1. An ultrasound system, comprising: an ultrasound data acquisition unit configured to transmit and receive ultrasound signals to and from a target object to thereby acquire ultrasound data corresponding to a plurality of frames; a volume data former configured to generate volume data corresponding to the plurality of frames based on the ultrasound data, the volume data including a plurality of voxels; and a processing unit configured to detect edges from frames included in the volume data, detect voxels of the edges connected to each other, label upon the detected edges, group the labeled voxels into a plurality of voxel groups, determine a voxel group based on the number of voxels among the voxel groups, set the determined voxel group as a region of interest (ROI), set a first parameter including a parameter associated with surface reflection and a second parameter for processing skin tone based on a user input, and perform surface rendering upon voxels within the ROI by using the first parameter and the second parameter to thereby form a 3-dimensional ultrasound image.