OpenCV 之基本绘图

OpenCV 虽是开源的计算机视觉库，但里面也有一些基础的绘图函数，本文将介绍几种常用绘图函数：直线、圆、椭圆、长方形、多边形等。

1 数据结构

1.1 二维向量

cv::Point 代表的是二维点 (int 型)，可用来表示图像坐标 (x, y)

// one way

Point pt;

pt.x = ;

pt.y = ;

// another way

Point pt = Point(, );

OpenCV 中，二维点类型可分为 Point2i, Point2l, Point2f, Point2d 四种，各自定义如下：

// 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 四维向量

cv::Scalar 代表的是四维向量，常用来传递像素值，尤其是 BGR 通道的像素值 (最后一个元素不用，则不定义)

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

2 绘图函数

2.1 line()

OpenCV 中，绘制直线段较简单，就是过两点画一条直线，函数为 line()

// pt1, first point
// pt2, second point

void cv::line ( InputOutputArray img, Point pt1, Point pt2, const Scalar& color, int thickness = , int lineType = LINE_8, int shift = )

2.2 circle() 和 ellipse()

知道圆心和半径，就可以绘制圆了，函数为 circle()

void cv::circle (

       InputOutputArray   img,

       Point  center,         // center of the circle

               int         radius,                       // radius of the circle

               const Scalar &     color,

       int      thickness = ,

       int      lineType = LINE_8,

       int      shift =

)

椭圆稍微复杂，椭圆中心，长、短轴半径，以及椭圆弧的旋转角度，则可得到一段椭圆弧 ellipse()

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 = ,

    int      lineType = LINE_8,

    int      shift =

)

2.3 rectangle()

长方形的绘制，主要是靠其对角线上的两个点 pt1 和 pt2，函数为 rectangle()

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 = ,

    int      lineType = LINE_8,

    int      shift =

)

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 = ,

    Point    offset = Point()

)

3 代码示例

3.1 直线和长方形

#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(,,));

    // draw lines

    line(img, Point(w/,w/), Point(*w/, w/), Scalar(, , ));

    line(img, Point(w/,w/), Point(*w/, w/), Scalar(, , ));

    line(img, Point(w/,*w/), Point(*w/, *w/), Scalar(, , ));

    // draw rectangle

    rectangle(img,Point(w/,w/),Point(*w/,*w/),Scalar(,,));

    // show lines in the image

    imshow("line and rectangle", img);

    waitKey();

}

3.2 圆和椭圆

// draw circle and ellipse

circle(img, Point(w/,w/), , Scalar(, , ));

ellipse(img, Point(w/,w/), Size(,), , , , Scalar(, , ));

3.3 多边形

Point rook_points[][];

rook_points[][]  = Point(    w/,   *w/ );

rook_points[][]  = Point(  *w/,   *w/ );

rook_points[][]  = Point(  *w/,  *w/ );

rook_points[][]  = Point( *w/, *w/ );

rook_points[][]  = Point( *w/,  *w/ );

rook_points[][]  = Point(  *w/,   *w/ );

rook_points[][]  = Point(  *w/,     w/ );

rook_points[][]  = Point( *w/,    w/ );

rook_points[][]  = Point( *w/,    w/ );

rook_points[][]  = Point( *w/,    w/ );

rook_points[][] = Point( *w/,    w/ );

rook_points[][] = Point( *w/,    w/ );

rook_points[][] = Point( *w/,    w/ );

rook_points[][] = Point( *w/,    w/ );

rook_points[][] = Point( *w/,    w/ );

rook_points[][] = Point(    w/,     w/ );

rook_points[][] = Point(    w/,   *w/ );

rook_points[][] = Point( *w/,  *w/ );

rook_points[][] = Point(  *w/, *w/ );

rook_points[][] = Point(    w/,  *w/ );

const Point* ppt[] = { rook_points[]};

int npt[] = {  };

// draw polygon

fillPoly(img, ppt, npt, , Scalar(, ,  ));

3.4 显示效果

参考资料:

OpenCV Tutorials / imgproc module / Basic Drawing

巴特西

OpenCV 之基本绘图

1 数据结构

1.1 二维向量

1.2 四维向量

2 绘图函数

2.1 line()

2.2 circle() 和 ellipse()

2.3 rectangle()

2.4 fillpoly()

3 代码示例

3.1 直线和长方形

3.2 圆和椭圆

3.3 多边形

3.4 显示效果

参考资料:

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热门文章

巴特西

OpenCV 之 基本绘图

1 数据结构

1.1 二维向量

1.2 四维向量

2 绘图函数

2.1 line()

2.2 circle() 和 ellipse()

2.3 rectangle()

2.4 fillpoly()

3 代码示例

3.1 直线和长方形

3.2 圆和椭圆

3.3 多边形

3.4 显示效果

参考资料:

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OpenCV 之基本绘图