How to Get Started with Computer Vision in Python

To get started with computer vision in Python, install the opencv-python library and use it to read, process, and display images. Begin by loading an image with cv2.imread(), then apply basic operations like resizing or converting to grayscale.

Syntax

Here is the basic syntax to load and display an image using OpenCV in Python:

• import cv2: Imports the OpenCV library.
• img = cv2.imread('path'): Loads an image from the given file path.
• cv2.imshow('title', img): Opens a window to display the image.
• cv2.waitKey(0): Waits for a key press to close the window.
• cv2.destroyAllWindows(): Closes all OpenCV windows.

python

import cv2

# Load an image from file
img = cv2.imread('image.jpg')

# Show the image in a window
cv2.imshow('Image Window', img)

# Wait until a key is pressed
cv2.waitKey(0)

# Close the window
cv2.destroyAllWindows()

Example

This example loads an image, converts it to grayscale, resizes it, and then displays both the original and processed images. It shows how to perform simple computer vision tasks with OpenCV.

python

import cv2

# Load the image
img = cv2.imread('image.jpg')

# Convert to grayscale
gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)

# Resize image to half its size
resized = cv2.resize(img, (img.shape[1]//2, img.shape[0]//2))

# Display original image
cv2.imshow('Original Image', img)

# Display grayscale image
cv2.imshow('Grayscale Image', gray)

# Display resized image
cv2.imshow('Resized Image', resized)

cv2.waitKey(0)
cv2.destroyAllWindows()

Common Pitfalls

Common mistakes when starting with computer vision in Python include:

• Not installing opencv-python before importing cv2.
• Using incorrect file paths causing cv2.imread() to return None.
• Forgetting to call cv2.waitKey() which prevents image windows from showing properly.
• Not handling color channels correctly; OpenCV uses BGR format, not RGB.

python

import cv2

# Wrong: File path typo leads to None
img = cv2.imread('wrong_path.jpg')
print(img)  # Output: None

# Right: Correct file path
img = cv2.imread('image.jpg')
print(type(img))  # Output: <class 'numpy.ndarray'>

Output

None
<class 'numpy.ndarray'>

Quick Reference

Here is a quick cheat sheet for common OpenCV functions to get started:

Function	Purpose
cv2.imread(path)	Load image from file
cv2.imshow(title, img)	Display image in window
cv2.waitKey(delay)	Wait for key press (0 = infinite)
cv2.destroyAllWindows()	Close all image windows
cv2.cvtColor(img, flag)	Convert image color space (e.g., BGR to Gray)
cv2.resize(img, size)	Resize image to given size

Key Takeaways

Install the opencv-python package to start computer vision in Python.

Use cv2.imread() to load images and cv2.imshow() to display them.

Always check that image paths are correct to avoid loading errors.

Remember to call cv2.waitKey() to show images properly.

OpenCV uses BGR color format, so convert if needed for other libraries.