Okay folks, want the only hint you need to implement it? Obviously, we are using renderscript, not the alpha android.support.v8 lib if below 11.
Okay, first do not do the full background image. 2nd, do not downscale it. 3d, parallel it as in compute the blur one line at a time. Detect the scroll and than start the blur operation and set it up to do so many lines per iteration and than change background per iteration.
Now, smile as you have the yahoo weather android app blur effect on android.