JPH0326140B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gradation image recording device, particularly in thermal recording in which heat is recorded on thermal paper using a thermal printing head. The present invention relates to a gradation image recording device that records a gradation image by changing the gradation image.

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 of the head must be controlled and determined according to the delicate coloring characteristics of the paper, so setting the heating conditions to obtain a stable gradation image is complicated and difficult.

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

(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) It had the disadvantage that paper with high smoothness was required to obtain stable gradation images (general thermal printing can be performed using paper that lasts about 200 seconds).

In the present invention, in order to eliminate these drawbacks, 1.
It is equipped with a unit that can break down one pixel into a matrix and a paper feed mechanism to express gradation by changing the color printing area within a pixel, and is equipped with a paper feed mechanism that can respond to changes in paper and environment. The aim is to obtain stable gradation images.

FIG. 1 shows an embodiment of the invention. 1 is a thermal printing head arranged perpendicularly to the paper feeding direction. 1' is a heating element. 2 is the original picture 1
This is an example of a printing result corresponding to a pixel. Reference numeral 3 denotes a printing unit corresponding to one side of one pixel and constituted by a plurality of heating elements. In the embodiment, one unit is composed of three heating elements. 4 is 1
This is a signal converting section for heating each heating element 1' with electricity according to the gradation of the pixel. 5 is a random number generation circuit section that acts on the signal conversion section 4. Reference numeral 6 denotes a line buffer for storing one line of information representing gradation for output. 7 is a sheet of paper, and 8 is a sheet feeding device that feeds the sheet a distance of 1/2 of the length of one pixel in the vertical direction in one operation. In the embodiment, one pixel is represented by a unit having three heating elements and two paper feeds, so it is represented by a (3×2) matrix. Therefore, as will be described later, seven gradations from gradation "0" to "6" can be obtained.

FIG. 2 shows an example of output of pixels having seven gradation levels from "0" to "6". In this figure, the colored area is indicated by diagonal lines. A plurality of output patterns may exist between the gradation level "2" and the gradation level "5". Then, when a certain gradation signal is applied, one of the plurality of possible output patterns is selected and output. If each heating element 1' is set to generate color at a saturation density, a more stable gradation image can be obtained than when, for example, halftone is introduced.

In order to operate this, in FIG. 1, when one line of information representing gradation is first transferred to the line buffer 6, the signal converter 4 reads information corresponding to the pixel from the line buffer 6, and
One of the gradation patterns shown in FIG. 2 is randomly selected based on the output from the random number generation circuit 5, and current is applied to the heating element 1' to generate heat according to the gradation pattern. In the embodiment, since one pixel is configured with a matrix of 3:2 (width x height), seven levels of gradation from "0" to "6" can be output. The pattern that should occur at each stage is
As shown in FIG. 2, there are a plurality of them. The random number generation circuit 5 uses random numbers to randomly output one of the gradation patterns, thereby preventing the same pattern from being repeated.

It goes without saying that substantially the same effect can be expected even if a plurality of patterns are used cyclically instead of random selection. Also, since the average density of one pixel is not linearly proportional to the area ratio, if the size of the heating elements in one unit is made variable and the gradation is expressed by the combination of the number of heating elements and the area, the image can be improved. can be reproduced more faithfully.

With such a structure, the effect is that a stable gradation image can be obtained using saturated density, and that copying is possible without the need for paper with high smoothness. Furthermore, since the printing pattern is generated randomly, for example, vertical stripes do not occur due to repetition of the pattern. Furthermore, since one pixel is represented by a combination of a plurality of heating elements and a plurality of paper feeds, a large number of gradations can be obtained.

As explained above, since the present invention uses a thermal printing means that develops color to saturation density, it is possible to obtain a gradation image that is stable against changes in the coloring characteristics of thermal paper and the environment, and also has a high level of smoothness. It has the advantage of not requiring special paper and making it possible to make copies. Furthermore, a random number generation circuit is used to prevent the appearance of vertical stripes due to repetition of the same pattern in outputs where the same gradation is continuous, resulting in an overall averaged, high-quality gradation image. It will be done.

[Brief explanation of the drawing]

FIG. 1 shows a configuration block diagram of the present invention, and FIG.
The figure shows an example of a gradation expression pattern obtained in the present invention. 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 converter, 5 is a random number generation circuit, 6 is a line buffer, and 8 is a paper feeding device.

Claims (1)

[Scope of Claims] 1. In an image recording device using thermal print heads arranged perpendicularly to the paper feeding direction, a printing unit consisting of a plurality of heating elements corresponding to one pixel is provided, and A paper feeding mechanism is provided in which the length in the feeding direction is given by multiple feedings, one side of one pixel corresponds to the plurality of heat generating elements on the printing unit, and the other side is set by feeding the paper multiple times. , and is configured to decompose one pixel into a matrix in accordance with the above-mentioned one pixel, and to decompose a plurality of heating elements corresponding to one side of the pixel in response to a gradation signal given corresponding to said one pixel. a signal converter for supplying an output signal, and an instruction means for instructing to select the output signal outputted by the signal converter, and the signal converter has at least a plurality of output signals expressing the same gradation level. one of the plurality of types of heating element selection patterns corresponding to the given gradation signal is selected based on an instruction from the instruction means, and the output signal is supplied. The instruction means is configured to instruct that each of the plurality of types of heating element selection patterns within the same gradation level are selected substantially equally, and the heating coloring area within one pixel 1. A gradation image recording device characterized in that the gradation of one pixel is expressed by changing the gradation of one pixel.