Feature Extraction and Feature Selection using Textual Analysis

VIVA-Tech International Journal for Research and Innovation Volume 1, Issue 3 (2020)
ISSN(Online): 2581-7280 Article No. 9
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www.viva-technology.org/New/IJRI
Feature Extraction and Feature Selection using Textual Analysis
Hemlata Badwal1
, Prof. Chandani Patel2
1
(Department of Computer Applications, VIVA School of MCA, Virar, Maharashtra, India)
Email: badwalhemlata@gmail.com
2
(Department of Computer Applications, VIVA School of MCA, Virar, Maharashtra, India)
Email: chandaniapatel@gmail.com
Abstract: After pre-processing the images in character recognition systems, the images are segmented based on
certain characteristics known as “features”. The feature space identified for character recognition is however
ranging across a huge dimensionality. To solve this problem of dimensionality, the feature selection and feature
extraction methods are used. Hereby in this paper, we are going to discuss, the different techniques for feature
extraction and feature selection and how these techniques are used to reduce the dimensionality of feature space
to improve the performance of text categorization.
Keywords – Character Recognition, Feature Extraction, Feature Selection, Image Segmentation, Pre-
processing.
1. INTRODUCTION
The conversion of textual documents in digital form have increased rapidly worldwide. This is where the
text classification becomes a dire need to handle these documents. The character recognition systems are thus
used to fulfill these needs. The main objective of character recognition systems is to recognize and classify the
text on the basis of predefined categories using some classifiers. Several analysis works have been done to evolve
newer techniques and strategies that would scale back the time interval for processing whereas providing higher
recognition accuracy.
In the following section, the four major steps used for handwriting recognition systems are described: -
Pre-processing, Image segmentation, Feature extraction and Classification. Section II describes the various
methods available for pre-processing, feature selection and feature extraction and the classifiers [1]. Section III
presents the conclusive idea regarding the reviewed methods.
2. WORKING PRINCIPLE
Handwritten character recognition is the ability of an automated system to recognize handwritten
character or sentence from photographs, documents, touchscreens and other such devices by a computer [1]. The
image of the written sentence / word / character may be gathered either offline or on-line. In off line technique it
may be from a scanned image of a paper. In on-line the sleuthing motion of the pen tip, for example by a pen-
based display screen surface capturing temporal frequency [2].

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Fig. 1 Block Diagram of Character Recognition
Fig. 1 describes the process of text classification. Although, text classification has one limitation. This
limitation includes high spatial property of feature area thanks to terribly sizable amount of options. The larger
the options, the bigger the complexity of methods used for text classification and also the smaller the accuracy
due to irrelevant or redundant terms within the feature space. Feature extraction and feature selection methods are
used to eradicate this downside.
The initial major step in textual classification is Pre-processing. The moot data existing in the document
is eliminated using the pre-processing. The subsequent step, image segmentation decomposes an image of a
sequence of characters into sub images of individual symbols. Then, each character image is resized into m x n
pixels towards the training network. These sub images are used to select the subset from the original feature set
on the basis of importance of features, known as Feature Extraction. The fundamental task of feature extraction
and selection is to identify a group of the most effective features for classification; so as to compress the high-
dimensional feature space to low-dimensional feature space, for efficient classification [4] [16].
2.1 PRE-PROCESSING
When a document is scanned it requires some preliminary processing. This pre-processing helps to
eliminate the irrelevant data in the scanned image in the form of noise and resize the image. For pre-processing
the document, noise reduction, binarization, skew correction, etc. techniques can be used. The main objectives of
pre-processing are [1]:
1. Noise reduction
2. Binarization
3. Skew correction
4. Stroke width normalization
Noise Reduction
The noise removal is achieved by converting RGB image into grayscale. It is then converted into binary
image consisting only pixels 0’s (white) and 1’s (black). Unnecessary background pixels are removed from
original image. To remove the redundant or irrelevant data, the threshold value is applied to the image.
Fig. 2 Grayscale image with noise
Fig. 3 Reduced noise image

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Stroke-width normalization
After normalization generally it reduces the amount of data to be processed. For e.g. by thinning the
shape information of a character can be gathered without losing the data.
Fig. 4 Stroke-width normalization image
Skew Correction and Slant Removal
Skew correction methods are used for the alignment of the coordinate system of the scanner with respect
to that of the document. Its main approaches include correlation, projection profiles and Hough transform etc [1].
The slant of any handwritten text(s) varies from one user to another. The characters can be normalized by using
the slant removal methods [1].
Fig. 5 Skew correction and Slant removal image
Binarization
In Binarization, a gray scale image if transformed to a binary image using global thresholding technique
[3]. Let’s assume f(x,y) is an input image. T is the threshold value and g(x,y) is the output image of thresholding
process then the mathematical equation of this conversion is g(x,y) =1 if f(x,y) ≥ T otherwise 0.
Fig. 6 Binarized image
2.2 IMAGE SEGMENTATION
Image Segmentation involves two major steps [4]:
1. Line Detection
2. Word Detection
Line detection
Lines are differentiated using the Hough Transform, horizontal projections, etc. technique.
Hough transform detects straight lines. The straight line y = mx + b can be represented as a point (b, m)
in the parameter space, where b represents the intercept parameter and m represents the slope parameter.
Horizontal Projection profile is the projection profile of an image along horizontal axis. It calculates each
row for all column pixels in that row.
Fig. 7 Line Segmentation

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Word detection
Words can be identified using vertical projections, connected component analysis, etc.
Vertical Projection profile is the projection profile of an image along vertical axis. Vertical projection
profile is calculated for each column as summation of all row pixel values inside the column.
Connected component labeling works by scanning an image, pixel-by-pixel (from top to bottom and left
to right) so as to identify connected pixel regions, [19] i.e. regions of adjacent pixels that share the same set of
intensity values V. For a binary image V={1} [20].
Fig. 8 Word Segmentation
2.3 FEATURE EXTRACTION
Feature extraction methods include principal component analysis (PCA), latent semantic indexing (LSI),
etc [3].
Principal Component Analysis (PCA): Principal Component Analysis is dimension reduction technique
that extracts the information from various dataset. PCA produces a set of lower-dimensional features from the
original dataset. PCA is sensitive to the relative scaling of the original variables [5]. PCA determines the number
of principal components using certain criterions. The dimensions representing the principal components at the
best are chosen. The number of principal components to be chosen varies depending upon the quality of the
dataset.
Latent Semantic Indexing (LSI): Latent Semantic Indexing (LSI) is a technique that projects queries and
documents into a space with “latent” semantic dimensions. LSI has fewer dimensions than the original space. It
works as a similarity matrix that is an alternative to word overlap measures like td.idf. LSI creates a matrix of
words and sentences in a document that determine the occurrences of similar words which can be used for
classification.
2.4 CLASSIFICATION
Classification is a supervised machine learning technique which identifies the category that a new
observation belongs to, based on the observations used in the training set. The classifier utilization depends on
several factors, such as available training set, range of free parameters. Some of the vital techniques which can be
used for classification are- decision Tree (DT), k-Nearest Neighbor (k-NN), Bayes Classifier, Neural Networks
(NN), Support Vector Machines (SVM), etc [1].
Decision Tree (DT) Classifier: In Decision tree classifier, the features are split into completely different
regions corresponding to the classes available. It uses Information Gain value to identify the node at each level of
the DT. The feature with the highest Information Gain is chosen as the node. The class is assigned along the path
of the assigned nodes containing the features.
k-Nearest Neighbor (k-NN) Classifier: The purpose of k-NN classifier is used to assign the class label to
a cluster of similar elements. It calculates the nearest neighbors using the Euclidean distance matrix. The similarity
score is used as the weight of the classes of the neighbor document.
Naive Bayes (MB) Classifier: Naive Bayes Classifier is a probabilistic classifier. It assumes the
independence of features. The value of a particular feature is independent of any other feature’s value, given the
class variable [17]. For example, a fruit can be considered to be an apple if it is round, red, and about 10 cm in
diameter. A naive Bayes classifier considers each and every feature contribute independently to the probability
that this fruit is an apple, regardless of any attainable correlations between the color, roundness, and diameter
features. Naive Bayes Classifier has surprisingly performed quite well in many complex real-world issues albeit
it considers naive assumptions. Training and testing phase in Naive Bayes is easy for implementation and
computation.

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Support Vector Machine (SVM) Classifier: Support Vector Machine belongs to supervised learning
classification technique. SVM algorithm consists of 2 types of versions: non-linear and linear versions [18]. In
non-linear version, classes are not separated i.e. no straight lines that separate the classes can be found. In linear
version, the classes are separated with the hyperplanes. Linear classifier is defined as wT x + b = 0. Where, w is
the direction of the hyperplane and b is the precise position of hyperplane [18].
Fig. 9 Linear SVM Classifier
SVM find this hyperplane by using margins and support vectors. The region between the two hyperplanes
wT x + b = 1 and wTx + b = -1 is known as margin. 2/||w|| is the width of the margin. The tuples that fall on the
two hyperplanes are known as support vectors.
3. CONCLUSION
With the rapid increase in the digital conversion of texts, the need for handwriting recognition systems
are soaring higher and higher. Here in this paper, we have discussed the techniques used in converting the text
into the digital form. The accuracy rate of the systems determines how well a system is. But the text classification
suffers from the higher dimensionality problem. To reduce the feature space and increase the accuracy of the
systems, we have reviewed the pre-processing techniques, image segmentation, feature extraction as well as the
classifiers available for text recognition.
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