How to get image width and height in OpenCV?

Getting the width and height of an image in OpenCV is a fundamental yet crucial operation that can be achieved in multiple ways. I will detail two commonly used methods to obtain this information.

Method 1: Using the shape Attribute

In OpenCV, images are typically represented as NumPy arrays. The NumPy array has a property called shape that contains the dimensions of the array. For images, this property returns a tuple with the height, width (and channel count if the image is color).

Below is an example code demonstrating how to use this method:

python
import cv2

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

# Get the image dimensions
dimensions = image.shape

# Height, width, and channel count
height = dimensions[0]
width = dimensions[1]
if len(dimensions) > 2:
    channels = dimensions[2]

print("Width: {}, Height: {}, Channels: {}".format(width, height, channels))

This code first loads an image and then uses the shape attribute to obtain its dimensions. shape[0] represents the height, shape[1] represents the width. If the image is color (e.g., RGB), shape also includes a third dimension representing the channel count.

Method 2: Using the get() Method

The Mat object in OpenCV (used for the C++ API) provides the get() method to retrieve specific image properties, such as width and height. In Python, we typically work with NumPy arrays, so this method is not applicable. However, if you are using C++ or other scenarios where this method is needed, consider consulting the relevant OpenCV documentation.

Conclusion

By using the shape attribute, we can easily obtain the width and height of the image. This is a fundamental and frequently used operation when processing images, and it is crucial for the development of image processing and computer vision applications. Understanding and mastering how to obtain and manipulate these basic attributes is highly beneficial in practical development.