KOETHEDGE_BASE - Base function for KOETHEDGE.

Contents

Syntax

   [emap, cmap, T] = ...
       KOETHEDGE_BASE(I, rho, sigma, der, int, map, samp, v1, v2, radius);

See also

Ressembles: KOETHEDGE, CANNYEDGE_BASE, EDGECORNER_BASE, CONGRUENCYEDGE_BASE, COMPASSEDGE_BASE, ANISOEDGE_BASE, ELDERZUCKEREDGE_BASE, ROTHWELLEDGE_BASE, SDGDEDGE_BASE, PETROUEDGE_BASE. Requires: GSTSMOOTH_BASE, GSTDECOMP, GSTFEATURE_BASE, FINDLOCALEXTREMA_BASE, CANNYEDGEMAP_BASE.

Function implementation

function [emap, cmap, T] = ...
    koethedge_base(I, rho, sigma, der, int, map, samp, v1, v2, radius )

% note : samp=2 and int='ani' corresponds to the method proposed by Koethe

% only parameters set to constant values
thez =8;  sigt = .4; gn = false; tn = false; hsize = [];

compute the gradient structure tensor

[T, ~, ~, gx2, gy2, gxy] = ...
 gstsmooth_base(I, rho, sigma, der, int, samp, hsize, gn, tn, thez, sigt);

perform the eigen decomposition

[l1,l2,e1,~] = gstdecomp(T);
% % compute Tedge = (l1-l2) e1 . e1^T
% Tedge = zeros(size(T));
% l1 = l1 - l2;
% Tedge(:,:,1,1) = l1 .* e1(:,:,1) .^2;
% Tedge(:,:,2,2) = l1 .* e1(:,:,2) .^2;
% Tedge(:,:,1,2) = l1 .* e1(:,:,1) .* e1(:,:,2);
% Tedge(:,:,1,2) = Tedge(:,:,2,1);
%
% % compute Tjunction = l2 * I
% Tjunction = zeros(size(T));
% Tjunction(:,:,1,1) = l2;
% Tjunction(:,:,2,2) = l2;

... and feed it to a Canny-like algorithm: non maxima suppression and hystheresis thresholding

switch map

    case 'canny'
        % transform the tensor back into a gradient-like vector
        mag = gstfeature_base(gx2, gy2, gxy, 'norm', v1, [], []);
        % compute the double angle of the gradient tensor
        or = gstfeature_base(gx2, gy2, gxy, 'orient', [], [], []);
        emap = cannyedgemap_base(e1(:,:,1), e1(:,:,2), 'matlab', mag, or, v2, []);

    case 'rothwell' % subpixel detection
        mag = sqrt(l1-l2);
        emap = rothwelledge_base(mag.*e1(:,:,1), mag.*e1(:,:,2), v1, v2);

end

detect corners

cmap = 2*l2; % trace(Tjunction)
cmap(abs(cmap)<eps) = 0;
cmap = findlocalextrema_base(cmap, 'max', samp*radius, 8, []);

end % end of koethedge_base