JPH02208064A - Thermal halftone recorder - Google Patents

Abstract

PURPOSE:To largely improve the quality of an image in the case of recording an image of intermediate density by employing an area modulation halftone thermal head for each element of 1Xn matrix for forming one pixel. CONSTITUTION:A halftone thermal head is employed as a thermal head 103, one pixel is composed of 1Xn matrix, each matrix element is area-modulated by using the head 103 to represent an image of each gradation. Here, two types are employed as a matrix pattern for specifying the change mode of a modulation area for the gradation. That is, a first matrix pattern is started for black coating from a matrix element m2 of a lower side in response to an increase in gradation, while a second matrix pattern is increased in the area of black coating on the matrix element m2 sequentially from the matrix element m1 of upper side.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a thermal halftone recording device that records halftone images by a thermal recording method.

(Prior Art) Conventionally, in order to record a halftone image using a thermal recording method, (I) one pixel is output in n times using a normal thermal head for recording binary images of white and black.

<n> Apply area modulation to each pixel using a half-tone thermal head whose heat generating area can be changed according to input energy.

Two methods were typical.

Among these, the thermal head used in method (1) has a rectangular heating element 703 between electrodes 701 and 702, as shown in FIG. The heating element 70 turns on and off.
3. Recording is performed by generating heat.

The recording characteristics of this thermal head are shown in FIG. The concentration reaches saturation.

Therefore, it is theoretically possible to obtain the required recording density by applying appropriate recording energy to the thermal head based on this recording characteristic, that is, to record a halftone image.

However, in actual recording operations, the dynamic range of recording energy that can be modulated, that is, the modulation energy width is 70
4 is too narrow, a slight error in the recording energy is amplified, causing variations in recorded density, and as a result, it is extremely difficult to produce a stable halftone recorded image in blue.

Here, we will verify that the modulation energy width 704 is narrow.

This can be determined by examining the heating state at each location inside the heating element 703, and in order to know this heating state, it is sufficient to examine the distribution of the current i involved inside the heating element 703.

This is because the amount of heat generated by the heating element 703 is determined by the input energy E, and this input energy E is determined by the current i.

In other words, when the resistance value is R, the input energy E can be expressed as E=R-i2 (1), and the current i in this can be expressed as the voltage ■ and the conductivity σ from electromagnetic observation. can be expressed as a vector.

Here, the voltage V is is the Laplace equation.

The above equation can be solved by the boundary element method, which is one of the computer calculation methods, and an example of the distribution of the current vector obtained by this method is shown in FIG.

FIG. 8 particularly shows the current distribution characteristics within the heating element 703 in a recording operation state in which the voltage of the electrode 701 is higher than that of the electrode 702, and the length of the current vector 705 corresponds to the strength of the current. are doing.

As is clear from the figure, since the magnitude of the current within the heating element 703 is uniform, it can be seen from equation (1) that the light heat is also generated uniformly.

Incidentally, a thermal transfer recording method is known as one type of image recording using such a thermal recording method.

This is a method of recording an image by applying heat-melting ink applied to an ink film, which is melted by the heat generated by the thermal head as described above, and then adhered to the recording paper, but the ink has wax as its main component. , a phase change from solid to liquid occurs at the melting point.

Therefore, in an actual recording operation, when the heating element 703 of the thermal head uniformly generates light and reaches the above-mentioned melting point, the ink in the ink film that is in close contact with the recording paper and in contact with the thermal head quickly solidifies. The phase changes from a phase to a liquid phase and is transferred to the recording paper, after which it is immediately attached to a solid phase and the recording is completed.

In the recording characteristics shown in FIG. 7(b), the modulation energy width is 70
This is why 4 is narrow.

A thermal head having such recording characteristics is originally suitable for recording binary images of white and black using saturated recording density.

For this reason, conventionally, when attempting to use this type of thermal head for recording halftone images, special measures for recording scanning were required.

One of them is a method of expressing a one-pixel image composed of a 1.times.n matrix by shifting n times, as shown in FIG.

Figure 9 is an example when n is 4, but nothing is recorded when the gradation is O, and once when the gradation is 1 (IX 1st stage element in a 1 x 4 matrix). Record only.

Similarly, when the gradation is 11g12, it is recorded twice (up to the IX 2nd stage element), and when the gradation is 3, it is recorded 3 times (up to the 1×3rd stage element).

And l? For i1!14, all four times (same, 1×4
If all elements (up to the step element) are recorded, it becomes possible to express a halftone image with five tones in total by area modulation of a black and white binary image.

On the other hand, method (n) is based on the idea of applying direct area modulation to one pixel in one scan, and as shown in FIG.
, a half-tone thermal head equipped with a heating element 1003 is used.

In this halftone thermal head, the shape of the heating element 1003 is given a characteristic so that the above-mentioned area modulation can be easily performed depending on the input amount of energy.

Here, in a recording operation state in which the heating element 1003 generates heat while applying a higher voltage to the electrode 1001 than the electrode 1002, the distribution of the current vector in the heating element 1003 is analyzed using the jM field element method described above. do.

Figure 11 shows the analysis results.
Looking at the distribution of the current vector 1005 in 003 (the length of the current vector 1005 corresponds to the strength of the current), it can be seen that the level increases as it approaches the center.

Furthermore, if we focus on the pixel size within the heating element 1003 during this recording operation, the pixel size at that time increases from 1006 to 100 as the input energy increases in order from the smallest to the largest.
You can see how it expands sequentially from 7 to 1008.

The recording characteristics of the halftone thermal head having such operating characteristics are shown in FIG. 10(b), and when compared with the recording characteristics of the non-halftone thermal head shown in FIG. 7(b),
It is clear that the modulation energy width 1004 of the former is significantly wider than the modulation energy width 704 of the latter, and from this it can be seen that by appropriately dividing the width, the setting of the halftone level in the former can be adjusted with respect to the latter. It turns out that it is easy to do.

In this way, conventionally, halftone images can be recorded by writing one pixel n times using a non-halftone thermal head, or by directly applying area modulation for each 1A pixel using a halftone thermal head. Met.

However, in any of these methods, deterioration in recording quality could not be avoided, especially when recording an intermediate density image.

The cause of this is the occurrence of so-called bridges in which transfer ink between adjacent pixels is connected during printing, which will be explained with reference to FIG. 12.

FIG. 12(a) shows the relationship between heating dots 1201 and transfer dots 1202 regarding adjacent pixels during low density image recording.

When recording a low-density image with a relatively small pixel size as described above, in order to ensure a sufficient distance d between the photothermal dots 1201 of adjacent pixels, the transfer dots of the ink melted and transferred from the ink film are 1202 as well, a correspondingly sufficient distance will be ensured.

On the other hand, a medium density image has a large pixel size, and when it is recorded, the distance d' between the heating dots 1203 of adjacent pixels becomes extremely small compared to the medium density image, as shown in FIG.

Therefore, the distance between the transfer dots 1204 of that pixel is also small, and when the recording paper is peeled off after transfer, the ink in unnecessary areas (other than the heat-generating dots 1203) is also peeled off and connected to the so-called bridge 12.
05 may occur.

The occurrence of such bridges 1205 causes the recording dots to collapse and makes the image quality unnatural, but this kind of unnatural image quality is not so noticeable in high-density images.
The most noticeable deterioration in image quality was felt in images with intermediate density.

(Problems to be Solved by the Invention) As described above, in the conventional thermal halftone recording device described above, one pixel is written n times using a non-halftone thermal head, or one pixel is written n times using a halftone thermal head. Although it is possible to record halftone images by applying area modulation,
Both methods have only 1@ type gradation patterns for the same gradation, and when recording images of intermediate density or higher, when pixels with similar dot sizes are adjacent, a bridge between the pixels with transfer ink is created. There is a problem in that image quality tends to deteriorate, especially when recording an intermediate density image.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to reduce as much as possible the occurrence of bridges due to transfer ink between adjacent pixels when recording images of intermediate density or higher, and particularly to improve the image quality of recorded images of intermediate density. The purpose of the present invention is to provide a thermal halftone recording device that can perform the following steps.

[Structure of the Invention] (Means for Solving the Problems) The thermal halftone recording device of the present invention has one pixel configured with a 1×n (n is an integer, n≧2) matrix, and each element of the matrix A thermal head that realizes the area modulation by a thermal recording method when expressing the floor WA degree for one pixel by the sum of the modulated areas while performing area modulation;
a pattern table that stores a matrix pattern that defines a change mode of the modulation area with respect to the gradation; and one of the matrix patterns stored in the pattern table.
The modulation area expands sequentially from the first matrix element to the nth matrix element in response to an increase in the gradation, and the pixel size, which is the modulation area, becomes smaller in the order of the matrix elements. A first matrix pattern lined up so as to change from a pixel size to a large pixel size, and another one of the matrix patterns stored in the pattern table, wherein the modulation is performed with respect to an increase in the gradation level. Contrary to the first matrix pattern, the area expansion progresses from the nth matrix element to the first matrix element in order, and the pixel size, which is the modulation area, increases from the large pixel size to the small pixel size in the order of the matrix elements. When the thermal head is driven to generate heat in synchronization with the conveyance of the thermal recording medium, the second matrix pattern is arranged so as to change in size, and when the thermal head is driven to generate heat in synchronization with the conveyance of the thermal recording medium, the second matrix pattern is The thermal head drive control means converts input image data into data for driving the thermal head and outputs the data while alternately using the first matrix pattern and the second matrix pattern.

(Function) The thermal halftone recording device of the present invention incorporates the advantages of both methods (I) and (n) described in the section of the prior art.
A xn matrix is used, and a predetermined gradation is obtained by writing n times while applying area modulation to every 1 x n matrix elements using an intermediate tone thermal bed.

At this time, the matrix pattern that defines the modulation area (pixel size) in accordance with the gradation level changes from a small pixel size to a large pixel size in the array direction of matrix elements as the gradation level increases. Prepare a first matrix pattern that changes from a large pixel size to a small pixel size, and a second matrix pattern that changes from a large pixel size to a small pixel size, and arrange them perpendicularly to the arrangement direction of the matrix elements of the recording pixels. They are used alternately in the recording scanning direction.

By doing so, on the recording rain, with respect to the dot arrangement of adjacent pixels in the direction perpendicular to the arrangement direction of the matrix elements, the interval between large and small pixel sizes is adjacent to each other, which is larger than before. will be presented.

The above-mentioned deterioration in image quality at intermediate densities is caused by the narrow spacing between these dots, which induces bridges caused by the transfer ink, and by eliminating this cause, it is possible to obtain good recorded images, especially at intermediate densities. become.

However, with this method, as the density increases, the dot spacing between adjacent pixels becomes smaller, making bridges more likely to occur; however, such high-density images are surjectively blackish, and bridges impair the apparent image quality. The impact will not be that large.

(Example) Hereinafter, an example of the present invention will be described in detail based on the accompanying drawings.

FIG. 1 is a conceptual diagram showing the configuration of main parts of a thermal halftone recording device according to the present invention.

In FIG. 1, the device drive system includes a pulse motor 101,
A conveyance roller 102 connected to this pulse motor 101 by a belt or the like, a thermal head 103 that comes into pressure contact with this conveyance roller 102, and a spring 104 that applies the pressure force.
, an ink film 105 interposed between the conveyance roller 102 and the thermal head 103, and this ink film 1
Ink film rollers 106 and 107 wind the ink film 1 at both ends, and the ink film 1 is
05, and a recording paper 110 that is supplied between the conveyance roller 102 and the thermal head 103 so as to be in close contact with the ink film 105 at the transfer position.

On the other hand, the control system includes a thermal head controller 111 that controls the heat generation drive of the thermal head 103, and a printer controller 112 that controls the rotation of the pulse motor 101.

Here, the thermal head controller 111 includes a dot counter 1111, a line counter 1112, and a pattern table 1113, and converts image data d1 inputted from a document reading section, etc., into thermal head control data d2 that can drive the thermal head 103. and output it.

The thermal head 103 is driven to generate heat based on the thermal head control data d2, and the generated energy melts the ink on the ink film 105 and transfers it to the recording paper 110.

On the other hand, the printer controller 112 starts a printing operation based on the printer control data d3, and conveys the ink film 105 and the recording paper 110 in the 31 scanning direction while rotating the pulse motor 101 in synchronization with the recording of the image data d1 described above.

Regarding this conveyance control, the dot counter 1111 outputs one line recording end data d4 each time one line of recording is completed, so the printer controller 112 outputs one line recording end data d4.
controls the rotation and angle of the pulse motor 101 at the timing of receiving this one-line recording end data d4, and transports the ink film 105 and the recording paper 110 by one line in the sub-scanning direction.

Due to the action of the guide shaft 108 accompanying this conveyance, the recording paper 110 is peeled off from the ink film 105 with the transfer ink still attached, so that a predetermined recorded image according to the image data d1 is obtained on the recording paper 110. become.

By the way, in the present invention, the first thermal head 103 is
A half-tone thermal head having an @ structure as shown in FIG. 1 is used.

Then, one pixel is formed into a 1×n matrix configuration, and the above-mentioned halftone thermal head 103 is used to perform area modulation for each matrix element to express an image of each gradation level.

Here, the following two types of matrix patterns are used as matrix patterns that define the manner in which the modulation area changes with respect to the gradation level.

The first of these matrix patterns is shown in FIG.

Fig. 2 is an example in which one pixel is formed into a 1x2 matrix in the main scanning direction x sub-scanning direction, and the size of the area of the black part within the elements m1゜m2 constituting this matrix is It shows how gradations from O to 16 are expressed.

Here, matrix element m1. The area of the black part in m2 increases with a certain regularity each time the l@ tone increases.

That is, in the first matrix pattern shown in FIG. 2, blacking starts from the matrix element m2 at the bottom of the figure for gradation 1, and thereafter, as the gradation increases, all matrix elements m2 become black. After being painted, the process proceeds to blacking the upper matrix element m1.

In actual recording, the area of the black portion in the matrix elements ml and m2 corresponds to the pixel size, so in other words, this first matrix pattern
l, it can be said that the pixel size changes from a small pixel size to a large pixel size in the second arrangement direction.

In contrast, a second matrix pattern used in the present invention is shown in FIG.

This second 7-trix pattern also moves one pixel in the main scanning direction
It is the same in that it is a matrix of IX2 in the IJ scanning direction, and the gradations from O to 16 are expressed depending on the size of the area of the black part in the matrix elements im1 and m2, but the matrix elements m1 and m2 are The manner in which the area of the blacked-out portion changes in this pattern is different from that of the first matrix pattern.

That is, in the first matrix pattern, blacking starts from the lower matrix element m2 according to the gradation h increase, whereas in the second matrix pattern, the matrix element is added in order from the upper matrix element im1. The area of the @ painted part increases toward Am2, and if we look at this change with respect to the matrix element m1 and the second arrangement direction, it can be seen that it is opposite to the first matrix pattern.

Therefore, when this second matrix pattern is captured at the pixel size 1iti mentioned above, the matrix element m1
, it can be said that the pixel size changes from a large pixel size to a small pixel size in the second arrangement direction.

This tendency of change in pixel size shows that the area of the black part in the upper matrix element m1 and the area of the black part in the lower matrix element m2 are significantly different from each other in FIGS. 2 and 3. Gradation, for example, 9-11m tone (A and A
') is especially clear when compared.

In the natural halftone recording apparatus of the present invention, the first and second matrix patterns are alternately used in the recording scanning direction perpendicular to the matrix element m1 of the second array direction.

Here, since the second arrangement direction of the matrix element m1 is set to the sub-scanning direction, the first matrix pattern and the second matrix pattern are used alternately in the main-scanning direction.

In order to achieve this, the thermal rad controller 111 determines which line, which dot, and what gradation, based on the image data d1 and the count values of the dot counter 1111 and line counter 1112 that match the input. The first or second matrix pattern corresponding to the @ key is read out alternately from the pattern table 1113 for each dot in the main scanning direction, and the thermal head 1
Supply to 03.

Here, each dot consists of two matrix elements m1. Since it is composed of a second line, it is necessary to write twice in order to completely record one line, and the conveyance of the ink film 105 and recording paper 110 in the sub-scanning direction for this purpose is controlled by the printer controller 112. There is.

In this way, the present invention uses a halftone thermal head to
Since area modulation is applied to each pixel and one pixel is expressed by writing n times, (I) and (
This recording method can be said to be a combination of method II).

An example of recording scanning performed under such control is shown in FIG.

In the figure, if attention is paid to the arrangement of matrix patterns in the main scanning direction for each line, it can be seen that the first matrix pattern and the second matrix pattern are used alternately for odd-numbered dots and even-numbered dots.

Further, FIG. 5 shows an enlarged schematic diagram of a recorded image, that is, a transferred dot, which is turned blue in accordance with this recording scan.

In the figure, a pixel 501 which is an adjacent pixel in the main scanning direction
and 502, the pixel 501 is recorded as a combination of a small pixel 5011 and a large pixel 5012 (first matrix pattern) in the same direction, whereas the pixel 502 is recorded in the same direction. On the other hand, large picture A5
021 and a small image 95022 (second matrix pattern).

Looking at this in the main scanning direction, the small pixel 5011 and large pixel 5021 are adjacent to each other in the first scan of pixels 501 and 502, and the large pixel 5012 and small pixel 5022 are adjacent to each other in the second scan. become.

Therefore, the separation distance in the main scanning direction of the transfer dots between these two pixels 501 and 502 is V71! This is much larger than ll', making it difficult for bridges to occur.

In particular, the occurrence of bridges at intermediate densities greatly reduces image quality, so eliminating the cause will greatly contribute to improving image quality.

The above embodiment relates to recording control using a 1×2 matrix in which the matrix elements are arranged in the sub-scanning direction, but in addition to this, an IX3 matrix can be used, and in that case An enlarged schematic diagram of the recorded image is shown in FIG.

In the figure, focusing on adjacent pixels 601 and 602 in the main scanning direction, pixel 601 is a small pixel a6 in the a1 scanning direction.
From 011 to medium pixel 6012 to large pixel a6
013 (the first matrix pattern), while the pixel 60
2 is recorded using a matrix pattern (second matrix pattern) that changes in order from a large pixel a6021 to a medium pixel 6022 to a small pixel a6023.

Here, if we look at each of these pixels 601 and 602 in the main scanning direction, for example, a small pixel a6011 and a large pixel 602
1, a sufficient distance D' between them in the main scanning direction can be secured, and the same effect as the above-mentioned one can be obtained in terms of preventing the occurrence of bridges.

Furthermore, this research can also use a matrix pattern in which the matrix elements are arranged in the main scanning direction, and in that case, the thermal head 1 can be adjusted according to this matrix pattern.
03, ink film 105 and recording paper 110
What is necessary is to change the control related to the conveyance of the .

〔Effect of the invention〕

As explained above, according to the thermal halftone recording device of the present invention, a halftone thermal head capable of area modulation is used for each element of a 1×n matrix constituting one pixel, and the matrix pattern is There are two types: one in which the pixel size changes from a large pixel size to a small pixel size in the arrangement direction of matrix elements according to the lit degree, and one in which the pixel size changes from a small pixel size to a large pixel size. Since seeds are prepared and recording scanning is performed while alternately using them in the direction perpendicular to the arrangement direction of the matrix elements of the recording pixels, the dot spacing between adjacent pixels becomes large and bridges due to the transfer ink are less likely to occur. In particular, it has the excellent advantage of being able to significantly improve the image quality when recording intermediate density images.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the main part configuration of a thermal halftone recording device according to an embodiment of the present invention, FIG. 2 is a diagram showing an example of a first matrix pattern used in the thermal halftone recording device of the present invention, Third
4 is a diagram showing an example of the second matrix pattern used in thermal halftone recording Iff of the present invention, FIG. 4 is a diagram showing an example of recording scanning using the matrix pattern shown in FIGS. 2 and 3, FIG. 5 is a schematic diagram showing a recording example in the thermal halftone recording device of the present invention, and FIG. 6 is a schematic diagram showing a recording example of the thermal halftone &! of the present invention when a 1×3 matrix is used for each pixel. A schematic diagram showing a recording example in a recording device, FIG. 7 is a diagram showing the electrode structure of a conventional thermal head and its recording characteristics, and FIG. 8 shows a current distribution in the heating element 703 of the thermal head shown in FIG. 9 is a schematic diagram for explaining the halftone recording method using the thermal head shown in FIG. 7. FIG. 10 is a diagram showing the structure of the electrode 4i of the halftone thermal head and its recording characteristics. FIG. 11 is a schematic diagram showing the current distribution in the heating element 1003 of the medium-Ha thermal head shown in FIG.
FIG. 8 is a diagram for explaining the cause of image quality deterioration in the eighth device. 101... Pulse motor, 102... Conveyance roller,
103... Thermal head, 104... Spring, 10
5... Ink film, 106, 107... Ink film roller, 108, 109... Guide shaft, 110... Recording paper, 111... Thermal head controller, 112... Printer controller, 11
11... Dot counter, 1112... Line counter, 1113... Pattern table, 501°50
2.601,602--pixels, 5011°5012.
5021, 5022, 6011゜6012.6013,
6021,6022°6023...Picture point, 701,7
02,1001゜1002-W pole, 703,1003・
l heating body, 704.1004...modulation energy width, 7o
5゜1005...Current vector!・Le, 1201.120
3...Heating dot, 1202.1204...Transfer dot, 1205...Bridge, ml, m2...Matrix pattern of Chapter 1 for matrix element n=2, Fig. 2, 7L=21. ：Akeru'12 matrix pattern Figure 3 Main direction i direction Main direction i8 clause ○○○ Figure 6 1 to 115 direction Figure 8 Figure 7 (a) ) Memory density main scanning direction Fig. 12(a) Fig. 12(b)

Claims (1)

[Claims] One pixel is constructed of a 1×n (n is an integer, n≧2) matrix, and area modulation is performed for each element of the matrix, and the sum of the modulated areas is used to determine the area of the one pixel. When expressing a gradation level, a thermal head realizes the area modulation by a thermal recording method, a pattern table that stores a matrix pattern that defines a change mode of the modulation area with respect to the gradation level, and a pattern table that stores a matrix pattern that defines a change mode of the modulation area with respect to the gradation level; One of the matrix patterns, in which the modulation area expands sequentially from the first matrix element to the nth matrix element as the gradation increases, and the pixel size that is the modulation area is the matrix pattern. A first matrix pattern whose elements are arranged in order of increasing pixel size from small pixel size to large pixel size, and another one of the matrix patterns stored in the pattern table, in which the pixel size increases On the other hand, the expansion of the modulation area progresses from the n-th matrix element to the first matrix element, contrary to the first matrix pattern, and the pixel size, which is the modulation area, increases in the order of the matrix elements. A second matrix pattern arranged in such a way that the pixel size changes from small to small, and a second matrix pattern that is arranged perpendicularly to the arrangement direction of each matrix element in the recording pixel when the thermal head is driven to generate heat in synchronization with the conveyance of the thermal recording medium. The thermal head drive control means converts input image data into data for driving the thermal head and outputs the data while alternately using the first matrix pattern and the second matrix pattern in the scanning direction. Features of thermal halftone recording device.