New example - warpPerspective_demo.cpp

An example program shows using cv::findHomography and cv::warpPerspective for image warping

modules/imgproc/include/opencv2/imgproc.hpp

@@ -2264,6 +2264,9 @@ CV_EXPORTS_W void warpAffine( InputArray src, OutputArray dst,
                               int borderMode = BORDER_CONSTANT,
                               const Scalar& borderValue = Scalar());
 
+/** @example warpPerspective_demo.cpp
+An example program shows using cv::findHomography and cv::warpPerspective for image warping
+ */
 /** @brief Applies a perspective transformation to an image.
 
 The function warpPerspective transforms the source image using the specified matrix:

samples/cpp/warpPerspective_demo.cpp

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