JP5017898B2 - Image processing method, image forming apparatus, and computer program - Google Patents

Description

  The present invention relates to an image processing method, an image forming apparatus, and a computer program in color printing.

  In recent years, digital multifunction peripherals or printers that can perform full-color printing have been widely used. In full-color printing, a plate for each basic color (cyan, magenta, yellow, and black) is created, and various colors are reproduced by overlaying them.

  Conventionally, such full-color printing has a problem that white spots occur at the boundary between colors. The white spot is a phenomenon in which, for example, when an object of a color different from the background is drawn on the background in the image to be printed, the boundary portion between the background and the object becomes white. This occurs when the plate that reproduces the background is shifted from the plate that reproduces the object (plate shift), and the background color is exposed at the shift portion. One type of image processing for preventing such white spots is trapping.

  In trapping, the object is slightly thickened at the boundary with the background, and even when a plate shift occurs, the blank portion does not occur by filling the shift portion with the color of the object.

  Further, when the object is a gray area (gray area) that can be reproduced only by black, which is one of the basic colors, the object may be reproduced by overprinting. In this method, the object is reproduced by superimposing black on the background. Therefore, the background color is not exposed regardless of the presence or absence of plate displacement, and white spots do not occur.

  Furthermore, the gray area may be reproduced by rich black using a mixed color including basic colors other than black. Even in this case, since the basic color of the object is superimposed on the background, white spots do not occur.

  As technologies related to the image processing as described above, devices as disclosed in Patent Documents 1 and 2 have been proposed.

  The color data conversion device in Patent Document 1 reads input image data for each pixel and determines whether or not it is gray. If it is gray and its neighboring pixels are gray or a continuous color, conversion processing by subtractive color mixing is performed. When the adjacent pixel is not gray and is not a continuous color, conversion processing using a single black color is performed. As a result, the optimum gray can be expressed.

According to Patent Document 2, in a printing control apparatus and a drawing control apparatus having a drawing means for drawing an input drawing command on a bitmap and a means for controlling an overprint function when drawing on the bitmap, When applying the function, the back color is lightened and the specified front color and back color are combined. Thereby, the difference between the original color and the reproduced color can be minimized.
JP 2002-135613 A JP 2004-174964 A

  However, in the conventional image processing, the color of the object and the background color overlap at the boundary portion of the object due to trapping, and the density of the overlapped portion may be more conspicuous than the surrounding area. In some cases, the boundary portion of the object appears to be edged (edge), and may appear different from the original image (see FIG. 7B).

  Further, due to overprinting, the toner in the overprinted region may cause a fixing failure or toner riding may be deteriorated. Further, when the density of black is low, the background color may be seen through in the overprinted area, and the color may look different from the original image. In addition, a phenomenon (suction) in which toner is sucked from the smaller amount of toner to the larger amount of toner may occur near the boundary between the overprinted region and the background. When the suction occurs, the density near the boundary of the area where the toner is sucked becomes low and the color becomes light (see FIG. 7C).

  If such a problem becomes conspicuous, the printed image becomes unnatural and gives a strange feeling to the person who sees it.

  In view of such problems, an object of the present invention is to enable overprinting and trapping to output an image that is less uncomfortable than in the past and to improve image quality by printing.

An image processing method according to the present invention is an image processing method in an image forming apparatus that forms a color image using a plurality of basic colors, and is a first method for acquiring color data of an adjacent region of an object included in the image. And a second step of selecting either trapping or overprinting based on the acquired color data as processing performed on the object in order to reduce unnaturalness in the vicinity of the boundary of the object And a third step of executing the process selected in the second step, and only one color obtained by mixing the plurality of basic colors is used in the adjacent region. in the first step, as the color data, collected by the number of colors used in one or more of the adjacent region adjacent to the object And, in the second step, when the number of the color is 1 in the case of two or more selected the overprint selects the trapping.

  Preferably, the object is a gray region that can be reproduced only by black, which is one of the basic colors, and when the overprint is executed in the third step, Reproduce gray with rich black using mixed colors.

  More preferably, in the second step, even if the number of colors is 1, the plate amount of the basic color used for the color is equal to or greater than a predetermined threshold or is used for the object. When the plate amount difference between the basic color used and the basic color used for the color is equal to or greater than a predetermined threshold, the trapping is selected.

In the image processing method, in the first step, as the color data, the maximum value and the minimum value of the plate amounts that one or more of the adjacent regions adjacent to the object have for the same basic color are respectively obtained. In the second step, if the maximum value is equal to or greater than a predetermined threshold value or the difference between the maximum value and the minimum value is equal to or greater than a predetermined threshold value, the trapping is selected and the maximum value is selected. When the value is less than a predetermined threshold and the difference between the maximum value and the minimum value is less than the predetermined threshold, the overprint is selected.

  The threshold used in the second step is determined according to the color of the object.

  The image forming apparatus in the present invention is, for example, a terminal device such as a personal computer or a workstation, an image output device such as a digital multifunction peripheral or a printer, or an image processing system including a terminal device and an image output device. It is.

  Further, in the present invention, overprinting refers to overlaying an object on a background, and includes both cases where the background color and the object color are adjusted and when no adjustment is made. Rich black is used as one method for overprinting.

  By using overprinting and trapping, it is possible to output an image that is less uncomfortable than in the past and to improve image quality by printing.

[First Embodiment]
1 is a diagram illustrating an image processing system 1 according to the present invention, FIG. 2 is a diagram illustrating an example of a schematic configuration of an image output device 3, and FIG. 3 is a diagram illustrating an example of a functional configuration of the image output device 3. 4 is a diagram illustrating an example of an image PR created by the user in the terminal device 2, and FIG. 5 is a diagram illustrating an example of the lookup table TL.

  As shown in FIG. 1, the image processing system 1 includes a terminal device 2, an image output device 3, and the like, which are connected to each other via a network 4 by a LAN. As the network 4, the Internet, an intranet, a public line, a dedicated line, or the like may be used.

  The terminal device 2 includes a processing device 11, a display 12, a keyboard 13, a mouse 14, and the like. As the terminal device 2, a personal computer, a workstation, a PDA (Personal Digital Assistant) or the like is used.

  The display 12 displays various documents or images on its display surface, and displays various application screens for creating the documents or images. As the display 12, a CRT, LCD (liquid crystal display), PDP, or the like is used.

  The keyboard 13 and the mouse 14 are input devices for the user to give instructions to the terminal device 2. The user operates these input devices to create an image or a document, and gives an instruction to the terminal device 2 to print the created image. When a printing instruction is given, image data PD relating to an image to be printed is transmitted to the image output device 3.

  Here, for example, the user creates an image PR as shown in FIG. The image PR includes objects GR1, GR2, GR3, GR4, and GR5, and adjacent regions CL1, CL2, and CL3 that are drawn as a background and are adjacent to these. The adjacent area CL1 is a white area.

  Hereinafter, the objects GR1, GR2, GR3, GR4, and GR5 may be collectively described as an object GR, and the adjacent areas CL1, CL2, and CL3 may be collectively described as an adjacent area CL. The same applies hereinafter.

  The object GR is a gray area (gray area) or a low-saturation color area that can be reproduced only with black (K), which is one of the basic colors. Each region has a different color, and one color is represented in each region.

  The image output device 3 executes printing based on data transmitted from the terminal device 2 via the network 4. During printing, trapping or overprinting (device color superimposition processing) is performed as necessary to process an image created with basic colors in accordance with the printing device.

  Note that the image output apparatus 3 is a digital multi-function peripheral or printer using an electrophotographic system, and includes, for example, a tandem print engine as shown in FIG.

  2, the image output apparatus 3 includes a control unit 21, transfer chargers 22C, 22M, 22Y, and 22K, an intermediate transfer belt 23, image forming units 24C, 24M, 24Y, and 24K, rollers 25 and 26, and a paper feed cassette. 27, a secondary transfer roller 28, a fixing unit 29, a paper discharge tray 30, a belt cleaner 31, a waste toner box 32, and the like.

  The control unit 21 performs image processing on the image data PD transmitted to the image output device 3 and then controls each unit of the image output device 3 to execute printing of the image. The control unit 21 includes a CPU 211, a memory 212, a control circuit 213, a communication interface 214, a magnetic storage device 215, and the like.

  Here, the communication interface 214 is a NIC (Network Interface Card) or a modem for performing communication with other devices. The memory 212 is a RAM or the like that temporarily stores data transmitted to the image output apparatus 3. The control circuit 213 is a circuit for controlling each part in the communication interface 214 and the image output apparatus 3.

  The magnetic storage device 215 stores programs and data for realizing each function of the image output device 3 shown in FIGS. 3 and 16. These are read into the memory 212 as necessary, and the program is executed by the CPU 211. Each function can be realized by a hardware circuit or a combination of a hardware circuit and software.

  The image forming unit 24 includes a charging charger 41, a photosensitive drum 42, an exposure unit 43, a developing device 44, a drum cleaner 45, and the like, and forms a toner image by a known electrophotographic process. The formed toner image is transferred onto the intermediate transfer belt 23 by the transfer charger 22, further transferred to the paper PA fed from the paper feed cassette 27, fixed by the fixing unit 29, and the printed paper PA is discharged. It is discharged to the paper tray 30.

  Next, processing of each unit of the image output device 3 will be described with reference to FIG.

  As shown in FIG. 3, the image output device 3 includes an image data receiving unit 301, a data storage unit 302, a color data acquisition unit 303, a process selection unit 304, an image processing unit 305, an image data output unit 306, and the like. It is done.

  The image data receiving unit 301 of the image output device 3 receives the image data PD sent from the terminal device 2. The data storage unit 302 stores the image data PD received by the image data receiving unit 301 and the lookup table TL shown in FIG.

  The color data acquisition unit 303 acquires color data CR related to the color of the object GR and the adjacent region CL included in the image data PD received by the image data reception unit 301. The color data CR includes the number of colors represented in the adjacent region CL for each object GR, and the basic colors (basic colors included in the object GR) used for the colors represented in the object GR. A plate amount that is a value related to the density, or a plate amount of a basic color included in the adjacent area CL is included. In the first and second embodiments, the plate amount is shown as a percentage value. That is, “10” as the plate amount means a density of “26” corresponding to 10% of 256 when the density of the basic color is expressed by 256 gradations (8 bits).

  The process selection unit 304 selects either overprinting or trapping as a process to be performed on the image data PD based on the color data CR.

  The image processing unit 305 executes the processing selected by the processing selection unit 304 on the image data PD, and creates processed image data PS that is data after the processing is performed.

  The image data output unit 304 outputs the processed image data PS to the image forming unit 24 at a predetermined timing.

  In the present embodiment, during overprinting, the gray color of the object GR is reproduced with rich black. In rich black, not only the basic color black but also other cyan (C), magenta (M), and yellow (Y) are used to reproduce the gray color. That is, using all these basic colors as candidate colors, a plurality of appropriate basic colors are selected from the candidate colors to reproduce a gray color.

  In the present embodiment, in order to further enhance the image quality improvement effect, the cyan, magenta, and yellow plate amounts used for rich black are changed in proportion to change the cyan contained in the adjacent region CL as the background. , Magenta, and yellow. As a method for obtaining such a plate amount, there is a method using a lookup table TL as shown in FIG. Here, a method for obtaining the plate amount (CMYK plate amount) of each basic color using the lookup table TL will be briefly described.

  In the look-up table TL shown in FIG. 5, the x-axis indicates the black printing amount when the gray color is expressed only by the basic color black. The y-axis represents the ratio between the plate amount of black and the plate amount of black when the colors of the same color, lightness, hue, and saturation are represented by the basic colors cyan, magenta, yellow, and black ( K component substitution amount). Further, each grid point is associated with a plate amount of each basic color for expressing a gray color corresponding to the grid point.

In obtaining the plate amount, first, a value X ₀ that is closest to the black plate amount necessary to reproduce the gray color of the object GR to be rich black and does not exceed the plate amount is obtained (FIG. 5). (A)). Next, an appropriate y coordinate value is obtained by referring to the lattice point corresponding to the obtained X ₀ in the positive direction of the y axis. Specifically, the cyan, magenta, and yellow plate amounts associated with each grid point are compared with the maximum values of the cyan, magenta, and yellow plate amounts in the adjacent region CL of the target object GR. Then, the value of the y coordinate at the time when the plate amount in the lattice point exceeds is defined as Y ₁ (FIG. 5B). Further, an x coordinate value 1 larger than X ₀ is X ₁ , and a y coordinate value 1 smaller than Y ₁ is Y _0, and lattice points (X ₀ , Y ₀ ), (X ₀ ) indicated by these values are set. , Y ₁ ), (X ₁ , Y ₀ ), and (X ₁ , Y ₁ ) are used for interpolation. Thus, the target CMYK plate amount is acquired (FIG. 5C). That is, cyan, magenta, and yellow have the same plate amount as cyan, magenta, and yellow included in the adjacent region CL, and can express the same brightness, the same hue, and the same saturation as the gray of the target object GR. Get the amount of CMYK plate.

  Here, the image processing of the present embodiment will be described with reference to a flowchart.

  FIG. 6 is a flowchart for explaining the flow of image processing in the first embodiment, and FIG. 7 is a diagram for explaining bordering and suction.

  When the user creates an image PR and gives an instruction to the terminal device 2 to print it, the image data PD is transmitted to the image output device 3.

  When the image output device 3 acquires the image data PD, the image output device 3 acquires the color data CR of the adjacent region CL of the object GR included in the image PR (# 11).

  After acquiring the color data CR, either trapping or overprinting is selected based on the acquired color data CR as a process to be performed on the object GR in order to reduce unnaturalness in the vicinity of the boundary of the object GR ( # 12). Subsequently, the selected process is executed (# 13).

  In the present embodiment, the above-described processing reduces problems that have conventionally occurred due to image processing for preventing white spots or color shifts. Here, this problem will be briefly described with reference to FIG.

  Each drawing in FIG. 7 shows a vicinity BR of the boundary between the object GR4 and the adjacent region CL2 when the image PR in FIG. 4 is printed. Here, FIG. 7A shows an image when printing is performed without image processing and no trouble occurs.

  FIG. 7B shows an image when printing is performed by trapping. When trapping is performed, as shown in this figure, the colors of the plates overlap at the boundary between the regions, and the color density of the overlapped portion may become conspicuous with respect to the surrounding colors, and bordering may occur. is there.

  FIG. 7C shows an image when overprinting is performed. In the overprint, as shown in this figure, for example, when the plate amount of the object GR4 is small with respect to the adjacent region CL2, the toner is transferred from the object GR4 having the smaller plate amount to the adjacent region CL2 having the larger plate amount. May be sucked in and the color on the object GR4 side may become lighter in the vicinity of the boundary BR.

Hereinafter, specific examples in the present embodiment will be described.
[First embodiment]
FIG. 8 is a flowchart for explaining an example of the flow of image processing in the first embodiment, and FIG. 9 is a flowchart for explaining an example of the flow of processing when executing trapping or overprinting.

  In this embodiment, the number of colors represented in the adjacent area CL adjacent to the object GR to be processed is acquired, and trapping or overprinting is selected based on the number. Specifically, overprinting is selected when the number of colors is “1”, and trapping is selected when the number of colors is “2” or more.

  However, it is not counted when the color of the adjacent region CL is white. Therefore, the number of colors is “0” for the object GR in which the color represented in the adjacent region is only white.

  Hereinafter, the flow of image processing in this embodiment will be described with reference to the flowchart of FIG.

  In FIG. 8, when receiving the image data PD from the terminal device 2, the image output device 3 converts the data into values relating to the densities of the basic colors cyan, magenta, yellow, and black (# 111). Based on the converted density value of the basic color, it is determined whether or not the image PD includes a gray area (object GR) that is equal to or higher than a certain density among areas represented only by the basic color black ( # 112). If it is not included (No in # 112), printing is executed as it is (# 123). If it is included (Yes in # 112), the area is extracted (# 113).

  Next, as the color data CR, the number of colors other than white among the colors represented in the adjacent region CL adjacent to the extracted object GR is acquired (# 114). In the case of the object GR1 in FIG. 4, the color represented in the adjacent region is only the white color of the adjacent region CL1, so the number of colors is “0”. In the case of the object GR2, since different colors are represented in the adjacent regions CL2 and CL3, which are colors other than white, the number of colors is “2”.

  Subsequently, it is determined whether the number of colors is “0”, that is, whether the color of the adjacent region is only white (# 115). If the number of colors is “0” (Yes in # 115), the processing after step # 120 is performed. When the color of the adjacent area is only white, white spots do not occur near the boundary between the object GR and the adjacent area CL. Therefore, the trapping process is not performed, and the object GR is displayed only by the basic color black. Reproduce.

  If the number of colors is not “0” (No in # 115), it is determined whether the number of colors acquired in Step # 114 is 2 or more (# 116). If the number of colors is “2” or more (Yes in # 116), trapping is selected as a process to be applied to the image PR (# 117). If the number of colors is “1” (No in # 116), overprint is selected (# 118). Then, the selected process is executed (# 119).

  When executing the processing in step # 119, the type of the selected processing is determined (# 131 in FIG. 9). If the selected process is trapping (trapping in # 131), trapping is executed between the object GR and the adjacent region CL adjacent thereto (# 132).

  If the selected process is overprinting (overprinting in # 131), the CMYK plate amount corresponding to the gray color of the object GR that is the input color is calculated (# 133). Here, the lookup table TL described with reference to FIG. 5 is used to calculate the CMYK plate amount.

  When the CMYK plate amount is obtained, data for replacing the gray color of the object GR by overprinting is created based on the plate amount (# 134).

  Returning to FIG. 8, after the process of step # 119, it is determined whether there is another gray area (# 120). If there is another gray area (Yes in # 120), the gray area is extracted (# 121), and the processes after step # 114 are repeated.

If there is no other gray area (No in # 120), processed image data PS including the data created in step # 119 is created (# 122), and printing is executed based on the data (# 123). )
In the image processing of the present embodiment, when overprinting is selected, that is, when trapping is not selected, the gray of the original image PR is reproduced by rich black that reproduces black and gray in a mixed color of a plurality of device colors. While maintaining the color tone, white spots can be prevented without generating a border (see FIG. 7B).

However, when the number of colors represented in the adjacent region CL is plural, it may be difficult to appropriately reproduce the object GR by rich black. In the present embodiment, since trapping is executed in this case, white spots can be appropriately prevented.
[Second Embodiment]
FIG. 10 is a diagram illustrating an example of the plate amount of each basic color included in the adjacent region CL2, FIG. 11 is a diagram illustrating an example of threshold values used in the second embodiment, and FIG. 12 is a diagram illustrating each basic color included in the object GR5. FIG. 13 is a flowchart for explaining an example of the flow of image processing in the second embodiment.

  In the second embodiment, in addition to the determination of the number of colors in the adjacent area CL (determination of the number of colors) in the first embodiment, the determination of the printing amount of the basic color included in the adjacent area CL (adjacent) Determination of the area plate amount) and a determination (plate amount difference determination) of the difference between the plate amounts of each basic color (plate amount difference) between the object GR and the adjacent area. That is, even if the number of colors is 1, overprinting is not selected unconditionally as in the first embodiment, but a predetermined condition is used in determining the adjacent area plate amount or determining the plate amount difference. If so, trapping is selected.

  In the determination of the adjacent area plate amount, trapping is selected when the plate amount of the basic color included in the adjacent region CL to be determined is large, that is, when the value of the plate amount is equal to or greater than a predetermined threshold value.

  For example, in the case of the object GR5 of FIG. 4, the area adjacent to this is only the adjacent area CL2. When the plate amount of each basic color included in the adjacent region CL2 is the value shown in FIG. 10A and the threshold value is the value shown in FIG. 11A, the basic color of each basic color in the adjacent region CL2 is displayed. The plate amounts (cyan = “75”, magenta = “80”, yellow = “90”, and black = “60”) are respectively threshold values for each basic color (cyan = “70”, magenta = “75”, Since yellow = “80” and black = “50”), trapping is selected as a process to be performed on the object GR5.

  Further, the plate amounts of the respective basic colors included in the adjacent area CL2 are the values shown in FIG. 10B (cyan = “40”, magenta = “45”, yellow = “65”, and black = “30”). In this case, the plate amount of each basic color is less than the threshold value shown in FIG. In this case, trapping is not selected in the determination of the adjacent area plate amount.

  On the other hand, in the determination of the plate amount difference, trapping is selected when the plate amount difference between the basic colors of the object GR and the adjacent area is large, that is, when the plate amount difference is equal to or greater than a predetermined threshold value.

  For example, in FIG. 4, the basic color plate amount included in the adjacent region CL2 is the value shown in FIG. 10B, and the basic color plate amount included in the object GR5 is the value shown in FIG. In the case of “5”, magenta = “5”, yellow = “0”, and black = “0”), the plate amount difference of each basic color is cyan = “35” (= 40−5), magenta = “40” (= 45-5), yellow = “65” (= 65-0), and black = “30” (= 30-0). When the threshold value of the plate amount difference is the value shown in FIG. 11B (cyan = “30”, magenta = “30”, yellow = “50”, black = “20”), the plate of each basic color The amount differences (cyan = “35”, magenta = “40”, yellow = “65”, and black = “30”) are each equal to or greater than the threshold value. In this case, trapping is selected as the process applied to the object GR5.

  That is, in this embodiment, even if the number of colors is 1, the basic color used for the color is equal to or larger than a predetermined threshold value or the basic color used for the object GR. Trapping is selected when the plate amount difference between the color and the basic color used for that color is equal to or greater than a predetermined threshold.

  In the above example, the threshold value is individually set for each basic color. This may be a common value for all basic colors.

  In this case, in determining the adjacent area plate amount, trapping is selected when the minimum value of the plate amount of the basic color is equal to or greater than the threshold value. For example, in the case of FIG. 10B, since the minimum value of the basic color plate amount is “30” (= black plate amount), trapping is selected when “30” is equal to or greater than the threshold value. Alternatively, the maximum value or the average value may be used instead of the minimum value.

  On the other hand, in determining the plate amount difference, the total value of the plate amounts of the basic colors is calculated in each of the object GR and the adjacent region CL, and trapping is selected when the difference between the total values is equal to or greater than a predetermined threshold value. To do. Alternatively, instead of the difference between the total values, a difference such as the maximum value, the minimum value, or the average value of the basic color plate amount in each region may be used.

  Next, the flow of image processing according to this embodiment will be described with reference to the flowchart of FIG.

  In FIG. 13, when the image output device 3 receives the image data PD from the terminal device 2, the image output device 3 converts the data into values relating to the density of each basic color (# 211). Further, based on the converted value, it is determined whether or not a gray area (object GR) is included in the image PD (# 212). If not included (No in # 212), printing is executed as it is (# 225). If it is included (Yes in # 212), the area is extracted (# 213).

  Next, as the color data CR, the number of colors represented in the area adjacent to the extracted object GR and the printing amount of the basic color included in the area are acquired (# 214).

  Subsequently, it is determined whether the number of colors is “0”, that is, whether the color of the adjacent region is only white (# 215). If the number of colors is “0” (Yes in # 215), the processing after step # 222 is performed.

  If the number of colors is not “0” (No in # 215), it is determined whether the number of colors acquired in Step # 214 is 2 or more (# 216).

  If the number of colors is 2 or more (Yes in # 216), trapping is selected as the processing to be performed on the image PR (# 219).

  If the number of colors is 1 (No in # 216), it is determined whether the plate amount of each basic color acquired as the color data CR is large, that is, whether it is greater than or equal to a predetermined threshold (# 217). If it is equal to or greater than the threshold value (Yes in # 217), trapping is selected (# 219). If it is not equal to or greater than the threshold value (No in # 217), it is determined whether or not the basic color plate amount difference between the target object GR and the adjacent area CL adjacent thereto is large, that is, whether it is equal to or greater than a predetermined threshold value ( # 218). If the plate amount difference is equal to or larger than the threshold value (Yes in # 218), trapping is selected (# 219). If it is not equal to or greater than the threshold (No in # 218), overprint is selected (# 220). Then, the selected process is executed (# 221). In step # 221, the process described in FIG. 9 is executed.

  Thereafter, it is determined whether there is another gray area (# 222). If there is another gray area (Yes in # 222), the gray area is extracted (# 223), and the processes after step # 214 are repeated.

If there is no other gray area (No in # 222), processed image data PS including the data created in step # 221 is created (# 224), and printing is executed based on the data (# 225). )
According to the image processing of the present embodiment, trapping is selected when the plate amount of the adjacent area CL is large. Therefore, even if a border is generated by trapping, the color of the adjacent region CL is dark, so that a portion darkened by the border is not conspicuous.

  In general, in the overprint, when the plate amount difference between the areas is large near the boundary between the areas, the adverse effect of the suction is noticeable. That is, in the vicinity of the boundary, the color of the area with the smaller plate amount becomes light, and the thinness becomes conspicuous. In the present embodiment, trapping is executed when there is a large difference in basic color between the object GR and the adjacent area. Accordingly, it is possible to prevent white spots while preventing the adverse effects due to suction from appearing conspicuously.

In addition, when both the color of the object GR and the adjacent area CL are light (the amount of the plate is small), the edge generated in the trapping is easily noticeable. However, according to the present embodiment, overprinting is executed when the plate amount of the adjacent region CL is small and the plate amount difference from the object GR is small, that is, when the colors of the object GR and the adjacent region CL are both light. Therefore, even in such a case, it is possible to prevent whiteout without causing edging.
[Third embodiment]
FIG. 14 is a diagram showing an example of the amount of basic colors included in the adjacent area CL, and FIG. 15 is a flowchart for explaining an example of the flow of image processing in the third embodiment.

  In the third embodiment, regardless of the number of colors in the adjacent area CL, the determination regarding the maximum value of the printing amount of each basic color included in the adjacent area CL (determination of the representative value), the maximum value and the minimum value, The processing to be performed on the object GR is determined by the determination of the difference (the determination of the maximum plate amount difference). That is, even if the number of colors is two or more, trapping is not selected unconditionally as in the first and second embodiments, but a predetermined value is determined in the determination of the representative value or the determination of the maximum plate amount difference. Overprint is selected when the condition is met.

  In the determination of the representative value, trapping is selected when the maximum value of the plate amount of each basic color included in the adjacent region CL is large, that is, when the value is equal to or greater than a predetermined threshold value.

  For example, in the case of the object GR2 in FIG. 4, the adjacent areas are adjacent areas CL1, CL2, and CL3. When the plate amount of each basic color used in each adjacent region CL is the value shown in FIG. 14A, the maximum value of the plate amount is the value of the adjacent region CL2 for cyan, magenta, and black. (Cyan = “75”, magenta = “80”, and black = “60”), and yellow, the value of the adjacent region CL3 (“85”). Furthermore, when the threshold value for this is the value shown in FIG. 11A (cyan = “70”, magenta = “75”, yellow = “80”, and black = “50”), Since the maximum value of the plate amount is equal to or greater than the threshold value, trapping is selected as a process performed on the object GR2.

  When the plate amounts of the respective basic colors included in the adjacent region CL2 are the values shown in FIG. 14B, the maximum plate amounts of the respective basic colors are all the values of the adjacent region CL2 (cyan = “60”). Magenta = “60”, yellow = “60”, and black = “40”). In this case, since each value is less than the threshold value shown in FIG. 11A, trapping is not selected in the determination of the representative value.

  On the other hand, in determining the maximum plate amount difference, trapping is selected when the difference between the maximum value and the minimum value of the basic color plate amount included in the adjacent region CL is large, that is, when the difference is equal to or greater than a predetermined threshold. Is done.

  For example, when the plate amounts of the basic colors included in the adjacent areas CL1, CL2, and CL3 are the values shown in FIG. 14B, the maximum value of each basic color is the value of the adjacent area CL2 (cyan = “60”). Magenta = “60”, yellow = “60”, and black = “40”). The minimum value is a value on the adjacent region CL3 side (cyan = “10”, magenta = “10”, yellow = “5”, and black = “0”). Here, the maximum value and the minimum value are obtained for a region other than white. Therefore, the printing amount of each basic color in the adjacent area CL1, which is a white area, is excluded.

  In this case, the difference between the maximum value and the minimum value in each basic color is cyan = “50”, magenta = “50”, yellow = “55”, and black = “40”.

  When the threshold values are those shown in FIG. 11B, the differences for each basic color are the respective threshold values (cyan = “30”, magenta = “30”, yellow = “50”, and black = “ 20 ") or more. In this case, trapping is selected.

  In other words, in the present embodiment, the maximum value and the minimum value of the printing amount of each basic color used for the color represented in the adjacent area CL are equal to or greater than a predetermined threshold value, or the maximum value and the minimum value. Trapping is selected when the difference from the value is greater than or equal to a predetermined threshold. If the maximum value is less than the predetermined threshold and the difference between the maximum value and the minimum value is less than the predetermined threshold, overprint is selected.

  In the above example, the threshold is individually set for each basic color. This may be a common value for all basic colors.

  In this case, in the determination of the representative value, the trapping is selected when the minimum value among the maximum plate amounts of the basic colors is equal to or greater than a predetermined threshold value. For example, in the case of FIG. 14A, the maximum value of the plate amount of each basic color is cyan = “75”, magenta = “80”, yellow = “85”, and black = “60”. The smallest is black “60”. Accordingly, trapping is selected when “60” is equal to or greater than a predetermined threshold. Alternatively, the maximum value, the average of the maximum values, the sum of the maximum values, or the like may be used instead of the minimum value among the maximum values of the plate amounts of each basic color.

  On the other hand, in the determination of the maximum plate amount difference, trapping is selected when the minimum of the differences between the maximum value and the minimum value of each basic color is equal to or greater than a predetermined threshold. Alternatively, instead of using the smallest difference among the basic colors, the largest, the average of the differences, or the sum of the differences may be used.

  In the determination of the representative value, the minimum value, the average value, or the total value may be used instead of the maximum value of the printing amount of each basic color.

  Next, the flow of image processing of this embodiment will be described with reference to the flowchart of FIG.

  In FIG. 15, when receiving the image data PD from the terminal device 2, the image output device 3 converts the data into values relating to the density of each basic color (# 311). Further, based on the converted value, it is determined whether or not a gray region (object GR) is included in the image PD (# 312). If not included (No in # 312), printing is executed as it is (# 324). If it is included (Yes in # 312), the area is extracted (# 313).

  Next, as the color data CR, the maximum value and the minimum value of the plate amount of each basic color included in the area adjacent to the extracted object GR are acquired (# 314).

  Subsequently, if the maximum value of the obtained plate amount of each basic color is “0”, that is, if the color of the adjacent region is only white (Yes in # 315), the processing after step # 321 is performed.

  If the maximum value of the plate amount is not “0” (No in # 315), it is determined whether the maximum value is large, that is, whether it is equal to or greater than a predetermined threshold (# 316). If it is equal to or greater than the threshold value (Yes in # 316), trapping is selected as processing to be performed on the image PR (# 318). If it is not equal to or greater than the threshold value (No in # 316), it is determined whether the difference between the maximum value and the minimum value acquired in Step # 314 is large, that is, whether it is equal to or greater than the predetermined threshold value (# 317).

  If it is equal to or greater than the threshold value (Yes in # 317), trapping is selected (# 318). If it is not equal to or greater than the threshold (No in # 317), overprint is selected (# 319). Then, the selected process is executed (# 320). In step # 320, the process described in FIG. 9 is executed.

  Thereafter, it is determined whether there is another gray area (# 321). If there is another gray area (Yes in # 321), the gray area is extracted (# 322), and the processes after step # 314 are repeated.

  If there is no other gray area (No in # 321), processed image data PS including the data created in step # 320 is created (# 323), and printing is executed based on the data (# 324). ).

  According to the image processing of the present embodiment, in the representative value determination, trapping is selected when the basic color plate amount included in the adjacent region CL is large. Therefore, even if a border is generated by trapping, the color of the adjacent region CL is dark, so that a portion darkened by the border is not conspicuous. In addition to this, it is possible to prevent white spots while preventing the adverse effects due to suction from appearing prominently.

  In the first and second embodiments, when the number of colors represented in the adjacent region CL is two or more, it may be difficult to appropriately reproduce the object GR by rich black (or overprint). , Trapping is selected unconditionally. However, even if the number of colors is two or more, if there is not much difference in the amount of basic colors used for those colors, it is often possible to reproduce an appropriate color by rich black. In this embodiment, even if the number of colors is 2 or more, if there is not much difference in the plate amount of the basic colors used for those colors, overprint is selected in the determination of the maximum plate amount difference. Is done. As a result, it is possible to prevent white spots without causing edging while maintaining the original color of the object GR.

Each threshold used in the present embodiment is determined from the color of the object GR.
[Second Embodiment]
FIG. 16 is a diagram illustrating an example of a functional configuration of the image output apparatus 3B according to the second embodiment, and FIG. 17 is a diagram illustrating an example of plate amounts of each basic color necessary for reproducing the object GR3 by overprinting. FIG. 18 is a flowchart for explaining the flow of image processing in the second embodiment.

  Hereinafter, processing of each unit of the image output apparatus 3B according to the second embodiment will be described with reference to FIG.

  As shown in FIG. 16, the image output device 3B includes an image data reception unit 301, a data storage unit 302, a color data acquisition unit 303, a process selection unit 304, an image processing unit 305, an image data output unit 306, a toner limit amount. An acquisition unit 307, a toner amount calculation unit 308, and the like are provided. The image output device 3B is similar to the image output device 3 in terms of hardware configuration and the like, and is used instead of the image output device 3 in the present embodiment.

  The processing in the image data receiving unit 301, data storage unit 302, color data acquisition unit 303, image processing unit 305, and image data output unit 306 is the same as that described in FIG.

  The toner limit amount acquisition unit 307 acquires the toner limit amount T1 of the image output device 3B. This toner limit amount T1 represents the upper limit of the total amount of toner to be used for performing appropriate printing. When printing, if the total amount of toner of each basic color exceeds the toner limit amount, the toner loading may be deteriorated or the toner may be peeled off due to poor fixing at the portion exceeding the toner limit amount.

  The toner amount calculation unit 308 calculates a toner amount T2 that is a total amount of toner of each basic color necessary for reproducing each object GR by overprinting based on the color data CR.

  The process selection unit 304 selects whether to perform overprinting or trapping on the image data PD based on the color data CR, the toner limit amount T1, and the toner amount T2. In the present embodiment, trapping is selected when the toner amount T2 exceeds the toner limit amount T1, and overprinting is selected when it does not exceed the toner limit amount T1. In this embodiment as well, during overprinting, a gray color is reproduced with rich black.

  Here, a method of selecting trapping or overprinting in the present embodiment will be specifically described with reference to FIG. In the present embodiment, the amount of toner is calculated by converting it into a plate amount.

  According to FIG. 17, the printing amount of each basic color necessary for reproducing the object GR3 by overprinting is cyan = “50”, magenta = “50”, yellow = “80”, and black = “40”. It is. Accordingly, the sum of the plate amounts (toner amount T2) is “220”. Here, for example, when the toner limit amount T1 is “200”, the toner amount T2 is equal to or greater than the toner limit amount T1, and therefore trapping is selected as a process to be performed on the object GR3.

  When the toner limit amount T1 is “250”, since the toner amount T2 is less than the toner limit amount T1, overprinting is selected.

  Hereinafter, the flow of image processing in the present embodiment will be described with reference to the flowchart of FIG.

  When receiving the image data PD from the terminal device 2, the image output device 3B acquires the color data CR of the adjacent region CL of each object GR included in the image PR (# 21). Next, the toner limit amount T1 is acquired (# 22). Subsequently, a toner amount T2 used when overprinting the object GR is calculated (# 23).

  Thereafter, as a process performed on the object in order to reduce unnaturalness in the vicinity of the boundary of the object GR, the trapping or overprinting is performed based on the comparison between the toner limit amount and the toner amount and the acquired color data CR. Either one is selected (# 24). Here, trapping is selected when the toner amount T2 is larger than the toner limit amount T1. Further, in addition to this, the determination of the number of colors, the determination of the adjacent area plate amount, the determination of the plate amount difference, the determination of the representative value, the determination of the maximum difference, or a combination thereof described in the first embodiment is performed. The trapping or overprinting may be selected by.

Then, the selected process is executed (# 25).
In general, in overprinting, since the object GR is reproduced by superimposing the toner of the object GR on the background toner, the toner amount T2 increases, and problems such as poor fixing are likely to occur. Also, for models with a small toner limit, if the amount of basic colors (cyan, magenta, yellow) in the background is large and the amount of basic colors (black) included in the object is small, it is appropriate for rich black. It may not be possible to obtain a large amount of CMYK plates. In such a case, overprinting cannot deal with it. In the image processing of the present embodiment, trapping is selected when the toner amount T2 exceeds the toner limit amount T1, so that the total amount of toner does not easily exceed the toner limit amount T1, and problems such as poor fixing occur. Can be suppressed.

  Conventionally, a user performs some processing on an image using an image editing application in order to reduce defects, or accepts some defects and performs only one process of trapping or overprinting. It was applied.

  However, when using an image editing application, the user needs knowledge and experience about image processing and is forced to bear a great burden. Further, when a single process is applied, conventional problems cannot be solved.

  According to the above-described embodiment, trapping or overprinting is performed based on the number of colors in adjacent regions, the plate amount of the region to be processed, the toner limit amount T1, the toner amount T2, or a combination thereof. Automatically selected under conditions suitable for each. As a result, problems in the conventional image processing can be greatly reduced. In addition, such image processing is automatically performed, so that high-quality printing can be realized without burdening the user.

  Furthermore, high-quality processing can be applied to products that are difficult to select, for example, controllers or printer drivers.

  In the above-described embodiment, an example in which the background region is the adjacent region CL in FIG. However, when there are overlapping objects GR, these objects GR are also adjacent areas CL to each other.

  Further, although the image processing in the above-described embodiment is performed on the image output device 3 or 3B side, this may be performed on the terminal device 2 side. In this case, the processing until the trapping or overprinting is performed in the image processing unit 305 is executed on the terminal device 2 side, and the processed image data PS created there is transmitted to the image output device 3 or 3B. Then, the image output device 3 or 3B executes printing based on the processed image data PS.

  The image output apparatus 3 or 3B is exemplified by an electrophotographic multifunction peripheral or a printer, but the image processing method according to the present embodiment is applied to any other image processing apparatus that performs trapping and overprinting. It is possible.

  In addition, the configuration of the entire image processing system 1, the terminal device 2, and the image output device 3 or each unit, the processing content, the processing order, the threshold value, each determination method, and the like may be appropriately changed in accordance with the spirit of the present invention. it can.

1 is a diagram illustrating an image processing system according to the present invention. It is a figure which shows the example of a schematic structure of an image output device. It is a figure which shows the example of a functional structure of an image output device. It is a figure which shows the example of the image which the user produced in the terminal device. It is a figure which shows the example of a look-up table. 4 is a flowchart for explaining a flow of image processing in the first embodiment. It is a figure for demonstrating edging and suction. 4 is a flowchart for explaining a flow of image processing in the first embodiment. It is a flowchart for demonstrating the example of the flow of a process at the time of performing trapping or overprint. It is a figure which shows the example of the plate amount of each basic color contained in an adjacent area | region. It is a figure which shows the example of the threshold value used in a 2nd Example. It is a figure which shows the example of the printing amount of each basic color contained in an object. It is a flowchart for demonstrating the flow of the image processing in a 2nd Example. It is a figure which shows the example of the printing amount of the basic color contained in an adjacent area | region. It is a flowchart for demonstrating the flow of the image processing in a 3rd Example. It is a figure which shows the example of a functional structure of the image output device in 2nd Embodiment. It is a figure which shows the example of the printing amount of each basic color required in order to reproduce an object by overprinting. It is a flowchart for demonstrating the flow of the image processing in 2nd Embodiment.

Explanation of symbols

1 Image processing system (image forming device)
2 Terminal device (image forming device)
3 Image output device (image forming device)
3B image output device (image forming device)
303 color data acquisition unit (color data acquisition means)
304 Process selection unit (selection means)
305 Image processing unit (execution means)
307 Toner limit amount acquisition unit (toner limit amount acquisition means)
308 Toner amount calculation unit (calculation means)
BR Near boundary CL Adjacent area (adjacent area)
CR color data (color data)
GR object (gray area)
PR Image T1 Toner limit amount T2 Toner amount

Claims (14)

An image processing method in an image forming apparatus for forming a color image using a plurality of basic colors,
A first step of obtaining color data of an adjacent area of an object included in the image;
A second step of selecting either trapping or overprinting based on the acquired color data as processing performed on the object in order to reduce unnaturalness in the vicinity of the boundary of the object;
A third step of executing the process selected in the second step,
In the adjacent area, only one color obtained by mixing the plurality of basic colors is used,
In the first step, the number of colors used in one or more adjacent areas adjacent to the object is acquired as the color data;
In the second step, the overprint is selected when the number of colors is 1, and the trapping is selected when the number is 2 or more.
An image processing method. The object is a gray area that can be reproduced only by black, which is one of the basic colors,
When performing the overprinting in the third step, gray is reproduced by rich black using a mixed color of the basic colors.
The image processing method according to claim 1. In the second step, even if the number of colors is 1, if the printing amount of the basic color used for the color is equal to or greater than a predetermined threshold, the trapping is selected.
The image processing method according to claim 1. In the second step, even if the number of colors is 1, the plate amount of the basic color used for the color is equal to or greater than a predetermined threshold or is used for the object If the plate amount difference between the basic color and the basic color used for the color is equal to or greater than a predetermined threshold, the trapping is selected.
The image processing method according to claim 1. An image processing method in an image forming apparatus for forming a color image using a plurality of basic colors,
A first step of obtaining color data of an adjacent area of an object included in the image;
A second step of selecting either trapping or overprinting based on the acquired color data as processing performed on the object in order to reduce unnaturalness in the vicinity of the boundary of the object;
A third step of executing the process selected in the second step,
In the adjacent area, only one color obtained by mixing the plurality of basic colors is used,
In the first step, as the color data, one or more adjacent regions adjacent to the object obtain a maximum value and a minimum value of the plate amounts of the same basic color, respectively ,
In the second step, when the difference between the maximum value and the minimum value is equal to or greater than a predetermined threshold, the trapping is selected, and the difference between the maximum value and the minimum value is less than the predetermined threshold. In case you choose the overprint,
An image processing method. An image processing method in an image forming apparatus for forming a color image using a plurality of basic colors,
A first step of acquiring color data of an adjacent area of an object included in the image, and processing performed on the object to reduce unnaturalness in the vicinity of the boundary of the object, A second step of selecting either trapping or overprinting based on;
A third step of executing the process selected in the second step,
In the adjacent area, only one color obtained by mixing the plurality of basic colors is used,
In the first step, as the color data, one or more adjacent regions adjacent to the object acquire a maximum value and a minimum value of plate amounts for the same basic color, respectively ,
In the second step, if the maximum value is equal to or greater than a predetermined threshold value, or the difference between the maximum value and the minimum value is equal to or greater than a predetermined threshold value, the trapping is selected, and the maximum value is equal to the predetermined value. If the difference between the maximum value and the minimum value is less than a predetermined threshold, the overprint is selected.
An image processing method. The object is a gray area that can be reproduced only by black, which is one of the basic colors,
When performing the overprinting in the third step, gray is reproduced by rich black using a mixed color of the basic colors.
The image processing method according to claim 5 or 6. The threshold used in the second step is determined according to the color of the object.
The image processing method according to claim 3. An image forming apparatus that forms a color image using a plurality of basic colors,
Color data acquisition means for acquiring color data of an adjacent area of an object included in the image;
Selection means for selecting either trapping or overprinting based on the acquired color data as a process performed on the object in order to reduce unnaturalness in the vicinity of the boundary of the object;
Execution means for executing the process selected by the selection means,
In the adjacent area, only one color obtained by mixing the plurality of basic colors is used,
The color data acquisition means acquires, as the color data, the number of colors used in one or more adjacent areas adjacent to the object ,
The selection means selects the overprint when the number of colors is 1, and selects the trapping when the number is 2 or more.
An image forming apparatus. An image forming apparatus that forms a color image using a plurality of basic colors,
Color data acquisition means for acquiring color data of an adjacent area of an object included in the image;
Selection means for selecting either trapping or overprinting based on the acquired color data as a process performed on the object in order to reduce unnaturalness in the vicinity of the boundary of the object;
Execution means for executing the process selected by the selection means,
In the adjacent area, only one color obtained by mixing the plurality of basic colors is used,
The color data acquisition means acquires, as the color data, a maximum value and a minimum value of plate amounts each having one or more adjacent regions adjacent to the object for the same basic color ,
The selecting means selects the trapping when the difference between the maximum value and the minimum value is equal to or greater than a predetermined threshold, and when the difference between the maximum value and the minimum value is less than the predetermined threshold. Select the overprint,
An image forming apparatus. An image forming apparatus that forms a color image using a plurality of basic colors,
Color data acquisition means for acquiring color data of an adjacent area of an object included in the image;
Selection means for selecting either trapping or overprinting based on the acquired color data as a process performed on the object in order to reduce unnaturalness in the vicinity of the boundary of the object;
Execution means for executing the process selected by the selection means,
In the adjacent area, only one color obtained by mixing the plurality of basic colors is used,
The color data acquisition means acquires, as the color data, a maximum value and a minimum value of plate amounts each having one or more adjacent regions adjacent to the object for the same basic color ,
The selection means selects the trapping when the maximum value is equal to or greater than a predetermined threshold value or the difference between the maximum value and the minimum value is equal to or greater than a predetermined threshold value, and the maximum value is equal to the predetermined threshold value. If the difference between the maximum value and the minimum value is less than a predetermined threshold, the overprint is selected.
An image forming apparatus. A computer program for performing image processing in an image forming apparatus that forms a color image using a plurality of basic colors,
A computer for controlling the image forming apparatus;
A first step of obtaining color data of an adjacent area of an object included in the image;
A second step of selecting either trapping or overprinting based on the acquired color data as processing performed on the object in order to reduce unnaturalness in the vicinity of the boundary of the object;
Performing a third step of executing the process selected in the second step,
In the adjacent area, only one color obtained by mixing the plurality of basic colors is used,
In the first step, the number of colors used in one or more adjacent areas adjacent to the object is acquired as the color data;
In the second step, when the number of colors is 1, the overprint is selected, and when the number is 2 or more, the trapping is selected.
A computer program to be executed. A computer program for performing image processing in an image forming apparatus that forms a color image using a plurality of basic colors,
A computer for controlling the image forming apparatus;
A first step of obtaining color data of an adjacent area of an object included in the image;
A second step of selecting either trapping or overprinting based on the acquired color data as processing performed on the object in order to reduce unnaturalness in the vicinity of the boundary of the object;
Performing a third step of executing the process selected in the second step,
In the adjacent area, only one color obtained by mixing the plurality of basic colors is used,
In the first step, as the color data, one or more adjacent regions adjacent to the object acquire a maximum value and a minimum value of plate amounts for the same basic color, respectively ,
In the second step, when the difference between the maximum value and the minimum value is equal to or greater than a predetermined threshold, the trapping is selected, and the difference between the maximum value and the minimum value is less than the predetermined threshold. In the case of selecting the overprint, processing,
A computer program to be executed. A computer program for performing image processing in an image forming apparatus that forms a color image using a plurality of basic colors,
A computer for controlling the image forming apparatus;
A first step of obtaining color data of an adjacent area of an object included in the image;
A second step of selecting either trapping or overprinting based on the acquired color data as processing performed on the object in order to reduce unnaturalness in the vicinity of the boundary of the object;
Performing a third step of executing the process selected in the second step,
In the adjacent area, only one color obtained by mixing the plurality of basic colors is used,
In the first step, as the color data, one or more adjacent regions adjacent to the object acquire a maximum value and a minimum value of plate amounts for the same basic color, respectively ,
In the second step, if the maximum value is equal to or greater than a predetermined threshold value, or the difference between the maximum value and the minimum value is equal to or greater than a predetermined threshold value, the trapping is selected, and the maximum value is equal to the predetermined value. The overprint is selected when the difference between the maximum value and the minimum value is less than a predetermined threshold.
A computer program to be executed.