The size of icons can be fixed without 'convert' by cropping them.

ChangeLog

@@ -6,6 +6,10 @@
 	images with/without wget.
 	(twittering-get-twits): retrieve images with
 	`twittering-retrieve-image'.
+	(twittering-use-convert): add a new variable specifying whether
+	the external command `convert' should be used.
+	(twittering-make-display-spec-for-icon): new function for
+	generating properties for icon with/without cropping the image.
 
 2009-12-04  Yuto Hayamizu  <y.hayamizu@gmail.com>
 

twittering-mode.el

@@ -289,16 +289,20 @@ directory. You should change through function'twittering-icon-mode'")
 
 (defvar twittering-image-stack nil)
 (defvar twittering-image-type-cache nil)
-(defvar twittering-convert-program "/usr/bin/convert")
+(defvar twittering-convert-program (executable-find "convert"))
 (defvar twittering-convert-fix-size nil)
+(defvar twittering-use-convert (not (null (executable-find "convert")))
+  "*This variable makes a sense only if `twittering-convert-fix-size'
+is non-nil. If this variable is non-nil, icon images are converted by
+invoking \"convert\". Otherwise, cropped images are displayed.")
 (defvar twittering-use-wget nil
   "*If non-nil, icon images are retrieved by invoking \"wget\".
 Otherwise, they are retrieved by `url-retrieve'.")
 
 (defun twittering-image-type (file-name)
   (if (and (not (assoc file-name twittering-image-type-cache))
 	   (file-exists-p file-name))
-      (if twittering-convert-fix-size
+      (if (and twittering-convert-fix-size twittering-use-convert)
 	  (let ((tmpfile (make-temp-file "emacstwit" nil ".png")))
 	    (let ((coding-system-for-read 'raw-text)
 		  (coding-system-for-write 'binary))
@@ -314,7 +318,8 @@ Otherwise, they are retrieved by `url-retrieve'.")
       			 ((string-match "JPEG" file-output) 'jpeg)
       			 ((string-match "PNG" file-output) 'png)
       			 ((string-match "GIF" file-output) 'gif)
-      			 ((string-match "bitmap" file-output)
+      			 ((and twittering-use-convert
+			       (string-match "bitmap" file-output))
       			  (let ((coding-system-for-read 'raw-text)
       				(coding-system-for-write 'binary))
       			    (with-temp-buffer
@@ -687,6 +692,32 @@ Otherwise, they are retrieved by `url-retrieve'.")
   (concat (md5 icon-url nil nil 'iso-2022-7bit)
 	  (or (ffap-file-suffix icon-url) ".img")))
 
+(defun twittering-make-display-spec-for-icon (fullpath)
+  "Return the specification for `display' text property, which limits
+the size of an icon image FULLPATH up to FIXED-LENGTH.
+
+If the size of the image exceeds FIXED-LENGTH, the center of the
+image are displayed."
+  (let* ((image-spec
+	  `(image :type ,(twittering-image-type fullpath)
+		  :file ,fullpath)))
+    (if (and twittering-convert-fix-size (not twittering-use-convert))
+	(let* ((size (if (file-exists-p fullpath)
+			 (image-size image-spec t)
+		       '(48 . 48)))
+	       (width (car size))
+	       (height (cdr size))
+	       (fixed-length twittering-convert-fix-size)
+	       (half-fixed-length (/ fixed-length 2))
+	       (slice-spec
+		(if (or (< fixed-length width) (< fixed-length height))
+		    `(slice ,(max 0 (- (/ width 2) half-fixed-length))
+			    ,(max 0 (- (/ height 2) half-fixed-length))
+			    ,fixed-length ,fixed-length)
+		  `(slice 0 0 ,fixed-length ,fixed-length))))
+	  `(display (,image-spec ,slice-spec)))
+      `(display ,image-spec))))
+
 (defun twittering-format-status (status format-str)
   ;; Formatting strategy:
   ;; 
@@ -716,11 +747,9 @@ Otherwise, they are retrieved by `url-retrieve'.")
 		    (add-to-list 'twittering-image-stack profile-image-url))
 
 		  (when (and icon-string twittering-icon-mode)
-		    (set-text-properties
-		     1 2 `(display
-			   (image :type ,(twittering-image-type fullpath)
-				  :file ,fullpath))
-		     icon-string)
+		    (let ((display-spec
+			   (twittering-make-display-spec-for-icon fullpath)))
+		      (set-text-properties 1 2 display-spec icon-string))
 		    icon-string)
 		  )))))
     (let ((cursor 0)