JP2009290612A - Image processing device, image processing method and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress scatter or explosion of a line image, according to the type of paper. <P>SOLUTION: An image processing device includes, for example, a paper type specification section, a line detection section, a line image processing section and a determination section. The paper-type specification section specifies a type of paper of a recording medium on which an image, based on image data is formed by a color material. The line detection section detects a main scanning direction line contained in image data. The line image processing section applies image processing to image data to prevent the definition of the main scanning direction line from being reduced. The determination section determines an image processing parameter which the line image processing section uses for image processing, according to the type of paper of the recording medium. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image processing apparatus and an image forming apparatus used for forming an image on a recording medium.

  2. Description of the Related Art Conventionally, in an image forming apparatus that employs an electrophotographic method, a phenomenon occurs in which the quality of an image is deteriorated due to a difference in the amount ratio of a color material (hereinafter referred to as toner) between a solid portion and a line portion. Was. For example, when the amount of applied toner for forming a line increases by edge enhancement, a phenomenon such as a scattered image or an explosion image may occur.

  FIG. 24 is a diagram illustrating an example of an image in which scattering or explosion has occurred. In this figure, an image in which scattering or explosion has occurred is captured by a scanner and binarized using the ISO 13660 method. It can be seen that the edge of the line is different between plain paper and coated paper. In this way, the degree of scattering and explosion varies depending on the paper type. Note that scattering and explosion often occur in the secondary transfer unit and the fixing unit of the image forming apparatus.

  FIG. 25 is an enlarged view of the secondary transfer portion. In the secondary transfer portion, the intermediate transfer body 2501 and the secondary transfer roller 2502 are pressed and contacted. This contacted portion is a so-called nip portion. The toner image is transferred when the recording medium P passes through the nip portion. Here, cross sections of line images 2503, 2504, and 2505 extending in the main scanning direction (direction parallel to the rotation axes of the intermediate transfer member 2501 and the secondary transfer roller 2502) are shown. The sub-scanning direction is a direction orthogonal to the main scanning direction. The main scanning direction is a direction that crosses the conveyance direction of the recording medium. In FIG. 25, the main scanning direction is orthogonal to the conveyance direction of the recording medium.

  As for the scattering / explosion phenomenon in the secondary transfer portion, the intermediate transfer body 2501 is manufactured from a material having a smooth surface property such as PI (polyimide) and high hardness, and the recording medium P also has a smooth surface property and hardness. It is easy to occur when is high.

  When the preceding line image 2504 passes through the nip portion, the secondary transfer roller and the recording medium P cannot withstand the height of the toner and are pushed down (solid line). After passing the preceding line image 2504, the secondary transfer roller 2502 and the recording medium P try to be restored to their original positions by the pressure of a spring or the like (dotted line). At this time, if the subsequent line image 2505 exists on the intermediate transfer body 2501, pressure is applied to the line image 2505 along with restoration, and scattering and explosion occur. Note that if the recording medium is high-quality paper, the pressure on the toner escapes moderately, so that scattering and explosion images are unlikely to occur. Thus, conventionally, there is a difference in the degree of occurrence of scattering and explosion for each paper type of the recording medium. In addition, scattering / explosion images are likely to occur in images or characters in which a plurality of main scanning direction lines such as graph ruled lines are arranged in the sub-scanning direction.

  On the other hand, even in the fixing portion, splattered / explosive images are generated by paper or film having high hardness. In addition to the above-described principle, the generation principle is that moisture contained in the paper is evaporated and released by the fixing process. This is because the toner layer on the paper surface is disturbed by the water vapor. Since coated paper or the like has a high electrical resistance value, the paper has less charge for holding toner. Therefore, it is easy to induce scattering and explosion when the fixing roller or the like is charged.

  As a technique for alleviating the above-described problem, a technique called Vcont that lowers the development contrast and lowers the height of the toner layer of the line image can be considered. Thereby, the quality of the line is maintained. However, when Vcont is lowered, the maximum image density is also lowered. That is, there is an adverse effect that the line width becomes narrow. Therefore, this method was not a sufficient solution.

According to Patent Document 1, a method for improving the quality of a line image by image processing while maintaining the maximum density is proposed. Specifically, the line image is detected, and a part of the detected line image is thinned out to form the line image on the recording medium.
JP 2006-303879 A

  The height of the toner carried on the intermediate transfer member for forming a line image varies depending on mechanical differences, environmental differences, durability differences, and the like. Therefore, if the thinning conditions are uniformly determined, the thinning amount is insufficient or too large. If the amount of thinning is not too much, it will not be possible to suppress scattering and explosion. On the other hand, if the thinning amount is too large, a part of the line or character is lost.

  In particular, the level of occurrence of scattering / explosive images occurring in the secondary transfer portion and the fixing portion varies depending on the paper type of the recording medium. For example, a non-coated paper having a rough surface and a low electrical resistance value, such as plain paper, is less likely to cause scattering and explosion. Scattered / explosive images are likely to occur on coated paper, such as coated paper or art paper, which has high hardness and resistance. As described above, if the image is corrected by applying a uniform thinning amount to different paper types, the correction tends to be insufficient.

  Therefore, an object of the present invention is to solve at least one of such problems and other problems. For example, the object is to suppress scattering and explosion phenomena according to the paper type. Other issues can be understood throughout the specification.

  The image processing apparatus includes, for example, a paper type identification unit, a line detection unit, a line image processing unit, and a determination unit. The paper type specifying unit specifies the paper type of the recording medium on which the image based on the image data is formed by the color material. The line detection unit detects a main scanning direction line included in the image data. The line image processing unit applies image processing for preventing deterioration of the quality of the main scanning direction line to the image data. The determining unit determines an image processing parameter used by the line image processing unit for image processing according to a paper type of the recording medium.

  According to the present invention, scattering and explosion of a line image are suppressed according to the paper type.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the relative arrangement, numerical formulas, numerical values, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified.

<Embodiment 1>
FIG. 1 is a block diagram of an image forming apparatus including an image processing apparatus according to the embodiment. In this example, an MFP (Multi Function Peripheral) is adopted as an example of the image forming apparatus. The MFP generally includes a network connection interface and an image processing apparatus that executes various image processes.

  The MFP has a copy function and a print function. The copy function is a function for copying a document by sending job data output from the scanner unit 200 to the printer unit 011. The print function is a function for printing job data output from an external device such as a computer by the printer unit 011. Note that the image forming apparatus may be a single function type image forming apparatus (SFP: Single Function Peripheral) having only a print function. As described above, the image forming apparatus of the present invention may be realized as a printing apparatus, a printer, a copying machine, or a facsimile.

  The MFP control unit 001 is a unit that comprehensively controls each unit. The input image processing unit 002 reads an image such as a paper document and performs image processing on the read image data. A FAX unit 003 transmits and receives image data using a telephone line typified by a facsimile. The NIC unit 004 transmits and receives image data using a network. NIC is an abbreviation for Network Interface Card. The dedicated I / F unit 005 transmits and receives image data and the like with a dedicated external device. I / F is an abbreviation for interface. A USB I / F unit 006 transmits and receives image data and the like to and from a USB device typified by a USB memory (a kind of removable media). USB is an abbreviation for Universal Serial Bus. Note that the MFP control unit 001 plays a role of temporarily storing image data and determining a destination according to a function designated by the operation unit 014 or the like.

  The document management unit 008 includes a memory such as a hard disk capable of storing a plurality of image data. For example, the document management unit 008 stores image data from the input image processing unit 002 and image data of a facsimile job received via the FAX unit 003. Also, the document management unit 008 stores image data input via the NIC unit 004, various image data input via the dedicated I / F unit 005 and the USB I / F unit 006, and the like. The MFP control unit 001 appropriately reads out image data from the document management unit 008 and transfers the image data to the printer unit 011, for example.

  The compression / decompression unit 007 compresses the image data and stores it in the document management unit 008, or conversely decompresses and reads out the stored image data. It is also generally known that compressed data such as JPEG, JBIG, and ZIP is used when image data passes through a network. The compression / decompression unit 007 also decompresses or decompresses these image data.

  The resource management unit 009 stores various commonly used resources such as fonts and gamma tables. Furthermore, the resource management unit 009 can store a new parameter table, or can modify and update it. Note that the line calibration information of this embodiment is stored in the resource management unit 009, read out by the MFP control unit 001 as necessary, and sent to the output image processing unit 012. The line calibration information includes at least an image processing parameter (for example, a line thinning pattern and a development contrast value) for suppressing scattering and explosion according to the paper type.

  The RIP unit 013 performs RIP processing on the input PDL data. PDL is an abbreviation for Page Description Language. RIP is an abbreviation for “Raster Image Processor”. Note that the document management unit 008 can also store intermediate data and print ready data (bitmap data for printing or data obtained by compressing the intermediate data) created by RIP processing as necessary.

  The printer unit 011 forms an image on a recording medium using a color material (for example, toner or ink). The post-processing unit 010 performs sorting processing and finishing processing on the recording medium ejected from the printer unit 011.

The transfer of image data by the MFP control unit 001 will be described by function as follows.
A) Copy function:
Input image processing unit 002 → output image processing unit 012 → printer unit 011
B) FAX transmission function:
Input image processing unit 002 → FAX unit 003
C) FAX reception function:
FAX unit 003 → output image processing unit 012 → printer unit 011
D) Network scan:
Input image processing unit 002 → NIC unit 004
E) Network print:
NIC unit 004 → RIP unit 013 → output image processing unit 012 → printer unit 011
F) Scan to external device:
Input image processing unit 002 → dedicated I / F unit 005
G) Printing from an external device:
Dedicated I / F unit 005-> output image processing unit 012-> printer unit 011
H) Scan to external memory:
Input image processing unit 002 → USB I / F unit 006
I) Printing from external memory:
USB I / F unit 006 → RIP unit 013 → output image processing unit 012 → printer unit 011
J) Scan box function:
Input image processing unit 002 → output image processing unit 012 → document management unit 008
K) Box print function:
Document management unit 008 → printer unit 011
L) Box reception function:
NIC unit 004 → RIP unit 013 → output image processing unit 012 → document management unit 008
M) Box transmission function:
Document management unit 008 → NIC unit 004
N) Preview function:
Document management unit 008 → operation unit 014.

  The operation unit 014 is a unit for selecting the various flows and functions described above and inputting operation instructions to the MFP control unit. The operation unit 014 includes a display device such as a liquid crystal device in addition to an input device such as a touch panel.

  FIG. 2 is a block diagram of the scanner unit 200. The monochrome single-line CCD sensor 020 reads an image of an original and outputs it as an analog image signal to the A / D converter 021. The A / D conversion unit 021 performs gain adjustment and offset adjustment on the analog image signal, and converts the analog image signal into 8-bit digital image data.

  Next, blocks arranged in the input image processing unit 002 of the scanner unit 200 will be described. The shading correction unit 022 corrects variations in sensitivity for each pixel cell in the CCD sensor 020, variations in the amount of light of the document illumination lamp, and the like using the reading signal of the reference white plate.

  The filter processing unit 024 performs convolution integration including the target pixel and a plurality of peripheral pixels located in the vicinity thereof, and performs processing for making the image sharper on the image data. The gradation correction unit 025 applies gradation correction to image data so as to achieve gradations according to a plurality of image modes such as a character mode, a photo mode, and a mixed mode thereof. Note that the one-dimensional lookup table (LUT) used for tone correction takes into account the output characteristics of the printer unit 011. Here, the character mode is a mode in which an LUT having a curve that reproduces an input image in extremely white or black is applied from a low density to a medium density in order to reproduce characters clearly. The photo mode is a mode in which a substantially linear curve LUT is applied to faithfully reproduce a document. The mixed mode is a mode in which an intermediate LUT is applied.

  The halftone processing unit 026 can alternatively apply different types of screening according to the function selected by the operation unit 014 or the like. In general, a halftone dot document such as a printed document uses an error diffusion system (generally, a pixel of interest and its surrounding pixels are weighted with an error filter) in which moiré is unlikely to occur. For a photographic paper document or the like, a screen system process (generally, a dither matrix is used to compare an input image with a threshold value to determine an output image) is used. In any case, a halftone is expressed in a pseudo manner by converting from a multi-value image to a binary image. The error diffusion processing is executed by the error diffusion processing unit 027, and the screen processing is executed by the screen processing unit 028. The notch processing unit 029 corrects unnecessary notches (jagged edges) using the window for the target pixel and its peripheral pixels.

  When instructed to perform line calibration, the line evaluation unit 023 performs quantitative evaluation on the line image formed on the recording medium. Note that a signal is input from the shading correction unit 022 to the line evaluation unit 023. The line evaluation unit 023 is an example of a determination unit that determines image processing parameters used by the line image processing unit for image processing according to the paper type of the recording medium. The line evaluation unit 023 is an example of an evaluation unit that evaluates the quality of each line image read from a recording medium of a specific paper type on which a specific line image is printed using different image processing parameters. Details of the line evaluation unit 023 will be described later.

  FIG. 3 is a block diagram of the RIP unit. In order to reproduce vector information such as characters, line drawings, and graphics described in PDL and image scanning line information such as colors, patterns, and photographs on one page, RIP uses a bitmap ( A raster image). The RIP was originally realized by hardware, but nowadays, it is often realized by software due to CPU speedup.

  The RIP unit 013 generally includes an interpreter unit 030 and a rendering unit 031. The interpreter unit 030 includes a PDL interpretation unit 032 that translates PDL, and a DL (Display List) generation unit 033 that generates an intermediate file called a display list from the interpreted PDL data.

  The rendering unit 031 includes a DL development unit 034, a gradation correction unit 035, and a screen processing unit 036. The DL development unit 034 develops the display list into a bitmap (raster image). The tone correction unit 035 performs brightness adjustment and printer tone correction instructed by the user. The screen processing unit 036 executes pseudo halftone processing for converting a multi-value grayscale image into a binary image.

  The PDL interpretation unit 032 analyzes various types of input PDL data. As the input format, the PostScript (registered trademark) language of Adobe, the PCL (Printer Control Language) language of Hewlett-Packard, etc. are well known. The PDL data is described by a printer control code for creating an image for each page, and includes not only a simple character code but also a graphic drawing code and a photographic image code. A document display file format developed by Adobe, called PDF (Portable Document Format), is also widely used in various industries. The PDL interpretation unit 032 also interprets PDFs that are thrown directly into the MFP without using a driver. In addition, the PDL interpretation unit 032 also supports a format for VDP called PPML, and a compression format for color images such as JPEG and TIFF. PPML is an abbreviation for Personalized Print Markup Language. VDP is an abbreviation for Variable Data Print. JPEG is an abbreviation for Joint Photographic Experts Group. TIFF is an abbreviation for Tagged Image File Format.

  FIG. 4 is a block diagram of the output image processing unit. A density error correction unit 040 at the time of zooming corrects a density error that occurs when the resolution is converted (for example, image data input at 200 dpi is output at 600 dpi) at the time of FAX reception or the like. When the resolution is converted, the density information may not be saved. Therefore, the magnification density error correction unit 040 divides the image into a plurality of blocks, performs pattern matching, and performs one-dimensional diffusion processing of errors on the matched blocks. As a result, the density is maintained.

  The toner save unit 041 is a unit that realizes toner saving by periodically replacing black pixels of an input image with white pixels. It is also possible to select the pattern used for replacement and the degree of saving. When printing PDL data, the edge portion is detected, the toner is not saved in the edge portion, and the toner is saved only in the non-edge portion, so that toner saving and a clear image can be achieved.

  The line image processing unit 042 thins out a part of the line image with the optimum thinning amount as much as possible. The line image processing unit 042 will be described in detail.

  FIG. 5 is a schematic cross-sectional view of an electrophotographic printer unit and a scanner unit. Here, a laser beam printer as the printer unit 011 is employed.

  The printer unit 011 includes a drum-type electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 100 as an image carrier. Around the photosensitive drum 100, a charging unit 101, an exposure unit 102, a developing unit 103, an intermediate transfer unit 104, a cleaning unit 105, and a pre-charger 106 are disposed almost in order along the rotation direction. A primary transfer unit 107 is provided opposite to the photosensitive drum 100 of the intermediate transfer unit 104. Further, a feeding / conveying unit 109, a secondary transfer unit 108, a conveying belt unit 110, a fixing unit 111, and a paper discharge tray 112 are arranged in this order from the upstream side along the conveying direction of the recording medium P. A scanner unit 200 is disposed above the printer unit 011.

  The above-described photosensitive drum 100 is manufactured, for example, by providing a layer of an a-Si photosensitive member on the outer peripheral surface of an aluminum cylinder. The photosensitive drum 100 is rotationally driven at a predetermined process speed in the direction of an arrow by a driving unit (not shown). The surface of the photosensitive drum 100 is uniformly charged by the charging unit 101 so as to have a predetermined polarity and a predetermined potential. As the charging unit 101, for example, a corona charger that is not in contact with the photosensitive drum 100 can be used. An electrostatic latent image is formed on the photosensitive drum 100 after charging by the exposure unit 102.

  The scanner unit 200 reads an image of the document D placed on the platen glass. Image data read by the scanner unit 200 is processed by the input image processing unit 002 and the output image processing unit 012 and input to the exposure unit 102. The exposure unit 102 includes a laser oscillator 102a, a polygon mirror 102b, a lens 102c, and a reflection mirror 102d. The exposure unit 102 exposes the surface of the photosensitive drum 100 according to the image data input from the scanner unit 200 to form an electrostatic latent image.

  The electrostatic latent image formed on the surface of the photosensitive drum 100 is developed as a toner image by being attached with toner by the developing unit 103. On the other hand, the recording medium P stored in the paper feeding cassette of the paper feeding / conveying unit 109 is fed by the paper feeding roller and conveyed to the secondary transfer unit 108 by the conveying roller. The recording medium is sometimes called a recording material, paper, sheet, transfer material, or transfer paper.

  The toner image formed on the photosensitive drum 100 by the developing unit 103 is primarily transferred onto the intermediate transfer unit 104 by applying a transfer bias at the primary transfer unit 107. Further, the toner image is transferred to the surface of the recording medium P by applying a transfer bias at the secondary transfer unit 108.

  The recording medium P onto which the toner image has been transferred is conveyed to the fixing unit 111 by the conveyance belt unit 110. The fixing unit 111 heats and pressurizes the recording medium P and the toner image by the fixing roller 111a and the pressure roller 111b. As a result, the toner image is fixed on the surface of the storage medium. Thereafter, the recording medium P is discharged onto the paper discharge tray 112.

  FIG. 6 is a schematic cross-sectional view of the scanner unit 200. The document D to be read is placed on the document table glass 201, and the scanning operation is started by using a trigger such as pressing the start key of the operation unit 014 or clicking the OK key of the scanner driver.

  When the scanning operation is started, the first mirror unit 202 and the second mirror unit 203 once return to the home position where the home position sensor 204 is located. Then, the document illumination lamp 205 is turned on and the document is illuminated. The reflected light from the document D passes through the first mirror 206 in the first mirror unit 202, the second mirror 207 and the third mirror 208 in the second mirror unit 203, and further onto the CCD sensor 020 through the lens 209. Imaged. Thus, the reflected light is input to the CCD sensor 020 as an optical signal. The first mirror unit 202 and the second mirror unit 203 are moved in the direction of the arrow by the scanner motor 210.

  Normally, the scanner unit 200 operates as a 600 dpi reading device. However, when line calibration is executed for a new paper type, the reading speed in the sub-scanning direction of the scanner unit 200 is set to a normal 1/4 speed. Thereby, only the resolution in the sub-scanning direction is set to 2400 dpi, and the line image is read. In line calibration, a line image formed on a recording medium of a specific paper type is read to determine an image processing parameter optimal for that paper type. Therefore, it is desirable to read a line image with as high accuracy as possible.

  In the line evaluation method described later, binarization is executed from a luminance difference between a white background portion and a black portion having a certain area. Therefore, highly accurate line image evaluation cannot be performed under conditions (such as light intensity and gain) that cause the image data of the white background portion to be saturated. For this reason, in the present embodiment, the light receiving condition of the scanner unit 200 is changed so that the gain is 85% as compared with normal image reading.

  FIG. 7 is a schematic configuration diagram of the operation unit 014. The operation unit 014 includes a key input unit 301 and a touch panel unit 302. The key input unit 301 includes a plurality of keys for performing routine operation settings. A user mode key 303 is a key for shifting to a system setting screen for each user. When the user mode key is pressed and the adjustment / CLN (cleaning) tab is touched, a line calibration start button 304 is displayed on the touch panel.

  FIG. 8 is a block diagram of the line image processing unit provided in the output image processing unit. The line image processing unit 042 detects a line image included in the image data, and executes a thinning process by replacing a part of the detected line image with a predetermined pixel.

  The buffer 400 and the delay circuit 401 are constituted by a memory, and temporarily store image data being processed. A window 402 is a block for determining whether the pixel of interest is a pixel that is undergoing pseudo halftone processing. The window 402 includes a halftone determination pattern 403 for determining whether the target pixel is a halftone. When a copy image is formed through error diffusion processing, a halftone image is reproduced to some extent. For this reason, the window 402 also holds a 175 lpi, 150 lpi, and 134 lpi halftone determination pattern 403 that is common in printing.

  FIG. 9 is a diagram illustrating an example of a halftone determination pattern. This halftone determination pattern is a halftone determination pattern for determining the dot growth of 141 lpi 45 degrees at 1200 dpi. According to this, a pixel of interest is arranged at a substantially central position of 9 pixels on the right and 9 pixels on the bottom, and it is determined whether or not there are other dots around the pixel of interest. In a 141 lpi halftone image, there are dots in the gray region (portion 1) in the figure. Therefore, 1 is output when a dot is detected in the gray area, and 0 is output when no dot exists. If 1 is returned, it means halftone. Such halftone determination patterns may be prepared according to the number of halftone processes, or other halftone determination patterns may be synthesized from several halftone determination patterns.

  The pixel of interest that is determined not to be halftone in the window 402 is determined by the pattern matching unit 404 as to whether or not it is a line image. The pattern matching unit 404 is an example of a line detection unit that detects main scanning direction lines included in image data. The pattern matching unit 404 uses the replacement pixel (line) determination pattern 405 to determine whether the target pixel is a line image. Here, as an example, the size of the replacement pixel (line) determination pattern 405 is 18 * 18 pixels.

  FIG. 10 is a diagram illustrating an example of a replacement pixel (line) pattern. In this replacement pixel (line) pattern, 1 means that there is an image. 0 means that there is no image. If the periphery of the target pixel is such a condition, it is determined that the target pixel is a line image. The line image detected in this way becomes a pixel replacement target pixel. In order to change the final thinning amount or thinning pattern, a plurality of replacement pixel (line) patterns corresponding to these conditions may be prepared. That is, the pattern matching unit 404 selects and uses a replacement pixel (line) pattern corresponding to the designated thinning amount and thinning pattern.

  It is not necessary to replace pixels that are determined not to be line images by the window 402 and the pattern matching unit 404. Therefore, the pixel matching unit 404 is notified that the pattern matching unit 404 does not require replacement. On the other hand, the pattern matching unit 404 notifies the pixel replacement unit 408 of a replacement signal indicating that replacement is necessary for an image determined to be a line image instead of a halftone. In addition, data used for replacement stored in the replacement pixel storage unit 407 is input to the replacement pixel input unit 406. The pixel replacement unit 408 replaces the line image using the data input to the replacement pixel input unit 406. The pixel replacement unit 408 is an example of a line image processing unit that applies image processing for preventing deterioration in the quality of a line in the main scanning direction to image data.

  FIG. 11 is a diagram illustrating a correspondence example between the determination result and the line image processing. According to this, if the target pixel is not a halftone but a line image, the replacement is executed. On the other hand, in the white block, halftone block, and black block, the pixel value of the target pixel to which the replacement is applied is directly output to the subsequent circuit.

  FIG. 12 is a diagram showing a list of line thinning patterns used in the pixel replacement unit. In the present embodiment, a test image that has been subjected to thinning processing based on the different line thinning patterns shown in FIG. 12 is output, and line evaluation is performed on the output test image to obtain an optimal thinning condition (line thinning pattern). ). The line thinning pattern may be called a line replacement pattern or a pixel replacement pattern due to its nature.

  As shown in FIG. 12, in each line thinning pattern, the amount of thinning (from 3% to 17% with respect to the whole) and the position of the thinned pixel are different. For example, in the line thinning patterns A and E, the number of pixels to be replaced (thinned out) is two. In the line thinning patterns B and F, the number of pixels to be replaced (thinned out) is four. In the line thinning patterns C and G, the number of pixels to be replaced (thinned out) is seven. In the line thinning patterns D and H, the number of pixels to be replaced (thinned out) is 12. As can be seen from FIG. 12, even if the number of pixels to be replaced (decimated) is the same, the positions of the pixels to be replaced are different.

  In each line thinning pattern, the positions of thinning pixels are set so that thinning is not performed at the edge of the line. This is because when line thinning is performed at the edge of the line, rattling occurs in the line and the quality is lowered. In this embodiment, as an example, pixel replacement is executed in units of 1200 dpi.

  FIG. 13 is a diagram showing an example of a test chart. The test chart includes a plurality of line calibration patterns arranged in the sub-scanning direction. Each line calibration pattern includes at least a specific line image printed using different image processing parameters. According to FIG. 13, the line calibration pattern includes a solid portion, eight line portions A to H from which some pixels are thinned, and a line portion (none) without thinning. Each of the line portions A to H corresponds to a different line thinning pattern (A to H shown in FIG. 12). For example, the line portion A includes four line images formed by applying the line thinning pattern A.

  For example, the solid portion and the line portion are arranged in an area of 1000 dpi × 1000 pixels (21.17 mm × 21.17 mm) of 1200 dpi. Each line part is formed by, for example, 8 dot lines (169.3 μm), the number of lines is 4, and the line interval is 250 dots (5.29 mm).

  According to FIG. 13, different image processing parameters are applied to the five line calibration patterns arranged in the sub-scanning direction. Here, development contrast (Vcont) is adopted as the image processing parameter. Note that the change in Vcont is executed by the printer unit 011. Accordingly, the five image data for forming the five line calibration patterns are all the same. That is, the test chart shown in FIG. 13 can be obtained by repeating the printing of the same image data five times while changing the image processing parameters. Here, the entire five line calibration patterns are called test charts. In order to change Vcont, the laser power or the PWM pulse width may be changed while Vgrid (grit bias) and Vdc (development bias) are kept constant.

  The printer unit 011 prints a test chart on a recording medium to be evaluated, and the scanner unit 200 reads the test chart from the recording medium. The line evaluation unit 023 evaluates the solid portion density, the line width of the line portion, and the scattering of the line portion as the quality of the line in the five line calibration patterns included in the read test chart.

  The line evaluation unit 023 performs various evaluations using the luminance information after the shading correction. Further, the line evaluation unit 023 determines optimal image processing parameters (eg, development contrast and thinning pattern) based on the evaluation result. The density of solid black can be obtained by converting the luminance information with a luminance-density conversion table. The luminance-density conversion table is created in advance in consideration of the characteristics of the scanner unit 200.

  As a line evaluation method, for example, “line width” and “blurness” defined in ISO 13660 can be used.

  “Line width” can be used as a scale for evaluating line width, and “blur” can be used as a scale for evaluating scattering. Below, these specific evaluation methods are demonstrated.

  FIG. 14A is a diagram showing an image edge threshold. The line evaluation unit 023 basically evaluates each line calibration pattern using a binary image. Let Rs be the luminance (reflectance) of the ground (white background in the test chart). The brightness of the solid portion is Ri. The line width is the average line width in the region when binarized by R60 (R60 = Rs−0.6 (Rs−Ri)), which is an image edge threshold. For example, assuming that 100% luminance is obtained from the ground and 0% luminance is obtained from the solid portion, R60 is set to 40% luminance.

  FIG. 14B is a diagram illustrating an inner boundary edge and an outer boundary edge. The blur is equivalent to the difference between the inner boundary edge and the outer boundary edge. According to ISO 13660, the inner boundary edge is defined as R90 (R90 = Rs−0.9 (Rs−Ri)). The outer boundary edge is defined as R10 (R10 = Rs−0.1 (Rs−Ri)). In this embodiment, the inner boundary edge is R70 (R70 = Rs−0.7 (Rs−Ri)), and the outer boundary edge is R30 (R30 = Rs−0.3 (Rs−Ri)). This is because when R90 and R10 are used as in ISO 13660, disturbances such as floating of the base, wrinkles after fixing, dirt, and fogging of the toner are picked up, and stable evaluation results cannot be obtained. As a result of studies by the inventors of the present invention, it has been found that the inner boundary edge is R80 to R70 and the outer boundary edge is R20 to R30, which is strong against disturbance. Therefore, in this case, R70 and outer boundary edge R30 are adopted as the inner boundary edge.

  FIG. 15A is a diagram illustrating an example of the density and the line width obtained from the test chart. FIG. 15A shows density and line width values for each Vcont.

  FIG. 15B is a diagram showing an example of density and blur obtained from the test chart. FIG. 15B shows the density and blur value for each Vcont.

  When determining an actual thinning pattern, it is desirable to determine an optimal thinning pattern according to a priority order based on a plurality of conditions. This is because the optimum thinning pattern varies depending on the importance of any of a plurality of conditions. Therefore, it is desirable to prioritize effective conditions in mitigating scattering and explosion.

Condition 1: Density is a predetermined threshold value (= 1.4) or more Condition 2: Line width is within a predetermined range (= 169 μm ± 15 μm) Condition 3: Blur is a predetermined threshold value (= 33) or less Condition 4: Condition 1 to 3 is satisfied When there are a plurality of candidates, the candidate having the smallest thinning amount (number of pixel replacements) is selected from these candidates. Further, when there are a plurality of candidates for the same thinning amount, C is given priority over the thinning pattern G, and D is given priority over the thinning pattern H. This is because, in general, the influence on the image quality is less when the positions of thinned pixels are dispersed. For example, because G and H thin out two consecutive pixels, the thinned out pixels may appear to be hollow.

  In this way, if the candidates (thinning patterns) can be narrowed down to one by the conditions 1 and 2, the condition 3 is applied. If the condition 3 cannot be narrowed down to one candidate, the condition 4 is narrowed down to two candidates.

  As described above, in the prior art, the quality of the line image was maintained by reducing the maximum density portion or reducing the line width, but this caused the quality of the other image portions to deteriorate. there were. Therefore, there is room for improvement in the prior art. In the present embodiment, blur evaluation is adopted as the condition 3 in particular.

  15A and 15B, it can be seen that Condition 3 is met if Vcont is standard and the thinning pattern is C, D, G, or H. Therefore, C is selected according to condition 4.

  The blur threshold is set to 33 because it is a value that can be achieved with plain paper even in each temperature and humidity environment and before and after durability. That is, even if the recording medium is another paper type that is likely to scatter or explode, if the blur value is 33 or less, the line quality equivalent to that of plain paper can be maintained. The value of 33 was determined by the inventors through subjective evaluation. Specifically, the threshold was determined based on the result that 80% or more of the subjects answered that the line quality was acceptable.

  FIG. 16 is a block diagram of a line evaluation unit according to the embodiment. The density determination unit 1601 determines whether the density of each image read from a recording medium of a specific paper type on which a specific line image is printed using different image processing parameters is greater than or equal to a threshold value. Different image processing parameters are, for example, the above-described development contrast and line thinning pattern.

  The line width determination unit 1602 determines whether or not the line width of each line image printed on the recording medium is within a predetermined range. The blur determination unit 1603 determines whether the blur of each line image printed on the recording medium is equal to or less than a threshold value. The comparison unit 1604 compares thinning amounts for thinning out images from the original image data between different image processing parameters.

  The selection unit 1605 selects an image processing parameter for a specific paper type based on the determination result of the density determination unit, the determination result of the line width determination unit, the determination result of the blur determination unit, and the comparison result of the comparison unit. Note that the selection unit 1605 prioritizes the determination condition used by the density determination unit first, and prioritizes the determination condition used by the line width determination unit. The selection unit 1605 gives priority to the determination condition used by the blur determination unit third, and gives priority to the comparison condition of the comparison unit fourth. In this way, one set of density and line thinning pattern that seems to be optimal is determined.

  FIG. 17 is a flowchart showing line calibration and normal image shapes according to the embodiment. Steps S002 to S007 correspond to normal image formation (copy function, print function, facsimile function). S009 to S021 correspond to line calibration (line CAL).

  In step S001, the MFP control unit 001 determines whether normal image formation is performed based on an operation instruction from the operation unit 014. If it is normal image formation, the process proceeds to step S002.

  In step S <b> 002, the MFP control unit 001 acquires paper information representing the paper type from the operation unit 014. Through the operation unit 014, the operator can specify the paper type. The paper type may be specified by the media sensor. The media sensor is a sensor that irradiates a recording medium with light and identifies a paper type based on transmitted light or reflected light from the recording medium. As described above, the MFP control unit 001 is an example of a paper type specifying unit that specifies the paper type of a recording medium on which an image based on image data is formed of a color material.

  In step S003, the MFP control unit 001 uses the acquired sheet information to inquire the resource management unit 009 about the line image processing condition, and acquires the line image processing condition corresponding to the acquired sheet information.

  In step S004, the MFP control unit 001 executes image processing using the tone correction unit 025 and the halftone processing unit 026 in the RIP unit 013.

  In step S005, the MFP control unit 001 performs halftone determination in the window 402 of the line image processing unit 042, performs line detection in the pattern matching unit 404, and executes replacement processing in the pixel replacement unit 408. In particular, the pixel replacement unit 408 performs pixel thinning (replacement) using the line thinning pattern determined by the line evaluation unit 023. In addition, the MFP control unit 001 notifies the pixel replacement unit 408 of a line thinning pattern corresponding to the paper type.

  In step S006, the MFP control unit 001 notifies the printer unit 011 of a development contrast value corresponding to the paper type specified by the paper information, and causes the printer unit 011 to form an image.

  In step S007, the MFP control unit 001 determines whether the job has ended. If not completed, the process returns to step S002. On the other hand, if it is finished, it shifts to the standby mode. If it is determined in step S001 that normal image formation is not performed, the process proceeds to step S008.

  In step S008, the MFP control unit 001 determines whether it is instructed to execute line calibration. If execution of line calibration is not instructed, the process returns to step S001. If execution of line calibration is instructed, the process proceeds to step S009.

  In step S009, the MFP control unit 001 acquires paper information indicating the paper type. The paper information acquisition process is as already described with respect to step S002.

  In step S010, the MFP control unit 001 prints a test chart (line calibration pattern) by the printer unit 011. A plurality of line calibration patterns are printed side by side in the sub-scanning direction, and Vcont is changed for each line calibration pattern. Therefore, the MFP control unit 001 must notify the printer unit 011 that it is a line calibration pattern and print it with a predetermined Vcont.

  In step S011, the MFP control unit 001 reads the printed line calibration pattern with the scanner unit 200. The line evaluation unit 023 converts the luminance information of the line calibration pattern into density data with reference to the luminance-density conversion table. The line evaluation unit 023 includes a luminance-density conversion unit.

  In step S012, the density determination unit 1601 extracts the development contrast that satisfies condition 1 regarding density based on the density of the line calibration pattern. For example, the density determination unit 1601 determines for each development contrast whether or not the density of the solid portion of the line calibration pattern is equal to or greater than a threshold value (reflection density 1.40).

  In step S013, the line width determination unit 1602 extracts a line width satisfying the condition 2 among the line widths of the line portions included in each line calibration pattern. Each line portion corresponds to a line thinning pattern (FIG. 13). Therefore, the line width determination unit 1602 extracts a line thinning pattern corresponding to the extracted line portion. Specifically, the line width determination unit 1602 calculates the line width of each line portion, and extracts a line portion (line thinning pattern) in which the calculated line width is within a predetermined range (eg, 169 μm ± 15 μm). .

  In step S014, the blur determination unit 1603 calculates a blur for each line part included in the line calibration pattern, and extracts a line part (line thinning pattern) that satisfies the condition 3. The blur determination unit 1603 extracts a line thinning pattern in which the blur is equal to or less than a predetermined threshold (for example, 33).

  In step S015, the selection unit 1605 determines whether or not there is a pair of development contrast and line thinning pattern that meets all of the conditions 1 to 3. If even one set exists, the process proceeds to step S016. In step S016, the selection unit 1605 determines whether there are a plurality of extracted sets. If there are not a plurality of extracted groups (that is, one group), the process proceeds to step S017. In step S017, the selection unit 1605 registers the extracted thinning pattern and development contrast in the resource management unit 009 in association with the paper type specified by the paper information. Thereafter, the image processing parameters (development contrast and line thinning pattern) corresponding to the paper type specified in step S002 are called from the resource management unit 009 and used.

  On the other hand, if there are a plurality of sets satisfying the conditions 1 to 3, the process proceeds to step S018. In step S018, the selection unit 1605 causes the comparison unit 1604 to compare the thinning amounts of the line thinning patterns. The comparison unit 1604 extracts the line thinning pattern belonging to the set satisfying the conditions 1 to 3 that has the smallest thinning amount. When a plurality of line thinning patterns having the smallest thinning amount are extracted, the distribution of thinning pixels is considered. That is, C is preferentially selected over the line thinning pattern G. Further, D is preferentially selected over the line thinning pattern H. The selection unit 1605 registers the extracted thinning pattern and development contrast in the resource management unit 009 in association with the paper type specified by the paper information.

  By the way, if there is no set that satisfies all of the conditions 1 to 3 in step S015, the process proceeds to step S019. In step S019, the selection unit 1605 determines whether there is a set satisfying the conditions 1 and 2. If there is a set that satisfies the conditions 1 and 2, the process proceeds to step S020.

  In step S020, the selection unit 1605 registers, in the resource management unit 009, the pair that satisfies the conditions 1 and 2 that has the smallest blur in association with the paper type specified by the paper information. If there is one set that satisfies the conditions 1 and 2, the blur comparison is omitted. That is, if there are a plurality of sets that satisfy the conditions 1 and 2, the sets of blurs are compared and the set that minimizes the blur is selected.

  In step S019, if there is no group that satisfies the conditions 1 and 2, the process proceeds to step S021. In step S021, the MFP control unit 001 displays an error on the display device of the operation unit 014. This is because there is a high possibility that the engine characteristics of the printer unit 011 are in an abnormal state, and it is considered that replacement or repair of parts is necessary.

  As described above, in the present embodiment, since image processing parameters corresponding to the paper type are used, scattering and explosion of line images are suppressed. The image processing parameter is a line thinning pattern used for converting the image data so that a part of the main scanning direction line is not formed on the recording medium. The thinning amount of the line is an important parameter from the viewpoint of maintaining the density of the solid portion while suppressing scattering and explosion. That is, the line thinning pattern is pattern data applied to image data in order to reduce the amount of color material used for forming at least the inside of the main scanning direction line. Therefore, it is important to select an optimum line thinning pattern from the viewpoint of maintaining the density of the solid portion while suppressing scattering and explosion.

  In this embodiment, a specific line image is printed on a recording medium of a specific paper type using different image processing parameters. Then, the quality of each line image read from the recording medium is evaluated, and the image processing parameter for the paper type is determined according to the evaluation result. As described above, since an image is actually formed in the image forming apparatus to be optimized and an optimum image processing parameter is determined, differences in installation environment, degree of durability, and model are taken into consideration.

  In this embodiment, the development contrast and the line thinning pattern are evaluated by using the scattering (blur) defined in ISO 13660 in addition to the solid portion density and the line width. Therefore, since the influence of scattering is sufficiently taken into consideration, a combination of a thinning pattern and a development contrast suitable for reducing scattering is selected.

  The determination condition used by the density determination unit has the highest priority, the determination condition of the line width determination unit has the second priority, the determination condition of the blur determination unit has the third priority, and the comparison condition of the comparison unit has the fourth priority. By giving priority to the above, it becomes possible to suitably select an image processing parameter for a specific paper type.

  Note that the width (line width) of line images used for line calibration and the interval between line images (line interval) may be changed for each image forming apparatus. For each model of the image forming apparatus, a plurality of line images having different line widths (thicknesses) and intervals may be evaluated in advance (scattering evaluation), and line widths and intervals at which the line quality is significantly deteriorated may be selected. This will improve the accuracy of the evaluation.

  For example, in order to determine the line width, the gap between the lines is secured as wide as possible (for example, about 20 mm). As shown in FIG. 6 of Japanese Patent Application Laid-Open No. 2006-098473, the line width on the chart is 1200 dpi, and about 5 to 20 dots is optimal. This is because the edge effect (solid line ratio) exists in electrophotography. In the thin line, scattering and explosion tend not to occur easily. On the contrary, when the toner is placed on the recording medium to some extent (that is, when the line becomes thicker), the toner tends to be excessively placed on the edge of the line.

  FIG. 18A is a diagram showing the relationship between the line width and the blur. Since the blur affects the edge, the blur value hardly changes if the line width is 100 μm or more. Therefore, it is desirable that the amount of toner used for line calibration is small. In this embodiment, a 1200 dpi 8-dot line (169.3 μm) is employed as the line width.

  FIG. 18B is a diagram illustrating the relationship between line spacing and blur. That is, FIG. 18B shows the measurement result of blur when the line interval is changed from 50 dots (1.06 mm) to 1000 dots (21.17 mm). If the line interval is too narrow, the degree of explosion and explosion cannot be measured accurately due to the light scattering of the scanner unit 200 and the internal scattering of the paper. Therefore, the minimum is about 50 dots (1.06 mm). As shown in FIG. 18B, a noticeable sensitivity to blur is confirmed when the resolution is about 250 dots (5.29 mm) at 1200 dpi. Therefore, in this embodiment, the line spacing is set to 250 dots (5.29 mm) with 1200 dpi.

  Of course, you can output a test chart with the line width changed for each paper type, determine the line width based on the output result, and then change the line interval to determine the line interval that is sensitive to blur. good. The line width and the line interval sensitive to blur depend on the diameters and nip widths of the fixing roller and the pressure roller, the intrusion amount of the secondary transfer roller, and the like. The nip width also changes depending on the thickness and hardness of the recording medium. Therefore, a line width determination step and a line interval determination step for determining a line calibration pattern may be added.

  The paper type (brand) is registered through the operation unit 014. The MFP control unit 001 may register a line calibration pattern corresponding to the paper type in the resource management unit or the like. In addition, when line calibration is to be executed with an unregistered paper type, processing for determining the line width and the line interval may be added to the flow.

<Embodiment 2>
In the present embodiment, rattling (hereinafter referred to as “raggedness”) is added to the line evaluation method. There may be cases where explosions are severe rather than splattering, or where the edge of the rear end becomes rattling due to excessive thinning of the line. In these cases, it is desirable to evaluate Raggedness to determine more suitable image processing parameters. Raggedness is a scale for evaluating rattling and is defined in ISO 13660.

  FIG. 19 is a conceptual diagram of evaluation using Raggedness. In order to evaluate Raggedness, the image edge threshold described in the first embodiment is used. That is, R60. An average edge is obtained for the line binarized with this threshold value. In FIG. 19, an upper average edge 1901 and a lower average edge 1902 are shown by broken lines. The average edge is a straight line. Raggedness is the difference between the actual edge and the average edge.

  Raggedness is calculated for the “front end” and “rear end” in the paper passing direction (conveyance direction), respectively. Furthermore, an “average of both” may be calculated. However, since the scattering of lines and the explosion phenomenon in the electrophotographic method are remarkably generated on the rear end side, in this embodiment, the rear end side of the line is an evaluation target.

  In the second embodiment, a condition relating to Raggedness is added to the four conditions described in the first embodiment.

Condition 1: Density is a predetermined threshold value (= 1.4) or more Condition 2: Line width is within a predetermined range (= 169 μm ± 15 μm) Condition 3: Blur is a predetermined threshold value (= 33) or less Condition 4: Ragedness is a predetermined threshold value (= 9) and below Condition 5: When there are a plurality of candidates that satisfy the conditions 1 to 4, a candidate having the smallest thinning amount (number of pixel replacements) is selected from these candidates. Further, when there are a plurality of candidates for the same thinning amount, C is given priority over the thinning pattern G, and D is given priority over the thinning pattern H.

Here, the reason why the threshold of Raggedness is set to 9 is that this value is a value that can be achieved by plain paper (an office planner 64 g / m ² manufactured by Canon Marketing Japan Inc.) before and after each temperature and humidity environment. That is, by setting the threshold of Raggedness to 9, it is possible to determine a line thinning pattern that enables output with the same line quality as plain paper even if paper that is likely to scatter or explode. Become.

  More specifically, condition 4 (Raggedness is 9 or less) is determined by the inventors based on subjective evaluation. That is, this value is based on the result that 80% or more of the subjects answered that the line quality is acceptable.

  FIG. 20 is a block diagram of a line evaluation unit according to the embodiment. The same reference numerals are assigned to the units described in the first embodiment to simplify the description. The rattling determination unit 2001 determines whether or not the ragedness representing the rattling of each line image printed on the recording medium is equal to or less than a threshold value (for example, 9).

  The selection unit 1605 is for a specific paper type based on the determination result of the density determination unit, the determination result of the line width determination unit, the determination result of the blur determination unit, the determination result of the shakiness determination unit, and the comparison result of the comparison unit. Select image processing parameters.

  Note that the selection unit 1605 prioritizes the determination condition used by the density determination unit first, and prioritizes the determination condition used by the line width determination unit. The selection unit 1605 gives priority to the determination condition used by the blur determination unit third, gives priority to the determination condition used by the rattling determination unit fourth, and gives priority to the comparison condition of the comparison unit fifth. That is, evaluation is performed according to these priorities until an optimal set is determined. An optimal set of narrowing-down methods is the same as in the first embodiment. In this way, one set of density (development contrast) and line thinning pattern that seems to be optimal is determined.

  According to the present embodiment, the image processing parameter is determined in consideration of line shakiness. Therefore, it is possible to suppress the deterioration of the line quality even in a case where the explosion is rather than scattering, or in a case where the line is excessively thinned and the trailing edge becomes rattling.

<Embodiment 3>
In this embodiment, a line dropout (hereinafter referred to as “Fill”) is added as an evaluation item.

  FIG. 21 is a diagram illustrating an example of a hollow. According to the cross section of the line image shown in FIG. 21, it can be seen that a thin portion of toner exists in the center of the line. Therefore, a white omission occurs in the center of the line, resulting in an image defect.

  Fill is likely to occur when the thinning amount is too large. Conversely, splashes and explosions are less likely to occur as the amount of thinning increases. Since Fill and splatter / explosion conflict, it is important to properly balance the two. Therefore, in the third embodiment, a fill is added as a line evaluation item in addition to a blur and a raggedness.

  Fill is expressed as a ratio of an area having a reflectance of 75% or more to the total area in the inner boundary edge (defined as R90 in ISO 13660 and R70 in the present invention).

  According to FIG. 21, Fill is a ratio between the number of pixels (a + b + c) in the inner boundary edge determined by R70 and the number of pixels (b) in the hollow portion divided by the threshold of 75%. Therefore, the calculation formula of Fill is as follows.

Fill = 100 (%) × b / (a + b + b)
In general, it should be assumed that nothing is missing. Therefore, it is desirable that Fill is 0. However, considering the influence of noise, dust, and gloss on the toner surface during line evaluation, the target value is 2% or less.

  In the third embodiment, a condition relating to Fill is added to the five conditions described in the second embodiment.

Condition 1: Density is a predetermined threshold value (= 1.4) or more Condition 2: Line width is within a predetermined range (= 169 μm ± 15 μm) Condition 3: Blur is a predetermined threshold value (= 33) or less Condition 4: Ragedness is a predetermined threshold value (= 9) or less Condition 5: Fill is 2% or less Condition 6: When there are a plurality of candidates satisfying the conditions 1 to 5, a candidate having the smallest thinning amount (number of pixel replacements) is selected from these candidates. Further, when there are a plurality of candidates for the same thinning amount, C is given priority over the thinning pattern G, and D is given priority over the thinning pattern H.

  FIG. 22 is a block diagram of a line evaluation unit according to the embodiment. The same reference numerals are assigned to the units described in the second embodiment to simplify the description.

  The dropout determination unit 2201 determines whether or not a Fill representing a dropout of each line image printed on the recording medium is equal to or less than a threshold value.

  The selection unit 1605 is based on the determination result of the density determination unit, the determination result of the line width determination unit, the determination result of the blur determination unit, the determination result of the rattling determination unit, the determination result of the dropout determination unit, and the comparison result of the comparison unit. Thus, image processing parameters for a specific paper type are selected.

  Note that the selection unit 1605 prioritizes the determination condition used by the density determination unit first, and prioritizes the determination condition used by the line width determination unit. The selection unit 1605 gives the third priority to the determination condition used by the blur determination unit, and gives the fourth priority to the determination condition used by the rattling determination unit. Furthermore, the selection unit 1605 gives priority to the determination condition used by the hollow-out determination unit in the fifth place, and gives priority to the comparison condition in the comparison unit in the sixth place. That is, evaluation is performed according to these priorities until an optimal set is determined. An optimal set of narrowing-down methods is the same as in the first embodiment. In this way, one set of density (development contrast) and line thinning pattern that seems to be optimal is determined.

  As described above, by setting the hollow out as an evaluation item, it is possible to obtain an image with good line quality with less fill while suppressing blur and ruggedness. However, not all of blur, ruggedness and fill need be provided. Further, the thinning conditions may be selected based on the evaluation result of Fill alone without using the conditions 1 to 4. In this case, the line evaluation unit will be configured by a dropout determination unit 2201, a selection unit 1605, and a comparison unit 1604.

<Other embodiments>
As shown in the first embodiment, the brand of the paper type can be specified, and the line calibration pattern and the thinning amount can be determined. On the other hand, the MFP control unit 001 may detect the paper type using a known paper type sensor, a barcode attached to a paper package, or the like. When a paper type for which image processing parameters are already registered is designated, the MFP control unit 001 may output a warning.

  It is assumed that there are generally many users who use the MFP. Therefore, even if one person registers the thinning amount for a specific paper type, another person may register the thinning amount for the same paper type again. Therefore, when determining the line calibration and the line calibration pattern, the MFP controller checks the paper type, and if it is new, executes it as it is. On the other hand, when there is an execution history in the past, it is desirable to be able to select from the operation unit 014 whether or not to re-register. Re-registration may be preferred. That is, this is a case where the durability has increased since the previous line calibration was executed. In this case, there is a possibility that the optimal image processing parameter has changed.

  When the optimum image processing parameter for any paper type is re-registered (changed) by line calibration, the MFP control unit 001 may automatically change the image processing parameters for other paper types. This is because when the optimum image processing parameter is changed for one paper type due to changes in the environment and durability, the same effect occurs for the other paper types.

  For example, suppose that the optimal line thinning pattern is B when a line calibration is previously executed for a certain paper type. It is assumed that the optimum line thinning pattern is C in the current line calibration. In this case, the line thinning pattern is changed by one level for a certain paper type. Therefore, the line thinning pattern is changed one level at a time for other paper types. For example, if the optimum line thinning pattern for other paper types is B, the MFP control unit 001 changes this to A. As described above, the MFP control unit 001 is an example of a changing unit that changes image processing parameters for other paper types when an image processing parameter selected for an arbitrary paper type is changed. The MFP control unit 001 is also an example of a changing unit that changes the image processing parameters for other paper types by a predetermined level when the image processing parameters for an arbitrary paper type are changed by a predetermined level.

  The detection method described above is a method using pattern matching. Pattern matching has the merit of sharing because the printer and copy processing can be executed by the same module. However, if the number of halftone determination patterns and replacement pixel (line) determination patterns increases, the memory capacity must be increased, resulting in an increase in cost. In addition, due to the nature of pattern matching, erroneous detection that detects a general image that is not a line image as a line may occur.

  Therefore, when printing is executed based on the PDL data, the PDL data may be analyzed to determine whether or not the image is a line image. When the line image is detected, the corresponding pixel information is notified from the RIP unit 013 to the replacement pixel storage unit 407 in the output image processing unit 012 via the MFP control unit 001. As a notification method, the input unit shown in FIG. 4 may be changed from 1 bit (2 values) to 2 bits (4 values). Of the 2-bit signal, 00 is white, 11 is black, and 01 is treated as information for notifying that it is a line pixel.

  Specific examples of these will be described using a postscript which is a mainstream PDL language in recent DTP (desktop publishing). The following example is a PostScript file that forms a simple line and uses the output destination as a file. As a simple line, it is described in the PDL language that a square of 100 × 100 points is printed by a printer with a 2-point line.

%! PS-Adobe-3.0
%% Title:. . . . . . . . . .
%% Creator:. . . . . . . .
.
newpath
100 100 moveto
200 100 lineto
200 200 lineto
100 200 lineto
closepath
2 setlinewidth Storoke
showpage
. .

  In the above example, “newpath”, “lineto”, “closepath”, “Storoke”, etc. are descriptions indicating execution instructions called operators. “Newpath” is an operator that creates a new path. “100 100 moveo” is an operator that moves the pen to the position of (100, 100) points (1 point is 1/72 inch) when the lower left corner of the page is the origin (0, 0). “Lineto” is an operator who moves the pen and adds a straight line to the path. “Closepath” is an operator that connects the end point and the start point of the path. “Storoke” is an operator who draws a line along a path. A condition for drawing a line such as “2 setlinewidth” is described before “Storoke”.

  In the present embodiment, operators such as “Storoke” and “Lineto” and “rlineto” with relative coordinates not described may be detected to determine whether the line is in the main scanning direction. This determination is performed by the PDL interpretation unit 032 provided in the RIP unit 013.

  In this embodiment, it is determined that the gray line is not a thinning target. Gray lines are less likely to scatter or explode because the screen processing unit 036 processes them in binary. For this reason, the line for executing the thinning process is conditional on being 0 at the gray level (in the postscript, black is 0 and white is 1).

  The width of the line can be easily grasped. If it is desired to set a range for the line width for performing thinning, an operator such as “setlinewidth” may be confirmed.

  FIG. 23 is a block diagram of the RIP unit. The PDL interpretation unit 032 synthesizes the line determination result as a (00 or 01) signal and a signal after screen processing (00 or 10). Therefore, the screen processing unit 036 may input an 8-bit gray scale and form a screen so as to output 2-bit signals of 00 and 10.

  Alternatively, each of the line information and the image information is sent as 1-bit information to the MFP control unit 001, and the MFP control unit 001 generates a 2-bit image signal by combining it, and transmits the output image processing unit 012. Also good.

  By adopting the above configuration, the window 402 in the output image processing unit 012 can be deleted. Since the pattern matching unit 404 creates a replacement pattern, it cannot be deleted. However, not a large 18 × 18 matrix but a matrix of about 5 × 9 that can be determined to be a line edge at the rear end will be sufficient.

  As described above, the line quality can be improved by optimizing the development contrast and the thinning amount for each paper type. In addition, usability will be improved because objective evaluation is automatically performed by line calibration executed for each specified paper type.

1 is a block diagram of an image forming apparatus including an image processing apparatus according to an embodiment. 2 is a block diagram of a scanner unit 200. FIG. It is a block diagram of a RIP part. It is a block diagram of an output image processing part. FIG. 2 is a schematic cross-sectional view of an electrophotographic printer unit and a scanner unit. 2 is a schematic sectional view of a scanner unit 200. FIG. It is a schematic block diagram of the operation part 014. It is a block diagram of the line image processing part with which the output image processing part was equipped. It is the figure which showed an example of the halftone determination pattern. It is the figure which showed an example of the replacement pixel (line) pattern. It is the figure which showed the example of a response | compatibility with a determination result and line image processing. It is the figure which showed the list | wrist of the line thinning pattern used by a pixel replacement part. It is the figure which showed an example of the line calibration pattern. It is the figure which showed the image edge threshold value. It is the figure which showed the inner side boundary edge and the outer side boundary edge. It is the figure which showed an example of the density | concentration and line width which were obtained from the test chart. It is the figure which showed an example of the density | concentration obtained from the test chart, and the blur. It is a block diagram of the line evaluation part which concerns on embodiment. It is the flowchart which showed the line calibration and normal image form which concern on embodiment. It is the figure which showed the relationship between line width and a blur. It is the figure which showed the relationship between a line space | interval and a blur. It is a conceptual diagram of evaluation using Raggedness. It is a block diagram of the line evaluation part which concerns on embodiment. It is the figure which showed an example of a hollow. It is a block diagram of the line evaluation part which concerns on embodiment. It is a block diagram of a RIP part. It is the figure which showed an example of the image which has scattered and exploding. It is an enlarged view of a secondary transfer part.

Claims (15)

An image processing apparatus,
A paper type specifying unit for specifying a paper type of a recording medium on which an image based on image data is formed of a color material;
A line detection unit for detecting a main scanning direction line included in the image data;
A line image processing unit that applies image processing for preventing deterioration in quality of the line in the main scanning direction to the image data;
An image processing apparatus comprising: a determining unit that determines an image processing parameter used by the line image processing unit for the image processing in accordance with a paper type of the recording medium. The image processing parameter is:
The image processing apparatus according to claim 1, wherein the image processing apparatus is a parameter used to convert the image data so that a part of the main scanning direction line is not formed on the recording medium. The image processing parameter is:
The image processing apparatus according to claim 2, further comprising pattern data applied to the image data in order to reduce a use amount of a color material for forming at least the inside of the main scanning direction line. The determination unit is
An evaluation unit that evaluates the quality of each line image read from a recording medium of a specific paper type on which a specific line image is printed using different image processing parameters;
The image processing apparatus according to claim 1, wherein the determination unit determines an image processing parameter for the specific paper type according to an evaluation result of the evaluation unit.   The image processing apparatus according to claim 4, wherein the evaluation unit evaluates at least one of blur, ruggedness, and fill defined in ISO 13660. The determination unit is
A density determination unit that determines whether the density of each line image read from a recording medium of a specific paper type on which a specific line image is printed using different image processing parameters is greater than or equal to a threshold;
A line width determination unit that determines whether or not the line width of each line image printed on the recording medium is within a predetermined range;
A blur determination unit that determines whether blur of each line image printed on the recording medium is equal to or less than a threshold;
A comparison unit for comparing a thinning amount for thinning an image from the original image data between the different image processing parameters;
Based on the determination result of the density determination unit, the determination result of the line width determination unit, the determination result of the blur determination unit, and the comparison result of the comparison unit, the image for the specific paper type from the different image processing parameters. The image processing apparatus according to claim 1, further comprising a selection unit that selects a processing parameter. The selection unit includes:
The determination condition used by the density determination unit is given first priority, the determination condition used by the line width determination unit is given second priority, the determination condition used by the blur determination unit is given third priority, The image processing apparatus according to claim 6, wherein the image processing parameter for the specific paper type is selected by giving priority to the comparison condition of the comparison unit fourth. The determination unit is
A density determination unit that determines whether the density of each image read from a recording medium of a specific paper type on which a specific line image is printed using different image processing parameters is greater than or equal to a threshold value;
A line width determination unit that determines whether or not the line width of each line image printed on the recording medium is within a predetermined range;
A blur determination unit that determines whether blur of each line image printed on the recording medium is equal to or less than a threshold;
A rattling determination unit that determines whether or not the ragedness representing the rattling of each line image printed on the recording medium is equal to or less than a threshold;
A comparison unit for comparing a thinning amount for thinning an image from the original image data included in the different image processing parameters;
The different image processing based on the determination result of the density determination unit, the determination result of the line width determination unit, the determination result of the blur determination unit, the determination result of the shakiness determination unit, and the comparison result of the comparison unit The image processing apparatus according to claim 1, further comprising a selection unit that selects an image processing parameter for the specific paper type from a parameter. The selection unit includes:
The determination condition used by the density determination unit is given first priority, the determination condition used by the line width determination unit is given second priority, the determination condition used by the blur determination unit is given third priority, The image processing parameter for the specific paper type is selected by giving the determination condition used by the rattling determination unit the fourth priority and giving the comparison condition of the comparison unit the fifth priority. The image processing apparatus according to claim 8. The determination unit is
A density determination unit that determines whether the density of each image read from a recording medium of a specific paper type on which a specific line image is printed using different image processing parameters is greater than or equal to a threshold value;
A line width determination unit that determines whether or not the line width of each line image printed on the recording medium is within a predetermined range;
A blur determination unit that determines whether blur of each line image printed on the recording medium is equal to or less than a threshold;
A rattling determination unit that determines whether or not the ragedness representing the rattling of each line image printed on the recording medium is equal to or less than a threshold;
A void determination unit that determines whether or not a fill representing a void in each line image printed on the recording medium is equal to or less than a threshold;
A comparison unit for comparing a thinning amount for thinning an image from the original image data included in the different image processing parameters;
Determination result of the density determination unit, determination result of the line width determination unit, determination result of the blur determination unit, determination result of the shakiness determination unit, determination result of the hollow out determination unit, and comparison result of the comparison unit 4. The image processing apparatus according to claim 1, further comprising: a selection unit that selects the image processing parameter for the specific paper type from the different image processing parameters based on the image processing parameter. 5. . The selection unit includes:
The determination condition used by the density determination unit is given first priority, the determination condition used by the line width determination unit is given second priority, the determination condition used by the blur determination unit is given third priority, The determination condition used by the rattling determination unit is given the fourth priority, the condition used by the hollow-out determination unit is given the fifth priority, and the comparison condition of the comparison unit is given the sixth priority. The image processing apparatus according to claim 10, wherein an image processing parameter for the paper type is selected.   12. The image processing apparatus according to claim 1, further comprising a changing unit that changes image processing parameters for other paper types when an image processing parameter selected for any paper type is changed. An image processing apparatus according to 1. The changing unit is
13. The image processing apparatus according to claim 12, wherein when the image processing parameter for an arbitrary paper type is changed by a predetermined level, the image processing parameter for another paper type is also changed by the predetermined level. An image forming apparatus,
An image forming apparatus comprising the image processing apparatus according to claim 1. An image processing method comprising:
A paper type specifying unit specifying a paper type of a recording medium on which an image based on image data is formed of a color material;
A line detection unit detecting a main scanning direction line included in the image data;
A line image processing unit applying image processing for preventing deterioration in quality of the main scanning direction line to the image data;
A determination unit determining an image processing parameter used for the image processing according to a paper type of the recording medium.