im2double.m

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function d = im2double(img, typestr)
%IM2DOUBLE Convert image to double precision.
%   IM2DOUBLE takes an image as input, and returns an image of
%   class double.  If the input image is of class double, the
%   output image is identical to it.  If the input image is of
%   class uint8, im2double returns the equivalent image of class
%   double, rescaling or offsetting the data as necessary.
%
%   I2 = IM2DOUBLE(I1) converts the intensity image I1 to double
%   precision, rescaling the data if necessary.
%
%   RGB2 = IM2DOUBLE(RGB1) converts the truecolor image RGB1 to
%   double precision, rescaling the data if necessary.
%
%   BW2 = IM2DOUBLE(BW1) converts the binary image BW1 to double
%   precision.
%
%   X2 = IM2DOUBLE(X1,'indexed') converts the indexed image X1 to
%   double precision, offsetting the data if necessary.
% 
%   See also DOUBLE, IM2UINT8, UINT8.

%   Chris Griffin 6-9-97
%   Copyright 1993-1998 The MathWorks, Inc.  All Rights Reserved.
%   $Revision: 1.5 $  $Date: 1997/11/24 15:35:13 $

if isa(img, 'double')
   d = img; 
elseif isa(img, 'uint8')
   if nargin==1
      if islogical(img)        % uint8 binary image
         d = double(img);
      else                   % uint8 intensity image
         d = double(img)/255;
      end
   elseif nargin==2
      if ~ischar(typestr) | (typestr(1) ~= 'i')
         error('Invalid input arguments');
      else 
         d = double(img)+1;
      end
   else
      error('Invalid input arguments.');
   end
else
   error('Unsupported input class.');
end