JP2013128219A - Image reading device and image reading method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make more precise corrections conforming to luminous energy reduction characteristics to keep abreast with further increase in a reading speed and also prevent unevenness in a read image due to a change in the luminous energy of a light source lamp.SOLUTION: A control unit 20 samples an auxiliary white reference plate immediately before reading the second and subsequent pages of a document to obtain the luminous energy of a light source lamp 18, and calculates a change amount from a luminous energy reference value in the light source lamp 18. A white reference value obtained when the first page of the document was read is corrected on the basis of this luminous energy change amount, β, and difference auxiliary profile data, α, to correct shading. At this time, the value of the difference auxiliary profile data α and a prescribed threshold value are compared, and if the value of the difference auxiliary profile data α is found to be larger than the prescribed threshold value, reference luminous energy data which was corrected by a correction value calculated using the difference auxiliary profile data α is used to correct shading. If the value of the difference auxiliary profile data α is found to be smaller than the prescribed threshold value, reference luminous energy data is used to correct shading.

Description

  The present invention relates to an image reading apparatus, and more particularly to an image reading apparatus and an image reading method that reduce the time spent for shading correction and increase the throughput of document reading.

  In an image reading apparatus, shading correction is performed in order to prevent unevenness of a read image due to non-uniform light amount of a light source lamp, change with time, sensitivity variation of an image reading element, and the like. In the shading correction, a white reference plate having a width equal to or larger than the main scanning width provided in the image reading apparatus is sampled to obtain a white reference value and create correction data for each pixel. Then, the image of the original is read, and the density of the read image is corrected according to the correction data.

  In the shading correction described above, it is necessary to prevent a decrease in throughput due to sampling the white reference plate every time a document is read. Therefore, for the first document reading, the white reference plate is sampled and normal shading correction is performed, and for subsequent readings, the light source lamp light quantity is measured without sampling the white reference plate, and from the time of the first document reading. A simple shading correction that corrects read data based on a decrease in the amount of light over time has been proposed.

  However, in general, the amount of light emitted from the light source lamp may vary depending on the position depending on the characteristics of the light source lamp, the temperature difference around the light source lamp due to the airflow of a cooling fan, or the like. For this reason, conventionally, as disclosed in Patent Document 1, for example, an improved technique has been proposed in which correction is performed in accordance with the light amount reduction characteristics of the light source lamp in the simple shading correction described above.

JP 2010-11439 A

  However, the characteristics of the light source lamp are various, and the usage environment of the image reading apparatus is also various, and more precise shading correction is required because it is necessary to follow a further increase in reading speed.

  Therefore, in the image reading apparatus, when the sampling value of the white reference plate is corrected in accordance with the light amount decrease of the light source lamp, a finer correction is performed in accordance with the light amount decrease characteristic to further increase the reading speed. An object of the present invention is to provide an image reading apparatus and an image reading method capable of preventing unevenness of a read image due to a change in the amount of light of a light source lamp.

In order to solve the above problems, an image reading apparatus according to a first aspect of the present invention includes:
A light source (for example, light source lamp 18 in FIG. 1B) and an image sensor in which reading elements are arranged in the main scanning direction (for example, image sensor 17 in FIG. 1B) are provided. An image reading device that emits light and reads reflected light with an image sensor (for example, the image reading device 10 in FIG. 1A),
A white reference plate (for example, the white reference plate 15 in FIG. 1A) having a length equal to or longer than the main scanning width in the image sensor;
An auxiliary white reference plate that is smaller than the white reference plate (for example, the auxiliary white reference plate 13 in FIG. 1A);
Difference profile data that is a change amount of a reading value for each reading element when a white reference plate is set as a reading target based on a change in the light amount of the light source (for example, light amount difference profile data Pro [1 to m] in FIG. 4). And storage means (for example, FIG. 3) that stores differential auxiliary profile data (for example, light amount difference auxiliary profile data α in FIG. 4) that is the amount of change in the representative value of the reading value when the auxiliary white reference plate is to be read. Storage unit 30),
When reading a plurality of originals, reference light quantity data (for example, reference light quantity line data P in FIG. 5), which is a reading value for each reading element when the white reference plate is read before the first original is read. [1 to m]) and reference light amount auxiliary data (for example, reference light amount auxiliary data M in FIG. 5), which is a representative value of the reading value when the auxiliary white reference plate is set as a reading target, are obtained. A normal shading correction unit (for example, a normal shading correction unit 231 in FIG. 3) for performing shading correction on the read data of the document using the reference light amount data;
The latest light amount auxiliary data (for example, the latest light amount auxiliary data N in FIG. 6), which is a representative value of the reading value when the auxiliary white reference plate is set as the reading target before reading the second and subsequent originals, is obtained, and the difference assist is obtained. Based on the ratio of the amount of change between the reference light amount auxiliary data and the latest light amount auxiliary data with respect to the profile data (for example, the ratio β / α in FIG. 7) and the difference profile data (for example, the white reference correction in FIG. 7). Correction value calculation means (for example, the correction value calculation unit 233 in FIG. 3) for calculating the value Adj [1 to m]),
When the difference auxiliary profile data value is compared with a predetermined threshold value and the difference auxiliary profile data value is smaller than the threshold value, the reference light amount data is used for the read data of the second and subsequent originals. When the value of the auxiliary supplemental profile data is larger than the threshold value, the reference light amount data (for example, FIG. 7) corrected using the correction value for the read data of the second and subsequent originals. Simple shading correction means (for example, the simple shading correction unit 232 in FIG. 3) that performs shading correction using the corrected white reference value aW [1 to m]).

  In the above invention, the reference light amount data is acquired when the first original is read, and the reference light amount auxiliary data that is the reference value of the light amount of the light source lamp is acquired by sampling the auxiliary white reference plate. Then, the auxiliary white reference plate is sampled immediately before reading the second and subsequent originals, the latest light amount auxiliary data that is the light amount of the light source lamp is obtained, and the amount of change from the reference light amount auxiliary data is calculated. With this amount of change, the simple light shading correction is performed by correcting the reference light amount data acquired when the first original is read. At this time, the reference light amount data is corrected for each pixel by referring to profile data in which the change amount of the sampling value for each pixel with respect to the light amount change is recorded. Thus, since the reference light amount data is corrected for each pixel with reference to the profile data, the correction can be performed in accordance with the actual light amount reduction characteristic.

  In particular, in the above invention, the difference auxiliary profile data value, which is the difference between the intrinsic light amount auxiliary data value and the latest light amount auxiliary data value, is compared with a predetermined threshold value, and the difference auxiliary profile data value is the threshold value. If it is larger, that is, if the light amount change is large, the shading correction processing is performed using the corrected reference light amount data. On the other hand, when the value of the differential auxiliary profile data is smaller than the threshold value, that is, when the light amount change is small, the shading correction process is performed using the reference light amount data as it is without using the corrected reference light amount data. Become. Therefore, for example, when acquiring the latest light quantity auxiliary data, a value larger than the actual value is acquired due to the influence of noise or the like, and as a result, the value of the differential auxiliary profile data becomes smaller than the threshold value. The shading correction process is performed using not corrected reference light amount auxiliary data but corrected reference light amount data. Thus, according to the present invention, for example, the latest light amount used as a reference when converting the change amount of the read value of the auxiliary white reference plate into the change of the read value of the white reference plate, which is a measure of the light amount change amount of the light source. When auxiliary data is acquired with a value larger than the actual value (small change in light amount) due to the influence of noise, etc., it is possible to prevent excessive correction processing. Thus, it is possible to prevent unevenness of the read image due to a change in the light amount of the light source lamp while following the increase in the reading speed.

Here, the shading correction performed by the normal shading correction means and the simplified shading correction means is the black reference value and the gradation of the read value acquired separately when the original read data is D and the corrected read data is Ds. Using numbers
Ds = (D−black reference value) × number of gradations / (reference light amount data−correction value−black reference value)
It is expressed by the correction formula. This shading correction is desirably performed for each RGB channel.

  Further, the representative value of the reading value when the auxiliary white reference plate is a reading target can be an average value of the reading values for each reading element when the auxiliary white reference plate is the reading target. More specifically, the average value of the reading values can be an average value of the reading values for each reading element in a predetermined region having a width in both the main scanning direction and the sub-scanning direction.

  Further, when the shading correction means satisfies a predetermined condition, the difference profile data and the difference auxiliary profile data are obtained using the latest acquired reference light amount data and the latest acquired reference light amount auxiliary data. May be updated.

  In this case, immediately after the difference profile data and the difference auxiliary profile data are updated, the shading correction unit corrects the shading using the latest acquired reference light amount data even for the second and subsequent originals. To do.

  The predetermined condition is that a difference between the reference light amount auxiliary data and the latest light amount auxiliary data is obtained when a predetermined number of originals are read after starting the original reading, or when a predetermined time has elapsed after starting the original reading. Any of cases where the differential auxiliary profile data is exceeded can be included.

  Further, when the white reference plate is to be read, the white reference plate may be read in a plurality of lines in the sub-scanning direction, and an average value in the sub-scanning direction may be used as a reading value for each reading element.

  Furthermore, instead of the amount of change in the reading value for each reading element when the white reference plate is the reading target, the amount of change in the reading value for each reading element when the white reference plate is the reading target is further Data averaged in the main scanning direction may be used as the difference profile data.

In order to solve the above problem, an image reading method according to a second aspect of the present invention includes:
An image reading method in an image reading apparatus comprising a light source and an image sensor in which a reading element is arranged in the main scanning direction, irradiating a reading object with light from the light source, and reading reflected light with the image sensor,
Reference light quantity data that is a reading value for each reading element when a white reference plate having a length equal to or larger than the main scanning width of the image sensor is read before reading the first original when reading a plurality of originals. And reference light quantity auxiliary data, which is a representative value of the reading value when an auxiliary white reference plate smaller than the white reference plate is read (for example, step S202 to step S203 in FIG. 5), the first sheet A normal shading correction step (for example, step S205 in FIG. 5) for performing shading correction on the read data of the original using the reference light amount data;
Prior to reading the second and subsequent originals, the latest light quantity auxiliary data, which is a representative value of the reading value when the auxiliary white reference plate is the reading target, is acquired (for example, step S302 in FIG. 5), and the white reference plate is read. The value of the differential auxiliary profile data, which is the amount of change in the read value for each reading element when the target is set, is compared with a predetermined threshold (for example, step S403 in FIG. 7), and the value of the differential auxiliary profile data is calculated. When it is smaller than the threshold value, the reading data of the second and subsequent originals is subjected to shading correction using the reference light amount data (for example, step S404 and step S406 in FIG. 7), and the value of the differential auxiliary profile data is set. If it is larger than the threshold value, the ratio of the change amount between the reference light amount auxiliary data and the latest light amount auxiliary data with respect to the difference auxiliary profile data, and the difference profile data It performs shading correction using the reference light quantity data corrected by using the correction value calculated based on the data (e.g., step S405, step S406 of FIG. 7) and a simplified shading correction step.

  According to the present invention, when correcting the sampling value of the white reference plate according to the light amount decrease of the light source lamp, performing a finer correction in accordance with the light amount decrease characteristic, and following the further increase in the reading speed, Unevenness of the read image due to a change in the light amount of the light source lamp can be prevented.

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. FIG. 3 is a block diagram illustrating a functional configuration of an image reading device and a control system of a host device that receives image data from the image reading device. Processing to acquire the intrinsic light amount line data P0 [1 to m] and the intrinsic light amount auxiliary data M0, processing to acquire the initial value of the light amount difference profile data Pro [1 to m], and the initial value of the light amount difference auxiliary profile data α It is a flowchart which shows. 10 is a flowchart for describing image reading processing of a first document during actual document reading. 10 is a flowchart for describing image reading processing of second and subsequent originals during actual original reading. It is a flowchart explaining simple shading correction. A graph showing the difference between the line data before the light intensity reduction, the line data after the light intensity reduction and the averaged light intensity difference profile data, and the light quantity not subjected to the averaging process with the line data before the light intensity reduction and the line data after the light intensity reduction. It is a graph which shows difference profile data. It is a graph which shows the light quantity ratio after N second with respect to the light quantity of the 1st sheet.

  Embodiments of the present invention will be described with reference to the drawings. The image reading apparatus according to this 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 the originals in the original placement area one by one. 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 lamp that irradiates light on the document and a mirror that captures reflected light from the document is fixed, and the document is automatically conveyed to perform reading. In the flat bed reading mode, the document is scanned. Is fixed and scanning is performed by scanning the carriage.

  In addition, with regard to shading correction performed when reading a document image, normal shading correction is performed in which a black reference value and a white reference value are sampled and corrected for each pixel before reading the document, and a change in the light amount of the light source lamp is detected. Thus, it is possible to perform simple shading correction for correction.

  FIG. 1 is a diagram illustrating a schematic configuration of an image reading surface of an image reading apparatus according to the present embodiment, where (a) is a plan view and (b) 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 normal shading correction. In normal shading correction, correction data is generated for each pixel. Therefore, the white reference plate 15 has a length longer than the width of the first mirror 4a mounted on the lamp carriage 16a, that is, a length longer than the width to be read. To have. In the present embodiment, the white reference plate 15 is sampled by reading the white reference plate 15 with the light source lamp ON, and the black reference value is sampled by reading the white reference plate 15 with the light source lamp OFF. . However, a black reference plate may be provided separately, or the black reference value may be sampled at another location. 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 lamp 18 and reflected from the document is guided to the image sensor 17 by the first mirror 4a, the second mirror 4b, the third mirror 4b, and the lens 3. Then, it is read as an image of a document by the image sensor 17. In the present embodiment, the light amount emitted from the light source lamp 18 includes a short wavelength component and a long wavelength component, and any wavelength component is measured by the image sensor 17.

  The lamp carriage 16a on which the light source lamp 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 the document G conveyed by an automatic document conveying mechanism (not shown). Read the image. In the flat bed reading mode, the white reference value for normal shading correction is sampled at the position B corresponding to the white reference plate 15 and moved toward the end position C of the document placement area 12 by a carriage movement mechanism (not shown). By moving horizontally, the image of the document placed on the document placement area 12 is read.

  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 lamp 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 in the automatic reading area 11. The auxiliary white reference plate 13 is read in order to detect a change in the light amount of the light source lamp. The auxiliary white reference plate 13 is disposed at a position where the lamp carriage 16a can be read while being fixed at a 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 lamp 18, and thus 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.

  FIG. 2 is a perspective view of the lamp carriage 16 a at the position A corresponding to the automatic reading area 11. As shown in the figure, the lamp carriage 16a includes a light source lamp 18 such as a cold cathode tube and a first mirror 4a, and the light reflected by the reading object of the light emitted from the light source lamp 18 is reflected by the first mirror 4a. Thus, it is configured to be 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 lamp 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 conveyance mechanism (not shown) in a direction (sub-scanning direction) orthogonal to the direction of the lamp 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. The “module” used in the description refers to a functional unit that is configured by hardware such as an apparatus or a device, software having the function, or a combination thereof, and achieves a predetermined operation. .

  As shown in the drawing, the image reading apparatus 10 includes a control unit 20, a storage unit 30, a carriage moving mechanism unit 40, a document conveying mechanism unit 50, and an operation panel 60 in addition to the image sensor 17 and the light source lamp 18 described above. Yes. 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 lamp 18 in accordance with the image reading conditions received by the image reading condition setting unit 22, and performs document reading processing. That is, in the sheet-through reading mode, the original is read by moving the lamp carriage 16 a to the position of the automatic reading area 11 and transporting the document by the document transport mechanism 50. In the flat bed reading mode, the document reading process is performed by moving the lamp 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. 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 normal shading correction processing, a simple shading correction unit 232 that performs simple shading correction, and a correction value calculation unit 233.

  The normal shading correction unit 231 reads the reference light amount data and the auxiliary white reference as reading values for each reading element when the white reference plate is read before reading the first original when reading a plurality of originals. This is a module that obtains reference light quantity auxiliary data, which is a representative value of a reading value when a plate is read, and performs shading correction on the read data of the first original using the reference light quantity data.

  The correction value calculation unit 233 acquires the latest light quantity auxiliary data, which is a representative value of the reading value when the auxiliary white reference plate is to be read before reading the second and subsequent originals. Thus, the correction value is calculated based on the ratio of the change amount between the reference light amount auxiliary data and the latest light amount auxiliary data with respect to the difference auxiliary profile data, and the difference profile data.

  The simplified shading correction unit 232 compares the difference auxiliary profile data with a predetermined threshold value, and based on the comparison result, the reference light amount data corrected using the correction value, or the reference light amount data with the correction amount set to 0 Is a module that performs shading correction using the selected reference light amount data.

  As described above, the image processing unit 23 can selectively perform normal shading correction and simple shading correction. The normal shading correction processing in the normal shading correction unit 231 is performed according to the following procedure. That is, prior to image reading of a document, the white reference value is obtained for each pixel by sampling the white reference plate 15 with the light source lamp 18 turned on. Then, reading of the document is started with the light source lamp 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.

If the read image data is D, the white reference value is W, and the black reference value is B, the image data Ds after shading correction is
Ds = (D−B) × the number of gradations / (W−B)
It can be. Note that shading correction is preferably performed for each RGB channel in order to improve correction accuracy.

  The general procedure for simple shading correction in the simple shading correction unit 232 is as follows. Note that the simple shading correction is performed on the second and subsequent originals, and the normal shading correction is performed on the first original. However, normal shading may be appropriately performed on the second and subsequent originals.

  In the simple shading correction, the reference value of the light amount of the light source lamp 18 is obtained by sampling the auxiliary white reference plate 13 when reading the first document. Then, the auxiliary white reference plate 13 is sampled immediately before reading the second and subsequent documents, the latest light amount of the light source lamp 18 is acquired, and the amount of change from the reference value in the light amount of the light source lamp 18 is calculated. Here, the simplified shading correction unit 232 compares the value of the differential auxiliary profile data with a predetermined threshold value, and based on the comparison result, the reference light amount data corrected using the correction value, or the uncorrected reference light amount data. One of the reference light quantity data is selected, and the white reference value acquired at the time of reading the first original is corrected by using the selected reference light quantity data to perform shading correction. Specifically, when the value of the differential auxiliary profile data is smaller than the predetermined threshold data, the reference light amount data calculated from the correction value calculated by the correction value calculation unit 233 is not used, and the reference is not corrected. Shading correction processing is performed based on the light amount data. On the other hand, when the value of the differential auxiliary profile data is larger than the predetermined threshold data, the shading correction process is performed using the reference light amount data using the correction value calculated by the correction value calculation unit 233. Thus, the simplified shading correction unit 232 switches the shading correction process. At this time, the white reference value is corrected for each pixel with reference to profile data in which the amount of change in the sampling value for each pixel with respect to the change in the amount of light is referred to. A detailed procedure of the simple shading correction will be described later.

  The color conversion processing unit 24 performs processing for converting image data in RGB format into CMYK format or 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 30 and a ROM 32. The ROM 32 includes a rewritable EEPROM 32a. A RAM 30 that is a volatile storage device includes a white reference value obtained by sampling the white reference plate 15, a black reference value, light amount data obtained by reading the auxiliary white reference plate 13, image reading data, threshold values. Data and the like are stored. The RAM 30 is also used as a work area. The threshold data is table data for comparison with the acquired differential auxiliary profile data, and a predetermined value is stored.

  A control program is stored in the ROM 32 which is a non-volatile storage device. The rewritable EEPROM 32a stores profile data, specific light quantity data, threshold value data, etc., which will be described in detail later. These data are transferred to the RAM 30 for use when the image reading apparatus 10 is activated. When the profile data is updated, it is written back to the EEPROM 32a.

  The carriage movement mechanism unit 40 can be constituted by a motor, a drive belt, and the like, and moves the lamp carriage 16a to the reading position or moves in the sub-scanning direction under the control of the image reading control unit 21. Further, the mirror carriage 16b is moved by a distance of 1/2 according to the moving direction of the lamp 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, characteristic processing performed by the image reading apparatus 10 configured as described above will be described with reference to flowcharts. First, the process for obtaining the intrinsic light amount line data P0 [1 to m] and the intrinsic light amount auxiliary data M0 of the image reading apparatus 10, the initial value of the light amount difference profile data Pro [1 to m], and the light amount difference auxiliary profile data α. The process for acquiring the initial value will be described with reference to the flowchart of FIG.

  Here, the intrinsic light amount line data P0 [1 to m] is a value for each pixel when the white reference plate 15 is sampled in a state where there is no light amount decrease immediately after the light source lamp 18 is turned on. Note that m is the number of pixels read by the image sensor 17. The inherent light amount auxiliary data M0 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 lamp 18 is turned on. In the present embodiment, the auxiliary light amount data is used as data indicating the light amount of the light source lamp 18, and therefore 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, an average value of a plurality of pixels in the main scanning direction may be used.

  The unique light amount line data P0 [1 to m] and the unique light amount auxiliary data M0 are recorded in the EEPROM 32a as unique information of the image reading apparatus 10. This processing is preferably performed, for example, before shipment of the image reading apparatus 10 or when the image reading apparatus 10 is installed. Alternatively, it may be performed when the image reading apparatus 10 is inspected.

  The light amount difference profile data Pro [1 to m] is data calculated by reading the white reference plate 15 when the lighting state of the light source lamp 18 continues for a while, and how much the sampling value decreases due to a decrease in the light amount. This is data indicating whether or not each pixel has been processed. The light amount difference auxiliary profile data α is data that is calculated by reading the auxiliary white reference plate 13 when the lighting state of the light source lamp 18 continues for a while and indicates how much the light amount of the light source lamp 18 has decreased. is there.

  Thus, in this embodiment, the light amount difference profile data Pro [1 to m] and the light amount difference auxiliary profile data α are used to calculate the light amount difference of the light source lamp 18 and the difference between the sampling values of the white reference plate 15 by continuing the lighting time. Are related. In the simple shading correction in the actual scan job, only the difference between the sampling values of the auxiliary white reference plate 13 is acquired, and the difference for each pixel in the sampling value of the white reference plate 15 is obtained using the profile data. presume.

  The initial values of the light amount difference profile data Pro [1 to m] and the light amount difference auxiliary profile data α are calculated by this processing and recorded in the EEPROM 32a. Both profile data are updated as necessary when the image reading process of the image reading apparatus 10 is performed by the user.

  As shown in the flowchart of FIG. 4, in this process, first, the light source lamp 18 is turned on (step S101). Then, the intrinsic light quantity auxiliary data M0 is acquired in a state before the light quantity decreases (step S102). In acquiring the intrinsic light quantity auxiliary data M0, the lamp carriage 16a is moved to the position of the automatic reading area 11 in order to sample the auxiliary white reference plate 13. Then, a predetermined area of the auxiliary white reference plate 13 is sampled, and an average value of the read values is calculated as the intrinsic light quantity auxiliary data M0. The predetermined area can be, for example, a square area of X pixels in the main scanning direction and X pixels in the sub scanning direction.

  Next, the intrinsic light amount line data P0 [1 to m] is acquired (step S103). In acquiring the intrinsic light amount line data P0 [1 to m], the lamp carriage 16a is moved to the position of the white reference plate 15 in order to sample the white reference plate 15. Then, the white reference plate 15 is sampled by a plurality of lines, and the average value for each pixel is set as the intrinsic light amount line data P0 [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. Further, the acquisition order of the intrinsic light quantity auxiliary data M0 and the intrinsic light quantity line data P0 [1 to m] may be reversed. The acquired intrinsic light quantity auxiliary data M0 and intrinsic light quantity line data P0 [1 to m] are recorded in the EEPROM 32a.

  Thereafter, in order to acquire data in a state where the light amount of the light source lamp 18 is reduced, the process waits for a predetermined time (step S104). The predetermined time can be, for example, 10 minutes.

  After a predetermined time has elapsed (Yes in step S104), the latest light quantity auxiliary data N is acquired (step S105). The latest light quantity auxiliary data N is the latest value, that is, a representative value when the auxiliary white reference plate 13 is sampled after the light quantity is reduced. The sampling of the auxiliary white reference plate 13 and the calculation method of the representative value can be the same as the processing for the specific light quantity auxiliary data M0.

  Further, the latest light quantity line data Q [1 to m] is acquired (step S106). The latest light amount line data Q [1 to m] is the latest value, that is, a value for each pixel when the white reference plate 15 is sampled after the light amount is reduced. The reading method of the white reference plate 15 can be the same as the processing for the specific light amount line data P0 [1 to m]. The acquisition order of the latest light quantity auxiliary data N and the latest light quantity line data Q [1 to m] may be reversed.

  Next, the light amount difference auxiliary profile data α is calculated and recorded in the EEPROM 32a (step S107). The light amount difference auxiliary profile data α is calculated by subtracting the latest light amount auxiliary data N from the inherent light amount auxiliary data M0. That is, the difference in light amount before and after the light amount of the light source lamp 18 is reduced.

  Further, the light amount difference profile data Pro [1 to m] is calculated and recorded in the EEPROM 32a (step S108). The light amount difference profile data Pro [1 to m] is calculated by subtracting the latest light amount line data Q [1 to m] from the unique light amount line data P0 [1 to m]. That is, it is the difference for each pixel in the sampling value of the white reference plate 15 before and after the light amount reduction of the light source lamp 18.

  When the above processing is completed, the light source lamp 18 is turned off, the inherent light amount line data P0 [1 to m] and the inherent light amount auxiliary data M0 are acquired, and the initial values of the light amount difference profile data Pro [1 to m]. Then, the process of acquiring the initial value of the light amount difference auxiliary profile data α is terminated.

  Next, processing of the image processing apparatus 10 at the time of actual document reading will be described with reference to the flowcharts of FIGS. In actual document reading, when a plurality of documents are continuously read, shading correction control differs between the first document and the second and subsequent documents.

  Specifically, for the first document, normal shading correction is performed and data serving as a reference for the amount of light is acquired. On the other hand, simple shading correction is performed on the second and subsequent originals. This increases the throughput of document reading. However, it is possible to update the profile data as necessary when reading the second and subsequent originals. At this time, normal shading correction is performed.

  When executing image reading, a reading condition such as a reading mode and color / monochrome is set by the user. This embodiment is particularly effective when the reading condition is a sheet-through reading mode in which a document is automatically and continuously read.

  In the image reading process, first, the light source lamp 18 is turned on (step S201). Then, the reference light quantity auxiliary data M before the light quantity reduction is acquired (step S202). The reference light quantity auxiliary data M is a reference light quantity for the current image reading job. In acquiring the reference light quantity auxiliary data M, the lamp carriage 16 a is moved to the position of the automatic reading area 11 in order to sample the auxiliary white reference plate 13. Then, a predetermined area of the auxiliary white reference plate 13 is sampled, and an average value of the read values is calculated as reference light amount auxiliary data M. The predetermined area can be the same as the predetermined area in the intrinsic light quantity auxiliary data M0.

  Next, reference light amount line data P [1 to m] is acquired (step S203). The reference light amount line data P [1 to m] becomes reference light amount line data in the current image reading job. In acquiring the reference light amount line data P [1 to m], the lamp carriage 16 a is moved to the position of the white reference plate 15 in order to sample the white reference plate 15. Then, the white reference plate 15 is sampled by a plurality of lines, and the average value for each pixel is set as the reference light amount line data P [1 to m].

  Next, the first original is read (step S204), and normal shading correction is performed on the image data of the read original (step S205). In the normal shading correction, the reference light amount line data P [1 to m] read immediately before is used as the white reference value, and the shading correction is performed according to the above formula.

  If there is no next original (No in step S206), the light source lamp 18 is turned off (step S207), and the original reading process is terminated. If there is a next original (Yes in step S206), it is determined whether or not to update the profile data (step S301).

  Here, various determination criteria can be used for determining whether to update the profile data. For example, the profile data can be updated after reading a predetermined number of documents. Alternatively, the profile data may be updated when the amount of decrease in the light amount of the light source lamp 18 exceeds a predetermined value as a result of obtaining the latest light amount auxiliary data N described later. Further, the profile data may be updated when the document reading time has passed a predetermined time.

  In general, the amount of decrease in the light amount of the light source lamp 18 depends on the environmental temperature. Therefore, it is desirable to update the profile data under the image reading environment in order to increase the accuracy of the shading correction corresponding to the actual light quantity reduction state.

  By updating the profile data, the accuracy of shading correction can be further increased. However, when updating the profile data, it is necessary to acquire the latest light amount line data Q [1 to m] as described later. In order to acquire the latest light amount line data Q [1 to m], the lamp carriage 16a has to be moved to the position of the white reference plate 15, which may reduce the productivity of the reading process.

  Therefore, a mode that emphasizes productivity and a mode that emphasizes image quality are prepared, and profile data may be updated more frequently when the user selects a mode that emphasizes image quality. . Further, the profile data may be updated after the end of the image reading job so as not to affect the productivity of the reading process.

  If the profile data is not updated (No in step S301), the latest light amount auxiliary data N is acquired before reading the document in order to grasp the current light amount of the light source lamp 18 (step S302). In obtaining the latest light quantity auxiliary data N, a predetermined area of the auxiliary white reference plate 13 is sampled, and an average value of the read values is calculated and used as the latest light quantity auxiliary data N. The auxiliary white reference plate 13 can perform sampling without moving the lamp carriage 16a in the sheet-through reading mode.

  Then, the original is read (step S303), and simple shading correction is performed on the read image data (step S304).

  Next, the simplified shading correction executed in step 304 will be described in detail. FIG. 7 is a flowchart showing a procedure of simple shading correction. As shown in this figure, in the simplified shading correction, the light amount difference auxiliary data β is calculated by subtracting the latest light amount auxiliary data N acquired immediately before from the reference light amount auxiliary data M acquired before reading the first image (step S401). ). The light amount difference auxiliary data β indicates the light amount reduction amount of the light source lamp 18 from the start of the image reading job.

  Next, the differential auxiliary profile data α is read from the RAM 31 (step S402), the value is compared with a threshold value (step S403), and the shading correction process is switched.

Specifically, if the value of the differential auxiliary profile data α is greater than a predetermined threshold (Yes in step S403), the following white reference correction value Adj [1 to m] = β / α × Pro [ 1-m]
As shown, the white reference correction value Adj [1-m] for each pixel is calculated by multiplying the ratio of the light amount difference auxiliary data β to the light amount difference auxiliary profile data α and the light amount difference profile data Pro [1 to m]. (Step S405).

  The white reference correction values Adj [1 to m] are values obtained by estimating how much the reference light amount line data P [1 to m] acquired before reading the first image is reduced for each pixel.

  Next, the corrected white reference value aW [1 to m] is calculated by subtracting the white reference correction value Adj [1 to m] from the reference light amount line data P [1 to m] (step S406). Then, shading correction is performed using the corrected white reference value aW [1 to m] as the white reference value (step S407).

  On the other hand, if the value of the differential auxiliary profile data α is smaller than the threshold value (No in step S403), the white reference correction value Adj [0] for each pixel with the correction amount set to 0 is calculated (step S404). Then, the corrected white reference value aW [1-m] is calculated by subtracting the white reference correction value Adj [0] with the correction amount set to 0 from the reference light amount line data P [1-m] (step S406). Then, shading correction is performed using the corrected white reference value aW [1 to m] as the white reference value (step S407). This completes the simple shading correction.

  When the simple shading correction is completed, it is determined whether there is a next original (step S311). If there is no next original (No in step S311), the light source lamp 18 is turned off (step S312), and the original reading process is terminated. If there is a next original (Yes in step S311), it is determined again whether or not to update the profile data (step S301).

  When the profile data is updated (Yes in step S301), first, the latest light amount auxiliary data N is acquired in order to grasp the current light amount of the light source lamp 18 (step S305). In obtaining the latest light quantity auxiliary data N, a predetermined area of the auxiliary white reference plate 13 is sampled, and an average value of the read values is calculated and used as the latest light quantity auxiliary data N.

  Then, the latest light quantity line data Q [1 to m] is acquired (step S306). In obtaining the latest light quantity line data Q [1 to m], the lamp carriage 16a is moved to the position of the white reference plate 15 in order to sample the white reference plate 15. Then, the white reference plate 15 is sampled by a plurality of lines, and the average value for each pixel is set as the latest light amount line data Q [1 to m].

  Next, the light amount difference auxiliary profile data α is calculated and updated (step S307). The light amount difference auxiliary profile data α is calculated by subtracting the latest light amount auxiliary data N acquired immediately before from the specific light amount auxiliary data M0.

  Further, the light quantity difference profile data Pro [1 to m] is calculated and updated (step S308). The light quantity difference profile data Pro [1 to m] is calculated by subtracting the latest light quantity line data Q [1 to m] acquired immediately before from the specific light quantity line data P0 [1 to m]. Thereby, both profile data are updated.

  The reference light amount auxiliary data M is the average value of the reading values by the image sensor 17 of the auxiliary white reference plate 13 immediately after the light source lamp 18 is turned on, like the specific light amount auxiliary data M0. Therefore, the light amount difference auxiliary profile data α may be calculated by subtracting the latest light amount auxiliary data N acquired immediately before from the reference light amount auxiliary data M. However, in this case, it is necessary to match the calculation method of the light amount difference profile data Pro [1 to m] with the calculation method of the light amount difference auxiliary profile data α. Therefore, the light amount difference profile data Pro [1 to m] is calculated by subtracting the latest light amount line data Q [1 to m] acquired immediately before from the reference light amount line data P [1 to m].

  Then, the original is read (step S309), and normal shading correction is performed on the read image data (step S310). That is, since the latest light amount line data Q [1 to m] is acquired when the profile data is updated, normal shading correction is performed using this data.

  Thereafter, it is determined whether or not there is a next original (step S311). If there is no next original (No in step S311), the light source lamp 18 is turned off (step S312), and the original reading process is terminated. If there is a next original (Yes in step S311), it is determined again whether or not to update the profile data (step S301).

  According to the present embodiment, when the simple shading correction is performed at the time of reading the second and subsequent originals, the value of the differential auxiliary profile data α is compared with a predetermined threshold value. When the value of the auxiliary auxiliary profile data α is larger than the threshold value, the shading correction process is performed using the corrected white reference correction value Adj [1 to m], and the value of the auxiliary auxiliary profile data α is set to the threshold. When the value is smaller than the value, the white reference correction value Adj [1 to m] is set to 0 and the shading correction process is performed.

  This makes it possible to prevent excessive correction processing when the change in the amount of light is small due to the influence of noise, etc. Therefore, unevenness of the read image due to a change in the light amount of the light source lamp can be prevented.

  A change in the amount of light caused by this noise will be described. Normally, as shown in FIG. 9, when the lighting state of the light source lamp 18 continues for a while, the change in the amount of light after lighting theoretically changes linear as shown by the dotted line in the graph. Due to the influence of the above, fluctuations occur up and down as shown by the solid line in the graph.

  When this variation occurs, the ratio β / α of the light amount difference auxiliary data β with respect to the light amount difference auxiliary profile data α varies. For example, the value of the difference auxiliary profile data α is calculated by subtracting the latest light amount auxiliary data N from the reference light amount auxiliary data M. When the latest light amount auxiliary data N is acquired, due to the influence of noise, FIG. As shown, there may be a case where the difference between the intrinsic light quantity auxiliary data M (P1) and the latest light quantity auxiliary data N (P2) becomes small. In this case, since the value of the differential auxiliary profile data α becomes small, as a result, the value of the ratio β / α becomes larger than usual.

  Further, in the calculation of the light amount difference auxiliary data β, when the latest light amount auxiliary data N acquired immediately before is acquired, as shown in FIG. 9, the latest light amount auxiliary data N is smaller than the original value (P3) due to the influence of noise. ) Indicates that the difference between the reference light amount auxiliary data M acquired before reading the first image and the latest light amount auxiliary data N acquired immediately before increases, and thus the calculated light amount difference auxiliary data β The value of increases. As a result, the ratio β / α of the light amount difference auxiliary data β with respect to the light amount difference auxiliary profile data α further increases.

  When the white reference correction value Adj [1 to m] is calculated using such a large value ratio β / α, the white reference correction value Adj [1 to m], which is an excessive correction amount, is calculated. As a result, excessive correction processing is performed even if the change in the amount of light is minute, and thus unevenness of the read image cannot be prevented stably.

  Therefore, as in the present embodiment, when performing simple shading correction, the value of the differential auxiliary profile data α is compared with a predetermined threshold value, and the value of the differential auxiliary profile data α is smaller than the threshold value. The shading correction process is performed by setting the white reference correction value Adj [0] to 0 without using the corrected white reference correction value Adj [1 to m], thereby preventing excessive correction processing and the like. It is possible to prevent unevenness in the read image due to a change in the light amount of the light source lamp while performing finer correction in line with the increase in the reading speed.

  In the above embodiment, the difference between the light amount line data before and after the light amount decrease of the light source lamp 18 is used as the light amount difference profile data. However, since the light amount line data is a sampling value of the white reference plate 15, there is a possibility that the influence of noise, dirt on the white reference plate 15 or the like is included. Sampling a plurality of lines in the sub-scanning direction at the time of acquiring light quantity line data and calculating the average value can reduce the influence of noise etc., but the light quantity difference profile data is a difference value. Noise may also appear as a large fluctuation.

  In addition, the light amount difference profile data is used for grasping the influence of the light amount decrease of the light source lamp 18 on each pixel at the time of shading correction for correcting the characteristics of each reading element. It is desirable to show a tendency.

  Therefore, the light amount difference profile data obtained by the difference between the light amount line data may be further averaged in the main scanning direction and used as the light amount difference profile data.

  The averaging process can be performed, for example, by calculating a weighted average using peripheral pixel values. In this case, for example, for data of Pro [n], Pro_Av [n] = Pro [n-2] / 16 + Pro [n-1] / 4 + Pro [n] / 4 + Pro [n] / 8 + Pro [n + 1] / 4 + Pro [n + 2 ] / 16 can be performed.

  Or, Pro_Av [n] = Pro [n-4] / 8 + Pro [n-3] / 8 + Pro [n-2] / 8 + Pro [n-1] / 8 + Pro [n] / 8 + Pro [n + 1] / 8 + Pro [n + 2] / An 8-pixel averaging process such as 8 + Pro [n + 3] / 8, a 16-pixel averaging process, or the like may be performed. Furthermore, the light amount difference profile data may be created by performing the averaging process in the main scanning direction after subtracting both the line data before the light amount decrease and the line data after the light amount decrease.

  FIG. 8A is a graph showing the line data before the light quantity reduction, the line data after the light quantity reduction, and the light quantity difference profile data subjected to the averaging process. Also, FIG. It is a graph which shows the light amount difference profile data which does not perform the line data before the light quantity fall, the line data after the light quantity fall, and the averaging process. As shown in the figure, by performing the averaging process of the light amount difference profile data, it is possible to suppress the influence of noise and the like and grasp a rough tendency of the light amount decrease in the main scanning direction. Since the graph of the light amount difference profile data has a small value, the range of the graph is different.

  Further, in the above-described embodiment, the light quantity measured by the image sensor 17 includes a short wavelength component and a long wavelength component. For example, the light quantity of the light source lamp 18 is measured only by the short wavelength component. May be. In this case, even when measurement is performed including a long wavelength component, the variation in the light amount decrease when the light is continuously lit is reduced, and the corrected white reference value with the white reference correction value Adj [0] set to 0 is set. The probability of performing simple shading correction processing using aW [1 to m] is reduced, and shading correction can be performed in accordance with the actual light quantity change.

3 lens 4a first mirror 4b second mirror 4c third mirror 10 image reading device 11 automatic reading area 12 document placing area 13 auxiliary white reference plate 14 position guide plate 15 white reference plate 16a lamp carriage 16b mirror carriage 17 image sensor 18 Light source lamp 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 Feeding Mechanism Unit 60 Operation Panel 80 Host Device 81 Host Controller 231 Normal Shading Correction Unit 232 Simple Shading Correction Unit 233 Correction Value Calculation Unit

Claims (2)

An image reading device comprising a light source and an image sensor in which a reading element is arranged in the main scanning direction, irradiating a reading object with light from the light source, and reading reflected light with the image sensor,
A white reference plate having a length longer than the main scanning width of the image sensor;
An auxiliary white reference plate that is smaller than the white reference plate;
Difference profile data that is the amount of change in reading value for each reading element when the white reference plate is a reading target based on a change in the amount of light of the light source and reading when the auxiliary white reference plate is a reading target Storage means for storing differential auxiliary profile data which is a change amount of a representative value of values,
When reading a plurality of documents, reference light amount data that is a reading value for each reading element and the auxiliary white reference plate are read when the white reference plate is read before reading the first document. Normal shading correction means for obtaining reference light amount auxiliary data that is a representative value of the read value when the image data is read, and performing shading correction on the read data of the first document using the reference light amount data;
Prior to reading the second and subsequent originals, the latest light quantity auxiliary data, which is a representative value of the reading value when the auxiliary white reference plate is the reading target, is acquired, and the reference light quantity auxiliary data for the differential auxiliary profile data and the A correction value calculation means for calculating a correction value based on the ratio of the amount of change with the latest auxiliary light amount data and the difference profile data;
When the value of the differential auxiliary profile data is compared with a predetermined threshold value, and the value of the differential auxiliary profile data is smaller than the threshold value, When the shading correction is performed using the reference light amount data, and the value of the differential auxiliary profile data is larger than the threshold value, the read data of the second and subsequent originals are corrected using the correction value. Simple shading correction means for performing shading correction using the reference light quantity data,
An image reading apparatus comprising: An image reading method in an image reading apparatus comprising a light source and an image sensor in which a reading element is arranged in a main scanning direction, irradiating a reading object with light from the light source, and reading reflected light with the image sensor,
When reading a plurality of documents, a reference value that is a reading value for each reading element when a white reference plate having a length longer than the main scanning width of the image sensor is read before reading the first document. Light amount data and reference light amount auxiliary data, which is a representative value of a reading value when an auxiliary white reference plate smaller than the white reference plate is read, are obtained, and the read data of the first original is obtained. A normal shading correction step for performing shading correction using the reference light amount data;
Prior to reading the second and subsequent originals, the latest light quantity auxiliary data, which is a representative value of the reading value when the auxiliary white reference plate is set as a reading target, is acquired, and the white reference is based on a change with time of the light quantity of the light source. The difference auxiliary profile data value, which is the amount of change in the reading value for each reading element when the plate is set as the reading target, is compared with a predetermined threshold value, and the value of the difference auxiliary profile data is compared with the threshold value. If it is smaller, shading correction is performed on the read data of the second and subsequent originals using the reference light amount data, and the difference assist profile data value is greater than the threshold value when the difference assist profile data value is greater than the threshold value. A correction value calculated based on the ratio of the amount of change between the reference light amount auxiliary data and the latest light amount auxiliary data with respect to profile data and the difference profile data is used. A simplified shading correction step of performing shading correction by using the reference light quantity data corrected Te,
An image reading method comprising:

Images