JP2009157596A - Image reading device and placement decision method in image reading device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image reading device for reliably deciding placement even under an environment in which the disturbance rays of light are strong without making it unnecessary to perform any mechanism or complicate signal processing to increase the luminance of a light source, and to provide a placement decision method in the image reading device. <P>SOLUTION: The image reading device includes: a light source for emitting the rays of light to a reading object placed on a reading surface; an image reading part for converting the incident rays of light into an electric signal, and to output it; and a placement decision part for deciding whether the reading object is placed on the reading surface based on the electric signal output from the image reading part. The placement decision part includes a disturbance light luminance decision means for deciding whether the luminance of the disturbance rays of light to be emitted from the outside of the image reading device is equal to or more than a prescribed value when the light source is turned off, and for deciding whether to compare the minimum values of electrical signals when the light source is turned on and off based on the results of the decision. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image reading apparatus and a placement determination method in the image reading apparatus, and more particularly to an image reading apparatus suitable for use in fingerprint detection and a placement determination method in the image reading apparatus.

  In recent years, from the viewpoint of security, an optical fingerprint that identifies an identity by reading an operator's fingerprint (reading object) for personal authentication in electronic devices such as computers and mobile communication devices such as mobile phones. It has been studied to provide a sensor. Conventional optical fingerprint sensors are broadly classified into a system that uses light reflected from the surface of the finger and a system that uses scattered light in the finger that scatters inside the finger and exits from the surface of the finger.

  FIG. 8 is a diagram illustrating a schematic configuration of a conventional fingerprint sensor using a light reflected by the finger surface. Referring to FIG. 8, the fingerprint sensor 10 includes a light source 11, a glass plate 12, a light receiving element 13, an analog-digital conversion circuit 14, and a signal processing control unit 15. Reference numeral 16 denotes a fingertip, 17 denotes outgoing light emitted from the light source 11, and 18 denotes reflected light reflected from the surface of the fingertip 16.

  In FIG. 8, the fingertip 16 is placed on the upper surface 12 a of the glass plate 12, and the emitted light 17 emitted from the light source 11 passes through the glass plate 12 and is reflected by the surface of the fingertip 16. The reflected light 18 reflected from the surface of the fingertip 16 passes through the glass plate 12 again and enters the light receiving element 13. The reflected light 18 incident on the light receiving element 13 is converted into an analog electric signal by the light receiving element 13 and input to the analog-digital conversion circuit 14. The analog electrical signal input to the analog-digital conversion circuit 14 is converted into digital data by the analog-digital conversion circuit 14, and then input to the signal processing control unit 15, where predetermined signal processing is performed.

  FIG. 9 is a diagram illustrating a schematic configuration of a conventional fingerprint sensor using a scattered light within a finger that is emitted from the surface of the finger. Referring to FIG. 9, the fingerprint sensor 20 includes a light source 11, a glass plate 12, a light receiving element 13, an analog-digital conversion circuit 14, and a signal processing control unit 15. Reference numeral 16 denotes a fingertip, 17 denotes outgoing light emitted from the light source 11, 21 denotes scattered light within the finger, and 22 denotes a part of scattered light within the finger.

  In FIG. 9, the fingertip 16 is placed on the upper surface 12 a of the glass plate 12, and the emitted light 17 emitted from the light source 11 enters the fingertip 16 and scatters in the finger to become scattered light 21 in the finger. . Intra-finger scattered light 22 that is a part of the intra-finger scattered light 21 exits from the surface of the fingertip 16, passes through the glass plate 12, and enters the light receiving element 13. The intra-finger scattered light 22 incident on the light receiving element 13 is converted into an analog electric signal by the light receiving element 13 and input to the analog-digital conversion circuit 14. The analog electrical signal input to the analog-digital conversion circuit 14 is converted into digital data by the analog-digital conversion circuit 14, and then input to the signal processing control unit 15, where predetermined signal processing is performed.

  In the fingerprint sensors 10 and 20 as shown in FIGS. 8 and 9, it is extremely important to stably read a fingerprint image regardless of the surrounding environment. As a method for stably reading a fingerprint image regardless of the surrounding environment, at least one control means for controlling the length and / or intensity of the light pulse of the emitted light is provided. / Or a method of accurately adjusting the intensity to the actually required light amount (see, for example, Patent Document 1), a method of having a plurality of reading modes, and switching the reading mode depending on the presence or absence of a fingerprint on the fingerprint sensor (for example, Patent Document 2), a method of determining whether or not the exposure amount is appropriate, and a method of controlling the exposure amount to an appropriate exposure amount (see, for example, Patent Document 3) has been proposed.

  Such a conventionally proposed fingerprint sensor has a placement determination function for determining whether the fingertip 16 is placed on the upper surface 12a of the glass plate 12 of the fingerprint sensor 10 or 20. For the placement determination, “finger placement determination” for determining whether or not the fingertip 16 is placed on the upper surface 12a of the glass plate 12 of the fingerprint sensor 10 or 20 before the fingerprint data acquisition is started, and fingerprint data is being acquired. In addition, there is a “finger separation determination” for determining whether or not a finger placed on the upper surface 12a of the glass plate 12 of the fingerprint sensor 10 or 20 has been released. Hereinafter, placement determination including finger placement determination and finger separation determination may be referred to as placement determination.

  The finger placement determination is performed based on the difference between the maximum signal level of the electrical signal output from the light receiving element 13 when the light source 11 is turned off and when the light source 11 is turned on. The finger placement determination will be described in more detail with reference to FIGS. 10 and 11. FIG. 10 is a diagram (part 1) for explaining a conventional finger placement determination method. FIG. 10 shows a light receiving element when the light source 11 is turned off and when the light source 11 is turned on in the case where the fingertip 16 is placed on the upper surface 12a of the glass plate 12 of the fingerprint sensor 10 or 20 under disturbance light with relatively weak luminance. The electric signal output from 13 is shown.

10, A indicates an electric signal (hereinafter referred to as “light source”) output from the light receiving element 13 when the light source 11 is turned off when the fingertip 16 is placed on the upper surface 12a of the glass plate 12 of the fingerprint sensor 10 or 20. A _max is the maximum value of the signal level of the electric signal A when the light source is off (hereinafter referred to as “maximum value A _max ”), and B is the glass of the fingerprint sensor 10 or 20. When placed on the upper surface 12a of the plate 12, an electrical signal output from the light receiving element 13 when the light source 11 is turned on (hereinafter referred to as “light source lighting electrical signal B”), B _max maximum value of the signal level of the signal B (hereinafter, referred to as "the maximum value B _max"), R is an analog - digital converter of the signal level that can be processed in 14 range (hereinafter, "process It is the ability signal level range R ").

  Since the signal levels of the electrical signal A when the light source is turned off and the electrical signal B when the light source is turned on shown in FIG. 10 are both within the processable signal level range R, the analog-digital conversion circuit 14 normally performs analog-digital conversion. Processing is performed. When the light source 11 is turned off, nothing is detected by the light receiving element 13, so in FIG. 10, the signal level of the electrical signal A when the light source is turned off is relatively small.

  In addition, since disturbance light such as a fluorescent light is incident on the fingerprint sensor 10 or 20, for example, an electrical signal (noise) having a slight signal level is output from the light receiving element 13. When the light source 11 is turned on, the light reflected by the surface of the fingertip 16 or the scattered light within the finger emitted from the surface of the fingertip 16 is detected by the light receiving element 13 and converted into an electrical signal. The signal level of the electrical signal B when turned on is higher than the signal level of the electrical signal A when the light source is turned off.

The analog-digital conversion circuit 14 performs an analog-digital conversion process on the electrical signal A when the light source is turned off and the electrical signal B when the light source is turned on as shown in FIG. The signal processing control unit 15 calculates the maximum value A _max and the maximum value B _max of the signal level of the electrical signal A when the light source is turned off and the electrical signal B when the light source is turned on, which is converted into digital data, and further, the maximum value A _max and The absolute value Dif (AB _max ) = | A _max −B _max | of the difference between the maximum values B _max is calculated.

Next, Dif (AB _max ) is compared with a predetermined threshold value V _th, and if Dif (AB _max ) ≦ V _th , the fingertip 16 is placed on the upper surface 12 a of the glass plate 12 of the fingerprint sensor 10 or 20. If Dif (AB _max )> _Vth, it is determined that the fingertip 16 is placed on the upper surface 12a of the glass plate 12 of the fingerprint sensor 10 or 20.

As shown in FIG. 10, when the fingertip 16 is placed on the upper surface 12a of the glass plate 12 of the fingerprint sensor 10 or 20, the signal levels of the electrical signal A when the light source is turned off and the electrical signal B when the light source is turned on. If the absolute value Dif (AB _max ) = | A _max −B _max | of the difference between the maximum value A _max and the maximum value B _max is a relatively large value and Dif (AB _max )> V _th , the fingertip 16 is It is determined that the fingerprint sensor 10 or 20 is placed on the upper surface 12a of the glass plate 12.

  FIG. 11 is a diagram (No. 2) for explaining a conventional finger placement determination method. In FIG. 10, the same parts as those in FIG. 10 are denoted by the same reference numerals, and the description thereof is omitted. FIG. 11 shows a light receiving element when the light source 11 is turned off and when the light source 11 is turned on in the case where the fingertip 16 is not placed on the upper surface 12a of the glass plate 12 of the fingerprint sensor 10 or 20 under disturbance light having relatively weak luminance. The electric signal output from 13 is shown.

In FIG. 11, C is an electric signal (hereinafter referred to as “light source”) output from the light receiving element 13 when the light source 11 is turned off when the fingertip 16 is not placed on the upper surface 12a of the glass plate 12 of the fingerprint sensor 10 or 20. _Cmax is the maximum value of the signal level of the electrical signal C when the light source is turned off (hereinafter referred to as “maximum value C _max ”), and D is the glass of the fingerprint sensor 10 or 20 at the fingertip 16. When the light source 11 is not placed on the upper surface 12a of the plate 12, an electrical signal output from the light receiving element 13 when the light source 11 is lit (hereinafter referred to as “light source lighting electrical signal D”), D _max This is the maximum value of the signal level of the signal D (hereinafter referred to as “maximum value D _max ”).

  Since the signal levels of the electrical signal C when the light source is turned off and the electrical signal D when the light source is shown in FIG. 11 are both within the processable signal level range R, the analog-digital conversion circuit 14 normally performs analog-digital conversion. Processing is performed.

  When the fingertip 16 is not placed on the upper surface 12a of the glass plate 12 of the fingerprint sensor 10 or 20, nothing is detected by the light receiving element 13 regardless of whether the light source 11 is off or on. In FIG. 11, the signal levels of the electrical signal C when the light source is turned off and the electrical signal D when the light source is turned on are both relatively small. In addition, since disturbance light such as a fluorescent light is incident on the fingerprint sensor 10 or 20, for example, an electrical signal (noise) having a slight signal level is output from the light receiving element 13.

The analog-digital conversion circuit 14 performs analog-digital conversion processing on the electrical signal C when the light source is turned off and the electrical signal D when the light source is turned on as shown in FIG. The signal processing control unit 15 calculates the maximum value C _max and the maximum value D _max of the signal level of the light source extinguishing electrical signal C and the light source lighting electrical signal D converted into digital data, and further, the maximum value C _max and The absolute value Dif (CD _max ) = | C _max −D _max | of the difference between the maximum values D _max is calculated.

Next, Dif (CD _max ) is compared with a predetermined threshold value V _th, and if Dif (CD _max ) ≦ V _th , the fingertip 16 is placed on the upper surface 12 a of the glass plate 12 of the fingerprint sensor 10 or 20. If Dif (CD _max )> _Vth, it is determined that the fingertip 16 is placed on the upper surface 12a of the glass plate 12 of the fingerprint sensor 10 or 20.

As shown in FIG. 11, when the fingertip 16 is not placed on the upper surface 12a of the glass plate 12 of the fingerprint sensor 10 or 20, the signal levels of the electrical signal C when the light source is turned off and the electrical signal D when the light source is turned on. Since there is no significant difference between the maximum value C _max and the maximum value D _max , Dif (CD _max ) ≦ V _{th is} satisfied, and the fingertip 16 is not placed on the upper surface 12a of the glass plate 12 of the fingerprint sensor 10 or 20. Determined.

  By the way, since the conventional fingerprint sensor 10 or 20 is used in various environments, the disturbance light may be relatively weak light such as a fluorescent lamp, or may be intense light such as sunlight. However, there is a problem when intense light such as sunlight becomes disturbance light. A problem of the conventional fingerprint sensor 10 or 20 will be described with reference to FIG.

  FIG. 12 is a diagram for explaining the problems of the conventional finger placement determination method under intense light disturbance light. In FIG. 10, the same parts as those in FIGS. 10 and 11 are denoted by the same reference numerals, and the description thereof is omitted. FIG. 12 shows the light receiving element 13 when the light source 11 is turned off and when the light source 11 is turned on when the fingertip 16 is placed on the upper surface 12a of the glass plate 12 of the fingerprint sensor 10 or 20 under intense light disturbance light. The electric signal output from is shown.

In FIG. 12, E is output from the light receiving element 13 when the light source 11 is turned off when the fingertip 16 is placed on the upper surface 12a of the glass plate 12 of the fingerprint sensor 10 or 20 under strong ambient light. Electrical signal (hereinafter referred to as “electric signal E when the light source is turned off”), E _max is the maximum value of the signal level of the electrical signal E when the light source is turned off (hereinafter referred to as “maximum value E _max ”), and F is intense In the case where the fingertip 16 is placed on the upper surface 12a of the glass plate 12 of the fingerprint sensor 10 or 20 under disturbance light of high brightness, an electrical signal (hereinafter referred to as “ _Fmax is the maximum value of the signal level of the electrical signal F when the light source is lit (hereinafter referred to as “maximum value F _max ”). The portion indicated by the alternate long and short dash line exceeds the processable signal level range R, and indicates a portion where the analog-digital conversion circuit 14 cannot normally perform analog-digital conversion processing.

The electric signal E at the time of turning off the light source shown in FIG. 12 has a very high signal level and exceeds the processable signal level range R even though the light source 11 is turned off. This is because disturbance light with intense luminance is transmitted through the fingertip 16 and input to the light receiving element 13. The light source lighting electric signal F shown in FIG. 12 is that the light source 11 is lit, so that the light reflected by the surface of the fingertip 16 or the scattered light in the finger emitted from the surface of the fingertip 16 is detected by the light receiving element 13 and becomes an electric signal. Therefore, the signal level of the electrical signal F when the light source is turned on is further larger than the signal level of the electrical signal E when the light source is turned off, and exceeds the processable signal level range R in the same manner as the signal level of the electrical signal E when the light source is turned off. ing. The portions exceeding the processable signal level range R cannot be normally subjected to analog-digital conversion processing in the analog-digital conversion circuit 14 and are all recognized as maximum value E _max = maximum value F _max .

Therefore, since the maximum value E _max and the maximum value F _max of the signal level of the electrical signal E when the light source is turned off and the electrical signal F when the light source is turned on are equal, the absolute value Dif (EF) of the difference between the maximum value E _max and the maximum value F _{max max) = | E max -F max} | = 0 ≦ V th , and the fingertip 16 despite being placed on the upper surface 12a of the glass plate 12 of the fingerprint sensor 10 or 20, the fingertip 16 is a fingerprint sensor 10 Alternatively, it is erroneously determined that the glass plate 12 is not placed on the upper surface 12a of the 20 glass plates 12.

  The conventional fingerprint sensor 10 or 20 fixes the sensitivity of the light receiving element 13 having the sensitivity adjustment function to the lowest possible value at the time of finger placement determination as a method for preventing erroneous determination caused by intense light of disturbance light. The method is taken. However, if the sensitivity of the light receiving element 13 is fixed as low as possible, the signal level of the electric signal output from the light receiving element 13 becomes too low when the disturbance light is relatively small. Therefore, a large current port is added to the IC that controls the LED, which is the light source 11, and the illuminance of the light source 11 is increased by increasing the LED current as necessary to ensure the signal level of the necessary electrical signal.

The finger separation determination is performed during the acquisition of fingerprint data, but the sensitivity of the light receiving element 13 is adjusted to an optimum value before starting the acquisition of fingerprint data, and is fixed at a constant sensitivity during the acquisition of fingerprint data. Has been. Therefore, since the finger separation determination cannot adopt a method of fixing the sensitivity of the light receiving element 13 to the lowest possible value like the finger placement determination, considering the influence of disturbance light with intense luminance, the finger placement determination As described above, it is difficult to obtain the maximum value of the signal level of the electric signal output from the light receiving element 13 when the light source 11 is turned off and when the light source 11 is turned on, and to perform determination based on the absolute value of the difference between the maximum values. is there. Therefore, the finger separation determination is not performed based on the absolute value of the difference between the maximum values, but is performed by performing complicated signal processing on the acquired fingerprint data in a subsequent application.
JP 2002-533848 A JP 2003-248817 A JP 2003-32453 A

  However, the conventional fingerprint sensor 10 or 20 employs a method of fixing the sensitivity of the light receiving element 13 to the lowest possible value as a countermeasure when strong ambient light is irradiated. There was a problem of requiring a mechanism to increase. Specifically, when the signal level of the electrical signal output from the light receiving element 13 becomes too low, the illuminance of the light source 11 is increased by increasing the current of the LED that is the light source 11. There is a problem that a large current port has to be added to the IC for controlling the current, and secondly, an LED capable of flowing a larger amount of current has to be selected, resulting in a low degree of design freedom.

  In addition, since the finger separation determination is performed by performing complicated signal processing on the acquired fingerprint data with a subsequent application, there is a problem that real-time processing is lost.

  The present invention has been made in view of the above, and does not require a mechanism for increasing the illuminance of a light source or complicated signal processing, and an image reading apparatus and an image that can reliably determine placement even in an environment with strong ambient light It is an object of the present invention to provide a placement determination method in a reading device.

  In order to achieve the above object, according to a first aspect of the present invention, a light source (112) that emits light to a reading object placed on a reading surface (S) and an incident light converted into an electrical signal and output. An image reading unit (115) and a mounting for determining whether the reading object is mounted on the reading surface (S) based on the electrical signal output from the image reading unit (115) An image reading device (100) having a determination unit (117), wherein the placement determination unit (117) is irradiated from the outside of the image reading device (100) when the light source (112) is turned off. Whether or not the luminance of the ambient light is greater than or equal to a predetermined value, and whether or not to obtain the minimum value of the electrical signal when the light source (112) is turned off and when the light source (112) is turned on based on the result of the determination It is characterized by having a disturbance light luminance determination means for determining.

  According to a second aspect of the present invention, in the image reading apparatus (100) according to the first aspect, the determination as to whether or not the luminance of the disturbance light is equal to or higher than a predetermined value is made from the image reading unit (115). It is performed based on the maximum value of the electric signal.

  According to a third invention, in the image reading apparatus (100) according to the first or second invention, the absolute value of the difference between the minimum values of the electric signal when the light source (112) is turned off and when the light source (112) is turned on. An absolute value calculation means for calculating, and when the disturbance light luminance determination means decides to compare the minimum value, based on the absolute value of the difference between the minimum values calculated by the absolute value calculation means , It is determined whether or not the reading object is placed on the reading surface (S).

  According to a fourth aspect of the present invention, in the image reading apparatus (100) according to any one of the first to third aspects, when the disturbance light luminance determination unit determines to compare the minimum values, It has an illuminance adjusting means for adjusting the illuminance of the light source (112) before obtaining the minimum value of the electrical signal when the light source (112) is turned on.

  The fifth invention comprises a light source (112) that emits light to a reading object placed on the reading surface (S), and an image reading unit (115) that converts incident light into an electrical signal and outputs it. A placement determination method for determining whether or not the object to be read is placed on the reading surface (S) of the image reading apparatus (100) having the image reading apparatus (100), wherein the image is displayed when the light source (112) is turned off. It is determined whether or not the intensity of disturbance light emitted from the outside of the reading device (100) is equal to or higher than a predetermined value, and based on the result of the determination, the light source (112) is turned off and turned on. It has a disturbance light luminance determination step (S101) for determining whether or not to acquire the minimum value of the signal.

  According to a sixth aspect of the present invention, in the placement determination method according to the fifth aspect, the determination as to whether or not the luminance of the disturbance light is equal to or higher than a predetermined value is performed by the electric signal output from the image reading unit (115). It is characterized in that it is performed based on the maximum value of.

  According to a seventh invention, in the mounting determination method according to the fifth or sixth invention, an absolute value of a difference between the minimum values of the electric signal when the light source (112) is turned off and when the light source is turned on is calculated. If there is an absolute value calculation step (S103, S105) and it is determined in the disturbance light luminance determination step (S101) that the minimum value is compared, the absolute value calculation step (S103, S105) is calculated. Whether or not the reading object is placed on the reading surface (S) is determined based on the absolute value of the difference between the minimum values.

  According to an eighth aspect of the present invention, in the placement determination method according to any one of the fifth to seventh aspects, when it is further determined in the disturbance light luminance determination step (S101) that the minimum value is compared. An illuminance adjustment step (S201) for adjusting the illuminance of the light source (112) before obtaining the minimum value of the electrical signal when the light source (112) is turned on.

  Note that the reference numerals in the parentheses are given for ease of understanding, are merely examples, and are not limited to the illustrated modes.

  According to the present invention, an image reading apparatus and a placement determination method in an image reading apparatus that can reliably determine placement even in an environment with strong ambient light without requiring a mechanism for increasing the illuminance of the light source or complicated signal processing. Can be provided.

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

  In an embodiment of the present invention, a light source that emits light to a reading object placed on a reading surface, an image reading unit that converts incident light into an electrical signal and outputs the output, and an output from the image reading unit A sweep type fingerprint reading device will be described as an example of an image reading device having a placement determination unit that determines whether or not the reading object is placed on the reading surface based on the electrical signal to be performed. .

  FIG. 1 is a block diagram illustrating a schematic configuration of a sweep type fingerprint reading apparatus according to the present invention. FIG. 2 is a perspective view illustrating a sweep type fingerprint reading apparatus according to the present invention. 1 and 2, a sweep type fingerprint reader 100 according to the present invention includes a printed wiring board 111, a light source 112, a light guide block 113, an image guide 114, a line image sensor 115, and an analog. A digital conversion circuit 116, a signal processing control unit 117, a memory 118, a connector 119, and a mold resin 120 are included.

  On the printed circuit board 111, a light source 112, a light guide block 113, an image guide 114, a line image sensor 115, an analog-digital conversion circuit 116, a signal processing control unit 117, a memory 118, and a connector 119 are mounted. It is sealed by.

  The light source 112 is driven by a drive signal from the signal processing control unit 117 to emit light. For example, an LED (light emitting diode) can be used as the light source 112. The light emitted from the light source 112 enters the light guide block 113. The light guide block 113 guides the light emitted from the light source 112 to the reading surface S and emits the light from the reading surface S in the arrow Z1 direction. As a material of the light guide block 113, for example, a transparent or translucent resin material can be used.

  On the reading surface S, a finger which is a reading object is placed and swept in the direction of the arrow X1, for example. The light emitted from the light guide block 113 is incident on the finger, is irregularly reflected inside the finger, and is incident on the image guide 114. The image guide 114 is, for example, a bundle of optical fibers fixed together, and both end surfaces thereof are mutually bonded. They are parallel and cut at a predetermined angle with respect to the extending direction of the optical fiber, and are arranged so that the longitudinal direction extends in the directions of arrows Y1 and Y2.

  The image guide 114 is in contact with the finger, that is, light from the convex portion of the fingerprint is incident and guided to the other end surface, and is separated from the finger, that is, light from the concave portion of the fingerprint is reflected, and the other end surface. Will not reach. As a result, light and dark according to the fingerprint occurs at the other end of the image guide 114. A line image sensor 115 is disposed on the other end surface of the image guide 114.

  The line image sensor 115 functions as an image reading unit, and is a sensor that converts an optical image appearing at the other end of the image guide 114 into an electrical signal and outputs the electrical signal. The line image sensor 115 includes photodiodes or phototransistors arranged in one or more columns in the directions of the arrows Y1 and Y2, and is configured to convert an optical image into an image signal for each line. At this time, the line image sensor 115 controls various timings such as a reading period, that is, a charge accumulation period and a transfer period, by a timing control signal supplied from the signal processing control unit 117.

  The image signal read by the line image sensor 115 is supplied to the analog-digital conversion circuit 116. The analog-digital conversion circuit 116 converts the image signal of each pixel of the line image sensor 115 into digital data. The digital data converted by the analog-digital conversion circuit 116 is supplied to the signal processing control unit 117.

  The signal processing control unit 117 is composed of an ASIC, a microcomputer, etc., and performs a process of assembling a fingerprint image from digital data supplied from the analog-digital conversion circuit 116 during the fingerprint reading operation, and moves the fingerprint image during the pointing operation. A process for creating data for moving the pointer or the like based on the above is performed.

  In the fingerprint reading operation, a fingerprint of a finger operated on the reading surface S is read for each line, and a process for assembling a fingerprint image is executed. Also, during the pointing operation, a movement amount and direction of the read fingerprint image are detected, data for moving the pointer is generated, and processing for transmitting to the host computer or the like via the connector 119 is executed.

  The signal processing control unit 117 controls the light emission timing of the light source 112. For example, the line image sensor 115 is controlled so that the reading interval is increased when the moving speed of the finger is slower than a predetermined speed. The signal processing control unit 117 controls the signal processing control unit 117 itself, the light source 112, and the line image sensor 115 to operate intermittently when the finger moving speed is slower than a predetermined speed. The signal processing control unit 117 also has a function as a placement determination unit that determines whether or not a reading object such as a finger is placed on the reading surface S.

  Specifically, when the light source 112 is turned off, it is determined whether or not the intensity of disturbance light emitted from the outside of the sweep type fingerprint reading apparatus 100 is equal to or higher than a predetermined value. Disturbance light luminance determination means for determining whether or not to compare the minimum value of the signal level of the electrical signal output from the line image sensor 115 when the light source is turned off and when the light source 112 is turned on, and the line image sensor 115 when the light source 112 is turned off and when it is turned on Absolute value calculating means for calculating the absolute value of the difference between the minimum values of the signal levels of the electrical signals output from the light source 112, and acquiring the minimum value of the signal level of the electrical signals output from the line image sensor 115 when the light source 112 is turned on. It has an illuminance adjusting means for adjusting the illuminance of the light source 112 before, and performs processing related to a finger placement determination operation and a finger separation determination operation. The memory 118 is composed of an SRAM or the like, and is used as a working storage area for the signal processing control unit 117.

Next, processing during the finger placement determination operation in the signal processing control unit 117 will be described. As shown in FIG. 12, in the conventional fingerprint sensor 10 or 20, when the finger placement determination is performed under strong light disturbance light, the strong light disturbance light passes through the fingertip 16 and the light receiving element 13 _Therefore, there is no difference between the maximum value E _max and the maximum value F _max of the signal level of the electrical signal E when the light source is turned off and the electrical signal F when the light source is turned on. However, since the light source lighting electric signal F is reflected by the surface of the fingertip 16 or scattered light within the finger emitted from the surface of the fingertip 16 is detected by the light receiving element 13 and converted into an electric signal, the electric signal E when the light source is turned off. The minimum value becomes larger than.

FIG. 3 is a diagram for explaining a method for solving the problems of the conventional finger placement determination method under intense light disturbance light. In FIG. 12, the same parts as those in FIG. 12 are denoted by the same reference numerals, and the description thereof is omitted. FIG. 3 shows the output from the line image sensor 115 when the light source 112 is turned off and when the light source 112 is turned on when the finger is placed on the reading surface S of the sweep type fingerprint reading device 100 under intense light disturbance light. The electric signal is shown. In FIG. 3, E _min is the minimum value of the signal level of the electrical signal E when the light source is turned off (hereinafter referred to as “minimum value E _min ”), and F _min is the minimum value of the signal level of the electrical signal F when the light source is turned on (hereinafter referred to as “minimum value E _min ”). , Referred to as “minimum value F _min ”).

In FIG. 3, attention is paid to the minimum value E _min and the minimum value F _min of the signal level of the electrical signal E when the light source is turned off and the electrical signal F when the light source is turned on shown in FIG. As shown in FIG. 3, even under strong ambient light, the minimum value E _min and the minimum value F _min are within the processable signal level range R, and the light source 11 is turned off and the light source 11 is turned on. There is a difference.

That is, when finger placement determination is performed under strong luminance disturbance light, the absolute difference between the minimum value E _min and the minimum value F _min of the signal level of the electrical signal E when the light source is turned off and the electrical signal F when the light source is turned on. By calculating the value Dif (EF _min ) = | E _min −F _min | and comparing Dif (EF _min ) with a predetermined threshold value, it is possible to determine finger placement. However, when the luminance of the ambient light is small, the signal levels of the electrical signal E when the light source is turned off and the electrical signal F when the light source is turned on are small, and therefore the absolute value Dif () of the difference between the minimum value E _min and the minimum value F _min EF _min ) also decreases, and accurate finger placement determination cannot be made.

  Therefore, in the sweep type fingerprint reading apparatus 100 according to the present invention, the signal processing control unit 117 having a function as a placement determination unit causes disturbance light emitted from the outside of the sweep type fingerprint reading apparatus 100 when the light source 112 is turned off. And the minimum value of the signal level of the electrical signal output from the line image sensor 115 when the light source 112 is turned off and when the light source 112 is turned on is compared based on the determination result. By determining whether or not to perform the placement determination, the placement determination including the finger placement determination can be surely performed even in an environment with weak disturbance light or an environment with strong disturbance light.

  A specific process at the time of finger placement determination in the signal processing control unit 117 of the sweep type fingerprint reading apparatus 100 according to the present invention will be described with reference to FIG. The finger placement determination operation is an operation for determining whether or not a finger is placed on the reading surface S of the sweep type fingerprint reading device 100 before starting fingerprint data acquisition. FIG. 4 is an example of a flowchart during the finger placement determination operation according to the present invention. In order to facilitate the description of each step, the electrical signals shown in FIGS. 5 and 6 will be described as an example as appropriate.

  FIG. 5 is a diagram (part 1) for explaining the processing of the flowchart at the time of the finger placement determination operation according to the present invention, and is the reading surface S of the sweep type fingerprint reading device 100 under disturbance light having a relatively weak luminance. 5 shows electrical signals output from the line image sensor 115 when the light source 112 is turned off and when the light source 112 is turned on.

In FIG. 5, G is an electric signal output from the line image sensor 115 when the light source 112 is turned off (hereinafter referred to as “electric signal G when the light source is turned off”), and G _max is a maximum value of the signal level of the electric signal G when the light source is turned off ( (Hereinafter referred to as “maximum value G _max ”), G _min is the minimum value of the signal level of the electrical signal G when the light source is turned off (hereinafter referred to as “minimum value G _min ”), and H is output from the line image sensor 115 when the light source 112 is lit. Electrical signal (hereinafter referred to as “electric signal H when the light source is turned on”), H _max is the maximum value of the signal level of the electrical signal H when the light source is turned on (hereinafter referred to as “the maximum value H _max ”), and R is analog-digital A range of signal levels that can be processed in the conversion circuit 116 (hereinafter referred to as “processable signal level range R”), TH ₁ is a range of the processable signal level range R. This is the first threshold value set in advance in the range.

  FIG. 6 is a diagram (part 2) for explaining the processing of the flowchart at the time of the finger placement determination operation according to the present invention, and is applied to the reading surface S of the sweep type fingerprint reading apparatus 100 under strong ambient light. The electrical signals output from the line image sensor 115 when the light source 112 is turned off and when the light source 112 is turned on when a finger is placed are shown.

In FIG. 6, I is an electric signal output from the line image sensor 115 when the light source 112 is turned off (hereinafter referred to as “electric signal I when the light source is turned off”), and I _max is the maximum signal level of the electric signal I when the light source is turned off. Value (hereinafter referred to as “maximum value I _max ”), I _min is the minimum value of the signal level of the electrical signal I when the light source is extinguished (hereinafter referred to as “minimum value I _min ”), and J is the line image sensor when the light source 112 is lit. 115, an electrical signal output from 115 (hereinafter referred to as “light source lighting electrical signal J”), J _min is the minimum value of the signal level of the light source lighting electrical signal J (hereinafter referred to as “minimum value J _min ”), and R is The signal level range that can be processed in the analog-digital conversion circuit 116 (hereinafter referred to as “processable signal level range R”), TH ₁ is the processable signal level This is a first threshold value set in advance within the range R.

In step 100 shown in FIG. 4, the signal processing control unit 117 turns off the light source 112, and the minimum and maximum values of the signal level of the electrical signal output from the line image sensor 115 (hereinafter, “minimum when the light source 112 is turned off”). Value and maximum value ”) (S100). The minimum value and the maximum value obtained when the light source 112 is turned off at this time are, for example, the minimum value G _min and the maximum value G _max shown in FIG. 5, the minimum value I _min and the maximum value I _{max shown} in FIG.

  In step 101, the signal processing control unit 117 determines whether or not the maximum value when the light source 112 acquired in step 100 is turned off is equal to or more than a preset first threshold, and based on the determination result, the light source 112. It is determined whether or not to compare the minimum value of the signal level of the electrical signal output from the line image sensor 115 when the light is turned off and when the light is turned on (S101, disturbance light luminance determination step).

  Here, determining whether or not the maximum value when the light source 112 is turned off is equal to or greater than a preset first threshold value is that the luminance of disturbance light emitted from the outside of the sweep type fingerprint reader 100 is equal to or greater than a predetermined value. It is synonymous with determining whether or not there is, and that the maximum value when the light source 112 is turned off is equal to or more than a preset first threshold value is that the strong intensity disturbance light is irradiated to the sweep type fingerprint reader 100. Means that the maximum value when the light source 112 is turned off is smaller than the preset first threshold value, that the disturbance light having a relatively low luminance is irradiated to the sweep type fingerprint reader 100. Means.

If it is determined in step 101 that the maximum value obtained when the light source 112 is turned off acquired in step 100 is smaller than the first threshold value, the process of step 102 is executed. If it is determined in step 100 that the maximum value obtained when the light source 112 is extinguished is greater than or equal to the first threshold value, the process of step 104 is executed. For example, the maximum value of the light source 112 unlit obtained in step 100 is smaller than the first threshold value TH ₁ as a maximum value _{G max} shown in FIG. 5, the process of step 102 is performed. Maximum value of the light source 112 unlit acquired in step 100 is equal to the first threshold value TH ₁ or more as the maximum value _{I max} shown in FIG. 6, the process of step 104 is performed.

In step 101, when it is determined that the maximum value when the light source 112 acquired in step 100 is turned off is smaller than the first threshold value, in step 102, the signal processing control unit 117 causes the light source 112 to be turned on by a predetermined drive signal. The maximum value when the light source 112 is turned on (hereinafter referred to as “the maximum value when the light source 112 is turned on”) of the signal level of the electric signal output from the line image sensor 115 is acquired (S102). For example, when the maximum value of the light source 112 unlit acquired in step 100 is smaller than the first threshold value TH ₁ as a maximum value _{G max} shown in FIG. 5, in step 102, the signal processing control unit 117, The light source 112 is turned on by a predetermined drive signal, and the maximum value H _max of the signal level of the light source lighting electric signal H shown in FIG. 5 is acquired.

In step 103, the signal processing control unit 117 calculates the absolute value of the difference between the maximum value obtained when the light source 112 is turned off acquired in step 100 and the maximum value obtained when the light source 112 is turned on in step 102 (S103, absolute value). Calculation step). For example, the absolute value Dif (GH) of the difference between the maximum value G _max of the signal level of the electrical signal G when the light source is turned off acquired at step 100 and the maximum value H _max of the signal level of the electrical signal H when the light source is turned on acquired at step 102. _max ) = | G _max −H _max |

In step 106, the signal processing control unit 117 performs finger placement determination by comparing the absolute value of the difference calculated in step 103 with a preset second threshold value. That is, if the calculated absolute value of the difference is equal to or smaller than the second threshold value, it is determined that the finger is not placed on the reading surface S. If the calculated absolute value of the difference is larger than the second threshold value, the reading is performed. It is determined that a finger is placed on the surface S (S106). For example, when the second threshold value is TH ₂ and the absolute value of the difference Dif (GH _max ) ≦ TH ₂ , it is determined that the finger is not placed on the reading surface S, and the absolute value of the difference Dif (GH _max )> TH ₂ , it is determined that the finger is placed on the reading surface S.

If it is determined in step 101 that the maximum value of the light source 112 acquired in step 100 when the light source 112 is turned off is equal to or greater than the first threshold value, in step 104, the signal processing control unit 117 causes the light source 112 to be turned on by a predetermined drive signal. The minimum value of the signal level of the electrical signal output from the line image sensor 115 (hereinafter referred to as “minimum value when the light source 112 is turned on”) is acquired (S104). For example, when the maximum value of the light source 112 unlit acquired in step 100 is the first threshold value TH ₁ or more as the maximum value _{I max} shown in FIG. 6, in step 104, the signal processing control unit 117, The light source 112 is turned on by a predetermined drive signal, and the minimum value J _min of the signal level of the electrical signal J when the light source is turned on shown in FIG. 6 is acquired.

In step 105, the signal processing control unit 117 calculates the absolute value of the difference between the minimum value obtained when the light source 112 is turned off acquired in step 100 and the minimum value obtained when the light source 112 is turned on in step 104 (S105, absolute value). Calculation step). For example, the absolute value Dif (IJ) of the difference between the minimum signal level I _{min of the} electrical signal I when the light source is extinguished acquired at step 100 and the minimum value J _min of the signal level J when the electrical signal J is turned on. _min ) = | I _min −J _min |

In step 106, the signal processing control unit 117 performs finger placement determination by comparing the absolute value of the difference calculated in step 105 with a second threshold value set in advance. That is, if the calculated absolute value of the difference is equal to or smaller than the second threshold value, it is determined that the finger is not placed on the reading surface S. If the calculated absolute value of the difference is larger than the second threshold value, the reading is performed. It is determined that a finger is placed on the surface S (S106). For example, if the second threshold is TH ₂ and the absolute value of the difference Dif (IJ _min ) ≦ TH ₂ , it is determined that no finger is placed on the reading surface S, and the absolute value of the difference Dif (IJ _min) )> TH ₂ , it is determined that the finger is placed on the reading surface S. This completes the processing of the flowchart shown in FIG.

  In step 101 (disturbance light luminance determination step) of the flowchart shown in FIG. 4, the signal processing control unit 117 determines whether or not the maximum value when the light source 112 acquired in step 100 is turned off is equal to or greater than a preset first threshold value. Based on the above, the luminance of disturbance light irradiated on the sweep type fingerprint reader 100 is determined. However, the luminance of disturbance light irradiated on the sweep type fingerprint reader 100 may be determined based on other signals. Absent.

  For example, the brightness of disturbance light applied to the sweep type fingerprint reader 100 may be determined based on the average value of the signal level of the electrical signal output from the line image sensor 115 when the light source 112 is turned off. A conversion element may be provided, and the brightness of disturbance light irradiated on the sweep type fingerprint reader 100 may be determined based on the level of the output signal.

  Further, in step 101 of the flowchart shown in FIG. 4, when it is determined that the maximum value obtained when the light source 112 is turned off acquired in step 100 is smaller than the first threshold value, the line image sensor 115 when the light source 112 is turned off and turned on. Although an example is shown in which the maximum value of the signal level of the electrical signal output from is acquired and the absolute value of the difference between the acquired maximum values is calculated, it is not necessary to acquire the maximum value.

  For example, the average value of the signal level of the electric signal output from the line image sensor 115 when the light source 112 is turned off and turned on, or the signal of the electric signal output from the line image sensor 115 when the light source 112 is turned off and turned on. You may make it acquire the average value etc. which remove | excluded the maximum value and minimum value of a level, and calculate the absolute value of those difference.

  In the description of FIG. 4, only the electrical signal when the finger is placed on the reading surface S of the sweep type fingerprint reading device 100 is illustrated in FIGS. 5 and 6, but reading of the sweep type fingerprint reading device 100 is performed. When the finger is not placed on the surface S, the electrical signal G when the light source is turned off is approximately equal to the electrical signal H when the light source is turned on, and the electrical signal I when the light source is turned off is approximately equal to the electrical signal J when the light source is turned on.

  Next, processing during the finger separation determination operation in the signal processing control unit 117 will be described. The finger separation determination operation is an operation for determining whether or not the finger placed on the reading surface S of the sweep type fingerprint reading apparatus 100 is separated from the reading surface S during fingerprint data acquisition. FIG. 7 is an example of a flowchart for the finger release determination operation according to the present invention. In the figure, the same parts as those in the flowchart shown in FIG. The difference from FIG. 4 is that the processing of S200 and S201 is added, and the finger placement determination in S106 is replaced with the finger separation determination in S206.

  In Step 101 shown in FIG. 7, when it is determined that the maximum value obtained when the light source 112 is turned off acquired in Step 100 is equal to or larger than the first threshold value, the process of Step 200 is executed. In step 200, the signal processing control unit 117 compares the lighting time of the light source 112 with a preset third threshold value. If the lighting time of the light source 112 is greater than or equal to the third threshold value, the process of step 104 is executed. If the lighting time of the light source 112 is shorter than the third threshold value, the process of step 201 is executed (S200).

  In step 200, the signal processing control unit 117 adjusts the driving signal of the light source 112 so that the lighting time of the light source 112 is equal to or longer than the third threshold value. That is, the drive signal of the light source 112 is adjusted so that the light source 112 is lit with sufficient illuminance (illuminance adjustment step). Next, the process of step 105 is executed.

  In step 206, the signal processing control unit 117 performs finger separation determination by comparing the absolute value of the difference calculated in step 103 or 105 with a second threshold value set in advance. That is, if the calculated absolute value of the difference is equal to or smaller than the second threshold value, it is determined that the finger placed on the reading surface S is separated from the reading surface S, and the calculated absolute value of the difference is the second threshold value. If it is larger, it is determined that the finger is placed on the reading surface S (S206). This completes the processing of the flowchart shown in FIG.

  In the flowchart shown in FIG. 7, the processing of S200 and S201 is added because the finger separation determination operation is performed during acquisition of fingerprint data, but the lighting time of the light source 112 is set short during acquisition of fingerprint data. Because there is a case. That is, if the lighting time of the light source 112 is set short, there is no problem in obtaining fingerprint data, but the illuminance of the light source 112 is insufficient for obtaining data for performing the finger separation determination operation.

  Therefore, the signal processing control unit 117 compares the lighting time of the light source 112 with a preset third threshold, and if the lighting time of the light source 112 is shorter than the third threshold, the illuminance of the light source 112 is insufficient. Before obtaining the minimum value of the signal level of the electric signal output from the line image sensor 115, the driving signal of the light source 112 is set so that the lighting time of the light source 112 is equal to or greater than the third threshold value. The light source 112 is turned on with sufficient illuminance. By doing in this way, sufficient data acquisition becomes possible in order to perform finger separation determination operation reliably.

  According to the sweep type fingerprint reader 100 according to the present invention, the minimum value and the maximum value of the signal level of the electric signal output from the line image sensor 115 when the light source 112 is turned off are acquired and acquired during the finger placement determination operation. It is determined whether the maximum value is equal to or greater than a first threshold value. When it is determined that the acquired maximum value is equal to or greater than the first threshold (corresponding to an environment with strong ambient light), the minimum value of the signal level of the electrical signal output from the line image sensor 115 when the light source 112 is turned on And the absolute value of the difference from the minimum value of the signal level of the electric signal output from the line image sensor 115 when the acquired light source 112 is extinguished is calculated, and the calculated absolute value of the difference is equal to or less than the second threshold value. If it is, it is determined that the finger is not placed on the reading surface S, and if the calculated absolute value of the difference is larger than the second threshold value, it is determined that the finger is placed on the reading surface S.

  Further, when it is determined that the acquired maximum value is smaller than the first threshold (corresponding to an environment where disturbance light is relatively weak), the signal level of the electric signal output from the line image sensor 115 when the light source 112 is turned on. Is obtained, the absolute value of the difference from the maximum value of the signal level of the electrical signal output from the line image sensor 115 when the acquired light source 112 is extinguished is calculated, and the calculated absolute value of the difference is the second value. If the absolute value of the calculated difference is larger than the second threshold, it is determined that the finger is placed on the reading surface S. judge. As a result, finger placement determination, which is one of placement determinations, can be reliably performed even in an environment with strong ambient light without requiring a mechanism for increasing the illuminance of the light source.

  Furthermore, in the finger separation determination operation, the lighting time of the light source 112 is compared with a preset third threshold value. If the lighting time of the light source 112 is shorter than the third threshold value, the lighting time of the light source 112 is A mechanism for increasing the illuminance of the light source by adjusting the driving signal of the light source 112 so as to be equal to or greater than the third threshold and adding the process of turning on the light source 112 with sufficient illuminance to the processing of the finger placement determination operation Therefore, it is possible to perform finger separation determination that is one of placement determinations reliably even in an environment with strong ambient light.

  Further, the finger separation determination operation according to the present invention is performed based on the absolute value of the difference between the minimum value or the maximum value of the signal level of the electric signal output from the line image sensor 115 acquired by the signal processing control unit 117. This eliminates the need for complicated signal processing as in the conventional finger separation determination operation, and does not lose real-time performance. it can.

  In addition, considering that the influence of disturbance light will become larger as the image reading apparatus such as the sweep type fingerprint reading apparatus 100 becomes smaller and thinner in the future, the sensitivity of the light receiving element is already set to the lowest possible value. Although it is difficult to further reduce the size and thickness of the conventional image reading apparatus employing the fixing method, the image reading apparatus can be further reduced in size by adopting the mounting determination method according to the present invention. Can be made thinner and thinner. Further, by combining the mounting determination method according to the present invention with the sensitivity adjustment function and the light source lighting time adjustment function, it is possible to further reduce the size and thickness.

  The preferred embodiment of the present invention has been described in detail above. However, the present invention is not limited to the above-described embodiment, and various modifications can be made to the above-described embodiment without departing from the scope of the present invention. And substitutions can be added.

  For example, in the embodiment of the present invention, the sweep type fingerprint reading apparatus has been described as an example of the image reading apparatus. However, since the present invention does not depend on whether or not it is swept in principle, the fingerprints other than the sweep type are used. The present invention can also be applied to a reading device.

  In the embodiment of the present invention, the sweep type fingerprint reading apparatus exemplified as the image reading apparatus is a fingerprint reading apparatus using the scattered light emitted from the finger surface. Since it does not depend on a method for reading a fingerprint, it can be applied to a fingerprint reading device that uses light reflected from the surface of a finger.

  Further, in the embodiment of the present invention, the example in which the finger as the reading object is placed on the reading surface S of the sweep type fingerprint reading apparatus as the image reading apparatus has been described. Therefore, the object to be read may be other than the finger, and the image reading apparatus may be other than the fingerprint reading apparatus.

1 is a block diagram illustrating a schematic configuration of a sweep type fingerprint reading apparatus according to the present invention. It is a perspective view which illustrates the sweep type fingerprint reader concerning the present invention. It is a figure for demonstrating the solution method of the problem of the conventional finger placement determination method under the intense light disturbance light. It is an example of the flowchart at the time of finger placement determination operation | movement which concerns on this invention. It is FIG. (1) for demonstrating the process of the flowchart at the time of the finger placement determination operation | movement which concerns on this invention. It is FIG. (2) for demonstrating the process of the flowchart at the time of the finger placement determination operation | movement which concerns on this invention. It is an example of the flowchart at the time of finger separation determination operation | movement which concerns on this invention. It is a figure which illustrates the schematic structure of the conventional fingerprint sensor of the system using the light reflected on the surface of the finger | toe. It is a figure which illustrates the schematic structure of the conventional fingerprint sensor of the system using the scattered light in the finger | toe emitted from the surface of a finger | toe. It is FIG. (1) for demonstrating the method of the conventional finger placement determination. It is FIG. (2) for demonstrating the method of the conventional finger placement determination. It is a figure for demonstrating the problem of the conventional finger placement determination method under the intense light disturbance light.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10,20 Fingerprint sensor 11,112 Light source 12 Glass plate 12a Upper surface of glass plate 12 13 Light receiving element 14,116 Analog-digital conversion circuit 15 Signal processing control unit 16 Fingertip 17 Emission light emitted from light source 11 18 Surface of fingertip 16 21 Reflected light reflected by 21 Finger scattered light 22 Part of finger scattered light 100 Sweep fingerprint reader 111 Printed wiring board 113 Light guide block 114 Image guide 115 Line image sensor 117 Signal processing control unit 118 Memory 119 Connector 120 Mold Resin A to J Electric signal A _{max to} J _max maximum value A _{min to} J _min minimum value R Processable signal level range TH ₁ threshold

Claims (8)

Based on a light source that emits light to an object to be read placed on the reading surface, an image reading unit that converts incident light into an electric signal and outputs the electric signal, and the electric signal output from the image reading unit A placement determination unit that determines whether or not the object to be read is placed on the reading surface,
The placement determination unit determines whether or not the luminance of disturbance light emitted from the outside of the image reading device is not less than a predetermined value when the light source is turned off, and based on the determination result, the light source An image reading apparatus comprising disturbance light luminance determination means for determining whether or not to compare the minimum value of the electrical signal between when the light is turned off and when the light is turned on.   The image reading apparatus according to claim 1, wherein whether or not the luminance of the disturbance light is equal to or greater than a predetermined value is determined based on a maximum value of the electric signal output from the image reading unit. Furthermore, it has an absolute value calculating means for calculating an absolute value of a difference between the minimum values of the electrical signal when the light source is turned off and when the light source is turned on,
When the disturbance light luminance determination unit determines to compare the minimum value, the reading object is placed on the reading surface based on the absolute value of the difference between the minimum values calculated by the absolute value calculation unit. 3. The image reading apparatus according to claim 1, wherein it is determined whether or not the image is placed.   In addition, when the disturbance light luminance determination unit determines to compare the minimum value, the luminance adjustment unit adjusts the illuminance of the light source before obtaining the minimum value of the electrical signal when the light source is turned on. The image reading apparatus according to claim 1, wherein the image reading apparatus is an image reading apparatus. The reading object is on the reading surface of an image reading apparatus having a light source that emits light to a reading object placed on the reading surface, and an image reading unit that converts incident light into an electrical signal and outputs the electric signal. A placement determination method for determining whether or not the device is placed,
When the light source is turned off, it is determined whether or not the luminance of disturbance light emitted from the outside of the image reading device is equal to or higher than a predetermined value. Based on the determination result, the light source is turned off and turned on. A placement determination method comprising a disturbance light luminance determination step for determining whether or not to compare the minimum value of the electric signal.   6. The placement determination method according to claim 5, wherein whether or not the luminance of the disturbance light is equal to or higher than a predetermined value is determined based on a maximum value of the electric signal output from the image reading unit. . Furthermore, an absolute value calculating step for calculating an absolute value of a difference between the minimum values of the electrical signal when the light source is turned off and when the light source is turned on,
When it is determined that the minimum value is compared in the disturbance light luminance determination step, the reading object is placed on the reading surface based on the absolute value of the difference between the minimum values calculated in the absolute value calculation step. The placement determination method according to claim 5 or 6, wherein it is determined whether or not it is placed.   Furthermore, when it is determined that the minimum value is compared in the disturbance light luminance determination step, there is an illuminance adjustment step of adjusting the illuminance of the light source before obtaining the minimum value of the electrical signal when the light source is turned on. The placement determination method according to claim 5, wherein the placement determination method is performed.

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