JP3504475B2 - Image forming method of image forming apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a recording head having a plurality of recording elements arranged in a line, and changes the dot size in each pixel based on multivalued input image data to perform dot recording on a recording medium. The present invention relates to an image forming method of an image forming apparatus that forms a multivalued image.

[0002]

2. Description of the Related Art Conventionally, a line LED (light emitting diode)
In an image forming apparatus such as a printer using a line head such as a head, a line thermal head, or a line inkjet head, the resolution of the head, that is, in the case of a line LED head, a plurality of recording elements arranged in a line are arranged. Raster direction spacing of LED light emitting elements, raster direction spacing of a plurality of heating resistors, which are recording elements arranged in a line in the case of a line thermal head, and recording elements arranged in a line in the case of a line inkjet head. That is, the binary image is formed by printing dots of the same size on the recording paper while keeping the plurality of ink ejection openings at intervals in the raster direction.

In these image forming apparatuses, the character image is simply reproduced as a binary image corresponding to the resolution of the head,
The photographic image was reproduced by pseudo gradation processing such as the systematic dither method or the error diffusion method. In this case, the reproducibility of the resolution of characters, line drawings, etc. depends on the resolution of the head, and in the case of a head with a low resolution, the shaded portions of characters, line drawings, etc. are jagged called jaggies.

On the other hand, in an image forming apparatus equipped with such a line head and performing high-speed printing line by line, in recent years, by using multi-valued image data, the printing area in one pixel is modulated to thereby set the area in one pixel. Something that can be expressed with several gradations has also appeared. FIG. 14 shows a recording head 1 in which a plurality of recording elements used in such an image forming apparatus are arranged in a line, and dots printed on the recording paper 2 by the recording head 1. In FIG. 14, for simplification, the case where one pixel is recorded in three values including white is shown as an example. In addition, such a recording head 1 is
For example, by arranging 4 or 3 in parallel, C
A color image can be recorded by a combination of four colors of (cyan), M (magenta), Y (yellow), and K (black), or a combination of three colors of C, M, and Y.

In such an image forming apparatus capable of recording multi-valued image data, an image recording operation is actually performed after various image processing such as color conversion processing, UCR (undercolor removal) processing, or γ correction. In order to reproduce the specified number of gradations peculiar to the printer engine, multi-valued pseudo gradation processing such as multi-valued dither processing using screen angles or multi-valued error diffusion processing is performed for each color, and the number of pixels is 1 pixel. It is designed to obtain multi-valued image data of bits. And
Image reproducibility is improved by concentrating a larger amount of information on one pixel.

[0006]

In the above-mentioned conventional structure, the gradation and color reproducibility are improved, but the resolution is not improved and jaggies are generated in the shaded areas of characters and line drawings. The problem that arises is not resolved. Also, in a low-resolution line head, when interpolating a portion where jaggies occur with small pixels, a gap occurs between dots, and if this is less than the resolution of human visual characteristics classification, the image will be reversed. There was a problem that it looked blurry.

Therefore, for example, in an electrophotographic image forming apparatus using a line LED head, the effect of controlling the light emission time of one pixel and superimposing the energy distribution of light on the photoconductor and the photoconductor itself. Due to the resolution, the density of dots is apparently higher than the spacing between the LED light-emitting elements, and the printing position is controlled to reduce the jaggedness of the shaded area of the printed image and improve the printing quality. Such a technique is referred to as an edge enhancement technique, and is a technique often used in an electrophotographic printer or the like in which the distribution of peripheral pixels has some influence on a pixel of interest and gives a printing effect.

However, such a method requires special hardware for smoothing, a special image code obtained there, and a driver and a drive waveform necessary for driving this with an LED, and further, a high-speed printer engine. It is difficult to achieve significant effects due to process limits or electrical limits.

Further, in a printer such as a line ink jet printer in which each pixel functions independently and has a strong independent factor that does not affect other pixels, a pulling effect between dots can be obtained. However, there is still a problem in that a gap still occurs between the dots. Further, in the line inkjet printer, due to the influence of misdirection and the like, due to the partial printing position accuracy, even if printing is performed under the same conditions, adjacent dots may be covered or separated depending on the position, which deteriorates the image quality. There was a problem.

Therefore, the inventions according to claims 1 to 6 provide an image forming method of an image forming apparatus capable of obtaining a smooth image with little blurring without generating a gap in the contour portion of the image. Further, the invention according to claim 2 further provides an image forming method of an image forming apparatus, in which adjustment is easier by changing a diameter of a dot having a larger gradation value. Also,
The invention according to claim 6 further provides an image forming method of an image forming apparatus capable of performing accurate contour correction on a contour portion of a character or a line drawing.

[0011]

According to the present invention, there is provided a recording head in which a plurality of recording elements are arranged in a line at a predetermined interval, and a recording medium for the recording head is provided in each recording element of the recording head. Are moved relative to each other in the direction orthogonal to the arrangement direction, and dot recording is performed pixel by pixel in the main scanning direction in each recording element of the recording head, and the dots in the main scanning direction are moved by the relative movement of the recording head and the recording medium. In an image forming apparatus for moving a recording in the sub-scanning direction and performing area modulation for changing a dot size in each pixel to form a multi-valued image, 1 pixel n bit, N (= 2 ⁿ ) gradation When image data is used and the gradation value of the minimum gradation pixel of a solid white dot is 0 and the gradation value of the maximum gradation pixel of a solid black dot is (N-1), a certain gradation value k (1 ≦ k <
N / 2) and a dot having a gradation value (N−k−1) that forms a paired relationship with this dot so that their outer peripheries intersect when the dots are juxtaposed vertically or horizontally on the recording medium. To change the diameter of the image to form an image.

[0012]

[0013]

[0014]

[0015]

[0016]

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to the drawings. In this embodiment, a case where the present invention is applied to a color inkjet printer will be described. FIG. 1 is a diagram showing the configuration of the entire printer. A rotary drum 12 that rotates in a direction indicated by an arrow in the figure at a constant peripheral speed is provided in a main body case 11, and the rotary drum 12 has paper feed rollers 13 and 14. The recording paper 15 which is a recording medium conveyed by is wound around.

That is, a paper feed cassette 16 is provided at the bottom of the main body case 11, the recording papers 15 are stacked and placed on a mounting plate 17 of the paper feed cassette 16, and the stacked recording papers 15 are placed. Are taken out one by one by the feeding roller 18 and fed to the paper feeding rollers 13 and 14. Further, the recording paper 15 that has been manually fed from the manual feed tray 19 that is mounted on the side of the main body case 11 so as to be openable and closable is fed by the feeding roller 20 to the paper feeding rollers 13 and 14. The feeding switching means 21 switches between feeding by the feeding roller 18 and feeding by the feeding roller 20.

A charging roller 22 that attracts the recording paper 15 conveyed by the paper feed rollers 13 and 14 to the drum surface is arranged opposite to the rotary drum 12. Also,
On the rotary drum 12, four ink jet recording heads 231 and 23 having a large number of recording elements arranged in a line.
The printing mechanism 24 in which 2, 233 and 234 are movably arranged in the rotation axis direction of the rotary drum 12 is arranged opposite to each other. Each of the recording heads 231 to 234 is a yellow inkjet recording head 231, which ejects a yellow (Y) ink, a cyan inkjet recording head 232, which ejects a cyan (C) ink, and a magenta inkjet recording, which ejects a magenta (M) ink. Head 23
3. A black inkjet recording head 234 that ejects black (K) ink.

The printing mechanism 24 includes the recording head 23.
1 to 234 mounted on the reciprocating mechanism 25, and a head moving device 26 having a linear motor for controlling the reciprocating mechanism 25 to move in the direction of the rotation axis of the rotary drum 12.
The head moving device 26 comprises an advancing / retreating means 27 for advancing / retreating the head 26 with respect to the drum surface of the rotary drum 12.

In the vicinity of the drum surface of the rotary drum 12, recording paper peeling means having a peeling claw 28 which can be inserted between the drum surface and the recording paper 15 is arranged.
Recording paper 15 wound around the rotating drum 12 by means of 8
Is peeled off, and the peeled recording paper 15 is discharged to the recording paper discharging / conveying means 29. The recording paper discharging / conveying means 29 conveys the recording paper 15 to the belt conveyor 30 which contacts the non-recording surface of the recording paper 15.
And a pressing means 31 that presses against the surface.

At the end of the belt conveyer 30, the recording paper 15 conveyed by the belt conveyer 30 is formed on the upper part of the main body case 11 and an upper discharge tray 32 is provided.
There is provided a direction switching means 34 for switching whether the sheet is discharged to the discharge tray 33 or to a removable discharge tray 33 provided on the side surface of the main body case 11. In addition, 35 is an ink drying means,
36 is an ink cassette, 37 is an ink buffer, and 38 is an ink supply tube.

FIG. 2 is a block diagram showing the entire hardware configuration, in which image data is transferred from the host computer 41 to the printer 42. That is, the host computer 41 transfers the code and raster data from the driver 411 to the printer controller 421 of the printer 42 according to the interface characteristics with the printer 42.

In the printer 42, the printer controller 421 drives and controls the printer engine 422. The printer engine 422
Is constituted by the rotary drum 12, the sheet feeding mechanism such as the sheet feeding rollers 13 and 14 and the sheet feeding cassette 16, the charging roller 22, the printing mechanism 24 having the inkjet recording heads 231 to 234, the recording sheet discharging and conveying means 29, and the like. I am configuring.

The printer controller 421 develops a coded image data sent from the host computer 41, for example, a page description language such as PDL into a bitmap and after performing each image processing, a page incorporated therein. Store in memory. The printer engine 422
Converts the bitmap image data from the printer controller 421 into a drive signal, and the rotary drum 1
2, paper feed mechanism, charging roller 22, each recording head 231
234 etc. are driven in a predetermined order.

The relationship between the host computer 41 and the printer 42 does not necessarily have to be one-to-one, and it may be used as a network printer in a network that has recently become widespread. In this case, there is a plural-to-one relationship. . Further, the printer controller 421 and the printer engine 4
The interface with 22 basically depends on the printer architecture and is not standardized.

FIG. 3 shows the printer controller 421.
FIG. 3 is a block diagram showing the configuration of an image processing unit in the figure, which is composed of a color conversion processing unit 51, a UCR processing unit 52, a pseudo gradation processing unit 53, and a smoothing processing unit 54. First, the typical RGB color signal is converted into the CMY color of the color reproduced by the printer 42 by the color conversion processing unit 51.

Next, in the UCR processing section 52, C
The black component is extracted from the MY colors, the subsequent CMY colors are determined, and finally the CMYK colors are converted. The pseudo gradation processing unit 53 compresses the data of one pixel into the data of about 2 to 4 bits for each color according to the printing ability of the printer 42 by the multi-value dither processing or the multi-value error diffusion processing for each color.
The smoothing processing unit 54 performs processing for interpolating the edge portion for each color to suppress line image jaggies.

FIG. 4 is a block diagram showing the hardware configuration of the printer engine 422, which is a control unit 6
1, the controller 61 drives and controls the recording heads 231 to 234 according to the image data from the printer controller 421, and also rotationally drives the head moving device 26, the paper feed rollers 13 and 14, and the like. The sheet conveying motor 62, the drum motor 63 that rotationally drives the rotary drum 2, and the charging roller 22 are driven and controlled.

The head moving device 26 moves the recording heads 231 to 234 in the rotational axis direction of the rotary drum 12 at a predetermined speed and timing in synchronization with printing.
The paper transport motor 62 controls the transport of the recording paper 15 picked up from the paper feed cassette 16 to the rotary drum 12. The recording paper 1 that has been peeled off after printing is completed
5 is discharged by the recording paper discharge / conveyance means 29 or the like by another motor.

Next, the dot recording method of this color ink jet printer will be described. The ink jet recording heads 231 to 234 have the same dot recording method, and the dot recording method of the yellow ink jet recording head 231 will be described here as a representative.
FIG. 5 shows a dot recording method on the recording paper 15 by the inkjet recording head 231. The ink jet recording head 231 has a plurality of ink ejection openings 231a as recording elements formed in a line at regular intervals.

The numbers 1 to 15 in the main scanning direction, which are the directions in which the ink ejection ports 231a of the ink jet recording head 231 are arranged, indicate the print dot positions in the main scanning direction on the recording paper 15, and the recording paper 15 The numbers 1 to 4, ... In the sub-scanning direction, which is the conveyance direction, indicate print dot positions in the sub-scanning direction on the recording paper 15. The conveyance of the recording paper 15 in the sub-scanning direction is performed by the rotation of the rotary drum 12.

One of the squares on the recording paper 15 represents one dot. The numbers in the squares represent the numbers of the ink ejection ports 231a that print the dots and the printing order. For example, 1-1 is a number No. 1 indicates the dots printed by the first ink ejection port 231a when the recording paper 15 is first conveyed, that is, the first rotation of the rotary drum 12, and 1-4 is the same number No. No. 1 ink ejection port 231a
7A and 7B indicate dots printed when the recording paper 15 is conveyed for the fourth time, that is, for the fourth rotation of the rotary drum 12.

The ink jet recording head 231 has an ink ejection port 231 during one rotation of the rotary drum 12.
Printing on the recording paper 15 is completed by moving in the main scanning direction by 1/2 of the interval between a and rotating the rotary drum 12 four times. That is, in the first first rotation of the rotary drum 12, each ink ejection port number. 1-No. Ink ejection from 8, ..., 1-1,2-1,3-1,4-1,5
Dots are printed at the positions of -1, 6-1, 7-1, 8-1, .... That is, in the first first rotation, printing is performed on the odd-numbered rows every other dot in the main scanning direction and on the odd-numbered lines in the sub-scanning direction. This can be realized by transferring the image data thinned out in advance so as to be printed with this pattern to the inkjet recording head 231 at the print timing. Then, while the rotary drum 12 is rotating, the inkjet recording head 231 moves in the main scanning direction at a constant speed. This is performed by controlling the drive of the head moving device 26 by a control signal from the control unit 61.

At the second rotation of the rotary drum 12, each ink ejection port number. 1-No. By ejecting ink from 8, ...
2,2-2,3-2,4-2,5-2,6-2,7-
Dots are printed at positions 2, ... In other words, printing is performed on even-numbered columns every other dot in the main scanning direction and on odd-numbered lines in the sub-scanning direction.

At the third rotation of the rotary drum 12, each ink ejection port number. 1-No. By ejecting ink from 8, ...
3,2-3,3-3,4-3,5-3,6-3,7-
Dots are printed at positions 3 ,. That is, printing is performed on odd-numbered columns every other dot in the main scanning direction and on even-numbered lines in the sub-scanning direction.

At the fourth rotation of the rotary drum 12, each ink ejection port number. 1-No. By ejecting ink from 8, ...
Dots are printed at the positions of 4,2,4,3,4,4,4,5,6-4, .... That is, printing is performed on even-numbered columns every other dot in the main scanning direction and on even-numbered lines in the sub-scanning direction. In this printing, the left and right two columns are in a state in which dots are thinned out, so this is not used for actual printing. This can be dealt with by setting blank data in regions of 2 dots each on the left and right when the control unit 61 thins out image data.

The ink jet recording head 231 is
One ink ejection port 231a can control ink ejection in eight steps including no ink ejection, and can reproduce an image with eight gradations per pixel. That is, as shown in FIG. 6, seven kinds of variable dot sizes from 1 gradation to 7 gradations are used for one pixel, and a total of 8 gradations including white can be expressed. Also,
The dot size of each gradation is adjusted in advance so as to have a linear density characteristic. This also applies to the other inkjet recording heads 232, 233, 234.

As the capability of the printer 42, 3 bits for each color are used.
, The pseudo gradation processing unit 53 converts the input 8-bit and 256-gradation image data into pseudo-halftone processing into 3 bits and 8 gradations of each color, for example. 8
For gradation image data, 0 is solid white, 7 is solid black, and 1 to 6
Will be described as an intermediate gradation.

FIG. 7 shows the configuration of one dot in the printer 42. Since the dots to be actually printed have an inclination at the edge portion, the solid density is visually 50% or measured with an optical microscope or the like. In that case, a threshold value is set at 40%, and the dot diameter is defined by what is binarized with this threshold value. When printing solid black on one side,
The dots are set with a diameter of a circle that completely covers the square grid with respect to the basic resolution of the printer so that white gaps do not occur diagonally. That is, the diameter of the 7th gradation dot, which is the maximum gradation value, is 119.73 μm if the width of one side of the square lattice is 84.66 μm, as shown in FIG.

FIG. 8 is a diagram showing how to set the dot diameter.
8A shows dots set in this embodiment,
FIG. 8B shows a dot set for conventional gradation reproduction. As shown in FIG. 8B, in the conventional dot, for example, 1-gradation and 6-gradation dots, 2-gradation and 5-gradation dots, and 3-gradation and 4-gradation dots are adjacent to each other. In this case, a gap is generated between the dots. On the other hand, in this embodiment, the dots are in contact with each other as shown in FIG. Here, the case where the outer diameters of the dots are in contact with each other at one point is shown as the minimum set diameter, but the point is that the outer circumferences of the dots forming a pair should intersect.

In this example, in 8 gradations of 0 to 7, for dots of arbitrary gradation values 1, 2, and 3, the dots of gradation values 6, 5, and 4 which form a paired relationship with this dot are It shows that the outer peripheries of the dots intersect each other when they are arranged side by side vertically or horizontally. If this is generalized, 1 pixel n bits, N (=
There is a case ^where image data of 2 ⁿ ) gradation is used, the gradation value of the minimum gradation pixel of the solid white dot is 0, and the gradation value of the maximum gradation pixel of the solid black dot is (N-1). Arbitrary gradation value k
When dots in (1 ≦ k <N / 2) and dots having a gradation value (N−k−1) that form a pair relationship with this dot are juxtaposed vertically or horizontally, the outer peripheries of the dots intersect each other. Will be set to.

The control for changing the diameter of the dot is a drive waveform used for the control for ejecting ink from the ink ejection ports of the ink jet recording heads 231 to 234 according to the image data value of each color inputted by the control unit 61 in FIG. It can be realized by controlling. It is assumed that the ink jet recording head in this case uses an electromechanical conversion element and applies a drive waveform to the electromechanical conversion element to give a pressure fluctuation in the ink chamber to eject ink from the ink ejection port. . Needless to say, the present invention is not limited to this.

For controlling the drive waveform, for example, even if the ejection amount of ink is controlled by finely adjusting the width of the driving pulse, the ejection amount of ink is controlled by controlling the voltage amplitude of the driving pulse. May be. For example, in the control by the pulse width, when the input image data is 1, the pulse width Aμ
m and Bμm when the input image data is 6, when the pulse width of the ejection waveform is changed to A′μm in order to change the dot diameter when the input image data is 1, the ejection for the input image data 6 is performed. The pulse width of the waveform is changed to B'μm so as to match the conditions of the pair of dots. Generally, the larger dot diameter is easier to adjust than the smaller dot diameter, and therefore, the one on the adjustment side that satisfies the setting condition of the paired dot diameter at this time is selected to have the larger gradation value. By doing so, adjustment can be made easier.

Next, a smoothing process for interpolating the edge portion of a character or line image using the set dots to reduce jaggies and obtain a smooth image will be described. Characteristic of a character or line image is that unlike a gradation image, it is basically composed of a combination of dots having a maximum gradation value of 7 when an original image is generated. As a smoothing method, a general pattern matching method is used. Further, in a printer such as a line inkjet printer in which the dot position cannot be controlled, in a configuration in which small dots are continuously formed, a gap occurs between pixels and an image is blurred, so that interpolation in a very large area cannot be performed. is there.

Therefore, the pattern size is 3 × 3.
The size will be described as an example. The principle of pattern matching is a well-known technique and will not be described. FIG. 9 shows a state in which a 3 × 3 pattern window is scanned at an arbitrary position. In this figure, 9 is the scanning window 7
In No. 1, the pattern in the scanning window 71 causes the pixel of interest 72 to reduce the diameter of the dot having the maximum gradation value 7 indicated by the dotted circle to, for example, about 5 gradation values, and in the scanning window 73, The pixel of interest 74 depending on the pattern in the scanning window 73
Indicates a state in which, for example, a pixel having a gradation value of 2 is added from the solid white state having a gradation value of 0 and interpolation pixels are set for each pixel.

As can be seen here, in a place where there is an edge in a certain oblique direction, a pattern in which pixels are added so as to suppress the occurrence of minute density fluctuations due to smoothing processing and to form a smoother line drawing. In most cases, there are pairs of patterns that reduce the maximum pixel. By using the pair of pixels shown in FIG. 8A as the pixels to be interpolated, white gaps are generated between the pixels not only in the sub-scanning direction but also in the main scanning direction, which is a problem in this example. Since an image can be formed without any need, a high-definition image with less blur can be obtained.

Which pair of pixels is selected as the interpolation pixel is determined from the pattern in the scanning window and the actual printing characteristics. Further, in the drawing, the very small gap 75 is not visually recognized by the superposition of the actual dot analog density characteristics as described in the dot configuration of FIG. 7.

On the other hand, when the diameter of the maximum gradation value 7 is set to be about 1.6 times larger than the basic dot size of FIG. 11A, the dot diameter of each gradation value is determined correspondingly. Consider, for example, the case where the dot diameter at each gradation value in FIG. 11B is set. At this time, an interpolation result corresponding to the same pattern as in FIG. 9 is shown in FIG. In FIG. 10, reference numeral 81 is a scanning window, 82 is a target pixel of the scanning window 81, 83 is another scanning window, and 84 is a target pixel of the scanning window 83.

Here, comparing FIG. 9 with FIG. 10, it is apparent that the result of FIG. 10 is improved in the smoothness of the diagonal line. This is a substantial tendency in the interpolation of dots whose position cannot be controlled. Therefore, the accuracy of interpolation is improved by setting the dot diameter of the maximum gradation value 7 larger than the diameter of the circle covering the square pixels corresponding to the basic resolution of the printer.

The range of this effect is as shown in FIG.
When the diameter of the circle covering the square pixels is 1, the larger the dot with the maximum gradation value 7 is set within the range of 1 <the diameter of the dot with the maximum gradation value 7 ≦ √2, the more the effect is obtained. In FIG. 12, (a) shows the case where the dot diameter of the maximum gradation value 7 is 1 times, (b) shows the case where the dot diameter of the maximum gradation value 7 is 1.13 times, and (c) shows The case where the dot diameter of the maximum gradation value 7 is 1.26 times is shown, and (d) shows the case where the dot diameter of the maximum gradation value 7 is √2 times, that is, 1.41 times.

As described above, a larger effect can be obtained by increasing the dots having the maximum gradation value 7 which is an important element forming the basic lattice of characters and line drawings within the above range. Note that here, for simplicity, 3
The smoothing process in the × 3 matrix has been described, but the present invention is not limited to this. Further, although the case of the image of 1 pixel 3 bits has been described, the present invention is not limited to this, and the number of bits may be arbitrary. Especially, 1 pixel 2bi
A large effect can be obtained even in a multi-value printer having a small bit of about t.

In the above description, the case where the outer peripheries of the dots of the adjacent pairs contact at one point has been described, but the present invention is not limited to this. Next, a method of setting dots in consideration of characteristics of printing accuracy will be described. In the case of an inkjet printer, the direction of ink ejected from an ink ejection port, which is a recording element, generally varies among individual ink ejection ports due to various factors such as misdirection. Although it is possible to suppress the value to a certain value or less so that the problem of variation does not occur, the processing accuracy is required so much, the manufacturing cost becomes very high, and it is difficult to actually commercialize it.

If the directions of the ink ejected from the ink ejection ports vary from one ink ejection port to another, the dots are likely to overlap at locations where adjacent dots are close to each other, and the dots are likely to separate at locations where adjacent dots are far apart. In particular, when the image is interpolated with small dots by the smoothing process, a gap is generated and the image quality is deteriorated.

Therefore, a method of setting the dot diameter which can solve this will be described. In FIG. 13 (a), the solid circles indicate the set diameters of the dots that form a pair. In the circle of the solid line in this figure, each outer circumference of the pair of dots intersects at two points. On the other hand, the circle shown by the dotted line in the figure shows the range in which the dot may deviate from the ideal print position due to the influence of misdirection, which is inherent in ink jet printers.

[0056] By setting the diameter of the dot as the outer periphery of where the two pairs dots against at least one another, in FIG. 13
As indicated by the solid circles in (b), the dots do not separate from each other even if the dots are worst misaligned due to the influence of misdirection, that is, even if a printing error occurs in the direction in which the dots are most separated from each other. Since there is no gap between the dots, an image with less blur can be obtained.

By incorporating the accuracy compensation for the expected printing accuracy in the setting of the dot diameter in this manner, no gap is generated at all positions within a possible range, and a smooth image with less blurring can be obtained. Obtainable.

In this embodiment, the recording paper is wound around the rotary drum and is moved relatively in the direction orthogonal to the direction in which the ink ejection ports of the ink jet recording head are arranged, but the present invention is not limited to this. Instead, it may be moved by placing it on a flat endless belt, or by fixing the recording paper and moving the inkjet recording head relatively.

Further, this embodiment has been described by applying the present invention to a color ink jet printer, but the present invention is not necessarily limited to this, and can be applied to a monochrome ink jet printer, a thermal printer, an LED printer and the like. Is.

[0060]

According to the inventions described in claims 1 to 6, it is possible to obtain a smooth image with little blurring without generating a gap in the contour portion of the image. Further, according to the second aspect of the present invention, the adjustment can be further facilitated by changing the diameter of the dot having the larger gradation value. Further, according to the invention of claim 6, it is possible to perform the contour correction with high accuracy for the contour portion of the character or the line drawing.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an entire printer showing an embodiment of the present invention.

FIG. 2 is a block diagram showing the overall hardware configuration of the same embodiment.

FIG. 3 is a block diagram showing a configuration of an image processing unit of the printer controller according to the embodiment.

FIG. 4 is a block diagram showing a hardware configuration of a printer engine according to the embodiment.

FIG. 5 is a diagram for explaining a dot recording method in the same embodiment.

FIG. 6 is a diagram for explaining a pixel size of each gradation.

FIG. 7 is a diagram for explaining the configuration of one dot.

FIG. 8 is a diagram showing a dot diameter setting method in the same embodiment in comparison with a conventional dot diameter setting method.

FIG. 9 is a diagram showing an example of interpolation by a 3 × 3 matrix according to the same embodiment.

FIG. 10 is a diagram showing another example of interpolation by the 3 × 3 matrix in the same embodiment.

FIG. 11 is a diagram showing another dot diameter setting method in the same embodiment in comparison with a conventional dot diameter setting method.

FIG. 12 is a diagram showing various interpolation examples using a 3 × 3 matrix according to the first embodiment.

FIG. 13 is a diagram for explaining a dot setting method in consideration of printing accuracy in the same embodiment.

FIG. 14 is a diagram showing an example of dot recording by a conventional line recording head.

[Explanation of symbols]

12 ... Rotating drum 15 ... Recording paper (recording medium) 231-234 ... Inkjet recording head 26 ... Head moving device

Claims (6)

(57) [Claims] 1. A recording head in which a plurality of recording elements are arranged in a line at a predetermined interval, and a recording medium with respect to the recording head is perpendicular to a direction in which the recording elements of the recording head are arranged. Relative to each other, dot recording is performed pixel by pixel in the main scanning direction in each recording element of the recording head, and dot recording in the main scanning direction is performed in the sub scanning direction by relative movement of the recording head and the recording medium. In an image forming apparatus that performs multi-valued image formation by performing area modulation for moving and changing the dot size of each pixel, image data of 1 pixel n bit and N (= 2 ⁿ ) gradation is used, When the gradation value of the minimum gradation pixel of the solid white dot is 0 and the gradation value of the maximum gradation pixel of the solid black dot is (N-1), a certain gradation value k (1≤k <N Dot in / 2) and this dot Gradation value (Nk-
When the dots in 1) are placed side by side vertically or horizontally on the recording medium, change the dot diameter so that the outer circumferences of the dots intersect.
An image forming method for an image forming apparatus, further comprising forming an image. 2. A recording head in which a plurality of recording elements are arranged in a line at a predetermined interval, and a recording medium with respect to the recording head is orthogonal to a direction in which the recording elements of the recording head are arranged. Relative to each other, dot recording is performed pixel by pixel in the main scanning direction in each recording element of the recording head, and dot recording in the main scanning direction is performed in the sub scanning direction by relative movement of the recording head and the recording medium. In an image forming apparatus that performs multi-valued image formation by performing area modulation for moving and changing the dot size of each pixel, image data of 1 pixel n bit and N (= 2 ⁿ ) gradation is used, When the gradation value of the minimum gradation pixel of the solid white dot is 0 and the gradation value of the maximum gradation pixel of the solid black dot is (N-1), a certain gradation value k (1≤k <N Dot in / 2) and this dot Gradation value (Nk-
When the dots of 1) are juxtaposed vertically or horizontally on the recording medium, an image is formed by changing the diameter of the dot having the larger gradation value so that the outer circumferences of the dots intersect with each other. Image forming method of device. 3. A recording head in which a plurality of recording elements are arranged in a line at a predetermined interval, and a recording medium with respect to this recording head is orthogonal to the direction in which the recording elements of the recording head are arranged. Relative to each other, dot recording is performed pixel by pixel in the main scanning direction in each recording element of the recording head, and dot recording in the main scanning direction is performed in the sub scanning direction by relative movement of the recording head and the recording medium. In an image forming apparatus that performs multi-valued image formation by performing area modulation for moving and changing the dot size of each pixel, image data of 1 pixel n bit and N (= 2 ⁿ ) gradation is used, When the gradation value of the minimum gradation pixel of the solid white dot is 0 and the gradation value of the maximum gradation pixel of the solid black dot is (N-1), a certain gradation value k (1≤k <N Dot in / 2) and this dot Gradation value (Nk-
When the dots of 1) are juxtaposed vertically or horizontally on the recording medium, the diameter of a dot having an arbitrary gradation value k and the diameter of a dot having a gradation value (N−k−1) paired with this dot are An image forming method of an image forming apparatus, wherein an image is formed by changing the outer circumferences of the dots so as to intersect each other. 4. The diameter of a solid black dot having the maximum gradation value (N-1) is set to be larger than the diameter of a circle covering a square pixel corresponding to the basic resolution of the device. 4. An image forming method of the image forming apparatus according to any one of 1 to 3. 5. The image forming method of an image forming apparatus according to claim 1, wherein the diameter of the dot of each gradation value is set based on the characteristic of the image forming accuracy of the apparatus. 6. A dot having a certain gradation value k and a dot having a gradation value (N−k−1) forming a pair relationship with this dot are mutually arranged in the vertical direction or the horizontal direction of the recording medium. 6. The outline of a character or a line drawing is corrected by changing the diameter of the dot so that the outer circumferences of the lines intersect.
2. An image forming method of the image forming apparatus according to any one of 1.