RGB 3D Visualization (Remove White Background)

The fonction allow to remove any white/gray component from a RGB Volume and only keep the color contrast from it. There is an option to increase dark value so that the function keeps the color contrast but, as the color is darker originally, it results in a brighter (more white) volume after processing. This later choice has a more natural final "look". The user can select also to keep only the color difference. The resulting volume have a "fluorescent look" and is more easily manageable with surfaces and spots functions.