| OpenCV 5.0.0alpha Open Source Computer Vision

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samples/cpp/snippets/warpPerspective_demo.cpp

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

#include "opencv2/imgproc.hpp"
#include "opencv2/imgcodecs.hpp"
#include "opencv2/highgui.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 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 inverse 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> midpoints(4);
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| right.jpg |}");
string filename = samples::findFile(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], FONT_HERSHEY_SIMPLEX, 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], FONT_HERSHEY_SIMPLEX, 0.8, Scalar(255, 0, 0), 2);
}
imshow( windowTitle, image );
midpoints[0] = (roi_corners[0] + roi_corners[1]) / 2;
midpoints[1] = (roi_corners[1] + roi_corners[2]) / 2;
midpoints[2] = (roi_corners[2] + roi_corners[3]) / 2;
midpoints[3] = (roi_corners[3] + roi_corners[0]) / 2;
dst_corners[0].x = 0;
dst_corners[0].y = 0;
dst_corners[1].x = (float)norm(midpoints[1] - midpoints[3]);
dst_corners[1].y = 0;
dst_corners[2].x = dst_corners[1].x;
dst_corners[2].y = (float)norm(midpoints[0] - midpoints[2]);
dst_corners[3].x = 0;
dst_corners[3].y = dst_corners[2].y;
Size warped_image_size = Size(cvRound(dst_corners[2].x), cvRound(dst_corners[2].y));
Mat M = getPerspectiveTransform(roi_corners, dst_corners);
Mat warped_image;
warpPerspective(original_image, warped_image, M, 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;
}
}
cv::CommandLineParser
Designed for command line parsing.
Definition utility.hpp:890
cv::Mat
n-dimensional dense array class
Definition mat.hpp:951
cv::Mat::cols
int cols
Definition mat.hpp:2425
cv::Point_< float >
cv::Scalar_< double >
cv::Size_
Template class for specifying the size of an image or rectangle.
Definition types.hpp:338
CV_VERSION
#define CV_VERSION
Definition version.hpp:19
cv::norm
double norm(InputArray src1, int normType=NORM_L2, InputArray mask=noArray())
Calculates the absolute norm of an array.
cv::String
std::string String
Definition cvstd.hpp:151
cvRound
int cvRound(double value)
Rounds floating-point number to the nearest integer.
Definition fast_math.hpp:200
cv::datasets::circle
@ circle
Definition gr_skig.hpp:62
cv::imshow
void imshow(const String &winname, InputArray mat)
Displays an image in the specified window.
cv::waitKey
int waitKey(int delay=0)
Waits for a pressed key.
cv::namedWindow
void namedWindow(const String &winname, int flags=WINDOW_AUTOSIZE)
Creates a window.
cv::setMouseCallback
void setMouseCallback(const String &winname, MouseCallback onMouse, void *userdata=0)
Sets mouse handler for the specified window.
cv::moveWindow
void moveWindow(const String &winname, int x, int y)
Moves the window to the specified position.
cv::imread
CV_EXPORTS_W Mat imread(const String &filename, int flags=IMREAD_COLOR_BGR)
Loads an image from a file.
cv::putText
void putText(InputOutputArray img, const String &text, Point org, int fontFace, double fontScale, Scalar color, int thickness=1, int lineType=LINE_8, bool bottomLeftOrigin=false)
Draws a text string.
cv::line
void line(InputOutputArray img, Point pt1, Point pt2, const Scalar &color, int thickness=1, int lineType=LINE_8, int shift=0)
Draws a line segment connecting two points.
cv::warpPerspective
void warpPerspective(InputArray src, OutputArray dst, InputArray M, Size dsize, int flags=INTER_LINEAR, int borderMode=BORDER_CONSTANT, const Scalar &borderValue=Scalar(), AlgorithmHint hint=cv::ALGO_HINT_DEFAULT)
Applies a perspective transformation to an image.
cv::getPerspectiveTransform
Mat getPerspectiveTransform(InputArray src, InputArray dst, int solveMethod=DECOMP_LU)
Calculates a perspective transform from four pairs of the corresponding points.
highgui.hpp
main
int main(int argc, char *argv[])
Definition highgui_qt.cpp:3
imgcodecs.hpp
imgproc.hpp
cv
Definition core.hpp:107
std
STL namespace.