JP4354785B2 - Image reading device - Google Patents

Description

  The present invention relates to, for example, an image reading apparatus that conveys documents set on a document table one by one and reads a reading surface of the conveyed document in color or monochrome according to a reading mode selected by a user.

  Conventionally, in an image reading apparatus having an automatic document feeder (ADF), a scanning position of a line sensor is fixed at a predetermined reading position, and an image on a document surface conveyed by the ADF is read. In the ADF, the reading surface of the document passes through a predetermined position at a specific position. In the conventional image reading apparatus having such an ADF, when reading the reading surface of the document conveyed by the ADF, the line is placed at a position where the reading surface of the document becomes the focal point of the line sensor at the specific position as described above. The scanning position of the sensor is set to be fixed.

  Further, in an image reading apparatus (color image reading apparatus) that reads an image of an original in color, conventionally, as a color CCD sensor, a red line sensor that outputs a red (red) component (R signal) and a green (green) A three-line CCD sensor comprising three CCD line sensors, a green line sensor that outputs a component (G signal) and a blue line sensor that outputs a blue component (B signal), is used. In such a three-line CCD sensor, when a monochrome image is read, a monochrome image is generated based on signals (RGB signals) output from the three CCD sensors.

  In other words, the conventional image reading apparatus as described above reads an image using the same line sensor regardless of whether it is in the color reading mode or the monochrome reading mode. For this reason, in the conventional 3-line CCD sensor image reading apparatus having an ADF, when the image is read using the ADF, the scanning position of each line sensor is optimal in both the color reading mode and the monochrome reading mode. The reading positions that become are the same positions.

However, in recent years, a line sensor in which a monochrome line sensor for reading a monochrome image is arranged in addition to the color line sensor as described above has been put into practical use. As such a line sensor, for example, there is a 4-line CCD sensor having a configuration in which a color 3-line CCD sensor and a monochrome line sensor are arranged in parallel. When such a 4-line CCD sensor comprising a color line sensor and a monochrome line sensor is fixed at a specific position, the scanning position by the color line sensor and the scanning position by the monochrome line sensor are different. . That is, in an image reading apparatus equipped with line sensors each having a color line sensor and a monochrome line sensor, one fixed reading is performed regardless of whether the reading is in the color reading mode or the monochrome reading mode. When the reading surface of the document conveyed by the ADF at the position is read, there is a problem in that the read image may be deteriorated due to a large focus shift in each line sensor due to a difference in scanning position between the line sensors. is there.
Japanese Patent Application No. 2002-314755

  The present invention solves the above-described problems, and reads an image of a document conveyed by a conveying unit using line sensors each having a color line sensor and a monochrome line sensor. Even if it exists, it aims at providing the image reading apparatus which can acquire a high quality image, without a read image deteriorating.

The image reading apparatus of the present invention reads an image of a document in color or monochrome, and is placed on a document table, photoelectric conversion means comprising a color line sensor and a monochrome line sensor. A conveying means for conveying the original, a scanning means on which an optical system for guiding light from the reading surface of the original conveyed by the conveying means to each line sensor of the photoelectric conversion means is mounted, and the conveying means conveys the original. Storage means for storing a reading position for one transported document set such that the scanning position of each line sensor with respect to the in-focus position with respect to the original document surface is a position corresponding to the sensitivity of each line sensor; and the transporting means The scanning unit is stored in the storage unit regardless of whether the image of the original conveyed by the scanner is read in color or monochrome. Driving means for moving the serial reading position for conveying the original, and conveys the document placed on the document table by the conveying means, by said scanning means to move the reading position for the transport document by the drive means Control means for reading a color image or a monochrome image of the document by photoelectrically converting the light from the reading surface of the document to be guided by each line sensor of the photoelectric conversion unit.

  As described above in detail, according to the present invention, even if an image is read using a line sensor having a color line sensor and a monochrome line sensor, a high-quality read image can be provided. It is possible to provide an image reading apparatus capable of

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram showing a configuration example of a 4-line CCD sensor 1 mounted in an image reading apparatus according to an embodiment of the present invention.

  As shown in FIG. 1, the 4-line CCD sensor 1 includes a red line sensor R that photoelectrically converts a red component of incident light into an R signal indicating a red density, and a green component of incident light. A green line sensor G that photoelectrically converts a blue component of incident light into a B signal indicating a blue density, and a black and white ( It is composed of a black and white line sensor BW that photoelectrically converts a black and white component into a BW signal indicating black and white density.

  The red line sensor R is composed of a CCD line sensor with a red filter. Thereby, the red line sensor R can capture only the red component of the incident light and output the R signal.

  The green line sensor G is a CCD line sensor with a green filter. As a result, the green line sensor G can capture only the green component of the incident light and output the G signal.

  The blue line sensor B is a CCD line sensor with a blue filter. Thus, the blue line sensor B can capture only the blue component of the incident light and output the B signal.

  In the 4-line CCD sensor 1, the line sensors R, G, B, and BW are arranged in parallel at predetermined intervals. In the example shown in FIG. 1, the line sensors are arranged in the order of R, G, B, and BW. Further, the distance between the red line sensor R and the green line sensor G and the distance between the green line sensor G and the blue line sensor B are 8 lines, and the distance between the blue line sensor B and the monochrome line sensor BW. Is for 12 lines.

  That is, the red line sensor R, the green line sensor G, and the blue line sensor B as color line sensors are arranged in parallel at intervals of 8 lines, and the monochrome line sensor BW as a monochrome line sensor. Are arranged in parallel to the blue line sensor B as a color line sensor at intervals of 12 lines.

  Next, the configuration of the image reading device 2 on which the 4-line CCD sensor 1 is mounted will be described.

  FIG. 2 is a diagram showing a configuration example of the image reading apparatus 2 according to the embodiment of the present invention.

  As shown in FIG. 2, the image reading apparatus 2 includes an ADF (auto document feeder) 4. The ADF 4 conveys a plurality of documents one by one to a reading position and functions as a document press against the document placed on the document placement glass 12.

  As shown in FIG. 2, the ADF 4 has a document table 5, a transport unit 6, a document discharge table 7, and the like. The document table 5 is for placing a document. The conveying unit 6 takes out the originals on the original table 5 one by one and conveys them on the conveying path 6a. The document discharge table 7 is for discharging a document transported through the transport path 6 a by the transport unit 6. A slit portion 8 in which a contact glass 8a is disposed is provided on the image reading apparatus main body side of the conveyance path 6a.

  Further, in the main body of the image reading apparatus 2, there is a first carriage (scanning means) 18 that can move below the contact glass 8 a and the document placing glass 12 in a direction parallel to the document placing glass 12. Is provided. The first carriage 18 deflects reflected light from the document in a predetermined direction, and an exposure lamp 14 as a light source for illuminating the document on the document placement glass 12 or the document passing on the surface of the contact glass 8a. A first mirror 16 is attached.

  The first carriage 18 is reciprocated below the document placing glass 12 by a drive motor (moving means) 30 connected via a toothed belt (not shown) or the like. The drive motor 30 includes a stepping motor that is driven and controlled by a drive pulse signal from a control unit (control board) 32.

  Further, a second carriage 20 that is movable in parallel with the document placing glass 12 is disposed in the main body of the image reading apparatus 2. A second mirror 22 and a third mirror 24 that sequentially deflect the reflected light from the document D deflected by the first mirror 16 are attached to the second carriage 20 at right angles to each other. The second carriage 20 is driven by the driving motor 30 by a toothed belt or the like connected to the first carriage 18 and is driven by the first carriage 18. The first carriage 18 is moved in parallel along the document placing glass 12 at a speed of 1/2.

  An image forming lens 26 and a 4-line CCD sensor 1 are further provided in the main body of the image reading apparatus 2. The imaging lens 26 is a lens that focuses light from the third mirror 24 mounted on the second carriage 20 and makes it incident on the 4-line CCD sensor. The 4-line CCD sensor 1 is configured as shown in FIG. 1, and receives the light focused by the imaging lens 26, and each line sensor R, G, B, BW photoelectrically processes each line of pixels. The data is converted and output to the control unit 32.

  Next, a document reading operation using the ADF 4 will be schematically described.

  First, the document D set on the document table 5 is transported along the transport path 6 a by the transport unit 6 and discharged onto the document discharge table 7. When the document D passes through the slit portion 8 on the transport path 6a, the reading surface of the document D contacts the surface of the contact glass 8a.

  Further, when reading an original using the ADF 4, it is assumed that the first carriage 18 in the main body is in a position where an image on the surface of the contact glass 8a can be read. As a result, when the image on the document surface conveyed by the ADF 4 at a constant speed through the conveyance path 6 a passes through the slit portion 8, the first mirror, the second mirror, the third mirror, and the connection are formed. The image is read by the 4-line CCD sensor through an optical system such as an image lens.

  Next, the configuration of the control system of the image reading apparatus 2 will be described.

  FIG. 3 is a block diagram schematically showing the configuration of the control system of the image reading apparatus 2.

  On the control board 32 of the image reading apparatus 2, a CPU 40, a ROM 41, a RAM 42, a signal processing unit 43, a drive control unit 44, and the like are provided. The CPU 40 controls the entire image reading apparatus 2.

  The ROM 41 is a memory in which a control program and control data for performing the image reading operation are stored. For example, the ROM 41 indicates a coordinate value (X value to be described later) indicating the standby position of the first carriage 18 and a reading position of the first carriage 18 as a reading position for a document conveyed by the ADF 14. A coordinate value (A value described later) and the like are stored in advance.

  The RAM 42 is a memory that temporarily stores data. For example, the RAM 42 stores coordinate values indicating the position of the first carriage 18 when driving the first carriage 18.

  The signal processing unit 43 processes the signal from the 4-line CCD sensor 1 and outputs it to the outside. The drive control unit 44 has a motor driver that controls the drive motor 30.

  The signal processing unit 43 includes a preprocessing circuit 51, a shading correction circuit 52, an interline correction circuit 53, and an image processing circuit 54.

  The preprocessing circuit 51 performs processing such as A / D conversion for converting an analog signal from the 4-line CCD sensor 1 into a digital signal.

  The shading correction circuit 52 performs pixel unit correction based on the reading result of the shading plate 11 by the 4-line CCD sensor 1.

  The inter-line correction circuit 53 performs alignment of data from the red line sensor R, data from the green line sensor G, and data from the blue line sensor B. That is, the line sensors R, G, and B of red, green, and blue as color line sensors are arranged with their lines shifted by several pixels. For this reason, in order to generate a color image, it is necessary to match the phases of the data from the line sensors R, G, and B according to the moving speed in the sub-scanning direction.

  For example, in the configuration example shown in FIG. 1, red, green, and blue line sensors R, G, and B as color line sensors are arranged in the order of RGB in the scanning order, and the red line sensor R and the green line are arranged. The sensor G, the green line sensor G, and the blue line sensor B are arranged so as to be shifted by 8 pixels. In this case, if the zoom ratio is 25% to 400%, for the data from each line sensor R, G, B, between 2 and 32 lines between R and G, between G and B Position correction of 2 to 32 lines is required.

  Here, for example, when the blue line sensor B is used as a reference, the inter-line correction circuit 53 is 4 to 64 lines for the red line sensor R data and 2 to 32 for the green line sensor G data. Align the line. By performing such alignment, the inter-line correction circuit 53 superimposes each data of the R signal, G signal, and B signal to generate a color image without any deviation.

  The image processing circuit 54 performs image processing and outputs image data to the outside. For example, in the color reading mode, the image processing circuit 54 performs color correction on the line-corrected data and outputs it to the outside. In the monochrome reading mode, the image processing circuit 54 performs processing such as filtering on the BW signal that has passed through the inter-line correction circuit 53 and outputs the result to the outside.

  The CPU 40 is connected to an operation unit 60 to which an operation instruction from a user is input. For example, the operation unit 60 is provided with a magnification setting key for setting a reading magnification, an image selection key for selecting color or monochrome, a start instruction key for instructing reading start, and the like. For example, when the user inputs a key for instructing to start reading by specifying a reading mode for the document using the operation unit 60, the CPU 40 starts reading the document image in the specified reading mode. Yes.

  Further, the CPU 40 is connected to a switching circuit 61 and a switching circuit 62. The switching circuit 61 is a circuit for switching between the G signal from the green line sensor G and the BW signal from the monochrome line sensor BW among the signals supplied from the 4-line CCD sensor 1 to the signal processing unit 43. The switching circuit 62 is a circuit that switches between the B signal from the blue line sensor B and the BW signal from the monochrome line sensor BW among the signals supplied from the 4-line CCD sensor 1 to the signal processing unit 43.

  That is, in the color reading mode, the CPU 40 validates the G signal by the switching circuit 61 and validates the B signal by the switching circuit 62. In this case, the 4-line CCD sensor 1 supplies the signal processing unit 43 with the R signal from the red line sensor R, the G signal from the green line sensor G, and the B signal from the blue line sensor B. As a result, the color image can be read by the 4-line CCD sensor 1.

  In the monochrome reading mode, the CPU 40 validates the BW signal by the switching circuit 61 and validates the BW signal by the switching circuit 62. In this case, the 4-line CCD sensor 1 supplies the BW signal from the monochrome line sensor BW to the signal processing unit 43.

  As a result, the monochrome image can be read by the 4-line CCD sensor 1. When the monochrome image is read with the configuration shown in FIG. 3 as described above, the 4-line CCD sensor CCD1 supplies a 2-channel BW signal to the signal processing unit 43. At this time, one side supplies BW signals for even lines, and the other side supplies BW signals for odd lines.

  Next, the sensitivity characteristic of each line sensor constituting the 4-line CCD sensor will be described.

  FIG. 4 is a diagram illustrating examples of sensitivity characteristics of the red line sensor R, the green line sensor G, and the blue line sensor B with respect to incident light. FIG. 5 is a diagram illustrating an example of sensitivity characteristics of the monochrome line sensor BW with respect to incident light.

  In the example shown in FIG. 4, in the visible light range (400 to 800 nm), the red line sensor R has a maximum sensitivity of “1” with respect to incident light (red light) of about 600 to 800 nm. In contrast, the green line sensor G has a maximum sensitivity of about “0.9 to 0.95” with respect to incident light (green light) of about 500 to 600 nm, and the blue line sensor B is The maximum sensitivity is about “0.8 to 0.85” with respect to incident light (blue light) of about 400 to 500 nm.

  In other words, in the example shown in FIG. 4, when the sensitivity of the red line sensor R is “1”, the green line sensor G is “0.9 to 0.95” and the blue line sensor B is “0”. .8 to 0.85 ". That is, the sensitivity of each of the line sensors R, G, and B has a characteristic that the red line sensor R, the green line sensor G, and the blue line sensor B are weak in this order.

  The sensitivity of the monochrome line sensor BW is “2” at the maximum, as is apparent from a comparison between FIGS. 4 and 5. That is, the sensitivity of the monochrome line sensor BW is approximately twice that of the red line sensor R.

  The red line sensor R, the green line sensor G, and the blue line sensor B are each composed of a CCD line sensor covered with a red filter, a green filter, and a blue filter, and the monochrome line sensor BW is a color filter. This is because it is composed of a CCD line sensor that is not covered. That is, the sensitivity of each color line sensor R, G, and B covered with the color filter is halved compared to the monochrome line sensor BW not covered with the color filter.

  As described above, in the 4-line CCD sensor, the sensitivity of the four line sensors constituting the 4-line CCD sensor is weak in the order of the monochrome line sensor BW, the red line sensor R, the green line sensor G, and the blue line sensor B. It has the characteristic.

  The exposure lamp 14 is prepared with a fluorescent agent so that the intensity of light of each color in the emitted light is constant. For example, the durability of the fluorescent agent for generating blue light is different. It may be inferior compared with the fluorescent agent for generating the color. That is, even if the fluorescent agent is mixed so that the intensity of light of each color is constant, or the fluorescent agent is mixed according to the sensitivity of each sensor, blue light is weakened due to secular change. Tend. As a result, in the output of the 4-line CCD sensor, the output of the blue line sensor B may be lowered due to aging compared to the outputs of other line sensors.

  In view of the above situation, it is preferable that a line sensor having poor sensitivity among a plurality of line sensors performs reading under better conditions than other line sensors. That is, the quality of the entire read image can be improved by making the line sensor with low sensitivity perform reading under the optimum conditions as much as possible.

  Moreover, it is preferable that the line sensor that reads light of a color that tends to be weakened due to secular change is also read under better conditions than other line sensors. In other words, it is possible to obtain a scanned image with little deterioration due to aging by making the line sensor that reads light of a color whose intensity tends to decrease with aging change under the most optimal conditions. It becomes.

  Next, the focal position of the 4-line CCD sensor with respect to the original reading surface will be described.

  FIG. 6 is a diagram illustrating the focal position of the line sensor at the first scanning position A and the focal position at the second scanning position B that is separated from the first scanning position by a distance a in the sub-scanning direction.

  In the ADF 4, the reading surface of the document D conveyed through the conveyance path 6 a comes into contact with the surface of the contact glass 8 a at the slit portion 8. It is assumed that the reading surface of the document D and the surface of the contact glass 8a are in contact at approximately one point (one line in the main scanning direction) with respect to the document transport direction. In the present embodiment, a description will be given assuming that the contact point (one line in the main scanning direction in contact) S between the reading surface of document D and the surface of contact glass 8a is constant.

  In the example shown in FIG. 6, at the second scanning position B, the reading surface of the document D is in contact with the surface of the contact glass 8a. At the first scanning position A, which is separated from the second scanning position B by a distance a, the contact glass 8a surface and the reading surface of the document D are separated by a distance b due to the curvature of the reading surface of the document D. ing.

  That is, the distance to the reading surface of the document at the first scanning position A is longer than the distance to the reading surface of the document at the second scanning position B by a distance b. Therefore, if the focal depth of the line sensor whose focal position is on the surface of the contact glass 8a is shallower than the distance b, the image read at the first scanning position A by the line sensor is out of focus.

  In the ADF 4, the document D is conveyed so that the reading surface of the document D is convex with respect to the surface of the contact glass 8 a, and the reading surface of the document D contacts the surface of the contact glass 8 a at the contact point S. It is like that. Therefore, in order to obtain a good image in the document reading process using the ADF 4, the contact is made so that the distance to the reading surface of the document D is within the focal depth of all the line sensors. It is necessary to perform reading scanning while fixing the scanning position of each line sensor in the vicinity of the contact point S where the surface of the glass 8a and the reading surface of the document D come into contact.

  Next, the relationship between the scanning positions of the line sensors R, G, B, and BW and the reading surface of the document D when passing through the slit portion 8 will be described.

  In the following description, the scanning position of the red line sensor R is Rs, the scanning position of the green line sensor G is Gs, the scanning position of the blue line sensor B is Bs, and the scanning position of the monochrome line sensor BW is BWs. To do. The focus of each line sensor is set on the contact surface, and the position of the contact point S where the focus position is optimal (the position where the document reading surface is in contact with the contact surface) is referred to as the in-focus position. .

  7, 8, and 9 show examples of the relationship between the scanning positions Rs, Gs, Bs, and BWs of the line sensors R, G, B, and BW constituting the 4-line CCD sensor and the reading surface of the document D. Is.

  FIG. 7 is a diagram illustrating the relationship between the scanning positions Rs, Gs, Bs, and BWs of the line sensors R, G, B, and BW and the depth of focus when the green line sensor G is set to the in-focus position.

  In the example shown in FIG. 7, the scanning position Gs as the central position of the scanning positions Rs, Gs, and Bs of the color line sensors R, G, and B is the in-focus position (contact point S). . In this case, as shown in FIG. 7, the depth of focus required by the red line sensor R and the blue line sensor B is F11 at the scanning position Rs and the scanning position Bs with respect to the scanning position Gs as the in-focus position.

  In the 4-line CCD sensor having the configuration shown in FIG. 1, the depth of focus F11 is a distance of 8 lines with respect to the curvature of the reading surface of the document, and the three line sensors R, G, For B, the depth of focus is the shallowest. For this reason, when the original image is read in color (when the original image is read using the line sensors R, G, and B), the depth of focus of the color line sensors R, G, and B is F11 or more. A good image can be read.

  However, as shown in FIG. 7, at the scanning position BWs, the depth of focus required by the monochrome line sensor BW is F12. The depth of focus F12 is deeper than the depth of focus F11, and is a distance corresponding to 20 lines with respect to the curvature of the document in the 4-line CCD sensor configured as shown in FIG.

  Therefore, when a monochrome image is read (when an image of a document is read by the monochrome line sensor BW), a good image can be read if the focal depth of the monochrome line sensor BW is F12 or more. However, as described above, since the depth of focus F12 is deep, it can be said that the position shown in FIG. 7 is an unfavorable scanning position for reading an image of a document by the monochrome line sensor BW.

  FIG. 8 shows the relationship between the scanning positions Rs, Gs, Bs, and BWs of the line sensors R, G, B, and BW and the depth of focus when the scanning position BWs of the monochrome line sensor BW is adjusted to the in-focus position. FIG.

  In the example shown in FIG. 8, the scanning position BWs of the monochrome line sensor BW is the in-focus position (contact point S). In this case, in the monochrome line sensor BW, the reading surface of the document coincides with the focal position. Therefore, when an original image is read in monochrome (when an original image is read using the monochrome line sensor BW), a good image can be read even when the focus depth of the monochrome line sensor BW is zero. It becomes possible.

  However, as shown in FIG. 8, the depth of focus increases in the order of Rs, Gs, and Bs for the scanning positions Rs, Gs, and Bs of the color line sensors R, G, and B. For example, at the scanning position Rs where the deepest depth of focus is required, the depth of focus is required to be F2 or more. In this case, unless the depth of focus of the red line sensor R is set to F2 or more, the red line sensor R cannot read a good image (red component image data). Similarly, for the green line sensor G and the blue line sensor B, the depth of focus according to the scanning positions Gs and Bs must be set. For this reason, it can be said that the scanning position shown in FIG. 8 is a disadvantageous scanning position for reading an image of an original in color by the color line sensors R, G, and B.

  FIG. 9 is a diagram showing focal positions at the respective scanning positions Rs, Gs, Bs, and BWs when the scanning position Bs is matched with the in-focus position (contact point S).

  In the example shown in FIG. 9, the scanning position Bs that is substantially the center of the scanning positions Rs, Gs, Bs, and BWs of the four line sensors is the in-focus position. In the example shown in FIG. 9, the scanning positions Rs, Gs, and BWs are displaced from the optimum focal position in the order of Gs, BWs, and Rs with respect to the scanning position Bs. In other words, the focus shift becomes larger as the scanning position is farther from the in-focus position. For example, in the example shown in FIG. 9, at the scanning position Rs of the red line sensor R where the scanning position is farthest from the in-focus position, a depth of focus F3 or more is required to read normal data.

  However, the focal depth F3 shown in FIG. 9 is smaller than the above-described focal depths F11 and F2, and is easily set as the focal depth allowed by the line sensor. On the other hand, considering the aspect of drive control of the first carriage 18, when reading an image using the ADF 4, it is preferable to execute reading at the same position regardless of color or monochrome. In this case, in an image reading apparatus using a 4-line CCD sensor, it is necessary to set a position where both color and monochrome can be read with good image quality as a reading position of an original image using ADF4.

  Hereinafter, setting of a reading position for a document conveyed by an ADF in an image reading apparatus using a line sensor having a monochrome line sensor and a color line sensor as described above will be described.

  First, in an image reading apparatus using a line sensor having a monochrome line sensor and a color line sensor, in order to reduce the depth of focus of all the line sensors at one fixed position, the center of all the line sensors is used. It is preferable to set the position to be the in-focus position. However, as shown in FIGS. 4 and 5, each line sensor has different sensitivity characteristics and the center position of the line sensor is not necessarily the optimum position.

  Therefore, in this embodiment, the optimum reading position is set based on the sensitivity characteristics of each line sensor, the arrangement of each line sensor, and the focal depth of each line sensor. In other words, as described above, when considering the sensitivity of each line sensor, it is possible to realize reading with better image quality by reducing the distance to the reading surface as much as possible for the line sensor having low sensitivity, and the sensitivity is high. As for the line sensor, if it is within the depth of focus, even when the distance to the reading surface is longer than that of other line sensors, it is possible to realize reading with good image quality.

  For example, when each line sensor constituting the 4-line CCD sensor has sensitivity characteristics as shown in FIGS. 4 and 5, as shown in FIG. 9, each line sensor has the weakest sensitivity of the blue line sensor. By setting the scanning position Bs to be the in-focus position, it is possible to set the reading position corresponding to the sensitivity characteristic of each line sensor.

  The example shown in FIG. 9 shows an example of the setting position when the 4-line CCD sensor shown in FIG. 1 has the sensitivity characteristics shown in FIGS. 4 and 5, for example, a blue line sensor and a green line sensor. The in-focus position may be set between When the arrangement of the line sensors in the 4-line CCD sensor is different, an optimum reading position is set based on the arrangement of the line sensors and the sensitivity characteristics of the line sensors.

  Further, if the light emission characteristics of the exposure lamp 14 have the characteristics described above, the reading position may be set in consideration of the characteristics. For example, when the light emitted from the exposure lamp 14 has a characteristic that the light of a specific color deteriorates (weakens) due to aging, that is, the light of a specific color weakens due to aging. In this case, the scanning position of the line sensor that detects light of a weak color is set to a position close to the in-focus position. Thereby, even if the light of a specific color becomes weak due to secular change, there is an effect that it is possible to realize reading with good image quality.

  As described above, in this embodiment, the optimum reading position based on the depth of focus, the arrangement, the sensitivity characteristics, the light emission characteristics of the exposure lamp, etc. of each line sensor is set as one fixed reading position. It is. As a result, it is possible to set one reading position where a document image can be read with good image quality for both monochrome images and color images, and for documents conveyed by ADF regardless of whether they are monochrome or color. Thus, reading can be performed at one reading position, and control of the carriage and the like can be simplified.

  For example, as in the above-described example, when the sensitivity of the blue line sensor is weak and the blue light tends to be weak due to secular change, the scanning position of the blue line sensor is set to be the in-focus position. Accordingly, the carriage drive control can be facilitated by setting a fixed reading position, and a document image can be read with good image quality regardless of whether it is monochrome or color. In addition, it is possible to realize reading of a document image with good image quality for a long time.

  Next, a document image reading operation using the ADF 4 will be described.

  FIG. 10 is a flowchart for explaining an operation of reading an image of a document set on the ADF 4.

  First, the user places a document on the document table 5 of the ADF 4 and instructs the operation unit 60 to start reading a document image. At this time, the user selects, as the document reading mode, whether the image of the document is read in color or monochrome. When the user gives an instruction to start reading, the operation unit 60 supplies information indicating the reading mode of the document together with a reading start request signal for requesting the CPU 40 to start reading.

  The CPU 40 that has received the reading start request from the operation unit 60 checks whether or not the first carriage 18 is in the standby position. When it is confirmed that the first carriage 18 is at the standby position, the CPU 40 sets the initialized coordinates indicating the position of the first carriage 18 in the RAM 42 (step S11), and waits as a value indicating the coordinates. A coordinate value X of the position is set (step S12). If the coordinate of the first carriage 18 is X, the CPU 40 selects whether the document reading mode is the color reading mode or the monochrome reading mode based on the information indicating the reading mode from the operation unit 60 (step S13). ).

  As a result, when the color reading mode is selected as the original reading mode (step S13), the CPU 40 starts moving the first carriage 18 at the standby position (step S14). Is read by the line sensors (red line sensor R, green line sensor G, and blue line sensor B) and shading correction is performed on the output signals (R signal, G signal, and B signal) from each line sensor R, G, B. This is performed (step S15).

  When the first carriage 18 that has read the white reference plate reaches a predetermined reading position, that is, the coordinates indicating the position of the first carriage 18 are coordinates of the predetermined reading position (X + A: A is predetermined from the standby position). The CPU 40 stops the first carriage 18 (step S16).

  As described above, the predetermined reading position is a position set in advance based on the sensitivity of each line sensor, the arrangement of each line sensor, the focal depth of each line sensor, and the like. This is the position where the sensor is positioned as shown in FIG. The coordinate A indicating the distance from the standby position to the predetermined reading position is stored in advance in the ROM 41 or the like. For example, as shown in FIG. 9, the scanning position Bs of the blue line sensor B is Pre-stored in the ROM 41 as coordinates for the contact point S.

  When the first carriage 18 stops, the CPU 40 starts taking in the R, G, and B signals from the color line sensors R, G, and B (step S17). At this time, the CPU 40 requests the ADF 4 to start document conveyance. In response to the transport start request, the ADF 4 starts transporting the document on the document table 5 by the transport unit 6 (step S18). As a result, the color line sensors R, G, and B read the color image of the image on the reading surface of the document D conveyed on the conveyance path 6a.

  Similarly, when the monochrome reading mode is selected as the original reading mode (step S13), the CPU 40 starts moving the first carriage at the standby position (step S14), and monochrome images of a white reference plate (not shown) are displayed. The shading correction is performed on the output signal (BW signal) from the monochrome line sensor BW after being read by the line sensor (monochrome line sensor BW) (step S15).

  When the first carriage 18 that has read the white reference plate reaches a predetermined reading position, that is, when the coordinates indicating the position of the first carriage 18 become the coordinates (X + A) of the predetermined reading position, The CPU 40 stops the first carriage 18 (step S16). The predetermined reading position is the same position as in the color reading mode, and is the position where the 4-line CCD sensor is positioned as shown in FIG.

  When the first carriage 18 stops, the CPU 40 starts taking in the BW signal from the monochrome line sensor BW as the monochrome line sensor (step S17). At this time, the CPU 40 requests the ADF 4 to start document conveyance. In response to the transport start request, the ADF 4 starts transporting the document on the document table 5 by the transport unit 6 (step S18). Thereby, the monochrome line sensor BW reads an image on the reading surface of the document D conveyed on the conveyance path 6a as a monochrome image.

  The color image or the monochrome image as described above is read until the document on the document table 5 runs out. That is, when there are no more documents on the document table 5 of the ADF 4, the CPU 40 determines the end of reading the document image (step S19). When it is determined that the reading of the document image has been completed, the CPU 40 starts moving the first carriage 18 to the standby position (step S20). When the first carriage 18 moves to the standby position, that is, when the coordinate indicating the position of the first carriage 18 becomes X, the CPU 40 ends the movement of the first carriage 18 and performs color reading mode. The image reading operation by is terminated (step S21).

  As described above, a predetermined reading position is set in accordance with the sensitivity characteristics, depth of focus or arrangement of each line sensor constituting the 4-line CCD sensor, and even in the color reading mode, the monochrome reading mode is set. Also, the first carriage is moved to a predetermined reading position, and the image of the original conveyed by the ADF at the predetermined reading position is read by a color line sensor or a monochrome line sensor.

  As a result, the original can be read at a predetermined reading position in both the color reading mode and the monochrome reading mode, and the image quality of the read image is not deteriorated, and a high-quality read image can be provided.

1 is a diagram showing a configuration of a 4-line CCD sensor mounted on an image reading apparatus according to an embodiment of the present invention. 1 is a diagram showing a schematic configuration of an image reading apparatus according to an embodiment of the present invention. FIG. 3 is a block diagram illustrating a configuration example of a control system of the image reading apparatus. The figure which shows the characteristic of the sensitivity of a red, green, blue line sensor. The figure which shows the characteristic of the sensitivity of a monochrome line sensor. The figure for demonstrating the change of the focal depth with respect to the change of a scanning position. The figure which shows the example of a relationship between a scanning position and a focal depth. The figure which shows the example of a relationship between a scanning position and a focal depth. The figure which shows the example of a relationship between a scanning position and a focal depth. 6 is a flowchart for explaining the operation of an image of a document using ADF.

Explanation of symbols

  R ... Red line sensor, G ... Green line sensor, B ... Blue line sensor, BW ... Monochrome line sensor, 1 ... 4-line CCD sensor (photoelectric conversion means), 2 ... Image reading device, 4 ... ADF, 5 ... Document base , 6 ... Conveying section (conveying means), 8 ... Slit, 8a ... Contact glass, 16 ... First mirror, 18 ... First carriage (scanning means), 20 ... Second carriage, 22 ... Second mirror , 24 ... third mirror, 30 ... drive motor (drive means), 32 ... control unit, 40 ... CPU (control means), 43 ... signal processing unit, 44 ... drive control unit

Claims (5)

An image reading apparatus that reads an image of a document in color or monochrome,
Photoelectric conversion means comprising a color line sensor and a monochrome line sensor;
Conveying means for conveying the document placed on the document table;
A scanning unit equipped with an optical system that guides light from the reading surface of the document conveyed by the conveying unit to each line sensor of the photoelectric conversion unit;
A memory for storing a reading position for one transported document set such that the scanning position of each line sensor with respect to the focal position with respect to the document surface transported by the transporting unit is a position corresponding to the sensitivity of each line sensor. Means,
The scanning unit is moved to the reading position for the transported document stored in the storage unit regardless of whether the image of the document transported by the transport unit is read in color or monochrome . Driving means;
The photoelectric conversion means converts the light from the reading surface of the original guided by the scanning means, which transports the original placed on the original table by the conveying means and moves to the reading position for the conveyed original by the driving means. Control means for reading a color image or a monochrome image of a document by performing photoelectric conversion with each of the line sensors;
An image reading apparatus comprising: The storage means has a scanning position of a line sensor having the weakest sensitivity among a plurality of line sensors within a range in which all line sensors are within a depth of focus with respect to a reading surface of a document conveyed by the conveying means. The image reading apparatus according to claim 1, wherein a reading position for a transported document set so as to be close to a focal position is stored . The storage means is further set so that the scanning positions of line sensors other than the weakest line sensor among the plurality of line sensors are positioned away from the in-focus position in order of decreasing sensitivity of each line sensor. The image reading apparatus according to claim 2, wherein a reading position for one transported document is stored . The photoelectric conversion means is composed of a monochrome line sensor having the strongest sensitivity and a color line sensor composed of three color line sensors having different sensitivities, and with respect to the document conveyance direction by the conveyance means. Each scanning position is arranged in the order of the monochrome line sensor, the third color line sensor, the second color line sensor, and the first color line sensor,
The storage means is such that the scanning position of the color line sensor having the weakest sensitivity among the color line sensors with respect to the reading surface of the document conveyed by the conveying means is closest to the in-focus position, and has the highest sensitivity. A scanning position of a color line sensor other than the weak color line sensor is stored as one reading position for a transported document set so as to be positioned away from the in-focus position in order of decreasing sensitivity;
The image reading apparatus according to claim 1, wherein: The first color line sensor is a red line sensor that photoelectrically converts a red component of incident light, and the second color line sensor is a green line sensor that photoelectrically converts a green component of incident light. The color line sensor 3 is a blue line sensor that photoelectrically converts a blue component of incident light, and the sensitivity decreases in the order of the red line sensor, the green line sensor, and the blue line sensor.
The storage means has a scanning position of the blue line sensor that is the least sensitive to the reading surface of the document conveyed by the conveying means, and is located closest to the in-focus position, and next to the blue line sensor. Storing a reading position for one transported document set so that the green line sensor with low sensitivity is positioned next to the in-focus position next to the blue line sensor;
The image reading apparatus according to claim 4, wherein:

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