gfcheckfilter.m

来自「外国人写matlab 的gobor特征运算工具箱」· M 代码 · 共 109 行

%GFCHECKFILTER Check filter parameters.
%
%   GFCHECKFILTER(F0,GAMMA,N,PT,PF)  Checks the constraints of the
%   discrete Gabor filter for given parameters and prints out
%   warning messages.
%
%     F0    - Central frequency
%     GAMMA - Sharpness factor
%     N     - Size of the filter
%     PT    - Time domain percent factor
%     PF    - Frequency domain Percent factor
%
%   Examples
%
%     gfcheckfilter(1/64, 1, 64, 0.998, 0.998);
%
%   See also GFCREATEFILTER, GFCREATEFILTERF.
%
% 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 $
%
function []=gfcheckfilter(f0,gamma,N,PT,PF)

% Set checking values
alpha = f0/gamma;
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

%% from [1]
%fPF = erf(pi/alpha*f0);

% more strict from [2] - works for positive and negative frequencies
f = f0;
L = N;
fPF = 1/2*erf(gamma*pi)+1/2*erf((gamma*pi)/abs(f)*(1/2-1/L)-gamma*pi);

if (fPF < PF)
  warning(['Filter envelope insufficiently located in the frequency domain. '...
	   ' Requested minimum envelope area inside domain is '...
	   num2str(100*PF) ' percent and currently area is ' ...
	   num2str(100*fPF)]);
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));

fPT = erf(abs(f)/gamma*(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;