| 摘要 |
A method for opto-electronic scanning, by pixel and by line, of screened master photographic images with a sensing device. From the actual scanning, at least one master photographic image area that contains the grid scale is detected in the screened master photographic image. Subsequently, the picture values present in the local area of the detected grid scale area of the master photographic image are transferred by Fourier transformation to the frequency range as a spatial frequency spectrum, and, from the spatial frequency spectrum, the screen ruling and raster angle of the raster of the master photographic image are determined. For the determined raster angle and the determined screen rulings of the grid scale of the master photographic image, the optimal scan frequencies for Moiré-free scanning are determined from the spatial frequency spectrum. The optimal scan frequencies which determined the scanning fineness are set at the sensing device and then the screened master photographic image is scanned with the set optical scan frequencies, to obtain the picture values necessary for reproduction of the screened master photographic image.
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