JP2012209876A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve accuracy of shading correction in an image reader in which white light consisting of light beams of a plurality of colors is set to be a light source and the light source is continuously lighted to read a manuscript.SOLUTION: Shading correction to all light components is performed from a light volume just after lighting of the light source, a measured value of a specified light component whose fluctuation of the light volume after continuous lighting is the largest, and a table in which light volume fluctuation to continuous lighting time is displayed for the previously stored light components.

Description

  The present invention relates to an image reading apparatus, and more particularly, to an image reading apparatus with improved shading correction accuracy.

In recent years, an image reading apparatus has an LED (Light Emitting Diode) as its light source.
Has come to be used. This is because LEDs have lower power consumption than conventionally used halogen lamps, fluorescent lamps, and xenon tubes, and can reduce the use of harmful substances.

  In the image reading apparatus, white light is required as the light source. White light is produced by using a LED emitting blue light as a light source in combination with a phosphor emitting a complementary yellow light excited by the blue light, or emitting light of three colors of red, green, and blue. It is made by combining LEDs.

  Although it is considered that LEDs are rich in stable light emission, in actuality, when continuous light emission is performed, the luminance and light amount vary with an increase in the amount of heat generated by the heating element. More specifically, the luminance and light amount of the heat generating element have characteristics that vary with increasing temperature. In addition, luminance and light quantity variation characteristics differ for each color (long wavelength, short wavelength).

  By the way, with the progress of technology, the productivity (number of printed sheets per unit time) of an image forming apparatus increases, and accordingly, there is a demand for increasing the document reading speed of the image reading apparatus.

  Normally, the image reading apparatus performs shading correction when reading an image. In Patent Document 1 below, when using an ADF (Auto Document Feeder) equipped with a sheet-through reading function in order to improve time loss related to the shading correction, an auxiliary white reference plate (simple An image reading apparatus is described that uses a shading plate) to simply perform shading correction using profile data that represents the relationship between the fluctuation amount of the sampling value for each pixel and the fluctuation in light amount stored in advance in the image reading apparatus. ing.

JP2010-011439

  When the document reading method of Patent Document 1 described above is carried out in an image reading device using an LED light source, each light component of R (red), G (green), and B (blue) is also emitted during continuous feeding of a document using ADF. The shading correction can be performed without reducing the productivity by measuring the light quantity fluctuation for each using a simple shading plate.

However, as described above, when using a plurality of colors of light to produce white light as a light source and reading the document with this light source continuously turned on, for the light component with little light amount fluctuation, the measurement time of the light amount It is difficult to measure the exact light quantity fluctuation rate in the case, and as a result, there is a problem that the accuracy of shading correction is lowered. In other words, the light amount fluctuation rate for the light component with small light amount fluctuation is greatly affected by the measurement error and the shading correction accuracy becomes low compared with the light amount fluctuation rate for the light component with large light fluctuation. There's a problem.
Furthermore, as the distance between the auxiliary white reference plate and the image sensor becomes longer, a sufficient amount of light cannot be obtained, and as a result, the accuracy of shading correction is lowered.

  SUMMARY An advantage of some aspects of the invention is that it provides an image reading apparatus capable of performing appropriate shading correction even on a light component with little light amount fluctuation.

In order to solve the above problems, a first feature of the image reading apparatus according to the present invention is as follows:
An image reading apparatus for reading a document image by creating white light from several colors of light and continuously turning on the white light as a light source, wherein the light source and the reading element are arranged in a main scanning direction. The sensor, a white reference plate longer than the main scanning width of the image sensor, an auxiliary white reference plate installed outside the document image reading area, and data relating to the following light quantities (1) to (3) are stored: Memory means to do;
(1) A linear white reference value for each light component, which is a light amount value obtained by reading the light amount of the reflected light of the white reference plate immediately after the light source is turned on,
(2) An auxiliary white reference value that is a light amount value of each light component obtained by reading the light amount of the reflected light of the white auxiliary reference plate immediately after the light source is turned on,
(3) Temporal light quantity fluctuation data associated with the temporal light quantity fluctuations of the plurality of colors of light obtained by reading the auxiliary white reference plate,
After the light source is turned on and continuously turned on for a predetermined period, the light amount fluctuation is maximum from the measured value of the reflected light amount of the auxiliary white reference plate measured by the image sensor and the auxiliary white reference value (2). A certain light component is specified and measured using the measured value of the specified light component, the auxiliary white reference value (2), the temporal light quantity fluctuation data (3), and the white reference value (1). And a shading correction unit that calculates light amount line data for all light components at the time and executes shading correction using the light amount line data.

In order to solve the above problem, a second feature of the image reading apparatus according to the present invention is as follows:
An image reading apparatus for reading a document image by creating white light from light of a plurality of colors and continuously turning on the white light as a light source, wherein the light source and the reading element are arranged in a main scanning direction. The sensor, a white reference plate longer than the main scanning width of the image sensor, an auxiliary white reference plate installed outside the document image reading area, and data relating to the following light quantities (1) to (4) are stored. Memory means to do;
(1) Among the light of the plurality of colors, specific light that is a light component with a temporal light amount variation amount being a predetermined value or more,
(2) A linear white reference value of each light component, which is a light amount value obtained by reading the light amount of the reflected light of the white reference plate immediately after the light source is turned on,
(3) An auxiliary white reference value that is a light amount value of the specific light obtained by reading the amount of reflected light of the white auxiliary reference plate immediately after the light source is turned on.
(4) Temporal light quantity fluctuation data associated with the temporal light quantity fluctuations of the plurality of colors of light obtained by reading the auxiliary white reference plate,
After the light source is turned on and continuously turned on for a predetermined period, the measured value of the light quantity of the specific light (1) among the reflected light of the auxiliary white reference plate measured by the image sensor, and the auxiliary white reference value (3), the light amount fluctuation data with time (4), and the white reference value (2) are used to calculate light amount line data for all light components at the time of measurement, and shading correction is performed using the light amount line data And a shading correction means for executing the above.

Here, the specific light may have the longest wavelength among the light of the plurality of colors.

The plurality of colors of light may be composed of short-wavelength light and long-wavelength light in which a part of the short-wavelength light is converted by a light conversion material.

The effect of the present invention is that, in an image forming apparatus that reads a document by continuously turning on a light source, a light component having a maximum light amount fluctuation (variation amount, fluctuation rate) with respect to continuous lighting is identified, and the light quantity fluctuation of the identified light component And shading correction by estimating the light intensity line values for all light components using the time-dependent light intensity fluctuation data, there is little light intensity fluctuation, and the actual measurement of the light intensity results in low measurement accuracy and appropriate shading It is also possible to execute more accurate shunning correction even for light components that cannot be corrected.

In addition, when the image forming apparatus stores a light component having a predetermined amount or more of light fluctuation amount corresponding to the continuous lighting time as a specific light in the storage unit, it is necessary to measure a light amount value for an unnecessary light component. In addition, the time required for shading correction can be shortened.

Further, in the present invention, when the white light of the light source is made from short-wavelength light and long-wavelength light in which a part of the short-wavelength light is converted by the light conversion material, that is, the light emission mechanism of each light component However, the present invention can also be used for an image reading apparatus using different light sources. When light converted in wavelength by a light conversion material is used as part of a light source, first, the light conversion material is irradiated with light, and is affected by the temperature change caused by the light conversion material. However, according to the present invention, this problem can be solved.

1 is a diagram illustrating a schematic configuration of an image reading surface of an image reading apparatus according to an embodiment. FIG. 4 is a perspective view of a carriage at a position corresponding to an automatic reading area. 2 is a block diagram illustrating a functional configuration of an image reading apparatus and a control system of a host apparatus that receives image data from the image reading apparatus. FIG. 6 is a flowchart for describing image reading processing during document reading. It is a figure showing the light quantity ratio of the light quantity of each light component measured when a light source is lighted continuously for a predetermined time, and the initial light quantity.

  Embodiments of the present invention will be described with reference to the drawings. The image reading apparatus according to the present embodiment includes a sheet-through reading mode operation in which a plurality of originals placed on an automatic original reading table are automatically taken to perform image reading, and a user places one by one in an original placement area. A flat bed reading mode operation for reading an image of a placed document can be selectively performed. In the sheet-through reading mode, a carriage equipped with a light source that irradiates light on the original and a mirror that captures reflected light from the original is fixed, and the original is automatically read to perform reading. In the flat bed reading mode, the original is read. Reading is performed by fixing and scanning the carriage.

  1A and 1B are diagrams illustrating a schematic configuration of an image reading surface of an image reading apparatus according to the present embodiment. FIG. 1A is a plan view and FIG. 1B is a side view. As shown in FIG. 1A, the image reading apparatus 10 includes an automatic reading area 11 serving as a document reading surface in the sheet-through reading mode and a document placement area 12 serving as a document reading surface in the flat bed reading mode. I have. Each of these document reading surfaces is formed of a glass plate, and the periphery of the document reading surface is covered with a light shielding member. As shown in FIG. 1B, a guide plate 19 serving as a document conveyance guide in the sheet-through reading mode is disposed above the automatic reading area 11.

  A position guide plate 14 serving as a light shielding member between the automatic reading area 11 and the document placement area 12 functions as a position alignment guide when placing a document on the document placement area 12 in the flat bed reading mode. Marks such as A3, A4 and the center position are displayed on the front side of the position guide plate 14, and a white reference plate 15 is provided on the back surface.

  The white reference plate 15 is read to obtain a white reference value in the shading correction. In the shading correction, in order to generate correction data for each pixel, the white reference plate 15 has a length longer than the width of the first mirror 4a mounted on the light source carriage 16a, that is, a length longer than the width to be read. Like that. In the present embodiment, the white reference value 15 is sampled by reading the white reference plate 15 with the light source ON, and the black reference value is sampled by reading the white reference plate 15 with the light source OFF. However, a black reference plate may be provided separately, or the black reference value may be sampled elsewhere. Since the present invention particularly deals with the white reference value, the description of sampling of the black reference value is omitted hereinafter.

  The light emitted from the light source 18 and reflected by the document is guided to the image sensor 17 by the first mirror 4a, the second mirror 4b, the third mirror 4c, and the lens 3. Then, it is read as an image of a document by the image sensor 17.

  The light source carriage 16a on which the light source 18 and the first mirror 4a are mounted is fixed at a position A corresponding to the automatic reading area 11 in the sheet-through reading mode, and an image of the original G conveyed by an automatic original conveying mechanism (not shown). Read. In the flat bed reading mode, sampling of a white reference value for shading correction is performed at a position B corresponding to the white reference plate 15, and the sample is horizontally moved toward the end position C of the document placement area 12 by a carriage movement mechanism (not shown). To read the image of the document placed on the document placement region 12.

  The mirror carriage 16b on which the second mirror 4b and the third mirror 4c are mounted moves at a distance of 1/2 according to the moving direction of the light source carriage 16a. The image reading apparatus 10 of the present embodiment employs a so-called full half-rate mirror scanning method, and keeps the distance between the image sensor 17 fixed to the housing and the document surface constant.

  An auxiliary white reference plate 13 is provided on the back surface of the light shielding member on the main scanning direction side of the automatic reading area 11. The auxiliary white reference plate 13 is read to detect fluctuations in the light amount of the light source 18. The auxiliary white reference plate 13 is arranged at a position where the light source carriage 16a can be read in a state where the light source carriage 16a is fixed at the position A corresponding to the automatic reading area 11. The auxiliary white reference plate 13 only needs to be able to measure the amount of light from the light source 18, so that a member smaller than the white reference plate 15 can be used. The auxiliary white reference plate 13 is a white plate (for example, a white mylar seal) having a uniform reflectance together with the white reference plate 15. However, other members may be diverted or arranged in other areas.

In the present embodiment, the auxiliary white reference value 13 is sampled by reading the auxiliary white reference plate 13 with the light source ON, and the auxiliary black reference value is sampled by reading the auxiliary white reference plate 13 with the light source OFF. To do. However, the auxiliary black reference value may be stored in advance in the storage unit 30 described later.

  FIG. 2 is a perspective view of the light source carriage 16 a at the position A corresponding to the automatic reading area 11. As shown in the figure, the light source carriage 16a includes a light source 18 composed of an LED that creates white light from a plurality of colors of light and a first mirror 4a. The light source 18 reflects light reflected from the reading object by the first object. The light is reflected by one mirror 4a and guided to the second mirror 4b of the mirror carriage 16b. However, a so-called contact type configuration in which a line-type image sensor is mounted on the light source carriage 16a and the reflected light of the document is directly read may be employed.

  In the sheet-through reading mode, the document G is guided and conveyed by the guide plate 19 by a document conveying mechanism (not shown) in a direction (sub-scanning direction) orthogonal to the direction of the light source carriage 16a (main scanning direction), and the image is line-by-line. Is read.

  FIG. 3 is a block diagram illustrating the functional configuration of the control system of the image reading apparatus 10 and the host device 80 that receives image data from the image reading apparatus 10. As shown in the figure, the image reading apparatus 10 includes a control unit 20, a storage unit 30, a carriage moving mechanism unit 40, a document transport mechanism unit 50, and an operation panel 60 in addition to the image sensor 17 and the light source 18 described above. . However, the operation panel 60 may be provided outside the image reading device 10, for example, on the host device 80 side.

  The control unit 20 includes a CPU, an image processing circuit, an interface circuit, and the like, and controls an image reading operation in the image reading apparatus 10. In the present embodiment, the control unit 20 includes an image reading control unit 21, an image reading condition setting unit 22, an image processing unit 23, a color conversion processing unit 24, and an image output unit 25. These are configured by the CPU executing a control program recorded in the ROM 32 described later.

  The image reading control unit 21 controls the operations of the carriage movement mechanism unit 40, the document transport mechanism unit 50, and the light source 18 according to the image reading conditions received by the image reading condition setting unit 22, and performs a document reading process. That is, in the sheet-through reading mode, the light source carriage 16 a is moved to the position of the automatic reading area 11, and the original is conveyed by the original conveying mechanism 50 to perform the original reading process. In the flat bed reading mode, the document reading process is performed by moving the light source carriage 16a in the sub-scanning direction with respect to the document placed in the document placement region 12.

  The image reading condition setting unit 22 receives setting of image reading conditions from the operation panel 60 or the connected host device 80. The reading conditions received by the image reading condition setting unit 22 can include, for example, sheet-through reading mode / flatbed reading mode, double-sided reading / single-sided reading, enlargement / reduction processing, color / monochrome, number of gradations, resolution, and the like. .

  The image processing unit 23 performs image processing on the image data read by the image sensor 17. Further, the image processing includes shading correction for correcting sensitivity variations between elements of the image sensor 17. Therefore, the image processing unit 23 includes a shading correction unit 231 that performs a shading correction process.

  The shading correction unit 231 performs shading correction according to the following procedure. That is, prior to image reading of a document, the white reference plate 15 is sampled with the light source 18 turned on to obtain a white reference value for each pixel. Then, reading of the document is started with the light source 18 turned on, and the read image data is corrected for each pixel using the acquired white reference value and the separately acquired black reference value. This operation is performed for each of the R, G, and B light components.

For example, the image data Dout after shading correction for a certain pixel can be expressed by the following Equation 1, where the value of the read image data is Din, the white reference value is W0, and the black reference value is B0.
Dout = number of gradations × (Din−B0) / (W0−B0) (Formula 1)
This calculation is applied to each of R, G, and B light components.

  In the shading correction, the auxiliary white reference value W1 and the auxiliary black reference value B1 of the light source 18 are obtained by sampling the auxiliary white reference plate 13 when reading the first original. Then, the auxiliary white reference plate 13 is sampled immediately before the subsequent document reading to obtain a measurement value of the light amount of the light source 18, and a ratio between the obtained measurement value and the auxiliary white reference value W1 is calculated. Using this light quantity fluctuation ratio and temporal light quantity fluctuation data, which will be described later, an estimated value of the light quantity of all light components at the time of measurement is calculated to perform shading correction. Details will be described later.

  The color conversion processing unit 24 converts the RGB format image data into the CMYK format and performs a process of reducing gradation. The image output unit 25 performs processing for transferring the read image data to the host device 80.

The storage unit 30 includes a RAM (Random Access Memory) 31 and a ROM (Read Only Memory) 32. The ROM 32 has a rewritable EEPROM (Electrically Erasable Programmable
Read-Only Memory) 32a is included.

In the RAM 31, which is a volatile storage device, reference light amount line data (corresponding to the white reference value W 0 in Equation 1), black reference line data (black in Equation 1), which is a reference value of the light amount of each element in the main operation direction of the light source 18. Reference light amount B0), reference light quantity auxiliary data (corresponding to the above-described auxiliary white reference value W1), image reading data, and the like are stored. The RAM 31 is also used as a work area.

  A control program is stored in the ROM 32 which is a non-volatile storage device. The rewritable EEPROM 32a stores temporal light amount fluctuation data (corresponding to the graph of FIG. 5) representing the relationship of the light quantity fluctuation with respect to the passage of continuous lighting time for each light component. These data may be transferred to the RAM 31 for use when the image reading apparatus 10 is activated.

  The carriage moving mechanism unit 40 can be constituted by a motor, a driving belt, and the like, and moves the light source carriage 16a to the reading position or moves in the sub-scanning direction according to the control of the image reading control unit 21. Further, the mirror carriage 16b is moved by a distance of ½ in accordance with the moving direction of the light source carriage 16a. The document transport mechanism 50 includes a document reversing mechanism. When double-sided scanning is set as a reading condition, the document transport mechanism 50 reverses the document to read the back side after reading the front side.

  The host device 80 may be, for example, a printer, a PC, or the like, and includes a host controller 81 that is connected to the image reading device and controls image data reception processing.

  Next, a process in which the image reading apparatus 10 acquires the reference light amount line data P [1 to m] and the reference light amount auxiliary data M will be described.

  Here, the reference light amount line data P [1 to m] is a value for each pixel when the white reference plate 15 is sampled in a state where there is no decrease in the light amount immediately after the light source 18 is turned on. Note that m is the number of pixels read by the image sensor 17. The reference light amount auxiliary data M is a representative value when the auxiliary white reference plate 13 is sampled in a state where there is no light amount decrease immediately after the light source 18 is turned on. In the present embodiment, since the reference light amount auxiliary data is used as data indicating the light amount of the light source 18, a representative value of the sampling value is used instead of each pixel.

  The representative value can be, for example, an average value of the values of a plurality of pixels read from the auxiliary white reference plate 13. As a result, the influence of dirt, unevenness, etc. on the auxiliary white reference plate 13 can be reduced. The plurality of pixels can be, for example, pixels in an area configured with a predetermined length in the main scanning direction and a predetermined length in the sub-scanning direction. However, the average value of a plurality of pixels in either the main scanning direction or the sub-operation direction may be used.

  The reference light amount line data P [1 to m] and the light amount auxiliary data M are acquired before the reading operation for one job is started. However, you may make it acquire again when continuous lighting time passes predetermined period.

Next, the document reading operation of the present invention will be described with reference to the flowchart of FIG. 4 and FIG.

Here, FIG. 5 will be described in advance. FIG. 5 shows the ratio between the measured value of the light quantity (initial light quantity value) measured immediately after turning on the light source 18 and the measured value of the light quantity of each light component measured when the light source 18 is continuously turned on for a predetermined time. FIG. The LED is considered to have excellent light emission stability over time, but the light amount fluctuates with the continuous lighting time, and the light amount fluctuation rate varies depending on R, G, and B light components. It became clear by study of. Furthermore, it has been found that a larger fluctuation rate is produced with a longer light wavelength interlocking rate. In addition, it was found that the former is larger when the light amount fluctuation with respect to the long wavelength light component converted by the light conversion material is compared with the light quantity fluctuation rate with respect to the light component emitted by direct light emission. FIG. 5 shows these relationships for each light component, with the continuous lighting time on the horizontal axis and the light quantity fluctuation rate with the initial light quantity value on the vertical axis. This corresponds to the temporal light quantity fluctuation data of the present invention.

Although the graph of FIG. 5 is based on the continuous lighting time, it may be a graph in which fluctuations of other light components are expressed based on the light component with the largest change in light amount. In addition, as long as the light quantity variation rate can be expressed by a function expression, the function expression may be stored instead of the graph. In the present invention, these graphs, function expressions, and the like are collectively referred to as data.

  Returning to the flowchart of FIG. In the image reading process in this embodiment, when reading is started, first, the light source 18 is turned on (S101). Then, the reference light amount line data P [1 to m] and the reference light amount auxiliary data M in the current reading operation are acquired in a state before the light amount changes (S103). These values are all reference values in the current image reading job. The reference light amount line data P [1 to m] corresponds to the white reference value W0 in Equation 1.

Here, in acquiring the reference light quantity auxiliary data M, the auxiliary white reference plate 13 is sampled. Therefore, the light source carriage 16a is moved to the position of the automatic reading area 11, a predetermined area of the auxiliary white reference plate 13 is sampled, and the read value It is necessary to calculate an average value. In this case, the predetermined area can be a square area of X pixels in the main scanning direction and X pixels in the sub scanning direction, for example.

  Further, the measurement of the reference light amount line data P [1 to m] samples the white reference plate 15, so that the light source carriage 16a is moved to the position of the white reference plate 15, the white reference plate 15 is sampled by a plurality of lines, and the pixel The average value for each is set as the reference light amount line data P [1 to m]. In this way, by calculating the average value in the sub-scanning direction, it is possible to reduce the influence of dirt, unevenness, etc. on the white reference plate 15. However, sampling of only one line may be used.

There is no problem regardless of which order of acquisition of the reference light quantity auxiliary data M and the reference light quantity line data P [1 to m] is first. The acquired reference light amount auxiliary data M and reference light amount line data P [1 to m] are recorded in the RAM 31.

  Next, the first original is read (S105), and shading correction is performed on the image data of the read original (S107 to S115).

The shading correction in steps S107 to S115 in the present invention will be specifically described. When reading a document, the image sensor 17 obtains the latest light amount auxiliary value N in order to grasp the current light amount of the light source 18. The light amount auxiliary value N is obtained by sampling a predetermined area of the auxiliary white reference plate 13 and calculating an average value of the read values. The predetermined area is preferably the same size as when the auxiliary light amount data is acquired. Here, the auxiliary white reference plate 13 can perform sampling without moving the light source carriage 16a in the sheet-through reading mode (S107).

Then, the shading correction unit 231 calculates the difference between the light amount values of the respective light components using the light amount auxiliary value N and the reference light amount auxiliary data M, and the light component having the largest difference, that is, the light amount fluctuation rate is the maximum. A certain light component is specified (S109).

Next, the shading correction unit 231 refers to the temporal light amount fluctuation data (corresponding to the data in FIG. 5) that is transferred from the EEPROM 32a to the RAM 31 and recorded in advance, and the light quantity fluctuation specified in step S109 is the maximum. Using the light amount fluctuation rate of the light component, an estimated value of the light amount of all the light components at the time of the measurement is calculated (S119). That is, the shading correction unit 231 performs (1) calculation of (N / M0) for the light component having the largest light quantity variation rate, and (2) is calculated by calculation (1) from the graph illustrated in FIG. The light amount fluctuation rate of other light components corresponding to the light amount fluctuation rate calculated is calculated, and (3) the light amount assistance is obtained by multiplying the reference light amount line data P [1 to m] corresponding to each light component by the calculated light amount fluctuation rate. A light amount line estimated value Pn [1 to m], which is light amount line data of all light components at the time of measurement of the value N, is calculated (S113).

Next, the shading correction unit 231 performs the shading correction at the time when the auxiliary light amount N is acquired for the document data read in step S105. In other words, in Equation 1, when the image data Dout after shading correction is Pout [1 to m], the Pout [1 to m] is a light amount line estimated value Pn [1 to m calculated from the input data Din in step S113. ], The reference light quantity line data P [1 to m] acquired before the start of the reading operation with the white reference value W0 and B0 as B [1 to m] are expressed by the following Equation 2.
Pout [1 to m] = tone number × (Pn [1 to m] −B [1 to m]) / (P [1 to m] −B [1 to m]) (Expression 2)

  Then, the control unit 20 confirms the presence or absence of the next read original. If there is no next read original (S117; YES), the controller 20 turns off the light source 18 and ends the original reading process (S119).

When there is a next read original (S117; No), the process returns to step S105 and the above-described operations (S105 to S117) are repeated. In this embodiment, the light source line estimated values Pn [1 to m] are calculated as needed in order to continuously turn on the high source 18 in the second and subsequent shading corrections. Certain reference light quantity line data P [1 to m] is assumed to be used as a constant one.

  As described above, according to the present invention, when the light source 18 is continuously turned on, the light component with the largest light amount fluctuation is specified from the auxiliary white reference value, and the other light components are measured from the light amount fluctuation of the light component. An estimated value of the light amount line data at the time is calculated, and shading correction is performed. Therefore, even when the accuracy of measuring the actual measurement value for the light component with small light amount fluctuation is low, more accurate shading correction can be performed.

Further, when a method of making white light in combination with a phosphor emitting a complementary yellow light excited by blue light is used as the light source 18, the mechanism for emitting light of blue and other components is different. As a result, the temperature characteristics with respect to the light component greatly fluctuate as compared with those of direct light emission due to the heat generated from the light conversion material. Even in this case, the same effect as described above can be obtained.
<Other embodiment 1>

In the present invention, the shading correction using the light amount auxiliary reference value M and the light amount auxiliary value N of the light component having the maximum light amount fluctuation with respect to the continuous lighting time has been described. For example, when the difference between the light amount auxiliary value N and the reference light amount auxiliary reference value M for a light component is greater than or equal to a predetermined value, light amount line data of light components other than the light component having the largest light amount fluctuation is acquired. In this case, the measured value can be used. In this case, as step S108 between step S107 and step S109 in the flowchart of FIG. 4, “whether the difference between the reference light amount auxiliary reference value M and the light amount auxiliary value N is equal to or greater than a predetermined value” for each light component. To make a judgment. For light components whose difference is greater than or equal to a predetermined value (threshold), the light amount line estimated value Pn [1 to m] may be estimated using the actual measurement value. When the difference is less than the predetermined value (threshold) The shading correction unit 231 may control so that the processing of steps S109 to S113 is performed.
<Other embodiment 2>

In addition, when it is known in advance that a specific light component has the largest light amount fluctuation as shown in FIG. 5, that is, when this information is stored in any one of the storage units 30, In performing the shading correction in the invention, the light amount auxiliary value N may be measured by extracting only the light amount value of the light component. This is because the estimated values can be used for the other light components by calculation using the temporal light amount fluctuation data. Here, in the case of FIG. 5, the R component with the longest wavelength corresponds. By processing in this way, it is not necessary to calculate measurement values for light components other than the light component with the largest amount of light fluctuation and to compare with the auxiliary white reference value, thereby reducing the time required for shading correction. Can be made. Specifically, a part of step S107 and step S109 can be omitted in the flowchart of FIG. In this case, step S111 is “calculate the light amount fluctuation rate of the extracted (identified) light component”. In addition, although the thing with the largest light quantity fluctuation | variation was demonstrated as a specific light component, if a light quantity fluctuation amount is more than predetermined (light quantity fluctuation is more than a predetermined threshold value), there is no problem. For example, instead of the R component, the G component light may be a specific light component.
<Other embodiment 3>

In the embodiment described above, simple shading correction is executed for each original (step S117 in FIG. 4; No and after). However, this determination is made by (A) “whether the continuous lighting time of the light source has exceeded a predetermined time since the previous shading correction was performed” or (B) “higher than the previous shading correction was performed. It may be determined whether or not the light amount fluctuation for the light component having the largest light amount fluctuation of the source exceeds a predetermined value (threshold value).

Specifically, in the case of (A), when there is a next read original (S117; No), before proceeding to step S105, “the continuous lighting time of the light source after executing the previous shading correction is predetermined. A determination step of “whether or not the time has been exceeded” is included. If “predetermined time has elapsed”, the processing from step S115 is executed as shown in the flowchart. If “predetermined time has not elapsed”, the light amount auxiliary value N and the light amount used in the previous shading correction. Shading correction is executed using the line data Pn [1 to m]. That is, the shading correction may be executed (S115) while skipping steps S107 to S113. The light quantity auxiliary value N and the light quantity line data Pn [1 to m] may be recorded in the RAM 31 at any time.

Alternatively, in the case of (B), if there is a next read original (S117; No), before proceeding to step S115, “light amount fluctuation for the light component that has the largest light quantity fluctuation since the previous shading correction was performed”. Is included in a determination step of “whether or not exceeds a predetermined value (threshold)”. In the case of “exceeding the predetermined value”, the processing from step S105 is executed as shown in the flowchart. In the case of “not exceeding the predetermined value”, the auxiliary light amount value N used in the previous shading correction, The shading correction is executed using the light amount line data Pn [1 to m]. That is, the shading correction may be executed (S115) while skipping steps S107 to S113. The light quantity auxiliary value N and the light quantity line data Pn [1 to m] may be recorded in the RAM 31 at any time.

Even in these cases, the number of times of measurement using the auxiliary white reference plate 13 can be reduced, the processing such as the identification of the light component having the maximum light amount fluctuation amount can be omitted, and the time required for the shading correction can be shortened.

In the case of determining whether or not “a predetermined time has elapsed”, the “predetermined time” is variable according to the continuous lighting elapsed time, that is, corresponding to the light quantity fluctuation characteristics. It is preferable. This is because, as can be seen from the graph of FIG. 5, there is a difference in the variation rate of the light amount immediately after the light source 18 is turned on and after a certain amount of time has passed. As a result, highly accurate shading correction can be executed.
<Other embodiment 4>

In the embodiment described above, the reference light amount line data P [1 to m], which is the white reference value, has been described as being constant regardless of the continuous lighting time of the light source 18. However, since the amount of light varies with time, it is necessary to update the white reference value as needed in order to perform more accurate shading correction. In this case, it is effective to execute the invention described in Patent Document 1 (Japanese Patent Application Laid-Open No. 2010-011439). That is, the light amount variation with time may be corrected individually for all pixels in the main operation direction of the light source 18.
<Other embodiment 5>

  In the above embodiments, sheet-through reading using ADF has been described. However, the present invention can be implemented even when the light source 18 is continuously turned on in a reading operation using a flat bed. Further, all of the above-described are described for correcting shading using values obtained by reading the auxiliary white reference plate. However, the continuous lighting time is a predetermined period, for example, a predetermined time, a predetermined number of originals to be read, When each reading interval elapses, shading correction may be executed using a value obtained by reading the white reference plate.

DESCRIPTION OF SYMBOLS 3 ... Lens, 4a ... 1st mirror, 4b ... 2nd mirror, 4c ... 3rd mirror, 10 ... Image reading apparatus, 11 ... Automatic reading area | region, 12 ... Original document mounting area, 13 ... Auxiliary white reference board, 14 ... Position guide plate, 15 ... white reference plate, 16a ... light source carriage, 16b ... mirror carriage, 17 ... image sensor, 18 ... light source, 19 ... guide plate, 20 ... control unit, 21 ... image reading control unit, 22 ... image reading Condition setting unit, 23 ... Image processing unit, 24 ... Color conversion processing unit, 25 ... Image output unit, 30 ... Storage unit, 31 ... RAM, 32 ... ROM, 40 ... Carriage movement mechanism unit, 50 ... Document transport mechanism unit, 60 ... Operation panel, 80 ... Host device, 81 ... Host controller, 231 ... Shading correction unit

Claims (4)

An image reading apparatus that creates white light from a plurality of colors of light, reads the original image by continuously turning on the white light as a light source,
A line-shaped image sensor in which the light source and the reading element are arranged in the main scanning direction;
A white reference plate having a length longer than the main scanning width of the image sensor;
An auxiliary white reference plate installed outside the document image reading area;
Storage means for storing data relating to the light quantity of (1) to (3) below;
(1) A linear white reference value for each light component, which is a light amount value obtained by reading the light amount of the reflected light of the white reference plate immediately after the light source is turned on,
(2) An auxiliary white reference value that is a light amount value of each light component obtained by reading the light amount of the reflected light of the white auxiliary reference plate immediately after the light source is turned on,
(3) Temporal light quantity fluctuation data associated with the temporal light quantity fluctuations of the plurality of colors of light obtained by reading the auxiliary white reference plate,
After the light source is turned on and continuously turned on for a predetermined period, the light amount fluctuation is maximum from the measured value of the reflected light amount of the auxiliary white reference plate measured by the image sensor and the auxiliary white reference value (2). A certain light component is specified and measured using the measured value of the specified light component, the auxiliary white reference value (2), the temporal light quantity fluctuation data (3), and the white reference value (1). Light amount line data for all light components at the time, and shading correction means for performing shading correction using the light amount line data; and
An image reading apparatus comprising: An image reading apparatus that creates white light from a plurality of colors of light, reads the original image by continuously turning on the white light as a light source,
A line-shaped image sensor in which the light source and the reading element are arranged in the main scanning direction;
A white reference plate having a length longer than the main scanning width of the image sensor;
An auxiliary white reference plate installed outside the document image reading area;
Storage means for storing data relating to the light quantity of (1) to (4) below;
(1) Among the light of the plurality of colors, specific light that is a light component with a temporal light amount variation amount being a predetermined value or more,
(2) A linear white reference value of each light component, which is a light amount value obtained by reading the light amount of the reflected light of the white reference plate immediately after the light source is turned on,
(3) An auxiliary white reference value that is a light amount value of the specific light obtained by reading the amount of reflected light of the white auxiliary reference plate immediately after the light source is turned on.
(4) Temporal light quantity fluctuation data associated with the temporal light quantity fluctuations of the plurality of colors of light obtained by reading the auxiliary white reference plate,
After the light source is turned on and continuously turned on for a predetermined period, the measured value of the light quantity of the specific light (1) among the reflected light of the auxiliary white reference plate measured by the image sensor, and the auxiliary white reference value (3), the light amount fluctuation data with time (4), and the white reference value (2) are used to calculate light amount line data for all light components at the time of measurement, and shading correction is performed using the light amount line data Shading correction means for executing
An image reading apparatus comprising: The image reading apparatus according to claim 2, wherein the specific light has the longest wavelength among the light of the plurality of colors. 4. The light according to claim 1, wherein the light of the plurality of colors includes short-wavelength light and long-wavelength light in which a part of the short-wavelength light is converted by a light conversion material. The image reading apparatus according to claim 1.