JP2943408B2 - Thermal transfer type image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of arranging a plurality of heating resistor elements in a line on a surface of a substrate, selectively heating the heating resistor elements according to pixel data, and discharging ink from an ink sheet or ink ribbon. The present invention relates to an image forming apparatus for forming dots on a recording sheet by fusing, more specifically, a gradation control technique and a color reproduction technique.

[0002]

2. Description of the Related Art A thermal transfer printer uses an ink sheet or a ribbon in which wax containing a pigment is coated on a polymer film, and transmits a signal based on pixel data to a print head in which minute heating resistance elements are integrated on a substrate. By supplying the ink, the ink in the minute area is melted to form dots on the recording paper. Such a thermal transfer image forming apparatus is often used in the field of full-color printing which requires high-density dot formation because a heating resistor element serving as a dot forming element can be easily formed in a minute size.

When full-color printing is performed by a printer, a process of normally using a total of four colors of three primary colors of yellow, magenta and cyan and black and returning the recording medium to the initial position for each primary color for printing is performed. Must be repeated multiple times. For this reason, there is a problem that a displacement occurs between the pixel data to be printed and the printing point of the recording medium, and the quality of the printed image is reduced. In order to solve such a problem, the printing position of each primary color is set in a certain direction with respect to the recording medium, that is, a so-called screen angle is set to prevent the color turbidity due to the displacement of the dot forming position as much as possible. Is being done. For example, in a printing method in which the size of a printable dot is constant, for example, in an ink jet method or a wire dot method, the density is represented by the number of dots formed in a fixed area, for example, a 4 × 4 dot area, and at least 1 A method has been proposed in which the positions at which two dots are formed are defined for each primary color so that the dot formation positions are aligned in a specific direction on a recording medium. However, in view of the fact that the density is expressed by the number of dots, if the density level that can be expressed is increased, 1
There is a problem that the number of dots to be assigned per pixel increases and the image becomes coarse. In order to solve such a problem, for example, as disclosed in Japanese Patent Application Laid-Open No. 61-189774, it is possible to express the density of dots formed on a recording medium itself and to read a unit of an original image, that is, a so-called pixel. A method has been proposed in which a threshold value is set in correspondence with the above, and a plurality of matrices serving as nuclei for constantly forming dots are set, thereby setting a density gradation and a screen nucleus.

When such a printing method is adopted, the improvement of the gradation and the setting of the screen angle can be realized at the same time. On the other hand, if the gradation is further increased, a huge amount of matrix data is required. There is a problem that the memory for storing the matrix data becomes large.
The present invention has been made in view of such a problem, and an object thereof is to reduce the screen angle setting data and set the screen angle while maintaining the gradation and the resolution. An object of the present invention is to provide a novel thermal transfer type image forming apparatus.

[0004]

According to the present invention, there is provided a print head having a plurality of heating resistance elements arranged in a line, and a recording paper and an ink sheet being conveyed at a predetermined pitch. Means for reading out pixel data constituting the input image data continuously for N lines (N ≧ 2), and image data reading means for reading the pixel data for the plurality of lines into N × N pixels. Sampling means for sampling in a matrix form, and for expressing the pixel density in dot size for each N × N pixel,
A first γ-conversion characteristic for outputting printing data for forming a main dot by performing γ-conversion proportionally from a low density to a high density, and a first γ-conversion characteristic for forming a sub-dot The second γ-conversion characteristic for outputting print data with a lower density than the third and fourth print characteristics in which dots are not formed in most areas.
And a conversion characteristic for selectively applying the γ conversion characteristic to each of the sampled N × N pixels so that dots according to the first γ conversion characteristic are aligned at a specific angle. The printing apparatus further includes a selection unit and a unit that supplies electric energy corresponding to the print data to the heating resistance element of the print head.

[0005]

The sampled pixel data of at least 2 × 2 pixels is limited by the γ-conversion means to two main dots and sub-dots in the low to medium density range. As a result, the thermal interference between the heating resistance elements constituting the dot forming means is reduced as much as possible, and the gradation is expressed by the area of the dot itself, thereby improving the gradation and the resolution. Further, by changing the application form of the γ-conversion characteristic, the position at which the main dot corresponding to at least 2 × 2 pixels is formed is changed for each primary color, thereby preventing the occurrence of mesh noise and preventing the color turbidity. To prevent.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the illustrated embodiments. FIG. 2 shows an embodiment of the present invention, and is composed of a thermal transfer printing mechanism and a control device. The thermal transfer printing mechanism uses a pickup roller 3 to pick up one sheet from the stacker 2 stocking the recording paper 1.
Paper feed mechanism 4 that pulls out a sheet of recording paper and conveys it to the printing area
A platen 5 for conveying the recording sheet 1 and the ink sheet 9 at a constant speed, a thermal transfer print head 6 pressed against the platen 5 at the time of printing, and a conveying roller 8 for returning the printed recording sheet to the stacker 2 side again. And a stock roller 10 for supplying the ink ribbon 9 and a take-up roller 11. Further, a circuit board 12 in which a control circuit described later is incorporated is accommodated in a lower portion of the housing. Thermal transfer print head 6
Are formed in a row at a constant pitch on the surface of the substrate 13 as shown in FIG.
Lead wires 15, 15, 15 ° in the direction of the paper feed direction
{, 16, 16, 16} are drawn out.

FIG. 4 shows an embodiment of the above-described control circuit. In the figure, reference numeral 17 denotes a microcomputer constituting a central part of the control device, which includes a CPU 18, a control program and data processing which will be described later. Program, and even γ
An external device such as a personal computer via an interface 21 and 22 and a print head drive circuit 2 comprising a ROM 19 storing conversion characteristics and a RAM 20 forming a buffer and a frame memory for data processing.
3. Connected to the motor drive circuit 24. The print head drive circuit 23 corresponds to the electric energy corresponding to the data representing the density outputted from the interface 22, for example, the densities B ₁ , B ₂ , B ₃ , B ₄ , ΔB _n as shown in FIG. And the pulse-like power in which the times T ₁ , T ₂ , T ₃ , T ₄ , and {Tn _} are sequentially increased is supplied to the heat-generating resistance elements 14, 14, 14} of the thermal transfer print head 6. I have. The motor drive circuit 24 drives a motor 25 connected to the pickup roller 3, the platen 5, and the transport roller 8, and has a rotation direction and a rotation speed corresponding to the command output from the interface 22. Thus, the driving pulse is output.

FIG. 1 shows an embodiment represented by functions required by the microcomputer 17 necessary for performing color printing by utilizing the basic printing function described above. Is an image memory for storing image data output from an external device, and stores a fixed amount of image data for each color output from the external device, for example, for one page. 31 is an image data reading means.
The image data stored in the image memory 30 is extracted for N lines (an integer of N ≧ 2). In this embodiment, the pixel data for two lines is extracted while being moved by N lines and output to the line buffer 32. It is. Reference numeral 33 denotes a sampling unit which samples N pixels (an integer of N ≧ 2) in the main scanning direction, that is, N × N dots, that is, 2 × 2 pixels in this embodiment, from the pixel data stored in the line buffer 32. And outputs it to the γ conversion means 34 described later.

Numeral 34 denotes the above-mentioned γ-conversion means, which functions as a filter and a print density setting means for the pixel data from the sampling means 33 so that the dot data corresponding to the density of the pixel data as shown in FIG. In order to specify the density (hereinafter, referred to as converted print data), data for defining the relationship between the density of the pixel data and the print conversion data is stored.

FIG. 6 shows an embodiment of a gamma characteristic conversion function set in the above-mentioned gamma conversion means 34. The gamma characteristic conversion function is constituted by storing a plurality of characteristics, in this embodiment four types of functions. ing. The gamma characteristic conversion function γ ₁ does not form a transfer dot when the density of pixel data is zero, but supplies the minimum energy enough to keep the temperature of the heating resistor element constant regardless of the surrounding environment. Is set to the maximum density Db in proportion to the entire intermediate density area, and the converted print data Db is maintained from the intermediate density area to the high density area. Has the characteristic of decreasing to a density Dc close to the density of By the way, the density De is a value that results in a dot density of 11.8 dots / mm when performing binary printing such as character printing, and is a value that can normally supply energy of about 0.125 millijoules / dot to the heating resistor element. Is set to Density Db
Is set to a value capable of supplying approximately twice the energy of the density De, the density Dc is set to a density slightly higher than De, and the density Dd is set to a density slightly lower than the density De. The gamma characteristic conversion function γ ₂ has a characteristic of generating a density Dd close to the density of pixel data only near the maximum density value of image data. The gamma characteristic conversion function γ ₃ is
Like the gamma characteristic conversion function γ _2, it has a characteristic that the density becomes Dd only near the maximum density of the pixel data. The gamma characteristic conversion function γ ₄ maintains the converted print data Da such that dots of the minimum size can be formed stably in the low density area of the pixel data, and thereafter converts the converted print data Da to the maximum converted print data Db from the middle density area to the high density area. And a characteristic that decreases to a density Dc close to the density of the pixel data in the highest density area.

[0011] as a result of being provided with such a characteristic, when being sampled assigning the gamma characteristic into four pixels matrix, dot becomes the center of the image represented by the conversion characteristic gamma _1, also adjacent thereto In addition, it becomes possible to express the sampling area by adding the conversion characteristics γ ₂ and γ ₃ to the pixel data indicating the sub-dots having the highest density and the conversion characteristics γ ₄ .

Numeral 35 is a conversion characteristic selecting means, which converts each of the _four gamma characteristic conversion functions γ _{1 to} γ ₄ corresponding to the primary colors output to the image memory 30 into sampled matrix pixel data D ₁₁ , D ₁₁ . ₁₂ , ‥‥ D ₁₄ ,
D ₂₁ , D ₂₂ ‥‥ D ₂₄ , D ₃₁ , D ₃₂ , ‥‥ D ₃₄ , D ₄₁ , D
₄₂ ‥‥ D ₄₄ is configured to store data to be allocated.

Next, in order to facilitate understanding of the present invention, a description will be given of a relationship between a driving mode of the heating resistor element and dots formed by the driving mode. As shown in FIG. 7, when only one heating resistor 14 is energized, and the adjacent heating resistors 14 ′ and 14 ″ are stopped and printing is performed, the driven heating resistor 14 is turned off. Since there is no thermal interference from the adjacent heating resistance elements 14 ′, 14 ″, it is possible to use the area of the other adjacent heating resistance elements 14 ′, 14 ″ as a dot forming area.
As a result, even if the relative input energy E supplied to the heating resistor element is divided into multiple stages of “32” as shown in FIG. 8, the size of the formed dot is proportional to the relative input energy. High gradation can be expressed, and therefore, dots having a density that is faithfully proportional to the density of the pixel data are formed. As a result, as shown in FIG. 9, as the energy increases, each dot is formed independently in the vicinity of the medium density and the high density, and a solid image is formed at the highest density.

Further, as shown in FIG. 10, while the two heating resistor elements 14 and 14 'are driven at the same time, and printing is performed with the heating resistor elements adjacent thereto being at rest, the heating resistor elements 14 Since the thermal interference can be sufficiently prevented in practice, dots can be formed with substantially the same gradation as in the case where the above-described heating resistance element is driven alone.

On the other hand, when the adjacent heating resistor elements are also driven, the thermal interference between the heating resistor elements becomes large as shown in FIG. 11, and therefore, as shown in FIG. In the density region, dots that should be formed independently are already connected in some places, causing variations in gradation expression ((I) in the figure), and there is a problem that the dots are completely connected near high density. (Fig. (II)).

Next, a case where the above-mentioned γ conversion characteristic is applied will be described. The conversion characteristic selection unit 34 is applied to each of the application forms as shown in FIG. 13, that is, the matrix-shaped 2 × 2 child pixel data D ₁₂ , D ₁₂ , D ₂₁ , and D ₂₂ extracted by the sampling unit 33. The following describes an example in which conversion characteristics γ ₁ , γ ₂ , γ ₃ , and γ ₄ are applied. Pixel data D ₁₁ that has been sampled by the sampling means 33 is converted into converted print data to be linearly proportional to its concentration by the gamma characteristic conversion function gamma ₁ of the conversion characteristic selection means 34 gamma converting unit 33 is selected by and the pixel data D ₁₂ is only the concentration Dd when the maximum concentration by the gamma characteristic conversion function gamma ₂ is, and otherwise is converted into converted print data not applying energy for dot formation. Moreover the pixel data D _21, the concentration of only density Dd when the highest value is converted into converted print data energy is not applied in other cases, further pixel data D _22, the energy is applied at a low concentration range However, the energy is applied to such an extent that a substantial dot cannot be formed, and is converted into converted print data which is linearly proportional to the density of the pixel data at a medium density or higher.

As a result, the first line of pixel data D ₁₁ ,
When printing a D _12, with respect to the intermediate density of the pixel data to be frequently occurring normal image is only dots are formed for the pixel data D _11, the pixel data D ₁₂ adjacent will not be printed. When printing of the first line is completed in this way, pixel data D ₂₁ and D _{22 of} the same sampling area are printed. Functions gamma ₃ is the pixel data D _21, and because the function gamma ₄ has been assigned to the pixel data D _22, only the pixel data D ₂₂ is printed in the intermediate density region, the pixel data D ₂₁ is Does not print. This second
In the printing of the line, similarly to the printing of the first line described above, since the other adjacent heating resistance elements are in the rest state, the pixel data to be printed has a density faithful to the density converted by γ _4. Will be formed as dots. Thereafter, printing is continued by alternately repeating the form as shown in FIG. 14, that is, the choreographic form of the gamma characteristic conversion function shown in FIG.

[0018] As a result, four pixels specified by the sampling area, the main dot pixel data D _11,
The pixel data D ₂₂ is to be printed as the sub-dot, four pixel data D ₁₁及至D ₂₂ is to be expressed in the form supplementing the main dots in the sub-dots. That is, when a low concentration in the region including four pixels that are sampled, only the dot corresponding to the pixel D ₁₁ the gamma characteristic conversion function gamma ₁ is assigned is printed (FIG. 15 ( I)). When the concentration of the sampled area is increased, so that the gamma characteristic conversion function gamma ₄ is printed dots 40, 40 ... also corresponding to the pixel D ₂₂ assigned (FIG. 15 (II)). When the density of the pixel data further increases, the size of the dots corresponding to the pixels D ₁₁ and D ₂₂ increases, and an image is printed so as to narrow the island-shaped blank portions 41 (see FIG. 15).
(III) (IV) (v)). Thus, the blank portions 41, 41
Are formed in an island shape, so that even when high-density data is printed, only ink having an area proportional to the density of the image data is reliably transferred to the recording paper without unnecessarily peeling off the ink on the ink sheet. Will be.

[0019] Figure 16 shows another specified embodiment of the conversion characteristics by the conversion characteristic selection means 34, with respect to four pixels D ₁₁ to D ₂₂ extracted by the sampling means 33, the pixel data D ₁₁ is the gamma characteristic conversion function gamma _1, gamma characteristic conversion function gamma ₃ in the pixel data D _12, the gamma characteristic conversion function gamma ₄ in the pixel data D _21, the gamma characteristic conversion function gamma ₂ in further pixel data D ₂₂ Assigned
Dot by the pixel data D _{1 1} According which is formed preferentially, also dots of pixel data D ₂₁ is formed as a by-. When such a form is applied by shifting one dot in the main scanning direction every two lines as shown in FIG.
When the concentration of the image data of the sampling area as shown is low in FIG. 18, only the dot corresponding to the pixel data D ₁₁ of the two 2 × is formed. Also, at the stage of moving two lines at this density, the sampling area is shifted by one pixel as described above, so that the sub dots 42, 42,... Are formed in the middle of the dots formed as the first line. When printing is continued by repeating such operations, the angle connecting the dots located at the shortest distance, that is, the screen angle becomes 63.4 degrees.

FIG. 19 shows another designation form of the conversion characteristic by the conversion characteristic selection means 34. As a first form, a gamma characteristic conversion function γ ₄ is provided for the pixel data D ₁₁ and a gamma characteristic conversion function γ _{4 is provided} for the pixel data D ₁₂ . The gamma characteristic conversion function γ ₁ is converted to pixel data D
₂₁ has a gamma characteristic conversion function γ ₃ and pixel data D
Assign the gamma characteristic conversion function gamma ₂ to ₂₂ (FIG. (A)), also the gamma characteristic conversion function gamma ₃ in the pixel data D ₁₁ as a second embodiment, the gamma characteristic conversion function gamma ₂ to D ₁₂ , Gamma characteristic conversion function γ ₄ for pixel data D ₂₁ ,
Further, a gamma characteristic conversion function γ ₁ is assigned to the pixel data D ₂₂ ((b) in the figure), and these first and second forms are shown in FIG.
In this case, they are used alternately as shown in FIG.
That is, the first embodiment with respect to the four pixel data D ₁₁ to the pixel data D ₂₂ of the first extraction region is selected,
Dot based on the pixel data D ₁₂ is printed preferentially, the next pixel data adjacent to the sampling area is selected, the pixel data D ₂₂ is printed preferentially. As a result, in the low density region, dots are formed at the screen angle plus or minus 26.6 degrees as shown in FIG. Also, when the image density of the extraction area increases,
Gamma characteristic conversion function γ ₄ in addition to gamma characteristic conversion function γ ₁
Since also to be printed dots, the pixel data D ₁₂ on odd lines as the main dots are printed in a form in which the pixel data D ₁₁ and the sub dots, also the pixel data D ₂₂ in even-numbered lines as the main dots, the printing is performed in a form subsidiary dots to D _21.

[0021] Figure 22 shows another specified embodiment of the conversion characteristics by the conversion characteristic selection 34, the gamma characteristic conversion function gamma ₁ is the pixel data D ₁₁ as a first embodiment, the gamma characteristic conversion to D ₁₂ the function gamma _2, the pixel data D _{1 1} gamma characteristic conversion function gamma ₃ to D _21, further assign the gamma characteristic conversion function gamma ₄ to D ₂₂ (FIG. (a)), and as the second embodiment
Gamma characteristic conversion function gamma _4, gamma characteristic conversion function gamma ₃ to D _12, the gamma characteristic conversion function gamma ₂ in D _21, further allocation (FIG gamma characteristic conversion function gamma ₁ to D ₂₂ to (B) Further, after two lines, as shown in FIG. 23, the application order of the first embodiment and the second embodiment is reversed and applied. That is, the first embodiment with respect to the four pixel data D ₁₁ to D ₂₂ of the first extraction region is selected, a dot based on the pixel data D ₁₁ is printed preferentially, adjacent to the pixel data When the next pixel data is selected, the pixel data D ₂₂ is printed preferentially.
As a result, in the low density area, dots are formed at a screen angle of 45 degrees as shown in FIG. The image density of the extraction area is increased, because in addition to the gamma characteristic conversion function gamma ₁ also dot gamma characteristic conversion function gamma ₄ comes to be printed, as Lord dot pixel data D ₁₁ on odd lines, adjacent Next pixel data D
₁₁ (pixel data D ₁₃ in FIG. 23 in the case of continuous use) is formed as sub-dots with one dot interval. In the even-numbered line, the pixel data D ₂₂ is used as a main dot, and one pixel before the pixel data D _22.
Are formed as sub dots.

[0022] Figure 25 shows another specified embodiment of the conversion characteristics by the conversion characteristic selection 34, the gamma characteristic conversion function gamma ₂ in the pixel data D ₁₁ as a first embodiment, the pixel data D
The gamma characteristic conversion function gamma ₄ to _12, the gamma characteristic conversion function gamma ₁ is the pixel data D _21, assign the gamma characteristic conversion function gamma ₃ further to the pixel data D ₂₂ (FIG. (A)), also the the pixel data D ₁₁ gamma characteristic conversion function gamma ₃ in the second embodiment, the pixel data D _{1 2} gamma characteristic conversion function gamma
₁ , a gamma characteristic conversion function γ ₄ is assigned to the pixel data D ₂₁ , and a gamma characteristic conversion function γ ₂ is assigned to the pixel data D ₂₂ ((b) in the same figure). Thus, the application order of the first mode and the second mode is reversed. That is, the first embodiment with respect to the four pixel data D ₁₁ to D ₂₂ of the first extraction region is selected,
Dot based on the pixel data D ₂₁ is printed preferentially, the next area is selected, the pixel data D ₁₂ is printed preferentially. As a result, in the low density area, dots are formed at a screen angle of 135 degrees as shown in FIG. The image density of the extraction area is increased, because in addition to the gamma characteristic conversion function gamma ₁ also dot gamma characteristic conversion function gamma ₄ comes to be printed, as Lord dot pixel data D ₁₂ on odd lines, adjacent previous region pixel data D ₁₂ of the (pixel data D ₁₂ in FIG. 26 in the form of a continuous) is formed as a by-made dots at a dot interval, and in even line, the pixel data D ₂₁ is as Lord dots, also printed as now dot pixel D ₂₁ is the sub after one dot. According to the application of the γ-conversion characteristics shown in FIGS. 13, 16 and 19, the blank portion is formed in a shape close to a circle and the blank portions are independent from each other. It is possible to prevent the ink in the dot forming portion from being unnecessarily peeled off. As a result, a gray scale faithful to the density of the pixel data can be expressed.

FIG. 28 shows a second embodiment of the gamma characteristic conversion function. The gamma characteristic conversion function γ ₁ has the same heating resistance as that of the above-mentioned density Da from the low density range to the middle density range. Enough to keep the thermal conditions of the element constant,
In addition, it is possible to supply energy that does not form dots, and the density increases from the density slightly lower than the density Da to the maximum density Db. Thereafter, the maximum density Db is maintained regardless of the density of the pixel data. It is set so as to decrease to the density Dc near the density. The gamma characteristic conversion functions γ ₂ and γ ₃ are both set so as to maintain a density Dg at which dots are not formed in a low density range, and to increase from a middle density range to a maximum density to a density Dd in proportion to the image density. ing. Only it is set to a concentration Dd at the highest concentrations for the more the gamma characteristic conversion function gamma _4. Such gamma characteristic conversion functions γ _{1 to} γ ₄ are converted into pixel data D ₁₁ , D ₁₂ , D ₂₁ , D ₂₂ as shown in FIG.
When continuous printing is applied, in a low concentration step of the pixel data of the extracted area, dots from the dot based on the pixel data D ₁₁ is formed, substantially a grid pattern as shown in (I) in FIG. 29 Are formed, and screen angles of 0 degree and 90 degrees are set. When the density of the pixel data increases, dots are formed by the gamma characteristic conversion functions γ ₂ and γ ₃ as shown in FIG. 3 (III).
_{The reference} numeral 21 designates a circular blank portion 45, 45, 45,...
The dot is formed while forming. As a result, it is possible to prevent the ink in the blank portion from being unnecessarily peeled off, and to form a dot having a gradation faithful to the density of the pixel data.

FIG. 14 shows the second gamma characteristic conversion function.
Although the description has been given of the case where the present invention is applied in such a form, it is apparent that the present invention can be applied in the forms shown in FIGS. 17, 20, 23, and 26 described above.

As described above, by changing the application form of the gamma characteristic conversion function, the position at which the main dot is formed also changes, so that the three primary colors for expressing the color corresponding to the pixel data are changed. By setting different application forms, clear color printing can be performed by utilizing the advantage of the screen angle setting performed in gravure printing or the like.

In the gamma characteristic conversion function shown in FIG. 6, the function γ ₁ decreases to the density Dc at the maximum density of the pixel data, and the functions γ ₂ and γ _{3 change at} the maximum density of the pixel data, respectively. Although the density Dd is taken, as shown in FIG. 30, the function γ ₁ maintains the density Db even in the highest density area, and the functions γ ₂ and γ ₃ maintain the density zero in the entire density area. Even if it is set, an image of practically sufficient quality can be obtained. In the gamma characteristic conversion function shown in the aforementioned FIG. 28, dropped to the concentration Dc function gamma ₁ is at the highest density of the pixel data and function gamma ₄ is to take the concentration Dd at the highest concentration of the pixel data But,
Function gamma ₁ as shown in FIG. 31 continues to maintain the highest concentrations, also function gamma ₄ can obtain practically sufficient quality images be set to continue to maintain the concentration zero.

[0027]

As described above, according to the present invention, a print head in which a plurality of heating resistance elements are arranged in a line, means for conveying recording paper and ink sheets at a predetermined pitch, and input pixels Image data reading means for continuously reading image data constituting data for N lines (N ≧ 2 integers);
Means for sampling in a matrix of N images, and N ×
In order to express the pixel density in dot size for each of the N pixels, the first is to perform gamma conversion proportionally from low density to high density and output print data for forming main dots.
Gamma characteristic conversion function, a second gamma characteristic conversion function for outputting print data having a lower density than the first gamma characteristic conversion function for forming sub dots, and forming dots in most areas. Gamma conversion means including third and fourth gamma characteristic conversion functions, and gamma characteristic conversion to each of N × N pixels sampled so that dots by the first gamma characteristic conversion function are aligned at a specific angle. A conversion characteristic selecting means for selecting and applying a function, and a means for supplying electric energy corresponding to print data to the heating resistor element of the print head, so that a combination of a common gamma characteristic conversion function is used as the conversion characteristic selecting means. If set, the dot formation position can be specified, so not only can the screen angle be set with as little data as possible, but also the fine gradation that changes the dot size With high performance and high resolution, dots formed for each primary color can be aligned at a fixed angle, and the area of the untransferred ink area can be subdivided to improve ink separation and realize rich color expression. .

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention with functions to be performed by a microcomputer.

FIG. 2 is a sectional view showing an embodiment of a thermal transfer printer to which the present invention is applied.

FIG. 3 is an enlarged front view showing an example of a print head used in the present invention.

FIG. 4 is a block diagram illustrating an example of a control device of the thermal transfer printer illustrated in FIG. 2;

FIG. 5 is a waveform chart showing an example of a signal for driving a print head in the present invention.

FIG. 6 is a diagram showing an example of a γ function used in the present invention.

FIG. 7 is an explanatory diagram illustrating a relationship between energy supplied to a print head and a heat generation area.

8 is a diagram showing a relationship between energy supplied to a heating resistor element and a dot size according to the driving method shown in FIG. 7;

9 is an explanatory diagram showing a relationship between the driving method shown in FIG. 7 and a print pattern.

FIG. 10 is an explanatory diagram showing a relationship between supply energy and a heat generation region in a print head driving method applied to the present invention.

FIG. 11 is an explanatory diagram illustrating an example of a conventional driving method of a print head.

FIG. 12 is an explanatory diagram showing a relationship between the conventional driving method shown in FIG. 11 and a printing pattern.

13 is an explanatory diagram showing an application example of the gamma characteristic conversion function shown in FIG.

FIG. 14 is an explanatory diagram showing a form in a case where the gamma characteristic conversion function shown in FIG. 13 is continuously applied.

FIG. 15 is an explanatory diagram showing a printing mode by applying the gamma characteristic conversion function shown in FIG.

FIG. 16 is an explanatory diagram showing another embodiment of an application example of the gamma characteristic conversion function shown in FIG.

FIG. 17 is an explanatory diagram showing a form in a case where the gamma characteristic conversion function shown in FIG. 16 is continuously applied.

FIG. 18 is an explanatory diagram showing a printing mode by applying the gamma characteristic conversion function shown in FIG.

FIG. 19 is an explanatory diagram showing another embodiment of the application example of the gamma characteristic conversion function shown in FIG. 6;

20 is an explanatory diagram showing a form in a case where the gamma characteristic conversion function shown in FIG. 19 is continuously applied.

FIG. 21 is an explanatory diagram showing a printing mode by applying the gamma characteristic conversion function shown in FIG.

FIG. 22 is an explanatory diagram showing another embodiment of the application example of the gamma characteristic conversion function shown in FIG. 6;

FIG. 23 is an explanatory diagram showing a form in a case where the gamma characteristic conversion function shown in FIG. 22 is continuously applied.

FIG. 24 is an explanatory diagram showing a printing mode by applying the gamma characteristic conversion function shown in FIG.

FIG. 25 is an explanatory diagram showing another embodiment of the application example of the gamma characteristic conversion function shown in FIG. 6;

FIG. 26 is an explanatory diagram showing a form in a case where the gamma characteristic conversion function shown in FIG. 25 is continuously applied.

FIG. 27 is an explanatory diagram showing a printing form by applying the gamma characteristic conversion function shown in FIG.

FIG. 28 is a diagram showing another embodiment of the gamma characteristic conversion function used in the present invention.

FIG. 29 is a diagram illustrating a printing form by applying the gamma characteristic conversion function of FIG. 28;

FIG. 30 is a diagram showing another embodiment of a gamma characteristic conversion function that can be used in the present invention.

FIG. 31 is a diagram showing another embodiment of a gamma characteristic conversion function that can be used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Recording paper 2 Stacker 3 Pickup roller 4 Paper feed mechanism 5 Platen 6 Thermal transfer print head 9 Ink sheet 12 Control circuit board 14 Heating resistance element

Claims (5)

(57) [Claims] 1. A print head having a plurality of heating resistance elements arranged in a line, means for conveying recording paper and an ink sheet at a predetermined pitch, and N, N, and N. Image data reading means for continuously reading out the data for the lines (an integer of N ≧ 2); sampling means for sampling the pixel data for the plurality of lines in a matrix of N × N pixels; A first gamma characteristic conversion function for outputting printing data for forming main dots by performing gamma conversion proportionally from low density to high density in order to express pixel density by dot size, A second gamma characteristic conversion function for outputting printing data having a lower density than the first gamma characteristic conversion function for forming dots; and third and fourth gas generators for forming dots in most density regions. Γ with a conversion function
Conversion means, and the sampled N × so that dots formed by the first gamma characteristic conversion function are aligned at a specific angle.
A thermal transfer image forming apparatus comprising: a conversion characteristic selecting unit for selectively applying the gamma characteristic conversion function to each of the N pixels; and a unit for supplying electric energy corresponding to the printing data to a heating resistor element of the print head. apparatus. 2. The thermal transfer type image forming apparatus according to claim 1, wherein said conversion characteristic selecting means sets a selection characteristic so that an angle at which dots are aligned differs for each primary color. 3. The conversion characteristic selecting means combines two adjacent dots in the main scanning direction in a low-density to medium-density region, and sets selection characteristics such that these two dots are aligned in a fixed direction. The thermal transfer image forming apparatus according to claim 1. 4. The conversion characteristic selecting means combines two adjacent dots in the sub-scanning direction in a low-density to medium-density region, and sets a selection characteristic such that these two dots are aligned in a fixed direction. The thermal transfer image forming apparatus according to claim 1. 5. A print head in which a plurality of heating resistance elements are arranged in a line, means for conveying recording paper and ink sheets at a predetermined pitch, and N, N, and N. Image data reading means for continuously reading out the data for the lines (an integer of N ≧ 2); sampling means for sampling the pixel data for the plurality of lines in an N × N matrix; A first gamma characteristic conversion function for performing gamma conversion proportionally from low density to medium density of pixel data to output printing data for forming a main dot in order to express density in dot size; The second and third gamma characteristic conversion functions for outputting print data whose density increases proportionally from the density range to the high density range, and the fourth for outputting print data in which dots are not formed in most areas. Γ conversion means comprising a gamma characteristic conversion function, a conversion characteristic selection means for selecting and applying a gamma characteristic conversion function such that dots formed by the first gamma characteristic conversion function are aligned at a specific angle, and Means for supplying corresponding electric energy to the heating resistor element of the print head.