JP2664803B2 - Thermal recording method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal recording method used for a thermal printer for recording a monochrome or color halftone image.

[Prior Art] Thermal recording methods include a thermal recording method in which color recording is performed by heating a thermal recording paper, and a thermal transfer recording method in which ink on a transfer sheet is transferred to recording paper by heating the back of a transfer sheet. . The latter thermal transfer recording method includes a thermal melting type in which ink is melted and transferred to a recording sheet, and a sublimation type in which ink (dye) of a transfer sheet is diffused and transferred to recording paper. Among these thermal recording methods, the thermal recording method and the sublimation type thermal transfer recording method record halftone images such as photographs because the recording density changes in accordance with the amount of heat (temperature) applied to the thermal recording material. Suitable for.

[Problems to be solved by the invention]

When printing the halftone image described above, a thermal head in which a large number of heating elements are arranged in a line is used, and the amount of heat generated by the heating elements is controlled in accordance with the recording density. However, it is difficult to obtain the amount of heat that accurately corresponds to the electric signal supplied to the heating element due to the problem of heat storage in the thermal head, etc.Therefore, it is necessary to record a reproduced image with a halftone faithful to the original image. Could not. Furthermore, since halftone expression is performed by controlling the amount of heat generated, there is a problem that it is difficult to control electric signals.

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermal recording method capable of easily expressing a halftone faithful to an original image.

[Means for solving the problem]

In order to achieve the above object, the present invention records one pixel in the main scanning direction with one heating element, and in this recording, controls the amount of heat generated by each heating element in a stepwise manner.
The recording area is changed by changing the recording length of the pixel in the sub-scanning direction, the halftone is expressed by a combination of the recording density and the recording area of the pixel, and the recording start positions of the heating elements are adjacent to each other. These are separated in the sub-scanning direction.

[Action]

According to the present invention, since the amount of heat generation is made stepwise and the area is complemented by area gradation, the control of the amount of heat of the thermal head is simplified, and the control circuit is simplified. Moreover, since one heating element records one pixel in the main scanning direction, and the recording area is changed by changing the recording length of the pixel in the sub-scanning direction, the resolution is reduced and the number of gradations is reduced. Images can be recorded. Therefore, a halftone faithful to the original picture can be easily expressed. Furthermore, since the recording start positions of the heating elements are separated in the sub-scanning direction between adjacent elements, the recording positions of the recording pixels are shifted in the sub-scanning direction. Thereby, the occurrence of moire is suppressed.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 2 shows a characteristic curve of the thermosensitive recording paper.
In the second embodiment shown in FIG., Each heating element, thermal energy J _a five _{stage, J b, J c, J} d, J e is selectively provided.
With this stepwise thermal energy, only five gradation levels can be expressed, so the recording area within the pixel area is changed between each gradation. For example, the concentration is not more than D _a is
The thermal energy _Ja is used to change the recording area within one pixel. Further, when the pixel density is between D _{a and} D _b , the thermal energy J _b is used to change the recording area within one pixel. As described above, by changing the thermal energy and the recording area stepwise, a multi-step gradation can be expressed. For example, when the recording density is 5 steps and the recording area is 25 steps, 125 gradations can be expressed.

FIG. 1 shows a state of thermal recording by a thermal head. The thermal head 10 has heating elements 11a to 1
1f are arranged in a zigzag pattern at appropriate intervals in the sub-scanning direction. In this embodiment, the distance D between two rows of heating elements
Is 1/2 of the length L of the one-pixel area 12 in the sub-scanning direction, and therefore, the recording position of adjacent pixels is shifted by L / 2. The shift of the recording position is for eliminating the occurrence of moire. In an apparatus used for image recording in which the influence of moire is small, each heating element is arranged on one line. Further, the heating elements are arranged in one line, and the recording position can be shifted between adjacent heating elements by delaying the electric signal.

The thermal recording paper 13 is moved in a direction indicated by an arrow at a constant speed so as to cross the thermal head 10 by a conveying means such as a roller or a belt. When the thermal recording paper 13 is moved, the heating elements 11a to 11f are given stepwise thermal energy for a time corresponding to the recording area. In FIG. 1, the recording density is represented by the dot density. For example, the density of a pixel recorded by the heating element 11a is higher than that of the heating element 11e. Further, one pixel has a length W in the main scanning direction,
The length in the sub-scanning direction is L.

The heating element 11a records, for example, a pixel having a recording density _Dc and a length L in the first pixel area. The heating pixel 11e records, for example, a pixel having a density Da and _a length L1 in the first pixel area. In this way, multiple gradations are expressed by the stepwise recording density and the recording area.

FIG. 3 shows an apparatus for carrying out the present invention. As the video signal input unit 20, for example, a video player, a TV camera, and a scanner are used, and an analog image signal is sent to an analog processing circuit 21. The analog processing circuit 21 performs tone correction, density conversion, shading correction, and color correction for a color image. The analog-processed image signal is converted to a digital signal by the A / D converter 22 and then written to the frame memory 23.

At the time of printing, an image signal for one line to be printed next is read out and written to the line memory 24.
The image signal for one line stored in the line memory 24 is sent to a halftone control circuit 25, where the image signal of each pixel is converted into temperature data and printing time data. These are sent to the shooting time setting circuits 27, respectively. The temperature data designates one of several temperatures, for example, five temperatures. The printing time data also designates one of several stages of printing time. The A / D converter 22, the frame memory 23, the line memory 24, and the halftone control circuit 25 are controlled by a digital section control circuit 28.

The temperature setting circuit 26 controls the power supplied to each of the heating pixels 11a to 11f of the thermal head 10 stepwise according to the temperature data of each pixel. The printing time setting circuit 27 controls the heating time of each heating element according to the printing time data of each pixel. The printing time is based on the recording area of the pixel and the thermal recording paper.
Thirteen moving speeds are considered. This thermal recording paper 13
Is moved at a constant speed in the main scanning direction by a roller 30 rotated by a pulse motor 29. The digital section control circuit 28 controls the rotation of the pulse motor 29 via the driver 31. In the apparatus shown in FIG. 3, halftone is expressed by changing the recording density and the recording area stepwise according to the image signal.

Although the above embodiment is directed to thermal recording, the present invention can also be applied to sublimation thermal transfer recording using a transfer sheet. Further, a single heat-sensitive recording paper is provided with a cyan coloring layer, a magenta coloring layer, and a yellow coloring layer, and is irradiated with an ultraviolet ray having a specific wavelength after the thermal recording of a certain color to selectively fix only the thermal-recorded layer. It can also be used for color thermal recording using a color thermal recording material that can be used, and sublimation type color thermal transfer recording that records color images by three-color surface sequential recording using cyan, magenta, and yellow transfer sheets. can do.

〔The invention's effect〕

The present invention having the above-described configuration expresses a halftone by combining several steps of density control and recording area control, so that it is not necessary to perform high-precision temperature control as in the related art. In addition, since the recording area is changed by changing the recording length of each pixel in the sub-scanning direction, the control of the recording area can be performed with a high accuracy by a simple circuit. In addition, one pixel is recorded in the main scanning direction by one heating element.
In order to control the amount of heat generated by each heating element in a stepwise manner and to change the recording area by changing the recording length of the pixel in the sub-scanning direction, one pixel is made up of a matrix element composed of several elements as in the related art. Unlike the method using the density pattern method composed of
In addition, an image can be recorded with a high number of gradations, and a halftone faithful to the original image can be reproduced.

Furthermore, since the recording start positions of the heating elements are separated from each other in the sub-scanning direction, the recording start positions are shifted in the sub-scanning direction, so that the recording start positions of the pixels in the main scanning direction are aligned. And the occurrence of moire is suppressed.

In addition, a thermal head in which heating elements are arranged in a line is used, and an electric signal is delayed between adjacent heating elements, so that the recording start position of each heating element is shifted in the sub-scanning direction between adjacent heating elements. Since the heating elements are separated from each other, it is not necessary to use a specially structured thermal head in which the arrangement of the heating elements is arranged in a staggered manner while maintaining an appropriate interval in the sub-scanning direction, and the configuration of the thermal head can be simplified. In addition, since the electric signal is delayed to generate heat, the peak of power consumption can be reduced by the delay compared to a general device that generates heat at the same time.
Power saving is achieved, and efficient thermal recording becomes possible.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a recording state according to the thermal recording method of the present invention. FIG. 2 is a characteristic curve showing the relationship between the thermal energy of the thermosensitive recording paper and the recording density. FIG. 3 is a block diagram showing an apparatus for implementing the method of the present invention. 10 Thermal head 11a-11f Heating element 12 Recording area 13 Thermal recording paper.

Claims (3)

(57) [Claims] 1. A thermal head, in which each heating element is arranged in a main scanning direction, moves a thermal recording material or a thermal head in a sub-scanning direction relative to a thermal recording material whose recording density changes in accordance with a calorific value. In the thermal recording method of recording an image, the one heating element records one pixel in the main scanning direction, and at the time of this recording, the amount of heat generated by each heating element is controlled in a stepwise manner. The recording area is changed by changing the recording length in the sub-scanning direction, and a halftone is expressed by a combination of the recording density and the recording area of the pixel. A thermal recording method, wherein the thermal recording method is separated in a scanning direction. 2. A thermal head in which heating elements are arranged in a line, and an electric signal is delayed between adjacent heating elements so that the recording start position of each heating element is set between adjacent heating elements. 2. The thermal recording method according to claim 1, wherein the thermal recording method is separated in the sub-scanning direction. 3. The thermal recording material has a cyan coloring layer, a magenta coloring layer, and a yellow coloring layer, and selectively irradiates ultraviolet rays of a specific wavelength after recording heat of a certain color to selectively select only the layer subjected to heat recording. 3. The thermal recording method according to claim 1, wherein the fixing is performed.