Keras; The API for Human Beings

Obviously deep learning is a hit! Being a subfield of machine learning, building deep neural networks for various predictive and learning tasks is one of the major practices all the AI enthusiasts do today. There are several deep learning frameworks out there that helps for building deep neural networks. TensorFlow, Theano, CNTK are some of the major frameworks used in the industry and in the research. These Frameworks has their own way of defining the tensor units and a way of configuring the connections between nodes. That is involves bit of a learning curve.

keras_1As shown in the graph, TensorFlow is the most popular and widely used deep learning framework right now. When it comes to Keras, it’s not working independently. It works as an upper layer for prevailing deep learning frameworks; namely with TensorFlow, Theano & CNTK (MXNet backend for Keras is on the way).  To be more précised, Keras act as a wrapper for these frameworks. Working with Keras is easy as working with Lego blocks. What you have to know is where to fix the right component. So it is the ultimate deep learning tool for human beings!


Architecture of Keras API

Why Keras?

  • Fast prototyping – Most of the cases, you may have to test different neural architectures to find the best fit. Building the models from the beginning may time consuming. Keras will help you in this with modularizing your task and giving you the ability to reuse the code.
  • Supports CNN, RNN & combination of both –
  • Modularity
  • Easy extensibility
  • Simple to get started, simple to keep going
  • Deep enough to build serious models.
  • Well-written document. – Yes! Refer
  • Runs seamlessly on CPU and GPU. – Keras support GPU parallelization that will boost your execution.

Keras follows a very simple design idea. Here I’ve sum-up the main four steps of designing a Keras model deep learning model.

  1. Prepare your inputs and output tensors
  2. Create first layer to handle input tensor
  3. Create output layer to handle targets
  4. Build virtually any model you like in between

Basically, Keras models go through the following pipeline. You may have to re-visit the steps again and again to come up with the best model.

keras_3Let’s start with a simple experiment that involves classifying Dog & Cat images from Kaggle. First make sure to download the training & testing image files from Kaggle (

Before playing with Keras, you may need to setup your rig. Please refer this post and make your beast ready for deep learning.

Then try this code! The code sections are commented for your reference. Here what I’m using is TensorFlow backend. You can change the configurations a bit and use Theano or CNTK as you wish.

# Convolutional Neural Network with Keras

# Installing Tensorflow
# pip install tensorflow-gpu

# Installing Keras
# pip install --upgrade keras

# Part 1 - Building the CNN

# Importing the Keras libraries and packages
import keras
from keras.layers import Conv2D
from keras.layers import MaxPooling2D
from keras.layers import Flatten
from keras.layers import Dense

# Initialising the CNN
classifier = Sequential()

# Step 1 - Convolution
#input_shape goes reverse if it is theano backend
#Images are 2D
classifier.add(Conv2D(32, (3, 3), input_shape = (64, 64, 3), activation = 'relu'))

# Step 2 - Pooling
#Most of the time it's (2,2) not loosing many. 
classifier.add(MaxPooling2D(pool_size = (2, 2)))

# Adding a second convolutional layer
#Inputs are the pooled feature maps of the previous layer
classifier.add(Conv2D(32, (3, 3), activation = 'relu'))
classifier.add(MaxPooling2D(pool_size = (2, 2)))


# Step 3 - Flattening

# Step 4 - Full connection
#relu - rectifier activation function
#128 nodes in the hidden layer
classifier.add(Dense(units = 128, activation = 'relu'))
#Sigmoid is used because this is a binary classification. For multiclass softmax
classifier.add(Dense(units = 1, activation = 'sigmoid'))

# Compiling the CNN
#adam is for stochastic gradient descent 
classifier.compile(optimizer = 'adam', loss = 'binary_crossentropy', metrics = ['accuracy'])

# Part 2 - Fitting the CNN to the images
#Preprocess the images to reduce overfitting
from keras.preprocessing.image import ImageDataGenerator

train_datagen = ImageDataGenerator(rescale = 1./255, #All the pixel values would be 0-1
shear_range = 0.2,
zoom_range = 0.2,
horizontal_flip = True)

test_datagen = ImageDataGenerator(rescale = 1./255)

training_set = train_datagen.flow_from_directory('dataset/training_set',
target_size = (64, 64),
batch_size = 32,
class_mode = 'binary')

test_set = test_datagen.flow_from_directory('dataset/test_set',
target_size = (64, 64),
batch_size = 32,
class_mode = 'binary')

steps_per_epoch = 8000, #number of images in the training set
epochs = 5,
validation_data = test_set,
validation_steps = 2000)

import numpy as np
from keras.preprocessing import image
test_image = image.load_img('dataset/single_prediction/cat_or_dog_2.jpg', target_size=(64,64))
test_image = image.img_to_array(test_image)
test_image = np.expand_dims(test_image, axis=0)
result = classifier.predict(test_image)
if result[0][0] == 1:
prediction = 'dog'
prediction = 'cat'