JP2009065417A - Image reader and image forming apparatus with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image reader and an image forming apparatus, capable of preventing the generation of lines while automatically adjusting density of pixels causing generation of lines due to dust, etc., by simple configuration. <P>SOLUTION: The image reader has: an original conveyance part; an image reading part which starts reading by starting of conveyance of an original; a conversion part which converts an output signal of the image reading part into a digital signal; a first memory which stores density data of pixels for one line, and is sequentially updated in accordance with the reading; a second memory which stores the read density data of the pixels for one initial line; and a comparison operation part 9 which compares between pieces of the density data of the first memory and the second memory per line, wherein the comparison operation part 9 outputs the density data of the pixels of the first memory for the pixels as the reading results of the original when the density of the first memory is higher than that of the second memory more than a threshold, and outputs density data of white to the pixels as the reading results of the original when the density of the first memory is not higher than that of the second memory more than the threshold. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image reading apparatus for reading a document such as a scanner. The present invention also relates to an image forming apparatus provided with the image reading apparatus.

  2. Description of the Related Art Conventionally, an image reading apparatus provided in a scanner, a copying machine, or the like automatically sends out (conveys) an original, irradiates light on the original that passes through the reading position, and performs CCD (Charge Coupled Device) or CIS Some image sensors such as (Contact Image Sensor) convert the reflected light into an electrical signal and optically read the image of the document. The reading position is generally provided with glass at the bottom (further, a light source, an image sensor, etc. are provided below the glass), and a white plate is provided above it, and the document passes between the glass and the white plate. .

  However, when a document is transported and scanned, if there is dust, dust, dirt, scratches, etc. at the scanning position, the image sensor scans the dust, and the direction parallel to the document transport direction (sub-scanning direction) ), Streaks appear in the read image data. For example, in a monochrome image, it appears as a black streak. This streak is not present in the document and reduces the quality of image reading.

An invention for preventing the occurrence of such streaks due to dust or the like is described in Patent Document 1. Patent Document 1 includes a document conveying unit that conveys a document, a reading unit that optically reads an image of a moving document on a reading glass, and a control unit that controls operations of the document conveying unit and the reading unit. The control unit has a function of moving the reading position when the reading unit reads an image of the document in the sub-scanning direction. If it is determined that there is streak noise, the scanning position is moved, the image is read by the reading means, and the presence / absence determination of streak noise using the image data is executed again. An image reading apparatus that sets the current reading position to the reading position to be applied in the moving document reading mode when it is determined is described. With this configuration, a position free from dirt and scratches is automatically detected on the reading glass of the image reading apparatus, and an excellent reading result without streak noise can be obtained without troublesome operations (Patent Literature). 1, see claim 1, paragraph 0058, FIG.
JP2004-179818

  Here, referring to Patent Document 1, control is performed to determine the presence or absence of streak-like noise and move the reading position. However, in order to determine the reading position, the document must be read a plurality of times. As a result, there is a problem that it involves a troublesome operation. In addition, in order to determine the reading position, the control means also performs complex control such as confirmation of the occurrence position of streak noise and confirmation of the position without noise, so the processing amount is large and there is no streak noise easily. There is a problem that the reading result cannot be obtained and the cost of the image reading apparatus may be increased.

  Further, when there are a large number of dusts, scratches, etc., or when the contact glass is dirty in the document transport direction, the reading position cannot be determined. In addition, even if the position where the number of dust or the like is the minimum is set as the reading position, streak noise is generated. Therefore, the invention described in Patent Document 1 has a problem that streaky noise may occur. In addition, when dust or the like does not move due to the conveyance of the document, the invention described in Patent Document 1 has a problem that it is necessary to set again.

  The present invention has been made in view of the above-described problems of the prior art, and with a relatively simple configuration, automatically adjusts the density of pixels that cause streaks due to dust and the like to generate streaks. It is an object of the present invention to provide an image reading apparatus capable of preventing the above and an image forming apparatus including the image reading apparatus.

  In order to achieve the above object, an image reading apparatus according to claim 1 irradiates a document conveying unit that conveys a document to be read and a document that passes through a reading position, photoelectrically converts the reflected light, An image reading unit that starts reading when a document starts to be transported, a conversion unit that converts an analog signal output as a reading result by the image reading unit into a digital signal as density data of each pixel, and the image reading unit A first memory that stores density data of pixels for one line and is sequentially updated as it is read; a density data of pixels for the first line read by the image reading unit; and the first memory A second memory capable of holding density data for comparison with each other, and a comparison operation unit that compares the density data for one line stored in the first memory and the second memory for each pixel. If the density of the pixel of the first memory is lower as a result of the comparison calculation of each pixel by the comparison calculation unit, the density data of the pixel of the second memory If the density of the first memory is higher than the second memory by a threshold value or more than the second memory as a result of the comparison calculation of each pixel, the comparison calculation unit updates the density of the pixel of the first memory. When the density of the first memory is not higher than the threshold value than the second memory, white density data is output to the pixel as a document reading result.

  According to this configuration, when dust, dust, dirt, scratches, etc. (hereinafter referred to as “dust”) are read, the density of the pixel usually increases. The second memory holds density data for one line indicating the position of the dust, etc., and the comparison operation unit compares each pixel of the first and second memory lines. White density data is output to the partial pixels. Therefore, since the dark stripe (for example, black) portion has the same density in both the first memory and the second memory, the stripe portion is replaced with white data, and the dark stripe can be erased. In this case, white streaks may occur in the read image data, but white streaks are less noticeable than black streaks and are confused. Therefore, the quality of the image data is not degraded.

  Further, as a result of the comparison of the density data of the line of the comparison operation unit, when the density of the pixel of the second memory is higher, the second memory stores the density data of the pixel of the first memory, and the line of the second memory Since the density data is kept in a lower density state, even if dust or the like moves as the document is transported, even if dark streaks are not generated, it is immediately reflected in the second memory. It is possible to prevent the density data in the first memory from being replaced with white. Furthermore, the configuration necessary for removing dark stripes is a simple configuration consisting of only two memories and an element that performs only a comparison operation, and since the processing can be performed automatically, it is a burden on the user. Nor.

  According to a second aspect of the present invention, in the image reading apparatus according to the first aspect, the second memory is reset every time reading of one original is completed.

  According to this configuration, the content of the second memory is refreshed every predetermined time (every time when one original is read), so the second memory reflects the latest state of attachment of dust or the like at the reading position. can do.

  According to a third aspect of the present invention, in the image reading apparatus according to the first or second aspect, the second memory is the first one read by the image reading unit at the time of starting the original reading and / or after being reset. The pixel density data for the line is not stored, and all the pixels for one line are set to the highest density.

  According to this configuration, all the pixels in the second memory line are first set to the darkest state, and the second memory is updated to a state in which the density is low according to the comparison result with the first memory by the comparison calculation unit. Even if it goes, dark streaks can be erased.

  According to a fourth aspect of the present invention, an image forming apparatus includes the image reading apparatus according to any one of the first to third aspects.

  According to this configuration, it is possible to provide an image forming apparatus that does not generate dark streaks even when image formation is performed on a read document.

  As described above, according to the present invention, with a relatively simple configuration, the pixel of the portion causing the streak due to dust or the like is automatically replaced with white density data, and the dark stripe is replaced with the white stripe. Thus, the generation of streaks can be made inconspicuous.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. However, each element such as configuration and arrangement described in this embodiment does not limit the scope of the invention and is merely an illustrative example.

  First, an outline of an electrophotographic copying machine 2 (corresponding to an image forming apparatus) provided with a scanner 1 (corresponding to an image reading apparatus) according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic cross-sectional view seen from the front showing a schematic configuration of a copying machine 2 according to an embodiment of the present invention.

  As shown in FIG. 1, the copying machine 2 according to the present embodiment has a main body 3 having a box shape, and a scanner 1 is disposed above the main body 3. The scanner 1 has an automatic document feeder 4 (corresponding to a document conveying unit) disposed above and an image reading unit 5 (corresponding to an image reading unit) disposed below. A detailed description of the scanner 1 will be described later with reference to FIG.

  Next, the internal configuration and operation of the main body 3 will be described. The main body unit 3 includes a sheet supply unit 21, a sheet conveyance path 25, an image forming unit 30, a fixing device 37, and the like, and a paper discharge space is provided at a position above the center of the main body unit 3. Accordingly, these configurations will be described along the sheet conveyance path. In FIG. 1, the sheet conveyance path in the main body 3 is shown by solid arrows.

  First, the sheet supply unit 21 is provided at the lowermost part of the main body unit 3, and sends out a sheet such as a copy sheet, an OHP sheet, a label sheet, or a thick sheet toward the image forming unit 30. The sheet supply unit 21 includes a sheet feeding cassette 22, a sheet placing plate 23, a sheet feeding roller 24, and the like. The sheet feeding cassette 22 stacks a plurality of sheets, has a box shape and an open top surface, and is detachable by being pulled out from the main body unit 3. A sheet mounting on which a plurality of sheets are placed in the sheet feeding cassette 22. A mounting plate 23 is provided.

  A paper feed roller 24 is provided on the upper part of the paper feed cassette 22 on the downstream side in the sheet conveyance direction (upper left position in FIG. 1). The sheet placing plate 23 always brings the uppermost sheet into contact with the sheet feeding roller 24 by a lift mechanism (not shown) using a spring or the like, and when the sheet is fed, the sheet feeding roller 24 has a predetermined direction (see FIG. 1 in the clockwise direction), and feeds the sheets one by one to the sheet conveyance path 25.

  In the present embodiment, the sheet conveying path 25 is formed so as to penetrate the main body 3 in the vertical direction. The sheet conveying path 25 conveys the sheet in the copying machine 2, and from the sheet supply unit 21 to the image forming unit 30 and the fixing device 37. After that, the sheet is conveyed to the discharge unit 26. The sheet conveyance path 25 is provided with a conveyance roller pair 27 that is rotationally driven by a drive mechanism (not shown), a plurality of guide plates for guiding the sheet, a registration roller pair 28, and the like. The registration roller pair 28 is provided in front of the image forming unit 30 on the upstream side in the sheet conveyance direction. The registration roller pair 28 temporarily stops the conveyed sheet and directs the sheet toward the image forming unit 30 at a predetermined timing and speed for transfer. Send it out.

  In FIG. 1, the image forming unit 30 is disposed at the center left position of the main body unit 3, and based on the original read by the scanner 1, the image data input to the copying machine 2, etc., the toner of the image to be formed An image is formed and transferred to a sheet. The image forming unit 30 includes a photosensitive drum 31 as an image carrier, a charging device 32, an exposure device 33, a developing device 34, a transfer roller 35, a cleaning device 36, and the like.

  The photoconductive drum 31 is disposed substantially at the center of the image forming unit 30 and is rotationally driven in a predetermined direction (clockwise in FIG. 1) by a driving device (not shown), for example, on the outer peripheral surface of an aluminum drum. Are configured to have a photosensitive layer of OPC or amorphous silicon.

  The charging device 32 is disposed to face the upper right of the photosensitive drum 31 in FIG. 1, and charges the peripheral surface of the photosensitive drum 31 with a predetermined potential. In this embodiment, a corona charger is used for the charging device 32, but it is sufficient that the surface of the photosensitive drum 31 can be charged to a predetermined potential, and a charging roller or a brush may be used.

  The exposure device 33 is disposed on the right side of the photosensitive drum 31 and the charging device 32 in FIG. 1, and emits light on the circumferential surface of the uniformly charged photosensitive drum 31 based on image data of an image to be formed. The photosensitive drum 31 is irradiated and the peripheral surface of the photosensitive drum 31 is scanned and exposed. Thereby, an electrostatic latent image is formed on the peripheral surface of the photosensitive drum 31.

  The developing device 34 is provided below the photosensitive drum 31 in FIG. 1, accommodates toner, charges the toner to a predetermined potential, and statically forms the toner on the peripheral surface of the photosensitive drum 31. Supply toward the electrostatic latent image. Specifically, the developing device 34 is provided with a developing roller 34 a that carries toner on the peripheral surface thereof, and the toner is supplied from the developing roller 34 a to the photosensitive drum 31.

  In FIG. 1, the transfer roller 35 is rotatably supported diagonally to the left of the photosensitive drum 31, and transfers the toner image formed on the photosensitive drum 31 to a sheet. For this reason, the transfer roller 35 contacts the photosensitive drum 31 to form a nip. Then, the sheet enters the nip, and a voltage having a polarity opposite to the charging polarity of the photosensitive drum 31 and the toner is applied to the transfer roller 35 to transfer the toner image onto the sheet. In FIG. 1, the cleaning device 36 is disposed above the photosensitive drum 31 and removes and collects residual toner, dust, and the like on the peripheral surface of the photosensitive drum 31.

  In the present embodiment, the fixing device 37 includes a heating roller 38, a pressure roller 39, and the like, and pressurizes and heats the toner image transferred to the sheet to fix it to the sheet. A heating element (not shown) is built in the heating roller 38, and the heating element warms the heating roller 38 to a temperature at which the toner can be melted. The pressure roller 39 is pressed against the heating roller 38 to form a nip, and a sheet on which the toner image is transferred enters the nip to fix the toner. The sheet after fixing is conveyed to the discharge unit 26 and discharged from the discharge roller pair 26a toward the discharge tray 2a provided on the side of the discharge unit 26.

  Next, the scanner 1 according to the embodiment of the present invention will be described in detail with reference to FIG. FIG. 2 is an enlarged schematic cross-sectional view of the scanner 1 portion of the copying machine 2 according to the embodiment of the present invention.

  As described above, the scanner 1 of the present embodiment is mainly composed of the image reading unit 5 having a rectangular parallelepiped housing and the automatic document feeder 4 disposed above the image reading unit 5.

  The automatic document feeder 4 automatically and continuously conveys a document to be read, and sequentially from the upstream side in the document conveyance direction, a document tray 41, a document conveyance path 42, a document pickup roller 43, and a document conveyance roller pair 44. A document discharge roller pair 45, a document discharge tray 46, a sensor 47, and the like. The automatic document feeder 4 is attached to the image reading unit 5 so that it can be opened and closed with the back side of the sheet of FIG. 2 as a fulcrum, and also functions as a cover for pressing the contact glass 51 of the image reading unit 5 from above.

  The document tray 41 can place a plurality of documents and is connected to the upstream end of the document transport path 42. The document pick-up roller 43 is disposed at a position where the document pick-up roller 43 comes into contact with the uppermost document among the documents on the document tray 41, and when an input to read or copy the document is made to the copying machine 2, The document is sent out toward the document conveyance path 42.

  The document sent to the document transport path 42 passes through the upper surface of the feed reading contact glass 51a while being guided by a plurality of document transport roller pairs 44 and guides. During this passage, the image reading unit 5 performs reading. The document that has been read is transported to the guide, the document transport roller pair 44 and the document discharge roller pair 45, connected to the downstream end of the document transport path 42, and the document discharge tray 46 for receiving the discharged document. To be discharged.

  A plurality of sensors 47 are provided, for example, at the entrance portion of the document conveyance path 42, in other words, at the end of the document tray 41 on the downstream side in the document conveyance direction, in the direction perpendicular to the paper surface of FIG. This sensor 47 confirms the size of the placed document, and detects the start of document transportation and the end of the document. Then, the scanner 1 determines the start and end of passage through the reading position of the document from the conveyance speed of the document and the distance to the reading position, and uses the density data read within that time as image data of the document.

  Next, the image reading unit 5 in this embodiment will be described with reference to FIG.

  As shown in FIG. 2, the image reading unit 5 in the present embodiment has a box-shaped housing provided on the upper portion of the main body 3, starts reading when the document starts to be transferred, and passes the reading position. Etc. are irradiated with light, and the reflected light is photoelectrically converted. A feed reading contact glass 51a and a placement reading contact glass 51b are arranged on the upper surface of the image reading unit 5 from the left side of FIG.

  The feed reading contact glass 51a is a surface through which a document transported by the automatic document feeder 4 comes into contact, and below the feed reading contact glass 51a, a first moving frame 52 and a second moving frame to be described later. 53, and the passing document is read. On the other hand, when the automatic document feeder 4 such as a book or a newspaper cannot be used, the placement reading contact glass 51b lifts the automatic document feeder 4 and lifts the document automatically. This is the surface on which the document is placed with the surface facing downward. Reading of the original on the placement reading contact glass 51b is performed by moving the first moving frame 52 and the second moving frame 53 horizontally from the home position to the right in FIG.

  White plates 48 and 49 formed of resin or the like are provided on the automatic document feeder 4 side on the upper surfaces of the feed reading contact glass 51a and the placement reading contact glass 51b. The original is conveyed between the white plate 48 and the feed reading contact glass 51a, or the original is placed between the white plate 49 and the placement reading contact glass 51b. The scanner 1 according to the present embodiment performs reading even between the sheets of the document before the document is conveyed to the reading position on the feed reading contact glass 51a. Therefore, the image reading unit 5 basically reads a white image.

  As shown in FIG. 2, a first moving frame 52, a second moving frame 53, a wire 54, a take-up drum 55, a lens 56, an image sensor 57 and the like are disposed in the scanner 1 housing. The first moving frame 52 supports the light source 58 above and the first mirror 591 below the light source 58. The second moving frame 53 supports the second mirror 592 on the upper side and the third mirror 593 on the lower side. The first moving frame 52 is arranged above and to the right of FIG. 2, and the second moving frame 53 is arranged below and to the left of FIG. A wire 54 is attached to the first moving frame 52 and the second moving frame 53, the other end of the wire 54 is connected to a winding drum 55, and a winding drum is driven by a driving mechanism (not shown) such as a motor or a gear. As the 55 rotates, the first moving frame 52 and the second moving frame 53 move in the horizontal direction.

  Further, the light source 58 supported by the first moving frame 52 is formed to extend in the direction perpendicular to the paper surface of FIG. 2 so as to face the lower side of the feed reading contact glass 51a and the placement reading contact glass 51b. The first mirror 591, the second mirror 592, and the third mirror 593 are formed to extend in the direction perpendicular to the paper surface of FIG. 2 and are coated with a material having high reflectivity.

  Here, reading of a document conveyed by the automatic document feeder 4 among actual reading operations of the scanner 1 will be described. First, the document conveyed from the document tray 41 is conveyed while passing between the feed reading contact glass 51 a and the white plate 48. Then, the first moving frame 52 and the second moving frame 53 are fixed below the feed reading contact glass 51a, and light is irradiated to the passing document.

  Specifically, the light emitted from the light source 58 strikes the original or white plate 48 on the feed reading contact glass 51 a and the first mirror 591 directs the reflected light toward the left side surface of the image reading unit 5. reflect. A second mirror 592 is disposed on the optical path, and the second mirror 592 reflects light downward. Further, a third mirror 593 is disposed on the optical path, and the third mirror 593 reflects light toward the right side of the scanner. After that, the reflected light is condensed on the lens 56, imaged by an image sensor 57 constituted by, for example, a CCD line sensor or the like, and converted into an analog electric signal corresponding to the image density. As described above, the reading unit performs reading in units of lines in the main scanning direction (direction perpendicular to the document conveying direction) of the document, and repeatedly performs reading in units of lines in the sub-scanning direction (document conveying direction). Thus, one original is read.

  On the other hand, when reading a document placed on the placement reading contact glass 51b, the first moving frame 52 and the second moving frame 53 are moved to the right side of the image reading unit 5 by the winding drum 55, the wire 54, or the like. The scanning operation is continuously performed up to the document edge while moving in the surface direction (right side in FIG. 2), whereby the entire document image is read and the document image is converted into an electrical signal.

  Next, a hardware configuration of the scanner 1 according to the embodiment of the present invention will be described with reference to FIG. FIG. 3 is a block diagram of the scanner 1 according to the embodiment of the present invention.

  As described above, the scanner 1 of this embodiment includes the automatic document feeder 4 and the image reading unit 5, and further includes a control unit 6, an amplification unit 61, and an A / D conversion unit 62 (conversion unit) inside the scanner 1. The line memory unit 63 and the image memory 64 are arranged.

  The amplification unit 61 amplifies the analog signal output from the image sensor 57 because the amplitude of the analog signal output from the image sensor 57 of the image reading unit 5 is generally small.

  The A / D converter 62 converts the analog signal amplified through the amplifier 61 into a digital signal. The A / D converter 62 samples and holds the analog signal and performs quantization in accordance with the output level of the analog signal. That is, by converting each pixel of the document into a digital signal, the document image is converted into data. In other words, the analog signal output from the image reading unit 5 is converted into a digital signal as density data of each pixel.

  Although details of the line memory unit 63 (corresponding to the first memory and the second memory) will be described later, in this embodiment, three line memories for storing the density data of the read document in line units (main scanning direction) are provided. Have a book. Further, in the present invention, it is a portion for performing processing for erasing dark streaks due to dust or the like. The memory used in the line memory unit 63 is not necessarily a line memory, and a memory other than the line memory can be used.

  The image memory 64 is a portion in which density data of all the pixels of the read original is stored, and stores density data for each original. That is, the image data is held. The image memory 64 uses a high-speed memory and secures a capacity capable of storing a plurality of image data of a document. Further, details of the image data before or after being stored in the image memory 64 are omitted. However, for example, various known methods such as γ correction processing, density adjustment processing, enlargement / reduction processing, binarization processing, etc. It is possible to perform image processing. Then, the image data is transmitted from the image memory 64 to the main body control unit 100 which is a control unit for controlling the main body of the copying machine 2, and is used for image formation and the like.

  The control unit 6 controls the operation of each part such as the automatic document feeder 4, the image reading unit 5, the amplification unit 61, the A / D conversion unit 62, the line memory unit 63, and the image memory 64 that constitute the scanner 1. And corresponds to a controller. For example, conveyance by the automatic document feeder 4, control of the positions and movements of the light source 58, the first moving frame 52, and the second moving frame 53 of the image reading unit 5, and the like are appropriately converted into image data. Control is performed as follows.

  For example, the control unit 6 can be configured to include a CPU 65 (Central Processing Unit), a RAM 66 (Random Access Memory), a ROM 67 (Read Only Memory), a timer 68, and the like. The CPU 65 is a central processing unit, reads out the control program and control data stored in the ROM 67, expands it in the RAM 66, and performs calculations. Thereby, the operation of each part of the scanner 1 is controlled.

  The timer 68 measures the document conveyance start time and the document end detection time by the sensor 47. Based on this timing, the document reading position (feed reading contact glass 51a) is determined from the document feeding speed of the automatic document feeder 4 to the document size, the document feeding speed and the distance from the document tray 41 to the feeding reading contact glass 51a. It is detected that the end of the document or the end of the document has passed the reading position. Therefore, the timer 68 is used for determining the image data actually read by the image reading unit 5.

  Next, details of the line memory unit 63 according to the embodiment of the present invention will be described with reference to FIG. FIG. 4A is a block diagram of the line memory unit 63 according to the embodiment of the present invention, and FIG. 4B is a diagram for explaining the comparison operation unit 9.

  First, as shown in FIG. 4A, the line memory unit 63 includes a first line memory 7 (corresponding to the first memory), a second line memory 8 (corresponding to the second memory), a comparison operation unit 9, A three-line memory 10 (corresponding to a third memory), a writing unit 81, a threshold input unit 91, and the like are provided.

  The first line memory 7 stores the density data of the document converted into a digital signal by the A / D converter 62 in units of lines. Here, the lines to be stored are lines in the main scanning direction in the image reading unit 5. That is, the density data of each pixel in the main scanning direction of the document is held. The first line memory 7 sequentially updates the density data sequentially in the sub-scanning direction in units of lines in accordance with the reading of the image reading unit 5.

  The second line memory 8 holds the density data in order to compare the density data stored in the first line memory 7 on a pixel basis, and each line of the first main scanning direction read by the image reading unit 5 is stored. Pixel density data is stored and stored in line units. Therefore, the contents stored in the first line memory 7 and the second line memory 8 are the same when the image reading unit 5 reads the original. Here, since the scanner 1 of the present embodiment starts reading before the document is conveyed to the reading position, the second line memory 8 maintains the adhesion state of dust and the like on the feed reading contact glass 51a. Keep memorizing. The second line memory 8 has a reset circuit 82, and the stored contents are reset when reading of one original is completed.

  The third line memory 10 stores density data output from the comparison calculation unit 9 and subjected to processing for erasing streaks according to the present embodiment in units of lines in the main scanning direction of the document. If the density data is sequentially output from the third line memory 10 to the image memory 64 in units of lines, and all the lines for one original are stored in the image memory 64, the image data of one original is stored. Has been read.

  As shown in FIG. 4B, the comparison operation unit 9 performs an operation for comparing the density data stored in the first line memory 7 and the second line memory 8 line by line. That is, the comparison calculation unit 9 compares and calculates the density data stored in the first line memory 7 and the second line memory 8 pixel by pixel (for each pixel) at corresponding positions. If the pixel density of the first line memory 7 is higher than the threshold, the density data of the first line memory 7 is sent to the third line memory 10 if the density data is lower than the threshold.

  For example, as shown in FIG. 4B, if the first line memory 7 and the second line memory 8 store density data of 1 to n pixels per line, the comparison operation unit 9 The density data of the first pixel in the 1-line memory 7 and the density data of the first pixel in the second line memory 8 are compared, and similarly, the second pixel, the third pixel, and so on, Each density data is compared up to the first pixel.

  Here, the comparison operation unit 9 may be realized by software by operating the CPU 65 based on a program, but in the present embodiment, it is realized by hardware by an ASIC (Application Specific Integrated Circuit) as a dedicated circuit. . Note that the calculation performed by the comparison calculation unit 9 is basically only the comparison calculation, and the design of the ASIC is not too complicated and the cost is not too high.

  Note that the number of pixels per line that can be stored in the first line memory 7, the second line memory 8, and the third line memory 10 varies depending on the resolution and document size that the scanner 1 can read. That is, the higher the resolution, the greater the number of pixels required, and the greater the size of the readable document, the greater the number of pixels required. Therefore, the storage capacity of each line memory is determined in accordance with the maximum resolution and the maximum document size that can be read by the scanner 1.

  If the first line memory 7 has a lower density pixel as a result of the comparison operation between the first line memory 7 and the second line memory 8, the writing unit 81 stores the first line memory 7 in the first line memory 7. The pixel density data is written to the corresponding pixel of the second line memory 8. As a result, the second line memory 8 is sequentially updated in accordance with the pixel having the lowest density when reading the document.

  The threshold value input unit 91 compares whether the pixel density of the first line memory 7 is higher or lower than the threshold value when the comparison operation unit 9 compares the first line memory 7 and the second line memory 8. Provides a threshold. Thereby, the threshold value can be changed in consideration of the document type, the amount of noise, the characteristics of the image reading unit 5 and the like, and reflecting the settings of the user. The threshold value input unit 91 may not be provided, and the comparison calculation unit 9 may store a fixed threshold value.

  Next, based on FIGS. 5 and 6, the cause of the streaks and the processing for the generated streaks will be described in detail.

  FIG. 5 is a diagram for explaining the cause of the generation of streaks, and is an explanatory diagram showing the feed reading contact glass 51a and an image in which the streaks are generated. FIG. 6 is a flowchart for explaining the stripe elimination process of the scanner 1 according to the embodiment of the invention.

  First, the feed reading contact glass 51a when the document is conveyed and read by the automatic document feeder 4 is shown in the upper part of FIG. In actual reading, the first moving frame 52 and the second moving frame 53 are fixed below the feed reading contact glass 51a (see FIG. 2), and the original passes above the feed reading contact glass 51a. Reading is performed in line units in the main scanning direction.

  When a document is sent out from the document tray 41, the light source 58 of the first moving frame 52 emits light before the document reaches the feed reading contact glass 51a, and the image sensor 5747 responds to the reflected light. Output an analog signal. In other words, the scanner 1 of the present embodiment starts reading between sheets before the document arrives.

  Here, if no dust or the like is attached to the feed reading contact glass 51a, the white plate 48 provided on the upper surface of the feed reading contact glass 51a and the lower surface of the automatic document feeder 4 has a white color. Should be read (see FIG. 2).

  However, as shown in FIG. 5, the toner peeled off from the original, fine paper pieces, ink, glue, etc. from the original, such as dust, dust, dirt, scratches, etc. Alternatively, if it is on the back surface, the portion absorbs light from the light source 58 or diffusely reflects it, so that it cannot be read as white. Note that black dots BP on the feed reading contact glass 51a in FIG. 5 indicate dust or the like.

  Specifically, when dust or the like is read, the light of that portion is generally difficult to be reflected, and is reflected in the read density data as gray or black having a higher density than white, for example. If this state continues during reading of the document, the read image data of the document is linear at the position corresponding to the black point BP in the sub-scanning direction (document transport direction) as shown in FIG. A dark streak (for example, black) appears. It should be noted that even if dust or the like adheres to the placement reading contact glass 51b, it is only read as a dot and does not cause a fatal image quality deterioration such as a streak. Therefore, the present invention is intended for reading a document by the automatic document feeder 4.

  The image data including the streak is difficult to use as it is, and it is necessary to read the original document again and form an image, and waste of time, toner, sheet, power, and the like becomes large. Further, if the image is continuously read and a plurality of copies are made without knowing that dust or the like has adhered to the feed reading contact glass 51a, the waste becomes even greater.

  Therefore, in the copying machine 2 of the present embodiment, the density data of the pixels in the dark streaks are replaced with white. Details of the processing will be described with reference to FIG.

  First, the start of FIG. 6 is a point in time when a document reading instruction is input to the copying machine 2 and the scanner 1. Then, the automatic document feeder 4 rotates the document pickup roller 43 and feeds it from the document tray 41 to the document conveyance path 42 (step # 1). Then, the sensor 47 starts detection, and thereafter, the sensor 47 detects the start of document transport, the document size, and the end of the document (step # 2). When conveyance of the document from the document tray 41 is started, the image reading unit 5 starts reading at the reading position (that is, the portion of the contact glass 51a for feeding reading) even before the document arrives (Step #). 3).

  Then, the density data of each pixel of the line at the first time when reading is started is simultaneously stored in the first line memory 7 and the second line memory 8 (step # 4). The density data in the first line memory 7 is continuously rewritten with the density data of each pixel in the next line read (step # 5). On the other hand, the second line memory 8 holds density data when the white plate 48 is read. That is, position information such as dust is kept retained.

  Each time the density data in the first line memory 7 is rewritten, the comparison operation unit 9 compares the first line memory 7 and the second line memory 8 for each pixel in units of lines (step # 6). At that time, it is confirmed whether or not the pixel density of the first line memory 7 is higher than the threshold (step # 7). For example, the comparison operation is as follows.

Density of pixels in first line memory 7−Density of pixels in second line memory 8> Threshold Here, in the scanner 1 of the present embodiment, density data is expressed as gradation. For example, if density data (density) is expressed by a general 8-bit per pixel, each pixel has a value of 0 to 255 (256 gradations). When reading in monochrome, for example, 0 can be assigned to white and 255 to black. The threshold value can be set to 2 to 5, more preferably about 3, in terms of 256 gradation values. This is because when reading an image, errors and wobble appear in the read density data due to the presence of noise. That is, even if the same dust or the like is read, the density data of the dust or the like in the first line memory 7 and the second line memory 8 is not always the same. Even if there are fluctuations, the dark streaks can be erased.

  Note that the number of bits per pixel is not limited to the above-described 8 bits (for example, if 10 bits are used, the gradation value is four times that of 8 bits). For this reason, the threshold value may be appropriately determined according to the number of bits per pixel.

  If the density of the pixel in the first line memory 7 is higher than the threshold (Yes in Step # 7), the comparison calculation unit 9 stores the first line memory in the third line memory 10 as the density data of the pixel. 7 is output (step # 8). On the other hand, if the density of the pixel in the first line memory 7 is lower than the threshold value (= not higher) (No in step # 7), white density data is transferred from the comparison calculation unit 9 to the third line for that pixel. The data is output toward the memory 10 (step # 9).

  That is, the second line memory 8 holds and stores the position of dust or the like that causes dark streaks in the main scanning direction. The second line memory 8 newly reads and stores the dust or the like stored in the first line memory 7. If the pixel density of the existing part is higher than the threshold, it can be determined that the part is also a dark part in the document, so it is sent to the third line memory 10 as it is, and if it is not higher than the threshold, The portion of pixels is replaced with white density data.

  This may cause white streaks, but there are few solid-colored images that are troubled by white streaks or images that have a solid background and white text. In view of the fact that white stripes are clearly less conspicuous than dark stripes and are confused with surrounding images, a practically sufficient effect of stripe elimination can be expected. Further, in the stripe elimination process of the present embodiment, it is only necessary to perform a comparison operation using a line memory, and there is no need for complicated calculation processes and circuits as in the prior art, and the stripe elimination process can be easily performed. .

  In addition, in step # 6 (comparison of density data of each pixel in the first line memory 7 and the second line memory 8 by the comparison operation unit 9), in addition to the confirmation in step # 7, the pixels in the first line memory 7 It is confirmed whether or not the density is lower than the density of the second line memory 8 (step # 10). For example, the comparison operation is as follows.

Pixel density of second line memory 8-Pixel density of first line memory 7> 0
If the density of the first line memory 7 is lower (Yes in Step # 10), the writing unit 81 uses the density data of the pixel of the first line memory 7 to correspond to the pixel of the second line memory 8. Is rewritten (step # 11). In other words, if the density of the pixel in the first line memory 7 is lower as a result of the comparison calculation of each pixel by the comparison calculation unit 9, the density data of the corresponding pixel in the second line memory 8 is stored in the first memory. The pixel density data is updated. As a result, when dust or the like is removed during conveyance of the document, the result is immediately reflected in the second line memory 8. If the density of the second line memory 8 is lower (No in step # 10), no particular processing is performed.

  These processes are performed for each original document and are continued until the reading of one original is completed, so it is confirmed whether or not the reading of one original has been completed (step # 12). Whether or not one document has been read may be determined from the time after the sensor 47 detects the start of document conveyance and the end of the document, the document conveyance speed, the document size, and the like. If the completion of reading one original is detected (Yes in step # 12), the final image data is determined (step # 13). This is because the scanner 1 of the present embodiment performs the reading operation before the document is conveyed to the reading position (between sheets), and the image memory 64 also stores density data between sheets. Remove the part (cut out the original image data). In this process, the image data of the portion where the document is read may be determined based on the document conveyance speed, the distance to the reading position, the document conveyance start time and the end detection time by the sensor 47, and the like.

  Further, the density data of the second line memory 8 is reset every time reading of one original is completed (step # 14). That is, at this time, the density data of all the pixels in the second line memory 8 may be set to the highest density at the same time as resetting (may be at the start of document reading). Thereby, the position information of adhesion of dust and the like stored in the second line memory 8 can be updated for each document. Even if the data in the second line memory 8 is set to the highest density, the data in the second line memory 8 is sequentially updated with reference to the data in the first line memory 7, and is darker in relation to the threshold value. Stripes can be erased more effectively.

  Then, it is confirmed whether or not the next document has been read (step # 15). If there is, the process returns to step # 1 to perform the same process, and if not, the process ends (END).

  As described above, according to the configuration of the present invention, when dust or the like is read, the density of the pixel is usually high. Therefore, the density data for one line indicating the position of the dust or the like is stored in the second line. The comparison calculation unit 9 compares each pixel of the data of the line of the first line memory 7 (first memory), which is held in the line memory 8 (second memory). Is output white density data. Therefore, in the pixel of the portion that becomes a dark streak (for example, black), the density is the same in both the first memory and the second memory, so the streak portion is replaced with white data, and the dark streak can be erased. it can. In this case, when the scanned image data of the original is viewed, white streaks may occur, but white streaks are less noticeable than black streaks. Is not reached.

  Further, as a result of the comparison of the density data of the line of the comparison operation unit 9, when the density of the pixel of the second memory is higher, the second memory stores the density data of the pixel of the first memory and stores the density data of the second memory. Since the density data of the line is kept at a lower density state, even if dust or the like moves as the document is transported and no dark streak occurs, it is immediately reflected in the second memory and is more than necessary. Therefore, it is possible to prevent the density data in the first memory from being replaced with white. In addition, the configuration necessary for removing dark streaks is a simple configuration consisting of only two memories and an element that performs only a comparison operation, and the processing can be performed automatically, so that the burden on the user is reduced. Nor.

  In addition, since the contents of the second memory are reset every predetermined time (every time when one original is read), the second memory can reflect the latest state of adhesion of dust or the like at the reading position. . In addition, first, all the pixels in the second memory line are set to the darkest state, and the second memory is updated so that each pixel is updated to a low-density state based on the comparison result with the first memory by the comparison calculation unit 9. Even so, dark streaks can be erased. If the scanner 1 of the present embodiment is applied to an image forming apparatus, an image forming apparatus that does not generate dark streaks can be provided even when image formation is performed on a read original.

  The embodiment of the present invention has been described above, but the scope of the present invention is not limited to this, and various modifications can be made without departing from the spirit of the invention.

  The present invention is applicable to an image reading apparatus such as a scanner and an image forming apparatus including the same.

1 is a schematic front sectional view showing a schematic configuration of a copying machine according to an embodiment of the present invention. 1 is an enlarged schematic cross-sectional view of a scanner portion of a copying machine according to an embodiment of the present invention. 1 is a block diagram of a scanner according to an embodiment of the present invention. It is a block diagram of the line memory part which concerns on embodiment of this invention, (b) is a figure for demonstrating a comparison calculating part. 4A and 4B are diagrams for explaining the cause of the occurrence of streaks, wherein FIG. 4A is an explanatory diagram showing the time of document reading, and FIG. 4B is an explanatory diagram showing an image in which the streaks are generated. 6 is a flowchart for explaining a stripe elimination process of the scanner according to the embodiment of the invention.

Explanation of symbols

1 Scanner (image reading device)
2 Copying machine (image forming device)
4 Automatic document feeder (document feeder)
3 Image reading unit (image reading unit)
62 A / D converter (converter)
7 First line memory (first memory)
8 Second line memory (second memory)
9 Comparison calculator

Claims (4)

A document transport unit that transports a document to be read; and
An image reading unit that irradiates light on a document passing through a reading position, photoelectrically converts the reflected light, and starts reading by starting conveyance of the document;
A conversion unit that converts an analog signal output as a reading result by the image reading unit into a digital signal as density data of each pixel;
A first memory which stores density data of pixels for one line read by the image reading unit and which is sequentially updated in accordance with the reading;
A second memory capable of storing density data for storing density data of pixels for the first line read by the image reading unit and comparing the density data with the first memory;
A comparison operation unit that performs pixel-by-pixel comparison of density data for one line stored in the first memory and the second memory;
As a result of the comparison calculation of each pixel by the comparison calculation unit, when the density of the pixel of the first memory is lower, the density data of the pixel of the second memory is updated to the density data of the pixel of the first memory. And
When the density of the first memory is higher than the second memory by a threshold value or more as a result of the comparison calculation of each pixel, the comparison calculation unit stores the density data of the pixel of the first memory in the pixel. When the density of the memory is not higher than a threshold value than the second memory, the image reading apparatus outputs white density data to the pixel as a reading result of the original.   The image reading apparatus according to claim 1, wherein the second memory is reset every time reading of one original is completed.   The second memory does not store the density data of pixels for the first line read by the image reading unit at the start of document reading and / or after resetting, and all pixels for one line have the highest density. The image reading apparatus according to claim 1, wherein the image reading apparatus is set as follows.   An image forming apparatus comprising the image reading apparatus according to claim 1.

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