REVIEW 3 major objections 5 minor 1 cited by
On Overlap Ratio in Defocused Electron Ptychography
T0 review · 3 major / 5 minor · reviewed 2026-08-09 · deepseek-v4-flash
Pith's one-line read The paper claims that a 40% overlap ratio is enough for stable, high-quality reconstructions in defocused electron ptychography.
desk verdict Useful geometric redundancy analysis, but the 40% overlap claim is a phase-object best case, not the universal guideline the abstract implies. 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 argument rests on a geometric overlap model plus a modified iterative algorithm. The function $\rho = R(\gamma)$ converts the ratio of scan step to probe diameter into an overlap fraction, and a piecewise Taylor-based inverse $R^{-1}(\rho)$ turns a desired overlap into a scan step. The quantities $D(\rho)$ (number of neighbouring illuminations overlapping a primary illumination) and $C(\rho)$ (number of times each pixel is illuminated) then measure data redundancy purely from scan geometry. On the algorithmic side, Constrained PIE (CPIE) is PIE with an added phase-object constraint that resets the object amplitude toward unity after each update, and it is this constraint that makes low-overlap reconstructions stable in the paper's simulations.
What would settle it
Simulate a 4D STEM dataset with a specimen that has known amplitude modulation (for example, amplitude varying by ±20% around unity) and run CPIE at 40% overlap. If the NRMSE gap versus 60% overlap widens relative to the pure-phase case, the 40% threshold depends critically on the phase-object assumption rather than on overlap alone.
Extended reading notes
Core claim
For a phase object and a known probe, an overlap ratio of 40% between adjacent illuminated areas is sufficient for stable, high-quality electron ptychography reconstructions. The paper demonstrates this by defining geometry-only redundancy measures and by benchmarking a Constrained PIE (CPIE) algorithm on simulated 4D STEM datasets for two phase images under noiseless and Poisson-noise conditions. In both test images, 40% overlap gave reconstruction quality comparable to 60% overlap; one of the images required 70% overlap to match the quality of 95% overlap. The paper also finds that the unconstrained PIE algorithm needs substantially larger overlaps, showing that the phase-object constraint is central to the 40% result.
Load-bearing premise
Everything rests on treating the specimen as a pure phase object whose transmission amplitude is close to one; if a real sample has strong amplitude contrast, the 40% overlap finding may not hold.
Editorial extensions
If this is right
- If the 40% threshold holds, experimentalists can use larger scan steps in defocused-probe ptychography, covering larger fields of view or reducing dose for a given field of view.
- The geometry-only quantities D(ρ) and C(ρ) allow users to estimate critical overlap values from the scan grid before running an experiment, without knowing the specimen or choosing a specific reconstruction algorithm.
- The phase-object constraint in CPIE is what makes 40% overlap viable; unconstrained PIE needs larger overlaps, so the constraint is a load-bearing part of the recipe.
- The 40% threshold is object-dependent in detail: the rice test image needed 70% overlap to match 95%-overlap quality, suggesting users check their specific specimen contrast before fixing an overlap.
Reading between the lines
- If the phase-object approximation is relaxed to allow amplitude contrast, the 40% threshold likely shifts; a natural test is to repeat the paper's simulations with mixed amplitude-and-phase objects.
- The same D(ρ) and C(ρ) redundancy measures could be applied to non-raster scan patterns, such as Fermat spirals, to predict whether the critical overlap changes with scan trajectory.
- Because CPIE enforces unit amplitude, real specimens with absorption or strong scattering may require a modified constraint; the 40% finding should be read as a best-case scenario for weakly scattering phase objects.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper studies how the overlap ratio between adjacent illuminated areas affects data redundancy and reconstruction quality in defocused-probe electron ptychography. It proposes a closed-form approximation to the inverse of the overlap-ratio function, defines two geometry-only quantities D(ρ) and C(ρ) that are independent of the object and of the reconstruction algorithm, and introduces a phase-object-constrained variant of PIE (CPIE). The numerical study uses two simulated phase objects (USAF-1951 chart and a rice image), three noise levels (noiseless and Poisson noise at 20 and 26 dB mSNR), and overlap ratios from 0% to 95%. The abstract claims that a 40% or greater overlap ratio yields stable, high-quality reconstructions, while the conclusion adds the qualifier 'within the parameter space considered'.
Significance. The geometric analysis in Sec. III is self-contained and provides a useful, algorithm-independent way to reason about overlap-induced redundancy; the error bound for the approximate inverse, |ρ − R(R^{-1}(ρ))| < 0.008, is a concrete and checkable quantitative claim. The paper also makes a practical algorithmic contribution by adding a phase-object projection to PIE, and it tests this algorithm across several noise levels. If the 40% threshold were robust, it would offer practical dose-saving guidance for 4D STEM acquisition. However, the current evidence is narrower than the central claim: only two pure phase objects are tested, the rice object requires 70% overlap to match the 95% case, and no repeat runs or error bars are provided despite random probe ordering and Poisson noise. The significance of the paper is therefore real but contingent on a careful restatement of the conditions under which the threshold holds.
major comments (3)
- [Abstract and §IV (Fig. 4)] The abstract's central sentence, 'a 40% or greater overlap ratio yields stable, high-quality reconstructions,' is not supported by the paper's own numerical results. Section IV states that the rice phase object requires a minimum overlap of 70% to achieve phase retrieval quality comparable to that obtained with 95% overlap, while the USAF object reaches that level at 40%. Thus, for one of the two test objects, 40% overlap does not yield the same quality as the high-overlap reference. The conclusion already limits the claim to 'within the parameter space considered,' but the abstract omits this qualifier. Please revise the abstract to state the object-dependent nature of the threshold, or redefine 'high-quality' operationally (for example, as 'comparable to 60% overlap') and apply that definition consistently.
- [§II, Algorithm 1 (line 10), and §III-C] The numerical validation is performed entirely under the phase-object approximation. Section II assumes 'the specimen is a phase object, meaning the amplitude of the object is small and close to one,' and Algorithm 1 line 10 enforces this assumption by replacing the updated object amplitude with unit amplitude. All simulated objects in Sec. IV are constructed as phase-only objects. This makes the 40% threshold a best-case result for pure phase objects. For real specimens with appreciable amplitude contrast, the constraint in line 10 is not valid, and the threshold may shift or disappear. Please either add simulations with amplitude-modulated and mixed amplitude/phase objects, or explicitly restrict the central claim to the phase-object case and state that extension to amplitude contrast is untested.
- [§IV (Fig. 4) and Algorithm 1] The reported NRMSE curves are single realizations with no error bars. Algorithm 1 processes probe locations in an order that the text describes as random, and the Poisson noise realizations are random as well, so the exact positions of the 40% and 70% crossover points are not established. The term 'stable' in the central claim therefore lacks statistical support. Please report the mean and standard deviation over multiple independent runs, especially at the threshold overlaps and noise levels, specify the random seed protocol, and state the NRMSE threshold used to classify a reconstruction as 'high-quality.'
minor comments (5)
- [§I (Introduction)] The sentence beginning 'The authors in [17–20] have established with applications in ptychography' is incomplete and should be rewritten or removed.
- [§III-C (Quality measure)] The statement 'NRMSE(o, co) = ∞' appears to be a sign error. With the given ν minimizing ||o − ν ohat||², the residual for ohat = co is zero, so the dB value is −∞, not +∞. Please correct the notation and define the normalization convention explicitly.
- [§III-B (Fig. 2)] The hypothesis that critical overlap ratios correspond to jump discontinuities in D, mC, or MC is stated but not tested. The paper would be strengthened by a direct comparison of the predicted critical ratios {18.2, 39, 45}% with the observed NRMSE transitions in Fig. 4.
- [§IV (Fig. 4)] The phrase 'the behaviour of the NRMSE of CPIE correlates with the σC(ρ)/µC(ρ) curve' is qualitative. Since σC/µC is a candidate predictor, please report a numerical correlation measure such as Spearman's ρ over the stated overlap range, or weaken the claim.
- [General] There are minor typographical issues, e.g., 'complex objects structures' in the introduction should read 'complex object structures.' A careful proofread would improve readability.
Circularity Check
No significant circularity: the overlap-ratio quantities are geometry-only, the 40% threshold is an observed simulation outcome, and the phase-object restriction is a scope limitation, not a fitted input.
full rationale
The claimed derivation chain is self-contained. D(ρ) and C(ρ) in Sec. III-B are computed purely from scan geometry via Eq. (6), with no fitted parameters derived from reconstruction quality. The inverse-overlap approximation R^{-1}(ρ) in Eq. (5) is a Taylor-series numerical approximation to the geometric function R(γ) in Eq. (4); its threshold parameters ρ0 and ρ1 are chosen to control the approximation error (|ρ - R(R^{-1}(ρ))| < 0.008), not to produce a target overlap threshold. The central 40% claim is reported as an observed result of the simulations in Sec. IV (Fig. 4), where CPIE's NRMSE at 40% is compared with the 60% and 95% cases; it is not a parameter fitted to those outcomes and renamed a prediction. The phase-object assumption is an explicit scope condition (Sec. II and Algorithm 1 line 10) and is stated again in the conclusion as 'within the parameter space considered'; it limits generality but does not make the result equivalent to its input. Self-citations [8,9,11,13] concern dose, compressive sensing, and low-dose regularisation, and are not load-bearing for the overlap threshold. No uniqueness theorem is imported, and no known result is renamed. The abstract's unconditional phrasing of the 40% claim is a presentation issue, not circularity.
Assumptions & free parameters
free parameters (4)
- rho_0 =
0.0448
- rho_1 =
0.5816
- alpha_o =
0.1
- Nitr =
100
assumptions (4)
- domain assumption Exit wave is the product of probe and object transmission function (Eq. 1)
- domain assumption Detector wave is the 2D DFT of the exit wave (Eq. 2)
- domain assumption Object amplitude is close to one (phase object)
- domain assumption Probe is known from aberration parameters
Cite this review
Pith. "Pith review of On Overlap Ratio in Defocused Electron Ptychography." pith.science (2026). https://pith.science/paper/MLP34QM5
@misc{pith2026250200762,
author = {Pith},
title = {Pith review of: On Overlap Ratio in Defocused Electron Ptychography},
year = {2026},
howpublished = {\url{https://pith.science/paper/MLP34QM5}},
note = {Machine review of arXiv:2502.00762}
}
read the original abstract
Four-dimensional Scanning Transmission Electron Microscopy (4D STEM) with data acquired using a defocused electron probe is a promising tool for characterising complex biological specimens and materials through a phase retrieval process known as Electron Ptychography (EP). The efficacy of 4D STEM acquisition and the resulting quality of EP reconstruction depends on the overlap ratio of adjacent illuminated areas. This paper demonstrates how the overlap ratio impacts the data redundancy and the quality of the EP reconstruction. We define two quantities as a function of the overlap ratio that are independent of both the object and the EP algorithm. Subsequently, we evaluate an EP algorithm for varying overlap ratios using simulated 4D STEM datasets. Notably, a 40% or greater overlap ratio yields stable, high-quality reconstructions.
Figures
Figures from the paper (2 more)
Forward citations
Cited by 1 Pith paper
-
LoRePIE: $\ell_0$ Regularised Extended Ptychographical Iterative Engine for Low-dose and Fast Electron Ptychography
LoRePIE, an l0-regularized ePIE with DCT-domain hard thresholding, reconstructs useful electron ptychography images from probe positions with as low as 56% overlap.
Reference graph
Works this paper leans on
-
[1]
Resolution beyond the information limit in transmission electron microscopy,
P. Nellist and B. McCallum, “Resolution beyond the information limit in transmission electron microscopy,” nature, vol. 374, no. 6523, pp. 630–632, 1995
work page 1995
-
[2]
A phase retrieval algorithm for shifting illumination,
J. M. Rodenburg and H. M. Faulkner, “A phase retrieval algorithm for shifting illumination,” Applied physics letters, vol. 85, no. 20, pp. 4795–4797, 2004
work page 2004
-
[3]
An improved ptychographical phase retrieval algorithm for diffractive imaging,
A. M. Maiden and J. M. Rodenburg, “An improved ptychographical phase retrieval algorithm for diffractive imaging,” Ultramicroscopy, vol. 109, no. 10, pp. 1256–1262, 2009
work page 2009
-
[4]
Probe retrieval in ptychographic coherent diffractive imaging,
P. Thibault, M. Dierolf, O. Bunk, A. Menzel, and F. Pfeiffer, “Probe retrieval in ptychographic coherent diffractive imaging,” Ultramicroscopy, vol. 109, no. 4, pp. 338–343, 2009
work page 2009
-
[5]
Relaxed averaged alternating reflections for diffraction imaging,
D. R. Luke, “Relaxed averaged alternating reflections for diffraction imaging,” Inverse problems, vol. 21, no. 1, p. 37, 2004
2004
-
[6]
Semi-implicit relaxed Douglas-Rachford algorithm (sdr) for ptychography,
M. Pham, A. Rana, J. Miao, and S. Osher, “Semi-implicit relaxed Douglas-Rachford algorithm (sdr) for ptychography,” Optics Express, vol. 27, no. 22, pp. 31 246–31 260, 2019
work page 2019
-
[7]
Maximum-likelihood refinement for coherent diffractive imaging,
P. Thibault and M. Guizar-Sicairos, “Maximum-likelihood refinement for coherent diffractive imaging,” New Journal of Physics , vol. 14, no. 6, p. 063004, 2012
work page 2012
-
[8]
A. Moshtaghpour, A. Velazco-Torrejon, A. W. Robinson, A. I. Kirkland, and N. D. Browning, “Ex- ploring low-dose and fast electron ptychography using l0 regularisation of extended ptychographical iterative engine,” Microscopy and Microanalysis, vol. 29, no. Supplement 1, pp. 344–345, 2023
work page 2023
Show all 23 references
-
[9]
Lorepie: ℓ0 regularised extended ptychographical iterative engine for low-dose and fast electron ptychography,
A. Moshtaghpour, A. Velazco-Torrejon, A. W. Robinson, N. D. Browning, and A. I. Kirkland, “Lorepie: ℓ0 regularised extended ptychographical iterative engine for low-dose and fast electron ptychography,” arXiv preprint arXiv:2411.14915 , 2024
2024 arXiv
-
[10]
Four-dimensional scanning transmission electron microscopy (4D-STEM): From scan- ning nanodiffraction to ptychography and beyond,
C. Ophus, “Four-dimensional scanning transmission electron microscopy (4D-STEM): From scan- ning nanodiffraction to ptychography and beyond,” Microscopy and Microanalysis , vol. 25, no. 3, pp. 563–582, 2019. 11
2019
-
[11]
High-speed 4-dimensional scanning transmission electron microscopy using compressive sensing techniques,
A. W. Robinson, A. Moshtaghpour, J. Wells, D. Nicholls, M. Chi, I. MacLaren, A. I. Kirkland, and N. D. Browning, “High-speed 4-dimensional scanning transmission electron microscopy using compressive sensing techniques,” Journal of Microscopy , 2024
2024
-
[12]
Atomic resolution defocused electron ptychography at low dose with a fast, direct electron detector,
J. Song, C. S. Allen, S. Gao, C. Huang, H. Sawada, X. Pan, J. Warner, P. Wang, and A. I. Kirkland, “Atomic resolution defocused electron ptychography at low dose with a fast, direct electron detector,” Scientific reports, vol. 9, no. 1, p. 3919, 2019
2019
-
[13]
Diffusion distribution model for damage mitigation in scanning transmission electron microscopy,
A. Moshtaghpour, A. Velazco-Torrejon, D. Nicholls, A. W. Robinson, A. I. Kirkland, and N. D. Browning, “Diffusion distribution model for damage mitigation in scanning transmission electron microscopy,” Journal of Microscopy , 2024
2024
-
[14]
Reducing electron beam damage through alternative STEM scanning strategies, part ii: Attempt towards an empirical model describing the damage process,
D. Jannis, A. Velazco, A. B ´ech´e, and J. Verbeeck, “Reducing electron beam damage through alternative STEM scanning strategies, part ii: Attempt towards an empirical model describing the damage process,” Ultramicroscopy, vol. 240, p. 113568, 2022
2022
-
[15]
Influence of the overlap parameter on the convergence of the ptychographical iterative engine,
O. Bunk, M. Dierolf, S. Kynde, I. Johnson, O. Marti, and F. Pfeiffer, “Influence of the overlap parameter on the convergence of the ptychographical iterative engine,” Ultramicroscopy, vol. 108, no. 5, pp. 481–487, 2008
2008
-
[16]
Optimization of overlap uniformness for ptychography,
X. Huang, H. Yan, R. Harder, Y . Hwu, I. K. Robinson, and Y . S. Chu, “Optimization of overlap uniformness for ptychography,” Opt. Express, vol. 22, no. 10, pp. 12 634–12 644, May 2014
2014
-
[17]
Near-optimal bounds for signal recovery from blind phaseless periodic short-time fourier transform,
T. Bendory, C.-y. Cheng, and D. Edidin, “Near-optimal bounds for signal recovery from blind phaseless periodic short-time fourier transform,” Journal of Fourier Analysis and Applications , vol. 29, no. 1, p. 1, 2023
2023
-
[18]
Blind phaseless short-time fourier transform recovery,
T. Bendory, D. Edidin, and Y . C. Eldar, “Blind phaseless short-time fourier transform recovery,” IEEE Transactions on Information Theory , vol. 66, no. 5, pp. 3232–3241, 2019
2019
-
[19]
Stft phase retrieval: Uniqueness guarantees and recovery algorithms,
K. Jaganathan, Y . C. Eldar, and B. Hassibi, “Stft phase retrieval: Uniqueness guarantees and recovery algorithms,” IEEE Journal of selected topics in signal processing , vol. 10, no. 4, pp. 770–781, 2016
2016
-
[20]
Phase retrieval for l 2 ([- π, π]) via the provably accurate and noise robust numerical inversion of spectrogram measurements,
M. Iwen, M. Perlmutter, N. Sissouno, and A. Viswanathan, “Phase retrieval for l 2 ([- π, π]) via the provably accurate and noise robust numerical inversion of spectrogram measurements,” Journal of Fourier Analysis and Applications , vol. 29, no. 1, p. 8, 2023
2023
-
[21]
P. W. Hawkes and J. C. Spence, Springer handbook of microscopy . Springer Nature, 2019
2019
-
[22]
Aberration correction in electron microscopy,
O. L. Krivanek, N. Dellby, and M. F. Murfitt, “Aberration correction in electron microscopy,” in Handbook of charged particle optics . CRC Press, 2017, pp. 601–640. 12
2017
-
[23]
Direct detectors and their applications in electron microscopy for materials science,
B. D. A. Levin, “Direct detectors and their applications in electron microscopy for materials science,” Journal of Physics: Materials , vol. 4, no. 4, p. 042005, 2021. 13
2021
Reviewed August 9, 2026 · model on record in the stance chip above.
Discussion (0). Continue with ORCID to comment.