Abstract:
A method to improve the image of a printed barcode by enhancing coverage of the print pixels within solid printed areas to improve the print uniformity and decrease the graininess of the typical ink jet printing by dissolving a small percentage of the colorant and distributing more uniformly. The parameter improved by the invention is the graininess or uniformity of coverage. The contrast ratio within barcode data elements can be also improved without causing unwanted image bleed into unintended areas. Hence, the printed barcode will contain more clearly defined printed and non printed areas to enable the barcode to be accurately read. The invention prevents also unwanted bleeding in areas where it could lower the quality of the printed material by avoiding application of enhanced coverage facilitators when desired white space is identified within a minimum distance.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to the field of printing and more particularly to improving the readability of printed matter. 
     BACKGROUND OF THE INVENTION 
     Printed matter needs to be printed with a high level of quality to ensure readability by automation equipment, especially when old technology readers require very high print contrast ratios to ensure readability. The problem is particularly evident when barcodes are automatically read by postal automation equipment and other barcode readers. 
     Barcodes have been used in a wide variety of applications as a source for information. Typically barcodes are used at a point-of-sale terminal in merchandising for pricing and inventory control. Barcodes are also used in controlling personnel access systems, mailing systems, and in manufacturing for work-in process and inventory control systems, etc. The barcodes themselves represent numbers or alphanumeric characters by series of adjacent stripes of various widths, (i.e. a width modulated universal product code), heights (i.e. a height modulated POSTNET barcode), or position (2D barcode). 
     An ordinary barcode is a set of binary numbers. It typically consists of black bars and white spaces. A wide black bar space may signify a one and a thin black bar or space may signify a zero. The binary numbers stand for decimal numbers or letters. There are several different kinds of barcodes. In each one, a number, letter or other character is formed by a pre-established number of bars and spaces. 
     Width modulated barcodes are “vertically redundant”, meaning that the same information is repeated vertically. They are in fact a one-dimensional code. The heights of the bars can be truncated without any lose of information. A two-dimensional code stores information along the height as well as the length of the symbol. Thus, in the same area more information may be stored in a two dimensional barcode than in a one dimensional barcode. 
     Current technology printers may leave small unintended voids between pixels which prevent achievement of the highest print contrast and uniform coverage of which the ink dyes or pigments are theoretically capable of. Such unintended voids are caused by the nature of ink jet printing of placing small drops (1-50 pL) on rough surface of paper with “peaks and valleys”. The ink jet drops do not reach the paper surface in a uniform way and therefore cause to “graininess” as defined by the Standard ISO 13660, herein incorporated by reference, or non uniform print coverage especially on plain paper. Therefore the result is a degradation of the print quality of printed images. In comparison the mass thermal transfer printing achieves a uniform print coverage with the melt wax bridging the irregularities of the paper surface. 
     These characteristics affect the uniformity of the modules printed in the 2 D bar codes which might be interpreted as background by scanners. Barcodes, are also very sensitive to ink in unwanted locations—the line of contact and the white spaces in barcodes must be preserved and readability can be severely impacted if ink is allowed to bleed into regions which are intended to be blank (print growth). 
     One of the problems of the prior art is that it is often difficult to automatically read printed information. 
     Another problem of the prior art is that s often difficult to automatically read printed information that has a low print contrast ratio which is due to non optimal print coverage. 
     SUMMARY OF THE INVENTION 
     This invention overcomes the disadvantages of the prior art by providing a method to improve barcode print image quality by printing the bar code ink from one printhead or trench and then applying the solvent from a second printhead on the first printed image in order to improve the printed area uniformity. The conditions of the 2 inks to be printed are the following: the first ink has to have a low percentage of colorant soluble in the post printed solvent and the solvent has to be able to wet the first print efficiently during the printing process. The invention utilizes a print head to cause localized improvement by applying a fluid that acts on prints generated by another print head. 
     The invention also prevents bleeding into unwanted areas where it could lower the quality of the printed material by utilizing the localized (targeted) print capabilities of print heads. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates in enlarged detail portions of code bars of an ideal one dimensional barcode; 
         FIG. 2  is a drawing of a two dimensional (2-d) barcode; 
         FIG. 3  illustrates in enlarged detail an idealized black rectangle  64  of  FIG. 2 ; 
         FIG. 4  illustrates in enlarged detail a barcode data element (black rectangle  64 ) of  FIG. 2  that comprises a matrix of 5 by 5 printed pixels; 
         FIG. 5  illustrates in enlarged detail a barcode data element (black rectangle  64 ) of  FIG. 2  that comprises a matrix of 5 by 5 printed pixels  66 , showing pixels  66  in the enhanced coverage area  68  of rectangle  64 ; 
         FIG. 6  illustrates in enlarged detail a barcode data element ( 64 ) of  FIG. 5  that that formed an almost solid black area  69  after the facilitator evaporated; 
         FIG. 7  illustrates a large black rectangle  70  that comprises a matrix of 10 by 10 printed pixels  66 , showing the pixel trimmed facilitator print area  71  with a subset rectangular reduced print area  72  for reduced facilitator print; 
         FIG. 8  illustrates in enlarged detail a black rectangle  70  of  FIG. 7  that that formed an almost solid black area  79  without pooling after the facilitator evaporates; 
         FIG. 9  is a process flow diagram of the printing of rectangle  64  of  FIG. 6 ; 
         FIG. 10  is a drawing of the apparatus of this invention showing two print heads (ink and facilitator) that print the enhanced barcode  60 ; 
         FIG. 11  is a drawing of the apparatus of this invention showing two print heads (ink and facilitator) as they move across the paper  204  leaving a trail of printed enhanced barcode data elements; and 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings in detail, and more particularly to  FIG. 1 , the reference character  11  represents an enlarged detail portion of a width modulated barcode. Barcode  11  contains bars  12 ,  13  and  14  and spaces  15 ,  16  and  17 . Bar  12  is three pixels wide, bar  13  is two pixels wide, and bar  14  is one pixel wide. Bar  12  represents a unique number (i.e., three), bar  13  represents a unique number (i.e., two), and bar  14  represents a unique number (i.e., one). Spaces  15 ,  16  and  17  are one unit wide. 
       FIG. 2  is a drawing of a two dimensional (2-d) barcode  60 . Barcode  60  includes: a start pattern  61 , that informs a scanner (not shown) when to begin reading data; a data portion  62 ; and a stop pattern  63 , that informs a scanner when to stop reading data. Data portion  62  comprises printed barcode data elements (rectangles)  64  and non printed barcode data elements (spaces)  65 . The coded information represented by data portion  62  is contained in the relative positions of the printed ( 64 ) and non printed ( 65 ) barcode data elements that are scanned. 
       FIG. 3  illustrates in enlarged detail an idealized black rectangle  64  of  FIG. 2 . 
       FIG. 4  illustrates in enlarged detail a black rectangle  64  of  FIG. 2  that comprises a matrix of 5 by 5 printed pixels  66 . The printed pixels  66  have unintended voids  67  between them. The print contrast within the printed area of rectangle  64  is diluted by the unintended voids  67  or white space between pixels  66  resulting in an average lower optical density and therefore lowered contrast ratio even in the presence of an “ideal” 100% black ink. 
       FIG. 5  illustrates in enlarged detail a black rectangle  64  of  FIG. 2  that comprise a matrix of 5 by 5 printed pixels  66 , including nine pixels  66  in the enhanced coverage area  68  of rectangle  64 . A facilitator (e.g. water) of the black ink that prints pixels  66  may be applied to the enhanced coverage area  68  (before or after printing). The pixel trimmed area  68  has been defined as the area remaining after trimming one row of pixels  66  off the top and bottom of the original rectangle  64  and one column off the left and right of the original rectangle  64 . This prevents any unwanted bleeding of the image outside the intended boundaries of rectangle  64 . This facilitator causes enhanced coverage of the pixels  66  in area  68  resulting in the image displayed in  FIG. 6  after the ink dries. Any number of pixels may be trimmed in different applications (more may be trimmed at higher print resolutions). The pixel trimming may also be different in different directions. For instance, the manufacturing process of paper results in a “grain” of preferred fiber orientation. Ink may show unintended bleed differently along the grain of the paper than across the grain of the paper. Therefore it may be desirable for the print area  68  for facilitator application to be trimmed more from the original rectangle  64  along the long axis (with the grain) of the paper than across the grain. A first print head may be used to apply a facilitator like water. The first print head may also be an existing print cartridge containing both ink and facilitator which is utilized for this function. And a second print head, like Xerox Y100 produced by Xerox Corporation, 100 South Clinton Avenue, Rochester, N.Y. 14644, may be used to print pixels  66  with a black ink. 
       FIG. 6  illustrates in enlarged detail a black rectangle  64  of  FIG. 5  that formed an almost solid black area  69  after the ink dried. The print quality and readability of rectangle  64  is improved because rectangle  64  is practically a solid black mass that contains no white areas or voids. The enhanced coverage printed area has been homogenized (resulting in a more uniform optical density within the area) by adding the facilitator. 
     The present invention recognizes that parameters may be set to define the number of pixels to trim (possibly different values in different axes or different values for the lead and trailing sides of print areas) from the outer perimeter of a rectangle to ensure that the facilitator induced enhanced coverage of individual pixels  66  does not cause unintended bleed beyond the boundaries of printed rectangles  64 .  FIG. 7  illustrates a print rectangle  70  from which two pixel columns ( 75 ) have been stripped from the right and left side (as well as pixel rows from the top and bottom) to define the reduced print area rectangle  71 . 
     A further embodiment of this invention recognizes that when large solid rectangles ( 70 ) are printed on paper, there may be a central area (rectangle  72 ) in which ink tends to pool because the paper fibers are saturated with ink. Therefore, a second parameter may be defined which further limits the maximum solid rectangular area ( 71 ) over which facilitator will be applied. In  FIG. 7 , while facilitator will be applied to the rectangular area  71 , it will be applied in reduced volume (e.g. 50%) in the inner rectangular reduced print area ( 72 ). Considering a cross section of this printed area therefore, we observe that the entire rectangle ( 70 ) has been printed with black ink. The facilitator raster print area has been defined as the original print area ( 70 ) less a two pixel boundary ( 75 ) on the right, left, top, and bottom resulting in a facilitator print area of rectangle  71 . We have further defined an inner rectangular reduced print area ( 72 ) in which the facilitator application will be at a reduced rate of 50%. This rectangle could be computed as the facilitator print area less a defined number of border pixels ( 76 ) resulting in 4 pixels ( 77 ) trimmed from the original rectangle height (and 4 from the width) to which the reduced facilitator volume is applied to prevent ink pooling. 
       FIG. 8  shows the result of this process in which region  79  provides enhanced coverage of the print area with homogenized optical density within the bounds of the rectangle  70 . 
       FIG. 9  is a process flow diagram of the printing of rectangle  64  of  FIG. 6 . The process begins in step  100  to activate in situ image enhancement. Then in step  101  the image is rasterized for the printing of rectangle  64  with black ink. The process of image rasterization for printing is well known in the industry. Rasterization means that the original two dimensional image is converted into a series of strips (rows) by the computer. For each potential print pixel a determination is made as to whether it should be printed in black or left unprinted (white). This raster data is then used to drive print commands or signals to the print head as it scans across the corresponding points on the unprinted paper. Now in step  102  the present invention takes the existing rasterized image and trims one (or more as desired) pixel from all contiguous solid print areas to generate the corresponding enhanced print area  68  facilitator print raster data. Pixels are not trimmed from rectangles  64  which are completely surrounded (within the contiguous print area) by other printed rectangles  64 . In step  103  the media is passed through the printer. As it passes through, in step  104  the first (facilitator) print head prints (overlays) facilitator on all subset areas  68  within rectangles  64 . Then in step  105  the second (ink) print head of the printer prints pixels  66  in all rectangles  64  as directed by the black ink raster data. Now in step  106  the facilitator and ink produce an enhanced coverage solid black area  69  that contains virtually no white areas or voids within the boundaries of rectangles  64 . 
       FIG. 10  is a drawing of the apparatus of this invention showing two print heads (ink  201  and facilitator  202 ) that print the enhanced barcode  60 . Print head controller  200  is coupled to print head  201  that ejects a black ink and controller  200  is coupled to print head  202  that ejects the facilitator for the aforementioned black ink. Controller  200  causes ink drops from print head  201  and facilitator from ink jet  202  to fall on paper  204  that moves in direction A. Ink jets  201  and  202  move in direction B. Controller  200  will cause print heads  201  and  202  to print bar code  60 . 
     It would be obvious to one skilled in the art that controller  200  may be used to control various print heads that eject colored inks so that bar code  60  may be a bar code that has multiple colors. Bidirectional print heads may utilize dual facilitator heads (either side) or ink which remain unfixed long enough for the facilitator to be effective when deposited after the ink is printed. 
       FIG. 11  illustrates the black and facilitator print heads ( 201 ,  202 ) as they progress across the paper ( 204 ) in direction B printing a strip of the rasterized barcode ( 60 ). Printed material is visible to the left of the print heads while the paper remains white in advance of the print operation to the right. When the print strip is complete, the paper will advance the height of a print strip, the print head will reset to the left position, and the print operation can repeat. The present invention recognizes that columns of pixels are printed simultaneously across the face of the print head as it advances across the paper but that pixels in subsequent strips will be printed with a significant latency. For this reason, under circumstances of fast drying and rapidly setting inks, it may be desirable to operate the pixel stripping algorithms only within the confines of each printing swatch rather than across the entire rasterized image. In this manner the facilitator may enhance coverage of the inks before they set. 
     The extraordinary diversity of ink vendors, ink formulations, printers, and paper types make it impractical to define specific ink formulations for use in the present invention. It is, however, possible to provide specific guidelines for their determination. First, each ink has a material, solvent, or fluid (“facilitator”) which facilitates the enhanced coverage of ink into nearby areas. If this facilitator is applied when the ink is printed as described in this application then the ink will be better able to spread into the unwanted voids  67  and enhance coverage. 
     The application describes the concept of taking the area to be printed and pixel trimming the dimensions of that area for application of the facilitator to prevent unintended bleed of the ink. A straightforward calibration process may be utilized to determine the desired facilitator load and pixel trimming of the print area for facilitator application. A monochrome black dot pattern, as presented in the application figures, may be printed and the unintended voids between pixels observed as well as the quality of test barcodes. Test patterns (A-Z) allow for a progressive series of dot or barcode tests in which the quantity of facilitator and number of pixels trimmed is varied: 
     
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Matrix Describing Print Quality Test Barcodes 
               
             
          
           
               
                 Pixels 
                   
                 % 
                 Maximum 
                 Facilitator 
                   
               
               
                 Trimmed 
                 0% 
                 25% 
                 50% 
                 75% 
                 100% 
               
               
                   
               
             
          
           
               
                 0 
                 A 
                 B 
                 C 
                 D 
                 E 
               
               
                 1 
                 F 
                 G 
                 H 
                 I 
                 J 
               
               
                 2 
                 K 
                 L 
                 M 
                 N 
                 O 
               
               
                 5 
                 P 
                 Q 
                 S 
                 T 
                 U 
               
               
                 10 
                 V 
                 W 
                 X 
                 Y 
                 Z 
               
               
                   
               
             
          
         
       
     
     The control test cases “A, F, K, P, and V” correspond to the instances in which no facilitator is applied (and therefore the trimming of the pixels is moot). At the opposite extreme, test cases in the final column represent instances in which the maximum facilitator is applied. Comparison of case “E” (no pixels trimmed) to cases with progressively greater numbers of pixels trimmed (“J, O, U, Z”) will reveal the point at which the enhanced coverage extends beyond the boundaries is the intended pattern and therefore is causing unwanted image distortion. This test pattern would easily fit on a single sheet of paper and therefore the test print is accomplished quickly. Selection of the “best” pattern in which black and white pixels are of equal size could be done by visual inspection (as alignment patterns are done on many printers today) or through automation. Test cases may also be included to identify the effects of paper grain and allow setting of different pixel trimming parameters in the horizontal and vertical axes. An automated solution would be to utilize a barcode reader/verifier to read each of the printed barcodes and identify the point at which the read rates and quality are highest. 
     Since print media differ considerably in porosity (capacity for unintended ink bleed), different settings would be expected to be required for blotting paper and plastic transparency film. Vendors might choose to pretest and calibrate their inks (they know what inks they sell with particular printer models) and incorporate the settings into the control systems or printer drivers for their printers. Printers that sense the paper media could then utilize the media types with the corresponding facilitator strength and pixel trimming parameters. Since paper grain is typically aligned with the long axis of the paper, printers could adapt pixel trimming algorithms accordingly based upon the landscape (horizontal) or portrait (vertical) orientation of the paper. 
     Some print heads may have the ability to delivery varying quantities of ink (underdrive or overdrive) resulting in reduced or enlarged pixels as described in other applications by Check and Sansone in U.S. Pat. No. 4,386,272 assigned to Pitney Bowes Inc. In such instances, the quantities of black ink delivered within regions  68  or  71  may be deliberately increased to produce enlarged pixels and the volumes of ink delivered to pixels within regions  72  may be reduced to produce reduced pixels. Dithering of pixels (deliberate omissions of pixels within a large region to reduce the overall intensity of the print while maintaining image integrity) may also be used to reduce unwanted pooling of ink due to saturation in large print areas  71 . 
     The above specification describes a new and improved method for improving the readability of printed matter. It has been described with reference to black ink on white paper. It is realized that the above description may indicate to those skilled in the art additional ways in which the principles of this invention may be used without departing from the spirit including the use of any ink colors with the corresponding facilitators to allow them to enhance coverage and provide a better quality of print and the use of bidirectional printers. It is, therefore, intended that this invention be limited only by the scope of the appended claims.