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OpenCV基础篇之绘图及RNG随机数对象.md

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程序及分析

/*
 * FileName : random_gen.c
 * Author   : xiahouzuoxin @163.com
 * Version  : v1.0
 * Date     : Tue 29 Jul 2014 08:31:41 PM CST
 * Brief    : 
 * 
 * Copyright (C) MICL,USTB
 */
#include <cv.h>
#include <highgui.h>
#include <iostream>

using namespace std;
using namespace cv;


const char wndname[] = "Drawing";
const int RAND_N = 100;

void help(void)
{
    cout<<"Usage:./drawing"<<endl;
}

static Scalar random_color(RNG& rng)
{
    int icolor = (unsigned)rng;

    return Scalar(icolor&0xFF, (icolor>>8)&0xFF, (icolor>>16)&0xFF);
}

int main(int argc, char *argv[])
{
    int line_type = CV_AA;
    int i = 0;
    int width = 1000;
    int height = 700;
    int x1 = -width/2;
    int x2 = width*3/2;
    int y1 = -height/2;
    int y2 = height*3/2;
    const int DELAY = 10;

    RNG rng(0xFFFFFFFF);
    Mat image = Mat::zeros(height, width, CV_8UC3);

    imshow(wndname, image);
    waitKey(DELAY);
    
    for (i=0; i<RAND_N; i++) {
        Point pt1;
        Point pt2;

        pt1.x = rng.uniform(x1, x2);
        pt1.y = rng.uniform(y1, y2);
        pt2.x = rng.uniform(x1, x2);
        pt2.y = rng.uniform(y1, y2);

        line(image, pt1, pt2, random_color(rng), rng.uniform(1,5), line_type);
    }
    imshow(wndname, image);
    waitKey(0);

    for (i=0; i<RAND_N; i++) {
    Point org;
    org.x = rng.uniform(x1, x2);
    org.y = rng.uniform(y1, y2);
    putText(image, "OpenCV",org, rng.uniform(0,8),rng.uniform(0,10)*0.5+0.1, 
            random_color(rng), rng.uniform(1, 10), line_type);
    }

    imshow(wndname, image);
    waitKey(0);
    return 0;
}

  1. RNG是OpenCV中的随机数生成类，其定义在core.hpp中，

    class CV_EXPORTS RNG
{
public:
    enum { UNIFORM=0, NORMAL=1 };

    RNG();
    RNG(uint64 _state);
    //! updates the state and returns the next 32-bit unsigned integer random number
    unsigned next();

    operator uchar();
    operator schar();
    operator ushort();
    operator short();
    operator unsigned();
    //! returns a random integer sampled uniformly from [0, N).
    unsigned operator()(unsigned N);
    unsigned operator ()();
    operator int();
    operator float();
    operator double();
    //! returns uniformly distributed integer random number from [a,b) range
    int uniform(int a, int b);
    //! returns uniformly distributed floating-point random number from [a,b) range
    float uniform(float a, float b);
    //! returns uniformly distributed double-precision floating-point random number from [a,b) range
    double uniform(double a, double b);
    void fill( InputOutputArray mat, int distType, InputArray a, InputArray b );
    //! returns Gaussian random variate with mean zero.
    double gaussian(double sigma);

    uint64 state;
};

    提供了两种随机数——均匀分布（uniform)和高斯正态分布（gaussian）。本文使用的是随机分布，两个参数分布表示均匀分布的下限和上限。RNG rng(0xFFFFFFFF);中的0xFFFFFFFF表示初始的随机值。

  2. Mat矩阵初始化：

    Mat image = Mat::zeros(height, width, CV_8UC3);

  3. line用于绘制直线，也定义在core.hpp中，

    //! draws the line segment (pt1, pt2) in the image
CV_EXPORTS_W void line(Mat& img, Point pt1, Point pt2, const Scalar& 	color,int thickness=1, int lineType=8, int shift=0);

    还有其它绘图函数circle、ellipse、rectangle等也也可以从core.hpp中找到原型，可用到时自行学习。

  4. putText可以将文字添加到图片中，

    //! renders text string in the image
CV_EXPORTS_W void putText( Mat& img, const string& text, Point org,
                         int fontFace, double fontScale, Scalar color,
                         int thickness=1, int linetype=8,
                         bool bottomLeftOrigin=false );

    其第一个参数img就是要添加文字的图像，第二个参数就是要添加的文字（程序中是"OpenCV"）

  5. 关于颜色：颜色是用RGB三通道表示的，因此上面函数中颜色参数的类型都是Scalar类型。Scalar在OpenCV中类似于向量，但其长度最大为4通道，源程序中

    Scalar(icolor&0xFF, (icolor>>8)&0xFF, (icolor>>16)&0xFF);

    将随机数的值取出分别作为RGB三个通道的颜色值。

效果

result1

随机线条的效果

result2

添加“OpenCV”文字后效果