JP6151887B2 - Image forming apparatus - Google Patents

Description

The present invention relates to images forming apparatus that generates a latent image to be visible under certain conditions.

  In recent years, the function of an image forming apparatus for copying an image by image reading and image formation has been improved, and the copying accuracy of the image has been improved, so that a document image such as a document can be copied easily and with high accuracy. In such a high-function image forming apparatus, for example, an illegal copy can be easily created by copying a document that should not be copied, and a highly accurate copy that cannot be distinguished from the original is obtained. be able to. Therefore, in order to prevent unauthorized copying of a document image, a technique for combining a copy prevention pattern or a watermark character with a document image that should be prohibited from being copied has been realized.

  In Patent Document 1, information identifying a person is printed on a base material with visible ink, and information obtained by encoding the person identification information is not absorbed in the visible light wavelength region but is absorbed only in the infrared light wavelength region. ID cards printed with external absorption inks have been proposed. For example, a face photograph image is printed as the person identification information, and a two-dimensional code is printed as the encoded information. This can prevent forgery of the ID card.

  In Patent Document 2, a plurality of first halftone dot regions and second halftone dot regions are arranged on a base material to form a visible image, and the first halftone dot region does not include an infrared absorption characteristic. The second halftone dot region is composed of a second halftone dot region composed of a color material including infrared absorption characteristics and a color material not including infrared absorption characteristics. There has been proposed a halftone dot printed matter having a 2b halftone dot area configured as described above and having a latent image formed by the second a halftone dot area.

JP 2000-309154 A Japanese Patent No. 4142262

  However, since the technique described in Patent Document 1 needs to print encoded information using an infrared absorbing ink that absorbs only the infrared light wavelength region without absorption in the visible light wavelength region, such infrared absorption. A special image forming apparatus for handling ink is required. Therefore, there is a problem that it is difficult to apply this technique to a general image forming apparatus.

  The technology described in Patent Document 2 is based on ink (or toner) of basic four colors of C (cyan), M (magenta), Y (yellow), and K (black) used in a general image forming apparatus. , K ink is a black pigment mainly composed of carbon black and exhibits absorption characteristics over the entire range from the ultraviolet region to the infrared region, whereas the process black with the CMY ink superimposed does not absorb infrared rays. is there. By configuring the 2a halftone dot area with K ink and the other areas with CMY ink process black, when the printed matter is observed with a special device such as an infrared camera, the latent potential formed with K ink Only the image can be visually recognized.

  As in the technique described in Patent Document 2, a latent image is used based on a difference in characteristics between two color materials, a first color material including at least one of CMY and a second color material of K. When forming an image, it is required that the latent image cannot be visually recognized under visible light. For this reason, it is important to optimize the combination of the first color materials and perform color control so as to be the same color as the second color material. However, conventional image forming apparatuses such as printers, copiers, and multi-function machines that employ an electrophotographic method, for example, have insufficient color control as described above, resulting in a color difference that can be recognized by humans. . For this reason, there is a case that the latent image can be visually recognized without using a special device such as an infrared camera, and there is a problem that the performance as the latent image is not sufficient.

The present invention was made in view of such circumstances, and it is an object to provide images forming device that can be generated latent image is low visibility under visible light There is.

The image forming apparatus according to the present invention uses a mixed color gray that includes a plurality of first color materials that reflect infrared rays and a single color gray that includes a second color material that absorbs infrared rays. In the original image , an image processing apparatus for performing image processing for forming an image including the latent image of the single color gray that is visually recognized in an infrared environment , and an image generated by the image processing apparatus are formed on a medium. An image forming apparatus comprising: an image forming unit , wherein the image processing apparatus includes a plurality of color grays that constitute the mixed-color gray so that the mixed-color gray and the single-color gray are substantially the same color under visible light. determining means for determining the concentration of one colorant, for each pixel of the original image C (cyan), M (magenta), Y (yellow), each pixel gray scale value and the latent image of K (black) of the multiplication of the gradation values of the CMYK The Ukoto, and a synthesizing means for synthesizing the original image and the latent image, said image forming means, said first color material and the second coloring material based on the concentration of the determining means has determined And an image synthesized by the synthesizing means is formed .

The image forming apparatus according to the present invention includes a forming process unit for performing a process for forming each color halftone image of the first color material to the image forming unit, the image forming unit by the processing of said formation processing unit Read image acquisition means for acquiring a read image obtained by reading the medium formed by the reading means, the determination means based on the halftone of each color included in the read image acquired by the read image acquisition means, The density of each first color material is determined.

In addition, the image forming apparatus according to the present invention includes a table in which an input gradation and an output gradation are associated with each color of the first color material, and an adjustment unit that performs image gradation adjustment using the table. And the determining means is configured so that a mixing amount of each first color material constituting the mixed color gray becomes a predetermined mixing amount based on a halftone of each color included in the read image acquired by the read image acquiring means. Further, the table is corrected.

The image forming apparatus according to the present invention, a plurality of the first color material mixing different amounts plurality of mixed color gray image, and to form an image including an image of the monochrome gray to said image forming means process And a read image acquisition means for acquiring a read image obtained by reading the medium formed by the image forming means by the reading means. The determination means includes the read image. The density of each first color material is determined based on the plurality of mixed color grays and the single color gray included in the read image acquired by the acquisition unit.

In addition, the image forming apparatus according to the present invention includes a table in which an input gradation and an output gradation are associated with each color of the first color material, and an adjustment unit that performs image gradation adjustment using the table. And the determining means includes a mixing amount of each first color material of the mixed-color gray that is substantially the same color as the single-color gray based on a halftone of each color included in the read image acquired by the read-image acquiring means And the table is corrected so that the mixing amount of each first color material constituting the mixed-color gray becomes the determined mixing amount.

The image forming apparatus according to the present invention, a plurality of the first color material mixing different amounts plurality of mixed color gray image, and to form an image including an image of the monochrome gray to said image forming means process And a selection receiving unit that receives selection of the halftone of the mixed color gray based on the image formed by the image forming unit by the processing of the formation processing unit, and the determination unit includes the selection receiving unit. The density of each first color material is determined on the basis of the selection of the mixed color gray accepted.

In addition, the image forming apparatus according to the present invention includes a table in which an input gradation and an output gradation are associated with each color of the first color material, and an adjustment unit that performs image gradation adjustment using the table. The determining means determines a mixing amount of each first color material of the mixed-color gray that is substantially the same color as the single-color gray based on the selection of the mixed-color gray received by the selection receiving means; The table is corrected so that the mixing amount of each first color material constituting the mixed color gray becomes the determined mixing amount.

In addition, the image forming apparatus according to the present invention includes a halftone image generation unit that generates a halftone image of the mixed-color gray and the single-color gray as an image including the latent image in the original image , and the halftone image And a superimposing unit that superimposes the halftone dot image generated by the generating unit on another image.

  In the present invention, a mixed color gray including a plurality of first color materials (for example, CMY chromatic color materials) that reflect infrared light and a second color material (for example, K achromatic color material) that absorbs infrared light are used. An image including a specific image of a single color gray is formed in the basic image of the mixed color gray and the single color gray using the single color gray included. Further, the image processing apparatus is provided with a means for determining the density of the first color material constituting the mixed-color gray so that the mixed-color gray and the single-color gray become substantially equal colors under visible light. Thereby, as for the formed image, a basic image is visually recognized under visible light, and a specific image is visually recognized under an infrared environment.

In the present invention, an image in which a halftone of each color of the first color material is drawn is formed on a medium such as recording paper by an image forming unit such as a printer, and the formed image is read by a reading unit such as a scanner. read. The image forming unit and the reading unit may be provided in the image processing apparatus, or may be provided in other apparatuses. Further, since the mixing amount of each color of the first color material for making the gray color substantially the same as the single color gray of the second color material is determined according to the characteristics of the image forming means, this is measured and stored in advance. .
Image processing is performed to adjust the gradation of each color of the image using a table or the like for image formation. Therefore, in the present invention, each first color material constituting the mixed-color gray is performed by correcting the table so as to obtain a predetermined mixing amount stored in advance based on the read image obtained by reading the sample image. Determine the concentration.

Further, in the present invention, an image in which a mixed gray of halftones in which the mixing amount of a plurality of first color materials is changed and a monochrome gray is drawn is formed on a medium such as recording paper by an image forming unit such as a printer. The formed image is read by reading means such as a scanner. The image forming unit and the reading unit may be provided in the image processing apparatus, or may be provided in other apparatuses. Based on the read image obtained by reading the sample image, it is possible to check the halftone of the mixed gray of the single color gray and the substantially equal color, and to check the mixing amount of the first color material in the mixed gray of the halftone. Thus, it is possible to determine the mixing amount of the first color material corresponding to the gradation of the single color gray.
Image processing is performed to adjust the gradation of each color of the image using a table or the like for image formation. Therefore, in the present invention, the density of each first color material constituting the mixed color gray is determined by correcting the table so that the mixing amount is determined based on the read image obtained by reading the sample image. Do.

Further, in the present invention, an image in which a mixed gray of halftones in which the mixing amount of a plurality of first color materials is changed and a monochrome gray is drawn is formed on a medium such as recording paper by an image forming unit such as a printer To do. When the user visually examines the formed sample image, it is possible to select a halftone between a single color gray and a substantially mixed color gray. Accordingly, the user selects the mixed gray color halftone, and determines the mixed amount of the first color material corresponding to the gradation of the single color gray by examining the mixed amount of the first color material in the mixed gray color that is the halftone. can do.
Image processing is performed to adjust the gradation of each color of the image using a table or the like for image formation. Therefore, in the present invention, the density of each first color material constituting the mixed color gray is determined by correcting the table so that the mixing amount determined based on the user's selection is obtained.

  Further, in the present invention, a halftone image with mixed color gray and single color gray is generated. This halftone dot image is an image in which a specific image of single color gray is embedded in a basic image of substantially equal color mixture gray and single color gray. By superimposing the generated halftone image and another image, an image in which the security latent image is embedded can be generated by a simple method.

  In the case of the present invention, since the single color gray and the mixed color gray can be made substantially the same color, an image in which a latent image having low visibility under visible light is embedded can be generated. In addition, it is easy to determine the density by forming a sample image and reading the formed image or accepting the user's selection based on the formed image to determine the density of each color constituting the mixed color gray. It is possible to provide an image processing apparatus or an image forming apparatus that can be performed and has high convenience and versatility.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a block diagram illustrating a configuration of an image forming apparatus. 6 is a flowchart illustrating a procedure of image forming processing by the image forming apparatus. It is a schematic diagram for demonstrating a latent image. It is a schematic diagram for demonstrating a latent image. It is a schematic diagram for demonstrating a latent image. It is a schematic diagram for demonstrating a latent image. 4 is a flowchart illustrating a procedure of density determination processing performed by the image forming apparatus according to the first embodiment. It is a schematic diagram which shows an example of a sample image. It is a schematic diagram which shows an example of a K-CMY correlation table. 10 is a flowchart illustrating a procedure of density determination processing performed by the image forming apparatus according to the second embodiment. It is a schematic diagram which shows an example of a sample image. It is a schematic diagram which shows an example of a K-CMY correlation table. 10 is a flowchart illustrating a procedure of density determination processing performed by an image forming apparatus according to a modification of the second embodiment.

(Embodiment 1)
Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof. FIG. 1 is a schematic diagram showing a configuration of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus 1 according to the present embodiment has multiple colors for a predetermined medium such as a sheet (recording paper) according to image data input from an external device such as a PC (Personal Computer) via a network. An apparatus for forming a monochrome image. The image forming apparatus 1 includes an exposure unit 11, developing devices 12a to 12d, photosensitive drums 13a to 13d, cleaner units 14a to 14d, chargers 15a to 15d, an intermediate transfer belt 17, a fixing unit 22, and the like. Yes.

  The image forming apparatus 1 according to the present embodiment adds 4 (black) to cyan (C), magenta (M), and yellow (Y), which are three subtractive primary colors obtained by color separation of a color image. Color image formation using colors can be performed. For this reason, the image forming apparatus 1 includes four developing devices 12a to 12d, photosensitive drums 13a to 13d, cleaner units 14a to 14d, and chargers 15a to 15d corresponding to the respective colors. An image station to be formed is configured. The four image stations are spaced apart by an appropriate length along the moving direction (sub-scanning direction) of the intermediate transfer belt 17.

  The photoconductive drums 13 a to 13 d have a cylindrical shape, and are arranged below the intermediate transfer belt 17 so that the axial direction thereof intersects the moving direction of the intermediate transfer belt 17. The chargers 15 a to 15 d are for charging the surfaces of the photosensitive drums 13 a to 13 d to a predetermined potential. In the illustrated example, a contact type roller charger is mounted on the image forming apparatus 1. However, a contact brush type charger or a charger type charger may be used.

  The exposure unit 11 is configured using a laser scanning unit including a laser irradiation unit and a reflection mirror. However, an EL (Electro Luminescence) or LED (Light Emitting Diode) writing head in which light emitting elements are arranged in an array may be used. The exposure unit 11 irradiates the photosensitive drums 13a to 13d with laser beams modulated by CMYK color image data. As a result, the charged photosensitive drums 13a to 13d are exposed according to the input image data, and electrostatic latent images are formed on the surface of the CMYK color image data. The developing units 12a to 12d store toners of CMYK colors, respectively supply the toner to the surfaces of the photosensitive drums 13a to 13d on which the electrostatic latent images are formed, and develop the electrostatic latent images into toner images. Image. The cleaning units 14a to 14d remove and collect the toner remaining on the surfaces of the photosensitive drums 13a to 13d after development and transfer of the toner image.

  The image forming apparatus 1 also includes intermediate transfer rollers 16a to 16d, an intermediate transfer belt 17, a driving roller 171, a driven roller 172, a cleaning unit 19, an intermediate transfer belt tension mechanism (not shown), and the like. The intermediate transfer rollers 16a to 16d, the driving roller 171, the driven roller 172, and the intermediate transfer belt tension mechanism are for rotating the intermediate transfer belt 17 in a predetermined direction (see an arrow in the drawing). The intermediate transfer belt 17 is disposed above the photosensitive drums 13a to 13d and is stretched between the driving roller 11a and the driven roller 11b. The intermediate transfer rollers 16a to 16d are rotatably supported at positions facing the respective photosensitive drums 13a to 13d with the intermediate transfer belt 17 interposed therebetween. The intermediate transfer rollers 16a to 16d have a polarity (+) opposite to the toner charging polarity (-) in order to transfer the toner image carried on the surface of the photosensitive drums 13a to 13d onto the intermediate transfer belt 17. A transfer bias is applied. The intermediate transfer belt 17 is provided so as to be in contact with the photosensitive drums 13 a to 13 d, and the toner images of the respective colors formed on the photosensitive drums 13 a to 13 d are sequentially superimposed on the outer peripheral surface of the intermediate transfer belt 17. By transferring, a color toner image is formed on the outer peripheral surface of the intermediate transfer belt 11. The intermediate transfer belt 17 is an endless film having a thickness of about 1100 μm to 1150 μm.

  Transfer of the toner image from the photosensitive drums 13 a to 13 d to the intermediate transfer belt 17 is performed by intermediate transfer rollers 16 a to 16 d that are in contact with the inner peripheral surface of the intermediate transfer belt 11. A high voltage transfer bias for transferring the toner image is applied to the intermediate transfer rollers 16a to 16d. The intermediate transfer rollers 16a to 16d are configured by covering a metal (for example, stainless steel) shaft having a diameter of about 18 to 110 mm with a conductive elastic material (for example, EPDM, urethane foam, or the like). A uniform high voltage can be applied to the intermediate transfer belt 17 by this conductive elastic material. Instead of the intermediate transfer rollers 16a to 16d, a brush-like intermediate transfer member can be used.

  Each of the photosensitive drums 13 a to 13 d is visualized according to each color, and the electrostatic image is an input image by being laminated on the intermediate transfer belt 17. The images stacked on the intermediate transfer belt 17 are conveyed to a position facing the transfer roller 21 by the rotation of the intermediate transfer belt 17 and transferred onto a sheet. At this time, the transfer roller 21 presses the intermediate transfer belt 17 with a predetermined nip pressure, and the transfer roller 21 has a voltage for transferring the toner onto the sheet (having a polarity (+) opposite to the toner charging polarity (−)). High voltage) is applied. In order to maintain the nip pressure between the transfer roller 21 and the intermediate transfer belt 17 at a predetermined value, either the transfer roller 21 or the drive roller 171 is made of a hard material (metal or the like), and the other is an elastic roller or the like. The soft material (such as an elastic rubber roller or a foaming resin roller) can be used.

  Toner adhering to the intermediate transfer belt 17 due to contact with the photosensitive drums 13a to 13d or toner remaining on the intermediate transfer belt 17 without being transferred onto the sheet by the transfer roller 21 prevents color mixing in the next step. Therefore, it is removed and collected by the cleaning unit 19. The cleaning unit 19 has, for example, a cleaning blade as a cleaning member that contacts the intermediate transfer belt 17. The intermediate transfer belt 17 in contact with the cleaning member is supported by a driven roller 172 from the opposite side.

  The sheet on which the toner image is transferred is guided to the fixing unit 22 and passes between the heat roller 24 and the pressure roller 25 and is heated and pressed. As a result, the toner image transferred to the paper is fixed on the surface of the paper. The paper on which the toner image is fixed is discharged onto the paper discharge tray 29 by the paper supply roller 27c.

  The image forming apparatus 1 also includes a paper feed tray 20, a manual feed tray 26, a paper discharge tray 29, a paper transport path S, and the like. The paper feed tray 20 is a tray for storing paper used for image formation, and is provided at the lower portion of the image forming apparatus 1. The paper discharge tray 29 is a tray for placing paper on which image formation has been performed face down, and is provided on the upper portion of the image forming apparatus 1. The paper transport path S is for sending the paper stored in the paper feed tray 20 to the paper discharge tray 29 via the transfer roller 21 and the fixing unit 22, and the inside of the image forming apparatus 1 is set in a substantially vertical direction. Has been placed. In the paper transport path S, a transfer roller 21, a fixing unit 22, a registration roller 23, transport rollers 27a to 27h, pickup rollers 28a and 28b, and the like are arranged.

  The transport rollers 27a to 27h are small rollers for promoting and assisting the transport of paper, and a plurality of the transport rollers 27a to 27h are provided along the paper transport path S. The pickup roller 28 a is a pull-in roller that is provided at the end of the paper feed tray 20 and supplies the paper stored in the paper feed tray 20 to the paper transport path S one by one. The registration roller 23 has a function of temporarily holding the sheet conveyed through the sheet conveyance path S and conveying the sheet to the transfer roller 21 at a timing when the leading edge of the toner image on the intermediate transfer belt 17 is aligned with the leading edge of the sheet. ing.

  The fixing unit 22 includes a heat roller 24, a pressure roller 25, and the like. The heat roller 24 and the pressure roller 25 are configured to rotate with a sheet interposed therebetween. The temperature of the heat roller 24 is detected by a temperature detector (not shown), and the temperature of the heat roller 24 is controlled to a predetermined fixing temperature by a printer controller described later. The heat roller 24 heat-presses the paper together with the pressure roller 25 to melt, mix and press the multicolor toner images transferred onto the paper, and heat-fix the paper on the paper.

  In addition, the image forming apparatus 1 is provided with a paper feed tray 20 for storing a large number of sheets in advance. When the user forms an image on a small number of sheets, the image forming apparatus 1 opens and closes the paper feed tray 20. A manual feed tray 26 on which a small number of sheets are placed is provided so as not to be performed. The pickup roller 28a or 28b guides the paper from the paper feed tray 20 or the manual feed tray 26 to the paper transport path S one by one.

  When image formation is performed on only one side of the paper, the paper stored in the paper feed tray 20 is fed by the pickup roller 28a and is transported through the paper transport path S to the registration roller 23 by the transport roller 27a. The toner image is transferred to a sheet of paper by being conveyed to the transfer roller 21 at the timing of matching the leading edge of the toner image on the transfer belt 17. Thereafter, the sheet passes through the fixing unit 22 so that unfixed toner is melted and fixed by heat, and is discharged onto the sheet discharge tray 29 through the conveyance rollers 27b and 27c.

  The paper placed on the manual feed tray 26 is fed by the pickup roller 28b, and is transported through the paper transport path S to the registration roller 23 through the transport rollers 27f, 27e, and 27d. Thereafter, the same processing as that for paper fed from the paper feed tray 20 is performed, and the paper on which the image is formed is discharged to the paper discharge tray 29.

  When image formation is performed on both sides of a sheet, the rear end of the sheet that has passed through the fixing unit 22 after the image formation on one side has been completed by the above processing is stopped by the conveyance roller 27c, and the conveyance roller 27c rotates backward. Is guided to the reverse path provided with the transport rollers 27g and 27h, and then the back side image is formed through the registration roller 23 and discharged to the paper discharge tray 29.

  The four-color toners of CMYK used by the image forming apparatus 1 are manufactured with a general prescription. Color materials used for these toners are organic pigments having absorption and reflection characteristics in the visible light region. For example, a cyan pigment is a copper phthalocyanine pigment, a magenta pigment is a dimethylquinacridone pigment, a yellow pigment is a benzimidazolone pigment, a black pigment is a carbon black pigment, both of which are It is a common organic material that is commercially available. Black pigments have absorption characteristics not only in the visible light region but also in the infrared region. For this reason, in an image formed using four color toners of CMYK, a portion formed of K toner is visually recognized under infrared rays.

  FIG. 2 is a block diagram illustrating a configuration of the image forming apparatus 1. The image forming apparatus 1 receives image data such as characters, graphics, or photographs input from an external device such as a PC 2 via a network in the form of a page description language, and uses it for image formation based on the received image data. It is a device such as a printer that generates data and forms an image. The PC 2 is connected to the scanner 3, acquires a read image obtained by the reading process of the scanner 3, and can give the read image to the image forming apparatus 1. The image forming apparatus 1 includes a printer controller 100, a print engine 110, an operation panel 120, and the like. The print engine 110 and the operation panel 120 are connected to the printer controller 100 and exchange data with the printer controller 100. The printer controller 100 is connected to an external device such as a PC 2 via a network.

  The printer controller 100 includes a central processing unit (CPU) 101, a random access memory (RAM) 102, a hard disk drive (HDD) 103, a network controller 104, a video controller 105, and the like. The CPU 101 performs control processing for each unit in the printer controller 100. The RAM 102 temporarily stores various types of information such as image data received from an external device, execution data generated based on the image data, and density correction information. The HDD 103 stores image data, execution data, characteristics of the print engine 110 (for example, characteristics such as density, gradation, or dot reproduction) data, and the like. The network controller 104 transmits / receives data to / from an external device such as the PC 2 via the network. The video controller 105 controls the operation of the print engine 110.

  The print engine 110 includes an image forming unit 111, a density sensor 112, a temperature / humidity sensor 113, and the like. The image forming unit 111 performs a process of forming an image on a sheet, and controls the operation of each mechanism shown in FIG. The density sensor 112 and the temperature / humidity sensor 113 are used when the image forming apparatus 1 is calibrated. The operation panel 120 receives an operation related to a user instruction such as an instruction to form an image stored in the HDD 103 and notifies the printer controller 100 of the operation.

  FIG. 3 is a flowchart showing a procedure of image forming processing by the image forming apparatus 1. When the user issues an image formation instruction of the original on the PC 2, an image is input to the image forming apparatus 1 from a printer driver or the like of the PC 2. The image forming apparatus 1 receives image input from the network controller 104 by receiving image data from the PC 2 (step S1). The image data input at this time is data represented by three colors of R (red), G (green), and B (blue).

  Next, the image forming apparatus 1 performs a color conversion process for converting the input RGB image data into CMYK image data (step S2). In the color conversion process, the CPU 101 performs a color conversion operation based on the color table of the ICC profile using a color management module installed in the firmware of the printer controller 100.

  Next, the image forming apparatus 1 performs gradation correction processing on the CMYK image data obtained by the color conversion processing (step S3). In the gradation correction processing, for example, low contrast processing that emphasizes output gradation reproducibility is performed by the CPU 101 using a gradation correction table stored in advance in the HDD 103. Thereafter, the image forming apparatus 1 performs halftone adjustment processing (step S4). The halftone adjustment process is a process that is performed in order to always maintain a constant state of an image to be formed by correcting variations in each color due to machine difference variations, temporal changes, environmental changes, and the like of the print engine 110 and is stored in the HDD 103 in advance. The CPU 101 executes the halftone table. Since these processes are general processes, a detailed description of the processing procedure is omitted. However, for example, the correspondence between the input gradation and the output gradation for each color of CMYK is stored in the halftone table, and the process of step S3 is performed. Processing for converting the gradation value of the processed image data according to the intermediate table can be performed. The CMYK image data obtained by the above steps S1 to S4 is stored in the RAM 102.

  The image forming apparatus 1 according to the present embodiment has a function of generating an image in which a latent image is embedded in an original image such as a document created by a user and forming the generated image. Although details of the latent image will be described later, the latent image is input from the PC 2 together with an image such as a document or stored in the HDD 103 in advance. When the user gives an instruction to embed a latent image, the image forming apparatus 1 performs the same processing as steps S1 to S4 on the latent image. However, the gradation correction table used in the gradation correction process in step S3 and the halftone table used in the halftone adjustment process in step S4 may be those for a latent image. The image data of the CMYK latent image obtained in the processes of steps S1 to S4 is stored in the RAM 102.

  Next, the image forming apparatus 1 determines whether or not there is a latent image (step S5). If there is a latent image (S5: YES), the original image such as a document and the latent image are read from the RAM 102 and combined. Processing is performed (step S6). In the image compositing process, calculation processing of pixels of the original image and pixels of the latent image is performed at the designated position of the original image. As the arithmetic processing, it is preferable to multiply the pixel values of both pixels. After performing the image composition process, the image forming apparatus 1 forms the image by providing the image data after the composition to the image forming unit 111 of the print engine 110 (step S7), and ends the process. If there is no latent image (S5: NO), the image forming apparatus 1 provides the data stored in the RAM 102 to the image forming unit 111 without performing the composition process, and performs image formation (step S7). Exit.

  In the above description, the image forming apparatus 1 performs all the processes of steps S1 to S6 in the flowchart shown in FIG. 3, but the present invention is not limited to this. A part or all of the processes in steps S1 to S6 may be performed in advance on the PC 2, and processed image data may be input to the image forming apparatus 1 to form an image.

  4 to 7 are schematic diagrams for explaining the latent image. In each figure, an enlarged image of a part of the image shown on the upper side is shown on the lower side. The latent image handled by the image forming apparatus 1 according to the present embodiment is a halftone dot image represented by a set of gray halftone dots as shown in FIG. In addition, the shape, size, arrangement, and the like of the halftone dots shown in the figure are merely examples, and the present invention is not limited to this. In the illustrated example, rectangular halftone dots having the same vertical and horizontal sizes (number of pixels) are used. Each pixel constituting the halftone dot is gray (or black), but a K single-color gray pixel and a CMY mixed-color gray pixel are mixed. Black shall be included in gray.

  FIG. 5 is an image obtained by extracting a K single-color gray portion from the halftone image shown in FIG. The image shown in FIG. 5 is an image obtained when the image shown in FIG. 4 is viewed under infrared rays, and becomes a latent image. Each halftone dot may be partly a monochrome gray pixel, or all may be a monochrome gray pixel. By changing the ratio of monochrome gray pixels included in the halftone dots, it is possible to realize area gradation expression. In the example shown in the lower part of FIG. 5, the dark portion of the image is composed of halftone dots of six single-color gray pixels, and the light portion of the image is composed of halftone dots of one single-color gray pixel. 5 constitutes the image shown on the upper side. The shape, size, arrangement, and the like of the monochrome gray dot are not limited to those shown in FIG.

  FIG. 6 is an image obtained by extracting the CMY mixed color gray portion from the halftone image shown in FIG. Each pixel constituting the halftone dot is composed of CMY mixed in a mixing amount determined so as to be the same color as a monochromatic gray under visible light. The image shown in FIG. 6 corresponds to an image obtained by subtracting the image shown in FIG. 5 from the image shown in FIG. 4, but the infrared ray is reflected under the infrared ray, and the image cannot be visually recognized.

  FIG. 7 is a composite image obtained by superimposing the halftone dot image shown in FIG. 4 on an image such as a document created by the user, and is an image obtained by the process in step S6 of the flowchart shown in FIG. Any method may be used for superimposing the two images, but it is preferable to use a multiplication process in order to retain the pixel value of the gray dot. When the synthesized image shown in FIG. 7 is viewed under infrared rays, only K single gray is visually recognized and becomes the image shown in FIG. 5 (however, the original image on which the latent image is superimposed (image such as a document) is K (It is assumed that monochrome gray is not used, and the image is a CMY color or monochrome image).

  As described above, the image forming apparatus 1 according to the present embodiment generates an image in which a latent image that is visible only under infrared rays is superimposed on an image such as a document, and forms the generated image on a sheet and outputs it. be able to. The formed image is visually recognized as an image such as a document under visible light, and only the latent image is visible under infrared light. However, in order that the latent image is not visually recognized under visible light, it is necessary that the K single color gray and the CMY mixed color gray be the same color under visible light. Therefore, the image forming apparatus 1 needs to appropriately determine the density of each color of CMY so that the mixed-color gray and the single-color gray are the same color. Therefore, the image forming apparatus 1 has a function of determining the density of each color of CMY, and performs density determination, for example, when the apparatus is maintained or when toner is replaced. Hereinafter, the density determination processing for each color of CMY constituting the mixed color gray by the image forming apparatus 1 will be described.

  FIG. 8 is a flowchart illustrating a procedure of density determination processing performed by the image forming apparatus 1 according to the first embodiment. In order to determine the mixing amount, the image forming apparatus 1 generates a sample image for each color of CMYK and forms the generated sample image (step S21). FIG. 9 is a schematic diagram illustrating an example of a sample image. The sample image is a predetermined image, for example, image data is stored in the HDD 103. The sample image is an image in which a plurality of halftones are drawn for each color of CMYK, and its layout, gradation, and the like are determined in advance. In the illustrated sample image, a plurality of rectangles that are long in the horizontal direction of the paper are drawn for each color of CMYK, and colors are given to the rectangles so that the gradation of each color gradually changes in the horizontal direction. Each color is expressed in halftone by changing the dot area ratio. The illustrated sample image is an example, and the present invention is not limited to this.

  The user reads the paper on which the sample image is formed by the scanner 3 and gives the read image obtained by the reading to the image forming apparatus 1 from the PC 2 via the network. In the case where the image forming apparatus 1 is configured to include a scanner such as a so-called multifunction machine, the sample image may be read using the scanner included in the image forming apparatus 1. The scanner 3 is corrected in advance so that the reading has a linear characteristic, and a read image having an RGB value corresponding to the gradation of each color of the sample image is obtained. The image forming apparatus 1 acquires a read image of the sample image given in this way (step S22). The image forming apparatus 1 stores the acquired read image in the RAM 102.

  Next, the image forming apparatus 1 performs K gradation correction processing (step S23). In the K gradation correction process, the preset K gradation of the sample image is compared with the K gradation of the read image obtained by reading, and an appropriate input value-output value correspondence is calculated. To do. The image forming apparatus 1 calculates the input value-output value correspondence, for example, for 16 points in the halftone of the K drawn in the sample image, and outputs the output value for the input value by calculation such as linear interpolation for the remaining points. Is calculated. The image forming apparatus 1 stores the calculated K input value-output value correspondence in the HDD 103 as a halftone table and uses it in the halftone adjustment process in step S4 of the flowchart of FIG.

  The density of each CMY color for making the CMY mixed color gray and the K single color gray equal is determined uniquely according to the output characteristics of the print engine 110. Therefore, the correspondence relationship between the K density and the CMY mixture amount is examined in advance and stored in the HDD 103 as a K-CMY correlation table. FIG. 10 is a schematic diagram showing an example of the K-CMY correlation table, and shows the correspondence between K and each color of CMY in a graph. The image forming apparatus 1 reads the K-CMY correlation table from the HDD 103 (step S24).

  Next, the image forming apparatus 1 performs CMY tone correction based on the K-CMY correlation table and the read image (step S25). In the CMY gradation correction, the gradation of each CMY color set in the K-CMY correlation table is compared with the gradation of each CMY color of the read image, and an appropriate input value−output value for each CMY color. The correspondence of is calculated. For example, the image forming apparatus 1 can obtain the actual density output for one gradation of K from the halftone table created in step S23, and the density of each color of CMY corresponding to the density of K. Since it can be acquired from the K-CMY correlation table, the correspondence between the input value and the output value for each color of CMY may be calculated based on the read image so that the density acquired in this way becomes an actual output. . The image forming apparatus 1 calculates an input value-output value correspondence for, for example, each of 16 CMY halftones, and calculates an output value for the input value for the remaining points by an operation such as linear interpolation. The image forming apparatus 1 stores the calculated input value-output value correspondence of each color of CMY in the HDD 103 as a halftone table, and uses it in the halftone adjustment process in step S4 of the flowchart of FIG.

  By these processes, the density of each color of CMY of the mixed color with respect to the K monochrome gray is appropriately determined, and by performing the halftone adjustment process on the latent image using the obtained halftone table, The density of CMY is appropriately controlled so that the mixed color of CMY becomes the same color.

  The image forming apparatus 1 having the above configuration forms a sample image in which halftones of each color of CMYK are drawn, and based on the read image obtained by reading this sample image, the single color gray of K and the mixed color of CMY are visible. By adopting a configuration in which the CMY density is determined so as to be the same color under light, an appropriate density according to the characteristics of the print engine 110 can be determined. As a result, an image including a latent image that is not visually recognized under visible light can be formed.

  In the present embodiment, the image forming apparatus 1 is configured not to include a scanner, but is not limited thereto, and may be configured to include a scanner. The image forming apparatus 1 is configured to use toner as a color material. However, the present invention is not limited to this. The image forming apparatus 1 may be an image forming apparatus that forms an image using other color materials such as ink. Further, although the image forming apparatus 1 performs the density determination process shown in FIG. 8, the present invention is not limited to this, and this process is performed by another apparatus such as the PC 2 and the processing result is given to the image forming apparatus 1. It may be a configuration.

(Embodiment 2)
The image forming apparatus 1 according to the first embodiment is configured to automatically determine the CMY density based on the read image obtained by reading the sample image with the scanner 3. On the other hand, the image forming apparatus 1 according to the second embodiment has a configuration in which the density of CMY is determined by a user visually confirming a sample image and inputting the result to the image forming apparatus 1.

  FIG. 11 is a flowchart illustrating a procedure of density determination processing performed by the image forming apparatus 1 according to the second embodiment. In order to determine the density, the image forming apparatus 1 generates a sample image in which a single color gray of K and a mixed color of CMY are drawn, and forms the generated sample image (step S31). FIG. 12 is a schematic diagram illustrating an example of a sample image. The sample image is a predetermined image, for example, image data is stored in the HDD 103. The sample image is an image in which one gradation of K monochromatic gray and a plurality of CMY mixed grays with different amounts of mixture are drawn, and its layout, gradation (density), etc. are predetermined. Yes. The monochrome gray of K expresses the gradation by changing the halftone dot area ratio, and the mixed color gray of CMY expresses the gradation by changing the mixing amount by overlapping the halftone dot area ratio of each color. Is.

  In the illustrated sample image, 125 mixed-tone grays are drawn for a single-color gray of K = 70%. The mixed color gray is obtained by calculating in advance the mixing amount of CMY that becomes a color close to a single gray, and increasing or decreasing the density of each color based on the calculated mixing amount. In the example shown in the figure, the mixed gray color close to the single color gray color with K = 70% is a case where C = 77%, M = 68%, and Y = 63%. Therefore, using these concentrations as a reference, 5 × 5 × 5 × 5 = 125 mixing amounts are considered for each color in consideration of the five types of reference concentration and −4%, −2%, + 2%, and + 4% of the concentration. Is generated. Although the illustrated sample image relates to a monochrome gray of K = 70%, a plurality of sample images under different conditions such as K = 80%, 90%, 100%, etc. are generated in the same manner (not shown). To do). However, the illustrated sample image is an example and is not limited thereto.

  The user of the image forming apparatus 1 visually confirms the sample image formed on the paper, selects a mixed-color gray having the closest density, color, etc. to one single-color gray drawn in the sample image, and operates it. The density of the mixed color gray selected on the panel 120 is input. Note that the user selects mixed gray for a plurality of sample images. The image forming apparatus 1 accepts a user selection based on the sample image on the operation panel 120 (step S32).

  Next, the image forming apparatus 1 generates a K-CMY correlation table based on the received user selection (step S33). FIG. 13 is a schematic diagram showing an example of the K-CMY correlation table, and shows the correspondence between K and each color of CMY in a graph. In this example, sample images are generated and selected for four conditions of K = 70%, 80%, 90%, and 100%, and the image forming apparatus 1 performs linear interpolation or the like other than these four conditions. Interpolate by processing.

  Thereafter, the image forming apparatus 1 performs CMY tone correction based on the K-CMY correlation table (step S34). In the CMY tone correction, the density of each color of CMY with respect to the density of K is determined so that the correspondence relationship of the K-CMY correlation table is obtained, and the input value-output value of the halftone table is set so as to be the determined density. Correct the correspondence. The image forming apparatus 1 stores the corrected halftone table in the HDD 103 and uses it in the subsequent halftone adjustment processing.

  With these processes, the CMY density is appropriately set, and the halftone adjustment process is performed on the latent image using the obtained halftone table, so that the K single color gray and the CMY mixed color gray become the same color. In addition, the concentration of CMY is appropriately controlled.

  The image forming apparatus 1 according to the second embodiment having the above-described configuration is configured such that the user visually confirms the sample image and selects a mixed-color gray that is close to a single-color gray, and therefore does not include the scanner 3 or uses the scanner 3. Even if this is not possible, it is possible to determine the density of each CMY color of mixed color gray.

(Modification)
The image forming apparatus 1 according to the above-described second embodiment has a configuration in which the user visually confirms the sample image shown in FIG. 12, but is not limited to this, and the sample image is read by the scanner 3. The image forming apparatus 1 may determine the mixing amount of the mixed color gray based on the read image. FIG. 14 is a flowchart illustrating a procedure of density determination processing performed by the image forming apparatus 1 according to the modification of the second embodiment. In order to determine the density, the image forming apparatus 1 according to the modification generates a sample image (see FIG. 12) in which a single color gray and a plurality of mixed color grays are drawn, and forms the generated sample image (step) S41).

  The user reads the paper on which the sample image is formed by the scanner 3 and gives the read image obtained by the reading to the image forming apparatus 1 from the PC 2 via the network. The image forming apparatus 1 acquires a read image of the sample image given in this way (step S42). Next, the image forming apparatus selects a mixed-color gray close to the K single-color gray based on the acquired read image (step S43), and generates a K-CMY correlation table based on the mixed amount of CMY of the selected mixed-color gray. (Step S44). Thereafter, the image forming apparatus 1 performs CMY tone correction based on the K-CMY correlation table (step S45).

  In this way, the sample image may be read by the scanner 3 instead of being visually confirmed by the user. When the image forming apparatus 1 is equipped with a scanner, the configuration of the modified example is suitable. is there.

  Since the other configuration of the image forming apparatus 1 according to the second embodiment is the same as the configuration of the image forming apparatus 1 according to the first embodiment, the same portions are denoted by the same reference numerals and detailed description is given. Is omitted.

  In the first and second embodiments, the sample image and the K-CMY correlation table are assumed on the assumption that the image forming apparatus 1 handles a color image or a grayscale image in which the gradation of each color is represented by 8 bits. The configuration of the above and the procedure of the processing using these have been described. However, it may be configured to handle a binary image (monochrome image) whose gradation is represented by 1 bit. In this case, only the maximum density point for each color is generated and the halftone table is generated. Processing such as correction may be performed. The sample image is preferably formed by dithering a halftone image, and the halftone dot of the sample image is preferably the same shape as the halftone dot shown in FIG.

1 Image forming apparatus 2 PC
3 Scanner (reading means)
DESCRIPTION OF SYMBOLS 11 Exposure unit 12a-12d Developing device 13a-13d Photosensitive drum 14a-14d Cleaner unit 15a-15d Charger 16a-16d Intermediate transfer roller 17 Intermediate transfer belt 20 Paper feed tray 21 Transfer roller 22 Fixing unit 23 Registration roller 24 Heat roller 25 Pressure roller 27a to 27h Conveying roller 28a, 28b Pickup roller 29 Paper discharge tray 100 Printer controller (image processing apparatus)
101 CPU (determination unit, formation processing unit, adjustment unit, halftone image generation unit, superimposition unit)
102 RAM
103 HDD
104 Network controller (read image acquisition means)
105 Video Controller 110 Print Engine 111 Image Forming Unit (Image Forming Unit)
112 Concentration sensor 113 Temperature / humidity sensor 120 Operation panel (selection accepting means)

Claims (8)

A mixed color gray including a plurality of first color materials that reflect infrared rays and a single color gray including a second color material that absorbs infrared rays are used in an original image of the mixed color gray and the single color gray in an infrared environment. An image forming apparatus comprising: an image processing apparatus that performs image processing for forming an image including a latent image of the monochrome gray that is visually recognized ; and an image forming unit that forms an image generated by the image processing apparatus on a medium. Because
The image processing apparatus includes:
Determining means for determining a density of each of the plurality of first color materials constituting the mixed-color gray so that the mixed-color gray and the single-color gray are substantially equal in visible light;
Wherein each pixel in the original image C (cyan), M (magenta), Y (yellow), by performing a multiplication of tone value and the tone value of CMYK of each pixel of the latent image of K (black) And combining means for combining the original image and the latent image .
The image forming unit forms an image synthesized by the synthesizing unit using the first color material and the second color material based on the density determined by the determining unit . And forming processing means for performing processing for forming each color halftone image of the first color material to the image forming means,
A read image acquisition means for acquiring a read image obtained by reading the medium formed by the image forming means by the processing of the formation processing means with a reading means;
2. The determination unit according to claim 1, wherein the determination unit determines a density of each first color material based on a halftone of each color included in the read image acquired by the read image acquisition unit. Image forming apparatus . A table in which an input gradation and an output gradation are associated with each color of the first color material;
Adjusting means for adjusting the gradation of the image using the table,
The determination unit is configured so that, based on a halftone of each color included in the read image acquired by the read image acquisition unit, the mixing amount of each first color material constituting the mixed color gray becomes a predetermined mixing amount. The image forming apparatus according to claim 2, wherein the table is corrected. A plurality of said first color material mixing different amounts plurality of mixed color gray image, and a form processing means for performing processing for forming an image including an image of the monochrome gray to said image forming means,
A read image acquisition means for acquiring a read image obtained by reading the medium formed by the image forming means by the processing of the formation processing means with a reading means;
The determining means determines the density of each first color material based on the plurality of mixed color grays and the single color gray included in the read image acquired by the read image acquiring means. The image forming apparatus according to claim 1. A table in which an input gradation and an output gradation are associated with each color of the first color material;
Adjusting means for adjusting the gradation of the image using the table,
The determining unit determines a mixing amount of each first color material of the mixed color gray that is substantially the same color as the single-color gray based on a halftone of each color included in the read image acquired by the read image acquisition unit. The image forming apparatus according to claim 4, wherein the table is corrected so that a mixing amount of each first color material constituting the mixed color gray becomes a determined mixing amount. A plurality of said first color material mixing different amounts plurality of mixed color gray image, and a form processing means for performing processing for forming an image including an image of the monochrome gray to said image forming means,
Selection accepting means for accepting selection of the halftone of the mixed color gray based on the image formed by the image forming means by the processing of the formation processing means,
The image forming apparatus according to claim 1, wherein the determining unit determines a density of each first color material based on the selection of the mixed color gray received by the selection receiving unit. A table in which an input gradation and an output gradation are associated with each color of the first color material;
Adjusting means for adjusting the gradation of the image using the table,
The determining unit determines a mixing amount of each first color material of the mixed color gray that is substantially the same color as the single color gray based on the selection of the mixed color gray received by the selection receiving unit, and determines the mixed color gray The image forming apparatus according to claim 6, wherein the table is corrected so that a mixing amount of each of the first color materials to be configured becomes a determined mixing amount. Halftone image generation means for generating a halftone image by the mixed color gray and the single color gray as an image including the latent image in the original image ;
The image forming apparatus according to claim 1, further comprising: a superimposing unit that superimposes the halftone dot image generated by the halftone dot image generating unit on another image.