Integrating OpenCV with Keras

Master the integration of OpenCV and Keras with this thorough tutorial. Learn to preprocess images, build deep learning models, and visualize predictions. Perfect for beginners and experts alike.

Updated March 21, 2023

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Welcome to this in-depth tutorial on integrating OpenCV with Keras! We’ll explore the theory behind how this integration works, provide multiple code examples, and discuss why someone might want to use it. Our goal is to make this tutorial as engaging and accessible as possible, even for beginners. So, let’s get started!

Introduction to OpenCV and Keras

OpenCV is a popular open-source computer vision library that offers a wide array of tools and functions for processing images and videos. It is designed to be efficient and performant, making it perfect for real-time applications.

Keras is a high-level neural networks API, written in Python, and capable of running on top of TensorFlow, Microsoft Cognitive Toolkit, Theano, or PlaidML. It enables fast experimentation with deep learning models through a user-friendly and modular interface.

Integrating OpenCV with Keras allows you to combine the power of computer vision with deep learning to create advanced applications, such as object recognition, facial recognition, and semantic segmentation.

Why Integrate OpenCV with Keras?

The primary reason to integrate OpenCV with Keras is to leverage OpenCV’s efficient image and video processing capabilities alongside Keras' deep learning functionality. Some common use-cases include:

  1. Preprocessing images and videos for input into Keras models.
  2. Augmenting training data with real-time image transformations.
  3. Visualizing intermediate results of Keras models on input images or videos.
  4. Implementing custom layers in Keras that utilize OpenCV functions for specialized tasks.

Setting Up the Environment

Before we begin, ensure that you have both OpenCV and Keras installed. If you haven’t installed them yet, follow the instructions on the official OpenCV installation guide and the official Keras installation guide.

Preprocessing Images with OpenCV for Keras Models

Let’s start by learning how to preprocess images using OpenCV before feeding them into a Keras model. We’ll use a simple example of loading an image, resizing it, and normalizing its pixel values.

Step 1: Import Libraries

First, we’ll import the necessary libraries.

import cv2
import numpy as np
from keras.preprocessing import image

Step 2: Load and Preprocess the Image

Next, we’ll load an image using OpenCV, resize it to the desired dimensions, and normalize its pixel values.

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

# Resize the image
desired_size = (224, 224)
resized_image = cv2.resize(input_image, desired_size)

# Normalize the image
normalized_image = resized_image.astype('float32') / 255.0

# Expand the dimensions to match Keras input format
input_data = np.expand_dims(normalized_image, axis=0)

Now, the input_data variable contains the preprocessed image, ready to be used as input for a Keras model.

Building a Simple Keras Model and Using OpenCV for Visualization

In this section, we’ll build a simple Keras model and use OpenCV to visualize the results. We’ll create a basic model that learns to distinguish between two classes of images, such as cats and dogs. We’ll use the popular CIFAR-10 dataset for training and validation.

Step 1: Import Libraries

First, we’ll import the necessary libraries.

import cv2
import numpy as np
import keras
from keras.datasets import cifar10
from keras.models import Sequential
from keras.layers import Dense, Flatten, Conv2D, MaxPooling2D
from keras.optimizers import Adam

Step 2: Load and Preprocess the Dataset

Next, we’ll load the CIFAR-10 dataset and preprocess it for input into our Keras model.

# Load the CIFAR-10 dataset
(x_train, y_train), (x_test, y_test) = cifar10.load_data()

# Select only cat (class 3) and dog (class 5) images
train_mask = np.isin(y_train, [3, 5]).flatten()
x_train = x_train[train_mask]
y_train = y_train[train_mask]

test_mask = np.isin(y_test, [3, 5]).flatten()
x_test = x_test[test_mask]
y_test = y_test[test_mask]

# Normalize the images
x_train = x_train.astype('float32') / 255.0
x_test = x_test.astype('float32') / 255.0

# Convert the labels to binary format
y_train = (y_train == 5).astype('float32')
y_test = (y_test == 5).astype('float32')

Step 3: Build the Model

Now, we’ll build a simple Keras model using the Sequential API.

# Build the model
model = Sequential()
model.add(Conv2D(32, (3, 3), activation='relu', input_shape=(32, 32, 3)))
model.add(MaxPooling2D(pool_size=(2, 2)))
model.add(Conv2D(64, (3, 3), activation='relu'))
model.add(MaxPooling2D(pool_size=(2, 2)))
model.add(Dense(64, activation='relu'))
model.add(Dense(1, activation='sigmoid'))

# Compile the model
model.compile(loss='binary_crossentropy', optimizer=Adam(lr=0.0001), metrics=['accuracy'])

Step 4: Train the Model

We’ll train our model using the preprocessed training dataset.

# Train the model, y_train, batch_size=64, epochs=20, validation_data=(x_test, y_test))

Step 5: Visualize Model Predictions with OpenCV

Now that our model is trained, we can use OpenCV to visualize the predictions on the test dataset.

# Visualize model predictions
for i in range(len(x_test)):
    img = x_test[i]
    label = y_test[i]

    # Make a prediction
    prediction = model.predict(np.expand_dims(img, axis=0))[0, 0]

    # Create a label for the prediction
    if prediction > 0.5:
        prediction_label = f'Dog ({prediction * 100:.2f}%)'
        prediction_label = f'Cat ({(1 - prediction) * 100:.2f}%)'

    # Prepare the image for display
    display_img = cv2.cvtColor((img * 255).astype('uint8'), cv2.COLOR_BGR2RGB)

    # Add the prediction label to the image

    # Display the image and prediction
    cv2.imshow('Predictions', display_img)

    # Exit if 'q' key is pressed
    if cv2.waitKey(0) & 0xFF == ord('q'):

    #Close the display window

That’s it! You’ve now built a simple Keras model and used OpenCV to visualize the predictions. This example demonstrates how seamlessly OpenCV and Keras can be integrated to create powerful computer vision applications.


In this tutorial, we’ve explored the integration of OpenCV with Keras, delving into the theory behind the process and providing code examples to illustrate the concepts. We’ve shown how OpenCV can be used to preprocess images for Keras models and how to visualize model predictions with OpenCV.

By integrating OpenCV with Keras, you can create powerful applications that leverage the best of both worlds: efficient image and video processing from OpenCV and deep learning capabilities from Keras. This integration enables you to tackle advanced computer vision tasks, such as object recognition, facial recognition, and semantic segmentation.

We hope you found this tutorial engaging, informative, and accessible, even for beginners. Keep experimenting with different datasets and model architectures to further your understanding of how OpenCV and Keras can be used together. Happy coding!