JPH0481381B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides printing heads arranged line by line at a distance from one another along an image line to print an image consisting of an assembly of pixels line by line. One line has N printing elements (N≧2), and the distance between them is 2 in the same image line.
The distance between each successive pixel is greater than the distance between each successive pixel, and during the printing stroke the print head is moved in the direction of the image line to be printed, and each pixel to be printed is 1
The present invention relates to a printing method for generating control signals.

Such a method is described in British Patent Application No. GB
Known from PA2025725. In this known method, an image consisting of an assembly of pixels is printed by moving the printing head in the direction of each image line to be printed. This ensures that each of the printing elements of the print head prints some successive position of such image line during the same printing stroke, and that each position of such image line is covered by only one printing element when printing the same color. Ru. A printing stroke corresponds to the mutual distance between two successive printing elements, which mutual distance is the same for all image elements of the printing head. After printing one image line, the carrier on which the image is being printed is shifted in a direction perpendicular to the image line and the next image line is printed. A first control signal is generated for each image to be printed whose intensity matches the pixel print value of that pixel. Pixels are then printed by activating printing elements covering image positions to be printed under the control of this first control signal.

However, this known method has the disadvantage that each position within a line is only covered by the same printing element. This creates interference patterns in the printed image, particularly during line-by-line printing or halftone printing of graphic images, which disturb the optical density of the printed image. These interference patterns are then characterized by large differences in optical density creating, for example, a pattern of successive bands of pixels printed by the same printing element. Interference and/or band patterns occur as a result of geometric and/or electrical inaccuracies in one or more printing elements of the printing head, such that bands of successive pixels in successive image lines This is even more pronounced when printed by the same printing element with inaccuracies.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for printing an image consisting of an assembly of pixels line by line by means of a printing head, in which the above-mentioned interference and/or band patterns are suppressed.

According to the method of the invention to achieve this objective:
The printing stroke is longer than the distance between two adjacent printing elements, extends perpendicularly to the image line direction, and has m pieces (2≦m) of each for each image line.
≦N) for each pixel located within the same image line and within such a strip for at least one pixel strip containing a number of pixels covered by these m printing elements; , and this assignment causes pixels located later in an image line to be printed by printing elements located earlier in said row, and pixels located earlier in an image line to be printed by elements located later in said row. The printing element is characterized in that each pixel is printed by energizing its assigned printing element under the control of a respective first control signal.

This results in a band of pixels in the image covered by m printing elements since the printing stroke is greater than the distance between two adjacent printing elements.
As a result, for each pixel in such a band, these m
An opportunity is given to select which of the printing elements will print that pixel. This allows successive pixels within such a band to be covered by different printing elements rather than being covered by the same printing element. Interferences in the image that occur because successive positions are printed by the same printing element with inaccuracies are thereby suppressed. Deceptively, according to the invention, one of the m printing elements is assigned to each pixel within such a band. However, this allocation is accompanied by the criterion that successive pixels of the same image line within such a band are printed by different printing elements. The actual printing of the pixels within such a band is effected by energizing the assigned printing elements under the control of the respective first control signals for the associated pixels.
Pixels lying outside this band are printed in a known manner with one printing element covering that position.

Also, the fact that two or more printing elements scan the same location improves the crossover to the characteristics of both the printing device and the printhead, and in some cases lessens the demands placed on the quality of the printhead.
Geometrical and electrical inaccuracies in printing elements are deceptively tolerated, or printing elements that perform less satisfactorily are tolerated. Interference patterns resulting from inaccuracies in one or more printing elements may be smoothed out by different printing elements covering relevant positions, or successive positions of a line may not necessarily be serviced by the same printing element. It is used for the sake of others. Thermal printing devices provide tolerances for the cooling time of the printing element.

Another method of suppressing the interference pattern is described in US Pat. No. 4,374,385. The method described therein uses a printing device in which the printing head comprises an assembly of thermal printing elements. and these thermal printing elements receive a second control signal derived from the first control signal.
is activated under the control of the control signal. In this known method, after printing the first number of positions, the carrier is shifted over a distance approximately equal to half the length of the distance formed by the printing elements arranged in a line. After this translation, the printing elements are reactivated and print the position that was between two successive printing elements during the previous printing, partially suppressing the interference pattern.

However, during this translation the carrier is shifted relative to the printing head, which is different from the method according to the invention. This method is expensive because the parallel movement of the carrier requires very strict precision on the carrier transport mechanism. If paper feeding is not accurate enough, interference patterns will not be suppressed sufficiently. Also, each location within the printing stroke is only covered by one printing element.

An embodiment of the method according to the invention is characterized in that the allocation of one of said m printing elements is achieved according to a predetermined distribution pattern.

This allows for a simple allocation of one of said m printing elements and provides an opportunity to create an appropriate distribution among said m printing elements for each position within such a band.

An embodiment of the method according to the invention is such that, if the strip contains more than one pixel, the allocation of one of said m printing elements is carried out according to a distribution pattern generated for each pixel line to be printed. It is characterized by

Generating a distribution pattern for each image line to be printed provides tolerance for the inaccuracies inherent in the printing head. This also allows certain printing elements to be used more or less frequently.

An alternative to the method of the present invention in which the strength of each first control signal is matched to the pixel print value of the associated pixel is to make the print stroke larger than the distance between two adjacent print pixels and with respect to the pixel line direction. Extending vertically, each image line has m pieces (2≦m≦N)
at least one pixel band comprising a number of pixels covered by printing elements, the pixels in such band being printed sequentially by p printing elements (2≦p≦m); For a strip of pixels, for each pixel printed by the p printing elements by activating each of the p printing elements, a portion of the strength of the first control signal for that pixel is applied. A second control signal is generated based on the pixel, and the sum of the intensities included in all the second control signals for the same pixel is at least equal to the intensity of the first control signal for that pixel.

Since one pixel location is covered by m printing elements, p of these m printing elements
related pixels can be printed sequentially. This results in successive pixels within such a band not being covered by the same printing element, but by different printing elements. In order to maintain the pixel print value of each pixel in such a band, the strength of the first control signal is divided into p second control signals, and each second control signal has a p value for that printing. It is necessary to energize one of the printing elements. Since the sum of the strengths contained in all the second control signals for the same pixel is at least equal to the strength of the first control signal for that pixel, the pixel print value for that pixel is preserved. It is even possible for the sum to be somewhat larger than the strength of the first control signal, for example when providing tolerances to the heating effect in the case of thermal printing elements.
Since each of the p printing elements now prints a portion of a pixel, the inaccuracies of each of the p printing elements are smoothed out as a whole.

An embodiment of the method of the present invention described above divides the intensity contained in the first control signal for each pixel belonging to one band into p parts according to a predetermined distribution code, and in each case The present invention is characterized in that p printing elements for printing each pixel within such a band are selected from the m printing elements according to a predetermined pattern.

This makes it easy to divide the intensity into p parts and select these p printing elements from said m printing elements.

An embodiment of the method of the present invention described above generates a distribution code for each pixel within one band and belonging to the same image line, and according to the distribution code is included in the first control signal for that pixel. dividing the intensity into p parts and selecting in each case p printing devices from said m printing elements according to a predetermined pattern to print each pixel in such a band; It is characterized by

Generating a distribution code creates a degree of freedom in the division of intensities.

An embodiment of the method of the present invention described above generates a distribution pattern for each pixel within one band and belonging to the same image line, and according to this distribution pattern p from m printing elements covering that pixel. The method is characterized in that the intensity included in the first control signal for each pixel belonging to such a band is divided into p parts according to a predetermined distribution code.

Generating the distribution pattern creates a degree of freedom in the selection of p printing elements.

Preferably, the distribution code and/or distribution pattern for each image line is left unchanged. This simplifies the control of the printing head and the printing according to the method of the invention.

A preferred embodiment of the method according to the invention provides that the distribution code for each pixel (j) to be printed contains p weighting factors P _ij (1≦i≦p), whereas is equal to _P 〓 ⁱ⁼¹ P _ij =C, where C is a constant value of 1≦C≦1.5.

Each of the weighting factors P _ij then represents a portion of the strength contained in the first control signal for the associated location. The sum of the p weighting factors for one pixel must in each case equal a constant value between 1 and 1.5. This is because the strength is not lost from the first control signal. The reason for this is that loss of strength from the first control signal means that the information will not be printed correctly.

A preferred embodiment of the above method determines p weighting factors for the same pixel according to a probability distribution,
It is characterized in that the constant C is equal to 1. The probability distribution is, for example, a delta (Δ) probability distribution or a sinusoidal probability distribution. Probability distributions are easy to generate and allow for a reasonable degree of smoothing.

One preferred embodiment of the method of the invention is to measure the distance traveled by a print head during a printing stroke by
characterized in that it is approximately an integral number (n) times the mutual distance between successive printing elements. The total number of times (n) mentioned above is less than or at most equal to the number of pixels that fall within the distance between two successive printing elements of the printing head. This simplifies the control system for shifting the print head and is sufficient to suppress interference patterns to a large extent.

The present invention also provides for printing an image line by line of an image consisting of an assembly of pixels, with N rows arranged at a distance from each other along an image line (N≧
2) a printing head comprising printing elements having a distance between them that is greater than the distance between two successive pixel locations within the same image line to be printed, and wherein said printing head is provided with printing elements during a printing stroke; a first control signal generator for generating a first control signal for each pixel to be printed;
A control signal generator is connected to a print head to provide a first control signal to a printing element.

Such a printing device is also known from the already mentioned British patent application no.
Known from GB PA2025725.

The printing device according to the invention is provided with said translation means for translating the printing head over a distance greater than the distance between two adjacent printing elements within one complete printing stroke, and wherein the printing device , the selection unit comprises at least one pixel position extending perpendicularly to the image line and comprising, for each image line, several pixel positions each printed by m (2≦m≦N) printing elements. Within a band of book pixel positions, for each pixel position located on the same image line within such a band, for a pixel position located backward within one image line, a pixel position located at the front within said line is The method is provided for assigning one of the m printing elements by selecting a printing element located at a position, and selecting a printing element located at a rear within said line for a pixel position located at the front in said image line. characterized in that the first control signal generator is connected to the selection unit and configured to apply the first control signal to the selected printing element.

The translation means and the selection unit make it possible to apply the method according to the invention.

A preferred embodiment of the printing device according to the invention is such that the selection unit comprises a first memory storing a distribution pattern so that one of said m printing elements can be selected at each pixel position according to this distribution pattern. It is characterized by the following.

With a fixed distribution pattern, a memory storing this distribution pattern, for example a ROM, provides an advantageous solution.

An alternative to the inventive printing device is that each first control signal includes a strength that matches the pixel print value of the associated pixel, but the translation means can be moved between two adjacent print elements within one complete stroke. provided for translating the printing head over a distance greater than the distance of
The printing device includes a second control signal generator for generating a second control signal connected to the first control signal generator, extending in a direction perpendicular to the image line direction and for each image line. (2≦m≦
N) printing pixel locations within a strip of at least one pixel location comprising a number of pixel locations printable by the printing element of N), and applying said second control signal generator to each pixel location within such strip; p (2≦p≦
m) provided for generating the second control signal of
Each of the p second control signals is generated for the same pixel location based on a portion of the strength of the first control signal for that pixel location; the sum of the included intensities is at least equal to the intensity of the first control signal for that pixel location, and the printing device further comprises a selection unit which selects p different printing elements from said m printing elements. the selection unit being connected to the printing head and the second control signal generator and configured to apply p second control signals to the p printing elements; Features.

The translation means and the second control signal generator make it possible to use an alternative method to the method of the invention.

Preferably, the printing head is provided with a thermal printing element. Geometrical and electrical inaccuracies of the printing element are common with thermal printing elements, and therefore when using such thermal printing printers interference patterns often occur, which can be caused by printing using several colors. Sometimes it is an eyesore.

The invention will be explained in detail with reference to the drawings.

FIG. 1a schematically illustrates the relative movement of the printing head and carrier in a preferred embodiment of a printing device in which the method according to the invention is used. The printing device comprises a printing head 2 movable across a carrier, e.g. a sheet of paper 1. The paper can move in the direction of arrow 5. Print head 2 is moved by arrow 4 when printing an image line.
It moves in the direction of arrow 4' during the return stroke. The printing head comprises N (N≧2) printing elements 6, which are arranged along a row having approximately the same direction as the direction of movement of the printing head. The printing elements 6 are therefore aligned perpendicular to the direction of paper movement. FIG. 1b shows the side of the printing head 2 that is in contact with the paper. Dot-like or linear printing elements 6 are arranged at a distance dp between each other, referred to as the "printing element pitch". This printing element pitch is greater than the distance between two successive pixels within the same image line. Each printing element is connected to a control line so that control signals can be sent to cause the printing element to operate. The various control lines are grouped together to form a control bus 3.
During the entire movement, referred to as the "print stroke," the print head travels a width b across the paper, printing an image line on the paper.

The invention will be described with reference to a preferred embodiment in which the printing element 6 takes the form of a thermal printing element. This printing device will therefore be described as a "thermal printing device". These printing elements include resistive elements and the control signals take the form of current pulses. The printing element is heated under the influence of such current pulses. This heat is transferred to the paper. For example, the paper may be previously treated with a chemical which changes locally as a result of the application of heat, or a layer of e.g. wax paper may be placed between the printing head and the carrier. put. Color printing is possible using colored wax paper. Obviously, the invention is also applicable in the case of other printing elements, such as, for example, printing needles or inkjet printers.

The image is printed on the paper line by line, each line consisting of an assembly of pixels printed by dot-like or linear printing elements. The printing elements are activated under the control of control signals, in each case during two successive control signal sequences the printing head moves slightly in the direction of arrow 4. In known printing devices, the printing stroke is approximately equal to the printing element pitch.

FIG. 2 shows an example of a device for printing information. This device includes a CPU 10, a read memory 11, and
ROM, read/write memory 17, e.g.
RAM and an input/output interface 12, which are interconnected by a system bus 14,
Data and addresses can be transmitted. Also connected to the system bus 14 is a printhead control element 13. This printhead control element 13 is then connected to the printhead 2 via a control bus 3. Furthermore, the print head control element 13 is connected to the motor 16.
Connect to. Motor 16 moves print head 2. The input/output interface 12 has several connection lines 15 along which the information to be printed (for example output from a teletext receiver) is sent. The read memory 11 stores, inter alia, programs for controlling the print head. These programs are
It is executed in a known manner under the control of the CPU.
With the help of a program under the control of the CPU the information supplied via the input/output interface 12 is converted into control signals, which are converted into control signals by the system bus 14.
to the printhead control elements. The strength of each control signal is matched to the pixel print value of the pixel to be printed and is converted into energy that activates the printing element at this point. For thermal printers, this energy takes the form of current pulses. The duration and/or intensity of these current pulses varies as a function of the pixel print value of the pixel to be printed. This changes the amount of heat transferred to the paper.

FIG. 3 shows in enlarged format several image elements that have been printed in such a way that the print stroke is equal to the print element pitch. The printing head comprises four printing elements designated by the capital letters A, B, C and D. The total number of printing strokes is several (5 in this example).
Each printing element prints one pixel on the paper during one such substroke. And these pixels are on the same line. Therefore, several pixels are printed during one printing stroke. At the top of FIG. 3, four sequential printing strokes are shown. An assembly of pixels a or b, c, d respectively is printed by printing elements A or B, C, D respectively. FIG. 3 illustrates the problem that arises when printing dotted pixels with a dotted printing head. An image includes a large number of pixels, where each pixel includes several image halftones or color intensities. Therefore, geometric and/or electrical inaccuracies in the various printing elements of the printing head (geometry and/or resistance values may vary for each printing element) ) As a result of this, the pixels printed by the printing element do not have a purely round or square geometric shape. The uniform shape of the geometric pattern is often disturbed as shown in pixel assemblies b, c and d. As a result, the optical density within the pixel assembly is often disturbed, which on the one hand results in small unprinted spots within the pixel assembly and bright vertical band structures within the plate. Each pixel assembly printed by the same printing element forms one individual band within the plate. Inaccurate positioning also creates gaps between successive bands. Looking at the whole image,
These gaps create an unsightly pattern of vertical lines that are sure to disrupt the image if it is a color plate.

The present invention provides several ways to reduce the effects of the above-described defects on printed images. What these methods have in common is that the print stroke is larger than the pixel pitch. As a result, each pixel is covered by two or more printing elements in the same line. Therefore, they extend perpendicularly to the print line direction, and for each image line there are m (2≦m
An opportunity arises to print that pixel with one or more of these m printing elements, such as at least one pixel comprising several pixels each covered by ≦N) printing elements.

The method of the present invention can be roughly divided into four examples. 1 assigning one of these m printing elements according to a predetermined distribution pattern to each pixel in such a band under the control of a control signal generated for that pixel; printing each pixel by energizing each of the printed printing elements.

2 Generate a distribution pattern for each image line to be printed in such a band, assign one of these m printing elements to each pixel in any band according to this distribution pattern, and Each pixel is printed by energizing each assigned printing element under the control of control signals generated for the pixel.

3 p of these m printing elements (2≦p≦
m) to each pixel in such a band according to a predetermined distribution pattern, each pixel is printed with a fraction of the intensity of the pixel print value at that point, and The image line is determined according to a predetermined distribution code or a distribution code generated for the image line.

4. Generate a distribution pattern for each image line to be printed from such a band, and according to this distribution pattern p (2≦p≦m) printing elements are distributed among the pixels in such a band. each pixel is printed with a fraction of the intensity of the pixel print value for that point, and that fraction is defined according to the distribution code generated for the associated image line.

These various methods will be explained in detail.

Figures 4a to 4e show illustrative embodiments of methods 2, 3 and 4. FIG. 4a shows a printing head 2 of a thermal printing device, known per se. Figure 4b
indicates a row of 30 pixels representing the 30 locations covered by the print head 2, and FIG. 4c gives a number to the successive locations of the pixels of FIG. 4b. FIG. 4d shows the distance covered by the various printing elements in this illustrative embodiment during one complete printing stroke. As can be seen from FIG. 4, in this illustrative embodiment of the method of the invention, the printing stroke is approximately twice the length of the printing element pitch. In relation to a customary printing stroke, this therefore means that the printing stroke is approximately twice as long. Print element A can print positions 1-12, and print element B can print positions 7-18. Printing elements C or D can print positions 13 to 24 or 19 to 30, respectively. This therefore implies, for example, that positions 7 to 12 can be printed with both printing elements A and B. As a result, the pixel assemblies covered by different printing elements overlap each other, so that the aforementioned band-like patterns are suppressed and optical variations in density are smoothed out.

Clearly, the method of the invention is not limited to printing strokes approximately equal to twice the printing element pitch. A printing stroke can have a length greater than twice the printing element pitch. However, the printing stroke may be only a small amount larger than the printing element pitch, and only a band of two or slightly more pixels may be covered by some printing elements. In this illustrative example, edge positions 1 to 6 and 25 to 30 are covered by only one printing element due to technical limitations.

the first representing the amount of energy or the time at which energy is applied to the printing element depending on the pixel print value for each pixel to be printed (in the latter case the amount of energy applied per unit time is constant);
generates a control signal. Considering that according to the invention it is covered by several printing elements,
The amount of energy (or time) stored in the first control signal covering the relevant position 1
need to be distributed over one or more printing elements.
The method of the invention may be used for this purpose by determining a weighting factor for each printing element covering that position, or one position for p of m printing elements, or for each printing element in a series of positions to be printed. gives some options, such as establishing a constant distribution pattern that is assigned to The series of positions is distributed over the path described by this time-related printing element.

The boundary condition when determining the weighting factor (P _ij ) is that the total sum of the weighting factors added over all (p) printing elements (i) covering a certain position (j) is _P 〓 ^{i= 1} P _ij = C (where 2≦p≦m and m is the number of printing elements covering the position j) and the constant C at that position.
It must be. The value of this constant is 1≦c≦1.5. This is because a given pixel must be printed without being reduced in that position. The weighting factors may be predetermined or may be determined, for example, by a probability distribution. Common probability distributions are, for example, delta probability distributions or sinusoidal probability distributions. FIG. 4e shows the delta probability distribution for printing elements A, B, C and D for positions 1-30. PA represents the weighting factor for printing positions 1 to 12 with printing element A. PB, PC
and PD are the respective positions 7 to 18, 13 to 24 printed by printing elements B, C and D, respectively.
and weighting factors for 19 to 30. As can be deduced from FIG. 4, printing element A prints position 7. Position 10 is printing element A
and B. In the case of this position 10, the energy stored in the first control signal for this position is distributed equally between the two printing elements A and B. Since position 10 is covered by two printing elements, the chances of optical density defects occurring as a result of inaccuracies in the printing elements (eg printing element B) are considerably reduced at this position. Also, a new set of weighting factors is generated for each line of the image to be printed. As a result, optical defects are further reduced when all lines of the image are viewed.

In a similar manner to defining a weighting factor for the energy distribution, it is also possible to define a distribution pattern for selecting p out of m printing elements.

Using probability distributions is, of course, one way to generate weighting factors. Another method of assigning weighting factors is shown in FIG. 4f.
In this case, a weighting factor representing a portion of the energy is assigned for each position to the printing element covering that position. Thus, for example, for position 14, printing elements B and C work, but a weighting factor of 2/3 is assigned to printing element B and a weighting factor of 1/3 is assigned to printing element C. When printing this position 14, 2/3 of the energy of the first control signal is applied to printing element B, and 1/3 of the energy
is given to printing element C. The sum of the weighting factors per position is equal to 1 in this case. Of course, this sum can also be made somewhat larger than 1. For example, weighting factors of 0.6 and 0.5 per position are also allowed. The total energy imparted to all printing elements acting on one position may be somewhat greater than the energy taken from the first control signal. Close the lid,
For example, because there are tolerances to the heating effects on the various printing elements.

The sequence of weighting factors is stored, for example, in a memory of the printing device, which memory functions as a distribution pattern generator.

FIG. 5 illustrates, on the basis of a flowchart, the operations that take place in a first preferred embodiment of the method of the invention. This first preferred embodiment uses probability distributions to generate the weighting factors. Assume that printing is done in a single color (for example, black). Printing of several colors will be dealt with later. As already noted in the discussion of FIG. 2, the print head is controlled by the CPU. In order to print an image consisting of dot-like or line-like image elements, when the user or the data processing device gives the necessary instructions, a program suitable for this purpose is called from memory and started under the control of the CPU ( 20). At the beginning of program execution,
A line counter that counts the number of lines to be printed is set to a starting position, eg, a "0" position. Next, for each position located within the line to be printed, a weighting factor is determined based on the probability distribution. The weighting factor is determined based on the Δ distribution, for example, as shown in e of FIG. These weighting factors are generated by a distributed code generator and readout memory that are part of the CPU. The weighting factors for each generated position are stored in read-write memory. After the weighting factor is generated, the index flag is set to the "0" position (23). This index flag serves to indicate within which position range the print head is located. Thus, in this illustrative example, where the print stroke extends approximately twice the length of the print element pitch, the index flag is in position 2, i.e., position "0" in the first half of the print stroke. ,
The second half of the printing stroke has position "1". The information to be printed on the first line is then retrieved (eg, via an input/output interface or from memory) (24). A first control signal (I _i ) sequence is called. This first control signal sequence is determined under the control of the CPU.
This first sequence of control signals is stored in a memory location designated for this purpose, called a "print table". Next, the position counter is set to the starting position, for example, the "0" position (25). This position counter counts the number of positions at one position of the pitch flat (eg, 6 as shown in FIG. 4b). An operation is then performed to apply the weighting factors stored in memory for the positions and a certain printing element to the first control signal for those positions (26). This operation will be explained with reference to the example given in FIG. When the position counter is in the starting position, printing element A covers position 1, printing element B covers position 7, and printing elements C and D cover positions 13 and 19, respectively. At this time, the first control signals for positions 1, 7, 13 and 19
Call I ₁ , I ₇ , I ₁₃ and I ₁₉ from the print table. weighting factors for different positions and different printing elements
Set P _A1 , P _B7 , P _C13 and P _D19 and recall these values from memory. This time, the CPU performs the next operation.

P _A1・I ₁ ＝S _A1 P _B1・I ₇ ＝S _B7 P _C13・I ₁₃ ＝S _C13 P _D19・I ₁₉ ＝S _D19 (Here, ・ represents "act". This is logical "AND" operation or multiplication). The result of this calculation is a second control signal S _j,I for the relevant position. This second control signal then represents the amount of energy (or the length of time that energy is applied to the printing element) to be applied to a certain printing element (j) covering position (i). A second set of control signals is stored in a buffer. and (27) activating the printing elements under control of the respective second control signals to print the information on the paper. Next, change the setting of the position counter by one unit (it increases or decreases depending on the starting position of the position counter), and check whether all the positions to be printed are covered by one setting of the index flag. That is, it is checked whether the position counter has reached the final setting (29). If the position counter has not reached its final setting (N), shift the print head to the next adjacent position and repeat step 26 for the next position. Referring again to the example in Figure 4, the second example below
The control signal for is determined.

P _A2・I ₂ = S _A2 P _B8・I ₈ = S _B8 P _C14・I ₁₄ = S _C14 P _D20・I ₂₀ = S _D20 Next, in step 27, these second control signals S _A2 ,
Activate the printing elements under the control of S _B8 , S _C14 and S _D20 . Steps 26, 27, 28, 29 and 33 are repeated until the position counter reaches the final position and all positions for the index flag setting ``0'' have been covered by the print head. step
If the position counter has reached the final position at step 29 (Y), then the setting of the index flag is checked (step 30). If the position is "0", proceed to step 31; if the position is "1", proceed to step 31.
Proceed to 38. In step 31, a new sum of weighting factors is calculated for the position covered by the new position of the index flag. This is necessary because a position that was already covered by another print element in a previous setting of the index flag will now be covered. In the example given in Figure 4, a Δ probability distribution is used and the index flag has only two settings, whereas this new probability factor is easily determined from the relation (Z-P _j,i ). . Here, z represents a constant value which is set equal to 1 in this example. In some cases z is greater than 1,
It is also possible to correct for certain switch-on effects, such as heating effects.

However, since the printing head has already been shifted through several positions, this must be taken into account when determining the second control signal. For this purpose, a shifting operation is carried out on the first control signal in the printing table and on the weighting factor in the memory (32). Referring again to the example of FIG. 4, this means that positions 7 through 30 are now covered. Printing element A then covers positions 7 to 12, printing element B covers positions 13 to 18, and printing elements C and D cover positions 19 to 2, respectively.
4 and 25 to 30. Thus, the shift operation is actually a modulo 6 shift operation, so, for example, I ₇ becomes I ₁ and P ₇ becomes P ₁ . This is necessary since step 25 is returned when the position counter is set to the starting position again, and step 26 is returned when the operation described above is performed again. Next, the print head is moved to the next position (34) and the index flag is set to the new position, in this example position "1" (35). The program then begins again at step 25. The various next steps are then repeated for the position to be printed when the index flag goes to position "1". However, if the answer is negative at step 30, which checks whether the index flag is in position "0", then the process proceeds from this point to step 38. step
At step 38, it is checked whether all lines to be printed have been covered. This is, for example,
This is done by interrogating the position of the line counter and checking whether it has already reached a set position before defining the number of lines to be printed. If all lines to be printed have been covered (Y), the printing process ends (39). However, if all the lines to be printed have not yet been covered (N), a return stroke pulse is given to the print head (36), setting the print head to the starting position and shifting the paper to print the next line. Make it possible to cover. The line counter is then changed (increased or decreased) by one position (37) and the above method is repeated from step 22 for the next line to be printed.

2-3 if color printing is required
The program must be modified in this respect. For example, step 24 retrieves only the information regarding the color to be printed and determines only the first control signal for the associated color. For example, if a colored video image is being printed, the recognition of the color to be printed can be derived from the RGB signals. At this time, the program shown in the flowchart of FIG. 6 is executed for each primary color RGB.

The flowchart shown in FIG. 5 is for illustrative purposes only.
It is clear that the invention is not limited thereto. Thus, for example, it is possible to change the selection of the probability distribution or to choose a printing stroke larger than twice the length of the printing element pitch. In this case, the index flag takes more than two positions. At this time, the position of the index flag is displayed and updated by, for example, an adjustable counter. Another embodiment of the method of the invention may include, for example, printing with a first position of the index flag during a forward stroke of the print head and printing with a second position of the index flag during a return stroke of the print head. is possible.

The use of probability distributions is only a preferred embodiment of the method of the invention. A fixed distribution pattern (Method 1) can also be chosen as described below. In a fixed distribution pattern, it is permanently determined which printing element will serve a position to be covered. An example of this is shown in FIG.
A in the figure shows six printing elements (A, B, C, D, E,
1 shows a known printing head of a thermal printer comprising F); FIG. 6b shows 24 different locations covered during one printing stroke. In this example, during one print stroke, the print head covers a distance equal to approximately three times the print element pitch (this therefore implies that the index flag has three positions). The positions covered by various printing elements during one printing stroke are
It is represented by a line segment f in the figure. Letters attached to line segments indicate printing elements. Thus, positions 1 to 9 are covered by printing element A.

Figures 6c, d and e illustrate first, second and third preferred embodiments, respectively, of such fixed distribution patterns. In FIGS. 6c, d and e, letters have been placed below the various locations shown in FIG. 6b to indicate which printing element of the print head services that location. If the distribution pattern shown in Fig. 6c is selected, for example, the sequential positions 7, 8
and 9 are served by different printing elements C, A and B. This also applies to positions 10 to 18. FIG. 6e shows a distribution pattern in which printing elements are alternately energized within the band. Since successive positions are now serviced by different printing elements, effects resulting from geometrical inaccuracies of the printing elements are smoothed out and the printing elements are allowed to cool down for a period of time between sequential operations.

The distribution pattern defining which printing elements serve a position during printing is stored in a memory of the printing device, which memory acts as a selection unit for selecting one of the m printing elements.

Printing information by using a fixed distribution pattern will be explained based on the flow section of FIG.
Assume again that only one color is to be printed. After the printing process has started (50), a line counter that counts the number of lines to be printed is set to a starting position, for example the 0 position. Next, the first
The information to be printed on the line is retrieved (52) under the control of the CPU, and based on this information to be printed (in a manner similar to that described in step 24 of the program in FIG. 5) a first control signal is sent. The sequence (I _i ) is determined and stored in a memory location allocated for that purpose, called a "print table". Next, the CPU
A distribution pattern, for example the distribution pattern given in d of FIG. 6, is recalled from memory under the control of (53). Next, a position counter is set to a starting position, eg, a "0" position (54). This position counter is the number of positions in one line, e.g.
In Figure 6 d, count 24. After setting this position counter, the second
performs calculations to obtain the control signal (55). The second control signal S _j is S _j where E represents the printing element given by the distribution pattern serving position j.
=E・I _j is determined for position j. Referring to the example of FIG. 6, at the starting position of the position counter, positions 1, 4, 7, 10, 13 and 16
will be covered.

When the distribution pattern d in FIG. 6 is selected, the second control signal for the starting position of the position counter is as follows.

S ₁ = A.I ₁ S ₄ = B. I ₄ S ₇ = 0 S ₁₀ = 0 S ₁₃ = 0 S ₁₆ = 0 This second control signal causes all assigned print elements to be attached at their respective positions. be encouraged. For these positions the strength of the second control signal is therefore equal to that of the first control signal.

Once the second control signal is determined, the printing element is activated 56 under control of the second control signal to print information. For the selected example, only print elements A and B are activated. This is because the values of the other second control signals S ₇ , S ₁₀ , S ₁₃ , and S ₁₆ are zero. This is because positions 7, 10, 13, and 16 are not currently selected by the printing element responsible for these positions (e.g., position 7 is serviced by printing element A, but now printing element A
is in position 1). Next, set the position counter to 1
(57) and then checks whether all positions within the line have been covered (58).
If not (N), shift the print head (59) and step for the next position to be covered.
Repeat the print program from 55. Referring again to the example above, these are positions 2, 5, 8, 11,
14 and 17. Now the second control signal is:

S ₂ = A・I ₂ S ₅ = B・I ₅ S ₈ = 0 S ₁₁ = 0 S ₁₄ = 0 S ₁₇ = F・I ₁₇ All positions of the line to be printed have been covered in step 58. Step 55 until it is confirmed.
Repeat steps 56, 57, 58, 59. When all positions have been covered (Y), check whether all lines to be printed have been covered (line counter position) (60). If so (Y), the print program is terminated (63). If not (N),
Return to the print head and apply a stroke pulse (61),
Set the print head to the starting position and shift the paper. Next, the setting of the line counter is changed (increased or decreased) by 1 (62) and the printing program is repeated from step 52 for the next line to be printed.

Such a distribution pattern, which assigns m printing elements to each location covered thereby, may be predetermined and stored in memory or may be generated by a distribution pattern generator (consisting of a CPU and memory). This distribution pattern is preferably the same for each image line, which simplifies the control of the printing process. The distribution pattern generator is, for example,
It operates using probability value distributions.

In determining this distribution pattern, several printhead parameters must be taken into account. These parameters include, for example, geometrical imperfections of the printing head, heating and cooling effects, different resistance values of the various printing elements from head to head, etc. Of course, the length of the print stroke required to service all locations must be taken into account in determining the distribution pattern.

In determining the distance over which a printing stroke extends, it is advantageous to make this distance an integral multiple of the printing element pitch (n*printing element pitch). An upper limit on the value of n is determined, for example, by choosing n to be no larger than the number of positions in one printing element pitch. 6
In the case of a print head with 4 print elements and a print element pitch of 4, the preferred solution is to make the print stroke 4 times the print element pitch.

[Brief explanation of the drawing]

FIG. 1a is an explanatory diagram schematically illustrating the relative movement of the printing head and carrier, FIG. 1b is an explanatory diagram of the surface of the printing head in contact with the carrier, and FIG. 2 is an illustrative embodiment of the printing device 3 is an enlarged view of some pixels printed in the conventional manner; FIGS. 4a to d are illustrations of a first preferred embodiment of the method of the invention; FIG. e is an explanatory diagram of the Δ probability distribution pattern used in the first preferred embodiment of the method of the present invention; f in FIG. 4 is an explanatory diagram showing the manner in which a weighting factor per position is assigned to a printing element; FIG. 6 is a flowchart showing the operations carried out in a first preferred embodiment of the method of the invention; FIGS. 6a to 6f are illustrations of a second preferred embodiment of the method of the invention; FIG. 5 is a flowchart illustrating operations performed in a second preferred embodiment of the method. 1... Carrier, 2... Printing head, 3... Control bus, 4, 4'... Direction of movement of the printing head, 5...
direction of movement of carrier, 6...printing element, 10...
CPU, 11...ROM, 12...I/O interface, 13...Print head control element, 14...
System bus, 15... connection line, 16... motor, 17... RAM.

Claims (1)

[Scope of Claims] 1. In order to print an image consisting of an assembly of pixels by a printing head line by line, the printing head has N pixels arranged in a row with a distance between them along one image line. (N≧2) printing elements;
This distance between each other is greater than the distance between two successive pixels in the same image line, and during the printing stroke the printing head is moved in the direction of the image line to be printed, so that each pixel is printed in a single color in this printing process. A printing method in which a first control signal is generated for each pixel to be printed each time the printing stroke is longer than the distance between two adjacent printing elements and extends perpendicular to the image line direction. within the same image line and for each image line at least one band of pixels each comprising a number of pixels covered by m (2≦m≦N) printing elements; assigning one of these m printing elements to each pixel located in the image line, and using this assignment, pixels located later in the image line are printed by printing elements located earlier in said line;
Pixels located in the foreground in an image line are printed by printing elements located later in said line, each pixel being printed by energizing its assigned printing element under the control of a respective first control signal. A printing method characterized by: 2. A printing method according to claim 1, characterized in that the allocation of one of the m printing elements is achieved according to a predetermined distribution pattern. 3. A patent claim characterized in that when a band includes two or more pixels, the allocation of one of the m printing elements is performed according to a distribution pattern generated for each pixel line to be printed. The printing method described in item 1 of the scope. 4. The printing method according to claim 2 or 3, characterized in that the pattern of each image line to be printed remains unchanged. 5. The printing method according to claim 4, wherein when m=2, the front printing element and the rear printing element are alternately energized according to a distribution pattern. 6. In order to print an image consisting of an assembly of pixels line by line by a printing head, a row of N (N≧2) printing heads are arranged along one image line with a distance between them. printing elements, the distance between them being greater than the distance between two successive pixels in the same image line, and moving said printing head in the direction of the image line to be printed during a printing stroke; A printing method in which a first control signal is generated for each pixel to be printed each time each pixel is printed in a single color, and the strength of the first control signal is matched to the pixel print value of that pixel. The stroke is larger than the distance between two adjacent printing pixels, extends perpendicularly to the pixel line direction, and is covered by m (2≦m≦N) printing elements each for each pixel line. a band of at least one pixel including several pixels, such that the number of pixels in such a band is p (2≦p≦
m) for each pixel printed by these p printing elements by activating each of the p printing elements, for a band of pixels printed sequentially by the p printing elements, generating a second control signal based in part on the strength of the first control signal;
The sum of the intensities included in all the second control signals for the same pixel is calculated as
A printing method characterized in that the strength of the control signal is equal to the strength of the control signal. 7. Divide the intensity contained in the first control signal for each pixel belonging to one band into p parts according to a predetermined distribution code, in each case for each pixel in such a band. 7. The printing method according to claim 6, wherein the p printing elements to be printed are selected from the m printing elements according to a predetermined pattern. 8 Generate a distribution code for each pixel within one band and belonging to the same image line, and divide the intensity included in the first control signal for that pixel into p parts according to the distribution code. p printing devices for printing each pixel in such a band in each case are selected from said m printing elements according to a predetermined pattern. The printing method described in Section 6. 9 Generate a distribution pattern for each pixel within one band and belonging to the same image line, select p from m printing elements that cover that pixel according to this distribution pattern, and The printing method according to claim 6, characterized in that the intensity included in the first control signal for each pixel belonging to the band is divided into p parts according to a predetermined distribution code. . 10. The printing method according to claim 7 or 8, characterized in that the distribution code is made constant for each image line. 11. The printing method according to claim 8, characterized in that the distribution code and the distribution pattern are made unchanged for each image line. 12 The distribution code for each pixel (j) to be printed contains p weighting factors P _ij (1≦i≦p), whereas the sum of all weighting factors is _P 〓 ⁱ⁼¹ p _ij =C Claims 7 and 8, wherein C is a constant value of 1≦C≦1.5.
The printing method according to item 9, item 10, or item 11. 13. The printing method according to claim 12, wherein p weighting factors for the same pixel are determined according to a probability distribution, and the constant C is equal to 1. 14 A set of probability values P _ij (i constant; j variable) consisting of all weighting factors for all pixels m covered by a certain printing element i takes the form of a delta probability distribution or a sinusoidal probability distribution. 14. The printing method according to claim 13, characterized in that: 15. Any of the preceding claims characterized in that the distance traveled by the printing head during a printing stroke is approximately an integral number (n) times the mutual distance between two successive printing elements of the printing head. Printing method described. 16. A printing method as claimed in claim 15, characterized in that the integer n is less than or at most equal to the number of pixels that fall within a space called printing element pitch between two successive printing elements of the printing head. 17. A printing head comprising a row of N printing elements (N≧2) arranged at a distance from each other along an image line for printing an image consisting of an assembly of pixels line by line. , the distance between them being greater than the distance between two successive pixel positions within the same image line to be printed, and translation means for causing said printing head to translate to be printed during a printing stroke. and further comprising a first control signal generator for generating a first control signal for each pixel to be printed, the first control signal generator being connected to the print head to generate the first control signal. in a printing device for imparting a printing head to a printing element, said translation means being provided for translating the printing head over a distance greater than the distance between two adjacent printing elements within one complete printing stroke; The printing device comprises a selection unit, which selection unit extends perpendicularly to the image line and for each image line has a number of pixels each printed by m printing elements (2≦m≦N). within a band of at least one pixel position containing the position, for each pixel position located on the same image line within such band, for pixel positions located later within one image line; One of the m print elements is selected by selecting the print element located at the front in the line, and for a pixel position located at the front in the image line, selecting the print element located at the rear in the line. 1. A printing device, characterized in that said first control signal generator is connected to said selection unit and configured to apply said first control signal to a selected printing element. 18. The selection unit comprises a first memory storing a distribution pattern, according to which one of the m printing elements can be selected at each pixel position. The printing device according to scope item 17. 19. Printing according to claim 17, characterized in that the selection unit comprises a distribution pattern generator for generating a distribution pattern, according to which one of the printing elements can be selected. Device. a printing head comprising a row of N printing elements (N≧2) arranged at a distance from each other along an image line for printing an image consisting of an assembly of 20 pixels line by line; , the distance between them being greater than the distance between two successive pixel positions in the same image line to be printed, and the printing head having a position in the direction of the image line to be printed during a printing stroke. and a first control signal generator for generating a first control signal for each pixel to be printed, the strength of the first control signal being determined by the intensity of the first control signal in a printing device, wherein the first control signal generator is connected to the print head so that the first control signal can be assigned to the printing element, the translation means being arranged within one complete stroke. the printing device for generating a second control signal connected to the first control signal generator; a second control signal generator, extending in a direction perpendicular to the image line direction and having m (2) second control signal generators for each image line;
≦m≦N), printing pixel locations within at least one swath of pixel locations including a number of pixel locations that can be printed by a printing element, ≦m≦N; p (2
≦p≦m), and each of the p second control signals has an intensity equal to a portion of the intensity of the first control signal for the same pixel position. wherein the sum of the strengths of all second control signals generated based on the same pixel location is at least equal to the strength of the first control signal for that pixel location, and the printing device further comprises a selection unit. , a selection unit is provided for selecting p different printing elements from said m printing elements, said selection unit being connected to the printing head and a second control signal generator, said selection unit being connected to said printing head and said second control signal generator; A printing apparatus characterized in that the control signal is configured to be applied to the p printing elements. 21 A second control signal generator comprises a second memory for storing a distribution code, according to which said p portions are defined for each pixel position in the band, and a selection unit stores a distribution pattern. 21. The printing apparatus according to claim 20, further comprising: 3 memories, which allow the p printing elements to be selected at each pixel position within the band according to the distribution pattern. 22, the selection unit comprising a distribution pattern generator for generating a distribution pattern, according to which said p printing elements can be selected for each pixel position in the strip; and generating a second control signal. Claim 20, characterized in that the device comprises a second memory for storing a distribution code, according to which the p portions are determined for each pixel position in the band. printing device. 23, the selection unit comprising a distribution pattern generator for generating a distribution pattern, according to which said p printing elements can be selected for each pixel position in the strip; and generating a second control signal. Claims characterized in that the device comprises a distribution code generator for generating a distribution code, according to which the p portions can be determined for each pixel position in the band. 21. The printing device according to item 20. 24 The distribution code is divided into p weighting factors p _ij (1≦
i≦p), and the sum of all weighting factors _P 〓 ⁱ⁼¹ p _ij =C is made equal to a constant value C (1≦C≦1.5). printing device. 25 Claim 23 or 2, characterized in that the distribution code generator is a probability value generator
The printing device according to item 4. 26. Printing device according to one of claims 17 to 25, characterized in that the printing head is provided with a thermal printing element.