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New example - warpPerspective_demo.cpp
An example program shows using cv::findHomography and cv::warpPerspective for image warping
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‎modules/imgproc/include/opencv2/imgproc.hpp

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int borderMode = BORDER_CONSTANT,
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const Scalar& borderValue = Scalar());
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/** @example warpPerspective_demo.cpp
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An example program shows using cv::findHomography and cv::warpPerspective for image warping
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*/
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/** @brief Applies a perspective transformation to an image.
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The function warpPerspective transforms the source image using the specified matrix:

‎samples/cpp/warpPerspective_demo.cpp

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/**
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@file warpPerspective_demo.cpp
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@brief a demo program shows how perspective transformation applied on an image
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@based on a sample code http://study.marearts.com/2015/03/image-warping-using-opencv.html
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@modified by Suleyman TURKMEN
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*/
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#include "opencv2/imgproc.hpp"
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#include "opencv2/imgcodecs.hpp"
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#include "opencv2/highgui.hpp"
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#include "opencv2/calib3d.hpp"
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#include <iostream>
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using namespace std;
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using namespace cv;
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static void help(char** argv)
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{
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// print a welcome message, and the OpenCV version
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cout << "\nThis is a demo program shows how perspective transformation applied on an image, \n"
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"Using OpenCV version " << CV_VERSION << endl;
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cout << "\nUsage:\n" << argv[0] << " [image_name -- Default ../data/right.jpg]\n" << endl;
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cout << "\nHot keys: \n"
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"\tESC, q - quit the program\n"
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"\tr - change order of points to rotate transformation\n"
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"\tc - delete selected points\n"
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"\ti - change order of points to invers transformation \n"
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"\nUse your mouse to select a point and move it to see transformation changes" << endl;
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}
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static void onMouse(int event, int x, int y, int, void*);
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Mat warping(Mat image, Size warped_image_size, vector< Point2f> srcPoints, vector< Point2f> dstPoints);
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String windowTitle = "Perspective Transformation Demo";
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String labels[4] = { "TL","TR","BR","BL" };
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vector< Point2f> roi_corners;
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vector< Point2f> dst_corners(4);
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int roiIndex = 0;
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bool dragging;
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int selected_corner_index = 0;
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bool validation_needed = true;
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int main(int argc, char** argv)
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{
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help(argv);
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CommandLineParser parser(argc, argv, "{@input| ../data/right.jpg |}");
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string filename = parser.get<string>("@input");
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Mat original_image = imread( filename );
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Mat image;
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float original_image_cols = (float)original_image.cols;
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float original_image_rows = (float)original_image.rows;
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roi_corners.push_back(Point2f( (float)(original_image_cols / 1.70), (float)(original_image_rows / 4.20) ));
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roi_corners.push_back(Point2f( (float)(original_image.cols / 1.15), (float)(original_image.rows / 3.32) ));
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roi_corners.push_back(Point2f( (float)(original_image.cols / 1.33), (float)(original_image.rows / 1.10) ));
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roi_corners.push_back(Point2f( (float)(original_image.cols / 1.93), (float)(original_image.rows / 1.36) ));
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namedWindow(windowTitle, WINDOW_NORMAL);
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namedWindow("Warped Image", WINDOW_AUTOSIZE);
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moveWindow("Warped Image", 20, 20);
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moveWindow(windowTitle, 330, 20);
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setMouseCallback(windowTitle, onMouse, 0);
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bool endProgram = false;
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while (!endProgram)
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{
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if ( validation_needed & (roi_corners.size() < 4) )
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{
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validation_needed = false;
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image = original_image.clone();
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for (size_t i = 0; i < roi_corners.size(); ++i)
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{
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circle( image, roi_corners[i], 5, Scalar(0, 255, 0), 3 );
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if( i > 0 )
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{
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line(image, roi_corners[i-1], roi_corners[(i)], Scalar(0, 0, 255), 2);
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circle(image, roi_corners[i], 5, Scalar(0, 255, 0), 3);
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putText(image, labels[i].c_str(), roi_corners[i], QT_FONT_NORMAL, 0.8, Scalar(255, 0, 0), 2);
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}
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}
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imshow( windowTitle, image );
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}
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if ( validation_needed & ( roi_corners.size() == 4 ))
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{
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image = original_image.clone();
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for ( int i = 0; i < 4; ++i )
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{
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line(image, roi_corners[i], roi_corners[(i + 1) % 4], Scalar(0, 0, 255), 2);
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circle(image, roi_corners[i], 5, Scalar(0, 255, 0), 3);
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putText(image, labels[i].c_str(), roi_corners[i], QT_FONT_NORMAL, 0.8, Scalar(255, 0, 0), 2);
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}
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imshow( windowTitle, image );
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dst_corners[0].x = 0;
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dst_corners[0].y = 0;
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dst_corners[1].x = (float)std::max(norm(roi_corners[0] - roi_corners[1]), norm(roi_corners[2] - roi_corners[3]));
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dst_corners[1].y = 0;
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dst_corners[2].x = (float)std::max(norm(roi_corners[0] - roi_corners[1]), norm(roi_corners[2] - roi_corners[3]));
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dst_corners[2].y = (float)std::max(norm(roi_corners[1] - roi_corners[2]), norm(roi_corners[3] - roi_corners[0]));
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dst_corners[3].x = 0;
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dst_corners[3].y = (float)std::max(norm(roi_corners[1] - roi_corners[2]), norm(roi_corners[3] - roi_corners[0]));
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Size warped_image_size = Size(cvRound(dst_corners[2].x), cvRound(dst_corners[2].y));
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Mat H = findHomography(roi_corners, dst_corners); //get homography
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Mat warped_image;
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warpPerspective(original_image, warped_image, H, warped_image_size); // do perspective transformation
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imshow("Warped Image", warped_image);
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}
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char c = (char)waitKey( 10 );
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if ((c == 'q') | (c == 'Q') | (c == 27))
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{
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endProgram = true;
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}
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if ((c == 'c') | (c == 'C'))
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{
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roi_corners.clear();
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}
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if ((c == 'r') | (c == 'R'))
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{
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roi_corners.push_back(roi_corners[0]);
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roi_corners.erase(roi_corners.begin());
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}
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if ((c == 'i') | (c == 'I'))
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{
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swap(roi_corners[0], roi_corners[1]);
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swap(roi_corners[2], roi_corners[3]);
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}
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}
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return 0;
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}
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static void onMouse(int event, int x, int y, int, void*)
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{
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// Action when left button is pressed
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if (roi_corners.size() == 4)
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{
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for (int i = 0; i < 4; ++i)
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{
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if ((event == EVENT_LBUTTONDOWN) & ((abs(roi_corners[i].x - x) < 10)) & (abs(roi_corners[i].y - y) < 10))
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{
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selected_corner_index = i;
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dragging = true;
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}
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}
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}
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else if ( event == EVENT_LBUTTONDOWN )
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{
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roi_corners.push_back( Point2f( (float) x, (float) y ) );
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validation_needed = true;
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}
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// Action when left button is released
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if (event == EVENT_LBUTTONUP)
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{
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dragging = false;
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}
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// Action when left button is pressed and mouse has moved over the window
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if ((event == EVENT_MOUSEMOVE) && dragging)
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{
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roi_corners[selected_corner_index].x = (float) x;
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roi_corners[selected_corner_index].y = (float) y;
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validation_needed = true;
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}
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}

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