JP4057594B2 - Copier - Google Patents

Description

  The present invention relates to a copying machine, and more particularly, to a technique for preventing forgery caused by copying important documents formed with an image.

A typical prior art for preventing forgery by copying as described above is disclosed in Patent Document 1. In the prior art, when obtaining printed matter such as insurance policies and securities that should be prevented from being counterfeited, the background and the warning image are made to have the same density (area ratio) using screens with different numbers of lines. By performing multiple printing, it is uniformly recognized by the naked eye as shown in FIG. 7 (a), but when copied, copy prohibition such as “copy” is prohibited as shown in FIG. 7 (b). An anti-counterfeit printed matter is disclosed in which a warning image is raised (visualized) from the background to prevent unauthorized copying.
JP-A-7-266770

  The above prior art is a response to printed matter. On the other hand, when copying important documents such as minutes and contracts in the copying machine, the background and warning images are printed using the same method by selecting special settings. An illegal copy prevention function called a mark is adopted.

  However, in the case of a copying machine, maintenance such as screen replacement in the case of the above-described printing is rarely performed. For example, in an electrophotographic copying machine, due to changes in the photosensitive body over time, changes in toner charge amount, etc. It is difficult to obtain a stable dot reproduction. For example, an airframe having a resolution of 600 dpi when it is new may be able to reproduce dots only at a resolution of about 300 dpi at the end of its life. As a result, there is a difference in density between the warning image portion and the background portion having different resolutions, and the warning image that should appear to be buried by the naked eye may not be recognized as the background portion and may be seen. (In particular, density changes occur in the background portion of the halftone dots.)

  An object of the present invention is to provide a copying machine capable of stably maintaining the effect of preventing unauthorized copying.

Copying machine of the present invention, the image data of the images processing means warning image and the background to create the print data to be used for the image formation number of lines using different screens to each other, the printing image forming means A screen for each of the warning image and the background image data in the image processing means in a copying machine in which the image is formed by data so as to obtain a copy which prevents the copying by embedding the warning image in the background. Of these, the screen changing means for changing the number of lines of at least one screen in accordance with the deterioration of the image forming ability of the image forming means, and the number of lines among the screens for the warning image and the background image data are large. Filter size setting means for setting the size of a smoothing filter for the image data corresponding to the number of lines on the screen.

  According to the above configuration, in a copying machine in which a warning image is embedded in the background, and when copying is performed, the warning image emerges from the background, thereby obtaining a copy that prevents unauthorized copying. Even if the formed image deviates from the intended density due to the deterioration of the image forming ability of the forming unit, and the warning image that should be buried in the background comes to the surface, the warning image and the warning image and By changing the number of screen lines of at least one of the screens for each background image data, the density difference between the warning image portion and the background portion is reduced within the reproducible resolution range of the image forming means again. be able to.

  However, if the number of screen lines is changed, when the copied image obtained by the copying machine is read again by the copying machine and copied, the spatial frequency of the input image data matches the spatial frequency of the smoothing filter. If it is lost and printed out as it is, it becomes difficult to distinguish the warning image from the background. Therefore, the filter size setting means sets the size of the smoothing filter for the image data corresponding to the number of lines of the screen having the larger number of lines among the screens for the warning image and the background image data. Therefore, the image data corresponding to the screen with a large number of lines is smoothed and the halftone dot is removed and does not appear in the print data, but the gradation of the image data corresponding to the screen with a small number of lines cannot be completely removed. It will come out.

  As a result, even when the image processing screen is changed due to the deterioration of the image forming means, the warning image can be displayed with a density difference between the warning image portion and the background portion when copying.

Also, in the copying machine of the present invention, the screen change means inputs the image data of the density of a test pattern predetermined in the image processing unit, the print respectively, using the number of lines is three or more screens different from each other Test pattern generating means for creating data, density detecting means for detecting the density of each test pattern imaged by the image forming means, and the warning image in the image processing means in response to the output of the density detecting means And screen line number setting means for setting the screen line number for each image data of the background.

  According to the above configuration, the frequency characteristics, that is, the resolution is lowered due to the time-dependent change of the image forming means, and the formed image is deviated from the intended density, and the warning image that should be buried in the background appears. Even if this happens, try to form an image of the test pattern, change the screen line number (resolution) so that the appropriate density can be reproduced, and use the different line numbers for the warning image and background image data. By processing, the difference in density between the warning image portion and the background portion can be reduced within the reproducible resolution range of the image forming means. As a result, the effect of preventing unauthorized copying can be stably maintained.

Furthermore , in the copying machine of the present invention, the smoothing filter is a Gaussian filter.

  According to the above configuration, even when the original is placed at an angle, the shading can be removed well regardless of the installation angle. Thereby, tolerance which has a deterrent effect can be raised.

  In the copying machine of the present invention, as described above, a warning image is embedded in the background, and when copying is performed, the warning image emerges from the background, thereby obtaining a copy that prevents unauthorized copying. In the copying machine, the formed image is deviated from the intended density due to the deterioration of the image forming ability of the image forming means, and a warning image that should be buried in the background comes to the surface. In order to suppress such problems by changing the number of screen lines of at least one of the screens for the warning image and the background image data, the filter size setting means includes a screen for the warning image and the background image data. The size of the smoothing filter for the image data is set corresponding to the number of lines on the screen having the larger number of lines.

  Therefore, the image data corresponding to the screen with a large number of lines is smoothed and the halftone dot is removed and does not appear in the print data, but the image data corresponding to the screen with a small number of lines cannot be completely removed. Even if the screen for image processing is changed due to the deterioration of the image forming means, the warning image portion and the background portion can have a density difference when copied, and a warning can be displayed. .

[Embodiment 1]
FIG. 1 is a block diagram showing an electrical configuration of a portion related to an image signal of a copying machine 1 according to an embodiment of the present invention, and drives a transport portion of a document or recording paper, and further a mechanical portion related to image formation. The electrical configuration relating to the configuration to be performed is omitted. The copying machine 1 is an electrophotographic copying machine. A document image from a reading device 2 such as an optical unit is converted into an electric signal by a photoelectric conversion element 3 such as a CCD, and further amplified by an analog circuit 4. Thereafter, the analog / digital conversion circuit 5 converts the image data into, for example, 8-bit digital image data and inputs the digital image data to the image processing circuit 6. When used as a scanner, the image data from the analog / digital conversion circuit 5 is output to an external device (not shown), and when used as a printer, the image data from the external device (not shown) is output. Input to the image processing circuit 6.

  The image processing circuit 6 is composed of an ASIC, IC, DSP, or the like, and uses an external image memory 7 to perform image processing such as color correction, spatial filter processing, γ correction, halftone processing, and superimposition of a plurality of images. In addition to editing processing such as alignment and image rotation, the watermark according to the present invention consisting of a warning image and a background is printed. Print data representing on / off of, for example, 1-bit dots obtained by these image processes is input to a printing device 8 such as a laser writing unit, and image formation is performed. The image memory 7 stores image data of the test pattern, which will be described later, together with image data of the warning image.

  On the other hand, a density sensor 11 for detecting the density of a toner patch for density correction formed on the photosensitive drum is provided in the vicinity of the photosensitive drum, and the detection output of the density sensor 11 is an amplifier 12. Is then converted into, for example, 8-bit digital density data by the analog / digital conversion circuit 13 and input to the CPU 9 realized by a microcomputer or the like. The density sensor 11 is a reflective sensor that irradiates the surface of the photosensitive drum on which the test pattern is formed with a specified amount of light, and reads the amount of reflected light with a spot diameter of 1 mm, for example. In response to the output from the CPU 9 corresponding to the output from the density sensor 11, the image processing circuit 6 performs density correction and the like, and selects the screen line number for printing a watermark according to the present invention to be described later. Process.

  FIG. 2 is a block diagram showing a part of the functional configuration of the image processing circuit 6. The image processing circuit 6 performs shading correction, scanner γ correction, and the like on the image data input from the analog / digital conversion circuit 5 or an external device, and then inputs the data to the configuration shown in FIG. First, spatial filter processing such as edge enhancement and averaging is performed in the spatial filter processing unit 21. Subsequently, γ correction is performed in the γ correction processing unit 22, and then input to the halftone processing unit 23.

  The halftone processing unit 23 selects an optimal halftone reproduction method (23 a to 23 e) corresponding to the number of gradations that can be reproduced by the printing device 8. In the example of FIG. 2, the error diffusion processing unit 23a, the high line number halftone screen processing unit 23b, the low line number halftone screen processing unit 23c, the high line number tens of thousands screen processing unit 23d, and the low line number One of the processing units of the line screen processing unit 23e is selected by the selector 23g, and processing is performed, whereby the 1-bit print data is created and supplied to the printing device 8. The high line number halftone screen processing unit 23b and the low line number halftone screen processing unit 23c express the density by changing the dot diameter, and the high line number tens of thousands screen processing unit 23d and the low line number halftone screen processing unit 23c The screen processing unit 23e expresses the density by changing the thickness of the line.

  In the copying machine 1 configured as described above, in the present invention, when printing of the watermark is selected by an operation from an operating means (not shown), the CPU 9 displays the warning image and background stored in the image memory 7. Is supplied to the image processing circuit 6 to generate print data for printing them out. At this time, the warning image portion and the background portion use screens having different line numbers of the high line number halftone screen processing unit 23b and the low line number halftone screen processing unit 23c, respectively. Then, the CPU 9 selects the screen line numbers of the high line number halftone screen processing unit 23b and the low line number halftone screen processing unit 23c. Note that either the warning image portion or the background portion may have a high screen line number.

  For this reason, the CPU 9 performs image processing on the test pattern image data stored in the image memory 7 at a predetermined timing, for example, when the power is turned on, when the number of copies reaches a predetermined number, or at the time of density adjustment. Output to the circuit 6, print data is created using three or more types of screens having different numbers of lines, and the print device 8 is composed of a toner patch of a solid image of a predetermined density on a photosensitive member or a transfer belt. A test pattern is formed. The toner density of the test pattern is detected by the density sensor 11, and the screen line numbers of the high line number halftone screen processing unit 23b and the low line number halftone screen processing unit 23c are selected in accordance with the detection result. . The test patterns may be collectively formed in the width direction of the photoconductor or the transfer belt. In this case, the density sensor 11 and the related configuration are required by the number of test patterns. By sequentially forming in the circumferential direction, the concentration sensor 11 and the related configuration can be made one.

  Specifically, the CPU 9 and the image memory 7 constitute test pattern generating means, and input test pattern data having an area ratio corresponding to the density of the warning image to the image processing circuit 6 as image processing means, A test pattern is formed on the printing device 8 which is an image forming means. FIG. 3 shows an example of a test pattern in which the area ratio is 50% of the intermediate density. From the highest resolution 424 lines / inch screen that can be reproduced in the new state of the airframe shown in FIG. Examples are shown in the screen of 212 lines / inch shown in FIG. 3B, the screen of 141 lines / inch shown in FIG. 3C, and the screen of 106 lines / inch of the lowest resolution shown in FIG. ing.

  As described above, the dot diameter reproducible by the printing device 8 changes due to changes in the photoreceptor over time, changes in the toner charge amount, etc., and this is preferable for reproducing the test pattern density (as expected). The number of screen lines can change). If the number of input bits to the CPU 9 of the detection result of the density sensor 11 serving as the density detection means is, for example, the aforementioned 8 bits, the data is in the range of 0 to 255, for example, and the 50% density is 127. Become. Therefore, when the density detection results when each screen shown in FIG. 3 is used are shown in Tables 1 and 2, density data in an allowable range at the 50% density is, for example, 112 to 144 (however, the density is It is assumed that the output of the density sensor 11 such as the gain of the amplifier 12 is calibrated so that the data is 0 for a complete white area and 255 for a solid black area. The screen line numbers selected by the high line number halftone screen processing unit 23b and the low line number halftone screen processing unit 23c are as follows.

  That is, in the example of Table 1, the density data is within the allowable range in the screens with 106 lines, 141 lines, and 212 lines in the number of lines (resolution). The high line number halftone screen processing unit 23b and the low line number halftone dot screen processing unit 23c are used so as to use a screen having 212 lines having the largest number of screen lines and 141 lines other than that. Set each. In the example of Table 2, the density data is within the allowable range for the screens having 141 lines and 106 lines. Therefore, the high line number halftone screen processing unit 23b The low line number halftone screen processing unit 23c is set to use each of these screens.

  With this configuration, when printing a watermark for preventing illegal copying, the frequency characteristics, that is, the resolution is lowered due to a change with time of the printing device 8 or the like, and the formed image is deviated from the intended density. Even if a warning image that should be buried in the background comes to emerge, the warning image portion and the background can be changed within the reproducible resolution range of the printing apparatus 8 by changing the number of screen lines. The density difference from the portion can be reduced. As a result, the effect of preventing unauthorized copying can be stably maintained.

  Even if the test pattern is formed with the same density as described above, if the number of screen lines used for creating the print data is different, the image should be formed in the same manner as the image density actually formed is different. When the density of the test pattern is different, the CPU 9 changes the density of the test pattern in accordance with the density of the warning image, corresponding to the appropriate number of screen lines (which can obtain the expected density). Thus, it is possible to select a screen having the most appropriate number of lines for the density of the warning image actually formed.

  It should also be noted that in the copying machine 1 of the present invention, the CPU 9 which is a screen changing means and a screen line number setting means, and is a filter size setting means, has a high line number halftone screen processing unit 23b as described above. When the screen line number of the low line number halftone screen processing unit 23c is changed, the size of the smoothing filter of the spatial filter processing unit 21 is changed in conjunction therewith. The smoothing filter is composed of a Gaussian filter. For example, when one line is smoothed, its frequency characteristic changes as shown in FIG. 4 depending on the filter size.

  In FIG. 4, reference numeral α1 represents a filter having a filter size of 5 × 1 dots. When the number of screen lines of the input image data is 200 or more, there is no change in shading, and the shading is barely recognized with about 175 lines, and 150 lines. The degree indicates that the shading can be clearly recognized. On the other hand, the reference symbol α2 represents a filter having a filter size of 7 × 1 dots, and the density cannot be recognized even with a smaller number of lines (lower resolution) than the 5 × 1 dot filter. Similarly, the reference symbol α3 has a filter size of This represents a 9 × 1 dot filter, indicating that even if the number of screen lines is about 125, light and shade can hardly be recognized.

  As the smoothing filter of the spatial filter processing unit 21, for example, Gaussian filters having respective dot sizes of 5 × 5, 7 × 7, and 9 × 9 are provided, and the CPU 9 is a high line number network having a large number of lines. According to the number of lines of the dot screen processing unit 23b, the image data processed by the screen having a large number of lines can be smoothed, and the density of the image data processed by the low line number halftone dot screen processing unit 23c is The Gaussian filter is selected for a size that cannot be removed.

  FIG. 5A and FIG. 6A show examples of weights in 7 × 7 and 9 × 9 Gaussian filters, respectively.

  For example, when the number of lines of the halftone screen processing unit 23b is 175, a 5 × 5 Gaussian filter is selected, when 150 lines, a 7 × 7 Gaussian filter is selected, and when 133 lines are used, a 9 × 9 Gaussian filter is selected. A filter is selected.

  Thus, for example, when the background portion is processed by the high line number halftone screen processing unit 23b and the warning image portion is processed by the low line number halftone screen processing unit 23c, the spatial filter processing unit 21 performs Gaussian filter processing. By applying to the entire surface, the shade of the halftone dot in the background portion is removed and does not appear in the print data, and the shade of the halftone dot in the warning image portion cannot be completely removed and is raised.

  As a result, even if the screen of the image processing circuit 6 is changed due to deterioration of the printing device 8, a warning display can be made with a difference in density between the warning image portion and the background portion when copying. In addition, by using a Gaussian filter as the smoothing filter, even when the original is placed at an angle, the shading of the halftone dot can be satisfactorily removed regardless of the installation angle. Thereby, tolerance which has a deterrent effect can be raised.

  The present invention is not limited to the integrated copying machine as described above, but can be applied to a configuration that realizes the function of the copying machine by combining a scanner and a printer.

1 is a block diagram showing an electrical configuration of a portion related to an image signal of a copying machine according to an embodiment of the present invention. FIG. 2 is a block diagram showing a part of a functional configuration in the image processing circuit of the copying machine shown in FIG. 1. It is a figure which shows the example of the test pattern using the screen of a different line number by the same area ratio 50%. It is a graph which shows the frequency characteristic of the Gaussian filter of 1 line. It is a figure which shows the characteristic of a 7 * 7 Gaussian filter. It is a figure which shows the characteristic of a 9x9 Gaussian filter. It is a perspective view which shows the printed matter in which the countermeasure for forgery prevention was given, and the copied matter at the time of copying it illegally.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Copy machine 2 Reading apparatus 3 Photoelectric conversion element 4 Analog circuit 5 Analog / digital conversion circuit 6 Image processing circuit 7 Image memory 8 Printing apparatus 9 CPU
11 Density sensor 12 Amplifier 13 Analog / digital conversion circuit 21 Spatial filter processing unit 22 γ correction processing unit 23 Halftone processing unit 23 a Error diffusion processing unit 23 b High line number halftone screen processing unit 23 c Low line number halftone screen processing unit 23 d High line tens of thousands screen processing unit 23e Low line tens of thousands screen processing unit 23g selector

Claims (3)

The image processing means creates print data for image formation using screens with different numbers of lines for the warning image and background image data, and the image forming means performs image formation with the print data. In the copying machine in which the warning image is embedded in the background to obtain a copy to prevent copying,
Of the screens for the warning image and background image data in the image processing means, a screen changing means for changing the number of lines of at least one screen in accordance with the deterioration of the image forming ability of the image forming means;
Filter size setting means for setting a size of a smoothing filter for the image data corresponding to the number of lines of the screen having a large number of lines among the screens for the warning image and the background image data. Copy machine to do. The screen changing means includes
Test pattern generating means for inputting image data of a test pattern having a predetermined density to the image processing means, and generating print data using three or more types of screens having different numbers of lines;
Density detecting means for detecting the density of each test pattern imaged by the image forming means;
The screen line number setting means for setting the screen line number for each of the warning image and background image data in the image processing means in response to the output of the density detection means. 1. The copying machine according to 1 . 3. The copying machine according to claim 1 , wherein the smoothing filter is a Gaussian filter .

Images