uquant.m

Matlab时频分析工具箱,希望能对大家有所帮助啊

function xo=uquant(p1,p2,p3,p4);
%UQUANT  Simulate uniform quantization.
%   Usage:  x=uquant(x,nbits);
%           x=uquant(x,nbits,xmax);
%           x=uquant(qtype,x,nbits,xmax);
%           x=uquant(qtype,x,nbits,xmax);
%
%   UQUANT(x,nbits) simulates the effect of uniform quantization of x using
%   nbits bit. The output is simply x rounded to 2^{nbits} different values.
%
%   UQUANT(x,nbits,xmax) does as above, but allows you to specify the
%   maximal value that should be quantifiable. If not specified, the
%   maximal value of the signal will be used.
%
%   UQUANT(qtype,x,nbits) or UQUANT(qtype,x,nbits,xmax) uses quantization
%   depending on qtype. qtype may be one of:
%
%    's','signed'   - Default quantization type. This assumes that the signal
%                     has a both positive and negative part. Usefull for sound
%                     signals.
%    'u','unsigned' - Assumes the signal is positive. Negative values are
%                     silently rounded to zero. Usefull for images.
% 
%
%   If this function is applied to a complex signal, it will simply be
%   applied to the real and imaginary part separately.
%

% This program is free software: you can redistribute it and/or modify
% it under the terms of the GNU General Public License as published by
% the Free Software Foundation, either version 3 of the License, or
% (at your option) any later version.
% 
% This program is distributed in the hope that it will be useful,
% but WITHOUT ANY WARRANTY; without even the implied warranty of
% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
% GNU General Public License for more details.
% 
% You should have received a copy of the GNU General Public License
% along with this program.  If not, see <http://www.gnu.org/licenses/>.

error(nargchk(2,4,nargin));

specified=0;
if ischar(p1)
  qtype=p1;
  xi=p2;
  if nargin==2
    error('Too few input parameters.');
  end;
  nbits=p3;
  if nargin==4
    specified=1;
    xmaxspecified=p4;
  end;

else
  qtype='unsigned';
  xi=p1;
  nbits=p2;
  if nargin==3
    specified=1;
    xmaxspecified=p3;
  end; 
end;

% ------ handle complex values ------------------
if ~isreal(xi)
  if ~specified
    xo = uquant(qtype,real(xi),nbits) + i* uquant(qtype,imag(xi),nbits);
  else
    xo = uquant(qtype,real(xi),nbits,xmaxspecified) + ...
	i* uquant(qtype,imag(xi),nbits,xmaxspecified);
  end;
  return
end;

if nbits<1
  error('Must specify at least 2 bits.');
end;

% Calculate number of buckets.
nbuck=2^nbits;    
    
switch(lower(qtype))
  case {'u','unsigned'}

    % ------------ unsigned case -----------------

    xmax=max(xi(:));
    xmin=min(xi(:));
    xminabs=abs(xmin);
    
    % Totally there is nbuck buckets to put all values in,
    % but since they are centered around zero, there will be nbuck/2
    % buckets for strictly positive values, and nbuck/2-1 buckets for
    % strictly negative values. This means, that if the coefficient with
    % the largest absolute value is negative, then the bucket size
    % must be slightly larger to cope with it.
    %
    % The messy code below deals with this phenomena.
    
    if specified
      if xmaxspecified<max(xmax,xminabs)
	error('Signal contains values higher than xmax.');
      end;
      
      bucksize=xmaxspecified/(nbuck/2-1);
    else
      
      posbuck=xmax/(nbuck/2);
      negbuck=xminabs/(nbuck/2-1);
      
      bucksize=max(posbuck,negbuck);
    end;
    
    xo=round(xi/bucksize)*bucksize;        
    
  case {'s','signed'}

    % ------------- signed case------------

    xmax=max(xi(:));
    xmin=0;
    xminabs=abs(xmin);
        
    if specified
      if xmaxspecified<max(xmax,xminabs)
	error('Signal contains values higher than xmax.');
      end;
      xmax=xmaxspecified;
    end;
    bucksize=xmax/(nbuck-.51);

    % Thresh all negative values to zero.
    xi=xi.*(xi>0);
    
    xo=round(xi/bucksize)*bucksize;        

    
  otherwise
    error(['Unknown quantization type: ',qtype]);
end;