如何使用openCV使用四个角点裁剪图像？

Posted 2023-02-25

【中文标题】如何使用openCV使用四个角点裁剪图像？

【英文标题】：How to crop image using four corner point using openCV?

【发布时间】：2014-01-31 10:45:35

【问题描述】：

我正在使用 code 获取图像的四个角：

cv::Mat CVSquares::detectedSquaresInImage (cv::Mat image, float tol, int threshold, int levels, int acc)

    vector<vector<Point> > squares;

    if( image.empty() )
        
        cout << "CVSquares.m: Couldn't load " << endl;
        

    tolerance = tol;
    thresh = threshold;
    N = levels;
    accuracy = acc;
    findSquares(image, squares);
    //drawSquares(image, squares);

    // The largest of them probably represents the paper
    vector<Point> largest_square;
    find_largest_square(squares, largest_square);
    drawSquares(image, largest_square);

    // Print the x,y coordinates of the square
    cout << "Point 1: " << largest_square[0] << endl;
    cout << "Point 2: " << largest_square[1] << endl;
    cout << "Point 3: " << largest_square[2] << endl;
    cout << "Point 4: " << largest_square[3] << endl;

    return image;

它给了我四个点，但现在我想将图像裁剪到那个点。谁能帮我解决这个问题？

我尝试使用来自this answer的代码

但是下面显示错误。

duplicate symbol __Z9getCenterNSt3__16vectorIN2cv6Point_IiEENS_9allocatorIS3_EEEE in:
    /Users/user/Library/Developer/Xcode/DerivedData/OpenCVSquares-gbnzjrefuxhjlchibreeqqdoaiqq/Build/Intermediates/OpenCVSquares.build/Debug-iphonesimulator/OpenCVSquares.build/Objects-normal/i386/UIImage+OpenCV.o
    /Users/user/Library/Developer/Xcode/DerivedData/OpenCVSquares-gbnzjrefuxhjlchibreeqqdoaiqq/Build/Intermediates/OpenCVSquares.build/Debug-iphonesimulator/OpenCVSquares.build/Objects-normal/i386/CVSquares.o
duplicate symbol __Z25sortSquarePointsClockwiseNSt3__16vectorIN2cv6Point_IiEENS_9allocatorIS3_EEEE in:
    /Users/user/Library/Developer/Xcode/DerivedData/OpenCVSquares-gbnzjrefuxhjlchibreeqqdoaiqq/Build/Intermediates/OpenCVSquares.build/Debug-iphonesimulator/OpenCVSquares.build/Objects-normal/i386/UIImage+OpenCV.o
    /Users/user/Library/Developer/Xcode/DerivedData/OpenCVSquares-gbnzjrefuxhjlchibreeqqdoaiqq/Build/Intermediates/OpenCVSquares.build/Debug-iphonesimulator/OpenCVSquares.build/Objects-normal/i386/CVSquares.o
ld: 2 duplicate symbols for architecture i386
clang: error: linker command failed with exit code 1 (use -v to see invocation)

【问题讨论】：

嘿，你怎么能得到这些正方形的CGPoint，这样我们就可以绘制uiview pointfro裁剪

【参考方案1】：

假设你的四个端点是 x1,y1,x2,y2

然后使用代码

src.copyTo(dst(Rect(x1,y1,x1+x2,y1+y2));

【参考方案2】：

使用 copyTo 加上 ROI rect 就可以了，示例代码如下：

Mat srcImg = imread('sample.jpg'), dstImg;
Rect rect = Rect( x, y, width, height ); // ROI rect in srcImg
// In your case, x=x1, y=y1, width=x2-x1, height=y2-y1; 
// (x1, y1) is the up-left corner, (x2, y2) is the bottom-right corner
srcImg(rect).copyTo(dstImg);  

希望这会有所帮助。

【参考方案3】：

$ c++filt __Z9getCenterNSt3__16vectorIN2cv6Point_IiEENS_9allocatorIS3_EEEE

getCenter(std::__1::vector, std::__1::allocator >>)

$ c++filt __Z25sortSquarePointsClockwiseNSt3__16vectorIN2cv6Point_IiEENS_9allocatorIS3_EEEE

sortSquarePointsClockwise(std::__1::vector, std::__1::allocator > >)

这是一个链接错误。它建议您将上述每个函数定义两次。