Abstract:
A sequence of steps for storing an image at a higher resolution in a rendering stage, and making a conversion of the image to a different asymmetrical print resolution. During the conversion corrections are made to avoid losing “on” pixels located on an eliminated row. In some embodiments, an initial narrowing step may occur along the axis of higher resolution and a final horizontal depletion may occur along a carriage scan axis.

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part of the commonly owned previously copending Alfaro U.S. Pat. No. 6,296,343 filed 21 Oct. 1996 entitled EDGE ENHANCEMENT DEPLETION TECHNIQUE FOR OVER-SIZED INK DROPS TO ACHIEVE HIGH RESOLUTION X/Y AXES ADDRESSABILITY IN INKJET PRINTING. 
     BACKGROUND OF THE INVENTION 
     This invention relates to techniques for converting stored images of a first resolution into a printed image of a second different resolution. 
     BRIEF SUMMARY OF THE INVENTION 
     A technique provides a sequence of steps for storing an image at a higher resolution such as 1200×1200 dpi in a rendering stage, and making a conversion of the image to a different asymmetrical print resolution such as 1200×600 dpi. 
     An exemplary embodiment of the invention eliminates alternate rows from the higher resolution image, with corrections made for certain “on” pixels in the eliminated rows. A final step may provide for horizontal depletion of the printed image which preserves left and right edge pixels, while an initial step may provide a narrowing of the printed image along the axis of higher resolution. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  show a printer for implementing the invention. 
         FIG. 2  shows a carriage for the printer of  FIGS. 1A–1B . 
         FIG. 3  shows a preferred print cartridge for the carriage of  FIG. 2 . 
         FIGS. 4A ,  4 B and  4 C show a flow chart of a preferred embodiment of the invention. 
         FIG. 5  is a block diagram corresponding to the flow chart of  FIGS. 4A–4C . 
         FIGS. 6–9  show examples of how the flow chart steps operate on vertical columns and horizontal rows of a stored image. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A typical embodiment of the invention is exemplified in a large format color inkjet printer/plotter as shown in  FIGS. 1A–1B . More specifically,  FIG. 1A  is a perspective view of an inkjet printer/plotter  210  having a housing  212  mounted on a stand  214 . The housing has left and right drive mechanism enclosures  216 ,  218 . A control panel  220  is mounted on the right enclosure  218 . A carriage assembly  300 , illustrated in phantom under a cover  222 , is adapted for reciprocal motion along a carriage bar  224 , also shown in phantom. The position of the carriage assembly  300  in a horizontal or carriage scan axis is determined by a carriage positioning mechanism  310  with respect to an encoder strip  320  (see  FIG. 1B ). A print medium  230  such as paper is positioned along a vertical or media axis by a media axis drive mechanism (not shown). As used herein the media axis is called the X axis denoted as  201 , and the carriage scan axis is called the Y axis denoted as  301 .  FIG. 1A   
       FIG. 1B  is a perspective view of the carriage assembly  300 , the carriage positioning mechanism  310  and the encoder strip  320 . The carriage positioning mechanism  310  includes a carriage position motor  312  which has a shaft  314  which drives a belt  324  which is secured by idler  326  and which is attached to the carriage  300 . 
     The position of the carriage assembly in the scan axis is determined precisely by the encoder strip  320 . The encoder strip  320  is secured by a first stanchion  328  on one end and a second stanchion  329  on the other end. An optical reader  366  is disposed on the carriage assembly and provides carriage position signals which are utilized by the invention to achieve optimal registration of images  240  in the manner described below. 
     Referring to  FIG. 2 , a carriage  102  is slidably mounted on support bar  172  through a bearing sleeve  171 , and includes four slots  121 ,  123 ,  125 ,  127  for removably receiving four inkjet print cartridges. From right to left in the carriage slots are respectively mounted a black ink print cartridge  120 , a magenta ink print cartridge  122 , a cyan ink print cartridge  124  and a yellow ink print cartridge  126 . 
     The enlarged perspective view of  FIG. 3  shows an exemplary refillable print cartridge  140  with two columns of nozzles  142 , a handle  144 , and an ink inlet housing  146  having a receptacle  148  for receiving an ink supply coupler (not shown). 
     The invention has been successfully demonstrated with four 600 dpi print cartridges of the type shown in  FIGS. 2 and 3 . In a currently preferred embodiment the black ink cartridge has a 600 dpi nozzle pitch resolution and a printer incorporates the invention to print monochrome images with 600 dpi sized drops on an asymmetrical 1200×600 pixel grid. 
     A modified carriage (not shown) may carry a removably mounted black ink cartridge similar to  120 , and a tri-compartment ink cartridge (not shown) which has separate ink reservoirs for cyan, magenta and yellow ink, respectively. 
     The embodiments described herein employ a new technique which allows an inkjet printer system to print A×B resolution monochrome bitmaps which A=B in a system where A dpi is addressable in the carriage scan axis and B/2 dpi is addressable in the media advance axis. Thus, the present system and methods may be used with asymmetrical sub-pixels that are only half as wide in the carriage scan direction as they are in the media advance direction. 
     The embodiments herein enable an inkjet printer system to utilize only the even width lines while preserving both edges without losing its ability to render one-pixel width lines. This enables it to keep the smallest detail in a bitmap image. 
     The present systems and methods may be accomplished in the steps illustrated in  FIGS. 4 and 5 . As shown in  FIG. 5 , the present systems and methods may be accomplished in three sequential steps  200 ,  202 ,  204 . First, as shown in  FIG. 4A  the A×B bitmap is processed by a narrowing process step  200  which in the exemplary embodiment comprises detecting the vertical edges ( 50 ), and then shifting one pixel distance to the left each right edge pixel which is not also a left edge pixel ( 52 ). 
     Referring again to  FIG. 5 , the next step is a logical combining  202  of rows of the pixel grid. In taking A to a A×A/2 bitmap for printing, a problem faced was that for certain images some horizontal rows would be lost and not shown on the final A×A/2 image. To solve this problem, several rows of data were taken together and a logical operation was performed on the rows such that no horizontal row would be removed while following through the process as shown and described in relation to  FIGS. 4B ,  6  and  7 . The logical combination of rows  202  ensures that the resulting row from the operation will have information from at least one of the rows involved in the operation and that no information will be lost. The actual dot location is in the middle between nonpreserved and preserved rows (see  FIG. 7 ). 
     The object of the logical combination step  202  is to downscale the raster (step  54 ) of the image (not reduce the ink) in the vertical axis without losing information. It is necessary with the present systems and methods to downscale in order to be able to work in an asymmetric writing system (where A/=B). Accordingly, the goals of this stage are different than other systems because the present embodiments are preparing a raster to be printed on an asymmetric system. Because the goals are different, the procedure also, as expected, will also be different. 
     In other systems two rows were worked with and processed at the same time. 
     In the present embodiments, there is no need to deplete in the vertical axis, because the system is only B=A/2 addressable. Accordingly, it is not possible to put double ink drops on the same pixel. With the present systems the goal for the vertical axis is then opposite of the other systems because with the present system, the logical combination step  202  serves to add pixels instead of deplete pixels. The logic combination step  202 , in current design shown in detail in  FIG. 4B  works with three rows at the same time of a 1200×1200 bitmap image (see step  62 ) instead of two rows like some other systems have and currently do. 
     Referring to  FIG. 6 , a pixel in a non-preserved row  80  is ignored (step  61 ) when at least one vertical adjacent pixel is “on” (see comparison tables  82 ). Alternatively a pixel in a non-preserved row  80  is “preserved” (see step  62 ) when no vertical adjacent pixel is “on” (see comparison tables  86 ). 
     The present system identifies isolated objects which would be lost in a media advance axis direction, directly a result of having a lower media advance axis resolution which eliminates odd numbered pixel rows in the 1220×1200 bit map (see  FIG. 7 ). Then the present system acts to save the image and moves these isolated objects one row upward such that the isolated object will not be lost. 
     The final step as shown in  FIG. 4C  is a horizontal depletion step  204 . This horizontal depletion step  204  is the same as some horizontal depletion methods described earlier except that the depletion is applied as a final step after the three row&#39;s logical operation step  202 , and only in the horizontal direction, that is, only in the carriage scan axis and not in the media advance axis. The horizontal depletion  204  saves each vertical left edge pixel (step  70 ), depletes alternate interior pixels (step  72 ) and thus preserved both the right and left vertical edges  74 ,  76  and the horizontal edges (see  FIG. 8 ). 
     By using this method and steps as described, the present embodiments are able to assume and store a 1200×1200 image in the rendering stage and produced a 1200×600 dpi image for the writing stage without losing any resolution for one-pixel width lines. Of course, the 1200 dpi is in the scan axis and the 600 dpi is in the paper axis. 
     The operation of the horizontal depletion technique is shown in  FIGS. 8 and 9 .