JPS58124667A - Ink jet printer - Google Patents

Abstract

PURPOSE:To form a picture print having a desired characteristics, by using a comparing output between each threshold of one matrix selected from a plurality of threshold matrices, different in random numbers, based on density conversion characteristics and an input picture signal containing gradation. CONSTITUTION:Four threshold matrices 2a, 2b, 2c and 2d are located based on different conversion characteristics, the four threshold matrices 2a, 2b, 2c and 2d are artificially selected, and the one matrix so selected is connected to an input terminal of a comparator 1. The comparing output of the comparator 1 is converted into an ink drop jet signal by a head drive circuit 4 through a picture element memory 3, and ink drops 6, 6... are jetted through an ink head 5.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inkjet printing apparatus that expresses the degree of shading by the adhesion density of ink droplets ejected per unit area.

When forming A-line and halftones using an inkjet printing device, this can be done by controlling the particle size of the ink jetted, but this particle size control depends on temperature, humidity, and use. It is not necessarily constant due to fluctuations in external elements such as ink.

On the other hand, depending on the number of inkjet printing apparatuses, there are also electric field control type inkjet printing apparatuses in which the particle size of ink droplets cannot be varied.

Conventionally, therefore, shading is expressed by controlling the adhesion density of ink droplets shot per unit area.

The applicant of the present application also filed a patent application in 1986-5081 in view of such density control.
The first application was filed for a color inkjet printing device.

FIG. 1 shows a main part of a color ink jet printing apparatus disclosed in Japanese Patent Application No. 55-50811, and shows only the signal series of one color. In the same figure.

(1) is a comparator that compares the input image signal vij and the threshold value Te1j, and 12; is the threshold value for the comparator +11? ij is a threshold matrix set in a matrix, and this ? ) The threshold pattern of risk (2) is, for example, input image signal Vij
contains gradation information of 17 gradations, then 1+
As shown in Figure 2, the numbers are randomly scattered between 0 and 15. The pattern of this threshold matrix (2) is determined by the dither method. The above-described dithering method compares the pixel level of the input image with a threshold value T1j (the level is set to 11 .tp'0.
In this method, the signal is converted into 200 million signals, and the binary signal is displayed on a binary display device, so that it appears to the human eye as if shading is formed.

The principle is that if cells that are turned on are grouped together and turned on, the area will appear white, and areas where cells that are turned on and off are gathered alternately will appear gray if you look at them from a distance. . The dithering method is as described above (an algorithm that determines which cells should be turned on in order to obtain a binary image that is as close to the original image as possible on a 200 million display device, and will be explained in more detail). is Nikkei Electronics 19
78°5-1. This is done on pages 50-65.

Returning to the explanation of FIG. 1 again, (31 is the above comparator +11
The pixel memo IJi41 temporarily stores the comparison output of the pixel memory (31), which is a head drive circuit that converts the pixel signal read out from the pixel memory (31) into an ink droplet ejection signal (5j is the ink droplet (6) from the seventh ejection signal number). (6) It is an ink head that ejects...

The transmitted image signal v1j is first passed through a comparator (1
) is introduced into the comparator (II) and the threshold value M7 (2
The input image signal v1 of comparator +11 is compared with the threshold value 〒1j of the location (row 11 column j) corresponding to the image signal of 1.
The 4×4 pixel matrix according to j is as shown in FIG.

The matrix of the comparison output R1j output to the pixel memory (31) is as shown in the 5th!1iQ(B), that is.

Between the input image signal v1a), the @value 〒ij, and the comparison output R1j.

Vij≦? 1 j OJ time R1j-QYl j>? i
The following relationship holds.

This ratio ψ output R1j is in the pixel memory 13+.

The data is stored until the comparison operation of the comparator (II) is performed for one row or one column in the ejection scanning direction of the ink head 15.

Then, the pixel 11 read out from this pixel memory (3:
．． Or 10. 1 in the head drive circuit (4). If 0. In this case no injection signal is formed. 1
．． The ejection signal is applied to the ink head (5) and ink droplets (61+61...) are ejected. That is, 11M5
In the matrix of comparison output 1'lij in Figure CB), @
1. An ink droplet (61 (6+...) adheres to the
0. It doesn't stick to places. As a result, ink droplets (61
16+ . . . is extremely useful because it is possible to print ＠儂 which is scattered with regularity based on the threshold value matrix (2) by the dither method and has a uniform halftone.

However, according to the conventional method, ink droplets +61+61... in proportion to each gradation of the input image signal Vij, which has a total of 17 gradations from 0 to 16, are ejected into a unit area, and one gradation is For the input image signal Vij of 4, as shown in FIG. 5 (4 ink droplets (61161...
The actual situation is that eight ink droplets f61i6+... are ejected.

However, assuming that the maximum reflection density (the darkest part) obtained by inkjet printing*'a is 1.0.

The relationship between this reflection density and the number of ink droplets ejected per 4×4 unit area is as shown in FIG. For example, 1 for input image signal Vij of floor wA4 as described above.
+5 If four inks 4f61+61... are applied as shown in the figure, the reflection density obtained is 0.58, which does not match the reflection density of floor m4, 0.25. Similarly, the reflection density obtained for floor [18] is 0.68.

The desired reflection density of 0.5 cannot be obtained. That is,
For the input image signal Vij of actual gradation 4, there is a print with a reflection density of 0.58 degrees Nm, which corresponds to the gradation wM6, and for the gradation 1118, a print with a reflection density of 0°68, which corresponds to gradation 11, is obtained. Therefore, the gradation of the input image signal Vij was not faithfully expressed. As a result, the density conversion characteristic expressed by the printing density for the gradation of the input image signal Vij is l! A curve as shown in Figure 5 was drawn, and the print obtained was hard.

In addition to such rigid density conversion characteristics, the present invention also provides a plurality of different density conversion characteristics, such as uniform density conversion characteristics that faithfully print the gradation of the input image signal Vij, and soft density conversion characteristics. Equipped with a threshold matrix.

The purpose is to form an image print having desired characteristics by selectively using the plurality of threshold values in view of the density conversion characteristics to be obtained.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1B6 is a schematic block diagram of the inkjet printing apparatus of the present invention. What differs from the conventional example shown in FIG. 181 is that four threshold matrices C2m)<2b)C2o)C2d) are provided based on different density conversion characteristics. , the four threshold matrices <2a)C2bJ(2o)(2d) are artificially selected and the selected one is connected to the input terminal of comparator +11.

For example, the contrasting density conversion characteristics include high contrast as mentioned above,
s, a soft density conversion characteristic and a characteristic in which halftones are emphasized; FIG. Density conversion characteristics and (DJ are soft dark FJrf conversion characteristics G) [Applicable. FIGS. The pattern of the threshold value matrix 121, that is, each threshold value 〒1j is l!7 (A) - (Based on DJ, the theoretical density which is the printing density for each gradation of the input image signal Vij is calculated, and this theoretical density and @ It is determined from the number of ink droplets that can obtain a reflection density approximately equal to the theoretical density by comparing the reflection density in FIG. 4.

Furthermore, the above! ! Figure 8 (A) to (D) 410 to 640
The input image signal Vij containing the J gradation information is printed with ink m (61 (6+-...) per unit area up to 16@). In other words, the input image signal Although the number of gradations of V1j (divided by 0 ( ) is 64, the number of ink droplets is 16, so if you simply calculate, there are 4 gradation widths for 1 ink droplet. This is more preferable than the case where the number of drops and the ratio of al@ are 1:1 because it is possible to realize precisely selected concentration conversion characteristics.

Next, the specific procedure for determining the pattern of IJ (threshold value) (2) is as follows: In the case of equal density conversion characteristics where one gradation and the printing density change linearly, the input image signal Vij is in the range of 0 to 16. A case will be explained in which 17 gradation information that changes within a range is included.This equal density conversion characteristic is defined as the input image signal Vij
The maximum level of gradation is the maximum value of printing density (1.0 in the inkjet printing apparatus of this embodiment, but it varies depending on the ink used, printing medium, etc.)
year.

It is divided equally for each gradation axis, and by using this equal density conversion characteristic, each gradation of the input image signal Vij can be faithfully converted into printing density.

Each threshold value Te1j of the dark value 7 trix 12) of this example is as follows.

Level 1--Theoretical density By calculating the number of gradations and comparing the theoretical density with FIG. 4, IJ can be easily determined from the number of ink droplets that can obtain a reflection density approximately equal to this theoretical density. It will look like Figure 9. More specifically, as mentioned above, when the number of gradations is 16, the theoretical density of the gradation m8 is 120.5, and the optimal number of ink droplets 5 to achieve this 0.5 is found from FIG. 4, and! ! What is the threshold value in the threshold matrix in Figure 2? The above 8 is placed at the location 1j-5.

The darkness value matrix (2) formed in this way has equal density conversion characteristics, and by selecting this matrix (21), it is possible to obtain an image print that is faithful to the input image signal Vij as intended. can.

Now, the explanation will be returned to the embodiment of the present invention shown in FIGS. 6 to 8.

Then, a pattern selection signal PS is applied to select the threshold matrix C2a)C2b(20)C2(3) based on the density conversion characteristics to be obtained.

As a result, the comparator (1) compares the input image signal Vij with each threshold value Tij of the selected one threshold value matrix drive.

Figure 1810 (AJ ~ (DJ is the threshold matrix (2 breath J (
2b) (ml as 2cJ (2d)!8 Figure (AJ ~ (D
This is a schematic representation of the adhesion state of ink droplets (61 (6+...) per unit area of 4 × 4 when the pattern of ) is selected, and the adhesion locations are hatched. In the figure, the row direction of (A) to (D) corresponds to each density conversion characteristic, and the column direction of (if to (g)) is a group for each gradation of the input image signal Vij, and is represented by an Arabic numeral. is the density conversion characteristic and (DJ
In the soft density conversion characteristic of (C), there is 0 ink, and in the hard density conversion characteristic of (C), there are 2 ink points? I(6)(61...) are attached respectively.

In the above explanation, monochromatic images were taken as an example, but if applied to the color inkjet printing apparatus of Japanese Patent Application No. 55-50811, color images with various tastes can be obtained. . Threshold value of this confrontation) IJ Kusu (2
) for the input image signal Vij or 64 gradation @11
Labeled on the diagram. In FIG. 11, rows (A] to (D) correspond to equal density conversion characteristics or soft density conversion characteristics, (column 13 is magenta, (rono column is cyan, (Hough column is black,
Corresponding to each color, yellow is 1! ! Figure 8 (AJ~(D
) is the same, so it will be omitted.

As is clear from the above description, the inkjet printing device fill of the present invention is an input image containing each threshold value of one matrix randomly selected from a plurality of 14 threshold value matrices based on density conversion characteristics and one gradation information. The signals are compared and the ink head is driven by the comparison output, so the ink droplets ejected from the ink head evaporate according to the selected conversion characteristic and are scattered in a unit area, and the ink droplets with different a numbers It is possible to easily obtain a printed image.

Table: Brief explanation of the drawings. Figure 1 is a block diagram showing the outline of a conventional inkjet printing device, WZ diagram is a diagram of a conventional threshold matrix X (/J pattern, Figure 6 (A) and (BJ are conventional example Pattern diagram of input 1ili signal and comparison output to explain, 18
Figure 4 is a reflection density characteristic diagram showing the relationship between the number of ink droplets per unit area and reflection density, and Figure s5 is a conventional density conversion characteristic diagram.
FIG. 6 is a block diagram schematically showing the inkjet printing apparatus of the present invention, Ig7 diagrams W(A) to (DJ are various density conversion characteristic diagrams for obtaining the present invention, and FIG. 1188 diagrams (A) to (D7)
Figures 11 to 9 are threshold matrix pattern diagrams corresponding to (A] to CD in Figures 12 and 7, Figures 11 and 9 are pattern diagrams of threshold matrices in other embodiments of the present invention, and Figures 1110 (Muno to C).
D) is a schematic diagram illustrating the state of ink droplets ejected into a unit area based on the threshold matrices of FIGS. 181
FIG. 1 shows a pattern diagram of a threshold matrix in still another embodiment of the present invention.

(1)... Comparator, (2)... Threshold matrix, (
5;...ink head.

〒、１（口） Figure 11 (stomach] , cj no C c)

Claims (1)

[Claims] (1) In an inkjet printing device that expresses the degree of shading by the adhesion density of ink droplets ejected per unit area, the value varies randomly according to the unit area, and the pattern or pattern a comparator that compares each threshold value of one threshold matrix selected from the plurality of matrices with an input image signal including gradation information, respectively; . an ink head driven by the comparative output of the comparator, the ink head being selected to scatter ink droplets deposited per unit area based on a pattern of a threshold matrix. Photography device. (2; Claim 111, characterized in that the pattern of the Uami threshold matrix is determined by a dither method.
The inkjet printing device described in Section 1.