JPH02260969A - Half tone recording system - Google Patents

Abstract

PURPOSE:To always make a recording density with the same gradation constant by providing a correcting means which accumulates exponents corresponding to gradation level signals at every prescribed heat generating resistors and corrects an impressed energy quantity supplied from a supplying means so that the recording density of the same gradation level may be constant based on the accumulated value. CONSTITUTION:A voltage drop exponent counting means 5 accumulates a voltage drop exponent outputted from a gradation level signal deciding means 4 on a front state by a portion corresponding to a simultaneous recording dot, for example, for one line, obtains a corrected coefficient corresponding to the accumulated value from a table, and outputs it to a pulse generating means 2. Next a pulse generating means 2 stores the inputted gradation level signal for the simultaneous recording dot, and based on the gradation level of each recording dot and the corrected coefficient outputted from the voltage drop exponent counting means 5, the means 2 obtains the number of optimal energizing pulses corresponding to the gradation level of each recording dot.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates to a halftone recording method in thermal transfer recording or thermal recording, and particularly to a method for eliminating density unevenness and obtaining high quality halftone images. be.

[Conventional technology]

Commonly used thermal recording devices and thermal transfer recording devices have relatively simple configurations, so they can be used as printers,
It is widely applied to various types of recording such as copying machines and facsimile machines. In these various recording devices, in order to record intermediate tones (ζ), for example, a thermal transfer recording method using a sublimation ink sheet is used. The dye ink is sublimated in an amount corresponding to the amount of heat generated by the applied electric energy (the plural heating resistors that make up the thermal head), and then this dye ink is transferred to a predetermined recording paper. This is for recording. The heating and crushing by the heating resistor described above is controlled by the number of electrical pulses applied thereto and the connection time width.

This thermal transfer recording method is easy to control and can achieve relatively good halftone recording.

Such a conventional halftone recording method is known, for example, from Japanese Patent Application Laid-Open No. 60
9271, and FIG. 6 is a waveform diagram of the energizing pulse applied to each heating resistor constituting the thermal head in this conventional halftone recording method tr-, and tw is the energizing pulse. , tp is the repetition period of the energizing pulse, and M is the number of energizing pulses (three in this case). The number of energizing pulses is selected and set in advance in accordance with the density of each gradation level.

In this way, by applying energizing pulses in the number of pulses corresponding to each gradation to each heating resistor, ink with energy corresponding to the number of pulses is sublimated, and halftone recording of each density is performed. Normally, a corresponding energizing pulse is applied all at once to each heating resistor arranged in line for one line in the thermal head to record one line at a time, and the recording paper is moved at a constant speed. In this method, printing is performed sequentially for each line while the sub-scanning feed is 1 step to perform planar printing.

[Problem to be solved by the invention]

In the conventional halftone recording method as described above, for example, the number of recorded N dots of black or gray pixels to which an energizing pulse is applied to the heating resistor and the number of non-recorded dots of white pixels to which the energizing pulse is not applied is determined. Since the ratio in one line or the size of the gradation level of the recording dots differs for each line, the applied energy, that is, the magnitude of the current that is collectively supplied for recording, also differs for each line. Therefore, the voltage drop due to wiring resistance from the power supply to the thermal head, or the voltage drop within the thermal head, changes for each line, and this change in voltage affects the energizing pulse to the heating resistor, making it difficult to maintain the same gradation level. Even if there were, there were problems such as the amount of heat generated by the heating resistor would be different, and the recording density would be different at the same gradation, resulting in uneven recording. That is,
There is a problem in that the recording density of the same gradation level varies because the total amount of energy applied to the heat generating resistors that perform recording at the same time differs from line to line.

This invention was made to solve the above-mentioned problems, and aims to provide a halftone recording method in which the recording density of the same tone level is constant regardless of the magnitude of simultaneously applied energy. purpose.

[Means to solve the problem]

This invention (this halftone recording method) includes a thermal head consisting of a plurality of heating resistors, applying energy according to a gradation level signal input corresponding to each of the heating resistors,
A supply means for supplying a batch to each predetermined number of heat generating resistors, a supply means that accumulates an index corresponding to the gradation level signal for each of the predetermined number of heat generating resistors, and calculates the recording density of the same gradation level based on the accumulated value. The apparatus is provided with a correction means for correcting the amount of applied energy supplied from the supply means so as to be constant.

[Effect]

In this invention, the correction means accumulates an index corresponding to the gradation level signal input corresponding to each heat generating resistor for each predetermined heat generating resistor, and collectively calculates the index for each predetermined heat generating resistor. A cumulative value indicating the total amount of applied energy supplied by the The recording density becomes constant for each key.

〔Example〕

FIG. 1 is a block diagram showing one embodiment of the present invention,
(1) is an input terminal into which, for example, a 6-bit tone level signal S is input, and (2) is an input terminal for each input terminal that constitutes the thermal head (3) based on the tone level signal S from this input terminal (1). Pulse generating means as a supply means which calculates the amount of applied energy to be supplied to the heating resistor, for example the number of energizing pulses, and supplies it to each heating resistor; (4) is the gradation level from the input terminal (1); This is a gradation level signal determining means that determines the signal S and outputs a voltage drop index corresponding to the signal S. Here, the voltage drop index is as follows. That is, the total amount of applied energy collectively supplied to the thermal head (3) differs for each line depending on the number of recording pixels (recording dots) of each recording line and the gradation level of each recording dot. As the load current of the source changes, the voltage drop at each part changes, and the voltage of the energizing pulse also changes, and the value used to estimate the amount of this change, that is, the amount of voltage drop, is the voltage drop index.

This voltage drop index can be calculated by determining the resistance value of the thermal head or each M(7), or can be easily determined by a recording experiment. (5) accumulates the voltage drop index from this gradation level signal determination means (4) for a predetermined number of heat generating resistors that are simultaneously recorded, for example, 1942 minutes, and calculates a correction coefficient corresponding to the cumulative voltage drop index. This is voltage drop index counting means for outputting to the pulse generating means (2). The /f pulse generating means (2) uses the correction coefficient from the voltage drop index counting means (5) to calculate the amount of applied energy, for example, the number of energizing pulses, determined from the gradation level signal S to the recording density of the same gradation. Correct the convolution so that it is constant and supply it to the thermal head.

Here, Fig. 2 is a characteristic diagram showing the change in recording density with respect to the number of simultaneously recorded dots when no correction is performed when one line consists of 1024 dots and the gradation level is 64 steps. There is, and each curve (goods) to (goods) indicates the following case 1.

curve? D: Curve when the gradation level of the recording dot is 8 (2): Curve when the gradation level of the recording dot is 16 - 2 Curve when the gradation level of the recording dot is 32 (goods): Recording dot As shown in Figure 2, when the gradation level is 64, first, when the gradation level is 8, as shown by the curve 3υ, even if the number of simultaneously recorded dots increases, the recording density will change. No change occurs. What is shown here is that since the gradation level is low, the load current is small, and the amount of voltage drop of the energization pulse is almost equal to zero.

Next, when the gradation level is 16, as shown by curve (2), the recording temperature changes somewhat as the number of simultaneously recorded dots increases.

Further, when the gradation level is 32 (as shown in song Bq, the recording density changes considerably as the number of simultaneously recorded dots increases. This is due to the number of energizing pulses.

Furthermore, when full-page printing is performed when the gradation level is 64, as shown by the curve, the degree of increase in the voltage drop of the energizing pulse increases as the number of simultaneously recorded dots increases. As a result, the recording density further becomes significantly lower.

As mentioned above, when the number of simultaneously recorded dots is large, the voltage of the energizing pulse decreases, the energy supplied by the energizing pulse decreases, and the recording density decreases. Based on such characteristics, the energizing pulse may be corrected so that the recording density remains constant regardless of the number of simultaneously recorded dots. That is, since the recording density changes differently depending on the gradation level of the recording dots, first, the voltage drop index corresponding to the gradation level of each dot is determined by the gradation level signal determining means +41, and then the voltage drop index is simultaneously determined. The voltage drop index counting means (5) calculates the cumulative value for each recording dot, and the pulse generating means (2) corrects the energizing pulse based on the cumulative value.

Here, as can be seen from the above, when determining the characteristic curve showing the relationship between the recording density and the number of simultaneously printed dots using the gradation level as a parameter, strictly speaking,
As many characteristic curves as there are gradation levels are obtained.

However, some of them can be considered to express almost the same characteristics, and by grouping these together, it is possible to divide them into an appropriate number of groups. That is, the N-level gradation level signal is divided into an appropriate number of groups (where N≧n), and the voltage drop index is set in advance in the gradation level signal determination means +41 for each group. put. FIG. 3 shows an example of this, in which 64 gradation levels are divided into four groups, and a voltage drop index is set for each group.

Then, the voltage drop index for each dot is accumulated by the voltage index counting means (5) for simultaneously recorded dots, for example, one line, and a correction coefficient corresponding to the accumulated value is determined.
This cumulative value is also divided into several groups, and a flea correction coefficient for each group is set in the voltage drop index counting means (5). FIG. 4 shows an example of this, in which the cumulative voltage drop index is divided into 16 groups, and a correction coefficient is set for each group.

Further, the pulse generating means (2) calculates the number of energizing pulses that will give the same recording density for the same gradation from the correction coefficient output for each line and the gradation level signal S, and calculates the number of energizing pulses that will give the same recording density for the same gradation. The pulse is supplied to the thermal head (3).

A part of a table showing the correspondence between the gradation level signal and correction coefficient and the number of energizing pulses is shown in FIG. 5, and such a table is set in the pulse generating means (2).

Next, the operation of the above embodiment will be explained. It is now assumed that gradation level signals corresponding to any one of gradation levels 1 to 64 of each dot are sequentially input to the input terminal (1). This signal is first input to the gradation level determination means (2), and a voltage drop index indicating the degree of voltage drop when recording one corresponding dot is determined. That is, referring to the table in FIG. 3, for example, when the input gray level signal is included between gray level 1, the corresponding voltage drop index O is determined from the gray level determining means (4). Output.

Similarly, for example, the input gradation side level signal is gradation level 33-64! When this is included, the corresponding voltage drop index 1 will be output from the gradation level determining means (4).

The voltage drop index counting means (5) accumulates the voltage drop indexes outputted from the previous gradation level signal determining means (4) by the number corresponding to simultaneously recorded dots, for example, one line, and calculates the cumulative value. A correction coefficient corresponding to the value is determined from the table shown in FIG. 4, and is output to the pulse generating means (2). For example, if the cumulative voltage drop index is 254, the corresponding correction coefficient is determined to be 1.02 from the table of FIG. 3, and is output to the pulse generating means (2).

Next, the pulse generating means (2) stores the inputted gradation level signal for the simultaneously recorded dots, and also stores the gradation level of each recorded dot and the correction coefficient outputted from the voltage drop index counting means (5). From the above, the optimum number of energizing pulses corresponding to the gradation level of each recording dot is determined with reference to FIG.

Here, even if the gradation level signal is the same, if the correction coefficient is different, different numbers of pulses are determined so that variations in the voltage drop of the energizing pulse can be absorbed and the same density can be achieved. Then, the determined number of energizing pulses are supplied to each heating resistor of the thermal head (3) to perform recording. For example, when the correction coefficient is 1.02 as described above at gradation level 6, the number of energizing pulses is determined to be 33.

As shown in FIG. In the embodiment, the correction means is comprised of a gradation level signal determining means (4), a voltage drop index counting means (5), and a pulse generating means (2).

In the above embodiment, the number of groups, correction coefficients, etc. when dividing the gradation level signal and cumulative voltage drop index as shown in FIGS. 3 and 4 are determined by the thermal head (
It may be determined based on the characteristics of 3.

Further, in the above embodiment, a case has been described in which a change in recording density due to a change in voltage drop is corrected by changing the number of energizing pulses to change the amount of applied energy. However, the present invention is not limited to this, for example, A similar effect can be obtained by changing the width and changing the applied energy to correct density changes.

Furthermore, by adding a heat accumulation correction function of the thermal head regarding changes in environmental temperature, etc., it is possible to improve the accuracy of keeping the recording density constant for the same gradation.

In addition, in the above embodiment, the accumulation of the voltage drop index was explained for dots recorded simultaneously, but in this case, the dots recorded simultaneously are not for one line, but for multiple lines. When recording by dividing into sections, accumulate the voltage drop index using this section as a unit.
A similar effect can be obtained by correcting the energization pulse.

〔Effect of the invention〕

As described above, according to the present invention, an index corresponding to a gradation level signal input corresponding to each heating resistor is accumulated for each predetermined number of heating resistors to which applied energy is supplied at once, and Since the amount of applied energy supplied to each of the predetermined number of heating resistors is corrected based on the cumulative value, changes in recording density for the same gradation due to differences in applied energy are corrected. This has the effect that the recording density of the same gradation is always constant and the quality of the recorded image is improved.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a characteristic diagram showing changes in recording density with respect to the number of simultaneously recorded dots when no correction is performed, and Fig. 3 is a gradation level and voltage drop index. 4 is a table diagram showing an example of the correspondence between the cumulative voltage drop index and the correction coefficient,
Figure 5 is a table diagram showing an example of the correspondence between the combination of gradation level and correction coefficient and the number of energizing pulses;
The figure is a waveform diagram of energizing pulses for explaining the operation of the halftone recording method. In the figure, (1) is an input terminal, (2) is a pulse generating means, (3) is a thermal head, (4) is a gradation level signal determining means, and (5) is a voltage drop index counting means. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] A thermal head consisting of a plurality of heat generating resistors, a supply means for collectively supplying applied energy to a predetermined number of heat generating resistors in accordance with a gradation level signal input corresponding to each of the heat generating resistors, and the above gradation level. An index corresponding to the level signal is accumulated for each of the predetermined number of heating resistors, and based on the accumulated value, the amount of applied energy supplied from the supply means is corrected so that the recording density of the same gradation level is constant. A halftone recording method characterized by being equipped with a correction means.