function g = intrans(f, varargin)
%INTRANS Performs intensity (gray-level) transformations.
%  G = INTRANS(F, 'neg') computes the negative of input image F
%
%  G = INTRANS(F, 'log', C, CLASS) computes C*log(1 + F) and
%  multiplies the result by (positive) constant C.  If the last two
%  parameters are omitted, C defaults to 1.  Because the log is used 
%  frequently to display Fourier spectra, parameter CLASS offers the 
%  option to specify the class of the output as 'uint8' or 
%  'uint16'. If parameter CLASS is omitted, the output is of the 
%  same class as the input.
%
%  G = INTRANS(F, 'gamma', GAM) performs a gamma transformation on
%  the input image using parameter GAM (a required input).
%
%  G = INTRANS(F, 'stretch', M, E) computes a contrast-stretching
%  transformation using the expression 1./(1 + (M./(F + eps)).^E).
%  Parameter M must be in the range [0, 1].  The default value for 
%  M is mean2(im2double(F)), and the default value for E is 4.
%
%  For the 'neg', 'gamma', and 'stretch' transformations, double
%  input images whose maximum value is greater than 1 are scaled 
%  first using MAT2GRAY. Other images are converted to double first
%  using IM2DOUBLE.  For the 'log' transformation, double images are
%  transformed without being scaled; other images are converted to 
%  double first using IM2DOUBLE.
%
%  The output is of the same class as the input, except if a 
%  different class is specified for the 'log' option.

%  Verify the correct number of inputs.
error(nargchk(2, 4, nargin))

%  Store the class of the input for use later.
classin = class(f);

%  If the input is of class double, and it is outside the range
%  [0, 1], and the specified transformation is not 'log', convert the 
%  input to the range [0, 1].
if strcmp(class(f), 'double') & max(f(:)) > 1 ...
      ~strcmp(varargin{1}, 'log')
   f = mat2gray(f);
else % Convert to double, regardless of class(f).
   f = im2double(f);
end

%  Determine the type of transformation specified.
method = varargin{1};

%  Perform the intensity transformation specified.
switch method
case 'neg'
   g = imcomplement(f);
case 'log'
   if length(varargin) == 1
      c = 1;
   elseif length(varargin) == 2
      c = varargin{2};
   elseif length(varargin) == 3
      c = varargin{2};
      classin = varargin{3};
   else
      error('Incorrect number of inputs for the log option.')
   end
   g = c*(log(1 + double(f)));
case 'gamma'
   if length(varargin) < 2
      error('Not enough inputs for the gamma option.')
   end
   gam = varargin{2};
   g = imadjust(f, [ ], [ ], gam);
otherwise
   error('Unknown enhancement method.')
end

%  Convert to the class of the input image.
g = changeclass(classin, g);