JP2815718B2 - Color thermal recording method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a color thermal recording method for expressing a halftone by changing the length of an ink dot in the sub-scanning direction.

[0002]

2. Description of the Related Art Thermal recording includes thermal recording in which an image is directly recorded on a thermal recording sheet, and thermal transfer recording in which ink of an ink film is transferred to recording paper. The thermal transfer recording includes a fusion type in which the melted ink is transferred to recording paper, and a sublimation type in which the amount of ink transferred to the recording paper changes according to thermal energy. Fused thermal transfer recording is widely used in personal word processors and the like, but has a problem that halftones cannot be expressed. The present applicant controls the energization time of the heating element according to the density of the pixel to be printed, and changes the length of the ink dot in the sub-scanning direction (the direction in which the recording paper is conveyed) to thereby provide a halftone image. (See, for example, Japanese Patent Application No. 15885/1990).

FIG. 6 shows a recording state of ink dots by the fusion type thermal transfer recording.
A total of six recording pixels (cells) in three rows and three columns are virtually represented by dotted lines. For each color, the pixel density in the main scanning direction and the sub-scanning direction is, for example, 100 lines / inch (8 dots / mm for dots), and the size of the recording pixels is 125 × 125.
μm. (A) shows a recording state of yellow, and yellow ink dots are recorded on all of the six recording pixels 2a to 2f as indicated by hatching.
(B) shows a magenta recording state, in which magenta ink dots are recorded in all of the six recording pixels 3a to 3f. (C) shows the recording state of cyan, and among the six recording pixels 4a to 4f, the recording pixels 4a, 4b, 4e,
At 4f, a cyan ink dot is recorded. If the color registration is complete, that is, if no color misregistration occurs, for example, the recording pixels 2a, 3a, and 4a will be at the same position on the recording paper, and the ink dots recorded on them will overlap, and Halftones are represented.

[0004]

When halftone is expressed by changing the length of ink dots in the sub-scanning direction,
Since the line extends in the main scanning direction, color moiré easily occurs. In addition, since recording is performed while moving the recording paper, the recording position is likely to shift in the sub-scanning direction. However, if this recording position shift occurs, the color tone of the image changes, and the color becomes different from that of the original image. When there is no color shift, for example, the color of the face is a yellowish tone, but when a color shift occurs, the color changes to a pinkish tone. This change in color tone is greatest when the displacement of the recording position in the sub-scanning direction is an integral multiple of half the pixel (half pitch). SUMMARY OF THE INVENTION It is an object of the present invention to provide a color thermal recording method capable of reducing the occurrence of color tone change and color moiré.

[0005]

According to the present invention, at least two types of ink dots are provided in the sub-scanning direction at intervals of one ink dot for one line arranged in the main scanning direction. Are shifted, and the shift amount is changed according to the color. According to the present invention, since the ink dots are arranged in a zigzag shape, the occurrence of color moiré can be reduced. Further, since good color reproducibility can be obtained in a state where the recording positions of the ink dots are shifted, even if the positions of the ink dots are slightly shifted at the time of recording, a change in the color tone is slight.

[0006]

FIG. 1 shows the arrangement of recording pixels for yellow, magenta and cyan. In order to clarify the overlapping state of the recording pixels of each color, a state is shown in which ink dots are recorded over the entire area of the recording pixels. It is represented by The yellow recording pixels 10a to 10f arranged in the main scanning direction have a zero shift amount in the sub-scanning direction (recording paper transport direction) between adjacent recording pixels. Magenta recording pixels 11a to 11f are 1
The dots are shifted by the distance L1 in the sub-scanning direction for every dot, and are recorded in a zigzag shape. Also,
The cyan recording pixels 12a to 12f are shifted by L2. The recording pixels shown in FIG. 1 are overlapped on the recording paper as shown in FIG.

In the embodiment shown in FIG. 1, L1 is １ ／ pitch and L2 is ピ ッ チ pitch. However, the shift amount can be arbitrarily determined according to the color tone change and the occurrence of color moiré. it can. In addition, the yellow recording pixels 10a to 10a
The position of f may be shifted every other dot.
These shift amounts are different depending on the type of the ink dot. However, since the yellow position shift has a small effect on the color tone change, the shift amount may be the same as the shift amount of cyan or magenta.

Next, with reference to FIGS. 3 to 5, a fusion type color thermal transfer recording apparatus embodying the present invention will be described.
In FIG. 3, a yellow ink area 15a, a magenta ink area 15b, and a cyan ink area 15c are formed on the ink film 15 at a constant pitch. When one hard copy is produced, three ink areas are formed. The color image is recorded on the recording paper 16 by three-color plane sequential recording. Note that a black ink area may be provided in the ink film 15 to record a color image in yellow, magenta, cyan, and black.

A thermal head 17 is arranged so as to press the back surface of the ink film 15, and heats and presses the ink film 15 from behind to transfer the melted ink to the recording paper 16. This thermal head 17
As shown in FIG. 4, a number of heating elements are formed in a line in the main scanning direction. In the drawing, only three heating elements 18a to 18c are shown.

The head vertical movement mechanism 20 is driven by a motor 21 to move the thermal head 17 in a direction indicated by an arrow, thereby pressing the thermal head 17 against the ink film 15 during recording. The motor 29 continuously rotates the platen 27 in the direction of the arrow via the platen roller drive mechanism 28. The recording paper 16 is wound around the outer periphery of the platen roller 27. The head driving unit 22 controls the energization time of each heating element while the recording paper 16 is moved by one recording pixel in the sub-scanning direction, and controls the energizing time in the sub-scanning direction according to the density of the pixel to be recorded. Determine the length of the ink dot.

The motor 23 rotates the take-up reel 24 to sequentially take up the used color areas, and after thermally transferring one color, pulls out the next color area to be recorded from the supply reel 25, and the leading end thereof. The thermal head 17
Set to the position facing. At the same time, the print head of the recording paper 16 is set at a position facing the thermal head 17 by rotating the platen roller 27. The controller 26 includes motors 21, 23, 2
9. Sequence control of the head drive unit 22.

FIG. 5 shows an example of a head driving section. The input unit 30 includes a video tape recorder or a scanner, and outputs a blue video signal B, a green video signal G,
The red video signal R is sent to the density conversion circuit 31. The density conversion circuit 31 converts the three-color video signal into a yellow density signal Y, a magenta density signal M, and a cyan density signal C,
The data is written into the frame memories 32 to 34, respectively.

At the time of producing a hard copy, the controller 26 sequentially sets the three frame memories 32 to 34 to the reading mode. In the frame memory set in the read mode, the density signals stored in the frame memory are read out line by line, and the three drive signal conversion units 35 to 37 are used.
Are converted to drive signals of the number of bits corresponding to the gradation step. For magenta, among the drive signals for one line, the drive signals for the odd-numbered pixels in the main scanning direction are, for example, the shift register 3.
8 and the drive signal of the even-numbered pixel is
After being delayed by 9, it is sent to the shift register 40. In the case of cyan, a drive signal of an odd-numbered pixel is sent to the delay circuit 39. The delay circuit 39 is set to a different delay time for each color by the controller 26.
In the case of yellow, the drive signal of the odd-numbered pixel is sent to the delay circuit 39. However, since the shift amount in the sub-scanning direction is zero for yellow, the delay time is set to zero.

In the drive signal, for example, in the case of 32 gradations, one pixel is composed of 32 bits, and the drive signal for one line is read out in 32 times. Therefore, at the start of recording of one line, only the first bit of the drive signal of each pixel is sequentially read out, sent to the shift registers 38 and 40 as serial signals, and converted into parallel signals. . In this way, the bits of each digit are sequentially read out at regular time intervals and sent to the shift registers 38 and 40. Each of the switch circuits 41 and 42
The shift register 3 is provided with a number of latch circuits and gate circuits corresponding to the number of heating elements of the thermal head 17.
The Parallel signals output from the 8, 40 latched at a predetermined timing. When this latch circuit is “1”,
The corresponding gate circuit is opened, while if it is "0", it is closed. When the gate circuit is opened, the heating element connected thereto is energized and heats the ink film 15.

Next, the operation of the above device will be described.
The video signal input from the input unit 30 is converted into a density signal and then written into the frame memories 32 to 34. When producing a hard copy, the controller 26 drives the motor 23 to rotate the take-up reel 24, and sets, for example, the head of the cyan ink area 15 a to the position of the thermal head 17. At the same time, the controller 26
Drives the motor 29 to rotate the platen roller 27 to set the recording paper 16 at the printing start position. Next, the controller 26 sets the frame memory 32 to the reading mode, and reads the yellow density signal line by line.
The read one-line yellow density signal is converted into a 32-bit drive signal by the drive signal conversion circuit 35, and is divided into an even number and an odd number in the main scanning direction. The drive signal of the even-numbered pixel is formed into a serial signal in which each bit is grouped for each digit, and the serial signal is sent to the shift register 38. The odd-numbered drive signal is converted into a serial signal, then delayed by a predetermined time in a delay circuit 39, and then sent to a shift register 40. Here, since the shift amount for yellow is zero, the shift amount is sent to the shift register 40 without being delayed by the delay circuit 39. These shift registers 38 and 40 convert a serial signal into a parallel signal and send it to switch circuits 41 and 42, respectively. These switch circuits 41 and 42 selectively turn on each heating element of the thermal head 17.

The recording paper 16 is continuously fed in the sub-scanning direction by a platen roller driving mechanism 28, and each heating element is determined by a drive signal while the recording paper 16 is fed by a distance in the sub-scanning direction of a recording pixel. It is energized only for a time. Since the ink film 15 is moved at the same speed as the recording paper 16, when each heating element of the thermal head 17 is energized according to the drive signal, the yellow ink area 15a is heated and pressurized from behind, and melts. Alternatively, the softened yellow ink dots are transferred to the recording paper 16. Thus, a yellow ink dot having a length corresponding to the density of the pixel is thermally transferred and recorded on each recording pixel.

Next, the yellow density signal of the second line is read from the frame memory 32, and the second line is recorded on the recording paper 16 as described above. When printing of one frame of yellow ink dots is completed, the motor 23 rotates to wind up the ink film 15, and the head of the magenta ink area 15 b is set at the position of the thermal head 17. In recording the magenta image, a magenta density signal is read from the frame memory 33 and converted into a drive signal. The drive signals of the even-numbered pixels are shifted by １ ／ pitch by the delay circuit 39. After the magenta image for one frame is recorded, the head of the cyan ink area 15c is set at the position of the thermal head 17, and the recording of the cyan image is started. In recording the cyan image, the odd-numbered pixels are shifted by １ ／ pitch by the delay circuit 39.

As is apparent from the above description, the main scanning method
Direction is the arrangement direction of the heating elements, and the sub-scanning direction is the main scanning direction.
The direction is orthogonal to the direction. In the above embodiment, therma
A head that records by moving the recording head or recording paper relative to one dimension.
Although it is an imprinter, the present invention
It can be applied to serial printers for recording.
Wear. In this serial printer, the thermal head
Move in the scanning direction, and the recording paper moves in the main scanning direction.
You. Further , in the sublimation type thermal transfer recording and the thermal recording, the coloring density changes in accordance with the heat energy. If this is used together with the area gradation method, high gradation image recording can be performed. The present invention can also be applied to sublimation type thermal transfer recording and thermal recording utilizing this area gradation method.

[0019]

As described in detail above, according to the present invention, at least two types of ink dots are used.
While shifting the recording position in the sub-scanning direction every dot,
Since this shift amount is changed according to the color, the occurrence of color moire can be reduced. Further, even when the three color ink dots are not recorded at the predetermined recording positions, the color tone change due to the ink dots can be minimized.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing positions of recording pixels of yellow, magenta, and cyan.

FIG. 2 is an explanatory diagram illustrating an overlapping state of three types of recording pixels on recording paper.

FIG. 3 is a schematic view showing a fusion-type color thermal transfer recording apparatus embodying the present invention.

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

FIG. 5 is a block diagram illustrating an example of a head driving unit.

FIG. 6 is an explanatory diagram showing positions of recording pixels when a conventional method is used.

[Explanation of symbols]

 10a to 10f Yellow recording pixels 11a to 11f Magenta recording pixels 12a to 12f Cyan recording pixels 15 Ink film 16 Recording paper 17 Thermal head 18a to 18c Heating element 27 Platen roller

Claims (1)

(57) [Claims] 1. A plurality of heating elements are arranged in a main scanning direction.
Of a pixel formed by at least three types of ink dots of yellow, magenta, and cyan using a thermal head
In a color thermal recording method of thermally recording a color image as a group , one pixel is formed according to gradation data obtained from the color image.
To obtain a gradation image by changing the recording width in the sub-scanning direction
In addition, the arrangement of pixels formed in the main scanning direction is such that pixels of each color formed by at least two types of ink dots
One pixel in the main scanning direction from a straight line whose position is parallel to the main scanning direction
Color thermal recording method characterized by changing the recording position for mind formed by shifting in the sub-scanning direction, and according to the shifting amount of this <br/> color.