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81 lines
3.6 KiB
Matlab
81 lines
3.6 KiB
Matlab
% IMSHEAR_FFT fft-based image shearing function for a stack of images along given axis
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%
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% img_stack = imshear_fft(img_stack, theta, shear_axis)
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%
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% Inputs:
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% **img_stack - stack of 2D images
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% **theta - shear angle, scalar
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% **shear_axis - image axis along which the image will be shared
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% *returns*:
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% ++img - shreared image
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%
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%*-----------------------------------------------------------------------*
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%| |
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%| Except where otherwise noted, this work is licensed under a |
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%| Creative Commons Attribution-NonCommercial-ShareAlike 4.0 |
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%| International (CC BY-NC-SA 4.0) license. |
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%| |
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%| Copyright (c) 2017 by Paul Scherrer Institute (http://www.psi.ch) |
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%| |
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%| Author: CXS group, PSI |
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%*-----------------------------------------------------------------------*
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% You may use this code with the following provisions:
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%
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% If the code is fully or partially redistributed, or rewritten in another
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% computing language this notice should be included in the redistribution.
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%
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% If this code, or subfunctions or parts of it, is used for research in a
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% publication or if it is fully or partially rewritten for another
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% computing language the authors and institution should be acknowledged
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% in written form in the publication: “Data processing was carried out
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% using the “cSAXS matlab package” developed by the CXS group,
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% Paul Scherrer Institut, Switzerland.”
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% Variations on the latter text can be incorporated upon discussion with
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% the CXS group if needed to more specifically reflect the use of the package
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% for the published work.
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%
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% A publication that focuses on describing features, or parameters, that
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% are already existing in the code should be first discussed with the
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% authors.
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%
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% This code and subroutines are part of a continuous development, they
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% are provided “as they are” without guarantees or liability on part
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% of PSI or the authors. It is the user responsibility to ensure its
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% proper use and the correctness of the results.
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function img = imshear_fft(img, theta, shear_axis)
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if theta == 0; return ; end
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assert(any(shear_axis == [1,2]), 'Shear axis has to be 1 or 2' )
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isReal = isreal(img);
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if abs(theta) > 45
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error('Out of valid angle range [-45,45], use rot90 to get into the valid range')
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end
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[M, N, ~] = size(img);
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theta = reshape(theta,1,1,[]); % allow different theta for each slice
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Nx = -sind(theta) .* ifftshift(-fix(M/2):ceil(M/2)-1)/M;
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Ny = tand(theta/2).* ifftshift(-fix(N/2):ceil(N/2)-1)/N;
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Mgrid = 2i*pi*((1:M)'-floor(M/2)) * ones(1,'like',img);
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Ngrid = 2i*pi*((1:N)'-floor(N/2)) * ones(1,'like',img);
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% rotate images by a combination of shears
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switch shear_axis
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case 1, img=ifft(fft(img,[],2).*exp(-Mgrid.*Ny), [],2);
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case 2, img=ifft(fft(img,[],1).*exp( Ngrid.*Nx)',[],1);
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otherwise
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error('Shear axis has to be 1 or 2')
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end
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if isReal
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img = real(img);
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end
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end |