C++ OpenCV cv::perspectiveTransform()
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Description::
This is a C++ program to rotate and warp the input file(image) by the use of wrafAffine funtion which is inbuilt in the opencv library. wrafAffine takes 4 parametres. FIrst is source image file , second is destination image file , third parameter is mat object that is ouput after rotating with some point taking into reference and last is taking the size.
A transformation that can be expressed in the form of a matrix multiplication (linear transformation) followed by a vector addition (translation) is affine transformation.
Here src: Input image
warp_dst: Output image
warp_mat: Affine transform
warp_dst.size(): The desired size of the output image
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Program::
#include "opencv2/imgcodecs.hpp"
#include "opencv2/highgui.hpp"
#include "opencv2/imgproc.hpp"
#include <iostream>
using namespace cv;
using namespace std;
int main( int argc, char** argv )
{
char* ImageFile = argv[1]; //taking input
Mat src = imread( ImageFile , IMREAD_COLOR ); //reading image file in mat object
if( src.empty() ) //if not opened correctly
{
cout << "Could not open or find the image!\n" << endl;
cout << "Usage: " << argv[0] << " <Input image>" << endl;
return -1;
}
Point2f srcTri[3]; //point 2f object for input file
srcTri[0] = Point2f( 0.f, 0.f );
srcTri[1] = Point2f( src.cols - 1.f, 0.f ); //Before transformation selecting points
srcTri[2] = Point2f( 0.f, src.rows - 1.f );
Point2f dstTri[3]; //point 2f object for destination file
dstTri[0] = Point2f( 0.f, src.rows*0.33f );
dstTri[1] = Point2f( src.cols*0.85f, src.rows*0.25f ); //After transformation by certain angle and distance
dstTri[2] = Point2f( src.cols*0.15f, src.rows*0.7f );
Mat warp_mat = getAffineTransform( srcTri, dstTri ); //apply an affine transforation to image and storing it
Mat warp_dst = Mat::zeros( src.rows, src.cols, src.type() );
warpAffine( src, warp_dst, warp_mat, warp_dst.size() );
Point center = Point( warp_dst.cols/2, warp_dst.rows/2 );
double angle = -50.0; //setting angle
double scale = 0.6; //setting scale value
Mat rot_mat = getRotationMatrix2D( center, angle, scale ); //rotating with some references and angle
Mat warp_rotate_dst; //mat object for storing in next step
warpAffine( warp_dst, warp_rotate_dst, rot_mat, warp_dst.size() );
imshow( "Source image", src );
imshow( "Warp", warp_dst ); //displaying three windows
imshow( "Warp + Rotate", warp_rotate_dst );
waitKey(0);
return 0;
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Commands to run program on terminal::
$ g++ -ggdb `pkg-config --cflags filename` -o `basename filename .cpp` filename `pkg-config --libs opencv`
$ ./cvopen filename
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Output::
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