JPS59191967A - Recording method of half-tone picture - Google Patents

Abstract

PURPOSE:To record a half-tone picture with high stability and high fidelity by setting the form of a heating resistor so that the width of the main scanning direction is larger than the width of the secondary scanning direction and then recording a large picture element after fractionating it in the secondary scanning direction. CONSTITUTION:For a heating resistor, the width (b) of the secondary scanning direction is set smaller than the width (a) of the arraying direction. At the same time, a/b>1.5 is satisfied. The pitches of both main and secondary scans are divided three times in the secondary direction and recorded in consideration of a large picture element of P. The half-tone is artificially obtained in response to the number of small picture elements printed within the large picture element. As shown by a pattern example of gradation 1 of a Fig. (a), it is avoided that the recording dots are arrayed on the same secondary scanning line when the same gradation is expressed. Thus the gradation expression capacity is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a halftone image recording method for recording a halftone image with good fidelity by ink thermal transfer recording or thermal recording.

FIG. 1 shows a typical structural diagram of a heat generating part of a conventional thermal recording head [4]. Here, (1) is a heating resistor, and (2
) indicates the drive circuit side, and (3) indicates the common electrode. As shown in this example, in the conventional thermal recording head (4), the heating resistor (1
) is usually larger in the sub-scanning direction than the width a in the arrangement direction (main-scanning direction).

When this conventional thermal recording head (4) is used to print on thermal recording paper, a pattern as shown in FIG. 2 can be obtained.

A printed pixel (hereinafter referred to as a large pixel) is usually somewhat longer in the sub-scanning direction than in the main scanning direction, as indicated by diagonal lines in the figure. To record a halftone image using a conventional thermal recording head (4) that uses such a large pixel as a unit, the power, pulse width, or number of pulses used to print one large pixel is modulated, and the density of the entire large pixel is modulated. It was common to do so.

The conventional methods described above work well when the recording medium itself is capable of reproducing halftones, such as thermal recording paper, but when the recording medium itself can reproduce halftones, such as thermal ink transfer recording, which is the main objective of this invention, it is difficult to change the recording density with respect to the amount of printing energy. In the case of a recording medium with an extremely steep gradient, printing conditions in a halftone state are unstable, making it impossible to record a faithful halftone image.

This invention was made to eliminate the drawbacks of the conventional ones as described above, and by further subdividing large pixels in the sub-scanning direction, it is possible to record halftone images stably and faithfully. This provides a method to do so.

FIG. 3 is an enlarged view showing an example of the structure of the heat generating part of the thermal recording head (6) used in the halftone image recording method of the present invention. Here, (101) is a heating resistor,
The width in the sub-scanning direction is significantly smaller than the width in the array direction.If a/b is expressed as the flatness ratio of the heating element, then k
It is preferable to select k so that it satisfies > 1.5. This example shows the case where k=3.

FIG. 4 shows a dot pattern printed by the head of FIG. 3. The dots printed by the head of this invention are small pixels (7) smaller than conventional pixels (large pixels).
becomes. In this example, the sub-scanning direction is 1 of the large pixel pitch P.
/3 width.

Recording of a halftone image by the thermal recording head (6) of the present invention is carried out as follows. Now, considering a large pixel with P in both the main scanning and sub-scanning pitches as shown in Fig. 5, the method of this invention divides the data into 3 degrees in the sub-scanning direction and records the small pixels printed in the large pixel. A pseudo halftone is obtained by the number of . Here, an example of a recording dot pattern of four gradations including 0 is shown. Figure 5(a)
As shown in the pattern example of gradation (1), when expressing the same gradation, the ability to express gradation can be increased by preventing the recording dots from being aligned on the same sub-scanning line. In this example, the 81st row of dots in the main scanning direction is printed on the sub-scanning line v1-1, and the 82nd row is printed on Vl-2, H3.
By printing each dot in the alignment Vl-3, adjacent dots are prevented from being lined up on the same sub-scanning line.

Solution: According to the method of the present invention, the image resolution in the main scanning direction is the same as that of conventional heads, so there is no difficulty in increasing the resolution of the head, and it is not possible to record halftone images using conventional methods. Even when applied to ink thermal transfer recording, 1. This makes it possible to record faithful halftone images.

Many variations are possible in practicing this invention, as described below. First, regarding the shape of the heating resistor,
Length a in the main scanning direction and length b in the sub-scanning direction of the heating resistor
As long as the ratio a/b is greater than 1.5, the value is not limited to a specific value and should be selected depending on the required resolution of the target device.

Further, as shown in FIG. 6, which shows another embodiment of the thermal recording head of the present invention, there is no restriction on the specific shape, and the dots that are finally printed are simply in the sub-scanning direction compared to the main scanning direction. All thermal recording heads whose width in the direction is narrow are included in the present invention. Here, the same numbers as in FIG. 3 indicate the same or corresponding parts, respectively.

Further, although the embodiments have been described with respect to ink thermal transfer recording, the present invention can be similarly applied to conventional thermal recording.

? :JS7 Figure shows another pattern example of the halftone expression method according to the present invention. In this case, 47) large pixels are used as the unit of halftone expression, and a total of 13 (including 0) pseudo gradations can be obtained. Here, up to the fourth gradation is displayed. In this way, the invention can be expanded to increase the number of gradations. Furthermore, many merging formats such as the Bayer type dither method or the halftone dot method can be used for the pixel arrangement of small pixels or large pixels.

As described in detail above, according to the present invention, it is possible to obtain halftones even when the recording medium itself, such as ink thermal transfer recording, is not capable of expressing halftones, and the resolution of the thermal recording head itself used is This has the advantage that it can be the same as the conventional one.

[Brief explanation of the drawing]

FIG. 1 is a partially enlarged view of the structure of the heat generating part of a conventional thermal recording head, FIG. 2 is a diagram showing a printed dot pattern by the conventional thermal recording head, and FIG. 3 is a diagram showing the heat generating part of the thermal recording head of the present invention. 4 is a diagram showing a printed dot pattern according to the present invention, FIG. 5 is a diagram illustrating one method of representing a halftone image, and FIG. 6 is a diagram showing a thermal recording head used in the present invention. FIG. 7 is a diagram showing a method for increasing the number of gradations. In the figure, (1) shows a heating resistor, (4) and (6) a thermal recording head, (5) a large pixel, and (7) a small pixel. Agent Masuo Oiwa 5th (C) (su (b) (2) (d> (O) 7th (0) (3) (b) (2) (4)

Claims (2)

[Claims] (1) Heating resistors are arranged in one or more rows on an insulating substrate, and the dimensions of the heating resistors in the sub-scanning direction are 1/k (k>1.5) compared to the arrangement direction. For the thermal recording head, by changing the distribution of current pulses that are applied to the heating resistor within the pitch length range in the sub-scanning direction of the large pixels that express the halftone, the halftone is created. A halftone image recording method characterized in that large pixels are obtained and a two-dimensional halftone image is obtained by a two-dimensional collection of these large pixels. (2) Adjust the timing of the current pulses that energize adjacent heating resistors to 1/4 to 3/2 of the pitch length in the sub-scanning direction of the large pixel.
2. The halftone image recording method according to claim 1, wherein the large pixels are arranged in a staggered manner by shifting the pixels by 4.