opencv-4.5.2入门——读写图片1

刺骨的言语ヽ痛彻心扉 2022-10-12 01:32 177阅读 0赞

一、官方下载地址，根据自己需要选择合适版本[opencv版本发布地址][opencv]

二、官方教程——[图像入门教程][Link 1]

三、目标

1.读取照片

**cv::imread (const string & filename,int flags = IMREAD\_COLOR)  **

第一个参数指定文件路径，第二个参数可选以下三种，如果读取失败返回NULL。

*  IMREAD\_COLOR 以 **BGR** 8 位格式加载图像。这是此处使用的**默认值**。
 *  IMREAD\_UNCHANGED 按原样加载图像（包括 alpha 通道，如果存在）。
 *  IMREAD\_GRAYSCALE 将图像加载为灰度图。
 *  更多在下面——[官网解释][Link 2]

//! Imread flags
    enum ImreadModes {
           IMREAD_UNCHANGED            = -1, //!< If set, return the loaded image as is (with alpha channel, otherwise it gets cropped).
           IMREAD_GRAYSCALE            = 0,  //!< If set, always convert image to the single channel grayscale image (codec internal conversion).
           IMREAD_COLOR                = 1,  //!< If set, always convert image to the 3 channel BGR color image.
           IMREAD_ANYDEPTH             = 2,  //!< If set, return 16-bit/32-bit image when the input has the corresponding depth, otherwise convert it to 8-bit.
           IMREAD_ANYCOLOR             = 4,  //!< If set, the image is read in any possible color format.
           IMREAD_LOAD_GDAL            = 8,  //!< If set, use the gdal driver for loading the image.
           IMREAD_REDUCED_GRAYSCALE_2  = 16, //!< If set, always convert image to the single channel grayscale image and the image size reduced 1/2.
           IMREAD_REDUCED_COLOR_2      = 17, //!< If set, always convert image to the 3 channel BGR color image and the image size reduced 1/2.
           IMREAD_REDUCED_GRAYSCALE_4  = 32, //!< If set, always convert image to the single channel grayscale image and the image size reduced 1/4.
           IMREAD_REDUCED_COLOR_4      = 33, //!< If set, always convert image to the 3 channel BGR color image and the image size reduced 1/4.
           IMREAD_REDUCED_GRAYSCALE_8  = 64, //!< If set, always convert image to the single channel grayscale image and the image size reduced 1/8.
           IMREAD_REDUCED_COLOR_8      = 65, //!< If set, always convert image to the 3 channel BGR color image and the image size reduced 1/8.
           IMREAD_IGNORE_ORIENTATION   = 128 //!< If set, do not rotate the image according to EXIF's orientation flag.
         };

2.使用opencv显示图像

**cv::namedWindow(const string & winname,int flags = WINDOW\_NORMAL);**

创建一个窗口，名字和下面要显示的窗口名对应，目的是对窗口其调节作用。（imshow可以直接指定窗口名，可以省去此函数（默认调用），但如果显示图像之前需要其他窗口操作时，需要调用此函数）

*  WINDOW\_NORMAL 使可以调整窗口大小
 *  WINDOW\_AUTOSIZE 会自动调整窗口大小
 *  WINDOW\_FREERATIO 或 WINDOW\_KEEPRATIO： WINDOW\_FREERATIO 不考虑其比例调整图像，而 WINDOW\_KEEPRATIO 保持图像比例。
 *  WINDOW\_GUI\_NORMAL 或 WINDOW\_GUI\_EXPANDED： WINDOW\_GUI\_NORMAL 是在没有状态栏和工具栏的情况下绘制窗口的旧方法

**cv::imshow(const string & winname,InputArray mat)     **

第一个为显示窗口名字，第二个为mat对象。

*  如果图像是 8 位无符号，则按原样显示。
 *  如果图像是 16 位无符号或 32 位整数，则将像素除以 256。即值范围 \[0,255\*256\] 映射到 \[0,255\]。
 *  如果图像是 32 位或 64 位浮点，则像素值乘以 255。即值范围 \[0,1\] 映射到 \[0,255\]。

3.保存图像

**cv::imwrite(const string & filename,InputArray img,const std::vector< int > & *params* = `std::vector<int>())`    **

**        **函数 imwrite 将图像保存到指定的文件中。图像格式是根据文件扩展名选择的，const std::vector& params表示为特定格式保存的参数编码，它有一个默认值std::vector< int >()，所以一般情况下不用写。

四、代码

#include <opencv2/core.hpp>
    #include <opencv2/imgcodecs.hpp>
    #include <opencv2/highgui.hpp>
    #include <iostream>
    
    #define  SAVE_KEY   115
    #define  PHOTO_PATH "../lena.png" //source photo path
    #define  PHOTO_SAVE "../lena1.png" //save photo path
    
    using namespace cv;
     
    int main()
    {
        //Get image
        Mat img = imread(PHOTO_PATH, IMREAD_COLOR);
        //check
        if(img.empty())
        {
            std::cout << "Could not read the image: " << PHOTO_PATH << std::endl;
            return 1;
        }
    
        //Creates a window
        namedWindow("Display window",WINDOW_NORMAL);
    
        //Show image
        imshow("Display window", img);
        
        int k = waitKey(0); // Wait for a keystroke in the window
        
        if(k == SAVE_KEY)
        {
           //Write image
           bool wr = imwrite(PHOTO_SAVE, img);
           if(wr == true)
             std::cout << "Write the image ok" << std::endl;
        }else
        {
             std::cout << "Key is not s: " << k << std::endl;
        }
    
      return 0;
    }

运行结果，有请lena

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2E2MTA3ODc5MzI_size_16_color_FFFFFF_t_70][]

[opencv]: https://opencv.org/releases/
[Link 1]: https://docs.opencv.org/4.5.2/db/deb/tutorial_display_image.html
[Link 2]: https://docs.opencv.org/4.5.2/d8/d6a/group__imgcodecs__flags.html#gga61d9b0126a3e57d9277ac48327799c80af660544735200cbe942eea09232eb822
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2E2MTA3ODc5MzI_size_16_color_FFFFFF_t_70]: /images/20221005/99737794c463476fa33b755108d60fff.png