CORNER - Corner detection techniques.

Contents

Description

Performs the implementation of and the call to various corner detection methods.

Syntax

   [cornermap, ptcorner] = CORNER(I, method, 'Property', propertyvalue, ...);

Inputs

I : input image, possibly multichannel.

method : (optional) string defining the method used for corner extraction; it is either:

note: currently, curve corner detection ('cur', outperformed by 'cpda'), compass corner detection ('com', very slow) are not included in this function, but could easily be added.

Property [propertyname propertyvalues]

'thres' : threshold parameter used by most of the corner detectors; see respective calls; default: thres=0.001 (as used by Harris detector).

'reduce' : logical value defining the way the different channels of a multispectral image are combined into the corner map; when set to true, the detector is applied channel by channel and the output corner map is taken as the logical OR of the output corner maps of the different channels; default: reduce=true.

'gap', 'thang' : parameters used by 'cpda', maximum gap between the successive edge-points and threshold on angle orientation;; default: gap=1 pixel and thang=157 degrees.

'kappa', 'radius' : parameters used by 'har' and/or 'nob'; default: kappa=0.06 and radius=3.

'sig' : numeric variable used when the selected method is any of 'cpda', 'har' or 'nob' as the standard deviation for smoothing the 1st order directional derivatives prior to edge detection; default: sig=1.

'rho' : numeric variable used when the selected method is any of 'har', or 'nob' as the standard deviation for averarging the 2nd order directional derivatives prior to edge detection; default: rho=1.

Outputs

cornermap : logical 2D map of corners.

ptcorner : matrix storing corners' coordinates.

References

[HS88]  C.G. Harris and M.J. Stephens: "A combined corner and edge
   detector", Proc. Vision Conference, pp 147-151, 1988.
   <http://www.bmva.org/bmvc/1988/avc-88-023.pdf>

[Noble89]  A. Noble: "Descriptions of Image Surfaces", PhD thesis, p45,
   Oxford University 1989.

[SB97]  S.M. Smith and J.M. Brady: "{SUSAN} - A new approach to low
   level image processing", International Journal of Computer Vision,
   23(1):45-78, 1997.
   <http://perception.inrialpes.fr/Publications/2000/SMB00/Schmid-ijcv00.pdf>

[HY04]  X.C. He and N.H.C. Yung: "Curvature scale space corner detector
   with adaptive threshold and dynamic region of support", Proc. ICPR,
   vol. 2, pp. 791-794, 2004.
   <http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=1334377>

[HY08]	X.C. He and N.H.C. Yung: "Corner detector based on global and
   local curvature properties", Optical Engineering, 47(5):057008, 2008.
   <http://spiedigitallibrary.org/oe/resource/1/opegar/v47/i5/p057008_s1>

[AL08]  M. Awrangjeb and G. Lu: "Robust image corner detection based
   on the chord-to-point distance accumulation technique", IEEE Trans.
   on Multimedia, 10(6):1059-1072, 2008.
   <http://www.gscit.monash.edu.au/gscitweb/loid.php?loid=905299&mimetype=application/pdf>

[ALFR09]  M. Awrangjeb, G. Lu, C.S. Fraser and M. Ravanbakhsh: "“A Fast
   Corner Detector Based on the Chord-to-Point Distance Accumulation
   Technique", Proc. DICTA, pp. 519-525, 2009.
   <http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=5384897>

See also

Ressembles: EDGECORNER, SUSANCORNER, HARRISCORNER, FASTCORNER, FASTCPDA, COMPASSEDGE, CONGRUENCYEDGE. Requires: CORNER_BASE.

Function implementation

function [cornermap, ptcorner] = corner(I, varargin)

parsing parameters

error(nargchk(1, 28, nargin, 'struct'));
error(nargoutchk(1, 2, nargout, 'struct'));

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

% optional parameters
p = createParser('CORNER');
p.addRequired('method',@(x)ischar(x) || ...
    any(strcmpi(x,{'harris','noble','susan','cpda', ...
    'fast9','fast10','fast11','fast12'})));
% used by FASTCORNER
p.addParamValue('nonmax', true, @(x)islogical(x));
% % used by SUSANCORNER
% p.addParamValue('md', 'flat', @(x)(ischar(x) && strcmp(x,flat)) || ...
%     (isscalar(x) && x>0));
% p.addParamValue('n', false, @(x)isscalar(x) && (x==true||x==false));
% p.addParamValue('q', true, @(x)isscalar(x) && (x==true||x==false));
% used by HARRISCORNER
p.addParamValue('kappa', 0.06, @(x)isscalar(x) && isfloat(x) && x>0);
p.addParamValue('radius', 3, @(x)isscalar(x) && round(x)==x && x>0);
% used by FASTCPDA
p.addParamValue('thang',157, @(x)x>=0 && x<=180);
p.addParamValue('gap',1, @(x)isscalar(x) && x>=1);
% used by FASTCPDA and HARRISCORNER
p.addParamValue('sig', 1, @(x) isnumeric(x) || ...
    (isscalar(x) && isfloat(x) && x>0));
p.addParamValue('rho', 1, @(x) isnumeric(x) || ...
    (isscalar(x) && isfloat(x) && x>0));
% used by COMPASS
% used by all
p.addParamValue('thres', 0.001, @(x)isscalar(x) && x>=0);
p.addParamValue('reduce',true, @(x)islogical(x));

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

main calculation

[cornermap, ptcorner] = ...
    corner_base(I, p.method, p.thres, p.kappa, p.radius, ...
    p.nonmax, p.gap, p.thang, p.sig, p.rho, p.reduce );

if p.disp
end

end % end of corner