Standard Android development is done in Eclipse, and creates four different sized images (LDPI, MDPI, HDPI, and XDPI) for different pixels densities. What you are observing is that the Desire has a lower DPI than the S4. Processing lacks the ability to load different resources like Eclipse can, however, you can achieve a similar effect by determining the pixel density of the device, loading the largest size image, and scaling it down accordingly (to prevent loss of quality).

You can get the screen's DPI by using Android's DisplayMetrics class. Check out this post on StackOverflow. You'll need to import DisplayMetrics ( android.util.DisplayMetrics).

Further reading on supporting multiple screens: Supporting Multiple Screens