Method for eliminating lens flare, imaging device, and image measuring instrument

Abstract

To provide a method for eliminating lens flare which contributes to elimination of lens flare reflected in an image captured by irradiating a target with coaxial epi-illumination light via a lens and receiving the reflected light via the lens.SOLUTION: A method for eliminating lens flare includes an image collection step of irradiating coaxial epi-illumination light while changing the irradiation intensity in a state where no target object is placed on a mounting table, and capturing images at each irradiation intensity to collect a plurality of images; a target object imaging step of irradiating the target object placed on the mounting table with coaxial epi-illumination light at an arbitrary irradiation intensity to capture an image of the target object; a correction image generation step of estimating, based on the plurality of images collected in the image collection step, a correction image which is an image at the irradiation intensity irradiated in the target object imaging step; and a flare elimination step of eliminating the lens flare from the image of the target object by taking the difference between the image of the target object and the correction image.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a lens flare elimination method, an imaging device, and an image measuring instrument that contribute to eliminating lens flare that occurs in an image when an object is irradiated with coaxial epi-illumination and an image is captured. [Background technology]

[0002] Coaxial epi-illumination is an illumination form in which the optical axis of light irradiating an object from above and the optical axis of an imaging unit that receives reflected light are aligned using a half mirror, and light is irradiated evenly onto the object, and only specularly reflected light from the light reflected from the object is received, making it possible to capture an image in which the unevenness of the object's surface can be clearly identified. Coaxial epi-illumination is used, for example, in image measuring instruments that measure the dimensions of each part of an object by detecting edges based on the brightness of the captured image (see, for example, Patent Document 1), and microscopes that perform bright-field observation of objects. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-225215 A Summary of the Invention [Problem to be solved by the invention]

[0004] When the coaxial epi-illumination light is irradiated onto an object via a lens such as a telecentric lens, the reflected light from the object also reaches the imaging unit via the lens. In this case, if the intensity of the coaxial epi-illumination light is high, part of the coaxial epi-illumination light is reflected by the lens, and the reflected light also reaches the imaging unit and appears in the captured image as flare. This causes problems such as inability to perform measurements with high accuracy in image measurements, and problems such as deterioration of the quality of the observed image in the case of a microscope.

[0005] An object of the present invention is to provide a lens flare elimination method, an imaging device, and an image measuring instrument that contribute to eliminating lens flare that appears in an image captured by irradiating a target with coaxial epi-illumination light through a lens and receiving the reflected light through the lens. [Means for solving the problem]

[0006] The lens flare elimination method of the present invention is a lens flare elimination method that eliminates lens flare reflected in an image captured by irradiating a mounting table on which an object is placed with coaxial epi-illumination light via a lens and receiving the reflected light via the lens, and includes the following steps: an image collection step in which, with no object placed on the mounting table, coaxial epi-illumination light is irradiated while changing the irradiation intensity, and images are captured at each irradiation intensity to collect a plurality of images; a measurement object imaging step in which coaxial epi-illumination light is irradiated at an arbitrary irradiation intensity onto an object placed on the mounting table to capture an image of the object; a correction image generation step in which a correction image is estimated based on the plurality of images collected in the image collection step, which is an image at the irradiation intensity irradiated in the object imaging step; and a corrected image generation step in which a corrected image in which lens flare has been eliminated from the image of the object is generated by taking the difference between the image of the object and the correction image.

[0007] The correction image may be estimated by an interpolation calculation based on a plurality of images acquired in the image acquisition step.

[0008] The imaging device of the present invention is an imaging device to which the lens flare elimination method of the present invention is applied, and is an imaging device that irradiates coaxial epi-illumination light from an illumination unit via a lens onto a mounting table on which an object is placed, and the imaging unit receives the reflected light via the lens to capture an image, and is equipped with a memory unit that irradiates coaxial epi-illumination light from the illumination unit while changing the irradiation intensity when no object is placed on the mounting table, and pre-stores multiple images captured by the imaging unit at each irradiation intensity, and a control and calculation unit that causes the illumination unit to irradiate coaxial epi-illumination light at an arbitrary irradiation intensity onto the object placed on the mounting table and causes the imaging unit to capture an image of the object, and estimates a correction image, which is an image at the irradiation intensity of the coaxial epi-illumination light when the image of the object was captured, based on the multiple images stored in the memory unit, and generates a corrected image in which lens flare has been eliminated from the image of the object by taking the difference between the image of the object and the correction image.

[0009] The image measuring instrument of the present invention is an image measuring instrument to which the lens flare elimination method of the present invention is applied, and performs image measurement based on an image captured by irradiating coaxial epi-illumination light from an illumination unit via a lens onto a mounting table on which a measurement object is placed, and receiving the reflected light via the lens and capturing the image, and is equipped with: a memory unit that irradiates coaxial epi-illumination light from the illumination unit while changing the irradiation intensity when the measurement object is not placed on the mounting table, and stores in advance a plurality of images captured by the imaging unit at each irradiation intensity; and a control and calculation unit that causes the illumination unit to irradiate the measurement object placed on the mounting table with coaxial epi-illumination light at an arbitrary irradiation intensity, causes the imaging unit to capture an image of the measurement object, estimates a correction image which is an image at the irradiation intensity of the coaxial epi-illumination light when the image of the measurement object was captured, based on the plurality of images stored in the memory unit, and generates a corrected image in which lens flare has been eliminated from the image of the measurement object by taking the difference between the image of the measurement object and the correction image, and performs image measurement on the corrected image. Effect of the Invention

[0010] According to the lens flare eliminating method of the present invention, it is possible to eliminate lens flare reflected in an image captured by irradiating a measurement object with coaxial epi-illumination light through a lens and receiving the reflected light through the lens. Also, according to the imaging device of the present invention, it is possible to obtain an image of the measurement object from which lens flare has been eliminated, and according to the image measuring instrument of the present invention, it is possible to improve the accuracy of image measurement. [Brief description of the drawings]

[0011] [Figure 1] 1 is a diagram showing an example of the appearance of an image measuring instrument 1 to which a method for eliminating lens flare of the present invention is applied. [Diagram 2] 1 is a schematic diagram showing the internal structure of an image measuring instrument 1. FIG. [Diagram 3] 1 is a schematic diagram showing a path of light in an image measuring instrument 1. FIG. [Figure 4] FIG. 2 is a flow diagram of the lens flare elimination method of the present invention. [Diagram 5] 1 is a functional block diagram of an image measuring instrument 1 to which a lens flare eliminating method of the present invention is applied. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following description and drawings, the same functional units are denoted by the same reference numerals, and the description of functional units that have already been described will be omitted or will be described only to the extent necessary.

[0013] The lens flare elimination method of the present invention can be applied to any type of device, such as an image measuring device, a microscope, etc., as long as the device is one in which coaxial epi-illumination light for imaging an object is irradiated onto the object via a lens. The following describes the application to an image measuring device as an example.

[0014] Fig. 1 is a schematic diagram showing the appearance of an image measuring instrument 1 to which a method for eliminating lens flare of the present invention is applied. Fig. 2 is a schematic diagram showing the internal structure of the image measuring instrument 1. Fig. 3 is a schematic diagram showing the path of light in the image measuring instrument 1.

[0015] The image measuring instrument 1 includes a mounting table 2, an imaging unit 3, a control and calculation unit 4, a storage unit 5, a display unit 6, a telecentric optical system 7, an illumination unit 8, and an operation unit 10.

[0016] The mounting table 2 is a table on which a measurement object (not shown) is placed.

[0017] The imaging unit 3 is provided opposite the mounting table 2 and captures an image by receiving light from the direction of the mounting table 2. The imaging unit 3 includes an image sensor and converts the brightness of the image formed on the light receiving surface into an electrical signal to generate image data. The image sensor may be a semiconductor solid-state imaging element such as a Charge-Coupled Device (CCD) or Complementary Metal Oxide Semiconductor (CMOS).

[0018] The control and calculation unit 4 controls each unit within the image measuring instrument 1 and performs necessary calculation processing in order to realize image capturing and image measurement by the image measuring instrument 1.

[0019] The telecentric optical system 7 includes an objective lens 71 that collects light from the direction of the mounting table 2, and an imaging lens 72 that forms an image of the light that has reached the objective lens 71 on the light receiving surface of the imaging unit 3. The objective lens 71 and the imaging lens 72 may each be provided on multiple surfaces.

[0020] The illumination unit 8 is a coaxial epi-illumination means including a light source 81 that emits illumination light, and a beam splitter 82 that causes the illumination light from the light source 81 to be split into the telecentric optical system 7 and irradiated toward the mounting table 2 as coaxial epi-illumination light whose optical axis coincides with the optical axis of the imaging unit 3. The illumination unit 8 may include transmitted illumination and side illumination in addition to the coaxial epi-illumination for the purpose of clarifying an image, etc.

[0021] As shown in FIG. 3, the coaxial epi-illumination light from the light source 81 is irradiated toward the mounting table 2 via the objective lens 71, is reflected by the mounting table 2 and the measurement object placed on the mounting table 2, and reaches the imaging unit 3 via the objective lens 71 again. When the coaxial epi-illumination light enters the objective lens 71, a part of the light is reflected and reaches the imaging unit 3 together with the reflected light from the mounting table 2 and the like. The light reflected by the objective lens 71 causes unnecessary flare in the image captured by the imaging unit 3. The occurrence of flare becomes more noticeable as the number of lens surfaces constituting the objective lens 71 increases. If flare is reflected in the image when the measurement object is captured, the accuracy of the image measurement is reduced.

[0022] Therefore, in the image measuring instrument 1 of the present invention, the lens flare reflected in the image of the measurement object is eliminated by applying the lens flare elimination method shown in the flow chart of FIG.

[0023] First, in a state where no measurement object is placed on the mounting table 2, coaxial epi-illumination light is irradiated while changing the irradiation intensity, and images are captured at each irradiation intensity to collect a plurality of images (image collection step S1). Note that when capturing images, light is blocked by hanging a blackout curtain or the like so that external light other than flare is not reflected in the images.

[0024] Flare occurs based on the presence of the objective lens 71, regardless of whether or not a measurement object is placed. Therefore, by capturing an image without a measurement object being placed, a flare image in which only flare is captured can be obtained. On the other hand, the degree of flare generated in the captured image depends on the irradiation intensity of the coaxial epi-illumination light. Therefore, by collecting flare images at a plurality of irradiation intensities, a flare image at an arbitrary irradiation intensity can be estimated and obtained as a correction image at the arbitrary irradiation intensity.

[0025] Next, the measurement object placed on the mounting table 2 is irradiated with coaxial epi-illumination light at an arbitrary irradiation intensity to capture an image of the measurement object (measurement object imaging step S2). The setting and input of the irradiation intensity may be made possible by, for example, configuring the display unit 6, which is a display means for information related to the measurement, as a touch panel display that also serves as the operation unit 10, which is an input means for information required for the measurement, and displaying an input interface on the display unit 6.

[0026] Further, based on the plurality of flare images collected in the image collecting step S1, a correction image at the irradiation intensity of the coaxial epi-illumination light in the measurement target imaging step S2 is estimated and generated (correction image generating step S3). The correction image may be estimated by, for example, an interpolation calculation based on the plurality of flare images collected in the image collecting step S1.

[0027] 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 input of the irradiation intensity setting.

[0028] Next, a difference is taken between the image of the measurement object captured in the measurement object imaging step S2 and the correction image, thereby generating a corrected image in which lens flare has been removed from the image of the measurement object (corrected image generating step S4).

[0029] According to the lens flare elimination method of the present invention described above, it is possible to eliminate lens flare that appears in an image of an object to be measured by irradiating the object to be measured with coaxial incident illumination light through a lens and receiving the reflected light through the lens.

[0030] The lens flare elimination method of the present invention can be realized by providing an image measuring instrument 1 with a storage unit 5 that stores a plurality of images captured under irradiation with coaxial epi-illumination light of a plurality of irradiation intensities with no measurement target placed on the placement stage, the images being collected based on an image collection step S1 executed in advance, and a control and calculation unit 4 that executes each of the subsequent steps. A functional block diagram is shown in FIG.

[0031] That is, the control and calculation unit 4 first causes the illumination unit 8 to irradiate coaxial epi-illumination light of an arbitrary irradiation intensity, and causes the imaging unit 3 to image the measurement object placed on the mounting table (measurement object imaging step S2). At the same time, a correction image for the irradiation intensity of the coaxial epi-illumination light from the illumination unit 8 is generated based on multiple images in the storage unit 5 (correction image generating step S3). Then, a corrected image is generated by taking the difference between the image of the measurement object and the correction image (corrected image generating step S4).

[0032] The functions of the control calculation unit 4 may be realized by executing a program in which the processing contents of each step are described by a CPU. The program may be read out from the memory unit 5, or may be read out from another memory means. The CPU and memory means such as the memory unit 5 may be provided in the main body of the image measuring instrument 1, or may be provided in a device such as a computer connected to the main body of the image measuring instrument 1 so as to be able to communicate with it.

[0033] After the corrected image is generated, the control and calculation unit 4 of the image measuring device 1 executes image measurement on the corrected image. The content of the image measurement is arbitrary. The result of the image measurement may be displayed on the display unit 6, or may be output using any output means.

[0034] According to the image measuring instrument 1 of the present invention to which the lens flare elimination method of the present invention described above is applied, image measurement can be performed on an image of the object to be measured from which lens flare has been eliminated, thereby improving the accuracy of image measurement.

[0035] It is also possible to configure an imaging device that can obtain an image of a measurement target object from which lens flare has been eliminated by excluding the image measurement function from the configuration of the image measuring instrument 1.

[0036] Furthermore, for example, by applying the lens flare elimination method of the present invention to a microscope using coaxial epi-illumination, the quality of the observed image can be improved.

[0037] The present invention is not limited to the above-mentioned embodiment and modified examples. The above-mentioned embodiment and modified examples are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included in the technical scope of the present invention. In other words, appropriate modifications are possible within the scope of the technical idea expressed in the present invention, and forms with such modifications and improvements are also included in the technical scope of the present invention. [Explanation of symbols]

[0038] 1...Image measuring device 2…Placement table 3. Imaging unit 4...Control and calculation section 5...Storage section 6...Display section 7...Telecentric optical system 8…Lighting section 10...Operation unit 71...Objective lens 72...Imaging lens 81...Light source 82...Beam splitter

Claims

1. A method for eliminating lens flare, which is performed by irradiating a coaxial epi-illumination light via a lens toward a mounting base on which an object is placed, and receiving reflected light via the lens, thereby eliminating lens flare reflected in an image captured, comprising: an image collecting step of irradiating the object with coaxial epi-illumination light while changing the irradiation intensity in a state where the object is not placed on the mounting table, capturing an image at each irradiation intensity, and collecting a plurality of images; an object imaging step of irradiating the object placed on the mounting table with coaxial epi-illumination light at an arbitrary irradiation intensity to capture an image of the object; a correction image generating step of estimating a correction image, which is an image at an irradiation intensity applied in the object imaging step, based on a plurality of images collected in the image collecting step; a corrected image generating step of generating a corrected image in which lens flare has been removed from the image of the object by calculating a difference between the image of the object and the correction image; How to remove lens flares.

2. 2. The method for eliminating lens flare according to claim 1, wherein the correction image is estimated by an interpolation calculation based on a plurality of images collected in the image collection step.

3. An imaging device that irradiates a coaxial epi-illumination light from an illumination unit through a lens onto a mounting table on which an object is placed, and captures an image by having an imaging unit receive reflected light through the lens, a storage unit that irradiates coaxial epi-illumination light from the illumination unit while changing the irradiation intensity in a state where no object is placed on the mounting table, and stores in advance a plurality of images captured by the imaging unit at each irradiation intensity; a control and calculation unit that causes the illumination unit to irradiate coaxial epi-illumination light at an arbitrary irradiation intensity onto an object placed on the mounting table, causes the imaging unit to capture an image of the object, and estimates a correction image, which is an image at the irradiation intensity of the coaxial epi-illumination light when the image of the object was captured, based on the plurality of images stored in the storage unit, and generates a corrected image in which lens flare has been eliminated from the image of the object by taking a difference between the image of the object and the correction image; An imaging device comprising:

4. 1. An image measuring instrument that performs image measurement based on an image captured by irradiating a coaxial epi-illumination light from an illumination unit through a lens onto a mounting table on which a measurement target is placed, and receiving reflected light from the imaging unit through the lens, a storage unit that irradiates coaxial epi-illumination light from the illumination unit while changing the irradiation intensity in a state where the measurement object is not placed on the placement stage, and stores in advance a plurality of images captured by the imaging unit at each irradiation intensity; a control and calculation unit that causes the illumination unit to irradiate a measurement object placed on the mounting table with coaxial epi-illumination light at an arbitrary irradiation intensity, causes the imaging unit to capture an image of the measurement object, estimates a correction image which is an image at the irradiation intensity of the coaxial epi-illumination light when the image of the measurement object was captured based on the multiple images stored in the storage unit, and generates a corrected image in which lens flare has been eliminated from the image of the measurement object by taking a difference between the image of the measurement object and the correction image, and performs image measurement on the corrected image; An image measuring machine comprising:

Images