Ink-jet color printing system

An ink-jet color printing system for painting a color image with complex colors arranged in ink-dot patterns; comprises a color image information input unit for reading out color image information from a color original, a color image information processing unit for memorizing the color image and carrying out a non-linear masking procedure, and color printer apparatus for painting a color image by depositing ink dots of yellow, magenta and cyan on a recording medium. New yellow, magenta and cyan ink dyes are also disclosed.

BACKGROUND OF THE INVENTION 
The present invention relates to an ink-jet color printing system for 
forming color images of complex color. More particularly, the invention 
pertains to the ink-jet color printing system in which a color image 
faithful to the original color reproduction can be produced by using a 
non-linear masking technique and by using cyan, magenta and yellow inks in 
combination in the ink-jet color printing apparatus. 
In the conventional ink-jet color printing apparatus for painting color 
images having complex color such as a color photograph, a color image is 
painted by means of a dot pattern wherein the injection of colored inks is 
regulated by driving the ink-jet heads for yellow, magenta and cyan which 
receive density signals of blue, green and red, respectively. However, in 
the heretofore known ink-jet color printing apparatus, it is difficult to 
paint a color image which is faithful to the original color in the 
original picture having complex color. 
It has become clear from investigation of deteriorated images that either 
insufficient color corrections in the masking procedure or inappropriate 
combinations of yellow, cyan and magenta inks will cause a deterioration 
in color reproducibility. 
That is to say, a conventional masking procedure by the use of a linear 
equation having variables which are the color density of three primary 
colors, namely, blue, green and red, is not desirable for obtaining a fine 
color correction on account of the fact that there is an extremely high 
degree of non-linearity between the amount of ink and the optical density. 
Inks usually used in ink-jet color printing apparatus contain water-soluble 
dyes such as direct dyes or acid dyes as described in Japanese Patent 
Examined Publication Nos. 54-16243, 54-16244, 54-16245 and 54-21765 and 
Japanese Patent Unexamined Publication Nos. 49-89534, 52-96105, 52-146307, 
53-77706 and 54-89811. Between the mixing ratio in which the inks 
containing water-soluble dyes aforementioned are mixed, and the hue of a 
color obtained by the mixing, there is a non-linearity in a subtractive 
mixture, and there is a tendency for the mixed color to appear as 
coloration unable to be absorbed, even though a polynominal function 
including non-linear terms is applied to a masking procedure. Therefore, 
in order to make improvements in color reproducibility, it is necessary to 
employ inks more suitable in coloration and to carry out a masking 
procedure having due consideration for the characteristics of the inks. 
OBJECTS OF THE INVENTION 
The principal object of the present invention is to provide an ink-jet 
color printing system which can reproduce a color image with hues closely 
similar to those of the color original. 
Another object of the present invention is to provide an ink-jet color 
printing system comprising means for performing color correction by using 
a non-linear masking technique. 
A further object of the present invention is to provide an ink-jet color 
printing system comprising means for improving the coloration by suitable 
combination of yellow, magenta and cyan inks. 
Finally, it is an object of the present invention to provide improved 
yellow, magenta and cyan ink dyes. 
SUMMARY OF THE INVENTION 
These and other objects of the present invention are attained in 
conjunction with the present invention by applying a non-linear masking 
procedure for color image information, regulating the amounts of colored 
inks which are ejected from the ink-jet head assembled, in corresponding 
to yellow, cyan and magenta depending upon color corrected color-image 
information, and supplying improved yellow, magenta and cyan inks to each 
ink-jet head in the ink-jet color printing apparatus using a digital data 
processing technique.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now in detail to the drawings, wherein like reference numerals 
denote the same or similar elements throughout the several views, in a 
preferred embodiment illustrated in FIG. 1, there is schematically shown 
an ink-jet color printing apparatus comprising a color image information 
input unit 1 which reads the color information of color picture images of 
an original by a two-dimensional scanning of the color images and then 
converts them into digital signals, a color image processing uint 2 for 
memorizing the color image information as digital signals input from the 
color image information input unit 1 and for carrying out image processing 
such as masking, and a color printer apparatus 3 for reproducing color 
pictures by ejecting colored ink-drops of a plurality of colors of inks 
from nozzles toward a recording medium, for instance a plain piece of 
paper, to form color pictures thereon. Although a digital color scanner 
is, in this embodiment, employed as a color image information input unit 
1, a device which can convert video signals from a color TV camera into 
digital signals to thus feed them to a color image information processing 
unit 2 can also be used. 
The color image information input unit 1 scans a color original 11 wrapped 
around a rotary drum 10 in two dimensions to measure the color densities 
of the three primary colors, namely blue, green and red, included in each 
picture element. The rotary drum 10 can be driven by means of a pulse 
motor 12 to scan primarily (in the direction of the rotation of the drum) 
the color original 11, while the actual position of the rotary drum 10 
undergoing rotation is, in the primary scanning direction, detected by a 
pulse counter 13 for counting driving pulses fed to the pulse motor 12. 
The counter 13 is adapted to reset the contents thereof each time the 
rotary drum 10 makes one revolution so that the actual position of the 
drum 10 undergoing rotation can be directly read from the pulse counter 13 
during each one revolution thereof. 
Light rays from light source 14 are condensed by means of a lens element 15 
to illuminate a spot on the color original 11. Light rays striking a 
half-mirror 17 through a lens element 16 after reflection from the color 
original 11 are separated into two beams, i.e. transmitted light ways and 
reflected light rays. The latter pass through a blue light transmitting 
filter 18 to impinge upon a light receiving device 19 responding only to 
blue light, thus being photoelectrically transmuted. 
The light rays transmitted by mirror 17 are further directed to another 
half-mirror 20 to be again separated thereby into two beams, i.e. 
transmitted light rays and reflected light rays. The latter transmitted 
light rays, after passing through a red light transmitting filter 23, will 
impinge upon a light receiving device 24 responding only to red light and 
the other reflected light rays after passing through a green light 
transmitting filter 21 will impinge upon a light receiving device 22 
responding only to green light, whereby red and green are also 
photoelectrically transmuted. Consequently, color components in the 
proportion of the three primary colors included in the light rays 
reflected from each picture element, can be measured by light receiving 
devices 19, 22 and 24, respectively. 
It is desirable to employ a blue color filter, a green color filter and a 
red color filter shown in the FIG. 1 having spectral characteristics of 
sensitivity equal or approximate to the CIE color matching function or its 
linear combinations. That is, although various colors of a color original 
are visually sensed as the same colors, it is possible that these colors 
are in fact multifarious as to their spectral characteristics. Thus it may 
be said that it is preferable to use a photometry system having a spectral 
characteristic which conforms to that of human eyes. 
The spectral characteristic of sensitivity described above may be that 
which satisfies the Luther condition. In FIG. 2, solid curves represent 
spectral characteristics of sensitivity of color filters used in practice 
with the present invention and are approximative to the CIE color matching 
function in its characteristic. But the dotted curves illustrate the ideal 
spectral characteristics of sensitivity based on the color matching 
function. 
All of light source 14, lens elements 15 and 16, half-mirrors 17 and 20, 
color filters 18, 21 and 23, and light receiving devices 19, 22 and 24 are 
firmly attached to a movable table 25 which is adapted to move parallel to 
the axis of the rotary drum 10 by means of a feed screw shaft 26 and a 
guide rod 27 in order thus to scan secondarily (in the direction 
perpendicular to the primary scanning direction) the color original 11. 
The feed screw shaft 26 is driven by means of a pulse motor 28 the total 
number of pulses fed to which being counted by another counter 29. 
Color component signals of three primary colors generated by light 
receiving devices 19, 22 and 24 are logarithmically converted into signals 
of color density of converters 30 and then converted into digital signals 
by A-D (analog-to-digital) converters 31 which are provided one for each 
color. It is desirable to carry out, prior to said analog-to-digital 
conversions of color signals, image processing such as noise reduction 
and/or image enhancement as required. Although the light source 14 is, in 
this embodiment, disposed outside of the rotary drum 10 so that one can 
measure the reflected light from the color original 11, in the case of 
using color originals with a high transmittance such as color films, color 
component measurements can be made by a color scanner which is comprised 
of a transparent rotary drum with a light source inside and light 
receiving devices for receiving light rays passing through the transparent 
color original. 
The color image processing unit 2 comprises an interface 33, a central 
processing unit (CPU) 34, a memory 35, line buffer memories 37 to 40, 
under color removal (UCR) circuits 41 to 44, dot pattern generates 45 to 
48 and printing head drivers 49 to 52. 
When reading color image information into the color image processing unit 
2, the CPU 34 feeds driving pulses to the pulse motor 12 to rotate the 
rotary drum 10 in the primary scanning direction followed by the rotation 
of the pulse motor 28 through a fixed angle every one revolution of the 
rotary drum 10 so that the color original 11 is two-dimensionally scanned 
to measure quantities of three primary color components of each picture 
element on a scanning line. Color density signals of the three primary 
colors, namely blue, green and red, are converted into digital signals, to 
be read into the CPU 34 through the interface 33. The said color density 
signals of three primary colors are memorized as color image information 
in memory cells the locations of which are addressed by position signals 
from counters 13 and 29 corresponding to the position of each picture 
element. 
A conventional mini-computer can be employed as the CPU described above for 
controlling the color image information input unit 1 and printer 3, for 
controlling the memorizing or reading out of the color image information, 
masking processing for color correction, character superimposition, and 
for carrying out the various image processings. 
When reading or reading out color density signals of three primary colors, 
the masking procedures is carried out in the CPU 34 by the use of a 
polynominal function including non-linear terms in order thus to obtain a 
fine color reproducibility faithful to the original color 11 having 
complex color. The form of the non-linear masking should be selected 
having regard for the characteristics of photometry and inks, and 
desirably utilizing quadratic terms, logarithmic terms, exponential 
function terms and the like as non-linear terms. 
The following matrix having variables which are, for example, color density 
signals of three primary colors, can be utilized in the non-linear 
masking: 
##STR1## 
The line-buffer memories 37 to 40 can memorize color image information for 
each picture element on four scanning lines which are sequentially read 
out from the memory 35. When simultaneously memorizing and reading out 
data, it is desirable to provide two line-buffer memories for every 
scanning line, and thus a total of eight line-buffer memories for four 
scanning lines. 
Four UCR circuits 41 to 44 are provided corresponding one to each 
line-buffer memory whereby the masking color density signals of yellow, 
magenta and cyan of each picture elements are reduced somewhat and whereby 
the amount of black ink to be used is determined, thereby to provide the 
color density signals of yellow, magenta, cyan and black. A dot pattern 
generator 45 to 48 is provided for each UCR circuit, with its input 
terminal connected with the output terminal of the latter. Consequently 
the dot pattern generator 45 receives only the color density signals of 
yellow output from the UCR circuit 41, the dot pattern generator 46 
receives only the color density signals of magenta output from the UCR 
circuit 42, the dot pattern generator 47 receives only the color density 
signals of cyan output from the UCR circuit 43 and the remaining one 
receives the density signals of black output from the UCR circuit 44. In 
each of the dot pattern generators 45 to 48, the locations and sizes of 
the ink dots to be depicted in a dot matrix, having n.times.m, for 
instance 3.times.3, possible positions for constructing an image element 
are determined in accordance with color density signals by referring to a 
predetermined table. Thus the dot pattern generator 45, when a series of 
yellow color density signals is fed thereto, converts these into three 
series of yellow color dot signals. In the case of a dot matrix of 
4.times.4 possible positions for an image element, a dot pattern generator 
for producing four series of color dot signals can be employed. 
Four printing head driving means 49 to 52, each of which includes three 
driving circuits, are provided corresponding to dot pattern generators 45 
to 48, respectively. Printing head driving means 49 to 52, each of which 
includes three printing head driving circuits for each color and thus a 
total of 12 circuits for four colors, receive three series of dot signals 
from dot pattern generators 45 to 48, respectively. Each printing head 
driving circuit selects one of a plurality of voltage values, for 
instance, one of six voltage values into which the voltage difference 
between 80 to 250 volts is divided, in accordance with a dot signal to 
provide a printing head driving signal by modulating the voltage with a 
carrier signal of, for instance, 20 kHz frequency. 
The ink-jet printer apparatus 3 ejects a series of ink drops from a head 
assembly onto a recording medium, for instance a white paper 55, wrapped 
around a rotary drum 54, to form a color image. The rotation of the rotary 
drum 54 is caused by a pulse motor 57 to which driving pulses are fed from 
the CPU 34. The pulses fed to the pulse motor 57 are counted by a pulse 
counter 58 which is adapted to reset to zero each time the rotary drum 54 
makes one revolution so that the position of a head assembly 56 relative 
to the white paper 55 is indicated in the primary scanning direction, 
while signals of the information of positions in the primary scanning 
direction can be fed to the CPU 34. 
As shown in FIG. 1, provided along and close to the outer surface of the 
rotary drum 54 is the head assembly 56 which is comprised of four groups 
of ink-jet heads 59 to 62 for yellow, magenta, cyan and black. Each group 
of ink-jet heads is comprised of three ink-jet heads of the conventional 
drop-on-demand type to which the particular printing fluid or ink is 
supplied from a reservoir (not shown). 
Furthermore, if the color printing speed is to be slow, a single ink-jet 
head for each color may be used. 
All the groups of ink-jet heads 59 and 62 are simultaneously driven to form 
three dot lines on the recording paper 55, so that a single color picture 
element is formed in the form of a dot matrix consisting of three dot 
lines on each of which three ink dots may be distributed. A picture 
element with half-tone can be formed in about 30 to 70 steps of gradation 
depending on the variation of sizes and arrangement of ink dots to be 
distributed in a single dot matrix having three possible positions in both 
the row and the column. A picture element having complex colors can be 
formed in such a way as to arrange ink dots of four kinds of colors having 
various sizes in a matrix; and this is an arranging color mixture (mean 
value color mixture) similar in its effects to the additive color mixture 
or the subtractive color mixture technique. 
A plurality of groups of ink-jet heads 59 to 62 are arranged in the 
secondary scanning direction with separation from each other a distance 
comprising the width of several tens of scanning lines therebetween; hence 
ink drops can be prevented from being turbid and flowing since the colored 
ink drops previously deposited on a recording paper 55, after they soak 
in, are laid by the other color ink drops. Furthermore, because it 
suffices to mount to plurality of groups of ink-jet heads 59 to 62 on a 
straight support member 63, the head assembly can be constructed with 
simplicity, whilst the adjustment of the distance between the head 
assembly and the rotary drum can be performed easily compared with 
conventional head assemblies arranged in the direction of the 
circumference of a rotary drum. The distances between each two adjacent 
groups of ink-jet heads can be adjusted to differ from each other 
depending on the characteristics of the inks and recording papers used. 
They can as well be adjusted to be equal distances. Consequently it is 
possible to make the distance between groups of ink-jet heads 59 and 60 
larger than that between groups of ink-jet heads 61 and 62 in order to 
prevent more completely ink drops from becoming turbid and flowing. 
The head assembly 56 is attached to a movable supporting member 66 which 
can be moved in a direction parallel to the axis of the rotary drum 54 by 
means of a feed screw shaft 64 and a guide rod 65. The feed screw shaft 64 
is adapted to be rotated by a pulse motor 67 which is caused to rotate by 
the output of driving pulse signals from the CPU 34. A counter 68 counts 
the driving pulses fed to the pulse motor 67 to indicate the number of 
driving pulse signals. Here, since a plurality of groups of ink-jet heads 
are arranged with separation in the secondary scanning direction, it is 
necessary for each group of ink-jet heads to detect its positions. For 
this, each group of ink-jet heads 59 to 62 is provided with a scanning 
counter 69 to 72, respectively, which begins to count driving pulses 
subsequently to a resetting thereof to the value initially set in 
accordance with the position of the group of ink-jet heads relative to the 
rotary drum 54. 
When printing a color image, the CPU 34 generates driving pulse signals to 
drive the pulse motors 57 to 67 in such a way as to move the head assembly 
56 in the secondary scanning direction by a regular distance equal to a 
scanning pitch every time the rotary drum 54 makes one revolution. As the 
positions of ink-jet heads 59 to 62 are detected by counters 69 to 72, 
respectively, color density signals of three primary colors of picture 
elements on four scanning lines are sequentially read out according to the 
respective line from the memory by addressing the lines depending on said 
positions detected when groups of ink-jet heads 59 to 62 should 
simultaneously eject ink drops toward a recording paper. Said color 
density signals of three primary colors are masked by non-linear equation 
to generate color density signals of the primaries, namely, yellow, 
magenta and cyan, the signals being written sequentially in an extremely 
short time into line buffer memories 37 to 40 provided for the respective 
groups of ink-jet heads 59 to 62. Furthermore, the color density signals 
of the primaries memorized in the line buffer memories 37 to 40 are 
converted into four color density signals of yellow, magenta, cyan and 
black by means of the UCR circuits 41 to 44 and thus fed to the dot 
pattern generators 45 to 48 for four colors in each of which a single 
series of color density signals fed thereto is converted into three series 
of dot signals. A series of dot signals is read out depending on the 
position signals from the counter 58 in order to position the head 
assembly 56 relative to the rotary drum 55. 
The three series of dot signals are fed to head driving means 49 and 52 and 
then are converted into analog head driving voltage. This head driving 
voltage causes the group of ink-jet heads to eject ink drops toward the 
recording paper 55 running in the primary scanning direction, thus 
painting three rows of ink dots. The same procedure described above is 
replicated for the other colors. Therefore four lines of different color, 
namely cyan, magenta, yellow and black, each line of which is constructed 
from three rows of the same color ink dots, are simultaneously painted. As 
a result, a dot matrix of three possible positions on the row and column 
constructing one picture element is filled with four different colors of 
ink dots by the motion of the head assembly 56 in the secondary scanning 
direction by steps of one scanning pitch equal to three times a dot's 
size, so as to compose the complex colors. 
Details of the structure and color printed ink dot patterns of the above 
color image information processing apparatus 2 and color printer 3 are 
disclosed in copending U.S. patent application Ser. No. 346,908 filed Feb. 
8, 1982, the disclosure of which is incorporated herein by reference. 
The image processed by the color image information processing unit 2 will 
be confirmed by the use of a television monitor and furthermore can be 
reformed following observation of the image displayed so as to reproduce a 
desirable image. Furthermore by memorizing processed image information 
signals into the memory 35, a plurality of identical images can be 
reproduced. 
According to the present invention, an improved color reproducibility can 
be obtained by the use of combinations of inks of yellow, magenta and cyan 
dyes to be described below as well as by the use of non-linear masking 
techniques described previously. 
Examples of yellow ink are aqueous inks comprising a yellow dye of the 
formula [I] 
##STR2## 
wherein R.sub.1 is amino or acylamino (e.g. acetylamino), R.sub.2 is 
phenyl, phenyl substituted by chlorine, alkoxy, alkyl, sulfo or carboxyl, 
C.sub.1-4 lower alkyl or lower alkyl substituted by sulfo or carboxyl, 
R.sub.3 is C.sub.1-4 lower alkyl or phenyl, X.sub.1 is halogen (e.g. 
chlorine), C.sub.1-4 lower alkyl, C.sub.1-4 alkoxy, sulfo, carboxyl, 
amino, substituted amino (e.g. acetylamino), cyano, C.sub.1-4 
alkylsulfonyl, nitro, hydroxyl, ureido or alkoxycarbonyl, j is 0, 1, 2 or 
3, provided that when j is 2 or 3, X.sub.1 can be the same or different, 
and the number of sulfo groups is 1-3. 
Examples of magenta ink are in aqueous ink comprising magenta dye of the 
formula [II-a], [II-b] or [II-c]: 
##STR3## 
wherein R.sub.4 is cyano, C.sub.1-4 alkylsulfonyl, arylsulfonyl (e.g. 
phenylsulfonyl, p-chlorophenylsulfonyl or p-chlorophenylsulfonyl), 
trifluoromethyl, trichloromethyl or halogen (e.g. chlorine or bromine), 
R.sub.5 is amino, acylamino (e.g. acetylamino), substituted ureido (e.g. 
with alkyl, C.sub.1-4 alkoxy, or acyloxy), R.sub.6 is hydrogen, C.sub.1-4 
lower alkyl, phenyl or ceyl (e.g. acetyl or benzoyl), and k is 0 or 1. 
##STR4## 
wherein R.sub.7 is hydrogen, acyl (e.g. acetyl or benzoyl), C.sub.1-4 
lower alkyl or phenyl, X.sub.2 is halogen (e.g. chlorine or bromine), 
C.sub.1-4 lower alkyl, C.sub.1-4 alkoxy, sulfo, carboxyl, amino, 
substituted amino (e.g. acetylamino), cyano, C.sub.1-4 alkylsulfonyl, 
nitro, hydroxyl, ureido or C.sub.2-5 alkoxycarbonyl, l is 0 or 1, and m is 
0, 1, 2 or 3, provided that when m is 2 or 3, X.sub.2 can be the same or 
different. 
##STR5## 
wherein R.sub.8 is hydrogen, C.sub.1-4 lower alkyl or phenyl, R.sub.9 is 
hydroxy, C.sub.1-4 lower alkyl, phenyl, C.sub.2-5 alkoxycarbonyl, carboxyl 
or cyano, X.sub.3 is C.sub.1-4 lower alkyl, halogen (e.g. chlorine or 
bromine), C.sub.1-4 alkoxy, carboxyl, cyano, hydroxyl or nitro, X.sub.4 is 
hydrogen or C.sub.1-4 lower alkyl, n is 1, 2 or 3, and p is 0, 1, 2, 3 or 
4 provided than when p is 3 or 4, X.sub.3 can be the same or different. 
An example of such a cyan ink is an aqueous ink comprising a cyan dye of 
the formula [III] 
##STR6## 
wherein q is 1 to 4. 
In the compounds of formulae [I], [II-a], [II-b], [II-c] and [III], the 
sulfo group can be an alkali metal salt such as a sodium or potassium 
salt, an ammonium salt or an organic amine salt such as triethylamine, 
pyridine or triethanolamine salt. 
The preferred groups in the compounds of formula [I] are amino for R.sub.1, 
phenyl or phenyl substituted by sulfo or chlorine, or sulfoalkyl, most 
preferably phenyl or phenyl substituted with chlorine or sulfo for 
R.sub.2, methyl or phenyl for R.sub.3, and chlorine, C.sub.1-3 lower alkyl 
(e.g. methyl or ethyl) or sulfo for X.sub.1. The number of sulfo groups in 
the compound of formula [I] is preferably 1 or 2. 
The preferred groups in the compounds of formula [II-a] are cyano, 
C.sub.1-2 alkylsulfonyl or halogen (e.g. chlorine or bromine) for R.sub.4, 
amino or acylamino (e.g. acetylamino), and hydrogen or acyl (e.g. acetyl) 
for R.sub.6. k is preferably 0. 
Preferred groups in the compounds of formula [II-b] are hydrogen or acyl 
(e.g. acetyl or benzoyl) for R.sub.7, and C.sub.1-4 alkoxy (e.g. methoxy 
or ethoxy), or halogen (e.g. chlorine or bromine) for X.sub.2. l is 
preferably 1. 
The preferred groups in the compounds of formula [II-c] are hydrogen or 
C.sub.1-3 lower alkyl (e.g. methyl or ethyl) for R.sub.8, hydrogen or 
C.sub.2-4 alkoxycarbonyl (e.g. methoxycarbonyl or ethyoxycarbonyl) for 
R.sub.9, C.sub.1-4 lower alkyl (e.g. methyl or ethyl), or halogen (e.g. 
chlorine) for X.sub.3, and hydrogen or methyl for X.sub.4. n is preferably 
1 or 2. 
In the compounds of formula [III], q is preferably 2 to 4. 
Embodiments of yellow, magenta and cyan dyes in the aqueous inks of the 
present invention are illustrated as follows, but are not to be construed 
as limiting the invention. 
Yellow dye: 
##STR7## 
Magenta dye: 
##STR8## 
Cyan dye: 
##STR9## 
The ratio of water-soluble dyes in the aqueous ink used in the present 
invention is usually 0.5-4 parts by weight per 100 parts by weight of ink. 
If the content is less than 0.5%, the coloring agent is ineffective. Use 
of more than 4% results in the precipitation of the dye from the ink in 
the course of time even though the dye is in solution, and is not suitable 
for jet-printing inks. 
Wetting agents are preferably added to the aqueous ink of the present 
invention for improving the dryness-resistance of the ink and to aid in 
dissolving the dye. The preferred wetting agents are non-volatile at 
normal temperature, have more than 30 dyne/cm of surface tension, and 
preferably more than 45 dyne/cm at normal temperature, and a viscosity of 
less than 5 cps in 3-40% solution. Furthermore it is preferred to use more 
than 1% of the water soluble dye described hereinbefore. 
Preferred examples of wetting agents are 2-pyrrolidones (Jap. Pat. 
Unexamined Publ. Nos. 50-71423, 51-5127 and 51-137505), carboxylic 
acidamide derivatives (ibid. Nos. 49-97620, 51-8031 and 51-8033), lactones 
(ibid. No. 55-48207), 2,2'-thiodiethanol (ibid. No. 51-5129), alcohol 
amines (ibid. No. 51-52004), N-formyl lactam derivatives (ibid. No. 
51-31525), polyalkyleneglycols and polyalkyleneglycol monoesthers (Jap. 
Pat. Examined Publ. No. 51-40484), Jap. Pat. Unexamined Publ. Nos. 51-1375 
and 54-12909), primary alcohols such as t-butylalcohol and n-amylalcohol 
(Jap. Pat. Unexam. Publ. No. 51-129310), cellulose derivatives such as 
hydroxypropyl cellulose and polyvinyl alcohol (ibid. No. 50-17840), 
polyoxyethylene sorbitan fatty acid esters, polyoxyethylene fatty acid 
esters, polyoxyethylene alkylphenyl ethers (ibid. No. 50-143602) and water 
soluble alginic acid salts, and 1,3-dialkyl-2-imidazolidinones such as 
N,N'-dimethyl-1,3-imidazolidinone-(2) (ibid. No. 54-62005). 
The amount of wetting agent used in the present invention can be varied 
according to its nature, and is preferably 0.2-30 parts by weight per 100 
parts by weight of ink. 
The aqueous ink used in the present invention can contain more than two 
kinds of wetting agents as described hereinabove. 
Black dye can be used together with the yellow, magenta and cyan dyes of 
the formulae [I], [II] and [III], respectively. 
Preferred black dyes are direct dyes or acid dyes disclosed in Jap. Pat. 
Unexamined Publ. Nos. 50-15622, 50-17840, 50-49004, 51-5127, 51-5128, 
51-52004, 51-137506, 53-61412 and 53-77706, and Jap. Pat. Examined Publ. 
No. 54-16243. 
Fungicides and oxygen absorption agents can be added to the ink used in the 
present invention. 
Preferred fungicides are sodium dehydro acetate (Jap. Pat. Unexamined Publ. 
No. 52-12008), benzisothiazolin-3-one, (ibid. No. 52-12009), 
6-acetoxy-2,4-dimethyl-m-dioxane (ibid. No. 52-12010), formalin and sodium 
pentachlorophenyl (ibid. No. 50-15622), and sodium benzoate (ibid. No. 
53-135707). 
Preferred oxygen absorption agents are sulfites such as sodium sulfite or 
sodium bisulfite (Jap. Pat. Unexam. Publ. Nos. 52-74406 and 53-61412). 
Anionic surface active agents such as sodium alkyl sulfate esters, cationic 
surface active agents such as alkylpyridinium sulfates and nonionic 
surface active agents such as polyoxyethylene alkyl ethers or amphoteric 
surface active agents can be added to the aqueous ink of the present 
invention as a surface tension modifier. 
In the ink-jet color printing system of the present invention, any 
recording medium commonly used in the conventional ink-jet recording 
systems using aqueous ink can be used. A typical recording medium is 
paper. Commercially available hign-quality paper, continuous strip paper, 
art paper or coated paper can be used for recording. Preferred papers are 
low-density manufactured papers without added sizing agent, ink-jet 
recording papers of good absorbancy and non-blurring papers (Jap. Pat. 
Unexam. Publ. Nos. 52-53012, 52-74340 and 53-49113) or specifically 
treated ink-jet recording papers (ibid. Nos. 55-144172 and 55-146786). 
Also cloth, plastic-film-coated surfaces with an ink-absorbing agent, wood 
plates or metal plates can be used. 
The present invention is explained in more detail with reference to the 
following example: 
EXAMPLE 
______________________________________ 
(1) Yellow ink: Parts by weight: 
______________________________________ 
Dye (Y-1) 2.8 
Diethyleneglycol 1.0 
2,2'-Thiodiethanol 16.0 
Nonionic surface active agent 
0.2 
##STR10## (z: about 9) 
Water 80.0 
______________________________________ 
The above mixture was stirred at 40.degree.-50.degree. C. for one hour, and 
press-filtered through a microfilter Type FM (0.8.mu., 47 .phi., Fuji 
Photo Film Co.) to prepare yellow ink. 
______________________________________ 
(2) Magenta ink: 
______________________________________ 
Dye (M-8) 1.2 
Diethyleneglycol monoethyl ether 
0.5 
Nmethyl-2-pyrrolidone 15.0 
Nonionic surface active agent 
0.3 
##STR11## (z: about 9) 
Water 83.0 
______________________________________ 
The above mixture was treated in the same way as hereinabove to prepare 
magenta ink. 
______________________________________ 
(3) Cyan ink: 
______________________________________ 
Dye (C-1) 2.4 
Diethyleneglycol monobutyl ether 
0.5 
Nmethyl-2-pyrrolidone 10.0 
Nhydroxyethyl lactamide 5.0 
Nonionic surface active agent 
0.1 
##STR12## (z: about 9) 
Water 82.0 
______________________________________ 
The above mixture was treated in the same way as hereinabove to prepare 
cyan ink. 
(4) Recording paper: 
100 parts by weight of LBKP were beaten in CSF (430 cc). Talc 5 parts, 
saponified rosin 1 part and band sulfate 2 parts were added thereto, and 
paper of the weight 152 g/m.sup.2 was produced on a paper machine. 
Oxidized starch was spread (2 g/m.sup.2) on the paper by a size-press. 
A spreading solution containing 12.3% solid matter, comprising synthetic 
zeolite 100 parts, gelatin 100 parts, hydroxyethyl cellulose 38.5 parts, 
hardening agent 10 parts and surface active agent 0.12 part was spread at 
the rate of 6.6 g/m.sup.2 on the surface of the above paper by a bar 
coating method and dried. The surface was smoothed with a super calender. 
(5) Ink-jet color printing apparatus: 
Color image information input unit: drum scanner; 
Characteristic of color filters used for color separation on color image 
information input unit: shown in FIG. 2; 
Memory device: magnetic disc (capacity 40 MB); 
Detecting means for position of the head: pulse counter; 
Image information processing unit: PANAFACOM U-1500 minicomputer; 
Ink-jet ejecting heads: drop-on-demand type head; 
Head driving frequency: 20 KHz. 
(6) Masking equation: 
In the matrix hereinbefore, a masking equation of 10 terms comprising 
primary, quadratic and constant terms, was used for color correction. 
The following coefficients A.sub.ij were used: 
______________________________________ 
A.sub.11 
0.062500 A.sub.21 
0.031250 
A.sub.31 
0.968750 
A.sub.12 
-0.046875 A.sub.22 
0.859375 
A.sub.32 
-0.375000 
A.sub.13 
0.953125 A.sub.23 
-0.109375 
A.sub.33 
0.140625 
A.sub.14 
0.031250 A.sub.24 
0.203125 
A.sub.34 
0.906250 
A.sub.15 
0.281250 A.sub.25 
0.281250 
A.sub.35 
-0.125000 
A.sub.16 
0.109375 A.sub.26 
-0.109375 
A.sub.36 
-0.0.5625 
A.sub.17 
-0.093750 A.sub.27 
-0.218750 
A.sub.37 
0.812500 
A.sub.18 
-0.187500 A.sub.28 
1.171875 
A.sub.38 
-0.843750 
A.sub.19 
0.531250 A.sub.29 
-0.265625 
A.sub.39 
-0.031250 
A.sub.110 
0.093750 A.sub.210 
0.203125 
A.sub.310 
0.093750 
______________________________________ 
The above values are standardized within the range of values from -2 to +2, 
and the terms A.sub.110, A.sub.210 and A.sub.310 are constants. 
In the above combination, the ink-jet print reproduction image was produced 
with a color paper printed from a negative obtained by photographing the 
24-color Macbeth Color Chart, as an original, to obtain the color 
reproduction characteristics shown in FIG. 3. In that figure, chromaticity 
is shown by the CIE (1964) (U*V*W*) color representation system. 
The present invention was compared with known ink-jet printing reproduction 
images prepared by ink-jet color printing systems. The color reproduction 
characteristics shown in FIG. 4 were obtained in the case of linear 
masking. But the improved color reproduction characteristics of the 
present invention were confirmed by comparison of FIGS. 3 and 4. 
__________________________________________________________________________ 
(1') 
Yellow ink: 
__________________________________________________________________________ 
Dye-1 (control) (refer to Jap. Pat. Unexam. Publ. No. 54-89811) 
1.4 
parts by weight 
##STR13## 
Diethyleneglycol 1.6 
2,2'-Thiodiethanol 10.0 
Nmethyl-2-pyrrolidone 6.0 
Nonionic surface active agent 0.2 
##STR14## (z: about 9) 
Water 80.0 
__________________________________________________________________________ 
Yellow ink as a control was prepared by the same preparation procedure as 
mentioned hereinbefore. 
______________________________________ 
(2') Magenta ink: 
______________________________________ 
Dye-2 (control) (refer to Jap. Pat. 
1.8 parts by 
Unexam. Publ. No. 54-89811) weight 
##STR15## 
Diethylene glycol 1.0 
2,2'-Thiodiethanol 10.0 
Nmethyl-2-pyrrolidone 6.0 
Nonionic surface active agent 
0.2 
##STR16## (z: about 9) 
Water 80.0 
______________________________________ 
Magenta ink as a control was prepared by the same procedure as mentioned 
hereinabove. 
______________________________________ 
(3') Cyan ink: 
______________________________________ 
Dye-3 (control) (refer to Jap. Pat. 
2.0 parts by 
Unexam. Publ. No. 54-89811) weight 
##STR17## 
Diethylene glycol monobutyl ether 
0.5 
Nmethyl-2-pyrrolidone 10.0 
Nhydroxyethyl lactamide 5.0 
Nonionic surface active agent 
0.1 
##STR18## (z: about 9) 
Water 82.0 
______________________________________ 
Cyan ink as a control was prepared by the same preparation procedure as 
described hereinabove. 
(4') Recording paper: 
The same recording paper as mentioned in item (4) hereinbefore. 
(5') Color ink-jet printing apparatus: 
The same color ink-jet printing apparatus as mentioned in item (5) 
hereinbefore. 
(6') Masking equation: 
In the matrix formula given hereinbefore, the cubic term masking equation 
consisting of a primary term, wherein the coefficient A.sub.ij was used 
for color correction as follows: 
______________________________________ 
A.sub.11 
0.062500 A.sub.21 
0.031250 
A.sub.31 
0.968750 
A.sub.12 
-0.046875 A.sub.22 
0.859375 
A.sub.32 
-0.375000 
A.sub.13 
0.953125 A.sub.23 
-0.109375 
A.sub.33 
0.140625 
______________________________________ 
in which the values thereof are standardized within the range from -2 to 
+2. 
In the preferred embodiments of the invention, a scanning apparatus is 
comprised of a rotary drum movable in the primary scanning direction and a 
scanning head assembly intermittently movable in the secondary scanning 
direction; however, in the case of color originals such as hard sheets 
like metal, it may be so modified as a planar scanning device or a TV 
camera device. 
As many apparently widely different embodiments of this invention may be 
made without departing from the spirit and scope thereof, it is to be 
understood that the invention is not limited to the specific embodiments 
thereof except as defined in the appended claims.