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Introduction to MATLAB

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1 Introduction to MATLAB
Iran University of Science and Technology, Computer Engineering Department, Introduction to MATLAB Ehsan Adeli M.

2 Outline Introduction MATLAB Environment Getting Help
Vectors, Matrices, and Linear Algebra Plotting User Defined Functions Image Manipulation and Processing Audio Processing Filters and Operations Multimedia Systems

3 Introduction MATLAB Stands for MATrix LABoratory.
The MATLAB environment allows the user to: manage variables import and export data perform calculations generate plots develop and manage files for use with MATLAB. A script can be made with a list of MATLAB commands like other programming language. Multimedia Systems

4 Environment Multimedia Systems

5 Getting Help Type one of following commands in the command window:
help – lists all the help topic help topic – provides help for the specified topic help command – provides help for the specified command help help – provides information on use of the help command helpwin – opens a separate help window for navigation lookfor keyword – Search all M-files for keyword Or simply press ‘F1’ and use the graphical help window. Multimedia Systems

6 Variables Variable names: when a semi-colon
Must start with a letter May contain only letters, digits, and the underscore “_” Matlab is case sensitive, i.e. one & OnE are different variables. Matlab only recognizes the first 31 characters in a variable name. when a semi-colon >> tutorial = 1234; >> tutorial = 1234 ”;” is placed at the end of each command, the result is not displayed. Multimedia Systems

7 Variables (Cont’d) Special variables: Commands involving variables:
ans : default variable name for the result pi: π = ………… eps: ∈ = e-016, smallest amount by which 2 numbers can differ. Inf or inf : ∞, infinity NaN or nan: not-a-number Commands involving variables: who: lists the names of defined variables whos: lists the names and sizes of defined variables clear: clears all variables, reset the default values of special variables. clear name: clears the variable name clc: clears the command window clf: clears the current figure and the graph window. Multimedia Systems

8 Vectors >> x = [ 0 0.25*pi 0.5*pi 0.75*pi pi ]
>> y = [ 0; 0 25*pi; 0 5*pi; 0 75*pi; ] y = 0.7854 y 2.3562 3.1416 Multimedia Systems

9 Vectors (Cont’d) Vector Addressing – A vector element is addressed in MATLAB with an integer index enclosed in parentheses. >> x(3) The colon notation may be used to address a block of elements (start : increment : end) start is the starting index, increment is the amount to add to each successive index, and end is the ending index. A shortened format (start : end) may be used if increment is 1. >> x(1:3) ans = NOTE: MATLAB index starts at 1. Multimedia Systems

10 Vectors (Cont’d) Multimedia Systems

11 Array Operations Scalar-Array Mathematics:
Element-by-Element Array-Array Mathematics: Multimedia Systems

12 Matrices A Matrix array is two-dimensional, having both multiple rows and multiple columns, similar to vector arrays: It begins with [, and end with ] spaces or commas are used to separate elements in a row semicolon or enter is used to separate rows. Matrix Addressing: matrixname(row, column) colon may be used in place of a row or column reference to select the entire row or column. Multimedia Systems

13 Matrices (Cont’d) Multimedia Systems

14 Matrices (Cont’d) Multimedia Systems

15 Example, Linear Equations
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16 Plotting Plotting Curves: Multiple Curves: Multiple Figures: Subplots:
plot (x,y) – generates a linear plot of the values of x (horizontal axis) and y (vertical axis). semilogx (x,y) – generate a plot of the values of x and y using a logarithmic scale for x and a linear scale for y semilogy (x,y) – generate a plot of the values of x and y using a linear scale for x and a logarithmic scale for y. loglog(x,y) – generate a plot of the values of x and y using logarithmic scales for both x and y Multiple Curves: plot (x, y, w, z) – multiple curves can be plotted on the same graph by using multiple arguments in a plot command. The variables x, y, w, and z are vectors. Two curves will be plotted: y vs. x, and z vs. w. legend (‘string1’, ‘string2’,…) – used to distinguish between plots on the same graph Multiple Figures: figure (n) – used in creation of multiple plot windows. place this command before the plot() command, and the corresponding figure will be labeled as “Figure n” close – closes the figure n window. close all – closes all the figure windows. Subplots: subplot (m, n, p) – m by n grid of windows, with p specifying the current plot as the pth window Multimedia Systems

17 Plotting (Cont’d) Multimedia Systems

18 Flow Control Multimedia Systems

19 Loops break – is used to terminate the execution of the loop.
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20 M-Files A M-file is a group of MATLAB commands.
MATLAB can open and execute the commands exactly as if they were entered at the MATLAB command window. To run the M-files, just type the file name in the command window. (make sure the current working directory is set correctly) Multimedia Systems

21 User Defined Functions
Add the following command in the beginning of your m- file: function [output variables] = function_name (input variables); Note that the file name should be the same as the function name. Multimedia Systems

22 Images in MATLAB MATLAB can import/export several image formats
BMP (Microsoft Windows Bitmap) GIF (Graphics Interchange Files) HDF (Hierarchical Data Format) JPEG (Joint Photographic Experts Group) PCX (Paintbrush) PNG (Portable Network Graphics) TIFF (Tagged Image File Format) XWD (X Window Dump) MATLAB can also load raw-data or other types of image data Data types in MATLAB Double (64-bit double-precision floating point) Single (32-bit single-precision floating point) Int32 (32-bit signed integer) Int16 (16-bit signed integer) Int8 (8-bit signed integer) Uint32 (32-bit unsigned integer) Uint16 (16-bit unsigned integer) Uint8 (8-bit unsigned integer)

23 Images in MATLAB • Binary images : {0,1} • Intensity images : [0,1] or uint8, double etc. • RGB images : m-by-n-by-3 • Indexed images : m-by-3 color map • Multidimensional images m-by-n-by-p (p is the number of layers)

24 Image import and export
Read and write images in Matlab >> I=imread('cells.jpg'); >> imshow(I) >> size(I) ans = (RGB image) >> Igrey=rgb2gray(I); >> imshow(Igrey) >> imwrite(lgrey, 'cell_gray.tif', 'tiff') Alternatives to imshow >>imagesc(I) >>imtool(I) >>image(I)

25 Images and Matrices How to build a matrix (or image)?
>> B = zeros(3,3) B = >> C = ones(3,3) C = >>imshow(A) (imshow(A,[]) to get automatic pixel range)

26 Image format conversion
Convert between intensity/indexed/RGB to binary format: dither() Convert between intensity format to indexed format: gray2ind() Convert between indexed format to intensity format: ind2gray() Convert between indexed format to RGB format: ind2rgb() Convert a regular matrix to intensity format by scaling: mat2gray() Convert between RGB format to intensity format: rgb2gray() Convert between RGB format to indexed format: rgb2ind() Multimedia Systems

27 Colormaps I = imread (‘lena.bmp’); imshow (I); colormap (cool);
Autumn, bone, colorcube, cool, copper, flag, gray, hot, hsv, jet, pink, prism, spring, summer, white, winter Multimedia Systems

28 Video mov = aviread(filename) mov = aviread(filename, index)
fileinfo = aviinfo(filename) Multimedia Systems

29 Digital Audio Multimedia Systems

30 Audio [road,fs]=wavread('road.wav');
The array road now contains the stereo sound data and fs is the sampling frequency.  This data is sampled at the same rate as that on a music CD (fs=44,100 samples/second). The left and right channel signals are the two columns of the road array:  left=road(:,1); right=road(:,2); Multimedia Systems

31 time=(1/44100)*length(left); t=linspace(0,time,length(left));
plot(t,left) xlabel('time (sec)'); ylabel('relative signal strength') soundsc(left,fs)       % plays left channel as mono  soundsc(right,fs)    % plays right channel mono (sound nearly the same)  soundsc(road,fs)     % plays stereo (ahhh…) Multimedia Systems


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