The detailed deep learning classification includes Pre-Processing, Learning, and Convolutional Neural Networks. Let’s understand each of them:
1. Pre-Processing
To understand how pre-processing takes place in Deep Learning, we first need background information on Variance and Covariance.
a. Variance and covariance
A variable’s variance describes the number of values spread. The covariance indicates the amount of dependency between any two variables. If the covariance value is positive, then the values of the first variables increase when the values of the second variable increase, and vice versa. If the value of covariance is negative, then the values of the first variables decrease when the values of the second variable increase, and vice versa.
Here is the formula to calculate variance:
Here, n = length of the vector
= the mean of the vector
The formula to calculate the covariance between two variables X and Y:
Pre-processing implies all the transformation of raw data before it is fed to deep learning or machine learning algorithms. For example, training a deep convolutional neural network on raw images may result in bad classification performances. The Pre-processing component is also vital to speed up training, for example, using centring and scaling techniques.
b. Mean normalisation
The next important component of Pre-processing is Mean normalisation, which refers to removing the mean from every observation.
The formula to calculate Mean Normalisation:
Here, X’: normalised dataset
X: original dataset
: mean of X.
Mean normalisation centres the data around 0.
c. Standardisation
Standardisation puts all features on an identical scale. Every zero-centred dimension is divided by the corresponding standard deviation.
Here, X’: standardised dataset
X: original dataset
x̅: mean of X
σx: standard deviation of X.
d. Whitening
Whitening (also called sphering) data means transforming the data to a covariance matrix, i.e. the identity matrix (1 in the diagonal and 0 for the remaining cells). It is called ‘Whitening’ because the values of the remaining cells are 0 in reference to the white noise.
Although whitening is slightly more complex than other pre-processing, all essential tools are available to perform it.
Whitening in Deep Learning involves the following steps:
1. Zero-center the data
2. Decorrelate the data
3. Rescale the data
2. Learning
The learning component is the most important one in Deep Learning. This component helps you create neurons in a computer. For that, we use an artificial structure known as an artificial neural network in which there are neurons and nodes. There are certain neurons for the input value and certain for the output value. In between, plenty of neurons in the hidden layer might be interrelated.
a. Deep Neural Network
It is a kind of neural network with some specific complexity level. Multiple hidden layers exist in between the input and output layers. These values can model and process non-linear relationships.
b. Deep Belief Network (DBN)
DBN is a multi-layer belief network belonging to a class of Deep Neural Networks.
Here are the steps to perform DBN for accurate learning in Deep Learning:
1. Firstly, learn a layer of features from visible units with the help of the Contrastive Divergence algorithm.
2. Treat activations of formerly trained features as visible units and subsequently learn features of features.
3. Lastly, the entire DBN is trained when the learning for the last hidden layer is completed.
c. Recurrent Neural Network
Based on the idea of performing the same task for each sequence element, the learning of recurrent neural networks enables sequential and parallel computation. Its working is identical to the human brain; there is a huge feedback network of connected neurons. The connected neurons can store essential information about the input they obtained, making them more accurate.
3. Convolutional Neural Networks
In simple terms, a neural network is a sequence of algorithms that undertakes to recognise underlying relationships in a data set via a process that resembles how the human brain works. Neural networks relate to systems of neurons that are either artificial or organic.
Convolutional Neural Networks are unique neural networks primarily used for deep learning image classification, image clustering, and object detection deep learning. DNNs allow unsupervised development of hierarchical deep learning image representations. But to attain the best accuracy, deep convolutional neural networks are more preferred than any other neural networks.
In other words, a Deep Learning Convolutional Neural Network (CNN) is a deep learning neural network implemented for processing organised arrays of data like images. CNN is widely used in computer vision, and now it has transformed into state-of-the-art for various visual applications like image classification. Also, it got successful in natural language processing for text classification.
In deep learning, a convolutional neural network (brief as CNN or ConvNet) represents a class of deep neural networks typically employed to analyse visual imagery. When discussing a neural network, we would think about the matrix multiplications; however, this is not the case with CNN. It implements a special technique known as Convolution. From a mathematics viewpoint, convolution is a mathematical operation performed on two functions that generates a third function that shows how the shape of one is altered by the other.
Convolutional neural networks choose the patterns in the input deep learning image efficiently. The patterns include lines, circles, gradients, faces, and eyes. With this property, convolutional neural networks become so efficient for computer vision. Contrasting formerly released computer vision algorithms, CNN can directly operate on a raw image and doesn’t require any pre-processing.
A CNN is a feed-forward neural network, usually consisting of up to 20 or 30 layers. Moreover, the huge power of a convolutional neural network derives from a unique type of layer known as the convolutional layer. CNN is extensively used for image identification and classification. It influences the present-day healthcare industry and enhances the outcome of patients’ cures.
a. Convolutional Layer
The fundamental building block in a convolutional neural network is a convolutional layer. You can envisage a convolutional layer as several tiny square templates known as convolutional kernels sliding across the image and looking for patterns. The kernel will return a huge positive value for the specific part of the image that matches the kernel’s pattern. The kernel will return 0 or a smaller value if there is no match.
Plenty of convolutional layers stacked on one another are present in CNNs. Each of these layers is competent in identifying more refined shapes. It is possible to identify transcribed digits using 3 or 4 convolutional layers. While using 25 convolutional layers, it is possible to differentiate human faces via face detection deep learning.
The use of convolutional layers in a CNN resembles the construction of the human visual cortex. Its construction shows a sequence of layers that processes an incoming image and gradually identifies more complex features.
Applications of Convolutional Neural Networks:
- Identify Faces, Tumors, Street Signs
- Image Recognition
- Video Analysis
- Anomaly Detection Deep Learning
- NLP deep learning
- Checkers Game
- Drug Discovery
- Time Series Forecasting