Method and apparatus for electrically controllable scanning device for moire-free scanning of rastered masters

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.

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 "offset 
rotogravure conversion" 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 "Der 
Polygraph", No. 18, 1968, the engraving of the rotogravure form occurs by 
means of the "Helio-Klischograph" 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:

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.sub.1 through 6.sub.n. The fringe 
fibers 4 are combined in a quadrant manner into quad groups 4.sub.1 
through 4.sub.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.sub.1 is 
connected to light receiver 6.sub.1 as are fibers 14.sub.II, 14.sub.III 
and 14.sub.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.sub.1 through 8.sub.n which are connected to the 
outputs of the light receivers 6.sub.1 through 6.sub.n. The switches 
8.sub.1 through 8.sub.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.sub.1 through 
8.sub.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 "Markt Und Technik", 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 "blanked out" in this manner and a "diaphragm" 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.sub.1 through 20.sub.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.sub.1 through 20.sub.n 
receives a clock signal T and supply outputs to AND gates 21.sub.1 through 
21.sub.n which receive control signal on lines B.sub.1 through B.sub.n 
according to the particular requirements. The control signals on lines 
B.sub.1 through B.sub.n cause the outputs of respective ones of the 
memories 20.sub.1 through 20.sub.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.