JP2009049690A - Image processing method, image processing device, image forming device, image forming system, program and storage medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that processing speed becomes low because of a complicated configuration for preventing moire from occurring in dither processing. <P>SOLUTION: In halftone processing, when a value which is smaller than a maximum value (n) of gradation sections 1-n (0<n≤m) composed of a minimum dot that is not smaller than 0 and can be formed at the time of an output or the thinnest dot is inputted as a value of a target pixel while a gradation level where 0 indicates white, and m(m>0) indicates a solid color is set, it is determined whether the target pixel exists at a corner position of an image section that is not a white background based on a value of an adjacently peripheral pixel of a 1/4 quadrant (vertical, horizontal, and oblique directions of the target pixel) with the target pixel as an origin. When it is determined that the target pixel exists at a corner position, an input value of the target pixel is converted to a value (n) before FM modulation dither processing is performed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image processing method, an image processing apparatus, an image forming apparatus, an image forming system, a program, and a storage medium.

  As an image forming apparatus such as a printer, a facsimile machine, a copying apparatus, and a multifunction machine of these, for example, a liquid ejection apparatus including a recording head composed of a liquid ejection head (droplet ejection head) that ejects liquid droplets of a recording liquid (liquid) As a liquid while transporting a medium (hereinafter also referred to as “paper”, but the material is not limited, and a recording medium, a recording medium, a transfer material, recording paper, etc. are also used synonymously). The recording liquid (hereinafter referred to as ink) is attached to a sheet to form an image (recording, printing, printing, and printing are also used synonymously). Some image forming apparatuses perform image formation using an electrophotographic process.

  The image forming apparatus means an apparatus for forming an image by discharging a liquid onto a medium such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramics, etc. This means not only giving images with meanings such as characters and figures to the medium, but also giving images without meaning such as patterns to the medium, forming a printing device and metal wiring. It also includes a device to perform. The liquid is not particularly limited as long as it is a liquid that can form an image.

In such an image forming apparatus provided with an image reading apparatus that reads an original image, when performing a copy process, since all input image data is captured as image data, a high-quality output image is obtained. Once the image data is separated into image areas, correction processing is performed according to each element of the input document (whether it is a character, continuous tone, or halftone).
Japanese Patent No. 3164400 Japanese Patent Laid-Open No. 06-176144 JP 2006-157331 A

  Also, in the halftone process for converting input data into an output dot pattern, an error diffusion process with excellent image reproducibility is generally applied.

  By the way, there is a strong trade-off relationship with the processing speed image quality in the image forming apparatus. In particular, in an image forming apparatus that includes an image reading apparatus and can be used in a copy mode, only a controller mounted on the image forming apparatus main body is used. Thus, since it is necessary to perform all image processing, the calculation load of image area separation and correction processing corresponding to the image region increases, and the processing speed is greatly reduced.

  Therefore, if the image area separation process is not performed, a correction process optimized for each image object (character, thin line, image, graphic) is applied in the copy process in which the input image can be recognized as only one piece of bitmap data. It becomes difficult.

  Therefore, it is conceivable to use error diffusion processing that provides excellent image reproducibility for any image object as a halftone processing method to prevent degradation of image quality, but in order to perform error diffusion processing An image processing device (image processing controller) having a high processing capability such as a large amount of buffer must be secured to hold the quantization error, and as a result, the cost of the entire device is greatly increased. There are challenges. In addition, error diffusion processing has a higher calculation load than dither processing, and similarly to image area separation, if the processing speed of the controller is slow, halftone processing takes time and throughput is affected.

  Therefore, by omitting image area separation and adopting dither processing for halftone processing, high-speed processing can be performed without using an image processing controller having high processing capability.

  However, when the image processing is simplified, so-called moire occurs. This moire is caused by the synchronization / asynchronization of the halftone dot component of the original and the dither mask pattern (dither matrix), so that the partially missing pixels appear on the output image as if they were a pattern, and the image quality is significantly reduced. It will be. Further, there is a problem that the image density itself is lowered due to the lack of dots.

  The present invention has been made in view of the above problems, and an object of the present invention is to suppress the occurrence of moiré and a decrease in density while maintaining high speed of dither processing and a light calculation load.

  In order to solve the above-described problems, an image processing method according to the present invention is an image processing method in which halftone processing using a threshold matrix is performed on input image data, where 0 is a white background and m (m> 0) Is a gradation level representing solid, 0 or more, and the maximum value n of gradation sections 1 to n (0 <n ≦ m) constituted by the smallest dots or the thinnest thinnest dots that can be formed at the time of output When a lower value is input as the value of the pixel of interest, the pixel of interest is white on the basis of the values of neighboring peripheral pixels in the ¼ quadrant (vertical, horizontal, and diagonal directions of the pixel of interest) with the pixel of interest as the origin. It is determined whether or not the pixel portion exists at a corner position of the image portion, and when it is determined that the target pixel is the corner position, the dither processing is performed after the input value of the target pixel is converted into the value n. did.

  Here, the position determination of the pixel of interest can be configured to determine that the pixel of interest is an angular position when the total input value of the adjacent peripheral pixels described above is zero. Alternatively, the position of the target pixel can be determined by pattern matching.

  An image processing method according to the present invention is an image processing method in which halftone processing using a threshold matrix is performed on input image data, wherein 0 is a white background, and m (m> 0) is a gradation level representing solid. In this case, a value of 0 or more and a value lower than the maximum value n of the gradation sections 1 to n (0 <n ≦ m) constituted by the smallest dot or the thinnest thinnest dot that can be formed at the time of output is the pixel of interest. When it is input as a value, it is determined whether or not it is an isolated point based on the input values of neighboring pixels adjacent to the target pixel. If the target pixel is determined to be an isolated point, the input value of the target pixel is set as a value. After conversion to n, a dither process is performed.

  Here, in determining whether or not the pixel of interest is an isolated point, the neighboring pixels in the range of k pixels or more (k ≧ 1) in the vertical and horizontal directions including all directions from the upper, lower, left and right diagonal directions around the pixel of interest. The pixel can be referred to. Alternatively, in the determination of whether or not the pixel of interest is an isolated point, an isolated point can be extracted using a Laplacian filter. Alternatively, the determination of whether or not the pixel of interest is an isolated point can be configured to extract isolated points by pattern matching.

  In these image processing methods according to the present invention, the dither processing can be configured to be FM modulation type dither processing.

  An image processing apparatus according to the present invention is an image processing apparatus that performs halftone processing using a threshold matrix on input image data, and has a gradation level in which 0 is a white background and m (m> 0) is solid. In this case, a value of 0 or more and a value lower than the maximum value n of the gradation sections 1 to n (0 <n ≦ m) constituted by the smallest dot or the thinnest thinnest dot that can be formed at the time of output is the pixel of interest. When input as a value, based on the values of neighboring peripheral pixels in the ¼ quadrant (vertical, horizontal, and diagonal directions of the pixel of interest) with the pixel of interest as the origin, the pixel of interest is positioned at the corner position of the image portion that is not white. When it is determined whether or not the pixel of interest exists and it is determined that the pixel of interest is in the angular position, the dither processing is performed after the input value of the pixel of interest is converted into the value n.

  An image processing apparatus according to the present invention is an image processing apparatus that performs halftone processing using a threshold matrix on input image data, and has a gradation level in which 0 is a white background and m (m> 0) is solid. In this case, a value of 0 or more and a value lower than the maximum value n of the gradation sections 1 to n (0 <n ≦ m) constituted by the smallest dot or the thinnest thinnest dot that can be formed at the time of output is the pixel of interest. When it is input as a value, it is determined whether or not it is an isolated point based on the input values of neighboring pixels adjacent to the target pixel. If the target pixel is determined to be an isolated point, the input value of the target pixel is set as a value. After conversion to n, a dither process is performed.

  An image forming apparatus according to the present invention is an image forming apparatus that forms an image by performing halftone processing using a threshold value matrix on input image data, where 0 is a white background and m (m> 0) is solid. When the gradation level to be expressed is 0 or more, it is lower than the maximum value n of gradation intervals 1 to n (0 <n ≦ m) constituted by the smallest dot or the thinnest thinnest dot that can be formed at the time of output. When the value is input as the value of the pixel of interest, an image in which the pixel of interest is not white based on the values of neighboring peripheral pixels in the ¼ quadrant (vertical, horizontal, diagonal direction of the pixel of interest) with the pixel of interest as the origin In the case where it is determined whether or not the pixel of interest exists at the corner position, and the pixel of interest is determined to be the corner position, the dither processing is performed after the input value of the pixel of interest is converted into the value n.

  An image forming apparatus according to the present invention is an image forming apparatus that forms an image by performing halftone processing using a threshold value matrix on input image data, where 0 is a white background and m (m> 0) is solid. When the gradation level to be expressed is 0 or more, it is lower than the maximum value n of gradation intervals 1 to n (0 <n ≦ m) constituted by the smallest dot or the thinnest thinnest dot that can be formed at the time of output. When the value is input as the value of the pixel of interest, it is determined whether or not the pixel is an isolated point based on the input values of neighboring pixels adjacent to the pixel of interest. After the input value is converted to the value n, the dither processing is performed.

  An image forming system according to the present invention includes an image processing apparatus according to the present invention and an image forming apparatus that forms an image.

  The program according to the present invention is a program that causes a computer to perform halftone processing using a threshold matrix on input image data, and 0 is a white background, and m (m> 0) is a gradation level representing solid. The value of the pixel of interest is 0 or more and a value lower than the maximum value n of the gradation sections 1 to n (0 <n ≦ m) constituted by the smallest dots or the thinnest thinnest dots that can be formed at the time of output. Is input at the corner position of the image area that is not a white background, based on the values of neighboring peripheral pixels in the quarter quadrant (vertical, horizontal, and diagonal directions of the target pixel) with the target pixel as the origin. When it is determined whether or not the pixel of interest is at the angular position, the computer converts the input value of the pixel of interest into a value n and then performs halftone processing for performing dither processing. .

  The program according to the present invention is a program that causes a computer to perform halftone processing using a threshold matrix on input image data, and 0 is a white background, and m (m> 0) is a gradation level representing solid. The value of the pixel of interest is 0 or more and a value lower than the maximum value n of the gradation sections 1 to n (0 <n ≦ m) constituted by the smallest dots or the thinnest thinnest dots that can be formed at the time of output. Is input as the isolated point based on the input values of the neighboring pixels adjacent to the target pixel. If the target pixel is determined to be an isolated point, the input value of the target pixel is set to the value n. After the conversion, the computer is configured to perform halftone processing for performing dither processing.

  The storage medium according to the present invention stores the program according to the present invention.

  According to the image processing method, the image processing apparatus, the image forming apparatus, the image forming system, the program, and the storage medium according to the present invention, when 0 is a gray level representing a white background and m (m> 0) is solid, A value lower than the maximum value n of the gradation sections 1 to n (0 <n ≦ m) configured by the minimum dots or the thinnest thinnest dots that can be formed at the time of output is input as the value of the target pixel. If the pixel of interest exists in the corner position of the image portion that is not a white background, based on the values of neighboring peripheral pixels in the ¼ quadrant (vertical, horizontal, and diagonal directions of the pixel of interest) with the pixel of interest as the origin If the pixel of interest is determined to be at the angular position, the dither processing is performed after the input value of the pixel of interest is converted to the value n. Suppresses the occurrence of moiré and concentration reduction while maintaining Door can be.

  According to the image processing method, the image processing apparatus, the image forming apparatus, the image forming system, the program, and the storage medium according to the present invention, when 0 is a gray level representing a white background and m (m> 0) is solid, A value lower than the maximum value n of the gradation sections 1 to n (0 <n ≦ m) configured by the minimum dots or the thinnest thinnest dots that can be formed at the time of output is input as the value of the target pixel. If the pixel of interest exists in the corner position of the image portion that is not a white background, based on the values of neighboring peripheral pixels in the ¼ quadrant (vertical, horizontal, and diagonal directions of the pixel of interest) with the pixel of interest as the origin If the pixel of interest is determined to be at the angular position, the dither processing is performed after the input value of the pixel of interest is converted to the value n. Suppresses the occurrence of moiré and concentration reduction while maintaining Door can be.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. An example of an image forming apparatus according to the present invention will be described with reference to FIGS. 1 is a schematic configuration diagram showing the overall configuration of the image forming apparatus, FIG. 2 is a plan explanatory view of an engine unit portion of the apparatus, and FIG. 3 is an enlarged front explanatory view.

  This image forming apparatus has an image forming part (means) 2 for forming an image, a sub-scanning conveying part (means) 3, etc. in the inside (enclosure) of the apparatus main body 1. A recording medium (hereinafter referred to as “paper”, but the material is not limited to paper) 5 serving as a transported member is separated and fed one by one from a paper feeding unit (means) 4 serving as a housing unit. Paper is formed and the sub-scanning conveyance unit 3 intermittently conveys the paper 5 at a position facing the image forming unit 2 while the image forming unit 2 ejects droplets onto the paper 5 to form (record) a desired image. After that, the paper 5 is discharged onto a paper discharge tray 7 formed on the upper surface of the apparatus main body 1 through the paper discharge conveyance unit 6. The image forming unit 2 and the sub-scanning conveyance unit 3 are unitized to form an engine unit 100 that is detachably attached to the apparatus main body 1.

  The image forming apparatus also has an image reading unit (scanner) for reading an image above the discharge tray 7 above the apparatus main body 1 as an input system for image data (print data) formed by the image forming unit 2. Part) 11. The image reading unit 11 includes a scanning optical system 15 including an illumination light source 13 and a mirror 14 and a scanning optical system 18 including mirrors 16 and 17. The scanned document image is read as an image signal by the image reading element 20 disposed behind the lens 19, and the read image signal is digitized and subjected to image processing, and the image-processed print data is printed. be able to. A pressure plate 10 is provided on the contact glass 12 for pressing the document.

  Here, as shown in FIG. 2, the image forming section 2 of the image forming apparatus is provided on a carriage guide (guide rod) 21 and a rear stay 101B which are horizontally mounted between the front plate 101F and the rear plate 101R. A guide stay (not shown) holds the carriage 23 movably in the main scanning direction, and the main scanning motor 27 moves and scans in the main scanning direction via a timing belt 29 spanned between the driving pulley 28A and the driven pulley 28B.

  On the carriage 23, recording heads 24k1 and 24k2 each composed of two droplet discharge heads for discharging black (K) ink, cyan (C) ink, magenta (M) ink, and yellow (Y). A total of five droplet ejection heads, recording heads 24c, 24m, and 24y each composed of one droplet ejection head that ejects ink (when not distinguishing colors and collectively referred to as “recording head 24”), are included. A shuttle type is mounted, in which the carriage 23 is moved in the main scanning direction, and droplets are ejected from the recording head 24 while the paper 5 is fed in the paper transporting direction (sub-scanning direction) by the sub-scanning transport unit 3. Yes.

  In addition, a sub tank 25 is mounted on the carriage 23 in order to supply a recording liquid of a required color to each recording head 24. On the other hand, as shown in FIG. 1, recording liquid containing black (K) ink, cyan (C) ink, magenta (M) ink, and yellow (Y) ink from the front of the apparatus main body 1 to the cartridge mounting portion 26A. Each color ink cartridge 26 can be detachably mounted, and ink (recording liquid) is supplied from each color ink cartridge 26 to each color sub-tank 25 via a tube (not shown). The black ink is supplied from one ink cartridge 26 to the two sub tanks 25.

  The recording head 24 uses a piezoelectric element as a pressure generating means (actuator means) for pressurizing the ink in the ink flow path (pressure generation chamber) to deform the vibration plate that forms the wall surface of the ink flow path. A so-called piezo type that discharges ink droplets by changing the volume in the flow channel, or discharges ink droplets with a pressure generated by heating the ink in the ink flow channel using a heating resistor to generate bubbles. The so-called thermal type, the diaphragm that forms the wall surface of the ink flow path and the electrode are placed opposite to each other, and the diaphragm is deformed by the electrostatic force generated between the vibration plate and the electrode, thereby the ink flow path inner volume It is possible to use an electrostatic type or the like that discharges ink droplets by changing the above.

  Further, as shown in FIG. 3, a linear scale 128 in which a slit is formed is stretched between the front plate 101F and the rear plate 101R along the main scanning direction of the carriage 23, and the linear scale 128 is provided on the carriage 23. An encoder sensor 129 made up of a transmissive photosensor for detecting the slit is provided, and the linear scale 128 and the encoder sensor 129 constitute a linear encoder that detects the movement of the carriage 23.

  Further, as shown in FIG. 2, a maintenance / recovery mechanism (device) 121 for maintaining and recovering the nozzle state of the recording head 24 is disposed in the non-printing area on one side of the carriage 23 in the scanning direction. . The maintenance / recovery mechanism 121 is a cap member for capping each nozzle surface 24a of the five recording heads 24, and includes one suction cap 122a that also serves as a moisture retention, and four moisture retention caps 122b to 122e. A wiper blade 124, which is a wiping member for wiping the nozzle surface 24a of the recording head 24, and an idle ejection receiver 125 for performing idle ejection are disposed.

  Further, an idle ejection receptacle 126 for performing idle ejection is disposed in the non-printing area on the other side of the carriage 23 in the scanning direction. Openings 127 a to 127 e are formed in the idle discharge receptacle 126.

  The sub-scanning conveyance unit 3 includes a conveyance roller 32 and a tension roller that are driving rollers for conveying the paper 5 fed from below by facing the image forming unit 2 by changing the conveyance direction by approximately 90 degrees. An endless conveyance belt 31 that is stretched between the driven rollers 33, a charging roller 34 that is a charging unit to which an AC bias voltage that is an alternating voltage is applied to charge the surface of the conveyance belt 31, and a conveyance belt 31 A platen guide member 35 that guides the sheet 5 in a region facing the image forming unit 2, a first pressure roller (inlet pressure roller) 36 that presses the sheet 5 toward the conveyance belt 31 at a position facing the conveyance roller 32, and conveyance Between the roller 32 and the recording head 34 as image forming means, a second pressure roller (front end) that presses the paper 5 toward the conveying belt 31 at a position facing the platen guide member 35. Pressure roller) 37, a pressing guide member 38 for pressing the paper 5 on which the image is formed by the image forming unit 2, and a separation claw for separating the paper 5 on which the image is formed by the image forming unit 2 from the conveying belt 31. 39.

  The transport belt 31 of the sub-scan transport unit 3 is rotated in the paper transport direction (sub-scan direction) in FIG. 2 by rotating the transport roller 32 from the sub-scan motor 131 through the timing belt 132 and the timing roller 133. It is configured to do.

  The paper feeding unit 4 is detachable from the apparatus main body 1 and separates the paper 5 in the paper feeding cassette 41 one by one from the paper feeding cassette 41 which is a storing means for stacking and storing a large number of papers 5. A sheet feeding roller 42 and a friction pad 43 for feeding out and a registration roller pair 44 for registering the sheet 5 to be fed are provided.

  The paper feed unit 4 includes a manual feed tray 46 for stacking and storing a large number of sheets 5, a manual feed roller 47 for feeding the sheets 5 from the manual feed tray 46 one by one, and the apparatus main body 1. On the lower side, an optional paper feed cassette and a vertical transport roller 48 for transporting the paper 5 fed from the duplex unit are provided. Members for feeding the paper 5 to the sub-scanning conveying unit 3 such as the paper feeding roller 42, the registration roller 44, the manual feeding roller 47, and the vertical conveying roller 48 are a paper feeding made of an HB type stepping motor via an electromagnetic clutch (not shown). The motor (drive means) 49 is rotationally driven.

  The paper discharge conveyance unit 6 includes a pair of paper discharge conveyance rollers 61 and 62 for conveying the paper 5 on which image formation has been performed, a paper discharge conveyance roller pair 63 and a paper discharge roller 64 for sending the paper 5 to the paper discharge tray 7. And.

Next, an overview of the control unit of the image forming apparatus will be described with reference to a block diagram shown in FIG.
The control unit controls the entire image forming apparatus, and includes a main control unit 301 configured by a microcomputer including a CPU, a ROM, a RAM, a VRAM, an I / O, and the like, and a print control configured by a microcomputer that controls the print control. Part 302. The program according to the present invention is stored in the ROM in the main control unit 301 and executed by the CPU.

  Then, the main control unit 301 uses the main scanning motor 27 and the sub-scanning motor 131 to form the main scanning motor driving circuit 311 and the sub-scanning motor 131 in order to form an image on the paper 5 based on the print processing information input from the communication circuit 303. Drive control is performed via the scanning motor drive circuit 312, and control such as sending print data to the print control unit 302 is performed.

  The main control unit 301 receives a detection signal from a carriage position detection circuit 313 that detects the position of the carriage 23, and the main control unit 301 controls the movement position and movement speed of the carriage 23 based on the detection signal. To do. The carriage position detection circuit 313 reads the number of slits of the linear scale (encoder sheet) 128 arranged in the scanning direction of the carriage 23 with a photo sensor (encoder sensor) 129 mounted on the carriage 23 and counts the carriage. 23 position is detected. The main scanning motor drive circuit 311 rotates the main scanning motor 27 according to the output value corresponding to the carriage movement amount input from the main control unit 301, for example, the PWM output value when performing PWM control, and the carriage 23 is moved to a predetermined position at a predetermined speed.

  The main control unit 301 receives a detection signal from a conveyance amount detection circuit 314 that detects the movement amount of the conveyance belt 31, and the main control unit 301 detects the movement amount and movement speed of the conveyance belt 31 based on the detection signal. To control. The carry amount detection circuit 314 detects the carry amount by reading and counting the number of slits of the encoder wheel attached to the rotation shaft of the carry roller 32 with a photo sensor (encoder sensor). The sub-scanning motor driving circuit 312 rotates the sub-scanning motor 131 in accordance with the conveyance amount input from the main control unit 301 and rotationally drives the conveyance roller 32 to bring the conveyance belt 31 to a predetermined position at a predetermined speed. Move.

  Further, the main control unit 301 performs control for charging the transport belt 31 by applying an AC bias to the charging roller 34 via the AC bias supply unit 315. The main control unit 301 rotationally drives the paper feed motor 49 via the paper feed motor drive circuit 316. The main control unit 301 rotationally drives a motor (not shown) of the maintenance / recovery mechanism 121 via the maintenance / recovery mechanism drive motor drive circuit 317, thereby raising and lowering the cap 122, raising and lowering the wiper blade 124, and driving a suction pump (not shown). And so on.

  The main control unit 301 also controls the image reading apparatus 11 via the scanner control unit 318. The main control unit 301 sends necessary display information to the operation panel 319 and takes in key information to be input.

  The print control unit 302 generates pressure for ejecting droplets of the recording head 24 based on the signal from the main control unit 301 and the carriage position and conveyance amount from the carriage position detection circuit 313 and the conveyance amount detection circuit 314. Data for driving the means is generated, and the above-mentioned image data is transferred to the head drive circuit 321 as serial data, and the transfer clock and latch signal necessary for transferring and confirming the transfer of the image data, droplet control, etc. In addition to outputting a signal (mask signal) etc. to the head drive circuit 321, it is composed of a D / A converter, a voltage amplifier, a current amplifier, etc. for D / A converting the pattern data of the drive signal stored in the ROM. Drive waveform generation means and drive waveform selection means to be given to the head driver, one drive pulse (drive signal) or a plurality of drive parameters. Scan to generate a composed drive waveform (drive signal) to the head drive circuit 321.

  The head drive circuit 321 selectively selects a drive signal constituting a drive waveform supplied from the print control unit 302 based on image data corresponding to one row of the print head 24 that is input serially. The recording head 24 is driven by applying it to a driving element (for example, a piezoelectric element as described above) that generates energy for discharging the ink. At this time, by selecting a driving pulse constituting the driving waveform, for example, dots having different sizes such as large droplets (large dots), medium droplets (medium dots), and small droplets (small dots) can be distinguished. it can.

  In this image forming apparatus configured as described above, the rotation amount of the conveyance roller 32 that drives the conveyance belt 31 is detected, the sub-scanning motor 131 is driven and controlled according to the detected rotation amount, and the AC bias is supplied. A positive and negative rectangular wave high voltage, which is an alternating voltage, is applied from the unit 315 to the charging roller 34, whereby positive and negative charges are alternately banded in the conveying direction of the conveying belt 31. When applied, charging is performed on the conveying belt 31 with a predetermined charging width, and an unequal electric field is generated.

  Therefore, the conveyance belt in which an unequal electric field is generated by the sheet 5 being fed from the sheet feeding unit 4 and fed between the conveyance roller 32 and the pressing roller 36 to form positive and negative charges. When fed onto the paper 31, the paper 5 is instantly polarized according to the direction of the electric field, and is attracted onto the transport belt 31 by the electrostatic attraction force, and is transported as the transport belt 31 moves.

  Then, while the paper 5 is intermittently transported by the transport belt 31, recording liquid droplets are ejected from the recording head 24 onto the paper 5 to record (print) an image, and the front end of the paper 5 on which printing is performed The side is separated from the conveyance belt 31 by the separation claw 37 and sent to the paper discharge conveyance unit 6 by the conveyance roller 38.

  During printing (recording) standby, the carriage 23 is moved to the maintenance / recovery mechanism 121 side, and the nozzle surface of the recording head 24 is capped by the cap 122, and the nozzles are kept in a wet state. To prevent. In addition, the recording liquid is sucked from the nozzle in a state where the recording head 24 is capped by the suction and moisture retention cap 122a (referred to as “nozzle suction” or “head suction”), and the recovered recording liquid and bubbles are discharged. Wiping is performed by the wiper blade 124 in order to clean and remove ink adhering to the nozzle surface of the recording head 24 by this recovery operation. In addition, a blank ejection operation is performed in which ink that is not related to printing is ejected toward the blank ejection receiver 125 before recording is started or during recording. Thereby, the stable ejection performance of the recording head 24 is maintained.

Next, an image processing method according to the present invention in this image forming apparatus will be described.
First, generally, the flow of image processing from reading an original image by an image reading device (scanner) to outputting it by an image forming device (printer unit) is as shown in FIG. On the other hand, in the input correction unit 401, the scanner γ correction unit 411, the RGB → YUV conversion unit 412, the smoothing unit 413, the edge enhancement unit 414, the YUV → RGB conversion unit 415, the background removal unit 416, and the edge enhancement unit 417 Correction of input document image data is performed.

  In other words, in the case of a copy in which a manuscript image is copied and printed out, all input image data is captured as “image” data. At this time, the scanner performance, the state of the input manuscript (recording quality, dirt and damage, etc.) , Surface gloss) and the like, the data is captured in a state of deterioration from the original. Therefore, the input correction processing unit 401 corrects this deterioration and emphasizes the characteristics of each object, thereby improving the image quality at the time of output.

  In this input correction processing unit 401, if there is processing capability, the image area separation unit 418 decomposes the image data into object elements, and reads the read image data into the object elements in order to read characters and pictures in an optimum mode. The above-described correction is performed on each image area by performing a process of decomposition every time. In other words, when scanning a manuscript with mixed text and design, halftone dots may be lost if text is given priority, and conversely, text may be faded if the design is wired. To be able to The object element indicates whether the input image data is classified as “character”, “thin line”, “image”, or “graphics”.

  In the output processing unit 402 for inputting the corrected image data output from the input correction processing unit 401, a CMM processing unit 421 that performs conversion into a color space (RGB color system → CMY color system), BG / UCR processing unit 422 that performs black generation / under color removal from values, scaling processing unit 423 that performs enlargement processing according to resolution, and printer γ correction unit that performs input / output correction reflecting device characteristics and user preferences 424, a necessary process is performed by the halftone processing unit 425 including a dither matrix that replaces the image data with the dot pattern arrangement ejected from the image forming apparatus. Although not shown, the print image data is obtained by the halftone process. A raster pattern that divides the dot pattern data into data for each scan and further develops the data in accordance with the position of each nozzle for recording. Performing grayed, and sends the print control unit 302 (printer output).

  In the output correction unit 402, the B / UCR processing unit 422, the printer γ correction unit 423, and the halftone processing unit 425 perform processing according to the separation result of the image area separation unit 218.

  By the way, the result of the image area separation by the image area separation unit 218 becomes important information in performing the processing of the correction processing unit and the output processing unit described above. If the image area separation result is wrong, the wrong processing is performed as it is. As a result, an abnormal image is generated, so that a high processing capability and performance are required for the image area separation part.

  Whether image separation can be performed accurately at high speed depends on the performance of the image processing controller. When an image processing controller that does not have sufficient processing capability is used, pattern matching, frequency analysis, etc. The image area separation calculation that makes full use of the image processing is heavy and results in a significant reduction in throughput. On the other hand, having an image processing controller with sufficient processing capability is costly for image forming apparatuses and image processing apparatuses. Cause the problem of high.

  In view of this, an image forming apparatus designed to reduce costs employs a configuration in which image area separation is omitted and only minimum correction processing (weak smoothing and background removal) is applied. The tone processing unit 425 may employ dither processing instead of error diffusion processing as halftone processing.

  As shown in FIG. 6, the dithering process compares the input multi-value image data shown in FIG. 6A with the threshold value of the dither matrix shown in FIG. This is a process of replacing with a dot pattern arrangement. Since the dither processing determines the ON / OFF of the dots by comparing the dither matrix with the input data, the processing is very light and a small amount of memory is required for the calculation.

  On the other hand, the error diffusion process performs, for example, the process shown in FIG. 7, and the calculation is performed by reflecting the peripheral quantization error in the ON / OFF determination of the dots. Even if the difference occurs, the difference is reflected as the ease of occurrence of dots in the surrounding pixels. As a result, missing dots are compensated for, and excellent image reproducibility is obtained. However, on the other hand, the calculation load is large and the memory capacity is large, so that the number of calculations is large and the influence on the processing speed and the cost becomes large.

  On the other hand, when the dither process is employed in the copy mode, moire occurs due to interference with the halftone dot pattern of the document. That is, as shown in FIG. 8, no matter how much data exists on the document image, no dot is generated unless the threshold value of the dither matrix is exceeded. When the data distribution is configured in a regular arrangement like a halftone document, the dot loss due to the dither processing may have regularity and appear as moire. For example, when the halftone dot original data as shown in FIG. 8A is dithered with a dither matrix having a line tone, as shown in FIG. Moire appears in the output image.

  As shown in FIG. 9, the dither processing can be divided into a concentrated type (AM modulation) and a distributed type (FM modulation) according to the dot generation method. Moire is likely to occur. This is because the centralized (AM modulation) dither focuses the dots according to a specific arrangement to make the gradation pattern uniform and aims at uniform image reproduction. This is because the occurrence of synchronization / asynchronization with the printing dot period (mutual interference) generates a regularity with a lower period (= coarse) and loses homogeneity.

  Therefore, in the present invention, as a means for suppressing this moire, a multi-value dispersion type (FM modulation) dither is first adopted. As long as the dither processing is performed, synchronization / asynchronization with the document data always occurs depending on the threshold arrangement of the dither matrix. However, the problem is that the halftone document has a fixed period as shown in FIG. It is arranged with. The halftone dots represent the gradation by always arranging dots at fixed intervals based on squares (including rhombuses), although the pitch between dots varies depending on the number of lines, and the dots gradually increase in size. . Since the generation coordinates of the halftone dots are fixed with regularity, even if the dither matrix has a regular threshold arrangement, even a slight misalignment will lead to the generation of interference moiré. May not be reproduced at all.

  In order to avoid this problem, it is necessary to use a threshold value arrangement that always has a portion that synchronizes with the halftone original and a threshold value arrangement that does not have periodicity in the synchronous / asynchronous portion. In order to prevent the synchronous / asynchronous part from having periodicity, the threshold arrangement of the dither matrix has no regularity, or the threshold arrangement with high frequency characteristics cannot be recognized by humans. It ’s fine. The former includes a random mask created using random numbers, and the latter includes a so-called Bayer mask, a green noise mask, a blue noise mask, and the like. By using these dither masks, even if a defect occurs, regularity is not seen in the defect part, so that it is difficult to be recognized as moire. .

  However, disordered defects are now recognized as “blurred”. The “blurring” deteriorates the graininess, and the quality of the copy image becomes lower as the original document that has been copied is a more homogeneous image. In order to avoid loss, it is always necessary to arrange the threshold values so as to synchronize with the pattern of the halftone original. However, it is expensive to have a function of dynamically updating the dither matrix according to the input original. Become.

  Therefore, by using a multi-value FM modulation dither, gradations where “blurring” occurs are narrowed down to a highlight portion. The “multi-value” mentioned here includes a combination of both a method of switching the size of the dot itself and a method of switching a colorant having the same color and a different density. In the embodiment, a method of switching the dot size will be described, but the present invention can be similarly applied to a method of switching the colorant.

  Here, with reference to FIG. 12, a method of expressing multi-values using three types of dot sizes of large, medium, and small will be described. Reproduction gradation sections are set in accordance with the droplet sizes (see FIG. 12 (a)). )), Gradation expression is performed by arranging dots in accordance with the order of threshold values of the dither matrix (gradation 0 is white and gradation 255 is solid).

  In this case, when the gradation section assigned to the small dots is “0 <small dot section ≦ gradation level n”, the paper surface is filled with small dots at the gradation level n. At the gradation level (n + 1), any of the filled small dots is replaced with medium dots, and the ratio of medium dots increases as the gradation increases (switching between medium dots and large dots is also possible). The same.) At this time, at a gradation level greater than or equal to the value n, no matter how regular the arrangement of the dither matrix thresholds is, small dots or medium dots are always assigned, and dots are not lost on the copy image. . Therefore, it is necessary to consider the influence of dot loss only for the gradation value n or less.

  An area of gradation value n or less is a highlight portion composed of a minimum (or lowest density) dot and a white background. Depending on the image data captured by the scanner, an “unevenness” as shown in FIG. May occur.

  FIG. 13 illustrates printing halftone dots and captured image data. Although the halftone dot size of the printing halftone dot changes depending on the gradation, the density of the halftone dot itself is basically constant.

  However, due to the characteristics of the scanner that performs the capture (the performance of the light receiving element, the performance of the light source, the capture resolution, etc.), the captured image is a deteriorated image than the actual one. Specifically, the image density may be partially reduced or the image may be lost due to insufficient resolution.

  In an area where a large halftone dot is used, such as a middle to shadow portion, the original size and density of the halftone dot are almost faithfully reproduced even if the density drop or loss occurs locally.

  On the other hand, when a very small halftone dot is captured as in the highlight portion, the size and density are smaller than the original halftone dot. In some cases, as shown in FIG. In some cases, it may be recognized only as a cluster of one pixel. FIG. 14 shows an example in which when a halftone dot is captured at 600 dpi, the protruding portion is missing due to the capture condition.

  In the dither processing, the threshold value matrix and the image data are compared, and the gradation expression is performed by controlling the dot generation ratio (or the area covered by the dots) per unit area. The higher the density and the larger the image area, the higher the probability of being compared with a lower threshold, and conversely, the lower the density and the smaller the image area, the more likely the missing dots. In particular, in the FM modulation type dither, the threshold is assigned so that the lower the density is, the larger the distance between the generated dots is. Therefore, the probability that the pixel of the highlight halftone dot is compared with the low threshold is low. It will be even smaller.

  Therefore, in addition to the use of multi-value FM modulation type dither, in the present invention, the highlight halftone image deteriorated at the time of capture by the scanner is enhanced to eliminate the missing dot. Specifically, the gradation value of the pixel considered as the highlight halftone dot is emphasized up to the gradation level (the gradation value n in the above example) to which the minimum dot is surely assigned. At this time, the emphasis is performed only up to the gradation value n in order to prevent conversion to a larger size dot by assigning a value of n or more.

  In other words, since the original image can be faithfully reproduced by the multi-value dither processing at the gradation of the value n or more, if the over-emphasized dots are mixed there, the reproduced gradation characteristics are lost, or There is a risk that the emphasized dots are recognized as foreign substances and the graininess deteriorates. As a result of emphasis, if the generated dots are the smallest dots that can be formed by the apparatus, the influence on the gradation and graininess can be minimized.

  Extraction of highlight halftone dots can use an isolated point extraction technique. In general, the method using the Laplacian filter processing shown in FIG. 15 and the method using pattern matching (not shown) are adopted as processing methods with a relatively small calculation load. These processes can be extracted with higher accuracy by expanding the reference range and increasing the combinations of judgment criteria and patterns. However, the memory cost and calculation load are increased by that amount. It is preferable to refer to the surrounding 8 pixels.

  As described above, whether or not the target pixel is an isolated point can be determined based on the input values of neighboring pixels adjacent to the target pixel. This is performed by referring to neighboring pixels in a range of k pixels or more in the vertical and horizontal directions including all directions (k ≧ 1), and more preferably, adjacent to a vertical and horizontal pixel that is directly adjacent to the pixel of interest and an oblique 45 degree position. It is performed in a range of 8 pixels including pixels.

  Furthermore, in order to reduce the burden on extraction / determination, as shown in FIG. 16, a method of extracting and enhancing the “corner position” on the captured image of halftone dots can be used. The loss of dots occurs because the originally highlighted halftone dot is captured as a small-sized and low-density dot image. The decrease in the concentration is small.) At this time, if even a part of the pixels constituting the captured halftone dot can be formed into dots, dots are arranged on the output image at a uniform cycle substantially the same as the original halftone dot pattern. Since the halftone dot period is a uniform dot arrangement based on each color and square, no blur is felt.

  In FIG. 16, the “upper left” corner position is pointed out. This is convenient when image processing scanning is performed sequentially from the upper left to the lower right of the document as shown in FIG. In the processing scan order, it is possible to determine whether or not the pixel of interest is the “upper left” corner position by simply referring to the processed pixels in the upper, left lateral, and upper left positions.

  Therefore, if the processing scanning order changes, it is only necessary to change the reference angle position to “upper right”, “lower left”, and “lower right” accordingly, and therefore, it is not necessarily limited to “upper left”. As for the determination method, it is possible to determine whether or not the position is a corner position when the sum of the pixel values of the upper, left side, and upper left positions is “0”, or by performing simple pattern matching (not shown).

  As described above, the determination of the angular position of whether or not the target pixel is present at the corner position of the image portion that is not white is performed in the ¼ quadrant (vertical, horizontal, and diagonal directions of the target pixel) with the target pixel as the origin. This can be done based on the values of adjacent peripheral pixels. In this case, when the total input value of the adjacent peripheral pixels is 0, it is determined that the pixel of interest is a corner position, or is determined by pattern matching. Can do.

  The image processing according to the present invention will be described with reference to the flowchart shown in FIG. Note that here, the present invention is applied to a recording apparatus (image forming apparatus) capable of multi-value output of three or more values, but for a binary recording apparatus (image forming apparatus) capable of realizing only one kind of dot size. Is also applicable. This is because, if high-resolution recording is possible even in binary recording, for example, the same effect as in multi-value recording can be obtained by emphasizing a plurality of pixels at angular positions.

  Referring to FIG. 18, simple correction is performed on the scanner input, halftone processing is performed after CMM processing and other processing (not shown) and printer γ correction processing are performed. In this halftone process, “0 <input value ≦ n” is determined. If “0 <input value ≦ n”, the angular position is determined (or isolated point is determined), and the angular position (or isolated) is determined. Point), after the input value is converted to a value n, multi-value FM dither processing as dither processing is performed.

  Further, when “0 <input value ≦ n” is not satisfied, or when “0 <input value ≦ n” but not the angular position (or isolated point), the multi-value FM dither processing as the dither processing is performed as it is.

  In this way, when 0 is a gradation level representing a white background and m (m> 0) is a solid gradation level, the gradation interval is composed of 0 or more and the smallest dot or the thinnest thinnest dot that can be formed at the time of output. When a value lower than the maximum value n of 1 to n (0 <n ≦ m) is input as the value of the target pixel, the quarter quadrant with the target pixel as the origin (vertical, horizontal, diagonal direction of the target pixel) Whether or not the pixel of interest exists at a corner position of the image portion that is not white, and if it is determined that the pixel of interest is a corner position, the input value of the pixel of interest Is converted to a value n, and then dithering is performed to eliminate moiré and blurring in the output image, which is a problem when copying a halftone image, with a minimum of image extraction / determination / value correction processing. Can maintain the high speed of dither processing and light computation load. , It is possible to suppress the occurrence and concentration reduction of moire.

  In addition, when the gradation level is such that 0 is white and m (m> 0) is solid, the level is composed of 0 or more and the smallest or thinnest thinnest dot that can be formed at the time of output. When a value lower than the maximum value n of the key intervals 1 to n (0 <n ≦ m) is input as the value of the pixel of interest, whether or not it is an isolated point based on the input values of adjacent peripheral pixels of the pixel of interest If the target pixel is determined to be an isolated point, the input value of the target pixel is converted to the value n, and then dither processing is performed to copy the halftone image. Moire and blur in the output image can be eliminated with minimal image extraction, judgment, and value correction processing, while maintaining the high speed of dither processing and light computation load, and the generation and density of moiré. The decrease can be suppressed.

  The above-described image processing is performed when image processing in an image forming apparatus such as an inkjet recording method or an electrophotographic method, or an image forming system in which the image forming apparatus and the image processing apparatus are combined, and image processing is performed by the image processing apparatus. It can be similarly applied to.

  In addition, there are liquid discharge type image forming apparatuses in which nozzles are arranged at a high density and perform high-quality recording. In this, bidirectional printing is performed by arranging the nozzle arrangement symmetrically in color. Some printers are designed to speed up printing while eliminating bidirectional color differences. Here, the symmetrical arrangement means that a plurality of nozzle rows composed of a plurality of nozzles arranged in the sub-scanning direction are arranged in the main scanning direction, and two or more nozzle rows for ejecting the same color ink are provided. One or more nozzle rows that eject inks of different colors are arranged between the nozzle rows that eject ink of the same color, and the nozzle rows that eject ink of the same color are symmetrical about the axis orthogonal to the main scanning direction. The arrangement is arranged.

  For example, as shown in FIG. 19, when bidirectional printing is performed using a head in which nozzle rows of each color are arranged one by one in the printing direction (for example, a head arranged with YMCK (the nozzles are also the same)), Bidirectional color difference will occur in the portion where the recording liquids are stacked. When overprinting yellow and cyan recording liquids, the color tone is different between printing in the order of yellow → cyan and printing in the order of cyan → yellow. As shown in FIG. 19, by performing bidirectional printing using the recording head in which the nozzles of the recording head are arranged in a line for each color, the droplet ejection order is yellow → cyan, reverse in the forward direction (outward). In the direction (return), cyan → yellow, and strip-like color unevenness with different color tones occurs.

  In order to solve this, a plurality of nozzle rows composed of a plurality of nozzles arranged in the sub-scanning direction are arranged in the main scanning direction, and two or more nozzle rows for ejecting the same color ink are provided. A configuration is adopted in which one or more nozzle rows that eject ink of different colors are arranged between the nozzle rows that eject ink.

  For example, as shown in FIG. 20, by arranging the nozzle rows for ejecting C and M inks between the nozzle rows for ejecting Y ink, they are overlapped in the order of C → Y regardless of the forward pass and the return pass. They can be combined, or they can be overlapped in the order of Y → C. Moreover, it is possible to superimpose in the order of M → Y regardless of the forward path and the return path, and it is also possible to superimpose in the order of Y → M. Accordingly, bidirectional printing can be performed while expanding the color reproduction range, and a color printed matter having a wide color reproduction range can be printed at high speed.

  In addition, a plurality of nozzle rows made up of a plurality of nozzles arranged in the sub-scanning direction are arranged in the main scanning direction, and there are two or more nozzle rows that eject the same color ink, and the nozzles that eject the same color ink One or more nozzle rows that eject ink of different colors are arranged between the rows, and the nozzle rows that eject ink of the same color are arranged symmetrically about an axis orthogonal to the main scanning direction. You can also.

  For example, as shown in FIG. 21, nozzle rows that eject ink of the same color are arranged symmetrically about an axis orthogonal to the main scanning direction. Here, C and M are horizontally arranged around K. By arranging in the order of Y and Y, it is possible to superimpose two or more types of color inks in an arbitrary superposition order for more colors regardless of the forward path and the backward path. As a result, bidirectional printing can be performed while obtaining a wider color gamut, and a color print having a wider color gamut can be printed at high speed.

  Further, as shown in FIG. 22, in addition to normal yellow (Y), magenta (M), cyan (C), and black (K), yellow, magenta, cyan, and black having low color density, that is, photo yellow. (PY), photomagenta (PM), and photocyan (PC) can also be used. In addition, photo gray (PG) can also be used. By using an ink having a low color density, it is possible to print a color printed matter in which graininess (roughness) is suppressed in addition to expanding the color reproduction range.

  In an image forming apparatus employing such a high-density nozzle and symmetric nozzle configuration, it is necessary to process high-density data at high speed, and the calculation load increases rapidly. By performing halftone processing using the dither matrix according to the present invention, it is possible to reduce the calculation load, and it is also possible to obtain effects such as ensuring processing speed and higher resolution.

  Further, the halftone processing using the dither matrix in the present invention is not only installed as hardware, but can be incorporated into the printer driver as a program, for example, as halftone processing for the printer mode, as described above. This can reduce the computation load, and particularly when applied to an image forming apparatus that prints out image data from the host side as well as the processing in the image forming apparatus having the copy mode as in the above embodiment. The host computer can be released from the printing task more quickly. Furthermore, the present invention can also be applied to an information processing apparatus that sends print data to an image forming apparatus (the information processing apparatus in this case is also an image processing apparatus according to the present invention).

  The dither processing according to the present invention can also be applied to a case where software processing is performed on a computer in a case where an information processing apparatus such as a host computer has high processing capability.

  It is also possible to switch between dither processing and another halftone processing in the present invention. Although the present invention is inferior in terms of moire suppression and calculation load on halftone originals, there are several halftone processes capable of higher quality output for continuous tone originals. These halftone processes are classified by mode, for example, the dither process of the present invention is used in the copy / fax mode in which halftone originals are frequently used, and the other halftone process is used in the printer mode mainly using continuous tone originals. Therefore, high-quality image reproduction is possible. Some applications have processing functions such as translucent processing and halftone processing for graphics data. Even if the data subjected to such processing is originally continuous tone data, it may be a pattern to which regularity such as printing halftone dots is added. The present invention is also effective when printing such data. These processes can be switched automatically according to the mode selection, or can be switched by a user instruction.

  In an image forming apparatus having a multifunction machine configuration having a function called “Scan to E-mail”, image data captured by a scanner may be distributed through a network. As described above, even if an image is captured by an external scanner, if the original is a halftone document, moire or blur may occur during output. The effects of the invention can be obtained.

  In addition, for example, when an arithmetic processing unit dedicated to image processing can be retrofitted, or when a part or all of image processing can be processed by software by connecting to a personal computer, more advanced arithmetic processing Is possible. When such an external arithmetic processing device can be utilized, it is possible to execute high-level input correction processing and halftone processing including image area separation and frequency analysis processing at high speed. By switching from 1 to more advanced processing, it becomes possible to create a high-quality copy image. Also in this regard, it may be switched automatically in accordance with the detection of the external processing unit, or may be switched according to a user instruction.

An overall configuration of a mechanism unit of an image forming apparatus according to the present invention, which includes an image processing apparatus according to the present invention, a program according to the present invention, and a dither matrix according to the present invention and forms an image by the image forming method according to the present invention. FIG. It is principal part plane explanatory drawing of the mechanism part. It is principal part expansion front explanatory drawing of the same apparatus. It is a block diagram which shows the outline | summary of the control part of the apparatus. It is explanatory drawing with which it uses for description of the flow of the image processing in a general copy mode. It is explanatory drawing with which it uses for description of a dither process. It is explanatory drawing with which it uses for description of an example of an error diffusion process. It is explanatory drawing with which it uses for description of generation | occurrence | production of a moire when the basics of a halftone image and a dither matrix correspond. It is explanatory drawing with which it uses for description of the dither of AM modulation system and FM modulation system. It is explanatory drawing with which it uses for description of the frequency characteristic of a halftone image. It is explanatory drawing with which it uses for description of the output image result at the time of performing a random dither process to a halftone image. It is explanatory drawing with which it uses for description of the expansion | deployment method to the multi-value dither of a dither matrix. FIG. 6 is an explanatory diagram for explaining a halftone image of an original and image data captured by a scanner. It is explanatory drawing with which it uses for description of deterioration of the halftone image at the time of scanner taking in. It is explanatory drawing which shows an example of the isolated point extraction method using a Laplacian filter. It is explanatory drawing with which it uses for description of the corner position on the capture image of a halftone dot. It is explanatory drawing with which it uses for description of the order of the image processed. It is a flowchart with which it uses for description of the flow of the image processing in this invention. It is explanatory drawing with which nozzle row arrangement | positioning uses for description of the head of asymmetric arrangement | positioning. It is explanatory drawing with which it uses for description of an example of the head of nozzle row arrangement | positioning symmetrical arrangement. It is explanatory drawing with which it uses for description of the other example of the head of nozzle row arrangement | positioning symmetrical arrangement. It is explanatory drawing with which it uses for description of the further another example of the head of nozzle row arrangement | positioning symmetrically.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Apparatus main body 2 ... Image formation part 3 ... Sub-scanning conveyance part 4 ... Paper feed part 5 ... Paper (recording medium)
DESCRIPTION OF SYMBOLS 7 ... Paper discharge conveyance part 8 ... Paper discharge tray 11 ... Image reading part 23 ... Carriage 24 ... Recording head 31 ... Conveyance belt 32 ... Conveyance roller 301 ... Main control part 313 ... Scanner control part 425 ... Halftone processing part

Claims (16)

In an image processing method for performing halftone processing using a threshold matrix on input image data,
When 0 is a white background and m (m> 0) is a solid level representing solid,
A value lower than the maximum value n of gradation intervals 1 to n (0 <n ≦ m) composed of the minimum dots or the thinnest thinnest dots that can be formed at the time of output is input as the value of the pixel of interest. The pixel of interest exists at a corner position of the image portion that is not a white background, based on the values of neighboring peripheral pixels in the ¼ quadrant (vertical, horizontal, and diagonal directions of the pixel of interest) with the pixel of interest as the origin. In the image processing method, dither processing is performed after the input value of the target pixel is converted into the value n when it is determined that the target pixel is a corner position.   2. The image processing method according to claim 1, wherein in the position determination of the target pixel, when the total input value of the adjacent neighboring pixels is 0, the target pixel is determined to be an angular position. Image processing method.   The image processing method according to claim 1, wherein the position of the target pixel is determined by pattern matching. In an image processing method for performing halftone processing using a threshold matrix on input image data,
When 0 is a white background and m (m> 0) is a solid level representing solid,
A value lower than the maximum value n of gradation intervals 1 to n (0 <n ≦ m) composed of the minimum dots or the thinnest thinnest dots that can be formed at the time of output is input as the value of the pixel of interest. When it is determined whether or not the pixel is an isolated point based on the input values of neighboring pixels adjacent to the pixel of interest. If the pixel of interest is determined to be an isolated point, the input value of the pixel of interest is An image processing method, wherein dither processing is performed after conversion to a value n.   5. The image processing method according to claim 4, wherein whether or not the pixel of interest is an isolated point is determined by determining whether the pixel of interest is an isolated point or not, including at least one of vertical and horizontal diagonal directions including all directions from the upper, lower, left, and right directions around the pixel of interest. An image processing method characterized by referring to neighboring adjacent pixels in a range of (k ≧ 1).   5. The image processing method according to claim 4, wherein in determining whether or not the target pixel is an isolated point, an isolated point is extracted using a Laplacian filter.   5. The image processing method according to claim 4, wherein in determining whether or not the target pixel is an isolated point, an isolated point is extracted by pattern matching.   8. The image processing method according to claim 1, wherein the dither process is an FM modulation type dither process. In an image processing apparatus that performs halftone processing using a threshold matrix on input image data,
When 0 is a white background and m (m> 0) is a solid level representing solid,
A value lower than the maximum value n of gradation intervals 1 to n (0 <n ≦ m) composed of the minimum dots or the thinnest thinnest dots that can be formed at the time of output is input as the value of the pixel of interest. The pixel of interest exists at a corner position of the image portion that is not a white background, based on the values of neighboring peripheral pixels in the ¼ quadrant (vertical, horizontal, and diagonal directions of the pixel of interest) with the pixel of interest as the origin. If the pixel of interest is determined to be a corner position, the dither processing is performed after converting the input value of the pixel of interest into the value n. In an image processing apparatus that performs halftone processing using a threshold matrix on input image data,
When 0 is a white background and m (m> 0) is a solid level representing solid,
A value lower than the maximum value n of gradation intervals 1 to n (0 <n ≦ m) composed of the minimum dots or the thinnest thinnest dots that can be formed at the time of output is input as the value of the pixel of interest. When it is determined whether or not the pixel is an isolated point based on the input values of neighboring pixels adjacent to the pixel of interest. If the pixel of interest is determined to be an isolated point, the input value of the pixel of interest is An image processing apparatus that performs dither processing after conversion to a value n. In an image forming apparatus that forms an image by performing halftone processing using a threshold matrix on input image data,
When 0 is a white background and m (m> 0) is a solid level representing solid,
A value lower than the maximum value n of gradation intervals 1 to n (0 <n ≦ m) composed of the minimum dots or the thinnest thinnest dots that can be formed at the time of output is input as the value of the pixel of interest. The pixel of interest exists at a corner position of the image portion that is not a white background, based on the values of neighboring peripheral pixels in the ¼ quadrant (vertical, horizontal, and diagonal directions of the pixel of interest) with the pixel of interest as the origin. In the image forming apparatus, the dither processing is performed after the input value of the target pixel is converted into the value n when it is determined that the target pixel is in the angular position. In an image forming apparatus that forms an image by performing halftone processing using a threshold matrix on input image data,
When 0 is a white background and m (m> 0) is a solid level representing solid,
A value lower than the maximum value n of gradation intervals 1 to n (0 <n ≦ m) composed of the minimum dots or the thinnest thinnest dots that can be formed at the time of output is input as the value of the pixel of interest. When it is determined whether or not the pixel is an isolated point based on the input values of neighboring pixels adjacent to the pixel of interest. If the pixel of interest is determined to be an isolated point, the input value of the pixel of interest is An image forming apparatus that performs dither processing after conversion to a value n.   12. An image forming system comprising the image processing apparatus according to claim 10 and an image forming apparatus for forming an image. In a program that causes a computer to perform halftone processing using a threshold matrix on input image data,
When 0 is a white background and m (m> 0) is a solid level representing solid,
A value lower than the maximum value n of gradation intervals 1 to n (0 <n ≦ m) composed of the minimum dots or the thinnest thinnest dots that can be formed at the time of output is input as the value of the pixel of interest. The pixel of interest exists at a corner position of the image portion that is not a white background, based on the values of neighboring peripheral pixels in the ¼ quadrant (vertical, horizontal, and diagonal directions of the pixel of interest) with the pixel of interest as the origin. If the pixel of interest is determined to be in the angular position, the input value of the pixel of interest is converted into the value n, and then the halftone processing for performing dither processing is performed on the computer. A program characterized by that. In a program that causes a computer to perform halftone processing using a threshold matrix on input image data,
When 0 is a white background and m (m> 0) is a solid level representing solid,
A value lower than the maximum value n of gradation intervals 1 to n (0 <n ≦ m) composed of the minimum dots or the thinnest thinnest dots that can be formed at the time of output is input as the value of the pixel of interest. When it is determined whether or not the pixel is an isolated point based on the input values of neighboring pixels adjacent to the pixel of interest. If the pixel of interest is determined to be an isolated point, the input value of the pixel of interest is A program for causing a computer to perform the halftone processing for performing dither processing after conversion to a value n.   15. A storage medium in which the program according to claim 13 or 14 is stored.

Images