Solved: change size of image and fir it into numpy array opencv

In the modern world, images are an essential part of communication and technology. With the advancements in artificial intelligence, machine learning, and computer vision, it has become increasingly important to understand how to process and manipulate images effectively. This article discusses a prevalent problem – resizing images and fitting them into a NumPy array using OpenCV, a popular Open-Source Computer Vision Library. We will go in-depth, providing a systematic approach, explaining the code step-by-step while mentioning libraries and functions involved, and their significance to the problem at hand.


Images are stored as matrices which contain pixel intensities. To work efficiently with image data, developers often need to resize an image to fit it into a NumPy array as per their requirements. One of the best libraries to achieve this is OpenCV, which seamlessly caters to diverse image processing needs. In this article, we will demonstrate how to resize an image and fit it into a NumPy array using Python and OpenCV.

Importing Required Libraries

To start, we need to import the necessary libraries into our Python environment.

import cv2
import numpy as np
  • cv2: The OpenCV library used for image processing tasks.
  • numpy: The NumPy library provides support for working with arrays and matrices effectively.

Loading and Resizing the Image

First, we need to load the image and then resize it using the OpenCV function cv2.resize():

# Load the image
image = cv2.imread('path/to/image.jpg')

# Define the new size (width, height)
new_size = (300, 300)

# Resize the image
resized_image = cv2.resize(image, new_size, interpolation=cv2.INTER_AREA)
  • cv2.imread(): This function reads an image from the specified file path.
  • new_size: A tuple containing the desired width and height of the resized image. In this case, we want to resize it to 300×300 pixels.
  • cv2.resize(): It resizes the image to the specified dimensions using a specified interpolation method.

Fitting the Resized Image into a NumPy Array

Once the image is resized, we need to fit it into a NumPy array:

# Create a NumPy array with the desired dimensions (width, height, channels)
array_shape = (300, 300, 3)

# Fit the resized image into the NumPy array
numpy_image = np.zeros(array_shape, dtype=np.uint8)
numpy_image[:resized_image.shape[0], :resized_image.shape[1]] = resized_image
  • array_shape: A tuple containing the desired dimensions for the NumPy array. It must have the same width, height, and number of channels as our resized image.
  • np.zeros(): This function creates an empty NumPy array with the specified dimensions and data type.
  • dtype: It defines the data type of the NumPy array. np.uint8 represents 8-bit unsigned integer, which is commonly used for image data.

After completing these steps, the image is now resized and fits into a NumPy array, ready for further processing.

Additional OpenCV Functions and Techniques

Here are some additional OpenCV functions and techniques related to resizing images:

  • cv2.INTER_LINEAR: Used for default interpolation in cv2.resize().
  • cv2.INTER_CUBIC: Provides better quality resizing for upscaling. It is slower compared to other interpolation methods.
  • cv2.INTER_NEAREST: Fastest method for resizing. However, the quality degrades due to the absence of interpolation.
  • Aspect Ratio Considerations: When resizing, preserving the aspect ratio is crucial, if not, the image may get distorted.

In summary, we have demonstrated how to resize an image and fit it into a NumPy array using OpenCV. By following the outlined steps, developers can efficiently manipulate images for various computer vision, machine learning, and other applications.

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