INTRODUCTION
The term image refer to two dimensional light intensity function f(x, y), where x and y denote spatial coordinates and the value of at any point (x, y) is proportional to the brightness (or gray level) of the image at that point. A digital image is an image f(x, y) that has been discretized both in spatial coordinate and brightness. A digital image can be considered a matrix whose row and column indices identify a point in the image and the corresponding matrix element value identifies the gray level at that point. The elements of such a digital array are called image elements, picture elements. The term digital image processing refers to processing of a two dimensional picture by a digital computer. An image given in the form of a transparency, slide, photograph or chart is first digitized and stored as matrix of binary digits in computer memory. This digitized image can be processed and/or displayed on a high resolution monitor. Segmentation subdivides an image into its constituent regions or objects .The level to which the segmentation is carried depends on the problem being solved. Segmentation is carried until we are able to distinguish the object from its backgrounds. Image segmentation is based on one of the two basic properties of intensity values: discontinuity and similarity. Thresholding is a similarity approach of segmenting an image. The simplest thresholding technique is to partition the image histogram by using a single global threshold T. But in case of uneven illumination, this is not possible .So the image is subdivided to carry out adaptive thresholding for better segmentation. Segmentation should stop when the object of interest in application have been isolated. TYPES OF DIGITAL IMAGES
For photographic purposes, there are two important types of digital images- colour and black and white. Colour images are made up of coloured pixels while black and white images are made of pixels in different shades of gray.
Black and White Images:-
A black and white image is made up of pixels each of which holds a single number corresponding to the gray level of the image at a particular location. These gray levels span the full range from black to white in a series of very fine steps, normally 256 different grays. Since the eye can barely distinguish about 200 different gray levels, this is enough to give the illusion of a stepless tonal scale as illustrated below:

Assuming 256 gray levels, each black and white pixel can be stored in a single byte (8 bits) of memory.
Colour Images:- A colour image is made up of each of which holds three numbers corresponding to the red, green and blue levels of the images at a particular location. Red, green, and blue (sometimes referred to RGB) are the primary colours for mixing light – these so-called additive primary colours are different from the subtractive primary colours used for mixing paints (cyan, magenta, and yellow). Any colour can be created by mixing the correct amounts of red, green, and blue light. Assuming 256 levels for each primary, each colour pixel can be stored in three bytes (24 bits) of memory.
This corresponds to roughly 16.7 million different possible colours.
Note that for images of the same size, a black and white version will use three times less memory than a colour version.