OpenCV之图像处理case(五) 透视校正

代码

#include "../common/common.hpp"

void main(int argc, char** argv) {
    Mat src = imread(getCVImagesPath("images/case3-5.png"));
    imshow("src3-5", src);

    // 二值分割 + 形态学方法 + Hough直线 +透视变换        OCR识别的前期工作
    // 二值处理
    Mat gray_src, binary, dst;
    cvtColor(src, gray_src, COLOR_BGR2GRAY);
    threshold(gray_src, binary, 0, 255, THRESH_BINARY_INV | THRESH_OTSU);
    imshow("binary image", binary);

    // 形态学操作
    Mat kernel = getStructuringElement(MORPH_RECT, Size(5, 5), Point(-1, -1));
    morphologyEx(binary, dst, MORPH_CLOSE, kernel, Point(-1, -1), 3); // 闭操作，填补社保卡上的黑洞
    imshow("morphology", dst);

    // 轮廓发现
    bitwise_not(dst, dst, Mat()); // 可有可无
    vector<vector<Point>> contours;
    vector<Vec4i> hireachy;
    findContours(dst, contours, hireachy, CV_RETR_TREE, CHAIN_APPROX_SIMPLE, Point()); // 也可使用 RETR_EXTERNAL
    cout << "contours.size=" << contours.size() << endl; // contours.size=5

    // 轮廓绘t制
    int width = src.cols;
    int height = src.rows;
    Mat drawImage = Mat::zeros(src.size(), CV_8UC3);
    for (size_t t = 0; t < contours.size(); t++) {
        Rect rect = boundingRect(contours[t]);
        if (rect.width > width / 2 && rect.width < width - 5) { // 社保卡宽大于图像宽一半
            drawContours(drawImage, contours, static_cast<int>(t), Scalar(0, 0, 255), 2, 8, hireachy, 0, Point());
        }
    }
    imshow("contours", drawImage);

    // 霍夫直线检测
    vector<Vec4i> lines;
    Mat contoursImg;
    int accu = min(width*0.5, height*0.5);
    cvtColor(drawImage, contoursImg, COLOR_BGR2GRAY);
    HoughLinesP(contoursImg, lines, 1, CV_PI / 180.0, accu, accu, 0);
    Mat linesImage = Mat::zeros(src.size(), CV_8UC3);
    for (size_t t = 0; t < lines.size(); t++) {
        Vec4i ln = lines[t];
        line(linesImage, Point(ln[0], ln[1]), Point(ln[2], ln[3]), Scalar(0, 0, 255), 2, 8, 0);
    }
    printf("number of lines : %d\n", lines.size()); // number of lines : 4
    imshow("lines image", linesImage);

    // 寻找与定位上下左右四条直线
    int deltah = 0;
    Vec4i topLine, bottomLine;
    Vec4i leftLine, rightLine;
    for (int i = 0; i < lines.size(); i++) {
        Vec4i ln = lines[i];
        deltah = abs(ln[3] - ln[1]);
        if (ln[3] < height / 2.0 && ln[1] < height / 2.0 && deltah < accu - 1) {
            if (topLine[3] > ln[3] && topLine[3]>0) {
                topLine = lines[i];
            }
            else {
                topLine = lines[i];
            }
        }
        if (ln[3] > height / 2.0 && ln[1] > height / 2.0 && deltah < accu - 1) {
            bottomLine = lines[i];
        }
        if (ln[0] < width / 2.0 && ln[2] < width / 2.0) {
            leftLine = lines[i];
        }
        if (ln[0] > width / 2.0 && ln[2] > width / 2.0) {
            rightLine = lines[i];
        }
    }
    // top line : p1(x, y) = 20,62 p2(x, y) = 467,54
    cout << "top line : p1(x, y) = " << topLine[0] << "," << topLine[1] << " p2(x, y) = " << topLine[2] << "," << topLine[3] << endl;
    // bottom line : p1(x, y) = 54, 316 p2(x, y) = 424, 322
    cout << "bottom line : p1(x, y) = " << bottomLine[0] << "," << bottomLine[1] << " p2(x, y) = " << bottomLine[2] << "," << bottomLine[3] << endl;
    // left line : p1(x, y) = 13, 70 p2(x, y) = 46, 309
    cout << "left line : p1(x, y) = " << leftLine[0] << "," << leftLine[1] << " p2(x, y) = " << leftLine[2] << "," << leftLine[3] << endl;
    // right line : p1(x, y) = 461, 315 p2(x, y) = 478, 63
    cout << "right line : p1(x, y) = " << rightLine[0] << "," << rightLine[1] << " p2(x, y) = " << rightLine[2] << "," << rightLine[3] << endl;

    // 拟合四条直线方程
    float k1, c1;
    k1 = float(topLine[3] - topLine[1]) / float(topLine[2] - topLine[0]);
    c1 = topLine[1] - k1*topLine[0];
    float k2, c2;
    k2 = float(bottomLine[3] - bottomLine[1]) / float(bottomLine[2] - bottomLine[0]);
    c2 = bottomLine[1] - k2*bottomLine[0];
    float k3, c3;
    k3 = float(leftLine[3] - leftLine[1]) / float(leftLine[2] - leftLine[0]);
    c3 = leftLine[1] - k3*leftLine[0];
    float k4, c4;
    k4 = float(rightLine[3] - rightLine[1]) / float(rightLine[2] - rightLine[0]);
    c4 = rightLine[1] - k4*rightLine[0];

    // 四条直线交点
    Point p1; // 左上角
    p1.x = static_cast<int>((c1 - c3) / (k3 - k1));
    p1.y = static_cast<int>(k1*p1.x + c1);
    Point p2; // 右上角
    p2.x = static_cast<int>((c1 - c4) / (k4 - k1));
    p2.y = static_cast<int>(k1*p2.x + c1);
    Point p3; // 左下角
    p3.x = static_cast<int>((c2 - c3) / (k3 - k2));
    p3.y = static_cast<int>(k2*p3.x + c2);
    Point p4; // 右下角
    p4.x = static_cast<int>((c2 - c4) / (k4 - k2));
    p4.y = static_cast<int>(k2*p4.x + c2);
    cout << "p1(x, y)=" << p1.x << "," << p1.y << endl; // p1(x, y) = 11, 62
    cout << "p2(x, y)=" << p2.x << "," << p2.y << endl; // p2(x, y) = 478, 53
    cout << "p3(x, y)=" << p3.x << "," << p3.y << endl; // p3(x, y) = 46, 315
    cout << "p4(x, y)=" << p4.x << "," << p4.y << endl; // p4(x, y) = 460, 322

    // 显示四个点坐标
    circle(linesImage, p1, 2, Scalar(255, 0, 0), 2, 8, 0);
    circle(linesImage, p2, 2, Scalar(255, 0, 0), 2, 8, 0);
    circle(linesImage, p3, 2, Scalar(255, 0, 0), 2, 8, 0);
    circle(linesImage, p4, 2, Scalar(255, 0, 0), 2, 8, 0);
    line(linesImage, Point(topLine[0], topLine[1]), Point(topLine[2], topLine[3]), Scalar(0, 255, 0), 2, 8, 0);
    imshow("four corners", linesImage);

    // 透视变换
    vector<Point2f> src_corners(4);
    src_corners[0] = p1; // 原图中社保卡的4个点
    src_corners[1] = p2;
    src_corners[2] = p3;
    src_corners[3] = p4;

    vector<Point2f> dst_corners(4);
    dst_corners[0] = Point(0, 0); // 原图中社保卡的4个点到图像的宽高上 的透视变换关系
    dst_corners[1] = Point(width, 0);
    dst_corners[2] = Point(0, height);
    dst_corners[3] = Point(width, height);

    // 获取透视变换矩阵
    Mat resultImage;
    Mat warpmatrix = getPerspectiveTransform(src_corners, dst_corners); // 获取上述关系的透视变换矩阵
    warpPerspective(src, resultImage, warpmatrix, resultImage.size(), INTER_LINEAR); // 透视变换
    imshow("Final Result", resultImage);

    waitKey(0);
}

效果图