JPS63266343A - Method and device for measuring surface property - Google Patents

Abstract

PURPOSE:To reduce the influence caused by a noise, and to obtain a result conforming with a result of a function test by a visual observation, by quantify ing separately the out-of-focus and distortion of an image. CONSTITUTION:A square wave pattern 1 is radiated from the rear side by a light source 2, its image is reflected by the surface of a body to be measured 5 by a lens 4, and it is formed on the image forming surface and measured by a linear image sensor 6. An output light intensity distribution signal is stored in a buffer memory through an A/D converter. In a data processing means 7, a data (light intensity distribution signal) is added by the number of times of setting to a real number part of a data area from the buffer memory, brought to a Fourier transformation, a power spectrum is derived, normalized by a DC component, and by the power strength of a basic space frequency component, the out-of-focus of the image is calculated. Subsequently, from the data, the base line strength is detected, subtracted from the data, brought to a Fourier transformation, normalized by a DC component, thereafter, each power strength of the basic space frequency component and a space frequency component of its integer multiple is added, and the distortion of the image is calculated.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates to a method for measuring the surface properties of an object, particularly the sharpness, gloss, etc. of a paint film, metal surface, plastic surface, plated surface, etc.; Regarding the equipment used.

[Conventional technology]

Gloss or surface roughness is an important factor that determines the properties of an object's surface, and the gloss measurement method, which is an important characteristic along with color, especially when evaluating the finished state of a paint film, is specified in JIS Z 8741. In addition to specular gloss, which is the amount of specular reflection according to the specified law of reflection on a mirror surface, contrast gloss, which is the ratio of the amount of specular reflection to the amount of total reflection, including diffuse reflection, and the amount of light that reflects the image of another object on the surface There are also sharpness and gloss to compare the sharpness. Compared to specular gloss and contrast gloss, which are based on physical measurements, sharpness gloss is the least quantifiable because it contains psychological elements, and even now, sensory evaluation is mainly done by visual inspection. .

According to the standard, the definition of sharpness gloss is "the degree to which the image of another object is transferred to the surface", and several sharpness gloss meters were devised based on this definition (Utility Model Publication No. 41-19039).
No. 50-153979, Japanese Patent Application Laid-Open No. 1982-153979
(Refer to Publication No.-138960, etc.). However, these methods have problems such as individual differences among the measurers and data variations due to factors unrelated to the gloss of the object to be measured.

On the other hand, Japanese Patent Application Laid-open No. 58-97608 and
There is a measurement method disclosed in JP-A-61-217708. These measuring methods attempt to measure sharpness and gloss based on the following concept.

■ Surface properties such as sharpness and gloss can be evaluated based on how sharply the edges of the rectangular wave pattern are reflected on the surface of the object to be measured.

■ The sharpness of the edges of the rectangular wave pattern reflected on the surface of the object to be measured can be evaluated by the sharpness of the light intensity distribution on the imaging plane where the rectangular wave pattern is imaged through reflection on the surface of the object to be measured. Moreover, the sharper the light intensity distribution is, the stronger the harmonic components will be if the light intensity distribution is subjected to spatial frequency analysis.

These measurement methods based on the above concept basically project and image a rectangular wave pattern onto an imaging plane using an imaging optical means through reflection on the surface of the object to be measured, and What they have in common is that the light intensity distribution is Fourier transformed and the sharpness and gloss of the surface of the object to be measured is quantified based on the magnitude of the power spectrum intensity (hereinafter referred to as "power intensity") at a specific spatial frequency.

The difference between the above two methods is that the latter (Japanese Unexamined Patent Publication No. 61-217708) is an improvement of the former (Japanese Unexamined Patent Application No. 58-97608) with the following configuration added. .

That is, in the latter method, in addition to the above basic configuration, the degree of image blur is quantified by the power intensity at the fundamental spatial frequency, and the degree of blurring of the image is quantified by the power intensity at the fundamental spatial frequency, which is an integral multiple of the fundamental spatial frequency. The degree of image distortion is quantified by the frequency or the ratio of the sum of power intensities at a plurality of frequencies near the fundamental spatial frequency.

In this way, the blur and distortion of the image are quantified separately.
According to the latter method, it is possible to detect the degree of minute blur in objects with large surface undulations and blur, which could not be measured with the former method. It becomes possible.

[Problem that the invention seeks to solve]

However, the power intensity at the fundamental spatial frequency, an integer multiple of the fundamental spatial frequency, or multiple frequencies near the fundamental spatial frequency used in this latter method is difficult to measure when the surface condition of the object to be measured is poor, such as orange skin or the like. When the degree of blur increases, the signal strength becomes extremely low, the S/N ratio during measurement deteriorates, and there is a high risk of erroneously determining that there is no blur.

This invention was made in view of the above-mentioned problems, and can quantify blurring and distortion of an image separately, has less influence from noise, and has results that agree well with the results of visual sensory tests. The object of the present invention is to provide a method for measuring the surface properties obtained and an apparatus for carrying out the method.

[Means for solving problems]

In order to achieve the above object, the first invention, a measuring method, is as follows:
A rectangular wave pattern is projected onto an imaging plane by an imaging optical system through reflection on the surface of the object to be measured, and the image is blurred by the power intensity of the fundamental spatial frequency of the power spectrum obtained from the imaging waveform. The degree of image distortion is determined by the sum of the power intensity of the fundamental spatial frequency and the power intensity of multiple frequencies that are integral multiples of the power spectrum obtained from the waveform obtained by subtracting the baseline intensity from the imaging waveform. , each is characterized by being individually quantified.

Further, as shown in FIGS. 1 and 5, the second invention apparatus has an illumination optical means 2 for illuminating the rectangular wave pattern
．． 3, an imaging optical means 4 for projecting and forming an image of the rectangular wave pattern onto an imaging plane through reflection on the surface of the object to be measured 5, and a spatial light intensity distribution of the imaging waveform on the imaging plane. The data processing means 7 includes a photoelectric conversion means 6 that converts the signal into an electrical signal, and a data processing means 7 that performs Fourier transform on the spatial light intensity distribution signal from the photoelectric conversion means and calculates the power intensity at a specific spatial frequency. is the sum of the power intensity at the fundamental spatial frequency of the imaged waveform, the power intensity at the fundamental spatial frequency of the waveform obtained by subtracting the baseline intensity from the imaged waveform, and the power intensity at multiple spatial frequencies that are integral multiples of the fundamental spatial frequency. It is characterized in that it calculates .

[For production]

Hereinafter, one embodiment of these inventions will be described in detail with reference to the accompanying drawings.

First, the measurement method, which is the first invention, will be explained.

The method of measuring the sample is the same as the conventional method. That is, as shown in FIG. is reflected on the surface of the object to be measured 5 by a lens 4, which is an imaging optical means, and is imaged onto an imaging plane on which a linear image sensor 6, which is a photoelectric conversion means, is installed. Then, the linear image sensor 6 measures the light intensity distribution on the imaging plane.

Although the spatial light intensity distribution in the rectangular wave pattern 1 can be considered to be an ideal rectangular wave, the pattern reflected by the surface of the object to be measured 5 and projected onto the imaging plane has the shape of the object to be measured. Diffusion and scattering depending on the surface condition of the waveform 5, that is, blurring and distortion of the image occur, resulting in a waveform that deviates from the ideal rectangular waveform, as shown in FIG. 2(a). In the figure, the horizontal axis indicates the spatial distance on the projected image where the linear image sensor 6 is arranged, and the vertical axis indicates the light intensity.

In the theory of Fourier series expansion, it is known that the boundary between the bright and dark parts of a waveform pattern changes sharply, that is, the closer the shape is to a rectangular wave, the stronger the spatial harmonic component becomes. . Therefore, when the spatial light intensity distribution of the imaged pattern obtained as described above is Fourier transformed and normalized by the DC component intensity, as shown in Fig. 2(b),
Fundamental spatial frequency component ν. and harmonic component 2ν. A power spectrum consisting of... is obtained. In the figure, the horizontal axis shows the spatial frequency, and the vertical axis shows the power intensity with the DC component intensity as 100.

As shown in Fig. 2 (a), if the imaged waveform deviates from the rectangular wave due to distortion or blurring of the surface to be measured, as shown in Fig. 2 (b)
), the overall power intensity becomes smaller and the fundamental spatial frequency ν. Spectra also occur at frequencies other than integer multiples of .

The degree of blur on the surface of the object to be measured 5 is determined by the fundamental spatial frequency ν. The power intensity Pν at . , or its square root F'7r
Defined by This is due to the following reasons.

The degree of blur on the surface of the object to be measured is determined by the light intensity RP at the brightest part and the light intensity RP at the darkest part of the image of the sinusoidal grating pattern (i.e., a repeating pattern in which the brightness and darkness changes in a sinusoidal manner). This corresponds to the difference in light intensity R6, that is, the contrast C of the imaged pattern. Contrast C is defined by 2(I) below.

On the other hand, the fundamental spatial frequency ν. The power intensity P at
ν. is the fundamental spatial frequency ν included in the imaged waveform. It is raining the power of a sine wave. Therefore, this power intensity Pν. The contrast, that is, the degree of blur on the surface of the object to be measured can be defined by the square root of the power intensity Pν. and its square root,
To define the degree of blur (NSIC*) on the surface of the object to be measured, for example, the power intensity Pv on a black glass plate used as a reference plate is used. It may be expressed as a percentage with respect to B and G. If this is expressed as a formula, the following formula (n) is obtained.

Distortion of the image on the surface of the object to be measured can be considered as follows.

In other words, if the surface of the object to be measured is undulated and the image is distorted, the change in the boundary between the bright and dark parts of the waveform pattern becomes slow, and based on the theory of Fourier series expansion, spatial harmonic components are strength becomes weaker. Therefore, when looking at the power spectrum obtained by Fourier transforming the spatial light intensity distribution of such an imaging pattern and normalizing it by the DC component intensity, the fundamental spatial frequency component ν. The power intensity Pν of
. and harmonic component 2ν. The power intensity Piν0(
(i is an integer of 2 or more) changes in proportion to the sharpness of the pattern. However, since these power intensities are normalized by the DC component, they are very small values, and the S/
There is a high risk that the N ratio will deteriorate and the degree of distortion will be incorrectly determined, as shown by (-Δ-Δ-) in FIG.

On the other hand, the baseline intensity (Fig. 2 (
By subtracting b) in a), the DC component becomes smaller, so
The power intensity normalized by the DC component becomes relatively large, and the influence of noise can be reduced. However, this effect is not so large that it does not eliminate erroneous judgments of the degree of distortion, such as the reversal shown in FIG.

Therefore, a new evaluation scale for the degree of distortion is desired, but as the degree of yuzu skin increases and the distortion in the shape of the imaged waveform increases, the contrast also decreases and the fundamental spatial frequency ν. The power intensity Pν. Based on the following formula (III), the degree of distortion was found to be similar to the degree of distortion determined by the sensory test, as shown by <-0-0-> in Figure 3. It turned out that the degree of blur (NSIC) in this figure is the same as the degree of blur described above, and is expressed as a percentage of the total sum on the black glass plate used as a reference plate.Also, The numbers on the horizontal axis of FIG. 3 indicate the size of yuzu skin (distortion) according to the sensory test, and B and G indicate the black glass plate (no distortion) as a reference plate.

In the above equation, the denominator side represents the total sum on the black glass plate, which is the reference plate.

Here, q=%, j=1, k= (2i −1)
, i=1.2, the equations of N5IC and N5IC* shown in FIG. 4 are obtained. The N5IC* value is the square root of the power of the fundamental spatial frequency of the power spectrum of the imaged waveform as seen on the left side of the same figure, normalized by the DC component intensity shown as d in the figure (shown as J'TrTv). is expressed as a percentage of that of the black glass plate serving as the reference plate (similarly, fT is expressed as 1r-). Also, N5I
The C value is the square root of the power of the fundamental spatial frequency and three times the frequency of the power spectrum of the imaged waveform obtained by subtracting the baseline intensity from the imaged waveform, and is standardized by the DC component intensity shown as d' in the figure. The sum of the abrasions is obtained as a percentage of that of the black glass plate. As shown, the fundamental spatial frequency ν. The power intensity at , and the frequency 3ν which is three times that. As shown in Figure 2, the degree of distortion (NSIC) can be represented by the sum of the power intensity at the fundamental spatial frequency ν. This is because the power intensity of spatial frequencies that are odd multiples of (3v., 5ν, . . . ) is larger than the power intensity of spatial dark wave numbers that are even multiples (2ν., 4ν, . . . ).

According to the method of the present invention as described above, it is possible to measure the blur and distortion on the surface of the object to be measured as separate parameters, and even when the degree of blur or citron skin is large, visual sensory tests can be performed. We can now obtain results that are in good agreement with the results of .

Next, an embodiment of an apparatus for carrying out the above method will be described in detail with reference to the accompanying drawings.

The apparatus of this embodiment has an internal configuration as shown in FIG. The operation of the device shown in the figure is as follows.

First, when the above-described pattern is projected onto the linear image sensor (photoelectric conversion means) 6 driven by a drive circuit, its light intensity distribution is output as a signal. The output optical intensity distribution signal is amplified by an amplifier, peak held by a peak hold circuit, converted into a digital signal by an A/D converter, and then temporarily stored in a buffer memory. The light intensity distribution signal stored in the buffer memory is processed by a microprocessing unit (MPU).
), read-only memory (ROM) for program storage
), read/write memory (RWM) for data storage,
Microcomputer section consisting of interface etc.
The data processing means 7) is a microcomputer that is used for arithmetic processing such as the Fourier transform, addition and subtraction, and outputs the arithmetic results, that is, the blurring and distortion data to a display device or printer. For example, the arithmetic processing flowchart of FIG. 0, in which the arithmetic processing is performed as shown in FIG.
M).

First, with the start of calculation, each data area in the RWM that constitutes the real part, imaginary part, and power:spectrum part is cleared. Next, after the number of additions has been set, the data (
light intensity distribution signal) is captured. When the data has been completely fetched, the data is added from the buffer memory to the real part of the data area by the set number of times. When added a predetermined number of times, the data is Fourier transformed and becomes a power spectrum. The obtained power spectrum is normalized by the DC component, and then the degree of image blur (NS
IC*) is calculated.

Next, the minimum light intensity value X sin, that is, the baseline intensity value, is found from the data of the light intensity distribution signal, and it is subtracted from the data. Then, the waveform data from which this baseline intensity has been subtracted is Fourier transformed to become a power spectrum. The obtained power spectrum is normalized by the DC component, and then the power intensities of the fundamental spatial frequency component and the spatial frequency components that are integral multiples of the fundamental spatial frequency component are added to calculate the degree of image distortion (NSIC).

Then, the N5IC* and N5IC calculated as described above are displayed on a display or output as a hard copy from a printer, and the process is completed.

〔Example〕

Examples of the present invention will be described below.

The properties of various coating film surfaces were measured using the method and apparatus described above. The results are shown in Figure 7 (a), (b
). In addition, these figures show the degree of image blurring (NSIC*) and the degree of image distortion (NSIC) on the black glass plate, which is the reference plate, respectively, expressed as percentages with 100. ◎ indicates the data for the black glass plate, and other symbols indicate the samples below.

−・−・−: Solid Akaichi Roro: Solid white − Mumuu: Solid red (skin sample board) −☆−☆−: Metallic silver−★−★−: Metallic silver (skin sample board) −◇−◇
-: Solid red (paste) In addition, the waveforms written next to each symbol above are those obtained by comparing the surface shape of the sample with the light intensity distribution of the imaged waveform formed on the linear image sensor. The more the waveform deviates from the rectangular wave, the more distorted the image becomes, and the larger the baseline becomes greater than 0, the more blurred the image becomes.

In order to understand the correlation between the light intensity distribution of the imaged waveform and the degree of blur and distortion, we investigated the N5ICI value and the
The values were measured and visually evaluated. The results are shown in Table 1.

According to the results shown in the above figure and table of Table 1, it was found that the surface shape of the sample, the degree of surface distortion (NSIC), and the degree of surface blur (NSIC*) were in good agreement.

〔Effect of the invention〕

Since the surface texture measuring method and device of the present invention are as described above, it is possible to individually quantify image blur and distortion, and even when the degree of blurring is large, it is possible to quantify the blurring and blurring of the image separately. Results that match well with test results can be obtained.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram for explaining the sample measurement method used in the surface texture measurement method of the present invention, FIG.
Figure (g)) is a graph showing an example of the power spectrum obtained by Fourier transforming the light intensity distribution waveform in figure (a), and Figure 3 shows the distortion of the image in the method of this invention and the conventional method. FIG. 4 is an explanatory diagram schematically explaining the process of deriving the N5IC value and N5IC* value from the imaged waveform in an embodiment of the present invention. FIG. 5 is a block diagram showing an example of the configuration of the apparatus of the present invention, and FIG. 6 is a flow chart showing an example of the calculation processing by the data processing means.
7(a) and 7(b) are graphs showing the results in the embodiment of the present invention, and FIG. 8 (al to (fl) are waveform diagrams showing examples of imaging waveforms obtained by measurement, respectively. 1... Rectangular wave pattern 2.3... Illumination optical means 5
...Object to be measured 4...Imaging optical means 6...Photoelectric conversion means 7...Data processing means N5IC*...
Degree of blur of the image N5IC... Degree of distortion of the image Representative Patent Attorney Takehiko Matsumoto 1st Figure 52 ~ Spatial Frequency Hayashi 1i311! ! 1 大嬌---Yur1几1んAL -111-小 MUSH! Figure 6 Chikuku Figure 8 Figure 8 (') (d) (b)
(e) (c)
(f) JD-Eμ 222]

Claims (2)

[Claims] (1) A rectangular wave pattern is projected and imaged onto the imaging plane by the imaging optical system through reflection on the surface of the object to be measured, and the spatial light intensity distribution of the imaged imaged waveform is identified by Fourier transformation. In a surface texture measurement method that quantifies the sharpness and gloss of the surface of an object to be measured based on the intensity of the power spectrum at the spatial frequency, the image is determined based on the intensity of the power spectrum at the fundamental spatial frequency of the power spectrum obtained from the imaging waveform. The degree of blur is determined by the sum of the intensity of the power spectrum of the fundamental spatial frequency and the intensity of the power spectra of multiple frequencies that are integral multiples of the power spectrum obtained from the waveform with the baseline intensity subtracted from the imaged waveform. A surface texture measuring method characterized by individually quantifying the degree of distortion of an image. (2) an illumination optical means for illuminating a rectangular wave pattern; an imaging optical means for projecting and forming an image of the rectangular wave pattern onto an image forming plane through reflection on the surface of the object to be measured; A photoelectric conversion means that converts the spatial light intensity distribution of the imaged waveform into an electrical signal, and a data processing means that performs Fourier transform on the spatial light intensity distribution signal from the photoelectric conversion means and calculates the intensity of the power spectrum at a specific spatial frequency. In this apparatus, the data processing means measures the intensity of the power spectrum at the fundamental spatial frequency of the imaged waveform and the baseline from the imaged waveform. 1. A device that calculates the sum of the intensity of a power spectrum at a fundamental spatial frequency of a waveform with reduced intensity and each intensity of the power spectrum at a plurality of spatial frequencies that are integral multiples of the fundamental spatial frequency.