Image processing apparatus and method

Abstract: The present invention is directed to discriminate in a high accuracy a specific pattern by using visible and invisible information. There is provided an image processing apparatus comprising a reading unit for obtaining visible and invisible information at an original as electric signals, and a comparing unit for comparing a visible reading signal with a invisible reading signal, both of which are obtained by the reading unit.

Description: This invention relates to a method and an apparatus for image processing that is applicable to devices such as a copying machine and an image scanner for the prevention of forgery. Copying machines have been improved to reproduce a color image of higher quality as close as an original one. Such improvement results in an increased chance for the copying machine of being abused to counterfeit banknotes or valuable securities. With respect to this, various systems have been developed that are capable of discriminating banknotes or the like. For example, EP 0463804 discloses a system for recognizing line drawing of a pattern on the original image. Another system is disclosed in EP 0382549 where color components are recognized on the original image. In addition, EP 0594446 (not published at the filing date of the present application) discloses to print a particular stamp on a banknote itself with an ink containing fluorescent dye, allowing discrimination between the genuine and counterfeit banknotes. The use of other types of ink such as the one having an infra-red absorption characteristic are also suggested. GB 1534403 discloses a system in which security documents are rendered resistant to copying by providing and detecting a security mark on each document. The security mark comprises a mark printed in each ink of at least one pair of inks, the inks of each pair being of the same visible colour but having different infra-red absorption properties. To detect the mark, the area bearing the mark is moved across a detector sensitive to infra-red radiation. The detector is influenced by two different levels of infra-red radiation reflected from the surface, and on this basis it is determined whether the document has the essential features of the security mark. A device designed to detect infrared comprises a reading sensor for infrared detection along with a reading sensor that is similar to those provided in typical devices for reproducing color images. The device of the type described is capable of detecting specific information involved in the original image according to the information about visible colour components and luminous energy of the infrared. When the infrared is used as a basis for discriminating a specific stamp, an erroneous detection may be made due to the presence of some infrared absorbing materials on the back of the original. More specifically, the infrared reaches the deep inside of a paper as well as being reflected from the face of the paper because it involves wavelengths longer than those of visible light. A portion of the infrared reached to the deep inside is reflected therefrom in an amount depending on the infrared absorbing materials, if any, present there. Carbon black, which is often contained in inks and pigments for printing, is one of the infrared absorbing materials. Thus, if the carbon black is present on the back of the original, the infrared reached to there is absorbed by this carbon black. However, less or no visible information is obtained from the back of the original. Thus, the visible information is obtained from the face of the original though the infrared information is obtained from the back of it. As a result, there is a disadvantage of erroneously detecting the infrared absorbing materials on the back of the original as the specific stamp. Another challenge to the security is to use a glazing color having specific reflecting characteristics to the infrared region and thereby detecting the latter. The glazing color can be printed independently of the visible colors, so that this technique is applicable to make any valuable securities. However, this optical characteristics specific to the infrared region is disadvantageous in that it is affected by various factors including the color material such as the carbon black, oil and dirt of fingers. Thus, incorrect discrimination may sometimes be caused. According to the present invention, there is provided an image processing apparatus as set out in claim 1. The invention further provides a method of operating an image processing apparatus as set out in claim 10. An embodiment of the present invention provides an image processing apparatus capable of discriminating a specific pattern in high accuracy by using visible and invisible information. Such embodiments aim to avoid incorrect or erroneous discrimination due to the information involved in the back of the original. Embodiments of the present invention provide a simple apparatus for such discrimination that is operated at a high speed. Embodiments can avoid counterfeit of a predetermined original. Embodiments improve a copying apparatus. These and other objects and features of embodiments will become more fully apparent from the following description and appended claims taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram of a specific pattern judging unit in a first embodiment of the present invention, Fig. 2 is a schematic view showing a structure of a color copying machine in the first embodiment; Fig. 3 is a view illustrating a specific pattern for discriminating an original; Fig. 4 is a block diagram of a secondary area signal generating unit for use in detecting a specific pattern; Fig. 5 shows reference pixels for use in detecting a specific pattern; Fig. 6A is a schematic perspective view showing a charged coupled device (CCD); Fig. 6B is a view showing CCD line sensors implemented in the CCD device of Fig. 6A; Fig. 7 shows spectral reflectance of a standard white plate; Fig. 8 shows spectral transmittance of a specific pattern; Fig. 9 shows spectral response of a visible line sensor and that of a filter for an infrared reading sensor, both in accordance with the first embodiment; Fig. 10 shows spectral response of an infrared cutoff filter; Fig. 11 shows spectral response of a far infrared-cutoff filter; Fig. 12 is a view showing geometry of radiation reflected from various originals and corresponding states of infrared reading signals; Fig. 13 illustrates relations between infrared reading signals and visible reading signals for various originals; Fig. 14 is comprised of Figs. 14A and 14B showing a block diagram showing an image signal controlling unit; Fig. 15 is a timing chart of image control signals; Fig. 16 is a control flow carried out by a CPU; Fig. 17 is a block diagram of a specific pattern judging unit in a second embodiment of the present invention; and Fig. 18 is a block diagram of a specific pattern judging unit in a third embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following embodiments an exemplified copying machine is described and illustrated. However, embodiments may be applicable to various other devices including a single image scanner and a sensor. 〈First Embodiment〉 One of the above mentioned problems is solved in the following first embodiment of the present invention by means of comparing, upon reading a invisible specific mark to be detected, a signal level of invisible read information with that of visible read information, thereby judging whether the invisible information in question is associated with the specific mark. Fig. 2 is an outside view of an apparatus according to the first embodiment of the present invention. In Fig. 2, the apparatus comprises an image scanner unit 201 and a printer unit 200. The image scanner unit 201 is for picking up an original image and digitizes it into an electrical signal. The printer unit 200 is for printing on a paper a full-color image corresponding to the original image picked up by the image scanner unit 201. The image scanner unit 201 comprises a pressing plate 202. An original 204 carried on an original carrier glass plate (hereinafter, referred to as a platen) 203 is illuminated with light produced by a halogen lamp 205. The halogen lamp 205, which serves as a light source, produces light beams involving wavelengths corresponding to the infrared region. The light reflected from the surface of the original is guided to mirrors 206 and 207 and is focused by a lens on a four-line sensor (hereinafter, referred to as a CCD) 210. The CCD 210 separates colors of the optical information obtained from the original. The separated colors are supplied to a signal processing unit as full-color information consisting of red (R), green (G) and blue (B) components and an infrared (IR) component. The entire area of the original is scanned by mechanical movement of the lamp 205 and the mirror 206 at a velocity v, and of the mirrors 207 at a velocity v/2, in a direction perpendicular (hereinafter, referred to as a sub scan direction) to the electrical scanning direction (hereinafter, referred to as a main scan direction) of the four-line sensor 210. A standard white plate 211 generates a correction data for correcting shading of read data 210-1 through 210-4 (correction of characteristics of an individual element of each line sensor) corresponding to the line sensors IR, R, G and B, respectively. The standard white plate 211 reflects light that is relatively balanced in all visible and infrared wavelengths. In other words, the standard white plate 211 reflects light at substantially uniform reflectance, as shown in Fig. 7, and appears white to the eyes. This standard white plate 211 is adapted to generate data used for shading correction on the output data of the IR sensor 210-1 and of the visible sensor 210-2 through 210-4. The signal processing unit electrically processes the signals obtained by the scanning operation to separate it into components of magenta (M), cyan (C), yellow (Y) and black (BK), which are sent to the printer unit 200. Either one of the components M, C, Y, and BK is supplied to the printer unit 200 at every one scanning operation of the image scanner unit 201, so that a complete color image corresponding to one original is obtained through four-time scanning operation. The image signals representing the respective components M, C, Y and BK supplied from the image scanner unit 201 are sent to a laser driver 212. The laser driver 212 drives a semiconductor laser 213 in response to the image signal supplied from the image scanner unit 201. The semiconductor laser 213 emits a laser beam and the emitted beam scans a photosensitive drum 217 through a polygon mirror 214, an f- lens 215, and a mirror 216. A developing unit is composed of a magenta developing station 219, a cyan developing station 220, a yellow developing station 221 and a black developing station 222. These four developing stations are successively brought into contact with the photosensitive drum 217, thereby developing electrostatic latent images of M, C, Y and BK formed on the photosensitive drum 217 with toners corresponding to the respective colors. A sheet fed from a sheet cassette 224 or 225 is wound on a transfer drum 223, and receives the transfer of the image developed on the photosensitive drum 217. After completion of transferring each of four color images of M, C, Y and BK, the sheet is discharged through a fixing unit 226. The halogen lamp 205 is commonly used for visible and infrared information readings. It produces light composed of a band of frequencies required for these readings. Such common source of light contributes to effective illumination of light with different wavelengths to the original which are required for visible and infrared information readings. Figs. 6A and 6B illustrate the CCD 210 applied to the present embodiment. The infrared sensor 210-1 is a photosensitive element line (CCD line sensor) used for sensing infrared radiation. The photosensitive element lines 210-2, 210-3, and 210-4 are for sensing R, G, and B waveform components (visible spectra), respectively. Each of the IR, R, G and B sensors 210-1 through 210-4 has openings of 10 µm in width and in length along the main and sub scan directions, respectively. These photosensitive element lines are different in optical characteristics from each other and are arranged monolithically on a single silicon chip such that the IR, R, G and B sensors are arranged in parallel to each other to sense the same line on the original. The above mentioned structure of the CCD allows common usage of optical system such as a lens for visible and infrared readings. This makes it possible to improve the accuracy of optical adjustment or the like and facilitate the adjustment as well. A reference numeral 210-5 represents a glass plate of approximately 300 µm in thick. The hatched portion of the glass is treated to have an infrared cutoff characteristic. For this purpose, the glass plate 210-5 is provided with a dichroic mirror 210-11 formed of a deposition film. The characteristic of this infrared cutoff region is shown in Fig. 10. In this event, the glass plate 210-5 is adhered to the surface of the chip with the deposited region facing to the sensors. Referring to Fig. 9, described is a filter spectral characteristic of each of the line sensors IR, R, G and B in the CCD 210. The sensor 210-2 is provided with a filter 210-8 having a characteristic indicated by R in Fig. 9 that has sensitivity to light of red and infrared spectra. Likewise, the sensor 210-3 is provided with a filter 210-9 having a characteristic indicated by G in Fig. 9 that has sensitivity to light of green and infrared spectra. The sensor 210-4 is provided with a filter 210-10 having a characteristic indicated by B in Fig. 9 that has sensitivity to light of blue and infrared spectra. The IR sensor 210-1 is sensitive only to the infrared radiation corresponding to the region represented by cross-hatched portion in Fig. 9. As apparent from the figure, the filters 210-8 through 210-10 are sensitive to the infrared radiation having a wavelength of 700 nm or more. With this respect, the infrared cutoff filter 210-11 used is so selected that it has the characteristic illustrated in Fig. 10. Fig. 6B is an enlarged illustration of the photosensitive elements. Each sensor is 10 µm in length for every one pixel along the main scan direction. Five thousand sensors are aligned along the main scan direction for each CCD line sensor to read the width (297 mm) of an A3-paper at a resolution of 400 dpi. In addition, the R, G and B line sensors are away from each other at a distance of 80 µm, which corresponds to an eight-line distance relative to a sub scan resolution of 400 lpi (line per inch). The IR sensor 210-1 is away from the R sensor 210-2 at a distance of 160 µm (16 lines), a double of other line distance. Fig. 8 shows spectral response of an infrared absorber SIR-159 (sold by Mitsui Toatsu Chemicals Inc., Chiyoda-ku, Tokyo, Japan) used in this embodiment as a detected mark on a specific original. In this embodiment, the IR sensor 210-1 is directed to sense the infrared with wavelength ranging between 750 and 850 nm to detect presence of this infrared absorber. To this end, the lens 208 is provided with a far infrared cutoff filter formed of a dichroic mirror having spectral response as illustrated in Fig. 11. This filter is harmless for the R, G and B sensors 210-2 through 210-4 as well as for the IR sensor 210-1, so that it is provided with a common lens unit, the lens 208. This allows a design for the filter provided for the lens 209 to be determined only by the consideration of the far infrared cutoff characteristic. As a result, superior far infrared cutoff characteristic can be achieved with a simple interference fringe structure. Fig. 14 is a block diagram for use in describing flow of the image signals in the image scanner unit 201. Each of the image signals is supplied from the CCD 210 to an analog signal processing unit 3001. The analog signal processing unit 3001 changes the magnitude of the image signal with a gain constant. The offset is also adjusted in the analog signal processing unit 3001. The image signals for the respective colors (including IR) are then supplied from the analog signal processing unit 3001 to respective A/D converters 3002 through 3005. Each of the A/D converters 3002 through 3005 converts the analog image signal into a digital image signal of 8 bits. The digital image signal is supplied to corresponding one of shading correction units 3006 through 3009 where it is subjected to known shading correction using a reading signal obtained for the standard white plate 211. A clock generator 3019 generates a clock signal at a speed corresponding to data of one pixel carried by the digital image signal. The clock signal is supplied to a line counter (a main scan address counter) 3020 that counts the number of clock signals to produce a pixel address output for one line. A decoder 3021 decodes a main scan address supplied from the main scan address counter 3020 to generate a CCD driving signal, a VE signal and a line synchronization signal HSYNC. The CCD driving signal may be shift pulses or reset pulses for every one line while the VE signal indicates a valid section in a one line reading signal supplied from the CCD. As shown in Figs. 6A and 6B, the line sensors 210-1, 210-2, 210-3 and 210-4 in the CCD 210 are spaced from each other at a predetermined distance. Line delay elements 3010, 3011 and 3012 are provided for correcting the spatial displacement. More specifically, the image signals obtained from the IR, R and G sensors 210-1, 210-2 and 210-3 proceed the image signal out of the B sensor 210-4 in the sub scan direction. With this respect, the line delay elements 3010, 3011 and 3012 line-delay the IR, R and G signal in the sub scan direction relative to the B signal. Light-to-density conversion (logarithmic) units 3013, 3014, 3015 are composed of look-up table ROMs and convert luminance signals of R, G and B into density signals of C, M and Y. A known masking and undercolor removal (UCR) circuit 3016 generates, from input signals Y, M and C representing three primary colors, output signals of Y, M, C, and Bk with a predetermined number of bits (for example, 8 bits), at each scanning operation carried out by the image scanner unit 201. A discrimination unit 3 detects a specific pattern on the original. A CPU 3018 carries out sequence control involving, for example, control to the original reading optical systems and ON/OFF control of the original illumination lamp 205. The CPU 3018 produces a pixel section signal VSYNC in the sub scan direction. The CPU 3018 also serves to control a selector 3017 in response to a result of judgment supplied from the discrimination unit 3 such that a port output rather than the reading signal is supplied to the printer, thereby effectively prohibiting copying operation for a specific original. Fig. 15 is a timing chart for each control signal. The VSYNC signal indicates the image valid section in the sub scan direction and assumes a level "1" in the entries for scanning the image to successively produce the output signals of (M), (C), (Y) and (Bk). VE is a signal indicating the image valid section in the main scan direction and takes, in the section of level "1", timing at the start position of the main scanning operation. A CLOCK signal is a pixel synchronization signal which causes the transfer of the image data at the leading edge from "0" to "1". Next, an image pattern to be detected is described referring to Fig. 3. Fig. 3 is a view illustrating an example of a pattern formed with a transparent ink containing a glazing dye having the spectral response as shown in Fig. 8. A triangular pattern a is printed with an ink excluding the infrared with a certain range of wavelength. A small square pattern b having sides of 120 µm in length is overlapped with the triangle and printed thereon with the above mentioned transparent ink. This pattern appears substantially same to the human eye, as shown in Fig. 8, in the visible spectrum. However, it can be detected in the infrared region by means of determining the infrared absorption characteristics of the pattern. While the square pattern having the sides of approximately 120 µm is illustrated here for the later description, the region corresponding to this pattern b requires four pixels as shown in the figure when being read at 400 lpi (line per inch). It is noted that a method of forming the pattern is not limited to that described here. Details of the discrimination unit is described with reference to Fig. 4 in which 10-1 through 10-4 represent image data line delay units. Each of the image data line delay units 10-1 through 10-4 is composed of a first-in-first-out (FIFO) memory. An address pointer thereof is initialized with a line synchronization signal HSYNC, which is not shown in this figure. The CLOCK signal is used for writing data into the FIFO memory for every one pixel and reading the same out of the memory. The image data line delay units 10-1 through 10-4 delay a 32-bit data (eight for each IR, R, G and B) by one line. More specifically, the input signal is delayed and latched by 2 pixels at flip-flops 11-1 and 11-2 to produce a pixel data A. The line memories 10-1 and 10-2 delay this signal by two lines to produce a pixel data C. This pixel data C is delayed by four pixels to produce a notable pixel data X and a pixel data B. All of these signals A, C and X are supplied to a judgment unit 12. Likewise, a pixel data D is produced and supplied to the judgment unit 12. Fig. 5 shows the positional relation between the notable pixel data X and other four pixels A, B, C and D therearound. As apparent from the figure, when the notable pixel X corresponds to the pattern b (Fig. 3), then the pixels A, B, C and D all correspond to the peripheral area, the image of the pattern a . Fig. 12 is a view showing geometry of visible and infrared radiation reflected from various originals and corresponding states of infrared reading signals. In Fig. 12, (a-1) is a cross-section of the specific original identification pattern shown in Fig. 3. An infrared absorbing ink 2802 is on the face of a paper 2801. The incident light from the halogen lamp 205 is reflected from the infrared absorption pattern and its peripheral portion. In this figure, R1, G1, B1, IR1 , R1', G1', B1', IR1' , R2, G2, B2, IR2 , R2', G2', B2', IR2' , R3, G3, B3, IR3 , R3', G3', B3' and IR3' are values obtained by means of sensing the reflected light by the R, G, B and IR sensors and converting these analog signal to the digital ones, following which the shading correction and line delay processings are made. These read values are given, for the R, G and B visible information, as the spectral characteristics corresponding to a combination of characteristics of the R, G and B sensors in Fig. 9 and the infrared cutoff filter in Fig. 10. In this event, R represents the light with wavelengths primarily in the 590 to 620 nm range, G represents the light with wavelengths primarily in the 500 to 580 nm range and B represents the light with wavelengths primarily in the 400 to 480 nm range. The infrared information, IR, is given as the spectral characteristic obtained by combining or multiplying the characteristics of R, B (the cross-hatched range in Fig. 9) and the far infrared cutoff characteristics shown in Fig. 11. More specifically, IR represents the light with wavelengths primarily in the 710 to 850 nm. The light in each of the wavelength ranges R, G, B and IR is corrected independently, during the shading correction, in sensitivity by using the standard white plate having a uniform reflectance to each wavelength in Fig. 7. In this embodiment, the light is corrected in sensitivity such that the R, G, B and IR reading values are equal to each other to the original having a relatively uniform spectral characteristic as the standard white plate as shown in Fig. 7. In Fig. 12, (a-2) is a graphical representation of the reading signal values obtained for the infrared absorption pattern and the peripheral portion thereof after the shading correction of the R, G, B and IR. The specific pattern in this embodiment has substantially same color in the visible region as shown (a) in Fig. 13 and the signal values of the visible R, G, and B become equal accordingly. The concentration of the infrared absorbing substances contained in the infrared absorbing ink is so adjusted that the infrared reading signal IR 2 obtained from the infrared absorption pattern is smaller than the minimum values of the visible information R2, G2 and B2 for the same infrared absorption pattern. The visible color of the specific original identification pattern consists of colors which are relatively high in saturation. This means that the minimum values of the visible color separation signals R, G and B for the identification pattern become relatively small. When the infrared absorbing ink does not satisfy the above mentioned conditions, the gain constant used for the shading correction on the above mentioned IR reading signal may be decreased, ensuring that the IR2 signal obtained from the infrared identification pattern to be detected is smaller than the minimum values of R2, G2 and B2. Described now is a case where the original is read under this reading conditions. An original (b-1) in Fig. 12 has a back on which a carbon black (having the infrared absorption characteristics) 2803 is printed. The visible reading signals for this original are similar to those obtained in (a-1). The infrared radiation is absorbed by the carbon black 2803 and, as a result, the infrared read value IR3 becomes smaller than the read value IR1 obtained from around the carbon black. Thus, the reading signal (b-2) exhibits similar characteristics to the reading signal (a-2) obtained from the infrared absorption pattern b. In this embodiment, the IR reading signal IR2 obtained from the infrared absorbing ink is smaller than any one of the visible reading signals R2, G2 and B2 . On the contrary, the infrared back-through component IR3 obtained from the typical carbon black is not smaller than the minimum values of the visible read values R3, G3 and B3 in most cases. This is because the identification pattern a has the visible colors of high saturation and the minimum values of R3, G3 and B3 are relatively small while the infrared back-through component is not sufficiently absorbed by the carbon black on the back of the original and thus the infrared information has a relatively large value. By detecting this characteristic, it becomes possible in this embodiment to discriminate the identification pattern printed with the infrared absorbing ink from the back through due to the carbon black. Described in conjunction with (c-1) and (c-2) in Fig. 12 is a case where the infrared back-through component IR3' is smaller than any one of the visible back-through components R3', G3' and B3'. This corresponds to a case where the carbon black is soaked into the original or where the original itself is a thin paper. The visible colors are different from the peripheral portions, according to which it is possible to discriminate the back-through from the identification mark in the form of the infrared absorption pattern in (a-1). This is because the identification pattern a has, as mentioned above, the visible colors of high saturation; the minimum values of R3', G3' and B3' are relatively small; the identification pattern is so determined that the IR3' is read with its value being smaller than any one of the minimum values of R3', G3' and B3'; and the sensitivity is set relative to the color separation reading for R, G, B and IR, so that if the infrared back-through component is smaller than the visible components R3', G3' and B3 as in (c-1) and (c-2), the back-through also affects the visible signals. The R, G, B and IR reading signals obtained from a dirt identification pattern is shown in (d-1) and (d-2) in Fig. 12. A banknote on which a specific pattern is printed is contaminated during circulation in the market for a long time. Such contamination or dirt affects on each of the R, G, B and IR signals as a uniform attenuation factor. Consequently, the infrared reading signal IR2' for the infrared absorbing pattern is smaller in value than the visible information R2', G2' and B2' even when the original is dirt. Fig. 13 shows the relation between the reading signals of the visible and infrared information for each of the above mentioned case. Now, described below is a judgment algorithm carried out by the judgment unit 12 of this embodiment. Let the R, G, B and IR components of the reading signal composing the pixel signal A be A R , A G , A B and A IR , respectively, then average values Y R , Y G , Y B and Y IR of the reading signals of the corresponding color components R, G, B and IR in each of the pixel signals B, C and D are given as follows: Y R = 1/4(A R + B R + C R + D R ), Y G = 1/4(A G + B G + C G + D G ), Y B = 1/4(A B + B B + C B + D B ), and Y IR = 1/4(A IR + B IR + C IR + D IR ). Judgment of the target pattern is made according to the difference between the notable pixel X and the average value Y obtained from the above equation. More specifically, let the R, G, B and IR components of X be X R , X G , X B and X IR , then ΔR = |Y R - X R |, ΔG = |Y G - X G |, ΔB = |Y B - X B |, and ΔIR = Y IR - X IR . In this event, the original is judged as the specific pattern when the following equations are satisfied: ΔR < K and ΔG < K and ΔB < K and ΔIR > L1 or Y IR /X IR > L2 and X IR < min (X R , X G , X B ), where K, L1 and L2 are constants. More specifically, the pattern is judged to be present when the difference in color is small (smaller than K) between the notable pixel X and the peripheral portions A, B, C and D in the visible region; when the difference is equal to or larger than the constant L1 in the infrared region or when the ratio of the level of the notable pixel X to that of the periphery is equal to or larger than the constant L2 in the infrared region; and when the signal value of the infrared notable pixel X is smaller than the visible color separation signal of the same notable pixel. In this event, the ratio is taken into consideration along with the difference in judging the infrared region in view of the reduction of the signal level of the infrared signal due to dirt on the original. In this embodiment, any affects of the dirt is eliminated by means of detecting the ratio, provided that the infrared reading signal is not entirely attenuated due to the dirt. Fig. 1 shows the structure of the judgment unit 12 for use in realizing the above mentioned algorithm. An adder 121 merely adds the color components of four pixels and produces the eight high-order bits of the sum to obtain Y R , Y G , Y B and Y IR . A subtractor 122 calculates a difference between the output of the adder 121 and corresponding component of the notable pixel signal to obtain ΔR, ΔG and ΔB components. The subtractor 122 supplies five high-order bits of the subtraction results to a judgment LUT 128 consisting of ROMs. The LUT 128 produces "1" when each of the ΔR, ΔG and ΔB components is smaller than a constant K (in this embodiment, the constant K is set at eight levels). Likewise, for the infrared reading signal, Y IR and X IR of eight bits each are supplied to address terminals of a judgment LUT 129 consisting of ROMs. The LUT 129 produces "1" when the above mentioned judgment result holds, that is, ΔIR > L1 or Y IR /X IR > L2 where ΔIR = Y IR - X IR . Simultaneously, a mm extraction unit 131 extracts the minimum value min (R, G, B) of the R, G, and B color separation signals X R , X G and X B , respectively for the notable pixel. A comparator 132 compares the min (R, G, B) with the infrared reading signal for the notable pixel. The comparator 132 produces "1" when X IR < C min (R, G, B) holds. The outputs of the LUTs and the comparator are supplied to an AND gate 130 to obtain a logical product thereof. The AND gate 130 produces an output signal MK. The output signal MK indicating "1" corresponds to the condition where presence of the specific pattern is detected. The judgment result is supplied to a latch 3022 in Figs. 14A and 14B. An output of the latch 3022 is supplied to an input port P10 of the CPU 3018. The CPU 3018 confirms that the specific mark is detected. The CPU 3018 clears the latch 3022 by an output port P9 signal before initiation of a copy sequence. The CPU 3018 is thus ready for the subsequent pattern detection. Referring to Fig. 16, description will be made in conjunction with a normal copying operation and an identification mark judging operation accompanying thereto carried out under control by the CPU 3018. When an operator put the original 204 on the platen 203 and initiates the copying operation through an operation unit (not shown), the CPU 3018 controls a motor (not shown) to move the reflection mirror 206 beneath the standard white plate 211. The halogen lamp 205 is turned on to illuminate the standard white plate 211. The shading correction units 3006 through 3009 sample the shading data for the IR, R, G and B signals (Step 1). Subsequently, the port output P is set into "0" to clear the output of the latch 3022 into "0" and, in turn, clear the P8 output into "0". The input A of the selector 3017 is selected such that the image signals masked and subjected to the undercolor removal (UCR) are supplied to the printer. The output P9 is set to "1" to stop the clear operation of the latch 3022 (Step 2). Next, the scanning operation is repeated four times as the printer unit 200 records four colors of M, C, Y and BK to complete one copy of the original. At the same time, presence of the identification mark is detected and the recording operation is controlled in accordance with the detection result. The CPU 3018 sets, for recording magenta, processing conditions for magenta into the masking UCR processing unit 3016. Subsequently, the CPU operates the optical system to supply a signal indicating magenta to the printer 200. After completion of the scanning operation, the optical system is turned back to an initial position of scanning (Step 3). The CPU periodically reads the input signal supplied to the port 10 during the scanning operation to determine whether the input signal indicates "1". If the P10 is "1", outputs of P0 through P7 are set into FFH at step 7 based on the decision that the predetermined original is to be copied. In addition, an output of P8 is set into "1" to supply the printer 200 a set-solid signal of FFH, whereby prohibiting further copying operation to avoid counterfeit of the specific original. Likewise, the recording control is also made for cyan, yellow and black through steps 4 to 6, during which the CPU periodically checks the P10. If the P10 is "1" the CPU supplies the set-solid FFH data to the printer 200 at step 7. For example, when P10 = 1 is detected during cyan recording, only magenta is recorded through a normal or proper copying operation. The remainders, cyan, yellow and black are recorded as solid of FFH. A way for prohibiting a normal copying operation may be, other than a set-solid, a batching processing, interruption of image forming means, turning off the power or the like. 〈Second Embodiment〉 Typical infrared absorbing inks are slightly colored in the visible region and sufficient level of the infrared absorbing characteristic may be achieved causing a difference in color between the infrared absorbing and non absorbing portions in the visible region. With such an infrared absorbing ink, it is difficult to lower the signal level of the infrared reading signal than the color separation signal in the visible region, though it is achieved in the first embodiment. This embodiment is directed to avoid incorrect or erroneous identification of the back-through on a normal original by means of using the visible information to a mark printed with the ink of the type described. The infrared absorbing mark to be detected in the second embodiment is so formed that the infrared reading signal value is lower than the luminosity level obtained by the values of the visible color separation signals of R, G and B. In addition, as in the first embodiment, the infrared reading signal is compared with luminosity signals generated from the visible color separation signals, thereby determining whether the read pixel is associated with a predetermined mark. Now, described below is a judgment algorithm carried out by the judgment unit 12 of this embodiment. In this embodiment, a luminosity signal L is obtained from the visible color separation signals of R, G and B according to the following equation: L = (R + 2G + B)/4. Let the R, G, B and IR components of the reading signal composing the pixel signal A be A R , A G , A B and A IR , respectively, then average values Y R , Y G , Y B and Y IR of the reading signals of the corresponding color components R, G, B and IR in each of the pixel signals B, C and D are given as follows: Y R = 1/4(A R + B R + C R + D R ), Y G = 1/4(A G + B G + C G + D G ), Y B = 1/4(A B + B B + C B + D B ), and Y IR = 1/4(A IR + B IR + C IR + D IR ). Judgment of the target pattern is made according to the difference between the notable pixel X and the average value Y obtained from the above equation. More specifically, let the R, G, B and IR components of X be X R , X G , X B and X IR , then ΔR = |Y R - X R |, ΔG = |Y G - X G |, ΔB = |Y B - X B |, ΔIR = Y IR - X IR , and XL = (X R + 2X G + X B )/4. In this event, the original is judged as the specific pattern when the following equations are satisfied: ΔR < K and ΔG < K and ΔB < K and ΔIR > L1 or Y IR /X IR > L2 and X IR < XL, where K, L1 and L2 are constants. More specifically, the pattern is judged to be present when the difference in color is small (smaller than K) between the notable pixel X and the peripheral portions A, B, C and D in the visible region; when the difference is equal to or larger than the constant L1 in the infrared region or when the ratio of the level of the notable pixel X to that of the periphery is equal to or larger than the constant L2 in the infrared region; and when the signal value of the infrared notable pixel X is smaller than the visible luminosity signal L of the same notable pixel. Fig. 17 shows the structure of the judgment unit 12 for use in realizing the above mentioned algorithm. The adder 121 merely adds the color components of four pixels and produces the eight high-order bits of the sum to obtain Y R , Y G , Y B and Y IR . The subtractor 122 calculates a difference between the output of the adder 121 and corresponding component of the notable pixel signal to obtain ΔR, ΔG and ΔB components. The subtractor 122 supplies five high-order bits of the subtraction results to the judgment LUT 128 consisting of ROMs. The LUT 128 produces "1" when each of the ΔR, ΔG and ΔB components is smaller than a constant K (in this embodiment, the constant K is set at eight levels). Likewise, for the infrared reading signal, Y IR and X IR of eight bits each are supplied to address terminals of the judgment LUT 129 consisting of ROMs. The LUT 129 produces "1" when the above mentioned judgment result holds, that is, ΔIR > L1 or Y IR /X IR > L2 where ΔIR = Y IR - X IR . Simultaneously, an AND calculation unit 131 extracts a luminosity signal XL of the R, G, and B color separation signals X R , X G and X B , respectively for the notable pixel. The comparator 132 compares the luminosity signal XL with the infrared reading signal for the notable pixel. The comparator 132 produces "1" when X IR <XL holds. The outputs of the LUTs and the comparator are supplied to the AND gate 130 to obtain a logical product thereof. The AND gate 130 produces an output signal MK. The output signal MK indicating "1" corresponds to the condition where presence of the specific pattern is detected. The result of judgment is processed by the CPU 3018 in the same manner as in the first embodiment. The similar processing to that in the first embodiment is performed for detection a specific original and avoiding counterfeit of it. 〈Third Embodiment〉 In this embodiment, to further improve the accuracy of detection on the specific mark, the signal level of the infrared reading signal at the infrared reflecting portion around the infrared absorbing ink portion of the mark is higher than the maximum value of the visible color separation signals. More particularly, possibility of the incorrect judgment of the back-through on the normal original is reduced by means of setting the infrared reading signal value at the infrared absorption portion is smaller than the minimum values of the visible color separation values. In addition, the infrared reading signal value at the infrared reflecting portion is larger than the maximum values of the visible color separation values. As a result, a feature less found in a normal original can be provided. Now, described below is a judgment algorithm carried out by the judgment unit 12 of this embodiment. Let the R, G, B and IR components of the reading signal composing the pixel signal A be A R , A G , A B and A IR , respectively, then average values Y R , Y G , Y B and Y IR of the reading signals of the corresponding color components R, G, B and IR in each of the pixel signals B, C and D are given as follows: Y R = 1/4(A R + B R + C R + D R ), Y G = 1/4(A G + B G + C G + D G ), Y B = 1/4(A B + B B + C B + D B ), and Y IR = 1/4(A IR + B IR + C IR + D IR ). Judgment of the target pattern is made according to the difference between the notable pixel X and the average value Y obtained from the above equation. More specifically, let the R, G, B and IR components of X be X R , X G , X B and X IR , then ΔR = |Y R - X R |, ΔG = |Y G - X G |, ΔB = |Y B - X B |, ΔIR = Y IR - X IR . In this event, the original is judged as the specific pattern when the following equations are satisfied: ΔR < K and ΔG < K and ΔB < K and ΔIR > L1 or Y IR /X IR > L2 and X IR < min (X R , X G , X B ) and Y IR > max (Y R , Y G , Y B ), where K, L1 and L2 are constants. More specifically, the pattern is judged to be present when the difference in color is small (smaller than K) between the notable pixel X and the peripheral portions A, B, C and D in the visible region; when the difference is equal to or larger than the constant L1 in the infrared region or when the ratio of the level of the notable pixel X to that of the periphery is equal to or larger than the constant L2 in the infrared region; when the signal value of the infrared notable pixel X is smaller than the visible color separation signal of the same notable pixel; and when the average value of the infrared signal values of the peripheral pixels is larger than the maximum value of the average values of the visible color separation signals. Fig. 18 shows the structure of the judgment unit 12 for use in realizing the above mentioned algorithm. The adder 121 merely adds the color components of four pixels and produces the eight high-order bits of the sum to obtain Y R , Y G , Y B and Y IR . The subtractor 122 calculates a difference between the output of the adder 121 and corresponding component of the notable pixel signal to obtain ΔR, ΔG and ΔB components. The subtractor 122 supplies five high-order bits of the subtraction results to the judgment LUT 128 consisting of ROMs. The LUT 128 produces "1" when each of the ΔR, ΔG and ΔB components is smaller than a constant K (in this embodiment, the constant K is set at eight levels). Likewise, for the infrared reading signal, Y IR and X IR of eight bits each are supplied to address terminals of the judgment LUT 129 consisting of ROMs. The LUT 129 produces "1" when the above mentioned judgment result holds, that is, ΔIR > L1 or Y IR /X IR > L2 where ΔIR = Y IR - X IR . Simultaneously, the min extraction unit 131 extracts the minimum value min (R, G, B) of the R, G, and B color separation signals X R , X G and X B , respectively for the notable pixel. The comparator 132 compares the min (R, G, B) with the infrared reading signal for the notable pixel. The comparator 132 produces "1" when X IR < min (R, G, B) holds. The outputs of the LUTs and the comparator are supplied to an AND gate 130 to obtain a logical product thereof. The AND gate 130 produces an output signal MK. The output signal MK indicating "1" corresponds to the condition where presence of the specific pattern is detected. Simultaneously, a Max extraction unit 134 extracts the maximum value max (R, G, B) of the R, G, and B color separation signals Y R , Y G and Y B , respectively for the notable pixel. A comparator 135 compares the max (R, G, B) with the average value of the infrared reading signals for the peripheral pixel. The comparator 135 produces "1" when Y IR > max (R, G, B) holds. The outputs of the LUTs and the comparator are supplied to the AND gate 130 to obtain a logical product thereof. The AND gate 130 produces an output signal MK. The output signal MK indicating "1" corresponds to the condition where presence of the specific pattern is detected. The result of judgment is processed by the CPU 3018 in the same manner as in the first embodiment. The similar processing to that in the first embodiment is performed for detection a specific original and avoiding counterfeit of it. As mentioned above, according to the embodiments 1 through 3 of the present invention, it is possible to detect the mark in a higher accuracy by means of comparing, upon detecting a specific mark using invisible information, the signal level of the reading signal thereof with the signal level of the visible reading signal. In addition, is possible to reduce significantly the incorrect or erroneous judgment to the normal original. As mentioned above, in the embodiments, it is possible to detect a specific pattern in a higher accuracy by an image processing device and to provide a pattern readily to be detected in a high accuracy. The above mentioned embodiments may be applied to any other devices and method in a single or a combined form. The judgment ROMs described above may be replaced with RAMs, gate arrays or softwares of the CPU to carry out equivalent judgment operation. The visible information is not limited to the RGB signal and may be other colors such as Lab and YIQ. It should be understood that the present invention is not limited to the particular embodiment shown and described above, and various changes and modifications may be made without departing from the scope of the appended claims.

Claims: An image processing apparatus for detecting copy-prohibited documents by detecting infra-red absorbing identification marks (b) thereon, characterised by: reading means (201; 210) for reading visible and infra-red wavelengths from a document, the infra-red wavelengths being in the absorption band of the identification marks; and judging means (3; 12; 3018) for judging whether the document is a copy-prohibited document by using the level of the visible and infra-red radiation to distinguish infra-red radiation reflected from the surface of the document from infra-red radiation reflected from the inside or rear surface of the document to determine whether or not an identification mark is present on the document. An image processing apparatus according to claim 1, wherein the judging means is arranged to judge whether the document is a copy-prohibited document by using the level of the visible and infra-red radiation read from first (X) and second (A) respective locations on the document separated such that, when the first location (X) corresponds to an infra-red absorbing identification mark (b), the second location (A) corresponds to a portion (a) outside the identification mark, to distinguish infra-red radiation reflected from the surface of the document from infra-red radiation reflected from the inside or rear surface of the document to determine whether or not an identification mark is present at the first location. An apparatus according to claim 1 or 2, wherein the judging means (3; 12; 3018) is arranged to use the level of the visible and infra-red radiation from the first location (X) with average values of radiation of the same wavelengths read from a plurality of different locations (A; B; C; D), each separated from the first location such that, when the first location corresponds to an identification mark (b), all of the other regions correspond to portions (a) of the document outside the identification mark. An apparatus according to any preceding claim, wherein the infra-red wavelengths are in the range 710 to 850nm. An apparatus according to any preceding claim, wherein the reading means comprises a first sensor for reading the visible wavelengths and a second sensor for reading the infra-red wavelengths. An apparatus according to claim 5, wherein the first sensor comprises respective R, G and B colour component sensors (210-2; 210-3; 210-4). An apparatus according to any preceding claim, further comprising processing means (200; 3017; 3018) for processing signals read from the document on the basis of the judgement result produced by the judging means. An apparatus according to claim 7, wherein the processing means comprises image forming means (200) for reproducing the document. An apparatus according to claim 8, wherein faithful reproduction is prevented if the judging means detects an identification mark. A method of operating an image processing apparatus to detect copy-prohibited documents by detecting infra-red absorbing identification marks thereon, characterised by the steps of: reading visible and infra-red wavelengths from a document, the infra-red wavelengths being in the absorption band of the identification marks; and judging whether the document is a copy-prohibited document by using the level of the visible and infra-red radiation to distinguish infra-red radiation reflected from the surface of the document from infra-red radiation reflected from the inside or rear surface of the document to determine whether or not an absorbing identification mark is present on the document. A method according to claim 10, wherein the judging step judges whether the document is a copy-prohibited document by using the level of the visible and infra-red radiation read from first (X) and second (A) respective locations on the document separated such that, when the first location (X) corresponds to an infra-red absorbing identification mark (b), the second location (A) corresponds to a portion (a) outside the identification mark, to distinguish infra-red radiation reflected from the surface of the document from infra-red radiation reflected from the inside or rear surface of the document to determine whether or not an absorbing identification mark is present at the first location. A method according to claim 10 or claim 11, wherein the judging step uses the level of the visible and infrared radiation from the first location (X) with average values of radiation of the same wavelengths read from a plurality of different locations (A; B; C; D), each separated from the first location such that, when the first location corresponds to an identification mark (b), all of the other regions correspond to portions (a) of the document outside the identification mark.

Inventors: ARIMOTO SHINOBU, HAYASHI TOSHIO, NAGASE TETSUYA, NAKAI TAKEHIKO, SASANUMA NOBUATSU, TANIOKA HIROSHI, UCHIDA YOSHIKI, UTAGAWA TSUTOMU, YOSHINAGA KAZUO, ARIMOTO, SHINOBU, HAYASHI, TOSHIO, NAGASE, TETSUYA, NAKAI, TAKEHIKO, SASANUMA, NOBUATSU, TANIOKA, HIROSHI, UCHIDA, YOSHIKI, UTAGAWA, TSUTOMU, YOSHINAGA, KAZUO, ARIMOTO, SHINOBU, C/O CANON KABUSHIKI KAISHA, HAYASHI, TOSHIO, C/O CANON KABUSHIKI KAISHA, NAGASE, TETSUYA, C/O CANON KABUSHIKI KAISHA, NAKAI, TAKEHIKO, C/O CANON KABUSHIKI KAISHA, SASANUMA, NOBUATSU, C/O CANON KABUSHIKI KAISHA, TANIOKA, HIROSHI, C/O CANON KABUSHIKI KAISHA, UCHIDA, YOSHIKI, C/O CANON KABUSHIKI KAISHA, UTAGAWA, TSUTOMU, C/O CANON KABUSHIKI KAISHA, YOSHINAGA, KAZUO, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1993
Main classification: G07D7
IPC codes: G07D7, G03G21, H04N1