Abstract:
A method for providing indications for conditioning ink flow valves of at least one inking unit of a printing press. The printing area of the inking unit is divided into a multiplicity of inking zones each supplied by one ink flow valve in order to prescribe a predetermined rate of ink flow for each ink zone in said at least one inking unit. The method includes determining by calculating, from a digital image being processed for printing, a representative ink density value for each ink zone and for each color separation and furnishing the ink flow valves respectively with the values for regulating the flow in the ink zones.

Description:
RELATED APPLICATION 
     This application is a continuation in part application of patent application Ser. No. 08/627,434 filed Apr. 4, 1996, now abandoned. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to control of the ink flow of a printing press. 
     BACKGROUND OF THE INVENTION 
     The prior art printing process is illustrated in FIG. 1 to which reference is now made. Each individual color page to be printed is prepared on a pre-press device  10 . When the designer finishes designing the page, the pre-press device  10  creates four digitized versions  12  of the page, one for each of the four color separations cyan, magenta, yellow and black (C, Y, M, and K). The digitized versions of the page will be known herein as “separation files”  12 . 
     When the designer has finished preparing all of the pages of the printed publication (magazine, newspaper, brochure, etc.) to be printed, he provides the separation files  12  for the entirety of pages to an imposition device  14  (such as provided within the WHISPER I/O Station manufactured by Scitex Corporation Ltd. of Herzlia, Israel) which “imposes” the pages into “signatures”  16 . Each signature typically has press marks  18  and eight pages on it where the order that the eight pages are laid out is a function of how the printing press will fold the press sheet after printing. The imposition device  14  produces four data files of the signature, one for each color separation. 
     The four files representing the signature  16  are provided to a film plotter  20  (such as the DOLEV 800 plotter manufactured by Scitex Corporation Ltd.) which plots each version of the signature  16  onto a film. The result are films  22  of the separations of the signature  16 . Blue-line proofs  26  are provided by blue line proofer  26  from films  22 . Blue-line proofs  26  is a blue and white print of the signature  16  and is utilized to ascertain that the text is correct, that the placement of the various elements of the pages are correct and aligned and that the general impression of the pages is correct. If it is not, the designer needs to make changes at the pre-press device  10  and the process needs to be repeated. 
     To determine whether or not the colors to be printed are the desired colors, the films  22  are sent to a Chromalin proofer  26  as produced by Dupont, Delaware, USA for producing a color CHROMALIN proof  29 . The film creation process is repeated if the colors are in any way unacceptable. 
     If the blue-line proof  26  and the color chromalin  29  indicate that there are no problems, the films  22  are provided to a printing press  30  for printing. Each film  22  is utilized to create a press plate and the press plates are placed on separate inking units of the press, onto which the ink of the proper color (cyan, magenta, yellow or black) will be spread. 
     Since the color varies widely across a page and across a signature, each press inking unit is divided into a plurality of “zones” where each zone has a separate ink flow regulator  32 , known as a “zone valve”. Each zone valve ensures that the amount of ink which is spread across its zone is compatible with the amount of color desired. 
     Usually, a press operator initially sets the zone valves  32  by looking at the colors in the Chromalin proof  29 . He then prints one sheet with the initial settings, to view the final result. If the colors are smeared in one zone, there is too much ink available and he will have to adjust down the zone valve  32  for the problematic zone. Similarly, if the color is too light, he will have to open up the zone valve  32 . The printing process is repeated for another sheet until the desired affect is achieved. After that, the printing press is operated with only spot checks to determine that the ink flow in each zone remains correct. 
     The Heidelberg Speedmaster 72 printing press, manufactured by Heidelberg Druckmaschinen AG of Germany, has a plurality of zone valves  32  (or fountain keys) which can be controlled directly or remotely. Presses may have 8 to 30 such zone valves. 
     It will be appreciated that, if the density of a given color is consistent across the zone, the setting for the zone valve  32  is straightforward. However, if the density of the color varies widely over a zone, it is difficult for the press operator to determine how much ink flow to provide. 
     U.S. Pat. No. 5,128,879 describes a method and apparatus which acquires the zone valve states and adjusts them automatically. The settings of the zone valves are calculated from the color density values provided in the page initially created by the pre-press devices  10 . The calculated zone valve settings are forwarded directly to the printing press, without intervention of the press operator. 
     European Patent Publication 495563 A2 describes an integrated computerized system for use in printing assigned to the common assignees of the present invention. The disclosure of its U.S. counterpart, allowed application No. 07/650,249 now U.S. Pat No. 5,875,288 is incorporated herein by reference. The system includes apparatus for providing and digitally storing at least one digital representation of at least one page. The digital representation is imposed and arranged in accordance with a desired plate layout to define a plate image. Press set-up apparatus then extracts the digital representation and providing press set-up data to a printing press. 
     SUMMARY OF THE PRESENT INVENTION 
     This invention is useful in printing presses which are manually (or remotely) controlled. It is an object of the present invention to provide the press operator with positive indication of the initial setting for the printing press zone valves. This is achieved by creating a proof which provides, in addition to a proof of the signature (placement, text, graphics), ink density indications for each zone of each color separation. 
     According to a preferred embodiment of the invention, there is provided a method for providing indications for conditioning or presetting ink flow valves of at least one inking unit of a printing press. The printing area of the inking unit is divided into a multiplicity of inking zones each supplied by one ink flow valve in order to prescribe a predetermined rate of ink flow for each ink zone in said at least one inking unit. The method includes determining by calculating, from a digital image being processed for printing, a representative ink density value for each ink zone and for each color separation and furnishing the ink flow valves respectively with the values for regulating the flow in the ink zones. 
     The ink density indications can be provided in any way. In one embodiment, the ink density indications are provided in strips, one per ink color, below the signature. The strips are divided into sections, one per zone, and each section has both a listing of the ink density of the zone and a swatch of ink having the average color density. 
     Moreover, in accordance with the preferred embodiment of the present invention, the representative ink densities are determined by dividing the image to be printed into a plurality of image zones associated with the inking zones of the press and determining a representative ink density of each ink color in each image zone. The operator is typically furnished with a reproduction of the representative ink densities as color proofs or alternatively on paper. 
     Furthermore, in accordance with the preferred embodiment of the present invention, the reproducing of the representative ink densities includes the step of creating color strips of the representative ink densities. The color strips have strip zones each of which is associated with one of the image zones. The strip zone has the representative density of the associated image zone. Numerical indications of the representative ink densities can be included. The step of reproducing can include the step of plotting the representative ink densities on a color proof or onto color separation films from which a color proof is produced. 
     Furthermore, in accordance with a second preferred embodiment of the present invention, there is provided a method of setting the amount of ink flow for each zone valve of a printing press for an image to be printed. The method includes determining, from the image to be printed, representative ink densities for each ink zone and for each separation, visually reproducing the representative densities and setting the amount of ink flow of each zone valve in accordance with the color of the corresponding representative ink density. Setting the amount of ink flow can provide the initial setting of the zone valves. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The file of this patent contains at least one drawing executed in color. Copies of this patent with color drawing(s) will be provided by the Patent and Trademark Office upon request and payment of the necessary fee. 
     The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which: 
     FIG. 1 is a schematic block diagram illustration of a prior art work flow for creating and printing color documents; 
     FIG. 2A is a color illustration of a part of a color proof having ink density strips thereon, said ink density strips being constructed in accordance with preferred embodiments of the present invention; 
     FIG. 2B is a schematic illustration of the complete proof of FIG. 2A, providing reference numerals to the elements of FIG. 2A; and 
     FIG. 3 is a schematic block diagram illustration of a first work flow for creating the color proof of FIG.  2 A. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention provides a press operator with indications, typically on a portable sheet of paper, of the ink flow rates to be set in each of the zones of the press. The ink-flow indication is provided as a swatch of ink, which has the desired density, accompanied by a percentage showing the setting of valve  32 , which according to the present invention may be carried out in each zone before beginning the printing job. Since the press operator generally knows the relationship between the swatch color and the setting of the zone valves, he can set each valve  32  in accordance with the percentage marked, using the corresponding ink-swatch as confirmation. The press operator typically then fine tunes the zone valves  32  as in the prior art. It will be appreciated that the visual indications of the present invention can be utilized at any point during the operation of the press. 
     Reference is now made to FIGS. 2A and 2B. FIGS. 2A and 2B provide an example of the present invention. FIG. 2A is a color illustration of part of a color  63  proof of a signature which also comprises strips of ink swatches having the representative density for each zone of the signature and FIG. 2B is a schematic illustration of the entire proof  63  of FIG. 2A indicating its elements and reference numerals. 
     It will be appreciated that the present invention is operative for all types of “pages” to be printed; thus, it can be implemented for a signature of many pages, as described hereinbelow, or it can be implemented for printing a poster of a single page. 
     As shown in FIGS. 2A and 2B, the proof has signature elements and color strips. The signature elements include eight pages  40 , registration marks  42  and folding marks  44 . There are four color strips, labeled  46   a,    46   b,    46   c  and  46   d,  one for each ink color, cyan, magenta, yellow and black, respectively. If other ink colors are utilized, the strips  46  will have the approximate colors of the inks utilized. 
     The color strips  46  are typically placed below or above the signature and the strips  46  are typically aligned with one another. Each color strip  46  is divided into swatches  50  where each swatch  50  of each strip  46  corresponds to a zone  52  of the signature thereabove or below. One zone  52  is illustrated in FIG.  2 B and is shown associated with swatches  50   a,    50   b,    50   c  and  50   d  of strips  46   a,    46   b,    46   c,  and  46   d,  respectively. The number of swatches correspond to the number of zone valves of the specific press in use. 
     Swatch  50   a  has a density of cyan which is the representative density of cyan in zone  52 . For the purposes of this description, “density” may be defined as the ink coverage as a percentage. Similarly, swatches  50   b,    50   c  and  50   d  have densities of magenta, yellow and black, respectively, which are the representative densities of magenta, yellow and black in zone  52 . The representative densities can be determined in any of a number of ways, some of which are described hereinbelow. 
     Over the color strip area is a notation  53  representing the number of the zone valve  32  to which each swatch refers. Below each zone of each color strip are numerical indications  54 , representing the zone valve positions as a percentage of the full open position. Alternatively, the indications  54  can indicate the ink density of the swatch  50  thereabove. Thus, swatches  50   a,    50   b,    50   c  and  50   d  have numerical indications,  54  for example, of 25%, 35%, 15% and 32%, respectively. 
     It will be appreciated that the press operator can determine, from both the visual indications of the representative color density and the numerical indications, what the appropriate initial setting for the zone valves  32  of each zone should be, and thus, condition or preset each of the zone valves  32 . 
     Reference is now made to FIG. 3 which is a schematic block diagram illustration of a first work flow for creating the color proof  63  of FIG.  2 A. Elements which are similar to those of FIG. 1 have the same reference numerals. 
     As in the prior art work flow of FIG. 1 the workflow of the invention as shown in FIG. 3 indicates that, the pre-press devices  10  produce color separations  12  of a plurality of pages. Then, in the prior art, an imposition device  14  imposes the page into a signature, whereas in the present invention, the imposition device  14 , after having composed the pages, provides them further to a density calculating device  61 , before being processed further in devices  62  and  20 . The device  61  determines a representative density value for each color and each zone of the imposed signature, as detailed hereinbelow. Each density value represents a zone allocated on the image, which corresponds to an ink zone of a printing machine inking unit in a printing press. According to the preferred embodiment, device  61  prepares strips, the color density value of which is based on the color density value placing a swatch of the calculated density above or below the associated zone and the numerical indications. Unit  61  then provides the signature and color strip information to a color printer  62 , such as the 650C color plotter manufactured by Hewlett-Packard Company of Boise, Id., to produce the color proof of FIG.  2 A. If the color proof of FIG. 2A is acceptable, device  61  also provides just the signature information to film plotter  20  which then plots the films  22 . The films are converted into plates which are then placed on the printing press  30  for printing. With the color proof  63  of FIG. 2A, produced by proofer  62 , the press operator can set the initial setting of zone valves  32 . 
     In one embodiment of the present invention, the representative densities are per color averages of the densities in each zone. The averages are determined by device  61  as follows: 
     1. First the imposed signature is divided into vertical zones  52  (FIG. 2B) the number of which reflects the number of zone valves in an inking unit of the press on which the signature intended to be printed; 
     2. Subsequent to their allocation each vertical zone  52  is divided into a multiplicity of squares  70  and the average color density of every square, for each color separation, is derived from the digital images of the color separations  12 . 
     3. The plurality of values thus obtained, one from each of the squares  70  comprising a vertical zone  52  are averaged, thereby obtaining a single value for an entire strip. 
     Consequently, each value representing a single vertical zone is then used according to a preferred embodiment, for assigning a specific color density manifested in swatches  50 . To achieve this, a transform function is employed, linking between the strip value and the color density scale, with instruction accordingly being sent to the color proofer  62 . 
     According to a preferred embodiment of the invention, device  61  exists virtually in software and all the operations involved are numeric calculations and other operations implemented by a computer such as a Personal Computer or a Workstation. 
     It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather the scope of the present invention is defined by the claims which follow.