获取车牌轮廓 c++ opencv

获取车牌轮廓的步骤如下：

1. 读取车牌图像

Mat img = imread("car_plate.jpg");

2. 灰度化

Mat gray_img;
cvtColor(img, gray_img, COLOR_BGR2GRAY);

3. 高斯模糊

Mat blur_img;
GaussianBlur(gray_img, blur_img, Size(3, 3), 0);

4. 边缘检测

Mat edges;
Canny(blur_img, edges, 80, 160);

5. 轮廓检测

vector<vector<Point>> contours;
vector<Vec4i> hierarchy;
findContours(edges, contours, hierarchy, RETR_TREE, CHAIN_APPROX_SIMPLE);

6. 遍历轮廓，找到最大的矩形轮廓

double max_area = 0;
Rect max_rect;
for (int i = 0; i < contours.size(); i++) {
    double area = contourArea(contours[i]);
    if (area > max_area) {
        max_area = area;
        max_rect = boundingRect(contours[i]);
    }
}

最终，`max_rect` 就是车牌的轮廓矩形。可以通过以下代码将其绘制在原图上：

rectangle(img, max_rect, Scalar(0, 0, 255), 2);
imshow("car plate", img);
waitKey(0);

完整代码如下：

#include <opencv2/opencv.hpp>
#include <iostream>

using namespace std;
using namespace cv;

int main() {
    Mat img = imread("car_plate.jpg");
    Mat gray_img;
    cvtColor(img, gray_img, COLOR_BGR2GRAY);
    Mat blur_img;
    GaussianBlur(gray_img, blur_img, Size(3, 3), 0);
    Mat edges;
    Canny(blur_img, edges, 80, 160);
    vector<vector<Point>> contours;
    vector<Vec4i> hierarchy;
    findContours(edges, contours, hierarchy, RETR_TREE, CHAIN_APPROX_SIMPLE);
    double max_area = 0;
    Rect max_rect;
    for (int i = 0; i < contours.size(); i++) {
        double area = contourArea(contours[i]);
        if (area > max_area) {
            max_area = area;
            max_rect = boundingRect(contours[i]);
        }
    }
    rectangle(img, max_rect, Scalar(0, 0, 255), 2);
    imshow("car plate", img);
    waitKey(0);
    return 0;
}