1. Introduction to MATLAB CS 534 Fall 2015

2. What you'll be learning today ●MATLAB basics (debugging, IDE) ●Operators ●Matrix indexing ●Image I/O ●Image display, plotting ●A lot of demos ●...

3. Who am I Jia-Shen Boon 文嘉绅

4. Who am I

5. Contact Office: 1302CS E-mail: boon@cs.wisc.edu Office hours: Tuesdays and Thursdays 4:00 - 5:00 p.m., and by appointment

6. Accessing MATLAB Get a local copy from the Campus Software LibraryCampus Software Library Also available in the Linux and Windows labs Also remotely accessible via ssh On Linux, type matlab into the terminal

7. What's great about MATLAB Matrices are treated as 1st class citizens Effortless to inspect images and plots

8. What's not so great about MATLAB Data structures besides matrices can feel like 2nd class citizens Proprietary ($$) Syntax sometimes not as elegant as other dynamically typed languages

9. Tip #1: Google is your friend.

10. MATLAB basics

11. Your first MATLAB command Arithmetic operators + - * / Assignment operator = >> total = 1 + 1; 1. MATLAB computes what's 1 + 1 2. Value from (1) is assigned to this variable 3. Semicolon suppresses output

12. MATLAB IDE COMMAND WINDOW Where you type commands Workspace List of your current variables Command History List of previous commands Current Path Filespace

13. Demo

14. What is a matrix? 534534 3 6 8 1 2 3 4 5 6 3x1 vector 1x3 vector 2x3 matrix MxNxP matrix Terms: row, column, element, dimension

15. What is a matrix? 1 2 3 4 5 6 First dimension Second dimension

16. What is a matrix? 24 72 78 236 252 255 An RGB image is a 3D MxNx3 matrix

17. The "layers" in a color image are often called channels red channelblue channelgreen channel

18. Expliciting defining a matrix >> A = [1 2 3; 4 5 6] A = 1 2 3 4 5 6 Bonus: you can define a matrix using other matrices too! What's the output of the following? a = [1 2]; b = [a 3 4]; c = [5 6 a; b]; disp(c); semicolon separates rows

19. Expliciting defining a matrix (cont'd) >> A = 1 : 5 A = 1 2 3 4 5 >> A = 1 : 2 : 10 A = 1 3 5 7 9 Colon creates regularly spaced vectors increment start valueend value

20. Demo

21. More arithmetic operators + Addition - Subtraction * Matrix Multiplication ^ Matrix Power ' Transpose \ Left Matrix Division (Solves A*x=B) / Right Matrix Division (Solves x*A=B).* Element by Element Multiplication./ Element by Element Division.^ Element by Element Power

22. How Operations Work 3 1 5 6 B = 1 2 3 4 A = 4 3 8 10 A+B = -2 1 -2 A-B = 13 29 27 A*B = 7 10 15 22 A^2 = solves A*x = B -.3077.3846.1538.6923 A/B = -1 4 2 1.5 A\B = solves x*A = B

23. Element-wise operations 3 2 15 24 A.* B =.333 2.6.666 A./ B = 1 2 243 4096 A.^ B = 3 1 5 6 B = 1 2 3 4 A =

24. Transpose 1 3 5 7 9 11 13 15 C = 1 5 9 13 3 7 11 15 C’ =

25. Demo

26. size() >> A = [1 2 3; 4 5 6]; >> size(A, 1) ans = 2 >> size(A, 2) ans = 3 1 2 3 4 5 6 A asks for first dimension asks for second dimension

27. size() cont'd >> A = [1 2 3; 4 5 6]; >> [height, width] = size(A) height = 2 width = 3 1 2 3 4 5 6 A

28. Matrix indexing A(2, 3) Element on 2nd row, 3rd column Note: indexing starts from 1, not zero! 1 2 3 4 5 6

29. Matrix indexing (cont'd) A(2, :) Returns 2nd row A(:, 3) Returns 3rd column 1 2 3 4 5 6

30. Matrix indexing (cont'd) >> A = [1 2 3; 4 5 6]; >> A(:, 2:end) ans = 2 3 5 6 Returns concatenation of 2nd, 3rd, …, last column 1 2 3 4 5 6

31. Matrix indexing (cont'd) >> A = [1 2 3; 4 5 6]; >> A(:, [1 end 1]) ans = 1 3 1 4 6 4 Returns concatenation of 1st, last and 1st column 1 2 3 4 5 6 Bonus: there's other ways to index a MATLAB matrix! Google 'linear indexing MATLAB' or 'logical indexing MATLAB'!

32. Indexing rules apply to 3D matrices too A(2, 4, 3) Element on 2nd row, 4th column of the 3rd channel 1 4 2 8 3 7 9 1 4 5 6 3

33. == is equal to = less/greater than ~ not ~= not equal to & logical AND | logical OR && short-circuit AND || short-circuit OR Logical operators

34. Flow control

35. Instead of using brackets, MATLAB uses “end” end keyword for(int a=0;a<=10;a++){ if( a>3){... … } C for (a=0:10) if (a>3)... … end MATLAB

36. if/elseif/else if (boolean) … elseif (boolean) … else … end Notice elseif is one word

37. while -loop while expression statement end A = 0; while A < 5 disp(A); A = A + 1; end

38. for index = values statements end Note: for- "condition" overwrites changes to index within the loop! for -loop

39. for A = 1 : 2 : 8 disp(A); end for -loop (cont'd) Bonus: values can be a 2D matrix too! What is the output of the following? for A = [1 2 3; 4 5 6]; disp(A); end;

40. Tip #2: Think in terms of matrices.

41. Time Cost Comparison Loop vs. No Loop A = rand(1000,1000);B = rand(1000,1000); for i = 1:size(A,1), for j = 1:size(A,2), C(i,j) = A(i,j) + B(i,j); end Using loop: Elapsed time is 1.125289 seconds.

42. Time Cost Comparison(cont.) Loop vs. no loop C = A + B Elapsed time is 0.002346 seconds. Try to take advantage of matrix/vector structure whenever possible

43. MATLAB file types

44. There's two types of.m files ●Matlab code is saved in.m files ●Function.m files ○Contain a function definition ○One function per file ○FILE NAME MUST MATCH FUNCTION NAME ●Script.m files ○Contain a list of commands ○Can be named anything ○Often used as drivers for functions you have implemented ○Kind of like main in other languages

45. Writing MATLAB functions ●Structure of a MATLAB function ●Functions Can Return Multiple values ●Make sure you initialize your return variables function returnVal = FunctionName (input1,input2) %Adds two numbers returnVal = input1+input2; end function [return1, return2] = FunctionName (input1,input2) return1 = input1+input2; return2= 0; end

46. How do these two files behave differently? %average1.m total = x + y; average = total / 2; %average2.m function average = average2(x, y) total = x + y; average = total / 2;

47. Matrices are effectively passed into functions "by value" %my_script.m vector = [6 3 2 5 4 1]; disp(vector) % (1) sort(vector); disp(vector) % same output as (1)

48. Debugging

49. Click along this column to set/remove breakpoints Check this option for the program to pause once an error occurs Click this to run program. Program pauses at checkpoints, if there's any. Before you enter debugging mode

50. Debugging mode works like any other IDE

51. Data types

52. Important data types logical true/false uint8 8-bit unsigned integer double 64-bit double-precision floating point single 32-bit single-precision floating point There's also uint16, uint32, int8, int16...

53. Be aware of your return types! imread() imfilter()

54. Be aware of your argument types! interp2() imhist()

55. Is there anything wrong with this script? im_original = imread('lena_gray.jpg'); [Xq, Yq] = meshgrid(0.5:99.5, 0.5:99.5); im_interp = interp2(im_original, Xq, Yq);

56. Demo

57. Images

58. Generic image processing script filename = 'badgers.jpg'; im_orig = imread(filename); im_processed = my_func(im_orig); figure; imshow(im_orig); figure; imshow(im_processed); imwrite(im_processed, 'hw.jpg');

59. Important image related functions imread Read image from disk imwrite Write image to disk figure Create new figure imshow Display image im2double Convert image datatype to double im2uint8 Convert image datatype to uint8

60. Histogram of each channel

61. im = imread('badgers.jpg'); for channel = 1:3 subplot(2, 3, channel); imshow(im(:, :, channel)); subplot(2, 3, channel + 3); imhist(im(:, :, channel)); end imhist expects a 2D matrix!

62. subplot() squeezes more into a figure subplot(m, n, p); 1 4 2 5 3 6 p is based on an m x n grid p determines location of this subplot; it's an index in row-major order

63. Useful MATLAB "hacks"

64. Problem - too many windows

65. Solution - dock figures set(0, 'DefaultFigureWindowStyle', 'docked')

66. How to time your code tic; % stopwatch starts here %-- Do some stuff here --% toc; % print time elapsed since tic

67. disp() without newline %Script disp('newline always included.'); fprintf('No newline here.'); fprintf(' Here is a newline.\n');

68. Reference https://www.google.com/ https://courses.engr.illinois.edu/cs445/fa2015/le ctures/Useful%20Functions%20in%20Matlab.p dfhttps://courses.engr.illinois.edu/cs445/fa2015/le ctures/Useful%20Functions%20in%20Matlab.p df MATLAB cheat sheet https://goo.gl/AZBlChhttps://goo.gl/AZBlCh This presentation