JP3235517B2 - Image recording device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image recording apparatus applied to a printer, a facsimile, a copier, and the like, and more particularly, to a color image recording apparatus for recording a color image by superimposing a plurality of color materials. It relates to a recording device.

[0002]

2. Description of the Related Art As a color image recording method used in a printer, a facsimile, a copying machine, etc., several methods such as an electrophotographic method, an ink jet method and a thermal transfer method have been put to practical use. Although these recording methods differ in the principle of recording, they are all common in that a color image is formed by superimposing images of a plurality of colors (usually three or four colors). In particular, the ink jet system, which performs printing by discharging minute ink droplets, is suitable for color printing because the size and cost of the printing head can be reduced, and is currently the mainstream in low-cost color printing apparatuses. ing. Therefore, in the present specification, the content of the invention will be described mainly with an example of an ink jet system, but the scope of the present invention is not necessarily limited to the ink jet system.

FIG. 7 shows a configuration of a conventional color ink jet recording apparatus. On the carriage 71, three recording heads 72 corresponding to three colors of yellow (Y), magenta (M), and cyan (C) are mounted. The recording head 72 includes a droplet forming unit 73 that forms and discharges ink droplets,
It is constituted by an ink tank 74 as a color material supply source.

A printer driver (not shown) sends a drive signal to each recording head after performing color separation of an output image and various data processing. Each recording head ejects minute ink droplets toward the recording paper 75 according to the drive signal. The recording head is scanned by the carriage in the width direction (A direction) of the recording paper, and the recording paper is transported in the length direction (B direction) in synchronization with the scanning of the carriage, so that recording is performed over the entire recording paper. Done.
Images of three colors of Y, M and C are superimposed on the recording paper to form a color image.

As described above, a color image is formed by using a plurality of recording heads that perform monochromatic recording. In the ink jet system, since individual recording heads can be reduced in size, it is easy to mount a plurality of heads on a carriage, which is an advantageous system as a color recording system.

[0006] In the above-described color recording apparatus, improvement of image quality is a major problem at present.
That is, in the conventional color ink jet recording apparatus and the like, there is a practical limit to the recording resolution, and it is difficult to freely control the density (gradation) of each pixel. For this reason, there is a certain limit in the image quality of the output image, and there is a problem that sufficient image quality cannot be obtained particularly when a pictorial image is output.

[0007] As a remedy for such a problem, it is effective to increase the kinds of color materials (inks) to be used. That is, while recording was conventionally performed in three colors of Y, M, and C, or four colors in which black (Bk) was added thereto, light yellow (LY), light magenta (LM), and light cyan with low density were used. By adding a color such as (LC), image quality can be significantly improved. Actually, a color ink jet printer using six color inks in which LM and LC are added to Y, M, C, and Bk has been developed, and an improvement in image quality has been realized.

[0008]

As described above, as the number of colors of the color materials (inks) used increases, the quality of an output image can be improved. However, in practice, the number of ink colors that can be used simultaneously is limited. This is because an increase in the number of ink colors means an increase in the number of recording heads, and thus an increase in the number of ink colors causes an increase in apparatus price and apparatus size. Therefore, it is practically difficult to unnecessarily increase the number of ink colors, and therefore, the image quality that can be obtained is limited.

Further, when the usable combination of ink colors is fixed, an increase in the number of ink colors may not lead to an improvement in image quality depending on an image to be output.
That is, a color material (ink) having a small number of pixels on an image
No matter how much is increased, the contribution to image quality improvement is low. This means that unless the ink color to be increased is selected according to the color distribution of the image, the image quality will not be improved. For example, assume that an image to be output is color-separated into Y, M, C, and Bk, and that a histogram as shown in FIG. 8 is obtained as a result of analyzing the pixel density distribution. In this image,
It can be seen that the M component is used most often and requires recording in a wide density region from low density to high density. On the other hand, the components of Y, C and Bk are small, and the required density region is also biased toward the low or high density side. If this image is to be printed by a printing apparatus using six colors of Y, M, C, Bk, LM, and LC, the ink color of C becomes almost unnecessary. In other words, in such a case, the image quality is almost the same as when using five ink colors, and even if the ink colors are increased to six colors, the effect of using six ink colors is obtained. It will be difficult to extract enough.

As described above, when the number of ink colors that can be used simultaneously is small, it is difficult to obtain sufficient color reproduction in an output image, and it is difficult to output a high quality color image. Was.

On the other hand, as a method of obtaining high color reproducibility with a limited ink color, there is a method of preparing and using an ink according to an image to be output. For example, in JP-A-7-81208,
In a charged-type inkjet device, by arbitrarily selecting and adjusting the color of the ink to be used corresponding to the image,
A method and apparatus for obtaining high color reproducibility are disclosed.
However, such a method of adjusting ink is a very effective method for printing a large amount of one image pattern in a light printing field or the like, but a variety of image patterns such as printers, copiers, and faxes are used. It is difficult to apply the present invention to an apparatus for printing a small amount at a time. In addition, as described above, if the color of the ink to be used is arbitrarily selected and adjusted, there is a problem that the image quality is not always improved.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has been developed in an image recording apparatus such as an ink jet printer in which the number of ink colors that can be used simultaneously is limited.
It is intended to enable high-quality color printing.

[0013]

SUMMARY OF THE INVENTION An image recording apparatus according to the present invention uses a plurality of recording heads having a single color material supply source and superimposes images of a plurality of colors on a recording medium such as recording paper. In the image recording apparatus for forming a color image, a recording head group or a colorant supply source group corresponding to the number of colors exceeding the number of colors that can be used simultaneously is provided inside or outside the apparatus, and the color components of the image to be output are provided. And an image processing unit for automatically selecting an optimal color combination to be used simultaneously from the recording head group or the colorant supply source group, based on the analysis result by the image processing unit. The recording head or the colorant supply source used for recording is replaceable.

For example, assuming that the number of color materials that can be used simultaneously is 6, a recording head or a color material supply source (ink tank) of 7 colors or more (for example, 12 colors) is prepared. When printing is performed, the most suitable six colors are selected from the twelve colors according to the image to be output, and printing is performed. By using such a method, the effect of using six colors can be maximized, and the quality of an output image can be improved.

[0015]

[0016]

FIG. 1 is a block diagram showing a first embodiment of the present invention. FIG. 2 shows the configuration of the image recording unit in this embodiment. In this embodiment, Y _{1 to} Y ₂ , M _{1 to} M ₄ , C _{1 to} C ₄ , B
A 12-color ink jet recording head of k _{1 to} Bk ₂ (subscripts indicate a difference in ink density, and the larger the number, the higher the density) is prepared outside the apparatus. Six print heads can be mounted on the carriage 21, so that up to six ink colors can be used simultaneously.

The printer driver 1 includes an image processing unit 2 for determining an ink color to be used. The image processing unit 2 includes a first color separation unit 4 that separates image data into four color components of Y, M, C, and Bk, and an ink color determination unit that determines an optimal combination of ink colors based on the color separation result. A second color separation unit 6 for performing color separation again according to the ink color to be used, and a pseudo gradation processing unit 7 for determining an array of pixels based on an error diffusion method, a dither matrix method, or the like. You.

The process of determining the ink color to be used by the image processing unit 2 will be described using a specific example. The image data is converted into Y, M, C, and Bk by the first color separation unit 4.
FIG. 3 shows an example of a result obtained by decomposing the image into color components and obtaining a pixel density distribution of each color image. In the actual processing, first, Y,
The Bk component was obtained by decomposing into three color components of M and C and performing an undercolor removal process on the result.

In the example shown in FIG. 3, the color component of M is the largest, and it is necessary to cover a wide density range from low density to high density. On the other hand, the components of Y, C, and Bk are relatively small, and the required density is biased toward the low density region or the high density region. The ink color determination unit 5 selects an ink color to be used based on the color separation result.

[0020] In this embodiment, as shown in FIG. 3, Y ₁ ~
_{Y 2, M 1 ~M 4,} C 1 ~C 4, Bk 1 ~Bk determined the number of pixels corresponding to each ink color of _2, was chosen large ink color number of pixels preferentially. However, since it is difficult to print a high-density area with low-density ink, the ink on the high-density side is given some priority. For example, the C component of FIG. 3, but towards the C ₁ than C ₂ is the number of pixels is greater, in such a case is to choose a C _2. Under the above criteria, in the example of FIG. 3, distribution is performed with a specific gravity on M that requires the widest density range, and Y ₂ ,
It was selected _{M 1, M 3, M 4} , 6 colors C _2, Bk _2.

When the ink color to be used is determined, the second color separation section 6 performs recolor separation of the image data corresponding to the ink color to be used. Thus, image data to be output by each recording head is obtained.

Further, the pseudo gradation processing section 7 performs pseudo gradation processing on the image data of each color. That is, since the recording head used in this embodiment cannot control the pixel density, it is necessary to appropriately arrange the pixels in order to perform pseudo multi-tone printing. In this embodiment,
The pixel arrangement was determined using the error diffusion method.

After the above-described image processing is completed, the work of replacing the recording head actually used is performed. In this embodiment, a method in which the user manually changes the recording head is used.
That is, the type of ink color used is determined by the ink color determination unit 5.
Is determined, the printer driver displays the recording head to be used on a display device (not shown) provided in the image recording unit with a number or a symbol, and urges the user to replace the recording head. The user selects a necessary print head from the print head group 26 according to the instruction of the printer driver, and mounts the print head on the carriage 21. Note that the instruction from the printer driver can be displayed by a message on a monitor of a computer connected to the printer.

When the exchange of the recording heads 22 is completed and the printer driver confirms that the recording heads of the designated colors are mounted, the head control unit 8 sends a driving signal to each recording head to execute recording. Each recording head ejects minute ink droplets in accordance with the transmitted drive signal while being scanned by the carriage. Recording head 22
Is composed of a droplet forming unit 23 for forming and discharging ink droplets, and an ink tank 24 as a color material supply source. In the present embodiment, a recording head based on an ejection principle utilizing a boiling phenomenon of ink is used. 6 on the recording paper 25
Six color images recorded by the individual recording heads are formed, and as a result, a full-color image is obtained.

As a result of an actual color image output experiment using the above-described apparatus, Y, M, C, Bk, LM, LC
It was confirmed that the granularity of the image could be reduced and the image quality could be improved as compared with the conventional printer using the six color inks.

In this embodiment, the ink color to be used is simply determined based on the pixel density histogram as shown in FIG. 3, but other factors such as human visual sensitivity are taken into consideration. You may select the ink color. For example,
Since humans have a lower discriminating ability than Y for other colors, the quality of an output image can be further improved by placing a higher priority on selecting colors M and C.

FIG. 4 shows a block diagram of a reference example of the present invention. Since the configuration of the image recording unit is the same as that of the first embodiment,
This will be described with reference to FIG. However, the display of the ink colors does not match FIG. The present embodiment is different from the first embodiment in that the user selects the used ink color by himself.

In this embodiment , as the recording head group 26,
A total of 11 recording heads including four colors of Y, M, C, and Bk plus seven colors of LM, LC, LY, red (R), green (G), blue (B), and skin color (S) Are prepared. As in the first embodiment, the number of ink colors that can be used simultaneously is six.

In order to execute image recording, first, the user selects an ink color to be used. For example, when a portrait of a person is output, S is added to the ink colors to be used because the skin color is frequently used. Also,
When the clothing color is red, the user selects the ink color to be used depending on the image to be output, such as adding R to the used ink color, and mounts the recording head on the carriage 21.

The printer driver 41 first detects the ink color of the mounted recording head 22 and the mounting position by the ink color detecting section 44. Next, the color separation unit 45 performs color separation according to the ink color using the image data. The color-separated image data is further subjected to pseudo gradation processing by a pseudo gradation processing unit 46, and finally, a drive signal is sent from the head control unit 47 to each print head, and printing is performed. .

When a portrait of a person was actually output using six color inks of Y, M, C, Bk, R, and S,
It was confirmed that the image quality could be improved as compared with the case where the conventional six-color inks (Y, M, C, Bk, LM, LC) were used. In particular, excellent color reproduction was able to be performed in a skin color portion where color reproduction was difficult. In addition, it was confirmed that since the total amount of ink used can be reduced, it is possible to reduce the penetration of the ink to the back surface of the recording paper (reverse back) and the occurrence of wrinkles on the recording paper.

FIG. 5 is a block diagram of a second embodiment of the present invention, and FIG. 6 is a block diagram of an image recording unit. In the present embodiment, the ejection part of the recording head is fixed on the carriage, the ink color is exchanged by exchanging an ink tank as a color material supply source, and the ink tank exchange is automatically performed using a switching mechanism. This is different from the first embodiment and the reference example in the point that it is executed.

In this embodiment, the ink tank group 66 includes Y ₁ -Y ₂ , M ₁ -M ₄ , C ₁ -C ₄ , Bk ₁ -B
12 color ink tank of k ₂ are prepared. Drop forming units 63 for six colors are mounted on the carriage 61 as an integral structure, and the ink color used can be changed by replacing the ink tank 64 connected to the drop forming unit 63. .

The processing at the time of recording in the printer driver 51 is almost the same as in the first embodiment. However, in the first embodiment, the user manually changes the recording head to be used, whereas in the present embodiment, the apparatus automatically changes the ink color (ink tank). That is, the ink color determination unit 55
When the ink color to be used is determined, a signal is sent to the switching mechanism 59, and the ink tank on the carriage is replaced. Specifically, first, the carriage 61 is moved in front of the ink tank group 66, and the ink tank on the carriage is pulled back by the switching bar 68, thereby returning the ink tank not used in the next recording to the ink tank group. . Next, the ink tank to be used for recording is pushed out by the switching lever, so that the ink tank is mounted on the carriage. When the ink tank is mounted on the carriage, ink is injected into the drop forming unit through a valve provided in the ink tank. When replacing an ink tank, before connecting a new ink tank, ink remaining in the print head is suctioned off by a head cleaner (not shown) to prevent color mixing of the ink in the print head. did.

When the replacement of the ink tank by the switching mechanism is completed, a drive signal is sent from the head control unit 58 to execute image recording. As described above, by automatically replacing the ink tank in the apparatus, high-quality color printing can be realized without bothering the user. Further, by exchanging the ink colors by exchanging only the ink tank, it is possible to prepare a large number of ink colors without greatly increasing the apparatus cost.

Although the present invention has been described in detail with reference to the embodiments, the present invention is not limited to these embodiments. For example, in the above-described embodiment, an ink ejection principle utilizing a boiling phenomenon of ink is used. However, other ejection principles such as a method using a piezoelectric actuator may be used. Also, the recording principle of the recording head is
Not only the ink jet method, but also other recording principles such as a thermal transfer method and an electrophotographic method can be used. Further, in the embodiment, the recording head is of a serial type in which the carriage is scanned by the carriage, but a line type recording head may be used.

[0037]

As described above, according to the present invention,
Since the most suitable ink color for the image data to be output can be used, high-quality image recording can be performed with a small number of recording heads (the number of ink colors). Therefore, a high-quality color recording apparatus can be realized with a low-cost and small-sized apparatus.

[Brief description of the drawings]

FIG. 1 is a block diagram of an apparatus according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of an image recording unit of the first embodiment of the present invention.

FIG. 3 is a diagram illustrating an example of a color separation result.

FIG. 4 is a block diagram of a device according to a reference example of the present invention.

FIG. 5 is a block diagram of a device according to a second embodiment of the present invention.

FIG. 6 is a configuration diagram of an image recording unit of the second embodiment of the present invention.

FIG. 7 is a configuration diagram of an image recording unit of a conventional device.

FIG. 8 is a diagram illustrating an example of a color separation result.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 21 Carriage 22 Recording head 23 Drop forming part 24 Ink tank 25 Recording paper 26 Recording head group

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ identification code FI H04N 1/60 H04N 1/46 Z (58) Field surveyed (Int.Cl. ⁷ , DB name) B41J 2/21 B41J 2 / 205 B41J 3/54 H04N 1/23 101 H04N 1/46 H04N 1/60

Claims (3)

(57) [Claims] An image forming apparatus comprising: a plurality of recording heads each having a single color material supply source;
In an image recording apparatus for forming a color image on a recording medium such as recording paper, a recording head group or a coloring material supply group corresponding to a number of colors exceeding the number of colors that can be used simultaneously is provided inside or outside the apparatus. An image processing unit for analyzing color components of an image to be output and automatically selecting an optimal color combination to be used simultaneously from the recording head group or the colorant supply source group; An image recording apparatus characterized in that a recording head or a colorant supply source used for recording can be replaced based on an analysis result. 2. An image recording apparatus according to claim 1, further comprising a switching mechanism for automatically exchanging said recording head or said color material supply source. 3. The image recording apparatus according to claim 1, wherein said recording head is an ink jet recording head for ejecting minute ink droplets.