JPH07223330A - Melt-type thermal transfer printing method - Google Patents

Abstract

PURPOSE:To record a high-quality halftone image in color and monochrome. CONSTITUTION:At the time of recording a color halftone image, a Y LUT 15, an M LUT 16, and a C LUT 17 are used. The length of a pixel of Y, C in a sub-scanning direction is twice longer than that of a pixel of M. With respect to all the pixels Y, M, C, adjacent pixels in a main scanning direction are shifted form each other in the same direction in the sub-scanning direction by 1/2 of the length of the pixel in the sub-scanning direction. In this pixel arrangement, a color image is recorded on recording paper 22 by a three-color face sequential manner. At the time of recording a monochrome halftone image, a monochrome halftone image LUT 18 is used. Ink dots of an odd-numbered pixel in a main scanning direction are increased from one end to the other. Ink dots of an even numbered pixel are increased from one end to the other in the reverse direction. In this pixel arrangement, ink dots are formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fusion type thermal transfer printing method in which halftones are expressed by changing the length of ink dots recorded in pixels, and more specifically, a color image and a monochrome image are selectively selected. It concerns a method for recording.

[0002]

2. Description of the Related Art A fusion type thermal transfer printing method uses a thermal head in which a large number of heating elements are arranged in the main scanning direction.
This is pressed against the back of the ink film to transfer the softened or melted ink to the recording paper. In this fusion type thermal transfer printing method, the amount of ink transferred onto the recording paper cannot be adjusted according to the amount of heat, and is therefore used for recording binary images such as line drawings and characters. The applicant uses a heating element that is elongated in the main scanning direction, controls the energization time of the heating element, the magnitude of the current, the number of drive pulses, and the like,
There has been proposed a method of recording a halftone image by changing the length of ink dots recorded in a pixel in the sub-scanning direction (for example, JP-A-3-219969).

In order to record a color halftone image by such a printing method, the dot patterns of three colors are printed in an overlapping manner, but when the overlap is shifted, the color tone changes. In order to prevent this, the Applicant has selected 2 out of 3 colors.
For the color, the pixel size in the sub-scanning direction is made twice as large as that of the other color, and for each color, a half pitch shift between adjacent pixels in the main scanning direction is proposed (for example, Japanese Patent Application No. 3-320521). When this method is used, even if the respective colors are slightly shifted, they shift due to the complementary color relationship, so that the change in color tone does not occur from a macro perspective.

[0004]

When a monochrome halftone image is recorded by the above method, a pixel array of one of the three colors is used, but this arrangement causes a half pitch shift between adjacent pixels. Ink dots are recorded in the
There was a drawback that the graininess was noticeable and the image quality deteriorated.

It is an object of the present invention to provide a fusion type thermal transfer printing method capable of recording a high quality halftone image in both color and monochrome.

[0006]

In order to achieve the above object, the fusion type thermal transfer printing method according to claim 1 changes the pixel arrangement between color recording and monochrome recording. However, high-quality print images can be obtained even in monochrome. Further, in the fusion type thermal transfer printing method according to claim 2, when a color image is recorded, the color image is composed of at least three types of ink dots of yellow, magenta and cyan, and two types of the three types of ink dots are used. The pixels in the sub-scanning direction have twice the length in the sub-scanning direction, and pixels adjacent to each other in the main scanning direction in the sub-scanning direction are adjacent to pixels of all colors. When printing a monochrome image by shifting in the same direction in the sub-scanning direction by 1/2 of the length, the number of ink dots in the odd-numbered pixels in the main-scanning direction increases from one end to the other end, and becomes an even number. In the pixel, the number of ink dots is increased from one end to the other end on the opposite side. In this way, since the pixel shift is not performed in the monochrome image, the roughness becomes inconspicuous.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows the outline of a thermal printer. Image data of a halftone image or a binary image to be printed is written in the frame memory 9. A print controller 12 that converts image data into print data and sends the print data to the thermal head 10 is connected to the frame memory 9. Five dot patterns referred to by the print controller 12 are provided according to the type of image, and each of them is a lookup table for yellow (LU for Y).
T) 15, magenta lookup table (LU for M
T) 16, cyan look-up table (C LU
T) 17, a monochrome halftone image lookup table (monochrome halftone image LUT) 18, and a binary image lookup table (binary image LUT) 19. Print controller 12 and LUTs 15-1
9 is connected via a switch SW, and this switching is performed by the system controller 13.

When printing a color halftone image, the LUT 15 for Y, the LUT 16 for M, and the LUT 17 for C
Are selected, and these are sequentially printed by the print controller 12
Connected to. When printing a monochrome halftone image, a monochrome halftone image LUT 18, and when printing a binary image such as a character or line drawing, a binary image LUT 1
9 are selected and connected to the print controller 12.

The thermal head 10 is arranged with an array of heating elements extending in the axial direction of the platen drum 21. A recording paper 22 is mounted on the outer periphery of the platen drum 21 and rotates intermittently or continuously in the sub-scanning direction indicated by the arrow. An ink film 23 is arranged between the recording paper 22 and the thermal head 10.
The recording paper 2 is guided by the guide rollers 24 and 25.
It moves in the sub-scanning direction together with 2. As is well known, the ink film 23 has cyan, magenta, and yellow ink areas formed at a constant pitch.

As shown in FIG. 2A, the thermal head 10 has a plurality of heating elements 10a, 10b, 10c, ... Arranged in a line in the main scanning direction (M). Each heating element has an elongated rectangular shape having a length L in the main scanning direction and a length D in the sub-scanning direction (S). Length L in the main scanning direction
Is, for example, 125 μm, and has a length D in the sub-scanning direction.
Is, for example, 25 μm. Note that a vertically long heating element that is shorter in the sub-scanning direction may be used.

As shown in FIG. 2B, the M LUT 16
Pixel 2 of magenta recorded according to the dot pattern of
6 has a square shape surrounded by a dotted line and having one side L. The length L in the main scanning direction corresponds to the length of the heating element in the main scanning direction, and the length in the sub scanning direction is determined by the energization state of the heating element. Pixels adjacent in the main scanning direction have a recording position L / L in the sub scanning direction so that moire and parallel lines do not occur.
It is off by 2. Ink dots 27 having an area ratio of 50% are recorded on each pixel 26 as indicated by hatching.

2C and 2D are LUT 1 for C
7 shows cyan and yellow pixels recorded according to the dot patterns of the Y and Y LUTs 15, respectively. The cyan pixel 28 and the magenta pixel 29 have a length L in the main scanning direction and a length 2L in the sub scanning direction. With respect to these colors as well, the pixels are shifted by 1/2 pitch between adjacent pixels in the main scanning direction.
The reference numerals 30 and 31 represent cyan ink dots and yellow ink dots.

FIG. 3 shows a state in which a gray color having an area ratio of 50% is recorded, which is obtained by superimposing pixels of each color shown in FIG. Black (K), green (G), magenta (M), and white (W) in the first row extending in the sub-scanning direction.
The color pattern of occurs periodically. In the second row adjacent to this, white (W), magenta (M), green (G), black (K)
Color pattern occurs. The two adjacent columns have the color patterns arranged in the opposite order, and the adjacent colors have a complementary color relationship.

FIG. 4A shows a state in which the registration deviation occurs in yellow and the pixels are displaced upward by ¼ pitch. In this state, Y, K, G, C,
A color pattern of M, W appears, and B, W,
Color patterns of M, R, G and K appear. These two color patterns also maintain the complementary color relationship. For example, in the first row, G in the first column is divided into G and C,
W is divided into W and Y. In the second column, M is divided into M and R, and K is divided into K and B. Since Y and B have a complementary color relationship and K and W have the opposite lightness, they are gray when viewed macroscopically. The colors of other rows are the same.

As described above, when the misregistration occurs in yellow, the color changes microscopically. However, the human eye does not identify small individual ink dots,
A color is identified from a group of ink dots. Therefore, although the color changes microscopically, since it changes while maintaining the complementary color relationship, the color tone does not change as a whole,
In addition, uneven color is not noticeable.

FIG. 4B shows a state in which cyan is shifted downward by ½ pitch of the pixel. When this cyan registration shift occurs, the color pattern changes, but since the complementary color relationship is still maintained, the color tone does not change as a whole. (C) shows a state in which magenta is shifted up by 1/2 pitch and yellow is shifted up by 1/4 pitch. Even if this misregistration occurs, the color tone does not change.

As shown in FIG. 5B, the monochrome halftone image pixel 32 surrounded by a dotted line has one side L and the other side 2L.
It has a rectangular shape. The length L in the main scanning direction corresponds to the length of the heating element in the main scanning direction, and the length 2L in the sub scanning direction is determined by the energization state of the heating element. In the present embodiment, a dot pattern in which the number of ink dots increases from one end to the other end is used for the odd-numbered pixels in the main scanning direction, and the ink dot is increased from the opposite end to the other end for the even-numbered pixels. Use a dot pattern that increases As a result, since the ink dots 33 are appropriately scattered, it is difficult to form a line that is connected in the main scanning direction, and it is possible to suppress the occurrence of moire. Further, each pixel has 10 gradations, and one pixel is composed of 10 sub-lines. For example, in the case of one gradation, one subline is recorded, and in the case of two gradations, two sublines are recorded.

FIG. 5C shows a state in which a monochrome binary image such as a character or a line drawing is recorded. Each of the binary image pixels 34 surrounded by the dotted line has a length L in the main scanning direction and a length in the sub scanning direction, and has a square shape. The dot pattern for a binary image is divided into pixels to be recorded and pixels not to be recorded according to a predetermined threshold value, printing data which becomes 100% painting is applied to pixels to be recorded, and 0 to pixels which are not.
Corresponds to% print data. The melted or softened ink is transferred to the binary image pixel 34 to be recorded, and the ink dot 35 shown by hatching is formed. In this embodiment, since L is 125 μm, the pixel density in the main scanning direction and the sub scanning direction is 8 dots / mm.

The operation of the thermal printer thus configured will be described. When printing a color halftone image, the system controller 13 switches the switch SW to first select the M LUT 16. The print controller 12 reads out the magenta dot pattern from the M LUT 16, converts the green image data written in the frame memory 9 line by line into magenta print data, and sends this to the thermal head 10. The magenta print data is in a signal form such that the pixels adjacent to each other in the main scanning direction are delayed by 1/2 pitch and the ink dot length is changed in the range of D to L.

The platen drum 21 rotates in the sub-scanning direction indicated by the arrow while holding the recording paper 22. At the same time, the ink film 23 is fed in the direction of the arrow, and the start end of the magenta ink area is set below the thermal head 10. Each time the platen drum 21 rotates by 25 μm, for example, the heating element is driven according to the print data,
The ink film 23 is heated and pressed from behind to transfer the melted ink to the recording paper 22. As a result, FIG.
As shown in (B), the length in the sub-scanning direction changes according to the recording density, and ink dots that are zigzag in the main scanning direction are recorded in the pixels 26. As the platen drum 21 rotates, magenta images are recorded on the recording paper 22 line by line.

When the platen drum 21 makes one rotation, the start end of the recording paper 22 returns to the recording start position, and the cyan ink area is set in the ink film 23. The system controller 13 switches the switch SW to change the LU for C.
Connect T17 to the print controller 12. The print controller 12 reads the cyan dot pattern from the C LUT 17, and converts the red image data in the frame memory 9 into cyan print data. This print data is sent to the thermal head 10, and a cyan image is recorded line by line as shown in FIG.

In recording a yellow image, the LUT 15 for Y is used.
Is connected to the print controller 12, and blue image data is converted into yellow print data. The yellow print data is supplied to the thermal head 10, and a yellow image is recorded on the recording paper 22 line by line. The print data of yellow and cyan is in a signal form such that the pixels adjacent to each other in the main scanning direction are delayed by 1/2 pitch and the length of the ink dot is changed in the range of D to 2L. There is. In addition, although a color halftone image is recorded in the three-color frame sequential manner as described above, the color order is determined according to the ink film.

When printing a monochrome halftone image, the system controller 13 connects the monochrome halftone image LUT 18 to the print controller 12. The print controller 12 reads the dot pattern for the monochrome halftone image from the monochrome halftone image LUT 18, converts the monochrome halftone image data in the frame memory 9 into print data, and sends the print data to the thermal head 10. Each time the platen drum 21 is rotated by, for example, 25 μm, the heating element is energized, and as shown in FIG. 5B, ink dots are formed between odd-numbered pixels and even-numbered pixels in the main scanning direction. A monochrome halftone image is recorded using dot patterns that increase in opposite directions. In addition,
For a mixed image of a binary image and a halftone image, the binary image is recorded and then the halftone image is recorded. Of course, the binary image may be recorded after the halftone image is recorded.

When printing a binary image such as a character or a line drawing, the system controller 13 switches the switch SW to connect the binary image LUT 19 to the print controller 12. The print controller 12 converts the image data into print data for a binary image based on the dot pattern for the binary image and sends the print data to the thermal head 10. Each time the platen drum 21 rotates by 25 μm, for example, the heating element is energized, and a binary image as shown in FIG. 5C is recorded on the recording paper 22.

In the above embodiment, the line printer is described as an example, but the present invention can be applied to a serial printer in which the thermal head moves in the sub scanning direction. In this serial printer, due to uneven paper feeding, the seams become a streak in the overlapping part,
Using the method of the present invention, this seam is less noticeable.
Further, although the above-mentioned embodiment is the fusion type thermal transfer recording, the present invention can be applied to sublimation type thermal transfer recording, thermal recording, ink jet recording, electrophotographic recording and the like.

[0026]

As described in detail above, according to the present invention, the pixel arrangement is changed to the optimum one depending on whether the image to be printed is color or monochrome, so that high image quality can be obtained in both color and monochrome. It is possible to obtain various printed images.

[Brief description of drawings]

FIG. 1 is a schematic view showing a fusion type thermal transfer recording apparatus for carrying out the present invention.

FIG. 2 is an explanatory diagram showing a recording state of each pixel of yellow, magenta, and cyan.

FIG. 3 is an explanatory diagram showing a color pattern when recording a gray area ratio of 50%.

FIG. 4 is an explanatory diagram showing a color pattern when misregistration occurs.

FIG. 5 is an explanatory diagram showing a recording state of each pixel of a monochrome halftone image and a binary image.

FIG. 6 is an explanatory diagram showing a dot pattern for a monochrome halftone image.

[Explanation of symbols]

 10 Thermal Head 12 Print Controller 13 System Controller 15 Y LUT 16 M LUT 17 C LUT 18 Monochrome Halftone Image LUT 19 Binary Image LUT 22 Recording Paper 23 Ink Film 26, 28, 29 Pixels 27, 30, 31, 33, 35 ink dots 32 monochrome halftone image pixels 34 binary image pixels

Claims (2)

[Claims] 1. A thermal head in which a plurality of heating elements are arranged in the main scanning direction is used to sequentially record a plurality of sub-lines constituting one pixel, and the halftone image is obtained from the area of ink dots recorded in the pixel. In the melt-type thermal transfer printing method, the pixel arrangement is changed when recording a color image and when recording a monochrome image. 2. A thermal head in which a plurality of heating elements are arranged in the main scanning direction is used to sequentially record a plurality of sub-lines constituting one pixel, and the halftone image is obtained from the area of the ink dot recorded in the pixel. In the fusion-type thermal transfer printing method that expresses, when a color image is recorded, the color image is composed of at least three types of ink dots of yellow, magenta, and cyan, and two types of pixels among these three types of ink dots are The length in the sub-scanning direction is made twice as long as that of the other type of pixel, and the pixel in the sub-scanning direction has a length of 1 between pixels adjacent to each other in the main scanning direction with respect to pixels of all colors. / 2 is shifted in the same direction in the sub-scanning direction, and when printing a monochrome image, the number of ink dots increases from one end to the other end in the odd-numbered pixels in the main scanning direction, Melt type thermal transfer printing method which is characterized in that so as to increase the ink dot from one end to the other end opposite to the pixel to be turn.