JPH10138546A - Thermal printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thermal printer capable of enhancing printing image quality by especially suppressing the so-called tailing phenomenon. SOLUTION: A peripheral pixel referring circuit 20 calculates a primary correction value Xa obtained by correcting a value X of an aiming pixel to be printed on the basis of the values B, C of the pixels adjacent to the aiming pixel and the value A of a previous pixel and further corrects the primary correction value Xa on the basis of the difference between the value X of the aiming pixel and the value D of a next pixel to calculate a secondary correction value X1. For example, the primary correction value Xa is corrected in proportion to the difference between the value X of the aiming pixel and the value D of the next pixel, that is, the difference between densities and the secondary correction value X1 is calculated according to formula X1=Xa-0.1(X-D). A heating control circuit 28 controls the generation of heat of a thermal head 30 on the basis of the set PA of the secondary correction value X1. By this constitution, it can be prevented that the density of a next pixel becomes dark by the effect of the heat of the aiming pixel and a tailing phenomenon can be especially suppressed and printing image quality is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal printer, and more particularly to a thermal printer capable of improving the printing quality by reducing unevenness in the density of printing pixels due to the influence of peripheral pixels.

[0002]

2. Description of the Related Art In a thermal printer (hereinafter sometimes simply referred to as a printer), when a specific pixel is continuously energized for several lines, heat is accumulated in that pixel and the recording density is reduced as compared with other heating pixels. In order to solve the problem of unevenness, there are, for example, those disclosed in Japanese Patent Application Laid-Open No. 63-319163 and Japanese Patent Publication No. 7-88097.
These control the energization time of the pixel of interest based on the data of the pixel of interest and its neighboring pixels and the pixel in the row before the pixel of interest and its neighboring pixels, and correct the effects of heat in the previous row and neighboring pixels Is what you do.

[0003]

FIG. 23 is an illustration in which the horizontal axis represents the sub-scanning direction, which is the paper feeding direction, the printing energy applied on the vertical axis is indicated by a solid line EN, and the printing density is indicated by a dotted line DN. FIG. As shown in FIG. 23, when there is a portion where printing is not performed in the sub-scanning direction which is the paper feeding direction, that is, when there is a pixel where the printing energy becomes zero, the printing density of the pixel of interest has the heat of the previous printing remaining. Therefore, the printing density is hardly reduced to zero. Therefore, there is a problem that a so-called trailing phenomenon occurs in which printing is performed when the user does not want to print, and printing quality cannot be sufficiently improved. In particular, when there is a horizontal line that is not printed in a solid print, the print immediately before the horizontal line cannot be determined as to whether or not there is a print on the next print line, so the print energy cannot be adjusted, and the horizontal line that is not printed is destroyed. Or it becomes thinner.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to obtain a printer capable of improving the printing quality, particularly the printing quality by suppressing the trailing phenomenon. It is another object of the present invention to provide a printer capable of performing more accurate or fine density correction. It is still another object of the present invention to obtain a printer which can reduce the density unevenness of a print at the boundary of a control block of a thermal head or change the print density systematically to make the density unevenness less noticeable and further improve the print quality. It is another object of the present invention to obtain a printer capable of reducing the density unevenness by correcting the influence of the common impedance of the thermal head. Another object of the present invention is to provide a printer that can select a simple print based on data of a target pixel that is not corrected.

[0005]

In order to achieve the above object, a thermal printer according to the present invention is a data printer which corrects target pixel data based on adjacent pixel data, previous pixel data and next pixel data to obtain correction data. A correction means and a heat generation control means for controlling the heat generation of the heating element of the thermal head based on the correction data to adjust the density of a print to be printed on a print medium are provided. As described above, since the target pixel data is corrected based on the data of the pixels around the target pixel, particularly the data of the peripheral pixels including the next pixel, the influence of the residual heat on the next pixel is corrected. Is prevented, and the printing quality is improved.

The data correcting means corrects the target pixel data based on the adjacent pixel data and the previous pixel data, and further corrects the corrected data based on the target pixel data or the difference between the corrected target pixel data and the next pixel data. Is what you want. Correction data is obtained based on the difference between the corrected pixel data of interest and the next pixel data, so that the influence of residual heat on the next pixel is corrected, and especially when the next pixel is not printed, collapse is prevented, and the so-called tailing phenomenon is also suppressed. Is done.

Further, the previous pixel data is correction data of the pixel of interest obtained in the row before the row. Since the target pixel data actually printed in the previous row is used as the previous pixel data, the influence of the residual heat is more accurately corrected.

The pixel data of interest, adjacent pixel data, previous pixel data, and next pixel data are each multi-value data. Since each is multi-valued data, finer correction data can be obtained to control the heating element, and the printing quality can be further improved.

Further, there is provided a re-correction means for further correcting the correction data based on the influence data which affects the print density of the target pixel to obtain re-correction data. Since the correction data is further corrected by the influence data that affects the printing of the target pixel, it is possible to cope with various changes in the influence data, and the density unevenness is further reduced.

Further, the thermal head has heating elements divided into a plurality of printing blocks and arranged, and the influence data is used as a signal of the boundary of the printing blocks. When the thermal head is divided into a plurality of printing blocks, there is a time difference between the printing of one printing block and the printing of the next printing block. For this reason,
After the ink of the printing block printed first cools down and solidifies, printing of the next printing block is performed. Therefore, the block to be printed after the first printed ink melts and the ink is sucked by the surface tension, so that the print at the end of the first print block becomes thinner and the print at the end of the later print block becomes darker. Phenomenon occurs. Since this phenomenon is corrected by further correcting the correction data based on the signal of the boundary of the print block by providing the print block correction means, the unevenness of the print density is reduced.

The influence data is a signal in the scanning direction of printing and a signal in the sub-scanning direction perpendicular to the scanning direction. Since the print density is systematically changed by the dither correction means, the change in the density is dispersed and the unevenness in the density becomes less noticeable.

Further, the influence data is the print rate of the row calculated from the pixel data of interest for one row of the row. When the printing rate is low, the voltage drop due to the common impedance of the thermal head is small, but the correction data is corrected based on the printing rate to obtain re-correction data. For example, when the printing rate is low, the re-correction data is made smaller than the correction data, and the current flowing through the heating element is reduced. As a result, a change in print density is suppressed, and uneven print density is reduced.

Further, data switching means for switching between the pixel data of interest and the correction data or switching between the pixel data of interest and the re-correction data is provided, and the heat generation control means is switched based on the switched pixel data of interest, the correction data or the re-correction data. The heat generation of the heating element is controlled to adjust the density of a print to be printed on a print medium. When printing is to be performed easily, the data can be switched by the data switching unit, and printing can be performed based on the target pixel data that is not corrected. There is no need to obtain correction data or re-correction data without using correction data or re-correction data.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. 1 to 6 show a printer according to an embodiment of the present invention. FIG. 1 is a block diagram showing the configuration, and FIG. 2 is an explanatory diagram showing the relationship between pixels on a sheet to be printed. FIG. 3 is an explanatory diagram for explaining the input / output relationship of the peripheral pixel reference circuit, and FIG. 4 is a sequence diagram showing the operation of the thermal head. FIG. 5 is an explanatory diagram for explaining the operation of the print data comparison circuit, and FIG. 6 is an explanatory diagram showing the relationship between print energy and print density in this embodiment.

In FIG. 1, reference numeral 12 denotes an engine interface circuit which receives binary data from an image processing unit (not shown) of the printer. Reference numeral 14 denotes a future data buffer circuit which receives and holds binary future data PF for one row in the future, that is, one row after the row of interest. Reference numeral 16 denotes an input data buffer circuit which receives and holds the binary input data PN for one row of interest. Reference numeral 18 denotes a past data buffer circuit, which receives one line of binary past data PP from the input data buffer circuit 16 and holds it. The future, input, and past data buffer circuits hold each binary data using a 1-bit memory element corresponding to the pixel to be printed.

Reference numeral 20 denotes a peripheral pixel reference circuit as data correction means, which has an addition circuit, a subtraction circuit, a multiplication circuit, a division circuit, and a correction coefficient storage circuit (not shown in detail). The peripheral pixel reference circuit 20 is based on the input data PN stored in the input data buffer circuit 16, the future data PF stored in the future data buffer circuit 14, and the past data PP stored in the past data buffer circuit 18. Perform a predetermined operation. That is, a secondary correction value X1 corrected by the addition / subtraction / multiplication / division circuit using the correction coefficient set in the correction coefficient storage circuit incorporated in the peripheral pixel reference circuit 20 is calculated.

Reference numeral 22 denotes a print data buffer circuit which holds the corrected and multivalued secondary correction value X1 for one line to be printed from now on, which is calculated by the peripheral pixel reference circuit 20, as corrected print data PA. A printer control circuit 24 controls the printer by inputting and outputting signals from other circuits. 26 is a printing data comparison circuit,
The corrected print data PA of the row output from the print data buffer circuit 22 and the signal from the printer control circuit 24 are input and compared, and head data PH is output. Reference numeral 28 denotes a heat generation control circuit as heat generation control means.
To control the heat generation of

A thermal head 30 receives the head data PH of the print data comparison circuit 26 and the output of the heat generation control circuit 28 as a head data signal and a strobe signal. Reference numeral 32 denotes a sensor input circuit, which converts outputs of a plurality of sensors (not shown) for detecting presence / absence of paper in the printer, paper size, positions of ink sheets, and the like into signals.
Output to the printer control circuit 24. Reference numeral 34 denotes a motor drive circuit which drives a paper feed motor, an ink feed motor, and the like from an output signal of the printer control circuit 24.

Next, the operation will be described. Binary data sent from an image processing unit of a printer (not shown), that is, data for each row in which one pixel corresponds to one bit and whether or not printing is performed is represented by 1-bit data, is the future row (input row). ,
The data is sequentially sent to and held in the past data buffer circuits 14, 16, and 18. Retained input and future data P
N and PF are input to the peripheral pixel reference circuit 20. Also,
The past data PP immediately before the row stored in the past data buffer circuit 18 is similarly input to the peripheral pixel reference circuit 20. Since there is no past data PP in the first line at the start of printing, the value is 0.

Here, the operation of the peripheral pixel reference circuit 20 will be described. In the printer, as shown in FIG. 2, the horizontal axis which is the horizontal direction of the paper is the scanning direction, and the vertical axis which is the vertical direction of the paper is the sub-scanning direction. Here, an arbitrary pixel of interest in the row to be printed is x, and there is a past pixel a as a previous pixel already printed on the pixel x. A pixel b adjacent to the left of the pixel x, a pixel c adjacent to the right of the pixel x, and a future pixel d as a next pixel to be printed next below the target pixel x
It will be explained as if there is.

In the peripheral pixel reference circuit 20, the previous (past) pixel,
The left and right (adjacent) pixels and the subsequent (future) pixels are referred to. The peripheral pixel reference circuit 20 refers to the value A of the previous pixel a as the previous pixel data and the values B and C of the left and right pixels b and c as the data of the adjacent pixels, and performs, for example, an operation represented by the following equation: The primary correction value Xa is calculated by correcting the value X of the target pixel x.
That is, the effects of the residual heat of the previous pixel and the heat of the left and right pixels are corrected. Here, when there is a print in the binary data, 10
0E and 0 when there is no print. E represents a unit of multi-level data when multi-level conversion is performed in the peripheral pixel reference circuit 20, and an arbitrary value may be selected. The multi-valued data takes the number of divisions in a range that can be controlled by the heat generation control circuit 28. For example, when the heat generation control circuit 28 controls the heat generation amount of a printing line or a printing block by dividing it into 100, the peripheral pixel reference circuit 20 controls the multi-valued data. Converted multi-valued data is from 0 to 1
Take the value of 00E.

The primary correction value Xa is obtained by the following equation (1). In the following formula, the unit E of the multilevel data is omitted. Xa = [1- {A · α + ((B + C) / 2)) · β} / 100 × 2] X (1) Next, the secondary correction value X1 is calculated by the following equation (2) or ( 3)
Ask at. The primary correction value Xa is corrected and used as the secondary correction value X1 only when the value X of the pixel of interest x is larger than the value D of the subsequent pixel d (X> D). The correction value Xa is used as it is as the secondary correction value X1. This is because when X ≦ D, the influence of the printing energy of the target pixel x on the subsequent pixel d is small. If X> D, X1 = Xa− (X−D) γ (2) If X ≦ D, X1 = Xa (3) where α, β, and γ are correction coefficients, and A and B , C, D, and X are the values of each pixel a, b, c, d, and x.

That is, in order to prevent the density of the subsequent pixel d from becoming high due to the influence of heat of the target pixel x, the difference between the value X of the target pixel x and the value D of the subsequent pixel d, that is, the density difference Correction is performed in proportion to decrease the density of the target pixel x. At this time, γ indicates the degree of influence. The correction coefficients α, β, and γ are respectively 0.8 in this embodiment,
0.2 and 0.1. These coefficients were determined in consideration of the effect of the preceding pixel a being the largest, the effect of the left and right pixels b and c being relatively small, and the effect of the following pixel d.
At this time, the above (1), (2), and (3) are expressed as follows.

Xa = [1- {A × 0.8 + ((B + C) / 2)) × 0.2} / 200] X (4) If X> D, X1 = Xa− (X−D) ) × 0.1 (5) If X ≦ D, X1 = Xa (6) Primary calculated by peripheral pixel reference circuit 20 based on equations (4), (5), and (6) Correction value Xa, secondary correction value X1
FIG. 3 shows an example. In these figures, row numbers 1, 2, 3,... Indicate the pixels on the row to be printed from now on with numbers for convenience. Then, it is assumed that the pixels are sequentially arranged in the scanning direction from the left end in FIG. 2 in the order of the numbers, and after printing several lines,
Next, an example of data for printing will be described.

In FIG. 3, since the pixel in row number 1 is the leftmost pixel, there is no left pixel b, so B is 0.
And As is clear from FIG. 3, the secondary correction value X1
When the value D of the rear pixel d is 100E, for example, row numbers 1 to
7, the correction is not performed on the primary correction value Xa. When the value D of the subsequent pixel d is 0, the correction is made to be smaller than the primary correction value Xa, for example, as shown in row numbers 8, 9, and 12. In this way, when X is large, the influence on the target pixel in the next row is reduced when printing the next row. 1 calculated sequentially as described above
The secondary correction values X1 for the rows are stored in the print data buffer circuit 22 as corrected print data PA.

Next, the print data comparison circuit 26 performs a sequence operation as shown in FIG. A control signal for instructing the print data buffer circuit 22 to output one line of corrected print data PA (a set of secondary correction values X1) is sent from the printer control circuit 24 to the print data buffer circuit 22. Corrected print data PA corresponding to the first heat generation number 1 is sent. The print data comparison circuit 26 compares the corrected print data PA with the heat generation number 1.

When the correction print data PA is equal to or larger than the heat generation number 1, the data of the head data PH is set to 1 and output to the thermal head 30. Corrected print data P
Data 0 not printed when A is smaller than heat generation number 1
(Zero) is output to the thermal head 30. The transmission of this data is repeated by the number of pixels of the thermal head in accordance with the head clock. Next, the printer control circuit 2
4 sends a latch signal to the thermal head 30 and data corresponding to each pixel sent to the thermal head 30 is held as head data in a latch circuit (not shown) of the thermal head 30.

The printer control circuit 24 includes a heat generation control circuit 28
The heating control circuit 28 sends a head strobe signal corresponding to the heating number 1 to the thermal head 30. In the thermal head 30, each pixel generates heat by a predetermined amount of energy corresponding to 1 and 0 of the head data. As shown in FIG. 4, the head strobe signal is compensated so that the initial heat is increased and the heating time is increased so that the heat at the time of rising is not insufficient. Next, the printer control circuit 24 increases the heat generation number by 1, and repeats the same operation until the heat generation number becomes equal to the number of divisions that the heat generation control circuit 28 can control. In this case, the process is repeated up to the heat generation number 100.

FIG. 5 is an explanatory diagram showing an output example of the print data comparison circuit 26. As shown in FIG. 5, the future, input, and past data PF are supplied to the future, input, and past data buffer circuits 14, 16, and 18, respectively. , PN, PP are held as 100E or 0. The secondary correction value X1 for one row as shown in FIG. 5 from the peripheral pixel reference circuit 20 (see FIG. 3).
Is output as corrected print data PA. The corrected print data PA is calculated as 100
The heat generation data is sent to the thermal head for each comparison. For example, since the secondary correction value X1 of the leftmost pixel is 55, the heat generation data becomes 1 when the heat generation number is 1 to 55, and heat is generated by the energy amount corresponding to 55, and when the heat generation number is 56 to 100, The heat generation data becomes 0 and no heat is generated. That is, the printing is performed with the energy of 55, and the calorific value is controlled.

For each pixel in the row, the secondary correction value X1
By controlling the heat generation amount in accordance with the above, when there is a non-printing portion in the pixel d of the next row in the sub-scanning direction, that is, when there is a future pixel whose printing energy becomes zero, the printing density of the target pixel x is changed. The correction is reduced so that little residual heat remains in the future pixel d. FIG. 6 shows the energy EN and the print density DN in the sub-scanning direction (paper feed direction) under such control.

In FIG. 6, the printing density is reduced in advance by reducing the energy at the pixel before the non-printing pixel, and the printing density at the next non-printing pixel is made substantially zero. In this way, it is possible to prevent a so-called trailing phenomenon in which printing is performed when printing is not originally desired, and to improve printing quality. In particular, when there is a horizontal line that is not printed in the solid print, in the print immediately before the horizontal line, the presence or absence of printing of the next print line is determined, and the print energy is adjusted. The horizontal line can be prevented from being crushed or thinned.

Embodiment 2 FIG. FIG. 7 is a main part configuration diagram showing a main part of another embodiment of the present invention, and FIG. 8 is an explanatory diagram for explaining an input / output relationship of a peripheral pixel reference circuit. FIG.
In the embodiment, for example, the value of the pixel x to be printed is 100E and the values A, B, C, and D of the pixels a, b, c, and d around the pixel x as shown in row number 1 in FIG. Is 100, 0, 10
0, 100 (E). The printing of the pixel of interest x is corrected by referring to the surrounding pixels (4), (5),
In the case of (6), printing is performed at a heating value of 55E of the pixel x. Then, when subsequently printing the next row, the pixel x in the previous row corresponds to the pixel a in the row to be printed this time. Therefore, for example, pixel a in row number 1 is actually 5
5E, the contents of the past data buffer circuit 18 referred to are the same as those of the input data buffer circuit 1.
6 because of the binary data transferred from 6
00E.

Therefore, in this embodiment, the past data buffer circuit 18 shown in FIG.
, A past data buffer circuit for storing multi-valued past data is provided. In FIG. 7, 4
Reference numeral 8 denotes a past data buffer circuit, which receives the secondary correction value X1 for one row calculated by the peripheral pixel reference circuit 20 in the previous row from the print data buffer circuit 22, and stores it as past data PP @ M.

Here, the past data buffer circuit 48
If the secondary correction value X1 is 100E at the maximum, it is held using a 7-bit memory element. The peripheral pixel reference circuit 20 calculates the equations (4), (5), and (2) based on the binary data PF and PN of the future data buffer circuit 14 and the input data buffer circuit 16 and the past data PP @ M of the past data buffer circuit 48. The secondary correction value X1 is calculated by (6), output to the print data buffer circuit 22, and held as multi-value corrected print data PA @ M.

The other components are the same as those shown in FIG. 1. Therefore, corresponding components are denoted by the same reference numerals and description thereof is omitted. Although not shown, a printer control circuit 24, a print data comparison circuit 26, a heat generation control circuit 28, a thermal head 30, a sensor 32, and a motor drive circuit 34 similar to those shown in FIG. 1 are provided.

Next, the operation result of the peripheral pixel reference circuit 20 will be described with reference to FIG. Assuming that printing is performed with the secondary correction value X1 shown in FIG. 3 in the previous row, the secondary correction value X1 in the previous row is stored in the past data buffer circuit 48 in the previous pixel a.
Is stored as a value A. Therefore, when printing the next line, the primary correction value X is determined according to the printing energy in the previous line.
a and the secondary correction value X1 are both corrected. That is, by storing multilevel data as past data in the past data buffer circuit 48, the secondary correction value X1 is 55E in the case of the row number 1 in FIG. As shown in row number 1 in FIG. 8, printing is performed with a larger energy 73E using the actual energy 55E of the previous row as the value A of the pixel a. In this manner, reference correction can be performed on the corrected pixels in the row before the pixels to be printed.

Although the case where the past data buffer circuit 48 stores the past data PP # M for one row has been described with reference to FIG. The data PP @ M may be referred to. In this case, the corrected print data PA # is sent from the print data buffer circuit 22 to the print data comparison circuit 26 (see FIG. 1).
Each time M is sent, the corrected print data PA @ M is taken into the past data buffer circuit 48 and held as a plurality of past data PP @ M.

The past data buffer circuit 48 obtains the secondary correction value X1 from the peripheral pixel reference circuit 20 and accumulates it as the past data PP @ M without obtaining the multivalued data PA @ M from the print data buffer circuit 22. However, the same effect can be obtained. Further, the values of the left and right pixels c and d in the current row do not refer to the secondary correction value X1, which is the actual output.
This is because the influence of the left and right pixels b and c is relatively small, so that there is no influence even if the value X that is not corrected is referred to. Although a long time is required for the calculation, the calculation may be performed until each value X1 at each pixel x converges, and the converged and corrected X1 may be used as the left and right values B and C.

In this embodiment, since the operation is performed as described above, binary data PP before correction is held in the past data buffer circuit 18 in FIG. Then, the corrected print data PP # M actually output is held as past data. Since the corrected print data PP # M is used for the calculation in the peripheral pixel reference circuit 20, it is possible to reduce the occurrence of a slight deviation from the actually printed energy and the uneven print density. By improving the reference accuracy of print data, reference of peripheral pixels is performed with high accuracy, and fine print energy correction is performed for the influence of peripheral pixels, thereby improving print quality.

Embodiment 3 9 to 13 show still another embodiment of the present invention. FIG. 9 is a block diagram showing a configuration of a printer, and FIG. 10 is an explanatory diagram for explaining an operation of a peripheral pixel reference circuit. is there. FIG. 11 is an explanatory diagram for explaining the operation of the peripheral pixel reference circuit by another expression, and FIGS. 12 and 13 are explanatory diagrams for explaining the operation of the peripheral pixel reference circuit by another expression. FIG.
Alternatively, in the embodiment of FIG.
N, the future data PF was binary data. However, in the case of a sublimation type printer, for example, it is common that input and future data are sent in multi-valued form. This embodiment corresponds to such multi-value data.

First, the configuration will be described. In FIG. 9, reference numeral 42 denotes an engine interface circuit which receives multivalued data (data range 0 to 100E) from an image processing unit (not shown) of the printer. Reference numeral 44 denotes a future data buffer circuit which receives and holds multi-valued future data PF # M of one line in the future, that is, one line after the line of interest. Reference numeral 46 denotes an input data buffer circuit,
The multi-valued input data PN @ M for a row is received and held.
Reference numeral 48 denotes a past data buffer circuit, which is a multi-valued past data PP of one row in the past from the input data buffer circuit 46.
￣ Receive and hold M. The future, input, and past data buffer circuits 44, 46, and 48 use a 7-bit memory element corresponding to the pixel to be printed, and hold each multi-value data.

The other components are the same as those shown in FIG. 1, and the corresponding components are denoted by the same reference numerals and description thereof will be omitted. Although not shown, a printer control circuit 24, a print data comparison circuit 26, a heat generation control circuit 28, a thermal head 30, a sensor 32, and a motor drive circuit 34 similar to those shown in FIG. 1 are provided.

The operation of the peripheral pixel reference circuit 20 is the same as that shown in FIG. 1, and based on the input multi-valued past, input, and future data PP @ M, PN @ M, and PF @ M, an equation ( 4), (5) and (6) are used to calculate a primary correction value Xa and a secondary correction value X1 as correction data. Figure 1 shows an example of calculation
0 is shown. The primary correction value Xa and the secondary correction value X1 are calculated corresponding to the multivalued values A, X, and D of the previous pixel a, the pixel of interest x, and the rear pixel d. As shown in FIG.
When (X−D)> 0, the secondary correction value X1 becomes the primary correction value X
It has been corrected to be smaller than a. That is,
When the printing energy of the rear pixel d is small, the printing energy of the target pixel x is corrected to be small, and the influence of the front pixel on the rear pixel is reduced. When (XD) ≦ 0, no secondary correction is performed. This is because when the value D of the subsequent pixel d is large (the density is high), the next pixel d is also printed, so that correction is not necessarily required.

In the above, the peripheral pixel reference circuit 20
As shown in the equations (5) and (6), the correction is made in proportion to the difference (XD) between the value of the target pixel and the value of the subsequent pixel d. However, the peripheral pixel reference circuit 20 can be configured as follows. That is, the primary correction value Xa is corrected only when the value D of the subsequent pixel d is equal to or less than a certain value. A second secondary correction value X2 as correction data is determined so that correction is performed only when the value D of the subsequent pixel d is equal to or smaller than a predetermined upper limit K. If D> K, X2 = Xa (7) If D ≦ K, X2 = X1 (8) For example, primary and secondary correction based on equations (4), (5), and (6) The values Xa and X1 are calculated, and the above (7), (8)
A second secondary correction value X2 as correction data is determined by the equation.

FIG. 11 is an explanatory diagram showing the primary correction value Xa, the secondary correction value X1, and the second secondary correction value X2 when K = 50. In FIG. 11, row numbers 1, 4, 6,
Since the value D of the subsequent pixel d of 7, 10, 11, 13 exceeds 50 (D> 50), the second secondary correction value X2 becomes the same value as the primary correction value Xa. Line numbers 2, 3, 5, 8, 9, 12,
Since the value D of the pixel d after 14 is 50 or less, the primary correction value Xa is corrected based on equation (8), and the secondary correction value X1 is output as the second secondary correction value X2.

Further, when the rear pixel d does not print, that is, when the value D of the rear pixel d is zero, it is conceivable to perform correction to reduce the tailing. This is because the trailing unevenness is not conspicuous when printing is performed even if the subsequent pixel d has a low density,
If no print is made, the tailing may be noticeable. This is due to the characteristics of the ink. In this case, the correction for lowering the density of the target pixel x is performed only when the value D of the subsequent pixel d is zero. That is, the third secondary correction value X3 as correction data is calculated as follows. If D> 0, X3 = X1 (9) If D = 0, X3 = X1Ｘδ (10) where δ is a correction coefficient. FIG. 12 shows the value of the third secondary correction value X3 when δ = 0.9. Line number 6
Since the value D of the subsequent pixel d is zero, the third secondary correction value X3 is reduced to 90% of the primary correction value Xa.

Further, if the difference between the value X of the pixel of interest x and the value D of the succeeding pixel d is equal to or less than a certain value, the effect of tailing is small, so that the correction is not performed, so that the printing quality is improved. Therefore, the peripheral pixel reference circuit 20 is configured to perform the following operation. When the difference (X-D) between the pixel values exceeds the predetermined value M, no correction is performed, and when the difference (X-D) is equal to or smaller than the predetermined value M, the correction is performed and a fourth secondary correction value X4 is output as correction data. That is, if (XD)> M, then X4 = Xa (11) If (XD) ≦ M, then X4 = X1 (12) FIG. 13 is an explanatory diagram illustrating a calculation example of the fourth secondary correction value X4 when M = 25. Line numbers 2, 4,
Difference (X-D) between 6, 8, and 10 target pixel x and subsequent pixel d
Is larger, the fourth secondary correction value X4 becomes the primary correction value X4.
The correction is reduced from a to the secondary correction value X1.

In the above embodiment, the secondary correction value X
Equations (2), (3), and
Alternatively, although the expressions (11) and (12) use the value X of the target pixel x, the corrected value Xa of the target pixel x may be used instead of X. That is, the secondary correction value X1
Is obtained by the following equations (2a) and (3a). If Xa> D, then X1 = Xa− (Xa−D) γ (2a) If Xa ≦ D, X1 = Xa (3a) Alternatively, the fourth equation is obtained by the following equations (11a) and (12a). The next correction value X4 is obtained. If (Xa-D)> M, then X4 = Xa. (11a) If (Xa-D) .ltoreq.M, then X4 = X1. (12a). Are replaced with one pixel around each of the pixels a, b, c,
d shows a case in which a total of four pixels (see FIG. 2) are referred to, but a pixel immediately before the previous pixel a, two pixels adjacent to the previous pixel a, and left and right pixels b and c, respectively. The same applies when referring to four or more surrounding pixels, such as referring to a total of twelve pixels: an adjacent pixel, two pixels adjacent to the subsequent pixel d, and a pixel further after the subsequent pixel d. can do.

Further, the secondary correction value may be obtained by using other expressions instead of the correction coefficients α to δ and the arithmetic expressions (1) to (12) as long as the object of the present invention is not impaired. Also,
Here, the correction print data PA (secondary correction values X1 to X4) is calculated by referring to the values of the peripheral pixels by using the peripheral pixel reference circuit 20 as the correction means, but is predetermined in the correction value storage means. Similar effects can be obtained by using the secondary correction values stored as a table.

As described above, according to these, the influence of each of the peripheral pixels a to d can be finely referenced by the peripheral pixel reference circuit 20, and fine print data can be corrected, so that print quality is improved. .

Embodiment 4 FIG. FIG. 14 is a main part configuration diagram showing a main part of still another embodiment of the present invention. When printing is performed by dividing the thermal head into printing blocks, density unevenness is likely to occur at the boundaries between the printing blocks. This is because there is a time difference between the printing of one printing block printed earlier and the printing of the next printing block printed next, and after the ink of the printing block printed earlier cools down and solidifies, Since the printing block to be printed is printed, the side of the block to be printed next melts after the ink printed earlier, and the ink is sucked by the surface tension, so the edge of the first printing block becomes thinner, and the later printing This is because the print at the end of the block becomes dark. Further, the density unevenness of the print block slightly differs due to the influence of peripheral pixels. In this embodiment, the density unevenness at the edge of the printing block is reduced.

In FIG. 14, the peripheral pixel reference circuit 20,
The print data buffer circuit 22 is the same as that shown in FIG. Reference numeral 52 denotes a printer control circuit which generates a signal POS for the printing position of the thermal head, and which is a block pixel position signal PO for distinguishing between the leftmost pixel of the printing block, the rightmost pixel of the printing block, and other pixels.
Output S. Reference numeral 54 denotes a block correction circuit as a re-correction unit. The block correction circuit 54 corrects the secondary correction value based on the secondary correction value X1 output from the peripheral pixel reference circuit 20 and the block pixel position signal POS output from the printer control circuit 52, and uses the corrected secondary correction value as re-correction data. The block correction value X1￣POS is stored in the print data buffer circuit 22
Output to The print data buffer circuit 22 converts the block correction value X1￣POS for one row into the block correction print data P
Store as A と し て POS.

Although not shown, an engine interface circuit 42 similar to that shown in FIG.
Input and past data buffer circuits 44, 46 and 48, print data comparison circuit 26, heat control circuit 28, thermal head 30, sensor 32, and motor drive circuit 34 are provided.

The printer control circuit 52 generates a block pixel position signal POS indicating the position of the pixel being transferred in one or more printing blocks of the thermal head.
For example, a signal is generated such as the left end of the print block, the right end of the print block, the center which is neither the left end nor the right end. The block correction circuit 54 corrects the secondary correction value X1 from the correction operation circuit 20 based on the block pixel position signal POS from the printer control circuit 52 to perform block correction print data PA
出力 Output POS.

For example, if the block pixel position signal POS is at the center of the block, the correction is not performed and the secondary correction value X1 is maintained, and if the block pixel position signal POS is at the left end of the block, 2 is subtracted from the secondary correction value X1. If the pixel position signal POS is at the right end of the block, 2 is added. That is, for example, when the secondary correction value X1 is 50, the block correction value X1
￣POS is 50, 48, 52 corresponding to the case of the block center, the left end, and the right end, respectively.

In this embodiment, since the configuration is as described above, the density of the boundary between the print of one print block to be printed first and the print of the next print block to be printed next is corrected. As a result, after the ink of the first printing block is cooled and solidified, printing of the next printing block is performed, and the block to be printed is melted after the first printing ink, and the ink is sucked by the surface tension. Can be prevented. That is, it is possible to prevent the print at the end of the first print block from becoming thin and prevent the print at the end of the subsequent print block from becoming dark, thereby reducing the density unevenness of the print. In this way, the print density correction at the end of the print block is performed in conjunction with the reference of the peripheral pixels to correct the print, thereby reducing the print density unevenness.

Embodiment 5 FIG. 15 is a main part configuration diagram showing a main part of still another embodiment of the present invention. FIG.
In 5, the peripheral pixel reference circuit 20 and the print data buffer circuit 22 are the same as those shown in FIG. Although not shown, the same engine interface circuit 42 as that shown in FIG. 9, future, input, past data buffer circuits 44, 46, 48, print data comparison circuit 26, heat generation control circuit 28, thermal head 30 , A sensor 32, and a motor drive circuit 34.

In FIG. 15, reference numeral 62 denotes a temperature detector which detects the temperature of the thermal head 30 (see FIG. 9). A printer control circuit 64 has a function similar to that of the printer control circuit 24 in FIG. 9 and detects a temperature detected by the temperature detector 62 as a temperature signal T of the thermal head.
Convert to E Reference numeral 66 denotes a temperature correction circuit as a re-correction unit.
A temperature signal TE is input from the printer control circuit 64, and a temperature correction value X1 @ TE as re-correction data is output to the print data buffer circuit 22.

Next, the operation will be described. The temperature of the thermal head not shown in FIG. 15 is detected by the temperature detector 62 and sent to the printer control circuit 64. The printer control circuit 64 sends a temperature signal TE corresponding to the temperature of the thermal head to the temperature correction circuit 66. The temperature correction circuit 66 performs the temperature correction of the secondary correction value X1 from the peripheral pixel reference circuit 20 on the basis of the temperature signal TE so as to be optimal for the temperature of the thermal head, calculates the temperature correction value X1￣TE, and prints the print data buffer circuit. 22. The print data buffer circuit 22
The temperature correction value X1 @ TE for the row is converted to the temperature correction print data PA
保持 Keep as TE.

The optimum temperature correction is, for example, as follows. When the temperature of the thermal head is low, the temperature correction value X
Correction is made so that 1 大 き く TE is larger than the value of the secondary correction value X1, so that printing is performed reliably even at low temperatures, and when the head temperature is high, correction is made so as to be smaller than the secondary correction value X1. Make sure that the prints are not crushed. That is, the temperature of the thermal head is 30 or less, more than 30 and 50 or less, more than 50 6
It is divided into four stages of 0 or less and over 60 (all in degrees Celsius), and the correction values of 5, 2, 0, and -3 are added to the secondary correction value X1 according to the respective levels, and the temperature correction value X1￣TE Output as

As for the temperature of the thermal head, the ambient temperature may be detected instead of detecting the temperature of the thermal head itself. In addition, although the temperature of the thermal head is divided into four stages and corrected, the temperature can be divided arbitrarily.
Alternatively, the correction value may be calculated according to the temperature of the head,
A similar effect is achieved. Generally, when the temperature of the thermal head is low, it cools before the heat flows between the pixels, so the influence of the peripheral pixels is small.When the temperature of the thermal head is high, the heat flowing between the pixels does not cool, so the peripheral pixels Many effects. On the other hand, the embodiment shown in this embodiment operates as described above, so that it is possible to correct the reference of the peripheral pixels to the temperature of the thermal head and to improve the printing quality. .

Embodiment 6 FIG. FIG. 16 is a main part configuration diagram showing a main part of another embodiment of the present invention. FIG.
In 6, the peripheral pixel reference circuit 20 and the print data buffer circuit 22 are the same as those shown in FIG. Although not shown, the same engine interface circuit 42 as that shown in FIG. 9, future, input, past data buffer circuits 44, 46, 48, print data comparison circuit 26, heat generation control circuit 28, thermal head 30 , A sensor 32, and a motor drive circuit 34.

In FIG. 16, reference numeral 72 denotes a printer control circuit, which outputs a pixel number DOT # N corresponding to a pixel position of a thermal head to be printed. A resistance value storage circuit 74 stores the pixel number DOT # N of the thermal head output from the printer control circuit 72 and the resistance value RES corresponding thereto, and outputs the resistance value RES. Reference numeral 76 denotes a heating element resistance correction circuit as a re-correction unit, and a peripheral pixel reference circuit 20 based on an output RES of the resistance value storage circuit 74.
, And outputs a resistance correction value X1 と し て RES as re-correction data. The print data buffer circuit 22 holds the resistance correction value X1 @ RES for one row as the resistance correction print data PA @ RES.

Next, the operation will be described. The head pixel number DOT # N is output from the printer control circuit 72 to transfer the print data. This is also output to the input data buffer circuit 46 and the past data buffer circuit 48, and the binary data corresponding to the head pixel number DOT @ N is stored in the future, input and past data buffer circuits 44,
6 and 48 are output to the peripheral pixel reference circuit 20. Based on this, the peripheral pixel reference circuit 20 calculates the secondary correction value X1 and outputs it to the heating element resistance correction circuit 76.

The heating element resistance correction circuit 76 stores the resistance value R for each pixel of the thermal head stored in the resistance value storage circuit 74.
A correction rate corresponding to the ES is calculated. The correction rate is calculated in accordance with the resistance value so that the print density of each print pixel is corrected so that the entire print density becomes a predetermined print density. Assuming that the voltage applied to each pixel of the thermal head is constant, the amount of heat generated is inversely proportional to the resistance value of the pixel of interest.
In order to keep the supplied energy constant, the correction rate RA [%]
Is calculated by the following formula, for example. RA = (r / rs) × 100 [%] (13) Here, r is the resistance value of the pixel of interest, and rs is the reference resistance value. The heating element resistance correction circuit 76 includes the peripheral pixel reference circuit 20.
Is multiplied by the correction factor for the pixel-based secondary correction value X1, and a resistance correction value X1￣RES is output to the print data buffer circuit 22.

When the pixel number DOT @ N of the thermal head is input to the heating element resistance correction circuit 76, the secondary head correction value X1 corresponding to the pixel number DOT @ N of the secondary correction value X1 is changed to the thermal head resistance value r. The resistance correction value X1ＸRES is calculated by multiplying the correction rate RA according to the above, and is output to the print data buffer circuit 22. Heating element resistance correction circuit 76
For example, a pixel whose resistance value r is the reference resistance value rs does not require correction and the correction rate is 100 [%]. A pixel having a large resistance value r has a low density, so that the resistance value r is high. If the reference resistance value rs is 102 [%], the correction value is 102
Set to [%]. A pixel having a small resistance value has a high density.
If 97% of s, the correction rate is selected as 97%.

Since the operation is performed as described above, it is possible to correct the unevenness of the density of the print due to the variation of the resistance value of the resistor of each pixel of the thermal head. Further, since the correction is performed in conjunction with the peripheral pixel reference circuit 20 that performs correction by referring to the peripheral pixels, the correction can be performed with high accuracy, and the printing quality is improved.

Embodiment 7 FIG. 17 is a main part configuration diagram showing a main part of still another embodiment of the present invention. FIG.
7, the peripheral pixel reference circuit 20 and the print data buffer circuit 22 are the same as those shown in FIG. Although not shown, the same engine interface circuit 42 as that shown in FIG. 9, future, input, past data buffer circuits 44, 46, 48, print data comparison circuit 26, heat generation control circuit 28, thermal head 30 , A sensor 32, and a motor drive circuit 34.

In FIG. 17, reference numeral 82 denotes a medium detecting means which detects the type of printing medium such as printing paper or ink sheet and outputs a medium type signal MED. In particular,
For example, a groove for identifying a photographic paper cassette is provided, and the groove is detected to detect, for example, types of photographic paper such as paper F and paper G. Further, the medium detecting means 82 identifies a mark on the ink sheet, for example, and detects the mark to detect the type of the ink sheet such as the ink sheet f and the ink sheet g. Then, a medium type signal MED is output based on these detection results. Reference numeral 86 denotes a medium correction circuit as a re-correction unit, and a peripheral pixel reference circuit 20
X1 and the medium type signal M of the printer control circuit 84
Enter ED.

The medium correction circuit 86 includes the printer control circuit 8
4 calculates a correction value based on the medium type signal MED output from the peripheral pixel correction circuit 2 based on, for example, the following equation.
The secondary correction value X1 output from 0 is corrected, and a medium correction value X1￣MED is output as re-correction data. If paper = F and ink sheet = f, X1 @ MED = X1 (14) if paper = G and ink sheet = g, X1@MED=X1.a+b (15)

Here, for example, a is 0.95 and b is 5
Is used. In this example, since the density of the low gradation portion is lower in the case of the sheet G and the ink sheet g than in the case of the sheet F and the ink sheet f, the corrected print data is used in the case of the sheet G and the ink sheet g. The correction for increasing the low gradation density of the PA is performed, and output as medium correction print data PA @ MED.

Since the operation is performed as described above, in this embodiment, the replacement of a printing paper or an ink sheet having a factor that causes a change in the printing density is detected, and the optimum printing correction is linked with the peripheral pixel reference. The printing quality can be improved. Note that the function expression (14) may be a certain function expression, and the expression (15) may not be a linear expression but may be another function expression such as a quadratic expression.

Embodiment 8 FIG. FIG. 18 is a main part configuration diagram showing a main part of another embodiment of the present invention. FIG.
In 8, the peripheral pixel reference circuit 20 and the print data buffer circuit 22 are the same as those shown in FIG. Although not shown, the same engine interface circuit 42 as that shown in FIG. 9, future, input, past data buffer circuits 44, 46, 48, print data comparison circuit 26, heat generation control circuit 28, thermal head 30 , A sensor 32, and a motor drive circuit 34.

Reference numeral 94 denotes a printer control circuit, which generates and outputs a scanning direction signal SWM and a sub-scanning direction signal SWS respectively corresponding to print pixels. The scanning direction signal SWM is
For example, if the dither correction is 2.times.2, the scanning direction signal is 1 bit, and outputs 0 for odd pixels and outputs 1 for even pixels. If the dither correction is 2 × 2, for example, the sub-scanning direction signal SWS is 1 bit, and outputs 0 for odd-numbered row printing and 1 for even-numbered row printing.

Reference numeral 96 denotes a dither correction circuit serving as a re-correction unit, and a secondary correction value X 1 from the peripheral pixel reference circuit 20.
Is output to the print data buffer circuit 22 as the re-correction data X1￣DIZ, which is further finely changed, based on the scanning direction signal SWM and the sub-scanning direction signal SWS. Specifically, the secondary correction value X1, the scanning direction signal SWM, and the sub-scanning direction signal SWS are input,
For example, a dither correction value X1￣DIZ, which is a result of performing an operation represented by the following equation, is output to the print data buffer circuit 22. Here, MOD (X, Y) is a function that returns a remainder obtained by dividing X by Y.

X1￣DIZ = X1-YY + ZZ (16) where YY = MOD (X1, 4) (17) ZZ = MOD ((SWM × 2 + SWS × 3), 4) (18) It is. An example of the calculation is shown in the explanatory diagram of FIG. FIG. 19 (a)
Is the calculation result of the above ZZ, and (b) is the calculation result of X1￣DIZ when X1 is 50, 54 or 56. As described above, since the print density is systematically minutely changed for 2 × 2 print pixels, it is possible to prevent a stripe pattern from being seen when a specific density is repeated. Further, when the print density is non-uniform, the change in density becomes dispersed and inconspicuous.

Embodiment 9 FIG. 20 is a main part configuration diagram showing a main part of another embodiment of the present invention. FIG.
At 0, the peripheral pixel reference circuit 20, print data buffer circuit 22, engine interface circuit 42, future, input, past data buffer circuits 44, 46, 48
Is similar to that shown in FIG. Although not shown, the same printer control circuit 24, print data comparison circuit 26, and heat generation control circuit 2 as those shown in FIG.
8, a thermal head 30, a sensor 32, and a motor drive circuit 34.

In FIG. 20, reference numeral 102 denotes a printing rate measuring circuit, which is a secondary correction value X for one row sent from the engine interface circuit 42 to the input data buffer circuit 46.
Calculate the print ratio of 1. The printing ratio is the ratio of the total value of the printing energy for one row to the total value of the energy when printing all the pixels for one row at an energy of 100E. Reference numeral 104 denotes a printing ratio correction circuit as a re-correction unit, which outputs the output of the peripheral pixel reference circuit 20 and the printing ratio measurement circuit 10
2, the secondary correction value X1 is corrected, and the printing ratio correction value X1￣PR as re-correction data is output to the printing data buffer circuit 22. The print correction circuit 104 calculates the print ratio PR (takes a value from 0 to 1) input from the print ratio measurement circuit 102 and the print ratio correction coefficient KD (takes a value from 0 to 1) of the printer measured in advance. Then, for example, correction is performed by the following equation.

X1￣PR = (KD (PR-1) +1) X1 (19) For example, when KD = 0.05,
When the printing ratio is 1, that is, when all the pixels print, X1￣PR = X1, and the printing ratio is not corrected. However, when the printing ratio is 0.1, that is, when the printing ratio is 10%, X1￣PR = (0.05 (0.1−1) +1) X1 ·· (20) = 0.955X1 ·· (21) Note that X1￣PR is actually a quadratic function, but is shown by approximation with a linear function for easy understanding.

Since the operation is performed as described above, when the printing ratio is low, the voltage drop due to the common impedance of the thermal head is reduced, and the printing density is reduced. Conversely, when the printing rate is high, it is possible to prevent the voltage drop due to the common impedance of the thermal head from increasing and the printing density from decreasing. In addition, correction for reducing unevenness in print density is performed in conjunction with reference to peripheral pixels. When the print block is divided into a plurality of blocks, the print ratio may be measured for each print block, and correction may be made for each print block, thereby obtaining the same effect.

The block pixel position signal POS, the temperature signal TE, the resistance value RES, the medium type signal MED, the scanning direction signal SWM and the sub-scanning direction signal SWS, the printing ratio PR, and the like in the above embodiment affect the present invention. This is an example of data that affects the print density of the target pixel in addition to the adjacent pixel data, the previous pixel data, and the next pixel data.

Embodiment 10 FIG. FIGS. 21 and 22 show still another embodiment of the present invention. FIG. 21 is a main part configuration diagram showing main parts, and FIG. 22 is an operation sequence diagram. 21, a peripheral pixel reference circuit 20, a print data buffer circuit 22, and a printer control circuit 24 are the same as those shown in FIG. Although not shown, an engine interface circuit 12 similar to that shown in FIG.
4, 16, and 18, a print data comparison circuit 26, a heat generation control circuit 28, a thermal head 30, a sensor 32, and a motor drive circuit 34 are provided.

In the figure, a switching circuit 114 switches between the output X1 of the peripheral pixel reference circuit 20 and the output PN of the input data buffer circuit 16 and outputs the output to the print data buffer circuit 22. Input data PN, which is binary data, is supplied in advance to a switching circuit 114 from an operation unit of a printer (not shown).
And information for selecting any one of the input of the secondary correction value X1 which is multi-value data. If binary data input is selected by switching circuit 114, input data buffer circuit 1
6 is output to the print data buffer circuit 22. When the input of the multi-value data is selected, the secondary correction value X1 output from the peripheral pixel reference circuit 20 is output to the print data buffer circuit 22.

FIG. 22 shows an operation sequence. The printing paper and the ink sheet are used in advance for printing binary data. Then, an instruction is made to print binary data from the operation unit of the printer, and the binary data PN for one row of the row held by the input data buffer circuit 16 is sent to the print data buffer circuit 22. Printing is performed in the same manner as in the embodiment. In this case, the print data comparison circuit 26 and the heat generation control circuit 28 (not shown) are set to 0 to 100 (E).
Is controlled so as to perform a two-stage comparison with 0 and 100E without performing successive comparisons up to. Next, the printing paper and the ink sheet are replaced with those for printing multi-valued data, and an instruction to print the multi-valued data is issued from the operation unit of the printer. The next correction value X1 is sent to the print data buffer circuit 22, and printing is performed in the same manner.

With the above configuration, in this embodiment, printing can be easily performed by switching to the input data PN which is binary data. The printing paper and the ink sheet for binary data are inexpensive, and the required color is obtained with a small printing energy, so that the printing speed is increased. This allows
The actual printing is performed using the multi-valued secondary correction value X1 as described above. However, prior to the actual printing, it is necessary to print at a high speed and at a low cost for checking the layout and performing galley printing. Can be. In addition, there is no need to obtain correction data or re-correction data, and there is no need to wait for the calculation, and since the heat generation control circuit 28 does not perform detailed successive comparisons, printing can be performed at a higher speed.

Also, when the input data is multi-valued, printing can be performed in the same manner using the printing paper and ink sheet for binary data. The switching circuit 114 is applied to, for example, the printers shown in FIG. 9, FIG. 14, FIG.
Multi-valued input data PN {M output from the input data buffer circuit 46, the secondary correction value X1, and the block correction value X1}
POS or the temperature correction value X1 @ TE can be switched.

In each of the above embodiments, for example, future, input, past data buffer circuits 44, 46, 4
8, peripheral pixel reference circuit 20, print data buffer circuit 2
2. The functions of the print data comparison circuit 26 and the like may be collectively executed by a microcomputer. It goes without saying that a printer can be used in combination with any of the printers described in the above embodiments as appropriate according to the intended use, required performance, and the like. Further, the printer may be a color printer, or in the future, the input data may be created by reading a document inside like a copier.

[0088]

Since the present invention is configured as described above, it has the following effects. Data correction means for correcting pixel data of interest based on adjacent pixel data, previous pixel data, and next pixel data to obtain correction data, and heat generation control means for controlling heat generation of a heating element of a thermal head based on the correction data are provided. Therefore, correction data is obtained based on the difference between the corrected pixel data of interest and the next pixel data, so that the influence of residual heat on the next pixel is corrected, and in particular, collapse in the next pixel when printing is not performed in the next pixel is prevented. The so-called tailing phenomenon is also suppressed.

Further, the target pixel data is corrected based on the adjacent pixel data and the previous pixel data, and the correction data is obtained based on the target pixel data or the difference between the corrected target pixel data and the next pixel data. The effect of the residual heat on the next pixel is reduced by reflecting the difference between the next pixel data and the pixels around the target pixel and the difference between the target pixel data and the next pixel data, and the printing quality is improved. Quality can be improved.

Further, since the previous pixel data is the correction data of the pixel of interest obtained in the row before the current row,
More accurate correction data is obtained using the correction data actually printed in the previous row, and the influence of residual heat on the next pixel is corrected more accurately, thereby improving printing quality.

Since the pixel data of interest, the adjacent pixel data, the previous pixel data, and the next pixel data are each multi-valued data, fine correction data is obtained, and the influence of residual heat on the next pixel is finely corrected. In addition, the printing quality can be further improved.

Further, since re-correction means for obtaining correction data by further correcting the correction data based on the influence data which influences the print density of the pixel of interest is provided, the re-correction means is provided in accordance with the influence data affecting the printing of the pixel of interest. Thus, the correction data can be further corrected to further reduce the density unevenness.

Further, in the thermal head, the heating elements are divided into a plurality of printing blocks and arranged, and the influence data is used as the signal of the boundary of the printing blocks.
It is possible to reduce uneven printing density at the end of the printing block due to the printing time difference between the printing blocks.

Since the influence data is a signal in the printing scanning direction and a signal in the sub-scanning direction which is a direction perpendicular to the scanning direction, the printing density is systematically changed and the change in density is dispersed. The unevenness of density can be made inconspicuous.

Since the influence data is the printing rate of the row calculated from the pixel data of interest of one row of the row, the influence of the voltage drop due to the common impedance of the thermal head is corrected to generate the heat of the heating element. , It is possible to suppress a change in print density and reduce uneven print density.

Since the data switching means for switching between the target pixel data and the correction data or for switching between the target pixel data and the re-correction data is provided, it is possible to easily print based on the target pixel which is not corrected.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a printer.

FIG. 2 is an explanatory diagram showing a relationship between pixels on a sheet to be printed.

FIG. 3 is an explanatory diagram for explaining an input / output relationship of a peripheral pixel reference circuit in the printer of FIG. 1;

FIG. 4 is a sequence diagram showing an operation of the thermal head in the printer of FIG.

FIG. 5 is an explanatory diagram for explaining an operation of a print data comparison circuit in the printer of FIG. 1;

FIG. 6 is an explanatory diagram showing a relationship between printing energy and printing density in the printer of FIG. 1;

FIG. 7 is a main part configuration diagram showing a main part of another embodiment of the present invention.

8 is an explanatory diagram illustrating an input / output relationship of a peripheral pixel reference circuit in the printer of FIG. 7;

FIG. 9 is a block diagram of a printer showing another embodiment of the present invention.

FIG. 10 is an explanatory diagram for explaining an operation of a peripheral pixel reference circuit of the printer in FIG. 9;

FIG. 11 is an explanatory diagram for explaining an operation based on another equation of the peripheral pixel reference circuit of the printer in FIG. 9;

12 is an explanatory diagram for explaining an operation of the peripheral pixel reference circuit of the printer in FIG. 9 using still another arithmetic expression.

FIG. 13 is an explanatory diagram for explaining an operation of the peripheral pixel reference circuit of the printer in FIG. 9 using still another arithmetic expression.

FIG. 14 is a main part configuration diagram showing a main part of another embodiment of the present invention.

FIG. 15 is a main part configuration diagram showing a main part of another embodiment of the present invention.

FIG. 16 is a main part configuration diagram showing a main part of another embodiment of the present invention.

FIG. 17 is a main part configuration diagram showing a main part of another embodiment of the present invention.

FIG. 18 is a main part configuration diagram showing a main part of another embodiment of the present invention.

FIG. 19 is an explanatory diagram showing an output example of the dither correction circuit of FIG. 18;

FIG. 20 is a main part configuration diagram showing a main part of another embodiment of the present invention.

FIG. 21 is a main part configuration diagram showing a main part of another embodiment of the present invention.

22 is an operation sequence diagram of the printer shown in FIG. 21.

FIG. 23 is an explanatory diagram showing printing energy and printing density in a conventional printer.

[Explanation of symbols]

 14: Future data buffer circuit 16: Input data buffer circuit 18: Past data buffer circuit 20: Peripheral pixel reference circuit 28: Heat generation control circuit 30: Thermal head 44: Future data buffer circuit 46: Input data buffer circuit 48: Past data buffer Circuit 54: Block correction circuit 66: Temperature correction circuit 76: Heating element resistance correction circuit 86: Medium correction circuit 96: Dither correction circuit 104: Print ratio correction circuit 114: Switching circuit

Claims (9)

[Claims] 1. A thermal head having a plurality of heating elements arranged in a scanning direction of printing, adjacent pixel data which is data of a pixel adjacent to a target pixel of a row to be printed, and a row preceding the row. The target pixel which is data of the target pixel based on the previous pixel data which is the data of the pixel corresponding to the target pixel and the next pixel data which is the data of the pixel corresponding to the target pixel in the next row of the row A thermal printer comprising: data correction means for correcting data to obtain correction data; and heat generation control means for controlling heat generation of the heating element based on the correction data to adjust the density of a print to be printed on a print medium. 2. A data correction means for correcting target pixel data based on adjacent pixel data and previous pixel data, and further correcting data based on the target pixel data or a difference between the corrected target pixel data and the next pixel data. 2. The thermal printer according to claim 1, wherein: 3. The thermal printer according to claim 1, wherein the previous pixel data is correction data of a pixel of interest obtained in a row before the row. 4. The thermal printer according to claim 1, wherein the pixel data of interest, adjacent pixel data, previous pixel data, and next pixel data are each multi-value data. 5. A re-correction means for obtaining correction data by further correcting the correction data based on the influence data which influences the print density of the pixel of interest, and controlling the heat generation control means to generate heat of the heating element based on the re-correction data. 2. The thermal printer according to claim 1, wherein the density of the print to be printed on the print medium is adjusted by controlling the print density. 6. The thermal printer according to claim 5, wherein the thermal head has heating elements divided and arranged in a plurality of printing blocks, and the influence data is a signal of a boundary between the printing blocks. . 7. The thermal printer according to claim 5, wherein the influence data is a signal in a printing scanning direction and a signal in a sub-scanning direction perpendicular to the scanning direction. 8. The thermal printer according to claim 5, wherein the influence data is a printing rate of the row calculated from pixel data of interest of one row of the row. 9. A data switching means for switching between target pixel data and correction data or re-correction data, wherein the heat generation control means controls heat generation of the heating element based on the switched target pixel data or correction data or re-correction data. 9. The thermal printer according to claim 1, wherein the density of a print to be printed on a print medium is adjusted by controlling the print density.