JP2010230423A - Instrument and method for measuring amount of displacement - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately detect movement of a target relating to an instrument for measuring the amount of displacement. <P>SOLUTION: A marker D is put on the target to be measured for photographing. First, a pixel constituting a reference image is weighted by luminance information of the pixel by using an initial image surface first photographed as a reference image surface, so as to calculate the center position coordinate of the reference image. The calculated value and an area expressed as the number of pixels are stored. After the lapse of a predetermined number of times, the marker D is similarly placed on the target to be measured for photographing. Its center position coordinate is calculated by the similar processing, and the value is compared with the stored center position coordinate of the reference image to obtain the difference (amount of displacement). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a displacement measuring apparatus and a measuring method using a photographed image.

Conventionally, a method of using an image to measure the movement or displacement of a specific measurement target is known. This image method has an advantage that a wide range of displacements of a plurality of objects can be measured at a time compared to other methods.
By the way, in the measurement of movement or displacement using an image, the amount of displacement is obtained two-dimensionally using an image photographed by one fixed camera, and three-dimensionally using images photographed by a plurality of fixed cameras. There are cases where the amount of displacement is obtained (see Patent Document 1), but when measuring with a single fixed camera, the amount of displacement on the image to be measured is converted to the amount of displacement in the actual three-dimensional space. For this reason, the accuracy of the actual displacement amount depends on the accuracy of the displacement amount on the image.
That is, in this image type displacement measuring device, the accuracy of the displacement can be actually increased by increasing the accuracy of the displacement in the image, but the measurement resolution is less than or equal to the pixels constituting the captured image, that is, less than one pixel. There is a problem that cannot be made.

JP 2004-77377 A

  The present invention has been made to solve the above-described conventional problems, and its purpose is to reduce the measurement resolution when measuring displacement using a plurality of captured images captured by a camera (imaging device). It is to be able to detect the movement of the object with high accuracy without being limited to one pixel or more as in the prior art.

The invention of claim 1 is a displacement amount measuring device for measuring a displacement amount of a measurement object based on a photographed image obtained by photographing the measurement object, comprising an image processing device and a display unit for processing the photographed image, and the image processing The apparatus includes a luminance measuring unit that measures the luminance of the pixels constituting the captured measurement target image, and weights the luminance information of the pixel obtained by the luminance measuring unit to the position coordinates of the pixels of the measurement target image. The coordinate calculation unit that calculates the center position of the measurement target image on the position coordinate is compared with the displacement amount between the center position of the reference image stored in advance on the position coordinate of the measurement target image and the calculated center position. And a comparison / determination unit that displays the determined displacement amount on the display unit.
According to a second aspect of the present invention, in the displacement amount measuring apparatus according to the first aspect, the coordinate calculation unit calculates the measurement target for each of a plurality of pairs of images obtained by photographing the measurement target in a symmetric direction. The displacement measuring device is characterized in that the center position is calculated by averaging.
According to a third aspect of the present invention, in the displacement amount measuring apparatus according to the first or second aspect, the measurement object is a predetermined shape drawn on an object whose displacement is to be measured or a predetermined shape fixed to the object. It is a displacement amount measuring device characterized by being a sign of.
The invention of claim 4 is a displacement amount measuring method for measuring a displacement amount of a measurement object based on a photographed image obtained by photographing the measurement object, the step of obtaining a photographed image obtained by photographing the measurement object, and the obtained measurement object image A luminance measurement step for measuring the luminance of the pixels constituting the pixel, and weighting the luminance information of the pixel obtained in the luminance measurement step to the position coordinates of the pixels of the measurement target image, on the position coordinates of the measurement target image A position coordinate calculation step for calculating a center position, and a comparison determination step for determining a displacement amount between the center position on the position coordinates of the reference image of the measurement object accumulated in advance and the calculated center position. A display control step of displaying a displacement amount on the display unit.
According to a fifth aspect of the present invention, in the displacement amount measuring method according to the fourth aspect, the position coordinate calculation step calculates the measurement calculated for each of a plurality of pairs of images obtained by photographing the measurement object in a symmetrical direction. A displacement amount measuring method characterized in that the center position of an object is a step of calculating by averaging processing.

  According to the present invention, the size and position of the measurement target image on the image can be measured with subpixel accuracy without being restricted by the size of the pixels constituting the image, so that the displacement detection accuracy is improved. be able to.

It is a figure for demonstrating the basic principle of the image type displacement meter of embodiment of this invention. It is a figure which shows the picked-up image in arrangement | positioning of the camera of FIG. FIG. 3A is a diagram showing a comparison between an initial image of a sign D and an image after a lapse of a predetermined time, in which FIG. 3A shows an initial value together with a cell representing a pixel, and FIG. It is a figure which shows the same image. 4A and 4B are diagrams showing a comparison between an initial image of a sign D and an image after a predetermined time, in which FIG. 4A shows the initial image, and FIG. 4B shows a pixel after the predetermined time has passed. It is the figure shown with the grid. It is the figure which contrasted and showed the image shown to FIG. 4B, and the image actually acquired about the same image, and is the figure shown with the cell which each shows a pixel. Each image when the image shown to FIG. 5B is binarized by changing a threshold value is shown. 6A is an image when the threshold is 80%, FIG. 6B is an image when the threshold is 50%, and FIG. 6C is an image when the threshold is 20%. FIG. 7A is an image for explaining the definition of the coordinate system of the target pixel when the luminance information of the pixel is used, and FIG. 7B is a diagram for explaining the principle of the subpixel processing according to the present embodiment. FIG. 7C is a graph of FIG. 7A along the Y axis (high → low) with the horizontal axis representing the Y coordinate and the vertical axis representing the luminance value. FIGS. 8A and 8B show images taken by panning the camera up and down, respectively, and are displaced 0.3 pixels below and above the image in FIG. 7. It is a functional block diagram of the apparatus for measuring the displacement of the measuring object which concerns on embodiment of this invention. It is a flowchart for demonstrating the displacement amount measurement procedure of the measuring object of this invention.

The present invention will be described based on embodiments shown in the drawings.
In the present embodiment, based on images of a plurality of measurement objects (labels D) photographed by one camera, the luminance information constituting the image is added to the initial image (reference image). ) And an image taken after a predetermined time so that the displacement of the marker D can be measured in less than a pixel unit. Before the description is given, first, the basic principle of the present invention will be described. explain.

FIG. 1 is a diagram for explaining the basic principle of a displacement measuring apparatus according to an embodiment of the present invention.
FIG. 1 is a diagram showing an arrangement relationship between a structure, for example, a bridge B, and a camera C used for measuring a displacement amount, which are displacement measurement targets. Here, a marker D to be measured prepared in advance on both sides of the bridge B is installed at an equal interval in the direction of the camera C by appropriate means such as pasting, and the camera C is displaced. It is installed so that the area you want to measure is within the shooting range.

FIG. 2 is a diagram showing a captured image in the arrangement of FIG.
The position of the sign D photographed first is set as an initial value, and after a predetermined time (period), how much each sign D has moved from that position is measured on the image (the measurement unit at this point is a pixel). . Here, since the size of the sign D is known, it is possible to know from the photographed image how large one pixel is shown at the place (distance) where the sign D is shown. Using this principle, it is possible to calculate how much the sign D is displaced in the real space.

That is, FIG. 3 is a diagram showing an image in which a certain marker D is displaced, FIG. 3A shows its initial value together with a grid representing a pixel, and FIG. 3B shows a similar image of the same marker D after a predetermined time has elapsed. FIG.
That is, as is clear from a comparison between FIG. 3A and FIG. 3B, when a certain period of time has elapsed, the marker D is displaced by two pixels from the initial value.
Here, if this marker D is, for example, a square having a side of 5 cm, the size viewed from the pixel is 5 cm ÷ 10 pixels = 0.5 cm / pixel, that is, the size per pixel of this marker D is 0. It will be 5 cm.
Therefore, when 2 pixels are lowered in FIG. 3B,
0.5 cm / pixel × 2 pixels = 1 cm, which indicates that the displacement amount of the marker D in the real space is 1 cm, that is, the marker D is lowered by 1 cm after a predetermined time.

However, the actual displacement is a continuous amount and is not displaced stepwise by one pixel.
4 is a diagram showing an initial image of a certain sign D compared with an image after a lapse of a predetermined time, as in FIG. 3, where FIG. 4A is the initial image, and FIG. 4B is a view after the lapse of the predetermined time. It is the figure which showed the image with the grid which each shows a pixel.
In FIG. 4B, the upper and lower contour portions of the sign D are hung on the mesh indicating the image, and are imaged in a state of being displaced from the mesh. In this case, the outline portion of the sign D appears or does not appear, that is, it is not an alternative state whether or not an image exists, but appears as a color (gray) between white and black (FIG. 5B). ).

FIG. 5 shows the image shown in FIG. 4B in comparison with the image actually acquired for the same image, and is a diagram showing each pixel together with a grid showing pixels.
In this example, a state where the pixel is displaced downward by approximately 0.3 pixels is shown. Here, when the acquired image is binarized as a general analysis method, the shape of the acquired image naturally changes depending on the threshold value used for binarization.

FIG. 6 shows each image when the image shown in FIG. 5B is binarized by changing the threshold value. 6A is an image when the threshold is 80%, FIG. 6B is an image when the threshold is 50%, and FIG. 6C is an image when the threshold is 20%.
If this is compared with the initial image of FIG. 4A, for example, the displacement amount to the image with the threshold value of 80% is 0.5 pixel, and the displacement amount to the image with the threshold value of 50% is 0 pixel, that is, no change. Yes, the amount of displacement to an image with a threshold of 20% is 0.5 pixels.
As is clear from this, the correct amount of displacement cannot be represented by any image.

Therefore, in the present embodiment, the amount of displacement of the image is expressed more accurately by using luminance information for each pixel measured by an arbitrary luminance measuring unit (not shown).
Next, the principle will be described.
FIG. 7A is a diagram for explaining the definition of the coordinate system of the target pixel when the luminance information of the pixel is used, and FIG. 7B is a diagram for explaining the principle of the sub-pixel processing according to the present embodiment. FIG. 7C is a graph of FIG. 7A along the Y axis (high → low) with the horizontal axis representing the Y coordinate and the vertical axis representing the luminance value.
In FIG. 7A, when the Y axis is taken vertically and the X axis is taken horizontally, the center of the white pixel is taken as the center (+) of the sign D. This is because when the outer black part and the background are black of the same color, the boundary is not known, that is, the boundary melts into the background, and it is impossible to know where the outer black part is.
Here, when the center coordinates are obtained,

図７Ａの場合、標識Ｄの中心座標は（０．５，０．５）になる。
図７Ｂは、図７Ａの画像から０．３画素下方に変位した画像である。
この画像について標識Ｄの中心座標を求めると、

In the case of FIG. 7A, the center coordinates of the marker D are (0.5, 0.5).
FIG. 7B is an image displaced 0.3 pixels downward from the image of FIG. 7A.
When the center coordinates of the sign D are obtained for this image,

  Since the initial value of the center (+) is (0.5, 0.5) and the position after displacement is (0.5, 0.2), the amount of displacement is −0.3 pixels in the Y-axis direction (that is, downward) 0.3 pixels), and the correct result is obtained.

Further, in this method, since the displacement amount of the marker D is calculated from the pixel base, the calculation is based on the size of the marker D, so this principle is effective even when the area is obtained.
Without this principle, the area (of the label D in the image) is wrong ⇒ the conversion amount is different ⇒ the displacement amount is also different, but in this embodiment, such an error does not occur.

When using the luminance information, for example, the luminance value is calculated for each pixel along the Y axis of the sign image in FIG. 7A.
That is, assuming that the upper half of the sign image in FIG. 7A is represented as black, gray, and white parts from the upper half of the sign image, the horizontal axis for each pixel in the upper half of the sign image along the Y axis (high → low) Is the Y coordinate and the vertical axis is the luminance value, the graph shown in FIG. 7C is obtained. Here, assuming that the luminance value of the black portion of the sign is L _A , the white portion is L _B , and the gray at the boundary between black and white is L _C , first, when looking at the upper half of the sign of FIG. Value: L _A ) continues from Y ₁ to Y ₂ of the Y coordinate, then Y ₂ to Y ₃ is a gray portion (luminance value: L _C ), Y ₃ to Y ₄ is a white portion (luminance value: L _B ). The width between the vertical lines in FIG. 7C is equal to the width of the pixel. In the actual imaging screen, the sign image is shifted with respect to the pixel arrangement of the imaging device. Therefore, in order to calculate the luminance value, the actual luminance value is calculated in consideration of the shifted width (less than the width of one pixel). . The weight of a specific pixel can be obtained by the following calculation formula.
_{W (L) = (L C} -L A) / (L B -L A)
Weight to be added to each pixel, obtained by normalizing to 1 0, L _B and L _A.

Next, the principle for improving the accuracy of sub-pixel calculation by camera pan / tilt will be described.
In the present embodiment, the accuracy of displacement measurement is improved based on the above principle, but there is a possibility that an error due to noise or the like may be included because it is based on luminance information.
Therefore, by panning and tilting the camera by a minute angle (less than one pixel is appropriate), a plurality of images are photographed while changing the blurry boundary of the sign D in the photographed image, and the average of the coordinates obtained from them is taken. This can alleviate the effects of errors. For this reason, when an image panned to the left is used, it is necessary to shoot with a pair in which the camera directions are always symmetrical, such as an image panned to the right. This is because if it is biased in either direction, the center position is also biased in the same way.

FIG. 8 is a symmetrical image taken by panning the camera direction up and down, FIG. 8A is an image taken by panning the camera up toward the sign D, and FIG. 8B is similarly panned downward. It is an image that was taken.
According to this embodiment, noise is canceled by changing the direction of the camera to a symmetric direction, and detection accuracy is further improved by taking the average of the center position coordinates on the two-dimensional coordinates calculated in each image. Can do.

FIG. 9 is a functional block diagram of an apparatus for measuring the displacement of the marker D, which is the measurement object described above, and thus the bridge B here.
That is, the displacement measuring apparatus according to the present embodiment performs, for example, the electronic camera 1 for capturing an image of the measurement object, the image processing apparatus 4, the operation of the image processing apparatus 4, setting values, and other inputs. Input device 2 and a display unit 3 for displaying an image or the like. Note that the display unit 3 is not limited to a visual display means such as liquid crystal, and may be one that performs display by sound or light.

The image processing device 4 includes an interface 10 for connecting the image processing device 4 to the camera 1, the input device 2, and the display unit 3, a CPU 12 that controls the entire image processing device 4, a RAM 14, and a luminance measuring unit 16. It consists of not ROM.
Here, the CPU 12 includes a camera control unit 120, a marker searching unit 122, and a comparison determination unit 124 as function realizing means obtained by executing a program stored in the ROM.
The camera control unit 120 periodically photographs the measurement object according to an instruction from the outside or based on a timer. In that case, in order to perform pan control of the camera, a signal for controlling a camera driving unit (not shown) is generated and transmitted to the camera 1 via the interface 10.

The marker searching unit 122 includes a preprocessing unit 122a and a coordinate calculating unit 122b that calculates the position coordinates of the marker D. The pre-processing unit 122a performs processing of the captured image before analyzing the captured image, and the coordinate calculation unit 122b calculates the displacement of the marker D calculated in consideration of the luminance information for each pixel obtained by the luminance measurement unit 16. In order to determine, the position coordinate value of the center of the sign D is calculated by the method described above.
The comparison / determination unit 124 determines whether a displacement has occurred by comparing the initial image and an image (current image) taken after a predetermined time, for example, with the respective center position coordinates, or whether the displacement exceeds a threshold value. When the threshold value is exceeded, control is performed to display the displacement amount on the display unit 3.

The RAM 14 stores an acquired image area 140 for storing an acquired image, an area 142 for storing an intermediate result of processing by the sign D searching unit 122, a reference data area 144 for storing reference data, and various setting values. Region 146 is provided.
The area 142 is provided with an average coordinate area 142a that accommodates the average coordinates of the sign D. The reference data area 144 includes a reference image (initial image) 144a, a reference coordinate 144b of the reference image, and various types of already described various types. The threshold 144c is stored.

FIG. 10 is a flowchart for explaining the procedure for measuring the amount of displacement of the object described above.
When measuring the displacement of the object, first, an image is acquired by a camera, for example, an electronic camera (S101). Before storing the acquired image in the RAM 14, the pixel of the captured image by the luminance measuring unit 16 (FIG. 9) is acquired. The brightness is measured and stored in the RAM 14 together with the image. Subsequently, image processing such as image quality correction performed on the image captured by the camera is performed as preprocessing (S102). Subsequently, a marker position search in the image is performed (S103), the above-described subpixel processing is performed on the marker D whose position has been searched, and an initial value of the marker D, for example, an XY coordinate value of the center thereof is calculated (S104). The calculated initial value and area of the sign D are calculated and stored in the storage device. The above processing is performed for all the labels D (S106).
After a predetermined time from the above processing, an image is acquired for the same sign D in the same manner as described above (S107), and in this case as well, before the acquired image is stored in the RAM 14, the luminance measurement unit 16 (FIG. 9) The luminance of the pixel is measured and stored in the RAM 14 together with the image. Subsequently, the same pre-processing as described above is performed (S108), the marker position search in the image is subsequently performed (S109), and the sub-pixel process similar to step S104 is performed for the marker D whose position has been searched (S110). The movement amount is calculated (S111). Subsequently, the movement amount is compared with a predetermined threshold value (S112), and whether or not the movement amount exceeds the threshold value is checked (S113). To a predetermined department or the like (S114). When the above process is completed for all the signs D (S115), it is determined again whether or not the process after step S107 is continued. When the process is not continued (S116, NO), the process is terminated.

  As described above, according to the present embodiment, by using the luminance information of the measurement target image, more detailed displacement, that is, one pixel of the measurement target image, which is impossible with the conventional pixel-based displacement detection. Displacement less than can be measured accurately. Also, by using multiple images taken at a pair of symmetrical shooting positions with the camera direction, noise in the luminance information can be removed, and the position coordinates of the center position calculated in each image are averaged Thus, the center coordinate position can be calculated with higher accuracy.

  DESCRIPTION OF SYMBOLS 1 ... Electronic camera, 2 ... Input device, 3 ... Display part, 4 ... Image processing apparatus, 10 ... Interface, 12 ... CPU, 14 ... RAM, 16 ... A luminance measuring unit, 120 ... a camera control unit, 122 ... a sign searching unit, 124 ... a comparison / determination unit.

Claims (5)

A displacement measuring device for measuring a displacement of a measurement object based on a photographed image obtained by photographing the measurement object,
An image processing apparatus for processing the captured image and a display unit;
The image processing apparatus includes a luminance measurement unit that measures the luminance of pixels constituting the captured measurement target image, and the weight of the luminance information of the pixel obtained by the luminance measurement unit in the position coordinates of the pixel of the measurement target image. In addition, a coordinate calculation unit that calculates a center position on the position coordinates of the measurement target image, and a displacement between the center position on the position coordinates of the reference image stored in advance and the calculated center position A comparison and determination unit that compares and determines the amount, and displays the determined displacement amount on the display unit;
A displacement amount measuring apparatus comprising: In the displacement amount measuring device according to claim 1,
The coordinate calculation unit calculates the displacement of the measurement object by averaging the center position of the measurement object calculated for each of a plurality of pairs of images obtained by photographing the measurement object in a symmetric direction. apparatus. In the displacement amount measuring apparatus according to claim 1 or 2,
The displacement measurement apparatus according to claim 1, wherein the measurement object is a mark having a predetermined shape drawn on the object whose displacement is to be measured or a predetermined shape fixed to the object. A displacement measurement method for measuring a displacement of a measurement object based on a photographed image obtained by photographing the measurement object,
A step of acquiring a photographed image obtained by photographing the measurement target, a luminance measurement step of measuring the luminance of the pixels constituting the acquired measurement target image, and the pixel obtained in the luminance measurement step in the position coordinates of the pixels of the measurement target image The position coordinate calculation step of calculating the center position on the position coordinates of the measurement target image with the weight of the luminance information is calculated, and the center position on the position coordinates of the reference image stored in advance is calculated. A comparison determination step of determining a displacement amount with respect to the center position, a display control step of displaying the determined displacement amount on the display unit,
A displacement measuring method characterized by comprising: In the displacement amount measuring method according to claim 4,
The position coordinate calculation step is a step of calculating a center position of the measurement object calculated for each of a plurality of pairs of images obtained by photographing the measurement object in a symmetrical direction, and calculating the average position. Displacement amount measurement method.

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