I am designing a background image in a Photoshop for 4 different types of handset ( xlarge screens are at least 960dp x 720dp, large screens are at least 640dp x 480dp, normal screens are at least 470dp x 320dp, small screens are at least 426dp x 320dp) according to (http://developer.android.com/guide/practices/screens_support.html).
Now my question is what is the good practice to start with (i.e. the biggest PSD file resolution and DPI before downsizing to specific those images) and what are the 4 sizes (resolution and dpi) for final output?