JP5335221B2 - Image forming apparatus and image forming method for controlling total amount of toner in trap - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of reducing the amount of toner at a position at which the trapping is carried out. <P>SOLUTION: The apparatus has an image deformation processing unit 110 where input image data is processed to deform the image shape or the trapping or overprinting is carried out on the respective color plates. The image deformation processing unit 110 determines whether or not the trapping should be carried out to the target pixels on the boundary between color plates in the adjacent different objects, determines the color plate having the trap color, obtains the amount of toner of the trap color, determines based on the amount of toner of the trap color and the target pixels whether or not the total amount of toner of the trap exceeds the limit value, and reduces the total amount of toner if the total amount of toner of the trap exceeds the limit value. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a technique for controlling the total amount of toner when printing a color image.

  Trapping means providing a portion (hereinafter referred to as “trap”) that slightly overlaps the boundary between two adjacent objects having different colors in order to prevent occurrence of misregistration. Therefore, the total amount of toner in the trap often exceeds a toner amount limit value set in advance in a printer unit or printer such as a copying machine. The total toner amount means the sum of the pixel values (toner amounts) of each pixel of each color plate, and the unit is percent (%). When the total amount of toner in the trap exceeds the limit value, toner scatters in the trap, resulting in a problem that image quality deteriorates. In order to avoid this problem, it is necessary to control the total amount of toner so that the total amount of toner in the trap does not exceed the limit value.

  As an example of a method for controlling the total amount of toner, for example, there is a method disclosed in Patent Document 1. This method will be briefly described below.

  5 and 7 are views for explaining a conventional mechanism for reducing the total amount of toner.

  701 in FIG. 7 shows an enlarged view of 501 in FIG. Reference numeral 701 denotes a state before trapping two adjacent objects. Reference numeral 702 denotes a state after trapping the two objects. Reference numeral 703 denotes a state where the total amount of toner in the trap is reduced. As can be seen from 702, the total amount of toner in the trap before trapping is 300% (C plate: 100%, M plate: 100%, Y plate: 100%, K plate: 0%). C, M, Y, and K indicate cyan, magenta, yellow, and black, respectively. Assuming that the toner amount limit value is 200%, the total toner amount of the trap exceeds the toner amount limit value. Therefore, in this method, as shown at 703, the total amount of toner in the trap is reduced by performing UCR (Under Color Removal). That is, in this method, the toner amounts of the C plate, M plate, and Y plate are reduced, while the K plate toner amount is newly added. Thus, the total toner amount of the trap is reduced from 300% to 200% (C plate: 50%, M plate: 50%, Y plate: 50%, K plate: 50%) while maintaining the brightness of the trap.

  FIG. 8 is a diagram illustrating the configuration of the color plate before the reduction of the total amount of toner and the configuration of the color plate after the reduction of the total amount of toner.

  As indicated by reference numeral 801 in the figure, it is assumed that the configuration of the toner amount of each color plate before reducing the total toner amount is C plate (100%), M plate (100%), and Y plate (100%). By performing UCR, the composition of the toner amount of each color plate becomes C plate (50%), M plate (50%), Y plate (50%), and K plate (50%).

  On the other hand, 704 shows an enlarged view of 502. Reference numeral 704 denotes a state before trapping two adjacent objects. Reference numeral 705 denotes a state after trapping the two objects. Reference numeral 706 denotes a state where the total amount of toner in the trap is reduced. As can be seen from 705, the total amount of toner in the trap before trapping is 300% (C plate: 100%, M plate: 100%, Y plate: 0%, K plate: 100%). Assuming that the limit value of the total toner amount is 200%, the total toner amount of the trap exceeds the limit value of the total toner amount. Therefore, in this method, as shown by reference numeral 706, the total toner amount of the C plate and the M plate is reduced to reduce the total toner amount of the trap from 300% to 200% (C plate: 50%, M plate: 50%, Y Plate: 0%, K plate: 100%).

  As indicated by reference numeral 802 in the figure, the constitution of the toner amount of each color plate before reducing the total toner amount is assumed to be C plate (100%), M plate (100%), and K plate (100%). By reducing the amount of toner for each of the C and M plates, the composition of the toner amount for each color plate becomes C plate (50%), M plate (50%), and K plate (100%).

JP 2005-161580 A

  However, there are two problems that must be solved in the above-described prior art.

  The first problem is that a K version is newly added in the trap as indicated by reference numeral 703 in FIG.

  The second problem is that the trap color toner amount becomes lower than the desired toner amount, as indicated by reference numeral 704 in FIG.

  The same can be said for a portion where overprinting is performed under which the surrounding color plate is inserted under the K plate.

  The first problem will be specifically described.

  As indicated by reference numeral 701 in FIG. 7, the color plate of the left object is composed of the C plate (100%) and the M plate (100%), and the color plate of the right object is the Y plate (100%). . Trapping is performed such that the right object overlaps the left object, as indicated by 702 in FIG. In this case, since the trap color is the color plate of the right object, that is, the Y plate (100%), by performing trapping, the trap color plate is the C plate (100%) and the M plate (100%). , Y composition (100%). That is, the total amount of toner in the trap after trapping is 300%. Generally, as indicated by reference numeral 702 in FIG. 7, an object composed of a color plate other than the C plate and the M plate is replaced with an object composed of the C plate and the M plate having a large total toner amount. Trapping is performed so that they overlap.

  In the case of electrophotography, the limit value of the total amount of toner is determined in advance as described above in consideration of the situation such as toner fixing and peeling. If the limit value of the total toner amount is 200%, the total toner amount in the trap is 300%, which exceeds the limit value. Therefore, the total toner amount is reduced to the limit value by performing the conventional processing for suppressing the total toner amount (hereinafter referred to as “toner reduction”). When toner reduction is performed, the total amount of toner in the trap is reduced to 200%. The composition of the color plate at that time is C plate (50%), M plate (50%), Y plate (50%), and K plate (50%). As shown in FIG. 6, the toner reduction is performed by superposing the C plate, M plate, and Y plate having the same toner amount, and the color of the K plate having the same toner amount as that of the color plate. It uses the property of being the same as brightness. By using toner reduction, 50% of the toner amount (100%) of the C plate, M plate, and Y plate is replaced with the K plate (50%), so that the total toner amount in the trap is changed from 300% to 200%. %. However, since the K plate is a color plate that did not originally exist, there arises a problem that when the K plate is shifted, a K plate that should not exist originally appears around the trap.

  Next, the second problem will be specifically described.

  As indicated by reference numeral 704 in FIG. 7, it is assumed that the color plate of the left object is composed of the C plate (100%) and the K plate (100%), and the color plate of the right object is the M plate (100%). . Trapping is performed such that the right object overlaps the left object, as indicated by reference numeral 705. In this case, since the trap color is the color plate of the object on the right side, that is, the M plate (100%), by performing trapping, the trap color plate is the C plate (100%) and the K plate (100%). , M version (100%). That is, the total amount of toner in the trap after trapping is 300%.

  As described above, in the case of electrophotography, the limit value of the total amount of toner is predetermined. If the limit value of the total toner amount is 200%, the total toner amount in the trap is 300%, which exceeds the limit value. Therefore, by performing toner reduction, as indicated by reference numeral 706, the total toner amount is lowered to the limit value. When toner reduction is performed, the total amount of toner in the trap is reduced to 200%. The composition of the color plate at that time is C plate (50%), M plate (50%), and K plate (100%). The total toner amount of the M plate, which is the trap color, was originally 100%, but the total toner amount of the M plate is reduced to 50% by toner reduction, and the toner amount of the trap color becomes smaller than the desired toner amount. Taking into account that the purpose of trapping is to make plate misalignment inconspicuous even when misregistration occurs, when the M plate reaches 50%, the effect of trapping is sufficiently obtained when misregistration occurs. I can't.

The image forming apparatus according to the present invention includes an input unit that inputs an image, a trap unit that traps a target pixel at a boundary between adjacent color plates of different objects, and a total toner amount of the target pixel after the trapping. Determining means for determining whether or not the limit value is exceeded, and reducing the toner amount of the color plate other than the black plate without changing the toner amount of the black plate when it is determined that the total toner amount exceeds the limit value By performing the processing for the pixel of interest, a reduction unit that reduces the total amount of toner and the trap unit perform trapping, and the image processed by the reduction unit is formed on a recording medium. Forming means.

In the image forming method of the present invention, an input step for inputting an image, a trap step for trapping a target pixel at a boundary between color plates of different adjacent objects, and a total toner amount of the target pixel after the trapping A determination step for determining whether or not the limit value is exceeded, and when it is determined that the total toner amount exceeds the limit value, the toner amount of the color plate other than the black plate is reduced without changing the toner amount of the black plate. By performing the process on the target pixel , the trapping is performed in the reduction step of reducing the total toner amount and the trap step, and the image processed in the reduction step is formed on the recording medium. Forming step.

  According to the present invention, it is possible to solve the problem that the K plate newly appears in the trap and the problem that the toner amount of the trap color is smaller than the desired toner amount.

  Further, according to the present invention, since the total amount of toner can be controlled to an optimum amount according to the brightness and density of the pixel, the image quality in the trap does not deteriorate.

  Furthermore, the present invention can be applied to locations where overprinting has been performed and locations where trapping has not been performed.

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

  The image forming apparatus according to the embodiment of the present invention is a copying machine such as a digital multifunction peripheral, but may be other printing devices such as a color printer in addition to the copying machine.

  First, the configuration of the image forming apparatus will be described with reference to the drawings.

  FIG. 1 is a block diagram illustrating a configuration example of the image forming apparatus 100.

  The image forming apparatus 100 includes a scanner 101, an image receiving unit 102, an image processing unit 103, a storage unit 104, a CPU 105, and an image output unit 106. The image processing unit 103 includes a scanner image processing unit 108, a printer image processing unit 109, and an image deformation processing unit 110. The image forming apparatus 100 is also connected to a server that manages image data and an external device such as a personal computer (PC) that instructs various image forming apparatuses to execute printing via a network 107 such as a LAN or the Internet. Is possible.

  Next, functions of the above-described components constituting the image forming apparatus 100 will be described.

  The scanner 101 outputs an input image (for example, RGB color signal) to the scanner image processing unit 108. The scanner image processing unit 108 performs image processing such as shading correction, image area separation processing, and color conversion on the received RGB color signal.

  The image receiving unit 102 outputs the PDL data received from the external device to the printer image processing unit 109. The printer image processing unit 109 interprets a command group included in the received PDL data and outputs an intermediate code.

  The printer image processing unit 109 converts the intermediate code into a bitmap image using a built-in RIP (Raster Image Processor). Further, the printer image processing unit 109 generates attribute information based on the attributes of the command group included in the PDL data.

  The image transformation processing unit 110 performs processing for changing the image shape of the image data received from the scanner image processing unit 108 and the image data received from the printer image processing unit 109, trapping, overprinting, and the like according to the present embodiment. Different processing is performed for each color plate.

  The quantization processing unit 112 or the like performs dither processing or the like.

  Next, configurations and functions of the storage unit 104, the CPU 105, and the image output unit 106 will be described.

  The storage unit 104 includes a RAM, a ROM, and the like. The CPU 105 executes various processes according to programs stored in the ROM. The image output unit 106 outputs an image on a recording sheet. That is, the image output unit 106 forms an image on the recording paper.

  In general, there are two types of processing, such as trapping and overprinting, which are different for each version, performed in the object database in the RIP and performed on the rendered bitmap. In this embodiment, both cases are applicable.

  Next, the structure of the image forming apparatus 100 will be described with reference to the drawings.

  FIG. 13 is a diagram illustrating the structure of the scanner 101, the image receiving unit 102, and the image output unit 106 of the image forming apparatus 100. In the drawing, a top view and a side view of a document table of the image forming apparatus 100 are shown together with a structural diagram of the image forming apparatus 100.

  The image forming apparatus 100 is a digital multi-function peripheral having a copy, printer, and FAX function.

  The image forming apparatus 100 includes a scanner 301, a document feeder 302, a print recording printer 313 including a color four-color drum, a paper feed deck 314, a finisher 315, and the like.

  A document reading operation by the scanner 301 will be described.

  First, a reading operation of a document placed on the document table 307 will be described.

  The user places a document on the document table 307 and closes the document feeder 302. When the open / close sensor 340 detects that the document table 307 is closed, the light reflection type document size detection sensors 331 to 335 detect the size of the document placed on the document table. When the size of the document is detected, the light source 310 irradiates the document. The CCD 343 receives the light reflected by the document via the reflecting plate 311 and the lens 312 and acquires an image signal. A controller (not shown) converts the image signal acquired by the CCD 343 into digital image data. Next, the controller performs desired image processing on the digital image data to generate print image data. Next, the controller temporarily stores the print image data in a memory in the controller.

  Next, a reading operation of a document placed on the document feeder 302 will be described.

  The user places the document face up on the tray of the document setting unit 303 of the document feeder 302. When the document presence / absence sensor 304 detects that a document is set in the document feeder 302, the document feed roller 305 and the transport belt 306 are rotated, whereby the document is transported to a predetermined position on the document table 307. . Next, an operation similar to the reading operation of the document placed on the document table 307 is performed, and the image data is temporarily stored in the memory in the controller.

  When the reading of the original is completed, the conveyance belt 306 rotates again. As a result, the document on the document table 307 is transported to the document discharge tray 309 via the discharge-side transport roller 308 and discharged outside the apparatus.

  When there are a plurality of documents, another document is placed at a predetermined position on the document table 307 via the feed roller 305 in parallel with the document on the document table 307 being conveyed to the document discharge tray 309. Then, the original is read.

  Next, a printing operation by the printer 313 will be described.

  The print image data once stored in the memory in the controller is sent to the printer 313. A laser unit in the printer 313 converts print image data into four colors of laser light of Yellow, Magenta, Cyan, and Black, and irradiates the photoconductor 316 of each color. Thereby, an electrostatic latent image is formed on each photoconductor 316. Next, the printer 313 develops and visualizes the electrostatic latent image formed on each photoconductor 316 using toner supplied from the toner cartridge 317. The image visualized on each photoconductor is primarily transferred to the intermediate transfer belt 321. When the recording paper conveyed through the paper feeding conveyance path 319 from the paper cassette 318 or the paper feeding deck 314 reaches the secondary transfer position 320, the image transferred to the intermediate transfer belt 321 is further transferred to the recording paper. The When the fixing device 322 applies pressure and heat to the recording paper on which the image is transferred, the toner is fixed on the recording paper. Next, the recording sheet is conveyed through a sheet ejection conveyance path to a face-down center tray 323, a finisher sheet ejection port 324, or a face-up side tray 325. The side tray 325 is a discharge port that can be used only when the finisher 315 is not attached. The flappers 326 and 327 switch these paper discharge ports by switching the transport path.

  In the case of duplex printing, when the recording paper passes through the fixing device 322, the flapper 327 switches the conveyance path, so that the recording paper is conveyed again to the secondary transfer position 320 through the duplex printing conveyance path 330. .

  Next, the operation of the finisher 315 will be described.

  The finisher 315 performs post-processing on the printed paper according to the setting by the user. Specifically, stapling (one or two stitches), punching (two or three holes), bookbinding saddle stitching, or the like is executed.

  The image forming apparatus 100 includes two paper discharge trays 328. The paper discharge tray 328 for the recording paper that has passed through the paper discharge port 324 to the finisher 315 is switched according to the setting (for example, copy, printer, FAX) by the user.

  The print engine 313 is a color 4 drum or color 1 drum printer engine or a monochrome recording printer engine. For the image forming apparatus 100, monochrome printing / color printing, paper size, 2UP / 4UP / N-UP printing, duplex printing, stapling, punching, bookbinding saddle stitching, slip sheet printing, front cover printing, back cover printing Etc. can be set.

<First Embodiment of Total Toner Reduction Processing>
A first embodiment of the total toner amount reduction process will be described with reference to the drawings.

  FIG. 2 is a flowchart showing a toner total amount reduction process.

  This processing is executed by the image deformation processing unit 110 in the image forming apparatus 100. This process is performed on image data read by the scanner 301 or image data after RIP, but may be performed on intermediate data before RIP.

  In step S <b> 202, the image transformation processing unit 110 determines whether or not to perform trapping on the pixel of interest at the boundary between color plates of different adjacent objects. Trapping is performed for each pixel.

  In step S203, the image transformation processing unit 110 determines a color plate to be used as a trap color.

  In step S <b> 204, the image deformation processing unit 110 calculates a trap color toner amount.

  In S205, the image transformation processing unit 110 determines whether the total toner amount of the trap exceeds the limit value based on the toner amount of the trap color and the toner amount of the target pixel, and the total toner amount of the trap exceeds the limit value. If so, a process for reducing the total amount of toner is performed.

  Finally, the image output unit 106 forms the trapped image on the recording medium.

  The total amount of toner in the trap is reduced by the image deformation processing unit 110 executing the above processing.

  FIG. 10 is a diagram for explaining a mechanism for reducing the total amount of toner according to the present embodiment.

  10 in FIG. 10 shows an enlarged view of 501 in FIG. Reference numeral 1001 denotes a state before trapping two adjacent objects. Reference numeral 1002 denotes information after the two objects are trapped. Reference numeral 1003 denotes a state in which the total amount of toner in the trap is reduced using the method according to the present embodiment.

  As indicated by 1001, the color plate of the left object is composed of the C plate (100%) and the M plate (100%), and the color plate of the right object is the Y plate (100%).

  The image transformation processing unit 110 determines whether or not to perform trapping on the pixel of interest at the boundary between the color plates of different adjacent objects (S202). In this example, there is no common color plate for the left object and the right object. Therefore, if trapping is not performed, when the Y plate is shifted to the right, whitening occurs between the left object including the C plate and the M plate and the right object including the Y plate. Therefore, the image transformation processing unit 110 determines to perform trapping.

  The image transformation processing unit 110 selects a color plate to be a trap color (S203). Here, the trap color is a color plate that an adjacent object excluding black among cyan, magenta, yellow, and black has a color plate that does not have a pixel of interest. The total amount of toner in the color plate of the left object is 200% (C plate: 100%, M plate: 100%), whereas the total amount of toner in the color plate of the right object is 100% (Y plate: 100%). Therefore, the Y plate is selected as the trap color.

  If the toner amount of the trap color is 100% (S204), the image transformation processing unit 110 performs trapping so that the right object overlaps the left object as indicated by 1002. At this time, the total toner amount of the trap is 300% (C plate (100%), M plate (100%), Y plate (100%)), which exceeds the limit value (200%) of the total toner amount. Therefore, the total amount of toner in the trap is lowered to the limit value using the method shown below (S205).

  Since the C plate and the M plate are visually darker than the trap color Y plate, the ratios of the reduction amounts of the C plate, M plate, and Y plate toners are set as follows.

here,
C_redu: C plate toner reduction amount M_redu: M plate toner reduction amount Y_redu: Y plate toner reduction amount That is, the C plate toner amount and the M plate toner amount are reduced by 20%, respectively. Reduce toner amount by 60%. As a result, as shown in 1003, the configuration of the color plate in the trap is C plate (80%), M plate (80%), and Y plate (40%), and the total amount of toner in the trap is changed from 300% to 200%. Decrease.

  There are two reasons why the reduction amount of the Y color, which is a trap color, is larger than that of other color plates. First, the Y plate is brighter than the other plates, so that it is not visually noticeable, and when there is no misregistration, there is visually little deterioration in image quality before and after trapping. Second, when plate misalignment occurs, the difference between the brightness of the Y plate (40%) and the brightness of the paper (paper white) is small. This is because the change is small and inconspicuous and has little effect on image quality.

  On the other hand, 1004 shows an enlarged view of 502. Reference numeral 1004 denotes a state before trapping two adjacent objects. Reference numeral 1005 denotes information after trapping the two objects. Reference numeral 1006 denotes a state in which the total amount of toner in the trap is reduced by using the method according to the present embodiment.

  As indicated by 1004, it is assumed that the color plate of the left object is composed of the C plate (100%) and the K plate (100%), and the color plate of the right object is the M plate (100%).

  The image transformation processing unit 110 determines whether or not to perform trapping on the pixel of interest at the boundary between the color plates of different adjacent objects (S202). In the case of this example, since there is no common color plate for the left object and the right object, if the M plate is shifted to the right unless trapping is performed, the left object including the C plate and the K plate, Whitening occurs between the right side object including the M version. Therefore, the image transformation processing unit 110 determines to perform trapping.

  The image transformation processing unit 110 selects a color plate to be a trap color (S203). Here, the trap color is a color plate that an adjacent object excluding black among cyan, magenta, yellow, and black has a color plate that does not have a pixel of interest. The total amount of toner on the color plate of the left object is 200% (C plate: 100%, K plate: 100%), whereas the total amount of toner on the color plate of the right object is 100% (M plate: 100%). Therefore, the M plate is selected as the trap color.

  If the toner amount of the trap color is 100% (S204), the image transformation processing unit 110 performs trapping so that the right object overlaps the left object as indicated by 1005. At this time, the total toner amount in the trap is 300% (C plate (100%), M plate (100%), K plate (100%)), which exceeds the limit value (200%) of the total toner amount. Therefore, the total amount of toner in the trap is lowered to the limit value using the method shown below (S205).

  The ratio of the reduction amount of toner for the C, M, and K plates is set as follows.

here,
C_redu: C plate toner reduction amount M_redu: M plate toner reduction amount K_redu: K plate toner reduction amount

  That is, the C plate toner amount is reduced by 90%, and the M plate toner amount is reduced by 10%. The amount of toner on the K plate is not reduced. As a result, as shown in 1006, the color plate composition in the trap is C plate (10%), M plate (90%), and K plate (100%), and the total amount of toner in the trap is reduced from 300% to 200%. To do.

  There are two reasons why the reduction amount of the M plate, which is a trap color, is less than the color plate other than the M plate (excluding the K plate), that is, the C plate. The first reason is as follows. The amount of toner on the K plate in the trap is 100% and the brightness is low. Therefore, if no plate misalignment occurs, even if the toner amount of the trap color is 100%, the brightness of “K plate (100%)” and “K plate (100%) + trap color (100%)” The difference in brightness is small. Therefore, there is little deterioration in image quality before and after trapping.

  Secondly, when a misregistration occurs, the M plate (90%) appears, so there is little change from the M plate (100%), which is the right object, to the M plate (90%) in the trap. In addition to realizing the effect of preventing, trapping effect is great. Further, since the amount of trap color reduction is small, a desired trap color can be prepared.

  The toner reduction amount ratio may be determined by calculating the value of L * a * b and determining the toner reduction amount of the trap color according to the L value or by using a lookup table. good.

<Second Embodiment of Total Toner Reduction Processing>
A second embodiment of the toner total amount reduction process will be described with reference to the drawings.

  S205-1 in FIG. 3 is a flowchart showing details of the process of controlling the total amount of toner in the trap (S205 in FIG. 2).

  In step S3010, the image deformation processing unit 110 determines whether the total value of the trap color toner amount calculated in step S204 and the toner amount of the target pixel exceeds the total toner amount limit value. If the total value of the trap color toner amount and the toner amount of the target pixel does not exceed the limit value, the process ends. On the other hand, when the total value of the toner amount of the trap color and the toner amount of the target pixel exceeds the limit value, the image transformation processing unit 110 performs the process of S3011.

  In step S3011, the image transformation processing unit 110 performs processing in step S3013 if the K plate toner amount of the target pixel is within a predetermined range, that is, if “θ1 <K plate toner amount of the target pixel ≦ θ2”. Do A. On the other hand, if “θ1 <K plate toner amount of target pixel ≦ θ2” is not satisfied, the image transformation processing unit 110 performs the process of S3012. Here, θ1 and θ2 are any value from 0 to 100%, as shown in FIG. 100% means 255 when the pixel data is 8 bits. Note that θ1 and θ2 may be set in advance by the service person from the operation unit of the image forming apparatus, or may be stored in the storage unit 104 at the manufacturing stage of the image forming apparatus.

  In step S3012, the image transformation processing unit 110 performs processing B in step S3014 when “θ2 <the amount of toner for the K plate of the target pixel”, and in step S3015 if “θ2 <the amount of toner of the K plate of the target pixel” is not satisfied. Process C is performed.

  Next, the contents of the processing A, processing B, and processing C will be described with reference to the drawings.

  First, the process A will be described. Hereinafter, for convenience of explanation, the limit value of the total toner amount is set to 200%.

  FIG. 4 is a diagram showing the contents of the process A shown in FIG. In the process A, the image deformation processing unit 110 compares the toner amount of the trap color with the toner amounts of the color plates other than the K plate and the trap color, and depending on the result, the process A-1 or the process A-2. I do. Here, color plates other than the K plate and the trap color (hereinafter referred to as color plates other than the K plate) are the C plate and the Y plate when the trap color is the M plate.

  When the toner amount of the trap color is larger than the toner amount of the color plate other than the K plate, the image transformation processing unit 110 performs the following calculation to obtain C ′, M ′, Y ′, and K ′ (Process A) -1).

  C ′, M ′, Y ′, and K ′ indicate the toner amounts of the C, M, Y, and K plates after the total toner amount is reduced.

If the amount of toner reduction is T, UCR (under color removal) is used, and CMY toner is replaced with K toner,
C ′ = C−T
M ′ = MT
Y '= Y-T
K '= K + T
It becomes. However, K ′ ≦ 100.

  Also, C ′ + M ′ + Y ′ + K ′ = C + M + Y + K−2T, where C ′ + M ′ + Y ′ + K ′ is the limit value (Limit) of the total toner amount, and C + M + Y + K is the total toner amount (Total) of the target pixel.

  Therefore, T = Total + Limit / 2.

  Since the toner reduction amount must be equal to or more than the toner amount of the color plate having the smallest color plate other than the K plate,

となる。かつ、Ｋ版にＴを加えた値は、Ｋのトナーを最大限使用する場合（Ｋ＝１００％）を超えてはいけない。したがって、

It becomes. The value obtained by adding T to the K plate must not exceed the case where K toner is used to the maximum (K = 100%). Therefore,

It becomes. By satisfying the above conditions, the toner amounts of the C plate, M plate, Y plate, and K plate are reduced using the following formula.
C ′ = C−a · min
M ′ = M−b · min
Y ′ = Y−c · min
K ′ = K + d · min
here,
C, M, Y, K: Toner amount of C plate, M plate, Y plate, K plate before reduction of total toner amount Total: Total toner amount of target pixel (Total = C + M + Y + K)
Limit: Limit value of total toner amount min: The smallest toner amount among C, M, and Y (a + b + cd) min = 2T (C ′ + M ′ + Y ′ + K ′ = C + M + Y + K−2T)
It is.

  In process A,

It is desirable to determine θ ₁ shown in FIG.

  By performing the processing A-1, the toner amount of the K plate is increased, while the total toner amount is reduced by decreasing the toner amount of the color plate other than the K plate.

  With the above configuration, the toner can be reduced under the restriction that the K-plate toner does not exceed 100% (maximum toner amount) and the smallest CMY toner does not disappear. Further, since the toner amount of the trap color is larger than the toner amount of the color plate other than the K plate, the trap color toner remains sufficiently even if the toner is reduced using the T. Therefore, the trapping effect can be sufficiently obtained even if plate misalignment occurs.

  On the other hand, when the toner amount of the trap color is smaller than the toner amount of the color plate other than the K plate, the image deformation processing unit 110 performs the following calculation to obtain C ′, M ′, Y ′, and K ′ ( Process A-2).

かつ

And

In this case, the toner amount of the C plate, M plate, and Y plate is reduced using the following formula.

here,
C, M, Y, K: Toner amount of C plate, M plate, Y plate, K plate before reduction of total toner amount Total: Total toner amount of target pixel (Total = C + M + Y + K)
Limit: Limit value of total toner amount α + β + γ = 1
It is.

  The values of α, β, and γ are coefficients that can be changed according to the color plate of the trap color or the characteristics of the copying machine (for example, the maximum amount of toner that can be output for each color plate varies depending on the copying machine).

  Regarding the setting of the values of α, β, and γ, the toner amount of the smallest color plate among the color plates other than the K plate is set as the conversion amount.

  By performing the processing A-2, the total toner amount can be reduced so that the trap color toner amount is not lost even though the trap color toner amount is smaller than the color plate toner amount other than the K plate.

  Next, processing B will be described. The process B is a process when the toner amount of the K plate is relatively large. In this case, when no misregistration occurs, control of the toner amount of the K plate, which has a large influence on the density, is performed in order to suppress the density change of the image after the toner reduction with respect to the image before the toner reduction. I refrain. Also, in order to obtain a trapping effect even when plate misregistration occurs, a reduction in the amount of trap color toner is refrained.

  In the process B, brightness is obtained using a lookup table for converting CMYK values to Lab values, and the following calculation is performed to obtain C ′, M ′, Y ′, and K ′.

  Note that C ′, M ′, Y ′, and K ′ may be obtained by replacing the brightness of each color plate with the toner amount of each plate and performing the following calculation.

here,
C, M, Y, K: Toner amount of C plate, M plate, Y plate, K plate before reduction of total toner amount Total: Total toner amount of target pixel (Total = C + M + Y + K)
Limit: Limit value of total toner amount L (i): L value of i-plane of target pixel α + β + γ = 1
It is.

  The values of α, β, and γ are coefficients that are set in mind that the color of the trap color is changed according to the situation of the copying machine or the like.

  FIG. 11 is a diagram illustrating a color plate configuration before the reduction of the total toner amount and a color plate configuration after the reduction of the total toner amount when the total toner amount is controlled according to the second embodiment.

  As indicated by 1104, 1105, and 1106 in the figure, the constitution of the toner amount of each color plate before the total toner amount reduction is C plate (100%), K plate (100%), and M plate (100%) that is a trap color. ).

  When (α, β, γ) = (1, 0, 0) is set, the constitution of the toner amount of each color plate after the total toner amount reduction is M plate (100%) and K plate (100%) ( Case 1).

  When (α, β, γ) = (0.8, 0.2, 0) is set, the composition of the toner amount of each color plate after the total toner amount reduction is M plate (80%), C plate (20%). ), K version (100%) (Case 2).

  When (α, β, γ) = (1, 0, 0) is set and the K plate is reduced, the configuration of the toner amount of each color plate after the total toner amount reduction is M plate (100%), C Version (20%), K version (80%) (Case 3).

  In all cases 1 to 3, the following two effects can be obtained by reducing the reduction rate of the K plate and the M plate which is the trap color.

  The first effect is that image quality deterioration after trapping can be suppressed. The second effect is that when the color plate is shifted, the trap color appears as desired, and whitening can be prevented.

  Accordingly, in the above example, the reduction rate of the C plate, which is a color plate other than the M plate and the K plate, which is a trap color, is 0.8 to 1.0, and thus the toner amount reduction amount of the C plate is large.

  Next, process C will be described.

  In process C, the amount of toner on the K plate is small, and the amount of toner on the K plate may be zero. Therefore, as described above, when the toner amount of the K plate is increased, the K plate which is not present in the first place is generated. Therefore, the toner amount of the K plate is not controlled. Then, only the toner amount of the trap color is adjusted. However, the reduction is within a range where the trap color toner does not disappear.

  In the process C, the toner amount of the color plate having the smallest toner amount among the plurality of color plates of the target pixel is set as the trap color toner amount.

In this case, the toner amount of the C plate, M plate, and Y plate is reduced using the following formula.

  Here, α + β + γ = 1.

In process C, it is desirable to determine θ ₂ in FIG. 9 so as to satisfy the above conditional expression.

  Note that C ′, M ′, Y ′, and K ′ may be obtained by replacing the brightness of each color plate with the toner amount of each plate and performing the following calculation.

  Here, α + β + γ = 1.

  The values of α, β, and γ are coefficients set in mind that the color of the trap color is changed according to the status of the printer main body such as a copying machine.

  Referring to FIG. 11 again, the configuration of the color plate before the reduction of the total toner amount and the configuration of the color plate after the reduction of the total toner amount will be described.

  As indicated by reference numerals 1101, 1102, and 1103 in the figure, the configuration of the toner amount of the target pixel before the total toner amount reduction is the C plate (100%), the M plate (100%), and the Y plate (100%) that is a trap color. ).

  When (α, β, γ) = (0.33, 0.33, 0.33) is set, the configuration of the toner amount of the target pixel after the toner amount reduction is Y plate (66%), M plate ( 67%) and C version (67%) (Case 1).

  When (α, β, γ) = (0.5, 0.25, 0.25) is set, the configuration of the toner amount of the target pixel after the toner amount reduction is Y plate (40%), M plate ( 80%) and C version (80%) (Case 2).

  When (α, β, γ) = (0, 0.5, 0.5) is set, the configuration of the toner amount of the target pixel after the toner amount reduction is Y plate (100%), M plate (50%). ), C version (50%) (Case 3).

The Y plate, which is a trap color, is a brighter color plate than the C plate and the M plate. Therefore, when the toner amount reduction rate of the Y plate is larger than the toner amount reduction rate of the C plate and M plate,
(Α, β, γ) = (0.5, 0.25, 0.25) is set.

  In general, it is preferable to set the values of α, β, and γ so that the brightness of pixels before trapping and the brightness of pixels after trapping are the same. However, depending on the degree of registration adjustment for each color plate, there are cases where the pixel of interest is prioritized over the trap color (Case 2) and cases where the trap color is prioritized (Case 3). However, in any of cases 1 to 3, an effect that image quality deterioration after trapping can be suppressed can be obtained. Further, since the Y plate, which is a trap color, is a bright color plate, even if whitening occurs, an effect that it is less noticeable can be obtained.

  Therefore, in the above example, the reduction rate of all color plates is 0.5-0.

<Third Embodiment of Total Toner Reduction Processing>
A third embodiment of the total toner amount reduction process will be described with reference to the drawings.

  S205-2 in FIG. 3 is a flowchart showing details of the process of controlling the total amount of toner in the trap (S205 in FIG. 2).

  In step S3020, it is determined whether or not the total value of the trap color toner amount calculated in step S204 and the toner amount of the target pixel exceeds the limit value of the total toner amount. When the total value of the trap color toner amount and the toner amount of the target pixel exceeds the limit value, the image transformation processing unit 110 performs the process of S3021. On the other hand, when the total value of the toner amount of the trap color and the toner amount of the target pixel does not exceed the limit value, the process ends.

  In step S3021, the image transformation processing unit 110 compares the brightness of the target pixel with the brightness of the trap color, and determines whether the difference is smaller than a predetermined value α. In other words, the image transformation processing unit 110 determines whether the brightness of the target pixel is the same as the brightness of the trap color. Note that the brightness of the trap color and the brightness of the target pixel are denoted as L * (trapping color) and L * (target pixel), respectively. When the brightness of the pixel of interest and the brightness of the trap color are approximately the same, the image transformation processing unit 110 performs the process D (S3023), and when not, the process of S3022 is performed.

  In S3022, it is determined whether or not the trap color is brighter than the target pixel. If the trap color is brighter than the target pixel, processing E is performed (S3024). Conversely, if the target pixel is brighter than the trap color. Performs processing F (S3025).

  In the above example, the brightness of the target pixel and the trap color are compared, but the toner amount of the target pixel and the trap color may be compared.

  Next, the contents of the above processing D, processing E, and processing F will be described with reference to the drawings.

  FIG. 12 is a diagram illustrating a color plate configuration before the reduction of the total toner amount and a color plate configuration after the reduction of the total toner amount when the total toner amount is controlled according to the third embodiment.

  First, the process D will be described.

  In process D, the image transformation processing unit 110 performs the following calculation to obtain C ′, M ′, Y ′, and K ′. C ′, M ′, Y ′, and K ′ indicate the toner amounts of the C, M, Y, and K plates after the total toner amount is reduced.

here,
C, M, Y, K: Toner amount of C plate, M plate, Y plate, K plate before reduction of total toner amount Total: Total toner amount of target pixel (Total = C + M + Y + K)
Limit: A limit value of the total amount of toner.

  As indicated by 1201 in FIG. 12, it is assumed that the configuration of the toner amount of each color plate before the total toner amount reduction is the C plate (100%), the M plate (50%), and the Y plate (100%). By performing the processing D, the composition of the toner amount of each color plate after the reduction of the total toner amount is C plate (80%), M plate (40%), and Y plate (80%). That is, by performing the processing D, the toner amount of each color plate is reduced uniformly, that is, at the same reduction ratio. In this example, the toner amount of each color plate is reduced by 20%.

  Next, process E will be described.

  In the process E, the image deformation processing unit 110 performs the following calculation to reduce only the trap color toner amount. X ′ represents the toner amount of the trap color after the toner amount is reduced.

X: trap color toner amount before reducing toner amount Total: total toner amount of target pixel (Total = C + M + Y + K)
Limit: Limit value of total toner amount

  As indicated by 1202 in FIG. 12, it is assumed that the configuration of the toner amount of each color plate before the total toner amount reduction is the C plate (100%), the M plate (50%), and the Y plate (100%). By performing the processing E, the composition of the toner amount of each color plate after the reduction of the total toner amount is C plate (80%), M plate (50%), and Y plate (70%).

  Next, processing F will be described.

  In processing F, the image transformation processing unit 110 performs the following calculation, and sets the toner amount of the color plate having the smallest toner amount among the plurality of color plates of the target pixel as the trap color toner amount.

here,
min: the smallest amount of toner among C, M, and Y trap: a trap coefficient.

  As indicated by reference numeral 1203 in FIG. 12, it is assumed that the configuration of the toner amount of each color plate before the total toner amount reduction is the C plate (100%), the M plate (50%), and the Y plate (100%). By performing the process F, the composition of the toner amount of each color plate after the reduction of the total toner amount is C plate (100%), M plate (50%), and Y plate (50%). That is, the toner amount of the Y plate that is the trap color is set so as not to exceed the smallest toner amount (C plate: 50%).

  The above three methods are selected according to the following conditions.

  As described above, in the third embodiment, the process D is performed when the brightness of the target pixel and the trap color are approximately the same, and the process E is performed when the trap color is brighter than the target pixel. If the pixel of interest is brighter than the trap color, processing F is performed.

<Other embodiments>
The present invention can take the form of a system, apparatus, method, computer program or computer-readable recording medium. Further, the present invention can be applied to a system composed of a plurality of devices or a single device.

  In the embodiment of the present invention, a computer program for realizing the above-described functions of the present invention is supplied to a system or apparatus via a recording medium or a network, and the computer included in the system or apparatus executes the program. included. The recording medium is a computer-readable recording medium. Therefore, the embodiment includes a computer program that realizes the functions of the present invention. The computer program includes computer executable instructions such as object code, a program executed by an interpreter, and script data supplied to the OS. The recording medium is a floppy (registered trademark) disk, hard disk, optical disk, magneto-optical disk, MO, CD-ROM, CD-R, CD-RW, magnetic tape, nonvolatile memory card, ROM, DVD or the like. As a program supply method, for example, there is a method of downloading from the Internet to a recording medium such as a hard disk using a browser of a client computer. In this method, a computer program file or a compressed file including an automatic installation function is downloaded from the Internet. Further, the embodiment includes dividing the program code constituting the computer program into a plurality of files and downloading each file from a different server. The embodiment also includes a server that allows a plurality of users to download a computer program file.

  The functions of the above-described embodiments can be realized by a computer executing a computer program. The functions of the above-described embodiments can also be realized by an OS running on a computer performing part or all of actual processing based on an instruction of the computer program.

  Even after the computer program read from the recording medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the functions of the above-described embodiments can be realized. That is, the functions of the above-described embodiments can also be realized when a CPU or the like provided in a function expansion board or a function expansion unit performs part or all of the actual processing based on instructions from a computer program.

1 is a block diagram illustrating a configuration example of an image forming apparatus 100 according to an embodiment. 7 is a flowchart illustrating a toner total amount reduction process according to the embodiment. 3 is a flowchart showing details of processing (S205 in FIG. 2) for controlling the total amount of toner in the trap. It is a figure which shows the content of the process A shown by FIG. It is a diagram for explaining a conventional mechanism for reducing the total amount of toner. It is a figure for demonstrating a toner reduction. It is a diagram for explaining a conventional mechanism for reducing the total amount of toner. FIG. 6 is a diagram illustrating a configuration of a color plate before reduction of the total amount of toner and a configuration of a color plate after reduction of the total amount of toner when a conventional method for reducing the total amount of toner is used. FIG. 10 is a diagram illustrating an example of controlling the total toner amount based on a toner amount of a K plate. FIG. 6 is a diagram for explaining a toner total amount reduction method according to the embodiment. FIG. 10 is a diagram illustrating a color plate configuration before reduction of the total toner amount and a color plate configuration after reduction of the total toner amount when the total toner amount is controlled according to the second embodiment. FIG. 10 is a diagram illustrating a configuration of a color plate before reduction of the total amount of toner and a configuration of a color plate after reduction of the total amount of toner when the total amount of toner is controlled according to the third embodiment. 1 is a diagram illustrating a structure of an image forming apparatus 100 according to the present embodiment.

Explanation of symbols

101 Scanner 102 Image Reception Unit 103 Image Processing Unit 104 Storage Unit 105 CPU
106 Image output unit 108 Scanner image processing unit 109 Printer image processing unit 110 Image deformation processing unit

Claims (13)

An input means for inputting an image;
Trap means for trapping the pixel of interest at the boundary between the color plates of different objects adjacent to each other;
Determination means for determining whether the total toner amount of the target pixel after the trapping exceeds a limit value;
When it is determined that the total toner amount exceeds the limit value, the processing for reducing the toner amount of the color plate other than the black plate without changing the toner amount of the black plate is performed on the target pixel. Reduction means for reducing the total amount of toner,
An image forming apparatus comprising: a forming unit that traps by the trap unit and forms the image processed by the reduction unit on a recording medium. The input means inputs an image read by a scanner or an image based on PDL data received from an external device,
The image forming apparatus according to claim 1, wherein the trapping unit traps the target pixel in the input image. The determination means, after trapping by the trap means is performed, the image forming apparatus according to claim 1 or 2, characterized in that determining whether the total amount of toner exceeds the limit value. The trap means selects a color plate of the object other than the black plate that does not include the target pixel as a trap color, and sets the toner amount of the selected trap color for the target pixel. Perform the trapping to increase,
The reduction means reduces the total toner amount by subtracting the reduction amount obtained based on the coefficient for each color plate from the toner amount of each color plate other than the black plate of the target pixel on which the trapping has been performed. The image forming apparatus according to claim 3 . 5. The image according to claim 4, wherein the reduction unit obtains the amount of reduction using a brightness look-up table of each color plate of the pixel of interest and obtains the reduction amount based on the obtained brightness of each color plate. Forming equipment. The image forming apparatus according to claim 1, wherein the color plate other than the black plate includes at least one of a cyan plate, a magenta plate, and a yellow plate. An input step for inputting an image;
  A trap step for trapping the pixel of interest at the boundary between the color plates of different objects adjacent to each other;
  A determination step of determining whether or not the total toner amount of the target pixel after the trapping exceeds a limit value;
  When it is determined that the total toner amount exceeds the limit value, the processing for reducing the toner amount of the color plate other than the black plate without changing the toner amount of the black plate is performed on the target pixel. Reduction steps to reduce the total amount of toner,
  A forming step in which trapping is performed in the trapping step and the image processed in the reduction step is formed on a recording medium;
  An image forming method comprising: The input step inputs an image read by a scanner or an image based on PDL data received from an external device,
  The trap step traps the pixel of interest in the input image.
  The image forming method according to claim 7. The image forming method according to claim 7, wherein the determination step determines whether or not the total amount of toner exceeds a limit value after trapping is performed in the trap step. The trap step selects a color plate of the object other than the black plate that does not include the pixel of interest as a trap color, and sets the toner amount of the selected trap color for the pixel of interest. Perform the trapping to increase,
  The reduction step reduces the total toner amount by subtracting a reduction amount obtained based on a coefficient for each color plate from the toner amount of each color plate other than the black plate of the target pixel on which the trapping has been performed.
  The image forming method according to claim 9. 11. The image forming method according to claim 10, wherein the reduction step obtains the amount of reduction using a brightness lookup table of each color plate of the target pixel, and obtains the reduction amount based on the obtained brightness of each color plate. Method. 12. The image forming method according to claim 7, wherein the color plate other than the black plate includes at least one of a cyan plate, a magenta plate, and a yellow plate. A program for causing a computer to execute the image forming method according to any one of claims 7 to 12.

Images