Return representation of last image as an hexadecimal-encoded string.
Input image must have values that are integers in [0,255].
G'MIC - GREYC's Magic for Image Computing: A Full-Featured Open-Source Framework for Image Processing
G'MIC is an open-source software distributed under the
CeCILL free software licenses (LGPL-like and/or GPL-compatible).
Copyrights (C) Since July 2008,
David Tschumperlé - GREYC UMR CNRS 6072, Image Team.