BASICS OPERATION OF IMAGE PROCESSING WITH MATLAB

DIGITAL SIGNAL PROCESSING

 BASICS OPERATION OF IMAGE PROCESSING WITH MATLAB

INTRODUCTION:

Digital image processing is transforming digital information representing images.

Image Processing Toolbox: The Image Processing Toolbox is a collection of functions that extend the capabilities of the MATLAB’s numeric computing environment. The toolbox supports a wide range of image processing operations.

MATLAB can import/export several image formats such as BMP (Microsoft Windows Bitmap), GIF (Graphics Interchange Files) and JPEG (Joint Photographic Experts Group) etc.

IMAGES IN MATLAB:

• Binary images: {0, 1}

• Intensity images: [0, 1] or uint8, double etc.

• RGB images: m × n × 3

Images and Matrices How to build a matrix (or image)

Example 1: Intensity Image:

row = 256;

col = 256;

img = zeros(row, col);

img(100:105, :) = 0.5;

img(:, 100:105) = 1;

figure;

imshow(img);

Example 2: Binary Image:

row = 256;

col = 256;

img = rand(row, col);

img = round(img);

figure;

imshow (img);

Basic commands of image processing

Imread

A = imread (filename, fmt) reads a gray scale or true color image named filename into A. If the file contains a gray scale intensity image, A is a two dimensional array. If the file contains a true color (RGB) image, A is a three dimensional (m by n by 3) array.

Note: when you read image you have to give the path of drive where image is placed along with image name and format.

A=imread('drive:/ folder_name/image_name')

Rotation:

B = imrotate (a,angle)

a is your image.

ANGLE is the angle (in degrees) you want to rotate your image in the counter clockwise direction.

Edge Tracing

b=rgb2gray (a); % convert to gray.

WE can only do edge tracing for gray images.

edge(b,'prewitt');

edge(b,'sobel');

edge(b,'sobel','vertical');

edge(b,'sobel','horizontal');

Scaling:

imresize Resizes the image.

B = imresize (A, M) returns an image that is M times the size of A. If M is between 0 and 1.0, B is smaller than A. If M is greater than 1.0, B is larger than A.

B = imresize (A, [MROWS MCOLS]) returns an image of size MROWS by MCOLS.

If the specified size does not produce the same aspect ratio as the input image has, the output image is distorted.

Note: you can check the size of image using command “size”.

Export image:

To display image we use the following command

imshow (a)

and to write an image we use command

 imwrite (a,'filename.format')

EXERCISE:

1. Generate the image that is reverse of example 1 (convert black area of image to white and white area to black).

row = 256;

col = 256;

img = ones(row, col);

img(100:105, :) = 0;

img(:, 100:105) = 0.5;

figure

imshow(img)

2. Read any image using “imread” and apply basic image processing commands studied and show the output image for each command.

READING IMAGE:

A=imread('logo.jpg')

figure

imshow(A)

ROTATE:

B=imrotate(A,60)

figure

imshow(B)

EDGE TRACING (Sobel):

C=rgb2gray(A)

D=edge(C,'sobel')

figure

imshow(D)

EDGE TRACING (Prewitt):

C=rgb2gray(A)

D=edge(C,'prewitt')

figure

imshow(D)

SCALING:

B=imresize(A,1/2)

figure

imshow(B)

3. Run the following code.

ima = zeros(100,100);

for  i = 1:100

for  j = 1:100

ima(i,j) = i+j;

end

end

imagesc(ima)