Patent Grant
9888149
Field of the Invention
The present invention relates to an image printing apparatus using color materials and an image printing method. In particular, the present invention relates to a color material for obtaining a smooth color image with reduced graininess.
Description of the Related Art
A printing apparatus for printing an image through a subtractive process by a pseudo halftoning method uses color materials of three primary colors for printing: cyan, magenta, and yellow. By adjusting the numbers of dots of the three primary colors and a balance among the three primary colors, various densities and colors are represented on a paper surface. Further, many color printing apparatuses use a black color material in addition to the above-mentioned three primary colors to improve contrast and color stability in an achromatic color image.
In an image printing apparatus using the pseudo halftoning method, graininess has been one of the problems to be solved. Recently, graininess has been made less visible, for example, by using a print head capable of ejecting a small droplet ink to reduce the size of a dot on the paper surface or by using ink having a higher lightness than cyan and magenta, such as light cyan ink and light magenta ink. However, preparing additional ink such as light cyan and light magenta may lead to upsizing of the apparatus and an increase in running costs.
Japanese Patent Laid-Open No. 2002-154240 discloses a method for preparing light blue instead of light cyan and light magenta by taking into consideration the fact that graininess caused by overlaying cyan ink and magenta ink, in particular, tends to be a problem associated with an image. Using light blue as disclosed in Japanese Patent Laid-Open No. 2002-154240 can effectively reduce graininess in an image while limiting the types of additional color materials to one.
Japanese Patent Laid-Open No. 2002-154240 discloses setting the lightness of light blue ink higher than that of cyan ink and magenta ink, but it does not particularly explain other features. Accordingly, even if graininess in, for example, a highlight in a blue image is reduced, graininess sometimes becomes conspicuous in other areas depending on gradations and hues. In particular, in a case where there is a great difference in lightness between light blue ink and cyan ink or magenta ink, graininess may be worse in an area in which cyan dots and magenta dots or blue dots formed by overlaying the cyan dots and the magenta dots are sparsely printed in a light blue image area.
The present invention has been made to solve the above problem. An object of the present invention is to provide an image printing apparatus capable of printing an image in which graininess is suppressed in all gradations and hues while using a color material of light blue, and an image printing method.
According to a first aspect of the present invention, there is provided an image printing apparatus for printing an image on a print medium by using a plurality of color materials including at least cyan, magenta, and light blue, wherein the color material of light blue satisfies:
ΔLB≧(ΔLC−ΔLB)>0 and
ΔLB≧(ΔLM−ΔLB)>0
where ΔLC represents a difference between lightness of the image printed on the print medium with the color material of cyan and lightness of a blank area in the print medium, ΔLM represents a difference between lightness of the image printed on the print medium with the color material of magenta and lightness of the blank area in the print medium, and ΔLB represents a difference between lightness of the image printed on the print medium with the color material of light blue and lightness of the blank area in the print medium; and
hC+(h(C+M)−hC)/2≦hB≦hM−(hM−h(C+M))/2
where hC represents a hue of the image printed on the print medium with the color material of cyan, hM represents a hue of the image printed on the print medium with the color material of magenta, h(C+M) represents a hue of the image printed on the print medium with the color material of cyan and the color material of magenta in the same amount, and hB represents a hue of the image printed on the print medium with the color material of light blue.
According to a second aspect of the present invention, there is provided an image printing method for printing an image on a print medium by using a plurality of color materials including at least cyan, magenta, and light blue, wherein the color material of light blue satisfies:
ΔLB≧(ΔLC−ΔLB)>0 and
ΔLB≧(ΔLM−ΔLB)>0
where ΔLC represents a difference between lightness of the image printed on the print medium with the color material of cyan and lightness of a blank area in the print medium, ΔLM represents a difference between lightness of the image printed on the print medium with the color material of magenta and lightness of the blank area in the print medium, and ΔLB represents a difference between lightness of the image printed on the print medium with the color material of light blue and lightness of the blank area in the print medium; and
hC+(h(C+M)−hC)/2≦hB≦hM−(hM−h(C+M))/2
where hC represents a hue of the image printed on the print medium with the color material of cyan, hM represents a hue of the image printed on the print medium with the color material of magenta, h(C+M) represents a hue of the image printed on the print medium with the color material of cyan and the color material of magenta in the same amount, and hB represents a hue of the image printed on the print medium with the color material of light blue.
Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings).
Preferable embodiments of the present invention will be described with reference to the attached drawings.
The print head 101 according to the present embodiment can eject inks of five colors: cyan, magenta, yellow, black, and light blue. The carriage 108 has the print head 101 and five ink tanks for supplying inks to the print head 101. When performing maintenance processing on the print head 101, the carriage 108 moves to a home position H shown in the figure. Various mechanisms are provided in the home position H for performing suction processing, wiping processing, and preliminary ejection processing on the print head 101.
On a print chip 102 for black ink, nozzles that eject black ink as droplets are arranged in Y direction. Meanwhile, on a print chip 103 for color inks, a nozzle array 203 for ejecting cyan ink, a nozzle array 204 for ejecting magenta ink, a nozzle array 205 for ejecting yellow ink, and a nozzle array 206 for ejecting light blue ink are provided. These five nozzle arrays are arranged in parallel in X direction as shown in
It should be noted that the configuration of the print head applicable to the present embodiment is not limited to the one shown in
In the image printing apparatus 100, constituent elements may be divided into software control units and hardware processing units. Examples of the software control units include processing units such as an image input unit 305, an image signal processing unit 306, and a central processing unit (CPU) 300 which has control over the image printing apparatus 100. The image input unit 305 is used to temporarily store an image received from the host device 200 via an interface (I/F) 318, and image data inputted to the image input unit 305 is sequentially processed by the image signal processing unit 306.
Meanwhile, examples of the hardware processing units include processing units such as an operation unit 303, a display unit 304, a maintenance operation control circuit 313, a head temperature control circuit 312, a head driving control circuit 310, a carriage driving control circuit 308, and a conveyance control circuit 309. The operation unit 303 receives a command from a user and the display unit 304 displays information provided to the user. The maintenance operation control circuit 313 operates a blade 315, a cap 316, and a suction pump 317 by using a recovery motor 314 so as to perform various kinds of maintenance processing on the print head 101 which has moved to the home position H. The head driving control circuit 310 drives the print head 101 according to a print signal generated by the image signal processing unit 306 and a detection result of a thermistor 311. The head temperature control circuit 312 adjusts a temperature of the print head 101 based on the detection result of the thermistor 311. The carriage driving control circuit 308 drives a carriage motor 326 for a reciprocation scanning of the carriage 108 in the X direction. The conveyance control circuit 309 drives a conveying motor 327 to rotate the conveying roller 106 and the discharge roller 104 and conveys the print medium P in the Y direction. The above mechanisms are connected to each other via a bus line 307 and controlled by the CPU 300.
The CPU 300 has a ROM 301 and a RAM 302. While using the RAM 302 as a work area, the CPU 300 generally controls the image printing apparatus 100 according to programs and various parameters stored in the ROM 301. For example, upon receiving a print command, the CPU 300 sets a driving pulse to be applied to the heater of the print head 101 according to a table stored in advance in the ROM 301 and provides the driving pulse to the head driving control circuit 310. Further, based on a print mode set by the user, the CPU 300 reads a corresponding driving condition of the carriage 108 and a corresponding conveying condition of the print medium from the table stored in advance in the ROM 301, and provides them to the carriage driving control circuit 308 and the conveyance control circuit 309. The ROM 301 stores also a timing chart program for performing maintenance processing on the print head. The CPU 300 controls the maintenance operation control circuit 313 and the print head 101 according to the timing chart program and appropriately performs a preliminary ejection operation and a suction recovery operation.
The host device 200 connected externally to the image printing apparatus 100 may be a mobile phone, a smartphone, a tablet, a digital camera, other portable/stationary terminals, and the like as well as a common PC. An internal configuration of the host device 200 changes depending on a main purpose of the apparatus, but generally includes a CPU 319, an operation unit 322, a display unit 323, and an interface I/F 324. These mechanisms are electrically connected to each other via a bus line 325. A keyboard and a mouse, for example, can be applied to the operation unit 322. An LCD, for example, can be applied to the display unit 323.
Next, an ink color separation processing unit converts an RGB luminance signal generated in the color correction unit 401 into a density signal corresponding to an ink color used in the printing apparatus 100. More specifically, with reference to the three-dimensional lookup table stored in advance in the ROM 301, an 8-bit RGB signal is converted into an 8-bit density signal of black (K), cyan (C), magenta (M), yellow (Y), and light blue (LB).
The 8-bit density signal after separation into an ink color is inputted to a γ correction unit 403, and a density value is corrected for each ink color. The γ correction is performed so that the inputted density signal and an optical density represented on the print medium have a linear relationship. More specifically, with reference to a one-dimensional lookup table stored in advance in the ROM 301, 8-bit density data for each ink color is converted into other 8-bit density data.
After that, the 8-bit density data corresponding to each ink color is subjected to quantization processing in a quantization unit 404. In the present embodiment, a method for quantization processing is not particularly limited, and a dither method, an error diffusion method, and the like may be employed. Furthermore, a signal value after the quantization may be binary or multi-valued.
In a case where data after the quantization is multi-valued, the quantized data is sent to an index-expansion unit 405 and converted into a binary signal in the index-expansion unit 405. More specifically, an index pattern in which printing (1) or non-printing (0) of a dot is defined for each print pixel is read and outputted for each 600 dpi input pixel. The index pattern will be described later in detail.
Then, the binary data is sent to a mask data conversion unit 406. The mask data conversion unit 406 determines in which printing scan a dot determined to be printed in index-expansion processing is to be printed in multi-pass printing of the printing apparatus. More specifically, a mask pattern in which allowance (1) or non-allowance (0) of the printing of a dot corresponding to each printing scan in the multi-pass printing is defined is ANDed with the binary signal outputted from the index-expansion unit 405, and dot print data is distributed to each printing scan. In a case where the multi-pass printing is 1-pass printing, processing by the mask data conversion unit 406 is omitted.
The binary signal outputted from the mask data conversion unit 406 is sent to the head driving control circuit 310, and the head driving control circuit 310 causes the print head 101 to perform the ejection operation according to the binary signal.
Incidentally, not all the series of processing described above with reference to
Here, a detailed description will be given of an index pattern suitable for the present embodiment used in the index-expansion unit 405.
S≦R≦S√2.
Meanwhile, in a case where a print resolution is anisotropic, each print pixel is a rectangle.
T≦R≦(T√5)/2.
In addition, the dot layout according to an increase in the gradation level also affects not only lightness but also graininess of an image. That is, if a plurality of dots are continuously arranged in a short side direction as shown in the right column of the figure from the stage of a low gradation level, an overlapping area may be large irrespective of the remaining blank area, and graininess may become conspicuous. Accordingly, as shown in the center column of the figure, the layout is preferable in which dots are arranged in print pixels in a dispersed manner as much as possible in the short side direction.
In a case where a plurality of pixels of input data at level 1 continue as shown in
It should be noted that in the above example, by making the index pattern characteristic, the overlaps of dots are minimized in a density from a highlight to a halftone. However, also in a case where, for example, binarization is performed in the quantization unit 404 without providing an index-expansion unit 405, employing a quantization processing method to increase dispersibility among dots in the density from a highlight to a halftone can suppress the overlaps of dots and make graininess less conspicuous.
(Characteristic Configuration)
A description will be given of a feature of color inks used as color materials in the present embodiment.
More specifically, a light blue ink (LB2) according to the present embodiment is prepared such that a difference in lightness ΔLB2 satisfies the following condition 1.
ΔLB≧(ΔLC−ΔLB)>0 and
ΔLB≧(ΔLM−ΔLB)>0 (condition 1)
The light blue ink as prepared under the condition 1 has a lightness that is higher than that of the cyan ink and the magenta ink, a dye density that is higher than that of a conventional light blue ink LB1, and a great difference in lightness ΔLB between the light blue ink and the blank area.
Meanwhile, in a case where LB2 having a great difference in lightness from the blank area is used, as can be seen in
Meanwhile, in a case where LB2 is used, cyan dots and magenta dots are not printed in the area [1], and only LB2 dots represent a predetermined gradation. Accordingly, graininess is low and a uniform image can be obtained (◯). In the area [2], LB2 dots, cyan dots, and magenta dots are mixed. However, since the LB2 dots have lightness that is not as high as that of the cyan dots and magenta dots, graininess is less likely to be detected (◯). Incidentally, in the area [3], since most part of the area is filled with cyan dots and magenta dots, whether LB1 is used or LB2 is used, graininess is not detected (◯).
Meanwhile,
Meanwhile, in the case of using LB2, as can be seen in
By the way, a description has been given on an assumption that the light blue ink has a hue that is just at the midpoint between the hues of the cyan ink and the magenta ink. However, the light blue ink for obtaining the above effect is not limited to this. According to the study of the inventors of the present invention, with respect to light blue ink LB, it is confirmed that the above-described effect of a decrease in graininess can be obtained as long as its hue angle hB, on an a*b* plane, satisfies the following condition 2.
hC+(h(C+M)−hC)/2≦hB≦hM−(hM−h(C+M))/2 (condition 2)
Here, hC is a hue angle of cyan ink, hM is a hue angle of magenta ink, and h(C+M) is a hue angle obtained in the case of printing cyan ink and magenta ink in the same amount. For example, if hC=210°, hM=330°, and h(C+M)=270°, the condition 2 is 240°≦hB≦300°. h(C+M) is not always an average of hC and hM, and for example if h(C+M)=280°, the condition 2 is 245°≦hB≦305°.
An example of color material components and color material densities of cyan ink, magenta ink, and light blue ink satisfying the above conditions 1 and 2 is shown below.
Each ink includes the following solvent: 10% of ethylene glycol, 10% of diethylene glycol, 1% of acetylenol E100, and pure water.
Preparing ink with the above components can satisfy both of the condition 1 and the condition 2, allowing output of an image having reduced graininess in all gradations and hues as compared to the conventional one.
It should be noted that in the above example, with respect to light blue ink, by taking into consideration continuity of hues in the case of applying cyan ink and magenta ink as well as light blue ink to a print medium, color material components used for the cyan ink and the magenta ink are mixed. However, such a mode does not limit the present embodiment. The light blue ink may contain a color material component that is different from those of the cyan ink and the magenta ink. In this example, a dye ink is used which includes a dye component as a color material, but a pigment ink including a pigment component may be used. In either case, as long as color materials of cyan, magenta, and light blue in a combination of satisfying the above conditions 1 and 2 are prepared, it is possible to produce an effect of a decrease in graininess.
As a modification example, a description will be given of a case where, while satisfying the above condition 2, a hue of light blue ink is shifted on purpose from an intermediate value between cyan ink and magenta ink. In the case of representing hues of blue and gray as shown in
Here, a description will be given of a case where a hue indicated by a star, which is a little closer to magenta than pure blue, is represented on the paper surface. In the case of using only cyan ink and magenta ink, the usage of magenta ink is greater than the usage of cyan ink as shown in the bar graphs of
In the case of using the light blue ink LB3 having a hue angle that is just at the midpoint between the hues of cyan ink and magenta ink, as shown in
Meanwhile, in the case of using the light blue ink LB4, since a hue of the light blue ink LB4 is a little inclined toward magenta, as shown in
It should be noted that in the above description, an example is given of the case where a hue to be represented is inclined toward magenta. Accordingly, an effect of LB4 having a hue inclined toward magenta is produced, and graininess of magenta ink is suppressed. However, in a case where the same ink is used to represent a color inclined toward cyan, a use frequency of cyan ink alone rather increases. However, as already described, in view of the fact that graininess of magenta ink is visually more conspicuous than graininess of cyan ink, the object of the present modification example is to suppress the use frequency of magenta dots alone as compared to the use frequency of cyan dots alone. Therefore, by preparing on purpose the light blue ink LB4 having a hue angle as shown in
In the above, a description has been given of the mode of using cyan, magenta, yellow, black, and light blue. However, combinations of color materials should not be limited to this. As long as cyan, magenta, and light blue are included, more color materials such as red and green may be added. Furthermore, in the above, a description has been given of the example of an ink jet printing apparatus that ejects ink as droplets, but the present invention should not be limited to such a mode. Any mode in which an image can be printed through a subtractive process may be applied to printing other than ink jet printing, such as an electrophotographic process. In either case, as long as the color materials of cyan, magenta, and light blue in a combination satisfying the above condition 1 and condition 2 are prepared, graininess can be suppressed in all gradations and hues as compared to the conventional one.
Embodiment(s) of the present invention can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a ‘non-transitory computer-readable storage medium’) to perform the functions of one or more of the above-described embodiment(s) and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described embodiment(s), and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s) and/or controlling the one or more circuits to perform the functions of one or more of the above-described embodiment(s). The computer may comprise one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2015-156823 filed Aug. 7, 2015, which is hereby incorporated by reference wherein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-156823 | Aug 2015 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5961703 | Fraas | Oct 1999 | A |
| 6061145 | Kanda | May 2000 | A |
| 6530638 | Shibata | Mar 2003 | B2 |
| 6652066 | Teshigawara | Nov 2003 | B2 |
| 7384460 | Hamajima | Jun 2008 | B2 |
| 9064202 | Tanaka | Jun 2015 | B2 |
| 20020063746 | Suzuki | May 2002 | A1 |
| 20020097412 | Shibata | Jul 2002 | A1 |
| 20020181987 | Kakutani | Dec 2002 | A1 |
| 20090058925 | Hayashi | Mar 2009 | A1 |
| 20120038708 | Ishii | Feb 2012 | A1 |
| 20120176432 | Hagiwara | Jul 2012 | A1 |
| 20170028739 | Ohnishi | Feb 2017 | A1 |
| Number | Date | Country |
|---|---|---|
| 1 403 334 | Mar 2004 | EP |
| 2002-154240 | May 2002 | JP |
| 2011-195783 | Oct 2011 | JP |
| Entry |
|---|
| European Office Action dated Dec. 19, 2016 during prosecution of related European application No. 16001641.6. |
| Number | Date | Country | |
|---|---|---|---|
| 20170041501 A1 | Feb 2017 | US |
