JPH02265749A - Image recording apparatus - Google Patents

Abstract

PURPOSE:To make it possible to obtain always fine image records even in an image recording apparatus wherein recording is conducted by superposing recording agents by implementing operation based on image signals which specify driving conditions of delivery energy generating elements corresponding to each delivery port of recording heads in a region of high ray level, and by making smaller the image signals to specify driving conditions of the elements in response to the result of the operation. CONSTITUTION:An operation unit 12 is an operation processing unit, wherein operation is applied to image signals 11C, 11M, 11Y, whereby signals 13C, 13M, 13Y are outputted therefrom as a result of the operation. And image signal correction unit 14C, 14M, 14Y correct input image signals 11C, 11M, 11Y respectively in response to the signals 13C, 13M, 13Y. In the case of cyanogen, for example, correction of the signal 11C in the input image signal correction unit 14 is made by converting the signal 11C to signal 15C using a look-up table. In the case of a binary printer, wherein input image signal is small, when the number of recorded dots per area is small, no conversion is made and when input image signal becomes larger and number of recorded dots increases in the binary printer, output signal is kept at lower values so that quantities of ink recorded in the boundary area decrease and hence black lines in the region of high gray level are reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an image recording device, and is particularly suitable for application to an image recording device that records images by serially scanning a plurality of recording heads. .

[Prior Art] Conventionally, as an image recording device, an inkjet recording device that performs recording by ejecting ink onto a recording material is known.

Inkjet recording devices are non-impact recording devices with features such as low noise and the ability to easily record color images by using multicolored inks, and have become rapidly popular in recent years. be.

FIG. 5 is a schematic perspective view of a conventional inkjet recording apparatus.

In FIG. 5, the recording material 5 wound into a roll is nipped by the feeding roller 3 via the conveying rollers 1 and 2, and is driven by the sub-scanning motor 50 connected to the feeding roller 3.
sent in the direction. A guide rail 6.7 is placed in parallel across the recording material 5, and a recording head unit 9 mounted on a carriage 8 scans left and right. The carriage 8 is equipped with inkjet recording heads 9Y, 9M, 9G, and 98K of four colors, yellow, magenta, cyan, and black, each having a plurality of ink ejection ports arranged in parallel, and four color ink tanks are arranged on these. has been done. Here, each recording head includes, for example, a group of ejection ports arranged in a direction perpendicular to the scanning direction, a liquid path communicating with each ejection port,
A recording element group includes ejection energy generating elements such as electrothermal transducers arranged corresponding to each liquid path. The recording material 5 is intermittently fed by the recording width in one scan of the recording head unit 9, but when the recording material 5 is stopped, the recording head unit 9 scans in the P direction, and the image signal is Recording is performed by ejecting ink droplets in accordance with the conditions.

In such an inkjet recording apparatus, the characteristics of the recording material are important, and in particular, the bleeding characteristics of the ink on the recording material have a large effect on image quality.

A "bleeding rate" is known as an index indicating the ink bleeding characteristics of a recording material. This indicates how many times the diameter of an ink droplet ejected from an inkjet nozzle spreads on the recording material, and is given by bleeding rate=dot diameter on the recording material/discharged ink droplet diameter. For example, the diameter of ink droplets in flight is 30 μm.
If a dot of 90 μm is formed on the recording material, the bleeding rate of the recording material will be 3.0.

Here, if a recording material with a small bleeding rate is used, the image density will be low, and a high-quality image with texture cannot be obtained.

On the other hand, with a recording material having a high bleeding rate, the image density becomes high, but the following problems occur.

In the serial scan type inkjet printing apparatus as shown in FIG. 5, as shown in FIG. The image records are shown in (1) and (2) in the same figure.
, (3) are repeated in this order. The width d is determined by the number of nozzles in the head and the recording density, and the number of nozzles is 256.
．． In the case of recording density 400 dots/inch (dpi), 256X 25.4/400 = 16.256mm
becomes.

When the amount of ink recorded is small, the ink absorption of the recording material is sufficient, so the width of the recorded image is equal to the recording width d.
Therefore, if printing is performed in the A direction after scanning the print head by d in the B direction, the seams between each printing scan will not pose a problem on the image, as shown in FIG. 6(^).

However, when recording an image in a high-density area, that is, a part where a large amount of ink is ejected onto the recording material, the recording material cannot absorb enough ink, and the ink smudges in the horizontal direction, causing the recorded image to disappear. The width is d+Δd. At this time, assuming that the scanning width of the recording head in the B direction is d, the images overlap with a width of Δd, and a black stripe occurs in this portion as shown in FIG. 6(B). Conversely, if the scanning width in the B direction is set to d+Δd, white streaks will appear in low density areas.

The amount of image width expansion Δd in a high-density area varies depending on the bleeding rate of the recording material and the amount of ink ejected onto the recording material.
becomes larger.

Therefore, in order to prevent black streaks, it is necessary to use a recording material with a low bleeding rate or to reduce the amount of ink used for recording, but in this case, as mentioned above, the image density will decrease and the appearance of solid matter will decrease. A problem arises in that a certain high-quality image cannot be obtained.

In order to solve the above-mentioned problems, the present applicant proposed in Japanese Patent Application No. 175341/1983 that the serial scan boundaries of the plurality of printheads are When the total of the image signals specifying the conditions for driving the recording element for printing in a certain area is large, the value of the image signal specifying the driving condition for the recording element is reduced to reduce black streaks in high-density areas. proposed a configuration to prevent this.

[Problems to be Solved by the Invention] However, in this proposal, for example, when recording a color image using four inkjet recording heads of cyan, magenta, yellow, and black, C, M,
The image signals specifying the conditions for driving the ejection nozzles for printing at the boundaries of the serial scans of the Y and Bk heads were simply added together, and differences in bleeding characteristics due to different ink colors were not considered.

However, in reality, the bleeding characteristics differ depending on the ink color, so even if the combination of cyan, magenta, yellow, and black image signals has the same total image signal, However, the value of Δd in Fig. 6 differs depending on each combination, and it is not necessarily appropriate to determine the correction amount by a simple addition value of each image signal of cyan, magenta, yellow, and black, and it is not possible to completely eliminate black streaks. There is a risk that you will not be able to eliminate it.

Furthermore, the bleeding characteristics differ greatly between when ink is later overlaid on previously recorded ink and when ink is recorded on a recording material for the first time.

For example, when recording blue where the recording amount of cyan and magenta are the same, you can record cyan first and then magenta, or record magenta first and then record cyan. The amount of cyan blur is larger in the latter than the former, and the amount of magenta blur is larger in the former than the latter. In other words, the ink color recorded later has a larger amount of bleeding than the first time the ink color was recorded on the recording material. Therefore, for example, ink is ejected onto the recording material in the order of cyan, magenta, yellow, and black. In an image recording apparatus that performs image recording, a blue image formed by a cyan image signal "128" and a magenta image signal "128", a magenta image signal "128" and a yellow image signal "1"
In the case of recording a red image formed by 28" on a recording material, for example, in the above proposal, the amount of correction for magenta is exactly the same for blue and red, but in reality, the amount of correction for magenta is exactly the same for blue and red. Since the amount of correction is large for blue and small for red, it is difficult to completely eliminate streaks at the boundaries of serial scans with a single correction amount.

The present invention improves the above-mentioned proposal, and even in an image recording apparatus that performs recording by superimposing recording agents such as ink, such as an image recording apparatus that has a plurality of recording heads corresponding to colors, etc., it is possible to always achieve good results. The purpose is to enable image recording.

[Means for Solving the Problems] To this end, the present invention provides an image recording apparatus that has n print heads in which a plurality of print elements are arranged side by side and performs image recording by serially scanning the print heads. When Xi (il2.3...n) is an image signal that specifies the drive condition of the recording element for recording the boundary area by scanning in the first recording head of the recording head, the following equation (1
) is characterized by comprising a correction means for correcting the value of the image signal specifying the driving condition of the recording element related to the recording of the boundary portion in the j-th recording head, according to the value of x'j determined by .

Cj; il; L2;----; Lnaal
, 2.3. -----, n:Q1ji+,
(12ii+iz, ---・-, an)t+-
--+*H4+, sheet] [Function] According to the present invention, for example, in a serial scan type color inkjet recording device, each inkjet recording head scans in a high density area, that is, an area where a large amount of ink is recorded. Based on the image signal that specifies the conditions for driving the ejection energy generating element corresponding to the ejection port for recording the boundary portion of By reducing the image signal that specifies the conditions for driving the ejection energy generating elements corresponding to the ejection ports involved in recording the boundary area, it is possible to reduce the difference in bleeding characteristics due to the difference in each ink color and the difference in the ink color recorded earlier. It is possible to more effectively prevent black streaks regardless of the presence or absence of black lines.

Note that the image signal that specifies the conditions for driving the recording element for recording at the boundary of a scan is, for example, in a binary input inkjet recording device, the image signal that specifies the ejection energy generation corresponding to the ejection port for recording at the boundary of the scan. Refers to a binary image signal input to an element, or generally a multi-value image signal input to a binary circuit before it, and in a multi-value input image recording device, it is used to record the boundary part of a scan. It can refer to an image signal recorded by a recording element.

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

(First Example) In this example, as an example of an image recording apparatus, a serial scan type inkjet recording apparatus that performs full-color image recording using three inkjet recording heads corresponding to cyan, magenta, and yellow will be described. . Here, it is assumed that the printing order of each ink color is cyan, magenta, and yellow. That is, in terms of configuration, the head 98k is omitted in FIG. 5, and the heads 9C, 9M, 9
It is assumed that the heads are arranged in the order of Y.

FIG. 1 is a block diagram showing a control system according to this embodiment. Here, IIC, IIM, and IIY are image signals specifying conditions for driving ejection energy generating elements arranged corresponding to ejection ports for recording boundary portions during serial scanning, and are respectively for cyan.

These are magenta and yellow image signals. 12 is an arithmetic processing unit that performs calculations such as the above equation (1) on the image signals +IC, 11M, and IIY, and the calculation results are 13G, 13M.
Outputs a 13Y signal.

14G, 14M, and I4Y are signals 13C and 13, respectively.
Human image signals 11C, IIM, I according to M, 1.3Y
This is a human image signal correction processing unit that corrects IY, and outputs a correction signal 15Cj5M15Y. Here, the operation of the input image signal correction processing section I4 will be explained using cyan as an example.

The correction of the human input image signal in the input image signal correction processing section 14 can be performed using, for example, a lookup table as shown in FIG. That is, input image signal 1
1C is converted into a signal 15G using a look-up table corresponding to the curve shown in FIG.

As is clear from FIG. 2, when the human input image signal is small, for example, in the case of a binary printer, when the number of recorded dots per certain area is small, no conversion is performed, but when the input image signal becomes large, In other words, when the number of recorded dots per area increases in a binary printer, for example, the output signal is suppressed to a small value, the amount of ink recorded at the border area decreases, and black streaks in high density areas are reduced. That's why.

The shape of the curve as shown in FIG. 2 is determined by the bleeding characteristics between the recording material and the ejected ink, and should be appropriately set according to these characteristics. Further, the shape of this curve does not need to be the same for each ink color.

Next, the arithmetic processing section 12 will be explained in detail.

The calculation processing unit 12 is basically a processing unit that performs calculations as shown in equation (1), but in this embodiment, all the coefficients of higher-order terms after the second term in equation (1) are Consider the case where it is 0''.

In the case of this embodiment, the number of recording heads is three, so n
=3. The image signals 11C, IIM, and IIY specifying the conditions for driving the ejection energy generating elements corresponding to the ejection ports for recording at the serial scan boundary of the three heads of cyan, magenta, and yellow are C, IIM, and IIY, respectively.
When written as M and Y, Xi is C, M, and Y. Therefore, in 13, 13M, 13Y, or x'j, are C', M'
, Y', equation (1) assuming that the coefficients of the higher-order terms after the second term are all 0 becomes C'-alccc"alc
-M◆alcyY -(2-1)M'-a
ll4(C+ali+MM+a1gyY
+++ (2-2) Y'mal,, C+alY, M+a
lYyY −(2-3), where a
lJ is a weighting coefficient.

According to these calculation results C' and M', one curve is selected from a group of curves as shown in FIG. 3 stored in the human image signal correction processing section, for example.

Here, the weighting coefficient a1'' will be explained in detail. The weighting coefficients alJ I l are set as appropriate, taking into consideration the differences in bleeding characteristics due to the differences in each ink color, the recording order of each ink color, etc., but for magenta as an example (2- To explain with reference to equation 2), for example, when magenta ink is used to record blue, the amount of bleeding of magenta ink is large because cyan ink has been recorded first.

For this reason, the correction amount must be increased, but as shown in FIG. 3, the correction amount is set so that when the value of <M' is large, the correction amount becomes a dog. In this case, it is sufficient to increase the value of Mo. Then, it becomes clear that the value of BIHc should be increased for the reasons described below.

When recording blue, since the value of C manually input is large, the influence of the first term of equation (2-2) is large. So all
, (If the value of When magenta ink is printed for the first time, the amount of bleeding is small, and if the correction amount used for blue printing described above is applied, the correction will be excessive, but this does not mean that cyan ink is not printed. Since the value of C is “0” or close to 0, at, ,c
Even if the value of is large, the first term of equation (2-2) has almost no effect, and the value of M" is not as large as it is when recording blue, and the correction is applied with an appropriate amount of correction. Become.

By setting other weighting coefficients in the same way, corrections can be made that take into account the influence of the printing order of each ink color, which is more effective than the method of determining the amount of correction from simple addition values. In particular, it is possible to prevent the occurrence of black streaks in the high 4 degree section.

Note that the above-mentioned processing is not performed on the ejection energy generating elements arranged at the ejection ports other than the ejection ports involved in recording the boundary portion of the scan, and the image signals specifying the drive conditions are sent to the heads 9G, 9M, and 9Y as they are. sent to.

(Second Example) In the first example above, we considered the case where the coefficients of the higher-order terms after the second term in equation (1) are all 0, but it is better to introduce higher-order terms. Black streaks can be effectively prevented.

In this embodiment, up to the second term of equation (1) is introduced, and the configuration is the same as that of the first embodiment except for the arithmetic expression applied to the arithmetic processing section 12 in FIG. In this example,
Rewriting equation (1) results in the following.

C'-alccC◆alc, M+alcYY+a2cc
cC'+a2. c, ICM+a2cc, CY+a2c,
,,,M'+a2c,,yMY+a2cyyY'・
...(3-1>M' ・al, I(C"al, ,,M
+a1.1iyY”azMcC(: 2+a2M,,C
M+a2. cyCY+a2b+MMM'a2xvyMY
”a2HyyY2- (3-2)Y' -a l Y
c C+a IYMM+ alyyY+ a2 Ycc
C2+ a2 ycxcllll” a2 ,,,CY”
a2yiimM2+a2yMyMY”a2yyyY2
-(3-3) However, C, M, and Y are image signals that specify the conditions for driving the ejection nozzles for recording the scan boundary portion of each head. Also, aFl+, a2”
Item 12 is a weighting factor as well.

The effect of introducing the quadratic term will be explained below, taking magenta as an example.

Considering recording blue in the same way as in the first embodiment, in the first embodiment, the value of Mo becomes large even when the C input signal is very large and the M input signal is relatively small. , the amount of magenta ink recorded at the scan boundary becomes small, which may result in excessive correction.

However, if we introduce a quadratic term as in this example, (3-2)
By increasing the value of 82MCM, which is the coefficient of CM in the formula, C
By making the coefficient almc smaller than the value in the first embodiment, the risk of excessive correction as described above is significantly reduced.

If other weighting coefficients are set in a similar manner, black streaks in high-density areas can be effectively prevented with less risk of excessive correction than in the first embodiment.

Note that in this example, as in the first embodiment, the image signal specifying the conditions for driving the ejection ports other than the ejection ports involved in recording the boundary portion of the scan is not processed as described above, and is directly sent to the head. 90. Sent to 9M, 9Y.

Also, terms after the cubic term may be introduced,
According to this, it is possible to effectively prevent black streaks in high-density areas while reducing the possibility of excessive correction.

(Third Example) In the first and second examples, the case where the present invention was applied to a color image recording device was described, but in the unimplemented example, the present invention was applied to a monochrome inkjet image recording device. Let's discuss the case where it is valid.

In order to solve the problem that dots stand out in highlighted areas in binary recording inkjet image recording devices, two inkjet heads eject ink of the same color in two shades of light and black, for example, to record an image. There are image recording devices that perform this. This method uses flame ink in highlighted areas to express the optical density with a large number of dots to alleviate the problem of conspicuous dots, and uses dark ink in areas with high optical density that cannot be expressed with light ink.

FIG. 4 shows a block diagram when the present invention is applied to such an inkjet image recording apparatus.

However, the same reference numerals as in FIG. 1 indicate similar elements.

here,? When using I4 tQ 2 fi class inks, the amount of bleeding is determined by the combination of the recorded amount of dark ink and the recorded amount of light ink and the recording order, and is calculated by simple addition, that is, (recorded amount of dark ink + light ink) Even if the values (recording amount) are the same, the amount of blurring is not necessarily constant.

Therefore, if a correction method using equation (1) as described in the first and second embodiments is used, black streaks can be more effectively prevented. However, the above correction process is performed only on the image signal that specifies the conditions for driving the ejection ports related to recording at the boundary of the scan, and only on the image signals that specify the conditions for driving the ejection ports for other areas. The signal is not subjected to the above processing and is sent to the head 9 as is.

(Roughly another example) Note that the recording element involved in recording the boundary part of the scan is as follows:
It does not need to be one recording element, but may be several recording elements. At this time, it is not necessary to use the same correction parameters for each recording element, and it is of course possible to appropriately set them depending on the position, for example.

In addition, for image recording devices that use multiple types of recording materials with different bleeding characteristics, the weighting coefficients and the shape of the correction curve shown in Figure 3 etc. can be adjusted as appropriate depending on the type of recording material. Just change it.

In addition, although the above explanation has given an example of an inkjet image recording device, the present invention can be applied extremely effectively and easily to any image recording device where bleeding is a problem, such as a thermal transfer printer using sublimation dye. Of course, it is.

In addition, it goes without saying that the type and number of recording agents, such as colors and shadings, and the corresponding number of recording heads can be adjusted as appropriate.

[Effects of the Invention] As explained above, according to the present invention, in an image recording apparatus in which bleeding is a problem such as an image recording apparatus having a plurality of serial scan type recording heads, simple addition, that is, the value of ΣXi Compared to determining the amount of correction from the above, black streaks can be prevented more effectively and high-quality images can be recorded.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the main parts of the first embodiment of the present invention, and FIGS. 2 and 3 are input image signals and input image signal correction processing unit output signals according to the first embodiment of the present invention. FIG. 4 is a block diagram showing another embodiment of the present invention; FIG. 5 is a perspective view showing an example of the mechanical configuration of a color inkjet recording device as a recording device to which the present invention can be applied. , FIGS. 6(^) and (B) are explanatory diagrams for explaining the mechanism of black streak occurrence. 4... Sub-scanning motor, 5... Recording material, 9G, 9M, 9Y,! lBk... Recording head, 12.
... Arithmetic processing section, 14.14G, 14M, 14Y... Input image signal correction processing section. Figure Figure Figure

Claims (1)

[Claims] 1) It has n recording heads in which a plurality of recording elements are arranged side by side,
In an image recording apparatus that performs image recording by serially scanning the recording head, specifying driving conditions of a recording element related to recording of a boundary portion by the scanning in the i-th recording head of the n recording heads. Xi (i=1, 2, 3・
...n), the value of the image signal that specifies the driving condition of the recording element related to recording of the boundary area in the j-th recording head is corrected according to the value of X'j determined by the following equation. An image recording device characterized by comprising a correction means. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ [j; i1; i2; −−−−−; in = 1, 2, 3, −
----, n: a1_j_i_1, a2_j_i_1_
i_2, -----, an_j_i_1 ---1n is a coefficient] 2) When the first to nth recording heads perform recording in this order and the X'j increases, the correction means When the amount of correction increases in the direction of decreasing the image signal that specifies the conditions for driving the recording element for recording the boundary portion in the j-th recording head, a1_m_−_1_i_1(i1<m−1)>a1_m
____1_i_1 (m-1<i1) [m=3, 4, 5,
---n] The image recording apparatus according to claim 1, wherein: