DE2728135A1 - DEVICE FOR REPRODUCING IMAGES - Google Patents

Description

In the production devices used in graphic institutions an adjustable computer is required for color separations, those of the photomultiplier tubes or photocells of the scanning head the device provided signals into signals

implement, using which the output unit of the pre-

I can produce color separations or printing plates which lead to a printed image which is an acceptable reproduction of the original used. With this modification of the
Signals, the computer must take the following points into account: The working characteristics of the input unit
Scanning head and the reproduction head representing the output unit, the tone or the gradation curve which are suitable for the object to be reproduced, the absorption and printing properties of the printing ink and the occasionally required! Change requests from the editor to the original picture.

However, the necessary corrections can only be saved as a
represent complicated functions and are by no means independent of one another. Rather, there is a strong interaction between)

I the corrections, and that makes it difficult for the printer to make the necessary settings with regard to the peculiarities of the template or the wishes of the editor. Ever
more complicated functions the correction circles in the electronic

j part of the device, the smaller the stability

; did this circle. j

• I

! I.

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In recent years, the modified analog signals have become

converted to digital signals in order to store them without deteriorating the quality of the ultimately obtained reproduction can. The signals are retrieved from memory as needed to display the surface of the reproduction medium to expose or otherwise treat. With such a storage, e.g. an enlargement of the original according to the in the method described in GB-PS 1 166 091 take place. If the signals are converted into digital signals, then of course one must be large number of digitization levels or quantization levels can be used. Namely, are the steps between the digitization levels too large, the transitions between two adjacent digitization levels on the finished image will be considered un ^ desired contours visible. However, the number of digitization levels cannot be used for reasons of the capacity of the memory be increased infinitely. The required number can be reduced somewhat by superimposing a noise signal on the signals will.

Because of the difficulties in setting and maintaining analog corrections and making Adjustments by an average good operator have been suggested in DT-OS 23 00 514, the correction using a digital look-up table. A memory with a matrix with corrected output values for the color and tone is used is assigned to a matrix of color component input signal combinations, each corresponding to a point in the color space.

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These values are entered into the calculator before an image is reproduced and take into account the changes requested by the operator for the job being done. the When the original is scanned by the photomultiplier tubes located in the scanning head, image signals are generated in this method converted into digital signals and then processed with the look-up table stored in the aforementioned memory, so that the values corrected in the required manner are obtained at the output of the memory. To load the Memory with the values of the matrix of the output values before the actual work, parameter values are set up, the with regard to the characteristic properties of the device for producing color separations and the characteristic Properties of the original to be reproduced are selected.

These values are entered into a programmed digital computer, which creates the necessary link between the output values and the input values and, for example, also can generate a black separation signal and the color component signals can free you from an under color.

By using a digital look-up table, one can get the The advantage that the correction of the color signals is stable and that which arises from the interaction between the corrections Problems have been resolved. Also the adjustment of the device for reproducing an image to reproduce the present one Submission is made easier through the use of a digital reference board. Some pictures or parts of pictures that are marked with

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such a device, however, show; a slight contouring. This could be overcome by increasing the number of digitization levels, which of course must be done together with a corresponding increase in the memory.

It has now been found that this contouring can be avoided even without increasing the number of digitization levels ^: while still obtaining a stable correction. For this purpose, a device according to the invention for reproducing templates has: a device for generating signals which correspond to the densities of the color components at the pixels of the template to be reproduced; a preset

j analog signal change circuit through which the signals j

changed in accordance with fixed change regulations

ι be that at least one of the modified signals of more j

depends as two unmodified color component signals; a ^ n Analog / digital converter, which derives from the changed analog signals

ι provides speaking digital signals; an adjustable j

ι digitally working correction circle for further modification of the signals in digital form such that desired color characteristics are obtained; a digital / analog converter, which produces analog signals corresponding to the further modified digital signals; and one with the latter analog signals acted upon output unit, through which the surfaces of a reproduction carrier for the purpose of manufacture of color separations corresponding to each of the color component images the template is being edited.

The invention also provides a method for reproduction of templates where most of the correction is made to the analog signals before the analog-to-digital conversion he follows.

The analog correction device can thus carry out a standard correction for each signal which, with regard to is chosen based on typical working conditions and in which the following points are taken into account: The working characteristics of the scanning unit and the reproduction unit the device, the transparency correction and the color correction for the absorption by the inks, etc. Instead, j the analog color correction also using j

i results of color theory are carried out, whereby in all j

Dividing the color space uniformly distributed quantization contours in the j

With regard to barely perceptible color differences in velvet '

borrowed directions can be used. The digital color correction!

then takes into account the difference between ₍

this signal range and the desired shape of the product. i

In both cases, the analog correction is chosen so that a relatively simple I transformation is carried out and j

very stable working is obtained. The correction that!

j nor by the operating staff for a single template or for the j Achieving a particular effect can be requested using the memory containing the look-up table carried out, with the bulletin board loaded into the device by the operator before the actual reproduction

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will.

In this way, good stability is obtained by simplifying the analog correction circuit, although this correction circuit still carries out most of the signal transformation between the scanning head and the reproduction head, avoiding any contour formation at the same time.
This failure to form a contour seems to be explained by the fact that in some parts of the three-dimensional
Color space, the eye is particularly sensitive to small changes in color. If the number of digitization levels is reduced, a contour formation appears in such parts before it becomes visible in other parts of the image.Usually, a logarithmic circuit is applied with the signal provided by the photomultiplier tube of the scanning head in order to determine the level of the signals provided by the photomultiplier tubes to modify. In the device described in DT-OS 23 00 514, the digitization levels are therefore distributed in a subjectively essentially uniform manner with respect to the image brightness. However, when use is made of the present invention, the digitization levels are essentially uniformly distributed in terms of the density of the color separation, since only a small part of the correction
after the analog-to-digital conversion is performed.

The invention is explained in more detail below using two exemplary embodiments with reference to the accompanying drawings
explained. In this show:

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FIG. 1 shows a color tone diagram, on the basis of which the object achieved by the invention is explained;

Figure 2 shows a first embodiment of an inventive Device for producing color separations; and

Figure 3 is a block diagram of a second according to the invention Device for the production of color separations.

First of all, with reference to FIG. 1, that on which the invention is based is intended Problem of color discrimination. A C.I.E. color tone diagram is shown in FIG. 1, in which ellipses are drawn around certain points, the radii of these ellipses being standard deviations for fit in different Represent directions. In this diagram, the size of the radii of the ellipses with respect to the scale unit is the Axes of the hue diagram enlarged to show the technical problem more clearly. An exhaustive explanation such a hue diagram can be found in that of H.D. Murray published book "Color in Theory and Practice" on pages 159 and 160. The different sizes of these Ellipses show the different sensitivity of the eye to color changes in different parts of the color space at.

A device for producing color separations is shown schematically in FIG. 2, in which the above problem is eliminated is. In this device, a template 10 is from a

? om

Cylinder 12 is carried, which is rotated about an axis 14. An ab- j probe 16 is moved linearly parallel to the axis of the cylinder and synchronously with the rotary movement of the cylinder. Based on these Movement scan the photomultiplier tubes provided in the scanning head the original on a helical path with a very slight incline around the cylinder 12. The template 10 is thus along a plurality of lines running parallel to one another; groped. The scanning head 16 contains color filters for the three photomultiplier tubes. The output signals of the photomultiplier tubes thus represent the red, blue and green components of the scanned points of the original. A fourth photomultiplier tube the original 10 scans through an opening that is larger than the openings of the other photomultiplier tubes. From her becomes a "fuzzy" signal is provided as is known to those skilled in the art. The "sharp" signals corresponding to the three color components and the fuzzy signal are amplified by logarithmic preamplifiers 18 so that signals are obtained which are in the I. change essentially linearly with density. These signals are given to a contrasting circle 20 in which the "unsharp" Signal is mixed in a known manner with each of the "sharp" signals i in such a way that a contrast enhancement in the j Margins is preserved.

The three color component signals are then from the contrasting circle 20 given to an analog correction circuit 22.

in which their amplitudes are changed so that non-linear

activities of the photographic components, the photochemical bej components and the printing units of the entire device for repro4

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Reduce images to be taken into account. The signal correction carried out in the correction circuit 22 is small and takes place in FIG
: fixed size. This correction is a standard correction for normal working conditions.

The three corrected analog signals are then given to an analog / digital converter 24, in which the level of the signals
can be sampled and converted into binary encrypted digital signals
being transformed. The digital signals can, for example, seven

digit binary numbers, which equates to 128 digitization levels

• I

receives. The digital signals representing binary numbers for j

each scanned point of the original are then mapped to a j digitally working enlarger 26 given, for example, in the

GB-PS 1 166 091 may have the structure described. One of those

digital enlarger essentially has an I memory and a device for changing the frequency of j

the sampling signals retrieved from the memory according to the desired < Magnification on. At the same time, the speed of the movement of the reproduction head becomes the axis of the reproduction tion cylinder changed in the parallel direction according to the desired magnification. j

The digital signals provided by the enlarger 26; are based on an adjustable, digitally working correction j

• j

given circle 28, which has a memory for a look-up table
as described in DT-OS 23 00 514. The- ι

Before the actual reproduction, this memory is marked with a j ί i

ι Matrix of tone and color corrected output values loaded wor-j

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those corresponding to a matrix of color component input signal combinations- J functions that each represent a point in the color space. In the device under consideration here, for each point des Color space, which is assigned to an input signal combination, four output values are provided that represent the three color component signals and represent a black separation signal. The levels of the three color component signals are dependent on the black separation signal changed to avoid an under color in the color separations. The one made in the correction circuit 28 Correction can be influenced to the extent that the values loaded into the memory for the look-up table can be influenced by an operator can be selected before the actual reproduction of the original begins. Make these corrections thus a fine trimming for the simple, unchangeable analog correction that is carried out in the analog correction circuit 22 is made.

The ones provided by the digitally operating correction circuit 28 Corrected signals are now sent to a digital / analog converter 30. The analog signals emitted by this are given using a switch 3 2 one at a time on a reproduction head 34 which is about a film 36 travels on a cylinder 38 rotating about axis 14 at the same speed as cylinder 12 is arranged. The film 36 is exposed to light by a light source provided in the reproduction head, and one is obtained by setting the switch 32, the printing color separation specified for the respective color being viewed (black, magenta, yellow

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or cyan).

Thereafter, the switch 32 is switched so that another output terminal of the digital / analog converter 30 is connected to the reproduction head 34 is connected and a new film is exposed, etc.

The arrangement of the scanning head and the reproduction head with respect to of the cylinder 12 or of the cylinder 34 is known to the person skilled in the art and can, for example, take place as described in GB-PS 1 166 091 is described. The logarithmic preamplifiers 18 are standard circuits for processing photomultiplier tubes provided signals. A "fuzzy" masking circle, which is suitable for use with the contrasting circle 20 is described in DT-OS 19 59 421.

Correction circles that work analogously are also known as such. Such a correction circuit is described for example in GB-PS 1,241,852. Analog-to-digital converters and digital-to-analog converters: are commercially available. In the DT-OS 23 00 514 already mentioned above, a digitally operating correction circuit and at the same time also an interpolation circuit is described, which can be used together with the analog / digital converter.

It is understood that the provided by the analog / digital converter Signals can also be stored over a long period of time, to then be used at a later time or at a other place to be used. You can also use all four

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expose extracts at the same time. This can be done, for example, by! that two films in a row around a trace of the circumference of the

Cylinder 34 are arranged and two other films along one parallel track. The reproduction head then has two light sources, and those for generating the various color separations Required signals are called up from a buffer in such a way that

I how this is the position of the color information carried by the cylinder 34 trains with regard to the corresponding light sources providing exposure in the reproduction head is required. j

The treated surface of the reproduction medium also needs

not necessarily being a photographic emulsion that j is exposed by a light source in the reproduction head. The surface of the reproduction medium can, for example, also contain a film be a very thin metal layer, in which, by exposure to a pulsed laser beam, one accommodated in the reproduction head Very small holes are produced by the laser. The reproduction head can also have a laser that directly processes material evaporated from the surface of the cylinder 38, the latter having a plastic coating carried by a metal core can be provided or formed in a metal base body and filled with plastic material recesses can.

A second embodiment of a device according to the invention for producing color separations is schematically shown in FIG using a more theoretical solution to the problem illustrated in Figure 1. In the case of the one shown in FIG

The signals provided by the scanning head 16 are device given to a transformation circuit 40 in which they are transformed such that differences in color signal values are the same Size correspond approximately to uniform differences in the color impression space; i.e. the transformation is a!

ι

; such that, expressed in signal differences, those in Figure 1;

j i

■ ellipses shown are all approximately the same size. The- ^! like transformations are known in the theory of color difference measurements and can be achieved using Operations

; amplify and analog working multiplication circuits in the

Perform in a known manner. The received! Signals are sent to the analog / digital converter 24. As ! In the exemplary embodiment shown in FIG. 2, the digital signals provided by the analog / digital converter 24 are generated a digital enlarger 26 is given.

From the enlarger 26, the digital signals come to a digitally operating correction circuit 44, which is in turn with a The reference table can be a working correction circle, which however Provides output signals with which the inverse transformation is carried out digitally in addition to the color and tone correction

; which is the counterpart to that in the transformation circuit,

'I.

j 40 represents the transformation performed. The in the Trans- ι

: j

The transformation carried out by the formation circuit 40 is again unchangeable, while the digital correction

! circle 42 carried out correction component of the signal change in

Can be adjusted with regard to the work carried out in each case. j [The corrected digital signals thus obtained become as in

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the embodiment of Figure 2 to a digital / analog converter 44 given, from where they reach the reproduction head 34.

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Claims (6)

Claims M Λ device for reproducing images with a signal generator device, the analog signals corresponding to the densities of the color components at the pixels of an original generated, and with a signal processing device acted upon by the analog signals, the analog output signals for treating the reproduction carrier surfaces for the purpose of producing color separations for each color component t image point of the original is generated and in which the analog input j output signals are converted into digital signals that are stored or processed and then converted into the analog output signals, characterized in that that the signal processing device has: a preset 709881 / Q9U ORIGINAL INSPECTED 272813a provided signal changing circuit (22; 40), which changes the analog: color component signals before their conversion into digital signals in accordance with predetermined, fixed processing ^{instructions L in} such a way that at least one of the modified analog signals depends on more than one unmodified analog signal, and an adjustable digital correction circuit (28; 42), which further modifies the signals in digital form in order to obtain the desired color characteristics. 2. Apparatus according to claim 1, characterized in that the analog signal change circuit (22; 40) a color correction by a fixed amount in order to give the analog signals predetermined, fixed color characteristics, and in that the adjustable digital correction circuit (28; 42) carries out a further color correction to that of the analog operating To trim the signal change circuit (22; 40) carried out fixed correction to the desired value. 3. Device according to claim 1 or 2, characterized in that that the preset analog signal change circuit (40) such a transformation of the from the scanning head obtained analog signals performs that for given differences between the color component signal combinations approximately uniform differences in the color impression in the color space can be obtained, and that the adjustable digital Correction circle (42) in addition to the adjustable color correction, the inverse transformation to the transformation in Performs signal change circuit. 709881/0914 -3- 4. A method of reproducing images, in which the density of the color components of the pixels of a to be reproduced Original corresponding analog signals are generated, these are processed in a signal processing device and thereafter used to control the treatment of the surfaces of a support to suit color separations to generate each one of the color component images of the original, with the obtained analog signals for storage or processing can be implemented in digital form and, prior to their use, to control the processing of the surface of the reproduction medium are converted back into analog form, characterized in that the color component signals before their conversion into digital form are subjected to a fixed predetermined modification, in the case of which is fixed for setting given color characteristics, at least one modified analog signal as a function of more than one unmodified Analog signal is changed. 5. The method according to claim 4, characterized in that the analog signals are first subjected to the unchangeable color correction and that the greater part of the total color correction is carried out on the analog signals before the Analog-to-digital conversion takes place. 6. The method according to claim 4 or 5, characterized in that the color component densities of the image to be reproduced Representative analog signals are subjected to such a transformation that the differences between color components 709881 / 09U ten signal combinations are essentially uniform in differences of the visual color impression in the color space, and that the adjustable color correction that corresponds to that in digital Form present signals are subjected to, at the same time with a digital transformation is carried out, which the is the inverse transformation of the transformation that was carried out with the analog signals. ; 709881/0914