Abstract:
Scanning apparatus and method for scanning rastered reproduction of differently rastered masters in reproduction technology using electronic means for selecting a shaped diaphragm which is variable in its geometry during scanning and wherein a center portion of the scanned picture can be added to different edge geometry scanning configurations so as to eliminate Moire effect.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates in general to reproduction technology as, for example, in printing wherein masters are commonly scanned which are unrastered or rastered with different raster width and/or screen angles. 
     2. Description of the Prior Art 
     The use of rastered offset masters for rotogravure so-called &#34;offset rotogravure conversion&#34; called OTC is gaining increasingly popularity and significance. The principle advantage of this method is that rastered offset positives can be more quickly and cheaply produced and corrected than the previously utilized half-tone separations for rotogravure. Proofs can be produced economically from OTC. Since the conversion conditions from offset to rotogravure are known, the printed results in rotogravure can be optimized before the expensive rotogravure form is produced by means of electronic engraving, for instance. 
     It is known from German Patent application P No. 32 17 752 which teaches a method for moire-free scanning wherein a diaphragm matched in shape, size and angular position to the raster of the master is employed for scanning. 
     This method, however, has limits when as described, for example, in &#34;Der Polygraph&#34;, No. 18, 1968, the engraving of the rotogravure form occurs by means of the &#34;Helio-Klischograph&#34; manufactured by Dr. Ing. Rudolf Hell GmbH or when scanning and re-recording occurs in rotating scanners or similar machines. 
     With such machines, a multitude of master montages of entire magazine pages are mounted on the scanning cylinder and a plurality are covered line-wise by scanning optics device during a scanning pass. It is entirely conceivable that masters to be scanned in common or even the individual images within one page are different in terms of raster widths and/or screen angle. Unrastered page montages or individual images can also occur. 
     The method disclosed in German Patent Application P No. 32 17 752 cannot operate successfully because a mechanical switch-over of diaphragm shapes and diaphragm angles for matching the respective master part to be scanned is much too slow. 
     Conditions which are somewhat similar exist in scanners. Offset positives would also be desirable as masters in scanner technique for the above-mentioned reasons of economic feasibility. Masters having different raster width and/or screen angle can also occur during one scanning pass. For example, different screen angles definitely always exist when the four color separations of one image are to be acquired in a single scanning by the so-called multi-color method and the masters are rastered offset color separations. 
     It is an object of the present invention to provide a method and apparatus which allows the electron-optical scanning of unrastered or rastered masters having different raster widths, raster configurations and/or screen angles during one scanning pass such that when the rasters are added during the reproduction process a moire will not occur with one of the master rasters during recording. 
     Other objects, features and advantages of the invention will be readily apparent from the following description of certain preferred embodiments thereof taken in conjunction with the accompanying drawings although variations and modifications may be effected without departing from the spirit and scope of the novel concepts of the disclosure and in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram illustrating the principles of the invention; 
     FIG. 2 is a schematic illustration illustrating the subdivision of the fiber optical waveguide bundle and the photo-electrical transducer; 
     FIG. 3 is a block diagram illustrating the diaphragm selection using read-write memories; and 
     FIG. 4 is a block diagram illustrating the diaphragm selection by means of a plurality of read-only memories. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates a master 2 mounted on a suitable drum which is driven by a suitable driving means not shown and which is scanned with a scanning optical device 1 which images a sub-image of the master and supplies it to one end of an arranged bundle 3 of fiber optical waveguides. The individual fiber diameters, the bundle diameter and the imaging scale are matched to each other. All of the fibers 5 of the bundle core 13 which is illustrated by shading in FIG. 2 have their opposite ends connected to a light receiver 7 which produces an output signal 7a which is supplied to an electrical summation point 10. In addition, to the fibers 5 of the bundle core 13 there are also a plurality of fringe fibers which surround the bundle core 13 and the second ends of the fringe fibers 4 are connected to various light receivers 6 1  through 6 n . The fringe fibers 4 are combined in a quadrant manner into quad groups 4 1  through 4 n . Each of the groups contains one fiber from each quadrant I through IV of the scanning end of the fibers and which are located within the respective quadrants at corresponding locations 14 as illustrated in FIG. 2, for example. Thus, for example, fiber 14 1  is connected to light receiver 6 1  as are fibers 14 II , 14 III  and 14 IV  illustrated in FIG. 2. It is to be noted that each quad group thus contains one fiber from each quadrant I through IV of the opposite end of the fibers and these are located within the respective quadrant at corresponding locations 14. By utilizing a control unit 9, the output signals can be locked onto the image signal 10 by utilizing electronic switches 8 1  through 8 n  which are connected to the outputs of the light receivers 6 1  through 6 n . The switches 8 1  through 8 n  are illustrated as simple switches in FIG. 2. The geometry of the effective area of the scanning ends of the fiber bundle 3 can be varied by switching on or off specific light receivers 6 for the outer area. 
     When the fringe fibers 4 of the fiber bundle 3 are divided into the four quadrants I through IV and when the four corresponding individual fibers 14 of each quadrant are combined at a light receiver 6, then the number of required light receivers 6 and switches 8 is reduced by one-fourth for obtaining the same effect. 
     By varying the effective area of the fiber bundle an effect equivalent to the variation of the diaphragm such as disclosed in German Patent Application P No. 32 17 752 is obtained in terms of shape, size and angular position. With the present invention, however, the matching on the basis of the electronic switches 8 in the control unit 9 can be accomplished so quickly that it changes the diaphragm geometry and the angularity between master parts during a scanning event in a manner such as required by the next master part to be scanned. The control unit 9 which decides which individual fibers 4 must be activated for the respective master part receives its instruction over the line 12 and said instruction can be obtained, for example, by scanning an on-line control mask. 
     The desired geometry and angular position can also be manually input over line 11 by means of setting the corresponding switches 8 1  through 8 n . 
     For scanning non-rastered continuous-tone masters, the fringe fibers 4 can be advantageously interconnected to accomplish unsharp masking areas scan. The core 13 of the bundle acts as the principle diaphragm. As a result, electronic unsharp masking for contrast enhancement is possible such as described in U.S. Pat. No. 2,691,696. 
     The central core region 13 which is not switched of the fiber bundle can also consist of a single thick individual fiber or it can also be a directly illuminated photo-electrical transducer as, for example, a photo-diode. 
     The complete fiber bundle can also be replaced with a correspondingly shaped array of photo-electrical transducers as, for example, diodes. This arrangement would also be in the shape illustrated in FIG. 2. The scanning optics 1 may be a zoom lens which matches the scanned image passage to the actual size of the array with the proper magnification scale. 
     Illustrated in FIGS. 3 and 4 are matrix-like arrangements of photo-electric transducers having memory properties which serve as the light receiver, for example, such as the charge coupled device imager chip CCD 15. The target of such chips is formed from a plurality of semiconductor elements in a regular arrangement which store an image which is projected onto the chip as a charged carrier image and such structures are disclosed, for example, in &#34;Markt Und Technik&#34;, No. 16, April 1982, pages 24 ff. 
     Given such charge coupled imager chips the charges stored in the individual image points are interrogated in a specific manner by a clock T and this sequence of analog luminance signals is read into a read-write memory 17 after being digitized in an analog-to-digital converter 16. The image originally projected onto the CCD chip can be intermediately stored in said read-write memory 17 as a charge carrier image. The selection of which of the image points are to be interpreted upon read-out and which are not to be interpreted can be determined by means of external wiring of the read-write memory. A specific part of the stored image portion can be electronically &#34;blanked out&#34; in this manner and a &#34;diaphragm&#34; can be formed of the respective requisite shape, size and angular position. This can occur as shown in FIG. 3 for example, by utilizing a second read-write memory 18 which has a bit pattern with a diaphragm shape, size and angular position which have been input therein and those image points of the part of the image which is presently stored in the read-write memory 17 can be interpreted. For purposes of illustration, a diaphragm shape is illustrated in FIG. 3 in the read-write memories 17 and 18. Read-in or, respectively, read-out of both read-write memories 17 and 18 as well as of the CCD chip 15 are controlled by a shared clock which produces a signal T illustrated in FIG. 3. The clock signal T can be advantageously generated by a clock generator not shown which is mounted on the same axis as the master cylinder upon which the master 2 is mounted of the scanner or, respectively, of the engraving machine. The coding of the diaphragm read-write memory 18 according to the objects given above, changes frequently during scanning and can be acquired by means of an on-line control mask or from a program memory synchronized with the rotation and can be supplied to the memory 18 over line B. 
     The output signals of the diaphragm memory 18 and of the image memory 17 are supplied to an AND gate 19 which emits an output signal only when both memories 17 and 18 emit a signal. 
     FIG. 4 illustrates a further modification of the device illustrated in FIG. 3 wherein a series of data memories 20 1  through 20 n  which have fast access are employed as the diaphragm memory and store various diaphragms shapes as illustrated in FIG. 4 which are stored in the different memories. Each of the memories 20 1  through 20 n  receives a clock signal T and supply outputs to AND gates 21 1  through 21 n  which receive control signal on lines B 1  through B n  according to the particular requirements. The control signals on lines B 1  through B n  cause the outputs of respective ones of the memories 20 1  through 20 n  to pass and be supplied to the AND gate 19. The control signal in the clock signal can be obtained from the same elements as utilized for the device illustrated in FIG. 3. 
     Although the invention has been described with respect to preferred embodiments, it is not to be so limited as changes and modifications may be made which are within the full intended scope of the invention as defined by the appended claims.