1. A method for processing a light-field image, comprising: acquiring a light-field image; acquiring an occlusion tag function for each of a plurality of unit images in the light-field image, and determining a cost function for offset estimation of each unit image according to intensity change information and gradient change information for each unit image in the light-field image and the occlusion tag function of each unit image; acquiring an offset of each unit image in the light-field image using the cost function; and reconstructing a high-resolution light field using the offset of each unit image, wherein the determining a cost function for offset estimation comprises: determining a cost function Γ intensity (u 1 ,v 1 ) for offset estimation of each unit image using a formula (6): ⁢ Γ intensity ⁡ ( u 1 , v 1 ) = Γ intensity ′ ⁡ ( u 1 , v 1 ) + β ⁢ ⁢ Γ smooth ⁡ ( u 1 , v 1 ) ⁢ ⁢ Γ intensity ′ ⁡ ( u 1 , v 1 ) = ∑ ( x , y ) ∈ χ ⁢ { ∑ k = 1 n 2 ⁢ f k ⁡ ( x , y ) ⁢ Φ ⁢ {  i k ⁡ [ x + u k ⁡ ( x , y ) , y + v k ⁡ ( x , y ) ] - i 1 ⁡ ( x , y )  } 2 + α ⁢  ∇ i k ⁡ [ x + u k ⁡ ( x , y ) , y + v k ⁡ ( x , y ) ] - ∇ i 1 ⁡ ( x , y )  2 } } , ⁢ ⁢ wherein , ⁢ ⁢ Γ smooth ⁡ ( u 1 , v 1 ) = ∑ ( x , y ) ∈ χ ⁢ Φ ⁡ [  ∇ u 1 ⁡ ( x , y )  2 +  ∇ v 1 ⁡ ( x , y )  2 ] , ( 6 ) χ is a pixel coordinate set of each unit image, Φ( ) is a concave function for acquiring robustness, ∇ is a gradient function, Γ intensity ′(u 1 ,v 1 ) is a cost subfunction for offset estimation of each unit image, Γ smooth (u 1 ,v 1 ) is a smoothing item of the cost function for offset estimation of each unit image, and β is an adjustment coefficient of the smoothing item.