JP2007081750A - Image forming apparatus, its method, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of outputting a tint block image with little visual density difference between a latent image and a background, and to provide its method and a program. <P>SOLUTION: The image forming apparatus 100 includes a photosensitive body 1, a patch detector 51, and a control unit 22. The gradation patches 801, 802 of screens to be used for the latent image and the background are respectively generated on the photosensitive body 1 with the use of the LED of the patch detector 51. Then, the density sensor of the patch detector 51 measures the densities of the gradation patches 801, 802 which are generated on the photosensitive body 1. The control unit 22 determines a signal level α corresponding to the density A of the latent image, and a signal level β corresponding to the density B of the background part respectively, based on the measured densities of the gradation patches 801, 802. The control unit 22 outputs the image including the tint block image, based on the two signal levels α, β. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, a method thereof, and a program, and more particularly to an image forming apparatus, a method thereof, and a program for printing a forgery-suppressing tint block on the background of a document.

  To prevent easy copying of important documents such as receipts, securities, certificates, etc., characters and images (hereinafter referred to as “latent images”) such as “copies” appear when copied. Some have anti-counterfeiting background patterns printed on the background.

  The forgery-inhibited tint block is composed of two areas having substantially the same density, an area where dots remain after copying (hereinafter referred to as “latent image portion”) and an area where dots disappear after copying (hereinafter referred to as “background portion”). It is configured. Since the latent image portion and the background portion have substantially the same density, it is visually unknown that the latent image that is a character or an image is hidden.

  For example, the latent image part is composed of a clustered dot in which each dot is concentrated, and the background part is composed of dots in which each dot is dispersed. Can produce.

  As shown in FIG. 22, the latent image portion 2201 is arranged with a plurality of dots concentrated, and the background portion 2202 is arranged with a plurality of dots dispersed.

  Generally, a copying machine has a limited image reproduction capability depending on the input resolution and output resolution of a copy document. Therefore, if a document including isolated minute dots exceeding the limit of the image reproduction capability of the copying machine is copied, the minute dots cannot be reproduced. In a manuscript including a forgery-inhibited tint block, dispersed dots constituting the background portion cannot be reproduced by copying, and concentrated dots constituting the latent image portion can be reproduced by copying, so that the latent image emerges by copying.

  Conventionally, printing paper manufacturers have previously printed a copy-forgery-inhibited pattern including a latent image on dedicated paper and sold it as copy-proof paper. In recent years, a technique for creating a forgery-inhibited background pattern and outputting a document in which the forgery-inhibited background pattern is arranged in the background by a laser printer (hereinafter referred to as “on-demand background pattern output method by a printer”) has been realized (for example, Patent Document 1).

  With this on-demand copy-forgery-inhibited pattern output method using a printer, it is possible to print a document with forgery-suppressed copy-forgery-inhibited patterns placed on the background using plain paper. The cost can be greatly reduced. In addition, the user can generate a tint block image including an arbitrary latent image.

Also, in order to correct the gradation of the printer, the gradation patch on the photoconductor or intermediate is read and fed back to the γ-LUT, or the gradation pattern is output to the recording paper, and the output is read by the reader. There is known a method for correcting the gray scale characteristics (see, for example, Patent Document 2).
JP 2001-197297 A Japanese Patent No. 3618777

  However, in the above-described on-demand background pattern output method using a printer, the density of the latent image portion and the density of the background portion vary depending on the printer engine characteristics, the printing environment such as temperature and humidity, and the state of the output paper. . Accordingly, it is necessary to appropriately adjust the density of the latent image portion and the background portion of the copy-forgery-inhibited pattern image so that the print density of the latent image portion and the background portion of the copy-forgery-inhibited pattern image is substantially equal and the latent image portion emerges after copying. .

  In this specification, a parameter that determines the print density of the background portion and the latent image portion of the copy-forgery-inhibited pattern image when generating the copy-forgery-inhibited pattern image is referred to as a “background pattern density parameter”. As a method of searching for the tint block density parameter, trial printing is performed before the document and the tint block image are synthesized. The density of the background pattern used to generate a copy-forgery-inhibited pattern image by visually searching for a copy-forgery-inhibited pattern image in which the latent image area and background area have almost the same density from the test print, and the latent image emerges after copying with a copier. A method for determining a parameter as an optimum tint block parameter is generally used. Thereafter, a copy-forgery-inhibited pattern image is generated based on the determined optimum copy-forgery-inhibited pattern density parameter.

  However, in the test printing method described above, taking into account printer engine characteristics and the like, trial printing is performed with a combination of a large number of background pattern density parameters in a relatively wide range from a light density to a dark density, and an optimum background pattern density parameter is determined. Must.

  In addition, the output value of the tint block image can be determined from the obtained gradation characteristic data by the method of correcting the gradation characteristic as described in Patent Document 2, but the gradation characteristic of the printer depends on the number of prints and the standing time. Since it changes, an appropriate copy-forgery-inhibited pattern image is not always obtained.

  An object of the present invention is to provide an image forming apparatus and method, and a program capable of outputting a tint block image having a small visual density difference between a latent image portion and a background portion.

  In order to achieve the above object, the image forming apparatus according to claim 1 is an image forming apparatus that prints a tint block image including a latent image portion and a background portion, and the density of the latent image portion and the density of the background portion. Correction means for correcting at least one of the gradation for the latent image portion and the gradation for the background portion so that each has a predetermined density, and the latent image portion based on the corrected gradation Output means for outputting the image signal for image and the image signal for the background portion, and printing means for printing the copy-forgery-inhibited pattern image based on each image signal.

  9. The image forming apparatus according to claim 8, wherein the image forming apparatus has two image forming modes: a normal image mode for forming a normal image and a tint block image mode for forming a tint block image including a latent image portion and a background portion. A gradation pattern forming means for forming a first gradation pattern on the image carrier or recording paper; and a reading means for reading the density of the first gradation pattern formed on the image carrier or recording paper; A changing unit that changes an image forming condition based on the read density; and an image forming unit that forms an image based on the image forming condition, and the gradation pattern forming unit is configured to select a copy-forgery-inhibited pattern image mode. A second gradation pattern is formed on the image carrier or recording paper.

  11. The image forming method according to claim 10, wherein an image forming method for printing a tint block image including a latent image portion and a background portion is configured such that the density of the latent image portion and the density of the background portion are respectively predetermined. A correction step for correcting at least one of the gradation for the latent image portion and the gradation for the background portion, and the image signal for the latent image portion and the background portion based on the corrected gradation Output steps for outputting the image signals, and a printing step for printing the copy-forgery-inhibited pattern image based on the image signals.

  The image forming method according to claim 17 is an image forming method having two image forming modes: a normal image mode for forming a normal image, and a tint block image mode for forming a tint block image including a latent image portion and a background portion. A gradation pattern forming step for forming a first gradation pattern on the image carrier or recording paper; and a reading step for reading the density of the first gradation pattern formed on the image carrier or recording paper; A change step of changing an image formation condition based on the read density; and an image formation step of forming an image based on the image formation condition, wherein the gradation pattern formation step is performed when the copy-forgery-inhibited pattern image mode is selected. A second gradation pattern is formed on the image carrier or recording paper.

  The program according to claim 19 is a program executed by an image forming method for printing a tint block image including a latent image portion and a background portion, and the density of the latent image portion and the density of the background portion are respectively set to predetermined densities. As described above, a correction module that corrects at least one of the gradation for the latent image portion and the gradation for the background portion, the image signal for the latent image portion based on the corrected gradation, and the An output module that outputs an image signal for a background portion, and a print module that prints the copy-forgery-inhibited pattern image based on each image signal.

  According to the present invention, at least one of the gradation for the latent image portion and the gradation for the background portion is corrected so that the density of the latent image portion and the density of the background portion become predetermined densities. A tint block image with a small visual density difference between the image portion and the background portion can be output.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
FIG. 1 is a diagram schematically showing an internal configuration of an image forming apparatus according to a first embodiment of the present invention.

  1, the image forming apparatus 100 includes an image scanner unit 18, an A / D converter 21, a control unit 22, a laser driver 24, a semiconductor laser 20, a polygon mirror 28, and a mirror 17e.

  The image forming apparatus includes a photosensitive member 1, a scorotron primary charger 2, a developing device 4, a surface potential sensor 41, a transfer roller 8, a cleaning device 13, a pre-exposure lamp 30, a fixing device 12, a charging control unit 50, and the like. A patch detection unit 51 is provided.

  The image scanner unit 18 includes a document glass table 14, an illumination lamp 16, mirrors 17 a, 17 b and 17 c, a lens 17 d, and a photoelectric conversion element 19.

  The illumination lamp 16 scans the document 15 placed on the document glass table 14. The mirrors 17a, 17b, and 17c guide reflected light from the document 15 scanned by the illumination lamp 16 to the lens 17d. The lens 17 d forms an image of the reflected light from the document 15 on the photoelectric conversion element 19. The photoelectric conversion element 19 converts the reflected light from the imaged document 15 into an electric signal and outputs it to the A / D converter 21.

  The A / D converter 21 digitizes the electrical signal output from the photoelectric conversion element 19. The control unit 22 converts the electrical signal digitized by the A / D converter 21 into an image signal of 256 gradations from 0 (00 hex) to 255 (FF hex) in proportion to the image density, and outputs it to the laser driver 24. To do.

  The photoconductor 1 is provided with a photoconductive layer on a cylindrical conductive substrate, and is rotatably supported in an arrow direction. The scorotron primary charger 2 charges the surface of the photoreceptor 1.

  The laser driver 24 modulates the light emission of the semiconductor laser 20 in accordance with the image signal output by the control unit 22. The semiconductor laser 20 irradiates the photosensitive member 1 with laser light modulated in accordance with the image signal via the polygon mirror 28 and the mirror 17e, and electrostatic latent image is charged on the photosensitive member 1 charged by the scorotron primary charger 2. Form an image.

  The developing device 4 attaches toner to the electrostatic latent image formed on the photoconductor 1 to form a toner image on the photoconductor 1. The transfer roller 8 transfers the toner image formed on the photoreceptor 1 onto the recording paper P.

  The cleaning device 13 removes residual toner on the photoreceptor 1 after the toner image is transferred. The pre-exposure lamp 30 removes residual charges on the photoreceptor 1.

  The recording paper P onto which the toner image has been transferred is separated from the photoreceptor 1 and then conveyed to the fixing device 12. The fixing device 12 fixes the toner image on the surface of the conveyed recording paper P, and discharges the recording paper P on which the image is formed to the outside of the image forming apparatus.

  Some photoreceptors 1 have good charging ability and others have poor charging ability due to manufacturing variations. Furthermore, the charging ability of the photosensitive member 1 also changes due to changes in the discharge characteristics of the scorotron primary charger 2 due to long-term use and changes in the usage environment of the image forming apparatus.

  The surface potential sensor 41 detects the surface potential of the photoconductor 1 in the vicinity of the developing position 4 and outputs a signal to the charge control unit 50 in order to absorb variations in the charging ability of the photoconductor 1. Based on the signal output from the surface potential sensor 41, the charging controller 50 changes the voltage applied to the grid of the primary charger 2 so as to keep the surface potential of the photoreceptor 1 at a desired potential.

  The patch detection unit 51 includes an LED for forming a reference patch on the photoconductor 1 and a density sensor that reads a reflected light amount of the patch formed on the photoconductor 1. Based on the read reflected light amount of the patch on the photoreceptor 1, the toner adhesion amount on the photoreceptor 1 is calculated, and the image control conditions (γ-LUT, charging potential, laser power, etc.) are controlled based on the result.

  In this embodiment, the one-component jumping development method is adopted as the development method of the image forming apparatus 100, but the present invention is not limited to this.

  The image forming apparatus 100 has a normal mode for printing a normal image and a tint block mode for printing a tint block image. In the tint block mode, the tint block image generated by the control unit 22 or the tint block image received by the control unit 22 from the external device is printed.

  The copy-forgery-inhibited pattern image is composed of two areas having substantially the same density, an area where dots remain after copying (hereinafter referred to as “latent image portion”) and an area where dots disappear after copying (hereinafter referred to as “background portion”). ing.

  In the present embodiment, the image corresponding to the background portion is designed so that dots are discretely arranged using a dot dispersion type dither matrix. The image corresponding to the latent image portion is designed so that the dots are concentrated by using a dot concentration type dither matrix. Hereinafter, the dither matrix used for generating the background image is referred to as a background dither matrix, and the dither matrix used for generating the latent image portion is referred to as a latent image dither matrix.

  The dither method is a method in which a multi-value input image signal is compared with a threshold value calculated according to a certain rule, and a binary image is output according to the magnitude relationship. The dither matrix is a threshold matrix in which thresholds for binarizing an input image signal by the dither method are two-dimensionally arranged.

  A binary image (threshold pattern) is obtained by binarizing the pixel value of the input image signal with the threshold value of the corresponding dither matrix. The binary image obtained here has one bit (for example, 0) in the pixel value when the gradation of the input image signal is less than the threshold value of the dither matrix, and the other bit (for example, 1) in the case of the threshold value or more. Assigned.

  Hereinafter, the binary image constituting the background portion is referred to as “background threshold pattern”, and the binary image constituting the latent image portion is referred to as “latent image threshold pattern”.

  Next, a method for arranging dots in the latent image portion and the background portion in this embodiment will be described. In the present embodiment, a case will be described in which a latent image portion is generated based on a dot concentration type dither matrix and a background portion is generated based on a dot dispersion type dither matrix. An example of the dot-concentrated dither matrix is the spiral dither matrix shown in FIG.

  FIG. 2 is a diagram showing a spiral dither matrix used in the image forming apparatus of FIG.

  In the 12 × 12 spiral dither matrix 600 of FIG. 2, the threshold values are arranged in a spiral shape so that the numerical value increases from the center. A threshold pattern generated by dithering an arbitrary input image signal with a 12 × 12 spiral dither matrix 600 is designed so that a plurality of dots are concentrated.

  When the input image signal 12 is subjected to threshold processing using the spiral dither matrix 600, the threshold pattern (dot arrangement) shown in FIG. 3 is obtained.

  FIG. 3 is a diagram showing a threshold pattern obtained by processing an image signal using the spiral dither matrix of FIG.

  In FIG. 3, the shaded portion indicates a threshold pattern obtained by performing threshold processing on the input image signal 12 with a 12 × 12 spiral dither matrix 600. The threshold pattern (dot arrangement) obtained here is a pattern in which a plurality of dots are arranged in a concentrated manner.

  On the other hand, the dot dispersion type dither matrix shown in FIG. 4 is used as the dot dispersion type dither matrix constituting the background portion.

  FIG. 4 is a diagram showing a dot dispersion type dither matrix used in the image forming apparatus of FIG.

  In the 12 × 12 dot dispersion dither matrix 800 of FIG. 4, the elements of the threshold matrix are sequentially arranged at positions where they are not in contact with each other as much as possible, and the threshold pattern has an isolated grid-like dot arrangement. The threshold pattern generated by dithering an arbitrary input image signal with a 12 × 12 dot dispersion dither matrix 800 is designed so that a plurality of dots are dispersedly arranged.

  FIG. 5 is a diagram showing threshold patterns obtained by processing image signals using the dot dispersion type dither matrix of FIG.

  In FIG. 5, shaded portions indicate threshold patterns obtained by performing threshold processing on the input image signal 12 with a 12 × 12 dot dispersion dither matrix 800. In the threshold pattern (dot arrangement) obtained here, a plurality of dots are arranged in a distributed manner.

  In the present embodiment, description will be made assuming that the dot dispersion type dither matrix 800 is used as the background dither matrix, but the present invention is not limited to this. Other dot dispersion type dither matrices such as a blue noise mask may be used.

  In this blue noise mask, all threshold patterns in an arbitrary gradation have blue noise characteristics, and the distribution of black pixels forming the threshold pattern is random but highly uniform, and the graininess is not conspicuous. The blue noise characteristic means that the output pattern of points when set to an arbitrary gradation is locally aperiodic and isotropic, and has low frequency components. The threshold pattern obtained from the blue noise mask has an advantage that a visually preferable output pattern can be obtained, for example, by preventing the occurrence of moire and making paper feed unevenness inconspicuous.

  In addition, a dot dispersion type dither matrix may be used that is not a blue noise mask but has a periodic (or pseudo-periodic) threshold pattern at a specific or arbitrary gradation, is anisotropic, and has low low-frequency components. . In addition to the method using the threshold pattern, it is possible to configure the background portion using the error diffusion method.

  In this embodiment, the size of the dither screen in the background portion and the latent image portion is the same 12 × 12. However, the sizes of the two screens may be different. Further, although the threshold pattern for each gradation is generated based on the dither matrix, the present invention is not limited to this. A background threshold pattern and a latent image threshold pattern may be independently generated for each gradation. In this case, there is also an advantage that threshold patterns having good image quality can be collected for each gradation.

  If the area ratio of black pixels is the same in the latent image portion and the background portion, the density is theoretically equal, and the boundary between the latent image portion and the background portion is difficult to understand and can be used as a tint block mode. However, actually, the gradation characteristics of the latent image dither matrix and the background dither matrix are not always the same due to the characteristics of the printer.

  The control unit 22 executes a tint block printing process of FIG. 9 to be described later, obtains the gradation characteristics of the latent image dither matrix and the gradation characteristics of the background dither matrix, and determines the signal level to be output based on the gradation characteristics.

  6 is a diagram showing the tone characteristics of the latent image dither matrix obtained by the control unit 22 in FIG. 1, and FIG. 7 is a diagram showing the tone characteristics of the background dither matrix obtained by the control unit 22 in FIG. It is.

  For example, the gradation characteristic of the latent image dither matrix is represented by a gentle S-curve as shown in FIG. 6, and the gradation characteristic of the background dither matrix is represented by a steep S-curve as shown in FIG. In such a case, the density of the background portion and the latent image portion at the time of printing is not the same even if the area ratio of the black pixels of the background threshold pattern and the latent image threshold pattern is set to be approximately equal.

  Further, when the copy-forgery-inhibited pattern image is actually output using a printer, the latent image portion and the background portion are not always output at the intended density due to various causes.

  Reasons include printer engine characteristics and dither matrix output of threshold patterns, individual printer differences, printing environment such as humidity and temperature, engine durability, recording paper (media) differences, printer ink and toner Concentration instability depending on various conditions such as differences in the above can be mentioned. That is, the optimum input gradation for each of the background portion and the latent image portion dither matrix differs depending on the printer model, dither matrix, individual printer, printing environment, recording paper, ink, toner, and the like.

  Therefore, even when the engine characteristics and the printing environment of the printer are different, it is necessary to generate a copy-forgery-inhibited pattern image after obtaining a background threshold pattern and a latent image threshold pattern having substantially the same density during printing. However, it is practically difficult to automatically calculate the optimum background threshold pattern and latent image threshold pattern in consideration of all the fluctuation factors including fluctuation due to the printing environment.

  Therefore, before executing the tint block synthesizing printing apparatus, a function for obtaining a background threshold pattern and a latent image threshold pattern in which the density of the background portion and the latent image portion are almost the same for each printer, that is, a tint block density calibration function is implemented. Necessary. Therefore, the patch detection unit 51 forms the gradation patches 801 and 802 shown in FIG. 8 on the photosensitive member 1 and detects the density thereof. Based on the density, the signal level output by the control unit 22 is controlled.

  FIG. 8 is a diagram showing the gradation patches formed by the patch detection unit 51 in FIG.

  In FIG. 8, the patch detection unit 51 is formed on the photoconductor 1 and the screen gradation patch 801 used for the latent image portion, the screen gradation patch 802 used for the background portion. The output levels of the gradation patches 801 and 802 are 0h, 10h, 20h... F0h and FFh, respectively.

  FIG. 9 is a flowchart showing the procedure of the tint block printing process executed by the image forming apparatus 100 of FIG.

  In FIG. 9, the user selects a tint block mode by using an operation unit (not shown) included in the image forming apparatus 100, and instructs to start printing (step S101). The gradation patch 801 of the screen used for the latent image portion is formed on the photoreceptor 1 by the LED of the patch detection unit 51 (step S102). Next, the density of the gradation patch 801 formed on the photoreceptor 1 is measured by the density sensor of the patch detection unit 51 (step S103). The controller 22 determines the signal level α corresponding to the latent image portion density A based on the measured density of the gradation patch 801 (step S104).

  Next, the gradation patch 802 of the screen used for the background portion is formed on the photoreceptor 1 by the LED of the patch detection unit 51 (step S105). Next, the density of the gradation patch 802 formed on the photoreceptor 1 is measured by the density sensor of the patch detection unit 51 (step S106). The controller 22 determines the signal level β corresponding to the background density B based on the measured density of the gradation patch 802 (step S107).

  The control unit 22 outputs an image including a copy-forgery-inhibited pattern image based on the two signal levels α and β (step S108), and ends the present process.

  Here, the concentrations A and B are predetermined values. The density A and the density B are not necessarily equal values, and are densities that are output by the image forming apparatus 100 so that the same density appears. Further, the values of the densities A and B are not one, but may be a combination of a plurality of values according to the density of the tint block pattern, or a relational expression or table indicating the correlation between A and B.

  According to the first embodiment, by performing calibration of the image pattern used in the background pattern before executing the background pattern mode, a background pattern image with a small visual density difference between the latent image portion and the background portion is obtained. Can be output.

  Further, there may be large density fluctuations due to differences in gradation reproduction characteristics between the latent image portion and the background portion due to printer engine characteristics, individual differences, etc., printing environment and durability. According to the present embodiment, even in such a case, the optimum latent image portion is necessary to generate a tint block image in which the print density of the latent image portion and the background portion approximates and the background portion disappears after copying. The tint block density parameter for determining the printing density of the background portion can be determined with high accuracy.

[Second Embodiment]
In the first embodiment, calibration is performed at the time of printing a monochrome background pattern image. In the second embodiment, calibration is performed at the time of printing a full color background pattern image.

  FIG. 10 is a diagram schematically showing an internal configuration of an image forming apparatus according to the second embodiment of the present invention.

  In FIG. 10, an image forming apparatus 200 includes a plurality of color process cartridges Pa to Pd, and sequentially forms toner images on the same transfer material.

  The image forming apparatus 200 includes an intermediate transfer belt (ITB) 128, a registration roller 132, a conveyance belt 127, a fixing device 129, a patch detection unit 133, and a cleaning blade 130.

  The ITB 128 travels in the arrow X direction. The ITB 128 is made of a dielectric resin such as polyimide, polycarbonate, polyethylene terephthalate, or polyvinylidene fluoride.

  The transfer material 108 taken out from a paper supply cassette (not shown) is supplied to the secondary transfer portion of the ITB 128 through the registration roller 132.

  Above the ITB 128, four image forming portions Pa, Pb, Pc, and Pd are arranged in series. These image forming units Pa, Pb, Pc, and Pd form magenta, cyan, yellow, and black toner images on the ITB 128, respectively. The polarity of these toners is negative.

  The patch detection unit 33 includes an LED for forming a reference patch on the ITB 128 and a density sensor that reads a reflected light amount of the patch formed on the ITB 128. The toner adhesion amount on the ITB 128 is calculated based on the read reflected light amount of the patch on the ITB 128, and the image control conditions (γ-LUT, charging potential, T / C ratio control, etc.) are controlled based on the result.

  The cleaning blade 130 removes residual toner on the ITB 128 after the secondary transfer. The recording paper 108 that has been secondarily transferred is conveyed to the fixing device 129 by the conveying belt 127. A fixing device 129 including a pair of heat rollers fixes toner on the surface of the conveyed recording paper 108 and discharges the recording paper 108 on which an image is formed to the outside of the image forming apparatus 200.

  The configuration of the process cartridges Pa, Pb, Pc, and Pd is basically the same. Hereinafter, the configuration of the process cartridge P will be described.

  FIG. 11 is a diagram schematically showing an internal configuration of the process cartridge P in FIG.

  In FIG. 11, the process cartridge P includes an exposure device 120, a photosensitive member 121, a primary charger 122, a developing device 123, a transfer roller 124, and a cleaner 125.

  The photoconductor 121 is pivotally supported in the direction of arrow R2. The primary charger 122 charges the surface of the photoconductor 121.

  The exposure device 120 is configured by, for example, an LED, a laser, and the like, and exposes the photosensitive member 121 charged by the primary charger 122 in accordance with an image signal output from a control unit (not shown) to electrostatically apply the photosensitive member 121 onto the photosensitive member 121. A latent image is formed.

  The developing sleeve 123 a of the developing device 123 attaches toner to the electrostatic latent image formed on the photoconductor 121 and forms a toner image on the photoconductor 121. The transfer roller 124 electrostatically transfers the toner image formed on the photoconductor 121 to the ITB 128. This toner image is carried on the ITB 128 and conveyed in the arrow X direction.

  The cleaner 125 includes a cleaning blade 125a and a waste toner conveying screw 125b. The cleaning blade 125a removes residual toner on the photoreceptor 121 after the toner image is transferred. The waste toner conveying screw 125b sends the residual toner removed by the cleaning blade 125a to a waste toner container (not shown). The process speed of the process cartridge P is 100 mm / s.

  FIG. 12 is a diagram showing the gradation patches formed by the patch detection unit 133 in FIG.

  In FIG. 12, the patch detection unit 133 forms on the ITB 128 a screen gradation patch 1201 used for the latent image portion and a screen gradation patch 1202 used for the background portion. The output levels of the gradation patches 1201 and 1202 are 0h, 10h, 20h... F0h and FFh, respectively. The gradation patches 1201 and 1202 include four-color gradation patches of Y, M, C, and K, respectively.

  FIG. 13 is a flowchart showing the procedure of the tint block printing process executed by the image forming apparatus 200 of FIG.

  In FIG. 13, the user selects a tint block mode by an operation unit (not shown) included in the image forming apparatus 200 and instructs to start printing (step S <b> 1301). All the colors (Y, M, C, K) of the screen gradation patches 1401 used for the latent image portion are formed on the ITB 128 by the LEDs of the patch detection unit 133 (step S1302). Next, the density of the gradation patch 1401 formed on the ITB 128 is measured by the density sensor of the patch detection unit 133 (step S1303). The control unit of the image forming apparatus determines the signal level α corresponding to the latent image portion density A for each of the colors Y, M, C, and K based on the measured density of the gradation patch 1401 (step S1304). .

  Next, all the colors (Y, M, C, K) of the screen gradation patches 1402 used for the background portion are formed on the ITB 128 by the LEDs of the patch detection unit 133 (step S1305). Next, the density of the gradation patch 1402 formed on the ITB 128 is measured by the density sensor of the patch detection unit 133 (step S1306). Based on the measured density of the gradation patch 1402, the control unit of the image forming apparatus determines a signal level β corresponding to the background part density B for each color of Y, M, C, and K (step S1307).

  The control unit of the image forming apparatus outputs an image including a copy-forgery-inhibited pattern image based on the two signal levels α and β for each color (step S1308), and ends the process.

  According to the second embodiment, by executing calibration of the image pattern used in the background pattern before executing the background pattern mode, a background pattern image with a small visual density difference between the latent image portion and the background portion is obtained. Can be output.

  Further, there may be large density fluctuations due to differences in gradation reproduction characteristics between the latent image portion and the background portion due to printer engine characteristics, individual differences, etc., printing environment and durability. According to the present embodiment, even in such a case, the optimum latent image portion is necessary to generate a tint block image in which the print density of the latent image portion and the background portion approximates and the background portion disappears after copying. The tint block density parameter for determining the printing density of the background portion can be determined with high accuracy.

  In this embodiment, a patch is formed on the ITB 128 and its density is read to obtain the relationship between the signal level and the density. However, a known gradation patch is output on the recording paper, and the output recording paper is read by a reader. The relationship between the output level and the density can also be obtained by reading. In this case, since the influence of secondary transfer and fixing can be taken into consideration, the difference in density between the latent image portion and the background portion of the tint block image can be further reduced.

[Third Embodiment]
In the second embodiment, the calibration is performed for all the colors Y, M, C, and K. In the third embodiment, the calibration is performed only for a specific color.

  When the color of the image used for the background pattern is determined to be Bk or the like, or when the user specifies the color of the background pattern, density calibration is performed only for the specified color as in the first embodiment. Thus, the calibration time can be shortened.

  The configuration of the image forming apparatus in the third embodiment is the same as the configuration of the image forming apparatus in the second embodiment of FIG.

  FIG. 14 is a diagram showing a gradation patch according to the third embodiment of the present invention.

  In FIG. 14, the patch detection unit 133 is a screen gradation patch 1601 used for a latent image portion of a designated color (here Cyan) and a screen used for a background portion of a designated color (here Cyan). The gradation patch 1602 is formed on the ITB 128. The output levels of the gradation patches 1601 and 1602 are 0h, 10h, 20h... F0h and FFh, respectively.

  FIG. 15 is a flowchart illustrating the procedure of the tint block printing process according to the third embodiment.

  In FIG. 15, the user designates a tint block color, selects a tint block mode, and instructs to start printing using an operation unit (not shown) included in the image forming apparatus 200 (step S <b> 1501). The LED of the patch detection unit 133 forms a gradation patch 1601 for the screen used for the latent image portion of the color (Cyan) designated on the ITB 128 (step S1502). Next, the density of the gradation patch 1601 formed on the ITB 128 is measured by the density sensor of the patch detection unit 133 (step S1503). The control unit of the image forming apparatus determines a signal level α corresponding to the latent image portion density A of the designated color (Cyan) based on the measured density of the gradation patch 1601 (step S1504).

  Next, the gradation patch 1602 of the screen used for the background part of the color (Cyan) designated on the ITB 128 is formed by the LED of the patch detection unit 133 (step S1505). Next, the density of the gradation patch 1602 formed on the ITB 128 is measured by the density sensor of the patch detection unit 133 (step S1506). The control unit of the image forming apparatus determines a signal level β corresponding to the background portion density B of the designated color (Cyan) based on the measured density of the gradation patch 1602 (step S1507).

  Based on the two signal levels α and β, the control unit of the image forming apparatus outputs an image including the copy-forgery-inhibited pattern image (step S1508), and the process is terminated.

  According to the third embodiment, by executing calibration of the image pattern used in the background pattern before executing the background pattern mode, a background pattern image with a small visual density difference between the latent image portion and the background portion is obtained. Can be output.

  Further, there may be large density fluctuations due to differences in gradation reproduction characteristics between the latent image portion and the background portion due to printer engine characteristics, individual differences, etc., printing environment and durability. According to the present embodiment, even in such a case, the optimum latent image portion is necessary to generate a tint block image in which the print density of the latent image portion and the background portion approximates and the background portion disappears after copying. The tint block density parameter for determining the printing density of the background portion can be determined with high accuracy.

  Furthermore, by performing density calibration only on the color of the image used for the background pattern, the time required for calibration can be shortened.

[Fourth Embodiment]
In the first to third embodiments, both the latent image portion and the background portion are calibrated. However, in the fourth embodiment, the latent image portion and the background portion have unstable gradation characteristics. Perform calibration only for the number of lines. The main body configuration is the same as that of the first embodiment.

  In an electrophotographic printer, generally, the lower the resolution (number of lines), the more stable the image. Therefore, since the latent image portion has a low number of lines, the image of the latent image portion is stable and the gradation characteristics do not change much. Therefore, in this embodiment, the calibration time can be shortened by performing calibration only for the background portion having a high number of lines with unstable gradation characteristics.

  The configuration of the image forming apparatus in the fourth embodiment is the same as the configuration of the image forming apparatus in the second embodiment of FIG.

  FIG. 16 is a diagram showing a gradation patch according to the fourth embodiment of the present invention.

  In FIG. 16, the patch detection unit 133 forms on the ITB 128 a screen gradation patch 1801 to be used for a background portion of a designated color (here, Cyan). The output level of the gradation patch 1801 is 0h, 10h, 20h... F0h, FFh.

  FIG. 17 is a flowchart illustrating the procedure of the tint block printing process according to the fourth embodiment.

  In FIG. 17, the user designates the tint block color, selects the tint block mode, and instructs the start of printing using an operation unit (not shown) included in the image forming apparatus 200 (step S1701). The screen gradation patch 1801 used for the background portion of the color (Cyan) designated on the ITB 128 is formed by the LED of the patch detection unit 133 (step S1702). Next, the density of the gradation patch 1801 formed on the ITB 128 is measured by the density sensor of the patch detection unit 133 (step S1703). The control unit of the image forming apparatus determines the signal level β corresponding to the background portion density B of the designated color (Cyan) based on the measured density of the gradation patch 1801 (step S1704).

  Based on the signal level β, the control unit of the image forming apparatus outputs an image including the copy-forgery-inhibited pattern image (step S1705), and ends the process.

  According to the fourth embodiment, by executing calibration of the image pattern used in the background pattern before executing the background pattern mode, a background pattern image with a small visual density difference between the latent image portion and the background portion is obtained. Can be output.

  Further, by performing calibration only for the higher number of lines where the gradation characteristics of the latent image portion and the background portion are unstable, the time required for calibration can be further shortened.

  Note that the output value α of the latent image portion may be a predetermined value. If automatic calibration of the latent image portion has been executed in the past, the signal level α corresponding to the density A determined at that time is set. May be used.

  In this embodiment, since the low number of lines is used for the latent image portion and the high number of lines is used for the background portion, only the background portion is executed. However, the reverse operation is performed using the high line number for the latent image portion and the low integer for the background portion. In this case, the same effect can be obtained by executing automatic calibration only for the latent image portion having a high number of lines.

[Fifth Embodiment]
In the first to third embodiments, both the latent image portion and the background portion are calibrated, but in the fifth embodiment, an image signal having a predetermined signal level on the high line number side is output. The signal level β on the low line number side that matches the density is set.

  In the case of the electrophotographic system, the gradation characteristic becomes nonlinear as the number of lines increases, so that it is necessary to increase the number of gradations of the patch in order to accurately determine the signal level β of the high number of lines. Therefore, by outputting an image signal having a predetermined signal level on the high line number side and setting a signal level β on the low line number side that matches the density, gradation control is accurately performed with a small number of gradations of patches. be able to. In addition, the time required for calibration can be further reduced.

  The configuration of the image forming apparatus in the fifth embodiment is the same as that of the image forming apparatus in the first embodiment of FIG.

  FIG. 18 is a diagram showing a gradation patch in the fifth embodiment of the invention.

  In FIG. 18, the patch detection unit 51 forms a screen gradation patch 2001 used for the background portion and a screen gradation patch 2002 used for the latent image portion on the photosensitive member 1. The output level of the screen gradation patch 2001 used for the background portion is level β0. The output level of the gradation patch 2002 of the screen used for the latent image portion is 0h, 10h, 20h... F0h, FFh.

  FIG. 19 is a flowchart illustrating the procedure of the tint block printing process according to the fifth embodiment.

  In FIG. 19, the user selects a tint block mode by an operation unit (not shown) included in the image forming apparatus 100 and instructs to start printing (step S <b> 1901). The gradation patch 2001 of the screen used for the level β0 background portion is formed on the photoreceptor 1 by the LED of the patch detection unit 51 (step S1902). Next, the density B0 of the gradation patch 2001 formed on the photoreceptor 1 is measured by the density sensor of the patch detection unit 51 (step S1903).

  Next, the gradation patch 2002 of the screen used for the latent image portion is formed on the photoreceptor 1 by the LED of the patch detection portion 51 (step S1904). Next, the density of the gradation patch 802 formed on the photoreceptor 1 is measured by the density sensor of the patch detection unit 51 (step S1905). The control unit 22 determines a signal level α corresponding to the latent image portion density B0 based on the measured density of the gradation patch 802 (step S1906).

  The control unit 22 outputs an image including a copy-forgery-inhibited pattern image based on the two signal levels α and β0 (step S1907), and ends the process.

  According to the fifth embodiment, a background pattern image with a small visual density difference between the latent image portion and the background portion is obtained by performing calibration of the image pattern used in the background pattern before executing the background pattern mode. Can be output. In addition, the time required for calibration can be further reduced.

[Sixth Embodiment]
In the first to fifth embodiments, gradation control is always performed when the copy-forgery-inhibited pattern mode is selected, but in the sixth embodiment, depending on the time since the previous gradation control was performed or the number of prints. To determine whether or not to execute gradation control.

  When outputting again in the tint block mode immediately after outputting in the tint block mode, the gradation characteristics are not changed so much and the time during which the gradation control is performed is wasted. Therefore, when the time since the previous gradation control or the number of printed sheets is equal to or less than a predetermined value, the tint block mode output time can be shortened by omitting the gradation control.

  The configuration of the image forming apparatus in the sixth embodiment is the same as that of the image forming apparatus in the second embodiment in FIG.

  FIG. 20 is a diagram showing a gradation patch according to the sixth embodiment of the present invention.

  In FIG. 20, the patch detection unit 133 forms on the ITB 128 a screen gradation patch 2001 used for the latent image portion and a screen gradation patch 2002 used for the background portion. The output levels of the gradation patches 2001 and 2002 are 9 gradations of 0h, 10h, 20h, 28h, 30h, 38h, 40h, 48h, and 50h, respectively.

  FIG. 21 is a flowchart illustrating the procedure of the tint block printing process according to the sixth embodiment.

  In FIG. 21, the user selects a tint block mode by an operation unit (not shown) included in the image forming apparatus 200, and instructs to start printing (step S2101). Next, it is determined whether or not the time and number of sheets since the previous tint block gradation control is performed are equal to or less than a predetermined value (step S2102). Here, it is determined whether or not the time since the gradation control for the background tint block was executed is 30 minutes or less and the number of sheets is 20 or less.

  As a result of the determination in step S2102, if the time since the previous gradation pattern gradation control was executed exceeds 30 minutes or the number of sheets exceeds 20, the process proceeds to step S2103.

  In step S2103, the gradation patch 2001 of the screen used for the latent image portion is formed on the ITB 128 by the LED of the patch detection portion 133. Next, the density of the gradation patch 2001 formed on the ITB 128 is measured by the density sensor of the patch detection unit 133 (step S2104). The control unit of the image forming apparatus determines the signal level α corresponding to the latent image portion density A based on the measured density of the gradation patch 2001 (step S2105).

  Next, the gradation patch 2002 of the screen used for the background part is formed on the ITB 128 by the LED of the patch detection unit 133 (step S2106). Next, the density of the gradation patch 2002 formed on the ITB 128 is measured by the density sensor of the patch detection unit 133 (step S2107). The control unit of the image forming apparatus determines the signal level β corresponding to the background portion density B based on the measured density of the gradation patch 2002 (step S2108).

  The control unit of the image forming apparatus outputs an image including the copy-forgery-inhibited pattern image based on the two signal levels α and β (step S2109), and ends this process.

  As a result of the determination in step S2102, when the time since the previous gradation control for the background pattern is executed is 30 minutes or less and the number of sheets is 20 or less, the gradation control is not performed and the background pattern image is included. An image is output (step S2109), and this process ends.

  According to the sixth embodiment, by executing calibration of the image pattern used in the background pattern before executing the background pattern mode, a background pattern image with a small visual density difference between the latent image portion and the background portion is obtained. Can be output. In addition, since the execution timing of the next gradation pattern gradation control is determined based on the previous execution timing of the gradation pattern control, it is possible to avoid unnecessary gradation control and execute it at an appropriate timing. can do. Furthermore, toner consumption can be suppressed.

[Seventh Embodiment]
In the sixth embodiment, whether or not automatic gradation correction is performed is determined based on the time and the number of sheets after the previous gradation pattern gradation control is executed. In the seventh embodiment, the background pattern mode is set. At the time of output, the user specifies whether or not to perform gradation correction, and outputs a tint block image.

  According to the seventh embodiment, useless gradation control can be omitted and the tint block mode output time can be shortened.

[Eighth Embodiment]
In the first to sixth embodiments, the output level of the gradation patch used for gradation correction before executing the tint block mode output is 17 gradations from 0h to FFh. In the eighth embodiment, as shown in FIG. 20, the output levels of the gradation patches used are 9 gradations of 0h, 10h, 20h, 28h, 30h, 38h, 40h, 48h, and 50h.

  In the known gradation control, since all gradations must be corrected, it is necessary to output patches in all density regions (17 gradations of 0h, 10h, 20h, to E0h, F0h, and FFh). However, since the density range used in the copy-forgery-inhibited pattern image is generally a low density range of 0.5 or less, a high density range such as FFh is not necessary. Therefore, in the present embodiment, the number of patches near the density range level (30h) to be actually used is increased, and the actual patches are reduced by eliminating the output of the high density portion patches. As a result, the control time can be shortened and the accuracy of gradation control can be increased.

  According to the eighth embodiment, by limiting the patches for automatic gradation correction before the copy-forgery-inhibited pattern mode to patches near the density used in the copy-forgery-inhibited pattern mode, the number of patches can be reduced and the time for gradation correction can be shortened. Became possible.

  Another object of the present invention is to supply a storage medium storing software program codes for realizing the functions of the above-described embodiments to a system or apparatus, and the computer of the system or apparatus (or CPU, MPU, or the like). Is also achieved by reading and executing the program code stored in the storage medium.

  In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the program code and the storage medium storing the program code constitute the present invention. .

  Examples of the storage medium for supplying the program code include a floppy (registered trademark) disk, a hard disk, a magneto-optical disk, a CD-ROM, a CD-R, a CD-RW, a DVD-ROM, a DVD-RAM, and a DVD. An optical disc such as RW or DVD + RW, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used. Alternatively, the program code may be downloaded via a network.

  Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an OS (Operating System) running on the computer based on the instruction of the program code Includes a case where the functions of the above-described embodiments are realized by performing part or all of the actual processing.

  Further, after the program code read from the storage medium is written in a memory provided in a function expansion board inserted in the computer or a function expansion unit connected to the computer, the expanded function is based on the instruction of the program code. This includes a case where a CPU or the like provided on the expansion board or the expansion unit performs part or all of the actual processing and the functions of the above-described embodiments are realized by the processing.

1 is a diagram schematically showing an internal configuration of an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is a diagram illustrating a spiral dither matrix used in the image forming apparatus of FIG. 1. It is a figure which shows the threshold value pattern obtained by processing an image signal using the spiral dither matrix of FIG. FIG. 2 is a diagram showing a dot dispersion type dither matrix used in the image forming apparatus of FIG. 1. FIG. 5 is a diagram showing a threshold pattern obtained by processing an image signal using the dot dispersion type dither matrix of FIG. 4. It is a figure which shows the gradation characteristic of the latent image dither matrix calculated | required by the control part in FIG. It is a figure which shows the gradation characteristic of the background dither matrix calculated | required by the control part in FIG. It is a figure which shows the gradation patch formed by the patch detection part in FIG. 3 is a flowchart illustrating a procedure of a tint block printing process executed by the image forming apparatus of FIG. 1. It is a figure which shows schematically the internal structure of the image forming apparatus which concerns on the 2nd Embodiment of this invention. It is a figure which shows schematically the internal structure of the process cartridge in FIG. It is a figure which shows the gradation patch formed by the patch detection part in FIG. 11 is a flowchart illustrating a procedure of a tint block printing process executed by the image forming apparatus of FIG. It is a figure which shows the gradation patch in the 3rd Embodiment of this invention. It is a flowchart which shows the procedure of the copy-forgery-inhibited pattern printing process in 3rd Embodiment. It is a figure which shows the gradation patch in the 4th Embodiment of this invention. It is a flowchart which shows the procedure of the copy-forgery-inhibited pattern printing process in 4th Embodiment. It is a figure which shows the gradation patch in the 5th Embodiment of this invention. It is a flowchart which shows the procedure of the copy-forgery-inhibited pattern printing process in 5th Embodiment. It is a figure which shows the gradation patch in the 6th Embodiment of this invention. It is a flowchart which shows the procedure of the tint block printing process in 6th Embodiment. It is a figure which shows the conventional tint block image.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 4 Developing apparatus 20 Semiconductor laser 22 Control part 24 Laser driver 50 Charging control part 51 Patch detection part

Claims (19)

In an image forming apparatus for printing a tint block image including a latent image portion and a background portion,
Correction means for correcting at least one of the gradation for the latent image portion and the gradation for the background portion so that the density of the latent image portion and the density of the background portion are respectively predetermined densities;
Output means for outputting the image signal for the latent image portion and the image signal for the background portion based on the corrected gradation;
An image forming apparatus comprising: a printing unit that prints the copy-forgery-inhibited pattern image based on each image signal.   The image forming apparatus according to claim 1, wherein the correction unit corrects gradations of all colors used by the printing unit.   The image forming apparatus according to claim 1, wherein the correction unit corrects a gradation of a color used for the copy-forgery-inhibited pattern image.   4. The image forming apparatus according to claim 1, wherein the correction unit corrects the higher-resolution gradation of the latent image portion and the background portion. 5.   5. The image forming apparatus according to claim 1, wherein the correction unit corrects the gradation every time the copy-forgery-inhibited pattern image is printed by the printing unit.   5. The correction unit according to claim 1, wherein the correction unit determines whether or not to correct the gradation according to at least one of a number of printed sheets and a time since the gradation is corrected last time. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, further comprising a setting unit configured to set whether or not the gradation is corrected by the correction unit. In an image forming apparatus having two image forming modes, a normal image mode for forming a normal image and a copy-forgery-inhibited pattern image mode for forming a copy-forgery-inhibited pattern image including a latent image portion and a background portion.
Gradation pattern forming means for forming a first gradation pattern on an image carrier or recording paper;
Reading means for reading the density of the first gradation pattern formed on the image carrier or the recording paper;
Changing means for changing image forming conditions based on the read density;
Image forming means for forming an image based on the image forming conditions,
The image forming apparatus, wherein the gradation pattern forming unit forms a second gradation pattern on the image carrier or recording paper when the copy-forgery-inhibited pattern image mode is selected.   9. The image forming apparatus according to claim 8, wherein the second gradation pattern is a gradation pattern of a density region used for the copy-forgery-inhibited pattern image. In an image forming method for printing a tint block image including a latent image portion and a background portion,
A correction step of correcting at least one of the gradation for the latent image portion and the gradation for the background portion so that the density of the latent image portion and the density of the background portion are respectively predetermined densities;
An output step of outputting the image signal for the latent image portion and the image signal for the background portion based on the corrected gradation, respectively;
And a printing step for printing the copy-forgery-inhibited pattern image based on each image signal.   The image forming method according to claim 10, wherein the correcting step corrects gradations of all colors used in the printing step.   The image forming method according to claim 10, wherein the correcting step corrects a gradation of a color used for the copy-forgery-inhibited pattern image.   13. The image forming method according to claim 10, wherein the correcting step corrects a gradation of a higher resolution of the latent image portion and the background portion.   14. The image forming method according to claim 10, wherein the correction step corrects the gradation every time the copy-forgery-inhibited pattern image is printed in the printing step.   14. The correction step determines whether or not to correct the gradation according to at least one of the number of printed sheets and time since the previous correction of the gradation. The image forming method according to any one of the above.   The image forming method according to claim 10, further comprising a setting step of setting whether or not the gradation is corrected in the correction step. In an image forming method having two image forming modes, a normal image mode for forming a normal image and a copy-forgery-inhibited pattern image mode for forming a copy-forgery-inhibited pattern image including a latent image portion and a background portion.
A gradation pattern forming step of forming a first gradation pattern on the image carrier or recording paper;
A reading step of reading the density of the first gradation pattern formed on the image carrier or the recording paper;
A change step of changing the image forming condition based on the read density;
An image forming step of forming an image based on the image forming conditions,
In the gradation pattern forming step, when the copy-forgery-inhibited pattern image mode is selected, a second gradation pattern is formed on the image carrier or recording paper.   The image forming method according to claim 17, wherein the second gradation pattern is a gradation pattern of a density region used for the copy-forgery-inhibited pattern image. In a program executed by an image forming method for printing a tint block image including a latent image portion and a background portion,
A correction module that corrects at least one of the gradation for the latent image portion and the gradation for the background portion so that the density of the latent image portion and the density of the background portion are respectively predetermined densities;
An output module that outputs the image signal for the latent image portion and the image signal for the background portion based on the corrected gradation, and
And a printing module that prints the copy-forgery-inhibited pattern image based on each image signal.

Images