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An introductory tutorial on MATLAB in Image Processing
ECE 178 (12pm Discussion batch, TA: Srivatsan Pallavaram)
I. GETTING STARTED
MATLAB is a dataanalysis and visualization
tool widely used by electrical engineers and
stands for “Mathematics Laboratory.” The most
important difference between MATLAB and C
(or C++) is that functions in MATLAB are
specifically written with a focus on large array
based operations in mind. Image processing is
heavy on the memory usage as well as the run
time of programs.
You would need the Image Processing toolbox
installed in your MATLAB to work with the
commands that are listed later in this worksheet.
You can check if the Image Processing toolbox
is installed using the
ver
command. Using “help
images” one can see all the commands that are
supported in this toolbox. If you find the help
document scrolling past very fast you can switch
the ‘more’ command using >> more on or for a
more formal help use >> doc ‘command’ A
MATLAB
function
is a keyword that accepts
various parameters, and produces output of some
sort. At times in this course, we may need to
write our own functions (and this is very easy as
you will see). A
command
is a particular usage
of a function.
Variables
are elements used to
store values. If you are using a windowed
version of MATLAB, you may find a Workspace
item in the View menu. This lists all your
currently defined variables, their data types, sizes
etc.
Exercise 1:
Explore the
whos
and
who
commands that are used to list the variables used
in the workspace.
At this point, I would like to stress that learning/
understanding MATLAB is impossible by just
reading this handout. The exercises in this
handout are motivated primarily by this reason.
Using standard MATLAB routines “efficiently”
Could mean the difference between a program
that runs for a day and one that runs in an hour.
Use of
for
loops is known to increase the run
time by a significant amount.
Exercise 2:
This exercise describes how ‘slow’
the
for
command can be. We can measure the
time that elapses between the executions of a
command using the
tic toc timer
of MATLAB.
tic starts a stopwatch timer and toc stops it and
prints out the elapsed time in seconds. Execute
the following code and compare the elapsed time
differences between the two.
>> tic; for i = 1:10ˆ6, sin(i);end; toc;
>> tic; i=1:10ˆ6; sin(i); toc; Understand how the
for
loop can slow down the process by quite a
bit.
II.
BASIC
MATRIX
OPERATIONS
IN
MATLAB
The standard data type of MATLAB operations
is the matrix. Images, of course, are matrices
whose elements are the gray values (or possibly
the RGB values) of its pixels. I am assuming that
most of you are aware of the basics of
MATLAB.
More
information
on
these
commands can be obtained using the
help
and
lookfor
commands. A standard 2
×
3 matrix
is defined as >> A = [a11 a12 a13; a21 a22
a23;]; Matrix elements can be obtained using the
standard row, column indexing scheme >> a(2,3)
The
reshape
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This note was uploaded on 12/28/2011 for the course ECE 178 taught by Professor Manjunath during the Fall '08 term at UCSB.
 Fall '08
 MANJUNATH
 Image processing

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