JP2012045796A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To more effectively reduce the amount of color material to be consumed without restricting color reproduction range.SOLUTION: A pre-reduction signal value of pixels where a black color material and other color materials than the black color material overlap each other for image data corresponding to color materials other than the black color material after pseudo half-tone processing by a pseudo half-tone processing section 140 is converted, by a color material reduction processing section 150, into a post-reduction signal value that is smaller than the pre-reduction signal value of at least one arbitrary color material among other color materials than the black color material, and into a post-reduction signal value that is equal to or smaller than the pre-reduction signal values of other color materials than the arbitrary color material. An image is formed based on image data of each color of the converted post-reduction signal value.

Description

  The present invention relates to an image forming apparatus.

  In an image forming apparatus such as a color laser beam printer or an inkjet color printer, color reproduction is performed by combining a plurality of color materials having different spectral characteristics and superposing them on a recording medium by changing the color material amount. Color materials used in general image forming apparatuses are four colors of black (K), cyan (C), magenta (M), and yellow (Y). When the spectral reflectance of a single-color image of each color formed on a white printer paper using a color laser beam printer is measured with a spectrophotometer at a certain wavelength, the K color material uniformly emits light in the visible wavelength range. Has the property of absorbing. On the other hand, CMY color materials other than the K color material have a characteristic of transmitting light in a specific wavelength range. Images having various colors are reproduced by superimposing the K color material and the CMY color material having such characteristics on the recording medium. The range of colors that can be reproduced is called the color reproduction range. Enlarging this color reproduction range is for more accurately reproducing input image data, and is an important issue in further developing the image forming apparatus.

  On the other hand, in recent years, due to increasing demands for reducing printing costs and environmental burdens, reducing the amount of color material consumed during image formation is also an important issue. As this color material consumption reduction method, the one described in Patent Document 1 is known. In this patent document 1, when the color material suppression mode is set, the amount of the color material that can be handled according to the characteristics of the device and is used in the color reproducible area, which is an area that can be reproduced by the toner as the color material. Suppress. For this reason, the image processing apparatus of Patent Document 1 converts the color information of the input image data so as to be within a color reproducible region and within a color material suppression region narrower than this. In other words, the color information of the input image data is converted into the color information of the output image data corresponding to the image forming apparatus, and the color material consumption is reduced by narrowing the color reproduction range than usual. Moreover, the thing of patent document 2 is also known as a coloring material consumption reduction method. This Patent Document 2 discloses an image forming apparatus that generates a color signal by subtracting a color component value having the smallest ratio from each color component value of an input color signal when a color material save mode is selected. . In Patent Document 2, the color material consumption is reduced by reducing the color reproduction range by reducing the signal value of each color after the color conversion process and before the pseudo halftone process. Thus, in the method of reducing the color material consumption, the color material consumption is reduced by intentionally narrowing the color reproduction range. In general, the amount of color material and the color to be reproduced have a relation that the color to be reproduced becomes lighter because the amount of absorption in the color material layer decreases as the amount of color material decreases. For this reason, it is possible to form an image with a small amount of color material by narrowing the color reproduction range by intentionally setting the color of the reproduced image to be light. Although these color material consumption reduction methods have no restrictions on the color reproduction range, they can reduce the color material consumption relatively greatly. However, as described above, the color reproduction range, which is an important issue for image forming apparatuses, is expanded. I can't do it.

  On the other hand, the techniques described in Patent Documents 3 and 4 are known as techniques for reducing the color material consumption without narrowing the color reproduction range. In Patent Document 3, when the first color signal is converted into an image recording signal of an image forming apparatus including black that is reproduced by CMYK or reproduced only by K, black that can reproduce the first color signal is disclosed. There is disclosed an image processing apparatus that obtains a plurality of image recording signals other than the amount and converts them into image recording signals other than only CMYK or K that reproduce the black so that the toner amount is minimized. That is, there are a plurality of combinations of CMY signal values that can reproduce a certain color, and the color material consumption is reduced by forming an image with a combination that minimizes the total value of the signals. Further, Patent Document 4 discloses an output in which color conversion parameters when an input color signal is converted into a plurality of color output color signals including black are calculated based on a plurality of sets of color-converted output image signals. A color conversion parameter generation method determined by an evaluation value related to image quality is disclosed. That is, the color gamut evaluation value increases as the size of the color gamut as the quality of the output image increases. The smaller the color material consumption amount, the larger the color material consumption evaluation value from the viewpoint that the color material consumption amount can be saved and the cost for image output can be reduced. By determining a color conversion parameter that maximizes both of these evaluation values, the color material consumption is reduced without significantly narrowing the color reproduction range.

  However, in Patent Document 3, the effect of reducing the color material consumption is mainly limited to the shadow area with low brightness. For this reason, the color material consumption which can be reduced is small. Also, in Patent Document 4, the effect of reducing the color material consumption is limited to low-lightness colors that mainly generate black ink. For this reason, it is difficult to reduce a large amount of color material consumption.

  The present invention has been made in view of the above background, and an object of the present invention is to provide an image forming apparatus capable of more effectively reducing the color material consumption amount without narrowing the color reproduction range.

In order to achieve the above object, the invention of claim 1 includes a pseudo halftone processing unit that performs pseudo halftone processing on target image data, and a visible wavelength region light absorption color that uniformly absorbs at least light in the visible wavelength region. An image forming apparatus that forms an image on a recording medium using a plurality of color materials including a material and a color material other than the visible wavelength region light-absorbing color material, wherein the visible wavelength region After the pseudo halftone process is performed on the target image data in which the light absorbing color material and the color material other than the visible wavelength range light absorbing color material overlap, it corresponds to a color material other than the visible wavelength range light absorbing color material. The pre-reduction signal value that is the signal value of the pixel in the image data is the post-reduction signal value that is smaller than the pre-reduction signal value in at least one arbitrary color material other than the visible light absorption color material. Convert to a signal value and use a color material other than the optional color material. Based on image data of each color after the color material amount reduction processing by the color material amount reduction processing unit, the color material amount reduction processing means for converting to the post-reduction signal value smaller than or equal to or less than the pre-reduction signal value An image forming apparatus characterized in that image formation is performed by the image forming means.
The invention according to claim 2 is the image forming apparatus according to claim 1, wherein the reduced signal value includes image data formed with the pre-reduction signal value and image data formed with the post-reduction signal value. The amount of change in the color value when formed on the recording medium by the image forming means is less than or equal to a specified value, and the total value of the amounts of change between the pre-reduction signal value and the post-reduction signal value of each color Is the maximum signal value.
Further, the invention of claim 3 is the image forming apparatus according to claim 2, wherein the change amount of the color value is the color value of the image formed by the signal value before reduction in the uniform color space and the signal after reduction. It is expressed by the distance between the color value of the image formed by the value.
According to a fourth aspect of the present invention, there is provided the image forming apparatus according to any one of the first to third aspects, wherein the pre-reduction signal value and the post-reduction signal value in the color material amount reduction processing unit are associated with each other. The color material amount reduction processing unit converts the pre-reduction signal value into the post-reduction signal value with reference to the storage unit.
The invention according to claim 5 is the image forming apparatus according to claim 4, further comprising recording medium information acquisition means for acquiring information relating to the type of recording medium on which image formation is performed, and the storage means can acquire the information. The color material amount reduction processing means selects the storage means corresponding to the type of the recording medium acquired by the recording medium information acquisition means, and refers to the selected storage means. The signal value before reduction is converted into the signal value after reduction.
The invention according to claim 6 is the image forming apparatus according to any one of claims 1 to 5, wherein a signal value of the target image data includes a signal corresponding to the visible light absorption color material. Black generation processing means for converting into a signal value after generation of black, and the black generation processing means is a color material other than the visible light absorption color material that overlaps with the visible light absorption color material based on target image data And calculating the signal value after the black generation based on the color material amount of the color material other than the visible wavelength region light absorbing color material overlapping the visible wavelength region light absorbing color material. Is.
Further, the invention according to claim 7 is the image forming apparatus according to claim 6, wherein the signal value after the black generation is a color material of the visible wavelength range light absorbing color material overlapping the visible wavelength range light absorbing color material. The signal value has the maximum amount.
The invention according to claim 8 is the image forming apparatus according to claim 6, wherein the signal value after black generation is a signal value calculated based on a change amount between the signal value before reduction and the signal value after reduction. It is characterized by being.
Further, the invention of claim 9 is the image forming apparatus according to claim 8, wherein the signal value after black generation is a signal value that maximizes the amount of change between the signal value before reduction and the signal value after reduction. It is characterized by being.
According to a tenth aspect of the present invention, in the image forming apparatus according to any one of the first to ninth aspects, the image forming apparatus includes a color misregistration correction unit that corrects a color misregistration amount of each color. Is.
Furthermore, an invention according to an eleventh aspect is the image forming apparatus according to the tenth aspect, wherein the color misregistration correction unit executes a color misregistration correction process at a predetermined timing.

  In the present invention, in order to form an image on a recording medium based on target image data after pseudo halftone processing, at least a visible wavelength range light-absorbing color material and a visible wavelength range that uniformly absorb light in the visible wavelength range A plurality of color materials including a color material other than the light absorbing color material is used. Then, by changing the combination of the visible wavelength range light-absorbing color material and the color material other than the visible wavelength range light-absorbing color material and the color material amount and superimposing them on the recording medium, images with various colors can be reproduced. Yes. In this way, when the visible wavelength region light-absorbing color material and the color material other than the visible wavelength region light-absorbing color material are superimposed on the recording medium to reproduce the color, the color other than the visible wavelength region light-absorbing color material The light transmitted through the material is absorbed by the visible wavelength region light absorbing color material. For this reason, the contribution to color reproduction in a color material other than the visible wavelength region light-absorbing color material is small. Then, in the target image data in which the visible wavelength region light absorbing color material and the color material other than the visible wavelength region light absorbing color material overlap, the color material other than the visible wavelength region light absorbing color material after the pseudo halftone process Even if the signal value before reduction, which is the pixel signal value, is reduced to reduce the amount of color material other than the light-absorbing color material in the visible wavelength range, the influence on color reproduction is small. Therefore, the color material amount reduction processing means converts the signal value before reduction, which is the signal value of the pixel in the image data corresponding to the color material other than the visible wavelength range light absorption color material after the pseudo halftone process, into the visible wavelength range light absorption. At least one arbitrary color material other than the color material is converted into a post-reduction signal value that is smaller than the pre-reduction signal value. In addition, in the color material other than at least one arbitrary color material other than the visible wavelength region light-absorbing color material, the signal value before the signal is smaller than or equal to the signal value before the reduction. Convert to reduced signal value. Then, image formation is performed by the image forming means based on the image data of these reduced signal values. As a result, the color material consumption can be reduced in the image data in which a plurality of color materials overlap and perform color reproduction without changing the color reproduction range.

  As described above, according to the present invention, it is possible to more effectively reduce the color material consumption amount without narrowing the color reproduction range.

FIG. 6 is a characteristic diagram illustrating spectral reflectance with respect to a wavelength of a formed image of each color material of CMYK. FIG. 6 is a characteristic diagram showing spectral reflectance with respect to wavelength of an image of a K color material and an image in which the K color material and the C color material overlap each other. It is explanatory drawing showing the process in a black generation process. FIG. 3 is a schematic diagram illustrating overlapping of color materials on a recording medium. 1 is a diagram illustrating a schematic configuration of an image forming apparatus according to a first embodiment. It is a glock figure showing the composition of the image processing part concerning a 1st embodiment. It is a flowchart which shows the process in the image process part which concerns on 1st Embodiment. 6 is a flowchart illustrating a color material amount reduction process and a color material amount reduction LUT creation procedure according to the first embodiment. It is a characteristic view which shows the color material reduction amount by the color material reduction process with respect to an input pixel value. It is a flowchart which shows the process of the color material amount reduction process which concerns on 2nd Embodiment. It is a flowchart which shows the black generation process which concerns on 4th Embodiment. It is a figure which shows schematic structure of the image forming apparatus which concerns on 5th Embodiment. FIG. 4 is a diagram illustrating a color misregistration correction pattern formed on an intermediate transfer belt.

First, the principle of the image forming apparatus of this embodiment will be outlined.
In the image forming apparatus of the present embodiment, the color material consumption is reduced by performing the color material amount reduction process on the image data after the pseudo halftone process. Therefore, it is also possible to carry out simultaneously with the techniques described in Patent Document 3 and Patent Document 4 for performing processing for reducing the amount of color material on the image data before pseudo halftone processing, thereby further increasing the color material. It is also possible to increase the consumption reduction effect.

  Then, for the image data corresponding to the color material other than black after the pseudo halftone process, the signal value before reduction of the pixel in which black and the color material overlap is converted into a signal value after reduction that is smaller than the signal value before reduction. Without reducing the color reproduction range by selecting and reducing the amount of color material of other colors (CMY, etc.) that have a small contribution to color reproduction that overlaps with the K color material, based on the image data after pseudo halftone processing. Colorant consumption can be reduced.

  Hereinafter, the reason why the color material of the other color overlapping with the K color material has a small contribution to the color reproduction will be described with an example in which image formation is performed with CMYK four color materials. As shown in FIG. 1, CMYK color materials used in a general image forming apparatus have different spectral characteristics. Of these, the K color material is different from other CMY color materials in that it absorbs light in the visible wavelength range uniformly. Therefore, in an image in which the K color material and the other CMY color materials overlap, the light transmitted through the CMY color material layer is eventually absorbed by the K color material layer, and the spectral reflectance detected as a result is K color. The shape is almost the same as the spectral reflectance of the material alone.

  FIG. 2 is a characteristic diagram showing an example in which the spectral reflectance is measured when an image of the K color material and an image in which the K color material and the C color material overlap are formed on the same recording medium. As shown in FIG. 1, the C color material absorbs light on the long wavelength side and transmits light on the short wavelength side, but the short wavelength side light transmitted through the C color material layer is also K color material layer. As shown in FIG. 2, the spectral reflectances of the K color image, the image in which the K color material and the C color material overlap as shown in FIG. In the case of an image in which the K color material overlaps with the M or Y color material, the change in spectral reflectance is small on the same principle. Therefore, it is determined whether or not the CMY color material overlaps the K color material from the image data after the pseudo halftone process, and the color reproduction range is narrowed by selecting and reducing the CMY color material overlapping the K color material. The amount of color material can be effectively reduced without any problem.

  Since the techniques of Patent Document 1 to Patent Document 4 perform processing for reducing the amount of color material on image data before pseudo halftone processing, CMY color materials overlapping with K remain in the formed image. As a result, the effect of reducing the amount of color material has been reduced. This will be described with reference to an example in which the color material consumption is reduced by black generation processing for converting the input color signal into a plurality of color output color signals including black, as in Patent Document 4. As shown in FIG. 3, before the black generation process, the input color signal of each CMY color is C = 100%, M = 50%, Y = 50%, and the black generation process is performed to replace the gray component with the K color. As a result, the output color signal is C = 50%, M = 0%, Y = 0%, and K = 50%. An output image when an image is formed by performing pseudo halftone processing on the output color signal so that the screen angle of C is 15 degrees and the screen angle of K is 45 degrees. A schematic diagram of is shown in FIG. At this time, in the output image, a C + K portion where the C line screen and the K line screen overlap is generated, and as described above, the C color material in this portion is a color material that does not contribute to color reproduction. In the case where M or Y color material is used or in the case of another screen shape such as a halftone dot type, even when another screen angle is used, a portion overlapping with the K color material similarly remains.

  Similarly, since the color material amount reduction process is performed before the pseudo halftone process for the other prior arts, there is a CMY color material that overlaps the K color material after the pseudo halftone process, and the color reproduction range. The color material that does not contribute to is left. Therefore, by performing color material amount reduction processing on the image data after pseudo halftone processing, it is possible to remove color materials that do not contribute to the color reproduction range and reduce color material consumption more effectively. it can.

  Furthermore, as shown in FIG. 2, when the K color material and another color material (CMY, etc.) overlap, generally the light transmitted through the color material layer other than K is eventually absorbed by the K color material layer. Therefore, even if the amount of color material other than K is reduced, the reproduced color hardly changes. However, even if the K color material overlaps with another color material, there are cases where the contribution to color reproduction by a color material other than K cannot be ignored. For example, when the amount of K color material placed on the recording medium is small and light absorption by the K color material layer is not sufficient, the spectral reflectance is also increased by absorption by another color material overlapping the K color material. Change and contribute to color reproduction. For such a problem, in the image forming apparatus, the amount of change in the color value of the image formed with the pre-reduction signal value and the image formed with the post-reduction signal value is equal to or less than the specified value, and the color material amount that can be reduced is It is stipulated that the CMY color material on the K color material is reduced so as to be maximized. That is, if the color does not change significantly even if the color material amount is reduced, the amount of the other color material on the K color material is greatly reduced, and the above-described absorption by the K color material is not sufficient and the color material is large. If the color changes when the amount is reduced, the amount of color material to be reduced is reduced. As a result, the color material consumption can be reduced without deteriorating the color reproducibility even in an image where the color materials overlap each other at any ratio.

Typical examples of the uniform color space include the L ^* a ^* b ^* color system and the L ^* u ^* v ^* color system, and the distance between two points in the color space is the difference in color perceived by humans. Is a color system corresponding to. Therefore, the amount of change in the color value before and after the color material amount reduction process is expressed as a distance in the uniform color space, and by setting a specified value for the allowable amount of change, the color change that humans feel when viewing the image can be further improved. Accurate evaluation can be performed, and the amount of color material can be effectively reduced within a range in which color change is not perceived.

  Further, a look-up table (LUT), which is a storage unit that is created in advance as a unit for converting a pre-reduction signal value into a post-reduction signal value and stored in the image forming apparatus, is a signal before reduction in the color material amount reduction processing unit. The correspondence between the value and the signal value after reduction is stored as a parameter. Therefore, the post-reduction signal value can be obtained by referring to the LUT based on the pre-reduction signal value after the pseudo halftone process. Conversion from the pre-reduction signal value to the post-reduction signal value has restrictions for reducing the amount of color material without reducing the color reproduction range. It is difficult to find a value. On the other hand, in the conversion using the LUT, the pre-reduction signal value and the post-reduction signal value can be associated with each other independently. Therefore, even in such a case, the conversion to the post-reduction signal value can be performed with high accuracy.

  Further, the amount of color material that can be reduced also varies depending on the type of recording medium. This is because the surface state of the image formed varies depending on the type of recording medium. For example, when image formation is performed on plain paper with a relatively large surface unevenness as a recording medium and coated paper with a relatively rough surface and a relatively small unevenness, the other color that overlaps with the K color material on the plain paper There is a tendency for the amount of change in color value to increase when the amount of color material (such as CMY) is changed. For this problem, a lookup table for performing color material amount reduction processing is stored for each type of recording medium, and after acquiring the type of recording medium on which image formation is performed based on the recording medium information acquisition unit, A reduced signal value is calculated using a corresponding lookup table. Therefore, it is possible to reduce the color material consumption amount without reducing the color reproduction range even if the type of recording medium on which image formation is performed changes.

  Furthermore, the color material consumption is reduced by reducing the color materials of other colors overlapping the K color material. Therefore, the effect of reducing the color material consumption becomes higher as the image has a larger amount of other color material overlapping the K color material. It is the black generation process that generates image data including a signal corresponding to the K color material from the target image data that greatly affects the amount of the color material of the other color that overlaps with the K color material. That is, if the black generation process is performed such that the amount of the color material of the other color that overlaps with the K color material is increased, the effect of reducing the color material consumption can be enhanced even with the same input image data.

  In addition, it has black generation processing means for converting the signal value of the target image data into a black generated signal value including a signal corresponding to the black color material, and the black generated signal value of other colors overlapping the black color material is included. The color material amount is calculated based on the color material amount that can be reduced. Thereby, it is possible to perform black generation processing corresponding to the amount of color material to be reduced. The amount of color material that can be reduced is accurately represented by the amount of change between the signal value before reduction and the signal value after reduction calculated by the color material amount reduction processing means. Calculate based on data. Therefore, the time required for the calculation can be shortened compared with the case of calculating the color material amount that can be reduced using the change amount of the signal value before reduction and the signal value after reduction.

  Further, the signal value after black generation calculated by the black generation processing means is determined so that the amount of the color material of the other color overlapping the black color material is maximized. By this process, image data after the black generation process is formed so that the color material amount of the other color overlapping the K color material is increased, and the effect of reducing the color material consumption amount in the color material amount reduction process can be enhanced.

  In addition, the effect of reducing the color material consumption can be enhanced by performing the black generation process that increases the amount of the color material of the other color that overlaps the K color material. The amount of color material that can be reduced is represented by the amount of change between the signal value before reduction and the signal value after reduction calculated by the color material amount reduction processing means, and the signal value after black generation is determined based on the change amount. As described above, even if K and other color materials overlap, the amount of color material that can be reduced without narrowing the color reproduction range varies depending on the color material overlap state and the recording medium. In order to obtain it accurately, it is necessary to check what value the change amount of the pre-reduction signal value and the post-reduction signal value takes with respect to the post-black signal value generated by the black generation processing means. Therefore, it is possible to more accurately perform the black generation process according to the amount of color material to be reduced.

  Further, the black generation signal value calculated by the black generation processing means is determined so that the amount of change between the pre-reduction signal value and the post-reduction signal value is maximized. By this processing, it is possible to form image data after the black generation processing that maximizes the amount of the color material of the other color that overlaps with the K color material, and the effect of reducing the color material consumption amount in the color material amount reduction processing can be enhanced.

  In addition, a phenomenon called “color misregistration” in which the color material of each color is formed at a position different from the original image position may be a problem. This occurs mainly due to the mechanical accuracy of the members constituting the image forming apparatus. For example, in the case of a tandem type full-color laser beam printer that forms an image with four color materials of yellow (Y), cyan (C), magenta (M), and black (K) as shown in FIG. When the movement speed of 40 is slightly changed, or when the shape and position of the member is changed due to environmental changes such as temperature, the optical path of the laser for writing is distorted, the above-described “color shift” occurs. Sometimes. By reducing the amount of color material that overlaps with the black color material that contributes little to color reproduction, the consumption of color material can be reduced without compromising color reproducibility. When the color material that should be above has shifted to another position, there is a possibility that the reproduced color may change by reducing the amount of the color material.

  In order to solve such a problem caused by “color misregistration”, in addition to the above-described color material amount reduction processing means, color misregistration correction means for further correcting “color misregistration” is provided. By executing the color misregistration correction process at a predetermined timing, it is possible to correct the influence of the color misregistration and to reduce the color material consumption without impairing the color reproducibility.

Hereinafter, embodiments of an image forming apparatus to which the present invention is applied will be described.
FIG. 5 is a schematic configuration diagram illustrating a configuration of the image forming apparatus according to the embodiment. The image forming apparatus 1 according to the first embodiment shown in FIG. 1 is a full-color laser beam printer that forms an image with four color materials of black (K), cyan (C), magenta (M), and yellow (Y). Yes, for image data corresponding to CMY color materials after pseudo halftone processing, a signal value before reduction, which is a signal value of a pixel in which K and color materials overlap at the time of image formation, is a signal value smaller than the signal value before reduction The color material consumption is reduced without narrowing the color reproduction range by performing color material amount reduction processing to be converted into post-signal values and performing image formation based on the image data of each color after the color material amount reduction processing.

  The configuration of the image forming apparatus 1 shown in FIG. 5 will be described. The image forming apparatus 1 includes an image processing unit (not shown) that generates output image data for forming an image in the image forming unit based on input image data, and an image forming unit that forms an image on a recording medium. It is configured to include. The image forming unit includes a writing unit 10 and photosensitive units 20-Y, 20-C, 20-M, 20-K, primary transfer rollers 30-Y, 30-C corresponding to color materials of YCMK as main components. 30-M, 30-K, an intermediate transfer belt 40, a secondary transfer roller 50, a fixing unit 60, a paper feed unit 70, and an engine controller 80. The photoconductor units are installed in the order of 20-Y, 20-C, 20-M, and 20-K from the upstream side of the image forming process, and each photoconductor unit is a photoconductor drum that is a latent image carrier, and a photoconductor. It comprises a charger that charges the drum to a desired potential, a developing device that develops the electrostatic latent image formed on the photosensitive drum with toner, a cleaner that collects transfer residual toner remaining on the photosensitive drum, and the like. . However, the photoconductor units of the respective colors do not have to be arranged in this order and may be arranged arbitrarily.

  The engine controller 80 has a role of controlling the image forming operation of the image forming apparatus. The engine controller 80 includes a writing control unit that controls the writing unit based on output image data input from the image processing unit, a drive control unit that controls paper feeding and conveying operations, a charging unit, a developing unit, a transfer unit, and the like. An image forming process control unit that comprehensively controls the image process, a CPU that controls these components, a ROM that stores a control program, a working storage area, a RAM that provides the work, and the like are provided.

  Here, the configuration of the image processing unit is shown in FIG. The image processing unit 100 includes a color conversion processing unit 110, a black generation processing unit 120, a total amount restriction processing unit 130, a pseudo halftone processing unit 140, and a color material amount reduction processing unit 150. Each processing unit includes a color conversion LUT 111, a total amount regulation value 131, a threshold matrix 141, and a color material amount reduction LUT 151 necessary for executing the processing.

  Next, a series of operations and processing when an image is formed by the image forming apparatus according to the embodiment will be described. The input image data is RGB image data in which each pixel is represented by three signal values (8 bits) of R, G, and B. The basic operation and processing are the same for other types of image data. Since the image forming apparatus according to the embodiment forms an image using four color materials of CMYK, the reproducible color reproduction range is different from the color reproduction range of the input image data represented by RGB data. In view of this, the image processing unit 100 converts the input image data into output image data for forming an image with four color materials of CMYK by the processing shown in FIG. The color conversion processing unit 110 converts RGB signal values of input image data into CMY signal values. In this embodiment, a memory map interpolation method using tetrahedral interpolation is used as a color conversion method. In the memory map interpolation method, R, G, and B color signal values are each divided into n, and CMY signal values corresponding to the respective grid points are created in advance as a three-dimensional lookup table (hereinafter referred to as color conversion LUT) 111. For RGB signal values located between grid points, CMY signal values corresponding to neighboring grid points are read from the color conversion LUT 111 and interpolated to calculate CMY signal values. The color change method is not limited to the memory map interpolation method using tetrahedral interpolation, and other known conversion methods may be used.

  Then, the black generation processing unit 120 obtains a CMYK signal value from the CMY signal value calculated by the color conversion processing unit 110. As shown in FIG. 3, the K signal value is generated by replacing the gray component of the CMY signal value (the signal component where C = M = Y). The CMY signal value is a signal value obtained by subtracting the amount replaced with the K signal value from each signal value. Such a black generation process may be a known method.

  Next, the total amount restriction processing unit 130 performs total amount restriction processing so that the total amount of CMYK color materials does not exceed a predetermined total amount restriction value 131 based on the CMYK signal value after the black generation processing. Then, the pseudo halftone processing unit 140 converts the CMYK signal value after the total amount restriction processing into a 2-bit CMYK signal value. Then, the pseudo halftone processing unit 140 determines the signal value (2 bits) after the pseudo halftone process by comparing the signal value of the target image data with a predetermined threshold value for each color of CMYK, and performs the pseudo halftone process of each color of CMYK Generate data. In the present embodiment, pseudo halftone processing is performed by a dither method. That is, the threshold values are stored in advance as three threshold matrixes 141, and the signal values after the pseudo halftone process are determined by comparing the signal values of the target image data with the threshold value matrix 141 for each color of CMYK. Pseudo halftone processing data is generated. In the pseudo halftone processing of the present embodiment, the quantized number of the processed signal value is described as 2 bits (4 values), but other quantized numbers may be used. For example, it may be a 1-bit, 4-bit, 8-bit, quantization number such as ternary or quinary. Further, the pseudo halftone processing method is not limited to the dither method, but can be similarly applied to the case where pseudo halftone processing is performed by other methods such as an error diffusion method and a blue noise method.

  Further, the color material amount reduction processing unit 150 performs color material amount reduction processing on the image data after the pseudo halftone processing, and generates output image data composed of CMYK signal values (2 bits). Details of the color material amount reduction processing will be described later.

  The output image data generated by each processing unit of the image processing unit 100 is output to the engine controller 80 in FIG. The engine controller 80 controls each image forming unit of the image forming apparatus based on the acquired output image data. First, the photosensitive drums in the photosensitive units 20-Y, 20-C, 20-M, and 20-K are uniformly charged to a desired potential by a charger. Based on an instruction from the writing control unit, the writing unit 10 exposes each charged photosensitive drum to form an electrostatic latent image on the surface. Based on the electrostatic latent image, each color toner is developed by the developing unit, and between the photosensitive drum on the intermediate transfer belt 40 and the primary transfer rollers 30-Y, 30-C, 30-M, and 30-K. Thus, transfer is performed in the order of Y, C, M, K from the belt side. The image transferred onto the intermediate transfer belt 40 is transferred onto the recording medium supplied from the paper supply unit 70 with the secondary transfer roller 50. Thereafter, heat and pressure are applied in the fixing unit 60 to fix the toner on the recording paper. The fixed image is discharged to a paper discharge tray. An output image corresponding to the input image data can be obtained by the series of operations and processes described above.

Next, the color material amount reduction process will be described in detail.
The color material amount reduction processing unit 150 in FIG. 6 compares the CMYK color image data generated by the pseudo halftone processing unit 140 with a predetermined threshold, and before the reduction of pixels in the CMY image data where K and the color material overlap. The signal value is converted into a post-reduction signal value that is a signal value smaller than the pre-reduction signal value of at least one color of CMY. Alternatively, it is converted into a post-reduction signal value that is smaller than or equal to the pre-reduction signal value of colors other than at least one of CMY. Here, a specific processing flow in the color material amount reduction processing is shown in FIG. In the figure, each pixel of the image data after pseudo halftone processing is numbered, and the i-th (i = 1, 2,..., N) pixel is represented as a pixel i (step S101). With respect to all the pixels i, it is determined whether at least one color of CMY and a K color material overlap with each other by referring to the pre-reduction signal value of the image data after the CMYK pseudo halftone process (step S102; YES, step S103). When the pre-reduction signal value of each color of CMYK in the pixel i is expressed as Vci, Vmi, Vyi, Vki (= 0, 1, 2, 3), the condition of the pixel where at least one color of KMY overlaps with the K color material is Vki ≠ 0 and Vci = Vmi = Vyi ≠ 0. When the K and CMY color materials do not overlap in the pixel i, the pre-reduction signal values Vci, Vmi, Vyi, and Vki are output as they are as the post-reduction signal values (step S103; NO). That is, assuming that the reduced signal values of each color of CMYK are Vci ′, Vmi ′, Vyi ′, and Vki ′, Vci ′ = Vci, Vmi ′ = Vmi, Vyi = Vyi, and Vki ′ = Vki. If it is determined that the K and CMY color materials overlap, a process of reducing the amount of the CMY color material overlapping K is performed (step S103; YES, step S104). If it is determined in step S102 that the color materials of K and CMY overlap in the pixel i, the pre-reduction signal values Vci, Vmi, and Vyi of the CMY colors are smaller than the pre-reduction signal value and smaller than the pre-reduction signal value or Converted to reduced signal values Vci ′, Vmi ′, and Vyi ′ that are equal to or less than the same. For K, Vki ′ = Vki. Conversion from the pre-reduction signal value to the post-reduction signal value is performed using the color material amount reduction LUT 151 of FIG. The color material amount reduction LUT 151 is a table in which the pre-reduction signal values Vci, Vmi, Vyi, Vki and the post-reduction signal values Vci ′, Vmi ′, Vyi, Vki ′ are associated with each other, and the pre-reduction signal values Vci, Vmi, Vyi. By referring to the color material amount reduction LUT 152 based on Vki, the reduced signal values Vci ′, Vmi ′, Vyi ′, and Vki ′ can be obtained. A method for creating the color material amount reduction LUT 151 will be described later.

  Through the series of processes described above, all the reduced signal values Vci ′, Vmi ′, Vyi ′, Vki ′ (i = 1, 2,..., N) can be determined. In the image forming apparatus of this embodiment, since the amount of the CMY color material overlapping with K, which has a small contribution to the color reproduction range, is reduced, it is possible to effectively reduce the color material consumption amount without impairing the color reproducibility. It is. By outputting the output image data having this signal value to the engine controller 80 of FIG. 1, the image forming unit forms an image.

A method for creating a color material amount reduction LUT used for converting a pre-reduction signal value into a post-reduction signal value will be described below. FIG. 8 shows a flow of a procedure for creating the color material amount reduction LUT. In the same figure, image data in which K and CMY color materials that can be reproduced with the pre-reduction signal values Vc, Vm, Vy, and Vk of the image data after pseudo halftone processing of each color of CMYK are created and recorded in the image forming unit. An image is formed on the medium (step S201). In the present embodiment, since the image data after the pseudo halftone process is represented by 2 bits, the pre-reduction signal values Vc, Vm, Vy, and Vk can take four values of 0, 1, 2, and 3. Therefore, there are a total of 189 types of image data that can be reproduced under the conditions of Vk ≠ 0 and Vc = Vm = Vy ≠ 0, where K and CMY color materials overlap. Each image data is output as data having an area sufficient for colorimetry performed in step S202. Then, the L ^* a ^* b ^* value of each image formed on the recording medium is measured (step S202). The L ^* a ^* b ^* value may be measured using a colorimeter that can measure the L ^* a ^* b ^* value. Alternatively, L ^* a ^* b ^* may be obtained indirectly by calculating an amount representing another color related to L ^* a ^* b ^* such as spectral reflectance or XYZ. Here, the signal value before reduction is expressed as V = (Vc, Vm, Vy, Vk), and the L ^* a ^* b ^* value of the image output with the signal value before reduction is expressed as L ^* (V), a ^* (V). , B ^* (V). Next, based on the measured L ^* (V), a ^* (V), b ^* (V), the signal value V ′ after reduction with respect to the signal value V before reduction V ′ = (Vc ′, Vm ′, Vy ′, Vk) ') Is obtained (step S203). The signal value after reduction is represented by 2 bits like the signal value before reduction. Here, the color difference ΔE between the pre-reduction signal value and the post-reduction signal value and the total value S of changes in the signal value are defined as follows.

ΔE = √ (ΔL ^{* 2} + Δa ^{* 2} + Δb ^{* 2} ) (Formula 1)
However, ΔL ^* = L ^* (V) −L ^* (V ′)
Δa ^* = a ^* (V) −a ^* (V ′)
Δb ^* = b ^* (V) −b ^* (V ′)
S = (Vc−Vc ′) + (Vm−Vm ′) + (Vy−Vy ′) (Formula 2)

At this time, the post-reduction signal value V ′ corresponding to the pre-reduction signal value V is obtained as a signal value that satisfies the following conditions [1] to [3].
[1]: The signal V ′ after reduction is smaller than the signal V before reduction in at least one arbitrary color material among the color materials, and the signal V ′ after reduction is smaller than the signal V before reduction in a color material other than any color material. Small or less than or equal.
[2]: ΔE ≦ X
[3]: S is the largest among the signal values satisfying the conditions [1] and [2]

  By satisfying the condition [1], the color material consumption can be reduced by converting the pre-reduction signal value to the post-reduction signal value using the color material amount reduction LUT.

  Condition [2] requires that the color difference ΔE that changes by converting the pre-reduction signal value to the post-reduction signal value is equal to or less than the allowable value X. This means that the color reproduction range is not narrowed by the color material amount reduction process. In the present embodiment, the allowable value X is set to 1.5. However, the allowable value X is not limited to 1.5, and may be set to another value according to the use of the output image and the user's request.

  Condition [3] is a signal value that satisfies the conditions [1] and [2], and has a maximum total value S of signal value changes before and after conversion, that is, a signal value that can reduce the color material consumption most before and after conversion. This indicates that the signal value after reduction is used. The post-reduction signal value V ′ corresponding to each pre-reduction signal value V can be obtained in step S203 of FIG.

  Then, in step S204 of FIG. 8, the color material amount reduction LUT 151 is created and stored based on the correspondence between the pre-reduction signal value V and the post-reduction signal value V ′ obtained in step S203.

  Through the above series of procedures, a color material amount reduction LUT capable of reducing the color material consumption amount without narrowing the color reproduction range can be created.

  FIG. 9 is a characteristic diagram showing changes in the color material reduction amount when image formation is performed using the image forming apparatus of the present embodiment. The formed image is a gray image in which the input signal value (R = G = B) of each color is changed with 8-bit RGB data. The horizontal axis corresponds to the input signal value, and the vertical axis represents the ratio of the color material consumption to the case where the color material amount reduction process is not performed. As can be seen from the figure, the present embodiment reduces the amount of color material of CMY that overlaps with K. Therefore, the effect of reducing the amount of color material is exhibited from the shadow portion where the K color material is used for image formation. The color material reduction amount increases as the value increases and the rate at which K and CMY color materials overlap increases.

  As described above, in the image forming apparatus according to the present embodiment, the color reproduction range is narrowed by performing the color material amount reduction process for reducing the CMY signal value overlapping K on the image data after the pseudo halftone process. Therefore, the color material consumption can be effectively reduced.

  Next, a second embodiment will be described in detail below with reference to the drawings. The image forming apparatus according to the present embodiment is a full-color laser beam printer that forms an image with four color materials of black (K), cyan (C), magenta (M), and yellow (Y). In addition, the color material amount reduction processing described in the first embodiment is performed, and the color material amount reduction LUT to be applied is changed according to the type of recording medium on which image formation is performed.

  In the image forming apparatus of the present embodiment, the operation unit (not shown) in the configuration of the image forming apparatus shown in FIG. 5 is configured by a touch panel type liquid crystal display, and the type of recording medium registered in advance is displayed on the display. To display. When the user selects the type of recording medium used for image formation, information regarding the type of recording medium can be acquired. In the image forming apparatus according to the present embodiment, two types of recording media, for example, “plain paper” and “coated paper” in which the surface of the base paper is coated are registered and can be selected from the operation unit. In the present embodiment, a touch panel type liquid crystal display is used as means for acquiring information on the type of recording medium. However, any other means may be used as long as it can acquire information on the type of recording medium. Absent. Also, the type of recording medium to be registered is not limited to this example, and other types of recording media or more types of recording media may be registered.

  In the main configuration of the image processing unit 100, the color material amount reduction processing unit 150 stores a single color material amount reduction LUT as a difference from the configuration shown in FIG. Two color material amount reduction LUTs corresponding to the types of recording media that can be designated are stored. The color material amount reduction LUT corresponding to each recording medium performs image formation on the recording media of plain paper and coated paper in step S201 of FIG. 8 of the procedure for creating the color material amount reduction LUT described in the first embodiment. It is the look-up table calculated | required by performing the process of step S202 to step S204 after performing.

Next, processing and operations performed in the image forming apparatus of this embodiment will be described. A series of processes and operations up to image output are shown in FIG.
First, information regarding the type of recording medium is acquired (step S301). As described above, the type of the recording medium is acquired by the user specifying the type of the recording medium used for image formation on the operation unit. The image processing unit 100 in FIG. 6 performs color conversion processing, black generation processing, total amount regulation processing, and pseudo halftone processing on the input image data, and generates image data after pseudo halftone processing corresponding to each color of CMYK. (Step S302). Details of these processes are as described in the first embodiment. Next, a color material amount reduction process is performed on the image data after the pseudo halftone process (step S303). As in the first embodiment, the color material amount reduction process is performed by using the color material amount reduction LUT 151 for the image data of each color of CMY after pseudo halftone processing before the reduction of the pixel value where the black and the color material overlap at the time of image formation. Is converted into a signal value after reduction. As the color material amount reduction LUT at this time, the color material amount reduction LUT corresponding to the type of the recording medium acquired in step S301 is selected and applied. The image data after the color material amount reduction processing is output as output image data. Based on the output image data, the image forming unit forms an image on the recording medium (step S304). The operation and processing at this time are as described in the first embodiment.

  As described above, in the image forming apparatus according to the present embodiment, the color material amount reduction process for reducing the CMY signal value overlapping K is performed on the image data after the pseudo halftone process without narrowing the color reproduction range. It is possible to effectively reduce the color material consumption. Furthermore, since the color material amount reduction LUT for converting the pre-reduction signal value into the post-reduction signal value in the color material amount reduction processing is selected and used according to the type of the recording medium, the type of the recording medium used for image formation is different. Even if it changes, it is possible to reduce the color material consumption without narrowing the color reproduction range.

  Next, a third embodiment will be described in detail with reference to the drawings. The image forming apparatus according to the present embodiment is a full-color laser beam printer that forms an image with four color materials of black (K), cyan (C), magenta (M), and yellow (Y). This is an image forming apparatus that performs color material amount reduction processing after performing black generation processing so that the amount of CMY color material overlapping K is maximized based on image data. The configuration of the image forming apparatus of the present embodiment is the same as that of the first embodiment, and includes an image forming unit shown in FIG. 5 and an image processing unit 100 shown in FIG.

  The operation and processing of the image forming apparatus are the same as those in the first embodiment except for the black generation processing unit 120. Based on the image data before the black generation process, the black generation processing unit 120 calculates a signal value after black generation that maximizes the amount of CMY color material overlapping K. In the present embodiment, an example will be described in which a general dither is used in which the screen angles of dither colors used in the pseudo halftone processing unit 140 are different and the colors do not completely overlap. That is, if the area ratio of the color material portion of the image formed with the signal value V1 is v1, and the area ratio of the color material portion of the image formed with the signal value V2 is v2, the area ratio of the overlapping portion of both images is v1. XV2 is considered to be obtained. At this time, if the CMY signal values of the image data before black generation processing are expressed as Vc, Vm, Vy, and the minimum value of the CMY signal values are expressed as min (Vc, Vm, Vy), the amount of CMY color material overlapping K is The maximum black generated signal values Vc ′, Vm ′, Vy ′, and Vk ′ for each color of CMYK that are maximized are obtained by the following equations.

[1]: When min (Vc, Vm, Vy) <(Vc + Vm + Vy) / 6 Vk ′ = min (Vc, Vm, Vy)
Vc ′ = Vc−Vk ′
Vm ′ = Vm−Vk ′
Vy ′ = Vy−Vk ′ (Formula 3)
[2]: When min (Vc, Vm, Vy) ≧ (Vc + Vm + Vy) / 6 Vk ′ = (Vc + Vm + Vy) / 6
Vc ′ = Vc−Vk ′
Vm ′ = Vm−Vk ′
Vy ′ = Vy−Vk ′ (Formula 4)

  The calculated CMYK signal values Vc ′, Vm ′, Vy ′, and Vk ′ are combinations of signal values that are predicted to have the largest amount of CMY color material overlapping K.

Thereafter, as in the first embodiment, total amount regulation processing, pseudo halftone processing, and color material amount reduction processing are performed, and an image is formed on the recording medium by the image forming unit based on the generated output image data.
In the image forming apparatus according to the present exemplary embodiment, the black material generation process is performed so that the amount of the CMY color material overlapping K is maximized as described above, and then the color material amount reduction process is performed. Therefore, the amount of color material that can be reduced is increased compared to the case where only the color material amount reduction processing is performed, and the color material consumption can be more effectively reduced. Further, since the amount of color material that can be reduced is calculated based on the target image data to be subjected to the black generation process, the processing can be performed in a shorter time compared to an image forming apparatus according to a fourth embodiment described later.

  Next, a fourth embodiment will be described in detail with reference to the drawings. The image forming apparatus according to the present embodiment is a full-color laser beam printer that forms an image with four color materials of black (K), cyan (C), magenta (M), and yellow (Y). The image forming apparatus performs the color material amount reduction processing after performing the black generation processing so that the change amount of the signal value before reduction and the signal value after reduction in the color material amount reduction processing is maximized. The configuration of the image forming apparatus of the present embodiment is the same as that of the first embodiment, and includes an image forming unit shown in FIG. 5 and an image processing unit 100 shown in FIG. The operation and processing of the image forming apparatus are the same as those in the first embodiment except for the black generation processing.

The black generation process, which is a feature of this embodiment, will be described below. FIG. 11 shows a process flow in the black generation process.
First, based on the CMY signal values Vc, Vm, and Vy of the image data before the black generation process and the set K signal values Vk ′ after the black generation process, the CMY signal values Vc ′, Vm ′, and Vy after the black generation process are set. 'Is calculated from the following equation (steps S401 and S402).

Vc ′ = Vc−Vk ′
Vm ′ = Vm−Vk ′
Vy ′ = Vy−Vk ′ (Formula 5)

  Then, a total amount restriction process is performed on the calculated signal value of each color after the black generation process (step S403). The total amount restriction process is as described in the first embodiment. Next, pseudo halftone processing is performed on the calculated image data after the total amount restriction processing (step S404). The pseudo halftone processing is as described in the first embodiment. Then, based on the calculated image data after pseudo halftone processing, a post-reduction signal value is calculated using the color material amount reduction LUT 151 of FIG. 6, and the amount of change between the pre-reduction signal value and the post-reduction signal value using Equation 2 above. S is calculated (step S405). Vk ′ at which the amount of change S between the pre-reduction signal value and the post-reduction signal value is maximized is obtained (step S406: YES, steps S407 and S408). By calculating the CMY signal values Vc ′, Vm ′, and Vy ′ after the black generation process from the above equation 5, based on the calculated Vk ′ where the change amount S between the pre-reduction signal value and the post-reduction signal value is the largest, It is possible to obtain a signal value after the black generation process in which the reduction amount of the color material is the largest. Thereafter, the total amount regulation process, the pseudo halftone process, and the color material amount reduction process are performed as in the first embodiment, and an image is formed on the recording medium by the image forming unit based on the generated output image data.

  In the image forming apparatus of the present embodiment, the black material amount reduction process is performed after the black generation process is performed so that the amount of change between the pre-reduction signal value and the post-reduction signal value in the color material amount reduction process is maximized. Therefore, the amount of color material that can be reduced is increased compared to the case where only the color material amount reduction processing is performed, and the color material consumption can be more effectively reduced. Further, since the amount of color material that can be reduced is obtained from the amount of change between the pre-reduction signal value and the post-reduction signal value that are actually calculated by the color material amount reduction processing means, it is more compared with the image forming apparatus of the third embodiment. It is possible to reduce the amount of color material that does not accurately contribute to the color reproduction range.

  Next, a fifth embodiment will be described in detail with reference to the drawings. The image forming apparatus of this embodiment is a full-color laser beam printer that forms an image with four color materials of black (K), cyan (C), magenta (M), and yellow (Y). An image forming apparatus that performs the color material amount reduction processing described in the first embodiment and performs color misregistration correction at a predetermined timing.

  FIG. 12 shows a schematic diagram of the image forming unit of the present embodiment. The image forming unit shown in the figure has, as main components common to the first embodiment of FIG. 5, a writing unit 10, and photoconductor units 20 -Y, 20 -C, 20 -M corresponding to color materials of each color of YCMK, 20-K, primary transfer rollers 30-Y, 30-C, 30-M, 30-K, an intermediate transfer belt 40, a secondary transfer roller 50, a fixing unit 60, a paper feed unit 70, and a main controller 80. Yes. Further, as a configuration different from that of the first embodiment, a color misregistration detection sensor 90 is installed on the intermediate transfer belt 40 at a position downstream of the primary transfer portion of K and upstream of the secondary transfer portion. The color misregistration detection sensor 90 is an optical sensor, and the pattern position information can be acquired by irradiating the pattern formed on the intermediate transfer belt with light and detecting the reflected light. The configuration of the image processing unit is the same as that in the first embodiment.

  Next, processing and operations performed in the image forming apparatus of this embodiment will be described. The image forming apparatus according to the present embodiment includes a color misregistration correction unit, and executes color misregistration correction processing at a predetermined timing. The color misregistration correction process is executed when a user instructs a color misregistration correction process from an operation unit (not shown), or when a predetermined condition is reached, for example, the output image reaches a certain number in the image forming apparatus. A known method may be used for the color misregistration correction process. For example, the pattern shown in FIG. 13 is formed on the intermediate transfer belt 40 at a predetermined timing. The pattern is composed of two types of patterns: a pattern 91 for detecting the color misregistration amount in the sub-scanning direction and a pattern 92 inclined at 45 degrees with respect to the sub-scanning direction for detecting the color misregistration amount in the main scanning direction. ing. The subscripts C, M, Y, and K represent the colors of the color materials, respectively. The pattern formed on the intermediate transfer belt 40 is detected by the color misregistration detection sensor 90, and the position of each pattern is calculated. The color misregistration can be corrected by calculating the color misregistration amount of each color based on the calculated position and correcting the writing timing so as to cancel the color misregistration amount.

  Other image processing and operations are the same as in the first embodiment, and after the color conversion processing, black generation processing, total amount regulation processing, and pseudo halftone processing are performed in the image processing unit 100, the color material amount reduction processing Output image data is generated, and an image is formed on a recording medium by the image forming unit in FIG. 12 based on the output image data.

  As described above, according to the embodiment, the color material amount reduction process for reducing the signal value of each CMY color material that overlaps the K color material with respect to the image data after the pseudo halftone process is at least one of CMY. The signal value after reduction with respect to the signal value before reduction of one arbitrary color material is smaller than the signal value before reduction, and the signal value after reduction with respect to the signal value before reduction other than any color material is smaller than or less than or equal to the signal value before reduction. As shown, it is a process of converting a signal before reduction into a signal after reduction. By performing such a color material amount reduction process, it is possible to effectively reduce the color material consumption amount without narrowing the color reproduction range.

  Further, according to the embodiment, the reduced signal value is a color value when formed on the recording medium by the image forming unit based on the image data formed with the signal value before reduction and the image data formed with the signal value after reduction. Is a signal value whose amount of change is not more than a specified value. The post-reduction signal value is a signal value that maximizes the total value of the amounts of change between the pre-reduction signal value and the post-reduction signal value for each color. The change amount of the color value is represented by the distance between the color value of the image formed with the signal value before reduction in the uniform color space and the color value of the image formed with the signal value after reduction. Thereby, the color material consumption can be effectively reduced.

  Furthermore, according to the embodiment, the color material amount reduction processing unit has a look-up table that stores a correspondence relationship between the pre-reduction signal value and the post-reduction signal value as a parameter. The color material amount reduction processing means converts the pre-reduction signal value into the post-reduction signal value with reference to the lookup table. Thereby, the color material consumption can be effectively reduced.

  In addition, according to the embodiment, the recording medium information acquisition unit that acquires information regarding the type of the recording medium on which image formation is performed is generated and stored in the lookup table for each type of recording medium that can be acquired. The amount reduction processing means selects a lookup table corresponding to the type of the recording medium acquired by the recording medium information acquisition means. Then, the pre-reduction signal value is converted into the post-reduction signal value with reference to the selected lookup table. Thereby, even if the type of the recording medium changes, the color material consumption can be reduced without narrowing the color reproduction range.

  Furthermore, according to the embodiment, there is a black generation processing means for converting the signal value of the target image data into a black generated signal value including a signal corresponding to the K color material. According to this black generation processing means, the amount of CMY color material overlapping with the K color material is calculated based on the target image data, and the signal value after black generation is calculated based on the amount of CMY color material overlapping with the K color material. As described above, if the black generation process is performed so that the amount of the CMY color material that overlaps with the K color material is increased, the effect of reducing the color material consumption can be enhanced even with the same input image data. Thereby, it is possible to perform black generation processing corresponding to the amount of color material to be reduced. The amount of color material that can be reduced is accurately represented by the amount of change between the signal value before reduction and the signal value after reduction calculated by the color material amount reduction processing means. Calculate based on data. Therefore, the time required for the calculation can be shortened compared with the case of calculating the color material amount that can be reduced using the change amount of the signal value before reduction and the signal value after reduction.

  Further, according to the embodiment, the signal value after the black generation is a signal value that maximizes the color material amount of the CMY color material overlapping the K color material. Accordingly, image data after the black generation process is formed such that the color material amount of the CMY color material overlapping the K color material is increased, and the effect of reducing the color material consumption amount in the color material amount reduction process can be enhanced. Alternatively, the signal value after generation of black is a signal value calculated based on the amount of change between the signal value before reduction and the signal value after reduction. Thereby, the black generation process according to the amount of color material to be reduced can be performed more accurately. Alternatively, the signal value after the black generation is a signal value that maximizes the amount of change between the signal value before reduction and the signal value after reduction. As a result, image data after the black generation process that maximizes the color material amount of the CMY color material overlapping the K color material is formed, and the effect of reducing the color material consumption amount in the color material amount reduction process can be enhanced. .

  Furthermore, according to the embodiment, the color misregistration correction unit that corrects the color misregistration amount of each color is provided. Further, the color misregistration correction unit executes color misregistration correction processing at a predetermined timing. As a result, even when color misregistration occurs due to changes in the state of the image forming apparatus over time or the environment, the effect of color misregistration can be corrected, and color material consumption can be reduced without impairing color reproducibility. Is possible.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Writing unit 20 (-Y, C, M, K) Photoreceptor unit 30 (-Y, C, M, K) Primary transfer roller 40 Intermediate transfer belt 50 Secondary transfer roller 60 Fixing unit 70 Supply Paper unit 80 Engine controller 90 Color misregistration detection sensor 100 Image processing unit

JP 2007-324900 A JP 2007-98771 A JP 2006-262367 A JP-A-2005-45454

Claims (11)

A pseudo halftone processing unit that performs pseudo halftone processing on target image data; a visible wavelength range light absorbing color material that uniformly absorbs light in at least a visible wavelength range; and a color material other than a visible wavelength range light absorbing color material. An image forming device that forms an image on a recording medium using a plurality of color materials including:
After the pseudo-halftone process is performed on the target image data in which the visible wavelength region light-absorbing color material and the color material other than the visible wavelength region light-absorbing color material overlap, a color other than the visible wavelength region light-absorbing color material A signal value before reduction which is a signal value of a pixel in image data corresponding to the material, and a signal value smaller than the signal value before reduction in at least one arbitrary color material other than the visible wavelength region light-absorbing color material A color material amount reduction processing means for converting to a post-reduction signal value that is, and for a color material other than the arbitrary color material, to convert the signal value to a post-reduction signal value that is smaller than or equal to or less than the pre-reduction signal value,
An image forming apparatus, wherein the image forming unit forms an image based on image data of each color after the color material amount reduction processing by the color material amount reduction processing unit. The image forming apparatus according to claim 1,
The post-reduction signal value is the amount of change in color value when formed on the recording medium by the image forming means based on the image data formed with the pre-reduction signal value and the image data formed with the post-reduction signal value. The image forming apparatus is characterized in that the signal value is equal to or less than a specified value, and a total value of each change amount of the pre-reduction signal value and the post-reduction signal value of each color is a maximum. The image forming apparatus according to claim 2,
The change amount of the color value is represented by a distance between a color value of an image formed with the signal value before reduction in a uniform color space and a color value of an image formed with the signal value after reduction. Image forming apparatus. The image forming apparatus according to any one of claims 1 to 3,
Storage means for storing a correspondence relationship between the pre-reduction signal value and the post-reduction signal value in the color material amount reduction processing means as a parameter; and the color material amount reduction processing means refers to the storage means and performs the reduction. An image forming apparatus that converts a previous signal value into the reduced signal value. The image forming apparatus according to claim 4,
Recording medium information acquisition means for acquiring information relating to the type of recording medium on which image formation is performed; the storage means is created and stored for each type of recordable recording medium; and the color material amount reduction processing means is the recording medium An image characterized in that the storage means corresponding to the type of recording medium acquired by the medium information acquisition means is selected, and the pre-reduction signal value is converted into the post-reduction signal value with reference to the selected storage means. Forming equipment. An image forming apparatus according to any one of claims 1 to 5,
A black generation processing means for converting the signal value of the target image data into a black generated signal value including a signal corresponding to the visible light absorption color material, and the black generation processing means is based on the target image data; Calculate the color material amount of the color material other than the visible wavelength range light absorption color material overlapping the visible wavelength range light absorption color material, and other than the visible wavelength range light absorption color material overlapping the visible wavelength range light absorption color material An image forming apparatus, wherein the post-black signal value is calculated based on a color material amount of a color material. The image forming apparatus according to claim 6, wherein
2. The image forming apparatus according to claim 1, wherein the black-generated signal value is a signal value that maximizes a color material amount of the visible wavelength light absorbing color material overlapping the visible wavelength light absorbing color material. The image forming apparatus according to claim 6, wherein
2. The image forming apparatus according to claim 1, wherein the black signal value is a signal value calculated based on a change amount of the pre-reduction signal value and the post-reduction signal value. The image forming apparatus according to claim 8, wherein
2. The image forming apparatus according to claim 1, wherein the black signal value is a signal value that maximizes a change amount between the pre-reduction signal value and the post-reduction signal value. An image forming apparatus according to any one of claims 1 to 9,
An image forming apparatus comprising color misregistration correction means for correcting a color misregistration amount of each color. The image forming apparatus according to claim 10, wherein
The image forming apparatus according to claim 1, wherein the color misregistration correction unit executes a color misregistration correction process at a predetermined timing.

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