1. A method for extracting salient object from stereoscopic video comprising the steps of: (A) dividing regions based on similarity of color and distance between pixels in a left-eye image and a right-eye image from an input stereoscopic image; (B) creating a disparity map of divided regions based on a disparity obtained from a pixel difference of the left-eye image and the right-eye image; (C) calculating a contrast-based saliency by comparing the regions in the step (A) and the divided regions of the disparity map in the step (B); (D) calculating a prior-knowledge-based saliency based on a prior-knowledge for the regions in the step (A) and the divided regions of the disparity map in (B) step, the prior-knowledge being comprised of features of the image being visually distinct; and (E) extracting salient regions of the image based on the contrast-based saliency and the prior-knowledge-based saliency, wherein in the step of calculating (C), the contrast-based saliency is determined based on color difference and disparity of the divided regions, wherein the contrast-based saliency is calculated by reliability of the disparity dependent upon quality of the disparity, wherein the reliability of the disparity is calculated by a curvature of cost function for a disparity calculation, and wherein the curvature is C f (x)=−2c(x,d)+c(x,d−1)+c(x,d+1) wherein c ⁡ ( x , d ) = 1  W ⁡ ( x )  ⁢ ∑ x ∈ N ⁡ ( x ) ⁢ ⅇ ⁡ ( x , d ) , ⅇ ⁡ ( x , d ) = ∑ ch ∈ ( R , G , B ) ⁢  I ch L ⁡ ( x ) - I ch R ⁡ ( x - d ) , d is a disparity, W(x) is a local window where a center is x, I ch L and I ch R are a left image and a right image normalized in a channel ch, respectively.