“…Its expression is as follows: where Ω x , y represent a spatial neighborhood pixel window which the size centered on ( x , y ) is (2 N + 1) × (2 N + 1), the larger the N , the better the smoothing effect. v ( x , y ) represents the center pixel value of Ω x , y , and u ( i , j ) represents the pixel value at ( i , j ) in the template; w s ( i , j ) is the spatial proximity factor; w r ( i , j ) is the gray similarity factor, w ( i , j ) = w s ( i , j ) × w r ( i , j ), which is the weight coefficient; σ s and σ r (Zhang et al, 2014), respectively control the attenuation degree of the weight factor in the spatial temporal progress and gray similarity. When σ s increases, more pixels participate in the weighting, and the image becomes blurred.…”