JP4653006B2 - Method, apparatus and program for determining density signal value of latent image and background image - Google Patents

Description

The present invention relates to a method, apparatus, and program for determining density signal values of a latent image and a background image by reading a sheet .

  There is a special paper called anti-counterfeit paper. In this forgery prevention paper, a character string such as “COPY” is embedded so that it cannot be seen at first glance. The embedded character string rises on a copy obtained by copying the forgery prevention paper. Therefore, a document created using such anti-counterfeit paper can be easily distinguished from the copy. In addition, the user can be hesitant to use a copy of the document.

  Anti-counterfeit paper has such effects and has been used to create resident cards and forms. However, there is a problem that anti-counterfeit paper is expensive compared to plain paper. In addition, there is a problem that only a character string embedded at the time of paper production is lifted on a copy.

  Under such circumstances, in recent years, a new technology that can obtain the same effect as that of the forgery prevention paper has been attracting attention (see Patent Document 1). This is a technique in which original data and copy-forgery-inhibited pattern (sometimes called copy-checked copy-forgery-inhibited pattern) created using a computer are combined inside the printer, and image data with a copy-forgery-inhibited pattern obtained by this combination is output to plain paper It is. A character string or the like is embedded in the copy-forgery-inhibited pattern image. For this reason, on the copy obtained by copying the image with the copy-forgery-inhibited pattern, the embedded character string appears as in the case of using the anti-counterfeit paper. Since this technology uses plain paper, there is an advantage that the original can be created at a lower cost than when using anti-counterfeit paper. Also, with this technique, new copy-forgery-inhibited pattern image data can be generated each time an original is created. Therefore, this technique has an advantage that the color of the copy-forgery-inhibited pattern image and the embedded character string can be freely set.

  By the way, the copy-forgery-inhibited pattern image is composed of a “remaining” region and a “disappearing” region (or “thinner than the remaining region”) on the copy. Note that the reflection densities in these two regions are substantially the same on the original. For this reason, it is not known that a character string such as “COPY” is embedded in the human eye. Here, “remaining” means that the image in the original is accurately reproduced on the copy. “Disappear” means that the original image is not reproduced on the copy. The reflection density is measured with a reflection densitometer.

  Hereinafter, the “remaining” area on the copy is referred to as a “latent image portion”, and the “disappearing” area (or “becomes thinner than the remaining area”) on the copy is referred to as a “background portion”.

  FIG. 38 is a diagram illustrating the state of dots in a tint block image. In the figure, the area where the dots are concentrated is the latent image part, and the area where the dots are dispersed is the background part. The dots in these two regions are generated by different halftone dot processing and different dither processing. For example, the dots in the latent image portion are generated by halftone dot processing with a low number of lines, and the dots in the background portion are generated by halftone dot processing with a high number of lines. Alternatively, the dots in the latent image portion are generated using a dot concentration type dither matrix, and the dots in the background portion are generated using a dot dispersion type dither matrix.

  Incidentally, the reproduction capability of a copying machine depends on the input resolution and output resolution of the copying machine. Therefore, there is a limit to the reproduction capability of the copying machine. As a result, when the dots in the latent image portion of the tint block image are formed larger than the dots that can be reproduced by the copying machine and the dots in the background portion are formed smaller than the dots that can be reproduced, the Then, the dots in the latent image portion are reproduced, but the dots in the background portion are difficult to reproduce. As a result, the latent image portion is reproduced darker than the background portion on the copy. Hereinafter, when the latent image portion is reproduced darker than the background portion on the copy, the embedded character string and the like appear to be raised, which is called visualization.

  FIGS. 39A and 39B are views showing this visualization. The figure conceptually shows that concentrated dots (large dots) are reproduced on the copy and dispersed dots (small dots) are not accurately reproduced on the copy.

  The copy-forgery-inhibited pattern image is not limited to the above-described configuration, and may be configured such that a character string such as “COPY”, a symbol, a pattern, or the like appears (visualizes) on the copy so that a human can recognize it. That's fine. Even if a character string such as “COPY” is shown in white on the copy, it can be said that the copy-forgery-inhibited pattern image has achieved the purpose. In this case, it goes without saying that the area of “COPY” is called the background portion.

  As described above, the copy-forgery-inhibited pattern image is created such that the reflection density of the latent image portion is substantially equal to the reflection density of the background portion. For example, Patent Document 1 describes that gradation correction is performed so that the gradation of a latent image portion that has been subjected to halftone processing and a background portion that has not been subjected to halftone processing substantially match at the time of output.

Although Patent Document 2 and Patent Document 3 do not describe the background pattern, the exposure amount and PWM parameters are adjusted in order to form an image of a small dot area having a reflection density that substantially matches the reflection density of the large dot area. A technique for doing this is described.
JP 2001-197297 A Japanese Patent Registration No. 0235926 JP 2000-196879 A

  However, the dot size output by the device (for example, MFP, printer, etc.) changes due to the influence of the environment in which the device is placed and the age of the device. As a result, the reflection density of the output image changes. For this reason, even if the initial setting is made so that the reflection densities of the latent image portion and the background portion substantially coincide with each other by the method described in Patent Document 1, the size of the output small dots is larger than the size of the previously output small dots. If it is slightly larger (or smaller), a background pattern image in which the background portion is darker (or lighter) than the latent image portion is generated. As a result, there is a problem that the latent image is visually recognized in the original (the latent image is not concealed).

  Further, when the size of the large dot becomes large (or small), a tint block image in which the latent image portion is darker (or lighter) than the background portion is formed. As a result, there is a problem that the latent image is visually recognized in the original.

  Furthermore, when both the large dot size and the small dot size increase, an original having a darker tint block image is created. As a result, there was a problem that the readability of the content (for example, the name of the resident's card) deteriorated, and the latent image portion and the background portion were reproduced on the copy and the latent image did not appear. On the other hand, the large and small dots are both reduced in size and the tint block image becomes thin. As a result, neither the latent image portion nor the background portion is reproduced on the copy and the latent image does not appear. did.

  To summarize the above, there is a problem that a copy-forgery-inhibited pattern image having a low latent image concealment property is formed in the original. There is also a problem that a tint block image with low content readability is formed. In addition, there is a problem in that a copy-forgery-inhibited pattern image is formed in the copy.

  By the way, in Patent Document 2 and Patent Document 3, a technique is disclosed in which, after outputting a test sheet having a plurality of patches, a user is allowed to determine a patch that appears to be equal in density to a predetermined patch. In Patent Document 2, density adjustment is performed by determining an optimum exposure amount based on a result determined by the user. Further, in Patent Document 3, density adjustment is performed by determining an optimum parameter of PWM based on a result determined by a user.

  However, the techniques described in Patent Document 2 and Patent Document 3 are visual adjustments by the user and do not necessarily provide accurate results, and are also burdensome to the user and highly convenient. It's hard to say.

A method for setting a density signal value used for generating a latent image and a density signal value used for generating a background image in the present invention for solving the above-described problems has the following configuration. To do. That is, a forming step of forming a plurality of latent image patches generated using a plurality of density signal values and a plurality of background patches generated using a plurality of density signal values on at least one sheet; and An acquisition step of acquiring the luminance values of the plurality of latent image patches and the luminance values of the plurality of background patches in the image data obtained by reading, and the luminances of the plurality of latent image patches acquired in the acquisition step Among the values, the density signal value used to generate the latent image patch having the luminance value closest to the predetermined value, and the luminance value of the plurality of background patches acquired in the acquisition step is the highest in the predetermined value. A setting step for setting a density signal value used for generating a background patch having a near luminance value to a density signal value for generating the latent image and a density signal value for generating the background image; Have And wherein the door.

  According to the present invention, the density of the tint block image can be automatically and optimally determined. As a result, a tint block image having an appropriate density can be generated easily and reliably.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  In the following embodiments, a latent image character string and a latent image symbol are set in a latent image portion of a copy-forgery-inhibited pattern image, and are combined with an arbitrary content image to output an original (original printed matter). Further, the description will be made assuming that the latent image character string and the latent image symbol appear to rise as the background portion becomes thinner than the latent image portion in the copy.

  However, the background pattern image in the present invention is not limited to this. For example, as described above, a latent image character string or a latent image symbol is set as a background portion, and an area around the background portion is set as a latent image portion. The symbol may be expressed in white.

  The present invention is not defined by the type of tint block image, its generation process, color, shape, size, or the like.

  Further, by arranging different dot patterns on the latent image portion and the background portion of the original, it is possible to cause different moiré in the latent image portion and the background portion on the copy, thereby causing a difference in reflection density.

  Various methods that can be taken into consideration, such as forming a tint block image using a line instead of a dot, can be substituted.

<Printing system (Fig. 1)>
Next, Example 1 will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a printing system according to an embodiment of the present invention. In this system, the host computer 40 and the three image forming apparatuses (10, 20, 30) are connected to the LAN 50. However, in the printing system according to the present invention, the number of connections is not limited. In this embodiment, LAN is applied as a connection method, but the present invention is not limited to this. For example, an arbitrary network such as a WAN (public line), a serial transmission method such as USB, and a parallel transmission method such as Centronics and SCSI can be applied.

  A host computer (hereinafter referred to as a PC) 40 has a function of a personal computer. The PC 40 can send and receive files and send and receive e-mails using the FTP and SMB protocols via the LAN 50 and WAN. Further, it is possible to issue a print command from the PC 40 to the image forming apparatuses 10, 20, and 30 via a printer driver.

  The image forming apparatuses 10 and 20 are apparatuses having the same configuration. The image forming apparatus 30 is an image forming apparatus having only a print function, and does not have the scanner unit included in the image forming apparatuses 10 and 20. In the following, for the sake of simplicity of explanation, the configuration will be described in detail focusing on the image forming apparatus 10 of the image forming apparatuses 10 and 20.

  The image forming apparatus 10 includes a scanner unit 13 that is an image input device, a printer unit 14 that is an image output device, a controller (controller unit) 11 that controls operation of the entire image forming apparatus 10, and an operation unit that is a user interface (UI). 12 is comprised.

<Image Forming Apparatus 10 (FIG. 2)>
An appearance of the image forming apparatus 10 is shown in FIG. The scanner unit 13 converts information of an image into an electrical signal by inputting reflected light obtained by exposing and scanning the image on the document to the CCD. The scanner unit further converts the electrical signal into a luminance signal composed of R, G, and B colors, and outputs the luminance signal to the controller 11 as image data.

  The document is set on the tray 202 of the document feeder 201. When the user instructs to start reading from the operation unit 12, a document reading instruction is given from the controller 11 to the scanner unit 13. Upon receiving this instruction, the scanner unit 13 feeds the documents one by one from the tray 202 of the document feeder 201 and performs a document reading operation. Note that the document reading method is not an automatic feeding method by the document feeder 201, but a method of scanning the document by placing the document on a glass surface (not shown) and moving the exposure unit.

  The printer unit 14 is an image forming device that forms image data received from the controller 11 on a sheet. In this embodiment, the image forming method is an electrophotographic method using a photosensitive drum or a photosensitive belt, but the present invention is not limited to this. For example, the present invention can also be applied to an ink jet system that prints on paper by ejecting ink from a micro nozzle array. The printer unit 14 is provided with a plurality of paper cassettes 203, 204, and 205 that allow selection of different paper sizes or different paper orientations. The paper after printing is discharged to the paper discharge tray 206.

<Detailed Description of Controller 11 (FIG. 3)>
FIG. 3 is a block diagram for explaining the configuration of the controller 11 of the image forming apparatus 10 in more detail.

  The controller 11 is electrically connected to the scanner unit 13 and the printer unit 14. On the other hand, the controller 11 is connected to the PC 40 or an external device via the LAN 50 or the WAN 331. As a result, image data and device information can be input and output.

  The CPU 301 comprehensively controls access to various connected devices based on a control program stored in the ROM 303, and also performs overall control of various processes performed in the controller. A RAM 302 is a system work memory for the operation of the CPU 301 and also a memory for temporarily storing image data. The RAM 302 includes an SRAM that retains stored content even after the power is turned off, and a DRAM that erases the stored content after the power is turned off. The ROM 303 stores a boot program for the apparatus. An HDD 304 is a hard disk drive and can store system software and image data.

  The operation unit I / F 305 is an interface unit for connecting the system bus 310 and the operation unit 12. The operation unit I / F 305 receives image data to be displayed on the operation unit 12 from the system bus 310 and outputs the image data to the operation unit 12 and outputs information input from the operation unit 12 to the system bus 310.

  A network I / F 306 is connected to the LAN 50 and the system bus 310 to input / output information. The Modem 307 is connected to the WAN 331 and the system bus 310, and inputs and outputs information. A binary image rotation unit 308 converts the direction of image data before transmission. The binary image compression / decompression unit 309 converts the resolution of the image data before transmission into a resolution that matches a predetermined resolution or the partner's ability. For compression and expansion, methods such as JBIG, MMR, MR, and MH are used. The image bus 330 is a transmission path for exchanging image data, and is configured by a PCI bus or IEEE1394.

  The scanner image processing unit 312 corrects, processes, and edits image data received from the scanner unit 13 via the scanner I / F 311. The scanner image processing unit 312 determines whether the received image data is a color document or a monochrome document, a character document, or a photographic document. Then, the determination result is attached to the image data. Such accompanying information is referred to as image area data. Details of processing performed by the scanner image processing unit 312 will be described later.

  The compression unit 313 receives the image data, and divides the image data into blocks of 32 pixels × 32 pixels. The 32 × 32 pixel image data is referred to as tile data. FIG. 4 conceptually shows this tile data. In a document (paper medium before reading), an area corresponding to the tile data is referred to as a tile image. The tile data is added with the average luminance information in the 32 × 32 pixel block and the coordinate position of the tile image on the document as header information. Further, the compression unit 313 compresses image data including a plurality of tile data. The decompression unit 316 decompresses image data composed of a plurality of tile data, raster-expands it, and sends it to the printer image processing unit 315.

  The printer image processing unit 315 receives the image data sent from the decompression unit 316 and performs image processing on the image data while referring to image area data attached to the image data. The image data after the image processing is output to the printer unit 14 via the printer I / F 314. Details of processing performed by the printer image processing unit 315 will be described later.

  The image conversion unit 317 performs a predetermined conversion process on the image data. This processing unit is composed of the following processing units.

  A decompression unit 318 decompresses the received image data. The compression unit 319 compresses the received image data. The rotation unit 320 rotates the received image data. The scaling unit 321 performs resolution conversion processing (for example, 600 dpi to 200 dpi) on the received image data. The color space conversion unit 322 converts the color space of the received image data. The color space conversion unit 322 performs a known background removal process using a matrix or a table, performs a known LOG conversion process (RGB → CMY), or performs a known output color correction process (CMY → CMYK). Can be. The binary multi-value conversion unit 323 converts the received two-gradation image data into 256-gradation image data. Conversely, the multi-level binary conversion unit 324 converts the received 256-gradation image data into 2-gradation image data using a technique such as error diffusion processing.

  The synthesizer 327 synthesizes the received two image data to generate one piece of image data. When combining two pieces of image data, a method of using an average value of luminance values of pixels to be combined as a combined luminance value, or a luminance value of a pixel having a brighter luminance level, A method for obtaining a luminance value is applied. In addition, it is possible to use a method in which the darker pixel is used as a synthesized pixel. Furthermore, a method of determining a luminance value after synthesis by a logical sum operation, a logical product operation, an exclusive logical sum operation, or the like between pixels to be synthesized is also applicable. These synthesis methods are all well-known methods. The thinning unit 326 performs resolution conversion by thinning out the pixels of the received image data, and generates image data such as 1/2, 1/4, and 1/8. The moving unit 325 adds a margin part to the received image data or deletes the margin part.

  The RIP 328 receives intermediate data generated based on PDL code data transmitted from the PC 40 or the like, and generates bitmap data (multi-value).

<Detailed Description of Scanner Image Processing Unit 312 (FIG. 5)>
FIG. 5 shows an internal configuration of the scanner image processing unit 312.

  The scanner image processing unit 312 receives image data composed of RGB 8-bit luminance signals. This luminance signal is converted by the masking processing unit 501 into a standard luminance signal that does not depend on the filter color of the CCD.

  The filter processing unit 502 arbitrarily corrects the spatial frequency of the received image data. This processing unit performs arithmetic processing using, for example, a 7 × 7 matrix on the received image data. By the way, in a copying machine or a multifunction machine, a character mode, a photo mode, or a character / photo mode can be selected as a copy mode by depressing the 704 tab in FIG. When the character mode is selected by the user, the filter processing unit 502 applies a character filter to the entire image data. When the photo mode is selected, a photo filter is applied to the entire image data. When the character / photo mode is selected, the filter is adaptively switched for each pixel in accordance with a character photo determination signal (part of image area data) described later. In other words, it is determined for each pixel whether to apply a photo filter or a character filter. Note that coefficients for smoothing only high-frequency components are set in the photographic filter. This is because the roughness of the image is not noticeable. In addition, a coefficient for performing strong edge enhancement is set in the character filter. This is to increase the sharpness of the characters.

  The histogram generation unit 503 samples the luminance data of each pixel constituting the received image data. More specifically, luminance data in a rectangular area surrounded by a start point and an end point specified in the main scanning direction and the sub scanning direction are sampled at a constant pitch in the main scanning direction and the sub scanning direction. Then, histogram data is generated based on the sampling result. The generated histogram data is used to estimate the background level when performing background removal processing. The input-side gamma correction unit 504 converts luminance data having nonlinear characteristics using a table or the like.

  A color / monochrome determination unit 505 determines whether each pixel constituting the received image data is a chromatic color or an achromatic color, and uses the determination result as a color / monochrome determination signal (part of image area data). To accompany. The character photo determination unit 506 determines whether each pixel constituting the image data is a pixel constituting a character or a pixel constituting a character other than a character (for example, a photograph). Then, the determination result is attached to the image data as a character photograph determination signal (part of image area data).

<Detailed Description of Printer Image Processing Unit 315 (FIG. 6)>
FIG. 6 shows the flow of processing performed in the printer image processing 315.

  The background removal processing unit 601 uses the histogram generated by the scanner image processing unit 312 to remove (remove) the background color of the image data. The monochrome generation unit 602 converts color data into monochrome data. The Log conversion unit 603 performs luminance density conversion. For example, the Log conversion unit 603 converts RGB input image data into CMY image data. The output color correction unit 604 performs output color correction. For example, image data input as CMY is converted into CMYK image data using a table or matrix. The output-side gamma correction unit 605 performs correction so that the signal value input to the output-side gamma correction unit 605 is proportional to the reflection density value after copying output. The halftone correction unit 606 performs arbitrary halftone processing in accordance with the number of gradations of the printer unit to be output. For example, the halftone correction unit 606 performs binarization or binarization on the received high gradation image data.

  Each processing unit in the scanner image processing unit 312 and the printer image processing unit 315 can output the received image data without performing each processing. Such passing of data without performing processing in a certain processing unit will be expressed as “through the processing unit” below. The description of the controller 11 has been described above.

<Description of Copy Operation and PDL Print Operation>
Next, a copy operation and a PDL print operation will be described with reference to FIGS. 2, 5, and 6. FIG.

  First, the copy operation will be described. The document read by the scanner unit 13 is sent as image data to the scanner image processing unit 312 via the scanner I / F 311. The scanner image processing unit 312 performs the processing shown in FIG. 5 on this image data, and generates image area data together with new image data. The image area data is attached to the image data. Subsequently, the compression unit 313 generates tile data by dividing the image data into blocks of 32 pixels × 32 pixels. Further, the compression unit 313 compresses the image data including the plurality of tile data. The image data compressed by the compression unit 313 is sent to the RAM 302 and stored. The image data is sent to the image conversion unit 317 as necessary, subjected to image processing, and then sent again to the RAM 302 for storage. Thereafter, the image data stored in the RAM 302 is sent to the decompression unit 316. The decompression unit 316 decompresses this image data. Further, the decompression unit 316 raster-expands image data composed of a plurality of tile data after decompression. The rasterized image data is sent to the printer image processing unit 315. The printer image processing unit 315 performs image data editing according to image area data attached to the image data. This process is the process shown in FIG. The image data that has been edited by the printer image processing unit 315 is sent to the printer unit 14 via the printer I / F 314. Finally, the printer unit 14 forms an image on the output paper.

  Note that the editing method in each processing unit in the scanner image processing unit 312 or the printer image processing unit 315, that is, each processing unit shown in FIGS. 5 and 6 is switched by register switching. This register switching is performed according to image area data, setting information (by the user) from the operation unit 12, or the like. Although omitted in the above description, it goes without saying that processing stored in the ROM 303 or HDD 304 and image data extraction processing stored in the ROM 303 or HDD 304 may be performed as necessary.

  Subsequently, the PDL operation will be described. PDL data sent from the PC 40 via the LAN 50 is sent to the RAM 302 via the Network I / F 306 and stored. Intermediate data generated by interpreting the PDL data stored in the RAM 302 is sent to the RIP 328. The RIP 328 renders the intermediate data to generate raster format image data. The generated raster format image data is sent to the compression unit 329. The compression unit 329 compresses the image data after dividing it into blocks. The compressed image data is sent to the RAM 302. The image data is accompanied by image area data corresponding to object data (data indicating a character image or a photographic image) included in the PDL data. When PDL printing is instructed, this image data is sent to the printer unit 14 and an image is formed on the output paper. Since this operation is the same as the copy operation, description thereof is omitted.

  Next, a method for setting a background pattern will be described.

<Explanation of operation screen>
FIGS. 7, 8, 9, and 10 show operation screens displayed when the initial screen and the background pattern are set.

  FIG. 7 shows an initial screen in the image forming apparatus 10. An area 701 indicates whether or not the image forming apparatus 10 is ready for copying, and indicates the set number of copies. A document selection tab 704 is a tab for selecting a document type. When this tab is depressed, three types of selection menus of text, photo, and text / photo mode are displayed in a pop-up. A finishing tab 706 is a tab for performing settings related to various finishings. A duplex setting tab 707 is a tab for performing settings relating to duplex reading and duplex printing. A reading mode tab 702 is a tab for selecting an original reading mode. When this tab is depressed, three types of selection menus of color / black / automatic (ACS) are popped up. Note that color copy is performed when color is selected, and monochrome copy is performed when black is selected. When ACS is selected, the copy mode is determined by the monochrome color determination signal described above.

  FIG. 8 is a screen displayed when the application mode tab 705 in FIG. 7 is pressed down. The user can make settings relating to the reduced layout, color balance, background pattern, and the like on this screen.

  FIG. 9 is a screen displayed when the copy-forgery-inhibited pattern tab 801 in FIG. 8 is pressed down. On this screen, the user can set character string information (confidential, copy prohibition, invalid, CONFIDENTIAL, confidential, copy), symbol information (★), and the like as latent images. For example, when the symbol information (★) is set as a latent image, the symbol information tab 901 may be pushed down and then the Next tab 902 may be pushed down.

  FIG. 10 is a screen displayed when the Next tab 902 in FIG. 9 is pressed down. The user can set the font size and color of the latent image on this screen. Font size candidates include large, medium, and small (1001), and color candidates include black, magenta, and cyan (1002). When the OK tab 1003 is pressed after the font and color settings are completed, the background pattern setting is completed.

<Image formation processing of image data with tint block>
In the following, a description will be given of the process from the original image data obtained by reading the original to the copy-forgery-inhibited pattern image data until the image is formed on the output paper. In executing each process, the CPU 301 performs overall control. The RAM 302 functions as a main memory or work area for the CPU 1.

  When an instruction to add a background pattern to a document is issued through the operation screen (FIGS. 8 to 10 and the like), the scanner unit 13 starts a document reading process. The document image data generated by this reading process is sent to the scanner image processing unit 312 and subjected to predetermined image processing. The document image data that has undergone predetermined image processing is sent to the compression unit 313 and compressed. The compressed document image data is sent to the RAM 302 and stored together with image area data attached to the document image data. The document image data stored in the RAM 302 is composed of a plurality of tile data. The above processing is the same as the processing described in <Copy operation>.

  Thereafter, the document image data stored in the RAM 302 is sent to the decompression unit 318. A decompression unit 318 decompresses the original image data. The expanded document image data is sent to the color space conversion unit 322. The color space conversion unit 322 performs background removal processing, monochrome generation processing, log conversion processing, and output color correction processing on the document image data. These processes correspond to the processes performed in the background removal processing unit 601, the monochrome generation unit 602, the log conversion unit 603, and the output color correction unit 604 in FIG. The document image data subjected to the above processing is sent to the compression unit 319. The compression unit 319 compresses the document image data that has been subjected to image processing by the color space conversion unit 322. The compressed document image data is sent to the RAM 302 and stored therein. On the other hand, copy-forgery-inhibited pattern image data generated by the processing described later is stored in the RAM 302 as uncompressed image data. Here, the copy-forgery-inhibited pattern image data is any one of C image data, M image data, and K image data. Which color of the image data is selected depends on which color is selected by the user using the display screen (FIG. 10). Note that the copy-forgery-inhibited pattern image data stored in the RAM 302 is composed of a plurality of tile data like the original image data.

  Subsequently, the document image data stored in the RAM 302 is sent to the decompression unit 318. A decompression unit 318 decompresses the original image data. The expanded document image data is sent to the synthesis unit 327. Similarly, the copy-forgery-inhibited pattern image data is sent to the synthesis unit 327 via the decompression unit 318. The decompressing unit 318 does not decompress the tint block image data. This is because the tint block image data is not originally compressed. The synthesizer 327 synthesizes these two image data. Since the two image data are both composed of a plurality of tile data, the combined image data is also composed of a plurality of tile data. The composite image data is sent to the compression unit 319. The compression unit 319 compresses the composite image data. The compressed composite image data is sent to the RAM 302 and stored therein. Further, the composite image data stored in the RAM 302 is sent to the decompression unit 316. The decompression unit 316 decompresses the composite image data. Furthermore, the expanded composite image data is rasterized. The rasterized composite image data is sent to the printer image processing unit 315.

  Subsequently, the printer image processing unit 315 performs output side gamma correction processing and halftone correction processing on the composite image data. These processes correspond to the processes performed by the output-side gamma correction unit 605 and the halftone correction unit 606 in FIG. On the other hand, background removal processing, monochrome generation processing, log conversion processing, and output color correction processing are not performed. These processes correspond to the processes performed by the background removal processing unit 601, the monochrome generation unit 602, the log conversion unit 603, and the output color correction unit 604 in FIG. The reason why the background removal process, the log conversion process, and the output color correction process are not performed on the composite image data is to prevent the copy-forgery-inhibited pattern image from being destroyed by performing these processes. Note that, as described above, these processes are performed on the document image data by the color space conversion unit 322 in advance.

  The composite image data subjected to the above processing in the printer image processing unit 315 is sent to the printer unit 14 via the printer I / F 314. The printer unit 14 forms an image of the composite image data on output paper. The above is the procedure of the image forming process for the image with a tint block (composite image).

  Although omitted in the above description, it goes without saying that the processing stored in the ROM 303 and the HDD 304 and the image data stored in the ROM 303 and the HDD 304 may be taken out as necessary.

<Flow of generation of tint block image data (FIG. 11)>
Next, the flow of processing when the copy-forgery-inhibited pattern image data is generated will be described with reference to FIG.

  First, bitmap data is generated based on latent image information (confidential, copy prohibition, symbol information, etc.) designated by the user. The symbol pattern 1101 is a conceptual diagram of bitmap data generated based on symbol information.

  Subsequently, a latent image pattern 1102 and a background pattern 1103 (both bitmap data) are generated by dither processing.

  Although the dither processing is a known technique, the case where both the dot concentration type dither matrix and the dot dispersion type matrix are 4 × 4 (FIGS. 12 and 13) is used as an example and is easily described with reference to FIGS. Give a simple explanation. FIG. 14 shows dot patterns generated by applying density signal values 3, 6, and 9 to the dot concentration type dither matrix shown in FIG. Here, when FIG. 12 is compared with FIG. 14, a dot is placed (on) at a pixel position where the numerical value in the dot concentration type dither matrix (FIG. 12) is equal to or less than the density signal value. You can see that Similarly, FIG. 15 shows dot patterns generated by applying density signal values 2, 4, and 5 to the dot dispersion type dither matrix shown in FIG. 14 and 15 are compared, it can be seen that the dot pattern in FIG. 14 is a concentrated dot pattern, whereas the dot pattern in FIG. 15 is a distributed dot pattern.

  This is the end of the description of the dither processing, and the description returns to the generation processing of the latent image pattern 1102 and the background pattern 1103.

  The HDD 304 stores a latent image portion generation dither matrix (hereinafter referred to as a latent image matrix) and a latent image portion generation density signal value to be applied to the dither matrix. In addition, a background portion generation dither matrix (hereinafter referred to as a background matrix) and background portion generation density signal values to be applied to the dither matrix are stored.

  In generating the latent image pattern 1102, the latent image matrix and the latent image portion generation density signal value are read from the HDD 304. The read latent image portion generation density signal value is applied to the latent image matrix. Then, a latent image pattern 1102 is generated. Similarly, a background pattern 1103 is generated.

  Subsequently, a pattern in which the latent image pattern 1102 and the background pattern 1103 are repeated a predetermined number of times (referred to as a latent image repeating pattern 1104 and a background repeating pattern 1105) is generated. Thereafter, latent image data 1106 is generated from the latent image repetition pattern 1104 and the symbol pattern 1101. Similarly, background image data 1107 is generated. Then, the generated latent image data 1106 and background image data 1107 are combined to generate copy-forgery-inhibited pattern image data 1108. The copy-forgery-inhibited pattern image data 1108 generated as described above is binary bitmap data. This bitmap data is accompanied by any color information of CMK. The color information may be determined by user settings or may be determined based on the color information of the document image data.

  As described above, in this embodiment, the copy-forgery-inhibited pattern image data is generated using the dither processing, but the present invention is not limited to this. For example, an error diffusion method or an average density method may be used to create a background pattern.

<Density adjustment of tint block image>
The reflection density of the tint block image in the original depends on the density signal value used in the above-described tint block image generation. That is, the reflection density of the latent image portion increases as the latent image portion generation density signal value increases. The reflection density of the background portion also increases as the background portion generation density signal value increases.

  By the way, as described above, the tint block image needs to be formed such that the reflection density of the latent image portion and the background portion is substantially equal in the output product. In practice, however, the reflection density of the output image changes due to external factors such as the characteristics of the image forming process, environmental changes, and aging. For this reason, it is very difficult to adjust the reflection density of the latent image portion and the background portion to be equal. Further, there is a problem that even if the reflection density of the latent image portion and the background portion in the original is equal, the reflection density must be such that the readability of the original synthesized with the background pattern is not impaired. In addition, when the original is copied, if the latent image is not readable in the copy, there is a problem that the effectiveness obtained by combining the copy-forgery-inhibited pattern image with the original is lost.

  Below, the technique which solves such a problem is demonstrated.

<Detailed description of density adjustment method for tint block image>
A processing flow for adjusting the density of the tint block image will be described. The following processing is centrally controlled by the CPU 301. The flowcharts shown in FIGS. 16 and 23 are preferred embodiments of the present invention. First, the processing flow of the first half in the density adjustment of a tint block image will be described with reference to FIG.

  In step 1601, a screen (not shown) for accepting the start of test sheet output is displayed on the operation unit 12. The operation unit 12 receives which color density adjustment the user wants to perform among the density adjustment of the cyan background pattern, the density adjustment of the magenta background pattern, and the density adjustment of the black background pattern. Then, when the operation unit 12 is instructed to start outputting a test sheet (details of the test sheet will be described later), the instruction information is received from the operation unit 12 and the process proceeds to step 1602.

  In step 1602, test sheet data 1 having each color patch received by the operation unit 12 is generated. At the same time, the patch number information, the patch position information, and the density signal value information used to generate the patch are associated with each other. These pieces of information are stored in the RAM 302. When associating each information, the table shown in FIG. 19 is created (test sheet data 1, patch number information, patch position information, density signal value information used to generate the patch, and FIG. 19). Details of the table shown will be described later). Thereafter, the test sheet data 1 is read from the RAM 302, and the test sheet data 1 is output to the printer unit 14 via the expansion unit 316, the printer image processing unit 315, and the printer I / F 314.

  Here, processing performed by the decompression unit 316 will be described. Before being sent to the decompression unit 316, the test sheet data 1 is stored in the RAM 302 without being compressed. Therefore, the decompression unit 316 does not perform decompression processing on the test sheet data 1.

  Next, processing performed by the printer image processing unit 315 will be described. The printer image processing unit 315 performs output side gamma correction processing and halftone correction processing on the test sheet data 1 received from the expansion unit 316. These processes correspond to the processes performed by the output-side gamma correction unit 605 and the halftone correction unit 606 in FIG. On the other hand, background removal processing, monochrome generation processing, log conversion processing, and output color correction processing are not performed. These processes correspond to the processes performed by the background removal processing unit 601, the monochrome generation unit 602, the log conversion unit 603, and the output color correction unit 604 in FIG. Note that the processing that the printer image processing unit 315 performs and does not perform on the test sheet data 1 in step 1602 is the processing and processing that the printer image processing unit 315 performs on the image data with the tint block when outputting the image with the tint block pattern. (See <Image formation processing of image data with copy-forgery-inhibited pattern>). This is because when the latent image patch (or background patch) of the test sheet and the latent image portion (or background portion) of the image with tint block are generated using the same density signal value, the latent image portion on the output sheet is used. This is because the reflection density value of the (or background portion) and the reflection density value of the latent image patch (or background patch) are matched.

  Here, details of the test sheet and the test sheet data 1 will be described. FIG. 17 is a diagram showing a test sheet, and is also a diagram conceptually showing test sheet data 1 generated for outputting the test sheet. The test sheet (and test sheet data 1) shown in FIG. 17 has a plurality of latent image patches and background patches generated using different density signal values. Each density signal value may be changed stepwise at regular intervals or may be changed randomly. Further, the density signal value used when generating these may be arbitrarily set from the operation unit 12. Reference numeral 1704 denotes a latent image patch group, and 1705 denotes a background patch group. Further, the number of patches of the latent image patch group and the number of patches of the background patch group are equal in FIG. 17 and both are n (an integer of 2 or more), but the number of patches of the latent image patch group and the background patch group are not equal. May be. The number of patches may be set on the operation screen or may be determined automatically. Reference numeral 1707 denotes a latent image patch number, and 1708 denotes a background patch number. This patch number is assigned to each patch of the latent image patch group and each patch of the background patch group, and is a numerical value from 1 to n corresponding to the number of patches. The test sheet further includes position patches 1702 and 1703 for determining whether or not the test sheet is correctly placed on the document table. The normal orientation of the test sheet can be known from the location where the position patches 1702 and 1703 are formed and the difference in shape between them. Further, device identification information (ID or serial number indicating the device that has been output, network IP address) that is information for identifying the device that has output the test sheet or the device that has generated the test sheet data 1 is embedded in the barcode 1706. . The barcode may be a two-dimensional barcode such as a QR code (registered trademark) instead of a one-dimensional barcode. The test sheet data 1 before output is accompanied by any color information of CMK, but the present invention is not limited to these colors.

  Here, patch number information, patch position information, density signal value information used to generate a patch, and details of the table shown in FIG. 19 will be described.

  The patch number information is a number shown in 1707 or 1708. The patch position information is the coordinate position of the patch in the test sheet and the coordinate position of the patch in the test sheet data 1. The density signal value information used for generating the patch is the density signal value applied to the dither matrix (latent image matrix and background matrix) when generating each patch included in the patch groups 1704 and 1705. That is. Note that these pieces of information are associated with each patch on the table shown in FIG. That is, on the table shown in FIG. 19, the number information of a patch, the position information of the patch, and the information of the density signal value used when generating the patch are arranged in the same line and associated with each other. Henceforth, when expressing that each information is linked | related, it means that the various information regarding one patch is linked | related for every patch.

  When the test sheet output is completed, a display for prompting the user to give an instruction to start reading the output test sheet is performed on an operation screen (not shown) (step 1603). When the user places the test sheet on the document table and instructs to start reading the test sheet, the information is received from the operation unit 12. Then, the process proceeds to step 1604.

  In step 1604, the scanner unit 14 performs a test sheet reading operation. The read image data is sent to the scanner image processing unit 312 via the scanner I / F 311.

  The scanner image processing unit 312 does not perform masking processing, filter processing, and input side gamma correction processing on the image data. Note that these processes correspond to the processes performed by the masking processing unit 501, the filter processing unit 502, and the input side gamma correction unit 504. Note that the histogram generation process, the color / monochrome determination process, and the character / photo determination process may or may not be performed. These processes are performed by the histogram generation unit 503, the color / monochrome determination unit 505, and the character / photo determination unit 506. Thereafter, the image data output from the scanner image processing unit 312 is sent to the compression unit 313. The compression unit 313 generates tile data by dividing the image data into blocks of 32 pixels × 32 pixels. Further, the image data composed of the plurality of tile data (hereinafter, this image data is referred to as test sheet data 2) is compressed. The image data compressed by the compression unit 313 is sent to the RAM 302 and stored therein. Note that step 1605 is from when the scanner image processing unit 312 receives image data obtained by scanning until it is stored in the RAM 302 via the compression unit 313.

  Note that the image data stored in step 1605 is composed of a plurality of tile data as described above. By the way, this tile image is sufficiently smaller than the size of the patch. FIG. 18 shows the relationship between patches and tile images. An area 1801 shows one tile image. An area 1802 shows one patch. An area 1803 shows nine tile images located at the center of the patch.

  In step 1606, it is determined whether or not the position patches 1702 and 1703 and the barcode can be read. If it is determined that reading is impossible, the process proceeds to step 1607. If it is determined that reading is possible, the process proceeds to step 1608.

  In step 1607, an error is displayed on the operation screen. This error display is a display prompting the user to correctly place a correct test sheet and give a reading start instruction again. Subsequently, when the test sheet is replaced by the user and a start key (not shown) is depressed, the process proceeds to step 1604.

  On the other hand, in step 1608, the device specifying information embedded in the barcode 1706 is read, and it is determined whether or not the device specifying information belongs to the image forming apparatus 200 itself. If it is determined that it is not the image forming apparatus 200 itself, the process proceeds to step 1609 and an error is displayed on the operation screen. This error display is the same as the error display displayed in step 1607. When the test sheet is replaced by the user and a start key (not shown) is depressed, the process proceeds to step 1604. If it is determined in step 1608 that the read apparatus specifying information is that of the image forming apparatus 10 itself, the process proceeds to step 1610.

  In step 1610, the position information of each tile data constituting the image data of the test sheet and the position information of each patch on the test sheet are acquired from the RAM 302, and it is determined whether or not each tile image exists in the patch. Then, an average value of average luminance values of tile data related to the tile image determined to be present in the patch is obtained. Here, when the test sheet is set to cyan in step 1601, only the luminance value of red (cyan complementary color) is considered. When the color of the test sheet is set to magenta in step 1602, only the green luminance value (magenta complementary color) is considered. The reason why only the luminance of the complementary color of the test sheet is taken into account is that if the luminance of the complementary color is known, the darkness of the test sheet can be known. However, when the color of the test sheet is set to black in step 1603, only the luminance value of green is considered (however, when the color of the test sheet is black, the luminance value of red is taken into consideration) In addition, green luminance values, blue luminance values, or all may be considered). This average value is stored in the RAM 302 as the luminance value of the patch. As described above, the position information (coordinate position on the document) of each tile image is added to each tile data as header information. Further, the position information of each patch generated when the test sheet data is formed exists in the table shown in FIG. Note that the position information in the table shown in FIG. 19 is not the position information of the tile data generated from the read image data but information indicating the patch formation position on the test sheet data when the test sheet data is generated. The average luminance value of each tile data (average luminance information in a block of 32 × 32 pixels) is generated when image data obtained by reading a test sheet is divided into a plurality of tile data and added as header information. ing.

  Subsequently, in step 1611, the brightness value of each patch and the table shown in FIG. 19 are read from the RAM 302, and each patch information (patch number and density signal value) obtained when the test sheet data 1 is formed is read and the test sheet is obtained. Associate the brightness value of the patch. The association is performed based on the position information of each patch stored when the test sheet data 1 is formed and the position information of the tile data described above. Then, a table including number information, density signal value, and luminance value information for each patch is generated. This table is shown in FIG.

  Subsequently, the luminance reflection density conversion table (FIG. 21) stored in advance in the HDD 304 is read. In step 1612, the reflection density value is obtained from the luminance value in the table shown in FIG. 20 stored in the RAM 302 with reference to the luminance density reflection conversion table. This table is prepared for each color. That is, a luminance reflection density conversion table for red and a luminance reflection density conversion table for green are prepared. Here, if the tint block color designated in step 1601 is cyan, the luminance reflection density conversion table for red is used.

  Subsequently, in step 1613, the obtained reflection density value and the table shown in FIG. 20 are read from the RAM 302, and the patch reflection density value is associated with the patch number and density signal value instead of the patch luminance value. This association is stored in the RAM 302. In the table shown in FIG. 22, the number information, reflection density value, and density signal value information used when generating the patch are associated with each patch.

  In step 1612, the reflection density value is obtained from the luminance value of the patch using a table, but the present invention is not limited to this. For example, the reflection density value may be obtained by calculation using a matrix. Further, a configuration having two tables (or matrices) (one for the latent image and one for the background) may be used. Furthermore, a configuration having a table (or matrix) for each color of black, cyan, magenta, and yellow may be employed.

<First Density Signal Value Determination Method>
The first density signal value determination method is intended to determine an appropriate density signal value used for generation of a tint block image in order to output a tint block image whose reflection density value is close to a predetermined value. The first density signal value determination method will be described with reference to FIG. In determining the density signal value, the processing shown in FIG. 24, FIG. 25, or FIG. 26 may be performed instead of the processing shown in FIG. 24, 25, and 26 will be described later.

  In step 2301, the reflection density value of each latent image patch is compared with the reflection density value of each background patch. As a result of the comparison, a latent image patch and a background patch whose reflection density value is closest to a predetermined value are extracted. In the extraction, if there are a plurality of latent image patches having the same difference from the predetermined value, either patch may be selected. The same applies to the background patch.

  The predetermined value is an optimum reflection density value of the tint block image obtained empirically. As described above, the optimum copy-forgery-inhibited pattern image needs to make it difficult to read characters, line drawings, and the like of a document on which a copy-forgery-inhibited pattern image is synthesized as a first condition. At the same time, as a second condition, it is necessary to make the latent image portion reproduced on the copied material and the background portion difficult to reproduce on the copied material in the copied material obtained by copying the output material synthesized with the copy-forgery-inhibited pattern image. The predetermined value is a value empirically obtained in order to satisfy these two conditions. For example, the predetermined value is 0.15 in the case of a black tint block image. As a result of experiments, the reflection density value in the case of a cyan tint block image and the reflection density value in the case of a magenta tint block image are both It is obtained in the same manner as the reflection density value in the case of a black background pattern image. In the following description (in all the embodiments including the present embodiment), the description will be made on the assumption that the density adjustment of the black background pattern image is performed. For example, when the table shown in FIG. 22 is targeted, the reflection density values of the latent image patches are 0.134, 0.145, 0.160, 0.172,. Of these, the value closest to 0.150 is 0.145. Therefore, patch 2 is extracted as a latent image patch. Similarly, patch 2 is extracted as a background patch.

  In step 2302, density signal values corresponding to the extracted latent image patch and background patch numbers are stored in the HDD 304. That is, in the case of FIG. 22, N + 1 is stored in the HDD 304 as a latent image portion density signal value and M + 1 is stored as a background portion density signal value in this step.

  If there are a plurality of combinations of finally extracted latent image patches and background patches, it is necessary to provide some rules and select one combination. As long as one combination can be selected, any rule may be used. For example, the following can be cited. A combination with the smallest reflection density difference is selected. A combination is selected in which the reflection density of the latent image patch is smaller (or greater) than the reflection density of the background patch. In the following examples and density determination methods, when there are finally a plurality of combinations, a certain rule may be provided as in this example to select one combination.

  This is the end of the density adjustment of the tint block image. A background pattern image generated after execution of this process uses these density signal values, and is an optimal background pattern image that satisfies the above two conditions.

  Note that all the above processing is performed by the image forming apparatus 10, but the present invention is not limited to this. For example, in the embodiment, the information is transferred to the server or the PC 40, each processing (for example, processing corresponding to steps 1610 to 1613 and step 2301) is performed, and the processing result is transmitted to the image forming apparatus 10. May be.

  Although omitted in the above description, it goes without saying that processing stored in the ROM 303 or HDD 304 and image data stored in the ROM 303 or HDD 304 may be taken out as necessary. The same applies to the following embodiments.

  As described above, according to the first density signal value determination method described above, in order to output a tint block image whose reflection density value is close to a predetermined value, an appropriate density signal value used for generating the tint block image is surely and automatically determined. Can be determined. Further, when the appropriate density signal value is determined, evaluation by the user's eyes is not required. Therefore, the same density signal value can be determined even if an arbitrary person adjusts the density of the tint block image. Further, it is not necessary for the user to input a patch number when determining an appropriate density signal value. Therefore, it is possible to prevent a non-optimal density signal value from being determined due to an input error or the like.

  By the way, in the embodiment described above, after calculating the reflection density value from the luminance value of each patch, the patch having the smallest difference from the predetermined value (the reflection density value of 0.150) is extracted, and the extracted patch The appropriate density signal value used for generating the tint block image is determined based on the above. However, the present invention is not limited to this. For example, an appropriate density signal value used for generating a tint block image can be determined without calculating a reflection density value. As an example, a patch having the smallest difference from a predetermined value (luminance value corresponding to a reflection density value of 0.150) is extracted, and an appropriate density signal value used for generation of a tint block image is determined based on the extracted patch. The method of doing is mentioned. The patch can be extracted without replacing the luminance value with the reflection density value in this way, as in the following density signal value determination methods (second to fifth), and the third and fourth embodiments. is there.

<Second Density Signal Value Determination Method>
Next, another method for determining the density signal value of the tint block image will be described. The first density signal value determination method described above is intended to determine an appropriate density signal value used for generation of a tint block image in order to output a tint block image whose reflection density value is close to a predetermined value. On the other hand, in the second density signal value determination method, the copy-forgery-inhibited pattern image not only has a reflection density value close to a predetermined value but also has a high latent image concealing property (the reflection density values of the latent image portion and the background portion in the original are substantially equal). Is to determine an appropriate density signal value used for generating a tint block image. This method will be described with reference to FIG.

  In step 2401, both the latent image patch and the background patch having a reflection density value of 0.150 + α (−0.010 ≦ α ≦ 0.010) obtained by giving the tolerance α to 0.150 which is the optimum reflection density value. Determine if it exists. In the determination, the difference between the reflection density value of each patch and 0.150 is compared with α. As a result of the determination, if it exists, the process proceeds to step 2403, and if it does not exist, the process proceeds to step 2402. However, this α can be changed by the user through the operation unit.

  In step 2402, an error is displayed on the operation screen. At the same time, a display for allowing the user to adjust the tolerance α is performed. Note that if the tolerance α is adjusted by the user and a start key (not shown) is pressed, the process returns to step 2401.

  Subsequently, in step 2403, a latent image patch and a background patch corresponding to the condition of step 2401 are extracted. For example, when the table shown in FIG. 22 is targeted, the latent image patches 2 and 3 and the background patches 1 to 3 are extracted in this step.

  Subsequently, in step 2404, a combination having the smallest difference in reflection density value is extracted from the latent image patch and background patch extracted in step 2402. In the extraction, the reflection density of each latent image patch included in the combination extracted in step 2403 is compared with the reflection density of each background patch. This means that in the original on which the copy-forgery-inhibited pattern image is printed, a combination that enhances the latent image concealment property is selected. That is, by selecting a combination having the smallest difference in reflection density, it is possible to generate a tint block printed matter in which the latent image is difficult to see in the original. That is, in the case of FIG. 22, the combination of the latent image patch 2 and the background patch 1 is extracted in this step.

  Subsequently, in step 2405, density signal values corresponding to the latent image patch and background patch numbers extracted in step 2404 are stored in the HDD 304. That is, in the case of FIG. 22, N + 1 is stored in the HDD 304 as a latent image portion density signal value and M as a background portion density signal value in this step.

  This is the end of the density adjustment of the tint block image. These density signal values are used for the copy-forgery-inhibited pattern image generated after execution of this processing.

  In the above-described method, when there is no patch corresponding to the condition of step 2401, α is adjusted by the user in step 2402. However, the test sheet may be output again by returning to step 2401 without letting the user adjust α. Needless to say, when re-outputting, it is necessary to create a test sheet that is different from the already output test sheet (a density signal value different from the density signal value used when the previous test sheet was created). Need to create a new test sheet). The same applies to the following embodiments.

  As described above, in the second density signal value determination method described above, in addition to the effects obtained when the first density signal value determination method is executed, the latent image concealability is high (the reflection density of the latent image portion and the background portion in the original). It is possible to output a tint block image having substantially the same value.

<Third Density Signal Value Determination Method>
Next, another method for determining the density signal value of the tint block image will be described. In the second density signal value determination method described above, a latent image patch and a background patch whose reflection density values are close to a predetermined value are extracted, and a combination that minimizes the reflection density difference is extracted from among the extracted patches. An appropriate density signal value used to generate a tint block image has been determined. However, there is a limit to the number of patches that can be formed on one test sheet. For this reason, when the density adjustment processing described in the second density signal value determination method is performed using a test sheet on which a small number of patches are formed, a combination in which the latent image concealment property is not high (a difference in reflection density value is a predetermined value). (A combination of the above) may be extracted. Of course, as a countermeasure against this situation, it is conceivable to use multiple test sheets to select the optimal combination from many patches. In that case, test sheet data generation, output, reading processing, etc. You will have to spend a lot of time.

  Therefore, this third density signal value determination method first extracts a combination of a latent image patch and a background patch whose reflection density value difference is equal to or smaller than a predetermined value, and then both reflection density values are in the vicinity of the predetermined value. The combination which is is extracted. Accordingly, in order to output a tint block image having a high latent image concealing property (a difference in reflection density between the latent image portion and the background portion in the original is surely kept within a predetermined value), an appropriate image used for generating the tint block image is used. The density signal value can be determined only by using a small number of test sheets. This method will be described with reference to FIG.

  In step 2501, it is determined whether or not there is a combination of reflection density value of latent image patch−reflection density value of background patch = β (β is −0.005 or more and 0.005 or less). In the determination, the difference between the reflection density of the latent image patch and the reflection density of the background patch is compared with β. As a result of the determination, if it exists, the process proceeds to step 2503, and if it does not exist, the process proceeds to step 2502. However, this β can be changed by the user through the operation unit.

  In step 2502, an error is displayed on the operation screen. At the same time, a display for allowing the user to adjust β is performed. If the start key (not shown) is pressed after β is adjusted by the user, the process returns to step 2501.

  In step 2503, a combination of a latent image patch and a background patch corresponding to the condition of step 2501 is extracted. For example, when the table shown in FIG. 22 is targeted, {(2,1), (2,2), (3,3), (3,4), (4,4),... } Combinations are extracted. (2, 1) means a combination of the latent image patch 2 and the background patch 1.

  Subsequently, in step 2504, a latent image patch having a reflection density value closest to 0.150 is searched from the combinations extracted in step 2503. In the search, the reflection density of each latent image patch and the reflection density of each background patch included in the combination are compared with 0.150. Then, a combination of the latent image patch having the latent image patch and the background patch is extracted. That is, in the case of FIG. 22, the combination of {(2,1), (2,2)} is extracted at this step.

  Subsequently, in step 2505, the background patch whose reflection density is closest to 0.150 is searched from the combination of the latent image patch and the background patch extracted in step 2504. Then, a combination of the latent image patch having the background patch and the background patch is extracted. That is, in the case of FIG. 22, the combination of (2, 2) is extracted at this step.

  In step 2506, the density signal values corresponding to the extracted latent image patch and background patch numbers are stored in the HDD 304. That is, in the case of FIG. 22, N + 1 is stored in the HDD 304 as a latent image portion density signal value and M + 1 is stored as a background portion density signal value in this step.

  This is the end of the density adjustment of the tint block image. These density signal values are used for the copy-forgery-inhibited pattern image generated after execution of this processing.

  In the above-described method, when there is no patch corresponding to the condition of step 2501, β is adjusted by the user at step 2502. However, it is possible to return to step 2501 and re-output the test sheet without letting the user adjust β. Needless to say, when re-outputting, it is necessary to create a test sheet that is different from the already output test sheet. The same applies to the following embodiments.

  As described above, in the third density signal value determination method described above, in addition to the effects obtained when the first and second density signal value determination methods are executed, the latent image concealment property can be obtained only by using a small number of test sheets. A high-quality copy-forgery-inhibited pattern image can be output (the difference in reflection density between the latent image portion and the background portion in the original is within a predetermined value).

<Fourth Density Signal Value Determination Method>
Next, another method for determining the density signal value of the tint block image will be described. This method will be described with reference to FIG.

  In step 2601, a latent image patch having a reflection density value closest to 0.150 is extracted. In the extraction, the reflection density of each latent image patch is compared with 0.150. If there are a plurality of latent image patches having a reflection density closest to 0.150, one of them may be selected. For selection, any rule may be used as described above. For example, when the table shown in FIG. 22 is targeted, the latent image patch 2 is extracted in this step.

  Subsequently, in step 2602, the latent image portion generation density signal value corresponding to the extracted latent image patch number is stored in the HDD 304. That is, in the case of FIG. 22, N + 1 is stored in the HDD 304 as a latent image portion generation density signal value in this step.

  In step 2603, a background patch having a reflection density value closest to the reflection density value of the latent image patch extracted in step 2601 is extracted. In the extraction, the reflection density of each background patch is compared with the reflection density of the latent image patch extracted in step 2601. If there are a plurality of background patches having a reflection density closest to the reflection density value of the latent image patch, one of them may be selected. For selection, any rule may be used as described above. That is, in the case of FIG. 22, the background patch 1 is extracted at this step.

  In step 2604, the background portion generation density signal value corresponding to the extracted background patch number is stored in the HDD 304. That is, in the case of FIG. 22, M is stored in the HDD 304 as the background portion generation density signal value in this step.

  This is the end of the density adjustment of the tint block image. These density signal values are used for the copy-forgery-inhibited pattern image generated after execution of this processing.

  In this method, the density signal value for background portion generation is determined after the density signal level for latent image portion generation is determined. However, the present invention is not limited to this. For example, after extracting one background patch having a reflection density closest to 0.150 and determining a background portion generation density signal value corresponding to the patch, the reflection density closest to the reflection density value of the background patch is obtained. One latent image patch may be extracted, and a latent image portion generation density signal value corresponding to the patch may be determined.

  In each density signal value determination method described above, the density signal value for latent image portion generation and the density signal value for background portion generation are obtained using the test sheet of FIG. However, in general, an image forming apparatus can stably form large dots, but cannot stably form small dots (the ability to form small dots is susceptible to external factors such as environmental changes and secular changes). is there. Therefore, once the density signal value for generating the latent image portion is adjusted, the reflection density of the latent image portion of the copy-forgery-inhibited pattern image formed on the sheet does not change much during a certain time. That is, the reflection density value of the latent image portion can be maintained near 0.150. The reverse is true for the background. Therefore, it is necessary to adjust the density in the background portion in a shorter cycle.

  The test sheet of FIG. 27 is a test sheet used for performing only the density adjustment of the background portion on the assumption that the reflection density value of the latent image portion is maintained in the vicinity of 0.150. . The density adjustment using FIG. 27 is performed as follows.

  First, on the assumption that the test sheet shown in FIG. 27 is output, the same processing as the flowchart shown in FIG. 16 is performed. In step 1602, test sheet data 1 is generated using the density signal value for latent image portion generation determined at the previous density adjustment, and the test sheet is output. Then, with reference to the table generated in step 1613, the reflection density value of the background patch having the reflection density value closest to the reflection density value of the latent image patch is determined. The tint block image density adjustment is thus completed.

  In FIG. 27, reference numeral 2701 denotes a test sheet. In FIG. 27, 2704 is a latent image patch, and 2705 is a background patch group. Reference numeral 2707 denotes a background patch number. Reference numerals 2702 and 2703 are position patches. 2706 is embedded with device specifying information (ID and serial number indicating the output device and generated device, network IP address) that is information for specifying the device that output the test sheet and the device that generated the test sheet data 1. It is a barcode.

  Further, in each density signal value determination method described above, the density signal value is finally stored in the HDD 304, thereby completing the density adjustment of the tint block image. However, the present invention is not limited to this. For example, a binary pattern (latent image pattern and background pattern) corresponding to the density signal value may be stored.

  By the way, in the density signal value determination method described above, an appropriate density signal value is determined from the density signal values used when creating any of the patches on the test sheet. However, the present invention is not limited to this. For example, it is possible to determine an appropriate density signal value by performing estimation as described below. This method will be described.

  First, a test sheet is generated and output with an interval between the density signal value for latent image portion generation and the density signal value for background portion generation (for example, an interval of 8 levels). Next, the latent image density signal value and the background density signal value corresponding to the reflection density value of 0.150 are estimated by interpolation using this test sheet.

  Here, the density signal value determination method will be described in more detail by taking as an example the case where the table shown in FIG. 28 is created. In the table shown in FIG. 28, the patch number, the reflection density value of the patch, and the density signal value for generating the patch are associated as in the table shown in FIG.

  Referring to FIG. 28, it is estimated that the density signal value of the latent image patch corresponding to the reflection density value 0.150 is L to L + 8, and the density signal value of the background patch is K + 8 to K + 16. Based on this estimation, the following interpolation calculation is performed to obtain an appropriate density signal value.

(For latent images)
Required concentration signal value = L + {(L + 8) −L} × (0.150−0.108) / (0.157−0.108) ≈L + 7 (rounded off)
(For background)
Required concentration signal value = K + 8 + {(K + 16) − (K + 8)} × (0.150−0.138) / (0.164−0.138) ≈K + 12 (rounded off)
The interpolation calculation may be non-linear interpolation calculation instead of linear interpolation calculation.

  In this density signal determination method, after calculating the reflection density value from the luminance value of each patch, the patch having the smallest difference from a predetermined value (a reflection density value of 0.150) is estimated by calculation. However, the present invention is not limited to this. For example, an appropriate density signal value used for generating a tint block image can be determined without calculating a reflection density value. As an example, there is a method of calculating a patch having the smallest difference from a predetermined value (a luminance value corresponding to a reflection density value of 0.150) by calculation. In this method, similarly to the above-described density signal determination method, first, it is estimated in which range the patch density signal value corresponding to a predetermined value (luminance value corresponding to the reflection density value 0.150) is included. Then, the density signal value is uniquely determined using the above-described interpolation calculation formula.

  In this embodiment, in order to output a tint block image having a high visible image effect (a large difference between the reflection density value of the latent image portion and the reflection density value of the background portion in a copy), an appropriate density used for generating the tint block image is used. The purpose is to reliably and automatically determine the signal value.

  In order to achieve the above object, in this embodiment, first, test sheet data 3 (image data as close as possible to an image obtained when the test sheet is actually copied) is generated. Subsequently, the density value of the latent image patch and the density value of the background patch in the test sheet data 3 are obtained. Then, a combination of patches having the largest density value difference is extracted. Finally, the density signal value corresponding to the extracted patch is stored in the HDD 304, and the density adjustment of the tint block image is completed.

  This process will be described in detail with reference to the flowcharts shown in FIGS. The first half of the processing flow in the density adjustment of the tint block image will be described below, focusing on the difference between FIG. 29 (the present embodiment) and FIG. 16 (the first embodiment). In FIG. 29 and FIG. 16, step 1605 and step 2905 are different. Further, step 1610 to step 1613 and step 2910 to step 2911 are different.

  First, the difference between step 1605 and step 2905 will be described. Since the processing of step 1605 is the same as that described above, description thereof is omitted. On the other hand, in step 2905, the scanner image processing unit 312 performs masking processing, filter processing, and input-side gamma correction processing on the received image data and outputs the result. The output image data is sent to and stored in the RAM 302 via the compression unit 313. Subsequently, the image data is sent to the color space conversion unit 322 via the decompression unit 318. The color space conversion unit 322 performs background removal processing, monochrome generation processing, log conversion processing, and output color correction processing on the image data, and outputs the result. The output image data is sent to the RAM 302 via the compression unit 319 and stored (as test sheet data 3). The reason for applying the masking process, the filter process, the input side gamma correction process, the background removal process, the log conversion process, and the output color correction process when generating the test sheet data 3 is a copy obtained when the test sheet is copied. This is to generate image data that is substantially the same as the above.

  Next, the difference between step 1610 to step 1613 and step 2910 to step 2911 will be described. In steps 1610 to 1613, the tables shown in FIGS. 20 and 22 are created based on the test sheet data 2. FIG. On the other hand, in steps 2910 to 2911, a table shown in FIG. 30 is created based on the test sheet data 3. In FIG. 30, the density value of the patch obtained by reading the test sheet is associated with the density signal value used to generate each patch and the number of each patch.

  Note that the test sheet data 2 is RGB luminance data that has not been subjected to log conversion processing (more specifically, as described in the first embodiment, when the test sheet color is cyan, the test sheet data 2 is red data. In the table shown in FIG. 20, the luminance value of the patch is associated with the density signal value and the patch number. On the other hand, the test sheet data 3 is CMY density data after log conversion processing (more specifically, when the test sheet color is cyan, it is cyan data, and the test sheet color is magenta or black. Therefore, in the table shown in FIG. 30, the density value of the patch is associated with the density signal value and the patch number.

<Density signal value determination method>
Subsequently, a density signal value determination method according to the second embodiment will be described with reference to FIG.

  In step 3101, a combination of a latent image patch and a background patch with the largest density difference is extracted by referring to the table shown in FIG. 30. In extraction, the reflection density of the latent image patch is compared with the reflection density of the background patch. This process means that a density signal value having the largest density difference between the latent image portion and the background portion is determined in a copy obtained by copying the original on which the copy-forgery-inhibited pattern image is formed.

  In step 3102, the density signal value corresponding to the extracted patch number is stored in the HDD 304.

  Further, the present invention is not limited to the above-described density signal value determination method (method for extracting a combination having the largest density difference). For example, instead of extracting the combination having the largest density difference, a latent image patch having a density value near a predetermined density value and a background patch having a density value near a different predetermined density value are respectively extracted in a copy. Also good.

  With the above, the density adjustment of the tint block image is completed. These density signal values are used for the copy-forgery-inhibited pattern image generated after execution of this processing.

  According to the present embodiment, an appropriate density used for generating a tint block image in order to output a tint block image having a high visual effect (a large difference in reflection density between the latent image portion and the background portion in a copy) The signal value can be determined reliably and automatically.

  In this embodiment, in order to output a tint block image having a high visible image effect (a large difference between the reflection density value of the latent image portion and the reflection density value of the background portion in the copy) and high latent image concealment property, An object is to reliably and automatically determine an appropriate density signal value used for generation of a tint block image.

  The first half of the processing necessary to achieve this object will be described in detail with reference to the flowchart shown in FIG.

  The process shown in the flowchart of FIG. 32 first generates test sheet data 2 (image data close to a test sheet) and test sheet data 3 (image data close to a copy of the test sheet). Subsequently, after obtaining the luminance value of each patch in the test sheet data 2, the reflection density value of each patch is obtained using the luminance reflection density table. Subsequently, the density value of each patch in the test sheet data 3 is obtained. The information of each patch is associated with the density value and reflection density value information.

  In the following, the processing flow of the first half in the density adjustment of the tint block image will be described first by paying attention to the difference between FIG. 32 (the present embodiment) and FIG. In FIG. 32 and FIG. 16, step 1605 is different from step 3205 to step 3206. Also, step 3215 and step 3216 are newly added in FIG.

  First, the difference between step 1605 and step 3205 to step 3206 will be described. In step 1605, test sheet data 2 is generated and stored in the RAM 302. On the other hand, in step 3205 to step 3206, test sheet data 2 and test sheet data 3 are generated and stored in the RAM 302.

  Next, step 3215 and step 3216 will be described. In step 3215, the density value of each patch assuming the reflection density in the copy is obtained from the test sheet data 3 by the same method as shown in the second embodiment. In step 3216, the table shown in FIG. 33 is created by associating the density value obtained in step 3215 with the patch number in the table shown in FIG. 22 generated based on the test sheet data 2. In the table shown in FIG. 33, the patch number, the patch density value corresponding to the reflection density in the copy, the patch reflection density value corresponding to the reflection density in the original, and the density signal used when the test sheet was generated. Associated with a value.

<Density signal value determination method 1>
Subsequently, the density signal value determination method in the present embodiment will be described with reference to FIG. The flowchart shown in this method outputs a copy-forgery-inhibited pattern image having a high visible image effect (a large difference between the reflection density value of the latent image portion and the reflection density value of the background portion in a copy) and high latent image concealing property. In addition, this is a method for reliably and automatically determining an appropriate density signal value used for generating a tint block image.

  In step 3401, by referring to the table shown in FIG. 33, whether or not there is a combination of reflection density value of latent image patch−reflection density value of background patch = β (−0.005 ≦ β ≦ 0.005). Determine whether. In the determination, the difference between the reflection density of each latent image patch and the reflection density of each background patch is compared with β. If it exists, the process proceeds to step 3403, and if it does not exist, the process proceeds to step 3402. Note that the range of the difference (β) between the reflection density value of the latent image patch and the reflection density value of the background patch is not limited to the above-described range.

  In step 3402, an error is displayed on the operation screen. At the same time, a display for allowing the user to adjust β is performed. If the start key (not shown) is pressed after β is adjusted by the user, the process returns to step 3401.

  In step 3403, a patch corresponding to the condition of step 3401 is extracted.

  Subsequently, in step 3404, by referring to the table shown in FIG. 33, the latent image patch having a reflection density value of 0.150 + α (α is −0.01 or more and 0.01 or less) from the patches extracted in step 3403. And whether a background patch exists. In the determination, the difference between the reflection density of the latent image patch and the reflection density of the background patch and 0.150 is compared with α. However, this α can be changed by the user through the operation unit. If it exists, the process proceeds to step 3405. If it does not exist, the process proceeds to step 3406.

  In step 3405, an error is displayed on the operation screen. At the same time, a display for allowing the user to adjust α is performed. If the start key (not shown) is pressed after α is adjusted by the user, the process returns to step 3404.

  In step 3406, patches corresponding to the conditions in step 3404 are extracted.

  Subsequently, in step 3407, a combination having the largest density value difference is extracted from the patches extracted in step 3406 by referring to the table shown in FIG.

  Subsequently, in step 3408, density signal values corresponding to the extracted latent image patch and background patch are stored in the HDD 304.

  This is the end of the density adjustment of the tint block image. These density signal values are used for the copy-forgery-inhibited pattern image generated after execution of this processing.

  In this density determination method, the visual effect is high (the difference between the reflection density value of the latent image portion and the reflection density value of the background portion in the copy is large), the reflection density value is close to a predetermined value, and the latent image concealment is performed. In order to output a high-quality copy-forgery-inhibited pattern image, an appropriate density signal value used for generating the copy-forgery-inhibited pattern image can be reliably and automatically determined.

  The object of this embodiment is to adjust the density of a tint block image generated by an image forming apparatus (apparatus 30) that does not have a scanner unit. In order to achieve the above object, in this embodiment, the image forming apparatus (apparatus 30) and an image forming apparatus (apparatus 10) having a scanner unit are linked.

  As described above, the device 10 and the device 30 are connected to the network. Further, it is assumed that the device 10 can instruct the device 30 to print via a network. It is also possible to instruct the registration of the density signal value.

<Method for adjusting density of tint block image>
The first half of the processing flow in the density adjustment of the tint block image according to the present embodiment will be described with reference to FIG.

  In step 3501, the screen shown in FIG. 36 is displayed on the operation screen of the apparatus 10. Reference numeral 3601 denotes a test sheet output printer selection screen. The printer selection tab 3602 is a tab for selecting a printer that outputs a test sheet. When the printer selection tab 3602 is depressed, the image forming apparatus that reverses the display and outputs the test sheet is selected. In FIG. 36, the image forming apparatus (apparatus 30) having the address 192.168.0.3 is selected. A cancel tab 3603 is a tab for canceling output of the test sheet, and an execution tab 3604 is a tab for instructing start of output of the test sheet. The local tab 3605 is used for an instruction to start output of the test sheet to the own device (device 10). When the execution tab 3604 is pushed down in the current state (the state in which the device 30 is selected), the process proceeds to step 3502.

  In step 3502, the table shown in FIG. 19 is created. Thereafter, the apparatus 30 is instructed to start outputting the test sheet. Upon receiving this instruction, the device 30 outputs a test sheet. When the output ends, the device 30 notifies the device 10 of the output end. Then, the process proceeds to step 3503.

  In step 3503, the display shown in FIG. Here, when the execution tab 3701 is pushed down after the test sheet is placed on the document table of the apparatus 10, the process proceeds to step 3504. In addition, when the barcode included in the test sheet does not include information indicating the device 30, an error display is performed.

  In step 3504, the apparatus 10 starts reading the placed test sheet.

  Note that step 3505 to step 3513, which are subsequent processes, are the same as step 1605 to step 1613. The processing in steps 3505 to 3513 is performed by the apparatus 10.

<Density signal value determination method>
Subsequently, density signal value determination processing is started in the apparatus 10. Any of the density signal value determination methods shown in the first embodiment can be applied to the density signal value determination method in the present embodiment. The density signal value determination method in the present embodiment is different from the density signal value determination method in the first embodiment in the following points.

  In this embodiment, after determining an appropriate density signal value in the apparatus 10, the determined density signal value is transmitted from the apparatus 10 to the apparatus 30. Further, the determined density signal value is stored in the HDD of the apparatus 30.

  With the above, the density adjustment of the tint block image is completed.

  In the present embodiment, a description has been given assuming that processing corresponding to the processing performed in the first embodiment is performed in cooperation with the device 10 and the device 30. However, the present invention is not limited to this. For example, a process corresponding to the process performed in the second embodiment or the third embodiment may be performed by cooperation between the device 10 and the device 30.

  According to the above embodiment, even in an image processing apparatus that does not have an image reading unit, an appropriate density signal value can be reliably and automatically determined when outputting a tint block image.

  In the above first to third embodiments, the method for adjusting the density of the copy-forgery-inhibited pattern image to be combined with the document image data obtained by scanning has been described. However, the present invention is not limited to this. For example, the present invention can be applied to density adjustment of a copy-forgery-inhibited pattern image to be combined with document image data generated by the PC 40.

  In this case, a case where the density adjustment processing result (appropriate density signal value) is stored in the apparatus 10 and a case where it is stored in the PC 40 are assumed. Hereinafter, the density adjustment method in each case will be briefly described.

  In the case where the density signal value is stored in the apparatus 10, the tint block image density adjustment method described in the first to third embodiments is applicable. However, it goes without saying that various displays (eg, step 1601, step 1607, and step 1609 in FIG. 16) need to be performed by the PC 40. It goes without saying that information needs to be exchanged between the PC 40 and the apparatus 10 as appropriate.

  On the other hand, even when the density adjustment processing result is stored in the PC 40, the density adjustment method for the tint block image described in the first to third embodiments can be applied. However, it goes without saying that the density signal value storage processing (eg, step 2302 in FIG. 23) needs to be performed by the PC 40 in addition to various displays. Therefore, it goes without saying that in this case also, it is necessary to exchange information appropriately between the PC 40 and the apparatus 10.

  Further, the present invention can be applied to a system constituted by a plurality of devices (for example, a computer, an interface device, a reader, a printer, etc.), and can also be applied to an apparatus (multifunction device, printer, facsimile machine, etc.) comprising a single device. It is also possible.

  Another object of the present invention is that a computer (or CPU or MPU) of a system or apparatus reads and executes the program code from a storage medium that stores the program code for realizing the procedure of the flowchart shown in the above-described embodiment. Is also achieved. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiment. Therefore, the program code and a storage medium storing the program code also constitute one of the present invention.

  As a storage medium for supplying the program code, for example, a floppy (registered trademark) disk, hard disk, optical disk, magneto-optical disk, CD-ROM, CD-R, magnetic tape, nonvolatile memory card, ROM, or the like is used. be able to.

  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) operating on the computer based on the instruction of the program code is actually used. A case where part or all of the processing is performed and the functions of the above-described embodiments are realized by the processing is also included.

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

Diagram showing the overall configuration of the image forming system External view of input / output device of image forming apparatus The figure which shows the whole structure of an image forming apparatus Diagram showing tile data conceptually Block diagram of the scanner image processing unit Block diagram of the printer image processing unit Explanatory drawing of the copy screen of the operation unit Explanatory diagram of the screen pattern setting screen of the operation part 1 Illustration 2 of the setting screen for setting the background pattern on the operation unit Illustration 3 of the setting screen for the screen pattern on the operation unit The figure which shows the generation method of copy-forgery-inhibited pattern image data Diagram showing dot concentration type dither matrix Diagram showing dot-dispersed dither matrix Diagram showing centralized dither pattern Diagram showing distributed dither pattern Flowchart 1 for explaining the density adjustment method (first half) Figure 1 showing the test sheet Diagram showing the relationship between patches and tile images Table 1 showing the association of parameters of each patch Table 2 showing the association of parameters of each patch The figure which shows a luminance reflection density conversion table Table 3 showing association of parameters of each patch Flowchart 1 for explaining the density adjustment method (second half) Flowchart 2 for explaining the density adjustment method (second half) Flowchart 3 for explaining the density adjustment method (second half) Flowchart 4 for explaining the density adjustment method (second half) Figure 2 shows the test sheet Table 4 showing association of parameters of each patch Flowchart 2 for explaining the density adjustment method (first half) Table 5 showing association of parameters of each patch Flowchart 5 for explaining the density adjustment method (second half) Flowchart 6 for explaining the density adjustment method (second half) Table 6 showing association of parameters of each patch Flowchart 7 for explaining the density adjustment method (second half) Flowchart 3 for explaining the density adjustment method (first half) Explanatory drawing of output printer selection screen of test sheet Explanatory drawing of test sheet loading screen A diagram showing the state of dots in a tint block image Diagram showing visualization

Claims (13)

A method of setting a density signal value used for generating a latent image and a density signal value used for generating a background image,
Forming a plurality of latent image patches generated using a plurality of density signal values and a plurality of background patches generated using a plurality of density signal values on at least one sheet;
An acquisition step of acquiring luminance values of the plurality of latent image patches and luminance values of the plurality of background patches in the image data obtained by reading the sheet;
Density signal values used to generate a latent image patch having a luminance value closest to a predetermined value among luminance values of the plurality of latent image patches acquired in the acquisition step, and acquired in the acquisition step A density signal value used to generate a background patch having a brightness value closest to the predetermined value among the brightness values of the plurality of background patches,
And a setting step of setting the density signal value for generating the latent image and the density signal value for generating the background image . The predetermined value is
By printing the latent image and the background image, it is not difficult to read characters and line drawings in the printed material,
The method according to claim 1, wherein the latent image is reproduced in a copy, and the value is experimentally determined so that the background image is difficult to be reproduced. 3. The method according to claim 1, wherein when the latent image patch and the background patch are black, the luminance value is green data. When the density signal value for generating the latent image changes, the size of the dots constituting the latent image changes, and when the density signal value for generating the background image changes, the background image is changed. The method according to any one of claims 1 to 3, wherein the number of constituent dots changes. The method according to claim 1, wherein the latent image is composed of dots larger than the background image. A method of setting a density signal value used for generating a latent image and a density signal value used for generating a background image,
Forming a plurality of latent image patches generated using a plurality of density signal values and a plurality of background patches generated using a plurality of density signal values on at least one sheet;
An acquisition step of acquiring the reflection density values of the plurality of latent image patches and the reflection density values of the plurality of background patches in the image data obtained by reading the sheet;
The density signal value used to generate a latent image patch having a reflection density value closest to a predetermined value among the reflection density values of the plurality of latent image patches acquired in the acquisition step, and acquired in the acquisition step Density signal values used to generate a background patch having a reflection density value closest to the predetermined value among the reflected density values of the plurality of background patches.
And a setting step of setting the density signal value for generating the latent image and the density signal value for generating the background image. The program for making a computer perform the method of any one of Claims 1 thru | or 6. An apparatus for setting a density signal value used for generating a latent image and a density signal value used for generating a background image,
Forming means for forming a plurality of latent image patches generated using a plurality of density signal values and a plurality of background patches generated using a plurality of density signal values on at least one sheet;
Acquisition means for acquiring the luminance values of the plurality of latent image patches and the luminance values of the plurality of background patches in the image data obtained by reading the sheet;
Density signal values used to generate a latent image patch having a luminance value closest to a predetermined value among luminance values of the plurality of latent image patches acquired by the acquisition unit, and acquired by the acquisition unit A density signal value used to generate a background patch having a brightness value closest to the predetermined value among the brightness values of the plurality of background patches,
An apparatus comprising: setting means for setting a density signal value for generating the latent image and a density signal value for generating the background image. The predetermined value is
By printing the latent image and the background image, it is not difficult to read characters and line drawings in the printed material,
9. The apparatus according to claim 8, wherein the latent image is reproduced in a copy and the value is experimentally determined so that the background image is difficult to be reproduced. 10. The apparatus according to claim 8, wherein when the latent image patch and the background patch are black, the luminance value is green data. When the density signal value for generating the latent image changes, the size of the dots constituting the latent image changes, and when the density signal value for generating the background image changes, the background image is changed. The apparatus according to any one of claims 8 to 10, wherein the number of constituent dots changes. The apparatus according to any one of claims 8 to 11, wherein the latent image is composed of dots larger than the background image. An apparatus for setting a density signal value used for generating a latent image and a density signal value used for generating a background image,
Forming means for forming a plurality of latent image patches generated using a plurality of density signal values and a plurality of background patches generated using a plurality of density signal values on at least one sheet;
Acquisition means for acquiring the reflection density values of the plurality of latent image patches and the reflection density values of the plurality of background patches in the image data obtained by reading the sheet;
The density signal value used to generate a latent image patch having a reflection density value closest to a predetermined value among the reflection density values of the plurality of latent image patches acquired by the acquisition unit, and acquired by the acquisition unit Density signal values used to generate a background patch having a reflection density value closest to the predetermined value among the reflected density values of the plurality of background patches.
An apparatus comprising: setting means for setting a density signal value for generating the latent image and a density signal value for generating the background image.

Images