Pictures in PDF have black background

I am trying to add a couple ,png pictures to a PDF generated in a web 2.0 app. In one picture the background is white but appears black in the PDF. In the other the background is light gray with some black designs on it with a big white area in the middle. There are some text and graphics in the white block. Everything in the PDF is black except the white block in the center. I dragged the ,png files into the IDE and referred to them by the names assigned.

Have you tried resaving the .png files so that they are not transparent?

Thank you. That did it.