WO1996023662A1 - Non-linear edge stitching apparatus and method - Google Patents

Non-linear edge stitching apparatus and method Download PDF

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Publication number
WO1996023662A1
WO1996023662A1 PCT/US1996/001050 US9601050W WO9623662A1 WO 1996023662 A1 WO1996023662 A1 WO 1996023662A1 US 9601050 W US9601050 W US 9601050W WO 9623662 A1 WO9623662 A1 WO 9623662A1
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WO
WIPO (PCT)
Prior art keywords
adjacent strips
printed
data
portions
image
Prior art date
Application number
PCT/US1996/001050
Other languages
French (fr)
Inventor
Carey W. Kriger
Marvin L. Freeman
Patrick T. Gilmore
Original Assignee
Summagraphics Corporation
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Publication date
Application filed by Summagraphics Corporation filed Critical Summagraphics Corporation
Publication of WO1996023662A1 publication Critical patent/WO1996023662A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/485—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by the process of building-up characters or image elements applicable to two or more kinds of printing or marking processes
    • B41J2/505—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by the process of building-up characters or image elements applicable to two or more kinds of printing or marking processes from an assembly of identical printing elements
    • B41J2/5056—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by the process of building-up characters or image elements applicable to two or more kinds of printing or marking processes from an assembly of identical printing elements using dot arrays providing selective dot disposition modes, e.g. different dot densities for high speed and high-quality printing, array line selections for multi-pass printing, or dot shifts for character inclination
    • B41J2/5058—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by the process of building-up characters or image elements applicable to two or more kinds of printing or marking processes from an assembly of identical printing elements using dot arrays providing selective dot disposition modes, e.g. different dot densities for high speed and high-quality printing, array line selections for multi-pass printing, or dot shifts for character inclination locally, i.e. for single dots or for small areas of a character
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K15/00—Arrangements for producing a permanent visual presentation of the output data, e.g. computer output printers
    • G06K15/02—Arrangements for producing a permanent visual presentation of the output data, e.g. computer output printers using printers
    • G06K15/10—Arrangements for producing a permanent visual presentation of the output data, e.g. computer output printers using printers by matrix printers
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K15/00—Arrangements for producing a permanent visual presentation of the output data, e.g. computer output printers
    • G06K15/02—Arrangements for producing a permanent visual presentation of the output data, e.g. computer output printers using printers
    • G06K15/10—Arrangements for producing a permanent visual presentation of the output data, e.g. computer output printers using printers by matrix printers
    • G06K15/102—Arrangements for producing a permanent visual presentation of the output data, e.g. computer output printers using printers by matrix printers using ink jet print heads
    • G06K15/105—Multipass or interlaced printing
    • G06K15/107—Mask selection
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K2215/00—Arrangements for producing a permanent visual presentation of the output data
    • G06K2215/111—Arrangements for producing a permanent visual presentation of the output data with overlapping swaths

Abstract

A method and apparatus for stitching the edges of adjacent strips (12) or swaths printed by a strip or swath printer in a manner which reduces the effects of visual artifacts caused by a difference in print quality, density or shape between pixels at or near the edge of the adjacent strips and other pixels in the strips. Two adjacent strips, each having a number of lines, are printed such that a portion (16) of one or more lines in one of the strips (12a) overlaps a portion (16) of a corresponding number of lines in the other strip (12b), with the pixels in corresponding overlapping line portions being superposed. When the strips are printed, certain predetermined pixels in all or some of the line portions in each of the two strips (12a, 12b) which will overlap are not printed. The pixels not to be printed may be selected such that the border or boundary between the adjacent edges of the two overlapping strips forms a nonlinear, predetermined pattern, such as a regular, repeating pattern, e.g., triangular, or a random or pseudo-random pattern. As a result of this process, overlapping line portions contain a mixture of pixels of higher and lower density or quality, thus reducing the effects of the visual artifacts caused by the clear contrast between such higher and lower density pixels when strips are not overlapped.

Description

NON-LINEAR EDGE STITCHING APPARATUS AND METHOD
RFJ,ATEn APPLICATION
The nonlinear edge stitching method and apparatus disclosed herein employs or may employ some or all of the subject matter disclosed in commonly-owned U.S. patent application Serial No. 07/920,186, filed on July 24, 1992 titled "Strip Mode Printing and Plotting Apparatus and Method". A corresponding application (PCT/US93/02724) was filed under the PCT, and was published on February 3, 1994 under WO 94/02320. The disclosures of Serial No. 07/920,186, and WO 94/02320 are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The invention disclosed herein relates to methods and apparatus for improved printing of monochrome and color images and indicia (collectively referred to herein as "images"). More particularly, the invention disclosed herein relates to methods and apparatus for "stitching" the edges of adjacent "strips" (also called "swaths" or "segments") in which portions of an image are printed to reduce the visibility of visual artifacts that may occur at the edges of the strips.
Modern color and monochrome computer or digital printers are of the matrix type which print an overall image on a sheet medium (such as paper, plastic, mylar. etc.) in small dots or other small geometric configurations, each of which consists of one or more pixels. By convention, the width direction of the medium being printed is referred to as the Y-axis or Y-direction, and the direction orthogonal thereto, i.e.. the length or feed direction of the medium, is referred to as the X-axis or X-direction. Such printers may utilize a so-called full width print head having a width at least equal to the width of the medium on which the image is to be printed to print an entire line at a time in each relative position of the print head and the medium ("line printer"), or a so-called flying or scanning print head to print the pixels in desired locations serially along a line as the print head is moved or scanned parallel to the Y-axis to also print a full line per scan ("serial" or "raster scan printer"). After each line is printed in a line or serial printer, the sheet medium is moved relative to the print head in a direction parallel to the X-axis and another full line is printed.
Modern matrix printers may also print in strips or swaths ("strip" or "swath printer"), as disclosed for example in commonly assigned U.S. Patent Application Serial No. 07/920,186. In strip printing the image to be printed is separated into strips or swaths, each having a width substantially less than the width of the medium, and each strip is separated into lines, each line having a width of one or more pixels and a length up to the length of the strip. The image is usually printed strip-by-strip, i.e., all lines of a strip are printed, then the print head is positioned to print another strip. However, the strips may be printed in another sequence, such as one line at a time. Strip printers may have a print head as wide as a strip, and thus have some attributes of a line printer, or a serial print head that scans a line at a time within a strip.
A problem arises in thermal transfer strip printers when pixels in lines at or near the edge of a strip are not printed with the same quality or density as pixels in other lines in the strip. During thermal transfer printing, thermal elements in the print head contact a thermal transfer ribbon and press the ribbon against the sheet medium which is supported by a platen. By heat and some pressure the print head activates and transfers the ink carried by the ribbon onto the sheet medium. The ribbon and the sheet medium are maintained in contact and heat is applied by the print head for a predetermined minimum "dwell" time sufficient to effect transfer of ink to the receptor sheet medium. Typically, the thermal transfer ribbon becomes temporarily adhered to the receptor sheet medium during the dwell time as the ink layer is melted and the ink is transferred to the sheet medium so that movement of the sheet medium also initially moves with it the thermal transfer ribbon and then effects separation of the two. The problem arises in thermal transfer strip printing when pixels near the edge do not have the same tone or size as pixels in other parts of the strip, or their shapes are distorted. This problem may arise because thermal elements at or near the edge of the thermal print head do not receive as much thermal energy as the other thermal elements in the print head, or because the thermal elements in other parts of the print head are hotter as a result of being surrounded by other thermal elements whereas the thermal elements at or near the edges of the strip are cooler. This problem is not necessarily symmetrical around the thermal print head. For example, it is possible that pixels on the side of the strip closest to the previous strip printed could be printed with slightly greater density or quality than pixels on the opposite side of the strip because of retained heat from the previous pass of the print head.
As a result of this problem, a visually perceptible straight band of less dense or distorted pixels appears on the image at the border of two adjacent strips. This visible artifact is often noticeable to the naked eye and can thus reduce the quality of the printed image. This problem may arise in other types of strip printers as well. Other examples of strip printers utilizing different mechanisms and/or printing methods are disclosed in U.S. Pat. Nos. 5,278,578 (Baek et. al.); 5,329,297 (Sanger et. al.); 5,274,397 (Grover et. al.); and 5, 164,742 (Baek et. al.). In these other types of printers, this problem may arise for other reasons, such as because of a large angle between the print head and the lines near the edge of a strip which causes pixels printed in lines near the edge to become oval shaped (see, for example, the discussion of this problem in the '397 Grover patent).
There is a need for apparatus and methods for reducing the visibility of the visual artifact or band appearing on or near the border between two adjacent strips printed by a strip printer and thus creating a higher quality image. Preferably, this should be accomplished without losing or altering any of the data representing the image, without requiring any additional printer components, and without requiring the relative movement between the print head and the medium in any direction other than parallel to the X- and Y- axes.
SUMMARY OF THE INVENTION
It is an object of the present invention to reduce the effects of the visual artifact caused by differences in the printing of pixels by strip printers at or near the edges of strips. It is a further object of the present invention to improve the quality of images printed by strip printers without losing, repeating, or altering any of the data representing the image.
It is a further object of the present invention to improve the quality of images printed by strip printers without requiring any additional printer components, and without requiring relative movement of the print head and the print medium in any direction other than parallel to the X- and Y- axes.
The present invention provides a method and apparatus for stitching the edges of adjacent strips or swaths printed by a strip or swath printer in a manner which reduces the effects of me visual artifacts described above. According to the invention, two adjacent strips, each having a number of lines, are printed such that a portion of one or more lines in one of the strips overlaps a portion of a corresponding number of lines in the other strip. In other words, the edges of the strips are overlapped in one or more lines. In the preferred embodiment, the pixels in corresponding overlapping line portions are superposed. When the strips are printed, certain predetermined pixels in all or some of the line portions in each of the two strips which will overlap are not printed. Pixels which are not printed may be referred to herein as "masked", with the understanding that masking may be accomplished in any suitable manner. As a result of this process, overlapping line portions contain a mixture of pixels of higher and lower density or quality, thus reducing the effects of the visual artifacts caused by the clear contrast between such higher and lower density pixels when strips are not overlapped.
In practicing the present invention, the strips may be printed in any order, i.e., each strip may be printed in its entirety (except for the masked pixels in the strip) before the next strip is printed, or portions of the strips may be alternately printed. In the preferred embodiment of the invention, each strip is printed in its entirety (except for the masked pixels) before the next strip is printed.
In the preferred embodiments of the present invention, the pixels masked in a subsequent or second strip are in complementary locations to the pixels masked in a previous or first strip. That is, when the second strip is printed, pixels are printed in and only in the locations at which the pixels in the first strip were masked. Thus, when both strips have been printed, no pixels in any of the lines in the overlapped portion between two adjacent strips will have been skipped and no pixels will have been prmted more than once. As a result, if the data in corresponding overlapping line portions of the first and second strips is identical, it is possible to prevent any of the data from being altered or repeated.
In the preferred embodiments, the pixels are masked according to a predetermined pattern so that the resulting border or boundary between the adjacent edges of the two strips is nonlinear, i.e., is not a straight line for the entire border. As a result, the effects of the visual artifact at this boundary will be less visible.
When the image is a color image, the colors in the image may be printed according to well known techniques by separating the colors into a number of colors. According to the present invention, the boundary pattern for each separate color in the overlapping portion of two adjacent strips may be different. In the preferred embodiment, the boundary pattern for each color is the same, the boundary patterns for the colors are offset. This offsetting of separate colors produces a diffusive effect which further reduces the effects of the visual artifacts appearing in the image.
A method of printing an image on a medium according to the present invention comprises arranging the data representing the image to be printed in a plurality of strips each having a length parallel to a first axis of the medium, with portions of at least two adjacent strips overlapping each other, arranging data representing each strip in a plurality of lines each having a width parallel to a second axis of the medium, with portions of respective lines in the overlapping portions of the two adjacent strips overlapping each other, and arranging data representing each line in a plurality of pixels each representing a location on the respective line where data is to be printed, with pixels of overlapping portions of respective lines in the overlapping portions of the two adjacent strips being superposed. The image is then printed by printing the data representing portions of the image in at least one line in a first of the two adjacent strips except for preselected pixels in the portions of the at least one line in the overlapping portions of the two adjacent strips and printing the data representing portions of the image in at least one line in a second of the two adjacent strips which is adjacent the line in the first adjacent strip except for preselected pixels in the portions of the at least one line in the second strip in the overlapping portions of the two adjacent strips, such that visual artifacts caused by a difference in print quality between pixels in the overlapping portions of the two adjacent strips are reduced.
An apparatus according to the present invention comprises an imaging means such as a print head for printing data representing the image on the medium and means for arranging the data into strips, each having a length parallel to the first axis of the medium, with portions of at least two adjacent strips overlapping each other, for arranging the data representing each strip in lines each having a width parallel to the second axis of the medium, with portions of respective lines in the overlapping portions of the two adjacent strips overlapping each other, and for arranging the data representing each line in a plurality of pixels each representing a location on the respective line where data is to be printed, with pixels of overlapping portions of respective lines in the overlapping portions of the two adjacent strips being superposed. The means for arranging the data in this fashion comprises a processing unit and memory device, such as may be found in a general purpose computer, microcomputer, microcontroller, etc., well known in the art, or as may be incorporated into the printer containing the imaging means, controlled by a software program as may be derived from this disclosure by one skilled in the art.
The apparatus also comprises means for relatively moving the imaging means and the medium in directions parallel to the first and second axes such that the position of the imaging means when printing a first of the two adjacent strips overlaps in the direction of the second axis the position of the imaging means when printing a second of the two adjacent strips. The means for relatively moving the imaging means and the medium may comprise any conventional printer, including a Y-axis drive for moving the imaging means relative to the medium and an X-axis drive for moving the medium relative to the imaging means, and the preferred embodiment of such a printer is as disclosed in the above referenced commonly assigned patent application. In addition, the apparatus comprises means for causing the imaging means to print the data representing portions of the image in at least one line in the first of the two adjacent strips except for preselected pixels in the portions of die at least one line in the overlapping portions of the two adjacent strips; and means for causing the imaging means to print the data representing portions of the image in at least one line in the second of the two adjacent strips except for preselected pixels in the portions of the at least one line in the second strip in the overlapping portions of the two adjacent strips, such that visual artifacts caused by a difference in print quality between pixels in the overlapping portions of the two adjacent strips are reduced. This means may comprise conventional printer structures for controlling the operation of the printer, a preferred embodiment of which is disclosed in the above referenced commonly assigned patent application.
BRIEF DESCRIPTION OF THE DRAWINGS The invention is illustrated in the figures of the accompanying drawings which are meant to be exemplary and not limiting, in which like references refer to like or corresponding parts, and in which:
Fig. 1 is a schematic view of a medium on which an image is printed in strips according to a know strip printing technique; Fig. 2 is a schematic view of two adjacent strips printed according to the technique illustrated in Fig. 1 by two adjacent, non-overlapping positions of a print head;
Fig. 3 is a schematic view of two adjacent strips printed by two adjacent, overlapping positions of a print head in accordance with the present invention, wherein the boundary between the two strips is a rectangular pattern;
Fig. 4 is a schematic view of two overlapping positions of a print head with the print head elements aligned to superpose pixels;
Fig. 5 is schematic view of two overlapping portions of adjacent strips showing registration of corresponding overlapped lines; Fig. 6 is a schematic view of adjacent strips with a boundary of pseudo- randomly arranged straight and angled segments, wherein the boundaries between adjacent pairs of strips are the same;
Fig. 7 is a schematic view of adjacent strips with a boundary of randomly arranged straight and angled segments, wherein the boundaries between some adjacent pairs of strips are different;
Figs. 8-11 show boundary patterns of different types in accordance with the present invention;
Figs. 12-13 show the triangular boundary pattern substantially as shown in Fig. 9 with different frequency (Fig. 12) and amplitude (Fig. 13);
Fig. 14a shows the triangular boundary pattern substantially as shown in Fig. 13 with colors offset along the X-axis;
Fig. 14b shows the triangular pattern substantially as shown in Fig. 13 with colors offset along the Y-axis; Fig. 15 is a schematic view of two adjacent, overlapping positions of a print head, illustrating a boundary pattern formed by lines in only part of the overlapping portion; and
Figs. 16A -16B show a flow chart which illustrates the procedure for generating boundary patterns in accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The preferred embodiments of the present invention will be described herein with respect to thermal transfer strip printing as described in the above-referenced commonly assigned application. However, the invention is applicable to other printing technologies and other strip or swath printing techniques, as described, for example, in the patents referenced above.
In the strip printer described in the above referenced commonly assigned application, an image is printed onto a medium such as paper, mylar or plastic, in a series of strips 12. The strips may run in either direction, i.e., with lengths πinning parallel to the Y or X axis. In a preferred embodiment, the strips run lengthwise parallel to the X-axis. Each strip consists of a plurality of lines running lengthwise along the strip, each line having a width of one or more pixels. In a preferred embodiment, each line is one pixel wide.
In a thermal strip printer, the strips are printed by a thermal print head having an array of thermal elements having a width parallel to the Y-axis which in the thermal printer disclosed in the above referenced commonly assigned application is longer than its width. The width of the strips is usually substantially equal to the length of the thermal print head array.
The strips may be printed in any sequence. In a preferred embodiment, the strips are printed in succession, i.e., the first strip is printed by positioning the thermal print head at the top comer of the medium, printing the first pixels in each line of the strip, relatively moving the print head and medium along the X-axis and printing the remainder of the data in the strip until the strip is printed in its entirety, then the print head and medium are relatively moved to position the print head at the top of the next, adjacent strip to be printed, and so on. For ease of reference, the printing process will be described herein as starting at the left of the medium 10 and moving to the right, although the strips 12 may be printed in either order. If the width of the image to be printed is not an integer multitude of the width of the strips, the width of one of the strips (the one furthest to the right in Fig. 1) will be smaller man other strips. In prior art strip printing (Fig. 2), the data in a first of two adjacent strips 12a is printed by moving the print head 14 to a first Y-axis position represented in broken lines and printing the strip 12a, and the data 12b in a second of two adjacent strips is then printed by moving the print head 14 to a second Y-axis position represented in solid lines and printing the strip 12b. (It is understood that references herein to "moving" the print head refer to relative motion between the print head and the medium). The print head is positioned as precisely as possible to print the second strip 12b exactly adjacent to the first strip 12a. As a result, the boundary 16 between the two strips is a straight line. As explained above, the pixels at or near the edge of the strips 12a and 12b, i.e., the pixels closest to the boundary 16, may not be printed with the same quality or density as, or may be distorted in shape in comparison to, pixels closer to the center of the strips 12a and 12b. As a result, a visually perceptible band or artifact may be seen on or near the boundary 16. The present invention reduces the visibility of this visual artifact as follows. With reference to Fig. 3, the position (solid lines) of the print head 14 when printing the second 12b of two adjacent strips 12b overlaps the position (broken lines) of the print head 14 when printing the first 12a of two adjacent strips. The extent of the overlap may vary according to the specific requirements of the printer and image to be printed. In a preferred embodiment of the invention, with a mermal print head of approximately 48 mm in length (Y-axis direction), with each line in the strips being one pixel wide, and with 16 lines/mm, the area of overlap may vary between 1-3 mm, i.e., 16-48 lines. The corresponding lines in the overlapping positions are aligned (registered) as closely as possible, and the locations of the pixels in the corresponding lines are superposed. It is possible with present technology, as described for example in the above-referenced commonly assigned application, to align corresponding lines of adjacent overlapped strips and to superpose corresponding pixels in overlapped lines without a visually-detectable registration problem, i.e., pixels located in the overlapping portion of adjacent strips are precisely registered along both the X and Y-axes. Thus, referring to Fig.4, the positions of the thermal elements 18 in printhead 14 which print in the overlapping portion of strips 12a and 12b in successive positions of the print head 14 are precisely registered. With reference to Fig. 3, when the first strip 12a is printed by the print head 14 in the first Y-axis position (broken lines), certain pixels in the overlapping portion between the two successive print head positions are "masked", i.e., are not printed. When the strip 12b is printed by the print head in the second Y-axis position (solid lines), certain pixels in the overlapping portion are masked. As a result, the boundary 16 between pixels from the first strip 12a and the second strip 12b becomes nonlinear. The same process may be repeated at the boundaries between all the strips in the image, except that the process is usually not necessary and therefore not done for the outside edges of the image, i.e., the left side of the first strip and the right side of the last strip of the image.
According to the invention, there need not be a relationship between the locations of the pixels masked when printing the first strip 12a and the locations of the pixels masked when printing the second strip 12b, as long as pixels are printed in either strip in a sufficiently diffused pattern to reduce the visibility of the boundary 16 without creating any visually perceptible gaps which reduce the desired quality of the image. However, it is preferred to precisely register pixels in the overlapping portions of adjacent strips to avoid holes and higher density printing. To prevent the appearance ofholes where pixels are masked in both strips, locations of the pixels masked in the first strip 12a are stored in memory and retrieved when printing the second strip 12b, which prevents the masking of pixels in any locations where pixels were masked in the first strip. To prevent the appearance of pixels of extra density as a result of the double printing of pixels or parts of pixels in the same locations, the locations of the pixels not masked in the first strip 12a are stored and then retrieved when printing the second strip 12b and used to mask pixels in any locations where pixels were printed in the first strip 12a.
In the preferred embodiment, both of these advantages are obtained by masking pixels in the second strip 12b in complementary locations to the locations of the pixels masked in the first strip 12a. This may be accomplished by storing in memory the locations of the pixels masked in the first strip 12a and printing pixels in and only in those locations in the second strip 12b. To reduce the reliance on memory, this may be accomplished by calculating the locations of the pixels to be masked in the first strip according to predetermined parameters, and then calculating the complementary locations of the pixels to be masked in the second strip according to the same parameters. If the boundary between two adjacent strips has a well defined pattern, as described below, and the boundary patterns between all adjacent strips are identical, this may also be accomplished by calculating the locations of the pixels to be marked on the left side of each strip according to predetermined parameters, and men calculating the complementary locations of the pixels to be marked on the right side of each strip according to the same parameters. The preferred methods of detemώύng which pixels to mask will be described in greater detail below.
According to the invention, the boundary 16 (Fig. 3) may but need not have a well defined shape. For example, the boundary pattern may be regular and repeating, irregular and repeating or non-repeating (e.g., pseudo-random), or irregular and non-repeating (e.g. random). In the preferred embodiment, the boundary follows a predetermined, repeating pattern. For example, the boundary 16 between strips 12a and 12b in Fig. 3 is a series of alternating rectangular blocks. Examples of some preferred predetermined patterns are illustrated schematically in Fig. 6 (rectangular and trapezoidal portions which are exactly duplicated in the overlapping strip portions) Fig. 7 (rectangular and trapezoidal portions which may or may not be exactly duplicated in all overlapping strip portions), Fig. 8 (rectangular), Fig. 9 (triangular), Fig. 10, (alternating blocks with diffused edges), and Fig. 11 (random pattern of straight and angled line segments). Use of a random or pseudo¬ random pattern of straight and angled line segments as shown in Fig. 11 will usually result in a greater reduction of the effects of the visual artifacts than use of a regular repeating pattern such as shown in Figs. 8 or 9 because a random or pseudo-random pattern is less detectable. However, regular patterns may be preferable for their ease of computation and generation. In a preferred embodiment, a relatively short random pattern (several inches in length) is used which is then repeated for the length of the strip. The frequency and amplitude of the boundary patterns may also vary. For example, the triangular pattern show in Fig. 9 may have the reduced amplitude and frequency shown in Fig. 12 or the increased frequency and amplitude shown in Fig. 13. The maximum amplitude of the pattern may be the maximum overlap of the print head in adjacent positions (Figs. 6 and 7), or less than the maximum overlap of adjacent positions of the print head (Fig. 15). Also, the axis of the pattern may be located at the midpoint of the overlap (Figs. 6 and 7), or offset from the midpoint (Fig. 15). Where the pattern is less than the total overlap as in Fig. 15, the pattern may be produced by masking pixels in less than all the lines 20a and 20b in the overlapped portion of the adjacent strips.
According to the invention, the data representing the image printed in the lines in the overlapping portion between two adjacent strips need not be identical provided the image does not become distorted in an undesired way. That is, with reference to Fig. 3, the data in the overlapping portion between the adjacent strips 12a and 12b may be different. For example, the data in the lines in the overlapping portions 12a and 12b in Fig. 3 may the same as the data in the corresponding lines in the strips 12a and 12b in Fig. 2. As a result, some data in the overlapping portion may be lost, but the image will be printed in no less time man if the image were printed without overlapping the positions of the print head. Alternatively, the data in some or all of the lines in the overlapping portions in Fig. 3 may be the same as data in the lines closest to the overlapping portion, such mat some data is repeated in the overlapping portion. In a preferred embodiment, with reference to Fig. 5, the data in the respective lines of the overlapping portion of a first of a pair of adjacent strips is identical to the data prmted in the respective lines of the overlapping portion of the second of the pair of adjacent strips. As a result, no data is lost, repeated or altered, although slightly more time is taken to print the image. If the image is a color image, the data representing the image to be printed is arranged not only into a plurality of strips and lines as described above, but also separated into two or more colors such that thermally printing respective parts of the image in respective colors of the separated colors prints the color image. For example, a color image may be separated into three colors - cyan, magenta, and yellow - and the colors in the image may be produced by mixing these three colors at different degrees of intensity. The process of producing color images in this manner is well known in the art. For example, in thermal transfer printing, a multi-colored thermal ribbon having a plurality of portions of different color may be used, and the ribbon appropriately positioned to print in the desired color. Or a plurality of different colored ribbons used, and a ribbon of the desired color moved into a printing position to print in the desired color, as described in the above-referenced commonly assigned application.
In accordance with the present invention, a separated color in the overlapping portion between two adjacent positions of a print head may be printed during printing of the two adjacent strips, as described above for monochrome, to create a given boundary pattern for that color. The other colors may be printed similarly, each with a given boundary pattern. The boundary patterns for the separate colors may be the same or different. Preferably, they are the same, but offset from each other. For example, the boundary patterns produced for each of the separate colors cyan (C), magenta (M), and yellow (Y) may be offset from each other in the Y-axis direction as shown in Fig. 14a or in the X-axis direction as shown in Fig. 14b. The offsetting of the separated colors often tends to increase the effects of the edge stitching and thus reduce the effects of the visual artifacts described above.
According to the present invention, the nonlinear edge stitching or boundary patterns described above are generated by mathematical calculation, reference to a table, or some combination of both. The flow chart in Fig. 16A and 16B represents the general, functional flow of a software routine used in one embodiment of the invention to generate the patterns and mask the pixels when printing the strips, wherein the strips are printed in succession from the right side of the medium to the left side. Sections of a routine called PRINTSTRIP used in the preferred embodiment of the invention are set forth below.
PRINTSTRIP is in the programming language C, although other programming languages would be suitable. It should be understood by those skilled in the art that there are many ways in which the same patterns may be generated.
The parameters used in PRINTSTRIP to generate the patterns, including the extent of the overlap between adjacent strips, the frequency and amphtude of the pattern, and whether and the extent to which the separate colors are offset from each other in the overlapping portion, may be predetermined for optimal effectiveness for a given application or may be changed by a user such as through the use of a standard user interface such as a menu driven system. The PRINTSTRIP routine initializes the settings for these parameters. The following are some of the variables utilized in the PRINTSTRIP routine, along with their default, minimum and maximum values in one preferred embodiment of the present invention:
Variable Default Min/Max
overlap 8 0/127 overstep 32 1/127 overplaneoff 11 0/63 overplanefreqx 0 0/63 overplanefreqy 8 0/63 interleave 0 0/255 The variable totaloverlap, representing the total number of lines in which two adjacent strips are overlapped, is calculated as follows:
totaloverlap =(overlap + ((numplanes-1) * overplanefreqy)) + (numplanes-1) * interleave);
where the variable numplanes represents the total number of separate colors to be printed to make all the colors in the image. The possible value for numplanes in accordance with the preferred embodiment are 1 (for monochrome images), 3 (for images which may be separated into cyan, magenta, and yellow), and 4 (for images utilizing the colors cyan, magenta, yellow, and black). Using the default settings set forth above and a value for numplanes=3, the default value of totaloverlap is 24, i.e., the two adjacent strips will overlap by 24 lines. If the edges are not to be stitched and a straight edge is to be printed, the default value of totaloverlap is set to 0. The PRINTSTRIP routine sets flags to watch whether the strip to be printed is the first or last strip in the image. For those strips, the PRINTSTRIP routine will not mask any pixels on the outside edges of the strips.
A variable plane is used in calculating the frequency and/or amphtude of the pattern, as described below, thus causing those parameters to change in each successive sweep of the strip printed in a different color of the separate colors. If the image is a monochrome image, or if the user has requested that the separate colors making up the image not be offset in the overlapping portions, the variable plane will be set to a constant, such as numplanes-l, causing each sweep through the strip to print the separate colors, if any, mat make up the image overlaid upon each other. If the separate colors are to be offset from each other, the variable plane will contain a value equal to the number of the current pass through the strip, i.e., on the first pass through the strip using the first color, plane=\, on the second pass using a different color, plane=2, etc.
The PRINTSTRIP routine calculates values for the vertical period of the pattern, represented by the variable zipvperiod, and the horizontal width or amphtude of the pattern, represented by the variable ziphwidth, in accordance with the following formulas: zipvperiod = overstep + (overplanefreqx*plane) ziphwidth = overlap + (overplanefreqy*plane).
Using the default values set forth above and a value of numplanes=3, the vertical period of the pattern zipvperiod would be 32 during all passes in the strip, and the width of the pattern ziphwidth would be a function of the color plane being printed, i.e., ziphwidth=l6 on the first sweep, ziphwidth=24 on the second sweep, and ziphwidth=32 on the third sweep. As a result, in this embodiment the separate colors would be offset in the Y-axis direction but not in the X-axis direction. Alternatively, setting a non-zero value for the variable overplanefreqx would cause the separate colors to be offset in the X-axis direction as well by changing the vertical period.
The location of the starting Y-axis position of the print head is offset by the number of lines in the variable totaloverlap, and the print head is caused to move to that Y-axis position The PRINTSTRIP routine loops through each X-axis value in the overlapping portion of the strip, deterrnines which pixels to mask, and clears those pixels from the strip. If, as in the preferred embodiment, the boundary pattern is to be the same between all adjacent strips, the pixels masked on one side of each strip are complementary to the pixels masked on the other side of the strip.
Particular patterns may be implemented by the following sections of the PRINTSTRIP routine:
1. to generate a triangular pattern substantially as shown in Fig. 9 which is the same at the boundary between all adjacent strips of the image (except for the outside edges of the first and last strips in the image):
for (x=0;x<MAX_X; x++, b+=WORDSPERLINE)
{ zipvndx = ((x + plane*overplaneoff) % (zipvperiod*2)); if (zipvndx >= zipvperiod) zipvndx - 2*zipvperiod - zipvndx; zipclrcnt = (ziphwidth*zipvndx/zipvperiod); clearbits((unsigned char*) b, 0, zipclrcnt); clearbits((unsigned char*) b, STRIPWIDTH - (totaloverlap - zipclrcnt, STRIPWIDTH); } where the variable WORDSPERLINE represents the total number of pixels in each line in the strips and the variable STRIPWIDTH represents the total number of lines in each strip. 2. to generate a pattern of alternating rectangular regions with diffused edges, substantially as shown in Fig. 10, with reference to a table containing predetermined values for the diffused pattern, the pixels to be masked may be determined as follows:
#ifdefDIFMASK for (x=0;x<MAX_X; x++, b+=WORDSPERLINE)
{ dm = difinask[zipper_mode-ZIPPER_DIFFUSE][(x»l) + plane*overplaneoff & 15]; *b &= dm; *(b + ACTIVEWORDS-1) &= -dm;
} #endif
3. to generate a pseudo-random pattern of straight and angled line segments, which produces a pattern 256 segments long and then repeats the pattern, which alternates between straight and 45 degree angled line segments of random length, and which is the same at the boundaries between all adjacent strips in the image (except for the outside edges of the first and last strips in the image):
if (ziphwidth <= 4) ziphwidth = 4; if (strip->no = 0) /*if this is the first strip to be printed*/ if (realplane = 0) /*if this is the first color plane to be printed*/ makezipper(ziphwidth, zipvperiod, zipdel, zippos, ZIPCMDCNT);
zcmdcnt = 0; zptr = zpdel + zcmdcnt; zpresx = * (zippos + zcmdcnt); zruncnt = *zptr-H-; zcmdcnt++; zdelx = 0; for (x=0;x<MAX_X; x++, b+=WORDSPERLINE)
{ zipchcnt = zpresx; clearbits((unsigned char*) b, 0, zipchcnt); clearbits((unsigned char*) b, STRIPWIDTH - (totaloverlap - zipchcnt), STRIPWIDTH);
zpresx +=zdelx; zruncnt— ; if (zruncnt == 0)
{ if (zcmdcnt&l)
{ zruncnt = *zptrt-+; if (zruncntO)
{ zdelx = -l zruncnt = -zruncnt; } else zdelx = +l;
} else
{ zruncnt = *zptr-H-; zdelx = 0;
zcmdcnt-H-; if (zcmdcnt >= ZIPCMDCNT)
{ zcmdcnt = 0; zptr = zipdel; }
^define ZIPCMDCNT 256 static char zipdelfZIPCMDCNT] static char ziρpos[ZIPCMDCNT] static void
makezipper(int ziphwidth, int zipvperiod, char *zipdel, char *zippos, int z ziinpddeellccnnttϊ) < int newx, dx, fcnt, presx, zipcnt; int centx; char *dstl; char *dst2; int i;
dstl = zipdel; dst2 = zippos; centx = ziphwidth/2 presx = centx; for(i = 0;i < zipdelcnt-l;i-H-)
{
*dst2++ = presx; if(i & 1) { do { again: newx=supeιrandO%ziphwidth; if(i = zipdelcnt-3)
{ dx = newx-centx; if((dx >= -2)&&(dx <= 2)) goto again; } dx = newx-presx; } while((dx >= -2) && (dx <= 2)); ♦dstl-H- = dx; presx = newx;
} else
{ fcnt = (superrandO % zipvperiod) + 2; *dstl++ = fcnt; }
}
*dst2++ = presx; newx = centx; dx = newx-presx; *dstl++ = dx;
}
These routines generate specific patterns according to predetermined parameters. Based on the techniques utilized in these routines, routines to generate other patterns, such as the rectangular pattern substantially as shown in Fig. 8 or patterns with different characteristics, may be developed in similar fashion by those skilled in the art. Also, other routines for generating patterns will be apparent to those of skill in the art from the disclosure herein. While the invention has been described and illustrated in connection with preferred embodiments, many variations and modifications as will be evident to those skilled in this art may be made without departing from the spirit and scope of the invention, and the invention as set forth in the appended claims is thus not to be limited to the precise details of methodology or construction set forth above as such variations and modifications are intended to be included within the scope of the appended claims.

Claims

WHAT IS CLAIMED IS:
1. A method of printing an image on a medium to be printed upon, comprising: arranging data representing the image to be printed in a plurality of strips each having a length parallel to a first axis of the medium, with portions of at least two adjacent strips overlapping each other; arranging data representing each strip in a plurality of lines each having a width parallel to a second axis of the medium, with portions of respective lines in the overlapping portions of the two adjacent strips overlapping each other; arranging data representing each line in a plurality of pixels each representing a location on the respective line where data is to be printed, with pixels of overlapping portions of respective lines in the overlapping portions of the two adjacent strips being superposed; and printing the image, including: printing the data representing portions of the image in at least one line in a first of the two adjacent strips except for preselected pixels in the portions of the at least one line in the overlapping portions of the two adjacent strips; and printing the data representing portions of the image in at least one line in a second of the two adjacent strips which is adjacent the line in the first adjacent strip except for preselected pixels in the portions of the at least one line in the second strip in the overlapping portions of the two adjacent strips, such that visual artifacts caused by a difference in print quality between pixels in the overlapping portions of the two adjacent strips are reduced.
2. The method of claim 1 wherein the step of arranging data representing the image in a plurality of strips comprises arranging the data with portions of all adjacent strips in the image overlapping each other.
3. The method of claim 1 wherein the step of printing the data in at least one line in a first of the two adjacent strips comprises printing the data in all of the lines in a first of the two adjacent strips and is done before the step of printing the data in at least one line in a second of the two adjacent strips.
4. The method of claim 1 further comprising retrievably storing the locations of the preselected pixels not printed in the at least one line in the first of the two adjacent strips, and wherein the step of printing the data in at least one line in a second of the two adjacent strips comprises printmg data in at least the locations of the preselected pixels not printed in the at least one line in the first of the two adjacent strips.
5. The method of claim 4 wherein the step of printing the data in at least one line in a second of the two adjacent strips further comprises printing the data in only the locations of the preselected pixels not printed in the at least one line in the first of the two adjacent strips.
6. The method of claim 1 wherein the step of arranging data representing the image in a plurality of strips comprises arranging the data such that the data arranged in the portions of the at least two adjacent strips overlapping each other is identical.
7. The method of claim 1 wherein the step of arranging data representing each strip in a plurality of lines comprises arranging the data with portions of a plurality of lines in each of the two adjacent strips overlapping each other.
8. The method of claim 7 wherein the step of printing the data in at least one line in a first of the two adjacent strips comprises printing the data in a plurality of lines in the first of the two adjacent strips and the step of printing the data in at least one line in a second of the two adjacent strips comprises printing the data in a plurality of lines in the second of the two adjacent strips such that a predetermined pattern is formed between the data printed in the plurality of lines in the first of the two adjacent strips and the data printed in the plurality of lines in the second of the two adjacent strips.
9. The method of claim 8 wherein the step of printing the data in a plurality of lines in the second of the two adjacent strips comprises printing the data such that a predetermined pattern is formed between the data printed in the plurality of lines in the first of the two adjacent strips and the data printed in the plurality of lines in the second of the two adjacent strips, wherein the predetermined pattern is a pattern of alternating rectangular blocks.
10. The method of claim 9 wherein the predetermined pattern of alternating rectangular blocks formed as a result of the step of printing the data in a plurality of lines in the second of the two adjacent strips is substantially as shown in Figure 8.
11. The method of claim 9 wherein the predetermined pattern of alternating rectangular blocks formed as a result of the step of printing the data in a plurality of lines in the second of the two adjacent strips is substantially as shown in Figure 10.
12. The method of claim 8 wherein the step of printing the data in a plurality of lines in a second of the two adjacent strips comprises printing the data such that a predetermined pattern is formed between the data printed in the plurality of lines in the first of the two adjacent strips and the data printed in the plurality of lines in the second of the two adjacent strips, wherein the predetermined pattern is a pattern of alternating triangular blocks.
13. The method of claim 12 wherein the predetermined pattern of alternating triangular blocks formed as a result of the step of printing the data in a plurality of lines in the second of the two adjacent strips is substantially as shown in Figure 9.
14. The method of claim 8 wherein the step of printing the data in a plurality of lines in a second of the two adjacent strips comprises printing the data such that a predetermined pattern is formed between the data printed in the plurality of lines in the first of the two adjacent strips and the data printed in the plurality of lines in the second of the two adjacent strips, wherein the predetermined pattern is a sequence of straight and angled line segments in a randomly generated pattern.
15. A method of claim 8 wherein the image is a color image, further comprising the step of separating the color image to be printed into two or more colors such that printing respective parts of the image in respective colors of the separated colors prints the color image, and wherein the step of printing the image includes: printing data representing respective parts of the image in the overlapping portions of the two adjacent strips in a first respective color of the two or more colors ; and printing data representing respective parts of the image in another respective color or colors of the two or more colors such that the predetermined pattern formed between the data printed in the first color in the first of the two adjacent strips and die data printed in the first color in the second of the two adjacent strips is offset in location from the predetermined pattern formed between the data printed in the other color or colors in the first of the two adjacent strips and the data printed in the other color or colors in the second of the two adjacent strips.
16. A method of printing an image on a medium to be printed upon using a thermal print head having a plurality of thermal elements arranged in an array having an overall length and an overall width, the medium having a first dimension parallel to a first axis and a second dimension parallel to a second axis, the length and width of the array being substantially less than the first and second dimensions of the medium, respectively, the method comprising: arranging data representing the image to be printed in a plurality of strips each having a length parallel to the first axis of the medium, with portions of at least two adjacent strips overlapping each other; arranging data representing each strip in a plurality of lines each having a width parallel to the second axis of the medium, with portions of respective lines in the overlapping portions of the two adjacent strips overlapping each other; arranging data representing each line in a plurality of pixels each representing a location on the respective line where data is to be printed, with pixels of overlapping portions of respective lines in the overlapping portions of the two adjacent strips being superposed; and printing the image, including: relatively moving the print head and the medium to relatively position the print head adjacent desired locations of the medium corresponding to strips to be printed with portions of adjacent strips overlapped; relatively moving the print head and the medium to relatively position the print head adjacent desired locations of the medium coπesponding to respective lines in the strips to be printed;
-1 thermally printing the data representing portions of the image in the respective lines in a first of two adjacent strips with overlapping portions except for preselected pixels in the portions of the respective lines in the overlapping portions of the two adjacent strips; and thermally printing the data representing portions of the image in the respective lines in a second of the two adjacent strips with overlapping portions except for preselected pixels in the portions of the respective lines in the second strip in the overlapping portions of the two adjacent strips, such that visual artifacts caused by a difference in print quality between pixels in the overlapping portions of the two adjacent strips are reduced.
17. A method of printing an image on a medium to be printed upon, wherein data representing the image to be printed is arranged in a plurality of strips each having a length parallel to a first axis of the medium, wherein data representing each strip is arranged in a plurality of lines each having a width parallel to a second axis of the medium, and wherein data representing each line is arranged in a plurality of pixels each representing a location on the line where data is potentially to be printed, the method comprising: for at least one pair of adjacent strips, arranging the data representing the image such that portions of lines in the adjacent strips overlap each other and pixels of overlapping portions of respective lines of the two adjacent strips are superposed; and printing the image, including: printing the data representing portions of the image in at least one line in a first of the two adjacent strips except for preselected pixels in the portions of the at least one line in the overlapping portion of the two adjacent strips; and printing the data representmg portions of the image in at least one line in a second of the two preselected pixels in the portions of the line in the second strip in the overlapping portions of the two adjacent strips, such that visual artifacts caused by a difference in print quality between pixels in the overlapping portions of the two adjacent strips are reduced.
18. A method of printing a color image on a medium to be printed upon using a thermal print head having a plurality of thermal elements arranged in an array having an overall length and an overall width, the medium having a first dimension parallel to a first axis and a second dimension parallel to a second axis, the length and width of the array being substantially less than the first and second dimensions of the medium, respectively, the method comprising: arranging data representing the image to be printed in a plurality of strips each having a length parallel to the first axis of the medium, with portions of all adjacent strips overlapping each other such that the data arranged in the portions of each pair of adjacent strips overlapping each other is identical; arranging data representing each strip in a plurality of lines each having a width parallel to the second axis of the medium, with portions of a plurality of respective lines in the overlapping portions of each pair of adjacent strips overlapping each other; arranging data representing each line in a plurality of pixels each representing a location on the respective line where data is to be printed, with pixels of overlapping portions of respective lines in the overlapping portions of each pair of adjacent strips being superposed; separating the color image to be printed into two or more colors such that printing respective parts of the image in respective colors of the separated colors prints the color image; and printing the image, including, for each pair of adjacent strips: relatively moving the print head and the medium to relatively position the print head adjacent desired locations of the medium corresponding to strips to be printed with portions of adjacent strips overlapped; relatively moving the print head and the medium to relatively position the print head adjacent desired locations of the medium corresponding to respective lines in the strips to be printed; causing the print head to thermally print the data representing portions of the image in the respective lines in a first of the pair of adjacent strips with overlapping portions except for preselected pixels in the portions of the respective lines in the overlapping portions of the pair of adjacent strips; retrievably storing the locations of the preselected pixels not printed in the respective lines in the first of the pair of adjacent strips; causing the print head to thermally print the data representing portions of the image in the respective lines in a second of the pair of adjacent strips with overlapping portions except for preselected pixels in the portions of the respective lines in the second strip in the overlapping portions of the pair of adjacent strips in only the locations of the preselected pixels not printed in the respective lines in the first pair of adjacent strips, such that a predetermined pattern is formed between the data printed in the respective lines in the first of the pair of adjacent strips and the data printed in the second of the pair of adjacent strips; causing the print head to thermally print data representing respective parts of the image in the overlapping portions of the pair of adjacent strips in a first respective color of the two or more colors ; and causing the print head to thermally print data representing respective parts of the image in another color or colors of the two or more colors such that the predetermined pattern formed between the data printed in the first color in the first of the two adjacent strips and the data printed in the first color in the second of the two adjacent strips is offset in location from the predetermined pattern formed between the data printed in the other color or colors in the first of the two adjacent strips and the data printed in the other color or colors in the second of the two adjacent strips.
19. Apparatus for printing an image on a medium to be printed upon, comprising: means for arranging data representing the image to be printed in a plurality of strips each having a length parallel to a first axis of the medium, with portions of at least two adjacent strips overlapping each other; means for arranging data representing each strip in a plurality of lines each having a width parallel to a second axis of the medium, with portions of respective lines in the overlapping portions of the two adjacent strips overlapping each other; means for arranging data representing each line in a plurality of pixels each representing a location on the respective line where data is to be printed, with pixels of overlapping portions of respective lines in the overlapping portions of the two adjacent strips being superposed; imaging means for printing the image on the medium in the plurality of strips; means for relatively moving the imaging means and the medium in directions parallel to the first and second axes such that the position of the imaging means when printing a first of the two adjacent strips overlaps in the direction of the second axis the position of the imaging means when printing a second of the two adjacent strips; image printing causing means for causing the imaging means to print the data representing portions of the image in at least one line in the first of the two adjacent strips except for preselected pixels in the portions of the at least one line in the overlapping portions of the two adjacent strips and for causing the imaging means to print the data representing portions of the image in at least one line in the second of the two adjacent strips except for preselected pixels in the portions of the at least one line in the second strip in the overlapping portions of the two adjacent strips, such that visual artifacts caused by a difference in print quality between pixels in the overlapping portions of the two adjacent strips are reduced.
20. The apparatus of claim 19 wherein the imaging means comprises a thermal print head.
21. The apparatus of claim 19 further comprising means for retrievably storing the locations of the preselected pixels not printed in the at least one line in the first of the two adjacent strips, and means for printing the data in at least the locations of the preselected pixels not printed in the at least one line in the first of the two adjacent strips.
22. The apparatus of claim 21 wherein the means for printing data in at least the locations of the preselected pixels not printed in the at least one line in the first of the two adjacent strips comprises means for printing the data in only the locations of the preselected pixels not printed in the at least one line in the first of the two adjacent strips.
23. The apparatus of claim 22 further comprising means for arranging the data such that the data arranged in the portions of the at least two adjacent strips overlapping each other is identical.
24. The apparatus of claim 19 wherein the means for arranging the data representing each strip in a plurality of lines arranges the data such that portions of a plurality of lines in each of the two adjacent strips overlap each other.
25. The apparatus of claim 19 wherein the image printing causing means causes the imaging means to print the data in a plurality of lines in the first of the two adjacent strips and in a plurality of lines in the second of the two adjacent strips such that a predetermined pattern is formed between the data printed in the plurality of lines in the first of the two adjacent strips and the data printed in the plurality of lines in the second of the two adjacent strips.
26. The apparatus of claim 25 wherein the image printing causing means causes the imaging means to print the data such that a pattern of alternating rectangular blocks is formed between the data printed in the plurality of lines in the first of the two adjacent strips and the data printed in the plurality of lines in the second of the two adjacent strips.
27. The apparatus of claim 26 wherein the pattern of alternating rectangular blocks is substantially as shown in Figure 8.
28. The apparatus of claim 26 wherein the pattern of alternating rectangular blocks is substantially as shown in Figure 10.
29. The apparatus of claim 25 wherein the image printing causing means causes the imaging means to print for printing the data such that a pattern of alternating triangular blocks is formed between the data printed in the plurality of lines in the first of the two adjacent strips and the data printed in the plurality of lines in the second of the two adjacent strips.
30. The apparatus of claim 29 wherein the pattern of alternating triangular blocks formed by the printing means is substantially as shown in Figure 9.
31. The apparatus of claim 25 further comprising means for printing the data such that a randomly generated pattern comprising a sequence of straight and angled line segments is formed between the data printed in the pluraUty of lines in the first of the two adjacent strips and the data printed in the plurality of lines in the second of the two adjacent strips.
32. The apparatus of claim 25 wherein the image is a color image, further comprising: means for separating the color image to be printed into two or more colors such that printing respective parts of the image in respective colors of the separated colors prints the color image; and wherein the image printing causing means causes the imaging means to print data representing respective parts of the image in the overlapping portions of the two adjacent strips in a first color of the two or more colors and to print data representing respective parts of the image in another color or colors of the two or more such that the predetermined pattern formed between the data printed in the first color in the first of the two adjacent strips and the data printed in the first color in the second of the two adjacent strips is offset in location from the predetermined pattern formed between the data printed in the other color or colors in the first of the two adjacent strips and the data printed in the other color or colors in the second of the two adjacent strips.
33. Apparatus for printing an image on a medium to be printed upon having a first dimension parallel to a first axis and a second dimension parallel to a second axis, comprising: processing means for at least: arranging data representing the image to be printed in a pluraUty of strips each having a length parallel to the first axis of the medium, with portions of at least two adjacent strips overlapping each other; arranging data representing each strip in a plurality of lines each having a width parallel to the second axis of the medium, with portions of respective lines in the overlapping portions of the two adjacent strips overlapping each other; and arranging data representing each line in a plurality of pixels each representing a location on the respective line where data is to be printed, with pixels of overlapping portions of respective lines in the overlapping portions of the two adjacent strips being superposed; a thermal print head having a plurality of thermal elements arranged in an elongated narrow array having an overall length of from about one inch to about four inches and an overall width, the length of the array being larger than the width of the array, the length and width of the array being substantially less than the first and second dimensions of the medium, respectively, said thermal print head being oriented relative to the medium with the length of the array extending parallel to the first axis; means for relatively moving said print head and the medium parallel to the second axis in each of the plurality of strips, and for relatively moving said print head and said medium parallel to the first axis to selectively position said print head adjacent desired locations of the medium corresponding to the overlapping portions of respective lines in the overlapping portions of the two adjacent strips to be printed; means for causing the print head to thermally print at least: the data representing portions of the image in the respective lines in a first of the two adjacent strips except for preselected pixels in the portions of the respective lines in the overlapping portions of the two adjacent strips; and the data representing portions of the image in the respective lines in a second of the two adjacent strips which is adjacent the lines in the first adjacent strip except for preselected pixels in the portions of the lines in the second strip in the overlapping portions of the two adjacent strips, such that visual artifacts caused by a difference in print quality between pixels in the overlapping portions in the two adjacent strips are reduced.
34. Apparatus for printing a color image on a medium to be printed upon having a first dimension parallel to a first axis and a second dimension parallel to a second axis, comprising: a thermal print head having a plurality of thermal elements arranged in an elongated narrow array having an overall length and an overall width, the length of the array being larger than the width of the array, the length and width of the array being substantially less than the first and second dimensions of the medium, respectively, said thermal print head being oriented relative to the medium with the length of the array extending parallel to the first axis; a plurality of thermal transfer media, there being a thermal transfer medium for each color in which at least a part of the image is to be printed; means for separating the color image to be printed into two or more colors such that thermally printing respective parts of the image in respective colors of the separated colors prints the color image; means for arranging data representing the image to be printed in a plurality of strips each having a length parallel to the first axis of the medium, with portions of at least two adjacent strips overlapping each other; means for arranging data representing each strip in a plurality of lines each having a width parallel to the second axis of the medium, with portions of respective lines in the overlapping portions of the two adjacent strips overlapping each other; and means for arranging data representing each line in a plurality of pixels each representing a location on the respective line where data is to be printed, with pixels of overlapping portions of respective lines in the overlapping portions of the two adjacent strips being superposed; means for relatively moving the print head and the medium in directions parallel to the first and second axes such that the position of the print head when printing a first of two adjacent strips overlaps in the direction of the second axis the position of the print head when printing a second of two adjacent strips; means for causing the print head to thermally print the data representing portions of the image in at least one line in a first of the two adjacent strips in a first of the respective colors except for preselected pixels in the portions of the at least one line in the overlapping portions of the two adjacent strips; means for causing the print head to thermally print the data representing portions of the image in at least one line in the first of the two adjacent strips in one or more other of the respective colors except for preselected pixels in the portions of the at least one line in the overlapping portions of the two adjacent strips, such that the locations of at least some of the preselected pixels not printed in the first color in the first of the two adjacent strips are different than the locations of at least some of the preselected pixels not printed in the one or more other of the respective colors in the first of the two adjacent strips; means for causing the print head to thermally print the data representing portions of the image in at least one line in a second of the two adjacent strips which is adjacent the line in the first adjacent strip in the first of the respective colors except for preselected pixels in the portions of the at least one line in the second strip in the overlapping portions of the two adjacent strips; and. means for causing the print head to thermally print the data representing portions of the image in at least one line in the second of the two adjacent strips in one or more other of the respective colors except for preselected pixels in the portions of the at least one line in the overlapping portions of the two adjacent strips, such that the locations of at least some of the preselected pixels not printed in the first color in the second of the two adjacent strips are different than the locations of at least some of the preselected pixels not printed in the one or more other of the respective colors in the second of the two adjacent strips.
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