+
+        # Limit PNG to 200K. If larger, convert to JPEG.
+        if th_format == 'PNG' and buffer.tell() > MAX_PNG_WEIGHT:
+            th_format, ext, media_type = 'JPEG', 'jpg', 'image/jpeg'
+            if th.mode != 'RGB':
+                buffer = io.BytesIO()
+                th = Image.alpha_composite(
+                    Image.new('RGBA', th.size, '#fff'),
+                    th.convert('RGBA')
+                )
+                th = th.convert('RGB')
+            th.save(buffer, format=th_format)
+