CANNYEDGE - Wrapping function for EDGE, CANNYEDGES and CANNYEDGEMAP.

Contents

Description

Nothing else than a wrapping function calling either EDGE, CANNYEDGES or CANNYEDGEMAP, written for convenience (and consistency with the other edge detection methods implemented in functions EDGE<METHOD>).

Syntax

   edgemap = CANNYEDGE(I,sigma);
   [edgemap, mag, or] = CANNYEDGE(I, sigma, ...
                             'Property', propertyvalue, ...);

Inputs

I : input image.

sigma : optional standard deviation of the Gaussian filter used for smoothing of the image; default: sigma=1.

Property [propertyname propertyvalues]

'der' : optional string storing the method used: 'edge' (or 'matlab'), 'vista', 'kovesi', or any of the other options used by GRDSMOOTH: 'fast', 'conv', 'fleck', 'opt', 'tap5', 'tap7', 'sob', 'prew', 'opt', 'circ', 'ana' or 'lue'; default: der='edge'.

'reduce' : logical value or string defining the way the different channels of a multispectral image are combined into the output edge map (see CANNYEDGE_BASE); it can be either:

in true case, it is set to 'sum'; default: reduce=false, ie. no 'combination' is used, a multichannel map is output; this parameter is naturally ignored when I is a scalar image.

'hyst' : vector [low high] setting low and high hystheresis threshold values with 0<=low<high<1 used with der='edge'; default: hyst=[], and the threshold values are chosen automatically (see EDGE).

'samp' : to perform (* samp) interpolation of the input image to avoid aliasing; default: samp=1.

Outputs

edgemap : logical map of detected edges.

mag, or : optional output matrices storing the magnitude and orientation of the estimated gradient field.

Reference

[Canny86] J.F. Canny: "A computational approach to edge detection", IEEE Trans. on Pattern Analysis and Machine Intelligence, 8(6):679-698, 1986. http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=4767851&tag=1

See also

Ressembles: CANNYEDGES, EDGECORNER, CANNYEDGEPROD, ROTHWELLEDGE, CONGRUENCYEDGE, COMPASSEDGE, ANISOEDGE, ELDERZUCKEREDGE, KOETHEDGE, SDGDEDGE, PETROUEDGE, CANNYEDGEPROD, GRDSMOOTH_BASE. Requires: CANNYEDGE_BASE.

Function implementation

function [edgemap,varargout] = cannyedge(I,varargin)

parsing parameters

error(nargchk(1, 18, nargin, 'struct'));
error(nargoutchk(1, 3, nargout, 'struct'));

if ~isnumeric(I)
    error('cannyedge:inputparameter','a matrix is required in input');
end

p = createParser('CANNYEDGE');
p.addOptional('sigma', 1, @(x)isscalar(x) && x>=0.05);
p.addParamValue('der', 'matlab', @(x)ischar(x) && ...
    any(strcmpi(x,{'edge','matlab','vista','kovesi','fast','conv','fleck', ...
    'opt','tap5','tap7','sob','prew','opt','circ','ana','lue'})));
p.addParamValue('reduce', false, @(x)islogical(x) || ...
    (ischar(x) && any(strcmpi(x,{'igray','imax','isum','gmax','eor'}))));
p.addParamValue('hyst', [], @(x)isempty(x) || ...
    (@(x)isvector(x) && length(x)<=2 && all(x>=0) && all(x<1)));
p.addParamValue('samp', 1, @(x)isscalar(x) && round(x)==x && x>=1 && x<=5);
% parse and validate all input arguments
p.parse(varargin{:});
p = getvarParser(p);

checking/setting variables

C = size(I,3);

if C==1 && ~(islogical(p.reduce) && ~p.reduce),
    warning('cannyedge:inputwarning', ...
        'ignored option ''reduce'' with scalar image');
    p.reduce = false;
end

if C~=3 && ischar(p.reduce) && strcmpi(p.reduce,'igray')
    error('cannyedge:inputerror', ...
         ['option ''reduce'' set to ' p.reduce ' for RGB images only']);
end

if strcmpi(p.der,'matlab')
    if nargout>=2
    warning('cannyedge:inputwarning', ...
        'no magnitude/orientation computed with method ''matlab''');
    varargout = [];
    elseif ischar(p.reduce) && strcmpi(p.reduce,'gmax')
        warning('cannyedge:inputwarning', ...
            'option ''gmax'' ignored with method ''matlab''');
        p.reduce = false;
    end
end

main calculation

if nargout==1
    edgemap = cannyedge_base(I, p.sigma, p.der, p.samp, p.hyst, p.reduce);

else
    [edgemap, mag, or] = cannyedge_base(I, p.sigma, p.der, p.samp, p.hyst, p.reduce);
    if nargout>=2,     varargout{1} = mag;     end
    if nargout==3,     varargout{2} = or;     end

end

display

if p.disp
    figure, imagesc(edgemap), axis image off, title('Canny edge map');
    if size(edgemap,3) == 1, colormap 'gray'; end;
    if nargout==3
        figure, subplot(1,2,1)
        imshow(mag), axis image off, title('gradient magnitude');
        subplot(1,2,2)
        imshow(rescale(or,0,1)), axis image off,
        title('gradient orientation');

    end
end

end % end of cannyedge