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What is OpenCV ?

OpenCV is a cross-platform library using which we can develop real-time computer vision applications. It mainly focuses on image processing; video capture and analysis including features like face detection and object detection.

Features of OpenCV Library

  • Read and write images
  • Capture and save videos
  • Process images (filter, transform)
  •  Perform feature detection
  • Detect specific objects such as faces, eyes, cars, in the videos or images.
  • Analyze the video, i.e., estimate the motion in it, subtract the background, and track objects in it.

How to install opencv3 with Anaconda ?


Steps to install Opencv

Step 1 : Create Virtual Environment in Anaconda

Go to Start Menu -open Anaconda Prompt then type below command

            conda create --name opencv-env python=3.6

Press Y and Enter, the environment will be installed

Step 2 : Install OpenCV

 2.1 Activate the environment using below command

        activate opencv-env

2.2 Install OpenCV and other important packages

pip install numpy scipy matplotlib scikit-learn jupyter

pip install opencv-contrib-python

pip install dlib

2.3 Test your installation

            Open the python prompt on the command line by typing python on the command prompt

import cv2

cv2.__version__

import dlib

dlib.__version__

Getting Started with Images

Read an image

  • Use the function cv2.imread() to read an image. The image should be in the working directory or a full path of image should be given.
  • Second argument is a flag that specifies way the image should be read.
  1. cv2.IMREAD_COLOR : Loads a color image. Any transparency of image will be neglected. It is the default flag.

  2. cv2.IMREAD_GRAYSCALE : Loads image in grayscale mode

  3. cv2.IMREAD_UNCHANGED : Loads image as such including alpha channel

Note :- Instead of these three flags, you can simply pass integers 1, 0 or -1 respectively.

image

Display an image

  • Use the function cv2.imshow() to display an image in a window. The window automatically fits to the image size.
  • First argument is a window name which is a string. second argument is our image. You can create as many windows as you wish, but with different window names.
  • cv2.destroyAllWindows() simply destroys all the windows we created. If you want to destroy any specific window, use the function cv2.destroyWindow() where you pass the exact window name as the argument.
  • cv2.waitKey() is a keyboard binding function. Its argument is the time in milliseconds. The function waits for specified milliseconds for any keyboard event. If you press any key in that time, the program continues. If 0 is passed, it waits indefinitely for a key stroke. 
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