Embodiments for providing a strain image in an ultrasound system are disclosed. In one embodiment, a processing unit sets windows on a pre-compression frame and a post-compression frame, and performs a correlation operation between the first and second frames within the windows to compute displacements for a third frame, wherein the processing unit selects at least one of previously set windows at an (N−i)th row by referring to current windows positioned at a Nth row in an axial direction, computes an initial displacement based on displacements corresponding to the selected at least one of windows, and determines a range for moving the current window on the second frame in the axial direction based on the computed initial displacement.
