JP2008271396A - Image reading apparatus, and density correcting method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image reading apparatus which is capable of performing proper light quantity correction by reducing the effect of dust deposited on a sub scan density reference or noise for the unit of a line and suppressing the influence of read level variation that occurs for the unit of a line. <P>SOLUTION: When reading a sub scan density reference that is provided outside a document placing area, image data for a plurality of pixels are added in a main scan direction, results of the addition are further added for a plurality of lines and a result thereof is defined as read data of the sub scan density reference, such that the sub scan density reference can be read as a plane area. On the basis of the read data of the sub scan density reference, density correction is performed with respect to read data of a document. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image reading apparatus and a density correction method for correcting a reading level fluctuation in a sub-scanning direction, which is caused by a temporal change in a light amount of a light source that illuminates a document.

  In general, an image reading apparatus is configured to place a document on a platen glass and form an image of reflected light from the document irradiated by a light source on a CCD line sensor through a reflection mirror and a lens.

  In the image reading apparatus, the sensitivity of the individual sensors constituting the CCD line sensor, non-uniformity of the reading level in the main scanning direction caused by the reduction in the amount of light at the edge by the lens and the main scanning light distribution characteristic of the illumination are corrected. Therefore, shading correction is performed.

  The shading correction is a process for correcting image density fluctuations caused by the above-described factors in the main scanning direction. In addition, the shading correction detects a non-uniformity of the reading level by reading a density reference member that is provided outside the document placement area and is long in the main scanning direction, and eliminates this non-uniformity to a predetermined reading level. The image correction is performed so that is obtained.

  Although it is possible to correct the nonuniformity of the reading level generated in the main scanning direction by this shading correction, the reading level fluctuation in the sub-scanning direction due to the light amount fluctuation of the light source generated during the reading scanning may occur. is there.

  A cold cathode discharge lamp may be used as a light source of the image reading apparatus. As a characteristic of the cold cathode discharge lamp, there is a feature that the rise of the light amount is very slow. FIG. 12 is a graph showing the light quantity rise characteristics of the cold cathode discharge lamp. The vertical axis indicates the amount of light and the horizontal axis indicates time. Time 0 indicates the start of lamp lighting control. It is shown that the amount of light gradually increases from the start of lighting control and converges to a predetermined amount of light with time.

  As shown in FIG. 12, when image reading is performed during a period in which the light quantity varies, image level fluctuations in the sub-scanning direction due to the light quantity fluctuations occur. With a cold cathode discharge lamp, it takes about several minutes from the start of lighting until the light quantity stabilizes.Therefore, if you want to scan an image with the light quantity stabilized, you must wait a few minutes after the instruction to start reading the original. Cannot start reading. An instruction to start reading a document is, for example, that a copy start key is pressed. If the time from the start of reading to the actual start of reading is long, the user will be burdened, and the lamp will be on for a long time, which is disadvantageous in terms of lamp life. .

  When trying to shorten the time from the start of lighting to the start of reading, reading must be performed before the light quantity enters the stable period. A time t1 in FIG. 12 indicates a read start timing. FIG. 13 is a diagram showing a reading result when reading is started at time t1. When reading is started at time t1, as shown in FIG. 13, the amount of lamp light is increasing, so that the reading result is darker at the leading edge than the rear end of the sub-scanning.

  For this reason, it is necessary to correct the reading level fluctuation due to the fluctuation of the lamp light amount occurring between the front end and the rear end of the sub-scan. An image reading apparatus that corrects this reading level variation is known (see Patent Document 1). In this image reading apparatus, a density reference member equivalent to the density reference used for the main scanning shading correction is also provided in the sub-scanning direction, and the reflected light from the density reference member is detected simultaneously with the document reading, and based on the result. It is possible to correct the sub-scanning reading level fluctuation caused by the light quantity fluctuation.

As described above, in this image reading apparatus, by providing the density reference member (reference reflection member) extending in the sub-scanning direction, the fluctuation of the reflected light from the density reference member is detected in the middle of the sub-scan, and the read output is obtained. On the other hand, light quantity correction is possible.
Japanese Patent Laid-Open No. 10-308849 FIG.

  However, in the above-described conventional image reading apparatus, no reference is made to an actual image processing method such as a sampling method or correction processing of a sub-scanning density reference member (simply referred to as a sub-scanning density reference). There was a problem.

  When performing light amount fluctuation correction based on the sub-scanning density reference, when using one line of the image signal output from the line sensor, if there is dust on the sub-scanning density reference, the image signal is affected by the dust, In some cases, the reading level based on the sub-scanning density cannot be acquired correctly.

  Further, when the reading speed is relatively fast or the light source light quantity is small immediately after the start of lighting, the S / N ratio is low. Therefore, when the image signal varies in line units, the sub-scanning density reference is accurate. The reading level could not be acquired. For this reason, the light quantity fluctuation correction cannot be performed with high accuracy.

  As described above, the conventional image reading apparatus does not provide a solution to the above-described dust on the sub-scanning density reference plate and line-unit noise in the image signal.

  Therefore, the present invention reduces the influence of dust adhering to the sub-scanning density reference, noise in units of lines, etc., suppresses the influence of fluctuations in reading level occurring in units of lines, and can perform appropriate light amount correction. It is another object of the present invention to provide a density correction method.

  In order to achieve the above object, an image reading apparatus according to the present invention includes an illuminating unit that illuminates a document, a sub-scanning density reference that is disposed outside a document placement region to detect the amount of light of the illuminating unit, Reading means for reading the sub-scanning density reference and the reflected light from the original and outputting each read data, and after starting reading of the original, the sub-scanning density reference read data is supplied to a plurality of sub-scanning lines. Adding means for adding in a predetermined range including the pixels and outputting the result of addition in the predetermined range for each predetermined sub-scanning line, and an output result output from the adding means for each predetermined sub-scanning line From the correction value calculating means for calculating a correction value for performing density correction, and based on the correction value calculated by the correction value calculating means, the density for the read data of the document Characterized in that a density correction means for performing positive.

  The control method of the image reading apparatus of the present invention includes an illuminating unit that illuminates a document, a sub-scanning density reference that is disposed outside a document placement region to detect the amount of light of the illuminating unit, the sub-scanning density reference, and A density correction method for an image reading apparatus comprising reading means for reading reflected light from the original and outputting each read data, wherein the reading of the sub-scanning density reference is performed after the reading of the original by the reading means is started. An addition step of adding data in a predetermined range including a plurality of pixels across a plurality of sub-scan lines, and outputting the result of addition in the predetermined range for each predetermined sub-scan line; and the predetermined step in the addition step A correction value calculating step for calculating a correction value for performing density correction from the output result output for each sub-scanning line, and the correction value calculating step. Based on the correction value, and having a density correction step of performing the density correction for read data of the document.

  According to the image reading apparatus of the first aspect of the present invention, the reading data based on the sub-scanning density is added within a predetermined range including a plurality of pixels over a plurality of sub-scanning lines, and the addition is performed within the predetermined range. The result is output every predetermined sub-scan line. Further, a correction value for performing density correction is calculated from the output result, and density correction is performed on the read data of the document based on the calculated correction value. Thus, the sub-scanning density reference can be read as a surface area. Therefore, when correcting fluctuations in the reading level in the sub-scanning direction caused by fluctuations in the light amount of the light source over time, the influence of dust adhering to the sub-scanning density reference or noise in line units is reduced, and occurs in line units. Appropriate light amount correction can be performed while suppressing the influence of reading level fluctuations.

  According to the image reading apparatus of the second aspect, the light amount correction can be performed relatively easily immediately after the start of reading. According to the image reading apparatus of the third aspect, it is possible to eliminate the influence of dust and the like adhering to the sub-scanning density reference and perform better light amount correction. According to the image reading apparatus of the fourth aspect, it is possible to remove read data affected by dust or the like attached to the sub-scanning density reference relatively easily.

  Embodiments of an image reading apparatus and its density correction method according to the present invention will be described with reference to the drawings. The image reading apparatus of this embodiment is applied to a scanner apparatus.

[First Embodiment]
FIG. 1 is a cross-sectional view showing an internal configuration of the image reading apparatus according to the first embodiment. The image reading apparatus 1 includes an automatic document feeder (ADF) 100 and a reader unit 200.

  The automatic document feeder 100 includes a document tray 130 on which a document bundle S composed of at least one sheet is placed, a separation that protrudes from the document tray 130 before starting document transportation, and restricts the downstream movement of the document bundle S. A pad 121 and a paper feed roller 101 are provided.

  The paper feed roller 101 falls on the original surface of the original bundle S placed on the original tray 130 and rotates. As a result, the uppermost document is fed from the document bundle. The original fed by the paper feed roller 101 is separated by the action of the separation roller 102 and the separation pad 121. The original document separated by the separation roller 102 and the separation pad 121 is conveyed to the registration roller 104 by the conveyance roller pair 103 and is abutted against the registration roller 104. As a result, the document is formed in a loop shape, and the skew in the conveyance of the document is eliminated.

  On the downstream side of the registration roller 104, a paper feed path is provided for feeding the document that has passed through the registration roller 104 and conveying it in the direction of the reading glass 211. The document sent to the paper feed path is conveyed onto the flow reading glass 211 by the large roller 107 and the feed roller 105.

  The large roller 107 is in contact with the flow reading glass 211, and at this time, the surface image of the document can be read by the CCD sensor 402. The document fed by the large roller 107 passes through the conveyance roller 106, moves between the roller 116 and the moving glass 118, and is discharged to the document discharge tray 131 via the discharge flapper 120 and the discharge roller 108. The At this time, the back side image of the document can be read by the back side image reading unit 117.

  On the other hand, when reading the document by reversing the document, the document is moved to the reversing path 119 by switching the sheet discharge flapper 120 by reversing the sheet discharge roller 108 while the document is caught in the sheet discharge roller 108. . The moved document is abutted against the registration roller 104 from the reversal path 119 and is formed again in a loop shape, thereby eliminating the skew in conveying the document. Thereafter, the original is again moved to the flow reading glass 211 by the feeding roller 105 and the large roller 107, so that the back side image of the original can be read by the flow reading glass 211. Further, the document tray 130 has a guide restricting plate (not shown) that is slidable in the sub-scanning direction of the placed document bundle, and a document width detecting sensor (not shown) that detects the document width in conjunction with the guide restricting plate. (Not shown) is provided.

  The combination of the document width detection sensor and the pre-registration sensor 111 makes it possible to determine the document size of the document bundle placed on the document tray 130. In addition, a document length detection sensor (not shown) provided in the conveyance path can detect the document length from the conveyance distance from the leading edge detection to the trailing edge detection of the document being conveyed. The document size can also be determined from the detected document length and the output of the document width detection sensor.

  The reader unit 200 optically reads image information recorded on a document and performs photoelectric conversion to obtain the image data. The reader unit 200 includes a flow reading glass 211, a platen glass 212, a scanner unit 219, mirrors 215 and 216, a lens 217, a CCD sensor 402, and the like. The scanner unit 219 is provided with a cold cathode discharge lamp 213 and a mirror 214. The main scanning density reference (main scanning shading white plate) 202 is used to create white level reference data by shading. In FIG. 1, a sub-scanning density reference (sub-scanning shading white plate) to be described later is not shown.

[Fixed reading mode]
As a document reading mode, an operation in a document fixed reading mode in which an image is read by moving the scanner unit 219 in the sub-scanning direction when reading a document printed on one side (single-sided document) will be described. When the reader unit 200 is instructed to start image reading, the scanner unit 219 moves immediately below the main scanning density reference 202 to perform white level reference in the main scanning direction and light distribution correction in the main scanning direction. Then, the scanner unit 219 moves to the home position where a sufficient distance is secured for acceleration. Thereafter, the scanner unit 219 moves in the sub-scanning direction and reads the reflected light with the CCD sensor 402 while irradiating the original S with the cold cathode discharge lamp 213. Further, the scanner unit 219 reads the reflected light from the sub-scanning density reference simultaneously with the reflected light from the original by the CCD sensor 402 as described later. After the reading to the right end of the document S is completed, the cold cathode discharge lamp 213 is turned off, the scanner unit 219 moves and returns to the original state.

[Original Scanning Mode]
As a document reading mode, an operation of a document flow reading mode in which an image is read by fixing the scanner unit 219 and moving a document when reading a document (single-sided and double-sided documents) will be described. When the automatic document feeder 100 is instructed to start document feeding, the scanner unit 219 moves immediately below the main scanning density reference 202, and a main scanning shading operation is performed. Simultaneously with the main scanning shading operation using the main scanning density reference 202, the shading operation using the white reference plate of the moving glass (not shown) of the back surface image reading unit 117 is performed. Further, in the original flow reading mode, as will be described later, the sub-scanning shading operation can be similarly performed by arranging the sub-scanning density reference outside the flow-read original region.

  Then, the paper feed roller 101 falls on the upper surface of the original, and only one uppermost original is separated from the original bundle by the action of the separation roller 102 and the conveying roller pair 103 and is fed to the registration roller 104. . At this time, the scanner unit 219 moves immediately below the point R.

  When the registration roller 104 rotates, the document is guided onto the flow reading glass 211 via the paper feed path. The document is conveyed at a predetermined speed at point R in the figure, and the image of the document is read by the scanner unit 219 and the CCD sensor 402 waiting under the point R.

  FIG. 2 is a diagram for explaining the arrangement of the main scanning density reference and the sub-scanning density reference. FIG. 4A is a view of the image reading apparatus viewed from above the platen glass 201, and FIG. 4B is a perspective view of FIG. As described above, the main scanning density reference (main scanning shading white plate) 202 is provided at the front end in the sub-scanning direction of the document table glass 201. The main scanning density reference is a density reference for calculating a correction value for correcting reading level unevenness (density unevenness) in the main scanning direction. Further, a sub-scanning density reference 203 is provided outside the document placement area (side edge) on the back side of the document table glass 201. The sub-scanning density reference 203 is a density reference for calculating a correction value for correcting reading level unevenness (density unevenness) in the sub-scanning direction, and is a length corresponding to the maximum sub-scanning size that can be handled by the image reading apparatus. Just prepared.

  The main scanning density standard 202 and the sub scanning density standard 203 are arranged so as to be covered with the size index 204 and can be referred to from the inside of the apparatus, that is, can be read by the optical system, but from the outside of the apparatus, that is, from the user side. It is configured so that its existence cannot be seen. The illumination system for illuminating the reading target and the optical system for guiding the reflected light from the document to the CCD line sensor can read both the main scanning maximum reading size and the sub-scanning density reference of the document. It has become.

  FIG. 3 is a diagram schematically showing read data in the vicinity of the sub-scanning density reference 203 that is simultaneously read when the reading scan is started. In the figure, squares indicate read data (image data) for one pixel. Further, the squares of the halftone dots indicate the reading data based on the sub-scanning density, and the white squares indicate the reading data on the platen glass 201. In the figure, the first line (document leading edge) shown as the uppermost image data indicates the reading start line of the document, and the reading lines continue from the second line to the third line. The image data on the platen glass 201 (original area) is read data of an area where an image is actually formed as original read data. The image data of the sub-scanning density reference region is read data of a region that is not used for image formation and is used only for detecting the light amount fluctuation of the light source.

  In the figure, a horizontal synchronization signal HSYNC is a horizontal synchronization signal indicating the reference position of one line of image data, and data of the start of the document area and the sub-scanning density reference according to the number of pixels from the horizontal synchronization signal HSYNC. An acquisition start position is determined. On the other hand, the vertical synchronization signal VSYNC is a vertical synchronization signal indicating the reference position of the image data in the sub-scanning direction, and the sub-scanning leading edge of the document image is determined according to the number of lines from the vertical synchronization signal VSYNC.

  In the present embodiment, the pixel position after X1 pixels from the falling edge of the horizontal synchronization signal HSYNC is set as the reading start position based on the sub-scanning density, and the pixel position after X2 pixels is set as the reading start position of the document area. Is set. The read data acquisition area based on the sub-scanning density is set to an area of image data of W pixels, that is, 4 pixels from the pixel that has passed X1 pixels. On the other hand, the falling line of the vertical synchronization signal VSYNC is set as the sub-scanning leading edge of the document image.

  FIG. 4 is a block diagram showing the configuration of the image processing circuit. The image processing circuit includes an analog front end IC (AFE) 403, a CCD / AFE drive signal generation unit 404, a density correction circuit 400, a CPU 409, and the like. The density correction circuit 400 is a circuit block for correcting density unevenness in the sub-scanning direction due to light quantity fluctuation, and includes a timing signal generation unit 401, a sub-scanning density reference read data addition unit 405, a reference data holding unit 406, a correction value. A calculation unit 407 and a correction calculation unit 408 are included. The timing signal generator 401 generates a horizontal synchronization signal HSYNC, a vertical synchronization signal VSYNC, and a clock signal for performing image processing and the like.

  The CCD sensor 402 outputs a read signal. An analog front end IC (AFE) 403 samples a CCD output signal, performs analog processing such as gain adjustment and offset adjustment, and converts the signal into a digital signal. The CCD / AFE drive signal generation unit 404 is a circuit that generates a signal for driving the CCD sensor 402 and a timing signal for driving the AFE 403. The CCD / AFE drive signal generation unit 404 operates based on the horizontal synchronization signal HSYNC output from the timing signal generation unit 401, and controls the CCD sensor 402 and the AFE 403 in units of lines. As a result, the document image is read in units of one line.

  The image data converted into digital data by the AFE 403 is sent to the density correction circuit 400, and a process for correcting density unevenness in the sub-scanning direction due to light quantity fluctuation is performed. First, the image data is sent to the sub-scanning density reference read data adding unit 405. A sub-scanning density reference read data adding unit 405 extracts image data in a predetermined range (area) having a predetermined pixel width and the number of lines from the sub-scanning density reference image data, and adds the level of the image data in that area. Perform the process.

  The predetermined pixel width and the number of lines are set by the CPU 409 setting an internal register (not shown). As described above, the addition start position and the number of added pixels are set based on the horizontal synchronization signal HSYNC, and the addition start position X1 and the added pixel width W are set by the CPU 409 as shown in FIG.

  The addition start timing in the sub-scanning direction is started in synchronization with the fall of the vertical synchronization signal VSYNC. In FIG. 3, image data for a predetermined number of lines set by the CPU 409 is added from the first line. Further, the addition start position X1 and the document area X2 based on the horizontal synchronization signal HSYNC are values that vary due to mechanical accuracy, and are values determined in an inspection process at the time of product shipment. The added pixel width W and the number of added lines are values determined by the sub-scanning density reference width and the like, and are parameters set in advance at the design stage.

[Addition processing of image data based on sub-scanning density]
The sub-scan density reference image data addition process will be described. When the number of added pixels W = 4 pixels and the number of added lines = 4 lines, image data for 4 pixels × 4 lines = 16 pixels is added together with the input of the vertical synchronization signal VSYNC.

  FIG. 5 is a diagram schematically showing the addition process in the sub-scan density reference addition region. Here, P indicates the main scanning pixel position in the addition area, p indicates the pixel at the main scanning pixel position P, l indicates the sub-scanning line position in the addition area, Dpl indicates the p pixel, and the l-th line Indicates the data value of the image data.

First, addition processing in the main scanning direction will be described. With the input of the vertical synchronization signal VSYNC, first, addition processing for the first line (l = 0) is started. The main scanning addition value sum_m ₀ calculated in the first line is expressed by Expression (1A).

  In the addition process of Formula (1A), the image data for four pixels at the main scanning pixel positions P = 0 to 3 in the addition area of the first line (l = 0) is added, and the addition value is equal to the number of main scanning pixels. Is obtained.

Further, as a general formula of the main scanning pixel number of added values, the main scanning addition value Sum_m _l calculated by addition processing l-th line is represented by the formula (1B).

  Here, n indicates the number of added pixels.

  Formula (1B) indicates that the addition processing for the n main scanning n pixels on the l-th line is performed.

  Formulas (1A) and (1B) are collectively referred to as Formula (1).

  This calculation is executed for each line. The added value for each line is held for a plurality of lines according to the added line number setting value.

  Next, addition processing in the sub-scanning direction will be described. Here, since the set number of addition lines is four lines, the main scanning addition results for four lines calculated by the equation (1) are added, and the addition values for the number of sub-scanning lines are obtained.

The result of addition processing in the sub-scanning direction that is first performed when the vertical synchronization signal VSYNC is input is used as reference data (reference value) sum _ref for calculating the correction amount, and is thus held in the reference data holding unit 406. . The addition formula of the reference value sum _ref is expressed by the formula (2).

After the calculation of the reference value sum _ref , addition processing in the sub-scanning direction is executed for each predetermined line. Here, the predetermined line is a value set in the sub-scanning density reference read data adding unit 405 by the CPU 409, and a line interval at which the addition process is performed is set by the set value. The line interval is controlled by counting the horizontal synchronization signal HSYNC output from the timing signal generator 401.

If the line interval at which addition processing is set to a value 1, the sub-scanning addition region after the reference value sum _ref calculation sub-scanning area calculated a reference value sum _ref to become one line shifted regions. Thereafter, addition processing is performed on the region shifted by one line, and the calculation result is sent to the correction value calculation unit 407. As a general formula, an addition value sum _k for which an addition operation is performed on the sub-scanning addition area is expressed by Formula (3).

Here, k represents an addition start sub-scanning line, and j represents the number of addition lines. When k = 0, sum _k = sum _ref .

By performing pixel addition processing in the main scanning direction based on the number of pixels set in this way, and line addition processing of pixel addition results based on the number of lines and line spacing, reading of the sub-scanning density reference for a predetermined number of pixels and a predetermined line Level addition values (sub-scanning addition values sum _k ) are sequentially calculated.

[Calculation of correction amount]
Next, a correction amount calculation method will be described. The correction value is calculated by the correction value calculation unit 407. The correction value C is calculated as a ratio between the reference value sum _ref held in the reference data holding unit 406 and the added value sum _k calculated after the reference value sum _ref , as shown in Equation (4). Obtained by.

Correction value C = sum _ref / sum _k (4)
The correction value calculation unit 407 reads the reference value sum _ref held in the reference data holding unit 406, acquires the value of the addition value sum _k calculated by the sub-scanning density reference read data addition unit 405, and the ratio thereof. Is calculated and sent to the correction calculation unit 408 in the subsequent stage.

FIG. 6 is a diagram showing the correction value calculated and the correction calculation performed on the image data of the document area. Since the correction value according to Equation (4) cannot be calculated until the addition value sum ₁ is calculated, the correction value calculation unit 407 does not correct the correction value within the range in which the set value of the addition line number does not exceed the number of lines from the front end of the image. = 1 is output.

In this embodiment, since the set value of the number of added lines is 4, the correction value is 1 until the fourth line (l = 3). Since the fifth line (l = 4) and thereafter, the added value sum _k is calculated, so that the correction value is calculated according to Equation (4), and the calculated correction value and one line of image data in the document area are calculated. The correction calculation is performed.

When the value of the addition value sum _k increases with respect to the reference value sum _ref calculated at the leading edge of the document, that is, when the amount of light source is increasing, the calculated correction amount is at the trailing edge of the document. It gets smaller as you go. On the other hand, when the sum value sum _n is smaller than the reference value sum _ref calculated at the leading edge of the document, that is, when the light source light amount is decreasing, the calculated correction amount is the value after the document. It gets bigger as you go to the edge.

  Based on the correction value calculated by the correction value calculation unit 407, the correction calculation unit 408 performs correction processing on the image data in the document area according to the correction calculation formula (5). Thereby, density correction processing of image data is performed.

Dout _nl = C _i * Din _nl (5)
Here, Dout _nl : input image data of the correction calculation unit 408 at the nth pixel and lth line of the document area, Din _nl : output image data of the correction calculation unit 408 at the nth pixel and lth line of the document area, C _i : Correction coefficient (correction value).

  The correction calculation is executed by sequentially multiplying one line of image data from the leading edge (l = 0) to the trailing edge of the document area by a correction coefficient. The correction calculation unit 408 performs correction calculation on the image data in the document area according to the horizontal synchronization signal HSYNC generated by the timing signal generation unit 401 and the pixel number setting value X2 set by the CPU 409.

FIG. 7 is a flowchart showing a correction value calculation processing procedure. This correction value calculation process is repeatedly executed by the density correction circuit 400 every time one line of sub-scanning is read after reading is started. First, the density correction circuit 400, the read data in the main scanning pixels output by adding one line from the AFE403, obtaining a main scanning addition value sum_m _l (step S1). Furthermore, the density correction circuit 400 adds the main scanning addition value Sum_m _l in the sub-scanning four lines, obtain the sub-scanning addition value sum _k (Step S2). Here, if the sub-scan line is less than the fourth line (l = 3), successively the main scanning addition value Sum_m _l is added. When the sub-scanning line is the fifth line (l = 4) or more, the upper four lines are added.

The density correction circuit 400 determines whether or not the sub-scanning line l has exceeded the fourth line (l> 3) (step S3). If the sub-scanning line l is not more than the fourth line, it is determined whether or not the sub-scanning line l is the fourth line (l = 3) (step S4). If the sub-scanning line l is less than the fourth line, the density correction circuit 400 sets the correction value C to the initial value 1 (step S5). Thereafter, the process proceeds to step S9 described later. On the other hand, when the sub-scanning line l is the fourth line in step S4, the density correction circuit 400 holds the sub-scan addition value sum _k as the reference value sum _ref in the reference data holding unit 406 (step S6), and step S5. Proceed to the process.

On the other hand, when the sub-scanning line l exceeds the fourth line in step S3 (l> 3), the density correction circuit 400 reads the reference value sum _ref held in the reference data holding unit 406 (step S7). The density correction circuit 400 calculates a correction value C from the ratio between the read reference value sum _ref and the sub-scanning addition value sum _k (step S8) and saves it in a storage unit (not shown) in the correction calculation unit 408. (Step S9). Thereafter, the density correction circuit 400 ends this process.

  FIG. 8 is a flowchart showing a read data correction processing procedure. This correction processing is performed on the read data for one pixel in the main scanning. The density correction circuit 400 first reads the correction value C stored in a storage unit (not shown) in the correction calculation unit 408 (step S11). The density correction circuit 400 multiplies the input image data Din by the correction value C and outputs the result as output image data Dout (step S12). Thereafter, the density correction circuit 400 ends this process.

  As described above, in the image reading apparatus according to the first embodiment, when detecting the light amount fluctuation of the lamp from the reading value based on the sub-scanning density, the addition value of the image data for a plurality of pixels in the main scanning direction is further added for a plurality of lines. to add. As a result, the sub-scanning density reference can be read as an area (surface area). Therefore, it is possible to reduce the influence of dust adhering to the sub-scanning density reference and image noise in units of lines on the correction value, and it is possible to correct favorable lamp light quantity fluctuation.

  In this embodiment, the processing system of image data corresponds to one system, that is, handles monochrome image data. However, when there are three processing systems and each performs processing independently, for example, each color of RGB Of course, it is possible to perform the density correction processing every time.

  In addition, in the case of performing so-called document flow scanning, in which the reading optical system is fixed and scanning is performed while the document is conveyed, a sub-scanning density reference equivalent to the sub-scanning density reference 203 is arranged outside the flow-reading document area. Similarly, it is possible to perform the density correction process.

[Second Embodiment]
In the second embodiment, a case will be described in which, when dust or the like is present in the sub-scanning density reference, the reading value of the sub-scanning density reference is calculated while eliminating the influence. The configuration of the image reading apparatus according to the second embodiment is the same as that of the first embodiment, and the description of the same components will be omitted by using the same reference numerals.

FIG. 9 is a diagram schematically showing a sub-scanning density reference in which dust adheres to the addition area in the second embodiment. Here, a state where dust or the like has adhered to the main scanning addition position P = 0, 1 of the sixth line (l = 5) is shown. When reading is started, as described in the first embodiment, the addition processing with respect to the main scanning addition position is performed in order from the first line, the main scanning addition value Sum_m _l is calculated. However, the main scan addition value sum_m _{6 on} the sixth line cannot be obtained as a normal addition result because dust is attached.

Figure 10 is a graph showing the relationship between the sub-scan line l and the main scanning addition value Sum_m _l. This graph shows that the main scanning addition value sum_m ₆ when the sub scanning line l = ₆ is small due to the influence of dust. In order to exclude a peculiar value such as the main scanning addition value sum_m _6, the calculation shown in Expression (6) is performed, and it is determined from the result whether or not the main scanning addition value is abnormal.

_{| Sum_m l -sum_m l-1 |} > th ...... (6)
Here, th is a determination threshold value.

Equation (6) is to compare the main scanning addition value Sum_m _l of the calculated the line and sum_m _l-1 calculated it to the previous line. That is, Equation (6) as a result of the comparison, when the absolute value of the difference between sum_m _l-1 calculated in the main scanning addition value Sum_m _l and previous line of the line is greater than the predetermined threshold th, This is for determining that the main scanning addition value of the line is abnormal. Since it is inappropriate to use the main scan addition value determined to be abnormal for the sub-scan addition operation, the sub-scan addition operation uses the main-scan addition value sum_m _l−1 calculated before the relevant line. the addition result replacement processing performed by replacing the main scanning addition value Sum_m _l of the line. In FIG. 10, the main scan addition value of the replaced line is indicated by sum_m _l ′.

FIG. 11 is a flowchart showing a correction value calculation processing procedure. The same step numbers as those in the first embodiment are denoted by the same step numbers, and the description thereof is omitted. Density correction circuit 400, at step S1, after obtaining the main scanning addition value Sum_m _l, absolute value a predetermined tooth of the difference between sum_m _l-1 calculated in the main scanning addition value Sum_m _l and previous line of the line It is determined whether or not it is larger than the threshold value th (step S1A). When the absolute value of the difference is larger than the predetermined threshold th, the density correction circuit 400 replaces the main scanning addition value sum_m _l−1 calculated before this line with the main scanning addition value sum_m _l of this line. (Step S1B). Thereafter, the process proceeds to step S2. On the other hand, if the absolute value of the difference is not larger than the predetermined threshold th in step S1A, or if there is no main scanning addition value calculated before this line (l = 0), the process of step S2 is performed as it is. Proceed to Subsequent processing is the same as in the first embodiment.

  As described above, according to the image reading apparatus of the second embodiment, dust on the sub-scanning density reference plate is corrected for the lamp light amount by determining the difference between the line and the main scanning addition value of the previous line. It is possible to eliminate the influence on the value and correct a favorable lamp light amount fluctuation.

  In the present embodiment, the determination is made using the difference between the main scanning addition values in the preceding and following lines, but instead of the main scanning addition value, the difference between the sub scanning addition value or the ratio between the reference value and the sub scanning addition value. You may determine using. In this case, if it is similarly determined that there is an abnormality, the sub-scan addition value or ratio of the previous line may be used, and similarly, the influence of dust on the sub-scan density standard is eliminated. Can do.

  Further, the present invention is not limited to the configuration of the above-described embodiment, and any configuration can be used as long as the functions shown in the claims or the functions of the configuration of the present embodiment can be achieved. Is also applicable.

  For example, in the above embodiment, a total of 16 pixels within a range (area) of 4 pixels * 4 lines of rectangle is used as the sub-scanning density reference read data. However, any number of pixels may be used as long as it is a surface area. Minute reading data may be used. The range is not limited to a rectangle, and may be any shape as long as the total number of pixels is equal.

  The image reading apparatus of the present invention is not limited to a scanner apparatus, but can be applied to a facsimile machine, a copying machine, and the like. In the present embodiment, the density correction processing is processed by a hardware circuit, but may be processed by software (control program) executed by the CPU.

1 is a cross-sectional view illustrating an internal configuration of an image reading apparatus according to a first embodiment. It is a figure explaining arrangement | positioning of the main scanning density reference | standard and a sub scanning density reference | standard. It is the figure which showed typically the reading data of the sub-scanning density reference | standard 203 vicinity read simultaneously when a reading scan is started. It is a block diagram which shows the structure of an image processing circuit. It is the figure which represented typically the addition process in the addition area | region of a subscanning density reference | standard. It is a figure showing the correction value performed with respect to the calculated correction value and the image data of a document area. It is a flowchart which shows a correction value calculation process procedure. It is a flowchart which shows the correction processing procedure of read data. FIG. 10 is a diagram schematically illustrating a sub-scanning density reference in which dust adheres to an addition area in the second embodiment. It is a graph showing the relationship between the sub-scan line l and the main scanning addition value Sum_m _l. It is a flowchart which shows a correction value calculation process procedure. It is a graph which shows the light quantity rise characteristic of a cold cathode discharge lamp. It is a figure which shows the reading result at the time of starting reading at time t1.

Explanation of symbols

203 Sub-scanning density reference 402 CCD sensor 405 Sub-scanning density reference read data addition unit 407 Correction value calculation unit 408 Correction calculation unit

Claims (5)

Illumination means for illuminating the document;
A sub-scanning density reference disposed outside the document placement area to detect the light quantity of the illumination means;
Reading means for reading reflected light from the sub-scanning density reference and the original and outputting respective read data;
After the reading of the original is started, the reading data based on the sub-scanning density is added within a predetermined range including a plurality of pixels over a plurality of sub-scanning lines, and the result of the addition within the predetermined range is added to the predetermined sub-scanning line. Adding means for outputting every time,
Correction value calculating means for calculating a correction value for performing density correction from an output result output for each of the predetermined sub-scanning lines from the adding means;
An image reading apparatus comprising: a density correction unit configured to perform the density correction on the read data of the document based on the correction value calculated by the correction value calculation unit. The adding means adds the reading data based on the sub-scanning density for a predetermined number of main scanning pixels according to the start of reading the document, and adds the result for the number of main scanning pixels for a predetermined number of sub-scanning lines. Adding and outputting the result of addition for the predetermined number of sub-scanning lines for each predetermined sub-scanning line,
The correction value calculating means performs the density correction based on a ratio between an initial output result after the start of reading of the document output from the adding means and an output result output for each predetermined sub-scanning line thereafter. The image reading apparatus according to claim 1, wherein a correction value for performing the calculation is calculated. The adding means compares the result of adding the number of main scanning pixels with the result of adding the number of main scanning pixels before that;
Addition result replacing means for replacing the result of addition for the number of main scanning pixels with the result of addition for the number of main scanning pixels before that based on the result of comparison by the comparison means;
The result obtained by adding the number of the main scanning pixels corresponding to the predetermined number of sub-scanning lines including the result obtained by adding the number of the replaced main scanning pixels is added, and the result obtained by adding the number corresponding to the predetermined number of sub-scanning lines is The image reading apparatus according to claim 2, wherein the image reading apparatus outputs the data every predetermined sub-scanning line.   When the absolute value of the difference between the result of adding the number of main scanning pixels and the result of adding the number of main scanning pixels before that is larger than a threshold value, the addition result replacing unit adds the number of main scanning pixels 4. The image reading apparatus according to claim 3, wherein the obtained result is replaced with a result obtained by adding the previous number of main scanning pixels. Illuminating means for illuminating the document, sub-scanning density reference arranged outside the document placement area for detecting the light quantity of the illuminating means, the sub-scanning density reference and the reflected light from the document are read and A density correction method for an image reading apparatus comprising reading means for outputting read data,
After the reading of the original by the reading unit is started, the reading data based on the sub-scanning density is added within a predetermined range including a plurality of pixels extending over a plurality of sub-scanning lines, and the result of the addition within the predetermined range is predetermined. An addition step of outputting for each sub-scan line,
A correction value calculating step for calculating a correction value for performing density correction from the output result output for each of the predetermined sub-scanning lines in the adding step;
A density correction method for an image reading apparatus, comprising: a density correction step for performing density correction on the read data of the document based on the correction value calculated in the correction value calculation step.

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