Display Image OpenCV

Basic reading and display of an image

import cv2

image_path= #put your image path here

#use imread() function to read image data to variable img.
img = cv2.imread(image_path) 

#display image data in a new window with title 'I am an image display window'
cv2.imshow('I am an image display window',img) 

#wait until user hits any key on keyboard
cv2.waitKey(0) 

#close any windows opened by opencv
cv2.destroyAllWindows()

To control the size of the display window on the screen, add the following commands before the cv2.imshow command:

window_width=800 #size of the display window on the screen
window_height=600

#open an empty window with a title.
#The flag cv2.WINDOW_NORMAL allows the window to be scaleable.
cv2.namedWindow('I am an image display window', cv2.WINDOW_NORMAL)

#scale the image display window to desired size
cv2.resizeWindow('I am an image display window', window_width, window_height)

see openCV docs for further details

Reading MJPEG from IP camera

import cv2
import numpy as np
import urllib

stream=urllib.urlopen('https://96.10.1.168/mjpg/video.mjpg')
bytes=''
while True:
    bytes+=stream.read(1024)
    a = bytes.find('\xff\xd8') # JPEG start
    b = bytes.find('\xff\xd9') # JPEG end
    if a!=-1 and b!=-1:
        jpg = bytes[a:b+2] # actual image
        bytes= bytes[b+2:] # other informations

        # decode to colored image ( another option is cv2.IMREAD_GRAYSCALE )
        img = cv2.imdecode(np.fromstring(jpg, dtype=np.uint8),cv2.IMREAD_COLOR) 
        cv2.imshow('Window name',img) # display image while receiving data
        if cv2.waitKey(1) ==27: # if user hit esc
            exit(0) # exit program

Every JPEG starts with 0xff 0xd8 and ends with 0xff 0xd9. Between those are actual image. Detailed information in this SO answer

Display Image OpenCV Java

Basic reading image from java

import org.opencv.core.Core;
import org.opencv.core.Mat;
import org.opencv.imgcodecs.Imgcodecs;
     
//Load native library
System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
//Mat object used to host the image
Mat imageArray;
//Read image file from vile system
imageArray=Imgcodecs.imread("path/to/image");

If you want to view images you can not use imshow because OpenCV-java does not have this method either. Instead, you can write the following method.

private static BufferedImage ConvertMat2Image(Mat imgContainer{
    MatOfByte byteMatData = new MatOfByte();
    //image formatting
    Imgcodecs.imencode(".jpg", imgContainer,byteMatData);
    // Convert to array
    byte[] byteArray = byteMatData.toArray();
    BufferedImage img= null;
    try {
        InputStream in = new ByteArrayInputStream(byteArray);
        //load image
        img= = ImageIO.read(in);
    } catch (Exception e) {
        e.printStackTrace();
        return null;
    }
    return img;
}

You can view the result object in the Jframe, Jlabel (jlabel icon) etc.