diff --git a/PIL/Image.py b/PIL/Image.py
index c11c4cb3f..c8315ba76 100644
--- a/PIL/Image.py
+++ b/PIL/Image.py
@@ -577,7 +577,7 @@ class Image(object):
         self.pyaccess = None
         self.readonly = 0
 
-    def _dump(self, file=None, format=None):
+    def _dump(self, file=None, format=None, **options):
         import tempfile
         suffix = ''
         if format:
@@ -592,7 +592,7 @@ class Image(object):
         else:
             if not file.endswith(format):
                 file = file + "." + format
-            self.save(file, format)
+            self.save(file, format, **options)
         return file
 
     def __eq__(self, other):
diff --git a/PIL/ImageShow.py b/PIL/ImageShow.py
index 33f059d74..a0978ab39 100644
--- a/PIL/ImageShow.py
+++ b/PIL/ImageShow.py
@@ -69,7 +69,7 @@ class Viewer(object):
             # FIXME: auto-contrast if max() > 255?
         else:
             base = Image.getmodebase(image.mode)
-        if base != image.mode and image.mode != "1":
+        if base != image.mode and image.mode != "1" and image.mode != "RGBA":
             image = image.convert(base)
 
         return self.show_image(image, **options)
@@ -77,6 +77,7 @@ class Viewer(object):
     # hook methods
 
     format = None
+    options = {}
 
     def get_format(self, image):
         """Return format name, or None to save as PGM/PPM"""
@@ -87,7 +88,7 @@ class Viewer(object):
 
     def save_image(self, image):
         """Save to temporary file, and return filename"""
-        return image._dump(format=self.get_format(image))
+        return image._dump(format=self.get_format(image), **self.options)
 
     def show_image(self, image, **options):
         """Display given image"""
@@ -115,7 +116,8 @@ if sys.platform == "win32":
 elif sys.platform == "darwin":
 
     class MacViewer(Viewer):
-        format = "BMP"
+        format = "PNG"
+        options = {'compress-level': 1}
 
         def get_command(self, file, **options):
             # on darwin open returns immediately resulting in the temp
@@ -142,6 +144,9 @@ else:
         return None
 
     class UnixViewer(Viewer):
+        format = "PNG"
+        options = {'compress-level': 1}
+
         def show_file(self, file, **options):
             command, executable = self.get_command_ex(file, **options)
             command = "(%s %s; rm -f %s)&" % (command, quote(file),