JP2008238644A - Image forming apparatus and system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus and system capable of obtaining a better image by preventing increase in viscosity of ink on the meniscus surface in a nozzle without complicating the structure of the apparatus. <P>SOLUTION: Out of pixels not being drawn, at least the pixel immediately before a pixel being drawn (black-dot ring) is set as a pixel (O) not rocking the meniscus surface, and other pixels are set appropriately as pixels (double circle) for rocking the meniscus surface. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an inkjet image forming apparatus that draws an image by ejecting ink, and an image forming system that includes the inkjet image forming apparatus.

  Some inkjet image forming apparatuses are always filled with ink in nozzles that eject ink so that printing can be performed immediately when a printing instruction is given. In such an image forming apparatus, on the ink meniscus surface of the nozzle opening, the solvent in the ink tends to evaporate, and the viscosity of the ink tends to increase. An increase in the viscosity of the ink on the meniscus surface causes ink ejection failure from the nozzles.

Therefore, various techniques have been proposed in the past so as not to increase the viscosity of the ink on the meniscus surface. Such techniques include, for example, periodically discharging ink separately from image formation and swinging the meniscus surface. Patent Document 1 describes that a porous member is provided on an orifice plate in which ink discharge ports are formed, and new ink is supplied to the meniscus surface through the porous member.
Japanese Patent Laying-Open No. 2005-246788 (published on September 15, 2005)

  However, when a porous member is provided as in Patent Document 1, the structure of the apparatus becomes complicated and processing is difficult. On the other hand, in an apparatus that swings the meniscus surface, immediately after the meniscus surface is swung, when ink is ejected from a nozzle that has swung the meniscus surface, ejection failure occurs due to the influence of the swing. May occur and a desired image may not be obtained.

  In view of the above-described conventional problems, an object of the present invention is to realize an image forming apparatus and an image forming system capable of obtaining a good image without complicating the structure of the apparatus.

  In order to solve the above-described problems, an image forming apparatus according to the present invention includes a plurality of nozzles that eject ink droplets onto a recording medium to perform recording of one pixel, a plurality of nozzles that communicate with each nozzle, and can accommodate ink therein. A pressure chamber, an inkjet head including a plurality of piezoelectric elements that discharge ink droplets from the nozzles by applying pressure to the ink in each pressure chamber, and drawing for each piezoelectric element corresponding to the nozzles For a pixel to be applied, a first drive signal for ejecting ink droplets is applied, and at least one pixel excluding a pixel immediately before the pixel to be drawn among pixels that are not drawn continuously by a predetermined number of two or more in the same nozzle. For the pixel immediately before the pixel to be drawn, a second drive signal that swings the meniscus in the nozzle but does not eject ink droplets is applied. Comprising a driving signal applying unit that none of the signals so as not to apply the.

  According to the above-described image forming apparatus, the ink droplet ejection defect is less likely to occur in the drawing of the pixel immediately after the pixel by not swinging the meniscus surface of the pixel immediately before the pixel to be drawn. As a result, according to the image forming apparatus, it is difficult to cause image drawing defects, and a desired image can be obtained.

  Further, the predetermined number is 3 or more, and the drive signal applying unit immediately after the pixel to be drawn among the pixels not drawn continuously for the piezoelectric element corresponding to the nozzle. It is preferable that neither the first drive signal nor the second drive signal is applied to the pixel.

  If the meniscus surface is swung immediately after ink droplets are ejected, the width of the swing becomes too large or conversely becomes too small, and ink leakage or an increase in ink viscosity tends to occur. On the other hand, the image forming apparatus can prevent such a problem from occurring by not swinging the meniscus surface of the pixel immediately after ejecting the ink liquid.

  In addition, the above problem is that image formation is performed by drawing ink droplets on a recording medium for pixels of gradation 1 or higher and not discharging ink droplets for pixels of gradation 0 according to image data. An image forming system comprising: an apparatus; and a control device that transmits the image data to the image forming apparatus, wherein the image forming apparatus ejects ink droplets onto a recording medium and records one pixel. A plurality of pressurizing chambers that communicate with each nozzle and that can accommodate ink therein, and a plurality of piezoelectric elements that apply pressure to the ink in each pressurizing chamber to eject ink droplets from the nozzles Depending on the head and the image data, the first drive signal for ejecting ink droplets is applied to the pixels of gradation 1 or higher (N-1) or lower, and the meniscus in the nozzle is applied to pixels of gradation N or higher. A second drive signal that oscillates the ink but does not eject ink droplets can be applied to the piezoelectric element, and neither the first drive signal nor the second drive signal is applied to a pixel with a gradation of zero. A drive signal applying unit configured as described above, and the control device applies the same nozzle to the same nozzle in the image data of the number of gradations N having a minimum gradation of zero and a maximum gradation of (N−1). Correspondingly, when a predetermined number of pixels having a gradation of zero or more continues for a predetermined number of pixels equal to or greater than 2, the number of gradations (N + 1) or more is set to the gradation N or more for at least one pixel excluding the pixel immediately preceding the pixel of gradation 1 or more. It can also be solved by an image forming system including an image data generation unit that generates and applies new image data.

  According to the image forming apparatus of the present invention, for the pixel immediately before the pixel to be drawn, the meniscus surface is not swung, so that the ink droplet ejection defect does not easily occur for the pixel to be drawn immediately after this pixel. As a result, the image forming apparatus is unlikely to cause image drawing defects. The object of the present invention can also be realized by the image forming system of the present invention.

  An image forming apparatus according to an embodiment of the present invention will be described below with reference to the drawings.

[1] Image forming apparatus 1
FIG. 1 is a block diagram illustrating a main configuration of the image forming apparatus 1 according to the present embodiment.

  As shown in FIG. 1, the image forming apparatus 1 of the present embodiment includes a control device 10 and an image forming unit 20.

  The control device 10 generates second print data (i) by adding the fourth gradation to the first print data (i) and the image processing unit 11 that generates the first print data (i) having the number of gradations 3 from the image data. a data processing unit 12 for generating ii);

  The image forming unit 20 includes a head 22 that draws an image by ejecting ink onto a sheet, and a head driving unit 21 that drives the head 22.

  The head drive unit 21 selects one of the drive pulse generation unit 21a that generates the drive pulses (1) to (3) and the drive pulses (1) to (3) according to the second print data (ii). A selector 21b is provided that selects and applies to the piezoelectric element 22a of the head 22 via a resistor, a capacitor, and the like. Details of the structure of the head 22 will be described later.

  Hereinafter, the maximum gradation number N of the first print data (i) is 3, the maximum gradation number N ′ of the second print data (ii) is (N + 1), that is, 4, and the drive pulses are (1) to ( Although it is assumed that there are three types of 3), the present invention is not limited to these.

[2] Control device 10
The operation of the control device 10 will be described in more detail with reference to FIGS. 2 and 3 focusing on the operation of the data processing unit 12. 2A shows an example of the first print data (i), FIG. 2B shows an example of the second print data (ii), and FIG. 2C shows another example of the second print data (ii). It is drawing which shows an example. In these drawings, the horizontal direction, that is, the row component, indicates a pixel in the scanning direction, and the vertical direction, that is, the column component, indicates a pixel in the sub-scanning direction. In these drawings, the components in the 1st to nth columns respectively represent pixels recorded by the same nozzle. That is, for example, one nozzle records pixels from the first row to the m-th row in the second column on the paper, and the other nozzle records pixels from the first row to the m-th row in the n-th column on the paper. To do.

  As shown in FIG. 2A, the first print data (i) has three gradations of “0 (zero)”, “1”, and “2”. In the first print data (i), when the predetermined number of pixels having gradation “0” continue in the column direction, the data processing unit 12 draws a pixel to be drawn among these pixels having gradation “0”. The gradation of at least one pixel selected from pixels other than the pixel immediately before is changed to “3”. In the example shown in FIG. 2A, “drawn pixels” are pixels of gradation “1” or gradation “2”. In this way, the data processing unit 12 generates the second print data (ii) whose gradation has been changed. The “predetermined number” is not particularly limited as long as it is an integer of 2 or more.

  In addition, among the pixels having a predetermined number of gradations “0”, the position of the pixel changed to gradation “3” is at least other than the pixel immediately before the pixel to be drawn, and the following [3] column As described in, it can be set as appropriate within a range in which ejection failure can be prevented, and is not particularly limited. When the predetermined number is 3 or more, it is preferable that the pixel to be changed from the gradation “0” to the gradation “3” is selected from other than the pixel immediately after the pixel to be drawn. In other words, the pixel of gradation “3” is arranged with at least one pixel of gradation “0” sandwiched between pixels of gradation “1” or “2” in the column direction (vertical direction). It is preferable.

  As an example of the second print data (ii), the print data shown in FIG. 2B includes three or more pixels of gradation “0” in the column direction in the print data (i) of FIG. At this time, among these pixels of gradation “0”, the gradations of all the pixels are changed to “3” except for the pixels immediately before and immediately after the pixel of gradation “1” or gradation “2”. ing. In other words, all pixels from the second pixel in the column direction from the pixel of gradation “1” or gradation “2” to the pixel immediately before the pixel of gradation “1” or gradation “2” are all on the floor. The key is “3”.

  Further, as another example of the second print data (ii), the print data shown in FIG. 2C includes pixels of gradation “0” in the column direction in the print data (i) of FIG. When three or more pixels are continuous, of the pixels of gradation “0”, the gradation “1” or gradation “2” from the second pixel in the column direction from gradation “1” or gradation “2” Every other pixel before the pixel has a gradation of “3”.

  In the above description, the maximum number of gradations N is 3. However, although the number of gradations to be added is “3”, the present invention is not limited to this. The first print data (i) having the maximum number of gradations N can include gradations of 0, 1, 2,... (N−1). The data processing unit 12 applies at least one gradation, that is, the (N + 1) th gradation (gradation “3” in the examples of FIGS. 2B and 2C) to the print data (i). It comes to add.

  FIGS. 3A to 3C show an example of the first print data (i) when the maximum number of gradations N is 2, that is, when the gradations are two of 0 and 1, and Two examples of the second print data (ii) obtained by processing this are shown. The second print data (ii) in FIG. 3B is generated by the data processing unit 12 through the same processing as in FIG. 2B, and from the pixel of gradation “1” to the second pixel in the column direction. The pixels up to two pixels before the pixel of gradation “1” are all of gradation “2”. Also, the second print data (ii) in FIG. 3C is generated by the data processing unit 12 through the same processing as in FIG. 2C, and from the second pixel in the column direction from the gradation “1”. The pixels up to two before the pixel of gradation “1” have gradation “2” every other pixel.

[3] Image forming unit 20
(3-1) Head 22
The head 22 is a so-called line type head. FIG. 4 is a plan view showing the main configuration of the head 22, and FIG.

  As shown in FIG. 4, the head 22 further includes an ejection surface 23 that faces the paper. The sheet is transported in a direction D shown in FIG. 4 by a transport unit (not shown), and receives ink droplets ejected from the ejection surface 23. The size of the discharge surface 23 in the longitudinal direction (direction perpendicular to the direction D) is larger than the maximum width E of the print area of the paper. The discharge surface 23 is provided with a plurality of discharge ports 25 having a minute diameter, which are openings of the nozzle 24, over at least the maximum width E in the longitudinal direction of the discharge surface 23.

  As shown in FIG. 5, the head 22 stores a water repellent film 23 a other than the discharge port 25 on the discharge surface 23, a pressurizing chamber 26 provided for each discharge port 25, and an ink storage. And a common flow path 27 that supplies ink from the ink tank to the plurality of pressurizing chambers 26. The pressurizing chamber 26 and the common channel 27 are connected by a supply hole 28, and ink is supplied from the common channel 27 to the pressurizing chamber 26 through the supply hole 28. The nozzle 24 continues from the pressurizing chamber 26 to the discharge port 25. Of the walls of the pressurizing chamber 26, the wall opposite to the discharge surface 23 is constituted by a diaphragm 29, and the diaphragm 29 is formed continuously over the plurality of pressurizing chambers 26. Similarly, a common electrode 30 formed continuously over the plurality of pressurizing chambers 26 is laminated. A separate piezoelectric element 22 a is provided for each pressurizing chamber 26 on the common electrode 30, and a separate individual electrode 31 is also provided for each pressurizing chamber 26 so as to sandwich the piezoelectric element 22 a together with the common electrode 30. It is done.

  By applying the driving pulse from the head driving unit 21b to the individual electrode 31, each piezoelectric element 22a is individually driven. The deformation of the piezoelectric element 22 a due to this driving is transmitted to the vibration plate 29, and the pressurizing chamber 26 is compressed by the deformation of the vibration plate 29. As a result, pressure is applied to the ink in the pressurizing chamber 26, and the ink that has passed through the nozzles 24 is ejected from the ejection port 25 as ink droplets onto the paper.

  While the ink droplets are not ejected, the ink is contained in the nozzle 24, and the ink forms a meniscus surface M in the nozzle 24.

(3-2) Head drive unit 21
The driving of the head 22 by the head driving unit 21 will be specifically described below with reference to FIGS.

  FIGS. 6A to 6C are diagrams respectively showing examples of waveforms of the drive pulses (1) to (3). FIGS. 7A to 7C are diagrams showing the drive pulses ( Drawing which shows the drive voltage concerning the piezoelectric element 22a when 1)-(3) is each selected, and the flow velocity (in-nozzle flow velocity [m / s]) of the ink in the nozzle 2 corresponding to this piezoelectric element 22a It is. FIG. 8A shows another example of the waveform of the drive pulse (3). FIG. 8B shows the drive pulse (3) having the waveform shown in FIG. 8A selected by the selector 21b. 6 is a drawing showing the driving voltage applied to the piezoelectric element 22a and the flow velocity in the nozzle corresponding to the piezoelectric element 22a.

  As shown in FIGS. 6A to 6C, the drive pulse (1) is composed of one pulse, and the drive pulse (2) has two pulses having the same width as the drive pulse (1). Thus, the drive pulse (3) is obtained by repeating a pulse having a width smaller than the pulse width of the drive pulse (1) a plurality of times.

  The pulse width of the drive pulse (1) is set to have a length (about 7 usec in this example) close to a half cycle of the natural vibration period (13 usec in this example) of the head channel. Here, the “head channel” means a portion including the nozzle 24, the pressurizing chamber 26, and the supply hole 28. Therefore, as shown in FIG. 7A, the pulse width of the driving voltage applied to the piezoelectric element 22a is also a length close to half of the natural vibration period of the head channel. According to such a drive voltage, since the flow velocity in the nozzle exceeds 10 m / s, one ink droplet is ejected from the ejection port 25.

  As shown in FIG. 7B, when the driving pulse (2) in which two pulses having the same width as the driving pulse (1) are continuously selected is selected, two ink droplets are ejected from the ejection port 25. That is, the volume of ink ejected per pixel is doubled compared to when the drive pulse (1) is selected.

  The pulse width of the drive pulse (3) is set to be considerably shorter than the natural vibration period of the head channel. Therefore, as shown in FIG. 7C, the pulse width of the drive voltage applied to the piezoelectric element 22a is also considerably shorter than the natural vibration period of the head channel. When such a short pulse continues, the flow velocity in the nozzle becomes a value at which ink droplets are not ejected although the meniscus surface M is swung.

  The waveform of the drive pulse (3) is not limited to the shape shown in FIG. 6C, and any waveform may be used as long as the meniscus surface M in the nozzle 24 is swung and ink droplets are not ejected. As an example of such a drive pulse (3), as shown in FIG. 8A, one having a pulse width close to the natural vibration period of the head flow path can be mentioned. FIG. 8 (a) According to this drive pulse (3), as shown in FIG. 8 (b), the vibration of the flow velocity in the nozzle is canceled, so that the meniscus surface M can be greatly shaken and no ink droplet is formed. Can be.

  In the second print data (ii) from the control device 10, the selector 21 b selects the drive pulse (1) for the gradation “1”, the drive pulse (2) for the gradation “2”, and the gradation “3”. For "", the drive pulse (3) is selected and applied to the piezoelectric element 22a, and no drive pulse is applied for the gradation "0".

  FIG. 9A is a diagram showing the operation of the head 22 when the selector 12b selects a drive pulse based on the first print data (i) of FIG. 2A. FIG. 9C shows the operation of the head 22 by the drive pulse selected by the selector 12 based on the second print data (ii) of FIGS. 2B and 2C, respectively. 9A to 9C, circles correspond to the pixels in FIGS. 2A to 2C, respectively. In addition, black circles (●) indicate pixels from which ink droplets are ejected, double circles (◎) indicate pixels from which the meniscus surface M is swung, and single circles (◯) indicate ink droplets ejected from the meniscus surface M. Pixels that are not swung are also shown. In FIGS. 9A to 9C, for convenience of explanation, ejection of ink droplets by drive pulses (1) and (2) is represented by the same black circle (●) without distinction.

  When the selector 21b selects the drive pulse based on the second print data (ii) as described above, as shown in FIG. 9B and FIG. At least one single circle (◯) is sandwiched between the circles (◎). That is, after the ink droplet is ejected from a certain nozzle 24 and recording of one pixel is performed, the time required to record at least one pixel until the meniscus surface M is swung is determined by this nozzle 24. No ink is ejected or the meniscus surface M is swung. Similarly, after the meniscus surface M is swung by a certain nozzle 24 and before the ink liquid is ejected, the time required to record at least one pixel is the same as the meniscus ejection of ink at this nozzle 24. The surface M is not swung.

  As shown in FIG. 9A, if the meniscus surface M is not swung at all for pixels that are not to be drawn, the viscosity of the ink increases in the nozzle 24, causing ejection failure.

  On the other hand, the waveform of the driving voltage for swinging the meniscus surface M is different in phase from the oscillation of the flow velocity in the nozzle, similarly to the waveform of the driving voltage for ejecting ink droplets (FIGS. 7A to 7). c) and FIG. 8B). Therefore, after the nozzle flow velocity is vibrated by the drive pulse (3) and the meniscus surface M is oscillated, the drive pulse (1) or (2) is applied before the vibration of the nozzle flow velocity becomes sufficiently small. If this is the case, ink droplets of a desired size cannot be stably formed, and ejection failure may occur.

  On the other hand, in the image forming apparatus 1 of the present embodiment, as described above, after the meniscus surface M is swung by a certain nozzle 24, one pixel is ejected from the same nozzle 24 until ink droplets are ejected. The nozzle flow velocity is not vibrated for more than the time required for recording (FIGS. 9B and 9C). Therefore, in the image forming apparatus 1, ink droplets can be ejected after the vibration of the nozzle flow velocity becomes small. As a result, the above-described ejection failure is less likely to occur.

  Also, after the ink droplet is ejected, if the drive pulse (3) is applied before the oscillation of the flow velocity in the nozzle caused by ejection is sufficiently reduced, the oscillation width of the meniscus surface M becomes too large and the ink is discharged. In some cases, the ink spills out from the ejection port 25, or on the contrary, the swinging width of the meniscus surface M is small, and the effect of preventing ink viscosity may not be sufficiently obtained.

  On the other hand, in the image forming apparatus 1 according to the present embodiment, as described above, after ink droplets are ejected from a certain nozzle 24, recording of one pixel is performed until the meniscus surface M is swung by the same nozzle 24. The nozzle flow velocity is not vibrated for more than this time (FIG. 9 (b) and FIG. 9 (c)). Therefore, in the image forming apparatus 1, the meniscus surface M can be oscillated after the oscillation of the flow velocity in the nozzle is reduced. As a result, the above-described problem is less likely to occur.

  Each block in the control device 10 may be realized by hardware logic, or may be realized by software using a computer. When implemented by software, the control device 10 includes a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and the like, and each block stores a program read from the ROM by the CPU on the RAM. It is realized by developing with. That is, the same effect as that of the present embodiment can be obtained by a program that causes a computer to function as the data processing unit 12.

  In the above embodiment, the object of the present invention is achieved by a single device called the image forming apparatus 1, but in addition to this, an apparatus that performs the function of the control device 10 and image formation separately from this apparatus. An image forming system including an apparatus that performs the function of the unit 20 is also included in the technical scope of the present invention.

1 is a block diagram illustrating a main configuration of an image forming apparatus 1 according to an embodiment. 2A shows an example of the first print data (i) when the maximum number of gradations N is 3. FIG. 2B shows the first print data (i) of FIG. 2A processed. FIG. 2C shows another example of the second print data (ii), and FIG. 2C shows another example of the second print data (ii). FIG. 3A shows an example of the first print data (i) when the maximum number of gradations N is 2. FIG. 3B shows the first print data (i) shown in FIG. FIG. 3C shows another example of the second print data (ii), and FIG. 3C shows another example of the second print data (ii). 3 is a plan view showing a main configuration of a head 22. FIG. FIG. 3 is a cross-sectional view showing a main part configuration of a head 22. FIGS. 6A to 6C are diagrams respectively showing examples of waveforms of the drive pulses (1) to (3). FIGS. 7A to 7C show the drive voltage applied to the piezoelectric element 22a when the drive pulses (1) to (3) are selected by the selector 21b, and the inside of the nozzle 2 corresponding to the piezoelectric element 22a. It is drawing which shows the flow velocity of the ink. FIG. 8A shows another example of the waveform of the drive pulse (3). FIG. 8B shows the drive pulse (3) having the waveform shown in FIG. 8A selected by the selector 21b. 6 is a diagram showing a driving voltage applied to the piezoelectric element 22a and a flow velocity in the nozzle corresponding to the piezoelectric element 22a. FIG. 9A is a diagram showing the operation of the head 22 when the selector 12b selects a drive pulse based on the first print data (i) of FIG. 2A. FIG. 9C shows the operation of the head 22 by the drive pulse selected by the selector 12 based on the second print data (ii) of FIGS. 2B and 2C, respectively.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Control apparatus 11 Image processing part 12 Data processing part 20 Image forming part 21 Head drive part 21a Drive pulse generation part 21b Selector (an example of a drive signal application part)
22 Head 22a Piezoelectric element 23 Discharge surface 23a Water repellent film 24 Nozzle 25 Discharge port 26 Pressurizing chamber 27 Common flow path 28 Supply hole 29 Diaphragm 30 Common electrode 31 Individual electrode M Meniscus surface (i) First printing data (ii) Second print data (1), (2) Drive pulse (first drive signal)
(3) Second drive signal

Claims (3)

A plurality of nozzles for ejecting ink droplets onto a recording medium to record one pixel, a plurality of pressure chambers communicating with each nozzle and accommodating ink therein, and pressure applied to the ink in each pressure chamber An inkjet head including a plurality of piezoelectric elements that discharge the ink droplets from the nozzles,
A first drive signal for ejecting ink droplets is applied to each of the piezoelectric elements corresponding to the nozzle, and drawing is performed among two or more predetermined numbers of pixels that are not drawn continuously in the same nozzle. For at least one pixel other than the pixel immediately preceding the pixel to be applied, a second drive signal that swings the meniscus in the nozzle but does not eject ink droplets is applied, and for the pixel immediately before the pixel to be drawn A drive signal applying unit configured not to apply any of the first and second drive signals;
An image forming apparatus comprising: The predetermined number is 3 or more,
The drive signal application unit applies the first and second drives for the pixels immediately after the pixel to be drawn among the pixels that are not drawn continuously for the piezoelectric elements corresponding to the nozzles. The image forming apparatus according to claim 1, wherein none of the signals is applied. In accordance with image data, an image forming apparatus that draws an image by ejecting ink droplets onto a recording medium for pixels of gradation 1 or higher, and does not eject ink droplets for pixels of gradation 0, and the above image formation An image forming system comprising: a control device that transmits the image data to the device;
The image forming apparatus includes:
A plurality of nozzles that eject ink droplets onto a recording medium to record one pixel, a plurality of pressure chambers that communicate with each nozzle, and that can contain ink therein, and a pressure applied to the ink in each pressure chamber An inkjet head comprising a plurality of piezoelectric elements that discharge ink droplets from the nozzles,
In accordance with the image data, the first drive signal for ejecting ink droplets is swung for pixels of gradation 1 or more (N-1) or less, and the meniscus in the nozzle is swung for pixels of gradation N or more. However, a second drive signal that does not cause ink droplets to be ejected can be applied to the piezoelectric element, and neither the first drive signal nor the second drive signal is applied to a pixel with a gradation of zero. A drive signal application unit,
The control device has a predetermined number of pixels equal to or greater than 2 corresponding to the same nozzle in the image data of the number N of gradations having a minimum gradation of zero and a maximum gradation of (N−1). An image data generation unit that generates and applies new image data of the number of gradations (N + 1) or more, which is the gradation N or more, to at least one pixel excluding the pixel immediately preceding the pixel of gradation 1 or more when continuous. An image forming system comprising:

Images