1. A noise reduction method, applied in a display, for use in reducing noise of a digital image, the method comprising steps of: providing a plurality of luminance threshold values; determining a plurality of luminance feature values according to a luminance value of a target pixel and luminance values of neighboring pixels of the target pixel by a calculating unit of the display; determining whether the target pixel is a noise point, by a comparing unit of the display, based on the comparison between each of the luminance feature values and each of the luminance threshold values corresponding thereto, respectively; and adjusting the luminance value of the target pixel, by an adjusting unit of the display, when the target pixel is determined as the noise point; wherein a first luminance feature value of the luminance feature values is determined by the luminance value of the target pixel and the luminance values of first four neighboring pixels, and the target pixel and the first four neighboring pixels form a cross shape; wherein a second luminance feature value of the luminance feature values is determined by the luminance value of the target pixel and the luminance values of second four neighboring pixels, and the target pixel and the second four neighboring pixels form an X shape.