Patent Publication Number: US-2023141957-A1

Title: Optical inspection device and inspecting method using the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2021-0152481, filed in the Korean Intellectual Property Office on Nov. 8, 2021, the entire content of which is incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     Aspects of embodiments of the present disclosure relate to an optical inspection apparatus and an inspection method using the same. 
     2. Description of the Related Art 
     An electronic device, such as a display device, includes a substrate and several films stacked on the substrate. After forming the films, an inspection step for the films is performed to determine whether foreign material is present, whether there is a defect in the films, whether there is a residual film that has not been removed, and the like by using an image acquired after imaging a target object to be inspected by using an optical camera. 
     The above information disclosed in this Background section is for enhancement of understanding of the background of the present disclosure, and therefore, it may contain information that does not form prior art that is already known to a person of ordinary skill in the art. 
     SUMMARY 
     Embodiments of the present disclosure provide accurate and easy inspection for foreign material presence, defects, or a residual film of a transparent film or an opaque film included in an electronic device, such as a display device. 
     An embodiment of the present disclosure provides an optical inspection device including: a barrel; a first light source unit at a first side of the barrel and configured to irradiate light of a first wavelength range through a first light path; a second light source unit at a second side of the barrel, the second side being different from the first side, and configured to irradiate light of a second wavelength range that is different from the first wavelength range through a second light path; and a camera. At least a portion of the first light path is different from the second light path. 
     The first light source unit may be configured to emit ultraviolet or infrared light, and the second light source unit may be configured to emit light of a visible range. 
     The second light source unit may include a white light source and a color selector between the white light source and the barrel, and the color selector may include a plurality of color filters. 
     The color selector may further include a rotatable turntable, and the color filters may be at an edge of the turntable. 
     The color filters may include a white filter and a plurality of color filters. 
     The optical inspection device may further include a driver configured to select one of the color filters and align it with the second light path according to a color or transparency of a target to be inspected. 
     The color filters may include a plurality of color filters having a complementary color relationship with each other. 
     The optical inspection device may further include an image processing unit configured to receive an image captured by the camera and to process the image to extract an image of a target to be inspected. 
     The image processing may include binarization processing. 
     Another embodiment of the present disclosure provides an optical inspection device including: a first light source unit configured to irradiate ultraviolet or infrared light through a first light path; a second light source unit configured to irradiate visible light through a second light path; and a camera configured to capture an image of a target object irradiated with light from the first light source unit or the second light source unit. At least a portion of the first light path is different from the second light path. 
     The second light source unit may include a white light source and a color selector including a plurality of color filters. 
     The color selector may further include a turntable configured to rotate the color filters. 
     The color filters may include a plurality of color filters having a complementary color relationship with each other. 
     Another embodiment of the present disclosure includes an inspection method using an optical inspection device. The optical inspection device includes a first light source unit and a second light source unit configured to irradiate light of different wavelength ranges, and the method includes: selecting the first light source unit or the second light source unit according to transparency or a color of a target object to be inspected; and capturing an image of the target object to be inspected by irradiating light from the selected one of the first light source unit or the second light source unit to the target object. 
     The first light source unit may be configured to irradiate ultraviolet or infrared light, the selecting the first light source unit or the second light source unit may include selecting the first light source unit when the target object to be inspected is a transparent film, and the captured image of the target object may include a fringe area corresponding to the target object to be inspected. 
     The inspection method may further include processing the captured image of the target object to be inspected to extract the fringe area. 
     The second light source unit may be configured to irradiate visible light, the selecting the first light source unit or the second light source unit may include selecting the second light source unit when the target object to be inspected is a colored film or an opaque film, and the second light source unit may include a white light source and a color selector including a plurality of color filters. 
     The inspection method may further include processing the captured image of the target object to be inspected to extract an image in which a deviation from surroundings of the image of the target object to be inspected is increased. 
     The capturing of the image of the target object may include irradiating visible light of a first color and a second color in a complementary color relationship with the first color to generate a first image and a second image having different luminance for an image of the target object to be inspected. 
     The inspection method of claim  19  may further include: processing the first image and the second image; and extracting an image in which cleanness of the image of the target object to be inspected is increased by merging luminance intensities of the processed first image and the processed second image. 
     According to embodiment of the present disclosure, an accurate and easy inspection for foreign material presence, a defect, or a residual film of a transparent film or an opaque film included in an electronic device, such as a display device, is provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates an optical inspection device according to an embodiment, 
         FIG.  2    illustrates a top plan view of a color selection unit included in an optical inspection device according to an embodiment, 
         FIG.  3    illustrates an image captured by an optical inspection device according to an embodiment, 
         FIG.  4    illustrates an image obtained by extracting a fringe area from the image of  FIG.  3   , 
         FIGS.  5  and  6    illustrate images captured by an optical inspection device according to an embodiment, 
         FIG.  7    illustrates an image obtained by processing the image of  FIG.  5    or  FIG.  6   , 
         FIG.  8    illustrates an image captured by an optical inspection device according to an embodiment, 
         FIG.  9    illustrates an image obtained by processing the image of  FIG.  8   , 
         FIG.  10    illustrates an image captured by an optical inspection device according to an embodiment, 
         FIG.  11    illustrates an image obtained by processing the image of  FIG.  10   , 
         FIG.  12    is a graph showing luminance of the image of  FIG.  9   , 
         FIG.  13    is a graph showing luminance of the image of  FIG.  11   , 
         FIG.  14    is a graph obtained by merging luminance intensity of the graph of  FIG.  12    and the graph of  FIG.  13   , 
         FIG.  15    is a graph obtained by removing noise from the graph of  FIG.  14   , and 
         FIG.  16    illustrates an image extracted according to the graph of  FIG.  15   . 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the present disclosure are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present disclosure. 
     To clearly describe the present disclosure, aspects, features, and parts that are irrelevant to the description may be omitted, and like numerals refer to like or similar constituent elements throughout the specification. 
     Further, because sizes and thicknesses of constituent members shown in the accompanying drawings are arbitrarily given for better understanding and ease of description, the present disclosure is not limited to the illustrated sizes and thicknesses. For example, in the drawings, the thicknesses of layers, films, panels, regions, etc., may be exaggerated for clarity. 
     The terminology used herein is for the purpose of describing embodiments of the present disclosure and is not intended to be limiting of the present disclosure. As used herein, the singular forms “a” and “an” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be understood that when an element, such as a layer, film, region, or substrate, is referred to as being “on,” “connected to,” or “coupled to” another element, it can be directly on, connected to, or coupled to the other element or intervening elements may also be present. When an element is referred to as being “directly on,” “directly connected to,” or “directly coupled to” another element, there are no intervening elements present. Further, in the specification, the word “on” or “above” can indicate an elements position on or below the object portion and does not necessarily mean positioned on the upper side of the object portion based on a gravitational direction. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” or “over” the other elements or features. Thus, the term “below” may encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations), and the spatially relative descriptors used herein should be interpreted accordingly. 
     In addition, unless explicitly described to the contrary, the words “have,” “include,” and “comprise,” and variations such as “has,” “having,” “includes,” “including,” “comprises,” or “comprising” will be understood to imply the inclusion of stated elements but not the exclusion of any other elements. 
     Further, in the specification, the phrase “in a plan view” means when an object portion is viewed from above, and the phrase “in a cross-sectional view” means when a cross-section taken by vertically cutting an object portion is viewed from the side. 
     As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Further, the use of “may” when describing embodiments of the present disclosure relates to “one or more embodiments of the present disclosure.” Expressions, such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. As used herein, the terms “use,” “using,” and “used” may be considered synonymous with the terms “utilize,” “utilizing,” and “utilized,” respectively. As used herein, the terms “substantially,” “about,” and similar terms are used as terms of approximation and not as terms of degree, and are intended to account for the inherent variations in measured or calculated values that would be recognized by those of ordinary skill in the art. 
     It will be understood that, although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers, and/or sections, these elements, components, regions, layers, and/or sections should not be limited by these terms. These terms are used to distinguish one element, component, region, layer, or section from another element, component, region, layer, or section. Thus, a first element, component, region, layer, or section discussed below could be termed a second element, component, region, layer, or section without departing from the teachings of example embodiments. 
     An optical inspection device according to an embodiment will be described with reference to  FIG.  1    and  FIG.  2   . 
       FIG.  1    illustrates an optical inspection device according to an embodiment, and  FIG.  2    illustrates a top plan view of a color selection unit included in an optical inspection apparatus according to an embodiment. 
     Referring to  FIG.  1   , an optical inspection device  500  according to an embodiment, which is an optical inspection device for inspecting various films formed in a manufacturing process of an electronic device, such as a display device, may inspect for presence (e.g., foreign object presence), a defect, and/or a residual film (e.g., a residual transparent or opaque film). 
     The optical inspection device  500  may include a first light source unit  510 , a second light source unit  520 , a barrel  540 , a camera  550 , and an optical unit  560 . 
     The first light source unit  510  and the second light source unit  520  may irradiate light of different wavelength ranges to a target object  100  to be inspected. 
     The first light source unit  510  may irradiate light in a wavelength range other than visible light. For example, the first light source unit  510  may irradiate ultraviolet light or infrared light to the target object  100  through a first optical path OP 1 . A width of a wavelength band of light irradiated from the first light source unit  510  may be about 300 nm or less, but the present disclosure is not limited thereto. 
     The second light source unit  520  may emit light in a visible range. For example, the second light source unit  520  may irradiate monochromatic light (e.g., a specific monochromatic light), such as white, red, green, or blue light to the target object  100  through a second optical path OP 2 . 
     The barrel  540  includes a space through which light irradiated from the first light source unit  510 , light irradiated from the second light source unit  520 , and/or light from the target object  100  passes. For example, the barrel  540  includes a space extending in a z direction inside so that the first optical path OP 1  of the light irradiated from the first light source unit  510 , the second optical path OP 2  of the light irradiated from the second light source unit  520 , or an optical path OB of the light from the target object  100  may pass in approximately the z direction. 
     The optical unit  560  may be positioned between the barrel  540  and the target object  100 . The first light path OP 1  of the first light source unit  510 , the second light path OP 2  of the second light source unit  520 , and/or the light path OB of light from the target object  100  may pass through the optical unit  560 . The optical unit  560  may include at least one optical member configured to control an optical path of the light irradiated from the first light source unit  510 , the light irradiated from the second light source unit  520 , and/or the light from the target object  100 . For example, the optical unit  560  may include at least one lens. 
     The first light source unit  510  may be positioned on a first side surface of the barrel  540 . A transparent portion (or a first light-transmitting portion)  541 , in the form of an opening through which light from the first light source unit  510  can pass, may be positioned on a first side surface of the barrel  540  adjacent to the first light source unit  510 . The barrel  540  may include at least one mirror positioned in the first light path OP 1  such that the first optical path OP 1 , through which light from the first light source unit  510  may be irradiated to the target object  100  positioned below the optical unit  560 , may be formed. 
     The second light source unit  520  may be positioned on a second side surface of the barrel  540 . A transparent portion (or a second light-transmitting portion)  542  in the form of an opening through which light from the second light source unit  520  can pass may be positioned on a second side surface of the barrel  540  adjacent to the second light source unit  520 . The barrel  540  may include at least one mirror positioned in the second light path OP 2  such that the second optical path OP 2 , through which light from the second light source unit  520  may be irradiated to the target object  100  positioned below the optical unit  560 , may be formed. 
     The second light source unit  520  may include a white light source  521  and a color selector  522 . The color selector  522  may be positioned between the barrel  540  and the white light source  521 . 
     The color selector  522  may pass the white light from the white light source  521  as it is or may filter it into a specific monochromatic light and pass it toward the barrel  540 . 
     Referring to  FIG.  2   , the color selector  522  may include, for example, a turntable  531  configured to rotate on an yz plane about a center CE and a plurality of color filters  532 ,  533 , . . . , and  539  positioned at an edge of the turntable  531 . 
     The color filters  532 ,  533 , . . . , and  539  may be positioned at a same distance (e.g., equidistant) from the center CE and may be arranged in a substantially circular shape. 
     The color filters  532 ,  533 , . . . , and  539  include a white filter  532  that can pass white light from the white light source  521  as it is (e.g., without modification or filtering), and color filters  533 , . . . , and  539  of red, green, and blue that can filter and pass light of specific colors. 
     Referring to  FIG.  1   , the color selector  522  may further include a driver  523  configured to rotate a plurality of color filters  532 ,  533 , . . . , and  539  with respect to the center CE. The color filters  532 ,  533 , . . . , and  539  selected by the driver  523  may be arranged on the second light-transmitting portion  542  of the barrel  540 , for example, the second light path OP 2 . Accordingly, the white light from the white light source  521  may pass through the color filters  532 ,  533 , . . . , and  539  arranged in the second light-transmitting portion  542  and may travel along the second optical path OP 2  to be irradiated to the target object  100  to be inspected. 
     The color filters  532 ,  533 , . . . , and  539  may include two or more color filters having a complementary color relationship with each other. 
     The color filters  532 ,  533 , . . . ,  539  may be modified with filters of different colors according to different embodiments. 
     The optical inspection device  500  according to an embodiment may select only one of the first light source unit  510  and the second light source unit  520  to irradiate light to the target object  100  when capturing an image of the target object  100 . That is, light may be irradiated to the target object  100  using only one of the first optical path OP 1  and the second optical path OP 2 . 
     The camera  550  may be a camera including a photosensor, such as a charge-coupled device, but the present disclosure is not limited thereto. 
     The target object  100  is an electronic device, such as a display panel or a part thereof, in a manufacturing process and may include a film or layer to be inspected. 
     The optical inspection device  500  according to an embodiment may further include an image processing unit (e.g., an image processor)  600 . The image processing unit  600  may be connected to the camera  550  to receive image information of the target object  100 . 
     The image processing unit  600  may extract an image of a target to be inspected from an image of the target object  100  captured by the camera  550  so as to be seen clearly. For example, the image processing unit  600  may extract an image of the target to be inspected by processing the image of the target to be inspected, such as a specific film or layer to make it stand out through binarization. Accordingly, the target to be inspected can be accurately and easily inspected by increasing visibility of only the image of the target to be inspected in the captured image including a background. 
     The binarization process may include, for example, a process in which wavelengths that are less than a wavelength of one specific color (e.g., a reference wavelength) are expressed as one type of color, and wavelengths above the wavelength (e.g., the reference wavelength) are expressed as a type of color that is different from the type of color. For example, one color may be black and the other may be white, or vice versa. 
     The first light source unit  510  may be used when a target to be inspected, such as a film to be inspected of the target object  100 , is a transparent film. A fringe phenomenon caused by interference may be well expressed by irradiating light from the first light source unit  510  to the transparent film, and an image of the target to be inspected may be extracted by extracting a fringe region through image processing by the image processing unit  600 . Herein, the transparent film may be a colorless transparent film, but the present disclosure is not limited thereto. 
     The second light source unit  520  may be used when a target to be inspected, such as a film to be inspected in the target object  100 , is a colored film or an opaque film. The image of the film to be inspected may appear clearer by a difference in reflectance or absorption of light of the target to be inspected compared to surroundings depending on a condition of the colored film or the opaque film to be inspected and a wavelength of light irradiated from the second light source unit  520 . The image of the target to be inspected may be clearly extracted by further increasing (or maximizing) a deviation thereof through image processing by the image processing unit  600 . 
     An inspection method using an optical inspection device according to an embodiment will be described with reference to  FIG.  3    to  FIG.  7    together with  FIG.  1    and  FIG.  2    described above. 
       FIG.  3    is an image captured by an optical inspection device according to an embodiment, and  FIG.  4    is an image obtained by extracting a fringe area from the image of  FIG.  3   . 
     When the target to be inspected in the target object  100  is a transparent film, the first light source unit  510  of the optical inspection device  500  is selected to irradiate the target object  100  with ultraviolet or infrared light through the first optical path OP 1  to the target object  100 . 
     Then, an image including a fringe area FA 1  corresponding to the target to be inspected may be captured by the camera  550  as illustrated in  FIG.  3    due to the occurrence of light interference in the target film to be inspected. A vicinity of the target to be inspected, that is, the background, may be a background area BA 1  without a fringe image. 
     The captured image illustrated in  FIG.  3    is transferred to the image processing unit  600 , and the image processing unit  600  extracts the fringe area FA 1 , which is an image to be inspected, through image processing, such as binarization processing. 
     As a result, a fringe area FA 2  may be clearly processed compared to a background area BA 2  processed illustrated in  FIG.  4   , thereby extracting an image of the target to be inspected with high visibility. It is possible to accurately and easily inspect foreign material presence, a defect, and/or a residual film of a film to be inspected through inspection of the extracted image, that is, the extracted fringe area FA 2 . 
       FIGS.  5  and  6    are images captured by an optical inspection device according to an embodiment, and  FIG.  7    is an image obtained by processing the image of  FIG.  5    or  FIG.  6   . 
     When the target to be inspected in the target object  100  is a colored film or an opaque film, the second light source unit  520  of the optical inspection device  500  is selected to irradiate the target object  100  with white or monochromatic visible light through the second optical path OP 2 . In this case, the color selector  522  may select a wavelength of an irradiated color by aligning a white (or other specific color) filter to a position of the second optical path OP 2 . 
     A color of the second light source unit  520  to be irradiated may be selected depending on a color of the colored film or transparency of the opaque film to be inspected. In this case, an image of the film to be inspected may be displayed more clearly due to a difference in reflectivity or absorbance of the film to be inspected to the irradiated light compared to a surrounding area of the film to be inspected. 
       FIG.  5    illustrates an image WA captured by selecting one color filter by the color selector  522 , and  FIG.  6    illustrates an image CA captured by selecting another color filter by the color selector  522 . For example,  FIG.  5    illustrates an image WA captured by selecting the white filter  532  by the color selector  522 , and  FIG.  6    illustrates an image CA obtained by selecting a color filter  533 , . . . , and  539  other than the white filter  532  by the color selector  522 . 
     Images WAa and CAa of each target object that is clearer or that has high visibility may be selected by comparing the two captured images WA and CA. The selected image WAa or CAa may be sent to the image processing unit  600  for image processing. 
     The image processing unit  600  may further increase the visibility of the image of the target to be inspected by further increasing (or maximizing) the deviation for a remaining surrounding area of the image WAa or CAa of the target to be inspected through image processing such as binarization. 
     Accordingly, as shown in  FIG.  7   , it is possible to extract an extracted image BPA including a clear image BPAa of the target to be inspected. It is possible to accurately and easily inspect foreign material presence, a defect, and/or a residual film of a film to be inspected through inspection of the image BPAa of the target of the extracted image BPA. 
     An inspection method using an optical inspection device according to an embodiment will be described with reference to  FIG.  8    to  FIG.  16    together with the drawings previously described. 
       FIG.  8    is an image captured by an optical inspection device according to an embodiment,  FIG.  9    is an image obtained by processing the image of  FIG.  8   ,  FIG.  10    is an image captured by an optical inspection device according to an embodiment, and  FIG.  11    is an image obtained by processing the image of  FIG.  10   . 
     The inspection method according to the present embodiment is similar to the inspection method of the embodiment described with respect to  FIGS.  5  to  7   , but two or more images irradiated with visible light of two or more colors for a same target to be inspected are captured and processed. Herein, the two or more colors may include two colors having, for example, a complementary color relationship to increase (or maximize) a deviation of the image of the target to be inspected. 
     When the target to be inspected in the target object  100  is a colored film or an opaque film, the second light source unit  520  of the optical inspection device  500  is selected to irradiate the target object  100  with visible light of a first single color through the second optical path OP 2 . In this case, the color selector  522  may select a wavelength of an irradiated color by aligning a color filter of the first color to a position of the second optical path OP 2 . 
     The first color may be, for example, a color of a wavelength having highest reflectivity of the visible light of the first color with respect to the film to be inspected in the target object  100 . 
     For example,  FIG.  8    is an image CA 1  captured by selecting a yellow color filter by the color selector  522 . An image CAa 1  of the target to be inspected in  FIG.  8    has higher luminance than its surroundings, which is due to the visible light of the high reflectivity of the first color (yellow) with respect to the film to be inspected. 
     Next, the image processing unit  600  further increases (or maximizes) the deviation of the remaining area of the image CAa 1  of the target to be inspected through image processing, such as binarization processing of the captured image CA 1 .  FIG.  9    is an image BPA 1  processed by binarizing the image CA 1  of  FIG.  8   . In the processed image BPA 1 , the image BPAa 1  of the target to be inspected has higher luminance and is more clearly visible compared to a surrounding background. 
     Next, the second light source unit  520  of the optical inspection device  500  is selected to irradiate the target object  100  with visible light of a second single color through the second optical path OP 2 . In this case, the color selector  522  may select a wavelength of an irradiated color by aligning a color filter of the second color to a position of the second optical path OP 2 . 
     The second color may be, for example, a color of a wavelength having highest absorption of the visible light of the second color with respect to the film to be inspected in the target object  100 . 
     For example,  FIG.  10    is an image CA 2  captured by selecting an indigo color filter, which is a complementary color of yellow, by the color selector  522 . An image CAa 2  of the target to be inspected in  FIG.  10    has lower luminance than its surroundings, which is due to the visible light of the high absorption of the second color, (indigo) with respect to the film to be inspected. 
     Next, the image processing unit  600  further increases (or maximizes) the deviation of the remaining area of the image CAa 2  of the target to be inspected through image processing, such as binarization processing for the captured image CA 2 .  FIG.  11    is an image BPA 2  processed by binarizing the image CA 2  of  FIG.  10   . 
     In the processed image BPA 2 , the image BPAa 2  of the target to be inspected has lower luminance and is more clearly visible compared to a surrounding background. 
     A difference in luminance of the corresponding area is maximized in the images BPA 1  and BPA 2 , obtained by irradiating the visible light of the first color and the second color in the complementary color relationship. For example, a difference in the luminance of the images BPAa 1  and BPAa 2  to be inspected in the processed images BPA 1  and BPA 2  is increased (or maximized) so that one is relatively bright and the other is relatively dark. 
     As such, it is possible to improve (or maximize) cleanness of the target object by merging luminance intensities of the images BPAa 1  and BPAa 2  of the target to be inspected with a maximum deviation. This will be described with reference to  FIGS.  12  to  16    together with  FIGS.  8  to  11   . 
       FIG.  12    is a graph showing luminance of the image of  FIG.  9   ,  FIG.  13    is a graph showing luminance of the image of  FIG.  11   ,  FIG.  14    is a graph obtained by merging luminance intensity of the graph of  FIG.  12    and the graph of  FIG.  13   ,  FIG.  15    is a graph obtained by removing noise from a graph of  FIG.  14   , and  FIG.  16    is an image extracted according to the graph of  FIG.  15   . 
       FIG.  12    is a graph GA 1  showing luminance of the processed image BPA 1  of  FIG.  9   , which has a peak PK 1  corresponding to the image BPAa 1  of the target to be inspected.  FIG.  13    is a graph GA 2  showing luminance of the processed image BPA 2  of  FIG.  11   , which has a peak PK 2  corresponding to the image BPAa 2  of the target to be inspected. 
     A graph GA 3  of  FIG.  14    is a graph showing the intensities of the graph GA 1  of  FIG.  12    and the graph GA 2  of  FIG.  13    to maximize the deviation in the luminance of the image of the target to be inspected from the surroundings. In this case, the graph GA 2  of  FIG.  13    is inverted to be positive and then merged with the graph GA 1  of  FIG.  12   . Accordingly, as shown in  FIG.  14   , a peak PK 3  may be obtained by merging the intensities of the peaks PK 1  and PK 2  of the two graphs GA 1  and GA 2 . 
     Next, as shown in  FIG.  15   , a graph GA 4 , in which a peak PK 4  corresponding to the target to be inspected is more clearly displayed, may be obtained by removing unnecessary noise from the graph GA 3  of  FIG.  14   . 
     The image processing illustrated in  FIGS.  12  to  15    may be performed by the image processing unit  600 .  FIG.  16    is an example of an extracted image FBPA including an image FBPAa of the target to be inspected corresponding to the graph GA 4  obtained through such image processing. 
     The image FBPAa of the extracted image FBPA of  FIG.  16    is sharper because the luminance deviation from the background is further improved (or maximized) compared to the image BPAa of the target to be inspected in the extracted image BPA of  FIG.  7   , described above. Accordingly, even when the film to be inspected does not have a large color difference from its surroundings, a clearer image of the target to be inspected may be extracted through processing of two or more images obtained by irradiating visible light of two or more colors. Accordingly, it is possible to accurately and easily inspect foreign material presence, a defect, and/or a residual film of the film to be inspected. 
     According to the present embodiment, the first light source unit  510  may be omitted (or may not be used or utilized) in the optical inspection device  500  shown in  FIG.  1   . 
     While the present disclosure has been described in connection with what is presently considered to be practical embodiments, it is to be understood that the present disclosure is not limited to the disclosed embodiments but is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims and their equivalents. 
     DESCRIPTION OF SOME SYMBOLS 
     
         
           100 : target object to be inspected 
           500 : optical inspection device 
           510 : first light source unit 
           520 : second light source unit 
           521 : white light source unit 
           522 : color selector 
           523 : driver 
           531 : turntable 
           532 : white color filter 
           533 ,  534 ,  535 ,  536 ,  537 ,  538 ,  539 : color filter(s) 
           540 : barrel 
           541 ,  542 : light-transmitting portion 
           550 : camera 
           560 : optical unit 
           600 : image processing unit 
         BA 1 , BA 2 : background area 
         BPA, FBPA: extracted image 
         BPA 1 , BPA 2 : processed image 
         BPAa, BPAa 1 , BPAa 2 , CAa, CAa 1 , CAa 2 , FBPAa, WAa: image of target to be inspected 
         CA, CA 1 , CA 2 , WA: captured image 
         CE: center 
         FA 1 , FA 2 : fringe region 
         GA 1 , GA 2 , GA 3 , GA 4 : graph 
         OB, OP 1 , OP 2 : optical path 
         PK 1 , PK 2 , PK 3 , PK 4 : peak