JPH03282335A - Colorimetric device for cylindrical surface - Google Patents

Abstract

PURPOSE:To facilitate the accurate colorimetry of the cylindrical surface by composing the device of a mechanism which moves the center axis of the cylindrical surface in parallel, a color sensor, a light source, and a device which transforms coordinate values in a color space measured on the cylinder surface into coordinate values in a plane. CONSTITUTION:The cylindrical surface 5 as an object of colorimetry has its center axis 6 moved horizontally in parallel by a stage 4. The color sensor 7 is arranged having its view axis perpendicularly to a reference horizontal plane drawn by the movement track of the center axis 6. The light source 8 is fitted so that its optical axis is in a plane which crosses the center axis 6 at right angles and is perpendicular to the reference horizontal plane while crossing the view axis of the sensor 7 on the cylindrical surface 5. Reflected light L2' is converted photoelectrically by the sensor 7, amplified 9, and A/D-converted 10 to input a numeral which is proportional to the quantity of reflected light L2' to a computer 11. The computer 11 transforms the coordinate values in the color space measured by the cylindrical surface 5 into the coordinate values in the color space on the plane by using the relational expression among reflection characteristics of the cylindrical surface 5, the relative position between the cylindrical surface 5 and sensor 7, the ratio of a visual field and the diameter of the cylindrical surface 5, and the quantity of reflected light L2' to the sensor 7.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a device for measuring the color of a cylindrical surface, and is applicable to, for example, automatic color code MS.

[Prior Art] First, the principle of colorimetry and color space will be explained, and then the stereoscopic colorimetry method and its problems will be described. The color measurement method quantifies the color of an object using the spectral distribution of the light source, the spectral reflectance of the object, and the color equivalence number that represents the color sensitivity characteristics of the human visual system. In order to determine color, three independent quantities are required as a basic law, and they are determined as follows (Masaharu Tominaga, Mapping method for computer color vision based on colorimetry, Information processing Academic journal, Vol, 26. No, 2. pll, 318
-327.1985).

Light emitted from a light source with a spectral distribution W(λ) is reflected by an object surface with a spectral reflectance ρ(λ), and enters the human eye as light with radiant energy W(λ)ρ(λ). do. The human eye has a spectral sensitivity characteristic called the isochromatic number x (λ), y (λ), 2 (λ) as shown in Figure 8, so the incident light has each spectral sensitivity characteristic. It is weighted and decomposed into three components, and the amount of integration in the visible region can be felt. This amount is called the object color stimulus value. The stimulus values X, Y, and Z corresponding to ×(λ), y(λ), and 2(λ) are: λ1...(1a) λ2 Y=ll W(λ) ρ(λ)y(λ)dλλ
1...(1b)λ2 Z=Kf W(λ)ρ(λ)2(λ) dλλ1
...-(1c).

However, K is the emmetropization constant, and ρ(λ)=1 [λ=λ
~λ2) = 100# W(λ)V(λ)dλ21 so that Y=100 for a completely white surface of λ2)
...(2) is given by. Note that λ and λ2 are the shortest in the visible range,
The longest wavelength is 380 nm and 780 nmF. Especially y(
Since λ) is the brightness sensitivity of the human eye, that is, it is a specific visual power curve, Y indicates the brightness of the object.

The above is a physical color measurement method using tristimulus values X, Y, and Z. However, the XYZ color space is not perceptually equidistant like the Munsell color space. That is, X
Even if two sets of colors are seen at the same distance in the YZ color space, the difference in color will be perceived differently. What is Munsell color space?
Colors are arranged perceptually evenly based on human psychological experiments. This color space has a cylindrical coordinate system consisting of hue H1 lightness ■ and saturation C as shown in Figure 9 (Ikeda Koryoku 5 Basics of Basai Engineering, Asakura Shoten, P11 Figure 1゜7 cited). ing. Hue H is related to the wavelength of light and indicates what kind of color it is, such as red, green, or blue. Brightness V is an amount that indicates the brightness of a color. Saturation C is an amount that indicates the purity of a color. . However, this space has no correspondence with physical quantities.

Therefore, in order to bring the XYZ color space obtained from physical quantities closer to perception, the XYZ color space is converted to the L*c*h3 color space. These *, C1, and h* are psychological quantities, that is, psychometric quantities that have a correlation with brightness, saturation, and hue, and are called metric brightness, metric chroma, and metric phase angle, respectively. L", c"h
This is the L*a*b8 color space or L” which is a perceptually uniform color space recommended by CIE (Commission Internationale de Illumination).
U"V' colored sky r + awo intert, -c, 3 stings 111X, Y.

The following is required from Z (Yoshinobu Naya, Shiroko Sangyo,
Asakura Shoten, 1987).

(a) In the case of passing through the L"a"b" color space A point in the XYZ color space is converted to a point in the L*a*b1 color space by the following equation.

However, X, Y, and Z are n tristimulus values for a standard white surface, and satisfy X/X, Y/Y, and Z/Zn. In addition, if the calculation method is not satisfied, please refer to “JI
S Z8729: L"a"b" color system and L* u*
■* Method of displaying object color using color system”.Furthermore, a” and b” can be expressed as
1(b”/a”) ・-(7) However, h*
is 0≦h”<360°.

Therefore, by using equations (3) to (7),
, Y, and Z, the corresponding L*c*h* can be obtained.

(b) When passing through shi*u*■8 color space, Lab
It is determined using equation (3) for the case through space. On the other hand, regarding the remaining u, v'', X, Y, Z
and L* are converted and obtained.

u"=131"(u'-u)-(8)
v = 131” (v' −v ) −
...(9) Here, u' = 4X/ (X+15Y+32) -(1o)
v' = 9Y/ (X+15Y+3Z) -(1
1) u, =4Xo/(Xo+15Yo+3Z,)・
...(12) vo' =9Y / (X, +15Yo+32.)・
...(13) It is ne. And c and h are from u v”,・
5F Ear C=...
・(14)h" = jan'(v"/u')
- Calculated by (15).

Next, I will explain the specific measurement method and its problems.

“JIS Z8727:101 [Method of displaying object color using XYZ system”] shows four types of illumination and light reception conditions. Condition 1 is selected because the device configuration is simple.
Alternatively, condition 2 is often used. Condition 1 means the 10th
As shown in the figure, a light source 2 illuminates a sample surface 1 with irradiation light L1 from a 45° direction, and a sensor 3 receives reflected light L2 in a direction perpendicular to the sample surface 1. The reason for this is that the specularly reflected light has the light source color, not the object color, and therefore needs to be removed. Note that condition 2 is the 10th
This is a case where the positional relationship between the light source 2 and the sensor 3 is reversed in the figure.

[Problems to be Solved by the Invention] Conventional color measurement is aimed at flat surfaces, and it has not been possible to perform accurate color measurements on cylindrical surfaces. The reason for this is that on a cylindrical surface, the direction of light reflection differs depending on the position on the cylindrical surface, so the reflected light is more diffused than on a flat surface. This is also because the method of diffusion differs depending on the diameter of the cylindrical surface and the reflection characteristics of the surface. That is, it was difficult to measure color while removing the influence of the curved surface. Therefore, in the conventional system, instead of measuring the correct color, the standard color data was obtained in advance using the measurement target, and the color was classified by comparing that data with the data measured one after another. . Further, if accurate color measurement is required for a cylindrical surface, a method of performing color measurement by greatly enlarging the cylindrical surface with a lens so that the cylindrical surface can be approximated to a plane may be considered.

However, in this case, since the amount of reflected light is reduced, there is a risk that the surface to be measured is susceptible to noise or damaged by strong illumination light. Since the field of view becomes narrower due to enlargement, it is necessary to shorten the measurement interval and increase the positioning accuracy of the measurement position, which causes problems such as making it difficult to speed up the processing.

In this respect, it is an object of the present invention to provide a cylindrical surface colorimeter that accurately measures the color of a cylindrical surface, which has conventionally been difficult to measure accurately.

[Means for Solving the Problems] The above-mentioned problems can be solved by using a cylindrical surface colorimeter according to the present invention, which includes a mechanism that moves the center axis of the cylindrical surface in parallel, and a mechanism that moves the central axis of the cylindrical surface in parallel and a reference plane that is drawn by a movement locus of the center axis. a color sensor arranged such that its axis is perpendicular; an optical axis is included in a plane that intersects the central axis and is perpendicular to the reference plane; and light sources intersecting on the cylindrical surface, reflection characteristics of the cylindrical surface, relative positions of the cylindrical surface and the color sensor, and incidence on the color sensor relative to the ratio of the field of view and the diameter of the cylindrical surface. This is achieved by employing the above configuration means comprising a device that converts coordinate values on the color space measured on the cylindrical surface into coordinate values on a plane using a relational expression such as the amount of light.

[Function] The present invention takes the above-mentioned means and provides a mechanism for moving the center axis of the cylindrical surface in parallel, a color sensor having a visual axis perpendicular to a reference plane drawn by a movement locus of the center axis of the cylindrical surface, and a color sensor that moves the center axis of the cylindrical surface in parallel. Using a light source whose optical axis is included in a plane that intersects the axis and is perpendicular to the reference plane, and whose optical axis intersects with the visual axis of the color sensor on the cylindrical surface, color measurement is performed while moving on the cylindrical surface. A sensor measures the amount of light reflected from the cylindrical surface, and based on that data, arithmetic conversion processing is performed and color measurement is performed. In this way, the constraints regarding the installation of the sample, color sensor, and light source are clarified, and measurements can be made while changing the position of the sample or color sensor.

[Example] Hereinafter, an example of the present invention will be described using FIGS. 1 to 2.

FIG. 1 is a schematic diagram of the entire color measuring device of this embodiment.

In the figure, a stage 4 causes a cylindrical surface 5, which is a colorimetric object, to move its central axis 6 in parallel in the horizontal direction. The color sensor 7 is disposed so that its visual axis is perpendicular to the reference horizontal plane drawn by the locus of movement of the central axis 6 of the cylindrical surface 5, and has the spectral sensitivity characteristics shown in FIG. There is. On the other hand, the light source 8 has its optical axis aligned in a plane perpendicular to the central axis 6 of the cylindrical surface 5 and perpendicular to the reference horizontal plane. It is attached so that it has a relationship of communion with. The light source 8 is the above-mentioned J
Referring to IS Z8727, as shown in FIG. 10, the irradiation light Ll' may be attached at an angle α of 45° with the central axis 6 of the cylindrical surface 5.

This angle α may be any angle as long as the specularly reflected light L2' of the cylindrical surface 5 is reflected on the color sensor 7. The light source 8 illuminates the cylindrical surface 5 with standard irradiation light Ll', and this reflected light L2' enters the color sensor 7.

In FIG. 1, reflected light L2' is photoelectrically converted by a color sensor 7, and its analog output is amplified by an amplifier 9. Furthermore, an A/D (analog/digital) converter 1
A numerical value that is quantized by 0 and is proportional to the amount of reflected light L2' is input to the computer 11. This calculator 11 uses a relational expression of the reflection characteristics of the cylindrical surface 5, the relative position of the cylindrical surface 5 and the color sensor 7, and the ratio of the field of view and the diameter of the cylindrical surface 5 to the light L2'l reflected to the color sensor 7. This is a device that converts the coordinate values on the color space measured on the cylindrical surface 5 to the coordinates rAi on the plane color space, and the principle thereof will be explained in the following colorimetric principle. 12 is a motor for driving the stage 4, and is controlled by the computer 11. Instead of moving the cylindrical surface 5 on the stage 4 as in the present device, the color sensor 7 may be moved.

Therefore, the principle of color measurement for the cylindrical surface 5 will be explained.

To summarize the principle, L* measured for the cylindrical surface 5
, C11, h* are corrected so that they become values measured on a plane as defined by JIS. That is, L*, CI.

A relational expression that holds true between the cylindrical surface 5 and the plane with respect to h* is theoretically derived, and correct coordinates in the color space are determined from measured values based on this relational expression. X, Y,
Since the relationship between Z binding, C, and h* differs depending on whether it is through the L*a$b* color space or the L"u"V1 color space, the relationship between the two is determined separately.

Here, the tristimulus value X between two objects with different shapes.

It is assumed that the ratio r of Y and Z can be regarded as equal if the colors of the two objects are the same. Here, the subscript C1p represents the cylindrical surface 5 and the plane, respectively.

(A) When passing through L*a*b* color space L*, a*, b* of the cylindrical surface 5 and the plane, respectively, are expressed by formula (3)
, (4), (5) Assuming X, Y, and Z shown by r*a*,
According to the relational expression with b*, it becomes. Furthermore, for C3 h8 shown in (7), the relationship between Equation (6) and am, b* holds between the cylindrical surface 5 and the plane. Similarly, equation (8)
- x, y, z and L8 shown in (13), *
The relational expression with v*, U shown in equations (14) and (15)
, the relational expression between V and h, and hH, and also equation (16)
By combining , we get . Formulas (17) to (22) are converted to formulas (23) to (26)
By substituting into , canceling am and b8, and also making equation (16) simultaneous, we find the relationship between L*, C* and h* that holds between the cylindrical surface 5 and the plane, h,
*==hc*.

(b) When passing through the L"a" bI color space...(29) is obtained. Note that Ll is given by equation (27).

Therefore, once r is determined, correct color measurement can be performed for the cylindrical surface 5 by substituting r and the measured value of the cylindrical surface 5 into equations (27), (28), or equation (30). Note that from equations (29) and (31), it can be seen that correct measurement of the metric phase angle can also be performed for the cylindrical surface 5.

This r is calculated as follows. As mentioned above, considering the irradiated light L1' with the angle α of 45° and the vertically reflected light L2', a calculation model thereof is shown in FIG.

In FIG. 2, the X axis is parallel to the central axis 6 of the cylindrical surface 5, the y axis is parallel to the moving direction of the cylindrical surface 5, and the two axes are parallel to the viewing axis of the color sensor 7. Also, the diameter of the cylindrical surface 5 is d, the size of the field of view is f1, the distance between the central axis 6 of the cylindrical surface 5 and the center of the field of view is △y
shall be. Further, it is assumed that the color sensor 7 is sufficiently far away from the cylindrical surface 5, and that reflected light r2' parallel to the Z-axis passing through the field of view is incident on the color sensor 7. Now, the field of view f is (2
The amount of light I(P
, ) to find the total amount of light I that enters the color sensor 7, I=f (Σ1(P, ))/(2m+1) =・
(32)+=m. On the other hand, since the stimulus value is the product of ■ and the spectral characteristics of the color sensor 7 integrated over the wavelength, 1 /I = r for ■, similarly to equation (16).
...(33) - holds true.

...(34) (Nomura, Sagara, Naruse, Attitude angle measurement using luminance changes 2, Transactions of the Japan Society of Mechanical Engineers, 54-506°C (Showa 6)
3>, 2481). K is a constant determined by the amount of reflected light L2', the reflectance of the surface, etc., and λ is a constant indicating reflection characteristics. is a unit vector in the normal direction of the cylinder surface, is a unit vector in the direction of the light source 8, and , , and δ are determined by the following equation.

Official= (-1,0,1)/Go-100 Ma δ-COS (,) ...(36) ...(37) '= (0,.,1) ...(39) V It is. Here, is a unit vector in the visual axis direction of the color sensor 7. The amount of light i reflected from the cylindrical surface 5 to the color sensor 7. Using equation (35a) and equations (36) to (39), the light llI in P expressed by equation (34)
(P,), further calculate the obtained I(P,), and further substitute the obtained I(P,) into Equation 32 to calculate the total light amount. On the other hand, the amount of light I(P,) from a plane can be found in the same manner using equation (35b) instead of equation (35a). r is calculated by substituting these results into equation (33). By substituting the calculated r into Equation 27, the correct metric lightness [* can be obtained from the measured value of the cylindrical surface 5. Similarly, the expression (
28), or by calculating L'',/L from equation (27) and substituting this result into equation (30), the metric chroma C9
Correct values can also be obtained for . L by changing f and λ
The influence on C8, that is, L "/L", c "/c" in field of view c p c
These are the results calculated using equations (27) to (39) while changing the c position. Also, Figure 5 (A) and (B) are L* u* ■
*For the case via color space, △y/d=o, △V/
This is the result of calculating C/C* when d=0.25 using the same * p as in FIG. 4. Note that there is no need to correct the metric phase angle h.

A specific color measurement method will be explained based on the above principle.

The measurement consists of four steps, from the first step to the fourth step.

(A) First step In this step, while relatively moving the color sensor 7 and the cylindrical surface 5, that is, while changing Δy,
This is the process of measuring Y and Z. The three measured curves are shown in FIG. However, the diameter d of the cylindrical surface 5 used for measurement
is 2 m, the thickness of the field of view f is lim, and the sampling interval is 0.11 MK. Normally, △y/d=
A curve with a peak at o is obtained.

(a) Second step This step is a step to be carried out only when the reflection characteristic λ of the cylindrical surface 5 to be measured is unknown.

Since it is difficult to analytically obtain λ from the curve, as shown in FIG. 7, using λ as a parameter, the reflected light L21 at each measurement point is calculated based on the measurement conditions of the first step, and the curve is obtained. The value that most closely matches the measurement results is determined as the reflection characteristic value λ of the cylindrical surface 5. In this example, λ−
It is 3. Note that the calculation was performed on the assumption that m=50.

(T) Third step In this step, the reflected light L2 incident on the color sensor 7 from the cylindrical surface 5 and the flat surface having the same reflection characteristic λ is obtained from equation (32).
'Quantity I, I. and the ratio r=(Io/Io
). As the position of stable colorimetry, the peak which is the characteristic point of the measured curve, i.e. Δy=0
The point shall be selected. In this example, r=0.0
87 was requested.

(1) Fourth step This process was measured using the cylindrical surface 5.

*, h* is corrected to obtain correct coordinates on the color space. Using r obtained in the third step, the body side value L*'' of the cylindrical surface 5 is corrected to remove the influence of the circle C/CC cylindrical surface 5. From the first step, L* when Δy=00 The measured value of 1 is 25.322.5C・C
c Ne8 is required. Also, h was measured to be 91°.

In contrast, the measured value L'' on a plane made of the same material
”, h are 81.4 lines and C p p C 52,5,94°, respectively. Therefore, the results measured by the device of the present invention and the results obtained by experiment agree, and the cylinder It was confirmed that correct measurements could also be made for surface 5.

[Effects of the Invention] As explained above, according to the present invention, there is a mechanism for horizontally translating the center axis of a cylindrical surface to be measured, and a line of sight perpendicular to the reference horizontal plane drawn by the movement locus of the center axis. A color sensor having an axis, and a light source whose optical axis is included in a plane perpendicular to the central axis and perpendicular to a reference horizontal plane, and whose optical axis intersects with the color sensor visual axis within the perpendicular plane and on a cylindrical surface. By using a cylindrical surface colorimeter consisting of the following, it is possible to accurately measure the color of a cylindrical surface, which has been difficult in the past.

Therefore, there is an advantage that errors in identifying the color of the color code can be reduced, or deterioration diagnosis can be performed based on color changes.

[Brief explanation of drawings]

FIG. 1 is a diagram schematically showing a configuration showing an embodiment of the present invention;
Figure 2 is a diagram for explaining the calculation model in the same configuration as above, and shows the geometric relationship of the illumination and light receiving parts, that is, the position of the light source, colorimetric cylindrical surface, and color sensor. A diagram showing the relationship,
Figures 3(A) and 3(B) are diagrams showing the ratio of metric brightness between a plane and a cylindrical surface calculated by changing the visual field size 1 reflection characteristics in the case of the L ab color space, respectively, Figures 4 (A) and (B) are diagrams showing the ratio of metric chromas obtained under the same conditions as Figures 3 (A) and (B), and Figures 5 (A) and (B) are respectively ) Similar to (B), but showing the ratio between the plane and the cylindrical surface for the metric chroma through the L"u"V" color space, FIG. Figure 7 shows an example of the stimulus value measurement results, Figure 7 shows an example of the curve of a cylindrical surface calculated using the calculation model in Figure 2, and Figure 8 shows the spectral sensitivity characteristic of isochromatic number × (λ), y (λ), and Z (λ), Figure 9 is a diagram to explain the Munsell color space, and Figure 10 is a plane that is one of the four conditions specified by JIS. It is a diagram for explaining 45° irradiation light and reflected light reception in the above. 1... Sample surface 2.8... Light source 3, 7... Sensor 4... Stage 5... Cylindrical surface 6 ... Central axis 9 ... Amplifier 10 ... A/D converter 11.
...Calculator 12...Motor 11.11'...Irradiated light 2.12'...Reflected light α...Angle Fig. 1 ΔY/d = 0.25 JcL 00 Fig. 6 ΔV/d c31δ δ1δ Fig. 7Δyld Three stings-Jt J! i Figure 10

Claims (1)

[Scope of Claims] 1. A mechanism for translating a central axis of a cylindrical surface, a color sensor disposed such that its visual axis is perpendicular to a reference plane drawn by a locus of movement of the central axis, and the center a light source whose optical axis is included in a plane intersecting the axis and perpendicular to the reference plane, and where the optical axis intersects with the visual axis in the perpendicular plane and on the cylindrical surface; The color measured on the cylindrical surface using a relational expression such as reflection characteristics, the relative position of the cylindrical surface and the color sensor, and the amount of light incident on the color sensor in item 1 with respect to the ratio of the field of view and the diameter of the cylindrical surface. A cylindrical surface colorimeter comprising: a device for converting coordinate values in space into coordinate values on a plane;