Make it possible to set fill value when reading images

satpy/readers/generic_image.py

@@ -54,11 +54,15 @@
 class GenericImageFileHandler(BaseFileHandler):
     """Handle reading of generic image files."""
 
-    def __init__(self, filename, filename_info, filetype_info):
+    def __init__(self, filename, filename_info, filetype_info, set_fill_value=None, nodata_handling=None):
         """Initialize filehandler."""
         super(GenericImageFileHandler, self).__init__(
             filename, filename_info, filetype_info)
         self.finfo = filename_info
+        self.set_fill_value = set_fill_value
+        if self.set_fill_value is not None and not isinstance(self.set_fill_value, (list, tuple)):
+            self.set_fill_value = [self.set_fill_value]
+        self.nodata_handling = nodata_handling
         try:
             self.finfo["end_time"] = self.finfo["start_time"]
         except KeyError:
@@ -82,13 +86,16 @@
         #   however, error is not explicit enough (see https://github.com/pydata/xarray/issues/7831)
         data = xr.open_dataset(self.finfo["filename"], engine="rasterio",
                                chunks={"band": 1, "y": CHUNK_SIZE, "x": CHUNK_SIZE}, mask_and_scale=False)["band_data"]
+
         if hasattr(dataset, "nodatavals"):
             # The nodata values for the raster bands
             # copied from https://github.com/pydata/xarray/blob/v2023.03.0/xarray/backends/rasterio_.py#L322-L326
             nodatavals = tuple(
                 np.nan if nodataval is None else nodataval for nodataval in dataset.nodatavals
             )
             data.attrs["nodatavals"] = nodatavals
+        if self.set_fill_value:
+            data.attrs["nodatavals"] = self.set_fill_value
 
         attrs = data.attrs.copy()
 
@@ -123,10 +130,12 @@
         ds_name = self.dataset_name if self.dataset_name else key["name"]
         logger.debug("Reading '%s.'", ds_name)
         data = self.file_content[ds_name]
+        if self.nodata_handling is not None:
+            info["nodata_handling"] = self.nodata_handling
 
         # Mask data if necessary
         try:
-            data = _mask_image_data(data, info)
+            data = _mask_image_data(data, info, self.set_fill_value)
         except ValueError as err:
             logger.warning(err)
 
@@ -135,15 +144,15 @@
         return data
 
 
-def _mask_image_data(data, info):
+def _mask_image_data(data, info, set_fill_value):
     """Mask image data if necessary.
 
     Masking is done if alpha channel is present or
     dataset 'nodata_handling' is set to 'nan_mask'.
     In the latter case even integer data is converted
     to float32 and masked with np.nan.
     """
-    if data.bands.size in (2, 4):
+    if data.bands.size in (2, 4) and not set_fill_value:
         if not np.issubdtype(data.dtype, np.integer):
             raise ValueError("Only integer datatypes can be used as a mask.")
         mask = data.data[-1, :, :] == np.iinfo(data.dtype).min
@@ -174,4 +183,6 @@
         if np.issubdtype(data.dtype, np.integer):
             fill_value = int(fill_value)
         data.attrs["_FillValue"] = fill_value
+        if "A" in data.bands:
+            data = data.drop_sel(bands="A")
     return data

satpy/tests/reader_tests/test_generic_image.py

@@ -73,7 +73,7 @@ def test_image_l(tmp_path, random_image_channel_l):
                         attrs={"name": "test_l", "start_time": DATA_DATE})
     dset["bands"] = ["L"]
     fname = tmp_path / "test_l.png"
-    _save_image(dset, fname, "simple_image")
+    _save_image(dset, fname, "simple_image", 255)
 
     return fname
 
@@ -162,7 +162,7 @@ def test_png_scene_l_mode(test_image_l):
     with pytest.warns(NotGeoreferencedWarning, match=r"Dataset has no geotransform"):
         scn = Scene(reader="generic_image", filenames=[test_image_l])
     scn.load(["image"])
-    _assert_image_common(scn, 1, None, None, np.float32)
+    _assert_image_common(scn, 1, None, None, np.uint8)
     assert "area" not in scn["image"].attrs
 
 
@@ -182,13 +182,23 @@ def test_png_scene_la_mode(test_image_la):
     """Test reading a PNG image with LA mode via satpy.Scene()."""
     with pytest.warns(NotGeoreferencedWarning, match=r"Dataset has no geotransform"):
         scn = Scene(reader="generic_image", filenames=[test_image_la])
-    scn.load(["image"])
+    scn.load(["image"], nodata_handling="fill_value")
     data = da.compute(scn["image"].data)
     assert np.sum(np.isnan(data)) == 100
     assert "area" not in scn["image"].attrs
     _assert_image_common(scn, 1, DATA_DATE, DATA_DATE, np.float32)
 
 
+def test_png_scene_la_mode_set_fill(test_image_la):
+    """Test reading a PNG image with L mode via satpy.Scene() setting input fill value."""
+    with pytest.warns(NotGeoreferencedWarning, match=r"Dataset has no geotransform"):
+        scn = Scene(reader="generic_image", filenames=[test_image_la],
+                    reader_kwargs={"set_fill_value": 255, "nodata_handling": "fill_value"})
+    scn.load(["image"])
+    _assert_image_common(scn, 1, DATA_DATE, DATA_DATE, np.uint8)
+    assert "area" not in scn["image"].attrs
+
+
 def test_geotiff_scene_rgb(test_image_rgb):
     """Test reading geotiff image in RGB mode via satpy.Scene()."""
     scn = Scene(reader="generic_image", filenames=[test_image_rgb])
@@ -205,6 +215,15 @@ def test_geotiff_scene_rgba(test_image_rgba):
     assert scn["image"].area == AREA_DEFINITION
 
 
+def test_png_scene_rgba_mode_set_fill(test_image_rgba):
+    """Test reading an image in RGBA mode via satpy.Scene() setting input fill value."""
+    scn = Scene(reader="generic_image", filenames=[test_image_rgba],
+                reader_kwargs={"set_fill_value": 255, "nodata_handling": "fill_value"})
+    scn.load(["image"])
+    _assert_image_common(scn, 3, None, None, np.uint8)
+    assert scn["image"].area == AREA_DEFINITION
+
+
 def test_geotiff_scene_nan_fill_value(test_image_l_nan_fill_value):
     """Test reading geotiff image with fill value set via satpy.Scene()."""
     scn = Scene(reader="generic_image", filenames=[test_image_l_nan_fill_value])
@@ -252,6 +271,8 @@ def __init__(self, filename, filename_info, filetype_info, file_content, **kwarg
         super(GenericImageFileHandler, self).__init__(filename, filename_info, filetype_info)
         self.file_content = file_content
         self.dataset_name = None
+        self.nodata_handling = kwargs.pop("nodata_handling", None)
+        self.set_fill_value = kwargs.pop("set_fill_value", None)
         self.file_content.update(kwargs)