JP2012044250A - Image processing apparatus, image forming apparatus, original determination method and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processing apparatus capable of authenticating originality of a manuscript without increase in cost.SOLUTION: An image processing apparatus 100 creating image data by reading a manuscript, comprises decoding means 31 extracting information record marks 30 from the image data and decoding image data information coded into the information record marks, of a manuscript that is an original of the image data, halftone region extraction means 34 extracting a halftone region on which halftone processing is performed from the image data, coincidence calculation means 32, 35 calculating a coincidence degree between image data read from the halftone region and original image data in the halftone region of the original based on the image data information, and original determination means 33 determining whether the manuscript of the image data is the original based on the coincidence degree.

Description

  The present invention relates to an image processing apparatus, an image forming apparatus, an original determination method, and an image forming method for evaluating the originality of a document.

  As color copiers are becoming more sophisticated, documents that should not be replicated, such as various certificates, rights documents, securities, and tickets, should be replicated as precisely as possible without knowing that they are duplicates. It has become. Such duplication may be a legal counterfeit, and the copier should have means to avoid it.

  As a method of avoiding forgery of documents, a method has been devised in which an invisible pattern is printed on the original with a transparent toner that cannot be read and printed by a normal copier, and the original is confirmed by reading this pattern with ultraviolet irradiation. (For example, refer to Patent Document 1).

  In a method that does not use special materials, the original is read in advance, image features that cannot be reproduced at the time of printing are extracted and recorded separately, and this is used to determine whether the original to be copied is an original. A determination method has been devised (see, for example, Patent Document 2). Image features that cannot be reproduced at the time of printing are, for example, the state of toner scattering and uneven penetration, which cannot be reproduced at the time of printing even if scanned by a scanner. These image features do not match.

  However, the method of using a special material at the time of printing disclosed in Patent Document 1 requires a special reading device such as applying a special material or ultraviolet rays, and thus has a problem of high cost.

  The method disclosed in Patent Document 2 does not require a special material at the time of printing. However, since it is necessary to read a very fine image feature at the time of reading the original and at the time of reading the original to be copied, a normal copying machine is used. Therefore, there is a problem that a higher-precision reading device is required and the cost is increased. In addition, since the fine features of the original may change due to slight dirt or rubbing of the image, it may be determined that the original is not the original when the original is read. In addition, the method disclosed in Patent Document 2 does not provide image characteristics unless the original is read with a scanner, so that it is necessary to read with the scanner each time the original is printed. To do.

  In view of the above problems, an object of the present invention is to provide an image processing apparatus, an image forming apparatus, an original determination method, and an image forming method capable of confirming the originality of a document while suppressing an increase in cost.

  In view of the above problems, the present invention is an image processing apparatus that reads an original and generates image data, and extracts an information recording mark from the image data and encodes the information recording mark. Decoding means for decoding image data information of a manuscript, halftone area extracting means for extracting a halftone area subjected to halftone processing from the image data, and the halftone area based on the image data information A degree-of-matching calculating means for calculating a degree of coincidence between the read image data of the area and the original image data of the original halftone area; And means.

  It is possible to provide an image processing apparatus capable of checking the originality of a document while suppressing an increase in cost.

It is an example of the figure explaining the determination method of an original. FIG. 3 is an example of a principle explanatory diagram of the present embodiment by processing at the time of copying a document. It is a figure which shows an example of a dither matrix. It is an example of the actual image data which shows the difference of a halftone process. 1 is an example of a hardware configuration diagram of an image forming apparatus. FIG. 2 is an example of a functional block diagram of original printing of the image forming apparatus. FIG. 3 is an example of a functional block diagram when the image forming apparatus reads a copied printed material. FIG. 6 is an example of a flowchart illustrating a procedure for determining whether or not a document scanned by the image forming apparatus is an original. FIG. 10 is an example of a functional block diagram of original printing of an image forming apparatus (second embodiment). FIG. 10 is an example of a functional block diagram when the image forming apparatus reads a copied printed material (Example 2). FIG. 10 is an example of a flowchart illustrating a procedure for determining whether or not a document scanned by the image forming apparatus is an original (second embodiment). It is an example of the figure explaining a Gabor filter. FIG. 10 is an example of a functional block diagram of original printing of an image forming apparatus (Example 3). FIG. 10 is an example of a functional block diagram when the image forming apparatus reads a copied printed material (Example 2). FIG. 10 is an example of a flowchart illustrating a procedure for determining whether or not a document scanned by the image forming apparatus is an original (third embodiment).

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 is an example of a diagram illustrating an original determination method according to the present embodiment. FIG. 1 (a) shows a printed material (hereinafter simply referred to as an original) that is an original, and FIG. 1 (b) shows a copy of the original (hereinafter referred to as a copied printed material). The original in the present embodiment refers to a document printed directly on a recording medium from an electronic file. In addition, when the original and the copy printed material are not distinguished, they are simply referred to as an original.

  When the original is printed, the image forming apparatus according to the present embodiment prints a barcode or a two-dimensional code (hereinafter simply referred to as a barcode) 30 that is not included in the original electronic file. The barcode 30 includes information on the original picture part.

  An image forming apparatus that expresses multi-valued image data as a set of dots expresses a halftone by quantizing a halftone region such as a pattern portion using a dither matrix. At this time, due to the influence of the screen angle of the dither matrix, a line-shaped dot pattern is formed as shown in the image data of the pattern portion. In the figure, the original dot pattern is 45 degrees downward to the right.

  On the other hand, the dot pattern of the same pattern portion of the copy print is 45 degrees to the left. As described above, even in the same image forming apparatus, the influence of the dither matrix appears in the halftone area, and the original and the copy print are often not the same. Therefore, even if the original and the copy printed matter look the same with the naked eye, if the halftone area is compared at the pixel level, a clear difference due to the influence of the dither matrix is detected in the original and the copied printed matter.

  By utilizing this phenomenon, the image forming apparatus can determine whether the original read by the scanner is an original or a printed copy. In other words, the image forming apparatus reads a document, extracts image data of a picture part, and decodes information related to the original picture part included in the barcode 30. The image forming apparatus can determine whether the read original is an original or a printed copy by verifying the image data of the pattern portion based on information on the pattern portion of the original.

  The information related to the picture part included in the barcode 30 is, for example, a pixel value (Example 1) of image data of the picture part or screen characteristic information (Example 2).

  FIG. 2 is an example of a principle explanatory diagram of the present embodiment by processing at the time of copying a document. The influence of the dither matrix on the original and the copy print described in FIG. 1 will be described in more detail.

  The scanner 11 includes a contact glass for placing a document, an exposure lamp, a mirror system, an image sensor (full color CCD), a drive system (stepping motor), and the like. When the document is read, the entire image surface of the document is optically scanned by moving the exposure lamp and the mirror system. The image on the image plane of the document is guided to the image sensor by the mirror system and subjected to photoelectric conversion, thereby generating color or monochrome image data.

  The plotter 12 is an image forming engine of an electrophotographic system or an inkjet system, and forms image data that has been subjected to character image processing or pattern image processing as a toner image or ink droplet image on a recording medium. . The electrophotographic plotter 12 has a charging unit, a developing unit, a cleaning unit, and the like arranged around the photoconductor, and an electrostatic latent image formed on the outer peripheral surface of the photoconductor according to color image data. A toner is attached and visualized. Thereafter, the toner image is transferred to a recording medium and fixed on the recording medium by a fixing device. Further, the inkjet plotter 12 has a recording head disposed in the entire area of the recording medium in the main scanning direction, and discharges recording liquid (ink) droplets according to image data from the recording head to form an image ( Line type). Alternatively, there is a type in which an image is formed by ejecting liquid droplets while the recording head reciprocates in the main scanning direction.

  From the viewpoint of improving image quality, the copying machine divides an image read from a document into an edge region and a non-edge region, and performs appropriate image processing on each. In general, an edge region is a region where characters and line drawings are drawn (hereinafter referred to as a character portion), and a non-edge region is a region where photographs and pictures are drawn (hereinafter referred to as a pattern portion).

  As a result, the image processing unit 22 of the image forming apparatus can perform optimum image processing on the pattern portion and the character portion, respectively.

  The area determination method for the character part and the picture part by the image processing unit 22 is known. For example, the image processing unit 22 performs vertical and horizontal edge detection processing from image data, and detects an edge having an edge strength equal to or greater than a predetermined value. To do. A region where an edge strength of a predetermined value or more is detected is a character portion, and the other region is a pattern portion.

  In the character portion, a region having a high pixel density and a region having a low pixel density (almost no pixels) are mixed, and two regions are continuous at the edge portion. By utilizing this, the character part may be extracted, and the part other than the character part may be used as the pattern part.

  The image processing unit 22 performs image processing for a character image on the character portion thus separated, and performs image processing for the pattern portion on the pattern portion. The image processing unit 22 performs edge enhancement processing by applying an edge enhancement filter to a character portion of an original binary image such as a character or a line, or performing binarization processing using a predetermined threshold. Thus, halftone processing is not performed on the character portion.

  On the other hand, the pattern portion (halftone portion expressed by a halftone dot or the like) has a cycle of a halftone processing screen line applied at the time of printing an original and a halftone processing screen line performed by the image forming apparatus. In general, the image processing unit 22 performs smoothing processing on the pattern portion and then performs halftone processing for output so as not to cause moire due to interference.

  Although the smoothing process is known, for example, the image processing unit 22 applies a predetermined smoothing filter to the pattern part. For example, the image processing unit 22 sets a value obtained by multiplying the pixel of interest by the coefficient of the smoothing filter and dividing the sum of each value by the number of coefficients as the pixel value of the pixel of interest. This process is performed for each of R, G, and B colors.

  In halftone processing, image data has multi-value data such as 8 to 12 bits per pixel, whereas when forming an image on a recording medium, the number of gradations that can be expressed per pixel (CMYK for toner) This is a technique that enables pseudo gradation expression with the number of dots (or the size of the dots).

  As the halftone processing, the dither method is often used, but the dither matrix used in the dither method is large and includes a dot concentration type (dot screen), a line type (line screen), and the like. These are characterized by the arrangement of the threshold values of the dither matrix.

  A dot concentration type (dot screen) dither matrix is a matrix that induces the distribution of pixels in dot units by periodically arranging small threshold values for a certain number of threshold values in the vertical direction and the horizontal direction. By adjusting the arrangement of the threshold values, it is possible to bring an angle to the periodicity, and such an angle is called a screen angle. The dot-concentrated dither matrix represents a pseudo halftone with a dot-like pattern.

  The line type (line screen) is a matrix that induces the distribution of pixels in a line by arranging small threshold values continuously in a desired angle direction. This angle of the line screen is also called the screen angle.

  In any dither matrix, the number of screen lines is determined from the definition of the image and the output resolution of the plotter 12, and the screen angle and the number of screen lines serve as indices that characterize the dither matrix.

  FIGS. 3A and 3B are diagrams showing an example of a line-type dither matrix when printing an original. In the halftone processing, the image processing unit 22 compares the pixel value of the pixel of interest with the threshold value of the corresponding dither matrix, and determines that a dot of that color is arranged if the pixel value exceeds the threshold value. If the value is less than the threshold value, it is determined that no dot of that color is to be arranged. By applying the dither matrix to the entire surface of the image data, a dot pattern as shown in the lower diagram of FIG. 3A is obtained. Further, in FIG. 3B in which the threshold arrangement is different, a dot pattern having an angle different from that in FIG. 3A is obtained.

  In this example, the binary data is 1 or 0. However, by preparing a plurality of dither matrices, 4-value data (3 dither matrices) and 8-value data (7 dither matrices) are prepared for each color. ) Or image data of 16-value data (15 dither matrices).

  As described above, the image processing unit 22 temporarily squeezes the halftone expression at the time of printing of the halftone portion (pattern part) of the image data of the original by smoothing processing, and then performs halftone expression using a predetermined dither matrix. Reconfigure.

  Accordingly, when viewed at the pixel level, the image data is not reproduced in the area (pattern part) on which the halftone process has been performed, even though the document is copied. In other words, the printed picture portion only has image data reconstructed so that it looks the same at the resolution of the naked eye and the degree of identification.

  By the way, the halftone expression of the image forming apparatus is different between the dither method and other methods, or the dither method, and the above-described matrix is different. Therefore, the halftone processing of the image forming apparatus is usually different for each model. It is. Even with the same image forming device (in the case of a multifunction device having a copy function and a printer function), there is an intermediate between printing as a printer (when printing an original) and copying a document (when printing a copy). The key expression is usually different.

  FIG. 4 is an example of actual image data showing the difference in halftone processing. 4A shows the original, and FIG. 4B shows the printed copy. The original image data is a square picture, and the black thin line frame is filled with lime. Specifically, a lime color patch is printed. FIGS. 4A and 4B are images scanned in color (R, G, B) at 600 dpi.

  When the original is printed, the image forming apparatus performs edge enhancement processing on the black frame line and halftone processing on the inner side of the frame line. When this original is read by the scanner 11 to print a copy, a black frame line is subjected to edge emphasis processing, the inside of the frame line is subjected to smoothing processing, and then halftone processing is performed.

  Although it is difficult to understand because it is black and white in the figure, it can be seen that the original was halftone processed by a dither matrix with a screen angle of 30 degrees to the right. Although the screen angle differs for each of C, M, Y, and K, the dither matrix of this screen angle is cyan because of the color tone.

  On the other hand, in a copy printed matter in which the image forming apparatus that printed the original is read by the scanner 11 and printed by the plotter 12, the screen angle is 30 degrees downward to the left (again, the dither matrix is cyan). . The copy printed material is subjected to a smoothing process, but the screen angle is not as clear as the original because the original screen components (high frequency components) are not sufficiently smoothed by the smoothing process. However, although it is difficult to understand in the figure, a dot pattern of 30 degrees descending to the left can be clearly confirmed.

  On the other hand, since the black thin line portion of the frame is determined as the character portion, there is almost no difference between the original and the copy printed matter even at the pixel level.

  In this way, if the fact that halftone processing is different between the original and the copy printed material is used, it can be determined whether the original read by the image forming apparatus is the original or not.

  FIG. 5 shows an example of a hardware configuration diagram of the image forming apparatus 100. The image forming apparatus 100 includes a system controller 20, a scanner 11, a plotter 12, and an operation display unit 13. The system controller 20 has a configuration in which the CPU 14, ROM 15, RAM 16 and HDD 17 are connected via a bus. The CPU 14 controls the entire image forming apparatus 100 such as management of a document or image data to be printed, reception and setting of printing conditions, and the like. The ROM 15 stores processing parameters for starting the image forming apparatus 100, and the RAM 16 serves as a working memory when the CPU 14 executes the program. The HDD 17 stores programs executed by the image forming apparatus 100, font data, documents, and image data. In addition to applications such as copy and scanner 11, this program includes a program 18 that enables the original determination method of the present embodiment.

  In addition, the system controller 20 includes an ASIC that performs various signal processing and image processing on image data, various input / output interfaces (NIC (Network Interface Card) connected via a bridge), an SD card, and a USB memory. Wireless LAN etc.). The program 18 is distributed from a server via a NIC (not shown) or is stored in an SD card or the like.

  The operation display unit 13 includes display means such as a liquid crystal display and operation accepting means including a touch panel integrated with the display means and surrounding hard keys, and provides a user interface with the user.

  FIG. 6 shows an example of a functional block diagram of the image forming apparatus 100 during original printing. The image forming apparatus 100 according to the present embodiment prints the barcode 30 on a recording medium such as paper. Therefore, first, the printing of the barcode 30 will be described.

  The image forming apparatus 100 in FIG. 6 includes a rasterization processing unit 21, a halftone area data encoding unit 23, and an image processing unit 22. In general, application software (word processing software, spreadsheet software, or the like) that is executed by a user operating a PC (Personal Computer) 200 generates document data. When the user performs a printing operation, the printer driver converts the document data into data that can be interpreted by the image forming apparatus 100 (referred to as PDL data or print data, but hereinafter referred to as print data). The PC 200 transmits print data to the image forming apparatus 100.

  The rasterization processing unit 21 of the image forming apparatus 100 performs rasterization processing on print data as general processing, converts the print data into bitmap data, and sends the bitmap data to the image processing unit 22.

  First, the image processing unit 22 performs general image processing (color conversion processing (RGB → CMYK), printer γ conversion processing, etc.) on rasterized print data (image data), and then performs dither processing on each. Apply.

  That is, the image processing unit 22 performs image area determination on the print data or the image data converted from the print data, and performs image processing optimal for the character part and the picture part. That is, the pattern portion is dithered using a dither matrix (for example, 300 dpi) having a low line number with a different screen angle for each of C, M, Y, and K color image data, and the character portion has a high height for characters. Dither processing is performed using a dither matrix (for example, 600 dpi) of the number of lines.

  By doing this, halftone processing can be applied to the pattern portion at a predetermined screen angle, and the edge of the character portion can be emphasized.

  The halftone area data encoding unit 23 encodes the image data of the pattern portion that has been subjected to the dither processing according to the encoding method of the barcode 30. Since the image data has already been converted to digital information by the image processing unit 22, the halftone area data encoding unit 23 may encode the image data as it is. Encoding is to convert image data into a two-dimensional barcode or a one-dimensional barcode. If the print data is converted into a monochrome dot pattern by a predetermined method based on the barcode 30 standard, the barcode 30 is obtained. Hereinafter, generating the barcode 30 from the image data of the pattern portion is referred to as “converting to the barcode 30”.

  If the image data can be stored, the barcode 30 may be stored in a semiconductor storage device such as an IC chip, for example.

  The image processing unit 22 superimposes the image data of the print data and the image data of the barcode 30 on one image data.

  The image data may be a picture part originally included in the print data, but it is a picture part in which a halftone area is printed in advance with a pixel value of C, M, Y, or K in a rectangular shape like patch data. It is preferable. By arranging the patch data and the barcode 30 at predetermined positions, the patch data and the barcode 30 can be easily detected.

  In the case of the pattern part originally included in the print data, since the image data is color-converted, the image data of the pattern part also includes image data for each of C, M, Y, and K. As described above, since the dither process is performed on all color images, it is preferable that the halftone area data encoding unit 23 converts the image data of the pattern portions of all colors into the barcode 30.

  Further, when there are a plurality of pattern parts, it is considered that it may be difficult to convert the entire pattern part or all of the plurality of pattern parts into the barcode 30 due to the limitation of the capacity of the barcode 30. In this case, it is possible to prevent the capacity of the barcode 30 from being limited by setting the position and size of the pattern portion to a rectangular area including the barcode 30. The position information of the picture part is, for example, the upper left vertex of the circumscribed rectangle of the picture part with the upper left vertex of the recording medium as the origin.

  As a method of making the position information unnecessary, there is a method of determining that the upper left pattern part is converted into the barcode 30. Also, the size can be determined in advance. When the size is larger than the smaller, the number of pixels to be compared increases, and the reliability of determining whether or not the original is the original increases.

  Note that a plurality of barcodes 30 may be generated so that the entire pattern portion or all of the pattern portions can be converted into the barcode 30.

  In addition, the image processing unit 22 arranges the barcode 30 in the upper right, lower right, upper left, upper left, or other blank portion of the recording medium so as not to overlap the image data of the print data transmitted from the PC 200. If necessary, the image processing unit 22 performs processing for emphasizing edges on the barcode 30, and superimposes the image data generated from the print data and the image data of the barcode 30 on one image data to the plotter 12. Output.

  Since the plotter 12 forms an image on the recording medium based on the image data, the image forming apparatus 100 can print on the recording medium including the image data generated from the print data transmitted from the PC 200 and the barcode 30. it can. This is the original.

  FIG. 7 is an example of a functional block diagram when the image forming apparatus 100 reads a copied printed material. The user places a document on the scanner 11 of the image forming apparatus 100 and inputs a scan operation from the operation display unit 13. The scanner 11 reads a document (a recording medium on which image data has already been printed) and generates image data of a color image (R, G, and B each 8 bits).

  First, the pattern part extraction processing unit 34 performs image area determination and specifies a pattern part. If there are multiple picture parts, all are extracted. Then, the following processing is performed for one of the picture portions. The pattern part extraction processing unit 34 specifies a pattern part and extracts image data (pixel value) of the area. Hereinafter, the image data of the pattern portion of the document read by the scanner 11 is referred to as inspection target image data.

  Here, since the image data is in color, the pattern portion extraction processing unit 34 extracts the image data for each of R, G, and B colors. Note that the image data converted into the barcode 30 is image data whose color space is CMYK and position information of the pattern portion.

  The barcode reading processing unit 31 extracts the barcode 30 from the read K image data based on a predetermined color of the barcode 30 (here, K). For the extraction of the barcode 30, for example, a premise that the barcode 30 is in a predetermined position may be used, or image area determination may be used. When the image area determination is used, the bar code 30 is a rectangular area where edge intensities of a predetermined value or more are dense.

  A method for decoding the barcode 30 is known. In the case of a QR code (registered trademark), the barcode reading processing unit 31 can specify three cut-out symbols and can specify the direction of the barcode 30, and can decode a two-dimensional monochrome pattern according to a rule. The image data obtained by decoding is referred to as original printing image data.

The image matching degree calculation processing unit 32 extracts part or all of the inspection target image data based on the position information, and calculates the degree of matching between the original printing image data and the inspection target image data. As described above, since the color space between the original printing image data and the inspection target image data is different, the image matching degree calculation processing unit 32 first converts the inspection target image data from CMYK to pixel values in the RGB color space. . The conversion formula is as follows, for example. Also, conversion may be performed using a direct lookup table (DLUT).
CMYK → RGB
R = 1-min (1, C x (1-K) + K)
G = 1-min (1, M × (1-K) + K)
B = 1-min (1, Y × (1-K) + K)
The meaning of min (A, B) means that the smaller of A and B is taken out. Thereby, inspection object image data is obtained for each of R, G, and B colors. Note that errors due to color space conversion are corrected in advance. Further, the color space may be converted from RGB to CMYK.

  The image matching degree calculation processing unit 32 matches the degree of matching between the R color original image data and the inspection target image data, the G color original printing image data and the inspection target image data, and the B color original printing image. The degree of coincidence between the data and the inspection target image data is calculated.

  The degree of coincidence is, for example, the absolute value sum of the differences between the pixel values of the original printing image data and the inspection target image data. As shown in FIGS. 3 and 4, if the screen angles are different, the pixel values do not match except at the intersection of the screen lines, so that the absolute value sum increases. In the average value and the most frequent value, the image data at the time of original printing and the image data to be inspected are approximately the same, but a difference in screen angle can be detected by comparing each pixel.

  Further, the normalized correlation between the original printing image data and the inspection target image data (a value between 0 and 1 is closer to 1 and the correlation is higher) R may be used as the degree of coincidence. In this case, the larger the value, the higher the matching degree. “G1” is the pixel value of the coordinates (ij) of the original image data, and “G2” is the pixel value of the coordinates (ij) of the image data to be inspected.

R = ΣΣG1 (i, j) G2 (i, j) / √ {ΣΣG1 (i, j) ² × ΣΣG2 (i, j) ² }
Here, since the original image printing image data and the inspection target image data exemplified are lime color regions, the pixel values of the inspection target image data are composed of two colors of yellow (Y) + cyan (C), and yellow and cyan Considering the intensity of C, M, Y, and K, the characteristics of the screen angle appear sufficiently in cyan. Further, the G component of the R / G / B image is most correlated with cyan. Therefore, the image matching degree calculation processing unit 32 may calculate the degree of matching between the original printing image data and the inspection target image data only for the G component image data. By calculating the degree of coincidence for only one color component, the processing load on the CPU 14 can be reduced.

  It is obvious from the characteristics of the lime color that the G component should be seen if it is a lime color, but if the characteristic hue of the pattern portion is not clear, the original image data at the time of original printing of each color of R, G, B Of these, the color component having the largest average value may be used for calculating the degree of coincidence. Therefore, the image matching degree calculation processing unit 32 can easily specify the color component for calculating the matching degree.

  The originality determination processing unit 33 compares the calculated degree of coincidence with a predetermined threshold value, and determines whether or not the document read by the scanner 11 is an original. When the degree of coincidence is the sum of absolute values of differences between image data in pixel units, the originality determination processing unit 33 determines that the original is the original if the sum of absolute values is smaller than a predetermined threshold value. When the degree of coincidence is a normalized correlation, the originality determination processing unit 33 determines that the original is the original if the normalized correlation value is greater than a predetermined threshold value.

  The predetermined threshold value may be determined as follows. Even when the original is repeatedly scanned, the degree of coincidence of the absolute value sum does not become zero and the degree of coincidence of the normalized correlation does not become 1 due to a slight deviation of the scanning position or deviation of the cutout position of the pattern portion. For this reason, the predetermined threshold value is determined in consideration of (a) the degree of coincidence calculated at the time of reading the original and (b) the degree of coincidence calculated at the time of reading the printed copy.

  That is, when the coincidence is the sum of absolute values, (a) <threshold << b), and when the coincidence is the normalized correlation, (b) <threshold <(a).

  The originality determination processing unit 33 displays the determination result on the operation display unit 13. For example, “This manuscript is an original” or “This manuscript is not an original” is displayed. In addition, for example, a message “The original to be copied is the original. Do you want to copy it” is displayed. The user can see this message and determine whether or not to copy. For example, when the original is an original, copying may be prohibited. In this case, the originality determination processing unit 33 displays “The original to be copied is an original. It cannot be copied”. The user can understand that the message cannot be copied by seeing this message.

  FIG. 8 is an example of a flowchart illustrating a procedure for determining whether or not a document scanned by the image forming apparatus 100 of the present embodiment is an original document.

  First, the scanner 11 scans a document (document to be inspected) (S10).

  Next, the barcode reading processing unit 31 extracts the barcode 30 from the image data, and decodes the original printing image data (S20).

  Next, the pattern part area extraction unit 34 specifies the pattern part and extracts the inspection target image data (S30).

  Next, the image matching degree calculation processing unit 32 calculates the degree of matching between the original printing image data and the inspection target image data (S40).

  The originality determination processing unit 33 compares the degree of coincidence with a threshold value and determines whether or not the original is the original (S50). If the original is not the original (No in S50), the originality determination processing unit 33 displays "The original to be copied is not the original" (S60).

  If it is an original (Yes in S50), the originality determination processing unit 33 displays “The original to be copied is the original” (S70).

  After the determination of whether or not it is the original in FIG. 8, the user can copy the original, but the copying operation of the image forming apparatus 100 is the same regardless of whether the original is an original or a printed copy. The image forming apparatus 100 extracts a character part (including the barcode 30) and a picture part from image data read by the scanner 11, performs an edge emphasis process on the character part, and smoothes and halftones the picture part. Apply processing. Accordingly, whether the original is an original or a copy print, the pattern portion is subjected to smoothing and halftone processing, and the copy print is generated from the original and the next copy print is generated from the copy print. In this case, the image data of the original picture portion is inherited while being stored in the barcode 30.

  As already described, the halftone processing performed on the pattern portion differs depending on the image forming apparatus 100 and also on the same image forming apparatus 100. Therefore, even if the possibility that the printed copy is printed with the original is almost zero. It's okay.

  As described above, the image forming apparatus 100 according to the present embodiment stores the original halftone area image data in the barcode 30 so that it can be compared with the inspection target image data read by the scanner 11. It is possible to determine whether the original is an original. There is no need to use special toner or to prepare a high-resolution scanner 11 as in the prior art.

  In the first embodiment, the image data itself is converted into the barcode 30. In this embodiment, the image forming apparatus 100 that stores the screen characteristics (screen angle, screen line number) of halftone expression in the barcode 30 will be described.

  FIG. 9 is an example of a functional block diagram at the time of original printing of the image forming apparatus 100 in the present embodiment. In FIG. 9, the description of the same part as in FIG. 7 is omitted. The image forming apparatus 100 according to the present exemplary embodiment includes a screen feature encoding unit 24 and stores a screen feature 25. The screen feature encoding unit 24 converts not the image data itself of the pattern portion but the screen feature 25 when the pattern portion is expressed in halftones into a barcode 30.

  The microscopic feature of the image data of the pattern portion subjected to the halftone process is characterized by a dither matrix. The periodic structure characteristic of the dither matrix is specified by the screen angle and the number of screen lines (pitch). At the time of printing the original, the image processing unit 22 performs halftone processing using a dither matrix. In this embodiment, the screen angle and the number of screen lines of the dither matrix are set as constants in the ROM 15 or HDD 17 (hereinafter referred to as “the dither matrix”). Simply stored in the ROM 15).

  The screen feature encoding unit 24 reads the screen feature (screen angle and screen line number) 25 from the ROM 15 only when printing the print data received from the PC 200 on the recording medium (only when printing the original), and the bar code 30 Convert to Even if there are a plurality of picture parts in the original, the screen feature 25 is common (the screen angle is different between CMYK), so the screen feature encoding unit 24 may store one screen feature 25 for each color.

  FIG. 10 is an example of a functional block diagram when the image forming apparatus 100 reads a copied printed material. 10, the description of the same part as in FIG. 7 is omitted. The image forming apparatus 100 according to the present exemplary embodiment includes a screen feature coincidence calculation processing unit 35.

  The bar code reading processing unit 31 decodes the original screen angle and screen line number, but the picture part extraction processing part 34 extracts the picture part image data itself (inspection target image data). . For this reason, the screen feature coincidence calculation processing unit 35 digitizes the inspection target image data by some method and calculates the degree of coincidence between the inspection target image data and the image data of the original pattern portion. In addition, since the screen feature 25 is common even if there are a plurality of pattern portions, any one or more inspection target image data may be extracted.

In this embodiment, a two-dimensional Gabor filter is used. Although the Gabor filter will be described later, the edge can be selectively detected by designating the edge detection interval and the edge detection direction. Accordingly, the screen angle (to be corrected if necessary) and the number of screen lines to be extracted may be set to θ (angle) and ω ₀ (sine wave frequency), respectively, among the Gabor filter parameters. If the number of screen lines is set to an appropriate constant, the degree of coincidence can be calculated to some extent even if only θ (angle) is specified.

  The screen feature coincidence calculation processing unit 35 sets the screen features (angle, pitch) 25 of the halftone expression at the time of printing of the original obtained by decoding the barcode 30 as parameters of the Gabor filter, and the scanner 11 reads them. The convolution integration processing is performed on the inspected image data. As a result, the edge strength corresponding to the screen angle and the number of screen lines of the image data to be inspected can be obtained, so the sum of absolute values for all pixels in the convolution integration process is calculated. As the absolute value sum is larger, the edge detection direction and the edge detection interval set in the Gabor filter tend to coincide with the screen angle and the screen interval of the inspection target image data.

  Strictly speaking, the calculated degree of coincidence is the screen feature 25 and the screen feature of the inspection target image data, but this degree of coincidence can also be regarded as the degree of coincidence between the inspection target image data and the original printing image data.

  As in the first embodiment, it is not necessary to calculate the degree of coincidence for all the color components of R, G, and B in the pattern portion. The screen feature coincidence calculation processing unit 35 calculates the coincidence for the G component if the color is lime. If the characteristic hue of the pattern portion is not clear, the color component having the largest average numerical value among the R, G, and B inspection target image data may be used for calculating the degree of coincidence.

  The method for determining the threshold is the same as in the first embodiment. That is, the predetermined threshold value is determined in consideration of (a) the degree of coincidence calculated when reading the original and (b) the degree of coincidence calculated when reading the copied printed material. In this embodiment, the higher the matching degree, the higher the possibility of matching, so that (b) <threshold value <(a).

  FIG. 11 is an example of a flowchart illustrating a procedure for determining whether or not a document scanned by the image forming apparatus 100 of the present embodiment is an original. 11 differs from FIG. 8 in the process of step S42.

  That is, the screen feature coincidence calculation processing unit 35 sets the screen feature 25 as a Gabor filter, and calculates the coincidence between the screen feature 25 and the screen feature of the inspection target image data (S42).

  The originality determination processing unit 33 compares the degree of coincidence with a threshold value and determines whether or not the original is the original (S50). If the original is not the original (No in S50), the originality determination processing unit 33 displays "The original to be copied is not the original" (S60).

  If it is an original (Yes in S50), the originality determination processing unit 33 displays “The original to be copied is the original” (S70).

  As described above, the image forming apparatus 100 according to the present exemplary embodiment stores the screen feature 25 of the image data of the original halftone area in the barcode 30 so that the image data to be inspected is the original halftone area. It can be determined whether or not the image data is the same as the original image data, and it can be determined whether or not the original is the original. There is no need to use special toner or to prepare a high-resolution scanner 11 as in the prior art.

<About Gabor Filter>
The Gabor filter will be briefly described. Since the Gabor filter is detailed in, for example, “http://fussy.web.fc2.com/algo/algo12-2.htm”, a part of it is summarized.

A Gabor filter is defined as the product of a “sine wave” and a “Gaussian function”.
g (t) = K ・ w (t) ・ exp (iφ) ・ s (t)
W (t) = exp (-t ² / 2σ ² ), s (t) = exp (iω ₀ t)
Extend the Gabor filter to two dimensions.
g (x, y) = K wr (x, y) s (x, y)
wr (x, y) is a Gaussian function in a one-dimensional Gabor filter, and s (x, y) is a sine wave.

wr (x, y) is expressed as the following equation.
wr (x, y) = exp (-(x ' ² + (γy') ² ) / 2σ ² )
However, (x ', y') is defined by the following formula, and is the result of rotating (x, y) clockwise by θ around the origin (0, 0).
x '= xcosθ + ysinθ
y '= -xsinθ + ycosθ
wr (x, y) becomes maximum at (x, y) = (0, 0), and decreases monotonously toward the periphery. Further, as shown in FIG. 12 (A), the cut edge when cut by a plane parallel to the x ′ axis and the y ′ axis and perpendicular to the xy plane is a bell-shaped curve by a Gaussian function.
s (x, y) is expressed as the following equation.
s (x, y) = exp (i (ω ₀ x '+ φ))
= exp (i (ω ₀ (xcosθ + ysinθ) + φ))
The formula which extracted only the real part and the imaginary part is as follows.
Re (s (x, y)) = cos (ω ₀ x '+ φ)
Im (s (x, y)) = sin (ω ₀ x '+ φ)
Since x ′ represents an axis tilted clockwise by θ, as shown in FIG. 12B, s (x, y) takes a form in which a wave advances along that axis.

From the above, the Gabor filter can be expressed by the following equation.
g (x, y) = K exp (-(x ' ² + (γy ') ² ) / 2σ ² ) exp (i (ω ₀ (xcosθ + ysinθ) + φ))) (1)
When the two waves in FIGS. 12 (a) and 12 (b) are superposed, the shape is as shown in FIG. 12 (c). FIG. 12C visually shows a two-dimensional Gabor filter from the left when ω ₀ = 3π, ω ₀ = 2π, and ω ₀ = π.

  When the image data and the Gabor filter are overlapped, only the value of the portion overlapping the peaks and valleys of the Gabor filter is amplified for each pixel of the image. If the image data is flat and there is no change in the range corresponding to the Gabor filter, the values amplified in the peaks and valleys cancel each other, and the total sum is close to zero. On the other hand, when the values are concentrated only on the peaks and valleys, the total sum of absolute values is increased.

  When the edge portion of the image overlaps with the wave, the values of the peaks and valleys are concentrated and emphasized on the edge portion, so that the Gabor filter is effective for edge extraction.

Further, if the frequency ω _{0 of the} sine wave is increased, the period of the wave becomes finer, so that a peak occurs many times while the periphery is attenuated by the Gaussian function. Conversely, if it is made smaller, the wave peak hardly occurs (if ω ₀ = 0, the sine wave becomes a constant (DC component) and becomes a Gaussian function itself).

  Therefore, an image with a rapid change (high frequency component) can be amplified by a Gabor filter with a high frequency, and an image with a slow change (a large low frequency component) can be amplified with a Gabor filter with a low frequency.

  Since θ can be expressed as an angle formed with the x-axis as shown in FIG. 12 (c), the Gabor filter has an edge in the vertical direction (parallel to the y-axis) at θ = 0 °, and at θ = 90 ° Edges in the horizontal direction (parallel to the x axis) can be emphasized. Since the screen angle converted to the bar code 30 is a value based on a certain reference direction, the screen angle is appropriately converted to the Gabor filter angle θ. For example, when the screen angle is 45 degrees to the right, θ = 45 degrees may be used, but when the screen angle is 45 degrees to the right, θ = 45 + 90 degrees.

  Further, if the screen angle is positive in the clockwise direction with respect to the 9 o'clock direction, 45 degrees downward to the right = 45 degrees and 45 degrees upward to the right = 135 degrees. Therefore, in this case, by setting θ = screen angle, a Gabor filter perpendicular to the screen can be generated.

  Note that the orientation of the document when the user sets the document depends on the method in which the user puts the document in the correct orientation, the position of the barcode 30 (the orientation is known in the case of a two-dimensional barcode), or the arrangement of the barcode 30 and patch data. There is a method for detecting the orientation of a document. When the orientation of the document is determined, the reference direction of the screen angle is also determined.

Further, since ω _{0 of the} Gabor filter is an angular frequency, it can be expressed as ω ₀ = 2πf = 2π / T (f is a frequency, T is a period). Assuming that one wavelength is advanced during the period T, the period T can be replaced with the wavelength λ in the three-dimensional space.
ω ₀ = 2π / λ
If the number of screen lines converted into the barcode 30 is, for example, 300 dpi in dpi units, the screen interval is 25.4 mm / 300 = about 0.085 mm. Therefore, this value can be the wavelength λ.

  Based on the above calculation, the screen feature coincidence calculation processing unit 35 obtains the screen angle decoded from the barcode 30 as the Gabor filter angle θ and the screen interval obtained from the screen line number decoded from the barcode 30. Is set to the expression (1). Thereby, the degree of coincidence between the screen feature 25 and the screen feature of the inspection target image data can be calculated.

  In the first and second embodiments, it is assumed that the halftone processing of the pattern portion is different between the original printing and the copy printing, but in the present embodiment, the middle of the pattern portion is different between the original printing and the copy printing. The image forming apparatus 100 that can determine whether or not the original is the same even when the tone processing is the same will be described.

  FIG. 13 is an example of a functional block diagram of the image forming apparatus 100 during original printing. The functional block diagram at the time of original printing of Example 1 and Example 2 is just combined, but the image processing unit 22 of this example has a function of dividing, rotating, and synthesizing the image data of the pattern part. Is provided.

  As in the first and second embodiments, the image processing unit 22 performs halftone processing on the pattern portion using a predetermined dither matrix. It is assumed that the cyan screen angle at the time of original printing is 45 degrees to the right. The image processing unit 22 processes the entire pattern portion with this dither matrix, and then divides it into 2 × 2 square blocks. Thus, four square blocks are obtained. Here, since the original picture part is not necessarily a square, the image processing part 22 preferably extracts a relatively large square area from the picture part.

  Then, the image processing unit 22 leaves one of the four blocks and rotates the remaining three by 90 degrees clockwise. For example, the upper right block is rotated by 90 degrees, the lower right block is rotated by 180 degrees, and the lower left block is rotated by 270 degrees. Therefore, the screen angle is the same as the upper left and lower right in appearance. For example, affine transformation is used for the rotation.

  However, the screen angles of upper left / lower right and upper right / lower left are different by 90 degrees. In this way, even when the image forming apparatus 100 uses a dither matrix with 45 degrees lower right as the cyan screen angle for halftone processing of the pattern portion when printing a printed copy, the upper right and lower left screen angles are The screen angle can be set differently from the original printing (upward 45 degrees). Therefore, even when a dither matrix having the same screen angle is used for halftone processing of the pattern portion when printing an original and when copying a printed matter, it is possible to reliably determine whether or not the original read by the scanner 11 is an original based on the degree of coincidence. .

  Note that the rotation of the block as shown in FIG. 13 is an example, and the pattern portion may be divided into two or more and only a part may be rotated. For example, any of the three rotated ones may be fixed, and the remaining three including the upper left block may be rotated. Also, the rotation angle need not be 90 degrees, for example, {60 degrees, 120 degrees, 180 degrees}, {30 degrees, 60 degrees, 90 degrees}, {15 degrees, 30 degrees, 60 degrees} Good.

  Further, the halftone area data encoding unit 23 of the present embodiment converts the image data of the divided pattern portion into the image data itself, and the screen feature encoding unit 24 converts the screen feature 25 into the barcode 30. Convert each one. When the screen feature 25 is converted to the bar code 30, only the screen feature 25 of the 45 ° downward dither matrix used for the image processing unit 22 to perform the halftone process may be converted. The screen feature 25 may be converted for each block.

  In this way, the degree of coincidence can be obtained from the image data as in the first embodiment, or the degree of coincidence can be obtained by a Gabor filter. In addition, the original determination can be stricter by using both determination methods.

  FIG. 14 is an example of a functional block diagram when the image forming apparatus 100 reads a copied printed material. In FIG. 14, the description of the same parts as those in FIGS.

  The image forming apparatus 100 according to the present exemplary embodiment includes the image matching degree calculation processing unit 32 and the screen feature matching degree calculation processing unit 35, but only one of them may be used.

Similar to the first embodiment, the image coincidence degree calculation processing unit 32 calculates the degree of coincidence between the original color printing image data of R, G, and B and the image data to be inspected. It is sufficient to calculate the degree.
In FIG. 14, since the screen angle of the copy printed material is 45 degrees downward to the right, it is the same as the screen angle used by the image processing unit 22 to perform halftone processing during original printing. However, in the present embodiment, since the original picture portion is rotated for each block, the calculated degree of coincidence can be set to a low value.

  In addition, since the picture part of the original is divided into four, and half of them have the same screen angle, even if the screen angle of the printed copy is different from the screen angle at the time of original printing, the images match in half the area. there is a possibility. For this reason, the threshold value is determined so that the originality determination processing unit 33 can determine whether or not the original is the original even if the images match in the half area. For example, it is determined in consideration of (a) the degree of coincidence calculated at the time of reading the original, and (b) the degree of coincidence when a copied printed material having a screen angle that coincides with half of the pattern portion is scanned.

  That is, when the coincidence is the sum of absolute values, (a) <threshold << b), and when the coincidence is the normalized correlation, (b) <threshold <(a).

  The screen feature coincidence calculation processing unit 35 of the present embodiment determines the coincidence using a two-dimensional Gabor filter, but changes the parameter θ of the Gabor filter for each 2 × 2 block. . Note that λ may be common to all blocks.

  The screen feature coincidence calculation processing unit 35 sets the screen angle decoded from the barcode 30 to the Gabor filter angle θ and applies the Gabor filter to the upper left block. Further, the screen feature coincidence calculation processing unit 35 adds 90 degrees to the screen angle decoded from the barcode 30 to set the Gabor filter angle θ, and applies the Gabor filter to the upper right block. Further, the screen feature coincidence calculation processing unit 35 adds 180 degrees to the screen angle decoded from the barcode 30 to set the Gabor filter angle θ, and applies the Gabor filter to the lower right block. Further, the screen feature coincidence calculation processing unit 35 adds 270 degrees to the screen angle decoded from the barcode 30, and sets the Gabor filter angle θ, and applies the Gabor filter to the lower left block.

  Then, absolute value sums for all pixels in the convolution integration processing of all blocks are obtained. The method for determining the threshold value is as described above, and (b) <threshold value <(a).

  FIG. 15 is an example of a flowchart illustrating a procedure for determining whether or not a document scanned by the image forming apparatus 100 of the present embodiment is an original document. 15 differs from FIG. 8 in the process of step S44.

  That is, the image coincidence degree calculation processing unit 32 calculates the degree of coincidence between the original printing image data and the inspection target image data, and the screen feature coincidence degree calculation processing unit 35 calculates the screen feature 25 for every four blocks. The degree of coincidence between the screen feature 25 and the screen feature of the inspection target image data is calculated (S44).

  The originality determination processing unit 33 compares the degree of coincidence with a threshold value and determines whether or not the original is the original (S50). The originality determination processing unit 33 determines that the original is the original when it can be considered that both the coincidence of the image data and the coincidence of the screen features match.

  If the original is not the original (No in S50), the originality determination processing unit 33 displays "The original to be copied is not the original" (S60).

  If it is an original (Yes in S50), the originality determination processing unit 33 displays “The original to be copied is the original” (S70).

  As described above, in addition to the effects of the first and second embodiments, the image forming apparatus 100 according to the present embodiment has the same halftone processing for the pattern portion when the original is printed and when the copy print is printed. It can be determined whether or not the original read by the scanner 11 is an original.

DESCRIPTION OF SYMBOLS 11 Scanner 12 Plotter 13 Operation display part 18 Program 20 System controller 21 Rasterization processing part 22 Image processing part 23 Halftone area data encoding part 24 Screen characteristic encoding part 25 Screen characteristic 31 Barcode reading processing part 32 Image coincidence calculation process Unit 33 Originality determination processing unit 34 Picture portion extraction processing unit 35 Screen feature coincidence calculation processing unit 100 Image forming apparatus

JP 2003-118276 A JP 2004-153405 A

Claims (11)

An image processing apparatus that reads a document and generates image data,
Decoding means for decoding the image data information of the document that is the original of the image data, the information recording mark being extracted from the image data and encoded in the information recording mark;
Halftone area extracting means for extracting a halftone area that has been subjected to halftone processing from the image data;
Based on the image data information, the degree-of-matching calculation means for calculating the degree of matching between the read image data of the halftone area and the original image data of the original halftone area;
Original determination means for determining whether the original of the image data is an original based on the degree of coincidence;
An image processing apparatus comprising: The image data information is a pixel value of a pixel unit of the halftone area,
The degree of coincidence calculating means calculates the degree of coincidence by comparing the pixel value of the read image data in pixel units and the pixel value of the original image data included in the image data information.
The image processing apparatus according to claim 1. The image data information is screen characteristic information of a dither matrix when halftone processing is performed on the halftone area,
The coincidence calculation unit uses a filter capable of selectively detecting an edge in a predetermined direction, sets a screen angle of the screen characteristic information as a parameter of the filter, performs a filtering process on the read image data, and Calculate the degree of match,
The image processing apparatus according to claim 1. The coincidence degree calculation unit sets a screen interval obtained from the number of screen lines of the screen feature information in the filter capable of detecting an edge for each predetermined distance, performs a filtering process on the read image data, and the coincidence degree To calculate,
The image processing apparatus according to claim 3.   5. The image processing apparatus according to claim 3, wherein the filter is a Gabor filter. An image forming apparatus for printing the document according to any one of claims 1 to 5,
Image data generating means for performing halftone processing on the pattern portion of the original print data received from the terminal and generating first original image data;
An information recording mark generating means for encoding the image data information of the halftone area of the first image data and generating second image data of the information recording mark;
Printing means for printing the first image data and the second image data on a single recording medium;
An image forming apparatus comprising: The image data generating means
Extracting a halftone area that has been subjected to halftone processing from the first image data, dividing the image data of the halftone area into two or more blocks, and rotating at least one block;
The image forming apparatus according to claim 6, wherein the printing unit prints the first image data in which a part of the halftone area is rotated together with the second image data on a single recording medium. apparatus. The image data generation means divides the image data of the halftone area into four blocks and rotates the three blocks to different angles of 90 degrees,
The image forming apparatus according to claim 7. An original determination method for determining the originality of a document read by an image processing apparatus,
Decoding means for extracting information record marks from the image data of the document and decoding the image data information of the document that is the original of the image data encoded in the information record marks;
A step of extracting a halftone area on which halftone processing has been performed from the image data;
A degree of coincidence calculating means, based on the image data information, calculating the degree of coincidence between the read image data of the halftone area and the original image data of the original halftone area;
A step of determining whether an original of the image data is an original based on the degree of coincidence;
An original determination method characterized by comprising: An image forming method of an image forming apparatus for printing the document according to claim 9,
Image data generating means performs halftone processing on a pattern portion of the original print data received from the terminal, and generates first original image data;
When the information recording mark generating means encodes the image data information of the halftone area of the first image data to generate the second image data of the information recording mark,
Printing means for printing the first image data and the second image data on a single recording medium;
An image forming method comprising: The image data generating means
Extracting a halftone area that has been subjected to halftone processing from the first image data, dividing the image data of the halftone area into two or more blocks, and rotating at least one block;
The printing means prints the first image data, in which a part of the halftone area is rotated, together with the second image data on a single recording medium.
The image forming method according to claim 10.