There is another way that you can try .
The api
CreateFile can read an existing file to the memory .So , if you know more about the foamat of png and bitmap , you can do the transform by yourself .In this case ,just like you implements the function that include in the GDI+ DLLs .This is a difficult way ,but you can learn more about the picture format and you will use it effective. By the way ,windows just provide the Bitmap struct ,and not provide the struct of png . So ,you must define your png's struct by yourself .Good luck!!!