feat: handle standardising paletted tiffs

scripts/gdal/gdal_bands.py

@@ -21,6 +21,7 @@ def find_band(bands: List[GdalInfoBand], color: str) -> Optional[GdalInfoBand]:
     return None
 
 
+# pylint: disable-msg=too-many-return-statements
 def get_gdal_band_offset(file: str, info: Optional[GdalInfo] = None, preset: Optional[str] = None) -> List[str]:
     """Get the banding parameters for a `gdal_translate` command.
 
@@ -36,19 +37,31 @@ def get_gdal_band_offset(file: str, info: Optional[GdalInfo] = None, preset: Opt
 
     bands = info["bands"]
 
-    alpha_band = find_band(bands, "Alpha")
-    alpha_band_info: List[str] = []
-    if alpha_band:
-        alpha_band_info.extend(["-b", str(alpha_band["band"])])
+    band_alpha_arg: List[str] = []
+    if band_alpha := find_band(bands, "Alpha"):
+        band_alpha_arg.extend(["-b", str(band_alpha["band"])])
 
-    grey_band = find_band(bands, "Gray")
-    if grey_band:
-        grey_band_index = str(grey_band["band"])
+    if band_grey := find_band(bands, "Gray"):
+        band_grey_index = str(band_grey["band"])
         if preset == "dem_lerc":
             # return single band if DEM/DSM
-            return ["-b", grey_band_index]
+            return ["-b", band_grey_index]
         # Grey scale imagery, set R,G and B to just the grey_band
-        return ["-b", grey_band_index, "-b", grey_band_index, "-b", grey_band_index] + alpha_band_info
+        return ["-b", band_grey_index, "-b", band_grey_index, "-b", band_grey_index] + band_alpha_arg
+
+    if band_palette := find_band(bands, "Palette"):
+        if colour_table := band_palette["colorTable"]:
+            palette_channels = len(colour_table["entries"][0])
+            if palette_channels == 4:
+                return ["-expand", "rgba"]
+            if palette_channels == 3:
+                return ["-expand", "rgb"]
+            get_log().error(
+                "unknown_palette_band_type",
+                palette_channels=palette_channels,
+                first_entry=colour_table["entries"][0],
+            )
+        get_log().error("palette_band_missing_colorTable")
 
     band_red = find_band(bands, "Red")
     band_green = find_band(bands, "Green")
@@ -61,12 +74,12 @@ def get_gdal_band_offset(file: str, info: Optional[GdalInfo] = None, preset: Opt
 
         # Not enough bands for RGB assume it is grey scale
         if len(bands) < 3:
-            return ["-b", "1", "-b", "1", "-b", "1"] + alpha_band_info
+            return ["-b", "1", "-b", "1", "-b", "1"] + band_alpha_arg
 
         # Could be RGB assume it is RGB
-        return ["-b", "1", "-b", "2", "-b", "3"] + alpha_band_info
+        return ["-b", "1", "-b", "2", "-b", "3"] + band_alpha_arg
 
-    return ["-b", str(band_red["band"]), "-b", str(band_green["band"]), "-b", str(band_blue["band"])] + alpha_band_info
+    return ["-b", str(band_red["band"]), "-b", str(band_green["band"]), "-b", str(band_blue["band"])] + band_alpha_arg
 
 
 def get_gdal_band_type(file: str, info: Optional[GdalInfo] = None) -> str:

scripts/gdal/gdalinfo.py

@@ -8,6 +8,12 @@
 from scripts.tile.tile_index import Point
 
 
+class GdalInfoBandColorTable(TypedDict):
+    palette: str
+    count: int
+    entries: List[List[int]]
+
+
 class GdalInfoBand(TypedDict):
     band: int
     """band offset, starting at 1
@@ -17,9 +23,10 @@ class GdalInfoBand(TypedDict):
     colorInterpretation: str
     """Color
     Examples:
-        "Red", "Green", "Blue", "Alpha", "Gray"
+        "Red", "Green", "Blue", "Alpha", "Gray", "Palette"
     """
     noDataValue: Optional[int]
+    colorTable: Optional[GdalInfoBandColorTable]
 
 
 class GdalInfo(TypedDict):

scripts/gdal/tests/gdal_bands_test.py

@@ -1,5 +1,5 @@
 from scripts.gdal.gdal_bands import get_gdal_band_offset, get_gdal_band_type
-from scripts.gdal.tests.gdalinfo import add_band, fake_gdal_info
+from scripts.gdal.tests.gdalinfo import add_band, add_palette_band, fake_gdal_info
 
 
 def test_gdal_grey_bands() -> None:
@@ -53,6 +53,24 @@ def test_gdal_rgb_bands_detection() -> None:
     assert " ".join(bands) == "-b 1 -b 2 -b 3"
 
 
+def test_gdal_rgba_palette_detection() -> None:
+    gdalinfo = fake_gdal_info()
+    add_palette_band(gdalinfo, colour_table_entries=[[x, x, x, 255] for x in reversed(range(256))])
+
+    bands = get_gdal_band_offset("some_file.tiff", gdalinfo)
+
+    assert " ".join(bands) == "-expand rgba"
+
+
+def test_gdal_rgb_palette_detection() -> None:
+    gdalinfo = fake_gdal_info()
+    add_palette_band(gdalinfo, colour_table_entries=[[x, x, x] for x in reversed(range(256))])
+
+    bands = get_gdal_band_offset("some_file.tiff", gdalinfo)
+
+    assert " ".join(bands) == "-expand rgb"
+
+
 def test_gdal_default_grey_scale() -> None:
     gdalinfo = fake_gdal_info()
     add_band(gdalinfo, color_interpretation="Pallette")

scripts/gdal/tests/gdalinfo.py

@@ -1,4 +1,4 @@
-from typing import Optional, cast
+from typing import List, Optional, cast
 
 from scripts.gdal.gdalinfo import GdalInfo, GdalInfoBand
 
@@ -27,3 +27,20 @@ def add_band(
             },
         )
     )
+
+
+def add_palette_band(gdalinfo: GdalInfo, colour_table_entries: List[List[int]], no_data_value: Optional[int] = None) -> None:
+    if gdalinfo.get("bands", None) is None:
+        gdalinfo["bands"] = []
+
+    gdalinfo["bands"].append(
+        cast(
+            GdalInfoBand,
+            {
+                "band": len(gdalinfo["bands"]) + 1,
+                "colorInterpretation": "Palette",
+                "noDataValue": no_data_value,
+                "colorTable": {"palette": "RGB", "count": len(colour_table_entries), "entries": colour_table_entries},
+            },
+        )
+    )