JP5794042B2 - Color material amount reduction method and image processing apparatus - Google Patents

Description

  The present invention relates to a color material amount reduction method and an image processing apparatus that reduce the total amount of color materials such as toner used when forming a color image composed of a plurality of color components.

  Conventionally, in an electrophotographic process, generally, toner of C (cyan), M (magenta), Y (yellow), and K (black) is used as a color material to form an image. At this time, in order to avoid problems such as securing fixing performance and toner scattering, the total amount of toner used for each pixel is limited so that the total amount of four colors is about 250%, with the maximum adhesion amount per color being 100%. There is a case. Furthermore, the upper limit may be set to around 200% depending on the purpose of reducing consumables costs, environmental conditions, and the like.

  Under such circumstances, the reproducibility of dark high-saturation colors is likely to be sacrificed, and is reproduced with C toner and M toner, blue reproduced with C toner and Y toner, and reproduced with M toner and Y toner. Since the color gamut is limited for the color reproducibility in the vicinity of red or the like, it is necessary to carefully control the color reproducibility.

  As one of countermeasures, there is a method of performing profile control using a four-dimensional lookup table that receives C, M, Y, and K image data values as inputs. This method also makes it possible to realize color reproduction that makes the most of the limited color gamut. However, a large amount of hardware resources such as memory is required, and detailed know-how is required for profile design, so there are significant restrictions due to hardware costs and development costs. For example, when it is desired to switch the upper limit of the toner amount finely according to conditions, it is necessary to prepare as many profiles as necessary.

  In order to solve the above problem, for example, various techniques using a simple toner amount increasing / decreasing unit based on undercolor removal have been proposed.

  As a simple toner amount increasing / decreasing means based on under color removal, for example, the black amount is determined based on the black amount determined based on the glossiness and the maximum black amount determined based on the input color signal. There is a method of determining C, M, Y, and K toner amount values based on the method (see Patent Document 1).

JP 2004-302652 A

  With the method disclosed in Patent Document 1 (method for controlling the ratio of K toner), it is possible to mainly control brightness reproducibility. However, the control of saturation reproducibility is limited, and when the ratio of K toner is controlled for the purpose of saturation reproduction, the brightness is greatly affected, so that the control as intended is difficult.

  In addition to the method disclosed in Patent Document 1, several methods for adjusting the amount of K toner have been proposed, but the ratios of C, M, and Y toners are basically maintained. In general, a method of reducing the amount of C, M, and Y by an equal amount or the like is used. Regardless of which method is used, high saturation color reproduction that makes full use of the color gamut should be realized for high saturation colors. Was difficult.

  The present invention is intended to solve the above-described problem, and the color material amount that can reduce the total color material amount while ensuring the reproducibility of saturation without requiring a large amount of hardware resources. It is an object of the present invention to provide a reduction method and an image processing apparatus.

  The gist of the present invention for achieving the object lies in the inventions of the following items.

[1] A total color material amount reduction method for reducing the total color material amount when forming a color image using color materials of a plurality of color components other than black and black,
For each pixel
Determining the total amount of colorant reduction;
Determining the amount of black colorant;
Determining a total reduction amount of the color material amount of a plurality of color components other than black;
A step for performing setting related to increase / decrease in the difference in color material amount between a plurality of color components other than black;
Obtaining a color material amount after the reduction of each color component other than black in such a manner that the total reduction amount is the total reduction amount and the difference is increased or decreased according to the setting;
I have a,
In the setting related to the increase / decrease of the difference, a saturation index value corresponding to the difference before reduction is obtained, and the difference is set so that the higher the saturation pixel value of the saturation index value is, the larger the difference is. Material reduction method.

  In the invention according to the above [1], when reducing the color material amount of color components other than black, it is set whether to increase the difference in color material amount between the color components or to reduce the difference. be able to. For example, if the setting for increasing / decreasing the difference is made according to the saturation of each pixel, the optimum color according to the saturation of the original image data in the limited color gamut under the condition that the total amount of color material is limited Saturation reproducibility can be realized.

In the invention according to the above [1] , when the saturation of the original pixel is high, the difference in the color material amount between the color components other than black is made larger than before the reduction by the total color material amount reduction process. . As a result, high chroma pixels can ensure high chroma reproducibility while reducing the total amount of color material. Note that when the saturation of the original pixel is low, the difference may be smaller than before the reduction or may be the same as before the reduction. The difference may be increased as the saturation of the original pixel is higher.

[ 2 ] The color material amount reduction according to [ 1] , wherein the color material amount after the reduction of each color component other than black is obtained by a predetermined arithmetic expression having a control parameter for adjusting increase / decrease in the difference. Method.

In the invention according to the above [ 2 ], the color material amount after the reduction of each color component other than black is obtained by a predetermined arithmetic expression having a control parameter for adjusting increase / decrease in the difference. As a result, the reduced color material amount can be obtained without requiring a large amount of hardware resources such as a multidimensional lookup table. Further, the difference in the amount of color material between the color components can be increased or decreased simply by changing the value of the control parameter.

[3] the colorant reduction method described in [2], wherein the determining the value of the control parameter in response to said saturation index value.

In the invention according to the above [3], a saturation index value representing the saturation of the pixel is obtained from the pixel value (image data of the pixel) of each color component of the pixel, and the control corresponding to the arithmetic expression is obtained from the saturation index value. Determine the value of the parameter. That is, the value of the control parameter is determined according to the saturation of the original pixel.
[4] A total color material amount reduction method for reducing a total color material amount when forming a color image using color materials of a plurality of color components other than black and black,
For each pixel
Determining the total amount of colorant reduction;
Determining the amount of black colorant;
Determining a total reduction amount of the color material amount of a plurality of color components other than black;
Obtaining a saturation index value according to a difference in the amount of color material between a plurality of color components other than black;
Obtaining a reduction amount of each color component in the total reduction amount based on the saturation index value, and determining a color material amount after reduction of each color component other than the black; and
Have
A method for reducing the amount of color material.

[5] The color material amount reduction method according to any one of [1] to [4], wherein the plurality of color components other than black are cyan, magenta, and yellow.

[6] Processing for executing the color material amount reducing method according to any one of claims 1 to 5 for image data of each pixel of a color image composed of a plurality of color components other than black and black An image processing apparatus.

  According to the color material amount reduction method and the image processing apparatus according to the present invention, the reproducibility of saturation can be ensured and the total color material amount can be reduced. For example, in a limited color gamut under conditions where the total colorant amount is limited, even if the original color is highly saturated, control to achieve optimal saturation reproducibility according to the saturation Is possible.

1 is a block diagram illustrating a schematic configuration of an image processing apparatus according to an embodiment of the present invention. It is a flowchart which shows the flow of the color material amount reduction process in this invention. FIG. 7 is a characteristic diagram showing a relationship between an input color material amount sum and a corresponding total color material amount after reduction (output color material amount sum) corresponding thereto. It is explanatory drawing which shows the specific example until it calculates | requires the total reduction amount of C, M, and Y. FIG. It is explanatory drawing which shows the example of a reduction in the case of reducing a color material amount so that the difference of the color material amount between each color component of C, M, and Y may become small. It is explanatory drawing which shows the example of a reduction in the case of reducing a color material amount by equal amount so that the difference of the color material amount between each color component of C, M, and Y may not change. It is explanatory drawing which shows the example of a reduction in the case of reducing a color material amount so that the difference of the color material amount between each color component of C, M, and Y may become large. It is explanatory drawing which shows the graph of the function which calculates | requires the saturation adjustment parameter from the saturation index value corresponding to the arithmetic expression (Formula 2) which calculates | requires the output value of C, M, and Y. It is explanatory drawing which shows the graph of the function which calculates | requires the saturation adjustment parameter from the saturation index value corresponding to the arithmetic expression (Formula 3) which calculates | requires the output value of C, M, and Y.

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

  FIG. 1 shows a schematic configuration of an image processing apparatus 10 that reduces (limits) the total color material amount by the color material amount reduction method according to the present invention. The image processing apparatus 10 is a color copy function that optically scans a document in color and prints a duplicate image on a recording sheet in color, stores the scanned document image data as a file, or transmits it to an external terminal via a network. This is a so-called color multifunction peripheral having a scanning function for performing printing, a PC printing function for forming an image related to print data received from an external terminal via a network, and printing it out on recording paper.

  The image processing apparatus 10 includes a CPU (Central Processing Unit) 11 as a control unit that performs overall control of the operation of the image processing apparatus 10. The CPU 11 includes an image reading unit 13, an image forming unit 14, a ROM (Read Only Memory) 15, a RAM (Random Access Memory) 16, a non-volatile memory 17, a display unit 18, and an operation unit 19. The image processing unit 21, the network I / F unit 22, and the hard disk device 23 are connected.

  Various programs are stored in the ROM 15, and each function (including a function for performing the color material amount reduction method) as the image processing apparatus 10 is realized by the CPU 11 executing processes according to these programs. The RAM 16 is used as a work memory for temporarily storing various data when the CPU 11 executes a program, an image memory for storing image data, and the like.

  The image reading unit 13 has a function of optically reading a document in color and acquiring image data. The image reading unit 13 includes, for example, a light source that irradiates light on a document, a color line image sensor that receives the reflected light and reads the document for one line in the width direction, and the reading position in units of lines in the length direction of the document. An optical path consisting of a moving means that sequentially moves the lens, a lens and a mirror that guides reflected light from the document to the line image sensor, and an image that is converted from the analog image signal output by the line image sensor into digital image data. It is configured with parts.

  The image forming unit 14 has a function of printing a color image corresponding to image data on a recording sheet. Here, it is configured as a tandem type color laser printer, and C, M, Y, and K toners are used as color materials for image formation.

  The image forming unit 14 includes an endless annular circumferentially driven intermediate transfer belt, and along the intermediate transfer belt, an image forming unit for C color, an image forming unit for M color, an image forming unit for Y color, and a K A color image forming unit is arranged. The C-color image forming unit forms a C-color toner image in accordance with the C-color image data and transfers it onto the intermediate transfer belt. The M-color image forming unit forms an M-color toner image in accordance with the M-color image data and transfers it onto the intermediate transfer belt. The Y-color image forming unit forms a Y-color toner image in accordance with the Y-color image data and transfers it onto the intermediate transfer belt. The K-color image forming unit forms a K-color toner image in accordance with the K-color image data and transfers it onto the intermediate transfer belt. The image forming unit 14 forms a full-color image by superimposing C, M, Y, and K color toners on the intermediate transfer belt.

  Specifically, each of the C, M, Y, and K image forming units has a cylindrical electrostatic latent image carrier on which an electrostatic latent image is formed, and a laser beam on the photosensitive member. The scanning unit includes a laser unit for scanning, a charging device, a developing device, and a cleaning device arranged around the photosensitive member. The photoconductor is driven to rotate in a constant direction at a constant speed, and the charging device uniformly charges the photoconductor. The laser unit scans the photoconductor with a laser beam modulated according to image data, and forms an electrostatic latent image on the surface of the photoconductor. The developing device visualizes the electrostatic latent image on the photoreceptor with toner. The toner image formed on the surface of the photoconductor is transferred to the intermediate transfer belt at a position where it contacts the intermediate transfer belt, and the cleaning device removes the toner remaining on the surface of the photoconductor after the transfer by rubbing with a blade or the like. to recover.

  The color toner image on the intermediate transfer belt formed by each of the C, M, Y, and K image forming units is transferred to a recording sheet conveyed from a paper feed cassette or the like at a predetermined transfer position. The transferred toner image on the recording paper is heated and pressed when the recording paper passes through the fixing device, and is fixed to the recording paper. The recording paper after fixing is discharged to a paper discharge tray in the case of single-sided printing. In the case of duplex printing, the recording paper is turned upside down and then sent back to the transfer position, the toner image is transferred from the intermediate transfer belt to the back side (second side) of the recording paper, and then discharged again through the fixing device. It is discharged to the tray.

  The nonvolatile memory 17 stores system information, user information, and the like. The system information includes various data for reducing the color material amount.

  The display unit 18 is configured by a liquid crystal display (LCD) and the like, and has a function of displaying various operation screens, setting screens, and the like. The operation unit 19 has a function of accepting various operations such as job setting / submission operations from the user. The operation unit 19 includes a touch panel that is provided on the screen of the display unit 18 and detects a pressed coordinate position, and includes a numeric keypad, a character input key, a start key, and the like.

  The image processing unit 21 performs rasterization processing for converting print data into image data, image data compression, expansion processing, and the like in addition to processing such as image enlargement / reduction and rotation.

  The network I / F unit 22 is connected to a network such as a LAN (Local Area Network) and performs a function of transmitting / receiving various data to / from a terminal device or server on the network. The hard disk device 23 is a large-capacity nonvolatile storage device, and is used, for example, for storing print data and image data.

  The image processing apparatus 10 according to the present embodiment includes a function (color material amount reduction function) that limits the amount of C, M, Y, and K toner used in pixel units. The control relating to the color material amount reduction function is performed by the CPU 11 in accordance with a program stored in the ROM 15. The image processing unit 21 may be configured to implement part or all thereof.

  Hereinafter, control related to the color material amount reduction function will be described.

  Basically, when the total color material amount of C, M, Y, and K is reduced, a process of reducing the color material amount of C, M, and Y and increasing K instead is performed. For example, if C, M, and Y are each reduced by 10% and K is increased by 10% instead, the total color material amount can be reduced by 20% while substantially maintaining the color and brightness. Further, according to the color material amount reduction method of the present invention, when determining the reduction amount of the color material of each of the C, M, and Y color components, the difference in color material amount (gap between the C, M, and Y color components). ) Is increased to reduce the amount of color material, or the difference in color material amount between each color component is reduced to reduce the amount of color material. Control regarding the increase / decrease of the difference is possible.

FIG. 2 shows a flow of color material amount reduction processing performed by the image processing apparatus 10. First, in the image data of the processing target image, a target pixel whose color material amount is to be adjusted is determined (step S201), and C, M, Y, and K data (a value indicating the color material amount) of the pixel is input ( Step S202). Next, an input color material amount sum T (T = C + M + Y + K), which is the sum of the input C, M, Y, and K color material amounts, is calculated (step S203). Further, an output color material amount total T ′, which is a sum of color material amounts after reduction of the color material amount corresponding to the input color material amount total T, is calculated by a function f ₁ (T) as shown in FIG. S204).

FIG. 3 shows an example of a graph of the function f ₁ (T) indicating the relationship between the input color material amount sum T and the output color material amount sum T ′. This graph is set according to the characteristics of the image forming unit 14. The value of the color material amount of each color component after the color material amount reduction process is also referred to as an output value. Further, in step S204 of FIG. 2, the output color material amount total T ′ may be obtained using a lookup table corresponding to the function f ₁ (T).

Returning to FIG. 2, the description will be continued. When the output color material amount total T ′ is obtained, the total reduction amount ΔT, the addition amount ΔK of K, and K ′ that is the output value of K are calculated (step S205). First, a total reduction amount ΔT = input color material amount sum T−output color material amount sum T ′ is obtained. By substituting this ΔT into the function f ₂ , ΔK that is the amount of addition of K is obtained. Then, a value obtained by adding the value of ΔK to K and limited under a condition not exceeding 100% is obtained as K ′ (K ′ = min (K + ΔK, 100%)) as an output value of K. Note that the maximum color material amount that can be used for one color component is 100%. The absolute amount indicated by 100% may vary depending on the color component.

  From the output color material amount total T ′ obtained in step S204 and K ′ obtained in step S205, the total of C, M, and Y output values (C ′ + M ′ + Y ′) is calculated as T′−K ′. (Step S206).

FIG. 4 shows a specific example of processing from step S203 to step S206. In the case of FIG. 4, C + M + Y + K = 100% + 90% + 80% + 60% = 330% is obtained in step S203 for obtaining the input color material amount total T of the processing target pixels. In step S204 for obtaining the total output color material amount T ′ from the total input color material amount T, T ′ = 250% is obtained by substituting T = 330% into the function f ₁ (T). In step S205, the total reduction amount ΔT = T−T ′ = 330% −250% = 80%. In the example of FIG. 4, the function f ₂ (ΔT) for obtaining ΔK is ΔK = ΔT × p. p is an adjustment parameter that suppresses a large change in brightness due to an excessive increase in the amount of the K color material. In FIG. 4, p = 0.2 and ΔK = 80% × 0.2 = 16%. From K ′ = min (K + ΔK, 100%) = min (60% + 16%, 100%), K ′, which is the color material amount of K after the reduction of the total color material amount, is 76%.

  In the case of the example of FIG. 4, in the calculation of step S206, C ′ + M ′ + Y ′ = T′−K ′ = 250% −76% = 174%. Thereby, the total reduction amount of the color material amounts of C, M, and Y can be obtained. In the example of FIG. 4, 270% -174% is 96%.

  Here, how the total reduction amount of the C, M, and Y color materials is allocated to C, M, and Y to determine the reduction amount of each color will be described.

  In the color material amount reduction method of the present invention, the color material amount is reduced by increasing the color material amount difference between the color components other than black, or the color material amount difference between the color components is reduced. Thus, it is possible to perform control related to increase / decrease in the difference in the color material amount between the color components, such as reducing the color material amount.

  5 illustrates a case where the difference is reduced before and after reduction, FIG. 6 illustrates a case where the difference does not change, and FIG. 7 illustrates a case where the difference is increased. In FIG. 5 to FIG. 7, the color material amounts of C, M, and Y before reduction are the same. In any case, the total reduction amount in C, M, and Y is 60%.

  When the reproducibility of the saturation when the reduction amount of C, M, and Y is equal is standard, the difference in the color material amount between C, M, and Y after reduction is reduced. If the reduction is made, the saturation becomes low, and if the reduction is made so that the difference in the color material amount among C, M, and Y after reduction becomes high, the saturation becomes high.

  FIG. 5 shows an example of reduction when the difference in color material amount among C, M, and Y after reduction becomes small. Here, the color material amounts of C, M, and Y are reduced so that the ratio of the color material amounts of C, M, and Y does not change before and after the reduction. In FIG. 5, the color material amounts of C, M, and Y before reduction were 100%, 70%, and 50%, whereas the color material amounts of C, M, and Y after reduction were 73%, 51% and 36%. The reduction amounts of the color materials of C, M, and Y are 27%, 19%, and 14%, and the reduction amount is larger as the color material amount before the reduction is larger. As a result, after the reduction, the difference in the color material amount between C, M, and Y becomes smaller than before the reduction.

  That is, the difference that was 100-70 = 30% before the reduction between CM was reduced to 73-51 = 22% after the reduction, and the difference between 70 and 20 = 20% before the reduction was reduced between MY. Later, 51−36 = 15%, and the difference between C−Y and 100−50 = 50% before the reduction is reduced to 73−36 = 37% after the reduction. When this reduction method is adopted, the saturation of the pixel after the reduction is lower than the original saturation before the reduction (low saturation).

  FIG. 6 shows a reduction example in the case where the color material amount is reduced by an equal amount from each of C, M, and Y. In this case, the difference in the color material amount between C, M, and Y does not change before and after the reduction. In FIG. 6, the color material amounts of C, M, and Y before reduction are 100%, 70%, and 50%, whereas the color material amounts of C, M, and Y after reduction are 80%, 50% and 30%. The reduction amounts of C, M, and Y color materials are unified to 20% for all of C, M, and Y. Before and after the reduction, the difference between CM is 30%, the difference between MY is 20%, and the difference between CY is 50. This reduction method is generally adopted.

  FIG. 7 shows an example of reduction when the difference in color material amount among C, M, and Y after reduction becomes large. In FIG. 7, the color material amounts of C, M, and Y before reduction are 100%, 70%, and 50%, whereas the color material amounts of C, M, and Y after reduction are 86%, 51% and 23%. The amount of reduction of C, M, and Y color materials is 14%, 19%, and 27%. The larger the color material amount before the reduction, the smaller the reduction amount, and the less the color material amount before the reduction. There is much reduction amount. Thereby, after the reduction, the difference in the amount of the color material in C, M, and Y becomes wider than before the reduction.

  That is, the difference that was 100-70 = 30% before the reduction between CM was 86-51 = 35% after the reduction, and the difference between 70 and 20 = 20% before the reduction was reduced between MY. Later, 51-23 = 28%, and the difference between CY and 100-50 = 50% before reduction increases to 86-23 = 63% after reduction. When this reduction method is employed, the saturation of the pixel after the reduction is higher (high saturation) than the original saturation before the reduction.

  Next, a method of obtaining the reduction amount of each color material will be described. In the present invention, each color material amount of C, M, and Y after reduction is obtained by an arithmetic expression. The arithmetic expression described below has a control parameter (saturation adjustment parameter) related to increase / decrease in the difference in color material amount between the color components, and when the color material amount is reduced by the value of the control parameter, The difference in the amount of color material between components increases or decreases. That is, of the reduction patterns described in FIG. 5, FIG. 6, and FIG. 7, which reduction pattern is adopted is determined by the value of the control parameter.

ここで、min（）は、括弧内の最小値を、max（）は、括弧内の最大値を示す。すなわち、Ｃ、Ｍ、Ｙの中の最大値と最小値との差分を最大値で除した値を彩度指標値Ｓとする。 The value α of the control parameter (referred to as saturation adjustment parameter) is obtained by obtaining the saturation index value S from the respective color material amounts of C, M, and Y before reduction, and substituting this saturation index value S into a predetermined function. (Or use a lookup table). The saturation adjustment parameter α is a parameter (control parameter) included in an arithmetic expression for obtaining each color material amount after reduction of C, M, and Y.
The saturation index value S is obtained by the following equation.

Here, min () indicates the minimum value in parentheses, and max () indicates the maximum value in parentheses. That is, a value obtained by dividing the difference between the maximum value and the minimum value among C, M, and Y by the maximum value is set as the saturation index value S.

この式中のαは彩度調整パラメータである。 The following expression is an example of an arithmetic expression for obtaining the color material amounts C ′, M ′, and Y ′ after reduction.

Α in this equation is a saturation adjustment parameter.

FIG. 8 is an example of a graph representing a function (α = f ₃ (S)) for obtaining the value of the saturation adjustment parameter α corresponding to the arithmetic expression from the saturation index value S. In the arithmetic expression shown in Formula 2, when the value of the saturation adjustment parameter α is 1 ≧ α> 0, the difference in the color material amount between C, M, and Y after reduction is small, and when α = 0. The difference in color material amount between C, M, and Y does not change from before reduction (the reduction amount becomes equal), and when α <0, the color material amount between C, M, and Y after reduction The difference becomes larger.

Returning now to FIG. The saturation index value S and the saturation adjustment parameter α described above are calculated (step S207). In this example, α is obtained by a function corresponding to the graph shown in FIG. 8, α = f ₃ (S), and S is obtained by the above-described equation (1). Thereafter, the C, M, Y, α, and K ′ values are substituted into the arithmetic expression shown in Equation 2 above to calculate the output values C ′, M ′, and Y ′ after reducing the total color material amount ( Step S208).

  If there is a pixel for which the process from step S201 to S208 has not been completed (step S209; No), the process returns to step S201 to continue the process. In step S201, the next pixel of interest is determined from pixels that have not been processed in steps S201 to S208. When the above process is completed for all pixels (step S209; Yes), the process of FIG. 2 is terminated.

Note that other arithmetic expressions may be used to obtain the output values C ′, M ′, and Y ′. The following expression is another example of an arithmetic expression for obtaining the color material amounts C ′, M ′, and Y ′ after reduction.

FIG. 9 shows an example of a graph representing a function (α = f ₄ (S)) for obtaining the value of the saturation adjustment parameter α corresponding to the above arithmetic expression from the saturation index value S. In the arithmetic expression shown in Equation 3, when the value of α is 1>α> 0, the difference in the color material amount between C, M, and Y after reduction is small, and when α = 1, C, The difference in the amount of color material between M and Y does not change from before reduction (the reduction amount becomes equal, neutralization and reduction), and when α> 1, between C, M, and Y after reduction The difference in the amount of color material increases. When Expression 3 is used as an arithmetic expression for obtaining the output values C ′, M ′, and Y ′, the value of the saturation adjustment parameter α is obtained by the function f ₄ (S).

According to the color material amount reduction method and the image processing apparatus according to the present invention, the following effects can be obtained.
1. Saturation reproducibility in color reproduction can be controlled without applying color conversion using a multi-dimensional lookup table that requires a lot of hardware resources in an image forming system that requires a limited amount of color material It becomes.
2. By adjusting the saturation reproducibility according to the saturation of the original color, to achieve the optimal saturation reproducibility in a limited color gamut under conditions where the total colorant amount is limited Control becomes possible.
3. High saturation color reproduction that makes the best use of the limited color gamut under the condition that the total colorant amount is limited with respect to the high saturation color.

  The embodiment of the present invention has been described with reference to the drawings. However, the specific configuration is not limited to that shown in the embodiment, and there are changes and additions within the scope of the present invention. Are also included in the present invention.

  In the embodiment of the present invention, in the color material amount reduction process, the value of the control parameter (saturation adjustment parameter α) related to increase / decrease in the difference in color material amount between the color components is used as the color material of each color component of the original pixel. The saturation index value S of the pixel is obtained from the quantity and determined from this S, but the method of determining the value of the saturation adjustment parameter α is not limited to this. For example, the saturation adjustment parameter α may be set by the user for the entire image to be processed or for each certain area.

  In the embodiment of the present invention, attention is paid to the saturation of each pixel as a reference for increasing / decreasing the difference in the amount of color material between color components. However, the present invention is not limited to saturation, and for example, increasing / decreasing the difference based on brightness is used. You may decide.

  The arithmetic expression for reducing the color material amount is not limited to the one (Equation 2 or 3) exemplified in the embodiment of the present invention. Any arithmetic expression for reducing the color material amount may be used as long as it includes a control parameter for reducing or increasing the difference in color material amount between color components other than black.

  The method of using an arithmetic expression including a control parameter that increases or decreases the difference in color material amount between color components used in the embodiment of the present invention can be achieved by simply changing the value of the control parameter to be set. Since the color material amount can be reduced by increasing or decreasing the difference in the color material amount between them, there is an advantage that the hardware can be shared. It should be noted that a plurality of types of arithmetic expressions with different differences may be prepared, and the arithmetic expressions may be switched instead of changing the control parameter value.

  In the embodiment, an example of a color image having four colors of CMYK as color components is shown, but the present invention is not limited to this, and six colors, eight colors, and the like may be used. Further, the present invention, which is not limited to toner, can also be applied to the case of printing with another type of image processing apparatus such as an ink jet type printer.

  In the embodiment, the purpose of reducing the color material amount is to limit the total color material amount, but the purpose of reduction is not limited.

  What is necessary is just to set suitably about the function which calculates | requires saturation adjustment parameter (alpha). What is necessary is just to determine according to the reproduction characteristic of a desired saturation and the characteristic of a printer. It should be noted that the function for obtaining α from S may be determined corresponding to the arithmetic expression for obtaining the output values C ′, M ′, and Y ′.

10. Image processing apparatus (MFP)
11 ... CPU
DESCRIPTION OF SYMBOLS 12 ... Bus 13 ... Image reading part 14 ... Image forming part 15 ... ROM
16 ... RAM
DESCRIPTION OF SYMBOLS 17 ... Nonvolatile memory 18 ... Display part 19 ... Operation part 21 ... Image processing part 22 ... Network I / F part 23 ... Hard disk apparatus 52 ... Image data (at the time of input)
53 ... Image data (after increase / decrease process)

Claims (6)

A total color material amount reduction method for reducing the total color material amount when forming a color image using color materials of a plurality of color components other than black and black,
For each pixel
Determining the total amount of colorant reduction;
Determining the amount of black colorant;
Determining a total reduction amount of the color material amount of a plurality of color components other than black;
A step for performing setting related to increase / decrease in the difference in color material amount between a plurality of color components other than black;
Obtaining a color material amount after the reduction of each color component other than black in such a manner that the total reduction amount is the total reduction amount and the difference is increased or decreased according to the setting;
Have
In the setting relating to the increase / decrease of the difference, a saturation index value corresponding to the difference before reduction is obtained, and the difference is set to be larger as the high saturation pixel has a larger saturation index value. Material reduction method. Color material amount after the reduction of the color components other than the black color material reduction method according to claim 1, characterized in that determined by the predetermined arithmetic expression having a control parameter for adjusting the increase or decrease of the difference. Colorant reduction method according to claim 2, characterized in that to determine the value of the control parameter in response to said saturation index value.   A total color material amount reduction method for reducing the total color material amount when forming a color image using color materials of a plurality of color components other than black and black,
  For each pixel
  Determining the total amount of colorant reduction;
  Determining the amount of black colorant;
  Determining a total reduction amount of the color material amount of a plurality of color components other than black;
  Obtaining a saturation index value according to a difference in the amount of color material between a plurality of color components other than black;
  Obtaining a reduction amount of each color component in the total reduction amount based on the saturation index value, and determining a color material amount after reduction of each color component other than the black; and
  Have
  A method for reducing the amount of color material. The color material amount reduction method according to claim 1, wherein the plurality of color components other than black are cyan, magenta, and yellow. 6. A processing unit that executes the color material amount reduction method according to claim 1 for image data of each pixel of a color image composed of a plurality of color components other than black and black. An image processing apparatus.

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