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## -*- texinfo -*-
## @deftypefn  {} {@var{img} =} gray2ind (@var{I})
## @deftypefnx {} {@var{img} =} gray2ind (@var{I}, @var{n})
## @deftypefnx {} {@var{img} =} gray2ind (@var{BW})
## @deftypefnx {} {@var{img} =} gray2ind (@var{BW}, @var{n})
## @deftypefnx {} {[@var{img}, @var{map}] =} gray2ind (@dots{})
## Convert a grayscale or binary intensity image to an indexed image.
##
## The indexed image will consist of @var{n} different intensity values.
## If not given @var{n} defaults to 64 for grayscale images or 2 for binary
## black and white images.
##
## The output @var{img} is of class uint8 if @var{n} is less than or equal to
## 256; Otherwise the return class is uint16.
## @seealso{ind2gray, rgb2ind}
## @end deftypefn

function [I, map] = gray2ind (I, n = 64)

  if (nargin < 1)
    print_usage ();
  elseif (! isreal (I) || issparse (I) || ! ismatrix (I))
    error ("gray2ind: I must be a grayscale or binary image");
  elseif (! isscalar (n) || n < 1 || n > 65536)
    error ("gray2ind: N must be a positive integer in the range [1, 65536]");
  endif

  ## default n is different if image is logical
  if (nargin == 1 && islogical (I))
    n = 2;
  endif

  cls = class (I);
  if (! any (strcmp (cls, {"logical", "uint8", "uint16", "int16", ...
                           "single", "double"})))
    error ("gray2ind: invalid data type '%s'", cls);
  elseif (isfloat (I) && (min (I(:) < 0) || max (I(:) > 1)))
    error ("gray2ind: floating point images may only contain values between 0 and 1");
  endif

  map = gray (n);

  ## Set up scale factor
  if (isinteger (I))
    low   = double (intmin (cls));
    scale = double (intmax (cls)) - low;
    I = double (I) - low;
  else
    scale = 1;
  endif
  I *= (n-1)/scale;

  ## Note: no separate call to round () necessary because
  ##       type conversion does that automatically.
  if (n <= 256)
    I = uint8 (I);
  else
    I = uint16 (I);
  endif

endfunction


%!assert (gray2ind ([0 0.25 0.5 1]), uint8 ([0 16 32 63]))
%!assert (gray2ind ([0 0.25 0.5 1], 400), uint16 ([0 100 200 399]))
%!assert (gray2ind (logical ([1 0 0 1])), uint8 ([1 0 0 1]))
%!assert (gray2ind (uint8 ([0 64 128 192 255])), uint8 ([0 16 32 47 63]))

%!test
%! i2g = ind2gray (1:100, gray (100));
%! g2i = gray2ind (i2g, 100);
%! assert (g2i, uint8 (0:99));

%!assert (gray2ind ([0 0.25 0.5 1], 256), uint8 ([0 64 128 255]))
%!assert (gray2ind ([0 (1/511) (1/510) 1-(1/509) 1-(1/510) 1], 256),
%!        uint8 ([0 0 1 254 255 255]))

%!test
%! assert (class (gray2ind ([0.0 0.5 1.0], 255)), "uint8");
%! assert (class (gray2ind ([0.0 0.5 1.0], 256)), "uint8");
%! assert (class (gray2ind ([0.0 0.5 1.0], 257)), "uint16");

## Test input validation
%!error <Invalid call> gray2ind ()
%!error <I must be a grayscale or binary image> gray2ind ({1})
%!error <I must be a grayscale or binary image> gray2ind ([1+i])
%!error <I must be a grayscale or binary image> gray2ind (sparse ([1]))
%!error <I must be a grayscale or binary image> gray2ind (ones (2,2,3))
%!error <N must be a positive integer> gray2ind (1, ones (2,2))
%!error <N must be a positive integer> gray2ind (1, 0)
%!error <N must be a positive integer> gray2ind (1, 65537)
%!error <invalid data type> gray2ind (uint32 (1))
%!error <values between 0 and 1> gray2ind (-1)
%!error <values between 0 and 1> gray2ind (2)
