OpenCV  4.10.0-pre
Open Source Computer Vision
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An example using the cv::linearPolar and cv::logPolar operations

#include <iostream>
using namespace cv;
int main( int argc, char** argv )
VideoCapture capture;
Mat log_polar_img, lin_polar_img, recovered_log_polar, recovered_lin_polar_img;
CommandLineParser parser(argc, argv, "{@input|0| camera device number or video file path}");
parser.about("\nThis program illustrates usage of Linear-Polar and Log-Polar image transforms\n");
std::string arg = parser.get<std::string>("@input");
if( arg.size() == 1 && isdigit(arg[0]) ) arg[0] - '0' );
if( !capture.isOpened() )
fprintf(stderr,"Could not initialize capturing...\n");
return -1;
namedWindow( "Linear-Polar", WINDOW_AUTOSIZE );
namedWindow( "Log-Polar", WINDOW_AUTOSIZE);
namedWindow( "Recovered Linear-Polar", WINDOW_AUTOSIZE);
namedWindow( "Recovered Log-Polar", WINDOW_AUTOSIZE);
moveWindow( "Linear-Polar", 20,20 );
moveWindow( "Log-Polar", 700,20 );
moveWindow( "Recovered Linear-Polar", 20, 350 );
moveWindow( "Recovered Log-Polar", 700, 350 );
Mat src;
capture >> src;
if(src.empty() )
Point2f center( (float)src.cols / 2, (float)src.rows / 2 );
double maxRadius = 0.7*min(center.y, center.x);
#if 0 //deprecated
double M = frame.cols / log(maxRadius);
logPolar(frame, log_polar_img, center, M, flags);
linearPolar(frame, lin_polar_img, center, maxRadius, flags);
logPolar(log_polar_img, recovered_log_polar, center, M, flags + WARP_INVERSE_MAP);
linearPolar(lin_polar_img, recovered_lin_polar_img, center, maxRadius, flags + WARP_INVERSE_MAP);
// direct transform
warpPolar(src, lin_polar_img, Size(),center, maxRadius, flags); // linear Polar
warpPolar(src, log_polar_img, Size(),center, maxRadius, flags + WARP_POLAR_LOG); // semilog Polar
// inverse transform
warpPolar(lin_polar_img, recovered_lin_polar_img, src.size(), center, maxRadius, flags + WARP_INVERSE_MAP);
warpPolar(log_polar_img, recovered_log_polar, src.size(), center, maxRadius, flags + WARP_POLAR_LOG + WARP_INVERSE_MAP);
// Below is the reverse transformation for (rho, phi)->(x, y) :
Mat dst;
if (flags & WARP_POLAR_LOG)
dst = log_polar_img;
dst = lin_polar_img;
//get a point from the polar image
int rho = cvRound(dst.cols * 0.75);
int phi = cvRound(dst.rows / 2.0);
double angleRad, magnitude;
double Kangle = dst.rows / CV_2PI;
angleRad = phi / Kangle;
if (flags & WARP_POLAR_LOG)
double Klog = dst.cols / std::log(maxRadius);
magnitude = std::exp(rho / Klog);
double Klin = dst.cols / maxRadius;
magnitude = rho / Klin;
int x = cvRound(center.x + magnitude * cos(angleRad));
int y = cvRound(center.y + magnitude * sin(angleRad));
drawMarker(src, Point(x, y), Scalar(0, 255, 0));
drawMarker(dst, Point(rho, phi), Scalar(0, 255, 0));
imshow("Src frame", src);
imshow("Log-Polar", log_polar_img);
imshow("Linear-Polar", lin_polar_img);
imshow("Recovered Linear-Polar", recovered_lin_polar_img );
imshow("Recovered Log-Polar", recovered_log_polar );
if( waitKey(10) >= 0 )
return 0;
Designed for command line parsing.
Definition utility.hpp:820
T get(const String &name, bool space_delete=true) const
Access arguments by name.
Definition utility.hpp:886
void about(const String &message)
Set the about message.
void printMessage() const
Print help message.
n-dimensional dense array class
Definition mat.hpp:812
MatSize size
Definition mat.hpp:2160
int cols
Definition mat.hpp:2138
int rows
the number of rows and columns or (-1, -1) when the matrix has more than 2 dimensions
Definition mat.hpp:2138
_Tp y
y coordinate of the point
Definition types.hpp:202
_Tp x
x coordinate of the point
Definition types.hpp:201
Template class for specifying the size of an image or rectangle.
Definition types.hpp:335
Class for video capturing from video files, image sequences or cameras.
Definition videoio.hpp:731
virtual bool open(const String &filename, int apiPreference=CAP_ANY)
Opens a video file or a capturing device or an IP video stream for video capturing.
virtual bool isOpened() const
Returns true if video capturing has been initialized already.
int cvRound(double value)
Rounds floating-point number to the nearest integer.
Definition fast_math.hpp:200
#define CV_2PI
Definition cvdef.h:381
int main(int argc, char *argv[])
Definition highgui_qt.cpp:3
"black box" representation of the file storage associated with a file on disk.
Definition core.hpp:102