Patent Grant
6923521
1. Field of the Invention
The present invention relates to an ink jet printer, and, more particularly, to a method of printing with high resolution using an ink jet printer.
2. Description of the Related Art
An ink jet printhead includes a plurality of nozzles arranged vertically, i.e., in the paper feed direction, with respect to a printed page. The nozzles have a fixed vertical spacing between them, such as 1/600 inch for a 600 dots per inch (dpi) printhead. Additionally, the array of nozzles travels horizontally repeatedly across the page, with some amount of advance of the paper in the vertical direction between such scans, dropping dots at a fixed horizontal distance, which can also be 1/600 inch. The term “horizontal”, as used herein, indicates the direction of printhead scan, perpendicular to the vertical, paper feed direction. According to the present example, the vertical pitch of the nozzles, in combination with the horizontal distance between dots as they are placed on the page, define a printing grid, or matrix, of a given vertical and horizontal resolution.
Typically, the combined behavior of the horizontal scanning of the nozzle array and the amount of vertical paper feed between consecutive scans allows exactly one drop of ink to be placed at every pixel position of the printing grid. In this condition, the grid is said to be “perfectly covered.” Each pixel position has one opportunity to be printed on exactly one scan of the printhead and by exactly one nozzle of the printhead.
The well known technique of “shingling” employs a method whereby the printing grid is “super covered”, meaning that the horizontal scanning behavior and the vertical paper feed allow that each pixel position has multiple opportunities in which a drop of ink can be placed at that position. Typically, these multiple opportunities are available in different scans of the head, which implies that the multiple opportunities are realized by different nozzles of the printhead.
A problem is that multiple passes of the printhead over the same raster line decreases the print speed of the printer. Another problem is that the amount of information that can be transferred to the print medium is limited by the fact that only one size of ink drop can be deposited on the print medium. Thus, only through the selection of locations at which the single-sized ink drops are deposited can the information be conveyed to the print medium.
What is needed in the art is a method of transferring more information to the print medium without requiring more passes of the printhead.
The present invention provides a method of printing at a higher resolution with fewer passes of a multiple-sized-nozzle printhead.
The invention, in one form thereof, relates to a method of printing with an ink jet printer. A printhead having a plurality of first nozzles with a first size and a plurality of second nozzles with a second size larger than the first size is provided. The first nozzles and the second nozzles are alternatingly disposed in a vertical direction. Print data corresponding to first columns of pixel locations is provided. The print data includes for each pixel location in the first columns both a respective large dot print datum and a respective small dot print datum. One of the respective large dot print datum and the respective small dot print datum is printed at a first pixel location of the corresponding pixel locations in the first columns. Second columns of pixel locations interleaved with the first columns of pixel locations are provided. The other of the respective large dot print datum and the respective small dot print datum not printed in the first pixel location of the first columns is printed at a first pixel location of the second columns of pixel locations.
In another form thereof, the method includes the steps of providing a printhead having a plurality of first nozzles with a first size and a plurality of second nozzles with a second size larger than the first size; providing print data corresponding to first columns of pixel locations, the print data including both a respective large dot print datum and a respective small dot print datum corresponding to each pixel location in the first columns of pixel locations; printing one of the respective large dot print datum and the respective small dot print datum onto the each pixel location in the first columns; providing second columns of pixel locations interleaved with the first columns of pixel locations, each pixel location in the second columns corresponding to a respective pixel location in the first columns; and printing an other of the respective large dot print datum and the respective small dot print datum not printed in the first columns onto each the corresponding pixel locations in the second columns.
The invention, in another form thereof, relates to a method of printing with an ink jet printer. A printhead has a plurality of first nozzles with a first size and a plurality of second nozzles with a second size larger than the first size. The first nozzles and the second nozzles are alternatingly disposed in a vertical direction. A first set of pixel locations is defined that receives ink only from the first nozzles. A second set of pixel locations is defined that receives ink only from the second nozzles. The pixel locations from the first set and the pixel locations from the second set are alternatingly disposed in a horizontal direction. The first nozzles jet ink onto the first set of pixel locations. The second nozzles jet ink onto the second set of pixel locations.
The invention, in yet another form thereof, relates to a method of printing with an ink jet printer. A printhead has a plurality of first nozzles with a first size and a plurality of second nozzles with a second size larger than the first size. The first nozzles and the second nozzles are alternatingly disposed in a vertical direction. Each first nozzle is separated from an adjacent second nozzle by a first distance. A matrix of pixel locations is defined that includes a plurality of first pixel locations and a plurality of second pixel locations. The first pixel locations receive ink only from the first nozzles. The second pixel locations receiving ink only from the second nozzles. The matrix includes adjacent rows separated from each other by a second distance equal to one-half of the first distance. Pairs of the first pixel locations and pairs of the second pixel locations are alternatingly aligned in each vertical column of the matrix. The printhead jets ink onto the matrix of pixel locations.
The invention, in a further form thereof, relates to a method of printing with an ink jet printer. A printhead has a plurality of first nozzles with a first size and a plurality of second nozzles with a second size larger than the first size. The first nozzles and the second nozzles are alternatingly disposed in a vertical direction. Each first nozzle is separated from an adjacent second nozzle by a first distance in the vertical direction. A matrix of pixel locations is defined that includes a plurality of first pixel locations, a plurality of second pixel locations, and a plurality of third pixel locations. The first pixel locations receiving ink only from the first nozzles. The second pixel locations receiving ink only from the second nozzles. The third pixel locations receive ink from the first nozzles and the second nozzles. The matrix includes adjacent rows separated from each other by a second distance equal to one-half of the first distance. Each first pixel location is separated from at least one second pixel location by the first distance in the vertical direction. Each second pixel location is separated from at least one first pixel location by the first distance in the vertical direction. Each third pixel location is separated from at least one other third pixel location by the first distance in the vertical direction. The printhead jets ink onto the matrix of pixel locations.
An advantage of the present invention is that the large nozzles can fill in dark colors with fewer passes of the printhead, and the small nozzles can be used where less grain is needed.
Another advantage of the present invention is that more information is transferred to the print medium without requiring additional passes of the printhead.
The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate preferred embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.
Referring now to the drawings and particularly to
As shown schematically in
Referring to
Printhead carrier 24 is guided by a pair of guide rods 34. The axes 34a of guide rods 34 define a bi-directional scanning path for printhead carrier 24, and thus, for convenience the bi-directional scanning path will be referred to as bi-directional scanning path 34a. Printhead carrier 24 is connected to a carrier transport belt 36 that is driven by a carrier motor (not shown) to transport printhead carrier 24 in a reciprocating manner along guide rods 34. Thus, the reciprocation of printhead carrier 24 transports ink jet printheads 26, 28 across a print medium sheet 38, such as paper, along bi-directional scanning path 34a to define a print zone 40 of ink jet printer 14. This reciprocation occurs in a main scan direction 42 that is parallel with bi-directional scanning path 34a, and is also commonly referred to as the horizontal direction. During each scan of printhead carrier 24, print medium sheet 38 is held stationary by print media sheet feed unit 23. Print media sheet feed unit 23 includes an index roller 39 that incrementally advances the print medium sheet 38 in a sheet feed direction 44, also commonly referred to as a sub-scan direction or vertical direction, through print zone 40. As shown in
Depending upon the particular design of ink jet printer 14, color ink reservoir 30 may be fixedly attached to color printhead 26 so as to form a unitary color printhead cartridge. Alternatively, color ink reservoir 30 may be removably attached to color printhead 26 so as to permit the replacement of color ink reservoir 30 separate from the replacement of color printhead 26, and in this alternative color ink reservoir 30 is located on-carrier in close proximity to color printhead 26. In another alternative, color ink reservoir 30 may be located off-carrier at a location remote from color printhead 26.
Likewise, black ink reservoir 32 may be fixedly attached to black printhead 28 so as to form a unitary black printhead cartridge. Alternatively, black ink reservoir 32 may be removably attached to black printhead 28 so as to permit the replacement of black ink reservoir 32 separate from the replacement of black printhead 28, and in this alternative black ink reservoir 32 is located on-carrier in close proximity to black printhead 28. In another alternative, black ink reservoir 32 may be located off-carrier at a location remote from black printhead 28.
A method of the invention will be described with reference to
In order to define a “perfectly covered” print mode with a two-nozzle-size printing array, realizing that a perfectly covered mode requires that each pixel position has an opportunity to receive exactly one of each of both a big dot and a small dot, twice as many printing scans are required relative to a one-nozzle-size printing array. For example, on one scan of the printhead, due to the vertical nozzle spacing of the alternating large and small nozzles, the even rasters (rows of pixels) can receive only big dots, and the odd rasters can receive only small dots. A second scan must be made in which the even rasters receive small dots and the odd rasters receive big dots.
It has been found that in order to achieve acceptable print quality, “perfectly covered” or “super covered” print modes are not required. Instead, a “sub covered” print mode, in which some pixel positions receive only big dots and some positions receive only small dots, is acceptable. Halftoning algorithms, such as error diffusion, operate on every pixel position of a printing grid to determine whether or not a dot of a given size should be printed, and generally are designed to expect at least a “fully covered” printing capability to faithfully carry out the request of the halftone algorithm's choice. A “sub covered” print mode could simply eliminate or ignore the halftone algorithm's decision to print a dot of a given size at a given pixel position if that pixel position has been chosen to not be covered on any printing scan by any nozzle corresponding to the dot size. However, this would result in an objectionable print quality degradation in the form of additional grain.
An attempt could be made to solve the aforementioned problem by embedding knowledge in the halftone algorithm as to whether the printhead is operated in a fully covered print mode or a sub covered print mode. In the event that the image will be rendered with a sub covered print mode that allows each pixel position to receive one of a large drop or a small drop, but not both, the halftone algorithm could be made to realize which of only a big dot or a small dot a given pixel can possibly receive. Then, the halftone algorithm can be constructed so as to “know better” than to request at a given location the printing of a drop that cannot actually be printed at that location. However, halftone algorithms with such “intelligence” are not widely available. The present invention provides a printing method using a conventional halftoning algorithm in conjunction with a sub covered print mode. Grain is prevented since the sub covered print mode does not simply drop out dots that the halftone algorithm requests at positions at which such drops are not allowed.
The present invention provides a method of printing with a two-nozzle-size printhead in a “sub covered” print mode. A halftone algorithm generates a pattern at half of a desired final resolution, and another hardware or software functional block takes the results from the halftone algorithm and shifts dots to produce the desired final resolution.
As used herein, the term “printing” data includes deciding whether to jet ink from nozzles onto pixel locations depending upon values of each respective print datum, the values each being, e.g., 0 or 1. Thus, ink is jetted onto selected ones of the pixel locations.
A single pass of printhead 26 prints on a 600×600 dpi grid, or matrix, (FIG. 5), so that drops of ink are spaced apart by a horizontal distance of 1/600 inch. The first half of the horizontal rasters, spaced 1/300 inch apart vertically, can receive only large drops. The other, second half of the horizontal rasters, also spaced 1/300 inch apart vertically and interleaved between the first half of rasters, can receive only small drops. By assumption, the first half of rasters (large drops) correspond to even rasters on the 600×600 dpi grid, and the second half of rasters (small drops) correspond to odd rasters on the 600×600 dpi grid.
A print mode that has “perfect coverage” requires two passes for every 600×600 dpi grid multiplied by the number of passes required to get any higher resolution. For example, a 4800×1200 dpi “perfectly covered” print mode requires 32 passes: 8 passes to get 4800 dpi horizontal resolution, times 2 passes to get 1200 dpi vertical resolution, times 2 passes for “perfect coverage”. The 4800×1200 dpi print mode, if implemented in such a way as to accomplish “perfect coverage”, has slow performance for two reasons. First, a halftone generating 4800×1200 dpi rasters is computationally expensive. Second, printing in 32 passes is also very slow. The present invention addresses both speed issues.
Consider a 4800×1200 dpi print mode. The halftone algorithm generates 2400×1200 dpi binary raster data by methods known to those skilled in the art. The halftone algorithm has no prior knowledge of where large and small drops can be placed. The halftone algorithm chooses no drops, a single small drop, a single large drop, or both a large and a small drop at each 2400×1200 dpi location. These data are then “separated” to make 4800×1200 dpi binary raster data. This is done by expanding each 2400 dpi horizontal raster into a 4800 dpi horizontal raster with alternating exclusively large and small drop locations.
A sample of pixel locations corresponding to the 2400×1200 binary raster data generated by the halftone algorithm is shown in FIG. 6. The print data corresponds to the pixel locations of FIG. 6. The small circles represent potential locations for small ink drops and the large circles represent potential locations for large ink drops. The halftone data are “separated” to make 4800×1200 dpi data corresponding to the matrix of pixel locations shown in FIG. 7. The numbers within the pixel locations illustrate the correspondence between adjacent pixel locations.
The halftone data includes a plurality of binary bits, with each bit or “datum” indicating whether a dot should be placed at a respective pixel location. Both a respective large dot print datum and a respective small dot print datum correspond to each pixel location of the first columns C1a, C2a, etc., shown in
The small dot pixel locations of
Each pixel location in the second set corresponds to a pixel location in the first set. As is evident from
The pattern of
For each pixel location in the first columns C1a, C2a, etc. of pixel locations, it is defined whether a small dot or a large dot is to be printed (Step S206). For example, a respective large dot print datum may be printed at a first corresponding pixel location of the first columns C1a, C2a, etc. of pixel locations, i.e., at pixel location 128 in column C1a. Respective small dot print data and large dot print data are printed in first columns C1a, C2a, etc. (Step S208). For this example, it is assumed that the print data will form an ink dot at each pixel location in the first columns.
The second columns of pixel locations, such as C1b, C2b, etc., are interleaved with the first columns of pixel locations, such as C1a, C2a, etc. For example, the separated respective small dot print datum is printed at a first corresponding pixel location of the second columns of pixel locations, i.e., at pixel location 130. In other words, respective separated data not printed in first columns C1a, C1b, etc., which may also be small dot print data and large dot print data, are printed in second columns C1b, C2b, etc. (Step S210).
As shown in
In another embodiment, non-integer multiples of resolution are achieved. By this it is meant, for example, that the driver reports a certain resolution to the application, say 1200 dpi, and desires to generate data at a resolution of 1800 dpi. Generating data at such a non-integer multiple of the original resolution of 1200 dpi falls beyond the scope of typical halftoning algorithms.
Because the spacing of the nozzles in the vertical paper feed direction is 600 dpi, and assuming paper feeds have been geared to provide 600 or 1200 dpi, a resolution of 600 or 1200 dpi, in both the horizontal and vertical directions, is reported to an application, such as a word processing program. When it is desired to achieve some horizontal resolution that is an odd multiple of the reported resolution, such as 1800 dpi, a different technique is needed. Among horizontal resolutions higher than that reported to the application, the easiest ones to achieve are those that are larger than the resolution reported to the application by multiples of two, since there are two sizes of nozzles. A resolution of 1800 dpi is either 3 or 1.5 times larger than the resolution reported to the application.
The first embodiment described above provides a method for processing 2400×1200 dpi data, assuming a “perfectly covered” print mode for a two nozzle size printhead (i.e., each location can receive one of each size drop), using traditional halftoning algorithms or techniques, yet yielding a 4800×1200 dpi printed output that is “sub-covered” (i.e., each location can receive either one or the other size drop). In this first embodiment, the driver can report a resolution of 1200 dpi to the application.
It may also be desirable to achieve an odd multiple of the reported resolution of 1200 dpi, such as 3600×1200 dpi printed output. According to the first embodiment described above, this would imply processing the data as a “perfectly covered” 1800×1200 dpi print mode, then expanding as described to obtain the 3600×1200 dpi printed output. However, traditional halftoning algorithms are not designed to process the data as 1800×1200 dpi, when reporting 1200 dpi to the application, as effectively and as efficiently as an integer or a power-of-two multiple.
The second embodiment described below not only provides a printing method (see
The same printhead 26 shown in
The numbers inside the circles in
The particular arrangement of pixel locations shown in
A third embodiment of the present invention is shown in FIG. 12. The discussion above with regard to
Compared to the 4800 dpi case described in the first embodiment, the second and third embodiments provide for a 3600 dpi print mode that utilizes the same data from the halftoning algorithm as the 4800 dpi case. This is accomplished by combining portions of each of the eight columns of
Another advantage of the present invention is that it can be easily extended to different printers to provide them with varying print resolutions. For instance the present invention is easily extended to 3000 or 4200 dpi resolution.
The present invention has been described as being implemented using color printhead 26. However, the present invention can also be implemented using black printhead 28.
While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.
This a Divisional of application Ser. No. 10/074,923, filed Feb. 11, 2002, now U.S. Pat. No. 6,592,203.
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| Number | Date | Country | |
|---|---|---|---|
| 20030197757 A1 | Oct 2003 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10074923 | Feb 2002 | US |
| Child | 10430634 | US |
