DD144468A5 - METHOD AND ARRANGEMENT FOR PRODUCING JAMMED PRESSURE FORMS - Google Patents

Description

--ι-

Berlin, the

Title of the invention

Method and arrangement for producing screened printing forms.

Field of application of the invention

The invention relates to a method for producing screened printing forms with screens of arbitrary screen angle and screen ruling by line-by-line photoreceptor scanning to obtain an image signal and by line recording by means of a recording element moved relatively over a recording medium, in which the recording medium is divided into area elements and oriented in the line direction. orthogonal coordinate system, in which the location coordinates of the surface elements currently being run over by the recording element are continuously determined and in which a recording signal for the recording element is continuously generated by comparing the image signal with a screen threshold value, the recording signal recording the individual screen points as a configuration of Controls surface elements in the coordinate system, and an arrangement for carrying out the method.

The field of technology to which the invention is intended to apply encompasses all electronic reproduction technology. The invention is intended, for example, in color scanners for

Position of electronically screened color separations application.

Characteristic of the Known Technical Solutions During the production of the print, it is not possible to exactly print the halftone dots of the individual separation colors. The result are Moire patterns, which make themselves disturbing in the printed image. The visibility of moiré effects is known to be reduced by the fact that the grating networks of the individual color separations of a color set are rotated against each other rotated over each other. By the screen angle is achieved that the resulting moire periods are either too small or too large to be perceived by the human eye as disturbing. For such a raster rotation one needs color separations in which the individual raster networks are rotated relative to the Jmfzeicnnungseinrichtung by different screen angles. For the four color separations therefore four different. Raster angles are needed. In order to produce a moire minimum, it has proved advantageous in four-color printing, the screen angle -15 for "magenta", the screen angle + 15 ° for "cyan", the screen angle 0 for "yellow" and the screen angle for "black" +45 to choose. The screen angles must be kept very accurately, since annoying moire effects occur even with small angular deviations.

Other screen angles are also required if you want to print more colors, use different print media, or print different screen rulings.

The direct screening of halftone templates in the color scanner can, for. B. by a so-called Kontaktrasterung (Handbook of printing technology, Bruckmann, 1976, Verlag F. Bruckmann, Munich, page 88- and f.), In which the recording light for generating the halftone dots in addition by the density profile

a contact scanning film arranged between the recording member and the recording medium is modulated.

From DE-PS 15 97 773 z. Example, a method for so-called "electronic screening" in which each raster dot is constructed in the manner of a pattern of individual pixels or writing lines. The image patterns of the different halftone dot sizes are stored as recording data for all tone values and for different screen angles. During the reproduction, those recording data are then continuously read out and recorded corresponding to the tone values determined during the original scanning.

While the device-related writing raster network, in which the raster dots are recorded, is oriented orthogonally in the recording direction and feed direction of the device, differently rotated raster webs are decisive for the exact location of the raster dots on the recording medium relative to the raster.

Now it is important to fit the various printed meshes into the system of writing lines. This is particularly easy according to DE-PS 19 01 101, if the tangent of the screen angle is a simple rational number. In such "rational grids", a common surface element results for both raster systems which has the basic structure of the raster pattern and which is repeated on the recording medium periodically in the recording and feed direction, whereby the recording is controllable by simple clock systems associated with the movement of the raster Recording medium or coupled to the feed movement of the recording member.

Raster nets with screen angles whose tangent is irrational can not be resolved by the method described above.

draw, so that even for a Moire minimum required screen angle of ^ 15 can not be realized.

In DE-OS 25 00 564, another method is described, with the "irrational master" can be recorded. In this known method XY pulse trains are derived from the movement of the recording drum and the advancing movement of the recording member, the evaluation of which the respective location of the lufzeichnungsorgans is determined with respect to the recording medium in a rectangular, oriented in the recording and feed direction coordinate system.

To generate a raster signal, the XY pulse trains are converted according to a predetermined function. This function, which is periodic and two-dimensional, represents the screen pattern rotated by the desired screen angle.

During the recording, the raster signal and the image signal are continuously compared and the decision is made from the comparison as to whether or not a raster point is to be recorded at a location characterized by XY pulse trains.

The function is electrically modeled in a function generator in which, among other things, further pulse trains are first formed by multiplying the frequencies of the XY pulse trains by certain factors, which factors are irrational or almost irrational and represent various functions of the screen angle selected for printing.

The multiplication is carried out by means of phase-locked loops ("phase-locked loop circuit), which, according to experience, have transient response and relatively low stability

_ 5 - A

desired screen angle can therefore be met only with a limited accuracy, so that, as already mentioned, disturbing Moire phenomena can occur at a certain angular deviation.

To improve the sharpness and printability of the halftone dots, it is often desirable to produce according to DE-PS 22 62 824 different halftone dot shapes or to break the halftone dot into sub-points.

In the method known from DE-OS 25 00 564 can indeed produce by various functions circular or rectangular grid points, but the possibilities for variation are very limited. In addition, some of the specified functions are difficult to replicate in a functional gene rotator, which is considered disadvantageous.

In the known device, the recording is carried out by a plurality of adjacent sub-beams emanating from a recording member. For controlling the partial beams, the image signal must be compared with different raster signals. The extraction of the raster signals, which must take into account the different impact points of the sub-beams on the recording medium, will not be described in detail.

Object of the invention

The aim of the invention is to improve both the reproduction quality and the method and arrangement for producing screened printing plates.

Explanation of the essence of the invention

The invention has for its object to provide a method and an arrangement for the production of screened printing forms, with which arbitrary screen angle, d. H. Screen angles whose tangent is rational or irrational can be generated with high accuracy.

The object is achieved in that the recorded rotated grid is associated with an orthogonal, oriented in the direction of the grid XY coordinate system, which includes the raster angle with the oriented in the direction of the line UV coordinate system that the grid of orthogonal, the predetermined raster correspondingly large Raster meshes and each grid consists of the surface elements, which are assigned to corresponding x; y location coordinates, that regardless of the screen angle the surface elements of at least one fictitious Ras.termasche arbitrary screen width depending on their x; y-location coordinates each assigned a raster Sehwellenwert that the u.v coordinate coordinates of the surface elements attributable to a raster masking with predetermined raster width are converted into the limited fourth region of the corresponding x, y spatial coordinates of the fictitious raster mesh et, and that with the aid of the converted x; y location coordinates, the grid threshold associated with each coordinate pair is determined which, when compared with the associated image signal, determines whether or not the area element in question is recorded in the U-V coordinate system as part of a grid point.

Preferably, it is provided that the conversion of the u, v location coordinates into the limited value range for the x, y location coordinates of the fictitious grid mesh digitally according to the relationships:.

x '= K «u'COsB + K« v-sin ^ O y' = -K * u «sinj + K» v-cos, where the coefficients 'K' and K are the ratio

take into account the respective given screen ruling to the screen ruling of the fictitious raster mesh, and that the restriction of the current x '; y' location coordinates to the limited value range for the x; y spatial coordinates of the fictitious raster mesh is done by omitting high-order bits.

Preferably, the current u v local coordinates are determined by counting basic steps (λ v).

An advantageous variant is that the current u, v location coordinates are determined by the continued addition of basic steps ($ u, £ v).

A development of the invention consists in determining the u, v location coordinates in basic steps 04u, £ v), and in that the corresponding x, y location coordinates are obtained by the continued addition of constant amounts D = K «4 ^U ' ^COS / S ^{+ K} * <av «sin / 3 (or D = -K * j &

to the previously determined location coordinates according to the relationship ^x (n + 1) ^{= X} n ^{+ D} x ( ^{or y} (n + 1) ^{= y} n ^{+ I} V, ^respectively ).

Advantageously, the x, y spatial coordinates of the surface elements and the raster threshold values (R) of the fictitious raster mesh are assigned according to a function R = g (x; y).

Preferably, the function has the form:

R = g (A χ + B y), where A and B are partial thresholds.

Furthermore, it is provided that the function R = g (A χ + B y) is generated digitally and that -the raster threshold values (R) are stored and the respectively assigned address by the sum (A χ + B y) are formed.

Alternatively, it is provided that the function R = g (A "x + B" y) is generated digitally and that the summands (Ax) and (B'y) are stored under the respectively assigned addresses χ and y and the read-out values are added ,

Preferably, the raster threshold values (R) of the notional raster mesh are stored among those addresses which correspond to the associated x, y location coordinates.

Advantageously, the raster threshold values (R) are stored in a two-dimensional memory matrix.

An advantageous development is that for simultaneous recording of multiple surface elements as parts of a raster point in the recording several, controllable by separate recording signals recording beams are generated and that for obtaining the recording signals for the χ; y-coordinate coordinate pairs of the individual recording beams (n) associated raster thresholds (R _n ) are determined and compared with the image signal.

In one variant of the invention, the raster threshold values (R) are determined in time-division multiplexing from the individual χ; y location coordinate pairs.

Preferably, it is provided that the u v location coordinates pairs of the other recording beams are continuously obtained from the u v coordinate coordinate pair determined by a recording beam by adding the distances of the respective recording beams from the one recording beam in the UV coordinate system 28, and that the each ^u _n ^v _n 5 -

Location coordinate pairs are transformed into corresponding χ; y location coordinate pairs.

A further embodiment of the invention consists in continuously extracting from the transformed x; y-location coordinate pair of a recording beam the χ; y-location coordinate pairs of the other recording beams by adding the distances of the respective recording beams transformed into the XY-coordinate system (30) from the one recording beam become. ·

An advantageous improvement is that for simultaneous

Recording a picture signal by document scanning along a scanning line associated with one of the recording lines, and comparing the image signal with the corresponding screen thresholds.

Another preferred improvement is that for simultaneously recording a plurality of recording lines for each of the recording lines, an image signal is obtained by document scanning along spatially-assigned scanning lines, and the image signals will be gated with the corresponding screen thresholds.

Preferably, in the original scan, each pixel is scanned for a plurality of pixels along a scanning line.

Advantageously, the location coordinates of the area elements are superimposed before the determination of the raster thresholds randomly generated values which are smaller than the 'location coordinate values.

Preferably, the randomly generated values are superimposed additively on the current x '; y' location coordinates.

In a variant of the invention it is provided that the basic clauses ($ u) are counted in the circumferential direction with the aid of a clock sequence (T) and that the clocks of this clock sequence are generated at random.

A preferred arrangement for carrying out the method is assigned by a raster generator, in which regardless of the screen angle the surface elements of at least one fictitious grid of any screen spacing is assigned a raster threshold value depending on their x, y location coordinates in an XY coordinate system the XY coordinate system aligned in the direction of the grid, compared with the oriented in the line direction UV coordinate system rotated by the Easter angle and constructed from the predetermined grid size correspondingly large grid, which in turn are divided into the area elements, and one between the means for the current determination of u; V-location coordinates and the grid generator arranged coordinate transformation stage marked to convert each attributable to a recording grid with a predetermined grid ruling u v location coordinates of the fictitious grid.

Execution objectives

The invention is explained in more detail below with reference to some embodiments and the accompanying drawings:

Show it:

FIG. 1: a block diagram of a color scanner,

FIG. 2: an enlarged section of the recording medium,

FIG. 3 shows an embodiment for the transformation stage,

FIG. 4 shows a further embodiment of the transformation stage,

FIG. 5 shows an exemplary embodiment of a recording element,

FIG. 6 shows an advantageous development of the tear formation stage;

FIG. 7 shows an exemplary embodiment of a pseudo-random number generator;

FIG. 8: a variant of a color scanner,

FIG. 9 shows an exemplary embodiment of a random clock generator.

Fig. 1 shows a schematic block diagram of a color scanner for the production of electronically screened and corrected color separations.

A scanning drum 1 and a recording drum 2 are coupled via a shaft 3 and are commonly driven by a motor 4 in the direction of an arrow 5.

On the scanning drum 1, a colored original 6 is spanned, which is scanned point by point and line by line of a light source of a light source, not shown. In a supervisory template passes the reflected and in a review template the transmitted, with the image content of the template 6 brightness modulated scanning into a scanning 7. In the scanning 7 are color separation by color filter and optoelectronic conversion of the scanning three color signals R, G and B, which represents the color components of the sampled pixels. ,

The scanning member 7 is moved by a motor 8 and a spindle 9 parallel to the scanning drum 1 in the direction of an arrow 10.

The analog color signals R, G, B pass from the scanning device 7 via a downstream amplifier 11 to A / D converters 12, 13 and 14, in which they by means of a Abtasttaktfolge T. in digital color signals R ¹ , G ^f and B 'with a Word length of z. B. 8 bits are converted, each clock of Abtasttaktfolge T. a sampled pixel is assigned.

The sampling clock sequence T. is formed by frequency division in a divider stage 15 from a clock sequence T _Q , which is generated in a coupled to the rotational movement of the drums clock generator 16. The sampling clock sequence is supplied to the A / D converters 12, and 14 via a line 17.

The digital color signals R *, G 'and B ^T are converted in a digital correction circuit 18 into the corrected color separation signals Mg, Cy, Ye for recording the color separations "magenta", "cyan" and "yellow".

In the digital correction circuit 18, a color and / or gradation correction takes place according to the requirements of the reproduction process. Such a correction circuit is z. As described in detail in the DT-AS 1 597 771.

The correction circuit 18 may be further downstream of a digital memory for temporarily storing the color separation signals to perform a scale change between template and recording according to DT-PS 1 193 534, or to save the image content of the entire template and time-shifted or optionally at a location for recording retrieve.

-13 - 2 t 3

In the exemplary embodiment, the digital color separation signals Mg, Cy, Ye reach a Farbauszug'sschalter 19, with each one of the digital color separation signals for rasterized recording of a color separation is selected. "

Of course, the invention can also be used if all the color separations are recorded parallel to one another or serially on the circumference of the recording drum 2 in one operation.

A recording member 20 moves by means of another motor 21 and a spindle 22 axially in the direction of the arrow on the rotating recording drum 2 along. The recording member 20 makes the dot and linewise exposure of the screen dots to a photosensitive recording medium 23 disposed on the recording drum 2.

The recording beams 24 focused on the recording medium 23 by the recording member 20 generate a number of exposure points P, which write lines 25 also extend the recording medium 23 by the relative movement between the recording member 20 and the recording drum 2 in the circumferential direction (recording direction).

Each grid point 26 is composed of a number of such closely spaced writing lines 25 together. The shape and the size of a raster point depends on the length of the writing lines 25 and on the respective duty cycle of the individual recording beams 24. The recording beams 24 are on and off by recording signals A, which are supplied to the recording member 20 via lines 27, switched on and off. An exemplary embodiment of the recording element '20 is shown in FIG.

It is within the scope of the invention to illuminate the writing lines 25 of the screen dot 26 by a single recording beam 24 deflectable transversely to the direction of recording.

In this case, the halftone dot · 26 is composed of writing lines running transversely to the recording direction. The deflection of the recording beam 24 can be effected by means of an electroacoustic deflection arrangement, as z. B. in the DT-OS 21 07 738 is given.

In the following, the method steps for obtaining the recording signals A will be explained in more detail.

The current location of the exposure points P on the recording medium 23 is determined by a device-related, independent of screen angle UV independent coordinate system 28 on the recording drum 2, whose U-axis is oriented in the circumferential direction of the recording drum 2 and its V-axis in the feed direction of the scanning and recording member , The U-V coordinate system 28 is divided into a plurality of area elements from which the halftone dots to be recorded are constructed.

The spatial position of the halftone dots 26 on the recording medium is predetermined by a grid network 29 in an XY coordinate system 30, which is rotated relative to the UV coordinate system 28 by the screen angle β .

The raster network 29 consists of a plurality of raster meshes whose size depends on the raster width to be recorded. Each raster mesh is made up of the area elements to which corresponding x ^T ; y 'location coordinates are assigned.

For a fictitious grid mesh independent of the screen angle and screen ruling of the screen to be recorded is a

given the spatial function R = g (x, y) with a range of values limited to the notional raster mesh, many of which define the size of the raster points as a function of different image signal amplitudes (tone levels) and the halftone dot shape. In this function, R is the grid threshold of a surface element and x; y is its associated location coordinates in the X-Y coordinate system -30.

The range of values of the x, y location coordinates belonging to the given function is limited in relation to the distance area, the x ¹ , y 'location coordinates of the exposure points P.

The spatial representation of the function R = g (x; y) is also referred to as "raster peak" whose base area fills the fictitious raster mesh and in which a cross-sectional area lying at the level of the instantaneous image signal amplitude indicates the raster point size for the respective tone value ,

During the reproduction, the current x '; y ^f coordinates of the exposure points P _n in the XY coordinate system 30 are determined, converted to the limited value range of the x, y spatial coordinates of the fictitious grid, and the grid threshold assigned by the function is called. The raster threshold value is compared with the image signal and the decision is derived from the comparison as to whether or not the pertinent area element is recorded in the UV coordinate system 28 as part of a raster point.

In order to determine the location coordinates u _n ; v of the exposure points P _n in the UV coordinate system 28, the U and V axes are divided into basic steps u u and v v. The length of the basic steps may vary on the axes.

The location coordinates u _n ; v _n are given as multiples of the basic steps ^ u and ^ v.

In a first method step, the instantaneous position coordinates u v of the exposure points P p are obtained by continuously counting or adding up the basic steps 4 u and 4 v with the aid of two clock sequences T and T in a transformation stage 31. determined. The clock sequence T is obtained by frequency division in a divider stage 32 from the clock sequence T of the clock generator 16 and the transformation stage 31 is supplied via a line 33. Each clock of the clock sequence T is assigned a basic step ^ u. The basic step length can be changed by the frequency of the clock sequence T and optionally adapted to the required Gena ability.

A circumferential encoder 34, which is also coupled to the recording drum 2, generates once per revolution, d. H. after each advancing step of the scanning member 7 and the recording member 20, a circumferential pulse T, to which a basic step ^ v is assigned. The circumferential pulses T are supplied to the transformation stage 31 via a line 35.

The location coordinates U ₁ Jv-. for the first point of reference, the equation follows:

= C _u «

= 0 _γ · Αν,

(D

where ^ Su and üv denote the basic steps in the U-V coordinate system 28 and C and C denote the number of clocks T and T, respectively.

The location coordinate pair for the other exposure points can be advantageous from the pair of location coordinates of one of the exposure points, z. B. the first exposure point P ₁ calculate. The position of the exposure points P to each other can be arbitrary, but in general the exposure points will lie on a straight line.

- ι? - ff-3 Hf 6

To produce a homogeneous density gradient over the grid point surface, the straight line according to Patent (Patent Application P 26 53 539.7) lies at an angle to the surface line of the recording drum 2.

In this case, the distances u * and v * of the exposure points from each other are constant and hur on the structural design of the recording member 20 and the imaging scale dependent. The location coordinates u _n ; v _{n of} the other exposure points P can therefore be calculated according to the equations u = U ₁ + (n-1) u * and v = V ₁ + (n-1) v *.

Often, however, the exposure points are directly on the envelope line of the recording drum 2, and then u * = 0.

Since the function R = (x; y) is independent of the screen angle und and the screen ruling, in a second method step in the transformation stage 31, the location coordinates u _n ; v _{n of} the UV location coordinate system 28 are continuously taken into account taking into account the screen angle β and the different Grid width of the recorded and the fictitious grid in the corresponding location coordinates x ', y' of the XY coordinate system 30 transformed.

In the transformation, at the same time, the larger value range of the spatial coordinates x ^! Occurring upon exposure of the entire area of the recording medium 23 is calculated ^. _n > y ' _{n is} limited to the limited range of values of the x, y location coordinates of the given function R = g (x; y). This process will be explained later.

The conversion of the location coordinates in the transformation stage. 31 takes place according to the equations:

^x n = VV ^COS / ^ ⁺ W ^sir 7 ^ - ^M x

^y n = -V ¹ V ³¹¹¹ V P ⁺ v _n * COS ^ - M _y

(2)

-18- 213 if 6

In equations (2), the coefficients K and K take into account the different screen rulings of the raster mesh and fictitious raster mesh to be recorded, and the expressions M and M consider limiting the continuous x '; y' location coordinates to the value range of the function.

The screen angle and the coefficients are preset at programming inputs 36 and 36 ^{f of} the transformation stage 31.

Exemplary embodiments of the transformation pieces 31 are indicated in FIGS. 3 and 4.

I The transformation stage 31 determines at its outputs for

each exposure point P corresponding coordinate pairs χ ^

V ι ·.

The raster generators 37, 38 and 39 generate from the offered coordinate pairs ^ _n JY _n according to the predetermined function R = g (x; y) corresponding digital raster threshold values R, which likewise have a word length of 8 bits like the digital color separation signals.

For comparison of the raster threshold values R on the lines 40 with the color separation signal selected on the color selection switch 19 on a line 41, digital comparisons 42, 43 and 44 are provided.

These comparators 42, 43 and 44 generate the recording signals A on the lines 27? with which the exposure of the halftone dots 26 to the recording medium 23 is controlled.

For the construction of the raster generators 37; 38; 39 offer various advantageous options.

- 19 - 1

In the exemplary embodiment, the raster generators consist of read-only memories, in each of which the same function R = g (x; y) is stored.

The read-only memory consists of a memory matrix with z. B. 32 χ 32 memory cells for the raster thresholds. The memory cells can be selected by 32 x addresses (5 bits) and 32 y addresses. In this case, the x, y value range for the function is "32", ie. H. each limited to the addresses 0 to 31.

It would also be conceivable to address all read-only memories with the x, y location coordinate values of one of the exposure points and to obtain the different grid threshold values R for the other exposure points by programming the individual read-only memories into the XY coordinate system 30 transformed distances u * and v * of the other exposure points is taken into account.

To save read only memories, the various x, y location coordinate pairs for the exposure points could successively address a single read only memory in multiplexed operation.

The raster generators 37, 38 and 39 could also be constructed of function generators which simulate the function R = g (x; y).

In this case, the function could preferably have the form R = g (D "x + E" y).

In the event that the function generator operates digitally, the function R = g (x; y) could be stored in a memory at whose address inputs the sum (D "x + E" y) is applied. Likewise, the products (D "x) and (E * y) could be stored in one or more memories, which are then directly addressable by the x, y coordinate values.

- 20 - Ä - 1 - <&

In the arrangement according to FIG. 1, the advancing movement of the scanning member 7 and the recording member 20 in the direction of the arrow 10 can be stepwise or continuous.

In a stepwise feed sampling and recording take place around the drums on circular image lines whose distance from each other corresponds to a feed step. On the other hand, in the case of a continuous feed, scanning and recording take place on image lines extending helically around the drums. In this case, small errors occur in the recording, which, according to an advantageous further development of the inventive concept, are provided by correction factors (S * sin $) or (S, »cos / l) in the transformation equations

Vj »VF

(2), where "S" denotes the pitch of the helix and "β" indicates the screen angle. The transformation equations have the following form:

χ = K _u -u »(cos> f + S _v » sin J) + K _y .v * siny $ - IV

^M x

y = K _u .u «(- sinp + S _v « cos #) + K _y - · yposiP- M

2 shows an enlarged section of the recording medium 23 ¹⁵¹ It the device-related UV coordinate system 28 (U direction = recording direction) and with the recorded rotated grating network 29 to which the XY coordinate system 30 is oriented, where the coordinate systems include the screen angle & $ .

The raster mesh 47 of the rotated raster mesh 29 with the raster point 26 represents to a certain extent the basic structure of the raster pattern, which continues periodically in the X and Y directions over the entire recording surface.

The halftone dot 26 is made up of a number of adjacent and in the recording direction extending write. lines 25 together. Each writing line 25 is made up of individual area elements 48 to which current u, v, x ', y ^f location coordinates are assigned.

In addition, a fictitious grid mesh 49 of any grid width is indicated, which is also composed of a number of surface elements 50. Each area element 50 is assigned a raster threshold R and an x; y location coordinate pair, but their value range is assigned to the fictitious one. Grid mesh 49 is limited.

During recording, for each area element 48 which is currently being driven over by an exposure point, the grid threshold corresponding to a congruent area element 50 in the fictive grid mesh 49 is determined according to the equations (2) given in FIG. 1 and compared with the image signal to obtain the recording signals.

There are various possibilities for image signal acquisition.

In the embodiment of FIG. 1, the recording member 20, which is only indicated in FIG. 2, generates several, for. B. three recording beams 24 and thus also a plurality of juxtaposed exposure points P, which simultaneously aufbelichten during a revolution of the recording drum 2 'a corresponding number of writing lines 25.

If there are three exposure points P ₁ to P-, as shown in FIG. 2, and if the halftone dot 26 consists of six writing lines 25, the halftone dot 26 is moved after two drum revolutions or advancing steps by the scanning element 7 and recording

20 illuminated. In this case, only two image data 51 of the original 6 scanned from adjacent image lines 51 are available for all writing lines 25 of the screen dot 26. The accuracy of the recording can be increased if, for each writing line 25, image information obtained from a spatially assigned image line 51 is available.

This can be achieved in an advantageous manner according to the patent ... (Patent Application P 26 58 502.4) in that in the template 6, a plurality of in the V direction of the UV coordinate system 28 adjacent pixels are sampled simultaneously and that in each case the image signal of that Pixel is selected to control the recording member whose location on the template 6 coincides with the writing line 25 to be recorded.

However, the recording element 20 can also generate only one recording beam 24 and thus only simultaneously an exposure point P. on the recording medium 23. In this case, one writing line 25 is irradiated per revolution of the recording drum 2, whereby the scanning member 7 and the recording member 20 execute a feeding step by one writing line width after each revolution. As a result, for each writing line 25 of the halftone dot 26, image information is obtained from an image line 51 of the original 6 which is associated with the location in the V direction. Although this procedure is very accurate, it works very slowly.

The distances of the pixels on an image line 51 are z. B. selected so that in the U direction per pixel 26 a pixel is scanned. Since each clock of the sampling clock sequence T "is associated with a pixel, their distance from each other. by changing the frequency of the sampling cycle T, set

-23-1

become. On the scale 52, the corresponding clocks of the sampling clock sequence T. are indicated.

Of course, it is also possible to scan several pixels per grid point 26 in the circumferential direction.

FIG. 3 shows an embodiment of the transformation stage 311 in which the current u, v-location coordinates of the UV coordinate system 28 are determined. Counting of the basic steps Au 'and Av determined and according to equation (2) in the coordinates χ; y for controlling the 'Rästergeneratoren 37,38 and 39 are converted.

The 'values K'. & U and K > Δν as well as oosp and sin / J are stored in memory registers 53 to 56.

The clocks T _u and T _y on the lines 33 and 35 are counted in counters 57 and 58. The counter readings correspond to factors C and C. According to the equations (2)

WV. _t

For example, multiply the factors in the multipliers 59-62 and then add the products in the adder stages and 64. The result is the current location coordinates x'-tiy ¹ "for the first exposure point P ₁ as 32-bit information.

Since the 32 x addresses and 32 y addresses of the read only memory in the raster generators 37, 38 and 39 are selectable by 5-bit information respectively, the computed location coordinates x'.jjy ¹ .. (32 bits) are limited to the χ . ; y - address range from 0-31 (5 bits) according to the relationship X ₁ = x ^ mod.32 or y- = y'j mod.32 converted in steps 65 and 66 respectively. The conversion is done by stripping the higher order bits. ,

The output signals χ. and y .. of the stages 65 and 66 are the address pair for the exposure point P. for selection of the read-only memory 37 ·

The further address pairs χ; y. for the other exposure points P, add the values (n-1) x * and (n-1) y * to the calculated location coordinates x ¹ ₁ and y '.. in the adder stages 67-70 and by stripping bits in the Steps 71 - 74 determined. The values x * and y * are calculated from the predetermined distances u ^s and v * of the exposure points P.

I

Of course, the pairs of addresses ^ _n JY _n for the other points of attachment P can also be obtained by adding the values (n-1) u * and _; (n-1) v® to the location coordinates u. and ν, 'of the first exposure point P and subsequent transformation.

H shows a further embodiment of a transformation stage 31 in which the location coordinates u v of the exposure points P are determined by adding up the basic steps u and v.

The values K »^ Lu · cos K" UEU · "sin A K <Άν * siniSund K Ά / ·" οο3 / 3 of the equation (2) in memory registers 75 - placed 78th

To add to these values, the storage registers 75 - "78 are respectively connected to the first inputs of adder stages 79 - 82. The adder stages 79-82 are followed by further memory registers 83-86, the outputs of which are respectively fed back to the second inputs of the associated adder stages 79-82 The transfer of the addition results into the storage _{registers 83-86} is effected by the clock sequences T _uncj -p

controlled on lines 33 and 35.

The operation of the Add'ierstufe 79 together with the storage register 83 is as follows. Assuming that the content of the memory register 83 is zero, then the summand at the second input of the adder 79 is also zero. With the first clock of the clock sequence T on the line 33, therefore, the value K »23u» cos # is taken over into the memory register 83. This value is returned and to the second input of the adder 79 adds up there, so that "taken with the second clock, the clock sequence T the value of 2K _and 4u-eos / $ in the memory register 83rd

The contents of the storage registers 83 and 84 are summed in an adder 87 and those of the storage registers 85 and 86 in a further adder 88. The results are the location coordinate ^ nx ¹ - and y ¹ .. for the first exposure point P-, which are converted by stripping in stages 89 and 90 into the location coordinate pair x-ijy-i.

The determination of the location coordinate pairs X _n JY _n for the other exposure points P takes place, as already described in FIG. 3, by means of the adder stages 91 - 94 and by means of the stages 95 -

The determination of the location coordinate pairs for the other exposure points P can also be done from the known fourth u * or v * or else by a suitable default setting of the memory register 83 - 86.

5 shows an exemplary embodiment of a recording member 20.

A laser generator 101 generates a polarized light beam 102 which successively passes through three partially transmissive mirrors 103. At this time, the recording beams 24 are reflected out of the light beam 102 and directed to the recording medium 23 by adjusting the mirrors 103. In the beam

Along the recording beams 24 are each a rotary crystal 105, a polarizing filter 106, and a lens. In unexcited rotary crystals 105, the polarization planes of the polarizing filters 106 are rotated by exactly 9Q ⁰ from the plane of polarization of the recording beams 24, so that they are turned off.

By a control voltage between the control electrode 108 and the counter electrode 109, which is at ground potential, is formed in a rotary crystal 105, an electric field. The electric field rotates the polarization plane of the recording beam 24 so that it no longer falls below the blocking angle on the downstream polarizing filter 106, whereby the recording beam 24 is turned on.

The rotary crystals 105 are thus used as light switches, which are turned on and off by the digital recording signals A on the lines 27. The recording signals A are converted into the control voltages for the rotary crystals 105 via amplifiers 110.

Instead of the mirror system, a separate laser generator 101 could also be present for each recording beam 24. The emerging from the polarizing filters 106 recording beams 24 could also be focused on optical fibers on the recording medium 23.

In one embodiment, the recording member 20 may also consist of a light-emitting diode row, wherein each individual light-emitting diode can be controlled by a recording signal A.

The method is also applicable when the halftone dots on another radiation source on a corresponding radiation sensitive. Medium be recorded.

The rasterization can be improved by storing a larger number than 32 × 32 raster threshold values in the read-only memories of the raster generators 37, 38 and 39. The improvement is advantageously achieved even without a corresponding increase in the storage capacity if the untransformed or transformed location coordinates of one of the exposure points before the interrogation of the fixed value spas are superimposed with auxiliary values whose amounts are determined at random.

In the exemplary embodiment, these randomly selected auxiliary values x, and y _{h become} the transformed, continuous location coordinates x '. and y'i of the first exposure point P- by the relationship

χ ¹ _Λ = χ ' _Λ + χ, Ί in

V ¹ Λ ~ V ' - I + Vl

* 1 * 1 ^y h added.

FIG. 6 shows a preferred development of the transformation stage according to FIG. 3 for carrying out this measure. For the sake of clarity, only those functional groups have been taken over from FIG. 3, which contribute to the understanding. The adder stages 63 and 64 are followed by additional adders 111 and 112 in which the transformed spatial coordinates x '.. and y' .. the auxiliary values x, and y are added to form the new spatial coordinates x '.. and y *. to obtain. The corresponding location coordinates of the further exposure points are then derived from these location coordinates. Such auxiliary values can also be added to the calculated location coordinates of the individual exposure points. The auxiliary values x, and y are stored in separate pseudo-random genes.

- 28 - £ 1: S © W ^

won 113 and 114 and supplied via the outputs 115 and 116 to the corresponding adders. The inputs 117 and 118 of the pseudo-random generators 113 and 114 are clocked by the clock sequence T _u on the line 33 (or of the clock sequence T on the line 35). Fig. 7 shows an embodiment for a pseudo-random generator. Of course, the specified measures can also be taken in the transformation stage of FIG. 4.

Fig. 7 shows an exemplary embodiment of a pseudo-random generator for generating the auxiliary values x, and y,.

The pseudo-random generator 113; 114 consists essentially of an n ^ bit shift register 120 and an exclusive-or-feedback network 121. The inputs 117; 118 of the shift register 120 are acted upon by the clock sequences T and T, respectively. Depending on which outputs of the shift register 120 are fed back via the feedback network 121, a quasi-random sequence of output values arises at the outputs 115, 116 which only repeats in a large time interval.

Such a pseudo-random generator is described in detail in the journal Electronics, May 27, 1976, page 107.

To improve grid generation, instead of superimposing auxiliary values, it would also be possible to find a timing sequence T ^f whose pitches are generated at random.

FIG. 8 shows a variant of the arrangement according to FIG. 1, in which a random clock generator 119 is arranged between the frequency divider 32 and the transformation stage.

9 shows an exemplary embodiment of a random clock generator 119. The clock sequence T _u obtained in the frequency divider 32 is applied to η delay stages 122 with different delay times T. "

The delay stages 122 are connected to the inputs 123 of a multiplexer 124, at the output 125 of which the random clock sequence T ^{f is} output. To the control input 126 of the multiplexer 124 is a pseudo-random generator 113 and connected to FIG. 7.

Claims (19)

Berlin, the Invention and claim . 1. A method for producing screened printing forms with screens of arbitrary screen angle and screen width by line-wise optoelectronic master scanning for obtaining an image signal and line by line recording by means of a relative moving over a recording medium recording member, wherein the recording medium is divided into area elements and aligned in the line direction, orthogonal coordinate system assigned in which the spatial coordinates of the surface elements currently being run over by the recording element are continuously determined and in which a recording signal for the recording element is continuously generated by comparison of the image signal with a raster threshold signal, the recording signal recording the individual raster points as a configuration of area elements in the Coordinate system controls, thereby marked etich et that the recorded rotated grid orthogonal, in the direction of Grid-oriented XY coordinate system (30) is associated, which with the oriented in the line direction UV coordinate system (28) the screen angle (ß) that the grid consists of orthogonal, the predetermined screen ruling correspondingly large grid and each raster mesh of the surface elements, which corresponding x; y location coordinates are assigned, that independent of screen angle (A) the surface elements of at least one fictitious grid of any screen width depending on their x; y location coordinates each assigned a grid threshold, that in the current coordinate determination, respectively a raster mesh to be recorded with predetermined raster width u u 'v spatial coordinates of the surface elements in the -at- limited by the x, y spatial coordinates of the fictive grid are converted, and that is determined with the help of the converted x; y location coordinates of each coordinate pair associated grid threshold, which determines when comparing with the associated image signal whether the area in question UV coordinate system (28) is recorded as part of a grid point or not. 2, method according to item 1, characterized in that the conversion of the u, v location coordinates in the limited value range for the x, y location coordinates of the notional raster mesh is digital according to the relationships: x ¹ = K _u .i r = -K _u .u.sin / * ₊ K _v . where the coefficients K and K take into account the ratio of the respective predetermined screen ruling to the screen ruling of the notional raster mesh, and that the restriction of the current x ¹ jy 'location coordinates to the limited value range for the x, y spatial coordinates of the notional raster mesh is omitted higher order bits. Method according to item 1 or 2, characterized in that the current u v location coordinates are determined by counting basic steps (4u; v). Method according to item 1 or 2, characterized in that the current u, v-location coordinates are determined by the continued addition of basic steps (J, Jv). 5. The method according to item 1 or 2, characterized in that the u v location coordinates in basic steps (^ Tu; ^ v) determined and that the corresponding x, y-location coordinates are obtained by the continued addition of constant amounts D = K »4li« cos / 5 + K »41V * sin / S (or D = -K« ^ u »sin / 2 + K i ^ v.cos to the previously determined Ortskoordi.naten according to the relationship ^x (n + 1) ^{= X} n ^{+ D} x ^ ^{or y} (n + 1) ^{= y} n ^{+ D} y ^{) Berecnnet} werden. 6. Method according to one of the items 1 to 5, characterized gekennzei chnet that the x; y-location coordinates of the surface elements. and assign the raster thresholds (R) of the notional raster mesh to a function R = g (x; y). 7. The method according to item 6, characterized in that the function is the form: R = g (A, x + By)
where A and B are partial thresholds. 8. The method according to item 7, characterized g ekennzeichnet that the function R = (A <x + B ^ y) is generated digitally and that the raster thresholds (R) stored and the respectively associated address by the sum (A χ + B y) are formed. 9. The method according to item 7, characterized in that the function R = g (A «x + B <-y) is generated digitally and that the summands (Ax) and (By) stored under the respectively assigned addresses χ and y and the read-out values are added. 10.A method according to item 6, characterized in that the raster threshold values (R) of the notional raster mesh are stored under those addresses which correspond to the associated x, y location coordinates. '' »5- 2 f 11. The method according to item 10, characterized in that the raster threshold values (R) are stored in a two-dimensional memory matrix. 12. The method according to any one of items 1 to 11, characterized in that for the simultaneous recording of a plurality of surface elements as parts of a raster point in the recording member a plurality of controllable by separate recording signals recording beams are generated and that for obtaining the recording signals for the χ; y place coordinate pairs of the individual Scanning thresholds (R _n ) associated with recording beams ( _n ) are determined and compared with the image signal. 13.-method according to item 12, characterized in that the raster threshold values (R »), in the time-division multiplex method of the individual x _n ; y _{n place} coordinate pairs are determined. 14. The method according to item 12 or 13, characterized in that continuously from the u v -location coordinate pair determined for a recording beam, the u v -location coordinate pairs of the other recording beams are added by adding the distances of the respective recording beams from the one recording beam in the UV coordinate system. 28), and that the individual u _n ; v _n -0th coordinate pairs are transformed into corresponding x »; y location coordinate pairs. 15. The method according to item 12 or 13, characterized in that continuously from the transformed xjy-location coordinate pair of a recording beam, the χ; y-location coordinate pairs of the other recording beams by adding the transformed into the XY coordinate system (30) distances · the corresponding recording beams of the a recording beam are obtained. & W 4P ^ 16. The method according to item 14 or 15, characterized in that for simultaneous recording of a plurality of recording lines, an image signal is obtained by document scanning along a scanning line which is assigned to one of the recording lines in a location, and the image signal is compared with the corresponding raster threshold values. 17. The method according to item 14 or 15, characterized in that for simultaneously recording a plurality of recording lines for each of the recording lines, an image signal is obtained by document scanning along spatially assigned scanning lines, and the image signals are compared with the corresponding screen thresholds. 18. The method according to any one of items 1 to 17, characterized in that in the template scanning for each grid point a plurality of pixels are scanned along 'a scan line. 19. The method according to one of the items 1 to 18, characterized in that the location coordinates of the surface elements before the determination of the raster thresholds randomly generated values are superimposed, which are smaller than the location coordinates values. 20. Method according to item 19, characterized in that the randomly generated values are additively superimposed on the current x ';y' location coordinates. 21. The method according to any one of items 1 to 18, characterized gek ennzeich net, that the basic steps (^ u) in the circumferential direction by means of a clock sequence (T) are counted and that the clocks, this clock sequence are generated randomly. 22. Arrangement for carrying out.The method according to item 1, consisting of an opto-electronic scanning element for obtaining an image signal from a line-wise movable relative to a recording medium and controllable by a recording signal recording member for generating arranged in the grid halftone dots, from a device for continuously determining the spatial coordinates of surface elements of the recording medium currently being traversed by the recording element in an orthogonal and line-oriented coordinate system, a raster generator for generating a raster threshold signal, and a comparison stage applied to the image signal and the raster threshold signal for obtaining the recording signal the recording signal controls the recording of the halftone dots as a configuration of the surface elements in the coordinate system, characterized by a halftone generator in which, independent of the halftone dot ny ty5) the area elements of at least one fictitious grid of any screen width is assigned a grid threshold value depending on their x, y location coordinates in an XY coordinate system (30) ', wherein the XY coordinate system (30) in the direction of the grid aligned, relative to the oriented in the direction of the line UV coordinate system (28) rotated by the screen angle (/ 5) and constructed from the predetermined grid size correspondingly large grid, which in turn are divided into the area elements, and one between the means for continuously determining the u v coordinate coordinates and the raster generator arranged coordinate transformation stage, in order to convert each of u-v spatial coordinates of the surface elements attributable to a raster grid with a predetermined screen ruling in the limited range of values of the corresponding x; y location coordinates of the fictitious grid. 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