Image Processing: A beginners Overview

Image Processing is a collection of numerous processes such as image enhancement, image acquisition, image analysis.

In other words Image processing is a  process of computer monitored routines which comprise of information extraction, retrieval which includes pattern recognition, classification and many more in order to get specific features of the image.

Category of Images in Image Processing:

  1. Indexed Images
  2. Intensity Images
  3. Binary Images
  4. RGB Images

What is Indexed Image in Image processing ?

An indexed image is a collection of two arrays. One of which is image matrix and other one is colormap. Image matrix is the collection of values which are called reference values or index values to the colormap.

Each pixel value of the image matrix is considered to be an index of colormap. Colormap is an m-by-3 ordered matrix having class ‘double’. As it is a three layered matrix, its first layer indicates red channel, second layer indicates green channel and third layer indicates blue channel.

So, for a single value of an image matrix, three corresponding values [reed, green, blue] can be obtained from a colormap in order to represent a RGB image. If the image matrix holds the value 1 then this would refer to the first row of the colormp and in the same way the value 2 would refer to the second row to the colormap and so on in image processing .

If the mage matrix holds the values of class unit8 type then the 0 value of pixel of image matrix would refer to the first row in the colormap and the 1 value of pixel of image matrix would refer to the second row in the colormap. Below figure describes an indexed image.

What is Indexed image
Indexed image

                                                               Image Processing

What is Intensity Image in Image Processing ?

In Image Processing, Intensity image refers to a single matrix of which each element of the matrix referencing to one image pixel.

If the matrix is of class double then it would hold the values in the range [0, 1] and if the matrix is of unit8 type then it would hold the values in the range [0,255]. It is to be noted here 0 indicates black pixel and 255 indicates white pixel. Below figure describes an intensity image.

Intensity image in Image Processing
Intensity image
What is Binary Image in Image Processing ?

In Image Processing, Binary image is a two dimensional matrix containing only discrete values that is 0 and 1. Two discrete values correspond to on and off. 0’s correspond to off pixels and 1’s correspond to on pixels. Below figure describes a binary image.

What is Binary image
Binary image
What is RGB Image in Image processing ?

In RGB image each pixel contains a set of 3 values which are representing the red, green and blue intensities to visible that color. Here the intensity values are stored in the image matrix itself.

In Image Processing, here is the difference between RGB and Intensity image. RGB image matrix is of m-by-n-by-3 dimension. Where first layer matrix represents red channel, second layer matrix represents green channel and third layer matrix represents blue channel.

Below figure describes an RGB image:

What is RGB image
RGB image

Various Image Conversion Functions Available in MATLAB for Image Processing:

dither = Binary from grayscale, indexed from RGB

gray2ind = Indexed from grayscale

grayslice = Indexed from grayscale by thresholding

im2bw = Binary from intensity, indexed or RGB image by luminance threshold

ind2gray =  Indexed to grayscale

ind2rgb = Indexed to RGB

mat2gray = Create a grayscale intensity image from data in a matrix, by scaling the data

rgb2gray = RGB to intensity

rgb2ind = RGB to indexed


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