JPS62249565A - Multilevel recording system - Google Patents

Abstract

PURPOSE:To suppress the random bridge of ink and to obtain smooth gradation characteristics by adding dots around a reference dot in accordance with the density level of a fixed pattern. CONSTITUTION:One picture element is formed by a matrix consisting of 3X3=9 dots and the center dot P shown in a drawing a0 is set up as a reference dot. Then, respective dots are divided into four density areas I-IV from a low density area to a high density area and respective fixed patterns a1-a4 are assigned to respective division areas. A fixed pattern with a higher density level than a certain fixed pattern is set up as a pattern adding dots with priority in a main scanning direction and a subscanning direction. Even if the fixed patterns with difference density levels are arranged adjacently, the recording dots are concentrated in the common main scanning directional position and subscanning directional position, so that the random bridge of ink can be suppressed. Thereby, smooth gradation characteristics can be obtained.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) This invention consists of one pixel in a matrix, and creates a pseudo gradation image by changing the area ratio of recording dots in this matrix. This invention relates to a multi-gradation recording method.

(Prior art) Conventionally, binary area gradation has been used to obtain images with gradation in recording methods such as melt-type thermal transfer recording methods that have to express density in the manner of "Q It, 141". Gradation expression is performed using area modulation called ``area modulation''.

In the 200 million area gradation method, the larger the size of the matrix constituting one pixel, the smoother the gradation can be obtained, and the smaller the matrix size, the higher the resolution of the image. therefore,
It is not possible to satisfy these contradictory demands at the same time.
Either gradation or resolution had to be sacrificed.

Therefore, as shown in Japanese Patent Application No. 60-16768 (unknown), small matrices can be formed by not only changing the number of recorded dots depending on the density level, but also multi-leveling the formation energy of each recording dot. Techniques have also been proposed in which a large number of gradations are obtained, thereby improving both gradation and resolution at the same time.

However, in the above method, when an arbitrary pattern is used as the fixed pattern, random ink adhesion may occur between adjacent dots or pixels in a specific density increasing area. For this reason, there is a problem in that unintended printing patterns, that is, random bridges of ink, occur in printing control, leading to a decrease in density reproducibility (linearity) and making it impossible to obtain smooth gradation characteristics.

(Problems to be solved by the invention) As described above, although it is possible to improve both gradation and resolution at the same time according to the prior art, smooth gradation characteristics cannot be obtained, leading to deterioration of image quality. There was a problem.

In view of the above circumstances, it is an object of the present invention to provide a multi-gradation recording method that provides smooth gradation characteristics and good image quality.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides a method for obtaining gradation by multi-leveling the formation energy of recording dots constituting a fixed pattern. A fixed pattern with a higher density level than this is characterized by being a pattern obtained by preferentially increasing dots in at least one of the main scanning direction and the sub-scanning direction around a predetermined reference dot.

(Function) In the present invention, even when fixed patterns of different density levels are adjacent to each other, recording dots are concentrated at common positions in the main scanning direction and in the sub-scanning direction, so that random bridging of ink is suppressed. Therefore, the linearity of the gradation characteristics is improved.

(Example) Hereinafter, the present invention will be explained in detail based on examples.

FIG. 1 is a diagram showing the relationship between the fixed pattern, the amount of implanted energy, and the recording density in one embodiment.

In this embodiment, a case where the present invention is applied to thermal transfer recording will be described as an example, and the amount of injected energy is determined by the drive pulse width of the thermal head, the drive pulse height, or a combination thereof. Further, in the figure, the horizontal axis represents the total amount of energy to be injected to form a pattern of one pixel.

In this example, one pixel is composed of a matrix of 3 x 3-9 dots, and the center dot P is set as the reference dot as shown in a(H). The region is shown <1. I[, 1[
, four of IV! ! Divide the density area into each divided density area 1. Fixed patterns a1, a2, a3, and a4 are assigned to IF, Dl, and IV, respectively. al is a pattern in which one recording dot is formed at the reference dot position of the matrix, a2 is an L-shaped pattern with a corner located at the reference lower dot position of the matrix, a3 is a cross pattern, and a4 is a cross pattern. This is a pattern with one dot added to the upper right. In this way, among the fixed patterns a1 to a4, a fixed pattern with a higher density level than one fixed pattern is a pattern in which dots are preferentially added in the main scanning direction and the sub-scanning direction with the reference dot as the center. is set to .

FIG. 2 shows an example of expressing 36 gradations using these four-stage fixed patterns. That is, in the first density region (gradation levels O to 6), the formation energy of one recording dot constituting the fixed pattern of al is varied from 0 to 6 to obtain seven gradations from gradation levels O to 6. I try to express myself.

In the second density region (gradation levels 7 to 18), the total implantation energy of the three recording dots constituting the fixed pattern a2 is changed from 7 to 18, and
I try to express gradations.

In the third density region Vj (gradation levels 19 to 30), the total implantation energy of the five recording dots constituting the fixed pattern a3 is varied from 19 to 3o, and the gradation level is 19.
I am trying to obtain 12111 tones of ~30.

Roughly speaking, in the fourth density region (gradation levels 31 to 36), the total amount of implanted energy of the six recording dots constituting the fixed pattern a4 is varied from 31 to 36, and the total amount of energy injected into the six recording dots constituting the fixed pattern a4 is varied from 31 to 36. It is designed to express six gradations.

As a result of the above, 36 levels of gradation can be obtained in a 3×3 matrix as a whole.

FIG. 3(a) is a diagram showing a pattern in which fixed patterns a1 to a4 are adjacent to each other in the main scanning direction. As is clear from this figure, even when fixed patterns of different density levels are adjacent, the recorded dots are concentrated in the main scanning direction column and sub-scanning direction column common between adjacent matrices. Thus, irregular bridges do not occur. On the other hand, FIGS. 3(c) and 3(d) are examples in which a conventional arbitrary fixed pattern is used in which the position of the recording dot row to be increased is not specified. Figure (C) shows the same density expression as Figure (a), but as shown in Figure (d), rampant bridges occur in the intermediate density region due to heat accumulation in the thermal head, etc. This has led to an extreme increase in the number of bells. Therefore, in this case, smooth gradation characteristics cannot be obtained.

Next, we will discuss the schematic configuration of a thermal printer that is capable of multi-gradation and also obtains smooth gradation characteristics in the fourth section.
This will be explained based on the diagram.

The output of the multi-gradation signal processing circuit 1 and the output of the matrix position determination circuit 2 are given to a multi-value pattern table 3. The output of the multi-value pattern table 3 is sent to the thermal recording circuit 4.
The signal is supplied to the thermal head drive circuit 5 via the following.

The multi-gradation signal processing circuit 1 processes multi-gradation/halftone signals input in the form of digital signals from a scanner, A/D converter, image memory, or demodulation or decoding circuit of a transmission system, according to the specifications and characteristics of the printer. , is a circuit that performs signal processing and outputs the signal.

The matrix position specifying circuit 2 is a circuit necessary for digital recording or pseudo halftone recording, and is a circuit for specifying the position of a pixel in a matrix array consisting of a plurality of pixel points. In the case of a normal line printer, it is linked with a dot counter in the main scanning direction and a line counter in the sub-scanning direction.

Further, depending on the case, processing is also performed to run on the image signal input clock used in the multi-gradation signal processing circuit 1, and to sample a signal in accordance with the matrix shape and arrangement as described above.

The multilevel pattern table 3 is a main part of this embodiment, and is a ROM that stores fixed patterns for each concentration region shown in FIG. 2 and the amount of energy to be injected into each dot of the fixed patterns. <ReadOnly
memory). This multi-value pattern table 3 outputs dot data at a position specified by the matrix position specifying circuit 2 among the fixed patterns corresponding to the output from the multi-gradation signal circuit 1 indicating the density level.

The thermal recording circuit 4 is a circuit for controlling the pulse width and pulse height of each dot of the thermal head in conjunction with the thermal head drive circuit 5, and is controlled by output data from the multi-value pattern table 3.

The thermal head drive circuit 5 is an IC circuit including a shift register, a latch, a gate, and a driver (not shown), and is mounted on the substrate of the thermal head.

The movement of the thermal head drive circuit 5 and the thermal recording circuit 4 is used to compensate for the heat accumulation phenomenon in conventional fused thermal transfer recording, but in this embodiment, the movement operation of the thermal head drive circuit 5 and the thermal recording circuit 4 is used to compensate for the heat accumulation phenomenon. used for control.

By performing the above-mentioned recording method using a thermal printer with such a configuration, it is possible to eliminate blank areas due to poor ink adhesion, roughness, and heat accumulation, which are causes of image quality deterioration that are particularly noticeable in the melt-type thermal transfer recording method. It is possible to select a pattern without smearing, etc., to obtain good image quality without random bridges of ink with adjacent pixels, and to express smooth 36 gradations in a 3×3 matrix, which could only be expressed in 10 levels conventionally.

Note that the above embodiment is just an example, and a pattern shown in FIG. 5 may be used as a pattern that achieves the same effect. This pattern is also the same 5! ! As shown in I(a), a reference dot P is set at the center of a 3×3 matrix, and the density level increases from (1) to (j) in the same figure.

The effects of the present invention can also be achieved by arbitrarily combining these fixed patterns, since recording dots are preferentially added to common main scanning direction columns and sub scanning direction columns.

In the above example, the position of the reference dot P is set at the center of the matrix, but it is not necessarily necessary to set it at the center of the matrix, and the effects of the present invention can be achieved even if it is set at any position on the matrix. FIG. 6 is an example in which the reference dot P is set at the upper left of the 3×3 matrix.

Even in this case, recording dots are preferentially added to the common main scanning direction column and sub-scanning direction column as shown in b1→b2→b3. Note that when all the dots are arranged at the same main scanning direction position and sub-scanning direction position as the reference dot P, b4. The density level is improved by adding recording dots at other positions in the main scanning direction and in the sub-scanning direction, such as b5.

Further, the present invention is not particularly limited in application to a 3×3 matrix, but for example, as shown in FIG.
It is similarly applicable to the matrix of Figure (a) shows an example in which a reference dot P indicated by CO is placed approximately at the center of the matrix, and the recording dot row is extended around the reference dot P as it reaches C1 to 05, increasing the density level. be. In addition, in (1) of the same figure, d is placed at the corner of the matrix.
.

This is an example in which a reference dot P shown in is set, and the recording dot row is extended from dl to d5 centering on the reference dot P to improve the density level.

Furthermore, the fixed patterns 81 to e4 shown in FIG.
~e3 is an example of a pattern that is symmetrical with respect to the sub-scanning direction axis that includes the reference dot P.

With such a pattern, since the directionality of the pattern is small, image quality with less texture noise can be obtained. Although the fixed pattern e2 has an asymmetrical relationship with respect to the main scanning direction axis passing through the reference dot P, the ink pattern formed on the recording medium due to heat accumulation in the thermal head is indicated by 02' in FIG. As shown, the recording dot at the position of the reference dot P has a shape slightly swollen downward. therefore,
This provides an effect of suppressing texture noise.

Further, although the fixed pattern e4 in the high 1 degree region does not have the above-mentioned symmetry, human visual characteristics in a high density region are generally lower than in a low density region, so it is unlikely to cause a sense of discomfort. However, when using a low resolution thermal head such as 4 resolutions/shoes, patterns 01 to e3
There is also a way to avoid expressing the concentration in the highest concentration range by using up to.

FIG. 10 is a diagram showing the amount of energy injected into each dot when the pattern of FIG. 8 is used.

In this way, it is desirable to have symmetry in the amount of energy implanted into each dot as well as the symmetry in the pattern, particularly in the region of concentration levels 7 to 19.

The above example is also not limited to a 3x3 matrix, but can be similarly applied to a 4x4 matrix as shown in FIG. That is, the patterns f1' to f5 are symmetrical patterns centered on the sub-scanning direction axis passing through point P. Here, f4゜fs is an asymmetric pattern, but since it is a fixed pattern in a high density area, it does not give a sense of discomfort to the visual sense, and when the same pattern is placed in adjacent pixels as shown in Figure 12, , 1/2 dot in the main scanning direction is regarded as a matrix frame, a symmetrical pattern is obtained, and the occurrence of texture noise is further suppressed than in the example shown in FIG.

Although each of the above embodiments is an example in which the present invention is applied to a fused thermal transfer type recording system, the present invention can be similarly applied to other multi-fill recording systems such as a thermal recording system.

[Effects of the Invention] As described above, according to the present invention, the positions of the formed recording dot rows in the main scanning direction and the sub-scanning direction are made common between different fixed patterns, so that the positions of the recorded dot rows are made common between different fixed patterns. No bridges will occur. For this reason,
Smooth gradation characteristics can be obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a fixed pattern according to an embodiment of the present invention and the relationship between the amount of energy injected into the pattern and the recording density, and FIG. 2 is a diagram showing the amount of energy injected into each dot of the same fixed pattern. , FIG. 3 is a diagram showing an example of recording using the same pattern in comparison with a conventional example, FIG. 4 is a block diagram showing an example of the configuration of a thermal printer that implements the method of this embodiment, and FIGS. 5 to 12 are FIG. 7 is a diagram for explaining other embodiments of the present invention. DESCRIPTION OF SYMBOLS 1... Multi-gradation signal processing circuit, 2... Matrix position specification circuit, 3... Multi-value pattern table, 4... Thermal recording circuit, 5... Thermal head drive circuit. Figure 1 (a) (b) (c) (d) Figure 5 (1)
) Figure 5 (2) Figure 6 Figure 7 Figure 8il Figure 9 Figure 11 Figure 12

Claims (3)

[Claims] (1) One pixel is composed of a matrix of multiple dots, and each pixel is formed by selecting a fixed pattern formed within the matrix and multileveling the formation energy of the recording dots that constitute the selected fixed pattern. In a multi-gradation recording method that obtains pixel gradation, a fixed pattern with a higher density level than one fixed pattern is formed by dots in at least one of the main scanning direction and the sub-scanning direction centered on a predetermined reference dot. A multi-gradation recording method characterized by a pattern obtained by preferentially increasing . (2) The multi-gradation recording method according to claim 1, wherein the reference dot is located at the center or center of gravity of the matrix. (3) The fixed pattern is a pattern having symmetry with respect to an axis in the sub-scanning direction that includes the reference dot at least in a low density area and a medium density area. Multi-gradation recording method.