iphone - 调整角并裁剪图像 openCV

Question

我在 IOS 中使用开放式 CV。我已经检测到图像中纸张的边界，如图所示，现在我必须在触摸时拖动这些边界线以调整裁剪框。我们如何调整边界线以及如何在边界内裁剪图像？

这在 openCV 中是可能的，还是我为此使用 openGL？

@moosgummi:我在下面的方法中调用了你的方法

- (cv::Mat)finshWork:(cv::Mat &)image
{

Mat img0 =image;

Mat img1;
cvtColor(img0, img1, CV_RGB2GRAY);

// apply your filter
Canny(img1, img1, 100, 200);

// find the contours
vector< vector<cv::Point> > contours;
findContours(img1, contours, CV_RETR_EXTERNAL, CV_CHAIN_APPROX_NONE);


// you could also reuse img1 here
Mat mask = Mat::zeros(img1.rows, img1.cols, CV_8UC1);

// CV_FILLED fills the connected components found
drawContours(mask, contours, -1, Scalar(255), CV_FILLED);


// let's create a new image now
Mat crop(img0.rows, img0.cols, CV_8UC3);

// set background to green
crop.setTo(Scalar(0,255,0));

// and copy the magic apple
img0.copyTo(crop, mask);

// normalize so imwrite(...)/imshow(...) shows the mask correctly!
normalize(mask.clone(), mask, 0.0, 255.0, CV_MINMAX, CV_8UC1);



std::vector<cv::Point> biggestContour = contours[contours.size()-1];

NSLog(@"%d",biggestContour[0].x);
NSLog(@"%d",biggestContour[0].y);

cv::Mat paperImage =[self getPaperAreaFromImage:image:biggestContour];


//return crop;
return paperImage;

}

谢谢大家

Answer 1

得到角后，您必须对纸张进行校正并将其“提取”为新图像。

您应该执行以下操作:

1. 对角点进行排序(顺序很重要；它们在两个向量中的顺序必须相同)
2. cv::getAffineTransform
3. cv::warpAffine

我自己写了一个辅助函数，它接受一个包含四个 cv::Point 的 std::vector 并从左上角开始按顺时针顺序对它们进行排序.有关此主题的更多信息，请查看以下主题:

• Sort points in clockwise order?
• Sort Four Points in Clockwise Order
• Sorting of Points in 2D space

您应该考虑的另一件事是要提取的纸张的大小。在我的示例中，我假设您正在提取 DIN A4 纸 (210x297mm)。请随意在我的代码中编辑 paperWidth 和 paperHeight。

组合一切看起来像这样:

// Helper
cv::Point getCenter( std::vector<cv::Point> points ) {

    cv::Point center = cv::Point( 0.0, 0.0 );

    for( size_t i = 0; i < points.size(); i++ ) {
        center.x += points[ i ].x;
        center.y += points[ i ].y;
    }

    center.x = center.x / points.size();
    center.y = center.y / points.size();

    return center;

}

// Helper;
// 0----1
// |    |
// |    |
// 3----2
std::vector<cv::Point> sortSquarePointsClockwise( std::vector<cv::Point> square ) {

    cv::Point center = getCenter( square );

    std::vector<cv::Point> sorted_square;
    for( size_t i = 0; i < square.size(); i++ ) {
        if ( (square[i].x - center.x) < 0 && (square[i].y - center.y) < 0 ) {
            switch( i ) {
                case 0:
                    sorted_square = square;
                    break;
                case 1:
                    sorted_square.push_back( square[1] );
                    sorted_square.push_back( square[2] );
                    sorted_square.push_back( square[3] );
                    sorted_square.push_back( square[0] );
                    break;
                case 2:
                    sorted_square.push_back( square[2] );
                    sorted_square.push_back( square[3] );
                    sorted_square.push_back( square[0] );
                    sorted_square.push_back( square[1] );
                    break;
                case 3:
                    sorted_square.push_back( square[3] );
                    sorted_square.push_back( square[0] );
                    sorted_square.push_back( square[1] );
                    sorted_square.push_back( square[2] );
                    break;
            }
            break;
        }
    }

    return sorted_square;

}

// Helper
float distanceBetweenPoints( cv::Point p1, cv::Point p2 ) {

    if( p1.x == p2.x ) {
        return abs( p2.y - p1.y );
    }
    else if( p1.y == p2.y ) {
        return abs( p2.x - p1.x );
    }
    else {
        float dx = p2.x - p1.x;
        float dy = p2.y - p1.y;
        return sqrt( (dx*dx)+(dy*dy) );
    }
}

cv::Mat getPaperAreaFromImage( cv::Mat image, std::vector<cv::Point> square )
{

    // declare used vars
    int paperWidth  = 210; // in mm, because scale factor is taken into account
    int paperHeight = 297; // in mm, because scale factor is taken into account
    cv::Point2f imageVertices[4];
    float distanceP1P2;
    float distanceP1P3;
    BOOL isLandscape = true;
    int scaleFactor;
    cv::Mat paperImage;
    cv::Mat paperImageCorrected;
    cv::Point2f paperVertices[4];

    // sort square corners for further operations
    square = sortSquarePointsClockwise( square );

    // rearrange to get proper order for getPerspectiveTransform()
    imageVertices[0] = square[0];
    imageVertices[1] = square[1];
    imageVertices[2] = square[3];
    imageVertices[3] = square[2];

    // get distance between corner points for further operations
    distanceP1P2 = distanceBetweenPoints( imageVertices[0], imageVertices[1] );
    distanceP1P3 = distanceBetweenPoints( imageVertices[0], imageVertices[2] );

    // calc paper, paperVertices; take orientation into account
    if ( distanceP1P2 > distanceP1P3 ) {
        scaleFactor =  ceil( lroundf(distanceP1P2/paperHeight) ); // we always want to scale the image down to maintain the best quality possible
        paperImage = cv::Mat( paperWidth*scaleFactor, paperHeight*scaleFactor, CV_8UC3 );
        paperVertices[0] = cv::Point( 0, 0 );
        paperVertices[1] = cv::Point( paperHeight*scaleFactor, 0 );
        paperVertices[2] = cv::Point( 0, paperWidth*scaleFactor );
        paperVertices[3] = cv::Point( paperHeight*scaleFactor, paperWidth*scaleFactor );
    }
    else {
        isLandscape = false;
        scaleFactor =  ceil( lroundf(distanceP1P3/paperHeight) ); // we always want to scale the image down to maintain the best quality possible
        paperImage = cv::Mat( paperHeight*scaleFactor, paperWidth*scaleFactor, CV_8UC3 );
        paperVertices[0] = cv::Point( 0, 0 );
        paperVertices[1] = cv::Point( paperWidth*scaleFactor, 0 );
        paperVertices[2] = cv::Point( 0, paperHeight*scaleFactor );
        paperVertices[3] = cv::Point( paperWidth*scaleFactor, paperHeight*scaleFactor );
    }

    cv::Mat warpMatrix = getPerspectiveTransform( imageVertices, paperVertices );
    cv::warpPerspective(_image, paperImage, warpMatrix, paperImage.size(), cv::INTER_LINEAR, cv::BORDER_CONSTANT );

    // we want portrait output
    if ( isLandscape ) {
        cv::transpose(paperImage, paperImageCorrected);
        cv::flip(paperImageCorrected, paperImageCorrected, 1);
        return paperImageCorrected;
    }

    return paperImage;

}

用法:

// ... get paper square ...

cv::Mat paperImage = getPaperAreaFromImage( srcImage, paperSquare );