OpenCV学习笔记一：图像基础操作

一、图像的读取、显示和保存

1、Mat imread(const string& filename, int flags=1)

filename:读入图像的完整路径

flags:读入图像的方式

• CV_LOAD_IMAGE_GRAYSCALE：单通道灰度图
• CV_LOAD_IMAGE_COLOR：三通道彩色图
• CV_LOAD_IMAGE_UNCHANGED保持不变

Mat image = imread("img.jpg",CV_LOAD_IMAGE_UNCHANGED);

2、void imshow(const string& winname, InputArray image)

//InputArray：接口类可以是Mat、Mat_< T >、Mat_< T, m, n >、vector< T >、vector< vector< T > >、vector< Mat >

winname:显示图像的窗口名

image:要显示的图像

namedWindow("Input");
imshow("Input",image);

3、bool imwrite(const string& filename, InputArray image, const vector< int >& params=vector< int >())

filename:保存的文件名

image:要保存的图像

params-Format-specific save parameters encoded as pairs paramId_1, paramValue_1, paramId_2, paramValue_2, … . The following parameters are currently supported:

• For JPEG, it can be a quality ( CV_IMWRITE_JPEG_QUALITY ) from 0 to 100 (the higher is the better). Default value is 95. 对于JPEG，图像质量。
• For PNG, it can be the compression level ( CV_IMWRITE_PNG_COMPRESSION ) from 0 to 9. A higher value means a smaller size and longer compression time. Default value is 3. 对于PNG，压缩等级。
• For PPM, PGM, or PBM, it can be a binary format flag ( CV_IMWRITE_PXM_BINARY ), 0 or 1. Default value is 1.

imwrite("out.jpg",output);

二、复制、翻转、颜色空间转换

1、void Mat::copyTo(OutputArray m) const

2、void Mat::copyTo(OutputArray m, InputArray mask) const

• mask为行列与源图相同的掩模矩阵（可以由图片复制），如果矩阵某元素为零，则对应位置像素无需覆盖，保留目标图中对应位置的像素值。

3、void flip(InputArray src, OutputArray dst, int flipCode)

flipCode:翻转模式

• flipcode = 0：沿x轴翻转
• flipcode > 0：沿y轴翻转
• flipcode < 0：x,y轴同时翻转

4、void cvtColor(InputArray src, OutputArray dst, int code, int dstCn=0 )

code:CV_BGR2GRAY, CV_BGR2YCrCb, CV_BGR2HSV……

dstCn: 输出图像通道数

示例

#include
#include
#include 

using namespace cv;

int main()
{
    Mat image = imread("img.jpg",CV_LOAD_IMAGE_UNCHANGED);
    if(!image.data)//图像载入失败
        return -1;
    namedWindow("Input");
    imshow("Input",image);

    Mat output;
    image.copyTo(output);//复制
    flip(output,output,-1);//翻转
    cvtColor(output,output,CV_BGR2RGB);//BGR->RGB
    imwrite("out.jpg",output);//保存
    namedWindow("Output");
    imshow("Output",output);

    waitKey(0);

    return 0;
}