JPS61148074A - Thermal image-recording system by alternate block printing system - Google Patents

Abstract

PURPOSE:To contrive a shorter printing time, by a system wherein a group of dots are divided into two blocks, and one of the blocks is used for printing with an odd-numbered gradation, while the other is used for printing with an even-numbered gradation. CONSTITUTION:When a block level data signal BLD111 is inputted to an input terminal of a shift register 65, the signal is transferred to the shift register 65 on a serial basis by a clock signal from a circuit 62, and is transferred to a latch circuit 66 on a parallel basis by a load signal from a circuit 63. Then, an output from the latch circuit 66 and a 'driving signal timed with a strobe signal SS1' from the circuit 64 are multiplied by each other by a NAND gate 67, and Joule heat is generated only at D1, D3, D5, D7, D9 corresponding to a signal '1' in the block B1, whereby a picture element with a density corresponding to gradation level 1 is printed. Next, to print with a density corresponding to gradation level 2 by level data LD12, a signal BLD122 obtained by multiplying the level data LD12 by a strobe signal SS2 for driving the block B2 is inputted to a data input terminal of the shift register 65, thereby printing a picture element with gradation level 2.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention prints one line of pixels on thermal recording paper by energizing the heating element dots of a thermal head to generate heat.
The present invention relates to an improvement in a thermal image recording method for obtaining a two-dimensional image by moving the recording paper or the like by a distance and sequentially printing pixels in each row.

[Background of the invention]

2. Description of the Related Art Methods of reproducing images in the form of hard copies such as photographs from electrical image signals obtained from televisions, video cameras, video discs, electronic cameras, etc. are being actively researched. The most powerful method among these is the thermal image recording method.
This is a process in which a line-type thermal head consisting of a group of heating element dots arranged in a horizontal line (corresponding to one line) is passed over a thermal recording paper (not only thermosensitive coloring type, but also an image receiving sheet and a thermal transfer ink sheet). While moving the dots (including stacked dots), only the predetermined heating element dots are energized to generate heat based on the input signal, and this heat is used to print one line of pixels on the recording paper, sequentially. A two-dimensional image is completed by printing each row of pixels (see FIG. 1).

In this case, the number of heating element dots corresponding to one row of pixels may reach, for example, 1280, depending on the size of the image. However, when there are many dots like this,
The maximum 'r that flows when all dots are heated! The L current value becomes extremely large, and therefore a large power supply is required.

Therefore, two blocks Ba are placed from the center of the heating element dot group.
, Bb, and each block is printed at a different time (a block printing method was proposed in which electricity is applied and heat is turned on). With this method, the time required to print one row of pixels is doubled. However, the required maximum current value is 1/2
That's enough.

By the way, the temperature distribution when one heating element dot is made to generate heat shows a mountain-shaped distribution as shown in Figure 2, and if each block is made to generate heat, if all the dots in the block are made to generate heat, Heat generating block B as shown in Figure 3A
The heat generation temperature at the boundary between a (dot area with hatching) and non-heat generating block Bb (dot area without hatching) is low. This is because the area outside the boundary is a non-heat generating block Ba, so the temperature is low and therefore heat escapes, and this phenomenon cannot be avoided.

This phenomenon also occurs when the energization and heat generation operation of the block Ba is completed and the next energization and heat generation operation of the block Bb is performed, resulting in a temperature distribution as shown in FIG. 3B. Therefore, the heat generation temperature at the boundary between the blocks is not high enough in either the first or the next operation (see Figure 3C), and as a result, the printed pixels are discontinuous at the boundary, resulting in white dots. Get out.

Naturally, these white spots appear as white streaks (referred to as white lines by the inventors) in the printed image in the direction of movement of the recording paper, etc. This white line becomes a fatal drawback when creating images such as photographs.

Therefore, instead of dividing the blocks at the center of the dot groups, we alternately number the dot groups starting from the end, so that the blocks to which odd-numbered dots belong and the blocks to which even-numbered dots belong. An alternating block printing method was proposed in which each block is divided into two blocks and each block is printed.

By the way, not only this alternating method but also other methods, it is not possible to obtain a high-quality image if the image consists of the presence or absence of a certain number of pixels. It is necessary to be different. That pixel 7jkp
It is important how many types L is divided into, and it is generally said to be 16 gradations, 32 gradations, 64 gradations, 128 gradations, or 256 gradations. The formation of pixels with such gradation density is generally done by shortening the time for one printing (thus, thinner pixels are printed).
This is done by printing over and over again over many summers. In other words, to form an image with the highest density of 64 gradations, for example,
This means that the same pixel is overprinted 64 times. However, for pixels that are thinner than that, printing is stopped in the middle of 64 times, and further overlapping printing is stopped. Therefore, when pixels with the highest 64 gradations are to be formed in that block, energization printing will be repeated 64 times for that block. Of course, during this time, the power supply to the dots forming pixels with low density is stopped midway.

The previously proposed alternating scheme has nth order v! in the first block.
4 (for example, n=64), and then in the next block, repeat printing with n1Vv4''1 is performed in the same way. Therefore, in the case of batch printing without block printing, , if the sum of the time required for one printing (equivalent to one gradation) and the pause time until the next printing is i
If it takes 17 seconds, it takes n X to print one line of pixels.
It will take t milliJ seconds, but in the case of block printing, it will take twice as long, 2XnXt milliseconds.

However, according to a follow-up experiment conducted by the inventors, in the alternating block printing method proposed earlier, the pixels and elements formed from the dots belonging to the block to be printed later are darker than those of the earlier ones. Therefore, it has been found that dark streaks appear in the obtained two-dimensional image at every other pixel in the direction of movement of the recording paper.

[Object of the Invention] Therefore, the object of the present invention is to reduce the time required for 2
The purpose is to shorten the printing time for a line and eliminate dark streaks.

[Summary of the Invention] Coincidentally, the inventors of the present invention discovered that by printing by alternating the plot for each gradation, the printing time required to print one line of pixels was nXtX. Despite this, the resulting image is streak-free, and the n
It was discovered that an image close to a gradation image can be obtained, and the present invention was completed.

Accordingly, the present invention provides a thermal image recording method for reproducing a two-dimensional image with gradation using a line-type thermal head consisting of a large number of groups of heating element dots, in which the dot groups are divided into groups to which odd-numbered dots belong. The thermal recording method is characterized in that it is divided into two blocks, a block and a block to which even-numbered dots belong, and one block prints in odd-numbered gradations, and the other block prints in even-numbered gradations. provide.

In the method of the present invention, at most n/
Since overlapping printing is performed only twice, originally, even at the highest density, only the n/2th density out of n gradations should be obtained, and the gradation should also be n,/2 gradations. It is thought that due to the heat accumulation phenomenon in the head, the higher the gradation, the higher the actual heat generation temperature of the dots (rg5), which results in darker printing, and as a result, an image close to n gradation is obtained. In particular, when n is set to 64, 128, or 256 gradations, they are completely comparable and almost indistinguishable.

Hereinafter, the present invention will be explained in more detail with reference to Examples.
The present invention is not limited to these. In the following example, in order to simplify the explanation, it is assumed that the electric flaw signal has already been decomposed into a monochrome image signal.

(How many units have been implemented... [Thermal sublimation transfer image recording method] The electrical image signal is inputted over time starting from the first line and ending with the last line. One row of image signals is shown in Fig. 4. This image signal is divided into 1 to 10 sections along the time axis, and each section corresponds to each pixel, that is, to an individual heating element dot.

Here, we will explain a method of expressing gradation y4 by the time to energize one heating element dot, but to simplify the explanation, the gradation is n = 6ii tones of 0, 1, 2, 3, 4, 5, 1 The number of pixels per row is 10.

Therefore, first, input the image signal for one line using five comparison levels LSIL! which are proportional to the density.・・・・・・L, and sequential comparison. As a result, if it is equal to or higher than the comparison level (darker), it is set as °1°, and if it is lower (lighter) than the comparison level, it is set as °0'', then the level expressed as 0,1. Data are obtained for each level of comparison.

The level data of the image signal shown in FIG. 4 is as shown in Table 1 below.

Table 1 (Pressure: In this level data, 0'' means non-printing, 01° means printing) When this level data is converted into an electric signal waveform, it becomes as shown in FIG.

FIG. 6 shows an example of the circuit used here, and there are 10 heating element dots DttDt corresponding to 10 pixels for one row.
+Ds...D. There is. 61 is a level data signal generation circuit, 6a is a clock signal generation circuit for timing, G1 is a load signal generation circuit, 64 is a thermal head drive signal generation circuit, 64 is a shift register,
6Q is a latch circuit, (51 is a Nant gate, 6th is a strobe signal switching circuit, and t5Lll is a strobe signal generation circuit.

Here, the heating element dots D, , D,...DI
) to the odd numbered dot DI ID!・・・・・・The first block (B,) to which D belongs, and the even numbered dot D,...
D,...D,. The second block (B,) to which belongs
Divide into. Then, printing of the first block (Bt) and printing of the second block (Bt) are performed at different times, thereby suppressing the maximum current value to half.

In order to print each block, six strobe signal generation circuits are used to generate strobe signals 5S1 (B,
Obtain (for driving) and SS, (B, for driving).

Strobe signals SS1 and SS are connected to the level data LDx via the strobe signal switching circuit 6Q (71, fa) alternately for each gradation. When combined, the block K handled by the strobe signal is energized for "Xth gradation printing corresponding to the level data LDx".

Therefore, first, level data LD 11th order K and block level data signals BI, Dl, . Then, this signal BLD, 11 is serially transferred to the shift register←OIC by the clock signal output from the block signal generation circuit 6a, and the transferred signal is
The load signal output from the load signal generation circuit 61 performs parallel transfer to the latch circuit.

Then, the output of the latch circuit GO and the strobe signal SS output from the thermal head drive signal generation circuit G4,
The driving signals with the same timing are combined at the Nant gate 61 to produce the block level data signal BLD,...
Based on 1, the heating element driver in charge of block B1)
DI-D, Norichi "1" signal (high level) K corresponding Dl t Dl l DI l n, t A current flows through DI for a unit time, generating Joule heat, and as a result,... -,, 1 line, ,) pixels with a density corresponding to 81 gradations of 1° element are printed. Pixels that are not printed here remain as a dark KO, that is, a white background.

Next, level data LD! at even-numbered gradations! ! This prints at a density corresponding to gradation level 2, but the present invention is characterized in that the blocks are alternately changed for each gradation, so level data LD, , is now used to drive block B. The strobe signal SS and the strobe signal SS are matched. As a result, the block level data signal BLD1. shown in FIG. get.

Then, this signal BI'I)+tt is transferred to the shift register I.
Manually input the signal BLD,,1 to the data input terminal of Q.
When a colleague processes this, pixels of gradation level 2 are printed between the pixels printed ahead of the M1 row of the image receiving sheet. Even though it is called gradation level 2, the background is still a white background with no printing, so the density of the printed pixels should originally be the same as that of gradation level 1, but gradation level l
Due to the residual heat effect of the neighboring dots that generated heat during printing, the dots that will be printed at gradation level 2 this time have already been warmed up, so the printing rIk degree is dark, and the dots that were originally printed twice are now warmed up. Even though it is not, pixels close to gradation level 2 are formed.

Level data LD,, After that, the strobe signal is changed alternately in the same way, and the next block level data signal is: LD,, X 881→BLD, 3°LDI4 X SS2→BLD, 4°LD,, BLD...

is obtained, and blocks B1 and Btt are printed alternately. As a result, a pixel column having six gradations is completed in the first row.

Therefore, the image receiving sheet is moved to the next line, and the image signal of the next line is similarly processed to complete printing. thus,
By repeating this process sequentially up to the last row, a monochrome two-dimensional image with gradations is formed on the image-receiving sheet. Yellow to get a full color image.

Images in three or four colors of magenta, cyan, and possibly black may be created in the same way and superimposed.

The full-color image reproduced in this way is created by batch printing instead of block printing, and has almost the same image quality as a friend full-color image, yet the printing time for one line is half that of batch printing, just like block printing. It's over.

Generally, at 16 gradations, false contours appear in the image obtained,
Although it does not appear in 32 gradations, according to the method of the present invention, when the input image signal is divided into 32 gradations, the reproduction time is the same as when it is divided into 16 gradations, and at the same time, it is possible to create an image without false contours. is obtained.

Incidentally, even if the dot is initially energized, no printing (pixel is formed) occurs in the case 1 in which the head is heated above a predetermined temperature. Therefore, when printing at gradation level 1, it is necessary to preliminarily energize the dots for a predetermined period of time to heat the head to a predetermined temperature. Heating to this predetermined temperature is called preheating, and it is desirable to conduct the preheating in a short time by passing as large a current as possible. This is because the head is designed to dissipate heat relatively easily, so if the dot's heat generation is low with a small current,
This is because even if the current is applied for a long time, the temperature will reach equilibrium at a point where the amount of heat generated and the amount of heat dissipated will reach equilibrium, and there is a possibility that the temperature will not reach the predetermined temperature. Therefore, a capacitor is used to temporarily store current, and the stored current is discharged during preheating.
It is preferable that all the dots be heated to a predetermined temperature at once.

In particular, the method of the present invention originally divides the dot group into two blocks and prints at different times in order to avoid the need for a large power supply. It is highly desirable to use a large power source in order to avoid using a large power source.

This is because capacitors are extremely compact and inexpensive.

(Conventional Example) In order to clarify the difference from the conventional alternating block printing, a conventional example will be explained with reference to the Meio side.

In the conventional example, first, the level data LD, , and the strobe signal SS are multiplied together to form the block level data BLD.
, , is obtained, and after printing at gradation level l for block B1 based on this, each block level data for block B is similarly obtained: LDtt ×SS+→BLD, ! LD,,X88. →BLDi,.

LD,, X SS, →B L D,,.

LDos X SSI → BLD...

and print each gradation level based on them.
Performs overlapping printing up to the highest gradation level 5.

This completes printing by block B.

After that, printing will be performed on block B this summer. 1v% First, level data LD□ and strobe signal SS,
Multiplying these together gives the block level data BLD,...
Based on this, printing at gradation level 1 is performed for block B. Then, in the same way, each block level data: LDtt X SS2 → BLD□LD,, X
SS, →BLD,.

LD, , X SS, -+ BLD, .

LD,, X SS, → BLD,,.

and print each gradation level based on them.
Printing of block B is completed. In this way, printing of the first line is completed.

Thereafter, each line is printed in the same manner to obtain a two-dimensional image.

However, in the image obtained in this way, dark streaks were observed in the direction of movement of the recording paper at every other pixel because the pixels of block B, which will be printed later, were printed in a concatenated manner.

θ bone fighting fever + ÷ ,　　　.

In addition, in order from the end of the dot group, 1.2, 3.4...
Block B+ to which odd-numbered dots belong and block B8 to which even-numbered dots belong.
When dividing into two blocks B+ and Bz, in some cases it may be necessary to number them one by one.
1.2,3.
They may be numbered as 4......

〔Effect of the invention〕

As described above, according to the present invention, in the alternating block printing method, a high-quality image close to a high-gradation image can be obtained, there is no streaking, and the printing time for one line, that is, the time required to create the entire image. is only half that of high gradation.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram illustrating a general thermal image recording method. FIG. 2 is a conceptual diagram showing the temperature distribution when one heating element dot generates heat. Figure 3A shows the thermal head blocked by B according to the conventional method.
It is a conceptual diagram which shows the temperature distribution when all aK is made to generate heat. FIG. 3B is also a conceptual diagram of block Bb. FIG. 3C is a composite diagram of FIGS. 3A and 3B. FIG. 4 is a graph showing the waveform or time chart of the first row of image signals used in the embodiment of the present invention. FIG. 5 is a waveform diagram of the level data signal. FIG. 6 is a driving circuit diagram of a thermal head used in the same Example. FIG. 7 is a waveform diagram of the strobe signal. FIGS. 8 and 9 are waveform diagrams of a level data signal, a strobe signal, and a block frequency data signal produced by multiplying the two signals. [Explanation of symbols of main parts] THE thermal head P...Platen roll R:
Image receiving sheet I... Thermal transfer ink sheet E: Electrical image signal input element D = Heating element dot 61 Double-level data signal generation circuit 62: Clock signal generation circuit 63: Hood signal generation circuit 64: Thermal head drive signal generation Circuit 65: Shift register 66 Two-latch circuit 67: NAND gate 68 Nistro single-pitch signal switching circuit 69 Nistro single-pig signal generation circuit 70, 71, 72: AND gate 73 Nior gate

Claims (1)

[Claims] In a thermal image recording method for reproducing a two-dimensional image having gradations using a line-type thermal head consisting of a large number of heating element dot groups, odd-numbered dots belong to the dot groups. A thermal recording method characterized in that it is divided into two blocks: a block and a block to which even-numbered dots belong, and one block prints in odd-numbered gradations, and the other block prints in even-numbered gradations.