JP2015201765A - Image reading device, control method and program, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image reading device that prevents a reduction in quality of read images.SOLUTION: An image reading device optically reads a white reference board provided on a document platen on which a document image is placed to require a gain correction value for outputting a read signal with predetermined image quality. The image reading device acquires the amount of light emission of a light source according to the position on the document platen on the basis of the acquired gain correction value, and reads the document image on the document platen with the acquired amount of light emission.

Description

  The present invention relates to an image reading apparatus that optically reads a document image, a control method and program, and an image forming apparatus.

  Conventionally, an image reading apparatus for reading a document image has been used as part of an image scanner and a copying machine. An image signal read by a CCD image sensor or a contact image sensor used in an image reading apparatus generally includes output distortion called shading. The causes of this output distortion are the non-uniformity of the light quantity distribution of the light source, the lens characteristics, the reduction of the peripheral light quantity corresponding to the angle of view, the non-uniformity due to the variation in the transmitted light quantity of the optical system, the sensitivity variation of the sensor itself, the CCD image A decrease in output with respect to the end of one scanning line due to the transfer efficiency of the sensor can be mentioned.

  In order to remove such output distortion, a shading correction technique (ac in FIG. 13) is known in which a reference plane is read in advance and distortion of an output image signal of an image sensor is corrected using the read value. The reference surface is a uniform white reference plate. Prior to reading the document, the sensor (image sensor or line sensor) reads the uniform white reference plate and uses the read value to increase the gain correction value. By reading the entire image, shading correction is performed to correct distortion of the output image signal of the image sensor (Patent Document 1).

JP 10-31769 A

  The white reference plate is often arranged on the document abutting portion side on the document table, and the glass support on the white reference plate side is weak in structure. Therefore, when a strong pressure is applied to the platen glass surface when reading a book document, the document glass on the white reference plate 101 side on the document abutment unit 104 side is distorted and attached to the back surface of the document glass as shown in FIG. The attached white reference plate is also distorted (FIG. 14A). As a result, the uniformity of the output image signal when reading the original placed on the original glass surface is lost, the light incident on the CCD image sensor or the contact image sensor is reduced, and the reading value of the white reference plate is reduced. Decrease. As a result, the white level of the read image is lowered.

  Further, the distortion amount gradually decreases from the white reference plate 101 on the document abutting portion 104 side toward the glass edge on the opposite side to the document abutting portion 104, and the document abutting position is as shown in FIG. There is a case where there is no distortion at the glass end opposite to the contact portion. As described above, when the platen glass is distorted, a difference is generated between a portion where the distortion is large and a portion where the distortion is small on the document glass surface. Since the white reference plate is often arranged on the document abutting portion side, the read value of the white reference plate becomes a read value of a portion with a large distortion. If the gain correction value at a position where the distortion is large is used as the gain correction value for the entire image, the gain correction value becomes larger than necessary at a position where the distortion of the platen glass is small, which causes image deterioration. .

  An object of the present invention is to solve such conventional problems. In view of the above, it is an object of the present invention to provide an image reading apparatus, a control method and a program, and an image forming apparatus that prevent deterioration in quality of a read image.

  In order to solve the above problems, an image reading apparatus according to the present invention irradiates a document image on a document table from a light source, reads reflected light from the document image, and outputs a read signal; A determination unit that determines whether a value read by the reading unit is within a predetermined range, and a determination unit that determines that the value is not within the predetermined range; And a light emission amount control unit that changes a light emission amount of the light source in accordance with a reading position of the reading unit in the sub-scanning direction on the document table.

  According to the present invention, it is possible to prevent deterioration in quality of a read image.

1 is a block diagram illustrating an overall configuration of an image forming apparatus. 1 is a diagram illustrating a schematic configuration of an image reading apparatus. 2 is a block diagram illustrating a configuration of an image processing system of the image reading apparatus. FIG. It is the figure which looked at the platen glass of a 1st embodiment from the top. It is the figure which looked at the platen glass of 2nd Embodiment from the top. It is a figure which shows a mode when the press of a platen glass is weak. It is a figure which shows a mode when the press of a platen glass is strong. It is a figure which shows a response | compatibility with the pixel value of a subscanning direction, and a gain correction value. It is a figure which shows the procedure of the control processing of an image reading apparatus. It is another figure which shows the procedure of the control processing of an image reading apparatus. It is a figure explaining the case where the press of the platen glass surface is strong. It is a block diagram which shows the structure for controlling the light-emission quantity. It is a figure explaining the conventional shading correction technique. The figure which shows a mode when the press of a platen glass is strong.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments do not limit the present invention according to the claims, and all combinations of features described in the embodiments are not necessarily essential to the solution means of the present invention. . The same constituent elements are denoted by the same reference numerals, and the description thereof is omitted.

[First Embodiment]
FIG. 1 is a block diagram showing the overall configuration of an image forming apparatus according to an embodiment of the present invention. As shown in FIG. 1, the image forming apparatus 100 includes an image reading device (image input device) 200, a printer unit 300, and a control device 110. The image reading apparatus 200 optically reads a document image and generates image data. The image reading apparatus 200 includes an image reading unit 210 for reading a document and an automatic document supply unit (ADF) 250 for conveying the document.

  A printer unit (image output device) 300 conveys a recording sheet (recording medium) as a sheet to an image forming position, prints image data as a visible image on the recording sheet, and discharges the recording paper outside the apparatus. The printer unit 300 includes a paper feed unit 360 having a plurality of types of recording paper cassettes, a marking unit 320 for transferring and fixing image data onto the recording paper, and a paper for discharging the printed recording paper out of the apparatus. A paper discharge unit 330 and a finisher 500 are included. The finisher 500 executes, for example, the stapling process and the sorting process on the printed recording paper, but may not be provided in the present embodiment.

  The control device 110 can control the image reading device 200 and the printer unit 300. The control device 110 is connected to external host computers (PCs) 701 and 702 via a network (hereinafter referred to as LAN) 700 so as to be able to communicate with each other. The control device 110 has a built-in modem (not shown) connected to the FAX line 128.

  When executing the copying function of the image forming apparatus 100, the control device 110 controls the image reading device 200 to read a document and generate image data, and controls the printer unit 300 to print the image data on recording paper. To do. Further, when executing the scan function of the image forming apparatus 100, the control apparatus 110 converts the image data generated by reading the document into code data, and transmits the image data to the host computers 701 and 702 via the LAN 700. The apparatus 200 is controlled. When executing the print function of the image forming apparatus 100, the control device 110 converts the code data received from the host computer 701 or 702 via the LAN 700 into image data and prints the printer unit 300 so as to print on the recording paper. It is also possible to control. The control device 110 is also connected to the operation unit 150. The operation unit 150 includes a display unit such as a liquid crystal touch panel, for example, and can receive an instruction to execute each function of the image forming apparatus 100 from the user.

  Next, the image reading unit 210 of the image reading apparatus 200 in FIG. 1 will be described with reference to FIG. FIG. 2 is a diagram illustrating a schematic configuration of the image reading apparatus 200. The image reading unit 210 includes an illumination member 210a as a light source for illuminating a document, an optical system 210d composed of a plurality of mirrors 210b and an imaging lens 210c, and a line sensor 210e. The reflected light emitted from the illumination member 210a and reflected by the document is imaged on the line sensor 210e via the optical system 210d, whereby the image signal of the document is photoelectrically converted.

  FIG. 3 is a block diagram illustrating a configuration of an image processing system of the image reading apparatus 200. The light source 201 is a light source such as an LED, and is the illumination member 210a in FIG. The sensor 202 is a CCD line sensor, for example. The amplifier 203 is a gain control amplifier whose gain can be controlled from the outside, and the A / D converter 204 converts an analog output from the gain control amplifier 203 into a digital signal. A shading correction unit 208 performs shading correction on the output data from the A / D converter 204. The CPU 205 comprehensively controls the entire image reading apparatus 200 via the system bus. The storage unit 206 stores a gain correction value in an initial state where the pressure applied to the platen glass 102 is weak (or not applied). The light emission amount correction calculation unit 207 controls the light emission amount of the light source 201 according to a command from the CPU 205. The image processing unit 209 performs various types of image processing such as smoothing processing on the image signal that has been subjected to the shading correction by the shading correction unit 208, and outputs it to the subsequent stage.

  Next, the image reading apparatus 200 of the present embodiment will be described with reference to FIG. FIG. 4 is a view of the platen glass of the image reading apparatus 200 as viewed from above. The first white reference plate 101 serves as a white reference for performing shading correction for correcting distortion of the output image signal, and is affixed to the platen glass 102. The flow reading glass 103 is a glass for a document fed from an automatic document feeding unit (ADF) 250. The document abutting unit 104 serves as a reference for setting the document on the document table glass 102 and is provided on the flow reading glass side of the document table glass 102. Hereinafter, the longitudinal direction of the first white reference plate 101 (the sensor arrangement direction of the line sensors described later) is the main scanning direction, and the direction orthogonal to the main scanning direction is the sub-scanning direction. When reading a document placed on the platen glass 102, the image is read while moving the image reading unit 210 in FIG. 2 in the sub-scanning direction. Further, the position in the sub-scanning direction is represented by the number of pixels with the position of the first white reference plate 101 as a reference.

  In general, as shown in FIGS. 6 and 7, the glass is bent by the pressure applied to the platen glass 102. FIG. 6 is a diagram showing a state where the pressure on the platen glass 102 is weak, and shows a state in which no bending occurs. FIG. 7 is a view showing a state where the original platen glass 102 is strongly pressed, and shows a state where the first white reference plate 101 is bent. The difference as shown in FIG. 6 and FIG. 7 is generally due to the structural feature that the glass support on the side of the first white reference plate 101 is weaker than the other three sides. .

  Next, the control operation of the image reading apparatus 200 in the present embodiment will be described with reference to FIGS. 1, 3, 4, and 8 according to the flowchart of the CPU 205 shown in FIG. Here, FIG. 8 is a diagram illustrating the correspondence between the pixel value in the sub-scanning direction and the gain correction value. First, the light source 201 irradiates the first white reference plate 101 with light, and the sensor 202 receives the reflected light and outputs an image signal from the received reflected light. At this time, the image signal output from the sensor 202 is amplified by the gain control amplifier 203 whose gain value is set to 1 time, converted into a digital signal by the A / D converter 204, and stored in the storage unit 206. .

  Then, the CPU 205 corrects the gain value set in the gain control amplifier 203 with a gain correction value that sets the output value of the gain control amplifier 203 to a predetermined output value (luminance or the like). Therefore, the image signal output from the sensor 202 thereafter is amplified with the gain value corrected with the gain correction value by the gain control amplifier 203 and converted into a digital signal by the A / D converter 204. The CPU 205 stores the gain correction value in the storage unit 206 (S1001).

  The CPU 205 calculates the difference between the gain correction value obtained from the first white reference plate 101 in S1001 and the reference gain correction value stored in advance in the storage unit 206 (S1002). Here, the reference gain correction value is such that the output value of the gain control amplifier 203 is set to a predetermined output value when the pressure applied to the platen glass 102 is weak (or not applied) as shown in FIG. This is a correct gain correction value.

  The CPU 205 determines whether or not the calculated difference is greater than or equal to a predetermined value (S1003). The predetermined value used in S1003 is a value that does not affect the image even if a uniform amount of light emission is used for all pixels in the sub-scanning direction if it is equal to or smaller than the predetermined value, and if it is equal to or larger than the predetermined value, it is a uniform gain. A value that affects the image when the correction value is used.

  If it is determined in S1003 that the difference is greater than or equal to a predetermined value, the CPU 205 acquires the light emission amount of the light source 201 from the difference from the reference gain correction value calculated in S1002 (S1004). In the present embodiment, the CPU 205 acquires the light emission amount (first light emission amount) of the light source 201 from the correspondence between the gain correction value difference and the light emission amount as shown in FIG.

  The correspondence relationship in FIG. 8 is a relationship in which the light emission amount increases as the difference in gain correction value increases. Here, the gain correction value stored in the storage unit 206 in S1001 is a gain correction value corresponding to the central image signal in the main scanning direction. For this reason, the light emission amount (first light emission amount) of the light source 201 obtained by obtaining the difference from the reference gain correction value is the light emission amount corresponding to the central image signal in the main scanning direction. Therefore, as the light emission amount of the light source 201, the light emission amount corresponding to the center image signal is used in the entire main scanning direction.

  When the pressure on the platen glass 102 is strong as shown in FIG. 7, the bending of the white reference plate 101 at the center in the longitudinal direction becomes remarkable. In this case, the amount of light received by the sensor 202 is smaller than that when the pressure is weak (or not applied) as shown in FIG. Therefore, a gain correction value that sets the output value of the gain control amplifier 203 to a predetermined output value is larger than when the pressure is weak (or not applied). In the present embodiment, the degree of bending due to pressing as shown in FIGS. 6 and 7 is determined based on whether or not the difference between the gain correction value and the reference gain correction value is equal to or greater than a predetermined value.

  The light emission amount correction calculation unit 207 corrects the light emission amount of the light source 201 so as to be the light emission amount acquired in S1004 (S1005). The light emission amount at this time is defined as a first light emission amount. When the pressure on the platen glass 102 is strong, the amount of light received by the sensor 202 becomes small. Therefore, it is necessary to increase the light emission amount of the light source 201 in order to obtain an image with a predetermined image quality. Therefore, the stronger the pressure on the platen glass 102, the higher the first light emission amount.

  Here, correction of the light emission amount of the light source 201 will be described with reference to FIG.

  FIG. 12 is a block diagram showing a configuration for controlling the light emission amount of the light source (LED) 201. The image reading unit 210 includes a sensor 202, an A / D converter 204, an LED 201, and an LED driver 1203. Here, the LED 201 indicates a light source. The LED driver 1203 drives the LED 201 by PWM control. The CPU 205 includes a gain correction value comparison control unit 1201 and a light emission amount setting control unit 1202.

  The gain correction value comparison control unit 1201 is a block that performs the processing of S1003, and the gain correction value obtained based on the digital signal output from the sensor 202 via the gain control amplifier 203 and the A / D converter 204 and It is determined whether or not the difference from the reference gain correction value is greater than or equal to a predetermined value. When the determination result from the gain correction value comparison control unit 1201 is equal to or greater than a predetermined value, the light emission amount setting control unit 1202 acquires the light emission amount corresponding to the difference from the correspondence relationship illustrated in FIG. The light emission amount setting control unit 1202 sets the duty ratio of PWM control for setting the acquired light emission amount in the LED driver 1203.

  The gain control amplifier 203 amplifies the image signal output from the sensor 201 with the first light emission amount by the reference gain correction value, and the shading correction unit 208 converts the image signal converted into a digital signal by the A / D converter 204. Then, shading correction is performed (S1006). The CPU 205 acquires the light emission amount for each position in the sub-scanning direction, and performs image reading in the sub-scanning direction while correcting the light emission amount of the light source 201. (S1007) The light emission amount acquisition method for each position in the sub-scanning direction will be described later. Thereafter, the image processing unit 209 performs image processing on the image data generated for each pixel position (S1008).

  As a method for acquiring the light emission amount in the sub-scanning direction performed in S1007, the CPU 205 determines, for example, the light source 201 for each pixel position in the sub-scanning direction from the correspondence between the number of pixels in the sub-scanning direction and the light emission amount as shown in FIG. Get the amount of luminescence. The point a in FIG. 9 changes in a direction increasing in the vertical axis direction in FIG. 9 as the pressure applied to the platen glass is stronger (the distortion of the first white reference plate 101 is larger). In the present embodiment, as shown in FIG. 9, the interval between the first light emission amount (point a in FIG. 9) and a predetermined reference light emission amount (point b in FIG. 9) is the sub-scanning direction. It is determined to change linearly. However, the CPU 205 may non-linearly determine between the first light emission amount and a predetermined reference light emission amount according to the structural characteristics with respect to the weight of the document table glass 102.

  As described above, the deflection in the longitudinal center of the white reference plate 101 is due to the structural feature that the glass support on the side on the first white reference plate 101 side is weaker than the other three sides. Accordingly, the further away from the white reference plate 101 in the sub-scanning direction, the smaller the amount of bending that occurs at the longitudinal center of the white reference plate 101. That is, in S1007, the light emission amount of the light source 201 is decreased as the distance from the white reference plate 101 in the sub-scanning direction is increased. In this case, the light emission amount is changed, but the reference gain correction value is uniformly used in the sub-scanning direction as the gain correction value of the gain control amplifier 203.

  If it is determined in S1003 that the difference is not greater than or equal to the predetermined value, the gain control amplifier 203 amplifies the image signal output from the sensor 202 with the above-described gain correction value with a predetermined reference light emission amount. The shading correction processing unit 209 performs shading correction on the image signal converted into a digital signal by the A / D converter 204 (S1009). The CPU 205 reads an image with a predetermined reference light emission amount at each position in the sub-scanning direction (S1010), and executes image processing by the image processing unit 209 for the image data generated at each pixel position ( S1008).

  As described above, in this embodiment, even if the white reference plate 101 is bent by changing the light emission amount of the light source 201 at each position in the sub-scanning direction, the image quality is stable in the sub-scanning direction. Can be obtained.

[Second Embodiment]
Next, the control device 110 for controlling the image reading device 200 of FIG. 1 in the second embodiment will be described with reference to FIG. FIG. 5 is a view of the original glass of the image reading apparatus as viewed from above. The first white reference plate 101 serves as a white reference for performing shading correction for correcting distortion of the output image signal, and is affixed to the platen glass 102. The flow reading glass 103 is a glass for a document fed from an automatic document feeding unit (ADF) 250. A document abutting portion 104 that serves as a reference for setting a document on the document table glass 102 is disposed on the side of the flow reading glass 103 of the document table glass 102. The second white reference plate 105 is affixed to the side opposite to the first white reference plate 101 in the sub-scanning direction on the platen glass 102. Here, the second white reference plate is provided at a position where the amount of deflection of the original table glass when the pressure applied to the original table glass is strong is smaller than that of the first white reference plate 101.

  The control operation of the image reading apparatus 200 in the present embodiment will be described according to the flowchart of the CPU 205 shown in FIG. 11 with reference to FIGS. 1, 3, 5, and 8. FIG. First, the light source 201 irradiates the first white reference plate 101 with light, and the sensor 202 receives the reflected light and outputs an image signal from the received reflected light. At this time, the image signal output from the sensor 202 is amplified by the gain control amplifier 203 whose gain value is set to 1 time, converted into a digital signal by the A / D converter 204, and stored in the storage unit 206. . Then, the CPU 205 corrects the gain value set in the gain control amplifier 203 with a gain correction value that sets the output value of the gain control amplifier 203 to a predetermined output value (luminance or the like). Therefore, the image signal output from the sensor 202 thereafter is amplified by the gain value corrected by the gain correction value by the gain control amplifier 203 and converted into a digital signal by the A / D converter 204. The CPU 205 stores the gain correction value in the storage unit 206 (S1101).

  The CPU 205 calculates the difference between the gain correction value obtained from the first white reference plate 101 in S1101 and the reference gain correction value stored in advance in the storage unit 205 (S1102). Here, the reference gain correction value is set so that the output value of the gain control amplifier 203 is a predetermined output value when the pressure applied to the platen glass 102 is weak (or not applied) as shown in FIG. This is a correct gain correction value. The CPU 205 determines whether or not the calculated difference is greater than or equal to a predetermined value (S1103). If it is determined that the difference is greater than or equal to the predetermined value, the CPU 205 acquires the light emission amount of the light source 201 from the difference calculated in S1102 (S1104). Also in the present embodiment, the CPU 205 acquires the light emission amount of the light source 201 (first light emission amount, point a in FIG. 9) from the correspondence between the gain correction value difference and the light emission amount as shown in FIG.

  The predetermined value used in S1003 is a value that does not affect the image even if a uniform amount of light emission is used for all pixels in the sub-scanning direction if it is equal to or smaller than the predetermined value, and if it is equal to or larger than the predetermined value, it is a uniform gain. A value that affects the image when the correction value is used. Here, the gain correction value stored in the storage unit 206 in S1101 is a gain correction value corresponding to the central image signal in the main scanning direction. For this reason, the light emission amount (first light emission amount) of the light source 201 obtained by obtaining the difference from the reference gain correction value is the light emission amount corresponding to the central image signal in the main scanning direction. Therefore, as the light emission amount of the light source 201, the light emission amount corresponding to the center image signal is used in the entire main scanning direction.

  Next, the control device 110 moves the image reading unit 210 to a position where the second white reference plate 105 can be read. The light source 201 irradiates the second white reference plate 105 with light, and the sensor 202 receives the reflected light and outputs an image signal from the received reflected light. The image signal output from the sensor 202 is amplified by the gain control amplifier 203 whose gain value is set to 1 in the same manner as in S1101, converted into a digital signal by the A / D converter 204, and stored in the storage unit 206. Is done. Then, the CPU 205 corrects the gain value set in the gain control amplifier 203 with a gain correction value such that the output value of the gain control amplifier 203 is set to a predetermined output value (luminance or the like). The CPU 205 stores the gain correction value in the storage unit 206 (S1105).

  The CPU 205 calculates the difference between the gain correction value obtained from the second white reference plate 105 and the reference gain correction value stored in advance in the storage unit 205. The CPU 205 obtains the light emission amount of the light source 201 (second light emission amount, point b in FIG. 9) from the correspondence between the gain correction value difference and the light emission amount as shown in FIG. 8 (S1106).

  The light emission amount correction calculation unit 207 corrects the light emission amount of the light source 201 so as to be the first light emission amount acquired in S1104 (S1107). The gain control amplifier 203 amplifies the image signal output from the sensor 201 with the corrected light emission amount by the reference gain correction value, and the shading correction processing unit 208 is converted into a digital signal by the A / D converter 204. Shading correction is performed on the image signal (S1108). The CPU 205 acquires the light emission amount for each position in the sub-scanning direction (S1109). A method for acquiring the light emission amount for each position in the sub-scanning direction will be described later. Then, image reading is performed while correcting the light emission amount of the light source 201 (S1110), and the image processing unit 210 performs image processing on the image data generated for each pixel position (S1111).

  As a method for acquiring the light emission amount in the sub-scanning direction performed in step S1007, the CPU 205 determines, for example, from the correspondence between the number of pixels in the sub-scanning direction and the first light emission amount and the second light emission amount as illustrated in FIG. The light emission amount of the light source 201 for each pixel position in the scanning direction is acquired. In this embodiment, since the point b in FIG. 9 is the amount of emitted light obtained from the second white reference plate 105, the pressure applied to the platen glass is strong as in the point a (the second white reference plate 105 As the distortion increases, the direction changes in the direction of the vertical axis in FIG. However, as described above, the amount of bending of the platen glass differs between the position where the first white reference plate 101 is provided and the position where the second white reference plate 105 is provided, and the second white reference plate is different. Since the document table glass on the 105 side has a small amount of deflection, the amount of change in FIG. 9 is also smaller in the second light emission amount.

  Further, in the present embodiment, as shown in FIG. 9, it is determined that the first light emission amount and the second light emission amount change linearly in the sub-scanning direction. However, the CPU 205 may determine the interval between the first light emission amount and the second light emission amount in a non-linear manner according to the structural characteristics with respect to the weight of the platen glass 102.

  If it is determined in S1103 that the difference is not greater than or equal to the predetermined value, the gain control amplifier 203 amplifies the image signal output from the sensor 201 with the predetermined reference light emission amount by the predetermined gain correction value. The shading correction processing unit 208 performs shading correction on the image signal converted into a digital signal by the A / D converter 204 (S1112). The CPU 205 reads an image with a predetermined reference light emission amount at each position in the sub-scanning direction (S1113), and executes image processing by the image processing unit 209 with respect to the image data generated at each pixel position ( S1111).

  In the second embodiment, by obtaining the second light emission amount from the second white reference plate 105, the light emission amount can be changed in accordance with the amount of deflection of the platen glass, so that more uniform image data can be obtained. Can be obtained, and deterioration of image quality can be prevented.

  In the second embodiment, the light emission amount is changed when the difference between the gain correction value obtained from the first white reference plate 101 and the reference gain correction value is equal to or greater than a predetermined value. Even if the light emission amount in the sub-scanning direction is changed when the difference between the gain correction value obtained from the first white reference plate 101 and the gain correction value obtained from the second white reference plate 105 is a predetermined value or more. Good.

  Further, in the present embodiment, when the difference between the two values of the gain correction value obtained from the first white reference plate 101 and the reference gain correction value is equal to or larger than a predetermined value, it corresponds to the distortion of the platen glass. Although the shading correction is performed, the light emission amount may be changed according to the deflection of the platen glass when there is a difference between the two values regardless of the magnitude of the difference between the two values.

  As described above, in each embodiment, when the white reference plate bends due to the pressure on the platen glass surface and the reading value of the white reference plate decreases, the light emission amount of the light source is read in the sub-scanning direction. By changing the position according to the reading position, it is possible to keep the white reference level constant and prevent deterioration of the image quality.

  In the embodiment described above, the light emission amount of the light source is changed according to the reading position in the sub-scanning direction. However, the light emission amount of the light source may be changed in the main scanning direction according to the distortion of the platen glass. . Also in this case, the light emission amount of the light source is set so that the value in the central portion in the main scanning direction, where the influence of the distortion of the platen glass is the largest, gradually decreases toward the end portion in the main scanning direction of the white reference plate. Change it. Further, the light emission amount in the distortion of the platen glass in the main scanning direction is applied to the distortion in the sub scanning direction, and the light emission amount for each pixel in the main scanning direction is linear in the sub scanning direction as in the embodiment described above. May be changed. By doing so, it is possible to further prevent a decrease in image quality.

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 110 Control apparatus 120 CPU
200 Image reader

Claims (16)

Reading means for irradiating a document image on a document table from a light source, reading reflected light from the document image, and outputting a reading signal;
Determining means for determining whether a value read by the reading means on a reference member provided on a document table on which an original is placed is within a predetermined range;
A light emission amount control unit configured to change a light emission amount of the light source according to a reading position of the reading unit in a sub-scanning direction on the document table when the determination unit determines that the light source is not within the predetermined range;
An image reading apparatus comprising: Reading means for irradiating a document image on a document table from a light source, reading reflected light from the document image, and outputting a reading signal;
Determining means for determining whether a value read by the reading means on a reference member provided on a document table on which an original is placed is within a predetermined range;
A light emission amount control unit configured to change the light emission amount of the light source in accordance with distortion of the document table when the determination unit determines that it is not within the predetermined range;
An image reading apparatus comprising:   The image reading apparatus according to claim 1, wherein the reference member is provided at a position affected by distortion of the document table.   The image reading apparatus according to claim 1, wherein the predetermined range is determined based on a preset value.   The predetermined range is determined based on a reading value obtained from a second reference member provided at a position that is different from the reference member and is not substantially affected by distortion of the document table. The image reading apparatus according to any one of claims 1 to 3. The reference member is a gain determining reference member for determining a gain correction value for outputting a read signal having a predetermined image quality,
2. The determination unit according to claim 1, wherein the determination unit determines whether or not a deviation between a gain correction value obtained from the gain determining reference member and a reference gain correction value is within a predetermined range. The image reading apparatus described.   The image reading apparatus according to claim 1, further comprising: a light emission amount acquisition unit configured to acquire a light emission amount that changes according to a position in the sub-scanning direction on the document table.   The image reading apparatus according to claim 7, wherein the light emission amount acquisition unit acquires a light emission amount that linearly changes in accordance with a position in a sub-scanning direction on the document table.   The light emission amount control means reduces the light emission amount of the light source as the reading of the reading means moves away from the reference member in accordance with a position in the sub-scanning direction on the document table. 9. The image reading apparatus according to any one of 8 above.   The light emission amount control means refers to a table in which a position in the sub-scanning direction on the document table is associated with a light emission amount, and the light emission amount of the light source according to the position in the sub-scanning direction on the document table The image reading apparatus according to claim 1, wherein the image reading apparatus is set.   The image reading apparatus according to claim 1, wherein the position in the sub-scanning direction on the document table is represented by the number of pixels from the reference member.   12. The reading device according to claim 1, wherein the reading unit reads the document image without changing the gain correction value at a position in the sub-scanning direction by the light emission amount set by the light emission amount control unit. The image reading apparatus according to claim 1. An image reading apparatus according to any one of claims 1 to 12,
Image forming means for forming an image on a recording medium based on a document image read by the reading device;
An image forming apparatus comprising: A control method executed in an image reading apparatus,
A reading step of irradiating a document image on a document table from a light source, reading reflected light from the document image, and outputting a reading signal;
A determination step of determining whether or not a value obtained by reading the reference member provided on the platen on which the document is placed in the reading step is within a predetermined range;
A light emission amount control step of changing the light emission amount of the light source according to the reading position in the reading step in the sub-scanning direction on the document table when it is determined that the predetermined range is not in the determination step;
A control method characterized by comprising: A reading step of irradiating a document image on a document table from a light source, reading reflected light from the document image, and outputting a reading signal;
A determination step of determining whether or not a value obtained by reading the reference member provided on the platen on which the document is placed in the reading step is within a predetermined range;
A light emission amount control step of changing the light emission amount of the light source in accordance with distortion of the document table when it is determined in the determination step that the range is not within the predetermined range;
A control method characterized by comprising:   A program for causing a computer to function as each unit of the image reading apparatus according to any one of claims 1 to 12 or the image forming apparatus according to claim 13.

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