JPH111016A - Heat-sensitive recording apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable recording of high-quality images with a stable density, by determining a heat generation maximum time for obtaining a required maximum density with the use of a gradation correction table under a record condition that a non-heat time between heat-generating blocks is zero, and forming a recording gradation correction table. SOLUTION: A platen roller 60 is rotated to transfer a heat-sensitive recording material A in a sub-scan direction. Many heat-generating elements 86 are arranged in a main scan direction of a thermal head 66. The heat-sensitive material A is colored with a predetermined gradation. Image data are divided in the sub scan direction to a plurality of data, and assigned to heat-generating blocks. One pixel is recorded by the generation of heat from each heat- generating block corresponding to the divided image data. In order to correct the gradation, a temporary gradation correction table is generated under a record condition that a non-heat time between the heat-generating blocks is 0, a heat generation maximum time required for a required maximum density is determined with the use of the temporary gradation correction table and, a recording gradation correction table is formed. Accordingly, high-quality images properly corrected in gradation can be recorded stably.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of a thermal recording apparatus, and more particularly, to a thermal recording apparatus capable of stably recording an image having an appropriate density in an apparatus for dividing and recording one image data. Related to the device.

[0002]

2. Description of the Related Art Thermal recording using a thermal recording material having a thermal recording layer formed on a support such as a film (hereinafter, referred to as a thermal material) is used for recording an ultrasonic diagnostic image. In addition, thermal recording does not require a wet development process,
In recent years, it has advantages such as easy handling, not only small image recording such as ultrasonic diagnosis,
For applications requiring large and high-quality images, such as CT diagnosis, MRI diagnosis, and X-ray diagnosis, use for image recording for medical diagnosis is also being studied.

[0003] As is well known, thermal recording uses a thermal head having a glaze in which heating elements are arranged in one direction (main scanning direction) for recording an image by heating a thermal recording layer of a thermal material. Glaze to heat-sensitive material (heat-sensitive recording layer)
In a state in which both are moved slightly in the sub-scanning direction orthogonal to the main scanning direction while slightly pressed, the respective glazes in accordance with the image data of the recording image supplied from an image data supply source such as MRI. By applying energy to the heating elements of the pixels to generate heat, the thermosensitive recording layer of the thermosensitive material is heated to perform image recording.

As a method of recording a gradation image in such thermal recording, a method of changing a heating time of a heating element by pulse (width or number) modulation according to a recording density is known. For example, an image with data D _P = 1 for recording is formed by heating the heating element for t seconds. Further, an image of data D _P = 2 to be recorded is recorded for 2t seconds.
Similarly, images of data D _P = 3 to 5 to be recorded are formed by heating the heating elements for 3 to 5 t seconds, respectively. As a result, pixels having different coloring areas and different coloring densities are formed on the heat-sensitive material in accordance with the data to be recorded in the range of one pixel width in the transport direction, and thereby a gradation image is recorded.

When a gradation image is recorded in this manner, each pixel is recorded from a fixed point in the sub-scanning direction, ie, a recording start position, and the other point in one pixel in the sub-scanning direction, ie, recording, is performed. Since the end position side is the non-recording portion, the recorded images concentrate on the recording start position side. Therefore, when the formed image is observed as a whole, there is a problem that the image becomes conspicuous and rough.

In order to solve such a problem, the present applicant divides image data of each pixel constituting an image into a plurality of substantially equal parts in the sub-scanning direction in image recording using a thermal head, a laser beam, or the like. There has been proposed an image recording method and apparatus in which one pixel is divided into a plurality of pieces in the sub-scanning direction and recorded (hereinafter, referred to as divided recording) using the divided image data (see Japanese Patent Application Laid-Open No. 7-96625). .
With this image recording method and apparatus, concentration of image recording portions in the sub-scanning direction can be avoided, and a high-quality image without roughness can be formed. In addition, in divided recording, one heat generation time is short, and a low density portion becomes unstable.
It is considered that the number of divisions of the image data and the number of heat generations are changed, but in this case, if the maximum heat generation time in one pixel printing is different, the density is high even if the total heat generation time in one pixel printing is the same. Will change.

The maximum heat generation time (maximum density) during recording of one pixel is defined as t _max . Here, assuming that one recording (heat generation) in divided recording is a heat generation block, the maximum length of one heat generation block is determined by this _tmax , and the time between each heat generation block, that is, the non-heat generation time is determined. The image data in the thermal recording is for determining the total heat generation time in the recording of one pixel, that is, the total of the heat generation times of all the heat generation blocks in the divided recording, but one image data is recorded over a plurality of heat generation blocks. In this case, as shown in FIG. 5, the length of t _max ((a) is t
_{When the max} is short, (b) indicates a long case), the length of the unheated time between the heat generating blocks changes.
The degree of temperature drop of the heating element of the thermal head differs between the heating blocks. Therefore, even if the total heat generation time in the printing of one pixel is the same, the total heat generation amount of the heating element differs, and the recording density changes.

[0008]

As is well known, in various image recording apparatuses including a thermal recording apparatus, gradation correction is performed in order to record an image having an appropriate density according to supplied image data. Is performed. This gradation correction is performed by using a gradation correction table set for each apparatus and correcting image data supplied from an image data supply source such as an MRI with the gradation correction table.

Here, in an apparatus aiming at higher-quality image recording, the maximum heat generation time t _max may be changed between normal image recording and image recording for creating a gradation correction table. In other words, when performing image recording for creating a tone correction table, it is necessary to create a tone correction table that can reliably record the highest density that is intended by the apparatus and can compensate up to the corresponding range. So t _max
And image recording is performed up to an area having a higher density than the target maximum density. On the other hand, in normal image recording,
In order to increase the density (gradation) resolution, high-quality image recording is performed by shortening _tmax . However, in this case, in a device that performs divided recording, the density does not match between the normal image recording and the gradation correction table, so that proper thermal recording cannot be performed.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problem of the prior art. In a thermal recording apparatus for performing divisional recording, in which image data is divided into a plurality of parts in the sub-scanning direction and recorded, the maximum heat generation time is reduced. It is an object of the present invention to provide a thermal recording apparatus which has an appropriate gradation correction table irrespective of a difference, that is, a difference in a non-heating time between heating blocks, and is capable of performing high-quality image recording with stable density.

[0011]

In order to solve the above-mentioned problems, the present invention relates to a thermal recording apparatus for recording on a thermal material by a thermal head, wherein one image data is divided into a plurality of heating blocks. In a thermal recording apparatus for recording, a relationship between a heating time and a reaction amount of a heat-sensitive material under a recording condition where the unheated time between the heating blocks is 0, a heating time and a test under a recording condition when a gradation correction table is created. From the relationship between the reaction amount of the thermosensitive material and the density of the thermosensitive recording image for preparing the tone correction table recorded on the test thermosensitive material, a tone correction table under the recording condition where the unheated time is 0 is created. The maximum heat generation time required to obtain the desired maximum density is determined using the gradation correction table, and the heat generation time and the heat-sensitive material under the recording conditions corresponding to the maximum heat generation time are determined. A recording gradation correction table is created from the relation between the reaction amount, the relation between the heat generation time and the reaction amount of the heat-sensitive material under the recording condition where the unheated time between the heat generating blocks is 0, and the gradation correction table. The present invention also provides a thermal recording apparatus characterized in that supplied thermal image data is corrected and thermal recording is performed using the recording gradation correction table.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a thermal recording apparatus according to the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings. FIG. 1 shows a schematic diagram of an example of a thermal recording apparatus according to the present invention. Thermal recording device 10 shown in FIG.
The recording device 10 (hereinafter, referred to as a recording device 10) performs thermal recording on a thermosensitive recording material (hereinafter, referred to as a thermosensitive material A) which is a cut sheet of a predetermined size such as a B4 size.
It comprises a loading section 14 into which a magazine 24 containing the thermal material A is loaded, a supply and transport section 16, a recording section 20 for performing thermal recording on the thermal material A by a thermal head 66, and a discharge section 22.

In such a recording apparatus 10, one heat-sensitive material A is pulled out of the magazine 24 and
The thermal material A is conveyed to the thermal head 66 while pressing the thermal head 66 against the thermal material A, and at right angles to the glaze extension direction of the thermal head 66, that is, the main scanning direction (the direction perpendicular to the plane of FIG. 1 and the direction of arrow X in FIG. 2). The heat-sensitive material A is conveyed in the sub-scanning direction (Y direction in FIG. 2), and each heating element 86 (see FIG. 2) according to a recording image (image data) supplied from an image data supply source such as CT or MRI. ), Heat-sensitive recording is performed on the heat-sensitive material A.

The heat-sensitive material A is a material in which a heat-sensitive recording layer is formed on one surface of a support such as a resin film such as a transparent polyethylene terephthalate (PET) film or paper as a support. In the illustrated example, the heat-sensitive recording layer is stored in the magazine 24 of the recording apparatus 10 with the heat-sensitive recording layer as the lower surface.

The magazine 24 is a housing having a lid 26 which can be opened and closed. The magazine 24 stores the heat-sensitive material A and is loaded in the loading section 14 of the recording apparatus 10. The loading unit 14 includes the recording device 10
Insertion hole 30 formed in housing 28 of
And guide rolls 34, 34, and a stop member 36.
The magazine 24 is inserted into the recording device 10 from the insertion port 30 with the lid 26 side first, and the guide plate 32 and the guide roll 3
4. It is loaded at a predetermined position by the stop member 36. Although not shown, the loading section 14 is provided with a known lid opening / closing mechanism for opening and closing the magazine lid 26.

The supply / conveyance means 16 takes out one heat-sensitive material A from the magazine 24 and conveys the heat-sensitive material A to the recording unit 20. The sheet conveyance mechanism using the suction cup 40, the conveyance means 42, the conveyance guide 44, and the regulating roller It has a pair 52. The conveying means 42 includes a conveying roller 46, a pulley 47 a coaxial with the conveying roller 46, and a pulley 4 connected to a rotation drive source.
7b, a tension pulley 47c, an endless belt 48 stretched over these three pulleys, and a nip roller 50 forming a roller pair with the transport roller 46. The heat-sensitive material A is transported by nipping the leading end between the transport roller 46 and the nip roller 50.

When an instruction to start recording is issued in the recording apparatus 10, the lid 26 is opened by the opening / closing mechanism.
The single-wafer mechanism using the suction cup 40 takes out one heat-sensitive material A from the magazine 24 and supplies the leading end of the heat-sensitive material A to the transport means 42. When the heat-sensitive material A is nipped by the conveyance roller 46 and the nip roller 50, the suction by the suction cup 40 is released, and the supplied heat-sensitive material A
The sheet is conveyed to the regulating roller pair 52 by the conveying means 42 while being guided by the roller. When the tip of the heat-sensitive material A reaches the regulation roller pair 52, the temperature of the thermal head 66 is confirmed. If the temperature is a predetermined temperature, the conveyance of the heat-sensitive material A by the regulation roller pair 52 is started. , Recording unit 2
Transported to zero.

The recording section 20 includes a thermal head 66, a platen roller 60, a cleaning roller pair 56, and a guide 5.
8, a cooling fan 76 for cooling the thermal head 66, and a guide 62 are provided. The thermal head 66 is capable of recording images up to a maximum B4 size, for example, about 300 mm.
The thermal head performs thermal recording at a recording density of dpi, and includes a thermal head body having a glaze formed by arranging a heating element 86 including a glaze layer (heat storage layer), a heating resistor, and an electrode in a main scanning direction; A heat sink fixed to the head body. This thermal head 66
Is supported by a support member 68 that is rotatable up and down around a fulcrum 68a. The platen roller 60 rotates in the direction of the arrow at a predetermined image recording speed while holding the heat-sensitive material A at a predetermined position, and conveys the heat-sensitive material A in the sub-scanning direction. The cleaning roller pair 56 is located at the upper side in the drawing (on the heat-sensitive recording layer side).
Has an adhesive rubber roller, and the adhesive rubber roller is a heat-sensitive material A.
It is possible to prevent dust and the like from adhering to the glaze and prevent dust from adversely affecting image recording.

In the recording apparatus 10 in the illustrated example, before the heat-sensitive material A is conveyed, the support member 68 is rotated upward, so that the thermal head 66 (glaze) and the platen roller 60 do not come into contact with each other. Has become. When the conveyance by the above-described regulating roller pair 52 is started and the leading end of the heat-sensitive material A is conveyed to a recording start position (a position corresponding to the glaze), the support member 68 rotates downward and the thermal head 66 (glaze). ) With the platen roller 60
, The glaze is pressed against the recording layer, and the heat-sensitive material A is held at a predetermined position by the platen roller 60, while the platen roller 60 (and the regulating roller pair 52 and the transport roller pair 64) is used in the sub-scanning direction. Transported to

Along with this conveyance, the heating elements 86 of each pixel of the glaze 66 are heated in accordance with the recorded image, whereby
Thermal recording is performed on the thermal material A. Here, in the recording apparatus 10 according to the present invention, one pixel of image data is divided into a plurality of pieces in the sub-scanning direction, and one heat is generated by a plurality of times of heat generation according to the divided image data (divided image data). Image recording is performed by divided recording in which image recording of pixels (one line in the main scanning direction) is performed. This will be described in detail later. The heat-sensitive material A on which the heat-sensitive recording has been completed is conveyed to the platen roller 60 and the conveyance roller pair 64 while being guided by the guide 62, and is discharged to the tray 72 of the discharge unit 22.

FIG. 2 is a schematic diagram of a recording control system of the recording unit 20. As shown in FIG.
Is rotated by a step motor 84 under the action of a control unit 82 of a recording control system 80 described later, and conveys the heat-sensitive material A in the sub-scanning direction (the direction of the arrow Y). As described above, the thermal head 66 is configured by arranging a number of heating elements 86 in the main scanning direction (the direction of the arrow X), and each heating element 86 is supplied from the thermal head driving unit 88 of the recording control system 80. The drive current generates heat so that the heat-sensitive material A is colored at a predetermined gradation.

The recording control system 80 includes a frame memory 90 for storing image data supplied from an image data supply source such as a CT or MRI, and an image data stored in the frame memory 90 for all pixels in the main scanning direction. A line memory 92 for storing each line, a divided image data memory 94 for storing divided image data obtained by dividing all image data that can be taken by the image data in the sub-scanning direction, and a thermal head based on the divided image data 66, a control unit 82 for controlling them, and a pixel clock signal PCLK output from the control unit 82.
The counter 96 outputs address data for outputting image data stored in the line memory 92 for each pixel in the main scanning direction, and the line clock signal LCLK output from the control unit 82 is counted. The lower three bits of the address data for outputting the divided image data from the divided image data memory 94 are supplied, and the timing signal TS for reading the image data from the frame memory 90 is sent from the timing signal generator 98 to the line memory 92. and a counter 100 for outputting count data B ₃ for generating.

Between the line memory 92 and the divided image data memory 94 and between the divided image data memory 94 and the thermal head driving unit 88, the control unit 82 transmits the divided image data to the divided image data memory 94. Are connected to each other. Further, the control unit 82 includes a memory 106 such as a ROM or a RAM.
The memory 106 stores at least all the divided image data described above. The divided image data stored in the memory 106 may be one type, but may be a plurality of types of divided image data. May be stored. Such divided image data is configured to be downloaded and stored in the memory 106 or directly in the divided image data memory 94 via the control unit 82 by a storage medium such as FD, HD, MD, and MO from the outside. In this case, the memory 1
06 may be omitted.

Further, the frame memory 90 is connected to an image processing unit 108 for performing predetermined image processing on image data supplied from an image data supply source such as CT. The image processing unit 108 is configured by combining a CPU (Central Processing Unit), an LUT (Look Up Table), a memory, an image processing circuit, and the like.
It has a gradation correction section, a temperature correction section, a shading correction section, a resistance correction section for a heating element, a black ratio correction section, and the like, and corrects image data supplied from an image data supply source in each of the above-described portions. The frame memory 9 is used as image data for thermal recording by the thermal head 66.
Send to 0. Here, the gradation correction unit of the image processing unit 108
This is a characteristic part of the present invention, in which image data is processed by a predetermined gradation correction table, and gradation correction of the image is performed. This gradation correction unit will be described later in detail.

In such a recording control system 80, first, prior to image recording, the divided image data is transferred from the memory 106 via the control unit 82 with the switches 102 and 104 connected to the contact b side. The data is stored in the divided image data memory 94. For example, the image data of one line of each pixel supplied from the line memory 92 to the divided image data memory 94 is 11 bits, and the output data (B _{0 to} B ₂ ) supplied from the counter 100 is 3 bits and the image of one line is provided. If the divided image data obtained by dividing the data is 8 bits, the divided image data read address data corresponding to one line of image data is set to the upper 11 bits (A _{3 to} A ₁₃ ) in the divided image data memory 94. , The lower three bits (A _{0 to} A ₂ ) thereof being 3-bit output data (B _{0 to} B ₂ ) from the counter 100, and all the corresponding 14-bit address data A _{0 to} A ₁₃ 8-bit divided image data is stored.

Table 1 below shows an example of the divided image data. In this example, one pixel of image data has 11 bits (0 to 0).
2047), the image data is equally divided into eight in the sub-scanning direction (that is, divided into eight heating blocks A to H), and the image data is divided into eight bits (0 to 255) of image data at a maximum of eight times. This is an example of recording one pixel by heat generation. In addition,
This example is described in detail in JP-A-7-96625 by the present applicant.

[0027]

[Table 1]

In the example shown in Table 1, since the image data is divided, the temperature of the heating element in each heating block does not rise sufficiently in the low density area, and the image density is lower than the target value in the low density area. There is a problem that it may become. In the division example described below, the image data is divided into a smaller number of heat-generating blocks (the number of heat-generating blocks that can be recorded per pixel), and the image data divided to a certain density (low-density portion) is divided into heat-generating blocks. Allocated only to a predetermined block, and when the density exceeds a certain level (high density area), it is allocated to the remaining heat generating blocks. As a result, the problem in the low density range shown in Table 1 can be solved, and higher-quality thermal image recording can be performed. In addition, according to this division method, even if the non-heating time between the heat-generating blocks changes, the thermal recording apparatus of the present invention has an appropriate gradation correction table in accordance therewith, and provides a high-density image with a stable density. The feature of the present invention of performing an excellent image recording can be more remarkably exhibited, and a more preferable result can be obtained. The dividing method and the recording method using the dividing method will be described in detail in Japanese Patent Application No. 8-202131 by the present applicant.

Table 2 below shows an example of divided image data in which the image data of each pixel is 11 bits, the heating block is divided into eight in the sub-scanning direction, and the image data is divided into four parts to form 8-bit image data. Show.

[0030]

[Table 2]

As shown in Table 2, in this example, each pixel is divided into eight heating blocks of block A to block H. In a low density portion up to a certain density portion, the image data is divided into the heating blocks. It is divided into only four substantially equal divided image data smaller than the number, and these four divided image data are allocated to only four heating blocks A, C, E and G out of eight heating blocks. And is not allocated to the remaining four heating blocks B, D, F and H. The low-density portion in this example means that the divided image data is 8
Bits, all four divided image data are 255
, Ie, the case where the image data of one pixel is 1020 or less. If the image data exceeds 1020, 1
Only the image data exceeding 020 is substantially equally divided into four divided image data, and the remaining four heat generation recording points B, D, F
And H. Therefore, the driving pulse (heating time) of each heating element in the low density region becomes large (about twice as large in this example), and the heating element is sufficiently heated even in the low density region, so that the color is sufficiently developed. It is possible to stably record a high-quality image whose low-density region is appropriate. FIG. 3 conceptually shows the relationship between the driving pulse based on the divided image data shown in Table 1 and the driving pulse based on the divided image data shown in Table 2 in the image recording in the low density region, and the thermal head temperature in both cases.

The division of the image data as described above is performed, for example, as follows. That is, the image data D _P, the division number M, the M pieces of divided image data after the division d
_1, d _2, ..., when the d _M, the image data D _{P is, D P = d 1 + d} 2 + ... + d M = [D P / M] + [(D P -d 1) / (M-1 )] +
_{[(D P -d 1 -d 2} ) / (M-2)] + ... + [(D P
−d ₁ −d ₂ −... −d _M−1 )]], and the M divided image data d ₁ , d ₂ ,.
It can be divided into d _M. In the example shown in Table 2, since the image data 2040 and above, all the divided image data of each heat generating block saturates at 255, all the divided image data take the same 255 for the image data beyond that.

According to this dividing method, it is possible to obtain a high-quality image in which low-density portions are sufficiently colored. However, if the image quality is further pursued, the image data of each heating block may become saturated in the low density portion, and unevenness that may occur when image data is assigned to a heating block that has not been assigned until now may be a problem. . For example, in Table 2, when the image data changes from 1020 to 1021, the divided image data 1 is allocated to the heat generation block H which has not been allocated until now. On the other hand, when the image data is switched from 1019 to 1020, the divided image data in the heat generation block A is increased by one from 254. At this time, the number of increments of the image data is 1 and the applied energy that increases is the same in both cases. However, in the heat generating block A, the heat is further applied when the heat is sufficiently generated. Since the voltage is applied where it is not performed, the rate of contribution to the overall heat generation differs.
For this reason, the linearity (linearity) of the gradation of the recorded image expressed by the sum of the image data and the eight heating blocks cannot be maintained, and discontinuity of the gradation may occur in the recorded image.

In order to prevent such unevenness and discontinuity of gradation and obtain a high-quality image, for example, in the case of dividing the heating block into eight parts and dividing the image data into four parts, instead of the dividing method shown in Table 2, The image data is divided into four in units of two heating blocks A + B, C + D, E + F, and G + H, and the divided image data is divided into two heating blocks, for example, A
And a method of allocating the data to B. By doing so, it is possible to balance the energy applied to both of the heat generating blocks A and B, and to prevent unevenness in the correction of the resistance value based on the difference in the contribution of the increased energy to the entire heat generation. Table 3 below shows one example.

Table 3 Example of image data division (part 3) A + B 0 0 0 0 1 1 1 ... 254 255 255 255 ... 510 510 510 ... 511 C + D 0 0 0 1 1 1 1 ... 255 255 255 255 ... 510 510 510 ... 512 E + F 0 0 1 1 1 1 2 ... 255 255 255 256 ... 510 510 511 ... 512 G + H 0 1 1 1 1 2 2 ... 255 255 256 256 ... 510 511 511 ... 512 Total value 0 1 2 3 4 5 6 ... 1019 1020 1021 1022 ... 2040 2041 2042 ... 2047

The distribution of the divided image data to the two heat generating blocks can be performed as follows, for example. For example, taking the heating blocks A and B as an example, the divided image data is represented by y (≦ 2 ^k -1; k is the number of bits of the divided image data), and the image data distributed to the heating blocks A and B are represented by D, respectively. _a, and D _B, fever blocks a, B
Is the maximum value of the image data assigned to K (= 2 ^k−1 −
Assuming 1), and assuming that the distribution ratio of the divided image data to the heat generating blocks B is N, the following formula can be used. D when D _A> K when _{A ≦ K D B = y /} N D A = K D A = y-D B D B = y-D A

According to this distribution method, the distribution ratio N
By selecting, it is possible to adjust the distribution balance of the divided image data to each heating block with respect to the increase in the image data. The distribution ratio N is preferably 3 to 50. Table 4 shows divided image data distributed to each of the heat generating blocks A to H when the image data is divided into four in units of two heat generating blocks shown in Table 3 and the distribution ratio N is set to 10.

Table 4 Example of Image Data Division (Part 4) A 0 0 0 0 1 1 ... 229 230 230 230 ... 255 255 ... 255 B 0 0 0 0 0 0 ... 25 25 25 25 ... 255 255 ... 255 C 0 0 0 1 1 1 ... 230 230 230 230 ... 255 255 ... 255 D 0 0 0 0 0 0 ... 25 25 25 25 ... 255 255 ... 255 E 0 0 1 1 1 1 ... 230 230 230 231 ... 255 255 ... 255 F 0 0 0 0 0 0 ... 25 25 25 25 ... 255 255 .. 255 G 0 1 1 1 1 2 ... 230 230 231 231 ... 255 255 ... 255 H 0 0 0 0 0 ... 25 25 25 25 ... 255 255 ... 255 Total value 0 1 2 3 4 5 ... 1019 1020 1021 1022 ... 2040 2041 ... 255

In the recording control system 80, all of such divided image data, for example, all of the divided image data shown in Table 2 are generated in advance and stored in the memory 106 or an external storage device. As described above, all the divided image data in the memory 106 or the external storage device is read out by the control unit 82 and stored in the divided image data memory 94. , 14-bit address data. Table 5 below shows the divided image data and address data stored in the divided image data memory 94, taking the divided image data shown in Table 2 as an example.

[0040]

[Table 3]

The divided image data memory 94 has the table shown in Table 5.
In the low density area, one pixel of image data is
The divided image data divided into four
4 blocks A, C, E and G up to block H
In the middle and high density part, the divided image data
Are assigned from block A to block H,
0,0,0,0,0,0,0,0 (image data D_P=
0) / 0,0,0,0,0,0,1,0 (D_P= 1) /
… / 255, 0, 255, 0, 255, 0, 255, 0
(D_P= 1201) /.../ 255, 255, 255, 2
55, 255, 255, 255, 255 (D_P= 204
7). Here, the 14-bit
Address data A₀~ A₁₃Lower 3 bits (A _Two,
A₁, A₀) Indicates the heat-sensitive material A by the thermal head 66.
Block A (A_Two= A₁= A₀= 0),
Lock B (A_Two= A₁= 0, A₀= 1) Block G
(A_Two= A₁= 1, A₀= 0), block H (A_Two= A
₁= A₀= 1) is specified. On the other hand,
Dress data A₀~ A₁₃Upper 11 bits (A_Three~
A₁₃) Represents the 11-bit image data before 1-pixel division.
Specify that the image data is the divided image data.

As described above, after the divided image data is stored in the divided image data memory 94, the switch 102,
The image recording is started according to the timing chart shown in FIG.

First, the control unit 82 outputs a drive signal SS to the step motor 84, and based on this, the step motor 84 drives the platen roller 60 to rotate, and the heat-sensitive material A moves at a predetermined speed in the sub-scanning direction ( (Y direction). On the other hand, the control unit 82 controls the pixel clock signal PC
LK and a line clock signal LCLK are generated and output to the counter 96 and the counter 100, respectively. At this time, the counter 100 outputs count data B _3,
Timing signal TS timing generating circuit 98 receives the count data B ₃ are synchronized or proportional to the drive signals SS
Is output. This timing signal TS is transmitted to the line memory 9
2, the image data of all pixels (one line of image data in the main scanning direction) is read out from the (two-dimensional) image data stored in the frame memory 90, and the line memory 92 is read out. Is transferred and stored.

Next, when the pixel clock signal PCLK is output from the control unit 82 to the counter 96, the counter 96 sequentially counts up the pixel clock signal PCLK and supplies it to the line memory 92 as address data. The line memory 92 stores the one line of image data for each pixel in accordance with the address data.
2 and output as address data to the upper 11 bits (A _{3 to} A ₁₃ ) of the divided image data memory 94.

On the other hand, when line clock signal LCLK is output from controller 82 to counter 100,
00 sequentially counts up the line clock signal LCLK, and counts 1 from the LSB (Least Significant Bit) side.
_First , second and third data B ₀ , B ₁ , B ₂ are transferred to lower 3 bits (A ₀ , A ₁ , A ₂ ) of divided image data memory 94 via switch 102 as address data. supplies, and supplies count data B ₃ of the fourth as a signal for generating a timing signal TS to the timing generating circuit 98.

As described above, the divided image data memory 94
, The upper 11 bits are composed of image data of each pixel before division, and the lower 3 bits are supplied with 14-bit address data indicating blocks A to H. For example, the divided image data and address data shown in Table 5 are stored in the divided image data memory 94, and as shown in Table 6, 1, 3, 401, 1022, 2040, 7, 0,
When performing image recording using image data of block A, block A
As an example, the data B ₀ , B ₁ , and B ₂ output from the counter 100 are the 0th line clock signal LC.
LK are reset to 0, and the lower 3 bits of address data are selected from the divided image data memory 94 stored at the address where A ₀ = A ₁ = A ₂ = 0. Drive unit 88
Supplied to

[0047]

The thermal head driving section 88 performs pulse width modulation on all the pixels in the main scanning direction in accordance with the divided image data of the block A selected from the divided image data memory 94, and performs time modulation of each pixel. A predetermined drive current corresponding to the width is supplied to each heating element 86 of the thermal head 66. Hereinafter, similarly, the address data of the lower three bits A ₀ , A ₁ , and A ₂ of the divided image data memory 94 are sequentially updated in accordance with the line clock signal LCLK, so that the blocks B, C,. A drive current according to the image data is sequentially supplied to each heating element,
An image of one pixel (one line) is recorded on the thermosensitive material A. The modulation may be pulse number modulation, or
Both pulse width modulation and pulse number modulation may be used together.

As described above, the image data is transferred in the sub-scanning direction.
In a thermal recording device that records separately, normal image recording and
Image recording for creating a gradation correction table
Concentration in the element, ie maximum heat generation time t_max(All shots
The sum of the maximum heating time of the heat block)
However, in this case, the unheated time between the blocks is t
_maxTemperature effect of the heating element
Of the image, the normal image recording and the gradation correction table
And the density does not match, preventing proper thermal recording.
U. On the other hand, in the recording apparatus 10 of the present invention,
The image processing unit 1 uses a predetermined gradation correction table shown below.
08 to perform the gradation correction in the gradation correction unit 08,
Large time t_maxUnaffected by concentration changes due to differences in
Appropriate image recording can be performed stably. Below,
Will be described.

As described above, the division recording means that the image data is divided into a plurality of parts (divided image data) in the sub-scanning direction, and each of the preset heat generating blocks (the eight blocks A to H in the above example). ) And intermittent heat generation in each heat generation block according to the divided image data.
This is a recording method for recording pixels. Therefore, the maximum value of the heat generation time for each heat generation block is determined by the maximum heat generation time t _max determined according to the target maximum density of one pixel.
The heat generation ratio of each heat generation block during image recording is determined by image data. That is, the heat generation time for one pixel is: heat generation time = (image data value / maximum image data value) × maximum heat generation time t _max .

In the present invention for performing such divided recording, when the gradation correction table is created, first, in the image recording of one pixel, the maximum heat generation when the unheated time between each heat generation block becomes 0 is set. The amount of reaction (that is, color development) of the thermosensitive material A with respect to the heat generation time under the recording condition of the time t _max 0 is calculated. This reaction amount is calculated by the Arrhenius equation using the temperature of the thermal head (heating element).

Temperature change of thermal head [dT] / [d
t] is proportional to the energy supplied to the heating element (constant is k _E ). Moreover, (the constants k _b) proportional to the difference between the ambient temperature T _b and the thermal head temperature T energy only by escape. Therefore, the temperature change of the thermal head [d
T] / [dt] can be obtained by the following equation: [dT] / [dt] = k _E −k _b (T−T _b ). Solving this equation, T _S T = as initial temperature ^T _S e -kbt + ([k _E / k _{b] + T b) (1-e} -kbt) ......... formula (1) In this formula ( 1) can be determined by actually measuring the temperature of the thermal head with a radiation thermometer or the like. In addition, the temperature change after the end of heat generation is k _{E in} equation (1).
= 0.

On the other hand, the reaction of the thermosensitive material A proceeds according to the Arrhenius equation, and the reaction amount P (t) is

(Equation 1) Is proportional to Therefore, by substituting the thermal head temperature T calculated by the equation (1) into the equation (2), the reaction amount of the thermosensitive material A can be calculated. This calculation can be performed numerically using Romberg method or the like.

Using the method of calculating the reaction amount of the heat-sensitive material A, as described above, the image under the recording condition of the maximum heat generation time t _max 0 when the non-heat generation time between each heat generation block becomes 0 is described. In the recording, the reaction amount of the heat-sensitive material A to the heat generation time is calculated. That is, assuming that the maximum data value set in one heat generation cycle is Dm, the reaction amount of the heat-sensitive material A corresponding to each image data value (that is, heat generation time) from the image data value 0 to the maximum image data value Dm is defined as The relationship between the heat generation time (image data value) and the reaction amount is obtained by performing calculation for one heat generation cycle using Expression (2). Here, the heat generation cycle is defined as a block of image data (A + B, C + D,...).
Etc.). The temperature of the heating element increases gradually when the heating time is prolonged cooling time is shortened, since the maximum concentration becomes high, the reaction amount calculation, the end temperature T _E of T _S and 1 heating cycle It is preferable to substitute the difference in which the temperature curve does not change below a certain value into the equation (2).

Further, in the same manner as the reaction amount of the heat-sensitive material A with respect to the heat generation time in the image recording at the setting of the heat generation maximum time t _max 0, the setting for performing the image recording for creating the gradation correction table is performed. The maximum heat generation time t _max
Heat-sensitive material A for heat generation time during recording under condition 1
Is calculated, and the relationship between the heat generation time (image data value) and the reaction amount is determined.

Next, image recording for preparing a gradation correction table under the recording condition of the maximum heat generation time t _max 1 is actually performed using the thermosensitive material A, and the density of the recorded image is measured. The image for creating the gradation correction table is
This may be the same as image recording used for creating a normal tone correction table, and includes, for example, a so-called wedge pattern in which a number of gray patches whose density changes stepwise are formed.

Using the above results, the maximum heat generation time t_max
0 corresponding to the image recording under the recording condition of 0
Create Bull First, the maximum heat generation time t calculated earlier
_maxThe relationship between the image data value (heat generation time) at 0 and the reaction amount
And the maximum heat generation time t_maxImage data value at 1
Heat generation time t_maxFor recording condition 1
Is the maximum heat generation time t _maxRecording condition of 0
Create a conversion table to convert to image data values in
You. Data value and recording density converted to the conversion table
From the maximum heat generation time t_{ma x}Image under recording condition of 0
A gradation correction table corresponding to recording (hereinafter, temporary gradation correction
Table). Here, the gradation correction table
Image (image density) and data for creating a file
Creates a gradation correction table by a known means of calculating from a value
can do.

Next, using the temporary gradation correction table, the maximum heat generation time t _max 2 required to obtain a desired maximum density in thermal recording by the recording apparatus 10 is determined.
Here, as described above, when the maximum heat generation time t _max is shortened, the reaction amount becomes smaller than the setting of the maximum heat generation time t _max 0 even at the same heat generation time, and the image density is reduced. _It is necessary to determine _max 2 in consideration of the margin. Note that this margin may be set to about 10% or less.

[0059] After determining the exothermic maximum time t _max 2, wherein in the same manner as during the heating up time t _max 0, in the image recording on the recording conditions of the heating up time t _max 2, to the heating time (image data values) The reaction amount of the heat-sensitive material A is calculated.

Next, based on the relationship between the image data value at the maximum heat generation time t _max 0 and the reaction amount, and the relationship between the calculated image data value at the maximum heat generation time t _max 2 and the reaction amount of the heat-sensitive material A, , to create a conversion table for converting the image data values of the recording conditions of the heating up time t _max 0 to the image data values of the recording conditions of the heating up time t _{ma x} 2. Using this conversion table and the temporary gradation correction table created earlier, a recording gradation correction table corresponding to image recording in the setting of the maximum heat generation time t _max 2 for thermal recording is created. Is set in the gradation correction unit of the image processing unit 108.
The gradation correction unit of the image processing unit 108 corrects image data using the gradation correction table for recording to perform gradation correction.

According to the recording apparatus 10 of the present invention, an actual image is obtained by utilizing the reaction amount of the heat-sensitive material A in the setting of the maximum heat generation time t _max 0 at which the _unheated time between the heat generation blocks becomes zero. Since the gradation correction table corresponding to the setting of the maximum heat generation time t _max 2 in recording is created, the influence of the density change due to the difference in the maximum heat generation time t _max between when the gradation correction table is created and when the image is actually recorded is considered. It is possible to perform appropriate gradation correction without receiving, and to stably perform high-quality image recording.

Although the thermal recording apparatus of the present invention has been described in detail above, the present invention is not limited to this example, and various improvements and modifications may be made without departing from the gist of the present invention. Of course.

[0063]

As described above in detail, according to the thermal recording apparatus of the present invention, in divided recording in which image data is divided and recorded in the sub-scanning direction, the density fluctuation due to the difference in the maximum heat generation time is obtained. It is possible to stably perform high-quality image recording that is not affected and is subjected to appropriate gradation correction.

[Brief description of the drawings]

FIG. 1 is a diagram conceptually illustrating an example of a thermal recording apparatus of the present invention.

FIG. 2 is a block diagram of a recording control system of the thermal recording apparatus shown in FIG.

FIG. 3 is a chart showing an example of a driving pulse of a thermal head and a change in temperature of the thermal head at that time.

FIG. 4 is a timing chart of thermal image recording by the thermal recording apparatus shown in FIG.

5A and 5B are conceptual diagrams for explaining a temperature difference of a thermal head due to a difference in a maximum heat generation time t _max , and FIG.
_{When max} is short, (b) indicates when it is long.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 (Thermal) recording device 14 Loading part 16 Supply / conveyance part 20 Recording part 22 Discharge part 60 Platen roller 66 Thermal head 80 Recording control system 82 Control part 84 Step motor 86 Heating element 88 Thermal head drive part 90 Frame memory 92 Line memory 94 Divided image data memory 96, 100 Counter 98 Timing signal generation circuit 102, 104 Switcher 106 Memory 108 Image processing unit

Claims (1)

[Claims] 1. A thermal recording apparatus for recording on a thermal material by a thermal head, wherein one image data is divided into a plurality of heating blocks and recorded, wherein a non-heating time between the heating blocks is provided. The relationship between the heat generation time and the reaction amount of the heat-sensitive material under the recording condition of 0, the relation between the heat generation time and the reaction amount of the test heat-sensitive material under the recording condition when the gradation correction table is created, and the relationship was recorded on the test heat-sensitive material. From the density of the thermal recording image for creating a gradation correction table, a gradation correction table is created under recording conditions where the unheated time is 0, and a necessary maximum density is obtained using the gradation correction table. The maximum heat generation time is determined, and the relationship between the heat generation time and the reaction amount of the heat-sensitive material under the recording conditions corresponding to the maximum heat generation time, and the unheated time between the heat generation blocks is 0. A recording gradation correction table is created from the relationship between the heat generation time and the reaction amount of the heat-sensitive material under the different recording conditions, and the gradation correction table, and the supplied image data is generated by using the recording gradation correction table. A thermal recording apparatus, wherein thermal recording is performed by correcting the following.