DE102015104574B3 - Method for optimizing halftone dot positioning in digital printing - Google Patents

Abstract

A method (500) of printing an image to be printed by a digital printing system (100) is described. In this case, a flexible positioning of pixels (201) within the raster cells (202) of a grid network (350, 400, 450) and a corresponding flexible timing of the pixel production units of the printing system (100). This allows a flexible adjustment of the printing costs / print quality of the printing system (100).

Description

The invention relates to methods and corresponding devices for determining screened image data for printing in a digital printing system.

The cost and / or expense of printing image data in a digital printing system typically depends on the ruling of rasterizing the image data to be printed. In this case, the expenditure for the printing system transversely to the printing direction consists in the fact that a number of pixel production units (eg inkjet nozzles, character generator) must be provided in the printing system, which corresponds to the screen width of the screening and the printing width on a recording medium. Furthermore, the pixel production units must be able to be controlled individually in order to implement the screen ruling grid.

On the other hand, in the printing direction, for a given screen ruling of the rasterization, there is a limitation for the transport speed of the recording medium and thus for the productivity of the printing system due to the (for example the maximum possible) driving frequency of the pixel production units. An increase in the transport speed can z. Example, by the use of a plurality of successively connected pixel generating units, wherein the adjustment (eg, the positioning and the adjustment of dot sizes) of these printing units typically means a considerable additional effort. Also, a time-offset control of the pixel generating units is required. Increasing the speed of transport of the printing system to increase the productivity of the printing system thus typically results in a significant increase in the cost of the printing system and additional quality or quality risks.

DE 695 31 142 T2 describes an image recording method in which dot pitches with respect to the pitch of different colors relative to each other are made variable.

The present document addresses the technical problem of providing means for a digital printing system to enable a more flexible and cost-efficient way of achieving an improved compromise between production cost and print quality.

The object is solved by the independent claims. Advantageous embodiments are u. a. in the dependent claims.

In one aspect, a method of printing an image to be printed on a record carrier using a digital printing system is described. The digital printing system includes a plurality of pixel generating units configured to print a corresponding plurality of pixels across the transport direction of the recording medium on the recording medium. A raster network for rasterizing the image to be printed has a multiplicity of raster cells. The method includes determining printing instructions for a first screen cell based on the image to be printed. The print instructions for the first screen cell indicate whether a pixel is to be printed by a first pixel creation unit in the first screen cell. In addition, the printing instructions indicate when a pixel is to be printed, at what level within the first screen cell the pixel is to be printed by the first pixel generating unit. Furthermore, the method comprises the activation of the first pixel generation unit as a function of the printing instructions for the first screen cell.

According to a further aspect, a printing system is described, which is adapted to print an image to be printed on a recording medium, which is guided in the transport direction by the printing system. A raster network for rasterizing the image to be printed has a multiplicity of raster cells. The printing system includes a plurality of pixel generating units configured to print a corresponding plurality of pixels across the transport direction onto the recording medium. In addition, the printing system includes a control configured to determine printing instructions for a first screen cell based on the image to be printed. The print instructions for the first screen cell indicate whether a pixel is to be printed by a first pixel creation unit in the first screen cell. In addition, when a pixel is to be printed, the printing instruction indicates at what level within the first screen cell the pixel is to be printed by the first pixel generating unit. Furthermore, the control is set up to control the first pixel generating unit in dependence on the printing instructions for the first grid cell.

It should be understood that the methods, devices and systems described herein may be used alone as well as in combination with other methods, devices and systems described in this document. Furthermore, any aspects of the methods, apparatus, and systems described herein may be combined in a variety of ways. In particular, the Characteristics of the claims can be combined in a variety of ways.

In the following, embodiments of the invention will be described in more detail with reference to schematic drawings. Show

1 a block diagram of an exemplary inkjet printing system;

2 an exemplary raster network for screening an image to be printed;

3a an exemplary raster network with simultaneous raster points or pixels;

3b an exemplary grid with temporally mutually offset grid points or pixels;

4a and 4b exemplary distributions of halftone dots in a raster network; and

5 a flowchart of an exemplary method for printing an image to be printed.

The present document addresses the technical problem of enabling an improved trade-off between printing costs and print quality of a digital printing system. In particular, the present document addresses the technical problem of increasing the print quality for a given printing system (without having to change the available hardware).

The digital printing system can z. B. include a printing system that uses an electrographic printing process to print the rasterized image data on a record carrier. Alternatively or additionally, the digital printing system may include an inkjet printing system. Hereinafter, an ink-jet printing system as an exemplary digital printing system will be described in more detail. It should be understood, however, that the methods described herein for rasterizing an image to be printed are generally applicable to digital printing systems.

1 shows a block diagram of an exemplary inkjet printing system 100 , This in 1 illustrated printing system 100 is for printing on a web-shaped record carrier 120 (also referred to as "continuous feed" designed). The award holder 120 is typically unwound from a roll (the unwinder) and then the printing unit of the printing system 100 fed. The printing unit becomes a printed image on the record carrier 120 applied, and the printed record carrier 120 is after fixing / drying of the printed image again wound on another roll (the rewinder) or cut into sheets. In 1 becomes the transport direction of the recording medium 120 represented by an arrow. The record carrier 120 may be made of paper, cardboard, cardboard, metal, plastic and / or other suitable and printable materials.

The printing unit of the printing system 100 includes four printhead assemblies in the illustrated example 102 (which are also referred to as pressure bar). The different pressure bars 102 can be used for printing with different color inks (for example, black, cyan, magenta, and / or yellow). The printing unit can still further pressure bar 102 for printing with other colors or other inks (eg, MICR ink).

A pressure bolt 102 includes one or more printheads 103 , In the illustrated example, a pressure latch comprises 102 five print heads each 103 , Every printhead 103 can turn into a variety of printhead segments 104 be divided, each printhead segment 104 typically comprises a plurality of nozzles or nozzle assemblies.

Every printhead 103 comprises a plurality of nozzles or nozzle arrangements, each nozzle arrangement being arranged, ink droplets on the recording medium 120 to fire or to splash. For example, a printhead 103 Comprise 2558 effectively used nozzle arrays along one or more rows transverse to the transport direction of the recording medium 120 are arranged. The nozzle arrangements in the individual rows can be arranged offset from one another. By means of the nozzle arrangements of a printhead 103 can each one line (line) on the record carrier 120 be printed transversely to the transport direction. By using a plurality of rows of (staggered) nozzle arrays, increased resolution can be provided. In sum, so by a in 1 illustrated printhead assembly 102 12790 drops along a transverse line on the record carrier 120 be sprayed. Every pressure bolt 102 can thus be set up, at a certain time, a transverse line of a particular color on the record carrier 120 to print.

The printing system 100 further comprises a control unit 101 (eg, drive hardware and / or controller) that is set up, the actuators of the individual nozzle arrays of the individual printheads 103 to enter, depending on screened print data Print image on the record carrier 120 applied. The rastered print data can be sent to a control module 105 a pressure bar 102 transmitted to the individual nozzle assemblies of the printheads 103 of the pressure bar 102 to cause the printed image on the record carrier 120 to print.

• • ob ein Bildpunkt 201 oder ob kein Bildpunkt 201 gedruckt werden soll (z. B. ob ein Tintenausstoß erfolgen soll oder nicht); und
• • ggf. eine Größe des zu druckenden Bildpunktes 201 (z. B. eine Größe des auszustoßenden Tintentropfens).

The rasterized print data typically includes a raster mesh (or raster array), with each raster cell of the raster mesh providing print instructions for a nozzle array of a print bar 102 includes. 2 shows an exemplary grid grid 200 , The grid network 200 includes a variety of lines 212 where each line 212 a variety of grid cells 202 includes. The grid cells 202 a line 212 are typically through the nozzle assemblies of a pressure bar 102 processed to a transverse line of a print image on the recording medium 120 to print. In this case, the grid cells include 202 a line 212 Printing instructions for each one nozzle array of the plurality of nozzle arrays of a printing bar 102 , For example, the pressure instructions for a nozzle assembly include information about it,

• • whether a pixel 201 or if no pixel 201 should be printed (eg whether an ink ejection is to take place or not); and
• • If necessary, a size of the pixel to be printed 201 (eg, a size of the ink drop to be ejected).

On the other hand, the grid network includes 200 a variety of columns 211 with a variety of grid cells 202 , The grid cells 202 a column 211 are typically through exactly one nozzle arrangement of a pressure bar 102 processed. In other words, the grid cells 202 a column 211 of the grid network 200 typically include instructions to exactly one nozzle assembly for printing from a corresponding plurality of temporally successive pixels 201 (Which along the transport direction on the recording medium 120 to print).

The in 2 illustrated arrow 203 shows the transport direction of the recording medium 120 on, ie the arrow indicates the chronological order with which the individual lines 212 on the record carrier 120 to be printed. The record carrier 120 is at a certain transport speed in the transport direction 203 on a pressure bolt 102 carried over.

A printing system 100 typically has one or more print quality limitations, particularly in terms of resolution. As stated above, the number of pixels is 201 across the record carrier 120 typically by the number of nozzle arrangements of a pressure bar 102 established. Furthermore, a nozzle assembly typically has a limitation on the number of drops that can be printed at a predefined time interval (eg, per second). In other words, a nozzle instruction typically has a maximum possible drive frequency (eg, number of pixels 201 / Time unit). Due to the limited number of pixels 201 per unit of time results in connection with the transport speed of the recording medium 120 a possible resolution of pixels 201 in the transport direction 203 of the record carrier 120 (ie longitudinal to the recording medium 120 ). Typically, a printing system 100 in the longitudinal direction of the recording medium 120 to a predefined resolution (eg 600 dpi). In particular, the transport speed of the recording medium 120 typically chosen such that the predefined resolution (eg 600 dpi) is achieved with the achievable number of drop ejections per unit of time.

The present document addresses the technical problem of providing an improved compromise between print quality and printing costs. One way to optimize for a trade-off between printing costs and print quality is to reduce the number of pixels 201 for an image to be printed (in the transport direction 203 ) With an increased distance to each other and thereby allow an increase in the transport speed. In this case, all, transversely to the transport direction 203 , adjacent pixels 201 (as in 2 represented) on a straight transverse line, ie the grid cells 202 for the different pixels 201 can be arranged on a straight transverse line. Typically, imaging is then done by a character generator or by an inkjet printhead 103 in the control of the individual transversely to the transport direction 203 No pixel offset or time offset due to the arrangement (e.g., in staggered rows) of the pixel generating units 103 is conditional. It is in the generation of the pixels 201 a print mesh a grid network 200 with grid cells 202 basis, which are arranged on a straight transverse line.

The individually controlled pixels 201 typically have a roundish shape on the record carrier 120 on. This is an example of a grid network 300 in 3a shown. This is typically also after spreading in an inkjet printing system 100 the case. As a result, on the record carrier 120 a pattern of visible lines is generated across the printing direction. These visible cross lines are particularly noticeable in full tones. Furthermore, the achievable cover of the recording medium 120 through the roundish pixels 201 limited as the pixels 201 transverse to the printing direction with the adjacent pixels 201 overlap and thus relatively large unprinted surfaces arise. The following describes measures that can be used to reduce the unprinted areas and thus increase the print quality. Reducing non-printed areas also increases the effect of "light trapping", which has a positive effect on the subjective perception of print quality.

3a shows two exemplary columns 311 . 313 of the grid network 300 , The columns 311 . 313 include corresponding grid cells 202 , each on straight cross lines 314 are arranged. Through a grid cell 202 can the pressure of one pixel 201 of the printed image. Due to the parallel arrangement of grid cells 202 in adjacent columns 311 . 313 a raster matrix 300 on straight cross lines 314 The above-mentioned disadvantages may arise with regard to print quality.

An improved use of the printing inks (in particular of ink and / or toner) while at the same time improving the print quality can be achieved in that, in particular, adjacent pixels 201 offset from each other to be printed and thus with an increased uniformity over the surface of the recording medium 120 be distributed. For this purpose, the control unit 101 and / or the control module 105 be configured, the individual nozzle arrangements (ie, the individual pixel generating units) of the printing system 100 to drive on an individual grid. In particular, those of the nozzle assemblies of a pressure bar 102 used columns 311 a grid network 300 be shifted to each other.

The control unit 101 and / or the control module 105 a printing system 100 can be set up for this purpose, for a raster cell to be printed 202 provide and process further printing instructions for a pixel production unit (eg, for a nozzle assembly). In particular, the further printing instructions may include a point in time at which a pixel is generated by the pixel production unit 201 on the record carrier 120 to be printed. This allows an individual and time-offset control of the individual pixel production units to pixels 201 flexible on a grid on the record carrier 120 to position. In particular, pixels can 201 relative to the transport direction 203 offset from each other in the grid cells 202 a line 212 the grid are arranged.

For example, the times for driving the individual pixel generating units can be selected according to a basic time grid, wherein the basic time grid has a resolution which is substantially greater than the screen width (in the transport direction 203 ) of the grid network 300 with which an image to be printed has been rasterized (eg by one or more orders of magnitude). So can a flexible shift of pixels 201 and a corresponding flexible driving of the pixel generating units are achieved while limiting the amount of information for providing the driving timing of the pixel generating units.

3b shows a grid network 350 at the adjacent columns 311 . 313 in the transport direction 203 are shifted from each other. This causes the grid cells 202 from neighboring pixels 201 in the transport direction 203 are shifted from each other. How out 3b can be seen, so the print quality can be increased. In particular, a streakiness of the printed image can be reduced. Furthermore, an increase in coloration by using the maximum coverage of the recording medium 120 and an increase in coloration can be achieved by maximizing light trapping. In addition, a reduction of coalescence (especially in inkjet printing) and / or a reduction of inter color bleed (especially in multi-color inkjet printing) can be effected. In sum, an optimization of the effect of ink and thus a minimization of costs can be effected. For example, even at higher transport speeds of the recording medium 120 Furthermore, an increased print quality can be achieved.

In a corresponding way to a shift of the grid cells 202 within a grid network 350 can be a different positioning of pixels 201 within the rest cells 202 a grid network 300 be made. In this case, one can continue in columns 211 . 311 . 313 and in lines 212 arranged grid network 300 (in particular a raster matrix) can be used. The shift of printed pixels 201 (as in 3b shown) can then by a vertical displacement of the pixels 201 within the fixed grid cells 202 of the grid network 300 be effected. The printing instructions for a grid cell 202 can then indicate or specify the height of the pixel 201 within the grid cell 202 is arranged. The height of the pixel 201 can then be used to that of the grid cell 202 to individually control the corresponding pixel generation unit individually. In particular, at different heights of pixels 201 from adjacent grid cells 202 the corresponding Pixel-generating units are time-shifted or asynchronously controlled to each other.

The asynchronous control of pixel production units of a printing bar 102 can be used to increase the print quality of specific elements (eg, contours) of an image to be printed, and thereby increase the perceived quality of a printed image. For example, the image to be printed can be analyzed to identify specific elements (eg, contours) in the image. The image to be printed can then be screened such that pixels 201 be placed directly on the specific elements. The other pixels 201 for further elements of the image to be printed can then take into account limitations of the printing system 100 (eg taking into account a maximum drive frequency of the individual pixel generating units).

4a shows an exemplary arrangement of pixels 401 . 402 in a grid network 400 , The pixels 401 for the contours have been placed as possible on the contours of the image to be printed in order to achieve a high-quality reproduction of the contours. The other pixels 402 are in 4a has been placed so that the maximum drive frequency of the pixel generating units is not exceeded. 4b shows another exemplary arrangement of pixels 401 . 402 at the other pixels 402 additional were arranged such that these pixels 402 in the grid cells of a regular grid network 450 lie.

As part of the rasterization of an image to be printed thus columns 311 for the printing of pixels 401 . 402 be created by individual pixel generating units. The pixels can 401 . 402 possibly without raster within a column 311 be placed (eg depending on the image to be printed). It is only necessary to ensure that the maximum drive frequency of the pixel production unit, the column 311 to print, is not exceeded. This can be done by a predefined minimum screen ruling between adjacent pixels 401 a column 311 be ensured.

The resulting rasterized image then includes for a pixel to be printed 401 an information about, at which time a corresponding pixel generating unit the pixel 401 to print. The control unit 101 and / or the control module 105 of the printing system 100 can be configured to drive the corresponding pixel generation unit (eg the corresponding nozzle arrangement) in such a way that the pixel 401 is printed at the right time, and thus in the right place on the printed image on the record carrier 120 appears.

5 shows an exemplary method 500 for printing an image to be printed on a recording medium 120 by means of a digital printing system 100 (For example, by means of an inkjet printing system and / or by means of a printing system that uses an electrographic toner transfer process to the image to be printed on the recording medium 120 to print).

The digital printing system 100 comprises a plurality of pixel generating units arranged to generate a corresponding plurality of pixels (or pixels) 201 . 401 . 402 transverse to a transport direction 203 of the record carrier 120 on the record carrier 120 to print. The pixel generating units may include an ink jet nozzle assembly or a character generator with an LED or laser line.

The rasterization of the image to be printed becomes a raster mesh 350 . 400 . 450 used a variety of grid cells 202 that has a lot of columns 211 . 311 . 313 and in a variety of lines 212 are arranged. The number of columns corresponds to this 211 . 311 . 313 typically the plurality of pixel generation units. In particular, one column becomes the plurality of columns 211 . 311 . 313 typically printed by exactly one pixel generating unit of the plurality of pixel generating units. It consists of the multiplicity of columns 211 . 311 . 313 and the plurality of pixel generating units typically have a one-to-one membership.

This document uses the lines 212 and the columns 211 . 311 . 313 a grid network 350 . 400 . 450 spoken (based on the 2 to 4b ). One line 212 of the grid network 350 . 400 . 450 corresponds to a line of printed by the plurality of pixel generating units printed image transverse to the transport direction 203 on the record carrier 120 , On the other hand, one column corresponds 211 . 311 . 313 of the grid network 350 . 400 . 450 a column of a print image printed by the plurality of pixel generating units, along the transport direction 203 on the record carrier 120 , It should be noted that the terms line 212 and column 211 . 311 . 313 a grid network 350 . 400 . 450 are mutually interchangeable, and depend on what orientation the image to be printed on the recording medium 120 is printed.

The procedure 500 includes determining 501 of printing instructions based on the image to be printed, for a first halftone cell 202 a first column 211 . 311 . 313 the multitude of columns 211 . 311 . 313 , The first column corresponds to this 211 . 311 . 313 a first pixel generation unit of the plurality of pixel generation units. That is, the printing instructions for the first halftone cell 202 are converted or printed by the first pixel generating unit.

The print instructions for the first screen cell 202 are determined such that the print instructions indicate whether in the first screen cell 202 a pixel 201 should be printed by the first pixel generating unit or not. Furthermore, the print instructions are determined such that the print instructions indicate (if a pixel 201 to be printed) on which level within the first screen cell 202 the pixel 201 should be printed by the first pixel generating unit. The term "height" refers to a shift in the position of a pixel 201 in a vertical direction in the 2 to 4b grid networks shown, ie in one direction, the transport direction 203 of the record carrier 120 equivalent. In other words, the print instructions indicate how the pixel to be printed 201 within the first grid cell 202 is to be arranged. In particular, it indicates the extent to which the pixel 201 from a default position (eg, from a position in the center of the first screen cell 202 ) upwards or downwards (in relation to the transport direction 203 of the record carrier 120 and assuming that an upper edge of the image to be printed is printed before a lower edge of the image to be printed).

The procedure 500 further includes driving 502 the first pixel generating unit in response to the printing instructions for the first halftone cell 202 , In this case, the driving of the first pixel generating unit may comprise determining based on the height within the first halftone cell 202 from a time point at which the first pixel generating unit the pixel 201 on the record carrier 120 to print. For example, the first pixel generation unit may be driven at a default time by one pixel 201 to print at the default position. By a control at a later time, a deviation from the default position down (in relation to the transport direction 203 of the record carrier 120 and, assuming that an upper edge of the image to be printed is printed from a lower edge of the image to be printed), and vice versa.

By the procedure 500 becomes a flexible positioning of pixels 201 on the record carrier 120 allows. As a result, the print quality can be increased with unchanged printing costs. Furthermore allows a flexible positioning of pixels 201 the provision of an improved compromise between printing costs and print quality.

The pixel generation units (in particular, the first pixel generation unit) typically have a maximum frequency at which the pixel generation units pixel 201 on the record carrier 120 can print. The procedure 500 may include determining, based on the maximum frequency, a minimum distance between two consecutive pixels 201 which can be printed by the first pixel generating unit. The minimum distance depends in addition to the maximum frequency typically also on the transport speed of the recording medium 120 (relative to the plurality of pixel generating units).

The procedure 500 may further comprise determining printing instructions based on the image to be printed for at least two consecutive halftone cells 202 the first column 211 . 311 . 313 , so that pixels 201 in the at least two consecutive grid cells 202 have a distance from each other, which does not fall below the minimum distance. In other words, the positioning of the pixels 201 within two consecutive grid cells 202 can be done such that within the grid cells 202 positioned pixels 201 have at least the minimum distance from each other. This ensures efficiently that the flexibly positioned pixels 201 by the pixel production units of the printing system 100 can be printed.

The procedure 500 may further comprise determining print instructions based on the image to be printed for a second screen cell 202 from a second column 211 . 311 . 313 the multitude of columns 211 . 311 . 313 which (possibly directly) next to the first column 211 . 311 . 313 is arranged. The first and the second grid cell 202 are in the same line 212 the multitude of lines 212 arranged, ie the pixels 201 the first and the second screen cell 202 should when positioning the pixels 201 at the default position next to each other (in relation to the transport direction 203 of the record carrier 120 ) on a straight cross line 314 to be printed. The positioning of the pixels 201 within the grid cells 202 However, it can be done such that the pixel 201 the first grid cell 202 has a first height and that the pixel 201 the second halftone cell 202 a second height, wherein the first height and the second height are different. By positioning adjacent pixels 201 (in terms of the transport direction 203 ) at different heights within the grid cells 202 can provide improved coverage with color on the record carrier 120 be achieved. Thus, the print quality can be increased (with the same printing costs) and / or the printing costs (with the same print quality) can be reduced.

The first grid cell 202 and the second screen cell 202 typically have a certain screen pitch (which is also referred to as the longitudinal screen pitch). The first height and the second height may be spaced apart by a distance greater than one quarter of the screen pitch and less than or equal to half the screen pitch. Thus, a particularly good coverage of the recording medium 120 be achieved with color (especially at a distance of about half the screen width corresponds).

The procedure 500 may further comprise determining, based on the image to be printed, whether the first halftone cell 202 has a predefined graphical element (eg, a contour) or not. The height of the pixel 201 in the first grid cell 202 may depend on a position of the predefined graphical element within the first screen cell 202 be determined when the first grid cell 202 a predefined graphical element (eg, a contour). In particular, the pixel may 201 be positioned at the position of the predefined graphical element. Similarly, the height of the pixels 201 for a variety of grid cells 202 (possibly in different lines 212 ) depending on a predefined graphical element (eg around the pixels 201 to position along a contour). By positioning the pixels 201 on predefined graphical elements, the subjective impression of the print quality (at unchanged printing costs) can be increased.

On the other hand, when it is determined that the first halftone cell 202 has no predefined graphical element, so the pixel 201 at a predefined height (ie at a default height) within the first screen cell 202 be positioned. In other words, if it is determined that the first halftone cell 202 has no predefined graphical element, the pixel 201 at the default position of the first screen cell 202 be positioned. So can an efficient positioning of pixels 201 take place, which have no special visual Prägnanz.

Furthermore, in this document, a printing system 100 described that is set up the procedure 500 perform. In particular, the printing system 100 set up, an image to be printed on a recording medium 120 to print in the direction of transport 203 through the printing system 100 to be led. It can be a grid network 350 . 400 . 450 be used to rasterize the image to be printed, which is a plurality of grid cells 202 that has a lot of columns 211 . 311 . 313 and in a variety of lines 212 are arranged.

The printing system 100 For example, a plurality of pixel generating units configured to have a corresponding plurality of pixels 201 . 401 . 402 transverse to the transport direction 203 on the record carrier 120 to print. The number of columns corresponds to this 211 . 311 . 313 of the grid network 350 . 400 . 450 the plurality of pixel generation units (typically according to a one-to-one mapping).

The printing system 100 further includes a control 101 . 105 configured to print instructions based on the image to be printed for a first raster cell 202 a first column 211 . 311 . 313 the multitude of columns 211 . 311 . 313 to determine where the first column 211 . 311 . 313 a first pixel generating unit of the plurality of pixel generating units. The print instructions for the first screen cell 202 indicate whether in the first grid cell 202 a "non-white" pixel 201 should be printed by the first pixel generating unit. Furthermore, the pressure instructions for the first grid cell show 202 on (if a pixel 201 to be printed), at which height (along the transport direction 203 of the record carrier 120 ) within the first screen cell 202 the pixel 201 should be printed by the first pixel generating unit. In addition, the control is arranged, the first pixel generating unit in response to the printing instructions for the first screen cell 202 head for.

The first pixel generation unit may be configured to be driven at predefined times on a predefined time grid by one pixel 201 on the record carrier 120 to print. By using a predefined time raster with a given temporal resolution, a number of bits can be used to signal the height of a pixel 201 within the first grid cell 202 limited / reduced. In particular, the height of the pixel 201 within the first grid cell 202 are displayed at a specific local resolution by the printing instructions corresponding to the temporal resolution of the time grid.

The grid network 350 . 400 . 450 typically has a particular screen ruling (ie, a longitudinal ruling) that is one size or length of the first raster cell 202 in the transport direction 203 of the record carrier 120 displays. In addition, the recording medium 120 typically with a certain transport speed past the first pixel production unit. The temporal resolution of the time raster is preferably smaller, in particular smaller by one or more orders of magnitude than a quotient of raster width and transport speed. Thus it can be ensured that even with a limited number of bits for signaling the height of a pixel 201 , furthermore, a precise and flexible positioning of the pixels 201 within the grid cells 202 is possible.

The control 101 . 105 may be configured to determine a rasterized image for the image to be printed. The rasterized image typically includes the printing instructions for the plurality of raster cells 202 of the grid network 350 . 400 . 450 , In particular, the rasterized image may include printing instructions for at least a first line 212 of the grid network 350 . 400 . 450 include a corresponding line of a print image on the record carrier 120 corresponds (transverse to the transport direction 203 of the record carrier 120 ). It can print the instructions for the first line 212 for at least two grid cells 202 pixels 201 show with a different height. The control 101 . 105 may be further configured, the plurality of pixel generating unit, in response to the printing instructions of the first line 212 to drive at different times to pixels 201 on the record carrier 120 to print according to the different heights indicated in the printing instructions, in the transport direction 203 are shifted from each other. This means that by a time-shifted control of the pixel production units, the different positioning of pixels 201 within the grid cells 202 on the print image on the record carrier 120 can be transferred.

In particular, pixels can 201 one line of the printed image are printed by the plurality of pixel generating units locally staggered. This is made possible by the fact that the printing instructions for a pixel generating unit next to the information about whether a "non-white" pixel 201 is to be printed, also information about it or include, at which time the "non-white" pixel 201 on the record carrier 102 to be printed (ie on which higher within a grid cell 202 the pixel 201 should be positioned).

The printing system 100 was in this document using the example of a printing system 100 described in which a record carrier 120 past a plurality of fixedly positioned image-forming units (eg inkjet nozzles). Similarly, the measures described in this document are also applicable to a printing system 100 applicable, wherein a plurality of movable image forming units on a (temporarily fixed) recording medium 120 is passed. For example, in a wide format printer or in a home inkjet printer, adjacent nozzles may be across the record carrier 120 be guided to simultaneously several lines on the record carrier 120 to print. These moving nozzles may then be individually driven as described in this document to make pixels in each line 201 to position individually. In this case results from the individual "height" within a grid cell 202 a transverse offset on a printed line.

LIST OF REFERENCE NUMBERS

100

printing system

101

Control unit of the printing system 100

102

Printhead assembly / pressure lock

103

printhead

104

Printhead segment

105

Control module of a printhead assembly

200, 300, 350, 400, 450

grid power

201, 401, 402

Pixel / pixel

202

grid cell

203

transport direction

211, 311, 313

Column of a grid network

212

Line of a grid network

314

Cross line of a grid network

500

Method for printing an image to be printed

501, 502

steps

Claims (9)

Method for printing an image to be printed on a recording medium ( 120 ) by means of a digital printing system ( 100 ); the digital printing system ( 100 ) comprises a plurality of pixel generating units arranged to generate a corresponding plurality of pixels ( 201 . 401 . 402 ) transversely to a transport direction ( 203 ) of the record carrier ( 120 ) on the record carrier ( 120 ) to print; where a grid network ( 350 . 400 . 450 ) for rasterizing the image to be printed a plurality of grid cells ( 202 ) having; the method ( 500 ), - Determine ( 501 ) of printing instructions based on the image to be printed, for a first halftone cell ( 202 ); wherein the printing instructions for the first screen cell ( 202 ) - whether in the first grid cell ( 202 ) a pixel ( 201 ) is to be printed by a first pixel generating unit; and - if a pixel ( 201 ) at what level within the first screen cell ( 202 ) the pixel ( 201 ) is to be printed by the first pixel generating unit; and - determining a minimum distance between two consecutive pixels ( 201 ) that can be printed by the first pixel generating unit; wherein the minimum distance depends on a maximum frequency with which the first pixel generation unit ( 201 ) on the record carrier ( 120 ) can print; Determine printing instructions, based on the image to be printed, for one on the first screen cell ( 202 ) the following grid cell ( 202 ) of a first column ( 211 . 311 . 313 ) of the grid ( 350 . 400 . 450 ), so that pixels ( 201 ) in the two successive grid cells ( 202 ) have a distance from each other that does not fall below the minimum distance; and - driving ( 502 ) of the first pixel generating unit in dependence on the printing instructions for the two successive halftone cells ( 202 ). Method according to claim 1, wherein - the plurality of grid cells ( 202 ) in a plurality of columns ( 211 . 311 . 313 ) and in a multiplicity of lines ( 212 ) is arranged; - the procedure ( 500 ), determining print instructions for a second screen cell ( 202 ) from a second column ( 211 . 311 . 313 ), which are next to the first column ( 211 . 311 . 313 ), wherein the first and the second grid cell ( 202 ) in a same line ( 212 ) are arranged; - a pixel ( 201 ) of the first screen cell ( 202 ) has a first height and a pixel ( 201 ) of the second screen cell ( 202 ) has a second height; and - the first height and the second height are different. Method according to claim 2, wherein - the first halftone cell ( 202 ) and the second grid cell ( 202 ) have a screen width; The raster width is one length of a raster cell ( 202 ) in the transport direction ( 203 ) of the record carrier ( 120 ) indicates; and - the first height and the second height are spaced apart by a distance greater than one quarter of the screen pitch and less than or equal to half the screen pitch. Method according to one of the preceding claims, wherein - the method ( 500 ), determining, based on the image to be printed, whether the first halftone cell ( 202 ) has a predefined graphical element; and - the height of the pixel ( 201 ) in the first grid cell ( 202 ), depending on a position of the predefined graphical element within the first screen cell ( 202 ) is determined when the first raster cell ( 202 ) has a predefined graphical element. Method according to claim 4, wherein the pixel ( 201 ) a predefined height within the first grid cell ( 202 ), when the first grid cell ( 202 ) has no predefined graphic element. Method according to one of the preceding claims, wherein the driving of the first pixel generating unit comprises determining, based on the height within the first grid cell ( 202 ), a point in time at which the first pixel generating unit sets the pixel ( 201 ) on the record carrier ( 120 ) should print. Printing system which is adapted to print an image to be printed on a record carrier ( 120 ) to be printed in the transport direction ( 203 ) by the printing system ( 100 ) to be led; where a grid network ( 350 . 400 . 450 ) for rasterizing the image to be printed a plurality of grid cells ( 202 ) having; the printing system ( 100 ), - a plurality of pixel generating units, which is arranged, a corresponding plurality of pixels ( 201 . 401 . 402 ) transversely to the transport direction ( 203 ) on the record carrier ( 120 ) to print; and - a control ( 101 . 105 ), which is set up, - printing instructions, based on the image to be printed, for a first screen cell ( 202 ) to investigate; wherein the printing instructions for the first screen cell ( 202 ) indicate whether in the first grid cell ( 202 ) a pixel ( 201 ) is to be printed by a first pixel generating unit; and if a pixel ( 201 ) at what level within the first screen cell ( 202 ) the pixel ( 201 ) is to be printed by the first pixel generating unit; A minimum distance between two consecutive pixels ( 201 ) which can be printed by the first pixel generating unit; wherein the minimum distance depends on a maximum frequency with which the first pixel generation unit ( 201 ) on the record carrier ( 120 ) can print; On the basis of the image to be printed, printing instructions for one on the first halftone cell ( 202 ) the following grid cell ( 202 ) of a first column ( 211 . 311 . 313 ) of the grid ( 350 . 400 . 450 ), so that pixels ( 201 ) in the two successive grid cells ( 202 ) have a distance from each other that does not fall below the minimum distance; and - the first pixel generating unit in dependence on the printing instructions for the two successive halftone cells ( 202 ) head for. Printing system according to claim 7, wherein - the first pixel generating unit can be driven at predetermined times on a time grid to a pixel ( 201 ) on the record carrier ( 120 ) to print; - the grid network ( 350 . 400 . 450 ) has a grid width which is one size of the first grid cell ( 202 ) in the transport direction ( 203 ) of the record carrier ( 120 ) indicates; - the record carrier ( 120 ) is passed past the first pixel production unit at a transport speed; A temporal resolution of the time raster is smaller, in particular smaller by one or more orders of magnitude, than the quotient of raster width and transport speed; and - the height of the pixel ( 201 ) within the first grid cell ( 202 ) is displayed with a resolution in the print instructions corresponding to the temporal resolution of the time grid. Printing system according to one of claims 7 to 8, wherein the control element ( 101 . 105 ) is arranged to: - determine a rasterized image for the image to be printed; the rasterized image printing instructions for at least a first line ( 212 ) of the grid ( 350 . 400 . 450 ); where the print instructions for the first line ( 212 ) for at least two grid cells ( 202 ) Pixels ( 201 ) with a different height within the grid cells ( 202 ) Show; and the plurality of pixel generating units, depending on the printing instructions for the first row ( 212 ), at different times to control pixels ( 201 ) on the record carrier ( 120 ) according to the different heights indicated in the printing instructions, in the transport direction ( 203 ) are shifted locally to each other.

Images