I've been working on this project during the last 15 years.

G'MIC is an open-source framework for digital image processing, distributed under the CeCILL free software licenses (LGPL-like and/or GPL-compatible).

It provides several user interfaces to convert / process / visualize generic image datasets, ranging from 1D scalar signals to 3D+t sequences of multi-spectral volumetric images, hence including 2D color images.