Render save() server-side via ginga

Use the ginga viewer's save_rgb_image_as_file renderer instead of writing out the JPEG-encoded widget buffer. This produces a file in the format implied by the extension (e.g. a real PNG for a .png filename) and does not depend on a running browser. The overwrite guard is unchanged. Co-written with Claude Opus 4.8
astropy · mwcraig · Jun 27, 2026 · Jun 27, 2026 · Jun 28, 2026 · Jun 28, 2026
commit 60287b794d45954c023f35c1bd75c9048fc47c37
diff --git a/astrowidgets/ginga.py b/astrowidgets/ginga.py
@@ -702,10 +702,9 @@ def save(self, filename, overwrite=False, **kwargs):
         overwrite : bool, optional
             If `True`, overwrite an existing file.
         """
-        # The widget value is already PNG-encoded, so just write it out. This
-        # requires a running browser to have populated the buffer.
         if not overwrite and Path(filename).exists():
             raise FileExistsError(f'File {filename} exists and overwrite=False')
 
-        with open(filename, 'wb') as f:
-            f.write(self._jup_img.value)
+        # Ginga renders the view server-side, so this works without a running
+        # browser and honors the image format implied by the file extension.
+        self._viewer.save_rgb_image_as_file(str(filename))
diff --git a/astrowidgets/tests/test_widget_api_ginga.py b/astrowidgets/tests/test_widget_api_ginga.py
@@ -95,13 +95,3 @@ def test_center_on_skycoord_updates_viewport():
 class TestGingaWidget(ImageAPITest):
     image_widget_class = ImageWidget
     cursor_error_classes = (ValueError, TraitError)
-
-    @pytest.mark.skip(reason="Saving requires a running browser to populate "
-                             "the image buffer.")
-    def test_save(self, tmp_path):
-        pass
-
-    @pytest.mark.skip(reason="Saving requires a running browser to populate "
-                             "the image buffer.")
-    def test_save_overwrite(self, tmp_path):
-        pass