JP2011091473A - Document reader - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent occurrence of a density difference between read images even when the inclination of a reflective surface of a document with respect to emitted light is different when reading an image while transporting the document. <P>SOLUTION: Document reading is started by control of a control section (S1); the system is determined to be a sheet through read system (S2); when it is determined that density correction is executed to read image data (S3), the document is irradiated with light for detecting the inclination of the document at a reading position, and image data are read at the reading position of the document (S4); a light reception position is detected by a reflection position detection portion (S5); a correction coefficient corresponding to the light reception position is read from a reference table based on the light reception position (S6); the read image data are multiplied by the correction coefficient to correct the density of the read image data (S7); and, when reading ends (S8), this processing is ended. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a document reading apparatus that reads an image of a document.

An original image in a document reading apparatus including a scanner (also referred to as an “image reading apparatus”) and an image forming apparatus including a facsimile machine, a copier, and a multifunction peripheral (also referred to as an “image processing apparatus”) including the document reading apparatus. For scanning, a pressure plate reading method that reads the image by moving the optical device while the original is fixed, and a sheet-through reading that reads and moves the original while moving the optical device without moving the optical device There is a method.
In the sheet-through reading method, when an inclination occurs during document conveyance, the amount of reflected light with respect to the document changes, so that a density difference occurs with respect to the pressure plate reading method.
In the conventional document reading apparatus, since the machine is large, the document transport path can be made long, so that the document can be prevented from being tilted.

However, in a document reading apparatus whose unit has become smaller and faster in recent years, the document transport path becomes shorter, the document incident angle to the reading position becomes steep, and the document tends to curl. There was a problem that the occurrence became more remarkable.
Conventionally, before feeding a document, after reading one or more lines of the document pressing surface and holding it as reference data, the image information fed by the document and read by the reading means is converted into digital image data. An image reading apparatus that determines a correction method with reference to the reference data of the image data of a plurality of lines selected from the above and the reference data, and corrects the digital image data based on the determined correction method (for example, And Patent Document 1).

  In addition, when an instruction for reading a document is given, an initial white reference value is acquired by reading the first reference white plate, the initial white reference value, the designated predetermined operation mode, variation in white reference value, and correction coefficient. The correction coefficient for the first document is set in accordance with the history of the document, and the reading of the conveyed document at the transported document reading position and the acquisition of the white reference value by reading the second reference white plate are performed simultaneously. There has been an image reading apparatus (for example, refer to Patent Document 2) that corrects the density of a read original in accordance with the amount of change in white reference value at the time of reading with respect to the initial white reference value.

However, due to differences in conditions such as the thickness, type, and curl amount of the document, the document surface with respect to the light irradiation direction when the document passes through the reading area (the portion irradiated with light for image reading). May tilt, and the slope may change during the conveyance.
The above-described conventional image reading apparatus has a problem that the density of a read image that changes in accordance with the behavior of the document surface being conveyed cannot be corrected.
The present invention has been made in view of the above points. When an image is read while conveying the original, even if the inclination of the reflection surface of the original with respect to the irradiated light is different, a density difference does not occur in the read image. The purpose is to.

  In order to achieve the above object, the present invention sequentially moves the document to a predetermined reading area, irradiates the document reaching the reading area with light for image reading, and based on the reflected light from the document. In the image reading apparatus for reading the image data of the original, light irradiating means for irradiating light for obtaining specular reflection light from the original that has reached the reading area, and the original that has reached the reading area by the light irradiating means In response to the light receiving position detecting means for detecting the light receiving position of the received regular reflected light and the light receiving position detected by the light receiving position detecting means in advance. Correction coefficient determination means for determining a correction coefficient for correcting the measured density, and image data obtained by reading the correction coefficient determined by the correction coefficient determination means from the original. Operation to provide a document reading device provided with density correction means for correcting the concentrations against.

The light emitted by the light irradiating means may be different from the visible length.
Furthermore, the light irradiating means and the light receiving position detecting means may be arranged on the back side of the document.
Further, a combination of the light irradiation means and the light receiving position detection means may be provided for each of a plurality of colors of the image data.
Further, the density correction means may correct the density of the image data in consideration of the delay time of the image data.

Further, the correction coefficient determining means may determine the correction coefficient from a plurality of lines of light receiving positions.
Further, a storage means for storing a correction coefficient for correcting the density measured in advance corresponding to the light receiving position is provided, and all the image data read from the original is temporarily stored, and the stored image data is stored in each stored image data. On the other hand, the density correction by the density correction means may be performed.
Furthermore, the density correction unit may be a unit that performs a process of correcting the density only in a region designated for the image data.

  The document reading apparatus according to the present invention can correct a density difference of a read image that occurs according to the inclination of the reflection surface of the light irradiated on the document when the image is read by irradiating light while the document is conveyed.

1 is a diagram illustrating a configuration of a document reading apparatus according to an embodiment of the present invention. It is explanatory drawing of the reflected light from a document. FIG. 6 is an explanatory diagram of a function unit that detects the degree of inclination of a document. FIG. 4 is a graph showing a relationship between a light receiving position and a density of read image data in a reflection position detection unit shown in FIG. 3.

It is a block diagram which shows each function part which concerns on the image process of the read image data. It is a figure which shows the procedure of a density correction process. It is a flowchart figure which shows the original reading process of the original reading apparatus of this Example.

Hereinafter, embodiments for carrying out the present invention will be specifically described with reference to the drawings.
〔Example〕
FIG. 1 is a diagram showing the configuration of an original reading apparatus according to an embodiment of the present invention.
This document reading apparatus is an image reading apparatus including a scanner. The document reading apparatus can be mounted on an image forming apparatus including a facsimile machine, a copying machine, and a multifunction machine. This document reading device reads an image of a document by a sheet-through reading method and acquires the image data.
Next, a conveyance system of the document reading apparatus will be described.
The document S placed on the document tray 1 is guided to the sheet feed roller 3 by the sheet feed roller 2, and is conveyed to the reading position P below the document pressing unit 5 through the first conveyance roller pair 4.

In the vicinity of the reading position P, the document pressing portion 5 presses the document S against the contact glass 6 with a constant urging force, so that the document S passes while being pressed to the contact glass 6 side. In this way, flapping near the reading position P can be suppressed when the document S is conveyed.
If the pressing force of the document pressing unit 5 is too strong, if the document S is thin, the document pressing unit 5 may not pass through the gap between the document pressing unit 5 and the contact glass 6. The pressing force may be adjusted based on the thickness of S.
Further, since the document pressing portion 5 is not essential for the embodiment of the present invention, the document pressing portion 5 may be omitted.
The document S that has passed the reading position P is discharged through the second conveying roller pair 7.

Next, the optical system will be described.
The original S passing through the reading position P is irradiated with light from the light source 8. As the light source 8, an Xe lamp, a cold cathode tube, an LED, or the like is used.
A reflector 9 is disposed at a position facing the light source 8, and the reflector 9 reflects the irradiation light from the light source 8 to the reading position P, so that the direct irradiation light from the light source 8 with respect to the document S is defined. Irradiate light from the opposite direction.
The light irradiated to the reading position P is reflected on the surface of the document S, and the reflected light is reflected at a predetermined angle with respect to the document S. The reflected light (scattered light) is the first light. The light is reflected by the mirror 10, the second mirror 11, and the third mirror 12 and guided to the lens 13.

The reflected light that has passed through the lens 13 is incident on the light receiving element 14 mounted on the substrate 15.
Further, the light source 16 is a light that emits light that is applied to the original S at the reading position P in order to detect the inclination of the original S.
The reflection position detection unit 17 functions as a light reception position detection unit, and receives the reflected light reflected from the reading position P with respect to the document surface of the document S by the light emitted from the light source 16 and detects the light reception position. .

FIG. 2 is an explanatory diagram of the reflected light from the document.
When the document surface is irradiated with light, the reflected light includes regular reflection light and diffuse reflection light (also referred to as “scattered light”).
For reading an image from an original, diffused reflected light of reflected light is incident on a light receiving element to obtain image data.
With respect to the reflected light, as shown in FIG. 5A, if the original surface of the original S is parallel to the contact glass, and if the original is not inclined, the reflected light with respect to the irradiation light L1 The central light L3 of the diffuse reflected light is reflected substantially perpendicular to the document surface, and the angle θa between the central light L3 of the diffuse reflected light and the regular reflected light L2 is the center light L3 of the irradiation light L1 and the diffuse reflected light. The angle is almost the same.

On the other hand, when the document surface of the document S is tilted with respect to the contact glass, as shown in FIG. 5B, the angle θb formed by the center light L3 of the diffuse reflected light and the regular reflected light L2 is irradiated. When the angle is smaller than the angle formed by the light L1 and the central light L3 of the diffuse reflected light, the intensity of the central light L3 of the diffuse reflected light is higher than that shown in FIG. The density of the image data is higher than that obtained from the diffusely reflected light in the case shown in FIG.
Further, as shown in FIG. 5C, when the angle θc formed between the center light L3 of the diffuse reflected light and the regular reflected light L2 is larger than the angle formed between the irradiation light L1 and the center light L3 of the diffuse reflected light. The intensity of the central reflected light L3 of the diffuse reflected light is weaker than that shown in (a) of the figure, and as a result, the density of the read image data is the same as that shown in (a) of the figure. It is thinner than that obtained from diffusely reflected light.

As described above, the intensity of the diffusely reflected light from the original varies depending on the angle of incidence on the original surface. The smaller the angle formed with the regular reflected light, the higher the intensity of the light. The greater the angle between the two, the lower the light intensity.
Therefore, even when images on the same document are read, a difference occurs in the density of the read image data depending on the inclination of the document.

As described above, when reading an image of an original, the density of the read image data changes depending on the inclination of the original surface with respect to the contact glass (or irradiation light).
In view of this, the document reading apparatus according to the present embodiment detects the inclination of the original with respect to the irradiation light when reading the document, and corrects the density of the read image data in accordance with the inclination.
FIG. 3 is an explanatory diagram of a functional unit that detects the degree of document inclination.
Regularly reflected light and diffusely reflected light from the light source 8 at the reading position P with respect to the original S1 with no inclination, and light emitted from the light source 8 at the reading position P with respect to the original S2 in an inclined state The regular reflection light and the diffuse reflection light are different.

Therefore, the light source 16 (light irradiating means) is disposed at a position where light is incident on the document S obliquely. For example, an LED may be used as the light source 16. In the case of the LED, since the directivity of light is narrow, the original surface can be irradiated without spreading the light, and different regular reflection light can be obtained according to the inclination of the original surface. Further, for example, a light source that emits light having a wavelength that is difficult for the light receiving element to read in a configuration of reading infrared light or the like may be used.
A reflection position detector 17 is disposed on the folded surface. For example, a PSD element may be used for the reflection position detection unit 17. Since the PSD element changes the output value in accordance with the light receiving position, it is possible to detect the inclination of the document based on the amount of change in the output value.
In addition, a method of providing a light receiving element such as a CCD and detecting the peak position is conceivable.

FIG. 4 is a graph showing the relationship between the light receiving position in the reflection position detection unit and the density of the read image data.
In the reflection position detection unit 17, when the light reception position of the regular reflection light from the document S1 (or S2) is detected in the A direction, the angle θb formed by the center light L3 of the diffuse reflection light and the regular reflection light L2 is This is a case where the angle between the irradiation light L1 and the central light L3 of the diffuse reflected light is smaller, and the intensity of the central light L3 of the diffuse reflected light is stronger than the reference reading (when the original is not tilted). As a result, the density of the read image data is higher than that obtained from the diffuse reflected light at the time of reading as a reference.

When the light receiving position of the regular reflection light from the document S1 (or S2) is detected in the B direction, the angle θc formed by the center light L3 of the diffuse reflection light and the regular reflection light L2 is diffused with the irradiation light L1. This is a case where the angle of the central light L3 of the reflected light is larger than the angle formed by the central light L3, and the intensity of the central light L3 of the diffusely reflected light becomes weaker than that at the time of the standard reading. It becomes thinner than that obtained from the diffusely reflected light at the time of reading.
That is, as the detected light receiving position approaches the reading position P, the light incident on the light receiving element becomes stronger in the reflection position detection unit 17, so that even if an original with the same density is read, the reflection position detection unit 17 Accordingly, the concentration received by the light receiving element changes.

Therefore, the amount of change in the density of each image data with respect to each light receiving position detected by the reflection position detection unit 17 is measured in advance by experiment, and the density of the image data different for each light receiving position is used as a reference based on the amount of change. Each correction coefficient (parameter) for matching with the density of the image data at the time of reading is obtained. For example, the correction coefficient for each light reception position detected by the reflection position detection unit 17 is associated with the memory of the control unit 27 described later. For example, the data is stored in a reference table format.
In this embodiment, the light source 16 and the reflection position detection unit 17 are shown separately. However, if the light source 16 and the reflection position detection unit 17 are arranged adjacent to each other, they can be integrated.
Further, the case where the reading position P of the document is set to the light irradiation position is shown, but if the inclination of the document can be detected, the light irradiation position on the document is set to a place other than the reading position P. Good.

Next, the density correction process of the read image data will be described.
FIG. 5 is a block diagram illustrating each functional unit related to image processing of read image data.
The control unit 27 is a CPU and includes a rewritable ROM (not shown).
The control unit 27 controls each of the following units, reads a correction coefficient from a reference table stored in the ROM, sends the correction coefficient to the density correction unit 24, and performs density correction of image data based on the correction coefficient to the density correction unit 24. Make it. That is, the control unit 27 functions as a correction coefficient determination unit, and the density correction unit 24 functions as a density correction unit.
Image data read from the document is output as R, G, and B analog data from a light receiving element (image sensor) 14.
The analog-to-digital converter 20 converts R, G, B analog data from the light receiving element 14 into digital data and outputs the digital data.

In the image processing unit 21, the inter-line correction unit 22 corrects the line interval of the light receiving element 14 for the R, G, B digital data.
Further, the black correction unit 23 corrects the black level.
Further, the density correction unit 24 performs density correction.
Further, the shading correction unit 25 performs shading correction.
Further, the other image processing unit 26 performs other image processing and outputs the result.
In FIG. 5, the density correction unit 24 is provided in front of the shading correction unit 25, but may be provided immediately after the shading correction unit 25.

FIG. 6 is a diagram illustrating a procedure of density correction processing.
When the reflection position detection unit 17 receives the regular reflection light at 30 in the figure, the control unit 27 detects the light reception position at 32 and reads the correction coefficient corresponding to the light reception position from the reference table at 33. do. On the other hand, the read image data inputted from the light receiving element 14 is inputted at 31.
Then, at 34, the read image data is multiplied by the correction coefficient, and the obtained image data is output at 35.

FIG. 7 is a flowchart showing the document reading process of the document reading apparatus of this embodiment.
Under the control of the control unit 27, when document reading is started in step (indicated by "S" in the figure) 1, it is determined in step 2 whether or not the sheet-through reading method is used. If it is not the sheet-through reading method, the process proceeds to step 10.
In step 3, it is determined whether or not density correction is performed on the read image data. If so, the process proceeds to step 4, and if not, the process proceeds to step 10.
In step 4, the light source 16 is turned on to irradiate the original with light for detecting the inclination of the original at the reading position P, and the image data at the original reading position P is read with the irradiation light from the light source 8. Go to step 5.

In step 5, the reflection position detection unit 17 detects the light receiving position using a line synchronization signal, which is a line start signal when reading an image from the document, as a trigger, and the process proceeds to step 6.
In step 6, based on the light reception position detected by the reflection position detection unit 17, a correction coefficient calculation process for reading a correction coefficient corresponding to the light reception position from the reference table is performed, and the process proceeds to step 7.
In step 7, the read image data is multiplied by the correction coefficient to correct the density of the read image data. The image data may be averaged only at the head of one line or by sampling a plurality of image data. All the image data of the line is multiplied by a correction coefficient corresponding to the light receiving position obtained in synchronization with one line. Then, it progresses to step 8.

In step 8, it is determined whether or not the reading of the document is finished. If finished, the process is finished. If not finished, the process proceeds to the process for the image data of the next line in step 9, and the process returns to step 5. The above process is repeated.
On the other hand, in step 10, the density correction function is disabled, normal image reading is performed in step 11, and this process ends.
In this way, the density correction is performed for each line of the image data, so that the variation in detection of the light receiving position of the regular reflection light during reading of the original, that is, the density change due to the inclination amount of the original can be corrected as needed. It becomes possible.

The document reading apparatus of this embodiment irradiates the document with light, detects the tilt of the document based on the light receiving position of the reflected light, and sequentially calculates the correction coefficient for each line to correct the image data. Even when the document is tilted, it is possible to prevent a difference in reading density of the document.
Further, since the correction coefficient is always derived and corrected, the correction can be performed without being affected by conditions such as the type of document, thickness, and curl.
In the embodiment of the present invention, the reflection position detection unit 17 may receive the reflected light of the irradiation light from the light source 8. In that case, it is not necessary to provide the light source 16, and the number of parts can be reduced to reduce the manufacturing cost of the document reading apparatus.
Further, when the light source 16 is an LED, it is conceivable that diffuse reflected light is input to the light receiving element depending on the way of reflection.
Therefore, if a light source such as an infrared LED having a low sensitivity at the light receiving element is used, there is no fear of input to the light receiving element if an infrared cut structure is employed.

Further, the light source 16 and the reflection position detection unit 17 are arranged under the contact glass 6 so that the inclination is detected by the reading surface of the document. However, there is a concern about the input of light to the light receiving element. The light source 16 and the reflection position detection unit 17 may be arranged on the document pressing unit 5 side so that the back side can be irradiated with respect to the document reading position P and the reflected light can be received.
In addition, since light receiving elements such as color CCDs need to read R, G, and B images at the same time, the light receiving elements of each color are arranged at positions that are separated by a certain distance.
In this case, since it is conceivable that the inclination of the original is different for each color, a plurality of light sources 16 and reflection position detectors 17 are provided to detect the inclination of the original corresponding to a light receiving element different for each color. It is preferable to perform density correction for each.
In this way, by estimating the actual document inclination amount from a plurality of detection results, it is possible to correct the density of each image data even when light receiving elements of each color are arranged at distant positions.

Further, with respect to the density correction processing, correction is performed by multiplying all the data of the line by a correction coefficient obtained in synchronization with one line. However, in the case of a color image as described above, correction between lines is performed. Depending on the color, it becomes delayed data. Therefore, it is possible to select a correction coefficient without deviation by setting a delay time for each color.
Further, as a correction coefficient calculation method, various methods such as an average value of one line or a plurality of lines and weight calculation (sudden fluctuation can be reduced) can be considered.
In view of this, since it is conceivable that the optimum is different for each model of the document reading apparatus, it is preferable that the correction coefficient calculation method is selectable based on a designation input from the user.
Further, in the above-described processing, the case of sequentially correcting the image data of one line read from the document has been shown. However, the image data of all the lines of the document is temporarily stored in the memory, and the reflection position is linked to each image data. The detection result may be stored, and the density correction may be performed after reading the document.

In addition, since it may be possible to partially correct the density of the image data, a correction area is designated for the entire image area of the document, and the density correction is performed only for the designated correction area. You can also.
Furthermore, for example, a distance measuring sensor that derives a distance by detecting a light bounce position may be used. In this case, it is preferable to correct the density of the image data based on the perspective of the position where the irradiation light is irradiated onto the document surface.

  The document reading apparatus according to the present invention can be applied to an image reading apparatus including a scanner, and an image forming apparatus including a facsimile machine, a copier, and a multifunction machine including the image reading apparatus.

1: Document tray 2: Paper feed roller 3: Paper feed roller 4: First transport roller pair 5: Document pressing unit 6: Contact glass 7: Second transport roller pair 8, 16: Light source 9: Reflector 10: First mirror DESCRIPTION OF SYMBOLS 11: 2nd mirror 12: 3rd mirror 13: Lens 14: Light receiving element 15: Board | substrate 17: Reflection position detection part 20: Analog digital conversion part 21: Image processing part 22: Interline correction part 23: Black correction part 24: Density correction unit 25: Shading correction unit 26: Other image processing unit 27: Control unit S, S1, S2: Document

JP 2002-374393 A JP 2007-208672 A

Claims (8)

In an image reading apparatus that sequentially moves an original to a predetermined reading area, irradiates the original that has reached the reading area with light for image reading, and reads image data of the original based on reflected light from the original ,
Light irradiating means for irradiating light for obtaining specularly reflected light from the document that has reached the reading area;
A light receiving position detecting means for receiving specularly reflected light from the original by light applied to the original that has reached the reading area by the light irradiating means, and detecting a light receiving position of the received specularly reflected light;
Correction coefficient determining means for determining a correction coefficient for correcting the density measured in advance corresponding to the light receiving position detected by the light receiving position detecting means;
An original reading apparatus, comprising: density correction means for correcting the density by calculating the correction coefficient determined by the correction coefficient determination means on the image data read from the original.   2. The document reading apparatus according to claim 1, wherein the light irradiated by the light irradiation unit is different from a visible length.   3. The document reading apparatus according to claim 1, wherein the light irradiating unit and the light receiving position detecting unit are arranged on the back side of the document.   4. The document reading apparatus according to claim 1, wherein a combination of the light irradiation unit and the light receiving position detection unit is provided for each of a plurality of colors of the image data. 5.   5. The document reading according to claim 1, wherein the density correction unit corrects the density of the image data in consideration of a delay time of the image data. apparatus.   The document reading apparatus according to claim 1, wherein the correction coefficient determination unit determines the correction coefficient from a plurality of lines of light receiving positions.   A storage means for storing a correction coefficient for correcting the density measured in advance corresponding to the light receiving position is provided to temporarily store all image data read from the original, and for each stored image data 7. The document reading apparatus according to claim 1, wherein density correction is performed by the density correction unit.   The document reading apparatus according to claim 1, wherein the density correction unit is a unit that performs a process of correcting the density only in a specified region with respect to the image data.

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