Image reader

Abstract

To provide an image reading device that can switch between a mode for controlling the lighting time of a light source and a mode for controlling a current flowing in the light source.SOLUTION: An image reading device has designation means that designates any one of a first control mode for adjusting the lighting time of a light source to adjust the amount of light received by reading means and a second control mode for controlling a current supplied to the light source to adjust the amount of light received by the reading means. The image reading device controls the light source according to one control mode of the first control mode and the second control mode designated by the designation means.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to an image reading device. [Background technology]

[0002] Image reading devices (image scanners, copiers, facsimile machines, etc.) use a CIS (contact image sensor) to read a document conveyed by an automatic document feeder (ADF). In order to ensure sufficient gradation in the reading quality of the document, the light source illumination time per line is adjusted so that the light receiving element does not become saturated. However, adjusting the illumination time creates periods when the light source is turned off, which causes image loss and resulting moire. According to Patent Document 1, moire in the read image is reduced by evenly distributing the illumination time of each RGB light emitting diode (LED). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2011-217049 A Summary of the Invention [Problem to be solved by the invention]

[0004] According to Patent Document 1, moire is reduced, but image loss occurs due to the existence of a time when the light source is off. In other words, if the light-on time is adjusted, gradation is ensured, but image loss and moire occur, and if the light-off time is eliminated by not adjusting the light-on time, image loss and moire do not occur, but gradation is not sufficiently ensured. Meanwhile, whether gradation should be given priority or image loss and moire should be given priority and reduced depends on the user's preference. Therefore, an object of the present invention is to provide an image reading device that can switch between a mode that controls the light source's light-on time and a mode that controls the current flowing through the light source. [Means for solving the problem]

[0005] The present invention relates to, for example, A light source that illuminates the object to be read; a reading means for receiving light from the object to be read that is illuminated by the light source and generating an image signal; By accepting the image scanning settings, Either a first control mode in which the amount of light received by the reading means is adjusted by adjusting the lighting time of the light source, or a second control mode in which the amount of light received by the reading means is adjusted by controlling the current supplied to the light source. Based on the image reading settings A designation means for designating the a control means for controlling the light source in accordance with a control mode designated by the designation means out of the first control mode and the second control mode; The present invention provides an image reading device comprising: Effect of the Invention

[0006] According to the present invention, there is provided an image reading device capable of switching between a mode for controlling the illumination time of a light source and a mode for controlling a current flowing through the light source. When the mode for controlling the illumination time of the light source is selected, the gradation of an image is easily ensured. When the mode for controlling the current flowing through the light source is selected, image loss and moire are less likely to occur. [Brief description of the drawings]

[0007] [Figure 1] FIG. 3 is a cross-sectional view illustrating the structure of the image reading device. [Diagram 2] FIG. 2 is a diagram illustrating an image reading unit. [Diagram 3] FIG. 2 is a diagram illustrating an image reading unit. [Figure 4] A diagram explaining the lighting time control mode [Diagram 5] Diagram explaining the current control mode [Figure 6] Diagram explaining the controller [Figure 7] Flowchart showing an image reading method [Figure 8] Flowchart showing the lighting time control mode [Figure 9] Flowchart showing current control mode [Figure 10] FIG. 2 is a diagram illustrating an image reading unit. [Figure 11] FIG. 2 is a diagram illustrating an image reading unit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, the embodiments will be described in detail with reference to the attached drawings. Note that the following embodiments do not limit the invention according to the claims. Although the embodiments describe a number of features, not all of these features are essential to the invention, and the features may be combined in any manner. Furthermore, in the attached drawings, the same reference numbers are used for the same or similar configurations, and duplicated descriptions are omitted.

[0009] <Structure of image reading device> As shown in Fig. 1, image reading device 100 uses a CIS to read a document conveyed by an ADF and generate image data. A loading platform 1 holds one or a plurality of conveying media S. The conveying media S are, for example, sheets such as office paper, checks, cards, etc., and may be thick or thin sheets. Cards are, for example, insurance cards, driver's licenses, credit cards, etc. The conveying media S also includes booklets such as passports.

[0010] The first conveying unit 10 is a feeding mechanism that feeds the conveying medium S to the path RT. The first conveying unit 10 has a feed roller 11 and a separation roller 12 arranged opposite to the feed roller 11. The separation roller 12 conveys only one of the conveying media S placed on the mounting table 1 in the conveying direction D1. The driving unit 3 is a motor or the like. The driving unit 3 transmits a driving force to the feed roller 11 via the transmission unit 4 to rotate the feed roller 11. The rotation direction of the feed roller 11 is counterclockwise (the direction in which the conveying medium S is conveyed along the path RT). The transmission unit 4 is, for example, an electromagnetic clutch, and connects and disconnects (disconnects / connects) the driving force from the driving unit 3 to the feed roller 11 according to an instruction from the control unit 8. The transmission unit 4 is in a state in which it transmits the driving force under normal circumstances, and disconnects the driving force when the conveying medium S is fed in the reverse direction. When the transmission of the driving force is interrupted by the transmission unit 4, the feed roller 11 is in a freely rotatable state. When the feed roller 11 is driven in only one direction, the transmission unit 4 may be omitted.

[0011] The separation roller 12 is a roller for separating the multiple conveying media S one by one, and is pressed against the feed roller 11 with a constant pressure. In order to secure this pressed state, the separation roller 12 is provided to be able to swing, and is urged against the feed roller 11 by a spring or the like. The separation roller 12 receives a driving force from the drive unit 3 via the torque limiter 12a, and rotates in a counterclockwise direction. The torque limiter 12a limits the driving force of the separation roller 12. Therefore, when the separation roller 12 is in contact with the feed roller 11, the separation roller 12 rotates together with the feed roller 11. As a result, when multiple conveying media S are conveyed to the pressure contact portion between the feed roller 11 and the separation roller 12, only one conveying medium S is conveyed downstream, and the remaining conveying media S are blocked so as not to be conveyed downstream. In this embodiment, the separation roller 12 and the feed roller 11 constitute a separation mechanism, but this is merely an example. The separation mechanism may be omitted, or a separation mechanism including a separation pad that applies a frictional force to the conveyed medium S and the feed roller 11 may be employed.

[0012] The second conveying section 20 is provided downstream of the first conveying section 10 in the conveying direction. The second conveying section 20 has a drive roller 21 and a driven roller 22 that is driven by the drive roller 21. The second conveying section 20 conveys the conveying medium S conveyed from the first conveying section 10 further downstream. A driving force is transmitted from the drive unit 3 to the drive roller 21, and the driven roller 22 rotates counterclockwise. The driven roller 22 is pressed against the drive roller 21 with a constant pressure, and therefore rotates together with the drive roller 21. The driven roller 22 may be biased against the drive roller 21 by a biasing unit (not shown) such as a spring.

[0013] The third conveying section 30 is provided downstream of the second conveying section 20 in the conveying direction. The third conveying section 30 has a drive roller 31 and a driven roller 32 that is driven by the drive roller 31. The third conveying section 30 conveys and discharges the conveyed medium S conveyed from the second conveying section 20 to the discharge tray 2. A driving force is transmitted from the drive section 3 to the drive roller 31, and the driven roller 32 rotates counterclockwise. The driven roller 32 is pressed against the drive roller 31 with a constant pressure, and rotates together with the drive roller 31. The driven roller 32 may be biased against the drive roller 31 by a biasing unit such as a spring.

[0014] Image reading units 70a and 70b are disposed between the second conveying section 20 and the third conveying section 30 on the path RT. The image reading unit 70a reads a first side of the conveying medium S. The image reading unit 70b reads a second side of the conveying medium S. To read the image, the second conveying section 20 and the third conveying section 30 convey the conveying medium S at a constant conveying speed. This conveying speed may always be set to be equal to or greater than the conveying speed of the first conveying section 10. This prevents the following conveying medium S from colliding with the preceding conveying medium S.

[0015] The double feed sensor 40 is disposed between the first conveying section 10 and the second conveying section 20. The double feed sensor 40 detects double feeding of the conveying media S. Double feeding is a phenomenon in which multiple conveying media S adhere to each other due to static electricity or the like and pass through the first conveying section 10. Various types of double feed sensor 40 can be used. For example, the double feed sensor 40 may be an ultrasonic sensor. In this case, the double feed sensor 40 has an ultrasonic transmitter 41 and a receiver 42. The attenuation of ultrasonic waves passing through the conveying medium S differs between when multiple conveying media S are being fed in a double feed and when one conveying medium S is being conveyed. Double feed is detected based on this principle.

[0016] A media sensor 50 is disposed downstream of the double feed sensor 40 in the conveying direction on the path RT. The media sensor 50 is disposed upstream of the second conveying section 20 and downstream of the first conveying section 10. The media sensor 50 detects the position of the conveying medium S conveyed by the first conveying section 10. More specifically, the media sensor 50 detects whether the end of the conveying medium S has reached or passed the detection position of the media sensor 50. Various media sensors can be used as the media sensor 50. The media sensor 50 may be, for example, an optical sensor. In this case, the media sensor 50 has an irradiation section 51 and a light receiving section 52 thereof. The light receiving intensity of the light receiving section 52 changes depending on the arrival or passage of the conveying medium S. The conveying medium S is detected based on this principle. The media sensor 50 is disposed downstream near the double feed sensor 40 so that when the leading edge of the conveying medium S is detected by the media sensor 50, the conveying medium S has reached a position where the double feed sensor 40 can detect the double feed. The medium sensor 50 may be a sensor capable of detecting the edge of the medium S (eg, an image sensor, etc.), or may be a lever-type sensor protruding into the path RT.

[0017] The media sensor 60 is disposed upstream of the image reading units 70a, 70b and downstream of the second conveying section 20. The media sensor 60 detects the position of the conveyed medium S conveyed by the second conveying section 20. As with the media sensor 50, various types of media sensor 60 can be used. Here, as an example, the media sensor 60 is an optical sensor equipped with a light-emitting section 61 and a light-receiving section 62. In FIG. 1, the media sensors 50, 60 are disposed on the upstream side and downstream side in the conveying direction of the second conveying section 20, respectively, but only one of them may be disposed.

[0018] The image reading units 70a and 70b, for example, optically scan the transport medium S and convert light from the transport medium S into an electrical signal to generate an image signal. The image reading units 70a and 70b include a light source such as an LED, a light guide, a light receiving sensor array, and the like. Only one of the image reading units 70a and 70b may be disposed on one side of the path RT. In FIG. 1, the image reading units 70a and 70b are disposed opposite each other across the path RT, but this is merely an example. The image reading units 70a and 70b may be disposed at an interval in the direction of the path RT.

[0019] When the control unit 8 receives an instruction to start image reading, it starts driving the first conveying unit 10, the second conveying unit 20, and the third conveying unit 30 by the drive unit 3. The media S to be conveyed loaded on the mounting table 1 are conveyed one by one starting from the lowest media S to be conveyed. During the conveying process, the double feed sensor 40 determines whether or not there is a double feed of the media S to be conveyed. If it is determined that there is no double feed, the conveying of the media S to be conveyed continues. If it is determined that there is a double feed, the control unit 8 stops the drive unit 3 and stops the conveying of the media S to be conveyed.

[0020] The control unit 8 causes the image reading units 70a and 70b to start reading the image of the conveyed medium S at a timing according to the detection result of the medium sensor 60. The control unit 8 converts the image signals output from the image reading units 70a and 70b into image data.

[0021] <Explanation of the structure of the image reading unit> 2 is a perspective view of the image reading units 70a and 70b as viewed from the path RT side. The image reading units 70a and 70b each have a light source 73. Since the image reading units 70a and 70b have a common structure, the structure of the image reading unit 70a will be described in detail here.

[0022] The light source 73 has a light emitting element (e.g., LED). The light source 73 is installed at least one end of the light guide 71. In FIG. 2, the light source 73 is installed at one end of the light guide 71, but it may be installed at the other end of the light guide 71. This compensates for the amount of light emitted. The light guide 71 uses a light-transmitting material such as a translucent molded resin or glass as a main member. The light output from the light source 73 propagates inside the light guide 71. A reflector (not shown) that reflects light toward the path RT is provided inside the light guide 71. The reflector reflects the light from the light source 73 toward the path RT. A plurality of reflectors may be provided at narrower intervals as the distance from the light source 73 increases. This may allow the path RT to be uniformly irradiated with light in the main scanning direction. A plurality of light guides 71 may also be provided.

[0023] The light emitted from the light guide 71 is reflected again by the surface of the transport medium S and enters the light receiving sensor array 72. The light receiving sensor array 72 has a plurality of photoelectric conversion elements, such as a CMOS (Complementary Metal Oxide Semiconductor) image sensor. The plurality of photoelectric conversion elements are arranged along the main scanning direction, forming one line in the main scanning direction. The light that reaches the light receiving sensor array 72 is converted into an electrical signal line by line. In general, the output value of a CMOS image sensor changes according to the amount of light acquired line by line. For example, when the amount of light emitted from the light source 73 is large, the output value becomes large. However, even if the amount of light emitted is the same, the output value becomes large if the scanning time per line is long. Finally, the electrical signal acquired line by line is converted into a digital signal by an A / D converter (ADC) to be described later. By combining the digital signals of multiple lines for the transport medium S transported along the route RT, image data of the transport medium S is created.

[0024] FIG. 3 is a cross-sectional view of the image reading units 70a and 70b as viewed from the main scanning direction. The light source 73 may be a white light source (e.g., white LED), or may be composed of a red light source 73r (e.g., red LED), a green light source 73g (e.g., green LED), and a blue light source 73b (e.g., blue LED) as shown in FIG. 3. The light sources 73r, 73g, and 73b each output light of a different wavelength. The light emission time of the light sources 73r, 73g, and 73b may be controlled on a line-by-line basis. The light emission time of the light sources 73r, 73g, and 73b is determined, for example, so that the output value of the light receiving sensor array 72 does not overflow. The light sources 73r, 73g, and 73b may start emitting light simultaneously on a line-by-line basis, or the light emission start timings may be shifted from one another. Depending on the format of the acquired image (e.g., dropout color), one or two of the light sources 73r, 73g, and 73b may not be turned on.

[0025] The amount of light emitted by the light source 73 and the amount of light received by the light receiving sensor array 72 may be adjusted by controlling the current (current value) supplied to the light source 73. In this case, the amount of light emitted and the amount of light received can be controlled while maintaining the light emission time of the light source 73 constant. The current values ​​of the light sources 73r, 73g, and 73b may be set individually. The light receiving sensor array 72 may have a red light receiving sensor array 72r, a green light receiving sensor array 72g, and a blue light receiving sensor array 72b. The light receiving sensor arrays 72r, 72g, and 72b each receive light in a corresponding wavelength range using a spectral filter or the like. Here, the light receiving sensor arrays 72r, 72g, and 72b are used, but a single light receiving sensor array 72 that covers all of the wavelength ranges assigned to the light receiving sensor arrays 72r, 72g, and 72b may be adopted. By using a single light receiving sensor array 72, the configuration of the image reading units 70a and 70b tends to be simple. However, it is necessary to switch the data of each color in units of one line. This means that while data of one color is being acquired, data of other colors cannot be acquired. Therefore, by using the light receiving sensor arrays 72r, 72g, and 72b, it becomes difficult for image data of each color to be missing in the sub-scanning direction.

[0026] <Explanation of the adjustment process for the amount of light emitted and the amount of light received> ●Lighting time control mode FIG. 4 shows an example (lighting time control mode) in which the light-on time of each of the light sources 73r, 73g, and 73b is controlled in units of one line. The SP (Start Pulse) section 80 represents the scanning time of the image data in units of one line. R, G, and B represent the light sources 73r, 73g, and 73b, respectively. The light source 73r is turned on during a lighting time 81r in the SP section 80, and is turned off during a lighting time 82r. The light source 73g is turned on during a lighting time 81g in the SP section 80, and is turned off during a lighting time 82g. The light source 73b is turned on during a lighting time 81b in the SP section 80, and is turned off during a lighting time 82b. In the lighting time control mode, the lighting times 81r, 81g, and 81b are adjusted so that the amount of light received by each of the light receiving sensor arrays 72r, 72g, and 72b becomes the target light amount. The target light amount can be set, for example, to a light amount that can maximize the S / N ratio of the document image. For example, the target light amount is set so that the reading result of the brightest document (e.g., white, which reflects the light of the light source 73 the most) generally expected is not saturated. Also, the lighting time of the light sources 73r, 73g, and 73b can be finely adjusted based on a clock of, for example, several MHz to several hundred MHz. Therefore, in the lighting time control mode, the lighting time is finely adjusted so that the amount of received light is not saturated and the S / N ratio is maximized.

[0027] On the other hand, in the light-on time control mode, off times 82r, 82g, and 82b occur in the SP section 80. The longer the off time is, the shorter the on time is. As a result, the sampling section of the document image becomes localized, which can cause aliasing in the image and moire.

[0028] ●Current control mode FIG. 5 shows an example (current control mode) in which the current values ​​of the light sources 73r, 73g, and 73b are controlled in units of one line. In the current control mode, the light-on time of the light sources 73r, 73g, and 73b in the SP section 80 is set to the maximum value. However, the current values ​​of the light sources 73r, 73g, and 73b are controlled, and the light-receiving sensor arrays 72r, 72g, and 72b receive light in an amount that is a target light amount. This reduces the time that the light sources 73r, 73g, and 73b are turned off, thereby suppressing degradation of image quality (e.g., moire) due to data loss. As an example of the maximum value of this light-on time, a time that is approximately equal to the scanning time of image data in units of one line is shown in FIG. 5.

[0029] On the other hand, circuit configuration for finely adjusting the current value leads to increased costs. As a result, it may not be possible to set continuous values ​​as the current value, and only discrete values ​​can be set. In this case, the amount of light emitted can only be roughly adjusted, making it difficult to maximize the S / N ratio of the amount of light received. As a result, it may be difficult to ensure sufficient gradation in the output image.

[0030] However, since the purpose of reading a document varies depending on the user, there are cases where the illumination time control mode is preferable and cases where the current control mode is preferable. Therefore, it would be convenient for the user if the illumination time control mode and the current control mode could be switched according to the user's preference.

[0031] Furthermore, in addition to the adjustment of the lighting time and the current value, gain adjustment may be combined to multiply the amount of received light by a predetermined coefficient. This can be achieved by multiplying the image data by a predetermined coefficient. The gain adjustment can increase the output value even in a situation where the scanning time per line is short and it is difficult to ensure a sufficient amount of received light. There are multiple methods for gain adjustment. Specifically, there is analog gain adjustment, in which the amount of received light is multiplied by a predetermined coefficient before being converted into a digital signal, and digital gain adjustment, in which the amount of received light is multiplied by a predetermined coefficient after being converted into a digital signal.

[0032] <Controller> 6 shows details of the control unit 8 that controls the image reading device 100. The control unit 8 may be, for example, a CPU (Central Processing Unit) that realizes various functions by executing a control program stored in a ROM area of ​​the storage device 620. The mode control unit 601 specifies, selects, or switches the control mode according to a user instruction input from an input device of the operation unit 621. For example, if the user wishes to ensure dynamic range or gradation, the mode control unit 601 selects the illumination time control mode. If the user wishes to reduce image loss or moire, the mode control unit 601 selects the current control mode.

[0033] When the lighting time control mode is specified, the lighting time control unit 602 adjusts the lighting time of the light sources 73r, 73g, and 73b so that the amount of light received by the light receiving sensor arrays 72r, 72g, and 72b becomes the target amount of light. When the current control mode is specified, the lighting time control unit 602 fixes the lighting time to a predetermined value and adjusts the current value of the light sources 73r, 73g, and 73b so that the amount of light received becomes the target amount of light. The current value may be set individually for each of the driving circuits 633r, 633g, and 633b. The driving circuits 633r, 633g, and 633b supply current of a set current value to the corresponding light sources 73r, 73g, and 73b for the lighting time set by the control unit 8. The gain control unit 604 adjusts the coefficient (gain) of the multiplication units 605r, 605g, and 605b and / or the AFEs 641r, 641g, and 641b. AFE is an abbreviation of an analog front-end circuit. The AFEs 641r, 641g, and 641b are optional. The AFEs 641r, 641g, and 641b adjust the gain of the image signal output from the corresponding light receiving sensor arrays 72r, 72g, and 72b, and output it to the corresponding ADCs 642r, 642g, and 642b. The ADCs 642r, 642g, and 642b convert the analog image signals input thereto into digital data, and output it to the control unit 8. The multiplication units 605r, 605g, and 605b multiply the image data output from the ADCs 642r, 642g, and 642b by a coefficient to adjust the gain, and output it to the image data generation unit 610. The image data generation unit 610 combines the image data output from the multiplication units 605r, 605g, and 605b to generate image data corresponding to the entirety of one conveying medium S, and stores it in the storage device 620.

[0034] <Flowchart> FIG. 7 is a flowchart showing an image reading method including a control mode switching process. The image reading unit 70a will be described below, but the same image reading method is also applied to the image reading unit 70b. In addition, the light sources 73r, 73g, and 73b will be collectively referred to as the light source 73, and the light receiving sensor arrays 72r, 72g, and 72b will be collectively referred to as the light receiving sensor array 72. However, the light sources 73r, 73g, and 73b may be individually adjusted in lighting time, gain, and current value so that the light receiving sensor arrays 72r, 72g, and 72b each receive a target light amount. In this adjustment process, the light sources 73r, 73g, and 73b are turned on in sequence one by one, and their lighting time, gain, and current value are individually adjusted, but when reading the conveyed medium S, the light sources 73r, 73g, and 73b may be turned on simultaneously.

[0035] In S701, the control unit 8 accepts image reading settings input by a user via a personal computer (PC) connected to the image reading device 100 or the operation unit 621. Here, the image reading settings may include the user's desired reading image quality (reduction of moire (reduction of image loss) or ensuring dynamic range (gradation)). The image reading settings may include information that directly or indirectly specifies the illumination time control mode or the current control mode.

[0036] In S702, the control unit 8 starts reading the stack of documents in accordance with a reading start command input by the user from the operation unit 621 or the like. In S703, the control unit 8 determines whether the user desires to reduce moire based on the image reading settings. For example, if the user selects a process related to moire removal in the image reading settings, it can be said that the user desires to reduce moire. If the user desires to reduce moire, the control unit 8 proceeds to S704, sets the control mode to the current control mode, and adjusts the amount of received light (amount of emitted light). If the user does not desire to reduce moire (if the user desires to ensure a dynamic range), the control unit 8 proceeds to S705, sets the control mode to the illumination time control mode, and adjusts the amount of received light (amount of emitted light).

[0037] In S706, the control unit 8 controls the drive unit 3 and the image reading units 70a, 70b, etc. to separate the document from the document stack and read the document. In S707, the control unit 8 determines whether or not the next document is present based on the detection results of the double feed sensor 40, the media sensor 50, etc. If the next document is present, the control unit 8 returns to S706 and reads the next document. If the next document is not present, the control unit 8 proceeds to S708 and ends reading the document stack.

[0038] ●Lighting time control mode 8 is a flowchart showing the lighting time control mode (S705). In S801, the control unit 8 sets an initial value stored in the storage device 620 as the current value of the drive current of the light source 73. The initial value varies depending on the configuration of the image reading device 100, and may be changed depending on the characteristics of the image reading device 100, the scanning time per line, the resolution setting, etc.

[0039] In S802, the control unit 8 sets the gain of the multiplication unit 605 (or AFE 641) to an initial value. The smaller the gain, the better the gradation of the reading result. For this reason, the initial value is set to approximately 1x. However, this is merely an example. For example, if it is known in advance that the amount of received light is small, a value larger than 1x may be set as the initial gain value. This will shorten the adjustment time. Note that the order of execution of S801 and S802 may be reversed.

[0040] In S803, the control unit 8 sets the lighting time of the light source 73 to an initial value (e.g., the maximum value that can be set as the lighting time). Setting the initial value to the maximum time that can be set is merely one example. If it is already known that the amount of received light will reach the target amount of light even if the lighting time is not set to the maximum value that can be set, the lighting time is set to a value smaller than the maximum value.

[0041] In S804, the control unit 8 controls the image reading unit 70a to acquire the amount of received light. Here, the amount of received light may be a luminance value. Here, a gain is applied to the amount of received light.

[0042] In S805, the control unit 8 determines whether the amount of received light exceeds a specified value. When a luminance value is used as the amount of received light, and the obtainable luminance value is 256 gradations from "0" to "255", the specified value may be set to a luminance value of "210". The illumination time and gain are adjusted so that the luminance value ultimately becomes "200", which is the target amount of light. If the amount of received light exceeds the specified value, the control unit 8 proceeds to S808. If the amount of received light does not exceed the specified value, the control unit 8 proceeds to S806.

[0043] In S806, the control unit 8 determines whether the current gain is less than the maximum value that can be set. If the gain is the maximum value, the control unit 8 proceeds to S830 and outputs a notice indicating an error to the display device of the operation unit 621 or the like. If it is determined in S806 that the gain is less than the maximum value, the control unit 8 proceeds to S807. In S807, the gain is increased by a predetermined value. Here, the predetermined value does not need to be constant, and a large predetermined value may be used so that the gain is increased by a large amount if the difference between the amount of received light and the specified value is large. This will result in a reduction in the adjustment time. Thereafter, the control unit 8 returns to S804.

[0044] If the amount of received light exceeds the specified value in S805, the control unit 8 proceeds to S808. In S808, the control unit 8 adjusts the lighting time (shortens the lighting time). In S809, the control unit 8 controls the image reading unit 70a to obtain the amount of received light. In S810, the control unit 8 determines whether the amount of received light reaches the target light amount "200". If the amount of received light has not reached the target light amount, the control unit 8 returns to S808. If the amount of received light has reached the target light amount, the control unit 8 completes the adjustment process. The control unit 8 stores the gain and the lighting time in the RAM area of ​​the storage device 620 so that they can be set in the multiplication unit 605 and the drive circuit 633. This determines the amount of light emitted by the light source 73 so that the dynamic range (S / N ratio) can be maximized within a range in which the read luminance value is not saturated, making it possible to obtain an image with a more appropriate amount of received light.

[0045] In the present embodiment, an example has been described in which the specified value and the final target light amount are different, but the present invention is not limited to this, and the specified value and the target light amount may be the same value.

[0046] ●Current control mode 9 is a flowchart showing the current control mode (S704). Since S801 to S807 have already been described, S908 and after will be described in detail. If the amount of received light exceeds the specified value in S805, the control unit 8 proceeds to S908.

[0047] In S908, the control unit 8 determines whether the amount of received light is saturated (whether the amount of received light has reached a maximum value). If the amount of received light is not saturated, the control unit 8 completes the adjustment process. If the amount of received light is saturated, the control unit 8 proceeds to S909.

[0048] In S909, the control unit 8 determines whether the current value set in the drive circuit 633 is the minimum value. If the current value is the minimum value, the control unit 8 proceeds to S803 and notifies an error. If the current value is not the minimum value, the control unit 8 proceeds to S910.

[0049] In S910, the control unit 8 reduces the current value, and the process returns to S802. As a result, the current value is adjusted while maintaining the lighting time of the light source 73 at the maximum time. This reduces image loss and moire.

[0050] <Modification> In FIG. 7, in S703, the control mode is determined based on whether the user desires to reduce moire. However, the control mode may be determined based on other conditions. The user may set a dropout color in S701. The dropout color is, for example, a color that causes a part of the color of the document to disappear from the read image when the document is read. For example, when the ruled lines of a document or the like are red, by setting red as the dropout color, it becomes possible to erase the ruled lines and read only the characters. In this way, when the user sets to drop out red, the mode control unit 601 selects the current control mode as the control mode. This reduces moire. However, even when the dropout color is set, the mode control unit 601 may set the lighting time control mode according to the user's desire. This may ensure a sufficient dynamic range.

[0051] Furthermore, even if the user does not set the desired control mode, the control unit 8 may automatically determine the control mode based on some condition in the reading setting. For example, when a specific process is specified as a post-processing of the read image in the reading setting, the control unit 8 may automatically set one of the control modes. Specifically, when character recognition (OCR) processing is specified as a post-processing of the read image, the control mode that improves the accuracy of the character recognition processing may be specified. Although it depends on the algorithm of the character recognition processing, for example, when character recognition processing is specified as a post-processing, the current control mode may be selected.

[0052] In this manner, in this embodiment, the control unit 8 is configured to specify one of the control modes when it is determined that the reading settings for reading the conveyed medium S satisfy a specific condition.

[0053] Either the illumination time control mode or the current control mode may be selected as a default. In this case, the user may specify a control mode different from the default control mode. For example, if the illumination time control mode, which has a large dynamic range, is set as the default control mode and the user wishes to reduce moire, the control mode may be switched to the current control mode.

[0054] In FIG. 2, one light guide 71 is provided, but as shown in FIG. 10, two light guides 71 may be provided. Two light guides 71 may be provided so as to sandwich the light receiving sensor array 72. Although one light source 73 is provided for each of the two light guides 71, two light sources 73 may be provided for each. In this case, the light source 73 is provided at one end of one light guide 71 and at the other end of the other light guide. This embodiment is also applicable to the case where two light guides 71 are provided in this manner. As shown in FIG. 11, by increasing the number of light guides 71 and the number of light sources 73, the conveying medium S is illuminated from the upstream side and the downstream side in the sub-scanning direction. This makes it difficult for shadows that may be caused by wrinkles in the document to appear on the image. The start and end timings of the emission of each light source 73 may be controlled individually.

[0055] <Technical ideas derived from the embodiment> [Point 1] The light source 73 is an example of a light source that illuminates a reading target (e.g., a conveying medium S). The image reading units 70a and 70b are an example of a reading means that generates an image signal by receiving light from a reading target illuminated by the light source 73. The mode control unit 601 and the operation unit 621 function as a designation unit that designates either a first control mode (e.g., a lighting time control mode) or a second control mode (e.g., a current control mode). The first control mode is a mode in which the amount of light received by the reading means is adjusted by adjusting the lighting time of the light source. The second control mode is a mode in which the amount of light received by the reading means is adjusted by controlling the current supplied to the light source. The control unit 8 (lighting time control unit 602, current control unit 603) functions as a control unit that controls the light source according to the control mode designated by the designation unit among the first control mode and the second control mode. In this way, according to the present invention, an image reading device capable of switching between a mode in which the lighting time of the light source is controlled and a mode in which the current flowing through the light source is controlled is provided.

[0056] [Point 2] The second control mode (e.g., current control mode) is a control mode in which the current supplied to the light source is controlled while the light source is turned on for the maximum lighting time that can be set in the first control mode, which makes it difficult for image loss to occur and also makes it difficult for moire to occur.

[0057] [Point 3] The image reading units 70a and 70b may be line sensors that read an image for each reading line while moving the reading target relatively. The maximum lighting time may be equal to the scanning time of the image for each line.

[0058] [Point 4] The gain control unit 604, the multiplication unit 605, and the AFE 641 function as an adjustment unit that adjusts the gain of the image signal. In the second control mode, the control unit 8 may set the adjustment unit to the minimum gain at which the amount of received light can reach a specified value (e.g., "210").

[0059] [Point 5] In the second control mode, the control unit (controller 8) may adjust the amount of received light to be equal to or less than a specified value (for example, to avoid saturation) by gradually reducing the current from the initial value. When the amount of received light falls below the specified value, the control unit (controller 8) may adjust the gain to make the amount of received light reach the specified value.

[0060] [Point 6] Even if the gain is increased to the adjustable maximum value, there may be cases where the amount of received light is below the target value. In this case, the operation unit 621 functions as an output unit that outputs a notification to the user.

[0061] [Point 7] The designation means (mode control unit 601) may designate either the first control mode or the second control mode when a specific condition is satisfied in the reading setting for reading the reading target.

[0062] [Point 8] The designation means (mode control unit 601) may designate the second control mode when the user requests reduction of moire or reduction of image loss. The designation means (mode control unit 601) may designate the first control mode when the user requests priority of gradation or dynamic range.

[0063] The invention is not limited to the above-described embodiment, and various modifications and variations are possible within the scope of the gist of the invention. [Explanation of symbols]

[0064] 73: light source, 70a, 70b: image reading unit, 8: control unit

Claims

1. A light source for illuminating an object to be read; a reading means for receiving light from the object to be read that is illuminated by the light source and generating an image signal; a designation means for designating, based on an image reading setting, either a first control mode in which the amount of light received by the reading means is adjusted by adjusting the lighting time of the light source, or a second control mode in which the amount of light received by the reading means is adjusted by controlling a current supplied to the light source, by accepting the image reading setting; a control means for controlling the light source in accordance with a control mode designated by the designation means out of the first control mode and the second control mode; 1. An image reading device comprising:

2. 2. The image reading device according to claim 1, wherein the second control mode is a control mode in which the current supplied to the light source is controlled while the light source is turned on for a maximum lighting time that can be set in the first control mode.

3. The image processing apparatus further includes an adjustment unit for adjusting a gain of the image signal, 2. The image reading apparatus according to claim 1, wherein the control means sets the adjustment means to a minimum gain at which the amount of received light can reach a specified value in the second control mode.

4. The image reading device described in claim 3, characterized in that in the second control mode, the control means adjusts the amount of received light to be below the specified value by gradually reducing the current from an initial value, and when the amount of received light falls below the specified value, the control means adjusts the gain to cause the amount of received light to reach the specified value.

5. 5. The image reading apparatus according to claim 4, further comprising an output unit that outputs a notification to a user when the amount of received light is less than the specified value even after the gain is increased to an adjustable maximum value.

6. The image reading device according to any one of claims 1 to 5, characterized in that the designation means designates either the first control mode or the second control mode when a specific condition is satisfied in a reading setting for reading the reading object.

7. 7. The image reading apparatus according to claim 1, wherein the designation unit designates the second control mode when a user requests reduction of moire or reduction of image loss.

8. 8. The image reading apparatus according to claim 1, wherein the designation unit designates the first control mode when a user requests priority over gradation or dynamic range.

Images