JP4254082B2 - Image processing device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image processing apparatus that performs image processing on an image read by a document conveyance type image reading device such as an automatic document conveyance device (ADF) in an image forming apparatus such as a copying machine or a facsimile.
[0002]
[Prior art]
In general, as shown in FIG. 10, the document conveyance type image reading apparatus is provided with a pair of rollers 102 </ b> A and 102 </ b> B disposed on the upstream side of the document reading unit 101 such as slit glass and the downstream side of the document reading unit 101. The two pairs of rollers 102A and 102B and 103A and 103B convert the image information on the original M into a photoelectric conversion element such as a CCD line sensor. Is supposed to be read by.
[0003]
By the way, when the front end of the document M enters the downstream roller pair 103A, 103B while the document M is being conveyed, and further when the rear end of the document M is separated from the upstream roller pair 102A, 102B, A load fluctuation is applied to a document conveyance drive motor (not shown). For this reason, there is a problem that unevenness in the document feeding accuracy is caused, leading to uneven reading in the reading unit 101, and the image quality is deteriorated in this portion.
[0004]
In order to solve this problem, Japanese Patent Application Laid-Open No. 9-235039 discloses a technique for correcting the load fluctuation by controlling the voltage or current value of the motor against the load fluctuation of the motor. ing.
[0005]
[Problems to be solved by the invention]
However, with the above conventional technology, it is difficult to adjust the timing of the motor voltage or current control, and since the control timing actually differs depending on the thickness of the document, the apparatus becomes complicated in order to perform stable operation. There were drawbacks. In addition, depending on the voltage or current control of the motor, it has been difficult to prevent uneven reading due to vibration in the thickness direction (vertical direction) of the document M during conveyance as described below.
[0006]
That is, the document M is being conveyed simultaneously by the upstream roller pair 102A, 102B and the downstream roller pair 103A, 103B, and the document M is being conveyed only by the upstream roller pair 102A, 102B. In addition, the tension applied to the document M differs from the state in which the document M is conveyed only by the roller pair 103A, 103B on the downstream side. For this reason, the front end of the original M enters the downstream roller pair 103A, 103B, or the rear end of the original M separates from the upstream roller pair 102A, 102B, and the tension applied to the original M is cut off. When the document is replaced, the document M vibrates so as to be violated in the thickness direction, and an impact is generated. However, in the conventional technique described above, it is insufficient to cope with reading unevenness due to such vibration.
[0007]
Generally, a line sensor in which linear R (red), G (green), and B (blue) chips extending in the main scanning direction are arranged at predetermined intervals in the sub-scanning direction is used for reading a color image. In such a case, a time lag in the reading timing of each chip is corrected by the distance between the chips. For this reason, for example, when a black ladder pattern is read, the corrected read waveforms of R, G, and B are overlapped in a state where reading unevenness does not occur.
[0008]
However, for example, when the reading unevenness occurs after the reading by the R and G chips and before the reading by the B chip, as shown in FIG. When an image is printed on paper without overlapping with the signal waveform, color misregistration occurs in the edge portion Pa of the ladder pattern P as shown in FIG. That is, the image quality is lowered corresponding to the portion where the reading unevenness occurs.
[0009]
The present invention has been made to solve the above-described conventional problems, and an original enters or leaves a pair of rollers disposed at upstream and downstream positions of an original reading unit in an original conveying type image reading apparatus. It is an object of the present invention to provide an image processing apparatus capable of suppressing deterioration in image quality against reading unevenness that occurs when reading.
[0010]
[Means for Solving the Problems]
  An object of the present invention is to provide an image processing apparatus for performing image processing on an image read by conveying a document using a pair of rollers respectively disposed upstream and downstream of a document reading unit. Means for identifying the occurrence site of uneven reading that occurs when entering or leaving the roller pair, and the occurrence of the specified uneven readingParts and otherWith partsγ curve in γ correction processingAnd an image processing means for performing image processing of a read image by changing the above.
[0011]
  In this image processing apparatus, even when reading unevenness occurs when a document enters or leaves the pair of rollers on the upstream side and downstream side of the reading unit, the part is specified, and the specified reading unevenness generation part And other parts,γ curve in γ correction processingThe image processing of the read image is executed with the change. For this reason,It is possible to make the image reading unevenness portion a soft and inconspicuous image.
[0013]
  An object of the present invention is to provide an image processing apparatus for performing image processing on an image read by conveying a document using a pair of rollers respectively disposed upstream and downstream of a document reading unit. Means for identifying the occurrence portion of the reading unevenness that occurs when entering or detaching from the roller pair, and changing the edge processing condition between the specified occurrence portion of the uneven reading and the other portion, An image processing apparatus characterized by comprising image processing means for performing processing is also solved.The image processing means performs image processing by changing edge processing conditions between the uneven reading portion and other portions.FromThe edge portion can be made inconspicuous due to a decrease in the toner adhesion amount at the edge portion in the portion where the image reading unevenness occurs.
[0015]
Further, the reading unevenness generation site may be specified based on detection signals from sensors that detect both ends of the document in the front-rear direction. In this case, it is possible to specify the reading unevenness portion with a relatively simple configuration.
[0016]
Further, the reading unevenness generation site may be specified based on a detection signal from a sensor that detects vibration when the document passes through the reading unit. In this case, the vibration of the document in the reading unit is directly detected, and it becomes easy to specify the portion where the reading unevenness occurs.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[0018]
FIG. 1 is a schematic sectional view showing an electrophotographic color copying machine equipped with an image processing apparatus according to an embodiment of the present invention.
[0019]
In FIG. 1, the color copying machine includes an image forming unit 1, an automatic document feeder (hereinafter referred to as ADF) 2, and a document conveyance type image reading device 3 including the ADF 2.
[0020]
First, the configuration of the image forming unit 1 is a general one, and a brief description will be given while also serving as an operation.
[0021]
When the ADF 2 is used, the first slider 117 having the exposure lamp 111 and the reflecting mirror 112 is driven by a scanner motor 116 to read an image on the one end side of the original table glass 100 in the sub-scanning direction. It moves to near the vicinity of the slit glass 110 and stops.
[0022]
The light from the exposure lamp 111 is applied to the image of the original M at a timing when the original M automatically fed one by one from the ADF 2 passes over the slit glass 110, and the reflected light from the original image is reflected by the reflection mirrors 112, 113, 114 is reflected toward the lens 115 side. The reflected light that has passed through the lens 115 is received by the CCD line sensor 10 that is an image sensor and converted into an electrical signal.
[0023]
When the ADF 2 is not used, by driving the scanner motor 116, the first slider 117 is at a speed V and the second slider 118 is V / 2 in a direction perpendicular to the electrical scanning direction of the CCD line sensor 10. To move the entire original.
[0024]
Image data received by the CCD line sensor 10 and converted into an electrical signal is sent to the signal processing unit 200. The signal processing unit 200 electrically processes the read image data and decomposes it into magenta (M), cyan (C), yellow (Y), and black (Bk) components, which will be described later in the signal processing unit 200. The print controller 5 that drives and modulates the semiconductor laser 214 in accordance with the image signal level. The laser beam scans on the photosensitive drum 206 via the polygon mirror 215, the f-θ lens 216, and the folding mirrors 217a and 217b.
[0025]
The developing unit includes C, M, Y, and Bk developing devices 208 a, 208 b, 208 c, and 208 d, and the developing devices 208 a, 208 b, 208 c, and 208 d are formed on the photosensitive drum 206. Develop the image with toner.
[0026]
On the other hand, the sheet fed by the sheet feeding units 201a, 201b, and 201c is conveyed to the transfer position of the transfer drum 202 by the timing roller 203, wound around the transfer drum 202 by the suction charger 204, and the photosensitive drum by the transfer charger 205. The image developed on 206 is transferred to a sheet. A suction push-up plate and a transfer push-up plate (not shown) are arranged on the sides of the suction charger 204 and the transfer charger 205.
[0027]
After the four colors C, M, Y, and Bk are sequentially transferred in this way, the sheet is separated from the transfer drum 202 by the separation chargers 209a and 209b and the push-up member 220, passes through the fixing rollers 210a and 210b, and is discharged. The paper is discharged to the paper tray 211. Reference numeral 233 denotes a cleaning device for cleaning the transfer drum 202, and reference numerals 242a and 242b denote neutralization chargers.
[0028]
Next, the configuration of the ADF 2 will be described with reference to FIG.
[0029]
In FIG. 2, a feed roller 153 and a separation roller 154, an intermediate roller (conveying roller) 155, a registration sensor 156, and the slit glass 110 are provided between the paper feed roller 152 at the downstream end of the paper feed tray 151 and the paper discharge tray 161. A pair of registration rollers 157 and 157 on the upstream side, a scooping guide body 158 on the downstream side of the slit glass 110, a pair of conveying rollers 159 and 159 on the downstream side of the scooping guide body 158, and a paper discharge roller 160, etc. They are arranged in order.
[0030]
A reversing roller 162 that guides the document M to the reversing path R1 and a reversing roller 163 that guides the document M to the re-reversing path R2 are provided above the downstream side conveyance roller 159 at the time of duplex copying.
[0031]
In the ADF 2, the original M is placed on the paper feed tray 151 with the image surface facing up. When a start key on an operation panel (not shown) is pressed, the document M is pushed up in conjunction with the rotation of a lever (not shown), and the uppermost document M is brought into contact with the pickup roller 152.
[0032]
A torque limiter is added to the separation roller 154, and when the document M fed by the pickup roller 152 is fed along, it is separated by the nip between the feed roller 153 and the separation roller 154, and 1 of the uppermost document M. Only the sheet is carried out.
[0033]
The fed document M is conveyed by an intermediate roller 155 or the like, and the front end of the document M is abutted against the nip between a pair of stopped registration rollers 157 and 157, so that a slight amount of loop is created. After the conveyance is temporarily stopped, the conveyance of the original M is resumed. As a result, the front edge registration and skew correction of the document M are performed.
[0034]
The original M whose conveyance has been resumed passes over the slit glass 110, advances between the downstream conveyance rollers 159 and 159 by the scooping guide body 158, and is discharged onto the paper discharge tray 161 via the paper discharge roller 160. Is done.
[0035]
When the double-sided copy mode of the original M is selected, a first switching claw (not shown) is changed, and the original M that has passed through the slit glass 110 passes through the downstream conveying rollers 159 and 159, and then the first reverse roller. After being reversed by 162 and 162, it is guided again to the pair of registration rollers 157 and 157 on the upstream side.
[0036]
Thereafter, the document M similarly passes over the slit glass 110 and is reversed by the second pair of reversing rollers 163 and 163 due to the change of the second switching claw (not shown) and then on the sheet discharge tray 161. To be discharged.
[0037]
FIG. 3 is a block diagram showing an electrical configuration of a main part of the color copying machine shown in FIG.
[0038]
In FIG. 3, 10 is the above-described CCD line sensor, 20 is an A / D converter, 4 is an image processing device, 5 is a print controller, 214 is a semiconductor laser, 156 is a registration sensor, and A / D converter 20 The signal processing unit 200 is configured by the image processing device 4 and the print control unit 5.
[0039]
As shown in FIG. 4, the CCD line sensor 10 is arranged with a predetermined interval d in the sub-scanning direction, and CCD chips 10r, 10g, 10g, respectively corresponding to R, G, and B3 colors that are long in the main scanning direction. 10b, and has a color separation filter (not shown) corresponding to each color.
[0040]
When the original M is read by the CCD line sensor 10 through the reading unit 110, a time lag of the read signal waveform occurs due to the positional relationship between the R, G, B CCD chips 10r, 10g, 10b. This deviation is corrected based on the distance difference d between the CCD chips 10r, 10g, and 10b. Although this correction is also performed by the image processing apparatus 4, since this correction is a conventionally known technique, a detailed description thereof is omitted.
[0041]
The A / D converter 20 converts analog image data read by the CCD line sensor 10 into digital image data.
[0042]
The image processing apparatus 4 includes an input image memory 30, an image processing unit 40, an output image memory 50, and a reading unevenness occurrence site specifying unit 60.
[0043]
The input image memory 30 stores the A / D converted digital image signal for each of R, G, and B colors.
[0044]
The image processing unit 40 performs image processing on the read image data, and includes a gamma (γ) correction processing unit 41, an edge processing unit 42, and a black discrimination processing unit 43.
[0045]
The γ correction processing unit 41 performs processing for converting the density of the input image and the density of the output image in accordance with a predetermined γ curve for image reproduction. The edge processing unit 42 detects the edge portion of the image and performs edge enhancement processing, and the black discrimination processing unit 43 discriminates whether or not the image is black. These γ correction processing, edge processing, and black discrimination processing are executed by changing the processing conditions for the uneven reading portion and other portions.
[0046]
The output image memory 50 temporarily stores image data that has been subjected to predetermined image processing by the image processing unit 40.
[0047]
The reading unevenness generation part specifying unit 60 specifies a reading unevenness generation part based on a signal from the registration sensor 156. The reading unevenness generation site specifying unit 60 includes a storage unit (not shown), and stores the specified reading unevenness generation site in the storage unit.
[0048]
The print controller 5 drives and modulates the semiconductor laser 214 in accordance with the C, M, Y, and Bk image signal levels.
[0049]
Next, the operation of the color copying machine having the above-described configuration will be described focusing on document reading and image processing.
[0050]
When the ADF 2 is used and the front end of the conveyed document M passes the registration sensor 156, the sensor 156 is turned on. The document M that has passed the sensor 156 is conveyed by receiving the conveying force of the registration rollers 157 and 157 after its front end has entered the upstream registration rollers 157 and 157. Further, the front end portion of the document M passes through the reading position on the slit glass 110 and then enters the downstream transport rollers 159 and 159, and the upstream registration rollers 157 and 157 and the downstream transport rollers 159 and 159. It is transported by receiving the transport force.
[0051]
Thereafter, the trailing edge of the document M passes through the registration sensor 156 and the sensor is turned off. Then, the trailing edge of the document M is separated from the upstream registration rollers 157 and 157, and the document M is transported downstream. 159 and 159 are transported by receiving the transport force. Then, after the trailing edge of the document M has passed through the reading position on the slit glass 110, the document M is also detached from the conveying rollers 159 and 159 on the downstream side.
[0052]
During this time, as the original M passes through the reading position on the slit glass 110 between the upstream registration rollers 157 and 157 and the downstream conveying rollers 159 and 159, the reflected light of the original image is reflected on the CCD line. Light is received by the sensor 10.
[0053]
An analog image signal corresponding to the original image is output from the CCD line sensor 10, and the analog image signal is converted into a digital image signal by the A / D converter 20 and then stored in the input image memory 30 as image data.
[0054]
Here, when the front end of the document M enters the downstream conveyance rollers 159 and 159 or when the rear end of the document M leaves the upstream registration rollers 157 and 157, the registration roller 157 and the conveyance roller 159. As a result, load fluctuations occur in the drive system, and uneven reading occurs. In addition, when the front end of the document M enters the downstream-side transport rollers 159 and 159 and when the registration rollers 157 and 157 are separated, the registration roller 157 and the transport roller 159 apply transport force to the document M. Since the tension applied to the original varies depending on the state, the original M at the reading position vibrates in the vertical direction, which also causes uneven reading.
[0055]
The occurrence site of the reading unevenness depends on the positions where the upstream registration rollers 157 and 157 and the downstream transport rollers 159 and 159 are disposed. Therefore, the reading unevenness occurrence site specifying unit 60 includes the sensor 156. Based on the document detection signal (ON / OFF edge signal), the region where the reading unevenness occurs is specified for the image data stored in the input image image memory 30.
[0056]
That is, as shown in FIG. 5, the distance between the center reading position of the slit glass 110 and the downstream transport rollers 159 and 159 is Da, and the distance between the upstream registration rollers 157 and 157 and the center reading position of the slit glass 110 is Assuming that the document transport distance between them is Db, for example, a position with a distance Da from the front end of the original M of the ladder pattern as shown in FIG. It becomes a part. In addition, since the distance between the registration sensor 156 and the central reading position of the slit glass 110 is also fixed, the position of the read image data corresponding to the front edge of the document M can also be grasped.
[0057]
In this embodiment, as shown in FIG. 6, the nonuniformity occurrence portion specifying unit 60 has a predetermined width including the front and back regions of the position Da from the front end of the document M and the position Db from the rear end of the document M. The region Px is identified as a nonuniformity generation site.
[0058]
FIG. 7 is a flowchart showing an image processing procedure in the color copying machine.
[0059]
In the following description and drawings, step is abbreviated as S.
[0060]
In FIG. 7, in S <b> 201, the top address of the document page stored in the input image memory 30 is acquired based on the ON edge signal from the registration sensor 156 at the time of reading the document image. In S202, the final address of the document page stored in the input image memory 30 is acquired based on the OFF edge signal from the registration sensor 156 when the document image is read.
[0061]
In S203, the address of the area (Px in FIG. 6) of the read original image in which the image processing is changed is specified. In S204, the image processing condition for the area is changed, and the γ correction processing section in the image processing section 40 is changed. 41, image processing by the edge processing unit 42 and the black discrimination processing unit 43 is performed.
[0062]
Note that these image processes do not have to be performed all, and any one or two of them may be performed.
[0063]
First, γ correction processing by the γ correction processing unit 41 will be described. For the uneven reading portion Px in the original image, a gently changing curve γB for the photo mode shown in FIG. For the part, correction processing is performed by applying a steeply changing curve γA for the text mode. The curve γB for the photo mode is used to blur the boundary with an emphasis on gradation as a whole, and the image γA for the text mode can obtain an image with clear contrast.
[0064]
As described above, by using the two types of γ curves, only the region Px in which character shakiness occurs due to uneven reading becomes a soft blurred image after printing and becomes inconspicuous.
[0065]
In the edge processing by the edge processing unit 42, edge enhancement processing is performed on a region where there is no uneven reading, and a sharp image is obtained. On the other hand, for the nonuniformity occurrence region Px, the edge emphasis process is not performed, or conversely, the process of reducing the toner adhesion amount of the edge is performed. As a result, the image in the reading unevenness generation region Px becomes a soft image with a blurred edge as compared with the images in other regions, and becomes inconspicuous.
[0066]
Further, the black discrimination processing by the black discrimination processing unit 43 will be described. In the black discrimination processing, as shown in FIG. 9, the gradation of C, M, and Y data obtained by color-converting R, G, and B data. If the difference T between the largest value (for example, M) and the smallest value (for example, C) is smaller than a predetermined threshold value, it is determined as “black”.
[0067]
In the example shown in FIG. 11 described above, when a black ladder pattern is read, if “blue” color misregistration occurs in the edge portion due to vibration during reading of the original image, the “blue” edge portion is directly “ Since it is determined not to be “black”, the developing devices 208a to 208d are faithfully developed to “blue” using C, M, and Y.
[0068]
In order to prevent this, the black discrimination standard at the time of reading is set gently to make it easy to discriminate “black”. For this purpose, the threshold value for black discrimination is changed. For example, threshold values 30 (level A) and 50 (level B) are prepared, and level B is applied to the read unevenness generation region Px, so that the case where the threshold value is 50 or less is set to “black”. Determine. For other areas, level A is applied to determine that the threshold value is 30 or less as “black”.
[0069]
By changing the black discrimination threshold in this way, for example, in reading a black ladder pattern, even if there is a color shift that causes the edge portion to be “blue” due to vibration during reading, the black discrimination criteria are loose. Therefore, the edge portion of “blue” is also determined as “black”, and the image in which the color shift is corrected is obtained.
[0070]
The image data subjected to the image processing as described above is stored in the output image memory 50 and then sent to the print control unit 5 to form an image.
[0071]
In the above embodiment, the portion where the reading unevenness of the document M is generated is specified based on the ON / OFF signal of the registration sensor 156. However, for example, vibration of the document M is generated in the vicinity of the document reading unit 110. A vibration sensor 170 (shown in FIG. 2) for detection may be provided, and the occurrence site of uneven reading may be specified from the vibration detection result. As an example of the vibration sensor 170, a sensor that monitors the distance to the document M and detects a vibration detection signal when the distance to the document M becomes smaller than a predetermined value can be exemplified.
[0072]
Further, without providing the registration sensor 156 and the vibration sensor 170, the size information of the document M given in advance by the operation panel may be used.
[0073]
【The invention's effect】
  According to the first aspect of the present invention, even when reading unevenness occurs when the original enters or leaves the pair of rollers on the upstream side and the downstream side of the reading unit, the portion is specified and specified. In the reading unevenness generation site and other sites,Since the image processing is performed by changing the γ curve in the γ correction processing, it is possible to make the image reading unevenness portion a soft and inconspicuous image.
[0075]
  Claim 2According to the invention described inIn the area where uneven reading occurs and other partsChange edge processing conditionsTo process the scanned imageTherefore, the edge portion can be made inconspicuous due to a decrease in the toner adhesion amount at the edge portion at the portion where the image reading unevenness occurs.
[0077]
  Claim 3According to the invention described in the above, since the occurrence site of the reading unevenness is specified based on the detection signals from the sensors that detect both ends of the document in the front-rear direction, the reading unevenness occurrence site can be determined with a relatively simple configuration. Identification becomes possible.
[0078]
  Claim 4According to the invention described in the above, since the portion where the reading unevenness is generated is specified based on the detection signal from the vibration sensor that detects the vibration when the document passes through the reading unit, the vibration of the document in the reading unit is directly detected. It is detected and it becomes easy to specify the occurrence site of the reading unevenness.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing an electrophotographic color copying machine provided with a document conveying type image reading apparatus according to an embodiment of the present invention.
FIG. 2 is a schematic sectional view showing an automatic document feeder in the same color copying machine.
FIG. 3 is a block diagram showing the electrical configuration of the main part of the color copying machine.
FIG. 4 is an enlarged plan view showing a CCD line sensor.
FIG. 5 is an explanatory diagram of a positional relationship between a document image reading position and an upstream roller and a downstream roller.
FIG. 6 is an explanatory diagram of a portion where pitch unevenness occurs in a document when reading the document.
FIG. 7 is a flowchart showing an image processing operation.
FIG. 8 is a characteristic diagram showing a γ curve used in processing by a γ correction processing unit.
FIG. 9 is an explanatory diagram of threshold values in black discrimination processing.
FIG. 10 is a configuration diagram of a main part of a document conveying type image reading apparatus for explaining a problem of the present invention.
FIG. 11 is a diagram for explaining color misregistration when a ladder pattern is read.
[Explanation of symbols]
4 ... Image processing device
40 ... Image processing unit
41... Γ correction processing section
42 ... Edge processing section
43 ... Black discrimination processing section
60... Uneven reading location specifying part
110 ... Reading section (slit glass)
156 ... ・ Regist sensor
157, 159 ... Roller pair
170 .... Vibration detection sensor
M ... Manuscript

Claims (4)

In an image processing apparatus that performs image processing on an image read by conveying a document using a pair of rollers respectively disposed upstream and downstream of a document reading unit,
Means for identifying a portion where uneven reading occurs when a document enters or leaves the roller pair;
Image processing means for performing image processing of a read image by changing the γ curve in the γ correction processing between the identified reading unevenness occurrence portion and another portion;
An image processing apparatus comprising: In an image processing apparatus that performs image processing on an image read by conveying a document using a pair of rollers respectively disposed upstream and downstream of a document reading unit,
Means for identifying a portion where uneven reading occurs when a document enters or leaves the roller pair;
Image processing means for performing image processing of a read image by changing edge processing conditions between the specified reading unevenness occurrence portion and another portion;
An image processing apparatus comprising: 3. The image processing apparatus according to claim 1, wherein the occurrence portion of the reading unevenness is specified based on a detection signal from a sensor that detects both ends of the document in the front-rear direction. 3. The image processing apparatus according to claim 1, wherein the occurrence portion of the reading unevenness is specified based on a detection signal from a sensor that detects vibration when the document passes through the reading unit.

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