基于opencv答题卡识别
2024-05-07 05:50:14
1.问题描述：
模拟考试答题卡的识别：如下图所示的一张答题卡，需要自动识别并标记出考生选择的选项，以及标记出正确答案。考生选择的选项用蓝色标记，标准答案用绿色标记。
2.解决思路：
2.1 首先打开相机拍摄一张答题卡
//用相机拍一张答题卡VideoCapture cap(0);if (!cap.isOpened()){cout << "open failed !";}Mat frame, gray;cap.read(frame);cvtColor(frame, gray, COLOR_BGR2GRAY);imwrite("C:\\Users\\86176\\Downloads\\visionimage\\testdetect.jpg", gray);imshow("frame", frame);waitKey(0);2.2对拍摄的答题卡图像进行预处理
颜色空间转换--------直方图均衡进行图像增强------高斯模糊去噪------canny边缘检测
Mat img = imread("C:\\Users\\86176\\Downloads\\visionimage\\testdetect.jpg");Mat binary, gry, equalhist;cvtColor(img, gry, COLOR_BGR2GRAY);equalizeHist(gry, equalhist);//imshow("eq", equalhist);GaussianBlur(equalhist, equalhist, Size(3, 3),10,20);Canny(equalhist, binary, 50, 300);imshow("can", binary);
2.3进行轮廓检测，筛选出答题卡纸张的区域，便于接下来的透视变换
vector<vector<Point>> bigcontour;vector<double>areas;double max = 0;int index = -1;findContours(binary, bigcontour, RETR_EXTERNAL, CHAIN_APPROX_SIMPLE);cout << bigcontour.size() << endl;for (int i = 0; i < bigcontour.size(); ++i){double area = contourArea(bigcontour[i]);if (area > max){max = area;index = i;}areas.push_back(area);//drawContours(img, bigcontour, i, Scalar( 0,0,200), 2);}cout << max << endl;cout << index << endl;筛选出最大的轮廓后，对该轮廓进行多边形逼近；从而得到透视变换前的四个顶点坐标；再计算出透视变化矩形的宽高，最后进行透视变换，将答题卡区域提取出来：
Mat result;Rect rec=boundingRect(bigcontour[index]);vector<Point2f>app;approxPolyDP(bigcontour[index], app, 10, true);//cout << app << endl;int curwidth = sqrt(pow((app[0].x - app[3].x), 2) + pow((app[0].y - app[3].y), 2));int curheight = sqrt(pow((app[0].x - app[1].x), 2) + pow((app[0].y - app[1].y), 2));vector<Point2f>currs;currs.emplace_back(Point(55, 30));currs.emplace_back(Point(55, 30+curheight));currs.emplace_back(Point(55+curwidth, 30+curheight));currs.emplace_back(Point(55 + curwidth, 30));Mat pers = getPerspectiveTransform(app, currs);Mat perspect;warpPerspective(img, perspect, pers, img.size());Mat out;Rect roi = Rect(55, 30, curwidth, curheight);perspect(roi).copyTo(out);
2.4采用OTSU阈值分割的方法将答题卡的图形信息找出来
Mat otsu, outgray, outdial;cvtColor(out, outgray,COLOR_BGR2GRAY);threshold(outgray, otsu, 100, 220, THRESH_OTSU|THRESH_BINARY_INV);imshow("otsu", otsu);//对图像进行膨胀Mat mod = getStructuringElement(MorphShapes::MORPH_RECT, Size(5, 5));morphologyEx(otsu, outdial, MORPH_DILATE, mod);
膨胀后的图形区域：
2.5再进行轮廓筛选，筛选出答题区域：
//再进行轮廓检测vector<vector<Point>>contoursagin, selectcontours;findContours(outdial, contoursagin, RETR_EXTERNAL, CHAIN_APPROX_SIMPLE);for (auto m : contoursagin){Rect bound = boundingRect(m);if ((bound.height < 45 && bound.height>20) && (bound.width < 45 && bound.width>20)){selectcontours.push_back(m);}}vector<Point2f>circlecenters;vector<Point2f>line1center;vector<Point2f >line2center;vector<Point2f>line3center;vector<Point2f>line4center;vector<Point2f>line5center;vector<vector<Point>>line1contour;vector<vector<Point>>line2contour;vector<vector<Point>>line3contour;vector<vector<Point>>line4contour;vector<vector<Point>>line5contour;vector<float>circiers;for (int n=0;n<selectcontours.size();++n){//画出所有选项的轮廓drawContours(out, selectcontours, n, Scalar(200, 0, 0), 2);//确定每个轮廓外接圆圆心Point2f center;float circler;minEnclosingCircle(selectcontours[n], center, circler);circiers.push_back(circler);if (center.y < 85){line1center.push_back(center);line1contour.push_back(selectcontours[n]);drawContours(out, selectcontours, n, Scalar(200, 0, 0), 2);}else if (center.y < 145){line2center.push_back(center);line2contour.push_back(selectcontours[n]);drawContours(out, selectcontours, n, Scalar(0, 200, 0), 2);}else if (center.y < 205){line3center.push_back(center);line3contour.push_back(selectcontours[n]);drawContours(out, selectcontours, n, Scalar( 0, 0,200), 2);}else if (center.y < 265){line4center.push_back(center);line4contour.push_back(selectcontours[n]);drawContours(out, selectcontours, n, Scalar(20, 0, 50), 2);}else if (center.y < 325){line5center.push_back(center);line5contour.push_back(selectcontours[n]);drawContours(out, selectcontours, n, Scalar(200, 200, 0), 2);}
2.6根据轮廓外接圆圆心的x,y坐标对轮廓进行排序：
//对每一行排序sort(line1center.begin(), line1center.end(), [](const Point2f& center1, const Point2f& center2){return (center1.x < center2.x);});sort(line2center.begin(), line2center.end(), [](const Point2f& center1, const Point2f& center2){return (center1.x < center2.x);});sort(line3center.begin(), line3center.end(), [](const Point2f& center1, const Point2f& center2){return (center1.x < center2.x);});sort(line4center.begin(), line4center.end(), [](const Point2f& center1, const Point2f& center2){return (center1.x < center2.x);});sort(line5center.begin(), line5center.end(), [](const Point2f& center1, const Point2f& center2){return (center1.x < center2.x);});vector<Point2f>sortedcenter;sortedcenter.insert(sortedcenter.end(), line1center.begin(), line1center.end());sortedcenter.insert(sortedcenter.end(), line2center.begin(), line2center.end());sortedcenter.insert(sortedcenter.end(), line3center.begin(), line3center.end());sortedcenter.insert(sortedcenter.end(), line4center.begin(), line4center.end());sortedcenter.insert(sortedcenter.end(), line5center.begin(), line5center.end());float meanrr=0;float tempr=0;for (int k=0;k<circiers.size();++k){ tempr += circiers[k];meanrr = tempr / circiers.size();}2.7已知答题卡选项的标准答案是A,DE,BE,C,D；用绿色标记标准答案：
//答题卡答案A,DE,BE,C,Dint answer[5][5] = {1,0,0,0,0,0,0,0,1,1,0,1,0,0,1,0,0,1,0,0,0,0,0,1,0};//用绿色标记处标准答案Mat resultout, selectout,studentsel;perspect(roi).copyTo(resultout);perspect(roi).copyTo(selectout);perspect(roi).copyTo( studentsel);for (int ii = 0; ii < 5; ++ii){for (int jj = 0; jj < 5; ++jj){if (answer[ii][jj] == 1){Point2f temp = sortedcenter[ii * 5 + jj];circle(resultout, temp, meanrr, Scalar(0, 200, 0), 2);}}}
2.8最后标记考生答题的选项：
//用蓝色标记考生答案Mat erodM = getStructuringElement(0, Size(17,17));erode(outdial, selectout, erodM);vector<vector<Point>>contours;vector<Point2f>tempcenters;findContours(selectout, contours, RETR_EXTERNAL, CHAIN_APPROX_SIMPLE);for (int t = 0; t < contours.size(); ++t){Point2f tempcenter;float tempr;minEnclosingCircle(contours[t], tempcenter, tempr);circle(studentsel, tempcenter, meanrr, Scalar(200, 0, 0),2);}//cout << contours.size() << endl;//cout << selectcontours.size();imshow("outdial", outdial);imshow("out", out);imshow("res", resultout);imshow("studentsel" , studentsel);//imshow("img", img);//imshow("gry", gry);waitKey(0);
}3.全部代码实现：
void VisionTest:: testdetect()
{//用相机拍一张答题卡/*VideoCapture cap(0);if (!cap.isOpened()){cout << "open failed !";}Mat frame, gray;cap.read(frame);cvtColor(frame, gray, COLOR_BGR2GRAY);imwrite("C:\\Users\\86176\\Downloads\\visionimage\\testdetect.jpg", gray);imshow("frame", frame);waitKey(0);*/Mat img = imread("C:\\Users\\86176\\Downloads\\visionimage\\testdetect.jpg");Mat binary, gry, equalhist;cvtColor(img, gry, COLOR_BGR2GRAY);equalizeHist(gry, equalhist);//imshow("eq", equalhist);GaussianBlur(equalhist, equalhist, Size(3, 3),10,20);Canny(equalhist, binary, 50, 300);imshow("can", binary);vector<vector<Point>> bigcontour;vector<double>areas;double max = 0;int index = -1;findContours(binary, bigcontour, RETR_EXTERNAL, CHAIN_APPROX_SIMPLE);cout << bigcontour.size() << endl;for (int i = 0; i < bigcontour.size(); ++i){double area = contourArea(bigcontour[i]);if (area > max){max = area;index = i;}areas.push_back(area);//drawContours(img, bigcontour, i, Scalar( 0,0,200), 2);}cout << max << endl;cout << index << endl;Mat result;Rect rec=boundingRect(bigcontour[index]);vector<Point2f>app;approxPolyDP(bigcontour[index], app, 10, true);//cout << app << endl;int curwidth = sqrt(pow((app[0].x - app[3].x), 2) + pow((app[0].y - app[3].y), 2));int curheight = sqrt(pow((app[0].x - app[1].x), 2) + pow((app[0].y - app[1].y), 2));vector<Point2f>currs;currs.emplace_back(Point(55, 30));currs.emplace_back(Point(55, 30+curheight));currs.emplace_back(Point(55+curwidth, 30+curheight));currs.emplace_back(Point(55 + curwidth, 30));Mat pers = getPerspectiveTransform(app, currs);Mat perspect;warpPerspective(img, perspect, pers, img.size());Mat out;Rect roi = Rect(55, 30, curwidth, curheight);perspect(roi).copyTo(out);imshow("roi", perspect(roi));Mat otsu, outgray, outdial;cvtColor(out, outgray,COLOR_BGR2GRAY);threshold(outgray, otsu, 100, 220, THRESH_OTSU|THRESH_BINARY_INV);imshow("otsu", otsu);//对图像进行膨胀Mat mod = getStructuringElement(MorphShapes::MORPH_RECT, Size(5, 5));morphologyEx(otsu, outdial, MORPH_DILATE, mod);//再进行轮廓检测vector<vector<Point>>contoursagin, selectcontours;findContours(outdial, contoursagin, RETR_EXTERNAL, CHAIN_APPROX_SIMPLE);for (auto m : contoursagin){Rect bound = boundingRect(m);if ((bound.height < 45 && bound.height>20) && (bound.width < 45 && bound.width>20)){selectcontours.push_back(m);}}vector<Point2f>circlecenters;vector<Point2f>line1center;vector<Point2f >line2center;vector<Point2f>line3center;vector<Point2f>line4center;vector<Point2f>line5center;vector<vector<Point>>line1contour;vector<vector<Point>>line2contour;vector<vector<Point>>line3contour;vector<vector<Point>>line4contour;vector<vector<Point>>line5contour;vector<float>circiers;for (int n=0;n<selectcontours.size();++n){//画出所有选项的轮廓drawContours(out, selectcontours, n, Scalar(200, 0, 0), 2);//确定每个轮廓外接圆圆心Point2f center;float circler;minEnclosingCircle(selectcontours[n], center, circler);circiers.push_back(circler);if (center.y < 85){line1center.push_back(center);line1contour.push_back(selectcontours[n]);drawContours(out, selectcontours, n, Scalar(200, 0, 0), 2);}else if (center.y < 145){line2center.push_back(center);line2contour.push_back(selectcontours[n]);drawContours(out, selectcontours, n, Scalar(0, 200, 0), 2);}else if (center.y < 205){line3center.push_back(center);line3contour.push_back(selectcontours[n]);drawContours(out, selectcontours, n, Scalar( 0, 0,200), 2);}else if (center.y < 265){line4center.push_back(center);line4contour.push_back(selectcontours[n]);drawContours(out, selectcontours, n, Scalar(20, 0, 50), 2);}else if (center.y < 325){line5center.push_back(center);line5contour.push_back(selectcontours[n]);drawContours(out, selectcontours, n, Scalar(200, 200, 0), 2);}}//对每一行排序sort(line1center.begin(), line1center.end(), [](const Point2f& center1, const Point2f& center2){return (center1.x < center2.x);});sort(line2center.begin(), line2center.end(), [](const Point2f& center1, const Point2f& center2){return (center1.x < center2.x);});sort(line3center.begin(), line3center.end(), [](const Point2f& center1, const Point2f& center2){return (center1.x < center2.x);});sort(line4center.begin(), line4center.end(), [](const Point2f& center1, const Point2f& center2){return (center1.x < center2.x);});sort(line5center.begin(), line5center.end(), [](const Point2f& center1, const Point2f& center2){return (center1.x < center2.x);});vector<Point2f>sortedcenter;sortedcenter.insert(sortedcenter.end(), line1center.begin(), line1center.end());sortedcenter.insert(sortedcenter.end(), line2center.begin(), line2center.end());sortedcenter.insert(sortedcenter.end(), line3center.begin(), line3center.end());sortedcenter.insert(sortedcenter.end(), line4center.begin(), line4center.end());sortedcenter.insert(sortedcenter.end(), line5center.begin(), line5center.end());float meanrr=0;float tempr=0;for (int k=0;k<circiers.size();++k){ tempr += circiers[k];meanrr = tempr / circiers.size();}//答题卡答案A,DE,BE,C,Dint answer[5][5] = {1,0,0,0,0,0,0,0,1,1,0,1,0,0,1,0,0,1,0,0,0,0,0,1,0};//用绿色标记处标准答案Mat resultout, selectout,studentsel;perspect(roi).copyTo(resultout);perspect(roi).copyTo(selectout);perspect(roi).copyTo( studentsel);for (int ii = 0; ii < 5; ++ii){for (int jj = 0; jj < 5; ++jj){if (answer[ii][jj] == 1){Point2f temp = sortedcenter[ii * 5 + jj];circle(resultout, temp, meanrr, Scalar(0, 200, 0), 2);}}}//用蓝色标记考生答案Mat erodM = getStructuringElement(0, Size(17,17));erode(outdial, selectout, erodM);vector<vector<Point>>contours;vector<Point2f>tempcenters;findContours(selectout, contours, RETR_EXTERNAL, CHAIN_APPROX_SIMPLE);for (int t = 0; t < contours.size(); ++t){Point2f tempcenter;float tempr;minEnclosingCircle(contours[t], tempcenter, tempr);circle(studentsel, tempcenter, meanrr, Scalar(200, 0, 0),2);}cout << contours.size() << endl;imshow("outdial", outdial);imshow("out", out);imshow("res", resultout);imshow("studentsel" , studentsel);waitKey(0);
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