JP2017173652A - Image formation device and white image formation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure a high whiteness level and a high performance of hiding a base color and achieve a high gradation reproducibility in image formation using a white toner.SOLUTION: An image formation device 1 is equipped with image formation units 6-5 to 6-7 filled with white (W) instead of image formation units 6-1 to 6-3 filled with cyanogen (C), magenta (M), and yellow (Y). The image formation device 1 generates a gray scale image 170 expressed by a single-color printing rate by converting a colored image into a gray scale image, corrects the printing rate of the gray scale image 170 based on the total printing rate and the number of image formation units 6-5 to 6-7 filled with white (W), and forms a white image 220 by printing a gray scale image 180 with the corrected printing rate using the image formation units 6-5 to 6-7 filled with white (W).SELECTED DRAWING: Figure 6

Description

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

  Conventionally, in an electrophotographic image forming apparatus, a photosensitive drum in a drum set is uniformly charged and initialized, a latent image is formed on the photosensitive drum by optical writing, and the latent image is transferred from a toner cartridge. A toner image is formed (developed) with the toner, and the toner image is directly or indirectly transferred to a printing medium and fixed by a fixing device.

  In the above image forming apparatus, as a method of printing a desired image or logo mark on a transfer medium such as a T-shirt, trainer, work clothes, or a transfer medium such as wood or metal plate, the image is transferred to a release sheet. There is known a method for producing a thermal transfer print sheet in which an image to be thermally transferred to a medium (color toner image) and a binder toner (transfer base material: thermoplastic resin) that serves to adhere to a transfer medium are fixed. Further, in the image forming apparatus, an image to be thermally transferred to a dark transfer medium such as black is being created only with white toner (hereinafter, white (W)).

  When an image is created using only white toner (hereinafter referred to as white toner), for example, in an image forming apparatus including four image forming units, one white, for example, cyan (C) image forming unit is used as one white toner. It is conceivable to replace the image forming unit (W) and print an image composed only of the white (W).

  FIG. 7A is a chart showing an original image (color), and FIG. 7B is a chart showing the density of a white image in which the original image (color) is formed by one white (W). It is. In the original image (color) 100 shown in FIG. 7A, in the upper stage, the density of cyan (C) is C0 (0%), C5 (5%), C10 (10) in the vertical direction from top to bottom. %), ..., C90, and the density of magenta (M) in the horizontal direction from right to left is M0 (0%), M5 (5%), M10 (10%), ..., C90 (90%), Each intersection block has a mixed color of cyan (C) and magenta (M).

  In the upper part of FIG. 7A, the difference in density is represented by the number of diagonal lines, the diagonal line from the upper left to the lower right indicates magenta (M), and the diagonal line from the upper right to the lower left indicates cyan (C). Represents. In the lower part of FIG. 7A, black (K), yellow (Y), magenta (M), cyan (C), green (G), red (R), and blue (B) color patch portions are shown. Is arranged. In the color patch portion, the difference in color is represented by the difference in hatching.

  When a white image is formed on a black transfer medium with a single white (W) from the original image (color) 100 shown in FIG. 7A, a white image 110 shown in FIG. 7B is obtained. It is done. For example, when cyan (C) is replaced with white (W), a white image 110 based on white (W) is obtained using only cyan (C) image data. In this case, in the original image (color) 100, the brightness difference due to the color, that is, the higher the luminance, the smaller the amount of white (W) applied (the background color is transparent), and the lower the luminance, the white (W ) Is increased.

  In the upper part of FIG. 7B, the density (monochrome) difference is indicated by the number of hatched lines. Further, the lower patch portion of FIG. 7B shows the density of the white image 110 (corresponding colors are indicated by alphabets in parentheses). Similar to the color chart, the difference in density is represented by the difference in hatching (see the density index at the bottom). In this case, the density of white (W) corresponding to yellow (Y) is low (the applied amount is small), the background color appears, and white (W) corresponding to black (K) and blue (B) Concentration is high (loading amount is increasing). On the other hand, white (W) corresponding to magenta (M), green (G), and red (R) has the same density, and the color difference cannot be reproduced.

  FIG. 8A is a chart showing the density of an image obtained by performing gray scale conversion on the original image (color) 100, and FIG. 8B shows one white (W) based on the gray scale converted image. It is a chart figure which shows the density | concentration of the white image formed by (). When the color chart of the original image (color) 100 shown in FIG. 7A is converted to gray scale, a gray scale image 120 shown in FIG. 8A is obtained. Further, when a white image is formed on a black transfer medium with one white (W) and white (W) based on the grayscale image 120 shown in FIG. 8A, the white color shown in FIG. 8B is obtained. An image 130 is obtained.

  When the gray scale conversion is performed, as shown in FIG. 8A, in the gray scale image 120, the density change of the mixed color of cyan (C) and magenta (M) in the upper stage is reproduced relatively faithfully. Has been. The lower patch portion shows the print rate after gray scale conversion in the color patch portion of the color chart of the original image (color) 100 (gray scale value when pure black is 100%). The print ratio after gray scale conversion is 95% for black (K) and 96% for blue (B), which is close to 100%.

  As for the black (K) and blue (B) of the patch portion, which shows a value close to 100% shown in FIG. 8A, when black and white printing is performed on black (K) on a blank sheet, it is almost pure black. Printed in black close to. However, when printing is performed with one white (W) image forming unit on a black background, as shown in FIG. 8B, in the white image 130, the black of the background is seen through the white (W), and the black portion Even in (K) and the blue portion (B), sufficient whiteness cannot be obtained. In the figure, it is shown by oblique lines with coarse intervals. When sufficient whiteness is obtained, “white (no hatching)” is obtained (see the density index at the bottom).

  As described above, when only one color toner image forming unit is replaced with one white (W) image forming unit, the amount of white (W) applied is insufficient. When transferred onto a transfer medium, the background concealing property is insufficient, and whiteness and gradation reproducibility cannot be obtained sufficiently.

  Therefore, for example, in Patent Document 1, in order to solve the whiteness deficiency at the time of printing with white (W), 2 to 4 image forming units of white (W) are mounted and black of a four-color stacking type is used. A technique for performing printing and a technique for performing printing in colors of two to three colors have been proposed. With respect to an image forming apparatus that cannot perform black printing in a four-color layered form, it is disclosed that printing is performed in dark brown or indigo.

JP 2014-126867 A

  However, the above-described conventional technique of Patent Document 1 is a technique for increasing the amount of white (W) applied in order to eliminate insufficient whiteness at the time of printing, and is white that is close to the gradation reproducibility of the original image (color). Since the purpose is not to obtain an image, it is possible to ensure the background concealment, but it is not possible to obtain the gradation reproducibility of the original image (color).

  Therefore, as proposed in the above-described prior art of Patent Document 1, all the color (CMY) image forming units (three units) are replaced with white (W) image forming units (three units). A method for obtaining high gradation reproducibility while ensuring the background concealment will be considered.

  FIG. 9 is a chart showing the density of a white image printed without grayscale conversion using three white (W) image forming units. All the color (CMY) image forming units are replaced with white (W) image forming units, respectively, and the original image (color) 100 data represented by the color chart shown in FIG. A white image shown in FIG. 9 is printed as it is (on a cyan (C), magenta (M), and yellow (Y) image) on a black transfer medium with three white (W) image forming units. 140 is obtained. As shown in FIG. 9, extremely high whiteness can be obtained, but as is apparent from the lower patch part, the color difference is hardly understood.

  This means that the CMY value of the color patch portion of the original image (color) 100 represented by the color chart shown in FIG. 7A is directly replaced with the density of white (W) and overprinted. ), The toner amounts of magenta (M) and cyan (C) are not different, and the brightness difference (luminance) due to the color cannot be reproduced. That is, 100% of yellow (Y) and 100% of cyan (C) are white (W) having the same density. Similarly, red (R) of “yellow (Y) 50% + magenta (M) 50%” and blue (B) of “magenta (M) 50% + cyan (C) 50%” have the same density of white (W The color difference cannot be reproduced.

  Further, in the prior art of Patent Document 1, a technique for performing printing with four-color stacked black is proposed. This is considered to be a technique for printing a monochrome image by so-called process black in which four colors are mixed.

  FIG. 10A is a chart showing the density of an image obtained by performing gray scale conversion on the three CMY colors of the original image (color) 100, and FIG. 10B shows the formation of three white (W) images. It is a chart figure which shows the density | concentration of the white image formed based on the image data which carried out the gray scale conversion using the unit. When the original image (color) 100 represented by the color chart shown in FIG. 7A is converted into gray scales for each of the three colors of CMY, as shown in FIG. ) Is generated in the lightness (the same as FIG. 8A). The numerical values in the lower patch part are the CMY values constituting the gray. That is, in order to express gray (black gradation) with three colors of CMY, CMY must be mixed and printed at an appropriate ratio. This CMY ratio is a CMY value. In other words, the gray scale image 150 obtained by the gray scale conversion is derived as a CMY value for realizing with three colors of CMY. In the illustrated example, for example, black (K) is composed of 82 for cyan (C), 73 for magenta (M), and 74 for yellow (Y). Similarly, for example, yellow (Y) is composed of 10 for cyan (C), 6 for magenta (M), and 6 for yellow (Y).

  When the gray scale image shown in FIG. 10A is printed on a black transfer medium using three white (W) image forming units, the luminance difference is reproduced in gradation as shown in FIG. 10B. A white image 160 that can be obtained and has sufficient whiteness in the dark portion is obtained. However, the CMY values constituting the gray of each density of the gray scale image 150 obtained here are not equal as shown in the patch portion of FIG. This CMY value is a value obtained by adjusting the blending amount of each CMY color in order to reproduce a well-balanced gray in which the colors are not biased, with a little more cyan (C), magenta (M), and yellow (Y). Is a little blended. As shown in FIG. 10B, the gradation reproduction of the white image 160 obtained by overprinting three white (W) of the same color with this CMY value is as shown in FIG. 10 (a). It is not an accurate reverse image.

  As described above, even if the conventional technique of Patent Document 1 and further the technique of Patent Document 1 are expanded, if the original image is in color, if the white image is printed in white (W), the original image It was difficult to reproduce the gradation of the image (color) 100.

  Accordingly, an object of the present invention is to achieve high gradation reproducibility while ensuring high background concealment when an image is formed with white toner.

  An image forming apparatus according to the present invention is an image forming apparatus in which a plurality of image forming units can be mounted. The image forming apparatus generates gray scale image data based on color image data, and the gray image generated by the generating means. Correction means for correcting the scale image data based on the number of mounted image forming units filled with white toner, and control for forming an image pattern made of the white toner based on the gray scale image data corrected by the correction means. Means.

  An image forming apparatus according to the present invention includes: a first conversion unit that generates a single-color grayscale image represented by a single-color print rate by performing grayscale conversion on a color image to be printed; and the first conversion unit that generates the color image. Correcting means for correcting the printing rate of the single-color gray scale image based on the total printing rate of the image forming apparatus and the number of image forming units filled with white toner, and correcting the single-color gray scale image Image forming control means for forming a white image by printing using the image forming unit filled with the white toner at a printing rate corrected by the means.

  The white image forming method according to the present invention includes a step of generating a monochrome grayscale image represented by a monochrome printing rate by performing grayscale conversion on a color image to be printed, and a printing rate of the generated monochrome grayscale image. Correcting based on the total printing rate of the image forming apparatus and the number of image forming units filled with white toner, and the monochrome grayscale image is filled with the white toner at the corrected printing rate. Forming a white image by printing using the image forming unit.

  According to the present invention, when forming an image with white toner, it is possible to ensure high background concealment and to realize high gradation reproducibility.

1 is a cross-sectional view illustrating an internal configuration of an image forming apparatus 1 according to an embodiment of the present invention. FIG. 3 is a conceptual diagram illustrating a combination of toners attached to the image forming apparatus 1 according to the present embodiment. 2 is a circuit block diagram including a control device of the image forming apparatus 1 according to the present embodiment. FIG. It is a chart for demonstrating the black monochrome grayscale conversion process by the image forming apparatus 1 of this embodiment. FIG. 6 is a chart showing the density of a white image formed based on a gray scale that has been subjected to black single-color gray scale conversion in the image forming apparatus 1 according to the present embodiment and whose CMY toner amount ratio has been corrected. 5 is a flowchart for explaining an operation (monochromatic image printing process) of the image forming apparatus 1 according to the present embodiment. FIG. 2 is a chart showing the color of an original image (color) 100 and a chart showing the density of a white image formed by using one white (W) for the original image (color) 100. FIG. 4 is a chart showing the density of an image obtained by performing gray scale conversion on an original image (color) 100, and a chart showing the density of a white image formed with one white (W) based on the gray scale converted image. FIG. 6 is a chart showing the density of a white image formed without grayscale conversion using three white (W) image forming units. Formed on the basis of a chart showing the density of an image obtained by performing gray scale conversion on three CMY colors of the original image (color) 100 and image data obtained by performing gray scale conversion using an image forming unit of three white toners (W). It is a chart figure which shows the density | concentration of the obtained white image.

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

A. Configuration of Embodiment FIG. 1 is a cross-sectional view showing an internal configuration of an image forming apparatus 1 according to an embodiment of the present invention. In the figure, the image forming apparatus 1 according to the present embodiment is not a system that directly transfers a toner image onto a sheet (a printing medium), but temporarily transfers the toner image onto an intermediate transfer belt, and then vertically extends to a secondary transfer unit. The toner image is secondarily transferred onto the conveyed paper via an intermediate transfer belt. However, the present invention is not limited to the secondary transfer method, and can be applied to other transfer methods such as a method of directly transferring a toner image onto a sheet.

  The image forming apparatus 1 includes an image forming unit 2, a duplex printing conveyance unit 3, a paper feeding unit 4, and a fixing unit 5. The image forming unit 2 has a configuration in which four image forming units 6 (6-1, 6-2, 6-3, 6-4) are arranged in a multistage manner, and each image forming unit 6 is not illustrated. It is configured to be detachable from the station (slot).

  The three image forming units 6-1, 6-2, and 6-3 each form a monocolor image using cyan (C), magenta (M), and yellow (Y) color toners that are subtractive three primary colors. To do. The fourth image forming unit 6-4 following the three image forming units 6-1, 6-2, 6-3 forms a monochrome image with black (K) toner.

  Below the image forming unit 6, an intermediate transfer belt 14 is disposed close to the lower surface of the photosensitive drum 7. A primary transfer roller 15 made of a conductive foam sponge is disposed so as to press the lower surface of the photosensitive drum 7 with the intermediate transfer belt 14 interposed therebetween. The intermediate transfer belt 14 is made of a conductive sheet-like member made of resin containing conductive carbon or an ion conductive substance, and has a flat loop shape from substantially the left and right sides of the figure at the center of the main unit. This is an endless transfer belt that extends.

  The intermediate transfer belt 14 is stretched around a driving roller 16 and a driven roller 17 and is circulated in a counterclockwise direction in the figure by the driving roller 16, and circulates in a counterclockwise direction indicated by arrows a, b, and c in the figure. Moving. The toner image formed by the image forming unit 6 is directly transferred (primary transfer) to the belt surface of the intermediate transfer belt 14 by the primary transfer roller 15 as the photosensitive drum 7 rotates. The intermediate transfer belt 14 conveys the toner image directly transferred (primary transfer) to the belt surface to a transfer position to the paper 22 for further transfer (secondary transfer) to the paper 22. A belt cleaner 20 is disposed in contact with the surface of the intermediate transfer belt 14. The belt cleaner 20 removes residual toner from the intermediate transfer belt 14 after the secondary transfer.

  The belt position control mechanism 18 includes three primary transfer rollers 15 corresponding to the three image forming units 6-1, 6-2, and 6-3 of cyan (C), magenta (M), and yellow (Y). Rotate and move in the same cycle around the saddle-shaped support shaft. The belt position control mechanism 18 rotates and moves one primary transfer roller 15 corresponding to the black (K) image forming unit 6-4 at a timing different from that of the three primary transfer rollers 15. 14 is separated from the photosensitive drum 7.

  That is, the belt position control mechanism 18 corresponds to the position of the intermediate transfer belt 14 in the full color mode (all four primary transfer rollers 15 are in contact with the intermediate transfer belt 14) and the monochrome mode (image forming unit 6-4). Only the primary transfer roller 15 is in contact with the intermediate transfer belt 14) and all non-transfer modes (all four primary transfer rollers 15 are separated from the intermediate transfer belt 14).

  The paper feed unit 4 includes two paper feed cassettes 21 arranged in two upper and lower stages. A large number of cut sheets 22 are accommodated in one or both of the sheet feed cassettes 21 of the sheet feed unit 4. Near the paper feed opening (right side in the figure) of the two paper feed cassettes 21, a paper feed roller 23, a feed roller 25, a separating roller 26, and a standby conveyance roller pair 27 are arranged, respectively. The sheet 22 is unloaded from the sheet feeding cassette 21 by one rotation of the sheet feeding roller 23, and is fed to the standby conveying roller pair 27 through the feeding roller 25 and the separating roller 26.

  A secondary transfer roller 30 that is in pressure contact with the driven roller 17 via the intermediate transfer belt 14 is disposed in the paper conveyance direction (vertical upward direction in the drawing) of the standby conveyance roller pair 27. The intermediate transfer belt 14, the driven roller 17, and the secondary transfer roller 30 form a secondary transfer portion to the paper 22.

  A fixing unit 5 composed of a belt-type heat fixing unit is disposed downstream (upward in the drawing) of the secondary transfer unit. On the further downstream side of the fixing unit 5, a pair of discharge rollers 31 that discharges the fixed sheet from the fixing unit 5 and a pair of discharge rollers that discharge the discharged sheet to a discharge tray 32 formed on the upper surface of the apparatus. 33 is arranged.

  The duplex printing conveyance unit 3 includes a return path that branches in the right lateral direction in the drawing from an intermediate conveyance path between the carry-out roller pair 31 and the paper discharge roller pair 33. This return path includes a start return path 34a, an intermediate return path 34b that bends downward, a terminal return path 34c that bends in the left lateral direction and finally reverses the return sheet, and four sets arranged in the middle of these return paths. A pair of return rollers 35a, 35b, 35c, and 35d is provided. The exit of the end return path 34 c communicates with a conveyance path to the pair of standby conveyance rollers 27 corresponding to the sheet feeding cassette 21 below the sheet feeding unit 4.

  The image forming apparatus 1 shown in FIG. 1 is a system that secondarily transfers the toner image primarily transferred to the intermediate transfer belt 14 to the paper 22 via the intermediate transfer belt 14, but is not limited thereto. A system in which a toner image is directly transferred to the paper 22 may be used.

Next, the image forming unit 6 will be described.
The image forming units 6-1 to 6-4 have the same configuration except for the color and type of toner stored in the toner cartridge 19. Therefore, hereinafter, the configuration of the image forming unit 6 will be described by taking the image forming unit 6-4 as an example.

  As described above, the image forming unit 6 includes a drum set 11 that can be attached to and detached from the station (slot), and a toner cartridge 19 that is configured to be attachable to and detachable from the station (slot) and is fitted to the corresponding drum set 11. Consists of. The drum set 11 includes a photosensitive drum 7 at the bottom. The peripheral surface of the photosensitive drum 7 is made of, for example, an organic photoconductive material. A developing device including a cleaner 8, a charging roller 9, an optical writing head 10, a developing roller 12, and the like is disposed in contact with or around the periphery of the photosensitive drum 7.

  Further, as shown by C, M, Y, and K in the drawing, the toner cartridge 19 accommodates any toner of cyan (C), magenta (M), yellow (Y), and black (K). ing. A toner supply mechanism for supplying toner from the toner cartridge 19 toward the drum set 11 is provided below the toner cartridge 19.

  The drum set 11 has the above-described developing roller 12 disposed in a lower side opening, a toner stirring member, a toner supply roller 13 for supplying toner to the developing roller 12, and a toner placed on the developing roller 12. A doctor blade or the like that regulates the layer to a certain layer thickness is provided. An optical writing head 10 on the main unit side is disposed in the vicinity of the upper surface located between the charging roller 9 and the drum set 11 of the photosensitive drum 7.

  The photosensitive drum 7 rotates in the clockwise direction in the figure. First, by applying charge from the charging roller 9, the peripheral surface of the photosensitive drum 7 is uniformly charged and initialized. Next, an electrostatic latent image is formed on the peripheral surface of the photosensitive drum 7 by optical writing from the optical writing head 10 based on the print information.

  The electrostatic latent image is converted into a toner image (development) by the toner stored in the toner cartridge 19 by the developing process by the developing roller 12. The toner image developed on the peripheral surface of the photosensitive drum 7 is directly transferred (primary transfer) to the belt surface of the intermediate transfer belt 14 by the primary transfer roller 15 as the photosensitive drum 7 rotates.

  FIG. 2 is a conceptual diagram showing a combination of toners mounted on the image forming apparatus 1 according to the present embodiment. In the present embodiment, when forming a white image for thermal transfer with a single color of white (W), cyan (C), magenta (M), yellow (Y) shown in FIG. 6-2 and 6-3 are replaced with white (W) image forming units 6-5, 6-6, and 6-7, and the black (K) image forming unit 6-4 is formed with the binder (B). Replace with unit 6-8. That is, a white image is formed in white (W) by the three image forming units 6-5, 6-6, and 6-7. In this case, the image forming unit 6-8 of the binder (B) is mounted. However, in order to simplify the explanation, printing with the binder (B) is not performed.

  FIG. 3 is a circuit block diagram including the control device of the image forming apparatus 1 according to the present embodiment. As shown in FIG. 3, the circuit block 39 has a central processing unit (CPU) 40 as a center, and an interface controller (I / F_CONT) 41 and a printer controller (PR_CONT) 42 are connected to the CPU 40 via data buses. It is connected. A printer printing unit 43 is connected to the PR_CONT 42.

  The CPU 40 is connected to a ROM (read only memory) 44, an EEPROM (electrically erasable programmable ROM) 45, an operation panel 46 of the main body operation unit, and a sensor unit 47 to which outputs from sensors arranged in the respective units are input. ing.

  A system program is stored in the ROM 44, and the CPU 40 performs processing by controlling each unit in accordance with the system program.

  The I / F_CONT 41 converts, for example, print data supplied from a host device such as a personal computer into bitmap data and develops it in the frame memory 48.

  In the frame memory 48, storage areas are set for each of cyan (C), magenta (M), yellow (Y), and black (K), and data of each color is developed in the corresponding area. The data developed in the frame memory 48 is output to the PR_CONT 42 and is output from the PR_CONT 42 to the printer printing unit 43. When image formation is performed in white (W), white (W) data is developed using a storage area corresponding to the replaced color. That is, a white image in white (W) is printed based on the data developed in the storage areas of cyan (C), magenta (M), and yellow (Y).

  The printer printing unit 43 is an image having a driven unit (not shown) including the photosensitive drum 7 shown in FIG. 1, a charging roller 9, an optical writing head 10, etc. under the control of the PR_CONT 42. A belt position control mechanism 18 for driving the forming unit 2 and the vertical transfer of the intermediate transfer belt 14 is provided.

  The printer printing unit 43, in normal color printing, corresponds to the image data of each color of cyan (C), magenta (M), yellow (Y), and black (K) shown in FIG. The feeding head 10 is supplied. In addition, when printing a white image in white (W), the printer printing unit 43 receives image data corresponding to cyan (C), magenta (M), and yellow (Y), which have been converted to a black single-color gray scale, which will be described later. This is supplied to the optical writing heads 10 of the corresponding white (W) image forming units 6-5 to 6-7. In addition, the printer printing unit 43 forms an electrostatic latent image on the photosensitive drum 7 based on the image data by the optical writing head 10 via the developing unit 49 and a color (corresponding to the formed electrostatic latent image). YMC) or development with white (W) toner is controlled.

  Further, the printer printing unit 43 performs various controls such as an applied voltage to a heat generating unit built in the heat roller of the fixing unit 5 and adjustment of pressure applied to the pressure roller that presses the heat roller via the fixing unit 50. Control the output. Further, the printer printing unit 43 outputs a driving output for performing the vertical movement of the belt position control mechanism 18 of the intermediate transfer belt 14 and the rotational driving of the driving roller 16 that circulates and moves the intermediate transfer belt 14 via the belt driving unit 51. Control.

  In normal color printing, the CPU 40 transfers cyan (C), magenta (M), and yellow (Y) to transfer toner images of three color images stored in the frame memory 48 at a predetermined timing. Are output to PR_CONT42. The PR_CONT 42 outputs image data of each color of cyan (C), magenta (M), and yellow (Y) to the printer printing unit 43 at the predetermined timing.

  The printer printing unit 43 sets the image forming units 6-1 to 6-3 to the printing state at the predetermined timing, and converts the image data of each color of cyan (C), magenta (M), and yellow (Y) into an image. The toner images are supplied to the optical writing heads 10 of the forming units 6-1 to 6-3, and toner images of cyan (C), magenta (M), and yellow (Y) are transferred onto the paper 22. Further, the printer printing unit 43 fixes the toner images of cyan (C), magenta (M), and yellow (Y) transferred to the paper 22.

  In addition, when printing a white image in white (W) (that is, image formation with white (W) on a thermal transfer sheet), the CPU 40 has three colors YMC stored in the frame memory 48 at a predetermined timing. The gray scale image reflecting the brightness difference (luminance) due to the color of the original image (color) 100 is generated by reading the image data of the original image and performing the black monochrome gray scale conversion.

  In addition, the CPU 40 assigns the CMY toner amount to the clay scale image based on the total print rate of toner overlap (up to 240% in this embodiment) defined by restrictions on transfer performance and fixing performance. Correct the alignment. The CPU 40 outputs, to the PR_CONT 42, grayscale image data that has been subjected to black-and-white grayscale conversion and the CMY toner amount ratio has been corrected at a predetermined timing.

  The PR_CONT 42 is an image of each color of cyan (C), magenta (M), and yellow (Y) that has been subjected to black monochrome grayscale conversion at the predetermined timing and the CMY toner amount ratio has been corrected. Output data. The printer printing unit 43 sets the image forming units 6-1 to 6-3 to the printing state at the predetermined timing, performs black single-color gray scale conversion, and corrects the CMY toner amount ratio cyan (C ), Magenta (M), and yellow (Y) image data are supplied to the optical writing heads 10 of the image forming units 6-5 to 6-7, and white (W) toner is placed on a thermal transfer sheet (not shown). Transfer the image. Further, the printer printing unit 43 fixes the white (W) toner image transferred onto a thermal transfer sheet (not shown).

B. Operation of Embodiment Next, the operation according to the embodiment of the present invention will be described.
FIGS. 4A and 4B are charts for explaining the black monochrome grayscale conversion processing by the image forming apparatus 1 of the present embodiment. In the present embodiment, the original image (color) 100 represented by the color chart shown in FIG. Thereby, the gray scale image 170 shown in FIG. 4A is obtained. In the present embodiment, the gray scale image 170 obtained by the black monochrome gray scale conversion is derived as a black print rate for realizing a single color.

  That is, 95% for black (K), 13% for yellow (Y), 66% for magenta (M), 51% for cyan (C), 64% for green (G), 70% for red (R), And blue (B) is 96%. This black printing rate is the black printing rate of each gray when pure black (color code # 000000) is 100%. As shown in the figure, the black printing rate of the patch portion of the gray scale image 170 reproduces the gray gradation reflecting the color luminance.

  In the present embodiment, the total printing rate of toner overlap is set to a maximum of 240% due to restrictions on transfer performance and fixing performance. Even when black is expressed by three colors of CMY, it is not necessary that each color is 100%, and it is possible to obtain a sufficient black reproduction by achieving a balance with a CMY total of about 240%. Accordingly, the total printing amount is expanded to a maximum of 240% based on the black printing rate shown in FIG. 4A, and the toner amount is changed to three colors of CMY, that is, three white (W) image forming units 6. Corrections are made such as -5, 6-6, and 6-7.

  The printing rate of the gray scale image 170 shown in FIG. 4A is [G1]. Let the printing rate after expansion to the total printing rate (240%) be [G2]. Based on the total printing rate (240%), the distribution of the toner amount in the gray scale image 170 printed by the three image forming units 6-5 to 6-7 for CMY is corrected. If the corrected printing rates are [Gc], [Gm], and [Gy], the conversion formula is expressed as follows.

Total printing rate = 240%
G2 = 240 × [G1] / 100
Gc = [G2] / 3
Gm = [G2] / 3
Gy = [G2] / 3

  That is, the gray printing rate range is expanded from 100% to 240%, which is the total printing rate, and is distributed evenly to the three image forming units 6-5 to 6-7. As a result, a gray scale image 180 shown in FIG. That is, black (K) is 76%, yellow (Y) is 10%, magenta (M) is 53%, cyan (C) is 41%, green (G) is 51%, red (R) is 56%, And blue (B) will be 77%. For example, in the case of black (K) in FIG. 4B, the cyan (C) printing rate is 76%, the magenta (M) printing rate is 76%, and the yellow (Y) printing rate is 76%. Is to do. In the case of yellow (Y) in FIG. 4B, the cyan (C) printing rate is 10%, the magenta (M) printing rate is 10%, and the yellow (Y) printing rate is 10%. Then, based on the corrected printing rate of the gray scale image 180 shown in FIG. 4B, each image forming unit 6-5 to 6-7 forms a white image with white (W).

  FIG. 5 is a chart showing the density of a white image formed on the basis of a gray scale that has been subjected to black single-color gray scale conversion and whose CMY toner amount ratio has been corrected in the image forming apparatus 1 according to the present embodiment. The upper part of FIG. 5 shows three white (W) based on the grayscale image 180 for CMY in which the toner amount distribution is corrected based on the total printing rate (240%) shown in FIG. The white images 190, 200, and 210 printed on the black transfer medium in each of the toner image forming units 6-5 to 6-7 are shown.

  A white image 220 shown in the lower part of FIG. 5 is formed by superimposing and fixing the white (W) white images 190, 200, and 210 on CMY. As a result, it is possible to secure the amount of white (W) applied in the dark color portion and to realize accurate gradation reproducibility as a single color image.

  FIG. 6 is a flowchart for explaining the operation (single-color image printing process) of the image forming apparatus 1 according to the present embodiment. When a print image is input to the image forming apparatus 1 (step S10), the CPU 40 determines whether white printing using white (W) is instructed by the user from the operation panel 46 (step S12).

  If white printing is not instructed, the image forming apparatus 1 includes cyan (C), magenta (M), yellow (Y), and black (K) image forming units as shown in FIG. 6-1 to 6-4 are attached, and when white printing is instructed, as shown in FIG. 2, the image forming apparatus 1 includes cyan (C) and magenta (M). This means that white (W) image forming units 6-5 to 6-7 are mounted instead of yellow (Y) image forming units 6-1 to 6-2.

  If white printing using white (W) is not instructed (NO in step S12), the CPU 40 analyzes the input print image and determines whether it is a color image or a monochrome image. Is determined (step S14). An image formed with process black mixed with color is regarded as a color image.

  If the image is a color image (“color” in step S14), the CPU 40 performs a normal grayscale image conversion process (step S16). The normal grayscale image conversion processing referred to here is processing for deriving CMY values so that grayscale can be output in three colors of cyan (C), magenta (M), and yellow (Y) (see FIG. 10). . As a result, a gray scale image represented by CMY values of three colors of cyan (C), magenta (M), and yellow (Y) is obtained. Thereafter, the process proceeds to step S26.

  On the other hand, if the image is a monochrome image (“monochrome” in step S14), the CPU 40 does not perform the gray scale conversion process and proceeds to step S26.

  Next, the CPU 40 outputs a gray scale image (CMY value) to each of the four image forming units 6-1 to 6-4, and cyan (C), magenta (M), and yellow (Y). , And black (K), a print image (black) is generated (step S26).

  Next, the CPU 40 outputs print images (black) formed by the image forming units 6-1 to 6-4 of cyan (C), magenta (M), yellow (Y), and black (K). (Step S28). That is, toner images output using cyan (C), magenta (M), yellow (Y), and black (K) are superimposed on the intermediate transfer belt 14, and the combined black toner image is secondary. The image is transferred and fixed on the paper 22 by the transfer roller 30 and output.

  On the other hand, when white printing using white (W) is instructed (YES in step S12), the CPU 40 analyzes the input print image and determines whether it is a color image or a monochrome image. Is determined (step S18). An image formed with process black mixed with color is regarded as a color image.

  If the image is a color image (“color” in step S18), the CPU 40 performs a black monochrome grayscale image conversion process (step S20). In the black monochrome grayscale image conversion process, as shown in FIG. 4A, a black print rate for realizing a single color is derived. Thereafter, the process proceeds to step S22.

  On the other hand, if the image is a monochrome image (“monochrome” in step S18), the CPU 40 does not perform the monochrome grayscale conversion process and proceeds to step S22.

  Next, as described above, the CPU 40 corrects the toner amount distribution (printing rate) in the grayscale image 170 that has been converted to the black monochrome grayscale image based on the total printing rate (for example, 240%) (step S22). ). As a result, the gray scale image 180 shown in FIG. 4B is obtained.

  Next, the CPU 40 sets the corrected and distributed grayscale image 180 as all CMY image data (step S24). That is, cyan (C), magenta (M), and yellow (Y) are the same image data.

  Next, the CPU 40 outputs a corrected and distributed gray scale image 180 to each of the three image forming units 6-5 to 6-7, and cyan (C), as shown in the upper part of FIG. White images 190, 200, and 210 for magenta (M) and yellow (Y) are generated (step S26).

  Next, the CPU 40 outputs a print image (white) formed by the white (W) image forming units 6-5 to 6-7 (step S28). That is, the toner images output using the three white (W) are superimposed on the intermediate transfer belt 14, and the combined white toner images are transferred onto a thermal transfer sheet (not shown) by the secondary transfer roller 30. Fixed and output. Finally, a white image 220 shown in the lower part of FIG. 5 is obtained, which is composed only of white (W) toner.

  As a result, even when the white (W) image forming units 6-5, 6-6, and 6-7 are used to transfer to a dark transfer medium such as black, a sufficient loading amount High whiteness and high background concealment can be ensured. Further, even if the original image is color, it is possible to print the white image 220 made of only white (W) toner with high gradation reproducibility.

  In the above-described embodiment, the three white (W) image forming units 6-5 to 6-7 are mounted. However, when the amount of applied toner per group is relatively large, that is, as desired. If the amount of applied toner can be obtained by two image forming units, a white image may be printed by the two image forming units 6-5 and 6-6. Further, when a desired amount of applied toner cannot be obtained by the three image forming units 6-5 to 6-7, a white image may be printed by the four image forming units.

  In the above-described embodiment, the same toner amount distribution (printing rate) is set for the three white (W) image forming units 6-5 to 6-7. Since the amount of remaining toner filled in the toner cartridge 19 is grasped, the amount of remaining toner filled in each of the three image forming units 6-5 to 6-7 is different. The toner amount distribution (printing rate) may be changed between an image forming unit having a large white (W) residual toner amount and an image forming unit having a small white (W) residual toner amount. That is, a larger amount of toner is distributed (printing rate) for image forming units with a large amount of white (W) residual toner, and a smaller amount of toner is used for image forming units with a small amount of residual toner. Distribution (printing rate) may be used. As a result, the residual toner amount can be made uniform.

  According to the above-described embodiment, the original image (color) is converted into a gray scale to generate the gray scale image 170 represented by a single color printing rate, and the printing rate of the gray scale image 170 is set to the image forming apparatus 1. Correction is made based on the total printing rate and the number of image forming units 6-5 to 6-7 filled with white (W), and the gray scale image 180 with the corrected printing rate is filled with white (W). Since the white image 220 is formed by printing using the image forming units 6-5 to 6-7, it is possible to secure a high background concealing property with a sufficient loading amount when forming an image with white toner. In addition, high gradation reproducibility can be realized.

  Further, according to the above-described embodiment, the image forming units 6-5 to 6-7 filled with white (W) are mounted instead of the image forming units 6-1 to 6-3 filled with color toner. The gray scale image 180 with the corrected printing rate is set as the printing rate of cyan (C), magenta (M), and yellow (Y). It is possible to ensure a high background concealment property with the applied amount and to realize high gradation reproducibility.

  Further, according to the above-described embodiment, since there are two or more image forming units filled with white (W), it is possible to secure a high background concealing property with a sufficient loading amount when forming an image with white toner. Can do.

  Further, according to the above-described embodiment, the gray scale image printing rate is increased to the total printing rate of the image forming apparatus 1, so that when the image is formed with white toner, the maximum capability of the image forming apparatus is utilized. A high base concealing property can be secured with a sufficient amount of loading.

  Further, according to the above-described embodiment, the white (W) is set so that the total printing rate of the image forming units 6-5 to 6-7 filled with white (W) becomes the total printing rate of the image forming apparatus 1. Since the printing rate is distributed to the image forming units 6-5 to 6-7 filled with (W), it is possible to secure a high background concealing property with a sufficient loading amount when forming an image with white toner.

  According to the above-described embodiment, the original image (color) is printed using the image forming units 6-5 to 6-7 filled with white (W), or cyan (C) or magenta (M). The image forming units 6-1 to 6-3 filled with yellow (Y) can be selected, and the image forming units 6-5 to 6-7 filled with white (W) are used. Image forming units 6-5 to 6-7 filled with white (W) at the corrected printing rate, the gray scale image 170 represented by a single color printing rate. When the image forming units 6-1 to 6-3 that are printed using cyan and filled with cyan (C), magenta (M), and yellow (Y) are selected, they are represented by a multicolor printing ratio. Grayscale images are converted to cyan (C), magenta (M), A black image is formed by printing using image forming units 6-1 to 6-3 filled with cyan (C), magenta (M), and yellow (Y) at a printing ratio of yellow (Y). Therefore, it is possible to easily select whether to print a white image by white (W) or a black image by CMY, and it is possible to ensure high background concealment with a sufficient amount of loading, High gradation reproducibility can be realized.

As mentioned above, although several embodiment of this invention was described, this invention is not limited to these, The invention described in the claim, and its equal range are included.
Below, the invention described in the claims of the present application is appended.

(Appendix 1)
The invention according to appendix 1 is an image forming apparatus in which a plurality of image forming units can be mounted, a generating unit that generates gray scale image data based on color image data, and a gray scale generated by the generating unit Correction means for correcting image data based on the number of mounted image forming units filled with white toner, and control means for forming an image pattern made of the white toner based on grayscale image data corrected by the correction means And an image forming apparatus.

(Appendix 2)
The invention according to appendix 2 is generated by a first conversion unit that generates a monochrome grayscale image represented by a single-color printing rate by performing grayscale conversion on a color image to be printed, and the first conversion unit. Correcting means for correcting the printing rate of the monochrome grayscale image based on the total printing rate of the image forming apparatus and the number of image forming units filled with white toner; and correcting the monochrome grayscale image with the correcting means. And an image forming control unit that forms a white image by printing using the image forming unit filled with the white toner at a printing rate corrected by the image forming apparatus.

(Appendix 3)
According to the third aspect of the present invention, the image forming unit filled with the white toner is mounted in place of the image forming unit filled with the color toner, and the monochrome grayscale image corrected by the correcting unit is used. The image forming apparatus according to claim 2, further comprising: setting a printing rate as a printing rate of the color toner by the image forming unit filled with the color toner.

(Appendix 4)
The invention according to appendix 4 is the image forming apparatus according to appendix 3, characterized in that there are two or more image forming units filled with the white toner.

(Appendix 5)
The image according to any one of appendices 2 to 4, wherein the correction means performs correction to enlarge the printing rate of the monochrome grayscale image at a predetermined ratio. Forming device.

(Appendix 6)
The invention according to appendix 6 is directed to the image forming unit filled with the white toner so that the correction means has a total printing rate of the image forming unit filled with the white toner equal to the enlarged printing rate. The image forming apparatus according to appendix 5, wherein the printing rate is distributed to the printer.

(Appendix 7)
The invention according to appendix 7 includes: a second conversion unit configured to generate a multicolor grayscale image represented by a multicolor print ratio by performing grayscale conversion on the color image to be printed; and the color image to be printed. Selecting means for printing using the image forming unit filled with the white toner or the image forming unit filled with the color toner, and the image forming control means When the selection unit selects to print using the image forming unit filled with the white toner, the white toner is applied to the monochrome grayscale image at the printing rate corrected by the correction unit. Printing is performed using the filled image forming unit, and printing is performed using the image forming unit filled with the color toner by the selection unit. In this case, a black image is formed by printing the multicolor grayscale image generated by the second conversion unit at the multicolor printing ratio using the image forming unit filled with the color toner. The image forming apparatus according to any one of appendices 3 to 6, wherein the image forming apparatus is characterized in that:

(Appendix 8)
The invention described in appendix 8 includes a step of generating a monochrome grayscale image represented by a monochrome printing rate by performing grayscale conversion on a color image to be printed, and a printing rate of the generated monochrome grayscale image. Correcting based on the total printing rate of the forming apparatus and the number of image forming units filled with white toner, and an image filled with the white toner at the corrected printing rate of the monochrome grayscale image. Forming a white image by printing using a forming unit.

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2 ... Image forming part, 3 ... Duplex printing conveyance unit, 4 ... Paper feed part, 5 ... Fixing part, 6 (6-1, 6-2, 6-3, 6-4) ... Image forming unit, 7 ... photosensitive drum, 8 ... cleaner, 9 ... charge roller, 10 ... optical writing head, 11 ... drum set, 12 ... developing roller, 13 ... toner supply roller, 14 ... intermediate transfer belt, 15 ... Primary transfer roller, 16 ... driving roller, 17 ... driven roller, 18 ... belt position control mechanism, 19 ... toner cartridge, 20 ... belt cleaner, 21 ... paper feed cassette, 22 ... paper (printing medium), 23 ... paper feed Roller, 25 ... Feed roller, 26 ... Separation roller, 27 ... Standby transfer roller pair, 30 ... Secondary transfer roller, 31 ... Unload roller pair, 32 ... Discharge tray, 33 ... Discharge roller pair, 34a ... Start return Road, 34b ... Intermediate return 34c ... Terminal return path, 39 ... Circuit block, 40 ... CPU (central processing unit), 41 ... Interface controller (I / F_CONT), 42 ... PR_CONT, 43 ... Printer printing unit, 44 ... ROM, 45 ... EEPROM, 46 ... Operation panel 47 ... Sensor part 48 ... Frame memory 49 ... Development part 50 ... Fixing part 51 ... Belt drive part 100 ... Original image (color) 110, 130, 140, 160, 190, 200, 210, 220 ... white image, 120, 150, 170, 180 ... grayscale image

Claims (8)

An image forming apparatus capable of mounting a plurality of image forming units,
Generating means for generating grayscale image data based on the color image data;
Correcting means for correcting the grayscale image data generated by the generating means based on the number of mounted image forming units filled with white toner;
Control means for forming an image pattern made of the white toner based on the grayscale image data corrected by the correction means;
An image forming apparatus comprising: First conversion means for generating a single-color grayscale image represented by a single-color printing rate by performing grayscale conversion on a color image to be printed;
Correction means for correcting the printing rate of the monochrome grayscale image generated by the first conversion unit based on the total printing rate of the image forming apparatus and the number of image forming units filled with white toner;
Image forming control means for forming a white image by printing the single color gray scale image at a printing rate corrected by the correcting means using an image forming unit filled with the white toner;
An image forming apparatus comprising: The image forming unit filled with the white toner is mounted in place of the image forming unit filled with the color toner,
Setting the printing rate of the single color grayscale image corrected by the correction means as the printing rate of the color toner by the image forming unit filled with the color toner;
The image forming apparatus according to claim 2, further comprising: The number of image forming units filled with the white toner is two or more.
The image forming apparatus according to claim 3. The correction means performs correction to enlarge the printing rate of the monochrome grayscale image at a predetermined ratio.
The image forming apparatus according to claim 2, wherein the image forming apparatus is an image forming apparatus. The correcting means distributes the printing rate to the image forming unit filled with the white toner so that the total printing rate of the image forming unit filled with the white toner becomes the enlarged printing rate;
The image forming apparatus according to claim 5. Second conversion means for generating a multicolor grayscale image represented by a multicolor print ratio by performing grayscale conversion on the color image to be printed;
Selecting means for selecting whether to print the color image to be printed using the image forming unit filled with the white toner or the image forming unit filled with the color toner;
The image formation control means
When the selection unit selects printing using the image forming unit filled with the white toner, the white toner is filled with the monochrome grayscale image at the printing rate corrected by the correction unit. The multi-color generated by the second conversion unit when the selection unit selects printing using the image forming unit filled with the color toner. Forming a black image by printing a grayscale image using the image forming unit filled with the color toner at the multicolor printing ratio;
The image forming apparatus according to claim 3, wherein the image forming apparatus is an image forming apparatus. Converting a color image to be printed to a gray scale to generate a single color gray scale image represented by a single color printing rate;
Correcting the printing rate of the generated monochrome grayscale image based on the total printing rate of the image forming apparatus and the number of image forming units filled with white toner;
Forming the white image by printing the monochrome grayscale image at the corrected printing rate using an image forming unit filled with the white toner; and
A white image forming method comprising:

Images