JP3499494B2 - Inkjet image forming method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method used in an ink jet type image forming apparatus, that is, a dot forming method, and more particularly, to dot forming at a black pixel position. The first dot formation using only the slow-drying black ink having a relatively long drying time and the second dot formation in which the quick-drying ink having a relatively short drying time and the slow-drying black ink are overlapped with each other And an ink-jet image forming method performed with variable dot size. 2. Description of the Related Art In an ink jet type image forming apparatus, the drying time of ink after image formation greatly affects the efficiency of the entire printing process. In particular, pigment-based black ink (hereinafter referred to as “slow-drying black ink”) has high black reproducibility and is easy to obtain high image quality, but it takes a long time to dry, so black dots can be formed using only this slow-drying black ink. If formed, an image with a large area ratio of black dots, such as black solids, takes a long time until the ink dries, and the printed surface is rubbed by transport before the ink is completely dried, and the image becomes dirty. There was a problem. Therefore, for example, Japanese Patent Application No. 7-1
No. 49036 proposes a dot forming technique in which printing is performed using a quick-drying ink (for example, a black ink obtained by mixing three colors of yellow, magenta, and cyan) as a base, and black dots by a slow-drying black ink are superimposed thereon. I have. By forming the quick-drying ink dots as the base in this way, the penetration of the slow-drying black ink into the paper is promoted, the drying time can be shortened, and the color between the adjacent color dots can be reduced. Bleeding and the like can also be suppressed. [0003] However, black dots formed by quick-drying ink have low reproducibility of black. Therefore, when black dots are formed from slow-drying black ink and quick-drying ink as described above, drying is difficult. However, there is a problem that the print density is easily lowered and the hue is easily changed. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an ink jet printer capable of sufficiently shortening a drying time while minimizing a change in print density and hue of black pixels. An object of the present invention is to provide an image forming method. FIG. 2 shows the relationship between the printing ratio (%) of the slow-drying black ink (shown simply as black ink in the figure) and the printing density, and the relationship between the printing density and the printing density of the yellow ink. (Y), magenta (M), and cyan (C) are shown for each printing ratio (%) of quick-drying black ink by mixing colors. In this figure, for convenience, the dot size (the ratio to the ideal dot size) is set as the printing ratio. Actually, the sum of the printing ratio of the slow-drying black ink and the printing ratio of the quick-drying black ink is 100%. However, in this experiment, the dots of the quick-drying black ink were fixed in dot size (0%, 17%).
%,...), And dots formed by slow-drying black ink are formed thereon while changing the dot size. Therefore, the sum of the printing ratios (dot sizes) of the two is not always 100%. As shown in the drawing, when the dot size (printing ratio) of the slow-drying black ink is 67% or more, the printing density is 1. regardless of the dot size (printing ratio) of the quick-drying black ink. It can be seen that the density was more than 20 and almost the same density as that obtained by printing with the slow drying black ink alone. That is, if the printing ratio of the slow-drying black ink is 67% or more (the printing ratio of the quick-drying black ink is 33% or less),
It can be said that a sufficient print density can be obtained. FIG. 3 shows the relationship between the printing ratio (%) of the slow-drying black ink and the color difference by using Y,
This is shown for each printing ratio (%) of the quick-drying black ink based on the mixed color of M and C. Here, the value of the color difference shown on the vertical axis is
Each corresponds to the following evaluations. 1: Color difference that cannot be distinguished 2: Color difference is not known 3: Judgment as the same color as a sensory impression 4: Judgment as the same system color 5: Judgment with another system color 6: Judgment with completely different color In FIG. 3, when the printing ratio (%) of the slow-drying black ink is 67% or more, the color difference is one of the above-mentioned 1 to 3, and the change in hue is hardly as compared with the printing using the slow-drying black ink alone. It can be determined that there is no. From the above results, when the quick-drying black ink is subjected to the base treatment to shorten the drying time of the slow-drying black ink, the printing ratio of the slow-drying black ink is set to 6%.
By setting it to 7% or more, it can be said that a decrease in image quality due to a decrease in density or a change in hue can be minimized. Accordingly, in order to achieve the above object, the present invention provides a method of forming dots at black pixel positions by changing the dot size.
Inkjet image forming method to be performed
The dot size for the ideal dot size of the black pixel is 50
% And a predetermined value centered on the target black pixel
When the area ratio of black dots in the region exceeds 50%, and / or
Or, the dot of the target black pixel with respect to the ideal dot size
The target black pixels whose size exceeds 50%
When a color dot exists in a predetermined area as the center
In addition, the drying time is relatively short, yellow, magenta and
Quick-drying produced by mixing cyan-dry inks
Dots made of neutral black ink are used as a base
In addition, the ink with the slow drying black ink
The ratio to the total with the above quick-drying black ink.
Both are formed on the above-mentioned base as 67%, and
Dot formation for black pixels
It is configured as an inkjet image forming method . This makes it possible to shorten the drying time while minimizing changes in the print density and hue of the black pixels. Also,
The ratio of the slow drying black ink is 67%, which is the smallest in the above range.
The drying time can be sufficiently shortened while maintaining the print density and hue change of the black pixel in a more appropriate range.
Is also possible. Further, when the dot size for an ideal dot size of the black pixels of interest more than 50%, and the black dot area ratio in a predetermined region around the black pixel to be the target is more than 50%, Dot as above
To formed, avoiding in particular due to adverse drying time increases the area of overlap between the black dots becomes extremely long
it can. Further, when the dot size of the target black pixel with respect to the ideal dot size exceeds 50% and a color dot exists in a predetermined area centered on the target black pixel, the dot is set as described above. To form
The inconvenience caused by the fact that the target black pixel and the color dot are adjacent to each other and that their overlap is large ,
It is possible to prevent the bleeding KazuSatoshi. Embodiments and examples of the present invention will be described below with reference to the accompanying drawings to provide an understanding of the present invention. The following embodiments and examples are mere examples embodying the present invention, and do not limit the technical scope of the present invention. The ink-jet image forming method according to the present embodiment uses three types of color inks of yellow (Y) ink, magenta (M) ink, and cyan (C) ink, and a pigment-based slow drying black ink. It is assumed that the present invention is applied to an ink jet image forming apparatus (here, an ink jet printer Z1) having a print head capable of discharging with variable dot sizes. FIG. 4 shows the ink jet printer Z1.
3 is a block diagram of a data processing circuit of FIG. This data processing circuit is provided, for example, in the control device of the inkjet printer Z1. In FIG. 4, R, G,
B, and Y, M, C, and K represent pixel data (color data) of red, green, blue, and yellow, magenta, cyan, and black, respectively. The number “3” or “4” added together with “//” in the line connecting each block indicates the number of data (the number of data lines) in that portion. The flow of pixel data in the data processing circuit will be briefly described. The RGB pixel data is passed through a frame memory 32 to an RGB / YMCK conversion circuit 34 where the YMCK
It is converted to system pixel data. The line memories 36Y, 36M, 3 corresponding to the respective color data (pixel data)
6C and 36K. Note that the original pixel data is YM
If it is CK data, RGB / YMCK conversion circuit 3
4 is unnecessary. Line memories 36Y, 36M, 36
Each color data input to C and 36K is sequentially sent to an area ratio processing circuit 38, where a data conversion process (FIG. 1) described later is performed.
Y, 36M, 36C, 36K. Then, based on each pixel data in the line memories 36Y, 36M, 36C, 36K, the head drivers 40Y, 40Y
M, 40C, 40K, yellow head 1 respectively
1Y, the magenta head 11M, the cyan head 11C, and the black head 11K are driven to form an image on a sheet. Here, each line memory 36Y, 36M,
36C and 36K have the same memory configuration,
In the following description, these are superimposed and described as one line memory for convenience. That is, each line memory 36
In Y, 36M, 36C, and 36K, it is assumed that one cell Co having the same address, which will be described below, is assumed to be one, and information of each color data is stored in this cell Co. FIG. 5 is a diagram showing a memory structure of the line memory.
Line memory is print data area (recorded image area)
And first and second correction data areas, first and second dummy data areas, and addresses assigned to rows and columns of each area. The print data area is composed of a memory map composed of m rows × n columns of cells Co... For storing a part of the print data. Each cell Co constituting this print data area has the above-described dot formation position and 1 cell.
Each cell Co stores data that is information on dots to be formed at each dot formation position by each cell Co. This data has a value of 1 or 0 depending on whether or not to form a dot. Specifically i row j
Regarding the data Dij stored in the cell Coij which is the cell Co of the column, when forming a dot at the dot forming position corresponding to the cell Coij, the data Dij = 1, and the dot is formed at the dot forming position corresponding to the cell Coij. Is not formed, the data Dij = 0. Note that the subscript “ij” indicates the i-th row and the j-th column, and in the following, will be added only when the position on the matrix is specified. Further, the data D is used in the case of a general description that does not distinguish each color data, and when representing the data D that distinguishes each color data, they are represented as data Y, M, C, and K, respectively. The print data area is configured to divide print data in the sub-scanning direction and store the divided print data sequentially. That is, cells Co... Included in one row of the print data area can store all data of one row in the main scanning direction (width direction of the recording paper), and cells Co included in one column of the print data area. Co ... can store one column of divided data in the sub-scanning direction. Also, in the cell Co of m rows × n columns in the print data area, row numbers (channel, row.) From 1 to m are respectively provided from the first row to the last row, and 1 to n are respectively provided from the first row to the last column. A column number (col.) Is assigned. The first and second correction data areas and the first and second dummy data areas are data areas corresponding to the periphery of a portion corresponding to the print data area in an actual print image. These are black dot area ratios Sk1 described later at the outermost periphery of the print data area.
The data used when calculating is stored. First
And the second correction data area are composed of cells Co... Constituting the row immediately before the first row and the row immediately after the last row of the print data area, and are assigned row numbers of 0 and m + 1. Then, in the first and second correction data areas, data of row = m (channel 1 correction data) stored in the print data area immediately before each, and in the print data area immediately thereafter,
Row = 1 data (channel m correction data) is stored. The first and second dummy data areas are
Immediately before the first column of the print data area (left side in the figure)
, And the cells Co in the column immediately after the last column (right side in the figure).
, And column numbers of 0 and n + 1 are respectively assigned. Since the first and second dummy data areas correspond to areas where no image is formed at both ends of the recording paper (areas where print data does not exist, blank areas), data D = 0 is set in all cells Co. Is stored. An address Rad and an address Cad are assigned to each row and each column constituting each area described above. The address Rad and the address Cad respectively represent a row number and a column number in binary numbers.
Note that the address Rad and the address Cad are sequentially assigned from the lower bit (first digit, second digit,...) To the address Rad2, respectively.
0, Rad21,... And addresses Cad20, Cad21. Next, the data conversion of the print data on the line memory 36 by the area ratio processing circuit 38 will be described. As described above, since the dot size of the inkjet printer Z1 is variable (dot size modulated), the data D stored in each cell Co of the line memory stores the dot size (the ratio to the ideal dot size). Shall be Here, the dot size is set to 100%, 83%, 75% of the ideal dot size.
%, 67%, 50%, 33%, 25%, and 17%. Here, the overlapping of the dots having the dot size when the dots of the respective dot sizes are formed will be described. When dots having the above dot sizes are formed at the target position, dots having the above dot sizes are formed at positions adjacent to the target position in the horizontal and vertical directions (row and column directions) and oblique directions. The presence / absence of overlap between the dot at the position of interest and the dot at the position adjacent thereto can be expressed as shown in Table 1. [Table 1] In Table 1, the case where there is an overlap between the dot at the target position and the dot at the position adjacent thereto is represented by "x", and the case where there is no overlap is represented by "o". The dot pitch ratio indicates the ratio of the dot size to the dot pitch. As can be seen from Table 1, when the dot size of the dot at the target position is 50% or less, the overlapping of the dots occurs only when the dot size of the dot at the target position is 50% and in the horizontal or vertical direction. This is only when there is an adjacent dot having a dot size of 100%. However, even in this case, when the dot pitch and each dot size are considered, it can be seen that the area of the overlapping portion is small. Therefore, in the present embodiment, the dot at the target position is a black dot whose dot size exceeds 50%.
That is, the data K stored in the cell of interest Ca is 50
% (Data K = 67%, 75%, 83%, 10%)
0%) is a condition for performing data conversion (condition 1). Next, conditions for performing data conversion according to the density of black dots in the area including the target position will be described. In the case where the dot size is modulated, the black dot area ratio Sk2 (dot area ratio) is calculated by Expression (1) as a value indicating the density of black dots in a predetermined region formed by m rows × n columns of dot formation positions. Define. (Black dot area ratio Sk2) = p2 / (m rows × n columns) (1) where p2 is the total (%) of the dot sizes of the black dots formed in the predetermined area, and m is the number of black dots in the predetermined area. The number of rows at the dot formation position is shown, and n is the number of columns at the dot formation position in a predetermined area. In the present embodiment, the above m = 3
n = 3, black dot area ratio Sk of a region of 3 rows × 3 columns (hereinafter referred to as a cell of interest) centered on cell of interest Ca
2 is the black dot area ratio Sk2 of the cell of interest Ca.
Then, the black dot area ratio Sk2 of the cell of interest Ca is 50%.
Is exceeded when the data conversion is performed (condition 2). For a black pixel that satisfies both the above conditions 1 and 2, if the dot formation is performed only with the slow-drying black ink, the drying time becomes extremely long. Therefore, the mixed color of the three color inks of Y, M, and C is used. A black dot formed by a quick-drying black ink is formed as a base, and a slow-drying black dot is formed thereon. Thus, the penetration of the slow-drying black dots into the paper is promoted by the quick-drying black dots formed as the base, and the drying time can be reduced. However, at this time, as the ratio of the slow-drying black ink becomes smaller, the image density and the change in the hue increase, and the image quality deteriorates. However, as described above, the slow-drying black ink and the quick-drying black ink are used. When both are used, by setting the ratio of the slow-drying black ink to 67% or more, it is possible to minimize a decrease in image density and a decrease in image quality due to a change in hue. In this embodiment, in order to shorten the drying time as much as possible while minimizing the deterioration of the image quality, when the above conditions 1 and 2 are satisfied, the ratio of the quick-drying black ink is 33%.
(Dot size 33%), slow drying black ink ratio 67%
(Dot size is 67%). Specifically, the correspondence between the data before conversion and the data after conversion is set as follows. [Table 2] Even when Condition 2 is not satisfied, if the cell of interest Ca is located at the boundary with the color area, it is necessary to prevent the black dots from bleeding into the color area and to reduce the drying time. It is desirable to use a quick-drying black ink in combination. Therefore, in the present embodiment, when there is a color dot in the target cell area (condition 3), and when the condition 1 is satisfied, the dot is set in the same manner as when the conditions 1 and 2 are satisfied. Form. Data conversion for forming dots as described above will be described with reference to FIGS.
6 to 8 are explanatory diagrams showing data conversion in the print data area of the line memory. FIG. 6 shows the data D before conversion, and FIG. 7 shows the black dot area ratio Sk2 of each cell Co.
Indicates data D after conversion. In FIGS. 6 to 8, cells Co forming black dots are hatched. In addition, "Y", "M", and "C" are simply displayed for cells Co that form color dots.
In the print data area having the data D shown in FIG. 6, the black dot area ratio Sk2 of each cell Co is sequentially obtained for all the cells Co having black data. As a result, the black dot area ratio Sk2 of each cell Co becomes as shown in FIG. Although the black dot area ratio Sk2 is not stored in each cell Co, the black dot area ratio Sk2 corresponding to each cell Co is shown in FIG. 7 for explanation. Based on the pre-conversion data D shown in FIG. 6, it is determined whether the cell of interest Ca satisfies the above condition 1 or condition 3. FIG.
It is determined whether or not the target cell Ca satisfies the condition 2 based on the black dot area ratio Sk2 shown in FIG. When the conditions 1 and 2 or the conditions 1 and 3 are satisfied, the data conversion shown in Table 2 is performed, and data D as shown in FIG. 8 is obtained. The above processing (processing in the area ratio processing circuit 38) will be described more specifically with reference to the flowchart shown in FIG. First, black pixel data (referred to as target cell data) k _{ij at the} i-th row and j-th column (initial values are i = 1 and j = 1) is obtained from the line memory 36, and whether or not the target cell data is a black pixel (Steps S0, S
1). Here, when the target cell data is not a black pixel (k
_(ij = 0), the process proceeds to step S8 described later. On the other hand, when the target cell data is a black pixel (k _ij = 1), the total p2 of the black dot sizes in the target cell region (here, 3 × 3 region) around the target cell is calculated. (Step S22), the area ratio Sk2 is obtained (Step S2)
3). Here, when the black dot area ratio Sk2 is obtained from the total black dot size p2, an area ratio conversion table showing the correspondence between the total black dot size p2 and the black dot area ratio Sk2 without performing division. By using (not shown), the time required for the arithmetic processing can be greatly reduced. Of course, the value of p2 may be used as it is for the determination in the next step S24. In the following step S24, the cell of interest Caij
Is determined for the black dot area ratio Sk2. If the black dot area ratio Sk2 exceeds 50% in step S24 (condition 2 above), data conversion processing using table 2 is performed on the cell data of interest in step S28. Further, even if the black dot area ratio Sk2 is 50% or less in the above step S24, the color dots in the cell area of interest are counted in the following step S5, and if the counted number ck is 1 or more (the above condition 3). In step S28, data conversion processing using Table 2 is performed on the cell data of interest. Otherwise, the conversion process of the cell data of interest is not performed (step S27). Here, in Table 2 above, data conversion is not performed when the dot size before conversion is 50% or less. Therefore, the data conversion is actually performed in step S28 because of the above conditions 1 and 2
Is satisfied, or the above conditions 1 and 3 are both satisfied. Also, the above step S2
In No. 8, when the dot size before conversion is 67% or more, the converted data has a dot size of 67% for a slow-drying black dot and a 33% dot size for a fast-drying black dot formed by mixing color inks. That is, when the slow-drying black ink and the quick-drying black ink are used in combination, the ratio of the slow-drying black ink is always 67%. Accordingly, it is possible to sufficiently shorten the drying time while minimizing the change in the print density and the hue of the black pixel. The processing after step S1 is
Repeated for all cells (Steps S8 to S1
1 → S1 → ...). As described above, according to the ink jet image forming method according to the present embodiment, the case where the black dots overlap and the drying time of the ink becomes particularly long (when both the above conditions 1 and 2 are satisfied) ) Or when the black dot is adjacent to the color dot (when both the above conditions 1 and 3 are satisfied), the drying time is shortened by forming the slow drying black dot on the quick drying black dot. It is possible to reduce the print density of the black pixels and the hue of the hue by using the quick-drying black dots together, by setting the ratio of the slow-drying black dots to 67% (the ratio of the quick-drying black dots to 33%). Changes can be minimized.
In the above example, when the slow-drying black dot is formed by superimposing the slow-drying black dot on the quick-drying black dot, the ratio of the slow-drying black dot is 67%.
However, it may be set to a higher value. However, it should be noted that as the ratio of the slow-drying black dots increases, the print density of black pixels increases and the change in hue decreases, but on the contrary, the drying property deteriorates. As described above, according to the present invention, the black pixel
Ink that forms dots at positions with variable dot size
A jet image forming method, in which the target black pixel
Dot size exceeds 50% of the expected dot size,
And black in a predetermined area centered on the target black pixel
If the dot area ratio exceeds 50% and / or
The dot size of the black pixel relative to the ideal dot size is
More than 50% and centered on the target black pixel
If color dots exist in the predetermined area,
Drying time is short, yellow, magenta and cyan
Quick-drying black ink produced by mixing fast-drying ink
Dot as a base and relatively dry
Quick drying of dots with slow drying black ink with long drying time
At least 67% of the total with black ink
To form a black pixel on the base,
Characterized by performing dot formation by using
Since it is configured as an image forming method , it is possible to shorten the drying time while minimizing the change in print density and hue of black pixels. Here, by setting the ratio of the slow-drying black ink to 67%, which is the smallest in the above range, it is possible to sufficiently shorten the drying time while maintaining the change in the print density and hue of the black pixels in a more appropriate range. Is also possible. Further, when the dot size for an ideal dot size of black pixels to be paired elephant than 50%, and the black dot area ratio in a predetermined region around the black pixel to be the target is more than 50% , Dot as above
Avoids inconvenience caused by an extremely long drying time due to the large overlapping area between black dots
can do. Further, when the dot size of the target black pixel with respect to the ideal dot size exceeds 50% and a color dot exists in a predetermined area centered on the target black pixel, the dot is changed as described above. Formation
Not because, moreover adjacent the black pixel and the color dot to be the target overlap thereof is large especially due to the
Convenience, ie, bleeding can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flowchart showing a processing procedure of an inkjet image forming method according to an embodiment of the present invention. FIG. 2 is a graph showing the relationship between the printing ratio (%) of the slow-drying black ink and the printing density for each printing ratio (%) of the quick-drying black ink mixed with Y, M, and C printed on the base. . FIG. 3 is a graph showing the relationship between the printing ratio (%) of the slow-drying black ink and the color difference for each printing ratio (%) of the quick-drying black ink by mixing Y, M, and C printed on the base. FIG. 4 is an inkjet printer Z to which the inkjet image forming method according to the embodiment of the present invention is applied.
FIG. 2 is a block diagram showing a schematic configuration of one data processing circuit. FIG. 5 is an explanatory diagram showing a memory structure of a line memory of the inkjet printer Z1. FIG. 6 is a diagram showing an example of pixel data D before data conversion. FIG. 7 is a view showing a black dot area ratio Sk2 in each cell Co of the pixel data D shown in FIG. 6; FIG. 8 is a diagram showing a result of performing a data conversion process on the pixel data D shown in FIG. 6; [Description of Signs] 11Y, 11M, 11C, 11K ... Inkjet heads 36Y, 36M, 36C, 36K ... Line memories 40Y, 40M, 40C, 40K ... Head driver 38 ... Area ratio processing circuit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-136310 (JP, A) JP-A-6-135006 (JP, A) JP-A-10-32409 (JP, A) JP-A-8-108 187880 (JP, A) JP-A-7-149036 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41J 2/21 B41J 2/01 B41M 5/00

Claims (1)

(57) [Claims 1] A dot size is formed at a black pixel position by a dot size.
An ink jet image forming method in which the size of a target pixel is different from the ideal dot size of a target black pixel.
The size exceeds 50%, and the center is around the target black pixel
If the area ratio of black dots in the predetermined region exceeds 50%
And / or the ideal dot size of the target black pixel
Dot size exceeds 50% and
Color dot exists in a predetermined area centered on the black pixel
When drying, yellow, magenta and shear
Quick-drying black produced by mixing the quick-drying inks of each color
Ink dots are formed as a base,
On the other hand, dots with slow drying black ink, which has a long drying time,
The ratio to the total with the quick-drying black ink is at least 6
7% is formed on the base, and dot formation is performed for the target black pixel.
Characteristic inkjet image forming method.