MATLAB - PRESENTATION for PG studentspdf

Introduction to Matlab
Instructor: Sanja Fidler
Presented by: KARTHIKSANKAR P

Outline
1. Introduction
1. Overview
2. Variables
3. Matrix
4. Misc.
2. Image Processing with Matlab
3. References

• Matrix Laboratory
– Dynamically typed language
• Variables require no declaration
• Creation by initialization (x=10;)
– All variables are treated as matrices
• Scalar: 1×1 matrix; Vector: N×1 or 1×N matrix
• Calculations are much faster
• Advantages
– Fast implementation and debugging
– Natural matrix operation
– Powerful image processing toolbox
What & Why

Matlab Main Screen
 Command Window
 type commands
 Current Directory
 View folders and m-files
 Workspace
 View variables
 Double click on a variable
to see it in the Array Editor
 Command History
 view past commands
 save a whole session
using diary

Variables
Defining variables
Variables are created when they are used
All variables are created as matrices with “some” type
(unless specified)
int a;
a=1;
double b;
b=2+4;
>>a=1;
>>b=2+4;
C/C++ Matlab

Variables
A = [1, 2, 3]
B = [1,2,3;4,5,6]
C=[1 2 3;4 5 6;7 8 9]

D=[1 ; 2 ; 3]
E=[1 2 3]’
Variables

C = ‘Hello World!';
Variables

Variables
A = zeros(3);
B = ones(5);
C = rand(100,2);
D = eye(20);
E = sprintf('%dn',9);

Matrix Index
Matrix indices begin from 1 (not 0!!!)
Matrix indices must be positive integers
Column-Major Order

Matrix Index
>> A(2,2:3)
ans =
5 6
>> A(2,1:end)
ans =
4 5 6
>> A(2,:)
ans =
4 5 6
>> A(2,1:2:3)
ans =
4 6
>> A(2,[1 3])
ans =
4 6
>> A(:)
ans =
1
4
7
2
5
8
3
6
9

Accessing Elements
A = rand(4);
A(2,3)
A(:,2)
A(end,:)
A([1,2],[1,3])
A(1:2,3:end)
http://www.mathworks.com/company/newsletters/articles/matrix-indexing-
in-matlab.html
Matrix Index

Matrix Operations
+ addition
- subtraction
* multiplication
^ power
‘ complex conjugate transpose

Given A and B:
Addition Subtraction Product Transpose
Slide credit: İ.Yücel Özbek
Matrix Operations

.* element-wise multiplication
./ element-wise division
.^element-wise power
Matrix Operations

A = [1 2 3; 5 1 4; 3 2 1]
A =
1 2 3
5 1 4
3 2 -1
y = A(3 ,:)
y=
3 4 -1
b = x .* y
b=
3 8 -3
c = x . / y
c=
0.33 0.5 -3
d = x .^y
d=
1 16 0.33
x = A(1,:)
x=
1 2 3
Matrix Operations

A/B Solve linear equation xA=B for x
AB Solve linear equation Ax=B for x
Matrix Operations

Matrix Concatenation
X=[1 2], Y=[3 4]

Strings
A =‘vision and geometry’
strfind(A,‘geometry')
strcmp(A,'computer vision')
B = strcat(A,' 12345')
c = [A,' 12345']
D = sprintf('I am %02d years old.n',9)
int2str, str2num, str2double
http://www.mathworks.com/help/matlab/ref/strings.html

Cell and Structure
• Cells
○ a = {}; a = cell(1)
○ b = {1,2,3}
○ c = {{1,2},2,{3}}
○ D = {'cat','dog','sheep','cow'}
○ E = {'cat',4}
• Structures
○ A = struct('name','1.jpg','height',640,'width',480);
○ b.name = '1.jpg‘
http://www.mathworks.com/help/matlab/matlab_prog/cell-vs-struct-arrays.html

Operators
== Equal to
~= Not equal to
< Strictly smaller
> Strictly greater
<= Smaller than or equal to
>= Greater than equal to
& And operator
| Or operator

Flow Control
• if, for, while ….
if (a<3)
Some Matlab Commands;
elseif (b~=5)
end
for ii=1:100
end
for j=1:3:200
end
for k=[0.1 0.3 -13 12 7 -9.3]
end
while ((a>3) & (b==5))
end
http://www.mathworks.com/help/matlab/control-flow.html

Vectorization
Optimize your code for Matrix operations
Examples
In other languages:
In MATLAB:
http://www.mathworks.com/help/matlab/matlab_prog/vectorization.html
tic; i = 0;
for t = 0:.001:1000
i = i + 1;
y(i) = sin(t);
end; toc;
tic; t = 0:.001:1000;
y = sin(t); toc;
Elapsed time is 0.509381 seconds.
Elapsed time is 0.011212 seconds.

M-File
Click to create
a new M-File
• A text file containing script or function
• Extension “.m”

Functions
For example,
Implement your own function Add3()
B = Add3(A)
How?
Create a M-file with the function name
Use the function definition at the beginning
function out1=functionname(in1)
function out1=functionname(in1,in2,in3)
function [out1,out2]=functionname(in1,in2)

Plotting
Plotting functions
plot, plot3d, bar, area, hist, contour, mesh
x = -pi:.1:pi;
y = sin(x);
plot(x,y)

Help & Doc
help functionName
doc functionName

Image Data Structure
• Image as matrices
– Gray image: m × n
– RGB image: m × n × 3
• Format:
– [0, 255] uint8
– [0, 1] double
I(m,n,1)
I(1,1,1)
I(1,1,3)
I(m,n,3)
n
m
I(1,n,3)

Image I/O/Display
% Read image (support bmp, jpg, png, ppm, etc)
I = imread('lena.jpg');
% Save image
imwrite(I, 'lena_out.jpg');
% Display image
imshow(I);
% Alternatives to imshow
imagesc(I);
imtool(I);
image(I);

Image Conversions
% Type conversion
I1 = im2double(I);
I2 = im2uint8(I);
% Convert from RGB to grayscale
I3 = rgb2gray(I);

Image Operations
% Resize image as 60% smaller
Ires = imresize(I, 0.6);
% Crop image from user’s input
imshow(I);
Rect = getrect;
Icrp = imcrop(I, Rect);
% Rotate image by 45 degrees
Irot = imrotate(I, 45);
% Affine transformation
A = [1 0 0; .5 1 0; 0 0 1];
tform = maketform('affine', A);
Itran = imtransform(I, tform);

Image Filtering / Convolution
• A filter (or called mask, kernel, neighborhood) is N×N matrix.
• Filters help us perform different kinds of operations:
Blurring Sharpening Edge Denoise

References
More tutorials
• Matlab course @ ETHZ (http://goo.gl/W2jmZJ)
• Introductory Digital Processing @ IIT (http://goo.gl/U0osD2)
Open source CV algorithms with Matlab interface
• VLFeat (http://www.vlfeat.org/)
• Piotr Dollar’s toolbox (http://vision.ucsd.edu/~pdollar/toolbox/)
• Mexopencv (http://www.cs.stonybrook.edu/~kyamagu/mexopencv/)

− Matlab Documentation
• http://www.mathworks.com/help/matlab/
− Cheat Sheets
• http://web.mit.edu/18.06/www/Spring09/matlab-cheatsheet.pdf
• http://www.geog.ucsb.edu/~pingel/210b/general/matlab_refcard.pdf
References

MATLAB - PRESENTATION for PG studentspdf

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