Opencv 传统形态学对填涂准考证号识别的一个例子

背景：.对于填涂类型的准考证号或则答案，用传统的边框检测，使用合适的阈值，将对象检测出来，然后根据排列，可以得到学号或则填涂的选项。

不足：挺依赖印刷的质量和填涂的规范性，对于大批量的识别，不能保证识别的准确性。

#include <iostream>
#include<opencv2/opencv.hpp>
using namespace std;
using namespace cv;

int main()
{
    Mat img = imread("d:\\Images\\stucard\\2.jpg", cv::IMREAD_UNCHANGED);
    if (img.empty())
    {
        printf("图像无法正常加载\n");
        return 0;
    }
    Mat gray;
    if (img.channels() > 1)
        cv::cvtColor(img, gray, COLOR_RGB2GRAY);
    else
        gray = img.clone();

    Mat result_Color_img;
    cvtColor(gray, result_Color_img, COLOR_GRAY2BGR);

    cv::Ptr<cv::CLAHE> clahe = cv::createCLAHE(2.0, cv::Size(8, 8));
    cv::Mat tmpresult;
    clahe->apply(gray, tmpresult);
    cv::GaussianBlur(tmpresult, tmpresult, cv::Size(3, 3), 0);
    cv::Mat binary;
    cv::threshold(tmpresult, binary, 0, 255, cv::THRESH_BINARY_INV | cv::THRESH_OTSU);

    std::vector<std::vector<cv::Point>> contours;
    cv::findContours(binary, contours, cv::RETR_EXTERNAL, cv::CHAIN_APPROX_SIMPLE);

    std::vector<cv::Rect> rectarray;
    double epsilon = 0.02;
    for (const auto& contour : contours) {
        cv::Rect rect = cv::boundingRect(contour);
        int rectsize = 0;

        if (rect.width < 60 && rect.height < 36 && rect.width>12 && rect.height >12) {

            double contourArea = cv::contourArea(contour);
            double rectArea = rect.width * rect.height;
            if (contourArea / rectArea > 0.4) {

                std::vector<cv::Point> approx;
                cv::approxPolyDP(contour, approx, epsilon * cv::arcLength(contour, true), true);
                if (approx.size() >= 4) {
                    rectarray.push_back(rect);
                    cv::rectangle(result_Color_img, rect, Scalar(0, 0, 255), 2);
                }
            }
        }
    }

    namedWindow("original", WINDOW_FREERATIO);
    int window_width = 400;
    resizeWindow("original", Size(window_width, window_width * img.rows / img.cols));
    imshow("original", result_Color_img);

    waitKey(0);
    destroyAllWindows();
    return 0;
}

结果：