Projects
Color-Accurate Camera Capture with Multispectral Illumination and Multiple Exposures
Hongyun Gao(1), Rafał K. Mantiuk(1), and Graham D. Finlayson(2).
(1) University of Cambridge, UK (2) University of East Anglia, UK
Presented at Pacific Graphics 2024

To improve the color accuracy of a camera, we capture an object in multiple exposures (between 1 and 3), each time illuminating the object with a different light spectrum. The spectra are optimized in such a way that a linear combination of captured RGB values can be transformed into the CIE XYZ tristimulus values. In this example, the color differences are subtle but noticeable. When the Rubik’s cube is captured under a D65 illuminant and transformed to the standard color space (BT.709), orange is mapped to a bright reddish color. Our optimized illuminants can correctly reproduce the original colors of the Rubik’s cube. All colors in the paper are reproduced for the sRGB color space.
Abstract
Cameras cannot capture the same colors as those seen by the human eye because the eye and the cameras’ sensors differ in their spectral sensitivity. To obtain a plausible approximation of perceived colors, the camera’s Image Signal Processor (ISP) employs a color correction step. However, even advanced color correction methods cannot solve this underdetermined problem, and visible color inaccuracies are always present. Here, we explore an approach in which we can capture accurate colors with a regular camera by optimizing the spectral composition of the illuminant and capturing one or more exposures. We jointly optimize for the signal-to-noise ratio and for the color accuracy irrespective of the spectral composition of the scene. One or more images captured under controlled multispectral illuminants are then converted into a color-accurate image as seen under the standard illuminant of D65. Our optimization allows us to reduce the color error by 20–60% (in terms of CIEDE 2000), depending on the number of exposures and camera type. The method can be used in applications in which illumination can be controlled, and high colour accuracy is required, such as product photography or with a multispectral camera flash.
Optimized illuminants and modulated color matching functions

Top: Optimized illuminant(s) of IDS U3-3800CP-C-HQ for 1, 2 and 3 exposures. Bottom: The product of the optimized illuminant(s) and camera sensitivity transformed via the color-correction matrix vs. the product of D65 and CIE 1931 color matching functions. The closer the solid line to the dashed lines of color matching functions is, the more accurate the color is.
Color checker visualization

The visualization of 30 patches of the PMCC, captured with IDS U3-3800CP-C-HQ. For each color patch, the bottom part is the reference color as measured with the spectroradiometer. The top half is horizontally split into 3 regions — left: the color captured under the approximated D65; center: color captured under 1 optimized illuminant; right: color obtained after merging information from 3 exposures, each captured under a different illuminant. The results are reported for real-image captures and with the color-correction fine-tuning step.
Materials
- Paper:
Color-Accurate Camera Capture with Multispectral Illumination and Multiple Exposures.
Hongyun Gao, Rafał K. Mantiuk, Graham D. Finlayson.
In Pacific Graphics 2024
[DOI] [paper PDF] - Code [Github]