JPH05116356A - Melting type color thermal transfer recording method - Google Patents

Abstract

PURPOSE:To enhance resolving power and a gradation number by preventing color shift, a color moire and a pattern moire from occurring. CONSTITUTION:Cell density in a sub-scanning direction S is changed according to a color. In cells becoming an odd number in a main scanning direction M, ink dots are recorded in the state approaching the start ends of the cells. In cells becoming an even number, ink dots are recorded in the state approaching the terminals of the cells. Magenta is lowest in gradation number but, by expressing one pixel using two cells arranged in the sub-scanning direction, the gradation number can be enhanced. The cell density in the sub-scanning direction is changed between cyan and magenta and the recording positions of ink dots are changed at every one with respect to a color low in cell density and the recording positions of ink dots are changed at every predetermined number in the main scanning direction with respect to a color high in cell density.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fusion-type color thermal transfer recording method suitable for recording halftone images.

[0002]

2. Description of the Related Art A melting type thermal transfer recording method uses a thermal head in which a large number of heating elements are arranged in the main scanning direction and presses it against the back of an ink film to transfer the softened or melted ink to a recording paper. Is. In this fusion type thermal transfer recording 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 of the present invention controls the energization time of the heating element, the magnitude of the current, the number of drive pulses, etc. to change the length of the ink dot recorded in the cell in the sub-scanning direction according to the density. Cyan and magenta are the cell density (pixel density) in the sub-scanning direction.
And a fusing color thermal transfer recording method in which even-numbered cells are shifted by a half pitch in the sub-scanning direction from odd-numbered cells in the main scanning direction. (Head 2 163726).

FIG. 6 shows a recording state of the above-mentioned fusion type color thermal transfer recording method, and each cell is virtually represented by a dotted line. One cell forms one pixel,
As shown by hatching, ink dots are recorded in half (50%) of each cell. These magenta ink dots, yellow ink dots, and cyan ink dots are overlapped, and a halftone image is represented by color mixing.

In magenta, the cell densities in the main scanning direction M, which is the arrangement direction of the heating elements, and the sub-scanning direction S orthogonal to the main scanning direction, are 8 dots / mm and 12 dots / mm, and the cells 2a to 2g are The size is 125 × 84 μm. The even-numbered cells are shifted by a half pitch with respect to the odd-numbered cells in the main scanning direction M, which reduces the effective cell density in the sub-scanning direction S to 2/3. That is, the effective cell size is 3/2 times larger.

Yellow has a cell density in the main scanning direction M of 8 dots / mm, which is the same as that of magenta, but a cell density in the sub scanning direction S is 9 dots / mm. Therefore, each of the cells 3a to 3g has a size of 125 × 110 μm. Further, one of the cells adjacent in the main scanning direction is shifted by a half pitch in the sub scanning direction S. As a result, the effective cell density in the sub-scanning direction S is reduced to 2/3. That is, the effective cell size is 3/2 times larger.

The cyan cells 4a to 4g are arranged in the main scanning direction M.
Has a cell density of 8 dots / mm, which is the same as magenta,
The cell density in the sub-scanning direction S is 6 dots / mm. Therefore, each of the cells 4a to 4g has a size of 125 × 166 μm. Further, one of the cells adjacent in the main scanning direction is shifted by a half pitch in the sub scanning direction S. As a result, the effective cell density in the sub-scanning direction S is reduced to 2/3.
That is, the effective cell size is 3/2 times larger.

[0007]

In the color thermal transfer recording method, since the size of the ink dots is changed, a gradation image can be expressed, and the cells are shifted by a half pitch. There is an advantage that the influence of the deviation is eliminated, and the occurrence of pattern moire and color moire can be suppressed. However, this recording method has a problem that it is not possible to express a sufficient gradation by colors.
For example, if an elongated heating element having a length in the sub-scanning direction S of 30 μm is used, the length of the smallest ink dot in the sub-scanning direction S is 30 μm for each color, and the feed pitch of the thermal head is 2 μm, then each ink is The dot area is 30μ
The number of gradations for each color is as follows, since it increases from m by 2 μm. Magenta: (84-30) ÷ 2 + 1 = 28 Cyan: (166-30) ÷ 2 + 1 = 69 As can be seen, magenta has too low a gradation when reproducing a photographic image.

Further, this recording method uses area gradation, and the resolution becomes lower as the number of gradations becomes higher, so that cyan has the lowest resolution. By the way, since the half pitch is shifted in the sub-scanning direction S, the overall resolution is reduced to ⅔ of that of cyan, which is the lowest resolution.

It is an object of the present invention to provide a fusion type color thermal transfer recording method capable of preventing the occurrence of color misregistration, pattern moire and color moire without lowering the resolution of the color having the lowest cell density. To do. Another object of the present invention is to provide a fusion-type color thermal transfer recording method in which the gradation number of the color having the maximum cell density is approximately the same as the gradation number of the color having the minimum cell density. It is a thing.

[0010]

In order to achieve the above object, the invention described in claim 1 is such that at least cyan and magenta have different cell densities in the sub-scanning direction, and each of these colors is Between the odd-numbered cells and the even-numbered cells in the main scanning direction, ink dots are printed closer to the start edge in the sub-scanning direction for one cell and sub-scanning for the other cell. Ink dots are recorded near the end of the direction. Further, for the color having the maximum cell density, it is preferable to express the gradation of one pixel by two cells arranged in the sub-scanning direction.

According to the third aspect of the present invention, at least cyan and magenta have different cell densities in the sub-scanning direction, and colors having a low cell density are odd-numbered cells and even-numbered cells in the main-scanning direction. Between the cells
For one cell, an ink dot is recorded by displacing it to the start end in the sub-scanning direction, and for the other cell, an ink dot is recorded by displacing it at the end in the sub-scanning direction. Two cells are grouped in the main scanning direction, and between the odd-numbered group and the even-numbered group in the main scanning direction, the cells of one group are moved closer to the start end in the sub-scanning direction. This is achieved by recording dots and then recording ink dots toward the other group of cells toward the end in the sub-scanning direction. Further, it is preferable to express the gradation of one pixel by one group.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the recording state of the invention described in claim 1, in which seven cells for each color are virtually represented by dotted lines. In the pixel of the maximum gradation level, ink dots are recorded in one cell, but in this embodiment, ink dots are recorded in half (50%) of the cells.

The cell density (pixel density) of magenta is 8 dots / mm in the main scanning direction M and 12 dots / mm in the sub scanning direction S, and the size of the cells 12a to 12g is 125 ×.
It is 84 μm. Odd numbered cells 12 in the main scanning direction M
a and 12c are ink dots 12a shown by hatching
i and 12ci are recorded in a state of being close to the start edge of the cell. On the other hand, the even-numbered cells 12b are recorded in a state where the ink dots 12bi are close to the end of the cells. Of course, ink dots may be printed from the end to odd-numbered cells and from the start to even-numbered cells.

The cell density of yellow is 8 in the main scanning direction M.
Dots / mm, the sub-scanning direction S is 9 dots / mm,
The size of the cells 13a to 13g is 125 × 110 μm. Odd numbered cells 13a and 13c in the main scanning direction M
Indicates ink dots 13ai and 13ci indicated by hatching.
Is recorded near the beginning of the cell. On the other hand, in the even-numbered cells 13b, the ink dots 13bi are recorded in a state in which the ink dots 13bi are close to the ends of the cells.

The cell density of cyan is 8 dots / mm in the main scanning direction M and 6 dots / mm in the sub scanning direction S, and the size of the cells 14a to 14g is 125 × 166 μm. Also for this cyan, the recording position of the ink dot 14bi is closer to the end of the cell 14b that is an even number in the main scanning direction M.

In this recording, the cells are not shifted by half pitch every other cell, so that the resolution in the sub-scanning direction S does not decrease. Further, since the ink dots of each color are not arranged in a line in the main scanning direction M, no pattern moire occurs, and the color densities do not occur because the cell densities of the respective colors are different. In general, color moire generated by the magenta line and the cyan line is conspicuous, but in this embodiment, as shown by the chain double-dashed line, since the screen angles of magenta and cyan are changed, the color moire can be ignored. ..

Although the cell densities in the main scanning direction M are the same for each color, the cell densities in the sub scanning direction S are different,
Magenta is the highest, and the size of one cell is 125 x 8
It is 4 μm. Therefore, as described above, 125 ×
When an ink dot is recorded in a cell with a heating bit of 30 μm and a feed bitch of 2 μm, only 28 gradations can be expressed.

The number of gradations of magenta can be increased by setting two adjacent cells in the sub-scanning direction S as one set and expressing one pixel by this one set. In this case, for gradation level 1, cell 1
2a minimum ink dot (length in the sub scanning direction is 30μ
Record m). At gradation level 2, 32 μm ink dots increased by 2 μm are recorded in the cell 12a.
In the same manner, if the ink dot size is increased by 2 μm, the size of the ink dot becomes 58 at the gradation level 15.
μm. At gradation level 16, cells 12a, 12d
Record the smallest ink dot on both. Gradation level 1
In the case of 7 or more, ink dots are recorded in the cells 12a and 12d alternately by 2 μm each.

As described above, when gradation expression is performed using two cells, a very low density portion (area ratio of about 0.18) is obtained.
Except for the cell density of 12 dots / mm, the number of gradations is (84 × 2-30) / 2 + 1 = 70, which is almost the same as the number of gradations of cyan (69). Therefore, although the resolution is reduced to half in this embodiment, the number of gradations can be greatly increased while preventing color moire, pattern moire, and color misregistration. Note that recording similar to magenta may be performed on yellow.

FIG. 2 shows a recording method described in claim 3. The cells of 1 row and 5 columns (5 in total) for magenta and 1 row and 3 columns (3 in total) of yellow and cyan are virtually displayed by dotted lines, and the ink dots are hatched. The cell density of magenta is 8 dots in the main scanning direction M and 12 dots in the sub scanning direction S.
The size of 2a to 22e is 125 × 84 μm. In the main scanning direction M, two cells are grouped, and in the odd numbered group and the even numbered group, one starts recording from the beginning of the cell and the other ends recording at the end of the cell. Ink dots are out of position. In this embodiment, cells 22a forming an odd group,
The ink dots of 22b are recorded near the beginning of the cell, and cells 22 forming an even group are formed.
The ink dots of c and 22d are closer to the end of the cell.
In this magenta recording, the resolution in the sub-scanning direction S is 12 dots / mm, as in the embodiment shown in FIG. 1, since the cells are not shifted by a half pitch. The resolution in the main scanning direction M is 8 dots / mm since the ink dots are the same regardless of whether they are near the start end or end of the cell.

The recording of yellow and cyan is exactly the same as that of the embodiment shown in FIG. That is, the cell density of yellow is 8 dots in the main scanning direction M and 9 dots in the sub scanning direction S, and the size of each of the cells 23a to 23c is 125 × 11.
It is 0 μm. In the cells 23a having an odd number in the main scanning direction M, the ink dots indicated by hatching are closer to the start end of the cells, and in the even cells 23b, the ink dots are closer to the end. The cell density of cyan is M in the main scanning direction.
Is 8 dots, the sub-scanning direction S is 6 dots, and each cell 2
The size of 4a to 24c is 125 × 166 μm. Similar to yellow, the printing positions of ink dots are also alternately shifted in the main scanning direction for cyan.

Also in this embodiment, as in the embodiment shown in FIG. 1, in addition to preventing pattern moire and color misregistration, the resolution in the sub-scanning direction S does not decrease. Further, as shown by the chain double-dashed line, the screen angle of magenta and the screen angle of cyan are larger than those in the embodiment shown in FIG. 1, so that the color moire can be further improved.

The number of magenta gradations is M in the main scanning direction.
It is possible to increase the number of gradations by grouping the two cells arranged in line and expressing the gradation by using these two cells as one set. In this case, for example, in the cell 22a,
The ink dot length in the sub-scanning direction S is 58 μm
Recording is performed until the gradation level reaches 15, and the gradation level is 1
When 6 or more, the minimum ink dot (30 μm) is recorded in the two cells 22a and 22b, and thereafter, the ink dot is alternately lengthened by 2 μm, whereby 70 gradations can be expressed. Similar recording may be performed for yellow.

Next, an apparatus for carrying out the recording method shown in FIG. 1 will be described with reference to FIGS. In FIG. 3, a cyan ink area 30a, a magenta ink area 30b, and a yellow ink area 30c are formed on the ink film 30 at a constant pitch, and when making one hard copy, three ink areas are formed. The color image is recorded on the recording paper 3 by three-color sequential recording.
It is recorded in 1. A black ink area may be provided in the ink film 30 to record a color image with cyan, magenta, yellow and black. When using this black, the cell density may be the same as that of yellow.

A thermal head 32 is arranged so as to press the back surface of the ink film 30, and the ink film 30 is heated from behind to transfer the melted ink to the recording paper 31. As shown in FIG. 4, the thermal head 32 has a large number of heating elements formed in a line in the main scanning direction. In the drawing, three heating elements 33a are provided.
Only ~ 33c is shown.

The head moving mechanism 34 is driven by a motor 35 and continuously moves the thermal head 32 in the sub-scanning direction indicated by the arrow. The head moving mechanism 34 is composed of, for example, a belt or a feed screw. The head drive unit 36 controls energization of each heating element while the thermal head 32 is moved by one cell in the sub-scanning direction S,
The length of the ink dot in the sub-scanning direction is changed according to the density of the pixel. In this embodiment, the thermal head 32 is 2μ.
Each heating element is driven every time it is moved by m. In addition to driving each heating element during continuous feeding of the thermal head 32,
The thermal head 32 may be intermittently fed by a constant distance, and each heating element may be driven while the thermal head 32 is stopped.

The motor 37 rotates the take-up reel 38b to wind up the used color area and draws out the next color area to be recorded from the supply reel 38a.
The recording sheet 31 is set at a recording position facing the recording sheet 31. The controller 39 controls the motors 35 and 37 and the head drive unit 36 in sequence.

FIG. 5 shows an example of the head drive section. The input section 40 is composed of a video tape recorder and a scanner, and has a green video signal G, a red video signal R,
The blue video signal B is sent to the density conversion circuit 41. The density conversion circuit 41 converts the three-color video signal into a magenta density signal M, a cyan density signal C, and a yellow density signal Y,
Write to the frame memories 42 to 44, respectively.

In order to prevent the change in color tone due to the color registration deviation, the interpolation circuits 45 and 4 are used in this embodiment.
6 is connected to the frame memories 42 and 44. These complementary circuits 45 and 46 are provided in the frame memories 42 and 4, respectively.
One pixel is interpolated for each fixed pixel in the sub-scanning direction with respect to the density signal read from each of the three, and the interpolated signals are written in the frame memories 47 and 48, respectively. For example, when performing 50% interpolation, it is sufficient to increase one pixel for every two pixels arranged in the sub-scanning direction. As the density of this interpolated pixel, the average value of the densities of two pixels, the density of the first pixel, or the like is used.

At the time of making a hard copy, the controller 39 sequentially sets the three frame memories 43, 47 and 48 in the read mode. In the frame memory set to the read mode, the density signals stored in the frame memory are read line by line, and the three drive signal conversion units 50 are
To 52, corresponding one of them is converted into a drive signal having the number of bits corresponding to the number of gradations. Of the drive signals for one line, the drive signals for the odd-numbered pixels in the main scanning direction are sent to the shift register 53, and the drive signals for the even-numbered pixels are delayed by the delay circuit 54 and then the shift register 55. Sent to. The delay circuit 54 shifts the recording start timing so that the ink dots recorded in the even-numbered cells are recorded closer to the end of the cells.

In the case of, for example, 69 gradations, the drive signal for one pixel is composed of 69 bits and is read out 69 times. Therefore, at the start of recording pixels for one line, only the first bit of the drive signal of each pixel is sequentially read and sent to the shift registers 53 and 55 as serial signals, where it is converted into parallel signals. To be done. In this way, the bits of each digit are sequentially read out at regular intervals, and the shift register 5
Sent to 3,55. The switching circuit 56 includes a number of latch circuits and switches corresponding to the heating elements of the thermal head 32, and latches the signals written in the shift registers 53 and 55 in the latch circuit at a predetermined timing. When this latch circuit is "1", the corresponding switch is turned on, while when it is "0", it is OF
F When the switch is turned on, the heating element connected thereto is energized to heat the ink film 30.

Next, the operation of the above device will be described.
The video signal input from the input unit 40 is converted into a density signal and then written in the frame memories 42 to 44. The magenta signal M and the cyan signal written in the frame memories 42 and 44 are interpolated in the sub-scanning direction by the interpolating circuits 45 and 46, and then the frame memory 47,
48 respectively.

At the time of producing a hard copy, the controller 39 drives the motor 37 to rotate the take-up reel 38b to set the cyan area 30a, for example, at a position overlapping the recording paper 31. Next, the controller 39 sets the frame memory 43 in the read mode and reads the cyan density signal line by line. The read cyan density signal for one line is converted into a drive signal by the drive signal conversion circuit 51, and is divided into an odd number and an even number in the main scanning direction. The bits of the odd-numbered pixel drive signal are grouped into digits to form a serial signal, and the serial signal is sent to the shift register 53. The even-numbered drive signals are converted into serial signals, delayed by the delay circuit 54 according to the gradation level, and then sent to the shift register 55. These shift registers 53 and 55 convert a serial signal into a parallel signal and send it to the switching circuit 56. The switching circuit 56 individually turns on each heating element of the thermal head 32.

The thermal head 32 is continuously fed in the sub-scanning direction by the head moving mechanism 34, and each heating element is driven every 2 μm movement. When the heating element is driven, it is heated and pressed from behind the cyan area 30a of the ink film 30 to transfer the softened or melted cyan ink dots to the recording paper 31. At this time,
In the even-numbered heating elements, the delay circuit 54 shifts the start of energization according to the gradation level, and the ink dots are recorded in a state of being close to the end of the cell.

Next, the cyan density signal of the second line is read from the frame memory 43, and the pixels of the second line are recorded on the recording paper 31 as described above. When the recording of the cyan ink dots for one frame is completed in this way, the motor 37 rotates to wind up the ink film 30 and set the yellow area on the recording paper 31. At the same time, the motor 35 reversely rotates to return the thermal head 32 to the recording start position. In the thermal transfer recording of the yellow image, the yellow density signal is read from the frame memory 48, and the ink dots are transferred in the same manner as the cyan recording described above. After the thermal transfer recording of the yellow image, the magenta area 30c is set on the recording paper 31, and the thermal transfer recording of the magenta image is started. These three types of ink dots are overlapped on the recording paper 31, and a halftone image is represented by subtractive color mixing or additive color mixing.

When the recording method shown in FIG. 2 is performed, the drive signal generation circuit 50 generates two drive signals from one cyan density signal, and these two adjacent heating elements are generated. Just drive. Further, in the above-mentioned embodiment, the cell density is changed by the interpolation process, but it may be changed by changing the sampling period when converting the video signal into the digital signal. The thermal head may be fixed, and the ink sheet and the recording paper may be transferred in the sub-scanning direction with the ink sheet and the recording paper stacked. Although the above embodiment is a line printer, the present invention can be applied to a serial printer.

[0037]

As described in detail above, according to the present invention, with respect to cyan and magenta, the positions of the cells adjacent to each other in the main scanning direction are shifted to the start end side of the ink dot cells without being displaced. Since the printing state and the printing state closer to the trailing end side are alternately performed, the resolution in the sub-scanning direction can be improved as compared with the conventional printing method while suppressing the occurrence of color shift, pattern moire, and color moire. Can be increased.

Between cyan and magenta, one pixel is represented by two cells adjacent in the main scanning direction or the sub scanning direction for a color having a high cell density in the sub scanning direction. The number of gradations can be increased since the recording is performed on the. Furthermore, since the difference in the screen angles becomes large, it has a remarkable effect in preventing color moire.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a recording method of the present invention.

FIG. 2 shows two adjacent cells in the sub-scanning direction
It is explanatory drawing which shows the method of recording a pixel.

3 is a schematic view of a fusion-type color thermal transfer recording apparatus for carrying out the recording method shown in FIG.

FIG. 4 is a bottom view of the thermal head.

FIG. 5 is a block diagram showing an example of a head drive unit.

FIG. 6 is an explanatory diagram showing a conventional recording method.

[Explanation of symbols]

 12a to 12g Magenta cells 12ai, 12bi, 12ci Magenta ink dots 13a to 13g Yellow cells 14a to 14g Cyan cells 22a to 12e Magenta cells 23a to 23c Yellow cells 24a to 24c Cyan cells 30 Ink film 31 Recording paper 32 thermal head 33a-33c heating element

Claims (4)

[Claims] 1. A thermal head in which a plurality of heating elements are arranged in the main scanning direction is used to change the length of an ink dot recorded in a cell in the sub scanning direction according to the density, and at least cyan, magenta, Yellow 3
In a fusion-type color thermal transfer recording method for recording a color image having a halftone on a recording paper with different types of ink dots, at least cyan and magenta have different cell densities in the sub-scanning direction, and Between the odd-numbered cells and the even-numbered cells in the main scanning direction, ink dots are printed closer to the start edge in the sub-scanning direction for one cell and sub-scanning for the other cell. 2. A fusion-type color thermal transfer recording method, characterized in that ink dots are recorded closer to the end of the direction. 2. The fusion type color thermal transfer according to claim 1, wherein for the color having the maximum cell density, the gradation of one pixel is expressed by two cells arranged in the sub-scanning direction. Recording method. 3. A thermal head having a plurality of heating elements arranged in the main scanning direction is used to change the length of ink dots recorded in the cells in the sub scanning direction according to the density, and at least cyan, magenta, Yellow 3
In the fusion-type color thermal transfer recording method for recording a color image with a halftone on a recording paper with different types of ink dots, at least cyan and magenta have different cell densities in the sub-scanning direction. Between the odd-numbered cells and the even-numbered cells in the main scanning direction, the ink dots are printed closer to the start end in the sub-scanning direction for one cell and for the other cell. Ink dots are printed closer to the end in the sub-scanning direction, and colors having a high cell density are grouped into two cells arranged in the main scanning direction, and become an odd number group and an even number group in the main scanning direction. With respect to the group, ink dots are printed at the beginning of the sub-scanning direction for the cells of one group, and at the end of the sub-scanning direction for the cells of the other group. A thermal color thermal transfer recording method of the melting type, characterized in that ink dots are recorded. 4. The fusion type color thermal transfer recording method according to claim 3, wherein the gradation of one pixel is expressed in each of the groups.