JP2010041651A - Color reproduction range evaluating method, color reproduction range evaluating device, and image forming device - Google Patents

Abstract

The present invention provides a color reproduction range evaluation method capable of appropriately evaluating a color image with only one evaluation value based on spectral reflectances of three colors of C, M, and Y.
In step 1 (S1), a user sets C, M, and Y spectral reflectances in a target color reproduction range, and the data is stored in a target color spectral reflectance data storage unit. Next, in step 2 (S2), the spectral reflectance measurement unit 12 measures C, M, and Y patch images of the evaluation sample, and the measurement data is stored in the spectral reflectance measurement data storage unit 13. In step 3 (S3), any one of the expressions (1) to (3), the expressions (5) to (7), the expressions (9) to (11) and (4), the expression (8), or the expression (12) An evaluation value E1, E2 or E3 is calculated using the evaluation formula. In step 4 (S4), the calculated evaluation values E1c, E1m, E1y, and E1 are displayed by a display method as shown in FIG. 10, for example.
[Selection] Figure 8

Description

  The present invention relates to a color reproduction range evaluation method and a color reproduction range evaluation for evaluating a color reproduction range of an image output by a color image forming apparatus such as a copying machine, a printer, an ink jet printer, or a printing machine using an electrophotographic method. The present invention relates to an apparatus and an image forming apparatus including the apparatus.

  The normal color reproduction range evaluation is performed based on the L * a * b * chromaticity value in the CIE-LAB uniform color space. The CIE-LAB uniform color space is a color space recommended by the CIE (International Lighting Commission) in 1976, and the values of L *, a *, and b * are defined by equations (13) to (15). Yes.

  Here, X, Y, and X are the tristimulus values of the object, and Xn, Yn, and Zn are the tristimulus values of the complete diffuse reflection surface. In the case of T / Tn ≦ 0.0008856 (T = X, Y, Z), the cubic root portion is set to 7.787 (T / Tn) +16/116.

  Next, tristimulus values will be described. Humans have a spectral reflectance of an object, which is a continuous function in the visible wavelength region (400 to 700 nm), and stimulation amounts of three types of cells called L cone, M cone, and S cone distributed on the retina. The color is perceived by. The values obtained by quantifying the amount of stimulation are tristimulus values X, Y, and Z, and the values of X, Y, and Z are based on the color matching function shown in FIG. 1 representing human spectral sensitivity characteristics (16). It is defined by the formula (18). In FIG. 1, curves 1, 2, and 3 are curves showing the relationship between the color wavelength and the color matching function in the stimulus values X, Y, and Z, respectively.

  In the conventional color gamut evaluation method, cyan (C), magenta (M), yellow (Y), red (R), green (G), and blue (B) (hereinafter, cyan, magenta, yellow, red) are used for paper. , Green, and blue are represented by C, M, Y, R, G, and B, respectively, and output by the image forming apparatus, and the spectral reflectance of each of the six colors is measured. L * a * b * values are calculated based on the definition formula.

  Next, as shown in FIG. 2, the values of (a *, b *) are plotted on 6 points of C, M, Y, R, G, B on the a * b * plane, and each plotted point is a straight line. Finally, a method is used in which the area (color gamut area) and shape of the region surrounded by the straight line is compared with the target color to evaluate the size of the color reproduction range. (In FIG. 2, a * b * values measured from C, M, Y, R, G, and B patch images of Japan Color 2001 coated paper produced by the Japan Printing Society Standardization Committee were used as target colors. However, in the evaluation on the a * b * plane, the lightness L * is not considered, and even if there is no difference from the target color on the a * b * plane, the difference in the lightness L * may be large. is there. As another color reproduction range evaluation method for avoiding this problem, there is a method of evaluating a color reproduction range using a color difference ΔE defined by the following equation (19) as in the example of Table 1.

  If the color difference ΔE is less than 3, the color difference cannot be distinguished with the naked eye. Therefore, the color reproduction range target is set for each of C, M, Y, R, G, and B so that the color difference ΔE is less than 3 for the target color. In many cases, a value is set and a toner or ink color material is designed.

  Since the evaluation method using the color difference yields six evaluation values, there is a method of evaluating by the size of the color gamut volume in the L * a * b * space in order to avoid it. First, 6 points are plotted from the L * a * b * values of C, M, Y, R, G, and B on the L * a * b * space, and then L * of black (Bk) and white (W). Set a * b * value or plot using Bk and W measurements. When the measured values Bk and W are used, the L * a * b * value measured by outputting a Bk patch image to the paper and W is the L * a * b * value of the used paper. The size of the color reproduction range is evaluated by the size of the color gamut volume obtained by connecting the above eight plot points with a straight line.

  As an evaluation method using the color gamut volume, there is a method in which the color gamut volume of the target color is evaluated by an inclusion rate representing how much the color gamut volume of the evaluation color is included (covered). Specifically, as described above for the evaluation color and the target color, eight plot points C, M, Y, R, G, B, Bk, and W on the L * a * b * space are straight lines. Are further projected onto the a * b * plane for each lightness L *. Next, in the color gamut area obtained by connecting the six points C, M, Y, R, G, and B projected on the a * b * plane for each brightness, the color gamut area of the target color and the evaluation color Evaluation is based on a ratio between a value (inclusion volume) obtained by integrating the areas of the overlapping color gamut areas in the brightness direction and the color gamut volume of the target color.

  As a simple evaluation method, a method of evaluating a color reproduction range using a density D defined by the following equation (20) in C, M, and Y images is also used.

  S (λ) × P (λ) is called a spectral product. FIG. 3 shows the spectral product of status A and status M defined by ISO. The density of each C, M, and Y is measured, and the color reproduction range is evaluated by comparison with the density of the target color. In particular, since the size of the color reproduction range of an image output by an electrophotographic method is greatly related to the amount of color material (toner) attached per unit area transferred onto a sheet, usually the color reproduction range described above is used. Using the evaluation method, obtain the pre-adhesion condition for a large color reproduction range, set the writing light intensity of the image forming device, the surface potential of the photoconductor drum, or the development bias, and control the toner adhesion amount per unit area. There are many cases to do.

  As a method of effectively using such a color reproduction range, taking into account human visual characteristics in advance, the toner adhesion amount per unit area that maximizes the saturation is calculated, and a γ table is created or a development bias is applied. An electrophotographic image forming apparatus to be controlled has been proposed. (For example, see Patent Document 1)

JP 2004-94027 A

  In the conventional color reproduction range evaluation method, the chromaticities of the six colors C, M, Y, R, G, and B are plotted on the a * b * plane and connected by a straight line, and the area of the area surrounded by the straight line ( Although a method for evaluating the size or shape of the color gamut area) is used, there is a problem that even if the area is the same size, if the shape is different, the color reproduction range is also different, so that it cannot be quantitatively evaluated. In addition, in the evaluation on the a * b * plane, the lightness L * is not taken into consideration, and even when the area and shape of the target color reproduction range are similar, the error from the lightness L * is large. , L * and the entire color reproduction range cannot be evaluated.

  In addition, as a method for quantitatively evaluating the color reproduction range, there is a method for evaluating the color reproduction range based on a color difference ΔE with respect to each of six target colors of C, M, Y, R, G, and B. Six evaluation values are required, and the color reproduction range cannot be evaluated with one evaluation value.

  As a method for evaluating the color reproduction range with one evaluation value including L *, there are methods such as the size of the color gamut volume in the L * a * b * three-dimensional space or the coverage ratio of the color gamut volume of the target color. However, since at least six chromaticity values of C, M, Y, R, G, and B are required, not only C, M, and Y but also R, G, and B patch images are output. And must be measured.

  Further, in order to set the toner adhesion amount per unit area so that the color reproduction range of the electrophotographic image can be widely used, the density values of the single color C, M, and Y patch images are matched with the target density value. Some image forming apparatuses control the amount of adhesion, but when the density value is used as the evaluation value of the color reproduction range, the density and L * a * b * chromaticity value correspond even if the density approaches the target density value. Therefore, there is a problem that the color difference ΔE increases even if the density value of the target color is the same.

  As another method for obtaining the optimum adhesion amount condition that can be used in a wide color reproduction range, C, M, Y, R, and G outputted by changing the adhesion amount of each C, M, and Y color material. There is also a method in which the optimal adhesion amount condition is obtained by evaluating from the patch images of the six colors B and B by the color gamut area, the color gamut volume or the coverage ratio of the target color gamut volume described above. However, it takes a very long time to evaluate the size of the color reproduction range by changing the adhesion amounts of C, M, and Y in several steps, creating and measuring samples of all combinations, and evaluating the size of the color reproduction range.

  Further, in the invention described in Japanese Patent Application Laid-Open No. H10-228867, an electronic device for obtaining an adhesion amount condition for widening the color reproduction range in consideration of a color reproduction range in consideration of human visual characteristics and controlling the toner adhesion amount per unit area for each color. Although a photographic image forming apparatus has been proposed, the color reproduction range is evaluated only by saturation, the lightness L * is not considered, and the entire color reproduction range is not correctly evaluated. The amount of adhesion is controlled. Therefore, even if the toner adhesion amount is controlled so that the saturation is maximized, it cannot be said that the image forming apparatus uses the maximum color reproduction range. Further, since the surface irregularities and spectral characteristics of the recording paper to be transferred are not taken into consideration, it is impossible to cope with a change in chromaticity of an image when the paper type is changed, that is, a change in color reproduction range.

  The present invention has been made in consideration of the above situation, and it is possible to appropriately evaluate a color image with a single evaluation value for the color reproduction range from only the spectral reflectances of the three colors C, M, and Y. An object is to provide a color reproduction range evaluation method and a color reproduction range evaluation apparatus.

  Another object of the present invention is to provide an image forming apparatus capable of forming an image with a wide color reproduction range.

  In order to solve the above-described problem, the present invention provides each spectral reflectance R ′ in the color reproduction range (color space) of the target color image and each spectral reflectance R in the color reproduction range of the color image to be evaluated. By performing correction by multiplying the difference value by a weight function, the evaluation value of each color is calculated, and the size of the color reproduction range in the color image is evaluated using the sum of the evaluation values of each color.

  That is, the invention described in claim 1 is a method for evaluating the size of the color reproduction range in a color image, and includes cyan (C), magenta (M), and yellow (Y) in the target color reproduction range. R'c (λ), R'm (λ), R'y (λ) for each spectral reflectance, and cyan (C), magenta (M), and yellow (Y) spectral reflectances for the image to be evaluated. Rc (λ), Rm (λ), Ry (λ), and weighting functions w1c (λ) = 1 / R′c (λ), w1m (λ) = 1 / R′m (λ), w1y (λ) = 1 / R′y (λ) and the sampling number of the wavelength λ of the color is N, using the following formulas (1) to (3), cyan (C), magenta (M), yellow ( Y) evaluation values (E1c, E1m, E1y) are calculated, and the color in the color image is calculated using the evaluation value E1 calculated by the following equation (4). It is obtained by the color reproduction range evaluation method and evaluating the magnitude of the current range.

  The invention according to claim 2 is a method for evaluating the size of the color reproduction range in a color image, and each spectrum of cyan (C), magenta (M), and yellow (Y) in the target color reproduction range. The reflectances are R′c (λ), R′m (λ), R′y (λ), and the spectral reflectances of cyan (C), magenta (M), and yellow (Y) of the image to be evaluated are Rc ( λ), Rm (λ), Ry (λ), and weighting functions w2c (λ) = (1-R′c (λ)), w2m (λ) = (1-R′m (λ)), w2y ( When λ) = (1−R′y (λ)) and the sampling number of the color wavelength λ is N, cyan (C), magenta (M) using the following equations (5) to (7): ) And yellow (Y) evaluation values (E2c, E2m, E2y) are calculated, respectively, and color evaluation in the color image is performed using the evaluation value E2 calculated by the following equation (8). It is obtained by the color reproduction range evaluation method and evaluating the size range.

  According to a third aspect of the present invention, there is provided a method for evaluating the size of a color reproduction range in a color image, wherein each spectrum of cyan (C), magenta (M), and yellow (Y) in a target color reproduction range. The reflectances are R′c (λ), R′m (λ), R′y (λ), and the spectral reflectances of cyan (C), magenta (M), and yellow (Y) of the image to be evaluated are Rc ( λ), Rm (λ), Ry (λ), color matching functions are x (λ), y (λ), z (λ), and weight function is w3 (λ) = x (λ) + y (λ) + z When (λ) and the sampling number of the wavelength λ of the color are N, the evaluation values (E3c) of cyan (C), magenta (M), and yellow (Y) are calculated using the following equations (9) to (11). , E3m, E3y), and using the evaluation value E3 calculated by the following equation (12), the size of the color reproduction range in the color image This is a color reproduction range evaluation method characterized by evaluating the thickness.

  According to a fourth aspect of the present invention, there is provided a color reproduction range evaluation apparatus for evaluating the size of a color reproduction range in a color image, wherein each spectrum of cyan (C), magenta (M), and yellow (Y) in the evaluation image. Obtained by means for obtaining the reflectance, means for setting the spectral reflectance of cyan (C), magenta (M), yellow (Y) in the target color reproduction range, and means for obtaining the spectral reflectance. The evaluation value is calculated using the color reproduction range evaluation method according to any one of claims 1 to 3, using each spectral reflectance data and each spectral reflectance data set by the means for setting the spectral reflectance. A color gamut evaluation apparatus characterized by comprising a means.

  According to a fifth aspect of the invention, in the color gamut evaluation apparatus according to the fourth aspect of the invention, cyan (C) and magenta (M) in an evaluation image in which the amount of color material deposited per unit area is changed in two or more stages. From the spectral reflectance data of each color acquired by the means for acquiring each spectral reflectance of yellow (Y) and the means for acquiring the spectral reflectance, the wavelength of each color with respect to the amount of color material attached per unit area Each color based on the spectral reflectance at the wavelength of each color with respect to the adhesion amount of the coloring material per unit area calculated by the means for calculating the spectral reflectance at the wavelength and the means for calculating the spectral reflectance at the wavelength of each color with respect to the adhesion amount Set by means for complementing spectral reflectance data for the amount of material adhering, each reflectance data supplemented by means for complementing the reflectance data, and means for setting the spectral reflectance A means for calculating an evaluation value by using the color reproduction range evaluation method according to claim 4 based on the spectral reflectance data, and a means for selecting an adhesion amount of the color material when the evaluation value is minimized. It is characterized by having.

According to a sixth aspect of the present invention, there is provided image forming means for forming a color image with at least cyan (C), magenta (M), and yellow (Y) color materials, and a transfer material for forming a color image with the image forming means. A color reproduction range evaluation device that calculates the adhesion amount of the color material for each color, and a control unit that controls the formation of the color image based on the color material adhesion amount calculated by the color reproduction range evaluation device. In the image forming apparatus,
The color reproduction range evaluation apparatus is a color reproduction range evaluation apparatus according to claim 4 or 5.

  According to the present invention, cyan (C), magenta (M), yellow () using the above formulas (1) to (3), formulas (5) to (7), or formulas (9) to (11). (Y) by calculating the evaluation value, and evaluating the size of the color reproduction range in the color image by using the evaluation value calculated by the above formula (4), (8) or (12). To provide a color reproduction range evaluation method and a color reproduction range evaluation apparatus capable of appropriately evaluating a color image with a single evaluation value for the color reproduction range from only the spectral reflectances of the three colors C, M, and Y. it can.

  In addition, according to the present invention, the color reproduction range is wide by calculating and controlling the amount of color material attached per unit area that maximizes the color reproduction range based on the evaluation of the color reproduction range evaluation apparatus. It is possible to provide an image forming apparatus that enables image formation.

  The color reproduction range evaluation method according to three embodiments according to the present invention will be described.

  First, the color reproduction range evaluation method according to the first embodiment is a method for evaluating the size of a color reproduction range in a color image, and each of C, M, and Y spectral reflectances in a target color reproduction range. R′c (λ), R′m (λ), R′y (λ), and C, M, and Y spectral reflectances of the image to be evaluated are Rc (λ), Rm (λ), Ry (λ ), W1c (λ) = 1 / R′c (λ), w1m (λ) = 1 / R′m (λ), w1y (λ) = 1 / R′y (λ) When N is the number of samplings, E1c, E1m, and E1y are calculated using the following formulas (1) to (3) and evaluated using the evaluation value E1 of formula (4). According to this method, by using the evaluation value E1, the color reproduction range can be evaluated with one evaluation value only from the spectral reflectances of the three colors C, M, and Y.

The experimental result confirmed about the validity at the time of using this evaluation value E1 is shown next. An electrophotographic copying machine was used to prepare samples of evaluation images used in the experiment. In addition, the spectral reflectance of the C, M, and Y patch images of JapanColor2001 coated paper was measured in advance as the target color.
First, the amount of toner adhered per unit area of C, M, and Y is changed as shown in Table 2 below (unit is mg / cm ² ), and patch images of C, M, Y, R, G, and B are respectively obtained. Is output on the transfer paper. Next, the spectral reflectance of each color is measured from the three color patch images of C, M, and Y, and the evaluation value E1 is calculated using the above equation (4). In addition, in order to confirm the validity of the evaluation value E1, six L * a * b * chromaticity values are acquired from the patch images of C, M, Y, R, G, and B output for evaluation, and the target From the color gamut volume connecting the C, M, Y, R, G, B, Bk, and W points of the color, the coverage of the color gamut volume with respect to the target color was calculated, and the correlation was examined. In order to obtain the coverage of the color gamut volume, at least six color L * a * b * chromaticity values of C, M, Y, R, G, and B are required, but the lightness L * value is also taken into consideration. Since the value represents the size of the color reproduction range, if there is a correlation between the coverage of the color gamut volume and the evaluation value E1, the validity of the proposed evaluation value E1 can be shown. In this experiment, the target color is Japan Color 2001 coated paper as described above, and the L * a * b * chromaticity values of Bk and W are Bk = (10, 0, 0), W = (95, 0, 0). And set. In addition, the calculation step width of each L * a * b * in the coverage ratio calculation is 1, and the X-RITE 938 is used to measure the spectral reflectance of the patch image, and measurement is performed under a light source D50 and a standard observation angle of 2 °. It was.

The experimental results are shown in FIG. FIG. 4 shows the relationship between the coverage of the target color gamut volume and the evaluation value E1. As is apparent from this result, very high and contribution ratio R ² is 0.96, indicating that can evaluate the magnitude of the color reproduction range in the evaluation value E1.

  The evaluation value E1 is obtained by dividing the difference value for each wavelength between the C, M, and Y evaluation colors and the spectral reflectance of the target color by the spectral reflectance of the target color. When a value of 0 exists in the rate, the evaluation value E1 cannot be calculated. As an evaluation method when the reflectance of the target color is 0, a second evaluation method using the equations (5) to (8) and a third evaluation method using the equations (9) to (12) are proposed. .

  First, expressions (5) to (8) related to the second evaluation method will be described. A method for evaluating the size of a color reproduction range in an electrophotographic image, in which C, M, and Y spectral reflectances in a target color reproduction range are represented by R′c (λ), R′m (λ), R′y (λ), C, M, and Y spectral reflectances of the image to be evaluated are Rc (λ), Rm (λ), Ry (λ), and the weight function is w2c (λ) = (1-R ′) c (λ)), w2m (λ) = (1−R′m (λ)), w2y (λ) = (1−R′y (λ)), and N is the number of wavelengths sampled, E2c, E2m, and E2y are calculated using the equations (5) to (7), respectively, and evaluated using the evaluation value E2 from the equation (8).

  Next, expressions (9) to (11) related to the third evaluation method will be described. A method for evaluating the size of a color reproduction range in a color image, wherein C, M, and Y spectral reflectances in a target color reproduction range are R′c (λ), R′m (λ), R 'y (λ), C, M, and Y spectral reflectances of the image to be evaluated are Rc (λ), Rm (λ), Ry (λ), and color matching functions are x (λ), y (λ), When z (λ) is set to w3 (λ) = x (λ) + y (λ) + z (λ) and the number of wavelength samplings is N, the following equations (9) to (11) are used. , E3c, E3m, and E3y are calculated and evaluated using the evaluation value E3 of equation (12).

  By using the evaluation value E2 of the above equation (8) and the evaluation value E3 of the equation (12), it is possible to evaluate the size of the color reproduction range even when the spectral reflectance of the target color is zero. Become. In the evaluation, either formula (8) or formula (12) may be used. The evaluation value E2 is obtained by subtracting the spectral reflectance of the target color from 1 and multiplying the difference value of the spectral reflectance as a weighting function. The evaluation value E3 is obtained by multiplying the sum of the color matching functions x (λ), y (λ), and z (λ) for each wavelength as a weighting function w3 (λ) by the difference value of the spectral reflectance. In order to show the validity of the evaluation values E2 and E3, the results obtained by the same method as in the validity verification experiment of the evaluation value E1 are shown below.

  In addition, for the target color, the spectral reflectance of the C, M, and Y patch images of JapanColor2001 coated paper is measured in advance. Next, the toner adhesion amount per unit area of C, M, and Y is changed as shown in Table 2 above, and the patch images of C, M, Y, R, G, and B are transferred by the image forming apparatus. Each spectral reflectance is output from the three color patch images of C, M, and Y, and the evaluation values E2 and E3 are calculated using equations (8) and (12). In addition, in order to confirm the validity of the evaluation values E2 and E3, six color L * a * b * chromaticity values are acquired from the output patch images of C, M, Y, R, G, and B, and the target The volume coverage ratio connecting the C, M, Y, R, G, B, Bk, and W points of the color is calculated. In this experiment, the target color is Japan Color 2001 coated paper, and Bk and W L * a * b * chromaticity values are set as Bk = (10, 0, 0) and W = (95, 0, 0). It was. The calculation conditions and measurement conditions are the same as in the experiment performed above.

  FIG. 5 shows the experimental results showing the relationship between the evaluation value E2 and the coverage ratio, and FIG. 6 shows the experimental results of the evaluation value E3. From these experimental results, the contribution ratio between the evaluation value and the coverage of the gamut volume of the target color is very high at 0.99 or more, and the size of the color reproduction range can be evaluated even at the evaluation values E2 and E3. Is shown.

  As described above, by using the evaluation values E1 to E3, a hexagonal shape connecting the plot points of C, M, Y, R, G, and B on the conventionally used a * b * plane, respectively. Unlike the color reproduction range evaluation method that evaluates from the shape and area, or the evaluation method that calculates the color difference from each target color of C, M, Y, R, G, and B for each of the six colors, C, M, and Y 3 A simple evaluation method that can evaluate the size of the color reproduction range including C, M, Y, R, G, and B in consideration of the lightness L * with one evaluation value based on the spectral reflectance of the color. It is understood that the evaluation can be performed with high accuracy.

  Further, means for obtaining the spectral reflectances of C, M, and Y in an evaluation image in which the amount of color material attached per unit area is changed in two or more stages, and C, M, and Y in a target color reproduction range Based on the means for setting the spectral reflectance and the acquired spectral reflectance data of C, M, and Y, a relational expression of the reflectance of each wavelength with respect to the amount of color material attached per unit area is calculated. Means for complementing the reflectance data for the adhesion amount of each color material based on this, and means for calculating the above-described E1c to E3c, E1m to E3m, E1y to E3y for the adhesion amount of each color material using the complemented reflectance data A color gamut evaluation apparatus comprising: a color material adhesion amount when E1c to E3c, E1m to E3m, and E1y to E3y are minimum, and calculating evaluation values E1 to E3 at that time; By doing C, M C, M, each of which can effectively use the color reproduction range without changing the adhesion amount of each of Y in many stages, creating and measuring all combinations of samples, and evaluating the size of the color reproduction range The optimum adhesion amount condition for Y can be obtained.

  Furthermore, by providing the above-described color reproduction range evaluation device in the image forming apparatus, optimum CMY adhesion amount conditions that can effectively use the color reproduction range for any paper type can be obtained. An image forming apparatus capable of outputting a wide image can be provided.

  Next, specific embodiments according to the present invention will be described in detail with reference to the drawings.

[Example 1]
FIG. 7 is a block diagram illustrating a schematic configuration of the color reproduction range evaluation apparatus according to the first embodiment of the present invention. In FIG. 7, reference numeral 11 denotes a color reproduction range evaluation apparatus main body. A spectral reflectance measurement unit 12 measures each spectral reflectance from the C, M, and Y patch images of the sample to be evaluated. The spectral reflectance measuring unit is composed of, for example, a spectrophotometer. Reference numeral 13 denotes a first data storage unit that stores C, M, and Y spectral reflectance data measured by the spectral reflectance measurement unit 12. Reference numeral 14 denotes a second data storage unit for storing the spectral reflectances of C, M, and Y in the target color reproduction range, which is set and stored in advance by the user. An evaluation value calculation unit 15 calculates an evaluation value using data stored in the first and second data storage units 13 and 14. Reference numeral 16 denotes an evaluation value display unit that includes a display such as a CRT or LCD, and displays the evaluation value calculated by the evaluation value calculation unit 15.

  Next, calculation processing of the color reproduction range evaluation apparatus according to the first embodiment will be described. FIG. 8 is a flowchart for explaining the evaluation process executed by the color reproduction range evaluation apparatus 11 according to this embodiment. First, in step 1 (S1), the user measures or sets the spectral reflectances of C, M, and Y in the target color reproduction range, and stores the data in the target color spectral reflectance data storage unit 14 of FIG. To do. In this embodiment, the target color reproduction range is Japan Color 2001-coated paper, and spectral reflectance data measured from C, M, and Y patch images of Japan Color 2001-coated paper is stored. As the target spectral reflectance, the spectral reflectance of the block waveform which is an ideal spectral reflectance of cyan, magenta, and yellow as shown in FIGS. 9A, 9B, and 9C is used. It doesn't matter.

  Next, in step 2 (S2), the spectral reflectance measurement unit 12 in FIG. 7 measures a patch image of C, M, and Y of the evaluation sample according to a user instruction, and the measurement data is stored in the spectral reflectance measurement data storage unit 13. Save to. In step 3 (S3), the above formulas (1) to (3), (5) to (7), (9) to (11) and (4), (8) or (12) The evaluation value E1, E2, or E3 is calculated using any evaluation formula. In the present embodiment, the evaluation value is calculated by the equation (4). Wavelength sampling is performed by measuring 400 to 700 nm at 10 nm intervals (sampling number N = 31). In this embodiment, sampling is performed at an interval of 10 nm. However, the sampling interval is not limited to this, and the sampling interval may be narrowed if it is desired to improve the accuracy of evaluation. Alternatively, it is possible to reduce the amount of calculation by widening the sampling interval. That is, the sampling interval can be changed according to the accuracy and calculation amount desired by the user. In step 4 (S4), the calculated evaluation values E1c, E1m, E1y, and E1 are displayed by a display method as shown in FIG. 10, for example.

  Next, details of the evaluation value calculation process in step 3 (S3) will be described with reference to FIG. First, in step 11 (S11), a difference value for each wavelength between the spectral reflectances targeted for C, M, and Y and the spectral reflectance to be evaluated is calculated. In step 12 (S12), the weight function w1 (cy) ([lambda]) = 1 / R '(cy) ([lambda]) is applied to the difference value for each wavelength of C, M, and Y. Next, the values obtained by applying the weighting function in step 13 (S13) are summed up in the visible wavelength region (400 to 700 nm), and values normalized by the number of samplings N of wavelengths are calculated as evaluation values E1c, E1m, and E1y, respectively. To do. In step 14 (S14), E1c, E1m, and E1y are further summed to calculate an evaluation value E1, and the values of E1c, E1m, E1y, and E1 are displayed as shown in the example of FIG.

  As described above, according to the first embodiment, color reproduction is evaluated from the shape and area of a hexagon connecting C, M, Y, R, G, and B plot points on the conventionally used a * b * plane. Unlike the range evaluation method or the evaluation method for obtaining color differences from the target colors of C, M, Y, R, G, and B for every six colors, it is based on the spectral reflectance of only three colors of C, M, and Y. The size of the color reproduction range including the entire C, M, Y, R, G, and B considering the lightness L * can be evaluated with a single evaluation value E1. This makes it possible to speed up the evaluation.

[Example 2]
Next, a second embodiment of the present invention will be described in detail with reference to the drawings. FIG. 12 is a block diagram showing a schematic configuration of a color reproduction range evaluation apparatus according to Embodiment 2 of the present invention. In FIG. 12, reference numeral 21 denotes a color reproduction range evaluation apparatus of the present embodiment. Reference numeral 22 denotes a spectral reflectance measuring unit that measures the spectral reflectances of C, M, and Y of the sample to be evaluated. The spectral reflectance measuring unit 22 is configured by, for example, a spectrophotometer. Reference numeral 23 denotes a first data storage unit that stores C, M, and Y spectral reflectance data measured by the spectral reflectance measurement unit 22. A second data storage unit 24 stores CMY spectral reflectances in a target color reproduction range, which is set and stored in advance by the user. Reference numeral 25 denotes a calculation unit that calculates the spectral reflectance at each wavelength with respect to the amount of color material attached based on the spectral reflectance data obtained in 24. An evaluation value calculation unit 26 calculates an evaluation value using the data stored in the second storage unit 24 and the data calculated by the calculation unit 25. A display unit 27 displays a toner adhesion amount per unit area and an evaluation value that maximizes the color reproduction range. The display unit 27 includes a display such as a CRT or LCD, and the value calculated by the evaluation value calculation unit 26. Is displayed.

  Next, calculation processing of the color reproduction range evaluation device 12 according to the second embodiment will be described. FIG. 13 is a flowchart illustrating an evaluation process executed by the color reproduction range evaluation device 21 according to the second embodiment. The outline is the same as that shown in FIG. 8 described above, but the step C22 (S22) in which the user inputs the number of measurements, and the C, M, and Y patch images of the sample with the adhesion amount changed in several stages. Step 23 (S23) of obtaining the spectral reflectance from the step, Step 24 (S24) of calculating the reflectance of each wavelength with respect to the adhesion amount from the obtained spectral reflectance, and the step of selecting the value with the smallest evaluation value 26 (S26) is added or changed.

  First, in step 21 (S21), the user measures or sets the spectral reflectances of C, M, and Y in the target color reproduction range, and stores the target color spectral reflectance data in the second data storage unit 24. . In the second embodiment, the target color reproduction range is Japan Color 2001 coated paper, and the spectral reflectance is measured from the C, M, and Y patch images of Japan Color and stored. As the target spectral reflectance, a spectral reflectance having a block waveform that is an ideal spectral reflectance as shown in FIGS. 9A, 9B, and 9C may be used.

  Next, in step 22 (S22), the user obtains samples in which the color material adhesion amount is changed in several stages, and inputs the number of samples in which the adhesion amount is changed, that is, the number of samples to be measured. In step 23 (S23), the C, M, and Y patch images of the evaluation sample are measured the same number of times as the input measurement number, and the evaluation color spectral reflectance measurement data is stored in the first data storage unit 23 shown in FIG. , And store together with the measured value of the amount of adhered sample. In this embodiment, the toner adhesion amount per unit area is divided into four stages, and the number of measurements is four.

  Next, in step 24 (S24), the relationship between the adhesion amount and the reflectance at each wavelength is calculated from the relationship between the measured spectral reflectance and the adhesion amount. In step 25 (S25), the above (1) to (3) are calculated. ), (5) to (7), or (9) to (11) and (4), (8) or (12) using the evaluation formula, the evaluation value for each adhesion amount E1, E2 or E3 is calculated. In the present Example 2, the evaluation value E1 was calculated by the above equation (4), and the number of wavelengths sampled at the time of measurement was 400 to 700 nm at 10 nm intervals. In the second embodiment, sampling is performed at an interval of 10 nm, but it is not limited to this. If it is desired to improve the accuracy of evaluation, the sampling interval may be narrowed. Alternatively, it is possible to reduce the amount of calculation by widening the sampling interval. That is, the sampling interval can be changed according to the accuracy and calculation amount desired by the user. Then, from step 25 (S25), the optimum adhesion amount that maximizes the minimum evaluation value and the color reproduction range is selected from the calculated adhesion amounts and the evaluation value E1 (step 26 (S26)). The optimum adhesion amount that maximizes the minimum evaluation value and the color reproduction range is displayed by a display method as shown in FIG. 14, for example (step 27 (S27)).

  Next, the calculation processing in steps 24 to 26 in FIG. 13 will be described in detail with reference to FIG. In the evaluation, first, based on the spectral reflectance data measured in step 23 (S23) in FIG. 13 while changing the adhesion amount to several stages, the adhesion amounts of C, M, and Y in step 31 (S31) in FIG. The spectral reflectance for each wavelength is calculated, and a relational expression between the spectral reflectance at each wavelength and the adhesion amount of C, M, and Y is obtained from the calculated spectral reflectance, and the reflectance data for the unmeasured adhesion amount is obtained. Complement. This relational expression can be applied to the physical characteristics of the toner, either by using a linear approximation between the measured adhesion amounts or by using logarithmic approximation or exponential approximation from the whole data measured in two or more steps. Any of them may be used. In Example 2, the reflectance data for each wavelength with respect to the adhesion amount was complemented by using logarithmic approximation for each wavelength from the spectral reflectances of C, M, and Y of the sample with the adhesion amount being changed in four stages. In the second embodiment, the adhesion amount is set to four stages. However, in practice, the adhesion amount may be set to four or more stages in order to improve the accuracy of evaluation.

As an example, each measurement value of C, M, and Y measured by changing the adhesion amount shown in Table 3 in four stages is shown. The unit of wavelength is nm, the unit of adhesion amount is mg / cm ² , and the unit of reflectance is%. Table 4 shows an example of cyan (C) data in which the reflectance for each wavelength with respect to the unmeasured adhesion amount is complemented using logarithmic approximation based on the measurement results in Table 3. The reflectance data is complemented in the same manner for M and Y. In the second embodiment, the interval between the adhering amounts of the supplemented data is set to 0.01 mg / cm ^2. However, when it is desired to improve the accuracy of evaluation, the adhering amount interval may be set to an interval narrower than 0.01 mg / cm ^2. Absent. Alternatively, it is possible to reduce the calculation amount by widening the adhesion amount interval to be complemented.

  Details of the evaluation value calculation process will be described. Based on the spectral reflectance data for each adhesion amount calculated in step 31 (S31), the evaluation values E1c, E1m, E1y of C, M, and Y for each adhesion amount using the equations (1) to (3). Is calculated. First, a difference value for each wavelength between the target spectral reflectance and the spectral reflectance to be evaluated is calculated. Next, in step 33 (S33), the weight function w1c (λ) = 1 / R′c (λ), w1m (λ) = 1 / R′m (λ), w1y (λ) = 1 / R′y (λ) is caused to act. Next, in step 34 (S34), the values obtained by applying the weight function are summed in the visible wavelength region (400 to 700 nm), and the values normalized by the sampling number N of wavelengths are calculated as evaluation values E1c, E1m, and E1y, respectively. . Subsequently, based on the evaluation values E1c, E1m, and E1y calculated in this way, E1c, E1m, and E1y for each adhesion amount are calculated based on the reflectance data supplemented as described above. Table 5 shows the relationship between E1c, E1m, and E1y thus calculated and the amount of adhesion.

  Next, in step 35 (S35), Ec1 (min), Em1 (min), Ey1 (min) that minimize the evaluation values E1c, E1m, and E1y and the adhesion amount at that time are selected. In the example of Table 5 above, (attachment amount, Ec1 (min)) = (0.38, 0.169), (attachment amount, Em1 (min)) = (0.42, 0.180), (attachment amount, Ey1 (min)) = (0.37, 0.084) is selected. Then, an evaluation value E1 (min) obtained by summing the selected values of Ec1 (min), Em1 (min), and Ey1 (min) is calculated (step 36 (S36)). The result thus calculated is displayed as in the example of FIG.

  In the conventional technology, the amount of adhesion of each of C, M, and Y is changed in several steps, and patch image samples of C, M, Y, R, G, and B are created and measured in all combinations, and the color reproduction range is large. However, according to the present embodiment, only the spectral reflectances of the three colors C, M, and Y of the sample image in which the adhesion amount is changed in two or more stages are evaluated. Thus, it is possible to obtain the optimum toner adhesion amount condition per unit area that maximizes the color reproduction range.

  Next, an image forming apparatus according to an embodiment provided with the color reproduction range evaluation apparatus described in Example 1 or 2 will be described. Hereinafter, as an image forming apparatus according to an embodiment of the present invention, an embodiment applied to a full-color laser beam printer will be described.

  FIG. 16 is an explanatory diagram showing a schematic configuration of a printer according to an embodiment of the present invention. This printer is an image forming apparatus that forms a color image by superimposing four color component images of Y, C, M, and Bk on a transfer material such as recording paper. This printer includes an image forming unit 28 in which four image forming units 30Y, 30C, 30M, and 30Bk are arranged as shown in FIG. 16 corresponding to the colors Y, C, M, and Bk. ing. The color toner images formed on the photosensitive drums 29Y, 29C, 29M, and 29Bk, which are latent image carriers provided in the image forming units 30Y, 30C, 30M, and 30Bk, are disposed in contact with the photosensitive drums. The images are sequentially transferred to the intermediate transfer belt 31 that is the belt-shaped image carrier so as to overlap each other. Since the intermediate transfer belt 31 is rotated at a predetermined timing by the illustrated driving unit, the toner images of the respective colors are superimposed on the intermediate transfer belt 31 at predetermined positions. The color component toner images superimposed on the intermediate transfer belt 31 are collectively transferred onto the recording paper 39 to form an image on the paper.

  In the present embodiment, each color image forming unit means 30Y, 30C, 30M, 30Bk has a common configuration, and therefore, one set 30Y will be described. The image forming unit 30Y includes a photosensitive drum 29, a charger 32 that charges the photosensitive drum 29 to a desired potential, and each color corresponding to output image data for the photosensitive drum 29 that is charged to a desired potential. A laser optical unit 33 as a latent image forming means for writing a latent image for each component, a developing device 34 as a developing means for developing the electrostatic latent image formed on the photosensitive drum 29 with toner, and a photosensitive member by this developing device. A transfer device (primary transfer device) 35 serving as transfer means for transferring the toner image developed on the drum 29 onto the intermediate transfer belt 31, and the transfer remaining on the photosensitive drum 29 without being transferred to the intermediate transfer belt 31. The cleaner 36 is configured to clean the remaining toner.

  The charger 32 is configured to apply a voltage obtained by superimposing an AC voltage on a DC voltage to a charging roller formed of a roller-shaped conductive elastic body. By causing a direct discharge between the charging roller and the photosensitive drum 29, the surface of the photosensitive drum is charged. The laser optical unit 33 is configured to form an image on the surface of the photosensitive drum of the laser light that has undergone light modulation from a laser diode (LD) element. By scanning this laser beam, a latent image is written on the photosensitive drum 29 corresponding to a desired image, and an electrostatic latent image is formed on the photosensitive drum 29.

  The light from the laser diode 33a forms parallel light in the collimate lens, and is cut into a light beam corresponding to a desired beam diameter by the aperture. The light beam after passing through the aperture passes through the cylindrical lens and enters the polygon mirror. The light beam reflected by the polygon mirror is condensed by a scanning lens, and after being folded by a folding mirror, an image is formed on the surface of the photosensitive drum 29. Thereby, an electrostatic latent image is formed on the surface of the photosensitive drum 29.

  The developing device 34 contains a two-component developer composed of a magnetic carrier and toner. The developing unit 34 includes a developing sleeve, a stirring member, and a toner supply device. The developing sleeve is a cylindrical member made of a nonmagnetic material whose surface is rotatably supported, and a magnet roller made of a permanent magnet is disposed inside the developing sleeve. The two-component developer held on the surface of the developing sleeve becomes a magnetic brush by the magnetic force of the magnet roller and comes into contact with the photosensitive drum 29. Further, the stirring member has a role of charging the toner to a predetermined charge amount by stirring the two-component developer. Further, the toner in the developer is adhered to the photosensitive drum 29 by applying a DC voltage as a developing bias to the developing sleeve. The primary transfer unit 35 is a roller-shaped conductive elastic roller, and is disposed so as to be pressed against the photosensitive drum 29 from the back surface of the intermediate transfer belt 31. The elastic roller is applied with a constant current controlled bias as a primary transfer bias.

  The secondary transfer unit 37 includes one of the rollers that support the intermediate transfer belt 31 and a secondary transfer roller that includes a conductive elastic roller that is disposed to face the intermediate transfer belt 31. To be pressed against the intermediate transfer belt 31. The secondary transfer roller of the secondary transfer unit 37 is applied with a constant current controlled bias as a secondary transfer bias. As for the recording paper, the recording paper 39 in the storage cassette 38 is taken out one by one by the paper feed roller 58 and conveyed to the registration roller 59. The registration roller 59 temporarily stops the recording paper 39 fed out by the paper supply roller 58 and measures the timing of the toner image from the intermediate transfer belt 31 to the recording paper 39 in the secondary transfer device 37 while measuring the timing of the secondary transfer device. The recording paper 39 is fed to 37. In the secondary transfer unit 37, the toner images (four color toner images) on the intermediate transfer belt 30 described above are collectively transferred to desired positions on the paper. The sheet on which the toner image is transferred is conveyed to the fixing device 40, heated and pressurized, and discharged outside the apparatus.

  Next, a correction processing unit that evaluates the size of the color reproduction range from the fixed image, obtains the optimum toner adhesion amount condition that maximizes the color reproduction range, and controls the adhesion amount will be described.

  By using the color gamut evaluation device 41 shown in the first embodiment, an optimum toner adhesion amount condition per unit area for a specific sheet is obtained in advance and stored in the memory of the image forming apparatus. By specifying the type (paper mode), it is possible to control to form an image with the toner adhesion amount that maximizes the color reproduction range. However, there are an infinite number of types of paper, and it is not possible to obtain the optimum adhesion amount condition in advance for all types of paper.

  Therefore, the color reproduction range evaluation device 41 similar to that described in the second embodiment is installed in the image forming apparatus of FIG. 16 and the image forming apparatus is provided with a correction processing mode so as to correspond to an infinite number of types of paper. It is possible. FIG. 17 is a functional block diagram of the image forming apparatus according to the present embodiment. First, the user sets the recording paper 39 to be used in the storage cassette 38 shown in FIG. 16, and confirms whether the recording paper 39 to be used is stored in the image forming apparatus in advance from the paper type-optimum adhesion amount data storage unit 48. To do. If not stored, optimum adhesion amount correction processing is started. When the correction process is instructed, signals of the patch images of C, M, and Y are generated, and the signals are sent to the image forming units 30C, 30M, and 30Y, and on the recording paper 39 by the series of image forming processes described above. C, M, and Y patch images are formed.

  At that time, the control unit 49 in FIG. 17 changes the intensity of writing light (exposure), the surface potential of the photosensitive drum 29, or changes the developing bias, thereby increasing the toner adhesion amount per unit area in two or more stages. The C, M, and Y patch images are output. At the time of output, the toner adhesion amount per unit area is detected by the adhesion amount detection unit 50 from the toner patch images on the photosensitive drums 29C, 29M, and 29Y and stored in the storage unit 43. After the toner is fixed on the paper by the fixing unit 40 and before being discharged out of the apparatus by the paper discharge roller 52, the spectral reflectance of the C, M, and Y patches whose adhesion amount has changed in two or more steps is spectrally reflected. Measurement is performed by the rate measuring unit 42.

  Here, an outline of the spectral reflectance measurement unit 42 for the C, M, and Y patch images will be described with reference to FIG. Before the image in which the C (or M, Y) toner 53 is fixed on the recording paper 39 by the fixing unit 40 is discharged to the outside by the paper discharge roller 52, the white light emitted from the light source 54 is spectroscope. The C, M, and Y spectral reflectances are obtained by causing the light to be spectrally separated by 55 and entering the C (or M, Y) toner 53 on the base substrate 57 and detecting the reflected light by the sensor 56. Can be measured. A CCD or photodiode array is used for the sensor 56, and a white reflector is used for the base substrate 57. Note that the above-described measurement method is one example, and other forms may be used as long as the spectral reflectance of the C, M, and Y patch images can be measured.

  Next, C, M, and Y spectral reflectance measurement data with respect to the adhesion amount changed in two or more steps are stored in the storage unit 43 of FIG. 17, and the optimum adhesion amount calculation processing is performed. The calculation process in this embodiment is the same as the calculation process described in the second embodiment with reference to the flowchart shown in FIG. The calculation units 45 to 47 in FIG. 17 calculate and select the adhering amount of each CMY that maximizes the color reproduction range, and the toner adhering amount per unit area that maximizes the color reproduction range for the sheet specified by the user is paper. It is stored in the seed-optimum adhesion amount storage unit 48. Next time when the user performs image formation using the specified paper, if the user designates the paper to be used from the paper mode, the toner adhesion amount condition per unit area that maximizes the color reproduction range is stored in the storage unit. The amount of adhesion is controlled by changing the intensity of the writing light, the surface potential of the photosensitive drum 29, or changing the developing bias in the control unit 49, and the size of the color reproduction range is maximized. It is possible to perform image formation under the adhesion amount condition.

  As described above, according to the present embodiment, the color reproduction range including C, M, Y, R, G, and B is maximized from the C, M, and Y patch images of the sample in which the adhesion amount is changed in two or more stages. Image forming apparatus that maximizes the color reproduction range for any paper type by calculating the amount of color material attached per unit area and controlling the amount of toner attached based on this result Can be provided. In the above description, a full color laser beam printer to which an electrophotographic method is applied using toner has been described. However, the image forming apparatus of the present invention is applied to an ink jet method using liquid ink, for example. Also good.

It is a figure which shows a color matching function. It is a figure showing the example of the color reproduction range evaluation in a * b * plane. It is a figure which shows the spectral product of status A and M. It is a graph which shows the relationship between the inclusion rate shown for demonstrating the validity of evaluation value E1 in the color reproduction range evaluation method of this invention, and evaluation value E1. It is a graph which shows the relationship between the inclusion rate shown for demonstrating the validity of the evaluation value E2 in the color reproduction range evaluation method of this invention, and the evaluation value E2. It is a graph which shows the relationship between the inclusion rate shown for demonstrating the validity of the evaluation value E3 in the color reproduction range evaluation method of this invention, and the evaluation value E3. It is a block diagram which shows schematic structure of the color reproduction range evaluation apparatus in Example 1 by this invention. It is a flowchart figure explaining the evaluation process of the color reproduction range evaluation apparatus in Example 1 by this invention. FIG. 6 is a block waveform diagram of ideal spectral reflectance used in the color reproduction range evaluation apparatus according to the present invention, where (A) is a block waveform diagram for cyan, (B) is a block waveform diagram for magenta, and (C) is a block waveform diagram for magenta. It is a block waveform diagram about yellow. It is a figure which shows the example which displayed the evaluation result of the color reproduction range evaluation apparatus in Example 1 by this invention. It is a flowchart figure explaining the specific example of the evaluation process of the color reproduction range evaluation apparatus in Example 1 by this invention. It is a block diagram which shows schematic structure of the color reproduction range evaluation apparatus in Example 2 by this invention. It is a flowchart figure explaining the evaluation process of the color reproduction range evaluation apparatus in Example 2 by this invention. It is a figure which shows the example which displayed the evaluation result of the color reproduction range evaluation apparatus in Example 2 by this invention. It is a flowchart figure explaining the specific example of step 24-step 26 of FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a functional block diagram illustrating toner adhesion amount control of the image forming apparatus according to the embodiment of the present invention. It is a schematic block diagram of the spectral reflectance measurement part used with the image forming apparatus which concerns on one Embodiment by this invention.

Explanation of symbols

11, 21, 41 Color reproduction range evaluation device 12, 22, 42 Spectral reflectance measurement unit 13, 23, 43 Evaluation color spectral reflectance data storage unit 14, 24, 44 Target color spectral reflectance data storage unit 15, 26, 46 Evaluation value calculation unit 16 Evaluation value display unit 25, 45 Spectral reflectance calculation unit for adhesion amount 27 Adhesion amount-evaluation value display unit 29Y, 29C, 29M, 29Bk Photosensitive drum 30Y, 30C, 30M, 30Bk Image forming unit 31 Intermediate transfer belt 32 Charging device 33 Optical unit 34 Developer 35 Primary transfer device 36 Cleaning device 37 Secondary transfer device 38 Storage unit 39 Recording paper 40 Fixing unit 47 Optimal adhesion amount calculation unit 48 Paper type / optimum adhesion portion storage unit 49 Control Unit 50 adhesion amount detection unit 52 paper discharge roller 53 toner 54 light source 55 spectroscope 56 sensor 57 Base substrate

Claims (6)

A method for evaluating the size of a color reproduction range in a color image, wherein the spectral reflectances of cyan (C), magenta (M), and yellow (Y) in a target color reproduction range are represented by R′c (λ). , R′m (λ), R′y (λ), and the spectral reflectances of cyan (C), magenta (M), and yellow (Y) of the image to be evaluated are Rc (λ), Rm (λ), Ry (Λ), the weighting function is w1c (λ) = 1 / R′c (λ), w1m (λ) = 1 / R′m (λ), w1y (λ) = 1 / R′y (λ), When the sampling number of the color wavelength λ is N, the evaluation values (E1c, E1m, E1y) of cyan (C), magenta (M), and yellow (Y) are calculated using the following equations (1) to (3). ) And evaluating the size of the color reproduction range in the color image using the evaluation value E1 calculated by the following equation (4). The color reproduction range evaluation method that.

A method for evaluating the size of a color reproduction range in a color image, wherein the spectral reflectances of cyan (C), magenta (M), and yellow (Y) in a target color reproduction range are represented by R′c (λ). , R′m (λ), R′y (λ), and the spectral reflectances of cyan (C), magenta (M), and yellow (Y) of the image to be evaluated are Rc (λ), Rm (λ), Ry (Λ), weighting functions w2c (λ) = (1−R′c (λ)), w2m (λ) = (1−R′m (λ)), w2y (λ) = (1−R′y (Λ)), where N is the sampling number of the wavelength λ of the color, the evaluation values of cyan (C), magenta (M), and yellow (Y) using the following equations (5) to (7) (E2c, E2m, E2y) are calculated, and the evaluation value E2 calculated by the following equation (8) is used to evaluate the size of the color reproduction range in the color image. The color reproduction range evaluation method with.

A method for evaluating the size of a color reproduction range in a color image, wherein the spectral reflectances of cyan (C), magenta (M), and yellow (Y) in a target color reproduction range are represented by R′c (λ). , R′m (λ), R′y (λ), and the spectral reflectances of cyan (C), magenta (M), and yellow (Y) of the image to be evaluated are Rc (λ), Rm (λ), Ry (Λ), the color matching functions are x (λ), y (λ), z (λ), the weighting function is w3 (λ) = x (λ) + y (λ) + z (λ), and the color wavelength λ When the sampling number is N, the evaluation values (E3c, E3m, E3y) of cyan (C), magenta (M), and yellow (Y) are calculated using the following equations (9) to (11), respectively. The color reproduction range in a color image is evaluated using an evaluation value E3 calculated by the following equation (12). Color reproduction range evaluation method.

A color reproduction range evaluation device for evaluating the size of a color reproduction range in a color image,
Means for obtaining each spectral reflectance of cyan (C), magenta (M), and yellow (Y) in the evaluation image, and cyan (C), magenta (M), and yellow (Y) in the target color reproduction range The spectral reflectance data acquired by the means for setting the spectral reflectance, the spectral reflectance data acquired by the means for acquiring the spectral reflectance, and the spectral reflectance data set by the means for setting the spectral reflectance are used. A color reproduction range evaluation apparatus comprising: means for calculating an evaluation value using the color reproduction range evaluation method according to any one of the above. In the color reproduction range evaluation apparatus according to claim 4,
Means for acquiring each of the spectral reflectances of cyan (C), magenta (M), and yellow (Y) in an evaluation image in which the amount of color material deposited per unit area is changed in two or more stages; Means for calculating the spectral reflectance at the wavelength of each color with respect to the amount of adhesion of the coloring material per unit area from the spectral reflectance data of each color acquired by the means for acquiring, and the spectral reflectance at the wavelength of each color with respect to the amount of adhesion Complementing the reflectance data with means for complementing the spectral reflectance data for the adhesion amount of each color material based on the spectral reflectance at the wavelength of each color with respect to the adhesion amount of the color material per unit area calculated by the means for calculating 5. The color reproduction range evaluation method according to claim 4, based on the reflectance data supplemented by the means for performing and the spectral reflectance data set by the means for setting the spectral reflectance. Means for calculating an evaluation value each, the color reproduction range evaluation device characterized by comprising a means for selecting the deposition amount of the color materials for which the evaluation value is minimized. An image forming unit that forms a color image with at least cyan (C), magenta (M), and yellow (Y) color materials, and the amount of each color material attached to the transfer material when the color image is formed by the image forming unit. In an image forming apparatus comprising: a color reproduction range evaluation device to calculate; and a control unit that controls the formation of the color image based on the color material adhesion amount calculated by the color reproduction range evaluation device.
6. The image forming apparatus according to claim 4, wherein the color reproduction range evaluation device is a color reproduction range evaluation device according to claim 4 or 5.

Images