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## -*- texinfo -*-
## @deftypefn  {} {} image (@var{img})
## @deftypefnx {} {} image (@var{x}, @var{y}, @var{img})
## @deftypefnx {} {} image ("CData", @var{img})
## @deftypefnx {} {} image ("XData", @var{x}, "YData", @var{y}, "CData", @var{img})
## @deftypefnx {} {} image (@dots{}, @var{prop}, @var{val})
## @deftypefnx {} {} image (@var{hax}, @dots{})
## @deftypefnx {} {@var{h} =} image (@dots{})
## Display a matrix as an image.
##
## @var{img} may be a 2-D matrix where each element is an index into the
## current colormap.  For floating point data, the value 1 chooses the first
## color in the colormap.  For integer data, the value 0 chooses the first
## color in the colormap.
##
## Or @var{img} may be a 3-D matrix where the third dimension is an RGB triplet
## specifying the color.  If the image data is floating point then the data
## must be in the range [0, 1].  If the image data is of integer type (uint8 or
## uint16) then the data must be in the range [0, INTMAX].
##
## @var{x} and @var{y} are optional 1-element (@code{[min]}) or 2-element
## vectors (@w{@code{[min, max]}}) which specify the coordinate(s) of the
## @emph{center} of a corner pixel.  If unspecified, the default minimum value
## is 1 and the maximum is the length of @var{img} along the specific
## dimension.  If a range is specified as @w{@code{[max, min]}}@ then the image
## will be reversed along that axis.  For convenience, @var{x} and @var{y} may
## be specified as vectors, however, only the first and last elements will be
## used to determine the axis limits.
##
## Multiple property/value pairs may be specified for the image object, but
## they must appear in pairs.
##
## If the first argument @var{hax} is an axes handle, then plot into this axes,
## rather than the current axes returned by @code{gca}.
##
## The optional return value @var{h} is a graphics handle to the image.
##
## Implementation Note: The origin (0, 0) for images is located in the upper
## left.  For ordinary plots, the origin is located in the lower left.  Octave
## handles this inversion by plotting the data normally, and then reversing the
## direction of the y-axis by setting the @code{ydir} property to
## @qcode{"reverse"}.  This has implications whenever an image and an ordinary
## plot need to be overlaid.  The recommended solution is to display the image
## and then plot the reversed ydata using, for example, @code{flipud (ydata)}.
##
## Calling Forms: The @code{image} function can be called in two forms:
## High-Level and Low-Level.  When invoked with normal options, the High-Level
## form is used which first calls @code{newplot} to prepare the graphic figure
## and axes.  When the only inputs to @code{image} are property/value pairs
## the Low-Level form is used which creates a new instance of an image object
## and inserts it in the current axes (as if @code{hold on} was in effect).
##
## Graphic Properties: The full list of properties is documented at
## @ref{Image Properties}.
## @seealso{imshow, imagesc, colormap}
## @end deftypefn

function h = image (varargin)

  [hax, varargin, nargin] = __plt_get_axis_arg__ ("image", varargin{:});

  chararg = find (cellfun ("isclass", varargin, "char"), 1, "first");

  do_new = true;
  if (nargin == 0)
    img = get (0, "defaultimagecdata");
    x = y = [];
  elseif (chararg == 1)
    ## Low-Level syntax
    do_new = false;
    x = y = img = [];
    idx = find (strcmpi (varargin, "cdata"), 1);
    if (idx)
      img = varargin{idx+1};
      varargin(idx:idx+1) = [];
    endif
    idx = find (strcmpi (varargin, "xdata"), 1);
    if (idx)
      x = varargin{idx+1};
      varargin(idx:idx+1) = [];
    endif
    idx = find (strcmpi (varargin, "ydata"), 1);
    if (idx)
      y = varargin{idx+1};
      varargin(idx:idx+1) = [];
    endif
  elseif (nargin == 1 || chararg == 2)
    img = varargin{1};
    x = y = [];
  elseif (nargin == 2 || chararg == 3)
    print_usage ();
  else
    x = varargin{1};
    y = varargin{2};
    img = varargin{3};
    chararg = 4;
  endif

  if (iscomplex (img))
    error ("image: IMG data can not be complex");
  endif

  oldfig = [];
  if (! isempty (hax))
    oldfig = get (0, "currentfigure");
  endif
  unwind_protect
    if (do_new)
      hax = newplot (hax);
    elseif (isempty (hax))
      hax = gca ();
    else
      hax = hax(1);
    endif

    htmp = __img__ (hax, do_new, x, y, img, varargin{chararg:end});

  unwind_protect_cleanup
    if (! isempty (oldfig))
      set (0, "currentfigure", oldfig);
    endif
  end_unwind_protect

  if (nargout > 0)
    h = htmp;
  endif

endfunction

## Generic image creation.
##
## The axis values corresponding to the matrix elements are specified in
## @var{x} and @var{y}.

function h = __img__ (hax, do_new, x, y, img, varargin)

  ## Initialize XDATA and YDATA to handle case where IMG is empty
  xdata = [];
  ydata = [];

  if (! isempty (img))

    if (! isempty (x))
      if (! isvector (x))
        error ("image: X must be a vector");
      endif
      if (isscalar (x))
        xdata = [x(1), x(1)+columns(img)-1];
      else
        xdata = x([1, end])(:).';  # (:).' is a hack to guarantee row vector
      endif
    endif

    if (! isempty (y))
      if (! isvector (y))
        error ("image: Y must be a vector");
      endif
      if (isscalar (y))
        ydata = [y(1), y(1)+rows(img)-1];
      else
        ydata = y([1, end])(:).';
      endif
    endif

  endif

  scale_axis = do_new && ! ishold (hax) && ! isempty (img);
  if (scale_axis)
    ## Set axis properties for new images
    ## NOTE: Do this before calling __go_image__ so that image is not drawn
    ##       once with default auto-scale axis limits and then a second time
    ##       with tight axis limits.
    if (isempty (get (hax, "children")))
      axis (hax, "tight");
    endif

    set (hax, "view", [0, 90], "ydir", "reverse", "layer", "top", "box", "on");

  endif

  h = __go_image__ (hax, "cdata", img, "xdata", xdata, "ydata", ydata,
                         "cdatamapping", "direct", varargin{:});

  if (scale_axis && isscalar (get (hax, "children")))
    ## Re-scale axis limits for an image in a new figure or axis.
    axis (hax, "tight");
  endif

endfunction


%!demo
%! clf;
%! colormap (jet (21));
%! img = 1 ./ hilb (11);
%! x = y = -5:5;
%! subplot (2,2,1);
%!  h = image (x, y, img);
%!  ylabel ("limits = [-5.5, 5.5]");
%!  title ("image (x, y, img)");
%! subplot (2,2,2);
%!  h = image (-x, y, img);
%!  title ("image (-x, y, img)");
%! subplot (2,2,3);
%!  h = image (x, -y, img);
%!  title ("image (x, -y, img)");
%!  ylabel ("limits = [-5.5, 5.5]");
%! subplot (2,2,4);
%!  h = image (-x, -y, img);
%!  title ("image (-x, -y, img)");

## test hidden properties x/ydatamode
%!test <*42121>
%! hf = figure ("visible", "off");
%! unwind_protect
%!   nx = 64; ny = 64;
%!   cdata = rand (ny, nx)*127;
%!   hi = image (cdata);             # x/ydatamode is auto
%!   assert (get (hi, "xdata"), [1 nx]);
%!   assert (get (hi, "ydata"), [1 ny]);
%!   set (hi, "cdata", cdata(1:2:end, 1:2:end));
%!   assert (get (hi, "xdata"), [1 nx/2]);
%!   assert (get (hi, "ydata"), [1 ny/2]);
%!
%!   set (hi, "xdata", [10 100]);    # xdatamode is now manual
%!   set (hi, "ydata", [10 1000]);   # ydatamode is now manual
%!   set (hi, "cdata", cdata);
%!   assert (get (hi, "xdata"), [10 100]);
%!   assert (get (hi, "ydata"), [10 1000]);
%!
%!   set (hi, "ydata", []);          # ydatamode is now auto
%!   set (hi, "cdata", cdata(1:2:end, 1:2:end));
%!   assert (get (hi, "xdata"), [10 100]);
%!   assert (get (hi, "ydata"), [1 ny/2]);
%! unwind_protect_cleanup
%!   close (hf);
%! end_unwind_protect

%!error <IMG data can not be complex> image ([1, i])