When one looks at the whole image, one sees a monochrome two value image for every pixel which is recognized as a pseudo halftone image. The visual model and the equivalent approximation method, which is performed respectively through the external world, the retina, and a brain, and proposed the quality-of-image evaluation method of various modulated images. The purpose of this paper is to solve the inconvenience of different window sizes of a modulated system in the usual equivalent approximation method. In addition, we are proposing that the fixed approximation method can be evaluated even when a difficult modulated system is used to find the size of a window. The size and the best approximation terms of a window were fixed, and the subjective superiority or inferiority of the pulse density four division method, ordered dither, average error minimum method, a simple two value method, and the random dither method are the degree of approximation, it could evaluate, and the validity of the fixed equivalent approximation method was shown. Furthermore, by comparing the fixed equivalent approximation method to the visual model and the equivalent approximation method the high-speed calculation was completed with the same accuracy in a much shorter time. Therefore, it is thought that this method can be used in future research.
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