Patent Publication Number: US-10322579-B2

Title: Inkjet printing system and method to reduce system-dependent streaking

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This patent application claims priority to German Patent Application No. 102016121497.3, filed Nov. 10, 2016, which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     The present disclosure relates to an inkjet printing system for reducing system-dependent streaking, and a corresponding method. 
     Inkjet printing systems may be used for printing to recording media (paper, for example). An inkjet printing system may comprise one or more print bars having respectively one or more print heads. Each print bar may thereby be used for the printing of a specific color. The recording medium may be directed in a transport direction past the one or more print bars in order to print a print image onto the recording medium row by row. 
     Each nozzle of a print head is configured to fire or eject ink droplets onto the recording medium. A nozzle thereby typically comprises a pressure chamber in which pressure is built up in order to generate an ink droplet. The pressure chambers of the individual nozzles of a print head may be connected with a common ink reservoir via one or more ink supply channels. Given a print head with a relatively high density of nozzles, interactions may therefore occur between adjacent nozzles of a print head. The print quality of an inkjet printing system may thereby be negatively affected. In particular, a (periodic) streaking of a print image (what is known as the corduroy effect) may occur due to interactions. 
     The German publication DE 10 2013 107942 A1 describes a method for compensation of streaking in which correction values for the nozzles of a print head are taken into account within the scope of a rastering process. However, the consideration of correction values in a rastering process is typically connected with relatively high computation costs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES 
       The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the embodiments of the present disclosure and, together with the description, further serve to explain the principles of the embodiments and to enable a person skilled in the pertinent art to make and use the embodiments. 
         FIG. 1  illustrates an inkjet printing system according to an exemplary embodiment of the present disclosure; 
         FIG. 2  illustrates a nozzle structure according to an exemplary embodiment of the present disclosure; 
         FIG. 3  illustrates an example print image having a corduroy effect according to an exemplary embodiment of the present disclosure; 
         FIG. 4  illustrates a plot of ejection pulses for the activation of different nozzles of a print head according to an exemplary embodiment of the present disclosure; and 
         FIG. 5  illustrates a flowchart of a method for reducing a periodic streaking of a print image according to an exemplary embodiment of the present disclosure. 
     
    
    
     The exemplary embodiments of the present disclosure will be described with reference to the accompanying drawings. 
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the present disclosure. However, it will be apparent to those skilled in the art that the embodiments, including structures, systems, and methods, may be practiced without these specific details. The description and representation herein are the common means used by those experienced or skilled in the art to most effectively convey the substance of their work to others skilled in the art. In other instances, well-known methods, procedures, components, and circuitry have not been described in detail to avoid unnecessarily obscuring embodiments of the disclosure. 
     An object of the present disclosure is to provide an inkjet printing system and a method with which a periodic streaking of a print image may be reduced in a resource-efficient manner. 
     According to an aspect of the disclosure, an inkjet printing system is described that comprises a print head having a first nozzle for printing image points of a first column of a print image, and having a second nozzle for printing image points of a second column of a print image. In an exemplary embodiment, the printing system may include at least one transporter that is configured to move the recording medium and the print head relative to one another in a transport device so that rows of the print image may be printed bit by bit by the print head, wherein the first column and the second column of the print image travel in a transport direction. Moreover, in an exemplary embodiment, the printing system includes a controller that is configured to activate the first nozzle to print a print image with a nominal quantity of ink with a first ejection pulse. The controller can furthermore be configured to activate the second nozzle to print a print image with the nominal quantity of ink with a second ejection pulse, wherein the first ejection pulse and the second ejection pulse are different. 
     According to an aspect of the disclosure, a method is described to reduce a system-dependent streaking of a print image printed by an inkjet printing system. In an exemplary embodiment, the printing system includes a print head having a first nozzle to print image points of a first column of the print image and a print head having a second nozzle to print image points of a second column of the print image. A recording medium and the print head may thereby be moved relative to one another in a transport direction to print sequential rows of the print image. The first column and the second column may then travel in the transport direction. In an exemplary embodiment, the method includes the determination that the first nozzle and the second nozzle for the printing of image points should respectively eject ink with a nominal ink quantity in a specific row. Moreover, the method can include the activation of the first nozzle for printing a print image of the determined row with a first ejection pulse, and the activation of the second nozzle for printing a print image of the determined row with a second ejection pulse, wherein the first ejection pulse and the second ejection pulse are different. 
     Exemplary embodiments described herein relate to the resource-efficient compensation of streaking effects—what is known as the corduroy effect—in inkjet printing systems.  FIG. 1  shows a block diagram of an example of an inkjet printing system  100  according to an exemplary embodiment. In an exemplary embodiment, the printing system  100  depicted in  FIG. 1  is designed for a continuous printing (i.e. for printing on a recording medium  120  that is “continuous” or in the form of a web (also designated as “continuous feed”)), but is not limited thereto. The recording medium  120  may be produced from paper, paperboard, cardboard, metal, plastic, textiles, and/or other materials that are suitable and can be printed to. In an exemplary embodiment, the recording medium  120  can be taken off a roll (the take-off) and then supplied to the print group of the printing system  100 . A print image is applied onto the recording medium  120  by the print group, and the printed recording medium  120  is taken up again on and additional roll (the take-up), possibly after fixing/drying of the print image. Alternatively, the printed recording medium  120  may be cut into sheets or pages by a cutting device. In  FIG. 1 , the transport direction  1  of the recording medium  120  is represented by an arrow  1 . The embodiments of the present disclosure are also applicable to a printing system for printing to recording media  120  in the form of sheets or pages. 
     With continued reference to  FIG. 1 , the print group of the printing system  100  can include, for example, four print bars  102 , but is not limited thereto. The different print bars  102  may be used for printing with inks of different colors (for example black, cyan, magenta and/or yellow) and/or different properties/characteristics. The print group may further include additional print bars  102  for printing with additional colors or additional inks (for example MICR ink). The printer group may include less than four print bars in other aspects. 
     In an exemplary embodiment, one or more print heads  103  (e.g. each print head  103 ) of the print bar  120  can include multiple nozzles  21 ,  22 , wherein each nozzle  21 ,  22  is configured to fire or push ink droplets onto the recording medium  120 . In an exemplary embodiment, a print head  103  may include 2558 effectively used nozzles  21 ,  22 , for example, which nozzles  21 ,  22  are arranged along one or more rows  41 ,  42  transversal to the transport direction  1  of the recording medium  120 . The number of nozzles, print groups, and print bars are not limited to the exemplary quantities described herein. In an exemplary embodiment, the nozzles  21 ,  22  in the individual rows  41 ,  42  may be arranged offset from one another. A row on the recording medium  120  may respectively be printed transversal to the transport direction  1  by means of the nozzles  21 ,  22  of a print head  103 . An increased image point resolution transversal to the transport direction  1  may be provided via the use of L rows having (transversally offset) nozzles (L&gt;1, for example L=32). In total, for example, K=12790 droplets may thus be fired by a print bar  102 , depicted in  FIG. 1 , along a row onto the recording medium  120  (for example for a print width of approximately 54 cm at 600 dpi (dots per inch)). 
     In an exemplary embodiment, the printing system  100  additionally includes a controller  101  (e.g. an activation hardware, processor, control circuit, etc.) that is configured to activate the actuators of the individual nozzles of the individual print heads  103  to apply a print image onto the recording medium  120  based on print data. In an exemplary embodiment, the controller  101  includes processor circuitry that is configured to perform one or more operations and/or functions of the controller  101 , including, for example, activating the actuators based on the print data. 
     In an exemplary embodiment, the printing system  100  includes at least one print bar  102  having K nozzles  21 ,  22  that may be activated with a specific line clock in order to print a line (transversal to the transport direction of the recording medium  120 ) with K pixels or K columns onto the recording medium  120 . Due to the arrangement in L rows, the nozzles  21 ,  22  of a print head  103  are typically activated with a (fixed) time offset relative to one another in order to print a row. In the presented example, the nozzles  21 ,  22  are immovable or installed fixed in the printing system  100 , and the recording medium  120  is directed past the stationary nozzles  21 ,  22  with a defined transport velocity. A specific nozzle  21 ,  22  thus prints a corresponding specific column  31 ,  32  (in the transport direction  1 ) onto the recording medium  120 . In other words, there may be a one-to-one association between  21 ,  22  and columns  31 ,  32  of a print image, such that the image points of a first column  31  of the print image are printed exclusively by a first nozzle  21  and the image points of a second column  32  of the print image are printed exclusively by a different, second nozzle  22 . Each nozzle  21 ,  22  of a print head  103  may thus be associated with precisely one column  31 ,  32 , and each column  31 ,  32  may be associated with precisely one nozzle  21 ,  22  of a print head  103 . A maximum of one ink ejection thus takes place via a specific nozzle  21 ,  22  per row of the print image. 
       FIG. 2  shows an example of a structure of a nozzle  21 ,  22  of a print head  103  according to an exemplary embodiment. In an exemplary embodiment, the nozzle  21 ,  22  includes walls  202  which, together with an actuator  220 , form a receptacle or a pressure chamber  212  to accommodate ink. The nozzle  21 , 22  can be configured to fire one or more ink droplets onto the recording medium  120  via a nozzle opening  201  of the nozzle  21 ,  22 . The ink forms what is known as a meniscus  210  at the nozzle opening  201 . Furthermore, the nozzle  21 ,  22  includes an actuator  220  (for example a piezoelectric element) that is configured to vary the volume of the pressure chamber  212  to take up ink, or to vary the pressure in the pressure chamber  212  of the nozzle  21 ,  22 . In particular, the volume of the pressure chamber  212  may be reduced, and the pressure in the pressure chamber  212  increased, by the actuator  220  as a result of a deflection  222 . An ink droplet is thus pushed from the nozzle  21 ,  22  via the nozzle opening  201 .  FIG. 2  shows a corresponding deflection  222  of the actuator  220  (dotted lines). Moreover, the volume of the pressure chamber  212  may be increased by the actuator  220  (see deflection  221 ) in order to draw new ink into the pressure chamber  212  via an ink supply channel  230 . 
     Via a deflection  221 ,  222  of the actuator  220 , the ink within the nozzle  21 ,  22  may thus be moved and the chamber  212  may be placed under pressure. A specific movement of the actuator  220  thereby produces a corresponding specific movement of the ink. The specific movement of the actuator  220  is typically produced by a corresponding specific waveform or a corresponding specific pulse of an activation signal of the actuator  220 . In particular, via a fire pulse (also designated as an ejection pulse) to activate the actuator  220 , it may be produced that the nozzle  21 ,  22  ejects an ink droplet via the nozzle opening  201 . In particular, ink droplets having different droplet size or having different ink quantities (for example 5 pl, 7 pl or 12 pl) may thus be ejected. In an exemplary embodiment, via a prefire pulse (also designated as a pre-ejection pulse) to activate the actuator  220 , the nozzle  21 ,  22  can produce a movement of the ink and an oscillation of the meniscus  210  while also preventing an ink droplet from being ejected via the nozzle opening  201 . 
     In an exemplary embodiment, the different nozzles  21 ,  22  of a print head  103  or of a print head segment are partially connected with one another, and with an ink reservoir, via one or more ink supply channels  230 . Ink may be drawn into the pressure chamber  212  of a nozzle  21 ,  22  via the ink supply channels  230  (e.g. when the actuator  220  is deflected as shown by the deflection  221 ). The nozzles  21 ,  22  of a print head  103  (or of a print head segment) may thereby mutually, indirectly affect one another via the one or more ink supply channels  230 . This may lead to negative effects on the print quality of an inkjet printing system  100 . 
     The mutual influencing of the nozzles  21 ,  22  (also designated as crosstalk) of a print head  103  may in particular lead to a corduroy effect upon printing a completely inked area, i.e. to a (possibly periodic) streaking with visible streaks or bars that travel in the transport direction  1 .  FIG. 3  shows an example of a print image  300  with groups  301 ,  302  of columns having different greyscale values. The transport direction  1  of the recording medium  120  is represented by an arrow. First groups  301  of columns have a relatively low greyscale value, and second groups  302  of columns have a relatively high greyscale value. The first groups  301  and the second groups  302  thereby alternate so that a periodic streak pattern appears. 
     Turning to  FIG. 3 , the different groups  301 ,  302  of columns are printed by different groups of nozzles  21 ,  22  of a print head  103 . In the example presented in  FIG. 3 , all nozzles  21 ,  22  of the print head  103  are activated with a specific standard pulse for a specific nominal ink quantity. Due to interactions between the nozzles  21 ,  22 , a first group  301  of nozzles ejects less ink than a second group  302  of nozzles, such that the streak pattern shown in  FIG. 3  results. 
     In an exemplary embodiment, different ejection pulses may be used for the different groups  301 ,  302  of nozzles  21 ,  22  to (at least partially) compensate for a streak pattern. In particular, a first ejection pulse for the specific nominal ink quantity may be used for the first group  301  of nozzles  21 , and a second ejection pulse for the specific nominal ink quantity may be used for the second group  302  of nozzles  22 .  FIG. 4  shows an example of a first ejection pulse  401  and an example of a second ejection pulse  402 . The first ejection pulse  401  typically produces a stronger deflection of the actuator  220  of a nozzle  21 ,  22  than the second ejection pulse  402 . In particular, the first ejection pulse  401  may be amplified, starting from the standard pulse to increase the ejected ink quantity. On the other hand, the second ejection pulse  402  may be weakened, starting from the standard pulse, in order to reduce the ejected ink quantity. The greyscale value of the image points  400  printed by the first group  301  of nozzles  21  may be increased, and/or the greyscale value of the image points  400  printed by the second group  302  of nozzles  22  may be reduced. As a result of this, a periodic streaking of print images  300  may be reduced. 
     The nozzles  21 ,  22  of a print head  103  may, if applicable, be activated to eject M different nominal ink quantities to generate M image points  400  of different sizes, wherein M is a whole number with M&gt;1, for example M=3. For each nominal ink quantity, different ejection pulses  401 ,  402  may be provided for the different groups  301 ,  302  of nozzles  21 ,  22 . In particular, M first ejection pulses  401  may be provided for the first group  301  and M second ejection pulses  402  may be provided for the second group  302 . 
     The respective pairs of ejection pulses  401 ,  402  may be determined in advance on the basis of full-area test print images  300 . For example, a test print image  300  may initially be printed with a uniform standard pulse for a specific, nominal ink quantity. The first ejection pulse  401  may then be amplified by a factor relative to the standard pulse, and the second ejection pulse  401  may be attenuated by the factor relative to the standard pulse. A full-area test print image  300  may then be printed with the first ejection pulse  401  for the first group  301  of nozzles  21 , and with the second ejection pulse  402  for the second group  302  of nozzles  22 . The factor may then be iteratively adapted (in particular increased) until the periodic streaking has been completed compensated, or has at least been partially compensated (for example has been compensated by 50%). Pairs of ejection pulses  401 ,  402  may accordingly be determined for all M ink quantities. 
     In the operation of a printing system  100 , the M pairs of ejection pulses  401 ,  402  may then be used to activate the different groups  301 ,  302  of nozzles  21 ,  22 . For printing a print image  300 , the print data typically show the nominal ink quantities to be ejected by the individual nozzles  21 ,  22  for each image point  400  of a row (for example as a 2-bit value for each image point  400 ). For each of the K nozzles  21 ,  22  of a print bar  102 , the ink quantity of an ink droplet to be ejected may thus be determined to print a row of a print image  300  on the basis of the print data (for example value “0”≠no ink ejection, value “1”—first ink quantity, value “2”—second ink quantity, value “3”—third ink quantity). Depending on whether a nozzle  21 ,  22  belongs to the first group  301  or to the second group  302  of nozzles  21 ,  22 , a first ejection pulse  401  or a second ejection pulse  402  may then be used in order to activate the nozzle  21 ,  22  for the printing of an image point  400  at a specific activation point in time  410 . The periodic streaking of print data-based print images  300  may thus be reduced. 
     As discussed above, what is known as the corduroy effect may occur upon printing with inkjet printing systems  100 . Due to the geometry and/or the design of a print head  103 , a specific set  302  of nozzles  22  thereby prints darker and a specific set  301  of other nozzles  21  prints lighter. For example, groups  301 ,  302  of eight respective nozzles  21 ,  22  may alternately print lighter or darker. Synchronous and/or periodic streaking may thus occur, which can be expressed to varying degrees for different droplet sizes. 
     The periods of the streaking may be different for different types of print heads  103 . In an exemplary embodiment, a fixed compensation of the streaking may be performed depending on the type of print head  103 . For example, an ejection pulse  401 ,  402  (also designated as a waveform) that is adapted with regard to droplet volume may be used for the respective group  301 ,  302  of nozzles  21 ,  22 . The light and/or dark regions of a test print image  300  may thus be at least partially adjusted to one another in order to at least partially reduce the corduroy effect. 
     In an exemplary embodiment, ejection pulses  401 ,  402  that vary depending on the nozzle are loaded in a non-volatile manner into a print head activator to reduce the corduroy effect. This is thereby enabled since the corduroy effect occurs repeatably and uniformly in full-area print images  300 . If applicable, only a partial compensation of the corduroy effect may thereby be performed for a full-area test print image  300  (for example between 40% and 60%) in order to prevent a degradation of the print quality for print images that do not cover the entire area. 
     In an exemplary embodiment, printing system  100  may have three different standard pulses Fire1, Fire2 and Fire3 for three different nominal ink quantities, but is not limited thereto. Three first ejection pulses  401  Fire1+, Fire2+, Fire3+ may then be determined, as well as three second ejection pulses  402  Fire1−, Fire2− and Fire3−, wherein the waveforms with “+” are stronger than the waveforms with “−”. During the printing of a print image  300 , the first ejection pulses  401  Fire1+, Fire2+ and Fire3+ are used for the weaker nozzles  21  (from the first group  301 ), whereas the stronger nozzles  22  (from the second group  302 ) use the second ejection pulses  402  Fire1−, Fire2− and Fire3. The association of the ejection pulses  401 ,  402  with the various nozzles  21 ,  22  may be performed via an association table. The association table may be predefined in one or more embodiments. The ejection pulses may additionally or alternatively be dynamically adjusted in more or more embodiments. The dynamic adjustment may be based on, for example, an analyzed print image. The analysis may be performed using a sensor such as a camera or one or more other types of sensors as would be understood by one of ordinary skill in the art. The analysis may be performed by the controller  101  and/or a user of the printer. 
       FIG. 5  shows a flowchart of a method  500  for reducing a system-dependent streaking of a print image  300  printed by an inkjet printing system  100  according to an exemplary embodiment. In an exemplary embodiment, the method  500  may be executed by a controller  101  of the printing system  100 . The controller  101  can include a memory storing instructions and/or code, that when executed by the controller  101 , controls the controller  101  to perform the method  500 . Additionally or alternatively, the controller  101  can be configured to access an external memory to obtain instructions and/or code to control the controller  101  to perform the method  500 . 
     The printing system  100  can include a print head  103  having a first nozzle  21  for printing image points  400  of a first column  31  of the print image  300 , and having a second nozzle  22  for printing image points  400  of a second column  32  of the print image  300 . The recording medium  120  for the print image  300  and the print head  103  may thereby be moved relative to one another in a transport direction  1  in order to print sequential rows of the print image  300 . A row of the print image  300  thereby travels transversal to the transport direction  1 , and a column  31 ,  32  of the print image  300  travels in the transport direction  1 . 
     The system-dependent streaking of a print image  300  may in particular be caused by the crosstalk between the first nozzle  21  and the second nozzle  22  of the print head  103 . The first nozzle  21  and the second nozzle  22  of the print head  103  are thereby typically substantially structurally identical (and therefore, in an isolated operation, might be activated with the same standard pulse in order to eject substantially the same nominal ink quantity). Furthermore, in the print head  103 , a uniform ink is may be used for all nozzles  21 ,  22  of the print head  103 . However, the crosstalk between the two nozzles  21 ,  22  may nevertheless lead to differences in the ejected ink quantity. 
     In an exemplary embodiment, the method  500  includes the determination  501  that the first nozzle  21  and the second nozzle  22  should respectively eject ink with a nominal ink quantity for the printing of image points  400  in a specific row. In other words, it may be determined that both the first nozzle  21  and the second nozzle  21  should eject the same nominal ink quantity (for example 5 pl, 7 pl or 12 pl) in the specific row. For example, this may be determined based on the print data for the print image  300  to be printed. 
     Moreover, the method  500  can include the activation  502  of the first nozzle  21  to print an image point  400  of the specific row with a first ejection pulse  401 , and the activation of the second nozzle  22  to print an image point  400  of the specific row with a second ejection pulse  402 . In an exemplary embodiment, the first ejection pulse  401  and the second ejection pulse  402  are different. A system-dependent streaking may be reduced in a resource-efficient manner via the different activation of the (structurally identical) first nozzle  21  and second nozzle  22  for the ejection of the same nominal ink quantity (of the same type of ink). 
     Accordingly, in the present disclosure, an inkjet printing system  100  is described, where the system  100  can include a print head  103  having a first nozzle  21  for printing of image points  400  of a first column  31  of a print image  300 , and having a second nozzle  22  for printing of image points  400  of a second column  32  of a print image  300 . The print image  300  may be printed by the print head  103  onto a recording medium  120 . The printing system  100  may include at least one transporter that is configured to move the recording medium  120  and the print head  103  relative to one another in a transport direction  1  so that a sequence of rows of the print image  300  may be printed by the print head  103 . The first column  31  and the second column  32  thereby travel in the transport direction  1 . In an exemplary embodiment, the printing system  100  may be configured such that the image points  400  of the first column  31  are printed only by the first nozzle  21 , and the image points  400  of the second column  32  are printed only by the second nozzle  22  (in a one-to-one relation). 
     In an exemplary embodiment, the printing system  100  includes a controller  101  that is configured to activate the first nozzle  21  for the printing of an image point  400  having a nominal ink quantity with a first ejection pulse  401 . The controller  101  can be additionally configured to activate the second nozzle  22  to print an image point  400  having a nominal ink quantity with a second ejection pulse  402  that differs from the first ejection pulse  401 . 
     In an exemplary embodiment, the printing system  100  may be configured to activate different (but structurally identical) nozzles  21 ,  22  of a print head  103  for the ejection of a specific nominal ink quantity (of a specific type of ink) with different ejection pulses  401 ,  402 . In an exemplary embodiment, non-uniformities between the different nozzles  21 ,  22  may exist, and the non-uniformities can be due to crosstalk. In this example, the non-uniformities resulting from crosstalk may thus be at least partially compensated. 
     In an exemplary embodiment, the print head  103  can be configured such that a first column  31  of a test print image  300  (the first column  31  being printed by the first nozzle  21 ) is lighter than a second column  32  of the test print image  300  (the second column  32  being printed by the second nozzle  22 ) if the first nozzle  21  and the second nozzle  22  (for the printing of the image points  400  of the first column  31  or the second column  32 ) are activated with a standard pulse for the printing of image points  400  with the nominal ink quantity. The test print image  300  may, for example, include a solid color print of image points  400  with the nominal ink quantity in the first column  31  and in the second column  32 . The activation (e.g. possibly simultaneous activation) of the first nozzle  21  and the second nozzle  22  with the same standard pulse may thus lead to lightness differences between the first column  31  and the second column  32 . In particular, the standard pulse may have the effect that the first nozzle  21  ejects a smaller quantity of ink than the second nozzle  22 . For example, the first nozzle  21  may eject an ink quantity that is smaller than the nominal ink quantity. On the other hand, the second nozzle  22  may eject an ink quantity that is greater than the nominal ink quantity. Such deviations of the actual ejected ink quantity from the nominal ink quantity may be produced by crosstalk between the first nozzle  21  and the second nozzle  22  (for example via a common ink supply channel  230 ). 
     In the aforementioned instance, the first ejection pulse  401  may be stronger than the second ejection pulse  402 . Alternatively or additionally, the first ejection pulse  401  may have more energy than the second ejection pulse  402 . Alternatively or additionally, the first ejection pulse  401  may lead to a stronger deflection of the actuator  220  of a nozzle  21 ,  22  than the second ejection pulse  402 . Furthermore, the first ejection pulse  401  may be stronger than the standard pulse. On the other hand, the standard pulse may be stronger than the second ejection pulse  402 . Via the first ejection pulse  401  and the second ejection pulse  402 , the differences in the ejected ink quantity of the nozzles  21 ,  22  of a print head  103  that are produced by the crosstalk may thus be at least partially compensated. 
     In particular, according to one or more embodiments, the first ejection pulse  401  and the second ejection pulse  402  may be such that the lightness difference between the first column  31  and the second column  32  of the test print image  300  is less. For example, the lightness difference can be at least half as great if the first nozzle  21  is activated with the first ejection pulse  401  and the second nozzle  22  is activated with the second ejection pulse  402  compared to if both the first nozzle  21  and the second nozzle  22  are activated with the standard pulse. Corduroy effects may thus be reliably reduced. 
     In an exemplary embodiment, the print head  103  may include a plurality of (possibly structurally identical) nozzles  21 ,  22  for printing a corresponding plurality of columns  31 ,  32  of a print image  300 , wherein the plurality of nozzles  21 ,  22  alternately includes first groups  301  and second groups  302  of nozzles  21 ,  22 . The print head  103  may be configured such that the first group  301  of nozzles  21  print lighter image points  400  in a test print image  300  (e.g. possibly on average) than the second group  302  of nozzles  22  if both the first group  301  and the second group  302  of nozzles  21 ,  22  are activated with the standard pulse. 
     The first groups  301  and/or the second groups  302  of nozzles  21 ,  22  may respectively include 4, 8 or more nozzles  21 ,  22 . The number of nozzles  21 ,  22  in a group  301 ,  302  may thereby depend on a type of the print head  103 . The first groups  301  and/or the second groups  302  typically respectively include multiple nozzles  21 ,  22  for printing the image points  400  of multiple directly adjacent columns  31 ,  32  of a print image  300 . The formation of first groups  301  and/or of second groups  302  may thereby in particular be caused by a crosstalk between at least some of the nozzles  21 ,  22  of the print head  103 . For example, multiple nozzles  21  of a nozzle row  41  of a print head  103  belong to a group  301 . Nozzles  21 ,  22  from different nozzle rows  41 ,  42  of a print head  103  may then belong to different groups  301 ,  302 . Alternatively, nozzles  21  (if applicable directly adjacent nozzles  21 ) from different nozzle rows  41 ,  42  of a print head  103  may belong to one group  301 . 
     In an exemplary embodiment, the controller  101  may be configured to activate the first group  301  of nozzles  21  for the ejection of the nominal ink quantity with the first ejection pulse  401 . On the other hand, the second group  302  of nozzles  22  for the ejection of the nominal ink quantity can be activated with the second ejection pulse  402 . In an exemplary embodiment, the first ejection pulse  401  and the second ejection pulse  402  depend on the respective type of print head  103 . 
     In an exemplary embodiment, the controller  101  can be configured to activate the first nozzle  21  for the printing of different image points  400  with M different nominal ink quantities with accordingly M different first ejection pulses  401 . In an exemplary embodiment, M is a whole number, with M&gt;1. On the other hand, the second nozzle  22  for printing different image points  400  with the M different nominal ink quantities are activated with accordingly M different second ejection pulses  402 . In other words, M different first ejection pulses  401  and M different second ejection pulses  402  may be provided for the printing of M image points  400  of different sizes. Corduroy effects for different image point sizes may thus be reliably reduced. 
     In an exemplary embodiment, the controller  101  can be configured to determine print data for printing a row of the print image  300 . For the first nozzle  21  and the second nozzle  22 , the print data thereby indicate whether the respective nozzle  21 ,  22  should eject ink or not in the row for the printing of an image point  400 . Furthermore, the print data may indicate what nominal ink quantity of the M different nominal ink quantities should be ejected by the respective nozzle  21 ,  22 . 
     In an exemplary embodiment, based on the print data, the controller  101  can be configured to the select a first ejection pulse  401  of the M different first ejection pulses  401  to activate the first nozzle  21 . Furthermore, based on the print data, the controller  101  can then select a second ejection pulse  402  of the M different second ejection pulses  402  to activate the second nozzle  22 . Corduroy effects may thus be reduced in the printing of print data-based print images. 
     Exemplary embodiments of the present disclosure enable a system-dependent streaking of a printing system  100  to be at least partially compensated given a low computing power in the rastering process. In one or more embodiments, a hard-set compensation or a pre-established offset may thereby be used so that no additional calculation costs arise during a running printing process. Furthermore, the use of redundant print heads  103  to reduce the streaking may be omitted. 
     CONCLUSION 
     The aforementioned description of the specific embodiments will so fully reveal the general nature of the disclosure that others can, by applying knowledge within the skill of the art, readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, and without departing from the general concept of the present disclosure. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance. 
     References in the specification to “one embodiment,” “an embodiment,” “an exemplary embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. 
     The exemplary embodiments described herein are provided for illustrative purposes, and are not limiting. Other exemplary embodiments are possible, and modifications may be made to the exemplary embodiments. Therefore, the specification is not meant to limit the disclosure. Rather, the scope of the disclosure is defined only in accordance with the following claims and their equivalents. 
     Embodiments may be implemented in hardware (e.g., circuits), firmware, software, or any combination thereof. Embodiments may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computer). For example, a machine-readable medium may include read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, instructions may be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions in fact results from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc. Further, any of the implementation variations may be carried out by a general purpose computer. 
     For the purposes of this discussion, “processor circuitry” can include one or more circuits, one or more processors, logic, or a combination thereof. For example, a circuit can include an analog circuit, a digital circuit, state machine logic, other structural electronic hardware, or a combination thereof. A processor can include a microprocessor, a digital signal processor (DSP), or other hardware processor. In one or more exemplary embodiments, the processor can include a memory, and the processor can be “hard-coded” with instructions to perform corresponding function(s) according to embodiments described herein. In these examples, the hard-coded instructions can be stored on the memory. Alternatively or additionally, the processor can access an internal and/or external memory to retrieve instructions stored in the internal and/or external memory, which when executed by the processor, perform the corresponding function(s) associated with the processor, and/or one or more functions and/or operations related to the operation of a component having the processor included therein. 
     In one or more of the exemplary embodiments described herein, the memory can be any well-known volatile and/or non-volatile memory, including, for example, read-only memory (ROM), random access memory (RAM), flash memory, a magnetic storage media, an optical disc, erasable programmable read only memory (EPROM), and programmable read only memory (PROM). The memory can be non-removable, removable, or a combination of both. 
     REFERENCE LIST 
     
         
           1  transport direction 
           21  first nozzle 
           22  second nozzle 
           31  first column 
           32  second column 
           41 ,  42  nozzle rows 
           100  printing system 
           101  controller of the printing system  100   
           102  print bar 
           103  print head 
           201  nozzle opening 
           202  wall 
           210  meniscus 
           212  chamber 
           220  actuator (piezoelectric element) 
           221 ,  222 ,  322  deflection of the actuator 
           230  ink supply channel 
           300  print image 
           301 ,  302  groups of columns of nozzles 
           400  image point 
           401 ,  402  ejection pulses 
           410  activation point in time for printing a row 
           500  method for reducing a system-dependent streaking 
           501 ,  502  method operations