1. A signal processing apparatus for performing a filtering process on an input image using a plurality of filters to generate an output image, the signal processing apparatus comprising: region variance value calculating means for calculating a region variance value for a region around a predetermined pixel used as a pixel of interest on the input image, the region variance value indicating a degree of variations of pixel values of pixels located in the region with respect to an average of pixel values of the pixels located in the region; filter processing means for applying a filtering process to a pixel value of the pixel of interest using the filters; reflection amount determining means for determining a reflection amount based on the region variance value, the reflection amount indicating a degree to which a filter output value obtained by the filtering process applied by the filter processing means contributes to generation of a pixel value of a pixel of the output image corresponding to the pixel of interest; and combining means for calculating the pixel value of the pixel of the output image corresponding to the pixel of interest, the calculation being based on each of filter output values obtained by filtering processes applied by a plurality of filter processing means, each of reflection amounts determined with respect to the filter output values, and the pixel value of the pixel of interest.