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47 lines
1.4 KiB
Matlab
47 lines
1.4 KiB
Matlab
function [pos_x, pos_y, mass, mu, sigma] = center(X, use_shift)
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% -----------------------------------------------------------------------
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% This file is part of the PTYCHOMAT Toolbox
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% Author: Michal Odstrcil, 2016
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% License: Open Source under GPLv3
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% Contact: ptychomat@gmail.com
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% Website: https://bitbucket.org/michalodstrcil/ptychomat
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% -----------------------------------------------------------------------
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% Description: find center of mass of matrix X, calculate variance if
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% needed
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% inputs:
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% X 2D stacked images
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% use_shift, if true, CoM will be calculated relatively to the center
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% of the image, default == true
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if nargin < 2
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use_shift = true;
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end
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[N,M,~] = size(X);
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mass = sum(sum(X));
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xgrid = (1:M);
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ygrid = (1:N)';
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pos_x = (sum(sum(X,1).*xgrid)./mass);
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pos_y = (sum(sum(X,2).*ygrid)./mass);
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if nargout > 3
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mu = [pos_x, pos_y]';
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end
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if nargout == 5
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pos_xx = (sum(sum(X,1).*((1:M)-pos_x).^2)/mass);
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pos_yy = (sum(sum(X,2).*((1:N)-pos_y)'.^2)/mass);
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pos_xy = ((X*((1:M)-pos_x)')'*((1:N)-pos_y)'/mass);
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pos_yx = ((X*((1:M)-pos_x)')'*((1:N)-pos_y)'/mass);
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sigma = [ pos_xx, pos_xy; pos_yx, pos_yy];
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end
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if use_shift
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pos_x = pos_x - M/2-0.5; % defined so that center(ones(N),true) == [0,0]
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pos_y = pos_y - N/2-0.5;
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end
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end
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