1. A signal processing apparatus, comprising: a first noise reduction processing means that performs first noise reduction processing on an image, in which each of multitudes of pixels has one of a plurality of color components and the color components are distributed regularly, based only on pixel arrangement to obtain a first processed image; a color component separation means that separates the first processed image into each of the color components to obtain a plurality of color component images; and a signal classification means 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.