1. A computerized method comprising: computing a blur difference between a first and a second image of a three-dimensional scene, the first image acquired through a camera lens focused at a first picture number and the second image acquired through the camera lens focused at a second picture number, wherein the first and second picture numbers represent different focus distances of the camera lens; retrieving a blur difference curve from one of a plurality of stored blur difference curves, wherein each of the plurality of stored blur difference curves is associated with a different picture number; and predicting a third picture number based on the computed blur difference, wherein the third picture number is subsequently used to autofocus the camera lens on the three dimensional scene and the predicting is further based on the blur difference curve associated with the first picture number.