WMEDFILT2 - Weighted median filtering.

Contents

Description

Perform weighted median filtering of a (possibly multispectral) image.

Syntax

   WMI = WMEDFILT2(I,wk);

Inputs

I : input image, possibly multispectral.

wk : kernel defining the neighbourhood and the local weights used for weighted median estimation; a negative weight indicates the position of the central pixel tested, otherwise the kernel is supposed to be square-shaped with odd size and the barycenter is considered.

Output

WMI : weighted median filtered image with same size as the input I each pixel in WMI contains the median value in the neighbourhood of I defined by the non-negative values of wk around the corresponding pixel in I.

References

[Brown84] D.R.K. Brownrigg: "The weighted median filter", Image Processing and Computer Vision, Communications of the ACM, 27(8): 807-818, 1984. http://dl.acm.org/citation.cfm?id=358222&bnc=1

[Yaros94] L. Yaroslavsky: "Local criteria: a unified approach to local adaptive linear and rank filters for image restoration and enhancement", Proc. IEEE ICIP, pp. 517-521, 1994. http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=413624&tag=1

[Yaros96] L. Yaroslavsky: "Local adaptative filters for image restauration and enhancement", LNCIS, vol. 219, pp. 31-39, 1996. http://www.springerlink.com/content/y45n7228700540n2/

See also

Ressembles: MEDIAN, MEDFILT2, ORDFILT2, WORDFILT2. Requires: WMEDFILT2_BASE.

Function implementation

function WMI = wmedfilt2(I,wk)

error(nargchk(2, 2, nargin, 'struct'));
error(nargoutchk(1, 1, nargout, 'struct'));

parsing and checking parameters

if ~isnumeric(I)
    error('wmedfilt2:inputerror','matrice is required in input');
end

p = createParser('WMEDFILT2');   % create an instance of the inputParser class.
p.addRequired('wk', @(x) isequal(round(x),x));

% parse and validate all input arguments
p.parse(wk);
p = getvarParser(p);

internal variables and further checking

C = size(I,3);
[x y c] = size(p.wk);

if ~isequal(round(p.wk),p.wk)
    warning('wmedfilt2:inputwarning',...
        'the input weighting matrix must have integer values');
end

if c~=1 && c~=C
    error('wmedfilt2:inputargument', ...
    'input kernel must have 1 channel or the same number as the input');
end

cpos = find(p.wk<0,1,'first');
if isempty(cpos) && (x~=y || mod(x,2)~=1)
    error('wmedfilt2:inputargument',...
        'input kernel must be square shaped with odd size');
end

main processing

WMI = wmedfilt2_base(I, p.wk);

display

if p.disp
    figure, imagesc(rescale(WMI,0,1)), axis image off;
    if C==1,  colormap gray; end;
    title('weighted median filtered image');
end

end % end of wmedfilt2