sbpdf.m

基于小波变换的特征检索算法

function [alpha, beta, K] = sbpdf(m1, m2)
% SBPDF Estimate generalized Gaussian pdf of an wavelet subband
%
% Input:
%	m1: average absolute values of subband coefficients
%	m2: variances of subband coefficients
%
% Output:
%	alpha, beta, K: paramaters of generalized Gaussian p.d.f.
%	f(x) = K * exp(-(abs(x) / alpha)^beta)

% beta = F^(-1)(m1^2 / m2);
% alpha = m1 * gamma(1/beta) / gamma(2/beta);
% K = beta / (2 * alpha * gamma(1/beta);

F = sprintf('fbeta(x) - %g', m1^2 / m2);

try
    beta = fzero(F, [.01, 5]);
catch
    warning('m1^2 / m2 is out of the expected range');
    if (m1^2 / m2) > fbeta(5)
	beta = 5;
    else
	beta = 0.01;
    end    
end

alpha = m1 * exp(gammaln(1/beta) - gammaln(2/beta));

if nargout > 2
    K = beta / (2 * alpha * gamma(1/beta));
end