OpenCV

Open Source Computer Vision Library is a library of programming functions mainly aimed at real-time computer vision.

Source: https://www.docs.opencv.org/master/

Installation: https://docs.opencv.org/2.4/doc/tutorials/introduction/windows_install/windows_install.html

Introduction

Image Recognition: https://blog.ieeemanipal.tech/image-recognition/

Image Analysis

//Importing Library
import cv2 as cv

//Reading an Image
img = cv.imread('name.jpg')

//Converting color image to grayscale
gray=cv.cvtColor(img,cv.COLOR_BGR2GRAY)

//Displaying the image
cv.imshow('name',img)
cv.waitKey(0)
cv.destroyAllWindows()
//here 'name' is the title of the displayed image

Video Analysis

//Reading a video file
cap= cv.VideoCapture('video.mp4',0)

//Capturing Live Video
cap= cv.VideoCapture(0)

//Displaying Video 
while True:
   ret, frame=cap.read()
   cv.imshow('video',frame)
   if cv.waitKey(1) & 0XFF==ord('q'):
      break
cap.release()
cv.destroyAllWindows()

//Writing Output to File
fourcc=cv.VideoWriter_fourcc(*'XVID')
out=cv.VideoWriter('output.avi',fourcc,20,(640,480))
out.release()

Drawing Images

1. Line

   cv.line(img,starting point,end position,colour(bgr))
   

2. Rectangle

   cv.rectangle(img,point, diagonal point,color, width)
   

3. Circle

   cv.circle(img,centre point,radius,color,-1(if circle is needed to be filled))
   

4. Polygon

   import numpy as np
   pts=np.array((bunch of points),np.int32)
   pts=pts.reshape((-1,1,2))
   cv.polylines(img,[pts],True(whether or not final point should be connected to initial point), color)
   

Text on Images

//Select a font
font=cv.FONT_HERSHEY_SIMPLX
cv.putText(img(on which text should be written), text to be written, starting point say (0,130),font, size(1), color, spacing b/w letters, cv.LINE_AA)

Basic Image Operations

    px=img[@location value]
    print(px)
    //gives color value at point

ROI => Region of Image

    roi=img[100:150,100:150]
    print(roi)
    //prints only that region

Changing a region of an Image

    img[100:150,100:150]=[255,255,255]
    
Shifting a part of image from one region to another

    roi=img[37:111,107:194]
    img[0:74,0:87]=roi
    //Both should be of same size

Image Arithmetic and Logic Operations

    add=img1+img2

    [OR]
 
    add=cv.add(img1,img2)
    //This adds all pixel values together, so we do not get a proper image as there will be variations in color

    [OR]

    weighted=cv.addWeighted(img1,0.6,img2,0.4,0)
    //adds 60% of first image and 40% of second image