JPH0326141B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gradation image recording device, particularly a thermal recording device that performs color recording on thermal paper using a thermal printing head. The present invention relates to a gradation image recording device for recording.

Conventionally, in order to output images with gradations in thermal recording, a device has been used to obtain stages in color density by controlling the power applied to a heating element or the width of a heating pulse.

This device had the following drawbacks. That is, (i) the heating conditions for the head must be controlled and determined according to the delicate coloring characteristics of the paper, making it complicated and difficult to set the heating conditions to obtain a stable gradation image.

(ii) Since the heating conditions are set depending on the paper type, it is difficult to obtain stable gradation images when the type of paper is changed.

(iii) It is difficult to obtain stable gradation images in response to environmental changes such as temperature and humidity.

(iv) When thermal copying paper is used, it is practically impossible to copy gradation images because the coloring characteristics of the upper and lower sheets are different.

(v) In order to obtain stable gradation images, paper with high smoothness is required. For example, Beck smoothness requires paper with a durability of 500 seconds or more (general thermal printing can be used with paper with a durability of around 200 seconds).

In order to eliminate these drawbacks, the present invention has a thermal print head arranged perpendicularly to the paper feeding direction, in which a plurality of heating elements are made to correspond to one pixel of the original image, so that a plurality of heating elements can be applied to one pixel. The purpose of this invention is to express the gradations by changing the color print area within one pixel using a plurality of heating elements. Furthermore, the present invention aims to improve the quality of printing results by changing the combination of heating elements that are energized when printing pixels having gradations of the same density, thereby avoiding repetition of the same combination.

FIG. 1 shows an embodiment of the invention. 1 is a thermal print head arranged perpendicular to the paper feeding direction. 1' is a heating element. 2 represents an example of a printing result corresponding to one pixel of the original image. Reference numeral 3 denotes a printing unit corresponding to one pixel and constituted by a plurality of heating elements. In the embodiment, the one unit is composed of three heating elements. Reference numeral 4 denotes a signal conversion circuit for energizing and heating the thermal printing head according to the gradation of one pixel. 5 is a random number generation circuit section that acts on the signal conversion circuit 4. Reference numeral 6 denotes a line buffer for storing one line of signals representing gradations for output. 7 represents paper. In this embodiment, it is assumed that a four-tone image is output.

FIG. 2 shows the printing result of one unit with gradation applied. Diagonal lines represent colored areas. Gradation levels “1” and “2” represent the same tone, but depending on the combination, 3
There are two cases. Note that by setting each coloring part to a saturation density, a stable gradation image can be obtained for each coloring part.

To operate this, information representing the gradation corresponding to each pixel is transferred to the line buffer 6 for one line in FIG. In the signal conversion circuit 4,
The gradation information corresponding to the pixel is received from the line buffer 6, and the printing unit 3 receives the gradation information corresponding to the gradation information from the line buffer 6.
Convert to a drive signal for. At this time, the random number generation circuit 5 acts on the signal conversion circuit 4 when selecting a drive signal for the printing unit, and works to randomly select one of the printing patterns belonging to the same gradation information. In the example, the aspect ratio of one pixel is 1:
1, recording by one heating element has an aspect ratio of 3:1.

In the case of the present invention, with such a configuration, one printing unit prints the gradation by changing the area within one pixel according to the gradation of each pixel of the original image in real time. It becomes possible to print in a manner that has a certain tone. Furthermore, since the heating elements to be driven in one printing unit 3 are randomly selected,
For consecutive pixels of the same gradation, it is possible to prevent vertical stripes from occurring due to repetition of the head selection pattern within the same unit. It goes without saying that substantially the same effect can be obtained even if, for example, a plurality of patterns belonging to the gradation level "1" are used cyclically instead of the random selection.
Also, since the average density of one pixel's perspective is not linearly proportional to the area ratio, the gradation can be adjusted by changing the size of the heating element within one unit and by combining the heating element and areas of different sizes. By expressing this, it becomes possible to obtain a more faithful reproduction of the image. That is,
3 corresponding to one printing unit 3 shown in FIG.
Among the heating elements 1', 1', 1', for example, the area of the central heating element is selected to be larger than the elements on both sides, and gradations are given by the combination of these elements. I can do it. Furthermore, for example, three heating elements 1', 1', 1' corresponding to one printing unit 3 shown in FIG. Therefore, by using three heating elements, it is possible to obtain a device that provides substantially eight levels of gradation. Furthermore, since the color developing portion is set to a saturated density, a stable gradation image can be obtained, and even paper that does not have high smoothness can be used.

As explained above, according to the present invention, it is possible to output an image with gradation stably against changes in the coloring characteristics of thermal paper or the environment, and the problems associated with conventional gradation image output are solved. . Furthermore, by using a random number generation circuit, etc., undesirable vertical stripes do not appear due to repetition of the same pattern even in output where the same gradation is continuous, and an overall averaged gradation image can be obtained. This has the advantage of improving image quality. Furthermore, by providing gradations based on the combination of the area and number of heating elements, it is possible to obtain a screen with high overall fidelity.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a driving circuit according to the present invention, and FIG. 2 shows an example of a gradation expression pattern when three dots are used in one pixel. In the figure, 1 is a thermal printing head, 1' is a heating element, 2 is a printing result, 3 is a printing unit, 4 is a signal conversion circuit, 5 is a random number generation circuit, 6 is a line buffer, and 7 is paper.

Claims (1)

[Scope of Claims] 1. In an image recording device using thermal print heads arranged perpendicular to the paper feeding direction, a printing unit consisting of a plurality of heating elements corresponding to one pixel of the same size is provided, and , After preparing in advance a plurality of types of heating element selection patterns expressing the same gradation level, the heating element selection pattern is used to select the heating element to be energized in the printing unit according to the gradation signal. The gradation of one pixel is expressed by providing a signal conversion means for selecting in the form of a heating element, and selecting a heating coloring area within one pixel in accordance with the number of energized heating elements. Gradation image recording device. 2. The signal conversion means includes a random number generating circuit, and randomly selects a heating element corresponding to one pixel by selecting the heating element selection pattern when selecting a heating element to be energized. A gradation image recording device according to claim 1, characterized in that: 3. The signal converting means includes a cyclic number generating circuit that cyclically generates a plurality of predetermined numbers, and selects the heating element selection pattern to select the heating element to be energized. 2. The gradation image recording apparatus according to claim 1, wherein the heating element corresponding to the gradation image recording device is cyclically selected. 4 The above printing unit is constructed by combining heating elements with different coloring areas, and 1
Claim 1, characterized in that the heating color development area corresponding to a pixel is made variable by combining the number of selected heating elements and the area of the heating elements, thereby expressing the gradation of one pixel. The gradation image recording device according to item 1 or 2 or 3.