JPS6235770A - Multi-value area gradation system - Google Patents

Abstract

PURPOSE:To record an excellent gradational image even when variance in intermediate density is large by constituting such a recording dot matrix that density level differences between picture elements and between adjacent recording dots in a picture element are largest and recording the image according to gradation data. CONSTITUTION:The gradation data is converted by a conversion part 1 into a recording dot pattern so that density level differences between picture elements and between adjacent recording dots in a picture element, and the conversion output is applied to a recording part 2 composed of a thermal head, etc., to record the gradational image by using multi-valued recording dots. Thus, the recording dot pattern which has the largest density level differences between picture elements and adjacent recording dots in a picture element is formed to obtain large periodicity, and when an area gradational picture element pattern having larger periodicity than intermediate recording density is employed, there is no deterioration in picture quality.

Description

[Detailed Description of the Invention] [Summary] One pixel is constructed by using a plurality of recording dots with multilevel density levels, and the difference in density level between pixels and between adjacent recording dots within a pixel is the widest (so that By selecting a recording dot pattern, it is possible to record a good gradation image even when there is a large variation in the intermediate density of recording dots.

[Industrial application field]

The present invention relates to a multivalue area gradation method for recording good gradation images by reducing the influence of variations in intermediate density of recorded dots.

[Conventional technology]

A thermal printer of the melt transfer type normally records by black and white binary recording dots.

When recording a gradation image using such binary recording dots, an area gradation method is used. The density pattern method and the dither method are known as typical examples of the area gradation method. In the density pattern method in which one pixel corresponds to N×N recording dot matrices, the number of gradations is N2+1. Therefore, in order to increase the number of gradations, it is necessary to increase the number of recording dots that make up one pixel, and there is a limit to reducing the size of the recording dots, so it is necessary to increase the number of gradations. As a result, the area of one pixel increases and the resolution decreases.

Furthermore, sublimation transfer type thermal printers can record with multi-value recording dots that correspond to the energy applied to the thermal head. It becomes possible to record images. Therefore, a gradation image can be recorded without reducing resolution.

However, the sublimation transfer type has problems such as slow recording speed and inability to perform recording on plain paper, so attempts are being made to perform multi-level recording using the melt transfer type.

The number of gradation levels for one recording dot is insufficient for recording a gradation image, but if a recording dot matrix of NXN is used, m-value recording dots are (m-1)XN''+1
It is possible to obtain a number of gradation levels, and it is possible to record a gradation image while suppressing a decrease in resolution.

FIG. 8 is an explanatory diagram of a conventional recording dot matrix, showing a case where one pixel is constructed of five-value recording dots of θ to 4 as a 2×2 matrix, and it is possible to record pixel densities of O to 15. It is said that For example, if the pixel density is 1 to 4, the recording dot? Consisting of only 74 degree 1 recording dots, if the pixel density is 5 to 7, the recording dots? Jflf degree 1
．． When the pixel density is 9 to 11, the recording dot density is 2 and 3. When the pixel density is 13 to 15, the recording dot density is 3.4. . Therefore, the density level difference between adjacent recording dots within a pixel is selected to be small.

[Problem that the invention seeks to solve]

In the conventional recording dot matrix, at an intermediate pixel density such as 8 to 11, the recording dot density is 2,
This method records using only medium-density recording dots such as those shown in No. 3, and as a result, the unsightly grid pattern caused by the periodicity of the area coverage modulation pixel pattern becomes less noticeable, and relatively good gradation images can be recorded. becomes possible. However, in order to obtain such a good image, the density variation of the recorded dots is sufficiently small (for example, the density dispersion σ is several tenths of the maximum density or less, and in the above case, the recorded dot density is 4 or less). This method has the disadvantage that image quality deteriorates rapidly as the dispersion in the intermediate density of recorded dots increases.

In particular, when using thermal paper or a melt-transfer thermal printer, which is relatively inexpensive and capable of high-speed recording, there is a large variation in the intermediate recording density of the recording dots, so gradation images are recorded using a multilevel area gradation method. When this occurs, the deterioration in image quality becomes significant, and even if multilevel recording is performed to reduce the deterioration in resolution, a sufficient effect cannot be obtained.

The present invention improves the above-mentioned conventional drawbacks, and even when there is a large variation in the intermediate recording density of recording dots,
The purpose is to reduce the deterioration of the image quality of gradation images.

[Means for solving problems]

The multi-level area gradation method of the present invention will be explained with reference to FIG. The pattern is converted into a pattern by a converting section 1, and the converted output is added to a recording section 2 using a thermal head or the like, and a gradation image is recorded using multi-valued recording dots.

[Effect]

By creating a recording dot pattern that maximizes the density level difference between pixels and between adjacent recording dots within a pixel, it is possible to have strong periodicity, which is stronger than the variation in intermediate recording density. In the case of an areal gradation pixel pattern having the following characteristics, no deterioration in image quality occurs, as can be seen from image recording by halftone dot printing.

Figure 7 is an explanatory diagram of density variations. When recording using a melt-transfer type ink sheet or thermal paper, the variation in recording density at intermediate gradations is determined by the permissible value (maximum density). (1/10). In such a case, if the area coverage modulation pixel pattern has strong periodicity, the image quality will be determined approximately by the average density within one cycle of the area coverage modulation pixel pattern. For example, in Figure 6 (a
), it is known that when the pixel pattern has no periodicity and there is variation in the recording density with respect to the target density, the image quality becomes extremely grainy and deteriorates rapidly. On the other hand, by selecting so that the density level difference between adjacent recording dots becomes large, the pixel pattern becomes periodic, as shown in FIG. Although the image becomes clear, the visual pixel density corresponds to its average value, and the effects of variations in intermediate density cancel each other out and are reduced by being masked by the periodicity of the pixel pattern. , the image quality will be thicker (improved).

As is clear from Figure 6 f8) and (b), by setting the difference in adjacent density levels within a pixel pattern to be larger than the amplitude of density variation, the periodicity of the pixel pattern is more important than the variation in recording density. It can be made stronger.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a block diagram of an embodiment of the present invention, in which 3 to 5 are delay circuits (DL), 6 is a launch circuit, 7 is a read-only memory (ROM), and 8 is a thermal head.

Also, LS is a line start signal, MSP is a main scanning pulse,
Dn is gradation data, MSA is main scanning direction address signal,
SSA is a sub-scanning direction address signal.

Further, FIG. 3 is an explanatory diagram of the operation, (a) is the line start signal L S , (bl is the main scanning pulse MSP, (C)
is the delayed signal by the delay circuit 3, (dl is the main scanning pulse MSP shown as an enlarged version of (bl), (el is the delayed signal by the delay circuit 4, tn is the gradation data Dn, and (g) is the main scanning direction address signal MSAlh. ) is the sub-scanning direction address signal S
SA, (1) is the launch output signal of the latch circuit 6, (jl
(k) shows the delayed signal from the delay circuit 5.

The thermal head 8 is composed of a heating element and a drive circuit. If the recording paper is A4 size and the recording dot density is 8 dots/mm, the number of heating elements is 1728.

Therefore, it is necessary to receive 1728 pieces of gradation data within the recording cycle of 1 line, convert it into a recording dot pattern, and transfer it to the thermal node 8, making the recording cycle of 1 line 10m5. Then, the conversion time per heating element is approximately 500 nS.

At the start of the recording cycle of each line, the line start signal LS shown in (al) in FIG. 3 is applied, and after a predetermined time from this line start signal LS, the main scanning pulse MSP shown in 1728 line start signals are applied at a constant period.The line start signal LS is applied by the delay circuit 3 for a time T2, which is longer than the time required to complete the input of the whole area scanning pulse Msp, as shown in FIG. 3(C). It is delayed and applied to the thermal head 8.

Furthermore, by the time the line start signal LS delayed by the time T2 is output by the delay circuit 3, the conversion process of the gradation data Dn for all the heating elements has been completed, and the line start signal delayed by the delay circuit 3 has been completed. The thermal head 8 is driven at the rising edge of the signal LS.

In addition, the main scanning pulse MSP shown in (bl, (dl) in FIG.
In synchronization with the rise of the gradation data Dn and the main scanning direction address signal MSA shown in (fl, (g) in FIG. The scanning direction address signal MSA is delayed by the time TO, which is longer than the time required for it to become valid, resulting in a delayed signal shown in (el) in FIG. Dn
, a main scanning direction address signal MSA, and a sub-scanning direction address signal SSA are latched.

The output signal of the latch circuit 6 shown in (11) of FIG. 3 becomes an address signal for the read-only memory 7, and successive data of the recording dot pattern shown in (j) of FIG. 3 is output from the read-only memory 7. Further, a delay signal shown in FIG. 3(k), which is delayed by the delay circuit 5 by a time T1 longer than the time during which successive data in the read-only memory 7 becomes valid, is applied to the thermal head 8, and at the rising edge of this delay signal, Synchronously, successive data from the read-only memory 7 is taken into the thermal head 8, and recording pulses corresponding to the successive data are applied to the heating element from a drive circuit (not shown), thereby forming multi-value recording dots on the recording paper. recorded.

FIG. 4 is an explanatory diagram of a recorded dot matrix according to an embodiment of the present invention. Similarly to the case shown in FIG. 8, one pixel is composed of five-value recorded dots from 0 to 4 in a 2×2 matrix. The recording angle between adjacent recording dots (between pixels and between adjacent recording dots within a pixel) is selected to be the largest at 98 degrees. For example, at a pixel density of 5, recording dots with a recording dot density of 1.4 are arranged diagonally opposite positions, and the density of adjacent recording dots is 0. Therefore, the periodic density changes are 1 and 4 in the horizontal and vertical directions. On the other hand, the matrix in FIG. 8 has O and 1, and the matrix in FIG. 4 has a much stronger periodicity.

Also, at pixel density 10, recording tons)? Two recording dots with M degree 4, one recording dot with recording dot density 2,
It is constructed using one recording dot with a recording dot density of 0, and a recording dot adjacent to a recording dot with a density of 4 becomes a recording dot with a density of 0 or 2. Therefore, the periodic density changes are 2 and 4 in the horizontal and vertical directions. on the other hand,
In the matrix of FIG. 8, 1 is 1, and the matrix of FIG. 4 has stronger periodicity than the grooves.

FIG. 5 is a clear diagram of the ROM successive data data, from read-only memory (ROM>7), gradation data Dn, main scanning direction address signal MSA, and sub-scanning direction address signal S.
It shows data read in response to SA. The gradation data Dn has a 4-bit configuration, and the gradation data Dn and the 1-bit sub-scanning direction address signal SSA
and the main scanning direction address signal MSA form an address signal for the read-only memory 7.

For example, in the case of gradation data "0010" indicating pixel density 2, the sub-scanning direction address signal becomes "1" and
When the main scanning direction address signal is “0”, the recording dot t
Since successive data of 74 degrees 2 is output, the recorded dot matrix of density 2 in FIG. 4 is obtained. Similarly, in the case of gradation data "0101" indicating a pixel density of 5, the recording dot matrix of density 5 in FIG. becomes.

The capacity of the read-only memory (ROM) 7 mentioned above is 2
Since b (number of addresses) x 3 (number of bits indicating recording dot density 0 to 4) = 192 (bits),
An inexpensive and high-speed bipolar ROM can be used. Next, a method for creating an area gradation pixel pattern will be explained.

Generally, there are a plurality of area coverage modulation pixel patterns that satisfy the condition that the periodicity of the area coverage modulation pixel pattern is greater than the variation in intermediate density, and that express density.

In this case, the variation in average density of the area coverage modulation pixel pattern is calculated from the characteristics of the variation in intermediate density, and the pixel pattern with the minimum variation is selected. The average density of the multilevel area gradation pixel consisting of the NXN dot matrix is D=-n7! og(1-Σ, a, (1-10-""
)). However, n is a coefficient related to light diffusion in paper (obtained experimentally), Di is the density of the i-th recording dot, ai is the area of the i-th recording dot, and 1≦i≦
It is N2.

The present invention can be applied not only to the density pattern method but also to the dither method, and since the only difference is the correspondence between the pixels of the original image and the area gradation pixels, the configuration shown in FIG. All that is required is to change the data stored in the read-only memory 7 or the addressing method. Furthermore, the present invention can be applied not only to thermal printers but also to inkjet printers and the like which have a recording section capable of recording using multivalued recording dots. Of course, the present invention can also be applied to a case where the number of recorded dots constituting one pixel is further increased.

〔Effect of the invention〕

As explained above, the present invention configures a recording dot matrix in which the density level difference between pixels and between adjacent recording dots within a pixel is the largest, and performs recording according to the gradation data Dn. , there is an advantage that good gradation images can be recorded even when there are large variations in intermediate density. Therefore, it is possible to record a gradation image with improved image quality using thermal paper or a melt transfer type thermal printer that is inexpensive and capable of high-speed recording.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the principle of the present invention, FIG. 2 is a block diagram of an embodiment of the present invention, and FIG. 3 is an explanatory diagram of the operation of an embodiment of the present invention.
FIG. 4 is an explanatory diagram of the recorded dot matrix of the embodiment of the present invention, FIG. 5 is an explanatory diagram of ROM successive data, FIG. 6 is an explanatory diagram of density variation and periodicity, and FIG. 7 is an explanatory diagram of density variation. FIG. 8 is an explanatory diagram of a conventional recording dot matrix. ■ is a conversion section, 2 is a recording section, 3 to 5 are delay circuits (DL)
, 6 is a latch circuit, 7 is a read-only memory (ROM
), 8 is a thermal head.

Claims (1)

[Claims] In a multi-value area gradation method in which a gradation image is recorded by forming one pixel with a plurality of recording dots of multi-value density levels, gradation data indicating the density level of a pixel is a converter (1) that converts into a pattern consisting of a plurality of recording dots of different density levels; and a recorder (1) that performs recording according to the conversion output of the converter (1).
2), wherein the conversion unit (1) has a function of converting the gradation data into a recording dot pattern in which the density level difference between pixels and between adjacent recording dots within a pixel is the largest. A multi-value area gradation method featuring: