Abstract: A method of gray value correction for binary image data, preferably screened image data, with a local gray value by a desired correction magnitude includes filtering the image data quantized with n bits with an asymmetrical low-pass filter whose filter window is smaller than a screen cell. By a threshold value operation, corrected binary image data is obtained from the filtered image data. Optimum threshold values are selected from a threshold value table as a function of the local gray value and of the desired correction magnitude.

Abstract: A process for the modeling of dots in the generation of a threshold matrix for a screen for the production of a screen form for the printing of image data. The dots are described by model points built up from computed points with an assigned density value. For modeling of ink-jet printing, in the area of overlap of neighboring model points the density values of the computed points are added to form a sum density, the sum density is limited to a maximum possible blackening, and the percentages of the sum density which exceed the maximum possible blackening are distributed to the neighboring computed points. For the modeling of offset printing, in the area of overlap of neighboring model points the maximum of the density values of the computed points is determined as the resulting density and with a filter operation a dilatation of the model points is effected.

Abstract: A method for generating a threshold value matrix is used in the frequency-modulated half-toning of the image data to be reproduced. A threshold value matrix for a basic screen is generated in that low-pass filters of different width are applied to the bit patterns generated and the threshold value distribution is changed on the basis of the filtered results. Furthermore, the bit patterns generated are examined for specific part patterns and the threshold value distribution is changed in such a way that undesired part patterns no longer occur and, instead, desired part patterns, preferably rounded forms, are contained in the bit patterns generated. By use of a combination of scaling and/or rotation and/or mirroring of the threshold value matrix of the basic screen, threshold value matrices are generated for the printing inks.

Abstract: In a method for converting the coordinates of image data, the positions of new picture elements in a new coordinate system are calculated by means of coordinate transformation equations from the positions of initial picture elements in an initial coordinate system. The positions of the new picture elements are randomly modified in a variation range around the positions calculated by way of the coordinate transformation. For this purpose, random values are added to the calculated coordinates of the new picture elements. The method can be used in case of scale conversions, image rotation, etc. to improve the quality of the converted image. The method avoids both the corruption of the image structures caused by coordinate conversion and the formation of disruptive moire patterns. The method can be combined with known methods for calculating the color values of the new picture elements, such as the nearest-neighbor method or the interpolation method.

Abstract: A method of gray value correction for binary image data, preferably screened image data, with a local gray value by a desired correction magnitude includes filtering the image data quantized with n bits with an asymmetrical low-pass filter whose filter window is smaller than a screen cell. By a threshold value operation, corrected binary image data is obtained from the filtered image data. Optimum threshold values are selected from a threshold value table as a function of the local gray value and of the desired correction magnitude.

Abstract: A method for calibrating image recording equipment is described. According to the method, raster areas such as images or color prints are recorded pixel by pixel, line by line in the form of screen dots on an image support by use of at least one exposure beam generated in an exposure unit. An image stored as a bit-map image and containing line data (binary image) is divided into fields. A raster percentage is determined for every field by calculating an average. A variation in the raster percentage is determined from a density-exposure curve. The parameters required for the variation are calculated by an algorithm and memorized in a variation table. The most suitable algorithm is read from the variation table and executed and the data determined thereby are memorized.

Abstract: 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.

Abstract: Binary screen image data redigitized in pixels are retouched, specifically to eliminate local screen defects such as dust artifacts and scratch artifacts. Defective screen dots are selected and recorded for the purpose of detecting screen defects. Then, dust artifacts and scratch artifacts or the like are removed from contaminated image data. Furthermore, missing points in the screen are also filled up, and inhomogeneous image regions are corrected in part. The production of visible moire effects in the retouched image data is avoided by the replacement of only small areas.

Abstract: A method for calibrating image recording equipment is described. According to the method, raster areas such as images or color prints are recorded pixel by pixel, line by line in the form of screen dots on an image support by use of at least one exposure beam generated in an exposure unit. An image stored as a bit-map image and containing line data (binary image) is divided into fields. A raster percentage is determined for every field by calculating an average. A variation in the raster percentage is determined from a density-exposure curve. The parameters required for the variation are calculated by an algorithm and memorized in a variation table. The most suitable algorithm is read from the variation table and executed and the data determined thereby are memorized.