This paper describes a marked reasonable technique extracting a two-valued picture from a scanning moiré picture in case of computer-input of moiré patterns. Recently, a variety of thresholding techniques are used for computer-input of moiré patterns. However, there are some troubles on post-treatment, since they are nothing but unreasonable for moiré pictures. In this study, by using basic properties of moiré patterns, a philosophy of moiré picture processing is suggested. By means of this technique, a thresholding of scanning moiré picture can be reasonably and quickly performed. Therefore, a two-valued picture for computer-input can be easily extracted. Results show that this method is useful in the 3-dimension auto-measurement with moiré topography.