JP5750846B2 - Image processing apparatus, image processing system, and program - Google Patents

Description

  The present invention relates to an image processing apparatus, an image processing system, and a program.

  For example, Patent Documents 1 and 2 show a technique that uses a random microscopic pattern inherent to the surface of an original image medium as a technique for guaranteeing the originality of an original such as a document / photo. . This technique reads an image of a document on a document using paper as an image medium, extracts and registers information on a random pattern (hereinafter referred to as a paper fingerprint) formed by paper fibers from the image, and collates it. The original is collated by comparing the paper fingerprint of the target original with the registered paper fingerprint.

JP 2005-038389 A JP 2004-102562 A

  The present invention relates to a paper fingerprint or the like from an image signal generated by an image reading device in which the amount of light received by a light receiving element that receives light reflected from the image medium and received from a light source is reduced by a change over time. An object of the present invention is to suppress the influence of noise when extracting pattern information relating to a microscopic pattern.

  An image processing apparatus according to a first aspect of the present invention irradiates an image medium with light from a light source, receives light reflected from the image medium by a light receiving element, reads an image on the image medium, and generates an original image signal. Amplification factor information for acquiring information relating to the amplification factor for the original image signal from an image reading device having an image reading unit for performing the operation and an image signal amplification unit for amplifying the original image signal to generate an image signal having a reference intensity An acquisition unit; a control unit that controls the image reading unit based on information acquired by the amplification factor information acquisition unit; and a control unit that controls the amount of light received by the light receiving element according to the amplification factor. Pattern information extracting means for extracting pattern information relating to a microscopic pattern on the surface of the image medium from the original image signal generated by the image reading means. .

  In the image processing apparatus according to the second aspect of the present invention, the control means adjusts the amount of received light by controlling the reading speed of the image reading means in the sub-scanning direction according to the amplification factor.

  In an image processing apparatus according to a third aspect of the present invention, the light source includes a semiconductor element that emits light when a voltage is applied thereto, and a drive circuit that periodically applies a voltage thereto, and the control unit includes the semiconductor element. The amount of received light is adjusted by controlling the ratio of the period during which the voltage is applied to the signal according to the amplification factor.

  An image processing apparatus according to a fourth aspect of the present invention irradiates an image medium with light from a light source, receives reflected light from the image medium with a light receiving element, reads an image on the image medium, and generates an image signal. Control means for controlling an image reading device and controlling the amount of light received by the light receiving element; and pattern information extracting means for extracting pattern information relating to a microscopic pattern on the image medium surface from the image signal; The control means increases the amount of received light when the image signal is used by the pattern information extraction means compared to when the image signal is not used by the pattern information extraction means.

  An image processing system according to the present invention is a system including an image reading device and an image processing device, wherein the image reading device irradiates image light from a light source to the image medium, and receives light from the image medium by a light receiving element. Image reading means for receiving reflected light to read an image on the image medium and generating an original image signal; and image signal amplification means for amplifying the original image signal to generate an image signal having a reference intensity. The image processing apparatus includes: an amplification factor information acquiring unit that acquires information about an amplification factor for the original image signal from the image reading device; and the image reading unit based on the information acquired by the amplification factor information acquiring unit. Control means for controlling the amount of light received by the light receiving element according to the amplification factor, and the image reading means controlled by the control means From said original image signal, comprising the A pattern information extracting means for extracting the A pattern information about the microscopic A pattern of image medium surface has a.

  The program according to the present invention is an image that irradiates a computer with irradiation light from a light source, receives reflected light from the image medium by a light receiving element, reads an image on the image medium, and generates an original image signal. Amplification factor information acquisition unit for acquiring information relating to the amplification factor for the original image signal from an image reading device having a reading unit and an image signal amplification unit for amplifying the original image signal to generate an image signal having a reference intensity The image reading unit is controlled based on the information acquired by the amplification factor information acquiring unit, and the control unit controls the amount of light received by the light receiving element according to the amplification factor. Pattern information extracting means for extracting pattern information relating to microscopic patterns on the surface of the image medium from the original image signal generated by the image reading means. To function as.

  According to the first, fifth, and sixth aspects of the present invention, the amount of light received by the light receiving element that receives the light irradiated from the light source and reflected from the image medium is reduced due to a change over time. The influence of noise when extracting pattern information related to a microscopic pattern such as a paper fingerprint from an image signal generated by the image reading apparatus can be suppressed as compared with the case where this configuration is not provided.

  According to the second aspect of the present invention, it is possible to suppress the influence of noise when extracting the pattern information without increasing the amount of light that irradiates the image medium, as compared with the case where the pattern information is not provided. it can.

  According to the third aspect of the present invention, it is possible to suppress the influence of noise when extracting the pattern information without lowering the scanning speed of the image medium as compared with the case without the present configuration.

  According to the fourth aspect of the present invention, the influence of noise when the pattern information is extracted from the image signal generated by the light receiving element in the image reading device is suppressed as compared with the case where this configuration is not provided. can do.

1 is a schematic functional block diagram of an image processing apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram schematically illustrating configurations of an image input unit, an image processing unit, a paper fingerprint processing unit, and a control unit of the image processing apparatus according to the embodiment of the present invention. It is a graph which shows the influence which the light quantity reduction has on collation performance. FIG. 5 is a schematic flowchart of an operation for compensating for a decrease in the amount of irradiation light by a decrease in scanning speed in the image processing apparatus according to the embodiment of the present invention.

  Hereinafter, embodiments of the present invention (hereinafter referred to as embodiments) will be described with reference to the drawings.

  The image processing apparatus 50 of the present embodiment is, for example, a multifunction machine having a copying function, a printer function, an image scanner function, a facsimile function, and the like, and the image processing apparatus 50 has a paper fingerprint registration function and a collation function. . A paper fingerprint is a microscopic pattern present on the surface of a document using paper as a medium. “Microscopic” means that the phenomenon is so fine that it cannot be discerned by human senses. Microscopic patterns differ from, for example, general characters and figures displayed on the surface of a manuscript. Basically, it is a fine pattern that cannot be recognized by the naked eye. Some types of media have microscopic patterns that are naturally formed on the surface. For example, the paper used for the original in the present embodiment is made by entwining fine fibers made from wood pulp, and the random entanglement of the natural fibers produces a paper fingerprint having a microscopic pattern. Hereinafter, in order to simplify the distinction from the paper fingerprint registration / collation function, the functions of the conventional multifunction peripherals such as a copying function, a printer function, an image scanner function, and a facsimile function are called general functions. I will decide. FIG. 1 is a schematic functional block diagram of the image processing apparatus 50. The image processing apparatus 50 includes an image input unit 52, an image processing unit 54, an image output unit 56, a communication unit 58, a paper fingerprint processing unit 60, a user interface unit 62, a control unit 64, and a storage unit 66.

  The image input unit 52 has a function of an image reading device that reads an image from a document and generates image data. Reading of the original image by the image input unit 52 is performed by general functions such as copying, image scanner, and facsimile transmission, for example, and the obtained image data is input to the image processing unit 54. The paper fingerprint processing unit 60 also uses the image data for the paper fingerprint registration / collation function.

  The image processing unit 54 performs various image processing on the image data input from the image input unit 52, processing for rasterizing into a bitmap format, and the like. The processing performed by the image processing unit 54 relates to image data used in general functions of the image processing apparatus 50, and is basically different from an image that is microscopic and difficult to recognize with the naked eye, such as a paper fingerprint. This is image processing relating to a visible image whose contents can be confirmed with the naked eye. The image processing unit 54 outputs the processed image data to the image output unit 56 or the communication unit 58. In the facsimile reception function, the image processing unit 54 processes the image data input from the communication unit 58 and outputs the processed image data to the image output unit 56, for example. The image processing unit 54 includes, for example, an arithmetic processing device such as a microprocessor.

  The image output unit 56 prints an image on a sheet based on the image data input from the image processing unit 54. The image output unit 56 includes an exposure unit, a photoreceptor, a developing device, a transfer device, and a fixing device.

  The communication unit 58 is connected to a transmission medium such as a network and performs communication processing with other devices connected to the transmission medium. For example, the communication unit 58 transmits the image data processed by the image processing unit 54 to another device, receives image data from another device, and inputs the image data to the image processing unit 54. The communication unit 58 is also used when transmitting / receiving information regarding paper fingerprints to / from other devices. The communication unit 58 includes a processor and the like.

  The paper fingerprint processing unit 60 performs a process of registering a paper fingerprint based on an image of a designated area in the document and a process of collating with an already registered paper fingerprint. The paper fingerprint processing unit 60 is composed of an arithmetic processing unit such as a microprocessor, for example, and its function is realized by executing a program.

  The user interface unit 62 includes a touch panel display, buttons, and the like. The user can give an operation instruction or the like to the control unit 64 by operating the user interface unit 62. In addition to the instruction screen and setting screen regarding various functions, the operation state of the image processing apparatus 50 and various messages are displayed on the touch panel display.

  The control unit 64 includes an arithmetic processing device such as a microprocessor, and directly or indirectly controls the operation of each unit of the image processing device 50 by executing a program.

  The storage unit 66 includes a storage device such as a semiconductor memory or a hard disk device, and stores, for example, a program for realizing processing of each unit using a processor, various parameters set by a user, and the like.

  The configuration and function of the image input unit 52 will be described in detail with reference to FIG. FIG. 2 is a block diagram schematically showing the configuration of the image input unit 52, the image processing unit 54, the paper fingerprint processing unit 60, and the control unit 64.

  The image input unit 52 irradiates a document (image medium) with light from a light source, reads an image of the document with an image sensor and generates an original image signal, and sets the reference level (reference intensity) of the image signal. Image signal amplifying means for amplifying the original image signal at an amplification factor set based on the generated image signal and generating an image signal having an intensity corresponding to the reference level.

  The image reading means reads an image by relatively moving the original and a line type image sensor in which light receiving pixels are arranged in the main scanning direction in the sub scanning direction orthogonal to the main scanning direction. There are an optical system moving method and a document moving method as relative movement in the sub-scanning direction. The optical system moving system is a scanner that moves a document placed on a platen glass (not shown) manually or under an automatic document feeder (ADF) (not shown) under the platen glass ( (Not shown). In the document moving method, the scanner is fixed at a predetermined position, and an image of the document is read while the document is conveyed at a constant speed by the ADF to the reading position of the scanner.

  The scanner includes a light source 100 that irradiates an original with irradiation light. The light source 100 includes, for example, a fluorescent lamp or a light emitting diode (LED). The light source driving circuit 102 is a circuit that generates a driving signal for turning on the light source 100, and its operation is controlled by the control unit 64. In the following description, the light amount of the light source 100 may be changed. In that case, the light source driving circuit 102 is configured to be capable of dimming the light source 100.

  In this image processing apparatus 50, a CCD (Charge Coupled Device) image sensor 104 is used as a line-type image sensor that is an imaging element (light receiving element) that receives reflected light from a document and converts it into an electrical signal. Note that a CMOS (Complementary Metal Oxide Semiconductor) image sensor or other solid-state imaging device can also be used as the image sensor. For example, the CCD image sensor 104 is arranged separately from the scanner, and the reflected light from the reading position of the scanner is input to the light receiving unit via a mirror or the like. The CCD image sensor 104 can also be arranged in a scanner. The CCD image sensor 104 generates a charge corresponding to the amount of light incident on each pixel at each light receiving pixel, converts the charge into a voltage signal at an output unit, amplifies the voltage signal with a preamplifier, and outputs the voltage signal. . The CCD image sensor 104 is, for example, for R, G, and R extending in the main scanning direction so that image information of red (R), green (G), and blue (B) can be obtained at each coordinate in the main scanning direction. The line sensor for B is arranged in parallel.

  The image sensor driving circuit 106 operates in response to a control signal from the control unit 64, generates a power source for driving the CCD image sensor 104 and various clock signals, and supplies the power to the CCD image sensor 104. Further, the image sensor driving circuit 106 performs correlated double sampling (CDS) on the output signal of the CCD image sensor 104 to generate an image signal from which reset noise and amplifier noise of the output portion of the CCD image sensor 104 are removed. To do.

  The motor 108 generates a mechanical driving force necessary for the movement of the scanner and the operation of the ADF. The motor drive circuit 110 is a circuit that generates an electrical signal for driving the motor 108, and its operation is controlled by the control unit 64. In the following description, the scanning speed of the document in the sub-scanning direction may be changed. In this case, the motor driving circuit 110 is configured to be able to adjust the speed of the motor 108.

  An amplification unit 120 is provided as an image signal amplification unit. The amplifying unit 120 receives an image signal output from the image sensor driving circuit 106. The amplifying unit 120 has an automatic gain control (AGC) circuit 122. The AGC circuit 122 feedback-controls the gain so that the output becomes the reference level. The output level of the CCD image sensor 104 changes according to the intensity of the irradiation light of the original even if the original is the same. Irradiation light intensity can be reduced due to deterioration of the light source 100 over time or internal contamination. The AGC circuit 122 absorbs and alleviates the influence of such fluctuations in illumination light intensity on the image signal. By using the AGC circuit, the conversion range of an analog-to-digital converter (ADC) 130 can be effectively used. For example, the reference level is set so that the amplitude of the image signal is, for example, about 80% of the input range of the ADC 130. Hereinafter, if necessary, an image signal that has not been amplified by the AGC circuit 122 (that is, a gain with respect to the image signal input to the amplification unit 120 is 1) is an original image signal, while an image that has been amplified by the AGC circuit 122 The signal is represented as an amplified image signal.

  The amplifying unit 120 can amplify and output the original image signal from the image sensor driving circuit 106 by the AGC circuit 122, or can output it without amplification, that is, as an original image signal. In order to make the configuration of the amplifying unit 120 easy to understand on the drawing, FIG. 2 shows a circuit example using a signal path 124 and a switch 126 that bypass the AGC circuit 122. In this example, the switch 126 that is switched by the control unit 64 outputs either the amplified image signal from the AGC circuit 122 or the original image signal from the signal path 124 from the amplification unit 120. The configuration of the amplifying unit 120 in FIG. 2 is an example, and other configurations can be used. For example, the control unit 64 sets the gain of the AGC circuit 122 to 1 without providing the signal path 124 and the switch 126. The original image signal may be output from the amplifying unit 120.

  The image input unit 52 further includes an ADC 130 and a signal correction circuit 140. The ADC 130 digitizes the output of the amplification unit 120 to generate image data. The signal correction circuit 140 includes a shading correction circuit 142 and a gap correction circuit 144. The shading correction circuit 142 corrects shading in the image data. Specifically, after adjusting the black output level by AOC (Auto Offset Control), non-uniform illumination in the main scanning direction, non-uniform image sensor light quantity due to lens properties, and non-uniform image sensor sensitivity Correct or remove the distortion caused by. The gap correction circuit 144 corrects the gap in the sub-scanning direction that exists between the three R, G, B line sensors that constitute the CCD image sensor 104. Specifically, the three line sensors read images at positions shifted from each other in the sub-scanning direction at the same time, and RGB signals corresponding to the same position of the document are output from the line sensors at timings shifted from each other. Is done. The gap correction circuit 144 delays the remaining two signals using a FIFO (First-In / First-Out) memory so as to match the timing of the most delayed signal among RGB, and each of R, G, B at the same position is delayed. Image data is obtained at the same time.

  The image input unit 52 outputs the RGB image data corrected by the signal correction circuit 140 to the image processing unit 54. The image processing unit 54 performs various image processing and the like as described above. For example, when the amount of illumination light decreases, the SN ratio decreases due to light shot noise, which is random noise, in the image sensor such as the CCD image sensor 104. When the decrease in the image signal corresponding to the amount of light is compensated by amplification by an AGC circuit or the like as described above, the amplitude of random noise is also amplified. The image processing unit 54 recognizes a plain background portion by performing filtering processing using a low-pass filter (LPF) or image processing for copying, scanning, and transmitting functions of original characters and photographs. Image quality deterioration due to the above-described random noise is prevented by processing such as masking a portion. The image processing unit 54 performs processes such as a color space conversion process 150, a noise removal process 152, and a background removal process 154, for example.

  The color space conversion processing 150 performs conversion from an RGB color system to, for example, an L * a * b * color system. As a result, the RGB data is converted into L * representing brightness and a * and b * representing hue and saturation. Instead of L * a * b *, it may be converted into a luminance / color difference separation color space system such as L * u * v *, YIQ, and YCrCb, which are the same uniform perceptual color space.

  The noise removal process 152 removes streak-like noise components along the sub-scanning direction included in the image data. Incidentally, for example, dirt and scratches present in the optical system of the image reading means are continuously read during scanning in the sub-scanning direction, thereby causing streak-like noise.

  In the background removal processing 154, for example, a histogram of document density is created by pre-scanning, the background density is detected, and pixel data below the background density is cut (invalidated).

  For example, the paper fingerprint processing unit 60 receives image data from the signal correction circuit 140 and performs a paper fingerprint registration process 160 and a paper fingerprint collation process 162.

  The paper fingerprint registration process 160 extracts feature information about the paper fingerprint from the image in the designated registration area, associates the feature information with the information of the registration area from which the feature information is extracted, and registers the registered paper fingerprint information 164 in the storage unit 66. Register as Here, the registration area is an area for extracting feature information about the paper fingerprint. For example, when the registration area is predetermined in a predetermined shape and size such as 32 × 32 pixels, the registration area Position information in the document is included in the registered paper fingerprint information 164 as information. For example, when selecting a registration area from preset candidate areas, identification information (candidate area ID) such as a number for discriminating each other is defined in the candidate area, and the candidate area ID is set to the position of the registration area. It can be information.

  Paper fingerprints are generally used as information indicating whether or not a document is an original. When it is necessary to distinguish a plurality of documents from each other, identification information for identifying the documents may be separately printed on the document. Done. As the document identification information, for example, a barcode, a two-dimensional code, an OCR (Optical Character Recognition) identification number, an image displayed on the document itself, or feature information extracted from the image is used. When such document identification information is defined in a document, the information can be included in the registered paper fingerprint information 164 of each document.

  The paper fingerprint collation process 162 collates whether or not the collation document that is the document to be collated is a registered document having the registered paper fingerprint information 164. The paper fingerprint collation process 162 sets a collation area in the collation document according to the registered area recorded in the registered paper fingerprint information 164, and the paper fingerprint of the collation document from the collation image which is an image in the collation area. Feature information is extracted. Then, the feature information is collated with the feature information about the registered document included in the registered paper fingerprint information 164.

  The collation area is set to a corresponding position based on the registration area position information included in the registration paper fingerprint information 164. If the collation area is the same size as the registration area, the collation area cannot be collated even if the reading position is slightly shifted. Therefore, the collation area is set slightly wider than the registration area, and registration is possible even if the document is misaligned. A part that matches the paper fingerprint of the registered area is searched for in the paper fingerprint of the collation area so that the area can be included. For example, the paper fingerprint collation processing 162 determines that the paper fingerprint of the collation document is the paper fingerprint of the registration manuscript if there is a portion in the image of the collation region where the correlation value of the pixel value with the image of the registration region is a predetermined threshold value or more. Is determined to match.

  Now, when the paper fingerprint processing unit 60 operates, the control unit 64 controls the operation of other units. Hereinafter, the operation of the image processing apparatus 50 at the time of paper fingerprint registration / collation will be described. As already described, the fluorescent lamp used in the light source 100 is relatively deteriorated with time. When the light amount of the illumination light with respect to the document decreases from the initial state due to such deterioration of the light source 100 with time and dirt in the apparatus, the output signal level of the CCD image sensor 104 also decreases accordingly. In the general function of the image processing apparatus 50, the image data input to the image processing unit 54 is generated based on the amplified image signal from the AGC circuit 122, and the influence of the light amount reduction is compensated, and the influence of the random noise amplification. Is avoided by noise removal processing.

  On the other hand, a paper fingerprint is a minute signal extracted from an image signal in a background portion where characters and photographs do not exist on a document and has properties similar to random noise. It is difficult to improve the signal-to-noise ratio between the signal and noise. If a paper fingerprint is extracted from a registration target document or a verification target document using an image signal from which noise has not been removed / reduced, the performance of paper fingerprint verification is degraded.

  FIG. 3 is a graph showing the influence of the light quantity reduction on the collation performance. FIG. 3 is a graph of FAR (False Acceptance Rate) and FRR (False Rejection Rate) with the horizontal axis representing the threshold value and the vertical axis representing the error rate (unit:%). Curve group 2 having an error rate of 100% in a low threshold range is a fake acceptance rate FAR that determines that a collation target document (false) different from a registration target document is the same document (true). Curve group 4 with a rate of 100% is a genuine rejection rate FRR that determines that the same collation target document (true) as the registration target document is a different document (false). The graph of FIG. 3 is an experimental result in which a neutral density filter (ND filter) is placed on the platen of the multifunction machine and the amount of light applied to the document is adjusted by reading the document to extract and collate the paper fingerprint. is there. In particular, the FRR curves 4a to 4e are the collation results with paper fingerprints registered in order of 0%, 20%, 33%, 50%, and 60% in light quantity reduction, and the curve 4f has a light quantity reduction of 0% during registration. Is a collation result in which the amount of light is reduced by 60% when the paper fingerprint to be collated is read. From these results, it can be seen that the FRR deteriorates as the amount of light decreases. In particular, it can be seen that if the amount of light is reduced by 50% or more during registration, it is difficult to secure a threshold value that can reduce both FAR and FRR to 0%.

  In this regard, in the paper fingerprint registration / collation function, the control unit 64 acquires information on the amplification factor for the original image signal by the AGC circuit 122 from the image input unit 52, and determines the speed of the motor 108 based on the information. The motor drive circuit 110 is controlled so as to reduce the scanning speed V in the sub-scanning direction at the time of reading an image of the document, and at the same time, the original image signal is output from the amplifying unit 120. If the scanning speed V in the sub-scanning direction is reduced, the exposure time of the CCD image sensor 104 is increased, the amount of accumulated charges is increased, and the output signal level is increased. Amplification of the image signal by the AGC circuit 122 is avoided or suppressed by compensating for the light amount decrease due to deterioration of the light source 100 or the like by increasing the exposure amount (light reception amount) of the CCD image sensor 104 due to the decrease in scanning speed.

FIG. 4 is a schematic flowchart of an operation for compensating for a decrease in the amount of irradiation light due to a decrease in scanning speed. For example, the control unit 64 refers to the gain control signal of the AGC circuit 122 as information regarding the gain, and acquires the gain G of the AGC circuit 122 (S170). If the gain G is 1 or less (in the case of “No” in S172), the scanning speed V is not controlled. That V scans the entire document remains the reference value _{V 0} (S174).

On the other hand, when the gain G is greater than 1 (in the case of “Yes” in S172), the control unit 64 calculates the set value V _S of the scanning speed V when it is lowered (S176). This V _S can basically be set to a value (V ₀ / G) that decreases in inverse proportion to the gain G. Since the paper fingerprint is read by the background portion of the document, an image signal in which the image of the background portion (blank paper portion) is not suitable is not suitable for the paper fingerprint registration / collation function. However, the set value V _S may be determined so that the output signal level of the CCD image sensor 104 is higher than the reference level set to, for example, about 80% of the input range of the ADC 130 within the range where whiteout does not occur. That is, since the output of the AGC circuit 122 is at the reference level at the gain G, V _S can be set to a speed slower than V ₀ / G. As the output signal level of the CCD image sensor 104 is increased, the influence of shot noise of the CCD image sensor 104 on the image from which the paper fingerprint is extracted is reduced.

The scanning speed V is basically decelerated only in the registration area / collation area of the paper fingerprint, and scanning can be performed at a speed equal to or higher than the reference value V ₀ in other portions. This shortens the document scanning time when reading the paper fingerprint. FIG. 4 shows this control method. Scanning in the sub-scanning direction is started using the reference value V ₀ as the initial value of the scanning speed V (S178), and the scanning position is a registration area during the paper fingerprint registration processing 160. When the paper fingerprint matching process 162 reaches the start position of the collation area (or the position near it) (S180), the scanning speed V is switched to V _S. (S182). On the other hand, the scanning position reaches the end position of the registration area or collating region (or near a position behind its) (S184), it switches the scanning speed V to _{V 0} (S186). Control unit 64 while lowering the scanning speed V to V _S controls the image sensor driving circuit 106 so as to increase in accordance with the charge accumulation period of the CCD image sensor 104 to the rate of decrease in V. The scanning speed switching processes S180 to S186 are repeated when a plurality of registration areas / collation areas are set (S188).

If it is desired to read the paper fingerprint simultaneously with the image reading of the general function of the image processing apparatus 50, the entire document may be scanned at a reduced constant speed V _S.

  The configuration in which the exposure amount of the CCD image sensor 104 is increased and compensated for the reduction in the light amount of the light source 100 with reference to FIG. 4 has been described. Compensation for the same purpose can also be realized by increasing the amount of exposure by increasing the amount of light from the light source 100. For example, the light source 100 is composed of an LED which is a semiconductor element that emits light when a voltage is applied, and the light source driving circuit 102 periodically applies a voltage to the LED to drive the LED at high frequency blinking (pulse driving). By changing the pulse duty according to the gain G by pulse width modulation (PWM), the ratio of the LED lighting period can be increased, and the exposure amount of the CCD image sensor 104 can be increased. Even when a fluorescent lamp is used as the light source 100, the exposure amount of the CCD image sensor 104 may be increased by increasing the light amount if the light source driving circuit 102 can increase the light amount.

  The compensation control of the exposure amount of the CCD image sensor 104 by reducing the scanning speed V or increasing the light amount of the light source 100 at the time of reading the above-described paper fingerprint indicates that the decrease in the light amount during image reading in the general function exceeds a predetermined threshold and is remarkable. You may go only when it becomes. For example, based on the experimental results shown in FIG. 3 and the like, the control unit 64 performs compensation control in a light quantity reduction state in which it is difficult to set a correlation value threshold value that can reduce both FAR and FRR to 0%. It can be set as the structure to do. For example, based on the result of FIG. 3, it is possible to set a light amount reduction threshold value for performing compensation control within a range of a light amount reduction rate of about 30 to 50%.

  Further, the control unit 64 can be configured to compensate for the decrease in the light amount based on information for determining the decrease in the light amount other than the gain of the AGC circuit 122. For example, it may be determined whether or not to perform compensation control with reference to a parameter relating to the exposure amount that is adjusted during maintenance inspection. Further, the control unit 64 may be configured to perform compensation control by integrating the lighting time / number of times of the fluorescent lamp, and estimating the light amount reduction based on the result.

  In the image processing apparatus 50 described above, the gain of the amplification unit 120 (or the AGC circuit 122) is 1 in the initial state, but the gain in the initial state may be a value larger than 1. That is, when the image signal is amplified by the amplifying unit 120 in the general function, the above-described compensation control is performed at the time of reading the paper fingerprint regardless of whether the amplification is performed to cover the light amount deterioration or the like. The action can be performed.

  As described above, when the exposure amount of the image sensor decreases, the influence of shot noise in the output signal increases and the SN ratio decreases. The SN ratio reduction due to the shot noise is not limited to the change over time targeted by the compensation control of the above embodiment. When an image sensor with a small aperture area and aperture ratio is used, the SN ratio is low from the beginning. It may be a ratio. Specifically, if the number of pixels of an image sensor such as a CCD image sensor or a CMOS image sensor is the same, the smaller the pixel size (opening area), the smaller the pixel size (opening area), and the accumulated charge amount decreases, resulting in a decrease in the SN ratio due to shot noise. Can occur. Further, for example, in a CCD image sensor with low performance, the dark current becomes large, and the SN ratio may be lowered due to dark current shot noise. The configuration for increasing the exposure amount of the CCD image sensor 104 in the compensation control of the above embodiment can also be adopted for reading a paper fingerprint in an image processing apparatus using an image sensor that is greatly affected by shot noise. Hereinafter, an image processing apparatus 50B employing this configuration will be described. In the following description, the reference numerals obtained by adding “B” to the constituent elements of the image processing apparatus 50 according to the above-described embodiment represent the corresponding constituent elements in the image processing apparatus 50B.

  The configuration described for the image processing device 50B is employed when the output signal of the CCD image sensor 104B is maintained at the reference level, and thus the gain G of the AGC circuit 122B is basically unity. When reading a paper fingerprint, the control unit 64B performs control to increase the light amount of the light source 100B or control to decelerate the scanning speed V, compared to when reading an image with a general function.

  The degree of the increase in the amount of light and the decrease in the speed are basically set in advance regardless of whether or not the output level of the CCD image sensor 104B is lowered. The level of the increase in the amount of light and the decrease in the speed do not exceed the input range of the ADC (analog-digital conversion circuit) 130B (referred to as ADC condition) and the saturation charge amount of the CCD image sensor 104B. (Referred to as CCD conditions).

  When the ADC condition is stricter than the CCD condition, the degree of increase in light amount and reduction in speed are set based on the ADC condition. In this case, for example, if the reference level is set to 80% of the input range of the ADC 130B in the general function, the control unit 64 determines the increase in the light amount and the decrease in the speed when reading the paper fingerprint, and the output of the CCD image sensor 104B. The level is set to increase by about 10 to 15% compared to the general function.

  Regarding the CCD conditions, the control unit 64 can employ a configuration in which the exposure amount of the CCD image sensor 104B is increased by increasing the light amount or the speed is decreased, and the number of times of charge reading of the CCD image sensor 104B is increased. For example, when the light amount of the light source 100 is m times (a real number where m> 1) or the scanning speed V is 1 / m, the charge accumulation operation and signal output operation in the CCD image sensor 104B are n times (n> If the frequency is an integer of m), the amount of charge accumulated in the pixel of the CCD image sensor 104B in one accumulation operation is only m / n (<1) times, and the CCD condition can be satisfied. In this case, an image signal of one line is generated at a certain scanning position in the general function, whereas an image signal of n lines is generated corresponding to the position in the paper fingerprint reading. The n lines are converted into image data by the ADC 130B and input to the paper fingerprint processing unit 60B. The paper fingerprint processing unit 60B adds the n lines of image data to generate one line of image data.

  Note that the multiple-reading configuration for the CCD conditions can also be used in the image processing apparatus 50 of the above-described embodiment.

  As described above, functions such as the paper fingerprint processing unit 60 and the control unit 64 in the image processing apparatus 50 are realized by executing a program. In the above embodiment, the program is stored in the storage unit 66, and the processor reads the program from the storage unit 66 and executes it as necessary. In another configuration, the program can be provided via a communication medium such as a network. In this case, the communication unit 58 acquires the program from the network or the like and provides the program to the processor or stores it in the storage unit 66. Further, the program can be provided by being stored in a recording medium such as a CD-ROM (Compact Disc Read Only Memory).

  Further, the image processing apparatus 50 according to the above-described embodiment is an apparatus including the image input unit 52 and the image processing unit 54 that realize general functions. On the other hand, a device such as a multifunction machine having the image input unit 52 and the image processing unit 54, an amplification factor information acquisition unit that acquires information about the amplification factor from the image input unit 52, and an image input unit based on the information 52, and the original image signal is input from the control means for controlling the amount of light received by the light receiving element according to the amplification factor, and the image input unit 52 controlled by the control means, and the paper fingerprint is extracted from the original image signal It is also possible to configure the image processing apparatus having the pattern information extracting means to separate. In this case, the image processing apparatus is directly attached and integrated inside or outside the apparatus that realizes a general function, or is connected and used in a form of exchanging information and signals through a network or the like.

  50 image processing device, 52 image input unit, 54 image processing unit, 56 image output unit, 58 communication unit, 60 paper fingerprint processing unit, 62 user interface unit, 64 control unit, 66 storage unit, 100 light source, 102 light source drive circuit 104 CCD image sensor, 106 image sensor drive circuit, 108 motor, 110 motor drive circuit, 120 amplifying unit, 122 AGC circuit, 130 ADC, 140 signal correction circuit, 142 shading correction circuit, 144 gap correction circuit, 150 color space conversion Processing, 152 noise removal processing, 154 background removal processing, 160 paper fingerprint registration processing, 162 paper fingerprint collation processing, 164 registration paper fingerprint information.

Claims (6)

Image reading means for irradiating the image medium from a light source and receiving light reflected from the image medium by a light receiving element to read an image on the image medium, and generating an original image signal; and amplifying the original image signal Then, amplification factor information acquisition means for acquiring information relating to the amplification factor for the original image signal from an image reading device having an image signal amplification unit that generates an amplified image signal having a reference intensity,
Visible image processing means for performing image processing on the visible image of the image medium with respect to the amplified image signal;
Pattern information extracting means for extracting pattern information relating to a microscopic pattern on the surface of the image medium from the original image signal;
At the time of generating the original image signal used by the pattern information extracting unit, the image reading unit is based on information acquired by the amplification factor information acquiring unit with respect to the amplification factor in the amplified image signal used by the visible image processing unit. Control means for controlling the amount of light received by the light receiving element according to the amplification factor,
An image processing apparatus comprising: The image processing apparatus according to claim 1.
The light source includes a semiconductor element that emits light when a voltage is applied thereto, and a drive circuit that periodically applies a voltage thereto.
The image processing apparatus characterized in that the control means adjusts the amount of received light by controlling a ratio of a period during which a voltage is applied to the semiconductor element in accordance with the amplification factor. Image reading means for irradiating the image medium from a light source and receiving light reflected from the image medium by a light receiving element to read an image on the image medium, and generating an original image signal; and amplifying the original image signal Then, amplification factor information acquisition means for acquiring information relating to the amplification factor for the original image signal from an image reading device having an image signal amplification unit that generates an amplified image signal having a reference intensity,
Control means for controlling the image reading means based on the information acquired by the gain information acquisition means, and for controlling the amount of light received by the light receiving element according to the gain;
Pattern information extraction means for extracting pattern information relating to a microscopic pattern on the surface of the image medium from the original image signal generated by the image reading means controlled by the control means;
The control means adjusts the amount of received light by controlling the reading speed of the image reading means in the sub-scanning direction according to the amplification factor;
An image processing apparatus. A light source irradiates the image medium with irradiation light, a light receiving element receives reflected light from the image medium, reads an image on the image medium, controls an image reading device that generates an image signal, and receives the light from the light receiving element. Control means for controlling the amount;
Pattern information extraction means for extracting pattern information relating to a microscopic pattern on the surface of the image medium from the image signal;
Have
The control means increases the amount of received light when the image signal is used by the pattern information extraction means compared to when the image signal is not used by the pattern information extraction means;
An image processing apparatus. An image processing system including an image reading device and an image processing device,
The image reading device irradiates an image medium with light from a light source, receives reflected light from the image medium with a light receiving element, reads an image on the image medium, and generates an original image signal; and Image signal amplification means for amplifying the original image signal to generate an amplified image signal having a reference intensity;
The image processing device includes amplification factor information acquisition means for acquiring information related to the amplification factor for the original image signal from the image reading device;
Visible image processing means for performing image processing on the visible image of the image medium with respect to the amplified image signal;
Pattern information extracting means for extracting pattern information relating to a microscopic pattern on the surface of the image medium from the original image signal;
At the time of generating the original image signal used by the pattern information extracting unit, the image reading unit is based on information acquired by the amplification factor information acquiring unit with respect to the amplification factor in the amplified image signal used by the visible image processing unit. And a control means for controlling the amount of light received by the light receiving element in accordance with the amplification factor. Computer
Image reading means for irradiating the image medium from a light source and receiving light reflected from the image medium by a light receiving element to read an image on the image medium, and generating an original image signal; and amplifying the original image signal An amplification factor information acquisition unit for acquiring information on the amplification factor for the original image signal from an image reading device having an image signal amplification unit for generating an amplified image signal having a reference intensity;
A visible image processing means for performing image processing on the visible image of the image medium with respect to the amplified image signal;
Pattern information extraction means for extracting pattern information relating to a microscopic pattern on the surface of the image medium from the original image signal; and
At the time of generating the original image signal used by the pattern information extracting unit, the image reading unit is based on information acquired by the amplification factor information acquiring unit with respect to the amplification factor in the amplified image signal used by the visible image processing unit. Control means for controlling the amount of light received by the light receiving element according to the amplification factor,
Program to function as.

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