a brief introduction to matlab digital image processing 2014 fall ntu

A Brief Introduction to MATLAB

Digital Image Processing 2014 Fall NTU

Outline• MATLAB overview• Matrix• 2-D plotting• 3-D plotting• Image Processing• more about MATLAB• Reference

Outline• MATLAB overview• Matrix• 2-D plotting• 3-D plotting• Image Processing• more about MATLAB• Reference

MATLAB• NTU AppShare (臺大雲端軟體運算銀行 )

– Windows & IE

• https://app.ntu.edu.tw/vdiportal/

MATLAB interface

basic operation

variables• English alphabet, number, underline

– first word must be English alphabet– variable length <= 32 characters

• variables need not be previously declared (default double)

• comments– %

operators• arithmetic operators

– +, -, *, /, ^

• relational operators– ==, ~=, >, >=, <, <=

• logical operators– &, |, ~

• bitwise operators– bitand, bitor, bitxor

flow control• conditional control– if-else– switch

• loop control– for– while– continue

script

• or type “edit filename.m” to create a script from command window

Click to create a new script

Outline• MATLAB overview• Matrix• 2-D plotting• 3-D plotting• Image Processing• more about MATLAB• Reference

matrix creation• row vector– R = [7 8 9 10];– R = [7, 8, 9, 10];

• column vector– C = [7; 8; 9; 10];

• build vector fast– start:step:end– linspace(start, end, num);

extract sub-matrix• A = [1 2 3 4; 5 6 7 8; 9 10 11 12];• B = A(1, 2:4);• C = A(2:3, 2:3);• D = A([1 3], [1 2 3]);

1 2 3 4

5 6 7 8

9 10 11 12

1 2 3 4

1

2

3

Matrix operations• add • Scalar

Matrix operation(Cont’d)• matrix multiplication • array multiplication

Outline• MATLAB overview• Matrix• 2-D plotting• 3-D plotting• Image Processing• more about MATLAB• Reference

2-D plotting• Example 1： plot sin(x) and cos(x) over [0, 2]

subplot• Example 2： create figure with multiple graphs

Axis control• Axis control example：

histogram• hist(data)： histogram plot– data = randn(1000, 3);– hist(data, 20);

Outline• MATLAB overview• Matrix• 2-D plotting• 3-D plotting• Image Processing• more about MATLAB• Reference

3-D plotting• Example 1： mesh graph

3-D plotting (Cont’d)• Example 2： surface graph

3-D plotting (Cont’d)• Example 3： 3-d curve

Outline• MATLAB overview• Matrix• 2-D plotting• 3-D plotting• Image Processing• more about MATLAB• Reference

overview• Basic commands：– img = imread(‘lena.jpg’, ‘jpg’);– imwrite(img, ‘my_lena.jpg’, ‘jpg’);– imfinfo(‘lena.jpg’)– image(img);

Image load and display

image scale• imresize(img, scale) – resize image

image rotation• I2 = imrotate(I, 60, ‘nearest’);• I3 = imrotate(I, 60, ‘bilinear’);

Nearest interpolation Bilinear interpolation

Original image

filter• h1 = fspecial(‘laplacian’);• f1 = filter2(h1, double(f)/255);• h2 = fspecial(‘sobel’);• f2 = filter2(h2, double(f)/255);

laplacian filter sobel filter

original image

edge detection• f3 = egde(f, ‘sobel’);• f4 = edge(f, ‘canny’);

edge detection by sobel method edge detection by canny method

original image

Outline• MATLAB overview• Matrix• 2-D plotting• 3-D plotting• Image Processing• more about MATLAB• Reference

more about MATLAB• more on, more off： control paged output for

command window• help function_name： help for functions in

command window• lookfor keyword： search for keyword in all

help entries

Outline• MATLAB overview• Matrix• 2-D plotting• 3-D plotting• Image Processing• more about MATLAB• Reference

reference• Mathworks document• Mathworks forum• Tutorial from Jyh-Shing Roger Jang