Detect the tile_format (png/webp/jpg) from tile

tests/test_tms_utils.py

@@ -9,6 +9,7 @@
     collect_zoom_stats,
     compute_bounds,
     detect_scheme,
+    detect_tile_format,
     generate_tilemapresource_xml,
     iter_tiles,
 )
@@ -161,6 +162,21 @@ def test_returns_both_bounds(self, tiny_tms_dir: Path):
         assert tms_bounds != xyz_bounds
 
 
+class TestDetectTileFormat:
+    def test_png(self):
+        assert detect_tile_format(b"\x89PNG\r\n\x1a\n" + b"\x00" * 8) == "png"
+
+    def test_jpeg(self):
+        assert detect_tile_format(b"\xff\xd8\xff\xe0" + b"\x00" * 8) == "jpg"
+
+    def test_webp(self):
+        # RIFF container with WEBP fourcc at offset 8
+        assert detect_tile_format(b"RIFF\x00\x00\x00\x00WEBPVP8 ") == "webp"
+
+    def test_unknown_falls_back_to_png(self):
+        assert detect_tile_format(b"not an image") == "png"
+
+
 class TestGenerateTimemapresourceXml:
     def test_contains_expected_elements(self):
         xml = generate_tilemapresource_xml(

tilepack/convert.py

@@ -6,7 +6,13 @@
 
 import click
 
-from tilepack.tms_utils import collect_zoom_stats, compute_bounds, detect_scheme, iter_tiles
+from tilepack.tms_utils import (
+    collect_zoom_stats,
+    compute_bounds,
+    detect_scheme,
+    detect_tile_format,
+    iter_tiles,
+)
 
 
 def run_convert(input_root: str, output_file: str, scheme: str | None = None) -> None:
@@ -50,6 +56,14 @@ def _convert_mbtiles(root: Path, out: Path, *, stats: dict, scheme: str) -> None
     bounds = compute_bounds(stats, scheme=scheme)
     flip_y = scheme == "xyz"
 
+    def _first_tile_format(root: Path) -> str:
+        """Detect the tile format from the first tile in the folder."""
+        for _z, _x, _y, tile_path in iter_tiles(root):
+            return detect_tile_format(tile_path.read_bytes())
+        return "png"
+
+    tile_format = _first_tile_format(root)
+
     # Create MBTiles database
     if out.exists():
         out.unlink()
@@ -75,7 +89,7 @@ def _convert_mbtiles(root: Path, out: Path, *, stats: dict, scheme: str) -> None
 
     meta = {
         "name": root.name,
-        "format": "png",
+        "format": tile_format,
         "bounds": bounds_str,
         "center": f"{center_lon:.6f},{center_lat:.6f},{center_zoom}",
         "minzoom": str(minzoom),
@@ -145,6 +159,13 @@ def tile_entries():
     click.echo("Reading and sorting tiles...")
     entries = sorted(tile_entries(), key=lambda e: e[0])
 
+    tile_format = detect_tile_format(entries[0][1]) if entries else "png"
+    tile_type = {
+        "png": TileType.PNG,
+        "jpg": TileType.JPEG,
+        "webp": TileType.WEBP,
+    }[tile_format]
+
     # Write PMTiles using the low-level writer
     from pmtiles.writer import Writer as PMTilesWriter
 
@@ -159,7 +180,7 @@ def tile_entries():
 
         writer.finalize(
             header={
-                "tile_type": TileType.PNG,
+                "tile_type": tile_type,
                 "min_zoom": minzoom,
                 "max_zoom": maxzoom,
                 "min_lon_e7": int(bounds[0] * 1e7),
@@ -170,7 +191,7 @@ def tile_entries():
             },
             metadata={
                 "name": root.name,
-                "format": "png",
+                "format": tile_format,
                 "bounds": f"{bounds[0]:.6f},{bounds[1]:.6f},{bounds[2]:.6f},{bounds[3]:.6f}",
                 "minzoom": str(minzoom),
                 "maxzoom": str(maxzoom),

tilepack/tms_utils.py

@@ -216,3 +216,16 @@ def generate_tilemapresource_xml(
   </TileSets>
 </TileMap>
 """
+
+
+def detect_tile_format(tile_data: bytes) -> str:
+    """Sniff the image format from a tile's magic bytes.
+
+    Returns an MBTiles/TileJSON ``format`` string ("png", "jpg", "webp").
+    Falls back to "png" for unrecognized data.
+    """
+    if tile_data[:4] == b"RIFF" and tile_data[8:12] == b"WEBP":
+        return "webp"
+    if tile_data[:2] == b"\xff\xd8":
+        return "jpg"
+    return "png"