JP6169008B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that prints a copy-forgery-inhibited pattern image including a latent image portion that is reproduced during copying and a background portion that disappears during copying.

  2. Description of the Related Art In recent years, the copying accuracy of image forming apparatuses that perform copying has improved, so that original images such as documents can be easily copied and reproduced with high accuracy. In such a high-performance image forming apparatus, for example, unauthorized copying such as copying a specific document image that should not be copied to create an unauthorized copy is easily performed. Therefore, in order to prevent illegal copying of a specific document image, a technique for synthesizing copy-forgery-inhibited pattern image data for preventing copying with specific document image data has been realized.

  The tint block image includes a latent image portion and a background portion. For example, the data of the latent image portion and the background portion are formed by arranging black pixel aggregates, which are aggregates of black pixels, in a predetermined pattern. The black pixel aggregate in the latent image data is larger in size than the black pixel aggregate in the background data. The small black pixel aggregate in the background data disappears at the time of copying due to the limit of the copying reproduction capability of the copying machine. As a result, when the copy-forgery-inhibited pattern image is copied, only the latent image portion remains.

  The copy-forgery-inhibited pattern image is printed so that the latent image portion cannot be distinguished from the background portion by human eyes. More specifically, the latent image portion and the background portion are printed so as to have the same density. In other words, if the densities of the latent image portion and the background portion do not match, the latent image portion and the background portion are identified by human eyes.

  However, the density of the latent image portion and the background portion may not match due to aging degradation of the image forming apparatus. In particular, the density of a background portion made up of an array of small black pixel aggregates is likely to fluctuate compared to the latent image portion due to aging degradation of the image forming apparatus.

  As a method for matching the densities of the latent image portion and the background portion, it is conceivable to adjust the density according to the shape of each black pixel aggregate. For example, Patent Document 1 proposes printing the black pixel aggregate at a desired density by determining the form of the black pixel aggregate of the image data and adjusting the laser output value according to the determined form. Has been.

JP 2004-306590 A

  However, in the density adjustment method described in Patent Document 1, a configuration for determining the form of the black pixel aggregate is separately required for the image forming apparatus, and the processing becomes complicated.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of printing a tint block image at a uniform density with a simple process with a simple configuration.

  An image forming apparatus according to the present invention refers to a storage unit that stores data of a tint block image composed of a latent image portion and a background portion and dithering image data, an input unit to which image data is input, and the storage unit, The composition unit that synthesizes the copy-forgery-inhibited pattern image data with the image data input to the input unit, and the storage unit is used to change the gradation of the synthesized image data using the dithering image data. A gradation changing unit; and a printing unit that prints based on the image data that has been changed in gradation by the gradation changing unit, wherein the dithering image data partially masks a pixel aggregate of the data in the background part It is characterized by comprising a pattern.

  The pixel aggregate is, for example, an aggregate of black pixels, but may be an aggregate of pixels of other colors. The gradation changing unit masks a part of the black pixel aggregate of the background data while maintaining the black pixel aggregate of the latent image data with the dithering image data, and converts the black pixel after masking to, for example, A white pixel is assumed. As a result, the gradation of the background portion is changed, and the density during printing decreases. The density of the background portion can be adjusted by changing the pattern of the dithering image data and changing the number of black pixels of the black pixel aggregate to be masked.

  Since the image forming apparatus of the present invention stores in advance dithering image data that adjusts the density of the background portion and matches the density of the latent image portion, only the gradation changing process using the dithering image data can be performed. A tint block image can be printed at a uniform density. In addition, since the image forming apparatus of the present invention does not determine the form of the pixel aggregate of the image to be printed, it does not require a separate configuration as in the prior art, and the dithering image data is kept in a simple configuration. A copy-forgery-inhibited pattern image can be printed with a uniform density only by using the gradation changing process.

  In the image forming apparatus of the present invention, since the background portion density matches the density of the latent image portion by simply changing the gradation of the background portion with the dithering image data while maintaining a simple configuration, Can print with uniform density.

1 is a block diagram illustrating a configuration of a printing system according to Embodiment 1. FIG. 3 is a flowchart illustrating image processing according to the first embodiment. (A) is a figure which shows the pattern of the data of the latent image part of the tint block image which concerns on Embodiment 1, (B) is a figure which shows the pattern of the data of the background part of a tint block image. (A), (B), and (C) are the figures which respectively show the pattern of the dithering image data which concerns on Embodiment 1. FIG. (A), (B), and (C) are figures which show the pattern of the data of the background part after the halftone process using the dithering image data, respectively. FIG. 5 is a diagram illustrating a relationship between an input tone value of dithering image data according to Embodiment 1 and a density of a tint block image subjected to halftone processing. It is a figure for setting the input gradation value of dithering image data. FIG. 10 is a diagram illustrating a plurality of dithering image data patterns of the printing system according to the second embodiment. FIG. 10 is a diagram illustrating a relationship between an input tone value of dithering image data of the printing system according to the second embodiment and a density of a tint block image subjected to halftone processing. FIG. 10 is a diagram illustrating a plurality of dithering image data patterns of the printing system according to the third embodiment. FIG. 10 is a diagram illustrating a relationship between an input tone value of dithering image data of a printing system according to a third embodiment and a density of a tint block image subjected to halftone processing.

  As shown in FIG. 1, a printing system 10 includes a digital color copying machine (corresponding to an image forming apparatus of the present invention, hereinafter simply referred to as “copying machine”) 22 that employs an electrophotographic system, and an information processing apparatus. Twelve. The copying machine 22 and the information processing apparatus 12 are connected to each other via a network 20 including, for example, a LAN line, and can transmit and receive various data including image data.

  The information processing apparatus 12 is a terminal device such as a PC, for example, and is operated by a user in order to use the copying machine 22. Although only one information processing device 12 is shown in FIG. 1, a large number may actually exist.

  In the printing system 10, first, for example, a printing instruction signal for instructing execution of printing processing and image data to be printed are transmitted from the information processing apparatus 12 to the copying machine 22. In response to the print instruction signal, the copying machine 22 performs a combining process for combining the copy-forgery-inhibited pattern image data with the image data, and then executes a printing process based on the combined image data.

  The copier 22 includes a control unit 24, an image input unit 30, an image processing unit 32, a printer unit 34, a scanner unit 35, an operation panel 36, and a power supply control unit 38.

  The control unit 24 is substantially a computer and includes a CPU 40, a ROM 42, a RAM 44, and an HDD 46. A BUS line 26 is electrically connected to the CPU 40, and a ROM 42, a RAM 44, and an HDD 46 are electrically connected to the BUS line 26. The CPU 40 executes various computer programs in response to instructions from the operation panel 36, the information processing apparatus 12 that is an external device, and the like, thereby operating each unit of the copier 22, communication with the information processing apparatus 12, and images. A desired process such as a process is executed.

  The various computer programs are stored in advance in the ROM 42 or the HDD 46, and are read out from the ROM 42 or the HDD 46, expanded in the RAM 44, and executed by the CPU 40 when desired processing is executed.

  The HDD 46 stores tint block image data and dithering image data used for various image processing. However, the tint block image data and the dithering image data may be stored in the ROM 42.

  Further, an image input unit 30, an image processing unit 32, a printer unit 34, a scanner unit 35, an operation panel 36, and a power supply control unit 38 are electrically connected to the BUS line 26.

  The image input unit 30 includes a NIC (Network Interface Card) (not shown). The NIC is connected to the network 20 and receives image data together with a print instruction signal from an external apparatus such as the information processing apparatus 12. As a result, image data is input to the image input unit 30. However, the print instruction signal and the image data may be input to the image input unit 30 from the information processing apparatus 12 via the USB cable, for example, without using the network 20. The image data input to the image input unit 30 is, for example, RGB (Red, Green, and Blue) image data.

  The image processing unit 32 includes an MPU (Micro Processing Unit) and an image memory (none of which is shown). The image processing unit 32 performs various image processing such as gradation change processing on the image data input to the image input unit 30 to create printing image data, and outputs the printing image data to the printer unit 34. To do. The detailed configuration of the image processing unit 32 will be described later.

  The printer unit 34 includes an image memory 48 and a printing unit 50. The image memory 48 includes a RAM and temporarily stores image data in units of pages. The image memory 48 temporarily stores image data to be transmitted to the printing unit 50, for example, printing image data input from the image processing unit 32 in units of pages in response to an instruction from the control unit 24 or the like. , Output to the printing unit 50. The printing unit 50 sequentially acquires printing image data from the image memory 48 in synchronization with the printing of the input printing image data. The printing unit 50 includes a photosensitive drum, a charger, an LSU (Laser Scanning Unit), a developing device, a transfer device, a cleaning device, a fixing device, and a toner cartridge that is detachably attached to the copying machine 22 (all of which are illustrated in the drawings). Not shown.) The printing unit 50 further includes a manual paper feed tray, a first paper feed tray, and a second paper feed tray (all of which are not shown). In response to an instruction from the control unit 24 or the like, the printing unit 50 prints image data for printing transmitted from the image memory 48 onto a recording sheet conveyed from one of the paper feed trays via the sheet conveying unit. Print the image based on.

  The scanner unit 35 includes a CCD line sensor (not shown) for reading image information of a document. The read image information is output as RGB image data. However, the scanner unit 35 is not essential to the present invention.

  The operation panel 36 includes a display output unit made up of a liquid crystal display and an operation interface unit made up of operation buttons, a touch panel and the like (none of them are shown). The display output unit provides the user with various types of information such as information regarding the status of the copying machine 22 and the status of various processes. The operation panel 36 is configured by overlapping a liquid crystal display and a touch panel to provide an interactive operation interface. The operation panel 36 includes a power button for inputting a power-on instruction and a power-off instruction, an image quality adjustment key for inputting an instruction for an image quality adjustment mode, and a print key for starting a printing process. The operation panel 36 also includes a test print key for confirming the density of the tint block image.

  The power control unit 38 is electrically connected to the external power source 52. The power control unit 38 acquires power necessary for the operation of each unit of the copying machine 22 from the external power source 52 and supplies the acquired power to each unit of the copying machine 22.

  The copying machine 22 operates the above-described units to read and record the image information of the document with the scanner unit 35 in accordance with an instruction by a user input operation from the operation panel 36 or an instruction from the information processing apparatus 12 or the like. A copy mode for printing an image on paper, a printer mode for receiving image data transmitted from the information processing apparatus 12 or the like and printing an image on recording paper, and reading the original image information by the scanner unit 35 to the information processing apparatus 12 or the like Various modes such as a scanner mode for transmitting image data and a storage mode for storing image data in the HDD 46 are executed.

  The CPU 40 of the control unit 24 and the MPU of the image processing unit 32 control the operations of the image input unit 30, the image processing unit 32, and the printer unit 34, so that input / output processing of image data and printing image data and image data are processed. Various image processing is executed. As described above, in the copying machine 22, the image input unit 30, the image processing unit 32, and the printer unit 34 function as an image processing system for performing image processing. The synthesizing unit and the gradation changing unit of the present invention are realized by the CPU 40 executing a program and operating according to the program in which the MPU of the image processing unit 32 is executed.

  As shown in FIG. 2, first, the CPU 40 outputs the image data input to the image input unit 30 to the image memory of the image processing unit 32 (S1).

  When the image data is input to the image memory, the MPU of the image processing unit 32 combines the copy-forgery-inhibited pattern image data with the input image data (S2). The tint block image includes a latent image portion and a background portion.

  As shown in FIG. 3A, the data pattern of the latent image portion is composed of a set of pixels arranged in a matrix. The matrix includes, for example, the same number of pixels (for example, 36) in the first direction and the second direction. For example, when the copy-forgery-inhibited pattern image is a monochrome image with two gradations, the pattern of the latent image portion includes white pixels and black pixels. As shown in FIG. 3A, the black pixel aggregate 100 includes a set of black pixels adjacent to each other in the first direction and the second direction. In the example shown in FIG. 3A, the black pixel aggregate 100 of the latent image portion data is composed of a matrix in which four black pixels are arranged in the first direction and the second direction, respectively. The plurality of black pixel aggregates 100 are arranged in the first direction and the second direction so as to be spaced apart by a predetermined number of white pixels. Note that one of the first direction and the second direction corresponds to the LSU movement direction (main scanning direction) of the printing unit 50, and the other direction corresponds to the sub-scanning direction.

  As shown in FIG. 3B, the data pattern of the background portion is different from the data pattern of the latent image portion in the shape, number, and arrangement of the black pixel aggregate. The description of the configuration overlapping with the data pattern of the latent image portion is omitted.

  The data pattern of the background portion includes a black pixel aggregate 110 and a black pixel aggregate 111. The black pixel aggregate 110 has a shape in which two black pixels are arranged in the first direction. The black pixel aggregate 111 has a shape in which two black pixels are arranged in the first direction and one black pixel is arranged in the second direction. That is, the black pixel aggregate 110 and the black pixel aggregate 111 are smaller in shape than the black pixel aggregate 100 of the latent image data. As shown in FIGS. 3A and 3B, the number of black pixel aggregates 110 and black pixel aggregates 111 is larger than that of the black pixel aggregate 100 in the latent image portion. The arrangement interval of the black pixel aggregates 110 is narrower than the arrangement interval of the black pixel aggregates 100.

  The background data pattern may be printed with the small black pixel aggregate 110 and the black pixel aggregate 111 missing, so that the density of black pixels is higher than the latent image data pattern. The number of black pixel aggregates 110 and black pixel aggregates 111 is set. Hereinafter, the density of black pixels is the number of black pixels in each data pattern of the latent image portion and the background portion. In the example shown in FIG. 3A, the data pattern of the latent image portion has 128 black pixels (because there are eight black pixel aggregates 100 made up of 16 black pixels). In the example shown in FIG. 3B, the data pattern of the background portion has 156 black pixels. As a result, even if some small black pixel aggregates 110 and black pixel aggregates 111 are printed without being printed, the latent image portion and the background portion are printed at the same density and cannot be identified by human eyes.

  The size of the data pattern of the latent image portion and the background portion is set so that the arrangement of the black pixel aggregate 100, the black pixel aggregate 110, and the black pixel aggregate 111 is continuous with a predetermined geometric pattern.

  The MPU of the image processing unit 32 combines the copy-forgery-inhibited pattern image data having the latent image portion with a predetermined shape and the background portion of the latent image portion with the image data input to the image input unit 30. The predetermined shape of the latent image portion is, for example, a figure or a character indicating the meaning of copy prohibition. Thus, the shape of the tint block image data is determined in advance. The position where the copy-forgery-inhibited pattern image data is combined with the image data input to the image input unit 30 is also determined. The composition is performed after converting the color space (for example, two gradations) of the copy-forgery-inhibited pattern image data into the color space (for example, RGB) of the image data input to the image input unit 30. However, it is not essential to convert the color space. For example, when the image data input to the image input unit 30 is a binary image, the MPU of the image processing unit 32 performs binary synthesis of the copy-forgery-inhibited pattern image data. You may carry out with the color space of an image.

  Returning to FIG. 2, when the MPU of the image processing unit 32 combines the copy-forgery-inhibited pattern image data, the MPU performs color space conversion on the combined image data (S2). The MPU of the image processing unit 32 converts, for example, the color space (RGB) of the combined image data into a color space (CMYK) that can be handled by the printer unit 34. The conversion is performed by calculating with a conversion matrix for converting the RGB gradation values into the CMYK gradation values, but may be performed by other methods.

  The MPU of the image processing unit 32 performs gradation correction on the image data obtained by converting the color space (S4). Gradation correction is performed to correct the brightness, contrast, and hue of the image. As gradation correction means, various conventional techniques are used. However, gradation correction is not an essential process for the present invention.

  Then, the MPU of the image processing unit 32 performs halftone processing on the area of the copy-forgery-inhibited pattern image data of the gradation-corrected image data (S5). This halftone process is to further change the gradation of the tint block image data so as to obtain a desired output gradation (density at the time of printing). The MPU of the image processing unit 32 performs halftone processing by a dithering method using a dithered image. However, the halftone process is not limited to the area of the copy-forgery-inhibited pattern image data, and may be performed on the entire image data.

  As shown in FIGS. 4A, 4B, and 4C, the dithering image data pattern is composed of a set of pixels arranged in a matrix. The matrix includes, for example, the same number of pixels (for example, 36) in the first direction and the second direction. That is, in the examples shown in FIGS. 4A, 4B, and 4C, the dithering image data pattern has the same size as the patterns of the latent image portion and the background portion data. . The dithering image data has, for example, two gradations, and the pattern is composed of white pixels and black pixels. In the pattern shown in FIG. 4A, all the pixels are black pixels. In the pattern shown in FIG. 4B, almost all pixels are black pixels, and some pixels are white pixels 120. In the pattern of FIG. 4C, the number of white pixels 120 is larger than the pattern shown in FIG. In the patterns shown in FIGS. 4B and 4C, the plurality of white pixels 120 are spaced apart in the first direction and the second direction, respectively. In other words, in the patterns shown in FIGS. 4B and 4C, the plurality of white pixels 120 are not adjacent to each other in the first direction and the second direction, respectively. In the pattern of FIG. 4C, some white pixels 120 are adjacent to each other in an oblique direction (first direction and second direction).

  Here, the number of black pixels in the dithering image data pattern is referred to as an input gradation value. For example, the input tone value of dithering image data is a value in the range of 0 to 255. The dithering image data has an input gradation value of 255 when all the pixels of the pattern are black pixels. The dithering image data has an input gradation value of 0 when all the pixels of the pattern are white pixels. Of the patterns shown in FIGS. 4A, 4B, and 4C, the pattern shown in FIG. 4A has the highest input gradation value 255, for example, and FIG. ) Has the lowest input gradation value of 200. The pattern shown in FIG. 4B has an input gradation value 220.

  In the dithering method, the MPU of the image processing unit 32 virtually superimposes the dithering image data on the copy-forgery-inhibited pattern image data, and according to the pixel of the dithering image data, the pixel of the copy-forgery-inhibited pattern image data superimposed on the pixel. Maintain or change the tone value.

  More specifically, when the pixel of the dithering image data is a black pixel, the tone value of the pixel of the tint block image data superimposed on the black pixel is maintained. When the pixel of the dithering image data is the white pixel 120, the pixel of the copy-forgery-inhibited pattern image data superimposed on the white pixel 120 has a gradation value of 0 and becomes a white pixel. That is, the white pixel 120 of the dithering image data is a mask pixel that masks the pixels of the copy-forgery-inhibited pattern image data. The black pixel of the dithering image data is a transmission pixel that transmits the pixel of the tint block image data.

  Here, the dithering image data maintains all black pixels constituting the black pixel aggregate 100 of the latent image portion data as black pixels, and the black pixel aggregate 110 and black pixels of the background data. The pattern is set so that some of the black pixels constituting the aggregate 111 are white pixels. Therefore, even if any of the dithering image data patterns shown in FIGS. 4A, 4B, and 4C is used, the data pattern of the latent image portion is the same as that shown in FIG. The pattern shown in FIG.

  As shown in FIG. 5A, when halftone processing is performed using the dithered image data having the input gradation value 255, the background data pattern shown in FIG. 3B is maintained as it is. As shown in FIG. 5B, when halftone processing is performed using the dithered image data having the input gradation value 220, the background data pattern shown in FIG. Part of the black pixels becomes white pixels. As a result, the density of the black portion of the background data after the halftone process is reduced due to a decrease in the density of the black pixels. As shown in FIG. 5C, when halftone processing is performed using dithered image data having an input gradation value of 200, the background data pattern shown in FIG. Not only the black pixel aggregate 110 but also some pixels are white pixels. As a result, the density of black pixels in the background data after halftone processing is further reduced as compared with the example shown in FIG.

  As shown by the solid line in FIG. 6, the density of the latent image portion at the time of printing is substantially constant regardless of the input gradation value of dithering image data. The density of the background portion (indicated by a broken line in FIG. 6) at the time of printing decreases substantially proportionally as the input tone value of the dithered image data decreases. However, when the dithered image data has an input gradation value of 0, the latent image portion and the background portion have a density of black pixels of 0 in each data, and therefore have a density of 0 at the time of printing.

  As described above, by using dithering image data having different input tone values, it is possible to adjust the density of the background portion while maintaining the density of the latent image portion. As a result, the copying machine 22 uses the dithered image data used in the halftone process even if the density of the background portion is higher than the density of the latent image portion due to, for example, deterioration of the printer portion 34 and individual variations of the printer portion 34. By changing, the density of the background pattern image can be made uniform by reducing the density of the background portion. Further, the copying machine 22 does not require a photo sensor or the like for determining the form of the black pixel aggregate of the image data as in the prior art, and the density of the tint block image can be made uniform only by performing halftone processing. it can.

  Further, since the white pixels 120 of the dithering image data are not arranged continuously in the first direction and the second direction, the copy-forgery-inhibited pattern image data area becomes two consecutive pixels in the main scanning direction or the sub-scanning direction. There is nothing. Thereby, the thin line extending in the main scanning direction or the sub-scanning direction in the image data is difficult to disappear. Furthermore, characters consisting of fine lines extending in the main scanning direction or the sub-scanning direction are difficult to disappear.

  In the above-described example, the dithering image data pattern has the same size as the pattern of each data of the latent image portion and the background portion, but it is not necessary to match. The size of the dithered image data pattern may be the least common multiple of the pattern size of each data of the latent image portion and the background portion. For example, the size of the data pattern of the latent image portion is a matrix of 15 pixels in the first direction and 20 pixels in the second direction, the size of the data pattern of the background portion is 10 pixels in the first direction, and 30 pixels in two directions. In this example, the size of the dithered image data pattern is 30 pixels in the first direction (number of pixels of the least common multiple of 15 and 10) and 60 pixels in the second direction (number of pixels of the least common multiple of 20 and 30). It is sufficient if it is a matrix. As a result, even if a plurality of patterns of dithering image data are arranged side by side, it is possible to prevent misalignment between the white pixels 120 of the dithering image data and the black pixel aggregate of the tint block image data.

  Returning to FIG. 2, when the halftone processing is completed, the MPU of the image processing unit 32 outputs the image data after the halftone processing to the printer unit 34 as image data for printing (S6). Then, the printing unit 50 performs printing based on the input printing image data.

  In the above example, the copy-forgery-inhibited pattern image data is combined with the image data input from the information processing apparatus 12 via the image input unit 30 and printed. However, the image data output by the scanner unit 35 is output. Even if the copy-forgery-inhibited pattern image data is synthesized, it is possible to print the copy-forgery-inhibited pattern image with a uniform density.

  In the above halftone processing, the black pixel of the background image data superimposed on the white pixel of the dithering image data is not set as a white pixel, and the gradation value of the black pixel is lowered, for example, a gray pixel (gradation value). 128). Even in this case, the density of the background portion decreases.

  In the above example, the copy-forgery-inhibited pattern image and the dithering image are two-tone black and white images, but may be RGB images.

  Here, selection of dithering image data will be described. As described above, the dithering image data having the input tone value that makes the density of the tint block image uniform is used during halftone processing. Therefore, when the copy-forgery-inhibited pattern image test print key is touched on the operation panel 36, the copying machine 22 prints the image shown in FIG.

  As shown in FIG. 7, the copying machine 22 prints a plurality of test patterns. Each test pattern includes a latent image portion and a background portion. Each test pattern is printed after halftone processing using dithering image data having different input tone values. Each test pattern is printed together with the input tone value of the dithering image data used for halftone processing. The administrator of the copying machine 22 visually recognizes the print result of the test pattern, and determines the input gradation value of the dithering image data corresponding to the test pattern in which the densities of the latent image portion and the background portion match with the operation panel 36 or information. Setting is made via the processing device 12.

  Next, dithering image data of the printing system according to the second embodiment will be described. In the dithering image data according to the second embodiment, the density of black pixels in the latent image data is changed stepwise, and the density of black pixels in the background data is periodically increased and decreased. This is different from the dithering image data shown in FIGS. 4 (A), 4 (B), and 4 (C).

  As shown in FIG. 8, halftone processing using dithered image data having an input gradation value 215 and an input gradation value 195 is performed by setting some pixels of the black pixel aggregate 100 of the latent image data to white pixels. The density of black pixels in the latent image portion data is reduced. The halftone process using the dithered image data having the input gradation value 175 and the input gradation value 155 further reduces the density of black pixels in the latent image data.

  In the examples shown in FIGS. 4A, 4B, and 4C, if the input tone value of the dithering image data decreases, the density of black pixels in the background data decreases. However, in the example shown in FIG. 8, when the input gradation value 235 is changed to the dithering image data having the input gradation value 215, the density of black pixels in the background data increases. The density of black pixels in the background data decreases as the input gradation value further decreases, but then increases again.

  As shown in FIG. 9, the density of the latent image portion is not substantially proportional but decreases step by step when the input tone value of the dithering image data decreases. The density of the background portion repeatedly decreases and increases as the input tone value of the dithering image data decreases. Also in this example, there is an input tone value of dithering image data that matches the density of the latent image portion and the density of the background portion. In this example, there are a plurality of input tone values of dithering image data that match the density of the latent image portion and the density of the background portion. Therefore, the copying machine 22 can print the copy-forgery-inhibited pattern image at a uniform density by performing intermediate processing using the dithering image data shown in FIG.

  Next, dithering image data of the printing system according to the third embodiment will be described. In the dithering image data according to the third embodiment, the density of the black pixels of both the latent image portion and the background portion is reduced at the same time, as shown in FIGS. 4 (A), 4 (B), and 4 (C). The dithering image data shown in FIG.

  As shown in FIG. 10, when the input gradation value of the dithering image data is lowered, the data pattern of the latent image portion and the background portion is such that some pixels of the black pixel aggregate are white pixels.

  As shown in FIG. 11, even in the third embodiment, there are input tone values of dithering image data in which the density of the tint block image is uniform. Therefore, the copying machine 22 can print the density of the copy-forgery-inhibited pattern image uniformly even using the dithering image data according to the third embodiment.

DESCRIPTION OF SYMBOLS 10 ... Printing system 12 ... Information processing apparatus 20 ... Network 22 ... Copy machine 24 ... Control part 26 ... BUS line 30 ... Image input part 32 ... Image processing part 34 ... Printer part 35 ... Scanner part 36 ... Operation panel 38 ... Power supply control Unit 40 CPU
42 ... ROM
44 ... RAM
46 ... HDD
48 ... Image memory 48 ... Sequential image memory 50 ... Printing unit 52 ... External power supply

Claims (3)

A storage unit for storing copy-forgery-inhibited pattern image data composed of a latent image portion and a background portion and dithering image data;
An input unit for inputting image data;
Referring to the storage unit, and a combining unit that combines the copy-forgery-inhibited pattern image data with the image data input to the input unit;
A gradation changing unit that changes the gradation of the synthesized image data using the dithering image data with reference to the storage unit;
A printing unit that prints based on the image data in which the gradation changing unit has changed the gradation,
The dithering image data, Ri pattern Tona masking some pixels collection of data of the background portion,
A plurality of transmission pixels of the dithering image data are adjacent to each other in the main scanning direction and the sub-scanning direction of printing of the printing unit;
Image forming apparatus. A storage unit for storing copy-forgery-inhibited pattern image data composed of a latent image portion and a background portion and dithering image data;
An input unit for inputting image data;
Referring to the storage unit, and a combining unit that combines the copy-forgery-inhibited pattern image data with the image data input to the input unit;
A gradation changing unit that changes the gradation of the synthesized image data using the dithering image data with reference to the storage unit;
A printing unit that prints based on the image data in which the gradation changing unit has changed the gradation,
The dithering image data consists of a pattern that partially masks the pixel aggregate of the background data,
The dithering image data pattern size is the least common multiple of the latent image data pattern size and the background data pattern size.
Images forming device. A scanner unit that reads image information of a document and generates image data;
An image generated by the scanner unit is input to the input unit.
The image forming apparatus according to claim 1.