JP2016116027A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device that can efficiently reduce a toner consumption amount while maintaining high image quality.SOLUTION: A digital composite machine 11 inputs image data from a computer (S11). Thereafter, the digital composite machine 11 executes, for example, image processing such as enlargement and contraction required by a user with respect to the input image data (S12). Next, the digital composite machine 11 executes identification of image attribute for the generated image data (S13). Thereafter, an edge portion and a portion other than the edge portion are identified for an identified character image (S14). Next, image density adjustment is executed (S15). After the image density adjustment, gradation processing is executed (S16). In this case, first gradation processing at the edge portion of the character image and second gradation processing at the portion other than the edge portion are controlled to be different from each other.SELECTED DRAWING: Figure 7

Description

  The present invention relates to an image forming apparatus.

  In an image forming apparatus typified by a digital multifunction peripheral or the like, after an image of a document is read by an image reading unit, light is irradiated to the photoconductor provided in the image forming unit based on the read image, and the photoconductor An electrostatic latent image is formed thereon. Thereafter, a developer such as charged toner is supplied onto the formed electrostatic latent image to form a visible image, and then transferred to a sheet, fixed, and discharged outside the apparatus.

  When an electrostatic latent image is formed by irradiating light to a charged photoreceptor, an edge effect that increases the electric field strength at the edge portion of the image may occur. When the edge effect occurs, a large amount of toner adheres to the edge portion as a result, which may cause uneven toner density.

  Japanese Patent Application Laid-Open No. 2009-118378 (Patent Document 1) discloses a technique for reducing the influence of the edge effect on image formation. According to Patent Document 1, an image forming apparatus converts an input image data into output image data having a predetermined gradation, and converts output image data converted by the image data processing apparatus into an exposure signal. And an exposure unit controller. The exposure unit control apparatus includes an edge detection unit for detecting an edge part of the output image data, and an edge correction unit for performing density correction on the edge part data detected by the edge detection unit. It is said.

JP 2009-118378 A

  According to the technique disclosed in Patent Document 1, in order to suppress the edge effect, an edge portion of output image data is detected, and density correction is performed on the detected edge portion data.

  However, for example, when an image having a narrow interval between edges, such as a character image, is to be formed, a large amount of toner may adhere to a region between the edges. In this case, the toner may be consumed more than necessary, and this situation is not preferable from the viewpoint of reducing the so-called running cost. In addition, a phenomenon such as so-called character thickening may occur. In such a case, the technique disclosed in Patent Document 1 cannot cope with this.

  Further, the toner adhesion amount may fluctuate due to changes over time in the environment or the image forming apparatus. It is difficult to obtain a high-quality image unless these changes are appropriately dealt with in the above situation.

  An object of the present invention is to provide an image forming apparatus capable of efficiently reducing toner consumption while maintaining high image quality.

  An image forming apparatus according to the present invention includes a photosensitive member, an exposure unit that irradiates light to the photosensitive member to form an electrostatic latent image on the photosensitive member, and supplies toner to the electrostatic latent image formed by the exposure unit. A developing unit that forms a visible image on the photosensitive member with a toner, a transfer member that transfers the visible image formed with the toner formed by the developing unit, and an exposure unit that irradiates the photosensitive member with light and is composed of characters. A plurality of character pattern image electrostatic latent images for adjusting the toner density of the character image to be formed are formed on the photosensitive member, and toner is supplied to the electrostatic latent images of the plurality of character pattern images by the developing unit. A visible image is formed by toner of a character pattern image, a visible image of a plurality of character pattern images is transferred onto a transfer body, and a plurality of character pattern images are transferred onto the transfer body by toner. A character pattern image forming unit that forms a visual image, and a toner concentration detection sensor that detects a toner concentration of each character pattern image formed by the character pattern image forming unit, and is formed on the transfer body at a predetermined timing. An image for discriminating between a character image and an image other than a character image from among a toner density adjustment unit that adjusts the toner density of a visible image with toner, an input unit that inputs image data, and image data that is input by the input unit An image based on the image data input by the determining unit, the edge identifying unit for identifying the edge of the character image and the portion other than the edge of the character image determined by the image determining unit, and the image data input by the input unit A tone processing unit that performs tone processing of an image based on the toner density adjusted by the toner density adjusting unit, and an image data input by the input unit. An output unit that performs gradation processing on the data by the gradation processing unit and forms and outputs an image based on the image data input by the input unit, and an edge portion of the character image identified by the edge identification unit And a control unit that controls so that the first gradation processing by the gradation processing unit and the second gradation processing by the gradation processing unit in a portion other than the edge portion of the character image are different.

  According to such an image forming apparatus, since gradation processing is performed based on the toner density adjusted by the toner density adjustment unit, gradation processing corresponding to fluctuations in the environment or the like can be performed. Further, different gradation processing is performed on the edge portion of the character image and the portion other than the edge portion of the character image. Then, gradation processing suitable for each part can be performed. Therefore, according to such an image forming apparatus, it is possible to efficiently reduce toner consumption while maintaining high image quality.

1 is a schematic diagram showing an external appearance of a digital multifunction peripheral when an image forming apparatus according to an embodiment of the present invention is applied to the digital multifunction peripheral. 1 is a block diagram illustrating a configuration of a digital multifunction peripheral when an image forming apparatus according to an embodiment of the present invention is applied to the digital multifunction peripheral. FIG. 2 is an external view illustrating a schematic configuration of an image forming unit. FIG. 3 is an external view illustrating a schematic configuration of a toner concentration detection sensor. FIG. 6 is a diagram illustrating a relationship between an electric field intensity in the vicinity of the surface of the photoreceptor and a toner adhesion amount on the surface of the transfer belt at a corresponding position. It is a figure which shows an example of the character pattern image for toner density adjustment. 6 is a flowchart showing the contents of processing when toner density is adjusted using a digital multi-function peripheral according to an embodiment of the present invention. It is a figure which expands and shows an example of the discriminated character image. FIG. 9 is an enlarged view of a portion indicated by a region IX in FIG. 8. It is a figure which shows the case where the pattern matching in each pixel is performed and an edge part is identified. It is a figure which shows the case where an edge part is identified by an image processing filter in each pixel. It is a figure which shows the case where a gradation process is performed.

  Embodiments of the present invention will be described below. First, the configuration of a digital multifunction peripheral when the image forming apparatus according to an embodiment of the present invention is applied to the digital multifunction peripheral will be described. FIG. 1 is a schematic diagram showing an external appearance of a digital multifunction peripheral when an image forming apparatus according to an embodiment of the present invention is applied to the digital multifunction peripheral. FIG. 2 is a block diagram showing a configuration of the digital multifunction peripheral when the image forming apparatus according to the embodiment of the present invention is applied to the digital multifunction peripheral.

  1 and 2, the digital multifunction peripheral 11 includes a control unit 12 that controls the entire digital multifunction peripheral 11, and a display screen 21 that displays information transmitted from the digital multifunction peripheral 11 side and user input contents. An operation unit 13 for inputting image forming conditions such as the number of copies to be printed and gradation and power on / off, and an ADF (Auto Document Feeder) 22 for automatically feeding a set document to a reading unit. A sheet to be supplied to the image forming unit 15, including an image reading unit 14 that reads an image of a document, a manual feed tray 28 that manually sets a sheet, and a sheet feeding cassette group 29 that can store a plurality of sheets of different sizes. Forming a sheet based on the scanned image and image data transmitted via the network 25 Unit 15, a discharge tray 30 that discharges a sheet after an image is formed on the sheet by image forming unit 15, hard disk 16 that stores transmitted image data, input image forming conditions, and the like, and public line 24 A facsimile communication unit 17 that is connected and performs facsimile transmission and reception and a network interface unit 18 for connecting to the network 25 are provided. The digital multi-function peripheral 11 includes a DRAM (Dynamic Random Access Memory) for writing and reading image data, and the illustration and description thereof are omitted. In addition, arrows in FIG. 2 indicate the flow of data regarding control signals, control, and images. As shown in FIG. 1, in this embodiment, the sheet cassette group 29 includes three sheet cassettes 23a, 23b, and 23c.

  The digital multifunction machine 11 operates as a copying machine by forming an image in the image forming unit 15 using the original read by the image reading unit 14. Further, the digital multifunction peripheral 11 forms an image in the image forming unit 15 and prints it on a sheet using image data transmitted from the computers 26a, 26b, and 26c connected to the network 25 through the network interface unit 18. It works as a printer. That is, the image forming unit 15 operates as a printing unit that prints the requested image. Further, the digital multifunction peripheral 11 forms an image in the image forming unit 15 via the DRAM using the image data transmitted from the public line 24 through the facsimile communication unit 17, and also by the image reading unit 14. The image data of the read original is transmitted to the public line 24 through the facsimile communication unit 17, thereby operating as a facsimile apparatus. The digital multifunction machine 11 has a plurality of functions such as a copying function, a printer function, and a facsimile function regarding image processing. Further, each function has functions that can be set in detail.

  An image forming system 27 including a digital multifunction peripheral 11 according to an embodiment of the present invention includes a digital multifunction peripheral 11 having the above-described configuration and a plurality of computers 26 a and 26 b connected to the digital multifunction peripheral 11 via a network 25. 26c. In this embodiment, three computers 26a to 26c are shown. Each of the computers 26 a to 26 c can print by making a print request to the digital multi-function peripheral 11 via the network 25. The digital multi-function peripheral 11 and the computers 26a to 26c may be connected by wire using a LAN (Local Area Network) cable or the like, or may be connected wirelessly. A configuration in which a digital multifunction peripheral or a server is connected may be used.

  Next, the configuration of the image forming unit 15 provided in the digital multifunction peripheral 11 will be described in more detail. FIG. 3 is a cross-sectional view showing a schematic configuration of the digital multi-function peripheral 11 according to the embodiment of the present invention. From the viewpoint of easy understanding, the members are not hatched in FIG. FIG. 3 is a cross-sectional view of the digital multifunction machine 11 cut along a plane extending in the vertical direction.

  Referring to FIG. 3, image forming unit 15 includes photoreceptors 31a, 31b, 31c, and 31d, respectively, and four image forming units 32a, 32b, and 32c corresponding to four colors of yellow, magenta, cyan, and black, respectively. , 32d, an LSU (Laser Scanner Unit) 34 as an exposure unit for exposing each of the four image forming units 32a to 32d based on the image read by the image reading unit 14, and an image forming unit A transfer belt 35 as an intermediate transfer member that is temporarily transferred before a visible image formed by the toners 32a to 32d is transferred to a sheet, and a transfer belt that removes toner remaining on the transfer belt 35 with a blade or the like. And a cleaning unit 37. About LSU34, it has shown roughly with the dashed-dotted line. The transfer belt cleaning unit 37 is also schematically shown. The image forming unit 15 is a so-called four-tandem development method.

The transfer belt 35 is endless, and a visible image formed by the four color image forming units 32a to 32d of yellow, magenta, cyan, and black is rotated in one direction by a pair of drive rollers 36a and 36b. Transcribed. Rotational direction of the transfer belt 35 is indicated by an arrow D ₁ of the in Figure 3. Of the image forming units 32a to 32d, the yellow image forming unit 32a is disposed on the most upstream side, and the black image forming unit 32d is disposed on the most downstream side in the rotation direction of the transfer belt 35. . The transfer belt cleaning unit 37 is disposed upstream of the yellow image forming unit 32a.

  The visible image formed by the toner transferred onto the transfer belt 35 is transferred to the conveyed paper and fixed on the paper by a fixing unit (not shown). After fixing, the sheet is discharged out of the digital multifunction peripheral 11, specifically, the discharge tray 30. After the visible image by the toner is transferred to the paper, the toner remaining on the transfer belt 35 is removed by the transfer belt cleaning unit 37. Then, the next image formation is performed.

  The digital multifunction peripheral 11 can perform monochrome printing using only the black image forming unit 32d. The digital multi-function peripheral 11 can perform color printing using at least one of a yellow image forming unit 32a, a magenta image forming unit 32b, and a cyan image forming unit 32c.

  The digital multifunction machine 11 includes a toner density adjustment unit 41 that adjusts the density of a visible image with toner at a predetermined timing. The predetermined timing is, for example, the timing at which the environment has changed, specifically, it is detected that the temperature value and the humidity value in the environment where the digital multi-function peripheral 11 is installed have exceeded a predetermined value. It is timing. The predetermined timing is, for example, a timing at which a member of the digital multi-function peripheral 11 changes over time, specifically, a timing at which the number of image formations is every 1000 sheets, an engine drive of the digital multi-function peripheral 11 For example, the timing when the time reaches a predetermined time. At such timing, the density of the visible image by the toner formed on the transfer belt 35 is adjusted.

  The toner density adjustment unit 41 separately adjusts the toner density of the character image and the toner density of the photographic image. When adjusting the toner density of a photographic image, the toner density adjusting unit 41 adjusts the toner density using halftone pattern images having different densities. The adjustment of the toner density of the character image will be described later.

  The toner density adjustment unit 41 includes a toner density detection sensor 42 that detects the toner density of the image formed by the image forming unit 15. The toner density adjusting unit 41 detects the toner density of the pattern image for adjusting the toner density formed by the image forming unit 15 by the toner density detecting sensor 42.

  Here, the configuration of the toner concentration detection sensor 42 will be briefly described. FIG. 4 is a schematic diagram showing the configuration of the toner concentration detection sensor 42. In FIG. 3, the toner concentration detection sensor 42 is schematically indicated by a two-dot chain line.

  1 to 4, the toner density detection sensor 42 is disposed on the downstream side of the black image forming unit 32 d in the rotation direction of the transfer belt 35. The toner concentration detection sensor 42 receives light by a light emitting element 43a that irradiates light on the surface 38 side of the transfer belt 35, a light receiving element 43b that receives reflected light reflected from the surface 38 side of the transfer belt 35, and a light receiving element 43b. A toner concentration calculation unit 44 that calculates the toner concentration from the amount of reflected light. In this embodiment, the light emitting element 43 a and the light receiving element 43 b are installed so as to be symmetrical with respect to a plane 45 extending in a direction perpendicular to the surface of the transfer belt 35. That is, the light receiving element 43b is provided at a position for receiving regular reflection light with respect to the light emitted by the light emitting element 43a. Specifically, an infrared light emitting diode that irradiates infrared light is employed as an example of the light emitting element 43a. As an example of the light receiving element 43b, specifically, an infrared light receiving element is employed.

Emitting element 43a is towards the visible image 39 by the surface 38 or the toner of the transfer belt 35 is irradiated with light 46a such infrared light to the left obliquely upward direction indicated by arrow E ₁ in FIG. When the visible image 39 made of toner is not formed, the light emitting element 43 a emits light 46 a toward the surface 38 of the transfer belt 35.

The light receiving element 43b is either one or toner, the reflected light 46b from the surface 38 of the reflected light 46b and the transfer belt 35 from the visible image 39 by the toner toward the lower left direction indicated by the arrow E ₂ in FIG. 4 The reflected light 46b from both the visible image 39 and the surface 38 of the transfer belt 35 is received. If the visible image 39 made of toner completely covers the surface 38 of the transfer belt 35, only the reflected light 46b from the visible image 39 made of toner is received. If the visible image 39 made of toner is not formed on the surface 38 of the transfer belt 35, only the reflected light 46b from the surface 38 of the transfer belt 35 is received. If the visible image 39 made of toner does not completely cover the surface 38 of the transfer belt 35 and the amount of toner in the visible image 39 made of toner is small, the reflection from both the visible image 39 made of toner and the surface 38 of the transfer belt 35 is reflected. The light 46b is received.

Toner concentration detecting sensor 42, the transfer belt 35 to a visible image 39 is formed by the toner on the surface 38 is irradiated with light 46a in the direction indicated by arrow E ₁ in FIG. The light 46 a is reflected when it hits either the visible image 39 made of toner or the surface 38 of the transfer belt 35, or both the visible image 39 made of toner and the surface 38 of the transfer belt 35. The reflected reflected light 46b is received by the light receiving element 43b. The light receiving element 43b outputs a current corresponding to the amount of received light. The toner concentration calculator 44 converts the current output from the light receiving element 43b into a voltage value. Then, the toner density is calculated based on this voltage value. In this way, the toner concentration detection sensor 42 detects the toner concentration.

  The toner density is adjusted using such a toner density detection sensor 42. Here, when adjusting the toner density of the character image, a pattern image of the character image is formed, and the toner density of the formed pattern image is detected by the toner density detection sensor 42 to adjust the toner density.

  Here, in the case of forming a pattern image of a character image, the state of toner adhesion on the surface of the photoconductors 31a to 31d, that is, the surface 38 of the transfer belt 35 onto which the toner is transferred from the surface of the photoconductors 31a to 31d. explain. FIG. 5 is a graph showing the relationship between the electric field strength in the vicinity of the surfaces of the photoconductors 31a to 31d and the amount of toner adhering to the surface 38 of the transfer belt 35 at the corresponding position. In FIG. 5, the vertical axis represents the electric field strength and the amount of toner attached to the surface 38 of the transfer belt 35, and the horizontal axis represents the areas exposed to the photoconductors 31 a to 31 d. A solid line 51 indicates the toner adhesion amount. The vertical axis indicates that the electric field strength is higher and the toner adhesion amount is increased toward the upper side. The exposed area is indicated by an area 52a and an area 52c in FIG. On the other hand, the unexposed area is indicated by an area 52b in FIG. 5 sandwiched between the area 52a and the area 52c.

  Referring to FIG. 5, when exposure is performed in region 52a and region 52c and non-exposure is performed in region 52b, it is ideal that an electric field strength as indicated by solid line 53a appears. That is, at the boundary between the exposure region 52a and the non-exposure region 52b and the boundary between the exposure region 52c and the non-exposure region 52b, the electric field strength changes greatly without causing an extreme decrease or increase in the electric field strength near the boundary. Is ideal.

However, due to the influence of the edge effect or the like, the electric field strength actually becomes as shown by the solid line 53b. That is, the electric field strength is extremely low at the point P ₁ slightly on the exposure region 52a side from the point P _{2 at} the boundary between the exposure region 52a and the non-exposure region 52b. Then, in the exposed areas 52a slightly unexposed regions 52b side becomes a point P ₃ than the point P ₂ of the boundary between the unexposed region 52b, the electric field strength is extremely high. Further, the P ₇ that a slight exposure area 52c side from the point P ₆ in the boundary between the exposed region 52c and the non-exposed regions 52 b, the electric field strength is extremely low. Then, the P ₅ that becomes slightly non-exposed regions 52b side from the point P ₆ in the boundary between the exposed region 52c and unexposed regions 52b, the electric field strength is extremely high. In the region between points P ₃ and the point P _5, the electric field strength is slightly lower than the position of the point P ₃ and the point P _5.

Here, in the case of a character image, that is, an image having a narrow space between the point P ₃ and the point P ₅ , the toner adhesion amount is affected by the point P ₃ and the point P ₅ at which the electric field strength is maximum, and the point P It becomes maximum at the point P ₄ which is the center between ₃ and the point P ₅ . That is, the toner adheres so as to gradually increase from the position of the points P ₃ and P ₅ toward the point P ₄ . When such a phenomenon occurs, the toner is consumed more than necessary. Further, a large amount of adhered toner is pushed to the edge portion side at the time of fixing, and as a result, a phenomenon such as so-called character thickening may occur.

  Such a tendency varies depending on a change in the environment where the digital multifunction peripheral 11 is placed. In other words, although such a tendency is similar between the high temperature and high humidity environment and the low temperature and low humidity environment, the degree of toner adhesion differs.

  Under such circumstances, a uniform toner amount reduction is inappropriate from the viewpoint of maintaining high image quality. Therefore, at a predetermined timing, the toner density is adjusted according to each environment. Specifically, an adjustment value of an appropriate toner density is obtained in advance according to each environment and the like, and image formation is performed using this adjustment value at the time of image formation.

  FIG. 6 is an enlarged view showing a part of the pattern image of the character image. Referring to FIG. 6, a pattern image 54 of a character image extends in a strip shape in the vertical direction, and is provided with two regions 55a and 55c to which toner is attached with a gap therebetween. In addition, a blank portion extending in a strip shape in the vertical direction, that is, a white region 55b where no toner is attached is provided between the region 55a and the region 55c. Further, a strip-like white region 55d is also provided in the vertical direction on the lateral side of the region 55c opposite to the region 55b. Each region 55a, 55b, 55c, 55d has a size of 2 pixels in the horizontal direction and 8 pixels in the vertical direction.

  The toner density is adjusted using the pattern image 54 of such a character image. That is, light is irradiated from the LSU 34 toward each of the photoreceptors 31a to 31d so as to form a pattern image 54 of a character image as shown in FIG. Next, toner is supplied to the surfaces of the photoreceptors 31 a to 31 d to be visualized, and a pattern image 54 shown in FIG. 6 is transferred and formed on the surface 38 of the transfer belt 35. Thereafter, the toner density of the pattern image 54 of the character image formed on the surface 38 of the transfer belt 35, specifically, the inner toner positioned between the edge portions of the regions 55a and 55c and between the edge portions. The density is detected by the toner density detection sensor 42. Then, a toner density adjustment value for adjusting the toner density is calculated based on the detected toner density in each part of each of the regions 55a and 55c. Thereafter, based on the calculated toner density adjustment value, the exposure amount in the exposure unit, the exposure pulse width, and the like are adjusted to obtain an appropriate toner adhesion amount. This will be described later.

  Next, a case where image data input from the computer 26a is output using the digital multifunction peripheral 11 according to an embodiment of the present invention as a printer will be described. FIG. 7 is a flowchart showing the contents of processing when image data input from the computer 26a is output using the digital multi-function peripheral 11 according to one embodiment of the present invention.

  Referring to FIG. 7, the digital multifunction peripheral 11 inputs image data from the computer 26a (in FIG. 7, step S11, hereinafter, “step” is omitted). Specifically, it accepts input of image data from the computer 26a and accepts a print request based on the image data. That is, a so-called print job request is accepted. Here, the control unit 12 operates as an input unit for inputting image data.

  Thereafter, the digital multi-function peripheral 11 performs image processing such as enlargement or reduction requested by the user on the input image data to generate image data (S12).

  Next, the digital multi-function peripheral 11 determines image attributes for the generated image data (S13). Regarding image attribute determination, image data requested to be printed is analyzed, and a character image and an image other than a character image are determined from the image data. That is, a part where image formation with characters is required is extracted. Here, the control unit 12 operates as an image discriminating unit that discriminates between a character image and an image other than the character image from the image data input by the input unit.

  Thereafter, an edge portion and a portion other than the edge portion are further identified from the determined character image (S14). Here, the control unit 12 operates as an edge part identification unit that identifies an edge part of a character image and a part other than the edge part of the character image determined by the image determination part.

  FIG. 8 is an enlarged view showing an example of the determined character image. FIG. 9 is an enlarged view showing a part of the character image shown in FIG. FIG. 9 is an enlarged view of a portion indicated by a region IX in FIG. With reference to FIG. 8 and FIG. 9, a so-called alphabetic lowercase letter “a” is identified as a character image 56.

  Here, the control unit 12 includes, in the character image 56, the edge portion 57a of the character image 56 and a portion other than the edge portion 57a, in this case, the inner portion 57b located between the edge portion 57a and the edge portion 57a. Identify.

Referring to FIGS. 8 and 9, the character edge portion 57 a in the character image 56 is directed from the portion indicated by the boundary 59 a between the background region 58 and the character image 56 toward the inner side of the character image 56. This is a region indicated by a portion having a certain width. The boundary 59a is identified by reading the appearance of a white image in the background area 58 and the appearance of a black image in the character image 56 with a line sensor. The inside 57b of the character in the character image 56 is a portion shown between the edge portion 57a and the edge portion 57a indicated by hatching in FIG. The width _{L 1} of the edge portion 57a is intended to be indicated by the length of the boundary 59a between the background region 58 and character image 56 to the boundary 59b between the edge portion 57a and the inner 57 b. In FIG. 9, for reference, the sub-scanning direction of the digital multifunction peripheral 11 that corresponds to the rotation direction of the transfer belt 35 is indicated by arrow D _1.

  At the time of identification, the control unit 12 identifies the edge portion 57a of the character image 56 and the interior 57b that is an area other than the edge portion 57a by pattern matching or an image processing filter in each pixel constituting the character image 56.

  FIG. 10 is a diagram illustrating a case where edge matching is performed by performing pattern matching in each pixel. FIG. 10 illustrates a pixel group 61 including nine pixels 62a, 62b, 62c, 62d, 62e, 62f, 62g, 62h, and 62i. In FIG. 10, a pixel having an image density equal to or higher than a predetermined value is indicated by a pixel 62d. A white pixel to which toner does not adhere is indicated by a pixel 62f. A pixel for identifying whether or not it corresponds to an edge portion is indicated by a pixel 62e. In this embodiment, the pixels 62d, 62e, and 62f are adjacent in the horizontal direction. In the adjacent pixels 62d, 62e, and 62f, when a pixel having an image density equal to or higher than a predetermined value is recognized as the pixel 62d and a white pixel to which toner is not attached is recognized as the pixel 62f, the pixel 62e positioned between the pixels 62d, 62e, and 62f It can be identified from the pixel 62e located at the edge. Such pattern matching is performed on the entire character image to identify the edge portion of the character image. In this embodiment, the pixel located in the edge portion is identified using the image density of the pixel adjacent in the horizontal direction. However, the present invention is not limited to this, and the edge portion is determined using the pixel adjacent in the vertical direction. The pixel located at may be identified.

  FIG. 11 is a diagram illustrating a case where an edge portion is identified by an image processing filter in each pixel. Referring to FIG. 11, in the image processing filter 63, the regions 64 a, 64 b, 64 c, 64 d, 64 e, 64 f, 64 g, 64 h, 64 i corresponding to nine pixels are sequentially −1 from the upper left to the lower right. , 0, 1, -2, 0, 2, -1, 0, 1 are assigned. The assigned coefficient is multiplied by each pixel and added to perform a convolution operation. Then, adjacent pixels may be compared based on the result of the convolution operation to identify the edge portion. Note that the above-described coefficients are merely examples, and other coefficients can be used.

  Next, image density adjustment is performed (S15). The image density adjustment is performed using the adjustment value adjusted by the toner density adjustment unit 41.

  After adjusting the image density, gradation processing is performed (S16). In this case, control is performed so that the first gradation processing at the edge portion of the character image is different from the second gradation processing at a portion other than the edge portion of the character image.

  Specifically, for example, the thinning amount for thinning the exposure pulse in the first gradation processing at the edge portion of the character image, and the thinning amount for thinning the exposure pulse in the second gradation processing in the portion other than the edge portion of the character image Less than. In this case, on the basis of the adjustment value of the toner density at the edge part adjusted by the toner density adjustment part 41 and the adjustment value of the internal toner density other than the edge part, the thinning amount at each part is calculated and thinned out. Tone processing is performed.

  Thereafter, that is, after gradation processing is performed, the output is performed (S17). In this way, the formed image is output for the input image data. Here, the control unit 12 or the like performs gradation processing on the image data input from the input unit by the gradation processing unit, and forms and outputs an image based on the image data input from the input unit. Operates as a part.

  With this configuration, gradation processing is performed based on the toner concentration adjusted by the toner concentration adjustment unit 41, and gradation processing corresponding to changes in the environment or the like can be performed. Further, different gradation processing is performed on the edge portion of the character image and the portion other than the edge portion of the character image. Then, gradation processing suitable for each part can be performed. Specifically, for example, gradation processing can be performed so that the amount of toner attached is less than the edge portion in the interior located between the edge portions. Therefore, according to such a digital multifunction peripheral 11, it is possible to efficiently reduce toner consumption while maintaining high image quality.

  Note that when the image discrimination is performed by the image discrimination unit, a third tone process in which the tone process is further changed may be performed on an image other than the character image. In other words, the control unit may control the gradation processing performed by the gradation processing unit in an image other than the character image determined by the image determination unit to be different from the first and second gradation processings. . In this way, for an image other than a character image, for example, an image including a photographic image, it is possible to reduce the toner consumption more efficiently as the entire image.

  Here, in the gradation processing, for example, the following processing may be performed. FIG. 12 is a diagram illustrating a case where gradation processing is performed.

Referring to FIG. 12, a case is assumed where gradation processing is performed to lower the image density of nine pixels having a high image density. In this case, for example, when adjusting the image density to be lower with respect to the pixel group 66a including nine pixels 67a, 67b, 67c, 67d, 67e, 67f, 67g, 67h, and 67i having relatively high image density. Further, as shown by the pixel group 66b in FIG. 12, the exposure pulse is thinned out to some extent, that is, the exposure pulse is spaced apart for exposure. Specifically, in the pixel group 66b, exposure is performed on a strip-shaped region 69a extending in the vertical direction, and the strip-shaped region 69c is exposed with an interval between the strip-shaped region 69a. A non-exposed band-like region 69b is formed between the region 69a and the region 69c. Similarly, an exposure area 69e and non-exposure areas 69d and 69f are formed. In this case, the width _{L 2} of the exposure area 69a indicated by the interval between the boundary 68a and the boundary 68b is made longer than the width _{L 3} of the unexposed areas 69b represented by the interval between the boundary 68b and the boundary 68c. The width _{L 2} is the length of about twice the width _{L 3.} The same applies to the regions 69c, 69d, 69e, and 69f. The pixel group 66a is an exposure area for all nine pixels 67a to 67i, whereas the pixel group 66b is an exposure area for six pixels. Such gradation processing may be performed.

  The gradation processing unit can perform a plurality of gradation processes, and the control unit 12 can select any one of the plurality of gradation processes according to the toner concentration adjusted by the toner concentration adjustment unit. You may control to perform gradation processing by selecting one. For example, when it is necessary to perform gradation processing to further reduce the image density for the pixel group 66b, as shown by the pixel group 66c in FIG. The gradation processing may be performed by opening the area, and as shown by the pixel group 66d in FIG. It is also possible to perform gradation processing by exposing the light. That is, when performing exposure corresponding to three pixels in accordance with the toner density, the gradation processing unit can perform the above-described two gradation processes. You may go.

Specifically, when performing gradation processing with further intervals between exposure pulses, in the pixel group 66c, the strip-shaped exposure areas 72a, 72c, and 72e and the strip-shaped non-exposure areas 72b, 72d, and 72f are set. The width _{L 4} of the exposure area 72a indicated by the interval between the boundary 71a and the boundary 71b constitute shorter than the width _{L 5} of the unexposed areas 72b represented by the interval between the boundary 71b and the boundary 71c. The width L ₅ is about twice as long as the width L ₄ . The same applies to the regions 72c, 72d, 72e, and 72f. In the pixel group 66b, an area corresponding to six pixels in all the pixels 67a to 67i is an exposure area, whereas in the pixel group 66c, an area corresponding to three pixels is an exposure area. Such gradation processing may be performed.

Further, in the case where gradation processing is performed by exposing three regions having different strip-like lengths extending in the horizontal direction, in the pixel group 66d, the strip-shaped exposure regions 74a, 74b, and 74c extending in the horizontal direction are extended in the horizontal direction. The strip-shaped non-exposed areas 74d, 74e, and 74f are used. The width _{L 6} of the exposure area 74a indicated by the interval between the boundary 73a and the boundary 73b is longest among the exposure areas 74 a - 74 c, the width L of the exposure area 74b indicated by the interval between the boundary 73a and the boundary 73c _7, within the exposure region 74 a - 74 c, longer to the next exposure area 74a, the width _{L 8} of the exposure area 74c indicated by the interval between the boundary 73a and the boundary 73d is the shortest among the exposed region 74 a - 74 c It is configured. In the pixel group 66b, an area corresponding to six pixels is used as an exposure area in all the pixels 67a to 67i, whereas in the pixel group 66d, an exposure area is used in three corresponding pixels. These exposure regions 74a, 74b, and 74c are configured such that the exposure regions 74a to 74c are not divided and are connected, as can be seen from comparison with the pixel group 66c.

  As described above, if the toner density is a predetermined value, that is, for example, in the case of the above-described embodiment, if the number of pixels is three or less, the floor exposed by the LSU 34 from a plurality of gradation processes is connected. You may make it control to select a tone process. By performing such gradation processing on the pixel group 66d in FIG. 12, it is possible to make the irradiation energy of exposure accompanying the lighting of the beam of the LSU 34 more uniform, resulting in higher image quality. In this case, of course, the order in the vertical direction of the exposure regions 74a to 74c may be changed according to the image, specifically, the shape of the edge portion of the character image.

  In the above embodiment, the pattern matching or the image processing filter identifies the edge portion of the character image and the inside that is an area other than the edge portion. You may decide to identify the edge part of a character image, and the inside which is area | regions other than an edge part.

  Further, the gradation processing may be configured such that one gradation processing can be performed. By doing so, the processing can be simplified.

  In the above-described embodiment, the same gradation processing may be performed on an image other than the character image as either one of the edge portion of the character image or the internal gradation processing other than the edge portion of the character image. . By doing so, the burden of image processing can be reduced.

  In the above embodiment, the transfer belt is applied as the transfer body. However, the present invention is not limited to this, and other transfer bodies may be used.

  It should be understood that the embodiments and examples disclosed herein are illustrative in all respects and are not restrictive in any respect. The scope of the present invention is defined by the scope of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the scope of the claims.

  The image forming apparatus according to the present invention is particularly effectively used when efficient reduction of toner consumption is required while maintaining high image quality.

  DESCRIPTION OF SYMBOLS 11 Digital multifunction device, 12 Control part, 13 Operation part, 14 Image reading part, 15 Image formation part, 16 Hard disk, 17 Facsimile communication part, 18 Network interface part, 19 Paper setting part, 21 Display screen, 22 ADF, 23a, 23b, 23c Paper cassette, 24 Public line, 25 Network, 26a, 26b, 26c Computer, 27 Image forming system, 28 Manual feed tray, 29 Paper feed cassette group, 30 Discharge tray, 31a, 31b, 31c, 31d Photoconductor 32a, 32b, 32c, 32d Image forming unit, 33 Imager, 34 LSU, 35 Transfer belt, 36a, 36b Driving roller, 37 Transfer belt cleaning unit, 38 Surface, 39 Visible image, 41 Toner density adjusting unit, 42 Toner Density detection sensor, 43a Light emitting element, 43b Light receiving element, 44 Toner density calculation unit, 45 surface, 46a, 46b Light, 51, 53a, 53b Solid line, 52a, 52b, 52c, 55a, 55b, 55c, 55d, 58, 64a 64b, 64c, 64d, 64e, 64f, 64g, 64h, 64i, 69a, 69b, 69c, 69d, 69e, 69f, 72a, 72b, 72c, 72d, 72e, 72f, 74a, 74b, 74c, 74d, 74e , 74f region, 54 pattern image, 56 character image, 57a edge portion, 57b inside, 61, 66a, 66b, 66c, 66d pixel group, 62a, 62b, 62c, 62d, 62e, 62f, 62g, 62h, 62i, 67a , 67b, 67c, 67d, 67e, 67f, 67g, 67h, 6 i, pixels, 63 image processing filters, 59a, 59b, 68a, 68b, 68c, 71a, 71b, 71c, 73a, 73b, 73c, 73d boundary.

Claims (5)

A photoreceptor,
An exposure unit that irradiates the photosensitive member with light to form an electrostatic latent image on the photosensitive member;
A developing unit that supplies toner to the electrostatic latent image formed by the exposure unit and forms a visible image on the photosensitive member with the toner;
A transfer body for transferring a visible image of the toner formed by the developing unit;
An electrostatic latent image of a plurality of character pattern images for adjusting a toner density of a character image composed of characters by irradiating the light onto the photoconductor by the exposure unit is formed on the photoconductor, A developing unit supplies the toner to the electrostatic latent images of the plurality of character pattern images to form a visible image of the plurality of character pattern images with the toner, and forms a visible image of the plurality of character pattern images with the toner. A character pattern image forming unit that forms a visible image of the plurality of character pattern images on the transfer member by the toner, and each character pattern image formed by the character pattern image forming unit. A toner concentration detection sensor for detecting the toner concentration of the toner, and the toner formed on the transfer body at a predetermined timing. A toner concentration adjustment unit for adjusting the toner density of the visual image,
An input unit for inputting image data;
An image discriminating unit for discriminating a character image and an image other than a character image from the image data input by the input unit;
Among the character images determined by the image determining unit, an edge part identifying unit that identifies an edge part of the character image and a part other than the edge part;
A gradation processing unit that performs gradation processing of the image based on the toner density adjusted by the toner density adjusting unit when forming an image based on the image data input by the input unit;
An output unit that performs gradation processing by the gradation processing unit on the image data input by the input unit, and forms and outputs an image based on the image data input by the input unit;
First gradation processing by the gradation processing unit at the edge portion of the character image identified by the edge portion identification unit, and second gradation by the gradation processing unit at a portion other than the edge portion of the character image. An image forming apparatus comprising: a control unit that controls the tone processing to be different. The gradation processing unit can perform a plurality of gradation processes,
The control unit controls to perform the gradation process by selecting any one of the plurality of gradation processes according to the toner density adjusted by the toner density adjustment unit. The image forming apparatus according to 1. 3. The control unit according to claim 2, wherein if the toner density is lower than a predetermined value, the control unit performs control so as to select a gradation process in which a region exposed by the exposure unit is continuous from the plurality of gradation processes. The image forming apparatus described. The control unit controls the gradation processing performed by the gradation processing unit in an image other than the character image determined by the image determination unit to be different from the first and second gradation processing. Item 4. The image forming apparatus according to any one of Items 1 to 3. 5. The image forming apparatus according to claim 1, wherein the edge part identifying part identifies an edge part of the character image and a part other than the edge part by pattern matching or an image processing filter.

Images