JP2005210492A - Manuscript reader, its correction method, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To automatically correct a region distinction parameter, and to acquire a right distinction result at all times regardless of production variation of the device or apparatus. <P>SOLUTION: The apparatus includes a scanner 11 which reads a reference chart 10 demarcating a character region composed of the character of a predetermined number of pixels preliminarily prepared, and a dot point region configured of a dot point of predetermined number of pixels; an image processing block 21 which respectively detects number of character pixels and number of dot pixels from the image data Din concerning the character region and the dot point region of the reference chart 10 read out here; and a control unit 35 which compares the number of character pixels and number of dot pixels detected here with preliminary established decision expected value, and corrects a region distinction parameter based on the comparison result. The apparatus can automatically corrects the region distinction parameter based on the image data Din obtained by reading the reference chart 10 by a pixel unit. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a document reading apparatus suitable for being applied to a scanner, a digital copying machine, a multi-function machine, or the like having an image area determination adjustment function for determining an image area read from a document and adjusting image data, and correction thereof The present invention relates to a method and an image forming apparatus.

  In recent years, black and white and color printers and copiers that form images based on arbitrary image information, and multi-function peripherals thereof are often used. For example, a digital copier for black and white includes an image forming unit including an exposure unit, a developing unit, a photosensitive drum, and a fixing device in addition to a scanner function.

  The original is read by a scanner, and the original image is binarized to become image information. The exposure means draws an electrostatic latent image on the photosensitive drum based on the image information after image processing. In the developing device, a black toner agent is attached to the electrostatic latent image drawn on the photosensitive drum and developed. The toner image is transferred from the photosensitive drum to a sheet and then fixed by a fixing device. As a result, an image can be formed on the paper fed from the paper feed tray.

  According to this type of digital copying machine, in order to ensure gradation and sharpness of an image read from a document, areas such as characters, photographs, and halftone dots are determined for each type of document image. For example, a dot image in which dots of a certain size are drawn with a certain period is a halftone dot image, and the halftone dot region is often determined using this periodicity. Image information is corrected based on these determination results. This correction eliminates the effects of misjudgment between characters and halftone dots even when the scanner's modulation transfer function (hereinafter referred to as MTF) is low or when the background of the original is detected darkly. The text is clear and the photos and halftone dots can be blurred.

  In relation to a copying machine having such an image area discrimination function, Patent Document 1 discloses a digital copying machine. According to this copier, the control means for controlling the halftone processing means and the binarization processing means based on the image area determination result is provided, and this control means is configured so that each area of the image read from the original is a halftone image. Alternatively, halftone processing or binarization processing is automatically switched based on the region determination result as to whether or not the image is a binary image. In this way, both a photograph and a character image can be clearly copied with respect to a document in which a halftone image such as a photograph and a binary image such as a character are mixed.

  Patent Document 2 discloses an image processing apparatus. According to this image processing apparatus, the mixed image determining means for performing image determination processing in units of pixels is provided, and the mixed image determining means is an image obtained by scanning a document in which character images, photographic images, half-line images, etc. are mixed. A signal is input, a harmonic component is reduced from the image signal, and the density information of the image signal with the reduced harmonic component is compared with a preset reference value. In this way, even an input image in which character images, photographic images, and line drawings are mixed can be reliably discriminated.

JP-A-62-104379 (page 4, FIG. 3) Japanese Patent Laid-Open No. 02-090868 (page 3, FIG. 3)

  By the way, according to the image forming apparatus according to the conventional example, when a region of a photograph, a halftone dot, or a character is discriminated from image information obtained by scanning a document, and image forming processing is performed based on the region discrimination result. There are the following problems.

  i. When discriminating the type of document image for each region, the optimum discrimination result is not necessarily due to variations in MTF due to variations in the optical system of the scanner, transmittance of the platen glass, circuit characteristics for digitally converting the document image, and the like. The current situation is that it has not been obtained. In general, when a document image area is determined, an image area determination unit is provided, and a determination threshold value (hereinafter referred to as an area determination parameter) for determining a halftone dot or a character area is set. This is because the area determination parameter is often manually corrected at the time of device assembly or maintenance.

  ii. Therefore, when the MTF of the scanner is low, or when the background of the original is detected as dark, there is a possibility that the character spacing is clogged and erroneously determined to be a halftone dot portion. In such a case, if the process shifts to image processing with halftone dots while being misidentified, the sharpness of characters after image formation will be lost.

  iii. In addition, if the area that should be determined as a halftone image is erroneously determined as a character area, the dot pitch may be increased during image formation, resulting in an image with more moire fringes. There is.

  Therefore, the present invention solves such a problem related to the conventional example, makes it possible to automatically correct the area determination parameter, and always makes a correct determination without being influenced by the manufacturing variation of the apparatus machine. An object of the present invention is to provide a document reading apparatus, a correction method thereof, and an image forming apparatus capable of acquiring a result.

  In order to solve the above-described problem, a document reading device is a device that performs region discrimination processing on a document including a character portion and a halftone dot portion based on a reading region discrimination parameter, and includes a character portion having a predetermined number of pixels. Image reading means for reading a reference original paper defining a character area to be read and a halftone dot area composed of a halftone dot portion having a predetermined number of pixels, and a character area and a halftone of the reference original paper read by the image reading means Pixel detecting means for detecting the number of pixels in the character part and the number of pixels in the halftone part from the image information relating to the dot area, and the number of pixels in the character part and the number of pixels in the halftone part detected by the pixel detecting means in advance Control means for comparing the set expected determination value and correcting the region discrimination parameter based on the comparison result is provided.

  According to the document reading apparatus of the present invention, when performing region determination processing on a document including a character portion and a halftone portion based on the reading region determination parameter, for example, in the parameter adjustment mode, the image reading unit is prepared in advance. The reference document sheet defining the character region composed of the character portion having the predetermined number of pixels and the halftone region composed of the halftone portion having the predetermined number of pixels is read.

  The pixel detecting means detects the number of pixels in the character portion and the number of pixels in the halftone dot portion from the image information relating to the character area and halftone dot area of the reference document sheet read by the image reading means. On the premise of this, the control means compares the number of pixels in the character part and the number of pixels in the halftone part detected by the pixel detection means with a predetermined determination expected value, and determines the region based on the comparison result. The parameters are corrected.

  Therefore, the area determination parameter can be automatically corrected based on the image information obtained by reading the reference document sheet in which the character area and the dot area are self-evident in advance in units of pixels. As a result, it is possible to always obtain a correct determination result without being affected by manufacturing variations of the apparatus machine.

  A correction method for a document reading apparatus according to the present invention is a method for correcting document reading means for performing region discrimination processing on a document including a character portion and a halftone dot portion based on a region discrimination parameter, wherein a character having a predetermined number of pixels is used. A reference document sheet in which a character area composed of a part and a halftone area composed of a halftone dot part having a predetermined number of pixels are defined, and the prepared reference document sheet is read by the document reading unit, The number of pixels of the character portion and the number of pixels of the halftone portion are detected from the image information relating to the character region and the halftone dot region of the reference document sheet read by the reading means, and the number of pixels of the character portion and the halftone dot detected here are detected. The number of pixels at the point portion is compared with a predetermined expected determination value, and the region determination parameter is corrected based on the comparison result.

  According to the correction method of the document reading apparatus according to the present invention, when performing region determination processing on a document including a character portion and a halftone portion based on a reading region determination parameter, for example, in the parameter adjustment mode, The area discrimination parameter can be automatically corrected based on the image information obtained by reading the reference original paper having a halftone dot area obvious in units of pixels.

  An image forming apparatus according to the present invention is an apparatus that forms an image based on arbitrary image information obtained by reading a document including a character portion and a halftone dot portion, and determines a region based on a reading region determination parameter. A document reading device that performs processing and an image forming unit that forms an image based on image information obtained by the document reading device. The document reading device includes a character portion having a predetermined number of pixels prepared in advance. Image reading means for reading a reference original paper defining a character area to be read and a halftone dot area composed of a halftone dot portion having a predetermined number of pixels, and a character area and a halftone of the reference original paper read by the image reading means Pixel detecting means for detecting the number of pixels in the character portion and the number of pixels in the halftone dot portion from the image information relating to the dot area, and the number of pixels in the character portion and the number of pixels in the dot portion detected by the pixel detecting means Comparing the preset determination expected value, it is characterized in that a control means for correcting the region discrimination parameter based on the comparison result.

  According to the image forming apparatus of the present invention, when the document reading unit of the present invention is applied and a region determination process is performed on a document including a character portion and a halftone portion based on a read region determination parameter, for example, parameter adjustment In the mode, the image reading unit reads a reference document sheet that defines a character area composed of a character portion having a predetermined number of pixels and a halftone area composed of a dot portion having a predetermined number of pixels. It is made like.

  The pixel detecting means detects the number of pixels in the character portion and the number of pixels in the halftone dot portion from the image information relating to the character area and halftone dot area of the reference document sheet read by the image reading means. The control means compares the number of pixels of the character part and the number of pixels of the halftone part detected by the pixel detection means with a preset expected expected value, and corrects the region discrimination parameter based on the comparison result. Made.

  Therefore, the area determination parameter can be automatically corrected based on the image information obtained by reading the reference document sheet in which the character area and the dot area are self-evident in advance in units of pixels. On the premise of this, the document reading means performs a region determination process based on a document reading region determination parameter. The image forming unit forms an image based on the image information after the area determination processing obtained by the document reading unit.

  Therefore, it is possible to form a high-quality image such as contour enhancement or blurring based on the region discrimination process without being affected by the manufacturing variation of the apparatus machine.

  According to the document reading apparatus of the present invention, when the region including the character portion and the halftone portion is subjected to the region determination process based on the read region determination parameter, the number of characters in the character portion and the number of pixels in the halftone portion are set in advance. Control means for comparing the set expected determination value and correcting the region discrimination parameter based on the comparison result is provided.

  With this configuration, it is possible to automatically correct the region determination parameter based on image information obtained by reading a reference document sheet in which the character region and the dot region are self-evident in advance in units of pixels. Therefore, it is possible to always obtain a correct determination result without being influenced by manufacturing variations of the apparatus machine.

  According to the correction method of the document reading apparatus according to the present invention, when correcting the document reading unit that performs the region determination process based on the region determination parameter, the reference document sheet prepared in advance is read by the document reading unit. The number of pixels of the character part and the number of pixels of the halftone part are detected from the image information relating to the character area and the halftone dot area of the reference document sheet read by the document reading means, and the number of pixels of the character part detected here and The number of pixels in the halftone dot portion is compared with a predetermined determination expected value.

  With this configuration, it is possible to automatically correct the region determination parameter based on image information obtained by reading a reference document sheet in which the character region and the dot region are self-evident in advance in units of pixels.

  According to the image forming apparatus of the present invention, the document reading apparatus of the present invention is applied, and the number of pixels in the character portion and the number of pixels in the halftone portion are compared with a predetermined determination expected value, and the comparison result is obtained. Based on this, the region discrimination parameter is corrected.

  With this configuration, it is possible to automatically correct the region determination parameter based on image information obtained by reading a reference document sheet in which the character region and the dot region are self-evident in advance in units of pixels. Therefore, it is possible to form a high-quality image such as contour enhancement or blurring based on the region discrimination process without being affected by the manufacturing variation of the apparatus machine.

  Next, an embodiment of a document reading apparatus, an image forming apparatus, and an image processing method according to the present invention will be described with reference to the drawings.

(1) Document Reading Apparatus FIG. 1 is a conceptual diagram showing a configuration example of a scanner 100 as an embodiment according to the present invention.
In this embodiment, when an area determination process is performed based on a reading area determination parameter for a document including a character area and a halftone area, the number of pixels in the character area, the number of pixels in the halftone area, and a predetermined determination expected value Control means for correcting the area discrimination parameter based on the comparison result, and image information obtained by reading a reference document sheet in which the character area and the halftone area are obvious in advance in units of pixels. Based on this, it is possible to automatically correct the region discrimination parameter and to eliminate the manufacturing variation of the apparatus machine so that a correct discrimination result can always be obtained.

  A scanner 100 shown in FIG. 1 is an example of an original reading apparatus, and is an apparatus that reads an original including a character part and a halftone part and performs area determination processing based on an area determination parameter. The scanner body 11a includes a scanner unit 11 as an example of an image reading unit, and reads a reference document sheet (hereinafter referred to as a reference chart 10) in the parameter adjustment mode.

  The parameter adjustment mode refers to an operation of automatically correcting the region discrimination parameter based on image information obtained by reading the reference chart in units of pixels. The reference chart 10 has a character area and a halftone dot area that are self-evident in advance, and is composed of a character area composed of a predetermined number of character portions and a halftone dot portion of a predetermined number of pixels. This is a sheet in which point areas are defined. Of course, the scanner reads a normal document image in addition to the reference chart 10 and converts it into digital data.

  The scanner 100 includes a scanner unit 11, a control unit 35, and an operation panel 48. For example, an automatic document feeder (ADF) 40 is attached to the scanner body 11a and operates to automatically feed an arbitrary document. The ADF 40 includes a document placing portion 41, a roller 42 a, a roller 42 b, a roller 43, a transport roller 44, and a paper discharge tray 46. One or a plurality of documents 20 are placed on the document placing portion 41.

  A roller 42 a and a roller 42 b are provided on the downstream side of the document placing portion 41. When the automatic paper feeding mode is selected, the document 20 fed out from the document placing portion 41 is U-shaped by the downstream roller 43. It is conveyed so as to rotate. When the automatic paper feeding mode is set, the recording surface of the document 20 is placed upward by the document placement unit 41.

  On the other hand, a control unit 35 is provided in the scanner body, and an operation panel 48 provided in the scanner body 11a is connected to the control unit 35. The operation panel 48 is operated to output image information (hereinafter referred to as image data Dout) obtained by reading an arbitrary document 20 to a printer or the like. A reduction type image sensor is used for the scanner unit 11. For example, when the document 20 is reversed into a U shape by the roller 43, the surface of the document 20 is read and image data Din is output.

  The scanner unit 11 includes a first platen glass 51, a second platen glass 52, a light source 53, mirrors 54, 55, and 56, an imaging optical unit 57, a CCD imaging device 58, and an optical drive unit (not shown). The document 20 read by the scanner unit 11 is transported by the transport roller 44 and discharged to the discharge tray 46. The scanner unit 11 is provided with a CCD imaging device 58 that constitutes a reduction type image sensor, and outputs a document reading signal Sin obtained by reading the document 20. A control unit 35 is connected to the output stage of the CCD imaging device 58.

  FIG. 2 is a block diagram illustrating a configuration example of a control system of the scanner 100. In the scanner 100 shown in FIG. 2, a control unit 35 is connected to the scanner unit 11. The control unit 35 includes an analog / digital (hereinafter referred to as A / D) conversion unit 12, a nonvolatile memory 16, an image area determination block 17, an image processing block 21, a system bus 22, a CPU 25, and a pixel counter 27.

  An A / D conversion unit 12 is connected to the scanner unit 11 so as to A / D convert the document reading signal Sin. The original reading signal Sin becomes digital image data Din after A / D conversion. An image area discrimination block 17 is connected to the A / D converter 12. The image area determination block 17 is provided with a memory of several lines (not shown) for developing the image data Din. The image area discrimination block 17 discriminates a character area and a halftone dot area from the image data Din developed in the memory based on the area discrimination parameter, and sets the rest as a photographic area.

  A pixel counter 27, which is an example of a pixel detection unit, is connected to the image area determination block 17 so as to count the number of character pixels and the number of halftone pixels in the output image according to the reference chart 10 read by the scanner unit 11. Made. That is, the pixel counter 27 is processed so as to detect the character pixel number N and the halftone pixel number M from the image data Din related to the character region and the halftone dot region of the reference chart 10, respectively. The pixel counter 27 has a register (not shown), and this register holds the number N of character pixels and the number M of halftone pixels as the number of detected pixels of characters and halftone dots in the parameter adjustment mode.

  The pixel counter 27 is connected to the system bus 22, and a CPU (Central Processing Unit) 25 as an example of a control unit is connected to the system bus 22. In addition to the image area determination block 17 and the CPU 25, the nonvolatile memory 16 and the operation panel 48 are connected to the system bus 22. The nonvolatile memory 16 stores a correction table for correcting the area determination parameter. In addition to the correction table, the non-volatile memory 16 stores the correction value of the area determination parameter. The area determination parameter is used to adjust the area determination result with respect to the image data Din.

  The operation panel 48 includes an operation unit 14 and a display unit 18 and is operated to set a document reading mode or a parameter adjustment mode. The CPU 25 is connected to a display unit 18 in addition to the operation unit 14 so as to display a document reading mode or a parameter adjustment mode selected and operated by the operation unit 14. For example, the document reading mode or the parameter adjustment mode is converted into display data D2 by the CPU 25 and output to the display unit 18. For example, the operation unit 14 includes a touch panel, and the display unit 18 includes a liquid crystal display panel. In this example, a touch panel constituting the operation unit 14 is combined with a liquid crystal display panel constituting the display unit 18 to constitute a GUI (Graphic User Interface) type operation panel 48.

  The CPU 25 compares the number N of character pixels and the number M of halftone pixels detected by the pixel counter 27 with a predetermined determination expected value, and corrects the region determination parameter based on the comparison result. In this example, the CPU 25 corrects the region determination parameter when the number of character pixels N and the number of halftone pixels M are included in the predetermined range of expected determination values.

  For example, the CPU 25 reads out the character pixel number N and the halftone pixel number M from the register of the pixel counter 27 as the detected number of characters and halftone dots, and refers to the correction table in the nonvolatile memory 16 created in advance to determine the region. The parameter correction value is calculated. In this way, it is possible to execute control such that the number of pixels in the character area and the halftone dot area obtained by reading the reference chart 10 is fed back to the area determination parameter. In addition, when the number of character pixels N and the number of halftone pixels M are outside the range of the predetermined expected determination value, the CPU 25 executes a warning process for the display unit 18.

  An image processing block 21 is connected to the image area determination block 17 described above. The image processing block 21 executes γ correction processing, shading correction, timing control, interline correction processing, and the like on the image data Din, and outputs the image data Dout after the image processing to a printer or the like. When the scanner 100 is configured in this manner, even when the read value of the background density of the original 20 or the MTF is different, the reference chart 10 can be read to check the determination result, and the region determination parameter can be automatically corrected. In addition, a correct determination result can always be obtained without being affected by machine variations.

  FIG. 3 is a block diagram showing an example of the internal configuration of the image area determination block 17. The image area discrimination block 17 shown in FIG. 3 includes a character detection unit 7, a halftone detection unit 8, and a signal synthesis unit 9. The halftone dot detection unit 8 further includes a halftone dot center point detection unit 81, a memory 82, a halftone dot center point periodicity detection unit 83, and a counter 84. The character detection unit 7 and the halftone dot detection unit 8 are connected to the A / D conversion unit 12 shown in FIG. 2 and receive image data Din.

  The character detection unit 7 includes a memory 82A, and detects a character image from the image data Din developed in the memory 82A based on the area determination parameter. For example, a character image is detected based on the character detection algorithm shown in FIGS. 6A and 6B.

  For example, the character detection unit 7 receives 8-bit image data Din, sets a window of X pixels × Y pixels for the image data Din, and further includes a plurality of matrices in the window. The block is divided into blocks, and an average value of luminance (density) is obtained for each block. Thereafter, the character detection unit 7 compares the average luminance value between the blocks with respect to the average luminance value of the pixels in the window, and calculates a difference between them. When the difference value exceeds a fixed determination threshold based on the region determination parameter, it is determined that all the pixels in the matrix are “characters” (see FIGS. 6A and 6B).

  The halftone dot detection unit 8 has a memory 82B, and detects a halftone dot image from the image data Din developed in the memory 82B based on the region discrimination parameter. For example, the halftone dot detection unit 8 compares the luminance average value of the pixel of interest and the surrounding 3 pixel × 3 pixel matrix in the window set in the image data Din, and the luminance of the pixel of interest is based on the region determination parameter. When the threshold value is smaller than the fixed determination threshold, the target pixel is specified as the rising portion of the halftone dot. At this time, the halftone dot detection unit 8 turns on the rising flag.

  In addition, the halftone dot detection unit 8 compares the luminance average value in the window W2 of the pixel of interest and the surrounding 3 pixels × 3 pixel matrix with the rising flag being ON, and the luminance of the pixel of interest is set as the region determination parameter. If it is larger than the fixed determination threshold based on that, the pixel of interest is identified as the fall of a halftone dot. At this time, the halftone dot detection unit 8 turns off the rising flag.

  Further, the halftone dot center point detector 81 detects the halftone dot center point of the halftone dot image from the 8-bit image data Din. For example, the halftone dot center point detection unit 81 refers to ON / OFF of the rising flag regarding the rising edge and falling edge of the halftone image obtained by the halftone dot detection unit 8, and sets the middle point of the target pixel as the center of the halftone dot. It is made a point.

  Further, the halftone dot center point periodicity detection unit 83 detects the periodicity of the halftone dot center point of the document image from the 8-bit image data Din. For example, the halftone dot center point periodicity detection unit 83 is connected to a counter 84 to detect the periodicity of the halftone dot center point obtained by the halftone dot center point detection unit 81.

  The above-described halftone dot detection unit 8 expands the halftone dot region detection process in the sub-scanning direction when it is determined that the target pixel is the halftone dot image Gi. In this example, when there is a halftone image Gi within 5 lines in the sub-scanning direction, processing is performed so that all the lines are halftone images Gi. As a result, the halftone dot area II consisting of the halftone dot images G1 to G22 can be finally detected (see FIGS. 7 to 11).

  A signal synthesis unit 9 is connected to the character detection unit 7 and the halftone detection unit 8 described above, and the image data Din relating to the character region I determined as the character part Ia by the character detection unit 7 and the halftone detection unit 8. The operation is performed to synthesize the image data Din related to the character region I determined as the character portion Ia. In this example, the character area I determined as a character by the character detection unit 7 and not determined as a halftone dot by the halftone detection unit 8 is finally determined as the character portion Ia. The signal synthesizer 9 outputs the character signal Sm to the pixel counter 37.

  FIG. 4 is a conceptual diagram illustrating a configuration example of the reference chart 10, and FIG. 5 is a diagram illustrating a relationship example of the number of detected pixels vs. the detection region. In FIG. 5, the vertical axis represents the number of detected pixels, and TH1 to TH4 are threshold values for determining the number of detected pixels. The four threshold values have a relationship of TH1 <TH2 <TH3 <TH4. The horizontal axis is a detection area, which is the size of a window (X element × Y pixel) when scanning the image data Din developed in the memory 82A.

  The reference chart 10 shown in FIG. 4 is composed of, for example, a sheet of A4 size vertically. The reference chart 10 is provided with a character area I and a halftone dot area II. The reference chart 10 has a constant background, the character portion Ia is drawn at a constant printing rate in the character region I, and the halftone dot portion IIa is drawn at a constant printing rate in the halftone region II. . In the reference chart 10, the number of pixels of the character part Ia drawn in the character area I is set to be smaller than the number of pixels of the halftone part IIa drawn in the halftone area II.

  In this example, the scanner 100 reads the reference chart 10 and counts the number of detected pixels of the character part Ia and the halftone dot part IIa. For example, if the character pixel number N is within the reference value Ref1 ± α in the relationship example of the detected pixel number vs. the detection region shown in FIG. 5, the region determination parameter is not corrected. Assuming that the upper limit threshold value is TH2 and the lower limit threshold value is TH1 as the expected determination value for the number N of character pixels, the CPU 25 first determines whether or not the relationship satisfies TH1 ≦ number of character pixels N ≦ TH2. It is determined whether or not the number N of character pixels is within an allowable range equal to or lower than the upper limit threshold TH2 and equal to or higher than the lower limit threshold TH1.

  After this determination, if the number N of character pixels satisfies TH1 ≦ N ≦ TH2 and is within the reference value Ref1 ± α, the region determination parameter is not corrected, but the number N of character pixels is either If the thresholds TH1 and TH2 are biased, correction is performed on the area discrimination parameter (detection threshold) of the character portion Ia. As a result, the region discrimination parameter can be corrected when the number of character pixels N is included in the range of the predetermined expected determination value and is other than the reference value Ref1 ± α.

  Similarly, if the number of halftone pixels M is within the reference value Ref2 ± β in the relational example of the number of detected pixels vs. the detection region shown in FIG. 5, the region discrimination parameter is not corrected. Assuming that the upper limit threshold value is TH4 and the lower limit threshold value is TH3 as an expected determination value for the number of halftone pixels M, the CPU 25 first determines whether TH3 ≦ the number of halftone pixels M ≦ TH4. It is determined whether or not the number of halftone pixels M is within an allowable range equal to or lower than the upper limit threshold TH4 and equal to or higher than the lower limit threshold TH3.

  After this determination, if the halftone pixel number M satisfies TH3 ≦ M ≦ TH4 and is within the reference value Ref2 ± β, the region determination parameter is not corrected, but the halftone pixel number M is either If the threshold values TH3 and TH4 are biased, correction is performed on the area discrimination parameter (detection threshold value) of the halftone dot portion IIa. Thus, the region discrimination parameter can be corrected when the number of halftone pixels M is included in the range of the predetermined expected determination value and other than the reference value Ref2 ± β.

  Further, when the deviation of the number of halftone pixels or the number of character pixels M is too large, that is, when the number of character pixels M or the number of halftone pixels detected by the pixel counter 27 is outside these ranges, The warning process to the display unit 18 is executed as an abnormality without executing the correction process of the area determination parameter. According to the example shown in FIG. 5, when the number of detected pixels of the character part Ia and the halftone dot part IIa is less than the threshold value TH1, exceeds the threshold value TH2, and is less than the threshold value TH3, and exceeds the threshold value TH4, warning processing is performed. It becomes the object of.

  These cases correspond to, for example, a case where the character part IIa is misidentified as the halftone dot part Ia, a case where the MTF is low, or a case where the background of the document 20 is read darkly. In such a case, the CPU 25 sets the threshold for determining a white pixel to be dark, or sets the dot period to be narrow when the dot interval is read narrowly due to a decrease in MTF. .

  The reference chart 10 has been described with respect to the case where it is separately prepared for the scanner body as shown in FIG. 4, but the present invention is not limited to this, and the reference chart 10 is arranged in the non-image area of the scanner unit 11. The description contents of 10 may be reduced and incorporated, and the region discrimination parameter correction process may be executed every certain period.

  6A and 6B are diagrams showing a window Wm and a character detection example when a character area is detected. The window Wm shown in FIG. 6A has a data matrix of X pixels in the main scanning (horizontal) direction and Y pixels in the sub-scanning (vertical) direction, and is used when scanning the image data Din developed in the memory 82A. Is set. In this example, X = 12 pixels and Y = 4 pixels.

  In this example, for the window Wm, the pixel numbers in the first column are (00, 01, 02, 03, 04, 05, 06, 07, 08, 09, 0a, 0b), and the pixels in the second column The numbers are (10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 1a, 1b), and the pixel numbers in the third column are (20, 21, 22, 23, 24, 25). 26, 27, 28, 29, 2a, 2b) and the pixel numbers in the fourth column are (30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 3a, 3b). is there.

  In this example, the image area discrimination block 17 shown in FIG. 2 discriminates the character area I and the dot area II from the image data Din developed in the memories 82A and 82B based on the area discrimination parameter. The For example, the character detection unit 7 shown in FIG. 3 receives 8-bit image data Din, and first, for the image data Din, a block ## consisting of a matrix of eight 3 pixels × 2 pixels in the window Wm. Dividing into i (i = 1 to 8), the average value of luminance (density) is obtained for each of these blocks.

  In this example, assuming that block # 1 shown in FIG. 6A is the pixel number (00, 01, 02, 10, 11, 12), the character detection unit 7 obtains the average value of the luminance of the pixels in block # 1, and this Is a luminance average value A1. Similarly, assuming that block # 4 is a pixel number (09, 0a, 0b, 19, 1a, 1b), the average value of the pixels in block # 4 is obtained, and this is set as the luminance average value A2.

  Furthermore, assuming that block # 5 is a pixel number (20, 21, 22, 30, 31, 32), the average luminance value of the pixels in block # 5 is obtained, and this is used as the average luminance value B1. Similarly, an average value of pixels of pixel numbers (29, 2a, 2b, 39, 3a, 3b) is obtained for block # 8, and this is used as a luminance average value B2.

  Further, the character detection unit 7 compares the average luminance values of the blocks (# 1 and # 8, # 5 and # 4) between the diagonal lines with respect to the average luminance value of each pixel in the window Wm shown in FIG. 6B. The difference between them (A1 and B2, A2 and B1) is calculated. When the difference value exceeds a fixed determination threshold based on the region determination parameter, it is determined that all the pixels in the matrix are “characters” (character detection algorithm).

  In this example, the image area determination block 17 outputs the character signal Sm to the pixel counter 27 only when it is determined as a character, and does nothing else. In this operation, the region discrimination process is executed while shifting the window W in the main scanning and sub-scanning directions pixel by pixel. Here, the image data Din is averaged for each block in order to remove equal density erroneous discrimination at the halftone dot portion in the area discrimination countermeasure for the halftone dot image.

  FIG. 7 is a diagram illustrating a detection example of the halftone image Gi when the halftone dot region is detected. Each grid (lattice) shown in FIG. 7 corresponds to one pixel of the CCD imaging device 58. In this example, a halftone dot portion IIa is configured with 22 halftone dot images Gi (i = 1 to 22) in a matrix of 24 pixels in the main scanning direction and 12 pixels in the subscanning direction. Show.

  In this example, halftone dot images G1 to G6 are drawn across three lines L1 to L3. Hereinafter, halftone dot images G7 to G11 are drawn across three lines L4 to L6, halftone dot images G12 to G17 are drawn across three lines L7 to L9, and halftone dot images G18 to G22 are drawn. Drawing is performed across three lines L10 to L12.

  8A and 8B are diagrams showing one halftone dot image G1 and a halftone dot detection example when a halftone dot region is detected. The vertical axis shown in FIG. 8B is the density (luminance) of each pixel, and the horizontal axis is the pixel position in the main scanning direction.

  The circular shape straddling the grid shown in FIG. 8A shows one halftone dot image G1. The windows W1 and W2 set on the left and right sides of the circular halftone dot image G1 each have a data matrix of 3 pixels in the main scanning direction and 3 pixels in the sub-scanning direction. The windows W1 and W2 are set when scanning the image data Din developed in the memory 82B when the halftone dot area is detected.

  FIG. 9 is a diagram illustrating an example of data expansion in the memory 82B when the periodicity of the halftone image is detected. In the line L2 shown in FIG. 9, the halftone dot center points of the halftone dot images G1 to G6 exist. Similarly, the halftone dot center points of the halftone dot images G7 to G11 exist on the line L5, and the halftone dot center points of the halftone dot images G12 to G17 exist on the line L8. The halftone dot center point of each of the halftone dot images G18 to G22 exists. In this example, the center points of the respective halftone dot images Gi (i = 1 to 22) exist at equal intervals on the lines L2, L5, L8, and L11. Therefore, after obtaining the center point of the halftone dot in FIG. 8, the process shifts to FIG. 9, and the periodicity of the halftone dot image is detected using this relationship.

  FIG. 10 is a diagram showing an example of expansion of the halftone dot region II in the main scanning direction of the halftone dot image Gi. In this example, when it is determined that the target pixel g shown in FIG. 7 is the halftone image Gi, and the periodicity of the halftone image Gi is detected in FIG. 9, the halftone detection unit 8 shown in FIG. The dot area detection process is extended in the main scanning direction.

  For example, when the counter 84 shown in FIG. 3 is incremented every time a halftone dot center point appears within 13 consecutive pixels in the main scanning direction, the counter 84 counts 16 pixels or more. In addition, the interval is set as a halftone dot region. At this time, 10 pixels before and after the target pixel g in the main scanning direction are expanded. From the next time, when the counter 84 counts 5 pixels or more, the halftone dot area is set. Further, when 15 or more white pixels having a luminance level of 200 gradations or more continue, the halftone dot region is not specified until the counter 84 counts 16 pixels or more.

  In this example, when there is a halftone image Gi within 5 pixels in the main scanning direction shown in FIG. 9, all the pixels are processed as a halftone image Gi as shown in FIG. The In the line L2, dot images G1 to G6 are continuously present. Similarly, halftone dot images G7 to G11 exist continuously on the line L5, halftone dot images G12 to G17 exist continuously on the line L8, and halftone dot images G18 to G18 appear on the line L11. It is specified that G22 exists continuously.

  FIG. 11 is a diagram illustrating an extension example of the halftone dot region II in the sub-scanning direction of the halftone dot image Gi. The halftone dot detection unit 8 shown in FIG. 3 expands the halftone dot area detection process in the sub-scanning direction when the halftone area detection process in the main scanning direction is extended. In this example, if there is a halftone image Gi within 5 lines in the sub-scanning direction shown in FIG. 11, processing is performed so that all the lines are halftone images Gi. As a result, the halftone dot region II including the halftone dot images G1 to G22 shown in FIG. 11 can be detected.

  Next, an example of correction processing in the scanner 100 will be described with respect to the correction method of the document reading unit according to the present invention. 12 is a flowchart (main routine) showing an example of correction processing in the scanner 100, FIG. 13 is a flowchart (discrimination algorithm) showing an example of area discrimination in the image area discrimination block 17, and FIG. 14 is halftone dot detection in the block 17 It is a flowchart (discrimination algorithm) which shows an example.

  In this embodiment, it is assumed that the area determination parameter of the scanner 100 is automatically corrected based on the parameter adjustment mode. In this example, it is assumed that the region correction parameter automatic correction processing is performed in the manufacturing process of the scanner 100 or in maintenance by a serviceman. As shown in FIG. 4, the reference chart 10 defines a character region I composed of a character portion Ia having a predetermined number of pixels and a halftone region II composed of a halftone portion IIa having a predetermined number of pixels. An example will be given in which the paper is prepared in advance. In the reference chart 10, the number of pixels of the character part Ia drawn in the character area I is set to be smaller than the number of pixels of the halftone part IIa drawn in the dot area II.

  With these as automatic correction processing conditions, the operator sets the reference chart 10 to the scanner 100 in step P1 of the flowchart shown in FIG. For example, the reference chart 10 is placed on the document placing portion 41 shown in FIG. 1 and automatically fed to the scanner portion 11 through the ADF 40. In this example, when the operator selects the parameter adjustment mode, the reference chart 10 fed out from the document placing portion 41 is conveyed by the downstream roller 43 so as to rotate in a U-shape. When the operation unit 14 is operated, the parameter adjustment mode is notified by outputting operation data D3 from the operation panel 48 to the CPU 25. Of course, the reference chart 10 may be placed on the platen glass 51.

  In step P2, the scanner 100 reads the reference chart 10 through the scanner unit 11 and acquires image data Din. In the above example, when the U-shaped rotation is performed by the roller 43, the reference chart 10 is read by the reduction type image sensor, and the document reading signal Sin is output to the control unit 35. When the reference chart 10 is placed on the platen glass 51, the document reading signal Sin is output from the CCD imaging device 58 to the control unit 35. The document reading signal Sin is output from the scanner unit 11 to the A / D conversion unit 12, and the A / D conversion unit 12 performs A / D conversion on the document reading signal Sin. The image data Din after A / D conversion is output to the image area determination block 17 and the image processing block 21.

  Thereafter, the process proceeds to step P3, where the image area discrimination block 17 develops the image data Din in the memories 82A and 82B, and discriminates the character area I and the dot area II based on the area discrimination parameter. . For example, in the discrimination algorithm shown in FIG. 13, in step Q1 of the flowchart, the image area discrimination block 17 inputs 8-bit image data Din from the A / D converter 12 to the memories 82A and 82B in the block.

  Thereafter, in step Q2, the image area determination block 17 executes a character detection process. For example, the character detection unit 7 shown in FIG. 3 detects the character region I by developing the image data Din of the reference chart 10 in the memory 82A. At this time, a window Wm with X = 12 pixels and Y = 4 pixels as shown in FIG. 6A is set in the image data Din developed in the memory 82A. The character detection unit 7 divides the window Wm for the image data Din into blocks #i (i = 1 to 8) formed of a matrix of eight 3 pixels × 2 pixels, and the luminance ( (Concentration) average values are obtained.

  At this time, according to the example shown in FIG. 6A, the character detection unit 7 obtains the average value of the luminance of the pixels in the block # 1, and sets this as the average luminance value A1. Similarly, the average value of the pixels in block # 4 is obtained, and this is set as the luminance average value A2. The average value of the luminance of the pixels in block # 5 is obtained, and this is set as the average luminance value B1. Similarly, the average value of the pixels of block # 8 is obtained, and this is set as the luminance average value B2.

  Further, the character detection unit 7 compares the luminance average values of the blocks (# 1 and # 8, # 5 and # 4) with respect to each other with respect to the luminance average value of each pixel in the window Wm shown in FIG. 6B. Then, the difference (A1 and B2, A2 and B1) is calculated. If the difference value exceeds a fixed determination threshold based on the region determination parameter, it is determined that all the pixels in the matrix are “characters”.

  In parallel with the character detection process, in step Q3, the image area determination block 17 executes a halftone dot detection process. For example, the halftone dot detection unit 8 develops the image data Din of the reference chart 10 in the memory 82B and detects the halftone dot region II. At this time, for example, in the discrimination algorithm shown in FIG. 14, the halftone dot detection unit 8 develops the 8-bit image data Din based on the reading of the reference chart 10 into the memory 82A in step R1 of the flowchart and displays the halftone dot image Gi. Is detected. According to the example shown in FIG. 7, the halftone dot portion IIa has 22 halftone dot images Gi (i = 1 to 22) in a matrix of 24 pixels in the main scanning direction and 12 pixels in the sub-scanning direction. And the windows W1 and W2 shown in FIG. 8A are set in the image data Din developed in the memory 82B.

  Then, the process proceeds to step R2, and the halftone dot detection unit 8 executes a halftone dot center point detection process. For example, the halftone dot detection unit 8 inputs the 8-bit image data Din to the halftone dot center point detection unit 81 and controls to detect the halftone dot center point of the document image. When the halftone dot detection unit 81 detects that the target pixel g is a halftone pixel, the halftone dot center point detection unit 81 obtains the halftone dot center point shown in FIG. 8B.

  Thereafter, the process proceeds to step R3, and the halftone dot detection unit 8 executes a halftone dot center point periodicity detection process. At this time, the halftone dot detection unit 8 inputs the 8-bit image data Din to the halftone dot center point periodicity detection unit 83 and controls to detect the periodicity of the halftone dot center point of the document image. As shown in FIG. 9, the halftone dot center periodicity detection unit 83 detects the periodicity of the halftone dot image. Further, as shown in FIG. 10, the halftone dot detection unit 8 extends the halftone dot region detection process in the main scanning direction. For example, when the counter 84 counts 16 pixels or more, the interval is set as a halftone dot region. At this time, 10 pixels before and after the target pixel g in the main scanning direction are expanded. From the next time, when the counter 84 counts 5 pixels or more, the halftone dot area is set.

  In step R4, the halftone detection unit 8 extends the area determination process in the sub-scanning direction. In this example, when the halftone dot image Gi exists within 5 lines in the sub-scanning direction shown in FIG. 11, the halftone dot detection unit 8 is processed so as to make all the halftone dot images Gi between the lines. The Thereby, the halftone dot detector 8 can detect a 1-bit discrimination signal in step R5. This discrimination signal indicates a halftone dot region II composed of halftone dot images G1 to G22 as shown in FIG.

  Thereafter, the process proceeds to step Q4 of the area discrimination algorithm shown in FIG. 13, and the signal synthesizer 9 synthesizes the character area I and the dot area II. Thereby, a discrimination signal can be obtained in step Q5. In step Q2, the character area of the original image is detected. Considering that there is an erroneous discrimination in the halftone area, the halftone image is detected by the halftone detecting unit 8 in step Q3, and the erroneous determination is made in step Q4. By removing another, only the character area I can be detected (area discrimination algorithm). And it returns to step P3 of the flowchart of the example of a correction process shown in FIG.

  In this example, the image area discrimination block 17 outputs the character signal Sm to the pixel counter 27 when it detects a character pixel according to the area discrimination algorithm, and outputs the halftone signal Sa when it detects a halftone pixel. 27 to output each. The pixel counter 27 receives the character signal Sm and the halftone signal Sa for each pixel, counts the number of character pixels N and the number of halftone pixels M, and stores the values of the number of character pixels N and the number of halftone pixels M in a register. It is made to hold. In this example, the character signal Sm and the halftone signal Sa are output to the image processing block 21 in addition to the pixel counter 27.

  Thereafter, in step P4, the CPU 25 detects the number N of character pixels and the number M of halftone pixels in the reference chart 10. For example, the CPU 25 reads the value of the register in the pixel counter 27 so that the number of character pixels M related to the character area I of the reference chart 10 read by the scanner unit 11 and the number of halftone pixels M related to the dot area II are read. Are detected.

  Then, the process proceeds to step P5, and the CPU 25 branches the number M of character pixels related to the character area I and the number M of halftone pixels related to the dot area II, and continues the image processing. For image processing relating to the character region I, the process proceeds to step P6, and the CPU 25 compares the number N of character pixels detected by the pixel counter 27 with a preset expected determination value. Assuming that the upper limit threshold value is TH2 and the lower limit threshold value is TH1 as an expected determination value for the number N of character pixels, the CPU 25 determines whether or not the relationship satisfying TH1 ≦ N ≦ TH2 is satisfied. It is determined whether or not it is within an allowable range that is equal to or lower than the upper threshold TH2 and equal to or higher than the lower threshold TH1. When the number N of character pixels detected by the pixel counter 27 is within these ranges, the process proceeds to step P7.

  In step P7, the CPU 25 further determines whether or not the number N of character pixels is within the reference value Ref1 ± α. If the number of character pixels N is within the reference value Ref1 ± α, the process is terminated without correcting the region discrimination parameter. When the character pixel number N is not within the reference value Ref1 ± α, that is, when the character pixel number N is biased to one of the threshold values TH1 and TH2, the process proceeds to step P8, and the CPU 25 determines the character portion Ia. Correction is performed on the region discrimination parameter (detection threshold). As a result, the region discrimination parameter can be corrected when the number of character pixels N is included in the range of the predetermined expected determination value and is other than the reference value Ref1 ± α.

  For example, the CPU 25 reads the number N of character pixels from the register of the pixel counter 27, refers to the correction table in the nonvolatile memory 16 created in advance, and calculates the correction value of the area determination parameter. The correction value calculated by the CPU 25 is stored in the nonvolatile memory 16.

  For image processing relating to the halftone dot area II, the process proceeds to step P9, and the CPU 25 compares the number of halftone pixels M detected by the pixel counter 27 with a preset expected expected value. Assuming that the upper limit threshold value is TH4 and the lower limit threshold value is TH3 as an expected determination value for the number of halftone pixels M, the CPU 25 determines whether or not the relationship satisfies TH3 ≦ M ≦ TH4. It is determined whether or not the upper limit threshold TH4 is within an allowable range equal to or lower than the lower limit threshold TH23. When the number M of halftone pixels detected by the pixel counter 27 is within these ranges, the process proceeds to Step P10.

  In Step P10, the CPU 25 further determines whether or not the number of halftone pixels M is within the reference value Ref2 ± β. If the number of halftone pixels M is within the reference value Ref2 ± β, the process is terminated without correcting the region discrimination parameter. When the number of halftone pixels M is not within the reference value Ref2 ± β, that is, when the number of halftone pixels M is biased to one of the threshold values TH3 and TH4, the process proceeds to Step P11, and the CPU 25 determines the halftone dot portion IIa. Correction is performed on the area discrimination parameter (detection threshold). Thus, the region discrimination parameter can be corrected when the number of halftone pixels M is included in the range of the predetermined expected determination value and other than the reference value Ref2 ± β.

  For example, the CPU 25 reads the number of halftone pixels M from the register of the pixel counter 27, refers to the correction table in the nonvolatile memory 16 created in advance, and calculates the correction value of the area determination parameter. The correction value calculated by the CPU 25 is stored in the nonvolatile memory 16. The CPU 25 reads an area determination parameter from the nonvolatile memory 16 and performs an area determination process in the normal image forming mode.

  In addition, when the number N of character pixels detected by the pixel counter 27 in step P6 is outside these ranges, and the number of halftone pixels M detected by the pixel counter 27 in step P9 is outside these ranges. In this case, the process proceeds to Step P12, and the warning process to the display unit 18 is executed without executing the correction process of the area determination parameter. At this time, a warning content such as “the area discrimination parameter cannot be automatically corrected because the number N of character pixels or the number M of halftone pixels is outside the allowable range” is displayed on the display unit 18.

  As described above, according to the scanner and the correction processing method thereof according to the embodiment of the present invention, in the parameter adjustment mode, the scanner unit 11 is a character region composed of the character part Ia having a predetermined number of pixels prepared in advance. The reference chart 10 defining I and a halftone dot region II composed of a halftone dot part IIa having a predetermined number of pixels is read.

  The image processing block 21 detects the number N of character pixels and the number M of halftone pixels from the image data Din related to the character area I and the halftone dot area II of the reference chart 10 read by the scanner unit 11. The CPU 25 obtains the number N of character pixels and the number M of halftone pixels detected by the pixel counter 27 and predetermined determination expected values such as threshold values TH1, TH2, TH3, TH4 and reference values Ref1 ± α, Ref2 ± β. The comparison is performed, and the region discrimination parameter is corrected based on the comparison result.

  Accordingly, the area discrimination parameter can be automatically corrected based on the image data Din obtained by reading the reference chart 10 in which the character area I and the halftone dot area II are obvious in advance in units of one pixel. As a result, a correct region discrimination result can always be obtained without being affected by manufacturing variations of the scanner 100.

  In this example, the case where an appropriate area determination parameter is determined by one scanning process has been described. However, the present invention is not limited to this, and an appropriate area determination parameter is determined by one scanning process by the scanner unit 11. If it is not possible, the CPU 25 may execute several scanning processes in the scanner unit 11 while changing the area determination parameter.

(2) Image Forming Apparatus FIG. 15 is a conceptual cross-sectional view showing a configuration example of an image forming apparatus 200 as an embodiment according to the present invention.
In this embodiment, the image forming apparatus 200 to which the scanner 100 shown in FIGS. 1 to 14 is applied is configured, and a reference chart in which the character area I and the halftone area II are obvious is read in units of one pixel. The area discrimination parameter can be automatically corrected based on the obtained image data Din, and manufacturing variations of the apparatus machine can be eliminated, so that a correct discrimination result can always be obtained.

  An image forming apparatus 200 shown in FIG. 15 is an apparatus that forms an image based on arbitrary image data Dout obtained by reading a document 20 including a character portion and a halftone dot portion. It is suitable for application to monochrome printers, copiers, and multi-function machines. This image forming apparatus 200 constitutes a direct transfer type multifunction peripheral or the like that obtains a monochrome image. The image forming apparatus 200 has a document reading means 101 in the apparatus main body, and performs area discrimination processing based on a reading area discrimination parameter. It is made to do. The scanner 100 shown in FIGS. 1 to 14 is applied to the document reading unit 101.

  In the apparatus main body, a scanner unit 11, paper feed trays 30A and 30B, a control unit 35, an image writing unit 60, an image forming unit 70, and the like are provided, and a manual feed tray 63 is provided on the side of the apparatus main body.

  An automatic document feeder (ADF) 40 is attached to the upper portion of the scanner unit 11 and operates to automatically feed an arbitrary document 20 or reference chart 10 as described with reference to FIG. On the other hand, the scanner unit 11 provided in the main body device operates so as to read an arbitrary document 20 or the reference chart 10. A control unit 35 is connected to the output stage of the CCD image pickup device 58 provided in the scanner unit 11, and the CCD image pickup device 58 outputs image data Dout to the control unit 35.

  The control unit 35 outputs the image data Dout after the image processing to the image writing unit 60. The image writing unit 60 generates laser light having a predetermined intensity based on the image data Dout. An image forming unit 70 is provided at a position facing the image writing unit 60, and an image is formed based on the image data Din obtained by the scanner unit 11.

  The image forming means 70 forms an image on the paper 30 fed out from one of the paper feed tray 30A, the paper feed tray 30B, the manual feed tray 63, and the like. The image forming unit 70 includes an organic photosensitive drum (hereinafter referred to as a photosensitive drum) 71, a charger 72, a developing unit 73, a transfer unit 74, a separator 75, a cleaning unit 76, a transport mechanism 77, and a fixing device 78. .

  A charger 72 is disposed above the photosensitive drum 71, and the photosensitive drum 71 is uniformly charged in advance based on a predetermined charging potential. For example, an image writing 60 is provided on the upper right side of the photosensitive drum 71, and laser light having a predetermined intensity based on the image data Dout after image processing is irradiated to expose the photosensitive drum 71. An electrostatic latent image is formed thereon.

  On the right side of the photosensitive drum 71, a developing device 73 containing toner and a carrier (developer) is disposed, and the electrostatic latent image exposed by the image writing unit 60 is developed by the toner agent. Below the developing unit 73, a registration roller 62, paper feed trays 30A and 30B, and the like are provided.

  A transfer device 74 is disposed below the photosensitive drum 71, and a toner image formed on the photosensitive drum 71 through charging, exposure, and development is transferred to a sheet 30 whose conveyance timing is controlled by a registration roller 62. Is done. A separator 75 is provided adjacent to the transfer device 74, and the paper 30 onto which the toner image has been transferred is separated from the photosensitive drum 71. A transport mechanism 77 is provided on the downstream side of the separator 75, and a fixing device 78 is provided at the end thereof. In the fixing device 78, the toner image transferred to the paper 30 is fixed. A cleaning unit 76 is provided between the transport mechanism unit 77 and the above-described charger 72 so as to face the photoconductive drum 71, and the toner remaining on the photoconductive drum 71 is cleaned.

  When duplex copying is selected in this example, an image is formed on one paper surface (front surface), and an image is also formed on the back surface of the paper 30 discharged from the fixing device 78. The sheet 30 discharged from the fixing device 78 is branched from the sheet discharge path by the branching unit 91, and the front and back are reversed by the lower reversing roller 92 and the reversing unit 93 constituting the sheet feeding unit 23. The sheet 30 passes through the reverse conveying path 94 and joins the normal sheet feeding path before the sheet feeding roller 61.

The paper 30 that has been transported in the reverse direction passes through the registration rollers 62 and is transported again to the transfer device 74, and the toner image is transferred onto the other surface (back surface) of the paper 30. The sheet 30 on which the toner image is transferred is fixed by the fixing device 78, is sandwiched between the discharge rollers 95, and is discharged to a discharge tray 96 or the like outside the apparatus. The time of forming these images, 52.3~63.9kg / m ² (1000 sheets) about thin and 64.0~81.4kg / m ² (1000 sheets) of approximately plain paper or a paper 30 83 .0~130.0kg / m ² (1000 sheets) about cardboard and 150.0kg / m ² (1000 sheets) about super thick paper is used. As the image forming conditions, it is preferable that the linear velocity is about 80 to 350 mm / sec, and the environmental conditions are a setting condition of a temperature of about 5 to 35 ° C. and a humidity of about 15 to 85%. The thickness of the paper 30 (paper thickness) is about 0.05 to 0.15 mm.

  FIG. 16 is a block diagram illustrating a configuration example of a control system of the image forming apparatus 200. An image forming apparatus 200 illustrated in FIG. 16 includes a scanner unit 11, an image memory 13, a communication unit 19, a paper feeding unit 23, a control unit 35, an operation panel 48, an image writing unit 60, and an image forming unit 70. The image forming apparatus 200 is an apparatus that forms an image on a desired sheet 30 through the photosensitive drum 71 shown in FIG. 12 based on arbitrary image data Din in the image forming mode. Here, the image forming mode refers to an operation of forming an image on a predetermined sheet 30 based on the image data Dout and outputting an image formed product. The control unit 35 includes a control unit 15 and an image processing block 21.

  The control unit 15 is connected to the scanner unit 11, the image memory 13, the image processing block 21, and the like. In the parameter adjustment mode, the scanner unit 11 defines a character area I composed of a character part having a predetermined number of pixels prepared in advance and a halftone dot area II composed of a halftone part having a predetermined number of pixels. The chart 10 is read. The image processing block 21 detects the number of character pixels N and the number of halftone pixels M from the image data Din related to the character area I and halftone area II of the reference chart 10 read by the scanner unit 11 in the parameter adjustment mode. To be made.

  The control means 15 expects determinations such as threshold values TH1, TH2, TH3, TH4, reference values Ref1 ± α, Ref2 ± β, etc., which are preset with the number of character pixels N and the number of halftone pixels M detected by the image processing block 21. The values are compared with each other, and the region discrimination parameter is corrected based on the comparison result.

  In this example, the control means 15 has a system bus 22. Connected to the system bus 22 are an A / D converter 12, a nonvolatile memory 16, an image area determination block 17, a ROM (Read Only Memory) 24, a RAM (Random Access Memory) 26, a CPU 25 and a pixel counter 27. In the A / D conversion unit 12, the document reading signal Sin output from the scanner unit 11 is A / D converted. The original reading signal Sin becomes digital image data Din after A / D conversion.

  In the image area discrimination block 17, for example, the image data Din output from the A / D conversion unit 12 is developed in the RAM 26 under the memory control of the CPU 25, and the image data Din developed in the RAM 26 is used as an area discrimination parameter. Based on this, the character region I and the dot region II are discriminated. When the document 20 includes a photograph, the photograph area is discriminated in addition to the character area I and the dot area II.

  The pixel counter 27 counts the number of character pixels N and the number of halftone pixels M in order to detect the number of character pixels N and the number of halftone pixels M from the image data Din obtained by reading the reference chart 10, respectively. . The pixel counter 27 has a register (not shown), and this register holds the number N of character pixels and the number M of halftone pixels as the number of detected pixels of characters and halftone dots in the parameter adjustment mode. The nonvolatile memory 16 stores a correction table for correcting the area determination parameter. In addition to the correction table, the non-volatile memory 16 stores the correction value of the area determination parameter.

  The ROM 24 stores system program data for controlling the entire apparatus and an area determination algorithm for executing an area determination process. The RAM 26 is used as a work memory. For example, the image data Din, the control command, and the like are temporarily stored during the area determination process of the image area determination block 17. In this example, when the power is turned on, the CPU 25 reads the system program data from the ROM 24 to start the system, and controls the entire apparatus based on the operation data D3 from the operation unit 14.

  In the image forming apparatus 200, in the image forming mode, the image data Din obtained by reading by the scanner unit 11 is subjected to memory control by the control unit 15 and subjected to image processing by the image processing block 21, and then the image memory 13 Stored in The image data Dout after the image processing is transferred to the image writing unit 60. The image writing unit 60 generates a laser beam having a predetermined intensity based on the image data Dout, and scans the photosensitive drum 71 with the laser beam. The image forming unit 70 develops the electrostatic latent image written on the photosensitive drum 71 by the image writing unit 60 and transfers the image onto a predetermined sheet 30.

  An operation unit 14 is further connected to the control unit 15 and is operated to set an image forming mode or a parameter adjustment mode. In the image forming mode, an operation is performed to select one of the paper feed trays 30A and 30B, the manual feed tray 63, and the like. The operation unit 14 is also used when setting image forming conditions. Image forming conditions, tray selection information, and the like are output to the control unit 15 as operation data D3.

  In addition to the operation unit 14, a display unit 18 is connected to the control unit 15 to display image forming conditions and the like selected and operated by the operation unit 14. For example, the image forming conditions are converted into display data D2 by the control unit 15 and output to the display unit 18. The control unit 15 controls the operations of the image writing unit 60 and the image forming unit 70 so as to form an image based on the contents set by the operation panel 48 in the image forming mode. For example, the control unit 15 outputs the image data Dout or the image data Din ′ after the image processing to the image writing unit 60, and outputs an image formation signal Sp to the image forming unit 70 to perform image formation control.

  In addition to the image writing unit 60 and the image forming unit 70, the communication unit 19 is connected to the control unit 15. The communication means 19 is connected to a communication line such as a LAN, and is used when communicating with an external computer or the like. When the image forming apparatus 100 is used as a printer, the communication unit 19 is used to receive image data Din ′ from an external computer in the print mode.

  The control unit 15 is connected to a sheet feeding unit 23, and drives and controls the sheet feeding trays 30A and 30B shown in FIG. 1 based on a sheet feeding control signal Sf in the image forming mode. The paper feed control signal Sf is supplied from the control means 15 to the paper feed means 23. As the sheet feeding means 23, a feed roller (not shown), a motor for driving the sheet feeding roller, etc., and a drive control IC for driving the motor are used. The paper feed trays 30A and 30B and the like constitute a sheet set tray, and a paper 30 having a predetermined size and quality is set in the paper feed trays 30A and 30B.

Next, an image forming method in the image forming apparatus 200 will be described. FIG. 17 is a flowchart illustrating an operation example in the image forming apparatus 200.
In this embodiment, selection of an image forming mode or parameter adjustment mode is accepted, control is branched based on these mode selections, and when an image forming mode (main scan) is selected, an area determination parameter is read from the nonvolatile memory 16. Is read and the parameter is set in the image area discrimination block 17.

  Under these image forming conditions, the control unit 15 monitors the detection of power-on information and waits for an image forming request or parameter adjustment request in step ST1 of the flowchart shown in FIG. In this example, the operation panel 48 shown in FIG. 16 is provided with a power save button (not shown). For example, power-on information is generated by pressing the power save button of the image forming apparatus 200 in the sleeping state. The The power-on information becomes operation data D3 and is output from the operation unit 14 to the control means 15.

  When this power-on information is detected, the process proceeds to step ST2, and the control means 15 displays a menu selection screen (not shown). For example, an icon or the like for selecting an image forming mode or a parameter adjustment mode is displayed on the menu selection screen. At this time, the operator (user) operates the operation unit 14 so as to select and set any mode (such as touching an icon).

  Thereafter, the process proceeds to step ST3, where the control unit 15 branches the control based on the previously selected mode. When the image forming mode is selected, the process proceeds to step ST4, and the control unit 15 inputs image forming conditions. At this time, for example, the image forming conditions are converted into display data D2 by the control unit 15 and output to the display unit 18. Further, the user operates the operation unit 14 to select one of the paper feed trays 30A and 30B, the manual feed tray 63, and the like, for example. The display unit 18 displays image forming conditions and the like selected and operated by the operation unit 14. Image forming conditions, tray selection information, and the like are output to the control means 15 as operation data D3.

  In step ST5, the scanner unit 11 reads an image from the document 20. At this time, the control unit 15 performs A / D conversion on the document reading signal Sin from the scanner unit 11 by the A / D conversion unit 12, and the image data Din after the A / D conversion is converted into the image area determination block 17 and the image. The data is output to the processing block 21.

  Thereafter, the process proceeds to step ST6, where the image area determination block 17 executes an area determination process. For example, the image area discrimination block 17 discriminates the character area I and the dot area II from the image data Din developed in the memories 82A and 82B shown in FIG. 3 based on the area discrimination parameter. . At this time, the control unit 15 reads the area determination parameter from the nonvolatile memory 16 and sets the parameter in the image area determination block 17. The image region determination block 17 and the like execute region determination processing according to the flowchart shown in FIG. 13, and the halftone detection unit 8 and the like execute halftone detection processing according to the flowchart shown in FIG. 14 (FIG. 13, FIG. 13). 14).

  In step ST7, the image processing block 21 executes image processing based on the region determination result determined for each pixel in the previous step. For example, the image processing block 21 receives the image data Din and executes density conversion processing, spatial filter processing, γ correction processing, shading correction processing, timing control, interline correction processing, and the like. Thereby, it is possible to execute character outline emphasis, halftone image blurring processing and the like based on the region discrimination processing. The image data Dout after the image processing is output to the image writing unit 60 and the like.

  In step ST8, the control unit 15 controls the image forming unit 70 to execute the image forming process. For example, the control unit 15 controls the operations of the image writing unit 60 and the image forming unit 70 so as to form an image based on the previously set image forming condition contents. The control unit 15 outputs the image data Dout after the image processing to the image writing unit 60, and outputs an image formation signal Sp to the image forming unit 70 to perform image formation control.

  In the image forming means 70, the photosensitive drum 71 shown in FIG. 15 is charged to a predetermined potential by the charger 72 based on the image forming signal Sp. An electrostatic latent image is written on the photosensitive drum 71 by the image writing unit 60, and the electrostatic latent image is converted into a toner image by the developing device 73. The toner image on the photosensitive drum 71 is transferred to the paper (transfer material) 30 by the transfer device 74, and the toner image on the paper 30 is fixed by the fixing device 78. Thereafter, the sheet (image formed product) 30 on which the toner image is fixed is discharged onto a discharge tray 96.

  In step ST9, the control unit 15 determines whether or not the page related to the image forming process is the last page. At this time, if it is determined that the page related to the image forming process is not the last page, the control unit 15 returns to step ST8 and repeats the image forming process. If it is determined that the page related to the image forming process is the last page, the process proceeds to step ST11. Note that the number of formed images is counted by a number counter (not shown). When the image forming process for the page is completed in step ST9, the process proceeds to step ST11.

  If the parameter adjustment mode is selected in step ST3, the process proceeds to step ST10 to execute an automatic correction process for the region discrimination parameter. As for the automatic correction process, the correction process is executed in the scanner unit 11 and the like according to the flowchart shown in FIG. In this correction processing, the image region determination block 17 and the like execute region determination processing according to the flowchart shown in FIG. 13, and the halftone detection unit 8 and the like execute halftone detection processing according to the flowchart shown in FIG. (See FIGS. 12 to 14). When the automatic correction processing of the area determination parameter is finished, the process proceeds to step ST11.

  In step ST11, the control unit 15 determines the end of the image forming process. For example, the control unit 15 detects the power-off information and ends the image forming process. If the power-off information is not detected, the process returns to step ST1 to repeat the above-described processing. The power-off information is generated when the power save button of the image forming apparatus 100 is pressed. The power-off information becomes operation data D3 and is output from the operation unit 14 to the control means 15. The control means 15 shifts the device 200 to the sleeping state based on the operation data D3. In the sleeping state, in addition to the monitoring function and the clock function of the CPU 25 and the like, the low power consumption mode for restricting energization is set.

  As described above, according to the image forming apparatus as an embodiment of the present invention, the scanner function (scanner 101) of the present invention is applied to read the document 20 including the character portion and the halftone portion, and based on the area determination parameter. When performing the area determination process, the scanner unit 11 reads the reference chart 10 prepared in advance in the parameter adjustment mode. The image processing block 21 detects the number N of character pixels and the number M of halftone pixels from the image data Din related to the character area I and the halftone dot area II of the reference chart 10 read by the scanner unit 11. The control means 15 compares the number N of character pixels and the number of halftone pixels M detected by the image processing block 21 with preset determination expected values, and corrects the region determination parameter based on the comparison result. The

  Accordingly, the area discrimination parameter can be automatically corrected based on the image data Din obtained by reading the reference chart 10 in which the character area I and the halftone dot area II are obvious in advance in units of one pixel. On the premise of this, the scanner 101 reads the document 20 and performs area determination processing based on the corrected area determination parameter. Therefore, the image forming unit 70 can form an image based on the image data Din after the region discrimination processing read by the scanner unit 11. As a result, it is possible to form a high-quality image such as character outline emphasis based on region discrimination processing, halftone image blurring processing, or the like, regardless of manufacturing variations of the apparatus machine.

  The present invention is extremely suitable when applied to a scanner, a digital copying machine, a multi-function machine, or the like having an image area discrimination adjustment function for discriminating an area of an image read from a document and adjusting image data.

1 is a conceptual diagram illustrating a configuration example of a scanner 100 as an embodiment according to the present invention. 2 is a block diagram illustrating a configuration example of a control system of a scanner 100. FIG. 3 is a block diagram showing an example of the internal configuration of an image area determination block 17. FIG. 3 is a conceptual diagram illustrating a configuration example of a reference chart 10. FIG. It is a figure which shows the example of a relationship of the detection pixel number vs detection area. A and B are views showing a window Wm and a character detection example when a character area is detected. It is a figure which shows the example of a detection of the halftone image Gi at the time of halftone dot area detection. A and B are diagrams illustrating one halftone dot image G1 and a halftone dot detection example when a halftone dot region is detected. It is a figure which shows the example of data expansion | deployment in the memory 82B at the time of the periodicity detection of a halftone image. It is a figure which shows the example of expansion of the halftone area | region II to the main scanning direction of the halftone image Gi. It is a figure which shows the example of expansion of the halftone dot area | region II to the subscanning direction of the halftone image Gi. 5 is a flowchart (main routine) showing an example of correction processing in the scanner 100. 5 is a flowchart (discrimination algorithm) showing an example of area discrimination in an image area discrimination block 17; 7 is a flowchart (discrimination algorithm) showing an example of halftone dot detection in the block 17; 1 is a conceptual cross-sectional view illustrating a configuration example of an image forming apparatus 200 as an embodiment according to the present invention. 3 is a block diagram illustrating a configuration example of a control system of the image forming apparatus 200. FIG. 5 is a flowchart illustrating an operation example in the image forming apparatus 200.

Explanation of symbols

7 character detection unit 8 halftone detection unit 9 signal synthesis unit 10 reference chart 11 scanner unit (document reading means)
15 Control means 17 Image area discrimination block 21 Image processing block (image processing means)
25 CPU (control means)
27 Pixel counter (pixel detection means)
35 Control unit (control means)
48 operation panel 60 image writing unit 70 image forming means 81 halftone dot center point detection unit 83 halftone dot center point periodicity detection unit 100 scanner (document reading apparatus)
101 Document Reading Unit 200 Image Forming Apparatus

Claims (6)

An apparatus for performing area discrimination processing based on a read area discrimination parameter for a document including a character portion and a halftone dot portion,
An image reading unit that reads a reference original sheet that defines a character region composed of a character portion having a predetermined number of pixels and a halftone region composed of a halftone portion having a predetermined number of pixels;
Pixel detecting means for detecting the number of pixels of the character part and the number of pixels of the halftone part from the image information relating to the character area and halftone dot area of the reference document sheet read by the image reading means;
Control means for comparing the number of pixels of the character part and the number of pixels of the halftone dot part detected by the pixel detection means with a predetermined expected determination value and correcting the region discrimination parameter based on the comparison result; An original reading apparatus comprising: When the number of pixels of the character part and the number of pixels of the halftone dot part are included in the predetermined range of expected determination values, the region determination parameter is corrected,
2. The document reading apparatus according to claim 1, wherein a warning process is performed when the number of pixels in the character portion and the number of pixels in the halftone dot portion are outside a predetermined expected value range.   2. The document reading apparatus according to claim 1, further comprising a pixel number counter for counting the number of pixels in the character portion and the number of pixels in the halftone dot portion. The control means includes
2. The scanning process of the image reading unit is performed several times while changing the region determination parameter when an appropriate region determination parameter cannot be determined by one scanning process by the image reading unit. The document reading device described in 1. A method of correcting a document reading device that performs region determination processing on a document including a character portion and a halftone portion based on a region determination parameter,
Preparing a reference manuscript paper in which a character region composed of a character portion having a predetermined number of pixels and a halftone region composed of a halftone portion having a predetermined number of pixels are defined;
The reference document sheet prepared in advance is read by the document reading device,
Detecting the number of pixels of the character portion and the number of pixels of the halftone dot portion from the image information relating to the character region and halftone dot region of the reference original paper read by the original reading device,
Compare the detected number of pixels of the character portion and the number of pixels of the halftone dot portion with a preset expected expected value,
A correction method for a document reading apparatus, wherein the region determination parameter is corrected based on the comparison result. An apparatus for forming an image based on arbitrary image information obtained by reading a document including a character portion and a halftone dot portion,
A document reading device that performs area determination processing based on a reading area determination parameter of the document;
Image forming means for forming an image based on image information obtained by the document reading device;
The document reading device includes:
An image reading unit that reads a reference original sheet that defines a character region composed of a character portion having a predetermined number of pixels and a halftone region composed of a halftone portion having a predetermined number of pixels;
Pixel detecting means for detecting the number of pixels of the character part and the number of pixels of the halftone part from the image information relating to the character area and halftone dot area of the reference document sheet read by the image reading means;
Control means for comparing the number of pixels of the character part and the number of pixels of the halftone dot part detected by the pixel detection means with a predetermined expected determination value and correcting the region discrimination parameter based on the comparison result; An image forming apparatus comprising:

Images