JP2015011254A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus which prevents degradation of a normal image other than a bar-code, and improve image quality of the bar-code.SOLUTION: A charging apparatus decreases a surface potential of a photoreceptor drum to V'[V]. During exposure, the potential of a toner image part is increased up to V[V]. In a white part, exposure is not performed in an area including a bar-code, while exposure is performed in the other area to increase the potential up to V[V]. A fog margin M[V] in the area including the bar-code is larger than a fog margin M[V] in the other area, thereby increasing printing accuracy of the bar-code.

Description

  The present invention relates to an image forming apparatus, and more particularly to a technique for improving printing accuracy by changing a fogging margin in an arbitrary region in an image.

  In recent years, image forming apparatuses such as printer apparatuses have increased opportunities to print barcodes, and further improvement in barcode printing accuracy has been strongly demanded as the bars become thinner. For this reason, for example, in consideration of ink bleeding, a bar code is printed thinner than the original line width, and the line width (number of dots) of each line is determined so that the original line width is obtained by ink bleeding. The technique to do is disclosed (refer patent document 1). In this way, black thick lines, black thin lines, white thick lines, and white thin lines constituting the barcode are printed with appropriate line widths.

  However, in order for the bar code reader to read the bar code properly, it is also important that not only the line width but also black lines and white lines are printed at an appropriate density without any defects. For this reason, there has been proposed a technique for controlling image forming conditions such as the frequency of the alternating voltage applied to the developing roller, the magnitude of the direct current voltage, and the transfer current supplied to the transfer roller. In this way, the barcode printing accuracy can be improved.

  For images other than barcodes, a good image cannot always be obtained if the same image formation conditions as barcodes are applied, and therefore image formation conditions different from barcodes are applied. As a result, excellent image quality can be achieved for images other than barcodes (see Patent Document 2).

Japanese Patent No. 3370711 JP 2009-193057 A

According to the above-described prior art, if the image forming conditions are changed while rotating the photosensitive drum, the image forming conditions can be changed along the rotation direction of the photosensitive drum, that is, the sub-scanning direction of the image. Therefore, when an image other than the barcode and the barcode are arranged in the sub-scanning direction, it is possible to apply an appropriate image forming condition suitable for each of these images.
However, since the developing roller and the transfer roller face the photosensitive drum throughout the main scanning direction, the same image forming conditions are applied throughout the main scanning direction, and the image forming conditions are changed. Can not do it. For this reason, when an image other than the barcode and the barcode are arranged in the main scanning direction, there is a problem that if one image quality is improved, the other image quality cannot be obtained.

  The present invention has been made in view of the above-described problems, and an image forming apparatus capable of improving the image quality of a barcode while reducing the quality deterioration of a normal image other than the barcode. The purpose is to provide.

  In order to achieve the above object, an image forming apparatus according to the present invention is an electrophotographic image forming apparatus that forms an electrostatic latent image by exposing a uniformly charged surface of a photoconductor. A region dividing means for dividing a page to be printed into a plurality of regions so as to have a boundary in both the main scanning direction and the sub-scanning direction by detection, and the types of images included in each region And an exposure amount control means for controlling the exposure amount for the white background portion to differ.

In general, when developing an electrostatic latent image on the surface of a photoreceptor, the surface potential of the white background portion in the electrostatic latent image and development are to be prevented in order to prevent the background fogging of the toner from adhering to the white background portion where the toner should not adhere. A potential difference is set with the bias potential of the agent carrier (hereinafter simply referred to as “development bias”), and this potential difference is referred to as a fogging margin.
If the cover margin is too narrow, background fog is generated, and if the cover margin is too wide, carrier adhesion is caused. In barcodes and the like, by making the fog margin in the white background portion wider than usual, the background fog can be suppressed and the image can be sharpened.

  Further, since the exposure amount can be adjusted for each pixel, it is possible to partition an area including a barcode and other areas not only in the sub-scanning direction but also in the main scanning direction. Therefore, since the area including the barcode and the other areas are exposed with an optimal exposure amount so as to have an appropriate fog margin, excellent image quality can be obtained while preventing background fog and carrier adhesion.

In this case, the area classification means classifies the area according to whether it includes a barcode, a two-dimensional code, or neither, and the exposure control means controls the area of the area including the barcode or the two-dimensional code. It is desirable to control so that the exposure amount for the white background portion is smaller than the exposure amount for the white background portion of other regions.
In particular, if the area including the barcode or the two-dimensional code includes the barcode and the peripheral pixels of the two-dimensional code, the area is clearly printed not only inside the barcode or the two-dimensional code but also the surrounding boundary portion. Can do.

  In addition, the area sorting unit classifies the area according to whether or not it includes a character having a predetermined size or less, the area including the character includes a peripheral pixel of the character, and the exposure amount control unit includes the exposure amount control unit You may control so that the exposure amount with respect to the white background part of the area | region containing a character becomes smaller than the exposure amount with respect to the white background part of another area | region. In this way, small-sized characters can be printed clearly. This is particularly effective when the character size is 7 points or less.

  In addition, the area classification means classifies the area depending on whether or not it includes an isolated dot or 1-dot thin line, and an area including the isolated dot or 1-dot thin line is the periphery of the isolated dot and 1-dot thin line. The exposure amount control means may include a pixel, and may control the exposure amount for the white background portion of the region including the isolated dot or 1-dot thin line to be larger than the exposure amount for the white background portion of the other region. In this way, it is possible to prevent the disappearance of isolated dots and the loss of one-dot fine lines by suppressing the fog margin in the white background.

Regardless of the area, the image forming apparatus further comprises a charge control means for uniformly charging the surface of the photosensitive member to a potential having a larger absolute value than the potential of the white background after exposure, and the exposure amount control means is provided in the area. It is more preferable to control the exposure amount so that the white background is exposed regardless of the case. This is because the exposure time can be shortened by performing so-called bias exposure.
In this case, the exposure amount control means first exposes only a region of the uniformly charged surface of the photosensitive member where the exposure amount for the white background portion is larger than the other regions, and then forms the static The exposure amount may be controlled so that all regions are exposed while maintaining the electrostatic latent image.

1 is a diagram illustrating a main configuration of an image forming apparatus according to an embodiment of the present invention. 2 is a diagram illustrating a main configuration of a control unit 110. FIG. It is a flowchart which shows operation | movement of the area | region discrimination | determination part 200a. It is a figure which illustrates the main structures of a barcode. It is a figure which illustrates the main structures of a two-dimensional code. It is an electric potential diagram which compares an image formation process with this Embodiment and a prior art. It is a figure which shows the relationship between the fog margin M and development image quality. It is an electric potential diagram which compares an image formation process with the modification of this invention, and a prior art. It is an electrogram which compares an image formation process with another modification of this invention, and a prior art.

Embodiments of an image forming apparatus according to the present invention will be described below with reference to the drawings.
[1] Configuration of Image Forming Apparatus First, the configuration of the image forming apparatus according to the present embodiment will be described.
As shown in FIG. 1, the image forming apparatus 1 is a so-called monochrome printer apparatus, and includes a charging device 101, an exposure device 102, a developing device 103, a transfer roller 104, a peeling claw along the outer periphery of the photosensitive drum 100. 105, a cleaning device 106, and a charge removal lamp 107 are provided, and these form a toner image under the control of the control unit 110.

  That is, when the charging device 101 uniformly charges the outer peripheral surface of the photosensitive drum 100 in a state where the photosensitive drum 100 is rotationally driven in the direction of arrow A, the exposure device 102 controls the laser under the control of the control unit 110. The image is exposed to light L to form an electrostatic latent image. The developing device 103 visualizes the electrostatic latent image by supplying toner while rotating the developing roller 103a disposed opposite to the photosensitive drum 100 and applied with a developing bias in the direction of arrow B. To do.

  In parallel with this, the recording sheets P accommodated in the paper feed cassette 108 are fed out one by one by the pickup roller 109, abut against the timing roller pair 111 and stop. A transfer roller 104 is in contact with the photosensitive drum 100 in a biased state to form a transfer nip. The recording sheet P is conveyed to the transfer nip in accordance with the timing at which the toner image reaches the transfer nip.

  The transfer roller 104 conveys the recording sheet P while rotating in the arrow C direction. In addition, a transfer bias is applied to the transfer roller 104, and the toner image carried by the photosensitive drum 100 is electrostatically adsorbed on the recording sheet P. The recording sheet P on which the toner image has been electrostatically transferred is further conveyed to the fixing device 112, where the toner image is thermally fixed. Thereafter, the recording sheet P is discharged onto the discharge tray 114 by the discharge roller pair 113.

After the transfer, the toner remaining on the outer peripheral surface of the photosensitive drum 100 is scraped off by a cleaning blade 106 a provided in the cleaning device 106. Thereafter, the photosensitive drum 100 is exposed to the charge removal lamp 107, and the residual charges are discharged.
The control unit 110 controls the operation panel 115 to present information to the user of the image forming apparatus 1 or accept an instruction input from the user. The control unit 110 receives a print job from an external device such as a PC (Personal Computer) via a network (not shown) such as a LAN (Local Area Network), and controls the operation of the image forming apparatus 1 according to the print instruction. .

[2] Configuration of Control Unit 110 Next, the configuration of the control unit 110 will be described.
As shown in FIG. 2, the control unit 110 includes a CPU (Central Processing Unit) 200, a communication interface (I / F) unit 201, a ROM (Read Only Memory) 202, and a RAM (Random Access Memory) 203. When the image forming apparatus 1 is powered on, the CPU 200 reads and boots the boot program from the ROM 202, and executes a control operation using the RAM 203 as a working storage area.

  The CPU 200 also communicates with the external device 210 via the network by the communication interface unit 201. When receiving a print job from the external device 210, the CPU 200 causes the image processing circuit 211 to process image data relating to the print job. The image processing circuit 211 executes image processing such as decompression of compressed image data at high speed.

In addition, the CPU 200 performs region determination in the image by the region determination unit 200a as described later.
The charging bias application unit 204, the exposure amount adjustment unit 205, and the development bias application unit 206 are all under the control of the CPU 200, and the charging bias application unit 204 adjusts the charging bias applied by the charging device 101.

  The exposure amount adjustment unit 205 adjusts the light amount of the exposure light source emitted from the exposure apparatus 102 in units of pixels. The adjustment of the exposure amount is performed by enlarging or reducing the dot area in the toner image portion or changing the pulse width (duty ratio) in the case of PWM (Pulse Width Modulation) control. In the white background portion, in the case of PWM control, the exposure amount is adjusted by changing the pulse width.

The development bias application unit 206 adjusts the development bias applied to the development roller 103 a of the development device 103.
[3] Operation of Control Unit 110 Next, the operation of the control unit 110 will be described.
Since the setting of the charging bias and the setting of the exposure amount are different from those of the prior art, the controller 110 will be described.

(1) Setting of Charging Bias The control unit 110 controls the charging bias applied by the charging device 101 so that the absolute value of the charging potential on the outer peripheral surface of the photosensitive drum 100 becomes the absolute value of the charging potential according to the related art. 10 to 50 [V]. This is a voltage range in which the fog margin can be increased within a range where carrier adhesion is not significant. In this embodiment, negatively charged toner is used, and the charging potential is lower by 30 [V] than the conventional charging potential.

(2) Region Discrimination The control unit 110 uses the region discrimination unit 200a to generate a bar code, a two-dimensional code, and characters of 7 points or less (hereinafter referred to as “small size characters”). These images are referred to as “predetermined images”. And a region composed of pixels in the vicinity of 24 of the predetermined image (hereinafter referred to as “predetermined region”) and a region other than the predetermined region (hereinafter referred to as “other region”). Is determined for each pixel, and one page is divided into a plurality of regions.

Note that the vicinity of 24 of a pixel means 24 pixels excluding the pixel from 25 pixels included in a square area of 5 pixels both in the vertical and horizontal directions centering on the pixel. Further, the vicinity of 24 in a certain region refers to a region that is in the vicinity of 24 of all pixels included in the region and excludes all the pixels.
FIG. 3 is a flowchart showing the operation of the area determination unit 200a. When the control unit 110 receives a print job, the area determination unit 200a first searches for a command that describes the print position of a barcode or a two-dimensional code in a page description language (PDL) in the print job. To do. If the command is detected (S301: YES), the range where the barcode or the like is to be printed and its vicinity are divided into predetermined areas (S302).

Further, when the point number of the character data is also designated as 7 points or less in the page description language during the print job (S303: YES), the small size character and its 24 neighborhood are divided into predetermined regions ( S304).
Next, when image data represented by compressed data such as bitmap data or GIF (Graphics Interchange Format) is included in the print job (S305: YES), first, a barcode or a two-dimensional code is used. It is searched whether the code pattern is included in the image data (S306).

  FIG. 4 is a diagram illustrating a barcode. As shown in FIG. 4, each bar code includes a left-bar, a center bar, and a right bar that are two lines. If the range of the numerical part is specified by detecting the range including these, the barcode printing range can be specified. In the present embodiment, a region 400 including the vicinity of 24 in the print range is set as a predetermined region.

  FIG. 5 is a diagram illustrating a two-dimensional code. As shown in FIG. 5, the two-dimensional code includes finder patterns 500 to 502, and the position of the two-dimensional code can be detected using these finder patterns 500 to 502. Depending on the two-dimensional code, an alignment pattern 503 may be added to correct distortion.

By these, a two-dimensional code printing range 504 is defined, and a data cell 505 is recorded therein. In the present embodiment, a region 506 including the vicinity of 24 of the two-dimensional code printing range 504 is set as a predetermined region.
Now, referring back to FIG. 3, if a code pattern is detected (S307: YES), the code pattern and 24 neighboring pixels are set as a predetermined area (S308). Further, a small size character is searched for in the image data (S309), and when the small size character is detected (S310: YES), the small size character and its 24 neighboring pixels are set as a predetermined region (S311).

In this embodiment, the case of designating whether or not each pixel is a predetermined region has been described. However, it goes without saying that the present invention is not limited to this, and instead of this, a minimum including pixels in the vicinity of 24 is included. The rectangular area may be a predetermined area. In this way, the predetermined area can be designated more easily.
The predetermined image may be monochrome or color.

  In the present embodiment, whether or not the image is a predetermined region is determined based on only the presence or absence of the predetermined image, so that an image other than the predetermined image may be included in the predetermined region. The barcode is defined by standards such as JAN (Japanese Article Code), Code 39, Code 128, and the like, and the two-dimensional code includes a QR (Quick Response) code, PDF417, DataMatrix, and the like.

(3) Control of exposure amount When the control unit 110 determines whether the region is a predetermined region or another region by the region determination unit 200a, the control unit 110 determines whether the exposure value adjustment unit 205 determines a gradation value and a predetermined region or another region for each pixel. To adjust the exposure. FIG. 6 is a diagram comparing the present embodiment and the prior art regarding the transition of the charging potential before and after exposure. In the figure, the upper part is described so that the potential is lower and the lower part is higher.

As shown in FIG. 6, in the prior art, the outer peripheral surface of the photosensitive drum 100 is uniformly negatively charged by the charging device 101, and the surface potential drops from 0 [V] to V ₀ [V]. Next, when the photosensitive drum 100 is exposed by the exposure device 102, the potential of the white background portion remains V ₀ [V], but the potential of the toner image portion ranges from V ₀ [V] to V _i [V]. The voltage rises. In other words, the absolute value of the charging potential is reduced by exposure.

In this way, an electrostatic latent image is formed. The white background fog margin M ₀ [V] is the absolute value of the potential difference between the charging potential V ₀ [V] and the developing bias V _dc [V] applied to the developing roller 103a | V ₀ −V _dc. Equal to [V].
On the other hand, in this embodiment, the charging device 101 by negatively charging the photosensitive drum 100, 30 than the surface potential V ₀ [V] [V] which is lower V ₀ 'is the voltage drop to [V]. Further, the exposure apparatus 102 increases the exposure amount of the toner image portion in both the predetermined area and the other areas as compared with the prior art, and increases the voltage to the potential V _i [V].

In other regions, the exposure device 102 also exposes the white background and raises the voltage to the potential V ₀ [V], thereby forming an electrostatic latent image having the same charging voltage as that of the prior art.
On the other hand, since exposure is not performed in a predetermined area, the white background potential is V ₀ ′ [V], which is 30 [V] lower than that of the prior art. Thereby, the head margin M ₁ in the predetermined region [V] is satisfied is greater than the head margin M ₀ [V] in the other regions, the head margin M ₀ according to the prior art [V] 30 [V] than just It is getting bigger.

FIG. 7 is a diagram showing the relationship between the fog margin M and the development image quality. As shown in FIG. 7, when the fog margin M [V], which is a potential difference between the white background potential V ₀ [V] and the development bias V _dc [V], is small, the toner adheres to the white background portion and the fog toner. It becomes. On the other hand, if the fog margin M is too large, the potential difference between the potential V _i [V] of the toner image portion and the developing bias V _dc [V] becomes small, so that not only the toner but also the carrier adheres to the toner image portion. End up.

On the other hand, in the present embodiment, the fog margin M ₁ [V] in the predetermined region is 30 [V] wider than the fog margin M ₀ [V] in the prior art, so that the carrier adhesion is not significant. The background fogging is suppressed. Therefore, black lines and white lines in a predetermined area are printed at an appropriate density without any defects. In other regions, since the exposure amount is adjusted for each pixel, a sufficient potential difference is taken between the potentials V ₀ [V], V _dc [V], and V _i [V] to achieve excellent image quality. Can be realized.

[4] Modifications As described above, the present invention has been described based on the embodiments. However, the present invention is not limited to the above-described embodiments, and the following modifications can be implemented. .
(1) In the above-described embodiment, the case where the exposure apparatus 102 does not perform exposure on the white background in the predetermined region has been described. However, the present invention is not limited to this, and instead, the following is performed. You may do it.

  In general, the light source used by the exposure apparatus 102 rises when shifting from a small amount of light to a large amount of light in a lighting state rather than shifting from a non-lighting state to a lighting state when shifting from a white background portion to a toner image portion. The response time is short. For this reason, the exposure time can be shortened by exposing the white background portion with a light amount (and hence a potential) at which no toner image is formed (hereinafter referred to as “bias exposure”).

FIG. 8 is a potential diagram comparing the prior art and this modification in the case of performing bias exposure. As shown in FIG. 8, in the prior art, the charging device 101 charges the outer peripheral surface of the photosensitive drum 100 to the charging potential V ₀ [V], and then the white background potential is V ₁ [by bias exposure. V]. Therefore, the fog margin M ₀ [V] is | V ₁ −V _dc | [V]. Further, the toner image portion is raised to V _i [V].

On the other hand, in this modification, the charging device 101 charges the outer peripheral surface of the photosensitive drum 100 to a charging potential V ₀ ′ [V] that is 30 [V] lower than the charging potential V ₀ [V] according to the related art. . Next, the exposure apparatus 102 raises the voltage to the charging potential V ₁ [V] by bias exposure in the same manner as in the conventional technique for the white background portion in other regions. As a result, the same fog margin M ₀ [V] as in the prior art is obtained.

The white background portion of the predetermined area is raised to the charging potential V ₁ ′ [V] by bias exposure. Since the charging potential V ₁ ′ [V] of the white background portion of the predetermined area is 30 [V] lower than the charging potential V ₁ [V] of the white background portion of the other area, the fog margin M of the white background portion of the predetermined area. ₁ (= | V ₁ ′ −V _dc |) [V] is 30 [V] larger than the fog margin M ₀ [V] of the white background portion of the other region.

Therefore, in the predetermined area, the background fogging on the white background portion is suppressed more than in the other areas. Further, the toner image portion increases in voltage to the potential V _i [V] by exposure in any of the other area and the predetermined area. As a result, carrier adhesion is also prevented, and excellent image quality can be realized.
In the above description, the case where the charging device 101 charges the outer peripheral surface of the photosensitive drum 200 to a charging potential V ₀ ′ [V] that is 30 [V] lower than the charging potential V ₀ [V] according to the related art. However, the following may be used instead. That is, the charging device 101 first charges the outer peripheral surface of the photosensitive drum 200 to the charging potential V ₀ [V] as in the conventional technique, and then performs image exposure only on the other regions.

Then, without developing or erasing, the photosensitive drum 200 is rotated once, and the charging device 101 further uses the difference between the charging potential V ₀ [V] and the charging potential V ₀ ′ [V] (in the present modification example). The charging potential is lowered by 30 [V]. In other words, the absolute value of the charging potential is increased. Then, the exposure apparatus 102 performs image exposure for both the predetermined area and other areas. In this way, bias exposure can be performed without increasing the maximum voltage applied to the charging device 101.

(2) In the above embodiment, the case where the exposure amount is controlled as the main purpose of preventing the background fogging in the white background portion of the predetermined region has been described, but it is needless to say that the present invention is not limited to this. May be controlled as follows.
In the prior art, even if the fog margin is set to an appropriate value as much as possible, depending on the characteristics of the developer and the photoconductor, toner is attached to only one pixel, and the surrounding pixels are white dots or lines. In an image such as a 1-dot thin line having a width of 1 dot and less than 0.1 [mm], the potential attenuation (decrease in the absolute value of the potential) due to exposure tends to be insufficient, and as a result, the image disappears. Or deficiencies may occur and affect readability.

On the other hand, as shown in FIG. 9, in this modification, first, the outer peripheral surface of the photosensitive drum 100 is uniformly charged to the charging potential V ₀ [V] by the charging device 101, as in the prior art. To do. Next, when an electrostatic latent image is formed by exposure, an image to be emphasized (hereinafter referred to as “predetermined image”) such as an isolated dot or 1-dot thin line in the image, and 24 of the predetermined image. The exposure amount of the white background portion is made different between an area composed of neighboring pixels (hereinafter referred to as “predetermined area”) and an area other than the predetermined area (hereinafter referred to as “other area”).

That is, in the white background portion of the other region, the exposure potential is set to V ₀ [V] by performing exposure processing in the same manner as in the conventional technique, and the fog margin is set to the fog margin M ₀ [V] optimized by the conventional technique. . On the other hand, in the white background portion of the emphasis region, by increasing the exposure amount, the charged potential after exposure is set to V ₁ [V] higher than the charging potential V ₀ [V] of the white background portion of the other region, and the fog margin the fog and the margin M ₀ [V] small head margin than M ₁ [V].

In this way, the white background around the image, which is likely to lose or be lost, such as isolated dots or 1-dot thin lines, is intentionally covered, so that the image is fattened to prevent loss or loss. In addition, readability can be improved.
Further, since the fog margin is adjusted by controlling the exposure amount as in the above embodiment, the fog margin can be switched in either the main scanning direction or the sub scanning direction.

In addition to the predetermined image and its vicinity, designation of a predetermined area may be received from the external device 210 such as a PC or the operation panel 115. In this way, it is possible to reduce the fog margin and minimize the area where the background fog is likely to occur.
Further, in the above embodiment, the fog margin of the white background portion is increased in the region including the barcode, and in the present embodiment, the fog margin of the white background portion is decreased in the region including the isolated dots. When performing both of these processes when forming an image for one page, the narrow bar width is 0.19 [mm], which is the narrowest line width in the barcode of Code 39, and the resolution is 600 dpi. Since the line width of the one-dot thin line is 0.042 [mm], the fog margin in the white background portion is increased depending on whether the line width included in the region is 0.1 [mm] or more. You may decide whether to make it small.

Alternatively, the increase or decrease of the cover margin may be determined by accepting designation of the barcode mode or 1200 dpi mode (registered trademark) from the external device 210 or the operation panel 115. Furthermore, when these areas overlap, it may be determined in advance which one has priority.
(3) In the above embodiment, the case where the predetermined area includes the vicinity of 24 of the predetermined image has been described, but the present invention is not limited to this, and the predetermined area may include only the predetermined image, It may include neighboring pixels of a predetermined image defined by criteria other than 24 neighborhoods. If the predetermined area does not always extend over the entire main scanning direction, it is possible to achieve an advantage over the conventional technique.

  (4) Although not particularly mentioned in the above embodiment, the predetermined area may be a rectangular area specified in units of pixels, or an indefinite shape that matches the shape of a barcode, small size character, or the like. The area may be specified in units of pixels. In addition, the entire image is divided into a plurality of regions (for example, a rectangular region or a hexagonal region) in units of pixels, and the exposure amount of the white background portion is changed for each region depending on whether or not the barcode is included. By doing so, it is possible to reduce the processing load of the area determination unit 200a.

(5) In the above embodiment, the case where a two-component developer containing a toner and a carrier is used has been described. Needless to say, the present invention is not limited to this. One-component developer not containing a carrier The same effect can be obtained by applying the present invention also to an image forming apparatus using the image forming apparatus.
(6) In the above embodiment, the case where negatively charged toner is used has been described as an example. However, it goes without saying that the present invention is not limited to this. The effect of the present invention can be obtained by controlling the absolute value of the charging potential in the same manner as in the embodiment.

  (7) In the above embodiment, the monochrome printer apparatus has been described as an example. However, it is needless to say that the present invention is not limited to this, and the present invention may be applied to a color printer apparatus instead. In addition to the printer device, the present invention is applied to a single-function device such as a copying device equipped with a document reading device, a facsimile device equipped with a communication function, or a multi-function peripheral (MFP) having these functions. The same effect can be obtained even if is applied.

  The image forming apparatus according to the present invention is useful as an apparatus for improving the printing accuracy by changing the fog margin in an arbitrary area in the image.

DESCRIPTION OF SYMBOLS 1 ......... Image forming apparatus 100 ... Photoconductor drum 101 ... Charging apparatus 102 ... Exposure apparatus 103 ... Developing apparatus 103a ... Developing roller 110 ... Control part 115 ... Operation panel 200a ... Area discriminating part 201 ... ... Communication interface unit 204 ... Charging bias application unit 205 ... Exposure amount adjustment unit 206 ... Development bias application unit 210 ... External device 211 ... Image processing circuit

Claims (8)

An electrophotographic image forming apparatus that forms an electrostatic latent image by exposing a uniformly charged photoreceptor surface,
An area dividing means for dividing a page to be printed into a plurality of areas so as to have a boundary in both the main scanning direction and the sub-scanning direction by detecting a predetermined image;
An image forming apparatus comprising: an exposure amount control unit configured to control, for each of the regions, an exposure amount with respect to a white background portion depending on a type of image included. The area segmentation means classifies the area according to whether it includes a bar code or a two-dimensional code, or neither.
The exposure amount control means controls the exposure amount for the white background portion of the region including the barcode or the two-dimensional code to be smaller than the exposure amount for the white background portion of another region. The image forming apparatus described in 1. The image forming apparatus according to claim 2, wherein the area including the barcode or the two-dimensional code includes a peripheral pixel of the barcode and the two-dimensional code. The area sorting means classifies the area according to whether or not it includes characters of a predetermined size or less,
The region including the character includes peripheral pixels of the character,
4. The exposure amount control unit according to claim 1, wherein the exposure amount control unit controls the exposure amount for the white background portion of the region including the characters to be smaller than the exposure amount for the white background portion of the other region. The image forming apparatus described in 1. The image forming apparatus according to claim 4, wherein the predetermined size is 7 points. The region segmentation unit classifies the region according to whether it includes an isolated dot or a 1-dot thin line, or neither.
The region including an isolated dot or 1-dot thin line includes peripheral pixels of the isolated dot and 1-dot thin line,
2. The exposure amount control unit controls the exposure amount with respect to a white background portion of an area including the isolated dot or 1-dot thin line to be larger than an exposure amount with respect to a white background portion of another region. The image forming apparatus described in 1. Regardless of the area, it comprises a charge control means for uniformly charging the surface of the photoreceptor to a potential having an absolute value larger than the potential of the white background after exposure,
The image forming apparatus according to claim 1, wherein the exposure amount control unit controls the exposure amount so that a white background portion is exposed regardless of the area. The exposure amount control means includes
Of the uniformly charged photoreceptor surface, first, only the area where the exposure amount for the white background portion is larger than the other areas is exposed,
7. The image forming apparatus according to claim 1, wherein the exposure amount is controlled such that all the areas are exposed while maintaining the formed electrostatic latent image. .

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