JP4328308B2 - Halftone dot evaluation method, halftone dot evaluation apparatus, and halftone dot evaluation program - Google Patents

Description

  The present invention relates to a halftone dot evaluation method, a halftone dot evaluation apparatus, and a halftone dot evaluation program for evaluating a halftone dot set for expressing a color image by superimposing halftone dots of a plurality of colors.

  Conventionally, when a color image is output by a printing machine or the like, a color image is expressed by using a halftone dot set including halftone dots of, for example, four colors of CMYK. As a halftone dot structure constituting such a halftone dot set, several types have been proposed from the past, and there is a theory about an ideal halftone dot. As digitization progresses, it has become possible to design the halftone dots constituting the halftone dot set in detail by defining the halftone dot structure with digital data. In addition, since the printing technology has improved, printing with high accuracy has become possible, and therefore, it is necessary to design a halftone dot set with excellent color reproducibility.

  In designing such a halftone dot set, it is necessary to appropriately evaluate the performance of the halftone dot set. In particular, when the halftone dot set is actually used for printing or the like, a so-called misregistration in which the halftone dot deviates from an ideal design overlay often occurs. Appropriate evaluation of changes is required for use in designing halftone dot structures that are resistant to misregistration.

  Therefore, conventionally, the spatial frequency of the halftone dot structure when a misregistration occurs is analyzed, or the halftone dot structure when the misregistration occurs is actually applied to the pixel values constituting the digital image to be printed. An evaluation method for analyzing a halftone dot structure obtained in this manner has been proposed (see, for example, Patent Document 1 and Patent Document 2).

According to the evaluation methods described in these patent documents, the stability of the halftone dot structure with respect to misregistration is evaluated. Therefore, a halftone dot set having a stable halftone dot structure should be designed using such an evaluation method. It is considered that a halftone dot set that is resistant to misregistration can be obtained.
JP 2003-298860 A JP 2003-296732 A

  However, in the techniques described in these patent documents, the structural characteristics of halftone dots that are thought to lead to the stability of the color reproduced by the halftone dot set are used for the evaluation. However, a halftone dot set with a good evaluation result is not guaranteed to have high color stability. Rather, even if the structure changes, the color reproduction of the halftone dot set is likely to be stable, and appropriate evaluation that directly reflects the stability of such reproduction color is desired. ing.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a halftone dot evaluation method, a halftone dot evaluation apparatus, and a halftone dot evaluation program for performing such evaluation with a computer. .

The halftone dot evaluation method of the present invention that achieves the above object is as follows.
A halftone dot evaluation method for evaluating a halftone dot set for expressing a color image by overlapping halftone dots of a plurality of colors,
A setting process for setting the shape and size of halftone dots of each color constituting the halftone dot set;
A position determination process for determining a relative position in the superposition of halftone dots;
An area ratio calculating process for calculating an area ratio occupied by each of the plurality of pure colors and the mixed colors, which is generated when the halftone dots set in the setting process are overlapped at the position determined in the position determining process; ,
Using the area ratio calculated in the area ratio calculation process and the spectral spectrum in each of the pure colors and mixed colors of the plurality of colors, a spectrum calculation process for calculating a spectral spectrum of superposition of halftone dots,
A tristimulus value calculation process for calculating a tristimulus value based on the spectral spectrum calculated in the spectrum calculation process;
And an evaluation process for evaluating the halftone dot set based on the tristimulus values calculated in the tristimulus value calculation process.

  Here, the position determination process may be a process of directly determining the relative position of the halftone dots, or may be a process of determining by a deviation from a predetermined reference position.

  According to the halftone dot evaluation method of the present invention, a spectral spectrum in superposition of halftone dots is obtained, and tristimulus values representing a reaction that the human retina reacts to light are obtained from the spectral spectrum. Since the halftone dot set is evaluated based on the value, an appropriate evaluation that directly reflects the reproduction color by the halftone dot set is possible.

  According to the halftone dot evaluation method of the present invention, “the tristimulus value calculation process is based on the spectrum calculated in the spectrum calculation process and the emission spectrum of the light source when observing the superposition of the halftone dots. The form of “calculating a value” is also suitable.

  According to such a suitable halftone dot evaluation method, it is possible to perform an evaluation in consideration of differences in observation light sources.

  The halftone dot evaluation method of the present invention is also preferably in a form that “the evaluation process is to evaluate the halftone dot set based on a Lab value obtained from tristimulus values”.

  According to such a preferable halftone dot evaluation method, it is possible to perform an evaluation that well reflects the human sense of color.

The halftone dot evaluation method of the present invention is
"The above position determination process determines multiple relative positions in the dot overlay,
The area ratio calculation process, the spectrum calculation process, and the tristimulus value calculation process include a plurality of area ratios, a plurality of spectral spectra, and a plurality of 3 corresponding to a plurality of positions determined in the position determination process. A process of calculating stimulus values,
The evaluation process evaluates the halftone dot set based on the difference in color generated at each of a plurality of positions determined in the position determination process based on the plurality of tristimulus values calculated in the tristimulus value calculation process. Is
This form is also suitable.

  According to such a suitable halftone dot evaluation method, it is possible to perform an evaluation that directly reflects color misregistration caused by so-called misregistration.

The halftone dot evaluation apparatus of the present invention that achieves the above object is as follows.
A halftone dot evaluation device for evaluating a halftone dot set for expressing a color image by superimposing halftone dots of a plurality of colors,
A setting unit for setting the shape and size for each color halftone dot constituting the halftone dot set;
A position determining unit for determining a relative position in superposition of halftone dots;
An area ratio calculating section that calculates an area ratio that each of the plurality of pure colors and each mixed color occupies when the halftone dots set by the setting section are overlapped at the position determined by the position determining section; ,
Using the area ratio calculated by the area ratio calculation unit and the spectral spectrum of each of the plurality of pure colors and the mixed colors, a spectrum calculation unit that calculates a spectral spectrum of superposition of halftone dots;
A tristimulus value calculation unit for calculating a tristimulus value based on the spectral spectrum calculated by the spectrum calculation unit;
And an evaluation unit that evaluates the halftone dot set based on the tristimulus values calculated by the tristimulus value calculation unit.

  According to the halftone dot evaluation apparatus of the present invention, a halftone dot set can be appropriately evaluated by the evaluation method of the present invention.

The halftone dot evaluation program of the present invention that achieves the above object is as follows.
A halftone dot evaluation program which is incorporated in a computer and causes the computer to evaluate a halftone dot set for representing a color image by superimposing halftone dots of a plurality of colors.
On the above computer,
A setting unit for setting the shape and size for each color halftone dot constituting the halftone dot set;
A position determining unit for determining a relative position in superposition of halftone dots;
An area ratio calculating section that calculates an area ratio that each of the plurality of pure colors and mixed colors occupies when the halftone dots set by the setting section are overlapped at the position determined by the position determining section; ,
Using the area ratio calculated by the area ratio calculation unit and the spectral spectrum of each of the plurality of pure colors and the mixed colors, a spectrum calculation unit that calculates a spectral spectrum of superposition of halftone dots;
A tristimulus value calculation unit for calculating a tristimulus value based on the spectral spectrum calculated by the spectrum calculation unit;
An evaluation unit that evaluates the halftone dot set is constructed based on the tristimulus values calculated by the tristimulus value calculation unit.

  According to the halftone dot evaluation program of the present invention, the elements constituting the halftone dot evaluation apparatus of the present invention are easily realized by a computer.

  Note that the halftone dot evaluation apparatus and halftone dot evaluation program according to the present invention are only shown here for their basic form, but this is merely to avoid duplication, and the halftone dot evaluation apparatus and the halftone dot evaluation apparatus according to the present invention. The halftone dot evaluation program includes not only the above basic form but also various forms corresponding to the above-described halftone dot evaluation methods.

  In addition, the elements such as a setting unit configured on the computer by the halftone dot evaluation program of the present invention may be configured such that one element is constituted by one program part, and one element is constituted by a plurality of program parts. It may be constructed, or a plurality of elements may be constructed by one program part. In addition, these elements may be constructed so as to execute such actions by themselves, or constructed by giving instructions to other programs and program components incorporated in the computer. May be.

  As described above, according to the halftone dot evaluation method, halftone dot evaluation apparatus, and halftone dot evaluation program of the present invention, a halftone dot set can be appropriately evaluated.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram illustrating a personal computer to which an embodiment of the present invention is applied.

  As shown in FIG. 1, a personal computer 100 includes a main body 110 incorporating a CPU, a main storage device, a hard disk, a communication board, and the like, and displays a screen and a character string on a display screen 121 according to instructions from the main body 110. By designating an arbitrary position on the display screen 121 by designating the display 120 for performing the display, the keyboard 130 for inputting user instructions and character information to the personal computer 100, the icon displayed at that position at the time of the designation A mouse 140 for inputting instructions according to the above is provided.

  The main body 110 has a CD loading slot 111 into which a CD-ROM or CD-R can be taken out freely, and reproduces information stored in the CD-ROM or CD-R loaded in the CD loading slot 111. A CD-ROM drive is built in. The main body 110 also has an FD loading port 112 into which a flexible disk (FD) is detachably loaded. An FD drive that records and reproduces information on the flexible disk (FD) loaded in the FD loading port 112. Also built-in.

  Here, an embodiment of the halftone dot evaluation program of the present invention is stored in a CD-ROM and loaded into the main body 110, and the halftone dot evaluation program stored in the CD-ROM is read by a CD-ROM drive, It is installed on the hard disk in the main body 110.

  When the halftone dot evaluation program installed on the hard disk is activated and executed, the personal computer 100 operates as an embodiment of the halftone dot evaluation apparatus of the present invention. That is, here, the personal computer 100 and one embodiment of the halftone dot evaluation program of the present invention are combined to constitute one embodiment of the halftone dot evaluation apparatus of the present invention. Here, the position embodiment of the halftone dot evaluation method of the present invention is executed by the operation as one embodiment of the halftone dot evaluation apparatus.

  FIG. 2 is a diagram showing an embodiment of the halftone dot evaluation program of the present invention. Here, the halftone dot evaluation program 300 is stored in the CD-ROM 200.

  The storage medium for storing the halftone dot evaluation program of the present invention is not limited to a CD-ROM, and may be other storage media such as an optical disk, MO, floppy (registered trademark) disk, and magnetic tape. Also, the halftone dot evaluation program of the present invention may be supplied directly to a personal computer via a communication network without using a storage medium.

  The halftone dot evaluation program 300 is executed in the personal computer 100 shown in FIG. 1, and operates the personal computer 100 as a halftone dot evaluation apparatus. The setting unit 310, the position determination unit 320, and the area ratio calculation unit 330 are used. A spectrum calculation unit 340, a Lab value calculation unit 350, and an evaluation unit 360.

  Details of each element of the halftone dot evaluation program 300 will be described later.

  FIG. 3 is a functional block diagram of an embodiment of the halftone dot evaluation apparatus of the present invention.

  The halftone dot evaluation apparatus 400 is configured by installing and executing the halftone dot evaluation program 300 of FIG. 2 on the personal computer 100 shown in FIG.

  The halftone dot evaluation apparatus 400 includes a setting unit 410, a position determination unit 420, an area ratio calculation unit 430, a spectrum calculation unit 440, a Lab value calculation unit 450, and an evaluation unit 460. Unit 420, area ratio calculation unit 430, spectrum calculation unit 440, Lab value calculation unit 450, and evaluation unit 460 are a setting unit 310, a position determination unit 320, and an area ratio that constitute the halftone dot evaluation program 300 shown in FIG. 2. The calculation unit 330, the spectrum calculation unit 340, the Lab value calculation unit 350, and the evaluation unit 360 are configured on the personal computer 100. As described above, each element of the halftone dot evaluation apparatus 400 shown in FIG. 3 corresponds to each element of the halftone dot evaluation program 300 shown in FIG. 2, but each element of FIG. 3 corresponds to the personal computer 100 shown in FIG. 2 is different from that shown in FIG. 2 in that each element is constituted only by the application program.

  The setting unit 410, the position determining unit 420, the area ratio calculating unit 430, the spectrum calculating unit 440, the Lab value calculating unit 450, and the evaluating unit 460 are respectively a setting unit and a position determining unit in the halftone dot evaluation apparatus of the present invention. , The area ratio calculation unit, the spectrum calculation unit, the tristimulus value calculation unit, and the evaluation unit.

  Details of each element of the halftone dot evaluation apparatus 400 will also be described later.

  FIG. 4 is a flowchart of one embodiment of the halftone dot evaluation method of the present invention.

  This halftone dot evaluation method is executed by the operation of the halftone dot evaluation apparatus 400 of FIG. 3, and includes a setting process (steps S101 to S103), a position determination process (steps S104 to S105), and an area ratio. It has a calculation process (steps S106 to S109), a spectrum calculation process (steps S110 to S111), a Lab value calculation process (steps S112 to S113), and an evaluation process (steps S114 to S116). Each of these processes is executed by each element of the halftone dot evaluation apparatus 400 shown in FIG. 3, and the processing contents of each process are defined by each element of the halftone dot evaluation program 300 shown in FIG. The setting process, position determination process, area ratio calculation process, spectrum calculation process, Lab value calculation process, and evaluation process are the setting process, position determination process, area ratio calculation process, spectrum in the halftone dot evaluation method of the present invention. This corresponds to an example of a calculation process, a tristimulus value calculation process, and an evaluation process.

  Hereinafter, the details of each step shown in FIG. 4 will be described, and each element of the halftone dot evaluation apparatus 400 shown in FIG. 3 and each element of the halftone dot evaluation program 300 shown in FIG.

  When the halftone dot evaluation method shown in FIG. 4 is started, a halftone screen is first set (step S101). This halftone screen defines a change in halftone dot shape accompanying a change in halftone dot structure and halftone dot area ratio, and halftone screen design means that these halftone screens are designed. . The halftone screen is composed of an array of threshold values to be compared with pixel values. A portion where the pixel value is equal to or greater than the threshold value is drawn as part of a halftone dot, and a portion where the pixel value is less than the threshold value is white. It becomes a missing part. In other words, the halftone screen has a role of converting an image represented by continuous tone pixel values into a binary image composed of drawing and blank areas. Such a halftone screen is prepared for each color of ink used when outputting a color image. In the present embodiment, three colors C (cyan), M (magenta), and Y (yellow) are used. Set for each color. The set of halftone screens for each color set in this way corresponds to an example of a halftone dot set according to the present invention.

  Next, a halftone dot area ratio (halftone%) is set for each of the three colors CMY (step S102). This halftone dot area ratio (halftone dot%) represents what percentage of the threshold value array constituting the halftone screen is the drawing position. If the halftone dot area ratio is 40%, for example, the threshold value array Of these, 40% of the smaller threshold values are drawn portions, and the remaining 60% portions are blank portions. Such a drawing portion and a white-out portion are obtained for each of the CMY three colors, and the shape and size of the halftone dots of the CMY three colors are determined (step S103).

  FIG. 5 is a diagram schematically showing CMY three-color halftone dots obtained in step S103 of FIG.

  The hatched portion in FIG. 5 is a drawing portion and constitutes a halftone dot. Further, a portion without hatching is a white portion. Each of the small squares that make up the halftone dots and white portions corresponds to each of the threshold values that make up the halftone screen, and each of these corresponds to the pixels that make up the image. To do.

  By setting the halftone screen and halftone for each color, as shown in FIG. 5, halftone dots of CMY three colors having different shapes, sizes, and halftone dot arrangements can be obtained.

  While such halftone dots of the CMY three colors are obtained in steps S101 to S103 in FIG. 4, in this halftone evaluation method, a maximum amount (maximum shift amount) by which the halftone dots shift each other due to misregistration is set. Then, a shift amount within the maximum shift amount is automatically set (step S105). In this embodiment, the shift amounts of the C and M halftone dots (C and M plates) with respect to the Y halftone dot (Y plate) are set. For convenience of explanation, the shift directions of the C and M plates are set. Are both in the vertical direction in FIG. 5 and the downward direction in the figure is positive. In the present embodiment, a small square (that is, a pixel) constituting a halftone dot or a white portion shown in FIG. 5 is adopted as a unit of the shift amount. In the present invention, when it is desired to increase the resolution of halftone dot evaluation, it is possible to set the shift amount in units smaller than the pixel unit.

  Thus, when the shape and size of the halftone dots are obtained and the shift amount between the halftone dots is obtained, an image representing a halftone dot structure in which the halftone dots of the CMY three colors are overlapped is created (step). S106, step S107). An image representing such a halftone dot structure is created for each of the case where the shift amount is set (step S106) and the case where the shift amount is “0” (step S107), and the white color in the created image is displayed. , CMY primary color (pure color), secondary color (R; red, Gn; green, B; blue), tertiary color (Gy; gray), and the area ratio of each color is calculated (step) S108, step S109).

  FIG. 6 is a diagram showing an example of a halftone dot structure obtained when the shift amount is “0”, and FIG. 7 is a diagram showing an example of a halftone dot structure obtained when a shift occurs.

  The halftone dot structure shown in FIGS. 6 and 7 is formed by overlapping the CMY three-color halftone dots shown in FIG. 5. In FIG. The state is shown when the M plate is shifted and the M plate is also shifted downward by 2 in the figure.

  As shown in FIG. 6 and FIG. 7 (Part A), the halftone dots of the CMY3 colors overlap, so that the secondary colors of RGnB and the tertiary of Gy other than the primary colors of each of the CMY3 colors. Color also appears on the image. The proportion of these colors existing on the image is statistically calculated, and the result is shown in each part (B) of FIGS. 6 and 7. As the halftone dots shift from each other due to misregistration or the like, for example, the white ratio shown in the column “No Pixel” changes from 44% to 49%, and the pure magenta ratio changes from 14% to 7%. %.

  When such an area ratio is calculated in step S108 and step S109 in FIG. 4, the spectral spectrum in the entire halftone dot structure is then synthesized and calculated from the spectral spectra of the respective colors (step S110, Step S111).

  FIG. 8 is a diagram illustrating an example of the spectrum of each color, where the horizontal axis represents wavelength and the vertical axis represents reflectance.

  FIG. 8 shows spectral spectra of reflectances for white, CMY primary color, secondary color, and tertiary color, respectively. Such a spectrum can be obtained by measuring each solid color actually output on a sheet or the like. The spectral spectra of these colors are added together with the above-described area ratio as a weight, so that the spectral spectra in the entire halftone dot structure are synthesized.

  FIG. 9 is a diagram illustrating an example of a synthesized spectral spectrum. Here, the horizontal axis of the figure represents the wavelength and the vertical axis represents the reflectance.

  FIG. 9 shows two spectrums, and the spectrum shown by the broken line is the spectrum when the shift amount is “0” shown in FIG. 6 and the spectrum shown by the solid line. The spectrum is a spectrum when the shift shown in FIG. 7 occurs. Comparing these spectral spectra, it can be seen that the wavelength dependence of the reflectance slightly changes before and after the shift.

  When such a spectrum is synthesized and calculated in step S110 and step S111 in FIG. 4, the color generated in the halftone dot structure as shown in FIGS. 6 and 7 is then measured based on the spectrum. Lab values expressed in color are calculated (steps S112 and S113). In calculating the Lab value, first, a spectrum of a light source for observing a halftone dot is used to obtain a spectrum of a color reflected by the halftone dot structure as described above.

  FIG. 10 is a diagram illustrating an example of a spectrum of a light source.

  As shown in FIG. 10, a typical light source has a hill-shaped portion extending over a wide wavelength range and several sharp peaks. The spectrum of light reflected by the halftone dot structure is obtained by multiplying the spectrum of such a light source and the reflectance spectrum shown in FIG.

  Next, tristimulus values (XYZ values) are calculated by multiplying and integrating the tristimulus value color matching function with the spectrum of the reflected light.

  FIG. 11 is a diagram illustrating color matching functions of tristimulus values.

  FIG. 11 shows trichromatic value (XYZ value) color matching functions. When such color matching functions are multiplied by the spectrum of reflected light and integrated over the entire wavelength region, XYZ values are obtained. Is obtained.

Finally, the XYZ values obtained in this way are converted into Lab values by a predetermined conversion formula determined internationally. For example, the Lab value finally obtained based on the spectrum shown in FIG. 9 and the spectrum of the light source shown in FIG. 10 is (L, a, b) = (80.068058, 1.8677918) when there is no shift. , 14.667547)
And when the shift occurs (L, a, b) = (82.7740753, -1.0719514, 14.274755)
It is.

When the Lab value is calculated in this manner at Step S112 and Step S113 in FIG. 4, the color difference ΔE between the unshifted state and the shifted state is then calculated from the Lab value.
ΔE = (ΔL ² + Δa ² + Δb ² ) ^1/2
However, ΔL; L value difference, Δa; a value difference, Δb; b value difference are calculated.

  For example, the color difference ΔE = 3.945245 is calculated from the Lab value exemplified above.

  Of each processing procedure described above, step S105, step S106, step S108, step S110, step S112, and step S114 are repeatedly executed while the shift amount is changed little by little and automatically set in step S105. A map representing the correspondence between the quantity and the color difference is created (step S115). Hereinafter, an example of this map is shown, but before that, a halftone dot set from which the map is based is shown.

  FIG. 12 is a diagram showing a halftone dot set as a map origin, and FIG. 13 is a diagram showing overlapping of halftone dots in the halftone dot set.

  FIG. 12 shows halftone dots for each of the three colors of CMY, and these halftone dots are used in place of the halftone dots schematically shown in FIG. 5 to obtain a color difference map to be described later.

  Part (A) of FIG. 13 shows a halftone dot structure when the shift amount is “0”, and Part (B) shows the shift amount with the maximum color difference in a map described later. A halftone dot structure is shown. The shift amount in the state shown in this part (B) is 1 shift upward in the figure for the C plate and 4 shifts in the lower part of the figure for the M plate.

  FIG. 14 is a diagram illustrating an example of a color difference map for a halftone dot set.

  The horizontal axis of the map shown here represents the shift amount of the C plate with respect to the Y plate, and the vertical axis represents the shift amount of the M plate with respect to the Y plate. In this figure, it can be seen that there is a region having a large color difference from the lower side to the right side with respect to the center of the map.

  When such a map is obtained in step S115 in FIG. 4, finally, the maximum color difference in the map is calculated (step S116). In the example shown in FIG. 14, as described in Part (B) of FIG. 13, the maximum color difference occurs when the shift of the C plate is +1 and the shift of the M plate is -4.

  The individual color differences calculated in step S114, the color difference map created in step S115, and the maximum color difference calculated in step S116 all indicate the degree of color shift in the halftone dot set. This is an evaluation value for evaluating the halftone dot set. In addition, since such an evaluation value is obtained by directly evaluating the color obtained by the halftone dot set, the stability of the color when the halftone dot set is actually used for printing or the like was appropriately evaluated. It has become a thing. Furthermore, in this embodiment, since the halftone dot set is evaluated based on the color difference based on the Lab value, the impression of color misregistration due to misregistration or the like is appropriately evaluated.

  In the above description, for the sake of convenience, the direction of misalignment between halftone dots has been described as being limited one-dimensionally. However, in the position determination process and position determination unit according to the present invention, a one-dimensional shift is determined. Also good.

  In the above description, an evaluation process based on the Lab value converted from the tristimulus values is shown as an example of the evaluation process and evaluation section referred to in the present invention. The part may be evaluated using the tristimulus values as they are. In such an evaluation, rather than the impression of a person, the evaluation is made with an emphasis on the color change itself of the color image obtained by the halftone dots.

  In the above description, as an example of the tristimulus value calculation process and the tristimulus value calculation unit referred to in the present invention, the tristimulus value is calculated in consideration of the spectrum of the light source. For example, when a simple evaluation is performed or when the observation light source is unknown, the spectrum of the light source may be ignored, and the tristimulus value may be calculated only from the spectrum of the halftone dot structure.

It is a figure which shows the personal computer with which one Embodiment of this invention is applied. It is a figure which shows one Embodiment of the halftone dot evaluation program of this invention. It is a functional block diagram of one Embodiment of the halftone dot evaluation apparatus of this invention. It is a flowchart of one Embodiment of the halftone dot evaluation method of this invention. FIG. 5 is a diagram schematically showing CMY three-color halftone dots obtained in step S <b> 103 of FIG. 4. It is a figure which shows the example of the halftone dot structure obtained when the amount of shifts is "0". It is a figure which shows the example of the halftone dot structure obtained when the shift has arisen. It is a figure which shows the example of the spectral spectrum of each color. It is a figure which shows the example of the synthetic | combination spectrum. It is a figure which shows an example of the spectrum of a light source. It is a figure showing the color matching function of a tristimulus value. It is a figure which shows the halftone dot set used as the origin of a map. It is a figure which shows the overlap of the halftone dot in the halftone dot set which becomes the origin of a map. It is a figure which shows an example of the map of the color difference with respect to a halftone dot set.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Personal computer 110 Main-body part 111 CD loading slot 112 FD loading slot 121 Display screen 120 Display 130 Keyboard 140 Mouse 200 CD-ROM
DESCRIPTION OF SYMBOLS 300 Halftone dot evaluation program 310 Setting part 320 Position determination part 330 Area ratio calculation part 340 Spectrum calculation part 350 Lab value calculation part 360 Evaluation part 400 Halftone dot evaluation apparatus 410 Setting part 420 Position determination part 430 Area ratio calculation part 440 Spectrum calculation part 450 Lab value calculation unit 460 evaluation unit

Claims (6)

A halftone dot evaluation method for evaluating a halftone dot set for expressing a color image by overlapping halftone dots of a plurality of colors,
A setting process for setting the shape and size of each color halftone dot constituting the halftone dot set;
A position determination process for determining a relative position in the superposition of halftone dots;
An area ratio calculation process for calculating an area ratio occupied by each of the plurality of pure colors and the mixed colors, which is generated when the halftone dots set in the setting process are overlapped at the position determined in the position determination process; ,
Using the area ratio calculated in the area ratio calculation process and the spectrum of each of the plurality of pure colors and the mixed colors, a spectrum calculation process of calculating a spectral spectrum of superposition of halftone dots,
A tristimulus value calculation process for calculating a tristimulus value based on the spectral spectrum calculated in the spectrum calculation process;
A halftone dot evaluation method comprising: an evaluation step of evaluating the halftone dot set based on the tristimulus values calculated in the tristimulus value calculation step.   The tristimulus value calculation process calculates a tristimulus value based on the spectral spectrum calculated in the spectrum calculation process and the emission spectrum of the light source when observing the overlapping of halftone dots. The halftone dot evaluation method according to claim 1.   2. The halftone dot evaluation method according to claim 1, wherein the evaluation step is to evaluate the halftone dot set based on a Lab value obtained from tristimulus values. The position determining process determines a plurality of relative positions in the superposition of halftone dots;
The area ratio calculation process, the spectrum calculation process, and the tristimulus value calculation process include a plurality of area ratios, a plurality of spectral spectra, and a plurality of 3 corresponding to a plurality of positions determined in the position determination process. A process of calculating stimulus values,
The evaluation process evaluates the halftone dot set based on a difference in color generated at each of a plurality of positions determined in the position determination process based on a plurality of tristimulus values calculated in the tristimulus value calculation process. The halftone dot evaluation method according to claim 1, wherein: A halftone dot evaluation device for evaluating a halftone dot set for expressing a color image by superimposing halftone dots of a plurality of colors,
A setting unit for setting the shape and size of each color halftone dot constituting the halftone dot set;
A position determining unit for determining a relative position in superposition of halftone dots;
An area ratio calculation unit for calculating an area ratio occupied by each of the pure colors of the plurality of colors and the mixed colors, which is generated when the halftone dots set by the setting unit are overlapped at the position determined by the position determination unit; ,
Using the area ratio calculated by the area ratio calculation section and the spectral spectrum in each of the pure colors and mixed colors of the plurality of colors, a spectrum calculation section that calculates a spectral spectrum of superposition of halftone dots,
A tristimulus value calculator that calculates tristimulus values based on the spectral spectrum calculated by the spectrum calculator;
A halftone dot evaluation apparatus comprising: an evaluation unit that evaluates the halftone dot set based on the tristimulus values calculated by the tristimulus value calculation unit. A halftone dot evaluation program incorporated in a computer and causing the computer to evaluate a halftone dot set for expressing a color image by superimposing halftone dots of a plurality of colors,
On the computer,
A setting unit for setting the shape and size of each color halftone dot constituting the halftone dot set;
A position determining unit for determining a relative position in superposition of halftone dots;
An area ratio calculation unit for calculating an area ratio occupied by each of the pure colors of the plurality of colors and the mixed colors, which is generated when the halftone dots set by the setting unit are overlapped at the position determined by the position determination unit; ,
Using the area ratio calculated by the area ratio calculation section and the spectral spectrum in each of the pure colors and mixed colors of the plurality of colors, a spectrum calculation section that calculates a spectral spectrum of superposition of halftone dots,
A tristimulus value calculator that calculates tristimulus values based on the spectral spectrum calculated by the spectrum calculator;
A halftone dot evaluation program that constructs an evaluation unit that evaluates the halftone dot set based on the tristimulus values calculated by the tristimulus value calculation unit.

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