JP5023789B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a printer, a copier, and a fax machine, and more particularly to a color image forming apparatus having a toner save mode.

  A toner save mode is installed in a color image forming apparatus for the purpose of draft printing or the like. When the toner save mode is set, the image forming apparatus performs development while reducing the amount of toner compared to the normal time.

  In Patent Document 1, in the toner save mode, among the four color toners of CMYK, the three color toners of CMY are suppressed (reduced) at the same ratio, and only the toner of K (black) is not suppressed. It has been proposed to output in the same amount as normal. Since all the CMY toner suppression rates are set at the same rate, the hue due to CMY does not change, only the saturation is lowered, and the image quality is unlikely to deteriorate. Also, by not suppressing K toner, black characters do not become intermediate density black, character quality deterioration due to binarization processing does not occur, and since the ratio of K toner is high for natural images, all CMYK are suppressed uniformly. Compared to the case, the image becomes clearer and the image quality becomes tighter. As a result, image quality deterioration due to toner saving can be suppressed.

  Further, in Japanese Patent Application Laid-Open No. 2004-228620, it is proposed to suppress K toner while suppressing CMY toner. For example, the CMY toner is suppressed to about 50%, the K toner is set to a higher suppression rate, and the amount of K toner is made larger than the amount of CMY toner to suppress the image quality deterioration.

  FIG. 1 is a configuration diagram of a conventional image forming apparatus. The color conversion unit 208 refers to the color conversion table 208T to convert the RGB input gradation IN to the CMYK gradation, and the gradation conversion unit 209 refers to the gradation conversion table 209T to convert the CMYK input gradation to C. The halftone processing unit 210 refers to the screen gamma table 210T and converts the input gradation of C′M′Y′K ′ to C ″ M ″. It is converted into Y "K" image reproduction data. The gradation conversion table 209T of the gradation conversion unit 209 normally has a predetermined conversion characteristic (linear in the figure) as in the table 209T. However, in the toner save mode, the input gradation of CMY is as in the table 209Tx. The input gradation of K is not reduced without converting the output gradation to a gradation value.

FIG. 2 is a diagram illustrating a conventional toner save mode. FIG. 2A shows the relationship between CMY input gradation and output density in a normal state where toner is not saved, and FIG. 2B shows the relationship between CMY input gradation and output density during toner saving. According to this, as a result of the above-described gradation conversion of CMY, the output density of the formed image is lowered. As a result, as shown in the color space of FIG. 2C, an image is formed in the color space indicated by the solid line in the normal state where the toner is not saved, but when the toner is saved, the hue is not converted as indicated by the broken line. However, an image is formed in a color space with reduced saturation.
Japanese Patent Laid-Open No. 2004-309662 Japanese Patent Application No. 2006-317985

  However, as shown in FIG. 2C, when the amount of CMY toner is suppressed, the saturation of the reproduced image is lowered, and the saturation of characters and graphics to be emphasized in the original image is lowered and becomes inconspicuous. Concerned.

  Further, in the conventional example, even if the amount of CMY toner is suppressed, CMY color toner is still consumed. CMY color toners are more expensive than K black toners, and cannot sufficiently contribute to toner cost reduction in the toner save mode.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of forming a sharp image while greatly reducing the consumption of color toner in the toner save mode.

  In order to achieve the above object, according to an aspect of the present invention, in an image forming apparatus that forms a color image based on image data having input gradations of a plurality of colors, the image data based on predetermined conversion characteristics A controller unit for generating image reproduction data from the input gradation, and a print engine for forming an image having an output density corresponding to the input gradation based on the image reproduction data. In the mode, for at least one of graphic and text image data included in the image data, when the input gradation of the plurality of colors is less than a predetermined reference saturation, the input gradation of the plurality of colors is changed to a monochrome input level. And an image forming apparatus that generates the image reproduction data from the converted input gradation.

  According to the above aspect of the present invention, the amount of color toner used can be reduced in the toner save mode.

  According to a preferred aspect of the above aspect of the present invention, the controller unit converts the input gradation of the plurality of colors into a monochrome input gradation for the image data of the image included in the image data in the toner save mode. The image reproduction data is generated from the converted input gradation after conversion.

  According to a preferred aspect of the above-mentioned aspect of the present invention, the controller unit further includes the plurality of color input gradations for at least one of graphic and text image data included in the image data in the toner save mode. Is converted to the input gradation of any one of the six RGBCMY colors, and the image reproduction data is converted from the converted input gradation. It is characterized by generating.

  According to a preferred aspect of the above aspect of the present invention, the controller unit converts the monochrome input gradation into a monochrome input gradation with enhanced contrast for the image image, graphic image, and text image. And

  According to a preferred aspect of the above aspect of the present invention, the controller unit includes an RGB gradation conversion unit that converts an RGB input gradation with a predetermined gradation characteristic, and an RGB output from the RGB gradation conversion unit. A color conversion unit that converts the input gradation of CMYK into an input gradation of CMYK, a CMYK gradation conversion unit that converts the input gradation of CMYK output from the color conversion unit with predetermined gradation characteristics, and the CMYK A halftone processing unit for converting the CMYK input gradation output from the gradation conversion unit into the image reproduction data, and the RGB gradation conversion unit is configured to input the plurality of color input gradations in the toner save mode. Is converted into a monochrome input gradation.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the technical scope of the present invention is not limited to these embodiments, but extends to the matters described in the claims and equivalents thereof.

  FIG. 3 is a configuration diagram of the image forming apparatus according to the present embodiment. FIG. 3 shows the configuration of a printer as an example of an image forming apparatus. In addition to printers, copiers and facsimiles with built-in scanner functions are similar image forming apparatuses.

  The printer 20 is connected to the host computer 10 via a network or the like, and receives print data from the printer driver 12 installed in the host computer 10. The printer 20 includes a controller unit 200 that generates image reproduction data based on print data, and a print engine 250 that forms an image based on image reproduction data.

  The controller unit 200 includes a CPU 202 that controls the entire controller unit, an image processing program storage memory 204, a memory 206 that stores image data, an interface IF that receives print data, and RGB ( An RGB gradation conversion unit 207 that converts gradations of red, green, and blue) with predetermined conversion characteristics, and RGB gradations of the output thereof are gradations of CMYK (respectively, cyan, magenta, yellow, and black). A color conversion unit 208 that performs color conversion, a CMYK gradation conversion unit 209 that performs gradation conversion on the color-converted CMYK gradations based on predetermined characteristics, and a CMYK level that is output from the CMYK gradation conversion unit 209. Image reproduction data for image formation based on a predetermined gamma characteristic (or screen) It converted to have a half-tone processing unit 210, and a pulse width modulator 121 for pulse width modulating the image reproduction data for CMYK.

  Further, the nonvolatile memory 214 includes an RGB gradation conversion table 207T, a color conversion table 208T, and a CMYK floor, which are referred to by the gradation conversion unit 207, the color conversion unit 208, the gradation conversion unit 209, and the halftone processing unit 210, respectively. A tone conversion table 209T and a screen gamma table 210T are recorded. The halftone processing unit 210 refers to a screen gamma table 210T having a gamma characteristic corresponding to an AM screen or FM screen, and converts CMYK input gradation values into respective image reproduction data. The halftone processing unit 210 may perform a smoothing process that improves the resolution of the edge portion of the image.

  The print engine 250 includes an engine controller 252, light emitting means 254 including a laser diode or a line-shaped light emitting element, a photosensitive drum 256, a developing unit, a transfer unit, and a fixing unit (not shown). The engine controller 252 irradiates a beam from the light emitting means 254 based on the image reproduction data generated by the controller unit 200 to form a latent image on the photosensitive drum 256, and the developing unit converts the latent image into a toner image. The toner image is transferred to a printing medium, for example, a sheet by a transfer unit, and the toner image is fixed on the sheet by a fixing unit.

  In the toner save mode according to the present embodiment, the RGB gradation conversion unit 207 converts RGB gradation data into desired data in accordance with image attributes (image, text, graphic). Alternatively, the CMYK gradation conversion unit 209 may perform a predetermined conversion process.

[Toner Save Mode]
FIG. 4 is a diagram showing an image in the toner save mode in the present embodiment. The image 30 by normal printing without toner saving includes a color image 32, a color graphic 34, and a color text 37. The color graphic 34 includes a high-saturation vivid color figure 35 and a low-saturation color figure 36, and the color text 37 includes a low-saturation color character 38 and a high-saturation vivid color figure. Color characters 39 are included.

  When the toner save mode of the present embodiment is selected when printing such an image, an image 40 is formed. In the image 40 formed in the toner save mode, the color image 32 is a monochrome image 42, the color graphic 34 is a graphic 44 in which a color graphic 45 and a monochrome graphic 46 are mixed, and the color text 36 is a color character 48 and a monochrome character 49. And the mixed text 47 are converted. Moreover, the vivid color figure 35 in the color graphic 34 is converted into a more vivid color figure 45 in the toner save mode image 40, and the vivid color characters 39 in the color text 37 are converted in the toner save mode image 40. It is converted into a more vivid color character 49. Everything else is converted to a monochrome image. Furthermore, all monochrome images are output as images with enhanced contrast.

  By using the above image, most of the image can be output as a monochrome image, the amount of color toner used can be greatly reduced, and high saturation is emphasized in graphics and text. By maintaining the portion in color, a sharp image can be formed. It should be noted that it is desirable to convert the image image into a monochrome image because it causes deterioration in image quality when color and monochrome are mixed.

  FIG. 5 is a configuration diagram of an RGB gradation conversion unit, a color conversion unit, a CMYK gradation conversion unit, and a halftone processing unit in the controller unit. Based on the print data received from the host computer 10, the CPU generates, for example, RGB gradation values and image attribute data X such as graphics, text, and images for each pixel of the image and inputs them to the RGB gradation unit 207. To do. The RGB gradation unit 207 performs gradation conversion on RGB gradation values based on predetermined conversion characteristics, and the color conversion unit 208 refers to the color conversion lookup table 208T to output RGB output from the RGB gradation conversion unit 207. Are converted into CMYK gradation values. The CMYK gradation conversion unit 209 converts the CMYK gradation value into the C′M′Y′K ′ gradation value with reference to the gradation conversion lookup table 209T having predetermined characteristics. This gradation conversion is for removing a solid error of the print engine 250, for example.

  The halftone processing unit 210 converts the input gradation value of C′M′Y′K ′ into an output gradation value of C ″ M ″ Y ″ K ″ with reference to the screen gamma table 210T. This output gradation value OUT corresponds to the image reproduction data. The output gradation value of C "M" Y "K" is subjected to pulse width modulation by the pulse width modulation unit 212 in FIG. 1, and the generated pulse signal is output to the print engine.

  FIG. 6 is a flowchart showing image processing in the toner save mode in the present embodiment. This image processing is performed by the RGB gradation conversion unit 207 in FIG.

  When the toner save mode is set, a command for instructing the toner save mode is included in the print data received from the host computer. In response to the toner save mode command, the CPU of the controller unit 200 instructs the RGB gradation conversion unit 207 in FIG. 5 to perform image processing in the toner save mode.

  The RGB gradation conversion unit 207 sequentially processes the RGB gradation data of the image data of each pixel and the image attribute data X. For example, the image attribute X includes three attributes: an image attribute such as a natural image, a graphic attribute such as a graph or a graphic, and a text attribute composed of characters.

  First, when the image attribute X of the image data of the processing target pixel is an image (YES in S10), the RGB gradation values are converted into luminance values (gray data Gray) (S12). This conversion process can be performed by the following calculation.

  Gray = 0.3 × R + 0.59 × G + 0.11 × B where R, G, and B are gradation values of red, green, and blue.

  Then, the RGB gradation conversion unit 207 converts the gray data Gray to a black gradation value K, which is monochrome data (S14). In this conversion processing, it is preferable to perform conversion that enhances contrast. This conversion process is performed with reference to the gray / black gradation conversion table 207T2.

  FIG. 7 is a diagram showing a conversion table for converting gray data Gray into a black gradation value K. The horizontal axis is gray data Gray which is an input gradation, and the vertical axis is black gradation value K which is monochrome data, both of which are gradation values 0-255. Gray data Gray = 0 corresponding to the luminance value corresponds to black, and Gray = 255 corresponds to white, so Gray = 0 corresponds to K = 255, Gray = 255 corresponds to K = 0, and halftone Gray is intermediate. Each key is converted to a K key.

  According to the conversion characteristic 50, the gray data Gray is simply converted into the black gradation value K, and the process of enhancing the contrast is not performed. Further, according to the conversion characteristic 51, the gray data Gray is converted into the black gradation value K, and the contrast is enhanced by making the gray close to black more black and making the gray close to white more white. . By generating the black gradation value K by enhancing the contrast in this way, the contrast of the output monochrome image can be increased, and the blur of the image due to the color image being changed to the monochrome image in the toner save mode, etc. Can be suppressed. When the conversion characteristic 51 is a characteristic between the conversion characteristics 50 and 51, contrast enhancement can be weakened, and when the conversion characteristic 51 is steeper than the conversion characteristic 51, contrast enhancement can be enhanced. A plurality of conversion characteristics 51 can be provided in the table in advance, and can be selected by option setting in the toner save mode.

  On the other hand, when the image attribute X of the image data of the processing target pixel is a graphic or text other than an image (NO in S10), the RGB gradation conversion unit 207 calculates the saturation S from the RGB gradation values (S16). ). The saturation S (Saturation) is calculated by the following equation (1).

ただし，ＭＡＸ（Ｒ，Ｇ，Ｂ）はＲＧＢの階調値のうち最大の階調値であり，ＭＩＮ（Ｒ，Ｇ，Ｂ）はＲＧＢの階調値のうち最小の階調値である。従って，上記式（１）により求められる彩度は最小値０（０％）から最大値１（１００％）の間のいずれかである。彩度Ｓとは，色空間内において，ＲＧＢの階調値が等しいグレー軸からの距離に対応する値であり，上記式（１）に示されるとおり，ＲＧＢの階調値が全て等しい場合は彩度Ｓ＝０になり，ＲＧＢの階調値のいずれかが０でいずれかが２５５の場合は彩度Ｓ＝１になる。

However, MAX (R, G, B) is the maximum gradation value among the RGB gradation values, and MIN (R, G, B) is the minimum gradation value among the RGB gradation values. Therefore, the saturation obtained by the above equation (1) is any value between the minimum value 0 (0%) and the maximum value 1 (100%). Saturation S is a value corresponding to the distance from the gray axis where the RGB gradation values are equal in the color space. As shown in the above equation (1), when all the RGB gradation values are equal, When the saturation S = 0, and any of the RGB gradation values is 0 and any of the gradation values is 255, the saturation S = 1.

  Then, when the saturation S is less than the threshold value Vth (for example, 0.85) that is the reference value (NO in S18), the RGB gradation conversion unit 207 converts the RGB gradation values by the above-described processing steps S12 and S14. Convert to black K tone value. This conversion formula is as described above. In other words, if the saturation S is not high in a graphic or text image, it is regarded that there is no need to emphasize it and is output as a monochrome image.

  In addition, when the saturation S is equal to or higher than a threshold value Vth (for example, 0.85) that is the reference value (YES in S18), the RGB gradation conversion unit 207 converts the RGB gradation value of the pixel to RGBCMY (red, green). , Blue, cyan, magenta, yellow) are converted into R′G′B ′ gradation values corresponding to any one of the six colors (S20). This gradation conversion is performed with reference to the RGB gradation conversion table 207T1.

  FIG. 8 is a diagram illustrating an example of the RGB gradation conversion table 207T1. The horizontal axis corresponds to the RGB gradation value of the pixel, and the vertical axis corresponds to the gradation value of R′G′B ′. According to this conversion table 207T1, when the input gradation value is less than 50%, the output gradation value is converted to 0, and when it is 50% or more, the output gradation value is converted to 255. As a result, the color of the pixel whose saturation S is equal to or higher than the threshold value Vth, which is the reference value, is converted to the closest color in the color space among the six colors RGBCMY. As a result, the output image becomes one of RGBCMY colors having the maximum saturation S. Due to this RGB gradation change, pixels with a saturation S higher than the reference value in graphics or text are converted to any color of RGBCMY, so that the portion emphasized in the original image is more emphasized and output. .

  The gradation conversion S20 may not be performed. In this case, when the saturation S is equal to or higher than the reference value, an image is formed with the RGB gradation values as they are.

  By the conversion process shown in FIG. 6, the image data can be converted into a sharp image with all pixels. The converted RGB gradation values are color-converted by the color conversion unit 208 into CMYK gradation values. The black gradation value K of the pixel converted into the monochrome image is supplied to the CMYK gradation conversion unit 209 or the halftone processing unit 210.

  When further suppression of the toner amount is required, the black gradation value K output from the RGB gradation conversion unit 207 is supplied to the CMYK gradation conversion unit 209, and the CMYK gradation conversion unit 209 further increases the toner amount. Gradation conversion for suppressing the above is performed.

  FIG. 9 is a diagram illustrating an example of the CMYK gradation conversion table 209T1. The horizontal axis corresponds to the CMYK input gradation, and the vertical axis corresponds to the C′M′Y′K ′ output gradation. When further suppression of the toner amount is required, the output of C′M′Y′K ′ in which the CMYK input tone is further suppressed based on the conversion characteristics corresponding to the desired suppression amount, respectively. Converted to gradation. FIG. 9 shows conversion characteristics when there is no toner amount suppression, conversion characteristics with a suppression rate of 75%, and conversion characteristics with a suppression rate of 50%.

  FIG. 10 is another configuration diagram of the RGB gradation conversion unit, the color conversion unit, the CMYK gradation conversion unit, and the halftone processing unit in the controller unit. In this example, the RGB gradation conversion unit 207 outputs the generated gray data Gray to the CMYK gradation conversion unit 209 without performing the processing step S14 of FIG. The CMYK gradation conversion unit 209 converts the gray data Gray into a black gradation value K with reference to the gray / black gradation conversion table 209T2. This gray / black gradation conversion table 209T2 is the same as the conversion table of FIG. Therefore, it is possible to convert to black gradation value K with enhanced contrast at the time of this conversion. Further, by the gradation conversion by the gray / black gradation conversion table 209T2, the black gradation value K can be uniformly suppressed to 75% or 50% and output as shown in FIG. Other configurations are the same as those in FIG.

[Output Image According to this Embodiment]
As shown in FIG. 4, in the toner save mode of this embodiment, the image forming apparatus outputs a color image as a monochrome image, and outputs color graphics and text in monochrome if the saturation is less than the reference value. , If the saturation is equal to or higher than the reference value, the color with the maximum saturation is output.

  FIG. 11 is a diagram illustrating a color space of a color image. In the color space 60, the central axis (axis perpendicular to the paper surface) is the gray axis 601 and both ends of the gray axis correspond to white W and black B. Further, the saturation S increases as the distance from the gray axis 601 increases. That is, the axis 603 of saturation S is an axis that goes outward from the gray axis 601. The outermost periphery 602 corresponds to the maximum saturation, and the RGBCMY color has the maximum saturation that is farthest from the gray axis 601.

  In the color spaces 61 and 62, white W is a reference 612 and black B is a reference 622 of both ends of the gray axis 601 of the color space 60, and an upward axis from the reference 612 and 622 corresponds to the saturation S. Therefore, the upper ends 602 of the color spaces 61 and 62 coincide with the outermost periphery 602 of the color space 60 and correspond to the MRYGCBM color from the left.

  FIG. 12 is a diagram showing a color space of an image in which graphic and text images are output in the toner save mode among the original images in the color space of FIG. The color spaces 60, 61, and 62 are converted into color spaces 70, 71, and 72, respectively. In the color spaces 70, 71, and 72, the reference threshold Vth for the saturation S corresponds to 704. Therefore, the color space 705 having a saturation lower than the reference value 704 is converted into a monochrome space. Further, the color space 706 having a saturation higher than the reference value 704 is converted into any of RGBCMY colors. Therefore, the graphic and text color images are not halftone, and the RGB gradation values are RGB = (255, 0, 0), (0, 255, 0), (0, 0, 255), ( 255, 255, 0), (255, 0, 255), (0, 255, 255) (corresponding to R, G, B, Y, M, and C, respectively).

  FIG. 13 is a diagram showing an example of RGB gradation values converted by the toner save mode for a text image. In FIG. 13, the left column includes RGB gradation values corresponding to the text image “test” of the image data of black K, red R, yellow Y, green G, and cyan C, and their saturation S, The text image “test” after toner save and the corresponding converted RGB gradation values are shown. In the right column, the RGB values corresponding to the text image “test” of the similar image data of blue B and magenta M, the saturation S, the image after the toner save and the RGB values are shown. . In the right column, similar values of R, Y, G, C, B, and M are further shown. The saturation S is indicated by%.

  As can be understood by referring to the example of FIG. 13, among the text images, an image having a saturation S of the reference value of 85% or more is set to an RGB gradation value of any color of RGBCMY (bold “test” in the figure). The converted image having a saturation S of less than 85% of the reference value is converted to a gradation value of a monochrome image (an underlined image in the figure) having the same RGB gradation values.

  As described above, according to this embodiment, when a color image is output in the toner save mode, the image is converted to a monochrome image, and a graphic or text image is converted to a monochrome image if the saturation is less than the reference value. If the saturation is above the reference value, the color image is output as it is. Further, if the saturation is equal to or higher than the reference value, the graphic or text image is converted into any one of RGBCMY colors with the saturation further maximized, so that the output image becomes more emphasized. Also, monochrome images such as image images, graphics, and text images are output as sharp images because the contrast is enhanced. Further, since the amount of color toner used is greatly reduced, the cost can be greatly reduced.

  In the above-described embodiment, when a color image is output in the toner save mode, the image is converted to a monochrome image, and the graphic or text image is converted to a monochrome image if the saturation is less than the reference value, and the saturation is the reference value. In the embodiment described above, the color image is output as it is. However, when the color image is output in the toner save mode, the image and one of the graphic and the text are converted into a monochrome image, and the other of the graphic and the text image is output. However, if the saturation is less than the reference value, it is converted to a monochrome image, and if the saturation is equal to or greater than the reference value, it may be output as a color image.

It is a block diagram of a conventional image forming apparatus. It is a figure which shows the conventional toner save mode. 1 is a configuration diagram of an image forming apparatus in the present embodiment. FIG. 6 is a diagram illustrating an image in a toner save mode in the present embodiment. FIG. 3 is a configuration diagram of an RGB gradation conversion unit, a color conversion unit, a CMYK gradation conversion unit, and a halftone processing unit in a controller unit. FIG. 6 is a flowchart illustrating image processing in a toner save mode in the present embodiment. It is a figure which shows the conversion table which converts the gray data Gray into the black gradation value K. FIG. It is a figure which shows an example of RGB gradation conversion table 207T1. It is a figure which shows an example of the CMYK gradation conversion table 209T1. It is another block diagram of the RGB gradation conversion part in a controller unit, a color conversion part, a CMYK gradation conversion part, and a halftone process part. It is a figure which shows the color space of a color image. FIG. 12 is a diagram illustrating a color space of an image in which graphics and text images are output in the toner save mode among images in the color space of FIG. 11. It is a figure which shows the example of the RGB gradation value converted by the toner save mode about the text image.

Explanation of symbols

20: Printer (image forming apparatus) 200: Controller unit 208: RGB gradation conversion unit 209: Color conversion unit 209: CMYK gradation conversion unit 210: Halftone processing unit

Claims (3)

In an image forming apparatus for forming a color image based on image data having input gradations of a plurality of colors,
A controller unit for generating image reproduction data from the input gradation of the image data based on predetermined conversion characteristics;
A print engine that forms an image having an output density corresponding to the input gradation based on the image reproduction data;
In the toner save mode, the controller unit inputs the plurality of colors when the input gradation of the plurality of colors is less than a predetermined reference saturation for at least one of graphic and text image data included in the image data. When the gradation is converted into a monochrome input gradation, and the input gradation of the plurality of colors is equal to or higher than the predetermined reference saturation, the input gradation of the plurality of colors is selected from any of the six colors RGBCMY. For the image data of the image included in the image data, the input gradation of the plurality of colors is converted into a monochrome input gradation, and the image reproduction data is converted from the converted input gradation. An image forming apparatus that generates In claim 1 ,
The image forming apparatus, wherein the controller unit converts the monochrome input gradation into a monochrome input gradation with enhanced contrast for the image image, graphic image, and text image. In claim 1 or 2 ,
The controller unit is
An RGB gradation converter for converting the RGB input gradation with a predetermined gradation characteristic;
A color conversion unit for converting an RGB input gradation output by the RGB gradation conversion unit into a CMYK input gradation;
A CMYK gradation converter that converts the input gradation of CMYK output by the color converter with a predetermined gradation characteristic;
A halftone processing unit for converting CMYK input gradation output from the CMYK gradation conversion unit into the image reproduction data;
The image forming apparatus, wherein the RGB gradation conversion unit converts the input gradation of the plurality of colors into a monochrome input gradation in the toner save mode.

Images