1. An ultrasonic imaging method comprising: sequentially emitting by each transducer group of respective regions, into which a plurality of transducers of an ultrasonic probe are divided, focused ultrasonic pulses to a same focal point of an object; sequentially acquiring, by each transducer group, ultrasonic echo signals reflected from the same focal point of the object in correspondence to the sequentially emitted ultrasonic pulses; calculating, via a processor of an ultrasound apparatus, a normal vector of a surface of the object using emission directions of the focused ultrasonic pulses emitted by at least three of the transducer groups and intensities of the acquired ultrasonic echo signals in correspondence to the focused ultrasonic pulses emitted by the at least three of the transducer groups; calculating, via the processor, an attenuation rate of the acquired ultrasonic echo signals using the calculated normal vector and the emission directions of the focused ultrasonic pulses emitted by the at least three of the transducer groups, and correcting the acquired ultrasonic echo signals based on the attenuation rate; beamforming the ultrasonic echo signals, an attenuation of which has been corrected, into ultrasonic image signals; and outputting, on a display, the ultrasonic image signals as an ultrasonic image.