How to draw a curve at breakpoints using opencv

Question

I want to draw a curve on control points so that I can move the curve to change colors, below is the code that got the help a very well-explained answer

 const int N=5; // number of control points (must be >= 4) float ctrl[N]= // control points y values initiated with linear function y=x { // x value is index*1.0/(N-1) 0.00, 0.25, 0.50, 0.75, 1.00, }; float correction(float col,float *ctrl,int n) { float di=1.0/float(n-1); int i0,i1,i2,i3; float t,tt,ttt; float a0,a1,a2,a3,d1,d2; // find start control point col*=float(n-1); i1=col; col-=i1; i0=i1-1; i2=i1+1; if (i2>=n) i2=n-1; i3=i1+2; // compute interpolation coefficients if (i0>=0) d1=0.5*(ctrl[i2]-ctrl[i0]); else d1=ctrl[i2]-ctrl[i1]; if (i3< n) d2=0.5*(ctrl[i3]-ctrl[i1]); else d2=ctrl[i2]-ctrl[i1]; a0=ctrl[i1]; a1=d1; a2=(3.0*(ctrl[i2]-ctrl[i1]))-(2.0*d1)-d2; a3=d1+d2+(2.0*(-ctrl[i2]+ctrl[i1])); // now interpolate new colro intensity t=col; tt=t*t; ttt=tt*t; t=a0+(a1*t)+(a2*tt)+(a3*ttt); return t; } int main (int argc, const char** argv) { Mat input = imread ("E:\\img2.jpg"); Mat input1 = input; for(int i=0 ; i<input1.rows ; i++) { for (int p=0;p<input1.cols;p++) { input1.at<cv::Vec3b>(i,p)[0] = 255*correction(input1.at<cv::Vec3b>(i,p)[0]/255.0,ctrl,N); //B input1.at<cv::Vec3b>(i,p)[1] = 255*correction(input1.at<cv::Vec3b>(i,p)[1]/255.0,ctrl,N); //G input1.at<cv::Vec3b>(i,p)[2] = 255*correction(input1.at<cv::Vec3b>(i,p)[2]/255.0,ctrl,N); //R } } imshow("image" , input); waitKey(); 

}

But the required output is similar to the curve the program is working , but the curves are not drawing on my screen like below , how to draw them using opencv or other approach . Thus, these lines can play the role of their specific color in the image and with their values, for example, below right one is the image of the original, and the rest is the result of changing the value through cuves , below the curves are control points per B,G,R

Answer 1

This code sketch allows you to edit the spline with the mouse, it uses the files for this link (attach to your project: overhauser.cpp overhauser. Hpp and vec3.hpp):

The left mouse button adds / moves a point, the right one deletes.

 #include <iostream> #include <vector> #include <stdio.h> #include <functional> #include <algorithm> #include <numeric> #include <cstddef> #include "opencv2/opencv.hpp" #include <iostream> #include <fstream> #include "overhauser.hpp" using namespace std; using namespace cv; Mat result; Mat Img; int current_color=0; vector<cv::Point2f> pts_red; vector<cv::Point2f> pts_green; vector<cv::Point2f> pts_blue; Mat curvesImg; int selectedPt=-1; CRSpline* spline_red = 0; CRSpline* spline_green = 0; CRSpline* spline_blue = 0; unsigned char LUT_RED[256]; unsigned char LUT_GREEN[256]; unsigned char LUT_BLUE[256]; // comparison function: bool mycomp (Point2f p1, Point2f p2) { return p1.x<p2.x; } float dist(Point2f p1,Point2f p2) { return sqrt((p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y)); } int findNEarestPt(Point2f pt, float maxDist) { vector<Point2f> current_pts_set; current_color=0; if(pt.x>255 && pt.x<512) { current_color=1; } if(pt.x>=512) { current_color=2; } float ptx=pt.x; switch(current_color) { case 0: current_pts_set=pts_red; break; case 1: current_pts_set=pts_green; pt.x-=255; break; case 2: current_pts_set=pts_blue; pt.x-=511; break; } float minDist=FLT_MAX; int ind=-1; for(int i=0;i<current_pts_set.size();++i) { float d=dist(pt,current_pts_set[i]); if(minDist>d) { ind=i; minDist=d; } } if(minDist>maxDist) { ind=-1; } return ind; } float F(float t,float x, CRSpline* spline) { vec3 rv = spline->GetInterpolatedSplinePoint(t); return x-rv.x; } float solveForX(float x,CRSpline* slpine) { float a=-1.0f,b=1.0,c,e=1e-2; c=(a+b)/2; while( (fabs(ba)>e) && (F(c,x,slpine)!=0) ) { if (F(a,x,slpine)*F(c,x,slpine)<0) { b=c; } else { a=c; } c=(a+b)/2; } return c; } int ind=-1; void mouseHandler(int event, int x, int y, int flags, void* param) { Point2f m; mx=x; my=y; curvesImg=Scalar(0,0,0); switch (event) { case cv::EVENT_RBUTTONDOWN: ind=findNEarestPt(m,5); if (ind==-1) { }else { switch(current_color) { case 0: pts_red.erase(pts_red.begin()+ind); break; case 1: pts_green.erase(pts_green.begin()+ind); break; case 2: pts_blue.erase(pts_blue.begin()+ind); break; } ind=-1; } break; case cv::EVENT_LBUTTONDOWN: ind=findNEarestPt(m,5); if (ind==-1) { switch(current_color) { case 0: pts_red.push_back(m); selectedPt=pts_red.size()-1; break; case 1: pts_green.push_back(Point2f(mx-255.0,my)); selectedPt=pts_green.size()-1; break; case 2: pts_blue.push_back(Point2f(mx-511,my)); selectedPt=pts_blue.size()-1; break; } }else { selectedPt=ind; } break; case cv::EVENT_MOUSEMOVE: if(ind!=-1) { switch(current_color) { case 0: pts_red[selectedPt].x=mx; pts_red[selectedPt].y=my; break; case 1: pts_green[selectedPt].x=mx-255; pts_green[selectedPt].y=my; break; case 2: pts_blue[selectedPt].x=mx-511; pts_blue[selectedPt].y=my; break; } } break; case cv::EVENT_LBUTTONUP: ind=-1; break; } std::sort(pts_red.begin(),pts_red.end(),mycomp); if(pts_red.size()>0) { pts_red[pts_red.size()-1].x=255; pts_red[0].x=0; } std::sort(pts_green.begin(),pts_green.end(),mycomp); if(pts_green.size()>0) { pts_green[pts_green.size()-1].x=255; pts_green[0].x=0; } std::sort(pts_blue.begin(),pts_blue.end(),mycomp); if(pts_blue.size()>0) { pts_blue[pts_blue.size()-1].x=255; pts_blue[0].x=0; } for(int i=0;i<pts_red.size();++i) { circle(curvesImg,pts_red[i],5,Scalar(0,0,255),-1,CV_AA); } for(int i=0;i<pts_green.size();++i) { circle(curvesImg,Point2f(pts_green[i].x+255,pts_green[i].y),5,Scalar(0,255,0),-1,CV_AA); } for(int i=0;i<pts_blue.size();++i) { circle(curvesImg,Point2f(pts_blue[i].x+511,pts_blue[i].y),5,Scalar(255,0,0),-1,CV_AA); } if (spline_red) {delete spline_red;} spline_red = new CRSpline(); if (spline_green) {delete spline_green;} spline_green = new CRSpline(); if (spline_blue) {delete spline_blue;} spline_blue = new CRSpline(); for (int i=0;i<pts_red.size();++i) { vec3 v(pts_red[i].x,pts_red[i].y,0); spline_red->AddSplinePoint(v); } for (int i=0;i<pts_green.size();++i) { vec3 v(pts_green[i].x,pts_green[i].y,0); spline_green->AddSplinePoint(v); } for (int i=0;i<pts_blue.size();++i) { vec3 v(pts_blue[i].x,pts_blue[i].y,0); spline_blue->AddSplinePoint(v); } vec3 rv_last(0,0,0); if(pts_red.size()>2) { for(int i=0;i<256;++i) { float t=solveForX(i,spline_red); vec3 rv = spline_red->GetInterpolatedSplinePoint(t); if(rv.y>255){rv.y=255;} if(rv.y<0){rv.y=0;} unsigned char I=(unsigned char)(rv.y); LUT_RED[i]=255-I; if(i>0) { line(curvesImg,Point(rv.x,rv.y),Point(rv_last.x,rv_last.y),Scalar(0,0,255),1); } rv_last=rv; } } rv_last=vec3(0,0,0); if(pts_green.size()>2) { for(int i=0;i<256;++i) { float t=solveForX(i,spline_green); vec3 rv = spline_green->GetInterpolatedSplinePoint(t); if(rv.y>255){rv.y=255;} if(rv.y<0){rv.y=0;} unsigned char I=(unsigned char)(rv.y); LUT_GREEN[i]=255-I; if(i>0) { line(curvesImg,Point(rv.x+255,rv.y),Point(rv_last.x+255,rv_last.y),Scalar(0,255,0),1); } rv_last=rv; } } rv_last=vec3(0,0,0); if(pts_blue.size()>2) { for(int i=0;i<256;++i) { float t=solveForX(i,spline_blue); vec3 rv = spline_blue->GetInterpolatedSplinePoint(t); if(rv.y>255){rv.y=255;} if(rv.y<0){rv.y=0;} unsigned char I=(unsigned char)(rv.y); LUT_BLUE[i]=255-I; if(i>0) { line(curvesImg,Point(rv.x+511,rv.y),Point(rv_last.x+511,rv_last.y),Scalar(255,0,0),1); } rv_last=rv; } } int cur_col=0; if(mx>255 && mx<512) { cur_col=1; } if(mx>=512) { cur_col=2; } Scalar col; switch(cur_col) { case 0: col=Scalar(0,0,255); break; case 1: col=Scalar(0,255,0); break; case 2: col=Scalar(255,0,0); break; } line(curvesImg,Point(0,my),Point(curvesImg.cols,my),col,1); line(curvesImg,Point(mx,0),Point(mx,curvesImg.rows),col,1); imshow("Correction curves",curvesImg); vector<Mat> ch; cv::split(Img,ch); LUT(ch[0],Mat(256,1,CV_8UC1,LUT_BLUE),ch[0]); LUT(ch[2],Mat(256,1,CV_8UC1,LUT_RED),ch[2]); LUT(ch[1],Mat(256,1,CV_8UC1,LUT_GREEN),ch[1]); cv::merge(ch,result); imshow("Transformed",result); } // --------------------------------- // // --------------------------------- //============================================================================== int main( int argc, char** argv ) { for (int i=0;i<256;++i) { LUT_RED[i]=i; LUT_GREEN[i]=i; LUT_BLUE[i]=i; } namedWindow("Image"); namedWindow("Correction curves"); namedWindow("Transformed"); Img=imread("D:\\ImagesForTest\\lena.jpg",1); imshow("Image",Img); curvesImg=Mat::zeros(256,768,CV_8UC3); setMouseCallback("Correction curves", mouseHandler, NULL); waitKey(0); getchar(); }