I need to convert each slide in a powerpoint presentation to a PNG with the command line. I have tried to convert it to a PDF then to individual PNGs but the images haven't exported properly. These images are graphs originally from Microsoft Excel. If I export it as a PNG from within LibreOffice the graph exports properly, but not if I convert it to a PDF first using unoconv or the export tool in LibreOffice Impress. Here is a couple of examples, in impress: As you can see the image works. But when this is exported to PDF it looks like:

So whats going wrong? As if its directly exported to PNG in libreoffice it looks exactly as is in the presentation. Also if I convert it to the LibreOffice file format this also happens.