KR101568726B1 - Quantitative method for constituents of sintered ore - Google Patents

Abstract

A method for quantifying sintered ores according to an embodiment of the present invention includes the steps of irradiating light to sintered light, obtaining luminance data of the reflected light, and generating an image so that lightness and darkness corresponding to the respective luminance values of the components included in the sintered light appear And quantifying the content of each component by quantifying the amount of each component in the image. The method of quantifying the components around the pores included in the sintered image on the image, A process of removing a region between desired component regions, and a process of calculating an area of a component region to be quantified and converting the calculated area into a content value.
Therefore, according to the embodiments of the present invention, it is possible to minimize the analysis error due to the pores included in the sintered ores, thereby minimizing the content analysis error of each component of the sintered ores. Further, in the area measurement of the pores, the pores are not cut off on one screen, but are recognized as one entity and measured, so that the pore area can be easily measured and the pore area measurement error can be reduced.

Description

[0001] The present invention relates to a method for quantifying sintered ores,

The present invention relates to a method of quantifying sintered ores, and more particularly, to a method of quantifying a sintered orbital component capable of reducing an analysis error.

The sintered ores are used as raw materials in the blast furnace production process and consist largely of hematite, magnetite, calcium ferrite, slag and pore.

As disclosed in Korean Patent No. 10-0896579, sintered ores are transported by being fed into a sintering hopper, in which the upper light stored in the upper hopper and the blending raw materials stored in the surge hopper are transported. Thus, the flame (that is, flame) injected from the ignition furnace is ignited to the sinter raw material accommodated in the sintered bogie, and the sintered bogie passes through the upper side of the wind box. As a result, a suction force is generated downward in the sintered bogie passing through the upper side of the windbox, and the flame ignited by the air sucked moves downward, and the sintered light is produced as the sintering is performed in the sintered bogie.

Such sintered ores result in quality variations of the sintered ores depending on the contents of hematite, magnetite, calcium ferrite, slag and pore components. Therefore, quantitative analysis for detecting the contents of hematite, magnetite, calcium ferrite, slag, and pore components of the sintered ores produced to confirm or improve the quality of the sintered ores is required.

In order to quantify the content of the components of the sintered ores, they are usually analyzed through an optical microscope. That is, light is irradiated to the sintered light through an optical microscope, luminance data of light reflected from the sintered light is obtained, and an image image is generated such that light and shade corresponding to the respective luminance values of the components included in the sintered light appear. The area or individual of each of hematite, magnetite, calcium ferrite, slag and pore can be analyzed on the image, and the area for each area can be measured and quantified.

On the other hand, since pores are vacant spaces, they absorb all the light, and when they are displayed as image images, they appear in black.

However, when quantifying the minerals such as hematite, magnetite, and calcium ferrite located in the vicinity of the pore, the outermost region of the pore or the region outside the edge region is a real mineral region, but exhibits a low luminance due to pores. That is, a mineral such as hematite, magnetite, or calcium ferrite is located on the outermost side of the pore to be adjacent to the pore, and an area just outside the outermost pore must be classified as a mineral. However, , Which causes an error to be measured with other components having lower luminance as compared with the mineral component to be analyzed.

Further, as the pore is larger and deeper, the center (or central portion) region of the pore is refracted, and an error is measured which is higher than that of the other regions, resulting in an error measured by the slag.

Another problem is that an epoxy resin which is superimposed on or similar to the slag and the reflected light luminance is mixed at the time of producing the sintered ores. When the epoxy resin is filled in the pores as the empty space, the pores are recognized as slags and errors are caused.

Thus, conventionally, due to the above-mentioned errors, there has been a problem that the components constituting the sintered ores, that is, the component contents of hematite, magnetite, calcium ferrite, slag and pore can not be accurately quantified.

Korean Patent No. 10-0896579

The present invention provides a method for quantifying components of highly reliable sintered ores.

The present invention also provides a method for quantifying sintered ores by using image images, and a method for quantifying components of sintered ores that can reduce the occurrence of analysis errors due to the brightness of each component.

A method of quantifying a component of an sintered ores according to the present invention includes the steps of irradiating light to sintered light, obtaining luminance data of light reflected from the sintered light, and generating an image image so that lightness and darkness corresponding to the respective luminance values of components included in the sintered light appear ; And quantifying the content for each component by calculating an area for each of the light and dark areas on the image image, and quantifying components around the pore included in the sintered light on the image image, Removing a region between a region classified as a pore and a component region intended to be quantified; And the area of the component region to be quantified is calculated and converted into a content value.

Quantifying a component around the pore on the image image, comprising: magnifying the pore and the pore surrounding area on the image image; Removing, on the image image, an area classified by the pore; And removing an outermost edge region of the region classified by the pore.

A method for quantifying sintered ores according to the present invention includes the steps of irradiating light to sintered light, obtaining luminance data of light reflected from the sintered light, and generating an image so that lightness and darkness corresponding to the respective luminance values of the components included in the sintered light appear process; Calculating an area for each of the light and dark areas on the image, and quantifying the content for each component; Wherein in quantifying the pores included in the sintered ores on the image, if it is determined that the inner region of the outermost region is relatively sharper than the other region, And the region having the relatively high contrast is adjusted to have the contrast of the pore.

After quantifying the content of the pores contained in the sintered ores, the content of the slag contained in the sintered ores is quantified.

In quantifying the content of the slag, an area of the area classified as slag on the image image is calculated to quantify the content of the slag, and in an area classified as pores on the image image, Is measured as a luminance value of the slag and is classified into slag, the area classified as slag is measured as the luminance value of the slag inside the outermost part of the area classified by the pore, and then the remaining area The area is calculated.

A method for quantifying sintered ores according to the present invention includes the steps of irradiating light to sintered light, obtaining luminance data of light reflected from the sintered light, and generating an image so that lightness and darkness corresponding to the respective luminance values of the components included in the sintered light appear process; And calculating an area for each of the light and dark areas on the image image, and quantifying the content for each of the components. When the area of one object classified as slag on the image image is equal to or larger than the reference area, it is determined as pore.

In the case where the area of one object classified as slag on the image image is equal to or larger than the reference area and the area of one object classified as slag has an area of 1/8 or more in the image of 200 pixels, .

According to the embodiments of the present invention, the analysis error due to the pores included in the sintered ores can be minimized, and the content analysis error for each component of the sintered ores can be minimized. Further, in the area measurement of the pores, the pores are not cut off on one screen, but are recognized as one entity and measured, so that the pore area can be easily measured and the pore area measurement error can be reduced.

Therefore, the quality state of the produced sintered ores can be determined more accurately than in the past, and the quality of the sintered ores can be improved or improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view showing the configuration of analytical conditions for carrying out a method for quantifying a component of a sample according to an embodiment of the present invention; FIG.
2 is a flowchart showing a method of quantifying a component of a sample according to an embodiment of the present invention
FIG. 3 is a graph showing a photograph represented by an image image using the luminance value of the reflected light by irradiating light to the sintered light
Fig. 4 is a graph showing the relationship between the pore size and the pore size
Fig. 5 is a graph showing the relationship between the amount of pores contained in the sintered ores
6 is a graph showing the relationship between the amount of slag contained in the sintered ores
Figs. 7 and 8 are schematic cross-sectional views of a microscope,
9 is a photograph showing a magnification of 50 magnifications and 200 magnifications in order to measure the area of the pores included in the sintered ores

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be understood, however, that the invention is not limited to the disclosed embodiments, but is capable of other various forms of implementation, and that these embodiments are provided so that this disclosure will be thorough and complete, It is provided to let you know completely.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a schematic configuration of analytical values for carrying out a method for quantifying a component of a sample according to an embodiment of the present invention; FIG. 2 is a flowchart showing a method of quantifying a component of a sample according to an embodiment of the present invention. 3 is a photograph showing an image image using the luminance value of the reflected light by irradiating the sintered light.

The present invention relates to a method for quantitatively analyzing the content of each component contained in a sample, and more particularly, a quantitative method for reducing an analysis error for each component.

First, a method of quantifying a component according to an embodiment of the present invention will be described with reference to Fig. 1, and an analyzing apparatus for performing a method of quantifying a component of the sample of the present invention will be described.

Referring to FIG. 1, the analyzer includes a microscope unit 100 for enlarging a sample while moving a sample placed on a stage 110, an image analyzing unit 100 for analyzing the image obtained by the microscope unit 100, And a computer unit 200 for setting the interval (x or y) between a plurality of measurement points, inputting other drive commands, and integrating the analysis results and outputting them on various screens.

The microscope unit 100 used in the embodiment of the present invention is a polarization microscope equipped with two polarizing lenses, that is, an upper Nicole and a lower Nicole. The lower Nicol passes light through the plane polarized light oscillating in the forward and backward directions, while the upper Nicol passes only the light vibrating in the left and right direction. In this case, it is assumed that the state in which the upper Nicol is operated to be placed on the light path is in the 'quadrature Nicoll' state, and if the upper Nicol is deviated from the light path, the vibration directions of the upper Nicol and the lower Nicol become parallel, 'Parallel Nicole' or 'Open Nicole'.

Further, the microscope section 100 is provided with light measuring means (not shown) for irradiating light of a specific wavelength with the analytical specimen and sensing the amount of light reflected from the analytical specimen. More specifically, the light measuring unit according to the embodiment of the present invention senses the amount of light (reflected light) reflected from the specimen, that is, the brightness, and transmits the sensed amount to the computer unit 200. The computer unit 200 acquires the obtained luminance data, and converts the obtained luminance data into an image image so that lightness and darkness corresponding to the respective luminance values of the components included in the sample are displayed.

On the other hand, the reflected light reflected by irradiating the specimen with light includes information on the brightness or brightness of the component or tissue constituting the specimen. Of the information on the analytical specimen, information indicating the brightness of the analytical specimen tissue is digitized, By subdividing it, it can be displayed as an image image so that light and shade corresponding to the luminance value are displayed. In other words, the brightness from the darkest black to the brightest white can be expressed as a number divided into several stages. For example, in the case of an 8-bit image, the color can be represented by 256 (= ²⁶ ) kinds of contrasting colors, thereby providing color information of the analysis sample organization. Of course, in case of 16bit, 65536 kinds of color information can be provided, and there is no particular limitation on the amount of color information to be provided.

When the analyzer irradiates the analysis specimen with light through the microscope 100, the reflected light is digitized as described above, and the analysis program embedded in the cup computer 200 calculates the amount of reflected light as a brightness value , And color or intensity information ranging from black to white, which is used to provide an image image that is expressed in different shades for each component.

Hereinafter, with reference to FIG. 2, a method of quantifying each component included in a sample by a method according to an embodiment of the present invention will be described. At this time, sintered ores are described as examples of samples to be analyzed and quantified.

Referring to FIG. 2, a method for quantifying the content of each component of a mineral according to an embodiment of the present invention includes a step (S100) of irradiating light to a sintered organd, which is a sample to quantify the content of each component (S100) A step of obtaining brightness data (S200), a step of generating an image image (S300) such that lightness and darkness according to brightness values of the components included in the sample are displayed (S300), a step of classifying each component by dark and light (S400) And calculating and quantifying the content of each component (S500).

First, the sintered ores, which are samples to be analyzed, will be described in more detail.

The sintered ores used as raw materials in the blast furnace are mainly composed of hematite, magnetite, calcium ferrite, slag and pore. Such sintered ores result in quality variations of the sintered ores depending on the contents of hematite, magnetite, calcium ferrite, slag and pore components. Therefore, quantitative analysis for detecting the contents of hematite, magnetite, calcium ferrite, slag, and pore components of the sintered ores produced to confirm or improve the quality of the sintered ores is required. To this end, in the present invention, the content of each component (hematite, magnetite, calcium ferrite, slag, and pore) is quantified by using the luminance of light (reflected light) reflected by irradiating the sintered light with light.

As described above, the sintered ores are composed mainly of hematite (H), magnetite (M), calcium ferrite (CF), slag (S) and pore (P), and the respective components (hematite, magnetite, calcium ferrite, And porosity) have different structures.

When the sintered light is irradiated with light (S100), each component absorbs and reflects light differently. At this time, the light measuring means obtains the amount of light reflected from the sintered organs, that is, luminance data (S200) The brightness of the reflected light from the light source is different. In the case of sintered ores, the magnitude of the luminance of the reflected light is in the order of hematite (H)> magnetite (M)> calcium ferrite (CF)> slag (S)> pore.

The computer unit 200 converts the luminance data provided from the light measuring unit into image images represented by different business cards according to the luminance of each component (S300). For this purpose, the computer unit 200 stores reference brightness values for hematite, magnetite, calcium ferrite, slag, and pores, respectively. The reference luminance value is set so that the hematite is in the order of hematite (H)> magnetite (M)> calcium ferrite (CF)> slag (S)> pore (P). For example, when the reference luminance value (first reference luminance value) is 200 to 255 cd / m ² , the reference luminance value (second reference luminance value) of magnetite is 171 to ²⁰⁰ cd / dm ² , 3 standard brightness value) of 91 to 170 cd / dm ² , a slag reference brightness value (fourth reference brightness value) of 50 to 90 cd / dm ² , a pore reference brightness value (fifth reference brightness value) of 0 to 50 cd / dm ² < / RTI >

The actual luminance data provided from the light measuring means is compared with the first to fifth reference luminance values as described above to determine which of the first to fifth reference luminance values is included in the reference luminance value range. Thereafter, it is imaged to have different contrasts according to the first to fifth reference luminance values, for example, divided into first to fifth contrast values. Here, the first to fifth brightness values can be divided into achromatic colors, and black and white contrasts (see FIG. 3A). In this case, the first lightness value corresponding to the first reference lightness value is, for example, black, and the fifth lightness value corresponding to the fifth reference lightness value is, for example, white. The second, third, and fourth contrast values according to the second, third, and fourth reference luminance values may be a color having a contrast between black and white, for example, a gray system, The third contrast value is larger than the second contrast value, and the fourth contrast value is larger than the third contrast value.

In addition, the first to fifth reference luminance values may be represented by a chromatic color system, and each reference luminance value may be displayed so as to show different chromatic colors (FIG. 3B).

For example, when the luminance of a certain region is included in the first reference luminance value range, entities represented by black, which is the darkest darkest color on the image, and black on the image are determined as pores.

Then, the brightness of the light reflected from the other area is compared with the first to fifth reference brightness values as described above, and the brightness is imaged with the brightness corresponding to the reference brightness value. (H), magnetite (M), calcium ferrite (CF), slag (S), pore (P), and so on are classified into 5 images by using the obtained luminance values. (S400).

The luminance obtained by irradiating light to one region of the sintered ores is image-imaged by the above-described method and displayed on a screen of, for example, 200 magnifications, for example, as shown in FIG. 3A, hematite (H), magnetite (M), calcium ferrite (CF), slag (S) and pores (P) are all included on an image displayed on one screen. As described above, such an image image can be expressed by varying the contrast depending on the brightness of the light reflected from the respective components and imaging it. According to FIG. 3A, halftone (H), magnetite (M), calcium slag (CF), slag (S) and pore (P) are classified in the achromatic series in descending order of light and shade.

In FIG. 3A, the image image expressed by varying the contrast in the achromatic series can be represented by different chromatic colors for each light and dark of each component as shown in FIG. 3B. For example, one individual of hematite (H), magnetite (M), calcium slag (CF), slag (S) and pore (P) can be converted into chromatic colors such as yellow, blue, red and green. This makes it easy to discriminate each component, and it is easy to calculate the area of each region classified into the respective components.

FIG. 4 is an image image showing pores and the periphery of the pores by magnifying through a microscope to quantify the content of each component of the sintered ores. 5 is an image image enlarged and shown through a microscope to quantify the pores contained in the sintered ores. 6 is an image image enlarged and shown through a microscope to quantify the slag contained in the sintered ores. Figs. 7 and 8 are image images enlarged and shown through a microscope to quantify the pores contained in the sintered ores. Fig. 9 is a photograph showing an enlarged image at a magnification of 50 and a magnification of 200 to measure the area of the pores included in the sintered ores.

Hereinafter, with reference to FIGS. 4 to 9, a method for quantifying the component content of a sample by a method according to an embodiment of the present invention will be described in detail.

First, referring to FIG. 4, a description will be given of a method for reducing errors due to pores P in quantifying the content of mineral components such as hematite (H), magnetite (M), or calcium ferrite (CF).

Since the pores P are voids, the level of the pores is low, and the amount of reflected light is extremely small. When the images are image-formed, the darkness P is lower than the other components as shown in FIGS. 4A, 4B, It is expressed in color. Thus, when a mineral such as hematite, magnetite, or calcium ferrite is located around the pore P, the outermost region A of the pore P or the outer region A of the edge region is a real mineral region, ). ≪ / RTI > That is, a mineral such as hematite, magnetite, or a calcium ferrite component is located outside the outermost periphery so as to be adjacent to the pore P, and the region A immediately outermost from the outermost pore P should be classified as a mineral, As described above, due to the pores P, a low luminance value is obtained, which causes an error to be measured with other components having low luminance as compared with the mineral component to be analyzed.

Therefore, in quantifying the components around the pores P included in the sintered light on the image of the present invention, it is necessary to remove the region between the region classified by the pore P and the component region to be quantified, Area is calculated and converted into a content value. 4A, when a mineral such as hematite, magnetite, or calcium ferrite is located around the pore P, the pore P and the mineral region around the pore P are selected to be included as shown in FIG. 4B , The selected area is enlarged as shown in Fig. 4C. On the image image, the region P classified as pores is removed, and a region having a lower brightness, that is, the outermost pore outer region A, as compared with the mineral to be quantified in the outer region of the outermost pore P After the removal, the area of the area classified as the component to be quantified which is the remaining part is calculated and converted into the content value.

Referring to Fig. 5, a method of reducing the error in the measurement of the porosity will be described.

In the case of pores, since the pores are larger and deeper, the center (or central portion) region C of the pores is refracted as shown in FIG. 5A, and an error is measured in which the luminance value is higher than the other regions. In most cases, the center (or central portion) region C of the pores P, which are measured to have a higher luminance value than the other regions, is measured at a higher luminance and appears as a darker color than the pores on the image image .

Accordingly, in the present invention, in at least one object classified into pores (P) on the image image, the outermost inner region of the pores (P) has a region (C) in which at least a portion exhibits a relatively high contrast, , The region C having a relatively high contrast is adjusted to have a contrast of the pore P (see FIG. 5C). For this purpose, when a fillhole, which is one of the functions of a polarizing optical microscope, is applied, a region (C) having a relatively high contrast within the outermost periphery of the pores (P) The lightness and darkness are reduced. When the chromatic color is represented by a chromatic color, a region classified as a pore P is expressed in the same color (for example, blue) as shown in FIG. 5C

Accordingly, even when a large and deep pore is used, by applying the above-described process, it is possible to prevent or reduce an error, which is measured by slag having at least a portion of the inside of the pore having one step higher luminance or shade.

As described above, after quantitating the porosity first, the slag is quantified. For this purpose, the brightness of the reflected light is measured by irradiating the sintered light with light, and is represented by an image image, for example, as shown in FIG. 6A. The luminance range of the slag to be measured is selected to be classified into a chromatic color, for example, blue, as shown in FIG. 6C.

However, in the case of a large or deep pore, as described above, the center or center (or central region) region C has a lower luminance value than the other region, and an error recognized as slag is generated as shown in FIG. 5B .

The region (C) recognized as slag in the pore inner region is already included in the pore calculation in the previous step of porosity quantification. Therefore, in the slag quantification process, the area C is removed, and the area of the area selected as the slag area S is calculated to calculate the content of the slag.

Referring to Figs. 7 and 8, a description will be given of a method for minimizing an error recognized by pores as slags in quantifying slag.

Since the pores P are vacant spaces, they absorb all the light, and when they are displayed as image images, they appear as black (P in FIG. 4A). On the other hand, the reflection luminance range of the epoxy resin used for mixing with the slag, which is one of the constituents of the sintered ores, is similar or overlapped. Thus, when the voids of the pores P1 are filled with the epoxy resin, the P1 region shows gray, which shows a level of contrast similar to that of slag. Therefore, if the luminous flux is simply classified according to the conventional method, an error occurs in which pores filled with epoxy, that is, the P1 region is measured by slag.

Accordingly, in the embodiment of the present invention, when the area of one object selected as slag (FIG. 7 and FIG. 8A) in the slag quantification process occupies 1/8 or more of the area of the screen of 200 magnification, (See Figs. 8A and 8B). Therefore, it is possible to reduce the error that the pores filled with the epoxy resin are measured by the slag.

On the other hand, when each component structure of the sintered ores is quantified, the final component content of each component is expressed as a percentage. Therefore, if the pores having a large area are filled with epoxy resin and the error measured by the slag can be reduced, the slag quantification error can be reduced as compared with the conventional method.

9 is an image image for explaining a method of measuring the size of pores by the method according to the embodiment of the present invention.

Basically, the magnification of the microscope used for the quantification of the texture of the sintered orbital component is 200 magnifications. However, when measuring at a magnification of 200 at the pore size, most of the pores do not enter the screen and are cut off (Fig. 9B).

In the case of measuring the porosity, even if a part of the pores is well seen on one screen of 200 magnification, it is not a problem since the pores are finally summed and quantified. However, since the size of the pores in the sintered ores is closely related to the reducing property, a comparative analysis according to the size of the pores is required. However, as described above, since a part of the pores are cut on a screen having a magnification of 200 (FIG. 9B), when measuring at a magnification of 200, most of the pores are cut off and an error that can not be recognized as one entity is generated.

Therefore, in the embodiment of the present invention, the microscopic magnification of 50 magnifications is used as shown in FIG. 9A to measure the size of the pores so that the pores are recognized as one entity without being cut off on one screen.

100: microscope part 200: computer part

Claims (7)

A step of irradiating the sintered light with light and obtaining luminance data of the light reflected from the sintered light to generate an image image so as to be classified into light and dark according to the luminance values of the minerals, pores and slag components included in the sintered light;
Calculating an area for each of the light and shade on the image, and quantifying the contents of the mineral, pore, and slag components;
/ RTI >
In quantifying the content of each of the pore periphery, pore, and slag components,
And a process of removing a part of the image on the image according to the component to be quantified, adjusting the contrast or converting the kind of the component according to the area,
In quantifying the components around the pores contained in the sintered ores on the image,
Removing an area between the area classified as the pore and the component area to be quantified on the image image; And
Calculating an area of a component region to be quantified, and converting the calculated area into a content value. The method according to claim 1,
In quantifying the component around the pore on the image image,
Enlarging the pore and the pore peripheral region on the image image;
Removing, on the image image, an area classified by the pore; And
Removing an outermost edge region of the region classified by the pore;
/ RTI > of claim < RTI ID = 0.0 > A step of irradiating the sintered light with light and obtaining luminance data of the light reflected from the sintered light to generate an image image so as to be classified into light and dark according to the luminance values of the minerals, pores and slag components included in the sintered light;
Calculating an area for each of the light and shade on the image, and quantifying the contents of the mineral, pore, and slag components;
/ RTI >
In quantifying the content of each of the pore periphery, pore, and slag components,
And a process of removing a part of the image on the image according to the component to be quantified, adjusting the contrast or converting the kind of the component according to the area,
In quantifying the pores contained in the sintered ores on the image,
In an individual classified into the pores, when it is determined that the inner region of the outermost region is relatively sharper than the other region, the composition of the sintered ores Quantification method. The method of claim 3,
And quantifying the content of the slag contained in the sintered ores after quantifying the content of the pores contained in the sintered ores. The method of claim 4,
In quantifying the content of the slag,
Calculating an area of a region classified as slag on the image image, quantifying the content of the slag,
In the region classified as pores on the image image, when the outermost inner region is measured as the luminance value of the slag and classified as slag,
And calculating the area of the remaining region classified by the slag after removing the region classified as slag by measuring the luminance value of the slag inside the outermost periphery of the region classified by the pore. A step of irradiating the sintered light with light and obtaining luminance data of the light reflected from the sintered light to generate an image image so as to be classified into light and dark according to the luminance values of the minerals, pores and slag components included in the sintered light;
Calculating an area for each of the light and shade on the image, and quantifying the contents of the mineral, pore, and slag components;
/ RTI >
In quantifying the content of each of the pore periphery, pore, and slag components,
And a process of removing a part of the image on the image according to the component to be quantified, adjusting the contrast or converting the kind of the component according to the area,
And determining an area of an object classified as slag on the image image as a pore when the area of the object is larger than a reference area. The method of claim 6,
Wherein when the area of one object classified as slag on the image image is equal to or larger than a reference area,
A method for quantifying a component of an ore that is judged as pores when an area of an individual classified as slag has an area of 1/8 or more in an image of 200 magnification.

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