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94 lines
4.1 KiB
Matlab
94 lines
4.1 KiB
Matlab
% INTERPOLATEFT_CENTERED Perform FT interpolation of provided stack of images using FFT so that
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% the center of mass is not modified after the resolution change
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% This function is critical for subpixel accurate up/down sampling
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%
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% imout = interpolateFT_centered(im,downsample,interp_sign)
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%
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% Inputs:
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% **im - Input complex 2D array or stacked 3D array
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% **Npix_new - (2x1 vector) Size of the interpolated array
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% **interp_sign - +1 or -1, sign that adds extra 1px shift. +1 is needed
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% if interpolation is used to downsample phase gradient which is used for
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% unwrapping, otherwise use -1
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% *returns*:
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% ++imout - Output complex 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 ] = interpolateFT_centered(img,Np_new, interp_sign)
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import utils.*
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import math.*
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Np = size(img);
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Np_new = 2+Np_new;
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isReal = isreal(img);
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scale = prod((Np_new-2)) / prod(Np(1:2));
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downsample = ceil(sqrt(1/scale));
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if isa(img, 'gpuArray')
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scale = Garray(scale);
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end
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% apply the padding to account for boundary issues
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img = padarray(img, double([downsample,downsample]), 'symmetric' ,'both');
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% go to the fourier space
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img = fft2(img);
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% apply +/-0.5 px shift
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img = imshift_fft(img, interp_sign*-0.5, interp_sign*-0.5, false);
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% crop in the Fourier space (can be speeded up similarly to example in utils.interpolateFT_ax )
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img = ifftshift_2D(crop_pad(fftshift_2D(img), Np_new));
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% apply -/+0.5 px shift in the cropped space
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img = imshift_fft(img, interp_sign*0.5, interp_sign*0.5, false);
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% return to the real space
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img = ifft2(img);
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% scale to keep the average constant
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img = img*scale;
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% remove the padding
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img = img(2:end-1, 2:end-1,:);
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if isReal
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img = real(img); % preserve complexity
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end
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end
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