JP2004241809A - Image reading apparatus, image forming apparatus, and image processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent image deterioration by preventing an originally lowest MTF value of image data from furthermore being lowered by inter-line correction processing. <P>SOLUTION: The image reading apparatus 10 is provided with: an inter-line correction processing circuit 15; a control section SC; and a ROM 19 for storing correction reference information, the correction reference information indicating a line sensor the image data of which have lowest optical evaluation values among image data of line sensors corresponding to R, G and B in order to perform inter-line correction. The image reading apparatus 10 reads the correction reference information from the ROM 19 in the case of reading an original image, and applies inter-line correction processing to the image data by each line sensor by using the image data obtained from the line sensor with a lowest MTF value corresponding to the correction reference information for a reference. Thus, image quality deterioration can be prevented by preventing the MTF value of the line sensor whose MTF value is lowest from being furthermore lowered by the inter-line correction processing. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image reading apparatus, an image forming apparatus, and an image processing method suitable for application to an image sensor including a plurality of image sensor rows, for example, a digital color copying machine using a three-line color CCD.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an image reading apparatus used in a copying machine or the like uses a line sensor (imaging element array). FIG. 9 is a diagram illustrating an image reading method using a one-dimensional image sensor. As shown in FIG. 9, an image is read by electrical scanning by a line sensor in the main scanning direction of the document, and the image is read by mechanical scanning by movement of the document or the carriage in the sub-scanning direction. The magnification in the sub-scanning direction can be changed by changing the sub-scanning moving speed. The magnification in the main scanning direction is performed by electrical enlargement / reduction processing.
[0003]
In the case of a color image reading apparatus, a color image sensor (that is, a three-line color CCD) including three R, G, and B line sensors is used. Such a color image sensor has three R, G, and B line sensors that are long in the main scanning direction. Each line sensor has a structure arranged in parallel with each other at a predetermined pitch d in the sub-scanning direction (see FIG. 2).
[0004]
In this case, since the three line sensors for R, G, and B are arranged at a predetermined pitch d, the original moves relatively in the sub-scanning direction with respect to the color image sensor during reading. Of the line sensor R is 2 d in distance from the last line sensor B, and the line sensor G is d in distance from the line sensor B in d. Therefore, when an image of one line of a document is read, a temporal shift occurs in the read R, G, and B color image signals due to a shift in the mounting position of the line sensor. In order to obtain a good image, it is necessary to correct this shift. In order to correct the time lag of the image signal, the first image data R is delayed by 2d and the next image data G is delayed by d, thereby correcting the position with the image data B (line-to-line correction). Processing is performed.
[0005]
Here, since d does not always coincide with the line unit of the sub-scan, in order to read without color shift, correction of less than one line is necessary in addition to correction of one line unit. In addition, when the magnification is changed in the sub-scanning direction, correction of less than one line is required.
[0006]
Therefore, for example, in a color image reading apparatus using a three-line color CCD, the position of a line sensor arranged in the sub-scanning direction is adjusted by a line delay using a FIFO (First In First Out) memory. At the time of zooming, the correction after the decimal point is performed by interpolation between two lines using an interpolation calculator. In this interpolation operation, each line is interpolated by delaying and interpolating the image signal from the line sensor preceding the line sensor in the sub-scanning direction with respect to the reading position of the line sensor corresponding to the rear end in the sub-scanning direction. Generally, the reading positions of the sensors are matched. Further, in order to avoid the G signal that is conspicuous being changed by the interpolation processing, a signal that performs interpolation processing on the R and B signals on the basis of the G signal for the decimal line is also used.
[0007]
In addition, when such correction is performed, when a black fine line included in the image data is detected, the decimal point correction operation is prohibited (that is, the decimal part is not corrected), and the reproducibility of the black fine line is reduced. There has been proposed an image processing apparatus that enhances image quality (for example, see Patent Document 1).
[0008]
Also, in order to prevent image deterioration due to interpolation processing, a color image processing apparatus has been proposed that performs density correction on image data having a low MTF value when performing line-to-line correction (for example, Patent Document 2). reference).
[0009]
Further, there has been proposed an image reading apparatus capable of setting a predetermined position as a reference for correction at an arbitrary position in the sub-scanning direction (for example, see Patent Document 3). In this case, for example, a resolution priority mode in which a reference position is set so that a difference between a reading position corresponding to any one line sensor and a predetermined reference position does not always include a fractional line, and a three-stage line There is a saturation priority mode in which a reference position is set so that sub-scanning reading position deviations included in each image signal output from the sensor are equivalent to a fractional number of lines.
[0010]
[Patent Document 1]
JP 2000-224417 A (pages 5 and 6)
[Patent Document 2]
JP 2000-287092 A (pages 3 and 4)
[Patent Document 3]
JP-A-2002-247292 (pages 4, 5, 7)
[0011]
[Problems to be solved by the invention]
However, in the above-described image reading apparatus according to the conventional method, when performing the line-to-line correction, one of the three colors is used as an interpolation reference to perform interpolation of the other two colors. With respect to, the optical evaluation (MTF) value of the image data is lower than the original data. For example, when interpolation processing is performed on image data of a color having the lowest MTF value of image data, the MTF value of the image data of this color is further reduced. There are problems such as deterioration, black characters and black lines being colored, a monochrome document being erroneously determined to be a color document, and a change in color depending on the magnification.
[0012]
Further, in the case of Patent Literature 1 and Patent Literature 3, when the image data having the lowest MTF value is used as the correction reference, it cannot be solved that the MTF value of the image data is further reduced by the interpolation calculation.
[0013]
Further, in the case of Patent Document 2, there is a problem that the cost is increased because a density correction unit for performing the density correction is required.
[0014]
In view of the above, the present invention has been made to solve the above-described problem, and it is possible to prevent the MTF value of image data having an originally low MTF value from being further reduced by performing the line-to-line correction processing, thereby preventing image deterioration. It is an object of the present invention to provide an image reading device, an image forming device, and an image processing method.
[0015]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, an image reading apparatus according to the present invention is an apparatus that reads an original image by exposing and scanning an arbitrary original, and has a predetermined pitch and one scanning direction with respect to one scanning direction of the original. Having a plurality of image sensor rows arranged in a line along the line, and an image sensor having the lowest optical evaluation (MTF) value among a plurality of image data obtained from each of the image sensor rows of the reading means Storage means for storing a row as correction reference information, line-to-line correction means for correcting a phase shift between image data due to a positional shift due to an arrangement pitch between image sensor rows, and storage means and a line-to-line correction means. Control means for controlling input and output, wherein the control means reads the correction reference information from the storage means and sets it in the line-to-line correction means when reading the original image, and It is characterized in that controlling the line correction means to correction processing between lines of image data by a plurality of imaging element arrays based on the image data obtained from the image pickup element arrays corresponding to.
[0016]
According to the image reading apparatus of the present invention, for example, at the time of shipment from a factory, for example, the imaging element array having the lowest optical evaluation value of the image data among the plurality of imaging element arrays of the reading unit is measured, and this optical evaluation value Are stored in the storage unit as correction reference information.
[0017]
Based on this, when reading the original image, the control unit reads the correction reference information from the storage unit and sets it in the line-to-line correction unit. The line-to-line correction means performs line-to-line correction processing on image data from each image sensor array based on image data obtained from the image sensor array having the lowest MTF value corresponding to the correction reference information.
[0018]
Accordingly, it is possible to prevent the MTF value of the image data obtained from the image sensor row having the lowest MTF value from becoming lower due to the inter-line correction processing. Further, since the MTF value of the image data of the other image data is reduced by the line-to-line correction processing, the difference in the MTF value between the image sensor rows can be reduced, and the balance of the entire MTF value can be improved. it can. Therefore, it is possible to eliminate the problem that a black-and-white document is erroneously determined to be a color document.
[0019]
An image forming apparatus according to the present invention is a device that reads a document image and forms an image based on image data obtained, and an image reading unit that reads a document image by exposing and scanning an arbitrary document. An image forming unit that forms an image based on image data obtained by the image reading unit, wherein the image reading unit has a predetermined pitch with respect to one scanning direction of the document and a line shape along the other scanning direction. Reading means having a plurality of image sensor rows arranged in a plurality of image data, and an image sensor row having the lowest optical evaluation (MTF) value among a plurality of image data obtained from each image sensor row of the reading means is referred to as correction reference information. Storage means for storing the image data, line-to-line correction means for correcting a phase shift between image data caused by a positional shift due to an arrangement pitch between image sensor rows, and input / output of the storage means and the line-to-line correction means Control means for controlling the readout of the original image, the control means reads out the correction reference information from the storage means, sets the correction reference information in the line-to-line correction means, and obtains the correction reference information from the image sensor array corresponding to the correction reference information. The inter-line correction means is controlled so as to perform inter-line correction processing on image data obtained by a plurality of image sensor rows based on image data obtained.
[0020]
According to the image forming apparatus of the present invention, the image reading device according to the present invention is applied to the image reading unit, and when reading the original image, the correction reference information is read from the storage unit by the control unit, and the image is read between the lines. It is set in the correction means. The line-to-line correction means performs line-to-line correction processing on image data from each image sensor array based on image data obtained from the image sensor array having the lowest MTF value corresponding to the correction reference information.
[0021]
As a result, the MTF value of the image data obtained from the image sensor row originally having the lowest MTF value does not further decrease due to the line-to-line correction processing, and it is possible to prevent the image quality from deteriorating during image formation. It becomes. Further, since the MTF value of the image data of the other image data is reduced by the line-to-line correction processing, the difference in the MTF value between the image sensor rows can be reduced, and the balance of the entire MTF value can be improved. it can. Therefore, it is possible to solve problems such as coloring of black characters and black lines, erroneous determination of a black-and-white document as a color document, and change in color tone depending on magnification.
[0022]
An image processing method according to the present invention includes a plurality of image reading devices having a plurality of image sensor rows arranged in a line at a predetermined pitch in one scanning direction of a document and along the other scanning direction. In a method of processing image data, a predetermined document image is read, and an optical evaluation (MTF) value of a plurality of image data obtained from a plurality of image sensor rows is measured. A low image sensor row is set as the correction reference information, the set correction reference information is stored, and when the document image is read, the correction reference information is read and set, and is obtained from the image sensor row corresponding to the correction reference information. It is characterized in that image data by a plurality of image sensor rows is subjected to line-to-line correction processing based on image data.
[0023]
According to the image processing method of the present invention, when reading a document image, the MTF value of the image data obtained from the image sensor array having the lowest MTF value does not decrease further by performing the line-to-line correction processing. In addition, it is possible to reduce the difference between the MTF values between the image sensor rows. Therefore, it is possible to improve the balance of the entire MTF value.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an image reading apparatus, an image forming apparatus, and an image processing method according to an embodiment of the present invention will be described with reference to the drawings.
[0025]
(1) Image reading device
An image reading apparatus according to an embodiment of the present invention includes a storage unit that stores a line sensor (imaging element row) having the lowest optical evaluation (MTF) value as correction reference information, and a line-to-line correction unit that corrects a phase shift between image data. A control unit for controlling the input / output of the correction unit; when reading the original image, the correction reference information is read from the storage unit and set in the line-to-line correction unit; and the lowest MTF value corresponding to the correction reference information is set. The MTF value of the image data of the line sensor having the lowest MTF value due to the line-to-line correction processing is further reduced by performing the line-to-line correction processing on the image data of each image pickup element line based on the image data obtained from the image pickup element line. Can be avoided.
[0026]
FIG. 1 is a block diagram illustrating a configuration example of an image reading apparatus 10 according to an embodiment of the present invention. As shown in FIG. 1, the image reading device 10 includes a color image sensor 1, an image data processing circuit 11, and a control unit SC.
[0027]
As shown in FIG. 2, the color image sensor 1 includes three line sensors (image sensor rows) Rs, Gs, and Bs for R, G, and B colors that are long in the main scanning direction at a predetermined pitch d in the sub-scanning direction. It has a structure arranged in parallel with each other. Note that the distance between Rs and Gs and the distance between Gs and Bs need not be the same.
[0028]
When reading a document image using the color image sensor 1, image information on the document is read by scanning in the main scanning direction and the sub-scanning direction. In the main scanning direction, an original image is read by electric scanning by the line sensors Rs, Gs, and Bs, and in the sub-scanning direction, an original image is read by a mechanical operation such as movement of the original or a carriage. The magnification in the sub-scanning direction can be changed by changing the sub-scanning moving speed. The magnification in the main scanning direction is performed by electrical enlargement / reduction processing.
[0029]
The image data processing circuit 11 includes analog processing circuits 12a, 12b, and 12c for processing image data of R, G, and B colors read by the color image sensor 1, A / D conversion circuits 13a, 13b, and 13c, and a shading correction circuit. 14a, 14b, 14c, and an inter-line correction circuit 15 (15a, 15b, 15c).
[0030]
The analog signal processing circuit 12a performs processing such as noise removal and amplification on the image data R under the control of the timing control unit 16. The analog signal processing circuit 12b performs processing such as noise removal and amplification on the image data G under the control of the timing control unit 16. The analog signal processing circuit 12c performs processing such as noise removal and amplification on the image data B under the control of the timing control unit 16. Image data (analog signals) processed by these analog signal processing circuits 12a to 12c are output to A / D conversion circuits 13a to 13c.
[0031]
The A / D conversion circuit 13a converts an analog signal of the image data R into a digital signal under the control of the timing control unit 16. The A / D conversion circuit 13b converts an analog signal of the image data G into a digital signal under the control of the timing control unit 16. The A / D conversion circuit 13c converts an analog signal of the image data B into a digital signal under the control of the timing control unit 16. Digital image data obtained by these A / D conversion circuits 13a to 13c are output to shading correction circuits 14a to 14c.
[0032]
The shading correction circuit 14a corrects the light amount unevenness of the image data R. The shading correction circuit 14b corrects the light amount unevenness of the image data G. The shading correction circuit 14c corrects the light amount unevenness of the image data B. The image data processed by these shading correction circuits 14a to 14c is output to an inter-line correction circuit 15 (15a to 15c).
[0033]
The line-to-line correction circuit 15 is a circuit that corrects a phase shift of the image data R, G, and B due to a positional shift between the line sensors Rs, Gs, and Bs of the color image sensor 1. FIG. 3 is a block diagram showing a schematic configuration of the line-to-line correction circuit 15.
[0034]
As shown in FIG. 3, the line-to-line correction circuits 15a and 15b each include a line delay FIFO (First In First Out) memory M _R , M _G And the interpolation calculator N _R , N _G It is composed of The line-to-line correction circuit 15c includes an interpolation calculator N _B It is composed of When correcting the shift between the image data R, G, and B, the correction in units of one line (correction of the integer part) is performed by the FIFO memory M as an integer part correction unit _R , M _G Is performed. Correction of less than one line (decimal part correction) is performed by an interpolation calculator N as a decimal part corrector. _R , N _G , N _B Is processed. In the line-to-line correction circuits 15a to 15c shown in FIG. 3, since the line sensor Bs is at the end, the line delay FIFO memory need not include only the reference color (B).
[0035]
FIG. 4 shows an interpolation operation unit N (N _R , N _G , N _B FIG. 2 is a block diagram showing the configuration of FIG. As shown in FIG. 4, the interpolation calculator N includes a subtractor N1, multipliers N2 and N3, and an adder N4. In FIG. 4, α and β are image data separated by one line (see FIG. 5 described later), RATIO is an interpolation coefficient, and C is an output of the arithmetic unit N. In FIG. 4, it is assumed that α, β, RATIO, and C are all 8-bit data.
[0036]
When performing the interpolation calculation using the interpolation calculator N, the interpolation calculation is performed based on the following equation.
C = α × (1-RATIO) + β × RATIO
When image data one line apart from α and β are input and an interpolation coefficient is input into RATIO, the result of the C interpolation operation is output. Here, the interpolation coefficient RATIO is supplied from the line-to-line correction control unit 17.
[0037]
The interpolation coefficient RATIO is obtained by calculation according to the interval between the line sensors Rs, Gs, Bs and the magnification, and is set in advance by the CPU 18. Here, the interpolation coefficient of the line sensor having the lowest MTF value of the image data is set to 0 and input to the interpolation calculator N to calculate the interpolation coefficient of another line sensor.
[0038]
In the interpolation calculator N, the subtractor N1 performs the calculation of (1-RATIO) to determine the difference between 1 and RATIO (the density of 256 gradations is set to 1). The multiplier N2 performs an operation of α × (1-RATIO), and obtains the product of α and the output of the subtractor N1. The multiplier N3 executes the calculation of β × RATIO, and obtains the product of β and RATIO. Finally, the operation of [α × (1-RATIO)] + [β × RATIO] is executed by the adder N4. As a result, image data corrected between lines is obtained.
[0039]
FIG. 5 is an explanatory diagram of an example of an inter-line correction process. In FIG. 5, when the image reading apparatus 10 reads a document image at 1.2 times, the image data G is delayed by 2.4 lines and the image data B is delayed by 4.8 lines with respect to the image data R. . In this case, RATIO for the image data G is 5-4.4 = 0.6. For the image data B, RATIO is 5-4.8 = 0.2. When correcting between lines, the FIFO memory M _R Delays the image data R by 5 lines. FIFO memory M _G Delays the image data R by two lines. And the interpolation calculator N _R RATIO = 0 (assuming that the MTF value of the image data R is the lowest) is input to the interpolation arithmetic unit N _G Input RATIO = 0.6 to the interpolation calculator N _B By inputting RATIO = 0.2 into the image data, interpolation processing is performed on the image data G and B. Thus, the line-to-line correction is performed.
[0040]
The control unit SC controls the operation of the color image sensor 1, the image data processing circuit 11, and the operation of the image forming unit 20 when reading a document image. The control unit SC includes a timing control unit 16, an inter-line correction control unit 17, a CPU 18, and a ROM 19. The operations of the timing control unit 16 and the line-to-line correction control unit 17 are controlled by the CPU 18 that controls the operation of the entire image forming apparatus 100.
[0041]
The timing control unit 16 controls the operations of the color image sensor 1, the analog processing circuits 12a to 12c, the A / D conversion circuits 13a to 13c, the shading correction circuits 14a to 14c, and the line-to-line correction control unit 17.
[0042]
The line-to-line correction control unit 17 forms a control unit together with the CPU 18 and controls the correction operation of the line-to-line correction circuit 15. For example, when reading the document image, the line-to-line correction control unit 17 reads information indicating that “the line sensor Rs is the correction reference” from the ROM 19 as a storage unit and sends it to the line-to-line correction circuit 15. The line-to-line correction circuit 17 is set so that the image data R, Gs, and Bs by the line sensors Rs, Gs, and Bs are subjected to line-to-line correction processing based on the image data R obtained from the line sensor Rs corresponding to the correction reference information. To be controlled.
[0043]
In this case, the correction reference information is obtained, for example, by measuring an optical evaluation (MTF) value of image data obtained from each of the line sensors Rs, Gs, and Bs before shipping the product, and determining a line sensor Rs having the lowest MTF value among the line sensors Rs. It is set as a reference for line-to-line correction, and this correction reference information is stored in the ROM 19. At the time of image reading, this correction reference information is read from the ROM 19 and used as a reference for line-to-line correction.
[0044]
The CPU 18 controls the overall operation of the image reading device 10 according to a control program stored in the ROM 19 while using a RAM (not shown) as a work area. For example, a document is conveyed, image information is read by the color image sensor 1, a line-to-line correction process is performed on the image data, and then output.
[0045]
The ROM 19 stores a control program and also stores correction reference information used in the inter-line correction processing. This correction reference information is read from the ROM 19 when reading the document image. The correction reference information read from the ROM 19 is used as a reference for line-to-line correction.
[0046]
Hereinafter, the image processing method will be described with reference to FIG. 6 regarding the operation of the image reading apparatus 10 when reading a document image. FIG. 6 is a flowchart showing an operation example when reading a document image.
[0047]
Here, in the image reading device 10, optical evaluation (MTF) values of the image data R, G, and B obtained from the line sensors Rs, Gs, and Bs are measured in advance before shipment, and the line sensor with the lowest MTF value is measured. Rs is set as a reference for line-to-line correction, which is stored in the ROM 19, and when reading a document image, the correction reference information is read from the ROM 19 and set in the line-to-line correction circuit 11 to correspond to the correction reference information. It is assumed that the image data R, Gs, and Bs by the line sensors Rs, Gs, and Bs are subjected to inter-line correction processing with reference to the image data R obtained from the line sensor Rs.
[0048]
Under these operating conditions, the CPU 18 of the image reading device 10 controls the image reading device 10 via the timing control unit 16 and the line-to-line correction control unit 17 as follows.
[0049]
First, in step S1 of the flowchart shown in FIG. 6, a document image is scanned by the color image sensor 1. Here, in the main scanning direction of the document, an image is read by electrical scanning by the line sensors Rs, Gs, Bs, and in the sub-scanning direction, the image is read by mechanical scanning such as movement of the document or carriage. As a result, the information of the original is converted into an electric signal by the color image sensor 1, and the obtained image data R, G, B are input to the analog signal processing circuits 12a, 12b, 12c, respectively.
[0050]
Next, in step S2, the image data R, G, and B are processed by the analog processing circuits 12a to 12c. In this case, processing such as noise removal and amplification of the image data R, G, and B is performed. In step S3, the image data R, G, and B processed by the analog processing circuits 12a to 12c are converted into digital signals. Thereafter, in step S4, shading correction is performed. Here, shading correction for correcting light amount unevenness in the main scanning direction is performed.
[0051]
Next, in step S5, the correction reference information is read from the ROM 19. This correction reference information is stored in advance, and is based on the line sensor having the lowest MTF value among the plurality of image data R, G, and B obtained from the line sensors Rs, Gs, and Bs of the color image sensor 1, respectively. Things. For example, it is information indicating the line sensor Rs.
[0052]
In step S6, a reference for line-to-line correction is set based on the correction reference information read from the ROM 19. In this example, since the correction reference information is the line sensor Rs, the image data R corresponding thereto is set as a reference, and the interpolation coefficient for the image data R is set to 0.
[0053]
In step S7, a line delay process of the image data is performed. In this case, correction is performed in units of integer lines so that each image data is aligned with a predetermined position (dotted line shown in FIG. 5) of the image data R. The image data R is delayed by five lines, and the image data G is delayed by two lines.
[0054]
In step S8, an interpolation process of the image data is performed. In this case, the interpolation calculation processing is performed based on the above-mentioned equation: C = α × (1−RATIO) + β × RATIO. Here, since the interpolation coefficient supplied from the line-to-line correction control unit 17 is 0 with respect to the image data R used as a reference for the interpolation processing, the input image data R is output as it is. The interpolation processing is performed on the image data G and B with the interpolation coefficient set.
[0055]
Here, as shown in FIG. 5, the image data G is delayed by 2.4 lines and the image data B is delayed by 4.8 lines with respect to the image data R. In order to correct this delay, the integer lines are corrected by the above-described line delay processing (step S7). Fractional lines are corrected by interpolation processing. For the image data G, the interpolation coefficient RATIO of the interpolation processing is 5-4.4 = 0.6. For the image data B, the interpolation coefficient RATIO is 5-4.8 = 0.2. These are input to an interpolation calculator N to perform an interpolation calculation.
[0056]
As shown in FIG. 5, the result of the processing by the interpolation calculator N is that the MTF value of the image data R remains 32% because no interpolation processing is performed, and the MTF value of the image data G is 38% to 35% by the interpolation processing. And the MTF value of the image data B changed from 35% to 33% by the interpolation processing. This prevents the MTF value of the image data R having the lowest MTF value from being further reduced. Further, the difference in the MTF value between the image sensor rows was reduced.
[0057]
In step S9, the image data R, G, and B after the inter-line correction processing are output to the image forming unit 20. After the image data R, G, and B output from the line-to-line correction circuit 15 are input to the image processing unit 2 of the image forming unit 20, the reading operation ends.
[0058]
As described above, in the present embodiment, in order to perform line-to-line correction, among the image data of the R, G, and B image sensor rows, the line sensor Rs having the lowest optical evaluation value of the image data is used as the correction reference information. This correction reference information is stored in the ROM 19, and when reading the original image, the correction reference information is read from the ROM 19, and the image obtained from the line sensor Rs having the lowest MTF value corresponding to the correction reference information is obtained. The image data G and B by the line sensors Gs and Bs are interpolated based on the data R.
[0059]
As a result, the MTF value of the image data of the line sensor originally having the lowest MTF value does not further decrease due to the line-to-line correction processing, so that the deterioration of the image quality can be prevented. In addition, since the difference between the MTF values between the line sensors can be reduced, the balance of the entire MTF value can be improved. For this reason, it is possible to solve a problem that a monochrome document is erroneously determined to be a color document.
[0060]
(2) Image forming apparatus
FIG. 7 shows a configuration example of an image forming apparatus 100 as an embodiment according to the present invention.
An image forming apparatus 100 according to an embodiment of the present invention employs the image reading apparatus 10 according to the present invention, and stores image data of a plurality of line sensors (imaging element arrays) of a reading unit in advance at the time of factory shipment or the like. The line sensor having the lowest optical evaluation value is measured, and the line sensor having the lowest optical evaluation value is stored in the storage means as correction reference information.When reading the document image, the correction reference information is read from the storage means. An MTF is originally set in the line-to-line correction means and line-to-line correction control is performed to perform line-to-line correction processing on image data from each line sensor based on image data obtained from the line sensor corresponding to the correction reference information. The MTF value of the image data of the image sensor row having the lowest value may be further reduced by performing the inter-line correction processing. Ku, in which to be able to prevent deterioration of image quality.
[0061]
As shown in FIG. 7, the image forming apparatus 100 includes an image reading unit 10A and an image forming unit 20.
The image reading unit 10A is an application of the image reading device 10 described above. The configuration of the image reading unit 10A is the same as that of the image reading device 10, and a detailed description thereof will be omitted. In this case, the CPU 18 controls the entire operation of the image forming apparatus 100 in accordance with the control program stored in the ROM 19 while using a RAM (not shown) as a work area. For example, a document is conveyed, image information is read by the image reading unit 10A, and an image is formed on a sheet based on the image data.
The image forming unit 20 includes an image processing unit 2, an image writing unit 3, an image generation unit 4, a cassette sheet feeding unit 5, a sheet feeding roller unit 6, a fixing device 7, a sheet discharging unit 8, an automatic double-sided copy sheet feeding unit (ADU). ) 9 is provided.
[0062]
When a document image is read using the image forming apparatus 100 and the read image data is formed on a sheet, the document image is placed on a document table of an automatic document feeder DF mounted on the upper part of the image forming apparatus 100. The placed document d is transported in the direction of the arrow, and an image on one or both sides of the document is read by the optical system of the image reading unit 10A, and is read by the color image sensor 1.
[0063]
The analog signal photoelectrically converted by the color image sensor 1 is subjected to analog processing, A / D conversion, shading correction, and line-to-line correction processing in the image processing circuit 11, and then image compression processing and the like in the image processing unit 2. , And sends a signal to the image writing unit 3.
[0064]
In the image writing section 3, output light from the semiconductor laser is irradiated on the photosensitive drum 4A of the image generation section 4 to form a latent image. In the image generation unit 4, processes such as charging, exposure, development, transfer, separation, and cleaning are performed, and an image is transferred to the sheet S conveyed from the cassette sheet feeding unit 5 or the sheet feeding roller unit 6.
The paper S carrying the image is fixed by the fixing device 7 and discharged from the paper discharge unit 8.
[0065]
Hereinafter, an operation when reading an original image in the image forming apparatus 100 will be described with reference to FIG. FIG. 6 is a flowchart showing an operation example when reading a document image.
[0066]
Here, in the image forming apparatus 100, the optical evaluation (MTF) values of the image data R, G, and B obtained from the line sensors Rs, Gs, and Bs are measured before shipping, and the line sensor with the lowest MTF value is measured. Rs is set as a reference for line-to-line correction, which is stored in the ROM 19, and when reading a document image, the correction reference information is read from the ROM 19 and set in the line-to-line correction circuit 11 to correspond to the correction reference information. It is assumed that the image data R, G, and B by the line sensors Rs, Gs, and Bs are subjected to line-to-line correction processing with reference to the image data R obtained from the line sensor Rs.
With this as an operating condition, the CPU 18 of the image forming apparatus 100 controls the image reading unit 10A and the image forming unit 20 as follows.
[0067]
First, in step S11 of the flowchart shown in FIG. 8, a document image is read. The operation in step S11 is performed according to the flowchart shown in FIG. For example, in order to perform the line-to-line correction, among the image data of the R, G, and B image sensor rows, the line sensor Rs having the lowest optical evaluation value of the image data is set as the correction reference information. When a document image is read, the correction reference information is read from the ROM 19, and the image data obtained by the line sensors Gs and Bs based on the image data R obtained from the line sensor Rs corresponding to the correction reference information is stored in the ROM 19. G and B are interpolated. The obtained image data R, G, and B after the inter-line correction processing are output to the image processing unit 2 of the image forming unit 20.
[0068]
Next, in step S12, processing such as image compression is performed. The processed image data is supplied to the image writing unit 3. In step S13, an image forming process is performed. Here, a latent image is generated on the photosensitive drum 4A of the image generation unit 4, and the image generation unit 4 performs processes such as charging, exposure, development, transfer, separation, and cleaning. The image is transferred onto the paper S conveyed from the paper feed roller 5 or the paper feed roller unit 6. Next, in step S14, the image transferred to the sheet S is fixed by the fixing device 7.
In step S15, the paper S on which the image has been fixed is discharged from the paper discharge unit 8. After the sheet S has been discharged, the operation ends.
[0069]
As described above, in the image forming apparatus 100 according to the embodiment of the present invention, since the above-described image reading apparatus 10 is applied, the MTF value of the image data of the line sensor originally having the lowest MTF value is subjected to the line-to-line correction processing. By doing so, the image quality can be prevented from deteriorating without being further reduced. In addition, since the difference between the MTF values between the line sensors can be reduced, the balance of the entire MTF value can be improved. For this reason, it is possible to solve problems such as coloring of black characters and black lines, erroneous determination of a black-and-white document as a color document, and change in color tone depending on magnification.
[0070]
In the above-described embodiment, the correction reference information is stored in the ROM 19 in advance, and when reading the original image, the correction reference information is read from the ROM 19, and the image obtained from the line sensor corresponding to the correction reference information is read. Although a case has been described where the image data by each line sensor is subjected to the inter-line correction processing based on the data, the present invention is not limited to this.
[0071]
For example, the image forming apparatus 100 may include a measuring unit that measures optical evaluation values of a plurality of image data obtained from a plurality of line sensors, and a line sensor that has the lowest optical evaluation point of the image data among a plurality of image data. Setting means for setting as a correction reference, reading a predetermined document image, measuring optical evaluation values of a plurality of obtained image data, and setting a line sensor having the lowest optical evaluation location of the image data as a correction reference Alternatively, the information may be stored in a ROM or a non-volatile memory as storage means.
[0072]
In this case, when the original image is read, as described above, the correction reference information is read from the storage unit, and the image data obtained by each line sensor is inter-lined based on the image data obtained from the line sensor corresponding to the correction reference information. Perform correction processing.
[0073]
Further, in the above-described embodiment, the image forming apparatus (copier) 100 having the image reading unit 10A has been described, but the present invention is not limited to this. The present invention can be applied to other image reading apparatuses, for example, a color scanner, and an image processing apparatus having a color scanner.
[0074]
【The invention's effect】
As described above, according to the image reading apparatus and the image processing method of the present invention, when an original is exposed and scanned to read the original image, the image sensor array having the lowest optical evaluation (MTF) value is corrected. A storage unit for storing as reference information; and a control unit for controlling input / output of a line-to-line correction unit for correcting a phase shift between image data. The control unit reads a correction reference from the storage unit when reading a document image. The information is read and set in the line-to-line correction means, and the image data from each image sensor row is subjected to line-to-line correction processing based on the image data obtained from the image sensor row having the lowest MTF value corresponding to this correction reference information. This is for performing line-to-line correction control.
[0075]
With this configuration, it is possible to prevent the MTF value of the image data of the image sensor row (for example, the line sensor) having the lowest MTF value from being further reduced due to the inter-line correction processing. In addition, since the difference in MTF values between the image sensor rows can be reduced, the balance of the entire MTF value can be improved. Therefore, it is possible to eliminate the problem that a black-and-white document is erroneously determined to be a color document.
[0076]
According to the image forming apparatus of the present invention, since the image reading apparatus of the present invention is applied, the MTF value of the image data of the image sensor array originally having the lowest MTF value is further corrected by performing the inter-line correction processing. The image quality can be prevented from deteriorating without being reduced. In addition, since the difference in MTF values between the image sensor rows can be reduced, the balance of the MTF values as a whole can be improved. For this reason, it is possible to solve such problems as coloring black characters and black lines, erroneously determining a black-and-white document as a color document, and changing the color tone depending on the magnification.
[0077]
The present invention is very suitable when applied to an image sensor including a plurality of line sensors, for example, a digital color copying machine using a three-line color CCD.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration example of an image reading apparatus 10 as an embodiment according to the present invention.
FIG. 2 is a diagram illustrating a configuration example of a color image sensor 1.
FIG. 3 is a block diagram illustrating a configuration example of an inter-line correction circuit 15;
FIG. 4 is a block diagram illustrating a configuration example of an interpolation calculator N;
FIG. 5 is an explanatory diagram of an example of an inter-line correction process.
FIG. 6 is a flowchart illustrating an operation example when reading a document image.
FIG. 7 is a diagram illustrating a configuration example of an image forming apparatus 100 according to an embodiment of the invention.
FIG. 8 is a flowchart illustrating an example of an image forming operation.
FIG. 9 is a diagram illustrating an image reading method using a unified image sensor.
[Explanation of symbols]
1 color image sensor (reading means)
2 Image processing unit
3 Image writing unit
4 Image generation unit
10 Image reading device
10A Image reading unit
11 Image data processing circuit
15 Line-to-line correction circuit (line-to-line correction means)
16 Timing control section
17 Line-to-line correction controller
18 CPU
19 ROM (storage means)
20 Image forming unit
M _R , M _G FIFO memory (integer correction unit)
N _R , N _G , N _B Interpolation operation circuit (decimal part correction unit)
SC control unit

Claims (11)

An apparatus for exposing and scanning an arbitrary original to read an original image,
Reading means having a plurality of image sensor rows arranged in a line along a predetermined pitch and one scanning direction of the document along the other scanning direction,
Storage means for storing, as correction reference information, an imaging element row having the lowest optical evaluation (MTF) value among a plurality of image data obtained from each imaging element row of the reading means;
Line-to-line correction means for correcting a phase shift between the image data due to a position shift due to an arrangement pitch between the image sensor rows,
Control means for controlling the input and output of the storage means and the inter-line correction means,
The control means,
When reading the original image,
The correction reference information is read out from the storage unit and set in the line-to-line correction unit, and the image data obtained by the plurality of image sensor rows is corrected for the line-to-line correction based on the image data obtained from the image sensor row corresponding to the correction reference information. An image reading apparatus, wherein the inter-line correction unit is controlled so as to perform processing. 2. The image reading apparatus according to claim 1, wherein the reading unit includes an image sensor array corresponding to three colors of red, green, and blue. The line-to-line correction unit includes:
An integer part correction unit that performs correction on a line-by-line basis;
3. The image reading apparatus according to claim 1, further comprising: a decimal part correction unit that performs correction of less than one line by an interpolation operation. The control means,
Controlling the line-to-line correction means to perform an interpolation operation on image data from another image sensor array using image data obtained from an image sensor array having the lowest optical evaluation value of the image data as a reference for the interpolation operation. The image reading device according to claim 3, wherein: Measuring means for measuring an optical evaluation value of a plurality of image data obtained from the plurality of image sensor rows,
5. The image processing apparatus according to claim 1, further comprising: a setting unit configured to set, as a correction reference, an imaging element row having the lowest optical evaluation value of the image data among the plurality of image data. 6. Image reading device. An apparatus for reading an original image and forming an image based on the obtained image data,
An image reading unit for exposing and scanning an arbitrary document to read a document image;
An image forming unit that forms an image based on image data obtained by the image reading unit,
The image reading unit,
Reading means having a plurality of image sensor rows arranged in a line along a predetermined pitch and one scanning direction of the document along the other scanning direction,
Storage means for storing, as correction reference information, an imaging element row having the lowest optical evaluation (MTF) value among a plurality of image data obtained from each imaging element row of the reading means;
Line-to-line correction means for correcting a phase shift between the image data due to a position shift due to an arrangement pitch between the image sensor rows,
Control means for controlling the input and output of the storage means and the inter-line correction means,
The control means,
When reading the original image,
The correction reference information is read out from the storage unit and set in the line-to-line correction unit, and the image data obtained by the plurality of image sensor rows is corrected for the line-to-line correction based on the image data obtained from the image sensor row corresponding to the correction reference information. An image forming apparatus, wherein the inter-line correction unit is controlled to perform processing. The image forming apparatus according to claim 6, wherein the reading unit includes an image sensor array corresponding to three colors of red, green, and blue. The line-to-line correction unit includes:
An integer part correction unit that performs correction on a line-by-line basis;
8. The image forming apparatus according to claim 6, further comprising: a decimal part correction unit that performs correction of less than one line by an interpolation operation. The control means,
Controlling the line-to-line correction means to perform an interpolation operation on image data from another image sensor array using image data obtained from an image sensor array having the lowest optical evaluation value of the image data as a reference for the interpolation operation. The image forming apparatus according to claim 8, wherein: Measuring means for measuring an optical evaluation value of a plurality of image data obtained from the plurality of image sensor rows,
10. The image processing apparatus according to claim 6, further comprising: a setting unit configured to set, as a correction reference, an image sensor row having the lowest optical evaluation value of the image data among the plurality of image data. Image forming device. In a method of processing a plurality of image data obtained by a plurality of imaging element rows arranged in a line along a predetermined pitch and one scanning direction of the original along the other scanning direction,
Read a predetermined document image,
Measuring an optical evaluation (MTF) value of a plurality of image data obtained from the plurality of image sensor rows;
An image sensor array having the lowest optical evaluation value among the plurality of image data is set as correction reference information,
Store the set correction reference information,
When reading the original image, read the correction reference information,
An image processing method, comprising: performing image-to-line correction processing on image data from the plurality of image sensor rows based on image data obtained from an image sensor row corresponding to the read correction reference information.

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