Field of the Invention
The invention relates to a method and system for producing screen or raster data for imaging units of a printing machine.
Printing machines with imaging units have become known heretofore. Imaging units of this type produce a printing image on a printing plate of the printing machine by scanning with a laser beam, the position and size of the screen or raster dots of the printing image being controlled by screen or raster data, with which the laser beam is modulated in the course of a scanning movement over the surface of the printing plate.
With the aid of imaging units of this type, as compared with the conventional film exposure technique, a plurality of processing stages on the path from an original image to the finished print are dispensed with, so that alternating print jobs can be processed speedily and cost-effectively. Nevertheless, even when such imaging units are used, the processing process from the original image to the finished print breaks down into a multiplicity of processing stages which have to be performed successively and which, to some extent, are time-consuming. In a conventional screen production system, as illustrated in FIG. 1 of the drawings herein, raw image data initially passes through a screen processor 1 (screen image processor RIP), which converts this data into a plurality of partial images, respectively, one partial image for each color to be printed, while simultaneously performing all of the necessary calibration operations. These partial images, respectively, are transferred by an administration unit 2 into a buffer storage unit 3. After the screen processor 1 has completely processed the original image, and all the necessary partial images are present in the buffer storage unit 3, they can be transferred therefrom to the imaging units 4 of a diagrammatically illustrated printing machine 5. Buffering the screen data in the unit 3 is necessary, because the imaging units 4, respectively, must be supplied with data without interruption at a data rate which is predefined or prescribed by the type of construction thereof, and a non-buffered imaging process will fail if the screen processor 1 is not capable of supplying the data at the required rate.
Consequently, the imaging units 4 remain inactive while the screen processor 1 is operating, and the reverse. Because the screen data for each screen dot to be produced by the imaging units must specify the size of the respective dot, they include a significantly greater quantity of data than the raw data originally input into the screen processor 1, which, for example, can be a file in Postscript or PDF format. Storing the screen data for the situation wherein they are used again for a subsequent print job is therefore rather complicated. In addition, if the screen processor 1 performs a high-quality calibration, the dot increases or growths of the individual imaging units of the various stages of the printing machine are taken into account in the specification of the screen dots. These dot increases or growths can vary from one imaging unit 4 to another, within certain limits, because of the scatter in the optical properties of the laser and the scanning system, which are used. Consequently, the screen processor 1 produces the screen data for a given printing ink, respectively, taking specifically into account the properties of the imaging unit 4 which sets the image on the printing plate for the relevant color. If a print job is to be repeated based upon stored screen data, it is consequently necessary for the distribution of the printing inks to the various stages of the printing machine 5, at the time the print job is repeated, to be the same as that for which the screen data were originally calculated. If, in the interim, jobs with a different sequence of colors have been processed, this would require lengthy washing and re-inking of the printing machine.
For a repetition of the print job on a different machine, renewed screening calibrated to the imaging units of the machine is always necessary, even if the machines are of identical construction and are equivalent in all the other relevant parameters, such as the printing material, the color used, the plate material, and so forth.
It is accordingly an object of the invention to provide a method and system for producing screen data for imaging units of a printing machine, which permit further acceleration of operating steps from the original raw image to the print.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a method of producing screen data for imaging units of a printing machine, which comprises the steps of breaking down raw image data into a plurality of partial images, respectively, corresponding to one printing ink; outputting the partial images to a plurality of screen processors, respectively, corresponding to the number of colors to the printed; and processing the partial images simultaneously for forming screen data by the screen processors for output to a respective one of the imaging units.
In accordance with another mode, the method of the invention includes performing by the screen processors, respectively, a calibration of the partial images relative to dot growth of the imaging unit with which it is associated.
In accordance with a further mode, the method of the invention includes breaking down the raw image data in a preprocessing unit that is separate from the screen processors.
In accordance with an added mode, the method of the invention includes performing a calibration by the preprocessing unit, relative to properties of at least one of the printing material, the printing ink, the blanket cylinder, and the plate material of the printing machine.
In accordance with an additional mode, the method of the invention includes, by the preprocessing unit, outputting partial image data to the screen processors before the step of breaking down the raw image data has been finished.
In accordance with yet another mode, the method of the invention includes buffering the screen data before outputting the screen data to the respective imaging units.
In accordance with yet a further mode of the method invention, the step of breaking down raw image data includes a trapping procedure.
In accordance with a concomitant aspect of the invention, there is provided a screen production system for a printing machine having imaging units, comprising a preprocessing unit for receiving raw image data and for breaking down the raw image data into a plurality of partial images, respectively, corresponding to one printing ink, and a plurality of screen processors, respectively, for screening the partial images, respectively, and for outputting to the imaging units, respectively, partial-image screen data obtained from the respective partial images.
Thus, instead of determining, in order, the sizes of the screen dots of the colors to be printed for each point or dot in an image to be printed here, initially, a separation into various colors is performed, and the partial image data, respectively, corresponding to one color, is processed by a screen processor which is specifically provided for the purpose and which is therefore capable of providing the screen data of the associated color significantly more rapidly than heretofore.
The calibration of the partial images relative to the dot growth of the imaging unit, the calibration being necessary for a high-quality print, is preferably performed by the screen processor which is associated with the imaging unit. Those partial images not yet screened, which form data files of a relatively small size, can comfortably be stored intermediately for a repetition of the print job. When the print job is to be repeated, the intermediately stored partial images are screened anew. If, in the interim, the distribution of the colors to the stages of the printing machine has changed, or another printing machine is to be used, the renewed screening can be performed by a screen processor that differs from the first one and can be calibrated to the dot growth of a different printing stage.
The step of breaking down the raw image data into partial images is preferably performed in a preprocessing unit that is separate from the screen processors. This preprocessing unit can perform a calibration relative to all those printing parameters which are standard for the various stages of the printing machine, thus, for example, the printing material used, the printing ink, the blanket cylinder or the plate material of the printing machine.
A particular advantage in using the preprocessing unit is the possibility of intermeshing in time the actions of breaking down and screening, by the preprocessing unit outputting partial image data to the screen processors before the step of breaking down the raw image data has been finished completely.
In order to be able to ensure a uniform data stream at the rate required by the imaging unit, the screen data are preferably buffered before being output to the imaging unit. However, such a buffer can be considerably smaller than that needed to store an entire partial image. If the computing power of the screen processors is sufficiently high so that they can ensure a stream of screen data at the rate required by the imaging unit, the buffer can even be omitted completely.
The step of breaking down the raw image data preferably also includes a trapping procedure.
The object of the invention is also achieved by a screen production system for a printing machine which includes a preprocessing unit for receiving raw image data and for breaking down the raw image data into a plurality of partial images, each of which corresponds to one printing ink, and a plurality of screen processors for screening one of the partial images, respectively, and for outputting the thus obtained partial-image screen data to an imaging unit.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as a method and embodied as a system for producing screen data, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: