JP2008167039A - Image processor, image forming apparatus, and image reader - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform proper shading correction of read images obtained by simultaneously reading both faces of an original D by two reading parts. <P>SOLUTION: An image processor includes a shading correcting means for preparing shading correction data for single lighting and both lighting in each image area divided in accordance with respective timing when light sources of two reading parts are turned on and performing proper shading correction by switching different shading data, wherein shading correction data for the single lighting is used to correct brightness difference that occurs when one of the two reading parts is turned on, and shading correction data for both lighting is used to correct brightness difference that occurs when both of a pair of reading parts are turned on. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image processing apparatus, an image forming apparatus, and an image reading apparatus that perform shading correction on a read image.

A reading unit that reads image data of a document includes, as main components, a light source that irradiates light on the document and a solid-state imaging device that converts a light amount signal into an electrical signal.
If two reading units are used and arranged at positions facing each other with the document sandwiched between them, a pair of reading units (one is a first reading unit and the other is a second reading unit), the first reading unit sets the document. The back side of the document can be simultaneously read by the second reading unit.

In the first reading unit, the light emitted from the light source is applied to the surface of the document, and the solid-state image sensor receives the reflected light from the surface of the document. On the other hand, the solid-state image sensor receives reflected light from the back side of the document in the same manner in the second reading unit.
That is, light is emitted from the light source of each reading unit toward both sides of the document, so that the illumination light from one light source passes through the document, and this transmitted light is received by the solid-state image sensor located on the other side. . This transmitted light causes a further luminance difference in the read image compared to when one of the light sources is turned on.

Therefore, in order to avoid the influence of the transmitted light on the opposite side, for example, a technique described in Patent Document 1 or 2 is disclosed.
According to Patent Document 1, switching control is alternately performed so that the light source of the first reading unit and the light source of the second reading unit are not turned on at the same time. During the first half of the document scanning process, the front side light source is turned on and the back side light source is turned off to read the front side of the document. In the second half of the document scanning process, the back side light source is turned on and the front side light source is turned off. Scan the back side of the document. That is, only one light source is lit at all times, so that each reading unit blocks transmitted light from the light source on the opposite side.

Further, according to Patent Document 2, when performing processing for reading both sides of a document by simultaneously turning on both the light sources on the front side and the back side of the document, turn on only one of the light sources on the front side and the back side. Processing to lower the reading density than when reading one side of the document is performed. Thus, a technique is disclosed in which the reading density is made equal between the case where transmitted light is received and the case where light is not received.
JP 9-321947 A Japanese Patent Laid-Open No. 2003-32443

  However, in the technique of Patent Document 1, it is necessary to operate so that only one of the light sources of the first reading unit and the second reading unit is always turned on in the process of reading both sides of the document. Therefore, the light source used for each reading unit requires excellent blinking performance and light output capability, which increases costs. In addition, when a normal light source is used, it is necessary to limit the reading speed of the document, which is not preferable because it lacks operability.

  In the technique disclosed in Patent Document 2, the first reading unit and the second reading unit are arranged relatively apart from each other in the moving direction of the document. Accordingly, the respective light sources are not always lit in all areas of the document, and the lighting timings of the light sources of the respective reading units vary. That is, in the read document image, only one of the first reading unit and the second reading unit is lit (that is, a region where there is no influence of transmitted light) and both are lit (that is, the region is not affected by transmitted light). A region affected by transmitted light). For this reason, if the reading density is lowered uniformly for all image areas as described above, appropriate shading correction cannot be performed.

  An object of the present invention is to perform appropriate shading correction on a read image obtained by simultaneously reading both sides of a document by two reading units.

The invention described in claim 1
An image area that is read when one of the two reading units is turned on with respect to a read image in which the images on the front and back sides of the document are read simultaneously by two reading units having a light source. And shading correction means for performing shading correction by switching different shading correction data in the image area when both of the two reading units are lit and read when both are lit.
It is characterized by having.

The invention according to claim 2 is the invention according to claim 1,
The shading correction data includes one-lighting shading correction data for correcting a luminance difference generated when one of the two reading units is lit, and luminance generated when both the pair of reading units are lit. Including shading correction data for both lighting for correcting the difference,
The shading correction means uses the one-lighting shading correction data for the one-lighted image area in the read image and performs the shading correction for the two-lighted image area using the two-lighting shading correction data. It is characterized by doing.

The invention according to claim 3 is the invention according to claim 1 or 2, wherein the shading correction data is data indicating a maximum luminance value or a minimum luminance value of an image read by the reading unit, and is a white reference plate or Created using a black reference plate,
The shading correction means calculates a shading function that uses the shading correction data to make the luminance value of the read image correspond to the gradation of the output image, and performs the shading correction by the shading function.

The invention according to claim 4
A reading device that simultaneously reads images on the front and back sides of a document by two reading units having a light source;
In the read images of the read front and back surfaces, the image area was read when one of the two reading units was lit, and was read when both the two reading units were lit. A shading correction means for performing shading correction by switching different shading correction data in the image area when both are lit;
It is characterized by having.

The invention described in claim 5
An image reading apparatus that reads images on the front and back sides of a document at approximately the same time by two reading units having a light source,
Shading correction data selection means for selecting shading correction data based on the position on the document image at the reading position of each reading unit and the lighting state of each light source of each reading unit;
Shading correction means for performing shading correction using the selected shading correction data;
It is characterized by having.

The invention according to claim 6 is the invention according to claim 5,
The shading correction data includes one-lighting shading correction data for correcting a luminance difference generated when one of the two reading units is lit, and luminance generated when both the pair of reading units are lit. Including shading correction data for both lighting for correcting the difference,
The shading correction means uses the one-lighting shading correction data for the one-lighted image area in the read image and performs the shading correction for the two-lighted image area using the two-lighting shading correction data. It is characterized by doing.

  According to the image processing apparatus of the present invention, shading correction data corresponding to a change in the amount of light in which reflected light and transmitted light are combined is applied to image data on both sides of a document that is simultaneously read by two reading units. Can be applied. Thereby, it is not necessary to use the flashing performance etc. which were excellent in the light source of the reading part, and it is preferable in terms of cost. Further, it is possible to generate image data in which a luminance difference is eliminated by reducing the influence of transmitted light.

Hereinafter, the configuration and operation of an optimum embodiment of an image processing apparatus according to the present invention will be described in detail with reference to the drawings.
In this embodiment, an example in which the present invention is applied to an image forming apparatus including two reading units will be described.

FIG. 1 shows an image forming apparatus 100.
The image forming apparatus 100 mainly includes a main body unit 30 including an automatic document feeder 10, a reading unit 20, a reading control device 200, and an image processing unit 40.

In addition, the image forming apparatus 100 includes a display unit 50, an operation unit 60, a printer unit 70, and the like.
The display unit 50 includes an LCD (Liquid Crystal Display), and displays various operation screens for performing a print operation on the LCD.
The operation unit 60 includes various function keys such as a start key and a numeric key for instructing the start of printing. When these function keys are operated, a corresponding operation signal is output to the control unit 41.
The printer unit 70 performs print output by the electrophotographic method based on the image data input from the image processing unit 40.

FIG. 2 is a diagram illustrating the configuration of the automatic document feeder 10 and the reading unit 20.
The automatic document feeder 10 includes a document tray 11, an introduction roller pair 12, a feed roller pair 13, a platen glass 14, a discharge roller pair 15, a discharge tray 16, and a document position sensor device 17.

  A document D is placed on the document tray 11. A plurality of documents D may be placed at one time, and the shape of the document D is a sheet.

  The introduction roller pair 12 separates the documents D placed on the document tray 11 one by one and conveys the documents D to the feed roller pair 13 on the conveyance path.

  The feed roller pair 13 transports the document D transported from the introduction roller pair 12 onto the platen glass 14 in a timely manner. The document D passes over the platen glass 14 and is conveyed to the discharge roller pair 15.

  The discharge roller pair 15 discharges the document D conveyed on the platen glass 14 to the discharge tray 16. The document D after the document reading process is discharged to the discharge tray 16.

  For example, an optical sensor or the like is applied to the document position sensor device 17 to detect the start and end of the document D on which the document D moves on the platen glass 14.

Next, the reading unit 20 will be described.
As shown in FIG. 2, the reading unit 20 includes a first reading unit 21 and a second reading unit 22 that are arranged at positions facing each other with the document D interposed therebetween. Here, the document surface read by the first reading unit 21 is referred to as the front surface, and the document surface read by the second reading unit 22 is referred to as the back surface. The first reading unit 21 and the second reading unit 22 output an image signal (analog signal) of the read document image to the image processing unit 40.

A schematic configuration diagram of the first reading unit 21 will be described with reference to FIG. 3. 3A is an external view of the first reading unit 21, and FIG. 3B is a sectional view in the sub-scanning direction.
The first reading unit 21 includes a light source 23, a rod lens array 24, and a CIS (Contact Image Sensor) 25.

  The light source 23 includes an LED 231, a light guide 232, and a holding member 233.

  A plurality of LEDs 231 are used and arranged two-dimensionally or three-dimensionally. By arranging in three dimensions, the amount of light emission can be increased compared to the case of arranging in two dimensions. If the required amount of light emission can be obtained, a single LED may be used instead of a plurality. The lighting timing of the LED 231 is controlled by the reading control device 200 described later.

  The light guide 232 is formed of a light transmission member such as glass. The light guide body 232 has a diffusing surface and an emitting surface (not shown), and the diffusing surface has a configuration in which a reflecting sheet having a high light reflectance is applied or a reflecting film is applied to increase the diffusing rate. It has become. The exit surface of the light guide 232 is disposed in the opening of the holding member 233, and the light emitted from the LED 231 enters. The light guide body 232 irradiates the original D with the light diffusely reflected inside.

  The holding member 233 is formed of a light impermeable member having a high light reflectance. The inner surface of the holding member 233 is configured such that a reflective sheet with a high light reflectance is applied or a reflective film is applied to increase the reflectance. The holding member 233 is disposed so as to cover the light guide 232 with the air layer interposed therebetween, and causes the light leaking from the light guide 232 to enter the light guide 232 again. By installing the holding member 233, the attenuation loss of light can be reduced.

The rod lens array 24 is composed of a plurality of cylindrical lenses (rod lenses) arranged in a line in the main scanning direction. Here, the main scanning direction is a direction perpendicular to the direction in which the document D moves on the conveyance path, and the direction in which the document D moves is referred to as a sub-scanning direction.
Each rod lens is arranged in one-to-one correspondence with CIS 25 described later. The rod lens array 24 receives the reflected light from the document D and forms an image of this light on the CIS 25 at the same magnification as the document D. As a result, an optical image of the reading portion of the document D is formed on the CIS 25.

  The CIS 25 includes a plurality of solid-state imaging elements 251 arranged in a line in the main scanning direction. The CIS 25 reads the amount of light imaged by the rod lens array 24 as an optical signal at a predetermined cycle. The CIS 25 converts the light amount signal into an electric signal, accumulates the converted charge for a predetermined time, and outputs it later. The time during which the light received by the CIS 25 is converted into electric charges and accumulated is the photoelectric conversion time, and the time for outputting the accumulated electric charges is the charge output time. These times are controlled by the reading control device 200 described later.

Next, a schematic configuration of the second reading unit 22 will be described with reference to FIG.
As shown in FIG. 4, the second reading unit 22 includes a scanning light source unit 26, a scanning mirror unit 27, an imaging lens 28, and a CCD image sensor 29.

  The scanning light source unit 26 includes a light source 261 and a first mirror 262. The light source 261 irradiates the document D with light, and the first mirror 262 receives reflected light from the document D and reflects it to the scanning mirror unit 27.

  The scanning mirror unit 27 includes a second mirror 271 and a third mirror 272. The second mirror 271 receives the reflected light from the scanning light source unit 26 and reflects it to the third mirror 272, and the third mirror 272 receives the reflected light from the second mirror 271 and reflects it to the imaging lens 28.

  The imaging lens 28 receives the reflected light from the scanning mirror unit 27 and forms an image on the light receiving surface of the CCD image sensor 29.

  The CCD image sensor 29 is composed of a CCD (Charge Coupled Device) which is a solid-state imaging device. The CCD image sensor 29 reads the amount of light imaged by the imaging lens 28 as a light amount signal, converts the light amount signal into an electrical signal, and outputs it.

  As described above, the reading unit 20 in the present embodiment includes the first reading unit 21 and the second reading unit 22. However, the present invention is not limited to this. For example, the second reading unit 22 may have the same configuration as the first reading unit 21.

Next, the reading control apparatus 200 will be described.
FIG. 5 is a functional block diagram of the reading control device 200 and the image processing unit 40.

  The reading control apparatus 200 includes a CPU 201, ROM 202, RAM 203, memory 204, motor driver 205, light source driver 206, and sensor driver 207.

The CPU 201 controls the operations of the motor driver 205, the light source driver 206, and the sensor driver 207, and controls the overall processing related to the document reading operation by the automatic document feeder 10, the first reading unit 21, and the second reading unit 22. Control.
Further, when a control signal is input from an external device via the input / output interface 80, control is performed to output digital image data to the external device in synchronization with the control signal.

  The ROM 202 stores programs for the CPU 201 to perform overall control and various reference data. The RAM 203 and the memory 204 temporarily store programs and various data.

  The motor driver 205 controls the rotation drive of the pulse motors of the introduction roller pair 12, the feed roller pair 13, and the discharge roller pair 15 of the automatic document feeder 10 to determine the rotation timing and rotation speed. In order to move the document D stacked on the document tray 11 at a predetermined timing and at a predetermined speed according to the rotation timing and rotation speed of the introduction roller pair 12, the feed roller pair 13, and the discharge roller pair 15, the introduction roller pair 12 The rotational drive of the pulse motor of the feed roller pair 13 and the discharge roller pair 15 is controlled.

  The light source driver 206 controls the timing of turning on and off the light sources of the first reading unit 21 and the second reading unit 22.

  The sensor driver 207 drives the solid-state imaging device 251 of the first reading unit 21 and the second reading unit 22 and controls the period of photoelectric conversion time and charge output time of the solid-state imaging device 251. The sensor driver 207 causes the image processing unit 40 to output the charges accumulated in the solid-state imaging device 251 during the photoelectric conversion time from the reading units 21 and 22 during the charge output time.

Next, each component of the main body 30 will be described.
The main body unit 30 includes an image processing unit 40, a control unit 41, a storage unit 42, a DRAM control unit 43, and a DRAM 44.
The image processing unit 40 will be described later, and the control unit 41 centrally controls the operation of each unit of the image forming apparatus 100 according to various control programs such as a system program and a print processing program stored in the storage unit 42.
In addition to the various control programs executed by the control unit 41, the storage unit 42 stores parameters and data necessary for each unit.
The DRAM control unit 43 controls input / output of image data stored in the DRAM 44.
The DRAM 44 is an image memory that stores image data.

Next, each component of the image processing unit 40 will be described.
The image processing unit 40 includes an analog signal processing unit 411 and a digital signal processing unit 422.
The analog signal processing unit 411 includes an analog signal correction unit 401 and an A / D conversion unit 402.

  The analog signal correction unit 401 performs signal processing such as offset correction, amplification correction, and noise removal on the image signals (analog signals) output from the reading units 21 and 22. The image signal subjected to signal processing is output to the A / D converter 402.

The A / D conversion unit 402 converts the image signal output from the analog signal correction unit 401 into a digital image signal (hereinafter referred to as image data) having a predetermined bit depth.

  The digital signal processing unit 422 includes a shading correction unit 403 and other signal processing units (not shown). The digital signal processing unit 422 performs digital signal processing such as shading correction, gamma correction, defective pixel interpolation processing, and filter processing on the image data output from the analog signal processing unit 411. A part or all of various digital signal processing performed by the digital signal processing unit 422 can be performed by the CPU 201 by a program.

Here, the shading correction performed by the shading correction unit 403 will be described.
The shading correction is a correction performed to eliminate luminance unevenness caused by the reading unit 20 such that the peripheral portion of the image is darker than the central portion in the image data read by the reading unit 20, This is correction that ensures that the entire image has a uniform brightness on average. The shading correction corrects a deviation of the illumination intensity of the light source, a deviation of the light amount due to the aberration of the condenser lens, a deviation of the sensitivity of each solid-state image sensor 251 and the like.
The shading correction unit 403 uses shading correction data for shading correction. The shading correction unit 403 stores shading correction data corresponding to the two reading units 21 and 22 in advance.

There are two types of shading correction data for one-side lighting and two-side lighting, and there are two types of shading correction data: white reference shading correction data and black reference shading correction data. That is, there are a total of four types of shading correction data.
Hereinafter, the white reference shading correction data for one lighting is white reference shading correction data for one lighting, black reference shading correction data for one lighting is black reference shading correction data for one lighting, and white reference shading correction data for both lighting is used. The white reference shading correction data for both lighting and the black reference shading correction data for both lighting are referred to as the black reference shading correction data for both lighting.

FIG. 6 shows the above four types of shading correction data.
Here, “one-side lighting” and “one-side lighting” refer to the case where one of the light sources of the first reading unit 21 or the second reading unit 22 is turned on or off. “Off” refers to the case where the light sources of both the first reading unit 21 and the second reading unit 22 are turned on or off.
Further, “white reference” indicates shading correction data created by the lighting-side reading unit 20 when a white reference plate is used, and “black reference” indicates an unlit reading unit 20 when a white reference plate is used. The shading correction data created in is shown. The white reference plate is a reference plate that has a length equal to or greater than the document width in the main scanning direction and is white and has uniform light reflection characteristics over the entire surface. In contrast, the black reference plate is entirely black. In the present embodiment described below, the white reference plate is used to create the “white reference” and “black reference” shading correction data. However, when the “black reference” shading correction data is created. It is also possible to create using a black reference plate.

Since the four types of shading correction data are created for each of the first reading unit 21 and the second reading unit 22, the shading correction data stored in the shading correction unit 403 is a total of eight.
Hereinafter, these eight shading correction data will be described.

On the other hand, lighting white reference shading correction data will be described.
The light source 23 of the first reading unit 21 is turned on, and the light source 261 of the second reading unit 22 is turned off. The first reading unit 21 on the lighting side receives reflected light from the white reference plate and performs photoelectric conversion. The photoelectric conversion value output to the image processing unit 40 indicates the light amount value received by the first reading unit 21 and indicates the luminance value of the read image. This luminance value is used as one-side lighting white reference shading correction data (for the front surface), and the shading correction unit 403 stores it.
Similarly, the light source 261 of the second reading unit 22 is turned on, the light source 23 of the first reading unit 21 is turned off, and the luminance value obtained by photoelectric conversion of the second reading unit 22 on the lighting side is for one side lighting. The shading correction unit 403 stores the white reference shading correction data (for the back surface).
That is, the one lighting white reference shading correction data becomes luminance value data in a state where there is no transmitted light from the light source of the other reading unit 21 or 22 in one reading unit 21 or 22.

On the other hand, the black reference shading correction data for lighting will be described.
The light sources 23 and 261 of both the first reading unit 21 and the second reading unit 22 are turned off. Then, the amount of light received by the first reading unit 21, that is, the luminance value of the read image is used as the one-side black reference shading correction data (for front side), and the luminance value of the read image from the second reading unit 22 is used as the one-side black reference for lighting. The shading correction data (for the back side) is stored in the shading correction unit 403.
By turning off both light sources, one-side black reference shading correction data is transmitted from the other first reading unit 21 or second reading unit 22 in one first reading unit 21 or second reading unit 22. It becomes the brightness value data in the absence.

The white reference shading correction data for both lighting will be described.
The light sources 23 and 261 of both the first reading unit 21 and the second reading unit 22 are turned on. Then, the luminance value obtained by photoelectric conversion in the first reading unit 21 is the white reference shading correction data for both lighting (for front surface), and the luminance value obtained in the second reading unit 22 is the white reference shading correction data for both lighting. These are stored in the shading correction unit 403.
By turning on both light sources, the white reference shading correction data for turning on both lights becomes light quantity value data in a state where one reading unit 21 or 22 receives transmitted light from the other reading unit 22 or 21.

The black reference shading correction data for both lighting will be described.
The light source 23 of the first reading unit 21 is turned off, and the light source 261 of the second reading unit 22 is turned on. At this time, the photoelectric conversion value of the amount of light received by the first reading unit 21 on the extinguishing side, that is, the luminance value of the read image is used as both black reference shading correction data for lighting (for front surface), and the shading correction unit 403 stores this. .
Further, the light source 261 of the second reading unit 22 is turned off, and the light source 23 of the first reading unit 21 is turned on. Then, the photoelectric conversion value of the amount of light received by the second reading unit 22 on the extinguishing side, that is, the luminance value of the read image is used as both black reference shading correction data for lighting (for the back side), and the shading correction unit 403 stores this.
By turning on one of the light sources, the black reference shading correction data for both lighting becomes light quantity value data in a state where one reading unit 21 or 22 receives transmitted light from the other reading unit 22 or 21.

  Next, shading correction using shading correction data will be described. The shading correction described below is an example performed on the image data of the surface of the document D, and is performed using the surface shading correction data stored in the first reading unit 21. The same shading correction is performed on the back side image data of the document D by using the back side shading correction data stored in the second reading unit 22.

FIG. 7 is a luminance characteristic diagram showing the relationship between the position of the first reading unit 21 in the main scanning direction and the luminance value of the read image obtained by the first reading unit 21 at that position.
Curve a is the luminance value of the read image when only the light source 23 of the first reading unit 21 is lit, curve b is the luminance value of the transmitted light received by the first reading unit 21 or the second reading unit 22, and curve c is the first value. The luminance values of the read image when the light sources 23 and 261 of the reading unit 21 and the second reading unit 22 are turned on are respectively shown.
As shown in FIG. 7, the luminance value is the largest in the central portion in the main scanning direction, and the luminance value decreases as it becomes the left and right end portions in the main scanning direction. That is, when the same luminance value is obtained from the same white reference plate, a luminance difference occurs depending on the position of the first reading unit 21 in the main scanning direction. This is due to the configuration of the first reading unit 21.

  The read image is quantized to output gradations, but inconvenience occurs when quantization is performed in a state where a luminance difference has occurred. At the time of quantization, gradation is assigned with the highest luminance value of the read image corresponding to the highest gradation and the lowest luminance value corresponding to the lowest gradation. For example, when 256 gradations from 0 to 255 are expressed by 8 bits, gradations are assigned with the lowest luminance value corresponding to gradation 0 and the highest luminance value corresponding to gradation 255. At this time, when the highest luminance value at the central portion in the main scanning direction is used, the highest luminance value at the end portion is smaller than that at the central portion, so that the luminance value at the end portion is assigned to the gradation 255 even though the luminance value is high. There is no. On the other hand, when the highest luminance value at the end is used for gradation assignment, all of the high luminance value areas in the center are assigned to gradation 255.

Furthermore, since the installation positions of the first reading unit 21 and the second reading unit 22 are shifted, the timing of the reading process is shifted. Therefore, in the read image, there are a region where only the first reading unit 21 is lit, a region where both the first reading unit 21 and the second reading unit 22 are lit, and a region where only the second reading unit 22 is lit. . That is, in the area where both are lit, the first reading unit 21 and the second reading unit 22 are affected by the transmitted light, and the luminance value should be larger than that when one is lit. Therefore, a luminance difference is generated depending on the lighting state of one-side lighting or both-side lighting.
Therefore, it is necessary to correct not only the luminance difference caused by the shading correction in the main scanning direction but also the luminance caused by the lighting state of the light source when performing both-side simultaneous reading.

Therefore, the shading correction unit 403 obtains a shading correction function for correcting a luminance difference generated according to the lighting state of the light source and the position in the main scanning direction using the shading correction data, and the shading function uses the shading correction data of the read image to be corrected. An image signal (luminance value) is input to obtain a luminance value after shading correction. The shading correction function can be obtained by the following equation (1).
K _out = [(((2 ⁿ −1) / (WB)) (K _in −B)] (1)
In the above equation (1), K _in is the luminance value before correction, K _out is the luminance value after correction, W is the white reference shading correction data, B is the black reference shading correction data, and n is the lowest gradation to the highest gradation. The number of bits indicating the number of gradations up to.

FIG. 8 is a diagram showing the shading correction function obtained by the above equation (1).
Straight lines d and e indicate shading correction functions when the light source of the reading unit 20 is lit on one side, and straight lines D and E indicate shading correction functions when both of the light sources of the reading unit 20 are lit. Straight lines d and D indicate shading correction functions corresponding to the center portion of the document D in the main scanning direction, and straight lines e and E indicate shading correction functions corresponding to the end portions in the main scanning direction.

First, the one-lighting shading correction function will be described.
A straight line d assigns the one lighting white reference shading correction data W1 which is the highest luminance value in the central portion of the read image in the main scanning direction to the highest gradation (2 ⁿ −1), and the one luminance black reference which is the lowest luminance value. By assigning the shading correction data B1 to the lowest gradation 0, it is a stair straight line that is quantized and assigned from the lowest luminance value to the highest luminance value to the gradation from the lowest gradation to the highest gradation. Based on the corrected luminance value (K _out ) obtained here, the image processing unit 40 can generate image data of the central portion in the main scanning direction subjected to the shading correction.

A straight line e assigns the one lighting white reference shading correction data W1 which is the highest luminance value at the left and right ends of the scanned image in the main scanning direction to the highest gradation (2 ⁿ −1), and the one lighting black which is the lowest luminance value. By assigning the reference shading correction data B1 to the lowest gradation 0, it is a stair straight line that is quantized and assigned from the lowest luminance value to the highest luminance value into gradations from the lowest gradation to the highest gradation. Based on the corrected luminance value (K _out ) obtained here, the shading correction unit 403 can generate image data of the left and right ends in the main scanning direction subjected to the shading correction.

As for shading correction in a range other than the central portion and the left and right end portions in the main scanning direction, shading correction indicated by a straight line within a range from a straight line d to a straight line e based on an electrical signal received by each solid-state imaging device 251. It is corrected by a function (not shown).
Thereby, the image processing unit 40 can generate image data having no luminance difference by smoothing the curve a shown in FIG.

Next, the shading correction function for both lighting will be described.
The both-lighting shading correction function is represented by straight lines D and E by inputting both-lighting white reference shading correction data W2 and both-lighting black reference shading correction data B2 into W and B of the above-described equation 1.

A straight line D assigns the white reference shading correction data W2 for both lighting, which is the highest luminance value at the center of the read image in the main scanning direction, to the highest gradation (2 ⁿ −1), and the black reference for both lighting that is the lowest luminance value. By assigning the shading correction data B2 to the lowest gradation 0, this is a stair straight line that is quantized and assigned from the lowest luminance value to the highest luminance value to the gradation from the lowest gradation to the highest gradation. Based on the corrected luminance value (K _out ) obtained here, the shading correction unit 403 can generate image data of the central portion in the main scanning direction subjected to the shading correction.

A straight line E assigns the white reference shading correction data W2 for both lighting that is the highest luminance value at the left and right ends of the read image in the main scanning direction to the highest gradation (2 ⁿ -1), and the black for both lighting that is the lowest luminance value. By assigning the reference shading correction data B2 to the lowest gradation 0, the stepwise straight line is obtained by quantizing and assigning the lowest luminance value to the highest luminance value to the gradation from the lowest gradation to the highest gradation. Based on the corrected luminance value (K _out ) obtained here, the shading correction unit 403 can generate image data of the left and right ends in the main scanning direction subjected to the shading correction.

For shading correction in a range other than the central portion and the left and right end portions in the main scanning direction, shading correction indicated by a straight line within the range from straight line D to straight line E based on the electrical signal received by each solid-state imaging device 251. It is corrected by a function (not shown).
As a result, the image processing unit 40 can generate image data having no luminance difference by smoothing the curve c shown in FIG.

Next, an operation when the image forming apparatus 100 simultaneously reads both sides of the document D will be described.
FIG. 9 is a flowchart for explaining reading processing by the first reading unit 21 and the second reading unit 22. In this process, the reading control apparatus 200 reads various control programs and controls the execution thereof.

First, when the double-sided reading operation of the document D is started, the reading control apparatus 200 sets four timers 1 to 4 at predetermined times (step S1), and rotates the introduction roller pair 12. (Step S2).
Timer 1 measures the lighting timing of the first reading section 21, timer 2 measures the lighting timing of the second reading section 22, timer 3 measures the lighting timing of the first reading section 21, and timer 4 measures the lighting timing of the second reading section 22. It is. The set times of the timers 1 to 4 are set in advance according to the paper size by measuring the time for the light sources 23 and 261 in the first reading unit 21 and the second reading unit 22 to be turned on and off. Shall.
Each of the timers 1 to 4 counts down, and the light sources 23 and 261 of the first reading unit 21 and the second reading unit 22 are turned on or off when the count reaches “0” from the set time.

One document D placed on the document tray 11 is introduced onto a predetermined transport path (step S3), and the rotation of the introduction roller pair 12 is temporarily stopped (step S4).
The reading control device 200 detects the statuses of the first reading unit 21 and the second reading unit 22, and rotates the feeding roller pair 13 when the document reading process can be executed (step S5; Yes). If this cannot be detected, the process waits (step S5; No).

The reading control device 200 rotates the feeding roller pair 13 and conveys the document D introduced by the introducing roller pair 12 onto the platen glass 14 (step S6).
The reading control apparatus 200 waits until the leading edge of the document D moving on the platen glass 14 passes the observation point of the document position sensor 7 (Step S7; No), and starts to pass (Step S7; Yes). The timer 2 starts to count down (step S8).

Until the count of the timer 1 reaches “0”, the document D has not reached the first reading unit 21 (step S9; No), and when the count of the timer 1 becomes “0” (step S9; Yes), the time when the leading edge of the document D reaches the reading point of the first reading unit 21 is reached. At this time, the reading control device 200 causes the first reading unit 21 to start a document reading process.
The first reading unit 21 turns on the light source 23 and starts a series of reading processes (step S10). The light of the light source 23 lit by the first reading unit 21 is irradiated on the surface of the document D, and the reflected light from the surface of the document D is received by the CIS 25.

When the count of the timer 2 reaches “0” after the count of the timer 1 ends (step S11; Yes), the time when the leading edge of the document D reaches the reading point of the second reading unit 22 is reached. The second reading unit 22 is caused to start the document reading process.
The second reading unit 22 turns on the light source 261 and starts a series of document reading processes (step S12). The light of the light source 261 turned on by the second reading unit 22 is irradiated on the back surface of the document D, and the reflected light from the back surface of the document D is received by the CIS 25.

  The reading control device 200 waits until the trailing edge of the document D moving on the platen glass 14 passes through the observation point of the document position sensor 7 (Step S13; No), and starts to pass (Step S13; Yes). 3 and timer 4 start to count down (step S14).

Until the count of the timer 3 reaches “0”, the trailing edge of the document D has not reached the reading point of the first reading unit 21 (step S15; No), and when the count of the timer 3 reaches “0”. (Step S15; Yes) Since the time when the trailing edge of the document D reaches the reading point of the first reading unit 21 is reached, the reading control device 200 causes the first reading unit 21 to end the document reading process.
The first reading unit 21 turns off the light source 23 and ends a series of document reading processing (step S16).

When the count of the timer 4 reaches “0” after the timer 3 finishes counting (step S17; Yes), the time when the trailing edge of the document D reaches the reading point of the second reading unit 22 is reached. At this time, the reading control device 200 causes the second reading unit 22 to finish the document reading process.
The second reading unit 22 turns off the light source 261 and ends a series of document reading processing (step S18).

  When the document D is conveyed to the discharge roller pair 15, the reading control device 200 rotates the discharge roller pair 15. The document D is discharged to the discharge tray 16 by the discharge roller pair 15 (step S21), and when the discharge is completed, the discharge roller pair 15 stops (step S22). A document D that has been subjected to the document reading process is stacked on the discharge tray 16. If there is a document D on the document tray 11 (step S23; No), the process proceeds to step S1, and the above-described processing is repeated. If there is no document D in the document tray 11 (step S23; Yes), this process is terminated.

Next, with reference to FIG. 10, the lighting and extinguishing timings of the light sources 23 and 261 of the first reading unit 21 and the second reading unit 22 will be described.
T1 is a timing chart at which the first reading unit 21 lights the light source 23, T2 is a timing chart at which the second reading unit 22 lights the light source 261, and T3 is the first reading unit 21 and the second reading unit in the timing charts T1 and T2. It is a figure which shows the lighting state of 22 light sources 23 and 261.

  When the timer 1 reaches the count “0”, the first reading unit 21 turns on the light source 23 (t1), and the second reading unit 22 turns off the light source 261 until the timer 2 reaches the count “0”. The surface image data generated during this time is subjected to shading correction using the one lighting white reference shading correction data and the one lighting black reference shading correction data.

  When the timer 2 reaches the count “0”, the second reading unit 22 turns on the light source 261 (t2), and the first reading unit 21 and the second reading unit 22 light sources 23 and 261 until the timer 3 reaches the count “0”. Lights up. The front and back image data generated during this time is subjected to shading correction using both the lighting white reference shading correction data and the lighting black reference shading correction data.

  When the timer 3 reaches the count “0”, the first reading unit 21 turns off the light source 23 (t3), and the second reading unit 22 turns on the light source 261 until the timer 4 reaches the count “0”. The back side image data generated during this time is subjected to shading correction using the one lighting white reference shading correction data and the one lighting black reference shading correction data.

When the timer 4 changes from “1” to “0”, the second reading unit 22 turns off the light source 261 (t4), and the light sources 23 and 261 of the first reading unit 21 and the second reading unit 22 are turned off. Ends.
The read image obtained by the first reading unit 21 is output to the image processing unit 40 as a read image on the front side of the document, and the read image obtained by the second reading unit 22 is output as a read image on the back side of the document. In the image processing unit 40, the front and back read images are processed by the analog signal processing unit 411 and then input to the digital signal processing unit 422. The digital signal processing unit 422 executes various processes including a shading correction process.

Next, with reference to FIG. 11, the shading correction process performed in the shading correction part 403 with respect to the read image obtained by the said reading process is demonstrated.
First, as shown in FIG. 11, the read images read by the first reading unit 21 and the second reading unit 22 are input to the image processing unit 40 (step S31).

  If the input read image is on the front side of the document D (step S32; Yes), the shading correction unit 403 reads the front-side shading correction data (step S33). If the input read image is on the back side of the document D (step S32; No), the shading correction data for the back side is read (step S34).

There are four types of shading correction data to be read, one for the front side and one for the back side.
The four shading correction data are one lighting white reference shading correction data, one lighting black reference shading correction data, two lighting white reference shading correction data, and both lighting black reference shading correction data.

Next, the shading correction unit 403 performs shading correction by switching the shading correction data in the read image according to the lighting state of the light source and the position of the read image in the main scanning direction.
The lighting state of the light source is obtained by acquiring timer control information at the time of reading processing from the reading control device 200 and, based on the timer control information, one of the first reading unit 21 and the second reading unit 22 is lit or both are Determine if it is lit.

  In the read image on the surface of the document D, only the light source 23 of the first reading unit 21 is turned on from the time when the count of the timer 1 becomes “0” to the time when the count of the timer 2 becomes “0”. From the time when the count of the timer 2 becomes “0” to the time when the count of the timer 3 becomes “0”, the light source of both the first reading unit 21 and the second reading unit 22 The image areas 23 and 261 are turned on and generated. This image area is a range set by the reading control apparatus 200 based on the timer control information, and the image processing unit 40 performs shading correction by applying shading correction data to each image area based on this setting. And

  In the read image on the back side of the document D, the light sources of both the first reading unit 21 and the second reading unit are from the time when the timer 2 reaches the count “0” to the time when the timer 3 reaches the count “0”. 23 and 261 are image areas generated by lighting, and only the light source 261 of the second reading unit 22 is lit from the time when the timer 3 reaches the count “0” to the time when the timer 4 reaches the count “0”. As a result, the image area is generated.

  Next, the shading correction unit 403 performs shading correction by switching different shading correction data according to the image area set by the reading control apparatus 200 (step S35). Specifically, a shading function is obtained for each lighting state of the light source and the position in the main scanning direction using the read shading correction data, and the shading function is applied to each image region.

For example, when the read image of the surface of the document D shown in FIG. 12 is obtained, the shading correction unit 403 turns on only one of the light sources 23 of the first reading unit 21 and generates one of the front-side lighting images. Using the white reference shading correction data and the one-lighting black reference shading correction data, the shading correction functions d and e (see FIG. 8) are obtained and applied.
On the other hand, for the image area generated by turning on the light sources 23 and 261 of both the first reading unit 21 and the second reading unit 22, both the lighting white reference shading correction data and the lighting both black reference shading correction data are used. The shading correction functions D and E (see FIG. 8) are obtained and used.

  The same applies to the read image on the back side of the document D. That is, in the image area generated by turning on the light sources 23 and 261 of both the first reading unit 21 and the second reading unit 22, the both-side lighting white reference shading correction data and the both-lighting black reference shading are displayed. With respect to an image region generated by applying only the light source 261 of the second reading unit 22 and lighting the shading correction functions D and E using the correction data, the white reference shading correction data for one lighting and the one lighting are generated. The shading correction functions d and e are obtained using the black reference shading correction data for use and applied.

In other words, the shading correction unit 403 switches shading correction data to be used in accordance with image regions having different luminance characteristics depending on the lighting state of the light source and the position in the main scanning direction in the read image of the front or back surface of the document D.
When the shading correction unit 403 outputs the read image subjected to the shading correction (step S36), the process ends.

  As described above, according to the present embodiment, the position (center portion and end portion) of the read image in the main scanning direction and the light sources 23 and 261 of the first reading unit 21 and the second reading unit 22 are turned on. Corresponding shading correction data is prepared, and shading correction is performed using shading correction data corresponding to image areas in which the position of the read image in the main scanning direction and the lighting state of the light source differ in the read image. Thus, not only the luminance difference caused by the position in the main scanning direction but also the luminance difference caused by the lighting states of the light sources 23 and 261 of the two reading units 21 and 22 can be corrected, and appropriate shading correction is performed. be able to.

  Further, according to the present embodiment, there is no restriction on the operation of the reading unit 20 such that one of the light sources 23 and 261 of the two reading units 21 and 22 facing each other is turned off when one is turned on. Therefore, it is not necessary to use a light source with excellent blinking performance and light output performance, and cost can be improved.

1 is a schematic configuration diagram of an image forming apparatus. 1 is a schematic configuration diagram of an automatic document feeder. It is a schematic block diagram of a 1st reading part. It is a schematic block diagram of a 2nd reading part. 2 is a functional block diagram of the image forming apparatus. FIG. It is a figure explaining the relationship between lighting on / off of a light source, and the shading correction data which a reading part acquires. It is a figure which shows the relationship between the position of a main scanning direction of a white reference board, and a light quantity signal. It is a figure which shows the relationship between before shading correction | amendment and after shading correction | amendment. 6 is a flowchart illustrating a reading operation for simultaneously reading both sides of a document. It is a timing chart explaining the lighting timing of a light source. It is a flowchart explaining a shading correction process. It is a figure which shows the image area divided in the read image.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Automatic document feeder 20 Reading part 21 First reading part 22 Second reading part 40 Image processing part 100 Image forming apparatus 200 Reading control apparatus 403 Shading correction part

Claims (6)

An image area that is read when one of the two reading units is turned on with respect to a read image in which the images on the front and back sides of the document are read simultaneously by two reading units having a light source. And a shading correction means for performing shading correction by switching different shading correction data in the image area when both of the two reading sections are lit and read when both are lit.
An image processing apparatus comprising: The shading correction data includes one-lighting shading correction data for correcting a luminance difference generated when one of the two reading units is lit, and luminance generated when both the pair of reading units are lit. Including shading correction data for both lighting for correcting the difference,
The shading correction means uses the one-lighting shading correction data for the one-lighted image area in the read image and performs the shading correction for the two-lighted image area using the two-lighting shading correction data. The image processing apparatus according to claim 1, wherein the image processing apparatus performs the processing. The shading correction data is data indicating the highest luminance value or the lowest luminance value of an image read by the reading unit, and is created using a white reference plate or a black reference plate,
The shading correction unit calculates a shading function that uses the shading correction data to associate a luminance value of a read image with a gradation of an output image, and performs shading correction using the shading function. 2. The image processing apparatus according to 2. A reading device that simultaneously reads images on the front and back sides of a document by two reading units having a light source;
In the read images of the read front and back surfaces, the image area was read when one of the two reading units was lit, and was read when both the two reading units were lit. Shading correction means for performing shading correction by switching different shading correction data depending on the image area when both are lit,
An image forming apparatus comprising: An image reading apparatus that reads images on the front and back sides of a document at approximately the same time by two reading units having a light source,
Shading correction data selection means for selecting shading correction data based on the position on the document image at the reading position of each reading unit and the lighting state of each light source of each reading unit;
Shading correction means for performing shading correction using the selected shading correction data;
An image reading apparatus comprising: The shading correction data includes one-lighting shading correction data for correcting a luminance difference generated when one of the two reading units is lit, and luminance generated when both the pair of reading units are lit. Including shading correction data for both lighting for correcting the difference,
The shading correction means uses the one-lighting shading correction data for the one-lighted image area in the read image and performs the shading correction for the two-lighted image area using the two-lighting shading correction data. The image reading apparatus according to claim 5, wherein the image reading apparatus is performed.

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