AgX is shorthand for silver based photo, Silver halide - Wikipedia, and here it more specifically relates to various algorithms seeking to emulate the behavior of film in the way it reacts to exposure (like what has been the basis for e.g. filmic modules).
Currently there are two projects going on her with AgX relevance:
kofa’s test development of a module implementing in darktable an algorithm used in Blender:
(There is also some kind of AgX-implementation in ART)
Then there is another project where one does a complete simulation of all the chemistry/physics in film based photography / image processing.
EDIT: Where in Norway is the picture taken?