JPH0269625A - Method for evaluating color difference based on colorimetric data - Google Patents

Abstract

PURPOSE:To make evaluation with visual sense agree with evaluation based on colorimetric value at the time of comparing a color with a color sample by multiplying each numeric value with which the color difference is calculated by visual sense correction coefficient so that it is made to approximate to visual sense characteristic and obtaining the color difference when the color is measured by a colorimetric machine so as to evaluate the color difference. CONSTITUTION:When the color is measured by the colorimetric machine so as to evaluate the color difference, the curve of visual sensitivity having a peak at about 550nm wavelength extending from 400nm wavelength to 700nm wavelength is used. Such color difference is obtained that the color difference obtained by the colorimetric machine is made to approximate to the curve by the curve of visual sensitivity 14 expressed by an L-axis 13, an a-axis 11 and a b-axis 12 which is determined by a CIE. The color difference is obtained by multiplying each calculated numeric value by the visual sense correction coefficient, so that the evaluation with visual sense is made to agree with that based on the colorimetric value at the time of comparing the color with the color sample.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in an evaluation method when measuring colors using a colorimeter and evaluating nine color differences.

[Conventional technology]

For example, it is necessary to evaluate whether a painted product has a desired color tone, that is, whether the color difference is within an acceptable range.

In this case, any specified color sample and the evaluation target are arranged visually (
The first thing to consider is to do this with the human eye. However, this kind of visual evaluation...

Depending on the individual differences of the person being evaluated, or the physical condition of the person being evaluated.

There is one aspect where evaluations tend to vary.

Therefore, a device called a colorimeter that automatically performs evaluation has been put into practical use. (For example, TC-180 manufactured by Tokyo Denshoku Co., Ltd.
0MKIl type) This type of colorimeter has a function that compares the data obtained by measuring any specified color sample with the data obtained by measuring the evaluation target, and outputs each colorimetric data and color difference. are doing.

The color difference determined by this colorimeter is CIE (Commis).
son International de l'Ec
lairaae). Lm, at,
It was measured based on the be color system, and was determined based on three data: , as, and b.

Figure 3 shows, for example, the magazine “Shikizai” Vol. 57, No. 10, page 566.
This is a diagram of the conventional CIE color system shown in Figure 1.
(13 is the L center axis.

Next, a color evaluation method will be explained. In Figure 3, a
The + side of the e-axis αυ represents red, and as the value increases, the saturation increases. Similarly, the negative side represents the edge, and the larger the value, the more the saturation. The + side of b-axis a3 represents yellow with a slight orange tinge, and the value becomes thicker (the saturation increases. The - side represents blue, and the value becomes thicker (the saturation increases. L-axis) a3 represents brightness and indicates the vertical direction of this figure.In other words, this figure is 2
It represents a cross section of a cylindrical shape. To explain further, ae
The lower side of the diagram on the + side of the axis aυ is set to 400 nm in terms of wavelength, and the wavelength increases clockwise so that one revolution reaches about 700 nm, so that the hue can be expressed in the circumferential direction. Also, since the saturation can be expressed in the radial direction, the hue and saturation can be determined by the numbers in a and b, and the brightness can be expressed numerically in the vertical direction of the surface by L-.

When quantifying, the sensitivity of nine people's eyes differs depending on the color tone, but the CIE color system is defined as a color space with equal intervals relative to visual perception, and is called CIELAB.

The evaluation of color difference in such C1εLAB is as follows.

It is determined by the following formula.

・・・・・・Il+ However, △E skewer ab; Color difference △LI; Difference in lightness data (L-) between the color sample and the evaluation target △a11- Same Saturation data (as
) Difference Δb Umbrella: Same < Difference (b-) This C1εLAB color system is an internationally accepted evaluation method and is excellent for quantifying two tones. However, when evaluating the color difference by comparing the color sample and the target object, the numerical special code is defined at equal intervals with respect to visual perception, so a difference with visual perception appears, and it is difficult to measure with a colorimeter. It has been found that the color difference obtained does not necessarily match the visual evaluation.

That is, it has been found that among the color differences that were evaluated by the colorimeter as having color differences that were outside the allowable range, there were some that were determined to be within the allowable range by visual evaluation without any problem.

[Problem to be solved by the invention]

As mentioned above, the evaluation of conventional colorimetry is evaluated by CIELAB, so it has the advantage of being accepted internationally, but since it is scaled at equal intervals with respect to visual perception, it cannot be used as a color sample using only numerical values. There was a problem in that when comparing the values, there was naturally a difference between the measured value and the visual observation.

This invention has been made to solve the above-mentioned problems, and aims to match visual evaluation and evaluation based on measured values when comparing with a single color sample.

[Means to solve the problem]

The evaluation method according to the present invention calculates the color difference by multiplying each numerical value for calculating the color difference by a visual correction coefficient so as to approximate the visual characteristics.

[For production]

The evaluation method in this invention is Lm that matches human vision,
Multiply each by a correction factor to obtain a and b umbrellas.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS Below, figures will be described to explain one embodiment of the present invention. In FIG. 11ζ, (4) is a curve representing the visibility, which is a curve ranging from a wavelength of 400 nm to a wavelength of 1100 nm and having a peak at about 550 nm. This characteristic is expressed in the LlIB*b fist color system of Figure 3 C1ε in the second
It is a diagram. As shown in the visibility curve α4 in Fig. 2,
In the CIELAB color system, brown colors are also modified to have circular shapes to ensure equal spacing.

This is convenient when expressing colors, but when expressing color differences, the results may differ from actual visual observation, especially in red and purple colors. This invention.

This was done to eliminate such problems and evaluate the color difference, and although this invention can of course be implemented using a calculation formula,
Here, an experimental example will be described.

The table below is a summary of the data obtained by making various colors A to ■ that can be visually detected, first selecting those within the permissible limits visually, and then measuring them with a colorimeter. DL for Lm is the difference between the maximum value and minimum value of about three sheets.
Dam for R,as, ob- for b・1ζ
It is raining. The CIELAB color difference △Ekushiab value at that time.

The largest one is written in 0EIIab.

Note that the numbers in Table 1 include a mixture of measured values and values obtained by data processing the measured values, so they do not necessarily match even if calculated using the calculation formula described later.

In C1εLAB, the color difference Δε umbrella ab is already given by a linear equation (as shown in equation 11).

In this formula, ΔL* and Δa−Δb are treated at the same ratio. On the other hand, when analyzing the characteristics from the above table, there is little difference in Dam, DL fist and D
It can be seen that the difference in b- is large. Therefore, in the case of only the color types in the table above, in order to reflect the magnitude of these differences in each data for calculating the two-color difference, a predetermined ratio was applied as a visual correction coefficient and calculated using the following formula (2). .

8ME”ab=1.65 (△L-/ 10.93
)2+(aasu2+(△b5/&31)2...
12+ The results were recorded in DME118b using the above-mentioned topsoil. The above coefficient is ob when Da· in the table of the above experiment is set to 1.
It is determined from the ratio of ・ and DL-.

Here, the maximum value was used, but the average value can also be used. Also, the coefficient of 1.65 is 5QR(++l+
I)=KXSQFl [(+/lo, o)"2-z+(
The coefficient K was calculated using +/F and 3D''z and was set to 1.65.

Comparing these results, even in samples that were within the permissible limit in visual evaluation, C1εLAB had a maximum ΔE1Tab of 6.03, but the evaluation method of this invention had a value of 1.57, which is generally said to be within the permissible range (taa ) is shown. When evaluating color differences in this way, results that match the actual situation can be obtained, improving the reliability of measurement.

The comparative example at the bottom of the table above shows the data and calculation results according to the present invention for an example in which the color difference was within the allowable range in the color difference evaluation using a colorimeter, but was judged to be outside the range in the visual evaluation. . From this comparative example, it will be understood that the color differences obtained by the evaluation method according to the above embodiments are not all smaller than the conventional color differences. In addition, as another example, divide the b-axis in FIG. When all is 10, multiply by a coefficient, such as not multiplying by a coefficient.

The coefficient can also be set to 1 when -. It is clear that precision will increase if the doses are divided more precisely.

In the above embodiment, △a◆ is multiplied by a coefficient of 1, but which element is multiplied by the coefficient does not depend on the implementation of the present invention. In addition, although the coefficients are determined experimentally in the example shown here, the coefficients are not limited to this, and B! It goes without saying that this can be derived by logical calculation, and it is obvious that this invention can be applied.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to obtain a color difference that matches the visual sense by multiplying each element by a visual correction coefficient based on the value measured by a colorimeter.

[Brief explanation of the drawing]

FIG. 1 shows a visibility curve for detailed explanation of this invention.
Figure 2 is a diagram showing the visibility curve on the CIELAB color system.
FIG. 3 is a diagram showing the conventional ClELAB color system. συ is the a-axis, 03 is the b-axis, (L3 is the L-axis, (4)
and σ is the visibility curve. In addition. In the figure. Same symbols are the same. or a corresponding portion.

Claims (1)

[Claims] A method for evaluating color differences based on colorimetric data, characterized in that in evaluating color differences based on data measured by a colorimeter, the colorimetric data is multiplied by a visual correction coefficient to approximate actual visual perception.