1 透視變換
透視變換(Perspective Transformation)是將成像投影到一個新的視平面(Viewing Plane),也稱作投影映射(Projective Mapping)。如下圖所示,通過透視變換ABC變換到A’B’C’。
2 使用OpenCV實現透視變換
2.1 getPerspectiveTransform
由四對點計算透射變換,返回由源圖像中矩形到目標圖像矩形變換的矩陣。
2.2 warpPerspective
使用getPerspectiveTransform
得到的透視變換矩陣,對圖像進行透視變換,返回的是相同size的圖片。
3 代碼實現
3.1 C++
#include "opencv2/opencv.hpp"
#include <iostream>
using namespace cv;
using namespace std;
/// 全局變量
const char* source_window = "Source image";;
const char* warpPerspective_window = "warpPerspective";
/**
* @主函數
*/
int main( )
{
Point2f srcTri[4];
Point2f dstTri[4];
Mat warpPerspective_mat(3, 3, CV_32FC1);
Mat src, warpPerspective_dst;
/// Load the image
src = imread("lena.bmp", IMREAD_COLOR);
/// Set the dst image the same type and size as src
warpPerspective_dst = Mat::zeros( src.rows, src.cols, src.type() );
/// 設置4組點,求出變換矩陣
srcTri[0] = Point2f( 0, 0);
srcTri[1] = Point2f( src.cols-1, 0 );
srcTri[2] = Point2f( 0, src.rows-1);
srcTri[3] = Point2f(src.cols-1, src.rows - 1);
dstTri[0] = Point2f( 0,src.rows*0.13 );
dstTri[1] = Point2f( src.cols*0.9,0 );
dstTri[2] = Point2f( src.cols*0.2,src.rows*0.7 );
dstTri[3] = Point2f( src.cols*0.8,src.rows );
//計算4個二維點對之間的仿射變換矩陣(2行x3列)
warpPerspective_mat = getPerspectiveTransform(srcTri, dstTri);
//應用仿射變換,可以恢復出原圖
warpPerspective( src, warpPerspective_dst, warpPerspective_mat, src.size() );
//顯示結果
namedWindow( source_window, WINDOW_AUTOSIZE );
imshow( source_window, src );
namedWindow( warpPerspective_window, WINDOW_AUTOSIZE );
imshow( warpPerspective_window, warpPerspective_dst );
/// 等待,直到用戶退出
waitKey(0);
return 0;
}
3.2 Python
import cv2 as cv
import numpy as np
img = cv.imread("test/scene2.png",0)
w,h = img.shape
point1 = np.array([[308,230],[500,230],[308,640],[500,640]],dtype = "float32")
point2 = np.array([[308,230],[500,230],[155,30],[835,30]],dtype = "float32")
M = cv.getPerspectiveTransform(point1,point2)
out_img = cv.warpPerspective(img,M,(w,h))
cv.imshow("img",out_img)
cv.waitKey(0)
4 參考
[1] OpenCV官方文檔:
getPerspectiveTransform
: https://docs.opencv.org/2.4.9/modules/imgproc/doc/geometric_transformations.html#getperspectivetransformwarpPerspective
: https://docs.opencv.org/2.4.9/modules/imgproc/doc/geometric_transformations.html#warpperspective
[2] https://www.cnblogs.com/aoru45/p/9763983.html
[3] https://blog.csdn.net/i_chaoren/article/details/78324184