# Beyond Fixed Luminance: Towards Panchromatic and Orthochromatic Image Colorization

Source: [Beyond Fixed Luminance: Towards Panchromatic and Orthochromatic Image Colorization](<https://www.sota2.com/research/paper/6a7bfe514b236a9bba1a1b3c>)

Collection index: [llms.txt](<https://www.sota2.com/research/llms.txt>)

Data updated: 2026-08-14T05:00:13.408Z

Authors: Swarnim Maheshwari, Syed Imam Ali, Vineeth N. Balasubramanian

Published: 2026-08-11T11:12:24.000Z

## Abstract

Most image colorization systems operate in $Lab$ space by predicting chroma ($ab$) while preserving an input-derived luminance channel ($L$). While effective on standard benchmarks, this fixed-luminance design restricts brightness changes and becomes unreliable when grayscale formation deviates from natural-image luminance, as in historical orthochromatic photography. We propose a luminance-agnostic colorization framework that formulates colorization as full-RGB image editing using a foundation image-editing model. To bridge modern panchromatic and historical orthochromatic conditions, we introduce a mixed grayscale objective that trains the model under both standard luminance grayscale and a red-insensitive grayscale formation. Experiments on COCO, ImageNet, and a multi-instance benchmark show that our method is competitive on standard grayscale inputs and substantially more robust under orthochromatic inputs, with qualitative comparisons and a human study indicating fewer visible color artifacts.

## Recorded benchmark results

A research result applies to its stated dataset, split, metric and evaluation configuration. Compare like-for-like settings, preserve the metric's unit and direction, and distinguish paper-reported results from independent reproduction. The best result recorded here is not a claim of exhaustive, current global coverage.

## Original sources and implementation

[Original paper](<https://arxiv.org/abs/2608.10798>)

[PDF](<https://arxiv.org/pdf/2608.10798.pdf>)