How to cross out everything outside the circle in Open CV
I am currently trying to cross out everything outside of the circle I found. I am currently drawing a circle with the following lines of code:
cv::Point center(cvRound(circles[i][0]), cvRound(circles[i][1])); // CVRound converts floating numbers to integer
int radius = cvRound(circles[i][2]); // Radius is the third parameter [i][0] = x [i][1]= y [i][2] = radius
circle( image, center, 3, cv::Scalar(0,255,0), -1, 8, 0 ); // Drawing little circle to Image Center , next Line of Code draws the real circle
circle( image, center, radius, cv::Scalar(0,0,255), 3, 8, 0 ); // Circle(img, center, radius, color, thickness=1, lineType=8, shift=0)
But this is not what I was looking for. If I have a Radius and a Center Point of my circle, what is the best approach for drawing the rest of my Mat black. Does OpenCV provide an easy way to do this, or should I iterate over all the pixels of my image and depending on the position color, are they black or not?
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Thanks to Abid for the hint, I ended up with this approach. Everything works fine:
cv::Mat src = someMethodThatReturnsSrcImage(); // src Image
cv::Mat maskedImage; // stores masked Image
std::vector<cv::Vec3f> circles = someMethodThatReturnsCircles(src);
cv::Mat mask(srcImageForDimensions.size(),srcImageForDimensions.type()); // create an Mat that has same Dimensons as src
mask.setTo(cv::Scalar(0,0,0)); // creates black-Image
// Add all found circles to mask
for( size_t i = 0; i < circles.size(); i++ ) // iterate through all detected Circles
{
cv::Point center(cvRound(circles[i][0]), cvRound(circles[i][1])); // CVRound converts floating numbers to integer
int radius = cvRound(circles[i][2]); // Radius is the third parameter [i][0] = x [i][1]= y [i][2] = radius
cv::circle( mask, center, radius, cv::Scalar(255,255,255),-1, 8, 0 ); // Circle(img, center, radius, color, thickness=1, lineType=8, shift=0)
}
src.copyTo(maskedImage,mask); // creates masked Image and copies it to maskedImage
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I think a comment on your question is the best solution. I made a modified version of your code for a 5M fisheye image. This image should also make all the points outside the circle black.
#include <Windows.h>
#include <Vfw.h>
#include <string>
#include <iostream>
#include "opencv2\core\core.hpp"
#include "opencv2\imgproc\imgproc.hpp"
#include "opencv2\imgcodecs\imgcodecs.hpp"
#include "opencv2\highgui\highgui.hpp"
using namespace std;
using namespace cv;
int _tmain(int argc, _TCHAR* argv[])
{
cv::Mat im_source_non_square = cv::imread("D:/FishLib/sample_02.bmp", CV_LOAD_IMAGE_COLOR);
cv::namedWindow("Image",CV_WINDOW_FREERATIO);
cv::imshow("Image", im_source_non_square);
Mat im_source_square;
int m_nCenterX=1280;
int m_nCenterY=960;
int m_nRadius=916;
Mat im_mask=im_source_non_square.clone();
im_mask.setTo(cv::Scalar(0,0,0));
circle( im_mask, cv::Point(m_nCenterX,m_nCenterY), m_nRadius, cv::Scalar(255,255,255), -3, 8, 0 );
cv::namedWindow("Mask image",CV_WINDOW_FREERATIO);
cv::imshow("Mask image", im_mask);
Mat im_source_circle;
cv::bitwise_and(im_source_non_square,im_mask,im_source_circle);
cv::namedWindow("Combined image",CV_WINDOW_FREERATIO);
cv::imshow("Combined image", im_source_circle);
cv::waitKey(0);
return 0;
}
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Just tried the code snippet and it works. Also if you want to change the background color instead of black, according to the opencv docs here , before the copyTo
matches the assignments will be initialized if needed, so just add the code below:
cv::Mat maskedImage(srcImageForDimensions.size(), srcImageForDimensions.type()); // stores masked Image
maskedImage.setTo(cv::Scalar(0,0,255)); // set background color to red
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