JPH04193553A - Thermal transfer recorder - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention particularly relates to a thermal transfer recording device that performs intermediate cylinder recording that is capable of expressing not only black and white binary values but also intermediate shading. This invention relates to a thermal transfer recording device that reproduces images.

[Prior Art] There have been various methods for recording images and characters used in hard copy output devices for information signals in communication devices and terminal output devices of electronic computers, hard copy devices for image information signals such as video signals, etc. A method has been proposed. Among these recording methods, an intermediate recording medium whose surface is coated with heat-melting or heat-sublimable ink is used, and this ink is selectively heated with a thermal head, etc., and the ink is transferred to the surface of the recording medium. A thermal transfer recording method has been put into practical use. Furthermore, a recording method has been put into practical use in which heat-sensitive coloring paper coated with a chemical that changes color due to heat is heated by the above-mentioned thermal head or the like to develop color without using an intermediate recording medium.

Among these recording methods, those capable of expressing not only binary gradations of black and white, but also intermediate densities between white and black, which are capable of expressing halftones, are being put into practical use.

As a method for performing halftone recording using a thermal transfer recording method, a density gradation method is generally used in which the density is controlled for each pixel. In this density gradation method, each heating element arranged in a row in a thermal head corresponds to a pixel, and the density is controlled by increasing or decreasing the amount of ink corresponding to the amount of energy applied to the heating element. Actually, for each heating element,
The energization time is often controlled to match the density (gradation) of the pixels to be recorded.

The structure of a thermal head that performs density gradation recording is as follows:
Consists of a heating element, switching elements individually connected to the heating element, a latch circuit that is a temporary storage circuit that turns on and off the switching element, and a shift register that stores on/off information input from the outside. has been done.

The method to control the energization time of each heating element is as follows.
Do it as follows.

First, image data is divided into the number of gradations (number of gradations) representing the maximum energization time. Then, the on/off of each heating element is controlled for each divided stage time (time slot). Since each heating element only needs to be energized for the required time, the time slots are connected to have the required length. The heating elements of each time slot are controlled to be turned on or off based on data stored in a latch circuit of the thermal head. and,
Data is input to this latch circuit from the outside via shift registers connected in parallel.

In other words, data is transferred to the shift register and energized a number of times corresponding to the number of gradations, and during this energization, image data of the next gradation is transferred, and this operation is repeated one after another until the predetermined number of gradations are completed. Obtain the energization time width.

As described above, when recording halftones, it is necessary to transfer energization on/off data into the thermal head a number of times corresponding to the number of manually inputted gradations.

Conventionally, examples of this type of implementation include, for example, Japanese Patent Application Laid-Open No. 57-48
As disclosed in Japanese Patent No. 868 "Thermal Recording Apparatus", there is known a device that records halftones by transferring on/off data of energization a number of times commensurate with the number of gradations.

In the conventional example described above, it was possible to record intermediate densities of a number corresponding to the number of input gradations. However, since this method uses a thermal head, there are phenomena such as a heat accumulation phenomenon in which the recording density is affected by the heat accumulated in the thermal head, and unevenness in the shape and resistance value of the heating element of the thermal head itself. It was not always possible to record an image with the desired density.

There is a new recognition that it is necessary to perform some kind of correction for these heat accumulation phenomena, resistance value unevenness phenomena, and the like.

As a conventional example of correcting the heat accumulation phenomenon in a thermal transfer recording apparatus, for example, the one disclosed in Japanese Patent Publication No. 64-2076 entitled "Thermal Recording Method" is known.

In the conventional example disclosed in the above-mentioned Japanese Patent Publication No. 64-2076, after correcting the heat accumulation phenomenon, the thermal energy input to each heating element is increased or decreased to reproduce the original image density. . However, in this conventional example, the target thermal transfer device uses heat-fusible ink in which the density of each pixel does not change due to thermal energy, and the density varies slightly depending on the area of the recorded pixel depending on the energy applied manually. Problems with controlling sublimable dyes were not fully recognized.

In other words, in the case of the heat-melting ink method, it is not possible to express intermediate shading for each pixel, but in the case of the sublimation dye method, it is possible to obtain the required density by controlling the thermal energy applied to each pixel. can.

In the above conventional example, the original image is a so-called binary image that either has color or not, and since only the area of the recording pixel changes with human energy, there is no scope for correction using one person's energy. It was sufficient to make rough settings such as ensuring that ink was applied to a sufficient area for the pixel area. However, in the case of sublimable dyes,
For example, if an attempt is made to express 256 gradations of light and shade, the corrected image must also have an expression range of 256 gradations.

That is, the setting accuracy of the correction energy also needs to be delicately controlled in accordance with the number of gradations of the original image, but this point has not been sufficiently recognized in the conventional example.

Furthermore, since the state of deterioration differs depending on the input image, it is necessary to change the correction contents and correction coefficients within the device depending on the image, but this point has not been fully recognized in the past. There wasn't.

In addition to thermal history correction processing, printers are required to perform internal processing such as color correction processing to remove color turbidity of color materials and processing to correct density unevenness during recording, and these image data correction processing It is necessary to operate without problems even when multiple combinations of . In the conventional example described above, this point was also not fully recognized.

[Problem to be solved by the invention]

Summarizing the above, in a thermal transfer recording device, (1) it is necessary to have an image data correction means, and the number of representation bits of the image data after correction is the number of bits of the source data of the image data. It must be more than that.

(2) It is necessary to have a means for selecting correction contents and correction coefficients corresponding to the type of input image.

(3) It is necessary to be able to change the gray scale range of the corrected image depending on the type of input image.

(4) It is necessary to provide a plurality of correction means in an appropriate combination.

The items listed above can be cited as issues. SUMMARY OF THE INVENTION An object of the present invention is to provide a thermal transfer recording apparatus that can solve the problems of the prior art described above and can perform high-quality recording at high speed.

[Means for Solving the Problems] In order to solve the above problems, the following technical means were adopted in the present invention.

(1) Correction processing of image data The number of bits of output data was set to be larger than the number of bits of input image data. The means for recording the image data after the correction process also controls the density of the number of gradations corresponding to the increased number of pixels.

(2) Means for selecting or changing the type of image data correction and processing coefficients is provided in accordance with the type of input image.

(3) The density reproduction range of the corrected image data recording means is changed in accordance with the type of input image.

(4) When a plurality of image data correction means are used in combination, the arrangement is such that correction specific to the recording means is performed at the final stage of correction.

[Effect]

The above technical means works as follows.

(1) Since the number of data bits output by the image data correction means is set to be larger than the number of bits of input image data, even in the part of the image that has been changed due to correction, the difference in density from the surrounding density is small. , the correction becomes less noticeable.

(2) The means for changing the type of correction and the coefficient of correction performs correction corresponding to a human image.

(3) The means for changing the gradation expression range of the corrected image selects a gradation expression range suitable for the type of image.

(4) By combining a plurality of image data correction means, the correction peculiar to the recording means is provided at the final stage, so that the other correction means are not affected by the correction peculiar to the 82 recording apparatus.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the overall configuration of a thermal transfer recording apparatus as a first embodiment of the present invention.

First, the schematic structure of the first cap body will be explained. The thermal transfer recording device 1 prints and records image information on a recording medium based on information such as a video signal 101 and digital image data 102 supplied from the outside.

A video signal 101 input from the outside is sent to the A/D circuit 1.
1, the signal is converted into digital data and sent to the memory circuit 12. Digital image data 102 supplied from the outside
is sent to the memory circuit 12 via the digital interface 14. Further, the digital image data from the memory circuit 12 is sent to the image data correction circuit 8 and subjected to predetermined correction, and then sent to the halftone control circuit 2.
After being subjected to predetermined processing, it is sent to the thermal head 3. This thermal head 3 is arranged inside the mechanism section 4, and operates together with an intermediate recording medium 401 and a platen drum 402 to perform print recording. A system control circuit 13 controls the overall operation of the thermal transfer recording apparatus 1.

In addition, following the image data correction circuit, one embodiment of the present invention shown in FIG. 1 will be described in detail using FIGS. 2 to 7.

FIG. 2 is a perspective view showing the overall structure of the thermal transfer recording apparatus l according to the embodiment shown in FIG. 1 according to the present invention.

In the figure, a recording medium 403 is connected to a recording medium feeding mechanism 40.
4, and is wound around the platen drum 402 for recording. The recording medium 403 after recording is sent out to the outside of the apparatus 1 via a paper discharge mechanism 405.

Further, an ink paper 401, which is an intermediate recording medium, is supplied from an ink paper cassette 406 and used for recording. The used ink paper 401 is wound up on the take-up reel of the ink paper cassette 406. - Volume of used ink paper 401
can be taken out of the apparatus 1 together with the ink paper cassette 406 and replaced.

A signal is sent to the thermal head 3 from the circuit section 5. As explained in FIG. 1 above, the circuit portion 5 includes the memory circuit 12 and halftone control circuit 2 shown in FIG.
, a print control circuit 13, an image data correction circuit 8, and the like. Also, the power used by the thermal head 3 is
It is supplied from the power source 6.

Next, referring to FIG. 3, the recording operation in the mechanism section will be explained. In the figure, there is a thermal head 3 placed around a platen drum 402, and during recording operation,
Recording medium 403 and ink paper 401 as an intermediate recording medium
is placed between the thermal head 3 and the platen drum 402 to perform recording.

A starch portion is provided on the surface of the platen drum 402, and a heating element 30 is provided on the surface of the thermal head 3.
In direct contact with 4. Further, from the back side of the thermal head 3, the thermal head 3 is pressed against the platen drum 402 by a spring 405, which is a suppressing means.

Furthermore, around the platen drum 402, there is an ink paper cassette 406 (the stepped surface of the outer case part is shown in FIG. 3), which is a supply means and a collection means for ink paper 401, which is an intermediate recording medium, and a recording A paper feed/discharge mechanism 420 for the medium 403 and a recording medium guide 421 are arranged.

The ink paper cassette 406 contains an ink paper 401 that is an intermediate J recording medium. One surface of the ink paper 401 is coated with sublimable dye ink, which has the property of sublimating due to heat, and thermal energy applied from the heating element 304 of the thermal head 3 through the surface opposite to the ink-coated surface causes the recording medium to be heated. It has the role of supplying 403 heink.

The ink paper 401 is passed from an ink paper supply reel 422 to a take-up reel 423.

Then, as recording progresses, a new portion of the ink paper 401 is supplied to the recording processing section between the thermal head 3 and the platen drum 402. Further, the used ink paper 401 used for recording is sent to a take-up reel 423 and wound up.

Recording is performed using heating elements 30 arranged on the surface of the thermal head 3.
4 (in the vertical direction of the page). 1
When the recording for one column is finished and the next column is to be recorded, the platen drum 40 is moved to the place where the next column is to be recorded.
2 is moving.

Each row of records is turned over to form a planar record on the recording medium 403.

Recording for one column is performed by appropriately energizing the heating element 304 of the thermal head 3. That is, the heating element 304 is energized to raise the temperature, thereby heating and sublimating the ink applied to the ink paper 401, and performing transfer recording onto the recording medium 403. The energy applied to the ink is controlled by the energization time at this time, and the density of the recording is controlled.

The ink paper 401 is painted with different tones of ink for each screen. And the same recording medium 403
By rotating the platen drum 402 once, it can be placed at the same recording position again. Here, color recording can be performed by overlapping S recording using ink paper 401 of different tones.

FIG. 4 is a characteristic diagram showing an example of the recording characteristics of the embodiment shown in FIG. 1 of the present invention. That is, FIG. 4 shows the relationship between the current application time during recording and the color density characteristics obtained as a result.

FIG. 4(a) shows the relationship between the color density and the energization time (manual energy) as an example of the recording characteristics of sublimation ink. As shown in Fig. 4(a), the coloring characteristics under the conditions of the combination of ink paper as an intermediate recording medium and recording paper as a recording medium generally have no coloring characteristics with respect to the input energy. Shows linear characteristics. That is, if an attempt is made to control the required concentration at equal intervals, the input energy must be controlled at irregular intervals.

As shown in FIG. 4(a), a relatively intermediate density portion 60
At 0a, the concentration corresponds almost linearly to the energization time (input energy). However, in the high-density portion 600b, the ink on the ink paper that supplies the ink is used up, and the increase in density reaches a plateau even if the energization time is increased. Further, in the relatively low concentration portion 600C, it takes time from the start of energization until the heating element of the thermal head is sufficiently heated, and color does not develop until a certain energization time is reached.

In this way, the recording characteristics change non-linearly mainly between relatively low-density areas and high-density areas.

FIG. 4(b) shows an example of setting input energy when controlling recording density.

In the example shown in FIG. 4, the variable range of color density is set to 64, for example.
It is divided into stages at equal intervals, and each stage is called a gradation number.

As shown in FIG. 4(b), for example, in order to realize the above-mentioned 64-gradation recording, 64 types of pulse widths may be prepared. Then, the energy input to the thermal head is changed by changing each pulse width in accordance with the required color density for each gradation number (.

Here, the first gradation #0 is assigned a pulse width of 10, and when current is applied with the pulse width 601 of this #O, the corresponding color density is the same as that of #0 in FIG. 4(a). Since it is assigned to the area of density (original density of paper), it is difficult to distinguish it from the area that is not actually recorded. This #0
The pulse width 602 of the second gradation number #l is set by increasing the current application time difference Δtl from the gradation number #1.

When recording is performed using this second #l energizing pulse, the #l density (assigned to the lightest density) in FIG. 4(a) is recorded. Thereafter, the pulse width of each gradation number is set corresponding to the set recording density. The time difference △tn in the energization time for each gradation was relatively wide near the low density portion 600C of the color density characteristics, but gradually narrowed, and remained almost the same near the intermediate density portion 600a. It gradually widens again near the concentration portion 600b (.

By setting energizing pulse widths of different lengths for each gradation as described above, it is possible to record a density corresponding to a preset gradation number.

In the above setting example, the number of gradations is set to 64 for explanation, but the number of gradations actually used is not only 64 (,
Gradation numbers such as 16, 32, 128, and 256 are also often used. Even when the number of gradations is other than 64, it is clear that shading can be expressed by changing the length of the energization time, as explained using FIG. 4 above.

Figure 5 shows ll! ! FIG. 3 is an explanatory diagram showing the relationship between the i key number and the corresponding recording result. In Figure 5, 1! is on the horizontal axis!
! The J key number is shown, and the vertical axis shows the density obtained.

The number of gradation numbers that can be set is determined by the number of bits of the input data line. That is, for example, when the number of bits is 6 bits, it is possible to set the number of gradations below 64 gradations.

Figure 5(a) shows a data line with a 1-bit gradation number (
This is the relationship between the gradation number and the recording density when the gradation number is set as a line) (one data line). In this case, there are two types of gradation numbers: gradation numbers #1 and #0. If the data of #O is O, the recording density O (paper background density white) is assigned, for example.

When the data #1 is 1, the maximum density (black) is assigned. In this way, when the gradation number is 1 bit, either white or black can be selected.

FIG. 5(b) shows the relationship between the gradation number and recording density when the gradation number is 2 bits. In this case, #0, #
Since four types of gradation, i.e., #2, and #3, can be selected, recording can be performed in four types of gradation corresponding to the assigned 2 bits.

FIG. 5(C) shows the relationship between the gradation number and the recording density when the gradation number is 3-pits 1 or more. In this case, since eight types of gradation from #0 to #7 can be selected, it is possible to perform recording with eight types of shading corresponding to the three allocated bits.

FIG. 5(d) shows the relationship between the gradation number and recording density when the gradation number is 6 bits. In this case, since 64 types of gradations from #0 to #63 can be selected, recording can be performed with 64 types of shading corresponding to the assigned 6 bits.

FIG. 5(e) shows the relationship between the gradation number and recording density when the gradation number is 8 bits 1. In this case, 256 types of gradation from #0 to #255 can be selected, so
It is possible to record in 256 types of shading corresponding to the assigned 8 bits.

As explained using Figure 5 above, the number of gradations that can be set is determined according to the number of bits of the input data line, and the level of shading that can be expressed in recording is determined according to the number of gradations. The number of gradation numbers is determined. Generally speaking, the higher the number of gradation numbers, the less noticeable the difference in density will be, and the more natural an image can be reproduced. However, when dealing with normal video signals, A/D (analog-to-digital) converters with a large number of bits are generally expensive, and the S/N (signal-to-noise ratio) of the video signal itself is often not very good; A number of bits of approximately 6 bits is often selected.

FIG. 6 is an explanatory diagram of the density reproduction range corresponding to input energy. Each figure in FIG. 6 shows the relationship between the recording density of one pixel on the recording screen and the energy input to one heating element of the thermal head used for recording.

FIG. 6(a) shows the density reproduction characteristic of a certain pixel when recording is performed with approximately the same gradation number around the pixel.

From the lowest gradation number #O to the highest gradation number # in this (a) diagram
20 to 100 human energy to express up to 63
Display as %. That is, if 100% input energy is used, the maximum density set by #63 of the maximum particle is recorded. Further, at an input energy of 20%, the lowest gradation x o t = the corresponding density (in this case, there is no change in density (the season is recorded).

Further, the density reproduction range is set as a range from 0.05 to 2.0, and this range is equally divided into 64 parts and assigned to gradation numbers. It is known that density is almost equal to visual characteristics, and it is reasonable to assign tone numbers to density at equal intervals.

In the characteristics shown in FIG. 6(a) above, the area around the pixel performing recording is performing a recording operation with almost the same gradation number, and the heating element of the thermal head is heated with the recording operation. Therefore, recording is performed under a certain temperature condition.

That is, the color density characteristics change depending on the surrounding conditions of each pixel.

Figure 6(b) shows an example of the color density characteristics when the surrounding area of a certain pixel is not recorded (the surrounding area is white and only one isolated pixel is black, which is often seen in text or line images). be. Since the area around the pixel is not generating heat and the temperature of the surrounding area is cold, an isolated whisker heating element loses heat to the surrounding low-temperature area, so the temperature does not rise sufficiently. Therefore, the color density corresponding to the input energy amount becomes thinner overall. As shown in Figure 6(b), when control is performed within the same human energy range as in the basic Figure 6(a), the required density range is from gradation number #0 to 0.05 to 2.0. This means that up to #63 cannot be expressed.

In this case, if you widen the control range of the energization pulse width, that is, the dynamic range, and set the length to, for example, 130% (compared to figure (a)) as shown in figure (b), A density of 2.0 at the required maximum gradation level #63 can be obtained.

FIG. 6(C) shows an example of color density characteristics when the area around the pixel to which printing is to be performed is already larger than the number of gradations of the pixel and is applied more than necessary.

In a case like this diagram (C), for example, immediately after recording a series of black areas, the lii! ii Occurs during raw recording.

The color density characteristic corresponding to the energization energy in case 2 becomes darker overall, and if control is performed within the same input energy range as in Figure 6(a), a density range that is larger than necessary will be expressed. Become.

In this case, narrow the energization time width corresponding to the entire gradation number (for example, to 80% in Figure (C)) and It is only necessary to set it to a value from #0 to #63). It is also necessary to narrow the energization time range until the start of color development.

As explained in FIG. 6, when performing gradation control within the same input energy range, recording is performed depending on whether or not each pixel is heated from the surroundings, depending on the relationship between each pixel and the gradation numbers of surrounding pixels. The recording density of the relevant pixel of the image to be printed changes significantly. In other words, compared to the normal human power energy range, it is necessary to change the energy control range (dynamic range) to a large range so that the overall input energy is large when the area around the thermal head is cold. . On the other hand, in a situation where the area around the thermal head is heated, it is necessary to change the energy control range (dynamic range) to a small range so that the overall human energy is small.

The operation of correcting changes in color density characteristics of individual pixels due to thermal characteristics caused by image data as described above will be referred to as thermal history correction.

FIG. 7 is a block diagram showing details of the internal configuration of the image data correction circuit 8 of the first embodiment of the present invention shown in FIG.

Inside the image data correction circuit 8, a thermal history correction circuit 800 as an example of a correction circuit and a thermal head density unevenness correction circuit 850 are provided.

These correction circuits are examples of circuits that perform correction, and the number and type of correction circuits can be arbitrarily selected when configuring the present invention.

FIG. 7 shows the configuration of a correction circuit as an example.

First, the internal configuration and operation of the thermal history correction circuit 800 will be explained.

The thermal history correction circuit 800 is for correcting density unevenness due to heat accumulation in a thermal head used in thermal transfer recording. It has a line memory for a total of 3 lines: a line memory that stores the image data of the current line being recorded, and a line memory that stores the image data of the previous two lines, and reads from each line memory. The obtained image data is multiplied by a predetermined coefficient and added.
The content is to create correction data and finally add it to the data to obtain correction data.

The digital data input line 801 is, for example, a 6-bit digital data line, and is composed of six lines for 6 bits, that is, six lines from the bit 0 data line to the bit 5 data line. Image data having 6 bits, that is, 64 types of shading information for each pixel, is input from outside the thermal history correction circuit 800 via a digital data input line 801.

The digital data input line 801 is connected to the line memory a802.
One continuous line of image data (corresponding to one line of recording) of image data input from the outside is stored in the line memory a802. This line memory a802 also has an internal configuration in which the number of bits of human input data is 6 bits, so the capacity of each storage element only needs to be 6 bits or more.

In parallel to line memory a802, line memory b80
3. Line memory C804 is provided.

The stored contents are sequentially transferred from line memory a802 to line memory b803 and line memory c to these line memories.
Transfer lines 805 and 806 are provided to transfer the data to 804. Further, a memory control signal line 807 that controls writing and reading of these line memories, transfer between memories, etc. is connected to the outside of the image data correction circuit 8.

Each line memory operates according to the signal on the memory control signal line 807.

The line memory output has a 6-bit data line a8.
08, data line b809 and data line c81O are provided. The data line a808 is composed of six data lines from bit 0 to bit 5. At the end of these output data lines, calculation means a811, calculation means b812,
A calculation means C813 is connected to each. Inside these calculation means, calculation processing is performed in which input 6-bit data is multiplied by a predetermined coefficient. That is, as a result of arithmetic processing, the human-powered 6-bit data representing 64 types of image shading is replaced with, for example, 8-bit information representing 256 types of shading. In the part that performs this arithmetic processing, if you try to output the same number of bits compared to the number of bits of the input data, some kind of rounding processing will be performed on the arithmetic processing result, resulting in so-called bit loss, i.e. This will cause deterioration of the image data later.

For example, eight sets of data lines a814 and data lines b' corresponding to 8 bits are output from the respective calculation means a, b, and C.
815 and data line c816 are connected to each other and connected to an adder circuit A317. The output lines from these calculation means are comprised of eight lines per set, and are assigned to each set from the bit O data line to the bit 7 data line.

Further, a correction coefficient selection control line 818 sent from outside the image data correction circuit 8 is connected to the three calculation means, and according to information on this correction coefficient selection control line 818,
Switches the calculation coefficients inside the calculation means. This coefficient switching will be explained in detail later using FIG. 11.

The addition circuit A317 performs addition processing on the 8-bit data sent from the calculation means. That is, for example, if the manually input data is of three types of 8 bits, the original information will not be lost if the data after addition processing is 9 bits.

The output of the adder circuit A317 is sent to a data line 819, which is a set of nine 9-bit data lines, and is sent to the second stage adder circuit B820.

Nine signals from the bit 0 data line to the bit 8 data line are assigned to the data line 819.

The second stage adder circuit B820 has the data line 8 of the original image.
08 is also connected, and correction data is added to the original image data.

The output from the second adder circuit B820 is sent to the next thermal head density unevenness correction circuit 850 via a data line 821 which is a set of nine 9-bit data lines. Nine signals from the bit 0 data line to the bit 8 data line are assigned to the data line 821.

Next, details of the configuration and operation of the thermal head density unevenness correction circuit 850 will be explained.

The thermal head density unevenness correction circuit 850 corrects density unevenness inherent in the thermal head and thermal transfer recording means. For example, it corrects density unevenness caused by resistance value unevenness of the thermal head itself, uneven shape, etc. on a pixel-by-pixel basis.

In the thermal head density unevenness correction circuit 850, 9-bit data is sent to the conversion circuit 851 via the data line 821.
is being sent to. A correction information storage element 852 is connected to the conversion circuit 851, and outputs corrected data by referring to the contents stored in the correction information storage element 852 based on the image data input to the conversion circuit 851. do.

That is, for the device-specific density unevenness, a value that becomes lighter for a dark portion and a value that becomes darker for a thin portion are set in the correction information storage element 852.

In this way, device-specific corrections can be made.

When changing the thermal head or recording section, the correction information storage element 852 can be replaced at the same time to perform the necessary correction.

A data bit compression circuit 853 is provided at the output of the thermal head density unevenness correction circuit 850, and the compressed 8-bit data line 854 is sent to the halftone control circuit 2 in FIG.
connected to. Eight signals from the bit 0 data line to the bit 7 data line are assigned to the data line 854.

That is, 8-bit image data is finally sent to the halftone control circuit.

In this way, by making the output after image data correction into 8 bits for the 6 bits on the digital data input line 801 of the image data correction circuit 8, recording can be made without damaging subtle changes in shading after correction. It can be performed.

FIG. 8 is an explanatory diagram before and after the correction process of the first embodiment of the present invention shown in FIG. 1.

A process for increasing the number of bits in the number of gradations after correction processing than the number of bits in the number of gradations before correction processing is explained using FIG. 8.

FIG. 8 shows a cross section of image data in the image recording direction (the direction in which the recording position moves as recording progresses, the so-called sub-scanning direction), and the horizontal axis represents the position in the sub-scanning direction; The vertical axis indicates the gradation number and the corresponding energization time and density, respectively.

FIG. 8(a) schematically shows a cross section of the original image data, and for explanation, the cross section 91O is the white part 91.
It suddenly moves from 0a to the black part 910b, and then again to the white part 9.
This is a simple configuration returning to 10c. Also, the number of floor translations is #
A case of a total of 64 gradations (6 bits) from 0 to #63 is shown. When the image data having the structure shown in FIG. 8(a) is printed, a density cross section as shown in FIG. 8(b) is obtained.

That is, in the portion 911a where the transition from white to black occurs, since the previously recorded portion was white, the temperature of the area around the thermal head where recording is to be performed has cooled, and sufficient recording density cannot be obtained. As the recording of the black portion progresses, the density of the black portion gradually becomes stable and the original density is obtained, but as the recording progresses further, the image data suddenly changes to white at a portion 91. With lb, the temperature around the thermal head has increased during black recording, making it difficult to record the original white area.

Problems in image recording as shown in FIG. 8(b) can be dealt with by applying correction processing to the image data used for recording in advance by using the correction means explained in FIG. can.

FIG. 8(C) is an example showing a correction result of input image data when data is corrected within a range of the number of bits corresponding to the number of gradations of the input image data. The number of bits of input image data before correction, 6 bits, was maintained after correction, and the dynamic range (setting range of energization time width) was expanded by correction, and the gradation numbering was changed. (C
) shows the case where correction is applied only to a portion 912a that changes from white to black. In this illustration,
The case where the number of data bits of the input image is 6 bits and the number of data bits after data correction is 6 bits is shown. FIG. 8(d) shows an example of a density cross section of a printing result when printing is performed using image data to which the correction shown in FIG. 8(C) has been added in advance. If correction is performed in a range where the number of gradations is relatively small (small number of gradations), the density section of the print result will be like 913. That is, in the part of the image where the image changes from white to black, the required density is insufficient, so large image data is input in advance so that a large amount of energy is applied. In this way, simply expanding the dynamic range of the original image recording increases the difference in density between each gradation. For example, the corrected portion 913a becomes darker than the required density,
In the portion 913b where the next stage of correction is performed, phenomena such as the density becoming thinner than necessary occur. The density difference generated during correction is approximately equal to the density difference for each gradation. If the density difference that is an error in correction is equivalent to the density difference for each gradation that can be expressed originally in the number of gradations of the original input image data, the correction will correct the original image data. This is undesirable because it impairs the image quality.

This is because the quantization noise of the original image data is about the density difference corresponding to the gradation difference, and noise of the same level as this noise is newly added.

FIG. 8(e) shows the gradation pitch 1 of the input image data.
This figure shows an example of a cross-section of input image data after correction when the control is made finer by making the number larger than the number. i after correction! I! The i key is set to 256 (8 bits), and numbers from #-5 to #250 are assigned as shown in (e). This corrected image data cross section 914 shows a cross section of image data when the number of bits of the input image data is, for example, 6 bits, and the number of gradations is 8 bits. An example of a density cross section when recording is performed using this image data is shown in FIG. 8(f). In the density cross-section 915 using the image data after correction in FIG. 1), and the deviation from the original recording density in the corrected portion becomes a value that can be relatively ignored as a system.

FIG. 9 is a diagram illustrating the correction contents of the first embodiment of the present invention shown in FIG. We will explain the correction details for the phenomenon that the value does not fall completely.

If the human image data cross section 920 shown in FIG. 9(a) is recorded as is, a density cross section 921 shown in FIG. In this case, a phenomenon 921b occurs in which a portion that changes from black to white does not become completely white. Since this defect in the part where black becomes white is caused by a thermal phenomenon of the thermal head, the present invention corrects the input image data as shown in FIG. 9(c). As shown in FIG. 9(C), in a portion 922a immediately after the transition from black to white, the energization time is set to increase stepwise from zero to small increments. When such input image data correction is performed, a faithful recording 923 that is quite close to the original image data can be obtained as a recording result as shown in FIG. 9(d).

The operation of the embodiment of the present invention explained in FIGS. 8 and 9 above can be summarized as follows.

1) The number of gradation bits after image data correction processing is thicker than the number of gradation bits of the input image data (by setting
By making the correction error during recording much smaller than the quantization error of the original image data, we have prevented the occurrence of defects due to correction.

2) Expand the gradation expression range (dynamic range) after correction of image data, perform recording control according to the density reproduction characteristics of each recording pixel after correction, and create faithful images that correspond to the original image data. I started recording.

In FIG. 10, the content explained using FIGS. 5 to 9 above will be comprehensively explained as applied to a specific embodiment of the present invention.

The horizontal axis in FIG. 10 is the gradation number, which approximately corresponds to the energization time width used for recording. The vertical axis indicates the color density obtained as a result of recording.

Note that the actual energization time will be recorded after conversion processing is performed for this gradation number to set the energization time width with the inverse of the non-linear characteristic of each energization time and recording density. . In FIG. 10, for the sake of explanation, the gradation numbers, which were arranged at approximately equal intervals, are shown at irregular intervals, and are shown at approximately equal intervals in proportion to the energization time.

The input gradation number 930 in FIG. 10 is for 64 gradations of 6 bits, and the gradation number is any number from #0 to #63. The gradation number 931 after correction processing is performed on the input is set to 256 8-bit gradation numbers. That is, the number of bits for the number of gradations after image correction is set to be larger than the number of bits for the number of gradations manually.

For convenience of explanation, 256 gradations from -5 gradation to +250250 gradation are assigned to the corrected gradation numbers.

As for the color density characteristics of the 8-color recording, three representative types are shown that are similar to those explained in FIG. That is, the characteristics 932 when image data having almost the same gradation numbers (normal image data has such similar gradation numbers) are recorded;
Characteristics when there is a sudden change from a white part to a black part 9
33, and characteristics 934 when there is a sudden change from a black part to a white part. Of course, in reality, there are various continuous characteristics between these three typical characteristics.
Correction of the image data is performed in accordance with one of the continuous characteristics during this period.

When normal image data with the same gradation number is input, the characteristics after correction basically do not need to change the value by correction, so the gradation number is moved in parallel by the amount of bit number increase. All you need to do is to assign it to the range from #0 to #200, for example. In this case, since recording is performed with the normal recording characteristic 932, the required recording density range, for example, from 0.05 to 2.0 can be obtained.

The color development density characteristic 933 when the image suddenly changes from a white part to a black part means that sufficient density will not be obtained if the gradation number setting range 932 of normal recording is maintained. It shows.

In this case, the corrected gradation number range (dynamic range) is reassigned to the range 935 from 10 to 250 gradations, for example, with respect to the gradation number range (dynamic range) of the input image data. good. This gradation number reassignment process is the content of image data correction at a location where the white portion is shifted to the black portion.

If the color development density characteristic 934 changes rapidly from the black part to the white part of the image, if the gradation number setting range 932 for normal recording is maintained, a density higher than necessary will be recorded. In this case, the corrected gradation number range (dynamic range) may be reassigned to the range 936 from -5 to 160, for example, with respect to the gradation number range (dynamic range) of the input image data. . This gradation number reallocation process is the content of the image data correction process at the location where the black part is shifted to the white part.

As described in detail above, by adjusting the dynamic range of input image data after correction according to the image data situation,
The required density can be faithfully recorded and reproduced.

In addition, in FIG. 10, for the sake of explanation, the gradation numbers after correction are set from -5 to 250, and the 0th gradation number is set as the preheating time for normal recording, but other settings may be used. The method may be set, for example, from -20 to 235, and the setting of the gradation number can be arbitrarily selected in constructing the present invention. In addition, although the number of input gradations has been explained using an example of 64 gradations with 6 bits, it is clear that the same configuration is possible with other numbers of gradations, such as 128 gradations with 7 bits. be.

FIG. 11 is a block diagram showing a means for computing coefficients in the arithmetic means explained in FIG. 7. In FIG. 7, calculation means are provided on three sides, but here, for the sake of explanation, calculation means a811 will be taken as a representative and explained. the other 2
The means also have a similar configuration.

The calculation means a811 receives an input data line a808 from the outside.
, correction coefficient selection control line 818, and output data line a8
14 are connected.

Note that a portion of the correction content command signal line 151 shown in FIG. 1 is connected to the calculation coefficient setting line 818.

Inside the calculation means a811, a calculation coefficient storage means 855, a coefficient switching means 856, and a calculation circuit 857 are provided. Then, the coefficients of the calculation contents are inputted to the calculation circuit 857 from the calculation coefficient input line 858. The calculation coefficient human power line 858 is connected to the coefficient switching means 856,
The calculation coefficients are sent out from the calculation coefficient storage means 855. At this time, the coefficient switching means 856 selects a signal line to be connected from among the plurality of coefficient output signal lines 859 sent out from the calculation coefficient storage means 855 based on a command from the correction coefficient selection control line 818.

That is, based on the setting contents sent to the correction coefficient selection control line 818 from outside the apparatus, the coefficients for calculation by the calculation means a811 can be switched and set.

Now, returning to FIG. 1 again, the overall operation of one embodiment of the present invention will be described.

Image data input to the thermal transfer recording device 1 is stored in the memory circuit 12 in six bits.

Then, it is read out from the memory circuit 12, passes through the image data correction circuit 8, is converted into an energizing pulse width by the halftone control circuit 2, and is sent to the thermal head 3. At this time, two types of correction are performed within the image data correction circuit 8. The first thermal history correction circuit 800 outputs 9-bit image data in response to 6-bit input image data to increase the number of bits of the data. The thermal head density unevenness correction circuit 8 is the second image data correction means.
The image data sent to the halftone control circuit 50 is a 9-bit output after density unevenness correction, which is finally compressed to 8 bits, and then delivered to the halftone control circuit 2. Looking at the 8 parts of this image data correction circuit as a whole, the number of bits is 8 compared to the number of human bits of 6.
The number of gradations will be reset to four times that of .

This increase in the number of bits, for example, not only simply narrows down the range of data that can be used, but also expands the expressible range (dynamic range). That is, if no correction processing is performed using only the original image data manually input, the gradation numbers from gradation number #0 to #200 are simply multiplied by approximately three times. Then, the expression range of the original input image data is divided three times as finely as possible to make it possible to express intermediate densities that are newly required by correction.

In addition, the range from gradation number #-5 to #250, which is the expression range of the corrected image data, compensates for the energization waveform that was insufficient in the expression range of the original image data. It is possible to record faithfully to the original image data.

By using a correction content setting switch 150 provided outside the thermal transfer recording apparatus 1, correction content can be set from outside the apparatus into the image data correction circuit 8 via a correction content command signal line 151.

Therefore, the type of image data correction can be set from outside the thermal transfer recording apparatus 1 according to the content of the image to be recorded.

In the internal configuration of the image data correction circuit 8, correction for recording unevenness inherent in the recording means, that is, the thermal head 3 and the mechanism section 4 is provided at a later stage.

Therefore, it is possible to accurately perform corrections related to the recording apparatus itself.

FIG. 12 is a block diagram showing the overall configuration of a second embodiment according to the present invention.

In FIG. 12, the correction coefficient of the image data correction circuit 8 is changed in accordance with correction content setting information sent from outside the thermal transfer recording apparatus l.

From the correction content setting knob 152, the correction content command signal line 1
53, the correction coefficient and the correction contents are sent to the correction coefficient setting circuit 154. Here, the correction coefficient setting circuit 154 includes an arithmetic processing means such as a microcomputer, and resets the coefficients of the image data correction circuit 8 in accordance with the input correction coefficient setting information, and transfers the correction coefficients. It is sent to the image data correction circuit 8 via line 155.

In this way, necessary correction details and correction coefficients can be set from outside the apparatus, and appropriate correction can be performed on the input image.

FIG. 13 is a block diagram showing the internal configuration of a third embodiment of the present invention.

In the embodiment shown in FIG. 13, a differentiation circuit 156 is provided as a means for extracting features of the input image data, and based on the extraction result of this image data extraction means, a correction coefficient setting circuit 154 Determine the type of data.

The result of the discrimination is that the gradation of the image changes rapidly (for example, from gradation #0 of a white background to #63 of a black character part), such as a character or line image. , it is possible to determine that the image is a character or line image by detecting its gradation discontinuity characteristics. In the case of such characters or line images, if the thermal head 3 corresponding to the pixel in question is relatively cold or black is continuous, the waveform of the current applied to the thermal head 3 must be changed significantly. Must be. In other words, use l! by changing the image data correction coefficients. ! This will expand the range of the J key.

Further, if the input image data is, for example, an image based on a video signal and in which gradations are continuous for each pixel, the output of the differentiating circuit 156 will be a small value. In such a case, if the image data is significantly corrected, the original image may be damaged, so for example, the correction coefficient is set to a relatively small value.

Furthermore, if the input image data is an artificial image such as computer graphics, and the gradation numbers are continuous for each pixel, the correction coefficient should not be made too large. Expand the data width of the output,
For example, make settings to create a sharp image.

In the embodiment according to the present invention described above, in order to simplify the explanation, the original number of gradations of the image data to be handled is assumed to be 64, but of course the number of gradations such as 16.32, 128.256, etc. It goes without saying that this can also be carried out in the same way. Also, the relationship between the N key number and the reproduced density is
For the sake of explanation, we have explained the case where they correspond linearly, but the relationship between tone number and density is the same even if it is set to have a relationship of other characteristics (for example, the inverse of the γ characteristic of a video signal). It is clear that it can be implemented.

Further, as an example of the present invention, the case of thermal transfer using a sublimable dye has been described, but it is also possible to control the recording density by applying heat energy in a method other than a sublimable dye, such as a method using heat-sensitive coloring paper. It goes without saying that gradation can be expressed in the same way using this method.

〔Effect of the invention〕

As described above in detail, the present invention has the following effects.

Since the number of bits after image data correction was set to be larger than the number of bits of the input image data, it is possible to express subtle density values due to correction, and the difference between areas with correction and areas without correction can be made. Smooth correction can be performed without creating visually discernable steps. In addition, a portion of the increased number of bits after correction is allocated to the expansion and contraction directions of the energization time, which reduces the temperature of isolated recording pixels even for characters and line images with a sharp contrast between artificial black and white. In the case of insufficient concentration due to this phenomenon, the problem can be solved by extending the energization time. Furthermore, even when a white area is covered with ink after a large area of black area continues, it is possible to maintain the white area by reducing the time period during which residual heat is applied without coloring.

In addition, since the type and coefficient of image data correction can be changed according to the type of image data being input, the appropriate correction method and correction coefficient can be set according to the image to be recorded. and can record good images.

Furthermore, by detecting the type of image and automatically inputting it to the means for setting the type and coefficient of image data correction described above,
You can set the correction type and coefficient suitable for the input image.
Good images can be recorded.

By placing the correction for the unique characteristics of each device at the final stage in the connection order of the plurality of image data correction means, the other correction means are not affected by the correction unique to the device.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the internal configuration of a thermal transfer recording device according to a first embodiment of the present invention, FIG. 2 is an external view of the thermal transfer recording device shown in FIG. 1, and FIG. 4 is an explanatory diagram of the color density characteristics and the energization time setting of the sublimable dye with respect to the energization time; FIG. 5 is an explanatory diagram of the number of gradations to be controlled; FIG. 6 is an explanatory diagram of changes in color density characteristics of a single pixel due to surrounding heating conditions, and FIG. 7 is a block diagram showing the internal configuration of an image data correction circuit according to an embodiment of the present invention shown in FIG. Figure, 8th
9 and 9 are explanatory diagrams of a two-dimensional section of the input image data example of the first embodiment shown in FIG. 1 and the effect of correction,
FIG. 10 is an explanatory diagram showing the relationship between the range of the number of gradations of input image data, the range of the number of gradations after image data correction, and the color density characteristics, and FIG. 11 is a correction coefficient of the image data correction means. FIG. 12 is a block diagram showing the configuration of the switching means.
FIG. 13 is a block diagram showing the internal configuration of a thermal transfer recording apparatus according to a second embodiment of the present invention. FIG. 13 is a block diagram showing the internal configuration of a thermal transfer recording apparatus according to a third embodiment of the present invention. 1. Thermal transfer recording device, 2. Halftone control circuit, 3. Thermal head, 4. Mechanism section, 8. Image data correction circuit, 800. Thermal history correction circuit, 850. Thermal head density unevenness correction. circuit, 801
...Digital data input line, 821...Output image data line, 150...Correction content setting switch, 152...Correction content setting knob. Kaya 50 N so-called scale number = (C) If-1000 - (C) Tsuji 9 10th figure well θ 31#Δ3 Manual gradation number No. II Ku

Claims (1)

[Scope of Claims] 1. A thermal transfer recording means and apparatus for appropriately heating a plurality of heating elements arranged in a row in a thermal head to transfer coloring material from an intermediate recording medium to which the coloring material is supplied onto the recording medium. Based on the gradation number for each pixel, which is an information signal sent from the outside,
A thermal transfer recording apparatus comprising means for controlling the energization waveform of a heating element corresponding to a pixel to control the gradation representing the density of recording for each heating element, the apparatus comprising: The present invention is characterized by comprising a correction means for setting image data having a number of bits greater than the number of gradation expression bits of the thermal transfer recording device, and further comprising a configuration in which the correction contents of the correction means can be changed by a command from outside the thermal transfer recording device. A thermal transfer recording device. 2. The thermal transfer recording apparatus according to claim 1, further comprising means for changing the correction coefficient of the image data from outside the apparatus. 3. The thermal transfer recording apparatus according to claim 1, further comprising a feature detecting means for inputted image data, and sending the detection result of the feature detecting means to a coefficient setting means of the image data correcting means, so as to correspond to the input image data. A thermal transfer recording device characterized by being configured to set image data correction details. 4. The thermal transfer recording device according to claim 1, wherein when the thermal transfer recording device has a plurality of image data correction means, correction of recording density unevenness inherent to the device is performed at the final stage. 5. The thermal transfer recording apparatus according to claim 1, further comprising means for changing the variable range of the injection energy for each pixel in image recording after correction, depending on the content of the correction.