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README.md
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---
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language:
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- en
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license: mit
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library_name: pytorch
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pipeline_tag: image-to-image
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tags:
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# Multinex: Lightweight Low-Light Image Enhancement via Multi-prior Retinex
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**Multinex** is a lightweight **low-light image enhancement
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Multinex
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- a **Retinex-guided residual enhancement formulation**
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- **analytic luminance and reflectance prior stacks**
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- a **dual-branch lightweight fusion network**
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This design allows the model to achieve strong perceptual enhancement quality and competitive paired-image restoration performance at a tiny parameter budget, including a lightweight version around **45K parameters** and an even smaller nano variant around **0.7K parameters**. The paper reports strong results on both enhancement and downstream detection benchmarks.
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**Keywords:** low-light image enhancement, LLIE, Retinex, image restoration, lightweight neural network, edge deployment, exposure correction, color correction, perceptual image enhancement, real-time enhancement.
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## Model Description
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Many low-light
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- use large neural networks that are hard to deploy on-device, or
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- operate in a single color space where illumination and color remain partially entangled.
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Multinex addresses this with a structured and lightweight design. Instead of learning a full reconstruction in a standard Retinex manner, it predicts an **enhancement delta** added to the input image. The correction is factorized into:
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- a **luminance correction**
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- a **reflectance correction**
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- mobile or embedded deployment
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- lightweight computer vision pipelines
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- preprocessing for downstream tasks such as object detection in dark scenes
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## Why Multinex?
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Multinex is useful when you
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### Main advantages
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- **Lightweight**:
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##
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Multinex
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\hat{\mathbf{I}} = \mathbf{I} + \Delta_{\mathbf{I}} = \mathbf{I} + \Delta_L \odot \Delta_R
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\]
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- \(\Delta_L\) is the learned luminance correction
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- \(\Delta_R\) is the learned reflectance correction
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- **Luminance stack** for brightness-related structure
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- **Reflectance stack** for color and chromatic structure
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These stacks are processed by lightweight fusion modules to produce the correction terms.
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## Prior Stacks
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A key
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### Luminance guidance stack
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- Rec.709 luminance
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- max-based luminance
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- lightness-based luminance
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- L2-based luminance
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### Reflectance guidance stack
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- \(C_b, C_r\)
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- normalized chromaticities \(r, g\)
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- saturation \(S\)
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## Intended Uses
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### Direct use
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- Enhance dark photos
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- Improve brightness and color visibility
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### Downstream use
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- Machine
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- Low-light object detection
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- Surveillance and nighttime
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- Embedded
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- Mobile photography enhancement
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- Robotics
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## Training Data
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- **LOL-v1**
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- **LOL-v2-real**
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- **LOL-v2-syn**
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- **NPE**
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- **ExDark** for downstream detection evaluation
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Please
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## Performance
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The paper reports that Multinex:
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- outperforms
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- achieves strong no-reference perceptual
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- remains competitive
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- improves downstream object detection performance in low-light
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### Example
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For the lightweight Multinex model, the paper reports:
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| Dataset | PSNR | SSIM | LPIPS |
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| LOL-v2-real | 23.04 | 0.860 | 0.178 |
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| LOL-v2-syn | 25.04 | 0.930 | 0.068 |
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### Example
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| Metric | Mean |
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| NIQE ↓ | 3.64 |
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| BRISQUE ↓ | 15.89 |
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### Efficiency
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| Variant | Parameters | GFLOPs |
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|---|---:|---:|
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| Multinex | 0.0447M | 2.50 |
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| Multinex-Nano | 0.0007M | very low |
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---
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language:
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- en
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library_name: pytorch
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pipeline_tag: image-to-image
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tags:
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# Multinex: Lightweight Low-Light Image Enhancement via Multi-prior Retinex
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**Multinex** is a lightweight model for **low-light image enhancement**. It is designed to brighten dark images, recover clearer colors, and improve visible detail while staying very small and efficient.
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Multinex is built around a simple idea: instead of relying only on raw RGB input, it uses multiple useful image cues related to brightness and color, then combines them through a compact network. This helps it perform strongly even at a very small model size.
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## Model Description
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Many low-light enhancement methods are either large and expensive to run, or they struggle to separate brightness changes from color correction cleanly.
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Multinex addresses this with a lightweight and structured design. It uses:
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- a brightness-oriented branch
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- a color-oriented branch
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- compact fusion modules
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- carefully chosen analytic image priors
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These priors give the model a stronger starting point, so it does not need to learn everything from scratch.
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## Why Multinex?
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Multinex is useful when you want:
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- strong low-light enhancement
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- a small and efficient model
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- better brightness and color recovery
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- a method suitable for edge or real-time use
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- a practical preprocessing step for downstream vision tasks
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### Main advantages
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- **Lightweight**: very small compared to many recent methods
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- **Efficient**: suitable for resource-constrained settings
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- **Structured**: uses separate cues for brightness and color
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- **Practical**: useful both for visual enhancement and downstream tasks
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- **Robust**: performs well across both reference and no-reference benchmarks
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## How It Works
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Multinex takes a dark RGB image and improves it using two types of guidance:
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- **luminance guidance**, which helps with brightness
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- **reflectance guidance**, which helps with color and appearance
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These two forms of guidance are processed by a lightweight network and combined into the final enhanced image.
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In simple terms, Multinex tries to answer two questions:
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- how should this image be brightened?
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- how should its colors and details be corrected?
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By handling these separately, the model can enhance low-light images more effectively.
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## Prior Stacks
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A key part of Multinex is its use of **prior stacks**.
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### Luminance guidance stack
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This stack provides different views of image brightness. It helps the model understand where the image is dark, how light is distributed, and how brightness should be adjusted.
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### Reflectance guidance stack
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This stack provides different views of image color and chromatic structure. It helps the model better recover color, preserve regions, and reduce unwanted artifacts.
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Together, these stacks give the model a richer and more stable representation of the image.
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## Intended Uses
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### Direct use
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- Enhance dark photos
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- Improve brightness and color visibility
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- Recover clearer low-light images
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- Preprocess images before other vision tasks
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### Downstream use
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- Machine vision
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- Low-light object detection
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- Surveillance and nighttime imaging
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- Embedded and edge systems
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- Mobile photography enhancement
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- Robotics in dim environments
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## Training and Evaluation Data
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Multinex is evaluated on common low-light image enhancement benchmarks, including:
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- **LOL-v1**
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- **LOL-v2-real**
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- **LOL-v2-syn**
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- **NPE**
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- **ExDark** for downstream detection evaluation
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Please refer to the paper and code for exact training details and evaluation settings.
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## Performance
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The paper reports that Multinex:
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- outperforms earlier lightweight and micro models in several settings
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- achieves strong no-reference perceptual quality
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- remains competitive with much larger methods
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- improves downstream object detection performance in low-light scenes
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### Example paired restoration results
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| Dataset | PSNR | SSIM | LPIPS |
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|---|---:|---:|---:|
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| LOL-v2-real | 23.04 | 0.860 | 0.178 |
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| LOL-v2-syn | 25.04 | 0.930 | 0.068 |
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### Example no-reference results
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| Metric | Mean |
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| NIQE ↓ | 3.64 |
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| BRISQUE ↓ | 15.89 |
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### Efficiency
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| Variant | Parameters | GFLOPs |
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| Multinex | 0.0447M | 2.50 |
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| Multinex-Nano | 0.0007M | very low |
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## Citation
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If you use Multinex in your work, please cite the paper.
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```bibtex
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@inproceedings{multinex2026,
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title = {Multinex: Lightweight Low-light Image Enhancement via Multi-prior Retinex},
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author = {Alexandru Brateanu and Tingting Mu and Codruta O. Ancuti and Cosmin Ancuti},
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booktitle = {Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR)},
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year = {2026}
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}
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