1. A signal processing apparatus, comprising: a first noise reduction processing section that performs first noise reduction processing on an image, in which a multitude of pixels has a predetermined pixel arrangement, each pixel of the multitude of pixels has one of a plurality of color components and the color components are distributed regularly, the first noise reduction processing being performed based on the signal values of target pixels which are targets of noise reduction, and the signal values of pixels located in the periphery of the target pixels, wherein said pixels located in the periphery of the target pixels include pixels having color components different from those of the target pixels, to obtain a first processed image; a color component separation section that separates the first processed image into each of the color components to obtain a plurality of color component images; and a signal classification section that compares a signal value of a target pixel for processing with a signal value of each pixel included in a predetermined range of area around the target pixel and classifies each pixel within the predetermined range of area into one of a plurality of groups based on the comparison result, wherein the signal classification section sets the target pixel as a processing target of a second noise reduction only when the number of pixels classified into a group having relatively small signal values within the predetermined range of area around the target pixel exceeds a predetermined threshold value.