JPH08297098A - Method and apparatus for measuring gloss irregularity of coated paper board - Google Patents

Abstract

PURPOSE: To quantitatively measure the gloss irregularity of a coated paper board. CONSTITUTION: A visible light is emitted from one light source 21 to the outer surface of a coated paper board 23, its reflected light is received by a television camera 24, and a two-dimensional image having obtained bright and dark gradation distribution is Fourier-transformed by an image analyzer 20. Then, the brightness and darkness of the image are bipolarized by using emphasizing coefficient in a specific wavelength range in the case of reversely Fourier- transforming it, the dark image region for forming a closed section is calculated in area as gloss irregular part, and the distribution parameter of the area is output as the measured result.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for measuring uneven gloss of coated paperboard, which quantitatively measures unevenness of gloss of the product surface of coated paperboard as one item of quality.

[0002]

2. Description of the Related Art In recent years, in addition to the strength of gloss on the surface of a product, uneven gloss has become more important in terms of product quality. For example, the "feel" of coated paper, the "flow mark" on the surface of molded plastic, and the "vividness" of automobile coating.

The surface feeling of the coated paper will be described. That is, it is said that the more the product has a uniform glossiness, the better the surface feeling. The evaluation has hitherto been made by an inspector visually observing the unevenness of gloss in the submillimeter region of the coated paper surface. In addition, the following inspection method has also been proposed, in which the appearance of a product is imaged by an imaging device such as a television camera, and the distribution of the brightness level (reflected light intensity) of the product appearance is calculated from the imaging result.

One of them is a modification of a chromatographic scanner, in which a luminous flux of 0.4 mmφ is scanned on the surface of coated paper at an incident reflection angle of 75 °, and the standard deviation of the intensity of reflected light is related to the visual order. (H. Fujiw)
ara et. al. , 1990 TAPPI Coa
t. Conf. Proc. , 209 (1990)).

The other is to analyze the surface reflection two-dimensional image of the printing paper input from the CCD camera to examine the correlation with the average visual order, and to find the correlation with the intensity of reflected light, that is, the variation coefficient of gradation. It's a good thing. But,
It is said that there were many cases where the uneven glossiness of white paper did not correlate <M. A. MacGregor et. a
l. , 1991 TAPPI Coat. Conf. P
rc. , 495 (1991)>.

In the proposal of Japanese Patent Laid-Open No. 222002/1994, unlike the conventional method, the uneven gloss is regarded as the size (area and its distribution) of a portion (bright portion) where the reflected light from the glossy surface is strong or a portion (dark portion) where the reflected light is weak. The range of glossiness is relatively narrow A0
For each glossy coated paper, measured for each A3 product, the correlation of the area of the dark part with the visual evaluation is obtained.

[0007]

However, in the inspection of the glossiness of the coated paperboard by visual inspection, the individual subjectivity easily enters the evaluation, and the quantitativeness is lacking. Therefore, a professional inspection is required to objectively judge the quality. Requires a large number of personnel.

On the other hand, the above-mentioned optical inspection method for uneven gloss of coated paperboard has the following drawbacks.

For the measurement of the optical unevenness of gloss, quantification has been attempted by the reflected light intensity distribution, but there is a drawback that it does not always correspond to the result of visual judgment. In particular, the blank surface feeling (surface feeling before printing) is strong in diffuse reflected light, and the uneven glossiness due to specular reflected light is weakened, and the optical inspection method for examining the reflected light intensity distribution has a large error. Further, the proposal of JP-A-6-222002 has room for improvement in measurement of coated paperboard.

In view of the above points, therefore, the present invention provides a measurement result of uneven glossiness of coated paperboard having a wide range of glossiness based on the size and distribution of uneven glossiness rather than the intensity distribution of light. An object of the present invention is to provide a method and apparatus for measuring uneven gloss of coated paperboard that can be quantified and expressed.

[0011]

In order to achieve such an object, the invention according to claim 1 takes an image of a coated paperboard by an image pickup device and selects an image obtained as an image pickup result by an image analysis device. An image area of a dark part forming a closed section is detected as an uneven gloss portion of the coated paperboard, an area of each of the detected closed section image areas is calculated, and a distribution of each of the calculated areas is calculated. It is characterized in that the calculation result is a quantified measurement result of uneven gloss.

According to a second aspect of the present invention, the lightness and darkness of the image pickup result is emphasized when the image area of the dark part forming the closed section is detected.

According to a third aspect of the present invention, an image pickup means for picking up an image of the coated paperboard, and an image area of a dark portion forming a closed section in the image obtained as a result of the image pickup is defined as uneven gloss of the coated paperboard. Detection means for detecting as a part, first calculating means for calculating the area of each of the detected closed partition image regions, and distribution of each of the calculated areas by calculating each distribution of the calculated area And a second calculation means for outputting the calculation result as the measurement result of the uneven glossiness of the coated paperboard.

The coated paperboard usually has a basis weight of 16
It refers to coated paper of 0 g / m ² or more, but there is no strict definition, and the glossiness of commercially available coated paperboard covers a wide range.

[0015]

In the inventions of claims 1 and 3, the inventor of the present application found that the dark portion forms a closed section in the captured image because the gloss unevenness of the coated paperboard causes a difference in lightness and darkness. The measurement result of uneven gloss is quantified by calculating the area distribution of the image of this closed section.

According to the second aspect of the present invention, the uneven gloss portion of the coated paper board can be accurately identified by emphasizing the lightness and darkness of the image pickup result.

[0017]

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

FIG. 1 shows the basic configuration of the embodiment of the present invention.
In FIG. 1, reference numeral 1000 denotes an image pickup means for picking up an image of coated paperboard. Reference numeral 1100 is a detection unit that detects an image area forming a closed section as an uneven gloss portion of the coated paperboard from an image obtained as a result of the imaging.

Reference numeral 1200 is a first calculating means for calculating the area of each of the detected closed section image regions.

Reference numeral 1300 is a second calculating means for calculating each distribution of the calculated areas and outputting the calculation result as a measurement result of uneven gloss.

As will be described later, the functions of the detecting means 1100 and the first and second calculating means 1200, 1300 are realized by the calculation function of the image analysis processing device.

FIG. 2 shows a schematic structure of a measuring apparatus to which the present invention is applied.

In FIG. 2, the object of inspection, that is,
An image pickup device (image pickup means 110 in FIG.
0) Light is projected from the light source 21 in 10 through the polarization filter 22. The light reflected by the object 23 is received by the television camera 24 via the polarization filter 25.
The television camera 24 converts the received light into an image signal for each pixel and outputs it to the image analysis device 20.

Visible monochromatic light or white light is preferably used for the light source 21 used in this embodiment. Further, the incident light on the surface of the coated paper board 23 is preferably parallel light or light in a state close to parallel light. If the light is not parallel light or light close to parallel light, uneven gloss may be difficult to capture over the entire image. The incident angle is preferably 15 ° to 35 °, but is not limited to this.

In the present embodiment, the reflected light received by the television camera 24 is −10 ° to +1 with respect to the value of the incident angle.
It is preferable to capture at a reflection angle of 0 °. If it deviates from this range, it becomes difficult to capture the specularly reflected light, which is the main component of gloss.

By passing the incident light and the reflected light through the polarization filters 22 and 25 having the same phase, the diffuse reflected light is blocked,
Transmits specularly reflected light. Therefore, uneven gloss is emphasized more.

The television camera 24 used in the present embodiment refers to a device for obtaining a two-dimensional (planar) image of the coated paperboard 23, and any one can be used as long as it can capture the change in brightness and darkness with respect to the position in the plane by an electric signal. May be. Although there are CCD cameras, video cameras and the like that are commercially available, it is preferable to use a CCD camera in which the brightness and the electric signal have a linear relationship. The focal length of the lens of the TV camera is 0.5 mm or less when the image resolution is expressed by the size of the coated paperboard surface, and the measured area of the coated paperboard corresponding to the entire image is 2 ×.
It is preferable to select 2 mm or more.

The present invention is characterized by an image signal analysis method, and the image analysis processing relating to the present invention will be described.

The image signal for one screen obtained by the television camera 24, that is, the brightness value (gradation expression) for each pixel is stored in the memory in the image analysis device 20 and then read by the central processing unit. The image is analyzed in the following processing steps.

(1) Fourier transform is applied to the two-dimensional image by the following equation.

[0031]

[Equation 1]

The result of the Fourier transform shows the intensity distribution for each frequency band and is called a power spectrum.

(2) When the inverse Fourier transform of the Fourier transform result is performed, the portion corresponding to the specific wavelength range that can be recognized by the naked eye is multiplied by the enhancement coefficient to obtain an enhanced image in which the lightness and darkness of the two-dimensional image at the time of image pickup is enhanced. . The inverse Fourier transform formula is represented by the following formula.

[0034]

[Equation 2]

(3) In the obtained emphasized image, an image area portion in which a white portion corresponding to a light portion or a black portion corresponding to a dark portion forms a closed section is detected as an uneven gloss portion, and the detected closed section is detected. The area, average area, standard deviation, coefficient of variation, or number of white or black portions per unit area for each of the regions is calculated as a gloss unevenness determination parameter corresponding to visual evaluation. Further, these parameter values quantitatively represent the degree (distribution) of uneven gloss.

Here, the white part and the black part refer to independent closed partition regions having gradations corresponding to white and black, respectively.

For reference, the formulas for calculating the above parameters are used.
The formula is shown below. Further, it goes without saying that the image analysis apparatus when executing this process operates as the detecting means 1100, the second calculating means 1200, and the second calculating means 1300 of FIG.

[0038]

(Equation 3)

[0039]

[Equation 4]

[0040]

(Equation 5)

The lower limit of the specific wavelength range is 0.
It is preferable to set the wavelength range such that the wavelength range is 004 to 2.0 mm and the upper limit is 2.0 to 200 mm. The lower limit is 0.
If it is out of the range of 004 to 2.0 mm, it is different from the resolution of human vision, and it becomes impossible to obtain an effective measurement value. Also, if the upper limit is outside the range of 2.0 to 200 mm, it is different from the size perceived by humans as a difference, and an effective measurement value cannot be obtained.

The emphasis coefficient in the equation (2) is preferably 2 to 50 times. If it is less than 2 times, the polarization of light and darkness cannot be obtained, and if it exceeds 50 times, the uneven shape does not match the visually recognized one, and it becomes difficult to obtain an effective measurement value.

When the above arithmetic processing is calculated by a computer, a two-dimensional image is divided into a set of pixels, and the gradation of each pixel is input by digitizing an image signal.

In the image analysis processing described above, the operation of Fourier transforming and inverse transforming a two-dimensional image to obtain a white part or a black part is a region setting which is conventionally called a "threshold" and which tends to be arbitrary. Since it can be set under the same conditions for all samples, measurement values with good reproducibility and reliability can be obtained.

The method and apparatus for quantitatively measuring the unevenness of gloss of the object to be inspected are suitable as a method for replacing the conventional method for visually judging the unevenness of gloss of the product surface, and do not require arbitrary operation. It has the feature that quantitative values with good reproducibility and reliability can be easily obtained without being influenced by the experience and judgment of the person.

Therefore, the present invention provides a coated paperboard blank surface,
Provided are a method and apparatus useful for quantitatively evaluating the minute gloss unevenness of molded plastic surfaces, various coated surfaces, and other articles where importance is attached to the aesthetics and smoothness of the surface, as well as the minute gloss unevenness of the printed surface. Is.

The measurement results of the uneven glossiness actually performed will be introduced for reference. As the coated paper sample, a commercially available coated paperboard (15 samples) was used. The glossiness of the 15 coated paperboard samples was in a wide range of 38 to 68%.

The device shown in FIG. 2 was used as a device for measuring the minute gloss unevenness of the coated paper blank. White visible parallel light (light irradiation device HT-2: Nikon) is polarized and irradiated on the surface of the coated paperboard at an incident angle of 25 ° with respect to the normal, and then at 25 °.
The reflected light of CC through the polarization filter of the same phase as the incident light
It was detected by a D camera (SONY: CE-75).

The photographing area of the surface of the object per pixel is 8
The measurement area was 0 × 80 μm and 20 × 20 mm.
The data were taken at 4 points per sample, and the arithmetic mean thereof was used as the value.

The brightness of each pixel was converted into a digital gradation by an A / D converter. 256 tones from black to white
The level was divided into 0 and black was set to 0 and white was set to 255. The amount of light was set so that the gradation distribution of the sample with the highest glossiness in each group of coated paper samples does not reach the gradation level 255.

Image analysis (Image analysis device IP-1000:
Asahi Chem. Ind. ) Conditions,
After the two-dimensional Fourier transform of the original image, the specific wavelength range that can be recognized by the naked eye at the time of the inverse transform is multiplied by an emphasis coefficient to emphasize the uneven brightness of the image. In the gradation of the image in which unevenness is emphasized, the range of 0 to 1 is <black part>, 254-2
The range of 55 was defined as <white part>.

After the area of each of the black part (dark part in the original image) and the white part (bright part in the original image) was determined, its standard deviation was calculated.

Regarding the visual level, eight experts involved in paper quality evaluation inside and outside the company gave a rank, and the arithmetic mean value of the rank was taken as the visual average rank. The order of ranking was given as integers such as 1, 2, 3, ...

The relationship between the average rank of the visual evaluation, the average area of the highlighted black portion corresponding to the uneven gloss of the coated paper, and the area standard deviation are shown in FIGS. 3 and 4. In this case, the emphasis wavelength range at the time of inverse Fourier transform was 0.5 to 20.0 mm, and the emphasis coefficient was 10 times. As is clear from FIGS. 3 and 4, the correlation coefficient was 20.92 in the case of the average area of the black portion and r = 0.91 in the case of the area standard deviation of the black portion. By the way, the correlation between the average rank of visual evaluation and the average area of the bright part is r
= 0.52, r = 0.45 in the case of the area standard deviation of the bright part
Met. From these results, it is understood that the visual evaluation of the coated paperboard is performed by observing the dark portion of the uneven gloss rather than the bright portion. Therefore, it is considered that the average area of the black area and the area standard deviation are the dominant factors for the visual sense.

In addition to this embodiment, the following example can be realized.

(1) In this embodiment, the processing up to the measurement of the uneven gloss is explained, but the appearance inspection can be automatically performed by using the measurement result. In this case, the presence or absence of abnormality is determined by comparing the parameter value obtained as the measurement result with a predetermined threshold value. At this time, it is advisable to display the inspection result and an image emphasizing the imaging result on the display.

(2) To visually output the measurement result of uneven glossiness, the following forms can be used.

(A) The calculated parameter value is numerically output by a display device or a printer.

(B) The calculated parameter value is graphically output by a display device or a printer.

(C) The degree of uneven glossiness is converted into a numerical value by a numerical operation expression using a plurality of parameter values, and the unevenness of glossiness or the degree of printing "large", corresponding to the numerical value,
Display a message such as "medium" or "small".

(3) In the present embodiment, detailed processing for detecting the image area of the closed section from the image was not described, but this processing can be performed by using various well-known methods as contour line extraction processing. Good.

(4) When it is desired to clarify the boundary of the uneven glossy portion, it is preferable to emphasize and display the contour line forming the closed section.

[0063]

As described above, according to the present invention, the gloss unevenness of the coated paperboard can be quantitatively measured, so that the degree of the gloss unevenness of the coated paperboard can be known.

[Brief description of drawings]

FIG. 1 is a functional block diagram showing a basic configuration of an embodiment of the present invention.

FIG. 2 is a structural diagram showing the structure of an embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between a visual average rank and a standard deviation of uneven gloss dark areas.

FIG. 4 is a diagram showing a relationship between a visual average order and an average area of uneven glossy dark areas.

[Explanation of symbols]

 10 Imaging Device 20 Image Analysis Device 21 Light Source 22, 25 Polarization Filter 23 Object 24 Television Camera

Claims (3)

[Claims] 1. A coated board is imaged by an imaging device, and an image analysis device detects an image area of a dark portion forming a closed section from an image obtained as an imaging result as a gloss uneven portion of the coated paperboard. The coated paperboard is characterized in that the area of each of the detected closed-section image regions is calculated, the distribution of each of the calculated areas is calculated, and the calculation result is used as a quantified gloss unevenness measurement result. Measurement method for uneven gloss. 2. The method for measuring uneven gloss of coated paperboard according to claim 1, wherein when detecting an image area of a dark part forming the closed section, the brightness of an image pickup result is emphasized. 3. An image pickup means for picking up an image of the coated paperboard, and a detection for detecting an image area of a dark portion forming a closed section as an uneven glossy portion of the coated paperboard from an image obtained as a result of the image pickup. Means, a first calculating means for calculating the area of each of the detected closed partition image regions, and a distribution of each of the calculated areas by calculating the distribution of each of the calculated areas. An apparatus for measuring uneven gloss of coated paperboard, comprising: second calculation means for outputting the calculation result as the result of measuring uneven gloss of the coated paperboard.