JP3094539B2 - 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.

[0003] 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 is easily formed in a minute size. . By the way, 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 and printing is repeated a plurality of times. There is a need.
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 fixed direction with respect to the recording medium, that is, a so-called screen angle is set, so that the color turbidity due to the displacement of the dot forming position is prevented as much as possible. Is being done.

For example, in a printing method in which the size of printable dots 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 the area is expressed. A method has been proposed in which the position at which one dot is formed is defined for each primary color, thereby aligning the dot formation positions in a specific direction of the 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 themselves formed on a recording medium and to read a unit of an original image. There has been proposed a method in which a threshold value is set in correspondence with a so-called pixel, and a plurality of matrices serving as nuclei for constantly forming dots are set, thereby setting a density gradation and a screen nucleus.

[0008]

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. It is to provide a novel thermal transfer type image forming apparatus capable of performing the above.

[0010]

In order to solve such a problem, a thermal transfer type image forming apparatus according to the present invention comprises a print head in which a plurality of heating resistance elements are arranged in a line, and a recording paper and an ink sheet. Means for conveying the image data at a pitch of N, image data reading means for continuously reading the pixel data constituting the input image data for N lines (N ≧ 2 is an integer), and N for reading the pixel data for the plurality of lines. Sampling means for sampling in a matrix of × N pixels;
In order to express the pixel density by dot size for each N × N pixel, a first conversion is performed, in which gamma conversion is performed proportionally from low density to high density to print data for forming main dots. A group of gamma characteristic conversion functions, a second group of gamma characteristic conversion functions for outputting printing data of lower density than the first group of gamma characteristic conversion functions for forming sub dots, Γ conversion means including a third group of gamma characteristic conversion functions that do not form dots in the density region, and the sampled N × N so that the dots by the first group of gamma characteristic conversion functions are aligned at a specific angle. Netsuten comprising: a conversion characteristic selection means for selecting applying the gamma characteristic conversion function to each pixel, and means for supplying electrical energy to the heating resistor elements of said print head relative to the printing data
A gamma characteristic conversion function, comprising:
Indicates a slightly different level of the mark in each group.
It consists of a plurality of types set by the printing data. Or the above
Set the gamma characteristic conversion function with 16 or less types of print data.
It is made up of multiple types that are specified. Alternatively,
Use the mark conversion function to mark 16 or less unequally spaced specific
It is made up of multiple types set by printing data.

[0011]

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 the color. Prevent turbidity.

[0013]

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, which comprises a thermal transfer printing mechanism and a control device. The thermal transfer printing mechanism includes a paper feed mechanism 4 that pulls out one recording sheet from a stacker 2 stocking the recording sheet 1 by a pickup roller 3 and conveys the recording sheet to a printing area. , A thermal transfer print head 6 pressed against the platen 5 during printing, and a stacker 2
The transport roller 8 returns to the side, a stock roller 10 that supplies the ink ribbon 9, and a winding 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.

As shown in FIG. 3, the thermal transfer print head 6 is provided on the surface of the substrate 13 with the heating resistance elements 14,
14, 14 ° are formed in a line, and the lead wires 15, 15, 15 °, 16, 16, 16 ° are oriented in the paper feed direction.
‥ is 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 or 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 outputs electric energy corresponding to the data representing the density output from the interface 22, for example, the densities B0, B1, and B as shown in FIG.
2, B3, ‥‥ Bn, corresponding to times T0, T1, T2, T3,
The pulse-like power in which {Tn increases sequentially} is supplied to each of the heat-generating resistance elements 14, 14, 14 of the thermal transfer print head 6.

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 rotation corresponding to a command output from the interface 22. It is configured to output a drive pulse so as to have a speed.

FIG. 1 shows an embodiment represented by functions required by the microcomputer 17 necessary for performing color printing by utilizing the basic printing functions 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. The density of the pixel data as shown in FIGS. 6 to 12 is provided so as to function as a filter or a print density setting means for the pixel data from the sampling means 33. In order to specify the dot density (hereinafter referred to as converted print data) for the image data, data defining the relationship between the density of the pixel data and the print conversion data is stored.

FIGS. 6 to 12 show an embodiment of the gamma characteristic conversion function set in the above-mentioned gamma conversion means 34. A plurality of characteristics, in this embodiment, 28 functions of 7 groups are shown. It is stored and configured.

Γ of a group of gamma characteristic conversion functions shown in FIG.
Does not form a transfer dot when the density of the pixel data is zero, but the converted print data Dd for supplying the minimum energy enough to keep the temperature of the heating resistor element constant regardless of the surrounding environment. Is set, and from there, it rises to the maximum density D0 in proportion to the entire intermediate density area,
Further, the converted print data D0 is maintained from the intermediate density area to the high density area. Has characteristics.

Γ11, γ1
Four types of γ having similar characteristics of 2, γ13, and γ14 are stored. These four types are set with converted print data slightly different from the pixel data by a predetermined amount, and the converted print data is set with data appropriately selected from 15 levels of Da to D0. I have.

By the way, the converted print data Dh is used to generate energy of a dot density of 11.8 dots / mm for binary printing such as character printing, and usually energy of about 0.125 mJ / dot. Is set to a value that can be supplied to

The density D0 is set to a value capable of supplying approximately twice the energy of the density Dh.

The gamma of the gamma characteristic conversion function 2 group shown in FIG.
Is a characteristic that maintains the converted print data De such that dots of the minimum size can be stably formed in the low density area of the pixel data, and thereafter increases from the middle density area to the high density area to the maximum converted print data D0. It has.

The second group of gamma characteristic conversion functions includes γ21, γ2
Four types of γ with similar characteristics of 2, γ23, and γ24 are stored. These four types are set with converted print data slightly different from the pixel data by a predetermined amount, and the converted print data is set with data appropriately selected from 15 levels of Da to D0. I have.

The γ of the gamma characteristic conversion function group 3 shown in FIG.
Has a characteristic that the density becomes Dh only near the maximum density of the pixel data.

The third group of gamma characteristic conversion functions includes γ31, γ3
Four types of γ 2 having similar characteristics of 2, γ 33 and γ 34 are stored. These four types are set with converted print data slightly different from the pixel data by a predetermined amount, and the converted print data is set with data appropriately selected from 15 levels of Da to D0. I have.

The gamma of the gamma characteristic conversion function 4 group shown in FIG.
Maintains the converted print data De such that dots of the minimum size can be formed stably in the low-density region to the medium-density region of the pixel data, and thereafter proportionally from the medium-density region to the high-density region to the converted print data Dm. It has characteristics that increase.

The fourth group of the gamma characteristic conversion functions includes γ41, γ4
Four types of γ with similar characteristics of 2, γ43 and γ44 are stored. These four types are set with converted print data slightly different from the pixel data by a predetermined amount, and the converted print data is set with data appropriately selected from 15 levels of Da to D0. I have.

Γ of the group of five gamma characteristic conversion functions shown in FIG.
Is converted print data Dc such that dots are hardly formed in a low density area to a medium density area of pixel data.
Is maintained, and thereafter, the print data is proportionally increased from the medium density area to the high density area up to the converted print data Di.

The gamma characteristic conversion function group 5 includes γ51, γ5
2, four types of γ with similar characteristics of γ53 and γ54 are stored. These four types are set with converted print data slightly different from the pixel data by a predetermined amount, and the converted print data is set with data appropriately selected from 15 levels of Da to D0. I have.

The γ of the group of six gamma characteristic conversion functions shown in FIG.
Is converted print data DC such that dots are hardly formed in a low density region to a high density region of pixel data.
Is maintained, and thereafter, the converted print data DJ increases in the high density area.

The gamma characteristic conversion function group 6 includes γ61, γ6
Four types of γ having similar characteristics of 2, γ63, and γ64 are stored. These four types are set with converted print data slightly different from the pixel data by a predetermined amount, and the converted print data is set with data appropriately selected from 15 levels of Da to D0. I have.

Γ of the gamma characteristic conversion function group 7 shown in FIG.
The conversion print data Db, DC, Dd, and De are maintained so that little or no dots are formed in the pixel data from the low-density region to the high-density region. Di, Dj, D
It consists of four types, γ71, γ72, γ73, and γ74, which have characteristics that rise to k. This is used in place of γ of the gamma characteristic conversion function group 3 shown in FIG. 8 and is used for correcting thermal history by printing. As a result of having such characteristics, for example, one group of gamma characteristic conversion functions as a first group for each pixel of the sampled matrix,
When the second group is assigned with the second group of gamma characteristic conversion functions and the third group is assigned with the third group of gamma characteristic conversion functions, γ of the first group of conversion characteristics causes the dot which is the center of the image expression to be adjacent to this. In addition, it becomes possible to express a sampling area by adding a dot which is a subordinate by the conversion characteristic 2 group of γ and further adding the conversion characteristic 3 group of γ to the pixel data showing the highest density.

Numeral 35 is a conversion characteristic selecting means. Matrix pixel data D11, D12,... D14 which are appropriately sampled from 28 kinds of 7 groups of gamma characteristic conversion functions corresponding to the primary colors output to the image memory 30. , D21, D22
‥‥ D24, D31, D32, ‥‥ D34, D41, D42 ‥‥ D44
(For example, FIG. 20).

Further, in order to uniformly correct the output density of each heating resistor element 14 of the thermal transfer print head 6, a gamma conversion characteristic is selected by the head density correction data 37, and the thermal effect is corrected by the history of each print. For this purpose, the gamma conversion characteristic is selected based on the thermal history correction data 38.

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. 13, current is applied to only one heating resistor element 14 while the adjacent heating resistor element 1 is turned on.
When printing is performed while 4 ′ and 14 ″ are paused, the driven heating resistor element 14 is turned off.
Since there is no thermal interference from 4 ′ and 14 ″, it is possible to use the area of other adjacent heating resistance elements 14 ′ and 14 ″ as a dot forming area. As a result, as shown in FIG. 14, even if the relative input energy E supplied to the heating resistance element is divided into multiple stages of “32”, the size of the formed dot is proportional to the relative input energy. High gradation can be expressed,
Therefore, a dot having a density that is directly proportional to the density of the pixel data is formed. As a result, as shown in FIG. 15, 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. 16, while the two heating resistor elements 14 and 14 'are driven at the same time, the printing is performed while the heating resistor elements adjacent to these are in a halt state. 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. 17, 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, the case where the above-mentioned γ conversion characteristic is applied will be described.

The conversion characteristic selecting means 34 applies the 2 × 2 pixel data D12, D12, D21 and D22 in the form of matrix extracted by the sampling means 33 to the application form as shown in FIG. A case will be described as an example in which four groups are appropriately applied from among a group of gamma characteristic conversion functions as a group of 1, a group of gamma characteristic conversion functions as a second group, and a group of gamma characteristic conversion functions as a third group. I do.

The pixel data D11 sampled by the sampling means 33 is converted linearly with respect to its density by applying γ11 of a group of gamma characteristic conversion functions of the γ conversion means 33 selected by the conversion characteristic selection means 34. The print data is converted into proportional print data, and the pixel data D12
By applying γ33 of the third group of gamma characteristic conversion functions, the density Dd is converted into converted print data only when the density is the highest value, and otherwise, the energy for dot formation is not applied. Further, the pixel data D21 is converted into converted print data to which the entire area energy is not applied by applying γ34 of the third group of gamma characteristic conversion functions, and the pixel data D22 is applied with γ21 of the second group of gamma characteristic conversion functions. As a result, energy is applied in a low-density region, but is applied to such an extent that a substantial dot cannot be formed. At a medium-density or higher, the converted print data is linearly proportional to the density of the pixel data. .

As a result, the first line of pixel data D11,
When D12 is printed, dots are formed only for the pixel data D11 for the intermediate density pixel data that frequently appears in a normal image, and the adjacent pixel data D12 is not printed.

When the printing of the first line is completed in this way, the pixel data D21 and D22 of the same sampling area are set.
Will be printed. Since the function γ34 is assigned to the pixel data D21 and the function γ21 is assigned to the pixel data D22, only the pixel data D22 is printed in the intermediate density area, and the pixel data D21 is not printed. Also in the printing of the second line, similar to the printing of the above-described first line, since the other adjacent heating resistor elements are in the rest state, the pixel data to be printed is faithful to the density converted by γ21. The dot is formed as a dot having an appropriate density. In the following, printing is continued by alternately repeating the choreography mode by slightly changing the form as shown in FIG. 20, that is, the gamma characteristic conversion function shown in FIG.

FIG. 20 shows a case where the basic 2 × 2 pixel data of FIG. 19 is arranged as a 4 × 4 matrix. The equivalent of D11, D12, D21, D22 is D13,
D14, D23, D24 and D31, D32, D41, D42 and D33, D
34, D43 and D44. Each converted print data is
They are slightly different and are converted as shown. Here, γ11, γ12, γ13, and γ14 of the gamma characteristic conversion function group 1 in FIG. 6 are appropriately applied to D11, D13, D31, and D33.
As for D12, D14, D32, and D34, γ31, γ32, and γ33 of the third group of gamma characteristic conversion functions in FIG. 8 are appropriately applied. Also,
As for D21, D23, D41, and D43, γ34 of the gamma characteristic conversion function group 3 in FIG. 8 is appropriately applied, and D22, D24, D42, and D44 are used.
Are γ21, γ22, γ2 of the gamma characteristic conversion function 2 group of FIG.
3, γ24 is applied as appropriate.

As a result, the 16 pixels specified by the sampling area are the pixel data D11, D13, D31, D33
Is a main dot, and pixel data D22, D24, D42,
D44 is printed so as to be a sub-dot, and the main dot is supplemented with the sub-dot to form 16 pixel data D
11 to D44 will be expressed.

That is, when the density of the region constituted by the 16 sampled pixels is low, the pixels D11, D13, and D3 to which γ of the group of gamma characteristic conversion functions is assigned are assigned.
1, only the dots corresponding to D33 are printed (FIG. 21 (I)). As the density of the sampled area increases, the dots 40, corresponding to the pixels D22, D24, D42, D44 to which γ of the second group of gamma characteristic conversion functions are assigned.
40 are also printed (FIG. 21 (II)). When the density of the pixel data further increases, the size of the dots corresponding to the pixels D11 and D22 increases, and
The image is printed so as to narrow 1, 41,... (FIGS. 21 (III), (IV), (v)). As a result, the blank portions 41, 41,... Are formed in an island shape. As a result, even when high-density data is printed, the ink on the ink sheet is not unnecessarily peeled off and only the ink having an area proportional to the density of the image data is used. Is reliably transferred to the recording paper.

FIG. 22 shows another specification form of the conversion characteristic by the conversion characteristic selecting means 34. For the four pixels D11 to D22 extracted by the sampling means 33, the pixel data D11 has a gamma characteristic conversion. Γ11 of group of functions
The pixel data D12 has γ34 of the gamma characteristic conversion function group 3
And the pixel data D21 includes γ21 of the gamma characteristic conversion function 2 group.
And a gamma characteristic conversion function group γ33 is assigned to the pixel data D22.
Is preferentially formed, and the pixel data D21
Are formed as sub-dots. When such a form is shifted by one dot in the main scanning direction for every two lines as shown in FIG. 23 and applied in a 4 × 4 matrix as in the previous embodiment and the gamma characteristic conversion function is slightly changed,
As shown in FIG. 24, when the density of the image data in the sampling area is low, the pixel data D11 of 4 × 4 pixels,
Only dots corresponding to D13, D31 and D33 are formed.
At the stage where two lines have been moved at this density, the sampling area is shifted by one pixel as described above.
.. Will be formed in the middle of the dots formed as lines. 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. 25 shows another specification form of the conversion characteristic by the conversion characteristic selection means 34, that is, the matrix-shaped 2 × 2 pixel data D12, D12, D21, D22 extracted by the sampling means 33. For each of them, the conversion characteristic selecting means 34 appropriately selects one group of gamma characteristic conversion functions as a first group, four groups of gamma characteristic conversion functions as a second group, and three groups of gamma characteristic conversion functions as a third group. This is a case where four types are applied.

As a first mode, pixel data D11 has γ41 of a group of four gamma characteristic conversion functions, pixel data D12 has γ11 of a group of gamma characteristic conversion functions, and pixel data D21 has a group of three gamma characteristic conversion functions. γ33 is assigned to the pixel data D22, and γ34 of three groups of gamma characteristic conversion functions is assigned to the pixel data D22 ((a) in the figure). As a second mode, γ31 of the three groups of gamma characteristic conversion functions is assigned to the pixel data D13 and D14. Assigns γ34 of the group of three gamma characteristic conversion functions, γ44 of the group of four gamma characteristic conversion functions to the pixel data D23, and further assigns γ14 of the group of gamma characteristic conversion functions to the pixel data D24 ((b) in the figure). The first and second embodiments are used alternately with a slight change in the gamma characteristic conversion function as shown in FIG.

That is, the pixel data D of the first extraction area
When the first mode is selected for the pixel data D11 to D44, the dot based on the pixel data D12 is preferentially printed. When the next pixel data adjacent to this sampling area is selected, the pixel data D24 is selected. Is preferentially printed.
As a result, in the low density area, dots are formed at a screen angle plus or minus 26.6 degrees as shown in FIG. Also, when the image density of the extraction area increases, dots of γ of the gamma characteristic conversion function 4 group are also printed in addition to γ of the gamma characteristic conversion function 1 group. ,
The pixel data D11 is printed in the form of sub-dots, and in even lines, the pixel data 24 is used as the main dot.
Printing is performed in a form in which 23 is sub-dotted.

FIG. 28 shows another specification form of the conversion characteristic by the conversion characteristic selection 34. As a first form, the pixel data D11 contains γ11 of a group of gamma characteristic conversion functions, D12
Γ33 of a group of three gamma characteristic conversion functions, γ34 of a group of three gamma characteristic conversion functions is assigned to D21, and γ21 of a group of two gamma characteristic conversion functions is assigned to D22 (FIG. 10A).
As a form, the pixel data D13 includes a gamma characteristic conversion function 2
Γ24 of the group and γ34 of the group 3 of the gamma characteristic conversion function
29, D23 is assigned gamma characteristic conversion function group 3 γ31, and D24 is assigned gamma characteristic conversion function group 1 γ14 (FIG. 29B). After two lines, as shown in FIG. The application order of the first mode and the second mode is reversed, and the gamma characteristic conversion function is slightly changed.

That is, when the first mode is selected for the four pixel data D11 to D22 of the first extraction area,
A dot based on the pixel data D11 is preferentially printed, and when the next pixel data adjacent to the pixel data is selected, the pixel data D24 is preferentially printed. As a result,
In the low-density area, dots are formed at a screen angle of 45 degrees as shown in FIG. When the image density of the extraction area is increased, dots of γ of the second group of gamma characteristic conversion functions are also printed in addition to γ of the first group of gamma characteristic conversion functions.
11 as a main dot, the next adjacent pixel data D13
Are formed as sub-dots with one dot interval. In the even-numbered lines, the pixel data D24 is formed as a main dot, and the pixel data D22 is formed as a sub-dot one dot before.

FIG. 31 shows another specification form of the conversion characteristic by the conversion characteristic selection 34. As a first form, the gamma characteristic conversion function group γ34 of the pixel data D11 and the gamma characteristic Γ21 of the second group of conversion functions, γ11 of the first group of gamma characteristic conversion functions are assigned to the pixel data D21, and γ33 of the third group of gamma characteristic conversion functions are assigned to the pixel data D22 (FIG. 10A). As a form of the pixel data D13, γ31 of a group of three gamma characteristic conversion functions, the pixel data D14 is γ14 of a group of gamma characteristic conversion functions, the pixel data D23 is γ24 of a group of two gamma characteristic conversion functions, and A gamma characteristic conversion function group 3 γ34 is assigned to the data D24 ((b) in the figure), and after two lines, the gamma characteristic conversion function is slightly changed in the first mode and the second mode as shown in FIG. Reversed application order A.

That is, when the first mode is selected for the four pixel data D11 to D22 of the first extraction area,
The dots based on the pixel data D21 are printed with priority, and when the next area is selected, the pixel data D14 is printed with priority. As a result, in the low density area, dots are formed at a screen angle of 135 degrees as shown in FIG. When the image density of the extraction area is increased, dots of γ of the second group of gamma characteristic conversion functions are also printed in addition to γ of the first group of gamma characteristic conversion functions. The pixel data D12 of the immediately preceding adjacent area is formed as sub-dots at one-dot intervals, and in even-numbered lines,
Pixel data D21 is the main dot,
After the dot, the pixel D23 is printed as a sub dot.

Of these embodiments, FIG. 19, FIG.
According to the application form of the γ-conversion characteristic shown in FIG. 25, the blank portion is formed in a shape close to a circle and the blank portions are independent from each other, so that the ink in the non-dot forming portion is unnecessarily peeled off. Can be prevented. As a result, a gray scale faithful to the density of the pixel data can be expressed.

FIG. 34 shows another embodiment of the gamma characteristic conversion function. The application form as shown in FIG. 34, that is, 2 × 2 pixel data of a matrix extracted by the sampling means 33 is shown. D12, D12, D21, D
For each of the 22 groups, the conversion characteristic selecting means 34 sets a gamma characteristic conversion function as a first group, a gamma characteristic conversion function as a second group, a gamma characteristic conversion function as a third group, and a gamma characteristic conversion function as a third group. The case where four types are appropriately applied from the three groups of the gamma characteristic conversion functions as the group of 4 will be described as an example.

The pixel data D11 sampled by the sampling means 33 is converted linearly with respect to the density by applying γ11 of a group of gamma characteristic conversion functions of the γ conversion means 33 selected by the conversion characteristic selection means. The print data is converted into proportional print data, and the pixel data D12
By applying γ64 of the gamma characteristic conversion function 6 group, the converted print data Db such that almost no dots are formed in the low density area to the middle density area of the pixel data is maintained, and thereafter, from the middle density area to the high density area, It is set so as to be converted into converted print data Dj. Further, by applying γ51 of the gamma characteristic conversion function 5 group, the pixel data D21 maintains converted print data DC such that dots are hardly formed in the pixel data from the low density region to the medium density region. Is set so as to be converted into converted print data Di over a range from to. Further, the pixel data D22 is set so as to be converted into converted print data to which the entire area energy is not applied by applying γ34 of the gamma characteristic conversion function 3 group.

As a result, the first line of pixel data D11,
When D12 is printed, dots are formed only for the pixel data D11 for the intermediate density pixel data that frequently appears in the normal image, and the adjacent pixel data D12 is the pixel data D11.
Take the form to assist. When the printing of the first line is completed in this manner, the pixel data D in the same sampling area
21, D22 will be printed. A function γ51 for the pixel data D21 and a function γ for the pixel data D22
Since 34 is assigned, in the intermediate density area, only the pixel data D21 takes the form of assisting the pixel data D11 of the first line.

Printing is continued by alternately repeating the choreography mode, with the form shown in FIG. 35, ie, the gamma characteristic conversion function shown in FIG. 34 slightly changed. When the density of the pixel data in the extraction area is low, the pixel data D11, D13,
Since dots based on D31 and D33 are formed, dots are formed in a substantially grid pattern as shown in (I) of FIG. 36, and screen angles of 0 ° and 90 ° are set. Become. When the density of the pixel data is increased, as shown in FIG.
Six groups of dots formed by γ are formed, but the dots formed by these are small, and the pixel data D21 does not form dots up to the maximum density. , 45... Are formed. 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.

The case where the gamma characteristic conversion functions of the first group, the second group, the fifth group, and the sixth group are applied in the form as shown in FIG. 35 has been described. However, FIG. 23, FIG. 26, FIG.
It is clear that the present invention can be applied in the form shown in FIG.

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.

Next, the gamma characteristic conversion function 7 shown in FIG.
The case where γ of the group is used will be described. The gamma of the gamma characteristic conversion function group 7 maintains the converted print data Db, DC, Dd, and De such that dots are hardly formed from the low-density region to the high-density region of the pixel data. It has a characteristic that rises to Di, Dj, and Dk. This is used in place of γ in the third group of gamma characteristic conversion functions of the third group shown in FIGS. 20, 23, 26, 29, and 32, and is used for thermal history correction by printing. .

FIG. 3 shows a case where one embodiment is applied to FIG.
7, FIG. 38, FIG. 39, FIG. 40, and FIG.

FIG. 37 shows a case where the first line before the corresponding line is printed every other dot in the paper transport direction, and all the lines before the second line are printed. At this time, γ of the group of three gamma characteristic conversion functions shown in FIG. 8 is applied as it is to D12 and D14 (, D16 and D18) of the corresponding line. FIG. 38 shows a case where the first line is printed every other dot and the second line is printed every other dot of a different digit from the first line in the paper transport direction. At this time, D12 and D14 (, D16 and D18) of the corresponding line are converted to converted print data higher than γ of the gamma characteristic conversion function group 3 shown in FIG. 8, and γ74 of the gamma characteristic conversion function group 7 shown in FIG. Is applied as a third group. FIG. 39 shows a case in which the preceding first line is printed every other dot and the second preceding line is not printed at all for the corresponding line in the paper transport direction. At this time,
D12 and D14 (, D16 and D18) of the corresponding line are γ73 slightly higher than γ74 of the gamma characteristic conversion function group 7 shown in FIG.
Apply FIG. 40 shows a case where the first line is not printed at all for the corresponding line in the paper transport direction and the second line is printed every other dot. At this time, γ72 slightly higher than γ73 of the gamma characteristic conversion function group 7 shown in FIG. 12 is applied to D12 and D14 (, D16 and D18) of the corresponding line.
FIG. 41 shows a case in which neither the first line nor the second line is printed on the corresponding line in the paper transport direction.
At this time, D12, D14 (, D16, D18) of the corresponding line are:
Γ71 which is slightly higher than γ72 of the gamma characteristic conversion function group 7 shown in FIG. 12 is applied.

[0069]

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.
And a gamma characteristic conversion function of a second group that outputs print data of lower density than the gamma characteristic conversion function of the first group to form sub dots. Gamma conversion means having a gamma characteristic conversion function of a third group that does not form dots in the region, and as another case, the main dots are obtained by performing gamma conversion proportionally from low density to high density. First to output print data to be formed
Gamma characteristic conversion function of the second group or the gamma characteristic of the second group or the third group that outputs printing data of lower density than the gamma characteristic conversion function of the first group to form sub dots. By setting the conversion function and gamma conversion means having a fourth group of gamma characteristic conversion functions that do not form dots in most areas, the dots by the gamma characteristic conversion function of the first group can be set at a specific angle. A conversion characteristic selection unit for selecting and applying a gamma characteristic conversion function to each of the N × N pixels sampled so as to be aligned; and a unit for supplying electric energy corresponding to print data to the heating resistor element of the print head. Therefore, if a common combination of gamma characteristic conversion functions is set in the conversion characteristic selection means, the dot formation position can be specified, so that the screen angle can be set with as little data as possible. In addition, by changing the size of the dots, the dots formed for each primary color are aligned at a fixed angle, and the area of the non-transferred ink area is subdivided while maintaining fine gradation and high resolution. To realize rich color expression. Also, by using a gamma characteristic conversion function that does not print in most areas for thermal history correction by printing, stable and clear color printing can be performed in any case,
This eliminates the need for a complicated heat history correction arithmetic circuit.

Further, since the gamma characteristic conversion function is set with 16 or less types of converted print data, the amount of memory can be reduced if the function is taken in the print buffer after gamma conversion.

[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 a diagram showing an example of a γ function used in the present invention.

FIG. 8 is a diagram showing one embodiment of a γ function used in the present invention.

FIG. 9 is a diagram showing an example of a γ function used in the present invention.

FIG. 10 is a diagram showing one embodiment of a γ function used in the present invention.

FIG. 11 is a diagram showing an example of a γ function used in the present invention.

FIG. 12 is a diagram showing an example of a γ function used in the present invention.

FIG. 13 is an explanatory diagram illustrating a relationship between energy supplied to a print head and a heat generation area.

FIG. 14 is a diagram illustrating a relationship between energy supplied to a heating resistor element and a dot size according to the driving method illustrated in FIG. 13;

15 is an explanatory diagram illustrating a relationship between the driving method illustrated in FIG. 13 and a print pattern.

FIG. 16 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. 17 is an explanatory diagram showing an example of a conventional driving method of a print head.

18 is an explanatory diagram showing a relationship between the conventional driving method shown in FIG. 17 and a print pattern.

FIG. 19 is an explanatory diagram showing an application example of the gamma characteristic conversion function shown in FIGS. 6, 7, and 8;

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 an application example of the gamma characteristic conversion function shown in FIGS. 6, 7, and 8;

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 an application example of the gamma characteristic conversion function shown in FIGS. 6, 8, and 9;

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 an explanatory diagram showing another embodiment of an application example of the gamma characteristic conversion function shown in FIGS. 6, 7, and 8;

FIG. 29 is an explanatory diagram showing a form in the case where the gamma characteristic conversion function shown in FIG. 28 is continuously applied.

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

FIG. 31 is an explanatory diagram showing another embodiment of an application example of the gamma characteristic conversion function shown in FIGS. 6, 7, and 8;

FIG. 32 is an explanatory diagram showing a form in a case where the gamma characteristic conversion function shown in FIG. 31 is continuously applied.

FIG. 33 is an explanatory diagram showing a printing form by applying the gamma characteristic conversion function shown in FIG. 31.

FIG. 34 is an explanatory diagram showing another embodiment of an application example of the gamma characteristic conversion function shown in FIGS. 6, 10, and 11;

FIG. 35 is an explanatory diagram showing a form in a case where the gamma characteristic conversion function shown in FIG. 34 is continuously applied.

FIG. 36 is a diagram illustrating a printing form by applying the gamma characteristic conversion function of FIG. 34;

FIG. 37 is an explanatory diagram showing an embodiment in which the gamma characteristic conversion function of the present invention is applied to thermal history correction by printing.

FIG. 38 is an explanatory diagram showing a form in which the gamma characteristic conversion function of the present invention is applied to thermal history correction by printing.

FIG. 39 is an explanatory diagram showing a form in which the gamma characteristic conversion function of the present invention is applied to thermal history correction by printing.

FIG. 40 is an explanatory diagram showing an embodiment in which the gamma characteristic conversion function of the present invention is applied to thermal history correction by printing.

FIG. 41 is an explanatory diagram showing a form in which the gamma characteristic conversion function of the present invention is applied to thermal history correction by printing.

[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 34 Gamma conversion means 35 Conversion characteristic selection means

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B41J 2/325 B41J 2/36 B41J 2/52

Claims (3)

(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; In order to express the pixel density by the dot size, a gamma characteristic conversion function of a first group for outputting printing data for forming a main dot by performing gamma conversion proportionally from low density to high density, And a second group of gamma characteristic conversion functions that output printing data having a lower density than the first group of gamma characteristic conversion functions to form dots, and a second group of gamma characteristic conversion functions that do not form dots in most density regions. A gamma conversion means having a gamma characteristic conversion function of a third group, and the gamma characteristic conversion is performed on each of the sampled N × N pixels so that dots according to the gamma characteristic conversion function of the first group are aligned at a specific angle. A thermal transfer type image forming apparatus comprising: a conversion characteristic selecting unit that selectively applies a function; and a unit that supplies electric energy for the print data to a heating resistance element of the print head, wherein the gamma characteristic conversion function is: A thermal transfer type image forming apparatus comprising a plurality of types which are set by printing data of slightly different levels by a predetermined amount in each group. 2. A print head in which a plurality of heating resistance elements are arranged in a row, means for conveying recording paper and ink sheets at a predetermined pitch, and pixel data constituting input image data are converted to 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; In order to express the pixel density by the dot size, a gamma characteristic conversion function of a first group for outputting printing data for forming a main dot by performing gamma conversion proportionally from low density to high density, And a second group of gamma characteristic conversion functions that output printing data having a lower density than the first group of gamma characteristic conversion functions to form dots, and a second group of gamma characteristic conversion functions that do not form dots in most density regions. A gamma conversion means having a gamma characteristic conversion function of a third group, and the gamma characteristic conversion is performed on each of the sampled N × N pixels so that dots according to the gamma characteristic conversion function of the first group are aligned at a specific angle. A thermal transfer type image forming apparatus comprising: a conversion characteristic selecting unit that selectively applies a function; and a unit that supplies electric energy for the print data to a heating resistance element of the print head, wherein the gamma characteristic conversion function is: A thermal transfer image forming apparatus comprising a plurality of types set by 16 or less types of printing data. 3. A print head in which a plurality of heating resistance elements are arranged in a line, means for conveying recording paper and an ink sheet at a predetermined pitch, and pixel data forming the input image data 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; In order to express the pixel density by the dot size, a gamma characteristic conversion function of a first group for outputting printing data for forming a main dot by performing gamma conversion proportionally from low density to high density, And a second group of gamma characteristic conversion functions that output printing data having a lower density than the first group of gamma characteristic conversion functions to form dots, and a second group of gamma characteristic conversion functions that do not form dots in most density regions. A gamma conversion means having a gamma characteristic conversion function of a third group, and the gamma characteristic conversion is performed on each of the sampled N × N pixels so that dots according to the gamma characteristic conversion function of the first group are aligned at a specific angle. A thermal transfer type image forming apparatus comprising: a conversion characteristic selecting unit that selectively applies a function; and a unit that supplies electric energy for the print data to a heating resistance element of the print head, wherein the gamma characteristic conversion function is: A thermal transfer type image forming apparatus comprising a plurality of types set at 16 or less specific printing data at unequal intervals.