JP2012151644A - Image reader, image formation apparatus provided with image reader, and image processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image reader capable of reducing color unevenness of a specific color occurring in image data on read document caused by unevenness in the properties of the light-emitting devices of a light source.SOLUTION: The document is irradiated with light from a light source comprising plural LED devices arrayed linearly, and the reflected light from the document is received by a CCD 3a to obtain image data. The obtained image data is converted to digital data by a gain adjustment circuit 100 and an A/D conversion circuit 101 and thereafter corrected by a shading compensation section 102. A color determination section 103 determines whether pixels in at least a part of the areas in the corrected image data is a preset specific color which generates the color unevenness. If determined to be the specific color, a color unevenness correction section 104 corrects the color unevenness of the specific color of the image data.

Description

  The present invention relates to an image reading apparatus used in an image forming apparatus such as a digital copying machine, a scanner, a facsimile, and a multifunction machine, an image forming apparatus including the image reading apparatus, and an image processing method. The present invention relates to an image reading apparatus having a function of reducing color unevenness, an image forming apparatus including the image reading apparatus, and an image processing method.

  2. Description of the Related Art Conventionally, image forming apparatuses such as digital copying machines, scanners, facsimile machines, and multifunction machines have been provided with an image reading apparatus that reads a document and digitizes it as image data, and various images for outputting the read image data. Various processing functions are provided, such as performing processing and performing print output in the apparatus as in copy processing, and performing output processing to an external device.

  In the image reading apparatus, light is emitted from a light source to a document, and the reflected light from the document is read in a line in the main scanning direction by a reading unit while relatively moving the document in the sub-scanning direction to obtain image data. Conventionally, a light source such as a halogen lamp or a xenon lamp has been used as a light source used in such an image reading apparatus. However, as a more efficient light source, a light source in which a plurality of LED (Light Emitting Diode) elements are linearly arranged is practical. It has become.

  When a light source in which a plurality of LED elements that emit white light are linearly arranged is used, a variation in chromaticity (color), which is one of the characteristics of the LED elements, becomes a problem. When the chromaticity of the LED elements varies, there is a problem that even if the original is colored in a uniform color, color unevenness occurs in the read image data. For the occurrence of such color unevenness, it is possible to realize an LED light source with less color unevenness by selecting and using LED elements having the same chromaticity in advance, but a sorting operation is required. Since LED elements having different chromaticities cannot be used, there is a problem that the manufacturing cost increases.

  As another countermeasure against the occurrence of color unevenness, for example, Japanese Patent Application Laid-Open No. H10-228561 uses a characteristic that the chromaticity is changed by changing the operating current of the LED element to control the LED element operating current. The point which correct | amends the dispersion | variation in chromaticity of the LED element arranged in the shape is described. Further, in Patent Document 2, in order to suppress variations in individual light emission intensities of LED elements, one line of gray balance correction data is created from line reference whiteboard data and line original data, and gray shading correction is performed at the time of shading correction. It also describes that gray balance fluctuations are also corrected by correcting the balance correction data together.

In Patent Document 1 described above, variation in chromaticity can be corrected by individually controlling the operating currents of a plurality of LED elements arranged in a line, but in order to individually control the amount of current applied to the LED elements. The drive circuit becomes complex and the drive circuit manufacturing cost increases. Further, even when the operating current is individually controlled, it is necessary to select the chromaticity of the LED elements to some extent.
Further, when looking at the spectral characteristics of the LED element, color unevenness may be more noticeable in a specific color. For example, a white LED element in which a blue light emitting diode and a yellow phosphor are combined has spectral characteristics as shown in FIG. When the peak wavelength P of the blue light emitting diode varies among elements, the chromaticity of each element varies. When a blue-type original is read by a reading unit using a light source in which such white LED elements are arranged in a line shape, the level of read data at pixel positions along the line shape is green (G ) And the red color (the graph indicated by R) have a greater variation in the level of the blue color (the graph indicated by B), and the color unevenness of the image data becomes more pronounced than the other colors when the document is read. .

  Accordingly, an object of the present invention is to reduce color unevenness of a specific color that occurs in image data obtained by reading a document due to variations in characteristics of light emitting elements of a light source in an image reading apparatus.

The invention according to claim 1 is a light source in which a plurality of light emitting elements are arranged in a line, a reading unit that irradiates light from the light source onto the document and obtains image data based on reflected light from the document, and Determination means for determining whether or not pixels in at least a part of the area of the image data have a preset specific color, and correction processing for color unevenness of the specific color of the image data when it is determined as the specific color An image reading apparatus comprising a correction unit.
The invention according to claim 2 is characterized in that the determination means determines whether or not a pixel in a region where the level fluctuation of the image data is within a predetermined range is the specific color. An image reading apparatus.
According to a third aspect of the present invention, in the image reading apparatus according to the first or second aspect, the determination unit makes a determination by comparing RGB data of a pixel with the RGB data of the specific color.
A fourth aspect of the present invention is the image reading apparatus according to any one of the first to third aspects, wherein the determination unit determines the image data subjected to the shading correction process.
The invention according to claim 5 is characterized in that the correction means performs a correction process using a correction value set in advance based on image data obtained by reading the reference document in advance by the reading means. The image reading apparatus described.
A sixth aspect of the present invention is an image forming apparatus comprising the image reading apparatus according to any one of the first to fifth aspects.
According to a seventh aspect of the present invention, there is provided a light source in which a plurality of light emitting elements are arranged in a line, a reading unit that irradiates a document with light from the light source and obtains image data based on reflected light from the document, An image processing method in an image reading apparatus comprising a processing unit that performs image processing of image data, wherein determination is made as to whether or not pixels in at least a partial area of the image data have a preset specific color An image processing method comprising: a processing step; and a correction processing step of correcting a color unevenness of the specific color of the image data when the specific color is determined.
The invention according to claim 8 is a program for causing a computer to perform each step of the image processing method according to claim 7.

  According to the present invention, in an image reading apparatus, it is possible to reduce color unevenness of a specific color that occurs in image data obtained by reading a document due to variations in characteristics of light emitting elements of a light source.

1 is a front view illustrating a schematic structure of an image forming apparatus including an image reading apparatus according to an embodiment of the present invention. It is a top view which shows the arrangement | sequence of the LED element of a light source. It is a block block diagram regarding image processing. It is a graph which shows distribution of the reading level in the pixel position of the main scanning direction before a shading correction process. It is a graph which shows distribution of the reading level after a shading correction process. It is a graph which shows the spectral characteristic of a white LED element. It is a graph which shows the reading level distribution of each color when color nonuniformity arises.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a front view showing a schematic structure of an image forming apparatus including an image reading apparatus according to an embodiment of the present invention. The image forming apparatus includes an original reading apparatus 1 that is an image reading apparatus that reads an original and obtains image data, and a printer 2 that forms an image on a sheet by electrophotography based on the image data read by the original reading apparatus 1. It has.

  The document reading device 1 includes a first reading unit 3 and a second reading unit 4 which are reading units for reading a document, a document tray 5 for setting a document, a document discharge tray 6 for discharging a document after reading, and a first document. A document conveyance path 7 that conveys the reading unit 3 and the second reading unit 4 so as to face each other, a plurality of conveyance rollers 8 that are arranged along the document conveyance path 7 and convey a document, and a first document such as a book. 1 contact glass 9, second contact glass 10 disposed opposite to the document to be conveyed, first reading roller 11 disposed opposite to the second contact glass 10, and second reading roller 12 disposed opposite to the second reading unit 4. It is constituted by.

  A document to be read is set on the document tray 5, and a document on which an image has been read is discharged to the document discharge tray 6. The document transport path 7 is a path set between the document tray 5 and the document discharge tray 6, and the documents set on the document tray 5 are sequentially transported one by one by the transport rollers 8. . In a normal use state, when a document reading operation is performed, the reading operation is performed by switching between one-sided or both-side reading modes. When the original is a single-sided original, the first reading unit 3 performs an image reading operation only on the surface of the original. When the original is a double-sided original, the first reading unit 3 performs an operation for reading the surface of the original. Then, the second reading unit 4 performs a reading operation on the back side of the document.

  The first reading unit 3 scans and moves the optical system in which the light source 3b and the mirror group 3c are combined with respect to the document placed on the first contact glass 9, and performs a reading operation with a CCD (Charge Coupled Device) 3a. Do. Light from the light source 3b is irradiated onto the document, and reflected light from the document is transmitted by the mirror group 3c, enters the imaging lens 3d, and forms an image on the light receiving surface of the CCD 3a to perform a reading operation. Further, the optical system is allowed to stand so as to face the second contact glass 10 with respect to the document transported through the document transport path 7, and between the second contact glass 10 and the first reading roller 11 (that is, When the document is transported on the document turn transport path 7), the light from the light source 3b is irradiated onto the document, and the reflected light from the document is imaged on the light receiving surface of the CCD 3a to perform the reading operation. When the document is transported to the document transport path 7, the first reading roller 11 is driven to rotate at the same speed as the transport roller 8 by a driving stepping motor (not shown), and the surface of the transported document is second contact glass. 10 acts to press. The first reading roller 11 is disposed to face the first reading unit 3 with a predetermined interval across the document conveyance path 7 and has a white peripheral surface for use as a white reference when generating shading data. ing.

  The second reading unit 4 is composed of a CIS (Contact Image Sensor) provided with a photoelectric conversion element. The second reading unit 4 reads the back side of the document conveyed on the document conveyance path 7 by the conveyance roller 8 with the photoelectric conversion element, and outputs image data. Can be obtained. The second reading roller 12 is disposed to face the second reading unit 4 with a predetermined interval across the document conveyance path 7 and has a white peripheral surface for use as a white reference when generating shading data. ing. The second reading roller 12 is rotationally driven at the same speed as the transport roller 8 by a stepping motor (not shown) when the second reading unit 4 performs the reading operation of the document, and the document is transferred to the second reading unit 4 and the second reading unit 4. It acts so as to move smoothly between the two reading rollers 12.

  The printer 2 includes a photosensitive member 14, a laser unit 15, a developing device 16, a transfer device 17, a fixing unit 18, and the like, and image forming processing is performed by an electrophotographic method. In the image forming process, the surface of the photoconductor 14 is uniformly charged by a charger (not shown), and the surface of the photoconductor 14 is read by the first reading unit 3 or the second reading unit 4 and subjected to image processing. A writing operation is performed by the laser unit 15 based on the image data, and an electrostatic latent image is formed. The toner is transferred from the developing device 16 to the electrostatic latent image formed on the surface of the photoconductor 14 so that the toner image is formed. The developed toner image is transferred to the paper 20 fed from the paper feed cassette 19 by the action of the transfer unit 17. The sheet 20 on which the toner image has been transferred is subjected to a fixing process by the fixing unit 18 and then discharged to a discharge tray 21.

  The first reading unit 3 uses a light source 3b in which a plurality of white LED elements are arranged in a line. FIG. 2 is a plan view showing the arrangement of the LED elements of the light source 3b. A plurality of white LED elements 30 are arranged in a line, and the arrangement direction is set to be along the main scanning direction when the reading operation is performed. The CCD 3a forms an image of reflected light from the original on the light receiving surface via the mirror group 3c and the imaging lens 3d, and converts it into an analog signal by photoelectric conversion.

  FIG. 3 is a block diagram showing image processing of an analog signal obtained by the CCD 3a. In the sensor block S that generates the read signal, the analog signal obtained from the CCD 3a is input to the gain adjustment circuit 100 and subjected to analog processing for amplifying to a preset gain, and the amplified analog signal is converted to A / A. The data is input to the D conversion circuit 101 and converted into digital data. Such analog processing and A / D conversion processing can be performed using, for example, an ASIC such as AFE (Analog Front End).

  The gain adjustment circuit 100 has a function of appropriately adjusting the gain, and amplifies and adjusts the gain so as to absorb variations in characteristics of the lamp and CCD line sensor used for the light source. The set value of the gain is determined so that a constant digital output is obtained when the reference white level of the first reading roller 11 is read. The gain setting is determined by performing gain adjustment processing when the power is turned on or for each reading operation.

Image data output as digital data from the sensor block S is input to the image processing block T. In the image processing block T, the shading correction unit 102 performs a shading correction process on the image data. Then, the color determination unit 103 determines whether or not the shading-corrected image data has a color that easily causes color unevenness. If it is determined that color unevenness is likely to occur, color unevenness correction is performed. In the unit 104, color unevenness correction processing of image data is performed.
As for the shading correction unit 102, the CCD 3a receives light in a state in which the light amount at both ends in the main scanning direction is reduced mainly due to the optical characteristics of the imaging lens 3d. A decrease in the amount of light can be corrected.

  FIG. 4 is a graph showing the distribution of the reading level at the pixel position in the main scanning direction before the shading correction process. The reading level decreases as it goes to both ends in the main scanning direction. In the shading correction processing, the reading level obtained by reading the reference white level of the first reading roller 11 with the CCD 3a is stored for each pixel, and the normalization processing is performed on the image data for each pixel using the stored reading level. By doing so, the distribution in the main scanning direction is corrected. FIG. 5 is a graph showing the distribution of the read level after the shading correction process. The reading level is almost uniform throughout, and the decrease in the amount of light at both ends is corrected.

  In addition, as a process for correcting variations in optical characteristics such as a light source, a lens, and a CCD, a gray balance correction process may be performed during the shading correction process. In the gray balance correction process, the reading levels of R, G, and B are corrected by multiplying a correction coefficient for each color so that the reading level of the reference document becomes a target value. The correction coefficient can be set by calculating from the amount of deviation between the data obtained by reading the reference document and the target value.

The shading correction process reads the reference white level and saves it as shading data for each pixel, and generates the data for each pixel of the image data obtained by reading the document based on the target value of the shading data and the reference white level. Processing is performed by multiplying the correction coefficient. Specifically, it is processed by the following equation.
Dout = Din × Dn / Ds
Here, Dout is data after shading correction, Din is input data, Ds is shading data, and Dn is a target value. In addition, the gray balance correction can be performed by adjusting the target value Dn itself in the above formula.

  In the color determination unit 103, data related to a specific color in which color unevenness is noticeably generated is set in advance based on the spectral characteristics of the LED element of the light source, and whether the image data subjected to the shading correction processing has the specified specific color Determine. The color determination unit 103 has a line memory of at least one line, and temporarily stores the image data after shading correction processing in the line memory sequentially while transferring it to the subsequent stage.

Color unevenness occurs when an area that should have the same density is formed in a document with a predetermined width or more. Therefore, the color determination unit 103 first stores image data (density data). In a line memory, a detection area that covers a plurality of pixels before and after the target pixel is set, and an average value, a maximum value, and a minimum value of image data (density data) in the detection area are calculated. Then, the level fluctuation Δ in the detection area is calculated by the following formula based on the maximum value and the minimum value.
If Δ = maximum value−minimum value Δ is less than or equal to a preset threshold value Δth, it is determined that the pixel of interest is image data having the same density, and is a specific color that causes color unevenness next to occur? Judge whether or not. In the determination of the specific color, the determination is made based on the RGB data (density data) of the average value of the detection area centered on the target pixel.

  For example, the ratios R / G and B / G of R and B data to G-related data are within a predetermined range compared with similar data ratios Rref / Gref and Bref / Gref of RGB data of a specific color. It is determined that the color is a specific color. By performing color determination using the data ratio of such RGB data. It is possible to determine whether or not the color is a specific color except for the difference in brightness of the image data. If color unevenness is easily noticeable at a certain lightness of a specific color, the color determination can be performed by directly comparing the image data and the RGB data of the specific color. By performing the determination process as described above, it is possible to determine whether or not color unevenness occurs based on the actual spectral characteristics of the LED element of the light source.

The color unevenness correction unit 104 performs color unevenness correction processing when it is determined based on the determination result obtained from the color determination unit 103 that the color irregularity is a specific color. The color unevenness correction unit 104 performs correction processing on the image data corrected by the shading correction unit 102. First, a reference document in which color unevenness significantly occurs after correction processing by the shading correction unit 102 is prepared in advance, and the reference document is read and the image data is stored as color unevenness data. In addition, a target value for each pixel for reducing color unevenness is set for the obtained color unevenness data. Then, the data for each pixel of the image data corrected by the shading correction unit 102 is processed by multiplying the color unevenness data and the correction coefficient generated by the target value for reducing the color unevenness. Specifically, it is processed by the following equation.
Mout = Min × Mn / Ms
Here, Mout is data after color unevenness correction, Min is input data, Ms is color unevenness data, and Mn is a target value.

  By performing color unevenness correction processing as described above, color unevenness caused by the actual spectral characteristics of the LED elements of the light source can be reduced. Therefore, when the light source is manufactured, it is based on the spectral characteristics of the LED elements. The selection range can be widened, and the manufacturing cost can be reduced. In addition, as described above, the color unevenness correction process can be performed by the same calculation process as the shading correction process. Therefore, the color unevenness correction process can be easily performed by setting a plurality of circuits having a shading correction processing function. It becomes possible. Therefore, it is not necessary to adjust the operating current according to the variation in the spectral characteristics of the LED elements, and color unevenness correction can be performed without using a complicated circuit configuration.

  Depending on the spectral characteristics of the LED elements used, there may be multiple specific colors with noticeable color unevenness. In that case, RGB data, color unevenness data, and color unevenness are reduced for each specific color. This can be dealt with by storing the target value for this purpose in the memory and correcting the color unevenness by determining each specific color.

  DESCRIPTION OF SYMBOLS 1 ... Document reading apparatus, 2 ... Printer, 3 ... 1st reading part, 3a ... CCD, 3b ... Light source, 3c ... Mirror group, 3d ... Imaging lens, 4 ... 2nd reading part, 11 ... 1st reading roller, 12 ... 2nd reading roller.

JP 2008-172327 A JP 2010-199898 A2

Claims (8)

  A light source in which a plurality of light emitting elements are arranged in a line; a reading unit that irradiates light from the light source onto a document and obtains image data based on reflected light from the document; and at least a part of the image data A determination unit configured to determine whether or not a pixel in the region is a specific color set in advance; and a correction unit configured to correct color unevenness of the specific color of the image data when the pixel is determined to be the specific color. An image reading apparatus.   The image reading apparatus according to claim 1, wherein the determination unit determines whether or not a pixel in a region where a level variation of the image data is within a predetermined range is the specific color.   3. The image reading apparatus according to claim 1, wherein the determination unit performs determination by comparing RGB data of a pixel with RGB data of the specific color.   The image reading apparatus according to claim 1, wherein the determination unit determines the image data subjected to shading correction processing.   4. The image reading apparatus according to claim 1, wherein the correction unit performs a correction process using a correction value set in advance based on image data obtained by reading the reference document by the reading unit. 5.   An image forming apparatus comprising the image reading apparatus according to claim 1.   A light source in which a plurality of light emitting elements are arranged in a line, a reading unit that irradiates light from the light source onto the document and obtains image data based on reflected light from the document, and performs image processing of the image data An image processing method in an image reading apparatus including a processing unit, wherein a determination processing step for determining whether or not pixels of at least a part of the area of the image data have a preset specific color, and the specific color An image processing method comprising: a correction processing step of correcting color unevenness of a specific color of the image data when it is determined.   The program for making a computer perform each process of the image processing method described in Claim 7.

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