JPH04212868A - Heat transfer picture forming device - Google Patents

Abstract

PURPOSE:To prevent the occurrence of heat interference by a method wherein picture element data of input picture data is fetched in a state to space a digit between adjoining digits and electric energy is fed to the heat generating resistance element of a printing head in response to a fetching pitch. CONSTITUTION:A heat transfer printing device conveys a recording sheet 1 from a sheet feeding mechanism 4 and an ink sheet 9 to a printing mechanism 7 wherein a heat transfer type printing head 6 is brought into contact with a platen 5. A microcomputer on a circuit substrate 12 stores inputted picture data equivalent to one line in a picture memory 25, and data equivalent to one line to be printed in a first color is stored in a line buffer 27 by means of a reading means 26. Every one, for example, odd picture element data in a main scanning direction is fetched by a fetching means 28 to output it to a printing buffer 29. Electric energy responding to density data is fed to the odd number-th heat generating resistance element of the printing head 6 to effect printing. A conveyance roller 8 is then reversed to return a sheet 1, and thereafter even number-th picture element data is printed in a similar manner described above.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention arranges a plurality of heating resistive elements in a line on the surface of a substrate, selectively generates heat in the heating resistive elements in accordance with print data, and ink on an ink sheet or ink ribbon. This invention relates to gradation control technology suitable for thermal transfer printers that form dots on recording paper by melting them.

0002

[Prior Art] A thermal transfer printer is equipped with an ink sheet or ribbon made by coating a polymer film with wax mixed with pigments, and a print head with minute heat-generating resistive elements integrated on a substrate. When the ink is energized, heat exceeding the ink melting temperature is generated in a minute area to melt the wax constituting the ink and transfer it to the recording paper. Such thermal transfer printers are often used in the field of full-color printing, which requires high-density dot formation, because it is easy to form heating resistive elements, which are dot-forming elements, in minute sizes.

By the way, full-color printing requires faithful representation of colors, but the pigments that can be used are
Usually, it is limited to the three primary colors yellow, magenta, cyan, and four colors, black. In order to express color tones under such restrictions, it is necessary to be able to arbitrarily adjust the density of the three primary colors of each dot printed by the heating resistor element. One way to meet these demands is to control the electrical energy supplied to the heating resistor elements of the print head, adjust the area at which the ink can melt, and reduce the dots formed by one heating resistor element. An image recording device has been proposed in which the area can be changed and a printed image faithful to the image data can be obtained by sampling the image data at fixed pixels in the vertical and horizontal directions and performing dither processing on the data multiple times. (IEICE Journal C-II, vol. J73-c-ii, no. 2,
pp38-45, January 1990).

0004

[Problems to be Solved by the Invention] However, at least 4×4 dots are required as the sampling area, and moreover, since the sampling data is subjected to dither processing by applying a 5-stage or 6-stage threshold matrix,
In addition to the problem that it takes time to generate print data from image data, there is also the problem that a textured image that does not exist in the original image data, so-called texture noise, is noticeable. SUMMARY OF THE INVENTION An object of the present invention is to provide a thermal transfer image forming apparatus that can obtain print data from image data at high speed and prevent as much as possible the textured noise pattern that tends to occur when setting a sampling area. It is in.

[0005]

[Means for Solving the Problems] In order to solve such problems, the present invention has a print head formed by arranging a plurality of heating resistor elements in a line, and a print head that conveys recording paper and ink sheets at a predetermined pitch. an extraction means for extracting pixel data constituting the input image data with digits spaced apart; A means for supplying corresponding electrical energy is provided.

[0006]

[Operation] Image data is extracted from externally inputted image data by an extraction means at intervals of at least one pixel in the main scanning direction, and heating resistive elements are arranged in a row in the main scanning direction. Output to a thermal transfer print head. As a result, the heating resistor element into which image data has been input will not receive thermal interference from adjacent heating resistor elements.
Therefore, even if electrical energy that generates a dot with a size larger than the dot size defined by the maximum density of the input image data is supplied, it is possible to generate a dot with an area proportional to the input electrical energy. As a result, it is possible to express density in more stages than conventional devices, which not only enables faithful gradation expression and color reproduction, but also allows for sufficient processing even when the sampling area is as small as possible. It becomes possible to express gradations, and therefore it is possible to prevent texture noise from occurring due to expansion of the sampling area.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be explained below based on illustrated embodiments. FIG. 1 shows an embodiment of the present invention, which is composed of a thermal transfer printing mechanism and a control device. The thermal transfer printing mechanism picks up recording paper 1 from a stacker 2 in which it is stocked by a pickup roller 3.
Paper feed mechanism 4 that pulls out a sheet of recording paper and conveys it to the printing area
, a printing mechanism 7 consisting of a platen 5 that transports the recording paper 1 and the ink sheet 9 at a constant speed, a thermal transfer print head 6 that is constantly pressed against the platen 5 during printing, and a stacker 2 that transports the printed recording paper again. It is composed of a conveyance roller 8 for returning the ink ribbon to the side, a stock roller 10 for supplying the ink ribbon 9, and a take-up roller 11. Further, a circuit board 12 incorporating a control circuit, which will be described later, is housed in the lower part of the housing.

As shown in FIG. 2, the thermal transfer print head 6 has heat generating resistive elements 14,
14, 14... are formed in a line, and lead wires 15, 15, 15..., 16, 16, 16... are formed in the paper feeding direction.
It is constructed by drawing out...

FIG. 3 shows an embodiment of the above-mentioned control circuit, and reference numeral 17 in the figure indicates a microcomputer constituting the central part of the control device, which includes a CPU 18, a control program, and a control program to be described later. It is composed of a ROM 19 that stores a data processing program, and a RAM 20 that constitutes a buffer and frame memory for data processing, and is connected to external devices such as a personal computer, a print head drive circuit 23, and a motor drive circuit via interfaces 21 and 22. 24.

The print head drive circuit 23 outputs electrical energy corresponding to the density data outputted from the interface 22, for example, as shown in FIG.
B4,... Time T1, T2, T3, T4 corresponding to Bn
, . . . is configured to supply pulsed power whose Tn increases sequentially to each heating resistor element 14, 14, 14, . . . of the thermal transfer print head 6.

The motor drive circuit 24 is configured to output drive pulses to the motor so that the rotation direction and rotation speed correspond to the command output from the interface 22.

FIG. 5 shows the microcomputer 17 mentioned above.
This diagram schematically shows the functions realized by the . The image memory 25 is configured to store one page worth of data input from the interface 21. The image data reading means 26 extracts one line of specific color data from the image memory 25 and stores it in the line buffer 27. The pixel extraction means 28 extracts image data one by one in the main scanning direction from the image data stored in the line buffer 27 and outputs it to the print buffer 29.

Next, the operation of the apparatus configured as described above will be explained. When image data is input from an external device such as a microcomputer, the microcomputer 17
One page's worth of image data is stored in the image memory 25, and from among the image data constituting the line to be printed, data to be printed in the first color, for example, data for cyan, is extracted and sent to the line buffer 27. Output to. Data D1, D2, D3, D4, D5, D1 in the line buffer 27
0, D11, and D12 (FIG. 6I), image data D1 of every other pixel in the main scanning direction, for example, odd-numbered pixels, is stored.
, D3, D5, . . . D11 (FIG. 5II) are extracted and output to the print buffer 29. The microcomputer 17 outputs the density data designated for each pixel data of the image data stored in the print buffer 29 to the thermal transfer print head drive circuit 23 via the interface 22 . Heat generating resistor elements 14, 14, of the thermal transfer print head 6
Electrical energy specified by the concentration data is supplied to every other one of 14, for example, an odd numbered one. This electrical energy is made proportional to the reciprocal of the extraction rate,
Also, a method is adopted in which the thinned out pixel data is added to other pixel data that is adjacent to the pixel targeted for thinning and that is to be printed.

[0014] As a result, the odd-numbered heating resistive elements 14, 14, 14, etc. that are to be driven do not receive thermal interference from other adjacent heating resistive elements, and therefore, the supplied electrical energy It is possible to faithfully transfer an area proportional to , and to make the average density of the entire printed surface comparable to that of the image data.

By the way, when the heat generating resistor element 13 is driven alone, the area of the ink sheet whose temperature rises to the temperature at which the ink can be melted by the electric energy supplied to it will, while the relative input energy is small, Since the periphery is in contact with the outside world, the degree of heat dissipation is greater at the outer periphery. Therefore, the temperature of the heating resistor element increases so that the center point has the highest temperature and forms a circular isothermal line.
Also, when the relative input energy increases, the heating resistor element 1
The heat generating area of No. 4 becomes larger than the area of the heat generating resistor element 14 itself and expands to the adjacent heat generating resistor element, and as a result, as shown in FIG. It is proportional to the size of E3, E4, E5...

That is, as shown in FIG. 8, even for a relative input energy E32 exceeding the conventionally used relative input energy E12, the melting area of the ink is expanded in proportion to the relative input energy, and the recording paper is Dots will be formed in the area.

On the other hand, two adjacent heating resistance elements 14,
When 14' are driven at the same time, the heat interferes with each other on the adjacent sides, so as shown in Figure 7(b), the melting temperature regions overlap each other, making it possible to change the melting area proportionally. The upper limit of the magnitude of the relative input electrical energy is limited to the magnitude E12 or less, and the melting area of the ink will be saturated for larger relative input energies E13 to E32.

As a result, according to the apparatus of the present invention, it is possible to raise the upper limit of the maximum reproducible density, thereby increasing the number of gradations that can be divided, and faithfully expressing the density defined by the image data. It is possible to form dots with a number of gradations that enable full-color printing.

When printing for one line is completed, the microcomputer 17 outputs a signal corresponding to the width of one line to the motor drive circuit 24 to rotate the conveying roller 8.
The recording paper 1 and the ink sheet are fed by one line width. As a result, a new ink sheet and unprinted recording paper are located in the print area of the print head 6. The image data reading means 26 reads the next one line of data D1, D2, D3, D4, D5, . . . D from the image memory 25.
10, D11, and D12 are stored in a buffer, and only the digits that were not printed last time, that is, even-numbered image data D2, D4, . . . D10, D12 are extracted and stored in a print buffer 29.

[0020] This data D2, D4,...D10, D1
2 is output to the print head drive circuit 23 via the interface 22, and each image data D2, D4, . . . D10
, D12, electrical energy proportional to the concentration specified by D12 is supplied to the even-numbered heating resistive elements 14, 14, 14, . . . . As a result, even-numbered heating resistor elements 14 of the print head 6
, 14, 14... are not subject to thermal interference from adjacent heating resistive elements, and the heating resistive elements contributing to dot formation this time were not driven last time, so they are maintained at room temperature. , heat is generated up to the ink melting temperature or higher with an area that is faithfully proportional to the supplied electrical energy.

When the printing of the second line is completed, the third line is printed again through the same process as the printing process of the first line described above. The heating resistive elements used in this third printing line have been completely cooled down since they were inactive during the previous printing process, and therefore generate heat over an area that is faithfully proportional to the electrical energy supplied. . Thereafter, odd-numbered digits and even-numbered digits are printed alternately for each line so that the areas shown by hatching in FIG. 9 are printed dots.

As a result, when the relative input energy is small as shown in FIG. 10(a) (I in the same figure), small-sized dots are also With the conventional device, even when the relative energy is input to saturation level (Figure II), independent dots are still created with sufficient margins, and when the highest relative energy is input (Figure III). , it is possible to form a sufficiently large dot without producing a blank space even though every other heating resistor element is activated.

On the other hand, the conventional device is shown in FIG.
As shown in Figure 10(b), even when a relative input energy that does not cause saturation is supplied, connections between dots occur in some places (I in Figure 10b), and the maximum size dots in the present invention are At the stage when about 1/3 of the relative input energy required for formation is injected, most of the dots have already been connected (II in FIG. 10b).

When printing for the first primary color is completed, the microcomputer 17 moves the print head 6 to the platen 5.
Then, the conveyance roller 8 is reversed to reset the recording paper to the printing start position, and the ink sheet take-up reel 11 is rotated to form a gap between the two.
Move the ink area of color to the print head. At the stage where the preparation is completed, printing for the second color is executed in the same process as the printing for the first color described above.

By repeating this process for the third color, dots are formed by separating the colors of each pixel, and the desired color can be printed. In this embodiment, dots are formed every other column, but dots are formed every three digits while sequentially shifting line by line, as shown in the hatched area in FIG. It is clear that the same effect can be achieved.

FIG. 12 shows a second embodiment of the present invention using the functions performed by a microcomputer. In the figure, reference numeral 31 denotes image data reading means, which reads one page of image data stored in the image memory 30. to N lines (N>1 integer)
In this embodiment, image data for two lines is extracted while being moved by N lines and output to the line buffer 32. 33 is a sampling means that samples N digits (N>1 integer) from the image data stored in the line buffer 32 in the main scanning direction, that is, N×N dots;
In this example, 2×2 pixel areas S1, S2, S3, S
4... is sampled and output to the pixel extraction means 34. 34 is the above-mentioned pixel extraction means, and for each pixel L1, L2, L3, L4 of the sampling area stored in the evaluation data storage means 35 (FIG. 13), the pixel L
1, the lowest density a1, e.g. "0", and the adjacent pixel L2, the highest density a2, e.g. "11".
The pixel L3 located directly below the lowest density has the second highest density a3, for example, "10", and the diagonally downward pixel L4 exists in a state independent from the pixel L1 that is always involved in dot formation. is the second lowest concentration a4, for example “2
” as the threshold value is set as the evaluation data storage means 35.
(FIG. 14b), it is configured to output only the image data exceeding the threshold value to the print buffer 36.

In this embodiment, when image data is output from an external device such as a personal computer and data for one page is stored in the image memory 30, the image data reading means 31 reads out the first two lines. and stores it in the line buffer 32. Of the read image data,
2×2 image data D1 of first sampling area S1
1, D12, D21, and D22 are evaluation data storage means 35
compared to the threshold. For example, when image data with gradation as shown in FIG. 15 is output, image data D exceeding the threshold value for this sampling area S1
Only 11 are output to the print buffer 36.

Next, the sampling means 33 extracts image data D13, D14, D23 from the next sampling area S2.
, D24 are read out and compared with the threshold value of the evaluation data storage means 35 in the same manner as described above. In this case, since the density of the image data D13 and D24 exceeds the threshold value, only the image data D13 and D24 are output to the print buffer 36. Thereafter, only data exceeding the threshold value is output to the print buffer 36 while sequentially moving the sampling area. As a result, one of the adjacent dots among the data existing on the same line is thinned out, as shown in FIG.
Tsuoki images D11, D13, D15, D17, D19
, and approximately every other pixel D24, D25, D26, D
Only 28 will be extracted.

When the extraction of print data from two lines of image data is completed, the microcomputer 17
The image data stored in the print buffer 36 is output to the print head drive circuit 23 via the interface 22. As a result, as described above, every other heating resistor element of the print head 6 is activated for the first line, so that even if the heating resistor element that is the target of dot formation is high-density data as described above, It is possible to express sufficient gradation. When the printing of the first line is completed in this way, the microcomputer 17 drives the pulse motor to feed the recording paper 1 and the ink sheet 9 by one line.
Next, data for the second line is printed from the print buffer 36 in the same manner.

When two lines of printing have been completed, the next two lines, that is, the third and fourth lines, are read out from the image memory 30, and the threshold value is determined by sampling each 2×2 pixel as described above. Only the image data exceeding the threshold value is output to the print buffer 36 and printed.

In this embodiment, by changing the data stored in the evaluation data storage means, it is possible to determine the image data to be thinned out in accordance with the density of the image data, so that high-density dots can be reliably expressed in density. In addition, it is possible to prevent the omission of adjacent high-density image data and perform printing faithful to the input image data.

[0032] In this embodiment, an area of 2 x 2 pixels is evaluated, but it is clear that the same effect can be obtained even if an area of 3 x 3 pixels or more is evaluated. Yes, and rectangular matrix N×M(N>
1, an integer of M>1), it is clear that the same effect can be achieved even if sampling and evaluation are performed.

In addition, in this embodiment, the threshold density of the evaluation data is set to "0", "11", "10", and "2", but if we take, for example, 2×2, the threshold density Setting two of the densities to a value that allows extraction of the highest density, for example "11", will reduce the pixel density to 1/2, and setting three to the maximum density of "11" will reduce the pixel density to 1/4. By changing the evaluation data for intermediate densities in various ways, it is possible to set the optimum printing condition according to the original image data and the quality of the recording paper.

FIG. 17 shows a third embodiment of the present invention using the functions performed by a microcomputer. In the figure, reference numeral 41 denotes image data reading means, which reads one page of image data stored in the image memory 40. to N lines (N>1 integer)
In this embodiment, two lines of image data are continuously extracted while being moved by N lines and output to the line buffer 42. 43 is a sampling means that samples N digits (N>1 integer) from the image data stored in the line buffer 42 in the main scanning direction, that is, N×N.
dots, in this example 2×2 pixel areas S1, S2,
S3, S4, etc. are sampled and output to the gradation determining means 44. Reference numeral 44 denotes the above-mentioned gradation determining means for each pixel L1, L2, L3, L4 of the sampling area stored in the evaluation data storage means 45 (FIG. 14a).
), the pixel L1 has a density a1 of, for example, "0", and the adjacent pixel L2 has the highest density a2, for example, "11".
The second highest density a3, for example "10", is applied to the pixel L3 located immediately below the lowest density, and the diagonally downward pixel L4, which is located independently from the pixel L1 that is always involved in dot formation, For example, the second lowest density a4, for example "2", is compared with the data in the evaluation data storage means 45 (FIG. 14b) set as the threshold value, and only image data exceeding the threshold value is extracted. The gradation of data below the threshold is added to the data above the threshold and output to the print buffer 46.

In this embodiment, when image data is output from an external device such as a personal computer and data for one page is stored in the image memory 40, the image data reading means 41 reads out the first two lines. and stored in the line buffer 42. Among the read data, data D11 for 2×2 pixels of the first sampling area S1,
D12, D21, and D22 are compared with the threshold values of the evaluation data storage means 45. For example, when image data with gradations as shown in FIG. Data "2""2""2" is the data D to be printed
The density "2" of the data D11 is added to the density "2" of the data D11, and the data D11 is finally outputted to the print buffer 46 as a density "8".

Next, the sampling means 43 extracts data D13, D14, D23, D from the next sampling area S2.
24 is read out and compared with the threshold value of the evaluation data storage means in the same manner as described above. In this case, since the density of D13 and D24 exceeds the threshold, the pixel D below the threshold
The densities "11" and "9" of 14 and D23 are respectively pixel D1
3. It is added to the density “12” and “3” of D24, and the data D
13 is corrected to the density "22", and data D24 is corrected to the density "13" and output to the print buffer 46. Next, the sampling means 43 extracts data D15, D16, D25, D26 from the next sampling area S3.
is read out and compared with the threshold value of the evaluation data storage means 45 using the same process as described above. In this case, the density of data D15, D25, and D26 exceeds the threshold value, so the density of pixel D16 that is below the threshold value is "6", and the density of pixels D15, D25, and D26 is "2", "11", and "7". '', data D15 is corrected to density "4," data D25 is corrected to density "13," data D26 is corrected to density "9," and output to the print buffer 46.

Thereafter, while sequentially moving the sampling area, the density of data exceeding the threshold value is added to the density of data below the threshold value, and the resultant data is output to the print buffer 46. As a result, as shown in FIG. 18, among the data existing on the same line, one of the adjacent pixels is thinned out, and almost every other pixel D11, D13, D15, D17, D
19, and approximately every other pixel D24, D25, D26
, D28 are extracted, and the density of the thinned out pixels is added to these data.

When the extraction of print data from two lines of image data is completed, the microcomputer 17
The data stored in the print buffer 46 is output to the print head drive circuit 23 via the interface 22. As a result, as described above, every other heating resistor element of the print head 6 is activated for the first line, so that the heating resistor element that is the object of dot formation can faithfully reproduce the density even with high density image data as described above. is reproduced, and as a result, the gradation can be expressed as a whole. When the printing of the first line is completed in this way, the microcomputer 17 drives the pulse motor to feed the recording paper 1 and the ink sheet 9 by one line, and then prints the data of the second line from the print buffer 46. .

When two lines of printing have been completed, the next two lines, that is, the third and fourth lines, are read out from the image memory 40, and the threshold value is determined by sampling each 2×2 pixel as described above. The density of the pixel to be thinned out is added to the image data exceeding the threshold value, and the result is output to the print buffer 46 for printing.

In this embodiment, the pixels to be thinned out are determined in accordance with the density of each pixel constituting the image data, and the density of the pixels to be thinned out can be reflected in the density of the pixels to be printed. In addition to being able to reliably express gradation of high-density dots, it is also possible to prevent adjacent high-density pixels from being omitted, allowing for printing that is more faithful to the input image data. In addition, since the size of the printed dots inevitably increases, it is possible to form dots with sufficient density even on recording paper of poor quality, and it is possible to improve the quality of printing. .

[0041] In this embodiment, an area of 2 x 2 pixels is evaluated, but it is clear that the same effect can be obtained even if an area of 3 x 3 pixels or more is evaluated. Yes, and rectangular matrix N×M(N>
1, an integer of M>1), it is clear that the same effect can be achieved even if sampling and evaluation are performed.

Furthermore, in this embodiment, the density of the image data not involved in dot formation is equally distributed to the image data involved in dot formation, but the density is distributed in inverse proportion to the threshold value of the evaluation data. You may also do so. In addition, by multiplying the extracted data by approximately the reciprocal of the extraction rate for each matrix or line, it is possible to prevent the overall density from decreasing due to thinning of the image data.

In the above embodiment, image data at a specific position is extracted from the sampled image data, but as shown below, the density of the sampled dots is converted in accordance with a specific characteristic curve. A similar effect can be obtained by doing so.

FIG. 19 shows an example in which γ conversion means is used in place of the pixel extraction means 44 and the evaluation data storage means 45 in the third embodiment, and the image memory 40, image data reading means 41, line buffer 42, The step of sampling the image data to be evaluated by the sampling means 43 is performed in the same manner as in the case described above. The γ conversion means 47 converts the sampled data D11 and D12 of the 2×2 pixel area S1 as shown in FIG.
, D21, D22 are converted into printing data using conversion characteristic function γ1, conversion characteristic function γ2, conversion characteristic function γ3, and conversion characteristic function γ4, and data D13, D1 of area S2 are
4, D23, and D24 respectively as conversion characteristic function γ1, conversion characteristic function γ2, conversion characteristic function γ3, and conversion characteristic function γ4.
The conversion characteristic is uniquely determined in accordance with the position of the dot data within the sampled area, such that the dot data is converted into print data by the following.

FIG. 21 shows an example of the γ characteristic set in the above-mentioned γ conversion means 47, and the conversion characteristic function γ1 is a conversion print corresponding to sufficiently high electrical energy with respect to the image data value. It has a conversion characteristic that changes approximately linearly with data Db being the maximum value, and the characteristic is such that when the image data value is the maximum value allowed by the heating resistor element, the converted print data Da is the same as the image data value. It is set. The conversion characteristic function γ4 has a substantially linear conversion characteristic with the maximum value being Da. Further, the conversion characteristic function γ2 and the conversion characteristic function γ3 output converted print data Da that is substantially the same as the image data only when the image data value is the highest density value,
It has a characteristic of outputting substantially zero converted print data when the density is lower than the maximum density value.

In this embodiment, the image data D11 of the sampled area S1 is converted into converted print data that is linearly proportional to the image data D11 by the conversion characteristic function γ1 characteristic of the γ conversion means 47, and the image data D12 is converted into converted print data that is linearly proportional to the image data D11. Due to the characteristic function γ2, the concentration D is increased only when the concentration is at its highest value.
a is converted into converted print data whose density is otherwise substantially zero. Furthermore, the image data D21 is
Similar to the image data D12 described above, the density Da is converted to converted print data only when the density is the highest value, and the density is substantially zero otherwise. Image data D22
is converted into almost linearly proportional conversion print data so that the highest density is Da. As a result, image data D1
Both 2D and 22 will be substantially thinned out.

When the two lines of image data have been converted into print data, the microcomputer 17 outputs the print data stored in the print buffer 46 to the print head drive circuit 23 via the interface 22. As a result, as mentioned above, for the first line, every other heating resistor element of the print head 6 operates with the conversion output indicated by the conversion characteristic function γ1, and even if the dot data is of high density, the electric current is sufficiently high. It receives energy and faithfully reproduces the density commanded by image data. Furthermore, the image data with the highest density is converted print data Da for both the conversion characteristic function γ1 and the conversion characteristic function γ4, and the conversion characteristic function γ2,
γ3 also becomes Da, forming continuous dots and reproducing a pattern with maximum density and high resolution.

When the printing of the first line is completed, the microcomputer 17 drives the pulse motor to feed the recording paper 1 and the ink sheet 9 by one line, and then prints the second line stored in the print buffer 46. The data is output to the print head drive circuit 23 to perform printing. In printing the second line, since the conversion characteristic function γ3 is set for the image data D21 of the sampled area S1, unless it is the highest density, it is substantially thinned out.
Furthermore, since the conversion characteristic function γ4 is set for the image data D22, the image data D22 is printed with a density proportional to the supplied electrical energy. As a result, the dot D printed on the second line
22 is printed at a position shifted one dot diagonally from the dot D11 printed on the first line. Therefore, dots can be formed by operating the heating resistor element corresponding to the image data D22 to its full capacity. Furthermore, for an extremely high density image area where all dots in the sampling area S have the highest density, all the sampled image data is to be printed, so the converted print data Da is output and the gradation is and the average concentration will be faithfully reproduced.

When printing for two lines is completed, the image data for the next two lines, that is, the third and fourth lines, is read out from the image memory 40 and sampled for each 2×2 pixel as described above. Perform γ conversion and print buffer 4
After outputting to step 6, print is executed.

In this embodiment, the conversion characteristic function γ1 is dominant in most areas, and the conversion characteristic function γ4 has an auxiliary function, so that for average image data, the sampling area 2
Among the ×2 dots, the number of pixels having the characteristic of the conversion characteristic function γ1 increases, and the actual number of pixels becomes 1/4 to 2/4. By the way, as mentioned above, the conversion characteristic function γ1 functions to supply about three times as much electrical energy to the heating resistor element as compared to the case of normal driving, so the ink on the ink ribbon can be reliably dissolved and recording It has the advantage of being less susceptible to variations in conditions such as paper quality. In addition, in the highest density part of the image data, there is a lot of data such as characters that need to be printed at high resolution, so all pixels in the 2 x 2 sampling area are set to the same density Da as the image data. There is.

FIG. 22 shows that the maximum converted print data is set to Dd lower than the above embodiment as the conversion characteristic function γ1,
Further, as the conversion characteristic function γ4, the supplied electric energy for the maximum conversion print data is set to Dc, which is higher than Da. According to this embodiment, in most areas, the pixel , it is possible to print at a higher resolution than in the above-described embodiments.

The γ conversion characteristics shown in FIG. 23 reduce the maximum converted print data to De even more than in the above-mentioned embodiment, but on the other hand, the dot sizes are determined at the same rate for the conversion characteristic function γ1 and the conversion characteristic function γ4. In addition, the conversion characteristic function γ2 and the conversion characteristic function γ3 have a characteristic of outputting the converted print data Da only when the image data shows the maximum value, and according to this embodiment, the conversion characteristic function γ2 and the conversion characteristic function γ3 are Dots are formed according to the characteristics of γ1 and conversion characteristic function γ4, and approximately half of the image data is to be printed. Therefore, when recording paper with excellent transfer characteristics is used, resolution can be further improved.

The γ conversion characteristic shown in FIG. 24 has a steep rise characteristic in the low density area of the image data, and only the conversion characteristic function γ1 set in the converted print data Df, that is, one pixel in the sampling area 2×2, has a steep rise characteristic. to be printed only,
When image data with a density higher than this is input, the conversion characteristic function γ4 in which the maximum dot size Dh is set is also taken into account when printing is performed. According to this embodiment, since the conversion characteristic function γ1 sets a characteristic in which the dot size is large compared to the density value of the image data in the low density region, stable transfer characteristics are exhibited.

The conversion characteristic function γ shown in FIG. 25 targets only one dot for printing when the density value of image data is low, while the conversion characteristic function γ shown in FIG. Since the proportional coefficient of the converted print data is set small, low density areas and high density areas have rich gradation characteristics, and in other intermediate gradation areas, the gradation is faithful to the density of the image data. characteristics can be obtained.

FIG. 26 shows another embodiment of the conversion characteristic function γ set in the γ conversion means 47, and the conversion characteristic function γ1 is such that no transfer dots are initially formed with respect to the image data value. It has a substantially linear characteristic in which the minimum value is the converted printing data Dk of the intermediate density area, and the maximum value is the converted printing data Dh, which is a sufficiently high supply electric energy for image data values in the intermediate density area. It has a characteristic that the converted print data Dh is maintained from the area to the high density area, and the converted print data Di is close to the image data in the highest density area.

The conversion characteristic function γ2 has a characteristic that the converted print data Dk is such that no transfer dots are formed in almost the entire area, and the converted print data Dj is close to the image data near the maximum density value.

Similar to the conversion characteristic function γ2, the conversion characteristic function γ3 is converted print data Dk that does not form transfer dots in almost the entire area, and converted print data Dj that is close to image data in the highest density area and its vicinity, or It has characteristics similar to Dj.

The conversion characteristic function γ4 takes the converted print data Dk at which no transfer dots are initially formed in the low density area of the image data as the minimum value, and rapidly rises to the converted print data Dj at which sufficient transfer dots can be formed. , after that, the value is maintained until the medium density area, and is changed almost linearly from the medium density area to the high density area so that it becomes the maximum converted print data Dh, and then the converted print data close to the density of the image data is changed in the highest density area. It has a conversion characteristic of Di.

According to this embodiment, since sufficiently high electrical energy is supplied to the image data by the conversion characteristic function γ4 at the beginning of printing, a large and stable transfer dot is formed, and the conversion characteristic function changes in the medium density region. γ1
The density increases smoothly with the transfer dots formed by the conversion characteristic function γ4 in the high density region.
The density is further increased while maintaining smoothness using the transfer dots formed by the process. In the vicinity of the highest density, dots based on the conversion characteristic function γ3 are added to increase the density, and in the highest density region, the converted printing data Di according to the conversion characteristic functions γ1 and γ4 and the converted printing characteristic Dj according to the conversion characteristic functions γ2 and γ3 are added, respectively. Transfer dots are formed. As a result, transfer dots are always stably formed in the entire area.

Furthermore, since the conversion characteristic functions γ1, γ2, γ3, and γ4 with different converted print data are applied to the same image data, the mutual interference of heating elements forming adjacent dots is reduced, and the input It is possible to form transfer dots that exhibit gradation faithful to print data.

As shown in FIG. 27, by setting one conversion characteristic function γ1 so that the conversion print data is gentle compared to the density of the image data, the gradation in the medium density region can be improved. Can be selectively enhanced.

Although seven typical types of conversion characteristic functions γ have been described above, it is clear that optimal printing results can be obtained by selecting the γ characteristics according to the printing object. That is, when printing with emphasis on high gradation, one conversion characteristic function γ1 may be set to have a steep characteristic, and the other conversion characteristic function γ4 may have a small slope. In addition, if it is desired to print with emphasis on high resolution, the conversion characteristic function γ4 may be set close to the conversion characteristic function γ1, or the conversion characteristic function γ2 or γ3 may be set loosely. Furthermore, by setting conversion print data that can supply electrical energy to the heating element to the extent that transfer dots are not formed even when there is no image data, thermal stability of the heating element during printing can be ensured. Transfer dots can be stably formed.

Furthermore, by supplying conversion print data whose supplied electrical energy is sufficiently higher than that of the image data to one of the conversion characteristic functions γ in the low density region of the image data, low density transfer that is likely to cause transfer defects can be achieved. Dots can be formed with stable gradation.

That is, by appropriately selecting the size and slope of the maximum and minimum values to be set in the print conversion data in accordance with the image to be printed and the type of paper to be printed,
Optimal gradation characteristics can be obtained.

In the above embodiment, for convenience of explanation, 1
28 (I) (II) (III) (IV
), conversion characteristic functions γ1, γ2, γ3 as shown in FIG. , γ4, and for magenta, the conversion characteristic function γ as shown in (II) of the same figure.
1, γ2, γ3, γ4 in the same figure for cyan (II
Conversion characteristic functions γ1, γ2, γ3, γ4 as shown in I)
Furthermore, for black, the conversion characteristic functions γ1, γ2, γ3, γ4 as shown in the same figure (IV),
By varying the allocation positions of the conversion characteristic functions γ1, γ2, γ3, and γ4, it is possible to obtain an effect similar to that of the halftone technique in so-called ordinary color printing, and colors can be reproduced clearly.

That is, an area S of N digits (N>1 integer) in the main scanning direction from the image data stored in the line buffer 32, that is, an area S of N×N dots, for example, 2×2 pixels.
1, S2, S3, S4..., when sampling and printing data D11, D12, which constitutes area S1,
In D21 and D22, data D1 for yellow
1, conversion characteristic function γ1 to data D12, conversion characteristic function γ2 to data D21, conversion characteristic function γ3 to data D22.
For the other color magenta, the conversion characteristic function γ3 is made to correspond to the data D11, and the conversion characteristic function γ3 is made to correspond to the data D11.
The positions of the data to which the conversion characteristics are assigned to each color of ink are made to differ, such as making the conversion characteristic function γ1 correspond to the data D21, the conversion characteristic function γ4 to the data D22, and the conversion characteristic function γ2 to the data D22. This makes it possible to prevent dots formed by inks of different colors from overlapping, thereby enabling clear color printing.

In this embodiment, the case where the sampling area is set to 2×2 dots has been described, but it is obvious that the invention can be applied to any size.

[0068]

[Effects of the Invention] As explained above, in the present invention,
A print head consisting of a plurality of heat-generating resistive elements arranged in a line, means for conveying recording paper and ink sheets at a predetermined pitch, and extracting pixel data constituting input image data with digits spaced apart. Since the extraction means and the means for supplying electric energy corresponding to the density specified by the pixel data to the heat generating resistive element of the print head in correspondence with the extraction pitch, the image data inputted from the outside can be In order to extract image data at intervals of at least one pixel in the scanning direction and prevent thermal interference from adjacent heating resistive elements, the dot size is larger than the maximum density of the input image data. It operates faithfully to the electrical energy that generates dots of the same size, and as a result, it is possible to express density in more stages than conventional devices. As a result, sufficient gradation expression and color reproduction can be achieved even if the sampling area is made small, and the number of dither processing steps can be reduced to shorten image data processing time and to prevent the occurrence of texture noise.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the configuration of a thermal transfer printing device of the present invention.

FIG. 2 is a front view of an example of a print head used in the present invention, with a surface coating layer removed to expose electrode portions.

FIG. 3 is a block diagram showing an embodiment of a control device in the apparatus shown in FIG. 1;

FIG. 4 is a diagram showing signals from a thermal transfer print head drive circuit in the same device.

FIG. 5 is a block diagram mainly illustrating functions realized by a microcomputer that constitutes the control device.

FIG. 6 is a schematic diagram showing image data and data supplied to the print head, where (I) and (I') respectively represent image data of odd lines and data supplied to the print head; (II) and (II') indicate image data of even lines and data supplied to the print head, respectively.

FIG. 7 is a schematic diagram illustrating the ink melting temperature range of the heat generating resistive elements constituting the print head, and FIG. , and FIG. 6(b) is a diagram showing a case where adjacent heating resistive elements are activated.

FIG. 8 is a diagram showing the relationship between relative input energy and dot size when printed by the apparatus shown in FIG. 1;

FIG. 9 is a diagram schematically showing a printing area by the same device.

FIG. 10(a) is an enlarged view schematically showing dots printed by the apparatus of the present invention, and FIG.
b) is an enlarged diagram schematically showing dots printed by a conventional device;

11 is a diagram schematically showing another printing form by the apparatus shown in FIG. 1. FIG.

FIG. 12 is a block diagram showing a second embodiment of the present invention by functions of a microcomputer that constitutes a control device.

FIG. 13 is a diagram schematically showing an example of data sampling in the second embodiment.

FIG. 14(a) is a diagram showing the data structure of the evaluation data storage means in the second embodiment, and FIG.
) is a diagram showing an example of data.

FIG. 15 is a diagram schematically showing image data stored in a line buffer in the second embodiment.

FIG. 16 is a schematic diagram showing an example of image data extracted from image data stored in a line buffer and stored in a print buffer in the second embodiment.

FIG. 17 is a block diagram showing a third embodiment of the present invention by functions of a microcomputer that constitutes a control device.

FIG. 18 is a diagram schematically showing an example of image data for printing created from input image data in the third embodiment.

FIG. 19 is a block diagram showing a fourth embodiment of the present invention by functions of a microcomputer that constitutes a control device.

FIG. 20 is a diagram showing the relationship between data sampling formats and γ conversion for each sampled pixel data in the fourth example.

FIG. 21 is a diagram showing an example of γ conversion characteristics applied to the present invention.

FIG. 22 is a diagram showing an example of γ conversion characteristics applied to the present invention.

FIG. 23 is a diagram showing an example of γ conversion characteristics applied to the present invention.

FIG. 24 is a diagram showing an example of γ conversion characteristics applied to the present invention.

FIG. 25 is a diagram showing an example of γ conversion characteristics applied to the present invention.

FIG. 26 is a diagram showing an example of γ conversion characteristics applied to the present invention.

FIG. 27 is a diagram showing an example of γ conversion characteristics applied to the present invention.

28 is a schematic diagram showing an example of the allocation of each conversion characteristic function γ in full-color printing using the γ conversion characteristics shown in FIGS. 26 and 27. FIG.

[Explanation of symbols]

2　Stacker 3 Pick up roller 4 Paper feeding mechanism 5 Platen 6 Thermal transfer print head 9 Ink sheet 12 Circuit board 14, 14 Heat generating resistor element 15, 16 Lead wire 17 Microcomputer

Claims (15)

[Claims] 1. A print head comprising a plurality of heating resistive elements arranged in a line, means for conveying recording paper and ink sheets at a predetermined pitch, and a means for conveying pixel data constituting input image data in digits. an extraction means for opening and extracting;
A thermal transfer type image forming apparatus comprising means for supplying electrical energy corresponding to a density defined by pixel data to a heating resistor element of a print head in a manner corresponding to the extraction pitch. 2. The thermal transfer image forming apparatus according to claim 1, further comprising gradation determining means for allocating image data excluded by the extracting means to extracted image data. 3. The thermal transfer image forming apparatus according to claim 1, wherein said extraction means extracts at least pixel data of a digit different from the previous extraction digit. 4. A print head comprising a plurality of heat generating resistive elements arranged in a line, a means for conveying recording paper and an ink sheet at a predetermined pitch, and a plurality of pixel data constituting input image data. means for continuously extracting lines, and image data for the plurality of lines N×M (M>1);
, an integer of N>1) dots, and a reference density determined as a matrix of N×M (M>1, an integer of N>1) dots is compared with the sampling data. A thermal transfer image forming apparatus comprising an extracting means for extracting image data exceeding a reference density, and a means for supplying electrical energy corresponding to the density of the extracted image data to a heating resistor element of a print head. 5. A print head formed by arranging a plurality of heat generating resistive elements in a line, means for conveying recording paper and ink sheets at a predetermined pitch, and a plurality of pixel data constituting input image data. means for continuously extracting lines, and image data for the plurality of lines N×M (M>1);
, an integer of N>1) dots, and a reference density determined as a matrix of N×M (M>1, an integer of N>1) dots is compared with the sampling data. gradation determining means for extracting image data exceeding a reference density and distributing the density of image data below the reference density to the extracted image data;
A thermal transfer type image forming apparatus comprising means for supplying electrical energy corresponding to the gradation-determined density of the extracted image data to a heating resistor element of a print head. 6. A print head formed by arranging a plurality of heat generating resistive elements in a line, means for conveying recording paper and ink sheets at a predetermined pitch, and a plurality of pixel data constituting input image data. means for continuously extracting lines, and image data for the plurality of lines N×M (M>1);
, an integer with N>1) dots in the form of a matrix, and γ converting each dot of N×M (an integer with M>1, N>1) dots to output printing data. A thermal transfer image forming apparatus comprising a converting means and a means for supplying electrical energy corresponding to printing data to a heating resistor element of a print head. 7. The thermal transfer image forming apparatus according to claim 6, wherein said γ conversion means includes a plurality of types of conversion characteristic functions for each dot in said sampling area. 8. The thermal transfer method according to claim 6, wherein the γ conversion means includes a conversion characteristic function that outputs density data substantially proportional to the density of a binary characteristic for at least one of the sampled image data. Image forming device. 9. The γ conversion means generates a conversion characteristic function for outputting density data for forming a dot expressing a density higher than a density defined by the image data for at least one of the sampled image data. 7. The thermal transfer image forming apparatus according to claim 6. 10. The thermal transfer image forming apparatus according to claim 6, wherein said γ conversion means includes a conversion characteristic function that outputs data for forming transfer dots of substantially different sizes in a medium density region. 11. The thermal transfer image forming apparatus according to claim 6, wherein said γ conversion means includes a conversion characteristic function that outputs density data substantially the same as image data in the highest density region. 12. The thermal transfer image forming apparatus according to claim 6, wherein said γ conversion means includes a conversion characteristic function that outputs density data different from image data in the highest density region. 13. The γ conversion characteristic is a conversion characteristic function that outputs density data from a low density region that is substantially the same as a maximum value defined in the image data for at least one of the sampled image data. 7. The thermal transfer image forming apparatus according to claim 6. 14. The thermal transfer image forming apparatus according to claim 6, wherein said γ conversion means includes a conversion characteristic function whose minimum value is such that no transfer dots are formed. 15. The thermal transfer image forming apparatus according to claim 6, wherein said γ conversion means assigns different conversion characteristic functions for each ink color to a plurality of image data to be printed.