JP2017199976A - Image processing apparatus, image processing method and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for preventing degradation of determination accuracy of a blank space due to false detection of edge in an image processing apparatus.SOLUTION: An edge detector in a blank page determination processing section detects a maximum value and a minimum value of pixel values in a region of a predetermined size in image data obtained by reading a document by a scanner (S111), and then calculates the difference value therebetween (S112). An edge detector generates an edge intensity signal by filtering the image data for extracting an edge (S113). When performing edge detection based on the edge intensity signal, the edge detector disables edge detection based on the edge intensity signal, when the calculated difference value is less than a first threshold (S114-S117). The blank page determination processing section determines whether or not a reading object document of the scanner is blank page, based on the edge detection results from the edge detector.SELECTED DRAWING: Figure 11

Description

  The present invention relates to an image processing apparatus, an image processing method, and a program.

  In an image reading apparatus such as a digital copying machine, there are mainly two types of document reading methods. The first method is a method (optical system moving method) that reads an original image by moving an optical system in a state where the position of the original is fixed by placing the original on a platen glass. The second method is a method (flow-reading method) in which the position of the optical system is fixed and the original image is read while the original is conveyed by an automatic document feeder (ADF).

  In general, in the scanning reading method using the ADF, even when a double-sided original and a single-sided original are mixed, reading is performed on both sides of the conveyed original paper. However, this method also reads a blank page on the back side of the paper on which the original image is printed on one side, which leads to unnecessary processing of data obtained by reading the blank page. Further, when outputting (printing) image data obtained by reading a document, if such blank page printing processing is executed, paper and power are wasted. On the other hand, wasteful consumption of paper and power can be suppressed by determining and deleting blank page image data from image data obtained by reading a document. In addition, when image data is transmitted as electronic data such as an e-mail, the amount of transmission data can be reduced by deleting image data of blank pages.

  Japanese Patent Application Laid-Open No. 2004-228561 proposes a technique for determining whether image data obtained by reading a document is image data obtained by reading a blank page (a plain document). Specifically, the histogram and the number of edge pixels of the image data obtained by reading the document are obtained, and it is determined whether or not the image data is blank page image data based on the obtained histogram and the number of edge pixels. ing. Further, by comparing a maximum density difference in a predetermined block including a pixel of interest and an edge determination threshold with a predetermined block, it is determined whether the pixel of interest is an edge pixel (that is, an edge is detected). Yes.

JP 2010-178377 A

  As described above, when an edge is detected based on the maximum density difference in a predetermined block, it is possible to avoid erroneously detecting a noise component having a relatively small amplitude due to the show-through of the original image as an edge. However, for example, when filter processing for emphasizing edges corresponding to print information is performed on image data while suppressing noise having high frequency or low frequency frequency components, noise components due to show-through are also emphasized. Edge detection may occur. Such an erroneous detection of the edge leads to a decrease in the accuracy of blank page determination based on the edge detection result.

  The present invention has been made in view of the above problems. An object of the present invention is to provide a technique for preventing a decrease in blank page determination accuracy caused by erroneous detection of an edge in an image processing apparatus.

  The present invention can be realized as an image processing apparatus, for example. An image processing apparatus according to an aspect of the present invention is a detection unit that detects a maximum value and a minimum value among pixel values in a region of a predetermined size including a plurality of pixels in image data obtained by reading a document. And filtering processing for extracting edges on the image data to generate an intensity signal indicating edge strength, and edge detection based on the intensity signal generated by the filtering processing means Edge detection means for performing edge detection based on the intensity signal if the difference between the maximum value and the minimum value is less than a first threshold, and the edge detection First determination means for determining whether the target document to be read is a blank page based on the edge detection result by the means. The features.

  According to the present invention, it is possible to prevent a decrease in blank page determination accuracy due to erroneous edge detection in an image processing apparatus. In particular, it is possible to suppress the false detection of edges due to noise caused by show-through while suppressing the false detection of edges due to noise having low frequency and high frequency components. Can be further enhanced.

External view showing a configuration example of a copier Sectional drawing which shows the structural example of the scanner part 110 and the document feeder 111 Block diagram showing a hardware configuration example of a copying machine External view showing a configuration example of the operation unit 120 A block diagram showing a configuration example of a scanner image processing unit 309 and a blank page determination processing unit 504 A block diagram showing a configuration example of a histogram generation unit 602, an edge information generation unit 604, and an edge detection unit 704 A block diagram showing a configuration example of the histogram analysis unit 603 and the edge information generation unit 604 The figure which shows the example of the effective area and invalid area of an original, and area division The figure which shows the example of the frequency characteristic of the filter used by the edge extraction part 754 Flow chart showing the copy processing procedure Flow chart showing the procedure of edge detection processing Figure showing an example of the paper type setting screen

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. The following embodiments do not limit the invention according to the claims, and all combinations of features described in the embodiments are not necessarily essential to the solution means of the invention.

[First Embodiment]
In the first embodiment, a copying machine having a copying function will be described as an example of an image processing apparatus. Note that this embodiment applies not only to a copying machine but also to image data provided from an image reading apparatus such as a multifunction peripheral (MFP) having a number of functions such as a reading function, a printing function, a copying function, and a scanner. The present invention can also be applied to a PC that can execute image processing.

<Copier>
FIG. 1 is an external view showing a configuration example of a copying machine according to the first embodiment. The copying machine includes a printer unit 100, a scanner unit 110, a document feeder 111, and an operation unit 120. The scanner unit 110 corresponds to an image input device, and the printer unit 100 corresponds to an image output device. The document feeder 111 corresponds to an automatic document feeder (ADF). A controller 300 (FIG. 3) is arranged inside the copying machine.

  The scanner unit 110 reads an image on a document, generates image data corresponding to the image, and outputs the generated image data to the controller 300 to perform a document reading operation. A document to be read by the scanner unit 110 is set on the tray 112 of the document feeder 111 or the document table glass 211 (FIG. 2). The scanner unit 110 conveys originals one by one from the tray 112 and reads an image on the original (hereinafter referred to as “flow-reading mode”), and on an original placed on the original platen glass 211. And an operation mode for reading the image. When the user instructs to start reading via the operation unit 120, the controller 300 transmits a document reading instruction to the scanner unit 110. Upon receiving a document reading instruction from the controller 300, the scanner unit 110 performs a document reading operation in any of these operation modes.

  The scanner unit 110 receives reflected light obtained by exposing and scanning an image on a document with light output from an illumination lamp by a linear image sensor (CCD sensor), and converts the image information into an electrical signal by the CCD sensor. Convert. The scanner unit 110 converts an electrical signal output from the CCD sensor into a luminance signal composed of R, G, and B colors, and outputs the luminance signal to the controller 300 as image data.

  The printer unit 100 forms an image on a sheet (paper) based on the image data received from the controller 300. The sheet may be referred to as recording paper, recording material, recording medium, paper, transfer material, transfer paper, or the like. As an example, the printer unit 100 according to the present embodiment forms an image by an electrophotographic method. The printer unit 100 includes a plurality of paper cassettes 101, 102, and 103 that can correspond to different paper sizes and different paper orientations, and a paper discharge tray 104. The printer unit 100 forms an image on a sheet fed from one of the sheet cassettes 101, 102, and 103, and discharges the sheet on which the image is formed to a discharge tray 104.

<Scanner 110 and Document Feeder 111>
FIG. 2 is a cross-sectional view illustrating a configuration example of the scanner unit 110 and the document feeder 111. Hereinafter, a case where the document feeder 111 is operated and the scanner unit 110 performs a document reading operation in the flow-reading mode will be mainly described.

  In FIG. 2, the document bundle 202 to be read is placed on the tray 112 of the document feeder 111. A delivery roller 221, a separation roller 222, and a registration roller 223 are sequentially arranged downstream in the conveyance direction of the document from the document feeder 111. For example, a stepping motor is used as a drive source (not shown) for driving these rollers. The feed roller 221 sends the document bundle 202 placed on the tray 112 to the transport path. A separation roller 222 disposed downstream of the feed roller 221 separates the uppermost document 201 from the conveyed document bundle 202 and conveys it downstream. The document 201 conveyed by the separation roller 222 stops at the position of the registration roller 223 where the rotation is stopped. Thereafter, when the rotation of the registration roller 223 starts at a predetermined timing, the conveyance of the document 201 is resumed. The timing at which the rotation of the registration roller 223 starts is a reference for the conveyance timing of the original 201 and the image reading timing.

  The document 201 that has started to be transported by the registration rollers 223 advances along the guide plate 227 and is then nipped by the large-diameter transport roller 224 and the driven rollers 225a, 225b, and 225c along the outer periphery of the transport roller 224 Be transported. At this time, the document 201 passes through the surface of the document table glass 211. When the document 201 passes through the surface of the document table glass 211, an image on the document 201 is read. After the image is read, the document 201 is further transported along the outer periphery of the transport roller 224. Thereafter, the document 201 is conveyed onto the document feeder 111 by being conveyed at a constant speed in the direction of the arrow shown in FIG. In such a flow reading mode, it is possible to continuously read a document image at a high speed while conveying a large amount of documents one by one in a certain direction.

  Next, the reading of the document image in the flow reading mode will be described in more detail. In the flow-reading mode, the document 201 passes through the surface of the document table glass 211 as described above. At this time, the first mirror unit 219 and the second mirror unit 220 are moved by the motor 218 and arranged at the positions shown in FIG. Light is emitted to the image on the original 201 by the illumination lamp 212 in the first mirror unit 219 at a timing when the image on the original 201 is opposed to the surface of the original table glass 211. The reflected light from the original 201 is reflected by the mirrors 213, 214, and 215 in order, passes through the lens 216, and forms an image on the CCD sensor 217. The reflected light incident on the CCD sensor 217 is converted into an electric signal of each pixel by the CCD sensor 217. The electrical signal output from the CCD sensor 217 is converted into digital data by an A / D converter (not shown), and the digital data is input to the controller 300 as a pixel signal Din.

  In the scanner unit 110 of this embodiment, a rod-shaped light source is used, and a reading line is set in parallel with the longitudinal direction of the light source. The document 201 is conveyed in a direction perpendicular to the reading line. In the present embodiment, a direction parallel to the reading line in the scanner unit 110 is defined as a main scanning direction, and a direction perpendicular to the reading line (original transport direction) is defined as a sub-scanning direction.

  When the scanner unit 110 operates in an operation mode for reading an image on a document placed on the document table glass 211, the scanner unit 110 includes a mirror 213 and an illumination lamp 212 under the document table glass 211 on which the document is placed. The first mirror unit 219 is moved at the speed v. Further, the scanner unit 110 moves the second mirror unit 220 including the mirrors 214 and 215 in the same direction as the movement direction of the first mirror unit 219 at a speed v / 2. In this way, the image on the original 201 is read while scanning in the sub-scanning direction.

<Controller 300>
FIG. 3 is a block diagram illustrating a hardware configuration example of the copying machine according to the present embodiment. The controller 300 is connected to the printer unit 100, the scanner unit 110, and the operation unit 120, and is also connected to a LAN 313 and a public line (WAN) 317. The controller 300 controls the operation of the entire copying machine and controls input / output of various information (data) such as image information and device information.

  A CPU 301 is a processor that controls the operation of the entire copying machine. The CPU 301 reads out and executes a control program stored in the ROM 303 or the HDD (hard disk drive) 304, thereby controlling the operation of each device in the copying machine and controlling various processes performed in the controller 300. A RAM 302 is a system work memory for the CPU 301 to operate, and is also used as an image memory for temporarily storing image data and the like. A ROM 303 is a boot ROM, and stores a system boot program. The HDD (hard disk drive) 304 stores various programs (system software, application programs, etc.) executed by the CPU 301 and various data such as image data. These data may be stored in a non-volatile memory (storage medium) other than the HDD 304.

  A LANC (LAN controller) 305 is connected to the LAN 313 and functions as a communication interface (IF) for communicating with an external device such as the user PC 314 connected via the LAN 313. The CPU 301 can communicate with an external device via the LANC 305, and can transmit and receive image data or control information (control data) to and from the external device. The local IF 306 is an IF such as a USB, and transmits / receives data to / from the user PC 316 or the printer connected via the cable 315. The modem 307 is connected to the public line 317 and transmits / receives data (for example, FAX data) to / from an external device via the public line 317.

  The printer image processing unit 308 functions as a printer IF for the printer unit 100 and communicates with a CPU mounted on the printer unit 100. The printer image processing unit 308 also performs image processing for image data (synchronous / asynchronous conversion) and image formation (printing) by the printer unit 100 on the image data. The scanner image processing unit 309 functions as a scanner IF for the scanner unit 110 and communicates with a CPU mounted on the scanner unit 110. The document feeder 111 is connected to the scanner image processing unit 309 via the scanner unit 110. Also, the scanner image processing unit 309 performs image processing (for example, blank page determination processing described later) on image data obtained by synchronous / asynchronous conversion of image data and reading of an original image by the scanner unit 110. Do.

  The image rotation unit 310 performs rotation processing on the input image data based on the processing conditions set by the user via the operation unit 120 or the orientation of the document. The image compression / decompression unit 311 compresses multi-value image data into JPEG image data, compresses binary image data into image data such as JBIG, MMR, and MH, and decompresses the compressed image data Perform the process. The operation unit IF 312 functions as an IF for the operation unit 120. The operation unit IF 312 outputs image data of an operation screen displayed on the operation unit 120 from the controller 300 side to the operation unit 120. The operation unit IF 312 outputs information input by the user via the operation unit 120 from the operation unit 120 to the controller 300 side.

<Operation unit 120>
FIG. 4 is an external view illustrating a configuration example of the operation unit 120. The operation panel 401 is a combination of a liquid crystal display and a touch panel. The operation panel 401 displays an operation screen, receives a user's touch operation on the operation screen, and transmits information indicating the operation content to the controller 300. A start key 402 is used to instruct the start of execution of a function of the copying machine such as copying (copying function) or reading function.

  The start key 402 incorporates green and red LEDs, and lighting of the green LED indicates that a start instruction is possible, and lighting of the red LED cannot be instructed to start. Indicates. A stop key 403 is used to instruct to stop the operation being executed. The hard key group 404 includes a ten key, a clear key, a reset key, a guide key, and a user mode key.

<Scanner Image Processing Unit 309>
FIG. 5A is a block diagram illustrating a configuration example of the scanner image processing unit 309. The scanner image processing unit 309 is connected to a register (not shown), and a control parameter is set in the register. The scanner image processing unit 309 operates based on the control parameters set in the register. Writing to the register is performed by the CPU 301 and the scanner image processing unit 309. The scanner image processing unit 309 includes a shading correction unit 501, a gamma correction unit 502, a DMAC 503, and a blank page determination processing unit 504.

  The pixel signal Din (image data) input to the scanner image processing unit 309 is input to the shading correction unit 501. The shading correction unit 501 performs shading correction on the input pixel signal Din, and outputs the pixel signal Dh subjected to the shading correction to the gamma correction unit 502. The shading correction is a correction process for removing luminance unevenness caused by the characteristics of the optical system.

  The gamma correction unit 502 performs gamma correction on the input pixel signal Dh, and outputs the pixel signal Dg subjected to gamma correction to the DMAC (DMA controller) 503 and the blank page determination processing unit 504. The gamma correction is a correction process for correcting a difference between the color characteristics of the scanner unit 110 (CCD sensor 217) and the color characteristics of the device on the output side of the scanner unit 110. The DMAC 503 performs control for writing the pixel signal Dg output from the gamma correction unit 502 as image data Dout directly into a specified area of the image memory (RAM 302) without using the CPU 301.

  As will be described in detail below, the blank page determination processing unit 504 determines whether the document (target document) read by the scanner unit 110 is a blank page based on the input pixel signal Dg (image data). The process which determines is performed. In other words, the blank page determination processing unit 504 determines whether or not the image data obtained by reading the document (target document) by the scanner unit 110 is blank page image data.

<Blank Page Determination Processing Unit 504>
FIG. 5B is a block diagram illustrating a configuration example of the blank page determination processing unit 504. The blank page determination processing unit 504 is connected to a register (not shown), in which control parameters are set and processing results are held. The blank page determination processing unit 504 operates based on the control parameter set in the register. Writing to the register is performed by the CPU 301 and the blank page determination processing unit 504. The blank page determination processing unit 504 includes an area control unit 601, a histogram generation unit 602, a histogram analysis unit 603, an edge information generation unit 604, an edge information analysis unit 605, and a blank page determination unit 606. 6 and 7 illustrate specific configuration examples of the histogram generation unit 602, the histogram analysis unit 603, the edge information generation unit 604, and the edge information analysis unit 605.

  In the present embodiment, the blank page determination processing unit 504 generates a histogram and edge information (information indicating the number of edges) based on the input image data. The generated histogram corresponds to a frequency distribution of gradation values (luminance values) expressed by the pixel signal Dg. For example, when the bit accuracy of the pixel signal Dg is 8 bits (256 gradations), the gradation of 256 gradations is obtained. This corresponds to the frequency distribution of each gradation value. The generated edge information corresponds to information indicating the number of edges in the target area. Further, the blank page determination processing unit 504 performs a process of determining whether or not the target document is a blank page based on the generated histogram and edge information analysis result. Hereinafter, the configurations and operations of the region control unit 601, the histogram generation unit 602, the histogram analysis unit 603, the edge information generation unit 604, the edge information analysis unit 605, and the blank page determination unit 606 will be described in detail.

(Region Control Unit 601)
The pixel signal Dg input to the blank page determination processing unit 504 is input to the area control unit 601 as image data corresponding to the document read by the scanner unit 110. A region control unit 601 controls a document region for generating histogram and edge information from input image data.

  Here, FIG. 8 is a diagram showing an example of the valid area and invalid area of the document and area division in the present embodiment. When the original is read by the scanner unit 110, the end of the original to be read (for example, the front end, the rear end, the left end, and the right end in the original transport direction) cannot be appropriately read, and a shadow of the original may occur. . This occurs depending on the configuration of the document transport system (document feeder 111) and the configuration of the light source of the scanner unit 110. When the image data of the shadow portion of the document is used for generating the histogram and the edge information, the determination accuracy by the blank page determination processing unit 504 decreases.

  For this reason, the area control unit 601 identifies such a shadow part, sets the shadow part as an invalid area so that the image data of the shadow part is not used for generation of the histogram and edge information, and other than the shadow part. The part is preset as an effective area. The area control unit 601 determines whether the position of the pixel corresponding to the currently input pixel signal Dg on the document is an effective area or an invalid area, and an area determination signal 701 indicating the determination result (FIG. 6). Is generated.

  Further, the area control unit 601 divides the effective area of the document into a plurality of areas in the main scanning direction and the sub-scanning direction. In the present embodiment, an example will be described in which an effective area of a document is divided into nine areas, area 1 to area 9, as shown in FIG. As described later, such region division is performed to generate histograms and edge information for each region from input image data.

  Here, when a histogram is generated from image data of the entire area of the original, an original on which a small amount of characters is printed locally and an original on a blank page in which impurities contained in the original paper are distributed over the whole, It may be difficult to determine based on the histogram. On the other hand, as shown in FIG. 8A, when histograms of a plurality of areas (divided areas) obtained by dividing an area (effective area) of a document are generated, the difference in histogram between the areas is determined. Based on this, it is possible to appropriately make such a determination.

  In addition, when edge information is generated from image data of the entire area of the original, an original on which a small amount of characters is printed locally and a blank page original in which impurities contained in the original paper are distributed throughout It may be difficult to determine based on the edge information. On the other hand, as shown in FIG. 8A, when the edge information is generated for each area obtained by dividing the area of the document, such a difference is determined based on the difference (variation) in the number of edges between the areas. Discrimination can be performed appropriately.

  The area control unit 601 indicates which of the plurality of divided areas (areas 1 to 9) the position of the pixel corresponding to the currently input pixel signal Dg on the document is. A signal 702 (FIG. 6) is generated. The region control unit 601 outputs the generated region determination signal 701 and region signal 702 to the histogram generation unit 602 and the edge information generation unit 604 together with the input image signal Dg.

  Note that, in the continuous scanning mode using the document feeder 111, there is a case where the size of the document to be read in the sub-scanning direction (document transport direction) is not fixed at the start of scanning by the scanner unit 110. If the size of the original in the sub-scanning direction is not fixed, the area division as shown in FIG. 8A cannot be performed. In this case, as shown in FIG. 8B, region division in the sub-scanning direction may be performed by repeatedly arranging regions of a predetermined size in the sub-scanning direction.

(Histogram generation unit 602)
FIG. 6A is a block diagram illustrating a configuration example of the histogram generation unit 602. The histogram generation unit 602 generates a histogram for each region obtained by region division based on the pixel signal Dg, the region determination signal 701, and the region signal 702. That is, the histogram generation unit 602 generates histograms (first to ninth histograms) indicating the frequency distribution of pixel values for each of the regions 1 to 9 (plural divided regions). Further, the histogram generation unit 602 outputs a histogram set 710 including the first to ninth histograms to the histogram analysis unit 603.

  Specifically, the data distribution unit 703 does not reflect the pixel signal Dg in the histogram when the region determination signal 701 indicates an invalid region. On the other hand, when the region determination signal 701 indicates an effective region, the data distribution unit 703 reflects the pixel signal Dg in the histogram. In this case, the data distribution unit 703 updates (increases) the frequency of the gradation value indicated by the pixel signal Dg in the histogram (any one of the first to ninth histograms) corresponding to the area indicated by the area signal 702.

  When generating a histogram with a bit accuracy lower than the bit accuracy of the pixel signal Dg, the target histogram may be updated using a value obtained by removing lower bits of the pixel signal Dg. For example, when a histogram is generated with an accuracy of 5 bits (32 gradations) based on an 8-bit (256 gradations) pixel signal Dg, a 5-bit value excluding the lower 3 bits of the pixel signal Dg may be used. .

(Edge information generation unit 604)
FIG. 6B is a block diagram illustrating a configuration example of the edge information generation unit 604. The edge information generation unit 604 generates edge information for each region obtained by region division based on the pixel signal Dg, the region determination signal 701, and the region signal 702. That is, the edge information generation unit 604 obtains the number of edges (the number of first to ninth edges) of each of the regions 1 to 9 (a plurality of divided regions) based on the edge detection result by the edge detection unit 704 described later. . Further, the edge information generation unit 604 generates edge information 720 indicating the number of edges in each region, and outputs the edge information 720 to the edge information analysis unit 605.

  The pixel signal Dg input to the edge information generation unit 604 is input to the edge detection unit 704. As will be described in detail below, the edge detection unit 704 performs edge detection processing (FIG. 11) based on the input pixel signal Dg, and generates an edge determination signal indicating whether or not the target pixel is an edge pixel. Generate and output.

  The data distribution unit 705 receives the edge determination signal, the region determination signal 701, and the region signal 702 output from the edge detection unit 704. The data distribution unit 705 does not reflect the edge determination signal output from the edge detection unit 704 in the edge information 720 when the region determination signal 701 indicates an invalid region. On the other hand, the data distribution unit 705 reflects the edge determination signal output from the edge detection unit 704 in the edge information 720 when the region determination signal 701 indicates an effective region. In this case, the data distribution unit 705 updates (increases) the number of edges in the region indicated by the region signal 702 (any one of the first to ninth edge numbers).

(Edge detection unit 704)
FIG. 6C is a block diagram illustrating a configuration example of the edge detection unit 704 for realizing the edge detection processing. The edge detection unit 704 includes a maximum value detection unit 751, a minimum value detection unit 752, a difference calculation unit 753, an edge extraction unit 754, and a determination unit 755. The edge detection unit 704 has a function of buffering the input image signal Dg for processing in each unit.

  The maximum value detection unit 751 and the minimum value detection unit 752 detect the maximum value and the minimum value, respectively, among pixel values in a region of a predetermined size including a plurality of pixels based on the pixel signal Dg. In this embodiment, an area of 9 pixels × 9 pixels is used as an area of a predetermined size. The difference calculation unit 753 calculates the difference between the maximum value and the minimum value detected by the maximum value detection unit 751 and the minimum value detection unit 752, respectively, and outputs the calculated difference value to the determination unit 755. In the present embodiment, the difference calculation unit 753 calculates (maximum value−minimum value) as a difference value.

  The edge extraction unit 754 performs a predetermined calculation based on the pixel signal Dg to generate an edge strength signal indicating the strength of the edge (that is, extract an edge), and output the generated edge strength signal to the edge determination unit 817. To do. Specifically, the edge extraction unit 754 performs a filtering process on the input pixel signal Dg using a filter having a frequency characteristic (frequency response) as shown in FIG. In the present embodiment, the edge extraction unit 754 performs such a filter operation by convolution of a pixel signal Dg in a region of a predetermined size (9 pixel × 9 pixel region) and a 9 × 9 matrix corresponding to a filter. Realize processing. Each coefficient of the 9 × 9 matrix used for the filter process may be stored in advance in a register (not shown) as a control parameter.

  The filter processing by the edge extraction unit 754 generally includes a filter coefficient that realizes a frequency characteristic that increases the weight of a frequency band corresponding to a halftone dot constituting thin print information (emphasizes the frequency component of the frequency band). Used. This is to enable detection of thin print information that is difficult to detect using the histogram generated by the histogram generation unit 602. When a non-blank portion (print information) is detected using a histogram, print information corresponding to a relatively large pixel value based on a difference from a pixel value corresponding to a background portion of the document (a portion where no print information exists) Can be detected. However, for example, it is difficult to detect print information (that is, light print information) having a density close to the background portion of the document. The edge extraction unit 754 performs a filter process for enabling detection of such thin print information.

  FIG. 9 is a diagram illustrating an example of the frequency characteristics of the filter used in the edge extraction unit 754. In FIG. 9, the DC component weight and the Nyquist frequency weight are set to 0, the weight of the intermediate frequency band corresponding to the halftone dot is increased, and the low frequency side and high frequency side frequency bands of the frequency band are increased. The frequency characteristic with a reduced weight is shown. The weight indicated by the frequency characteristic corresponds to the enhancement amount of each frequency component. A halftone dot of a general printed material is composed of 150 to 170 lines. For this reason, for example, when the printing resolution of an original is 600 dpi, it is only necessary to detect a frequency component in the vicinity of 6 [lp / mm] by filtering and to suppress other frequency components. Filtering using a filter having frequency characteristics as shown in FIG. 9 can suppress erroneous detection of noise having frequency components in the low frequency side and high frequency side frequency bands as edges relative to the intermediate frequency band. . Note that such frequency bands on the low frequency side and the high frequency side can be determined based on the type of paper, the MTF characteristics of the optical device, and the like. For example, the frequency bands on the low frequency side and the high frequency side are respectively defined as a frequency band of 2 [lp / mm] or less and a frequency band of 10 [lp / mm] or more.

  Note that when paper containing a large amount of impurities (recycled paper or the like) is used for a document, it may not be possible to suppress erroneous detection of edges due to impurities only by the filter processing by the edge extraction unit 754. However, since such impurities are generally distributed over the entire sheet, as described later, such a false detection is performed by making a determination using the difference (variation) in the number of edges between regions. It is possible to suppress.

  In the present embodiment, the sizes of the regions to be processed by the maximum value detection unit 751, the minimum value detection unit 752, and the edge extraction unit 754 are the same, but they may be different sizes. For example, the size of the region to be processed by the maximum value detection unit 751 and the minimum value detection unit 752 may be larger than the size of the region to be processed by the edge extraction unit 754. As a result, it is possible to detect edges by excluding noise having frequency components on the lower frequency side.

  The determination unit 755 determines whether or not the target pixel is an edge pixel based on the outputs from the difference calculation unit 753 and the edge extraction unit 754, and generates an edge determination signal indicating the determination result. The determination unit 755 outputs the generated edge determination signal to the data distribution unit 705. In the present embodiment, the determination unit 755 generates an edge intensity signal output from the edge extraction unit 754 based on a result of comparison between the difference value output from the difference calculation unit 753 and a predetermined threshold (first threshold). Control edge detection based.

  Here, the reason why the determination unit 755 performs such edge detection control based on the difference value output from the difference calculation unit 753 will be described. Generally, when a document is read by a scanner, print information on the back side (for example, the back surface) of the surface to be read (for example, the front surface) is shown through, and noise due to the show-through occurs in the reading result. Sometimes. The noise caused by the show-through in this manner depends on the thickness and surface property of the original paper, and becomes random noise although the amplitude is not large. Such random noise may have a frequency component to which a large weight is given (that is, emphasized) by the filter processing in the edge extraction unit 754. In this case, noise caused by show-through is emphasized by the filter processing in the edge extraction unit 754, and as a result, such noise may be erroneously detected as an edge. As described above, the noise caused by the show-through generated in the read result is not distributed over the entire sheet like the impurities contained in the recycled paper, but depends on the position and density of the print-out information showing through. Thus, in order to prevent erroneous detection of an edge due to noise caused by show-through, processing for preventing the amplitude of noise caused by show-through from being detected as an edge pixel is required.

  In the present embodiment, whether or not noise due to show-through affects the edge intensity corresponding to the target pixel output from the edge extraction unit 754 in order to prevent the erroneous detection of edges as described above. Is determined based on the difference value output from the difference calculation unit 753. The determination unit 755 compares the difference value output from the difference calculation unit 753 with a predetermined threshold (first threshold), thereby controlling whether or not to perform edge detection based on the edge intensity signal for the target pixel. . The first threshold value is determined in advance based on the amplitude of noise generated in the image data due to the show-through of the original image, for example, by measuring in advance the amplitude of the noise due to the show-through of the original image. Is possible.

  When the difference between the maximum value and the minimum value of the pixel values within an area of a predetermined size is less than the threshold value, noise caused by show-through affects the edge strength corresponding to the target pixel output from the edge extraction unit 754. Can be determined. In this case, the determination unit 755 does not use the edge strength for determining whether or not the target pixel is an edge pixel. On the other hand, when the difference is greater than or equal to the threshold value, it can be determined that noise due to show-through does not affect the edge intensity corresponding to the target pixel output from the edge extraction unit 754. In this case, the determination unit 755 determines whether the target pixel is an edge pixel using the edge strength.

  Specifically, edge detection based on the edge intensity signal output from the edge extraction unit 754 is controlled as follows. When the difference value output from the difference calculation unit 753 is greater than or equal to the threshold value, the determination unit 755 detects an edge based on the edge intensity signal output from the edge extraction unit 754 (whether or not the target pixel is an edge pixel). Is determined). In this case, the determination unit 755 compares the edge intensity corresponding to the pixel of interest indicated by the edge intensity signal output from the edge extraction unit 754 with a predetermined threshold value, so that the pixel of interest is an edge pixel. Determine whether or not. Further, according to the determination result, the determination unit 755 indicates that the target pixel is an edge pixel (set to “ON”), or indicates that the target pixel is not an edge pixel (“OFF An edge determination signal (set to "") is generated and output. On the other hand, when the difference value output from the difference calculation unit 753 is less than the threshold value, the determination unit 755 does not perform edge detection based on the edge intensity signal output from the edge extraction unit 754. In this case, the determination unit 755 generates and outputs an edge determination signal indicating that the target pixel is not an edge pixel (set to “OFF”) regardless of the edge strength signal.

  The edge detection processing as described above in the edge detection unit 704 suppresses erroneous detection of edges caused by noise due to show-through while suppressing erroneous detection of edges caused by noise having low frequency and high frequency components. It becomes possible. As a result, it is possible to prevent the blank page determination accuracy by the blank page determination processing unit 504 (blank page determination unit 606) from being deteriorated due to erroneous detection of an edge.

(Histogram analysis unit 603)
FIG. 7A is a block diagram illustrating a configuration example of the histogram analysis unit 603. The histogram analysis unit 603 determines whether the target document is a blank page (candidate) based on the histogram set 710 generated by the histogram generation unit 602. The histogram analysis unit 603 includes an average value calculation unit 801, a variance value calculation unit 802, an average value determination unit 803, a variance value determination unit 804, and a histogram determination unit 805. The histogram set 710 output from the histogram generation unit 602 is input to the average value calculation unit 801 and the variance value calculation unit 802.

  The histogram analysis unit 603 determines whether the target document is a blank page (candidate) based on the respective histograms (first to ninth histograms) of the regions 1 to 9 (plural divided regions). Specifically, the histogram analysis unit 603 calculates the average value and the variance value of the pixel values in each divided region based on the first to ninth histograms corresponding to the regions 1 to 9. Further, the histogram analysis unit 603 determines whether each divided area is a blank area based on the calculated average value and variance value, and based on the determination result, the target document is a blank page. It is determined whether or not. Hereinafter, the operation of each unit illustrated in FIG. 7A will be described in more detail.

  The average value calculation unit 801 calculates the average values (first to ninth average values corresponding to the regions 1 to 9) of the first to ninth histograms included in the histogram set 710. The average value calculation unit 801 outputs the calculated first to ninth average values to the variance value calculation unit 802 and the average value determination unit 803.

Based on the first to ninth histograms included in the histogram set 710 and the first to ninth average values calculated by the average value calculation unit 801, the variance value calculation unit 802 corresponds to the first to ninth regions. First to ninth dispersion values are calculated. Specifically, the variance value calculation unit 802 calculates (average value−luminance value) ² × frequency for each gradation value (luminance value) of the histogram and obtains the sum of the calculated values corresponding to all luminance values. . Further, the variance value calculation unit 802 calculates the variance value by dividing the sum by the total frequency included in the histogram. The variance value calculated in this way is a high value when characters or the like are printed in the corresponding area, and a low value when nothing is printed in the corresponding area (background color only). Become.

  The average value determination unit 803 compares the first to ninth average values calculated by the average value calculation unit 801 with a predetermined threshold value, so that each of the regions 1 to 9 has a dark image (for example, a photo It is determined whether or not (dark part) is printed. When the average value is relatively low, it can be determined that such a dark image is printed in the corresponding area (that is, not a blank area). For this reason, for each of the regions 1 to 9, the average value determination unit 803 determines a determination signal indicating a blank area when the comparison target average value is equal to or greater than the threshold value, and the comparison target average value is less than the threshold value. Generates a determination signal indicating a non-blank area (not a blank area). The average value determination unit 803 outputs the generated determination signal to the histogram determination unit 805.

  The variance value determination unit 804 determines the variation in the luminance value in each of the regions 1 to 9 by comparing the first to ninth variance values calculated by the variance value calculation unit 802 with a predetermined threshold value. As described above, when the variance value is relatively high and the luminance value varies greatly, it can be determined that characters or the like are printed in the corresponding area (that is, not a blank area). For this reason, for each of the regions 1 to 9, the variance value determination unit 804 determines a determination signal indicating a non-blank region when the comparison variance value is greater than or equal to the threshold value, and the comparison target average value is less than the threshold value. A determination signal indicating a blank area is generated. The variance value determination unit 804 outputs the generated determination signal to the histogram determination unit 805.

  The histogram determination unit 805 is based on the determination signal corresponding to the regions 1 to 9 output from the average value determination unit 803 and the determination signal corresponding to the regions 1 to 9 output from the variance value determination unit 804. It is determined whether or not the target document is a blank page (candidate). The histogram determination unit 805 outputs a determination signal indicating a blank page candidate when all of the determination signals corresponding to the regions 1 to 9 output from the average value determination unit 803 and the variance value determination unit 804 indicate blank regions, respectively. Is generated. On the other hand, when any of the determination signals corresponding to the regions 1 to 9 indicates a non-blank region, the histogram determination unit 805 generates a determination signal indicating a non-blank page candidate (not a blank page candidate). The histogram determination unit 805 outputs the generated determination signal to the blank page determination unit 606.

  Note that the histogram determination unit 805 indicates that a determination signal corresponding to a predetermined number (for example, three) or more of the regions 1 to 9 indicates a non-blank region instead of any of the determination signals corresponding to the regions 1 to 9. In some cases, a determination signal indicating a non-blank page candidate may be generated.

(Edge information analysis unit 605)
FIG. 7B is a block diagram illustrating a configuration example of the edge information analysis unit 605. The edge information analysis unit 605 determines whether the target document is a blank page (candidate) based on the edge information 720 generated by the edge information generation unit 604. The edge information analysis unit 605 includes a maximum value detection unit 811, a minimum value detection unit 812, an upper limit determination unit 813, a lower limit determination unit 814, a division unit 815, a correlation value determination unit 816, and an edge determination unit 817. The edge information 720 output from the edge information generation unit 604 is input to the maximum value detection unit 811 and the minimum value detection unit 812.

  The edge information analysis unit 605 determines whether the target document is a blank page based on the number of edges (the number of first to ninth edges) of each of the areas 1 to 9 (plural divided areas). Specifically, the edge information analysis unit 605 detects the maximum edge number and the minimum edge number among the first to ninth edge numbers corresponding to the regions 1 to 9. Further, the edge information analysis unit 605 includes a first determination process based on the maximum number of edges (upper limit determination unit 813), a second determination process based on the minimum number of edges (lower limit determination unit 814), the maximum number of edges, and the minimum number of edges. And a third determination process (correlation value determination unit) based on the correlation value. Based on the results of these determination processes, the edge information analysis unit 605 determines whether or not the target document is a blank page. Hereinafter, the operation of each unit illustrated in FIG. 7B will be described in more detail.

  The maximum value detection unit 811 detects the maximum value (maximum edge number) among the first to ninth edge numbers included in the edge information 720 output from the edge information generation unit 604, and sets the maximum edge number as an upper limit determination unit. 813. The minimum value detection unit 812 detects the minimum value (minimum edge number) among the first to ninth edge numbers included in the edge information 720 output from the edge information generation unit 604, and sets the minimum edge number as a lower limit determination unit. To 814. Thus, the maximum value detection unit 811 and the minimum value detection unit 812 detect the maximum edge number and the minimum edge number among the first to ninth edge numbers corresponding to the regions 1 to 9, respectively.

  The upper limit determination unit 813 determines whether the target document is a blank page (candidate) by comparing the maximum number of edges output from the maximum value detection unit 811 with a predetermined threshold, and the determination result Is output to the edge determination unit 817. Specifically, the upper limit determination unit 813 receives a determination signal indicating a non-blank page candidate when the maximum number of edges is equal to or greater than a threshold, and a determination signal indicating a blank page candidate when the maximum number of edges is less than the threshold. Output.

  Here, in an image forming apparatus such as a digital multi-function peripheral, security dots or the like for restricting copying of a document (printed material) may be printed on the entire sheet of the document. When the number of edges in each area is obtained from image data corresponding to such a document, the number of edges may be the same in all areas. In this case, when blank page determination processing is performed by comparing the number of edges between regions, the document is determined to be a blank page even if printing is performed on the entire original sheet. The upper limit determination unit 813 performs a determination process (first determination process) based on the maximum number of edges for the purpose of avoiding such a determination error.

  On the other hand, the lower limit determination unit 814 determines whether or not the target document is a blank page (candidate) by comparing the minimum number of edges output from the minimum value detection unit 812 with a predetermined threshold. A signal indicating the determination result is output to the edge determination unit 817. Specifically, the lower limit determination unit 814 generates a determination signal indicating a non-blank page candidate when the minimum number of edges is greater than or equal to a threshold, and a determination signal indicating a blank page candidate when the minimum number of edges is less than the threshold. Output.

  Here, when the original paper is general plain paper, the correlation value of the number of edges between regions, which is obtained by a division unit 815 described later when the original is a blank page, is a high value. For example, if the maximum number of edges is 320 and the minimum number of edges is 300, the correlation value is 0.93 (= 300/320), indicating a high value. However, when the original paper is a good quality paper such as a coated paper, the correlation value of the number of edges between the areas obtained by the dividing unit 815 when the original is a blank page may be a low value. This is because when the number of edges in each area is obtained from image data corresponding to such a document, few edges are detected, and the number of edges in any area can be very small. For example, if the maximum number of edges is 10 and the minimum number of edges is 0, the correlation value is 0 (= 0/10), which is the minimum value. As a result, even if the document is a blank page, it is determined that the document is a non-blank page. In order to avoid such a determination error, the lower limit determination unit 814 performs a determination process (second determination process) based on the minimum number of edges.

  As described above, the division unit 815 and the correlation value determination unit 816 calculate the correlation value of the number of edges between regions, and determine whether or not the target document is a blank page (candidate) based on the correlation value. To do. Specifically, the division unit 815 divides the maximum number of edges detected by the maximum value detection unit 811 and the minimum number of edges detected by the minimum value detection unit 812, thereby correlating the number of edges between regions. The value is calculated, and the calculated correlation value is output to the correlation value determination unit 816. In the present embodiment, the division unit 815 calculates (minimum edge number / maximum edge number) as a correlation value.

  The correlation value determination unit 816 performs a determination process (third determination process) based on the correlation value between the maximum number of edges and the minimum number of edges calculated by the division unit 815. Specifically, the correlation value determination unit 816 determines whether or not the target document is a blank page (candidate) by comparing the correlation value calculated by the division unit 815 with a predetermined threshold value. A signal indicating the determination result is output to the edge determination unit 817. Specifically, correlation value determination section 816 outputs a determination signal indicating a blank page candidate when the correlation value is equal to or greater than a threshold value (that is, the difference between the maximum edge number and the minimum edge number is small). On the other hand, correlation value determination section 816 outputs a determination signal indicating a non-blank page candidate when the correlation value is less than the threshold value (the difference between the maximum edge number and the minimum edge number is large).

The edge determination unit 817 determines whether the target document is a blank page (candidate) based on the results of the determination processing performed by the upper limit determination unit 813, the lower limit determination unit 814, and the correlation value determination unit 816. Specifically, the edge determination unit 817 generates a determination signal indicating the result of the determination process and outputs the determination signal to the blank page determination unit 606 as follows.
When the determination signal from the upper limit determination unit 813 indicates a non-blank page candidate, the determination signal indicating the non-blank page candidate is output without referring to the determination signals from the lower limit determination unit 814 and the correlation value determination unit 816.
When the determination signal from the upper limit determination unit 813 indicates a blank page candidate and the determination signal from the lower limit determination unit 814 indicates a blank page candidate, the blank is not referred to the determination signal from the correlation value determination unit 816. A determination signal indicating a page candidate is output.
When the determination signal from the upper limit determination unit 813 indicates a blank page candidate and the determination signal from the lower limit determination unit 814 indicates a non-blank page candidate, the determination signal from the correlation value determination unit 816 is output as it is.

(Blank page determination unit 606)
The blank page determination unit 606 finally determines whether or not the target document is a blank page based on the determination signal output from the histogram analysis unit 603 and the determination signal output from the edge information analysis unit 605. . Specifically, the blank page determination unit 606 determines that the target document is blank when both the determination signal output from the histogram analysis unit 603 and the determination signal output from the edge information analysis unit 605 indicate blank page candidates. Judged to be a page. On the other hand, when at least one of the determination signal output from the histogram analysis unit 603 and the determination signal output from the edge information analysis unit 605 indicates a non-blank page candidate, the blank page determination unit 606 is blank. It is determined that it is not a page. The blank page determination unit 606 writes information indicating the result of the determination process to the register and notifies the CPU 301 of the completion of the determination process.

<Copy processing>
FIG. 10A is a flowchart showing a copy processing procedure executed in the copying machine according to the present embodiment. The processing of each step shown in FIG. 10A is realized in the copying machine by the CPU 301 reading and executing the program stored in the HDD 304.

  In step S <b> 101, the CPU 301 determines whether or not pressing of the start key 402 of the operation unit 120 is detected. When pressing of the start key 402 is detected, the process proceeds to step S <b> 102 to start document copy processing. In step S <b> 102, the CPU 301 performs a document reading process using the scanner unit 110. In the present embodiment, the scanner unit 110 reads a plurality of pages of documents in the above-described flow reading mode using the document feeder 111. Specifically, the document feeder 111 conveys a plurality of pages of documents placed on the tray 112 to the scanner unit 110 one by one. The scanner unit 110 sequentially reads the images of the document conveyed by the document feeder 111 and generates image data corresponding to the plurality of pages. The image data corresponding to a plurality of pages generated by the scanner unit 110 is output to the scanner image processing unit 309.

  In step S <b> 103, the CPU 301 controls the scanner image processing unit 309 to execute the image processing described with reference to FIGS. 5 to 9 on the image data output from the scanner unit 110. The scanner image processing unit 309 performs image processing such as shading correction and gamma correction on the image data output from the scanner unit 110, and stores the image data after image processing in the image memory (RAM 302). Further, the scanner image processing unit 309 performs blank page determination processing in the blank page determination processing unit 504 based on the image data output from the scanner unit 110. Thereafter, the scanner image processing unit 309 writes information indicating the result of the determination process in a register and notifies the CPU 301 of the completion of the determination process.

  In step S104, the CPU 301 acquires information indicating the result of the determination process by the blank page determination processing unit 504 from the register, and deletes the image data corresponding to the blank page from the image data stored in the image memory. I do. Specifically, the CPU 301 performs a deletion process for deleting the document data corresponding to the document determined to be a blank page by the blank page determination processing unit 504 (blank page determination unit 606), and the image data after the deletion process. Is stored in the image memory.

  When the deletion process is completed, in step S105, the CPU 301 controls the printer image processing unit 308 to perform a printing process by the printer unit 100 based on the image data after the deletion process. When the printing process by the printer unit 100 is completed, the CPU 301 ends the process. In S105, instead of the printing process, a process of transmitting to an external device via a network (such as the LAN 313) may be performed by transmitting an e-mail or the like.

<Edge detection processing>
FIG. 11 is a flowchart showing a procedure of edge detection processing executed in the copier according to the present embodiment. In this embodiment, the processing of each step shown in FIG. 11 is executed by the scanner image processing unit 309 (edge detection unit 704), and is realized by the CPU 301 reading and executing the program stored in the HDD 304. Is also possible.

  As described above, the image data (pixel signal Dg) obtained by reading the document by the scanner unit 110 is input to the edge detection unit 704. In step S111, the edge detection unit 704 (maximum value detection unit 751 and minimum value detection unit 752) has a maximum value and a minimum value among pixel values in a predetermined size area including a plurality of pixels in the input image data. Detect value. In step S112, the edge detection unit 704 (difference calculation unit 753) calculates a difference between the maximum value and the minimum value detected in step S111 and generates a difference value.

  After the processing of S111 and S112, in S113, the edge detection unit 704 (edge extraction unit 754) performs edge filtering on the input image data by performing filter processing for extracting an edge. Intensity signal generation (edge extraction) is performed. In this filter processing, as described above, a filter having frequency characteristics as shown in FIG. 9 is used to emphasize frequency components corresponding to halftone dots included in the original image. Note that the process of S113 may be performed in parallel with the processes of S111 and S112.

  Thereafter, in S114, the edge detection unit 704 (determination unit 755) determines whether or not the difference value calculated in S112 is greater than or equal to a predetermined threshold (first threshold). If the difference value is greater than or equal to the threshold value, the edge detection unit 704 advances the process to S115. In S115, the edge detection unit 704 (determination unit 755) performs edge detection based on the edge intensity signal generated in S113. Here, the edge detection unit 704 (determination unit 755) determines whether or not the pixel of interest is the edge intensity indicated by the edge intensity signal generated in S113 is greater than or equal to a predetermined threshold (second threshold). It is determined whether the pixel is an edge pixel. The edge detection unit 704 advances the processing to S116 when the edge strength is greater than or equal to the threshold, and advances to S117 when the edge strength is less than the threshold.

  In S116, the edge detection unit 704 (determination unit 755) generates an edge determination signal set to “ON” indicating that the target pixel is an edge pixel, and ends the processing. On the other hand, in S117, the edge detection unit 704 (determination unit 755) generates an edge determination signal set to “OFF” indicating that the pixel of interest is not an edge pixel, and ends the processing.

  On the other hand, in S114, the edge detection unit 704 (determination unit 755) advances the process to S117 when the difference value is less than the threshold value. In this case, the edge detection unit 704 invalidates edge detection based on the edge intensity signal generated in S113. Specifically, the edge detection unit 704 generates an edge determination signal set to “OFF” indicating that the pixel of interest is not an edge pixel in S117 regardless of the edge strength signal, and ends the processing. .

  The edge detection unit 704 generates and outputs an edge determination signal as an edge detection result by executing the edge detection process shown in FIG. The blank page determination processing unit 504 performs processing for determining whether or not the target document read by the scanner unit 110 is a blank page based on the edge detection result by the edge detection unit 704.

  In the present embodiment, as described with reference to FIGS. 5 to 9, whether or not the target document is a blank page is determined only by the edge information 720 obtained from the edge detection result by the edge detection unit 704. Not based on the histogram set 710. Thereby, it is possible to further improve the determination accuracy of the blank page.

  As described above, in the present embodiment, the edge detection unit 704 in the blank page determination processing unit 504 performs the filtering process for extracting the edge of the image data obtained by reading the document by the scanner unit 110. To generate an edge strength signal. The blank page determination processing unit 504 determines whether or not the target document read by the scanner unit 110 is a blank page based on the edge detection result by the edge detection unit 704. The edge detection unit 704 detects the maximum value and the minimum value among the pixel values in a region of a predetermined size in the image data, and performs edge detection based on the edge intensity signal if the difference between them is less than the first threshold value. To disable.

  In this way, false detection of edges caused by noise due to show-through can be suppressed while suppressing false detection of edges caused by noise having low-frequency and high-frequency frequency components by filtering the image data. become. As a result, it is possible to prevent the blank page determination accuracy by the blank page determination unit 504 from being lowered due to erroneous edge detection, and it is possible to further increase the blank page determination accuracy.

  The image processing by the scanner image processing unit 309 described in the present embodiment is an information processing apparatus (image processing apparatus) such as a PC that can perform image processing on image data provided from an image reading apparatus such as a scanner. It is also possible to execute in

[Second Embodiment]
In the first embodiment, the document image show-through is performed by controlling whether or not to perform edge detection based on the edge strength obtained by the filtering process on the image data obtained by reading the document according to the determination result of S114. The false detection of the edge resulting from the is suppressed. Here, the noise generated in the reading result due to the show-through of the document image shows different characteristics depending on the paper type of the document. For this reason, when a fixed value is used as the threshold value (first threshold value) used in the determination of S114, the influence of noise caused by show-through on edge detection may not be appropriately suppressed depending on the paper type of the document. There is sex.

  For example, when a paper (thin paper, etc.) that is likely to show through is used as a document paper, the edge strength is increased in a region where noise due to the show-through occurs unless the first threshold is increased. The possibility of performing edge detection based on the signal increases. As a result, erroneous detection of edges can easily occur. On the other hand, when paper (thick paper or the like) in which show-through hardly occurs is used as a document sheet, noise due to show-through is reduced. For this reason, for example, if the first threshold value is set based on thin paper, there is a high possibility that edge detection based on the edge intensity signal is not performed in a region where no show-through occurs. As a result, it may be difficult to detect print information.

  In the second embodiment, by setting (changing) the first threshold value used in the determination of S114 by the edge detection unit 704 in accordance with the paper type of the document, erroneous detection of edges is more appropriately suppressed, and a blank page is set. It is possible to improve the accuracy of determination. In the following, the present embodiment will be described focusing on the differences from the first embodiment.

  FIG. 12 is a diagram illustrating an example of a paper type setting screen 1200. An OK button 1201 is used to save a setting value indicating the setting content on the setting screen 1200 and instruct to close the screen. A cancel button 1202 is used to invalidate the setting contents on the setting screen 1200 and instruct to close the screen. Setting buttons 1203 to 1205 are buttons for setting the paper type of the document, and correspond to plain paper, thick paper, and thin paper, respectively. When any of the setting buttons 1203 to 1205 is pressed and the OK button 1201 is pressed, the CPU 301 sets the type corresponding to the pressed button among the setting buttons 1203 to 1205 as the paper type of the document. The CPU 301 stores a setting value indicating the set paper type in the RAM 302 or the HDD 304. In this way, the CPU 301 sets the paper type of the document to be read by the scanner unit 110.

  FIG. 10B is a flowchart showing a copy processing procedure executed in the copying machine according to the present embodiment. The processing in each step shown in FIG. 10B is realized in the copying machine by the CPU 301 reading and executing the program stored in the HDD 304. Note that the processing of S101 to S105 is the same as that of the first embodiment (FIG. 10A). In step S <b> 101, the CPU 301 determines whether or not pressing of the start key 402 of the operation unit 120 is detected. If pressing of the start key 402 is detected, the process proceeds to step S <b> 201.

  In step S <b> 201, the CPU 301 acquires a set value of the paper type set on the setting screen 1200. Furthermore, in S202, the CPU 301 sets a threshold value (first threshold value used in S114) used in the determination process based on the difference value by the determination unit 755 according to the acquired setting value. That is, the CPU 301 sets the first threshold according to the paper type set as the paper type of the document to be read.

  In S202, for example, when thick paper thicker than plain paper is set as the document paper type, the first threshold is set to a value lower than a threshold (threshold corresponding to plain paper) used when plain paper is set. Set as. On the other hand, when thin paper thinner than plain paper is set as the original paper type, a value higher than the threshold (threshold corresponding to plain paper) used when plain paper is set is set as the first threshold. . The CPU 301 causes the scanner image processing unit 309 to use the threshold value by writing the set threshold value as a control parameter in the register for the scanner image processing unit 309. Note that the CPU 301 may set a lower value as the first threshold value as the paper thickness of the paper type set as the paper type of the document to be read is larger.

  When the setting of the threshold value in S202 is completed, the CPU 301 advances the process to S102 and starts the document copying process. Since the processing of S102 to S105 is the same as the processing in the first embodiment, description thereof is omitted.

  As described above, according to the present embodiment, even if the amount of noise generated in the reading result (image data) of the document due to the show-through of the document image changes depending on the paper type of the document, It is possible to appropriately set the threshold used in the determination of S114. As a result, it is possible to more appropriately suppress erroneous detection of edges due to noise caused by show-through and increase blank page determination accuracy.

[Other Embodiments]
The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read and execute the program This process can be realized. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

100: Printer unit, 110: Scanner unit, 111: Document feeder, 120: Operation unit, 301: CPU, 309: Scanner image processing unit, 504: Blank page determination processing unit, 601: Area control unit, 604: Edge information generation , 704: edge detection unit, 751: maximum value detection unit, 752: minimum value detection unit, 753: difference calculation unit, 754: edge extraction unit, 755: determination unit

Claims (16)

Detecting means for detecting a maximum value and a minimum value among pixel values in an area of a predetermined size including a plurality of pixels in image data obtained by reading a document;
Filter processing means for generating an intensity signal indicating edge intensity by performing filter processing for extracting an edge on the image data;
Edge detection means for performing edge detection based on the intensity signal generated by the filter processing means, and if the difference between the maximum value and the minimum value is less than a first threshold, the edge based on the intensity signal The edge detection means for disabling detection; and
First determination means for determining whether or not the target document to be read is a blank page based on an edge detection result by the edge detection means;
An image processing apparatus comprising: The edge detection unit determines whether the target pixel is an edge pixel based on the intensity signal, and generates an edge determination signal indicating whether the target pixel is an edge pixel,
The edge detection means generates an edge determination signal indicating that the pixel of interest is not an edge pixel regardless of the intensity signal if the difference is less than the first threshold value. An image processing apparatus according to 1. The edge detection means determines that the pixel of interest is an edge pixel if the edge intensity indicated by the intensity signal is greater than or equal to a second threshold, and if the edge intensity indicated by the intensity signal is less than the second threshold. The image processing apparatus according to claim 2, wherein the target pixel is determined not to be an edge pixel. The filter processing means performs the filter processing on the image data using a filter having a frequency characteristic that emphasizes a frequency component corresponding to a halftone dot included in an image of a document. 4. The image processing device according to any one of items 1 to 3. 5. The image processing according to claim 1, wherein the first threshold value is determined in advance based on an amplitude of noise generated in the image data due to a show-through of an image of a document. apparatus. First setting means for setting a paper type of the document to be read;
6. The image processing apparatus according to claim 1, further comprising: a second setting unit configured to set the first threshold according to a paper type set by the first setting unit. The image processing apparatus according to claim 6, wherein the second setting unit sets a lower value as the first threshold value as the thickness of the set sheet type is larger. The second setting means includes
If the set paper type is a paper type thinner than plain paper, a value lower than the threshold value corresponding to the plain paper is set as the first threshold value.
8. If the set paper type is thicker than the plain paper, a value higher than a threshold corresponding to the plain paper is set as the first threshold. Image processing apparatus. First generating means for generating a histogram indicating a frequency distribution of pixel values for each of a plurality of divided areas obtained by dividing a document area based on the image data;
Second generation means for generating edge information indicating the number of edges of each of the plurality of divided regions based on an edge detection result by the edge detection means;
The image according to any one of claims 1 to 8, wherein the first determination unit determines whether or not the target document is a blank page based on the histogram and the edge information. Processing equipment. Second determination means for determining whether the target document is a blank page based on the histogram of each of the plurality of divided regions;
A third determination unit that determines whether or not the target document is a blank page based on the number of edges of each of the plurality of divided regions;
The first determination means includes
When both the second determination unit and the third determination unit determine that the target document is a blank page, information indicating that the target document is a blank page is output;
When at least one of the second determination unit and the third determination unit determines that the target document is not a blank page, information indicating that the target document is not a blank page is output. The image processing apparatus according to claim 9. The second determination unit calculates an average value and a variance value of pixel values in each of the plurality of divided regions based on the histogram of each of the plurality of divided regions, and calculates the calculated average value and variance value. 11. The method according to claim 10, further comprising: determining whether each divided area is a blank area based on the determination result, and determining whether the target document is a blank page based on a result of the determination. The image processing apparatus described. The third determination means detects the maximum number of edges and the minimum number of edges among the number of edges of each of the plurality of divided regions, and based on the first determination process based on the maximum number of edges and the minimum number of edges A second determination process and a third determination process based on a correlation value between the maximum edge number and the minimum edge number are performed, and the results of the first determination process, the second determination process, and the third determination process are obtained. The image processing apparatus according to claim 10, wherein the image processing apparatus determines whether the target document is a blank page based on the determination. Document conveying means for conveying a plurality of pages of documents one by one;
Reading means for sequentially reading images of originals conveyed one by one by the original conveying means to generate image data corresponding to the plurality of pages;
A deletion unit that performs a deletion process of deleting image data corresponding to a document that has been determined to be a blank page by the first determination unit from image data corresponding to the plurality of pages generated by the reading unit;
The image processing apparatus according to claim 1, further comprising: a printing unit that performs a printing process based on image data corresponding to the plurality of pages after the deletion process. Document conveying means for conveying a plurality of pages of documents one by one;
Reading means for sequentially reading images of originals conveyed one by one by the original conveying means to generate image data corresponding to the plurality of pages;
A deletion unit that performs a deletion process of deleting image data corresponding to a document that has been determined to be a blank page by the first determination unit from image data corresponding to the plurality of pages generated by the reading unit;
The image according to any one of claims 1 to 12, further comprising transmission means for transmitting image data corresponding to the plurality of pages after the deletion process to an external device via a network. Processing equipment. A detection step of detecting a maximum value and a minimum value among pixel values in a region of a predetermined size including a plurality of pixels in image data obtained by reading a document;
A filtering process for generating an intensity signal indicating an edge intensity by performing filtering on the image data to extract an edge;
An edge detection step of performing edge detection based on the intensity signal generated in the filter processing step, and if the difference between the maximum value and the minimum value is less than a threshold value, the edge detection based on the intensity signal is performed. Invalidating the edge detection step;
A determination step of determining whether or not the target document to be read is a blank page, based on an edge detection result in the edge detection step;
An image processing method comprising:   The program for making a computer perform each process of the image processing method of Claim 15.

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