JP4915517B2 - Spectral radiance spectrum processing method and color monitor calibration method using the same - Google Patents

Description

  The present invention relates to a spectral radiance spectrum processing method suitable for obtaining a colorimetric value in a desired color system based on a spectral radiance spectrum obtained by measurement with a spectral radiance meter, and using the same. The present invention relates to a color monitor calibration method for soft proofing.

  In recent years, in the field of printing, as a method for confirming the color of the finished print, a soft proof that displays the image to be printed on the screen of a color monitor and confirms the color finish when printed there has been widely used. It is becoming. In this specification, the color monitor refers to all color display devices that can emit light and display color images by additive color mixing, such as a color CRT, a color liquid crystal display, and a color plasma display. To do.

  By the way, soft proofing is a technique for confirming the color of the finished print on the screen of the color monitor, so the color of the image displayed on the color monitor must be the same as the actual printed image. Therefore, when soft proofing is performed, before displaying the image on the color monitor, the white color of the color monitor used for soft proofing must match the white color of the paper actually used for printing, that is, the ground color of the printing paper. Is done. This is the color monitor calibration.

  In color monitor calibration, various adjustments such as color balance adjustment, white color temperature adjustment, and brightness adjustment are performed. In the present invention, what and how are adjusted when calibration is performed. Since this is not an essential matter, detailed description is omitted. Hereinafter, it is simply referred to as adjusting or calibrating the color monitor.

There are the following two methods for matching the white color of the color monitor with the white color of the printing paper. One is to measure the white color of the color monitor with a non-contact colorimeter and calibrate the color monitor so that the colorimetric value matches the white colorimetric value of the printing paper (for example, patents) The other is a method in which the operator calibrates the color monitor by trial and error while visually comparing the white color of the color monitor and the white color of the printing paper (for example, Patent Document 2). Non-Patent Document 1).
Japanese Patent No. 3783869 Japanese Patent Laying-Open No. 2005-20144 Liquid Crystal Color Monitor Standardization Work Report for the Printing Industry (issued in May 2006, Printing Industry Color Monitor Specification Review Committee, ISO / TC130 National Committee, Japan Printing Industrial Machinery Manufacturers Association) 28 pages

  However, it has been found that any method has a problem. For example, the inventor conducted the following experiment. In the experiment, measurement was performed with a spectral radiance meter while the printing paper was illuminated, and a colorimetric value was obtained from the spectral radiance spectrum obtained by the measurement. Here, the colorimetric values are tristimulus values XYZ in the XYZ color system. On the other hand, the white color of the color monitor is measured with the same spectral radiance meter, and the tristimulus value XYZ is calculated as a colorimetric value from the measured spectral radiance spectrum so that the tristimulus values XYZ of the two coincide. The color monitor was calibrated.

  Here, as printing paper, OK Top Coat Plus manufactured by Oji Paper Co., Ltd. was used. This is a coated paper generally used in printing. As a color monitor, ColorEdge CG210 manufactured by Nanao Co., Ltd. was used. Illumination was performed using a color rendering color AAA for color evaluation and a fluorescent lamp with a color temperature of 5000K so that the illuminance on the observation surface of the printing paper was about 500 lux. The spectral radiance meter used was PR-705 manufactured by Photo Research. Note that the color rendering property for color evaluation of a fluorescent lamp is AAA, which indicates that it is optimal for use in color evaluation.

  Then, with the color monitor calibration completed, that is, with the colorimetric values of both the white color of the color monitor and the white color of the printing paper matched, the eight subjects were given the white color of the color monitor and the printing paper. They were compared at the same time visually. As a result, all subjects replied that the color monitor looks more red and yellow than the print paper.

  In other words, even if the color monitor is calibrated so that the colorimetric values of the white of the printing paper and the white of the color monitor match, there is a problem that the two colors appear to be different in human appearance. It was.

  The inventor conducted another experiment. In this experiment, a single operator calibrated the color monitor while visually comparing the white of the printing paper with the white color of the color monitor, and the operator judged that the white color of both of them matched. In the state, both were measured with the spectral radiance meter, and each tristimulus value XYZ was calculated from the measured spectral radiance spectrum. The printing paper, illumination, color monitor, and spectral radiance meter used are the same as those used in the above experiment.

  The result is as shown in FIG. 6, and it was found that the white color of the color monitor was shifted in the blue direction compared with the white color of the printing paper. FIG. 6 shows the xy chromaticity obtained from the tristimulus values XYZ of both the white color of the color monitor and the white color of the printing paper, and plotted on the xy chromaticity coordinates. As is well known, the relationship between xy chromaticity and tristimulus values XYZ is expressed by the following equations (1) and (2).

x = X / (X + Y + Z) (1)
y = Y / (X + Y + Z) (2)

  As described above, in a method in which the operator visually compares the white color of the color monitor and the white color of the printing paper and calibrates the color monitor by trial and error, the calibration is completed and the operator can Even when it was determined that the colors matched, when the colors were measured, it was found that the colorimetric values of the two did not match.

  Although the latter experiment was actually performed with a plurality of subjects, the result is the same tendency as described above, and the colorimetric values of the white color of the color monitor and the white color of the printing paper do not match, and both It was found that the difference in the colorimetric values varies depending on the subject, and even if the same subject performs several times.

  As described above, in any calibration method, there is a difference between the human appearance and the colorimetric value. However, this is not desirable, and when the color monitor calibration is completed, if the colorimetric values of both the white color of the color monitor and the white color of the printing paper match, Obviously, the whites of the two are substantially the same, and conversely, when the whites of the two are the same, it is clear that the colorimetric values of the two are preferably the same.

  Therefore, as a result of various considerations, the present inventor looks different from the human appearance even when the colorimetric values of the white color of the color monitor and the white color of the printing paper match, and vice versa. The reason for the difference between the colorimetric values of the color monitor when the white color of the color monitor and the white color of the printing paper match is the cause of the spectral emission used to determine the colorimetric value. Because the spectral sensitivity characteristics of the luminance meter are not ideal and are distorted, the waveform of the obtained spectral radiance spectrum, especially the peak part, is distorted. It has been found that the colorimetric value calculated based on the obtained spectral radiance spectrum is deviated from the value that should be.

  This is as follows. As is well known, the spectral radiance meter includes a large number of light receiving elements, and the light having a predetermined wavelength width is guided to each light receiving element by a spectroscopic optical system including a diffraction grating and a lens. A spectral radiance spectrum is obtained by combining the outputs of the light receiving elements.

  Then, the inventor of the present invention has a spectral radiance meter having a total spectral sensitivity characteristic including the spectral sensitivity characteristic of the spectral optical system from the entrance to the light receiving element and the sensitivity characteristic of the light receiving element. It has been found that not all of the light receiving elements are ideal, but in fact, the sluggish and broadband characteristics are the cause of the above-mentioned problems.

  That is, FIG. 7 is a diagram for explaining spectral sensitivity characteristics of each light receiving element of the spectral radiance meter, FIG. 7A is a diagram schematically showing ideal spectral sensitivity characteristics, and FIG. 7B. Fig. 7 is a diagram schematically showing an example of actual spectral sensitivity characteristics. As shown in Fig. 7 (a), the total spectral sensitivity characteristics of all the light receiving elements are measured over a measurement wavelength interval n for each light receiving element. If it is constant, it is ideal and does not cause any problem. However, the actual overall spectral sensitivity characteristic is broadened for each light receiving element as shown in FIG. 7B. This is a characteristic with a wide band. This is because the light incident on each light receiving element is blurred due to the aberration of the spectroscopic optical system. As shown in FIG. 7B, the interval between adjacent spectral sensitivity characteristic peaks is the same as the measurement wavelength interval n. In FIG. 7 (b), the spectral sensitivity is shown normalized by setting the peak value to 1, and the width of one peak at the position where the value is 0.5 is referred to as a half-value width.

Therefore, when light having a single wavelength λ ₀ is measured, if the spectral sensitivity characteristic is an ideal spectral radiance meter as shown in FIG. 7A, the obtained spectral radiance spectrum is shown in FIG. As shown in FIG. 8 (b), the spectral radiance spectrum is a broad line as shown in FIG. 8 (b). In addition to widening the band, the peak intensity is also smaller than the emission line spectrum.

  That is, since the spectral sensitivity characteristic is dull, the spectral radiance spectrum is dull, especially in the peak portion. This means that an actual spectral radiance meter having a distorted spectral sensitivity characteristic as shown in FIG. 7B cannot accurately measure the spectral radiance. In particular, it is difficult to accurately measure a sharp spectral intensity characteristic such as an emission line spectrum. For this reason, the colorimetric value calculated based on the spectral radiance spectrum is shifted from the original value.

  FIG. 9 shows an example of the spectral radiance spectrum when the white color of the color monitor (color liquid crystal display) and the white of the printing paper are measured. As can be seen from FIG. There are strong peaks at wavelengths near green and orange, but due to the above reasons, when measured, the intensity of these peaks will appear smaller than the original value, which will reduce the measurement accuracy. is there. The color monitor, printing paper, illumination, and spectral radiance meter are the same as those described above, and the measurement wavelength interval of the spectral radiance meter is 2 nm.

  Therefore, the present invention uses a spectral radiance spectrum obtained by a spectral radiance meter as a spectral radiance spectrum closer to the original shape, and thus colorimetry obtained by calculation based on the spectral radiance spectrum. It is an object of the present invention to provide a method for processing a spectral radiance spectrum that can bring the value closer to the original value.

  It is another object of the present invention to provide a method of calibrating a color monitor when performing soft proofing using the spectral radiance spectrum processing method.

In order to achieve the above object, a spectral radiance spectrum processing method according to the present invention is configured such that a spectral radiance spectrum measured by a spectral radiance meter has a measurement wavelength interval of n. , Q (λ) is the measured spectral radiance at the wavelength λ, Q ′ (λ) is the spectral radiance at the wavelength λ after sharpening, and α is a positive coefficient.
Q ′ (λ) = α {Q (λ) −Q (λ−n)} + Q (λ) + α {Q (λ) −Q (λ + n)}
(However, when the value on the right side becomes negative, Q ′ (λ) is rounded to 0)
A sharpening process for emphasizing the peak intensity by performing the calculation is performed, and a colorimetric value of a predetermined color system is calculated based on the spectral radiance spectrum subjected to the sharpening process. .

The spectral radiance spectrum processing method according to the present invention is a spectral radiance spectrum obtained by measuring with a spectral radiance meter. The luminance is Q (λ), the spectral radiance at the wavelength λ after the sharpening process is Q ′ (λ), and α1 and α2 are both positive coefficients.
Q ′ (λ) = α 2 {Q (λ−n) −Q (λ−2n)}
+ Α1 {Q (λ) −Q (λ−n)}
+ Q (λ)
+ Α1 {Q (λ) −Q (λ + n)}
+ Α2 {Q (λ + n) −Q (λ + 2n)}
(However, when the value on the right side becomes negative, Q ′ (λ) is rounded to 0)
A sharpening process for emphasizing the peak intensity by performing the calculation is performed, and a colorimetric value of a predetermined color system is calculated based on the spectral radiance spectrum subjected to the sharpening process. .

Furthermore, the color monitor calibration method according to the present invention measures the ground color of the printing paper and the white color of the color monitor with the same spectral radiance meter, and the spectral radiance spectrum obtained is spectrally analyzed. The measurement wavelength interval of the radiance meter is n, the measured spectral radiance at the wavelength λ is Q (λ), the spectral radiance at the wavelength λ after sharpening treatment is Q ′ (λ), and α is a positive coefficient.
Q ′ (λ) = α {Q (λ) −Q (λ−n)} + Q (λ) + α {Q (λ) −Q (λ + n)}
(However, when the value on the right side becomes negative, Q ′ (λ) is rounded to 0)
By performing the sharpening process that emphasizes the peak intensity by performing the above calculation, the colorimetric values in the predetermined color system are calculated based on the spectral radiance spectrum that has been sharpened. The color monitor is adjusted so that the white colorimetric value of the monitor matches the colorimetric value of the ground color of the printing paper .

In addition, the color monitor calibration method according to the present invention measures the ground color of the printing paper and the white color of the color monitor with the same spectral radiance meter, and the spectral radiance spectrum obtained is spectrally analyzed. The measurement wavelength interval of the radiance meter is n, the measured spectral radiance at the wavelength λ is Q (λ), the spectral radiance at the wavelength λ after sharpening is Q ′ (λ), and α1 and α2 are both positive coefficients. As
Q ′ (λ) = α 2 {Q (λ−n) −Q (λ−2n)}
+ Α1 {Q (λ) −Q (λ−n)}
+ Q (λ)
+ Α1 {Q (λ) −Q (λ + n)}
+ Α2 {Q (λ + n) −Q (λ + 2n)}
(However, when the value on the right side becomes negative, Q ′ (λ) is rounded to 0)
By performing the sharpening process that emphasizes the peak intensity by performing the above calculation, the colorimetric values in the predetermined color system are calculated based on the spectral radiance spectrum that has been sharpened. The color monitor is adjusted so that the white colorimetric value of the monitor matches the colorimetric value of the ground color of the printing paper .

  In the spectral radiance spectrum processing method according to the present invention, first, the spectral radiance spectrum obtained by measurement is sharpened. By this sharpening process, the peak intensity of the measured spectral radiance spectrum can be emphasized and corrected to a shape close to the spectral radiance spectrum that should originally be.

  Then, a colorimetric value is calculated based on the spectral radiance spectrum resulting from the sharpening process. As a result, the spectral radiance spectrum is corrected to a shape close to the original shape by the sharpening process, so that the colorimetric value calculated from it is closer to the original value and is measured more than before. The accuracy of the color value can be improved.

  Further, according to the color monitor calibration method of the present invention, the ground color of the printing paper and the white color of the color monitor are measured with a spectral radiance meter, and a peak is obtained for each obtained spectral radiance spectrum. Based on the spectral radiance spectrum that has been sharpened to emphasize the intensity of the color, the colorimetric values in the specified color system are calculated, respectively, and the white colorimetric value of the color monitor However, since the color monitor is adjusted so as to match the colorimetric value of the ground color of the printing paper, the spectral radiance spectrum is corrected to a shape close to what it should be by sharpening and is calculated from there. Since the colorimetric value is close to the original value, when the calibration is completed, the white color of the color monitor and the white color of the printing paper match well even when viewed by humans. The things.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, a sharpening process used in the spectral radiance spectrum processing method according to the present invention will be described. As described above, the spectral radiance spectrum processing method according to the present invention corrects a rounded spectral radiance spectrum to a spectral radiance spectrum closer to the original shape, and obtains it by calculation based on the spectral radiance spectrum. The colorimetric value to be obtained is made closer to the original value, but what is important for this purpose is to emphasize and increase the intensity of the peak in the spectral radiance spectrum.

  As described above, in the spectral radiance spectrum obtained by measurement, the peak intensity is smaller than the original intensity, so it would be desirable to restore it to the original intensity, but in practice how much the peak intensity is Since it is not known whether it is small, it is impossible to completely restore the spectral radiance spectrum that should have been originally obtained. However, it will be apparent that at least by increasing the peak intensity, it can be brought closer to a shape that is close to the spectral radiance spectrum that should originally exist.

  Also, it is desirable for the base of the broadened peak to be corrected so that the base spread can be narrowed, but if it is difficult to narrow the base spread, the peak intensity will be increased. As a result, the spread of the base of the peak becomes relatively small.

  From the above, in the processing of the spectral radiance spectrum according to the present invention, processing for enhancing and enhancing the peak intensity in the spectral radiance spectrum obtained by measurement with the spectral radiance meter is performed. This process is a sharpening process.

In this sharpening process, Q ′ (λ) is the spectral radiance at the wavelength λ after the sharpening process, Q (λ) is the measured spectral radiance at the wavelength λ, the measurement wavelength interval of the spectral radiance meter using n, Q ′ (λ) = α {Q (λ) −Q (λ−n)} where α is a positive coefficient
+ Q (λ) + α {Q (λ) −Q (λ + n)} (3)
This is done by performing the calculation. However, since Q ′ (λ) takes 0 or a positive value, when the value on the right side becomes negative, rounding is performed to 0.

  Note that, as described above, since the spectral radiance meter can measure the spectral radiance only by the width of the measurement wavelength interval n as described above, Q (λ) may be the output of a certain light receiving element. (Λ−n) and Q (λ + n) may be outputs of a light receiving element that receives light having a wavelength width of n adjacent to the shorter wavelength side and the longer wavelength side than the wavelength range received by the light receiving element, respectively. It is.

  The coefficient α must be a positive value, but the optimum value or desirable range of the coefficient α cannot be determined unconditionally because it varies depending on the characteristics of the spectral optical system of the spectral radiance meter. It is necessary to determine for each spectroradiometer by trial and error. However, according to experiments by the present inventors, it has been found that there is a high possibility that there is an optimum value of the coefficient α between 0.5 and 2.5.

  Now, this sharpening process is expressed by the above equation (3), but the form of this equation (3) is actually the processing for performing edge enhancement in the horizontal scanning direction in image processing. It is the same as the shape of the simple processing formula. That is, for example, the spectral radiance spectrum obtained by measuring the white color of the color monitor and the white color of the printing paper shown in FIG. 9 can be regarded as one waveform diagram although it is a spectrum. That is, the spectral radiance spectrum can be regarded as an image signal in one horizontal scanning direction. Therefore, if a process called edge enhancement or contour correction is applied to this, the peak intensity in the spectrum can be increased. This is the idea of sharpening processing for the spectral radiance spectrum.

Although the meaning of the above equation (3) is clear, it will be briefly described with reference to FIG. FIG. 1 is a diagram schematically showing an example of a measured spectral radiance spectrum. Q ₁ , Q ₂ , Q ₃ , and Q ₄ have wavelengths λ ₁ , λ ₂ , λ ₃ , and λ ₄ as center wavelengths, respectively. The measured spectral radiance of the measured wavelength interval n is Q, and the measured fractional radiance of Q ₂ is a in the figure. In FIG. 1, b, c, and d are all positive values.

Now, Q ₂ in FIG. 1 is considered as Q (λ) in equation (3). In FIG. 1, the measured fractional radiance Q ₂ has a peak. At this time, since Q (λ−n) = a−b and Q (λ + n) = ac, the spectral radiance Q ′ ₂ after the sharpening process for the measured spectral radiance is
Q ′ ₂ = αb + a + αc (4)
Thus, it can be seen that the intensity of this peak is greater than the measured spectral radiance a.

Next, Q ₃ in FIG. 1 is considered as Q (λ) in the equation (3). At this time, since Q (λ) = ac, Q (λ−n) = a, and Q (λ + n) = ac−d, the spectral radiance after the sharpening process for this measured spectral radiance Q _'3 is,
Q ′ ₃ = a− (α + 1) c + d (5)
It becomes. Examining how much this changed from the measured spectral radiance Q ₃ before sharpening,
Q ′ ₃ −Q ₃ = (a− (α + 1) c + d) − (ac)
= Α (dc) (6)
If c and d are as shown in FIG. 1, it can be seen that the strength is lower than that before the sharpening process. In this case, the peak base can be narrowed by the sharpening process.

  As described above, the peak intensity of the measured spectral radiance spectrum can be increased by the sharpening process, and in some cases, the spread of the peak base can be narrowed.

  Note that the value of Q ′ (λ) in equation (3) is negative depending on the magnitude relationship between the values of Q (λ), Q (λ−n), and Q (λ + n), and the value of the coefficient α. May be 0, may be positive, but the spectral radiance does not take a negative value, so if the value on the right side of equation (3) is negative, Round the value of Q ′ (λ) to zero. This is the meaning of the proviso attached to the expression (3).

  Next, an example of sharpening processing is shown. FIG. 2 is a diagram illustrating an example of a white spectral radiance spectrum of a color monitor, where a solid line is a measured spectral radiance spectrum, that is, a spectral radiance spectrum before sharpening processing, and a wavy line is after sharpening processing. The spectral radiance spectrum is shown. Similarly, FIG. 3 is a diagram illustrating an example of a white spectral radiance spectrum of a printing paper, in which a solid line is a measured spectral radiance spectrum, and a wavy line is a spectral radiance spectrum after sharpening processing. Yes. Printing paper, color monitor, spectral radiance meter, and illumination are the same as those described above. In both the case of FIG. 2 and the case of FIG. 3, the value of the coefficient α is 0.84.

  2 and 3, there is no significant change in the portion where the spectral radiance changes gently even if sharpening is performed, but the peak portion is corrected so that the intensity is increased by the sharpening processing. I understand. Note that the measurement was performed by illuminating the printing paper. In FIG. 3, the peak near 440 nm and the peak near 540 to 550 nm are bright lines of illumination light.

  In the part where the spectral radiance changes gently, there is no big change even if sharpening processing is performed. Since such a part is not the part corresponding to the contour of the image, the edge enhancement or contour correction processing for the image signal is performed. Even if the same sharpening process is applied, there is no significant change. On the other hand, the peak portion of the spectral radiance spectrum is a portion corresponding to the contour of the image, and can be increased by performing sharpening processing similar to edge enhancement or contour correction processing on the image signal. It can be done.

  As described above, the spectral radiance spectrum obtained by measurement can be corrected to a shape close to the spectral radiance spectrum that should be originally obtained by this sharpening process.

  While one embodiment of the sharpening process for the measured spectral radiance spectrum has been described above, another embodiment of the sharpening process will be described. According to the above equation (3), in the sharpening process for the measured spectral radiance of a certain wavelength λ, in other words, the measured spectral radiance Q (λ) in the wavelength region including the wavelength λ, the short wavelength in that wavelength region The measured spectral radiances Q (λ−n) and Q (λ + n) of the wavelength range adjacent to the side and the wavelength range adjacent to the long wavelength side are used. Whether to use up to the measured spectral radiance in a distant wavelength region is determined by the measurement wavelength interval n of the optical radiance meter and the half-value width of the spectral sensitivity characteristic of the spectral radiance meter.

  For example, if the half-value width of the spectral sensitivity characteristic is up to about three times the measurement wavelength interval n, sharpening may be performed according to the equation (3). This is because, in this case, the measured spectral reflection luminances of three wavelength widths of Q (λ−n), Q (λ), and Q (λ + n) are used, but these three measured spectral reflection luminances are continuous. This is because the measured spectral reflection luminance in the adjacent wavelength range affecting the measured spectral reflection luminance Q (λ) may be considered to be included.

  On the other hand, when the half-value width of the spectral sensitivity characteristic is about 5 times the measurement wavelength interval n, it is not possible to perform a good sharpening process using the equation (3). This is because in this case, it is necessary to consider that the measured spectral reflection luminance Q (λ) is influenced not only by light in the adjacent wavelength range but also by light in the wavelength ranges on both sides thereof.

Therefore, when the half width of the spectral sensitivity characteristic is about 5 times the measurement wavelength interval n,
Q ′ (λ) = α 2 {Q (λ−n) −Q (λ−2n)}
+ Α1 {Q (λ) −Q (λ−n)}
+ Q (λ)
+ Α1 {Q (λ) −Q (λ + n)}
+ Α2 {Q (λ + n) −Q (λ + 2n)} (7)
To perform sharpening. Where Q ′ (λ) is the spectral radiance at the wavelength λ after the sharpening process, Q (λ) is the measured spectral radiance at the wavelength λ, the measurement wavelength interval of the spectral radiance meter using n, α1, α2 Is a positive coefficient, and Q ′ (λ) is rounded to zero when the value on the right side of equation (7) becomes negative.

  According to the equation (7), since the five measurement spectral reflection luminances used cover the continuous wavelength region of 5n, the measurement spectral in the wavelength region affecting the measurement spectral reflection luminance Q (λ). It can be considered that the reflected luminance is included. Therefore, it can be seen that a good sharpening process can be performed by the equation (7).

  So far, we have proposed a sharpening process for spectral radiance spectra as a method to solve the problems during calibration of color monitors when performing soft proofing, and explained the sharpening process. The sharpening process that has been described can be generally performed on a spectral radiance spectrum obtained by measurement using a spectral radiance meter. For example, a colorimetric value is used when an ICC profile is created. Needless to say, the present invention can also be suitably applied to a spectral radiance spectrum used in the case of obtaining.

  The sharpening process for the measured spectral reflection luminance spectrum has been described above. Next, a color monitor calibration method using the above-described sharpening process will be described. FIG. 4 is a flowchart showing the steps of the color monitor calibration method according to the present invention. First, the white of the printing paper is measured with a spectral radiance meter to obtain the white spectral radiance spectrum of the printing paper. (Step S1).

  Next, the sharpening process described above is performed on the spectral radiance spectrum acquired in step S1 (step S2), and a colorimetric value is calculated based on the spectral radiance spectrum subjected to the sharpening process (step S2). Step S3). It is arbitrary which colorimetric stimulus value is adopted as the colorimetric value, but here, the XYZ colorimetric tristimulus value XYZ generally used is used.

  Next, similarly, white is displayed on the color monitor, and the white is measured with a spectral radiance meter to obtain a white spectral radiance spectrum of the color monitor (step S4). The spectral radiance meter used in step S4 is the same as the spectral radiance meter used in step S1. And the sharpening process mentioned above is performed with respect to the spectral radiance spectrum acquired at step S4 (step S5). In the sharpening process in step S5, the same expression as that used in the sharpening process in step S2 is used. Then, based on the spectral radiance spectrum subjected to the sharpening process, a colorimetric value, that is, a tristimulus value XYZ is calculated (step S6).

  Next, it is determined whether or not the white colorimetric value of the printing paper obtained in step S3 matches the white colorimetric value of the color monitor obtained in step S6 (step S7). If so, the color monitor calibration process ends. If they do not match, the color balance of the color monitor is adjusted (step S8). Then, the white color obtained by these adjustments is set as a new white color, and the processes in and after step S4 are repeated again.

  Note that in the determination performed in step S7, all of the XYZ tristimulus values are of course the case where the white tristimulus values XYZ of the printing paper and the white tristimulus values XYZ of the color monitor completely coincide. If they are within a predetermined allowable range, it may be determined that they match.

  Now, the color monitor calibration process shown in FIG. 4 is different from the conventional process in that steps S2 and S5 are added. In other words, conventionally, after the spectral radiance spectrum for white of the printing paper is measured in step S1, the process of step S3 for calculating the colorimetric value is performed immediately. Similarly, the color monitor also performs color processing in step S4. After measuring the spectral radiance spectrum for the white color of the monitor, the process of step S6 for calculating the colorimetric value is performed immediately. In the process of the color monitor calibration method, the process is performed in steps S1 and S4. A sharpening process is performed on the spectral radiance spectrum measured with the spectral radiance meter (steps S2 and S5), and a colorimetric value is calculated based on the spectral radiance spectrum on which the sharpening process has been performed. (Step S3, Step S6).

  And the process of this step S1-S3 and the process of step S4-S6 are the processes regarding the processing method of the spectral radiance spectrum which concerns on this invention.

  Incidentally, it is known that when calculating a colorimetric value based on a spectral radiance spectrum, the intensity of the peak of the spectral radiance spectrum is greatly affected. Then, as described above, by performing the sharpening process, the peak intensity of the measured spectral radiance spectrum can be emphasized and corrected to a shape close to the spectral radiance spectrum that should be originally. From this, the colorimetric value is brought close to the original value by calculating the colorimetric value after performing the sharpening process as in the process of steps S1 to S3 and the process of steps S4 to S6 in FIG. I can see that That is, this spectral radiance spectrum processing method makes it possible to improve the accuracy of the colorimetric values as compared with the prior art.

  Actually, when the color monitor was calibrated by the process shown in FIG. 4 and an experiment was conducted to visually compare the color of the printing paper and the white color of the color monitor, the color difference between the two was much greater than in the past. It was a good result to say that it was small and fit well.

  Another experiment was conducted. In that experiment, one operator had the color monitor calibrated while visually comparing the white of the printing paper and the white of the color monitor, and the operator judged that the white color of both of them matched. In the state, measure the white of the printing paper and the white of the color monitor with a spectral radiance meter, sharpen the measured spectral radiance spectrum, from the resulting spectral radiance spectrum, Tristimulus values XYZ were calculated for each, and the measured values were compared.

  The printing paper, illumination, color monitor, and spectral radiance meter used at this time are the same as those used in the above experiment. Moreover, the sharpening process was performed using (3) Formula. The coefficient α is 0.84.

  The result is shown in FIG. FIG. 5 is a diagram in which the white colorimetric value of the color monitor obtained in the above experiment and the white colorimetric value of the printing paper are plotted on the xy chromaticity coordinates, and the chromaticities of the two match well. I understand. The fact that the chromaticities of the two match is the same as the good match between the colorimetric values of the two.

  Also, comparing FIG. 5 with FIG. 6 showing an example of the prior art, if the spectral radiance spectrum processing method according to the present invention is performed, the white color of the color monitor and the white human of the printing paper It can be seen that the appearance and the colorimetric values of both can be matched well.

  As described above, by the spectral radiance spectrum processing method according to the present invention, colorimetric values can be made more accurate than in the past, and accordingly, the color using the spectral radiance spectrum processing method can be made. According to the monitor calibration method, when the calibration is completed, the white color of the color monitor and the white color of the printing paper are well matched with each other even when viewed by humans.

It is a figure which shows typically the example of a measurement spectral radiance spectrum. It is a figure which shows the example of sharpening processing, Comprising: It is a figure which shows the example of the white spectral radiance spectrum of a color monitor, A solid line shows the spectral radiance spectrum before sharpening processing, and a wavy line after sharpening processing A spectral radiance spectrum is shown. It is a figure which shows the example of sharpening processing, Comprising: It is a figure which shows the example of the white spectral radiance spectrum of a printing paper, A solid line shows the spectral radiance spectrum before sharpening processing, and a wavy line after sharpening processing A spectral radiance spectrum is shown. 4 is a flowchart showing steps of a color monitor calibration method according to the present invention. The color monitor is calibrated while visually comparing the white of the printing paper and the white of the color monitor, and the white color of the printing paper and the white color of the color monitor are Is measured with a spectral radiance meter, and each measured spectral radiance spectrum is sharpened. From the resulting spectral radiance spectrum, tristimulus values XYZ calculated for each are expressed on xy chromaticity coordinates. It is the figure compared. The color monitor is calibrated while visually comparing the white of the printing paper and the white of the color monitor, and the white color of the printing paper and the white color of the color monitor are Is measured using a spectral radiance meter, and tristimulus values XYZ calculated for the spectral radiance spectra are compared on the xy chromaticity coordinates. FIGS. 7A and 7B are diagrams for explaining spectral sensitivity characteristics of each light receiving element of the spectral radiance meter. FIG. 7A schematically shows ideal spectral sensitivity characteristics, and FIG. It is a figure which shows the example of a sensitivity characteristic typically. FIG. 8A is a diagram for explaining a problem to be solved by the invention, and FIG. 8A is a diagram showing an example of a spectral radiance meter having a single wavelength with an ideal spectral radiance meter as shown in FIG. FIG. 8B shows a spectral radiance spectrum obtained by measuring a single wavelength with a spectral radiance meter having a spectral sensitivity characteristic as shown in FIG. 7B. It is a figure which shows typically the acquired spectral radiance spectrum. It is a figure which shows the example of a spectral radiance spectrum when measuring the white of a color monitor and the white of a printing paper.

Claims (4)

With respect to the spectral radiance spectrum obtained by measuring with the spectral radiance meter, the measurement wavelength interval of the spectral radiance meter is n, the measured spectral radiance at the wavelength λ is Q (λ), and the wavelength λ after the sharpening process is Spectral radiance is Q ′ (λ), α is a positive coefficient,
Q ′ (λ) = α {Q (λ) −Q (λ−n)} + Q (λ) + α {Q (λ) −Q (λ + n)}
(However, when the value on the right side becomes negative, Q ′ (λ) is rounded to 0)
A sharpening process for emphasizing the peak intensity by performing the calculation is performed, and a colorimetric value of a predetermined color system is calculated based on the spectral radiance spectrum subjected to the sharpening process. Spectral radiance spectrum processing method. With respect to the spectral radiance spectrum obtained by measuring with the spectral radiance meter, the measurement wavelength interval of the spectral radiance meter is n, the measured spectral radiance at the wavelength λ is Q (λ), and the wavelength λ after the sharpening process is Spectral radiance is Q '(λ), α1 and α2 are both positive coefficients.
Q ′ (λ) = α 2 {Q (λ−n) −Q (λ−2n)}
+ Α1 {Q (λ) −Q (λ−n)}
+ Q (λ)
+ Α1 {Q (λ) −Q (λ + n)}
+ Α2 {Q (λ + n) −Q (λ + 2n)}
(However, when the value on the right side becomes negative, Q ′ (λ) is rounded to 0)
A sharpening process for emphasizing the peak intensity by performing the calculation is performed, and a colorimetric value of a predetermined color system is calculated based on the spectral radiance spectrum subjected to the sharpening process. Spectral radiance spectrum processing method. Measure the background color of the printing paper and the white color of the color monitor with the same spectral radiance meter, and measure the measurement wavelength interval of the spectral radiance meter at n and wavelength λ for each spectral radiance spectrum obtained. Spectral radiance is Q (λ), spectral radiance at wavelength λ after sharpening is Q ′ (λ), α is a positive coefficient,
Q ′ (λ) = α {Q (λ) −Q (λ−n)} + Q (λ) + α {Q (λ) −Q (λ + n)}
(However, when the value on the right side becomes negative, Q ′ (λ) is rounded to 0)
By performing a sharpening process that emphasizes the intensity of the peak by performing the calculation of, based on the spectral radiance spectrum that has been subjected to the sharpening process, respectively, to calculate a colorimetric value in a predetermined color system,
A color monitor calibration method comprising adjusting a color monitor so that a white colorimetric value of the color monitor matches a colorimetric value of a ground color of a printing paper. Measure the background color of the printing paper and the white color of the color monitor with the same spectral radiance meter, and measure the measurement wavelength interval of the spectral radiance meter at n and wavelength λ for each spectral radiance spectrum obtained. The spectral radiance is Q (λ), the spectral radiance at the wavelength λ after the sharpening process is Q ′ (λ), and α1 and α2 are both positive coefficients.
Q ′ (λ) = α 2 {Q (λ−n) −Q (λ−2n)}
+ Α1 {Q (λ) −Q (λ−n)}
+ Q (λ)
+ Α1 {Q (λ) −Q (λ + n)}
+ Α2 {Q (λ + n) −Q (λ + 2n)}
(However, when the value on the right side becomes negative, Q ′ (λ) is rounded to 0)
By performing a sharpening process that emphasizes the intensity of the peak by performing the calculation of, based on the spectral radiance spectrum that has been subjected to the sharpening process, respectively, to calculate a colorimetric value in a predetermined color system,
A color monitor calibration method comprising adjusting a color monitor so that a white colorimetric value of the color monitor matches a colorimetric value of a ground color of a printing paper.

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