Fix compositing multi source with alpha

CHANGELOG.md

@@ -9,6 +9,9 @@
 - Infer DICOM file size, when possible ([#1448](../../pull/1448))
 - Swap styles faster in the frame viewer ([#1452](../../pull/1452))
 
+### Bug Fixes
+- Fix an issue with compositing sources in the multi source caused by alpha range ([#1453](../../pull/1453))
+
 ## 1.27.1
 
 ### Improvements

large_image/tilesource/utilities.py

@@ -8,6 +8,7 @@
 from typing import Any, Dict, List, Optional, Set, Tuple, Union, cast
 
 import numpy as np
+import numpy.typing as npt
 import PIL
 import PIL.Image
 import PIL.ImageColor
@@ -729,16 +730,17 @@ def getAvailableNamedPalettes(includeColors: bool = True, reduced: bool = False)
     return sorted(palettes)
 
 
-def fullAlphaValue(arr: np.ndarray) -> int:
+def fullAlphaValue(arr: Union[np.ndarray, npt.DTypeLike]) -> int:
     """
     Given a numpy array, return the value that should be used for a fully
     opaque alpha channel.  For uint variants, this is the max value.
 
     :param arr: a numpy array.
     :returns: the value for the alpha channel.
     """
-    if arr.dtype.kind == 'u':
-        return np.iinfo(arr.dtype).max
+    dtype = arr.dtype if isinstance(arr, np.ndarray) else arr
+    if dtype.kind == 'u':
+        return np.iinfo(dtype).max
     return 1
 
 

sources/multi/large_image_source_multi/__init__.py

@@ -931,36 +931,34 @@
             return tile
         if base is None:
             base = np.zeros((0, 0, tile.shape[2]), dtype=tile.dtype)
-            if tile.shape[2] in {2, 4}:
-                base[:, :, -1] = fullAlphaValue(tile)
         base, tile = _makeSameChannelDepth(base, tile)
         if base.shape[0] < tile.shape[0] + y:
             vfill = np.zeros(
                 (tile.shape[0] + y - base.shape[0], base.shape[1], base.shape[2]),
                 dtype=base.dtype)
             if base.shape[2] in {2, 4}:
-                vfill[:, :, -1] = fullAlphaValue(base)
+                vfill[:, :, -1] = fullAlphaValue(self.dtype)
             base = np.vstack((base, vfill))
         if base.shape[1] < tile.shape[1] + x:
             hfill = np.zeros(
                 (base.shape[0], tile.shape[1] + x - base.shape[1], base.shape[2]),
                 dtype=base.dtype)
             if base.shape[2] in {2, 4}:
-                hfill[:, :, -1] = fullAlphaValue(base)
+                hfill[:, :, -1] = fullAlphaValue(self.dtype)
             base = np.hstack((base, hfill))
         if base.flags.writeable is False:
             base = base.copy()
         if base.shape[2] in {2, 4}:
             baseA = base[y:y + tile.shape[0], x:x + tile.shape[1], -1].astype(
-                float) / fullAlphaValue(base)
-            tileA = tile[:, :, -1].astype(float) / fullAlphaValue(tile)
+                float) / fullAlphaValue(self.dtype)
+            tileA = tile[:, :, -1].astype(float) / fullAlphaValue(self.dtype)
             outA = tileA + baseA * (1 - tileA)
             base[y:y + tile.shape[0], x:x + tile.shape[1], :-1] = (
-                tile[:, :, :-1] * tileA[..., np.newaxis] +
+                np.where(tileA[..., np.newaxis], tile[:, :, :-1], 0) +
                 base[y:y + tile.shape[0], x:x + tile.shape[1], :-1] * baseA[..., np.newaxis] *
                 (1 - tileA[..., np.newaxis])
-            ) / outA[..., np.newaxis]
-            base[y:y + tile.shape[0], x:x + tile.shape[1], -1] = outA * fullAlphaValue(base)
+            ) / np.where(outA[..., np.newaxis], outA[..., np.newaxis], 1)
+            base[y:y + tile.shape[0], x:x + tile.shape[1], -1] = outA * fullAlphaValue(self.dtype)
         else:
             base[y:y + tile.shape[0], x:x + tile.shape[1], :] = tile
         return base
@@ -1030,8 +1028,9 @@
         }
         if output['maxWidth'] <= 0 or output['maxHeight'] <= 0:
             return None, 0, 0
-        srcImage = ts.getRegion(
-            format=TILE_FORMAT_NUMPY, region=region, output=output, frame=frame)[0]
+        srcImage, _ = ts.getRegion(
+            region=region, output=output, frame=frame,
+            format=TILE_FORMAT_NUMPY)
         # This is the region we actually took in our source coordinates, scaled
         # for if we took a low res version
         regioncorners = np.array([