You can export diagrams as PNG/JPEG/EMF/SVG by using the command line in Astah. (EMF/SVG export is available in Astah Professional edition only.)
Each diagram will be stored under the packages which will be automatically created where the diagrams belong to accordingly. See the tree structure of this .asta file in the right figure, for example, an image of Activity Diagram will be exported under the [Activity] folder.
You can export all the diagrams at once or choose which diagram types you want to export by using the following options.
all: All of the diagrams
cl: Class Diagram
uc: UseCase Diagram…etc
png, jpg, emf or svg
Please refer to the Command Line Tool User Guide (CommandRunner.html file in the Astah Installation folder) for all the options.