BWSHRINK1D - Shrinking of 1D binary signals.

Contents

Description

Shrink a 1D binary signal by reducing sequence of points with true value to isolated true points. Similarly to BWMORPH (which it uses when the Image toolbox is available), it removes points so that a true sequence shrinks to a point halfway of it.

Syntax

     S = BWSHRINK1D(X);

Input

X : 1D binary signal; if not binary, it is converted using LOGICAL.

Output

S : output shrinked signal with same size as the input X.

See also

Requires: BWMORPH, DIFF, FIND.

Function implementation

function S = bwshrink1D(X)

check the inputs

if ~islogical(X),  X = logical(X);  end

if nb_dims(X)~=1,
    error('bwshrink1D:errorinput',...
        '1D signals required in input - use BWMORPH when available');
end

in the case the Image toolbox is available, simply call the morphological function BWMORPH

if ~isempty(ver('images'))
    S = bwmorph(X, 'shrink', Inf);
    return
end
% else...

initialize the output

S = false(size(X));

characterize the logical changes in sequences

x1 = [X(1); diff(X(:))];
x2 = [-diff(fliplr(X(:))); X(end)];

extract those isolated 'true' points that are shrinked on themselves

isolated = find(x1==1 & x2==1);
S(isolated) = true;

extract the starting and ending points of a 'true' sequence

x1(isolated) = 0;  x1 = find(x1==1);
x2(isolated) = 0;  x2 = find(x2==1);

shrink the sequence to its central point

S(ceil((x1+x2)/2)) = true; % with CEIL, returns the same output as BWMORPH
% S(floor((x1+x2)/2)) = true;

final output

S = reshape(S,size(X));

end % end of bwshrink1d