From 90237da8f3485b22cdb794274f5da929788478bc Mon Sep 17 00:00:00 2001
From: Gerrit Holl <gerrit.holl@dwd.de>
Date: Mon, 19 Aug 2024 11:39:10 +0200
Subject: [PATCH] Adapt fill value after palettizing.

Adapt fill value after palettizing.
---
 trollimage/tests/test_image.py | 10 ++++++++++
 trollimage/xrimage.py          |  1 +
 2 files changed, 11 insertions(+)

diff --git a/trollimage/tests/test_image.py b/trollimage/tests/test_image.py
index 0aaf6a9..1883323 100644
--- a/trollimage/tests/test_image.py
+++ b/trollimage/tests/test_image.py
@@ -2600,6 +2600,16 @@ def test_palettize_geotiff_tag(self, tmp_path, colormap_tag, keep_palette):
                 np.testing.assert_allclose(new_brbg.values, loaded_brbg.values)
                 np.testing.assert_allclose(new_brbg.colors, loaded_brbg.colors)
 
+    def test_palettize_fill_value(self):
+        """Test that fill values are adapted."""
+
+        arr = np.arange(25, dtype="float32").reshape(5, 5)/25
+        arr[2, 2] = np.nan
+        data = xr.DataArray(arr.copy(), dims=['y', 'x'], attrs={"_FillValue": np.nan})
+        img = xrimage.XRImage(data)
+        img.palettize(brbg)
+        assert img.data[0, 2, 2] == img.data.attrs["_FillValue"]
+
 
 class TestXRImageSaveScaleOffset:
     """Test case for saving an image with scale and offset tags."""
diff --git a/trollimage/xrimage.py b/trollimage/xrimage.py
index 6c56b3e..afd70ff 100644
--- a/trollimage/xrimage.py
+++ b/trollimage/xrimage.py
@@ -1483,6 +1483,7 @@ def palettize(self, colormap):
 
         self.data.data = new_data
         self.data.coords['bands'] = list(mode)
+        self.data.attrs["_FillValue"] = colormap.values.shape[0]-1
         # See docstring notes above for how scale/offset should be used
         scale_factor, offset = self._get_colormap_scale_offset(colormap)
         self.data.attrs.setdefault('enhancement_history', []).append({