JP2018097205A - Image formation apparatus and image formation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To appropriately suppress a user's discomfort due to show-through in accordance with a user's feeling. An image forming apparatus includes an intermediate transfer unit that first transfers a white toner image on a colored toner image to form a synthetic toner image, and secondarily transfers the synthetic toner image onto a printing medium, and a printing medium. Represents a plurality of patches having different densities in a stepwise manner, such as a transport unit that inverts the front and back sides of the above and supplies the intermediate transfer unit, a halftone processing unit that generates dot data for colored toner and dot data for white toner. A test sheet output unit that forms a patch image on the first surface of the print medium and an identification image for identifying the plurality of patches on the second surface that is the back surface of the first surface of the print medium. Then, a predetermined threshold value is set based on the information input using the identification image, and a region where the colored toner image shows through is extracted from the region where the colored toner image is formed based on the predetermined threshold value. It is equipped with an image analysis unit. [Selection diagram] Fig. 1

Description

  The present invention relates to an image forming apparatus and an image forming method, and more particularly to a technique using white toner.

  Many image forming apparatuses are capable of double-sided printing, and are widely used. In double-sided printing, an image is formed on both the front and back sides of the printing paper, which may cause a problem of show-through. The show-through is also called show-through, and is a state in which the printed image on the front side can be seen through from the back side. In order to solve this problem, a technique for suppressing show-through using a white color material has been proposed. For example, in Patent Document 1, when an image is formed on both sides of a transfer material, an area in which a front image area and a back image area overlap and a front image area and a back image area do not overlap. A technique for changing the amount of white toner attached has been proposed. According to this technique, it is possible to prevent a sense of incongruity that the images on the opposite side are transmitted and the images on both sides are seen overlapping or the color of the image is changed. Patent Document 2 proposes a technique for forming a white toner image in an area corresponding to an image area formed on the back surface at least on the front surface of the transfer material when images are formed on both surfaces of the transfer material. According to this technology, in a double-sided image forming apparatus using batch fixing, even if a positional deviation occurs between the front image and the back image of the transfer material, transmission of the color toner image on the opposite surface of the transfer material through the transfer material is prevented. You can do that.

JP 2002-304035 A JP 2002-304091 A

  However, in the show-through, the degree and color of the show-through that is anxious depends on the user's personal feeling, and the discomfort due to the show-through of the user is different. From the viewpoint of appropriately suppressing the user's discomfort due to the show-through in response to such a user's sense, sufficient studies have not been made.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a technique for appropriately suppressing user discomfort due to show-through in correspondence with the user's sense.

  The present invention provides an image forming apparatus that uses colored toner and white toner and forms an image on a print medium based on image data. The image forming apparatus includes: a colored toner photosensitive drum; a white toner photosensitive drum; and a colored toner developing unit that forms a colored toner image on the colored toner photosensitive drum using the colored toner. A white toner developing unit that forms a white toner image using the white toner on the white toner photosensitive drum; and the colored toner image is primarily transferred from the colored toner photosensitive drum; An intermediate transfer section for primary transfer of the white toner image from the photosensitive drum for white toner on the toner image to form a composite toner image, and secondary transfer of the formed composite toner image onto a print medium; A conveying unit that reverses the front and back of the print medium and supplies the intermediate transfer unit, a fixing unit that fixes the composite toner image secondarily transferred onto the print medium, and the presence A halftone processing unit that generates color toner dot data for forming toner dots and white toner dot data for forming white toner dots, and a plurality of patches whose densities are stepwise different A test sheet on which a patch image representing the image is formed on a first surface of a print medium and an identification image for identifying the plurality of patches is formed on a second surface which is the back surface of the first surface of the print medium A predetermined threshold value is set based on the information input using the output unit and the identification image, and the colored toner image is backed out of an area where the colored toner image is formed based on the predetermined threshold value. An image analysis unit that extracts a region to be reflected, and the halftone processing unit generates the white toner dot data so as to form the white toner image in the extracted region.

  The present invention provides an image forming method for forming an image on a print medium based on image data using colored toner and white toner. The image forming method includes a color toner developing step for forming a color toner image using the color toner on the color toner photosensitive drum, and a white toner using the white toner on the white toner photosensitive drum. A white toner developing step for forming a toner image; and the primary transfer of the colored toner image from the photosensitive drum for colored toner; and the white toner image from the photosensitive drum for white toner is superimposed on the colored toner image. Primary transfer forms a composite toner image, and an intermediate transfer process for secondary transfer of the formed composite toner image onto a print medium, and the print medium is reversed and supplied to the intermediate transfer process. A conveying step, a fixing step for fixing the composite toner image secondarily transferred onto the print medium onto the print medium, and a color toner dot device for forming the color toner dots. And a halftone processing step for generating white toner dot data for forming the white toner dots, and a patch image representing a plurality of patches whose densities are stepwise different from each other. A test sheet output step for forming an identification image for identifying the plurality of patches on a second surface which is a back surface of the first surface of the print medium, and an input using the identification image An image analysis step of setting a predetermined threshold based on the information and extracting an area where the colored toner image shows through from an area where the colored toner image is formed based on the predetermined threshold. The halftone processing step includes a step of generating the white toner dot data so as to form the white toner image in the extracted region.

  ADVANTAGE OF THE INVENTION According to this invention, the user's discomfort by a show-through can be suppressed appropriately corresponding to a user's sense.

2 is a block diagram showing a functional configuration of the image forming apparatus 1 according to the first embodiment of the present invention. 1 is a cross-sectional view illustrating an overall configuration of an image forming apparatus 1 according to a first embodiment. 3 is a flowchart showing the contents of a show-through suppression process of the image forming apparatus 1 according to the first embodiment. 12 is a flowchart showing the contents of set value adjustment processing of the image forming apparatus 1 according to the second embodiment. It is explanatory drawing which shows the printing surface and back surface of a show-through test sheet which concern on 2nd Embodiment. It is explanatory drawing which shows HSV color space utilized as a reference | standard by the show-through suppression process of the image forming apparatus 1 which concerns on 2nd Embodiment. It is explanatory drawing which shows the printing surface and back surface of a show-through test sheet which concerns on 3rd Embodiment.

Hereinafter, modes for carrying out the present invention (hereinafter referred to as “embodiments”) will be described in the following order with reference to the drawings in the following order.
A. First embodiment:
B. Second embodiment:
C. Third embodiment:
D. Variations:

A. First embodiment:
FIG. 1 is a block diagram showing a functional configuration of an image forming apparatus 1 according to the first 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, a fixing unit 80, and an operation display unit 90. The image reading unit 50 reads an image from a document and generates an image data ID that is digital data.

  The operation display unit 90 includes a display (not shown) that functions as a touch panel, various buttons, and switches (not shown), and receives user operation inputs. The operation display unit 90 functions as an operation mode setting unit, displays a user interface screen (not shown), and enables selection of “back-through prevention mode” in the duplex printing mode.

  The image forming unit 20 includes a color conversion processing unit 21, a halftone processing unit 22, an exposure unit 29, a colored toner photosensitive drum (image carrier) 30 c to 30 k which is an amorphous silicon photosensitive member, and an amorphous silicon photosensitive member. White toner photosensitive drum 30w, colored toner developing units 100c to 100k, colored toner developing units 100c to 100k for supplying colored toner to each of colored toner developing units 100c to 100k, and white toner The developing unit 100w includes a white toner supply unit 200w that supplies white toner to the white toner developing unit 100w, and charging units 25c to 25w.

  The photosensitive drums 30c to 30w include four colored toner photosensitive drums 30c, 30m, 30y, and 30k, and one white toner photosensitive drum 30w. The developing units 100c to 100w include four colored toner developing units 100c, 100m, 100y, and 100k, and one white toner developing unit 100w. The charging units 25c to 25w include four colored toner charging units 25c, 25m, 25y, and 25k, and one white toner charging unit 25w.

  The colored toner photosensitive drums 30c to 30k, the colored toner developing units 100c to 100k, and the colored toner charging units 25c to 25k are colored toners using colored developers including colored toners of cyan, magenta, yellow, and black. Development can be performed. On the other hand, the white toner photosensitive drum 30w, the white toner developing unit 100w, and the white toner charging unit 25w can perform white toner development using a white developer containing white toner. The white toner is a toner using a white pigment such as zinc oxide or titanium oxide.

  The color conversion processing unit 21 color-converts the image data ID, which is RGB data, into CMYK data. The halftone processing unit 22 performs halftone processing on the CMYK data to generate color toner dot data that is CMYK halftone data. The halftone processing unit 22 further generates white toner dot data, which is halftone data for white toner, such that the white toner dots have a preset dot density. The CMYK halftone data and the white toner halftone data constitute the print data PD.

  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 controller functions related to various I / O, USB (Universal Serial Bus), bus, and other hardware interfaces, and controls the entire image forming apparatus 1. The control unit 10 includes an image analysis unit 11 and a test sheet output unit 12. The functions of the image analysis unit 11 and the test sheet output 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 setting data SD for using white toner for suppressing show-through.

  FIG. 2 is a cross-sectional view illustrating the overall configuration of the image forming apparatus 1 according to the embodiment. The image forming apparatus 1 of the present embodiment is a tandem type color printer. In the housing 70, the image forming apparatus 1 includes a white toner photosensitive drum 30w, and colored toner photosensitive drums (image carriers) 30m, 30c corresponding to magenta, cyan, yellow, and black. 30y and 30k (image carrier) are arranged in a line. A white toner developing unit 100w is disposed adjacent to the white toner photosensitive drum 30w. Colored toner developing units 100m, 100c, 100y, and 100k are disposed adjacent to the colored toner photosensitive drums 30m, 30c, 30y, and 30k, respectively.

  The color toner photoreceptor drums 30c to 30k and the white toner photoreceptor drum 30w are irradiated (exposed) with laser light Lm, Lc, Ly, Lk, and Lw for each color from the exposure unit 29. By this irradiation, electrostatic latent images are formed on the color toner photosensitive drums 30c to 30k and the white toner photosensitive drum 30w. The colored toner developing units 100m, 100c, 100y, and 100k attach the toner to the electrostatic latent images formed on the surfaces of the colored toner photosensitive drums 30m, 30c, 30y, and 30k while stirring the colored toner.

  The white toner developing unit 100w adheres the toner to the electrostatic latent image formed on the surface of the white toner photosensitive drum 30w while stirring the white toner. As a result, the development process is completed, and a colored toner image of each color is formed on the surface of the photosensitive drums 30c to 30k for colored toner, and a white toner image is formed on the surface of the photosensitive drum 30w for white toner. The white toner photosensitive drum 30w is disposed on the downstream side of the colored toner photosensitive drums 30c to 30k.

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

  For example, a white toner image, which is a white toner image on the white toner photosensitive drum 30w, sandwiches the intermediate transfer belt 27 between the white toner photosensitive drum 30w and the primary transfer roller 23w, and the intermediate transfer belt 27 is circulated. As a result, primary transfer is performed on the intermediate transfer belt 27. This also applies to cyan, yellow, magenta and black colored toners. The surface of the intermediate transfer belt 27 is subjected to primary transfer so as to be superimposed on each other at a predetermined timing, so that a white toner image is formed on the full color toner image. A full-color toner image is also called a colored toner image.

  The color toner image and the white toner image formed on the color toner image are also collectively referred to as a synthetic toner image. Thereafter, the composite toner image is secondarily transferred onto the printing paper P supplied from the paper feed cassette 60 by a pair of transfer rollers 26 a and 26 b sandwiching the intermediate transfer belt 27. As a result, on the printing paper P, a white toner image is formed below the colored toner image (the printing paper P side). The fixing unit 80 (see FIG. 1) can fix the white toner image and the colored toner image on the printing paper P as a printing medium by the fixing roller pair 81.

  In order to convey the printing paper P as a printing medium, the image forming apparatus 1 includes a manual feed tray 35, a paper feed cassette 60, a first conveyance path 71, a second conveyance path 72, and a third conveyance path 73. A transport drive system having a fourth transport path 74 and a reverse transport path 75 is provided. The reverse conveyance path 75 is a conveyance path (also referred to as a conveyance unit) used in double-sided printing.

  The printing paper P is transported from the manual feed tray 35 to the second transport path 72 through a first transport path 71 disposed on the upper side of the paper feed cassette 60, for example. The second transport path 72 is connected to the paper feed cassette 60 and the first transport path 71. The second transport path 72 transports the printing paper P supplied from the paper feed cassette 60 or the like to the registration rollers 33. A registration switch (not shown) detects that the printing paper P has reached the registration roller 33.

  The image forming apparatus 1 can secondarily transfer the composite toner image transferred onto the surface of the intermediate transfer belt 27 onto the printing paper P in the third conveyance path 73. Secondary transfer is performed by a pair of transfer rollers 26a and 26b having a drive roller 26a and a secondary transfer roller 26b. When the printing paper P is detected, the registration roller 33 can perform secondary transfer by starting conveyance of the printing paper P to the pair of transfer rollers 26a and 26b in synchronization with the synthesized toner image on the intermediate transfer belt 27. And The intermediate transfer belt is also called an intermediate transfer portion.

  In duplex printing, after the first secondary transfer, the printing paper P is fixed on the printing paper P as a printing medium with a white toner image and a colored toner image on the surface, and then returned to the reverse conveyance path 75 to The back (front and back) is reversed. At this time, a synthetic toner image for the back surface is formed on the intermediate transfer belt 27. When the printing paper P is detected, the registration roller 33 starts conveying the printing paper P to the pair of transfer rollers 26a and 26b in synchronization with the synthesized toner image for the back surface on the intermediate transfer belt 27. Secondary transfer can be performed.

  FIG. 3 is a flowchart showing the contents of the show-through suppressing process of the image forming apparatus 1 according to the first embodiment. The show-through suppression process is a process for forming a white toner layer on the lower side (printing paper side) of the color toner image when the brightness of the color toner image is low and show-through is expected.

  In step S10, the control unit 10 determines whether or not the operation mode of the image forming apparatus 1 is a show-through prevention mode in double-sided printing. If the control unit 10 is in the show-through prevention mode, the process proceeds to step S20. If the control unit 10 is not in the show-through prevention mode, the process ends. This is because if the mode is not the show-through prevention mode, the show-through is not a problem for the user, and it is not necessary to suppress show-through.

  In step S20, the image analysis unit 11 executes a luminance calculation process. In the luminance calculation process, the control unit 10 calculates the luminance value of each pixel of the image data ID in this embodiment. The luminance value can be calculated from the RGB gradation values of each pixel using a predetermined calculation formula (luminance value≈0.3R + 0.6G + 0.1B).

  In step S30, the image analysis unit 11 determines whether or not a low luminance area exists. In the present embodiment, the control unit 10 assumes that the low luminance area is an area where show-through occurs. Human visual characteristics are standards that focus on the point that even small changes can be discriminated with respect to changes in luminance.

  The control unit 10 advances the process to step S40 when the low luminance area exists, and ends the process when the low luminance area does not exist. This is because show-through does not occur when there is no low-luminance region, and it is not necessary to suppress show-through.

  In step S40, the image analysis unit 11 performs a low luminance area extraction process. In the low luminance region extraction process, the control unit 10 reads the setting data SD from the storage unit 40, and the low luminance region is a region where show-through occurs based on the luminance threshold value that is the luminance threshold value included in the setting data SD. Extract luminance region.

  In step S50, the halftone processing unit 22 executes white toner halftone data generation processing. In the white toner halftone data generation processing, the halftone processing unit 22 generates white toner halftone data based on the luminance of the region extracted as the low luminance region. Specifically, the halftone processing unit 22 generates dot data such that the lower the luminance, the thicker the white toner layer or the higher the density.

  The dot data is generated using a table (for example, LUT) prepared in advance that represents the relationship between the brightness and the dot data included in the setting data SD. The white toner halftone data may be configured to have a uniform thickness or a uniform density in the low luminance region.

  The region for generating the white toner dot data is determined based on the color toner dot data corresponding to the region determined as the low luminance region based on the RGB image data ID. That is, the white toner dot data is formed in an area where colored dots are formed corresponding to the area determined as the low luminance area based on the RGB image data ID in consideration of resolution conversion and the like. .

  In step S60, the image forming unit 20 executes a white toner layer forming process. In the white toner layer forming process, the image forming unit 20 forms white dots in the low luminance area based on the halftone data for white toner. Since the white toner layer is formed on the lower side of the color toner image (the side of the print paper P) on the printing paper P as described above, the colored toner image is blocked by the white toner layer and cannot be visually recognized. Thereby, show-through in double-sided printing is suppressed.

  The white toner layer is not limited to between the colored toner image and the printing paper P, and may be formed on the corresponding surface of the printing paper P opposite to the colored toner image.

  As described above, according to the image forming apparatus 1 according to the first embodiment, the show-through is recognized by the human vision based on the criterion focusing on the human visual characteristic that the luminance change can be discriminated to a small and fine change. Since the white toner layer is formed when it is easy to be done, the white toner can be used efficiently to prevent see-through.

  Note that the brightness threshold value for setting the low brightness region and the table representing the relationship between the brightness and the dot data vary depending on the type of printing paper, etc. The image forming apparatus 1 may be configured so that the threshold value can be adjusted.

  In addition, the brightness threshold and the table, for example, when the paper type to be replenished to the paper feed cassette 60 is always the same and the paper type is unknown only when manually feeding, the printing paper P of the paper feed cassette 60 is used. The setting data SD may be set so as to be used. Further, when the image forming apparatus 1 includes a unit that can determine the type of the print medium, a luminance threshold value or a table may be registered and used in the setting data SD in association with the determined print medium.

B. Second embodiment:
FIG. 4 is a flowchart showing the contents of the set value adjustment processing of the image forming apparatus 1 according to the second embodiment. FIG. 5 is an explanatory diagram showing the printing surface TP1f and the back surface TP1r of the show-through test sheet according to the second embodiment. The image forming apparatus 1 according to the second embodiment is different from the image forming apparatus 1 according to the first embodiment in that fine setting is possible based on the brightness, hue, and saturation of the color.

  In step S71, the test sheet output unit 12 of the control unit 10 executes a test sheet output process. In the test sheet output process, the test sheet output unit 12 outputs test sheets TP1f and TP1r in response to a user input from the operation display unit 90. The test sheets TP1f and TP1r have a printing surface TP1f as a surface on which a test chart is formed and a back surface TP1r.

  The print surface TP1f is formed as a mixed color of a subtractive primary color patch, which is a primary color formed with CMY color toners, a gray patch formed with black toner (K toner), and a CMY color toner. An additive three primary color (RGB) patch that is a secondary color and an achromatic gray patch that is a tertiary color formed as a mixed color of CMY colored toners are formed. Each color patch has a higher density for each color on the upper side and a lower density on the lower side, and the densities differ in stages. On the other hand, a plurality of patches formed on the printing surface TP1f show through on the back surface TP1r.

  In step S72, the user executes a test sheet measurement process. In the test sheet measurement process, the user uses the image reading unit 50 to read the print surface TP1f of the test sheet. Thereby, the image forming apparatus 1 can acquire the optical characteristics of the colored toner actually formed by the image forming unit 20. Optical properties can include brightness, hue, saturation, and brightness. However, in this example, the brightness value is measured.

  In step S73, the user executes test sheet show-through determination processing. In the test sheet show-through determination process, the user counts the number of patches show-through of each color. Specifically, the number of cyan patches on the rightmost side (the leftmost side on the printing surface TP1f) on the back surface TP1r is seven. Similarly, on the back surface TP1r, the numbers of magenta, yellow, black (K toner), red, green, blue, and black (CMY toner) are 6, 5, 5, 7, 5, and 6, respectively. And 6 pieces.

  In the test sheet show-through determination process, the user may read the back surface TP1r of the test sheet using the image reading unit 50. Thereby, the image analysis part 11 can perform the same process based on the read image. The method of counting by the user has an advantage that it can be set in accordance with the preference and sensitivity of each user, and the method of causing the image analysis unit 11 to analyze has the advantage of ensuring objectivity.

  In step S74, the image analysis unit 11 performs a threshold value determination process. In the threshold value determination process, the image analysis unit 11 determines a lightness threshold value for determining the low lightness region based on the count by the user or the analysis result of the read image by the image analysis unit 11.

  FIG. 6 is an explanatory diagram showing an HSV color space used as a reference in the show-through suppressing process of the image forming apparatus 1 according to the second embodiment. The HSV color space is a color space including three components of hue H, saturation S, and brightness V. The image analysis unit 11 determines a lightness threshold value that is determined according to lightness, hue, and saturation in the HSV color space.

  First, the image analysis unit 11 sets a lightness threshold for each color of C, M, Y, R, G, and B. Next, the image analysis unit 11 can determine threshold values of other colors as interpolation of the hue direction in the HSV color space of these threshold values. A plurality of patches (C, M, Y, K, R, G, and B) formed on the printing surface TP1f have saturation as the maximum value that can be realized by the image forming apparatus 1. Thereby, the image analysis part 11 can determine appropriately the brightness threshold value defined according to the brightness and the hue.

  Furthermore, K (CMY) can be used for interpolation in the saturation direction. Thereby, the image analysis part 11 can determine appropriately the lightness threshold value defined according to a saturation and a hue. In the second embodiment, the threshold value can also be defined as a lightness threshold value determined for each combination of hue and saturation.

  In step S75, the image analysis unit 11 executes setting data adjustment processing. In the setting data adjustment process, the lightness threshold value stored in the setting data SD is changed to a lightness threshold value newly defined as a lightness threshold value determined for each combination of hue and saturation.

  As described above, according to the image forming apparatus 1 according to the second embodiment, when the brightness threshold value of the show-through varies according to the hue and the saturation, the white toner layer is formed when the show-through is likely to occur. Therefore, the white toner can be efficiently used to suppress show-through.

  Instead of the lightness threshold value, it may be newly defined as a luminance threshold value determined for each combination of hue and saturation. Furthermore, instead of the combination of hue and saturation, a brightness threshold value determined for each hue or a brightness threshold value determined for each saturation may be newly defined. In the HSV color space, it is not always necessary to perform interpolation calculation. For example, the HSV color space is divided (quantized) for each of six colors (C, M, Y, R, G, B). It may be.

C. Third embodiment:
FIG. 7 is an explanatory diagram showing the printing surface TP2f and the back surface TP2r of the show-through test sheets TP2f and TP2r according to the third embodiment. The back surface TP2r according to the third embodiment is printed on the back surface TP2r by the symbols A to H representing a plurality of two-dimensionally arranged rows of patches and the numbers 1 to 7 representing rows. This is different from the back surface TP1r according to the second embodiment in which is not formed. The same image as the printing surface TP1f according to the second embodiment is formed on the printing surface TP2f according to the third embodiment.

  The set value adjustment process according to the third embodiment includes a test sheet output process (Step S71) and a set data adjustment process (Step S71) in order to appropriately suppress user discomfort due to show-through in correspondence with the user's sense. S75) is different from the set value adjustment processing according to the second embodiment.

  In the test sheet output process (step S71), the operation display unit 90 requests user login in order to execute the set value adjustment process. The operation display unit 90 displays a user interface screen (not shown) that enables output of a test sheet in response to user login.

  The test sheet output unit 12 outputs the show-through test sheets TP2f and TP2r in response to a user input requesting output of the test sheet. The show-through test sheets TP2f and TP2r are printed by the double-sided printing function of the image forming apparatus 1. The show-through test sheets TP2f and TP2r are formed on the printing surface TP2f based on the patch data read from the setting data SD. The patch data can be common data for all users.

  On the printing surface TP2f, there are patch images, that is, patches of subtractive three primary colors that are primary colors formed with CMY colored toners, gray patches formed of black toner (K toner), and CMY colored toners. An additive three primary color (RGB) patch that is a secondary color formed as a mixed color and an achromatic gray patch that is a tertiary color formed as a mixed color of CMY colored toners are formed. Each color patch has a higher density for each color on the upper side and a lower density on the lower side, and the densities differ in stages. The printing surface TP2f is also referred to as a first surface.

  An identification image for identifying a plurality of patches is displayed on the back surface TP1r. The identification image includes symbols A to H representing a plurality of patch rows arranged two-dimensionally and numbers 1 to 7 representing rows. The back surface TP1r is also called a second surface. The identification image is formed at a position that does not overlap a plurality of patches in order to ensure the visibility.

  According to the show-through test sheets TP2f and TP2r, the user can easily input the show-through states of a plurality of patches from the operation display unit 90 using the symbols A to H and numbers. On the other hand, when the image reading unit 50 is caused to read the back surface TP2r, the image analysis unit 11 can perform analysis using the symbols A to H and numbers. The image analysis unit 11 can set a lightness threshold value or a luminance threshold value based on information input using the symbols A to H and numbers.

  In the setting data adjustment process (step S75), the image analysis unit 11 can store the luminance threshold value and the brightness threshold value in the storage area prepared for the login user in the setting data SD. Thereby, the login user can realize the show-through suppressing process corresponding to his / her sense.

  As described above, according to the image forming apparatus 1 according to the third embodiment, information that can be used by the user or the image analysis unit 11 is printed on the back surface TP2r of the test sheet. The user's discomfort due to the show-through can be appropriately suppressed corresponding to the user's feeling.

  Note that the image analysis unit 11 may be configured so that the use of the setting data SD set for other users can be permitted so that the clerk or secretary can output the supervisor's printed matter.

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

D. Variations:
Modification 1: In the above embodiment, the lightness threshold and the brightness threshold set for each hue or each combination of hue and saturation are used. However, the lightness threshold and brightness set regardless of the hue and saturation. A threshold value may be used.

  Variation 2: In the above embodiment, an image representing the signs A to H and numbers for easily specifying the show-through state of a plurality of patches is formed on the back side of the show-through test sheet. For example, an image storing information such as a QR code (registered trademark) can be displayed. Such an image can include, for example, the density of each patch and other information available for analysis.

  Modification 3: In the above embodiment, cyan, magenta, yellow, and black toners can be used as the colored toners. However, in the present invention, monochrome printing that uses only black toners or cyan, magenta, and yellow toners can be used. It can also be applied to available color printing.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Control part 20 Image forming part 21 Color conversion process part 22 Halftone process part 27 Intermediate transfer belt 29 Exposure part 30c-30k Photosensitive drum for colored toner 30w White toner photosensitive drum 40 Storage part 50 Image reading Unit 60 paper feed cassette 70 housings 100c to 100k color toner development unit 100w white toner development unit 200w white toner supply unit

Claims (7)

An image forming apparatus that uses colored toner and white toner to form an image on a print medium based on image data,
A photosensitive drum for colored toner;
A photosensitive drum for white toner;
A colored toner developing unit that forms a colored toner image on the photosensitive drum for colored toner using the colored toner;
A white toner developing unit that forms a white toner image using the white toner on the white toner photosensitive drum;
Primary transfer of the color toner image from the photosensitive drum for colored toner, and primary transfer of the white toner image from the photosensitive drum for white toner superimposed on the colored toner image to form a composite toner image; An intermediate transfer portion for secondary transfer of the formed synthetic toner image onto a print medium;
A conveying unit that reverses the front and back of the printing medium and supplies the intermediate transfer unit;
A fixing unit for fixing the synthetic toner image secondarily transferred onto the print medium onto the print medium;
A halftone processing unit for generating color toner dot data for forming the color toner dots and white toner dot data for forming the white toner dots;
A patch image representing a plurality of patches having different densities in stages is formed on the first surface of the print medium, and an identification image for identifying the plurality of patches is formed on the back surface of the first surface of the print medium. A test sheet output section formed on a second surface;
A predetermined threshold value is set based on information input using the identification image, and an area where the colored toner image shows through from the area where the colored toner image is formed based on the predetermined threshold value. An image analysis unit to extract;
With
The halftone processing unit generates the white toner dot data so as to form the white toner image in the extracted region. The image forming apparatus according to claim 1,
The predetermined threshold is a luminance threshold;
An image forming apparatus, wherein the image analysis unit calculates a luminance of each pixel represented by the image data, and extracts an area where the luminance is smaller than the luminance threshold as an area where the colored toner image shows through. The image forming apparatus according to claim 1,
The predetermined threshold is a lightness threshold,
The image analysis unit is an image forming apparatus that calculates brightness of each pixel represented by the image data, and extracts an area where the brightness is smaller than the brightness threshold as an area where the colored toner image shows through. The image forming apparatus according to claim 3, wherein
The brightness threshold is set according to the hue,
The image analysis unit calculates the lightness and hue of each pixel represented by the image data, and sets the area where the calculated lightness is smaller than a lightness threshold value set in advance according to the hue as the colored toner. An image forming apparatus that extracts a region where an image shows through. The image forming apparatus according to claim 3, wherein:
The brightness threshold is set according to the saturation,
The image analysis unit calculates the brightness and saturation of each pixel represented by the image data, and the calculated brightness is a region smaller than a brightness threshold set in advance according to the saturation. An image forming apparatus that extracts a colored toner image as a show-through area. The image forming apparatus according to any one of claims 1 to 5,
The halftone processing unit determines in accordance with the luminance or brightness of each pixel represented by the image data such that the lower the brightness or brightness, the thicker the white toner image layer. An image forming method for forming an image on a print medium based on image data using colored toner and white toner,
A colored toner developing step of forming a colored toner image on the photosensitive drum for colored toner using the colored toner;
A white toner developing step of forming a white toner image on the white toner photosensitive drum using the white toner;
Primary transfer of the color toner image from the photosensitive drum for colored toner, and primary transfer of the white toner image from the photosensitive drum for white toner superimposed on the colored toner image to form a composite toner image; An intermediate transfer step of secondarily transferring the formed synthetic toner image onto a print medium;
Inverting the front and back of the print medium, supplying the intermediate transfer step,
A fixing step of fixing the synthetic toner image secondarily transferred onto the print medium onto the print medium;
A halftone processing step of generating color toner dot data for forming the color toner dots and white toner dot data for forming the white toner dots;
A patch image representing a plurality of patches having different densities in stages is formed on the first surface of the print medium, and an identification image for identifying the plurality of patches is formed on the back surface of the first surface of the print medium. A test sheet output process to be formed on a second surface;
A predetermined threshold value is set based on information input using the identification image, and an area where the colored toner image shows through from the area where the colored toner image is formed based on the predetermined threshold value. An image analysis process to be extracted;
With
The halftone processing step includes a step of generating the white toner dot data so as to form the white toner image in the extracted region.