JP2549620B2 - Thermal recording method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal recording method for stabilizing recording density and improving gradation characteristics.

[Technical background of the invention and its problems]

2. Description of the Related Art Conventionally, a thermal recording device such as a thermal transfer recording device or a thermal recording device that records an image or character information by energizing a plurality of heating resistors is known. In such a thermal recording device, as the recording density and the recording speed are improved, the effect of the heat storage of the heat generating resistor becomes remarkable, and there is a problem that the density unevenness of the recorded image and the crushing phenomenon of the characters occur. is there. Therefore, various energy injection methods for removing heat storage have been conventionally proposed.

For example, in the method disclosed in Japanese Patent Laid-Open No. 59-98878, four kinds of energizing pulses having different pulse widths are prepared, and 16 kinds of energizing energy can be selected by a combination of these, so that the thermal storage state of the thermal head is obtained. The optimum energizing pulse is selected from these 16 kinds of energizing pulses according to the above. At this time, the heat storage state is estimated based on the history of past energization states.

However, it is practically difficult to quantitatively grasp how much the influence of the heat storage energy due to the energization of each past image point affects the current heat storage amount. This is because an extremely large number of experiments must be performed to understand these effects, and the obtained results apply only to the device. For this reason, the conventional thermal recording system does not always perform appropriate heat storage compensation control.

[Object of the Invention]

The present invention has been made based on such a conventional problem, and it is possible to eliminate the influence of heat storage of the thermal head to stabilize the recording density and to improve the gradation characteristics by a simpler method. It is an object of the present invention to provide a thermal recording method capable of performing thermal recording.

[Outline of Invention]

The thermal recording method according to the present invention reduces the amount of energy used for recording the target image point as the number of mark dots existing in the reference area including the target image point to be recorded decreases,
In addition, the total amount of energy used for recording all the image points in the reference area is increased.

〔The invention's effect〕

According to the present invention, the larger the number of mark dots in the reference area including the target image point, the smaller the amount of energy used for recording the target image point (injection energy amount). The effect can be eliminated, and conversely, sufficient energy can be injected in a region where the effect of heat storage is small, and an image and characters that are uniform and have no crushing phenomenon can be obtained as a whole.

Further, according to the present invention, since the energy amount is simply calculated from the number of marked dots in the reference area without considering the influence of each image point, the optimum maximum energy amount and minimum energy amount for each recording device can be obtained. By obtaining the amount of energy and interpolating it with a monotone function, various amounts for heat storage control can be obtained very easily.

By the way, if the above-described control is performed in which the energy amount (implantation energy amount) used for recording the target image point is reduced as the number of mark dots in the reference region is increased, depending on the setting of the implantation energy amount, The total amount of energy used for recording all the image points may not decrease monotonically but may decrease due to the increase in the number of mark dots. In this way, in the area where the total energy amount decreases with the increase in the number of mark dots, the change in the output image level with respect to the change in the input image level is reversed, and the gradation characteristics are significantly deteriorated.

According to the present invention, the larger the number of mark dots in the reference area, the smaller the amount of energy used for recording the target image point, and the larger the number of mark dots in the reference area including the target image point, the more the reference area. Since the control is performed to increase the total energy amount used for recording all the image points in the inside, the above-mentioned inversion phenomenon of the change of the output image level with respect to the change of the input image level can be avoided. Therefore, the change in the output image level with respect to the input image level becomes smooth, and good gradation characteristics can be obtained.

Example of Invention

 Hereinafter, details of the present invention will be described based on examples.

FIG. 1 shows an example in which the present invention is applied to a thermal recording system in which an image signal having gradation is binarized by a dither pattern to obtain a recorded image, and a dither matrix is 8 as shown in FIG. It consists of threshold data.

Now, assuming that the point at which a dot is to be formed (hereinafter referred to as the target image point P) is the n-th line and the i-th dot, the reference area is centered on the target image point as shown in FIG. Two
One, one on the bottom, one on the left and one on the left, and one on the diagonally above. Then, each time the target image point P changes by one, the reference region is newly set at a position satisfying the above relationship. The amount of energy to be injected into the target picture point P is shown in FIG. 1 (c). That is, when the number of image points of "1" in the reference area is 1, the effect of heat storage of the thermal head is the least, and the energy required for recording the image point P of interest is the maximum energy P (1) = Pmax. Is set. On the other hand, when the number of image points of "1" in the reference area is eight, the effect of heat storage is the largest, and the energy amount required to record the image point of interest is the minimum energy amount P (8).
= Suppressed to Pmin. Hereinafter, by connecting Pmax and Pmin with a monotonically decreasing function (a straight line in the illustrated example), the amount of implantation energy when the number of "1" dots in the reference region is 2 to 7 is determined. In addition to the above setting method, the reference area may be set to 4 lines × 2 dots including the target image point P as shown in FIG. 2, for example. When the dither matrix is 4 × 4, the reference area is 4 lines × 4 including the recording image point P, as shown in FIG.
The size of the dots may be set. The reference area is preferably the same as the size of the dither matrix, but when the size of the dither matrix is large, it is sufficient to refer to the necessary minimum size.

Next, an example of an apparatus that realizes the above thermal recording method will be described with reference to FIGS. In this example, pulse width control is used as energy control for injection into the thermal head.

In FIG. 4, the binarized image data Di of the (n + 1) th line, which is inputted from the image input means (not shown) and binarized by the dither method, is serial / parallel converted by the shift register 2. 2 converted to parallel data
The binarized image data is supplied to the dither discrimination unit 3 and the data update unit 4. The dither discriminating unit 3 and the data updating unit 4 store the n-th data stored in the line buffer 5.
The binarized data of the (n−1) th and nth lines are also supplied.

The data updating unit 4 discards the data of the (n-2) th line input most recently, and adds the newly input data of the (n + 1) th line to update the line data. Then, after this update, data for three lines is output to the line buffer 5.

The dither determination unit 3 counts the number of image points of "1" in the reference area determined for each image point P of interest from the input data of three lines, and from this image point, one dot shown in FIG. Data indicating the amount of energy to be injected per hit is output. This energy amount may be different depending on the individual characteristics of the apparatus or the thermal head, but if the energy determination method as in this embodiment is used, one image point is formed in the reference area. If the optimum maximum energy Pmin and the minimum energy amount for forming the eight image points in the reference area are obtained by simple experiments, then the intermediate energy amount should be obtained by simple interpolation. You can

Data indicating the amount of injected energy is given to the pulse width conversion unit 6. The pulse width conversion unit 6 sets the width of the pulse required to drive the thermal head according to the amount of injected energy, and outputs it as pulse width data Dp. The pulse width data Dp is given to a pulse width control unit (not shown), and the pulse width control unit sets the pulse width.
A method of setting the pulse width is shown in FIG. 5, for example. In other words, this method uses four energizing pulses EN ₁ with different pulse widths.
~ EN ₄ is prepared and a maximum of 16 kinds of energizing pulses can be obtained by combining these 4 energizing pulses EN _{1 to} EN ₄ . The pulse width data Dp is given as 4-bit data,
Each bit corresponds to each energizing pulse EN _{1 to} EN ₄ . Therefore, when the pulse width data is 1011 as shown in FIG. 5B, the energizing pulses EN ₁ , EN ₃ and EN ₄ are selected. As a result, the heating resistor of the thermal head (not shown) is energized for the time of T ₁ + T ₃ + T ₄ . The amount of energy injected into the thermal head is controlled by such control.

Although the dither discriminating unit 3 and the pulse width converting unit 6 are separately provided in the above-mentioned embodiment, as shown in FIG. 6, these are provided in the dither-pulse converting unit 8 composed of ROM or RAM. You can also put them together. That is, the dither-pulse converter 8 extracts the data of the reference area centering on the target image point P from the inputted four lines of binarized image data, and each bit of these data is shown in FIG. Are associated with address data A _{0 to} A ₇ . Then, the address data A _{0 to} A ₇ are given to the ROM 9 shown in FIG. RO
In M9, as shown in FIG. 9, P is set in the memory location of the address where the added value of all the bits of the address data A _{0 to} A ₇ is n.
The data of (n) is stored. With such a configuration, the hardware configuration becomes extremely simple.

Further, in this embodiment, in addition to controlling the amount of energy to be injected into the target picture point P in the reference area as described above, as shown in FIG. The total amount of energy injected into the dither matrix is controlled accordingly. Although the total implantation energy amount increases according to the number of image points of "1", the energy injection amount per dot also decreases in this case as the number of image points increases. In such a system, the amount of energy to be injected into one dot is arbitrary, and it is sufficient that the entire dither matrix has a predetermined amount of energy. Therefore, as shown in FIG. The influence of an error when the power amount P (n) and the amount P '(n) of the energizing pulse actually obtained by combining a plurality of pulses do not match should be smaller than that of the above example. You can

That is, if the amount of energy to be injected into the target image point P is decreased as the number of image points of “1” in the reference region is increased as described above, recording of all image points in the reference region may be performed depending on the setting of the injection energy amount. The total amount of energy used may not decrease monotonically but may decrease due to an increase in the number of "1" dots. In this way, in the area where the total energy amount decreases with the increase in the number of mark dots, the change in the output image level with respect to the change in the input image level is reversed, and the gradation characteristics are significantly deteriorated.

On the other hand, in addition to decreasing the amount of energy injected into the target image point P as the number of “1” image points in the reference region increases, for example, as shown in FIG. (The area of the area is set equal to the size of the dither matrix) The total energy amount Pt (1) when there is only one image point of "1" in the reference area is set to the minimum value Ptmin, and "1" is set in the reference area. The total amount of energy Pt (8) injected into all the image points in the reference area when all the image points of
By determining the total amount of energy to be injected into all the image points in the reference region as max according to a monotonically increasing function that connects the minimum value and the maximum value, the more the number of “1” image points in the reference region, the more the reference region. If the control for increasing the total amount of energy injected to all image points in the inside is performed, the above-mentioned inversion phenomenon of the change of the output image level with respect to the change of the input image level can be avoided. Therefore, the change in the output image level with respect to the input image level becomes smooth, and good gradation characteristics can be obtained.

Further, according to the present invention, as shown in FIG. 12, the injection energy per dot may be exponentially reduced according to the number of image points of "1".

FIG. 13 is an example in which the present invention is applied to a printer for outputting a character pattern. Here, the reference area is set to the formation area for one character. Energy control is performed by a voltage control method.

The character pattern generator 11 that has input the character code data D0 from an input device (not shown)
The character pattern data corresponding to is output serially to the temporary storage circuit 12 and the character dot density determination unit 13. The temporary storage circuit 12 is composed of a shift register or the like, and stores at least one character pattern data. The character dot density determination unit 13 includes a counter 13a and a character dot density determination unit 13b. The counter 13a counts the number of “black” dots in the serially input character pattern data (the number of “white” dots may be counted) and outputs it to the character dot density setting unit 13b. To do.
The character dot density setting unit 13b is a memory that stores in advance a table of outputs corresponding to the total number of print dots (for example,
The count value output from the counter 13a is classified into dot density data D1 corresponding to the total number of print dots for one character and output to the voltage setting unit 14. The voltage setting unit 14 uses the dot density data D1 and the data
The output data corresponding to the dot density addition data D2, which is the cumulative addition value in the adder 15 of D1, is configured by a memory (for example, ROM) in which the output data corresponding to the table is stored in advance and indicates the voltage value applied to the thermal head. Outputs digital data. This data is converted into analog data by the digital-analog converter 16 and supplied to the power supply unit 17. The power supply unit 17 is a thermal head according to the input voltage.
The applied voltage applied to 18 is determined. This applied voltage is the applied voltage necessary for recording a character pattern having a large number of print dots per character as shown in FIG. 14 (a), and is a recording of a character pattern having a small number of print dots as shown in FIG. 14 (b). So that it is less than the applied voltage required for
It is set to a monotonically decreasing function as shown in the figure. The applied voltage is maintained during the printing time for one character described later.

On the other hand, the temporary storage circuit 12 outputs each print data in synchronization with the print cycle. The energization pulse width setting unit 19 determines the energization pulse width of the thermal head 18, and drives the driver 20 of the thermal head 18 with this pulse width. As a result, each heating element (not shown) of the thermal head 18 is energized by the energizing pulse of the above-mentioned applied voltage, and a character dot is formed on the thermal paper (not shown) or the plain paper through the thermal transfer ink.

The effect of heat storage due to continuous printing of a plurality of characters is suppressed by the following operation.

That is, the dot density data D1 output from the character dot density setting unit 13b is set to be positive when the character pattern has a high character dot density and negative when the character pattern has a low character dot density. Therefore, the adder
The dot density addition data D2 output from 15 increases when the dot density is equal to or higher than a predetermined value, and decreases when the dot density is equal to or lower than the predetermined value. Therefore, for example, when printing a character pattern with a high print dot density continuously,
The applied voltage decreases as shown by the curve A in Fig. 16, and conversely the applied voltage increases as shown by the curve B when continuously printing a character pattern with low print dot density from point Q in the figure during continuous printing. To do. Further, in general, characters to be printed continuously include high-density character patterns and low-density character patterns irregularly / discontinuously, and the value of the dot density data D1 is involved. It is expected that the voltage value will take a value like the curve D in FIG. By such control, an appropriate voltage value corresponding to the increase / decrease in the heat storage amount of the thermal head 18 is set. When the character pattern having a low print dot density is continuous and the applied voltage to the thermal head increases, the adder 15 is set so that the dot density addition data D2 does not become less than a predetermined value. Therefore, the voltage applied to the thermal head 18 does not exceed a predetermined value as shown by the curve C in the figure, and the excessive voltage application to the thermal head is prevented.

According to the above-described embodiment, in the case of a character pattern having a large total number of printed dots per character, the applied voltage is relatively suppressed to be lower than that of a character pattern having a small total number of printed dots. It is possible to reduce the difference between the total energy to be injected into a character and the total energy to be injected into a low density character. Therefore, it is possible to obtain a print output with little heat storage and a small variation in the density of recorded characters. As a method of omitting the temporary storage circuit 12 in FIG. 13 described above, the circuit configuration can be simplified by re-outputting the character pattern data from the character pattern generator 11 and inputting it to the energization pulse width setting unit 19.

FIG. 17 is a character dot density discriminating unit in the above embodiment.
The figure shows an example in which 16 is configured by one memory. That is, the character dot density determination unit 21 is composed of a ROM or the like, and the character pattern dot density data corresponding to the character code data is written in advance. When the character code data D0 is input to the character dot density determination unit 21, the dot density data D1 is output to the voltage setting unit 14 and the adder 15. The character dot density discriminating unit 21 performs both functions of counting the number of print dots and setting the character dot density based on this count value in the above-described embodiment, so that the circuit configuration can be simplified. Note that such a counter 13a
If the method is not used, the parallel data can be directly output from the character pattern generator 11 to the energization pulse width setting unit 19.

If the character dot data discriminating unit 21 is written at the time of starting the device or at any time, a volatile memory such as a RAM can be used as the character dot data discriminating unit 21.

Further, in the above embodiment, the dot density data D1 is set to a positive or negative value, and the dot density addition data D2 is increased or decreased by adding in the adder 15, but it is not always necessary to set the dot density data D1 to a positive or negative value. However, any data may be used as long as the dot density addition data D2 increases or decreases. According to the above embodiment, even if the reference area is relatively wide, the circuit scale does not increase.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram for explaining an embodiment in which the present invention is applied to a thermal recording system for image recording, and FIG. 1 (a) is a schematic diagram showing a reference area. (B) is a schematic diagram showing a dither matrix, (c) is a relationship diagram showing the relationship between the number of mark dots in the reference area and the amount of implantation energy per dot, and FIGS. 2 and 3 are reference areas. FIG. 4 is a schematic diagram for explaining each of the other setting methods, FIG. 4 is a block diagram showing a configuration of a thermal recording apparatus that realizes the thermal recording method, and FIG. 5 is a diagram for explaining a form of energizing pulses in the apparatus. 6 is a block diagram showing a configuration example of another apparatus for realizing the above-mentioned thermal recording system, and FIGS. 7 to 9 are for explaining the details of the dither-pulse converter of the recording apparatus. Fig. 10 and Fig. 12 show the same thermal description. The relationship diagram for explaining another injection energy control system of the thermal head in the system, FIG. 13 is a block diagram showing the configuration of a thermal recording apparatus according to an embodiment in which the present invention is applied to a thermal recording system for character recording, FIG. 14 is a diagram showing an example of a character pattern, FIG. 15 is a relational diagram between the total number of print dots and the applied voltage of the thermal head in the same device, and FIG. 16 is a number of printed character patterns and the applied voltage of the thermal head in the same device. FIG. 17 is a block diagram showing a configuration example of another device that realizes the thermal recording method. 2 ... Shift register, 3 ... Dither discriminating unit, 4 ... Data updating unit, 5 ... Line buffer, 6 ... Pulse width converting unit, 8 ... Dither-pulse converting unit, 9 ... ROM, 11 ...
… Character pattern generator, 12… Temporary storage circuit, 13, 21…
… Character dot density discrimination unit, 13a …… Counter, 13b …… Character dot density setting unit, 14 …… Voltage setting unit, 15 …… Adder, 16 …… Digital-analog converter, 17 …… Power supply unit, 18 ...... Thermal head, 19 ...... energization pulse width setting part, 20 ...... Driver.

Claims (7)

(57) [Claims] 1. In a thermal recording method for forming mark dots by heat generation of a heating element, the larger the number of mark dots existing in a reference area including a target image point to be recorded, the more energy used for recording the target image point. The thermal recording method is characterized in that the amount is reduced and the total amount of energy used for recording all the image points in the reference area is increased. 2. When the amount of energy used for recording the target image point is the maximum value when only one mark dot exists in the reference area, and all mark dots are formed in the reference area The energy amount used for recording the target image point is set as a minimum value, and the energy amount used for recording the target image point is determined according to a monotonically decreasing function connecting the maximum value and the minimum value. First
The thermal recording method described in the item. 3. A total energy amount used for recording all image points in the reference area when only one mark dot exists in the reference area is set to a minimum value, and all mark dots are formed in the reference area. If the total energy amount used for recording all the image points in the reference area is the maximum value, the total energy amount used for recording all the image points in the reference area is connected to the minimum value and the maximum value. The thermal recording method according to claim 1, wherein the thermal recording method is determined according to a monotonically increasing function. 4. An area of the reference region is set to be substantially equal to a size of a matrix used in a dither method or a density pattern method or a font size of a character pattern. 4. The thermal recording method according to any one of 3 above. 5. The shape of the reference area is set to be substantially equal to the shape of the matrix used in the dither method or the density pattern method or the shape of the font of the character pattern. 4. The thermal recording method according to any one of 3 above. 6. The amount of energy used for recording the target image point is determined from dot density data corresponding to the number of mark dots in the reference area and dot density addition data which is a cumulative addition value of the data. The thermal recording method according to claim 1, wherein: 7. The dot density data is a positive value when the number of mark dots in the reference area is a predetermined value or more, and is a positive value when the number of mark dots is less than the predetermined value. 7. The thermal recording method according to claim 6, which is a negative value.