title: Quantitative optical image subtraction by means of pulse-width modulation through one-dimensional contact screens.
abstract: A quantitative optical image-subtraction method based on the principle of spatial pulse-width modulation through a one-dimensional contact-screen process and superposition of positive and negative halftone photographs is described. The difference in intensity transmittance of two images A and B can be measured by either superposing the halftone positive of A onto the halftone negative of B or vice versa. Not only subtle differences between the two photographs but also the polarity of such differences can be found.
authors.forename: D Z
authors.initials: DZ
authors.lastname: Zhao
authors.forename: C K
authors.initials: CK
authors.lastname: Chiang
authors.forename: H K
authors.initials: HK
authors.lastname: Liu