![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)](https://image.slidesharecdn.com/intromatlab-131004113053-phpapp01/85/Intro-matlab-4-320.jpg)
![Images and Matrices
• How to build a matrix (or image)?
>> A = [ 1 2 3; 4 5 6; 7 8 9 ];
A = 1 2 3
4 5 6
7 8 9
>> B = zeros(3,3)
B = 0 0 0
0 0 0
0 0 0
>> C = ones(3,3)
C = 1 1 1
1 1 1
1 1 1
>>imshow(A) (imshow(A,[]) to get automatic pixel range)](https://image.slidesharecdn.com/intromatlab-131004113053-phpapp01/85/Intro-matlab-6-320.jpg)
![Logical Conditions
• equal (==) , less than and greater than (< and >), not equal (~=) and not (~)
• find(‘condition’) - Returns indexes of A’s elements that satisfies the
condition.
>> [row col]=find(A==7)
row = 3
col = 1
>> [row col]=find(A>7)
row = 3
3
col = 2
3
>> Indx=find(A<5)
Indx = 1
2
4
7
A =
12 3
45 6
7 8 9](https://image.slidesharecdn.com/intromatlab-131004113053-phpapp01/85/Intro-matlab-9-320.jpg)
![Working with M-Files
• Create a new empty m-file
function B=test(I)
[row col]=size(I)
for r=1:row
for c=1:col
if r==c
A(r, c)=1;
elseif abs(r-c)==1
A(r, c)=2;
else
A(r, c)=0;
end
end
end
B=A;](https://image.slidesharecdn.com/intromatlab-131004113053-phpapp01/85/Intro-matlab-14-320.jpg)
Intro matlab
- 1. Introduction to MATLAB and image processing Amin Allalou [email protected] Centre for Image Analysis Uppsala University Computer Assisted Image Analysis April 4 2008
- 2. MATLAB and images • The help in MATLAB is very good, use it! • An image in MATLAB is treated as a matrix • Every pixel is a matrix element • All the operators in MATLAB defined on matrices can be used on images: +, -, *, /, ^, sqrt, sin, cos etc.
- 3. 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)
- 4. 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)
- 5. Image import and export • Read and write images in Matlab >> I=imread('cells.jpg'); >> imshow(I) >> size(I) ans = 479 600 3 (RGB image) >> Igrey=rgb2gray(I); >> imshow(Igrey) >> imwrite(lgrey, 'cell_gray.tif', 'tiff') Alternatives to imshow >>imagesc(I) >>imtool(I) >>image(I)
- 6. Images and Matrices • How to build a matrix (or image)? >> A = [ 1 2 3; 4 5 6; 7 8 9 ]; A = 1 2 3 4 5 6 7 8 9 >> B = zeros(3,3) B = 0 0 0 0 0 0 0 0 0 >> C = ones(3,3) C = 1 1 1 1 1 1 1 1 1 >>imshow(A) (imshow(A,[]) to get automatic pixel range)
- 7. Images and Matrices • Accesing image elements (row, column) >> A(2,1) ans = 4 • : can be used to extract a whole column or row >> A(:,2) ans = 2 5 8 • or a part of a column or row >> A(1:2,2) ans = 2 5 X Y A = 12 3 45 6 7 8 9
- 8. Image Arithmetic • Arithmetic operations such as addition, subtraction, multiplication and division can be applied to images in MATLAB – +, -, *, / performs matrix operations >> A+A ans = 2 4 6 8 10 12 14 16 18 >> A*A ans = 30 36 42 66 81 96 102 126 150 • To perform an elementwise operation use . (.*, ./, .*, .^ etc) >> A.*A ans = 1 4 9 16 25 36 49 64 81 A = 12 3 45 6 7 8 9
- 9. Logical Conditions • equal (==) , less than and greater than (< and >), not equal (~=) and not (~) • find(‘condition’) - Returns indexes of A’s elements that satisfies the condition. >> [row col]=find(A==7) row = 3 col = 1 >> [row col]=find(A>7) row = 3 3 col = 2 3 >> Indx=find(A<5) Indx = 1 2 4 7 A = 12 3 45 6 7 8 9
- 10. Flow Control • Flow control in MATLAB - if, else and elseif statements (row=1,2,3 col=1,2,3) if row==col A(row, col)=1; elseif abs(row-col)==1 A(row, col)=2; else A(row, col)=0; end A = 1 2 0 2 1 2 0 2 1
- 11. Flow Control • Flow control in MATLAB - for loops for row=1:3 for col=1:3 if row==col A(row, col)=1; elseif abs(row-col)==1 A(row, col)=2; else A(row, col)=0; end end end A = 1 2 0 2 1 2 0 2 1
- 12. Flow Control • while, expression, statements, end Indx=1; while A(Indx)<6 A(Indx)=0; Indx=Indx+1; end A = 12 3 45 6 7 8 9 A = 0 2 3 0 5 6 7 8 9
- 13. Working with M-Files • M-files can be scripts that simply execute a series of MATLAB statements, or they can be functions that also accept input arguments and produce output. • MATLAB functions: – Are useful for extending the MATLAB language for your application. – Can accept input arguments and return output arguments. – Store variables in a workspace internal to the function.
- 14. Working with M-Files • Create a new empty m-file function B=test(I) [row col]=size(I) for r=1:row for c=1:col if r==c A(r, c)=1; elseif abs(r-c)==1 A(r, c)=2; else A(r, c)=0; end end end B=A;