Apply MinIsWhite inversion across GeoTIFF read backends (#1804)

* Apply MinIsWhite across GeoTIFF backends (#1795)

* Add MinIsWhite GPU parity coverage

* Correct MinIsWhite test issue filename

Author: brendancol

xrspatial/geotiff/__init__.py

@@ -2450,6 +2450,7 @@ def _read(http_meta):
             from ._reader import (
                 _fetch_decode_cog_http_tiles,
                 MAX_PIXELS_DEFAULT,
+                _apply_photometric_miniswhite,
             )
             header, ifd = http_meta
             if _is_http_src:
@@ -2469,6 +2470,7 @@ def _read(http_meta):
             if (arr.ndim == 3 and ifd.samples_per_pixel > 1
                     and band is not None):
                 arr = arr[:, :, band]
+            arr = _apply_photometric_miniswhite(arr, ifd)
         else:
             _r2a_kwargs = {}
             if max_pixels is not None:
@@ -3323,6 +3325,13 @@ def _read_once():
         geo_info = _apply_orientation_geo_info(
             geo_info, orientation, file_h=height, file_w=width)
 
+    if (ifd.photometric == 0 and samples == 1 and not arr_was_cpu_decoded):
+        gpu_dtype = np.dtype(str(arr_gpu.dtype))
+        if gpu_dtype.kind == 'u':
+            arr_gpu = np.iinfo(gpu_dtype).max - arr_gpu
+        elif gpu_dtype.kind == 'f':
+            arr_gpu = -arr_gpu
+
     # Apply nodata mask + record sentinel so the GPU read agrees with the
     # CPU eager path (issue #1542). Without this, integer rasters keep the
     # literal sentinel value and float rasters keep the sentinel rather

xrspatial/geotiff/_reader.py

@@ -1954,6 +1954,8 @@ def _read_cog_http(url: str, overview_level: int | None = None,
         arr, geo_info = _apply_orientation_with_geo(
             arr, geo_info, ifd.orientation)
 
+    arr = _apply_photometric_miniswhite(arr, ifd)
+
     return arr, geo_info
 
 
@@ -2303,6 +2305,16 @@ def _apply_orientation_with_geo(
     return arr, geo_info
 
 
+def _apply_photometric_miniswhite(arr: np.ndarray, ifd: IFD) -> np.ndarray:
+    """Apply TIFF MinIsWhite inversion for single-band grayscale images."""
+    if ifd.photometric == 0 and ifd.samples_per_pixel == 1:
+        if arr.dtype.kind == 'u':
+            return np.iinfo(arr.dtype).max - arr
+        if arr.dtype.kind == 'f':
+            return -arr
+    return arr
+
+
 def read_to_array(source, *, window=None, overview_level: int | None = None,
                   band: int | None = None,
                   max_pixels: int = MAX_PIXELS_DEFAULT,
@@ -2444,12 +2456,7 @@ def read_to_array(source, *, window=None, overview_level: int | None = None,
             arr, geo_info = _apply_orientation_with_geo(
                 arr, geo_info, orientation)
 
-        # MinIsWhite (photometric=0): invert single-band grayscale values
-        if ifd.photometric == 0 and ifd.samples_per_pixel == 1:
-            if arr.dtype.kind == 'u':
-                arr = np.iinfo(arr.dtype).max - arr
-            elif arr.dtype.kind == 'f':
-                arr = -arr
+        arr = _apply_photometric_miniswhite(arr, ifd)
     finally:
         src.close()
 

xrspatial/geotiff/tests/test_miniswhite_backend_parity_1797.py

@@ -0,0 +1,120 @@
+"""MinIsWhite photometric handling must be backend-consistent (#1797)."""
+from __future__ import annotations
+
+import http.server
+import importlib.util
+import socketserver
+import threading
+
+import numpy as np
+import pytest
+
+from xrspatial.geotiff import open_geotiff
+
+tifffile = pytest.importorskip("tifffile")
+
+
+def _gpu_available() -> bool:
+    """True if cupy is importable and CUDA is initialised."""
+    if importlib.util.find_spec("cupy") is None:
+        return False
+    try:
+        import cupy
+        return bool(cupy.cuda.is_available())
+    except Exception:
+        return False
+
+
+_HAS_GPU = _gpu_available()
+_gpu_only = pytest.mark.skipif(
+    not _HAS_GPU,
+    reason="cupy + CUDA required",
+)
+
+
+class _RangeHandler(http.server.BaseHTTPRequestHandler):
+    payload: bytes = b''
+
+    def do_GET(self):  # noqa: N802
+        rng = self.headers.get('Range')
+        if rng and rng.startswith('bytes='):
+            spec = rng[len('bytes='):]
+            start_s, _, end_s = spec.partition('-')
+            start = int(start_s)
+            end = int(end_s) if end_s else len(self.payload) - 1
+            chunk = self.payload[start:end + 1]
+            self.send_response(206)
+            self.send_header('Content-Type', 'application/octet-stream')
+            self.send_header(
+                'Content-Range',
+                f'bytes {start}-{start + len(chunk) - 1}/{len(self.payload)}',
+            )
+            self.send_header('Content-Length', str(len(chunk)))
+            self.end_headers()
+            self.wfile.write(chunk)
+            return
+        self.send_response(200)
+        self.send_header('Content-Type', 'application/octet-stream')
+        self.send_header('Content-Length', str(len(self.payload)))
+        self.end_headers()
+        self.wfile.write(self.payload)
+
+    def log_message(self, *_args, **_kwargs):
+        pass
+
+
+def _serve(payload: bytes):
+    handler_cls = type(
+        'RangeHandler1797', (_RangeHandler,), {'payload': payload}
+    )
+    httpd = socketserver.TCPServer(('127.0.0.1', 0), handler_cls)
+    port = httpd.server_address[1]
+    thread = threading.Thread(target=httpd.serve_forever, daemon=True)
+    thread.start()
+    return httpd, port
+
+
+@pytest.fixture
+def miniswhite_http_url(tmp_path, monkeypatch):
+    monkeypatch.setenv('XRSPATIAL_GEOTIFF_ALLOW_PRIVATE_HOSTS', '1')
+    stored = np.array([[0, 1, 2], [10, 128, 255]], dtype=np.uint8)
+    path = tmp_path / "tmp_1797_miniswhite.tif"
+    tifffile.imwrite(str(path), stored, photometric='miniswhite')
+    httpd, port = _serve(path.read_bytes())
+    try:
+        yield f'http://127.0.0.1:{port}/tmp_1797_miniswhite.tif', stored
+    finally:
+        httpd.shutdown()
+        httpd.server_close()
+
+
+def test_http_miniswhite_matches_local_reader(miniswhite_http_url):
+    url, stored = miniswhite_http_url
+
+    got = open_geotiff(url)
+
+    np.testing.assert_array_equal(got.values, np.iinfo(stored.dtype).max - stored)
+
+
+def test_http_dask_miniswhite_matches_local_reader(miniswhite_http_url):
+    url, stored = miniswhite_http_url
+
+    got = open_geotiff(url, chunks=2).compute()
+
+    np.testing.assert_array_equal(got.values, np.iinfo(stored.dtype).max - stored)
+
+
+@_gpu_only
+def test_gpu_miniswhite_matches_cpu_reader(tmp_path):
+    from xrspatial.geotiff._writer import write
+
+    stored = np.array([[0, 1, 2], [10, 128, 255]], dtype=np.uint8)
+    path = str(tmp_path / "tmp_1797_miniswhite_gpu.tif")
+    write(stored, path, compression='deflate', tiled=True, tile_size=16,
+          photometric='miniswhite')
+
+    cpu = open_geotiff(path)
+    gpu = open_geotiff(path, gpu=True)
+
+    np.testing.assert_array_equal(cpu.values, np.iinfo(stored.dtype).max - stored)
+    np.testing.assert_array_equal(gpu.data.get(), cpu.values)