JP2009033704A - Original reading device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an original reading device capable of achieving dust detection with a small memory capacity. <P>SOLUTION: The present invention relates to an original reading device in which an original to be read is fed on contact glass in a sub-scanning direction and a line image sensor is provided for reading an image of a reading position on the contact glass by a plurality of lines in a main scanning direction. When there are a first pixel whose read values of read data outputted from a plurality of read lines are smaller than a predetermined black threshold, and an adjacent pixel whose two arbitrary read values have differences larger than a predetermined threshold near the first pixel, and when the first pixel remains at the same pixel position in a predetermined number of continuous main scanning periods, read data of the adjacent pixel and a predetermined number of subsequent pixels are replaced with white pixel data. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention provides a document reading apparatus provided with a line image sensor that reads a plurality of lines of images in the main scanning direction at the reading position of the contact glass while conveying a reading document on the contact glass in the sub-scanning direction, and The present invention relates to an image forming apparatus including a document reading device.

  Conventionally, a so-called sheet scan type equipped with a line image sensor that conveys a read original on the contact glass in the sub-scanning direction and reads an image for one line or a plurality of lines at the reading position of the contact glass in the main scanning direction. In an image reading apparatus (also referred to as a sheet-through type), if dust adheres to the contact glass, the image of the dust is also read. If the dust does not move, a vertical streak black image is displayed on the read image. The situation of appearing occurred.

  When the black image of the vertical stripe appears in the read image as described above, the user needs to clean the contact glass and perform the reading operation again.

As a technique for coping with such a situation, as disclosed in Patent Document 1, in order to detect the presence of dust on the reading surface at the time of sheet-through (automatic document feeding, flow reading) reading, The determination is made based on whether there is a straight line extending in the sub-scanning direction where the position of the main scanning pixel or the data size does not change. That is, no matter how straight the straight line on the document is, the position of the main scanning pixel or the size of the data does not change at all due to a skew or the like when the document is conveyed, so that it can be determined by that.
JP 2006-229719 A

  In this conventional example, in order to detect whether there is dust on the reading surface, in order to detect the presence of dust on the reading surface, the position of the main scanning pixel or the size of data does not change in the sub-scanning direction. Judgment was made based on whether there was an extended straight line.

  Therefore, in this detection method, detection corresponding to the number of lines in the sub-scanning direction is required, so that the capacity of the memory for storing the read image data for the detection becomes large and the apparatus cost increases. May occur.

  SUMMARY An advantage of some aspects of the invention is that it provides a document reading device capable of realizing dust detection with a small memory capacity and an image forming apparatus including the document reading device. .

  The present invention is an original reading apparatus provided with a line image sensor for reading an image of a plurality of lines in a main scanning direction at a reading position of the contact glass while conveying a read original on the contact glass in a sub-scanning direction, There is a first pixel in which the reading values of the plurality of reading data respectively output from the plurality of reading lines in the same main scanning period are smaller than a predetermined black threshold, and the difference between any two reading values A neighboring pixel having a value greater than a predetermined threshold is present around the first pixel, and the first pixel is present at the same pixel position in a predetermined number of consecutive main scanning periods; and The read data of a predetermined number of pixels following the adjacent pixels is replaced with white pixel data.

  An original reading apparatus comprising a line image sensor that conveys a read original on a contact glass in a sub-scanning direction and reads an image for a plurality of lines in a main scanning direction at a reading position of the contact glass. There are first pixels in which the read values of a plurality of read data respectively output from the read line in the same main scanning period are smaller than a predetermined black threshold, and the difference between any two read values is predetermined. If there are neighboring pixels larger than the threshold value around the first pixel, and the first pixel exists at the same pixel position in a predetermined number of consecutive main scanning periods, a plurality of the first pixels are determined. In such a case, the read data of the pixels sandwiched between the first pixels and including the adjacent pixels are replaced with white pixel data.

  The line image sensor has a color separation function for three primary colors and includes three reading lines.

  The predetermined number of the continuous main scanning lines is set according to the reading magnification.

  The predetermined black threshold value, the predetermined threshold value, and the predetermined number are set to different values in the monochrome reading mode and the color reading mode, respectively.

  An original reading apparatus comprising a line image sensor that conveys a read original on a contact glass in a sub-scanning direction and reads an image for a plurality of lines in a main scanning direction at a reading position of the contact glass. A dust detection unit that detects that all outputs from the line image sensor are larger than a predetermined threshold as dust detection, and a pixel that the dust detection unit detects dust detection has a white pixel value. Output value rewriting means for rewriting outputs from the plurality of line image sensors to values corresponding to.

  Further, when the dust detection unit detects dust detection while reading one page of the document image, the display unit further includes a display unit that displays dust detection after reading the document image of the page. is there.

  An image forming apparatus for forming an image read by a document reading device on a recording sheet, wherein the document reading device includes the document reading device according to claim 1.

  Therefore, according to the present invention, dust is determined by referring to the read values of the image data for a plurality of lines obtained in one scan, so that dust is detected when a linear image parallel to the sub-scanning direction is detected. As compared with the conventional method for determining that the target is detected, it is possible to perform appropriate dust detection with a small memory capacity.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 shows an example of an image forming apparatus according to an embodiment of the present invention.

  The image forming apparatus includes a controller unit UN1 for controlling operations of the units constituting the apparatus, an operation display unit UN2 for configuring a user interface for a user to operate the image forming apparatus, and the image forming apparatus. Power unit UN3 that supplies power to each unit, connected to an external device or network, exchanges various information with the external device, and exchanges various information between other terminal devices, etc. via the network The communication unit UN4 includes a scanner unit UN5 for reading an original image to form image data, and a plotter unit UN6 for recording and outputting a copy image, a print image, and the like on a recording sheet.

  Among the units constituting the image forming apparatus, the scanner unit UN5 and the plotter unit UN6 are configured to be detachable, and have predetermined interface rules (physical requirements, signal input / output requirements, etc.) If there is, a plurality of types can be appropriately exchanged and connected. For example, the scanner unit UN5 includes an ADF (automatic document feeder), a monochrome reading function, and a color reading function. The plotter unit UN6 includes a recording paper post-processing function (sorting function, stapling function, fold function, etc.), a monochrome printing function, and a color printing function.

  Similarly, the communication unit UN4 can be selected and connected from a plurality of types according to the device configuration. For example, two types, a host I / F connected to a host device such as a personal computer device and a network I / F for connecting to a network, and a host I / F only connected, are appropriately connected. Is possible. Depending on the configuration of the image forming apparatus, the communication unit UN4 may not be connected (a so-called stand-alone configuration (such as a copying machine)).

  For example, when the scanner unit UN5 and the plotter unit UN6 are connected together, an image forming apparatus having a copying function, a printer function, a network printer function, a network facsimile function, a network scanner function, and the like can be realized. Further, a communication unit UN4 having an appropriate function is connected according to the function provided in the image forming apparatus.

  Further, when only the printer unit UN6 is connected, an image forming apparatus having a printer function and a network printer function can be realized. Also in this case, similarly, the communication unit UN4 having an appropriate function is connected according to the function of the image forming apparatus.

  FIG. 2 shows a schematic configuration of an image reading apparatus (corresponding to the scanner unit UN5 of FIG. 1) 1 according to an embodiment of the present invention. The image reading apparatus 1 includes an automatic document conveyance unit 1a that separates read documents from the document table 2 one by one and conveys them to a reading position RL, and an image reading unit 1b that reads a document image at the reading position line by line. The image reading unit 1b has two document reading functions, a sheet scan type document reading function and a book scan type document reading function. Since the present invention mainly relates to a sheet scan type document reading function, a description of the book scan type document reading function is omitted in the following description. The automatic document conveyance unit 1a is provided so as to be openable and closable with respect to the image reading unit 1b, and can cope with a jam of a read document. In the book scan type document reading function, the automatic document transport unit 1a serves as a pressure plate that presses the document from the back.

  In the automatic document feeder unit 1 a, the read document PP placed on the document table 2 is taken out by the pickup roller 3 at the uppermost position and sent to the separation unit 4. They are separated one by one and delivered to the delivery roller 5. The delivery roller 5 sends out one read original in the transport direction through the guide member GG.

  As a result, the read original PP is sandwiched between the transport roller 6 and the transport drum 7, transported in close contact with the surface of the transport drum 7, passes through the reading position RL, and is transported to the discharge roller 8. The paper is discharged onto the paper discharge tray 9 by the discharge roller 8.

  In the document reading unit 1b, a sheet scanning contact glass 10 is disposed corresponding to the reading position RL. The dimension of the contact glass 10 in the sub-scanning direction is about 4 (mm).

  Further, a contact glass 11 for book scanning is disposed on the right side of the contact glass 10. The white reference plate WW is used to construct a white reference image for shading correction.

  The lamp 12 illuminates the original surface of the read original PP at the read position RL, and reflected light from the read position RL sequentially reflects the first mirror 13, the second mirror 14, and the third mirror 15. Then, the light is guided to the lens 18, converged by the lens 18, and irradiated to the color CCD line image sensor 20 provided on the substrate 19.

  The lamp 12 and the first mirror 13 are mounted on the first carriage 16 and reciprocated in the sub-scanning direction SS, and the second mirror 14 and the third mirror 15 are mounted on the second carriage 17 and connected to the sub-scanning direction SS. Reciprocates in the scanning direction SS. Further, in order to maintain the optical path length from the contact glass 10 to the CCD line image sensor 20, the second carriage 17 is moved at a speed half that of the first carriage 16.

  The scanner motor 21 is for driving the first carriage 16 and the second carriage 17.

  In this embodiment, as shown in FIG. 3, the color CCD line image sensor 20 includes a red CCD line image sensor 20R that reads a red component of an image, a green CCD line image sensor 20G that reads a green component of an image, The three CCD line image sensors of the blue CCD line image sensor 20B for reading the blue component of the image are provided at a predetermined distance (in this case, three lines) in the sub-scanning direction. In this case, when the reading position of each CCD line image sensor is used as a reference, it is arranged at intervals of 4 lines in the sub-scanning direction.

  At the time of image reading, for example, as shown in the figure, the read original PP enters from the blue CCD line image sensor 20B side, so the image of the read original PP is first read by the blue CCD line image sensor 20B, and then green. It is read by the CCD line image sensor 20G and finally read by the red CCD line image sensor 20R.

  Here, considering the coordinates (line numbers) of the main scanning line read by the red CCD line image sensor 20R in the sub-scanning direction, it is four lines before the main scanning line read by the green CCD line image sensor 20G. This is 8 lines before the main scanning line read by the blue CCD line image sensor 20B.

  Therefore, the red image data output from the red CCD line image sensor 20R, the green image data output from the green CCD line image sensor 20G, and the blue image data output from the blue CCD line image sensor 20B are combined. When forming color image data, it is necessary to consider the shift of coordinates in the sub-scanning direction of each main scanning line.

  In this case, the green image data is passed through a data buffer that delays four main scanning lines, and the blue image data is passed through a data buffer that delays eight main scanning lines, so that it is the same as red image data. Data of the main scanning line can be obtained. Then, the color-read image data can be obtained by color-combining the delayed green image data, blue image data, and red image data at the same pixel position (coordinate in the main scanning direction). Processing for eliminating such a delay between lines is called “inter-line correction processing”.

  FIG. 4 shows an example of a read signal processing system of the image reading apparatus 1 according to an embodiment of the present invention.

  In the figure, a red reading signal PR, a green reading signal PG, and a blue reading signal PB output from the color CCD line image sensor 20 are respectively output by analog signal processing units (AFE (Analog Front End)) 25, 26, and 27. Predetermined image signal processing and analog / digital conversion are performed.

  A predetermined number of lines of red reading data RD, green reading data GD, and blue reading data BD output from the analog signal processing units 25, 26, and 27 are accumulated in the buffer memory 28.

  The dust detection processing unit 29 determines that “the number of pixels around the black vertical line is colored and how many lines in the sub-scanning direction are based on the red read data RD, green read data GD, and blue read data BD accumulated in the buffer memory 28. Also, it is detected whether or not there is image data that matches “the read data hardly changes”.

  When the dust detection processing unit 29 detects “present”, the data correction circuit 30 deletes the image data of that portion including the black vertical line at that location and surrounding colored pixels (described later). Here, the capacity of the buffer memory 28 is sufficient even from several to several tens of lines necessary for the determination processing of the dust detection processing unit 29.

  Unlike the conventional example in which there is an image in which the read data of the main scanning does not change in the sub-scanning direction, the number of lines is much smaller because the coloring around the black vertical line is detected.

  This is the most excellent effect of the present invention. That is, it is possible to simultaneously remove reading data of several to several tens of lines when it is detected as dust while sequentially detecting the reading data.

  Next, a method for detecting dust on the contact glass 10 will be described.

  5, 6, and 7, dust GBa, GBb, and GBc having different shapes formed on the color CCD line image sensor 20 and read data for each of the R, G, and B pixels (red read data RD, green read) are shown. Data GD, blue reading data BD) are shown.

  Here, in this embodiment, dust detection determination processing is performed based on the read data. At this time, the read data to be referred to is red read data RD, green read data GD, which are obtained at the same main scanning timing. Blue reading data BD is used. That is, the red reading data RD, green reading data GD, and blue reading data BD in this case are at different sub-scanning positions.

  First, as shown in FIG. 5, the dust GBa having a shape parallel to the sub-scanning direction has the same shape as a straight line parallel to the sub-scanning direction. Cannot be detected as.

  However, as recognized in Patent Document 1, straight lines parallel to the sub-scanning direction hardly appear in an actual read image due to skew of the read original PP at the time of conveyance. Even if the dust GBa cannot be detected, there is no practical problem.

  Next, as shown in FIG. 6, a dust GBb having a substantially elliptic shape and a long axis parallel to the sub-scanning direction is considered. In this case, at the pixel where both ends of the dust GBb are applied, the image of the dust GBb is applied to each of the reading window (aperture) of the red CCD line image sensor 20R and the reading window of the blue CCD line image sensor 20B. The reading window of the green CCD line image sensor 20G has an image of dust GBb over the entire area.

  Accordingly, in this case, the red read data RD and the blue read data BD are, for example, “192” as an 8-bit digital value, and the green read data GD is “0” as an 8-bit digital value. The read value is “dark magenta” (see FIG. 8; color number “3” in FIG. 8).

  That is, at the pixels at both ends of the dust GBb, when the red reading data RD, the green reading data GD, and the blue reading data BD are combined, the reading values other than black (the red reading data RD, the green reading data GD, and the blue reading data BD) Is obtained). Here, the specific numerical values (“192” in the above description) of the red reading data RD, the green reading data GD, and the blue reading data BD in the description of the dust GBb described above are an example, and other appropriate values. Can take a value.

  If the dust GBb does not move, the same read value is continuously generated at the same pixel position in different main scanning lines.

  That is, when the same read value is continuously generated at the same pixel position in a plurality of main scanning lines, it can be predicted that the pixel position from which the read value is obtained corresponds to the pixels at both ends of the dust GBb.

  Therefore, the red correction data RD, the green read data GD, and the blue read data BD of the portion including this pixel position and sandwiched between two pixels are all expressed by white by an 8-bit digital value by the data correction circuit 30 “255”. , The dust component can be removed from the read image.

  Further, as shown in FIG. 7, a garbage GBc having a shape in which the major axis is inclined with respect to the sub-scanning direction is considered. In this case, the left side of the garbage GBc covers 2 pixels, and the right side covers 3 pixels.

  Therefore, at the pixel position where the left and right sides of the dust GBc are covered, a reading value of an intermediate color which is neither white nor black is obtained. Further, a black read value is obtained at the pixel position where the central portion of the dust GBc is covered.

  As described above, if the dust GBc does not move, the same read value is continuously generated at the same pixel position in different main scanning lines.

  That is, when the same read value is continuously generated at the same pixel position in a plurality of main scanning lines, the pixel position from which the read value is obtained can be predicted to be a pixel on which both sides of the dust GBc are applied. .

  Therefore, the red correction data RD, the green read data GD, and the blue read data BD of the portion including the pixel position where the read value of the intermediate color is obtained and sandwiched between these pixels are all converted into 8-bit digital values by the data correction circuit 30. By converting to “255” representing white, the dust component can be removed from the read image.

  That is, dust has an irregular shape with a larger area than the pixels of the color CCD line image sensor 20, and can be detected by the method described above.

  FIG. 9 shows an example of the dust detection method.

  First, the threshold for determining the black level (threshold for black level) is set to the constant Xd, the threshold for the number of pixels colored in the main scanning direction is set to the constant Sd, the threshold for the RGB data difference is set to the constant Dd, and the coloring is set in the sub-scanning direction. A threshold value for the number of lines is set to each constant Fd (process 101).

  Then, the reading operation is started (process 102), and (RD-GD)> Dd or (DG-DB)> Dd or (within the peripheral Sd pixels of the pixels whose read data RD, GD, and BD are less than or equal to the threshold value Xd. DB-DR)> Dd is examined to determine whether there is a relationship satisfying (Determination 103).

  When a pixel satisfying the relationship of the processing 103 is found (the result of the determination 104 is YES), it is checked whether or not the pixels satisfying the relationship continue for the Fd line or more (determination 105). If the result of determination 105 is YES, the values of the pixels up to the periphery Sd of the pixels whose read data RD, GD, and BD are less than or equal to the threshold value Xd are all changed to “255”, so that the pixel It is removed (process 106).

  The above processing is continuously performed until the reading operation is finished (NO loop of determination 107).

  Here, if the determination conditions are severe, that is, if the values (threshold values) of the constants Xd, Sd, Dd, and Fd that determine the determination conditions are large, the frequency of detecting dust decreases, and conversely, if the determination conditions are loose. Even the vertical lines of the original are judged as dust and removed.

  Accordingly, these threshold values can be set by a service person or a user, and can be set according to a document of a type that the user reads relatively well, thereby reducing the above erroneous determination.

  In addition, when scanning an original with enlargement or reduction, the detection can be performed in the same manner by setting the number of lines (or the number of pixels) corresponding to the magnification in the sub-scanning direction (or main scanning direction) as a threshold value.

  Although an example of the countermeasure for reducing the erroneous determination is shown above, another case where the user selects monochrome reading or the original reading apparatus or the image forming apparatus has an automatic color selection mode is determined as a monochrome original. In such a case, it is preferable to loosen the above threshold value for determination and increase the frequency of detecting dust.

  This is because the original is monochrome, and if there is colored read data, there is a high possibility that it is dust on the reading surface.

  By the way, the shape of the dust described above shows a case where dust is applied to any of the RGB lines, and the determination condition is “several pixels around the black vertical line are colored, and there are many lines of read data in the sub-scanning direction. There is a case where only two or one of RGB is dusty.

  In this case as well, it is sufficient to detect only a colored portion without a black image. However, in this case, since the document is read data similar to the graph paper or the ruled line of the note paper, it is easy to erroneously determine the image on the document as dust. Therefore, the determination is different from the case where there is a black image (difficult to determine as dust). It is preferable to set a threshold value in the direction).

  10 and 11 show an example of a configuration for realizing the dust removal process of the flowchart shown in FIG. 9 in hardware.

  In this case, the red read data RD output from the analog signal processing unit 25 in FIG. 4 is added to the input terminal A of the comparator CA1, and one input terminal (input terminal for the subtracted value) of the subtractor GA1 and It is added to the other input terminal (input terminal of the subtraction value) of the subtractor GA3.

  Further, the green read data GD output from the analog signal processing unit 26 of FIG. 4 is added to the input terminal A of the comparator CA2, and one input terminal (input terminal for the subtracted value) and subtraction of the subtractor GA2. It is added to the other input terminal (input terminal of the subtraction value) of the device GA1.

  Further, the blue read data BD output from the analog signal processing unit 27 in FIG. 4 is added to the input terminal A of the comparator CA3, and one input terminal (input terminal for the subtracted value) and subtraction of the subtractor GA3. It is added to the other input terminal (input terminal of the subtraction value) of the device GA2.

  A constant Xd (threshold for determining the black level) held in the register RG1 is added to the input terminal B of the comparators CA1, CA2, and CA3. When the input value of A is smaller than the input value of the input terminal B, the output is set to the logic H level. In other cases, the output is set to the logic L level. The outputs of CA1, CA2 and CA3 are respectively applied to the input terminals of a 3-input AND circuit AN.

  The AND circuit AN sets the output to the logic H level when all three input terminals are at the logic H level, and sets the output to the logic L level in all other cases.

  Therefore, the output signal S1 of the AND circuit AN for the pixel in which all of the red read data RD, the green read data GD, and the blue read data BD are smaller than the constant Xd, that is, for the pixel determined to be a black pixel. Becomes a logic H level.

  The output signal S1 of the AND circuit AN is applied to the shift register SR1. The shift register SR1 stores an output signal S1 corresponding to a pixel of interest X to be subjected to dust determination and Sd pixels (threshold for the number of pixels colored in the main scanning direction) before and after the pixel of interest X.

  Accordingly, in the shift register SR1, in the range of Sd pixels before and after the target pixel X, “1 (= logic H level)” is set for pixels that are determined as black pixels, and “0 (= logic level) is set for other pixels. "L level)" is stored.

  The subtractor GA1 calculates (RD-GD), and its output is applied to the input terminal A of the comparator CB1. The subtractor GA2 calculates (GD-BD), and its output is applied to the input terminal A of the comparator CB2. The subtractor GA3 calculates (BD-RD), and its output is applied to the input terminal A of the comparator CB3.

  A constant Dd (threshold value of RGB data difference) held in the register RG2 is added to the input terminal B of the comparators CB1, CB2, and CB3. The comparators CA1, CA2, and CA3 are input to the input terminal A. When the value is larger than the input value of the input terminal B, the output is set to the logic H level. In other cases, the output is set to the logic L level. The comparators CB1, CB2 , CB3 are respectively applied to the input terminals of a three-input OR circuit RR.

  The OR circuit RR sets its output signal S2 to a logic H level when a signal applied to any input terminal becomes a logic H level, and outputs an output when a signal applied to all the input terminals becomes a logic L level. Signal S2 is set to logic L level.

  Therefore, the output signal S2 of the OR circuit RR becomes a logic H level for a pixel that satisfies the relationship of (RD-GD)> Dd or (DG-DB)> Dd or (DB-DR)> Dd.

  The output signal S2 of the OR circuit RR is applied to a shift register SR2 having the same number of transfer stages as the shift register SR1.

  Therefore, in the shift register SR2, regarding the range of the Sd pixels before and after the target pixel X, “RD-GD)> Dd or (DG-DB)> Dd or (DB-DR)> Dd regarding the pixels satisfying the relationship. “1 (= logic H level)” and “0 (= logic L level)” are stored for the other pixels.

  The stored value of the shift register SR1 and the stored value of the shift register SR2 are respectively added to the data comparison processing unit MM. For each pixel position, the data comparison processing unit MM checks whether or not there is a pixel having a stored value of “1” in the shift register SR1 and a stored value of “1” in the shift register SR2, and satisfies the relationship. When there is one or more, the output signal S3 is set to "1", otherwise the output signal S3 is set to "0". The output signal S3 of the data comparison processing unit MM is applied to a shift register SR3 having the same number of transfer stages (m) as the number of main scanning pixels.

  Therefore, the output signal S3 of the data comparison processing unit MM corresponds to the result of the determination 104 in FIG. That is, the determination result “YES” corresponds to the value “1” of the signal S3, and the determination result “NO” corresponds to the value “0” of the signal S3.

  For this reason, the result of the determination 104 is held in the shift register SR3 for each pixel position for one line. The holding value at each pixel position of the shift register SR3 is added to the input terminal EN of the counters CT1 to CTm.

  The counters CT1 to CTm have the value of the input terminal EN at the rising timing of the clock SC (substantially output at every one line cycle) output at the timing after completion of processing for one line of the data comparison processing unit MM. Counts up when the logic H level (= “1”), and clears the count value when the value of the input terminal EN is at the logic L level (= “0”) at the rising timing of the clock SC. Is done.

  Therefore, the counters CT1 to CTm hold the number of continuous lines for the pixel position where the result of determination 104 is YES.

  The count values of the counters CT1 to CTm are added to the input terminal A of the comparators CC1 to CCm. A constant Fd (threshold of the number of lines colored in the sub-scanning direction) held in the register RG3 is added to the input terminal B of the comparators CC1 to CCm, and the comparators CC1 to CCm are connected to the input terminal A. When the input value is equal to or higher than the input value at the input terminal B, the output is set to the logic H level. In other cases, the output is set to the logic L level. The comparators CC1 to CCm Are added to the data correction unit PA.

  Therefore, the outputs of the comparators CC1 to CCm correspond to the result of determination 105 in FIG. That is, the result “YES” of determination 105 corresponds to the output value “1” of the comparators CC1 to CCm, and the result “NO” of determination 109 corresponds to the output value “0” of the comparators CC1 to CCm.

  On the other hand, the red read data RD, the green read data GD, and the blue read data BD are respectively added to the data rewriting unit PB having a line buffer of a plurality of lines. Then, the data correction unit PA controls the data rewriting unit PB for the pixel positions where the outputs of the comparators CC1 to CCm are “1”, and the values correspond to the white pixels within the range of the peripheral Sd pixels. The value is rewritten (corresponding to processing 106).

  As a result, the red read data DR, the green read data DG, and the blue read data DB output from the data rewriting unit PB become image read data from which the influence of dust is removed, and are output to the next-stage device.

  In the embodiment described above, dust is detected by paying attention to the color change in the main scanning direction of the CCD line image sensor 20 that has read the dust. However, other methods can be used as the dust detection method. be able to.

  For example, as shown in FIG. 12, when considering a case where a black vertical line image on a read original is read by the CCD line image sensor 20, the leading edge of the black vertical line image is initially only the blue CCD line image sensor 20B. (Reading color is “cyan”), and after 4 lines, it is read by the blue CCD line image sensor 20B and the green CCD line image sensor 20G (reading color is “blue”). Reading is performed by the CCD line image sensor 20B, the green CCD line image sensor 20G, and the red CCD line image sensor 20R (the reading color is “black”).

  Considering the rear end of the black vertical line image, when the rear end passes through the blue CCD line image sensor 20B, the black vertical line is read by the green CCD line image sensor 20G and the red line image sensor 20R (reading). After 4 lines, the trailing edge of the black vertical line passes through the green CCD line image sensor 20G, so the black vertical line is read only by the red CCD line image sensor 20R (the read color is “ yellow").

  Therefore, considering the read color before the line-to-line correction of the CCD line image sensor 20, the black vertical line image represents a color change as shown in FIG.

  However, when dust is adhered, as shown in FIGS. 5 to 7, dust is detected simultaneously by the red CCD line image sensor 20R, the green CCD line image sensor 20G, and the blue CCD line image sensor 20B. In the stage before the interline correction, as shown in FIG. 13B, the read color is “black” from the beginning to the end.

  Therefore, as shown in FIG. 14, the red reading signal PR, the green reading signal PG, and the blue reading signal PB output from the color CCD line image sensor 20 are converted into comparators CP1 and CP2, respectively, before the line-to-line correction. , CP3 and the threshold value TH output from a signal generator (not shown), the outputs of the comparators CP1, CP2, CP3 are added to the 3-input AND circuit AN2, and the outputs of the comparators CP1, CP2, CP3 are When all are at logic H level, the output signal SG of the AND circuit AN2 rises to logic H level.

  The signal SG is applied to the selection control signal terminals of the selectors SL1, SL2, and SL3 and is output to the controller unit UN1. A white value WT output from a signal generator (not shown) is added to one input terminal A of the selectors SL1, SL2, and SL3, and a red reading signal PR, a green reading signal PG, In addition, a blue reading signal PB is added.

  The selectors SL1, SL2, and SL3 output the red reading signal PR, the green reading signal PG, and the blue reading signal PB applied to the input terminal B, respectively, when the signal SG is at the logic L level. When the signal SG is at the logic H level, that is, when dust is detected, the white value WT added to the input terminal A is output.

  The output signals from the selectors SL1, SL2, and SL3 are corrected as red read signal PR, green read signal PG, and blue read signal PB, respectively, as analog signal processing units (AFE (analog front end)) 41, 42, 43.

  The analog signal processing units (AFE (Analog Front End)) 41, 1, 42, and 43 perform predetermined image signal processing and analog / digital processing for the red reading signal PR, the green reading signal PG, and the blue reading signal PB, respectively. A conversion process is applied. The output signal of the analog signal processing unit 41 is applied to the image processing unit 44, and the output signals of the analog signal processing units 42 and 43 are applied to the image processing unit 44 via the inter-line correction memories 45 and 46.

  Here, as long as the value of the threshold TH is a value suitable for detecting dust, it can be set to an appropriate value with a smaller value rather than a value for determining the black value. It is preferable to determine by experiment according to the necessity of detecting what kind of dust.

  FIG. 15 shows an example of processing of the controller unit UN1 when performing a document reading operation in this case.

  When the user sets a document on the automatic document transport unit 1a (process 201), turns on the start key (not shown) of the operation display unit UN2 and instructs the start of a reading operation (the result of determination 202 is YES). The read original is fed (process 203), and the reading operation is started (process 204).

  Then, a reading operation for one page is performed (NO loop of processing 205 and determination 206). When the reading operation for one page is completed (the result of determination 206 is YES), the read original is discharged (process 207).

  Here, during the reading operation for one page, it is checked whether or not the signal SG has changed to the logic H level to check whether dust has been detected (decision 208). If no dust is detected and the result of determination 208 is NO, it is checked whether or not the next page is set in the automatic document feeder unit 1a (decision 209), and when the result of determination 209 is YES. Returning to the process 203, the next document is fed to read the document image.

  Further, when all the document reading operations are completed and the result of determination 209 is NO, the image reading operation at this time is ended.

  On the other hand, when the dust detection is confirmed and the result of determination 208 is YES, a guidance message that prompts the user to clean the contact glass 10 is displayed (processing 210, NO loop of determination 211). If the user opens the pressure plate (automatic document conveyance unit 1a), cleans the contact glass 10, and returns the pressure plate in response to the display of the guidance message, whether or not the next page is set in the automatic document conveyance unit 1a. When the result of determination 212 is YES, a guidance message prompting the user to turn on the start key is displayed (processing 213), and the process returns to determination 202 to read the next original image. Move to operation.

  Further, when all the document reading operations are completed and the result of determination 212 is NO, the image reading operation at this time is terminated.

  In this way, in this embodiment, at the end of reading one page of the document image, if dust is detected during image reading of the page, the user is prompted to clean the contact glass 10. Therefore, the influence of dust can be suppressed as much as possible.

  In the above-described embodiment, the case where the color CCD line image sensor 20 having three reading lines is used has been described. However, a CCD line image sensor having two reading lines, or four or more CCD line image sensors. The present invention can be similarly applied to the case where a CCD line image sensor having a reading line is used.

  In the above-described embodiments, the case where the present invention is applied to the image reading apparatus has been described. However, the present invention is similarly applied to an image processing apparatus and an image forming apparatus having a color document reading function. Can do.

1 is a block diagram showing an example of an image forming apparatus according to an embodiment of the present invention. 1 is a schematic configuration diagram showing a schematic configuration of an image reading apparatus (scanner unit UN5) 1 according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram for explaining an example of a configuration of a color CCD line image sensor 20. 1 is a block diagram showing an example of a read signal processing system of an image reading apparatus according to an embodiment of the present invention. Schematic for demonstrating an example of dust detection. Schematic for demonstrating the other example of dust detection. Schematic for demonstrating the further another example of dust detection. Schematic for demonstrating the relationship between reading data and a color (reading value). The flowchart which showed an example of the dust detection method. FIG. 10 is a block diagram showing an example of a configuration for realizing the dust removal processing of the flowchart shown in FIG. 9 in hardware (continuing to FIG. 10). FIG. 10 is a block diagram showing an example of a configuration for realizing the dust removal process of the flowchart shown in FIG. 9 in hardware (continuation of FIG. 10). FIG. 3 is a schematic diagram for explaining a case where a black vertical line image on a read document is read by a CCD line image sensor. Schematic which illustrated the comparison with the color change at the time of black vertical line reading (before correction between lines), and the reading mode at the time of dust reading. FIG. 3 is a block diagram illustrating an example of dust detection and reading signal correction. The flowchart which showed an example of the process of controller unit UN1 when performing original reading operation | movement.

Explanation of symbols

20 Color CCD Line Image Sensor 25, 26, 27 Analog Signal Processing Unit 28 Buffer Memory 29 Dust Detection Processing Unit 30 Data Correction Circuit

Claims (8)

A document reading apparatus provided with a line image sensor that conveys an image on a contact glass in a sub-scanning direction and reads an image for a plurality of lines in a main scanning direction at a reading position of the contact glass,
There is a first pixel in which the reading values of the plurality of reading data respectively output from the plurality of reading lines in the same main scanning period are smaller than a predetermined black threshold, and the difference between any two reading values A neighboring pixel having a value greater than a predetermined threshold is present around the first pixel, and the first pixel is present at the same pixel position in a predetermined number of consecutive main scanning periods; and An original reading apparatus, wherein read data of a predetermined number of pixels following the adjacent pixels is replaced with white pixel data. A document reading apparatus provided with a line image sensor that conveys an image on a contact glass in a sub-scanning direction and reads an image for a plurality of lines in a main scanning direction at a reading position of the contact glass,
There is a first pixel in which the reading values of the plurality of reading data respectively output from the plurality of reading lines in the same main scanning period are smaller than a predetermined black threshold, and the difference between any two reading values Are adjacent pixels around the first pixel, and the first pixel exists at the same pixel position in a predetermined number of main scanning periods,
When a plurality of the first pixels are determined, the read data of the pixels sandwiched between the first pixels and including the adjacent pixels are replaced with white pixel data. Document reader.   3. The document reading apparatus according to claim 1, wherein the line image sensor has a color separation function of three primary colors and includes three reading lines.   4. The document reading apparatus according to claim 1, wherein the predetermined number of the continuous main scanning lines is set according to a reading magnification.   4. The document reading apparatus according to claim 3, wherein the predetermined black threshold value, the predetermined threshold value, and the predetermined number are set to different values in the monochrome reading mode and the color reading mode, respectively. A document reading apparatus provided with a line image sensor that conveys an image on a contact glass in a sub-scanning direction and reads an image for a plurality of lines in a main scanning direction at a reading position of the contact glass,
Dust detection means for detecting as dust detection that all of the outputs from the plurality of line image sensors are larger than a predetermined threshold;
An original reading unit comprising: an output value rewriting unit that rewrites the output from the plurality of line image sensors to a value corresponding to a white pixel value for a pixel in which the dust detection unit detects dust detection. apparatus.   When the dust detection unit detects dust detection while reading one page of the document image, the display unit further includes a display unit for displaying the detection of dust after reading the document image of the page. The document reading device according to claim 6. An image forming apparatus for forming an image read by a document reading device on a recording sheet,
An image forming apparatus comprising the document reading device according to claim 1 as the document reading device.