1. A color degradation compensation method for an image, comprising: capturing two images by only an image capturing device, wherein the two images have an overlapped area; constructing, by a processor, a semi-Gaussian model, wherein the semi-Gaussian model is represent as: Gau ⁡ ( X , σ ) = A ⁢ ⁢ exp ⁡ ( -  X - C  2 2 ⁢ σ 2 ) ; where X is a coordinate value of any points in the overlapped area; A is a maximum color value, referred to a white color; C is a coordinate value of the center point of the image; and ∥X−C∥ is a distance between X and C; applying, by a processor, the semi-Gaussian model to the two images, wherein a correlation between the two images is represented as: ∏ i = 1 N ⁢ O 1 ⁢ ⁢ i R O 2 ⁢ ⁢ i R = ⁢ ∏ i = 1 N ⁢ Gau ⁡ ( X 1 ⁢ ⁢ i , σ R ) Gau ⁡ ( X 2 ⁢ ⁢ i , σ R ) ; and = ⁢ exp ( - ∑ i = 1 N ⁢  X 1 ⁢ ⁢ i - C 1  2 - ∑ i = 1 N ⁢  X 2 ⁢ ⁢ i - C 2  2 2 ⁢ σ R 2 ) ; where C 1 and C 2 are the coordinate values of center points of the two images respectively: X 1i and X 2i are coordinate values of any points of the same position (overlapped points) corresponded to the two images respectively in the overlapped area S; O 1i and O 2i are the color values of the points X 1i and X 2i on the two images respectively; and O 1i R and O 2i R are color values of red color portion of O 1i and O 2i respectively; calculating, by a processor, a degradation standard division of a red color portion, a degradation standard division of a green color portion and a degradation standard division of a blue color portion respectively, wherein the degradation standard division of each color portion is represented as: σ R = ⁢ - ∑ i = 1 N ⁢  X 1 ⁢ ⁢ i - C 1  2 + ∑ i = 1 N ⁢  X 2 ⁢ ⁢ i - C 2  2 2 · log ⁡ ( ∏ i = 1 N ⁢ O 1 ⁢ ⁢ i R O 2 ⁢ ⁢ i R ) ; σ G = ⁢ - ∑ i = 1 N ⁢  X 1 ⁢ ⁢ i - C 1  2 + ∑ i = 1 N ⁢  X 2 ⁢ ⁢ i - C 2  2 2 · log ⁡ ( ∏ i = 1 N ⁢ O 1 ⁢ ⁢ i G O 2 ⁢ ⁢ i G ) ; and σ B = ⁢ - ∑ i = 1 N ⁢  X 1 ⁢ ⁢ i - C 1  2 + ∑ i = 1 N ⁢  X 2 ⁢ ⁢ i - C 2  2 2 · log ⁡ ( ∏ i = 1 N ⁢ O 1 ⁢ ⁢ i B O 2 ⁢ ⁢ i B ) ; where O 1i R , O 1i G and O 1i B are color values of the red color portion, the green color portion and the blue color portion of O 1i respectively; O 2i R , O 2i G and O 2i B are color values of the red color portion, the green color portion and the blue color portion of O 2i respectively; σ R ,σ G and σ B are the degradation standard divisions of each color; eliminating, by a processor, color degradation of all points on the overlapped area and a non-overlapped area of each of the two images by applying σ R , σ G and σ B to the semi-Gaussian model again, wherein compensated color values is generated by the following relationship: O ^ i ⁢ ⁢ j R = ⁢ O i ⁢ ⁢ j R / exp ⁡ ( -  Y i ⁢ ⁢ j - C i  2 2 ⁢ ( σ R ) 2 ) ; O ^ i ⁢ ⁢ j G = ⁢ O i ⁢ ⁢ j G / exp ⁡ ( -  Y i ⁢ ⁢ j - C i  2 2 ⁢ ( σ G ) 2 ) ; and O ^ i ⁢ ⁢ j B = ⁢ O i ⁢ ⁢ j B / exp ⁡ ( -  Y i ⁢ ⁢ j - C i  2 2 ⁢ ( σ B ) 2 ) ; where O ij R , O ij G and O ij B are color values of the red color portion, the green color portion and the blue color portion of the point Y ij on the image I I (before calibration); Ô ij R , Ô ij G and Ô ij B are compensated color values of the red color portion, the green color portion and the blue color portion calibrated from O ij R , O ij G and O ij B in accordance with σ R , σ G and σ B (after calibration); j is any points on the image I i (including the overlapped area and the non-overlapped area); and N is a number of all points in the overlapped area S of the two images I 1 and I 2 ; and compositing Ô ij R , Ô ij G , and Ô ij B and obtaining two compensated images I 1 and I 2 .