Like RenderWindow.SaveRenderImageAs(string,Guid,bool), but with Guid set to Guid.Empty.
|SaveRenderImageAs(String, Guid, Boolean)|
Save current RenderWindow contents as an image file with the given name. The filetype will be determine. Pass in render engine Guid if an engine implements saving to a format that is not supported by Rhino. Guid.Empty if there is no need for that.