--- a/scripts/image/imwrite.m	Wed Jul 10 22:31:46 2013 +0100
+++ b/scripts/image/imwrite.m	Thu Jul 11 02:07:10 2013 +0100
@@ -1,4 +1,5 @@
 ## Copyright (C) 2008-2012 John W. Eaton
+## Copyright (C) 2013 Carnë Draug
 ##
 ## This file is part of Octave.
 ##
@@ -45,25 +46,23 @@
   if (nargin < 2)
     print_usage ();
   endif
+  [filename, ext] = imwrite_filename (varargin{2:end});
 
-  ## This input checking is a bit convoluted to support the multiple
-  ## ways the function can be called. Basically, after the image we
-  ## can have the filename or a colormap. If we have a colormap, then
-  ## the filename becomes the third argument. After that, we may have
-  ## the optional file extension.
-  if (ischar (varargin{2}))
-    filename_idx = 2;
-  elseif (nargin >= 3 && iscolormap (varargin{2}) && ! ischar (varargin{3}))
-    filename_idx = 3;
+  fmt = imformats (ext);
+  ## When there is no match, fmt will be a 1x1 structure with
+  ## no fields, so we can't just use `isempty (fmt)'.
+  if (isempty (fieldnames (fmt)))
+    if (isempty (ext))
+      error ("imwrite: no extension found for %s to identify the image format",
+             filename);
+    endif
+    warning ("imwrite: unlisted image format %s (see imformats). Trying to save anyway.",
+             ext);
+    core_imwrite (varargin{:});
   else
-    error ("imwrite: no FILENAME specified");
-  endif
-  filename = {varargin{filename_idx}};
-  if (nargin > filename_idx + 1 && ischar (varargin {filename_idx + 1}))
-    filename{2} = varargin{filename_idx + 1};
+    fmt.write (varargin{:});
   endif
 
-  imageIO (@core_imwrite, "write", filename, varargin{:});
 endfunction
 
 %% Test input validation

--- a/scripts/image/private/core_imwrite.m	Wed Jul 10 22:31:46 2013 +0100
+++ b/scripts/image/private/core_imwrite.m	Thu Jul 11 02:07:10 2013 +0100
@@ -27,43 +27,15 @@
     print_usage ("imwrite");
   endif
 
-  map = [];
-  fmt = "";
+  [filename, ext, map, param_list] = imwrite_filename (varargin{2:end});
 
-  offset = 1;
-  if (isnumeric (varargin{1}))
-    map = varargin{1};
-    if (! iscolormap (map))
-      error ("imwrite: invalid COLORMAP");
-    endif
-    offset = 2;
-  endif
-  if (offset <= length (varargin) && ischar (varargin{offset}))
-    filename = varargin{offset};
-    offset++;
-    if (rem (length (varargin) - offset, 2) == 0 && ischar (varargin{offset}))
-      fmt = varargin{offset};
-      offset++;
-    endif
+  if (isempty (options))
+    has_param_list = false;
   else
-    print_usage ("imwrite");
-  endif
-  if (offset < length (varargin))
     has_param_list = true;
-    for ii = offset:2:(length (varargin) - 1)
-      options.(varargin{ii}) = varargin{ii + 1};
+    for ii = 1:2:(length (param_list))
+      options.(param_list{ii}) = param_list{ii + 1};
     endfor
-  else
-    has_param_list = false;
-  endif
-
-  filename = tilde_expand (filename);
-
-  if (isempty (fmt))
-    [~, ~, fmt] = fileparts (filename);
-    if (! isempty (fmt))
-      fmt = fmt(2:end);
-    endif
   endif
 
   if (isempty (img))
@@ -95,9 +67,9 @@
       error ("imwrite: %s: invalid class for truecolor image", img_class);
     endif
     if (has_param_list)
-      __magick_write__ (filename, fmt, img, options);
+      __magick_write__ (filename, ext, img, options);
     else
-      __magick_write__ (filename, fmt, img);
+      __magick_write__ (filename, ext, img);
     endif
   else
     if (any (strcmp (img_class, {"uint8", "uint16", "double"})))
@@ -121,11 +93,11 @@
     tmp = uint8 (cat (3, r, g, b) * 255);
 
     if (has_param_list)
-      __magick_write__ (filename, fmt, tmp, options);
-      ## __magick_write__ (filename, fmt, img, map, options);
+      __magick_write__ (filename, ext, tmp, options);
+      ## __magick_write__ (filename, ext, img, map, options);
     else
-      __magick_write__ (filename, fmt, tmp);
-      ## __magick_write__ (filename, fmt, img, map);
+      __magick_write__ (filename, ext, tmp);
+      ## __magick_write__ (filename, ext, img, map);
     endif
   endif
 

--- a/scripts/image/private/imageIO.m	Wed Jul 10 22:31:46 2013 +0100
+++ b/scripts/image/private/imageIO.m	Thu Jul 11 02:07:10 2013 +0100
@@ -16,8 +16,8 @@
 ## along with Octave; see the file COPYING.  If not, see
 ## <http://www.gnu.org/licenses/>.
 
-## This function simply connects the function that calls it to all
-## other imageIO functions. It does it by checking the file extension
+## This function simply connects imread and imfinfo() to the function
+## to be used based on their format. It does it by checking the file extension
 ## of the file and redirecting to the appropriate function after checking
 ## with imformats.
 ##
@@ -47,15 +47,11 @@
   ## should completely ignore filename{2}. It won't even be used by
   ## imformats() at all, even if filename{1} has no extension to use with
   ## imformats().
-  ##
-  ## To further complicate things, when we are going to be writing a
-  ## file, whether the file exists or not does not matter.
-  if (isscalar (filename) || (strcmp (fieldname, "write") &&
-      ! isempty (file_in_path (IMAGE_PATH, filename{1}))))
+  if (isscalar (filename) || ! isempty (file_in_path (IMAGE_PATH, filename{1})))
     [~, ~, ext] = fileparts (filename{1});
     if (! isempty (ext))
       ## remove dot from extension
-      ext(1) = [];
+      ext = ext(2:end);
     endif
   else
     ext = filename{2};

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/scripts/image/private/imwrite_filename.m	Thu Jul 11 02:07:10 2013 +0100
@@ -0,0 +1,68 @@
+## Copyright (C) 2013 Carnë Draug
+##
+## This file is part of Octave.
+##
+## Octave is free software; you can redistribute it and/or modify it
+## under the terms of the GNU General Public License as published by
+## the Free Software Foundation; either version 3 of the License, or (at
+## your option) any later version.
+##
+## Octave is distributed in the hope that it will be useful, but
+## WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+## General Public License for more details.
+##
+## You should have received a copy of the GNU General Public License
+## along with Octave; see the file COPYING.  If not, see
+## <http://www.gnu.org/licenses/>.
+
+## The input check for imwrite needs to be done twice, once when imwrite
+## is called the first time to find where the filename is, and a second
+## time by core_imwrite after imformats decides what function to use.
+## Because a user can, and is encouraged to, get a function handle to
+## core_imwrite, the input check is also done there.
+## In addition, the input check for imwrite is not that straightforward
+## in order to support the multiple ways the function can be called,
+## and interpretations of Matlab documentation.
+##
+## Anyway, this will only do the input check until it finds the filename
+## to be used, the only part that imwrite actually needs.
+
+function [filename, ext, cmap, options] = imwrite_filename (varargin)
+
+  ## First, we check if the first argument is a colormap or a filename.
+  cmap = [];
+  if (ischar (varargin{1}))
+    filename_idx = 1;
+  elseif (numel (varargin) >= 2 && iscolormap (varargin{1}) && ischar (varargin{2}))
+    filename_idx = 2;
+    cmap = varargin{1};
+  else
+    error ("imwrite: no FILENAME specified");
+  endif
+  filename = tilde_expand (varargin{filename_idx});
+
+  ## Next, we get the file extension.
+  ## if we have an odd number of leftover arguments, and the next argument
+  ## is a string, we consider it the file extension. Otherwise we will
+  ## extract what we can from the previously found filename.
+  options_idx = filename_idx + 1;
+  if (numel (varargin) > filename_idx &&
+      rem (length (varargin) - filename_idx, 2) != 0 &&
+      ischar (varargin{filename_idx + 1}))
+    ext = varargin{filename_idx + 1};
+    filename = [filename "." ext];
+    options_idx++;
+  else
+    [~, ~, ext] = fileparts (filename);
+    if (! isempty (ext))
+      ## remove dot from extension
+      ext = ext(2:end);
+    endif
+  endif
+
+  ## After all the work finding where the filename was, we might as well
+  ## send the leftovers list (they should be in key value pairs)
+  options = varargin(options_idx:end);
+
+endfunction