JP2019128408A - Image forming apparatus, image forming method, and image forming program - Google Patents

Abstract

To improve image quality by using an organic relationship between a method for halftone processing and an edge effect.SOLUTION: An image forming apparatus comprises: an image analysis unit that analyzes image data to estimate the degree of occurrence of accumulation of toner at a rear end, when the estimated degree of occurrence of accumulation of toner at a rear end exceeds a first threshold, selects a line screen, and when the estimated degree of occurrence of accumulation of toner at a rear end is equal to or less than the first threshold, selects a dot screen; developing units that each form, on a developing roller, a toner layer having a thickness according to a toner layer forming potential difference between a magnetic roller and the developing roller, and attach a toner from the toner layer to a photoreceptor on the basis of a developing bias potential that is the potential of the developing roller and an electrostatic latent image; and a calibration processing unit that adjusts the developing bias potential of the developing unit within an adjustment range set in advance to execute first calibration processing, and sets a dot area ratio for forming a solid image when the developing bias potential reaches a potential limiting value within the adjustment range in the first calibration processing to execute second calibration processing.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus, an image forming method, and an image forming program.

  In the technical field of image formation, various techniques for suppressing edge effects have been proposed. The edge effect is a phenomenon in which toner as a developer is concentrated on the edge portion (end portion) of an image area and the density of the image becomes uneven. Specifically, for example, in Patent Document 1, the edge region is detected according to the distance from the boundary of the edge region detected by the edge detection unit and the toner adhesion amount obtained from the image pattern formed at a predetermined timing. A technique has been proposed for controlling the writing exposure amount or the width of a correction value for image data. When adjusting the exposure amount of the edge part, this technology has a large influence on the change in the thickness of characters and lines with respect to the change in the exposure amount in pixels close to the edge boundary, while the exposure amount in pixels far from the edge boundary. This technology was created focusing on the fact that the change in the thickness of the characters and lines is small.

JP, 2015-219407, A

  However, conventionally, the organic relationship between the halftoning method and the edge effect has not been sufficiently studied.

  The present invention has been made in view of such a situation, and an object of the present invention is to provide a technique for improving image quality by utilizing an organic relationship between a halftone processing method and an edge effect.

  The image forming apparatus according to the present invention performs halftone processing using any one of a plurality of halftone processing methods including halftone processing using a line screen and halftone processing using a dot screen. And the image data are analyzed to estimate the degree of occurrence of rear end accumulation, and when the estimated degree of occurrence of rear end accumulation exceeds a first threshold, the line screen is selected, and the estimation is performed. When the degree of occurrence of the trailing edge accumulation is equal to or less than the first threshold value, the image analysis unit that selects the dot screen, a rotatable photoconductor, and the photoconductor is exposed based on the image data. And an exposure unit for forming an electrostatic latent image, a magnetic roller, and a developing roller, and a toner layer having a thickness corresponding to the toner layer forming potential difference between the magnetic roller and the developing roller A developing portion formed on the developing roller and configured to attach toner from the toner layer to the photoreceptor based on a developing bias potential which is a potential of the developing roller and the electrostatic latent image; and a developing bias potential of the developing portion A dot area for forming a solid image when the first calibration process is executed by adjusting the value within a preset adjustment range and the potential limit value is within the adjustment range in the first calibration process. And a calibration processing unit that sets a rate and executes a second calibration process.

  The image forming method of the present invention is a halftone process that performs halftone processing using any one of a plurality of halftone processing methods including halftone processing using a line screen and halftone processing using a dot screen. Analyzing the process and image data to estimate the degree of occurrence of rear end accumulation, and if the estimated degree of occurrence of rear end accumulation exceeds a first threshold, select the line screen, and If the degree of occurrence of the trailing edge accumulation is equal to or less than the first threshold value, the image analysis step for selecting the dot screen, the rotatable photosensitive member, and the photosensitive member are exposed based on the image data. Using an exposure unit for forming an electrostatic latent image, a magnetic roller, and a developing roller, and having a thickness corresponding to the toner layer forming potential difference between the magnetic roller and the developing roller. A developing step of forming a layer on the developing roller, and attaching toner from the toner layer to the photoconductor based on a developing bias potential which is a potential of the developing roller and the electrostatic latent image; and developing in the developing step A first calibration process is executed by adjusting the bias potential within a preset adjustment range, and a solid image is formed when the potential limit value is within the adjustment range in the first calibration process. And a calibration process step of setting a dot area rate and executing a second calibration process.

  The present invention provides an image forming program for controlling an image forming apparatus that forms an image on an image forming medium according to image data. The image forming apparatus includes a rotatable photosensitive member, an exposure unit that exposes the photosensitive member based on the image data to form an electrostatic latent image, a magnetic roller, and a developing roller, A toner layer having a thickness corresponding to a toner layer forming potential difference between the roller and the developing roller is formed on the developing roller, and the developing bias potential which is the potential of the developing roller and the electrostatic latent image A developing unit that attaches toner from the toner layer to the photoconductor, and the image forming program includes any of a plurality of halftone processing methods including a halftone process using a line screen and a halftone process using a dot screen. A halftone processing unit for performing halftone processing using the image, analyzing the image data to estimate the degree of occurrence of the trailing edge accumulation, and the estimated trailing edge accumulation Image analysis in which the line screen is selected when the degree of occurrence exceeds a first threshold, and the dot screen is selected when the degree of occurrence of the estimated trailing edge accumulation is less than or equal to the first threshold. And the developing bias potential of the developing unit is adjusted within a preset adjustment range and the first calibration processing is executed, and the potential limit value within the adjustment range is reached in the first calibration processing. The image forming apparatus functions as a calibration processing unit that sets a dot area ratio for forming a solid image on the image forming apparatus and executes a second calibration process.

  According to the present invention, it is possible to improve the image quality by utilizing the organic relationship between the method of halftone processing and the edge effect.

2 is a block diagram illustrating a functional configuration of the image forming apparatus 1 according to an embodiment of the present disclosure. 1 is a cross-sectional view illustrating an overall configuration of an image forming apparatus 1 according to an embodiment. FIG. 2 is a side cross-sectional view showing the structure of the developing unit 100 according to an embodiment of the present invention. It is a conceptual diagram which shows a mode that a back end accumulation generate | occur | produces in the image development process which concerns on one Embodiment. 4 is a flowchart showing the contents of a half patch calibration processing procedure of the image forming apparatus 1 according to an embodiment. 5 is a flowchart showing the contents of development bias adjustment processing and dot area ratio adjustment processing according to an embodiment. FIG. 2 is an explanatory diagram showing an outline of a line screen and a dot screen that can be used by the image forming apparatus 1 according to an embodiment. 5 is a flowchart showing the contents of an image forming processing procedure of the image forming apparatus 1 according to an embodiment.

  Hereinafter, modes for carrying out the present invention (hereinafter, referred to as “embodiments”) will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a functional configuration of an image forming apparatus 1 according to an embodiment of the present invention. The image forming apparatus 1 includes a control unit 10, an image forming unit 20, a storage unit 40, an image reading unit 50, and a fixing unit 80. The image reading unit 50 reads an image from a document and generates an image data ID that is digital data.

  The image forming unit 20 includes a color conversion processing unit 21, a halftone processing unit 22, a density sensor 28 for calibration, an exposure unit 29, and photosensitive drums (image carriers) 30c to 30k, which are amorphous silicon photosensitive members. , And developing units 100c to 100k and charging units 25c to 25k. The color conversion processing unit 21 converts the color space of the image data ID, which is RGB data, into CMYK data in a color space that can be reproduced by the developing units 100c to 100k. The halftone processing unit 22 performs halftone processing on the CMYK data to generate print data PD as CMYK halftone data. The halftone data represents the formation state of dots formed by each toner of CMYK, and is also called dot data.

  The control unit 10 includes main storage means such as RAM and ROM, and control means such as MPU (Micro Processing Unit) and CPU (Central Processing Unit). The control unit 10 also has a controller function related to interfaces such as various I / O, USB (Universal Serial Bus), bus, and other hardware, and controls the entire image forming apparatus 1. The control unit 10 includes a calibration processing unit 11 and an image analysis unit 12. The functions of the calibration processing unit 11 and the image analysis unit 12 will be described later.

  The storage unit 40 is a storage device including a hard disk drive or a flash memory that is a non-temporary recording medium, and stores a control program and data for processing executed by the control unit 10. In the present embodiment, the storage unit 40 further stores calibration data CD1 and screen data CD2. The calibration data CD1 can be configured, for example, as a LUT (Look Up Table). The screen data CD2 is data for using a screen that can be used by the halftone processing unit 22. Details of the calibration data CD1 and the screen data CD2 will be described later.

  FIG. 2 is a cross-sectional view showing the overall configuration of the image forming apparatus 1 according to an embodiment. The image forming apparatus 1 of the present embodiment is a tandem type color printer. In the image forming apparatus 1, photosensitive drums (image carriers) 30 m, 30 c, 30 y and 30 k are arranged in a line in a casing 70 corresponding to each color of magenta, cyan, yellow and black. Developing units 100m, 100c, 100y and 100k are disposed adjacent to the photosensitive drums 30m, 30c, 30y and 30k, respectively.

  The laser beams Lm, Lc, Ly and Lk for respective colors are irradiated (exposed) from the exposure unit 29 to the photosensitive drums 30m, 30c, 30y and 30k. By this irradiation, electrostatic latent images are formed on the photosensitive drums 30m, 30c, 30y and 30k. The developing units 100m, 100c, 100y and 100k cause the toner to adhere to the electrostatic latent images formed on the surfaces of the photosensitive drums 30m, 30c, 30y and 30k while stirring the toner. Thus, the developing process is completed, and toner images of respective colors are formed on the surfaces of the photosensitive drums 30c to 30k.

  The image forming apparatus 1 has an endless intermediate transfer belt 27. The intermediate transfer belt 27 is stretched around a tension roller 24, a drive roller 26a and a driven roller 26b. The intermediate transfer belt 27 is driven to circulate by the rotation of the driving roller 26a.

  For example, a black toner image on the photosensitive drum 30k is primarily transferred to the intermediate transfer belt 27 by sandwiching the intermediate transfer belt 27 between the photosensitive drum 30k and the primary transfer roller 23k, and the intermediate transfer belt 27 being driven to circulate. Ru. The same applies to the three colors of cyan, yellow and magenta.

  A full-color toner image is formed on the surface of the intermediate transfer belt 27 by performing primary transfer so as to be superimposed on each other at a predetermined timing. The calibration density sensor 28 is disposed at a position where the primary transfer is completed and the density of the toner image before the secondary transfer can be measured. Thereafter, the full-color toner image is secondarily transferred to the printing paper P supplied from the paper feed cassette 60 and fixed on the printing paper P as a printing medium by the fixing roller pair 81 of the fixing unit 80.

  FIG. 3 is a side sectional view showing the structure of the developing unit 100 according to an embodiment of the present invention. The developing units 100m, 100c, 100y and 100k have the same configuration, and these are also simply referred to as the developing unit 100. The developing unit 100 includes two agitating and conveying members 141 and 142, a magnetic roller 143, a developing roller (developer carrying member) 144, a developing container 145, and a regulating blade 146.

  The developing container 145 constitutes the outline of the developing unit 100. At the lower part of the developing container 145, a partition part 145b is provided. The partitioning portion 145 b partitions the inside of the developing container 145 into a first transfer chamber 145 a and a second transfer chamber 145 c. The first transfer chamber 145a and the second transfer chamber 145c extend in a column shape in a direction perpendicular to FIG. 3, and contain a two-component developer (also simply referred to as a developer) made of a magnetic carrier and black toner.

  The developing container 145 further holds the magnetic roller 143 and the developing roller 144. The developing container 145 is formed with an opening 147 for exposing the developing roller 144 toward the photosensitive drum 30 (30 k).

  The two agitating and conveying members 141 and 142 are cyclically moved while stirring the developer inside the first conveying chamber 145a and the second conveying chamber 145c, respectively. The stirring and conveying member 142 supplies a positively charged developer to the magnetic roller 143 as a magnetic brush. The magnetic roller 143 includes a nonmagnetic rotating sleeve 143a and a fixed magnet body 143b fixed inside the rotating sleeve 143a. The magnetic roller 143 and the developing roller 144 face each other with a predetermined clearance. The regulation blade 146 adjusts the magnetic brush to a predetermined height.

  The developing roller 144 includes a rotatable nonmagnetic developing sleeve 144a and a developing roller side magnetic pole 144b fixed inside the developing sleeve 144a. A magnetic roller potential Vmag is applied to the magnetic roller 143. A developing bias potential Vslv is applied to the developing roller 144.

  In the present embodiment, in the photosensitive drum 30, the surface potential is set to 20 V, and a developing electric field is formed between the photosensitive drum 30 and the developing roller 144. On the other hand, an alternating bias in which a DC potential of 20 to 80 V as the developing bias potential Vslv and a sine wave potential of a peak-to-peak value of 2000 V at a frequency of 2 kHz are superimposed is applied to the developing roller 144. A DC potential of 200 V is applied to the magnetic roller 143 as a magnetic roller potential Vmag during development, and a DC potential of −200 V is applied during non-development.

  As a result, during development, the time of developing bias potential Vslv <magnetic roller potential Vmag (the potential state in which toner is supplied to developing roller 144) is lengthened, and the time for supplying toner to developing roller 144 is lengthened. At the time of non-development, the time of developing bias potential Vslv> magnetic roller potential Vmag (a potential state in which toner is collected from the developing roller 144) becomes longer, and the time for collecting toner from the developing roller 144 becomes longer.

  Furthermore, by adjusting the magnetic roller potential Vmag applied to the magnetic roller 143 during development and non-development, the toner layer formation potential difference ΔV during development between the development bias potential Vslv and the magnetic roller potential Vmag is changed. Can. Accordingly, a thin toner layer (simply a toner) having a thickness D (see FIG. 4A described later) corresponding to the toner layer forming potential difference ΔV between the developing bias potential Vslv and the magnetic roller potential Vmag is applied to the developing roller 144. Also called a layer) is formed.

  The developing roller 144 attaches toner to the photosensitive drum 30 through a facing portion (developing nip) having a predetermined clearance with the photosensitive drum 30 to form a toner image on the surface of the photosensitive drum 30. . The toner image is formed based on the potential difference between the electrostatic latent image potential on the surface of the photosensitive drum 30 and the developing bias potential Vslv applied to the developing roller 144.

  Amorphous silicon photoconductors have a characteristic that the relative permittivity is about three times higher than that of organic photoconductors (OPC), and the amount of toner that can be held by the photoconductor is larger than the development contrast potential. For this reason, the amorphous silicon photosensitive member can hold more toner than the solid density which is usually used. Therefore, when used in a saturated state, the amorphous silicon photosensitive member is held in excess of the amount required for the solid density. Therefore, in the present embodiment, the amorphous silicon photosensitive member is used in the non-saturated state even in the solid density, and the toner formed on the developing roller 144 is almost entirely developed on the photosensitive member, and the development is completed. Is used to be determined.

  FIG. 4 is a conceptual diagram illustrating how the trailing edge accumulation occurs in the developing process according to the embodiment. FIG. 4A shows a state in which an image is formed at the front end portion and the center portion of the image. FIG. 4B shows that the image is formed at the rear end of the image. In the present specification, the front end portion, the central portion, and the rear end portion are defined as the front end portion, the central portion, and the rear end portion in order from the traveling direction with reference to the traveling direction of the photosensitive drum 30.

  In this embodiment, as shown in FIG. 4A, the photosensitive drum 30 is supplied with toner from the developing sleeve 144a of the developing roller 144 while neutralizing the potential of the latent image. At this time, the developing process is configured to be completed when the toner thin layer formed on the developing sleeve 144a is consumed in the non-saturated state, not in the saturation of the potential. The thickness D of the toner thin layer is set to have a thickness T1 for achieving the maximum density at the time of solid development in image formation.

  As shown in FIG. 4B, the developing sleeve 144a has a peripheral speed Vs and is configured to form an image while overtaking the photosensitive drum 30 at the peripheral speed Vd. For this reason, the surface of the developing sleeve 144a in which the toner is not consumed exists near the rear end of the solid at the time of solid development. The surface on which the toner is not consumed will overtake the rear end of the solid latent image on the amorphous silicon photosensitive member 30.

  At this time, since the photosensitive drum 30 as the amorphous silicon photosensitive member is not saturated, the toner is further developed from the surface of the developing sleeve 144a where the toner is not consumed. By this development, the trailing edge stagnation (thickness T2) as a solid density higher than the density assumed in advance becomes apparent.

  FIG. 4C shows, as an example, the adhesion state (stacked state) of the toner at the time of image formation of the line image TP. In the line image TP, the toner layer is raised at the rear end portion at the time of image formation. This rise of the toner layer is called a rear end reservoir.

  FIG. 5 is a flowchart showing the contents of the half patch calibration process procedure (step S100) of the image forming apparatus 1 according to an embodiment. FIG. 6 is a flowchart showing the contents of the development bias adjustment process and the dot area ratio adjustment process according to an embodiment. FIG. 7 is an explanatory view showing an outline of a line screen and a dot screen which can be used by the image forming apparatus 1 according to an embodiment. In the present embodiment, since the amorphous silicon photosensitive members are adopted for the photosensitive drums 30c to 30k, the image forming apparatus 1 is configured to express a solid by a half patch in order to suppress the problem of the rear end accumulation. There is.

  Such a problem of rear end accumulation can be suppressed by expressing a solid with a half patch. In this example, it is assumed that the image forming apparatus 1 expresses a solid by a half patch having a dot area rate of 65% to 90%. In the present embodiment, the solid density by the half patch is calibrated by adjusting the developing bias potential Vslv, which is the applied potential of the developing units 100m, 100c, 100y, and 100k, and the dot area ratio.

  In step S110, the calibration processing unit 11 of the control unit 10 executes a developing bias adjustment process using the line screen LS. The line screen LS has a property that the rear end accumulation can be made less visible compared to the dot screen DS, but the gradation is easily crushed in the high gradation portion (high density portion).

  In step S <b> 111, the calibration processing unit 11 forms a chart having a plurality of half patches on the intermediate transfer belt 27. The halftone processing unit 22 generates halftone data for reproducing a plurality of half patches using the line screen LS. Halftone data represents the formation state of dots formed by CMYK toners.

  The plurality of half patches are formed by stepwise changing the developing bias potential Vslv. Specifically, the calibration processing unit 11 forms on the intermediate transfer belt 27 a chart having a plurality of half patches in which the developing bias potential Vslv is different at a dot area ratio (65% in this example) as an initial value before calibration. Do. The plurality of half patches include those having the development bias potential Vslv having the maximum value.

  A plurality of half patches in which the development bias potential Vslv is changed in stages are used because the toner image has an electrostatic latent image potential on the surface of the photosensitive drum 30 and a development bias potential Vslv applied to the development roller 144. It is because it is formed based on the potential difference. A plurality of half patches are formed for each of CMYK. Hereinafter, a cyan (C) half patch will be described as an example.

  In step S112, the calibration processing unit 11 measures the density of the patch of each color (for example, cyan (C)) using the calibration density sensor 28. The density of the patch can be measured, for example, the amount of red reflected light which has a complementary color relationship of cyan (C). The same process is performed for MYK.

  In the present embodiment, the calibration concentration sensor 28 emits infrared light from, for example, an LED (not shown), passes through a polarizing filter that transmits only P waves, and irradiates the patches with infrared P waves. The density is detected based on the ratio of P wave and S wave of the reflected light detected by the light receiving element. The calibration density sensor 28 includes a regular reflection method for detecting regular reflection light from the patch and a diffuse reflection method for detecting diffuse reflection light from the patch.

  In step S113, the calibration processing unit 11 executes a developing bias setting process. In the developing bias setting process, the calibration processing unit 11 detects a patch which has reached a preset solid image target density among a plurality of cyan (C) half patches in which the developing bias potential Vslv is changed stepwise. Is present, it is executed by selecting the developing bias potential Vslv corresponding to the patch. Specifically, when there is a half patch in which the ratio of the P wave to the S wave is equal to or less than a preset threshold, the calibration processing unit 11 calibrates the lowest developing bias potential Vslv among the half patches. It is adjusted to the potential of the later development bias.

  In step S120, the calibration processing unit 11 executes development bias adjustment processing using the dot screen DS. The development bias adjustment process in step S120 is the same process as the development bias adjustment process in step S110 except that a plurality of half patches are formed using the dot screen DS instead of the line screen LS. The dot screen DS has the property of being able to reproduce the gradation smoothly in all the gradations as compared with the line screen LS, but is likely to generate the trailing edge accumulation.

  In step S130, the calibration processing unit 11 determines, for each of the line screen LS and the dot screen DS, whether or not half patch calibration using the line screen LS and the dot screen DS is possible within the adjustment range of the developing bias. . If the half patch calibration is possible within the adjustment range of the development bias, the calibration processing unit 11 proceeds to step S150, and if the half patch calibration is not possible within the adjustment range of the development bias potential Vslv. Advances the process to step S140.

  In step S150, the calibration processing unit 11 stores the development bias potential Vslv after calibration in the storage unit 40 as part of the calibration data CD1 for each of the line screen LS and the dot screen DS. Calibration by adjusting the development bias potential Vslv is also referred to as first calibration processing.

  The case where half patch calibration is not possible within the adjustment range of development bias means that there is no patch which has reached a preset solid image target density among a plurality of cyan (C) patches. ing. Normally, any one of the plurality of half patches reaches the solid image target density, but the solid image target density may not be reached in a state where the toner charge amount is increased due to, for example, an environmental change. However, when half-patch calibration is not possible within the adjustment range of the developing bias, the effect of improving the trailing edge accumulation is reduced by increasing the dot area ratio as will be described later.

  In step S140, the calibration processing unit 11 executes dot area ratio adjustment processing. The dot area ratio adjustment process is performed on the line screen LS and the dot screen DS for which half patch calibration is not possible within the adjustment range of the development bias.

  In step S141, the calibration processing unit 11 sets the development bias potential Vslv to the maximum value, and starts an operation mode in which the dot area ratio is adjusted and calibrated. The maximum value of the developing bias potential Vslv is also referred to as a potential limit value, and is set from the viewpoint of, for example, the output limit of the developing bias and an adverse effect (fogging etc.) on the image.

  In step S142, the calibration processing unit 11 forms, on the intermediate transfer belt 27, a chart having a plurality of half patches in which the dot area ratio is changed stepwise. In this example, the dot area rate is changed stepwise in the dot area rate ranging from 66% to 90%.

  In step S143, the calibration processing unit 11 measures the density of the cyan (C) patch using the calibration density sensor 28. The calibration concentration sensor 28 measures the ratio of the P wave and the S wave. The same process is performed for MYK.

  In step S144, the calibration processing unit 11 executes dot area ratio setting processing. In the dot area ratio setting process, when there is a half patch whose ratio between the P wave and the S wave is equal to or less than a preset threshold, the calibration processing unit 11 has the lowest dot area ratio among the half patches. The dot area rate of the half patch is acquired as calibration data. Calibration by setting the dot area rate is also referred to as a second calibration process. The calibration processing unit 11 stores the dot area ratio after calibration in the storage unit 40 as a part of the calibration data CD1.

  FIG. 8 is a flowchart showing the contents of an image forming process procedure (step S200) of the image forming apparatus 1 according to an embodiment. In step S210, the image analysis unit 12 of the control unit 10 executes an image analysis process. In the image analysis process, the image analysis unit 12 detects a specific pixel in which the rear end accumulation is likely to occur, and counts the number of the detected specific pixels.

  The image analysis unit 12 detects the rear end pixel of the solid image using, for example, a contour detection filter such as a differential filter or a Sobel filter, and sets a preset threshold A on the upstream side of the rear end pixel in the sub-scanning direction. A specific pixel can be extracted as a pixel forming a solid image with an exceeding number of pixels, that is, a pixel in which the number of connected dots exceeds a preset threshold A.

  In step S220, the image analysis unit 12 determines whether the number of specific rear end pixels, which are specific pixels in which rear end accumulation tends to occur, exceeds the threshold value B. The image analysis unit 12 advances the process to step S230 when the number of specific rear end pixels exceeds the threshold B, and advances the process to step S240 when the number of specific rear end pixels is equal to or less than the threshold B. . The threshold value B is also called a first threshold value.

  In step S230, the image analysis unit 12 selects the line screen LS. Thereby, the image analysis unit 12 selects the line screen LS that can make the rear end accumulation less visible compared to the dot screen DS for image data in which the rear end accumulation is relatively likely to occur. Can.

  In step S240, the image analysis unit 12 selects a dot screen DS. Thereby, the image analysis unit 12 can reproduce the gradation smoothly for all gradations compared to the line screen LS for the image data in which the trailing edge accumulation is relatively unlikely to occur. Choose As described above, the image analysis unit 12 analyzes the image data to estimate the degree of occurrence of the trailing edge accumulation, and selects an appropriate screen of the line screen LS and the dot screen DS based on the estimation. be able to.

  In step S250, the halftone processing unit 22 executes a dot data generation process. In the dot data generation processing, the halftone processing unit 22 performs halftone processing using a screen selected from the line screen LS and the dot screen DS, and represents dots forming states of CMYK toner dots. Generate data.

  In step S260, the image forming unit 20 forms dots on a printing medium (image forming medium) based on the dot data and outputs a printed matter.

  As described above, the image forming apparatus 1 according to the embodiment analyzes the image data to estimate the degree of occurrence of the trailing edge accumulation, and selects an appropriate screen from the line screen and the dot screen based on the estimation. can do. Specifically, the image forming apparatus 1 selects the line screen LS that can make the rear end accumulation difficult to see for image data that tends to cause the rear end accumulation. For data, it is possible to select a dot screen DS which can reproduce tones smoothly in all tones.

  The present invention can be implemented not only in the above embodiment but also in the following modifications.

  Modification 1: In the above embodiment, the image analysis unit selects either halftone processing using a line screen or halftone processing using a dot screen. For example, error diffusion is applied to the halftone processing method. Some may be used. The image analysis unit 12 only needs to select one of a plurality of halftone processing methods including halftone processing using a line screen and halftone processing using a dot screen.

  Modification 2: In the above-described embodiment, the image analysis unit selects either the line screen LS or the dot screen DS based on the degree of occurrence of the trailing edge accumulation, but the screen is displayed using other factors. You may choose. Specifically, the image analysis unit generates, for example, a gradation histogram and uses a line screen LS to assume that the gradation is crushed (for example, a high-density image in a preset gradation range). When the ratio of the image area occupied by the pixel exceeds the predetermined threshold (also referred to as a second threshold), the dot screen DS may be selected.

  Modification 3: In the above embodiment, the image analysis unit selects the screen regardless of whether the development bias potential is adjusted within a preset adjustment range, but the development bias potential is preset. The screen may be selected depending on whether or not adjustment is made within the adjustment range. Specifically, the image analysis unit executes the second calibration process for the line screen LS, for example, and the dot screen DS when the developing bias potential is calibrated within the adjustment range in the first calibration process. A dot screen may be selected.

  Modification 4: In the above embodiment, an amorphous silicon photoconductor is used, but the present invention is not limited to the use of an amorphous silicon photoconductor. The present invention is generally applicable to an image forming apparatus that reproduces a solid density with a non-saturated photoconductor.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Control part 11 Calibration processing part 12 Image analysis part 20 Image forming part 21 Color conversion processing part 28 Calibration density sensor 29 Exposure part 40 Storage part 50 Image reading part 60 Paper feed cassette 70 Case

Claims (6)

A halftone processing unit that performs halftone processing using any one of a plurality of halftone processing methods including halftone processing using a line screen and halftone processing using a dot screen;
The image data is analyzed to estimate the degree of occurrence of the rear end accumulation, and when the estimated degree of occurrence of the rear end accumulation exceeds the first threshold, the line screen is selected, and after the estimation An image analysis unit that selects the dot screen when the degree of occurrence of edge accumulation is not more than the first threshold;
A rotatable photosensitive member; an exposure unit that exposes the photosensitive member based on the image data to form an electrostatic latent image; a magnetic roller; and a developing roller; the magnetic roller and the developing roller; A toner layer having a thickness corresponding to a toner layer forming potential difference between the toner layer and the photosensitive member from the toner layer based on a developing bias potential which is a potential of the developing roller and the electrostatic latent image. A developing unit for attaching toner to
When the developing bias potential of the developing unit is adjusted within a preset adjustment range, the first calibration process is executed, and a solid image is obtained when the potential limit value is within the adjustment range in the first calibration process. A calibration processing unit that sets the dot area ratio for forming the second and executes the second calibration process;
An image forming apparatus comprising: The image forming apparatus according to claim 1,
The image analysis unit determines that the ratio of the image area occupied by the high-density image in the preset gradation range is the second even when the estimated degree of occurrence of the trailing edge exceeds the first threshold. The image forming apparatus which selects the dot screen when exceeding a threshold. An image forming apparatus according to claim 1 or 2, wherein
The image analysis unit performs the second calibration process for the line screen and the dot screen for the dot screen when the estimated degree of occurrence of the trailing edge exceeds the first threshold. An image forming apparatus that selects the dot screen when a developing bias potential is calibrated within the adjustment range in the first calibration process. The image forming apparatus according to any one of claims 1 to 3, wherein
The photoconductor is an amorphous silicon photoconductor,
The image forming apparatus, wherein the amorphous silicon photosensitive member forms the solid image in a non-saturated state. A halftoning step of performing halftoning using any of a plurality of halftoning methods including halftoning using a line screen and halftoning using a dot screen;
The image data is analyzed to estimate the degree of occurrence of the rear end accumulation, and when the estimated degree of occurrence of the rear end accumulation exceeds the first threshold, the line screen is selected, and after the estimation An image analysis step of selecting the dot screen when the degree of occurrence of edge accumulation is not more than the first threshold;
A rotatable photosensitive member, an exposure unit that exposes the photosensitive member based on the image data to form an electrostatic latent image, a magnetic roller, and a developing roller. A toner layer having a thickness corresponding to the toner layer formation potential difference between the toner layer and the electrostatic latent image is formed on the developing roller based on a developing bias potential which is a potential of the developing roller and the electrostatic latent image. A development process for adhering toner;
When the development bias potential of the development step is adjusted within a preset adjustment range, the first calibration process is executed, and a solid image is obtained when the potential limit value is within the adjustment range in the first calibration process. A calibration process step of setting the dot area ratio to form the second calibration process and executing the second calibration process;
An image forming method comprising: An image forming program for controlling an image forming apparatus for forming an image on an image forming medium according to image data, comprising:
The image forming apparatus includes a rotatable photosensitive member, an exposure unit that exposes the photosensitive member based on the image data to form an electrostatic latent image, a magnetic roller, and a developing roller. A toner layer having a thickness corresponding to a toner layer forming potential difference between the roller and the developing roller is formed on the developing roller, and the developing bias potential which is the potential of the developing roller and the electrostatic latent image A developing unit for attaching toner from a toner layer to the photoreceptor;
The image forming program includes:
A halftone processing unit that performs halftone processing using any one of a plurality of halftone processing methods including halftone processing using a line screen and halftone processing using a dot screen;
Analyzing the image data to estimate the degree of occurrence of rear end accumulation, and if the estimated degree of occurrence of rear end accumulation exceeds a first threshold, select the line screen, and the estimated An image analysis unit that selects the dot screen when the degree of occurrence of rear end accumulation is not more than the first threshold; and
When the developing bias potential of the developing unit is adjusted within a preset adjustment range, the first calibration process is executed, and a solid image is obtained when the potential limit value is within the adjustment range in the first calibration process. An image forming program that causes the image forming apparatus to function as a calibration processing unit that executes a second calibration process by setting a dot area ratio for forming the image.