<< Chapter < Page Chapter >> Page >

Questions or comments concerning this laboratory should be directedto Prof. Charles A. Bouman, School of Electrical and Computer Engineering, Purdue University, West Lafayette IN 47907;(765) 494-0340; bouman@ecn.purdue.edu


This is the first part of a two week experiment in image processing. During this week, we will cover the fundamentalsof digital monochrome images, intensity histograms, pointwise transformations, gamma correction, and image enhancement based on filtering.

In the second week, we will cover some fundamental concepts of colorimages. This will include a brief description on how humans perceive color, followed by descriptions of two standard color spaces.The second week will also discuss an application known as image halftoning .

Introduction to monochrome images

An image is the optical representation of objects illuminated by a light source. Since we want to process images using acomputer, we represent them as functions of discrete spatial variables. For monochrome (black-and-white) images, a scalar function f ( i , j ) can be used to represent the light intensity at each spatial coordinate ( i , j ) . [link] illustrates the convention we will use for spatial coordinates to represent images.

Spatial coordinates used in digital image representation.

If we assume the coordinates to be a set of positive integers, for example i = 1 , , M and j = 1 , , N , then an image can be conveniently represented by a matrix.

f ( i , j ) = f ( 1 , 1 ) f ( 1 , 2 ) f ( 1 , N ) f ( 2 , 1 ) f ( 2 , 2 ) f ( 2 , N ) f ( M , 1 ) f ( M , 2 ) f ( M , N )

We call this an M × N image, and the elements of the matrix are known as pixels .

The pixels in digital images usually take on integer values in the finite range,

0 f ( i , j ) L m a x

where 0 represents the minimum intensity level (black), and L m a x is the maximum intensity level (white) that the digital image can take on. The interval [ 0 , L m a x ] is known as a gray scale .

In this lab, we will concentrate on 8-bit images, meaning that each pixel is represented by a single byte.Since a byte can take on 256 distinct values, L m a x is 255 for an 8-bit image.


Download the file yacht.tif for the following section. Click here for help on the Matlab image command .

In order to process images within Matlab, we need to first understand their numerical representation.Download the image file yacht.tif . This is an 8-bit monochrome image.Read it into a matrix using

A = imread('yacht.tif');

Type whos to display your variables. Notice under the "Class" column that the A matrix elements are of type uint8 (unsigned integer, 8 bits). This means that Matlab is using a single byte to represent each pixel.Matlab cannot perform numerical computation on numbers of type uint8 , so we usually need to convert the matrix to a floating point representation.Create a double precision representation of the image using B = double(A); . Again, type whos and notice the difference in the number of bytes between A and B . In future sections, we will be performing computations on our images,so we need to remember to convert them to type double before processing them.

Display yacht.tif using the following sequence of commands:

Questions & Answers

what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!

Source:  OpenStax, Purdue digital signal processing labs (ece 438). OpenStax CNX. Sep 14, 2009 Download for free at http://cnx.org/content/col10593/1.4
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Purdue digital signal processing labs (ece 438)' conversation and receive update notifications?