KR102074073B1 - Method for detecting vehicles and apparatus using the same - Google Patents

Abstract

Disclosed are an image processing-based vehicle recognition method and an apparatus using the same, which can reduce an amount of computation while maintaining a recognition rate. The vehicle recognition method acquires a road image, forms two windows having variable sizes in an area of a moving object in the road image, slides two windows to overlap each other, and compares similarities between histograms of the two windows. Based on the comparison result of the similarity, the vehicle recognizes whether the vehicle is located or the area of the vehicle, where the two windows show the front side of the vehicle corresponding to the moving object and split in half. Have

Description

Vehicle recognition method and apparatus using same {METHOD FOR DETECTING VEHICLES AND APPARATUS USING THE SAME}

Embodiments of the present invention relate to a vehicle recognition method, and more particularly, to an image processing-based vehicle recognition method and apparatus using the same that can reduce the amount of computation while maintaining the recognition rate.

The next-generation Cooperative Intelligent Transport Systems (C-ITS), which is being actively researched recently, has a separate system for collecting and providing traffic information, unlike existing ITS, which has limitations in providing information according to space. As a result, continuous and rapid information sharing between the vehicle and the vehicle (V2V) and the vehicle and the road infrastructure (V2I) enables active proactive response and prevention.

The advanced road infrastructure that collects traffic information through video in C-ITS provides a variety of information necessary for driving of autonomous cars, thereby limiting the cost issues such as limited perception range of autonomous cars and expensive sensor equipment. It can be overcome.

On-road vehicle awareness is critical for C-ITS and advanced road infrastructure. The Scale-Invariant Feature Transform (SIFT) algorithm, which is typically used to recognize a specific object in the image recognition field, has a problem that a large amount of computation and reference models (images) of various vehicles are required in advance, thus realizing an unspecified number of vehicles in real time. There is no way to implement a system that recognizes this as a system.

More specifically, the most important factor in collecting traffic information using images is a problem of accurately recognizing a moving object suspected as a vehicle as one complete vehicle. Until now, the vehicle has been recognized using motion history, scale-invariant feature transform (SIFT), mean shift using histogram back-projection, and machine learning algorithms.

The motion history algorithm is an algorithm for estimating the motion of a moving object by binarizing values above a threshold value in each result image through difference operations of adjacent frames, and then superimposing the result images for a short time. However, there is a disadvantage that the moving object is not recognized when the image frame is stopped for a long time due to the congestion of the vehicle.

In the case of the SIFT algorithm, the vehicle is recognized through object matching between frames based on the feature points, so that the vehicle can be recognized regardless of time. However, the amount of computation to process is so large that real-time processing is impossible. In some cases, two to three seconds are performed in one frame calculation. In addition, since it is necessary to input the vehicle model images in advance, it is very limited to detect an unspecified number of vehicles.

Mean-Shift using the histogram inverse projection technique measures the similarity in the input image using a Hue channel histogram and performs Mean-Shift on the probability distribution obtained by changing the pixel value of the image into a probability value. However, as with SIFT, it requires practical information, so it is virtually impossible to detect an unspecified number of vehicles.

Recently, a lot of vehicle detection methods using machine learning have been studied. Like SIFT, computational complexity is so large that real-time processing is impossible.

As such, there is a need for a vehicle recognition method capable of reducing the amount of computation for real time recognition while maintaining or increasing the recognition rate for a plurality of unspecified vehicles.

The present invention overcomes the problem of detecting high computational complexity (not run-time processing) of the existing algorithms or only a vehicle that has been promised in advance, and reduces the amount of computation while increasing the recognition rate, and uses a histogram-based decalcomani matching algorithm. A recognition method and an apparatus using the same are provided.

Another object of the present invention is to overcome the problems of existing vehicle recognition methods, which are difficult to process in real time due to high computational complexity, and are useful in vehicle detection methods using a histogram-based decalcommani matching algorithm and apparatus using the same. To provide.

In order to achieve the above technical problem, the vehicle recognition method according to an aspect of the present invention defines a road area through a preprocessing process for an image input from a road infrastructure camera, accumulates input frames to generate a background image, The moving object on the road is detected through a difference operation between the background image and the current input frame, the detected moving object is separated into a separate image window, and a histogram-based decalcomani matching process is performed within the separated image window. The similarity is calculated, and the similarity value is analyzed to determine the authenticity of the vehicle.

According to another aspect of the present invention, there is provided a vehicle recognition method, which defines a road area as an ROI in an image input from a camera, generates a background image by accumulating input frames, and generates a background image. It detects moving objects on the road by performing the difference operation between the current input frames, separates the detected moving objects into image windows, measures similarity by applying histogram decalcomani matching within the separated image windows, and a certain number of images The above processes are repeated until they accumulate, and the similarity coefficients according to the histogram decalcomani matching are analyzed to determine the authenticity of the vehicle.

According to another aspect of the present invention, there is provided a vehicle recognition method, comprising: generating a binary polygon image by receiving a plurality of coordinates in an input frame, wherein the polygon image is defined as a region of interest; Accumulating input frames to generate a background image; Obtaining only a polygonal inner region through a logical operation between the polygonal image and the currently input frame; The result of the difference operation between the background image and the current input frame is set as an absolute value, binarization is performed by comparing with a predetermined threshold value, and a moving object on the road is detected by estimating a coordinate having a pixel value equal to or greater than a predetermined threshold value as a coordinate at which movement occurs. step; Dividing a rectangular area defined as an outline of the moving object in half with respect to a vertical center line; Obtaining a histogram using original pixel values of the left and right window regions divided in half and comparing them with each other; Calculating the histogram similarity of the left and right window areas by gradually increasing the width of the left and right window areas, and finding the center of the vehicle by stopping the sliding at the point where the calculated value is the highest; And determining whether the moving object is a vehicle based on a similarity coefficient or a comparison coefficient of the histograms for the left and right window regions.

In one embodiment, the method for recognizing a vehicle may include: performing median filtering to remove noise in an image including the moving object after detecting the moving object; Performing a morphology operation such that object separation of the mobile object is suppressed or the divided object chunks of the mobile object are merged; And slicing the part of the object inflated to the outside by the morphology call operation or the expansion operation to restore the original size to the original size through an erosion operation.

In one embodiment, the step of performing a morphology operation, if there is a division in the vertical direction in the moving object, by defining the size of the mask used for merging to 2X8 to be more dilation in the vertical direction Can be.

Here, the morphology call operation is a value of all the pixels in the area covered by the mask as the center pixel value of the area covered by the mask while passing the center of the mask to all pixel positions of the object portion or the white area of the input image. It may refer to a process of converting to or converting to a center coordinate pixel. The shape and size of the mask can be tuned or determined differently depending on the installation position of the camera.

In an embodiment, the generating of the background image may include accumulating consecutive input frames with a predetermined weight to obtain the background image, and the background image may include a two-lane road portion having a predetermined length in front of the vehicle. have.

In an exemplary embodiment, the dividing may include calculating a rectangular region by examining outermost pixel coordinates in up, down, left, and right directions having a white pixel value in the object image of the moving object, and calculating brightness values of an input frame. By separating the object area of the moving object, a new image for the moving object can be created.

In one embodiment, the step of finding the center of the vehicle, in the calculation of the degree of similarity if the similarity coefficient is out of a predetermined range to widen the step of sliding and enter the range by a little increase in the sliding step to control the operation speed and precision Can be.

According to another aspect of the present invention, there is provided a vehicle recognition apparatus, including: a setting unit defining a road area in an input image; An accumulator for accumulating the input image or the input frame to generate a background image; A difference calculation unit for detecting a moving object on a road through a subtraction between the background image and a current input frame; A separator that separates the ROI corresponding to the detected moving object into two image windows; A similarity measurer comparing the similarity of the histograms of the two image windows; And a determination unit determining whether the vehicle is authentic or the vehicle area based on the similarity coefficient obtained through the similarity measuring unit.

In one embodiment, the setter, the accumulator, the difference calculator, the separator, the similarity measurer, the determiner, or a combination thereof are stored in a memory in the form of one or more software modules or programs. A processor that executes the program may be connected.

In order to achieve the above technical problem, a vehicle recognition method according to another aspect of the present invention, acquires a road image, forms two windows having a variable size in the area of the moving object in the road image, and two windows Sliding and overlapping each other, comparing the similarity between the histograms of the two windows, and recognizes whether the vehicle or the vehicle area based on the comparison result of the similarity, where the two windows are viewed from the front of the vehicle corresponding to the moving object When divided into two parts, the divided parts are symmetrical to each other.

In an embodiment, the process of acquiring a road image and forming two windows may set an ROI, detect an object through background removal, and correspond to the process. After the object detection process by setting the ROI and removing the background, the morphology calculation used as the shape feature may be performed. The histogram decalcomani matching performed after the morphology operation and the morphology operation may correspond to a process of comparing similarities between histograms of two windows.

As described above, according to an embodiment of the present invention, when the vehicle is viewed from the front, the vehicle (vehicle region) in the image is halved on the basis of the physical or morphological characteristics that when the vehicle is divided in half, the left and right are the same in symmetrical form. In order to accurately measure the similarity of the left and right images obtained by dividing, a histogram comparison technique is used. Here, the histogram represents the frequency of the intensity value (that is, the pixel value) of the image and may be used to determine the characteristics of the image.

According to another aspect of the present invention, there is provided a vehicle recognition method, including: defining a road area in an input image, generating a background image by accumulating an input image or an input frame, a background image, and a current input. Detecting a moving object on the road through a difference operation between frames, superimposing two image windows of the same size in the area of the detected moving object, comparing the similarity of the histograms of two image windows arranged by sliding side by side; And determining the authenticity of the vehicle and the vehicle area based on the similarity coefficient obtained as a result of the similarity comparison.

In another aspect of the present invention to achieve the above technical problem, a setting unit for defining a road area in the input image, the accumulation unit for accumulating the input image or input frame to generate a background image, the background image and the current input frame ( A difference calculation unit for detecting a moving object on the road through subtraction between the current frame), a separation unit for separating the moving object into two image windows, a similarity measuring unit comparing the similarity of the histograms of the two image windows, and the measured The vehicle recognition apparatus may include a determination unit that determines whether the vehicle is authentic and / or the vehicle area based on the similarity coefficient.

In another aspect of the present invention, a memory for storing a program, and a processor coupled to the memory, the processor performs a program to define a road area in the input image, the input image or Accumulate input frames to create a background image, detect moving objects on the road by calculating the difference between the background image and the current input frame, separate the moving objects into two image windows, compare the similarity of histograms of the two image windows, The vehicle recognition apparatus may determine whether the vehicle is authentic and / or the vehicle region based on the similarity coefficient obtained as a result of the similarity comparison.

According to an embodiment, the program may include a setting module that defines a road area in an input image, a cumulative module that accumulates an input image or an input frame, and generates a background image. Vehicle authenticity and vehicle area based on the similarity coefficient measured in the difference calculation module for detecting, the separation module for separating the moving object into two image windows, the similarity measuring module for comparing the similarity of histograms of the two image windows, and the similarity measuring module. It may include a determination module or a combination thereof to determine the.

According to the embodiments of the present invention as described above, when looking at the vehicle from the front and divided in half relatively precisely for the determination of the vehicle which is the moving object on the road, the vehicle is effectively utilized by using the visual feature that both sides are symmetrical. Can be recognized reliably. The vehicle recognition method of this embodiment may be referred to as a vehicle recognition method using histogram decalcomani matching.

According to the present exemplary embodiment, two windows having a variable size may be slid to a moving object area on a road, and the vehicle area, that is, the vehicle may be recognized by comparing the similarity of the histograms of the two windows. As a result of the actual measurement, it was confirmed that the vehicle recognition rate of more than 97.2% is achieved in real time for the vehicles located within 20 ~ 40m. As described above, according to the present exemplary embodiment, there is an advantage in that a vehicle which is a moving object on a road can be efficiently recognized with a small amount of calculation.

In addition, using the vehicle recognition method and apparatus of the present embodiment, it is possible to implement in a small, low-power, low-cost mobile embedded platform through a low computational image processing algorithm to the back roads without a current loop detector or VDS installed Cameras can be installed in every corner of the road to contribute to the collection and provision of key traffic information (traffic volume, etc.) between all roads.

1 is a flowchart illustrating a vehicle recognition method according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating a process of setting a region of interest in which object detection is to be performed in the method of FIG. 1.
FIG. 3 is an exemplary diagram of a background image using a running average that may be employed in the method of FIG. 1.
FIG. 4 is a diagram illustrating an object detection result using background removal employed in the method of FIG. 1.
FIG. 5 is a diagram illustrating a noise removal process using median filtering employed in the method of FIG. 1.
FIG. 6 is a view for explaining object mass disambiguation using morphology operations that may be employed in the method of FIG. 1.
FIG. 7 is a view for explaining window separation using a moving object image that may be employed in the method of FIG. 1.
FIG. 8 is a diagram for describing a window sliding process that may be employed in the method of FIG. 1.
FIG. 9 is a diagram for describing a histogram decalcomani matching technique that may be employed in the method of FIG. 1.
10 is an exemplary view showing an experimental result for the method of FIG.
11 is a block diagram of an apparatus using a vehicle recognition method according to another embodiment of the present invention.

As the invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description. However, this is not intended to limit the present invention to specific embodiments, it should be understood to include all changes, equivalents, and substitutes included in the spirit and scope of the present invention. In describing the drawings, similar reference numerals are used for similar elements.

Terms such as first, second, A, and B may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as the second component, and similarly, the second component may also be referred to as the first component. The term and / or includes a combination of a plurality of related items or any item of a plurality of related items.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. As used herein, the terms “comprise,” “having,” and the like are intended to indicate that there is a feature, number, step, action, component, part, or combination thereof described in the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, components, or a combination thereof.

Unless otherwise defined herein, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in the commonly used dictionaries are to be interpreted in a meaning consistent with the contextual meaning of the related art, and are not to be construed in ideal or excessively formal meanings unless expressly defined herein.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a flowchart of a vehicle recognition method according to an embodiment of the present invention.

The overall process or operating algorithm execution process of the image detection system implementing the vehicle recognition method of the present embodiment includes preprocessing (S10) and looping (loop, S20) procedures as shown in FIG.

The road area is defined through the preprocessing process of the image input from the road infrastructure camera to block the effects of noise from the non-road area. Then, the average background image is generated by accumulating the input frames, and the moving objects on the road are detected by performing a difference operation between the background image and the current input frame. After that, each object is separated into a separate image window, and the similarity is calculated through histogram-based decalcomani matching. Finally, the similarity value is analyzed to determine the authenticity of the vehicle.

In other representations, the road region is defined as a region of interest (ROI) in the image (First Frame, S12) input from the fixed camera based on the infrastructure in the preprocessing (S10) (S14). Minimize the effect due to the area noise.

Next, in the loop S20, input frames are accumulated (S22) to generate a background image, and a subtraction between the background image and the current input frame is performed (S24) to detect a moving object on the road. do.

Next, the object obtained previously in the loop (S20) process is separated into each image window, and histogram decalcomani matching (S26) is applied in the separated window to measure similarity. The above steps S22, S24, and S26 may be repeatedly performed until a predetermined number of images are accumulated (S28). Then, it is possible to determine the authenticity of the vehicle by analyzing the similarity coefficient according to the histogram decalcomani matching.

Hereinafter, each step of the preprocessing S10 and the loop S20 will be described in more detail.

FIG. 2 is a diagram illustrating a process of setting a region of interest in which object detection is to be performed in the method of FIG. 1.

The first process of the vehicle detection algorithm (corresponding to the vehicle recognition method) according to the present embodiment is to set a region of interest in an input frame. An area excluding a road area in which a vehicle is detected in a frame input through a fixed camera may be noise in an operation to be performed in a later step. Therefore, the road area is set as the area of interest to minimize noise and errors caused by factors outside the area.

The ROI setting may be performed as shown in FIG. 2. A region of interest is defined by generating a binarized polygonal image 22 having an internal pixel value of 255 and an external pixel value of 0 by receiving a plurality of coordinates in the first input frame. Then, only the polygonal inner region may be obtained through a logic (AND) operation between the polygon image 22 and the currently input frame 21 (see 23).

Moving objects on the road in vehicle detection are important information suspected to be vehicles. Most commonly used moving object detection algorithms include background subtraction, motion history, optical flow, and the like. However, in the present embodiment, a relatively small amount of computation and a simple implementation are performed. To detect objects on moving roads.

Object detection using background removal is the simplest and most effective method of motion detection. It calculates the difference operation between the background image and the current input frame and converts coordinates with pixel values above a certain threshold It can be estimated.

FIG. 3 is an exemplary diagram of a background image using a running average that may be employed in the method of FIG. 1.

Referring to FIG. 3, a running average is obtained by accumulating consecutive input frames with a predetermined weight to obtain a background image (see 25). The background image includes a portion of the two-lane road of a certain length in front of the vehicle.

The running average may be represented by a calculation formula such as Equation 1 below.

는 현재 프레임

에서 입력된 영상의 픽셀 값,

는

까지의 평균 픽셀 값, 그리고

는 가중치로 새로이 입력된 영상

가 이전까지 평균값

에 얼마만큼 영향을 주는지에 대한 값으로, 적절한 이동평균배경을 얻기 위해서 적절하게 설정해 주어야 한다. 예를 들어 200프레임의 영상을 누적하여 배경을 획득할 경우

의 값은 0.005의 값이 된다.In Equation 1 above

Is the current frame

Pixel value of the image input from

Is

Average pixel values up to and

Is the newly input image with weight

Averaged until

It is a value that affects how much it affects, and should be set appropriately to obtain an appropriate moving average background. For example, if you acquire a background by accumulating 200 frames of video

The value of becomes 0.005.

FIG. 4 is a diagram illustrating an object detection result using background removal employed in the method of FIG. 1.

As shown in FIG. 4, extracting a background image from an input frame is performed by using Equation 2 below, and sets a result of a difference operation between the current input frame and the accumulated background image as an absolute value and a predetermined threshold value. Image binarization is performed by comparison (see 27).

As a result, after the pixel in which the motion in the input frame is generated is obtained through the difference operation with the background image, the moving object can be extracted through the binarization by selecting the pixel having the extreme value change larger than a certain level. . The extreme change in value may correspond to the motion suspected pixel. The dotted circle portion of the binarized image 27 is shown enlarged below (see 28).

) 내 객체 추출에 적용된 계산 수식을 나타낸다.Equation 2 is the input image (

) Shows the calculation formula applied to extract objects.

FIG. 5 is a diagram illustrating a noise noise removing process using median filtering employed in the method of FIG. 1.

In the binarized object image obtained in the previous step as a moving object, the difference between the pixel brightness of the background image and the object does not exceed the threshold value, so that a single object is divided into multiple chunks. Therefore, at this stage, you can apply morphology operations to suppress object separation.

As shown in FIG. 5, before merging the separated object masses into one object, the difference in pixel values between the background image and the input frame changes drastically and appears as white in the binarized object image. White spots within the portion) (see 31). Area-based treatments that are effective against this salt noise include median filtering (see 32).

Median filtering is a representative nonlinear filtering that selects the middle value among the overlapping pixel values and performs filtering. White (black is 255) and black (zero is pixel), such as salt noise or salt and pepper noise. It can be effectively used to suppress noise close to.

After removing the noise, we can perform the morphology operation for merging the chunks of the divided objects.

FIG. 6 is a view for explaining object mass coupling using morphology calculation that may be employed in the method of FIG. 1. 6 illustrates an example in which connection elements of an object are correctly combined through morphology calculation.

As shown in FIG. 6, the mobile object suspected of being a vehicle can be seen that the division occurred in the vertical direction by the installation angle of the camera installed to face the road in front (see 33). Therefore, in the present exemplary embodiment, the size of the mask used for merging the divided object chunks may be defined as 2 × 8 so that more dilation occurs in the vertical direction (see 34).

If the size of the mask is empirically determined in the above manner, the mask must be artificially manipulated according to the distance (perspective) between the vehicle and the camera. Generally, when the camera of the VDS recognizes the vehicle for traffic measurement, the vehicle is viewed in front of the vehicle. The distance between the camera and the subject becomes constant because the vehicle recognizes when the vehicle passes through a specific reference point (ROI), so it is only necessary to artificially determine the first camera installation. In addition, since the reference point is generally set at a certain distance not far from the camera installation point, the tuning time for determining the shape and size of the mask does not take much even if the installation environment is different.

The morphology called operation described above may be performed as in Equation 3 below.

의 객체 부분(white 영역)의 모든 픽셀 위치로 마스크

의 중심좌표가 지나다니면서 마스크

이 덮치는 부분은 모두 화이트(white) 픽셀로 전환하는 과정을 지칭한다. 예컨대, 씌워지는 영역의 중심좌표픽셀 값이 255일 때, 마스크로 씌워지는 영역을 255로 바꾸는 과정이다. 결과적으로 차량으로 의심되는 객체를 마스크 크기만큼 외부로 팽창시켜 끊어져있던 요소들을 상호 연결해주는 역할을 하게 된다(도 6의 33 참조).In Equation 3, the morphology call operation is input image.

Mask to all pixel positions in the object portion of the (white region) of

Mask as the center coordinates pass by

All of these overlapping parts refer to the process of converting to white pixels. For example, when the center coordinate pixel value of the area to be covered is 255, the process of changing the area covered by the mask to 255. As a result, the object suspected of being a vehicle is inflated to the outside by the size of a mask to serve to interconnect broken elements (see 33 in FIG. 6).

Then, ie, if the object connection element is preferably coupled, after the expansion operation is performed through the erosion operation, the part of the object that has been expanded outwardly is cut back to its original size (see 34 in FIG. 6). Equation 4 below represents an erosion operation.

In the present embodiment, a histogram is used to determine the presence or absence of a moving object on a road. A histogram is a representative image processing technique that analyzes the characteristics of an image and calculates the frequency of pixel values of an image to indicate how many times the pixel value is included in the image. In this embodiment, when the vehicle is viewed from the front or the rear, it has a visual characteristic that the left and right are symmetrical (decalcomani) when divided in half. Therefore, the rectangular area (box area in 36 in FIG. 7) defined as the coutour of the moving object obtained in the previous steps is divided in half with respect to the vertical center line, and the histogram is obtained from the original pixel values of the left and right areas. Comparing with each other, it can be seen that it has a high similarity. This high similarity coefficient can be used as an important measure for determining whether the moving object is a vehicle.

Incidentally, the above characteristics remind us of Decalcomanie, one of the painting techniques of art where the two sides have the same pattern by applying paint on paper and folding it in two layers or squeezing and peeling another paper over it. . Therefore, if the two histograms are compared by dividing the object area in the moving object image obtained in the previous step in half, a high comparison coefficient can be obtained in a specific region. Therefore, in the present embodiment, such a comparison coefficient can be used as a measure for determining a vehicle of an object.

FIG. 7 is a view for explaining window separation using a moving object image that may be employed in the method of FIG. 1.

Referring to FIG. 7, outline information of an object is used to separate an object area from an input frame 35. In the object image, the rectangular area may be calculated by examining the outermost pixel coordinates in four directions of up, down, left, and right of each object having a white pixel value 255 (see 35). Separation can be performed by making the calculated area a new image. If each area of the calculated object image is imported as it is, only two values of binarized 0 and 255 will be calculated when the histogram is calculated (see 36). Accordingly, new images 371, 372, and 373 may be obtained by separating an object region from a gray-scale image in which brightness values of input frames are calculated.

On the other hand, to calculate the decalcomani characteristics of the object, it is necessary to calculate the histogram of two divided images by dividing the object vertically and then compare them. However, the object estimated to be a vehicle in the separated image includes the shadow component. When the vehicle estimation object in the image is divided in half by these shadows, the center cannot be the center of the vehicle. Accordingly, the vehicle recognition method according to the present embodiment calculates the histogram similarity of the left and right window regions by gradually increasing the width of the left and right windows and gradually sliding the left or right side to increase the accuracy when determining the vehicle using the separated object. The true vehicle center can be found by stopping the sliding at the point with the highest calculated value.

FIG. 8 is a diagram for describing a window sliding process that may be employed in the method of FIG. 1. FIG. 8 shows a process of sliding two region windows to perform a similarity calculation using the decalcomani characteristic.

As mentioned above, since there is a high probability of containing unnecessary shadows, the two left and right windows for which the histogram is to be calculated are increased by a certain weight, that is, from left to right and sequentially from right to left, to calculate the similarity in both directions. The results can be compared. In this case, the direction in which the shadow is generated has a low similarity compared to the opposite direction, thereby eliminating errors due to the shadow. That is, it is possible to suppress the recognition of unnecessary shadow components as objects through a sliding process that effectively removes a specific surrounding background including a shadow.

As described above, in the present embodiment, when calculating the decalcomani characteristic of the object, that is, the shadows are generated when the two windows 38 and 39 for which the histogram is calculated are increased by a certain weight and compared from left to right and right to left. The error caused by the shadow can be eliminated by using the point that the inclined direction has a lower similarity than the opposite direction.

For the above-described histogram comparison calculation, the Battacharyya matching technique, which is a representative histogram comparison technique, may be used as a similarity calculation formula in this embodiment. Batchaya matching is a statistical algorithm that measures the similarity of the data represented by the histogram, and can be defined as shown in Equation 5 in the histogram on which normalization is performed.

와

는 이전 단계에서 분할된 객체의 좌우 이미지의 히스토그램으로 i에 따른 각 빈(bin)의 값을 의미한다.

는 히스토그램의 모든 빈의 값을 빈의 개수로 나눈 평균값으로서

로 나타낼 수 있다.

은 히스토그램 빈의 수를 나타낸다. 이렇게 얻어진 비교 계수

는

의 범위를 가지고 있으며 d의 값이 0에 가까울수록 두 히스토그램이 유사한 히스토그램임을 나타낸다. 완벽하게 일치하는 이미지일 경우 0의 값을 갖는다.In Equation 5 above

Wow

Is a histogram of the left and right images of the object divided in the previous step, and means the value of each bin according to i.

Is the average of all bins in the histogram divided by the number of bins.

It can be represented as.

Represents the number of histogram bins. The comparison coefficient thus obtained

Is

It has a range of and the closer d is to 0, the more similar histograms are. If the image is a perfect match, it has a value of zero.

FIG. 9 is a diagram for explaining an example of a histogram decalcomani matching technique employed in the method of FIG. 1.

As shown in FIG. 9, the histogram comparison is performed for each window of each size while performing the window sliding described in the previous step (see FIG. 8). As a result of the comparison, the window with the lowest coefficient (the two most similar images) can be detected by the vehicle. In the present embodiment, the comparison coefficient has the smallest value in the example (X).

Therefore, experiments were performed using more than 1000 vehicle image samples to find average comparison coefficients of vehicles, and the center of gravity of the vehicle was found in the similarity coefficient ranging from 0 to 0.376. In other words, when the similarity coefficient is not within the range, the sliding step can be widened, and when the similarity coefficient is within the range, the sliding step can be increased little by little to increase the computation speed and precision.

10 is an exemplary view showing an experimental result for the method of FIG.

Referring to FIG. 10, a performance analysis result of the histogram decalcomani matching technique described above may be confirmed.

Calculate the difference (error) between the center coordinates of the actual vehicle area and the center coordinates of the vehicle area automatically recognized by the decalcommani matching algorithm of the present embodiment for the performance evaluation of the algorithm (decalcomani matching algorithm) implementing the vehicle recognition method of this embodiment. Looked.

The unit of measurement of the error distance is pixels, and the error ratio is expressed as a ratio obtained by dividing the number of error pixels by the width of an area determined to be an area of an actual vehicle. For example, an error pixel is expressed as a ratio of the size of the actual vehicle area by dividing an error pixel by a width of an area manually determined as an area of the actual vehicle in consideration of the relative size of one pixel according to the distance. In addition, the recognition rate was tested by expressing the shared area between the real vehicle area and the recognized vehicle area by the ratio divided by the real vehicle area.

Table 1 above shows the result of applying the decalcomani matching algorithm for a vehicle moving at a distance of 20 to 40 meters from the camera during a sunny day. The average error and average vehicle calculated by applying this algorithm while photographing roads for a certain period of time. Recognition rate is shown.

In addition, as shown in FIGS. 10A to 10D, it can be seen that the result of the embodiment indicated by the blue region 41 and the actual vehicle region indicated by the red region 42 substantially coincide.

As can be seen from the calculated data, it can be seen that the algorithm according to the present embodiment has a relatively very accurate recognition rate and a small error when the weather is clear.

On the other hand, the recognition rate and error by bad weather and time are also important, so experiments were conducted for various situations and the results are summarized in Table 2.

As expected, the rate of error was high in the case of rain and the rate increased sharply in the rainy evening. This was confirmed because headlights reflected by rainwater at the bottom of the road interfered with matching. As a result, the recognition rate drops sharply. On the other hand, if the amount of snow comes, the recognition rate was higher than the clear weather. The reason is that the floor surface turns white so that the obstacles such as lanes and shadows on the road surface are removed and the background separation becomes clear. In the case of a snowy evening, the accuracy is reduced, which is better than that of a rainy evening.

11 is a block diagram of an apparatus using a vehicle recognition method according to another embodiment of the present invention.

Referring to FIG. 11, the apparatus according to the present embodiment may include a processor 50 and a memory 60 to use a vehicle recognition method. Such a device may be one of a vehicle controller mounted on a vehicle. In addition, such a device may be implemented as at least some functional units or components of a user terminal detachable from a vehicle or an intelligent mobile system of the user (see 100 of FIG. 1). The user terminal may be implemented as one or more terminals selected from a navigation, a black box, a smart phone, a mobile terminal, a tablet computer, and the like having a camera and image processing means.

The processor 50 may execute a program or software modules stored in the memory 60 to perform an operation according to the vehicle recognition method. In one example, the processor 50 defines a road area in the input image, generates a background image by accumulating the input image or the input frame, and generates a road through subtraction between the background image and the current input frame (current frame). The moving object may be detected, the moving object may be separated into two image windows, the similarity of the histograms of the two image windows may be compared, and whether the vehicle may be determined based on the compared similarity coefficients.

The memory 60 may include software modules for implementing a vehicle recognition method. The software modules may include a setting unit 61 defining a road area in the input image, an accumulator 62 accumulating the input image or an input frame to generate a background image, and a difference operation between the background image and the current input frame (current frame). a difference calculation unit 63 for detecting a moving object on the road through subtraction, a separating unit 64 for separating the moving object into two image windows, a similarity measuring unit 65 for comparing the similarity between the histograms of the two image windows, and The determination unit 66 may determine the authenticity of the vehicle based on the measured similarity coefficient. In addition, software modules may be grouped into preprocessing modules and loop modules in a group form (see FIG. 1).

The above-described processor 50 may include at least one central processing unit, and the central processing unit (CPU) may include an SOC (microcontrol unit) and a peripheral device (an integrated circuit for an external expansion unit). system on chip), but is not limited thereto. The core is a register that stores instructions to be processed, an arithmetic logical unit (ALU) that is responsible for comparison, determination, and operation, and a controller that internally controls the CPU for interpretation and execution of instructions. (control unit), and an internal bus connecting them.

In addition, the processor 50 may include, but is not limited to, one or more data processors, an image processor, or a codec. The processor 50 may have a peripheral device interface and a memory interface. The peripheral interface may connect the processor 50 to the input / output system and various other peripheral devices, and the memory interface may connect the processor 50 to the memory 60.

In addition, the above-described memory 60 may include volatile memory such as non-volatile random access memory (NVRAM), dynamic random access memory (DRAM), a hard disk drive (HDD), an optical storage device, It may be implemented as a flash memory, and may store an operating system, a program, a command set, etc. in addition to software modules for implementing a vehicle recognition method.

According to the embodiments described above, a new vehicle recognition method using a histogram decalcomani matching technique can be provided. In other words, it uses the visual or morphological characteristics that the left and right are the same when the vehicle is divided in half, and additionally moves the half objects on the road from side to side through the sliding step to overcome the influence of obstacles such as shadows. In comparison, vehicle recognition can be effectively performed.

On the other hand, the results of the performance analysis according to the above embodiments confirmed that the vehicle has an error rate of 97.2% and an error rate of the actual vehicle center point of 9.58%. The most common cause of this error is decalcomani matching based on object detection through background removal.Therefore, there is an error according to background removal performance and another weighting factor is given by the weight of the width of the sliding window to be compared. Since the number of partitions of the window is small, the number of comparisons of an object may be reduced, thereby causing an error. Therefore, in another embodiment of the present invention, the vehicle recognition rate may be higher than 97.2% by lowering the width weight of the sliding window. However, in this case, since the decrease in weight may cause an increase in the amount of calculation, the weight may be appropriately adjusted or set according to the performance of the apparatus.

Thus, according to this embodiment, it can contribute to the accurate vehicle recognition based on infrastructure. Infra-based accurate vehicle recognition can be usefully used in advanced road infrastructure-based vehicle information providing system and C-ITS related fields. Vehicle recognition using the decal comany characteristic according to the present embodiment has the advantage that it is easy to drive in a low-cost device because it does not use the SIFT, machine learning, etc. that require a high amount of conventional operation. In addition, if the analysis based on the decalcomani characteristics provided in this embodiment also analyzes the characteristics of the rear of the front and the front of the rear of the vehicle in a black box inside the vehicle other than the infrastructure-based camera, the vehicle recognition can be usefully performed by substituting the existing high-computation system. Can be.

Although described above with reference to a preferred embodiment of the present invention, those skilled in the art will be variously modified and changed within the scope of the invention without departing from the spirit and scope of the invention described in the claims below I can understand that you can.

Claims (8)

delete delete Generating a binarized polygonal image by receiving a plurality of coordinates in an input frame, wherein the polygonal image is defined as a region of interest;
Accumulating input frames to generate a background image;
Obtaining only a polygonal inner region through a logical operation between the polygonal image and the currently input frame;
The result of the difference operation between the background image and the current input frame is set as an absolute value, and binarization is performed by comparing with a predetermined threshold value. step;
Dividing a rectangular area defined as an outline of the moving object in half with respect to a vertical center line;
Obtaining a histogram using original pixel values of the left and right window regions divided in half and comparing them with each other;
Calculating the histogram similarity of the left and right window areas while increasing the width of the left and right window areas while sliding to the left or right, and finding the center of the vehicle by stopping the sliding at the highest point; And
Determining whether the moving object is a vehicle based on a similarity coefficient or a comparison coefficient of the histogram for the left and right window regions;
Vehicle recognition method comprising a. The method according to claim 3,
After detecting the moving object,
Performing median filtering to remove noise in an image including the moving object;
Performing a morphology operation such that object separation of the mobile object is suppressed or the divided object chunks of the mobile object are merged; And
And slicing the part of the object inflated to the outside by the morphology expansion operation of the morphology operation and restoring it to its original size. The method according to claim 3,
The generating of the background image may include obtaining a background image by accumulating a continuous frame input with a predetermined weight, wherein the background image includes a two-lane road portion having a predetermined length in front of the vehicle,
In the dividing step, the rectangular area is calculated by examining the outermost pixel coordinates in the up, down, left, and right directions having white pixel values in the object image of the moving object, and the object area of the moving object is calculated from the image in which the brightness value of the input frame is calculated. Separating to generate a new image for the moving object, vehicle recognition method. delete delete delete

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