Heidelberger Druckmaschinen Ag

Bernd Stritzel

Michael Kaiser

Peter Weinholz

Uwe-Jens Krabbenhoeft

Dirk Kirchhoff

A method for compensating for position-dependent density fluctuations in an inkjet printing machine includes the steps of assigning, by using a look-up table, specific halftone patterns to specific gray values of a color separation to be screened of an image in the course of the calibration of a raster image processor of the inkjet printing machine, using the halftone patterns in the image screening process by using the computer and printing the halftone image on the inkjet printing machine. The look-up table contains the position of every printing nozzle of the print heads in the inkjet printing machine as an additional variable and the computer enters a complete set of gray values with associated adapted halftone patterns into the look-up table for every position of a printing nozzle.

Method for density fluctuation compensation in an inkjet printing machine

A method for carrying out a printing operation on an inkjet printing machine compensates for failed printing nozzles by using a computer. After a screening process in which a halftone image is created for an image to be printed, failed printing nozzles are compensated for by increased ink application from neighboring printing nozzles by precalculating at least one corrective halftone image for the adjacent printing nozzles by using the computer, replacing the halftone image created in the screening process by the corrective halftone image in the at least one column of the neighboring printing nozzles, and carrying out the printing operation on the inkjet printing machine using the corrected halftone.

Method for compensating for defective printing nozzles in inkjet printing

A method for preserving the black composition of at least one object positioned to overprint a special color in a print image for preprint color management of a printing operation using a computer, includes transforming the special color and the object into a combination of process colors of the printing operation during the color management process and then using this combination of process colors to generate the print image in a printing machine. The color transformation into the process colors of the printing operation is achieved in two stages. In a first stage, the color transformation into the process colors is carried out while keeping the special colors, then checking if the object is overprinted onto the special color, then removing the black proportion of the object and then in a second stage, transforming the special color into the process colors and subsequently maximizing the black proportion of the object.

Method for preserving the black composition of objects

A method for compensating tone value fluctuation in inkjet printing includes generating multi-bit halftone images of pixels on a computer during prepress screening for color separations with multiple tone values out of print image data, forwarding multi-bit halftone images to a control unit of an inkjet printing machine, and printing the multi-bit halftone on the machine, wherein encoded binary values of multi-bit halftone images correspond to ink drop sizes to be generated by the machine. The computer introduces additional binary values of multi-bit halftone images not corresponding to ink drop sizes in pixel positions of multi-bit halftone images where occurring tone value fluctuations are to be compensated for by modified ink drop sizes, causing additional binary values to be ignored by the machine in a regular print mode, and assigning additional binary values to modified ink drop sizes in a correction print mode.

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Goosefeld, Germany

Bernd Stritzel