EP2349718B1 - Method for illustrating printed image carriers - Google Patents

Description

The invention relates to a method for imaging a predetermined desired printing characteristic during printing, namely a predetermined relationship between prepress-based printing surface coverage values and print image area coverage values that actually form during printing, and thus a defined dot gain, ensuring print image carriers such. B. printing plates.

Fig. 1 illustrates the known from the prior art approach for producing offset printed products. From a file 10 for a print template, a so-called RIP file 12 is generated in a raster image processor 11, wherein the RIP file 12 is used in an imagesetter 13 to print forms such. B. printing plates 14 to expose and thus produce. For each ink involved in printing a printing plate 14 is produced, which are used in the printing units of a printing machine 15 to print a printed product 16. When assessing the print quality of such a printing process, a so-called printing characteristic plays an essential role, wherein a printing characteristic describes the relationship between the areal coverage values of the file 10 and thus the artwork and the areal coverage values that actually form during the printing of the printed copies 16. So shows Fig. 1 By way of example, a printing characteristic 17 is plotted on the horizontally extending axis 18 of the printing surface cover values of the file 10 and on the vertical axis 19 of printed image surface coverage values of the printed copy 16. Further visualized Fig. 1 the so-called dot gain 20, which depends, inter alia, on the type and setting of the printing press used for printing, the quality of the printing material used for printing and on the properties of the ink used for printing. To ensure a good print quality, for each ink involved in the printing, an actual pressure characteristic forming during printing must correspond as far as possible to a predetermined desired pressure characteristic. Otherwise, z. B. in the print image, a so-called color cast or other color errors occur, which adversely affects the print quality and can lead to the printing of waste.

So far, there is great difficulty that during printing an actual printing characteristic actually forming during printing corresponds to a predetermined nominal printing characteristic, ie a defined relationship is provided between pre-printed surface coverage values and print image area coverage values actually forming during printing, and thus a defined tone value increase.

From the WO 01/91453 A1 a method for calibrating printing presses is known. The tone value increase or dot gain is measured on a wedge and from this a profile is calculated which corresponds to the maximum dot gain or the maximum dot gain measured.

On this basis, the present invention is based on the problem to provide a novel method for imaging printed image carriers. This problem is solved by a method according to claim 1. The method according to the invention comprises at least the following steps: a) a test print image carrier is produced for at least one printing ink, namely such that a RIP file is produced from a test print original which images a gradation fine wedge with a defined number of gradation levels for the respective printing ink is generated, based on which the respective test print image carrier is imaged; b) the or each test print image carrier produced according to step a) is used to print a test print image, the test print image for at least one ink involved in printing comprising the respective gradation fine wedge having the defined number of gradation levels; c) the print image printed in step b) with the or each test print image carrier is measured such that for each gradation level of the or each gradation fine wedge an actual test print image area coverage value is determined, from the test artwork area coverage values of each gradation step of the gradation fine wedge and actually during printing forming test print image area coverage values of each gradation level of the gradation fine wedge an actual pressure characteristic is determined for the respective printing ink; d) the or each determined in step c) Istdruckkennlinie is compared with the predetermined for the respective ink target pressure characteristic such that determined for each in the target pressure characteristic for a defined Druckvorlageflächungungsgröße print image area coverage value of the printing in step b) forming test print image area coverage value and to form a Ratio with in order to provide a corrected target pressure characteristic in the target pressure characteristic, the print image area coverage values are replaced by values resulting from the multiplication of the original image area coverage values and the ratio values obtained therefor; e) taking advantage of the or each generated in step d) corrected target pressure characteristic is generated from the print template of the actual print image to be printed a RIP file, which is used for imaging the print image carrier.

With the present invention, it can be ensured in a simple and secure manner that during printing for each ink involved in the printing a predetermined desired pressure characteristic is maintained. The method according to the invention can be carried out fully automatically or semi-automatically. The method is for all known printing form based printing methods, such. B. for offset printing, gravure, planographic printing, book printing or through-pressure. The method according to the invention can also be used for digital printing systems according to the direct imaging method. It is suitable for use with sheetfed presses and web presses.

Fig. 1:

ein Blockschaltbild zur Verdeutlichung eines Druckprozesses; und

Fig. 2:

ein Diagramm zur Verdeutlichung des erfindungsgemäßen Verfahrens zum Bebildern von im Druckprozess eine vorgegebene Solldruckkennlinie gewährleistenden Druckbildträgern.

Preferred embodiments of the invention will become apparent from the dependent claims and the description below. Embodiments of the invention will be described, without being limited thereto, with reference to the drawings. Showing:

Fig. 1:

a block diagram illustrating a printing process; and

Fig. 2:

a diagram illustrating the process of the invention for imaging of a predetermined target pressure characteristic curve in the printing process image carriers.

The invention relates to a method for imaging or producing print image carriers which guarantee a predetermined desired printing characteristic during printing, wherein a predetermined desired characteristic describes a predetermined relationship between pre-print-based print cover area values and print image area coverage values actually forming during printing, and thus a defined tone value increase.

The following describes the process for the production of printing plates. However, the method is not limited to this. Rather, the method can also be used for imaging other print media.

The predetermined desired pressure characteristic may be a normalized nominal pressure characteristic or a desired pressure characteristic defined in-house by a printing company in order to produce printed products in a desired print quality.

Fig. 2 shows such a predetermined target pressure characteristic 21, wherein in Fig. 2 on the horizontally extending axis 22, in each case printed copy surface coverage values X _n and on the vertically extending axis 23, in each case print screen area coverage values Y _{n are} plotted. Print image area coverage values of the desired pressure characteristic 21 are marked Y _n-SOLL .

In the context of the method according to the invention, a test printing plate is produced in a first step for at least one printing ink, namely such that a preferably linear test printing original, which images a gradation fine wedge with a defined number of gradation levels for the respective printing ink, preferably a linear RIP Is generated, based on which the respective test pressure plate is preferably exposed linearly. The number of gradation levels for the gradation fine wedge of the respective printing ink is arbitrary. Thus, a gradation fine wedge of an ink can comprise up to 100 gradation levels, which then each represent a gradation of the area coverage values of 1%. It is also possible for a gradation fine wedge to comprise 20 gradation levels, with each gradation grade then grading area coverage values by 5%.

It should already be pointed out at this point that in the first step of the method according to the invention alternatively from the preferably linear test printing original also a non-linear RIP file can be generated, based on which the respective test printing plate is then exposed non-linearly.

Such a non-linear RIP file is preferably generated using a pre-determined corrected target pressure characteristic stored in the raster image processor. Thus, the previously determined target pressure characteristic z. B. also be determined by this method, but under no longer valid printing conditions such as a different temperature, using a different ink type, another type of printing material or the like.

In a second step of the method of the invention, the test printing plate or plates produced in the first step are used to print a test print image, the test print image for at least one ink involved in printing, namely the or each ink for which in the first step a corresponding test printing plate is exposed linearly was included a gradation fine wedge with the defined number of gradation levels. Accordingly, in the second step of the method according to the invention, the or each linearly exposed test printing plate is used for printing, the printing in the second step of the method according to the invention being used on the printing machine to be used for printing the actual printed image, on the printing substrate to be used for printing the actual printed image, and under Use of the print to be used for printing the actual image to be used ink and possibly the dampening solution to be used.

In a third step of the method according to the invention, the printed image printed with the or each test printing plate is measured, namely such that for each gradation level of the or each printed gradation fine wedge, a test print image area coverage value actually formed during printing is determined.

From the test print surface coverage values X _{n of} each gradation step of the gradation fine wedge and the test print image area coverage values Y _{n-IST of} each gradation level of the corresponding gradation fine wedge actually formed during printing, an actual pressure characteristic is determined for the respective printing ink. In Fig. 2 Such an actual pressure characteristic curve 24 is shown by way of example, such an actual pressure characteristic line 24 thus showing for a printing ink the relationship between the print image area coverage values and the print surface area coverage values which occurs when printing a gradation fine wedge with a linearly exposed test printing plate. Furthermore, in Fig. 2 a straight line 25 is plotted against which the so-called dot gain is determined and for which the following applies: X _n = Y _n .

The metrological evaluation of the gradation levels of the or each printed gradation fine wedge for determining the respective Istdruckkennlinie for each ink is preferably carried out using a densitometer. Alternatively, however, another color measuring device can be used.

The measurement of the gradation levels of the or each printed gradation fine wedge may be offline for printing e.g. with the help of handheld instruments or fully automated measuring instruments or inline for printing with the help of fully automated measuring instruments.

In a fourth step of the method according to the invention, the actual printing characteristic curve 24 determined for a printing ink is subsequently compared with the desired printing characteristic curve 21 specified for the respective printing ink such that for each printing image area coverage value Y _n-SOLL specified in the nominal printing characteristic curve 21 for a defined printing surface area coverage value X _n Print forming test printing image area coverage value Y _n-iS is determined and taken into consideration to form a ratio value using the same, wherein the print image area coverage values are replaced by values Y _{n-sET NEW} for providing a corrected desired pressure characteristic in the target pressure curve resulting from the multiplication of the master area coverage values X _n and the ratio values determined for the same. It therefore applies: $$Y_{n-\mathit{SHOULD}-\mathit{NEW}}=X_n*\frac{Y_{n-\mathit{SHOULD}}}{Y_{n-\mathit{IS}}}$$

In Fig. 2 this is illustrated by way of example for the print original area coverage value X _n of 40%, which should guarantee a print image area coverage value Y _n-SOLL of 65% according to the target print characteristic 21. On the actual printing characteristic 24, the test printing original area coverage value X _n corresponding to 40% of the printing original area coverage value X _{n is determined} as 40% of the test printing image area coverage Y _n-IST which forms in the printing and which corresponds to the _actual printing characteristic 24 of FIG Fig. 2 here is 53%. The thus obtained print image area coverage value Y _n-SOLL of 65% and the thus-determined test image area coverage value Y _n-ACT of 53% are proportioned and multiplied by the print surface area coverage value X _n of 40%, thus providing the corrected target pressure characteristic in the target pressure characteristic for the print original area coverage value or test print area coverage value X _n of 40%, the print image area coverage value is replaced by the following value Y _n-SOLL-NEW : $${\mathrm{Y}}_{\mathrm{n}\mathrm{-}\mathrm{SHOULD}\mathrm{-}\mathrm{NEW}}\mathrm{=}\mathrm{40}\mathrm{\%}\mathrm{*}\left(\mathrm{65}\mathrm{/}\mathrm{53}\right)\mathrm{=}\mathrm{49}\mathrm{\%}\mathrm{,}$$

Taking advantage of the generated in the fourth step of the method according to the invention corrected target pressure curve for the respective ink is generated from the artwork of the actually printed image in the raster image processor a corrected RIP file used to expose the printing plates required for printing the actually printed image becomes. The determined, corrected target pressure characteristic therefore represents a correction characteristic for the raster image processor, using the same for a print job printing plates are generated, by means of which then the predetermined target pressure curve 21 can be maintained for the respective ink, so which can be ensured that the actual pressure characteristics correspond to the respective desired pressure characteristics.

Preferably, for each ink involved in printing the actual printed image, in the above manner, an ink-specific actual printing characteristic is determined, on the basis of which an ink-corrected corrected desired printing characteristic for the raster image processor is determined.

In this case, a corresponding test printing plate with a corresponding gradation fine wedge is then generated for each ink involved in the printing, in which case the respective gradation fine wedges printed with the aid of the test printing plates for the determination of the actual pressure characteristics are metrologically evaluated.

Are z. B. in an offset printing after the autotypical Zusammendruck next to the four process colors cyan, magenta, yellow and black still involved two offprint colors, then corresponding test printing plates would be generated with corresponding gradation fine wedges for all six inks to a corrected target pressure characteristic for the raster image processor for each of the inks to determine ink individually.

In contrast to this, it is also possible for ink colors to be used for only a subset of the printing inks used for printing the actual printed image in the sense of the invention, as well as for individual printing ink-specific actual printing characteristics and for individual printing ink corrected nominal printing characteristics.

For the or each printing ink for which no actual printing characteristic curve is determined by printing and metrological evaluation of a gradation fine wedge, a corrected nominal pressure characteristic can be determined on the basis of the nominal pressure characteristic correction of a reference ink, for which an actual pressure characteristic and an ink corrected corrected nominal pressure characteristic were determined.

The method described above is for all known printing form based printing methods, such. B. for offset printing, gravure, planographic printing, book printing or through-pressure. The method according to the invention can also be used for digital printing systems according to the direct imaging method. It is therefore not limited to the production of printing plates, but rather can also be used in the production or imaging of other print media or printing plates.

LIST OF REFERENCE NUMBERS

10

A master file

11

Raster Image Processor

12

RIP file

13

imagesetter

14

printing plate

15

press

16

printed copy

17

Pressure characteristic curve

18

A master coverage values

19

Print image area coverage values

20

Dot gain

21

Target pressure curve

22

A master coverage values

23

Print image area coverage values

24

Istdruckkennlinie

25

Just

Claims (9)

1. A method for imaging print image carriers which during printing ensure a predetermined set value characteristic, namely a predetermined relationship between printing prestage based print copy area coverage values and print image area coverage values actually forming during printing and thus ensure a defined tonal value increase, with the following steps:

   a) for at least one printing colour involved in the printing, a test print image carrier is generated, namely such that from a test print copy, which for the respective printing colour depicts a gradation precision wedge with a defined number of gradation steps, an RIP-file is generated based on which the respective test print image carrier is imaged:

   b) the or each test print image carrier generated according to step a) is used for printing of a test print image, wherein the test print image for at least one printing colour involved in the printing comprises the respective gradation precision which with the defined number of gradation steps;

   c) the print image printed in step b) with the or each test print image carrier is measured in such a manner that for each gradation step of the or each gradation precision wedge a test print image area coverage value actually forming during printing is determined, wherein from the test print copy area coverage values of each gradation step of the gradation precision wedge at the test print image area coverage values of each gradation step of the gradation precision wedge actually forming during the printing, an actual print characteristic for the respective printing colour is determined;

   d) the or each set print characteristic determined in step c) is compared with the set print characteristic predetermined for the respective printing colour in such a manner that for each print image area coverage value predetermined in the set print characteristic for a defined print copy area coverage value the test print image area coverage value forming during printing in step b) is determined and for forming a ratio value is put in relation with the latter, wherein for providing a corrected set print characteristic in the set print characteristic the print image area coverage values are replaced with values which are obtained for these determined ratio values;

   e) utilising the or each corrected set print characteristic generated in step d), an RIP-file is generated out of the print copy of the print image actually to be printed, which is used for imaging the print image carrier, wherein for each printing colour involved in the printing of the actual print image in terms of the steps a) to e), an individual actual print characteristic and an individual corrected set print characteristic is determined.
2. A method for imaging print image carriers which during printing ensure a predetermined set value characteristic, namely a predetermined relationship between printing prestage based print copy area coverage values and print image area coverage values actually forming during printing and thus ensure a defined tonal value increase, with the following steps:

   a) for at least one printing colour involved in the printing, a test print image carrier is generated, namely such that from a test print copy, which for the respective printing colour depicts a gradation precision wedge with a defined number of gradation steps, an RIP-file is generated based on which the respective test print image carrier is imaged:

   b) the or each test print image carrier generated according to step a) is used for printing of a test print image, wherein the test print image for at least one printing colour involved in the printing comprises the respective gradation precision which with the defined number of gradation steps;

   c) the print image printed in step b) with the or each test print image carrier is measured in such a manner that for each gradation step of the or each gradation precision wedge a test print image area coverage value actually forming during printing is determined, wherein from the test print copy area coverage values of each gradation step of the gradation precision wedge at the test print image area coverage values of each gradation step of the gradation precision wedge actually forming during the printing, an actual print characteristic for the respective printing colour is determined;

   d) the or each set print characteristic determined in step c) is compared with the set print characteristic predetermined for the respective printing colour in such a manner that for each print image area coverage value predetermined in the set print characteristic for a defined print copy area coverage value the test print image area coverage value forming during printing in step b) is determined and for forming a ratio value is put in relation with the latter, wherein for providing a corrected set print characteristic in the set print characteristic the print image area coverage values are replaced with values which are obtained for these determined ratio values;

   e) utilising the or each corrected set print characteristic generated in step d), an RIP-file is generated out of the print copy of the print image actually to be printed, which is used for imaging the print image carrier,
   wherein for a part quantity of the printing colours involved in the printing of the actual print image in terms of the steps a) to e) an individual actual print characteristic and individual corrected set print characteristic is determined, and in that for the or each printing colour, for which no individual actual print characteristic is determined, a corrected set print characteristic based on the set print characteristic correction of a reference printing colour is determined, for which in terms of the steps a) to e) an individual actual print characteristic as well as individual corrected set print characteristic was determined.
3. The method according to any one of the Claims 1 to 2, characterized in that in step b) the test print image is printed on the printing press to be used for printing the actual print image and under the printing conditions which prevail for the printing of the actual print image.
4. The method according to any one of the Claims 1 to 2, characterized in that in step c) the test print image is measured with the help of a densitometer.
5. The method according to any one of the Claims 1 to 4, characterized in that in terms of the steps a) to e) print forms as print image carriers are exposed.
6. The method according to Claim 5, characterized in that as print forms, printing plates are exposed.
7. The method according to any one of the Claims 1 to 4, characterized in that in terms of the steps a) to e) as print image carriers, erasable and rewritable print forms are directly imaged.
8. The method according to any one of the Claims 1 to 7, characterized in that in step a) from a test print copy a linear RIP-file is generated, based on which the respective test print image carrier is linearly imaged.
9. The method according to any one of the Claims 1 to 7, characterized in that in step a) from a test print copy making use of a corrected set print characteristic determined for an non-linear RIP-file is generated, based on which the respective test print image carrier is non-linearly imaged.

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