Showing 1–50 of 189 results for abstract: "color difference"

Perceptual Color Difference Modeling Using Machine Learning and Human Similarity Judgments

Authors: Elnara Kadyrgali, Muragul Muratbekova, Adilet Yerkin, Nuray Toganas, Ayan Igali, Malika Ziyada, Aruzhan Burambekova, Jamaladdin Hasanov, Pakizar Shamoi

Abstract: Accurate assessment of color… ▽ More Accurate assessment of color differences is essential for applications ranging from digital design to quality control. While existing color difference metrics, such as CIEDE2000, aim to approximate human perception, they may still exhibit inconsistencies with perceptual judgments. In this study, we investigate a data-driven approach to color-difference estimation based directly on human evaluations. We collect similarity judgments for 2,000 systematically generated color pairs, each rated by seven observers using a four-point ordinal scale. These judgments are then used to train regression models using different color representations, including RGB channel differences, HSI differences, and COLIBRI fuzzy linguistic categories. Experiments with five regression algorithms show that the choice of color model has a greater influence on prediction performance than the choice of regression algorithm. Using COLIBRI features alone, linear regression achieves an R2 of 0.595, outperforming RGB and HSI representations, which achieve R2 values of 0.479 and 0.493, respectively. The best performance is obtained by LightGBM using the combined representation, reaching an R2 of 0.703. The results indicate that human perceptual color differences are better captured when numerical color coordinates are complemented by graded perceptual categories, highlighting the potential of data-driven models for perceptually aligned color-difference estimation. △ Less

Submitted 30 September, 2026; originally announced September 2026.

Comments: This manuscript has been submitted to IEEE Access for consideration

A conformally-Euclidean Line Element for evaluating color differences

Authors: Patrick De Visschere, Patrick Candry, Kristiaan Neyts

Abstract: …simplified version which matches experimental datasets equally well and resulted into a conformally-Euclidean line element, which is conceptually much simpler than any existing color difference metrics. The color difference is written as an… ▽ More Starting from our previously proposed line element and considering more ``surface color'' datasets, we derive a simplified version which matches experimental datasets equally well and resulted into a conformally-Euclidean line element, which is conceptually much simpler than any existing color difference metrics. The color difference is written as an Euclidean difference multiplied with a simple factor which depends on the luminance only. In a subspace with constant luminance, as considered by MacAdam, this factor becomes constant and the subspace is flat. The same holds for sufficiently large luminances. Based on this LE we derive perceptual coordinates $\left(A,l_{c},s_{c}\right)$ very similar to the CIELab $\left(L^{*},a^{*},b^{*}\right)$. △ Less

Submitted 23 September, 2026; v1 submitted 10 June, 2026; originally announced June 2026.

Opacity Is Not Just Opacity

Authors: Chunran Zhang, Tianrui Li

Abstract: …appearance depend on its background, yet is usually understood only as how much the object obscures it. In fact, opacity controls the scaling of the object-background color difference; transparency is only one effect of this relationship. Zero places the output at the background and one at the source color, but differe… ▽ More Web graphics travel with content across pages and themes, where changing backgrounds can require recoloring and maintenance. Opacity already makes a fixed object's appearance depend on its background, yet is usually understood only as how much the object obscures it. In fact, opacity controls the scaling of the object-background color difference; transparency is only one effect of this relationship. Zero places the output at the background and one at the source color, but difference scaling need not stop at either position. We retain the compositing expression and extend the coefficient domain from $[0,1]$ to the real numbers: negative values reverse the difference, whereas values above one expand it in the same direction. We focus on same-direction expansion for reusing Web graphics across backgrounds. Each object carries a fixed source color and coefficient, while the actual background determines the enhancement direction. Background-adaptive contrast enhancement thus becomes part of the object's compositing properties, reducing the design and maintenance of separate color variants. The implementation reuses the original equation without increasing the per-pixel arithmetic operation count within the same pipeline. Enumerating all 8-bit sRGB source colors on 16 predefined light and dark canvases, a fixed $α=1.1$ increases the contrast ratio in 99.8145% of combinations. Without changing source colors, 4.8346% of all combinations newly reach the $3:1$ contrast threshold. Output validation and timing across three browsers demonstrate implementation in the same WebGL pipeline, with no sustained additional runtime observed. △ Less

Submitted 22 September, 2026; v1 submitted 13 September, 2026; originally announced September 2026.

Comments: 10 pages, 8 figures, 1 table. Code: https://github.com/ln-one/opacity-is-not-just-opacity

Magnetic Fields and Asymmetric Accretion in the Class 0 Protostellar System L1527 IRS

Authors: Hanju Nam, Woojin Kwon, Youngwoo Choi, Ian W. Stephens, Leslie W. Looney

Abstract: …the outflow axis, while those in the western region show a pinched morphology, overall aligned with the outflow cavity. These distinct bipolar outflow regions also have a clear color difference in near infrared observed by James Webb Space Telescope. In addition, the spectral index derived from 450 μm and 850 μm observ… ▽ More Magnetic fields play a crucial role in regulating the collapse of dense molecular clouds, shaping the early stages of protostellar evolution. We present polarization observations in submillimeter wavelengths with the SCUBA-2/POL-2 instrument on James Clerk Maxwell Telescope toward the Class 0 protostellar system L1527 IRS (IRAS 04368+2557). The magnetic field morphology varies across the core of L1527 IRS. Magnetic fields in the eastern region are perpendicular to the outflow axis, while those in the western region show a pinched morphology, overall aligned with the outflow cavity. These distinct bipolar outflow regions also have a clear color difference in near infrared observed by James Webb Space Telescope. In addition, the spectral index derived from 450 μm and 850 μm observations reveals that the northwestern region of the protostellar system is colder and denser compared to the southeastern region. Furthermore, in the large-scale structures and magnetic fields revealed by Herschel and Planck, we find a ~0.1 pc scale filamentary structure parallel to the large-scale magnetic fields in the eastern region and a relatively isotropic mass distribution in the western region. Based on these results, we propose an accretion scenario of the protostellar system in which an asymmetric mass distribution causes the distinct features observed in near-infrared and submillimeter wavelengths. △ Less

Submitted 11 September, 2026; originally announced September 2026.

Comments: 18 pages, 13 Figures, 1 table, Accepted for publication in ApJ

Gemini and Apache Point Multi-band Optical Imaging Characterization of Fragmenting Long-period Comet C/2025 K1 (ATLAS)

Authors: Carl Ingebretsen, Bryce T. Bolin, Meredith A. MacGregor, Carey M. Lisse, Matthew Belyakov, Gracyn Jewett, Mukremin Kilic, Marco Micheli, Davide Farnocchia, Brian Lemaux, Hyewon Suh

Abstract: …0.40. The color difference between the comet and its fragments at the two epochs may be explained by particle size and light-scattering effects. We used the Gemini observations to calculate dust mass-loss rates for fragments A, C, and D. We conclude that C/2025 K1 has moderate dust mass-loss rates for millimeter-sized… ▽ More We present results from multi-band g, r, and i, observations of C/2025 K1 (ATLAS) taken with the Gemini North 8.1-m/GMOS imager on 2025 December 6 and December 24, and u, g, r, i, and z observations with the Astrophysical Research Consortium (ARC) 3.5-m/ARCTIC imager on 2025 December 8. We identify at least four distinct fragments in the Gemini and ARC images, designated as A, C, D, and E in these data taken between 2025 December 6 and 24. Color indices are determined from the December 8 ARC observations of fragments A and C, and from the Gemini observations on December 24 for A, C, and D. K1 has an unusually blue g-r color of $\sim$0.40. The color difference between the comet and its fragments at the two epochs may be explained by particle size and light-scattering effects. We used the Gemini observations to calculate dust mass-loss rates for fragments A, C, and D. We conclude that C/2025 K1 has moderate dust mass-loss rates for millimeter-sized dust of $\sim$50 kg/s for the A and C fragments. △ Less

Submitted 30 August, 2026; originally announced August 2026.

Comments: 11 pages, 5 figures, Submitted to the Astronomical Journal

A Passive Daytime Colored Radiative Cooler with DBR-Engineered Color Selectivity

Authors: Rajib Lochan Ghadei, Rohit Gupta, Rishi Maiti

Abstract: …of 92% in the atmospheric window and an average reflectivity of 93.3% over 0.75-6 micrometers. CIE 1931 chromaticity analysis confirms high-contrast CMY colors with low color differences from standard subtractive primary colors. Under daytime conditions with a heat-transfer coefficient of 6 W m-2 K-1, the proposed cool… ▽ More Passive daytime colored radiative cooling (PDCRC) offers an attractive approach to thermal management while enabling structural coloration. However, achieving both strong daytime cooling and vivid, stable colors remains challenging. Here, we propose a lithography-free PDCRC comprising a polydimethylsiloxane (PDMS) emitter, SiC/SiO2 distributed Bragg reflector (DBR), MgF2 spacer, and Ag back reflector. The DBR and MgF2 spacer enable selective visible-spectrum reflection for cyan, magenta, and yellow (CMY) color generation, while the PDMS layer provides strong thermal emission within the atmospheric transparency window (8-14 micrometers). Finite-difference time-domain (FDTD) simulations, validated using the transfer matrix method (TMM), yield an average emissivity of 92% in the atmospheric window and an average reflectivity of 93.3% over 0.75-6 micrometers. CIE 1931 chromaticity analysis confirms high-contrast CMY colors with low color differences from standard subtractive primary colors. Under daytime conditions with a heat-transfer coefficient of 6 W m-2 K-1, the proposed cooler achieves cooling powers of approximately 140-145 W m-2 and a temperature reduction of about 12 degrees C below ambient. The color characteristics remain stable over a broad range of incidence angles, with only a gradual reduction in color intensity at larger angles, while the spectral response remains nearly insensitive to TE and TM polarizations. Simulations using meteorological conditions from different global cities further demonstrate robust cooling performance under diverse environmental conditions. The combination of high cooling performance, vivid coloration, simple multilayer architecture, and fabrication feasibility makes the proposed PDCRC promising for energy-efficient thermal management in buildings, vehicle coatings, wearable devices, and other outdoor applications. △ Less

Submitted 16 August, 2026; originally announced August 2026.

Comments: 20 pages, 8 figures, 2 tables

Type Ib supernovae are bluer than Type Ic supernovae

Authors: Harim Jin, Selma E. de Mink, Sebastian Holzner, Jakub Klencki, Géza Csörnyei, Sung-Chul Yoon, Iair Arcavi, Wolfgang E. Kerzendorf

Abstract: …tests confirming that the distributions differ (p<0.05). The difference in their host galaxy reddening, as currently constrained, is too small to fully explain it. The color difference therefore most likely has an intrinsic origin, reflecting progenitors with different degrees of stripping -- helium-rich for SNe Ib… ▽ More Type Ib and Ic supernovae (SNe Ib/Ic) are the bright finale of massive stars that have lost their hydrogen envelopes, making them powerful probes of mass stripping in massive star evolution. The advent of modern large photometric and spectroscopic surveys presents a unique opportunity to investigate systematic differences between these two kinds of SNe. In this study, we analyze a large, homogeneous sample of SNe Ib/Ic light curves from the Zwicky Transient Facility. We find a systematic difference in their apparent optical colors at peak: SNe Ib are, on average, bluer than SNe Ic, with two-sample tests confirming that the distributions differ (p<0.05). The difference in their host galaxy reddening, as currently constrained, is too small to fully explain it. The color difference therefore most likely has an intrinsic origin, reflecting progenitors with different degrees of stripping -- helium-rich for SNe Ib and helium-poor for SNe Ic. In addition, we find that SNe Ib/Ic with narrow lines (SNe Ibn/Icn) are bluer than those without, which might originate from circumstellar matter interaction, with potential connection to fast blue optical transients. We demonstrate that SN colors offer a promising probe of mass stripping in massive stars, potentially providing a useful tool for analyzing large photometric data and improving predictions for the final outcomes of stripped massive stars. △ Less

Submitted 16 July, 2026; v1 submitted 1 May, 2026; originally announced May 2026.

Comments: Accepted for publication in A&A Letters

Region-Specific Calibration Achieves Excellent Inter-Device Reliability for Smartphone Dermatology: A Multi-Device Benchmark on Korean Facial Skin

Authors: Sungwoo Kang, Jong-Kook Kim

Abstract: …and region-specific CCM trained per anatomical region, both applied in Commission Internationale de l'Eclairage Lab* (CIELAB) space. Results: Linear CCM reduced inter-device color differences by 61-74% and placed both Melanin Index (intraclass correlation coefficient [ICC] = 0.80) and Individual Typology Angle (ITA… ▽ More Background: Smartphone-based dermatology requires inter-device colorimetric reliability that holds across calibration regimes, yet quantitative multi-device benchmarks remain scarce. Materials and Methods: We analyzed matched facial images from 965 Korean subjects captured by a digital single-lens reflex (DSLR) camera, a consumer tablet, and a consumer smartphone, and evaluated two calibration methods against the DSLR reference. The methods are standard global linear Color Correction Matrix (CCM) normalization and region-specific CCM trained per anatomical region, both applied in Commission Internationale de l'Eclairage Lab* (CIELAB) space. Results: Linear CCM reduced inter-device color differences by 61-74% and placed both Melanin Index (intraclass correlation coefficient [ICC] = 0.80) and Individual Typology Angle (ITA, ICC = 0.78) in the good reliability band. Region-specific CCM raised both indices into the excellent reliability band (MI ICC = 0.95, ITA ICC = 0.93), with anatomical region exceeding the source device as the largest pre-calibration variance contributor (analysis-of-variance $η^2 = 0.18$ versus 0.12). Conclusion: Consumer-device skin colorimetry therefore achieves clinically useful inter-device reliability using standard calibration, with region-aware calibration the largest remaining source of improvement. △ Less

Submitted 2 July, 2026; v1 submitted 26 December, 2025; originally announced December 2025.

Convex Recoloring of General Graphs: Formulations, Polyhedra, and Computational Experiments

Authors: Boyue Lin, Phablo F. S. Moura, Roel Leus

Abstract: …a connected subgraph. In the convex recoloring problem (CR), the goal is to find a convex coloring while minimizing the weight of recolored vertices, i.e., vertices assigned a color different from their original one. This problem was originally motivated by the study of phylogenetic trees in bioinformatics and is NP-ha… ▽ More A vertex coloring of a graph is convex if the vertices of each color induce a connected subgraph. In the convex recoloring problem (CR), the goal is to find a convex coloring while minimizing the weight of recolored vertices, i.e., vertices assigned a color different from their original one. This problem was originally motivated by the study of phylogenetic trees in bioinformatics and is NP-hard even on paths. Most existing research focuses on trees, with only limited results available for general graphs. We advance the state of the art by developing exact solution methods for CR on general graphs. In particular, we propose four mixed-integer linear programming formulations, including a compact flow-based model and a representatives model, and design corresponding solution methods. We compare the polytopes associated with the linear relaxation of the proposed formulations. Computational experiments on benchmark instances and on new synthetic instances show that a branch-and-cut algorithm based on the representatives formulation performs best overall. △ Less

Submitted 29 June, 2026; originally announced June 2026.

Comments: 29 pages,6 figures

Plasma Etch Process Optimization for Photonic-Grade Diamond-on-Insulator Substrates and Thickness Evaluation using Colorimetry

Authors: Tianyin Chen, Alessio Miranda, Leyla Rami, Ryoichi Ishihara, Salahuddin Nur

Abstract: …and quantify color differences across thicknesses in common colorimetric spaces. This analysis enables automatic diamond-thickness extrapolation from standard optical microscope images with 5 nm resolution, in good agreement with white-light interferometry (WLI) measurements. The DOI substrate and colorimetric thickne… ▽ More Diamond color-center qubits integrated with photonic circuits can be initialized, manipulated, entangled, and read individually with high fidelity, making them attractive for large-scale modular quantum computers, quantum networks, and distributed quantum sensing. However, the limited size of heteroepitaxially grown single-crystal diamond (SCD) and photonic-grade diamond-on-insulator (DOI) substrates remains a challenge for integration with existing manufacturing processes. Here, we develop a plasma etch recipe to thin direct-bonded (100) SCD membranes (<50 $μ$m) into large-area, thin-film DOI substrates, and demonstrate free-standing photonic chiplets fabricated from the resulting DOI. The ICP-RIE recipe preserves diamond bonding, provides sufficient micromasking and surface-quality control, and enables thin-film DOI manufacture. We thin a 10 $μ$m diamond plate bonded to SiO$_2$/Si and obtain a photonic-grade DOI substrate with diamond thickness $\leq$300 nm. The DOI film is around 300 nm thick over 0.5 $\times$ 0.5 mm$^2$, with surface roughness < 0.5 nm, while the bonding interface remains intact. Diamond photonic chiplets are fabricated on this DOI substrate using a standard two-step lithography process, without complex thin-film transfer, under-etching, or pedestal formation. We also present a colorimetric study of diamond visibility on SiO$_2$ and quantify color differences across thicknesses in common colorimetric spaces. This analysis enables automatic diamond-thickness extrapolation from standard optical microscope images with 5 nm resolution, in good agreement with white-light interferometry (WLI) measurements. The DOI substrate and colorimetric thickness-evaluation method provide an effective fabrication platform and reliable validation route for scalable manufacturing of diamond nanophotonic devices, opening a path toward large-scale integrated quantum systems. △ Less

Submitted 19 June, 2026; v1 submitted 18 June, 2026; originally announced June 2026.

Oklch+: A Three-Parameter Extension of Oklab for Improved Color Difference Prediction

Authors: Naoyuki Uchida

Abstract: Oklab and its cylindrical representation Oklch are widely adopted in interpolation and design workflows as perceptually motivated color spaces, but their color… ▽ More Oklab and its cylindrical representation Oklch are widely adopted in interpolation and design workflows as perceptually motivated color spaces, but their color difference prediction accuracy falls short of CIEDE2000. We propose Oklch+, a three-parameter extension of Oklab comprising a power transformation on the L-axis and a Naka-Rushton compression on the C-axis, with Euclidean distance computed in the resulting transformed Oklab coordinates. The Naka-Rushton function is bounded in [0,1], reflecting the saturating nature of chroma sensitivity at high colorimetric values. Evaluated on COMBVD -- 3,813 suprathreshold color difference pairs spanning six independent experimental datasets -- Oklch+ achieves STRESS = 29.09, closely matching CIEDE2000 (29.13; difference = 0.04), using only three parameters optimized against color difference data compared to approximately 17 for CIEDE2000. Cross-validation on a held-out BFD-P D65 subset (2,028 pairs) confirms generalization (STRESS = 26.14), with Oklch+ substantially outperforming Oklab (51.45) and achieving STRESS comparable to CIEDE2000 (24.12) on the held-out set. Improvement over Oklab (47.35) is confirmed across all six COMBVD sub-datasets. Because Oklch+ defines a coordinate system in which Euclidean distance approximates perceptual distance, linear interpolation in the transformed space offers substantially improved perceptual uniformity relative to Oklab. Current evaluation is limited to the sRGB-centered COMBVD dataset; validation in high-chroma regions with empirical observer-rated discrimination data remains future work. △ Less

Submitted 3 June, 2026; originally announced June 2026.

Comments: 3 figures, 8 tables. Submitted to Color Research & Application

Review of Measures Used for Evaluating Color Difference Models

Authors: Patrick De Visschere

Abstract: We made a detailed review of the difference measures which have been used to judge the differences between experimentally determined color differences and theoretically defined ones, so-called line elements, for the human visual system. To eliminate the statistical errors due to variable and usually arbitrary sampling… ▽ More We made a detailed review of the difference measures which have been used to judge the differences between experimentally determined color differences and theoretically defined ones, so-called line elements, for the human visual system. To eliminate the statistical errors due to variable and usually arbitrary sampling of the directions in a color point, we integrate the measures over a complete ellipsoid/ellipse. It turns out that in the limit for small deviations from circularity all proposed measures ($V_{AB}$, $γ-1$, $CV$ and $\mathrm{STRESS}$) are equivalent. For greater deviations the measures become distinct with $γ-1$ the most sensitive and $\mathrm{STRESS}$ the least. Ideally a difference measure should be coordinate independent and then it is advantageous to apply an affine transformation to both sets, e.g. turning the theoretical one into the unit ball. Although MacAdam already used this method but sampled the transformed ellipse, we integrate over the ellipsoid/ellipse. Comparing the results with the base measures we show that only $\mathrm{STRESS}$ is coordinate independent. Judging whether a single ellipsoid/ellipse resembles a unit ball can easily be done by comparing the eigenvalues with one and we show that our previously proposed error measure $d_{ev}$ (Candry e.a. Optics Express, 30, 36307, 2022) is the eigenvalue version of $γ-1$. We show why the short lived correlation coefficient $r$ was justly abandoned, being very coordinate dependent, but that Pant's recent geometric measure $1-R$ on the other hand is coordinate independent. All measures are routinely made scale invariant by the introduction of a scaling parameter, to be optimized. Lastly we show that from all measures the $γ-1$ ones are the only ones permitting the simple derivation of the globally optimized difference measure from the locally defined ones. △ Less

Submitted 23 May, 2026; v1 submitted 19 January, 2026; originally announced January 2026.

From Pixels to Primitives: Scene Change Detection in 3D Gaussian Splatting

Authors: Chamuditha Jayanga Galappaththige, Jason Lai, Timothy Patten, Donald Dansereau, Niko Suenderhauf, Dimity Miller

Abstract: …comparison hard is the under-constrained nature of Gaussian splatting representation: independent optimizations yield primitive solutions whose count, positions, shapes, and colors differ even where nothing has changed. We address this challenge with anisotropic models of geometric and photometric drift, complemented b… ▽ More Scene change detection methods built on Gaussian splatting universally follow a render-then-compare paradigm: the pre-change scene is rendered into 2D and compared against post-change images via pixel or feature residuals. This change detection problem with Gaussian Splatting has been treated as a question about pixels; we treat it as a question about primitives. We provide direct evidence that native primitive attributes alone -- position, anisotropic covariance, and color -- carry sufficient signal for scene change detection. What makes primitive-space comparison hard is the under-constrained nature of Gaussian splatting representation: independent optimizations yield primitive solutions whose count, positions, shapes, and colors differ even where nothing has changed. We address this challenge with anisotropic models of geometric and photometric drift, complemented by a per-primitive observability term that reflects the extent to which each Gaussian is constrained by the camera geometry. Operating directly on primitives gives our method, GD-DIFF, two properties that distinguish it from render-then-compare methods. First, change maps are multi-view consistent by construction, where prior work had to learn this through an additional optimization objective. Second, geometric and appearance changes are scored separately, identifying not just where but what kind of change occurred, distinguishing structural changes (e.g., an added object) from surface-level ones (e.g., a color change) without supervision or external model dependencies. On real-world benchmarks, GS-DIFF surpasses the prior state-of-the-art approach by $\sim$17% in mean Intersection over Union. △ Less

Submitted 10 May, 2026; v1 submitted 7 May, 2026; originally announced May 2026.

Comments: Project Page: https://chumsy0725.github.io/GS-DIFF/

Helmlab: A Two-Space Family of Analytical, Data-Driven Color Spaces for UI Design Systems

Authors: Gorkem Yildiz

Abstract: …present Helmlab, a family of two purpose-built color spaces for UI design systems sharing a common 11-stage analytical structure: MetricSpace, a 72-parameter space optimized for color-difference prediction, and GenSpace, a 44-parameter space optimized for gradient and palette generation. The forward transform maps CIE… ▽ More We present Helmlab, a family of two purpose-built color spaces for UI design systems sharing a common 11-stage analytical structure: MetricSpace, a 72-parameter space optimized for color-difference prediction, and GenSpace, a 44-parameter space optimized for gradient and palette generation. The forward transform maps CIE XYZ to a perceptually-organized Lab representation through learned matrices, per-channel power compression, Fourier hue correction, and embedded Helmholtz-Kohlrausch lightness adjustment. A post-pipeline neutral correction holds gray-axis chroma below 1e-5 on a 21-step ramp, and a rigid rotation of the chromatic plane improves hue-angle alignment without affecting the distance metric (which is invariant under isometries). On COMBVD (3,813 color pairs), MetricSpace v21 achieves STRESS 22.48, a 23 percent reduction from CIEDE2000 (29.20). On the held-out MacAdam 1974 dataset it scores 19.51 (CIEDE2000: 22.13; CAM16-UCS leads at 18.71). On a self-collected 3,552-judgement screen-condition set it scores 23.26 vs 62.54 for CIEDE2000. On academic He et al. 2022 (82 3D-printed pairs) MetricSpace scores 35.9 vs CIEDE2000 32.6, a regression we own. Averaging the three primary datasets, MetricSpace scores 21.75 vs the next-best baseline CIECAM02-UCS at 35.98. GenSpace v0.11.1 trades distance accuracy for generation quality: on a 90-metric, 3,038-pair gradient/palette benchmark across sRGB, P3, and Rec.2020, it wins 65 of 90 vs OKLab. The transform is invertible with round-trip errors below 1e-13. Production implementations ship on PyPI, npm, Color.js (PR 722, merged), and as a PostCSS plugin. △ Less

Submitted 6 May, 2026; v1 submitted 26 February, 2026; originally announced February 2026.

Comments: 16 pages, 7 figures, 4 tables. Code, datasets, and live benchmark at https://github.com/Grkmyldz148/helmlab and https://helmlab.space

ACM Class: I.4.10; I.3.7; D.2.13

Beyond Pixel Fidelity: Minimizing Perceptual Distortion and Color Bias in Night Photography Rendering

Authors: Furkan Kınlı

Abstract: …on the dataset introduced in the NTIRE 2025 challenge on NPR confirm our approach achieves competitive fidelity while establishing new state-of-the-art results in both CIE2000 color difference and LPIPS. This validates our perceptually-driven design for high-quality nighttime imaging. ▽ More Night Photography Rendering (NPR) poses a significant challenge due to the extreme contrast between dark and illuminated areas in scenes, stemming from concurrent capture of severely dark regions alongside intense point light sources. Existing methods, which are mainly tailored for fidelity metrics, reveal considerable perceptual gaps and often detract from visual quality. We introduce pHVI-ISPNet, a novel RAW-to-RGB framework built on the robust HVI color space. Our network integrates four distinct key refinements: RAW-domain feature processing and Wavelet-based feature propagation to mitigate high-frequency detail loss; sample-based dynamic loss coefficients to ensure stable learning across varying exposure levels; and loss term based on feature distributions to maintain rigorous color constancy. Evaluations on the dataset introduced in the NTIRE 2025 challenge on NPR confirm our approach achieves competitive fidelity while establishing new state-of-the-art results in both CIE2000 color difference and LPIPS. This validates our perceptually-driven design for high-quality nighttime imaging. △ Less

Submitted 30 April, 2026; originally announced April 2026.

Comments: 6 pages, 3 figures, Accepted to 2026 IEEE International Conference on Image Processing

A Metric for Three-Dimensional Color Discrimination Derived from V1 Population Fisher Information

Authors: Michael Menke

Abstract: …chromaticity ellipses, the Koenderink et al. (2026) three-dimensional ellipsoids, Wright's (1941) wavelength discrimination function, and the Huang et al. (2012) threshold color difference ellipses, covering 96 independently measured discrimination conditions across varied chromaticities and luminances. The joint f… ▽ More We derive a Riemannian metric on three-dimensional color space from the Fisher information of neural population codes in the visual pathway. Photoreceptor adaptation, retinal opponent channels, and cortical population encoding each map onto a geometric construction, producing a metric tensor whose components correspond to measurable neural quantities. The resulting 17-parameter model is fitted jointly to four independent threshold datasets: MacAdam's (1942) chromaticity ellipses, the Koenderink et al. (2026) three-dimensional ellipsoids, Wright's (1941) wavelength discrimination function, and the Huang et al. (2012) threshold color difference ellipses, covering 96 independently measured discrimination conditions across varied chromaticities and luminances. The joint fit achieves STRESS of 23.9 on MacAdam, 20.8 on Koenderink et al., 30.1 on Wright, and 30.8 on Huang et al. △ Less

Submitted 25 March, 2026; originally announced March 2026.

Comments: 20 pages, 3 figures

Multi-contrast laser endoscopy for in vivo gastrointestinal imaging

Authors: Taylor L. Bobrow, Mayank Golhar, Suchapa Arayakarnkul, Anthony A. Song, Saowanee Ngamruengphong, Nicholas J. Durr

Abstract: …demonstrate MLE in vivo during clinical colonoscopies. MLE images from 31 polyps demonstrate an approximate three-fold improvement in contrast and a five-fold improvement in color difference compared to white light and narrow band imaging. With the ability to reveal multiple complementary types of tissue contrast while… ▽ More White light endoscopy is the clinical gold standard for detecting diseases in the gastrointestinal tract. Most applications involve identifying visual abnormalities in tissue color, texture, and shape. Unfortunately, the contrast of these features is often subtle, causing many clinically relevant cases to go undetected. To overcome this challenge, we introduce Multi-contrast Laser Endoscopy (MLE): a platform for widefield clinical imaging with rapidly tunable spectral, coherent, and directional illumination. We demonstrate three capabilities of MLE: enhancing tissue chromophore contrast with multispectral diffuse reflectance, quantifying blood flow using laser speckle contrast imaging, and characterizing mucosal topography using photometric stereo. We validate MLE with benchtop models, then demonstrate MLE in vivo during clinical colonoscopies. MLE images from 31 polyps demonstrate an approximate three-fold improvement in contrast and a five-fold improvement in color difference compared to white light and narrow band imaging. With the ability to reveal multiple complementary types of tissue contrast while seamlessly integrating into the clinical environment, MLE shows promise as an investigative tool to improve gastrointestinal imaging. △ Less

Submitted 13 March, 2026; v1 submitted 15 May, 2025; originally announced May 2025.

One Color Makes All the Difference in the Tractability of Partial Coloring in Semi-Streaming

Authors: Avinandan Das

Abstract: …of its neighbors are assigned colors different from its own. This framework naturally extends classical coloring problems: specifically, $k$-partial $(k+1)$-coloring and $k$-partial $k$-coloring generalize $(Δ+1)$-proper coloring and $Δ$-proper coloring, respectively. Prior works of Assadi, Chen, and Khanna [SODA~20… ▽ More This paper investigates the semi-streaming complexity of \textit{$k$-partial coloring}, a generalization of proper graph coloring. For $k \geq 1$, a $k$-partial coloring requires that each vertex $v$ in an $n$-node graph is assigned a color such that at least $\min\{k, °(v)\}$ of its neighbors are assigned colors different from its own. This framework naturally extends classical coloring problems: specifically, $k$-partial $(k+1)$-coloring and $k$-partial $k$-coloring generalize $(Δ+1)$-proper coloring and $Δ$-proper coloring, respectively. Prior works of Assadi, Chen, and Khanna [SODA~2019] and Assadi, Kumar, and Mittal [TheoretiCS~2023] show that both $(Δ+1)$-proper coloring and $Δ$-proper coloring admit one-pass randomized semi-streaming algorithms. We explore whether these efficiency gains extend to their partial coloring generalizations and reveal a sharp computational threshold : while $k$-partial $(k+1)$-coloring admits a one-pass randomized semi-streaming algorithm, the $k$-partial $k$-coloring remains semi-streaming intractable, effectively demonstrating a ``dichotomy of one color'' in the streaming model. △ Less

Submitted 21 February, 2026; originally announced February 2026.

Efficient HDR Reconstruction from Real-World Raw Images

Authors: Qirui Yang, Yihao Liu, Qihua Cheng, Huanjing Yue, Kun Li, Jingyu Yang

Abstract: …4K resolution using one RTX 3090 GPU. While being highly efficient, our model also achieves comparable performance to state-of-the-art HDR methods in terms of PSNR, SSIM, and a color difference metric. ▽ More The growing prevalence of high-resolution displays on edge devices has created a pressing need for efficient high dynamic range (HDR) imaging algorithms. However, most existing HDR methods either struggle to deliver satisfactory visual quality or incur high computational and memory costs, limiting their applicability to high-resolution inputs (typically exceeding 12 megapixels). Furthermore, current HDR dataset collection approaches are often labor-intensive and inefficient. In this work, we explore a novel and practical solution for HDR reconstruction directly from raw sensor data, aiming to enhance both performance and deployability on mobile platforms. Our key insights are threefold: (1) we propose RepUNet, a lightweight and efficient HDR network leveraging structural re-parameterization for fast and robust inference; (2) we design a new computational raw HDR data formation pipeline and construct a new raw HDR dataset, RealRaw-HDR; (3) we design a plug-and-play motion alignment loss to suppress ghosting artifacts under constrained bandwidth conditions effectively. Our model contains fewer than 830K parameters and takes less than 3 ms to process an image of 4K resolution using one RTX 3090 GPU. While being highly efficient, our model also achieves comparable performance to state-of-the-art HDR methods in terms of PSNR, SSIM, and a color difference metric. △ Less

Submitted 10 February, 2026; v1 submitted 17 June, 2023; originally announced June 2023.

Toward a Universal Color Naming System: A Clustering-Based Approach using Multisource Data

Authors: Aruzhan Sabitkyzy, Maksat Shagyrov, Pakizar Shamoi

Abstract: …diverse sources. After data cleaning and normalization, we converted the colors to the perceptually uniform CIELAB color space and applied K-means clustering using the CIEDE2000 color difference metric, identifying 280 optimal clusters. For each cluster, we performed a frequency analysis of the associated names to assi… ▽ More Is it coral, salmon, or peach? What seems like a simple color can have many names, and without a standard, these variations create confusion across design, technology, and communication. Color naming is a fundamental task across industries such as fashion, cosmetics, web design, and visualization tools. However, the lack of universally accepted color naming standards leads to inconsistent color standards across platforms, applications, and industries. Moreover, these systems include hundreds or thousands of overlapping, perceptually indistinct shades, despite the fact that humans typically distinguish only a limited number of unique color categories in practice. In this study, we propose a clustering-based multisource data framework to build a standardized color-naming system. We collected a dataset of over 19,555 RGB values paired with color names from 20 diverse sources. After data cleaning and normalization, we converted the colors to the perceptually uniform CIELAB color space and applied K-means clustering using the CIEDE2000 color difference metric, identifying 280 optimal clusters. For each cluster, we performed a frequency analysis of the associated names to assign representative labels. The resulting system reflects naturally occurring linguistic patterns. We demonstrate its effectiveness in automatic annotation and content-based image retrieval on a clothing dataset. This approach opens new opportunities for standardized, perceptually grounded color labeling in practical applications such as generative AI, visual search, and design systems. △ Less

Submitted 30 January, 2026; originally announced April 2026.

Comments: Submitted to Wiley for consideration

Chameleon: Automated Color Palette Adaptation for Dark Mode Data Visualizations

Authors: Manusha Karunathilaka, Songheng Zhang, Anthony Tang, Kotaro Hara, Jiannan Li, Yong Wang

Abstract: …transforms light mode visualizations into dark mode while maintaining visual clarity and color semantics. By optimizing for luminance contrast, color consistency, and adjacent color differences, Chameleon ensures that the transformed visualizations are legible and visually coherent. Our evaluation includes case study,… ▽ More Dark mode has gained widespread adoption across mobile platforms due to its benefits in reducing eye strain and conserving battery life. However, while the mobile system switches to dark mode, most visualizations remain designed for light mode, causing visual disruptions. Existing methods, such as manual adjustment or color inversion, are either time-consuming or fail to preserve the semantic meaning of colors in visualizations, making them less effective in dark mode. To address this challenge, we propose Chameleon, an algorithm that automatically transforms light mode visualizations into dark mode while maintaining visual clarity and color semantics. By optimizing for luminance contrast, color consistency, and adjacent color differences, Chameleon ensures that the transformed visualizations are legible and visually coherent. Our evaluation includes case study, expert interview, system evaluation, and a user study, and these demonstrate that Chameleon is effective at translating visualizations for dark mode. △ Less

Submitted 5 January, 2026; v1 submitted 29 November, 2025; originally announced December 2025.

Perceptually-Minimal Color Optimization for Web Accessibility: A Multi-Phase Constrained Approach

Authors: Lalitha A R

Abstract: …of successful corrections exhibiting imperceptible color difference ($ΔE_{2000} < 2.0$) as defined by standard perceptibility thresholds. The median perceptual change for successful adjustments is only $0.76\ ΔE_{2000}$, and the algorithm achieves this with a median processing time of $0.876\text{ms}$ per color pai… ▽ More Web accessibility guidelines require sufficient color contrast between text and backgrounds; yet, manually adjusting colors often necessitates significant visual deviation, compromising vital brand aesthetics. We present a novel, multi-phase optimization approach for automatically generating WCAG-compliant colors while minimizing perceptual change to original design choices. Our method treats this as a constrained, non-linear optimization problem, utilizing the modern perceptually uniform OKLCH color space. Crucially, the optimization is constrained to preserve the original hue ($\text{H}$) of the color, ensuring that modifications are strictly limited to necessary adjustments in lightness ($\text{L}$) and chroma ($\text{C}$). This is achieved through a three-phase sequence: binary search, gradient descent, and progressive constraint relaxation. Evaluation on a dataset of 10,000 procedurally generated color pairs demonstrates that the algorithm successfully resolves accessibility violations in $77.22\%$ of cases, with $88.51\%$ of successful corrections exhibiting imperceptible color difference ($ΔE_{2000} < 2.0$) as defined by standard perceptibility thresholds. The median perceptual change for successful adjustments is only $0.76\ ΔE_{2000}$, and the algorithm achieves this with a median processing time of $0.876\text{ms}$ per color pair. The approach demonstrates that accessibility compliance and visual design integrity can be achieved simultaneously through a computationally efficient, perceptually-aware optimization that respects brand identity. The algorithm is publicly implemented in the open-source cm-colors Python library. △ Less

Submitted 4 December, 2025; originally announced December 2025.

An optical--mid-infrared color evolution tool for nova identification using WISE data

Authors: Joseph Onuegbu, Dafne Guetta, Yael Hillman, Volker Perdelwitz, Massimo Della Valle

Abstract: …on well-defined infrared criteria, and leveraging this pipeline, we successfully identified 41 optically confirmed novae in the WISE catalog. In particular, we focus on the color… ▽ More We present a novel approach for characterizing nova candidates by exploiting the infrared capabilities of the Wide-field Infrared Survey Explorer (WISE) catalog. We developed a pipeline to identify novae based on well-defined infrared criteria, and leveraging this pipeline, we successfully identified 41 optically confirmed novae in the WISE catalog. In particular, we focus on the color difference between the optical V band and the WISE 3.4 microns W1 band as a diagnostic. We compared their infrared light curves with their optical counterparts. We identified a strong correlation from which we proposed a color difference model that can be used for further identification and characterization of novae. Our analysis validates the mass-loss timescale theory, which predicts that systems with lower accretion rates accumulate larger envelopes and produce more massive ejecta. We also confirm models' prediction that the early color evolution of novae is governed by ejecta expansion and cooling. From our sample statistics, we infer a Galactic nova rate of approximately 40 to 50 novae per year, consistent with modern and infrared-corrected estimates. The resultant model from this work paves the way for future large-scale investigations of nova candidates. △ Less

Submitted 14 November, 2025; originally announced November 2025.

List-recoloring of two classes of planar graphs

Authors: Chenran Pan, Weifan Wang, Runrun Liu

Abstract: …-colorings where consecutive colorings differ at exactly one vertex. We prove the existence of such a recoloring sequence in which every vertex is recolored at most a constant number of times under two conditions: (i) $G$ is planar, contains no $3$-cycles or intersecting $4$-cycles, and $L$ is a $6$-assignment; or (ii)… ▽ More For a graph $G$ with a list assignment $L$ and two $L$-colorings $α$ and $β$, an $L$-recoloring sequence from $α$ to $β$ is a sequence of proper $L$-colorings where consecutive colorings differ at exactly one vertex. We prove the existence of such a recoloring sequence in which every vertex is recolored at most a constant number of times under two conditions: (i) $G$ is planar, contains no $3$-cycles or intersecting $4$-cycles, and $L$ is a $6$-assignment; or (ii) the maximum average degree of $G$ satisfies $\mathrm{mad}(G) < \frac{5}{2}$ and $L$ is a $4$-assignment. These results strengthen two theorems previously established by Cranston. △ Less

Submitted 20 October, 2025; originally announced October 2025.

Comments: 10 pages

MSC Class: 05C

Color2Struct: efficient and accurate deep-learning inverse design of structural color with controllable inference

Authors: Sichao Shan, Han Ye, Zhengmei Yang, Junpeng Hou, Zhitong Li

Abstract: …predictions. By utilizing sampling bias correction, adaptive loss weighting, and physics-guided inference, Color2Struct improves the prediction of tandem networks by 65% (color difference) and 48% (short-wave near-infrared reflectivity) in designing RGB primary colors. These improvements make Color2Struct highly promis… ▽ More Deep learning (DL) has revolutionized many fields such as materials design and protein folding. Recent studies have demonstrated the advantages of DL in the inverse design of structural colors, by effectively learning the complex nonlinear relations between structure parameters and optical responses, as dictated by the physical laws of light. While several models, such as tandem neural networks and generative adversarial networks, have been proposed, these methods can be biased and are difficult to scale up to complex structures. Moreover, the difficulty in incorporating physical constraints at the inference time hinders the controllability of the model-predicted spectra. In this work, we propose Color2Struct, a universal framework for efficient and accurate inverse design of structural colors with controllable predictions. By utilizing sampling bias correction, adaptive loss weighting, and physics-guided inference, Color2Struct improves the prediction of tandem networks by 65% (color difference) and 48% (short-wave near-infrared reflectivity) in designing RGB primary colors. These improvements make Color2Struct highly promising for applications in high-end display technologies and solar thermal energy harvesting. In experiments, the nanostructure samples are fabricated using a standard thin-film deposition method and their reflectance spectra are measured to validate the designs. Our work provides an efficient and highly optimized method for controllable inverse design, benefiting future explorations of more intricate structures. The proposed framework can be further generalized to a wide range of fields beyond nanophotonics. △ Less

Submitted 1 October, 2025; originally announced October 2025.

Vertex-partitions of 2-edge-colored graphs

Authors: Jørgen Bang-Jensen, Francois Pirot, Anders Yeo

Abstract: …has at least as many out-neighbours of color different from its own color as it has out-neighbours with the same color as itself. Majority colorings have received much attention in the last years and many interesting open problems remain. Inspired by this and the fact that digraphs can be modelled via 2-edge-color… ▽ More A {\bf $\mathbf{k}$-majority coloring} of a digraph $D=(V,A)$ is a coloring of $V$ with $k$ colors so that each vertex $v\in V$ has at least as many out-neighbours of color different from its own color as it has out-neighbours with the same color as itself. Majority colorings have received much attention in the last years and many interesting open problems remain. Inspired by this and the fact that digraphs can be modelled via 2-edge-colored graphs we study several problems concerning vertex partitions of 2-edge-colored graphs. In particular we study vertex partitions with the property that for each $c=1,2$ every vertex $v$ has least as many edges of colour $c$ to vertices outside the set it belongs to as it has to vertices inside its own set. We call such a vertex partition with $k$ sets a {\bf $\mathbf{k}$-majority partition. Among other things we show that every 2-edge-coloured graph has a 4-majority partition and that it is NP-complete to decide whether a 2-edge-coloured graph has a 3-majority partition. We also apply probabilistic tools to show that every $2$-edge-colored graph $G$ of minimum color-degree $δ$ and maximum degree $Δ\le \frac{e^{δ/18}}{9δ}-2$ has a balanced majority $3$-partition. △ Less

Submitted 26 August, 2025; originally announced August 2025.

MSC Class: 05C07; 05C15; 05C20; 05C69

Generalizing Brooks' theorem via Partial Coloring is Hard Classically and Locally

Authors: Jan Bok, Avinandan Das, Anna Gujgiczer, Nikola Jedličková

Abstract: …neighbors colored differently. Das, Fraigniaud, and Ros{é}n~[OPODIS 2023] showed that the problem of $k$-partial $(k+1)$-coloring admits efficient centralized and distributed algorithms and posed an open problem about the status of the distributed complexity of $k$-partial $k$-coloring. We show that the problem become… ▽ More We investigate the classical and distributed complexity of \emph{$k$-partial $c$-coloring} where $c=k$, a natural generalization of Brooks' theorem where each vertex should be colored from the palette $\{1,\ldots,c\} = \{1,\ldots,k\}$ such that it must have at least $\min\{k, °(v)\}$ neighbors colored differently. Das, Fraigniaud, and Ros{é}n~[OPODIS 2023] showed that the problem of $k$-partial $(k+1)$-coloring admits efficient centralized and distributed algorithms and posed an open problem about the status of the distributed complexity of $k$-partial $k$-coloring. We show that the problem becomes significantly harder when the number of colors is reduced from $k+1$ to $k$ for every constant $k\geq 3$. In the classical setting, we prove that deciding whether a graph admits a $k$-partial $k$-coloring is NP-complete for every constant $k \geq 3$, revealing a sharp contrast with the linear-time solvable $(k+1)$-color case. For the distributed LOCAL model, we establish an $Ω(n)$-round lower bound for computing $k$-partial $k$-colorings, even when the graph is guaranteed to be $k$-partial $k$-colorable. This demonstrates an exponential separation from the $O(\log^2 k \cdot \log n)$-round algorithms known for $(k+1)$-colorings. Our results leverage novel structural characterizations of ``hard instances'' where partial coloring reduces to proper coloring, and we construct intricate graph gadgets to prove lower bounds via indistinguishability arguments. △ Less

Submitted 22 August, 2025; originally announced August 2025.

ACM Class: F.2.2; G.2.2

Colored Sandpile

Authors: S. S. Manna

Abstract: …painted the sand particles using a few distinct colors, and restrict them to move in linear trajectories only along their assigned lattice axes, one axis reserved for one color. Different colored particles interact among themselves through the toppling of unstable sand columns. Consequently, the avalanches or in… ▽ More After the introduction of sandpile model a number of different variants have been studied. In most of these models sand particles are indistinguishable. Here we have painted the sand particles using a few distinct colors, and restrict them to move in linear trajectories only along their assigned lattice axes, one axis reserved for one color. Different colored particles interact among themselves through the toppling of unstable sand columns. Consequently, the avalanches or in general the self-organization processes in the sandpile has no overall preferred direction, though the individual particles execute directed motion. For such non-abelian colored sandpiles the steady states are found to be different and also the avalanche size distributions. This sandpile so defined has a non-trivial spatial structure and belongs to a different universality class of sandpile models. Dynamics of a granular heap with grains of different colors and properties may be described using this sandpile. △ Less

Submitted 14 August, 2025; originally announced August 2025.

Comments: 6 page, 6 figures

List strong and list normal edge-coloring of (sub)cubic graphs

Authors: Borut Lužar, Edita Máčajová, Roman Soták, Diana Švecová

Abstract: …of a graph is a proper edge-coloring, in which the edges of every path of length 3 receive distinct colors; in other words, every pair of edges at distance at most 2 must be colored differently. The least number of colors needed for a strong edge-coloring of a graph is the strong chromatic index. We consider the list v… ▽ More A strong edge-coloring of a graph is a proper edge-coloring, in which the edges of every path of length 3 receive distinct colors; in other words, every pair of edges at distance at most 2 must be colored differently. The least number of colors needed for a strong edge-coloring of a graph is the strong chromatic index. We consider the list version of the coloring and prove that the list strong chromatic index of graphs with maximum degree 3 is at most 10. This bound is tight and improves the previous bound of 11 colors. We also consider the question whether the strong chromatic index and the list strong chromatic index always coincide. We answer it in negative by presenting an infinite family of graphs for which the two invariants differ. For the special case of the Petersen graph, we show that its list strong chromatic index equals 7, while its strong chromatic index is 5. Up to our best knowledge, this is the first known edge-coloring for which there are graphs with distinct values of the chromatic index and its list version. In relation to the above, we also initiate the study of the list version of the normal edge-coloring. A normal edge-coloring of a cubic graph is a proper edge-coloring, in which every edge is adjacent to edges colored with 4 colors or to edges colored with 2 colors. It is conjectured that 5 colors suffice for a normal edge-coloring of any bridgeless cubic graph which is equivalent to the Petersen Coloring Conjecture. Similarly to strong edge-coloring, list normal edge-coloring is much more restrictive and consequently for many graphs the list normal chromatic index is greater than the normal chromatic index. We show that there are cubic graphs with list normal chromatic index at least $9$, there are bridgeless cubic graphs with its value at least 8, and there are cyclically 4-edge-connected cubic graphs with value at least 7. △ Less

Submitted 18 July, 2025; v1 submitted 1 October, 2024; originally announced October 2024.

MSC Class: 10C05

Strong list-chromatic index of subcubic graphs is at most 10

Authors: Yunfang Tang, Zhiwei Bi

Abstract: …such that two distinct edges are colored differently if they are incident to a common edge or share an endpoint. The strong chromatic index of a graph $G$, denoted by $χ_{s}'(G)$, is the minimum number of colors needed for a strong edge coloring of $G$. The edge weight of a graph $G$ is defined to be… ▽ More A strong edge coloring of a graph $G$ is an assignment of colors to the edges of $G$ such that two distinct edges are colored differently if they are incident to a common edge or share an endpoint. The strong chromatic index of a graph $G$, denoted by $χ_{s}'(G)$, is the minimum number of colors needed for a strong edge coloring of $G$. The edge weight of a graph $G$ is defined to be $\max\limits_{uv\in E(G)}\{(d_G(u)+d_G(v))\}$. It was proved in Chen et al in 2020 that every graph with edge weight at most 6 has a strong edge-coloring using at most 10 colors. In this paper, we consider the list version of strong edge-coloring. We strengthen this result by showing that every graph with edge weight at most 6 has a strong list-chromatic index at most 10. Specially, every subcubic graph has a strong list-chromatic index at most 10, which improves a result of Dai et al. in 2018. △ Less

Submitted 16 July, 2025; originally announced July 2025.

Comments: 6 pages,4 figures

PRISM: Perceptual Recognition for Identifying Standout Moments in Human-Centric Keyframe Extraction

Authors: Mert Can Cakmak, Nitin Agarwal, Diwash Poudel

Abstract: …for Identifying Standout Moments), a lightweight and perceptually-aligned framework for keyframe extraction. PRISM operates in the CIELAB color space and uses perceptual color difference metrics to identify frames that align with human visual sensitivity. Unlike deep learning-based approaches, PRISM is interpretable, t… ▽ More Online videos play a central role in shaping political discourse and amplifying cyber social threats such as misinformation, propaganda, and radicalization. Detecting the most impactful or "standout" moments in video content is crucial for content moderation, summarization, and forensic analysis. In this paper, we introduce PRISM (Perceptual Recognition for Identifying Standout Moments), a lightweight and perceptually-aligned framework for keyframe extraction. PRISM operates in the CIELAB color space and uses perceptual color difference metrics to identify frames that align with human visual sensitivity. Unlike deep learning-based approaches, PRISM is interpretable, training-free, and computationally efficient, making it well suited for real-time and resource-constrained environments. We evaluate PRISM on four benchmark datasets: BBC, TVSum, SumMe, and ClipShots, and demonstrate that it achieves strong accuracy and fidelity while maintaining high compression ratios. These results highlight PRISM's effectiveness in both structured and unstructured video content, and its potential as a scalable tool for analyzing and moderating harmful or politically sensitive media in online platforms. △ Less

Submitted 23 June, 2025; originally announced June 2025.

Evaluating Fairness and Mitigating Bias in Machine Learning: A Novel Technique using Tensor Data and Bayesian Regression

Authors: Kuniko Paxton, Koorosh Aslansefat, Dhavalkumar Thakker, Yiannis Papadopoulos

Abstract: …AI. In this paper, we focus on Machine Learning (ML) and the performance of model predictions when dealing with skin color. Unlike other sensitive attributes, the nature of skin color differs significantly. In computer vision, skin color is represented as tensor data rather than categorical values or single numerical p… ▽ More Fairness is a critical component of Trustworthy AI. In this paper, we focus on Machine Learning (ML) and the performance of model predictions when dealing with skin color. Unlike other sensitive attributes, the nature of skin color differs significantly. In computer vision, skin color is represented as tensor data rather than categorical values or single numerical points. However, much of the research on fairness across sensitive groups has focused on categorical features such as gender and race. This paper introduces a new technique for evaluating fairness in ML for image classification tasks, specifically without the use of annotation. To address the limitations of prior work, we handle tensor data, like skin color, without classifying it rigidly. Instead, we convert it into probability distributions and apply statistical distance measures. This novel approach allows us to capture fine-grained nuances in fairness both within and across what would traditionally be considered distinct groups. Additionally, we propose an innovative training method to mitigate the latent biases present in conventional skin tone categorization. This method leverages color distance estimates calculated through Bayesian regression with polynomial functions, ensuring a more nuanced and equitable treatment of skin color in ML models. △ Less

Submitted 13 June, 2025; originally announced June 2025.

Tunable Coloration in Core-Shell Plasmonic Nanopixels Based on Organic Conductive Polymers: A First-Principles and FDTD Study

Authors: Md. Shariful Islam, Ahmed Zubair

Abstract: …and gear were utilized to model the nanopixels studied and a significant absorption peak shift was observed. Chromaticity coordinates in the CIE 1931 color space and CIELAB2000 color difference quantify color change capabilities during the redox cycle, and a comparative analysis of organic and inorganic materials highl… ▽ More From raindrops to planets, the scattering of electromagnetic fields introduces exciting phenomena that can be utilized for display devices. Here, we designed an electrochromic nanoparticle on mirror (eNPoM) structure with core-shell geometries for low-power nanoscale pixels with rapid coloration abilities based on four electrochromic organic conducting polymers utilizing the first-principles calculations based on density functional theory (DFT) and the finite-difference time-domain (FDTD) simulations. Au nanoparticles are coated with electrochromic conductive polymers (such as PANI, PEDOT, PPy, and PTh) and positioned on the metal mirror. The electric field enhancement and the impact of shell thickness are analyzed. Dielectric properties of all polymers resulting from atomistic calculation were utilized for FDTD simulation, which helps to correlate the direct relationship between polymer structure and optical properties. Notably, the study reveals significant wavelength tunability of 100nm, 40nm, 70nm, and over 40nm using PANI, PEDOT, PPy, and PTh shells, respectively. Additionally, the potential for RGB color production using a TiN layer on the mirror is explored. For the first time, complex structures such as bow tie and gear were utilized to model the nanopixels studied and a significant absorption peak shift was observed. Chromaticity coordinates in the CIE 1931 color space and CIELAB2000 color difference quantify color change capabilities during the redox cycle, and a comparative analysis of organic and inorganic materials highlights the prospects of the proposed plasmonic nanopixels. △ Less

Submitted 9 June, 2025; originally announced June 2025.

Geometry-guided Online 3D Video Synthesis with Multi-View Temporal Consistency

Authors: Hyunho Ha, Lei Xiao, Christian Richardt, Thu Nguyen-Phuoc, Changil Kim, Min H. Kim, Douglas Lanman, Numair Khan

Abstract: …The key innovation of our approach lies in using global geometry to guide an image-based rendering pipeline. To accomplish this, we progressively refine depth maps using color difference masks across time. These depth maps are then accumulated through truncated signed distance fields in the synthesized view's imag… ▽ More We introduce a novel geometry-guided online video view synthesis method with enhanced view and temporal consistency. Traditional approaches achieve high-quality synthesis from dense multi-view camera setups but require significant computational resources. In contrast, selective-input methods reduce this cost but often compromise quality, leading to multi-view and temporal inconsistencies such as flickering artifacts. Our method addresses this challenge to deliver efficient, high-quality novel-view synthesis with view and temporal consistency. The key innovation of our approach lies in using global geometry to guide an image-based rendering pipeline. To accomplish this, we progressively refine depth maps using color difference masks across time. These depth maps are then accumulated through truncated signed distance fields in the synthesized view's image space. This depth representation is view and temporally consistent, and is used to guide a pre-trained blending network that fuses multiple forward-rendered input-view images. Thus, the network is encouraged to output geometrically consistent synthesis results across multiple views and time. Our approach achieves consistent, high-quality video synthesis, while running efficiently in an online manner. △ Less

Submitted 24 May, 2025; originally announced May 2025.

Comments: Accepted by CVPR 2025. Project website: https://nkhan2.github.io/projects/geometry-guided-2025/index.html

Improved Algorithms for Overlapping and Robust Clustering of Edge-Colored Hypergraphs: An LP-Based Combinatorial Approach

Authors: Changyeol Lee, Yongho Shin, Hyung-Chan An

Abstract: …approach for handling categorical data. Given a hypergraph with (hyper)edges labeled by colors, ECC aims to assign vertex colors to minimize the number of edges where the vertex color differs from the edge's color. However, traditional ECC has inherent limitations, as it enforces a nonoverlapping and exhaustive clu… ▽ More Clustering is a fundamental task in both machine learning and data mining. Among various methods, edge-colored clustering (ECC) has emerged as a useful approach for handling categorical data. Given a hypergraph with (hyper)edges labeled by colors, ECC aims to assign vertex colors to minimize the number of edges where the vertex color differs from the edge's color. However, traditional ECC has inherent limitations, as it enforces a nonoverlapping and exhaustive clustering. To tackle these limitations, three versions of ECC have been studied: Local ECC and Global ECC, which allow overlapping clusters, and Robust ECC, which accounts for vertex outliers. For these problems, both linear programming (LP) rounding algorithms and greedy combinatorial algorithms have been proposed. While these LP-rounding algorithms provide high-quality solutions, they demand substantial computation time; the greedy algorithms, on the other hand, run very fast but often compromise solution quality. In this paper, we present an algorithmic framework that combines the strengths of LP with the computational efficiency of combinatorial algorithms. Both experimental and theoretical analyses show that our algorithms efficiently produce high-quality solutions for all three problems: Local, Global, and Robust ECC. We complement our algorithmic contributions with complexity-theoretic inapproximability results and integrality gap bounds, which suggest that significant theoretical improvements are unlikely. Our results also answer two open questions previously raised in the literature. △ Less

Submitted 23 May, 2025; originally announced May 2025.

Research on Defect Detection Method of Motor Control Board Based on Image Processing

Authors: Jingde Huang, Zhangyu Huang, Chenyu Li, Jiantong Liu

Abstract: The motor control board has various defects such as inconsistent color… ▽ More The motor control board has various defects such as inconsistent color differences, incorrect plug-in positions, solder short circuits, and more. These defects directly affect the performance and stability of the motor control board, thereby having a negative impact on product quality. Therefore, studying the defect detection technology of the motor control board is an important means to improve the quality control level of the motor control board. Firstly, the processing methods of digital images about the motor control board were studied, and the noise suppression methods that affect image feature extraction were analyzed. Secondly, a specific model for defect feature extraction and color difference recognition of the tested motor control board was established, and qualified or defective products were determined based on feature thresholds. Thirdly, the search algorithm for defective images was optimized. Finally, comparative experiments were conducted on the typical motor control board, and the experimental results demonstrate that the accuracy of the motor control board defect detection model-based on image processing established in this paper reached over 99%. It is suitable for timely image processing of large quantities of motor control boards on the production line, and achieved efficient defect detection. The defect detection method can not only be used for online detection of the motor control board defects, but also provide solutions for the integrated circuit board defect processing for the industry. △ Less

Submitted 23 May, 2025; originally announced May 2025.

The chromatic number of the plane with an interval of forbidden distances is at least 7

Authors: Vsevolod Voronov

Abstract: …, are colored differently. The conjecture proposed by G. Exoo in 2004, states that for arbitrary positive $\varepsilon$ at least 7 colors are required. Also, with a sufficiently small $\varepsilon$ the number of colors is exactly 7. The main result of the present paper is that the conjecture is true for the Euclidean p… ▽ More The work is devoted to one of the variations of the Hadwiger--Nelson problem on the chromatic number of the plane. In this formulation one needs to find for arbitrarily small $\varepsilon$ the least possible number of colors needed to color a Euclidean plane in such a way that any two points, the distance between which belongs to the interval $[1-\varepsilon, 1+\varepsilon]$, are colored differently. The conjecture proposed by G. Exoo in 2004, states that for arbitrary positive $\varepsilon$ at least 7 colors are required. Also, with a sufficiently small $\varepsilon$ the number of colors is exactly 7. The main result of the present paper is that the conjecture is true for the Euclidean plane as well as for any Minkowski plane. △ Less

Submitted 13 April, 2025; v1 submitted 20 April, 2023; originally announced April 2023.

Comments: 16 pages, 6 figures. Extended the bibliography and details of proofs concerning arbitrary norm. Added a theorem on covering a disk of radius 3 by closed sets. Corrected some inaccuracies

MSC Class: 52C10

Undertrained Image Reconstruction for Realistic Degradation in Blind Image Super-Resolution

Authors: Ru Ito, Supatta Viriyavisuthisakul, Kazuhiko Kawamoto, Hiroshi Kera

Abstract: …enhancing performance on real-world LR images. Furthermore, an analysis of the datasets reveals that degradation diversity contributes to performance improvements, whereas color differences between HR and LR images may degrade performance. 11 pages, (11 figures and 2 tables) ▽ More Most super-resolution (SR) models struggle with real-world low-resolution (LR) images. This issue arises because the degradation characteristics in the synthetic datasets differ from those in real-world LR images. Since SR models are trained on pairs of high-resolution (HR) and LR images generated by downsampling, they are optimized for simple degradation. However, real-world LR images contain complex degradation caused by factors such as the imaging process and JPEG compression. Due to these differences in degradation characteristics, most SR models perform poorly on real-world LR images. This study proposes a dataset generation method using undertrained image reconstruction models. These models have the property of reconstructing low-quality images with diverse degradation from input images. By leveraging this property, this study generates LR images with diverse degradation from HR images to construct the datasets. Fine-tuning pre-trained SR models on our generated datasets improves noise removal and blur reduction, enhancing performance on real-world LR images. Furthermore, an analysis of the datasets reveals that degradation diversity contributes to performance improvements, whereas color differences between HR and LR images may degrade performance. 11 pages, (11 figures and 2 tables) △ Less

Submitted 4 March, 2025; originally announced March 2025.

Comments: 11 pages, 11 figures, 2 tables

The Diversity of Cold Worlds: a blended-light binary straddling the T/Y transition in brown dwarfs

Authors: Daniella C. Bardalez Gagliuffi, Jacqueline K. Faherty, Genaro Suarez, Sherelyn Alejandro Merchan, Brianna Lacy, Ben Burningham, Klara Matuszewska, Rocio Kiman, Johanna M. Vos, Austin Rothermich, Jonathan Gagne, Caroline Morley, Melanie J. Rowland, Dan Caselden, Aaron Meisner, Adam C. Schneider, Marc J. Kuchner, Charles A. Beichman, Peter R. Eisenhardt, Christopher R. Gelino, Ehsan Gharib-Nezhad, Eileen C. Gonzales, Federico Marocco, Niall Whiteford, J. Davy Kirkpatrick

Abstract: …mag redder than the primary in [3.6]-[4.5]. Despite the large color difference between the best fit primary and secondary, their temperature difference is only $92\pm23$\,K, a feature reminiscing of the L/T transition. Carbon disequilibrium chemistry strongly shapes the mid-infrared spectra of these sources, as a comp… ▽ More We present the first brown dwarf spectral binary characterized with JWST: WISE J014656.66+423410.0, the coldest blended-light brown dwarf binary straddling the T/Y transition. We obtained a moderate resolution (R$\sim$2700) G395H spectrum of this unresolved binary with JWST/NIRSpec and we fit it to late-T and Y dwarf spectra from JWST/NIRSpec, and model spectra of comparable temperatures, both as individual spectra and pairs mimicking an unresolved binary system. We find that this tightly-separated binary is likely composed of two unequal-brightness sources with a magnitude difference of $0.50\pm0.08$ mag in IRAC [4.5] and a secondary $1.01\pm0.13$ mag redder than the primary in [3.6]-[4.5]. Despite the large color difference between the best fit primary and secondary, their temperature difference is only $92\pm23$\,K, a feature reminiscing of the L/T transition. Carbon disequilibrium chemistry strongly shapes the mid-infrared spectra of these sources, as a complex function of metallicity and surface gravity. While a larger library of JWST/NIRSpec spectra is needed to conclusively examine the peculiarities of blended-light sources, this spectral binary is a crucial pathfinder to both understand the spectral features of planetary-mass atmospheres and detect binarity in unresolved, moderate-resolution spectra of the coldest brown dwarfs. △ Less

Submitted 3 March, 2025; originally announced March 2025.

Comments: 21 pages, 7 figures

CAR-LOAM: Color-Assisted Robust LiDAR Odometry and Mapping

Authors: Yufei Lu, Yuetao Li, Zhizhou Jia, Qun Hao, Shaohui Zhang

Abstract: …LiDAR scan, the edge and planar features are extracted and colored using the corresponding image and then matched to a global map. Specifically, we adopt a perceptually uniform color difference weighting strategy to exclude color correspondence outliers and a robust error metric based on the Welsch's function to mi… ▽ More In this letter, we propose a color-assisted robust framework for accurate LiDAR odometry and mapping (LOAM). Simultaneously receiving data from both the LiDAR and the camera, the framework utilizes the color information from the camera images to colorize the LiDAR point clouds and then performs iterative pose optimization. For each LiDAR scan, the edge and planar features are extracted and colored using the corresponding image and then matched to a global map. Specifically, we adopt a perceptually uniform color difference weighting strategy to exclude color correspondence outliers and a robust error metric based on the Welsch's function to mitigate the impact of positional correspondence outliers during the pose optimization process. As a result, the system achieves accurate localization and reconstructs dense, accurate, colored and three-dimensional (3D) maps of the environment. Thorough experiments with challenging scenarios, including complex forests and a campus, show that our method provides higher robustness and accuracy compared with current state-of-the-art methods. △ Less

Submitted 24 February, 2025; originally announced February 2025.

On the Age Calibration of Open Clusters using Red Clump Stars

Authors: Abigail R. Chriss, Guy Worthey

Abstract: …color difference between the red giant branch (RGB) and red clump to younger cluster ages. We perform membership analysis on fourteen galactic open clusters using Gaia DR3 astrometry, then compute the difference in color of the RGB and red clump $d_{B-R}$ using Gaia photometry. We also compute $d_{B-R}$ for five field… ▽ More In this study, we extend the dust-independent Hatzidimitriou (1991) relation between cluster age and $d_{B-R}$ color difference between the red giant branch (RGB) and red clump to younger cluster ages. We perform membership analysis on fourteen galactic open clusters using Gaia DR3 astrometry, then compute the difference in color of the RGB and red clump $d_{B-R}$ using Gaia photometry. We also compute $d_{B-R}$ for five fields surrounding Small Magellanic Cloud (SMC) clusters. We find that the trend derived from older clusters does not extrapolate to younger ages and becomes double-valued. We confirm that $d_{B-R}$ is independent of metallicity. Current stellar evolutionary isochrones do not quantitatively reproduce the trend and furthermore predict an increased color gap with a decrease in metallicity that is not echoed in the data. Integrated light models based on current isochrones exaggerate the color change over the $-0.5 <$ [Fe/H] $< 0$ interval at the few-percent level. △ Less

Submitted 4 February, 2025; v1 submitted 28 February, 2024; originally announced February 2024.

Comments: 12 pages, 12 figures

Journal ref: AJ 169:81 (2025) 13pp

Evaluating Model Perception of Color Illusions in Photorealistic Scenes

Authors: Lingjun Mao, Zineng Tang, Alane Suhr

Abstract: We study the perception of color illusions by vision-language models. Color illusion, where a person's visual system perceives color differently from actual color, is well-studied in human vision. However, it remains underexplored whether vision-language models (VLMs), trained on large-scale human data, exhibit sim… ▽ More We study the perception of color illusions by vision-language models. Color illusion, where a person's visual system perceives color differently from actual color, is well-studied in human vision. However, it remains underexplored whether vision-language models (VLMs), trained on large-scale human data, exhibit similar perceptual biases when confronted with such color illusions. We propose an automated framework for generating color illusion images, resulting in RCID (Realistic Color Illusion Dataset), a dataset of 19,000 realistic illusion images. Our experiments show that all studied VLMs exhibit perceptual biases similar human vision. Finally, we train a model to distinguish both human perception and actual pixel differences. △ Less

Submitted 8 December, 2024; originally announced December 2024.

Inter-Camera Color Correction for Multispectral Imaging with Camera Arrays Using a Consensus Image

Authors: Katja Kossira, Jürgen Seiler, André Kaup

Abstract: …a consensus image as basis for calibration. This way, we managed to improve the PSNR values for the linear regression color correction algorithm by 1.15 dB and the improved color difference (iCID) values by 2.81. ▽ More This paper introduces a novel method for inter-camera color calibration for multispectral imaging with camera arrays using a consensus image. Capturing images using multispectral camera arrays has gained importance in medical, agricultural, and environmental processes. Due to fabrication differences, noise, or device altering, varying pixel sensitivities occur, influencing classification processes. Therefore, color calibration between the cameras is necessary. In existing methods, one of the camera images is chosen and considered as a reference, ignoring the color information of all other recordings. Our new approach does not just take one image as reference, but uses statistical information such as the location parameter to generate a consensus image as basis for calibration. This way, we managed to improve the PSNR values for the linear regression color correction algorithm by 1.15 dB and the improved color difference (iCID) values by 2.81. △ Less

Submitted 13 November, 2024; v1 submitted 30 October, 2024; originally announced October 2024.

The Lie algebraic structure of colored networks

Authors: Fahimeh Mokhtari, Jan Sanders

Abstract: …-dimensional vector fields with C colors (different functions describing different types of cells in the network) this Lie algebra $net_{C,N}$ is isomorphic to the semidirect sum of a semisimple part, consisting of two simple components $\mathfrak{sl}_C$ and $\mathfrak{sl}_B$, with $B=N-C$, which we write as a block-ma… ▽ More In the computation of the normal form of a colored network vector field, following the semigroup(oid) approach in [19], one would like to be able to say something about the structure of the Lie algebra of linear colored network vector fields. Unlike the purely abstract approach in [10], we describe here a concrete algorithm that gives us the Levi decomposition. If we apply this algorithm to a given subalgebra, it does put the elements in the subalgebra in the block form given by the Levi decomposition, but this need not be the Levi decomposition of the given subalgebra. We show that for $N$-dimensional vector fields with C colors (different functions describing different types of cells in the network) this Lie algebra $net_{C,N}$ is isomorphic to the semidirect sum of a semisimple part, consisting of two simple components $\mathfrak{sl}_C$ and $\mathfrak{sl}_B$, with $B=N-C$, which we write as a block-matrix and a solvable part, consisting of two elements representing the identity $C$ in $c\simeq glC$ and B in $b \simeq glB$, and an abelian algebra $a\simeq\mathfrak{Gr}(C,N)$, the Grassmannian, consisting of the $C$-dimensional subspaces of $\mathbb{R}^N$. The methods in this paper can be immediately applied to study the linear maps of colored networks. △ Less

Submitted 20 September, 2024; v1 submitted 23 September, 2021; originally announced September 2021.

Realistic and Efficient Face Swapping: A Unified Approach with Diffusion Models

Authors: Sanoojan Baliah, Qinliang Lin, Shengcai Liao, Xiaodan Liang, Muhammad Haris Khan

Abstract: Despite promising progress in face swapping task, realistic swapped images remain elusive, often marred by artifacts, particularly in scenarios involving high pose variation, color differences, and occlusion. To address these issues, we propose a novel approach that better harnesses diffusion models for face-swapping b… ▽ More Despite promising progress in face swapping task, realistic swapped images remain elusive, often marred by artifacts, particularly in scenarios involving high pose variation, color differences, and occlusion. To address these issues, we propose a novel approach that better harnesses diffusion models for face-swapping by making following core contributions. (a) We propose to re-frame the face-swapping task as a self-supervised, train-time inpainting problem, enhancing the identity transfer while blending with the target image. (b) We introduce a multi-step Denoising Diffusion Implicit Model (DDIM) sampling during training, reinforcing identity and perceptual similarities. (c) Third, we introduce CLIP feature disentanglement to extract pose, expression, and lighting information from the target image, improving fidelity. (d) Further, we introduce a mask shuffling technique during inpainting training, which allows us to create a so-called universal model for swapping, with an additional feature of head swapping. Ours can swap hair and even accessories, beyond traditional face swapping. Unlike prior works reliant on multiple off-the-shelf models, ours is a relatively unified approach and so it is resilient to errors in other off-the-shelf models. Extensive experiments on FFHQ and CelebA datasets validate the efficacy and robustness of our approach, showcasing high-fidelity, realistic face-swapping with minimal inference time. Our code is available at https://github.com/Sanoojan/REFace. △ Less

Submitted 11 September, 2024; originally announced September 2024.

Comments: Accepted as a conference paper at WACV 2025

Resolved UV and optical color gradients reveal environmental influence on galaxy evolution at redshift z$\sim$1.6

Authors: William J. Cramer, A. G. Noble, G. Rudnick, A. Pigarelli, G. Wilson, Y. M. Bahé, M. C. Cooper, R. Demarco, J. Matharu, T. B. Miller, A. Muzzin, J. Nantais, W. Sportsman, E. van Kampen, T. M. A. Webb, H. K. C. Yee

Abstract: …The presence of these observed differences, along with evidence from ancillary data from previous studies, strongly suggests that the environment drives these population-level color differences, by affecting the stellar populations and/or dust content. ▽ More The changes in colors across a galaxy are intimately connected to the galaxy's formation, growth, quenching history, and dust content. A particularly important epoch in the growth of galaxies is near $z \sim 2$ often referred to as `cosmic noon', where galaxies on average reach the peak of their star formation. We study a population of 125 cluster galaxies at $z \sim 1.6$ in three Hubble Space Telescope (HST) filters, F475W, F625W, and F160W, roughly corresponding to the rest-frame FUV, NUV, and r band, respectively. By comparing to a control sample of 200 field galaxies at similar redshift, we reveal clear, statistically significant differences in the overall spatially resolved colors and color gradients in galaxies across these two different environments. On average, cluster galaxies have redder UV colors in both the inner and outer regions bounded by $r_{\mathrm{50}}$, as well as an overall wider dispersion of outside-in color gradients. The presence of these observed differences, along with evidence from ancillary data from previous studies, strongly suggests that the environment drives these population-level color differences, by affecting the stellar populations and/or dust content. △ Less

Submitted 8 September, 2024; v1 submitted 10 April, 2024; originally announced April 2024.

Comments: Accepted for publication in ApJ

Multiscale Sliced Wasserstein Distances as Perceptual Color Difference Measures

Authors: Jiaqi He, Zhihua Wang, Leon Wang, Tsein-I Liu, Yuming Fang, Qilin Sun, Kede Ma

Abstract: Contemporary color difference (CD) measures for photographic images typically operate by comparing co-located pixels, patches in a ``perceptually uniform'' color space, or features in a learned latent space. Consequently, these measures inadequately capture the human color perception of misaligned image pairs,… ▽ More Contemporary color difference (CD) measures for photographic images typically operate by comparing co-located pixels, patches in a ``perceptually uniform'' color space, or features in a learned latent space. Consequently, these measures inadequately capture the human color perception of misaligned image pairs, which are prevalent in digital photography (e.g., the same scene captured by different smartphones). In this paper, we describe a perceptual CD measure based on the multiscale sliced Wasserstein distance, which facilitates efficient comparisons between non-local patches of similar color and structure. This aligns with the modern understanding of color perception, where color and structure are inextricably interdependent as a unitary process of perceptual organization. Meanwhile, our method is easy to implement and training-free. Experimental results indicate that our CD measure performs favorably in assessing CDs in photographic images, and consistently surpasses competing models in the presence of image misalignment. Additionally, we empirically verify that our measure functions as a metric in the mathematical sense, and show its promise as a loss function for image and video color transfer tasks. The code is available at https://github.com/real-hjq/MS-SWD. △ Less

Submitted 14 July, 2024; originally announced July 2024.

Comments: ECCV 2024

A Comprehensive Study of Multimodal Large Language Models for Image Quality Assessment

Authors: Tianhe Wu, Kede Ma, Jie Liang, Yujiu Yang, Lei Zhang

Abstract: …We assess three open-source and one closed-source MLLMs on several visual attributes of image quality (e.g., structural and textural distortions, geometric transformations, and color… ▽ More While Multimodal Large Language Models (MLLMs) have experienced significant advancement in visual understanding and reasoning, their potential to serve as powerful, flexible, interpretable, and text-driven models for Image Quality Assessment (IQA) remains largely unexplored. In this paper, we conduct a comprehensive and systematic study of prompting MLLMs for IQA. We first investigate nine prompting systems for MLLMs as the combinations of three standardized testing procedures in psychophysics (i.e., the single-stimulus, double-stimulus, and multiple-stimulus methods) and three popular prompting strategies in natural language processing (i.e., the standard, in-context, and chain-of-thought prompting). We then present a difficult sample selection procedure, taking into account sample diversity and uncertainty, to further challenge MLLMs equipped with the respective optimal prompting systems. We assess three open-source and one closed-source MLLMs on several visual attributes of image quality (e.g., structural and textural distortions, geometric transformations, and color differences) in both full-reference and no-reference scenarios. Experimental results show that only the closed-source GPT-4V provides a reasonable account for human perception of image quality, but is weak at discriminating fine-grained quality variations (e.g., color differences) and at comparing visual quality of multiple images, tasks humans can perform effortlessly. △ Less

Submitted 11 July, 2024; v1 submitted 16 March, 2024; originally announced March 2024.

Spin Parity of Spiral Galaxies IV -- Differential Reddening of Globular Cluster Systems of Nearby Spiral Galaxies

Authors: Masanori Iye, Masafumi Yagi

Abstract: …model to evaluate the visibility of the effect and its application to published CCD photometry on globular cluster systems of three spiral galaxies, M31, M33, and NGC253. The color difference of globular cluster systems due to differential reddening was confirmed for M31 and NGC253; however, the data for M33 were insuf… ▽ More The northwest side of the disk of M31 is known to be the near side because of the differential reddening of globular clusters found from their photographic photometry. This paper reports a simple geometric model to evaluate the visibility of the effect and its application to published CCD photometry on globular cluster systems of three spiral galaxies, M31, M33, and NGC253. The color difference of globular cluster systems due to differential reddening was confirmed for M31 and NGC253; however, the data for M33 were insufficient. The analysis reaffirms the currently adopted interpretation that the side on the minor axis of the galactic disk, where more conspicuous dust features and interstellar reddening are visible, is the nearer side to us and provides an additional basis for using spiral galaxies with identified spiral windings, S-wise or Z-wise, to study the large-scale spin distribution of galaxies in the universe. △ Less

Submitted 8 July, 2024; originally announced July 2024.

Comments: 8 pages, 11 figures, 4 tables

Artwork Protection Against Neural Style Transfer Using Locally Adaptive Adversarial Color Attack

Authors: Zhongliang Guo, Junhao Dong, Yifei Qian, Kaixuan Wang, Weiye Li, Ziheng Guo, Yuheng Wang, Yanli Li, Ognjen Arandjelović, Lei Fang

Abstract: …crucial in the context of artistic works. To comprehensively assess the color-mattered tasks, we propose the Adversarial Color Distance Metric (ACDM), designed to quantify the color difference of images pre- and post-manipulations. Experimental results confirm that attacking NST using LAACA results in visually inferior… ▽ More Neural style transfer (NST) generates new images by combining the style of one image with the content of another. However, unauthorized NST can exploit artwork, raising concerns about artists' rights and motivating the development of proactive protection methods. We propose Locally Adaptive Adversarial Color Attack (LAACA), empowering artists to protect their artwork from unauthorized style transfer by processing before public release. By delving into the intricacies of human visual perception and the role of different frequency components, our method strategically introduces frequency-adaptive perturbations in the image. These perturbations significantly degrade the generation quality of NST while maintaining an acceptable level of visual change in the original image, ensuring that potential infringers are discouraged from using the protected artworks, because of its bad NST generation quality. Additionally, existing metrics often overlook the importance of color fidelity in evaluating color-mattered tasks, such as the quality of NST-generated images, which is crucial in the context of artistic works. To comprehensively assess the color-mattered tasks, we propose the Adversarial Color Distance Metric (ACDM), designed to quantify the color difference of images pre- and post-manipulations. Experimental results confirm that attacking NST using LAACA results in visually inferior style transfer, and the ACDM can efficiently measure color-mattered tasks. By providing artists with a tool to safeguard their intellectual property, our work relieves the socio-technical challenges posed by the misuse of NST in the art community. △ Less

Submitted 5 July, 2024; v1 submitted 17 January, 2024; originally announced January 2024.

Comments: 9 pages, 5 figures, 4 tables