s/image_format/format

IPython/html/static/notebook/js/widgets/widget_image.js

@@ -31,7 +31,7 define(["notebook/js/widgets/widget"], function(widget_manager){
             //
             // Called when the model is changed.  The model may have been 
             // changed by another view or by a state update from the back-end.
-            var image_src = 'data:image/' + this.model.get('image_format') + ';base64,' + this.model.get('_b64value');
+            var image_src = 'data:image/' + this.model.get('format') + ';base64,' + this.model.get('_b64value');
             this.$el.attr('src', image_src);
             
             var width = this.model.get('width');

IPython/html/widgets/widget_image.py

@@ -27,8 +27,8 class ImageWidget(DOMWidget):
     view_name = Unicode('ImageView')
     
     # Define the custom state properties to sync with the front-end
-    keys = ['image_format', 'width', 'height', '_b64value'] + DOMWidget.keys
-    image_format = Unicode('png')
+    keys = ['format', 'width', 'height', '_b64value'] + DOMWidget.keys
+    format = Unicode('png')
     width = Unicode()
     height = Unicode()
     _b64value = Unicode()