CODEWITHSUNDEEP
matlabimage-processing
rossy
rossy

Reputation: 29

How to find orientation of image using Fourier transform?

How can i find orientation using fft? Here is the idea (reference paper)

1. Find the fft2 x(u,v)=fft2(x(x,y))

2. ur=sqrt(u.^2+V.^2),theta=atan2(v,u)  

3. X(ur,theta)=x(ur*cos(theta),ur*sin(theta))  

4. power of dft p(ur,theta)=abs(X(ur,theta).^2)  

5. found the angular DFT by summing the power of annual band between radial frequency ur1 and ur2  
A(theta)=sum(p(ur,theta))

My problem is how can I implement the last step? Here is the code that I tried but could not understand the last step. Matlab code:

    t=imread('untitled5.png');
    fontSize=12
    [m,n]=size(t);
    img=fftshift(t(:,:,2));
    g=fft2(img);
    c = g .* conj(g) ;
    d=fft2(c);

image for orienatation

Upvotes: 0

Views: 2506

Answers (1)

Rijul Sudhir
Rijul Sudhir

Reputation: 2132

imgOrg=imread('untitled5.png');
imgGray=rgb2gray(imgOrg);
dft=fft2(imgGray);
dftCentered=fftshift(dft);
ur=abs(dftCentered);
theta=angle(dftCentered);
X_new=ur.*(cos(theta)+(1i.*sin(theta)));
P=abs(X_new).^2;
imshow(mat2gray(log(P)));

Now you have to create masks. Here is a reference for how mask should be. Read Frequency Orientation Page 70

Here is something to start with Pixels between 2 intersecting lines

Create a mask with same dimension as image and multiple it with P and sum the matrix. You will get the A(Theta) for that direction. If first mask is at mask(:,:,1) and if you have 4 masks (mask(:,:,1),mask(:,:,2),mask(:,:,3),mask(:,:,4)). Then rest of the code will be.

for indexTheta=1:4
    A(indexTheta)=sum(sum(P.*mask(:,:,indexTheta)));
end

Now you will have A for four directions. Now you are done.

Upvotes: 3

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