JP2005205685A - Image processing device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently prevent a Moire fringe from occurring by a simple processing without increasing speed and accuracy of the detecting and smoothing processes of a halftone region, in an image processing device for generating recording image data for imaging based on input image data. <P>SOLUTION: In the image processing device, an image processing circuit 50 is designed to restrain a Moire fringe to be generated in an image formed using the recording image data acquired by an error diffusion circuit 60 by detecting the halftone region of an input image using a halftone detection circuit 52 and smoothing image data in the halftone region with the help of a smoothing/highlighting circuit 54. In this circuit 50 and further, the error diffusion circuit 60, a threshold value setting circuit 62 is provided which changes a threshold value to be used for deciding whether a dot with a large diameter (or a dot of a high density ink) of the halftone region, is to be set, among the threshold values to be used for setting the diameter of an ink dot (or the thickness of the ink) to either of "large", "small" or "zero" per pixel, in the error diffusion circuit 60, to a large value than the threshold value to be used in a character region. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image processing apparatus and an image processing method for generating recording image data necessary for forming an image corresponding to input image data on a recording medium.

  2. Description of the Related Art Conventionally, ink jet image forming apparatuses (printers, copiers, facsimile machines, etc.) use an input image data representing an image to be formed on a recording medium such as recording paper to control the image forming unit to the recording medium. An image processing apparatus is provided that generates recorded image data necessary to form an image.

  This image processing apparatus uses a known pseudo gradation process in accordance with an error diffusion method, a dither method, etc., from the gradation information of each pixel constituting the input image data to the position on the recording medium corresponding to each pixel. In some cases, the dot size (dot diameter) and the ink density when forming the ink dots on the recording medium are further determined. Recorded image data is generated with the parameters for each pixel as pixel information of the formed image.

In this type of image processing apparatus, if input image data is used as it is when generating recorded image data, moire is likely to occur in the halftone dot area of the formed image, or characters are blurred in the character area of the formed image. Therefore, usually, before generating recorded image data by pseudo gradation processing, the input image data is divided into a halftone area and a character area. A smoothing process for smoothing gradation information between pixels in the area is performed, and an edge emphasis process for emphasizing the edge of the character is performed on the input image data in the character area ( For example, see Patent Documents 1 and 2).
JP 2002-28313 A Japanese Patent Application Laid-Open No. 7-111602

  By the way, in the conventional image processing apparatus, in order to more reliably prevent the moiré that occurs in the formed image, the detection accuracy of the halftone area of the input image data is improved, and the type of the detected halftone area is determined. Smoothing processing must be performed.

  However, in order to prevent the occurrence of moiré in this way, the detection accuracy of the halftone dot area of the input image data is improved, and the smoothing process is executed according to the type of the detected halftone dot area. There is a problem in that an arithmetic processing circuit capable of executing point area detection processing and smoothing processing at high speed and with high accuracy is required, resulting in an increase in cost of the image processing apparatus.

  The present invention has been made in view of these problems, and in an image processing apparatus that generates recorded image data for image formation from input image data, speeding up and increasing the accuracy of halftone dot area detection processing and smoothing processing. It is an object of the present invention to prevent the occurrence of moiré efficiently with a simple arithmetic processing.

  In the image processing apparatus according to claim 1, which is made to achieve such an object, when input image data to be processed is input from the outside, first, an area separation unit is configured by the input image data. The entire image area is separated into a halftone dot area and a character area, and the smoothing processing means smoothes the input image data in the halftone dot area separated by the area separation means.

  In other words, in the halftone dot area, when an image corresponding to the input image data is formed on the recording medium, moire is likely to occur on the formed image. In addition, the input image data is separated into a halftone dot area and a character area by the area separation means, and in the image area separated as the halftone dot area, the smoothing processing means so that the ink dots are dispersed during image formation. Thus, the input image data in the halftone dot region is smoothed.

  The input image data that has been smoothed in this way is input to an error diffusion processing unit, and converted into recording image data for forming an image on a recording medium by the error diffusion processing unit. That is, the error diffusion processing means sets at least the dot diameter of the ink when forming each pixel on the recording medium based on the gradation information of each pixel constituting the input image data in accordance with a preset error diffusion method. By setting one of large, small, and zero, recording image data for forming an image corresponding to the input image data on the recording medium using dots having the same color and different diameters is generated.

  In this way, the error diffusion processing means sets the dot diameter of the ink used when forming each pixel on the recording medium based on the gradation information of each pixel constituting the input image data. In the image processing apparatus described in the above, the threshold value changing means uses the area separation means as a halftone dot area among the threshold values used by the error diffusion processing means to determine whether or not to set the ink dot diameter to a large value. The threshold value used in the determined image region is changed to a value larger than the threshold value used in the image region separated as the character region by the region separation unit.

  Therefore, according to the image processing apparatus of the first aspect, in the recorded image data after the error diffusion processing, each pixel in the halftone dot area is more easily assigned a dot having a smaller diameter than a large diameter dot. In addition, pixels to which dots having a small diameter are assigned are arranged in a distributed manner without being partially biased in the halftone dot region. Therefore, if an image is formed on a recording medium using the recording image data generated by the image processing apparatus, the occurrence of moire on the formed image can be suppressed.

  Further, according to the image processing apparatus of the first aspect, in order to enhance the effect of suppressing the occurrence of moire on the formed image, the detection accuracy of the halftone dot area by the area separating means and the smoothing processing means as in the prior art. Since there is no need to increase the accuracy of the smoothing process, it is only necessary to change the threshold value when performing the error diffusion process in the halftone area to a value larger than the threshold value when performing the error diffusion process in the character area. The generation of moire can be suppressed very easily and efficiently.

  In the image processing apparatus according to claim 1, when the recorded image data is generated from the input image data, the error diffusion processing unit performs error diffusion processing according to the error diffusion method. This is because it is possible to more reliably suppress the occurrence of moire by dispersing small diameter dots in the halftone dot region.

  That is, as the pseudo gradation processing for generating the recording image data from the input image data, as described in the section of the prior art, two types of methods, an error diffusion method and a dither method, are known. In the dither method, when a pixel value such as a dot diameter is set for a target pixel, the setting error of the pixel value is not distributed to surrounding pixels, so the threshold value is changed as in the present invention. Even so, it is difficult to set a dot having a large diameter for each pixel, and it is not possible to increase a dot having a small diameter.

  In contrast, in the error diffusion method, when an ink dot diameter is set for a specific pixel, a pixel when an image is formed on the recording medium with the set dot diameter, and a pixel corresponding to input image data, And the error is reflected to surrounding pixels for which the dot diameter is not set, so that the threshold value changing means determines whether the error diffusion processing means sets the ink dot diameter to a large value. If the threshold value used for this is changed to a large value, instead of setting dots having a large diameter in the halftone dot region, more dots having a small diameter are set.

  Therefore, according to the first aspect of the present invention, in the image processing apparatus provided with the error diffusion processing means for performing the pseudo gradation processing in accordance with the error diffusion method, the error diffusion processing means includes a dot of each pixel in the halftone dot region. Changed the threshold used to determine whether to set a large diameter to a value larger than the threshold used to determine whether to set a large dot diameter for each pixel in the text area. By doing so, in the halftone dot area, instead of dots having a large diameter, dots having a small diameter are more dispersed and arranged so as to suppress the occurrence of moire on the formed image. .

  By the way, in the image processing apparatus according to claim 1, the error diffusion processing means divides the ink dot diameter when forming the pixels on the recording medium into three stages of large, small and zero, or more stages. For example, the dot diameter may be set to any one of large, medium, small, and zero.

  In this way, when the error diffusion processing unit is configured to set the dot diameter of ink for each pixel to one of large, medium, small, and zero, the error diffusion unit performs error diffusion. The threshold used by the processing means to set the dot diameter of each pixel to either large or medium in the halftone dot area, and the dot diameter of each pixel to either large or medium in the character area, respectively. It may be changed to a value larger than the threshold value used for this.

  According to the first aspect of the present invention, the input image data is monochrome image data, and the error diffusion processing means uses a single color (generally black) ink based on the input image data and applies a single color to the recording medium. Even if it is an image processing device for a single color image configured to generate recorded image data for forming an image, or the input image data is multicolor image data, and the error diffusion processing means The present invention can be applied even to an image processing apparatus for a multicolor image configured to generate recording image data for forming a multicolor image on a recording medium using a plurality of colors of ink based on the input image data. .

  In particular, the input image data is color image data having gradation information for a plurality of colors including black for each pixel, and the error diffusion processing means determines the dot diameter of the ink of each color based on the gradation information of each color. In an image processing apparatus for a multicolor image configured to set a color dot, a problem arises that dots of a color other than black are formed in a black image area, and the dots of that color become conspicuous. Therefore, in this type of image processing apparatus, as described in claim 2, black area detection means for detecting a black area in which black pixels occupy a large proportion in the input image data is provided, and threshold value changing means is provided. For the image area detected by the black area detection means as a black area and separated as a halftone dot area by the area separation means, the error diffusion processing means sets a large dot diameter for each pixel and each color. You The threshold value used to determine whether or not the error diffusion means sets a large dot diameter for each pixel and each color in the image area separated as a character area by the area separation means. It may be configured to change to a value larger than the threshold value used for this.

  That is, as described in claim 2, when generating recorded image data from color image data, if it is difficult to form a dot having a large diameter only in a halftone dot region that is a black region, It is possible to prevent a large color dot from being formed, making the dot stand out, or causing moire due to the dot, thereby improving the image quality of the formed image.

  In addition, when the threshold value is changed in all halftone dot areas to prevent the formation of large-diameter dots, the size of the dots in the halftone dot area may be unnecessary depending on the content of the color image data. However, according to the image processing apparatus of the second aspect of the present invention, in the halftone dot area, the black image quality is likely to deteriorate. Since the formation of large-diameter dots is suppressed only in the region, the image quality of the formed image can be improved without causing such problems.

  On the other hand, in the image processing apparatus according to claim 3, when input image data to be processed is input from the outside, first, similarly to the apparatus according to claim 1, first, the region separation means performs the input image data. The whole image area constituted by is divided into a halftone dot area and a character area, and the smoothing processing means smoothes the input image data in the halftone dot area separated by the area separation means, The input image data after the smoothing process is input to the error diffusion processing means. This error diffusion processing means, unlike the one described in claim 1, generates the recorded image data as follows.

  That is, in the image processing apparatus according to claim 3, the error diffusion processing means sets each pixel of the ink based on the gradation information of each pixel constituting the input image data in accordance with a preset error diffusion method. An image corresponding to input image data using inks of the same color and different densities is set by setting the density of ink when forming on the recording medium with dots to one of dark, light, and zero. Record image data to be formed is generated.

  In the image processing apparatus according to claim 3, the threshold value changing unit uses the threshold value used by the error diffusion processing unit to determine whether the ink density is set to dark or light for each pixel. Among these, the threshold value used in the image area separated as the halftone dot area by the area separating means is changed to a value larger than the threshold value used in the image area separated as the character area by the area separating means.

  Therefore, according to the image processing apparatus of the third aspect, in the recorded image data after the error diffusion processing, each pixel in the halftone dot area includes a dark ink dot and a dark ink dot in two types of dark and light ink dots. As a result, it is easier to assign the light ink dots, and the pixels to which the light ink dots are assigned are arranged in a distributed manner without being partially biased in the halftone dot region. Therefore, if an image is formed on a recording medium using the recording image data generated by the image processing apparatus according to claim 3, the recording image data generated by the apparatus according to claim 1 is used. As in the case of using, the occurrence of moire on the formed image can be suppressed.

  Further, according to the image processing apparatus of the third aspect, in order to enhance the effect of suppressing the occurrence of moire on the formed image, the halftone dot area detection accuracy by the area separating means and the smoothing processing means as in the prior art. Since it is not necessary to increase the accuracy of the smoothing process by the method, and it is only necessary to change the threshold value when the error diffusion process is performed in the halftone dot region, as in the apparatus according to claim 1, it is extremely simple and efficient. Generation of moiré can be suppressed.

  In the image processing apparatus according to claim 3, the pseudo gradation processing when generating the recording image data from the input image data is performed in accordance with the error diffusion method. This is because of the same reason as that of the image processing apparatus. In other words, according to the third aspect of the present invention, in the image processing apparatus provided with the error diffusion processing means for performing the pseudo gradation processing according to the error diffusion method, the error diffusion processing means is provided for each pixel in the halftone dot region. The threshold used to determine whether the ink density is set to dark or light is used to determine whether the ink density is set to dark or light for each pixel in the character area. By changing the value to a value larger than the threshold value to be used, an image in the halftone dot area is formed by dispersing and arranging light ink dots, and the occurrence of moire in the formed image can be suppressed. -ing

The invention described in claim 3 can be applied to an image processing apparatus for a single color image or an image processing apparatus for a multicolor image, as in the case of the first aspect.
In particular, the input image data is color image data having gradation information for a plurality of colors including black for each pixel, and the error diffusion processing means is a specific color excluding black among the plurality of colors. On the other hand, in an image processing apparatus for a multicolor image that is configured to set the density of ink of that color to one of dark, light, and zero, an image area that has a large black ratio has an area other than black. In this type of image processing apparatus, since the problem that a dot of a dark color ink is formed and the dot becomes conspicuous is likely to occur. The black area detecting means similar to the above is provided, and the threshold value changing means is an error diffusion processing means in an image area detected as a black area by the black area detecting means and separated as a halftone dot area by the area separating means. Is a specific color dot for each pixel. The error diffusion means uses a specific color for each pixel in the image area separated as the character area by the area separation means. It may be configured to change the ink density to a value larger than a threshold value used to determine whether to set the ink density to dark or light.

  In other words, as described in claim 4, when generating the recording image data from the color image data, if it is difficult to form dark ink dots only in the halftone dot area, which is the black area, It is possible to prevent the dots of the color from becoming conspicuous or the moire from being generated by the dots, thereby improving the image quality of the formed image.

Next, the invention described in claims 5 to 8 relates to an image processing method suitable for realizing the image processing apparatuses described in claims 1 to 4 described above.
In other words, the image processing method according to claim 5 is a method for forming each pixel on a recording medium based on gradation information of each pixel constituting input image data in accordance with a preset error diffusion method. By setting the dot diameter of the ink to at least one of large, small and zero, print image data for forming an image corresponding to the input image data on the print medium with dots having the same color and different diameters is generated. An image processing method in which an entire image area composed of input image data is separated into a halftone dot area and a character area, and when the image area is separated as a halftone dot area, an image is formed on a recording medium. In the input image data before conversion to the recording image data, the input image data in the halftone dot area is smoothed so that the ink dots are dispersed, and in the image area separated as the halftone dot area, The threshold used to determine whether or not to set a large dot diameter for each pixel when generating recorded image data is set to a large dot diameter for each pixel in the image area separated as a character area. It is characterized in that it is changed to a value larger than the threshold value used to determine whether or not. Therefore, if the image processing method according to claim 5 is used, the image processing apparatus according to claim 1 can be realized, and the same effect as that of claim 1 described above can be obtained.

  Next, an image processing method according to a sixth aspect is the image processing method according to the fifth aspect, wherein at the time of generation of the recorded image data, as input image data, a scale for a plurality of colors including black is provided for each pixel. Using color image data with tone information, based on the tone information of each color, set the dot diameter of the ink of each color, and set the threshold used when generating the recorded image data within the image area separated as the character area When changing to a value larger than the threshold used to determine whether to set a large dot diameter for each pixel, first, a black area in which black pixels occupy a large proportion in the input image data is selected. In order to determine whether or not to set a large dot diameter for each pixel and each color in an image area detected as a black area by the detection operation and then separated as a halftone dot area. use Value, and changing the dot diameter in an isolated image area for each pixel, each color as a character region to a value greater than the threshold value used to determine whether to set larger. Therefore, if the image processing method according to claim 6 is used, the image processing apparatus according to claim 2 can be realized, and the same effect as that of claim 2 described above can be obtained.

  According to a seventh aspect of the present invention, in accordance with a preset error diffusion method, each pixel is transferred to a recording medium with ink dots based on gradation information of each pixel constituting the input image data. Recording for forming an image corresponding to input image data on a recording medium using ink of the same color and different density by setting the density of ink at the time of formation to one of dark, light, and zero An image processing method for generating image data, wherein an entire image area constituted by input image data is separated into a dot area and a character area, and the image area separated as a dot area is stored on a recording medium. The input image data in the halftone dot area of the input image data before conversion to the recorded image data is smoothed so that the two types of dark and light dots are dispersed when the image is formed. In an image area separated as an area The threshold value used to determine whether to set the ink density for each pixel at the time of recording image data generation is the ink density for each pixel in the image area separated as the character area. It is characterized in that the value is changed to a value larger than a threshold value used for determining whether to set darkness or lightness. Therefore, if the image processing method according to claim 7 is used, the image processing apparatus according to claim 3 can be realized, and an effect similar to that of claim 3 described above can be obtained.

  The image processing method according to claim 8 is the image processing method according to claim 7, wherein when the recorded image data is generated, the input image data is a plurality of colors including black for each pixel. Using color image data with gradation information, for a specific color other than black among the multiple colors, set the ink density of the color to dark, light, or zero, and record The threshold value used when generating image data is set to a value larger than the threshold value used to determine whether the ink density is set for each pixel in the image area separated as the character area. When changing, first, a black region in which black pixels occupy a large proportion in the input image data is detected, and then the black region is detected by the detection operation, and the image region is separated as a halftone dot region. Special for each pixel The threshold used to determine whether to set the darkness or darkness of the ink of the specific color is the darkness of the ink of a specific color for each pixel in the image area separated as the character area. -It is characterized in that it is changed to a value larger than a threshold value used for determining which one to set to light. Therefore, if the image processing method according to claim 8 is used, the image processing apparatus according to claim 4 can be realized, and the same effect as in claim 4 described above can be obtained.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a perspective view illustrating an appearance of a multifunction machine 1 according to an embodiment to which the present invention is applied.
The multifunction machine 1 of this embodiment has functions as a copying machine (copy machine), a printer, a scanner, and a facsimile machine. As shown in FIG. The upper body 2b is provided with a clam shell type opening / closing structure in which the upper body 2b can be opened and closed. Further, the upper body 2b has a scanner unit 3 for reading an image from a document, and the lower body 2a has an opening / closing structure. A printer unit 4 (see FIG. 2) for forming an image on a recording sheet (corresponding to a recording medium) is provided.

  Further, on the front side of the lower main body 2a, there is provided an operation panel 5 in which an LCD 5a for displaying the operation state of the multifunction machine 1 and a keyboard 5b made up of various keys for operation input are integrally assembled. Further, below the operation panel 5, a paper discharge tray 6 for discharging recording paper on which an image is formed by the printer unit 4 is provided.

  Here, the scanner unit 3 provided in the upper body 2b is a type of scanner having both a flat bed mechanism (FB) and an automatic paper feed mechanism (ADF). The scanner unit 3 itself is also used as a document table. A clamshell type opening / closing structure is provided in which a cover portion 3b as a document table cover is attached to the flat bed portion 3a so as to be openable and closable.

  The cover 3b is provided with a document supply tray 7 and a document discharge tray 8 that are used when documents are automatically fed. Further, a platen glass (not shown) for placing a document is provided on the upper surface of the flat bed portion 3a, and an image sensor 9a (see FIG. 3) is provided in the lower part thereof.

  The scanner unit 3 conveys the original held on the original supply tray 7 one by one to the front of the image sensor 9a in a stationary state at a predetermined position, reads the original image, and then discharges the original to the original discharge tray 8. It is well known to read paper or to read an image of a stationary document placed on the platen glass by moving the image sensor 9a along the platen glass of the flat bed portion 3a. A sensor / document transport mechanism 9b (see FIG. 3) is provided.

  On the other hand, the printer unit 4 includes a recording head 10 as shown in FIG. The recording head 10 includes an ink cartridge 11 that is detachable, and includes an actuator 13 that discharges ink stored and held in the ink cartridge 11 onto a recording sheet via a nozzle plate 12.

  The actuator 13 includes a piezoelectric element, and is a well-known one that discharges ink from the nozzle plate 12 by expanding according to a driving voltage applied from the outside and pressurizing ink near the nozzle plate 12. In this embodiment, by switching the drive voltage waveform, the ink discharge amount is changed in two steps, large and small, so that two types of dots having different diameters can be selectively formed on the recording paper. Yes.

  As shown in FIG. 2B, four recording heads 10 are provided corresponding to four colors of magenta (M), yellow (Y), cyan (C), and black (K) ( (See 10m, 10y, 10c, and 10k shown in FIG. 2B.) Each of the color recording heads 10 stores inks of colors (M, Y, C, and K) corresponding to the recording heads 10, respectively. Ink cartridges 11m, 11y, 11c, and 11k are mounted.

  Each of the recording heads 10 is mounted on a carriage 15 that is movable along a guide 14 in a direction orthogonal to the recording sheet conveyance direction. A maintenance member such as a suction cap 16 that performs a suction operation on the nozzles provided on the nozzle plate 12 and a wiper 17 that wipes the nozzle plate 12 is provided on one end side in the moving direction of the carriage 15. Further, a flushing area for each recording head 10 to perform flushing is set in the vicinity thereof.

  The printer unit 4 takes out recording sheets one by one from a plurality of recording sheets stored in a stacked state in a paper cassette (not shown) in addition to the recording heads 10 and carriages 15 of the respective colors. 15 is a paper feed roller that is fed to the image forming position that is transported through 15, a transport roller that transports the recording paper image-formed at this image forming position to the paper discharge tray 6, and a paper for driving these rollers. A transport mechanism (head / paper transport mechanism 18 shown in FIG. 3) including a transport motor and a carriage motor for moving the carriage 15 in both directions along the guide 14 is also provided.

  In the multifunction machine 1, when an image is formed on a recording sheet, the recording sheet and the carriage 15 (and thus the recording head 10 of each color) are moved through the head / sheet transport mechanism 18, and each color of each color is moved. By ejecting ink from the recording head 10, an image is formed on the recording paper.

  Returning to FIG. 1, a rectangular through hole 5c is formed in the upper end surface of the lower main body 2a (more precisely, the upper end surface of the operation panel 5 as a part thereof), and constitutes a part of the upper main body 2b. On the lower end surface of the flat bed portion 3a, a projecting portion 20 that clicks and engages with the through hole 5c is provided. The flat bed portion 3a is held closed by the lower main body 2a by the engagement between the protruding portion 20 and the through hole 5c. For this reason, the operation of opening only the cover portion 3b and reading the document image by the flat bed mechanism (FB) is also facilitated. That is, the flat bed portion 3a and the cover portion 3b are configured to have substantially the same rectangular shape in plan view, and can be opened and closed with one end (long side) on the same side as the center of rotation. It is easy to open only the upper cover portion 3b.

Next, FIG. 3 is a block diagram illustrating the configuration of the control system of the multifunction machine 1 according to the present embodiment.
As shown in FIG. 3, this control system is mainly composed of a microcomputer comprising a CPU 21, a ROM 22, a RAM 23, and a bus 24 for connecting them. Further, the scanner unit 3, the printer unit 4, and the operation panel 5 described above are driven to the bus 24 via a scanner driving circuit 27, a printer driving circuit 28, and a panel interface (panel I / F) 29. An ASIC (Application Specific Integrated Circuit) 25 is connected to control various types of data from these units and process the data at high speed.

  The scanner driving circuit 27 drives the image sensor 9a of the scanner unit 3 in accordance with a command from the ASIC 25, and inputs image data of the original read by the image sensor 9a to the ASIC 25 along with the driving, or according to a command from the ASIC 25. This is for driving the sensor / document conveying mechanism 9b of the scanner unit 3 to convey the image sensor 9a or the document, and the printer drive circuit 28 is configured by the recording head 10 and the head / paper of the printer unit 4 in accordance with a command from the ASIC 25. The transport mechanism 18 is driven to form an image on the recording paper, and the state (position, etc.) of each part is fed back to the ASIC 25 during the drive. The panel I / F 29 is a keyboard of the operation panel 5. The command from the user input via 5b is sent to the ASIC 25 Or force is used to display various messages to LCD5a of the operation panel 5 in accordance with the display instruction from the ASIC 25.

  The ASIC 25 includes a parallel interface (parallel I / F) 31 for communication via a parallel cable, a USB interface (USB I / F) 32 for communication via a USB cable, and a public line such as a telephone line. An NCU (Network Control Unit) 33 for performing communication via a communication network is also connected. The NCU 33 is also connected to the bus 24 via a modem (MODEM) 34.

  In the MFP 1 of this embodiment configured as described above, functions as a copying machine, a printer, a scanner, and a facsimile machine are realized by the operations of the CPU 21 and the ASIC 25.

  For example, in the function as a copying machine, when a user inputs a copy command via the keyboard 5b of the operation panel 5, the ASIC 25 drives and controls the scanner unit 3 via the scanner drive circuit 27 in accordance with the command. As a result, an image is read from the document placed on the document supply tray 7 or the flat bed unit 3a, and the read image data is converted into recorded image data necessary for image formation by the printer unit 4, This is realized by executing a series of operations such as driving the printer unit 4 via the printer drive circuit 28 in accordance with the converted recorded image data and forming an image read from the document on a recording sheet. In this case, the CPU 21 operates the ASIC 25 in accordance with copy conditions (such as enlargement / reduction of the original, the number of copies, etc.) preset by the user via the keyboard 5b of the operation panel 5.

  Further, for example, as a function of a printer, print data for printing is transmitted from an external information processing apparatus (such as a personal computer) connected via a parallel cable or a USB cable, and the print data is converted into a parallel I / F 31. Alternatively, when the ASIC 25 receives the print data via the USB I / F 32, the CPU 21 identifies the print conditions given to the print data, and the CPU 21 forms an image corresponding to the print data under the print conditions. It is realized by operating. In this case, the ASIC 25 converts the print data transmitted from the external information processing apparatus into print image data necessary for image formation by the printer unit 4, and the printer according to the converted print image data. The printer unit 4 is driven and controlled via the drive circuit 28 to form an image on the recording paper.

  In this way, when the printer unit 4 is driven and controlled to form an image on a recording sheet, the ASIC 25 receives input image data (image data read from a document, an external information processing apparatus) to be image-formed. Since the print data, facsimile data received by the NCU 33, etc.) are converted into recording image data necessary for forming an image on recording paper by the printer unit 4, the ASIC 25 has an image processing circuit for this purpose. 50 is incorporated.

Hereinafter, the configuration and operation of the image processing circuit 50 will be described.
First, FIG. 4 is a block diagram showing the configuration of the image processing circuit 50.
As shown in FIG. 4, the image processing circuit 50 detects a halftone dot region from the input image data, thereby separating the entire image represented by the input image data into a halftone dot region and other regions (character regions). Of the input image data, the halftone dot detection circuit 52 performs smoothing processing on the input image data in the area identified as the halftone dot area by the halftone dot detection circuit 52, and performs the smoothing process on the area identified as the character area. A smoothing / enhancement circuit 54 that performs edge enhancement processing on the input image data, and the input image data that has been subjected to image processing by the smoothing / enhancement circuit 54 are converted into the original color system (for example, RGB color system, YIQ table). The color conversion circuit 56 for color conversion from the color system) to the CMYK color system image data that can be formed using the four-color recording head 10 described above, and the color-converted image by the color conversion circuit 56 In response to commands from the CPU 21 An enlargement / reduction circuit 58 that cuts out image data that can be formed on a recording sheet by the printer unit 4 and that is enlarged or reduced at an appropriate magnification, and image data for one sheet of recording paper that is cut out by the enlargement / reduction circuit 58 Is generated in accordance with a well-known error diffusion method to generate recording image data indicating whether the dot diameter of each color is large, small, or zero for each pixel constituting the image data. And a diffusion circuit 60, and the recording image data generated by the error diffusion circuit 60 is output to a printer control circuit 70 in the ASIC 25.

  In addition, the error diffusion circuit 60 uses a large dot determination threshold value used when converting image data of an area identified as a halftone dot area by the halftone dot detection circuit 52 to print image data. A threshold value setting circuit 62 is provided for changing to a value larger than a threshold value (hereinafter simply referred to as an initial value) used when converting the image data of (region) into the recorded image data.

  That is, the error diffusion circuit 60 uses the two types of threshold values for the gradation information for each color (C, M, Y, K) for each pixel of the image data input from the enlargement / reduction circuit 58, respectively. By digitizing, whether or not to form dots for each color in the pixel (whether or not the dot diameter is made zero), and when forming dots, the dot diameter is either large or small The threshold value setting circuit 62 determines whether or not the error diffusion circuit 60 forms a large dot having a large diameter for each pixel and each color of the image data. By changing the threshold value to be used to a value larger than the initial value, the operation of the error diffusion circuit 60 prevents the setting of large dots having a large diameter in the halftone dot region of the recorded image data.

  Specifically, in this embodiment, as shown in FIG. 5, a halftone dot detection circuit 52 detects a halftone dot region from input image data and separates the image into a halftone dot region and a character region. After executing the point detection process (S100: S represents a step), a threshold value change flag is set and assigned to each pixel in the area determined as a halftone dot area in this process (S110). ), The threshold value change flag is reset and applied to each pixel outside the halftone dot area (that is, in the character area) (S120). As described above, the threshold change flag given to each pixel of the input image data by the halftone dot detection circuit 52 is a smoothing / enhancement circuit 54, a color conversion circuit 56, an enlargement / reduction as parameters representing the detection result of the halftone area. It is input via the circuit 58.

  Therefore, in the error diffusion circuit 60, when the image data input from the enlargement / reduction circuit 58 is processed for each pixel in accordance with the error diffusion method, as shown in FIG. The threshold change flag is read (S200), it is determined whether or not the read threshold change flag is set (S210). If the threshold change flag is set, the threshold is set as a large dot determination threshold. In step S220, if the threshold value change flag is reset, the initial value is set as it is as a large dot determination threshold value (S230). Processing as the threshold setting circuit 62 is executed, and then, for each color (C, M, Y, K) of the target pixel, two types of gradation information and dot formation determination and large dot determination are used. By sequentially comparing the values with each other, dots of each color (C, M, Y, K) are formed on the target pixel at the time of image formation, or when forming dots, the diameter is made larger or smaller. In this procedure, pixel information indicating whether or not to be generated is generated, and further, a color reproduction error occurring in the target pixel is obtained from the pixel information after the generation, and the pixel information is reflected in gradation information of surrounding pixels that are not set. An error diffusion process (S240) for the target pixel is executed.

  Therefore, according to the multifunction device 1 of the present embodiment, the smoothing process for the input image data in the halftone area executed by the smoothing / enhancing circuit 54 is formed on the recording paper via the printer unit 4. Even in the case where moire generated on the formed image cannot be sufficiently suppressed, it is difficult to set a large-diameter dot in each pixel in the halftone dot region by the operation of the threshold setting circuit 62 in the error diffusion circuit 60 (in other words, In this case, it is possible to suppress the occurrence of moire by making it easy to set each pixel with a small diameter.

  For example, FIG. 7A shows a dot formation state in a halftone dot region in a conventional apparatus that does not include the threshold setting circuit 62 of this embodiment, and FIG. 7B shows a dot in the halftone dot region in this embodiment. As is apparent from this figure, the input image data in which large dots of K, M, and C are assigned to the pixels in the halftone dot area in the conventional apparatus is shown in FIG. When the image is input to the multi-function peripheral 1, the pixels to which the large dots of K, M, and C are allocated in the same halftone dot area as before are eliminated, and instead of the pixels to which the small dots of K, M, and C are allocated. By increasing the number, the dots can be distributed to more pixels, and as a result, the occurrence of moire on the formed image can be suppressed.

  Further, according to the multifunction device 1 of the present embodiment, it is not necessary to improve the halftone dot detection circuit 52 and the smoothing / enhancement circuit 54 in order to increase the effect of suppressing the occurrence of moiré on the formed image. Since it is only necessary to provide the threshold value setting circuit 62 for changing the threshold value used to determine the formation of large dots in the error diffusion circuit 60 based on the detection result of the output circuit 52, it is extremely simple (in other words, low cost) and efficient. It is possible to suppress the occurrence of moire well.

  In FIG. 7, a circle described with a dotted line represents the position of each pixel constituting the recorded image data, a black circle represents a black K dot formed on the pixel, and a circle given M or C is M and C dots formed on the pixel are shown.

  FIGS. 5 and 6 are flowcharts showing the operation of the halftone detection circuit 52 and the operation of the error diffusion circuit 60 including the threshold setting circuit 62 (image data processing procedure). Since 62 is one circuit that constitutes the ASIC 25, it is needless to say that it actually comprises a logic circuit configured to operate according to the procedure shown in FIGS.

  In this embodiment, the image processing circuit 50 corresponds to the image processing apparatus of the present invention, and the halftone dot detection circuit 52 constituting the image processing circuit 50 corresponds to the region separation means of the present invention. The circuit 54 corresponds to the smoothing processing means of the present invention, the error diffusion circuit 60 corresponds to the error diffusion processing means of the present invention, and the threshold value setting circuit 62 also corresponds to the threshold value changing means of the present invention.

As mentioned above, although one Embodiment of this invention was described, this invention is not limited to the said embodiment, A various aspect can be taken in the range which does not deviate from the summary of this invention.
For example, in the above-described embodiment, the halftone dot detection circuit 52 in the image processing circuit 50 detects a halftone dot region from the input image data, thereby converting all the images represented by the input image data into a halftone dot region and other regions ( The halftone dot detection circuit 52 detects the character area from the input image data, and the image is divided into the character area and the other area (halftone area) as shown in FIG. When the character area detecting process (S100 ′) is separated, the threshold value is set for each pixel in the area determined as the character area by the character area detecting process. The change flag is reset and added (S110 ′), and the threshold value change flag is set and assigned to each pixel outside the character area (that is, in the halftone dot area) (S120 ′). That's fine.

  In the above embodiment, four color inks of C, M, Y, and K are used, and the color of the color image is changed by changing the dot diameter of the ink into two stages of large and small (three stages when zero is inserted). The multi-function device 1 having the image forming apparatus (printer unit 4) for forming the image has been described. However, the present invention is applicable to the ink dot diameters in three stages of large, medium, and small (four stages when zero is inserted), or Even an image forming apparatus configured to form an image by dividing it further, or dark and light (dark (D) and light (L)) as magenta (M) and cyan (C) inks By using two types of inks, the present invention can be applied to an image forming apparatus that forms an image using a total of six colors (DC, LC, DM, LM, Y, K).

  That is, for example, in the above embodiment, when the error diffusion circuit 60 is configured to set the ink dot diameter to one of large, medium, small, and zero for each pixel, the error The large dot determination threshold used to determine whether the ink dot diameter is to be large or medium in the diffusion circuit 60, or the ink dot system is large, medium or medium Of the thresholds for determining large dots and the thresholds for determining medium dots used to determine which one is small, only the threshold used in the halftone area is larger than the initial value by the threshold setting circuit 62. If the value is set, the same effect as in the above embodiment can be obtained.

  Further, for example, in the above embodiment, when the error diffusion circuit 60 sets whether or not to form C, M, Y, and K ink dots for each pixel, the size (diameter) of the dots to be formed. Instead of setting the dark (D) or light (L) ink density (LC / DC, LM / DM) for cyan (C) and magenta (M) dots. In such a case, the error diffusion circuit 60 including the threshold setting circuit 62 may be configured to operate as shown in FIG.

  That is, the error diffusion circuit 60 first reads the threshold value change flag given to the target pixel (S300), determines whether or not the read threshold value change flag is set (S310), and sets the threshold value. If the change flag is set, dark used to determine whether the cyan (C) and magenta (M) inks are dark ink (DC, DM) or light ink (LC, LM). The determination threshold is set to a value obtained by adding a correction value to the initial value of the threshold (S320). Conversely, if the threshold change flag is reset, the initial value is set as the dark determination threshold (S330). ), The processing as the threshold setting circuit 62 is executed, and then whether or not to form a dot for each color (C, M, Y, K) of the target pixel is determined. Pixel information indicating whether the density of the ink used for dot formation is dark or light is generated, and further, color reproduction errors occurring in the target pixel are calculated from the pixel information after the generation. The error diffusion process (S340) for the target pixel may be executed by a procedure such as obtaining and reflecting the pixel information in the gradation information of surrounding pixels that have not been set.

  In this way, light ink (lighter than light dark ink (DC, DM)) is used as light when forming cyan (C) or magenta (M) dots in the halftone dot region. LC, LM) can be easily selected, and the number of dots of the light ink (LC, LM) is increased and dispersed in the dot area by the error diffusion method. Similarly, the occurrence of moire on the formed image can be suppressed.

  By the way, in the above-described embodiment and the modification shown in FIG. 9, all of the image areas to be formed on the recording paper are all large dots in the image area identified as the halftone dot area by the halftone dot detection circuit 52. The threshold value for determination (or the threshold value for dark determination) is changed to a value larger than the initial value to suppress the formation of large diameter dots (or dots with dark ink), but the input image data Depending on the content of the color image data (in other words, the color image data), the dot size (or ink density) may be unnecessarily limited, and the image quality of the formed image may be deteriorated.

  On the other hand, when a color image is formed using four colors of C, M, Y, and K, or six colors including dark and light, as in the above-described embodiments and modifications, the problem is that This is when a dot of a color other than black is formed independently in a black region where an image is formed mainly with black (K) ink, and the dot of that color becomes conspicuous.

  Therefore, in the above-described embodiments and modifications, the large dot determination threshold value or darkness is limited only to the black region in which the proportion of black pixels is large in the image region identified as the halftone dot region by the halftone dot detection circuit 52. The determination threshold value may be changed to a value larger than the initial value to suppress the formation of dots with large diameters or dots with dark ink.

  For this purpose, for example, as shown in FIG. 10, a black area detection circuit 64 as black area detection means is provided between the color conversion circuit 56 and the enlargement / reduction circuit 58 of the image processing circuit 50. The black area detection circuit 64 detects a black area in which the ratio of black (K) pixels is large using the image data after color conversion, and among the halftone area detected by the halftone detection circuit 52, The threshold value change flag output from the halftone dot detection circuit 52 is set so that the threshold value change flag is set in the halftone dot region of the black region, and the threshold value change flag is reset even in the non-black region even in the halftone dot region. Is updated and output to the enlargement / reduction circuit 58 (and thus the threshold setting circuit 62).

  For example, as illustrated in FIG. 11, the black area detection circuit 64 may include black (K) of a plurality of pixels in a predetermined area including the target pixel for each pixel of the image data output from the color conversion circuit 56. The average density of black (K) in the area is calculated from the gradation information (S200), and it is determined whether or not the calculated average density is smaller than a preset black area determination value Kref. Then, it is determined whether or not the target pixel is outside the black region (S210), and if it is determined that the average density is smaller than the black region determination value Kref and the target pixel is outside the black region, the threshold value for the target pixel is changed. What is necessary is just to comprise so that a flag may be reset compulsorily irrespective of the setting result by the halftone detection circuit 52 (S220).

  However, as a method for detecting a black region (in other words, an achromatic region), various methods are conventionally known (see, for example, Japanese Patent Laid-Open Nos. 2000-125139 and 2003-259135). Thus, as in the case of detection of a halftone dot region, a conventionally known method can be used.

  As described above, if the large dot determination threshold or the dark determination threshold is changed to a value larger than the initial value only in the black halftone area, the dot size or the ink density is not improved. It can prevent restricting to necessity.

  In the above embodiment, the case where the present invention is applied to the multifunction machine 1 having functions as a copying machine, a printer, a scanner, and a facsimile machine has been described. Even an image forming apparatus provided with the above-described printer unit 4 or an information processing apparatus such as a personal computer that outputs recording image data for image formation to this type of image forming apparatus. The same effect can be obtained by applying in the same manner as in the embodiment.

1 is a perspective view illustrating an appearance of a multifunction machine according to an embodiment to which the present invention is applied. FIG. 3 is an explanatory diagram illustrating a configuration of a printer unit of the multifunction peripheral according to the embodiment. It is a block diagram showing the structure of the control system of the multifunctional machine of an Example. FIG. 3 is a block diagram illustrating a configuration of an image processing circuit incorporated in an ASIC of the multifunction peripheral according to the embodiment. 6 is a flowchart showing the operation of the halftone dot detection circuit shown in FIG. 5 is a flowchart showing the operation of the error diffusion circuit shown in FIG. It is explanatory drawing which represents the dot formation state in the halftone dot area | region in the multifunction machine of an Example compared with the conventional apparatus. 6 is a flowchart illustrating a modification example of the operation of the halftone dot detection circuit illustrated in FIG. 4. 6 is a flowchart illustrating a modification example of the operation of the error diffusion circuit illustrated in FIG. 4. It is a block diagram showing the other structural example of an image processing circuit. It is a flowchart showing operation | movement of the black area | region detection circuit shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Multifunction machine, 3 ... Scanner part, 4 ... Printer part, 5 ... Operation panel, 5a ... LCD, 5b ... Keyboard, 9a ... Image sensor, 9b ... Sensor and document conveyance mechanism, 10 ... Recording head, 18 ... Head Paper transport mechanism, 21 ... CPU, 22 ... ROM, 23 ... RAM, 24 ... bus, 25 ... ASIC, 27 ... scanner drive circuit, 28 ... printer drive circuit, 29 ... panel I / F, 31 ... parallel I / F, 32 ... USB I / F, 33 ... NCU, 34 ... modem, 50 ... image processing circuit, 52 ... dot detection circuit, 54 ... smoothing / enhancement circuit, 56 ... color conversion circuit, 58 ... enlargement / reduction circuit, 60 ... error Diffusion circuit 62... Threshold setting circuit 64. Black area detection circuit 70.

Claims (8)

In accordance with a preset error diffusion method, based on the gradation information of each pixel constituting the input image data, the dot diameter of the ink when forming each pixel on the recording medium is at least one of large, small and zero Error diffusion processing means for generating recording image data for forming an image corresponding to the input image data on the recording medium with dots of the same color and different diameters,
A region separating means for separating the entire image region composed of the input image data into a halftone dot region and a character region;
In the image area separated as the halftone dot area by the area separating means, input image data inputted to the error diffusion processing means so that the ink dots are dispersed when an image is formed on the recording medium. Smoothing processing means for smoothing input image data in the halftone dot region,
In an image processing apparatus comprising:
In the image region separated as the halftone dot region by the region separation unit, the threshold value used by the error diffusion processing unit to determine whether or not to set a large dot diameter for each pixel, A value larger than a threshold used by the error diffusion processing unit to determine whether or not to set a large dot diameter for each pixel in the image region separated as the character region by the region separation unit. Threshold changing means for changing,
An image processing apparatus comprising: The input image data is color image data having gradation information for a plurality of colors including black for each pixel, and the error diffusion processing means determines the dot diameter of the ink of each color based on the gradation information of each color. And is configured to set
Furthermore, a black area detecting means for detecting a black area in which the proportion of black pixels in the input image data is large,
The threshold value changing means is an image area detected as a black area by the black area detecting means and separated as the halftone dot area by the area separating means. The threshold value used to determine whether or not to set a large dot diameter every time is determined by the error diffusion processing unit in the image region separated as the character region by the region separation unit. The image processing apparatus according to claim 1, wherein the image processing apparatus is changed to a value larger than a threshold value used for determining whether or not to set a large dot diameter every time. In accordance with the error diffusion method set in advance, based on the gradation information of each pixel constituting the input image data, the density of the ink when forming each pixel on the recording medium with ink dots is set to dark / light. An error diffusion processing means for generating recording image data for forming an image corresponding to the input image data on a recording medium using ink of the same color and different densities by setting to any one of zero;
A region separating means for separating the entire image region composed of the input image data into a halftone dot region and a character region;
In the image area separated as the halftone dot area by the area separation means, the two types of dark and light dots are input to the error diffusion processing means when an image is formed on the recording medium. Smoothing processing means for smoothing the input image data in the halftone dot region of the input image data
In an image processing apparatus comprising:
In the image area separated as the halftone dot area by the area separating means, the threshold value used by the error diffusion processing means to determine whether the ink density is set to dark or light for each pixel. Is used by the error diffusing means to determine whether to set the ink density for each pixel in the image area separated as the character area by the area separating means. Threshold changing means for changing to a larger value than
An image processing apparatus comprising: The input image data is color image data having gradation information for a plurality of colors including black for each pixel, and the error diffusion processing means applies a specific color excluding black among the plurality of colors. On the other hand, the ink density of the color is configured to be set to dark, light, or zero,
Furthermore, a black area detecting means for detecting a black area in which the proportion of black pixels in the input image data is large,
The threshold value changing means is an image area that is detected as a black area by the black area detecting means and separated as the halftone dot area by the area separating means, and the error diffusion processing means is provided for each pixel. The threshold value used to determine whether the darkness or darkness of the specific color ink is set is determined by the error diffusion means in the image area separated as the character area by the area separation means. 4. The image processing according to claim 3, wherein for each of the pixels, the specific color ink is changed to a value larger than a threshold value used to determine whether to set darkness or lightness of the ink. apparatus. In accordance with a preset error diffusion method, based on the gradation information of each pixel constituting the input image data, the dot diameter of the ink when forming each pixel on the recording medium is at least one of large, small and zero An image processing method for generating recording image data for forming an image corresponding to the input image data on a recording medium with dots having the same color and different diameters,
Separating the entire image area composed of the input image data into a halftone dot area and a character area;
In the image area separated as the halftone dot area, the halftone dot area of the input image data before conversion to the recording image data is dispersed so that the dots of the ink are dispersed when an image is formed on the recording medium. Smoothing the input image data in
In addition, in the image area separated as the halftone dot area, a threshold value used to determine whether or not to set a large dot diameter for each pixel when the recorded image data is generated is separated as the character area. An image processing method comprising: changing a dot diameter to a value larger than a threshold used for determining whether or not to set a large dot diameter for each pixel in the image area. At the time of generation of the recording image data, color image data having gradation information for a plurality of colors including black is used for each pixel as the input image data, and ink dots of each color are based on the gradation information of each color. While setting the diameter,
A threshold value used when generating the recording image data is larger than a threshold value used for determining whether or not to set a large dot diameter for each pixel in the image area separated as the character area. First, a black area in which black pixels occupy a large proportion in the input image data is detected, and then detected as a black area by the detection operation and separated as the halftone area. In the image area, a threshold value used to determine whether or not to set a large dot diameter for each pixel and each color is set for each pixel and each color in the image area separated as the character area. 6. The image processing method according to claim 5, wherein the image processing method is changed to a value larger than a threshold value used for determining whether or not the dot diameter is set to be large. In accordance with the error diffusion method set in advance, based on the gradation information of each pixel constituting the input image data, the density of the ink when forming each pixel on the recording medium with ink dots is set to dark / light. An image processing method for generating recording image data for forming an image corresponding to the input image data on a recording medium using ink of the same color and different densities by setting to any one of the following:
Separating the entire image area composed of the input image data into a halftone dot area and a character area;
In the image area separated as the halftone dot area, the input image data before conversion to the recording image data is dispersed so that the two types of dark and light dots are dispersed when an image is formed on the recording medium. , Smoothing the input image data in the dot area,
In addition, in the image area separated as the halftone dot area, a threshold value used to determine whether the ink density is set to dark or light for each pixel when the recorded image data is generated is set to the character area. An image processing method comprising: changing an ink density for each pixel in the image area separated as an area to a value larger than a threshold value used to determine whether to set dark or light. . When generating the recorded image data, color image data having gradation information for a plurality of colors including black is used for each pixel as the input image data, and a specific color excluding black among the plurality of colors In contrast, the ink density of the color is set to dark, light, or zero,
The threshold value used when generating the recording image data is set to be higher than the threshold value used to determine whether the ink density is set for each pixel in the image area separated as the character area. When the value is changed to a larger value, first, a black area in which black pixels occupy a large proportion in the input image data is detected, and then detected as a black area by the detection operation, and the halftone dot area In the separated image area, the image area separated as the character area has a threshold value used to determine whether the darkness or darkness of the ink of the specific color is set for each pixel. 8. The method according to claim 7, wherein the value is changed to a value larger than a threshold value used to determine whether the darkness or darkness of the ink of the specific color is set for each pixel. Image processing method.

Images