added alternative stripe removal function

1 files changed, 54 insertions, 0 deletions

diff --git a/striperemoval.m b/striperemoval.m
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+function [img_cleaned]=striperemoval(img, varargin)
+% Cleans an image from the stripes produced by interference fringes.
+%  img - image with stripes to be removed
+%  varargin - not used, it is here for compatibility
+% By Eugeniy E. Mikhailov 2014/11/25
+% 
+% be aware of "slow" spatial stripes their Fourier components will overlap with Gaussian.
+% Such parallel fringes appears like strong isolated peaks in the Fourier transformed image.
+% What is even nice they appear symmetrical with respect to origin but not symmetrical to 
+% fold
+%
+%                 ^
+%                 |
+%               * |
+%                 |
+%                oOo
+%   -------------O0O-------------->
+%                oOo <- gaussian beam fft
+%                 |
+%                 | * <- stripe fft peak
+%                 |
+%
+%
+% so it easy to clean them, especially if their spatial frequency is high.
+%
+
+img_fourier=fftshift(fft2(img)); % move to Fourier space
+
+imgfa= abs(img_fourier); % amplitude of Fourier components
+imgfa= imgfa/max(imgfa(:)); % normalized amplitudes
+
+[Ny, Nx] = size (img);     % image size
+
+mask = img_fourier.*0;
+for xi = 1:Nx
+    % strictly speaking one of dimensions can be only half sampled due to symmetry of the mask
+    for yi = 1:Ny
+        xr = Nx - xi + 1; % reflected x
+        yr = Ny - yi + 1; % reflected y
+        mt = imgfa( yi, xi ); % test point
+        ms = imgfa( yr, xr ); % symmetrical point with respect to origin 
+        mr = imgfa( yi, xr ); % symmetrical point with respect to Y axis (right)
+        md = imgfa( yr, xi ); % symmetrical point with respect to Y axis (down)
+
+        m = ( mt + ms ) - ( mr + md ); % high value to the points shown at figure
+        m = m/max([mt, ms, mr, md]);
+        mask(yi,xi) = m;
+    end
+end
+
+threshold = max(mask(:))/2;
+mask = mask < threshold; % points due to stripes need to be removed
+
+img_cleaned = abs( ifft2(ifftshift(img_fourier.*mask)) );