JP4466041B2 - Image forming apparatus and image forming method - Google Patents

Description

  The present invention relates to an image forming apparatus and an image forming method.

  In general printing such as offset printing, gradation is expressed by controlling the area on which ink is placed. By changing the size of a periodic shape pattern (hereinafter referred to as “screen”), it is possible to express light and shade. In the case of performing color printing, in order to prevent the occurrence of color unevenness, the screen angle is changed for each color and then printing is performed in an overlapping manner.

  In recent years, electrophotographic printers (copiers) have been proposed that perform color expression using halftone dot screen processing similar to printing. However, due to the difference between general printing and electrophotographic printing processes, interference moiré between screens tends to be noticeable in electrophotographic printers. Of course, moire occurs even in general printing, but an electrophotographic printer has a moire generation factor due to the printing method, and moire is more conspicuous than in general printing.

  Next, a conventional electrophotographic printing process and a moire generation mechanism will be described (Prior Art 1). FIG. 1 is a block diagram of a conventional electrophotographic printer. As shown in FIG. 1, a printer (image forming apparatus) 1 includes an image processing unit 2, a screen processing unit 3, a laser driving unit 4, a charging unit 5, an exposure unit 6, a photoconductor 7, a developing unit 8, and a transfer belt 9. A sheet conveyance path 10 and a fixing unit 11. The printer 1 primarily transfers the toner image developed on the photosensitive member 7 to an intermediate transfer member such as a transfer belt 9, and then retransfers the toner image to a sheet conveyed through the sheet conveyance path 10. Fix the toner on top. When the printer 1 is a color printer, four color toner images are sequentially transferred onto the transfer belt 9.

  FIG. 2 is an enlarged view of the image on the transfer belt when the secondary color image is printed. FIG. 2 shows a state in which a B color toner image is superimposed and transferred onto an A color toner image. At this time, even if the B color toner image is transferred to the flat surface where the A color toner image does not exist below, the halftone dot shape of the B color screen is maintained and transferred. On the other hand, if the B color toner image is superimposed and transferred to the portion where the A color toner image exists, the halftone dot shape of the B color is slightly collapsed as compared with the case where the image is transferred to a flat surface. As a result, the halftone dot shape periodically changes between the part where the toner image is broken and the part where the toner image is not. This will appear as moire on the paper.

  In addition, when the toner image is secondarily transferred from the intermediate transfer member such as the transfer belt 9 to the sheet, the halftone dot shape is easily broken because the pile height is high at the portion where the toner overlaps. Therefore, there is a problem that moire is further emphasized during the secondary transfer. This moire is called pile height moire, which is caused by using powder toner having a large particle size.

  Patent Document 1 is a conventional technique that suppresses such pile height moire. In the image forming apparatus described in Patent Document 1, the yellow screen angle is set to be the same as the other screen angles of any one of cyan, magenta, and black, and the phase of the yellow screen is changed to that of the other screen. By differentiating the phase by a predetermined angle, in addition to low-contrast moiré that occurs in the low-frequency range due to the superposition of yellow, it suppresses the occurrence of pile height moiré that is unique to electrophotographic images in the low-frequency range. is there.

  In addition, a conventional technique for avoiding moire by using a screen having a non-conspicuous shape has been proposed (Prior Art 3). FIG. 3 is a diagram showing an example of a conventional screen having an inconspicuous shape, in which FIG. 3A is cyan, FIG. 3B is magenta, FIG. 3C is black, and FIG. Indicates the yellow screen shape. Conventionally, at the time of designing screen parameters, moire has been avoided by using a screen having a line shape that does not make moire visible as shown in FIG.

JP 2002-112047 A

  However, although the conventional image forming apparatus can suppress moire, it cannot realize a screen shape similar to printing, and uses screen parameters having a shape specialized for an electrophotographic printer. There was a problem that the image quality was lowered.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus and an image forming method capable of suppressing generation of moire peculiar to electrophotography due to screen interference.

In order to solve the above-described problems, an image forming apparatus according to the present invention forms toner images of different colors on an image carrier using a screen that expresses the gradation of an image. The toner image on the image carrier is primarily transferred to an intermediate transfer member, and the toner image formed on the intermediate transfer member is secondarily transferred onto a recording material at a secondary transfer portion, In an image forming apparatus that performs a process of fixing a toner image on a recording material secondarily transferred by a secondary transfer unit at a fixing unit, the recording material fixed by the fixing unit is moved to a secondary transfer position by the secondary transfer unit. A transport unit that transports, a control unit that controls each unit to perform the process for each predetermined color unit when a plurality of color toner images are formed on the image carrier , the number of lines of the screen , Angle of the screen, halftone dot of each color Moire caused by interference, or on the basis of the screen information including the angular difference of each screen, the toner images of the plurality of colors, the same process of each process, whether transferring to the intermediate transfer member or the recording medium And a determination unit that determines the above.

According to the first aspect of the present invention, when a toner image of a plurality of colors is formed, the process is performed for each predetermined color unit. Therefore, the occurrence of moire peculiar to electrophotography due to screen interference can be suppressed, and a print output with good image quality can be obtained. In addition, based on the screen information, colors that do not stand out in moire can be performed in the same process, so that the number of processes can be reduced.

According to a second aspect of the present invention, there is provided the image forming apparatus according to the second aspect, wherein toner images of different colors are formed on the image carrier by a toner forming unit using a screen that expresses the gradation of the image. In an image forming apparatus for performing a process of transferring a toner image on an image carrier onto a recording material by a transfer unit and fixing the toner image on the recording material transferred by the transfer unit by a fixing unit, fixing by the fixing unit A transport unit that transports a subsequent recording material to a transfer position by the transfer unit; and when forming a plurality of color toner images on the image carrier, the units are configured to perform the process for each predetermined color unit. a control unit for controlling the line speed of the screen, the angle of the screen, the moire pitch caused by the interference of each color dot, or on the basis of the screen information including the angular difference of each screen, the toner of the plurality of colors And the same process of each process, and having a determining section for determining whether or not to transfer to the recording material.

According to the second aspect of the present invention, when the toner image of a plurality of colors is formed, the process is performed in a predetermined color unit, so that the change in the halftone dot shape due to the collapse of the toner image is prevented. Therefore, it is possible to suppress the generation of moiré peculiar to electrophotography due to screen interference, and a print output with good image quality can be obtained. In addition, based on the screen information, colors that do not stand out in moire can be performed in the same process, so that the number of processes can be reduced.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the control unit controls the respective units to perform the process for each different color. It is characterized by. According to the third aspect of the invention, by performing the process for each different color, it is possible to prevent a periodic change in the halftone dot shape due to the collapse of the toner image. Can be suppressed, and a print output with good image quality can be obtained.

According to a fourth aspect of the present invention, there is provided an image forming method comprising: a first step of forming a toner image on an image carrier using a screen that expresses the gradation of the image; and the image carrier. A second step of primarily transferring the upper toner image to an intermediate transfer member; a third step of secondarily transferring the toner image formed on the intermediate transfer member onto a recording material at a secondary transfer portion; A fourth step of fixing the toner image on the recording material secondarily transferred by the secondary transfer unit by the fixing unit, and conveying the recording material fixed by the fixing unit to the secondary transfer position by the secondary transfer unit The plurality of color toner images based on screen information including the number of lines of the screen, the angle of the screen, the moire pitch caused by the interference of the halftone dots of each color, or the angle difference of each screen . Said first step And a sixth step of determining whether or not to transfer to the intermediate transfer member or the recording material in the same step of the fourth step, and forming a multi-color toner image on the image carrier. In this case, the first to fourth steps are performed for each predetermined color unit.

According to the fourth aspect of the present invention, when the toner images of a plurality of colors are formed, the first step to the fourth step are performed for each predetermined color unit. Therefore, the occurrence of moiré peculiar to electrophotography due to screen interference can be suppressed, and a print output with good image quality can be obtained. In addition, based on the screen information, colors that do not stand out in moire can be performed in the same process, so that the number of processes can be reduced.

According to a fifth aspect of the present invention, there is provided an image forming method comprising: a first step of forming a toner image on an image carrier using a screen that expresses the gradation of the image; and the image carrier. A second step of transferring the toner image on the recording material by the transfer unit onto the recording material; a third step of fixing the toner image on the recording material transferred by the transfer unit by the fixing unit; and fixing by the fixing unit. A fourth step of conveying a subsequent recording material to a transfer position by the transfer unit, and a screen including the number of lines of the screen, the angle of the screen, the moire pitch generated by the interference of halftone dots of each color, or the angle difference of each screen A fifth step of determining whether to transfer the plurality of color toner images to the recording material in the same step of the first step to the third step based on the information, When toner images of plural colors on Kizo bearing is formed, and performing the third step from the first step for each predetermined color units.

According to the fifth aspect of the present invention, when the toner images of a plurality of colors are formed, the first step to the third step are performed for each predetermined color unit. Since the change in the halftone dot shape can be prevented, the occurrence of moire peculiar to electrophotography due to screen interference can be suppressed, and a print output with a good image quality can be obtained. In addition, based on the screen information, colors that do not stand out in moire can be performed in the same process, so that the number of processes can be reduced.
The present invention, as described in claim 6, in the image forming method according to claim 4 or 5, said screen information, the moire pitch or the either of the angular difference of each screen Features.

  According to the present invention, it is possible to suppress the generation of moiré peculiar to electrophotography due to screen interference, and a print output with good image quality can be obtained.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to examples.

  FIG. 4 is a block diagram of the system 100 according to the first embodiment. FIG. 5 is a configuration diagram of the printer according to the first embodiment. As shown in FIG. 4, the system 100 includes a personal computer (PC) 110 and a printer 120. The printer 120 corresponds to an image forming apparatus. The printer 120 draws an image according to the drawing data described in PDL from the PC 110, and forms the drawn image on a sheet.

  The PC 110 includes application software 111 and a printer driver 112. The PC 110 sends print data such as character / graphic information and color information indicating image information created by the application software 111 as a result of user operation to the printer 120 in the form of PDL (page description language). send. The printer 120 includes an image processing unit 130 and a printer engine 140. The image processing unit 130 includes a PDL interpretation unit 131, a drawing unit 132, a rendering unit 1233, a halftone generation unit 134, and a pulse generation unit 135. The image processing unit 130 includes, for example, a central processing unit (CPU), a read only memory (ROM), and a random access memory (RAM).

  The PDL interpretation unit 131 interprets drawing data described in PDL sent from the PC 110 and controls operations according to various commands. The drawing unit 132 includes a color conversion unit 132a and a TRC / γ correction unit 132b, and generates an intermediate code for drawing according to the interpretation of the drawing data by the PDL interpretation unit 131. The color conversion unit 132a converts a drawing color (for example, a color in the RGB color space) specified by the drawing data described in PDL into a color (for example, a color in the YMCK color space) used in the printer engine 140.

  The color conversion unit 132a can be configured by, for example, a three-dimensional lookup table (hereinafter referred to as a DLUT), a matrix operation using a conversion matrix, or the like. The TRC / γ correction unit 132b performs gradation correction processing for outputting to the printer engine 140 in accordance with a TRC (Tone Reproduction Curve) and a γ value. The TRC / γ correction unit 132b can be configured by, for example, a one-dimensional lookup table (LUT).

  The rendering unit 133 performs rendering processing on image data for one page suitable for the printer engine 140 based on the intermediate code generated by the drawing unit 122. Note that the image data is generated in accordance with the drawing resolution in the printer engine 140.

  The halftone generation unit 134 includes a storage unit 134a and performs screen processing using a halftone reproduction screen (screen) that expresses the gradation of an image by the size of the area of a point or a line. The storage unit 134a stores screen information related to a screen that is necessary when determining a screen process or a printing process (printing order). This screen information is referred to by the control unit 136 as necessary. Here, the screen information includes the number of screen lines, the screen angle, the moire pitch, the angle difference between the screens, and the like. The number of screen lines and the screen angle are referred to as screen parameters. In the first embodiment, an example in which a set of screen parameters is stored in the storage unit 134a will be described.

  When a toner image of a plurality of colors is formed, the control unit 136 controls each unit so that the process from transfer to fixing is performed for each predetermined color unit. That is, the control unit 136 controls the pulse signal output from the pulse generation unit 135 based on the screen information stored in the storage unit 134a and the position of the paper reverse conveyance unit 101, and performs a predetermined process from transfer to fixing. This is done in color units. Here, an example in which Y, M, C, and K are used as the predetermined color units and printing is performed for each color will be described. However, for example, Y and M may be used by using a plurality of colors as the predetermined color units. May be printed in the same process, and C and K may be printed in the next process.

Note that when there is only one set of screen parameters, the control unit 136 performs printing in a predetermined printing process (printing order). The control unit 136 corresponds to a determination unit, and determines whether to transfer a plurality of color toner images to the intermediate transfer member or the recording material in the same process among the processes based on the screen information.
The control unit 101 controls the transport unit 101.

  The pulse generation unit 135 converts the image data screen-processed by the halftone generation unit 134 into a pulse signal for driving the printer engine 140 according to a control signal from the control unit 136 and outputs the pulse signal. The printer engine 140 forms an image on a sheet in accordance with a drive signal such as a pulse signal output from the pulse generator 135. In this embodiment, the electrophotographic method is used as the image forming method, but the present invention is not limited to this. For example, an arbitrary image forming method such as an inkjet method, a thermal transfer method, a thermal recording method, a dot impact method, or the like can be used. In the present embodiment, since the storage unit 134a has only one set of screen parameters, printing is executed by a predetermined printing process.

  Next, the configuration of the printer 120 will be described with reference to FIG. As shown in FIG. 5, the printer 120 includes an image processing unit 2, screen processing units 3Y, 3M, 3C, and 3K, laser driving units 4Y, 4M, 4C, and 4K, charging units 5Y, 5M, 5C, and 5K, and an exposure unit. 6Y, 6M, 6C, 6K, photoconductors 7Y, 7M, 7C, 7K, developing units 8Y, 8M, 8C, 8K, transfer belt 9, paper transport path 10, fixing unit 11, transport unit 101, secondary transfer unit 102 Have The same parts as those of the electrophotographic apparatus 1 according to the conventional example will be described with the same reference numerals.

  5, the PDL interpretation unit 131, the drawing unit 132, and the rendering unit 133 in FIG. 4 are in the image processing unit 2, the halftone generation unit 134 is in the screen processing unit 3, the laser driving unit 4 and the like are in the printer engine 140. Equivalent to. In FIG. 5, the pulse generation unit 135 shown in FIG. 4 is omitted. The laser driving unit 4, the charging unit 5, the exposure unit 6, and the developing unit 8 correspond to toner forming means, and the photoconductor corresponds to an image carrier. The transport unit 101 is for transporting the paper fixed by the fixing unit 11 back to the secondary transfer position by the secondary transfer unit 102 again. In addition, it is also possible to perform reverse paper conveyance using a general double-sided paper conveyance unit.

  Next, the operation of the printer 120 according to the first embodiment will be described. In order to prevent the occurrence of the moire, the transfer to fixing process may be performed in a plurality of times. As described above, in this embodiment, since a set of screen parameters is not stored in the storage unit 134a, printing is executed by a predetermined printing process. Specific methods are shown below. In the following, it is assumed that the fixing process is performed a plurality of times in the order of Y, M, C, and K.

  The control unit 136 outputs a control signal to the pulse generation unit 135 with reference to the sheet conveyance position by the sheet reverse conveyance unit 101 and the screen parameters stored in the halftone generation unit 134 at predetermined intervals. First, when developing the first color (yellow Y), the pulse generation unit 135 converts the image data screen-processed by the halftone generation unit 134 into the printer engine 140 in accordance with a control signal from the control unit 136. It converts into the pulse signal for driving, and outputs it to the laser drive part 4Y.

  The laser driving unit 4Y irradiates light based on the pulse signal from the pulse generating unit 135 to form an electrostatic latent image pattern on the photoreceptor 7Y. Thereafter, toner is supplied from the developing unit 8Y onto the photoreceptor 7Y, and the toner image is developed. The toner image developed on the photoconductor 7Y is primarily transferred to a transfer belt 9 as an intermediate transfer member, and the secondary transfer unit 102 performs secondary transfer onto a sheet conveyed through the sheet conveyance path 10, and the fixing unit 11 To fix the toner on the paper. The conveyance unit 101 reversely conveys the fixed sheet to the secondary transfer unit 102.

  When developing the second color (magenta M), the pulse generation unit 135 drives the printer engine 140 with the image data screen-processed by the halftone generation unit 134 in accordance with a control signal from the control unit 136. Is converted into a pulse signal for output to the laser drive unit 4M. The laser driver 4M irradiates light based on the pulse signal from the pulse generator 135 to form an electrostatic latent image pattern on the photoreceptor 7M. Thereafter, toner is supplied from the developing unit 8M onto the photoreceptor 7M, and the toner image is developed. The toner image developed on the photoconductor 7M is primarily transferred to a transfer belt 9 which is an intermediate transfer member, and is subjected to secondary transfer on the reversely conveyed paper sheet by the secondary transfer unit 102, and then the fixing unit 11 performs the secondary transfer. Fix the toner on the paper. The conveyance unit 101 reversely conveys the fixed sheet to the secondary transfer unit 102.

  When developing the third color (cyan C), the pulse generation unit 135 drives the printer engine 140 with the image data screen-processed by the halftone generation unit 134 in accordance with a control signal from the control unit 136. Is converted into a pulse signal for output to the laser drive unit 4C. The laser driver 4C irradiates light based on the pulse signal from the pulse generator 135 to form an electrostatic latent image pattern on the photoreceptor 7C. Thereafter, toner is supplied from the developing unit 8C onto the photoreceptor 7C, and the toner image is developed. The toner image developed on the photoconductor 7C is primarily transferred to a transfer belt 9 as an intermediate transfer member, and then, the secondary transfer unit 102 performs secondary transfer on the reversely conveyed paper, and the fixing unit 11 performs paper transfer. Fix the toner on top.

  Finally, when developing the fourth color (black K), the pulse generator 135 converts the image data screen-processed by the halftone generator 134 into the printer engine 140 in accordance with a control signal from the controller 136. Is converted into a pulse signal for driving the laser beam and output to the laser driving unit 4K. The laser driver 4K irradiates light based on the pulse signal from the pulse generator 135, and forms an electrostatic latent image pattern on the photoconductor 7K. Thereafter, toner is supplied from the developing unit 8K onto the photoreceptor 7K, and the toner image is developed. The toner image developed on the photoconductor 7K is primarily transferred to a transfer belt 9 as an intermediate transfer member, and then the secondary transfer unit 102 performs secondary transfer on the reversely conveyed paper, and the fixing unit 11 performs paper transfer. Fix the toner on top.

  According to the first embodiment, by repeating the printing process from transfer to fixing for each color four times, it is possible to prevent a periodic change in the halftone dot shape due to the collapse of the toner image. Occurrence of moiré peculiar to photographs can be suppressed, and a print output with good image quality can be obtained.

  Next, a second embodiment will be described. In the second embodiment, the printing process is controlled using the moire pitch obtained by calculation. Since the second embodiment has the same configuration as the system 100 of the first embodiment, it will be described with reference to FIG. The conspicuousness of moiré is due to the moire pitch (periodic interval) generated by the interference of halftone dots of each color. Generally, the larger the moire pitch, the more noticeable. Therefore, the moire pitch can be used as a reference for the conspicuousness of the moire.

  The control unit 136 determines whether the moire pitch stored in the storage unit 134a is different from each other by comparing the moiré pitch stored in the storage unit 134a with a predetermined threshold, and if the moire pitch is larger than the set threshold. Separate the printing process. On the contrary, when the array pitch is smaller than the set threshold value, it is determined that the moire generated between the two colors is not noticeable, and both are printed in the same process. The moire pitch can be obtained by calculation from the number of screen lines and the screen angle stored in advance in the storage unit 134a. The moire pitch obtained by calculation is stored in advance in the storage unit 134a.

  When the halftone generation unit 134 has only one set of screen parameters, the control unit 136 may always perform printing using the printing process determined by this method. Note that, here, an example of using a moiré pitch obtained by calculation is shown as a criterion for determining how moiré is conspicuous. However, how moiré is conspicuous may be determined by other methods.

  Next, a method for determining a printing process will be described with reference to FIG. FIG. 6 is an example in which the printing operation ends in the second process. In addition, when the transfer order to the intermediate transfer member is the order of Y, M, C, and K, the control unit 136 sets the process priority order as Y, M, C, and K.

  FIG. 6 is a diagram for explaining a printing process determination method based on the moire pitch according to the second embodiment. FIG. 6A shows yellow and magenta stored in the storage unit 134a of the halftone generation unit 134. FIG. The figure which shows the combination of the screen angle of cyan and black, and the number of screen lines, the figure (b) is a figure explaining the determination method in a 1st process, The figure (c) is the determination method of a 2nd process. FIG.

  As shown in FIG. 6A, the four screen lines of yellow, magenta, cyan, and black are all 175 lines, and the screen angles are 0 degree, 15 degrees, 75 degrees, and 45 degrees, respectively. The moire pitch calculated based on these is stored in advance in the storage unit 134a. Here, the threshold for determining whether or not to perform the same process is 0.5 [mm], and the control unit 136 performs control so that the printing process is divided when the moire pitch is larger than the threshold of 0.5 [mm]. To do.

  As shown in FIG. 6B, the control unit 136 first prints yellow Y in the first process. Next, for magenta M, since the moire pitch generated by yellow Y and magenta M is about 0.6 [mm], control unit 136 rotates magenta M after the next process. For cyan C, the moire pitch generated in yellow Y and cyan C is about 0.6 [mm], so that the cyan C is printed after the next process. The control unit 136 prints the black B in the same process as the yellow Y because the moire pitch generated in the black Y is about 0.2 [mm].

  As shown in FIG. 6C, in the second process, the control unit 136 determines that yellow Y has already been printed, and performs printing processing for magenta M. For cyan C, the moire pitch generated between magenta M and cyan C is about 0.3 [mm], and therefore cyan C is printed in the same process as magenta M.

  According to the second embodiment, the printing process of each color is determined using the moire pitch, the pulse generator 135 is controlled, yellow Y and black K are processed in the first process, and the second process is performed. Since magenta M and cyan C are processed, print output with good image quality can be obtained with a small number of times while suppressing the occurrence of moire due to screen interference.

  In the above description, the control unit 136 compares the moire pitch stored in advance in the storage unit 134a with a predetermined threshold value, and if three colors are not conspicuous in the same manner, the three colors may be processed in the same process. Good. In addition, the control unit 136 may not separately perform the process of the color plane where no image exists. That is, the control unit 136 may refer to the input image data to the halftone generation unit 134, and may not perform the cyan printing process when, for example, a cyan image does not exist.

  A third embodiment will be described. In the third embodiment, similarly to the second embodiment, the printing process is controlled by using the moire pitch obtained by calculation. However, the screen angle is different from that of the second embodiment. For this reason, the moire pitch determined by the number of screen lines and the screen angle is also different from that of the second embodiment. This moire pitch is also obtained in advance by calculation and stored in the storage unit 134a. Since the third embodiment has the same configuration as the system 100 of the first embodiment, it will be described with reference to FIG.

  A method for determining the printing process will be described with reference to FIG. FIG. 7 is a diagram for explaining a printing process determination method based on the moire pitch according to the third embodiment. FIG. 7A shows yellow and magenta stored in the storage unit 134a of the halftone generation unit 134. FIG. The figure which shows the combination of the screen angle | corner and screen line number of cyan and black, the figure (b) is a figure for demonstrating the determination method of a 1st process, The figure (c) demonstrates the determination method of a 2nd process. It is a figure for doing.

  As shown in FIG. 7A, the four screen lines of yellow, magenta, cyan, and black are all 175 lines, and the screen angles are 75 degrees, 15 degrees, 0 degrees, and 45 degrees, respectively. The number of screen lines and the screen angle are stored in advance in the storage unit 134a. The moire pitch calculated based on these is also stored in the storage unit 134a in advance.

  Here, the threshold for determining whether or not to perform the same process is 0.5 [mm], and the control unit 136 divides the printing process when the moire pitch is larger than the threshold of 0.5 [mm]. FIG. 7 shows an example in which the printing operation ends in the second process. When the transfer order to the intermediate transfer member is the order of Y, M, C, and K, the control unit 136 sets the process priority to the order of Y, M, C, and K. The control unit 136 compares the predetermined threshold value with the moire pitch stored in the storage unit 134a and determines the printing process as follows.

  As shown in FIG. 7B, in the first process, the control unit 136 first prints yellow Y. Next, for magenta M, the control unit 136 prints magenta M in the same process as yellow Y because the moire pitch generated between yellow Y and magenta M is about 0.3 [mm]. Next, for cyan C, the moire pitch generated in yellow Y and cyan C, magenta M and cyan C is about 0.6 [mm] for cyan C. Turn

  Next, for black K, the moire pitch generated by yellow Y and black K is about 0.3 [mm], so that black K is printed in the same process as yellow Y or the like. . As shown in FIG. 7C, the control unit 136 determines that yellow Y and magenta M have been printed in the second process, and prints cyan C in the second process.

  As described above, according to the third embodiment, the printing process of each color is determined using the moire pitch, the pulse generator 135 is controlled, and yellow Y, magenta M, and black K are printed in the first process. Since cyan C is printed in the second process, it is possible to obtain a print output with good image quality with a small number of times of printing while suppressing the occurrence of moire peculiar to electrophotography due to screen interference. .

  A fourth embodiment will be described. In the fourth embodiment, the printing process is controlled by using the angle difference of the screen as a reference for the conspicuousness of moire. Since the fourth embodiment has the same configuration as the system 100 of the first embodiment, it will be described with reference to FIG. Note that the screen angle difference is stored in the storage unit 134a as in the above embodiment.

  When the number of screen lines of the two colors is the same, the moire pitch increases as the screen angle decreases. Therefore, the angle difference of the screen can be used as a reference for the conspicuousness of moire. The control unit 136 compares the screen angle difference stored in the storage unit 134a with a predetermined threshold value, determines whether the moiré colors are inconspicuous, and determines whether the process is divided. When the angle difference is small, the printing process is divided.

  On the contrary, when the screen angle difference is larger than the set threshold, it is determined that the moire generated between the two colors is not noticeable, and both are printed in the same process. The screen angle difference can be obtained by calculation from the screen angle stored in advance in the storage unit 134a, and the screen angle difference obtained by the calculation is stored in advance in the storage unit 134a.

  A method for determining the printing process will be described with reference to FIG. FIG. 8 is a diagram for explaining a printing process determination method based on the screen angle difference according to the fourth embodiment. FIG. 8A shows yellow stored in the storage unit 134 a of the halftone generation unit 134. The figure which shows the combination of the screen angle of magenta, cyan, and black, and the number of screen lines, the figure (b) is a figure for demonstrating the determination method of a 1st process, The figure (c) is the determination method of a 2nd process It is a figure for demonstrating.

  As shown in FIG. 8A, the four screen lines of yellow, magenta, cyan, and black are all 175 lines, and the screen angles are 0 degree, 15 degrees, 75 degrees, and 45 degrees, respectively. Here, the threshold of the screen angle difference when determining whether to perform the same process is 20 degrees, and the control unit 136 divides the printing process when the screen angle difference is smaller than 20 degrees. FIG. 8 shows an example in which the printing operation ends in the second process. When the transfer order to the intermediate transfer member is the order of Y, M, C, and K, the control unit 136 sets the process priority to the order of Y, M, C, and K.

  The control unit 136 determines the printing process as follows by comparing the predetermined threshold value with the angle difference of the screen stored in the storage unit 134a. As shown in FIG. 8B, in the first process, the control unit 136 first prints yellow Y. Next, for magenta M, the control unit 136 rotates magenta M after the next process because the angle difference between yellow Y and magenta M is 15 degrees. Next, for cyan C, since the angle difference between yellow Y and cyan C is 15 degrees, the control unit 136 rotates cyan C after the next process. Next, for black K, the angle difference between yellow Y and black K is 45 degrees, so black K is printed in the same process as yellow Y.

  As shown in FIG. 8C, the control unit 136 determines that yellow Y has been printed in the second process, and prints magenta M in the second process. Next, since the angle difference between magenta M and cyan C is 30 degrees, the control unit 136 prints cyan C in the same process as magenta M.

  As described above, according to the fourth embodiment, the printing process of each color is determined using the angle difference of each color screen, the pulse generator 135 is controlled, and the printing of yellow Y and black K is performed in the first process. In the second process, printing of magenta M and cyan C is performed, so that print quality with good image quality can be achieved with a small number of printings while suppressing the occurrence of moire peculiar to electrophotography due to screen interference. Can be obtained.

  A fifth embodiment will be described. In the fifth embodiment, as in the fourth embodiment, the printing process is controlled by using the angle difference of the screen as a reference for the conspicuousness of moire. The fifth embodiment has the same configuration as the system 100 of the first embodiment, and will be described with reference to FIG. Note that the screen angle difference is stored in the storage unit 134a as in the above embodiment.

  A method for determining the printing process will be described with reference to FIG. FIG. 9 is a diagram for explaining a printing process determination method based on the screen angle difference according to the fifth embodiment. FIG. 9A shows yellow stored in the storage unit 134 a of the halftone generation unit 134. , M, magenta, cyan and black showing the combination of the screen angle and the number of screen lines, FIG. 5B is a diagram explaining the determination process of the first process, and FIG. 4C is a diagram explaining the determination process of the second process. It is a figure to do.

  As shown in FIG. 9A, the four screen lines of yellow, magenta, cyan, and black are all 175 lines, and the screen angles are 75 degrees, 15 degrees, 0 degrees, and 45 degrees, respectively. Here, the threshold of the screen angle difference when determining whether to perform the same process is 20 degrees, and the control unit 136 divides the printing process when the screen angle difference is smaller than 20 degrees. FIG. 9 shows an example in which the printing operation ends in the second process. When the transfer order to the intermediate transfer member is the order of Y, M, C, and K, the control unit 136 sets the process priority to the order of Y, M, C, and K.

  The control unit 136 determines the printing process as follows by comparing the predetermined threshold value with the angle difference of the screen stored in the storage unit 134a. As shown in FIG. 9B, in the first process, the control unit 136 first prints yellow Y. Next, for magenta M, the control unit 136 prints magenta M in the same process as yellow Y because the angle difference between yellow Y and magenta M is 30 degrees.

  Next, for cyan C, since the angle difference between yellow Y and cyan C is 15 degrees, the control unit 136 rotates cyan C after the next process. Next, for black K, the angle difference between yellow Y and black K is 30 degrees, so black K is printed in the same process as yellow Y. As shown in FIG. 9C, since the yellow Y and magenta M have already been printed in the second process, the control unit 136 determines to print cyan C in the second process.

  As described above, according to the fifth embodiment, the angle difference between the color screens is used to determine the printing process for each color, and the pulse generator 135 is controlled so that yellow Y, magenta M, and black K are used in the first process. In the second process, Cyan C is printed. Therefore, it is possible to produce prints with good image quality with a small number of printings while suppressing the occurrence of moiré unique to electrophotography due to screen interference. Obtainable.

  Next, a sixth embodiment will be described. In the present embodiment, a plurality of combinations of screen parameters are stored in the ROM of the intermediate generation unit 234 so that the screen parameters can be switched according to the mode specified by the user.

  FIG. 10 is a block diagram of a system 200 according to the sixth embodiment. As shown in FIG. 10, the system 200 includes a PC 210 and a printer 220. The PC 210 has an application 111 and a print driver 212. The printer 220 includes an image processing unit 230 and a printer engine 140. The image processing unit 230 includes a PDL interpretation unit 131, a drawing unit 132, a rendering unit 133, a halftone generation unit 234, a pulse generation unit 135, and a control unit 236. Note that the same portions as those in the above embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  The printer driver 212 includes a command for designating a screen in the PDL and outputs it to the printer 220. That is, when the printer driver 212 outputs the image data created by the application software 211 to the printer 220, the printer driver 212 includes a command for designating a plurality of screens that the halftone generation unit 234 has in the PDL.

  The PDL interpretation unit 131 interprets the PDL as a command and outputs a command for designating a screen to the control unit 236. The drawing unit 132 generates an intermediate code for drawing according to the interpretation of the image data by the PDL interpretation unit 131, and performs color conversion, γ correction, and the like as necessary. The rendering unit 133 renders the image data for one page suitable for the printer engine 140 together with the intermediate code generated by the drawing unit 122.

  The halftone generation unit 234 has a plurality of screens A and B, and performs screen processing on the image data output from the rendering unit 133 according to a screen-designated command included in the PDL. The halftone generation unit 234 includes the storage unit 134a described in the first embodiment, although not illustrated.

  The control unit 236 controls the pulse signal output from the pulse generation unit 135 based on the command from the PDL interpretation unit 131, the screen parameter stored in the intermediate generation unit 234, and the position of the transport unit 101. For example, as described in the above embodiment, the control unit 236 prints yellow Y and black B in the first process and prints magenta M and cyan C in the next second process in response to the screen designation command. To do. The printer engine 140 executes printing in a printing process corresponding to the screen designation command.

  According to the sixth embodiment, the screen parameters are switched in accordance with the screen designation command from the printer driver 212 to divide the process, so that good image quality can be obtained in any mode.

  Next, a seventh embodiment will be described. In the seventh embodiment, the user can freely specify the number of lines and the angle of the screen from the printer driver. In this case, the control unit 336 makes the moire inconspicuous by changing the printing process according to the parameter designated by the user.

  FIG. 11 is a block diagram of a system 300 according to the seventh embodiment. As shown in FIG. 11, the system 300 includes a PC 310 and a printer 320. The PC 310 has an application 311 and a print driver 312. The printer 320 includes an image processing unit 330 and a printer engine 140. The image processing unit 330 includes a PDL interpretation unit 131, a drawing unit 132, a rendering unit 133, a halftone generation unit 334, a pulse generation unit 135, and a control unit 336. About the same location as the said Example, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

  The printer driver 312 calculates a printing process in which moire is not conspicuous based on the number of lines and angle specified by the user, inserts the printing process into the PDL as a command, and sends it to the printer 320. Here, the printer driver 312 calculates a printing process using a screen line number, a moire pitch based on a screen angle, and a screen angle as a printing process in which moire is not noticeable.

  The PDL interpretation unit 131 interprets the PDL command and outputs a command for designating a screen to the control unit 336. The drawing unit 132 generates an intermediate code for drawing according to the interpretation of the image data by the PDL interpretation unit 131, and performs color conversion, γ correction, and the like as necessary. The rendering unit 133 renders the image data for one page suitable for the printer engine 140 together with the intermediate code generated by the drawing unit 122.

  The halftone generation unit 334 performs screen processing on the image data output from the rendering unit 133 according to a user-designated screen. The halftone generation unit 334 includes the storage unit 134a described in the first embodiment, although not illustrated.

  The control unit 336 controls the pulse signal output from the pulse generation unit 135 based on the command from the PDL interpretation unit 131, the screen parameters stored in the halftone generation unit 334, the position of the paper reverse conveyance unit 101, and the like. For example, as described in the above embodiment, the control unit 336 prints yellow Y and black B in the first process and prints magenta M and cyan C in the next second process in response to the screen designation command. To do. The printer engine 140 executes printing in a printing process corresponding to a command designated by the user.

  According to the seventh embodiment, according to the screen command designated by the user, the screen parameters are switched to divide the process, so that good image quality can be obtained in any mode.

  Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications, within the scope of the gist of the present invention described in the claims, It can be changed. For example, although the present embodiment has been described using a printer, the image forming apparatus of the present invention can also be applied to, for example, a digital electrophotographic copying machine, a FAX, or the like. In each of the above embodiments, an electrophotographic printer having an intermediate transfer member has been described as an example of a printing method. However, in the case of a printer that directly transfers from a photosensitive member to paper without using an intermediate transfer member. However, the technique of the present invention can be applied by replacing the intermediate transfer member with paper.

It is a block diagram of a conventional electrophotographic printer. FIG. 6 is an enlarged view of an image on a transfer belt when a secondary color image is printed. It is a figure which shows the example of the screen of the shape where the conventional moire is not conspicuous. 1 is a block diagram of a system according to a first embodiment. 1 is a configuration diagram of an image forming apparatus according to a first embodiment. It is a figure for demonstrating the printing process determination method 1 on the basis of the moire pitch by 2nd Example. It is a figure for demonstrating the printing process determination method 2 on the basis of the moire pitch by 3rd Example. It is a figure for demonstrating the printing process determination method 1 on the basis of the screen angle difference by 4th Example. It is a figure for demonstrating the printing process determination method 2 on the basis of the screen angle difference by 5th Example. It is a block diagram of the system concerning a 6th example. It is a block diagram of the system concerning a 7th example.

Explanation of symbols

100 System 101 Transport unit 110, 210, 310 PC
111, 311 Application 112, 212, 312 Printer driver 120, 220, 320 Printer 130, 230, 330 Image processing unit 131 PDL interpretation unit 132 Rendering unit 133 Rendering unit 134, 234, 334 Halftone generation unit 134a Storage unit 135 Pulse generation Part 136, 236 control part 140, printer engine

Claims (6)

The toner image forming unit forms toner images of different colors on the image carrier using a screen that expresses the gradation of the image, and primarily transfers the toner image on the image carrier to the intermediate transfer member. An image in which a toner image formed on a body is secondarily transferred onto a recording material at a secondary transfer portion, and a toner image on the recording material secondarily transferred by the secondary transfer portion is fixed at a fixing portion. In the forming device,
A transport unit that transports the recording material fixed by the fixing unit to a secondary transfer position by the secondary transfer unit;
A control unit that controls each of the units so that the process is performed for each predetermined color unit when a plurality of color toner images are formed on the image carrier;
Based on the screen information including the number of lines of the screen, the angle of the screen, the moire pitch generated by the interference of halftone dots of each color, or the angle difference of each screen, the toner images of the plurality of colors are the same in each of the processes. An image forming apparatus comprising: a determination unit that determines whether to transfer to the intermediate transfer member or the recording material in a process. Toner images of different colors are formed on the image carrier by a toner forming means using a screen expressing the gradation of the image, and the toner image on the image carrier is transferred onto a recording material by a transfer unit, In an image forming apparatus that performs a process of fixing a toner image on a recording material transferred by a transfer unit by a fixing unit,
A transport unit that transports the recording material fixed by the fixing unit to a transfer position by the transfer unit;
A control unit that controls each of the units so that the process is performed for each predetermined color unit when a plurality of color toner images are formed on the image carrier;
Based on the screen information including the number of lines of the screen, the angle of the screen, the moire pitch generated by the interference of halftone dots of each color, or the angle difference of each screen, the toner images of the plurality of colors are the same in each of the processes. An image forming apparatus comprising: a determination unit that determines whether or not to transfer to the recording material in a process. The image forming apparatus according to claim 1, wherein the control unit controls the units so as to perform the process for each different color. A first step of forming a toner image on the image carrier using a screen expressing the gradation of the image; a second step of primarily transferring the toner image on the image carrier to an intermediate transfer member; A third step in which the toner image formed on the intermediate transfer member is secondarily transferred onto the recording material by the secondary transfer unit; and a toner image on the recording material secondarily transferred by the secondary transfer unit. A fourth step of fixing by the fixing unit, a fifth step of conveying the recording material fixed by the fixing unit to a secondary transfer position by the secondary transfer unit, the number of lines of the screen, the angle of the screen, and each color Based on screen information including a moire pitch generated by the interference of halftone dots or an angle difference between the screens, the toner images of the plurality of colors are subjected to the intermediate step in the same step from the first step to the fourth step. Transcription Or and a sixth step of determining whether to transfer to the recording material,
An image forming method, wherein when a plurality of color toner images are formed on the image carrier, the first to fourth steps are performed for each predetermined color unit. A first step of forming a toner image on the image carrier using a screen expressing the gradation of the image, and a second step of transferring the toner image on the image carrier onto a recording material by a transfer unit; A third step of fixing the toner image on the recording material transferred by the transfer unit by the fixing unit, and a fourth step of conveying the recording material fixed by the fixing unit to a transfer position by the transfer unit; Based on the screen information including the number of lines of the screen, the angle of the screen, the moire pitch caused by the interference of halftone dots of each color, or the angle difference of each screen, the toner images of the plurality of colors are obtained from the first step. A fifth step of determining whether to transfer to the recording material in the same step of the third step,
An image forming method, wherein when a plurality of color toner images are formed on the image carrier, the first step to the third step are performed for each predetermined color unit. Wherein the screen information, the moire pitch or image forming method according to claim 4 or 5, wherein said either of the angular difference of each screen.

Images