From what I found, Samsung galaxy s2 has 480x800 resolution and s3 has 1280x720 resolution. So I believe I should ask my graphics designer to provide me hdpi graphics that contain 480x800 background images and to implement same background image in galaxy s3 mobile. Can I use image of size 1280x720 and put it in xhdpi folder so that it can work on s3.
The background image is something which covers whole available area for mobile app. so am I right in this approach ??
You should read Supporting multiple screens. You must define dpi on your emulator. 240 is hdpi, 160 is mdpi and below that are usually ldpi.
Extract from Android Developer Guide link above:
320dp: a typical phone screen (240x320 ldpi, 320x480 mdpi, 480x800 hdpi, etc).
480dp: a tweener tablet like the Streak (480x800 mdpi).
600dp: a 7” tablet (600x1024 mdpi).
720dp: a 10” tablet (720x1280 mdpi, 800x1280 mdpi, etc).