--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/scripts/image/private/__tiff_imread__.m	Thu Sep 01 01:56:20 2022 +0200
@@ -0,0 +1,150 @@
+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
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