JP2006101288A - Image reading apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image reading apparatus for decreasing the noise generated in images due to dust found on original platen. <P>SOLUTION: The image reading apparatus includes line sensors; an original platen; a mobile mechanism for moving the original platen with respect to the line sensors; a dust size detection section for moving the original platen over an entire movable range of the original platen, before reading the original to extract a dust size, while moving the original platen; a degree of dirt calculation section for determining the degree of dirt by each relative position of the original platen, on the basis of the extracted dust size and the relative position of the original platen; a noise detection processing section for detecting noise, while the line sensors scan the carried original; and a selector 313 for detecting the relative position of the original platen, when the line sensors read the original, with respect to the line sensors and selecting the output of a first detection section 310 or the output of a second detection section 320, in response to the degree of dirt corresponding to the detected relative position. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image reading apparatus, and more particularly to an image reading apparatus that reads an original while conveying the original.

  Conventionally, a so-called panning technique has been used in an image reading apparatus such as a digital copying machine. In this technique, a document is read by conveying the document in a sub-scanning direction orthogonal to the line sensor with respect to a fixed line sensor.

  In this image reading apparatus, a transparent document table is provided between the document and the line sensor in order to fix the reading position of the conveyed document. Light reflected from the document is received by the line sensor via the document table.

  Therefore, when foreign matters such as dust, paper dust, dust, and scratches (hereinafter collectively referred to as “dust”) adhere to the reading position of the document table, they are conveyed by the line sensor. While reading a document, dust is always read. Therefore, there has been a problem that streak noise in the sub-scanning direction is generated in the output image.

  An image reading apparatus that reads a document conveyed while vibrating the document table in the main scanning direction in order to detect noise generated due to dust adhering to the reading position of the document table glass from the read image -278485 (Patent Document 1). This image reading apparatus detects a specific waveform appearing in an image as noise generated by reading dust.

However, since the image reading apparatus described in Japanese Patent Laid-Open No. 2000-278485 detects a specific waveform appearing in an image by pattern matching, it is erroneously detected when such a pattern is drawn on a document. There was a problem such as.
JP 2000-278485 A

  The present invention has been made to solve the above-described problems, and it is an object of the present invention to provide an image reading apparatus with improved accuracy in detecting noise generated in an image due to dust existing on a document table.

  In order to achieve the above-described object, according to one aspect of the present invention, an image reading apparatus includes a line sensor for scanning a document in the sub-scanning direction, a document table that forms a part of a document transport path, and A moving means for moving the document table relative to the line sensor; a position detecting means for detecting a relative position of the document table with respect to the line sensor; and an entire movable range of the document table before reading the document. Extraction means for extracting a feature pixel having a predetermined feature from data output from the line sensor while moving the document table, and the extracted feature pixel and the feature pixel are extracted On the basis of the relative position of the document table at the time when the read data is read by the line sensor, a contamination level determination unit for determining the contamination level for each relative position of the document table, a document conveyance unit for conveying the document, and the document Carrying Noise detecting means for detecting noise from data output by the line sensor while scanning the original conveyed by the means, and moving means while scanning the original conveyed by the original conveying means by the line sensor. Moves the document table, the position detection unit detects the relative position of the document table to the line sensor at the time when the line sensor reads the document, and the noise detection unit detects the degree of contamination corresponding to the detected relative position. Noise is detected from the data output by the line sensor with appropriate accuracy.

  According to the present invention, the document table is moved relative to the line sensor, and the relative position of the document table to the line sensor is detected. A feature pixel having a predetermined feature is obtained from data output from the line sensor while the document table is moved by moving the document table over the entire movable range of the document table before reading the document. Based on the extracted feature pixels and the relative position of the document table at the time of reading the extracted data of the feature pixels by the line sensor, the degree of contamination for each relative position of the document table is determined. Then, while the original conveyed by the original conveying means is scanned by the line sensor, the relative position of the original platen with respect to the line sensor at the time when the line sensor reads the original is detected, and the degree of contamination corresponding to the detected relative position is detected. Noise is detected from the data output by the line sensor with appropriate accuracy. For this reason, the greater the degree of contamination, the higher the probability that noise will be detected from the data.Therefore, the detection accuracy is increased to reduce false detections.If the probability that noise is detected is low, the detection accuracy is lowered to reduce the detection rate. Can be high. As a result, the detection rate can be improved while reducing erroneous detection.

  Preferably, the noise detection unit is a region determination unit that determines a specific region with a small amount of dust on the document table based on the determined degree of contamination for each relative position, and a first that detects noise from data output by the line sensor. According to the detection means, the second detection means for detecting noise from the data output by the line sensor with lower accuracy than the first detection means, and whether or not the detected relative position is a specific region, Switching means for switching between the output of the first detection means and the output of the second detection means.

  Preferably, the switching unit selects the output of the first detection unit when the detected relative position is in the specific region, and selects the output of the second detection unit when the detected relative position is not the specific region.

  Preferably, a plurality of line sensors are arranged at a distance in the sub-scanning direction, and the first detection means has a first level first having a predetermined characteristic from each of a plurality of data output by the plurality of line sensors. The first extraction means for extracting the feature pixels is compared with the pixels obtained by reading the same position of the document between the plurality of data, and the first feature pixel extracted from one data among the plurality of data First noise pixel detection means for detecting the data as a noise pixel on condition that the data is not the first feature pixel, and the second detection means has a predetermined feature from each of the plurality of data output from the plurality of line sensors. The second extraction means for extracting the second feature pixel at the second level is compared with the pixels that read the same position of the document between the plurality of data, and the second feature extracted from one of the plurality of data The element, for all other data and a second noise pixel detection means for detecting a noise pixel on the condition that it is not a second feature pixel, the first level is higher than the second level.

  Preferably, the first extraction means includes first edge extraction means for extracting an edge region by comparing a value calculated using the edge extraction filter with a first threshold, and the first edge extraction means The pixel included in the extracted edge region is extracted as a first feature pixel, and the second extraction means extracts the edge region by comparing the value calculated using the edge extraction filter with the second threshold value. A second edge extraction unit that extracts pixels included in the edge region extracted by the second edge extraction unit as second feature pixels, and the first threshold value is greater than the second threshold value. .

  Preferably, the first extraction unit includes a first region extraction unit that extracts a region having a small change in lightness and having a lightness difference from the surrounding region equal to or greater than a first threshold value. The second extraction means extracts a region where the change in brightness is small and the difference in brightness from the surrounding region is greater than or equal to a second threshold value. An area extraction unit is included, and the extracted area is extracted as the second feature pixel, and the first threshold value is larger than the second threshold value.

  Preferably, the noise detection means is based on the determined degree of contamination for each relative position, the specific area determination means for determining a specific area with less dust on the document table, and a threshold given from the data output from the line sensor. Noise pixel detecting means for detecting a noise pixel using a value, and when the detected relative position is a specific area, a first threshold value is given to the noise pixel detecting means, and the detected relative position is the specific area If not, it further comprises control means for giving the noise pixel detection means a second threshold value smaller than the first threshold value.

  Preferably, a plurality of line sensors are arranged at a distance in the sub-scanning direction, and the noise pixel detection unit is given a value calculated using an edge extraction filter from each of data output from the plurality of line sensors. Edge extraction means to extract the edge area compared to the threshold value, and extract the pixels included in the extracted edge area as feature pixels, and compare the pixels that read the same position of the document between multiple data Then, a feature pixel extracted from one data among a plurality of data is detected as a noise pixel on condition that it is not a feature pixel in all other data.

  Preferably, a plurality of line sensors are arranged at a distance in the sub-scanning direction, and the noise pixel detecting means is a region where the brightness change is small from each of the data output from the plurality of line sensors. A region extraction unit that extracts a region having a brightness difference from a surrounding region that is equal to or greater than a given threshold value, and extracts pixels included in the extracted region as a feature pixel; Pixels read at the same position on the document are compared, and a feature pixel extracted from one of a plurality of data is detected as a noise pixel on condition that it is not a feature pixel in all other data.

  Preferably, the contamination degree determination unit includes a size detection unit that detects a continuous number of feature pixels for each relative position of the document table.

  Preferably, the stain level determination unit includes a brightness detection unit that detects the brightness of the feature pixel for each relative position of the document table. Preferably, a plurality of line sensors are arranged at a distance in the sub-scanning direction, and the contamination degree determination unit reads the extracted feature pixels and the data from which the feature pixels are extracted by the plurality of line sensors. Size determining means for determining the number of consecutive feature pixels for each relative position of the document table based on the relative position of the document table, and the noise detecting means is configured to determine whether the document is based on the determined size for each relative position. Specific area determining means for determining a specific area with a small amount of dust and a plurality of edge extraction filters corresponding to the size of the edge area to be extracted, and using all or any one of the plurality of edge extraction filters An edge area is extracted by comparing the calculated value with a threshold value, and an edge extraction means for extracting a pixel included in the extracted edge area as a feature pixel; Noise pixel detection means for comparing pixels that have read the same position and detecting a feature pixel extracted from one of a plurality of data as a noise pixel on the condition that it is not a feature pixel in all other data In the case where the detected relative position is a specific area, the edge extraction means is used to extract the edge area using all edge extraction filters, and when the detected relative position is not the specific area, the detected relative position is Control means for extracting an edge region using an edge extraction filter corresponding to the consecutive number of feature pixels is further provided.

  Preferably, a plurality of line sensors are arranged at a distance in the sub-scanning direction, and the contamination degree determination unit reads the extracted feature pixels and the data from which the feature pixels are extracted by the plurality of line sensors. Size determining means for determining the number of consecutive feature pixels for each relative position of the document table based on the relative position of the document table, and the noise detection means includes a plurality of edges corresponding to the size of the edge region to be extracted. The extracted edge region has an extraction filter, compares the value calculated using the edge extraction filter corresponding to the consecutive number of feature pixels at the detected relative position with a threshold value, and extracts the edge region The edge extraction means for extracting the pixels included in the image as feature pixels and the pixels obtained by reading the same position of the document between the plurality of data are compared, and the feature image extracted from one of the plurality of data And for all other data and a noise pixel detection means for detecting a noise pixel on the condition that it is not a feature pixel.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

  FIG. 1 is a perspective view of an MFP (Multi Function Peripheral) provided with an image reading apparatus according to one embodiment of the present invention. Referring to FIG. 1, the MFP includes an image reading device 10 for reading a document image and an image forming device 20 provided at a lower portion of the image reading device 10. The MFP forms an image read by the image reading apparatus 10 on a recording medium such as paper. The MFP also includes a communication interface for connecting to a network such as a facsimile device, a local area network (LAN), or a public line.

  FIG. 2 is a diagram showing an outline of the internal configuration of the image reading apparatus 10. The image reading apparatus 10 includes an automatic document feeder (ADF) 101 for automatically feeding a document to a document reading position, and a main body 103. The automatic document feeder 101 conveys a document that has passed through the reading position, an upper regulating plate 203 for guiding the conveyance of the document in the vicinity of the document reading position, a pair of timing rollers 201 for conveying the document to the document reading position, and the like. And a roller pair 202 for the purpose.

  The main body 103 includes a document table 205 made of a transparent member, a paper passing guide 207 that forms part of the document transport path, a light source 206 for irradiating the document at a reading position, and light from the light source. A reflection member 208 that reflects the light beam, a reading unit 213 in which three line sensors are arranged in the sub-scanning direction, a reflection mirror 209 that reflects reflected light from the document and guides it to the reading unit 213, and the reflection mirror 209. A lens 211 for forming an image of the reflected light on the reading unit 213, an image processing unit 215 for processing an electric signal output from the reading unit 213, a motor 219 for moving the document table 205, and an image A motor control unit 217 that controls driving of the motor 219 based on a control signal from the processing unit 215.

  The document 200 is conveyed between the document table 205 and the upper regulating plate 203 in the direction of the arrow D1 by the timing roller pair 201. The image is sequentially read by the reading unit 213 at the reading position L while being conveyed. The direction in which the document is conveyed by the automatic document conveying device 101 is the sub-scanning direction at the reading position L. During the image reading operation, the document table 205 is moved by the motor 219 in the direction of the arrow D2. The moving direction of the document table 205 is substantially parallel to the sub-scanning direction.

  The surface of the upper regulating plate 203 on the side of the document table 205 is a gray achromatic color.

  The reading unit 213 includes three line sensors. Each of the three line sensors has a plurality of photoelectric conversion elements arranged in a main scanning direction substantially perpendicular to the sub-scanning direction. Each of the three line sensors has filters having different spectral sensitivities, and receives light reflected from the document through the filters. Specifically, a filter that transmits light of each wavelength of red (R), green (G), and blue (B) is included. For this reason, the line sensor having a red (R) filter outputs an electric signal (R signal) indicating the intensity of red light out of the light reflected from the document, and the line sensor having a green (G) filter is The line sensor having a blue (B) filter that outputs an electric signal (G signal) indicating the intensity of green light out of the light reflected from the original, calculates the intensity of blue light out of the light reflected from the original. The electric signal (B signal) shown is output.

  The three line sensors are arranged in a predetermined order at a predetermined distance in the sub-scanning direction. Here, the document reading lines are arranged in the order of red, green, and blue in the document transport direction with a distance of 3 lines in terms of the document reading line. In addition, the space | interval and order which arrange | position a line sensor are not limited to these.

  Since the three line sensors are arranged in the order of red, green, and blue at a distance of three lines, the three line sensors receive light reflected at different positions on the document at the same timing. Therefore, the light reflected at a certain position on the document is first received by a line sensor that receives red light, then received by a line sensor that receives green light, and finally received by a line sensor that receives blue light. Received light. This delay is adjusted by an image processing unit 215 described later.

  In the present embodiment, the reading unit 213 is provided with three line sensors. However, four or more line sensors may be provided.

  FIG. 3 is a perspective view showing a mechanism for moving the document table. Referring to FIG. 3, document table 205 is held by document table holder 221. The document table holder 221 is held by the guide 220 so as to be slidable in the sub-scanning direction. The guide 220 is fixed to the main body of the image reading apparatus 10. Two arms 222 are joined to one surface of the document table holder 221. The other end of the arm 222 has a circular hole.

  Two cams 223 are attached to the shaft 224 at positions corresponding to the two arms 222. A gear 225 is attached to one end of the shaft 224. The gear 225 is disposed so as to mesh with a gear 226 joined to the drive shaft of the motor 219 with a belt. When the motor 219 rotates, the rotation is transmitted to the gear 226 via the belt, and the gear 226 rotates. As the gear 226 rotates, the gear 225 and the shaft 224 rotate.

  The cam 223 is disposed in the circular hole of the arm 222. Therefore, the rotational motion of the two cams 223 accompanying the rotation of the shaft 224 is converted into the reciprocating motion of the document table holder 221.

  Note that the mechanism for moving the document table 205 is not limited to this, and may be a mechanism using a drive source that generates a linear motion such as a piston using an electromagnet, air pressure, hydraulic pressure, or the like.

  The document table 205 is moved in parallel with the sub-scanning direction. While the document table 205 is moving in the direction opposite to the document conveyance direction, the document table 205 is moved in the direction opposite to the document, so that the relative speed of the document table 205 with respect to the line sensors 213R, 213G, and 213B, The relative speed of the document with respect to the line sensors 213R, 213G, and 213B is different. In the present embodiment, the document table 205 is moved in the direction opposite to the document conveyance direction while the document is being read. However, the document table 205 may be moved in the document conveyance direction. In this case, the direction of the document table 205 and the document conveyance speed are the same. It is preferable to vary the speed. Here, the document table 205 is moved in parallel with the sub-scanning direction, but the direction is not limited to this.

  Here, the principle that the image reading apparatus 10 according to the present embodiment detects noise generated by dust attached to the document table 205 from the read image will be described. FIG. 4 is a diagram for explaining the principle of detecting noise generated by reading dust from a read image. Here, the document and document table 205 are conveyed in the direction of the arrow in the figure, and the movement speed of the document table 205 is the same as the document conveyance speed and is twice as fast. The three line sensors are arranged in the order of a line sensor that receives red light, a line sensor that receives green light, and a line sensor that receives blue light at a distance of three lines in the document conveyance direction. It is assumed that The output of the line sensor that receives red light is indicated by R, the output of the line sensor that receives green light is indicated by G, and the output of the line sensor that receives blue light is indicated by B.

  FIG. 4A is a diagram for explaining line-to-line correction. First, a partial image of a document is read by a line sensor that receives red light arranged at the most upstream in the document transport direction. Then, the image of the original is conveyed by a distance of 4 lines and read by a line sensor that receives green light. Further, the image of the original is conveyed by a distance of 4 lines and read by a line sensor that receives blue light.

  As described above, since images at the same position on the document are read by the three line sensors at different timings, timing deviations occur in signals output from the three line sensors. In the interline correction, the timings of the signals output from the three line sensors are matched so that each signal is at the same position on the document. Specifically, the output R is delayed by 8 lines, and the output G is delayed by 4 lines.

  A combined output obtained by combining the output R, the output G, and the output B corrected between the lines is an output obtained by combining the output R, the output G, and the output B read at the same position on the original.

  FIG. 4B is a diagram for explaining a composite output that is output when dust attached to the document table is read. The dust adhering to the document table 205 is first read by a line sensor that receives red light arranged at the most upstream in the document conveyance direction. Then, the dust is conveyed by a distance corresponding to four lines and read by a line sensor that receives green light. Here, the document table 205 moves in the same direction at a speed twice as high as the document conveyance speed, so that the dust moves for four lines in a time required for the line sensor to read the document for two lines. For this reason, the time when dust is read by the red line sensor and the time when dust is read by the green line sensor are shifted by the time for reading two lines. Further, the dust is conveyed by a distance of 4 lines and read by a line sensor that receives blue light. Since the document table 205 moves in the same direction at twice the speed of the document conveyance, there are two points when the dust is read by the green line sensor and when the dust is read by the blue line sensor. The time for reading the line is shifted.

  Then, due to the interline correction, the output R that the line sensor that receives red light reads and outputs dust is delayed by 8 lines, and the output G that the line sensor that receives green light reads and outputs dust is 4 Delayed by line. Therefore, in the combined output obtained by combining the output R, the output G, and the output B corrected between lines, if the output R from which dust is read, the output G from which dust is read, and the output B from which dust is read are at the same timing. No, two lines are misaligned

  In the figure, white dust such as paper dust is attached to the document table 205, and a combined output when a black document is read is shown. In this case, although white dust is read, the composite output is not white but blue, green, and red divided into three lines.

  FIG. 4C is another diagram for explaining a composite output that is output when dust attached to the document table is read. FIG. 4C shows an example in which dust having a size of 10 lines is read in the sub-scanning direction. Since the document table 205 moves in the same direction at twice the document conveyance speed, dust is read as a size corresponding to five lines.

  The dust adhering to the document table 205 is first read by a line sensor that receives red light arranged at the most upstream in the document conveyance direction. Then, the dust is conveyed by a distance corresponding to four lines and read by a line sensor that receives green light. The time at which dust is read by the red line sensor and the time at which dust is read by the green line sensor are shifted by the time for reading two lines. Further, the dust is conveyed by a distance of 4 lines and read by a line sensor that receives blue light. The time when the dust is read by the green line sensor and the time when the dust is read by the blue line sensor are shifted by the time for reading two lines.

  Then, due to the interline correction, the output R that the line sensor that receives red light reads and outputs dust is delayed by 8 lines, and the output G that the line sensor that receives green light reads and outputs dust is 4 Delayed by line. Therefore, in the combined output obtained by combining the output R, the output G, and the output B corrected between lines, the output R for 5 lines from which dust is read, the output G for 5 lines from which dust is read, and the dust are read. The output B for 5 lines does not have the same timing but is shifted by 2 lines. In the figure, white dust such as paper dust is attached to the document table 205, and a combined output when a black document is read is shown. In this case, although the white dust is read, the combined output is an output in which the color changes in the order of blue, blue-green, white, yellow, and red.

  In this way, the dust adhering to the document table 205 is divided into a plurality of lines in the image. Noise is detected by extracting the divided lines as feature points for each color. Further, the noise generated by reading the dust by being divided is reduced.

  FIG. 5 is a plan view of the document table viewed from the back side. Referring to FIG. 5, document table 205 has a mark 205A at one end. The mark 205 </ b> A has a shape in which the length in the main scanning direction varies depending on the position in the sub-scanning direction and is a single color. Here, the mark 205A has a triangular shape and is black. Further, one side of the mark 205A is arranged in parallel with one side of the document table 205.

  By using the reading unit 213 or using a sensor provided separately from the reading unit 213 and fixed to the main body unit 103, the length of the mark 205A in the main scanning direction is detected, thereby reading the document table 205. It is possible to detect a relative position with respect to the part 213.

  FIG. 6 is a diagram showing a position on the document table 205 read by the reading unit 213. The reading unit 213 includes a line sensor 213R having a red (R) filter, a line sensor 213G having a green (G) filter, and a line sensor 213B having a blue (B) filter. Are arranged in the order of the line sensors 213R, 213G, and 213B.

  The line sensor 213R receives light transmitted through the region 205R of the document table 205. The line sensor 213G receives light transmitted through the region 205G of the document table 205. The line sensor 213B receives light transmitted through the area 205B of the document table 205. In the areas 205R, 205G, and 205B, the line sensors 213R, 213G, and 213B are arranged so as to have an interval of three lines. The document first passes through the region 205R, then passes through the region 205G, and finally passes through the region 205B. Therefore, the light reflected at a certain position of the document is first received by the line sensor 213R that receives red light, then received by the line sensor 213G that receives green light, and finally the line that receives blue light. Light is received by the sensor 213B. As described above, the line sensors 213R, 213G, and 213B are arranged at a distance of three lines, so that the line sensors 213R, 213G, and 213B do not receive the light reflected at the same position on the document at the same time. .

  Here, it is assumed that dust 300 having a maximum length of 4 lines or less adheres on the document table 205. In this case, since the document table 205 moves parallel to the sub-scanning direction, the dust 300 does not exist in two or more of the areas 205R, 205G, and 205B at the same time. FIG. 6 shows a case where the dust 300 exists in the area 205G. In this case, the light reflected by the dust 300 is received only by the line sensor 213G and not received by the line sensors 213R and 213B.

  Further, the area where the dust 300 is present due to the movement of the document table 205 is the area 205R first, then the area 205G, and the last when the document table 205 is moved in the document transport direction D1. Changes in the order of the region 205B. Conversely, when the document table 205 moves in the direction opposite to the document conveyance direction D1, the area changes first in the order of the area 205B, then in the area 205G, and finally in the area 205R.

  Therefore, the order in which the light reflected by the dust 300 is received is the line sensor 213R first, then the line sensor 213G, and finally the line sensor 213B when the document table 205 is moved in the document transport direction D1. . When the document table 205 is moved in the direction opposite to the document conveyance direction D1, the line sensor 213B is first, the line sensor 213G is next, and finally the line sensor 213R.

  FIG. 7 is a block diagram illustrating a configuration of an image processing unit of the image reading apparatus according to the present embodiment. Referring to FIG. 7, R signal, G signal, and B signal are input from reading unit 213 to image processing unit 215. The image processing unit 215 includes an analog / digital conversion unit (A / D conversion unit) 251 for converting an analog signal input from the reading unit 213 into a digital signal, and shading correction for correcting illumination unevenness of the light source 206. A unit 253, an interline correction unit 255 for synchronizing the R signal, the G signal, and the B signal to be on the same line of the document, and a chromatic aberration correction unit 257 for correcting distortion in the main scanning direction caused by the lens 211. Before reading a document, the document table 205 is read to detect dust adhering to the document table 205, and a pre-read detection unit 271 detects noise from each of the R signal, G signal, and B signal. A processing unit 259, a noise correction unit 260 that executes a process of correcting noise pixels, a control unit 263 for controlling the entire image processing unit 215, an image And a printer interface 261 for outputting to an image forming apparatus 20.

  The interline correction unit 255 delays the R signal by 8 lines and delays the G signal by 4 lines, thereby synchronizing the R signal, the G signal, and the B signal to be on the same line of the document. As described above, the line sensors 213R, 213G, and 213B are arranged at a distance of three lines in the sub-scanning direction.

  The pre-reading detection unit 271 receives the R signal, the G signal, and the B signal from the chromatic aberration correction unit 257, and receives the position of the document table 205 from the control unit 263. The pre-reading detection unit 271 detects dust attached to the document table 205. The time when the pre-reading detection unit 271 detects dust attached to the document table 205 may be any time before the document is read. For example, when the power is turned on, any time after the power is turned on, or when the start button for instructing the start of reading of the document is pressed by the user.

  The pre-reading detection unit 271 executes processing for detecting dust attached to the document table 205 based on an instruction from the control unit 263. When detecting dust adhering to the document table 205, the image reading apparatus 10 executes the following processing.

  (1) The control unit 263 outputs a movement start signal to the motor control unit 217 to move the document table 205 from the initial position. While the document table 205 is moving, the reading unit 213 reads the entire document table 205.

  (2) The size of dust attached to the document table 205 is detected from the read data. Since the document table 205 is transparent, the light reflected by the upper regulating plate 203 is received by the reading unit 213 unless dust is attached to the document table 205. If dust adheres to the document table 205, the light reflected by the dust is received by the reading unit 213. The pixel value obtained by receiving the light reflected by the upper regulating plate 203 is different from the pixel value obtained by receiving the light reflected by dust. The pre-reading detection unit 271 detects the size of dust from the continuous number of pixel values obtained by receiving light reflected by dust.

  (3) The position of dust on the document table 205 attached to the document table 205 is detected. The pre-reading detection unit 271 always receives the position of the document table 205 from the control unit 263. Therefore, the pre-reading detection unit 271 detects the position of the document table 205 when dust is detected from the signal output from the reading unit 213.

  (4) The pre-reading detection unit 271 determines a use area with less dust from the document table 205 based on the size and position of the document table 205 and outputs the use area to the control unit 263.

  When reading the document, the control unit 263 controls the motor control unit 217 and the ADF control unit 273 to move the document table 205. As a result, the document table 205 is reciprocated once by a movement at the time of reading and a movement at the time of return in one reading operation of the document. Further, the reciprocation may be performed a plurality of times in one document reading operation.

  The noise detection processing unit 259 receives the R signal, the G signal, and the B signal from the chromatic aberration correction unit 257, and receives the position of the document table 205 and the moving direction of the document table 205 from the control unit 263. The noise detection processing unit 259 detects a noise pixel for each of the R signal, G signal, and B signal input from the chromatic aberration correction unit 257. Then, a logic signal in which the noise pixel is “1” and the other pixels are “0” is output to the noise correction unit 260 and the control unit 263. Details thereof will be described later.

  The noise correction unit 260 receives the R signal, the G signal, and the B signal from the chromatic aberration correction unit 257, and the noise detection processing unit 259 outputs a logical signal that sets the noise pixel to “1” and the other pixels to “0”. Are input for each of the R signal, the G signal, and the B signal.

  The noise correction unit 260 determines the color of a pixel that is a noise pixel from logic signals corresponding to the R signal, the G signal, and the B signal. At this time, the color of the noise pixel continuous in the sub-scanning direction is determined. If the noise pixels are not continuous in the sub-scanning direction, the color of the pixel between the two noise pixels is determined. Then, when the color change in the sub-scanning direction is in the following order at the same position in the main scanning direction, all of those pixels are set as noise pixels.

(1) CBMRY or YRMBC
(2) CBKRY or YRKBC
(3) RYGCB or BCGYR
(4) RYWCB or BCWYR
However, R is red, G is green, B is blue, C is blue-green, M is magenta, Y is yellow, K is black, and W is white. Here, only the order of color change is shown, and two or more pixels of the same color may be continuous. For example, the color may change from CCBBMMRRYY.

  As a result, even if the size of dust is simultaneously read by a plurality of line sensors, here, it is possible to detect noise caused by reading the dust.

  In addition, the noise correction unit 260 replaces the pixel value determined as a noise pixel with the pixel value of a pixel that is not a surrounding noise pixel based on the corresponding logic signal for each of the R signal, the G signal, and the B signal. The average value, maximum value, or minimum value of a plurality of pixels that are not surrounding noise pixels may be replaced. The noise correction unit 260 outputs an R signal, a G signal, and a B signal obtained by replacing the noise pixel with surrounding pixels to the printer interface.

  In the control unit 263, the position of the document table 205 is input from the position detection unit 265, and a logic signal is input from the noise detection processing unit 259 that sets the noise pixel to “1” and the other pixels to “0”. The control unit 263 specifies the position of dust on the document table 205 from these signals. More specifically, the position of the document table 205 in the sub-scanning direction is specified from the position of the document table 205 and the line number of the logic signal, and the position of the document table 205 in the main scanning direction is determined from the position of the noise pixel of the logic signal. Identify.

  FIG. 8 is a block diagram illustrating a schematic configuration of the pre-reading detection unit. Referring to FIG. 8, pre-reading detection unit 271 includes a peak value detection unit 291 for detecting a peak value from input R, G, and B signals, and a dust size for detecting the size of dust. The detection unit 292, a dust information storage memory 293 for storing the detected dust size and the position of the document table 205 in association with each other, and the contamination for each position of the document table 205 based on the dust size and the position of the document table 205. A degree-of-dirt calculation unit 294 for calculating the degree of use; and a use region determination unit 295 for determining a use region that is a partial region of the document table 205 and is used for reading by the reading unit 213 from the calculated degree of stain. including.

  The peak value detector 291 receives RGB signals for each line. The peak value detection unit 291 performs the following process for each pixel on the input RGB signal of one line.

  (1) A maximum value and a minimum value are selected from RGB signals.

  (2) If the maximum value is less than or equal to the threshold value for detecting black dust, the pixel is determined to be a pixel from which dust has been read.

  (3) If the minimum value is greater than or equal to the threshold value for detecting white dust, the pixel is determined as a pixel from which dust has been read.

  (4) Output to the dust size detection unit 292 a logic signal that sets the value of the pixel from which the dust has been read to “1” and the value of the pixel that has not been read from the dust to “0”. To do.

  The dust size detection unit 292 receives a logical signal that sets the value of the pixel from which dust is read from the peak value detection unit 291 as “1”. The dust size detection unit 292 detects the size of dust from the number of consecutive pixels from which dust has been read. For example, if the value “1” continues three times, the size of the dust is set to 3 pixels. Then, the detected dust size and the position of the document table 205 are associated with each other and stored in the dust information storage memory 293. The garbage information storage memory 293 may be a non-volatile semiconductor memory such as a random access memory (RAM). The dust information storage memory 293 stores dust information that associates the size of dust obtained by reading the entire range in which the document table 205 can be moved in the sub-scanning direction with the reading unit 231 and the position of the document table 205. .

  The degree-of-dirt calculation unit 294 stores a weighting coefficient table 296 in advance. The weighting coefficient table 296 is used for calculating the degree of contamination for each position of the document table 205, and defines weighting coefficients corresponding to the size of dust. The dirt level calculation unit 294 reads dust information from the dust information storage memory and calculates the dirt level for each position of the document table 205. The degree of contamination is defined by a value obtained by multiplying the weighting coefficient by the number of dust. Then, the contamination level calculation unit 294 outputs the contamination level calculated for each position of the document table 205 to the use area determination unit 295.

  FIG. 9 is a diagram illustrating an example of the weighting coefficient table. The weighting factor increases as the size of the dust increases. For the dust size of 1 to 9 pixels (dot), the weighting coefficient is defined as the square of the dust size, and for the dust size of 10 pixels (dot) or more, the weighting coefficient is defined as “255”. Is done.

  Returning to FIG. 8, the use area determination unit 295 determines an area with less dust as a use area from the degree of contamination for each position of the document table 205. Specifically, the document table 205 is divided in the sub-scanning direction by a predetermined number, and an area where the total sum of the degree of contamination is the smallest among the divided areas is used.

  FIG. 10 is a diagram showing an area obtained by dividing the document table into three in the sub-scanning direction. The arrows in the figure indicate the direction of movement of the document table. Here, the three areas obtained by dividing the document table 205 into three parts in the document table movement direction are referred to as the front region 281A, the region that moves first to the reading position, the next region as the middle region 281B, and the last region as the last region. This is referred to as a rear region 281C.

  Here, an example is shown in which the document table 205 is divided by a length equal to the document table movement direction. However, for example, the use area is determined from the distribution of the degree of contamination calculated for each position of the document table 205. May be. Specifically, the sum of the degree of contamination is calculated in the front region 281A having a length of L / 3 in the document table moving direction with respect to a document having a length of LT / 3 in the sub-scanning direction, and the front region 281A is calculated as the document table. The sum total of the degree of contamination is calculated in the region translated by one line in the direction opposite to the moving direction. Each time the front area 281A is translated by one line to the end of the document table 205, the total sum of the stain levels is calculated. Then, the region of the parallel movement amount that minimizes the total sum of the contamination levels is set as the use region.

  Further, the size of the use area may not be determined by the size of the document, but may be determined in advance, or may be determined from the distribution of the degree of contamination calculated for each position of the document table 205. When determining the size of the area to be used from the distribution of the degree of contamination calculated for each position of the document table 205, for example, the region having the maximum number of consecutive lines among the regions in which the lines having a degree of contamination equal to or less than a predetermined value are continuous. And it is sufficient.

<Modification of the detection unit before reading>
FIG. 11 is another block diagram illustrating a schematic configuration of the pre-reading detection unit. Referring to FIG. 11, the modified pre-reading detection unit 271A replaces the dust size detection unit 292 in the above-described pre-reading detection unit 271 with a dust lightness detection unit 292A, and a stain level calculation unit 294 and a weighting coefficient table 296. Is a change. Since other configurations are the same, different points will be mainly described here.

  The dust lightness detection unit 292A receives a logic signal for setting the value of a pixel from which dust is read from the peak value detection unit 291 to “1” and an RGB signal. The dust brightness detection unit 292A detects the average brightness of the brightness of pixels from which dust is read. For example, if there are three consecutive values “1” in the ethical signal, the average brightness of these three pixels is calculated. Then, dust information that associates the calculated average brightness of the dust area with the position of the document table 205 is stored in the dust information storage memory 293. The dust information storage memory 293 stores the average brightness of dust at all positions on the document table 205.

  The degree-of-dirt calculation unit 294A stores a weighting coefficient table 296A in advance. The weighting coefficient table 296A is used for calculating the degree of contamination for each position of the document table 205, and defines weighting coefficients corresponding to the brightness of dust. The stain level calculation unit 294A reads the dust information from the dust information storage memory 293, and calculates the stain level for each position of the document table 205. The degree of contamination is defined by a value obtained by multiplying the weighting coefficient by the number of dust. Then, the contamination level calculation unit 294A outputs the contamination level calculated for each position of the document table 205 to the use area determination unit 295.

  FIG. 12 is another diagram illustrating an example of the weighting coefficient table. The weighting coefficient is the smallest when the lightness of dust is the middle, and the larger the lightness, or the smaller the lightness, the larger the weighting coefficient. For a lightness of dust of “100 to 179”, a weighting coefficient “36” is defined, and for a lightness of dust of “60 to 99” and “180 to 209”, a weighting coefficient of “49” is defined. Is defined for the lightness of dust from “30 to 59” and “210 to 229”, and “64” is defined as the weighting coefficient, and for the lightness of dust from “10 to 29” and “230 to 249” Thus, “81” is defined as the weighting coefficient, and “255” is defined as the weighting coefficient for the lightness of dust “0 to 9” and “250 to 259”.

  Next, detection of noise caused by dust on the platen from the read image will be described.

  Next, the noise detection process will be specifically described. As described with reference to FIG. 6, the line sensors 213R, 213G, and 213B read different positions of the document at the same timing. The line correction unit 255 synchronizes the lines of the R signal, the G signal, and the B signal, thereby obtaining the R signal, the G signal, and the B signal obtained by reading the same position of the document.

Therefore, any one of the R signal, G signal, and B signal obtained by reading the same position of the document is affected when dust adheres to the document table 205.
FIG. 13 is a block diagram illustrating a configuration of a noise detection processing unit of the image reading apparatus according to the present embodiment. Referring to the figure, a noise detection processing unit 259 includes a first detection unit 310 for detecting a noise pixel from each of an inputted R signal, G signal, and B signal, and an inputted R signal, G signal, B A second detector 320 for detecting a noise pixel from each signal, and a selector 313 for selecting and outputting either the output of the first detector or the output of the second detector 320 are included.

  An R signal, a G signal, and a B signal are sequentially input to the first detection unit 310 line by line. The first detection unit 310 detects a noise pixel from each of the input R signal, G signal, and B signal for each line. Details of the first detection unit 310 will be described later. The first detection unit 310 outputs a logic signal in which the noise pixel is “1” and the other pixels are “0” for each line corresponding to each of the input R signal, G signal, and B signal. A logic signal corresponding to each of the R signal, the G signal, and the B signal output from the first detection unit 310 is a signal indicating the position of the noise pixel.

  The second detection unit 320 receives the R signal, the G signal, and the B signal in order line by line. The second detection unit 320 detects the noise pixel by a method with a lower accuracy of detecting the noise pixel than the first detection unit 310. In response to the detection signal for the R signal being input, the second detection unit 320 sets the noise pixel to “1” for each R signal, G signal, and B signal input for each line, and sets the other pixels to A logic signal to be “0” is output.

  The selector 313 receives position information of the document table 205 and a use area from the control unit. The position information indicates the position of the document table 205 at the reading position L at the time when the RGB signal corresponding to the logic signal output from the first detection unit 310 and the second detection unit 320 is read. The selector 313 selects and outputs the output of the first detection unit 310 when the position of the document table 205 is included in the use region, and the output of the second detection unit 320 when it is not included in the use region. Select to output. As a result, the output of the first detection unit 310 is validated for RGB signals read in a non-use area that is known to have dust in advance, and it is known that there is little or no dust. The output of the second detection unit 320 is validated for RGB signals read in the use area. Since the second detection unit 320 has lower detection accuracy than the first detection unit 310, the first detection unit 310 has fewer false detections but a lower detection rate than the second detection unit 320. In this way, for RGB signals that are expected to contain a lot of noise in advance, it is possible to reduce false detection by selecting the output of the first detection unit 310, and it is expected that there will be little noise in advance. For the RGB signals to be processed, the detection rate can be improved by selecting the output of the second detector 320. Thereby, the detection rate can be improved while reducing erroneous detection.

<First detection unit>
FIG. 14 is a diagram illustrating an example of RGB signals output by the reading unit. FIG. 14A shows an example in which black dust is attached to the area 205R corresponding to the line sensor 213R on the document table, and the white area of the document is read. When the area of the original when the line sensor 213R reads black dust moves to the areas 205G and 205B corresponding to the line sensors 213G and 213B, the dust enters the areas 205G and 205B corresponding to the line sensors 213G and 213B. Does not exist. This is because the document and the document table 205 move at different speeds. For this reason, the line sensors 213G and 213B read the white area of the document. As a result, only the R signal output from the line sensor 213R has low brightness, and the G and B signals output from the line sensors 213G and 213B have high brightness. Here, the output values of the three line sensors 213R, 213G, and 213B corresponding to the reflected light are referred to as brightness.

  The RGB signal combination shown in FIG. 14A is rarely output when a document is read in a dust-free state. The closest combination is when a blue-green region which is a complementary color of red is read. FIG. 14B is a diagram illustrating RGB signals output from the reading unit 213 when a blue-green region of a document is read. The brightness of the R signal is greatly lowered, but the brightness of the G signal and the B signal is also lowered. Therefore, a change in the brightness of the R signal whose brightness is greatly reduced can be detected using the threshold value Ref1 (R).

  There is a big difference between the RGB signal shown in FIG. 14A and the RGB signal shown in FIG. 14B whether the B signal and the G signal are affected or not. By detecting this difference, black dust can be detected as noise without erroneously detecting the blue-green line as noise. Therefore, a change in the brightness of the B signal is detected using the threshold value Ref2 (B). The threshold value Ref2 (B) may be the smallest value among the following values. In the following, threshold values Ref2 (R), Ref2 (G), and Ref2 (B) are shown.

(1) When detecting achromatic dust with high brightness When reading blue-green, which is a complementary color of red, so that a blue-green line is not erroneously detected as noise, a line other than the line sensor 213R is detected. The difference between the lightness output from one of the sensors 213G and 213B and the maximum lightness value (255) may be set as Ref2 (G) and Ref2 (B). The brightness and maximum output by either one of the line sensors 213R and 213B other than the line sensor 213G when reading the magenta complementary color of green so that the magenta line is not erroneously detected as noise. Differences from brightness (255) may be set as Ref2 (R) and Ref2 (B). In order to prevent the yellow line from being erroneously detected as noise, the brightness and maximum brightness (one of the line sensors 213R and 213G other than the line sensor 213B output when reading yellow, which is a complementary color of blue) ( And Ref2 (R) and Ref2 (G).

(2) When detecting achromatic dust having low lightness Any of the line sensors 213G and 213B other than the line sensor 213R is read when red is read so that the red line is not erroneously detected as noise. The difference between the lightness output by one and the minimum value (0) of lightness may be Ref2 (G) and Ref2 (B). The difference between the lightness output by one of the line sensors 213R and 213B other than the line sensor 213G and the minimum value (0) when green is read so that the green line is not erroneously detected as noise. Ref2 (R) and Ref2 (B) may be used. The difference between the lightness output by one of the line sensors 213R and 213G other than the line sensor 213B and the minimum value (0) when blue is read so that the blue line is not erroneously detected as noise. Ref2 (R) and Ref2 (G) may be used.

  In this way, a plurality of threshold values Ref2 (R), Ref2 (G), and Ref2 (B) can be obtained, and the minimum value thereof may be used.

  Here, detection of black dust as noise will be described, but it is possible to detect non-black dust if it is achromatic. This is because an achromatic color dust affects all of the R signal, the G signal, and the B signal.

  Although a case where a white document is read will be described as an example here, the color of the document is not limited to white and may be any color.

  FIG. 15 is a block diagram illustrating a configuration of the first detection unit of the noise detection processing unit of the image reading apparatus according to the present embodiment. Referring to FIG. 15, the first detection unit 310 includes first brightness difference detection units 301R, 301G, and 301B for extracting regions having predetermined characteristics from the input R signal, G signal, and B signal. Second lightness difference detection units 302R, 302G, and 302B, detection result expansion processing units 303R, 303G, and 303B for extending the regions extracted by the second lightness difference detection units 302R, 302G, and 302B to the periphery; Sum elements 305R, 305G, and 305B, AND elements 307R, 307G, and 307B, and detection area expansion processing units 309R, 309G, and 309B are included.

  The R signal, the G signal, and the B signal are input to the first detection unit 310 one line at a time. Note that the R signal, the G signal, and the B signal may be input together for a plurality of lines, or may be input for the entire image.

  The first lightness difference detector 301R receives the R signal and the threshold value Ref1 (R). The first brightness difference detection unit 301R extracts a region having a first level predetermined feature from the R signal. The region having the first level predetermined feature is a region where the change in lightness is small and a difference in lightness from the surrounding region is a threshold value Ref1 (R) or more. Such a region may have a size of one pixel or more. Here, a pixel included in a region having a predetermined feature at the first level is referred to as a first feature pixel.

  The region having the first level predetermined feature may be extracted using an edge extraction filter. A plurality of edge extraction filters are prepared for each size of the edge region, and the value obtained as a result of the filtering process is compared with the threshold value Ref1 (R). The pixel that satisfies the condition of the threshold value Ref1 (R) is set as the center pixel of the edge region, and the size of the edge region is obtained from the edge extraction filter that satisfies the condition.

  FIG. 16 is a diagram illustrating an example of an edge extraction filter. FIG. 16A shows an edge extraction filter used for detecting an edge region having a size of one pixel when an R signal is input line by line. FIG. 16B shows an edge extraction filter used to detect an edge region having a size of one pixel when a plurality of R signals are input together.

  FIG. 16C shows an edge extraction filter used for detecting an edge region having a size of 3 pixels when the R signal is input line by line. FIG. 16D shows an edge extraction filter that is used to detect an edge region having a size of 3 pixels when a plurality of lines of R signals are input.

  FIG. 16E shows an edge extraction filter used to detect an edge region having a size of 5 pixels when an R signal is input line by line. FIG. 16F shows an edge extraction filter used to detect an edge region having a size of 5 pixels when a plurality of R signals are input together. The conditions for establishing these edge extraction filters are as follows.

  (1) The determination condition for the edge region with high brightness is when the value obtained by subtracting the average brightness of pixel C from the average brightness of pixels A and B is equal to or greater than threshold value Ref1 (R).

Average (pixel A and pixel B) -average (pixel C)> Ref1 (R)
The central pixel in this case is the pixel having the maximum brightness among the pixels A, B, and C.

  (2) The determination condition for the edge region with low brightness is when the value obtained by subtracting the average brightness of the pixels A and B from the average brightness of the pixel C is equal to or greater than the threshold value Ref1 (R).

Average (pixel C) -average (pixel A and pixel B)> Ref1 (R)
The central pixel in this case is a pixel having the minimum brightness among the pixel A, the pixel B, and the pixel C.

  For the G signal and the B signal, the same edge extraction filter as that used for the R signal can be used.

  In the first lightness difference detection units 301R, 301G, and 301B, the values calculated by the above-described edge extraction filter are compared with the threshold values Ref1 (R), Ref1 (G), and Ref1 (B).

  Returning to FIG. 15, a logic signal in which the first feature pixel extracted by the first brightness difference detection unit 301 </ b> R is “1” and the other pixel is “0” is output to the AND element 307 </ b> R.

  The second lightness difference detection unit 302R receives the R signal and the threshold value Ref2 (R). The second brightness difference detection unit 302R extracts a region having a second level predetermined feature from the R signal. The region having the second level predetermined feature is a region where the change in lightness is small, and is a region where the difference in lightness from the surrounding region is equal to or greater than the threshold value Ref2 (R). Such a region may have a size of one pixel or more. Here, a pixel included in an area having a second level predetermined feature is referred to as a second feature pixel. The threshold value Ref2 (R) is smaller than the threshold value Ref1 (R).

  The region having the second level predetermined feature may be extracted using an edge extraction filter. A plurality of edge extraction filters are prepared for each size of the edge region, and a value obtained as a result of the filtering process is compared with a threshold value Ref2 (R). Then, the pixel that satisfies the condition of the threshold value Ref2 (R) is set as the center pixel of the edge region, and the size of the edge region is obtained from the edge extraction filter that satisfies the condition.

  In the second brightness difference detection units 302R, 302G, and 302B, the values calculated by the edge extraction filter described above are compared with the threshold values Ref2 (R), Ref2 (G), and Ref2 (B).

  A logic signal in which the second feature pixel extracted by the second brightness difference detection unit 302R is set to “1” and the other pixel is not set to “0” is output to the detection result extension processing unit 303R.

  The detection result expansion processing unit 303R expands an area having a predetermined feature of the second level by setting a pixel around the second feature pixel extracted by the second brightness difference detection unit 302R as the second feature pixel. . That is, the value of the pixel having the value “0” around the pixel having the logic signal value “1” input from the second brightness difference detection unit 302R is changed to “1”. Thereby, the accuracy of noise detection can be improved. The logic signal in which the area is expanded is output to the negative OR elements 305G and 305B.

  The first lightness difference detection unit 301G receives the G signal and the threshold value Ref1 (G). The first brightness difference detection unit 301G extracts a region having a first level predetermined feature from the G signal. The region having the first level predetermined feature is a region where the change in lightness is small and a difference in lightness from the surrounding region is a threshold value Ref1 (G) or more.

  The region having the first level predetermined feature may be extracted using an edge extraction filter. A plurality of edge extraction filters are prepared for each size of the edge region, and the value obtained as a result of the filtering process is compared with the threshold value Ref1 (G). Then, the pixel that satisfies the condition of the threshold value Ref1 (G) is set as the center pixel of the edge region, and the size of the edge region is obtained from the edge extraction filter that satisfies the condition.

  A logic signal in which the feature pixel extracted by the first brightness difference detection unit 301G is “1” and the other pixel is “0” is output to the AND element 307G.

  The second lightness difference detection unit 302G receives the G signal and the threshold value Ref2 (G). The second brightness difference detection unit 302G extracts a region having a second level predetermined feature from the G signal. The region having the second level predetermined feature is a region where the change in brightness is small and a difference in brightness from the surrounding region is a threshold value Ref2 (G) or more. Such a region may have a size of one pixel or more. Here, a pixel included in an area having a second level predetermined feature is referred to as a second feature pixel. The threshold value Ref2 (G) is a value smaller than the threshold value Ref1 (G).

  The region having the second level predetermined feature may be extracted using an edge extraction filter. A plurality of edge extraction filters are prepared for each size of the edge region, and a value obtained as a result of the filtering process is compared with a threshold value Ref2 (G). The pixel that satisfies the condition of the threshold value Ref2 (G) is set as the center pixel of the edge region, and the size of the edge region is obtained from the edge extraction filter that satisfies the condition.

  A logic signal in which the second feature pixel extracted by the second brightness difference detection unit 302G is set to “1” and other pixels are not set to “0” is output to the detection result extension processing unit 303G.

  The detection result expansion processing unit 303G expands the region having the second level predetermined feature by setting the pixels around the second feature pixel extracted by the second brightness difference detection unit 302G as the second feature pixel. . The logical signal with the expanded area is output to the negative OR elements 305R and 305B.

  The first lightness difference detection unit 301B receives the B signal and the threshold value Ref1 (B). The first brightness difference detection unit 301B extracts a region having a first level predetermined feature from the B signal. The region having the first level predetermined feature is a region where the change in lightness is small and a difference in lightness from the surrounding region is a threshold value Ref1 (B) or more.

  The region having the first level predetermined feature may be extracted using an edge extraction filter. A plurality of edge extraction filters are prepared for each size of the edge region, and the value obtained as a result of the filtering process is compared with the threshold value Ref1 (B). Then, the pixel that satisfies the condition of the threshold value Ref1 (B) is set as the center pixel of the edge region, and the size of the edge region is obtained from the edge extraction filter that satisfies the condition.

  A logic signal in which the feature pixel extracted by the first brightness difference detection unit 301B is set to “1” and the other pixels are set to “0” is output to the AND element 307B.

  The second lightness difference detection unit 302B receives the B signal and the threshold value Ref2 (B). The second brightness difference detection unit 302B extracts a region having a second level predetermined feature from the B signal. The region having the second level predetermined feature is a region where the change in lightness is small, and is a region where the difference in lightness from the surrounding region is equal to or greater than the threshold value Ref2 (B). Such a region may have a size of one pixel or more. Here, a pixel included in an area having a second level predetermined feature is referred to as a second feature pixel. The threshold value Ref2 (B) is smaller than the threshold value Ref1 (B).

  The region having the second level predetermined feature may be extracted using an edge extraction filter. A plurality of edge extraction filters are prepared for each size of the edge region, and a value obtained as a result of the filtering process is compared with a threshold value Ref2 (B). The pixel that satisfies the condition of the threshold value Ref2 (B) is set as the center pixel of the edge region, and the size of the edge region is obtained from the edge extraction filter that satisfies the condition.

  A logic signal in which the second feature pixel extracted by the second lightness difference detection unit 302B is set to “1” and other pixels are not set to “0” is output to the detection result extension processing unit 303B.

  The detection result expansion processing unit 303B expands the region having the second level predetermined feature by setting the pixels around the second feature pixel extracted by the second brightness difference detection unit 302B as the second feature pixel. . The logic signal in which the area is expanded is output to the negative OR elements 305R and 305G.

  To the negative OR element 305R, a logic signal obtained by extending the area is input from each of the detection result expansion processing units 303G and 303B. The negative logical sum element 305R outputs a logical signal obtained by inverting the logical sum of the two input logical signals to the logical AND element 307R. That is, a logic signal is output that sets a pixel that is not the second feature pixel to “1” in either the G signal or the B signal and at least one pixel that is the second feature pixel to “0”.

  The logical product element 307R outputs the logical product of the logical signal input from the first brightness difference detection unit 301R and the logical signal input from the negative logical sum element 305R to the detection area expansion processing unit 309R. In other words, a logical signal is output in which the pixel that is the first feature pixel in the R signal and is not the second feature pixel expanded by either the B signal or the G signal is set to “1”, and the other pixels are set to “0”. The A pixel having a value “1” in this logical signal indicates a noise pixel. Therefore, a pixel that has not been extracted as the second feature pixel in either the G signal or the B signal from among the first feature pixels extracted from the R signal by the negative OR element 305R and the AND element 307R is a noise pixel. Is determined.

  The detection area expansion processing unit 309R expands the range of the noise pixel by setting the pixels around the pixel that is set to “1” by the logic signal input from the AND element 307R to “1”. This is to improve the accuracy of noise pixel correction. A logic signal that sets the noise pixel whose range has been expanded to “1” is output to the noise correction unit 260.

  A logical signal obtained by extending the area from each of the detection result expansion processing units 303R and 303B is input to the negative logical sum element 305G. The negative logical sum element 305G outputs a logical signal obtained by inverting the logical sum of two input logical signals to the logical AND element 307G. In other words, a logic signal is output that sets a pixel that is not the second feature pixel to “1” in both the R signal and the B signal, and at least one pixel that is the second feature pixel to “0”.

  The logical product element 307G outputs the logical product of the logical signal input from the first brightness difference detection unit 301G and the logical signal input from the negative logical sum element 305G to the detection area expansion processing unit 309G. In other words, a logical signal is output in which the pixel that is the first feature pixel in the G signal and is not the second feature pixel expanded by either the R signal or the B signal is set to “1”, and the other pixels are set to “0”. The A pixel having a value “1” in this logical signal indicates a noise pixel. Therefore, a pixel that is not extracted as a second feature pixel in either the R signal or the B signal is a noise pixel among the first feature pixels extracted from the G signal by the negative OR element 305G and the AND element 307G. Is determined.

  The detection area expansion processing unit 309G expands the range of the noise pixel by setting the pixels around the pixel that is set to “1” by the logic signal input from the AND element 307G to “1”. This is to improve the accuracy of noise pixel correction. A logic signal that sets the noise pixel whose range has been expanded to “1” is output to the noise correction unit 260.

  A logical signal obtained by extending the area from each of the detection result expansion processing units 303R and 303G is input to the negative logical sum element 305B. The negative logical sum element 305B outputs a logical signal obtained by inverting the logical sum of two input logical signals to the logical product element 307B. That is, a logic signal is output that sets a pixel that is not the second feature pixel to “1” in either the R signal or the G signal, and at least one pixel that is the second feature pixel to “0”.

  The logical product element 307B outputs the logical product of the logical signal input from the first brightness difference detection unit 301B and the logical signal input from the negative logical sum element 305B to the detection area expansion processing unit 309B. In other words, a logical signal is output in which a B signal is a first feature pixel and a pixel that is not a second feature pixel expanded by either the R signal or the G signal is set to “1” and the other pixels are set to “0”. The A pixel having a value “1” in this logical signal indicates a noise pixel. Therefore, a pixel that is not extracted as a second feature pixel in either the R signal or the G signal is a noise pixel among the first feature pixels extracted from the B signal by the negative OR element 305B and the AND element 307B. Is determined.

  The detection area expansion processing unit 309B expands the range of the noise pixel by setting the pixels around the pixel that is set to “1” by the logical signal input from the AND element 307B to “1”. This is to improve the accuracy of noise pixel correction. A logic signal that sets the noise pixel whose range has been expanded to “1” is output to the noise correction unit 260.

  As described above, the first detection unit 310 extracts the first feature pixel and the second feature pixel from the R signal, the G signal, and the B signal output from the three line sensors 213R, 213G, and 213B, respectively. The next pixel is a noise pixel.

  (1) Pixels that are first feature pixels extracted from the R signal, and that all of the pixels that read the same positions of the first feature pixel and the original in the G signal and B signal are not second feature pixels.

  (2) First feature pixels extracted from the G signal, and all of the pixels that read the same position of the original feature pixel and the original in the R signal and the B signal are not second feature pixels.

  (3) The first feature pixels extracted from the B signal, and all of the pixels that have read the same position of the original feature pixel and the original in the R signal and the G signal are not second feature pixels.

  For this reason, it is possible to detect noise generated by dust existing on the document table from an image obtained by reading the document.

<Second detection unit>
The second detection unit 320 has substantially the same configuration as the first detection unit 310. The second detector 320 is different from the first detector 310 in that the threshold value is different. More specifically, in the second detector 320, the threshold values given to the first lightness difference detectors 301R, 301G, 301B are the threshold values Ref1 (R), Ref1 ( G), Ref1 (B) is a smaller value at which the edge is more easily detected, and the threshold value given to the second brightness difference detection units 302R, 302G, 302B is the threshold value Ref2 used by the first detection unit 310. (R), Ref2 (G), and Ref2 (B) are set to a smaller value at which the edge is more easily detected.

  In addition, the second detection unit 320 deletes the second brightness difference detection units 302R, 302G, and 302B from the first detection unit 310, and outputs the outputs of the first brightness difference detection units 301R, 301G, and 301B to the detection result extension processing unit 303R. , 303G, and 303B.

  Alternatively, the second detection unit 320 may convert the input RGB signal into the L * a * b * color system and detect an edge region from the luminance signal L *. In order to detect the edge region, the edge extraction filter shown in FIG. 16 is used. Pixels included in the extracted edge region are set as noise pixels.

  Further, the second detection unit 320 may detect an isolated point from the luminance signal L *. For detection of an isolated point, an isolated point is detected using an isolated point detection filter. The detected isolated point is used as a noise pixel.

<First Modification of Noise Detection Processing Unit>
FIG. 17 is a block diagram illustrating another configuration of the noise detection processing unit. Referring to the drawing, noise detection processing unit 259A in the first modification includes a first detection unit 310. The first detection unit 310A has the same configuration as that of the first detection unit 310 illustrated in FIG. 15 except that the first detection unit 310A is connected to the control unit 263 and has two types of threshold values.

  The first detection unit 310A has threshold values with high edge detection accuracy for the threshold values Ref1 (R), Ref1 (G), and Ref1 (B) given to the first brightness difference detection units 301R, 301G, and 301B. Two types of threshold values, that is, a low threshold value, are provided. In addition, the threshold value Ref2 (R), Ref2 (G), and Ref2 (B) given to the second brightness difference detection units 302R, 302G, and 302B has a threshold value with high edge detection accuracy and a low threshold value. There are two types of thresholds with values. These two types of threshold values can be selected.

  The first detection unit 310A receives the threshold selection signal from the control unit 263, selects one of the two thresholds according to the input threshold selection signal, and detects the first brightness difference. To the units 301R, 301G, and 301B and the second brightness difference detection units 302R, 302G, and 302B.

  When the position of the document table 205 is in the use area, the control unit 263 outputs a threshold selection signal for selecting a threshold with high detection accuracy to the first detection unit 310A. In addition, when the position of the document table 205 is not in the use area, the control unit 263 outputs a threshold selection signal for selecting a threshold with low detection accuracy to the first detection unit 310A.

  As described above, when the document table is in the use area, a noise pixel is detected using a threshold value with high detection accuracy. When the document table is not in the use area, a threshold value with low detection accuracy is set. The noise pixel is detected using this. Therefore, when the document table 205 is in the use area, the detection rate is low but the detection accuracy can be increased without being erroneously detected. When the document table 205 is not in the use area, the detection rate is increased. Can be improved.

<Second Modification of Noise Detection Processing Unit>
FIG. 18 is a block diagram showing still another configuration of the noise detection processing unit. Referring to the figure, noise detection processing unit 259B in the second modification example has the same configuration as that of first detection unit 310 shown in FIG. 15, but selects a point connected to control unit 263 and a filter to be used. It differs in possible points.

  The first detection unit 310 </ b> B receives a filter selection signal from the control unit 263. Similar to the first detection unit 310, the first detection unit 310B includes a plurality of edge extraction filters having different sizes in the first lightness difference detection units 301R, 301G, and 301B and the second lightness difference detection units 302R, 302G, and 302B. ing. The first detection unit 310B can perform edge extraction processing using any one of a plurality of edge extraction filters. Similarly to the first detection unit 310, it is possible to perform edge extraction processing using all edge extraction filters. The filter selection signal is a signal for designating a filter used for edge extraction from among a plurality of edge extraction filters.

  When the position of the document table 205 is in the use area, the control unit 263 outputs a filter selection signal indicating that the edge extraction filters of all sizes are used to the first detection unit 310B. Further, when the position of the document table 205 is not in the use area, the control unit 263 reads out dust information corresponding to the position of the document table 205 from the dust information storage memory 293, and an edge having a size corresponding to the size of the dust. A filter selection signal for selecting an extraction filter is output to the first detection unit 310B.

  The first detection unit 310B selects a filter according to the filter selection signal input from the control unit 263, and detects a noise pixel.

  As described above, when the document table is in the use area, noise pixels are detected by using edge extraction filters of all sizes, and when the document table is not in the use area, it is detected at the position of the document table 205. Noise pixels are detected using an edge extraction filter having a size corresponding to the size of dust. Therefore, when the document table 205 is in the use area, the detection accuracy is low but the detection accuracy can be increased without being erroneously detected. When the document table 205 is not in the use area, the detection accuracy is improved. Noise pixels can be detected while maintaining a constant level.

  Note that the control unit 263 reads out dust information corresponding to the position of the document table 205 from the dust information storage memory 293 regardless of whether or not the position of the document table 205 is the use area, and corresponds to the size of the dust. A filter selection signal for selecting a size edge extraction filter may be output to the first detection unit 310B.

  The image reading apparatus 10 described above includes the following inventive concept.

(1) The first extraction unit further includes a first enlargement unit that uses a pixel around the extracted first feature pixel as a first feature pixel,
5. The image reading apparatus according to claim 4, wherein the second extraction unit further includes a second enlargement unit that uses a pixel around the extracted second feature pixel as a second feature pixel.

(2) Each of the plurality of line sensors includes filters having different spectral sensitivities,
The image reading apparatus according to claim 3, wherein the light reflected from the document is received through the filter.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 is a perspective view of an MFP including an image reading apparatus according to one embodiment of the present invention. 2 is a diagram illustrating an outline of an internal configuration of an image reading apparatus. FIG. It is a perspective view which shows the mechanism for moving an original table. It is a figure for demonstrating the principle which detects the noise which generate | occur | produces by reading dust from the read image. FIG. 3 is a plan view of the document table viewed from the back side. It is a figure which shows the position on the original stand read by a reading part. 3 is a block diagram illustrating a configuration of an image processing unit of the image reading apparatus according to the present embodiment. FIG. It is a block diagram which shows schematic structure of the detection part before reading. It is a figure which shows an example of a weighting coefficient table. It is a figure which shows the area | region which divided the original table into 3 in the subscanning direction. It is another block diagram which shows schematic structure of the detection part before a reading. It is another figure which shows an example of a weighting coefficient table. It is a block diagram which shows the structure of the noise detection process part of the image reading apparatus in this Embodiment. It is a figure which shows an example of the RGB signal which a reading part outputs. It is a block diagram which shows the structure of the noise detection process part of the image reading apparatus in this Embodiment. It is a figure which shows an example of an edge extraction filter. It is a block diagram which shows another structure of a noise detection process part. It is a block diagram which shows another structure of a noise detection process part.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Image reading apparatus, 20 Image forming apparatus, 101 Automatic document conveying apparatus, 103 Main body part, 200 Document, 201 Timing roller pair, 202 Roller pair, 203 Upper restriction plate, 205 Document stand, 205A mark, 206 Light source, 207 Passing paper Guide, 208 reflection member, 209 reflection mirror, 211 lens, 213 reading unit, 213R, 213G, 213B line sensor, 215 image processing unit, 217 motor control unit, 219 motor, 253 shading correction unit, 255 interline correction unit, 257 Chromatic aberration correction unit, 259 noise detection processing unit, 261 printer interface, 263 control unit, 271 pre-reading detection unit, 273 ADF control unit, 291 peak value detection unit, 292 dust size detection unit, 292A dust lightness detection unit, 293 dust information Storage memory, 294, 294A Contamination level calculation unit, 296, 296A Weighted coefficient table, 295 Use area determination unit, 301R, 301G, 301B First brightness difference detection unit, 302R, 302G, 302B Second brightness difference detection unit, 303R , 303G, 303B detection result expansion processing unit, 305R, 305G, 305B negative OR element, 307R, 307G, 307B logical product element, 309R, 309G, 309B detection area expansion processing unit.

Claims (13)

A line sensor for scanning the document in the sub-scanning direction;
A document table that forms part of the document transport path;
Moving means for moving the document table relative to the line sensor;
Position detecting means for detecting a relative position of the document table with respect to the line sensor;
The document table is moved over the entire movable range of the document table before reading the document, and predetermined characteristics are obtained from the data output from the line sensor while the document table is moved. Extraction means for extracting feature pixels having;
Based on the extracted feature pixel and the relative position of the document table at the time when the data from which the feature pixel was extracted is read by the line sensor, the degree of contamination for each relative position of the document table is determined. A degree of contamination determination;
An original conveying means for conveying an original;
Noise detecting means for detecting noise from data output by the line sensor while scanning the original conveyed by the original conveying means with the line sensor;
While scanning the original conveyed by the original conveying means with the line sensor,
The moving means moves the document table,
The position detecting means detects a relative position of the document table with respect to the line sensor at the time when the line sensor reads the document;
The noise detection unit is an image reading apparatus that detects noise from data output from the line sensor with an accuracy corresponding to a degree of contamination corresponding to the detected relative position. The noise detection means, based on the determined degree of dirt for each relative position, an area determination means for determining a specific area of the document table with less dust;
First detection means for detecting noise from data output by the line sensor;
Second detection means for detecting noise from data output by the line sensor with lower accuracy than the first detection means;
2. The image according to claim 1, further comprising switching means for switching between the output of the first detection means and the output of the second detection means in accordance with whether or not the detected relative position is the specific region. Reader.   The switching means selects the output of the first detection means when the detected relative position is in the specific area, and outputs the output of the second detection means when the detected relative position is not the specific area. The image reading apparatus according to claim 2, wherein the image reading apparatus is selected. A plurality of the line sensors are arranged at a distance in the sub-scanning direction,
The first detection means extracts first feature pixels of a first level having a predetermined feature from each of a plurality of data output from the plurality of line sensors;
Comparing pixels that read the same position of the document between the plurality of data, the first feature pixel extracted from one of the plurality of data is not a first feature pixel in all other data First noise pixel detection means for detecting as a noise pixel in the condition,
The second detection means extracts second feature pixels of a second level having a predetermined feature from each of a plurality of data output from the plurality of line sensors;
Compare the pixels that read the same position of the document between the plurality of data, and determine that the second feature pixel extracted from one of the plurality of data is not the second feature pixel in all other data. Second noise pixel detection means for detecting as a noise pixel in the condition,
The image reading apparatus according to claim 2, wherein the first level is higher than the second level. The first extraction means includes first edge extraction means for extracting an edge region by comparing a value calculated using an edge extraction filter with a first threshold value, and the first edge extraction means extracts the edge area. A pixel included in the edge region is extracted as the first feature pixel;
The second extraction means includes second edge extraction means for extracting an edge region by comparing a value calculated using an edge extraction filter with a second threshold value, and the second edge extraction means extracts the edge region. A pixel included in the edge region is extracted as the second feature pixel;
The image reading apparatus according to claim 4, wherein the first threshold value is larger than the second threshold value. The first extraction means includes first area extraction means for extracting an area having a small change in brightness and having a brightness difference with a surrounding area equal to or greater than a first threshold value. Extracting a region as the first feature pixel;
The second extraction means includes second area extraction means for extracting an area having a small change in brightness and having a brightness difference with a surrounding area equal to or greater than a second threshold value. Extracting a region as the second feature pixel;
The image reading apparatus according to claim 4, wherein the first threshold value is larger than the second threshold value. The noise detection means, based on the determined degree of dirt for each relative position, a specific area determination means for determining a specific area of the document table with less dust;
Noise pixel detection means for detecting a noise pixel using a threshold value given from data output by the line sensor,
When the detected relative position is in the specific area, a first threshold value is given to the noise pixel detecting means, and when the detected relative position is not in the specific area, the noise pixel detecting means has a first threshold value. The image reading apparatus according to claim 1, further comprising a control unit that provides a second threshold value smaller than the threshold value. A plurality of the line sensors are arranged at a distance in the sub-scanning direction,
The noise pixel detection means extracts an edge region from each of data output from the plurality of line sensors by comparing a value calculated using an edge extraction filter with a given threshold, and the extracted Including edge extraction means for extracting pixels included in the edge region as feature pixels;
The pixels that read the same position of the document between the plurality of data are compared, and the feature pixel extracted from one of the plurality of data is determined to be a noise pixel on the condition that all the other data are not feature pixels. The image reading apparatus according to claim 7, which is detected as: A plurality of the line sensors are arranged at a distance in the sub-scanning direction,
The noise pixel detecting means is an area in which the noise pixel detecting means is an area where the change in brightness is small from each of data output from the plurality of line sensors, and a difference in brightness from surrounding areas is given. A region extracting means for extracting a region having a value equal to or greater than the value and extracting a pixel included in the extracted region as a feature pixel;
The pixels that read the same position of the document between the plurality of data are compared, and the feature pixel extracted from one of the plurality of data is determined to be a noise pixel on the condition that all the other data are not feature pixels. The image reading apparatus according to claim 7, which is detected as:   The image reading apparatus according to claim 1, wherein the contamination degree determination unit includes a size detection unit that detects a continuous number of the feature pixels for each relative position of the document table.   The image reading apparatus according to claim 1, wherein the stain level determination unit includes a brightness detection unit that detects the brightness of the feature pixel for each relative position of the document table. A plurality of the line sensors are arranged at a distance in the sub-scanning direction,
The contamination level determining means is configured to determine the extracted feature pixel and the relative position of the document table at the time when the data extracted from the feature pixel is read by the plurality of line sensors. Sizing means for determining a consecutive number of said feature pixels for each relative position;
The noise detection means, based on the determined size for each relative position, a specific area determination means for determining a specific area of the document table with less dust;
A plurality of edge extraction filters corresponding to the size of the edge region to be extracted, and the edge region is obtained by comparing a value calculated using all or any one of the plurality of edge extraction filters with a threshold value. Edge extraction means for extracting and extracting pixels included in the extracted edge region as feature pixels;
The pixels that read the same position of the document between the plurality of data are compared, and the feature pixel extracted from one of the plurality of data is determined to be a noise pixel on the condition that all the other data are not feature pixels. Noise pixel detecting means for detecting as,
When the detected relative position is the specific area, the edge extraction unit extracts the edge area using all edge extraction filters, and when the detected relative position is not the specific area, the edge detection unit detects the detected area. The image reading apparatus according to claim 1, further comprising a control unit that extracts an edge region using an edge extraction filter corresponding to a continuous number of the feature pixels at a relative position. A plurality of the line sensors are arranged at a distance in the sub-scanning direction,
The contamination level determining means is configured to determine the extracted feature pixel and the relative position of the document table at the time when the data extracted from the feature pixel is read by the plurality of line sensors. Sizing means for determining a consecutive number of said feature pixels for each relative position;
The noise detection means has a plurality of edge extraction filters corresponding to the size of the edge region to be extracted, and is calculated using an edge extraction filter corresponding to the consecutive number of the feature pixels at the detected relative position. Edge extraction means for comparing the obtained value with a threshold value to extract an edge region and extracting pixels included in the extracted edge region as feature pixels;
The pixels that read the same position of the document between the plurality of data are compared, and the feature pixel extracted from one of the plurality of data is determined to be a noise pixel on the condition that all the other data are not feature pixels. The image reading apparatus according to claim 1, further comprising: a noise pixel detection unit that detects a noise pixel.

Images