JPH0542706A - Multigradation thermal recording method - Google Patents

Abstract

PURPOSE:To obtain a multigradation thermal recording method wherein boundary line is natural and desired hue can be obtained by arranging sequentially heating pulses to be added before and after a first heating pulse as the center, inserting dummy pulses before the heating pulses, and making adjustment so that the first heating pulse is always in the same place. CONSTITUTION:In the gradation 1, a heating pulse P1 is allocated in the center of energizing time timewise. In the gradation 2, a heating pulse P2 is allocated in a position immediately before it. Likewise, heating pulses P3 and P4 are allocated before and after the heating pulse P1 sequentially. A position of a first heating pulse Pi to which a dummy pulse DP is inserted is made to coincide with the position of the first heating pulse P1 by inserting a comparatively short dummy pulse DP when temperature of a thermal head is comparatively low and a comparatively long dummy pulse is inserted when the temperature is comparatively high. Thus, even when a boundary line becomes oblige with respect to the scanning direction, unnaturalness will be undistinguishable and change of hue when printing is performed by superposing multiple colors becomes comparatively small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal recording method for recording with multiple gradations. More specifically, it eliminates the unnaturalness at the boundary where the density of the entire image changes, and further improves the thermal recording. The present invention relates to a multi-gradation thermal recording method capable of avoiding the influence of correction of printing conditions due to the temperature of a thermal head used.

[0002]

2. Description of the Related Art Conventionally, a multi-tone image is printed on a recording paper by a multi-tone thermal recording method, that is, by sublimating or melting the ink of an ink sheet using a thermal head and thermally transferring it to the recording paper. In the thermal recording device, the number of heating pulses corresponding to the gradation of the dot is applied to all the gradations to the heating elements of the thermal head to thermally transfer the ink of the density corresponding to the gradation to each dot. , So that the gradation of each dot is expressed.

The case of printing an image of n gradations will be described below with reference to the schematic diagrams of FIGS. 1 (a) to 1 (h).

When a gradation 0, that is, a white dot is printed, 0 heat generation pulses are assigned as shown in FIG. 1 (a). When the lowest density dot is printed for gradation 1, that is, for the entire gradation n, one heat generation of the first heat generation pulse 1 (P1) as shown in FIG. 1 (b). Pulses are assigned. Gradation 2, that is, 2 for the whole gradation n
When printing the second low-density dot, as shown in Fig. 1 (c), two heat pulses, the first heat pulse 1 (P1) and the second heat pulse 2 (P2) Is assigned. Similarly, as the gradation shifts from the low density side to the high density side, the heating pulse 1 (P1) at the beginning is sequentially changed according to the gradation.
In other words, the higher the density to be printed, the more heat pulses are allocated. Therefore, although not shown in FIG. 1, when the gradation n, that is, the black dot is printed, n heating pulses from the heating pulse 1 (P1) to the heating pulse n (Pn) are generated. Will be applied to.

In the usual case, a heating element for one line is arranged in the main scanning direction in the thermal head, and the ink sheet and the recording sheet are superposed on the thermal head and moved relative to each other integrally. Heat the heating element.
At this time, the time required to record one line is defined by the time for moving one dot in the sub-scanning direction by the relative moving speed between the thermal head and the recording paper.
It is constant regardless of the print density. For this reason, in the conventional thermal head, when recording a low density, the heating element is energized to generate heat for a part of the time required to record one line. Therefore, the dots formed on the recording paper do not have uniform density. That is, only the part corresponding to the energization heat generation time develops high-density color, while the other parts remain white without coloring, for example, 1/3 of 1 dot.
The phenomenon that the area is printed in black appears as if it were printed with a density of 1/3 for the entire dot.

When the number of heating pulses for heating the heating element changes according to the printing density, the center position of the heating pulse group also changes, causing the following problems. Figure 2
(a) And (b) is a schematic diagram showing a dot printing state when a boundary line between a portion expressed in black and a portion expressed in white is inclined with respect to both scanning directions. ..

In the schematic diagram of FIG. 2 (a), since the change from black to white is in the same direction as the printing direction by the thermal head, the boundary line of the original gradient of 1: 3 and each dot are shown. The relationship with is relatively natural. That is, the dot a is black
100%, dot b is the same 20%, dot d is the same 50%, dot f is the same 80%, but only a part of them is printed black. The area to be filled is on the side of the black portion as a whole.

On the other hand, in the case of FIG. 2 (b) in which the color changes from white to black in the same direction as the printing direction of the thermal head, the dots are marked black like dots a ', c'and e'. The 80%, 50%, and 20% parts that are copied are on the side of the white part as a whole. For this reason, the boundary line between the two is in a very unnatural state.

Under these circumstances, as shown in FIG. 3, for example, in the case of 8 gradations, the heat generation pulse is in the order of 7th, 5th, 3rd, 1st, 2nd, 4th and 6th. Are arranged, and only the first heat generation pulse (P1) is provided in the case of gradation 1 and the first and second heat generation pulses (P1, P2) are provided in the case of gradation 2, so that the density is high. There is also known a method of sequentially allocating from the central heating pulse in the heating pulse group.

By the way, since the print density by the thermal head varies depending on the temperature, in order to obtain the same print density, the energization heat generation time, in other words, the pulse width of the heat generation pulse, is set according to the temperature of the thermal head. Need to change. Therefore, when the above-mentioned method is adopted, if the thermal head has a low temperature, each pulse width becomes long as shown in FIG. 4 (a), and if the thermal head has a high temperature, As shown in 4 (b), correction is performed so that each pulse width becomes shorter. However, if such a correction is performed, the first heating pulse (P1) at the center of the heating pulse group
That is, the position of the first heat generation pulse (P1) during the heat generation time assigned to one dot changes depending on the temperature of the thermal head.

More specifically, if the temperature of the thermal head is low, as shown in FIG. 4 (a), the entire length of the heating pulse group from the beginning to the end becomes long and the center thereof is assigned to 1 dot. If the temperature of the thermal head is high, on the contrary, as shown in Fig. 4 (b), the whole of the heating pulse group from the beginning to the end becomes shorter and the center of the heating pulse group also becomes shorter. Move to the beginning of the energized heat generation period. Therefore, even if dots of the same gradation are printed, if the thermal head is at a low temperature, as shown in FIG. If the range is expanded and the entire dot has a predetermined gradation, and if the thermal head is at a high temperature, as shown in Fig. 5 (b), the printing range within the dot is relatively high density. Is reduced and the entire dot has a predetermined gradation.

As described above, since the dots themselves are printed with a predetermined gradation regardless of the temperature of the thermal head, when printing is performed with only a single color, for example, black, there is no such problem. Does not happen. However, when performing multi-color printing, the temperature of the thermal head often rises each time each color is printed, so for example, when the first color is printed, the temperature is relatively low. Is printed as shown in Fig. 5 (a), and at the time when the second color is printed, it is printed at a relatively high temperature as shown in Fig. 5 (b). Become. When inks of different colors are sequentially printed by thermal transfer as shown in FIGS. 5 (a) and 5 (b), a desired hue can be obtained in the overlapping portions. Since only one color is printed in the non-overlapping portion, the desired hue cannot be obtained as a whole.

[0013]

As described above, in the conventional multi-gradation thermal recording method, when the boundary line of the areas having different gradations is inclined with respect to the scanning direction, the boundary portion is unnatural. And the problem that the desired shade cannot be obtained because the areas to which each color is printed are different in order to correct the temperature change of the thermal head when performing multicolor printing. There is a point.

The present invention has been made in view of the above circumstances, and prints in a natural state even when the boundary lines of regions having different gradations are inclined with respect to the scanning direction. It is also an object of the present invention to provide a multi-gradation thermal recording method capable of obtaining a desired color tone even when multi-color printing is performed by correcting the temperature of the thermal head.

[0015]

In the first invention of the multi-gradation thermal recording method of the present invention, the first heating pulse is positioned at the temporal center within the energization period of the heating element corresponding to one dot. Then, the heat generation pulse added around the first heat generation pulse as the concentration becomes higher is sequentially arranged before and after the first heat generation pulse.

Specifically, in the case of gradation 0 (white), FIG.
As shown in (a), no heat pulse is used, but in case of gradation 1, as shown in FIG. 6 (b),
One heating pulse 1 (P1) is assigned to the temporal center of the energization period assigned to one dot. In the case of gradation 2, as shown in FIG. 6 (c), the heat pulse 2 (P2) is assigned to the position immediately before (or immediately after) the heat pulse 1 (P1). As shown in FIGS. 6 (d) to 6 (h), as the gradation increases, the heat pulse 1 (P1) is centered and the heat pulse 3 (P3), heat is sequentially generated before and after that. Allocate pulse 4 (P4) ... and heat pulse.

Further, in the second invention of the multi-gradation thermal recording method of the present invention, a dummy pulse having a pulse width corresponding to the temperature of the thermal head is inserted before the heating pulse group, and the first heating pulse is 1 The dot is adjusted so that it is always at the same position during the energization period.

Specifically, the position of the first heat generation pulse (P1) when the dummy pulse DP in the normal case shown in FIG. 7 (a) is inserted and the position shown in FIG. 7 (b). When the thermal head being heated is at a relatively low temperature, each heating pulse is extended, so a relatively short dummy pulse DP is inserted to match the position of the first heating pulse (P1). When the thermal head shown in c) has a relatively high temperature, each heating pulse is shortened, so a relatively long dummy pulse DP is inserted to match the position of the first heating pulse (P1).

[0019]

In the first and second aspects of the present invention, the heat pulse added as the printing density becomes higher is sequentially arranged around the temporal center of the energization period assigned to one dot. To be done. Therefore, the actual printing is always performed in a state in which the central portion of the dot is expanded to both sides thereof according to the density.

Specifically, in the first aspect of the invention, as shown in FIG. 8, for example, the boundary line when changing from a white region to a black region is oblique with respect to the scanning direction. Even in such a case, since the dots are equally printed from the center of the dot to both sides, the unnaturalness becomes less noticeable than in the past.

In the second aspect of the invention, as shown in FIG. 9, the center of color development within one dot is always at a fixed position even if the temperature of the thermal head is different. Therefore, the change in hue when printing multiple colors is relatively small.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings showing the embodiments.

FIG. 10 is a block diagram showing the structure of an apparatus for carrying out the first invention of the multi-gradation thermal recording method according to the present invention.

In FIG. 10, reference numeral 1 is a line buffer, which stores print data with gradation for one line to be printed, that is, data representing the gradation of each dot forming one line. Has been done. The print data stored in the line buffer 1 is read in the order of each dot according to the read address given from the address counter 2, and is input to one input terminal of the comparator 3. The address counter 2 is controlled by an address counter control signal supplied from the timing controller 8 to generate an address.

Reference numeral 4 is a pulse counter, which is controlled by a pulse counter control signal output from the timing controller 8 to sequentially output pulse numbers.
This pulse number is input to the pulse / gradation conversion table ROM5, and the gradation number currently being processed (processed gradation number) is output. This processed gradation number is input to the other input of the comparator 3 and the pulse width table ROM6.

As described above, since the print data with gradation output from the line buffer 1 is also input to the comparator 3, the comparator 3 compares the gradation of the print data with the processed gradation, "1" if the gradation of the print data is not smaller than the processing gradation, and "0" if it is smaller than 2
Outputs the print data of the value. The binary print data is input to the data input terminal of the thermal head 7.

The energization heat generation time data of the pulse corresponding to the processing gradation number is read from the pulse width table ROM 6 and input to the timing controller 8. The energization heat generation time data output from the pulse width table ROM6 corresponds to the processing gradation number input from the pulse / gradation conversion table ROM5 as shown in FIGS. 6 (a) to 6 (h). The pulse width data representing the relationship is output.

The timing controller 8 controls each part while monitoring the states of the address counter 2 and the pulse counter 4 in addition to the pulse width, and controls the thermal head 7 according to the energization heat generation time data given from the pulse width table ROM6. The strobe signal for controlling the heat generation time width and the shift clock necessary for reading the binary print data are generated.

The thermal head 7 reads the binary print data from the comparator 3 in accordance with the shift clock, and heats the energization in accordance with the strobe signal. As a result, pulse energization control as shown in FIGS. 6A to 6H is performed. As a result, printing as shown in FIG. 8 is possible.

FIG. 11 is a block diagram showing the arrangement of an apparatus for carrying out the second invention of the multi-gradation thermal recording method according to the present invention.

In the configuration of the apparatus used in the method of the second invention, the temperature sensor 9 is added to the thermal head 7 as compared with the apparatus used in the first invention shown in FIG. The difference is that the detection output is given to the pulse width table ROM6.

Line buffer 1, address counter 2,
The configurations and operations of the comparator 3 and the pulse counter 4 are the same as in the case of FIG.

The pulse / gradation conversion table ROM5 outputs the gradation number currently being processed according to the pulse number input from the pulse counter 4. The maximum value of the processed gradation number is the dummy pulse DP, and the others are heat generation. It is assigned to a pulse. The processed gradation number output from the pulse / gradation conversion table ROM5 is input to the pulse width table ROM6.

The energization heat generation time data output from the pulse width table ROM6 corresponds to the processing gradation number input from the pulse / gradation conversion table ROM5 and the temperature of the thermal head input from the temperature sensor 9 shown in FIG. As shown in (a) to (c), the dummy pulse DP is added and the time-related pulse width data in which the time of each heat generation pulse is corrected is output. This data is input to the timing controller 8.

The structure and operation of the timing controller 8 are the same as in the case of FIG. As a result, FIG.
Pulse energization control is performed as shown in (c). As a result, printing as shown in FIGS. 9 (a) and 9 (b) becomes possible.

[0036]

As described in detail above, according to the first and second aspects of the present invention,
In the second aspect of the invention, the heat pulse added as the printing density increases is sequentially arranged in the front-rear direction around the temporal center of the energization period assigned to one dot. Therefore, the actual printing is always performed in a state in which the central portion of the dot is expanded to both sides thereof according to the density.

Thus, in the first aspect of the invention, for example, even when the boundary line when changing from the white region to the black region is inclined with respect to the scanning direction, the dot is moved from the center to both sides. Since it is printed in equal parts, unnaturalness is less noticeable than in the past.

According to the second aspect of the invention, the center of color development within one dot is always at a fixed position even if the temperature of the thermal head is different. Therefore, in addition to the effect similar to that of the above-described first invention, the change in the hue when the multiple colors are superposed and printed is relatively small.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an arrangement of heat generation pulses in a conventional multi-gradation thermal recording method for printing an image of n gradations.

FIG. 2 is a schematic diagram showing a printed state of dots when a boundary line between a portion expressed in black and a portion expressed in white in the conventional method is inclined with respect to the scanning direction.

FIG. 3 is a schematic diagram showing an arrangement of heat generation pulses in a conventional multi-gradation thermal recording method when printing an 8-gradation image.

FIG. 4 is a schematic diagram showing an arrangement of heat generation pulses in a multi-gradation thermal recording method for performing correction according to the temperature of a conventional thermal head when printing an image with 8 gradations.

FIG. 5 is a schematic diagram showing variations in the printing position within a dot when the temperature of the thermal head is corrected by the conventional method.

FIG. 6 is a schematic diagram showing an array of heat generation pulses for explaining the first invention of the multi-gradation thermal recording method of the present invention.

FIG. 7 is a schematic diagram showing an arrangement of dummy pulses and heat generation pulses for explaining the second invention of the multi-gradation thermal recording method of the present invention.

FIG. 8 is an image printed by the first invention of the multi-gradation thermal recording method of the present invention, the boundary line of which changes from a white region to a black region inclines with respect to the scanning direction. It is a schematic diagram which shows a result.

FIG. 9 is a schematic diagram showing a printing result when the temperature of the thermal head is different according to the second invention of the multi-gradation thermal recording method of the present invention.

FIG. 10 is a block diagram showing a configuration of an apparatus for carrying out the first invention of the multi-gradation thermal recording method according to the present invention.

FIG. 11 is a block diagram showing the configuration of an apparatus for carrying out the second invention of the multi-gradation thermal recording method according to the present invention.

[Explanation of symbols]

 P1, P2 ... Heat pulse

Claims (2)

[Claims] 1. A heating element of a thermal head applies as many heating pulses as necessary to obtain a printing density corresponding to a gradation of a dot to be printed to the heating element during an energized heating period assigned to one dot. Thus, in the multi-gradation thermal recording method for printing each dot at a density corresponding to the gradation, the number of heat generation pulses necessary to obtain the printing density corresponding to each dot during the energization heat generation period. Is continuously applied to the heating element with its center aligned with the center of the energized heat generation period. 2. The number of heating pulses required to obtain the printing density corresponding to the gradation of dots to be printed by the heating element of the thermal head is corrected by adjusting the pulse width according to the temperature of the thermal head. In a multi-gradation thermal recording method in which each dot is printed at a density corresponding to its gradation by applying to each heating element during the energization heat generation period assigned to the dot, A dummy pulse having a length corresponding to the temperature of the thermal head is inserted, and the heat generation pulse at the center of the number of heat generation pulses required to obtain the printing density corresponding to each dot coincides with the center of the energization heat generation period. A multi-gradation thermal recording method characterized by applying to each heating element as described above.