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Framework for Illumination Estimation and Segmentation in Multi- Illuminant Scenes

Color constancy is an important part of the human visual system, as it allows us to perceive the colors of objects invariant to the color of the illumination that is illuminating them. Modern digital cameras have to be able to recreate this property computationally. However, this is not a simple task, as the response of each pixel on the camera sensor is the product of the combination of spectral characteristics of the illumination, object, and the sensor. Therefore, many assumptions have to be made to approximately solve this problem. One common procedure was to assume only one global source of illumination. However, this assumption is often broken in real-world scenes. Thus, multi-illuminant estimation and segmentation is still a mostly unsolved problem. In this paper, we address this problem by proposing a novel framework capable of estimating per-pixel illumination of any scene with two sources of illumination. The framework consists of a deep-learning model capable of segmenting an image into regions with uniform illumination and models capable of single- illuminant estimation. First, a global estimation of the illumination is produced, and is used as input to the segmentation model along with the original image, which segments the image into regions where that illuminant is dominant. The output of the segmentation is used to mask the input and the masked images are given to the estimation models, which produce the final estimation of the illuminations. The models comprising the framework are first trained separately, then combined and fine-tuned jointly. This allows us to utilize well researched single-illuminant estimation models in a multi-illuminant scenario. We show that such an approach improves both segmentation and estimation capabilities. We tested different configurations of the proposed framework against other single-and multi-illuminant estimation and segmentation models on a large dataset of multi-illuminant images. On this dataset, the proposed framework achieves the best results, in both multi-illumination estimation and segmentation problems. Furthermore, generalization properties of the framework were tested on often used single-illuminant datasets. There, it achieved comparable performance with state- of-the-art single-illumination models, even though it was trained only on the multi-illuminant images.

Color Constancy ; Segmentation ; Multi-Illuminant ; Illumination Estimation ; Deep Learning ; Framework

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