JP2012204849A - Image reading apparatus and light quantity adjustment method - Google Patents

Abstract

Light amount adjustment is performed based on a low reflectance member.
An image reading apparatus includes a gray reference plate having a reflectance Rf3 lower than a reflectance Rf1 of a white reference plate, and a light source that emits light to the document or the gray reference plate. And a reading unit 24 including light receiving units 32 and 42 that receive light reflected from the document or the gray reference members 33 and 43. In the image reading apparatus 1, the light receiving units 32, 42 irradiate light to the gray reference members 33, 43 and receive the reflected light reflected by the gray reference members 33, 43. The irradiation time of the light sources 31 and 41 is adjusted so that the output value to be output becomes a value corresponding to the reflectance Rf1 of the white reference plate, and the light source is obtained by multiplying the adjusted time by the ratio of the reflectance Rf3 to the reflectance Rf1. 31 and 41 are determined as the irradiation times, and the original is read using the irradiation times.
[Selection] Figure 3

Description

  The present invention relates to a technique for adjusting the amount of light using a reference member having a low reflectance.

  Conventionally, an image reading apparatus including a reading unit and a reference member having a low reflectance is known (for example, Patent Document 1). In these apparatuses, when the document is read using the reading unit, the reference member is disposed at a position facing the reading unit via the document. Then, the original is irradiated with light, and the light reflected by the original is read using the reading unit. In these apparatuses, since the reference member has a low reflectance, when the original is irradiated with light, the light passing through the original is suppressed from being reflected by the reference member. As a result, when reading the contents of the surface facing the reading section of the document, the content described on the surface not facing the reading section of the document is read by the reading section, so-called “show-through” phenomenon. Is said to be suppressed.

JP 2000-125044 A

  In these apparatuses, the reading unit may be fixed so as not to move relative to the reference member. In this case, the reading unit performs light amount adjustment using the reference member. As in the prior art, the reference member is configured to be exchangeable with another reference member having high reflectivity, so that the light amount of the reading unit is appropriately adjusted using the reference member having high reflectivity. Is possible. However, it is necessary to provide the apparatus with a reference member replacement function, which causes a problem that the apparatus becomes complicated.

  Further, in the conventional technique such as Patent Document 1, the reflection density (output value) measured using a reference member having a low reflectance is corrected, and the measurement is performed using a reference member having a high reflectance. A technique for calculating the output value of is disclosed. In this technique, the light amount is adjusted by a light amount adjustment circuit using the calculated output value. However, the calculation method that simply uses the reflectance ratio is based on the premise that the output value is simply proportional to the reflectance ratio, and does not consider the nonlinearity of the actual reading device. Therefore, when the correction is performed simply using the reflectance ratio, there arises a problem that the output value exceeds the output range of the reading unit.

  The present specification discloses a technique for performing light amount adjustment based on a low reflectance member.

  An image reading device disclosed in this specification includes a reference member having a second reflectance lower than the first reflectance, a light source that irradiates light to the document or the reference member, and a reflection from the document or the reference member. A light receiving element that receives the received light, and the light source outputs light based on an amount of light received by the light source irradiating the reference member with light reflected by the reference member. An irradiation time adjusting unit that adjusts an irradiation time of the light source so that an output value to be a value corresponding to the first reflectance, and the second reflectance of the second reflectance at a time adjusted by the irradiation time adjusting unit An irradiation time determination unit that multiplies a ratio to the first reflectance and determines the multiplied time as an irradiation time of the light source, and an irradiation time of the light source determined by the irradiation time determination unit when reading the original. make use of And a control unit for controlling to read the serial document.

  The image reading apparatus includes a conversion unit that converts an output value of an analog signal output from the light receiving element into an output value of a digital signal, and the irradiation time adjusting unit outputs the light receiving element, It is good also as a structure which adjusts the irradiation time of the said light source so that the maximum value of the output value converted by the conversion part may turn into the maximum output value of the said conversion part.

  In the image reading apparatus, the reading unit may be supported so as not to move relative to the reference member.

  In addition, the image reading apparatus includes a transport unit that transports a document on a transport path, and the reading unit includes a first reading unit disposed on one side along the transport path, and the transport path. And a second reading unit disposed on the other side along the reference path, and the reference member includes a first reference member disposed on the other side along the transport path and one along the transport path. A second reference member disposed on the first side, and the first reading unit may be disposed to face the second reading unit via the transport path.

  In the image reading apparatus, the first reflectance may be a reflectance of a white reference plate.

  The present invention can be realized in various modes such as a light amount control method using the image reading apparatus in addition to the image reading apparatus described above.

  In the image reading device disclosed in this specification, when the light amount is adjusted based on a reference member that is a low reflectance member having a reflectance lower than the first reflectance, the reflectance is higher than that of the reference member. An irradiation time is determined based on the first reflectance. According to this image reading apparatus, since the irradiation time is determined based on the amount of received light corresponding to the first reflectance, even if the reading unit has nonlinearity when setting the output value from the amount of received light, It is not affected by nonlinearity. Therefore, the irradiation time can be appropriately determined using a reference member that is a low reflectance member, and the light amount can be adjusted with high accuracy.

Perspective view of the image reading apparatus 1 Schematic sectional view of the image reading apparatus 1 The figure for demonstrating the structure of the reading part 24 Block diagram schematically showing the electrical configuration of the image reading apparatus 1 Flow chart showing the reading process Flow chart showing light amount adjustment processing Graph showing white reference data WD and white reference data WD of each light receiving element Diagram showing problems with the prior art The figure for demonstrating the determination method of the irradiation time T of this embodiment.

<Embodiment>
This embodiment will be described with reference to FIGS.

1. FIG. 1 is a perspective view illustrating an appearance of an image reading apparatus 1 according to the present embodiment. The image reading apparatus 1 includes a paper feed tray 2, a main body unit 3, and a paper discharge tray 4. The image reading apparatus 1 according to the present embodiment transports a plurality of documents placed on a paper feed tray 2 by a user to a paper discharge tray 4 and also reads a document being transported in a reading unit 24 (see FIG. 2).

  The paper feed tray 2 has guides 7A and 7B at both ends in the width direction of the paper feed tray 2 indicated by arrows 8 in FIG. The guides 7A and 7B are movable in the width direction of the paper feed tray 2. In the image reading apparatus 1, the distance between the guides 7 </ b> A and 7 </ b> B is adjusted to be equal to the width of the original by the user pushing and narrowing the guides 7 </ b> A and 7 </ b> B. A document is placed between the two.

  As shown in FIG. 2, the main body 3 is provided with a conveyance path 22 that connects the paper feed tray 2 and the paper discharge tray 4. A pickup roller 20 and a separation pad 21 are disposed around the conveyance path 22. A feed roller 23, a reading unit 24, and a discharge roller 25.

  The pickup roller 20 draws a plurality of documents placed on the paper feed tray 2 into the main body 3 by friction force. The separation pad 21 separates a plurality of documents into each document by a frictional force. The plurality of originals placed on the paper feed tray 2 are separated into individual originals and drawn into the main body 3.

  The feed roller 23 is driven by a motor (not shown) and conveys the document drawn into the main body 3 onto the conveyance path 22. The reading unit 24 reads a document conveyed in the conveyance path 22 by the feed roller 23.

  The discharge roller 25 sends the document transported on the transport path 22 to the paper discharge tray 4. Documents supplied to the paper discharge tray 4 by the discharge rollers 25 are stacked on the paper discharge tray 4. That is, the pickup roller 20, the feed roller 23, and the discharge roller 25 form a transport unit 26 that transports the document placed on the paper feed tray 2 onto the transport path 22.

  As shown in FIG. 3, the reading unit 24 includes a pair of CISs 30 and 40 that are opposed to each other with the conveyance path 22 interposed therebetween. As shown in FIG. 3, the CIS (an example of the first reading unit) 30 is disposed on the upper side (an example of one side) along the conveyance path 22, and covers the back side of the document passing under the platen glass 34. read. The CIS (an example of the second reading unit) 40 is disposed on the lower side (an example of the other side) along the conveyance path 22 and reads the surface of the document passing over the platen glass 44. The CISs 30 and 40 are supported so as not to move relative to each other across the conveyance path 22.

  In addition to the platen glass 34, the CIS 30 includes a light source 31 including light emitting diodes, a light receiving unit 32 in which a plurality of light receiving elements are linearly arranged in a direction perpendicular to the paper surface of FIG. 3, and a carriage on which these are mounted. 35 etc. are included. Note that the structure of the CIS 40 is basically the same as the structure of the CIS 30, and redundant description is omitted.

  A gray reference plate (an example of a second reference member) 33 is disposed on the platen glass 34 of the CIS 30 at a position facing the light receiving portion 42 of the CIS 40. The CISs 30 and 40 are supported so as not to move relative to each other across the conveyance path 22, and the CIS 40 is supported so as not to move relative to the gray reference plate 33.

  The gray reference plate 33 is disposed on the lower surface of the platen glass 34 facing the conveyance path 22 so that the surface thereof is at the same height as the lower surface of the platen glass 34. The gray reference plate 33 has a reflectance (an example of the second reflectance) Rf3 that is lower than the reflectance (an example of the first reflectance) Rf1 of the white reference plate and higher than the reflectance Rf2 of the black reference plate. Yes.

  Further, a gray reference plate (an example of a first reference member) 43 is disposed on the platen glass 44 of the CIS 40 at a position facing the light receiving unit 32 of the CIS 30. The CISs 30 and 40 are supported so as not to move relative to each other across the conveyance path 22, and the CIS 40 is supported so as not to move relative to the gray reference plate 33.

  The gray reference plate 43 is arranged on the upper surface of the platen glass 44 facing the conveyance path 22 so that the surface thereof is at the same height as the upper surface of the platen glass 44. Similar to the gray reference plate 33, the gray reference plate 43 has a reflectance Rf3.

  As shown in FIG. 1, the main body unit 3 includes a power switch and various setting buttons, an operation unit 5 that receives an operation command from the user, a liquid crystal display, and the image reading apparatus 1. And a display unit 6 that displays an image of the original read by the reading unit 24.

2. FIG. 4 is a block diagram schematically showing the electrical configuration of the image reading apparatus 1. As shown in FIG. 4, the image reading apparatus 1 includes an ASIC (application specific integrated circuit) 10 that controls each unit of the image reading apparatus 1. The ASIC 10 includes a central processing unit (hereinafter referred to as “CPU”) 11, ROM 12, and RAM 13, and an operation unit 5, a display unit 6, an analog front end (an example of a conversion unit, hereinafter referred to as “AFE”) 15, and a lighting via the bus 14. A circuit 16, a driving circuit 17 that drives each roller included in the transport unit 26, CISs 30 and 40, and the like are connected.

  Various programs for controlling the operation of the image reading apparatus 1 are stored in the ROM 12, and the CPU 11 performs an image processing unit 50, an irradiation time adjustment unit 51, and an irradiation time determination unit 52 according to the programs read from the ROM 12. , Functions as the control unit 53 and the like, and controls each unit.

  The lighting circuit 16 is connected to each of the CISs 30 and 40, and transmits a signal for controlling the lighting of the light sources 31 and 41 and the irradiation time T to the CISs 30 and 40 based on a command from the CPU 20. When receiving signals from the lighting circuit 16, the CISs 30 and 40 turn on the light sources 31 and 41 and irradiate the light sources 31 and 41 over the irradiation time T. At that time, the CISs 30 and 40 receive the reflected light reflected from the original or the gray reference plates 33 and 43 conveyed on the conveyance path 22 using the light receiving units 32 and 42 based on a command from the CPU 20. A reading voltage (an example of an output value) that is an analog signal corresponding to the amount of light received by the light receiving units 32 and 42 is output to the AFE 15. The CISs 30 and 40 receive the reflected light using the respective light receiving elements of the light receiving units 32 and 42 and sequentially output read voltages corresponding to the amount of light received by the respective light receiving elements to the AFE 15.

  The AFE 15 is connected to each of the CISs 30 and 40, and based on an instruction from the CPU 20, the AFE 15 converts the reading voltage output from the CISs 30 and 40 into reading data (another example of an output value) that is a digital signal. A conversion circuit is included. The AFE 15 has a predetermined input range Q and resolution B (for example, gradation of 0 to 255 if it is 8 bits). The AFE 15 performs A / D conversion on the read voltage output from the CISs 30 and 40 into 8-bit (0 to 255) read data. The read data A / D converted by the AFE 15 is stored in the RAM 13 via the bus 14.

3. Reading Processing Next, processing in the CPU 20 when reading an original using the reading unit 24 will be described with reference to FIGS. In the reading unit 24, each of the CISs 30 and 40 separately performs the same reading process. Here, a description is given of reading the front side of the document using the CIS 40, and a description of reading the back side of the document using the CIS 30. Is omitted.

  FIG. 5 shows a flowchart of the present embodiment executed by the CPU 11 according to a predetermined program. The CPU 11 starts processing when a document is placed on the paper feed tray 2 of the image reading apparatus 1 and a document reading instruction by the CIS 40 is input via the operation unit 5. When starting the process, the CPU 11 first executes a light amount adjustment process (S2).

  As shown in FIG. 6, in the light amount adjustment process, the CPU 11 sets the irradiation time T of the light source 41 to a predetermined longest irradiation time Tmax (S22), and transmits the content to the CIS 40 via the lighting circuit 16. Accordingly, in the CIS 40, the light source 41 irradiates the gray reference plate 33 with light over the longest irradiation time Tmax. At that time, the CPU 11 reads the reflected light reflected by the gray reference plate 33 over one line using the light receiving unit 42 (S24). The read voltage corresponding to the amount of light received by the light receiving unit 42 is converted into read data by the AFE 15 and stored in the RAM 13.

  The CPU 11 detects the maximum gradation value KAmax from the read data stored in the RAM 13, and compares this maximum gradation value KAmax with the maximum gradation value KBmax (255 in the case of 8 bits) of the resolution of the AFE 15 (S26). . When the maximum gradation value KAmax is larger than the maximum gradation value KBmax (S26: NO), the CPU 11 functioning as the irradiation time adjustment unit 51 sets the irradiation time T of the light source 41 by a reference interval ΔT that is set in advance from the current time. Adjustment is made so as to shorten it (S28). And CPU11 performs the process of S22 and S24 again.

  On the other hand, as shown in FIG. 7, when the maximum gradation value KAmax becomes equal to the maximum gradation value KBmax (S26: YES), the CPU 11 temporarily stores the currently set time T1 in the RAM 13 (S30). ). In the present embodiment, the reference interval ΔT is set relatively short with respect to the longest irradiation time Tmax. Therefore, when the irradiation time T is shortened by the reference interval ΔT, the state where the maximum gradation value KAmax is larger than the maximum gradation value KBmax is changed to the state where the maximum gradation value KAmax is equal to the maximum gradation value KBmax. It is possible to prevent the maximum gradation value KAmax from changing from the state where the maximum gradation value KAmax is larger than the maximum gradation value KBmax to the state where the maximum gradation value KAmax is smaller than the maximum gradation value KBmax.

The RAM 13 stores a reflection ratio R that is a ratio of the reflectance Rf3 to the reflectance Rf1. After storing the time T1, the CPU 11 reads the reflection ratio R from the RAM 13, calculates a time T2 obtained by multiplying the time T1 by the reflection ratio R (S32), and stores it in the RAM 13 (S34). After storing the time T2, the CPU 11 functions as the irradiation time determination unit 52, determines the calculated time T2 as the irradiation time T (S36), and ends the light amount adjustment processing.
R = Rf3 / Rf1, T2 = T1 × R = T1 × Rf3 / Rf1

  After the light amount adjustment processing, the CPU 11 creates shading correction data (hereinafter referred to as correction data) H of the light receiving unit 42 (S4). The CPU 11 performs the correction data creation process in a state where no document is placed on the conveyance path 22. In the correction data creation processing, as shown in FIG. 7, the CPU 11 uses the CIS 40 to acquire black reference data (solid line) KD when the light source 41 is not irradiated, and the irradiation time from the light source 41 to the gray reference plate 33. T, that is, white reference data (dotted line) WD in the case of irradiation over time T2 is acquired. The CPU 11 creates correction data H using the black luminance data and the white luminance data, and stores the created correction data H in the RAM 13. With the correction data H, the black reference data KD of each light receiving element included in the light receiving unit 42 is corrected to the minimum gradation value KBmin of the AFE 15, and the white reference data WD of each light receiving element becomes the maximum gradation value KBmax of the AFE 15. It is corrected. Note that the method for creating the correction data H is the same as the method for creating the correction data in the prior art, and a description thereof will be omitted.

  After creating the correction data, the CPU 11 drives the transport unit 26 using the drive circuit 17 and starts transporting the document (S6). The CPU 11 reads the document when the leading end in the document transport direction reaches the position facing the light receiving unit 42 of the CIS 40 after starting the document transport (S8). At this time, the CPU 11 functioning as the control unit 53 controls the CISs 30 and 40 for reading the document by irradiating the document with light for one line and for the irradiation time T. Further, the CPU 11 functions as the image processing unit 50, and performs correction processing such as shading correction on the read data (gradation value) obtained by reading the document. When the CPU 11 finishes reading the document, it ends the process.

4). Advantages of the present embodiment (1) In the image reading apparatus 1, in order to correct the mutual characteristic variation of the plurality of light receiving elements included in the light receiving units 32 and 42, correction data is read prior to reading the original using the CIS 30 and 40. It is necessary to acquire H, and at that time, white reference data WD is acquired. Since the white reference data WD is converted into the maximum gradation value KBmax of the AFE 15 by the correction data H, the white reference data WD is often measured using a member having a high reflectance in order to suppress errors due to conversion or the like. Normally, the white reference data WD is acquired using a white reference plate having the reflectance Rf1. That is, the maximum gradation value KBmax of the AFE 15 can be said to be a value corresponding to the reflectance Rf1 of the white reference plate.

  In the image reading apparatus 1 of this embodiment, gray reference plates 33 and 43 are provided instead of the white reference plate, and white reference data WD is acquired using the gray reference plates 33 and 43. At this time, the irradiation time T of the light sources 31 and 41 when acquiring the white reference data WD (which is equal to the irradiation time T of the light sources 31 and 41 when reading the document) is the maximum gradation value KBmax of the AFE 15. To be determined. That is, in this embodiment, when the light amount adjustment is performed using the gray reference plates 33 and 43 having the reflectance Rf3 lower than the reflectance Rf1 of the white reference plate, the value corresponds to the reflectance Rf1 of the white reference plate. Based on this, the irradiation time T is determined.

For example, as shown in FIG. 8, when the light amount adjustment is performed using the gray reference plates 33 and 43, it corresponds to the reflection ratio R of the reflectance Rf3 of the gray reference plates 33 and 43 and the reflectance Rf1 of the white reference plate. A method of setting the target gradation value KBmid of the AFE 15 as follows and setting the irradiation time T based on the target gradation value KBmid is also conceivable. In this method, for example, in the light amount adjustment process, a time T3 when the maximum gradation value KAmax is equal to the target gradation value KBmid is calculated, and a time T4 obtained by multiplying the time T3 by the reciprocal of the reflection ratio R is used as the irradiation time T. decide.
KBmid = KBmax × R = KBmax × (Rf3 / Rf1)
T4 = T3 × (1 / R) = T3 × (Rf1 / Rf3)

  However, time T2 and time T4 are not necessarily equal. In the image reading apparatus 1, the amount of light received by the light receiving elements of the light receiving units 32 and 42 is amplified and output as a read voltage in the CIS 30, 40 and AFE 15, and is nonlinear until the read voltage is converted into read data. As shown in FIG. 8, the linearity between the irradiation time T and the acquired gradation value may be lost as shown in FIG. Therefore, even if the target gradation value KBmid is calculated by performing linear processing on the maximum gradation value KBmax, linear processing is performed on the irradiation time T corresponding to the target gradation value KBmid to correspond to the maximum gradation value KBmax. The irradiation time T to be calculated is not necessarily calculated. For example, as shown in FIG. 8, the time T4 may be set longer than the time T2, and in this case, the gradation value acquired using each light receiving element exceeds the maximum gradation value KBmax of the AFE 15. As a result, the amount of light cannot be adjusted. In contrast to FIG. 8, the time T4 may be set shorter than the time T2, and in this case, the gradation value obtained using each light receiving element is lower than the maximum gradation value KBmax of the AFE 15. An error due to conversion or the like cannot be suppressed.

  In the image reading apparatus 1 of the present embodiment, when adjusting the light amount using the gray reference plates 33 and 43, the irradiation time T is set based on the maximum gradation value KAmax of the AFE 15, and for example, the target gradation value KBmid or the like. The irradiation time T is not set using gradation values other than the maximum gradation value KAmax. In the present embodiment, even when the gray reference plates 33 and 43 are used, each light receiving element determines the irradiation time T based on the amount of received light corresponding to the first reflectance, so that the amount of received light is converted into read data. Even if processing involving nonlinearity is performed, it is not affected by the nonlinearity.

  Further, in the image reading apparatus 1 of the present embodiment, the irradiation time T is determined using the fact that the reflectance and the amount of received light are proportional and the irradiation time and the amount of received light are proportional. That is, the irradiation time T1 that is prolonged by measuring using the gray reference plates 33 and 43 having the reflectance Rf3 lower than the reflectance Rf1 of the white reference plate is compensated by the reflection ratio R, and the irradiation time T2 is determined. To do. As a result, as shown by the one-dot chain line in FIGS. 8 and 9, the irradiation time T2 set using the white reference plate can be appropriately determined using the gray reference plates 33 and 43, and the amount of light can be accurately determined. Adjustments can be made.

(2) In the image reading apparatus 1 of the present embodiment, since the irradiation time T is adjusted based on the maximum gradation value KAmax of the AFE 15, when the AFE 15 converts the reading voltage output from the CIS 30, 40, It is possible to reliably prevent the converted gradation value from exceeding the maximum gradation value KAmax of the AFE 15.

(3) In the image reading apparatus 1 of the present embodiment, the CISs 30 and 40 are supported so as not to move relative to each other across the conveyance path 22. The CIS 30 is supported so as not to move relative to the gray reference plate 43, and the CIS 40 is supported so as not to move relative to the gray reference plate 33. Therefore, when performing the light amount adjustment processing of the CIS 30 and 40, even when the irradiation time cannot be set using another reference member that is not provided in the image reading apparatus 1 such as a white reference plate, the gray reference plate 33 , 43 can be used to appropriately set the irradiation time.

(4) In the image reading apparatus 1 of the present embodiment, when the CIS 30 or 40 reads a document, the document is placed between the gray reference plates 33 and 43 and the CIS 30 or 40 and the document is read. According to the image reading apparatus 1, since the reflectance of the gray reference plates 33 and 43 is suppressed to be lower than the first reflectance of the white reference plate, it is possible to suppress see-through when reading a document. .

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and the drawings, and for example, the following various aspects are also included in the technical scope of the present invention.
(1) Although the above embodiment has been described using the image reading apparatus 1, the present invention is not limited to this. For example, a multifunction machine having at least one function such as a printer function, a scanner function, a copy function, and a facsimile function may be used.

(2) In the above embodiment, the image reading apparatus 1 has one ASIC 10, and one CPU 20 in which the ASIC 10 has functions such as the image processing unit 50, the irradiation time adjustment unit 51, the irradiation time determination unit 52, and the control unit 53. However, the present invention is not limited to this. For example, each unit may be configured by different CPUs, ASICs, or the like, or may be configured by using independent circuits or devices such as an image processing circuit.

1: image reading device, 3: main body, 10: ASIC, 11: CPU, 15: AFE, 16: lighting circuit, 22: conveyance path, 24: reading unit, 26: conveyance unit, 30, 40: CIS, 31 , 41: light source, 32, 42: light receiving unit, 33, 43: gray reference plate, 34, 44: platen glass, 50: image processing unit, 51: irradiation time adjusting unit, 52: irradiation time determining unit, 53: control Part, Rf1: reflectance of white reference plate, Rf2: reflectance of black reference plate, Rf3: reflectance of gray reference plate, R: reflection ratio, T: irradiation time

Claims (6)

A reference member having a second reflectance lower than the first reflectance;
A reading unit including a light source that irradiates light on the document or the reference member, and a light receiving element that receives light reflected from the document or the reference member;
The light source irradiates the reference member with light, and the output value output from the light receiving element based on the amount of light received by the reflected light reflected by the reference member is a value corresponding to the first reflectance. And an irradiation time adjusting unit for adjusting the irradiation time of the light source,
An irradiation time determination unit that multiplies the time adjusted by the irradiation time adjustment unit by a ratio of the second reflectance to the first reflectance, and determines the multiplied time as the irradiation time of the light source;
A control unit that controls to read the document using the irradiation time of the light source determined by the irradiation time determination unit when reading the document;
An image reading apparatus comprising: The image reading apparatus according to claim 1,
A converter that converts an output value of an analog signal output by the light receiving element into an output value of a digital signal;
With
The irradiation time adjustment unit adjusts the irradiation time of the light source so that the maximum value of the output value output from the light receiving element and converted by the conversion unit becomes the maximum output value of the conversion unit,
An image reading apparatus. The image reading apparatus according to claim 1 or 2,
The reading unit is supported so as not to move relative to the reference member;
An image reading apparatus. An image reading apparatus according to any one of claims 1 to 3,
A transport unit for transporting a document onto a transport path;
With
The reading unit includes a first reading unit disposed on one side along the conveyance path, and a second reading unit disposed on the other side along the conveyance path,
The reference member includes a first reference member disposed on the other side along the transport path, and a second reference member disposed on one side along the transport path,
The first reading unit is disposed to face the second reading unit via the transport path;
An image reading apparatus. An image reading apparatus according to any one of claims 1 to 4,
The image reading apparatus, wherein the first reflectance is a reflectance of a white reference plate. A reference member having a second reflectance lower than the first reflectance;
A reading unit including a light source that irradiates light on the document or the reference member, and a light receiving element that receives light reflected from the document or the reference member;
A light amount adjustment method for an image reading apparatus comprising:
An irradiation step of irradiating the reference member with light from the light source;
An output step of outputting an output value based on the amount of light received by the light receiving element that is reflected from the light source and reflected by the reference member;
An adjustment step of adjusting the irradiation time of the light source so that the output value becomes a value corresponding to the first reflectance;
A determination step of multiplying the time adjusted in the adjustment step by a ratio of the second reflectance to the first reflectance and determining the multiplied time as an irradiation time of the light source;
A control step of controlling to read the original using the irradiation time of the light source determined in the determination step when reading the original;
A method for adjusting the amount of light of an image reading apparatus including:

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