Image Classification and its Applications By Anush Ramsurat (106111035) Vignesh S (106111082) Nishant K M (106111063)

Introduction – What is Image Classification? It is the task of extracting and categorizing useful information from a multi-band raster image. This extracted information is further used to create thematic maps.  The image is classified according to its visual content. The classification scheme/criteria depends on the need of the end user.

Why Classify Images? The intent of the classification process is to categorize all pixels in a digital image into one of several land cover classes, or "themes“. This categorized data may then be used to produce thematic maps of the land cover present in an image. The objective of image classification is to identify and portray, as a unique grey level (or colour), the features occurring in an image in terms of the object or type of land cover these features actually represent on the ground.

Types of Image Classification Unsupervised Classification: Unsupervised classification is a method which examines a large number of unknown pixels and divides into a number of classes based on natural groupings present in the image values. Unsupervised classification does not require analyst-specified training data. The basic premise is that values within a given cover type should be close together in the measurement space (i.e. have similar grey levels), whereas data in different classes should be comparatively well separated (i.e. have very different grey levels).

Types of Image Classification Supervised Classification: With supervised classification, we identify examples of the Information classes (i.e., land cover type) of interest in the image. These are called "training sites". The image processing software system is then used to develop a statistical characterization of the reflectance for each information class. Once a statistical characterization has been achieved for each information class, the image is then classified by examining the reflectance for each pixel and making a decision about which of the signatures it resembles most. 

Supervised Classification - Steps

Supervised Classification – Some Advanced Techniques and Concepts Neural Networks: Use flexible functions to partition the spectral space. Contextual Classifiers: Incorporate spatial or temporal conditions in classification. Linear Regression: Instead of discrete classes, apply proportionate value of classes to each pixel.

Maximum Likelihood Classification Maximum likelihood Classification is a statistical decision criterion to assist in the classification of overlapping signatures; pixels are assigned to the class of highest probability. The maximum likelihood classifier is considered to give more accurate results. However, it assumes that classes in the input data have a Gaussian distribution and that signatures were well selected; this is not always a safe assumption.

Applications of Image Classification Remote Sensing: Used in classifying raw satellite image of land area, taken from space, into useful segregators based on geography. STEPS Acquisition of suitable satellite imagery. Visual Interpretation of satellite image. Radiometric and Geometric correction. Stretch and filter logarithm Supervised classification: Every object class in the image will be coordinated to reference areas called ‘training areas’, and this enhances the statistical classification. We get a Land Classification Map as the output.

Sample Satellite Image Classification

Applications of Image Classification Infrared Thermal Imagery All objects emit infrared energy (heat) as a function of their temperature. This is called ‘heat signature’. The hotter an object is, the more radiation it emits. A thermal camera captures heat signatures and classifies the image of an object or area based on differences in temperature. The distinction between areas with high and low heat signatures is clearly visible in the image. This is used in many popular real-world scenarios such as in cricket to detect if the ball has touched the bat or not for contentious catch appeals.

Image of IR Camera used in Cricket