Introduccion a matlab

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Introduction to MATLAB (Basics)

Reference from: Azernikov Sergei mesergei@tx.technion.ac.il

MATLAB Basics
• Where to get help? 1) In MATLAB’s prompt type: help, lookfor,helpwin, helpdesk, demos. 2) On the Web: http://www.mathworks.com/support
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MATLAB’s Workspace
• • • • who,whos - current variables in workspace save - save workspace variables to *.mat file load - load variablesfrom *.mat file clear all - clear workspace variables

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Matrices in MATLAB
• Matrix is a main MATLAB’s data type • How to build a matrix? A = [ 1 2 3; 4 5 6; 7 8 9 ]; Creates matrix A with size 3x3. • Special matrices : zeros(n,m), ones(n,m),eye (n,m)
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Basic Operations on Matrices
• All the operators in MATLAB defined on matrices : +, -, *, /, ^, sqrt, sin, cos etc. • Element wiseoperators defined with preceding dot : .*, ./, .^ . • size(A) - size vector • sum(A) - columns sums vector • sum(sum(A)) - all the elements sum
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Logical Conditions
• == , < , > , (not equal)~= ,(not)~ • find(‘condition’) - Returns indexes of A’s
elements that satisfies the condition.

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Logical Conditions(cont.)
• Example:
>> A = [1 2; 3 4], I = find(A 0, E = E + F; F = A*F/N; N = N +1; end
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Scripts and Functions
• There are two kinds of M-files:
– Scripts, which do not accept input arguments or return output arguments. They operate on data in the workspace. – Functions, which can accept input arguments and return output arguments. Internal variables are local to the function.
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Functions in MATLAB

• FUNCTION Add new function. • New functions may be added toMATLAB' s vocabulary if they are expressed in terms of other existing functions.
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Functions in MATLAB (cont.)
• Example :
The existence of a file on disk called STAT.M with: function [mean,stdev] = stat(x) %STAT Interesting statistics. n = length(x); mean = sum(x) / n; stdev = sqrt(sum((x - mean).^2)/n); defines a new function called STAT that calculates the mean and standard deviation ofa vector.
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Visualization and Graphics
• • • • • • • • plot(x,y), plot(x,sin(x)) - plot 1-D function figure , figure(k) - open a new figure hold on, hold off - refreshing mesh(x_ax,y_ax,z_mat) - view surface contour(z_mat) - view z as top. map subplot(3,1,2) - locate several plots in figure axis([xmin xmax ymin ymax]) - change axes title(‘figure title’) - add title to figure
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ImageProc. with MATLAB
(Please refer to Matlab Demo for more details of Image Processing Tool Box)

What Is the Image Processing Toolbox?
• The Image Processing Toolbox is a collection of functions that extend the capability of the MATLAB ® numeric computing environment. The toolbox supports a wide range of image processing operations, including:
– – – – – – – Geometric operations Neighborhoodand block operations Linear filtering and filter design Transforms Image analysis and enhancement Binary image operations Region of interest operations
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MATLAB Image Types
• • • • Indexed images Intensity images Binary images RGB images : m-by-3 color map : [0,1] or uint8 : {0,1} : m-by-n-by-3

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Indexed Images
» [x,map] = imread(' trees.tif' ); » imshow(x,map);

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IntensityImages
» image = ind2gray(x,map); » imshow(image);

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Binary Images
» imshow(edge(image));

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RGB Images

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Image Display
• • • • • • • image - create and display image object imagesc - scale and display as image imshow - display image colorbar - display colorbar getimage- get image data from axes truesize - adjust display size of image zoom - zoom in and zoom out of 2D plot28

Some Points to Note
Pixel values are accessed as matrix elements.
2D Image with intensity values: I(row,col) 2D RGB images I(row,col,color) - Color : Red = 1; Green = 2 ; Blue = 3

Displaying images
figure, imshow(I)

Displaying pixel position and intensity information
pixval on
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Points to Note
All arithmetic operations performed on matrices may be performed on images...
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