OpenCV学习（一）基础篇

OpenCV 2 计算机视觉编程手册读书笔记1

矩阵创建

　　Mat类是OpenCV中非常有用类，用来创建和操作多维矩阵。可以有很多方法构造它。

// 构造函数
//! constructs 2D matrix of the specified size and type
// (_type is CV_8UC1, CV_64FC3, CV_32SC(12) etc.)
Mat(int rows, int cols, int type);
Mat(Size size, int type);
//! constucts 2D matrix and fills it with the specified value _s.
Mat(int rows, int cols, int type, const Scalar& s);
Mat(Size size, int type, const Scalar& s);

// 感兴趣区域，部分区域，子区块，新的矩阵和m共同使用内存
//! creates a matrix header for a part of the bigger matrix
Mat(const Mat& m, const Range& rowRange, const Range& colRange=Range::all());
Mat(const Mat& m, const Rect& roi);
Mat(const Mat& m, const Range* ranges);

// create()函数
Mat mat(2, 2, CV_8UC3); //构造函数创建矩阵
M.create(3, 2, CV_8UC2); //释放内存重新创建

// Matlab风格的创建方法
Mat zero = Mat::zeros(2, 3, CV_8UC1);
Mat one = Mat::ones(2, 3, CV32F);
Mat eye = Mat::eye(2, 3, CV_64F);

　　其中 type参数的值CV_8UC3，表示的是CV_8U类型，3通道，CV_8U即无符号8为数据。3通道相当于BGR通道。

图像读取

cv::imread( const string& filename, int flags);

读取指定的图片，flags可以有以下的值：

enum
{
/* 8bit, color or not */
    CV_LOAD_IMAGE_UNCHANGED  =-1,
/* 8bit, gray */
    CV_LOAD_IMAGE_GRAYSCALE  =0,
/* ?, color */
    CV_LOAD_IMAGE_COLOR      =1,
/* any depth, ? */
    CV_LOAD_IMAGE_ANYDEPTH   =2,
/* ?, any color */
    CV_LOAD_IMAGE_ANYCOLOR   =4
};

图像显示

// 先命名一个窗口，再使用
namedWindow( "output", CV_WINDOW_AUTOSIZE );
imshow("input", img);

　　窗口可以有以下Type：　　

enum
{
    //These 3 flags are used by cvSet/GetWindowProperty
    CV_WND_PROP_FULLSCREEN = 0, //to change/get window's fullscreen property
    CV_WND_PROP_AUTOSIZE   = 1, //to change/get window's autosize property
    CV_WND_PROP_ASPECTRATIO= 2, //to change/get window's aspectratio property
    CV_WND_PROP_OPENGL     = 3, //to change/get window's opengl support

    //These 2 flags are used by cvNamedWindow and cvSet/GetWindowProperty
    CV_WINDOW_NORMAL       = 0x00000000, //the user can resize the window (no constraint)  / also use to switch a fullscreen window to a normal size
    CV_WINDOW_AUTOSIZE     = 0x00000001, //the user cannot resize the window, the size is constrainted by the image displayed
    CV_WINDOW_OPENGL       = 0x00001000, //window with opengl support

    //Those flags are only for Qt
    CV_GUI_EXPANDED         = 0x00000000, //status bar and tool bar
    CV_GUI_NORMAL           = 0x00000010, //old fashious way

    //These 3 flags are used by cvNamedWindow and cvSet/GetWindowProperty
    CV_WINDOW_FULLSCREEN   = 1,//change the window to fullscreen
    CV_WINDOW_FREERATIO    = 0x00000100,//the image expends as much as it can (no ratio constraint)
    CV_WINDOW_KEEPRATIO    = 0x00000000//the ration image is respected.
};

图像存储

cv::imrwite("output.jpg", imgOut);

图像像素操作

　　at函数

void salt(cv::Mat &image, int n)
{
    for(int k =0; k<n; ++k)
    {
        int i=rand()%image.cols;
        int j=rand()%image.rows;
        if(image.channels() == 1) // gray image
        {
            image.at<uchar>(j, i) = 255;
        }
        else if(image.channels() == 3) // color image
        {
            image.at<cv::Vec3b>(j, i)[0] = 255;
            image.at<cv::Vec3b>(j, i)[1] = 255;
            image.at<cv::Vec3b>(j, i)[2] = 255;
        }
    }
}

　　其中Vec3b的定义为：typedef Vec<uchar, 3> Vec3b。上述代码是在一个图片上随机产生盐点。

　　迭代器

cv::Mat Iterator_<cv::Vec3b> it;
// 定义在Mat_内部的迭代器
cv::Mat_<cv::Vec3b>::iterator it;

// 迭代器使用
void colorReduce(cv::Mat &image, int div=64)
{
    // 得到初始位置的迭代器
    cv::Mat_<cv::Vec3b>::iterator it = image.begin<cv::Vec3b>();
    // 得到种植位置的迭代器
    cv::Mat_<cv::Vec3b>::iterator itend = image.edn<cv::Vec3b>();
    // 遍历所有像素
    for(; it!=itend; ++it)
    {
        // 处理每个像素
        (*it)[0] = (*it)[0]/div*div+div/2;
        (*it)[1] = (*it)[0]/div*div+div/2;
        (*it)[2] = (*it)[0]/div*div+div/2;
    }
}

　　指针操作

// 得到image图像的第index行的首地址
image.ptr<uchar>(index);

图像算术运算

　　图像的算术运算可以有加减乘除，可以对图片有亮度有影响，具体的后续再了解。

图像感兴趣区域

　　图像感兴趣区域指的是，对一个图片的部分区域感兴趣，则可以只操作感兴趣的部分区域，也即子区域。