| 摘要 |
<p>Method and apparatus for improving contour reproduction particularly of thin lines and serifs for engraving rastered printing forms, where the engraving of the cups arranged in a printing screen is carried out by electromagnetic engraving means which is controlled by a raster signal. The image pattern to be reproduced is scanned point-by-point and line-by-line by opto-electrical scanning means with a resolution higher in the scanning direction than that of the printing screen and the image signal obtained is converted point-by-point into digital image values. Based on the higher resolution additional intermediate image values are obtained between the principal image values which are produced with the frequency of the raster signal. The principal image values and the intermediate image values are converted back into an analog image signal in the sequence of their creation, said image signal being superimposed on the raster signal with a time relationship to the amplitude values of the raster signal which determine the moments for the engraving of the cups by the engraving tool of said engraving means. Thus, for a contour in the image pattern to be reproduced, two partial steps of the image signal are produced during a particular time interval rather than a single larger step (prior art). The first partial step, corresponding to the intermediate image value of the contour, is superimposed onto the raster signal prior to said amplitude value of the raster signal and the second partial step, corresponding to the principal image value of the contour, is superimposed onto said amplitude value of said raster signal. Whereby the cups representing a contour on the printing form are shifted toward the high level of density of the contour, thus, the contour is improved.</p> |
