数字图像处理之作业2

%This script shows how to perform linear filtering directly in the Fourier domain.
%By Li Jiechu 1252853, codes for homework 2 ,programming 1.

%imread an image , use rgb2gray if it is necessary
Image = imread('C:\Users\asus\Desktop\LIHYU作业\homework2\baby.jpg');
%Image = rgb2gray(Image);
[rows,colums] = size(Image);

%Choose test mode:
% default:centered the image and surrounded it by a border of zeros
mode = 1;
% Image padding:the Image locates in the Top,Left Corner with a border of zeros surrounded
% mode = 2;

%Step1: image padding
if(2 == mode)
ImagePadded = padarray(Image,[rows,colums],0,'post');  %put the image on left,top corner
else
ImagePadded = padarray(Image,[rows/2,colums/2],0,'both');%put the image on center
end

figure(1);
subplot(2,2,1),imshow(Image),title('Original Picture');
if(2 == mode)
subplot(2,2,2),imshow(ImagePadded),title('Image Padded in Corner');
else
subplot(2,2,2),imshow(ImagePadded),title('Image Padded in Center');
end

[m,n]=size(ImagePadded);

% Step 2: Multiply fp(x,y) by (-1)^(x+y) to center its transform
% [m,n]=size(ImagePadded);
% for i = 1:m
%     for j = 1:n
%     ImagePadded(i,j) = ImagePadded(i,j)*((-1)^(i+j));
%     end
% end

% Step 3: Discrete Fourier Transform,DFT
J=fftshift(fft2(ImagePadded));
subplot(2,2,3),imshow(log(abs(J)),[]),title('frequency spectrum');

% Step 4: construct a low-pass filter in the Fourier domain
% Let D0 = 50,We can change it here,Ideal Low-Pass filter;
D0=50;
result = zeros(m,n);
rows_center = fix(m/2);
cols_center = fix(n/2);
for i = 1:m
for j = 1:n
d = sqrt((i-rows_center)^2+(j-cols_center)^2);
if(d<=D0 )
D = 1;
else
D = 0;
end
result(i,j) = J(i,j)* D;
end
end

% Step 5: go back to the spatial domain
result = ifftshift(result);
J2 = ifft2(result);
J3 = uint8(real(J2));

% Step 6:
% for i = 1:m
%     for j = 1:n
%     J3(i,j) = J3(i,j)*((-1)^(i+j));
%     end
% end

%extract the final processed result
if(2 == mode)
subplot(2,2,4),imshow(J3(1:rows,1:colums)),title('Final Result');
else
subplot(2,2,4),imshow(J3(rows/2:3*rows/2,colums/2:3*colums/2)),title('Final Result');
end

% -----------------------------------------------------------------------
%            The following are some notes I take in this program.       |
% -----------------------------------------------------------------------
% -----------------------------------------------------------------------
%                          1.About padarray                             |
% -----------------------------------------------------------------------
% B = padarray(A,PADSIZE,PADVAL,DIRECTION) pads A in the direction;
% String values for DIRECTION
% 'pre'         Pads before the first array element along each dimension .
%
% 'post'        Pads after the last array element along each dimension.
%
% 'both'        Pads before the first array element and after the
%               last array element along each dimension.
% --------------------
4000
---------------------------------------------------
%                          2.My own padarray                            |
% -----------------------------------------------------------------------
%I also write my personal padarray function and test it after.
%Just see the mypadarray.m and TestMyPadaray.m including in my homework
% -----------------------------------------------------------------------