JP2010113070A - Image forming apparatus and control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of improving faithful reproducibility of a copied image, a printed image and line width of image data, and to provide a control method. <P>SOLUTION: The line width correction part 40 of the image forming apparatus includes a controller 400, a data storage part 401, a data comparison part 402, a correction value calculation part 403, and a line width correction processing part 406. The data comparison part 402 compares data 1 obtained by reading a reference image for line width correction by a reader-scanner with data 2 obtained by reading the copied image formed on recording material by a printer on the basis of the data 1 by the reader-scanner. The correction value calculation part 403 calculates a correction value A based on a difference between the data 1 and the data 2. The line width correction processing part 406 performs thinning processing that dots are thinned or thickening processing that dots are added on the basis of the correction value A to the image data when outputting copies so that line width of the image of an original may be equal to the line width of the copied image. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and a control method for forming an image by an electrophotographic method.

  2. Description of the Related Art Conventionally, in an image forming apparatus (copier) having a copying function, the following problems occur particularly when an image is formed on a sheet by reading a barcode (one-dimensional barcode and two-dimensional barcode) or a drawing. To do. If the width of the lines constituting the image (line width) is not a predetermined value, the embedded information of the image such as a barcode cannot be read accurately, and the design differs between the image before copying and the image after copying. Problems occur. Therefore, image forming apparatuses are required to faithfully reproduce (copy) a copy target.

  Further, it is known that an electrophotographic image forming apparatus has a difference in line width between a vertical line and a horizontal line of an image formed due to structural factors of the image forming apparatus. Here, the horizontal line is a straight line in a direction (main scanning direction) parallel to the direction of the rotation axis of the photosensitive drum, and the vertical line is a direction (sub-scanning direction) orthogonal to the rotation axis of the photosensitive drum. It is a straight line.

  When reproducing (copying) a halftone such as a photographic original, the optical signal accompanying the reading of the original is photoelectrically converted into an electrical signal, the electrical signal is converted into a laser beam by image processing, and the photosensitive member is exposed. A digital copying machine that develops a latent image formed on a photoconductor to visualize it is suitable.

  In a digital copying machine equipped with an image forming unit that forms an image by electrophotography, the sensitivity characteristics of a reading element such as a CCD and the density characteristics of the image forming unit are not linear. An image is formed on the paper. Further, the density characteristics of the image forming unit vary greatly, and fluctuations in the environment and time occur. Furthermore, since individual variations of the reading system including the reading element also occur, density fluctuation, that is, line width fluctuation is likely to occur even in the entire digital copying machine.

  In view of the above, conventionally, image quality control in image forming apparatuses (copiers and printers) has been widely performed. In particular, regarding an electrophotographic image forming apparatus that forms an image using a plurality of processes, various control methods have been proposed for each process.

  First, a method has been proposed in which a reference image is formed on a photoconductor, the reference image is monitored, and each process is controlled so that a predetermined image is obtained (see, for example, Patent Document 1). In addition, a method has been proposed in which the toner density after the toner image formed on the photoconductor is transferred to a sheet is monitored and each process is controlled (see, for example, Patent Document 2). However, since these methods are controls at an intermediate stage of the image forming process, they are not methods for adjusting the image that the user actually obtains, that is, the fixed image itself, and errors are likely to occur.

  In addition, a method has been proposed in which a reference image is read using an image reading unit provided in an image forming apparatus and used for γ correction control in an actual image forming process (see, for example, Patent Document 3 and Patent Document 4). Since these proposals are controlled using a fixed image that the user actually has, there is an advantage that the control accuracy is improved. However, with these methods, it is possible to adjust the density (gradation density), but there is a problem that the difference in line width between the main scanning direction and the sub-scanning direction cannot be corrected.

  In addition, a method has been proposed in which an optical sensor is disposed in the vicinity of a discharge port from which a sheet is discharged, a reference image and an actual image are read, and an output image is corrected and controlled based on the difference (for example, Patent Document 5, (See Patent Document 6). In these methods, there is an advantage that it is possible to save the user from having to read the output image by the image reading unit provided in the image forming apparatus. However, there is a problem that the reading error of the image reading unit cannot be fed back to the correction control.

  In addition, a method has been proposed in which control is performed in the order of maximum density control, line width control, and gradation correction control, and the line width control changes the amount of exposure light (see, for example, Patent Document 7). In this method, maximum density control is corrected by the number of rotations of the developing sleeve, line width control is corrected by laser power, and tone correction control is γ-corrected. Since there is an image forming apparatus in which the maximum density control is corrected with laser power, in such a case, there is a problem that the maximum density control and the line width control overlap. Furthermore, the line width control detects and corrects both the vertical line (line in the sub-scanning direction) and the horizontal line (line in the main scanning direction) or an oblique line, but cannot correct the vertical line and the horizontal line separately. There is a problem.

In addition, a method for preventing toner scattering at an edge portion of an image formed by superposing a plurality of color toners has been proposed (for example, see Patent Document 8). This method does not mention line width correction of a black monochromatic image such as a barcode, and further reduces the line width in order to prevent toner scattering and to form a thick line width. Since there is only a method of making the line width, there is no mention of a correction method for making the line width thicker.
Japanese Patent Laid-Open No. 3-087768 JP-A-4-193576 Japanese Patent Laid-Open No. 4-077060 JP-A-4-367165 JP-A-8-328322 JP 2003-287930 A JP-A-9-146313 JP-A-9-149281

  The conventional line width control described above has the following problems. Since the line width control is a control at an intermediate stage of the image forming process, there is a problem that an error is likely to occur because it is not a method for adjusting an image that the user actually obtains, that is, a fixed image. Further, it is possible to adjust the density (gradation density), but there is a problem that the difference in line width between the main scanning direction and the sub-scanning direction cannot be corrected. Further, there is a problem that the reading error of the image reading unit provided in the image forming apparatus cannot be fed back to the line width correction. There is also a problem that the maximum density control and the line width control overlap. Further, there is a problem that there is only a method for reducing the line width in order to prevent toner scattering.

  An object of the present invention is to provide an image forming apparatus and a control method capable of improving the faithful reproducibility of a line width of a copy image, a print image, and image data.

  In order to achieve the above object, the present invention provides an image forming apparatus including an image reading unit that reads an image and an image forming unit that forms an image on a recording material. The first image data obtained by reading is compared with the second image data obtained by reading the copy image formed on the recording material by the image forming unit based on the first image data by the image reading unit. Comparing means, calculating means for calculating a first correction value based on a difference between the first image data and the second image data by comparison of the comparing means, line width and copy of the document image By performing thinning processing for thinning out dots or thickening processing for adding dots based on the first correction value to image data at the time of copy output so that the line width of the image becomes equal, the line width The A positive correcting means, characterized in that it comprises a.

  According to the present invention, in an image forming apparatus including an image reading unit that reads an image and an image forming unit that forms an image on a recording material, a first image obtained by reading a reference image for line width correction using the image reading unit. Image data, second image data obtained by reading the copy image formed on the recording material by the image forming unit based on the first image data by the image reading unit, and stored in the image forming apparatus. Comparing means for comparing the print image obtained by forming the recording material by the image forming means on the basis of the reference image data for line width correction with the third image data obtained by reading the image reading means; By the comparison by the comparison means, the first correction value based on the difference between the first image data and the second image data, and the difference between the first image data and the third image data. A second correction value to be calculated, a calculation means for calculating a third correction value based on a difference between the first correction value and the second correction value, a line width of the original image, and a line width of the copy image The line width is corrected by performing a thinning process for thinning dots or a thickening process for adding dots based on the first correction value for image data at the time of copy output so that the The thinning process or the thickening process is performed on the image data at the time of print output based on the second correction value so that the line width of the print image becomes a predetermined line width. Thus, the second correcting means for correcting the line width, and the third width of the image data to be transmitted to the external device so that the line width of the image of the original and the line width of the image read from the original are equal. The thinning process or the fattening process based on the correction value of By performing, characterized by comprising a third correcting means for correcting the line width, the.

  According to the present invention, the image data at the time of copy output is subjected to the thinning process or the thickening process based on the first correction value so that the line width of the original image is equal to the line width of the copy image. Further, the image data at the time of print output is thinned or thickened based on the second correction value so that the line width of the print image becomes a predetermined line width. Further, the image data to be transmitted is thinned or thickened based on the third correction value so that the line width of the image of the document is equal to the line width of the image read from the document. This makes it possible to improve the faithful reproducibility of the line width of the copy image obtained by copying the original image, and improve the fidelity reproducibility of the line width of the print image and image data other than the copy image. It becomes possible to make it.

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

  First, an outline of an embodiment of the present invention will be described. The following control is performed by a line width correction unit that can increase or decrease the line width. A correction value is determined from the fixed image after the final process obtained by the user, the line widths in the main scanning direction and the sub-scanning direction are separately corrected, and correction values relating to all of the image reading unit and the image forming unit are determined. . Further, line width correction control that does not overlap with the maximum density correction control and gradation correction control is performed. Further, the correction value related to all of the image reading unit and the image forming unit, the correction value related to the image forming unit, and the correction value related to the image reading unit are respectively determined, and the output image (copy image, print image, image to be transmitted to the outside) Each correction value is applied according to the data. This improves the faithful reproducibility of the line width.

[First Embodiment]
FIG. 1 is a configuration diagram illustrating a configuration example of an image forming apparatus according to a first embodiment of the present invention.

  In FIG. 1, the image forming apparatus includes a reader scanner 100 (image reading means) and an image forming apparatus main body 200 (image forming means). An image forming apparatus forms a color image by a plurality of image forming units respectively corresponding to a plurality of colors (yellow (Y), magenta (M), cyan (C), and black (K)), and uses an intermediate transfer method as a recording material. It is configured as a tandem type electrophotographic image forming apparatus that performs transfer. The tandem type is suitable for speeding up because one image can be formed by almost one rotation of the intermediate transfer belt. However, the tandem type is not limited to the tandem type image forming apparatus, but a one-drum type color image forming apparatus or monochrome image forming apparatus is used. It may be used.

  The reader scanner 100 includes a mirror unit 21 having a document illumination lamp and a mirror, an image pickup device 22 including a CCD array, and a document loading unit. When reading an image from the document G set in the document loading unit, the mirror unit 21 scans the document G to form an optical image of the document G on the image sensor 22. A luminance image signal obtained by photoelectrically converting the optical image of the original G by the image sensor 22 is converted into a digital image signal by an A / D converter (not shown), and then a gamma (γ ) Perform image processing such as correction.

  An image forming apparatus main body (hereinafter referred to as a printer) 200 includes a black (K) image forming unit, a cyan (C) image forming unit, a magenta (M) image forming unit, a yellow (Y) image forming unit, an intermediate transfer belt 10, A secondary transfer roller 14 and a fixing unit 16 are provided. The printer 200 forms an image on the recording material P (paper or transparent film) based on the image data output from the controller 30 and outputs the image. The printer 200 includes a storage unit (not shown) that stores image data as will be described later.

  The black image forming unit includes a photosensitive drum 1K, a charging roller 2K, an exposure unit 3K, a developing unit 4K, a primary transfer roller 5K, and a cleaning unit 6K. The cyan image forming unit includes a photosensitive drum 1C, a charging roller 2C, an exposure unit 3C, a developing unit 4C, a primary transfer roller 5C, and a cleaning unit 6C. The magenta image forming unit includes a photosensitive drum 1M, a charging roller 2M, an exposure unit 3M, a developing unit 4M, a primary transfer roller 5M, and a cleaning unit 6M. The yellow image forming unit includes a photosensitive drum 1Y, a charging roller 2Y, an exposure unit 3Y, a developing unit 4Y, a primary transfer roller 5Y, and a cleaning unit 6Y.

  An image forming operation by the yellow image forming unit among the image forming units of the plurality of colors (yellow, magenta, cyan, black) will be described as an example. The photosensitive drum 1Y rotates in the direction of arrow A, and the surface of the photosensitive drum 1Y is uniformly charged by the charging roller 2Y. An electrostatic latent image is formed on the photosensitive drum 1Y by irradiating the surface of the photosensitive drum 1Y with laser light corresponding to the image information from the controller 30 by the exposure unit 3Y.

  The developing unit 4Y develops the electrostatic latent image on the photosensitive drum 1Y with yellow toner, thereby forming a yellow toner image on the photosensitive drum 1Y. The yellow toner image on the photosensitive drum 1Y is primarily transferred by the primary transfer roller 5Y onto the intermediate transfer belt 10 that rotates in the arrow B direction via the rollers 11, 12, and 13. After the primary transfer, the primary transfer residual toner on the photosensitive drum 1Y is removed by the cleaning unit 6Y, and then ready for the next image formation.

  Similarly, in the black image forming unit, the cyan image forming unit, and the magenta image forming unit, the magenta toner image, the cyan toner image, and the black toner image are sequentially superimposed on the yellow toner image on the intermediate transfer belt 10 and are primarily transferred. To do.

  The four-color superimposed toner images formed on the intermediate transfer belt 10 formed by the primary transfer are secondarily transferred onto the recording material P by the secondary transfer roller 14 and then conveyed to the fixing unit 16. After fixing the color image on the recording material P by the fixing unit 16, it is discharged to a discharge tray (not shown) provided in the image forming apparatus. After the secondary transfer, the secondary transfer residual toner on the intermediate transfer belt 10 is removed by the cleaning unit 15 and then prepared for the next image formation.

  FIG. 2 is a block diagram illustrating a configuration example centering on a controller 30 that controls the image forming apparatus.

  2, the controller 30 includes a control unit 300, a network interface (I / F) 301, a PDL processing unit 303, an operation unit 304, and an image processing unit 305. The control unit 300 controls each unit. When the user instructs the reading of the document by the operation unit 304, the control unit 300 reads the document by the reader scanner 100 and outputs image data corresponding to the image read from the document. Control to output to the image processing unit 305. Moreover, the control part 300 performs the process shown to each flowchart of FIG. 5 (1st Embodiment) and FIG. 11 (2nd Embodiment) based on a program.

  The image processing unit 305 performs image processing on the image data output from the reader scanner 100. For example, in the case of copying, the image data output from the reader scanner 100 is subjected to image processing suitable for copy output, and the image data after image processing is output to the printer 200. Thereby, a copy image is formed on the recording material. The control unit 300 is connected to the reader scanner 100 and the printer 200 via a predetermined interface. The control unit 300 acquires status information indicating the operation states of the reader scanner 100 and the printer 200, and controls the operations of the reader scanner 100 and the printer 200 based on the status information.

  A network interface (I / F) 301 is connected to a network 302 such as a local area network (LAN), communicates with a personal computer (hereinafter referred to as a PC) connected to the network 302, and exchanges various commands and data. For example, when the image forming apparatus receives a print signal including image data (PDL data) described in a description language (for example, PDL) from the PC, the control unit 300 supplies the PDL data to the PDL processing unit 303.

  The PDL processing unit 303 outputs image data obtained by processing the PDL data to the image processing unit 305. The image processing unit 305 performs image processing suitable for print output on the image data output from the PDL processing unit 303, and outputs the image data after the image processing to the printer 200. As a result, the printer 200 forms a print image on the recording material. The operation unit 304 transmits an instruction input from the user to the control unit 300 and displays the state of the image forming apparatus.

  The control unit 300 causes the reader scanner 100 to read a document when an instruction to read the document is given by the operation unit 304 from the user. Further, the control unit 300 causes the image processing unit 305 to generate image data corresponding to the image read from the document by the reader scanner 100, and transmits the image data to the PC or the like via the network 302 as a file format. The controller 30 includes a facsimile transmission / reception unit, an interface with a telephone line, etc., but the description thereof is omitted here.

  FIG. 3 is a block diagram illustrating a functional configuration example of the image processing unit 305 of the controller 30.

  In FIG. 3, an image processing unit 305 includes a shading correction unit 3051, an input color processing unit 3052, a spatial filter unit 3053, a LOG processing unit 3054, an output color processing unit 3055, a gamma (γ) correction unit 3056, and a smoothing processing unit 3057. I have.

  The image data output from the reader scanner 100 is generally RGB image data. The luminance image signal obtained by photoelectrically converting the optical image of the document by the image sensor 22 in the reader scanner 100 is converted into a digital image signal (RGB image data) by the A / D converter, and is output to the image processor 305. The image processing unit 305 performs white reference correction on the RGB image data output from the reader scanner 100 by the shading correction unit 3051 and performs input masking processing by the input color processing unit 3052. Thereby, the turbidity of the color caused by the CCD spectral characteristics of the image sensor 22 is removed.

  Further, the frequency characteristics of the RGB image data are corrected by the spatial filter 3053, and the RGB image data (RGB signal), which is a luminance signal, is inverted by the LOG processing unit 3054 and converted into a density signal, thereby obtaining a YMC signal. Further, the output color processing unit 3055 converts the YMC signal into a YMCK signal using a known output masking method or a three-dimensional lookup table (LUT) interpolation calculation, and inputs the YMC signal to the gamma correction unit 3056.

  The image processing unit 305 outputs the RGB image data (copy output image data) obtained by the above processing or the RGB image data (print output image data) generated by the PDL processing unit 303 into four colors. The color processing unit 3055 performs color separation into YMCK signals. In some cases, the PDL processing unit 303 outputs YMCK image data. In this case, the output color processing unit 3055 performs color processing on the YMCK image data.

  Next, in the image processing unit 305, the color-separated signal is input to the gamma (γ) correction unit 3056. The gamma correction unit 3056 performs tone correction using an independent lookup table (LUT) for each color, and corrects output characteristics (gamma correction) to the color separation signal. Finally, the signal subjected to gamma correction is input to the smoothing processing unit 3057. The smoothing processing unit 3057 performs a smoothing process on the signal and outputs it to the printer 200. As a result, an image is formed on the recording material by the printer 200.

  FIG. 4 is a block diagram illustrating a configuration example of the line width correction unit 40.

  In FIG. 4, the line width correction unit 40 includes a control unit 400, a data storage unit 401, a data comparison unit 402, a correction value calculation unit 403, a correction value interpolation unit 404, a line width correction reference image storage unit 405, a line width correction. A processing unit 406 is provided.

  The control unit 400 controls each unit of the line width correction unit 40. In the data storage unit 401, the line width of the reference image for line width correction read by the reader scanner 100 is stored as data 1 (first image data). In the data storage unit 401, the line width of the image obtained by further reading the copy image obtained by forming the reference image for line width correction read by the reader scanner 100 on the recording material by the printer 200 by the reader scanner 100 is data 2. It is stored as (second image data).

  The data comparison unit 402 (comparison means) compares data 1 and data 2. In addition, as will be described in a second embodiment described later, the data comparison unit 402 compares data 1 and data 3. The correction value calculation unit 403 (calculation means) corrects the correction value A (first correction value) so that the line width of the original image and the line width of the copy image are equal based on the difference between the data 1 and the data 2. Is calculated. Further, as will be described in a second embodiment described later, the correction value calculation unit 403 calculates a correction value B based on the difference between the data 1 and the data 3, and further, the correction value A and the correction value B. The correction value C, which is the difference between the two, is calculated.

  The correction value interpolation unit 404 determines the correction amount by linearly interpolating the horizontal line width correction amount and the vertical line width correction amount shown in FIG. Line width correction reference image data is stored in the line width correction reference image storage unit 405. The line width correction processing unit 406 (correction unit) applies the line width to the image data read from the document based on the correction value A so that the line width of the image of the document is equal to the line width of the copy image. Correction processing (thinning processing for thinning out dots or thickening processing for adding dots) is performed. Further, as will be described in a second embodiment described later, the line width correction processing unit 406 performs line width correction processing based on the correction value B and the correction value C, respectively.

  Next, the operation of the image forming apparatus of the present embodiment having the above configuration will be described with reference to FIGS.

  FIG. 5 is a flowchart illustrating an example of line width correction control.

  In FIG. 5, the controller 30 first reads the line width correction reference image shown in FIG. 6, for example, with the reader scanner 100, and outputs the line width correction reference image to the line width correction unit 40. Further, the controller 30 causes the control unit 400 of the line width correction unit 40 to store the line width of the reference image for line width correction as data 1 in the data storage unit 401 of the line width correction unit 40 (step S1). Here, the reference image for line width correction may be either of the following. Based on the image stored in the image forming apparatus as a master chart or the reference image data for line width correction stored in the line width correction reference image storage unit 405, an image is formed on a recording material by the printer 200 and output. Either print image can be used.

  In addition, the controller 30 performs image processing on the image data obtained by reading the line width correction reference image with the reader scanner 100 by the image processing unit 305, and then uses the printer 200 as a recording material for a copy image of the line width correction reference image. Form and output to the discharge tray (step S2). Thereafter, the user takes out the recording material from the discharge tray and sets it on the document loading portion of the reader scanner 100.

  Along with this, the controller 30 reads a copy image of the reference image for line width correction from the recording material set in the document loading section by the reader scanner 100 and outputs it to the line width correction section 40. Further, the controller 30 causes the control unit 400 of the line width correction unit 40 to store the line width of the copy image as data 2 in the data storage unit 401 (step S3).

  Next, the controller 30 compares the data 1 and the data 2 by the data comparison unit 402 (step S4). Next, the controller 30 calculates a correction value A based on the difference between the data 1 and the data 2 so that the line width of the data 2 is substantially equal to that of the data 1 (the line widths of both data are equal). Calculated by the unit 403 (step S5). Thereby, the line width correction control is finished (step S11). The correction value A (first correction value) is a line width correction value including the reader scanner 100 and the printer 200. This completes the calculation of the line width correction value at the time of outputting the copy image.

  At the time of copy output in which an image of an actual document is formed on a recording material, image data obtained by reading the document with the reader scanner 100 is output to the line width correction unit 40 by the controller 30. Next, the following processing is performed by the line width correction processing unit 406 of the line width correction unit 40. Thinning processing for thinning out dots or thickening processing for adding dots based on the correction value A so that the line width of the original image and the line width of the copy image are equal. The line width correction process is performed.

  Thereafter, the image data after the line width correction processing is output from the line width correction unit 40 to the controller 30, the image is formed by the printer 200 under the control of the controller 30, and a copy image is output.

  If the correction value differs between the horizontal line (line in the main scanning direction parallel to the direction of the rotation axis of the photosensitive drum) and the vertical line (line in the sub-scanning direction orthogonal to the rotation axis of the photosensitive drum), the correction value is calculated. The unit 403 calculates a horizontal line correction value A1 and a vertical line correction value A2. It is more preferable that the correction amount of the image data is different between the main scanning direction and the sub scanning direction. Patent Document 7 described above describes that the horizontal line is thin and the vertical line is thick, but this differs depending on the configuration of the image forming apparatus. In the case of the jumping development method in which the photosensitive drum and the developing sleeve are not in contact with each other, an image formation in which the horizontal line is thick and the vertical line is thin because the amount of toner attached to the trailing edge of the image increases due to a phenomenon called “sweeping”. There is also a device.

  The ratio of the line width between the horizontal line and the vertical line is determined to some extent by the configuration of the image forming apparatus. For this reason, for example, if one of the horizontal line and vertical line correction values is calculated by the above method and then the other correction value is calculated by a calculation formula, the line width correction control time can be shortened. In addition, after calculating the correction value of the middle of the horizontal line and the vertical line, that is, for example, the oblique line of 45 degrees oblique (the line not parallel to the rotation axis of the photosensitive drum) by the above method, the correction value of the horizontal line and the vertical line is calculated. A method of calculating by an equation may be used.

  An example of calculating the correction values for the horizontal and vertical lines is as follows. For example, as shown in FIG. 6, a case is assumed in which three line width correction reference images are set for each of 8 horizontal lines and 1200 vertical lines (dot per inch). For the line width, nine points are measured in total at three points per line, and an average value obtained by averaging the measured values at seven points excluding the upper limit value and the lower limit value is used. This is calculated for each of the horizontal and vertical lines. From the difference between data 1 and data 2 calculated using this average value, for example, a horizontal line correction value A1 = + 10 μm and a vertical line correction value A2 = + 20 μm are calculated.

  In the present embodiment, the following line image is used as the reference image for line width correction. That is, in the main scanning direction, the sub-scanning direction, both the main scanning direction and the sub-scanning direction, or the oblique direction (direction not parallel to the rotation axis of the photosensitive drum), single colors (Y, M, C) A plurality of types of line images composed of K) or a plurality of colors (R, G, B) are used.

  Next, thinning processing for thinning out dots and thickening processing for adding dots will be described as line width correction processing in the line width correction processing unit 406 of the line width correction unit 40. In the present embodiment, the resolution of the original image read, image data, image formation, and line width correction by the reader scanner 100 is 1200 dpi, and the 1-dot size of 1200 dpi is approximately 21 μm.

  FIG. 7 shows image data of a vertical line (line in the sub-scanning direction) with correction level 0 (no correction), and FIGS. 8A to 8D show images of vertical line thickening processing correction level + 1 to correction level + 4. Data, FIGS. 9A to 9D show correction level-1 to correction level-4 of the thinning process of the vertical line. One square of the grid is one dot of 1200 dpi.

  In the thickening process of FIGS. 8A to 8D, dot addition is performed in four stages of level + 1 to level + 4, and line width correction in units of about 10 μm from about +10 μm to +40 μm is possible. In the thinning process of FIGS. 9A to 9D, dot thinning is performed in four stages of level-1 to level-4, and line width correction in units of about 10 μm to −40 μm is possible.

  Although the line width correction processing of the horizontal line (line in the main scanning direction) is not shown, it is the same as the case where FIGS. 7 to 9 are each rotated 90 degrees.

  In the calculation example of the horizontal line correction value A1 = + 10 μm and the vertical line correction value A2 = + 20 μm, the following processing is performed at the time of copy output for forming an actual original image on a recording material. After the line width correction process is performed on the image data by the line width correction processing unit 406 of the line width correction unit 40, the correction level + 1 thickening process in the main scanning direction and the correction level +2 thickening process in the sub-scanning direction are performed. An image is formed at 200 and a copy image is output.

  In the present embodiment, as shown in FIGS. 8 and 9, the correction level is set to four stages of 10 μm increments. However, the present invention is not limited to this. For example, in order to enable correction in increments of 5 μm, such as the correction level +0.5 (line width correction value: +5 μm) shown in FIG. 10, the dot thinning method or dot addition method is further subdivided to correct the line width. It is good also as a structure which can subdivide a value further.

  As described in detail above, according to the present embodiment, the line width correction reference image and the copy image of the line width correction reference image are read by the reader scanner 100, and the correction value is obtained by comparing the line widths. calculate. Further, the image data is corrected based on the correction value at the time of copy output for copying an image of an actual document on a recording material.

  This makes it possible to correct line width fluctuations due to structural factors including all of the reader scanner 100 and the printer 200, so that a copy image that faithfully reproduces the line width of the original image can be obtained. . Accordingly, it is possible to accurately extract the embedded information in the information embedded image such as a barcode, and it is possible to clearly reproduce the design in the copy image such as the drawing.

  Further, the line width correction of the present embodiment does not change the image forming conditions (image forming conditions such as laser power and developing bias potential), so that the horizontal line (main scanning direction line) and the vertical line are maintained while maintaining the solid density. The line width can be corrected independently of the line (line in the sub-scanning direction). In addition, it is possible to correct the difference in line width between the horizontal line and the vertical line due to structural factors of the image forming apparatus.

  Summarizing the above, it is possible to improve the fidelity of the line width of a copy image obtained by copying an image of a document, and at the same time, a horizontal line (line in the main scanning direction) and a vertical line (line in the sub scanning direction). ) Can be corrected independently. As a result, an image forming apparatus with improved line width faithful reproducibility can be provided.

[Second Embodiment]
The second embodiment of the present invention differs from the first embodiment in the following points. Since the other elements of the present embodiment are the same as the corresponding ones of the first embodiment (FIGS. 1 to 4), description thereof is omitted.

  FIG. 11 is a flowchart illustrating an example of line width correction control of the image forming apparatus according to the present embodiment.

  In FIG. 11, for example, the controller 30 reads the reference image for line width correction shown in FIG. 6 with the reader scanner 100 and outputs the reference image for line width correction to the line width correction unit 40. Further, the controller 30 causes the control unit 400 of the line width correction unit 40 to store the line width of the reference image for line width correction as data 1 in the data storage unit 401 of the line width correction unit 40 (step S1). Here, an image stored in the image forming apparatus as a master chart is used as the reference image for line width correction. Hereinafter, the processing procedure from step S2 to step S5 for calculating the correction value A, which is the line width correction value at the time of outputting the copy image, is the same as that in the first embodiment, and thus the description thereof is omitted.

  Next, the controller 30 uses the printer 200 to draw a line on the recording material based on the line width correction reference image data (master chart) stored in advance in the line width correction reference image storage unit 405 of the line width correction unit 40. A reference image for width correction is formed and output to the discharge tray (step S6). Thereafter, the user takes out the recording material from the discharge tray and sets it on the document loading portion of the reader scanner 100.

  Accordingly, the controller 30 reads the print image of the reference image for line width correction from the recording material set in the document loading section by the reader scanner 100 and outputs it to the line width correction section 40. Further, the controller 30 causes the control unit 400 of the line width correction unit 40 to store the line width of the print image as data 3 (third image data) in the data storage unit 401 (step S7).

  Next, the controller 30 compares the data 1 and the data 3 with the data comparison unit 402 (step S8). Further, based on the difference between the data 1 and the data 3, the controller 30 calculates a correction value B such that the line width of the data 3 is substantially equal to that of the data 1 (the line widths of both data are equal). It calculates by 403 (step S9). This correction value B (second correction value) is a correction value for the line width of the printer 200 only.

  Next, the controller 30 calculates a correction value C (third correction value) that is a difference between the correction value A and the correction value B by the correction value calculation unit 403 (step S10). Thereby, the line width correction control is finished (step S11). This correction value C is a correction value for the line width of the reader scanner 100 only. This completes the calculation of the line width correction value.

  At the time of copy output in which an image of an actual document is formed on a recording material, image data obtained by reading the document with the reader scanner 100 is output to the line width correction unit 40 by the controller 30. Next, the following processing is performed by the line width correction processing unit 406 (first correction unit, second correction unit, and third correction unit) of the line width correction unit 40. Thinning processing for thinning out dots or thickening processing for adding dots based on the correction value A so that the line width of the original image and the line width of the copy image are equal. The line width correction process is performed.

  Thereafter, the image data after the line width correction processing is output from the line width correction unit 40 to the controller 30, the image is formed by the printer 200 under the control of the controller 30, and a copy image is output.

  In the case of print output for forming an image based on image data transmitted from a PC or the like connected to the image forming apparatus, the transmitted image data is output to the line width correction unit 40 by the controller 30. Next, the line width correction processing unit 406 of the line width correction unit 40 performs line thinning processing for thinning out dots or thickening processing for adding dots to image data at the time of print output based on the correction value B. Perform correction processing.

  Thereafter, the image data after the line width correction processing is output from the line width correction unit 40 to the controller 30, the image is formed by the printer 200 under the control of the controller 30, and the print image is output.

  When image data obtained by reading a document with the reader scanner 100 is transmitted as a file (for example, a PDF file) to, for example, a PC connected to the image forming apparatus, the image data is sent to the line width correction unit 40 by the controller 30. Output. Next, the line width correction processing unit 406 of the line width correction unit 40 performs thinning processing for thinning dots on the image data to be transmitted to the PC (external device) based on the correction value C, or a thickness for adding dots. The line width correction process of the cutting process is performed.

  Thereafter, the image data after the line width correction processing is output from the line width correction unit 40 to the controller 30, and the image data is transmitted to the PC as a file under the control of the controller 30. When the image forming apparatus has a facsimile function, the image data after the line width correction processing is transmitted by facsimile.

  Further, when image data obtained by reading a document with the reader scanner 100 is stored in the printer 200 and the image data is formed and output at a later date, the image data is output to the line width correction unit 40 by the controller 30. To do. Next, the line width correction processing unit 406 of the line width correction unit 40 performs line width correction processing of thinning processing for thinning out dots or thickening processing for adding dots based on the correction value C. To do.

  Thereafter, the image data after the line width correction processing is output from the line width correction unit 40 to the controller 30, and the image data is stored in a storage unit (not shown) of the printer 200 under the control of the controller 30.

  This is used, for example, when a standard format such as a form is stored in the storage unit of the printer 200, and the standard format is output and the contents are entered as necessary. When the image data stored in the storage unit of the printer 200 is printed out at a later date, the image data is output to the line width correction unit 40 by the controller 30. Next, the line width correction processing unit 406 of the line width correction unit 40 performs line width correction processing of thinning processing for thinning out dots or thickening processing for adding dots based on the correction value B. To do.

  Thereafter, the image data after the line width correction processing is output from the line width correction unit 40 to the controller 30, the image is formed by the printer 200 under the control of the controller 30, and the print image is output.

  In this manner, the image data after the line width correction process is performed using the correction value C is stored in the storage unit of the printer 200. As a result, when an image is formed and output by the printer 200 at a later date, a line width correction process is necessary with the correction value B. However, when the image data is output as a file or transmitted by facsimile, a new line width is required. This is preferable because correction processing is unnecessary.

  When the correction values are different between the horizontal line (line in the main scanning direction) and the vertical line (line in the sub-scanning direction), the correction value calculation unit 403 calculates the correction value for the horizontal line and the correction value for the vertical line as follows. . That is, by calculating the correction value A1 and the correction value A2, the correction value B1 and the correction value B2, and the correction value C1 and the correction value C2, if the correction amount of the image data is different between the main scanning direction and the sub-scanning direction, Is preferred.

  As described above, the ratio of the line width between the horizontal line and the vertical line is determined to some extent by the configuration of the image forming apparatus. For this reason, if one of the horizontal line and vertical line correction values is calculated by the above method and then the other correction value is calculated by a calculation formula, the line width correction control time can be shortened. Alternatively, the correction value of the horizontal line and the vertical line may be calculated by the above-described method after calculating the correction value of the middle of the horizontal line and the vertical line, that is, for example, the oblique line of 45 degrees.

  An example of calculating the correction values for the horizontal and vertical lines is as follows. For example, as shown in FIG. 6, a case in which three line width correction reference images, each of horizontal lines and vertical lines, are set with 8 dots of 1200 dpi is taken as an example. For the line width, nine points are measured in total at three points per line, and an average value obtained by averaging the measured values at seven points excluding the upper limit value and the lower limit value is used. This is calculated for each of the horizontal and vertical lines. From the difference between data 1 and data 2 calculated using this average value, for example, the horizontal line correction value A1 = + 10 μm and the vertical line correction value for copy output (document reading by the reader scanner 100 and image formation by the printer 200). A2 = + 20 μm is calculated.

  Similarly, from the difference between the average value data 1 and the data 3, for example, the horizontal value correction value B1 = 0 μm and the vertical line correction value B2 = + 20 μm of the print output are calculated. Then, from the difference between the correction value A1 and the correction value B1, and the difference between the correction value A2 and the correction value B2, the horizontal line correction value C1 = + 10 μm and the vertical line correction value of the image data output (document reading by the reader scanner 100). C2 = 0 μm is calculated.

  Next, thinning processing for thinning out dots and thickening processing for adding dots will be described as line width correction processing in the line width correction processing unit 406 of the line width correction unit 40. In the present embodiment, the resolution of original image reading, image data, image formation, and line width correction by the reader scanner 100 can be 1200 dpi, and the 1 dot size of 1200 dpi = about 21 μm. It is the same as the form. The correction levels in FIGS. 7 to 9 are the same as those in the first embodiment.

  In the calculation example of the horizontal line correction value A1 = + 10 μm and the vertical line correction value A2 = + 20 μm, the following processing is performed to output a copy image at the time of actual document copy output. After the line width correction processing 406 of the line width correction section 40 performs line width correction processing (correction level + 1 thickening processing in the main scanning direction and correction level + 2 thickening processing in the sub-scanning direction) on the image data. Then, the printer 200 forms an image on the recording material and outputs a copy image.

  In the calculation example of the horizontal line correction value B1 = 0 μm and the vertical line correction value B2 = + 20 μm, the following processing is performed to output a print image at the time of actual print output. After the line width correction processing unit 406 of the line width correction unit 40 performs line width correction processing (correction level 0 (no correction) in the main scanning direction, thickening processing of correction level +2 in the sub-scanning direction) on the image data. Then, the printer 200 forms an image on the recording material and outputs a print image.

  In the case of the above calculation example of the horizontal line correction value C1 = + 10 μm and the vertical line correction value C2 = 0 μm, the following processing is performed at the time of actual image data output (document reading by the reader scanner 100). After performing line width correction processing (correction level + 1 thickening processing in the main scanning direction, correction level 0 (no correction) in the sub-scanning direction) on the image data by the line width correction processing unit 406 of the line width correction unit 40 The image data is transmitted to a PC or facsimile. Alternatively, it is stored in the storage unit of the printer 200 as image data.

  As described above in detail, according to the present embodiment, the reader scanner 100 reads a line width correction reference image, a copy image of the line width correction reference image, and a print image of the line width correction reference image. The correction value is calculated by comparing the line width data. Further, the image data is corrected at the time of actual document copy output, print output, and image data output.

  As a result, line width variation due to structural factors including all of the reader scanner 100 and the printer 200, line width variation due to structural factors only of the printer 200, and line width variation due to structural factors only of the reader scanner 100, etc. , Each can be corrected appropriately. As a result, it is possible to obtain an image or image data in which the line width is faithfully reproduced according to the outputs of the reader scanner 100 and the printer 200.

  Accordingly, it is possible to accurately extract the embedded information in the information embedded image such as a barcode, and it is possible to obtain a copy image or a printed image in which the design is clearly reproduced in the image such as a drawing. Also in the image data file, it is possible to obtain image data and an image data file in which the line width is faithfully reproduced.

  In addition, the line width correction according to the present embodiment does not change the image forming conditions (image forming conditions such as laser power and developing bias potential), so that the horizontal line and the vertical line are independent while maintaining the solid density. The width can be adjusted.

  For example, even in a print output image in which image information received from the PC by the image forming apparatus is printed, it is possible to faithfully reproduce a desired line width set on the PC. In addition, for example, in the output of image data (electronic information) in which an image read by a reader scanner of an image forming apparatus is transmitted as an image file to a PC, the line width of an image of a document can be faithfully reproduced.

  In addition, since the line width of the horizontal line (line in the main scanning direction) and the vertical line (line in the sub scanning direction) can be corrected independently, the line width of the horizontal line and the vertical line due to structural factors of the image forming apparatus. It is possible to correct the difference.

  In summary, the faithful reproducibility of the line width of the copy image can be improved, and the fidelity reproducibility of the print image other than the copy image and the line width of the image data can also be improved.

[Third Embodiment]
The third embodiment of the present invention differs from the first embodiment in the following points. Since the other elements of the present embodiment are the same as the corresponding ones of the first embodiment (FIGS. 1 to 4), description thereof is omitted.

  In the present embodiment, the order of control in density correction control (maximum density correction control, gradation correction control) and line width correction control of the image forming apparatus will be described.

  First, the maximum density correction control is a control for creating a test patch for maximum density correction control on a photosensitive drum or an intermediate transfer belt, and detecting the reflection density of the test patch to correct the maximum density of toner. In the present embodiment, as shown in FIG. 1, a method is employed in which the optical sensor 50 detects the reflection density of a test patch created on the intermediate transfer belt 10. The reflection density of the intermediate transfer belt 10 itself is subjected to background correction, and the optical sensor 50 is corrected so that the reflection density corresponds to a change in the amount of toner applied to the intermediate transfer belt 10.

  The test patch is created for each color (Y, M, C, K, R, G, B) by changing image forming conditions such as laser power and developing bias potential for a plurality of types. For each color, the laser power and developing bias at which the test patch has a predetermined density are set. The test patch at this time has a solid density.

  The maximum density correction control is to reduce the maximum density fluctuation of the printer 200 due to the environment and changes with time. By fixing the maximum amount of applied toner of each color on the intermediate transfer belt 10, the maximum density of the toner of each color is fixed. It is what. That is, this is to reduce the variation in color tone when a plurality of colors of toner are superimposed on the intermediate transfer belt 10.

  Next, tone correction control creates a test patch for tone correction control on a photosensitive drum or an intermediate transfer belt, detects the reflection density of the test patch, and detects the tone (in a certain color) in color image formation. This is a control for correcting the stage of changing to another color. In the present embodiment, as shown in FIG. 1, a method is used in which a test patch created on the intermediate transfer belt 10 is detected by the optical sensor 50. Similar to the maximum density correction control, the reflection density of the intermediate transfer belt 10 itself performs background correction.

  The test patch has a gradation pattern including a halftone from a solid part of 256 gradations for each color (Y, Y, etc.) based on image forming conditions such as laser power and developing bias potential determined by the maximum density correction control. M, C, K, R, G, B). The reference numeral 255 is the same solid portion as the test patch for maximum density control. Actually, the optical sensor 50 detects the reflection density of the test patch for every 15 gradations, that is, the test patch for 17 gradations, and the gradation correction control time is shortened by linearly interpolating the reflection density between them. May be. By correcting this reflection density signal by γ correction, each color is corrected so that the density of 256 gradations becomes linear.

  FIG. 12 is a diagram showing an example of a gradation correction (γ correction) table of the image forming apparatus according to the present embodiment.

  In FIG. 12, the gradation correction table is a table indicating what level of the output image signal is output from the input image signal. The horizontal axis is the input image signal, and the vertical axis is the output image signal. L1 indicates an actual gradation curve by a thin solid line. L2 represents an ideal gradation curve by a one-dot chain line. L3 indicates the corrected curve with a solid solid line. L4 indicates an ideal gradation curve with an emphasis on line width indicated by a broken line. L5 indicates a corrected curve with emphasis on line width indicated by a thick solid line.

  The actual gradation curve L1 corresponds to the reflection density signal of the above-described gradation pattern test patch. In the example of FIG. 12, the actual gradation curve L1 has a lower output at the low density portion and a higher output at the high density portion than the ideal gradation curve L2. Therefore, the actual gradation curve L1 is corrected and replaced with the corrected curve L3 so that the output level approaches the ideal gradation curve L2.

  By making the output image signal using the corrected curve L3 with respect to the input image signal, the image density becomes linear with respect to the input image signal. In this way, an appropriate output image signal can be obtained by correcting the actual gradation curve L1 in the gradation correction table and replacing it with the corrected curve L3. This gradation correction is called γ correction.

  As a test patch, a line image, a halftone image by a dither method, a screen method, or the like has been proposed. In this embodiment, as shown in FIG. Adopts a diagonal line of degrees. By adopting diagonal lines, even in an image forming apparatus in which line widths of horizontal lines (lines in the main scanning direction) and vertical lines (lines in the sub-scanning direction) are different, gradation correction is performed with the density of the intermediate line width. Thus, it is possible to prevent the line widths of the horizontal line and the vertical line after gradation correction from greatly changing from the desired line width. The numbers displayed beside the test patch in FIG. 13 indicate the number of gradations.

  Further, the gradation correction table may be changed as follows according to the image output by the image forming apparatus. For example, in the case of an image having many dots, such as a photograph, a corrected curve L3 that becomes an ideal gradation curve L2 may be used. Alternatively, in the case of an image having a large number of line images, a corrected curve L5 that emphasizes line width may be used so that an ideal gradation curve L4 that emphasizes line width is obtained.

  In this way, by using the line width-oriented gradation correction table, the correction value of the line width correction after gradation correction can be made smaller, so that dot thinning by line width correction and image quality by dot addition are improved. The influence can be reduced.

  Next, the control sequence in the maximum density correction control, gradation correction control, and line width correction control will be described.

  In the conventional line width correction control, the image forming conditions such as the laser power and the developing bias potential are corrected. Therefore, when the line width correction control is executed last, the image forming conditions determined by the maximum density correction control and the gradation correction control. Will be changed. Therefore, as in Patent Document 7, control is executed in the order of maximum density correction control, line width correction control, and gradation correction control.

  On the other hand, in the present embodiment, control is executed in the order of maximum density correction control, gradation correction control, and line width correction control. The line width correction control according to the present embodiment is control for correcting the line width by increasing or decreasing the dots of the image data without changing the image forming conditions as described above. Therefore, the maximum density is not changed and the influence on the gradation correction control is small.

  In the present embodiment, in the above-described gradation correction control, by using the diagonal test patch, the line width is intermediate between the horizontal line and the vertical line, so the first embodiment and the second embodiment. The line width correction of the horizontal and vertical lines described in the embodiment only needs to be finely adjusted.

  As in the present embodiment, by controlling in the order of maximum density correction control, gradation correction control, and line width correction control, the influence on image density (maximum density and halftone density) is minimized. By doing so, it is possible to execute line width correction. This is more preferable because the line width can be corrected to a desired value in a state where the image density is appropriate.

  In the present embodiment, the maximum density correction control and the gradation correction control are exemplified as a configuration in which the density of the test patch is detected and corrected on the intermediate transfer belt. However, the present invention is not limited to this. . Similar to the line width correction control, a reference image for maximum density correction control or gradation correction control is copied or printed out, and the output image is read by the reader scanner 100. The difference between the reference image and the output image May be used for correction control. In this case, the image density can be corrected not by the intermediate process but by the image density finally obtained by the user.

  The reference image for maximum density correction control or gradation correction control may be either of the following. It may be an image stored in the image forming apparatus as a master chart. Alternatively, it may be a print image output by forming an image on a recording material with the printer 200 based on the reference image data stored in the storage unit of the printer 200.

  As described above in detail, according to the present embodiment, by performing line width correction control after controlling the image density to be in an appropriate state by maximum density correction control and gradation correction control, It is possible to achieve both the formation of a gradation image such as a photograph and the faithful reproducibility of the line width of the line image.

[Fourth Embodiment]
The fourth embodiment of the present invention differs from the first embodiment in the following points. Since the other elements of the present embodiment are the same as the corresponding ones of the first embodiment (FIGS. 1 to 4), description thereof is omitted.

  In line width correction control, the line width differs between horizontal lines (main scanning direction lines) and vertical lines (sub scanning direction lines) due to structural factors of the image forming apparatus. As described above, the line width reproducibility is improved by setting different values for and.

  Furthermore, since the line width reproducibility varies depending on the dot width of the line, the line width correction amount may be changed. For example, a thin 1-dot line or 2-dot line of 1200 dpi is relatively thin, and a thick 10-dot line or 20-dot line is relatively thick. This is because the latent image on the photosensitive drum is not formed digitally but is formed in an analog manner with a certain inclination.

  FIG. 14 is a diagram illustrating an example of a latent image formed on the photosensitive drum of the image forming apparatus according to the present embodiment. FIG. 14A is a diagram illustrating an ideal shape of the latent image, and FIG. FIG. 14 is a diagram showing the actual shape of the latent image, and FIG. 14C is a diagram showing the actual shape of the latent image.

  14A, 14B, and 14C, VD is a dark portion potential (non-image portion potential) that is charged on the photosensitive drum and is not irradiated with the laser. VL is the bright portion potential (image portion potential) irradiated with the laser on the photosensitive drum. Vdc is a developing bias potential. The toner T is developed on the VL portion on the photosensitive drum by the potential difference between VL and Vdc.

  FIG. 14A shows an ideal shape of a latent image in which 2-dot lines of 1200 dpi are digitally formed, and the line width at this time is a line width W1 of 2-dot width.

  FIG. 14B shows an actual shape of a latent image in which 2-dot lines of 1200 dpi are formed in an analog manner, and the line width at this time is a line width W2 smaller than the line width W1 of 2-dot width. It becomes. Since the latent image is formed with a certain inclination as shown in FIG. 14B, the line width is smaller than that in the ideal shape.

  FIG. 14C shows an actual shape of a latent image in which 1200 dpi 4-dot lines are formed in an analog manner. The line width at this time is smaller than twice the line width W1, and the line width W2 The line width W3 is larger than twice this.

  Therefore, it is necessary to increase the line width correction amount for the fine line to be image formed, but the line width correction amount may be small for the thick line to be image formed. Depending on the image forming apparatus, one dot line of 1200 dpi may not be reproduced and may be lost.

  FIG. 15 is a diagram illustrating the relationship between the line width correction amount and the line dot width.

  In FIG. 15, the horizontal axis represents the dot width of a line for image formation, and the vertical axis represents the line width correction amount (μm) at the time of line width correction. The larger the dot width of the line, that is, the smaller the line width correction amount, the thicker the line. A thin solid line connecting white circles is a horizontal line (line in the main scanning direction), and a thick solid line connecting black circles is a vertical line (a line in the sub scanning direction). The line width correction amount is set in a plurality of stages according to the line width, density, and color. A plurality of stages of line width correction amounts between the white circle correction amount and the black circle correction amount may be determined by linear interpolation by the correction value interpolation unit 404 of the line width correction unit 40.

  Therefore, as a reference image for line width correction, line images having a plurality of types of dot widths as shown in FIG. 16 are used, for example, in the method of the first embodiment or the second embodiment, as shown in FIG. A line width correction amount as shown is calculated and a line width correction process is performed. As a result, the line width correction amount can be changed in accordance with the line width to be formed, so that an appropriate line width correction process can be executed even for various line widths, thereby further improving the line width reproducibility. it can. FIG. 16 shows an example of a single color image. Similarly, when a line image having a plurality of dot widths in a plurality of colors (Y, M, C, K, R, G, B) is used as a reference image for line width correction, More preferred.

  Here, the line width of the image formed on the actual recording material depends on the transfer efficiency in the transfer process after forming the latent image on the photosensitive drum, the scattering of the toner, and the pressurization and heating in the fixing process after transfer. It is finally measured through a process such as crushing the toner. In the above, for the sake of simplicity, only the influence on the line width in the latent image process has been described.

  In addition, since the reproducibility of the line width varies depending on the amount of toner applied to the line, the line width correction amount may be changed. FIG. 15 is a graph in which the dot width of the line is changed when the amount of applied monochromatic toner is 100%. On the other hand, FIG. 17 shows the relationship of the line width correction amount to the applied toner amount (%) on the recording material in the 8-dot line. The horizontal axis represents the amount of applied toner (%), and the vertical axis represents the correction amount at the time of line width correction. Here, the maximum amount of applied toner for each of the single colors (Y, M, C, K) is assumed to be 100%.

  Regarding the amount of toner applied to the line, the black line generally has a black (K) toner applied amount of 100%, while the gray (gray) line has, for example, a black toner applied amount of 50%. Further, the red line may be, for example, a total of 200% of two colors of yellow (Y) toner applied amount 100% and magenta (M) toner applied amount 100%.

  When the amount of toner applied on the recording material is different, the amount of toner spread by pressing and heating at the fixing unit 16 is different. Therefore, if the applied toner amount changes even in the same 8-dot line, it is necessary to change the line-width correction amount in order to obtain a predetermined 8-dot line width.

  As shown in FIG. 17, when the amount of applied toner is small, the amount of toner spread on the fixing unit 16 is small, so the line becomes thin and the line width correction amount is on the plus side. On the other hand, when the amount of applied toner is large, the amount of toner spread on the fixing unit 16 is large, so the line becomes thick and the line width correction amount is negative. In FIG. 17, a thin solid line connecting white circles is a horizontal line, and a thick solid line connecting black circles is a vertical line. The line width correction amount between the white circle correction value and the black circle correction value may be determined by linear interpolation by the correction value interpolation unit 404 of the line width correction unit 40.

  Therefore, as a reference image for line width correction, line images having a plurality of densities as shown in FIG. 18 are used, for example, by the method of the first embodiment or the second embodiment, as shown in FIG. A line width correction process is performed by calculating an appropriate line width correction amount. That is, the line width correction amount is changed according to the density of the formed line image. As a result, an appropriate line width correction process can be executed even for line images of various densities, so that the line width reproducibility can be further improved.

  Further, FIG. 18 shows an example of a monochromatic line image. Similarly, a line image having a plurality of densities in a plurality of colors (Y, M, C, K, R, G, B) is used as a reference image for line width correction. The line width correction amount may be calculated according to each color, and the line width correction process may be performed according to each color. As a result, the line width variation due to each color toner can be corrected, which is more preferable. This is because the applied toner amount (g) at the maximum density, that is, when the applied toner amount is 100%, is slightly different depending on each color toner, and therefore the line width slightly varies even if the applied toner amount (%) is the same. It is.

  A typical monochrome image forming apparatus has a maximum toner loading amount of 100%, and a color image forming apparatus has a maximum toner loading amount of about 200 to 280%.

  As described above, according to the present embodiment, since line width correction processing is performed using a plurality of types of dot width line images as line width correction reference images, various line width correction operations can be performed. It becomes possible to determine the correction value of the condition. In addition, by setting a plurality of line width correction amounts, more detailed line width correction can be performed. In addition, it is possible to faithfully reproduce the line width in various images by determining the line width correction amount by linear interpolation for images with various line widths and toner applied amounts other than the reference image for line width correction. It becomes.

[Fifth Embodiment]
The fifth embodiment of the present invention differs from the first embodiment in the following points. Since the other elements of the present embodiment are the same as the corresponding ones of the first embodiment (FIGS. 1 to 4), description thereof is omitted.

  In this embodiment, the image forming apparatus has an image area separation function for determining an image area such as a photograph, a line drawing (graphic), and a character (character). For each image area, it is possible to arbitrarily set whether to perform line width correction including adjustment of the line width correction amount or not to perform line width correction. As a result, an image forming apparatus capable of executing line width correction in an image area with little change in image density and gradation and high image quality and requiring line width correction is provided.

  FIG. 19 is a diagram showing an example of image area separation of the image forming apparatus according to the present embodiment.

  FIG. 19 shows a state in which image areas are separated in one recording material, and image data is separated into, for example, a picture, a line drawing (graphic), and a character.

  Here, since a graphic (graphic) generally has few line images and many dot parts such as a solid part and a halftone, it does not require an accurate adjustment of the line width. Is done. Further, when dots of a photographic image are excessively thinned or dots are excessively added, there arises a problem that image density and gradation are greatly changed. Accordingly, for a photograph (image), for example, 50% of the correction value determined in FIG. 15 or 17 is executed as the line width correction process, or the line width correction process is not executed. As a result, it is possible to obtain an image with high gradation without any image deterioration in a photograph (image).

  On the other hand, line drawings (graphics) and characters (characters) generally have many straight lines and curves, and line width is regarded as important. The line drawing (graphic) is particularly a barcode or drawing, and an accurate line width is regarded as important. Accordingly, the line width is improved by applying the correction values determined in FIG. 15 and FIG. 17 as they are to the line drawing (graphic), for example. Thereby, it is possible to improve the reading accuracy of the barcode or to improve the reproducibility of the drawing and the design.

  With regard to characters, especially in small-point characters, the reproducibility of line width is regarded as important in terms of readability, such as thin characters or thick characters that are crushed. Therefore, for the character, the line width reproducibility is improved by applying the correction value determined in FIG. 15 or FIG. 17 as it is, for example, as in the case of the line drawing (graphic). As a result, it is possible to improve character discrimination.

  In the case of characters, it is particularly small point characters that require line width reproducibility. Large point characters have no problem in distinguishability even if the line width is slightly narrower or thicker. In a small-point character, if the line width is too thin, the character disappears, and if the line width is too thick, the character is crushed, so that the character cannot be read. Therefore, in the case of a character, for example, by applying the line width correction process only to characters of 8 points or less, the character identification can be improved and the line width correction processing time can be shortened. Further, by applying a line width correction process to a white character, an image of a white character having an appropriate line width can be obtained.

  As described above, according to the present embodiment, image data is separated into photo, line drawing, and character image areas, and line width correction is performed for each image area / line width correction is not performed. Therefore, it is possible to perform line width correction without causing image quality degradation. In addition, the line width correction processing time can be shortened.

[Other Embodiments]
In the first to fifth embodiments, a copying machine has been described as an example of an electrophotographic image forming apparatus, but the present invention can also be applied to an electrophotographic printer, a facsimile, or the like.

  In the first to fifth embodiments, the numerical values and drawings used are examples for simplifying the description of the embodiment and can be arbitrarily determined according to the configuration and settings of the image forming apparatus. it can.

  In the first to fifth embodiments, as described above, each embodiment has been described separately. However, the embodiments can be arbitrarily combined without departing from the gist of the present invention. .

1 is a configuration diagram illustrating a configuration example of an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is a block diagram illustrating a configuration example centering on a controller that controls the image forming apparatus. It is a block diagram which shows the function structural example of the image processing part of a controller. It is a block diagram which shows the structural example of a line | wire width correction | amendment part. It is a flowchart which shows the example of line | wire width correction control. It is a figure which shows the example of the reference | standard image for line | wire width correction | amendment. It is a figure which shows the example of the correction level 0 (no correction | amendment) of a line | wire width correction process. (A)-(d) is a figure which shows the example of the thickening process which adds the dot of a line | wire width correction process. (A)-(d) is a figure which shows the example of the thinning process which thins out the dot of a line | wire width correction process. It is a figure which shows the other example of the fattening process which adds the dot of a line | wire width correction process. 10 is a flowchart illustrating an example of line width correction control of the image forming apparatus according to the second exemplary embodiment of the present invention. It is a figure which shows the example of the gradation correction table of the image forming apparatus which concerns on the 3rd Embodiment of this invention. It is a figure which shows the example of the test patch for gradation correction control. FIG. 10 is a diagram illustrating an example of a latent image formed on a photosensitive drum of an image forming apparatus according to a fourth embodiment of the present invention, where (a) is a diagram illustrating an ideal shape of the latent image, and (b) is a latent image. The figure which shows the actual shape of an image, (c) is a figure which shows the actual shape of a latent image. It is a figure which shows the relationship of the line | wire width correction amount with respect to the dot width of a line | wire. It is a figure which shows the example of the reference | standard image for line | wire width correction | amendment. FIG. 6 is a diagram illustrating a relationship between a line width correction amount and a toner applied amount. It is a figure which shows the other example of the reference | standard image for line | wire width correction | amendment. It is a figure which shows the example of the image area separation of the image forming apparatus which concerns on the 5th Embodiment of this invention.

Explanation of symbols

1Y, 1M, 1C, 1K Photosensitive drum 30 Controller 40 Line width correction unit 50 Optical sensor 100 Reader scanner 200 Image forming apparatus main body 300 Control unit 303 PDL processing unit 305 Image processing unit 400 Control unit 401 Data storage unit 402 Data comparison unit 403 Correction value calculation unit 404 Correction value interpolation unit 405 Line width correction reference image storage unit 406 Line width correction processing unit

Claims (9)

In an image forming apparatus comprising an image reading means for reading an image and an image forming means for forming an image on a recording material,
First image data obtained by reading the reference image for line width correction by the image reading unit, and a copy image formed on the recording material by the image forming unit based on the first image data by the image reading unit. A comparing means for comparing the second image data obtained by reading;
Calculating means for calculating a first correction value based on a difference between the first image data and the second image data by comparison of the comparing means;
Thinning processing for thinning dots based on the first correction value or thickening for adding dots to image data at the time of copy output so that the line width of the original image and the line width of the copy image are equal. Correction means for correcting the line width by performing processing;
An image forming apparatus comprising: In an image forming apparatus comprising an image reading means for reading an image and an image forming means for forming an image on a recording material,
First image data obtained by reading the reference image for line width correction by the image reading unit, and a copy image formed on the recording material by the image forming unit based on the first image data by the image reading unit. Based on the second image data obtained by reading and the reference image data for line width correction stored in the image forming apparatus, the image reading means forms a print image obtained on the recording material by the image forming means. A comparison means for comparing with the third image data obtained by reading by
Based on a comparison between the first image data and the second image data, and a difference between the first image data and the third image data based on the comparison by the comparison unit. Calculating means for calculating a third correction value based on a second correction value and a difference between the first correction value and the second correction value;
Thinning processing for thinning dots based on the first correction value or thickening for adding dots to image data at the time of copy output so that the line width of the original image and the line width of the copy image are equal. A first correcting means for correcting the line width by performing processing;
By performing the thinning process or the thickening process on the image data at the time of print output based on the second correction value so that the line width of the print image becomes a predetermined line width, the line width is reduced. Second correcting means for correcting;
Based on the third correction value, the thinning process or the thickening process is performed on the image data to be transmitted to the external device so that the line width of the image of the document is equal to the line width of the image read from the document. A third correction unit that corrects the line width by performing processing;
An image forming apparatus comprising: The image forming unit includes a photosensitive drum on which a latent image of an image to be transferred to a recording material is formed.
3. The line width correction is performed independently in a main scanning direction parallel to the rotation axis of the photosensitive drum and a sub-scanning direction orthogonal to the rotation axis of the photosensitive drum. Image forming apparatus. The reference image for line width correction is the main scanning direction parallel to the rotation axis of the photosensitive drum, the sub-scanning direction orthogonal to the rotation axis of the photosensitive drum, both the main scanning direction and the sub-scanning direction, or the A plurality of types of line images composed of a single color or a plurality of colors having a plurality of densities in an oblique direction not parallel to the rotation axis of the photosensitive drum;
4. The image forming apparatus according to claim 3, wherein the correction amount of the line width is a correction amount in a plurality of stages set according to the line width, density, and color.   The image forming apparatus according to claim 4, wherein the correction amount is determined by linear interpolation between the plurality of correction amounts.   Maximum density correction control for correcting the maximum density of toner used for developing a latent image of an image transferred to a recording material, gradation correction control for correcting gradation in color image formation, and line width correction control for correcting the line width The image forming apparatus according to claim 1, wherein the image forming apparatus is executed in the following order. An image area separating function for determining which image area is a character (character), graphic (graphic), or photograph (image) in image data obtained by reading from a document by the image reading means;
3. A setting for performing line width correction including adjustment of a line width correction amount or a setting for not performing the line width correction is possible for each image area. Image forming apparatus. In a control method for an image forming apparatus, comprising: an image reading unit that reads an image; and an image forming unit that forms an image on a recording material.
First image data obtained by reading the reference image for line width correction by the image reading unit, and a copy image formed on the recording material by the image forming unit based on the first image data by the image reading unit. A comparison step of comparing the second image data obtained by reading;
A calculation step of calculating a first correction value based on a difference between the first image data and the second image data by comparison in the comparison step;
Thinning processing for thinning dots based on the first correction value or thickening for adding dots to image data at the time of copy output so that the line width of the original image and the line width of the copy image are equal. And a correction step of correcting the line width by performing processing. In a control method for an image forming apparatus, comprising: an image reading unit that reads an image; and an image forming unit that forms an image on a recording material.
First image data obtained by reading the reference image for line width correction by the image reading unit, and a copy image formed on the recording material by the image forming unit based on the first image data by the image reading unit. Based on the second image data obtained by reading and the reference image data for line width correction stored in the image forming apparatus, the image reading means forms a print image obtained on the recording material by the image forming means. A comparison step for comparing with the third image data obtained by reading,
Based on the comparison in the comparison step, based on the first correction value based on the difference between the first image data and the second image data, and on the difference between the first image data and the third image data. A calculation step of calculating a second correction value and a third correction value based on a difference between the first correction value and the second correction value;
Thinning processing for thinning dots based on the first correction value or thickening for adding dots to image data at the time of copy output so that the line width of the original image and the line width of the copy image are equal. A first correction step of correcting the line width by performing processing;
By performing the thinning process or the thickening process on the image data at the time of print output based on the second correction value so that the line width of the print image becomes a predetermined line width, the line width is reduced. A second correction step to correct;
Based on the third correction value, the thinning process or the thickening process is performed on the image data to be transmitted to the external device so that the line width of the image of the document is equal to the line width of the image read from the document. And a third correction step of correcting the line width by performing processing.

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