1. An apparatus filtering a digital image signal, comprising: a noise reduction filter which selectively outputs one of results obtained by temporally and spatially filtering pixel values of pixels of each frame of an image as a temporal or spatial filtering value in response to magnitudes of the results of the temporal and spatial filtering; and a sharpness enhancement filter which highlights and outputs a high pass component of the selected temporal or spatial filtering value, wherein the noise reduction filter comprises a temporal filter which temporally filters the pixel values; a spatial filter which spatially filters the pixel values; and a filter selector which selectively outputs one of the results of the temporal and spatial filtering as the respective temporal or spatial filtering value in response to a result of a comparison between a local spatial mean value and each of the results of the temporal and spatial filtering, wherein the filter selector selects the temporal or spatial filtering value according to an Equation f ^ s ⁡ ( x ρ , t ) = { f ^ ⁡ ( x ρ , t ) , if ⁢ ⁢  f σ ⁡ ( x ρ , t ) - f _ ⁡ ( x ρ , t )  >  f ^ ⁡ ( x ^ ; t ) - f _ ⁡ ( x ρ , t )  f σ ⁡ ( x ρ , t ) , else where “{circumflex over (f)} s ( ,t)” denotes the temporal or spatial filtering value, “{circumflex over (f)}( ,t)” denotes the results of temporal filtering of the pixel values, “f 94 ( ,t)” denotes the results of spatial filtering of the pixel values, and “ f ( ,t)” denotes the local spatial mean value.