What is the meaning of EP-Format for saving pictures?
If you try to save a picture from any graphical window of ESA, you will find among others choice of formats, where you can find also: EP3, EP2, EPD. Which ones are available, depends on a kind of a window.
To EP2 it is possible to export contents of 2D window (eg. cross-sections database manager).
EP3 can be used for export from a 3D window (normal ESA window, gallery etc.).
EPD is a window of a paperspace. All formats can be inserted to a paperspace with keeping the original sense, that's a main reason of existence of those formats. (eg. EP3 works as fully 3D on paperspace, including lateral change of view direction, hidden lines removal etc.)