{"id":"2759d4c6-1834-4e24-b84b-33a74377d9a8","arxiv_id":"2411.10189","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":4,"one_line_summary":"NeISF++ generalizes the dielectric-only NeISF polarized inverse renderer to conductors by adding a complex-refractive-index Fresnel term and a DoLP-based geometry initialization, improving metal and dielectric reconstruction.","lead":"A polarized inverse rendering method is extended so it can reconstruct both shiny metals and plastics from multi-view polarization images, not just plastics. It does this with a generalized material model and a new geometry initialization based on polarization properties that ignore highlight brightness.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Table 2 reports K (imaginary refractive index) errors of 0.43 and 0.65, roughly six times the eta errors, so the claim of accurate conductor material decomposition is not supported by the reported evidence.","rationale":"The reader's weakest assumption was the user-specified conductor-dielectric mask. That is a real limitation, but it is explicitly acknowledged and can be mitigated by providing a correct mask. My concern is more fundamental to the central claim: even with a perfect mask, the reported K errors in Table 2 suggest the imaginary refractive index is not accurately recovered. Since the paper's headline contribution is a pBRDF supporting conductors and estimating complex refractive index, large K errors mean the material-decomposition claim is not established by the evidence. The paper has no code or dataset release, no error bars, and only two synthetic scenes, so these numbers cannot be independently checked. The DoLP initialization is a plausible contribution and the ablation shows improvement, but it does not fix K estimation. The appropriate verdict remains conditional: the authors should release code/data and report unnormalized K errors and per-pixel K accuracy. If the K errors are confirmed, the claim should be narrowed to geometry, roughness, and albedo improvement, not full conductor material recovery.","tokens_in":13683,"tokens_out":5267,"duration_ms":54832,"concrete_test":"Recompute Table 2's K errors after undoing the normalization used for visualization, converting normalized values back to physical units (e.g., for gold, k is roughly 3.4 at 633 nm). If the physical imaginary-index mean absolute error on the two synthetic scenes exceeds 1.0, the conductor material decomposition is quantitatively unreliable and the material claim should be weakened. Also report per-pixel correlation between estimated and ground-truth K; a correlation below 0.8 would confirm poor constraint.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim that NeISF++ reconstructs conductor materials rests on estimating the complex refractive index (eta, k). Table 2 reports mean absolute errors for K of 0.4300 (Stanford scan) and 0.6526 (Helmet), versus Eta errors of 0.0685 and 0.0717. Even if the reported values are normalized for visualization, the K errors are roughly six times larger than the eta errors, indicating that the imaginary part of the refractive index is weakly constrained by the Stokes L1 and DoLP losses. Conductor appearance, especially under relighting, depends strongly on k, so large K errors directly undermine the material-decomposition and relighting claims. Moreover, no baseline method estimates k, so the K column cannot substantiate the 'surpasses existing methods' claim for material decomposition. This is internal evidence of a limitation, not merely a missing baseline: the optimization objective does not appear to constrain k tightly. The user-specified mask of Sec. 4.1 is an additional practical limitation, but the K accuracy problem occurs even when the mask is correct, making it the more load-bearing concern for the central claim.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"NeISF++ proposes a polarized inverse rendering pipeline that extends the dielectric-only NeISF framework to scenes containing both conductors and dielectrics. The material model modifies Baek's pBRDF by inserting a binary conductor/dielectric indicator in front of the diffuse polarization term and by computing the Fresnel reflection Mueller matrix with a complex refractive index. Geometry is initialized with a VolSDF trained jointly on DoLP and intensity images, followed by joint optimization of the SDF, BRDF fields (roughness, albedo, complex IOR), and incident Stokes fields. The authors also contribute a synthetic and real multi-view polarimetric dataset and report normal/material metrics on two synthetic scenes, qualitative real-data and relighting results, and an ablation of the proposed DoLP initialization.","tokens_in":13931,"tokens_out":5618,"duration_ms":57720,"significance":"If the results hold, this is a useful step beyond NeISF: it is the first polarized inverse rendering treatment of conductors with a pBRDF, and the DoLP-based geometry initialization is a simple idea that could transfer to other inverse rendering pipelines. The proposed dataset, with ground-truth complex IOR, roughness, and conductor/dielectric masks, is a potentially valuable resource for the community. The quantitative evidence, however, is narrow (two synthetic scenes, no error bars), and the complex-Fresnel derivation and the relighting protocol are not present in the main paper. The contribution is plausible and worth developing, but the broad claims of accurate conductor material decomposition and improved relighting need stronger support before acceptance.","major_comments":[{"comment":"The material decomposition claim is not adequately supported by Table 2 as reported. The mean absolute errors for K (0.4300 and 0.6526) are much larger in absolute value than those for Eta (0.0685 and 0.0717), but the real and imaginary parts of the refractive index have very different physical scales for metals (for example, gold at 633 nm has eta around 0.18 and k around 3.4). Reporting absolute MAE alone does not tell the reader whether the K estimates are accurate in relative terms. Please report relative errors, per-material ground-truth IOR values, or error maps for both synthetic scenes, and state whether the reported numbers are raw or normalized.","section":"Table 2, Sec. 5.3"},{"comment":"The central ingredient of the paper, namely the general Fresnel reflection term supporting complex refractive indices, is described only by a pointer to the supplementary document after Eq. (5). Since this term is what makes the proposed pBRDF applicable to conductors, the manuscript should include the complex-Fresnel Mueller matrix derivation, or at least the final expressions for R+, R-, R×, and the phase delay Delta, in the main text or in an appendix included with the submission. Without this, Eq. (4) and the central claim cannot be independently checked.","section":"Sec. 4.1, Eq. (5)"},{"comment":"The relighting comparison in Fig. 7 is presented without a description of how relighting is performed. The paper does not state whether the estimated geometry and material are re-rendered with a new illumination environment, whether the incident Stokes field is reused or replaced, or how the 'Relit1' and 'Relit2' results are generated. Since improved downstream relighting is one of the central claims, the evaluation protocol should be specified and preferably accompanied by quantitative metrics.","section":"Sec. 5.3, Relighting and Fig. 7"},{"comment":"The quantitative evaluation is restricted to two synthetic scenes with no error bars or multiple runs, and the real-data results are qualitative only. Given the broad claim of surpassing existing polarized inverse rendering methods for geometry and material decomposition, the evidence is thin. Additional scenes, especially with different conductor materials and with imperfect conductor/dielectric masks, would materially strengthen the claim. The mask-sensitivity point is acknowledged in Sec. 6 but is never tested, despite the fact that an incorrect binary indicator m directly corrupts the estimated complex IOR and geometry.","section":"Sec. 5.1, Tables 1 and 2; Sec. 6"}],"minor_comments":[{"comment":"The notation in Eq. (6) is a little confusing: the MLP fDoLP is defined on sampled points along a ray, but the input list (x_j, omega_o, n_j, v_j) is not fully explained; please clarify what v_j is and how the per-point DoLP values are alpha-blended.","section":"Sec. 4.2, Eq. (6)"},{"comment":"There are two captions labeled 'Figure 4' in the manuscript, one for the geometry initialization pipeline and one for the joint optimization stage; the figure numbering should be corrected.","section":"Figures 3 and 4"},{"comment":"In the material paragraph, 'support conducts' should read 'support conductors'.","section":"Sec. 2.1"},{"comment":"The phrase 'NeISF [33] is the second best choice' is unclear; presumably it means 'the best available baseline' given the absence of a direct conductor-aware competitor.","section":"Sec. 5.2"}],"recommendation":"major_revision","confidential_remarks":"The reader's concern about K errors should be interpreted with care: an absolute MAE of 0.43 on k is not directly comparable to 0.07 on eta because the physical scales differ by an order of magnitude. The more serious issues in my view are the missing complex-Fresnel derivation, the unspecified relighting protocol, and the very small quantitative evaluation. These are fixable in revision: including the derivation, reporting relative IOR errors, adding more scenes or error bars, and providing a precise relighting procedure would turn a plausible contribution into a well-supported one."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"The paper does something real. It takes the NeISF pipeline and extends the pBRDF to conductors via a binary diffuse switch and a complex-number Fresnel term, and adds a DoLP-based geometry initialization. That combination is new in the cited literature, and the DoLP initialization looks like the most robust contribution—the ablations show it improves geometry over plain VolSDF initialization. Credit is also due for building an HDR dataset with both conductors and dielectrics, which the community lacks.\n\nThe soft spots are in proportion. The evaluation is thin: two synthetic scenes, no error bars, and real-data results that are qualitative only. The stress-test note is accurate and more serious: Table 2 reports K (imaginary refractive index) errors of 0.43 and 0.65, roughly six times the eta errors. That internal evidence says the optimization objective does not constrain k tightly, which matters because conductor appearance under relighting depends strongly on k. The material decomposition claim is therefore not supported by the reported numbers. Also, since no baseline estimates k, the 'surpasses existing methods' claim for material decomposition lacks a comparison point. The user-specified mask is a practical limitation the authors acknowledge, but the k problem exists even with a correct mask, so it is the more load-bearing concern.\n\nThat said, the paper is honest about the mask limitation, the equations are coherent, and the geometry improvements are plausible. The central idea—that DoLP helps geometry initialization and that a binary diffuse switch plus complex Fresnel is a reasonable way to extend a dielectric pBRDF—holds up as a contribution worth building on.\n\nThis paper is for researchers working on polarization-based inverse rendering specifically. It is not a field-opener, but it is a legitimate new technique with an instructive failure mode. I would send it to peer review rather than desk reject, but I would push the authors to add more scenes, report error bars, and analyze why k is weakly constrained—perhaps by adding ablations on loss weighting or showing relighting sensitivity to k. The claims should be softened to match the evidence. A serious referee can help the authors turn this into a solid, more honest paper.","headline":"A sensible incremental extension of NeISF to conductors, but the paper overclaims material accuracy: the imaginary refractive index is weakly constrained and the evaluation is too thin to support the 'surpasses' claims.","tokens_in":14454,"tokens_out":1474,"would_cite":false,"duration_ms":16513,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"NeISF++ introduces a polarized inverse rendering pipeline that, for the first time, reconstructs geometry and material for scenes containing both conductors and dielectrics using a general polarimetric BRDF and DoLP-based geometry…","keywords":["polarized inverse rendering","polarimetric BRDF","conductors","dielectrics","complex refractive index","degree of linear polarization","signed distance field","relighting"],"falsifier":"Run NeISF++ on a mixed scene with a deliberately corrupted mask (for example, labeling part of a metal object as dielectric) and compare the resulting normal-error and complex-refractive-index error to the correct-mask run; if the errors do not rise substantially, the mask assumption is not load-bearing, whereas a sharp rise confirms it is.","tokens_in":13498,"feed_emoji":"📸","tokens_out":5765,"duration_ms":48684,"temperature":0.7,"pith_summary":"The paper introduces NeISF++, an inverse rendering pipeline that reconstructs 3D geometry, roughness, albedo, and complex refractive index from multi-view polarized images of scenes that contain both conductors and dielectrics. The central claim is that a general polarimetric BRDF (pBRDF) with a binary conductor/dielectric switch and a complex-number Fresnel term makes this joint reconstruction possible, and that a geometry initialization using degree of linear polarization (DoLP) images handles the strong specular reflections typical of glossy conductors. This matters because conductors such as metal are everywhere, and prior polarized inverse rendering methods only modeled dielectrics, producing visibly wrong shape and material estimates on metal parts.","feed_headline":"Inverse rendering pipeline now handles conductors and dielectrics","feed_subtitle":"NeISF++ uses a polarimetric BRDF and DoLP-based initialization to recover shape, material, and complex refractive index.","key_machinery":"The key machinery is the generalized polarimetric BRDF: a sum of a diffuse Mueller term gated by the binary mask m and a specular microfacet term whose Fresnel reflection matrix FR supports complex refractive indices. The diffuse term is m·(a/π cosθi) FT o · D · FT i, and the specular term is ksD G/(4 cosθo) FR, with FR computed from Fresnel wave theory so that reflection coefficients and phase delay are correct for conductors. Alongside this, the geometry initialization replaces intensity-only volume rendering with a DoLP field, training an MLP to predict per-point DoLP values that are alpha-blended along rays and supervised by the captured DoLP images, which are intensity-invariant and geometry-related.","core_discovery":"The paper's discovery is that the dielectric-only Baek pBRDF can be extended to conductors by making two changes: multiplying the diffuse polarization term by a binary indicator m (set to 0 for conductors, where subsurface scattering is absent, and 1 for dielectrics), and replacing the fixed real-index Fresnel reflection term with one derived from Fresnel wave theory that accepts a complex refractive index η - ki. With these changes, the renderer produces correct Stokes-vector predictions for both material classes, and the optimization simultaneously estimates SDF geometry, roughness, diffuse albedo, and the two components of the conductor's complex refractive index. The paper also establishes that a DoLP-based initialization of the SDF, which is invariant to light intensity, gives better geometry for glossy objects than intensity-only initialization.","pith_inferences":["If the conductor-dielectric mask could be predicted automatically, the pipeline would extend to unconstrained scenes; the paper itself suggests data-driven and error-driven mask generation as future work.","The binary mask is a discrete material prior; a continuous metallic parameter (like Disney's) might blur the physical distinction, but the paper argues discrete is more physical—this is a testable design choice.","The robustness of DoLP to intensity could transfer to other inverse rendering settings where specular highlights corrupt intensity-based geometry initialization.","The complex-Fresnel implementation should match laboratory measurements of known conductors (e.g., gold at a given wavelength); validating this on a calibrated target would strengthen the physical correctness claim."],"forward_implications":["The method reconstructs complex refractive indices of conductors, enabling physically plausible relighting with metallic gloss.","DoLP-based geometry initialization improves normal estimation for glossy and specular objects compared to intensity-only initialization.","The same pipeline handles both conductors and dielectrics within one optimization, removing the need to treat them separately.","The proposed synthetic and real HDR datasets provide a benchmark for polarized inverse rendering of mixed material scenes.","Downstream tasks such as material editing can use the estimated complex refractive index and roughness for realistic appearance changes."],"supporting_citations":[{"why":"Supplies the dielectric pBRDF that the proposed general pBRDF extends to conductors.","marker":"[4]"},{"why":"Provides the Fresnel wave theory used to compute reflection coefficients and phase delay for complex refractive indices.","marker":"[13]"},{"why":"The prior incident Stokes field framework and baseline that NeISF++ builds on and compares against.","marker":"[33]"},{"why":"The volume rendering geometry initialization approach that the DoLP-based method replaces.","marker":"[55]"},{"why":"The first polarized inverse rendering method, used as a geometry reconstruction baseline.","marker":"[14]"}],"fun_headline_variants":["NeISF++: Polarized inverse rendering now includes conductors","One pBRDF to rule conductors and dielectrics in polarized inverse rendering","DoLP-based initialization recovers glossy conductors in inverse rendering","Complex refractive index via polarized pBRDF for conductor rendering","Extending pBRDF to conductors: binary indicator and complex Fresnel"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing assumption is that the conductor-versus-dielectric mask is correct and given by the user; if the mask is wrong, the diffuse term is switched incorrectly and the reconstructed geometry, complex refractive index, and relighting results are corrupted.","fun_headline_variants_meta":{"raw":{"variants":["NeISF++: Polarized inverse rendering now includes conductors","One pBRDF to rule conductors and dielectrics in polarized inverse rendering","DoLP-based initialization recovers glossy conductors in inverse rendering","Complex refractive index via polarized pBRDF for conductor rendering","Extending pBRDF to conductors: binary indicator and complex Fresnel"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000672,"raw_usage":{"total_tokens":3028,"prompt_tokens":880,"completion_tokens":2148,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":496,"completion_tokens_details":{"reasoning_tokens":2059}},"tokens_in":496,"tokens_out":2148,"duration_ms":16479,"temperature":1.0,"reasoning_tokens":2059,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-12T19:52:40.140183+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Run NeISF++ on a mixed scene with a deliberately corrupted mask (for example, labeling part of a metal object as dielectric) and compare the resulting normal-error and complex-refractive-index error to the correct-mask run; if the errors do not rise substantially, the mask assumption is not load-bearing, whereas a sharp rise confirms it is.","supporting_citations":[{"cited_title":"Simultaneous acquisition of polarimetric svbrdf and normals","cited_arxiv_id":null,"evidence_quote":"Supplies the dielectric pBRDF that the proposed general pBRDF extends to conductors."},{"cited_title":"Field guide to polarization","cited_arxiv_id":null,"evidence_quote":"Provides the Fresnel wave theory used to compute reflection coefficients and phase delay for complex refractive indices."},{"cited_title":"Neisf: Neural incident stokes field for geometry and material estimation","cited_arxiv_id":null,"evidence_quote":"The prior incident Stokes field framework and baseline that NeISF++ builds on and compares against."},{"cited_title":"V olume rendering of neural implicit surfaces","cited_arxiv_id":null,"evidence_quote":"The volume rendering geometry initialization approach that the DoLP-based method replaces."},{"cited_title":"Pan- dora: Polarization-aided neural decomposition of radiance","cited_arxiv_id":null,"evidence_quote":"The first polarized inverse rendering method, used as a geometry reconstruction baseline."}],"review_version":1}