OpenCV 之基本繪圖

時間 2020-05-19

標籤 opencv 基本繪圖简体版

原文原文鏈接

OpenCV 雖是開源的計算機視覺庫，但裏面也有一些基礎的繪圖函數，本文將介紹幾種經常使用繪圖函數：直線、圓、橢圓、長方形、多邊形等。html

1 數據結構

1.1 二維向量

cv::Point 表明的是二維點 (int 型)，可用來表示圖像座標 (x, y)
數據結構

// one way
Point pt; pt.x = 10; pt.y = 8; // another way
Point pt = Point(10, 8);

OpenCV 中，二維點類型可分爲 Point2i, Point2l, Point2f, Point2d 四種，各自定義以下：函數

// 4 type of Point
typedef Point_<int> cv::Point2i typedef Point_<int64> cv::Point2l typedef Point_<float> cv::Point2f typedef Point_<double> cv::Point2d // cv::Point
typedef Point2i cv::Point

1.2 四維向量

cv::Scalar 表明的是四維向量，經常使用來傳遞像素值，尤爲是 BGR 通道的像素值 (最後一個元素不用，則不定義)ui

$\texttt{Scalar} (blue \_ component, green \_ component, red \_ component)$spa

2 繪圖函數

2.1 line()

OpenCV 中，繪製直線段較簡單，就是過兩點畫一條直線，函數爲 line()
code

// pt1, first point
// pt2, second point
void cv::line ( InputOutputArray img, Point pt1, Point pt2, const Scalar& color, int thickness = 1, int lineType = LINE_8, int shift = 0)

2.2 circle() 和 ellipse()

知道圓心和半徑，就能夠繪製圓了，函數爲 circle()
component

void cv::circle ( InputOutputArray img, Point center, // center of the circle
               int         radius,                       // radius of the circle
               const Scalar & color, int      thickness = 1, int      lineType = LINE_8, int      shift = 0 )

橢圓稍微複雜，橢圓中心，長、短軸半徑，以及橢圓弧的旋轉角度，則可獲得一段橢圓弧 ellipse()htm

void cv::ellipse (     
    InputOutputArray   img,
    Point       center,         // center of the ellipse
    Size        axes,           // half size of the main axes
    double      angle,          // ellipse rotation angle in degrees
    double      startAngle,
    double      endAngle,
    const Scalar &   color,
    int      thickness = 1,
    int      lineType = LINE_8,
    int      shift = 0 
)

2.3 rectangle()

長方形的繪製，主要是靠其對角線上的兩個點 pt1 和 pt2，函數爲 rectangle()blog

void cv::rectangle (
    InputOutputArray  img,
    Point      pt1,          // vertex of the rectangle
    Point      pt2,          // vertex of the rectangle opposite to pt1
    const Scalar &    color,
    int      thickness = 1,
    int      lineType = LINE_8,
    int      shift = 0 
)

2.4 fillpoly()

void cv::fillPoly (     
    InputOutputArray  img,
    const Point **   pts,   //
    const int *      npts,  //
    int      ncontours,
    const Scalar &  color,
    int      lineType = LINE_8,
    int      shift = 0,
    Point    offset = Point() 
)

3 代碼示例

3.1 直線和長方形

#include <opencv2/core.hpp>
#include <opencv2/imgproc.hpp>
#include <opencv2/highgui.hpp>

using namespace cv;

#define w 300

int main()
{
    // creat a white background image
    Mat img;
    img.create(w,w,CV_8UC3);
    img.setTo(Scalar(255,255,255));

    // draw lines
    line(img, Point(w/4,w/4), Point(3*w/4, w/4), Scalar(255, 0, 0));
    line(img, Point(w/6,w/2), Point(5*w/6, w/2), Scalar(0, 255, 0));
    line(img, Point(w/10,3*w/4), Point(9*w/10, 3*w/4), Scalar(0, 0, 255));
    
    // draw rectangle
    rectangle(img,Point(w/12,w/12),Point(11*w/12,9*w/10),Scalar(200,200,100));

    // show lines in the image
    imshow("line and rectangle", img);

    waitKey(0);
}

3.2 圓和橢圓

// draw circle and ellipse
circle(img, Point(w/2,w/2), 50, Scalar(255, 0, 0));
ellipse(img, Point(w/2,w/2), Size(100,50), 0, 0, 360, Scalar(0, 255, 0));

3.3 多邊形

Point rook_points[1][20];
rook_points[0][0]  = Point(    w/4,   7*w/8 );
rook_points[0][1]  = Point(  3*w/4,   7*w/8 );
rook_points[0][2]  = Point(  3*w/4,  13*w/16 );
rook_points[0][3]  = Point( 11*w/16, 13*w/16 );
rook_points[0][4]  = Point( 19*w/32,  3*w/8 );
rook_points[0][5]  = Point(  3*w/4,   3*w/8 );
rook_points[0][6]  = Point(  3*w/4,     w/8 );
rook_points[0][7]  = Point( 26*w/40,    w/8 );
rook_points[0][8]  = Point( 26*w/40,    w/4 );
rook_points[0][9]  = Point( 22*w/40,    w/4 );
rook_points[0][10] = Point( 22*w/40,    w/8 );
rook_points[0][11] = Point( 18*w/40,    w/8 );
rook_points[0][12] = Point( 18*w/40,    w/4 );
rook_points[0][13] = Point( 14*w/40,    w/4 );
rook_points[0][14] = Point( 14*w/40,    w/8 );
rook_points[0][15] = Point(    w/4,     w/8 );
rook_points[0][16] = Point(    w/4,   3*w/8 );
rook_points[0][17] = Point( 13*w/32,  3*w/8 );
rook_points[0][18] = Point(  5*w/16, 13*w/16 );
rook_points[0][19] = Point(    w/4,  13*w/16 );

const Point* ppt[1] = { rook_points[0]};
int npt[] = { 20 };

// draw polygon
fillPoly(img, ppt, npt, 1, Scalar(0, 255, 255 ));