The soul is dyed the color of its thoughts. Think only on those things that are in line with your principles and can bear the light of day. The content of your character is your choice. Day by day, what you do is who you become. Your integrity is your destiny - it is the light that guides your way. - Heraclitus
If all you're doing is displaying the image on the screen, then changing the DPI doesn't make much sense, because screens have a fixed DPI. Are you talking about scaling the image? Then you can use the java.awt.Image.getScaledInstance() method.