Vortex effect on image with OpenCV - c++

Question

I am beginning in image processing, I would like to make a vortex in the center of an image with OpenCV in C++.
My first intuition would be to make a rotation and a translation, but I can't figure it out how to make the equation, or there is a simple way to make it.
There is an example of what I want to achieve : Image

Answer 1

You can try the code I shamelessly stole from here:
#include <iostream>
#include <cmath>
#include <opencv2/opencv.hpp>
using namespace cv;
using namespace std;
void trackbar_callback(int value, void* userdata)
{
Mat* image = (Mat*)userdata;
const float width = (float)image->rows;
const float height = (float)image->cols;
Mat result(image->rows, image->cols, image->type());
for (int i = 0; i < image->rows; i++) {
for (int j = 0; j < image->cols; j++) {
float x = (j / height) - 0.5f;
float y = (i / width) - 0.5f;
float angle = atan2f(y, x);
float radius = sqrtf((x * x) + (y * y));
angle += radius * (value / 10.0f);
float xr = ((radius * sinf(angle)) + 0.5f) * width;
float yr = ((radius * cosf(angle)) + 0.5f) * height;
int k = (int)std::min(width - 1, std::max(0.0f, xr));
int m = (int)std::min(height - 1, std::max(0.0f, yr));
uchar* src = image->ptr<uchar>(k, m);
uchar* out = result.ptr<uchar>(i, j);
out[0] = src[0];
out[1] = src[1];
out[2] = src[2];
}
}
imshow("Result Image", result);
}
int main(int argc, char** argv)
{
Mat image = imread("data/lena.jpg", CV_LOAD_IMAGE_COLOR);
if (image.empty())
{
printf("No image data \n");
return -1;
}
try
{
const cv::String name_window = "Twirl Image";
const cv::String name_trackbar = "Twirl";
namedWindow(name_window);
createTrackbar(name_trackbar, name_window, NULL, 200, trackbar_callback, &image);
setTrackbarPos(name_trackbar, name_window, 80);
imshow(name_window, image);
waitKey(0);
destroyAllWindows();
}
catch (cv::Exception& e)
{
const char* err_msg = e.what();
std::cout << "exception caught: " << err_msg << std::endl;
}
return 0;
}