gfcheckfilter2.m

外国人写matlab 的gobor特征运算工具箱

function gfcheckfilter2(f0,theta,gamma,eta,n,pt,pf)
%GFCHECKFILTER2 Check 2-d filter parameters.
%
%   GFCHECKFILTER2(F0,THETA,GAMMA,ETA,N,PT,PF)  Checks the
%   constraints of the discrete Gabor filter for given parameters
%   and prints out warning or error messages.
%
%     F0    - Central frequency
%     THETA - Orientation
%     GAMMA - Width parallel to wave
%     ETA   - Orthogonal width
%     N     - Size of the filter
%     PT    - Spatial domain percent factor
%     PF   - Frequency domain Percent factor, (major and minor axes)
%
%   Examples
%
%     gfcheckfilter2(1/64, pi/2, 1, 1, 64, 0.998, 0.998);
%     gfcheckfilter2(1/64, pi/2, 1, 1, 64, 0.998, [0.998 0.95]);
%
%   See also GFCREATEFILTER2, GFCREATEFILTERF2.
%
% References:
%   [1] Kamarainen, J.-K., Kyrki, V., Kalviainen, H., Gabor
%       Features for Invariant Object Recognition, Research
%       report 79, Department of Information Technology,
%       Lappeenranta University of Technology 
%   [2] Kamarainen, Joni-Kristian, Feature Extraction with Gabor
%       Filters, PhD thesis, Lappeenranta University of Technology,
%       2003. 
%
% Author(s):
%    Joni Kamarainen <[e-mail]>
%    Ville Kyrki <[e-mail]>
%
% Copyright:
%
%   The Gabor Features in Signal and Image Processing Toolbox is
%   Copyright (C) 2000 by Joni Kamarainen and Ville Kyrki.
%
%
%   $Name:  $ $Revision: 1.7 $  $Date: 2003-05-02 12:11:06 $
%

% Check filter size parameter
if length(n)>1,
  nx=n(1);
  ny=n(2);
else
  nx=n;
  ny=n;
end;

% Check if different values for major and minor axes of Frequency
% domain Gaussian envelope
if length(pf)>1,
  pf1 = pf(1);
  pf2 = pf(2);
else
  pf1 = pf;
  pf2 = pf;
end;

% Set checking values
alpha = f0/gamma;
beta = f0/eta;
nyqf = 0.5; % Nyquist frequency 

%
% 1. Checking Nyquist criterion
if (abs(f0) > nyqf)
  warning(['Nyquist criterion violated. Allowed intervals are' ...
	  ' ]0,0.5[ for positive and ]-0.5,0[ for negative frequencies']);
end;


%
% 2. Checking zero frequency constraint
if (f0 == 0)
  error(['Zero frequency is not allowed due to the filter normalization ' ...
	 '(division by zero).']);
end;


%
% 3. Checking frequency constraint

% more strict from [2] - works for positive and negative frequencies
PF = min([pf1 pf2]);
f = f0;
L = min([nx ny]);
fPF = 1/4*(erf(gamma*pi)+erf((gamma*pi)/abs(f)*(1/2-1/L)-gamma*pi))*...
      (erf(eta*pi)+erf((eta*pi)/abs(f)*(1/2-1/L)-eta*pi));

if (fPF < PF)
  warning(['Filter envelope insufficiently located in the frequency domain. '...
	   ' Requested minimum envelope area inside legal area ]0,0.5[ or ]-0.5,0[ in frequency domain is '... 
	   num2str(100*PF) ' percent and currently area is ' ...
	   num2str(100*fPF) '. Thus aliasing occurs!']);
end;


%
% 4. Checking time constraint

% Symmetric part of the filter must contain pt percent of the
% full filter envelope 

%% from [1]
%fPT = erf(alpha*floor((N-1)/2));
PT = pt;
fPT = erf(abs(f)/gamma*(L/2-1))*erf(abs(f)/eta*(L/2-1));

if (fPT < PT)
  warning(['Spatial filter size may be too small. '...
	   ' Requested minimum spatial envelope size is '...
	   num2str(PT*100) ' percent and current size is '...
	   num2str(100*fPT)]);
end;




% DEPRICATED FROM [1]
%%
%% Checking spatial constraints
%
%% Symmetric part of the filter must contain pt percent of the
%% full filter envelope 
%% Lasketaan 'leveydet' aallon suunnassa ja aaltoa vastaan kohtisuoraan
%lx=max(abs([cos(theta)*nx sin(theta)*ny]));
%ly=max(abs([sin(theta)*nx cos(theta)*ny]));
%	   
%% Filtterin symmetrisen osan tulee sis鋖t滗 pt prosenttia 
%fpt = abs(erf(alpha*floor((lx-1)/2))*erf(beta*floor((ly-1)/2)));
%if (fpt < pt)
%  warning(['Spatial filter size may be too small. '...
%	   ' Requested minimum spatial envelope size is '...
%	   num2str(pt*100) ' percent and current size is '...
%	   num2str(100*fpt)]);
%end;
%
%%
%% Checking frequency constraints
%
%% marjor axis constraints
%fpf1 = erf(pi/alpha*f0);
%if (fpf1 < pf1)
%  warning(['Filter envelope insufficiently located along the major axis in the frequency domain. '...
%	   ' Requested minimum envelope area inside domain is '...
%	   num2str(100*pf1) ' percent and currently area is ' ...
%	   num2str(100*fpf1)]);
%%  warning(['Area of filter envelope along the major axis insufficient' ...
%%	   ' in frequency domain']); 
%end;
%
%% minor axis constraints
%fpf2 = erf(pi/(beta)*1/2);
%if (fpf2 < pf2)
%  warning(['Filter envelope insufficiently located along the minor axis in the frequency domain. '...
%	   ' Requested minimum envelope area inside domain is '...
%	   num2str(100*pf2) ' percent and currently area is ' ...
%	   num2str(100*fpf2)]);
%%  warning(['Area of filter envelope along the minor axis insufficient' ...
%%	   ' in frequency domain']); 
%end;