JPH06229931A - Method and equipment for calibration for image measuring apparatus - Google Patents

Abstract

PURPOSE:To obtain a method and equipment for calibration for an image measuring apparatus which enable such flexible setting of parameters as to enable absorption of an error of an image apparatus being used for measurement. CONSTITUTION:In a state wherein an image from a TV camera 8 is taken in and stored by a means 31 for taking in and storing the image and displayed in CRT 25, the position of the center of the image and the size thereof are determined by using a cross cursor display indicating means 35 for indicating the position of the center of the image and a circular cursor display indicating means 36 for indicating the size of the image, and determination of parameters of an imaging formula of an image pickup optical system is conducted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a calibration method for an image measuring device and a calibration device for measuring from an image obtained by an endoscope.

[0002]

2. Description of the Related Art In recent years, endoscopes have been widely used in the medical field and industrial field. In addition, the endoscope may be used to measure the size of a lesion or a wound that cannot be directly measured.

When performing measurement using an endoscope, it is necessary to know the characteristics of the lens incorporated in the endoscope to be used and use the parameters that determine the characteristics. The coefficients required for this characteristic are the focal length of the lens, the imaging formula of the lens, the coefficient for correcting the lens distortion, the maximum angle of view of the lens, and the center position of the image. The center position of the image among these has been obtained from the image by the conventional method. Other coefficients (this operation is called calibration) were selected from a list of endoscope names prepared in advance.

That is, the photographing adapter and the TV camera to be used in combination with the name of the endoscope are confirmed, and the number of the coefficient set corresponding thereto is selected from the list.
At this time, the focal length of the lens, the imaging formula of the lens, the coefficient for correcting the distortion aberration of the lens, and the maximum angle of view of the lens are prepared in advance corresponding to the numbers.

[0005]

When the coefficient is set in this way, the following problems occur with respect to the focal length of the lens. The image size of the endoscope on the TV screen may differ from the calculated value due to variations in the image forming lens system of the endoscope, the photographing adapter, and the TV camera. This error becomes a measurement error.

Further, when an endoscope having a new optical system was put on the market, the coefficient of this endoscope could not be registered in the list. In addition, since there are many combinations of shooting adapters and TV cameras, it is difficult to select a coefficient set from the list.

Further, the size of the image taken by the TV camera is the sum of the errors of the eyepiece lens of the endoscope, the lens of the photographing adapter, and the size of the image pickup surface of the TV camera. There is a drawback that this error is neglected by the parameter decided in advance, and the measurement error becomes large.

The present invention has been made in view of the above points, and a calibration method and calibration for an image measuring device capable of performing flexible parameter setting capable of absorbing an error of an image device used for measurement. The purpose is to provide a device.

[0009]

Since the present invention is provided with a means for determining the center of an image from an image used for measurement and a means for determining the size of the image, the present invention provides an imaging lens system for an endoscope. , Due to variations in shooting adapter and TV camera,
It is possible to eliminate the error caused by the size of the image of the endoscope on the TV screen being different from the calculated value.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 10 relate to a first embodiment of the present invention,
FIG. 1 is an overall configuration diagram of an endoscopic image measuring device including the first embodiment, FIG. 2 is an explanatory diagram showing the principle of image formation by an imaging optical system, and FIG. 3 is an explanatory diagram showing a simplified version of FIG. FIG. 4 is a block diagram showing the configuration of the measuring device, and FIG. 5 is an explanatory diagram of the operation for obtaining the size and center of the image.

An endoscope image measuring apparatus 1 having the first embodiment shown in FIG. 1 includes a TV camera external scope 2 having an image pickup means, and a light source for supplying illumination light to the TV camera external scope 2. A device 3, a camera control unit (hereinafter referred to as CCU) 4 that performs signal processing for the image pickup means of the TV camera external scope 2, and measurement that is connected to the CCU 4 and measures the size of an object such as a scratch. Device 5
The measuring device 5 is used to perform calibration necessary for measurement from an image, and the size of the object can be measured with high accuracy.

The TV camera external scope 2 has a fiberscope 6 and a TV camera 8 connected to the fiberscope 6 via a photographing adapter 7. This fiberscope 6 has an elongated insertion part 9 and this insertion part 9
Has an operation section 10 provided on the proximal side and an eyepiece section 11 provided on the rear end of the operation section 10, and the light guide cable 12 extends from the side of the operation section 10. .

A connector 13 provided at the end of the light guide cable 12 is detachably connected to the light source device 3 so that the illumination light supplied from the light source device 3 is inserted into the light guide cable 12 and is not shown. Supplied to the guide. The illumination light transmitted by this light guide is emitted forward from an illumination window (not shown) of the distal end portion 14 of the insertion portion 9 to illuminate the affected area or the like.

An observation window is formed adjacent to the illumination window at the tip portion 14, and an objective optical system 16 is attached to the observation window as shown in FIG. Connect 17 statues. The front end surface 18a of the image guide 18 is arranged at this image forming position, and the image is transmitted to the rear end surface 18b on the eyepiece 11 side.

An eyepiece optical system 19 is arranged in the eyepiece portion 11 so as to face the rear end surface 18b, and the transmitted image can be magnified and observed. When the photographing adapter 7 is attached to the eyepiece section 11, an image is formed on the surface of the CCD 22 housed in the TV camera 8 by the adapter optical system 21 facing the eyepiece optical system 19.

The image formed on the CCD 22 is photoelectrically converted into an electric signal, which is sent to the CCU 4 by the camera cable 23 extended from the TV camera 8, and this CCU 4
Therefore, the signal is processed and converted into a video signal. This video signal is transmitted to the measuring device 5 by the video cable 24.

Then, the video signal shown in FIG.
As shown in, the image of the object 17 is displayed on the CRT 25 surface of the measuring device 5. That is, the image of the endoscope can be observed by the CRT 25. A keyboard 26 and a mouse 27 are connected to the measuring device 5. Next, the principle of image formation will be described with reference to the image pickup optical system in FIG.

An image of the object 17 by the objective optical system 16 is formed on the tip surface 18a of the image guide 18. Since the image guide 18 is twisted by 180 degrees, the images of the object 17 are interchanged vertically and horizontally, and the rear end surface 1 of the image guide 18 is rotated.
Sent to 8b.

The image on the rear end face 18b is an eyepiece optical system 19.
An image is formed on the surface of the CCD 22 by the adapter optical system 21. The image formed on the CCD 22 is displayed on the surface of the CRT 25. As a result, the image of the object 17 is projected on the screen of the CRT 25. FIG. 3 shows the principle by further simplifying this relationship. θ is an incident angle at which the object 17 is seen. A light ray incident at an incident angle θ passes through the lens 29 and forms an image at a focal length f at an image height h. In FIG. 2, the lens 29 is an objective optical system 16, an image guide 18 for transmitting the image, an eyepiece optical system 19, and an adapter optical system 21.
Represents

Here, as the aberration of the lens 29, distortion is a problem for measurement. In this embodiment, only aberration is corrected. As a formula for correcting this aberration, for example, one of formulas (1), (2), and (3) shown in FIG. 3 is used. This equation shows that the light ray having the incident angle θ has the image height h. Use this formula properly according to the actual optical system.

The variables that must be known are the focal length f,
The distortion correction coefficient k. The distortion correction coefficient k is a constant determined by the optical system, and it is difficult to obtain it by measurement. Therefore, it is given in advance depending on the type of the optical system.

Further, which of the formulas (1), (2) and (3) is used is also given in advance. Under such conditions, it is necessary to give a set of image height h and incident angle θ in order to obtain the focal length f. Since it is difficult to capture an image with an arbitrary known angle θ, it is convenient to use the maximum angle of view as the known angle θ.

That is, the relationship between the image height h and the incident angle θ can be easily understood from the maximum angle of view and the image height at that time (maximum image height).
The maximum angle of view is determined by the optical system and is difficult to measure, so give it in advance. The last remaining maximum image height can be obtained from the screen.

On the other hand, since the image formation formula expressed by the above formula is point-symmetric with respect to the optical axis, it is necessary to find the center of the screen within the screen. From the above, if the center of the image and the size of the image (maximum image height) can be obtained on the screen, the focal length f can be obtained. Therefore, the relational expressions (1), (2), and (3) of the image formation are Can be used. Therefore, measurement can be performed using this imaging formula.

FIG. 4 is a block diagram of the measuring device 5 constituting the first embodiment. The image signal from the TV camera 8 is connected to the image capture storage means 31. The image capturing and storing means 31 temporarily stores the endoscopic image.

The output of the image storage means 31 is connected to the superimposing means 32. The superimposing means 32 superimposes and displays a figure on the endoscopic image.

The output of the superimposing means 32 is connected to the image display means 33. The image display means 33 converts the signal so that it can be displayed on the CRT 25. The superimposing means 32 is controlled by the display control means 34 and synthesizes necessary information with the captured image signal and displays it.

The display control means 34 is connected to a cross cursor display instruction means 35 for instructing the center position of the image and a circular cursor display instruction means 36 for instructing the size of the image. The superimposing means 32 displays a crosshair on the surface of the CRT 25 according to the information from the crosshair cursor display means 35.

The superimposing means 32 displays a circular cursor on the surface of the CRT 25 according to the information from the circular cursor display instruction means 36. On the other hand, integrated control calculation means 37 is provided and connected to the image capture storage means 31, display control means 34, cross cursor display instruction means 35, circle cursor display instruction means 36, position information / quantity information input means 38. Has been done.

The overall control calculation means 37 determines the operation of the measuring device 5 based on the information from the position information / quantity information input means 38. The position information / quantity information input means 38 obtains position and quantity information from the keyboard 26 and the mouse 27.

Next, the operation of this embodiment will be described. First,
The operation will be described with reference to FIG. In the light source device 3, light from a lamp (not shown) enters a light guide (not shown).
A light guide (not shown) passes through the connector 13, the light guide cable 12, the operation section 10, and the insertion section 9,
It is guided to the tip portion 14. An illumination lens (not shown) of the tip portion 14 spreads the light beam to illuminate an object 17 to be observed. This is a normal endoscope operation.

An image of the object 17 to be observed is formed by the objective optical system 16 and transmitted by the image guide 18, and then, by the eyepiece optical system 19 and the adapter optical system 21, the CCD 22 of the TV camera 8 as described above. Is formed. C
The image formed on the CD 22 is converted into a normal TV signal by the CCU 4 and sent to the measuring device 5. In the measuring device 5, as shown in FIG. 4, the image capture storage means 31 receives the transmitted TV signal.

When the user operates the keyboard 26 to instruct to capture an image, the information is sent from the position information / quantity information input means 38 to the overall control arithmetic means 37, and the overall control arithmetic means 37 displays the image. The acquisition is instructed to the image acquisition storage means 31. Based on the command, the image capture storage means 31 stores the image from the TV camera 8.

An image output signal of the image acquisition / storage means 31 passes through a superimposing means 32 and an image display means 33.
And converted into a signal that can be displayed on the CRT 25.
That is, the image of the TV camera 8 is displayed on the CRT 25 with characters and graphics combined. An image on a normal endoscope becomes a circular image as shown in FIG. The image on the circular frame is the maximum angle of view of this endoscope. This circle is mask 3
Call it 9. As described in the explanation of the principle, the center and size of the image are obtained here.

When the keyboard 26 is operated to operate the calibration function for measurement, the overall control calculation means 37 issues a command to the cross cursor display instruction stage 35 to display the cross cursor. Based on the command, the cross-cursor display instruction means 35 sends the cross-cursor data to the display control means 34.

In response to the data, the display control means 34 sends a signal for displaying the cross cursor to the superimposing means 32, and the superimposing means 32 superimposes the crosshair information on the image signal based on the signal, so that the CRT 25 is used. A cross cursor 40 is displayed on the surface.

This image is shown in FIG. 5 (b). When the central axis of the TV camera 8 is displaced in the endoscopic image, the mask 39 is not at the center of the screen as shown in FIG. 5B and is displaced. The operator moves the cross-shaped cursor 40 while seeing the shifted state, and performs an operation of aligning it with the center of the mask 39.

Based on the amount information from the mouse 27 moved by the operator, the overall control calculation means 37 instructs the cross cursor display instruction means 35 to change the cross cursor display position. As a result, the cross-shaped cursor 4 displayed on the CRT 25
The position of 0 is changed.

When the cross cursor 40 is located at the center position of the image of the endoscope, that is, at the center of the mask 39, the operator presses the value fixing key on the keyboard 26. Based on this information, the overall control calculation means 37 calculates the position of the cross cursor 40 when the value confirmation key is pressed. That is, this position becomes the coordinates of the center point of the image.

Next, the size of the mask 39 is set. Therefore, the overall control calculation means 37 instructs the circle cursor display instruction means 36 to display the circle cursor 41. FIG. 5C shows how the circular cursor 41 is displayed on the CRT 25.

The operator moves the mouse 27 to increase or decrease the size of the circular cursor 41,
Perform the operation to match the image on the endoscope. That is, the general control calculation means 37 instructs the circle cursor display instruction means 36 to change and display the size of the circle cursor based on the information from the mouse 27.

As a result, the center does not change on the CRT 25, circular cursors 41 having different sizes are displayed, and the size changes according to the movement of the mouse 27. The operator places the circular cursor 41 on the mask 39 of the endoscope and presses the value confirmation key of the keyboard 26. Based on this information, the overall control calculation means 37 calculates the size of the frame of the endoscopic image.

Next, a method of selecting coefficients for measurement in the first embodiment will be described. The coefficients to be calculated are the coefficients f and k of the equations (1), (2) and (3) as described above.
This formula is a calculation formula for calculating the coefficient f when an image is formed on the CCD surface.

In the first embodiment, the size on the CCD surface and CR
Since the size on the T screen is simply a multiplication of the size, h in equations (1), (2) and (3) is considered to be the size on the CRT screen. Then, the focal length f becomes the focal length including the magnification, and equations (1), (2), and (3)
The image height on the CRT screen can be calculated by using.
That is, it is possible to perform the measurement using the image at the coordinates on the CRT screen.

As described above, the center of the endoscopic image on the CRT screen can be seen. In addition, since the radius of the circle corresponding to the maximum image height of the endoscopic image is known, let d be the maximum angle of view, and let d = f · k · sin (θ / k) (Equation (1) In this case, the focal length f including the magnification can be obtained. That is, the coefficients required for measurement can be calibrated.

After that, the size of the object can be measured by using the focal length f determined by this calibration. Although not described, since other coefficients are set in advance by the keyboard 26, the measurement using the image can be performed in this state.

According to this embodiment, since the image is formed by the actually used optical system and is displayed on the CRT screen to set the characteristics of the optical system, there is a variation in each lens. Even in the case, the error due to the variation can be absorbed, and the error can be reduced.

In other words, the parameters of the scope used for measurement are not set from the list, but are taken from the image according to the actual product and the parameters are calculated according to the actual product, so errors due to variations in the scope and adapter are absorbed. It is possible to do things, and it enables highly accurate measurement. It can also support new scopes.

More accurate measurement becomes possible. Also, when a new scope is released, it can be handled at the user level.

When the focal length f including the magnification is determined by this embodiment, the fiberscope 6 used,
Along with the shooting adapter 11 and ID number of the TV camera 8,
The focal length f including this magnification is registered, and in the case of the same combination next, the measurement is performed without performing the calibration or the calibration is performed again next time according to the operator's selection. Is also good.

Next, a second embodiment of the present invention will be described. Second
The embodiment differs from the first embodiment in that the detection of the center position of the image and the detection of the size of the image are obtained by using image processing. FIG. 6 shows a block diagram of the measuring device 5 in the second embodiment.

The difference from the first embodiment is that an image center position detecting means 41 and an image size detecting means 42 are added to the measuring device 5.

Both are connected to the image acquisition / storage means 31 and the overall control calculation means 37. The image center position detecting means 41 receives the image data from the image storage means 31 in response to a command from the overall control calculating means 37.

In this image data, the brightness of the point where the image exists and the point where the image does not exist is discriminated, and the binarized image is generated. Next, the center of the image is obtained by obtaining the center of gravity of the image. This method is known.

Further, the image size detecting means 42 searches in the direction of the entire circumference 44 from the center 43 of the obtained image as shown in FIG. For example, the line indicated by the search line 45 is sequentially searched from the center 43 of the image. The area on the searched line where the image disappears is the radius on the search line 45. The size of the mask 39 can be detected by averaging the radii thus obtained. This method is also known.

As described above, in the second embodiment, the necessary parameters can be automatically detected from the image by the image processing. Next, a third embodiment of the present invention will be described.

As a third embodiment, the pipe measuring apparatus using the method described in this embodiment is targeted. The pipe measuring method is described in the specification of Japanese Patent Application No. 4-84066 and Japanese Patent Application No. 4-217049 of the present applicant.

In this embodiment, circles corresponding to four sections of the pipe-shaped measurement model 52 assumed for the endoscope 51 shown in FIG. 8 are synthesized on the screen as shown in FIG. ing. This is called a guide 53.

In normal use, since the central axis of the measurement model 52 is aligned with the central axis of the optical system of the endoscope 51, the four circles of the guide 53 are four circles of different sizes. The difference in size indicates the difference in the distance from the endoscope 51 to each cross section. By specifying two points on this screen, the length shown in the above specification is measured.

In this embodiment, the position of the measurement model 52 can be changed manually. The measurement model can be translated or tilted according to the information from the position information / quantity information input means. The shape of the guide 53 when translated is shown in FIG. This figure shows the screen when the measurement model 52 is moved to the lower left of the screen.

The shape of the guide 53 when tilted is shown in FIG. This figure shows a screen when the measurement model 102 is tilted upward. On the other hand, in this embodiment, it is possible to display a double circle guide 54 for confirming the length of the pipe in the sectional direction. This state is shown in FIG. The distance between the double circle guides 54 is displayed as 1 mm at the lower left, for example.

The state of the measurement model at this time is shown in FIG. The double circle guide 54 has a first circle 55 corresponding to the cross section of the model and a second circle for confirming the length of the pipe in the cross sectional direction.
A circle 56 is assumed for the model 52. FIG. 13 shows a double circle guide 54 used when the inside of the pipe is carved.

Although not shown, the double circle guide 54 is a second circle 56 when the object to be observed is overhanging inside the pipe.
Will be inside the first circle 55.

Of course, when performing the above measurement, it is necessary to calibrate the optical system of the endoscope by the method shown in the first and second embodiments.

[0065]

As described above, according to the present invention, the size of the image of the endoscope on the TV screen varies due to variations in the imaging lens system of the endoscope, the photographing adapter, and the TV camera. It is possible to eliminate the measurement error due to the difference from the calculated value.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an image measuring device including a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing the principle of image formation by the image pickup optical system.

FIG. 3 is an explanatory view showing a simplified version of FIG.

FIG. 4 is a block diagram showing a configuration of a measuring device.

FIG. 5 is an explanatory diagram of an operation for obtaining the size and center of an image.

FIG. 6 is a block diagram showing a configuration of a measuring device according to a second embodiment of the present invention.

FIG. 7 is an explanatory diagram of an operation of detecting the size of a mask.

FIG. 8 is an explanatory view showing a state of measuring a pipe in the third embodiment of the present invention.

FIG. 9 is an explanatory diagram showing a state in which a guide is displayed.

FIG. 10 is an explanatory diagram showing a shape of a guide when a measurement model is translated.

FIG. 11 is an explanatory diagram showing the shape of the guide when the measurement model is tilted.

FIG. 12 is an explanatory diagram showing a state in which a double circle guide is displayed.

13 is an explanatory diagram showing a state of a measurement model corresponding to the case of FIG.

[Explanation of symbols]

 1 ... Endoscopic image measuring device 2 ... TV camera external scope 3 ... Light source device 4 ... CCU 5 ... Measuring device 6 ... Fiberscope 7 ... Imaging adapter 8 ... TV camera 11 ... Eyepiece 16 ... Objective optical system 17 ... Object 18 ... Image guide 19 ... Eyepiece optical system 22 ... CCD 25 ... CRT 26 ... Keyboard 27 ... Mouse 29 ... Lens 31 ... Image capture storage means 32 ... Superimpose means 34 ... Display control means 35 ... Cross cursor display instruction Means 36 ... Circle cursor display instruction means 37 ... Overall control calculation means 38 ... Position information / quantity information input means

Claims (2)

[Claims] 1. As constants used for measurement from an image obtained by an image input device, at least a focal length of a lens, a coefficient for correcting lens distortion aberration, a maximum angle of view of the lens, and a maximum An image measuring method using image height and image center position, which comprises a step of obtaining at least an image center and an image size from an image used for measurement, and a calibration for an image measuring apparatus. Method. 2. A constant used for measurement from an image obtained by an image input device, at least a focal length of the lens, a coefficient for correcting distortion of the lens, a maximum angle of view of the lens, and a maximum A measuring device that uses the image height and the center position of the image is characterized by having a center position detecting means for obtaining at least the center of the image from the image used for measurement, and a size detecting means for obtaining the size of the image. Calibration device for image measurement device.