JP3141609B2 - Thermal halftone 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 a halftone recording method for performing color printing using a thermal printing head (thermal head) in which a plurality of heating resistors are juxtaposed in the main scanning direction. .

[0002]

2. Description of the Related Art Conventionally, there are (1) a sublimation type thermal transfer recording method and (2) a color halftone recording method using a thermal head.
There are a fusion type thermal transfer recording method and (3) a heat sensitive halftone recording method. (1) The sublimation type thermal transfer recording method has a problem in that it requires a large amount of energy, it takes a long time to print, or a special paper is used, so that the cost is high. (2) In the fusion type thermal transfer recording method, printing can be performed with small energy and the cost is low. However, since the ink donor film itself cannot obtain gradation even if the applied energy is changed, it is difficult to perform multi-gradation recording. Therefore, a matrix method such as a dither method, and a method of taking a gradation by reducing a heating region such as sub-scanning division and heat concentration have been proposed. (3) In the heat-sensitive halftone recording method, halftone recording is performed using a heating element whose width in the sub-scanning direction is shorter than the width in the main scanning direction (JP-A-60-248074, 219969). This method is called a sub-scanning division method and has the following configuration.

FIG. 11 is a plan view of a heat generating portion of a thermal head used in this method. The electrode structure is a comb-like common electrode 10 (electrodes 11 to 16) and comb-like selection electrodes 31 to 35.
And an alternate lead type in which the strip-shaped resistors 20 arranged in one row in the main scanning direction on the selection electrode are arranged. The width of the heating element of the heating resistor 20 in the sub-scanning direction is shorter than the width in the main scanning direction. Printing by the thermal head is performed by selecting electrodes 31 to 31
When 35 is selected and energized, the resistor sandwiched between the selected electrode and the common electrode on both sides of the selected electrode generates heat. FIG. 12 shows an example of print recording when halftone recording is performed using this thermal head. In color recording, three colors of yellow, magenta, and cyan (black) are overprinted. The printing record shown in FIG. 12 shows a printing state for each color. For example, FIG. 12A shows the printing state of each pixel (pixels 41 to 45) of the resistor 20 of the first color, (b) shows the printing state of the second color, and (c) shows the printing state of the third color. Is shown. As shown in this figure, in the halftone recording, each pixel is often printed and recorded, and the recording start timing of each pixel 41 to 45 is the same. Are aligned, and a line is formed in the main scanning direction. For this reason, the formed line is emphasized, and a streak noise in the main scanning direction occurs in the printed image, thereby deteriorating the image quality. In addition, if registration in each color is not accurately performed for each print, the degree of overlap of the lines formed in each color is changed, and the degree of polymerization differs for each print, causing a problem of color shift.

[0004]

In view of the foregoing, the present invention has been made in consideration of the above-described problems, and has been described in view of the above problem. A halftone recording method is proposed.

[0005]

According to the present invention, a halftone using a thermal head in which a plurality of heating resistors whose width in the sub-scanning direction is shorter than the width of one pixel in the sub-scanning direction is arranged in the main scanning direction. The recording method has a configuration in which the recording start position of one pixel in the sub-scanning direction is shifted by a fixed amount within the width of one pixel with respect to the recording start position of an adjacent pixel.

Further, a thermal halftone recording method for color printing is to make the resolution in the sub-scanning direction and the resolution in the main scanning direction of one pixel different for each color of cyan, magenta, yellow and black, and to perform the sub-scanning of one pixel. The recording start position in the direction is shifted from the adjacent pixel by a certain amount within the width of one pixel, and the halftone density of each color is recorded.

Also, image data of the same gradation in the main scanning direction
When a continuous thin line or character is detected, the recording start position of each pixel at the detection position is set to the same position.

[0008]

Since the recording start position in the sub-scanning direction is shifted by a fixed amount within the width of one pixel from the recording start position of the adjacent pixel, a line due to the connection with the adjacent pixel is less likely to occur. In the case of color printing, by changing the resolution in the sub-scanning direction and the resolution in the main scanning direction of one pixel for each color of cyan, magenta, yellow, and black, the line generated in each color is It has different angles, the overlapping of dots recorded by each resistor is different, and macroscopic problems such as streak noise and color misregistration are solved, and good halftone recording can be realized. . Furthermore, fine lines and
Recording of thin lines and dots indicating characters when characters are detected
Simultaneous timing allows halftone images and color
A good image can be obtained in the halftone image.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described in detail with reference to the drawings.

Embodiment 1 FIG. 1 is a diagram for explaining a basic halftone expression by a thermal halftone recording method. FIG. 1A is an explanatory diagram of a thermal head, and FIG. (C) is an explanatory diagram of the pulse generation timing. The electrode structure of the thermal head shown in this embodiment has a comb-like shape of electrodes 51.
., 78 alternately arranged on the common electrode 50 having the electrodes 59 and the electrodes 51,.
Are arranged on a substrate, and have an alternate lead type having a strip-shaped heating resistor 60 on an electrode. The print record of this thermal head is composed of one selection electrode and common electrodes on both sides,
For example, the selection electrode 71 and the common electrodes 51 and 52 on both sides thereof
This is performed in a region A indicated by hatching of the heating resistor 60 sandwiched between the two. The width h of the resistor 60 in the sub-scanning direction is
The width dimension is set shorter than the width H of one pixel in the sub-scanning direction.

Next, a case where halftone recording is executed by a thermal head will be described. In this embodiment, the width h of the resistor 60 in the sub-scanning direction is about 1 / the width H of one pixel in the sub-scanning direction.
4 indicates a case where halftone printing of eight gradations is executed. The recording paper is conveyed at a constant speed in the sub-scanning direction. The recording paper speed is a speed at which the recording paper is fed by a width of one pixel in the sub-scanning direction during one cycle T, where the printing cycle is a cycle T. The first gradation 81 does not apply a printing pulse within the printing cycle T, and printing in one pixel is expressed as non-printing. In the second gradation 82, as shown in the print record, a print pulse having a pulse width Tp for recording a dot having substantially the same area as the resistor 60 is applied to the resistor 62, and a dot having the same area as the resistor 62 is formed. Express as a print record. This means that 1/4 (2/8) of one pixel has been recorded. 3
First, the first gradation pulse 83 is applied to the resistor 63 by applying the first printing pulse which is the same as the second gradation, and then printing is performed.
A second print pulse having a pulse width Tp is applied to the resistor 63 at a timing delayed by 8, that is, the recording paper is conveyed by 1/8 of the width H of one pixel in the sub-scanning direction. Expressed as Thus, ／ of one pixel is recorded. The fourth gradation 84 is a timing delayed by ８ of the printing period T after printing the same as the third gradation, that is, the recording paper has a width H in the sub-scanning direction of one pixel further than the third gradation. A third print pulse having a pulse width Tp, which is sent by 1/8, is applied to the resistor 64, and is expressed as a print record. As a result, half of one pixel (4
/ 8) is recorded. As described above, the number of print pulses applied sequentially is increased. The eighth gradation 88 applies a sixth print pulse having a print pulse width Tp to the resistor 68 every ８ of the print cycle T, as in the case of the seventh gradation. The recording paper is advanced by one-eighth of the width H in the sub-scanning direction of one pixel further than the seventh gradation, and the recording paper is delayed by the seventh pulse width Tp.
Is applied to the resistor 68 to express it as a print record. Thus, the entire area of one pixel is recorded. Thus, by providing a fixed time lag for adjacent pixels and increasing the number of print pulses to be sequentially applied, halftone recording of eight gradations can be performed as shown in FIG.

In this embodiment, for simplicity of explanation, 8
Although the gradation was used, in a thermal head having a resolution of 300 dpi, the width in the sub-scanning direction was set to about 20 μm, and a high-resolution ink donor film (PET material thickness: 3.5 μm, ink coating amount: 2.0 g / m ² ) was used. And the printing cycle T is 2
With 0 ms / line, halftone recording of 64 gradations is possible. Also, if the print cycle is shortened or the number of gradations is increased, the interval between each print pulse is shortened and heat storage occurs. In this case, the area recorded by each pulse is almost equal to that of the resistor. It is necessary to adjust the pulse width to have the same area.

Next, a recording method in which the recording start position of one pixel in the sub-scanning direction is shifted from the adjacent pixel by a certain amount within a width of one pixel will be described with reference to FIG. FIG. 2 shows an example of a recording pixel that expresses three gradations. FIG. 2A is an explanatory diagram of the thermal head, which has the same configuration as the above-described thermal head. Therefore, the same portions are denoted by the same reference numerals and description thereof will be omitted. (B) is an explanatory diagram of a printing state,
(C) is an explanatory diagram of pulse generation when the printing cycle is set to cycle T.

If printing of all pixels is started at the first timing of the printing cycle T, printing is performed in which the printing area gradually increases, similar to the printing printing shown in FIG. 1 (b). The printing start timing is shifted by 1/8 to 5/8 of the printing cycle for each pixel so that the printing start position in the sub-scanning direction is fixed by a fixed amount within a width of one pixel from the adjacent pixels. It is shifted. To the first pixel 801, a print pulse having a pulse width Tp for recording a dot having substantially the same area as the resistor 60 is applied to the resistor 61 for one dot, and the timing is further delayed by ８ of the print cycle ( The recording paper is 1/8 of the width H of one pixel in the sub-scanning direction.
), A second print pulse is applied to the resistor 61. Thus, ３ of the area of one pixel is recorded. The second pixel 802 includes an adjacent pixel 80
At a timing delayed by 1/8 of the print cycle from the start of recording of 1 (recording paper is conveyed by 1/8 of the width H of one pixel in the sub-scanning direction), the first print pulse is output by a resistance of one dot. Apply to body 62. Further, a timing delayed by の of the printing cycle (the recording paper is １ ／ of the width H of one pixel in the sub-scanning direction)
), A second print pulse is applied to the resistor 62. Thus, ３ of the area of one pixel is recorded. The third pixel 803 has two-eighths (１ ／) of the printing period from the start of recording of the pixel 801 and the adjacent pixel 8
At the timing delayed by 1/8 from the start of recording of the second pixel (recording paper is conveyed by 1/8 of the width H of one pixel in the sub-scanning direction from the start of recording of the adjacent pixel 802), the first print pulse is output. The voltage is applied to the resistor 63 for one dot. Further, the second print pulse is applied to the resistor 63 at a timing delayed by 印字 of the print cycle (the recording paper is conveyed １ ／ of the width H of one pixel in the sub-scanning direction). Thus, ３ of the area of one pixel is recorded.

As described above, printing is started at a timing delayed by 1/8 from the printing start of the adjacent pixels, and a second printing pulse having a pulse width Tp is applied at a timing of 1/8 of the printing cycle T. Thus, １ ／ of the area of one pixel is sequentially recorded while shifting the １ ／ printing position from the adjacent pixel, and halftone recording of three gradations is executed.

Next, a method for making the resolution of one pixel of each color in the sub-scanning direction different from that in the main scanning direction in color printing will be described with reference to FIG. For color printing, yellow
Since there are cases where three colors of magenta and cyan and further black are used, color printing can be performed if there are at least four types of patterns having different resolutions. For example, 300 dpi
If the resolutions in the sub-scanning direction and the main scanning direction are properly used at 150 dpi and 300 dpi, four types of patterns having different resolutions can be generated as shown in FIG. That is, a pattern P ₁ having 300 dpi in both the main scanning direction and the sub-scanning direction,
Pattern P of 0 dpi and 150 dpi in the sub-scanning direction
_2. 150 dpi in the main scanning direction and 300 d in the sub-scanning direction
There are four types of patterns, a pattern P _{3 having} a resolution of p.pi and a pattern P ₄ having a resolution of 150 dpi in both the main scanning direction and the sub-scanning direction. The four types of patterns having different resolutions are employed, and the recording start position of one pixel in the sub-scanning direction is set to be 1 / 8H of the width H of one pixel in the sub-scanning direction within one pixel. When halftone recording by the recording method of shifting each halftone recording 64 gradation pattern P _1, the pattern P ₂
In 64 to 126 gray scale, halftone recording 64-127 gradation pattern P _3, it is possible to halftone recording 64-252 gradation pattern P _4.

Next, by adopting four types of patterns, the amount of deviation from adjacent pixels is set to 1/2 of one pixel, and the area ratio of the printing area (dotted portion) in one pixel is set to 25%. Examples of printing in this case are shown in FIGS. Figure 4 is the print example of adopting the pattern P _1, the printing example 5 employing the pattern P _2, FIG. 6
The print example of adopting the pattern P _3, FIG. 7 is a print example of adopting the pattern P _4. According to the conventional recording method, when the print start portions are connected, they overlap on a straight line and appear on the image as streak noise. Therefore, when the printing start portions are connected by straight lines by each pattern, the connecting straight lines in each pattern have components of different angles.
From this fact, it has been found that, in the color printing, when the printing pattern is changed for each color and the respective colors are overprinted, the stripe noise is not emphasized. FIG. 8 shows an example of a print record in the case of four-color printing using an area ratio of 25% using this method. Here, the first color resolution pattern is the pattern P _1, 2-color resolution pattern is resolved pattern of the pattern P _2, 3 color the resolution pattern of the pattern P _3, 4 color employing a pattern P4. Assuming that the print area ratio of each pattern is 25%, a portion represented by oblique lines and straight lines is printed for each pattern by one print pulse. For each color, the amount of deviation from the adjacent pixel is set to の of one pixel.

As can be seen from the print record example, there are various cases where the print portions of the four colors overlap. For this reason, registration deviation occurs for each color.
However, although the overlapping manner of each printed dot differs depending on the place, it becomes equivalent in a macroscopic region visible to human eyes, and is not recognized as a color shift.

Although the embodiment of the four-color printing has been described above, it is also possible to execute the three-color printing using three types of patterns without using all the four patterns shown in FIG. Further, the amount of printing deviation from adjacent pixels is not limited to １ ／, ４, ８ of one pixel, etc., and may be within the range of one pixel. In addition, for one color, 30 pixels per pixel as in the conventional case.
A similar effect can be obtained when the resolution is set to 0 dpi and the amount of deviation from adjacent pixels is eliminated. As described above, by controlling the recording method, the resolution pattern, and the print pulse generation timing for the paper conveyance according to the present invention, the problem of color shift and stripe noise in color printing, which cause deterioration in image quality, is solved, and good halftone Recording became feasible.

Next, a method of arbitrarily selecting the resolution in the sub-scanning direction will be described with reference to FIG. For example, FIG.
The case where the printing cycle of 0 dpi is T and one cycle T is printed as one pixel is shown. In this case, as described with reference to FIG. 2, gradation can be expressed by 300 dpi pixels. One pixel is 1.5 times the period T. As shown in FIG.
= 1.5, gradation can be expressed with 200 dpi pixels. Two times the period T is defined as one pixel. If printing is performed with Tx = 2.0 as shown in FIG.
The gradation can be expressed by the pixel of i. As described above, the resolution in the main scanning direction is only allowed to be a multiple of the resolution of the resistor, but in the sub-scanning direction, an arbitrary resolution can be selected to achieve gradation recording. In this manner, printing can be performed at an arbitrary resolution in the sub-scanning direction.

In the recording method of the present invention, since the resolution of each color and the resistor and the deviation between the image data and the recording start position are different, the image data at the position where the resolution is different and the recording start timing is deviated is required. is there. So 6
A method of generating image data when performing printing at four gradations will be described with reference to the flowchart of FIG. In this embodiment, since the recording start timing and the resolution differ depending on the number of lines, resistors, and colors, information on the current number of lines, resistors, and colors is stored in a counter or a buffer in step ST100. In step ST200, using this data, a shift amount of the recording start timing is calculated by a microprocessor or the like, and it is determined whether there is a shift. If it is determined that the shift amount is not zero, the process proceeds to step ST300, and print image data is used. If the shift amount is not zero and it is determined that there is a shift amount, image data at a position shifted by に in the sub-scanning direction is required. The data is averaged to generate image data. If the resolution is different in the main scanning direction, averaging is performed in step ST500 including data in the main scanning direction. In step ST600, the image data of 1 to 256 tones obtained from the previous shift amount is converted to 64 tones by the tone conversion circuit while performing γ correction. Step S
From the n gradation data converted in T700 and the calculated shift amount, the print data generating circuit generates binary data (for 63 bits) for the thermal head. Step S
At T800, the data is rearranged, parallel-serial converted, and the like, transferred to the thermal head, and printing is performed. A series of these processes is executed by a not-shown microprocessor for controlling a thermal head or a look-up table using a ROM.

The method of generating image data at a position where the recording start timing is shifted is not limited to the present embodiment. If the amount of shift is not 1/2 of one pixel, for example,
Depending on the amount of shift, data near four or eight may be used. Further, if the shift amount is within half of one pixel, a pictorial image can be sufficiently reproduced, so that image data of adjacent dots in the sub-scanning direction may be used without interpolation. As described above, according to this recording method, the overlapping manner of the print dots recorded by the respective heating resistors is different, so that the problem of image quality deterioration such as macroscopic color shift is solved, and the angle of the line formed by each color is solved. The streak noise is reduced due to the deviation.
Thus, according to the recording method of this embodiment, a good halftone image can be obtained.

Embodiment 2 However, if there are fine lines and characters in the main scanning direction in the input data, the fine lines will be uneven, and the reproducibility of the fine lines and characters will be poor. Therefore, in this embodiment, a thin line or character detection algorithm is applied to the print data generation circuit, for example, a line is determined to be a thin line when the same gradation data continues for x bits or more in the main scanning direction. Then, the same gradation data in the main scanning direction is x
If it is determined that the line is a thin line or a character that continues for more than a bit, control is performed such that the recording start timings of the dots indicating the thin line or the character are simultaneous. By making recording start of adjacent pixels at the same time, the print line in the main scanning direction is emphasized, and the reproducibility of fine lines and characters is improved. Thus, according to this embodiment,
Good image quality can be obtained not only for halftone images but also for images containing characters and fine lines.

[0024]

As described above, the halftone recording method of the present invention can achieve multitone halftone recording by shifting the printing timing between adjacent pixels by a fixed amount. In addition, when the resolution in the sub-scanning direction and the resolution in the main scanning direction are made different from each other so that the overlapping of the print dots recorded by each heating resistor is recorded differently, even if there is no accurate registration, each The overlap of each color is different in the print dot, and the problem of deterioration in image quality due to color shift in the entire image does not occur. In addition, the streak noise due to line formation in the main scanning direction is different from the printing start portion in the main scanning direction for each color, so that no emphasis due to overprinting occurs, the streak noise can be reduced, and color shift and streak noise can be reduced. The problem of image quality degradation, which is noise, is solved, and good halftone recording can be realized.

Further, by adding a thin line or character detection algorithm, when a thin line or a character is detected, the recording start timing of the dot indicating the fine line or the character is made simultaneous. Good image quality can be obtained even in a color halftone image including fine lines and fine lines.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a halftone expression by an intermediate recording method of the present invention.

FIG. 2 is an explanatory diagram of a recording method of three gradation expression.

FIG. 3 is an explanatory diagram of a print pattern.

FIG. 4 is a printing example using a printing pattern.

FIG. 5 is a printing example using a printing pattern.

FIG. 6 is a printing example using a printing pattern.

FIG. 7 is a printing example using a printing pattern.

FIG. 8 is an explanatory diagram of a printing example in a halftone recording method.

FIG. 9 is a diagram illustrating a method for adjusting the resolution in the sub-scanning direction.

FIG. 10 is a flowchart of a halftone recording method.

FIG. 11 is a plan view of a conventional thermal head.

FIG. 12 is an example of a conventional halftone recording print.

[Explanation of symbols]

50: common electrode, 60: heating resistor, 70: selection electrode, 81 to 88: pixel, 801 to 806: pixel.

Continuation of front page (56) References JP-A-4-363261 (JP, A) JP-A-4-257459 (JP, A) JP-A-3-132366 (JP, A) JP-A-5-155057 (JP) (A) JP-A-5-155051 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41J 2/36 B41J 2/52 B41J 2/525

Claims (2)

(57) [Claims] A recording head for one pixel in the sub-scanning direction is started using a thermal head in which a plurality of heating resistors having a width in the sub-scanning direction shorter than the width of one pixel in the sub-scanning direction are arranged in the main scanning direction. thermal halftone recording method for position by shifting one by a fixed amount within the width of one pixel for the record of the adjacent pixel recorded
A means for determining the presence / absence of a shift amount based on image data is provided.
Is detected, the halftone is determined and the recording of adjacent pixels is performed.
The start position is shifted by a fixed amount, and when it is detected that there is no shift amount , an image of the same gradation in the main scanning direction is detected.
The image data is determined to be continuous thin lines and characters, and
The original recording start position is the same in the main scanning direction.
And a heat-sensitive halftone recording method. 2. Using the sub-scanning direction of the thermal head width is arranged in the sub-scanning direction a plurality of shorter than the width of the heat generating resistor of 1 pixel in the main scanning direction, un, magenta, yellow, black The resolution of one pixel in the sub-scanning direction and the resolution in the main scanning direction of each color are made different , and one pixel of
Set the recording start position in the scanning direction to the width of one pixel and the adjacent pixel
Color printing with halftone density
In the thermal halftone recording method to be performed, a means for determining the presence or absence of a shift amount based on image data is provided.
Is detected, the halftone is determined and the recording of adjacent pixels is performed.
The start position is recorded with a certain amount of shift, and no deviation is detected.
When the image data of the same gradation continues in the main scanning direction
Judge as a thin line or character, and set the recording start position of the adjacent pixel.
A thermosensitive halftone recording method, wherein recording is performed in the same direction in the main scanning direction .