在图片上画直线比画框更简单。线形的控制还是通过对Pen的设置来实现的。
 
 
 

  
  
          
  /**/
  /// <summary>
        /// 在图片上画线
        /// </summary>
        /// <param name="bmp">原始图</param>
        /// <param name="p0">起始点</param>
        /// <param name="p1">终止点</param>
        /// <param name="RectColor">线的颜色</param>
        /// <param name="LineWidth">线宽</param>
        /// <param name="ds">线条样式</param>
        /// <returns>输出图</returns>
  

  
          
  public
   
  static
   Bitmap DrawLineInPicture(Bitmap bmp, Point p0, Point p1, Color LineColor, 
  int
   LineWidth, DashStyle ds)
        
  ...
  {
            if (bmp == null) return null;

            if (p0.X == p1.X || p0.Y == p1.Y) return bmp;

            Graphics g = Graphics.FromImage(bmp);

            Brush brush = new SolidBrush(LineColor);

            Pen pen = new Pen(brush, LineWidth);
            //pen.Alignment = PenAlignment.Inset;

            pen.DashStyle = ds;

            g.DrawLine(pen,p0,p1);

            g.Dispose();

            return bmp;
        }
 

因为需要在图片上标记直线，所以从网上找了相应的参考资料。但大多都是c风格的，于是自己就按照此博主的c++风格的代码进行了简单的修改。
 代码如下：
 
#pragma warning(disable:4996)
#include <opencv2/opencv.hpp>
#include <opencv2\highgui\highgui.hpp>
#include <opencv2\imgproc\imgproc.hpp>
#include <iostream>
#include <string.h>

using namespace std;
using namespace cv;
Mat src;
Mat dst;
void on_mouse(int event, int x, int y, int flags, void* ustc)
{
 static CvPoint pre_pt = { -1, -1 };
 static CvPoint cur_pt = { -1, -1 };
 char temp[16];
 if (event == CV_EVENT_LBUTTONDOWN)
 {
  dst.copyTo(src);
  sprintf(temp, "(%d,%d)", x, y);
  pre_pt = Point(x, y);
  putText(src, temp, pre_pt, FONT_HERSHEY_PLAIN,1,Scalar(0,0,255),1,8,0);
  circle(src, pre_pt, 3, cvScalar(255, 0, 0, 0), CV_FILLED, CV_AA, 0);
  imshow("src", src);
  src.copyTo(dst);
 }
 else if (event == CV_EVENT_MOUSEMOVE && (flags & CV_EVENT_FLAG_LBUTTON))
 {
  sprintf(temp, "(%d,%d)", x, y);
  dst.copyTo(src);
  cur_pt = Point(x, y);
  putText(src, temp, cur_pt, FONT_HERSHEY_PLAIN, 1, Scalar(0, 0, 255), 1, 8, 0);
  line(src, pre_pt, cur_pt, cvScalar(0, 255, 0, 0), 1, CV_AA, 0);
  imshow("src", src);
 }
 else if (event == CV_EVENT_LBUTTONUP)
 {
  sprintf(temp, "(%d,%d)", x, y);
  dst.copyTo(src);
  cur_pt = Point(x, y);
  putText(src, temp, cur_pt, FONT_HERSHEY_PLAIN, 1, Scalar(0, 0, 255), 1, 8, 0);
  circle(src, cur_pt, 3, cvScalar(255, 0, 0, 0), CV_FILLED, CV_AA, 0);
  line(src, pre_pt, cur_pt, cvScalar(0, 255, 0, 0), 1, CV_AA, 0);
  imshow("src", src);
  src.copyTo(dst);
 }
}
int main()
{
 namedWindow("src", CV_WINDOW_AUTOSIZE);
 src = imread("1.jpg", 1);
 if (src.empty())
 {
  cout << "not find the image" << endl;
 }
 src.copyTo(dst);
 setMouseCallback("src", on_mouse, 0);
 imshow("src", src);
 waitKey(0);
 return 0;
}
 
注：#pragma warning(disable:4996)是为了规避4996的错误。

OpenCV在图像中添加文字，画点，画直线
   【尊重原创，转载请注明出处】 http://blog.csdn.net/guyuealian/article/details/77870983

#include "stdafx.h"
#include <iostream>
#include <string.h>
#include<opencv2\opencv.hpp>
using namespace cv;
using namespace std;
int main()
{

	Mat src = imread("images/2.jpg");//图片必须添加到工程目录下

	// 将原图像转换为灰度图像    
	//cvtColor(src, src, CV_BGR2GRAY)

	//在原图画一个圆圈点
	cv::Point point;//特征点，用以画在图像中  
	point.x = 20;//特征点在图像中横坐标  
	point.y = 50;//特征点在图像中纵坐标  
	cv::circle(src, point, 4, cv::Scalar(0, 0, 255));//在图像中画出特征点，2是圆的半径 

	//在原图画一条直线
	cv::Point start = cv::Point(10, 100); //直线起点
	cv::Point end = cv::Point(50, 200);   //直线终点
	cv::line(src, start, end, cv::Scalar(0, 0, 255));

	//在原图某个位置添加文字标记
	//char str[4];
	//int num = 100;
	//_itoa_s(num, str, 10);//数字需要转为字符串来显示
	string str = "Love100";
	putText(src, str, end, cv::FONT_HERSHEY_DUPLEX, 0.5, cv::Scalar(0, 255,0 ), 2);
	imshow("src", src);
	waitKey(0);
}
运行结果：

clc;

 clear all;

 I=imread('test.jpg');

 figure;

 imshow(I);

 I=rgb2gray(I);

 rot1=imrotate(I,33,'crop');  %旋转图像

 bw=edge(rot1,'canny');   %使用边缘检测形成二值图像

 [H,T,R]=hough(bw);   %生成点的叠加矩阵和坐标T,R

 figure;

 imshow(H,[],'XData',T,'YData',R,'InitialMagnification','fit');  %显示统计点的图形

 title('变换结果');

 xlabel('\theta'),ylabel('\rho');

 axis on,axis normal;hold on; %使坐标易于观察

 p=houghpeaks(H,5,'threshold',ceil(0.3*max(H(:))));  %提取5个极值点，p中为极坐标的位置

 x=T(p(:,2));y=R(p(:,1));

 plot(x,y,'s','color','blue');

 lines=houghlines(bw,T,R,p,'FillGap',5,'MinLength',7);  %生成这五个点在图像中的直线矩阵

 figure;

 imshow(rot1);,hold on;

 max_len=0;

 for k=1:length(lines)  %计算线的数量

     xy=[lines(k).point1;lines(k).point2];  %

     plot(xy(:,1),xy(:,2),'LineWidth',2,'Color','green'); %通过直线的起点和终点画出直线

     plot(xy(1,1),xy(1,2),'x','LineWidth',2,'Color','red');  %标出起点和终点

     len=norm(lines(k).point1-lines(k).point2);

     if(len>max_len)  %算出最大的直线

         max_len=len;

         xy_long=xy;

     end

 end

 
plot(xy_long(:,1),xy_long(:,2),'LineWidth',2,'Color','Cyan');  %标记出最大的直线