title: Setting DPI for PNG files
body: <p>I have a bunch of diagrams created using a Java diagramming tool that I wrote - they are mostly black and white diagrams, with the blocks in aqua, and occasional other colours.  They are currently being saved as JPG files, and I want to insert them into a book that I am preparing for Print On Demand. </p>
  
  <p>The book is an OpenOffice ODT file, which will later be converted to a PDF.</p>
  
  <p>Currently I use JPG files, but the print facility they use requires 300 DPI, so I modified my diagramming tool to set the xDensity and yDensity to 300, and resUnits to 1, using getAsTree(), and then expand the diagram by a factor of 3 (300/96).  IMO the result looks pretty good!</p>
  
  <p>Unfortunately, someone on another forum pointed out that line diagrams are "fuzzed" on JPG files, so suggested that I change over to PNG, or possibly BMP files, both of which ODT files allow to be inserted.</p>
  
  <p>My problem is that BMPs don't seem to have a DPI, and PNGMetadata doesn't seem to support getAsTree().  Can someone point me in the right direction?  Thanks.</p>