Abstract:
A method for printing on a receiver with a plurality of colored dry inks including dry black ink and a dry white ink, the method includes the steps of providing a set of multidimensional look-up tables for transforming a set of color channel inputs to a set of colored channel outputs; inputting a set of color values to the multidimensional look-up table, which values corresponds to a color rendition at each pixel location of the receiver; wherein the multidimensional look-up table outputs a new set of laydown values corresponding to the input channels and a white laydown at each pixel location; and printing the laydown values at each pixel location with the plurality of colored dry inks and dry white ink.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Reference is made to commonly assigned U.S. patent application Ser. No. 14/519,170 filed Oct. 21, 2014 by Chung-Hui Kuo, entitled “Method For Printing Colored And White Toner Using A Look-Up Table”, and commonly assigned U.S. patent application Ser. No. 14/519,183 filed Oct. 21, 2014 by Chung-Hui Kuo, entitled “An Apparatus For Printing Colored And White Toner”. 
     FIELD OF THE INVENTION 
     The present invention generally relates to electrophotographic printers and, more particularly, to electrophotographic printers that deposit “dry” white ink (commonly referred to as white toner) in a controlled amount for cost efficiencies and image quality. 
     BACKGROUND OF THE INVENTION 
     Electrophotographic printers produce images by depositing toner on receivers (or “imaging substrates”), such as pieces or sheets of paper or other planar media, glass, fabric, metal, or other objects. Printers typically operate using subtractive color: a substantially reflective receiver is over-coated image-wise with cyan (C), magenta (M), yellow (Y), black (K), and other colorants. Other toner compositions can also be used to produce effects beyond simple image appearance. 
     In electrophotography, there is a need to deposit white toner in combination with colored toner for various purposes such as image quality and the like. The prior art discussed below deposits white ink and other color toner on the receiver. 
     For example, U.S. Patent Publication 2009/0220695 A1 discloses a method of creating a record medium using an ink jet process by which a non-white background can be completely hidden. This is achieved by printing a metallic ink first and then a white pink. Wherever there is an overlap between the two layers, an opaque layer is formed which completely hides the background color or transparency of the medium. A combination of metallic and white layers creates the opaque layer which is extremely white because of the scattering by the white layer and reflecting properties of the metallic layer. 
     U.S. Patent Publication 2011/0234660 A1 discloses a method of printing on a transparent medium by IJ process using color inks, metallic ink and white ink. The opaque areas are created by the process described in the &#39;695 disclosure above. Use of white and metallic provides the cost advantage as well as be able to provide the desired luster effects. The image is viewed from the non-printed side for transparent substrate where the white layer is uniformly applied farthest from the medium. From opaque medium, white is applied first and then metallic and finally the color inks are jetted. The metallic layer serves as a specialty gloss layer to provide different effects and opacity. 
     U.S. Patent Publication 2013/0145383 A1 discloses an inkjet recording method which uses a white overlaying layer. The process is designed for remote proofing in which a longitudinal film is passed through two separate IJ stations. The substrate may contain an ink reception layer. 
     If the substrate is opaque, white is first laid down uniformly and after white layer is dried, color image is applied above it and dried again. On the other hand, when the substrate is transparent, color image is applied first and then dried. This is followed by the uniform application of white inkjet drops over the entire color image areas which are then dried again. In another variation, the white can be applied on the opposite surface in the case of a transparent substrate. Because the white is inkjet based, the preferred pigments are hollow or porous to avoid settling of heavy titania based white pigment. It further discloses an “inverse” type white ink application [0054 and 0057]; however, the white usage is based on total amount allowed by the substrate. 
     Although satisfactory, in U.S. Patent Publication 2009/0220695 A1, there is no adjustment of the white laydown with respect to the subsequent color inks, and two layers or more layers are required to create this opaque image. In U.S. Patent Publication 2011/0234660 A1, which is an inkjet process, there is no control of white ink based on color ink density; white is printed farthest from the viewing side, behind colors, not alongside. In U.S. Patent Publication 2013/0145383 A1, two printing stations are used, not one printing station, and the total white amount can exceed the total non-white amount ink. The present invention includes the advantages of adjusting the white laydown relative to color toner layers which reduces total toner cost, preserves the possible special visual effect provided by specialized substrates such as metallic/pearlescent substrate, and optimizes printable color gamut. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the invention, the invention resides in a method for printing on a receiver with a plurality of colored dry inks including dry black ink and a dry white ink, the method comprising the steps of providing a set of multidimensional look-up tables for transforming a set of color channel inputs to a set of colored channel outputs; inputting a set of color values to the multidimensional look-up table, which values corresponds to a color rendition at each pixel location of the receiver; wherein the multidimensional look-up table outputs a new set of laydown values corresponding to the input channels and a white laydown at each pixel location; and printing the laydown values at each pixel location with the plurality of colored dry inks and dry white ink. 
     These and other objects, features, and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described an illustrative embodiment of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features, and advantages of the present invention will become more apparent when taken in conjunction with the following description and drawings wherein identical reference numerals have been used, where possible, to designate identical features that are common to the figures, and wherein: 
       While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter of the present invention, it is believed that the invention will be better understood from the following description when taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is an electrophotographic printer useful for implementing the present invention; 
         FIG. 2  is a block diagram illustrating details of the logic and control unit and its interaction with printing modules of the present invention; 
         FIG. 3  is an alternative embodiment of the logic and control unit and its interaction with printing modules of the present invention; 
         FIG. 4  is a third embodiment of the logic and control unit and its interaction with printing modules of the present invention; and 
         FIG. 5  is a fourth embodiment of the logic and control unit and its interaction with printing modules of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Before discussing the present invention, it is useful to understand the term “dry ink” as used herein. In this regard, dry ink refers to toner particles deposited on a substrate which are later fixed to the substrate by pressure, heat or both. In contrast, liquid ink refers to inkjet processes where liquid ink is deposited which then dries for forming an image on a substrate. 
     In the following description, some embodiments will be described in terms that would ordinarily be implemented as software programs. Those skilled in the art will readily recognize that the equivalent of such software can also be constructed in hardware. Because image manipulation algorithms and systems are well known, the present description will be directed in particular to algorithms and systems forming part of, or cooperating more directly with, embodiments described herein. Other aspects of such algorithms and systems, and hardware or software for producing and otherwise processing the image signals involved therewith, not specifically shown or described herein, are selected from such systems, algorithms, components, and elements known in the art. Given the system as described herein, software not specifically shown, suggested, or described herein that is useful for implementation of the invention is conventional and within the ordinary skill in such arts. 
       FIG. 1  is an elevational cross-section illustrating portions of a typical electrophotographic printer  100  useful with various embodiments. Printer  100  is adapted to produce print images, such as single-color (monochrome), CMYK, CMYKF (five-color), or with the addition of a 6 th  development station (which is not shown) hexachrome images, on a receiver (multicolor images are also known as “multi-component” images). Images can include either or a combination of text, graphics, photos, and other types of visual content. One embodiment involves printing using an electrophotographic print engine having six sets of single-color image-producing or printing stations or modules arranged in tandem, but more or fewer than six colors can be combined to form a print image on a given receiver. Other electrophotographic writers or printer apparatus can also be included. Various components of the printer  100  are shown as rollers; other configurations are also possible, such as configurations having belts. 
     The printer  100  is an electrophotographic printing apparatus having a number of tandemly arranged electrophotographic image-forming printing modules  31 ,  32 ,  33 ,  34 ,  35 , also known as electrophotographic imaging subsystems. Each printing module  31 ,  32 ,  33 ,  34 ,  35  produces a single-color toner image for transfer using a respective transfer subsystem  50  (for simplicity and clarity, only one is labeled) to a receiver  42  successively moved through the modules. The receiver  42  is transported from a supply unit  40 , which can include active feeding subsystems as known in the art, into the printer  100 . In various embodiments, the visible image can be transferred directly from an imaging roller to the receiver  42 , or from an imaging roller to one or more transfer roller(s) or belt(s) in sequence in transfer subsystem  50 , and then to the receiver  42 . The receiver  42  is, for example, a selected section of a web of, or a cut sheet of, planar media such as paper or transparency film. 
     Each printing module  31 ,  32 ,  33 ,  34 ,  35  includes various components. For clarity, these are only shown in the printing module  32 . Around photoreceptor  25  are arranged, ordered by the direction of rotation of photoreceptor  25 , a charger  21 , an exposure subsystem  22 , and toning station  23 . 
     In the EP process, an electrostatic latent image is formed on photoreceptor  25  by uniformly charging photoreceptor  25  and then discharging selected areas of the uniform charge to yield an electrostatic charge pattern corresponding to the desired image (a “latent image”). The charger  21  produces a uniform electrostatic charge on photoreceptor  25  or its surface. The exposure subsystem  22  selectively image-wise discharges photoreceptor  25  to produce a latent image. The exposure subsystem  22  can include a laser and raster optical scanner (ROS), one or more LEDs, or a linear LED array. 
     After the latent image is formed, charged toner particles are brought into the vicinity of the photoreceptor  25  by the toning station  23  and are attracted to the latent image to develop the latent image into a visible image. Note that the visible image may not be visible to the naked eye depending on the composition of the toner particles (for example clear toner). The toning station  23  can also be referred to as a development station. The toner can be applied to either the charged or discharged parts of the latent image. The toner particles can have a range of diameters, for example less than 8 micrometer, on the order of 10-15 micrometer, up to approximately 30 micrometer, or larger (“diameter” refers to the volume-weighted median diameter, as determined by a device such as a Coulter Multisizer). 
     After the latent image is developed into a visible image on photoreceptor  25 , a suitable receiver  42  is brought into juxtaposition with the visible image. In the transfer subsystem  50 , a suitable electric field is applied to transfer the toner particles of the visible image to the receiver  42  to form the desired print image  38  on the receiver  42 , as shown on receiver  42 A. The imaging process is typically repeated many times with reusable photoreceptors  25 . 
     The receiver  42 A is then removed from its operative association with photoreceptor  25  and subjected to heat or pressure to permanently fix (“fuse”) print image  38  to receiver  42 A. Plural print images are overlaid on one receiver before fusing to form a multi-color print image  38  on the receiver  42 A. 
     Each receiver  42 , during a single pass through the six printing modules  31 ,  32 ,  33 ,  34 ,  35 , can have transferred in registration thereto up to five single-color toner images to form an image. In one embodiment, printing module  31  forms black (K) print images,  32  forms yellow (Y) print images,  33  forms magenta (M) print images,  34  forms cyan (C) print images and  35  forms white (W) print images. The receiver  42 A is shown after passing through the printing module  36 . The print image  38  on receiver  42 A includes unfused toner particles. 
     Subsequent to transfer of the respective print images  38 , overlaid in registration, one from each of the respective printing modules  31 ,  32 ,  33 ,  34 ,  35 , the receiver  42 A is advanced to a fuser  60 , i.e. a fusing or fixing assembly, to fuse the print image  38  to receiver  42 A. A transport web  81  transports the print-image-carrying receivers (e.g.,  42 A) to the fuser  60 , which fixes the toner particles to the respective receivers  42 A by the application of heat and pressure. The receivers  42 A are serially de-tacked from transport web  81  to permit them to feed cleanly into fuser  60 . The transport web  81  is then reconditioned for reuse at cleaning station  86  by cleaning and neutralizing the charges on the opposed surfaces of the transport web  81 . A mechanical cleaning station (not shown) for scraping or vacuuming toner off the transport web  81  can also be used independently or with cleaning station  86 . The mechanical cleaning station can be disposed along the transport web  81  before or after the cleaning station  86  in the direction of rotation of the transport web  81 . 
     The fuser  60  includes a heated fusing roller  62  and an opposing pressure roller  64  that form a fusing nip  66  therebetween. In one embodiment, the fuser  60  also includes a release fluid application substation  68  that applies release fluid, e.g. silicone oil, to fusing roller  62 . Alternatively, wax-containing toner can be used without applying release fluid to the fusing roller  62 . Other embodiments of fusers, both contact and non-contact, can be employed. For example, solvent fixing uses solvents to soften the toner particles so they bond with the receiver  42 . Photoflash fusing uses short bursts of high-frequency electromagnetic radiation (e.g. ultraviolet light) to melt the toner. Radiant fixing uses lower-frequency electromagnetic radiation (e.g. infrared light) to more slowly melt the toner. Microwave fixing uses electromagnetic radiation in the microwave range to heat the receivers (primarily), thereby causing the toner particles to melt by heat conduction, so that the toner is fixed to the receiver  42 . 
     The receivers (e.g., receiver  42 B) carrying the fused image (e.g., fused image  39 ) are transported in a series from the fuser  60  along a path either to a remote output tray  69 , or for duplex printing, back to the printing modules  31 ,  32 ,  33 ,  34 ,  35  to create an image on the backside of the receiver (e.g., receiver  42 B), i.e. to form a duplex print. Receivers (e.g., receiver  42 B) can also be transported to any suitable output accessory. For example, an auxiliary fuser or glossing assembly can provide a clear-toner overcoat. Printer  100  can also include multiple fusers  60  to support applications such as overprinting, as known in the art. 
     In various embodiments, between the fuser  60  and the output tray  69 , the receiver  42 B passes through the finisher  70 . Finisher  70  performs various media-handling operations, such as folding, stapling, saddle-stitching, collating, and binding. 
     The printer  100  includes the main printer apparatus logic and control unit (LCU)  99 , which receives input signals from the various sensors associated with the printer  100  and sends control signals to the components of the printer  100 . The LCU  99  can include a microprocessor incorporating suitable look-up tables and control software executable by the LCU  99 . It can also include a field-programmable gate array (FPGA), programmable logic device (PLD), microcontroller, or other digital control system. The LCU  99  can include memory for storing control software and data. Sensors associated with the fusing assembly provide appropriate signals to the LCU  99 . In response to the sensors, the LCU  99  issues command and control signals that adjust the heat or pressure within fusing nip  66  and other operating parameters of fuser  60  for receivers. This permits the printer  100  to print on receivers of various thicknesses and surface finishes, such as glossy or matte. 
     Image data for writing by the printer  100  can be processed by a raster image processor (RIP; not shown), which can include a color separation screen generator or generators. The output of the RIP can be stored in frame or line buffers for transmission of the color separation print data to each of the respective LED writers, e.g. for black (K), yellow (Y), magenta (M), cyan (C), and white (W), respectively. The RIP or color separation screen generator can be a part of printer  100  or remote therefrom. Image data processed by the RIP can be obtained from a color document scanner or a digital camera or produced by a computer or from a memory or network which typically includes image data representing a continuous image that needs to be reprocessed into halftone image data in order to be adequately represented by the printer. The RIP can perform image processing processes, e.g. color correction, in order to obtain the desired color print. Color image data is separated into the respective colors and converted by the RIP to halftone dot image data in the respective color using matrices, which comprise desired screen angles (measured counterclockwise from rightward, the +X direction) and screen rulings. The RIP can be a suitably-programmed computer or logic device and is adapted to employ stored or computed matrices and templates for processing separated color image data into rendered image data in the form of halftone information suitable for printing. These matrices can include a screen pattern memory (SPM). 
     Further details regarding printer  100  are provided in U.S. Pat. No. 6,608,641, issued on Aug. 19, 2003, to Peter S. Alexandrovich et al., and in U.S. Publication No. 20060133870, published on Jun. 22, 2006, by Yee S. Ng et al., the disclosures of which are incorporated herein by reference. 
     Referring to  FIG. 2 , there is shown in block diagram details of the portion of the LCU  99  for rendering white toner based on the amount of colored toner being rendered. The LCU  99  receives images files, such as, but not limited to, RGB, CMYK, pdf, raster or vector files, that are sent to a CMYK rendering engine  102  which converts the particular image file into a standard CMYK format and then separates the CYMK format file into individual color components—Cyan component, Magenta component, Yellow component, and Black component. These individual color components are then each sent to either a one-dimensional transform  105   a  or a one-dimensional look-up table (LUT)  105   b . The transform  105   a  or LUT  105   b  takes the particular color component and obtains the corresponding white laydown at each pixel location. It is noted that the white color component varies according to the amount of the particular color component as illustrated schematically in  FIG. 2 . The LUT  105   b  is in a table format in which corresponding values are stored; transform  105   a  is a real-time look-up in which an algorithm determines the corresponding white laydown; and look-up table as used herein refers to either embodiment. The basic algorithm is to deposit maximal amount of white toner on the area of the media corresponding to the white point of the image, and gradually reducing monotonically the amount of white toner laydown relative to each increasing color toner laydown. The rate of white toner laydown reduction is dependent on the opacity of each color toner, the intended substrate&#39;s background color, and the toner laydown sequence. For example, the black toner has very high opacity. As a result, the white toner reduction rate relative to the black toner can be higher than other color toners such as yellow. Furthermore, the background color of the intended substrate will also affect the white toner reduction rate relative to each color toner laydown. For example, if the substrate is metallic, since the substrate surface is very reflective, the purpose of the white toner is simply to sufficiently block the underlying metallic texture structure without losing the metallic appearance. The white toner reduction rate will be much higher than that on a colored card board substrate. The four 1-D transforms or LUTs ( 105   a  or  105   b ), one for each colorant, each output a value for the white laydown (W1, W2, W3, W4). Those values are input to a computational engine  110  that determines the print value for each pixel location based on the white laydown values from each transform or LUT ( 105   a  or  105   b ). 
     The determined value for W could be simply the smallest of the set of white values (W1, W2, W3, W4), or it could be an overage of the set of white values (W1, W2, W3, W4), or it could even be the largest of the set of white values (W1, W2, W3, W4). The value for the white ink laydown W and the original values for the colorants (CMYK) are provided to the printing module  31 - 15  for rendering and physical lay down and finishing of the colorants on the receiver. 
     Referring to  FIG. 3 , there is shown an alternative embodiment for rendering white toner based on the amount of colored toner being rendered. The LCU  99  receives images files, such as, but not limited to, RGB, CMYK, pdf, raster or vector files, that are sent to the CMYK rendering engine  102  which converts the received image file into a standard CMYK format and then separates the CYMK format file into individual color components—C component, M component, Y component, and K component. The CMY values are combined in an effective laydown engine  120  to determine an effective laydown of the colorants and then the effective laydown is sent to either the one dimensional transform  105   a  or the one dimensional LUT  105   b , which is used to determine the desired laydown of white ink W5 at each pixel location (the y values) depending on the effective laydown of the colored inks (CMY). The opaque black value K is provided to either a separate one dimensional transform  105   c  or one dimensional LUT  105   d  which correlates the laydown of the black ink (K) to another white laydown W6 based on the black ink. In other words, the two 1-D transforms or LUTs (either  105   a  or  105   b  and either  105   c  or  105   d ), one for the effective CMY and one for the black K laydown, each output a value for the white laydown (W5, W6). The W5 and W6 values are input to the computational engine  110  that determines the print value for each pixel location based on the white laydown values from each transform or LUT (either  105   a  or  105   b  and either  105   c  or  105   d ). To determine the effective laydown of the colored ink (CMY), first treat each distinct color toner as the same type of toner. Within a unit area, then compute the percent of averaged coverage of this new toner where the overlapped area of two of more color toner is counted only once. This averaged coverage can also change with respect to the halftone screen structure. 
     The determined value for W in this embodiment could be simply the smallest of the set of white values (W5, W6), or it could be an overage of the set of white values (W5, W6), or it could even be the largest of the set of white values (W5, W6). The value for the white ink laydown W and the original values for the colorants (CMYK) are provided to the print engine modules  31 - 35  for rendering and physical lay down and finishing of the colorants on the receiver. 
     Referring to  FIG. 4 , there is shown a third embodiment for rendering white toner based on the amount of colored toner being rendered. The LCU  99  receives images files, such as, but not limited to, RGB, CMYK, pdf, raster or vector files, that are sent to a CMYK rendering engine  102  which converts the received image file into a standard CMYK format and then separates the CYMK format file into individual color components—C component, M component, Y component, and K component. The CMYK values are combined in an effective laydown engine  120  to determine an effective laydown of the colorants and black and then the effective laydown is sent to either the one dimensional LUT  105   a  or  105   b , which is used to determine the desired laydown of white ink W7 at each pixel location (the y values) depending on the effective laydown of the colored inks and black dry ink (CMYK). The 1-D transform or LUT ( 105   a  or  105   b ) outputs a value for the white laydown (W7). That value determines the white ink print value for each pixel location based on the effective laydown of CMYK. The value for the white ink laydown W7 and the original values for the colorants (CMYK) are provided to the printing module  31 - 35  for rendering and physical lay down and finishing of the colorants on the receiver. 
     Referring to  FIG. 5 , there is shown a fourth embodiment for rendering white toner based on the amount of colored toner being rendered. The LCU  99  receives images files, such as, but not limited to, RGB, CMYK, pdf, raster or vector files, that are sent to a CMYK rendering engine  102  which converts the received image file into a standard CMYK format and then separates the CYMK format file into individual color components—C component, M component, Y component, and K component. The CMYK values are then combined using a color profile known as the Device Link Profile  130  to determine the desired laydown of all the dry inks, C′M′Y′K′ and W′. The effective laydowns are provided to the printing modules  31 - 35  for rendering and physical lay down and finishing of the colorants on the receiver. The advantage of utilizing a Device link profile to provide proper white toner laydown relative to the color toner laydown, such as C,M,Y,K, and possibly other supplemental accent color toners, from the digital controller is its capability to specify different amount of white toner laydown at different color toner laydown composition on the intended printing substrate. A printer output device link profile is composed of a multidimensional LUT from N-color input channels to M-Color output channels. In the case of creating a separate white toner layer, the dimension of the input/output color channels is N and N+1 respectively. In one embodiment, each color toner is assigned with its own opacity coefficient ranging from 0 to 1, where 0 means complete transparent and 1 means complete opaque. For example, the opacity coefficient for yellow toner is usually set as the lowest among all color toners and the black toner is usually set to be 1. Based on a chosen halftone screen set for every color channel, the effective substrate-blocking ratio, Br, on a unit area by all color toner laydown combined in the multidimensional LUT of the Device link profile can be computed. The white toner laydown, W′, is inversely correlated with the computed substrate-blocking ratio, for example, W=1−Br. This correlation function will also be dependent on the selected substrate. At the same time, C′M′Y′K′ are computed taking into account grey component removal and the type of substrate used. 
     Grey component removal is used by the Device link profile to substitute a quantity of black ink for the grey component of the CMY inks. The Device link profile uses properties of the receiver to determine the multidimensional look-up table transforms, and properties of the receiver include the color of the receiver, type of the receiver or reflectance of the receiver. The Device link profile also depends on order of laydown of the colored, black and white toner on the receiver. 
     The present invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 
     PARTS LIST 
     
         
           21  charger 
           22  exposure subsystem 
           23  toning station 
           25  photoreceptor 
           31  printing module 
           32  printing module 
           33  printing module 
           34  printing module 
           35  printing module 
           38  print image 
           39  fused image 
           40  supply unit 
           42  receiver 
           42 A receiver 
           42 B receiver 
           50  transfer subsystem 
           60  fuser 
           62  fusing roller 
           64  pressure roller 
           66  fusing nip 
           68  release fluid application substation 
           69  output tray 
           70  finisher 
           81  transport web 
           86  cleaning station 
           99  logic and control unit (LCU) 
           100  printer 
           102  CMYK rendering engine 
           105   a  transform 
           105   b  one-dimensional look-up table (LUT) 
           105   c  transform 
           105   d  one dimensional look-up table (LUT) 
           110  computational engine 
           120  effective laydown engine 
           130  Device link profile