JPH0795809B2 - Multi-gradation recording method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Industrial field of application) The present invention forms a pseudo-gradation image by forming one pixel in a matrix and changing the area ratio of recording dots in this matrix. The present invention relates to an obtained multi-gradation recording method.

(Prior Art) Conventionally, in order to obtain a gradation image by a recording method such as a fusion type thermal transfer recording method in which density expression must be “0” or “1”, a binary area Gradation expression is performed by area modulation called gradation.

In the binary area gradation method, smoother gradation can be obtained as the size of the matrix forming one pixel is larger, and the resolution of the image is increased as the size of the matrix is smaller. Therefore,
It is not possible to simultaneously satisfy such conflicting requirements,
There was no choice but to sacrifice either gradation or resolution.

Therefore, as shown in, for example, Japanese Patent Application No. 60-16768 (unknown), not only is the number of recording dots changed according to the density level, but the formation energy of each recording dot is also multi-valued to create a small matrix. A technique has been proposed in which a large number of gradations are obtained by using, and thereby both the gradation and the resolution are simultaneously improved.

However, in the above method, when an arbitrary pattern is used as the fixed pattern, a random ink adhesion state may occur between adjacent dots or adjacent pixels in a specific density increase area. For this reason, there is a problem that a print pattern unintended for print control, that is, a random bridge of ink is generated, resulting in deterioration of density reproducibility (linearity), and smooth gradation characteristics cannot be obtained.

(Problems to be Solved by the Invention) As described above, according to the prior application technique, although both the gradation and the resolution can be improved at the same time, a smooth gradation characteristic cannot be obtained, which causes deterioration of image quality. There was a problem.

SUMMARY OF THE INVENTION Under the circumstances, it is an object of the present invention to provide a multi-gradation recording method which can obtain smooth gradation characteristics and has good image quality.

[Configuration of the Invention] (Means for Solving the Problems) In the present invention, one pixel is composed of a matrix of a plurality of dots, and a fixed pattern formed in the matrix is composed of a plurality of fixed patterns corresponding to different density regions. In the multi-gradation recording method, in which the gradation of each pixel is obtained by multi-valued formation energy of the recording dots that form the selected fixed pattern while selecting from the patterns, a higher level than one fixed pattern is used. It is characterized in that the fixed pattern corresponding to the density area of the density is a pattern obtained by increasing the dots in the main scanning direction and the sub scanning direction centering on a predetermined reference dot in preference to other dots. .

(Operation) In the present invention, even when the fixed patterns of different density areas are adjacent to each other, the recording dots are concentrated in the common main operation direction and sub-scanning direction positions, so that the recording dots are adjacent to each other in the main scanning direction and the sub-scanning direction. As a result of minimizing the area in contact with the fixed pattern (pixel), a random bridge of image points formed by ink or the like is controlled. Therefore, the linearity of gradation characteristics is improved.

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

FIG. 1 is a diagram showing a relationship between a fixed pattern and an implantation energy amount and a recording density in one embodiment. In this embodiment, the case of applying to thermal transfer recording will be described as an example, and the implantation energy amount has a value determined by the driving pulse width of the thermal head, the driving pulse height, or a combination thereof. Also, in the figure, the horizontal axis represents the total amount of energy to be injected to form a pattern of one pixel.

In this embodiment, one pixel is composed of a matrix of 3 × 3 = 9 dots, and its central dot P is set as a reference dot as indicated by a ₀ . Then, the entire concentration region from the low concentration region to the high concentration region is divided into four concentration regions I, II, III, IV as shown in the figure, and these divided concentration regions I, II, III, IV
And to allocate the respective fixed pattern _{a 1, a 2, a 3} , a 4 against. a ₁ is a pattern in which one recording dot is formed at the reference dot position of the matrix, a ₂ is an L-shaped pattern in which a corner is located at the reference dot position of the matrix, a ₃
Is a cross pattern, and a ₄ is a pattern in which one dot is added at the upper right of the cross pattern. Thus, of the fixed patterns a _{1 to} a ₄ , one fixed pattern has a higher density level than this fixed pattern, and dots are added preferentially in the main scanning direction and the sub-scanning direction with the reference dot as the center. Is set to the pattern.

FIG. 2 shows an example in which 36 gradations are expressed by using these four-stage fixed patterns. That is, in the first density area (gradation levels 0 to 6), the formation energy of one recording dot forming the fixed pattern of a ₁ is changed from 0 to 6 to obtain 7 gradations from gradation levels 0 to 6. I am trying to express.

In the second density region (gradation levels 7 to 18), the total injection energy of the three recording dots forming the fixed pattern a ₂ is changed to 7 to 18 to express 12 gradations of gradation levels 7 to 18. I am trying to do it.

In the third density region (gradation levels 19 to 30), the total implantation energy of the five recording dots forming the fixed pattern a ₃ is
By changing from 19 to 30, 12 gradations of gradation levels 19 to 30 are obtained.

Further, in the fourth density region (gradation levels 31 to 36), the total injection energy amount of the six recording dots forming the fixed pattern a ₄ is changed to 31 to 36 to change the gradation levels 31 to 36. 6 gradations are expressed.

As a result, 36 gradations can be obtained in a 3 × 3 matrix as a whole.

FIG. 3A is a diagram showing a pattern when the fixed patterns a _{1 to} a ₄ are adjacent to each other in the main scanning direction. As is clear from this figure, even when fixed patterns having different density levels are adjacent to each other, the print dots are concentrated in the common main scanning direction row and common sub scanning direction row between the adjacent matrices. So irregular bridging does not occur. On the other hand, (c) and (d) in the figure are columns using a conventional fixed pattern in which the position of the recording dot column to be increased is not specified. The figure (c) expresses the same density as that of the figure (a), but as shown in the figure (d), a Lambum bridge occurs in the intermediate density region due to the effect of heat storage of the thermal head, This has led to an extreme increase in concentration levels. Therefore, in this case, smooth gradation characteristics cannot be obtained.

Next, a schematic structure of a thermal printer for achieving such multi-gradation and smooth gradation characteristics will be described below.
A description will be given based on the figure.

The output of the multi-gradation signal processing circuit 1 and the output of the matrix position specifying circuit 2 are given to the multi-valued pattern table 3. The output of the multi-valued pattern table 3 is given to the thermal head drive circuit 5 via the thermal recording circuit 4.

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

The matrix position specifying circuit 2 is a circuit required for digital recording or pseudo-halftone recording, and is a circuit for specifying the positions of pixels in a matrix array composed of a plurality of image points. In the case of a normal line printer, the dot counter in the main scanning direction and the line counter in the sub scanning direction are interlocked. In some cases, the multi-gradation signal processing circuit 1
In conjunction with the image signal input clock used in, the processing for sampling the signal according to the matrix shape and arrangement as described above is also performed.

The multi-valued pattern table 3 is an essential part of this embodiment, and stores a fixed pattern for each density region shown in FIG. 2 and the amount of energy injected into each dot of the fixed pattern (ROM ( Read Only Memory). The multi-valued pattern table 3 outputs the dot data at the position designated by the matrix position designating circuit 2 in the fixed pattern corresponding to the output indicating the density level from the multi-gradation signal circuit 1.

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 the output data from the multi-valued 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 interlocking operation of the thermal head drive circuit 5 and the thermal recording circuit 4 is used for compensating the thermal storage development in the conventional fusion thermal transfer recording, but in the present embodiment, it is used for gradation expression. Used for energy control.

By performing the above-described recording using the thermal printer having such a configuration, the blank due to ink adhesion defects, roughness, and heat accumulation, which are factors of image quality deterioration that are particularly noticeable in the fusion thermal transfer recording method, are caused. It is possible to select a pattern that does not have a part collapse and to obtain a good image quality without random bridging of ink with adjacent pixels, and to express 36 smooth gradations in a 3 x 3 matrix that could only be expressed in 10 steps. it can.

The above embodiment is an example, and the pattern shown in FIG. 5 may be used as a pattern that achieves the same effect. This pattern is also 3 × 3 as shown in FIG.
The reference dot P is set at the center of the matrix, and the pattern is such that the density level increases from (b) to (j) in FIG. By arbitrarily combining these fixed patterns, the recording dots are preferentially added to the common main scanning direction row and common sub-scanning direction row, so that the effect of the present invention can be obtained.

Although the position of the reference dot P is set at the center position of the matrix in the above-mentioned example, it is not always necessary to set it at the center of the matrix, and the effect of the present invention can be achieved at any position of the matrix. FIG. 6 shows an example in which the reference dot P is set at the upper left of the 3 × 3 matrix.
Even in this case, the print dots are preferentially added to the common main scanning direction row and common sub-scanning direction row as shown by b ₁ → b ₂ → b ₃ . When all the dots are arranged at the same position in the main scanning direction and the position in the sub scanning direction as the reference dot P, the recording dots at the other positions in the main scanning direction and the sub scanning direction such as b ₄ and b _5. Is added to improve the concentration level.

Further, the present invention is not particularly limited to application to a 3 × 3 matrix, and for example, as shown in FIG.
The matrix can be similarly applied. The same figure (a)
Is an example in which the reference dot P indicated by c ₀ is arranged at a substantially central position of the matrix, and the print dot row is extended around the reference dot P from c ₁ to c ₅ to increase the density level. Further, in FIG. 9B, the reference dot P indicated by d ₀ is set at the corner of the matrix, and the reference dot P is set from d ₁ to d _5.
This is an example in which the recording dot row is extended around the center to improve the density level.

Also, fixed pattern e ₁ to e ₄ shown in FIG. 8, a fixed pattern e ₁ to e ₃ in the low density area and intermediate density region (I to III)
Is an example of a pattern that is line-symmetric with respect to the sub-scanning direction axis including the reference dot P. With such a pattern, since the directionality of the pattern is small, an image quality with less texture noise can be obtained. Although the fixed pattern e ₂ has asymmetry with respect to the main scanning direction axis passing through the reference dot P, the ink pattern formed on the recording medium is e ₂ ′ in FIG. 9 due to heat storage of the thermal head. As shown by, the recording dot at the position of the reference dot P has a shape that slightly expands downward. Therefore, this has the effect of suppressing texture noise. Further, the fixed pattern e ₄ in the high-density area does not have the above-mentioned symmetry, but since the human visual characteristics in the high-density area are generally lower than those in the low-density area, a sense of discomfort is less likely to occur. However, when using a low resolution thermal head with a resolution of 4 lines / mm, there is also a method of using the patterns e _{1 to} e ₃ to avoid expressing the density in the maximum density range.

FIG. 10 is a diagram showing the amount of energy injected into each dot when the pattern of FIG. 8 is used. As described above, it is desirable that the amount of energy injected into each of the dodds has symmetry as well as the symmetry of the pattern, especially in the region of the concentration levels 7 to 19.

The above example is not limited to the 3 × 3 matrix, and can be similarly applied to the 4 × 4 matrix as shown in FIG. That pattern f ₁ ~f ₅ is a symmetrical pattern around the sub-scanning direction axis passing through the point P. Here, f ₄ and f ₅ are asymmetrical patterns, but since they are fixed patterns in the high-density region, there is little visual discomfort, and when the same pattern is arranged in adjacent pixels as shown in FIG. In addition, if a position shifted by 1/2 dot in the main scanning direction is regarded as a matrix frame, a symmetrical pattern is formed, and the generation of texture noise is further suppressed as compared with the example shown in FIG.

Although each of the above embodiments is an example in which the present invention is applied to a fusion thermal transfer type recording system, the present invention can be similarly applied to other multi-gradation 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 to different fixed patterns. There is no such a bridge. For this reason,
Smooth gradation characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a fixed pattern according to an embodiment of the present invention, and a 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 fixed pattern. FIG. 3 is a diagram showing a recording example of the same pattern in comparison with a conventional example, FIG. 4 is a block diagram showing a configuration example of a thermal printer which realizes the method of the present embodiment, and FIGS. It is a figure for explaining another example of the present invention, respectively. 1 ... Multi-gradation signal processing circuit, 2 ... Matrix position designation circuit, 3 ... Multi-valued pattern table, 4 ... Thermal recording circuit, 5 ... Thermal head drive circuit.

Claims (3)

[Claims] 1. A recording in which one pixel is composed of a matrix of a plurality of dots, a fixed pattern formed in the matrix is selected from a plurality of fixed patterns corresponding to different density regions, and the selected fixed pattern is formed. In the multi-gradation recording method that obtains the gradation of each pixel by making the dot formation energy multi-valued, a fixed pattern corresponding to a density area of higher density than one fixed pattern is set to a predetermined reference. A multi-gradation recording method, characterized in that a pattern obtained by giving priority to and increasing dots in the main scanning direction and the sub scanning direction centering on a dot over other dots. 2. The multi-gradation recording method according to claim 1, wherein the reference dot is located at the center or the center of gravity of the matrix. 3. The fixed pattern is a pattern having symmetry with respect to a sub-scanning direction axis including the reference dot in at least a low density region and a medium density region. Multi-gradation recording method described.