Allow to change downsample function

ome_zarr/scale.py

@@ -77,9 +77,7 @@ def methods() -> Iterator[str]:
 
     def scale(self, input_array: str, output_directory: str) -> None:
         """Perform downsampling to disk."""
-        func = getattr(self, self.method, None)
-        if not func:
-            raise Exception
+        func = self.func
 
         store = self.__check_store(output_directory)
         base = zarr.open_array(input_array)
@@ -94,6 +92,14 @@ def scale(self, input_array: str, output_directory: str) -> None:
             print(f"copying attribute keys: {list(base.attrs.keys())}")
             grp.attrs.update(base.attrs)
 
+    @property
+    def func(self) -> Callable[[np.ndarray], List[np.ndarray]]:
+        """Get downsample function."""
+        func = getattr(self, self.method, None)
+        if not func:
+            raise Exception
+        return func
+
     def __check_store(self, output_directory: str) -> MutableMapping:
         """Return a Zarr store if it doesn't already exist."""
         assert not os.path.exists(output_directory)

ome_zarr/writer.py

@@ -906,7 +906,7 @@ def _create_mip(
                 "Can't downsample if size of x or y dimension is 1. "
                 "Shape: %s" % (image.shape,)
             )
-        mip = scaler.nearest(image)
+        mip = scaler.func(image)
     else:
         LOGGER.debug("disabling pyramid")
         mip = [image]

tests/test_scaler.py

@@ -36,6 +36,26 @@ def test_nearest(self, shape):
         downscaled = scaler.nearest(data)
         self.check_downscaled(downscaled, shape)
 
+    def test_nearest_via_method(self, shape):
+        data = self.create_data(shape)
+
+        scaler = Scaler()
+        expected_downscaled = scaler.nearest(data)
+
+        scaler.method = "nearest"
+        downscaled = scaler.func(data)
+        self.check_downscaled(downscaled, shape)
+
+        assert (
+            np.sum(
+                [
+                    not np.array_equal(downscaled[i], expected_downscaled[i])
+                    for i in range(len(downscaled))
+                ]
+            )
+            == 0
+        )
+
     # this fails because of wrong channel dimension; need to fix in follow-up PR
     @pytest.mark.xfail
     def test_gaussian(self, shape):
@@ -58,6 +78,26 @@ def test_local_mean(self, shape):
         downscaled = scaler.local_mean(data)
         self.check_downscaled(downscaled, shape)
 
+    def test_local_mean_via_method(self, shape):
+        data = self.create_data(shape)
+
+        scaler = Scaler()
+        expected_downscaled = scaler.local_mean(data)
+
+        scaler.method = "local_mean"
+        downscaled = scaler.func(data)
+        self.check_downscaled(downscaled, shape)
+
+        assert (
+            np.sum(
+                [
+                    not np.array_equal(downscaled[i], expected_downscaled[i])
+                    for i in range(len(downscaled))
+                ]
+            )
+            == 0
+        )
+
     @pytest.mark.skip(reason="This test does not terminate")
     def test_zoom(self, shape):
         data = self.create_data(shape)
@@ -80,6 +120,20 @@ def test_scale_dask(self, shape):
 
         assert np.array_equal(resized_data, resized_dask)
 
+    def test_scale_dask_via_method(self, shape):
+        data = self.create_data(shape)
+
+        chunk_size = [100, 100]
+        chunk_2d = (*(1,) * (data.ndim - 2), *chunk_size)
+        data_delayed = da.from_array(data, chunks=chunk_2d)
+
+        scaler = Scaler()
+        expected_downscaled = scaler.resize_image(data)
+
+        scaler.method = "resize_image"
+        assert np.array_equal(expected_downscaled, scaler.func(data))
+        assert np.array_equal(expected_downscaled, scaler.func(data_delayed))
+
     def test_big_dask_pyramid(self, tmpdir):
         # from https://github.com/ome/omero-cli-zarr/pull/134
         shape = (6675, 9560)