Yoshitsugu Hirose

Perceptual characteristics of image noise in color hard-copy images

Perceptual characteristics of image noise vs its spatial frequency and colors were deduced from color hardcopy images. The following experiments were carried out: (1) A regular distribution random noise based on the Box & Mueller algorithm was generated. (2) Several noise patterns with a specific spatial frequency were prepared. (3) The noise patterns were superimposed on an arbitrary L*A*B* space of the original image. (4) Simulation prints were made on a xerographic color printer. (5) The prints were evaluated by noise perception tests. (6) Perception characteristics of the noise for spatial frequency were derived. The relationship between noise perception score and noise intensity was estimated on each noise pattern. The experimental results were compared with the visual response in display images. As a result, it has been found that the characteristics of visual perception vs noise intensity are non-linear and depend on the spatial frequency of the noise. The characteristics of image noise perception vs spatial frequency obtained by this experiment agree well with H. Sakatas VTF (Visual Transfer Function) according to Horsts experimental method in lightness space (L*). The magnitudes, however, do not agree with the noise perceptual characteristics in the display images as reported by Barstow. It is also shown that the noise perceptual characteristics in chromatic spaces (a*b*) have a wider band spatial frequency response than H. Sakatas VTF.