opencv4.5.1自学（1）——图像输入输出

1、命名空间

opencv的命名空间为cv，using namespace cv;

2、Mat类型

opencv中的Mat类用于保存图像以及其他矩阵数据。
比如输入一张图片，就用以下代码

Mat myMat = imread("myimage.jpg");

3、图像载入和显示

图像载入函数：

CV_EXPORTS_W Mat imread( const String& filename, int flags = IMREAD_COLOR );

第一个参数为图片路径名，第二个参数取值如下

enum ImreadModes {
IMREAD_UNCHANGED
= -1, //Ignore EXIF orientation.
IMREAD_GRAYSCALE
= 0,
//the single channel grayscale image
IMREAD_COLOR
= 1,
//the 3 channel BGR color image.
IMREAD_ANYDEPTH
= 2,
//the corresponding depth, otherwise convert it to 8-bit.
IMREAD_ANYCOLOR
= 4,
//any possible color format.
IMREAD_LOAD_GDAL
= 8,
//use the gdal driver for loading the image.
IMREAD_REDUCED_GRAYSCALE_2
= 16, //always convert image to the single channel grayscale image and the image size reduced 1/2.
IMREAD_REDUCED_COLOR_2
= 17, //always convert image to the 3 channel BGR color image and the image size reduced 1/2.
IMREAD_REDUCED_GRAYSCALE_4
= 32, //always convert image to the single channel grayscale image and the image size reduced 1/4.
IMREAD_REDUCED_COLOR_4
= 33, //always convert image to the 3 channel BGR color image and the image size reduced 1/4.
IMREAD_REDUCED_GRAYSCALE_8
= 64, //always convert image to the single channel grayscale image and the image size reduced 1/8.
IMREAD_REDUCED_COLOR_8
= 65, //always convert image to the 3 channel BGR color image and the image size reduced 1/8.
IMREAD_IGNORE_ORIENTATION
= 128 //do not rotate the image according to EXIF's orientation flag.
};

创建窗口

CV_EXPORTS_W void namedWindow(const String& winname, int flags = WINDOW_AUTOSIZE);

第一个参数为窗口名称，第二个参数取值如下

enum WindowFlags {
WINDOW_NORMAL
= 0x00000000, //!< the user can resize the window (no constraint) / also use to switch a fullscreen window to a normal size.
WINDOW_AUTOSIZE
= 0x00000001, //!< the user cannot resize the window, the size is constrainted by the image displayed.
WINDOW_OPENGL
= 0x00001000, //!< window with opengl support.
WINDOW_FULLSCREEN = 1,
//!< change the window to fullscreen.
WINDOW_FREERATIO
= 0x00000100, //!< the image expends as much as it can (no ratio constraint).
WINDOW_KEEPRATIO
= 0x00000000, //!< the ratio of the image is respected.
WINDOW_GUI_EXPANDED=0x00000000, //!< status bar and tool bar
WINDOW_GUI_NORMAL = 0x00000010, //!< old fashious way
};

图像显示函数：

CV_EXPORTS_W void imshow(const String& winname, InputArray mat);

第一个参数为窗口名称，第二个参数为要显示的图像

4、图像输出——imwrite

CV_EXPORTS_W bool imwrite( const String& filename, InputArray img,const std::vector<int>& params = std::vector<int>());

第一个参数为文件名，第二个参数为Mat类型图像数据，第三个参数表示为特定格式保存的参数编码

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