These options affect the standalone image viewer.

Viewer title bar
Custom title bar

You can use several special "tokens" in the title string to insert various pieces of information:

%Pfull path of the currently viewed image
%Nname of the current displayed image
%Rdrive root of the current image
%Edisplays * if the image's metadata has been modified and not saved
%Icurrent image's index (number) in the list of images
%Ototal number of images in the list
%Wwidth of the current image
%Hheight of the current image
%Ddepth of the current image (bits per pixel)
%Mcurrent image's dimensions
%Sfile size on disk
%Ffolder name
%Ccollection name if current image is marked
%Lany labels assigned to the current image
%Tcomplete original title (useful for simply adding a prefix or suffix to the title)
%%insert a literal % character
%!hide empty blocks within %!…%! (see below)

The %! code is special in that it should be used in pairs around the things you want to hide. They will be hidden if all tokens within the block expand to empty values.

Consider %!Dimensions: %W x %H%!, for example: If %W and %H (width and height) are unavailable (e.g. because the viewer isn't displaying an image) then this will output nothing at all instead of a meaningless "Dimensions: 0 x 0".