Digital Picture Processing
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Document information often includes image data (eg. handwritten annotations, signatures, maps, sketches and photos) as well as alphanumeric and other coded data. Thus, the capability of handling these image data plays an important role in reforming current office-work activities. This paper presents a high-speed scaling method to enlarge or reduce digital images defined as two-dimensional pixel arrays. Scale factors are assumed to be rational numbers R/r and S/s for the vertical and horizontal directions, respectively, where R, S, r, s denote positive integers. Under this assumption, coordinate determination for image scaling is performed by simple table look-up and shift operations. This method excludes time-consuming arithmetic operations for coordinate determination. Thus, high-speed scaling is realized. Experiments showed that the execution time per output pixel is about 150 ns when the shift clock frequency is 8 MHz. The proposed algorithm has been successfully applied to a multi-functional office workstation featuring integrated functions of data processing, document processing and image processing.