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+math/get_img_grad.m

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+% get vertical and horizontal gradient of the image using FFT
+%
+%  [dX, dY] = get_img_grad(img, axis, split)
+%
+% Inputs:
+%   **img   - stack of images 
+%   **split - split for GPU fft_partial 
+%   **axis  - direction of the derivative 
+% *returns*
+%  ++[dX, dY]  - image gradients 
+
+%*-----------------------------------------------------------------------*
+%|                                                                       |
+%|  Except where otherwise noted, this work is licensed under a          |
+%|  Creative Commons Attribution-NonCommercial-ShareAlike 4.0            |
+%|  International (CC BY-NC-SA 4.0) license.                             |
+%|                                                                       |
+%|  Copyright (c) 2017 by Paul Scherrer Institute (http://www.psi.ch)    |
+%|                                                                       |
+%|       Author: CXS group, PSI                                          |
+%*-----------------------------------------------------------------------*
+% You may use this code with the following provisions:
+%
+% If the code is fully or partially redistributed, or rewritten in another
+%   computing language this notice should be included in the redistribution.
+%
+% If this code, or subfunctions or parts of it, is used for research in a 
+%   publication or if it is fully or partially rewritten for another 
+%   computing language the authors and institution should be acknowledged 
+%   in written form in the publication: “Data processing was carried out 
+%   using the “cSAXS matlab package” developed by the CXS group,
+%   Paul Scherrer Institut, Switzerland.” 
+%   Variations on the latter text can be incorporated upon discussion with 
+%   the CXS group if needed to more specifically reflect the use of the package 
+%   for the published work.
+%
+% A publication that focuses on describing features, or parameters, that
+%    are already existing in the code should be first discussed with the
+%    authors.
+%   
+% This code and subroutines are part of a continuous development, they 
+%    are provided “as they are” without guarantees or liability on part
+%    of PSI or the authors. It is the user responsibility to ensure its 
+% 
+
+
+
+function [dX, dY] = get_img_grad(img, axis, split)
+    import math.* 
+    
+    if nargin < 3 || isempty(split)
+        split = 1;
+    end
+    isReal = isreal(img); 
+    Np = size(img);
+    if nargin < 2 || any(axis == 2)
+        X = 2i*pi*ifftshift(-fix(Np(2)/2):ceil(Np(2)/2)-1)/Np(2);
+        dX = bsxfun(@times,fft_partial(img,2,1,split,false),X);
+        dX = fft_partial(dX,2,1,split,true);
+        if isReal; dX = real(dX);end 
+    end
+    if nargout == 2 || (nargin > 1 && any(axis == 1))
+        Y = 2i*pi*ifftshift(-fix(Np(1)/2):ceil(Np(1)/2)-1)/Np(1);
+        dY = bsxfun(@times, fft_partial(img,1,2,split,false),Y.');
+        dY = fft_partial(dY,1,2,split,true);
+        if isReal; dY = real(dY);end 
+        if nargout == 1; dX = dY; end
+    end
+end
+