1. An ultrasound system, comprising: an ultrasound data acquisition unit configured to transmit and receive ultrasound signals to and from a target object based on a plurality of steering angles to thereby output a plurality of ultrasound data for obtaining a plurality of ultrasound images corresponding to the steering angles; and a processing unit in communication with the ultrasound data acquisition unit, the processing unit being configured to form the ultrasound images based on the ultrasound data, decompose each of the ultrasound images into a low pass image having a low frequency component and a high pass image having a high frequency component, perform a blending process for removing a seam artifact upon the low pass image and the high pass image corresponding to each of the ultrasound images, form a plurality of restoration images by composing the blending-processed low and high pass images corresponding to each of the ultrasound images, and form an ultrasound spatial compound image based on the restoration images, wherein the processing unit is configured to perform the blending process upon the low pass image or the high pass image of one of the plurality of ultrasound images with the low pass image or the high pass image, respectively, of another one of the plurality of ultrasound images.