Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
- 13~980
METHOD OF IMP~OVIIJG DOT-OI~-DOT GRAPHICS AREA-FILL
USI~G A~ INK-JET DEVICE
1 TECHtJICAL FIELD
T~le present invelltion relates to ink-~et devlces for
printing colors on a prlnt medlum, and, more partlcularly,
to a method of improvlng the percel~ed quality of color
graphicc thereorl.
BACKGROUI~D A~T
Ink-~et devlces flre droplets of lnk toward a print-
lng medlum, 8uch as paper or mylar. Typlcal lnk-~et
printheads comprlse at least one group of nozzles, called
a primitive, through whlch the droplets of ink are flred.
For full color prlntlng, three primitlves are employed,
with the nozzles of each fluldlcally connected to a reser-
voir of a different color ink ~cyan, yellow, magenta).
The firing, or propelllng of lnk droplets, may be done by
piezoelectric means or by reslstive heat~ng (thermal).
In green, red and blue soltd area-flll, the colors
are generated by placlng one dot of a flrst color on top
of anot~ler dot of a 6econd color, whlch produces the de-
~ired t~llrd color (e.g., yellow on cyan creates greenJ.
In the normal prlnting mode, the dots are put down on
each other ln the same pass of the prlnthead across the
medium. When prlrltlng a block of area-fill, bands occur
between swaths of prlnt rows, due to absorptlon of the
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first color printed on the medium, which may be a
specially coated paper used for color ink-jet printing.
The banding tends to reduce the perceived quality of the
output.
Accordingly, a method of producing a substantially
uniform block of color, without the perceived banding or
at least with reduced perceived banding is desired.
DISCLOSURE OF INVENTION
In accordance with the invention, a method of
forming dot-on-dot graphics area-fill with reduced
perceived banding is provided. The method comprises
overlapping a portion of one print row or print swath
with a portion of another print row or print swath.
In particular, the invention provides a method of
generating dot-on-dot graphics area fill on a print
medium using an ink-jet device including at least one
printhead having a set of primitives, each primitive
comprising a plurality of nozzle~ one dot apart
fluidically connected to a reservoir of a given colour,0 the method comprising:
printing a first row of a first colour;
printing a second row of a second colour; and
printing further rows of alternating first and
second colours, each further row of each colour being5 contiguous with the previous row of that colour;
characterised in that each row of the second colour
is offset from its respective row of the first colour by
a predetermined displacement toward the previous row of
the first colour.
The offset printing may be done by moving either
the print medium or the printhead relative to the other.
Also, primitives on the printhead may be staggered to
achieve the desired effect.
B
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2~P
By overlapping, or interleaving, swaths of the
individual colors, the bands present in the conventional
print mode are eliminated. This results in improved
print quality and homogeneity of graphics output.
Other aspects of this invention are as follows:
An improved method or generating dot-on-dot
graphics area fill on a print medium using an ink-jet
device, said device including at least one printhead
having a set of primitives, each primitive comprising a
plurality of adjacent nozzles one dot apart fluidically
connected to a reservoir of a given color, said method
comprising:
(a) printing a first swath of a first color by
ejecting ink through said plurality of nozzles;
(b) partially overprinting said first swath with a
narrower swath of a second color such that part of said
first swath is exposed as a partial swath of said first
color, said overprinting being accomplished by ejecting
inX through a ~econd plurality of nozzles;
¢c) printing a second swath of said first color
abutting said partial swath;
(d) printing another swath of said second color
over said partial and an adjacent portion of said second
swath of said first color;
(e) repeating steps (c) and (d) until said graphic
area is completely colored; and
(f) finally overprinting any remaining narrow
swath of said first color with a partial swath of said
second color.
An improved method of generating dot-on-dot
graphics area fill on a print medium using an ink-jet
device including at least on¢ printhead having a set of
primitives, each primitive comprising a plurality of
nozzles one dot apart fluidically connected to a
3S reservoir of a given color, said method comprising:
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2b
(a) printing a first swath of a first color by
ejecting ink through said plurality of nozzles
associated with said first color;
(b) overprinting approximately the top 50% of said
first swath with a swath of a second color by ejecting
ink through a second plurality of nozzles;
(c) printing a second swath of said first color
abutting said first swath;
(d) printing another swath of said second color
over approximately the lower 50% of said first swath and
the top 50~ of said second swath of said first color;
(e) repeating steps (c) and (d) until said graphic
area is completely colored; and
(f) overprinting the remaining 50% of the last
swath of said first color with a 50% swath of said
second color.
~RIEF DESC~TION OF THE DRAW~GS
PIGS. la-d are top plan views of printing two
colors to achieve a third color, employing a
conventional print
.~
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1 mode used ln t~le pr~or art: a~ld
FIGS. 2a-e are top plan vlews of prlrltillg two colors
to acllleve a thlrd color ln accorda~lce wlth the ~nventlon.
BEST MODES FOR CARRYI~G OUT THE Ir~VENTION
Referrll~g now to the drawlngs wherei~ llke numerals
of reference designate li~e elements throughout, FIGS. la-
d deplct the sequence of events ln fllling in an area of a
third color achleved by printing multlple rowY of two
colors. In the descriptlon wh~ch follows, the color green
ls acl~leved by pr1tltlng alternatlng rows of cyan and yel-
low. However, it wlll be understood that other comblna-
tions suffer from the same effect to be described, and
that such other combinations wlll also benefit from em-
ploying the method of the lnventlon.
FIG. la illustrates the prlntlng of a first row 10 of
a first color, here, cyan, on a print medlum 12. Employ-
lng ink-~et techllology, tlle row lO, and sub6eque~lt rows,
are generated by flrlng all nozzles of a prlmltlve on the
prlnthead. As an example, a prlmltive may contaln ten
nozzles, although fewer or greater numbers of nozzles may
be employed.
In FIG. lb, a row 14 of a second color, here, yellow,
i~ overlald directly over the flrst row 10, elther in the
same pass across the medium 12 or ln a subsequent pass.
However, the print medlum 12 is saturated with the flrst
color, so the second color tends to run off the flrst
color, creating tlle thlrd color ln the central portion 16
and a border 18 of the second color.
In FIG. lc, a second row 20 of tllé flrst color 19
printed, and lts top edge is allgned substantlally ad~a-
cent tlle bottom edge of the first row 10 of the first
color. Whlle tllat portlon 22 of the border 18 overlald by
~5 the second row 20 suffers from the saturatlon effect~
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1 discussed 11l conneeti~n wlt}) FIG. la, lt llevertheless i~
converted to t~le t~llrd color. I~owever, w~lereas the cen-
tral portlon 16 compr~ses the second color on top of the
first color, t~le border portlo~l 22 comprlses t~,e flrst
color Oll top of t~le secor~d color. T~lls dlstlnction wlll
be dlscussed s~lortly.
Irl FIG. ld, another row 24 of the second color ls
overlaid dlrectly over the second row 20. Again, due to
saturatlon of the prlnt medlum, the thlrd color i9 gener-
ated in the central portion 16', and a border 18' of thesecond color i9 formed, as ln FIG. lb.
It wlll be appreclated that prlntiny of subsequent
rows of the flrst color overlald wlth rows of the ~econd
color generates two reglons of a th~rd color, namely a
central portlon 16 (and 16', etc.) and a border portlon 22
~and 22', etc,). Whlle both are of the same color, the
~ormer reglon ls a thlrd color of the ca~t of the first
color (due to the prlor absorptlon of the flrst color
therein1, while the latter reglon 15 a thlrd color of the
cast of the second color ~due to the prior absorption of
the second color thereln).
Thus, in the case of rows 10, 20 of cyan overlaid
with rows 14, 24 of yellow, the central portions 16, 16'
are green wlth a blulsh cast, whlle the border portionY
22, 22' are green with a yellowish cast. The resultlng
area-flll comprlses large swaths of one shade of green
separated by narrow bands of another shade of green. The
dlstinct banding is consldered ob~ectionable.
In accordance wlth the invention, the percelved qual-
ity of the area fill is improved by overlapping, or lnter-
leavlng, swat~ls of the indlvldual colors. The preferred
sequence of the overlapplng is depicted in FIGS. Za-e.
FIG. 2a shows a flrst row 3~ of a first color, agaln,
cyar~, for example, prlr~ted on a medlum 12. ~ complete
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1 flrst row ts ~ritlted. Rey~on "A" comprlses the flrst
color.
In FIG. 2b, only a portlon of a second row 32 of a
second color, agaln, yellow, for example, ls prlnted,
off~et from the,flrst row by a speclflc, predetermined
amount. The portlon (reglon "A"') not prlnted by the
second color relates to the amount of over~ap, or offset,
and here 15 one-half of a row. Thus, one-half row is
lnitially printed, and tl~e offset ls one-~lalf row, so that
lo the second row 32 covers the top one-half of the prlnted
portlon of the flrst row 30. The row 32 creates the thlrd
color, again, green, for example, whlle the bottom half of
the row 30 remalns the ftrst color. Region l'B" is now the
third color, whlle that portlon of region "A" not prlnted
on i5 denoted IIA"'.
In FIG. 2c, a thlrd row 3~ of the flrst color ls
prlnted adJacent the row 30, agaln, offset from the ~econd
row 32 by the predetermlned amoullt, here, one-half row.
Thus, the top of row 34 butts agalnst the bottom of row
30. Region "B", beirlg unaffected in thl~ step, remalns
the third color, reglon "A"', also unaffected, remalns the
flr~t color, and region "A" is the newly-printed flrst
color.
In FIG. 2d, a fourth row 36 of the second color ls
printed, offset from the thlrd row 34 by the predetermlrled
amount, agaln, one-half row. Region "B", being unaffected
ln this step, remains the third color, reglon "A"' and the
upper portion of region "A" are now the third color, as
denoted by "B", and the lower portion of region "A" not
printed on t5 denoted "A "', the first color.
The method may be continued as many times a~ deslred,
printing of rows of alternating flrst and second colors,
untll the area ls filled. In order to termlnate the la~t
row of the area to provide only one color, only a portion
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of the last row is printed, and is the amount of offset,
here, one-half of a row 38, as shown in FIG. 2e.
It will be appreciated that in the preferred
embodiment, one color (the first color, here, cyan) is
always overlaid by another color (the second color,
here, yellow), so that the resulting third color is
always of the same cast. Thus, the objectionable
banding achieved with the prior art method is avoided.
The offsetting of one color relative to another
color can be done using several methods, so that the
nozzles in each primitive are located one dot apart.
First, individual primitives on a single printhead
containing separate colors can be physically offset
relative to each other. Second, if the primary colors
are contained in separate pens, the pens themselves can
be offset relative to one another. Third, w].th a print-
head having primitives not offset, or with a pen fixturing
con~iguration not having the pens offset, les~ than the full
number of nozzle~ in each primitive, or pen, can be used in
order to allow for offsetting of the remaining nozzles.
The third method allows for offsetting without
having to make a physical change to an existing pen or
to the pen fixturing (in the case when each color is in
a separate pen).
By physically offsetting the nozzles of one color
relative to the nozzles of the other color using any of
the methods stated previously, the two colors can be
deposited during the sam~ pass of the printhead across
the medium. In FIG. 2, this would be accomplished by
depositing the rows 30 and 32 represented in FIGS. 2a
and 2b in the same pass, as well as the rows 34 and 36
represented in FIGS. 2c and 2d during the same pass.
Two additional methods can be used to create the
offset of the two colors. In the fourth method, the print
medium 12 can be moved relative to the printhead. In the
fifth method, the printhead can be moved relative to the
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1 prlnt medlum 12. T~lese mettlods requlre that the medium or
prlntllead deperldl~lg ~n w~1c~l is being mcved move back-
ward (opposlte the dlrectlon of the progression of print-
ing down tlle page) to allow for the offsettlng of t~le
second color relative to the f lrst color. The prlnthead
or medlum must then be moved ~orward to depo61t the first
color oJI a~l ut~printed section of medlum again tllen move
backward to prlnt the second color and continue in thls
fashion untll the area-fill block is complete. Thus
lo these methods require that one pass of the prlnthead
across the medium be made for each primary color depos-
ited.
The advantage of printing the first and second colors
during the same pass of the printhead or prlntheads across
the medlum is that the tlme required to print a section of
area-fill ls approximately halved. However, with the
off~et conflguration, tl)e prlnt quality 18 better w~len tlle
sectlon 19 prlnted ln two pass modeR rather than ln a
slllgle pass mode. Ttle reason for t~lis 18 t}~at one sectlon
of the thlrd color ls created by combinlng the flrst and
second colors in the same pass, and another section 18
created by depositlng the second color on top of the first
color which was deposited in the prevlous pas~ of the
printhead across the medium. The d~fference creates a
variation in hue between the two sections whlch ls no-
tlceable.
In the two-pass mode, the second color ls depos'ted
on two sectlons of the flrst color. ~ne sectlon was de-
posited in tlle previous pass arld t~e ot~ler was put down
three passes pr~or to the pass of the cecond color. The
two sectlons oP the flrst color are very simllar, s~nce
both have ~lad sufficient time to dry and result ln a
uniform area of the third color.
The extent of offset may be var'ed. In the one-pa~
mode maximum print quality is achieved at an offset of
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100%, while slight improvement is made with slight
amounts of offset of at least about 10%, such as an
offset of at least one nozzle or one dot row. In the
two-pass mode, maximum print quality is achieved at an
offset of 100% also, but major improvements are obtained
with slight amounts of offset of at least about 10%,
such as an offset of at least one nozzle or one dot row.
INDUSTRIAL APPLICABILITY
The use of offset partial row printing in
accordance with the invention is expected to find use in
color ink-jet printers.
Thus, there has been disclosed a method of
improving dot-on-dot graphics area fill using an ink-jet
device. It will be clear to one of ordinary skill in
the art that various changes and modifications of an
obvious nature may be made, and all such changes and
modi~ications are considered to fall within the scope of
the invention as defined by the appended claims.
B
