Opencv learning notes -day1 (image reading display imread, imshow, namedwindow)

day1- Image reading display

  use OpenCV Development module , Open a picture in the host Directory ,
  And displayed on the desktop 

function ：

highug Module imread,imshow,namedWindow,imwrite function

1. imread() Read images

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

Parameters	explain
filename	Read the address file name of the file
flags	Read the color category of the image （flags=1：( Default parameters ) Said to return to 3 Channel image ;CV_LOAD_IMAGE_ANYEPTH： return 16bit or 32bit Images ( When entering the same depth ), Otherwise return to 8bit Images ;CV_LOAD_IMAGE_COLOR： Returns a monochrome image ;CV_LOAD_IMAGE_GRAYSCALE： Return to channel image ;0: Return to single channel image ;<0： Do not channel the image ;>0： Cast to 3 Channel image .

example 1

// Image reading 
Mat scr = imread("D:\\ Study \\OpenCV Study \\pictures\\image\\1.jpg");

2. ,imshow() Display an image in the specified window
   void imshow(const String& winname, InputArray mat);

Parameters	explain
winname	const string& Type of winname, Refers to the window identification name to be displayed
mat	InputArray Type of mat, Refers to the image to be displayed

notes：imshow() 1, Only support 8 Bits and floating-point numbers display RGB Color space ;
2, RGB Color space :B G R Three channels Three color combination 255255255 And transparent channels

example 2

imshow(" window 1",scr);// In the created window 1 Show 

3. namedWindow() Create a new window

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

Parameters	explain
winname	const String& Of winname, The window name used as the window identifier
flags	The identification of the window , The general default is WINDOW_AUTOSIZE The size of the window is constrained by the displayed image

notes：
CV_WINDOW_NORMAL Change the window to normal size or make it resizable ..
CV_WINDOW_AUTOSIZE The size of the window is constrained by the displayed image . The window is not resizable ..
CV_WINDOW_FULLSCREEN Change the window to full screen .
CV_WINDOW_FREERATIO Make windows resizable without ratio constraints .
CV_WINDOW_KEEPRATIO Make the window resizable , But keep the scale of the displayed image

example 3

namedWindow(" window 1", WINDOW_NORMAL);// establish  WINDOW_FREERATIO window 

4. waitkey() Waiting for typing

int waitKey(int delay = 0);
waitKey The function is to constantly refresh the image , Frequency time delay, Unit is ms, The return value is the value pressed by the current keyboard , Return when there is no key -1

example 4

waitKey(0);// Infinite loop 
while(1){
     if(waitKey(100)==27)break; }
// In this program , tell OpenCv Wait for the user to trigger the event ,
// The waiting time is 100ms, If within this time period ,  The user presses ESC(ASCII Code for 27), And then jump out of the loop , otherwise , And then jump out of the loop 

Code ：

QuickDemo.cpp

#include <iostream>
#include <opencv2\highgui.hpp>
#include <opencv2\imgproc.hpp>

using namespace cv;
using namespace std;

int main()
{
    
	Mat scr = imread("D:\\ Study \\OpenCV Study \\pictures\\image\\1.jpg");// Open a picture 
	if (!scr.data == 1)// Sentenced to empty 
		return -1;
	namedWindow(" window 1", WINDOW_FREERATIO);// establish  WINDOW_FREERATIO window 
	imshow(" window 1",scr);// Show in the created window 
	waitKey(0);// Time delay  0-> Constant delay  1-> Time delay 1ms
	return 0;
}

notes:
The conditions for judging null （ As shown in the complete code above ）：
1,scr.empty();// Determine whether it is a form ,if If it is not loaded successfully, it is blank ,print： could not laod image;
2,scr.data;//if(!scr.data)==1 Failed to read