JP2007318228A - Image reader, image reading control program, and image reading method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image reader, an image reading control program, and an image reading method, capable of preventing occurrence of show-through by discriminating an original likely to cause show-through without the need for revising the image reading mechanism. <P>SOLUTION: A contact glass 201 is arranged on an upper face of a main body of a scanner 200, an original of a reading object is placed thereon, and a cover 204 is closed. A contactless angular sensor 205 detects a prescribed angle of the cover 204 before the cover 204 is closed, and a cover closing sensor 206 detects that the cover 204 is completely closed. Whether or not an original is likely to cause show-through is discriminated by comparing reading results of particular parts of the original at two sensing points of time, and the show-through is prevented by adjusting a gradation level of a background. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image reading apparatus, an image reading control program, and an image reading method for reading a sheet-like document, and in particular, an image on the back side of a relatively thin document can be read from the front side by a scanner, a facsimile machine or a copying machine. The present invention relates to an image reading apparatus, an image reading control program, and an image reading method.

  Reading a sheet-like document is actively performed by, for example, a scanner for inputting an image to a computer, a facsimile machine, or a copying machine. When such a sheet-like document is comparatively thin or made of a material having a high light transmittance, the platen cover surface in contact with the document reading side is stained or written on the side opposite to the document reading side. There is a possibility that image information such as characters and figures that have been read is mixed with image information on the reading side of the document. When a color image is read, the color of the surface of the platen cover may be seen through to the reading side and affect the background color of the image information on the front side. Such a phenomenon is generally called “show-through”.

  If there is a show-through, the characters and graphics on the front side will be mixed with the characters and figures on the front side, making it difficult to read the characters read on the front side, and noise such as smudges in some parts of the image. Will be greatly reduced. The same applies when the stain on the platen cover surface is added to the information on the reading side of the document. Further, when the color of the contact glass is read from the reading side of the document, a color that does not originally exist on the reading side is recognized as the background color of the document. This is also not preferable because the reading result is different from that of the original.

  FIG. 15 shows the principle of show-through. A sheet-like document 102 is placed on a transparent contact glass 101, and a platen cover 103 covers it. A light source 104 is disposed below the contact glass 101, and a light beam 105 emitted from the light source 104 is reflected by a reading side surface (a lower surface in the drawing) of the original 102, and is reflected as a reflected light 106 by a CCD ( It enters the reading element 107 such as a charged coupled device. At this time, a part of the light beam 105 is transmitted to the back side of the document 102 and reflected by the surface opposite to the reading side (upper surface in the drawing) or the surface of the platen cover 103 (lower surface in the drawing). The reflected light 108 enters the reading element 107.

  Here, the color of the reflected light 108 is a composite color of the background color as the material of the document 102 and the surface color of the platen cover 103. Therefore, when the reflection surface (the lower surface in the drawing) of the platen cover 103 is a relatively bright white color, the reflected light 108 is bright near white.

  It is assumed that characters are written on the surface of the document 102 opposite to the reading side. In this case, light absorption occurs according to the density of the character. Therefore, the light beam 105 is absorbed more at the portion where the character density is high, and the intensity of the reflected light 108 reflected from the platen cover 103 is reduced accordingly. On the other hand, the intensity of the reflected light 108 is relatively strong in the ground portion where no character is written on the surface opposite to the reading side of the document 102. Such a difference in intensity depending on the location of the reflected light 108 enters the reading element 107 in a form combined with the reflected light 106.

  The signal level corresponding to the light intensity at each location read by the reading element 107 is binarized or multivalued through a predetermined emphasis processing circuit (not shown) for character reproduction. At this time, if the signal level obtained by adding the reflected light 108 to the reflected light 106 corresponds to the density reproduced as a character, even if there is no character in that portion on the reading side, that portion is “black”. ”Or the like, and show-through occurs.

  As above, the show-through of characters has been described. For an apparatus that expresses a halftone image such as a photograph, if the signal level obtained by adding the reflected light 106 and the reflected light 108 is a density level to be printed, show-through occurs on the same principle.

  In recent years, in scanners and image processing apparatuses using the same, the speed of processing and the rate of reading in color are increasing. At the same time, there is a tendency that a light source is brighter than in the past, and there are many situations in which the amplitude of the output signal of the image reading unit must be made larger. If the color of the surface of the platen cover 103 is set to a dark color such as black, most of the light rays reaching the surface opposite to the reading side of the original are absorbed here. As an advantage, such an image processing apparatus does not need to consider the influence of the reflected light 108.

  However, if the surface of the platen cover 103 is dark, there arises a problem that when the document is smaller than the reading area, a portion exceeding the area is read in dark color. Further, when the original is thin and relatively easy to transmit light, there is a problem that the reflected light is insufficient in the reading area of the original and the read image becomes blackish as a whole. In order not to cause such a problem, the surface of the platen cover 103 needs to be a bright color such as white. However, this causes a problem that characters and images existing on the side opposite to the reading side of the document are likely to show through.

  In view of this, the first proposal is to obtain an optimum image when the document presser is opened and closed by setting and changing the threshold for estimating the show-through corresponding to the open / closed state of the platen cover. (For example, refer to Patent Document 1). In the first proposal, a sensor for detecting whether the document presser is open or closed is provided. When the document presser is in a closed state, data relating to various show-through corrections such as a threshold value stored in advance corresponding to the closed state is called from the RAM to set the image reading apparatus. When the document presser 7 is in the open state, data relating to various show-through corrections such as threshold values stored in advance corresponding to the open state is called from a RAM (Random Access Memory) to set the image reading apparatus. . Accordingly, it is possible to appropriately set the threshold for show-through regardless of whether the document presser is open or closed.

  In this first proposal, since the opening and closing of the document presser are detected, a threshold value that prevents show-through in a situation where the document presser is open and the document show-through is likely to occur is set. By preparing, it is possible to prevent show-through. However, as described with reference to FIG. 15, even when the document presser is closed, show-through occurs when the document is thin and relatively easy to transmit light. In the first proposal, the threshold value can be set for each of when the document presser is opened and when it is closed, but it is left to the operator of the image forming apparatus to determine what kind of document is likely to show through. Therefore, if the operator does not have knowledge about the show-through of the original, even if the original press is closed when the original press is closed, it is difficult to read an image such as a show-through in the read image. There was a risk of many situations.

Therefore, the same part of the document is read at two different conditions, the brightness data is compared, and the reading control variable of the contact type line sensor is changed based on the comparison result, thereby reducing or preventing show-through. This is proposed as a second proposal (see, for example, Patent Document 2). In the second proposal, a portion where the surface is painted black and a portion where the surface is painted white are arranged on the document conveyance path, and the contact type line sensor is moved to each position so that the brightness of these portions is increased. Get data.
JP 2004-104402 A (paragraph 0032, FIG. 3) Japanese Unexamined Patent Publication No. 2003-198810 (paragraphs 0048 and 0049, FIG. 2)

  In the second proposal, the light transmittance of the document is calculated by comparing the acquired luminance data. From this calculation result, it is determined that the paper thickness of the document is thick when the light transmittance is low. When the light transmittance is high, it is determined that the paper thickness of the document is thin. When the control unit determines that the light transmittance is high, the control unit changes the reading control variable of the contact type line sensor in order to reduce or prevent the show-through. For example, increase or decrease the amount of light that irradiates the original, change the binary slice level to make the light gray part white instead of black when binarizing, or change the curve of the γ table Or contriving to increase or decrease the coefficient of the edge enhancement filter.

  However, in the image processing apparatus of the second proposal, it is necessary to move the contact type line sensor to a plurality of positions in order to compare luminance data before starting reading a document. For this reason, a moving mechanism for the contact type line sensor is required, and there is a problem that the cost of the image reading apparatus is increased correspondingly, and the apparatus is increased in size. In addition, since the processing for changing the reading control variable of the contact type line sensor is performed as necessary after the contact type line sensor is moved, there is a problem that rapid image reading is impossible.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image reading apparatus, an image reading control program, and an image reading method capable of discriminating a document that is easy to show through and preventing the show-through without changing the image reading mechanism. It is in.

  According to the first aspect of the present invention, (a) the first mode in which external light is incident from other than the reading surface of the document and the second mode in which the periphery of the reading surface is shielded are alternately switched before the document reading starts. (B) a document specific part reading unit that reads a specific part of a document in both the first mode and the second mode; and (c) a reading result of the document specific part reading unit. An image reading apparatus comprising: a show-through discriminating means for discriminating whether or not the document is easily show-through from the document and (d) a reading condition setting means for setting the reading condition of the document based on the discrimination result of the show-through discrimination means To provide.

  That is, according to the present invention, before the reading of the document, the document is alternately set to two modes, a first mode in which external light is incident from other than the reading surface and a second mode in which the periphery of the reading surface is shielded. Thus, the document specific part reading unit reads the specific part of the document in both the first mode and the second mode. Thus, since it is possible to determine whether or not the document is likely to transmit light, the show-through determination unit can determine whether or not the document is likely to show through from the reading result of the document specific part reading unit. it can. The reading condition setting unit can prevent the show-through even if the document is to show through by setting the document reading condition based on the determination result of the show-through determining unit.

  According to the second aspect of the present invention, (a) a transparent flat plate member on which a document is placed, and (b) outside light from a surface opposite to the reading surface at the time of image reading of the document placed on the flat plate member. A lid member that can be freely opened and closed so as not to be incident; and (c) a lid closing detection unit that detects a time when the lid member is closed at a predetermined angle before the document is completely closed before the document is read. (D) a document specific part reading unit that reads a specific part of the document both when the cover closing detection means is detected and when the lid member is closed; and (e) a reading result of the document specific part reading unit. An image reading apparatus comprising: a show-through discriminating unit that discriminates whether or not the document is easily show-through and (f) a reading condition setting unit that sets an original reading condition based on the discrimination result of the show-through discriminating unit To provide.

  That is, in the present invention, a lid member that can be opened and closed with respect to a transparent flat plate member on which an original is placed is used to detect when the lid member is at a predetermined angle before the lid member is completely closed by the lid closing detection means. Then, the document specific part reading unit reads the specific part of the document both when it is detected by the lid closing detection unit and when the lid member is closed. Here, the closed state of the lid member is not particularly detected, but this may be detected using a special detection means. The show-through determination unit can determine whether the document is likely to show through from the reading result of the document specific site reading unit from the reading result of the document specific site reading unit. Can be determined. The reading condition setting means can set the original reading conditions based on the result of the show-through discrimination means, thereby preventing the show-through even in the case of the show-through document.

  In the image reading control program according to the sixth aspect of the present invention, (a) the computer of the apparatus that reads an image is (b) the light shielding lid member is closed with respect to the document placement surface prior to reading the document. A lid member angle detection process for detecting both a point at which a specific angle during closing and a closed point are detected, and (c) a specific part of the document at two points detected by the lid member angle detection process. A document specific part reading process for reading, (d) a show-through determination process for determining whether or not a document is likely to show through from the reading result of the document specific part read process, and (e) a show-through determination process. It is characterized in that a reading condition setting process for setting a reading condition for a document based on the determination result is executed.

  That is, according to the present invention, the computer of the image reading apparatus is closed at a specific angle in the middle of closing when the light shielding lid member is closed with respect to the document placement surface prior to reading the document. The lid member angle detection process is performed to detect both of the points in time, and a specific part of the document is read at these two points in time. In the show-through determination process, it is determined from these reading results whether or not the document is easily show-through. In the reading condition setting process, the reading condition of the document is set based on the determination result in the show-through determination process, so that the show-through can be prevented even for a document that shows through.

  9. The image reading method according to claim 8, wherein (a) when the light-shielding lid member is closed with respect to the document placement surface prior to reading the document, a specific angle during closing and a time when it is closed. A lid member angle detection step for detecting both of the above, (b) a document specific part reading step for reading a specific part of the document at two time points detected in the lid member angle detection step, and (c) this document specification. A show-through determination step for determining whether or not a document is likely to show through from the reading result in the part reading step; and (d) a reading condition setting for setting a document reading condition based on the determination result in the show-through determination step. And a step.

  That is, according to the present invention, a specific part of a document is read at two points in time by using a normal operation in which a light-shielding lid member is closed with respect to the document placement surface prior to reading the document. It is determined from the read result whether the document is easy to show through. Then, based on the determination result, the document reading condition is set.

  As described above, according to the first aspect of the present invention, the first mode and the second mode are realized by a simple method of the presence / absence of external light to determine whether or not the document is likely to show through. I am going to do it. For this reason, it is possible to determine a document that is easy to show through without the intervention of an operator, and it is possible to prevent show-through by appropriately setting a reading condition for this document. In addition, for other originals that are difficult to show through, gradation can be faithfully reproduced even in a bright gradation part.

  Further, according to each of the inventions according to claim 2, claim 6 and claim 8, by using a normal operation of closing a lid for holding the press when reading the document, In addition, it is possible to easily realize an environment in which external light is irradiated or not irradiated from the side opposite to the reading surface, and to quickly switch between these environments. Therefore, it is possible to realize a reading process that does not show through quickly. In addition, for other originals that are difficult to show through, gradation can be faithfully reproduced even in a bright gradation part.

  Hereinafter, the present invention will be described in detail with reference to examples.

  FIG. 1 shows the appearance of a scanner as an image reading apparatus in an embodiment of the present invention. The scanner 200 includes an apparatus main body 202 in which a contact glass 201 as a transparent flat plate member is disposed at the center of the upper surface thereof, and a lid section 204 that can be opened and closed with respect to the apparatus main body 202 by a hinge mechanism (not shown). It is configured. In the hinge mechanism, a non-contact angle sensor 205 is arranged in such a manner that its shaft 205A is interlocked. Of course, this figure shows in principle, and the non-contact angle sensor 205 is disposed in a place where there is no hindrance to the opening and closing of the lid 204.

  A lid closing sensor 206 is built in a position close to the front of the apparatus main body 202. The lid closing sensor 206 is a sensor that detects a state in which the lid portion 204 is closed. Various sensors can be used as the lid closing sensor 206. For example, the lid closing sensor 206 is constituted by an optical sensor, and a projection (not shown) provided at a corresponding portion of the lid portion 204 when the lid portion 204 is completely closed bites into the upper portion of the apparatus main body 202 and is not shown. You may detect the state which the cover part 204 closed by interrupting | blocking the light path between a light emission part and a light-receiving part. Further, the lid closing sensor 206 may be constituted by a reed switch or a magnetic sensor, and a permanent magnet may be disposed at a corresponding portion of the lid portion 204 so that the closed state of the lid portion 204 is detected by magnetic detection. .

  A white reference plate 207 is disposed at the left end portion of the contact glass 201 in the figure. The white reference plate 207 reads the image when the image scanning unit 209 which is reciprocally movable in the direction of the arrow 208 inside the apparatus main body 202 exists at the position of the home position or just before the start of normal scanning, It is a plate-like member for use in shading correction. The image scanning unit 209 is provided with an optical system, a light source, and a reading element (not shown), and when moved to the home position, the white reference plate 207 is positioned immediately above it.

  FIG. 2 shows the main part of the scanner with the lid closed. A document 221 is placed on the contact glass 201. A strip-shaped white reference plate 207 is attached to the lower surface of the opaque guide member 222 that regulates the position of the left end portion of the document 221. The image scanning unit 209 is provided with a light source lamp 224 on the top thereof, and irradiates light toward the upper contact glass 201. The light reflected from the original or the white reference plate 207 is incident on an optical system (not shown) in the image scanning unit 209, and finally an R (red) color CCD (Charged Coupled Device) 226 disposed on the reading plate 225. , G (green) color CCD 227 and B (blue) color CCD 228 are imaged.

  FIG. 3 shows an outline of the circuit configuration of the scanner of this embodiment. The scanner 200 includes a main control unit 241 that controls the whole. The main control unit 241 includes a CPU (Central Processing Unit) 242, and executes various control operations such as image scanning by executing a control program stored in a storage medium such as a ROM (Read Only Memory) 243. Is supposed to do. A RAM (Random Access Memory) 244 is a working memory that temporarily stores various data necessary for this control. The main control unit 241 is connected to each part of the apparatus via signal transmission means 245 such as a data bus. However, at least a part of each of these units may be configured by software by a functional unit realized by the CPU 242 executing the control program.

  The operation input unit 246 constituting the scanner 200 is configured by an input device such as a key switch (not shown) used when the operator operates this apparatus. The operation display unit 247 is for displaying visual data such as operation contents, and is configured by a display (not shown) and its display drive circuit. The image memory 248 is a memory that stores the read image in units of lines. The image output unit 249 includes various signal output means such as a USB (Universal Serial Bus) port (not shown) that outputs the read image. The image input unit 251 includes the image scanning unit 209 shown in FIG. 2, and is a part that inputs (reads) an image of the document 221 (FIG. 2). The image scanning unit driving unit 252 is a mechanism that reciprocates the image scanning unit 209 in the sub-scanning direction. The image pre-processing unit 253 performs pre-processing on the image data read by the image input unit 251 so as to amplify the electrical signal after photoelectric conversion and perform A / D (analog / digital) conversion or shading correction. Circuit. A circuit for preventing the show-through described later is also arranged here. The image processing unit 254 is a circuit that performs various corrections such as color correction on the pre-processed image data. The sensor input unit 255 is configured to input the outputs of various sensors such as the non-contact angle sensor 205 and the lid closing sensor 206 shown in FIG. 1 for control purposes. This includes a sensor (not shown) for detecting and controlling the moving position of the image scanning unit driving unit 252.

  FIG. 4 specifically shows a circuit portion for preventing show-through in the scanner shown in FIG. Image data 261 obtained by the image input unit 251 is input to the show-through determination unit 262 after correcting the output level for each reading element by a shading correction circuit (not shown) of the image preprocessing unit 253. It has become. The show-through determination unit 262 includes a data storage unit 263 that stores image data, and a show-through analysis unit 264 for analyzing presence or absence of show-through.

  In order to enable the show-through analysis unit 264 to analyze the show-through determination unit 262, the previous line storage memory 265 and the current line storage memory 266 constituting the image memory 248 store image data for one line of the previous line, respectively. Image data for one line of the current line is stored. When reading the original 221 (FIG. 2) in monochrome (monochrome), the previous line storage memory 265 and the current line storage memory 266 correspond to one line representing the previous line and the current line, respectively, for one monochrome color. Save the image data. When reading a color image, image data representing the previous line and the current line is stored for each of the three colors of R (red), G (green), and B (blue).

The show-through analysis unit 264 scans all pixels by taking a moving average for each of n pixels (where n is an arbitrary integer equal to or greater than 2) with respect to serial image data stored in the previous line storage memory 265. Then, the previous line maximum value P _max1 is calculated as the maximum value of the moving average. Similarly, the show-through analysis unit 264 scans image data for one line in the current line storage memory 266, takes a moving average for every n pixels, and scans all pixels. Also in this case, the current line maximum value P _max2 is calculated as the maximum value of the moving average. Based on these calculation results, the show-through analysis unit 264 analyzes whether the document 221 to be read causes a show-through as described later.

  The image pre-processing unit 253 outputs pre-processed image data 267 and a show-through determination signal 268 indicating the presence or absence of show-through, and these are input to the image processing unit 254. It has become. The image processing unit 254 performs image processing such as background removal, image smoothing, or enhancement processing while inputting / outputting data to / from the histogram storage area 269 and the current line storage memory 266 that constitute a part of the RAM 244. It has become.

  FIG. 5 shows the overall control flow when the scanner having such a configuration reads and scans a document. The description will be made with reference to FIGS.

  The main control unit 214 monitors whether the operator presses an image reading start button (not shown) of the operation input unit 246 (step S301). When the start button is pressed (Y), the image scanning unit driving unit 252 moves the image scanning unit 209 to the home position (step S302). Here, the home position refers to a position in the sub-scanning direction with the white reference plate 207 as an image reading position.

By the way, before performing reading scanning by the scanner 200, the operator places the document 221 on the contact glass 201 so that the reading surface is on the lower side. And the operation which closes the cover part 204 is started. The main control unit 214 monitors the detection output of the non-contact angle sensor 205 via the sensor input unit 255, and the angle θ that the cover unit 204 makes with the contact glass 201 is less than a predetermined angle θ ₁ (however, 90 degrees> When θ ₁ > 0 degree) (step S303: Y), the image input unit 251 is instructed to turn on the light source lamp 224 (step S304). The angle θ ₁ is set to a value of about 20 degrees in the present embodiment because of the need to reduce the influence of external light as much as possible. However, the angle θ ₁ is not limited to this. For example, the angle range suitable for the angle θ ₁ varies depending on the shape of the lid portion 204.

  The light source lamp 224 of the present embodiment uses a xenon tube lamp, and is lit using an inverter circuit (not shown). In this case, the light source lamp 224 can obtain stable lighting characteristics after about 300 milliseconds have elapsed since the start of lighting. Accordingly, the first show-through measurement is performed, for example, when 300 msec elapses after the light source lamp 224 is turned on in step S304 (step S305). That is, if the scanner 200 reads a color image, the image of one line for the first show-through measurement is read by the R color CCD 226, the G color CCD 227, and the B color CCD 228 at the home position. Is done. The image data obtained at this time is stored in the previous line storage memory 265.

  After the first show-through measurement is performed in this way, the main control unit 214 monitors the timing at which the lid closing sensor 206 is completely closed by the lid closing sensor 206 via the sensor input unit 255 (step S306). When it is detected that the lid 204 is completely closed (Y), the main control unit 214 instructs the image input unit 251 to read the color image, and if the color image is read, the R color CCD 226, The second show-through measurement is performed in which the image for one line is read by the G color CCD 227 and the B color CCD 228 (step S307). The image data obtained at this time is stored in the current line storage memory 266.

  It is assumed that the operator performs an operation of closing the lid portion 204 at a normally assumed operation speed. In such a case, the first show-through in step S305 is performed after the light source lamp 224 is turned on in step S304 in FIG. 5 until the lid 204 is detected to be closed in step S307. There is a time margin for performing the measurement. For this reason, after the reading of the image for one line for the first show-through measurement is completed, the lid portion 204 is closed, and the second show-through measurement can be performed thereafter.

  However, for example, it is conceivable in some cases that the operator quickly performs an operation of closing the lid 204. In such a case, the lid 204 may be closed before the reading of the image for one line for the first show-through measurement started in step S305 is completed. When such a situation occurs, for example, an error display is performed on the operation display unit 247, or an error sound is output from a speaker (not shown), and the lid unit 204 is closed again at a normally assumed operation speed. You may make it indicate.

  When two reading operations are performed at the home position as described above (steps S305 and S307), the main control unit 214 instructs the image scanning unit driving unit 252 to start reading the document 221 with the image scanning unit 209. While moving to a position, a show-through calculation process is performed to prevent show-through during this movement (step S308). When the image scanning unit 209 moves to the reading start position of the document 221 by detection of a sensor (not shown), the main control unit 214 controls the image scanning unit driving unit 252 so that the image scanning unit 209 is moved in the sub scanning direction. The scanning is started while moving (step S309). When the scanning to the end of the original 221 by the image scanning unit 209 is completed (step S310: Y), the original reading control is completed (end).

FIG. 6 specifically shows the flow of the show-through calculation process shown in step S308 of FIG. The description will be made with reference to FIGS. In the show-through calculation process, the show-through analysis unit 264 performs a scanning average of every n pixels on the serial image data stored in the previous line storage memory 265 as described above, and scans all pixels in the line. The previous line maximum value P _max1 as the maximum value of the moving average is calculated (step S321). Then, the image data for one line in the current line storage memory 266 is scanned, the moving average is taken every n pixels, and the scanning for all the pixels of the line is similarly performed, and the maximum value of the moving average is obtained. The current line maximum value P _max2 is calculated (step S322). The show-through analysis unit 264 calculates the absolute value “| D |” of the difference D between the previous line maximum value P _max1 and the current line maximum value P _max2 obtained in this way (step S323).

| D | = | P _max1 −P _max2 |

  The difference D indicates that the transmitted light of the document 221 returns to the reading surface when the lid portion 204 is in contact with the surface on the opposite side of the reading surface of the document 221 and the surface on the opposite side of the reading surface. This represents a difference in brightness on the reading surface side from the case where there is not. In general, when the ratio of transmitting light increases due to a decrease in the thickness of the document 221, for example, more light reaches the surface opposite to the reading surface accordingly. At this time, if the lid portion 204 does not exist on the surface opposite to the reading surface, the reached light is diffused without returning to the reading surface. As a result, when viewed from the reading surface, the brightness of the original 221 becomes darker by the amount of the diffused light.

  On the other hand, when the ratio of transmitting light is reduced due to the thickness of the original 221 or the like, the ratio of the light reaching the surface opposite to the reading surface decreases. Accordingly, since the ratio of light that is diffused without returning to the reading surface is reduced, the brightness of the document 221 is increased by that amount when viewed from the reading surface. Regardless of the thickness of the original 221, if a surface having a high reflectivity of the lid portion 204 faces the surface opposite to the reading surface, the ratio of light reflected from this surface to the reading surface increases. Therefore, as in the case where the original 221 is thick, the brightness of the original 221 becomes bright when viewed from the reading surface.

The show-through analysis unit 264 compares the absolute value “| D |” of the difference D thus obtained with the predetermined threshold value P _thr (step S324). As a result, when the absolute value “| D |” of the difference D is larger than the threshold value P _thr (Y), the determination “1” is output as the determination result (step S325). In other cases (step S324: N), the determination “0” is output (step S326). These determination results are stored in a predetermined determination result storage area of the RAM 244.

FIG. 7 shows an example of a measurement result when a document with show-through is used, and FIG. 8 shows an example of a measurement result when a document with no show-through is used. In these drawings, the horizontal axis represents pixels for one line in the main scanning direction, and the vertical axis represents the gradation of the original read. Further, as a premise, the reading surfaces of the originals used for the two measurements in FIGS. 7 and 8 have the same color tone and the same reflectance. As an example, the background on the reading surface of the document is a sufficiently white surface. Under such conditions, the current line maximum value P _max2 when the lid 204 (FIG. 1) is completely closed has the same gradation L _{1 in} both FIG. 7 and FIG.

On the other hand, when the front line maximum value P _max1 is viewed, for example, when the document 221 is thin and show-through occurs, the read gradation L ₂ is shown in FIG. 8 as shown in FIG. It becomes lower (darker) than the gradation L ₃ when the show-through shown does not occur. Therefore, when the gradation level L _thr that is the threshold value for determination is set to a level that is lower (darker) than the gradation level L ₁ by a certain level (threshold value P _thr ), the show-through shown in FIG. 7 occurs. In such a case, the difference D is larger than the threshold value P _thr . Further, when the show-through as shown in FIG. 8 does not occur, the threshold value P _thr becomes larger than the difference D. Therefore, as described above, by comparing the absolute value “| D |” of the difference D with a predetermined threshold value P _thr , it is possible to determine whether or not the document 221 causes show-through. It will be possible.

  As described above, the determination result “1” indicates that the corresponding document 221 causes show-through. The determination “0” indicates that the corresponding document 221 does not cause show-through.

  In this embodiment, whether or not the show-through occurs is not checked for the entire area of the document 221, but the first show-through measurement when the operation of closing the lid 204 is performed (step S 305 in FIG. 5). ) And the second show-through measurement (step S307 in FIG. 5). Therefore, the image pre-processing unit 253 shown in FIG. 4 stores the determination result in the above-described determination result storage area of the RAM 244 and then uses this as the show-through determination signal 268 applied to the entire original 221. Will be shed.

  FIG. 9 shows a process of creating and storing a histogram after determining the show-through of the document, and embodies the process positioned at the beginning of the process shown in step S309 of FIG. is there. The description will be made with reference to FIGS. When the determination of the show-through of the document 221 is completed (step S341: Y), the image processing unit 254 reads the image data for one line from the current line storage memory 266, and creates a histogram including the gradations and their frequencies. (Step S342). Then, the created histogram is stored in the histogram storage area 269 (step S343).

  FIG. 10 shows an example of a histogram created based on a certain original. In this figure, the horizontal axis represents the gradation from black to white in the corresponding line of the original 221, and the vertical axis represents the appearance frequency of the pixel in each gradation. The creation of the histogram is performed on the data for one line obtained from the current line storage memory 266 shown in FIG. The created histogram is stored in the histogram storage area 269 in the RAM 244 as described above.

Next, processing for obtaining the background level based on the created histogram will be described. In order to search on the original 221 for the background, that is, the background portion that is normally white, the scanner 200 of the present embodiment previously has the white scanning section minimum gradation abc _min and the white scanning section maximum floor shown in FIG. The key abc _max is set. Of course, a plurality of these values may be prepared so that the operator can select them, or the operator can select the white scanning section minimum gradation abc _min and the white scanning section maximum gradation abc according to the state of the original 221. You may be able to adjust _max each time.

  Incidentally, since the scanner 200 of this embodiment performs image processing such as γ correction as digital processing, quantization noise is generated in the middle of these processing. As a result, the output density may be equal even when the input density as the image density is different. As a result, when a histogram such as that shown in FIG. 10 is created, frequency deviations may occur in specific densities where output densities are equal. For this reason, it is necessary to devise a method for correctly searching for the background density of the corresponding document 221 using the created histogram.

In this embodiment, for this reason, when the frequency variation is larger than the predetermined variation range H _thr as shown in FIG. 10, these are treated as quantization noise. Therefore, this variation range H _thr is also set in the scanner 200 at the time of factory shipment. Further, in this embodiment, before starting the background level acquisition process described below, a lower limit threshold value H _lim of the frequency regarded as the background level is also set in advance. The variation range H _thr and the lower limit threshold value H _lim may be selected by the operator from several sets or adjusted appropriately.

FIG. 11 shows the flow of processing for obtaining the background level for the corresponding document. FIG. 11 is a process included in step S309 of FIG. 5, and is a process performed subsequent to the process shown in FIG. First, the image processing unit 254 shown in FIG. 4 starts scanning at a frequency from the white scanning section maximum gradation abc _max (see FIG. 10) as a background candidate (step S361). Then, it is determined whether the obtained current frequency exceeds the lower limit threshold H _lim (step S362). In the example shown in FIG. 10, the lower limit threshold H _lim is not exceeded (N). In such a case, the gradation is scanned in the direction of the white scanning interval minimum gradation abc _{min to} the position indicated by the next gradation (step S363).

If the position of the gradation after the scanning does not reach the white scanning section minimum gradation abc _min (step S364: N), it is determined whether or not the frequency exceeds the lower limit threshold H _lim at the gradation position. (Step S362). If not (N), the process returns to step S363 again.

When the frequency exceeds the lower limit threshold value H _lim at a certain gradation position in this way (step S362: Y), the subsequent variation in the waveform representing the m frequencies is confirmed (step S365). In FIG. 10, a fluctuation exceeding the variation range H _thr is observed in the vicinity of the left side in the white scanning section maximum gradation abc _max . As described above, when there is a case where the variation is equal to or larger than the variation range H _thr (step S366: Y), it is regarded as the quantization noise range, and the gradation a and the frequency b are stored. (Step S367). Then, the next gradation is scanned by shifting the scanning range by one in the direction of the white scanning interval minimum gradation abc _min (step S363).

On the other hand, if the variation does not exceed the variation range H _thr in step S366 (N), the frequency at that time is compared with the maximum frequency value obtained so far, and the frequency is higher than this. It is determined whether or not (step S368). As a result, if the frequency of this time is larger (Y), the frequency c and the gradation d are stored (step S369). Then, the next gradation is scanned by shifting the scanning range by one in the direction of the white scanning interval minimum gradation abc _min (step S363). If the current frequency is not increased in step S368 (N), the scanning range is set to one in the direction of the minimum gray level abc _min without storing the frequency c and the gray level d. The next gradation is scanned while being shifted by a distance (step S363).

By sequentially performing the scanning as described above, the position of the gradation after scanning finally reaches the white scanning interval minimum gradation abc _min (step S364: Y). When all the scans in the preset scan range are completed in this way, it is checked whether the maximum value c of the frequency at which the variation does not exceed the variation range H _thr and the corresponding gradation d exist. (Step S370). If it exists (Y), the frequency c is set as the maximum frequency H _{max and the} tone d is set as the background tone W ₁ (step S371).

On the other hand, when the maximum value c of the frequency that did not exceed the variation range H _thr in step S370 and the gradation d corresponding thereto do not exist (N), the frequency a is set as the maximum frequency H _max. Is set as the background gradation W ₁ (step S372).

FIG. 12 shows the background gradation correction processing obtained as described above and the actual document reading processing subsequent thereto. The processing in the latter half of step S309 and the processing in step S310 in FIG. It is a materialization. When the gradation d or gradation b is set as the background gradation W ₁ as described with reference to FIG. 11, the image processing unit 254 shown in FIG. 4 displays the show-through determination signal 268 output from the show-through determination unit 262. Is read (step S391). The determination if the result is determined "1" (step S392: Y), the document 221 (Fig. 2) is because if the likely occurrence of show-through, the correction to the gradation W ₁ it is determined that the base A value obtained by adding the offset W ₂ is set as a new background gradation (step S393).

Here, when reading the document 221 that is easy to show through, at the stage of second show-through measurement (step S307) shown in FIG. The line maximum value P _max2 tends to be brighter. Since the offset W ₂ is for performing processing as a background even for a gradation somewhat darker than the gradation W ₁ , the offset W ₂ takes a negative value.

Next, the case where the determination result of the show-through determination signal 268 is “0” will be described. In this case (step S392: N), since it is difficult for the document 221 (FIG. 2) to show through, the gradation W ₁ determined as the background is not particularly corrected, and this is changed to a new background gradation. Setting is made (step S394).

When the gradation to be the background is set as described above, reading of the actual portion of the original 221 by the image scanning unit 209 shown in FIG. 2 is started. That is, the scanning position of the image scanning unit 209 is first positioned at the leading end (left end in FIG. 2) position of the document 221 (step S395), and image reading processing is performed while removing the background for the reading line (step S395). Step S396). Taking black-and-white image reading as an example, specifically, the processing of fixing all the gradations on the white side to the gradation W ₁ or the gradation obtained by adding the offset W ₂ to the background (white). Done.

  When the image reading process for the corresponding line is performed, it is checked whether reading of the document 221 is completed at that time (step S397). If not completed (N), the process returns to step S395 to return to R The reading positions of the color CCD 226, G color CCD 227 and B color CCD 228 are moved to the next scanning line. Then, the image reading process is performed while performing the background process for the line in the same manner as described above (step S396). When the reading process for all the areas to be read of the original 221 is completed in this way (step S397: Y), all the processes are ended (END).

In the above description, the background removal is performed for all the originals 221. In the actual scanner 200, it is often the case that the operator decides whether or not to remove the background. If the operator has set not to remove the background, the gradation W ₁ may be set to the maximum white level (“255” when the gradation of the image is represented by 8 bits). . Thereby, even when the background removal is not performed, it is possible to read an image with reduced show-through.

  According to the scanner 200 of the embodiment described above, the second show-through measurement (step S307) is performed in addition to the first show-through measurement (step S305) shown in FIG. These measurements make it possible to determine whether the document 221 is likely to show through or not before the reading of the document 221 starts. When the original 221 is determined to be a paper that is easy to show through, for example, a thin paper, the deterioration of image quality due to the show-through can be suppressed by changing the background level with a preset threshold.

  <Modification of the invention>

In the previous embodiment, the background density is determined before the reading of the document 221 is started. As a result, uniform and quick processing of the background removal for the entire area of the original 221 is possible. In this embodiment, one line of image data is read from the current line storage memory 266 and a histogram is created. However, in a modified example, a histogram for a predetermined band unit in the sub-scanning direction, that is, for a predetermined sub-scan line. And the histogram stored in the histogram storage area 269 is sequentially updated in band units. Then, the gradation W ₁ shown in FIG. 10 is obtained again based on the histogram updated for each band, and the background removal is performed by performing the addition process of the offset W ₂ for each band using this. . Accordingly, when the image processing of the first band is performed at the leading end portion of the document 221, the same processing as in the embodiment is performed. Further, in this modification, the logic of the show-through determination signal 268 shown in FIG. 4 is assumed not to change during the image reading operation, and the show-through analysis unit 264 for analyzing the presence or absence of show-through also operates after the first band. I will not let you.

  FIG. 13 shows a process of creating and storing a histogram in this modification, and corresponds to FIG. 9 of the embodiment. Therefore, the same parts as those in FIG. 9 are denoted by the same reference numerals. In the modified example of the present invention, the processing in steps S301 to S307 in FIG. 5 is executed in the same manner as in the embodiment, and the description thereof will be omitted. When the second show-through measurement in step S307 in FIG. 5 is performed and the show-through determination by the show-through calculation process in FIG. 6 is completed (step S341: Y), the image processing unit 254 reads one line from the current line storage memory 266. Minute image data is read out, and a histogram including gradations and their frequencies is created (step S342). Then, the created histogram is stored in the histogram storage area 269 (step S343).

  At this time, it is checked whether or not all reading of the document 221 has been completed (step S401). If the reading has not been completed (N), only a predetermined line corresponding to the above band is further sub-scanned. It is determined whether or not it has moved (step S402). When the predetermined line is further moved in the sub-scanning direction (Y), the process returns to step S342, and at that time, the latest one line of image data is read from the current line storage memory 266 shown in FIG. A new histogram is created (step S342). This histogram is stored in the histogram storage area 269. In this way, the creation and storage of the histogram is repeated for each band until reading of all the images on the document 221 is completed (step S401: Y, end).

  FIG. 14 shows the state of the background gradation correction process and the actual document reading process subsequent to this modification, and corresponds to FIGS. 9 and 11 of the embodiment. Therefore, the same parts as those in FIG. 9 are denoted by the same reference numerals. Also in the modified example, the image processing unit 254 illustrated in FIG. 4 reads out the show-through determination signal 268 output from the show-through determination unit 262 (step S391).

Next, reading of the actual portion of the original 221 by the image scanning unit 209 shown in FIG. 2 is started. That is, the scanning position of the image scanning unit 209 is first positioned at the leading end (left end in FIG. 2) position of the document 221 (step S395), and then the background level acquisition processing shown in FIG. Necessary corrections are performed on the gradation W ₁ determined as the background according to the show-through state of the original 221 shown in steps S392 to S394 in FIG. 12 (step S421). Thereafter, an image reading process is performed while removing the background for the corresponding reading line (step S422). The processing so far is the same as the embodiment.

Thereafter, the image processing unit 254 checks whether reading of all images on the document 221 is completed (step S423). At this stage, reading of the first band of the document 221 has just started, and reading of all images has not been completed (N). Therefore, it is determined whether or not the processing for the current band has been completed (step S424). Since the reading of the first line of the band has only been completed (N), the scanning position of the image scanning unit 209 is moved to the next reading line (step S425). Then, the process proceeds to step S422 by performing a correction process for the same gradation W ₁ and the previous reading processes of the image while the background removal for the relevant read line is performed.

  Thereafter, a reading completion check (step S423) and a check whether the current band is completed (step S424) are performed. While the reading is not completed and the band is the same, the image reading process in step S422 proceeds while sequentially moving to the next reading line.

As a result of the image reading process of a predetermined line, when the reading of the corresponding band is completed (step S424: Y), the scanning position is moved to the first reading line of the next band (step S395). Then, necessary correction for the gradation W ₁ determined as the background is performed for the new band using the background level newly obtained in FIG. 11 (step S421), and then the background removal is performed on the corresponding reading line. The image reading process is performed while performing (step S422). That is, at this point, the image reading process corresponding to the second band is started.

  In the same manner, the background level is calculated and corrected at the start of each band (step S421). While the band continues, the scanning position is sequentially moved in the sub-scanning direction while the image of the background is removed. The reading process proceeds. As described above, the reading of the original 221 is finally completed (step S423: Y), and the process ends (END).

  In the modification described above, a histogram is created for each band in the sub-scanning direction, and the background level is calculated and corrected. For this reason, it is possible to read an image in which the background level is changed for each band.

  In the modification, it is assumed that one band is constituted by a plurality of lines, but may be constituted by one line. In this case, the background level is calculated and corrected for each line.

  Moreover, although the specific angle when the cover part 204 closes was detected using the non-contact angle sensor 205 in the Example and the modification, it is not necessary to always use an angle sensor. For example, it is possible to detect the angle by providing a projection that moves the rotation angle in accordance with the rotation of the lid 204 on a hinge mechanism (not shown), and detecting the angle at which the projection shields light with an optical sensor. is there.

  Further, in the embodiment, the state in which external light is incident from the periphery where the document is placed and the state where the periphery of the document is shielded are created by opening and closing the lid, but for example, light is irradiated from the back of the document. A similar reading environment may be created by or not. In this case, the mode setting means for alternately setting the two modes of the first mode in which external light is incident from other than the reading surface of the document and the second mode in which the periphery of the document is shielded before starting the document reading is performed. It will be provided in the reader. In the latter case, the book glass in which contact glass 201 as a transparent flat plate member is arranged on the upper part of the casing as shown in FIG. The present invention can be applied to other than a typical image reading apparatus. For example, even a device that reads a sheet-like document exclusively and does not have the lid 204 opening and closing structure as shown in FIG. 1, for example, by irradiating light from the back of the document. The mode can be switched between the second mode and the second mode, whereby the present invention can be applied.

  In the embodiment, the scanner 200 is taken up as an image reading apparatus. However, the present invention is naturally applicable to other image reading apparatuses such as a copying machine and a facsimile machine.

1 is a perspective view illustrating an outline of an appearance of an image reading apparatus according to an embodiment of the present invention. It is sectional drawing of the principal part in the state which closed the cover part about the image reading apparatus of a present Example. 1 is a block diagram illustrating an outline of a circuit configuration of an image reading apparatus according to an embodiment. FIG. 4 is a block diagram specifically showing a circuit portion for preventing show-through in the image reading apparatus shown in FIG. 3. 3 is a flowchart showing an overall control flow when the image reading apparatus performs scanning of a document in this embodiment. 5 is a flowchart specifically showing a flow of show-through calculation processing shown in step S308. FIG. 6 is a characteristic diagram illustrating an example of a measurement result when using a document in which show-through occurs. FIG. 6 is a characteristic diagram illustrating an example of a measurement result when a document that does not show through is used. It is a flowchart showing the mode of the creation process of a histogram in a present Example. FIG. 6 is a characteristic diagram illustrating an example of a histogram created based on a document in the present embodiment. 6 is a flowchart showing a flow of processing for obtaining a background level of an original in the embodiment. 6 is a flowchart showing a background gradation correction process and an actual document reading process following the background gradation correction process in the present embodiment. It is a flowchart of the process of creation and preservation | save of a histogram in the modification of this invention. 10 is a flowchart showing a background gradation correction process and an actual document reading process in the modified example. It is explanatory drawing which showed the principle which show-through occurs.

Explanation of symbols

200 Scanner (image reading device)
DESCRIPTION OF SYMBOLS 201 Contact glass 202 Apparatus main body 204 Cover part 205 Non-contact angle sensor 206 Cover closure sensor 209 Image scanning unit 226 R color CCD
227 G color CCD
228 B color CCD
241 Main control unit 242 CPU
243 ROM
253 Image pre-processing unit 254 Image processing unit 262 Show-through determination unit 263 Data storage unit 265 Previous line storage memory 266 Current line storage memory 267 Image data 268 Show-through determination signal 269 Histogram storage region

Claims (9)

Mode setting means for alternately setting two modes, a first mode in which external light is incident from other than the reading surface of the document, and a second mode in which the periphery of the reading surface is shielded before the reading of the document is started;
A document specific part reading means for reading a specific part of the document in both the first mode and the second mode;
Show-through discriminating means for discriminating whether or not the original is easily show-through from the reading result of the document specific part reading means;
An image reading apparatus comprising: a reading condition setting unit that sets a reading condition of a document based on a determination result of the show-through determination unit. A transparent flat plate member on which the document is placed;
A lid member that is openable and closable so that external light does not enter from a surface opposite to the reading surface when reading an image of a document placed on the flat plate member;
When the lid member is closed prior to reading the document, a lid closing midway detecting means for detecting a time when the lid member reaches a predetermined angle before being completely closed;
A document specific part reading means for reading a specific part of the document both at the time of detection by the cover closing midway detection means and in a state in which the lid member is closed;
Show-through discriminating means for discriminating whether or not the original is easily show-through from the reading result of the document specific part reading means;
An image reading apparatus comprising: a reading condition setting unit that sets a reading condition of a document based on a determination result of the show-through determination unit.   The show-through determination means includes an absolute value calculation means for obtaining an absolute value of a difference between two reading results of the specific part of the document by the document specific part reading means, and an absolute value calculated by the absolute value calculation means in advance. Comparison means for comparing with a predetermined threshold value, and document determination for determining that the original document is likely to show through when the absolute value is larger than the threshold value based on the comparison result of the comparison means, and otherwise determining that the original document is difficult to show through. The image reading apparatus according to claim 1, further comprising: means.   The reading condition setting means creates a histogram representing each gradation and appearance frequency for a predetermined line of image data of a document, and a gradation that is a candidate for a background from the histogram created by the histogram creation means Gradation range narrowing means for narrowing down the range of the image, quantization noise removing means for removing the quantization noise generated during image processing from the histogram of the gradation range narrowed down by the gradation range narrowing means, and the quantization noise removal 3. The image reading apparatus according to claim 1, further comprising: a background gradation specifying means for specifying a gradation as a background from the peak waveform of the histogram after the quantization noise is removed.   5. The image reading apparatus according to claim 4, further comprising a background gradation correction unit that corrects a background gradation specified by the background gradation specifying unit in accordance with a determination result of the show-through determination unit. . In the computer of the device that reads the image,
A lid member angle detection process for detecting both when the light shielding lid member is closed with respect to the document placement surface prior to reading the document and when the light shielding lid member is closed at a specific angle and when it is closed;
A document specific part reading process for reading a specific part of the document at two time points detected by the lid member angle detection process;
Show-through determination processing for determining whether the document is easy to show-through from the reading result of the document specific part reading processing;
An image reading control program for executing a reading condition setting process for setting a reading condition of a document based on a discrimination result of the show-through discrimination process.   The reading condition setting process includes a histogram creation process for creating a histogram representing each gradation and appearance frequency for a predetermined line of image data of a document, and a gradation that is a candidate for a background from the histogram created by the histogram creation process. Gradation range narrowing process for narrowing down the range, quantization noise removal process for removing quantization noise generated during image processing from the histogram of the gradation range narrowed down by this gradation range narrowing process, and this quantization noise removal 7. The image reading control program according to claim 6, wherein the computer is caused to execute background gradation specifying processing for specifying a background gradation from a peak waveform of a histogram after quantization noise is removed by processing. A lid member angle detecting step for detecting both when the light shielding lid member is closed with respect to the document placement surface prior to reading the document and when the light shielding lid member is closed at a specific angle and when the lid member is closed;
A document specific part reading step for reading a specific part of the document at two time points detected in the lid member angle detection step;
A show-through determination step for determining whether or not the document is easily show-through from the reading result of the document specific part reading step;
An image reading method comprising: a reading condition setting step for setting a reading condition of a document based on a determination result of the show-through determination step.   The reading condition setting step includes a histogram creation step for creating a histogram representing each tone and appearance frequency for a predetermined line of image data of a document, and a tone to be a background candidate from the histogram created in the histogram creation step. A gradation range narrowing step for narrowing down the range, a quantization noise removing step for removing quantization noise generated during image processing from the histogram of the gradation range narrowed down by the gradation range narrowing step, and this quantization noise removal 9. The image reading method according to claim 8, further comprising: a background gradation specifying step for specifying a background gradation from the peak waveform of the histogram after removing quantization noise in the step.

Images