JPH0661953B2 - Image printing method and image printing apparatus - Google Patents

Description

The present invention relates to an image printing apparatus that prints (hardcopy) television images, computer-generated graphic images, and the like.

[Conventional technology]

FIG. 6 is a schematic diagram of an example of a conventional image printing apparatus. In the figure, 101 is an input terminal for an image signal, 102 is an input terminal for a synchronizing signal such as vertical and horizontal, 103 is an A / D converting means for an image signal, 104 is a digital image memory means, and 105 is a white image data. Density conversion means necessary to obtain a print density gradation corresponding to a change from black to black, 10
7 is a counter that generates a clock for obtaining a desired operation in synchronization with a synchronization signal and a signal required for each circuit,
A system control means by a gate circuit or the like, 106 a comparator for comparing the data C5 converted by the density conversion means 105 and the output C4 of the counter in the system control means 107, 108 a thermal head, and the running of the image receiving paper. The printer is composed of a mechanism section mainly composed of means and the like.

Next, the operation will be described.

For example, 6-bit quantization is performed by the A / D conversion unit 103 from the reference black level to the reference white level of the image signal that is applied to the input terminal 101 and that consists of the luminance component of the NTSC television signal, for example. Next, the quantized image data is written in the image memory 104 in order from the previously designated address. At this time, assuming that the sampling data of one horizontal scanning line is 640 and one frame is composed of 480 horizontal scanning lines, the memory capacity is 640 (H) × 480 (V) × 6 bits≈1.8. It will be about Mbit. The image data of one frame written in the image memory 104 is read out in a predetermined order, and the density conversion means 105 makes the printing density on the image receiving paper a linear gradation of 6 bits and 64 gradations. Is converted into, for example, 8-bit time axis data. Further, the system control means 107
It has a counter that represents an 8-bit time for counting 256 within the printing time of one scanning line, and the output C of this counter
A comparator 106 compares the density-converted data C5 with the comparison data C6, and the comparison data C6 determines whether or not the thermal head of the printer 108 is turned on / off to perform printing.

FIG. 7 is a diagram showing a configuration of the thermal head and an example of driving the head. The thermal head is composed of, for example, 640 resistors, but if all of the 640 resistors are turned on / off at once, there is a problem that the electric power becomes too large. Therefore, the thermal head is divided into several blocks. Print each block in turn. Here, consider a case where the thermal head is composed of five blocks B1 to B5. 12 resistors for each block
Eight. 64 from one scanning line from the image memory 104
0 data is read while the 8-bit counter output C4 counts 1. The data group is the density conversion means 105.
Is converted into 8-bit time axis data, and sequentially compared with the data C4 by the comparator 106. At this time, C4 ≧ C
At "5", the "L" signal to turn off the thermal head is sent to C6.
An "H" signal that turns on at <C5 is output. This process is continuously executed for all group data, and the printer 10
The C6 signal is sent to the register in the thermal head 8 of FIG. 8 together with the transfer clock in the signal C7 for temporary storage. Then, division driving signals for each block of the thermal head during signal C7 by time _{T 1, T 2, T 3} , T 4, T 5 section by sequentially turning on operation, Shirushiutsushi 1/256 of N scanning lines I do.
Since the printing of "0" (address) of the signal C4 is finished, the image data group of N scanning lines is read again from the image memory 104, and the density conversion means 105 converts the image data group into the time axis data group C5 in order and updates it. The on / off signal C of the resistor is compared by the comparator 106 with the "1" of the generated C4 signal.
6 are sequentially generated. Thereafter, the same operation as that of the address "0" is executed to finish the printing of the address "1" of the signal C4. This operation is continuously repeated up to 255 to complete printing of N scanning lines. Subsequently, the same operation of N scanning lines is repeated for (N + 1) scanning lines, and printing is continuously executed for 480 scanning lines to obtain one hard copy image.

At this time, the mechanical portion of the printer 108 intermittently or continuously feeds the image receiving paper, and controls the traveling so that the aspect ratio of one screen becomes 3 to 4 of the NTSC standard screen ratio. The system control means 107 uses the synchronization signal input to the input terminal 102 and the internally generated clock signal to
A / D conversion clock signal C1, address signal and read /
Control signal C of the image memory 104 including a write signal
2, a clock signal C3 required for density conversion, an output C8 of a counter representing time lapse of 8 bits, a clock signal C7 required for operation of the thermal head, a signal C8 required for sequence control of the mechanical section, and the like. Let With the above configuration and operation, a 64-tone black-and-white hard copy image of a desired image can be obtained.

[Problems to be solved by the invention]

Since the conventional image printing apparatus is configured as described above, thermal history density unevenness occurs between adjacent pixels in the paper feeding direction of the printing paper. In the case of low-density printing, the thermal head-on section is concentrated toward the beginning of the one-pixel printing, resulting in a visually rough printing state. There was a problem of degrading image quality.

The present invention has been made to solve the above-mentioned problems, and the printing rate between pixels arranged in the sub-scanning direction,
That is, it is possible to reduce the adverse effect of thermal history density unevenness between adjacent pixels due to the proportion of the printing area in each pixel in the sub-scanning direction, and further, especially in the case of printing low-density image data, a hard copy image. To improve the visually rough printing state that appears as a result because the section in which the thermal head is turned on in the paper feed direction, that is, the sub-scanning direction is concentrated at the beginning of one pixel printing. An object of the present invention is to obtain an image printing method and an image printing apparatus capable of performing the above.

[Means for solving problems]

The image printing method according to the present invention, by controlling the heat generation time of each resistor provided in the thermal head, each pixel, a hard copy image having a multi-tone density corresponding to the original image,
In the method of printing on a recording medium that moves with respect to the thermal head, a plurality of portions of each pixel except for both ends in the sub-scanning direction, that is, the moving direction of the recording medium serve as the pixel center, and The heating time of each resistor is controlled so that the printing area of each pixel expands around the pixel center as the corresponding multi-tone density value increases.

An image printing apparatus according to the present invention includes a thermal head having a plurality of resistors and a recording medium that moves relative to the thermal head, and each pixel is controlled by controlling the heating time of each resistor. In a device for printing a hard copy image having multi-tone density corresponding to an image on the recording medium,
Print data corresponding to the multi-tone density and data comparison means for comparing control data for controlling the heat generation time, and control means for controlling the heat generation time based on the comparison result, At the time of printing due to heat generation of the resistor of each pixel, the printing area is centered on a portion corresponding to a plurality of intermediate times between the start time and the end time, excluding the portions corresponding to the start time and the end time. A control data creating means for creating the above control data is provided so as to spread.

[Action]

According to the present invention, the printing area of each pixel is enlarged around the pixel center as the multi-tone density value corresponding to each pixel is increased. It is possible to reduce the adverse effect of thermal history density unevenness between adjacent pixels due to the printing rate, that is, the ratio of the printing area in each pixel in the paper feed direction (sub-scanning direction).

In addition, since the center position when the printing area expands in accordance with the increase in the density level as described above, that is, the pixel centers are located at a plurality of locations in one pixel, the low density printing is performed. The picture part will be dispersed and located in one pixel,
As a result, the thermal head in the sub-scanning direction of the hard copy image becomes O when the image data of low density is printed.
Since the section of N is concentrated at the beginning with respect to the printing of one pixel, it is possible to improve the resulting visually rough printing state.

〔Example〕

 Examples of the present invention will be described below.

FIG. 1 is a diagram showing a block configuration of an image printing apparatus according to a first embodiment of the present invention, and FIGS. 2 and 3 are diagrams for explaining the operation thereof.

In the figure, reference numeral 1 indicates the total printing time of one scanning line in the system control means 107, for example, 256 counts of 8 bits, and the output signal C4 of the counter showing the elapsed time of printing within one scanning line is another. It is an address converting means for converting into data, and the data (control data) C10 and the data (printing data) C5 converted by the address converting means 1 are compared by a comparator 106, and a head on / off signal C
6

Here, the converted data C10, as shown in FIGS. 2B and 2C, corresponds to the start time and end time of each pixel when printing is performed by heat generation of the resistor. Except for the part, the two intermediate times between the start and end times, that is, the part corresponding to the address "0" or "1" as shown in FIGS. In FIG. (C), the printing area is created so as to expand centering on a plurality of parts of addresses "0" and "1". The other structure is the same as the conventional one.

Next, the function and effect will be described.

As shown in the conventional example, the quantization of this image printing apparatus is 6
C4 is the output of the 8-bit counter. However, here, in order to simplify the explanation, it is assumed that the quantized 2-bit counter and C4 are 4-bit counters. C4 is a value that monotonically increases from 0 to 15 for each printing of one scanning line, as shown in FIG.

Here, for example, when the counter output C4 is converted by the address conversion means 1 as shown in FIG. 2B, when the converted data C10 is C10 <C5, the head is turned on. In the past, since the ON / OFF signal was determined by comparison with a monotonically increasing counter, the printing was gathered at the beginning of one line. In this case, after the conversion of FIG. As can be seen in, there is an OFF signal at the beginning and end of one line, so a cooling period is provided between dots (pixels), and the next dot with the highest density as shown in Fig. 3 also has a cooling period. Therefore, it is possible to avoid thermal history density unevenness in the sub-scanning direction, that is, in the moving direction of the recording medium. In the case of continuous printing with the highest density shown in FIG. 3, there is no cooling period between dots, and thermal history density unevenness exists, but in other cases, the unevenness does not appear,
Has been greatly improved.

However, in the case of the address conversion shown in FIG. 2 (B), the low-density printing part is concentrated in the central part of the dot, and this part is visually rough and the printing quality is favorable. is not.

Therefore, in this embodiment, the data conversion of the counter output C4 is performed as shown in FIG. 2C, and at the time of printing each pixel (dot) by the heat generation of the resistor, the start time and Except for the part corresponding to the end time, the printing area is expanded around the part corresponding to the two intermediate times between the start and end times, in this case, "0" and "1".

As a result, the low-density printed portion is dispersed and positioned at two places within one pixel, and the width between a certain printing position and the next printing position becomes 1/2 pixel, and especially, the hard copy image It is possible to improve the visually rough printing state of the portion printed at low density, and it is possible to make the printing quality extremely good.

FIG. 4 is a diagram showing a block configuration of an image printing apparatus according to the second embodiment of the present invention, and FIG. 5 is a diagram for explaining its operation. In this embodiment, the image data or the density data is used as it is for the print data C9,
As the control data C10, data obtained by converting 256 time-lapse data C4 into a data string in which at least one numerical value of the 64 numerical value groups expressing the gradation density is used multiple times is used. This is the same as the above-mentioned embodiment in that the quantization is 2
The bit, C4, is the output of the 4-bit counter. In the conventional example and the above-described embodiment, the 2-bit quantized image signal is converted into 4-bit time axis data by the density conversion means 105 and input to the comparator 106. However, in the present embodiment,
Without performing density conversion, 4-bit C4 is converted into 2-bit gradation data by the address conversion means 1 and the image data is compared with the comparator 2 to switch the head on / off signal.

FIG. 5 shows the density when the 0th gradation is printed with a pulse of 0 count, the density when the 1st gradation is printed with a pulse of 7 counts, and the density when the 2nd gradation is 12 counts. The same result as the conversion example of (B) and (C) in Fig. 2 is obtained when the density when printed with a pulse is the density when the third gradation is the density when printed with a pulse for 16 counts. The conversion examples are shown as (B) 'and (C)'.

When the relationship between the print data C9 representing the print gradation and the conversion data C10 is C10 ≧ C9, the “L” signal that turns the head off, and when C10 <C9, the “H” signal that turns the head on is the comparator. 2 is output to the printer. Therefore, in this conversion example, when C9 is 0, it is not turned on, when it is 1, 7 counts of 0, which is less than 1, the converted data is on, and when it is 2, the converted data is 2 12 counts that are smaller than 0 or 1 are turned on 3
If the converted data is less than 3, 0 or 1 or 2
6 counts, that is, in all cases, it is turned on. As a result, the gradation expression as shown above can be obtained.

Note that, in each of the above-mentioned embodiments, for convenience of explanation, quantization 2 bits,
The case where the time counter is 4 bits is shown, but the present invention is not limited to this, and according to the same idea, if the number of quantization bits is equal to or less than the number of bits of the time counter, such as quantization 6 bits and time counter 8 bits. Can also be expanded. Further, the conversion example is not limited to (B), (C), (B) ', and (C)', and may be any conversion that is performed for at least one of prevention of thermal history unevenness and improvement of the low-density printing state. .

Further, the head configuration is not limited to 5 blocks, and the printing method is not limited to this method.

Further, by replacing the A / D conversion means 103 with a digital interface means, it is possible to print a graphic image other than a pictorial image.

〔The invention's effect〕

As described above, according to the image printing method and the image printing apparatus of the present invention, a plurality of parts of each pixel except for both ends in the sub-scanning direction, that is, the moving direction of the recording medium are the pixel centers, and Since the heat generation time of each resistor is controlled so that the print area of each pixel expands around the pixel center as the multi-tone density value corresponding to each pixel increases, the sub-scanning is performed. Between adjacent pixels lined up in the direction,
It is possible to reduce the adverse effect of thermal history density unevenness between adjacent pixels due to the printing rate, that is, the ratio of the printing area in each pixel, and further, especially in the case of printing low-density image data, hard copy Since the section in which the thermal head is ON in the sub-scanning direction of the image is concentrated at the beginning with respect to the printing of one pixel, it is possible to improve the visually rough printing state that appears as a result. is there.

[Brief description of drawings]

FIG. 1 is a block diagram of an image printing apparatus according to an embodiment of the present invention, FIG. 2 is a diagram showing an example of address conversion of the present invention, and FIG. 3 is a diagram showing an example of printing of the above-mentioned embodiment. FIG. 4 is a block diagram of an image printing apparatus according to another embodiment of the present invention,
FIG. 5 is a diagram showing an example of address conversion used in FIG. 4, and FIGS. 6 and 7 are schematic diagrams showing a configuration and a printing operation of a conventional image printing apparatus. In the figure, 1 is address conversion, 2 is a comparator, 101 is an image signal input unit, 102 is a synchronization signal input unit, and 103 is A.
/ D conversion, 104 is an image memory, 105 is density conversion, 1
06 is an 8-bit comparator, 107 is system control, 10
Reference numeral 8 is a printer. The same reference numerals in the drawings indicate the same or corresponding parts.

Claims (4)

[Claims] 1. A recording in which a hard copy image having a multi-tone density in which each pixel corresponds to an original image is moved with respect to the thermal head by controlling the heat generation time of each resistor provided in the thermal head. In the method of printing on a medium, a plurality of parts of each pixel except for both ends in the moving direction of the recording medium are the pixel centers, and as the multi-tone density value corresponding to each pixel increases, An image printing method, wherein the heat generation time of each resistor is controlled so that the printing area of each pixel expands around the center of the pixel. 2. A thermal head having a plurality of resistors and a recording medium moving relative to the thermal head, wherein each pixel corresponds to an original image by controlling the heating time of each resistor. In a device for printing a hard copy image having a gradation density on the recording medium, a data comparing means for comparing the printing data corresponding to the multi-gradation density and the control data for controlling the heat generation time. And a control means for controlling the heat generation time based on the comparison result, and at the time of printing by the heat generation of the resistor of each pixel, a portion corresponding to the print start time and print end time. Excluding the above, a control data creating means for creating the control data is created so that the printing area expands with an increase in the multi-tone density value, centering on a portion corresponding to a plurality of intermediate times between the start and end times. Equipment Image Shirushiutsushi apparatus characterized by a. 3. The print data is data obtained by converting image data into a time axis, and the heat generation time control data is time elapsed data obtained by dividing the whole print time of one pixel into N pieces. 3. The image printing apparatus according to claim 2, wherein the control data is converted into a data string that does not include a simple increase or a simple decrease by the data creating means. 4. The image data or the density data is used as it is for the printing data, and the control data is N indicating an elapsed time from a reference time.
A data string made up of a plurality of time-lapse data is used by converting it into a data string in which at least one numerical value of a numerical value group of 0 to M expressing gradation density is used a plurality of times. The image printing apparatus according to the second aspect.