1. A noise filter, comprising: a first filter performing as an edge detector to detect a high-frequency component area of an image; a second filter performing a noise filtering function for remaining areas of the image while conserving the high-frequency component area detected by the first filter; and a function processor that controls operations of the first filter and the second filter, wherein the second filter is defined by an equation of BF ⁡ [ I ] p = ⁢ 1 W p ⁢ ∑ q ∈ S ⁢ G σ s ⁡ (  p - q  ) ⁢ G σ r ⁡ ( I p - I q ) ⁢ I q ≈ ⁢ ∑ q ∈ S ⁢ G S ⁢ G σ r ⁡ ( I p - I q ) ⁢ I q ∑ q ∈ S ⁢ G S ⁢ G σ r ⁡ ( I p - I q ) = ⁢ ∑ q ∈ S ⁢ ⅇ - ( I q - I p ) 2 2 ⁢ σ r 2 ⁢ G S ⁢ I q ∑ q ∈ S ⁢ ⅇ - ( I q - I p ) 2 2 ⁢ σ r 2 ⁢ G S , where G σ s (∥p−q∥)≈G s represents a matrix function of ( 1 / 16 ) × [ 6 8 9 10 9 8 6 8 10 12 13 12 10 8 9 12 14 15 14 12 9 10 13 15 16 15 13 10 9 12 14 15 14 12 9 8 10 12 13 12 10 8 6 8 9 10 9 8 6 ] .