Lens flash elimination method, image capturing device and image measuring device

Abstract

The invention discloses a lens flash elimination method, an image capturing apparatus and an image measuring apparatus. The lens flash elimination method performs the steps of: acquiring an image by irradiating the coaxially reflected illumination light at varying irradiation intensities and capturing an image at each irradiation intensity when the object is not placed on the stage; a step for capturing an image of the object by irradiating the object placed on the stage with coaxially reflected illumination light at any irradiation intensity; a step for estimating an image for correction on the basis of the image acquired in the image acquisition step, the image for correction being an image at an irradiation intensity irradiated when the measurement object is captured; and a step for generating a corrected image in which lens flash is eliminated from the image of the object by obtaining a difference between the image of the object and the image for correction.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This nonprovisional application claims priority under 35 U.S.C. §119(a) to Japanese Patent Application No. 2023-125243 filed on August 1, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to a lens flare elimination method, an image capturing device and an image measuring device, which helps to eliminate lens flare that occurs in an image captured when an object is illuminated by coaxial reflected illumination. Background Art

[0004] Coaxial reflection illumination is a form of illumination in which a half mirror is used to align the optical axis of light irradiating an object from above with the optical axis of an image capture unit that receives the reflected light. With coaxial reflection illumination, light is uniformly irradiated onto the object, and only the normally reflected light from the object is received, thereby capturing an image in which the convex and concave surfaces of the object surface can be clearly identified. Coaxial reflection illumination is applied to, for example, an image measuring device that measures the size of each part of an object by performing edge detection via the brightness or darkness of a captured image, or a microscope that performs bright-field observation of an object (see, for example, JP 2015-225215A). Summary of the invention

[0005] Problems to be solved by the present invention

[0006] When the coaxial reflected illumination light is irradiated onto the object through a lens (e.g., a telecentric lens), the reflected light from the object will also reach the image capture unit through the lens. If the intensity of the coaxial reflected illumination light is high, a part of the coaxial reflected illumination light is reflected by the lens, and the reflected light here also reaches the image capture unit and appears as a light spot in the captured image. Therefore, in the case of image measurement, there are problems such as inaccurate measurement, and in the case of a microscope, there are problems such as deterioration in the quality of the observed image.

[0007] An object of the present invention is to provide a lens flare elimination method, an image capturing device and an image measuring device, which helps to eliminate lens flare that appears in an image captured by illuminating an object through a lens with coaxial reflected illumination light and receiving reflected light through the lens.

[0008] Solutions to the problem

[0009] The lens flare elimination method according to the present invention eliminates lens flare in an image captured by irradiating coaxial reflected illumination light through a lens onto a stage on which an object is placed and receiving reflected light through the lens. The lens flare elimination method performs: an image acquisition step for acquiring a plurality of images by irradiating the coaxial reflected illumination light with varying illumination intensities and capturing images at each illumination intensity when the object is not placed on the stage; a measurement object imaging step for capturing an image of the object by irradiating the object placed on the stage with the coaxial reflected illumination light at an arbitrary illumination intensity; a correction image generation step for estimating an image for correction based on the plurality of images acquired in the image acquisition step, the image for correction being an image at the illumination intensity irradiated in the measurement object imaging step; and a corrected image generation step for generating a corrected image in which the lens flare is eliminated from the image of the object by obtaining a difference between the image of the object and the image for correction.

[0010] The image used for correction may be estimated by interpolation calculation based on the plurality of images acquired in the image acquisition step.

[0011] The image capture device of the present invention is an image capture device to which the lens flare elimination method of the present invention is applied. In the image capture device, coaxial reflected illumination light from an illumination unit is irradiated through a lens onto a stage on which an object is placed, and the reflected light is received by the image capture unit through the lens to capture an image. The image capture device includes: a storage unit that pre-stores a plurality of images captured by the image capture unit with different illumination intensities by irradiating the coaxial reflected illumination light from the illumination unit when the object is not placed on the stage; and a control processing unit that causes the illumination unit to irradiate the object placed on the stage with the coaxial reflected illumination light at an arbitrary illumination intensity, causes the image capture unit to capture an image of the object, estimates an image for correction based on the plurality of images stored in the storage unit, the image for correction being an image at the illumination intensity of the coaxial reflected illumination light when the image of the object is captured, and generates a corrected image in which the lens flare is eliminated from the image of the object by obtaining a difference between the image of the object and the image for correction.

[0012] The image measuring device of the present invention is an image measuring device to which the lens flare elimination method of the present invention is applied. The image measuring device performs image measurement based on an image captured by irradiating coaxial reflected illumination light from an illumination unit through a lens onto a stage on which a measurement object is placed, and the image measuring device has an image capturing unit that receives reflected light through the lens. The image measuring device includes: a storage unit that pre-stores a plurality of images captured by the image capturing unit by irradiating coaxial reflected illumination light from the illumination unit with different irradiation intensities when the measurement object is not placed on the stage; and a control processing unit that causes the illumination unit to irradiate the measurement object placed on the stage with coaxial reflected illumination light at an arbitrary irradiation intensity, causes the image capturing unit to capture an image of the measurement object, estimates an image for correction based on the storage unit image stored in the storage unit, the image for correction being an image at the irradiation intensity of the coaxial reflected illumination light when capturing the image of the measurement object, generates a corrected image in which lens flare is eliminated from the image of the measurement object by obtaining a difference between the image of the measurement object and the image for correction, and performs image measurement on the corrected image.

[0013] Effects of the Invention

[0014] According to the lens flare elimination method of the present invention, the lens flare in the image captured by irradiating the measurement object through the lens with coaxial reflected illumination light and receiving the reflected light through the lens can be eliminated. In addition, the image acquisition device can obtain the image of the measurement object with the lens flare eliminated, and the imaging measurement device can improve the accuracy of image measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 An example of the appearance of the vision measuring apparatus 1 to which the lens flare eliminating method is applied is shown.

[0016] Figure 2 A schematic diagram showing the internal structure of the vision measuring device 1 is shown.

[0017] Figure 3 is a schematic diagram showing the optical path in the image measuring device 1 .

[0018] Figure 4 It is an execution flow chart of the lens flare elimination method according to the present invention.

[0019] Figure 5 1 is a functional block diagram of an image measuring device 1 to which the lens flare elimination method of the present invention is applied. DETAILED DESCRIPTION

[0020] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description and the accompanying drawings, the same reference numerals are attached to the same functional components, and once these functional components are explained, these functional components are omitted or explained only to the extent necessary.

[0021] The lens flare elimination method according to the present invention can be applied to any type of equipment, such as an image measuring device and a microscope, and an image capturing device, as long as the coaxial reflected illumination light for imaging an object is irradiated onto the object through a lens. Hereinafter, an example of application to an image measuring device will be described.

[0022] Figure 1 : is a schematic diagram showing the appearance of a vision measuring device 1 to which the lens flare eliminating method of the present invention is applied. Figure 2 A schematic diagram showing the internal structure of the vision measuring device 1 is shown. Figure 3 is a schematic diagram showing the optical path in the image measuring device 1 .

[0023] The vision measuring device 1 includes a stage 2 , an image capturing unit 3 , a control processing unit 4 , a storage unit 5 , a display unit 6 , a telecentric optical system 7 , an illumination unit 8 , and an operation unit 10 .

[0024] The mounting table 2 is a platform on which a measurement object (not shown) is placed.

[0025] The image capturing unit 3 is disposed opposite to the stage 2 and captures an image by receiving light from the direction of the stage 2. The image capturing unit 3 includes an image sensor that converts the brightness or darkness of an image formed on its light receiving surface into an electrical signal, thereby generating image data. For the image sensor, a semiconductor solid-state imaging device such as a CCD (charge coupled device) and a CMOS (complementary metal oxide semiconductor) is used.

[0026] The control processing unit 4 controls each part in the vision measuring device 1 , and performs necessary arithmetic processing to realize image capturing and image measurement by the vision measuring device 1 .

[0027] The telecentric optical system 7 includes an objective lens 71 that collects light from the direction of the stage 2 and an imaging lens 72 that forms an image of the light arriving through the objective lens 71 on the light receiving surface of the image capture unit 3. The objective lens 71 and the imaging lens 72 may each have a plurality of lens surfaces.

[0028] The illumination unit 8 is a coaxial reflected illumination device, which is provided with a light source 81 that emits illumination light and a beam splitter 82 that blocks the illumination light from the light source 81 from entering the telecentric optical system 7 and guides the light to the stage 2 as coaxial reflected illumination light, the optical axis of which coincides with the optical axis of the image capturing unit 3. The illumination unit 8 includes transillumination or side illumination as well as coaxial reflected illumination for image clarity and other purposes.

[0029] like Figure 3 As shown, the coaxial reflected illumination light from the light source 81 is irradiated toward the stage 2 through the objective lens 71, is reflected by the stage 2 and the object to be measured placed on the stage 2, and passes through the objective lens 71 again to reach the image capture unit 3. When the coaxial reflected illumination light enters the objective lens 71, a portion of the light is reflected and reaches the image capture unit 3 together with the reflected light from the stage 2 and the like. The light reflected by the objective lens 71 causes unwanted light spots in the image captured by the image capture unit 3. As the number of lens surfaces constituting the objective lens 71 increases, the flare occurs more significantly. If light spots appear in the image when imaging the object to be measured, the accuracy of the image measurement will be reduced.

[0030] Therefore, the image measuring device 1 applies Figure 4 The lens flare elimination method shown in the flowchart in FIG. 1 is used to eliminate the lens flare that appears in the image of the measurement object.

[0031] First, when the measuring object is not placed on the stage 2, a plurality of images are acquired by irradiating coaxial reflected illumination light with varying irradiation intensity and capturing images at each irradiation intensity (image acquisition step S1). When imaging, light should be shielded by a light-shielding curtain or other device to prevent external light other than flash from being reflected in the image.

[0032] Regardless of whether the measurement object is placed on the stage, the flash will appear based on the presence of the objective lens 71. Therefore, by performing imaging without placing the measurement object, a spot image can be obtained, which is an image that captures only the flash. On the other hand, the degree of flash on the captured image depends on the intensity of the coaxial reflected illumination light. Therefore, by acquiring the spot image at multiple illumination intensities, the spot image at any illumination intensity can be estimated, and the estimated spot image can be used as an image for correction at any illumination intensity.

[0033] Then, an image of the measured object placed on the stage 2 is captured by irradiating the measured object with coaxial reflected illumination light at an arbitrary irradiation intensity (measurement object imaging step S2). The setting input of the irradiation intensity can be realized, for example, by configuring the display unit 6 (which is a device for displaying information related to the measurement) as a touch panel display (which is a device for inputting information required for the measurement) also serving as the operation unit 10 and displaying an input interface on the display unit 6.

[0034] Based on the multiple images acquired in the image acquisition step S1, an image for correction with the illumination intensity of the coaxial reflected illumination light in the measurement object imaging step S2 is estimated and generated (correction image generation step S3). For example, the image for correction can be estimated by interpolation calculation based on the multiple images acquired in the image acquisition step S1.

[0035] Note that the measurement object imaging step S2 and the correction image generating step S3 may be performed in parallel or in any order based on the setting input of the illumination intensity.

[0036] Then, by obtaining the difference between the image of the measuring object captured in the measuring object imaging step S2 and the image for correction, a corrected image in which the lens flare is eliminated from the image of the measuring object is generated (corrected image generating step S4 ).

[0037] According to the lens flare eliminating method of the present invention described above, it is possible to eliminate lens flare in an image captured by illuminating a measurement object with coaxial reflected illumination light through a lens and receiving reflected light through the lens.

[0038] The lens flare elimination method of the present invention can be implemented in the image measuring device 1 by, for example, providing a storage unit 5 and a control processing unit 4, wherein the storage unit 5 stores a plurality of images captured under the illumination of coaxial reflected illumination light of a plurality of illumination intensities without placing a measurement object on a stage, the plurality of images being acquired in an image acquisition step S1 performed in advance, and the control processing unit 4 executes subsequent steps. Figure 5 is a functional block diagram of the vision measuring device 1.

[0039] That is, the control processing unit 4 first causes the lighting unit 8 to irradiate coaxial reflected illumination light of arbitrary intensity, and causes the image capture unit 3 to capture an image of the object to be measured placed on the stage (measurement object imaging step S2). At the same time, the lighting unit 8 generates an image for correction based on a plurality of images in the storage unit 5 at the irradiation intensity of the coaxial reflected illumination light (correction image generation step S3). Then, a corrected image is generated by obtaining the difference between the image of the object to be measured and the image for correction (corrected image generation step S4).

[0040] The function of the control processing unit 4 can be realized by executing a program describing the process of each step by the CPU. The program can be read from the memory unit 5 or from another storage medium. The CPU and a storage device such as the memory unit 5 can be provided in the main body of the vision measuring device 1, or in a computer or other device communicatively connected to the main body of the vision measuring device 1.

[0041] After generating the corrected image, the control processing unit 4 of the image measuring device 1 performs image measurement on the corrected image. The content of the image measurement is arbitrary. The result of the image measurement can be displayed on the display unit 6 or output using any other output device.

[0042] According to the image measuring apparatus 1 to which the lens flare eliminating method of the present invention described above is applied, the accuracy of image measurement can be improved because image measurement can be performed on an image of a measurement object from which lens flare has been eliminated.

[0043] By excluding the function of image measurement from the configuration of the image measuring apparatus 1 , it is possible to configure an image capturing apparatus capable of obtaining an image of a measurement object from which lens flare has been eliminated.

[0044] In addition, for example, by applying the lens flare elimination method of the present invention to a microscope with coaxial reflected illumination, the quality of the observed image can be improved.

[0045] The present invention is not limited to the above-mentioned embodiments and modifications. The above-mentioned embodiments and modifications are merely examples, and any content having substantially the same configuration as the technical concept described in the claims of the present invention and producing similar effects is included in the technical scope of the present invention. In other words, changes can be made appropriately within the scope of the technical concept expressed in the present invention, and forms with such changes and improvements are also included in the technical scope of the present invention.

Claims

1. A lens flare elimination method for eliminating lens flare in an image captured by irradiating coaxial reflected illumination light through a lens onto a stage on which an object is placed and receiving the reflected light through the lens, wherein: The lens flare elimination method performs: an image acquisition step for acquiring a plurality of images by irradiating the coaxial reflected illumination light with varying irradiation intensities and capturing an image at each irradiation intensity when the object is not placed on the mounting table; a measurement object imaging step for capturing an image of the object by irradiating the object placed on the stage with coaxial reflected illumination light at an arbitrary illumination intensity; a correction image generating step for estimating an image for correction based on the plurality of images acquired in the image acquiring step, the image for correction being an image at an irradiation intensity irradiated in the measurement object imaging step; and A corrected image generating step for generating a corrected image in which lens flare is eliminated from the image of the object by obtaining a difference between the image of the object and the image for correction.

2. The lens flare elimination method according to claim 1, wherein: An image for correction is estimated by interpolation calculation based on the plurality of images acquired in the image acquisition step.

3. An image capturing device that captures an image by irradiating coaxial reflected illumination light from an illumination unit through a lens onto a mounting table on which an object is placed and receiving light reflected by the image capturing unit through the lens, the image capturing device comprising: a storage unit that pre-stores a plurality of images captured by the image capture unit by irradiating coaxial reflected illumination light from the illumination unit with different illumination intensities when the object is not placed on the mounting table; as well as a control processing unit that causes the illumination unit to illuminate the object placed on the stage with coaxial reflected illumination light at an arbitrary illumination intensity, causes the image capture unit to capture an image of the object, estimates an image for correction based on the storage unit image stored in the storage unit, the image for correction being an image at the illumination intensity of the coaxial reflected illumination light when capturing the image of the object, generates a corrected image in which lens flare is eliminated from the image of the object by obtaining a difference between the image of the object and the image for correction, and performs image measurement on the corrected image.

4. An image measuring device that performs image measurement based on an image captured by irradiating coaxial reflected illumination light from an illumination unit through a lens onto a stage on which a measurement object is placed, and that has an image capturing unit that receives reflected light through the lens, the image measuring device comprising: a storage unit that pre-stores a plurality of images captured by the image capture unit by irradiating the coaxial reflected illumination light from the illumination unit with different illumination intensities when the measuring object is not placed on the stage; as well as a control processing unit that causes the illumination unit to illuminate the object to be measured placed on the stage with coaxial reflected illumination light at an arbitrary illumination intensity, causes the image capture unit to capture an image of the object to be measured, estimates an image for correction based on the storage unit image stored in the storage unit, the image for correction being an image at the illumination intensity of the coaxial reflected illumination light when capturing the image of the object to be measured, generates a corrected image in which lens flare is eliminated from the image of the object to be measured by obtaining a difference between the image of the object to be measured and the image for correction, and performs image measurement on the corrected image.

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