You don't really need a journal for this as it is a built in command. Use File, Export, [PNG, JPEG, GIF, TIFF, BMP].
You can put the UI into customize mode and drag the command (hold down <Ctrl> to make a copy) to add it to any ribbon bar or menu that you want.
The dialog includes a browse button for selecting the file name and a toggle to use a white background.
Have a look at C:\Program Files\Siemens\NX 11.0\UGOPEN\SampleNXOpenApplications\.NET\SnagImage