FINDLOCALEXTREMA - Local neighbourhood extrema of a map.

Description
Syntax
Inputs
Property [propertyname propertyvalues]
Outputs
See also
Function implementation

Description

Extract the extrema (min or max) of any multispectral image in local square neigbourhoods and outputs a logical map.

Syntax

   M = FINDLOCALEXTREMA(I);
   M = FINDLOCALEXTREMA(I, ord, win, 'Property', propertyvalue, ... );

Inputs

I : input image of size [X,Y,C], possibly multichannel when C>1. rank : string variable defining the extrema to be computed locally; it is either 'min' or 'max' to compute local minima or maxima resp.

win : width of the window of analysis.

Property [propertyname propertyvalues]

'graph' : parameter defining the implicit graph connectivity assumed when computing the local rank filter; it is either 4 or 8; default: graph=8.

'corr' : string defining the way the channels of the input image are combined in the output extrema map when C>1; it can be:

'forall' if the pixels to be output are the extrema considered separately in the different channels,
'inall' if the pixels are the extrema simultaneously found in all channels
'inone' if the pixels are extrema in one channel at least;

corr is naturally ignored with grayscale images; default: corr='forall'.

Outputs

M : logical output map where extrema are assigned true; depending on the input variable corr (see above), M can be of size (X,Y) (cases 'inall' and 'inone') or of size (X,Y,C) (case 'forall').

Function implementation

function M = findlocalextrema(I,varargin)

parsing parameters

error(nargchk(1, 15, nargin, 'struct'));
error(nargoutchk(1, 1, nargout, 'struct'));

% mandatory parameter
if ~isnumeric(I)
    error('findlocalextrema:inputerror','a matrix is required in input');
end

% optional parameters
p = createParser('FINDLOCALEXTREMA');   % create an instance of the inputParser class.
p.addOptional('ord', 'max', @(x) ischar(x) && any(strcmpi(x,{'min','max'})));
p.addOptional('win',3, @(x)isscalar(x) && isfloat(x) && x>=3);
p.addParamValue('graph',8, @(x)isscalar(x) && (x==4 || x==8));
p.addParamValue('corr',[], @(x)ischar(x)&& ...
    any(strcmpi(x,{'forall','inall','inone'})));

% parse and validate all input arguments
p.parse(varargin{:});
p = getvarParser(p);

setting internal variables

C = size(I,3);

if isempty(p.corr),   p.corr = 'forall';
elseif C==1
    warning('findlocalextrema:inputwarning', 'variable corr ignored with scalar image');
end

main computation

M = findlocalextrema_base(I, p.ord, p.win, p.graph, p.corr);

display

if p.disp
    figure, imagesc(rescale(M,0,1)), axis image off, title('local extrema')
    if ~strcmp(p.corr,'forall'), colormap gray; end;
end

end % end of findlocalextrema