Convert all pfg pages to png with unoconv

How can I convert all the pages of a pdf document to jpg/png ? This line below converts only one page. Any ideas ?

C:\Program Files (x86)\LibreOffice 4\program>python.exe unoconv -f jpg d:\class.pdf

This type of conversion is best done using an external tool / method like those indicated in this StackOverflow thread or this SuperUser thread.