JPH03197149A - Heat sensitive transfer gradation controller - Google Patents

Abstract

PURPOSE:To obtain a color printing record of high quality by performing a first electrification with density correction data corresponding to an irregularity in the resistance value of each heat generating resistor at the time of preheating and a second electrification with video data corrected corresponding to an irregularity in the resistance value of the resistor at the time of printing. CONSTITUTION:In a first electrification, density correction data corresponding to an irregularity in the resistance values of heat generating resistors R1 - Rn from density correction data recorder 23 are electrified to heat generating resistors R1 - Rn to be preheated, and in a second electrification, image data corrected corresponding to an irregularity in the resistance values of the heat generating resistors R1 - Rn from other calculator 25 are electrified to the resistors R1 - Rn to be printed. A line thermal head 6 is not simultaneously electrified at the time of preheating, but the first conduction with the density correction data corresponding to the irregularity in the resistance values of the resistors R1 - Rn at the time of preheating and the second electrification with the video data corrected corresponding to the irregularity at the time of printing are executed to eliminate an irregularity in the density on a part having low density, thereby obtaining a color printing record of high quality.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a thermal transfer gradation control device, and particularly to a thermal transfer gradation control device that controls current flow during preheating, which is applied to a plurality of heat generating resistors constituting a line thermal head, and during printing. The present invention relates to a thermal transfer IW adjustment control device that controls 1Wi11 by applying current in accordance with the variation in resistance value of each heating resistor.

(Prior Art) A thermal transfer printing device has conventionally been used in the business or consumer field as a stamp ψJ device for printing images such as still images or computer graphic figures. As shown in FIG. 7, this thermal transfer printing device uses an ink film 1 in which one side of a polyester film 2 with a thickness of 5 to 6 μm is coated with heat-melting ink or heat-sublimable ink. The ink surface is brought into contact with the recording paper 4, a line thermal head 6 is applied to the back surface, the recording paper 4 and the ink film 1 are pressed together with a platen roller 5 by the line thermal head 6, and the platen roller 5 is rotated.

A current is applied to the line thermal head 6 to generate heat, melting or sublimating the ink on the ink film 1 at a position corresponding to the line thermal head 6, and transferring the ink onto the recording paper 4. Further, the ink is composed of a plurality of colors such as yellow, magenta, cyan, and black.

The line thermal head 6 has a plurality of heat generating resistors arranged in a line, and current is sequentially applied to each heat generating resistor to print images, figures, characters, etc. in color.

The density that determines the gradation of color-printed images, figures, characters, etc. is determined depending on the area of each dot on the transferred recording paper 4 when heat-melting ink is used; When used, it is determined by the amount of sublimation of ink in each dot.

In general, the longer the current is applied to the heating resistor, the more heat it generates, and the larger the area of the dots printed with heat-melting ink becomes.On the other hand, the area of dots printed with heat-sublimable ink increases. The amount of sublimation becomes large. Therefore, the density of the printed recording paper 4 becomes high, and the gradation becomes close to the saturation density.

The transfer characteristics of heat-melting ink or heat-sublimating ink (hereinafter also referred to as ink) are as shown in Figure 8. Point X1 in Figure 0 is the ink threshold point at which the ink begins to melt or sublimate. .

As shown in the figure, the transfer characteristics of the ink have non-linearity almost in the shape of an "S", so various controls are performed to make the characteristics as linear as possible during printing.

For example, in the section up to the ink threshold point in the figure (section o-xi >, the line thermal head 6 is heated by a batch energization in which each heating resistor of the line thermal head 6 is energized at a constant current for a fixed period of time. Preheat each heating resistor,
Controls the rise of ink density characteristics. In addition, in the section after point X1 (section Xi - He is acting as a governor. Then, during the period of printing for a line, preheating is performed by energizing each heating resistor at once, and printing is performed by energizing each heating resistor in accordance with its resistance value, and these operations are repeated multiple times to complete color printing. can get.

(Problem to be Solved by the Invention) By the way, in tone control using the conventional thermal transfer printing device configured as described above, the line thermal head 6
There is variation in the resistance value of each heating resistor. Further, the pressing force of the thermal head 6 that presses against the platen roller 5 also varies.

Therefore, due to these causes, differences occur in the amount of heat generated and the amount of heat transfer during printing.

As mentioned above, each heating resistor of the line thermal head 6 is energized and preheated up to the ink threshold point, but due to variations in each heating resistor, the ink reaches the threshold point. Some heat generating resistors are present, while others do not reach the threshold point of the ink. Therefore, variations in the heat generating resistors during preheating have an effect even during printing, and affect the low density portion (high-color portion) of the printed recording paper 4. That is, density differences (density unevenness) occur in areas of low density on the printed recording paper 4.
In addition, stains on the base material occur in low-density areas of the recording paper 4. For example, when hot-melt ink is used, if the heat-generating resistor reaches a threshold point or higher during preheating and becomes overheated, this stain on the substrate can occur even in areas that are not printed during printing. In addition, if heat sublimation ink is used, the heat sublimation ink sublimates slightly even at low temperatures, and the heat generating resistor causes a small amount of ink to be transferred to the recording paper 4. It will be transcribed. This phenomenon is called soiling of the substrate.

As a result, the quality of color printed images is significantly degraded, and the reliability of the printing apparatus is impaired.

(Means for Solving the Problems) The present invention has been made in view of the above problems, and uses a line thermal head in which a plurality of heat-generating resistors are arranged in a row, and is based on an input video signal. A thermal transfer gradation control device that prints an image, etc. by controlling the amount of current applied to each heating resistor, the density correction storing density correction data corresponding to the variation in resistance value of each heating resistor. a data storage device; an arithmetic circuit that combines the input video signal and the density correction data to form video data that is corrected in accordance with variations in the resistance values of the heating resistors; and the density correction a level counter with an up/down counter function that sends a signal for comparing the data and the corrected video data; and the density correction data and the corrected video data, which are selectively switched by a switching means. a density data comparison circuit that compares the signal of the level counter with the signal of the level counter, and sets the level counter to the down counter side during a period in which each heating resistor prints one line, and calculates the density correction data. By comparing the signal of the level counter and the signal of the level counter,
By first energizing each heat generating resistor, setting the level counter to the up counter side, and comparing the corrected video data and the signal of the level counter, each heat generating resistor is energized. It is characterized by comprising a second energization that energizes the resistor.

The present invention also provides a thermal transfer gradation control device characterized in that a non-energizing period is provided between the first energizing and the second energizing.

(Embodiment) An embodiment of the thermal transfer Wll sub-control device according to the present invention will be described in detail below with reference to FIGS. 1 to 6. Note that the same reference numerals are given to the same components as those of the conventional example.

FIG. 1 is a circuit diagram showing a first embodiment of the thermal transfer gradation control device of the present invention, and FIG. FIG. 3 is a circuit diagram showing a second embodiment of the thermal transfer gradation control device of the present invention, and FIG. 4 is a diagram showing the first energization state and the second energization state during the period in which The second control device
In the embodiment, a diagram showing the first energization state and the second energization state during the period of printing for -line, FIG. 5 is a control signal waveform diagram in the thermal transfer gradation control device of the present invention, and FIG. FIG. 7 is an operation flow diagram of first energization and second energization in the thermal transfer gradation control device of the invention.

The thermal transfer IW adjustment sub-control device of the present invention, roughly speaking, preheats each heat-generating resistor by applying density correction data corresponding to the variation in resistance of each heat-generating resistor arranged in a line in a line thermal head. The second energization process consists of a first energization step in which the heating resistors are energized and image data corrected in accordance with the variation in the resistance value of each heat-generating resistor element is printed. Then, during the period of printing for -line, first energization and second energization are performed, and these operations are repeated a plurality of times to obtain color printing.

[First Embodiment] As shown in FIG. 1, the line thermal head 6 includes a plurality of n heating resistors R1 on a ceramic substrate (not shown).
~R, are arranged in a row.

The configuration of this line thermal head 6 is the same as that of a conventional thermal transfer printing device, and extends in the width direction of the ink film 1, as shown in FIG.

In the figure, an ink film 1 serving as a transfer paper has a polyester film 2 coated with heat-melting ink or heat-sublimable ink 3 (hereinafter referred to as ink) on the surface of the polyester film 2 to a predetermined thickness. The recording paper 4 is sent along with the ink film 1 in the direction of arrow A by the platen roller 5 with its recording surface facing the ink 3 surface of the ink film 1 . Further, a line thermal head 6 is provided opposite the platen roller 5, and is in contact with the back surface of the ink film 1. Among the heating resistors R1 to R of the line thermal head 6, the ink 3 of the ink film 1 corresponding to the energized heating resistor is melted or sublimated and transferred onto the recording paper 4. After passing through the line thermal head 6, the ink film 1 is guided by a roller rough and separated from the recording paper 4, and the used ink film 1 is placed on a take-up roll (not shown).
It is wound up as a. The transferred ink 3a remains on the printed recording paper 4a. For convenience of illustration, the transferred ink 3a is shown as having a large area, but it actually consists of a collection of small dots.

One dot is formed by a - heating resistor element,
The size of the - dot is determined by the current value or the duration of current flowing through the - heating resistor element. The shading, that is, the gradation, of the printed figure is determined depending on the size of each dot or the amount of sublimation.

Further, an encoder 5b that rotates integrally with the platen roller 5 is attached to a coupling 5 at the shaft end of the platen roller 5.
They are connected via a. This encoder 5b generates one absolute pulse and one pulse per one rotation of the platen roller 5.
For example, 1500 Y pulses are generated for each rotation.

The operation of the thermal transfer F@adjustment sub-controller is controlled by the number of Y pulses based on the absolute pulse.

Further, one wavelength of the Y pulse corresponds to a period during which the line thermal head 6 prints one line.

The present invention is a thermal transfer gradation control device (hereinafter also referred to as device) that can be applied to such a thermal transfer type printing device, and is explained below using FIGS. 1, 2, 5, and 6. explain.

In FIG. 1, input means for inputting a video signal into the apparatus is a video signal input device 8. A/D converter9. It consists of a data storage device 10.

That is, the analog video signal supplied from the video signal input device 8 is converted into a digital video signal by the A/D converter 9, and sent to the data storage device 10 for storage. Note that these input means for inputting video signals are not provided in advance in the device, but are constructed as a separate part of the above configuration, and are digitized between this separate part and the arithmetic circuit 25 described later. Alternatively, the video i-signal may be a synchronized digitized sequential video signal without being stored in the data storage device 10 as in this embodiment. . However, the synchronized sequential video signal must satisfy the control processing speed of the device address, etc.

On the other hand, the Y pulse output from the encoder 5b described above is input to the pulse generator 22, and the start pulse J (J
1, J2) and a data switching pulse from the pulse generator 22. As shown in FIG. 5, the start pulse J consists of a J1 pulse synchronized with the rising edge of the Y pulse of the encoder 5b, and a J2 pulse delayed by a certain period of time from Jl.
Consists of pulses. Further, the data switching pulse 1 is formed as shown in the figure with reference to the start pulses Jl and J2.

Returning to FIG. 1, the data switching pulse 1 is a control signal for the electronic switch 24 that is connected to the electronic switch 24 (SWI) and switches between the concentration correction data storage device 23 side and the arithmetic circuit 25 side, which will be described later. .

The level counter 15 is an up/down counter, and the up/down setting is switched by 1 in the data switching pulse. As will be described later, the down counter is used during the first energization, and the up counter is used during the second energization. Note that it is necessary to align the ends of the first energization of each heating resistor R1 to Ro and to align the starts of the second energization, and the output of the level counter 15 input to the grayscale data comparison circuit 14, which will be described later, is , is set as a down counter during the first energization, and is set as an up counter during the second energization.

Then, the first energization process is performed to preheat the heat generating resistors R1 to Rn by applying the density correction data corresponding to the variation in the resistance values of the heat generating resistors R1 to Rn from the density correction data storage bag W23. On the other hand, the image data corrected according to the variation in the resistance value of each heat generating resistor R1 to R1 from the arithmetic circuit 25 is printed by energizing each heat generating resistor #R1 to R. This is called second energization. Note that the address 1. which is output from the address counter 11, which will be described later.
2...n correspond to each heating resistor R1 to Ro.

First, the first energization will be explained.

This first energization is not a batch energization to each of the heat generating resistors KR1 to Rn during preheating as in the conventional example described above, but a method of energizing during preheating that accommodates variations in the resistance values of the respective heat generating resistors R1 to R. It is. That is, in the density correction data storage device 23,
Concentration correction data corresponding to variations in resistance values of each heat generating resistor R1 to Ro is stored in ROM (READ) in advance.
ONLYMEMORY), etc. This density correction data is, for example, based on the average value of the resistance values of the heating resistors R1 to R1, and is corrected so that the amount of heat generated by each heating resistor R1 to Rn is constant depending on whether it is higher or lower than the average value. data, or each heating resistor R1 to R
Based on either the highest or lowest resistance value of o,
This data is corrected so that the amount of heat generated by each heating resistor R1 to Ro becomes constant.

First, the address counter 11 is supplied with a reference clock signal (ctoc...3MHz) supplied from a terminal 12 and a start pulse J1 from a pulse generator 22.
The first address (first address) at the first energization
The address of the second heating resistor R1) is sent to the density correction data storage device 23.

At this time, the electronic switch 24 (SWI) is connected to the density correction data storage device 23 side by a data switching pulse of 1. The above configuration is the density correction data storage device 23.
The density correction data output from the arithmetic circuit 2 to be described later
This is a switching means for switching between the corrected video data outputted from 5 and the corrected video data outputted from 5.

In addition, level counter 1 is set by 1 in the data switching pulse.
5 is set as a down counter, and is set to a value (signal) of [m] greater than or equal to the maximum value of the density correction data stored in the density correction data storage device 23 by the start pulse J1. Note that the value [m] in the level counter 15 is, for example, a value within 6 bits [within 63].

Then, the density correction data corresponding to the first address of the first energization of the density correction data storage device 23 is sent to the density data comparison circuit 14, while the value [m] of the level counter 15 is also The data is sent to the data comparison circuit 14. Here, both values are compared, and if the density correction data is larger than [m] of the level counter 15, control data [1] is sent to the shift register 16, and if it is equal to or smaller than [m], the control data is sent to the shift register 16. [0]
send. When the processing at the first address in the first energization is completed in this way, the address counter 11 sequentially counts 2.3 at the first address in the first energization.
．． ..., the n-th address (the address of the n-th heating resistor Rn) is sent to the data storage device 10, and the data storage device 10 writes density correction data corresponding to the 2nd to nth addresses each time. The data is sequentially sent to the grayscale data comparison circuit 14.

During this time, the level counter 15 remains set at [m]. Then, the same processing as above is performed sequentially, and the grayscale data comparison circuit 14 outputs the control data [O or [
1] to the shift register 16, and the operation of step 1 as shown in FIG. 6 is completed.

On the other hand, the n-stage shift register 16 outputs the first 1 to
The control data [0 or [1] corresponding to the n-th address is sequentially fetched and sent to the latch circuit N117 (
Step 2 in Figure 6).

When the address counter 11 finishes counting the first to nth addresses during the first energization, the address counter 11 transmits the data transfer pulse L1 to the level counter 15 and the latch circuit 17.
send to

The latch circuit 17 latches the control data [0] or [1] output from the shift register 16 at the time when the data transfer pulse L1 is input, and gate circuits 01 to 17 latch the control data [0] or [1] output from the shift register 16.
Go to each one of the input terminals, and then to each heat generating resistor R1 to R1, and each heat generating resistor R1 to
R, is preheated (steps 3 to 4 in FIG. 6).

Furthermore, when the next data transfer pulse L1 is sent, the level counter 15 changes from [m] to [m-1
] value.

Then, in the same way as Step 1 in FIG. 6, processing corresponding to the 1st to nth addresses in the second time during the first energization is performed, Step 5 is executed, and the value of the level counter 15 is sequentially decreased. The same process is repeated until the value of 0 reaches the value [0], and the operations up to step 6 in FIG. 6 are performed.

The above operation flow is the first energization at the time of preheating, in which energization is performed according to the density correction data.

Next, the second energization will be explained.

This second energization is completed after the first energization during preheating, and the recording paper 4
Each heating resistor R1 to R is printed on.

This is energizing.

As mentioned above, the data storage device 10 stores digitized video signals.

First, from the address counter 11, the first address (the first address of the first heating resistor R1
address) to the data storage device 10 and density correction data storage device 23. As described above, the density correction data storage device 23 stores density correction data corresponding to variations in the resistance values of the heat generating resistors R1 to Ro. Then, the video signal output from the data storage bag W10 corresponding to the first address of the first time during the second energization and the second
The density correction data output from the density correction data storage device 23 corresponding to the first address at the time of energization is sent to the arithmetic circuit 25 at the same time. The video signal and the density correction data are combined and processed in the calculation circuit 25 to form video data that has been corrected in response to variations in the resistance values of the heating resistors R1 to Rn. Incidentally, if the input means described above is a digitalized sequential video signal, it is also possible to input the video signal synchronized with the address to the arithmetic circuit 25.

On the other hand, when the first energization ends, the level counter 15 is set to an up counter by the start pulse J2 and the data switching pulse of 1. At this time, level counter 15
The inside is set to a value (signal) of [0]. In addition, during the second energization, the maximum value of the corrected video data is [p]
Therefore, as shown in FIG. 6, the maximum value of the up counter in the level counter 15 is the value [p], for example, a value within 8 bits [within 255].

Further, the connection of the electronic switch 24 to the arithmetic circuit 25 side is switched by the data switching pulse 1.

Then, the first time when the arithmetic circuit 25 is energized for the second time.
The corrected video data corresponding to the th address is sent to the grayscale data comparison port F#114, while the value [0] of the level counter 15 is also sent to the grayscale data comparison circuit 14, where both values are After comparison, if the video data is greater than [01 of the level counter 15, control data [1] is sent to the shift register 16, and if it is equal to or smaller than [0], control data [0] is sent to the shift register 16.

In this way, when the processing at the first address in the first time during the second energization is completed, the address counter 11 is sequentially updated to 2.3.・・・
・, nth (address of nth heating resistor Rn)
The address of data storage device 10. The data is sent to the density correction data storage device 23, and the data storage device 10 and the density correction data storage device
The inputted video signals and density correction data corresponding to the addresses from .

Note that during this time, the level counter 15 remains set to [0]. Then, the same processing as above is performed sequentially, and the gray data comparison circuit 14 outputs the control data [0] or [
1 is sent to the shift register 16, and the operation of step 7 shown in FIG. 6 is completed.

After that, similarly to the first energization, the n-stage shift register 16
sequentially takes in n-bit control data corresponding to the 1st to nth addresses of the first time during the second energization supplied from the gray data comparison circuit 14, and outputs the n-bit control data to the latch circuit 17.
Send to.

When the address counter 11 finishes counting the first to nth addresses during the second energization, the address counter 11 transmits the data transfer pulse L1 to the level counter 15 and the latch circuit 17.
send to

The latch circuit 17 latches the control data [0] or [1] output from the shift register 16 at the time when the data transfer pulse L1 is input, and gates 1 to 4G.
The signals are sent to one of the input terminals 1 to Go, respectively, and to each of the heating resistors R1 to R0, and printing is performed on the recording paper 4 here.

Further, when the data transfer pulse L1 is sent to the level counter 15, the level counter 15 increases from [0] to the value [1].

Then, in the same way as step 7 in FIG. The same process is repeated until the value of [p] is reached, and the operations up to step 10 in FIG. 6 are performed to complete the printing of -line.

The above operation flow is the second energization during printing in which energization is performed according to the corrected video data.

Note that the time required for the second energization during printing is longer than the time required for the first energization during preheating. This is done by level counter 1 in order to send the video data to be printed finely to each heating resistor R1 to Rn and obtain high quality color printing.
This is because the maximum setting value of 5 is set to a value greater than the first energization value, for example, within 8 bits, as described above. Therefore, during the period of printing for -line, the first energization and the second energization are performed as shown in FIG. Then, by repeating printing for -lines multiple times, high-quality color printing can be obtained.

As a result of the above, instead of energizing the line thermal head 6 all at once during preheating as in the conventional method, it is possible to perform a correction process based on density correction data that corresponds to the variation in the resistance value of each heat generating resistor R1 to R during preheating. By performing the first energization and the second energization based on the video data corrected in accordance with the variation in the resistance value of each heating resistor R1 to Rn during printing, it is possible to ) is eliminated, and the base of the recording paper 4 is not smudged (background smudge), resulting in a high-quality color print record. Therefore, it is possible to greatly contribute to improving the quality of the thermal transfer gradation control device.

[Second Embodiment] The second embodiment is a method of providing a short non-energization period between the first energization and the second energization in the first embodiment. Explain using.

The second embodiment is almost the same as the first embodiment except for a part as shown in FIG.
The second embodiment has the same configuration as the first embodiment, and therefore, detailed explanations of parts that have the same configuration and the same operation as the first embodiment will be omitted.

In the first embodiment, the density correction data storage device 2 at the time of first energization
The electronic switch 24 (SWI) is switched by using the data switching pulse 1 to switch between the 3 side and the arithmetic circuit 25 side during the second energization, but the second embodiment further uses the data switching pulse shown in FIG. 2, the electronic switch 26 (SW2) connected in series with the electronic switch 24 is also switched. The data switching pulse 2, the data switching pulse 1, and the start pulses J1 and J2 are logically summed by an OR element 27 as shown in FIG. Note that the above-mentioned control means is not limited, and for example, one terminal 28 of the gate elements 01 to Go is separated from the VCC (fixed voltage) side,
It is also possible to input a strobe pulse (not shown) equivalent to the data switching pulse 3, which is obtained by inverting 2 to the data switching pulse shown in FIG. 5, to one terminal 28 of the gate elements 01 to Gn.

Therefore, the electronic switch 26 is connected to the arithmetic circuit 25 side later than the electronic switch 24 by the period of the start pulse J2. Therefore, in the second embodiment, as shown in FIG. 4, there is a short non-current period (T1) between the first energization and the second energization.
is provided.

The effect of the second embodiment described above is due to the voltage drop in the power supply voltage during the first energization of the power supply (not shown) supplied to the line thermal head 6 in the thermal transfer gradation control device of the present invention.
It is recovered during a short non-current period (T1). Therefore, the power required to drive the line thermal head 6 is reduced, and it is possible to contribute to an improvement in productivity due to cost reduction of the thermal transfer gradation control device.

(Effects of the Invention) As described in detail above, the thermal transfer gradation control device of the present invention is capable of controlling each heating resistor during preheating without energizing the line thermal head all at once during preheating as in the conventional case. By performing the first energization based on density correction data corresponding to variations in resistance value and the second energization based on image data corrected corresponding to variations in resistance value of each heating resistor during printing, the conventional example is improved. This eliminates density differences (density unevenness) in low-density areas (high-print areas), eliminates stains on the base of the recording paper (background stains), and provides high-quality color print records. Therefore, it is possible to greatly contribute to improving the quality of the thermal transfer PLL sub-control device.

Further, in the thermal transfer gradation control device of the present invention, for example, a voltage drop in the power supply voltage during the first energization of the power supply to the line thermal head is recovered during a short period of non-energization. Therefore, the power supply for driving the line thermal head becomes smaller, and it becomes possible to contribute to an improvement in productivity due to cost reduction of the thermal transfer gradation control device.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the thermal transfer gradation control device of the present invention, and FIG. FIG. 3 is a circuit diagram showing a second embodiment of the thermal transfer gradation control device of the present invention, and FIG. 4 is a diagram showing the first energization state and the second energization state during the period in which The second control device
In the embodiment, a diagram showing the first energization state and the second energization state during the period of printing for -line, FIG. 5 is a control signal waveform diagram in the thermal transfer gradation control device of the present invention, and FIG. In the thermal transfer gradation control device of the invention, an operation flow diagram of first energization and second energization, FIG. 7 is a perspective view of a part of the main part of a conventional thermal transfer type printing device, and FIG. 8 is an ink paper FIG. 3 is a diagram showing the ink characteristics of 6... Line thermal head, 8... Video signal input device, 9... A/D conversion device,
10... Data storage device, 11... Address counter, 14... Grayscale data comparison circuit, 15... Level counter, 16... Shift register, 17... Latch circuit, 2
2... Pulse generator, 23... Concentration correction data storage device, 24... Electronic switch (SWI), 25... Arithmetic circuit, 26... Electronic switch (SW2), 27... OR Element, 01~Go... Gate element, R1~Ro... Heat generating resistor.

Claims (2)

[Claims] (1) Thermal transfer that uses a line thermal head in which multiple heat generating resistors are arranged in a row to print images, etc. by controlling the amount of current applied to each heat generating resistor based on the input video signal. The gradation control device includes a density correction data storage device that stores density correction data corresponding to variations in resistance values of the heat generating resistors; an arithmetic circuit that forms video data corrected in response to variations in the resistance values of the heating resistors; and an up/down circuit that sends a signal for comparing the density correction data and the corrected video data.
comprising a level counter with a down counter function, and a grayscale data comparison circuit that compares the density correction data and the corrected video data selectively switched by a switching means with the signal of the level counter, By setting the level counter to the down counter side and comparing the density correction data and the signal of the level counter during a period in which each of the heat generating resistors prints one line, each of the heat generating resistors energizing each of the heating resistors by first energizing the resistor, setting the level counter to the up counter side, and comparing the corrected video data and the signal of the level counter; A thermal transfer gradation control device characterized by comprising a second energization for performing. (2) The thermal transfer gradation control device according to claim 1, characterized in that a non-energization period is provided between the first energization and the second energization.