function [A, cmap, alpha] = __tiff_imread__ (filename, varargin)
  img = Tiff (filename);
  dir_count = img.numberOfDirectories ();
  
  ## A lot of the input sanitising logic here is copied from
  ## scripts/image/__imread__.m and adapted to the needs of the Tiff
  ## interface

  pages = [1];
  offset = 1;
  if (nargin > 1 && ! ischar (varargin{1}))
    if (! is_valid_index_option (varargin {1}))
      error ("imread: IDX must be a numeric vector");
    endif
    pages = varargin{1};
    offset = 2;
  endif

  if (rem (numel (varargin) - offset + 1, 2) != 0)
    error ("imread: PARAM/VALUE arguments must occur in pairs");
  endif

  ## Check for Index/Frames argument
  idx = strcmpi ("index", varargin) | strcmpi ("frames", varargin);
  if (any (idx))
    if (sum (idx) > 1)
      error ("imread: Index or Frames may only be specified once");
    endif
    val = varargin{circshift (idx, 1)};
    if (! is_valid_index_option (val) && ! strcmpi (val, "all"))
      error ("imread: %s must be a vector or the string 'all'", varargin{idx});
    endif
    if (strcmpi (val, "all"))
      pages = 1:dir_count;
    else
      pages = val;
    endif
  endif
  
  if (any ((pages < 1) | (pages > dir_count)))
    error ("imread: index/frames specified are outside the number of images");
  endif

  img.setDirectory (pages(1));
  info = get_image_info (img);

  ## Verify that all images have the same dimensions, number of channels,
  ## bit-depth, and data type
  for page_idx = 2:numel (pages)
    img.setDirectory (pages(page_idx));
    dir_info = get_image_info (img);
    if (info.width != dir_info.width || info.height != dir_info.height)
      error ("imread: all frames must have the same size but frame %d is different",
             pages(page_idx));
    endif
    if (info.bitdepth != dir_info.bitdepth)
      error ("imread: all frames must have the same bit depth but frame %d is different",
             pages(page_idx));
    endif
    if (info.nchannels != dir_info.nchannels)
      error ("imread: all frames must have the same number of channels but frame %d is different",
             pages(page_idx));
    endif
    if (info.datatype != dir_info.datatype)
      error ("imread: all frames must have the same data type but frame %d is different",
             pages(page_idx));
    endif
    if (info.photometric != dir_info.photometric)
      error ("imread: all frames must have the same photometric interpretation but frame %d is different",
             pages(page_idx));
    endif
  endfor

  region = {1:info.height, 1:info.width};
  for idx = offset:2:(numel (varargin) - offset + 1)
    switch (tolower (varargin{idx}))

      case {"frames", "index"}
        ## Do nothing.  This option was already processed before the loop.

      case "pixelregion"
        region = varargin{idx+1};
        if (! iscell (region) || numel (region) != 2)
          error ("imread: %s must be a 2-element cell array",
                 varargin{idx});
        endif
        for reg_idx = 1:2
          if (numel (region{reg_idx}) == 3)
            ## do nothing
          elseif (numel (region{reg_idx}) == 2)
            region{reg_idx}(3) = region{reg_idx}(2);
            region{reg_idx}(2) = 1;
          else
            error ("imread: range for %s must be a 2 or 3 element vector",
                   varargin{idx});
          endif
          region{reg_idx} = floor (region{reg_idx}(1)): ...
                            floor (region{reg_idx}(2)): ...
                            floor (region{reg_idx}(3));
        endfor
        if (region{1}(end) > info.height)
          error ("imread: end ROWS for PixelRegions option is larger than image height");
        elseif (region{2}(end) > info.width)
          error ("imread: end COLS for PixelRegions option is larger than image width");
        endif

      case "info"
        ## We ignore this option.  This parameter exists in Matlab to
        ## speed up the reading of multipage TIFF by passing a structure
        ## that contains information about the start on the file of each
        ## page.  We can't control it through GraphicsMagic but at least
        ## we allow to load multiple pages with one command.

      otherwise
        error ("imread: invalid PARAMETER '%s'", varargin{idx});

    endswitch
  endfor

  A = [];
  cmap = [];
  alpha = [];
  for page_idx = 1:numel(pages)
    img.setDirectory (pages(page_idx));
    ## FIXME: This an ineffecient way to read pixel regions because it
    ## always reads the entire image first. A better way is to figure
    ## out which strips/tiles are needed for the region and read only those.
    data = img.read ();
    data = data (region{1}, region{2}, :);
    A = cat (4, A, data);
    if (info.photometric == Tiff.Photometric.Palette)
      cmap = cat (3, cmap, img.getTag (Tiff.TagID.ColorMap));
    endif
  endfor

  img.close ();
endfunction

function bool = is_valid_index_option (arg)
  bool = isvector (arg) && isnumeric (arg) && isreal (arg);
endfunction

function info = get_image_info (img)
  info.height = img.getTag (Tiff.TagID.ImageLength);
  info.width = img.getTag (Tiff.TagID.ImageWidth);
  info.bitdepth = img.getTag (Tiff.TagID.BitsPerSample);
  info.nchannels = img.getTag (Tiff.TagID.BitsPerSample);
  info.datatype = img.getTag (Tiff.TagID.SampleFormat);
  info.photometric = img.getTag (Tiff.TagID.Photometric);
endfunction