Matlab Tutorial. Yi Gong

Transcription

1 Matlab Tutorial Yi Gong

2 Contact Info Keep an eye on latest announcement on course website Office HFH 3120B M 10am-12pm, W 12pm-2pm, F 3pm-5pm Discussion Fri ygong@umail.ucsb.edu Grading problems refer to reader first Sammay sanmaypatil@cs.ucsb.edu

3 Programming Homework Matlab & turnin CSIL ECI Need csil account matlab and turnin are in /usr/bin turnin is in /usr/bin matlab is in /fs/ece/matlab_r2009a/bin Remote access section8 turnin <foldname or filelist>

4 Prog 1 Due next Wed 5pm function [mean1,mean2] =ProcessImage(filename) function [sd1,sd2] = NoisyImage(filename) Otherwise, write a readme file (not recommended) function should work on all other images too.

5 Prog1 Upate For the first problem, you need to scale the sqrt-ed image value to make the minimum value to be 0.0 and maximum value be 255. It s not only make sure the range is [0,255], but also enlarge the dynamic range - after sqrt, the image s dynamic range shrinked to [0,sqrt(255)]. You need to scale the image value to make the values fill the range from 0~255.

6 Matlab Matlab = Matrix Laboratory Works almost exclusively with matrics. Scalars are just 1x1 matrics; string are 1xn char matrix Weakly dynamically typed programming language - types of variables are implicitly converted. Example: a = 3*2 b = a^2 a =[3; 2] BTW: upper case and lower case are different for variables name

7 The MATLAB Environment MATLAB window components: Workspace > Displays all the defined variables Command Window > To execute commands in the MATLAB environment Command History > Displays record of the commands used File Editor Window > Define your functions

8 More about the Workspace who, whos current variables in the workspace save save workspace variables to *.mat file load load variables from *.mat file clear clear workspace variables

9 row a = [1 0 0 ] or a = [1,0,0] column b = [1; 0; 0] or b=[1 0 0] matrix c= [1 2 3; 4 5 6; 7 8 9] Create Matrix Special matrices: zeros(n,m), ones(n,m), eye(n,m), rand(), randn()

10 Access Matrix Blocks can be operated like scalars as long as reasonable. d = [c c; c c] e = c(1:2, 1:2) % get the 2x2 upper left part of matrix c f = c(:,2) get the 2nd column of c Much efficient than be operated one by one in loops

11 Basic Operations on Matrices All operators in MATLAB are defined on matrices: +, -, *, /, ^, sqrt, sin,cos,,etc, Element-wise operators defined with a preceding dot:.*,./,.^ eg: A.*A size(a) size vector sum(a) columns sums vector sum(sum(a)) sum of all the elements min, max are similar to sum

12 Logical Operators ==, <, >, (not equal) ~=, (not) ~ find( condition ) Returns indexes of A s elements that satisfy the condition

13 Logical Operators (cont.) Example: >>A=[7 3 5; 6 2 1], Idx=find(A<4) A= Idx=

14 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 function [output1,output2] = functionname(input1,input2 ) functionname have to be the same name as.m file outputs need to be assigned value in function

15 Scripts and Functions (cont.) Example: A file called STAT.M: function [mean, stdev]=stat(x) %STAT Interesting statistics. n=length(x); mean=sum(x)/n; stdev=sqrt(sum((x-mean).^2)/n); Above defines a new function called STAT that calculates the mean and standard deviation of a vector (matrix version need some modification). Function name and file name should be the SAME!

16 Visualization and Graphics plot(x,y),plot(x,sin(x)) plot 1D function figure, figure(k) open a new figure hold on, hold off refreshing figure axis([xmin xmax ymin ymax]) change axes title( figure titile ) add title to figure mesh(m_3d) view 2D function

17 Loop and Branch for i = 1:100 for j = 1:100 Isub(i,j) = I(i,j); end end if (b ~= 0) && (a/b > 18.5) %do 1 (% means comment) elseif %do 2 else %do 3 end while is similar

18 Image Processing with MATLAB

19 Images in MATLAB Binary images : {0,1} Intensity images : uint8 [0,255], double [0,1] etc. RGB images : m n 3

20 Image Import and Export Read and write images in Matlab img = imread('apple.bmp'); dim = size(img); figure; imshow(img); imwrite(img, 'output.jpg', jpg');

21 Images and Matrices How to build a matrix (or image)? Intensity Image: o [0, 0] row = 256; col = 256; img = zeros(row, col); img(100:105, :) = 0.5; img(:, 100:105) = 1; figure; imshow(img); Row 1 to 256 Column 1 to 256 o [256, 256]

22 Images and Matrices(cont.) Binary Image: row = 256; col = 256; img = rand(row, col); img = round(img); figure; imshow(img);

23 Image Conversion gray2ind - intensity image to index image im2bw - image to binary im2double convert to [0,1] double, different from double(i), which only convert type. Consider which one you need in your prog1 im2uint8 - image to 8-bit unsigned integers im2uint16 - image to 16-bit unsigned integers ind2gray - indexed image to intensity image mat2gray - matrix to intensity image rgb2gray - RGB image to grayscale rgb2ind Remember - covert RGB image integers to to indexed double before image doing fft

24 More Demo