function Y = ind2gray(X,map)

# Convert an octave indexed image to a gray scale intensity image.
#
# Y = ind2gray(X) converts an indexed image to a gray scale intensity
# image.  The current colormap is used to determine the intensities.
# The intensity values lie between 0 and 1 inclusive.
#
# Y = ind2gray(X,map) uses the specified colormap instead of the current
# one in the conversion process.
#
# SEE ALSO: gray2ind, rgb2ntsc, image, colormap

  if (nargin == 1)
    map = colormap;
  endif

  # Convert colormap to intensity values.
  yiq = rgb2ntsc(map);
  y = yiq(:,1);

# We need Fortran indexing capability, but be sure to save the user's
# preference.

  pref = do_fortran_indexing;

  unwind_protect

    do_fortran_indexing = "true";

# Replace indices in the input matrix with indexed values in the output
# matrix.

    [rows, cols] = size(X);
    Y = y(X(:));
    Y = reshape(Y,rows,cols);

  unwind_protect_cleanup
    do_fortran_indexing = pref;
  end_unwind_protect

endfunction