JPS63286357A - Ink jet recording device - Google Patents

Abstract

PURPOSE:To enhance gradation and control the quality of a color image such as degree of tint precisely without changing the size of pixels by discharging, in a plurality of dots, ink droplets continuously at the same position on a material to be recorded in accordance with the density or color tone of an input image and making the interval of ink droplet discharging time variable. CONSTITUTION:When a discharge pulse S2 is applied to data S1 prepared in a shift register, ink droplets 24 are discharged from a nozzle 23 at 1 indicated by data S1. This ink discharging interval is shown as t, and the shorter this interval t becomes, the higher growth rate of dot diameter of printing dots 25 as a whole. On the contrary, the longer the interval t becomes, the lower growth rate of the dot diameter. The growth of dot diameter becomes slower in proportion to the interval t of ink dot printing which becomes wider. However, the degree of tint and color can be changed by chromatic superimposing. In addition, the density of printed dots slightly improves.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an inkjet recording device, and in particular, inputs multivalued image data, binarizes it, and creates a halftone image by modulating the dot diameter by overlapping ejected inks. □Relates to an inkjet recording device that reproduces □.

[Prior Art] In a dot recording device such as an inkjet recording device in which the size of ink droplets ejected from a nozzle is constant, so-called so-called color images and gradation images (halftone images) sent from a host computer, etc. When printing image data having depth information, a fixed threshold pattern matrix is called from memory and compared with input image data to perform binarization.

This is because image data with such depth information is multivalued data that indicates pixel gradation (density and brightness) etc. in digital quantities, so a binary image recording device cannot handle such image data. This is because it is not possible to print as is without binarizing, and in this binarizing, a collection of multiple dots is defined as one pixel, and it is necessary to decide whether or not to print dots in one pixel. There is also a way to express gradation, but if you print an image in this way,
The quantization error makes it impossible to maintain balance with other pixels, resulting in false contours. Therefore, a recording method is generally adopted in which a threshold pattern separate from these pixels is defined, and binary image processing is performed by comparison with the threshold pattern to express gradation over a large range. .

A conventional example of a circuit that performs such binarized image processing is
Input image data 1 shown in the figure is digital multi-value data given as 8-bit digital values, etc., but in order to be printed on an output device such as a dot printer, it is passed through a latch circuit 2 to a comparator ( Parallel comparator) 3 is input to one input terminal of the comparator 3, and the comparator 3 compares it with the threshold matrix data read from the pattern matrix 4 and input to the other input terminal of the comparator 3. 2) Dots are expanded to petrification data. In this way, it is not possible to express gradation by simply converting multivalued data into binarized data, so when input image data 1 is prepared in the comparator 3, it is processed from the pattern memory 4 in which the threshold value (threshold value matrix) is written. Comparison data (threshold values) are sequentially output and binarized to 0.1, but for example, one image data 1 is divided into 4×4 pixels (pi
xel) When expanding and binarizing, the threshold data is called 16 times for that one image data 1, and is sequentially compared with that one image data to binarize with 4x4 dot expansion. be done.

FIGS. 11(^) to (D) show the operation of the conventional circuit in pixel expansion of 1×1 to 4×4. Input multilevel image data 1 is pixel-developed according to the pixel size, and by comparing with 4×4 threshold value data 8, a binarized density pattern is output on printing surface 9. Note that "1" on the printing surface 9 indicates dot printing, and θ" indicates no printing. In this figure, pixel expansion is shown from 1 x 1 to 4 x 4, but one input multi-value The size of a pixel is determined by the number of ink dots that image data 1 is represented by.Therefore, compared to an image with 1x1 pixel expansion, an image with 4x4 pixel expansion is are printed at 16 times the size.Also, each threshold matrix 8 is 4x4
Therefore, 17 gradations (including white) can be expressed using the area gradation method.

12(^) to (C) show examples of actual threshold data of the 4×4 threshold matrix 11-1, an ideal printing model printed using the threshold matrix, and 8
An example of the actual threshold data of ×8 threshold matrix 8-2 is shown. Here, the numbers 1 to 16 in this figure (B) indicate the number of gradations, and the threshold data in this figure (C) is in hexadecimal. The 8×8 threshold matrix 8-2 shown in Figure (C) is a threshold pattern matrix that corresponds to the 8-bit multivalued image data l, but it is still only able to express up to 65 (including white) gradations. Can not.

[Problems to be Solved by the Invention] However, in an inkjet recording device that performs dot printing using such a conventional binary image processing method, the 13th dot printing device is designed to make the gap in the paper surface invisible during solid printing.
As shown in the figure, the dot diameter of the printed dots is usually made larger than the dot pitch P. In other words, one is used that can produce printed dots with a dot pitch larger than the circumscribed circle of a square. Furthermore, when printing in multiple colors using yellow, magenta, cyan, and black color inks, a method is adopted in which ink droplets are overlapped to mix the colors. In that case, the print dots are set to be large so that the print dots overlap each other as much as possible.

Therefore, the relationship between the brightness (Lo) of the conventional printed matter and the input multivalued image data obtained in this way is the 14th
As shown in the figure, the relationship is not linear, and when the image data exceeds a certain density, the brightness becomes saturated, causing the problem that faithful reproduction of the input image data cannot be performed. .

In addition, the characteristics of yellow, magenta, and cyan monochrome inks are shown on the am -b* plane (+a" indicates the red direction, -al indicates the edge direction, +b" indicates the forward direction, and -b" indicates the forward direction). This is shown in Figure 15. The broken line in this figure is a measurement of a sample printed with an actual inkjet recording device where ink overlaps, and the solid line shows an ideal situation where ink does not overlap. As shown in this figure, the ideal curve is a straight line, but the actual printed line draws an arc.The reason for this is that the printed line as shown in Figure 13 This is because there are overlapping areas of the dots, and even if the same density of ink is used to print, there is a problem that the tone will be different in the light density area, the middle area, and the dark area.In other words, In this way, even if the same ink is used, the colors will be different, which means that the saturation (vividness) and hue (color) will differ due to the overlapping of the inks.
This is because it changes.

That is, the conventional device has the following problems.

■ Since printing is performed with a dot diameter larger than the dot pitch, a linear relationship between image data and print brightness or density cannot be obtained.

■ Even for the same color, the color changes due to overlapping dots.

■ It is not possible to accurately control the color tone of standards that represent colors such as saturation and hue.

■ Since the threshold pattern matrix size is increased to increase gradation, there are drawbacks such as decreased resolution and noticeable graininess.

The present invention was made to solve the above-mentioned problems, and it is possible to increase the gradation and accurately control the image quality of color images such as saturation without changing the pixel size. An object of the present invention is to provide an inkjet recording device that can perform the following steps.

[Means for Solving the Problems] In order to achieve the above object, the present invention expresses one pixel by a plurality of groups of dots whose minimum dot diameter is smaller than the dot implantation pitch, and uses a threshold matrix or density pattern data. A plurality of ink droplets are continuously ejected at the same position on the recording material according to the density and color tone of the input image using a plurality of ink droplets, and the ejection time interval of the ink droplets is made variable.

[Function] The present invention, by overlapping ejected ink in inkjet recording, (1) modulates the dot diameter, thereby smoothly changing the area ratio, and (2) increases the density of printed dots by overlapping dots. The saturation and hue are controlled, and the time interval for dot overlapping is set to approximately 1 m5ec or less to grow the dot diameter, and the time interval for dot overlapping is set to approximately 1 m5ec or more to allow ink to overlap without growing the dot diameter. By combining these operations, it is possible to obtain smooth gradation, and at the same time, it is possible to control the chroma-1 hue, which plays an important role in color reproduction.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows the circuit configuration of an embodiment of the present invention. In this figure, 11 is a pattern memory in which a plurality of threshold matrices 10-1 to 10-4 as shown in FIG. This is an address generator for reading threshold values in the Z direction. 15 is the dot expanded 2@! in comparator (parallel comparator) 3. 16.17.18 are the line memory 15 that temporarily stores the
This is an address generator for writing in the Z direction. 19 is a read controller that controls the read timing of output data from the line memory 15; 20 is a pulse generator that generates ejection pulses; and 21 is a shift register. The data read from the line memory 15 enters the shift register 21 via the read controller 19, and is transferred to the inkjet rad 2 according to the ejection pulse from the pulse generator 20.
It is supplied to a driving element such as a heating element in the nozzle of No. 2.

The conventional threshold matrix was only in the x-y direction of the row direction and the column direction, as shown in FIGS. 11 and 12.
As shown in FIG. 2 in the present invention, the Z direction of the stacking direction is further increased. For example, in the case of stacking 4 dots with a 4 x 4 threshold matrix, the 4 x 4 x 4 threshold matrix 10
-1-10-4 is prepared in the pattern memory 11, sent to the comparator 3, and compared with input image data 1. in this way,
Since the threshold value matrix 1O-INlo-4 of this example also prepares threshold value data in the overlapping direction (Z), in the case of 4 dots overlapping, it is four times as large as the conventional 4×4 threshold value matrix. At the same time, the number of comparisons of input image data is quadrupled.

According to the overlapping pattern design of the threshold matrix IQ-IN10-4, the image data binarized to 0.1 code is then input to the line memory 15, and the ejection signal 51 ( Figure 3 (^)~
(See (C)). For example, the data binarized by the comparator 3 is sent to one nozzle 2 of the inkjet head 22.
3 (see Figure 3) is given as "1100", then ink droplets are ejected from the nozzle 23 in succession, one dot and two dots, resulting in overlapping printing at the same position on the paper. executed.

Next, the operation of the embodiment of the present invention shown in FIG. 1 will be explained.

When the input multi-level image data 1 is latched by the latch circuit 2, the input multi-level image data 1 is transferred from the pattern memory 11 to the address generators 12, 13, .
The threshold data of the X, Y, and Z addresses designated by 14 are supplied to the comparator 3, and the image data 1 supplied from the latch circuit 2 is successively compared with the threshold data by the comparator 3 and binarized. Ru. The data binarized to 0.1 by the comparator 3 is stored in the line memory 15 indicated by x, y, and z addresses similarly to the pattern memory.

On the other hand, on the inkjet printer side, line memory 1
The read controller 19 reads data (ejection signals) prepared in the inkjet head 5 and sends it to the inkjet head 22 through the shift register 21. That is, when data for the inkjet heads 22 is prepared in the shift register 21, the ejection pulse S2 is applied from the pulse generator 20 to the shift register 21, and the ejection signal is outputted from the shift register 21 at the timing shown in FIG. (data)
is supplied to the heating element in the nozzle 23 of the inkjet head 22, and the nozzle 23 ejects ink in response to this ejection signal, and repeats the same operation again.

To manipulate the time interval between dots with the circuit configuration shown in FIG. 1, prepare a plurality of threshold patterns in advance as shown in FIG. While the data of "32" of image data 1 was input, the threshold value issued for each overprint is "7".
"14", "21".

28”, ”35’”, ”42’”, ”49
”, “56”, image data 1 is binarized as “1111000G” for one nozzle, but the threshold values are “7”, “35”, 14”, “42”.
″、′″21″.

If they are “49”, “28”, and “56”,
Image data 1 of "32" becomes 10101010",
The printing results for both are the same three dots overlapping, but because the ink ejection interval (time interval) is different, the diameter of the printed dots is different as will be described later.

FIGS. 3 and 4 show the output timings of the print data S1 and the ejection pulse S2 in the embodiment of the present invention. When the ejection pulse S2 is applied to the data 51 prepared in the shift register 21, the data Sl Ink droplets 24 are ejected from the nozzle 23 only when the time is 1.

The interval between these ink discharges is indicated by t, and as shown in FIG. Indeed, the dot diameter growth rate tends to decrease.

That is, when the ejection signal 51 of the inkjet printer is continuously applied to the inkjet head 22, the sixth
As shown in C of the figure, the ink 26 blends and bleeds on the paper surface 27, and the dot diameter grows. On the other hand, if the distance t increases when the ink dots are ejected, then a in FIG.
As shown in FIG. 6b and a and b in FIG. 6, although the dot diameter growth is slowed down, it is possible to change the zero saturation hue due to superimposition, and the density of the printed dot itself is improved to some extent. In this way, in Figures 5 and 6, the ink spread of the dots printed as l) -h B -*c increases because the first dot is cut into the paper surface and the next dot is This is because if the time t is short until the ink is printed, the supply of ink droplets will be faster than the rate at which the ink penetrates into the paper, 1 dot, 2 dots, 3 dots, etc., and the ink will easily spread on the paper surface. . On the right side of FIG. 6, arrows indicate how the ink penetrates into the paper. 7th
The figure shows the relationship between the number of overlapping dots and the size of the dot diameter, and it can be seen that the longer the overlapping interval, the lower the dot diameter growth rate f.

Therefore, 8 types or 9 types of bidirectional threshold matrices can be used.
If you prepare a large number of types, for example, ■11100000 for the same image data. ■10101000. ■100
10010... can be binarized, smooth gradation can be obtained, and brightness, saturation, and hue can be appropriately controlled.

As described above, by utilizing the dot diameter growth caused by overlapping ink droplets, it is possible to obtain smooth gradation that could not be expressed using conventional techniques. In particular, when a linear relationship between the input image data 1 and brightness as shown in FIG. 8 is obtained, the threshold matrix is configured so that the dot diameter becomes small in the highlighted area shown by A. The graininess becomes less noticeable. Until now, when reproducing an image of a person's face, the skin color could not be reproduced well, but with this example, smooth gradation can be obtained, making it possible to properly reproduce the skin color. can. Furthermore, by increasing the interval t between overlapping dots, the area ratio does not change, but the effect of overlapping ink, that is, changing the saturation, can increase the vividness, which expands the range of expression and significantly improves the image quality. .

Therefore, the effects of the embodiments of the present invention can be summarized as follows.

■ Since it is possible to use smaller dots than conventional methods, bright areas can be expressed in more detail.

■ By scattering printing with small dot diameters throughout the dots and gradually increasing the dot diameter by overprinting, the difference in gradation (
Sudden changes) become less noticeable and smooth color tones can be expressed.

■ By overlapping the dots without changing the dot diameter,
The vividness and color tone of the reproduced image can be changed, and clear image quality can be obtained.

Furthermore, in order to express fine gradation and adjust saturation and hue, it is sufficient to change the bit ejection interval, and the following can be considered for this.

(2) Adjust the dot spacing using the Z-direction data of the threshold matrix as described above.

■ By manipulating the Z address of the threshold matrix and Tx,
If it is desired to set the value data to 0, read out 255 threshold data that always yields O even when compared with the threshold value, and compare it with the image data.

■ Change the frequency of the ejection pulse.

FIG. 9 shows the main part configuration of another embodiment of the present invention. In this embodiment, for human multilevel image data 1, binary data is obtained from lookup table 30 along with addresses indicated by X, Y, and Z. is called and output to the line memory 15.

Binarized data is called from the lookup table 30 by adding the address indicated by the size of image data 1 and the matrix address generated by the X and Y address generators 31 and 32, but the Due to the difference in the two addresses, the superimposed data can be read out with different values. The rest of the configuration is the same as that of the first embodiment shown in FIG. 1, so a detailed explanation thereof will be omitted.

[Effects of the Invention] As explained above, according to the present invention, in addition to dot diameter modulation in which printing of small dot diameters is made into larger dot diameters by overlapping them, the dot striking time interval is adjusted. Not only can fine gradation be obtained, but also the degree of saturation and hue, which play an important role in color reproduction, can be appropriately adjusted and controlled.

As a result, according to the present invention, when smooth gradation is obtained but the image quality is not so good, the printed image can be made clear by adjusting the vividness. It is also possible to do so. Further, the present invention is highly practical because it is easy to use and improve conventional existing inkjet recording apparatuses almost as they are.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the circuit configuration of an embodiment of the present invention, FIG. 2 is a schematic diagram showing an example of the configuration of the threshold matrix stored in the pattern memory of FIG. 1, and FIGS. 3 (A) to (C)
is a timing chart showing the relationship between ejection data and ejection pulses in an embodiment of the present invention, FIG. 4 is a timing chart showing an example of ink ejection intervals in an embodiment of the present invention, and FIG. 5 is a timing chart showing an example of ink ejection intervals in an embodiment of the present invention. FIG. 6 is a plan view showing the relationship between the ejection interval and dot diameter growth, FIG. 6 is an elevational view showing the state of ink adhesion due to the difference in ink ejection interval in the embodiment of the present invention, and FIG. A characteristic diagram showing the relationship between the ink ejection interval and the growth of the dot diameter. Figure 8 shows the brightness (L'') versus the value of the input multi-valued image data.
FIG. 9 is a block diagram showing the main circuit configuration of another embodiment of the present invention; FIG. 1θ is a block diagram showing the circuit configuration of the conventional device; FIG. 11 (^)~ (D) is a schematic diagram showing the operational relationship between the pixel size and the threshold matrix when input multilevel image data is binarized using a conventional device. An explanatory diagram showing a configuration example and an ideal printing pattern when printing using the threshold matrix, Fig. 13 is a plan view showing how actual printing overlaps with the conventional device, and Fig. 14 shows the conventional device. The value and brightness of the input image data (L
FIG. 15 is a characteristic diagram showing the characteristics of a conventional apparatus in the a*-bm plane when yellow, magenta, and cyan inks overlap with each other and when they do not overlap. 1... Input image data, 2... Latch circuit, 3... Comparator, 10-1 to 10-4-... Threshold matrix, 11-...
battle pattern memory, 15--line memory, 19--read controller, 20--pulse generator, 21--shift register, 22--inkjet head, 23--nozzle, 24-- Ink drop, 3G--look up table. - See how the ink adheres to the ink on the 1st large gloss example and the 5th Senmenguchi, which shows the relationship between the tpt and the shokigicho. Figure 8: A block diagram of the series of lectures by the great Hiroba series. Fronk diagram for each bond Figure 10 Figure 10 shows the conventional blank f straight matrix and Shiu pattern, light concave No. 12
centroid map

Claims (1)

[Claims] 1) One pixel is expressed by a group of multiple dots whose minimum dot diameter is smaller than the dot implantation pitch, and the same position on the recording material is expressed according to the density and color tone of the input image using a threshold matrix or density pattern data. An inkjet recording apparatus characterized in that a plurality of ink droplets are continuously ejected in a plurality of dots, and the ejection time interval of the ink droplets is made variable.