JP2003237114A - Color imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To represent a uniform color taste through a simple head arrangement even when a recording sheet is to be printed with ink of more than one color by superposing. <P>SOLUTION: Depending on the color information of each pixel of an image being recorded, a plurality of nozzles are divided into a plurality of nozzle groups (dividing positions 1-4) on the order of performing print in the same color. A recording sheet 12 is printed sequentially for each nozzle group by scanning it a plurality of times by means of an ink jet head 10 thus altering the order of superposing the inks depending on the color information of each pixel. The order of superposing the inks is determined according to the number of ink components when the color information of each pixel is converted into the ink component. The maximum number of times of scanning the recording sheet with the ink jet head 10 is set within a specified range. Each nozzle performs gray level modulation by ejecting a plurality of ink drops of arbitrary number to the same position. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus for printing a recording material by ejecting a plurality of colors of ink from a recording head.

[0002]

2. Description of the Related Art Conventionally, an ink jet printer has been known as a device for ejecting a plurality of colors of ink onto a recording material such as paper to print a color image. The need for color reproduction has arisen.
For example, taking a four-color ink system as an example, in order to form a color image other than the four mounted colors on a recording medium, ink droplets of a plurality of colors are landed at the same position and mixed on the recording medium. Let

FIG. 7 shows the state of ink droplets when performing unidirectional printing using a conventional ink jet printer.
First, a case will be described in which the head 100 is arranged so as to perform recording on the recording medium in the order of K (black), C (cyan), M (magenta), and Y (yellow) in the main scanning direction. . When performing unidirectional printing with such an ink jet printer, for example, if G (green) is to be recorded, C first lands on the recording medium, and then Y lands. At this time, first, the C ink permeates the recording medium and spreads on the surface and inside of the recording medium. Then, Y that has landed next will also dig into the lower part of the C ink.
That is, as shown in FIG. 7A, when viewed from the surface of the recording medium, the Y ink appears to have spread to the outside of the C ink. The CY color mixing portion on the inside is G, and G is recorded with the naked eye.

Next, the head 101 is
A case will be described in which the main scanning direction is arranged so that recording is performed in the order of Y, M, C, and K. When unidirectional printing is performed with such an ink jet printer, C is printed after Y ink.
Since the ink lands, as shown in FIG. 7B, the C ink sneaks under the Y ink, and Y becomes dominant in the YC color mixing portion as compared with G described above.

For this reason, even if the same C and Y mixed color portions have different head configurations, or if reciprocal printing is performed and the ink ejection order is different, a different tint will result. There was a problem. In order to solve such a problem, in the technique disclosed in Japanese Patent Application Laid-Open No. 8-295034, a head configuration (“Y, M, C” in which the ink superposition order does not change between forward scan and backward scan) , K, C, M,
Y ”).

[0006]

However, in the technique disclosed in the above-mentioned Japanese Patent Laid-Open No. 8-295034, seven heads are arranged in the main scanning direction for four colors. As the size increases, a new problem arises that the number of nozzles increases and the cost increases. In other words, if you try to simplify the head configuration,
When printing two or more colors of ink on the recording paper, there is a problem that the tint may be different depending on the order of ink overlapping, so that the order of ink overlapping does not change between forward scanning and backward scanning. When the number of nozzles is increased, the head configuration becomes complicated, the apparatus becomes large, and the cost increases.

The present invention has been proposed in view of the above-mentioned circumstances, and has a uniform color tone even when two or more colors of ink are overlaid and printed on a recording paper with a simple head configuration. An object is to provide a color image forming apparatus capable of expressing.

[0008]

In a color image forming apparatus according to the present invention, an ink jet head having a plurality of nozzles for ejecting inks of a plurality of different colors is made to relatively scan on a recording medium to print data. In a color image forming apparatus for forming a color image based on, according to the color information for each pixel of the image to be recorded, the plurality of nozzles are divided into a plurality of nozzle groups in the same color in the printing execution order, It is characterized in that the ink jet head is scanned a plurality of times to perform printing sequentially for each of the nozzle groups, thereby changing the ink superposition order according to the color information for each pixel.

In this case, the ink may be superposed in the order in which the color information of each pixel is converted into an ink component and the ink component is contained in a large amount.

The maximum value of the number of times the ink jet head is scanned can be defined by the following equation. Maximum number of times the inkjet head is scanned = (number of ink colors) × (number of masks) × (image recording resolution) ÷
(Nozzle resolution)

Further, each of the nozzles is capable of performing density modulation by ejecting arbitrary plural drops of ink to the same location.

In the present invention, a plurality of nozzles are divided into a plurality of nozzle groups within the same color in the printing execution order, the ink jet head is scanned a plurality of times to perform printing sequentially for each nozzle group, and color information for each pixel is obtained. Since the order of overlapping inks is changed depending on the situation, even if two or more inks are overlaid on the recording paper, a uniform tint can be expressed without increasing the number of heads. It is possible to reproduce various colors.

[0013]

DETAILED DESCRIPTION OF THE INVENTION An inkjet printer, which is an embodiment of a color image forming apparatus according to the present invention, will be described below with reference to the drawings. In the following explanation, K
Represents black, C represents cyan, M represents magenta, Y represents yellow, and R represents red.

The color ink jet printer according to the embodiment of the present invention may be a binary printer that ejects or does not eject ink, but is preferably a multi-drop printer. That is, a binary printer can perform color reproduction in which the tint is faithful according to the order in which ink is ejected, but a multi-drop printer changes the number of ink ejected per pixel, the drop size, and the like. By doing so, gradation expression can be performed, and the color tone becomes even more faithful.

FIG. 1 is a schematic diagram for explaining the order of ejecting ink in a color ink jet printer according to an embodiment of the present invention. In the example shown in FIG.
Image data exists for each pixel. For example, as for “Ry” of the original image (upper left corner in the figure), yellow is ma
It means Red which is stronger than genta. That is, even for the same Red, the stronger color is shown in lowercase for the constituent y and m (Ry, Rm, etc.).

Next, this image data is converted into C plane, M
Plane and Y plane. At this time, for example, R
y is divided into My and Yy, and the density of each color is My <Yy. Therefore, when the inks are overlaid, the color printed earlier is the dominant color than the color printed later, so Yy is printed first and My is printed later.

In order to realize this, each of the C plane, the M plane, and the Y plane is further divided, and the same uppercase and lowercase letters (Cc, Mm, Yy) in FIG. 1 are printed in the first scan, and Other color components are printed in the second scan. For example, in Ry, My is printed after Yy, and in Rm, Ym is printed after Mm.

As described above, in the present embodiment, the number of scans which is twice the normal number is required. However, in order to obtain a high image quality in consideration of the tint, the above-described printing method is used, and conversely, the image quality is changed. In the case where speed is important, by selecting a normal print mode that does not consider the ink stacking order, it is possible to perform printing suitable for the purpose without increasing the size of the apparatus and increasing the cost.

Next, with reference to FIGS. 2 and 3, the actual scanning and the appearance of the printed image will be described. 2 and 3
In the example shown in, the head resolution is 300 dpi and 60
Image data of 0 dpi shall be printed. Further, for simplicity, the number of Y, M, C, and K nozzles is 16 nozzles, but in general, in order to achieve higher image quality with a low-resolution head, 64, 128, 256 nozzles, etc. ,
There are many multiples of a power of 2 (8 or 16).

Further, the maximum number of colors to be superimposed in the same pixel is "2". When the number of overlapping is 3 or more, the number of divisions may be increased accordingly.
Since the image resolution is twice the head resolution and the maximum value of the number of overlapping inks is 2, the head 10 is divided into four (divided portions 1 to 4 in FIG. 2) and four nozzles are arranged at each divided portion. To be done. The number of masks is "1".

As shown in FIG. 2A, in the first scan, four nozzles are printed in the order of K, C, M, and Y using the divided portion 1 on the head 10. Further, as shown in FIG. 1, the data to be printed is divided, and color data having a strong tint (data having the same uppercase and lowercase letters) is printed first. The area a of the recording paper 12 is printed as shown by the dividing points 1 of the head 10.

As shown in FIG. 2B, in the second scan, the recording paper 12 is moved in the sub-scanning direction by 4.5 nozzles (9 nozzles in image resolution). And head 1
At the divided portion 2 of 0, the portion to be interpolated in the sub-scanning direction is printed on the area a of the recording paper 12, and at the same time, the head 1
At the division location 2 of 0, color data having a strong tint is printed in the area b. Therefore, for the area a, the head 1
It means that the printing is performed by the division points 1 and 2 of 0 and the printing is performed by the division point 1 of the head 10 on the region b.

As shown in FIG. 3A, in the third scan, the recording paper 12 is moved in the sub-scanning direction by 3.5 nozzles (7 nozzles in image resolution). And head 1
At the division location 3 of 0, the second color ink having a weak tint to be printed on the same pixel printed in the first scan is printed in the area a. However, at the division location 2 of the head 10, a location interpolated in the sub-scanning direction of the second scan is printed on the region b, and at the division location 1 of the head 10,
Color data having a strong tint is printed in each area c. Therefore, the area a is printed by the divided portions 1, 2, 3 of the head 10, and the area b is printed by the divided portions 1, 2 of the head 10,
The area c is printed by the divided portion 1 of the head 10.

As shown in FIG. 3B, in the fourth scan, the recording paper is moved in the sub-scanning direction by 4.5 nozzles. Then, in the divided portion 4 of the head 10, a color having a weak tint is printed on the area a and the area b for overlapping printing, and a color having a strong hue is printed on the area c and the area d. To do. Therefore, the area a is printed by the divided portions 1, 2, 3, 4 of the head 10, and the area b is printed by the divided portions 1, 2, 3 of the head 10, The area c is printed by the division points 1 and 2 of the head 10, and the area d is printed by the division point 1 of the head 10.

By repeating such scanning, it is possible to print with an image resolution of 600 dpi with a head having a resolution of 300 dpi without making the tint different. That is, the number of divisions of the head 10 is (the number of overlapping colors) × (image resolution) ÷ (head resolution)
X (number of masks). Also, the number of nozzles of the head 10 is often set to an integral multiple of the number of divisions, and unnecessary nozzles are eliminated. In the above-described embodiment, bidirectional printing is used, but unidirectional printing can be performed by the same procedure.

Here, the value of each color is set from "0 (light)" to "25".
5 (dark) ”, for example, as shown in FIG. 4, Rm at the left end has a value of M (136) + Y (78), and Ry at the right end is M (86) + Y (123). ) Value. At this time, in the first scan, Rm at the left end is M
(136) is printed, Ry at the right end is printed with Y (123), and in the second scan, Rm at the left end is printed with Y (7).
8) is printed, and M (86) is printed at Ry at the right end.
Therefore, printing is performed with the number of drops corresponding to the density value.

Assuming that the number of drops corresponding to the density value can be expressed by 8 gradations of "0" to "7" drops per color, for example, it becomes as shown in FIG. Also,
Since the slope of the gamma value becomes gentle at the time of multi-gradation, the range of density values corresponding to 7 drops becomes wider than that at the time of low density value. Similarly, since the remaining colors are printed in the second scan, it is possible to reproduce colors faithful to the data even with the same Red.

2 and 3, the dots are arranged with a gap of one pixel in the main scanning direction for ease of explanation, but in reality there is no gap in the main scanning direction. Each dot is arranged. Further, when a mask is applied (for example, the number of masks is “2”), as shown in FIG. 6, the dots are arranged so that there is a gap of one pixel in the main scanning direction. Further, in order to print at an image resolution twice the head resolution, interpolation in the main scanning direction and interpolation in the sub scanning direction are performed, and ink is superimposed on each dot. For example, when the number of masks is “2”, the number of divisions of the head 11 is 2 (mask) × 2 (resolution) × 2 (overlay), which is “8” in total, and one pitch in the sub-scanning direction is It has 2 nozzles. Therefore, as shown in FIG. 6, the head 11 divides the 16 nozzles of Y, M, C, and K into 2 nozzles into 8 portions (division points 1 to 8).

[0029]

The image forming apparatus according to the present invention divides a plurality of nozzles into a plurality of nozzle groups in the same color in the printing execution order, scans the ink jet head a plurality of times, and sequentially prints for each nozzle group. By changing the ink stacking order according to the color information of each pixel, a uniform color tone can be obtained even when two or more colors of ink are stacked and printed on the recording paper even with a simple head configuration. Can be expressed.

By converting the color information for each pixel into an ink component and stacking the inks in the order of increasing ink components, the tint closest to the desired color can be obtained.

Further, by defining the maximum value of the number of times of scanning the ink jet head to be a predetermined value, it is possible to faithfully reproduce the tint without increasing the cost and to shorten the printing time. It can be shortened.

Further, it is possible to perform the density modulation in one pixel by ejecting an arbitrary plurality of drops of ink to the same location and performing the density modulation. In this case, since different inks having a high gradation number are overlaid, the tint changes, and the color can be reproduced more reliably for a desired color.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining the order of ejecting ink.

FIG. 2 is a schematic diagram illustrating an example of printing when an actual scan is performed.

FIG. 3 is a schematic diagram illustrating an example of printing when an actual scan is performed.

FIG. 4 is a schematic diagram showing a printing method in the case of considering the order in which inks are superposed due to the difference in components with respect to almost the same color.

FIG. 5 is an explanatory diagram showing a relationship between a density value and the number of drops.

FIG. 6 is a schematic diagram for explaining an ink ejection order.

FIG. 7 is a schematic diagram showing a state of ink droplets when performing unidirectional printing using a conventional inkjet printer.

[Explanation of symbols]

1-8 Head division points 10, 11 heads 12 Recording paper K black C cyan M magenta Y yellow R red

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shiro Wakahara             22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka             Inside the company (72) Inventor Hiroshi Doshoda             22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka             Inside the company F-term (reference) 2C056 EA11 EC75 EC76 ED03 EE03                       EE10

Claims (4)

[Claims] 1. A color image forming apparatus for forming a color image on the basis of print data by relatively scanning an ink jet head having a plurality of nozzles for ejecting inks of different colors, on a print medium. In accordance with the color information for each pixel of the image to be recorded, the plurality of nozzles are divided into a plurality of nozzle groups in the same color in the print execution order, and the inkjet head is scanned a plurality of times to make each nozzle group A color image forming apparatus, characterized in that the order of superimposing ink is changed according to the color information for each pixel by sequentially performing printing on the. 2. The color image forming apparatus according to claim 1, wherein the ink is superposed in the order in which the color information of each pixel is converted into an ink component and the ink component is contained in a large amount. 3. The color image forming apparatus according to claim 1, wherein the maximum value of the number of times the inkjet head is scanned is defined by the following formula. Maximum number of times the inkjet head is scanned = (number of ink colors) × (number of masks) × (image recording resolution) ÷
(Nozzle resolution) 4. The color image forming apparatus according to claim 1, wherein each of the nozzles ejects a plurality of arbitrary drops of ink to the same location to perform density modulation. .