Do not store instance of an Image in cache, store its value respectively.

Do handle well case between 'display' argument and its pixel size representation by storing in cache only 'display' argument.

product/ERP5/Document/Image.py

@@ -279,19 +279,23 @@ class Image(TextConvertableMixin, File, OFSImage):
     quality = kw.get('quality', _MARKER)
     if quality is _MARKER:
       quality = self.getDefaultImageQuality(format)
-    #print "image._convert", kw, quality, self.getRelativeUrl(), self.getPortalType()
-    convert_kw = {'quality': quality,
-                  'resolution': kw.get('resolution'),
-                  'frame': kw.get('frame'),
-                  'image_size': image_size,
-                  'format': format,
-                 }
+    kw['format'] = format
+    kw['quality'] = quality
     try:
-      mime, image = self.getConversion(**convert_kw)
+      mime, image_data = self.getConversion(**kw)
     except KeyError:
-      mime, image = self._makeDisplayPhoto(**convert_kw)
-      self.setConversion(image, mime, **convert_kw)
-    return mime, image.data
+      # we need to convert string representation (i.e. display=small) to a 
+      # pixel (number of it = 128x128)
+      kw['image_size'] = image_size    
+      display = kw.pop('display', None)
+      mime, image = self._makeDisplayPhoto(**kw)
+      image_data = image.data
+      # as image will always be requested through a display not by passing exact
+      # pixels we need to restore this way in cache
+      kw['display'] = display
+      image_size = kw.pop('image_size', None)
+      self.setConversion(image_data, mime, **kw)
+    return mime, image_data
 
   # Display
   security.declareProtected(Permissions.View, 'index_html')