image_processing_basics.m

%% DSP TUTORIAL -- UNDERSTANDING IMAGE PROCESSING ON MATLAB
% This tutorial gives a beginner level introduction to image processing
% using MATLAB(R) 2013.

%% INTRODUCTION
% Digital Image Processing refers to the manipulation of iamge data which
% is motivated by conversion between Spacial and Frequency domains.
%%
% A _filter_ is a matrix, typically 3x3, 4x4, 5x5 which is
% applied to the input pixels one at a time, resulting in an output pixel
% in the filtererd image.


%% Reading and displaying the image
% imread() and imshow() functions are used to load and display an image
% respectively.

image = imread('image.jpg');
imshow(image);

%% Displaying individually the red, green and blue components.
% WE know that a digital jpeg image is comp;losed of red, blue and green
% components. The loaded image is 3 Dimensional matrix with dimensions
% mxnx3, where m and n are the length and width of the image.

% Displaying red-components
figure(1)
imshow(image(:,:,1));

% Displaying green-components
figure(2)
imshow(image(:,:,2));

% Displaying blue-components
figure(3)
imshow(image(:,:,3));
%% Converting an image to Gray Scale
% A colored image is converted into a grayscale image by simply calling the
% rgb2gray() function.
gray_image = rgb2gray(image);
imshow(gray_image);

%% Using kernel matrices with images -- EDGE DETECTION
%%
% In image processing, many filter operations are applied to in image by
% performing a special operation called convolution with a matrix. this
% matrix is called a KERNEL.
% Kernels are typically 3x3 square matrices, although kernels of size 4x4,
% 5x5 are also used.
% The values stored in a kernel directly relates to the result after
% applying the filter, and filters are characterised solely by kernel
% matrix. For example, the following kernels are used for detecting the
% horizontal and vertical edges in an image.

% Define the Sobel kernels
kernel_horizontal = [1 2 1;0 0 0;-1 -2 -1];
kernel_vertical = [1 0 -1;-2 0 2;-1 0 1];

% Convolve the gray image with Sobel Kernels
M1 = conv2(double(gray_image), double(kernel_horizontal));
M2 = conv2(double(gray_image), double(kernel_vertical));

%%
% double is used because the loaded image was by defauls in Unit8 format,
% which needs to be converted in numbers before processing.
    %% Displaying the horizontal and vertical edges seperately
    figure(4)
    imshow(abs(M1),[]);
    title('horizontal parts');
    
    figure(5)
    imshow(abs(M2),[]);
    title('vertical parts');
    
    
    %% Displaying the normalized vertical and horizontal edges combined
    figure(2);
    imshow((M1.^2+M2.^2).^0.5,[]);