingly support its central claims.
major comments (2)
- [Section IV-B, Eq. (10)] The memory bank mechanism as described stores predicted quality scores from previous batches and epochs as gradient-free scalars, and Eq. (10) is computed over the union of these stale values and the current batch's outputs. Because the network parameters change between updates, the stored predictions are produced by an earlier parameter state and are not faithful to the current model. The paper asserts that this 'decouple[s] the isolation effect incurred by batch size and achieve[s] global consistency' (Section I), but no analysis or experiment is provided to justify that optimizing this mixed objective improves true global SROCC of the current model. Concretely, the authors should add an oracle-refresh ablation in which the memory bank is refreshed with the current model's predictions (with gradient blocked) at each iteration, and compare it to the proposed stale-bank version; they should also report the sensitivity of results to the memory bank retention length. Without such evidence, the global-consistency claim is unsupported.
- [Section V-C, Tables I-II and Section V-D, Tables III-IV] The experimental support for the central claim is weak. Across all reported conditions, the largest gain is 0.011 in SROCC (PQA-Net on WPC, Table II) and the paper does not report error bars, confidence intervals, or repeated-run variances. The HyperIQA/CSIQ pair in Table I shows a SROCC regression from 0.922 to 0.914, which is neither mentioned in the text nor reconciled with the statement that the method 'exhibits performance gain under most testing conditions.' Given the small effect sizes and the absence of statistical significance testing, the claim that the proposed strategy 'can improve the metric performance without changing the metric framework' (Section I) is not convincingly established. The authors should add multiple seeds or cross-validation fold-level statistics, perform paired significance tests, and discuss the regression case explicitly.
minor comments (6)
- [Eq. (1)] The summation term in Eq. (1) is typeset as 'LP' instead of 'L'; it should be '6 \sum_{i=1}^{L} (m_i - n_i)^2 / (L(L^2 - 1))'.
- [Eqs. (7)-(12)] The notation x(k) is undefined and confusing: it appears to denote the set of K samples, but the subscript/superscript structure suggests a dependence on k. Please clarify, e.g., by using \mathbf{x} for the full set and x_k for individual samples.
- [Fig. 1] The caption for Figure 1 appears but the actual figure is not visible in the manuscript; please ensure the figure is included and referenced in the text.
- [Tables III and IV] The 'initial performance' baseline is not defined; please specify which loss function (e.g., MSE or PLCC) is used for the reproduced metrics before adding the proposed loss.
- [Section V-B] The text says '10-fold cross-validation is adopted' but then states that CSIQ and LIVE use a 4:1 training-testing ratio. A 4:1 split corresponds to 20% test, not a 10-fold (90/10) protocol; please clarify the exact evaluation protocol and whether the reported numbers are medians or means over folds.
- [References] Several references are to arXiv preprints or self-citations of the authors' prior work (e.g., [10], [15], [16], [30]); please ensure these are necessary and identify peer-reviewed versions where available.
Circularity Check
No significant circularity: the differentiable SROCC loss is a designed surrogate for the target metric, and the paper's few self-citations are not load-bearing.
full rationale
The paper's central method is a differentiable approximation of SROCC used as a training loss. Equation (10) computes a PLCC over differentiable rank approximations from Equations (11)-(12); this is an objective function chosen by the authors, not a prediction derived from an input. No fitted constant is later renamed as a result, and no equation reduces to another by construction. The nearest potential concern is whether optimizing a differentiable SROCC surrogate and then reporting SROCC improvements is trivial, but that is an empirical effectiveness question, not a circular derivation: the loss is not the evaluation protocol, and the paper evaluates held-out data with the actual SROCC. The memory bank mechanism stores stale gradient-free predictions from earlier batches, and the paper does not analyze the distribution shift between those stale scores and current-model outputs; this is a correctness or robustness weakness, not a circularity, because the method's stated behavior is exactly to mix current and historical predictions. The self-citations [15] and [16] describe prior linear-programming SROCC losses, but the paper explicitly contrasts its approach with those works and does not rely on any theorem or result from them to justify its own loss or memory bank. Therefore the derivation chain is self-contained, and the only mild concern is incidental self-citation that is not load-bearing.
Assumptions & free parameters
free parameters (3)
- k (tanh steepness) =
not specified
- memory bank retention length (epochs) =
not specified
- loss weight lambda =
not specified
assumptions (3)
- domain assumption The soft rank with finite k closely approximates the true rank for SROCC
- domain assumption Historical predictions in the memory bank are a faithful proxy for the current model's global outputs
- domain assumption The reproduced baselines (DBCNN, HyperIQA, ResSCNN(D), PQA-Net) are faithful implementations with identical training hyperparameters
Cite this review
Pith. "Pith review of Differentiable Low-computation Global Correlation Loss for Monotonicity Evaluation in Quality Assessment." pith.science (2026). https://pith.science/paper/DUKIFNFD
@misc{pith2026250115485,
author = {Pith},
title = {Pith review of: Differentiable Low-computation Global Correlation Loss for Monotonicity Evaluation in Quality Assessment},
year = {2026},
howpublished = {\url{https://pith.science/paper/DUKIFNFD}},
note = {Machine review of arXiv:2501.15485}
}
read the original abstract
In this paper, we propose a global monotonicity consistency training strategy for quality assessment, which includes a differentiable, low-computation monotonicity evaluation loss function and a global perception training mechanism. Specifically, unlike conventional ranking loss and linear programming approaches that indirectly implement the Spearman rank-order correlation coefficient (SROCC) function, our method directly converts SROCC into a loss function by making the sorting operation within SROCC differentiable and functional. Furthermore, to mitigate the discrepancies between batch optimization during network training and global evaluation of SROCC, we introduce a memory bank mechanism. This mechanism stores gradient-free predicted results from previous batches and uses them in the current batch's training to prevent abrupt gradient changes. We evaluate the performance of the proposed method on both images and point clouds quality assessment tasks, demonstrating performance gains in both cases.
Figures
Reference graph
Works this paper leans on
-
[2]
A morphing-based 3D point cloud reconstruction framework for medical image processing,
Q. Cheng, P. Sun, C. Yang et al. , “A morphing-based 3D point cloud reconstruction framework for medical image processing,” Computer Methods and Programs in Biomedicine , vol. 193, p. 105495, 2020
work page 2020
-
[3]
Point cloud generation using deep local features for augmented and mixed reality contents,
S. Lim, M. Shin, and J. Paik, “Point cloud generation using deep local features for augmented and mixed reality contents,” in IEEE International Conference on Consumer Electronics , 2020, pp. 1–3
work page 2020
-
[4]
S. Chen, B. Liu, C. Feng et al. , “3D point cloud processing and learning for autonomous driving: Impacting map creation, localization, and perception,” IEEE Signal Processing Magazine , vol. 38, no. 1, pp. 68–86, 2021
work page 2021
-
[5]
3d is here: Point cloud library (PCL),
R. B. Rusu and S. Cousins, “3d is here: Point cloud library (PCL),” in IEEE International Conference on Robotics and Automation , 2011, pp. 1–4
work page 2011
-
[6]
Comparison of four subjective methods for image quality assessment,
R. K. Mantiuk, A. Tomaszewska, and R. Mantiuk, “Comparison of four subjective methods for image quality assessment,” Computer Graphics Forum, vol. 31, no. 8, pp. 2478–2491, 2012
work page 2012
-
[7]
A survey of DNN methods for blind image quality assessment,
X. Yang, F. Li, and H. Liu, “A survey of DNN methods for blind image quality assessment,” IEEE Access, vol. 7, pp. 123 788–123 806, 2019
work page 2019
-
[8]
Point cloud quality assessment: Dataset construction and learning-based no-reference metric,
Y . Liu, Q. Yang, Y . Xu, and L. Yang, “Point cloud quality assessment: Dataset construction and learning-based no-reference metric,” ACM Transactions on Multimedia Computing Communications and Applica- tions, vol. 19, no. 2s, pp. 1–26, 2023
work page 2023
-
[9]
Reduced reference quality assessment for point cloud compression,
Y . Liu, Q. Yang, and Y . Xu, “Reduced reference quality assessment for point cloud compression,” in IEEE International Conference on Visual Communications and Image Processing , 2022, pp. 1–5
work page 2022
Show all 39 references
-
[10]
GMC-IQA: Exploiting global- correlation and mean-opinion consistency for no-reference image qual- ity assessment,
Z. Chen, J. Wang, B. Li et al. , “GMC-IQA: Exploiting global- correlation and mean-opinion consistency for no-reference image qual- ity assessment,” arXiv preprint arXiv:2401.10511 , 2024
2024 arXiv
-
[11]
MM-PCQA: Multi-modal learning for no-reference point cloud quality assessment,
Z. Zhang, W. Sun, X. Min et al. , “MM-PCQA: Multi-modal learning for no-reference point cloud quality assessment,” in International Joint Conference on Artificial Intelligence , 2023, pp. 1–1
2023
-
[12]
A deep learning based no- reference quality assessment model for ugc videos,
W. Sun, X. Min, W. Lu, and G. Zhai, “A deep learning based no- reference quality assessment model for ugc videos,” in ACM Interna- tional Conference on Multimedia , 2022, p. 856–865
2022
-
[13]
Novel no-reference image quality assessment metric based on joint relative features,
X. Zeng and H. Lu, “Novel no-reference image quality assessment metric based on joint relative features,” IEEE Transactions on Image Processing, vol. 27, no. 8, pp. 4010–4022, 2018
2018
-
[14]
RankIQA: Learning from rankings for no-reference image quality assessment,
X. Liu, J. van de Weijer, and A. D. Bagdanov, “RankIQA: Learning from rankings for no-reference image quality assessment,” in IEEE International Conference on Computer Vision , 2017
2017
-
[15]
Once-Training-All-Fine: No-reference point cloud quality assessment via domain-relevance degradation de- scription,
Y . Liu, Q. Yang, Y . Zhang et al., “Once-Training-All-Fine: No-reference point cloud quality assessment via domain-relevance degradation de- scription,” arXiv preprint arXiv:2307.01567 , 2023
2023 arXiv
-
[16]
Beyond score changes: Adversarial attack on no-reference image quality assessment from two perspectives,
C. Yang, Y . Liu, D. Li et al., “Beyond score changes: Adversarial attack on no-reference image quality assessment from two perspectives,” arXiv preprint arXiv:2404.13277, 2024
2024 arXiv
-
[17]
No-reference image quality assessment in the spatial domain,
A. Mittal, A. K. Moorthy, and A. C. Bovik, “No-reference image quality assessment in the spatial domain,” IEEE Transactions on Image Processing, vol. 21, no. 12, pp. 4695–4708, 2012
2012
-
[18]
A feature-enriched completely blind image quality evaluator,
L. Zhang, L. Zhang, and A. C. Bovik, “A feature-enriched completely blind image quality evaluator,”IEEE Transactions on Image Processing, vol. 24, no. 8, pp. 2579–2591, 2015
2015
-
[19]
Blind image quality assessment based on high order statistics aggregation,
J. Xu, P. Ye, Q. Li et al., “Blind image quality assessment based on high order statistics aggregation,” IEEE Transactions on Image Processing , vol. 25, no. 9, pp. 4444–4457, 2016
2016
-
[20]
Fully deep blind image quality predictor,
J. Kim and S. Lee, “Fully deep blind image quality predictor,” IEEE Journal of Selected Topics in Signal Processing , vol. 11, no. 1, pp. 206–220, 2017
2017
-
[21]
Blind image quality assessment using a deep bilinear convolutional neural network,
W. Zhang, K. Ma, J. Yan et al., “Blind image quality assessment using a deep bilinear convolutional neural network,” IEEE Transactions on Circuits and Systems for Video Technology , vol. 30, no. 1, pp. 36–47, 2020
2020
-
[22]
Which has better visual quality: The clear blue sky or a blurry animal?
D. Li, T. Jiang, W. Lin, and M. Jiang, “Which has better visual quality: The clear blue sky or a blurry animal?” IEEE Transactions on Multimedia, vol. 21, no. 5, pp. 1221–1234, 2019
2019
-
[23]
Deep cnn-based blind image quality predictor,
J. Kim, A.-D. Nguyen, and S. Lee, “Deep cnn-based blind image quality predictor,” IEEE Transactions on Neural Networks and Learning Systems, vol. 30, no. 1, pp. 11–24, 2019
2019
-
[24]
Hallucinated-iqa: No-reference image quality assessment via adversarial learning,
K.-Y . Lin and G. Wang, “Hallucinated-iqa: No-reference image quality assessment via adversarial learning,” in IEEE/CVF Conference on Computer Vision and Pattern Recognition , 2018
2018
-
[25]
Blind predicting similar quality map for image quality assessment,
D. Pan, P. Shi, M. Hou et al. , “Blind predicting similar quality map for image quality assessment,” in IEEE/CVF Conference on Computer Vision and Pattern Recognition , 2018
2018
-
[26]
dipIQ: Blind image quality assessment by learning-to-rank discriminable image pairs,
K. Ma, W. Liu, T. Liu et al. , “dipIQ: Blind image quality assessment by learning-to-rank discriminable image pairs,” IEEE Transactions on Image Processing, vol. 26, no. 8, pp. 3951–3964, 2017
2017
-
[27]
Blindly assess image quality in the wild guided by a self-adaptive hyper network,
S. Su, Q. Yan, Y . Zhu et al., “Blindly assess image quality in the wild guided by a self-adaptive hyper network,” in IEEE/CVF Conference on Computer Vision and Pattern Recognition , 2020
2020
-
[28]
Point cloud projection and multi-scale feature fusion network based blind quality assessment for colored point clouds,
W. Tao, G. Jiang, Z. Jiang, and M. Yu, “Point cloud projection and multi-scale feature fusion network based blind quality assessment for colored point clouds,” in ACM International Conference on Multimedia, 2021, p. 5266–5272
2021
-
[29]
PQA-Net: Deep no reference point cloud quality assessment via multi-view projection,
Q. Liu, H. Yuan, H. Su et al., “PQA-Net: Deep no reference point cloud quality assessment via multi-view projection,” IEEE Transactions on Circuits and Systems for Video Technology , vol. 31, no. 12, pp. 4645– 4660, 2021
2021
-
[30]
No-reference point cloud quality assessment via domain adaptation,
Q. Yang, Y . Liu, S. Chen et al. , “No-reference point cloud quality assessment via domain adaptation,” in IEEE/CVF Conference on Com- puter Vision and Pattern Recognition , 2022, pp. 21 179–21 188
2022
-
[31]
A no-reference quality assessment metric for point cloud based on captured video sequences,
Y . Fan, Z. Zhang, W. Sun et al. , “A no-reference quality assessment metric for point cloud based on captured video sequences,” in IEEE International Workshop on Multimedia Signal Processing , 2022, pp. 1–5
2022
-
[32]
Evaluating point cloud from moving camera videos: A no-reference metric,
Z. Zhang, W. Sun, Y . Zhu et al. , “Evaluating point cloud from moving camera videos: A no-reference metric,” arXiv preprint arXiv:2208.14085, 2022
2022 arXiv
-
[33]
GPA-Net: No-reference point cloud quality assessment with multi-task graph convolutional network,
Z. Shan, Q. Yang, R. Ye et al. , “GPA-Net: No-reference point cloud quality assessment with multi-task graph convolutional network,” IEEE Transactions on Visualization and Computer Graphics, pp. 1–13, 2023
2023
-
[34]
Most apparent distortion: full- reference image quality assessment and the role of strategy,
E. C. Larson and D. M. Chandler, “Most apparent distortion: full- reference image quality assessment and the role of strategy,” Journal of Electronic Imaging , vol. 19, no. 1, p. 011006, 2010
2010
-
[35]
A statistical evaluation of recent full reference image quality assessment algorithms,
H. Sheikh, M. Sabir, and A. Bovik, “A statistical evaluation of recent full reference image quality assessment algorithms,” IEEE Transactions on Image Processing , vol. 15, no. 11, pp. 3440–3451, 2006
2006
-
[36]
Predicting the perceptual quality of point cloud: A 3d-to-2d projection-based exploration,
Q. Yang, H. Chen, Z. Ma et al. , “Predicting the perceptual quality of point cloud: A 3d-to-2d projection-based exploration,” IEEE Transac- tions on Multimedia , vol. 23, pp. 3877–3891, 2021
2021
-
[37]
Perceptual quality assessment of 3D point clouds,
H. Su, Z. Duanmu, W. Liu et al., “Perceptual quality assessment of 3D point clouds,” in IEEE International Conference on Image Processing , 2019, pp. 3182–3186
2019
-
[38]
Perceptual quality assessment of colored 3D point clouds,
Q. Liu, H. Su, Z. Duanmu et al. , “Perceptual quality assessment of colored 3D point clouds,” IEEE Transactions on Visualization and Computer Graphics, vol. 29, no. 8, pp. 3642–3655, 2023
2023
-
[39]
Deep neural networks for no-reference and full-reference image quality assessment,
S. Bosse, D. Maniry, K.-R. M ¨uller et al. , “Deep neural networks for no-reference and full-reference image quality assessment,” IEEE Transactions on Image Processing , vol. 27, no. 1, pp. 206–219, 2018
2018
-
[40]
A probabilistic quality represen- tation approach to deep blind image quality prediction,
H. Zeng, L. Zhang, and A. C. Bovik, “A probabilistic quality represen- tation approach to deep blind image quality prediction,” arXiv preprint arXiv:1708.08190, 2017
2017 arXiv
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